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ArticleJuly 26, 2016

Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface Traps
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Cite this: ACS Omega 2016, 1, 1, 148–159

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https://doi.org/10.1021/acsomega.6b00107

Published July 26, 2016

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Abstract

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Photoluminescence (PL) of organometal halide perovskite materials reflects the charge dynamics inside of the material and thus contains important information for understanding the electro-optical properties of the material. Interpretation of PL blinking of methylammonium lead iodide (MAPbI₃) nanostructures observed on polycrystalline samples remains puzzling owing to their intrinsic disordered nature. Here, we report a novel method for the synthesis of high-quality single-crystal MAPbI₃ nanorods and demonstrate a single-crystal study on MAPbI₃ PL blinking. At low excitation power densities, two-state blinking was found on individual nanorods with dimensions of several hundred nanometers. A super-resolution localization study on the blinking of individual nanorods showed that single crystals of several hundred nanometers emit and blink as a whole, without showing changes in the localization center over the crystal. Moreover, both the blinking ON and OFF times showed power-law distributions, indicating trapping–detrapping processes. This is further supported by the PL decay times of the individual nanorods, which were found to correlate with the ON/OFF states. Furthermore, a strong environmental dependence of the nanorod PL blinking was revealed by comparing the measurements in vacuum, nitrogen, and air, implying that traps locate close to crystal surfaces. We explain our observations by proposing surface charge traps that are likely related to under-coordinated lead ions and methylammonium vacancies to result in the PL blinking observed here.

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Introduction

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Reporting power-conversion efficiencies exceeding 20%, (1, 2) the recent emergence of organometal halide perovskites (OHPs), methylammonium lead iodide (MAPbI₃) in particular, has enabled new possibilities for cost-efficient photovoltaic (PV) devices. (3, 4) OHP properties such as photoluminescence (PL), charge mobility, trap density, and their PV performance, however, are found to vary largely depending on the material preparation and processing methods, (5) likely due to differences in the defect density and crystal morphology. The conventionally employed deposition method for OHP solar-cell fabrication is by annealing a spin-casted precursor film at elevated temperatures, (6, 7) resulting in a polycrystalline film composed of densely packed crystal grains of a few hundred nanometers up to micrometers in size. The crystal grains in the film show large variations in their size and morphology. PL and cathodoluminescence from such OHP films, reflecting local charge dynamics, (8-12) have recently been shown to be highly heterogeneous from grain to grain. (6, 13, 14) Moreover, a recent study using simultaneous light and electron microscopy has revealed significant variations in both PL and morphology evolution of perovskite crystals upon light- and electron-beam-induced degradation. (15) The aforementioned heterogeneity found in submicron-sized perovskites is closely related to variations in the local ion mobility, (13, 15-18) trap densities, (19) and local chemical composition, (6, 13, 16, 20) which ultimately determine the device performance on mesoscopic and macroscopic scales. (17, 18, 21-23) Besides OHP crystals themselves, the inherent grain boundaries in the polycrystalline films are also found to play an important role in the properties of OHP-based devices. (24, 25)

To best resolve such heterogeneity in the crystal properties and the role of grain boundaries, the link between morphology and material properties needs to be established at the single-crystal level. Applying super-resolution localization microscopy on individual particles on a glass cover slide prepared using the conventional film deposition method, Tian et al. reported on light-activated quenching sites in single perovskite particles that cause giant PL blinking. (7) Super-resolution localization on these blinking events revealed that the localization center position was jumping for the sub-diffraction-limit nanocrystals studied. (7) Furthermore, the authors reported a strong correlation between PL intensities and the corresponding localization center positions. (7) Whereas these data represent a first-of-its-kind report on OHP nanocrystal PL blinking, studies correlating optical localization with morphology at the nanometer scale are still missing, leaving the mechanism behind the PL blinking phenomenon elusive. In particular, the sample preparation method employed in the previous study by Tian et al. (7) cannot exclude the existence of multiple crystal grains within a diffraction-limited spot. Therefore, single-crystalline OHP nanocrystals, nanorods in particular, are required to minimize the effects caused by polycrystallinity in the aforementioned super-resolution optical studies.

Although a few studies have reported on the solution synthesis of single-crystal OHP nanostructures, (26, 27) such as quantum dots, (28) rod- and wire-type crystals, (29-32) and platelets, (33) controlled synthesis of OHP rods (100–300 nm) remains challenging. The surface-initiated solution growth of a single-crystalline OHP gives well-isolated OHP wires and plates of high quality. (29, 30) However, this method requires an initial step that uses a solid surface and results in crystals of a few microns in size. (29, 30) A total solution-based synthesis of OHP nanorods (an average dimension of 800 × 50 nm²) was recently demonstrated by Zhu et al. by employing n-octylammonium cations as capping agents. (31) Nevertheless, these nanorods (800 nm in length) are much longer than the diffraction limit of visible light (200–300 nm). This makes them not ideal for super-resolution localization studies in which 2D Gaussian is usually used to approximate the point-spread function (PSF) of single emitters. (34, 35) Very recently, Aharon et al. used octylammonium iodide and oleic acid (OA) to control the OHP nanocrystal morphology and reported on high-yield synthesis of OHP nanorods of 11 × 2 nm². (32) Such crystals are too small to draw useful conclusions from the super-resolution localization studies because the resolution of this imaging modality is only several tens of nanometers (34-36) and spatial-related PL phenomena on the sub-10 nm length scale are out of reach.

In this study, we first present a novel method to synthesize single-crystalline MAPbI₃ nanorods with an average dimension of 160 × 35 nm², using a combination of oleylamine (OAm) and OA as capping agents. It is noteworthy that the resulting MAPbI₃ nanorods are exceptionally stable in toluene suspension even after 8 weeks of storage in the dark. Next, we investigate the PL blinking of the as-prepared individual MAPbI₃ nanorods using correlative super-resolution localization optical microscopy and scanning electron microscopy (SEM). (15) Finally, we discuss our experimental observations by proposing under-coordinated lead ions and methylammonium vacancies to be the surface traps that lead to PL blinking of MAPbI₃ nanorods observed in this study.

Results and Discussion

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MAPbI₃ Nanorods

MAPbI₃ nanorods were prepared via a two-step synthesis. The capping agents, OAm and OA, were first dissolved in toluene. On injecting the precursor acetonitrile solution into the capping agent toluene solution under vigorous stirring, tiny MAPbI₃ nuclei started to form, resulting in a color change of the suspension to red. Further crystal growth was achieved by gradually introducing additional amounts of pure toluene into the mixture to drive further precipitation of MAPbI₃ precursors. A detailed description of the synthesis method can be found in Experimental Section.

The concentration ratio between the two capping agents is crucial for the anisotropic growth of MAPbI₃ nanocrystals. On the one hand, when OA was used as the only capping agent, the MAPbI₃ nanocrystals grown consisted mostly of large bulky clusters of small nanoparticles. On the other hand, elongated thin wires were found when OAm was used as the only capping agent. However, MAPbI₃ nanocrystals are found to be stable only in the presence of OA. In the absence of OA, the nanowires quickly aggregate within several hours of stirring during synthesis, leading to a clear and transparent suspension. The anisotropic growth of nanorods is likely due to the complex dynamic binding of OAm and OA onto certain crystal facets of MAPbI₃ during crystal growth, similar to other capping agents used in the literature. (31, 37-39) However, the detailed role of OA and OAm during crystal growth remains elusive and will be investigated in future.

The synthesis resulted in a mixture of MAPbI₃ nanorods (∼68%), nanoplatelets (∼22%), and cuboids (∼10%), as is also visible in the scanning electron micrograph in Figure 1a. The bulk X-ray diffraction (XRD) pattern, shown in the upper panel of Figure 1b, matches that of the MAPbI₃ film prepared by conventional thermal annealing (the lower panel of Figure 1b), confirming the crystalline nature of MAPbI₃ nanocrystals. The average dimensions of the nanorods are 160 ± 80 nm in length, 35 ± 20 nm in width, and 32 ± 12 nm in thickness [deduced from SEM and atomic force microscopy (AFM) measurements], well below the diffraction limit. Although their physical dimensions are broadly distributed, these nanocrystals show little variation in their PL emission peak wavelengths (763 ± 2 nm). However, we do notice that the individual nanorods have a narrower full-width at half-maximum (FWHM) of ∼40 nm (Figure 2d) in comparison with the PL spectrum of a bulk sample shown in Figure 1c inset (∼60 nm).

Figure 1. (a) Scanning electron micrograph of the synthesized perovskite nanocrystals. (b) XRD patterns of solution-processed perovskite nanocrystals and a thermal-annealed polycrystalline perovskite film. (c) Time-resolved PL decay histogram measured on an individual perovskite nanorod (red curve) and thermal-annealed polycrystalline perovskite films (cyan curve) under 485 nm pulsed excitation with an average power density of 80 mW/cm². The repetition rate was 100 kHz. The instrumental response function (IRF) is shown in black (FWHM ≈ 0.4 ns). The red decay curve can be fitted with three exponential decay components of 665.5 ns (10%), 143.4 ns (51%), and 22.2 ns (39%). The cyan decay curve can be fitted with three exponential decay components of 65.3 ns (4%), 13.5 ns (31%), and 2.2 ns (65%). The inset shows the emission spectrum of bulk perovskite nanocrystals (FWHM ≈ 60 nm).

Figure 2. (a) Scanning electron micrograph of an individual perovskite nanorod, 140 nm in length and 40 nm in width. (b) PL image of the same perovskite nanorod. (c) Plot of the localization events by applying 2D Gaussian fitting. (d) PL spectrum of the same perovskite nanorod. The red curve is a Lorentzian fitting. (e–i) PL time traces (normalized intensities) and the corresponding intensity histograms (in percentage) of the same perovskite nanorod under different excitation power densities, that is, 1, 10, 40, 160, and 630 mW/cm².

Remarkably, the individual MAPbI₃ nanorods showed PL lifetimes that are about 1 order of magnitude longer than those observed on the polycrystalline MAPbI₃ films under identical experimental conditions (a 100 kHz repetition rate and an excitation power density of 80 mW/cm²). Figure 1c shows the PL decay histogram of an individual nanorod (the red curve) and that of a polycrystalline film prepared by the conventional thermal-annealing method (the cyan curve). Both decay curves were fitted with a triple-exponential function. (40, 41) The individual nanorod reveals characteristic decay times of 665.5, 143.4, and 22.2 ns. The polycrystalline film sample that we measured for comparison showed characteristic decay times of 65.3, 13.5, and 2.2 ns. The longer PL lifetimes observed on the individual nanorods are inherently related to an improved crystallinity associated with the reduced defect density and longer charge diffusion lengths. (10, 13, 30, 42) Moreover, it is noteworthy that the PL lifetimes of individual nanorods differ from each other, likely due to variations in defect densities in each nanocrystal. On average, individual MAPbI₃ nanorods showed characteristic PL decay times of 485 ± 270, 127 ± 79, and 23 ± 13 ns.

PL of Individual MAPbI₃ Nanorods under Ambient Conditions

Figure 2 shows the PL of an individual nanorod under continuous-wave (CW) laser illumination. The nanorod in Figure 2a is 150 nm in length and 40 nm in width. The PL intensity image of the nanorod, given in Figure 2b, closely resembles a 2D Gaussian PSF, with a slight elongation along the longitudinal axis of the nanorod. The observed elongation is due to the fact that the nanorod (150 nm in length) is comparable in size with the diffraction-limited in our experiments (∼180 nm). Therefore, the nanorod cannot be treated as an ideal point emitter. Nevertheless, 2D Gaussian is still a reasonable approximation of the PSF in this case. In particular, the localization fitting will yield widths that are sensitive to changes in the shape of the PSF and emission center positions that are sensitive to changes in quenching or emission sites. Applying a 2D Gaussian fitting on the observed emission patterns for localizing the center of mass of the emission over 10 000 frames resulted in a spread of localizations within a 10 nm radius around the geometrical center of the nanorod (Figure 2c). Even though PL blinking was observed on the nanorod (Figure 2e–i), the localization position and widths of Gaussian fittings did not show apparent changes throughout the entire measurement, regardless of the PL intensity changes during blinking (Figure S1), suggesting little changes in the nanorod PSF during PL blinking. Such observations from super-resolution localization microscopy are in contrast to the report by Tian et al., (7) where super-resolution localization microscopy revealed changes in the positions of the localization centers alongside PL blinking in most of the studied nanostructures. The difference in observations could be related to the presence of multiple crystal grains within a diffraction-limited area in nanostructures prepared by the conventional film preparation method in the work of Tian et al. (7) This point will be further demonstrated and discussed in a later section, Super-Resolution Localization Microscopy on Individual Nanorods and Nanorod Clusters (vide infra), and is also shown in Figures S1–S3.

Next, we look into the temporal evolutions in the PL intensity of the same single-crystal nanorod. The nanorod was not exposed to laser light or electron beam irradiation before optical measurements. The nanorod PL was first measured under a low laser excitation power density of 1 mW/cm², which is approximately one-hundredth of the typical solar power density at the earth’s surface. Because of the large absorption coefficient of MAPbI₃, the light penetration depth is constrained so that surface-related phenomena dominate the experimental observations at this low excitation power density. PL blinking observed at a very low light excitation power readily implies that the surface defects or traps play an important role. The laser excitation power density was then gradually increased to 10, 40, 160, and 630 mW/cm². At each excitation power density, the PL of the nanorod was recorded for a fixed duration of 500 s, with a frame integration time of 50 ms. The corresponding normalized PL intensity time traces are given in Figure 2e–i, respectively. PL blinking was observed on this nanorod under all excitation power densities. However, the PL intensity levels, intensity histograms, blinking frequencies, and OFF-time durations at these different illumination power densities vary largely. Under a low excitation power density of 1 mW/cm², the PL blinking between two steady intensity levels (ON and OFF) is clearly distinguishable in both the intensity time trace and the intensity histogram in Figure 2e. It is worth noticing that the nanorod does not become completely nonemissive in its OFF state. In many cases, the OFF-state intensity is less than one-fifth of that of the ON state (Figures 2 and S1).

Surprisingly, the often-reported “light soaking” or “photo-brightening” that describes a significant increase in PL intensity upon light illumination (7, 40, 43) was not observed in this experiment on individual nanorods. The “photo-brightening” phenomenon reported in the literature is often related to the high density of traps in perovskites prepared by the conventional method and their passivation by a yet-unclear photo-induced mechanism. (7, 43, 44) Therefore, the rare observation of “photo-brightening” on single-crystalline OHP nanocrystals, which was also noticed by Zhu et al., (31) is most likely a consequence of inherently lower trap densities in the MAPbI₃ nanorods, which is also evident from the long PL lifetimes (Figure 1c).

Upon increasing the laser excitation power density, we noticed significant changes in the ON state of the PL intensity time traces (Figure 2f–i). Intermediate PL blinking levels that differ from the previously observed ON/OFF states started to appear in the intensity histograms (Figure 2f–h). The fluctuation in the ON-state intensity occurred in a continuous fashion, which is different than the single-step PL blinking. Moreover, it started to appear only when elevated excitation powers were applied but not at the lowest excitation power density of 1 mW/cm² (Figure 2e). Therefore, the changes in the ON-state intensity are likely due to the photo-induced process and of different origin than PL blinking. Photo-degradation, on the other hand, is unlikely because of the low laser excitation power densities applied in these experiments; the applied power densities here are two orders of magnitude lower than those reported to cause distinct photo-degradation (tens of W/cm²) within the measurement duration of hundreds of seconds. (15, 45) Moreover, photo-induced changes in the ON-state intensity of PL blinking were mostly observed under ambient conditions, in the presence of air, but were rarely observed in vacuum. These observations indicate that the presence of oxygen and water vapor in air plays an important role, likely related to the photochemical reactions at the perovskite crystal surface. (40, 46-49) A detailed discussion on this point can be found in a later section, where PL blinking under different environmental conditions is reported (Figure 6).

Super-Resolution Localization Microscopy on Individual Nanorods and Nanorod Clusters

Super-resolution localization results on individual nanorods and clusters of nanorods are compared in Figure 3. Figure 3a shows a PL image of two MAPbI₃ nanostructures, whose morphology can be seen in Figure 3d. The two PL emitting structures are an individual nanorod (420 nm in length and 60 nm in width) and a nanorod cluster (about 500 nm in dimension). Both nanostructures showed symmetric PSFs that are larger than the diffraction limit due to their large dimensions. Applying Gaussian approximation on their PSFs, localization results are illustrated in Figure 3b,c, respectively. The individual nanorods showed a single localization position at the center of the nanorod, even though the nanorod length clearly exceeded the diffraction limit (∼180 nm). The widths of the Gaussian fitting (∼250 nm) at the ON state were almost constant throughout the entire measurement (Figure S2), which indicates an almost static PSF of the ON state during the nanorod PL blinking. The PL image acquired by averaging several frames during the OFF state (Figure S1c) showed an almost identical PSF as that of the ON state. Furthermore, localization fitting on the same nanorod at different PL blinking states yielded overlaid emission center position (Figure S1). The dim PL intensities of the OFF events lead to less accurate position determination and thus broader distributions. Nevertheless, localization positions at the OFF events spread closely around the localization center position of the ON state (Figure S1f). These observations indicated that the entire rod, up to several hundred nanometers in length, blinks as one whole structure. Generally, it agrees with the earlier reports. (7, 50) However, contrary to those studies, we did not observe clear shifts of the emission localization positions accompanied by PL intensity fluctuations. At the moment, we speculate that the observed differences may be related to our different sample preparation methods.

Figure 3. (a) PL image of two bright spots. The spot on the left side is because of the PL emission from an individual perovskite nanorod. The spot on the right side comes from a random cluster of several perovskite nanorods. The corresponding scanning electron micrograph on the same sample area is given in (d). The color bar shows the PL intensity in the unit of counts per frame (50 ms). The excitation power density was 16 mW/cm². (b and c) Plots of super-resolution localization events over the two bright spots in (a). The color bars represent the numbers of localization events. (e and f) scanning electron micrographs of the two nanostructures that correspond to (b) and (c), respectively. Solid lines in orange and in green colors outline the two nanostructures, respectively.

In contrast, localization on the cluster of a few nanorods revealed an elongated shape in the histogram plot (Figure 3c). Not only were multiple blinking intensity levels observed for the cluster, the Gaussian fittings also varied in width over time (Figure S2). This indicates changes in PSFs that are most likely due to stochastic blinking of each nanorod within the cluster. Therefore, the elongation in the localization found in the cluster is thus due to mixed PSFs of the closely located blinking nanorods.

Power-Law Distributions of the ON and OFF Times

Figure 4 shows statistics of the ON and OFF times of blinking events recorded on 14 individual nanorods. Time traces of each nanorod were recorded for 500 s at each excitation power density. The PL blinking OFF time and ON time histograms of the individual MAPbI₃ nanorods showed clear power-law distributions as illustrated in Figure 4a,b. Power-law emission intermittency, which has been generally observed on single-quantum emitters, (51-58) can be expressed by the formula p(t_OFF/ON) ∝ t^α, that is, the probability of ON or OFF times p(t_OFF/ON) is proportional to the time interval t with an exponent α. As demonstrated in Figure 4a,b, the power-law exponent (α) of both ON time and OFF time is independent of the applied laser excitation power density. The ON- and OFF-time distributions can be well simulated by the power-law exponent α = −1.6 and −1.9, respectively. To the best of our knowledge, the power-law blinking behavior of individual MAPbI₃ nanorods is revealed for the first time. The revealed power-law distributions of the ON and OFF times are direct evidence for the presence of trapping and detrapping processes. (43, 59)

Figure 4. (a) Probability distributions of ON times under different laser excitation power densities. The red solid line shows a power-law profile with the power parameter α = −1.6. (b) Probability distributions of OFF times under different laser excitation power densities. The red solid line shows a power-law profile with the power parameter α = −1.9. (c) The OFF-time PL blinking histogram of 14 individual perovskite nanorods resembles the power law. Different excitation power densities were examined, that is, 1 mW/cm² (blue triangles), 16 mW/cm² (green dots), and 160 mW/cm² (orange squares).

Both the total number of OFF events and duration of OFF times were found to decrease when the laser excitation power density was increased, as can be recognized from the OFF-time histograms in Figure 4a. Although this effect as such has been reported and suggested to occur because of trap filling, (7) a quantitative assessment as presented here has been missing. Red solid lines, as guide for the eye, highlight the shift of histograms toward fewer occurrences and shorter OFF times upon higher excitation power densities. When the power density was increased from 1 to 160 mW/cm², the total number of OFF events reduced by a factor of 2; the average OFF time decreased from 1.16 to 0.76 s; and the longest OFF time reduced from 93.8 to 14 s. In addition, PL blinking became very rare when increasing the excitation power density above 2 W/cm².

Correlation between PL Decay Time and Intensity of Individual Nanorods

PL decay times were found to correlate with PL intensity during PL blinking of individual nanorods, as shown in Figure 5. Figure 5a displays an intensity time trace (red) of an individual nanorod and the corresponding average photon arrival times (blue), with a bin time of 1 s. Average photon arrival times were found to shorten when the PL intensity dropped. The ON state yielded average photon arrival times around 300 ns, whereas the OFF state yielded them around 283 ns. The scatter plot of the average photon arrival times within 1 s time bins versus the PL intensity is shown in Figure 5b. A correlation between the PL intensity and average arrival times can be clearly observed. The normalized PL decay curves of ON and OFF states are given in Figure 5c. At the low excitation power density employed here, we did not find changes in the PL decay times to be correlated with ON/OFF states as a function of time nor any correlation between OFF-state decay times and OFF times.

Figure 5. (a) Time traces of PL intensity (red) and average arrival times measured on an individual OHP nanorod. (b) Correlation scattered plot of average arrival times versus PL intensities. Dashed cycles are used to highlight the ON and OFF states. (c) PL decay time histograms of ON and OFF states.

The shortened average PL decay time found at the OFF states indicates the presence of rapid nonradiative pathways. One commonly reported mechanism is Auger recombination, which is often found in the PL blinking of semiconductor quantum dots (60) and inorganic perovskite quantum dots. (58) The Auger recombination pathways in the charged states of these systems facilitate rapid nonradiative decay, resulting in prominently faster decay in the OFF state connected to PL blinking. (58, 60, 61) However, PL blinking here showed only minor shortening in PL decay in conjunction with the OFF state (Figure 5c), in contrast to what is expected for Auger recombination. Nevertheless, it is difficult to exclude the presence of Auger recombination. It is noteworthy that the OFF states found during PL blinking were not completely dark, which may indicate that the traps affect only a part of the nanocrystals. If this is the case, the Auger recombination can be overwhelmed by the emission that is not affected by the traps. This point requires further investigation.

On the other hand, PL blinking linked to mechanisms other than Auger recombination, (60, 62, 63) resulting only in minor changes in PL decay, has also been reported and attributed to “electron-accepting surface sites” (60) or charge carrier traps that are associated with the surface of quantum dots where coordination of ions is incomplete. (61, 62) Therefore, the observation of minor changes of PL decay alongside OHP nanorods PL blinking in this study is likely related to surface defects or surface charge trap sites, similar to their semiconductor quantum dot counterparts. If this is the case, it can be expected that the environment that surrounds the crystal can have an important impact on the PL blinking behavior.

PL of MAPbI₃ Nanorods in Different Atmospheres

PL blinking of nanorods is strongly dependent on the atmosphere, namely, vacuum, nitrogen, and air. Typical PL time traces of MAPbI₃ nanorods at different conditions are illustrated in Figure 6a–c, respectively, in vacuum (10^–6 mbar), in nitrogen atmosphere (1 bar), and in air (1 bar, approximately 30% humidity).

Figure 6. PL blinking time traces and histograms of perovskite nanorods under different environments, that is, under vacuum (a), in nitrogen under the ambient pressure (b), and in air under the ambient pressure (c). The same excitation power density of 16 mW/cm² was applied. The inset shows the scanning electron micrograph of the cluster of three perovskite nanorods. The red lines are guide for the eye, generated using vbFRET package. (64)

We next look into the effect of environment on the PL intensity of the same nanorod cluster. A cluster of three nanorods of similar dimensions can be identified in the scanning electron micrograph (inset of Figure 6a). The three nanorods are outlined with dashed lines. The PL intensity of this nanorod cluster was enhanced by more than 3 times by transferring it from vacuum (∼600 counts per frame) to ambient conditions (∼2800 counts per frame), as previously reported. (15) Applying state-recognizing analysis, (64) four PL intensity levels can be found in Figure 6a,b, representing the ON/OFF blinking states of the cluster in vacuum and in nitrogen. The number of levels identified corresponds well with the presence of three nanorods, each with an independent ON/OFF state. However, five intensity levels were recognized by applying the same algorithm on the same cluster in ambient atmosphere. Note that the continuous intensity fluctuations are significantly larger than the measurement noise. These intensity fluctuations in the ON-state PL are highlighted with red arrows in Figure 6c. Such fluctuations in the ON state were found on both individual nanorods (Figure 2g,h) and small clusters but only under relatively high laser excitation power densities in air. Therefore, we propose that the continuous PL intensity fluctuations of the ON state come from surface reactions involving oxygen (40, 46) and/or water molecules. (48, 49) Moreover, the reactions are likely enhanced by photo-generated charges and photo-induced ion mobility in the MAPbI₃ nanocrystals, (13) leading to an apparent excitation power dependence.

PL blinking of the same cluster behaved markedly differently in the various tested environments (vacuum, nitrogen, and air) without shifts in the emission spectrum. Blinking was found to be short-lived and most frequent in nitrogen, whereas blinking of the nanorods in air and in vacuum is less frequent. Among the three environmental conditions, vacuum resulted in the longest OFF states. In vacuum, 18 transition events between ON and OFF states among four intensity levels can be recognized within 120 s (Figure 6a). In air, the cluster showed 27 transition events in the same time window (Figure 6c). By contrast, 62 transition events were observed for the same cluster in nitrogen, which is about three times more frequent than that in vacuum or air. However, the duration of blinking OFF states in nitrogen was at most several seconds or less, which is much shorter than that observed in vacuum (tens of seconds on average) and in air (up to 10 s). The distinctly different PL blinking behaviors of the same cluster in the three different environmental conditions lead to apparent differences in the PL intensity histograms in Figure 6. The extreme sensitivity of PL blinking to the environmental conditions suggests the charge traps to be located at or close to the crystal surface. Interestingly, we also found a small fraction of nanorods whose PL blinking was less sensitive to environmental conditions. This observation implies the existence of charge traps inside of the nanocrystals as well, but with a much lower possibility. This observation supports a very recent report on trap densities on the surface of single OHP crystals that are two orders of magnitude higher than those in bulk. (65) Hence, the traps that induce PL blinking of single-crystal MAPbI₃ are more likely at or close to the crystal surface.

Discussion on the Possible Nature of Charge Traps

In summary, the key findings on PL blinking of perovskite nanorods are listed as follows.

(1)	PL “photo-brightening” under light illumination is rarely observed on the as-synthesized MAPbI₃ nanorods.
(2)	ON/OFF PL blinking was observed on the individual MAPbI₃ nanorods under low-power laser excitation.
(3)	Large fluctuations in the PL ON-state intensity and multiple intensity levels appear at elevated excitation power densities under ambient conditions without leading to severe structural damage.
(4)	Power-law ON-/OFF-time statistics suggest trapping and detrapping processes in PL blinking of individual nanorods.
(5)	PL blinking of most nanorods strongly depends on their surrounding atmosphere, indicating their sensitivity to the surface charge traps. A small fraction of the nanorods show less environmental dependence on their PL blinking, suggesting the presence of trapping sites inside of the crystals.

Like other ionic materials, under-coordinated ions and vacancies may be present in single OHP crystals. On the basis of the formation mechanism, such as light-induced/charge-driven (17) or surface reactions, (66) under-coordinated ions and vacancies can be located at different positions, either inside of the crystal or on the crystal surface. Because of the low activation energies, ionic species including methylammonium ions, iodine ions, and their vacancies can be mobile in the crystal, driven by light, (17, 67-69) and influence the PL properties. (13, 15, 16)

The surface traps that result in PL blinking of the single-crystal MAPbI₃ nanorods are most likely related to under-coordinated lead ions and ion vacancies. A recent study has revealed spectral shifts alongside iodine redistribution in MAPbI₃, (16) which indicates a high density of iodine ions in the iodine-rich regions and a high density of iodine vacancies in the iodine-poor regions. The differences in the local iodine contents are strongly correlated with the local PL emission spectra. (16) However, spectral shifts were found to be absent during MAPbI₃ PL blinking in this work. Moreover, photo-induced iodine migration has very recently been probed using time-of-flight secondary-ion mass spectrometry and correlated with photo-brightening without PL blinking. (13) Therefore, iodine ions/vacancies are unlikely to be responsible for PL blinking in the MAPbI₃ nanorods. On the other hand, Yuan et al. recently reported on instant quenching in MAPbI₃ PL by a focused electron beam. (15) Taking into account the organic nature of methylammonium and its low boiling point, local removal of methylammonium is a logical consequence of applying a focused electron beam on the perovskite surface, resulting in high densities of methylammonium vacancies and under-coordinated lead ions. The instant drop in PL upon applying a scanning electron beam on MAPbI₃ supports this assumption. (15)

Moreover, chemical surface passivation of under-coordinated lead ions has been found to enhance MAPbI₃ PL in several recent studies. (6, 66) Therefore, besides dedicated passivation agents, surface reactions of perovskite crystals with oxygen and water have also been reported to result in passivation of under-coordinated lead ions by the formation of lead oxide and hydroxide species, (66) leading to improved PL. Such passivation by surface binding involving oxygen and water may be a contributing factor for the reported “photo-brightening” and enhancement of MAPbI₃ PL in air. (40, 50)

The observed power-law behavior of the PL blinking ON and OFF times, in observation (4), suggests trapping and detrapping processes. In the following, we address each of our key observations one by one by proposing under-coordinated lead ions and methylammonium vacancies as possible charge traps responsible for PL blinking in MAPbI₃ nanorods. In this study, the excess amounts of methylammonium iodide during the synthesis and the good crystallinity of the resulting nanorods are believed to reduce the amount of under-coordinated lead ions. Under a very low laser excitation, PL blinking reflects the charge traps formed during crystal growth. Because under-coordinated lead ions are expected to be rare in the synthesized crystals in this study, the often-reported phenomenon of “photo-brightening” by passivation of under-coordinated lead ions with oxygen or water will be eliminated, as noticed in observation (1). However, PL blinking can still be observed even at a low density of under-coordinated lead ions. Because of the exceptional charge diffusion lengths up to several microns in OHP crystals, (10, 42) a single charge trap may control the PL blinking of a nanosized crystal. (7, 43) Therefore, PL blinking can take place even at very low charge trap densities in single-crystalline OHP nanorods, leading to observation (2).

The strong environmental dependence of PL blinking outlined in observations (3) and (5) can be related to the differences in charge trap formation probabilities because the detrapping rates in different atmospheres are different. Furthermore, charge trap formation rates are different for nanorods in different environmental conditions. Because of the low boiling points of methylammonium, detachment can be promoted by a vacuum. (70) Moreover, water vapor in air promotes the removal of methylammonium from a perovskite surface. (49, 71) Therefore, both environmental conditions of vacuum and air can easily result in methylammonium vacancies and under-coordinated lead ions on the crystal surface, leading to higher charge trap formation probabilities than in an inert atmosphere. In contrast, charge trap formation in an inert nitrogen atmosphere relies only on the thermal detachment of methylammonium from the surface. Hence, the trap formation probability in nitrogen is expected to be the lowest among the three environmental conditions. On the other hand, detrapping rates can differ in different atmospheres. In vacuum and in nitrogen, detrapping most likely involves mobile ions in the crystal driven by light. In air, extra detrapping pathways by surface reactions with oxygen or water may be present. PL blinking of a nanorod is therefore controlled by trap-formation rates and detrapping rates.

It is noteworthy that the OFF state of PL blinking may not necessarily correspond to a single trap because of the ability of a single charge trap to quench the PL of an entire nanocrystal. Therefore, multiple traps could result in a long-lived OFF state, and this cannot be identified based on the intensity in this experiment. Assuming the same detrapping rates for MAPbI₃ nanorods in vacuum and in nitrogen, the very long OFF times observed in vacuum can be understood through the higher possibility to form multiple traps. By contrast, short-lived OFF events found on MAPbI₃ nanorods in nitrogen, where the trap formation rate is the lowest, are likely due to single traps, resulting in similar detrapping time (OFF time). PL blinking of nanorods in air is, however, more complex as a result of the interplay between detrapping processes by mobile ions and surface reactions, leading to broadly distributed OFF times ranging from tens of seconds to hundreds of milliseconds. However, to verify this point, further investigation is necessary.

The fluctuations in the ON-state intensity levels in air under relatively high excitation power densities found in observation (3) are most likely due to surface photochemical reactions of MAPbI₃ with oxygen and water. Because it occurs only at relatively high laser excitation power, such surface chemical reactions are likely promoted by light or light-generated charges. (72) This could also contribute to the absence of PL blinking at the high laser excitation power density above 2 W/cm². The promoted surface chemical reactions by strong laser excitation result in rapid passivation of vacancies and under-coordinated lead ions, resulting in blocking possible trapping sites.

In summary, the experimental observations presented in this work yielded strong evidence for the following: (i) charge traps that cause PL blinking of MAPbI₃ nanorods, likely methylammonium vacancies and under-coordinated lead ions; (ii) the environmental conditions surrounding the MAPbI₃ nanorods affect the PL blinking behavior of OHP nanorods by influencing trap formation rates and detrapping rates on the crystal surface; (iii) a single charge trap on the surface of an MAPbI₃ nanorod can dictate the PL blinking of the entire crystal; (iv) the OFF state during PL blinking may result from one or multiple charge traps; (iv) the light-promoted surface chemical reactions of MAPbI₃ with oxygen and water may lead to large variations in the ON-state PL intensity and may be responsible for the lack of PL blinking at high excitation power densities.

Conclusions

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In conclusion, we demonstrated a novel approach for the synthesis of highly crystalline MAPbI₃ nanorods and performed a systematic investigation on the PL blinking of individual MAPbI₃ nanorods. We revealed two-level PL blinking of individual nanorods under low laser excitation power densities. Moreover, super-resolution localization study on these blinking nanorods shows single perovskite nanorods (several hundred nanometers) to blink and to emit as a whole, demonstrating the ability of charge traps to dominate PL emission in a single nanorod of several hundred nanometers in length, which is qualitatively in agreement with the earlier observations. (7) Furthermore, PL blinking of nanorods showed strong light illumination power dependence as well as environmental dependence that are related to charge trapping and detrapping processes, evident from the power-law behavior of the experimentally recorded ON/OFF times shown here for the first time. PL lifetime measurements suggest processes other than Auger recombination to contribute to the blinking of nanorods. On the basis of the PL blinking observations on MAPbI₃ nanorods in these experiments, the charge traps that are likely related to the under-coordinated lead ions and methylammonium vacancies on the crystal surface are proposed to cause the PL blinking observed here. Nevertheless, a deeper understanding on the nature of traps and the detrapping process requires further experimental and theoretical investigations.

Experimental Section

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Materials

All the chemicals were used as received from Sigma-Aldrich, including lead(II) iodide (99%), hydriodic acid (57 wt % in water), methylamine (33 wt % in absolute ethanol), OA, OAm (70%, technical grade), acetonitrile, γ-butyrolactone, diethyl ether, ethanol for spectroscopy, absolute ethanol, and toluene.

Preparation of Methylammonium Iodide (CH₃NH₃I)

Methylammonium iodide was synthesized by a typical procedure. (7) Methylamine (27.8 mL) and hydriodic acid (30 mL) were reacted in a 150 mL round-bottom flask at 0 °C for 2 h under stirring. The precipitate was recovered by using a rotary evaporator by removing the solvents at 50 °C. The obtained product was redissolved in 80 mL of ethanol, recrystallized by the addition of 300 mL of diethyl ether twice, and finally dissolved with absolute ethanol. Methylammonium iodide was then collected by drying at 60 °C in a vacuum oven for 24 h.

Polycrystalline Perovskite Crystals

Methylammonium iodide (92 mg) and 32 mg lead(II) iodide were dissolved in 2 mL of γ-butyrolactone at 60 °C. A perovskite film sample was prepared by spin-coating the 60 °C solution onto a glass cover slide, with a speed of 1500 rpm for 60 s. Right after spin-coating, the sample was heated at 70 °C for 10 min. The sample was then subjected to optical experiments right after preparation.

Synthesis of Perovskite Nanorods

Solution A: 2.8 μL of OAm and 5.2 μL of OA were dissolved in 5 mL of toluene. Solution B: 9.2 mg lead iodide and 9.2 mg methylammonium iodide were dissolved in 10 mL acetonitrile. Magnetic stirring (600 rpm) was applied throughout the entire synthesis. Solution B (1.3 mL) was injected into Solution A. The solution turned red in color, indicating the formation of OHP crystals of very small sizes. After 30 s, 7 mL of toluene was added to the mixed solution dropwise, after which the solution was kept under stirring in the dark for 4 h. The dark brownish suspension was then washed and redispersed in 4 mL toluene two times by centrifuging at 3000 rpm for 30 min. The final suspension was maintained in the dark.

XRD

XRD measurements on the prepared perovskite materials were carried out on a STOE STADI P COMBI instrument equipped with an imaging plate (IP position sensitive detector) as the detector. The diffraction was measured using Cu Kα₁ radiation in transmission mode with a focusing Ge(111) monochromator.

AFM

A Smart-1000 AFM (AIST-NT) was used for AFM measurements under ambient conditions in tapping mode with a Si tip (cantilever length, 140 μm; resonant frequency, 200–400 kHz; spring constant, 25–95 N/m) at a scanning rate of 0.5 Hz and a sample line of 1024.

Integrated Optical and Electron Microscope (iLEM)

The iLEM system consists of an FEI Quanta FEG-250 environmental scanning electron microscope, equipped with a modified door assembly provided by Delmic BV, the Netherlands. This door features an optically transparent window which enables the transmission of excitation and emission light and holds both an EM-CCD camera (Image-EM X2, Hamamatsu) and optomechanics. Additionally, the original SEM stage is replaced by one that is capable of holding a high-numerical-aperture oil-immersion objective lens (Plan Apo VC 100×, NA 1.4, Nikon), which enables high-resolution imaging in combination with vacuum-compatible immersion oil. The ILEM instrument is further equipped with a laser illumination system featuring six distinct continuous-wave laser sources (405, 445, 488, 532, 561, and 642 nm, LightHub, Omicron). The 532 nm output is employed as the excitation source in this study. A compact spectrometer (USB4000, Ocean Optics) is used for spectral measurements. Super-resolution localization fitting was applied using a set of home-developed Matlab code. A detailed description can be found in previous reports. (73, 74) PL time traces shown in Figure 2 were normalized by the initial ON-state intensity after background subtraction. Half the ON-state intensity was used as the threshold to determine the ON/OFF times.

Confocal Optical Microscope for Time-Resolved Measurements

The confocal microscopy results were obtained on an inverted optical microscope (Olympus IX71) equipped with a set of galvo scanning mirrors (Yanus IV, Till Photonics, Chromaphor). A pulsed 485 nm laser (PicoQuant, LDH-D-C-485) was used as the excitation source. Laser repetition rates of 100 kHz or 1 MHz were applied. Circular polarization at the sample was achieved by a set of half-wavelength (λ/2) and quarter-wavelength (λ/4) waveplates. An oil-immersion objective lens from Olympus which has a numerical aperture of 1.4 and 100× magnification was used. Time-resolved single-photon counting (TCSPC) data were acquired with fiber-coupled avalanche photon diodes and a HydraHarp 400 system (PicoQuant).

Sample Preparation

For SEM characterization, 5 μL of OHP nanorod suspension was drop-casted onto a 5 mm × 5 mm silicon chip and was dried in a fume hood. For AFM measurements, 100 μL was dropped onto a clean glass cover slide for about 60 s and was then dried by a nitrogen flow. For optical measurements, 100 μL of OHP nanorod toluene suspension was dropped onto a clean glass cover slide and was spin-casted at 1500 rpm for 60 s. For correlative SEM measurements after optical experiments, the sample was coated with a thin gold film using a JOEL auto fine film coater.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.6b00107.

PL intensity correlated super-resolution localization mapping on a single-crystal MAPbI₃ nanorod, Gaussian fitting widths time evolution during PL blinking of a single-crystal nanorod and a cluster of several nanorods, super-resolution localization mapping on polycrystalline deposits, and PL decays of nanorods and polycrystalline films (PDF)

ao6b00107_si_001.pdf (671.31 kb)

Terms & Conditions

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Author Information

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Corresponding Authors
- Haifeng Yuan - Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium; Email: [email protected]
- Maarten B. J. Roeffaers - Centre for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium; Email: [email protected]
Authors
- Elke Debroye - Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
- Giorgio Caliandro - Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
- Kris P. F. Janssen - Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
- Jordi van Loon - Centre for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium
- Christine E. A. Kirschhock - Centre for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium
- Johan A. Martens - Centre for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium
- Johan Hofkens - Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium; RIES, Hokkaido University, N20W10, Kita-Ward, Sapporo 001-0020, Japan
Notes
The authors declare no competing financial interest.

Acknowledgment

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We thank Prof. Ivan Scheblykin and his co-workers as well as Dr. Rafael Camacho for stimulating discussions. We thank Marike Wolberg for assistance with the XRD measurements. We acknowledge financial support from the Research Foundation-Flanders (FWO, grant G.0197.11, G.0962.13, G0B39.15, postdoctoral fellowship to H.Y., E.D., and K.P.F.J.), KU Leuven Research Fund (OT/12/059 and C14/15/053), the Flemish government through long-term structural funding Methusalem (CASAS², Meth/15/04), the Hercules foundation (HER/11/14), the Belgian Federal Science Policy Office (IAP-PH05), the EC through the Marie Curie ITN project iSwitch (GA-642196), and the ERC projects LIGHT (GA-307523).

References

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This article references 74 other publications.

1
Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange Science 2015, 348, 1234– 1237 DOI: 10.1126/science.aaa9272
Google Scholar
1
High-performance photovoltaic perovskite layers fabricated through intramolecular exchange
Yang, Woon Seok; Noh, Jun Hong; Jeon, Nam Joong; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
Science (Washington, DC, United States) (2015), 348 (6240), 1234-1237CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). An approach is reported for depositing high-quality FAPbI3 films, involving FAPbI3 crystn. by the direct intramol. exchange of dimethylsulfoxide (DMSO) mols. intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallog. orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepd. by this technique, the FAPbI3-based PSCs are fabricated with max. power conversion efficiency greater than 20%.
2
Saliba, M.; Orlandi, S.; Matsui, T.; Aghazada, S.; Cavazzini, M.; Correa-Baena, J.-P.; Gao, P.; Scopelliti, R.; Mosconi, E.; Dahmen, K.-H.; De Angelis, F.; Abate, A.; Hagfeldt, A.; Pozzi, G.; Graetzel, M.; Nazeeruddin, M. K. A molecularly engineered hole-transporting material for efficient perovskite solar cells Nat. Energy 2016, 1, 15017 DOI: 10.1038/nenergy.2015.17
Google Scholar
2
A molecularly engineered hole-transporting material for efficient perovskite solar cells
Saliba, Michael; Orlandi, Simonetta; Matsui, Taisuke; Aghazada, Sadig; Cavazzini, Marco; Correa-Baena, Juan-Pablo; Gao, Peng; Scopelliti, Rosario; Mosconi, Edoardo; Dahmen, Klaus-Hermann; De Angelis, Filippo; Abate, Antonio; Hagfeldt, Anders; Pozzi, Gianluca; Graetzel, Michael; Nazeeruddin, Mohammad Khaja
Nature Energy (2016), 1 (2), 15017CODEN: NEANFD; ISSN:2058-7546. (Nature Publishing Group)
Soln.-processable perovskite solar cells have recently achieved certified power conversion efficiencies of over 20%, challenging the long-standing perception that high efficiencies must come at high costs. One major bottleneck for increasing the efficiency even further is the lack of suitable hole-transporting materials, which ext. pos. charges from the active light absorber and transmit them to the electrode. In this work, we present a molecularly engineered hole-transport material with a simple dissym. fluorene-dithiophene (FDT) core substituted by N,N-di-p-methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for a family of potentially low-cost hole-transport materials. We use FDT on state-of-the-art devices and achieve power conversion efficiencies of 20.2% which compare favorably with control devices with 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). Thus, this new hole transporter has the potential to replace spiro-OMeTAD.
3
Park, N. G. Perovskite solar cells: an emerging photovoltaic technology Mater. Today 2015, 18, 65– 72 DOI: 10.1016/j.mattod.2014.07.007
Google Scholar
3
Perovskite solar cells: an emerging photovoltaic technology
Park, Nam-Gyu
Materials Today (Oxford, United Kingdom) (2015), 18 (2), 65-72CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
A review. Perovskite solar cells based on organometal halides represent an emerging photovoltaic technol. Perovskite solar cells stem from dye-sensitized solar cells. In a liq.-based dye-sensitized solar cell structure, the adsorption of methylammonium lead halide perovskite on a nanocryst. TiO2 surface produces a photocurrent with a power conversion efficiency (PCE) of around 3-4%, as first discovered in 2009. The PCE was doubled after 2 years by optimizing the perovskite coating conditions. However, the liq.-based perovskite solar cell receives little attention because of its stability issues, including instant dissoln. of the perovskite in a liq. electrolyte. A long-term, stable, and high efficiency (∼10%) perovskite solar cell was developed in 2012 by substituting the solid hole conductor with a liq. electrolyte. Efficiencies have quickly risen to 18% in just 2 years. Since PCE values over 20% are realistically anticipated with the use of cheap organometal halide perovskite materials, perovskite solar cells are a promising photovoltaic technol. In this review, the opto-electronic properties of perovskite materials and recent progresses in perovskite solar cells are described. In addn., comments on the issues to current and future challenges are mentioned.
4
Yusoff, A. R. b. M.; Nazeeruddin, M. K. Organohalide lead perovskites for photovoltaic applications J. Phys. Chem. Lett. 2016, 7, 851– 866 DOI: 10.1021/acs.jpclett.5b02893
Google Scholar
4
Organohalide Lead Perovskites for Photovoltaic Applications
Yusoff, Abd. Rashid bin Mohd; Nazeeruddin, Mohammad Khaja
Journal of Physical Chemistry Letters (2016), 7 (5), 851-866CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Perovskite solar cells have recently exhibited a significant leap in efficiency due to their broad absorption, high optical absorption coeff., very low exciton binding energy, long carrier diffusion lengths, efficient charge collection, and very high open-circuit potential, similar to that of III-IV semiconductors. Unlike silicon solar cells, perovskite solar cells can be developed from a variety of low-temp. solns. processed from inexpensive raw materials. When the perovskite absorber film formation is optimized using solvent engineering, a power conversion efficiency of over 21% has been demonstrated, highlighting the unique photovoltaic properties of perovskite materials. Here, we review the current progress in perovskite solar cells and charge transport materials. We highlight crucial challenges and provide a summary and prospects.
5
Sharenko, A.; Toney, M. F. Relationships between lead halide perovskite thin-film fabrication, morphology, and performance in solar cells J. Am. Chem. Soc. 2016, 138, 463– 470 DOI: 10.1021/jacs.5b10723
Google Scholar
5
Relationships between Lead Halide Perovskite Thin-Film Fabrication, Morphology, and Performance in Solar Cells
Sharenko, Alexander; Toney, Michael F.
Journal of the American Chemical Society (2016), 138 (2), 463-470CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A review. Soln.-processed lead halide perovskite thin-film solar cells have achieved power conversion efficiencies comparable to those obtained with several com. photovoltaic technologies in a remarkably short period of time. This rapid rise in device efficiency is largely the result of the development of fabrication protocols capable of producing continuous, smooth perovskite films with micrometer-sized grains. Further developments in film fabrication and morphol. control are necessary, however, in order for perovskite solar cells to reliably and reproducibly approach their thermodn. efficiency limit. This Perspective discusses the fabrication of lead halide perovskite thin films, while highlighting the processing-property-performance relationships that have emerged from the literature, and from this knowledge, suggests future research directions.
6
deQuilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Impact of microstructure on local carrier lifetime in perovskite solar cells Science 2015, 348, 683– 686 DOI: 10.1126/science.aaa5333
Google Scholar
6
Solar cells. Impact of microstructure on local carrier lifetime in perovskite solar cells
deQuilettes Dane W; Vorpahl Sarah M; Nagaoka Hirokazu; Ziffer Mark E; Ginger David S; Stranks Samuel D; Eperon Giles E; Snaith Henry J
Science (New York, N.Y.) (2015), 348 (6235), 683-6 ISSN:.
The remarkable performance of hybrid perovskite photovoltaics is attributed to their long carrier lifetimes and high photoluminescence (PL) efficiencies. High-quality films are associated with slower PL decays, and it has been claimed that grain boundaries have a negligible impact on performance. We used confocal fluorescence microscopy correlated with scanning electron microscopy to spatially resolve the PL decay dynamics from films of nonstoichiometric organic-inorganic perovskites, CH3NH3PbI3(Cl). The PL intensities and lifetimes varied between different grains in the same film, even for films that exhibited long bulk lifetimes. The grain boundaries were dimmer and exhibited faster nonradiative decay. Energy-dispersive x-ray spectroscopy showed a positive correlation between chlorine concentration and regions of brighter PL, whereas PL imaging revealed that chemical treatment with pyridine could activate previously dark grains.
7
Tian, Y.; Merdasa, A.; Peter, M.; Abdellah, M.; Zheng, K.; Ponseca, C. S.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Giant photoluminescence blinking of perovskite nanocrystals reveals single-trap control of luminescence Nano Lett. 2015, 15, 1603– 1608 DOI: 10.1021/nl5041397
Google Scholar
7
Giant Photoluminescence Blinking of Perovskite Nanocrystals Reveals Single-Trap Control of Luminescence
Tian, Yuxi; Merdasa, Aboma; Peter, Maximilian; Abdellah, Mohamed; Zheng, Kaibo; Ponseca, Carlito S.; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
Nano Letters (2015), 15 (3), 1603-1608CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Fluorescence super-resoln. microscopy showed correlated fluctuations of luminescence intensity and spatial localization of individual perovskite (MeNH3PbI3) nanocrystals of size ∼200 × 30 × 30 nm3. The luminescence blinking amplitude caused by a single quencher was a hundred thousand times larger than that of a typical dye mol. at the same excitation power d. The quencher probably is a chem. or structural defect that traps free charges leading to nonradiative recombination. These trapping sites can be activated and deactivated by light.
8
Li, Y.; Yan, W.; Li, Y.; Wang, S.; Wang, W.; Bian, Z.; Xiao, L.; Gong, Q. Direct observation of long electron-hole diffusion distance in CH₃NH₃PbI₃ perovskite thin film Sci. Rep. 2015, 5, 14485 DOI: 10.1038/srep14485
Google Scholar
8
Direct Observation of Long Electron-Hole Diffusion Distance in CH3NH3PbI3 Perovskite Thin Film
Li, Yu; Yan, Weibo; Li, Yunlong; Wang, Shufeng; Wang, Wei; Bian, Zuqiang; Xiao, Lixin; Gong, Qihuang
Scientific Reports (2015), 5 (), 14485CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
In high performance perovskite based solar cells, CH3NH3PbI3 is the key material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. By coating the film with an electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid Me ester (PCBM) or 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) resp., we obsd. the charge transfer directly through the fluorescence quenching. One-dimensional diffusion model was applied to obtain long charge diffusion distances in thick films, which is ∼1.7 μm for electrons and up to ∼6.3 μm for holes. Short diffusion distance of few hundreds of nanosecond was also obsd. in thin films. This thickness dependent charge diffusion explained the formerly reported short charge diffusion distance (∼100 nm) in films and resolved its confliction to thick working layer (300-500 nm) in real devices. This study presents direct support to the high performance perovskite solar cells and will benefit the devices' design.
9
Tian, W.; Zhao, C.; Leng, J.; Cui, R.; Jin, S. Visualizing carrier diffusion in individual single-crystal organolead halide perovskite nanowires and nanoplates J. Am. Chem. Soc. 2015, 137, 12458– 12461 DOI: 10.1021/jacs.5b08045
Google Scholar
9
Visualizing Carrier Diffusion in Individual Single-Crystal Organolead Halide Perovskite Nanowires and Nanoplates
Tian, Wenming; Zhao, Chunyi; Leng, Jing; Cui, Rongrong; Jin, Shengye
Journal of the American Chemical Society (2015), 137 (39), 12458-12461CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Single-crystal MeNH3PbX3 (X = I-, Cl-, Br-) perovskite nanowires (NWs) and nanoplates (NPs), which demonstrate ultracompact sizes and exceptional photophys. properties, offer promises for applications in nanoscale photonics and optoelectronics. However, traditional electronic and transient techniques are limited by the dimensions of the samples, and characterizations of the carrier behavior (diffusion coeff., charge mobility and diffusion length) in these NWs and NPs are extremely difficult. Herein, the authors report the direct visualization of the carrier diffusion process in individual single-crystal MeNH3PbI3 and MeNH3PbBr3 NWs and NPs using time-resolved and photoluminescence-scanned imaging microscopy. The authors report the diffusion coeff. (charge motility), which varies significantly between different NWs and NPs, ranging from 1.59 to 2.41 cm2 s-1 (56.4 to 93.9 cm2 V-1 s-1) for MeNH3PbI3 and 0.50 to 1.44 cm2 s-1 (19.4 to 56.1 cm2 V-1 s-1) for MeNH3PbBr3 and find this variation is independent of the shape and size of the sample. The av. diffusion length is 14.0 ± 5.1 μm for MeNH3PbI3 and 6.0 ± 1.6 μm for MeNH3PbBr3. These results provide information that is essential for the practical applications of the single-crystal perovskite NWs and NPs, and the imaging microscopy may also be applicable to other optoelectronic materials.
10
Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber Science 2013, 342, 341– 344 DOI: 10.1126/science.1243982
Google Scholar
10
Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber
Stranks, Samuel D.; Eperon, Giles E.; Grancini, Giulia; Menelaou, Christopher; Alcocer, Marcelo J. P.; Leijtens, Tomas; Herz, Laura M.; Petrozza, Annamaria; Snaith, Henry J.
Science (Washington, DC, United States) (2013), 342 (6156), 341-344CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
Org.-inorg. perovskites showed promise as high-performance absorbers in solar cells, 1st as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, the authors report transient absorption and photoluminescence-quenching measurements to det. the electron-hole diffusion lengths, diffusion consts., and lifetimes in mixed halide (MeNH3PbI3-xClx) and triiodide (MeNH3PbI3) perovskite absorbers. The diffusion lengths are >1 μm in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. But the triiodide absorber has electron-hole diffusion lengths of about 100 nm. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a crit. parameter to optimize for future perovskite absorber development.
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Christians, J. A.; Manser, J. S.; Kamat, P. V. Multifaceted excited state of CH₃NH₃PbI₃. Charge separation, recombination, and trapping J. Phys. Chem. Lett. 2015, 6, 2086– 2095 DOI: 10.1021/acs.jpclett.5b00594
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Multifaceted Excited State of CH3NH3PbI3. Charge Separation, Recombination, and Trapping
Christians, Jeffrey A.; Manser, Joseph S.; Kamat, Prashant V.
Journal of Physical Chemistry Letters (2015), 6 (11), 2086-2095CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
A review. A need to understand the excited-state behavior of org.-inorg. hybrid perovskites, such as CH3NH3PbI3, has arisen due to the rapid development of perovskite solar cells. The photoinduced processes leading to the efficient charge sepn. obsd. in these materials remain somewhat elusive. This Perspective presents an overview of the initial attempts to characterize the excited-state and charge recombination dynamics in the prototypical material CH3NH3PbI3. While much has been accomplished in designing high-efficiency solar cells, the multifaceted nature of the CH3NH3PbI3 excited state offers ample challenges for the photovoltaic community to better comprehend. Building on this foundation may enable us to tackle the stability concerns that have shadowed the rise of perovskite solar cells. Furthermore, a better understanding of the excited-state properties can provide insight into the specific properties that have thrust this material to the forefront of photovoltaic research.
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Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination kinetics in organic–inorganic perovskites: excitons, free charge, and subgap states Phys. Rev. Appl. 2014, 2, 034007 DOI: 10.1103/physrevapplied.2.034007
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Recombination kinetics in organic-inorganic perovskites: excitons, free charge, and subgap states
Stranks, Samuel D.; Burlakov, Victor M.; Leijtens, Tomas; Ball, James M.; Goriely, Alain; Snaith, Henry J.
Physical Review Applied (2014), 2 (3), 034007CODEN: PRAHB2; ISSN:2331-7019. (American Physical Society)
Org.-inorg. perovskites are attracting increasing attention for their use in high-performance solar cells. Nevertheless, a detailed understanding of charge generation, interplay of excitons and free charge carriers, and recombination pathways, crucial for further device improvement, remains incomplete. Here, we present an anal. model describing both equil. properties of free charge carriers and excitons in the presence of electronic subgap trap states and their time evolution after photoexcitation in CH3NH3PbI3-xClx. At low fluences the charge-trapping pathways limit the photoluminescence quantum efficiency, whereas at high fluences the traps are predominantly filled and recombination of the photogenerated species is dominated by efficient radiative processes. We show exptl. that the photoluminescence quantum efficiency approaches 100% at low temps. and at high fluences, as predicted by our model. Our approach provides a theor. framework to understand the fundamental physics of perovskite semiconductors and to help in designing and enhancing the material for improved optoelectronic device operation.
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deQuilettes, D. W.; Zhang, W.; Burlakov, V. M.; Graham, D. J.; Leijtens, T.; Osherov, A.; Bulović, V.; Snaith, H. J.; Ginger, D. S.; Stranks, S. D. Photo-induced halide redistribution in organic–inorganic perovskite films Nat. Commun. 2016, 7, 11683 DOI: 10.1038/ncomms11683
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Photo-induced halide redistribution in organic-inorganic perovskite films
deQuilettes Dane W; Ginger David S; Zhang Wei; Burlakov Victor M; Leijtens Tomas; Snaith Henry J; Burlakov Victor M; Graham Daniel J; Osherov Anna; Bulovic Vladimir; Stranks Samuel D; Stranks Samuel D
Nature communications (2016), 7 (), 11683 ISSN:.
Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.
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Bischak, C. G.; Sanehira, E. M.; Precht, J. T.; Luther, J. M.; Ginsberg, N. S. Heterogeneous charge carrier dynamics in organic–inorganic hybrid materials: nanoscale lateral and depth-dependent variation of recombination rates in methylammonium lead halide perovskite thin films Nano Lett. 2015, 15, 4799– 4807 DOI: 10.1021/acs.nanolett.5b01917
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Heterogeneous Charge Carrier Dynamics in Organic-Inorganic Hybrid Materials: Nanoscale Lateral and Depth-Dependent Variation of Recombination Rates in Methylammonium Lead Halide Perovskite Thin Films
Bischak, Connor G.; Sanehira, Erin M.; Precht, Jake T.; Luther, Joseph M.; Ginsberg, Naomi S.
Nano Letters (2015), 15 (7), 4799-4807CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
The authors reveal substantial luminescence yield heterogeneity among individual subdiffraction grains of high-performing methylammonium lead halide perovskite films by using high-resoln. cathodoluminescence microscopy. Using considerably lower accelerating voltages than is conventional in SEM, the authors image the electron beam-induced luminescence of the films and statistically characterize the depth-dependent role of defects that promote nonradiative recombination losses. The highest variability in the luminescence intensity is obsd. at the exposed grain surfaces, which the authors attribute to surface defects. By probing deeper into the film, it appears that bulk defects are more homogeneously distributed. By identifying the origin and variability of a surface-specific loss mechanism that deleteriously impacts device efficiency, probably producing films homogeneously composed of the highest-luminescence grains found in this study could result in a dramatic improvement of overall device efficiency. Also although cathodoluminescence microscopy is generally used only to image inorg. materials it can be a powerful tool to study radiative and nonradiative charge carrier recombination on the nanoscale in org.-inorg. hybrid materials.
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Yuan, H.; Debroye, E.; Janssen, K.; Naiki, H.; Steuwe, C.; Lu, G.; Moris, M.; Orgiu, E.; Uji-i, H.; De Schryver, F.; Samorì, P.; Hofkens, J.; Roeffaers, M. Degradation of methylammonium lead iodide perovskite structures through light and electron beam driven ion migration J. Phys. Chem. Lett. 2016, 7, 561– 566 DOI: 10.1021/acs.jpclett.5b02828
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Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration
Yuan, Haifeng; Debroye, Elke; Janssen, Kris; Naiki, Hiroyuki; Steuwe, Christian; Lu, Gang; Moris, Michele; Orgiu, Emanuele; Uji-i, Hiroshi; De Schryver, Frans; Samori, Paolo; Hofkens, Johan; Roeffaers, Maarten
Journal of Physical Chemistry Letters (2016), 7 (3), 561-566CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degrdn. pathways. Here, the authors apply simultaneous luminescence and electron microscopy on perovskites for the 1st time, allowing the authors to monitor in situ morphol. evolution and optical properties upon perovskite degrdn. Morphol., photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degrdn. driven by electron beam (e-beam) or by light. A transversal elec. current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degrdn. results in material decompn. to scattered particles and shows little PL spectral shifts. The differences in degrdn. can be ascribed to different elec. currents that drive ion migration. Also, soln.-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphol. The authors' results reveal the essential role of ion migration in perovskite degrdn. and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphol. and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degrdn. and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using SEM or TEM techniques.
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Hentz, O.; Zhao, Z.; Gradečak, S. Impacts of ion segregation on local optical properties in mixed halide perovskite films Nano Lett. 2016, 16, 1485– 1490 DOI: 10.1021/acs.nanolett.5b05181
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Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films
Hentz, Olivia; Zhao, Zhibo; Gradecak, Silvija
Nano Letters (2016), 16 (2), 1485-1490CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Despite the recent astronomical success of org.-inorg. perovskite solar cells (PSCs), the impact of microscale film inhomogeneities on device performance remains poorly understood. In this work, we study CH3NH3PbI3 perovskite films using cathodoluminescence in scanning transmission electron microscopy and show that localized regions with increased cathodoluminescence intensity correspond to iodide-enriched regions. These observations constitute direct evidence that nanoscale stoichiometric variations produce corresponding inhomogeneities in film cathodoluminescence intensity. Moreover, we observe the emergence of high-energy transitions attributed to beam induced iodide segregation, which may mirror the effects of ion migration during PSC operation. Our results demonstrate that such ion segregation can fundamentally change the local optical and microstructural properties of org.-inorg. perovskite films in the course of normal device operation and therefore address the obsd. complex and unpredictable behavior in PSC devices.
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Meloni, S.; Moehl, T.; Tress, W.; Franckevičius, M.; Saliba, M.; Lee, Y. H.; Gao, P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Rothlisberger, U.; Graetzel, M. Ionic polarization-induced current–voltage hysteresis in CH₃NH₃PbX₃ perovskite solar cells Nat. Commun. 2016, 7, 10334 DOI: 10.1038/ncomms10334
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Ionic polarization-induced current-voltage hysteresis in CH3NH3PbX3 perovskite solar cells
Meloni, Simone; Moehl, Thomas; Tress, Wolfgang; Franckevicius, Marius; Saliba, Michael; Lee, Yong Hui; Gao, Peng; Nazeeruddin, Mohammad Khaja; Zakeeruddin, Shaik Mohammed; Rothlisberger, Ursula; Graetzel, Michael
Nature Communications (2016), 7 (), 10334CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
CH3NH3PbX3 (MAPbX3) perovskites have attracted considerable attention as absorber materials for solar light harvesting, reaching solar to power conversion efficiencies above 20%. In spite of the rapid evolution of the efficiencies, the understanding of basic properties of these semiconductors is still ongoing. One phenomenon with so far unclear origin is the so-called hysteresis in the current-voltage characteristics of these solar cells. Here we investigate the origin of this phenomenon with a combined exptl. and computational approach. Exptl. the activation energy for the hysteretic process is detd. and compared with the computational results. First-principles simulations show that the timescale for MA+ rotation excludes a MA-related ferroelec. effect as possible origin for the obsd. hysteresis. On the other hand, the computationally detd. activation energies for halide ion (vacancy) migration are in excellent agreement with the exptl. detd. values, suggesting that the migration of this species causes the obsd. hysteretic behavior of these solar cells.
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Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.; Huang, J. Giant switchable photovoltaic effect in organometal trihalide perovskite devices Nat. Mater. 2014, 14, 193– 198 DOI: 10.1038/nmat4150
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Draguta, S.; Thakur, S.; Morozov, Y. V.; Wang, Y.; Manser, J. S.; Kamat, P. V.; Kuno, M. Spatially non-uniform trap state densities in solution-processed hybrid perovskite thin films J. Phys. Chem. Lett. 2016, 7, 715– 721 DOI: 10.1021/acs.jpclett.5b02888
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Spatially Non-uniform Trap State Densities in Solution-Processed Hybrid Perovskite Thin Films
Draguta, Sergiu; Thakur, Siddharatha; Morozov, Yurii V.; Wang, Yuanxing; Manser, Joseph S.; Kamat, Prashant V.; Kuno, Masaru
Journal of Physical Chemistry Letters (2016), 7 (4), 715-721CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
The facile soln.-processability of methylammonium Pb iodide (MeNH3PbI3) perovskites has catalyzed the development of inexpensive, hybrid perovskite-based optoelectronics. Apparently, soln.-processed MeNH3PbI3 films possess local emission heterogeneities, stemming from electronic disorder in the material. The spatially resolved emission properties of MeNH3PbI3 films were studied through detailed emission intensity vs. excitation intensity measurements. These studies enable establishing the existence of nonuniform trap d. variations wherein regions of MeNH3PbI3 films exhibit effective free carrier recombination while others exhibit emission dynamics strongly influenced by the presence of trap states. Such trap d. variations lead to spatially varying emission quantum yields and correspondingly impact the performance of both methylammonium Pb halide perovskite solar cells and other hybrid perovskite-based devices. The obsd. spatial extent of the optical disorder extends over length scales greater than that of underlying cryst. domains, suggesting the existence of other factors, beyond grain boundary-related nonradiative recombination channels, which lead to significant intrafilm optical heterogeneities.
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Klein, J. R.; Flender, O.; Scholz, M.; Oum, K.; Lenzer, T. Charge carrier dynamics of methylammonium lead iodide: from PbI₂-rich to low-dimensional broadly emitting perovskites Phys. Chem. Chem. Phys. 2016, 18, 10800– 10808 DOI: 10.1039/C5CP07167D
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Charge carrier dynamics of methylammonium lead iodide: from PbI2-rich to low-dimensional broadly emitting perovskites
Klein, Johannes R.; Flender, Oliver; Scholz, Mirko; Oum, Kawon; Lenzer, Thomas
Physical Chemistry Chemical Physics (2016), 18 (16), 10800-10808CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
The authors provide a study of the charge carrier dynamics of the (MAI)x(PbI2)1-x system in the range x = 0.32-0.90 following the recently published pseudobinary phase-compn. processing diagram of Song et al. (Chem. Mater., 2015, 27, 4612). The dynamics were studied using ultrafast pump-supercontinuum probe spectroscopy over the pump fluence range 2-50 μJ cm-2, allowing for a wide variation of the initial carrier d. At high MAI excess (x = 0.90), low-dimensional perovskites (LDPs) are formed, and their luminescence spectra are significantly blue-shifted by ∼50 nm and broadened compared to the 3-dimensional perovskite. The shift is due to quantum confinement effects, and the inhomogeneous broadening arises from different low-dimensional structures (predominantly 2-dimensional, but presumably also 1-dimensional and 0D). Accurate transient carrier temps. are extd. from the transient absorption spectra. The regimes of carrier-carrier, carrier-optical phonon and acoustic phonon scattering are clearly distinguished. Perovskites with mole fractions x ≤ 0.71 exhibit extremely fast carrier cooling (∼300 fs) at low fluence of 2 μJ cm-2, however cooling slows down significantly at high fluence of 50 μJ cm-2 due to the hot phonon effect (∼2.8 ps). A kinetic anal. of the electron-hole recombination dynamics provides 2nd-order recombination rate consts. k2 which decrease from 5.3 to 1.5 × 10-9 cm3 s-1 in the range x = 0.32-0.71. In contrast, recombination in the LDPs (x = 0.90) is more than one order of magnitude faster, 6.4 × 10-8 cm3 s-1, which is related to the confined perovskite structure. Recombination in these LDPs should be however still slow enough for their potential application as efficient broadband emitters or solar light-harvesting materials.
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Liu, M.; Johnston, M. B.; Snaith, H. J. Efficient planar heterojunction perovskite solar cells by vapour deposition Nature 2013, 501, 395– 398 DOI: 10.1038/nature12509
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Efficient planar heterojunction perovskite solar cells by vapour deposition
Liu, Mingzhen; Johnston, Michael B.; Snaith, Henry J.
Nature (London, United Kingdom) (2013), 501 (7467), 395-398CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based 1st-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between 2 charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport pos. and neg. charges in spatially sepd. phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapor-deposited perovskite as the absorbing layer can have solar-to-elec. power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). Perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.
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Kutes, Y.; Zhou, Y.; Bosse, J. L.; Steffes, J.; Padture, N. P.; Huey, B. D. Mapping the photoresponse of CH₃NH₃PbI₃ hybrid perovskite thin films at the nanoscale Nano Lett. 2016, 16, 3434– 3441 DOI: 10.1021/acs.nanolett.5b04157
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Mapping the Photoresponse of CH3NH3PbI3 Hybrid Perovskite Thin Films at the Nanoscale
Kutes, Yasemin; Zhou, Yuanyuan; Bosse, James L.; Steffes, James; Padture, Nitin P.; Huey, Bryan D.
Nano Letters (2016), 16 (6), 3434-3441CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Perovskite solar cells (PSCs) based on thin films of organolead trihalide perovskites (OTPs) hold unprecedented promise for low-cost, high-efficiency photovoltaics (PVs) of the future. While PV performance parameters of PSCs, such as short circuit current, open circuit voltage, and max. power, are always measured at the macroscopic scale, it is necessary to probe such photoresponses at the nanoscale to gain key insights into the fundamental PV mechanisms and their localized dependence on the OTP thin-film microstructure. Here we use photoconductive at. force microscopy spectroscopy to map for the first time variations of PV performance at the nanoscale for planar PSCs based on hole-transport-layer free methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) thin films. These results reveal substantial variations in the photoresponse that correlate with thin-film microstructural features such as intragrain planar defects, grains, grain boundaries, and notably also grain-aggregates. The insights gained into such microstructure-localized PV mechanisms are essential for guiding microstructural tailoring of OTP films for improved PV performance in future PSCs.
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Li, C.; Tscheuschner, S.; Paulus, F.; Hopkinson, P. E.; Kießling, J.; Köhler, A.; Vaynzof, Y.; Huettner, S. Iodine migration and its effect on hysteresis in perovskite solar cells Adv. Mater. 2016, 28, 2446– 2454 DOI: 10.1002/adma.201503832
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Iodine Migration and its Effect on Hysteresis in Perovskite Solar Cells
Li, Cheng; Tscheuschner, Steffen; Paulus, Fabian; Hopkinson, Paul E.; Kiessling, Johannes; Koehler, Anna; Vaynzof, Yana; Huettner, Sven
Advanced Materials (Weinheim, Germany) (2016), 28 (12), 2446-2454CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
In brief, we used three different methods to reveal the underlying processes relating to hysteresis. First we employed electroabsorption(EA) spectroscopy, a noninvasive in situ characterization approach to det. the built-in potential ( VBI) in solar cell devices. In a second expt. we applied a staircase voltage pro le to these devices and measured the time dependent current at a series of temps. in order to study the activation energy of the migrating species in perovskite based devices. In the last expt. we used X-ray photoemission spectroscopy (XPS) measurements to study the redistribution of elements within laterally configured devices after long-term elec. biasing. Our results suggest that the hysteresis in J-V curves originates from the interfacial barrier assocd. with the drift of iodide ions or the resp. interstitial under an elec. field.
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Yun, J. S.; Ho-Baillie, A.; Huang, S.; Woo, S. H.; Heo, Y.; Seidel, J.; Huang, F.; Cheng, Y.-B.; Green, M. A. Benefit of grain boundaries in organic–inorganic halide planar perovskite solar cells J. Phys. Chem. Lett. 2015, 6, 875– 880 DOI: 10.1021/acs.jpclett.5b00182
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Benefit of grain boundaries in org.-inorg. halide planar perovskite solar cells
Yun, Jae S.; Ho-Baillie, Anita; Huang, Shujuan; Woo, Sang H.; Heo, Yooun; Seidel, Jan; Huang, Fuzhi; Cheng, Yi-Bing; Green, Martin A.
Journal of Physical Chemistry Letters (2015), 6 (5), 875-880CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
The past 2 years have seen the uniquely rapid emergence of a new class of solar cell based on mixed org.-inorg. halide perovskite. Grain boundaries are present in polycryst. thin film solar cell, and they play an important role that could be benign or detrimental to solar-cell performance. Here we present efficient charge sepn. and collection at the grain boundaries measured by KPFM and c-AFM in CH3NH3PbI3 film in a CH3NH3PbI3/TiO2/FTO/glass heterojunction structure. We observe the presence of a potential barrier along the grain boundaries under dark conditions and higher photovoltage along the grain boundaries compare to grain interior under the illumination. Also, c-AFM measurement presents higher short-circuit current collection near grain boundaries, confirming the beneficial roles grain boundaries play in collecting carriers efficiently.
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Shao, Y.; Fang, Y.; Li, T.; Wang, Q.; Dong, Q.; Deng, Y.; Yuan, Y.; Wei, H.; Wang, M.; Gruverman, A.; Shield, J.; Huang, J. Grain boundary dominated ion migration in polycrystalline organic–inorganic halide perovskite films Energy Environ. Sci. 2016, 9, 1752– 1759 DOI: 10.1039/C6EE00413J
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Grain boundary dominated ion migration in polycrystalline organic-inorganic halide perovskite films
Shao, Yuchuan; Fang, Yanjun; Li, Tao; Wang, Qi; Dong, Qingfeng; Deng, Yehao; Yuan, Yongbo; Wei, Haotong; Wang, Meiyu; Gruverman, Alexei; Shield, Jeffery; Huang, Jinsong
Energy & Environmental Science (2016), 9 (5), 1752-1759CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
The efficiency of perovskite solar cells is approaching that of single-cryst. silicon solar cells despite the presence of a large grain boundary (GB) area in the polycryst. thin films. Here, by using a combination of nanoscopic and macroscopic level measurements, we show that ion migration in polycryst. perovskites dominates through GBs. Atomic force microscopy measurements reveal much stronger hysteresis both for photocurrent and dark-current at the GBs than on the grain interiors, which can be explained by faster ion migration at the GBs. The dramatically enhanced ion migration results in the redistribution of ions along the GBs after elec. poling, in contrast to the intact grain area. The perovskite single-crystal devices without GBs show negligible current hysteresis and no ion-migration signal. The discovery of dominating ion migration through GBs in perovskites can lead to broad applications in many types of devices including photovoltaics, memristors, and ion batteries.
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González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Organometal halide perovskites: bulk low-dimension materials and nanoparticles Part. Part. Syst. Charact. 2015, 32, 709– 720 DOI: 10.1002/ppsc.201400214
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Organometal Halide Perovskites: Bulk Low-Dimension Materials and Nanoparticles
Gonzalez-Carrero, Soranyel; Galian, Raquel E.; Perez-Prieto, Julia
Particle & Particle Systems Characterization (2015), 32 (7), 709-720CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
Organometal halide perovskites (hybrid perovskites) contain an anionic metal-halogen-semiconducting framework and charge-compensating org. cations. As hybrid materials, they combine useful properties of both org. and inorg. materials, such as plastic mech. properties and good electronic mobility related to org. and inorg. material, resp. They are prepd. from abundant and low cost starting compds. The perovskite stoichiometry is assocd. with the dimensionality of its inorg. framework, which can vary from three to zero, 3D consisting of corner-sharing MX6 octahedra, and 0D consisting of isolated octahedra. Small-sized org. cations can fit into the MX6 octahedra of the 3D framework and in all dimensions org. cations surround the inorg. framework. Regarding the low dimensionality in the material, this refers to at least one of its dimensions being shorter than approx. 100 nm. These materials should be considered as genuine nanomaterials or as bulk materials depending on whether they have three or less than three dimensions on the nanoscale, resp. In principle, hybrid perovskite nanoparticles can be prepd. with different shapes and with inorg. framework dimensionalities varying from 0D to 3D, and this also applies to the bulk material. This report is mainly focused on the unique properties of organometal halide perovskite nanoparticles.
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González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Organic–inorganic and all-inorganic lead halide nanoparticles Opt. Express 2016, 24, A285– A301 DOI: 10.1364/oe.24.00a285
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Schmidt, L. C.; Pertegás, A.; González-Carrero, S.; Malinkiewicz, O.; Agouram, S.; Espallargas, G. M.; Bolink, H. J.; Galian, R. E.; Pérez-Prieto, J. Nontemplate synthesis of CH₃NH₃PbBr₃ perovskite nanoparticles J. Am. Chem. Soc. 2014, 136, 850– 853 DOI: 10.1021/ja4109209
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Nontemplate Synthesis of CH3NH3PbBr3 Perovskite Nanoparticles
Schmidt, Luciana C.; Pertegas, Antonio; Gonzalez-Carrero, Soranyel; Malinkiewicz, Olga; Agouram, Said; Minguez Espallargas, Guillermo; Bolink, Henk J.; Galian, Raquel E.; Perez-Prieto, Julia
Journal of the American Chemical Society (2014), 136 (3), 850-853CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
To date, there is no example in the literature of free, nm-sized, organo-Pb halide MeNH3PbBr3 perovskites. The prepn. is reported of 6 nm-sized nanoparticles of this type by a simple and fast method based on the use of an NH4Br with a medium-sized chain that keeps the nanoparticles dispersed in a wide range of org. solvents. These nanoparticles can be maintained stable in the solid state and in concd. solns. for >3 mo, without requiring a mesoporous material. This makes it possible to prep. homogeneous thin films of these nanoparticles by spin-coating on a SiO2 substrate. Both the colloidal soln. and the thin film emit light within a narrow bandwidth of the visible spectrum and with a high quantum yield (∼20%); this could be advantageous in the design of optoelectronic devices.
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Zhu, H.; Fu, Y.; Meng, F.; Wu, X.; Gong, Z.; Ding, Q.; Gustafsson, M. V.; Trinh, M. T.; Jin, S.; Zhu, X.-Y. Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors Nat. Mater. 2015, 14, 636– 642 DOI: 10.1038/nmat4271
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Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors
Zhu, Haiming; Fu, Yongping; Meng, Fei; Wu, Xiaoxi; Gong, Zizhou; Ding, Qi; Gustafsson, Martin V.; Trinh, M. Tuan; Jin, Song; Zhu, X.-Y.
Nature Materials (2015), 14 (6), 636-642CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same phys. properties that are ideal for semiconductor lasers. Here, we show room-temp. and wavelength-tunable lasing from single-crystal lead halide perovskite nanowires with very low lasing thresholds (220 nJ cm-2) and high quality factors (Q ∼ 3,600). The lasing threshold corresponds to a charge carrier d. as low as 1.5 × 1016 cm-3. Kinetic anal. based on time-resolved fluorescence reveals little charge carrier trapping in these single-crystal nanowires and gives estd. lasing quantum yields approaching 100%. Such lasing performance, coupled with the facile soln. growth of single-crystal nanowires and the broad stoichiometry-dependent tunability of emission color, makes lead halide perovskites ideal materials for the development of nanophotonics, in parallel with the rapid development in photovoltaics from the same materials.
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Fu, Y.; Meng, F.; Rowley, M. B.; Thompson, B. J.; Shearer, M. J.; Ma, D.; Hamers, R. J.; Wright, J. C.; Jin, S. Solution growth of single crystal methylammonium lead halide perovskite nanostructures for optoelectronic and photovoltaic applications J. Am. Chem. Soc. 2015, 137, 5810– 5818 DOI: 10.1021/jacs.5b02651
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Solution Growth of Single Crystal Methylammonium Lead Halide Perovskite Nanostructures for Optoelectronic and Photovoltaic Applications
Fu, Yongping; Meng, Fei; Rowley, Matthew B.; Thompson, Blaise J.; Shearer, Melinda J.; Ma, Dewei; Hamers, Robert J.; Wright, John C.; Jin, Song
Journal of the American Chemical Society (2015), 137 (17), 5810-5818CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Understanding crystal growth and improving material quality is important for improving semiconductors for electronic, optoelectronic, and photovoltaic applications. Amidst the surging interest in solar cells based on hybrid org.-inorg. lead halide perovskites and the exciting progress in device performance, improved understanding and better control of the crystal growth of these perovskites could further boost their optoelectronic and photovoltaic performance. Here, new insights are reported on the crystal growth of the perovskite materials, esp. cryst. nanostructures. Specifically, single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide perovskites (CH3NH3PbI3 and CH3NH3PbBr3) are successfully grown via a dissoln.-recrystn. pathway in a soln. synthesis from lead iodide (or lead acetate) films coated on substrates. These single crystal nanostructures display strong room-temp. photoluminescence and long carrier lifetime. It is also reported that a solid-liq. interfacial conversion reaction can create a highly cryst., nanostructured MAPbI3 film with micrometer grain size and high surface coverage that enables photovoltaic devices with a power conversion efficiency of 10.6%. These results suggest that single-crystal perovskite nanostructures provide improved photophys. properties that are important for fundamental studies and future applications in nanoscale optoelectronic and photonic devices.
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Zhu, F.; Men, L.; Guo, Y.; Zhu, Q.; Bhattacharjee, U.; Goodwin, P. M.; Petrich, J. W.; Smith, E. A.; Vela, J. Shape evolution and single particle luminescence of organometal halide perovskite nanocrystals ACS Nano 2015, 9, 2948– 2959 DOI: 10.1021/nn507020s
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Shape Evolution and Single Particle Luminescence of Organometal Halide Perovskite Nanocrystals
Zhu, Feng; Men, Long; Guo, Yijun; Zhu, Qiaochu; Bhattacharjee, Ujjal; Goodwin, Peter M.; Petrich, Jacob W.; Smith, Emily A.; Vela, Javier
ACS Nano (2015), 9 (3), 2948-2959CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Organometallic halide perovskites MeNH3PbX3 (X = I, Br, Cl) have quickly become 1 of the most promising semiconductors for solar cells, with photovoltaics made of these materials reaching power conversion efficiencies of ∼20%. Improving the ability to harness the full potential of organometal halide perovskites will require more controllable syntheses that permit a detailed understanding of their fundamental chem. and photophysics. MeNH3PbX3 (X = I, Br) nanocrystals with different morphols. (dots, rods, plates, or sheets) were systematically synthesized by using different solvents and capping ligands. MeNH3PbX3 nanowires and nanorods capped with octylammonium halides show relatively higher luminescence (PL) quantum yields and long PL lifetimes. MeNH3PbI3 nanowires monitored at the single particle level show shape-correlated PL emission across whole particles, with little photobleaching obsd. and very few off periods. This work highlights the potential of low-dimensional organometal halide perovskite semiconductors in constructing new porous and nanostructured solar cell architectures, as well as in applying these materials to other fields such as light-emitting devices and single particle imaging and tracking.
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Aharon, S.; Etgar, L. Two dimensional organometal halide perovskite nanorods with tunable optical properties Nano Lett. 2016, 16, 3230– 3235 DOI: 10.1021/acs.nanolett.6b00665
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Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties
Aharon, Sigalit; Etgar, Lioz
Nano Letters (2016), 16 (5), 3230-3235CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Facile low-temp. synthesis of 2-dimensional (2D) Pb halide perovskite nanorods (NRs) is presented. These NRs show a shift to higher energies in the absorbance and in the luminescence compared to the bulk material, which supports their 2D structure. XRD anal. of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. By alternating the halide compn., the authors were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, the authors were able to provide the formation mechanism of these novel 2D perovskite NRs.
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González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Maximizing the emissive properties of CH₃NH₃PbBr₃ perovskite nanoparticles J. Mater. Chem. A 2015, 3, 9187– 9193 DOI: 10.1039/c4ta05878j
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Maximizing the emissive properties of CH3NH3PbBr3 perovskite nanoparticles
Gonzalez-Carrero, Soranyel; Galian, Raquel E.; Perez-Prieto, Julia
Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (17), 9187-9193CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
Highly luminescent and photostable MeNH3PbBr3 nanoparticles were prepd. by fine-tuning the molar ratio between MeNH3Br, PbBr2, a medium-size alkyl-chain NH4+ salt, and 1-octadecene. The nanoparticles exhibit an excellent photoluminescence quantum yield (∼83%) and av. recombination lifetime (∼600 ns) in toluene dispersion.
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Huang, B.; Bates, M.; Zhuang, X. Super-resolution fluorescence microscopy Annu. Rev. Biochem. 2009, 78, 993– 1016 DOI: 10.1146/annurev.biochem.77.061906.092014
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Super-resolution fluorescence microscopy
Huang, Bo; Bates, Mark; Zhuang, Xiaowei
Annual Review of Biochemistry (2009), 78 (), 993-1016CODEN: ARBOAW; ISSN:0066-4154. (Annual Reviews Inc.)
A review. Achieving a spatial resoln. that is not limited by the diffraction of light, recent developments of super-resoln. fluorescence microscopy techniques allow the observation of many biol. structures not resolvable in conventional fluorescence microscopy. New advances in these techniques now give them the ability to image three-dimensional (3D) structures, measure interactions by multicolor colocalization, and record dynamic processes in living cells at the nanometer scale. It is anticipated that super-resoln. fluorescence microscopy will become a widely used tool for cell and tissue imaging to provide previously unobserved details of biol. structures and processes.
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Habuchi, S. Super-resolution molecular and functional imaging of nanoscale architectures in life and materials science Front. Bioeng. Biotechnol. 2014, 2, 20 DOI: 10.3389/fbioe.2014.00020
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Super-resolution molecular and functional imaging of nanoscale architectures in life and materials science
Habuchi Satoshi
Frontiers in bioengineering and biotechnology (2014), 2 (), 20 ISSN:.
Super-resolution (SR) fluorescence microscopy has been revolutionizing the way in which we investigate the structures, dynamics, and functions of a wide range of nanoscale systems. In this review, I describe the current state of various SR fluorescence microscopy techniques along with the latest developments of fluorophores and labeling for the SR microscopy. I discuss the applications of SR microscopy in the fields of life science and materials science with a special emphasis on quantitative molecular imaging and nanoscale functional imaging. These studies open new opportunities for unraveling the physical, chemical, and optical properties of a wide range of nanoscale architectures together with their nanostructures and will enable the development of new (bio-)nanotechnology.
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Neely, R. K.; Dedecker, P.; Hotta, J.-i.; Urbanavičiu̅tė, G.; Klimašauskas, S.; Hofkens, J. DNA fluorocode: a single molecule, optical map of DNA with nanometre resolution Chem. Sci. 2010, 1, 453– 460 DOI: 10.1039/c0sc00277a
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DNA fluorocode: A single molecule, optical map of DNA with nanometre resolution
Neely, Robert K.; Dedecker, Peter; Hotta, Jun-ichi; Urbanaviciute, Giedre; Klimasauskas, Saulius; Hofkens, Johan
Chemical Science (2010), 1 (4), 453-460CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
We present a new method for single-mol. optical DNA mapping using an exceptionally dense, yet sequence-specific coverage of DNA with a fluorescent probe. The method employs a DNA methyltransferase enzyme to direct the DNA labeling, followed by mol. combing of the DNA onto a polymer-coated surface and subsequent sub-diffraction limit localization of the fluorophores. The result is a 'DNA fluorocode'; a simple description of the DNA sequence, with a max. achievable resoln. of less than 20 bases, which can be read and analyzed like a barcode. We demonstrate the generation of a fluorocode for genomic DNA from the lambda bacteriophage using a DNA methyltransferase, M.HhaI, to direct fluorescent labels to four-base sequences reading 5'-GCGC-3'. A consensus fluorocode that allows the study of the DNA sequence at the level of an individual labeling site can be generated from a handful of mols.
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Chen, Y.; He, M.; Peng, J.; Sun, Y.; Liang, Z. Structure and growth control of organic–inorganic halide perovskites for optoelectronics: From polycrystalline films to single crystals Adv. Sci. 2016, 3, 1500392 DOI: 10.1002/advs.201500392
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Structure and Growth Control of Organic-Inorganic Halide Perovskites for Optoelectronics: From Polycrystalline Films to Single Crystals
Chen Yani; He Minhong; Peng Jiajun; Sun Yong; Liang Ziqi
Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2016), 3 (4), 1500392 ISSN:2198-3844.
Recently, organic-inorganic halide perovskites have sparked tremendous research interest because of their ground-breaking photovoltaic performance. The crystallization process and crystal shape of perovskites have striking impacts on their optoelectronic properties. Polycrystalline films and single crystals are two main forms of perovskites. Currently, perovskite thin films have been under intensive investigation while studies of perovskite single crystals are just in their infancy. This review article is concentrated upon the control of perovskite structures and growth, which are intimately correlated for improvements of not only solar cells but also light-emitting diodes, lasers, and photodetectors. We begin with the survey of the film formation process of perovskites including deposition methods and morphological optimization avenues. Strategies such as the use of additives, thermal annealing, solvent annealing, atmospheric control, and solvent engineering have been successfully employed to yield high-quality perovskite films. Next, we turn to summarize the shape evolution of perovskites single crystals from three-dimensional large sized single crystals, two-dimensional nanoplates, one-dimensional nanowires, to zero-dimensional quantum dots. Siginificant functions of perovskites single crystals are highlighted, which benefit fundamental studies of intrinsic photophysics. Then, the growth mechanisms of the previously mentioned perovskite crystals are unveiled. Lastly, perspectives for structure and growth control of perovskites are outlined towards high-performance (opto)electronic devices.
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De Roo, J.; Ibáñez, M.; Geiregat, P.; Nedelcu, G.; Walravens, W.; Maes, J.; Martins, J. C.; Van Driessche, I.; Kovalenko, M. V.; Hens, Z. Highly dynamic ligand binding and light absorption coefficient of cesium lead bromide perovskite nanocrystals ACS Nano 2016, 10, 2071– 2081 DOI: 10.1021/acsnano.5b06295
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Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals
De Roo, Jonathan; Ibanez, Maria; Geiregat, Pieter; Nedelcu, Georgian; Walravens, Willem; Maes, Jorick; Martins, Jose C.; Van Driessche, Isabel; Kovalenko, Maksym V.; Hens, Zeger
ACS Nano (2016), 10 (2), 2071-2081CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects of their chem. and photophysics such as surface chem. and quant. light absorption. Here, we elaborate on the synthesis of CsPbBr3 NCs and their surface chem. In addn., the intrinsic absorption coeff. was detd. exptl. by combining elemental anal. with accurate optical absorption measurements. 1H soln. NMR spectroscopy was used to characterize sample purity, elucidate the surface chem., and evaluate the influence of purifn. methods on the surface compn. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purifn. procedures. However, when a small amt. of both oleic acid and oleylamine is added, the NCs can be purified, maintaining optical, colloidal, and material integrity. In addn., we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid.
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Ma, Q.; Mimura, K. i.; Kato, K. Tuning shape of barium titanate nanocubes by combination of oleic acid/tert-butylamine through hydrothermal process J. Alloys Compd. 2016, 655, 71– 78 DOI: 10.1016/j.jallcom.2015.09.156
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Tuning shape of barium titanate nanocubes by combination of oleic acid/tert-butylamine through hydrothermal process
Ma, Qiang; Mimura, Ken-ichi; Kato, Kazumi
Journal of Alloys and Compounds (2016), 655 (), 71-78CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
The shape and surface morphol. of mono-dispersed barium titanate (BaTiO3) nanocrystals were controlled by tuning the compn. of hydrothermal reaction system. High-quality BaTiO3 nanocubes with the smooth surface and 90° std. corner angle were synthesized by the hydrothermal method using a relatively low concn. of oleic acid and tert-butylamine, which were used as surfactant and additive, resp. The av. size of BaTiO3 nanocubes was ∼25 nm and the size distribution was relatively narrow. As a large amt. of surfactant and additive was employed, BaTiO3 nanocrystals with convex structure were synthesized. The terrace structure were developed at the {100} surface of the nanocrystals. Here, we analyzed systematically the role of oleic acid and tert-butylamine on the surface morphol. of BaTiO3 nanocrystals. Our study demonstrates the possibility of synthesizing high-quality BaTiO3 nanocubes for com. application. These findings can be applied on other perovskite nanomaterials.
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Tian, Y.; Peter, M.; Unger, E.; Abdellah, M.; Zheng, K.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold Phys. Chem. Chem. Phys. 2015, 17, 24978– 24987 DOI: 10.1039/C5CP04410C
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Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold
Tian, Yuxi; Peter, Maximilian; Unger, Eva; Abdellah, Mohamed; Zheng, Kaibo; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
Physical Chemistry Chemical Physics (2015), 17 (38), 24978-24987CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
A light-induced luminescence (PL) enhancement in surface-deposited methylammonium lead iodide (MeNH3PbI3) perovskites was studied using time-resolved luminescence microscopy. The authors found the PL intensity to increase up to 3 orders of magnitude upon light illumination with an excitation power d. of 0.01-1 W cm-2. The PL enhancement is accompanied by an increase of the PL lifetime from several nanoseconds to several hundred nanoseconds and also by an increase of the initial amplitude of the PL decay. The latter suggests excited state quenching at the sub-ps timescale. A model is proposed where the trapping sites responsible for nonradiative charge recombination can be de-activated by a photochem. reaction involving O. The reaction zone is spatially limited by the excitation light-penetration depth and diffusion length of the charge carriers. The latter increases in the light-curing process making the reaction zone spreading from the surface towards the interior of the crystal. The PL enhancement can be reversed by switching on/off the excitation light or switching the atm. between O and N. Slow diffusion of the reactants and products and equil. between the active and cured trapping sites probably are the reasons for peculiar responses of PL to such varied exptl. conditions.
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Kim, B. J.; Kim, D. H.; Lee, Y.-Y.; Shin, H.-W.; Han, G. S.; Hong, J. S.; Mahmood, K.; Ahn, T. K.; Joo, Y.-C.; Hong, K. S.; Park, N.-G.; Lee, S.; Jung, H. S. Highly efficient and bending durable perovskite solar cells: toward a wearable power source Energy Environ. Sci. 2015, 8, 916– 921 DOI: 10.1039/C4EE02441A
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Highly efficient and bending durable perovskite solar cells: toward a wearable power source
Kim, Byeong Jo; Kim, Dong Hoe; Lee, Yoo-Yong; Shin, Hee-Won; Han, Gill Sang; Hong, Jung Sug; Mahmood, Khalid; Ahn, Tae Kyu; Joo, Young-Chang; Hong, Kug Sun; Park, Nam-Gyu; Lee, Sangwook; Jung, Hyun Suk
Energy & Environmental Science (2015), 8 (3), 916-921CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
Perovskite solar cells are promising candidates for realizing an efficient, flexible, and lightwt. energy supply system for wearable electronic devices. For flexible perovskite solar cells, achieving high power conversion efficiency (PCE) while using a low-temp. technol. for the fabrication of a compact charge collection layer is a crit. issue. Herein, we report on a flexible perovskite solar cell exhibiting 12.2% PCE as a result of the employment of an annealing-free, 20 nm thick, amorphous, compact TiOx layer deposited by at. layer deposition. The excellent performance of the cell was attributed to fast electron transport, verified by time-resolved photoluminescence and impedance studies. The PCE remained the same down to 0.4 sun illumination, as well as to a 45° tilt to incident light. Mech. bending of the devices worsened device performance by only 7% when a bending radius of 1 mm was used. The devices maintained 95% of the initial PCE after 1000 bending cycles for a bending radius of 10 mm. Degrdn. of the device performance by the bending was the result of crack formation from the transparent conducting oxide layer, demonstrating the potential of the low-temp.-processed TiOx layer to achieve more efficient and bendable perovskite solar cells, which becomes closer to a practical wearable power source.
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Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals Science 2015, 347, 519– 522 DOI: 10.1126/science.aaa2725
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Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals
Shi, Dong; Adinolfi, Valerio; Comin, Riccardo; Yuan, Mingjian; Alarousu, Erkki; Buin, Andrei; Chen, Yin; Hoogland, Sjoerd; Rothenberger, Alexander; Katsiev, Khabiboulakh; Losovyj, Yaroslav; Zhang, Xin; Dowben, Peter A.; Mohammed, Omar F.; Sargent, Edward H.; Bakr, Osman M.
Science (Washington, DC, United States) (2015), 347 (6221), 519-522CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
The fundamental properties and ultimate performance limits of organolead trihalide MAPbX3 (MA = CH3NH3+; X = Br- or I-) perovskites remain obscured by extensive disorder in polycryst. MAPbX3 films. The authors report an antisolvent vapor-assisted crystn. approach that enables the authors to create sizable crack-free MAPbX3 single crystals with vols. exceeding 100 cubic millimeters. These large single crystals enabled a detailed characterization of their optical and charge transport characteristics. The authors obsd. exceptionally low trap-state densities ∼109 to 1010 per cubic centimeter in MAPbX3 single crystals (comparable to the best photovoltaic-quality silicon) and charge carrier diffusion lengths exceeding 10 μm. These results were validated with d. functional theory calcns.
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Ponseca, C. S., Jr.; Tian, Y.; Sundström, V.; Scheblykin, I. G. Excited state and charge-carrier dynamics in perovskite solar cell materials Nanotechnology 2016, 27, 082001 DOI: 10.1088/0957-4484/27/8/082001
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Excited state and charge-carrier dynamics in perovskite solar cell materials
Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundstrom, Villy; Scheblykin, Ivan G.
Nanotechnology (2016), 27 (8), 082001/1-082001/16CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technol. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved cond., transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.
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Wen, X.; Feng, Y.; Huang, S.; Huang, F.; Cheng, Y.-B.; Green, M.; Ho-Baillie, A. Defect trapping states and charge carrier recombination in organic–inorganic halide perovskites J. Mater. Chem. C 2016, 4, 793– 800 DOI: 10.1039/C5TC03109E
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Defect trapping states and charge carrier recombination in organic-inorganic halide perovskites
Wen, Xiaoming; Feng, Yu; Huang, Shujuan; Huang, Fuzhi; Cheng, Yi-Bing; Green, Martin; Ho-Baillie, Anita
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (4), 793-800CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
Org.-inorg. perovskite solar cells have attracted huge research interest due to rapid improvement in device performance showing great potential to be the next generation flexible solar cells. Unique defect properties in perovskite have been considered as the possible mechanism for the superior performance, and closely relevant to the effects of hysteresis and light soaking. To date, the quant. correlation and in-depth understanding of defects in org.-inorg. perovskite are still lacking although extensive investigation have been undertaken. Here we study defect trapping states and carrier recombination dynamics in org.-inorg. halide perovskites. At low excitation the photoluminescence (PL) intensity exhibits a super-linear increase with increasing excitation, due to the slow depopulation rate of the defect states. The steady state and time-resolved photoluminescence (PL) carried out in this work reveal that the carrier recombination dynamics is ultimately correlated with both the defect d. and the relaxation rate of the carriers in defects. A model is established for the relationship between the properties of the defect trapping state and steady state PL intensity. Two key parameters, (i) the ratio of the trap-state d. to the depopulation rate of trapped states and (ii) ratio of the max. d. of covalence band electrons to the trapping rate, can be extd. from the model based on the excitation dependent steady state PL. This work demonstrates that the properties of defect trapping states are closely related to the fabrication technique, and suggests that the org.-inorg. halide perovskite is partly defect-tolerant.
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Merdasa, A.; Bag, M.; Tian, Y.; Källman, E.; Dobrovolsky, A.; Scheblykin, I. G. Super-resolution luminescence micro-spectroscopy reveals mechanism of photoinduced degradation in CH₃NH₃PbI₃ perovskite nanocrystals J. Phys. Chem. C 2016, 120, 10711– 10719 DOI: 10.1021/acs.jpcc.6b03512
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Super-Resolution Luminescence Microspectroscopy Reveals the Mechanism of Photoinduced Degradation in CH3NH3PbI3 Perovskite Nanocrystals
Merdasa, Aboma; Bag, Monojit; Tian, Yuxi; Kaellman, Elin; Dobrovolsky, Alexander; Scheblykin, Ivan G.
Journal of Physical Chemistry C (2016), 120 (19), 10711-10719CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Photoinduced degrdn. of individual methylammonium lead triiodide (MAPbI3) perovskite nanocrystals was studied using super-resoln. luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degrdn. process, indicating that the degrdn. needs a high concn. of mobile photogenerated charges to occur. Probably the mechanistic process of degrdn. occurs as the three-dimensional MAPbI3 crystal structure smoothly collapses to the two-dimensional layered PbI2 structure. The degrdn. starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA+), which distorts the lattice structure causing alterations to the Pb-I-Pb bond angle and in turn changes the effective band gap.
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Kong, W.; Rahimi-Iman, A.; Bi, G.; Dai, X.; Wu, H. Oxygen intercalation induced by photocatalysis on the surface of hybrid lead halide perovskites J. Phys. Chem. C 2016, 120, 7606– 7611 DOI: 10.1021/acs.jpcc.6b00496
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Oxygen Intercalation Induced by Photocatalysis on the Surface of Hybrid Lead Halide Perovskites
Kong, Weiguang; Rahimi-Iman, Arash; Bi, Gang; Dai, Xusheng; Wu, Huizhen
Journal of Physical Chemistry C (2016), 120 (14), 7606-7611CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Methylammonium lead iodide (MAPbI3) perovskite has emerged as a dazzling nova in the solar cell realm. However, the robustness or stability of the material exposed to different ambiences is a key issue. In this paper, resonance Raman spectroscopy is combined with surface and bulk crystal characterizations to interpret the oxygen intercalation phenomenon on the surface of MAPbI3. We observe that oxygen can intercalate into the frameworks of MAPbI3 with the assistance of laser radiation excitation. By lowering down the pressure in the exptl. chamber, the intercalated oxygen can be readily removed. XPS and X-ray diffraction characterizations suggest that Pb-O bonds are mainly formed on the surface of MAPbI3 but are constrained to avoid the formation of PbO compd. The quantum chem. calcn. based on d. functional theory supports the above conclusions. The understanding of oxygen intercalation in MAPbI3 shall benefit the improvement of stability of the important solar cell materials.
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Aristidou, N.; Sanchez-Molina, I.; Chotchuangchutchaval, T.; Brown, M.; Martinez, L.; Rath, T.; Haque, S. A. The role of oxygen in the degradation of methylammonium lead trihalide perovskite photoactive layers Angew. Chem., Int. Ed. 2015, 54, 8208– 8212 DOI: 10.1002/anie.201503153
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The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers
Aristidou, Nicholas; Sanchez-Molina, Irene; Chotchuangchutchaval, Thana; Brown, Michael; Martinez, Luis; Rath, Thomas; Haque, Saif A.
Angewandte Chemie, International Edition (2015), 54 (28), 8208-8212CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
In this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2O3/CH3NH3PbI3 photoactive layers rapidly decomp. yielding methylamine, PbI2, and I2 as products. We show that this degrdn. is initiated by the reaction of superoxide (O2-) with the methylammonium moiety of the perovskite absorber. Fluorescent mol. probe studies indicate that the O2- species is generated by the reaction of photoexcited electrons in the perovskite and mol. oxygen. We show that the yield of O2- generation is significantly reduced when the mp-Al2O3 film is replaced with an mp-TiO2 electron extn. and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.
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Müller, C.; Glaser, T.; Plogmeyer, M.; Sendner, M.; Döring, S.; Bakulin, A. A.; Brzuska, C.; Scheer, R.; Pshenichnikov, M. S.; Kowalsky, W.; Pucci, A.; Lovrinčić, R. Water infiltration in methylammonium lead iodide perovskite: fast and inconspicuous Chem. Mat. 2015, 27, 7835– 7841 DOI: 10.1021/acs.chemmater.5b03883
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Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous
Mueller, Christian; Glaser, Tobias; Plogmeyer, Marcel; Sendner, Michael; Doering, Sebastian; Bakulin, Artem A.; Brzuska, Carlo; Scheer, Roland; Pshenichnikov, Maxim S.; Kowalsky, Wolfgang; Pucci, Annemarie; Lovrincic, Robert
Chemistry of Materials (2015), 27 (22), 7835-7841CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
While the susceptibility of CH3NH3PbI3 to water is well-documented, the influence of water on device performance is not well-understood. Herein, the authors use IR spectroscopy to show that water infiltration into CH3NH3PbI3 occurs much faster and at a humidity much lower than previously thought. The authors propose a mol. model in which water mols. have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb-I cage. Also, the exposure of CH3NH3PbI3 to the ambient environment increases the photocurrent of films in lateral devices by >1 order of magnitude. The obsd. slow component in the photocurrent buildup indicates that the effect is assocd. with enhanced proton conduction when light is combined with water and oxygen exposure.
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Mosconi, E.; Azpiroz, J. M.; De Angelis, F. Ab initio molecular dynamics simulations of methylammonium lead iodide perovskite degradation by water Chem. Mat. 2015, 27, 4885– 4892 DOI: 10.1021/acs.chemmater.5b01991
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Ab Initio Molecular Dynamics Simulations of Methylammonium Lead Iodide Perovskite Degradation by Water
Mosconi, Edoardo; Azpiroz, Jon M.; De Angelis, Filippo
Chemistry of Materials (2015), 27 (13), 4885-4892CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
Protecting organohalide perovskite thin films from H2O and ambient humidity represents a paramount challenge for the com. uptake of perovskite solar cells and, in general, of related optoelectronic devices. Therefore, understanding the perovskite/H2O interface is of crucial importance. As a step in this direction, here the authors present ab initio mol. dynamics simulations aimed at unraveling the atomistic details of the interaction between the methylammonium lead iodide (MAPbI3) perovskite surfaces and a liq. H2O environment. According to the calcns., MAI-terminated surfaces undergo a rapid solvation process, driven by the interaction of H2O mols. with Pb atoms, which prompts the release of I atoms. PbI2-terminated surfaces, instead, seem to be more robust to degrdn., by virtue of the stronger (shorter) Pb-I bonds formed on these facets. The authors also observe the incorporation of a H2O mol. into the PbI2-terminated slab, which could represent the 1st step in the formation of an intermediate hydrated phase. PbI2 defects on the PbI2-terminated surface promote the rapid dissoln. of the exposed facet. Surface hydration, which is spontaneous for both MAI- and PbI2-terminated slabs, does not modify the electronic landscape of the former, while the local band gap of the PbI2-exposing model widens by ∼0.3 eV in the interfacial region. Finally, H2O incorporation into bulk MAPbI3 produces almost no changes in the tetragonal structure of the perovskite crystal (∼1% vol. expansion) but slightly opens the band gap. Probably this work, unraveling some of the atomistic details of the perovskite/H2O interface, may inspire new interfacial modifications and device architectures with increased stabilities, which could in turn assist the com. uptake of perovskite solar cells and optoelectronic devices.
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Tian, Y.; Merdasa, A.; Unger, E.; Abdellah, M.; Zheng, K.; McKibbin, S.; Mikkelsen, A.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Enhanced organo-metal halide perovskite photoluminescence from nanosized defect-free crystallites and emitting sites J. Phys. Chem. Lett. 2015, 6, 4171– 4177 DOI: 10.1021/acs.jpclett.5b02033
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Enhanced Organo-Metal Halide Perovskite Photoluminescence from Nanosized Defect-Free Crystallites and Emitting Sites
Tian, Yuxi; Merdasa, Aboma; Unger, Eva; Abdellah, Mohamed; Zheng, Kaibo; McKibbin, Sarah; Mikkelsen, Anders; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
Journal of Physical Chemistry Letters (2015), 6 (20), 4171-4177CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Luminescence (PL) of organo-metal halide perovskite semiconductors can be enhanced by several orders of magnitude by exposure to visible light. PL microscopy and super-resoln. optical imaging were applied to study this phenomenon with spatial resoln. better than 10 nm using films of MeNH3PbI3 prepd. by the equimolar soln.-deposition method, resulting in crystals of different sizes. PL of ∼100 nm crystals enhances much faster than that of larger, μm-sized ones. This crystal-size dependence of the photochem. light passivation of charge traps responsible for PL quenching allowed concluding that traps are present in the entire crystal vol. rather than at the surface only. Because of this effect, dark μm-sized perovskite crystals can be converted into highly luminescent smaller ones just by mech. grinding. Super-resoln. optical imaging shows spatial inhomogeneity of the PL intensity within perovskite crystals and the existence of <100 nm-sized localized emitting sites. The possible origin of these sites is discussed.
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Cichos, F.; von Borczyskowski, C.; Orrit, M. Power-law intermittency of single emitters Curr. Opin. Colloid Interface Sci. 2007, 12, 272– 284 DOI: 10.1016/j.cocis.2007.07.012
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Power-law intermittency of single emitters
Cichos, F.; von Borczyskowski, C.; Orrit, M.
Current Opinion in Colloid & Interface Science (2007), 12 (6), 272-284CODEN: COCSFL; ISSN:1359-0294. (Elsevier B.V.)
A review. We summarize exptl. observations of fluorescence intermittency of single semiconductor nanocrystals and single mols. We review the main models proposed earlier to explain the broad power-law distributions of on- and off-blinking times. We argue that a self-trapping model with a distribution of trapping distances can account for most, if not all, observations to date. We propose possible scenarios for photo-ionization, the switching to states with long on-times and the influence of disorder and surfaces on the trapping dynamics.
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Frantsuzov, P.; Kuno, M.; Janko, B.; Marcus, R. A. Universal emission intermittency in quantum dots, nanorods and nanowires Nat. Phys. 2008, 4, 519– 522 DOI: 10.1038/nphys1001
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There is no corresponding record for this reference.
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Clifford, J. N.; Bell, T. D. M.; Tinnefeld, P.; Heilemann, M.; Melnikov, S. M.; Hotta, J.-i.; Sliwa, M.; Dedecker, P.; Sauer, M.; Hofkens, J.; Yeow, E. K. L. Fluorescence of single molecules in polymer films: sensitivity of blinking to local environment J. Phys. Chem. B 2007, 111, 6987– 6991 DOI: 10.1021/jp072864d
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Fluorescence of Single Molecules in Polymer Films: Sensitivity of Blinking to Local Environment
Clifford, John N.; Bell, Toby D. M.; Tinnefeld, Philip; Heilemann, Mike; Melnikov, Sergey M.; Hotta, Jun-Ichi; Sliwa, Michel; Dedecker, Peter; Sauer, Markus; Hofkens, Johan; Yeow, Edwin K. L.
Journal of Physical Chemistry B (2007), 111 (25), 6987-6991CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
The single-mol. fluorescence blinking behavior of the org. dye Atto 647N in various polymer matrixes such as Zeonex, PVK, and PVA and aq. media was studied. Fluorescence blinking with off-times in the millisecond to second time range is assigned to dye radical ions formed by photoinduced electron transfer reactions from or to the environment. In Zeonex and PVK, the measured off-time distributions show power law dependence, whereas, in PVA, no such dependence is obsd. Rather, in this polymer, off-time distributions can be best fitted to monoexponential or stretched exponential functions. Furthermore, treatment of PVA samples to mild heating and low pressure greatly reduces the frequency of blinking events. We tentatively ascribe this to the removal of water pockets within the polymer film itself. Measurements of the dye immobilized in water in the presence of methylviologen, a strongly oxidizing agent, reveal simple exponential on- and off-time distributions. Thus, our data suggest that the blinking behavior of single org. mols. is sensitive to their immediate environment and, moreover, that fluorescence blinking on- and off-time distributions do not inherently and uniquely obey a power law.
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Hoogenboom, J. P.; Hernando, J.; van Dijk, E. M. H. P.; van Hulst, N. F.; García-Parajó, M. F. Power-law blinking in the fluorescence of single organic molecules ChemPhysChem 2007, 8, 823– 833 DOI: 10.1002/cphc.200600783
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Power-law blinking in the fluorescence of single organic molecules
Hoogenboom, Jacob P.; Hernando, Jordi; van Dijk, Erik M. H. P.; van Hulst, Niek F.; Garcia-Parajo, Maria F.
ChemPhysChem (2007), 8 (6), 823-833CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
The blinking behavior of perylene diimide mols. is investigated at the single-mol. level. We observe long-time scale blinking of individual multi-chromophoric complexes embedded in a poly(methylmethacrylate) matrix, as well as for the monomeric dye absorbed on a glass substrate at ambient conditions. In both these different systems, the blinking of single mols. is found to obey analogous power-law statistics for both the on and off periods. The obsd. range for single-mol. power-law blinking extends over the full exptl. time window, covering four orders of magnitude in time and six orders of magnitude in probability d. From mol. to mol., we observe a large spread in off-time power-law exponents. The distributions of off-exponents in both systems are markedly different whereas both on-exponent distributions appear similar. Our results are consistent with models that ascribe the power-law behavior to charge sepn. and (environment-dependent) recombination by electron tunneling to a dynamic distribution of charge acceptors. As a consequence of power-law statistics, single mol. properties like the total no. of emitted photons display non-ergodicity.
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Kuno, M.; Fromm, D. P.; Hamann, H. F.; Gallagher, A.; Nesbitt, D. J. Nonexponential “blinking” kinetics of single CdSe quantum dots: a universal power law behavior J. Chem. Phys. 2000, 112, 3117– 3120 DOI: 10.1063/1.480896
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Nonexponential "blinking" kinetics of single CdSe quantum dots: A universal power law behavior
Kuno, M.; Fromm, D. P.; Hamann, H. F.; Gallagher, A.; Nesbitt, D. J.
Journal of Chemical Physics (2000), 112 (7), 3117-3120CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
Single mol. confocal microscopy is used to study fluorescence intermittency of individual ZnS overcoated CdSe quantum dots (QDs) excited at 488 nm. The confocal app. permits the distribution of on and off times (i.e., periods of sustained fluorescence emission and darkness) to be measured over an unprecedentedly large dynamic range (109) of probability densities, with nonexponential behavior in τoff over a 105 range in time scales. In dramatic contrast, these same τoff distributions in all QDs are described with remarkable simplicity over this 109-fold dynamic range by a simple inverse power law, i.e., P(τoff).varies.1/τoff1+α. Such inverse power law behavior is a clear signature of distributed kinetics, such as predicted for (i) an exponential distribution of trap depths or (ii) a distribution of tunneling distances between QD core/interface states. This has important statistical implications for all previous studies of fluorescence intermittency in semiconductor QDs and may have broader implications for other systems such as single polymer mols.
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Peterson, J. J.; Nesbitt, D. J. Modified power law behavior in quantum dot blinking: a novel role for biexcitons and Auger ionization Nano Lett. 2009, 9, 338– 345 DOI: 10.1021/nl803108p
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Modified Power Law Behavior in Quantum Dot Blinking: A Novel Role for Biexcitons and Auger Ionization
Peterson, Jeffrey J.; Nesbitt, David J.
Nano Letters (2009), 9 (1), 338-345CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Single photon detection methods are used to acquire fluorescence trajectories from single CdSe/ZnS colloidal quantum dots (QDs) and analyze their blinking behavior. Although the "off-time" distributions follow ideal power law behavior at all wavelengths and intensities, significant deviations from power law behavior are obsd. for the "on-times". Specifically, with improved time resoln., trajectory durations, and photon statistics, we report a near-exponential falloff of on-time probability distributions at long times. Investigation of this falloff behavior as a function of laser wavelength and power demonstrate that these deviations originate from multiexciton dynamics, whose formation probabilities can be very low on a "per laser pulse" basis, but become nearly unity on the time scales of the longest on-times. The near quadratic, power-dependent results indicate the predominant role of biexcitons in the long time on-to-off blinking dynamics, which can be interpreted in terms of an Auger ionization event. In conjunction with Poisson modeling of the photon statistics, the data is consistent with QD ionization efficiencies of order ≈10-5 and highlight a novel role for biexcitons and Auger ionization in QD blinking.
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Hu, F.; Zhang, H.; Sun, C.; Yin, C.; Lv, B.; Zhang, C.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Superior optical properties of perovskite nanocrystals as single photon emitters ACS Nano 2015, 9, 12410– 12416 DOI: 10.1021/acsnano.5b05769
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Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters
Hu, Fengrui; Zhang, Huichao; Sun, Chun; Yin, Chunyang; Lv, Bihu; Zhang, Chunfeng; Yu, William W.; Wang, Xiaoyong; Zhang, Yu; Xiao, Min
ACS Nano (2015), 9 (12), 12410-12416CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Single photon emission was obsd. from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. The radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temps. to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.
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Park, Y.-S.; Guo, S.; Makarov, N. S.; Klimov, V. I. Room temperature single-photon emission from individual perovskite quantum dots ACS Nano 2015, 9, 10386– 10393 DOI: 10.1021/acsnano.5b04584
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Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots
Park, Young-Shin; Guo, Shaojun; Makarov, Nikolay S.; Klimov, Victor I.
ACS Nano (2015), 9 (10), 10386-10393CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Lead-halide-based perovskites have been the subject of numerous recent studies largely motivated by their exceptional performance in solar cells. Electronic and optical properties of these materials have been commonly controlled by varying the compn. (e.g., the halide component) and/or crystal structure. Use of nanostructured forms of perovskites can provide addnl. means for tailoring their functionalities via effects of quantum confinement and wave function engineering. Furthermore, it may enable applications that explicitly rely on the quantum nature of electronic excitations. Here, we demonstrate that CsPbX3 quantum dots (X = I, Br) can serve as room-temp. sources of quantum light, as indicated by strong photon antibunching detected in single-dot photoluminescence measurements. We explain this observation by the presence of fast nonradiative Auger recombination, which renders multiexciton states virtually nonemissive and limits the fraction of photon coincidence events to ∼6% on av. We analyze limitations of these quantum dots assocd. with irreversible photodegrdn. and fluctuations ("blinking") of the photoluminescence intensity. On the basis of emission intensity-lifetime correlations, we assign the "blinking" behavior to random charging/discharging of the quantum dot driven by photoassisted ionization. This study suggests that perovskite quantum dots hold significant promise for applications such as quantum emitters; however, to realize this goal, one must resolve the problems of photochem. stability and photocharging. These problems are largely similar to those of more traditional quantum dots and, hopefully, can be successfully resolved using advanced methodologies developed over the years in the field of colloidal nanostructures.
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Verberk, R.; van Oijen, A. M.; Orrit, M. Simple model for the power-law blinking of single semiconductor nanocrystals Phys. Rev. B 2002, 66, 233202 DOI: 10.1103/PhysRevB.66.233202
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Simple model for the power-law blinking of single semiconductor nanocrystals
Verberk, Rogier; van Oijen, Antoine M.; Orrit, Michel
Physical Review B: Condensed Matter and Materials Physics (2002), 66 (23), 233202/1-233202/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
We assign the blinking of nanocrystals to electron tunneling towards a uniform spatial distribution of traps. This naturally explains the power-law distribution of off times, and the power-law correlation function we measured on uncapped CdS dots. Capped dots, on the other hand, present extended on times leading to a radically different correlation function. This is readily described in our model by involving two different, dark and bright, charged states. Coulomb blockade prevents further ionization of the charged dot, thus giving rise to long, power-law distributed off and on times.
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Galland, C.; Ghosh, Y.; Steinbruck, A.; Sykora, M.; Hollingsworth, J. A.; Klimov, V. I.; Htoon, H. Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots Nature 2011, 479, 203– 207 DOI: 10.1038/nature10569
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Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots
Galland, Christophe; Ghosh, Yagnaseni; Steinbrueck, Andrea; Sykora, Milan; Hollingsworth, Jennifer A.; Klimov, Victor I.; Htoon, Han
Nature (London, United Kingdom) (2011), 479 (7372), 203-207CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Luminescence blinking - random switching between states of high (ON) and low (OFF) emissivities - is a universal property of mol. emitters found in dyes, polymers, biol. mols. and artificial nanostructures such as nanocrystal quantum dots, C nanotubes and nanowires. For the past 15 years, colloidal nanocrystals were used as a model system to study this phenomenon. The occurrence of OFF periods in nanocrystal emission was commonly attributed to the presence of an addnl. charge, which leads to luminescence quenching by nonradiative recombination (the Auger mechanism). This charging model was recently challenged in several reports. Time-resolved luminescence studies of individual nanocrystal quantum dots were performed while electrochem. controlling the degree of their charging, with the goal of clarifying the role of charging in blinking. Two distinct types of blinking are possible: conventional (A-type) blinking due to charging and discharging of the nanocrystal core, in which lower luminescence intensities correlate with shorter luminescence lifetimes; and a 2nd sort (B-type), in which large changes in the emission intensity are not accompanied by significant changes in emission dynamics. B-type blinking is attributed to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept hot electrons before they relax into emitting core states. Both blinking mechanisms can be electrochem. controlled and completely suppressed by application of an appropriate potential.
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Rabouw, F. T.; Kamp, M.; van Dijk-Moes, R. J. A.; Gamelin, D. R.; Koenderink, A. F.; Meijerink, A.; Vanmaekelbergh, D. Delayed exciton emission and its relation to blinking in CdSe quantum dots Nano Lett. 2015, 15, 7718– 7725 DOI: 10.1021/acs.nanolett.5b03818
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Delayed Exciton Emission and Its Relation to Blinking in CdSe Quantum Dots
Rabouw, Freddy T.; Kamp, Marko; van Dijk-Moes, Relinde J. A.; Gamelin, Daniel R.; Koenderink, A. Femius; Meijerink, Andries; Vanmaekelbergh, Daniel
Nano Letters (2015), 15 (11), 7718-7725CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
The efficiency and stability of emission from semiconductor nanocrystal quantum dots (QDs) is neg. affected by blinking on the single-nanocrystal level, i.e., random alternation of bright and dark periods. The time scales of these fluctuations can be as long as many seconds, orders of magnitude longer than typical lifetimes of exciton states in QDs. The authors study luminescence from QDs delayed over microseconds to milliseconds. The results prove the existence of long-lived charge-sepd. states in QDs. The authors study the properties of delayed emission as a direct way to learn about charge carrier sepn. and recovery of the exciton state. A new microscopic model is developed to connect delayed emission to exciton recombination and blinking from which bright periods in blinking are in fact not characterized by uninterrupted optical cycling as often assumed.
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Rosen, S.; Schwartz, O.; Oron, D. Transient fluorescence of the off state in blinking CdSe/CdS/ZnS semiconductor nanocrystals is not governed by Auger recombination Phys. Rev. Lett. 2010, 104, 157404 DOI: 10.1103/PhysRevLett.104.157404
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Transient Fluorescence of the Off State in Blinking CdSe/CdS/ZnS Semiconductor Nanocrystals Is Not Governed by Auger Recombination
Rosen, Shamir; Schwartz, Osip; Oron, Dan
Physical Review Letters (2010), 104 (15), 157404/1-157404/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
The obsd. intermittent light emission from colloidal semiconductor nanocrystals has long been assocd. with Auger recombination assisted quenching. The authors test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the obsd. decay dynamics seem inconsistent with those expected from Auger processes. Rather, the data suggest that in the off state the quantum dot cycles in a 3-step process: photoexcitation, rapid trapping, and subsequent slow nonradiative decay.
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Cordones, A. A.; Bixby, T. J.; Leone, S. R. Direct measurement of off-state trapping rate fluctuations in single quantum dot fluorescence Nano Lett. 2011, 11, 3366– 3369 DOI: 10.1021/nl2017674
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Direct Measurement of Off-State Trapping Rate Fluctuations in Single Quantum Dot Fluorescence
Cordones, Amy A.; Bixby, Teresa J.; Leone, Stephen R.
Nano Letters (2011), 11 (8), 3366-3369CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Fluorescence decay times measured during the off-state of single CdSe/ZnS quantum dot blinking decrease with increasing off-state duration, contradicting the charging model widely considered to explain the blinking phenomenon. The change in the nonradiative process of a short off-state duration compared to a long one was studied here through simultaneous measurement of fluorescence decay and blinking behavior. The results were studied in the framework of two models based on fluctuating trapping rates.
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Bronson, J. E.; Fei, J.; Hofman, J. M.; Gonzalez, R. L., Jr.; Wiggins, C. H. Learning rates and states from biophysical time series: a Bayesian approach to model selection and single-molecule FRET data Biophys. J. 2009, 97, 3196– 3205 DOI: 10.1016/j.bpj.2009.09.031
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Learning rates and states from biophysical time series: a Bayesian approach to model selection and single-molecule FRET data
Bronson, Jonathan E.; Fei, Jingyi; Hofman, Jake M.; Gonzalez, Ruben L., Jr.; Wiggins, Chris H.
Biophysical Journal (2009), 97 (12), 3196-3205CODEN: BIOJAU; ISSN:0006-3495. (Cell Press)
Time series data provided by single-mol. Forster resonance energy transfer (smFRET) expts. offer the opportunity to infer not only model parameters describing mol. complexes, e.g., rate consts., but also information about the model itself, e.g., the no. of conformational states. Resolving whether such states exist or how many of them exist requires a careful approach to the problem of model selection, here meaning discrimination among models with differing nos. of states. The most straightforward approach to model selection generalizes the common idea of max. likelihood-selecting the most likely parameter values-to max. evidence: selecting the most likely model. In either case, such an inference presents a tremendous computational challenge, which we here address by exploiting an approxn. technique termed variational Bayesian expectation maximization. We demonstrate how this technique can be applied to temporal data such as smFRET time series; show superior statistical consistency relative to the max. likelihood approach; compare its performance on smFRET data generated from expts. on the ribosome; and illustrate how model selection in such probabilistic or generative modeling can facilitate anal. of closely related temporal data currently prevalent in biophysics.
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Wu, B.; Nguyen, H. T.; Ku, Z.; Han, G.; Giovanni, D.; Mathews, N.; Fan, H. J.; Sum, T. C. Discerning the surface and bulk recombination kinetics of organic–inorganic halide perovskite single crystals Adv. Energy Mater. 2016, 6, 1600551 DOI: 10.1002/aenm.201600551
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There is no corresponding record for this reference.
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Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. Enhanced photoluminescence and solar cell performance via Lewis base passivation of organic–inorganic lead halide perovskites ACS Nano 2014, 8, 9815– 9821 DOI: 10.1021/nn5036476
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Enhanced Photoluminescence and Solar Cell Performance via Lewis Base Passivation of Organic-Inorganic Lead Halide Perovskites
Noel, Nakita K.; Abate, Antonio; Stranks, Samuel D.; Parrott, Elizabeth S.; Burlakov, Victor M.; Goriely, Alain; Snaith, Henry J.
ACS Nano (2014), 8 (10), 9815-9821CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Org.-inorg. metal halide perovskites have recently emerged as a top contender to be used as an absorber material in highly efficient, low-cost photovoltaic devices. Soln.-processed semiconductors tend to have a high d. of defect states and exhibit a large degree of electronic disorder. Perovskites appear to go against this trend, and despite relatively little knowledge of the impact of electronic defects, certified solar-to-elec. power conversion efficiencies of up to 17.9% have been achieved. Here, through treatment of the crystal surfaces with the Lewis bases thiophene and pyridine, the authors demonstrate significantly reduced nonradiative electron-hole recombination within the MeNH3PbI3-xClx perovskite, achieving photoluminescence lifetimes which are enhanced by nearly an order of magnitude, up to 2 μs. Probably this is due to the electronic passivation of under-coordinated Pb atoms within the crystal. Through this method of Lewis base passivation, the authors achieve power conversion efficiencies for soln.-processed planar heterojunction solar cells enhanced from 13% for the untreated solar cells to 15.3% and 16.5% for the thiophene and pyridine-treated solar cells, resp.
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Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic transport in hybrid lead iodide perovskite solar cells Nat. Commun. 2015, 6, 7497 DOI: 10.1038/ncomms8497
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Ionic transport in hybrid lead iodide perovskite solar cells
Eames, Christopher; Frost, Jarvist M.; Barnes, Piers R. F.; O'Regan, Brian C.; Walsh, Aron; Islam, M. Saiful
Nature Communications (2015), 6 (), 7497CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
Solar cells based on org.-inorg. halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behavior such as current-voltage hysteresis and a low-frequency giant dielec. response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chem. origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extd. from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and exptl. study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.
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Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F. Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation Energy Environ. Sci. 2015, 8, 2118– 2127 DOI: 10.1039/C5EE01265A
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Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation
Azpiroz, Jon M.; Mosconi, Edoardo; Bisquert, Juan; De Angelis, Filippo
Energy & Environmental Science (2015), 8 (7), 2118-2127CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
In spite of the unprecedented advance of organohalide lead perovskites in the photovoltaics scenario, many of the characteristics of this class of materials, including their slow photocond. response, solar cell hysteresis, and switchable photocurrent, remain poorly understood. Many exptl. hints point to defect migration as a plausible mechanism underlying these anomalous properties. By means of state-of-the-art first-principles computational analyses carried out on the tetragonal MAPbI3 (MA = methylammonium) perovskite and on its interface with TiO2, we demonstrate that iodine vacancies and interstitials may easily diffuse across the perovskite crystal, with migration activation energies as low as ∼0.1 eV. Under working conditions, iodine-related defects are predicted to migrate at the electrodes on very short time scales (<1 μs). MA and Pb vacancies, with calcd. activation barriers of ∼0.5 and 0.8 eV, resp., could be responsible for the slow response inherent to perovskites, with typical calcd. migration times of the order of tens of ms to minutes. By investigating realistic models of the perovskite/TiO2 interface we show that neg. charged defects, e.g. MA vacancies, close to the electron transport layer (TiO2 in our case) modify the perovskite electronic state landscape, hampering charge extn. at selective contacts, thus possibly contributing to the obsd. solar cell hysteresis. We further demonstrate the role of the electron transport layer in affecting the initial concn. of defects close to the selective contacts, highlighting how charge sepn. at the perovskite/TiO2 interface may further change the defect distribution. We believe that this work, identifying the mobile species in perovskite solar cells, their migration across the perovskite material, and their effect on the operational mechanism of the device, may pave the way for the development of new materials and solar cell architectures with improved and stabilized efficiencies.
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Klein-Kedem, N.; Cahen, D.; Hodes, G. Effects of light and electron beam irradiation on halide perovskites and their solar cells Acc. Chem. Res. 2016, 49, 347– 354 DOI: 10.1021/acs.accounts.5b00469
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Effects of Light and Electron Beam Irradiation on Halide Perovskites and Their Solar Cells
Klein-Kedem, Nir; Cahen, David; Hodes, Gary
Accounts of Chemical Research (2016), 49 (2), 347-354CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review is presented. Hybrid alkylammonium lead halide perovskite solar cells have, in a very few years of research, exceeded a light-to-electricity conversion efficiency of 20%, not far behind cryst. silicon cells. These perovskites do not contain any rare element, the amt. of toxic lead used is very small, and the cells can be made with a low energy input. They therefore already conform to two of the three requirements for viable, com. solar cells-efficient and cheap. The potential deal-breaker is their long-term stability. While reasonable short-term (hours) and even medium term (months) stability has been demonstrated, there is concern whether they will be stable for the two decades or more expected from com. cells in view of the intrinsically unstable nature of these materials. In particular, they have a tendency to be sensitive to various types of irradn., including sunlight, under certain conditions. This Account focuses on the effect of irradn. on the hybrid (and to a small degree, all-inorg.) lead halide perovskites and their solar cells. It is split up into two main sections. First, we look at the effect of electron beams on the materials. This is important, since such beams are used for characterization of both the perovskites themselves and cells made from them (electron microscopy for morphol. and compositional characterization; electron beam-induced current to study cell operation mechanism; cathodoluminescence for charge carrier recombination studies). Since the perovskites are sensitive to electron beam irradn., it is important to minimize beam damage to draw valid conclusions from such measurements. The second section treats the effect of visible and solar UV irradn. on the perovskites and their cells. As we show, there are many such effects. However, those affecting the perovskite directly need not necessarily always be detrimental to the cells, while those affecting the solar cells, which are composed of several other phases as well as the perovskite light absorber, are not always due to the perovskite itself. While we cannot yet say whether perovskite solar cells will or will not be stable over the long-term, the information in this Account should be a useful source to help achieve this goal.
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Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A. Atomistic origins of CH₃NH₃PbI₃ degradation to PbI₂ in vacuum Appl. Phys. Lett. 2015, 106, 131904 DOI: 10.1063/1.4916821
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Atomistic origins of CH3NH3PbI3 degradation to PbI2 in vacuum
Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A.
Applied Physics Letters (2015), 106 (13), 131904/1-131904/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
We study the mechanisms of CH3NH3PbI3 degrdn. and its transformation to PbI2 by means of X-ray diffraction and the d. functional theory. The exptl. anal. shows that the material can degrade in both air and vacuum conditions, with humidity and temp.-annealing strongly accelerating such process. Based on ab initio calcns., we argue that even in the absence of humidity, a decompn. of the perovskite structure can take place through the statistical formation of mol. defects with a non-ionic character, whose volatility at surfaces should break the thermodn. defect equil. We finally discuss the strategies that can limit such phenomenon and subsequently prolong the lifetime of the material. (c) 2015 American Institute of Physics.
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Zhang, L.; Sit, P. H.-L. Ab initio study of interaction of water, hydroxyl radicals, and hydroxide ions with CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ surfaces J. Phys. Chem. C 2015, 119, 22370– 22378 DOI: 10.1021/acs.jpcc.5b07000
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Ab Initio Study of Interaction of Water, Hydroxyl Radicals, and Hydroxide Ions with CH3NH3PbI3 and CH3NH3PbBr3 Surfaces
Zhang, Linghai; Sit, Patrick H.-L.
Journal of Physical Chemistry C (2015), 119 (39), 22370-22378CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Although there have been tremendous breakthroughs in perovskite solar cells over the past few years, degrdn. of perovskite has been a huge problem. Recently, a no. of exptl. studies have demonstrated that org.-inorg. halide perovskite materials are sensitive to humid air, and several degrdn. mechanisms have been proposed. However, the decompn. process of perovskites is only partially known and controversial. In this paper, we theor. study the structures of the tetragonal CH3NH3PbI3 and CH3NH3PbBr3 (110) surfaces and the degrdn. mechanism using d. functional theory calcns. both with and without the van der Waals correction. The computed results indicate that the CH3NH3+ (MA) cations preferentially orient with the NH3 group pointing into the surface. This allows the formation of more hydrogen···halide hydrogen bonds between the MA cations and the halides. Moreover, the interactions of water mols., hydroxyl radicals, and hydroxide ions with the perovskite surfaces are investigated. It has been suggested that the deprotonation of the MA cations followed by the desorption of the CH3NH2 mols. is a key step in the degrdn. mechanism. We found that the hydroxyl radicals and hydroxide ions facilitate this desorption process while water mols. have little effect on it. These present findings are pertinent to revealing the decompn. mechanisms of perovskite materials.
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Bryant, D.; Aristidou, N.; Pont, S.; Sanchez-Molina, I.; Chotchunangatchaval, T.; Wheeler, S.; Durrant, J. R.; Haque, S. A. Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells Energy Environ. Sci. 2016, 9, 1655– 1660 DOI: 10.1039/C6EE00409A
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Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells
Bryant, Daniel; Aristidou, Nicholas; Pont, Sebastian; Sanchez-Molina, Irene; Chotchunangatchaval, Thana; Wheeler, Scot; Durrant, James R.; Haque, Saif A.
Energy & Environmental Science (2016), 9 (5), 1655-1660CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
Here, we demonstrate that light and oxygen-induced degrdn. is the main reason for the low operational stability of methylammonium lead triiodide (MeNH3PbI3) perovskite solar cells exposed to ambient conditions. When exposed to both light and dry air, unencapsulated MeNH3PbI3 solar cells rapidly degrade on timescales of minutes to a few hours. This rapid degrdn. is also obsd. under elec. bias driven current flow in the dark in the presence of O2. In contrast, significantly slower degrdn. is obsd. when the MeNH3PbI3 devices are exposed to moisture alone (e.g. 85% relative humidity in N2). We show that this light and oxygen induced degrdn. can be slowed down by the use of interlayers that are able to remove electrons from the perovskite film before they can react with oxygen to form O2-. These observations demonstrate that the operational stability of electronic and optoelectronic devices that exploit the electron transporting properties of MeNH3PbI3 will be critically dependent upon the use of suitable barrier layers and device configurations to mitigate the oxygen sensitivity of this remarkable material.
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Su, L.; Lu, G.; Kenens, B.; Rocha, S.; Fron, E.; Yuan, H.; Chen, C.; Van Dorpe, P.; Roeffaers, M. B. J.; Mizuno, H.; Hofkens, J.; Hutchison, J. A.; Uji-i, H. Visualization of molecular fluorescence point spread functions via remote excitation switching fluorescence microscopy Nat. Commun. 2015, 6, 6287 DOI: 10.1038/ncomms7287
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Visualization of molecular fluorescence point spread functions via remote excitation switching fluorescence microscopy
Su, Liang; Lu, Gang; Kenens, Bart; Rocha, Susana; Fron, Eduard; Yuan, Haifeng; Chen, Chang; Van Dorpe, Pol; Roeffaers, Maarten B. J.; Mizuno, Hideaki; Hofkens, Johan; Hutchison, James A.; Uji-i, Hiroshi
Nature Communications (2015), 6 (), 6287CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
The enhancement of mol. absorption, emission and scattering processes by coupling to surface plasmon polaritons on metallic nanoparticles is a key issue in plasmonics for applications in (bio)chem. sensing, light harvesting and photocatalysis. Nevertheless, the point spread functions for single-mol. emission near metallic nanoparticles remain difficult to characterize due to fluorophore photodegrdn., background emission and scattering from the plasmonic structure. Here, we overcome this problem by exciting fluorophores remotely using plasmons propagating along metallic nanowires. The expts. reveal a complex array of single-mol. fluorescence point spread functions that depend not only on nanowire dimensions but also on the position and orientation of the mol. transition dipole. This work has consequences for both single-mol. regime-sensing and super-resoln. imaging involving metallic nanoparticles and opens the possibilities for fast size sorting of metallic nanoparticles, and for predicting mol. orientation and binding position on metallic nanoparticles via far-field optical imaging.
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Su, L.; Yuan, H.; Lu, G.; Rocha, S.; Orrit, M.; Hofkens, J.; Uji-i, H. Super-resolution localization and defocused fluorescence microscopy on resonantly coupled single-molecule, single-nanorod hybrids ACS Nano 2016, 10, 2455– 2466 DOI: 10.1021/acsnano.5b07294
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Super-resolution Localization and Defocused Fluorescence Microscopy on Resonantly Coupled Single-Molecule, Single-Nanorod Hybrids
Su, Liang; Yuan, Haifeng; Lu, Gang; Rocha, Susana; Orrit, Michel; Hofkens, Johan; Uji-i, Hiroshi
ACS Nano (2016), 10 (2), 2455-2466CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Optical antennas made of metallic nanostructures dramatically enhance single-mol. fluorescence to boost the detection sensitivity. Moreover, emission properties detected at the optical far field are dictated by the antenna. Here we study the emission from mol.-antenna hybrids by means of super-resoln. localization and defocused imaging. Whereas gold nanorods make single-crystal violet mols. in the tip's vicinity visible in fluorescence, super-resoln. localization on the enhanced mol. fluorescence reveals geometrical centers of the nanorod antenna instead. Furthermore, emission angular distributions of dyes linked to the nanorod surface resemble that of nanorods in defocused imaging. The exptl. observations are consistent with numerical calcns. using the finite-difference time-domain method.

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Bhawna, Supriti Ghorui, Aftab Alam, M. Aslam. Advances in Synthesis and Defect Properties of Halide Perovskite Nanocrystals: Experimental and Theoretical Perspectives. 2023, 3-37. https://doi.org/10.1007/978-981-99-1350-3_1
S.L. Choon, H.N. Lim, I. Ibrahim, Z. Zainal, K.B. Tan, C.Y. Foo, C.H. Ng. New potential materials in advancement of photovoltaic and optoelectronic applications: Metal halide perovskite nanorods. Renewable and Sustainable Energy Reviews 2023, 171 , 113037. https://doi.org/10.1016/j.rser.2022.113037
Subhasis Adhikari, Michel Orrit. Progress and perspectives in single-molecule optical spectroscopy. The Journal of Chemical Physics 2022, 156 (16) https://doi.org/10.1063/5.0087003
Ruiyun Chen, Bo Xia, Wenjin Zhou, Guofeng Zhang, Chengbing Qin, Jianyong Hu, Ivan G. Scheblykin, Liantuan Xiao. Environment‐Dependent Metastable Nonradiative Recombination Centers in Perovskites Revealed by Photoluminescence Blinking. Advanced Photonics Research 2022, 3 (1) https://doi.org/10.1002/adpr.202100271
Handong Jin, Julian A. Steele, Ruolin Cheng, Nagma Parveen, Maarten B. J. Roeffaers, Johan Hofkens, Elke Debroye. Experimental Evidence of Chloride‐Induced Trap Passivation in Lead Halide Perovskites through Single Particle Blinking Studies. Advanced Optical Materials 2021, 9 (23) https://doi.org/10.1002/adom.202002240
Sudipta Seth, Eduard A. Podshivaylov, Jun Li, Marina Gerhard, Alexander Kiligaridis, Pavel A. Frantsuzov, Ivan G. Scheblykin. Presence of Maximal Characteristic Time in Photoluminescence Blinking of MAPbI 3 Perovskite. Advanced Energy Materials 2021, 11 (44) https://doi.org/10.1002/aenm.202102449
Marina Gerhard, Boris Louis, Pavel A. Frantsuzov, Jun Li, Alexander Kiligaridis, Johan Hofkens, Ivan G. Scheblykin. Heterogeneities and Emissive Defects in MAPbI 3 Perovskite Revealed by Spectrally Resolved Luminescence Blinking. Advanced Optical Materials 2021, 9 (18) https://doi.org/10.1002/adom.202001380
Tao Wang, Sumin Hou, Huafang Zhang, Yi Yang, Wen Xu, Tianyong Ao, Miao Kang, Gencai Pan, Yanli Mao. Highly controllable synthesis of MAPbI3 perovskite nanocrystals with long carrier lifetimes and narrow band gap for application in photodetectors. Journal of Alloys and Compounds 2021, 872 , 159589. https://doi.org/10.1016/j.jallcom.2021.159589
Ivan Yu. Eremchev, Aleksandr O. Tarasevich, Jun Li, Andrey V. Naumov, Ivan G. Scheblykin. Lack of Photon Antibunching Supports Supertrap Model of Photoluminescence Blinking in Perovskite Sub‐Micrometer Crystals. Advanced Optical Materials 2021, 9 (3) https://doi.org/10.1002/adom.202001596
Ruiyun Chen, Bo Xia, WenJin Zhou, Wenling Guan, Guofeng Zhang, Chengbing Qin, Jianyong Hu, Liantuan Xiao, Suotang Jia. Underestimated effect of the polymer encapsulation process on the photoluminescence of perovskite revealed by in situ single-particle detection. Optics Express 2021, 29 (2) , 1851. https://doi.org/10.1364/OE.415596
Seunghyun Rhee, Kunsik An, Kyung-Tae Kang. Recent Advances and Challenges in Halide Perovskite Crystals in Optoelectronic Devices from Solar Cells to Other Applications. Crystals 2021, 11 (1) , 39. https://doi.org/10.3390/cryst11010039
Xiaoming Wen, Weijian Chen, Baohua Jia. Charge Carrier and Mobile ion Dynamic Processes in Perovskite Solar Cells: Progress and Prospect. 2020, 2-1-2-34. https://doi.org/10.1063/9780735422414_002
Xue Han, Guofeng Zhang, Bin Li, Changgang Yang, Wenli Guo, Xiuqing Bai, Peng Huang, Ruiyun Chen, Chengbing Qin, Jianyong Hu, Yifei Ma, Haizheng Zhong, Liantuan Xiao, Suotang Jia. Blinking Mechanisms and Intrinsic Quantum‐Confined Stark Effect in Single Methylammonium Lead Bromide Perovskite Quantum Dots. Small 2020, 16 (51) https://doi.org/10.1002/smll.202005435
Géraud Delport, Stuart Macpherson, Samuel D. Stranks. Imaging Carrier Transport Properties in Halide Perovskites using Time‐Resolved Optical Microscopy. Advanced Energy Materials 2020, 10 (26) https://doi.org/10.1002/aenm.201903814
Tejmani Behera, Nithin Pathoor, Chinmay Phadnis, Susmita Buragohain, Arindam Chowdhury. Spatially correlated photoluminescence blinking and flickering of hybrid-halide perovskite micro-rods. Journal of Luminescence 2020, 223 , 117202. https://doi.org/10.1016/j.jlumin.2020.117202
Yani Chen, Shengdong Zhang, Jinjie Wang. Electrospinning of Perovskite Crystals with Strong Emission and Improved Electrical Conductivity. 2020, 715-719. https://doi.org/10.1109/AIEA51086.2020.00159
Binbin Zhao, Liqing Zhu, Liaoxin Sun, Shaowei Wang, Jian Lu, Jian zhang, Qi Han, Hongxing Dong, Bing Tang, Beier Zhou, Feng Liu, Xuechu Shen, Wei Lu. Strong fluorescence blinking of large-size all-inorganic perovskite nano-spheres. Nanotechnology 2020, 31 (21) , 215204. https://doi.org/10.1088/1361-6528/ab7250
Xin Liu, Zhao Luo, Wenxu Yin, Aleksandr P. Litvin, Alexander V. Baranov, Jiaqi Zhang, Wenyan Liu, Xiaoyu Zhang, Weitao Zheng. Methanol-induced fast CsBr release results in phase-pure CsPbBr 3 perovskite nanoplatelets. Nanoscale Advances 2020, 2 (5) , 1973-1979. https://doi.org/10.1039/D0NA00123F
Handong Jin, Elke Debroye, Masoumeh Keshavarz, Ivan G. Scheblykin, Maarten B. J. Roeffaers, Johan Hofkens, Julian A. Steele. It's a trap! On the nature of localised states and charge trapping in lead halide perovskites. Materials Horizons 2020, 7 (2) , 397-410. https://doi.org/10.1039/C9MH00500E
Jing Wang, Wei Li, Wan‐Jian Yin. Passivating Detrimental DX Centers in CH 3 NH 3 PbI 3 for Reducing Nonradiative Recombination and Elongating Carrier Lifetime. Advanced Materials 2020, 32 (6) https://doi.org/10.1002/adma.201906115
Guo-Feng Zhang, Chang-Gang Yang, Yong Ge, Yong-Gang Peng, Rui-Yun Chen, Cheng-Bing Qin, Yan Gao, Lei Zhang, Hai-Zheng Zhong, Yu-Jun Zheng, Lian-Tuan Xiao, Suo-Tang Jia. Influence of surface charges on the emission polarization properties of single CdSe/CdS dot-in-rods. Frontiers of Physics 2019, 14 (6) https://doi.org/10.1007/s11467-019-0916-1
Marina Gerhard, Boris Louis, Rafael Camacho, Aboma Merdasa, Jun Li, Alexander Kiligaridis, Alexander Dobrovolsky, Johan Hofkens, Ivan G. Scheblykin. Microscopic insight into non-radiative decay in perovskite semiconductors from temperature-dependent luminescence blinking. Nature Communications 2019, 10 (1) https://doi.org/10.1038/s41467-019-09640-w
Young‐Hoon Kim, Joo Sung Kim, Tae‐Woo Lee. Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes. Advanced Materials 2019, 31 (47) https://doi.org/10.1002/adma.201804595
Brett W. Boote, Himashi P. Andaraarachchi, Bryan A. Rosales, Rafael Blome‐Fernández, Feng Zhu, Malinda D. Reichert, Kalyan Santra, Jingzhe Li, Jacob W. Petrich, Javier Vela, Emily A. Smith. Unveiling the Photo‐ and Thermal‐Stability of Cesium Lead Halide Perovskite Nanocrystals. ChemPhysChem 2019, 20 (20) , 2647-2656. https://doi.org/10.1002/cphc.201900432
Yongli Zhao, Jinhang Li, Yuhui Dong, Jizhong Song. Synthesis of Colloidal Halide Perovskite Quantum Dots/Nanocrystals: Progresses and Advances. Israel Journal of Chemistry 2019, 59 (8) , 649-660. https://doi.org/10.1002/ijch.201900009
Lata Chouhan, Sushant Ghimire, Vasudevanpillai Biju. Blinking Beats Bleaching: The Control of Superoxide Generation by Photo‐ionized Perovskite Nanocrystals. Angewandte Chemie 2019, 131 (15) , 4929-4933. https://doi.org/10.1002/ange.201900061
Lata Chouhan, Sushant Ghimire, Vasudevanpillai Biju. Blinking Beats Bleaching: The Control of Superoxide Generation by Photo‐ionized Perovskite Nanocrystals. Angewandte Chemie International Edition 2019, 58 (15) , 4875-4879. https://doi.org/10.1002/anie.201900061
Yu Zhong, Carlos Andres Melo Luna, Richard Hildner, Cheng Li, Sven Huettner. In situ investigation of light soaking in organolead halide perovskite films. APL Materials 2019, 7 (4) https://doi.org/10.1063/1.5086125
Soranyel Gonzalez-Carrero, Lorena Bareño, Elke Debroye, Cristina Martin, Patricia Bondia, Cristina Flors, Raquel E. Galian, Johan Hofkens, Julia Pérez-Prieto. Linear assembly of lead bromide-based nanoparticles inside lead( ii ) polymers prepared by mixing the precursors of both the nanoparticle and the polymer. Chemical Communications 2019, 55 (20) , 2968-2971. https://doi.org/10.1039/C8CC10287B
Yanyu Lei, Jie Yang, Daocheng Hong, Sushu Wan, Yan Hua, Mingcai Xie, Xiaosheng Tang, Yuxi Tian. A Single Nonblinking Cs 4 PbBr 6 Nanoparticle as a Nanothermometer. ChemNanoMat 2019, 5 (3) , 364-369. https://doi.org/10.1002/cnma.201800619
Xiaorong Zhang, Chengbing Qin, Yani Gong, Yunrui Song, Guofeng Zhang, Ruiyun Chen, Yan Gao, Liantuan Xiao, Suotang Jia. Co-adsorption of an anionic dye in the presence of a cationic dye and a heavy metal ion by graphene oxide and photoreduced graphene oxide. RSC Advances 2019, 9 (10) , 5313-5324. https://doi.org/10.1039/C8RA09438A
Linghai Zhang, Patrick H.-L. Sit. Ab initio study of the dynamics of electron trapping and detrapping processes in the CH 3 NH 3 PbI 3 perovskite. Journal of Materials Chemistry A 2019, 7 (5) , 2135-2147. https://doi.org/10.1039/C8TA09512D
Wenjun He, Chengbing Qin, Zhixing Qiao, Yani Gong, Xiaorong Zhang, Guofeng Zhang, Ruiyun Chen, Yan Gao, Liantuan Xiao, Suotang Jia. In situ manipulation of fluorescence resonance energy transfer between quantum dots and monolayer graphene oxide by laser irradiation. Nanoscale 2019, 11 (3) , 1236-1244. https://doi.org/10.1039/C8NR07858K
S. Ananthakumar, S. Moorthy Babu. Progress on synthesis and applications of hybrid perovskite semiconductor nanomaterials—A review. Synthetic Metals 2018, 246 , 64-95. https://doi.org/10.1016/j.synthmet.2018.10.003
Toshio Ando, Satya Prathyusha Bhamidimarri, Niklas Brending, H Colin-York, Lucy Collinson, Niels De Jonge, P J de Pablo, Elke Debroye, Christian Eggeling, Christian Franck, Marco Fritzsche, Hans Gerritsen, Ben N G Giepmans, Kay Grunewald, Johan Hofkens, Jacob P Hoogenboom, Kris P F Janssen, Rainer Kaufmann, Judith Klumperman, Nyoman Kurniawan, Jana Kusch, Nalan Liv, Viha Parekh, Diana B Peckys, Florian Rehfeldt, David C Reutens, Maarten B J Roeffaers, Tim Salditt, Iwan A T Schaap, Ulrich S Schwarz, Paul Verkade, Michael W Vogel, Richard Wagner, Mathias Winterhalter, Haifeng Yuan, Giovanni Zifarelli. The 2018 correlative microscopy techniques roadmap. Journal of Physics D: Applied Physics 2018, 51 (44) , 443001. https://doi.org/10.1088/1361-6463/aad055
Nithin Pathoor, Ansuman Halder, Amitrajit Mukherjee, Jaladhar Mahato, Shaibal K. Sarkar, Arindam Chowdhury. Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals. Angewandte Chemie 2018, 130 (36) , 11777-11781. https://doi.org/10.1002/ange.201804852
Nithin Pathoor, Ansuman Halder, Amitrajit Mukherjee, Jaladhar Mahato, Shaibal K. Sarkar, Arindam Chowdhury. Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals. Angewandte Chemie International Edition 2018, 57 (36) , 11603-11607. https://doi.org/10.1002/anie.201804852
Changgang Yang, Guofeng Zhang, Liheng Feng, Bin Li, Zhijie Li, Ruiyun Chen, Chengbing Qin, Yan Gao, Liantuan Xiao, Suotang Jia. Suppressing the photobleaching and photoluminescence intermittency of single near-infrared CdSeTe/ZnS quantum dots with p-phenylenediamine. Optics Express 2018, 26 (9) , 11889. https://doi.org/10.1364/OE.26.011889
Haifeng Yuan, Elke Debroye, Eva Bladt, Gang Lu, Masoumeh Keshavarz, Kris P. F. Janssen, Maarten B. J. Roeffaers, Sara Bals, Edward H. Sargent, Johan Hofkens. Imaging Heterogeneously Distributed Photo‐Active Traps in Perovskite Single Crystals. Advanced Materials 2018, 30 (13) https://doi.org/10.1002/adma.201705494
Antonio Aloi, Ilja K. Voets. Soft matter nanoscopy. Current Opinion in Colloid & Interface Science 2018, 34 , 59-73. https://doi.org/10.1016/j.cocis.2018.03.001
Martin Vacha, Dharmendar Kumar Sharma, Shuzo Hirata. Single-molecule studies beyond optical imaging: Multi-parameter single-molecule spectroscopy. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2018, 34 , 121-136. https://doi.org/10.1016/j.jphotochemrev.2017.11.003
Wanyi Nie, Hsinhan Tsai, Jean‐Christophe Blancon, Fangze Liu, Costas C. Stoumpos, Boubacar Traore, Mikael Kepenekian, Olivier Durand, Claudine Katan, Sergei Tretiak, Jared Crochet, Pulickel M. Ajayan, MercouriG. Kanatzidis, Jacky Even, Aditya D. Mohite. Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide. Advanced Materials 2018, 30 (5) https://doi.org/10.1002/adma.201703879
Himchan Cho, Joo Sung Kim, Young-Hoon Kim, Tae-Woo Lee. Influence of A-site cation on the thermal stability of metal halide perovskite polycrystalline films. Journal of Information Display 2018, 19 (1) , 53-60. https://doi.org/10.1080/15980316.2018.1424652
Daocheng Hong, Sushu Wan, Yuxi Tian. Characterization of quenching defects in methylammonium lead triiodide (CH3NH3PbI3). Journal of Luminescence 2017, 192 , 1191-1195. https://doi.org/10.1016/j.jlumin.2017.08.055
Marc‐Antoine Stoeckel, Marco Gobbi, Sara Bonacchi, Fabiola Liscio, Laura Ferlauto, Emanuele Orgiu, Paolo Samorì. Reversible, Fast, and Wide‐Range Oxygen Sensor Based on Nanostructured Organometal Halide Perovskite. Advanced Materials 2017, 29 (38) https://doi.org/10.1002/adma.201702469
Dominik Wöll, Cristina Flors. Super‐resolution Fluorescence Imaging for Materials Science. Small Methods 2017, 1 (10) https://doi.org/10.1002/smtd.201700191
Fabian Panzer, Cheng Li, Tobias Meier, Anna Köhler, Sven Huettner. Impact of Structural Dynamics on the Optical Properties of Methylammonium Lead Iodide Perovskites. Advanced Energy Materials 2017, 7 (16) https://doi.org/10.1002/aenm.201700286
Chinnadurai Muthu, Anuja Vijayan, Vijayakumar C. Nair. CH 3 NH 3 PbBr 3 Perovskite Nanocrystals as Efficient Light‐Harvesting Antenna for Fluorescence Resonance Energy Transfer. Chemistry – An Asian Journal 2017, 12 (9) , 988-995. https://doi.org/10.1002/asia.201601672
Elke Debroye, Haifeng Yuan, Eva Bladt, Wouter Baekelant, Mark Van der Auweraer, Johan Hofkens, Sara Bals, Maarten B. J. Roeffaers. Facile Morphology‐Controlled Synthesis of Organolead Iodide Perovskite Nanocrystals Using Binary Capping Agents. ChemNanoMat 2017, 3 (4) , 223-227. https://doi.org/10.1002/cnma.201700006

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Abstract
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Figure 1
Figure 1. (a) Scanning electron micrograph of the synthesized perovskite nanocrystals. (b) XRD patterns of solution-processed perovskite nanocrystals and a thermal-annealed polycrystalline perovskite film. (c) Time-resolved PL decay histogram measured on an individual perovskite nanorod (red curve) and thermal-annealed polycrystalline perovskite films (cyan curve) under 485 nm pulsed excitation with an average power density of 80 mW/cm². The repetition rate was 100 kHz. The instrumental response function (IRF) is shown in black (FWHM ≈ 0.4 ns). The red decay curve can be fitted with three exponential decay components of 665.5 ns (10%), 143.4 ns (51%), and 22.2 ns (39%). The cyan decay curve can be fitted with three exponential decay components of 65.3 ns (4%), 13.5 ns (31%), and 2.2 ns (65%). The inset shows the emission spectrum of bulk perovskite nanocrystals (FWHM ≈ 60 nm).
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Figure 2
Figure 2. (a) Scanning electron micrograph of an individual perovskite nanorod, 140 nm in length and 40 nm in width. (b) PL image of the same perovskite nanorod. (c) Plot of the localization events by applying 2D Gaussian fitting. (d) PL spectrum of the same perovskite nanorod. The red curve is a Lorentzian fitting. (e–i) PL time traces (normalized intensities) and the corresponding intensity histograms (in percentage) of the same perovskite nanorod under different excitation power densities, that is, 1, 10, 40, 160, and 630 mW/cm².
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Figure 3
Figure 3. (a) PL image of two bright spots. The spot on the left side is because of the PL emission from an individual perovskite nanorod. The spot on the right side comes from a random cluster of several perovskite nanorods. The corresponding scanning electron micrograph on the same sample area is given in (d). The color bar shows the PL intensity in the unit of counts per frame (50 ms). The excitation power density was 16 mW/cm². (b and c) Plots of super-resolution localization events over the two bright spots in (a). The color bars represent the numbers of localization events. (e and f) scanning electron micrographs of the two nanostructures that correspond to (b) and (c), respectively. Solid lines in orange and in green colors outline the two nanostructures, respectively.
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Figure 4
Figure 4. (a) Probability distributions of ON times under different laser excitation power densities. The red solid line shows a power-law profile with the power parameter α = −1.6. (b) Probability distributions of OFF times under different laser excitation power densities. The red solid line shows a power-law profile with the power parameter α = −1.9. (c) The OFF-time PL blinking histogram of 14 individual perovskite nanorods resembles the power law. Different excitation power densities were examined, that is, 1 mW/cm² (blue triangles), 16 mW/cm² (green dots), and 160 mW/cm² (orange squares).
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Figure 5
Figure 5. (a) Time traces of PL intensity (red) and average arrival times measured on an individual OHP nanorod. (b) Correlation scattered plot of average arrival times versus PL intensities. Dashed cycles are used to highlight the ON and OFF states. (c) PL decay time histograms of ON and OFF states.
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Figure 6
Figure 6. PL blinking time traces and histograms of perovskite nanorods under different environments, that is, under vacuum (a), in nitrogen under the ambient pressure (b), and in air under the ambient pressure (c). The same excitation power density of 16 mW/cm² was applied. The inset shows the scanning electron micrograph of the cluster of three perovskite nanorods. The red lines are guide for the eye, generated using vbFRET package. (64)
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References
This article references 74 other publications.
1. 1
  Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange Science 2015, 348, 1234– 1237 DOI: 10.1126/science.aaa9272
  1
  High-performance photovoltaic perovskite layers fabricated through intramolecular exchange
  Yang, Woon Seok; Noh, Jun Hong; Jeon, Nam Joong; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
  Science (Washington, DC, United States) (2015), 348 (6240), 1234-1237CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). An approach is reported for depositing high-quality FAPbI3 films, involving FAPbI3 crystn. by the direct intramol. exchange of dimethylsulfoxide (DMSO) mols. intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallog. orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepd. by this technique, the FAPbI3-based PSCs are fabricated with max. power conversion efficiency greater than 20%.
2. 2
  Saliba, M.; Orlandi, S.; Matsui, T.; Aghazada, S.; Cavazzini, M.; Correa-Baena, J.-P.; Gao, P.; Scopelliti, R.; Mosconi, E.; Dahmen, K.-H.; De Angelis, F.; Abate, A.; Hagfeldt, A.; Pozzi, G.; Graetzel, M.; Nazeeruddin, M. K. A molecularly engineered hole-transporting material for efficient perovskite solar cells Nat. Energy 2016, 1, 15017 DOI: 10.1038/nenergy.2015.17
  2
  A molecularly engineered hole-transporting material for efficient perovskite solar cells
  Saliba, Michael; Orlandi, Simonetta; Matsui, Taisuke; Aghazada, Sadig; Cavazzini, Marco; Correa-Baena, Juan-Pablo; Gao, Peng; Scopelliti, Rosario; Mosconi, Edoardo; Dahmen, Klaus-Hermann; De Angelis, Filippo; Abate, Antonio; Hagfeldt, Anders; Pozzi, Gianluca; Graetzel, Michael; Nazeeruddin, Mohammad Khaja
  Nature Energy (2016), 1 (2), 15017CODEN: NEANFD; ISSN:2058-7546. (Nature Publishing Group)
  Soln.-processable perovskite solar cells have recently achieved certified power conversion efficiencies of over 20%, challenging the long-standing perception that high efficiencies must come at high costs. One major bottleneck for increasing the efficiency even further is the lack of suitable hole-transporting materials, which ext. pos. charges from the active light absorber and transmit them to the electrode. In this work, we present a molecularly engineered hole-transport material with a simple dissym. fluorene-dithiophene (FDT) core substituted by N,N-di-p-methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for a family of potentially low-cost hole-transport materials. We use FDT on state-of-the-art devices and achieve power conversion efficiencies of 20.2% which compare favorably with control devices with 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). Thus, this new hole transporter has the potential to replace spiro-OMeTAD.
3. 3
  Park, N. G. Perovskite solar cells: an emerging photovoltaic technology Mater. Today 2015, 18, 65– 72 DOI: 10.1016/j.mattod.2014.07.007
  3
  Perovskite solar cells: an emerging photovoltaic technology
  Park, Nam-Gyu
  Materials Today (Oxford, United Kingdom) (2015), 18 (2), 65-72CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
  A review. Perovskite solar cells based on organometal halides represent an emerging photovoltaic technol. Perovskite solar cells stem from dye-sensitized solar cells. In a liq.-based dye-sensitized solar cell structure, the adsorption of methylammonium lead halide perovskite on a nanocryst. TiO2 surface produces a photocurrent with a power conversion efficiency (PCE) of around 3-4%, as first discovered in 2009. The PCE was doubled after 2 years by optimizing the perovskite coating conditions. However, the liq.-based perovskite solar cell receives little attention because of its stability issues, including instant dissoln. of the perovskite in a liq. electrolyte. A long-term, stable, and high efficiency (∼10%) perovskite solar cell was developed in 2012 by substituting the solid hole conductor with a liq. electrolyte. Efficiencies have quickly risen to 18% in just 2 years. Since PCE values over 20% are realistically anticipated with the use of cheap organometal halide perovskite materials, perovskite solar cells are a promising photovoltaic technol. In this review, the opto-electronic properties of perovskite materials and recent progresses in perovskite solar cells are described. In addn., comments on the issues to current and future challenges are mentioned.
4. 4
  Yusoff, A. R. b. M.; Nazeeruddin, M. K. Organohalide lead perovskites for photovoltaic applications J. Phys. Chem. Lett. 2016, 7, 851– 866 DOI: 10.1021/acs.jpclett.5b02893
  4
  Organohalide Lead Perovskites for Photovoltaic Applications
  Yusoff, Abd. Rashid bin Mohd; Nazeeruddin, Mohammad Khaja
  Journal of Physical Chemistry Letters (2016), 7 (5), 851-866CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Perovskite solar cells have recently exhibited a significant leap in efficiency due to their broad absorption, high optical absorption coeff., very low exciton binding energy, long carrier diffusion lengths, efficient charge collection, and very high open-circuit potential, similar to that of III-IV semiconductors. Unlike silicon solar cells, perovskite solar cells can be developed from a variety of low-temp. solns. processed from inexpensive raw materials. When the perovskite absorber film formation is optimized using solvent engineering, a power conversion efficiency of over 21% has been demonstrated, highlighting the unique photovoltaic properties of perovskite materials. Here, we review the current progress in perovskite solar cells and charge transport materials. We highlight crucial challenges and provide a summary and prospects.
5. 5
  Sharenko, A.; Toney, M. F. Relationships between lead halide perovskite thin-film fabrication, morphology, and performance in solar cells J. Am. Chem. Soc. 2016, 138, 463– 470 DOI: 10.1021/jacs.5b10723
  5
  Relationships between Lead Halide Perovskite Thin-Film Fabrication, Morphology, and Performance in Solar Cells
  Sharenko, Alexander; Toney, Michael F.
  Journal of the American Chemical Society (2016), 138 (2), 463-470CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A review. Soln.-processed lead halide perovskite thin-film solar cells have achieved power conversion efficiencies comparable to those obtained with several com. photovoltaic technologies in a remarkably short period of time. This rapid rise in device efficiency is largely the result of the development of fabrication protocols capable of producing continuous, smooth perovskite films with micrometer-sized grains. Further developments in film fabrication and morphol. control are necessary, however, in order for perovskite solar cells to reliably and reproducibly approach their thermodn. efficiency limit. This Perspective discusses the fabrication of lead halide perovskite thin films, while highlighting the processing-property-performance relationships that have emerged from the literature, and from this knowledge, suggests future research directions.
6. 6
  deQuilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Impact of microstructure on local carrier lifetime in perovskite solar cells Science 2015, 348, 683– 686 DOI: 10.1126/science.aaa5333
  6
  Solar cells. Impact of microstructure on local carrier lifetime in perovskite solar cells
  deQuilettes Dane W; Vorpahl Sarah M; Nagaoka Hirokazu; Ziffer Mark E; Ginger David S; Stranks Samuel D; Eperon Giles E; Snaith Henry J
  Science (New York, N.Y.) (2015), 348 (6235), 683-6 ISSN:.
  The remarkable performance of hybrid perovskite photovoltaics is attributed to their long carrier lifetimes and high photoluminescence (PL) efficiencies. High-quality films are associated with slower PL decays, and it has been claimed that grain boundaries have a negligible impact on performance. We used confocal fluorescence microscopy correlated with scanning electron microscopy to spatially resolve the PL decay dynamics from films of nonstoichiometric organic-inorganic perovskites, CH3NH3PbI3(Cl). The PL intensities and lifetimes varied between different grains in the same film, even for films that exhibited long bulk lifetimes. The grain boundaries were dimmer and exhibited faster nonradiative decay. Energy-dispersive x-ray spectroscopy showed a positive correlation between chlorine concentration and regions of brighter PL, whereas PL imaging revealed that chemical treatment with pyridine could activate previously dark grains.
7. 7
  Tian, Y.; Merdasa, A.; Peter, M.; Abdellah, M.; Zheng, K.; Ponseca, C. S.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Giant photoluminescence blinking of perovskite nanocrystals reveals single-trap control of luminescence Nano Lett. 2015, 15, 1603– 1608 DOI: 10.1021/nl5041397
  7
  Giant Photoluminescence Blinking of Perovskite Nanocrystals Reveals Single-Trap Control of Luminescence
  Tian, Yuxi; Merdasa, Aboma; Peter, Maximilian; Abdellah, Mohamed; Zheng, Kaibo; Ponseca, Carlito S.; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
  Nano Letters (2015), 15 (3), 1603-1608CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Fluorescence super-resoln. microscopy showed correlated fluctuations of luminescence intensity and spatial localization of individual perovskite (MeNH3PbI3) nanocrystals of size ∼200 × 30 × 30 nm3. The luminescence blinking amplitude caused by a single quencher was a hundred thousand times larger than that of a typical dye mol. at the same excitation power d. The quencher probably is a chem. or structural defect that traps free charges leading to nonradiative recombination. These trapping sites can be activated and deactivated by light.
8. 8
  Li, Y.; Yan, W.; Li, Y.; Wang, S.; Wang, W.; Bian, Z.; Xiao, L.; Gong, Q. Direct observation of long electron-hole diffusion distance in CH₃NH₃PbI₃ perovskite thin film Sci. Rep. 2015, 5, 14485 DOI: 10.1038/srep14485
  8
  Direct Observation of Long Electron-Hole Diffusion Distance in CH3NH3PbI3 Perovskite Thin Film
  Li, Yu; Yan, Weibo; Li, Yunlong; Wang, Shufeng; Wang, Wei; Bian, Zuqiang; Xiao, Lixin; Gong, Qihuang
  Scientific Reports (2015), 5 (), 14485CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
  In high performance perovskite based solar cells, CH3NH3PbI3 is the key material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. By coating the film with an electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid Me ester (PCBM) or 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) resp., we obsd. the charge transfer directly through the fluorescence quenching. One-dimensional diffusion model was applied to obtain long charge diffusion distances in thick films, which is ∼1.7 μm for electrons and up to ∼6.3 μm for holes. Short diffusion distance of few hundreds of nanosecond was also obsd. in thin films. This thickness dependent charge diffusion explained the formerly reported short charge diffusion distance (∼100 nm) in films and resolved its confliction to thick working layer (300-500 nm) in real devices. This study presents direct support to the high performance perovskite solar cells and will benefit the devices' design.
9. 9
  Tian, W.; Zhao, C.; Leng, J.; Cui, R.; Jin, S. Visualizing carrier diffusion in individual single-crystal organolead halide perovskite nanowires and nanoplates J. Am. Chem. Soc. 2015, 137, 12458– 12461 DOI: 10.1021/jacs.5b08045
  9
  Visualizing Carrier Diffusion in Individual Single-Crystal Organolead Halide Perovskite Nanowires and Nanoplates
  Tian, Wenming; Zhao, Chunyi; Leng, Jing; Cui, Rongrong; Jin, Shengye
  Journal of the American Chemical Society (2015), 137 (39), 12458-12461CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Single-crystal MeNH3PbX3 (X = I-, Cl-, Br-) perovskite nanowires (NWs) and nanoplates (NPs), which demonstrate ultracompact sizes and exceptional photophys. properties, offer promises for applications in nanoscale photonics and optoelectronics. However, traditional electronic and transient techniques are limited by the dimensions of the samples, and characterizations of the carrier behavior (diffusion coeff., charge mobility and diffusion length) in these NWs and NPs are extremely difficult. Herein, the authors report the direct visualization of the carrier diffusion process in individual single-crystal MeNH3PbI3 and MeNH3PbBr3 NWs and NPs using time-resolved and photoluminescence-scanned imaging microscopy. The authors report the diffusion coeff. (charge motility), which varies significantly between different NWs and NPs, ranging from 1.59 to 2.41 cm2 s-1 (56.4 to 93.9 cm2 V-1 s-1) for MeNH3PbI3 and 0.50 to 1.44 cm2 s-1 (19.4 to 56.1 cm2 V-1 s-1) for MeNH3PbBr3 and find this variation is independent of the shape and size of the sample. The av. diffusion length is 14.0 ± 5.1 μm for MeNH3PbI3 and 6.0 ± 1.6 μm for MeNH3PbBr3. These results provide information that is essential for the practical applications of the single-crystal perovskite NWs and NPs, and the imaging microscopy may also be applicable to other optoelectronic materials.
10. 10
  Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber Science 2013, 342, 341– 344 DOI: 10.1126/science.1243982
  10
  Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber
  Stranks, Samuel D.; Eperon, Giles E.; Grancini, Giulia; Menelaou, Christopher; Alcocer, Marcelo J. P.; Leijtens, Tomas; Herz, Laura M.; Petrozza, Annamaria; Snaith, Henry J.
  Science (Washington, DC, United States) (2013), 342 (6156), 341-344CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  Org.-inorg. perovskites showed promise as high-performance absorbers in solar cells, 1st as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, the authors report transient absorption and photoluminescence-quenching measurements to det. the electron-hole diffusion lengths, diffusion consts., and lifetimes in mixed halide (MeNH3PbI3-xClx) and triiodide (MeNH3PbI3) perovskite absorbers. The diffusion lengths are >1 μm in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. But the triiodide absorber has electron-hole diffusion lengths of about 100 nm. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a crit. parameter to optimize for future perovskite absorber development.
11. 11
  Christians, J. A.; Manser, J. S.; Kamat, P. V. Multifaceted excited state of CH₃NH₃PbI₃. Charge separation, recombination, and trapping J. Phys. Chem. Lett. 2015, 6, 2086– 2095 DOI: 10.1021/acs.jpclett.5b00594
  11
  Multifaceted Excited State of CH3NH3PbI3. Charge Separation, Recombination, and Trapping
  Christians, Jeffrey A.; Manser, Joseph S.; Kamat, Prashant V.
  Journal of Physical Chemistry Letters (2015), 6 (11), 2086-2095CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  A review. A need to understand the excited-state behavior of org.-inorg. hybrid perovskites, such as CH3NH3PbI3, has arisen due to the rapid development of perovskite solar cells. The photoinduced processes leading to the efficient charge sepn. obsd. in these materials remain somewhat elusive. This Perspective presents an overview of the initial attempts to characterize the excited-state and charge recombination dynamics in the prototypical material CH3NH3PbI3. While much has been accomplished in designing high-efficiency solar cells, the multifaceted nature of the CH3NH3PbI3 excited state offers ample challenges for the photovoltaic community to better comprehend. Building on this foundation may enable us to tackle the stability concerns that have shadowed the rise of perovskite solar cells. Furthermore, a better understanding of the excited-state properties can provide insight into the specific properties that have thrust this material to the forefront of photovoltaic research.
12. 12
  Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination kinetics in organic–inorganic perovskites: excitons, free charge, and subgap states Phys. Rev. Appl. 2014, 2, 034007 DOI: 10.1103/physrevapplied.2.034007
  12
  Recombination kinetics in organic-inorganic perovskites: excitons, free charge, and subgap states
  Stranks, Samuel D.; Burlakov, Victor M.; Leijtens, Tomas; Ball, James M.; Goriely, Alain; Snaith, Henry J.
  Physical Review Applied (2014), 2 (3), 034007CODEN: PRAHB2; ISSN:2331-7019. (American Physical Society)
  Org.-inorg. perovskites are attracting increasing attention for their use in high-performance solar cells. Nevertheless, a detailed understanding of charge generation, interplay of excitons and free charge carriers, and recombination pathways, crucial for further device improvement, remains incomplete. Here, we present an anal. model describing both equil. properties of free charge carriers and excitons in the presence of electronic subgap trap states and their time evolution after photoexcitation in CH3NH3PbI3-xClx. At low fluences the charge-trapping pathways limit the photoluminescence quantum efficiency, whereas at high fluences the traps are predominantly filled and recombination of the photogenerated species is dominated by efficient radiative processes. We show exptl. that the photoluminescence quantum efficiency approaches 100% at low temps. and at high fluences, as predicted by our model. Our approach provides a theor. framework to understand the fundamental physics of perovskite semiconductors and to help in designing and enhancing the material for improved optoelectronic device operation.
13. 13
  deQuilettes, D. W.; Zhang, W.; Burlakov, V. M.; Graham, D. J.; Leijtens, T.; Osherov, A.; Bulović, V.; Snaith, H. J.; Ginger, D. S.; Stranks, S. D. Photo-induced halide redistribution in organic–inorganic perovskite films Nat. Commun. 2016, 7, 11683 DOI: 10.1038/ncomms11683
  13
  Photo-induced halide redistribution in organic-inorganic perovskite films
  deQuilettes Dane W; Ginger David S; Zhang Wei; Burlakov Victor M; Leijtens Tomas; Snaith Henry J; Burlakov Victor M; Graham Daniel J; Osherov Anna; Bulovic Vladimir; Stranks Samuel D; Stranks Samuel D
  Nature communications (2016), 7 (), 11683 ISSN:.
  Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.
14. 14
  Bischak, C. G.; Sanehira, E. M.; Precht, J. T.; Luther, J. M.; Ginsberg, N. S. Heterogeneous charge carrier dynamics in organic–inorganic hybrid materials: nanoscale lateral and depth-dependent variation of recombination rates in methylammonium lead halide perovskite thin films Nano Lett. 2015, 15, 4799– 4807 DOI: 10.1021/acs.nanolett.5b01917
  14
  Heterogeneous Charge Carrier Dynamics in Organic-Inorganic Hybrid Materials: Nanoscale Lateral and Depth-Dependent Variation of Recombination Rates in Methylammonium Lead Halide Perovskite Thin Films
  Bischak, Connor G.; Sanehira, Erin M.; Precht, Jake T.; Luther, Joseph M.; Ginsberg, Naomi S.
  Nano Letters (2015), 15 (7), 4799-4807CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  The authors reveal substantial luminescence yield heterogeneity among individual subdiffraction grains of high-performing methylammonium lead halide perovskite films by using high-resoln. cathodoluminescence microscopy. Using considerably lower accelerating voltages than is conventional in SEM, the authors image the electron beam-induced luminescence of the films and statistically characterize the depth-dependent role of defects that promote nonradiative recombination losses. The highest variability in the luminescence intensity is obsd. at the exposed grain surfaces, which the authors attribute to surface defects. By probing deeper into the film, it appears that bulk defects are more homogeneously distributed. By identifying the origin and variability of a surface-specific loss mechanism that deleteriously impacts device efficiency, probably producing films homogeneously composed of the highest-luminescence grains found in this study could result in a dramatic improvement of overall device efficiency. Also although cathodoluminescence microscopy is generally used only to image inorg. materials it can be a powerful tool to study radiative and nonradiative charge carrier recombination on the nanoscale in org.-inorg. hybrid materials.
15. 15
  Yuan, H.; Debroye, E.; Janssen, K.; Naiki, H.; Steuwe, C.; Lu, G.; Moris, M.; Orgiu, E.; Uji-i, H.; De Schryver, F.; Samorì, P.; Hofkens, J.; Roeffaers, M. Degradation of methylammonium lead iodide perovskite structures through light and electron beam driven ion migration J. Phys. Chem. Lett. 2016, 7, 561– 566 DOI: 10.1021/acs.jpclett.5b02828
  15
  Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration
  Yuan, Haifeng; Debroye, Elke; Janssen, Kris; Naiki, Hiroyuki; Steuwe, Christian; Lu, Gang; Moris, Michele; Orgiu, Emanuele; Uji-i, Hiroshi; De Schryver, Frans; Samori, Paolo; Hofkens, Johan; Roeffaers, Maarten
  Journal of Physical Chemistry Letters (2016), 7 (3), 561-566CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degrdn. pathways. Here, the authors apply simultaneous luminescence and electron microscopy on perovskites for the 1st time, allowing the authors to monitor in situ morphol. evolution and optical properties upon perovskite degrdn. Morphol., photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degrdn. driven by electron beam (e-beam) or by light. A transversal elec. current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degrdn. results in material decompn. to scattered particles and shows little PL spectral shifts. The differences in degrdn. can be ascribed to different elec. currents that drive ion migration. Also, soln.-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphol. The authors' results reveal the essential role of ion migration in perovskite degrdn. and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphol. and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degrdn. and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using SEM or TEM techniques.
16. 16
  Hentz, O.; Zhao, Z.; Gradečak, S. Impacts of ion segregation on local optical properties in mixed halide perovskite films Nano Lett. 2016, 16, 1485– 1490 DOI: 10.1021/acs.nanolett.5b05181
  16
  Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films
  Hentz, Olivia; Zhao, Zhibo; Gradecak, Silvija
  Nano Letters (2016), 16 (2), 1485-1490CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Despite the recent astronomical success of org.-inorg. perovskite solar cells (PSCs), the impact of microscale film inhomogeneities on device performance remains poorly understood. In this work, we study CH3NH3PbI3 perovskite films using cathodoluminescence in scanning transmission electron microscopy and show that localized regions with increased cathodoluminescence intensity correspond to iodide-enriched regions. These observations constitute direct evidence that nanoscale stoichiometric variations produce corresponding inhomogeneities in film cathodoluminescence intensity. Moreover, we observe the emergence of high-energy transitions attributed to beam induced iodide segregation, which may mirror the effects of ion migration during PSC operation. Our results demonstrate that such ion segregation can fundamentally change the local optical and microstructural properties of org.-inorg. perovskite films in the course of normal device operation and therefore address the obsd. complex and unpredictable behavior in PSC devices.
17. 17
  Meloni, S.; Moehl, T.; Tress, W.; Franckevičius, M.; Saliba, M.; Lee, Y. H.; Gao, P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Rothlisberger, U.; Graetzel, M. Ionic polarization-induced current–voltage hysteresis in CH₃NH₃PbX₃ perovskite solar cells Nat. Commun. 2016, 7, 10334 DOI: 10.1038/ncomms10334
  17
  Ionic polarization-induced current-voltage hysteresis in CH3NH3PbX3 perovskite solar cells
  Meloni, Simone; Moehl, Thomas; Tress, Wolfgang; Franckevicius, Marius; Saliba, Michael; Lee, Yong Hui; Gao, Peng; Nazeeruddin, Mohammad Khaja; Zakeeruddin, Shaik Mohammed; Rothlisberger, Ursula; Graetzel, Michael
  Nature Communications (2016), 7 (), 10334CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  CH3NH3PbX3 (MAPbX3) perovskites have attracted considerable attention as absorber materials for solar light harvesting, reaching solar to power conversion efficiencies above 20%. In spite of the rapid evolution of the efficiencies, the understanding of basic properties of these semiconductors is still ongoing. One phenomenon with so far unclear origin is the so-called hysteresis in the current-voltage characteristics of these solar cells. Here we investigate the origin of this phenomenon with a combined exptl. and computational approach. Exptl. the activation energy for the hysteretic process is detd. and compared with the computational results. First-principles simulations show that the timescale for MA+ rotation excludes a MA-related ferroelec. effect as possible origin for the obsd. hysteresis. On the other hand, the computationally detd. activation energies for halide ion (vacancy) migration are in excellent agreement with the exptl. detd. values, suggesting that the migration of this species causes the obsd. hysteretic behavior of these solar cells.
18. 18
  Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.; Huang, J. Giant switchable photovoltaic effect in organometal trihalide perovskite devices Nat. Mater. 2014, 14, 193– 198 DOI: 10.1038/nmat4150
  There is no corresponding record for this reference.
19. 19
  Draguta, S.; Thakur, S.; Morozov, Y. V.; Wang, Y.; Manser, J. S.; Kamat, P. V.; Kuno, M. Spatially non-uniform trap state densities in solution-processed hybrid perovskite thin films J. Phys. Chem. Lett. 2016, 7, 715– 721 DOI: 10.1021/acs.jpclett.5b02888
  19
  Spatially Non-uniform Trap State Densities in Solution-Processed Hybrid Perovskite Thin Films
  Draguta, Sergiu; Thakur, Siddharatha; Morozov, Yurii V.; Wang, Yuanxing; Manser, Joseph S.; Kamat, Prashant V.; Kuno, Masaru
  Journal of Physical Chemistry Letters (2016), 7 (4), 715-721CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  The facile soln.-processability of methylammonium Pb iodide (MeNH3PbI3) perovskites has catalyzed the development of inexpensive, hybrid perovskite-based optoelectronics. Apparently, soln.-processed MeNH3PbI3 films possess local emission heterogeneities, stemming from electronic disorder in the material. The spatially resolved emission properties of MeNH3PbI3 films were studied through detailed emission intensity vs. excitation intensity measurements. These studies enable establishing the existence of nonuniform trap d. variations wherein regions of MeNH3PbI3 films exhibit effective free carrier recombination while others exhibit emission dynamics strongly influenced by the presence of trap states. Such trap d. variations lead to spatially varying emission quantum yields and correspondingly impact the performance of both methylammonium Pb halide perovskite solar cells and other hybrid perovskite-based devices. The obsd. spatial extent of the optical disorder extends over length scales greater than that of underlying cryst. domains, suggesting the existence of other factors, beyond grain boundary-related nonradiative recombination channels, which lead to significant intrafilm optical heterogeneities.
20. 20
  Klein, J. R.; Flender, O.; Scholz, M.; Oum, K.; Lenzer, T. Charge carrier dynamics of methylammonium lead iodide: from PbI₂-rich to low-dimensional broadly emitting perovskites Phys. Chem. Chem. Phys. 2016, 18, 10800– 10808 DOI: 10.1039/C5CP07167D
  20
  Charge carrier dynamics of methylammonium lead iodide: from PbI2-rich to low-dimensional broadly emitting perovskites
  Klein, Johannes R.; Flender, Oliver; Scholz, Mirko; Oum, Kawon; Lenzer, Thomas
  Physical Chemistry Chemical Physics (2016), 18 (16), 10800-10808CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  The authors provide a study of the charge carrier dynamics of the (MAI)x(PbI2)1-x system in the range x = 0.32-0.90 following the recently published pseudobinary phase-compn. processing diagram of Song et al. (Chem. Mater., 2015, 27, 4612). The dynamics were studied using ultrafast pump-supercontinuum probe spectroscopy over the pump fluence range 2-50 μJ cm-2, allowing for a wide variation of the initial carrier d. At high MAI excess (x = 0.90), low-dimensional perovskites (LDPs) are formed, and their luminescence spectra are significantly blue-shifted by ∼50 nm and broadened compared to the 3-dimensional perovskite. The shift is due to quantum confinement effects, and the inhomogeneous broadening arises from different low-dimensional structures (predominantly 2-dimensional, but presumably also 1-dimensional and 0D). Accurate transient carrier temps. are extd. from the transient absorption spectra. The regimes of carrier-carrier, carrier-optical phonon and acoustic phonon scattering are clearly distinguished. Perovskites with mole fractions x ≤ 0.71 exhibit extremely fast carrier cooling (∼300 fs) at low fluence of 2 μJ cm-2, however cooling slows down significantly at high fluence of 50 μJ cm-2 due to the hot phonon effect (∼2.8 ps). A kinetic anal. of the electron-hole recombination dynamics provides 2nd-order recombination rate consts. k2 which decrease from 5.3 to 1.5 × 10-9 cm3 s-1 in the range x = 0.32-0.71. In contrast, recombination in the LDPs (x = 0.90) is more than one order of magnitude faster, 6.4 × 10-8 cm3 s-1, which is related to the confined perovskite structure. Recombination in these LDPs should be however still slow enough for their potential application as efficient broadband emitters or solar light-harvesting materials.
21. 21
  Liu, M.; Johnston, M. B.; Snaith, H. J. Efficient planar heterojunction perovskite solar cells by vapour deposition Nature 2013, 501, 395– 398 DOI: 10.1038/nature12509
  21
  Efficient planar heterojunction perovskite solar cells by vapour deposition
  Liu, Mingzhen; Johnston, Michael B.; Snaith, Henry J.
  Nature (London, United Kingdom) (2013), 501 (7467), 395-398CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based 1st-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between 2 charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport pos. and neg. charges in spatially sepd. phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapor-deposited perovskite as the absorbing layer can have solar-to-elec. power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). Perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.
22. 22
  Kutes, Y.; Zhou, Y.; Bosse, J. L.; Steffes, J.; Padture, N. P.; Huey, B. D. Mapping the photoresponse of CH₃NH₃PbI₃ hybrid perovskite thin films at the nanoscale Nano Lett. 2016, 16, 3434– 3441 DOI: 10.1021/acs.nanolett.5b04157
  22
  Mapping the Photoresponse of CH3NH3PbI3 Hybrid Perovskite Thin Films at the Nanoscale
  Kutes, Yasemin; Zhou, Yuanyuan; Bosse, James L.; Steffes, James; Padture, Nitin P.; Huey, Bryan D.
  Nano Letters (2016), 16 (6), 3434-3441CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Perovskite solar cells (PSCs) based on thin films of organolead trihalide perovskites (OTPs) hold unprecedented promise for low-cost, high-efficiency photovoltaics (PVs) of the future. While PV performance parameters of PSCs, such as short circuit current, open circuit voltage, and max. power, are always measured at the macroscopic scale, it is necessary to probe such photoresponses at the nanoscale to gain key insights into the fundamental PV mechanisms and their localized dependence on the OTP thin-film microstructure. Here we use photoconductive at. force microscopy spectroscopy to map for the first time variations of PV performance at the nanoscale for planar PSCs based on hole-transport-layer free methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) thin films. These results reveal substantial variations in the photoresponse that correlate with thin-film microstructural features such as intragrain planar defects, grains, grain boundaries, and notably also grain-aggregates. The insights gained into such microstructure-localized PV mechanisms are essential for guiding microstructural tailoring of OTP films for improved PV performance in future PSCs.
23. 23
  Li, C.; Tscheuschner, S.; Paulus, F.; Hopkinson, P. E.; Kießling, J.; Köhler, A.; Vaynzof, Y.; Huettner, S. Iodine migration and its effect on hysteresis in perovskite solar cells Adv. Mater. 2016, 28, 2446– 2454 DOI: 10.1002/adma.201503832
  23
  Iodine Migration and its Effect on Hysteresis in Perovskite Solar Cells
  Li, Cheng; Tscheuschner, Steffen; Paulus, Fabian; Hopkinson, Paul E.; Kiessling, Johannes; Koehler, Anna; Vaynzof, Yana; Huettner, Sven
  Advanced Materials (Weinheim, Germany) (2016), 28 (12), 2446-2454CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
  In brief, we used three different methods to reveal the underlying processes relating to hysteresis. First we employed electroabsorption(EA) spectroscopy, a noninvasive in situ characterization approach to det. the built-in potential ( VBI) in solar cell devices. In a second expt. we applied a staircase voltage pro le to these devices and measured the time dependent current at a series of temps. in order to study the activation energy of the migrating species in perovskite based devices. In the last expt. we used X-ray photoemission spectroscopy (XPS) measurements to study the redistribution of elements within laterally configured devices after long-term elec. biasing. Our results suggest that the hysteresis in J-V curves originates from the interfacial barrier assocd. with the drift of iodide ions or the resp. interstitial under an elec. field.
24. 24
  Yun, J. S.; Ho-Baillie, A.; Huang, S.; Woo, S. H.; Heo, Y.; Seidel, J.; Huang, F.; Cheng, Y.-B.; Green, M. A. Benefit of grain boundaries in organic–inorganic halide planar perovskite solar cells J. Phys. Chem. Lett. 2015, 6, 875– 880 DOI: 10.1021/acs.jpclett.5b00182
  24
  Benefit of grain boundaries in org.-inorg. halide planar perovskite solar cells
  Yun, Jae S.; Ho-Baillie, Anita; Huang, Shujuan; Woo, Sang H.; Heo, Yooun; Seidel, Jan; Huang, Fuzhi; Cheng, Yi-Bing; Green, Martin A.
  Journal of Physical Chemistry Letters (2015), 6 (5), 875-880CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  The past 2 years have seen the uniquely rapid emergence of a new class of solar cell based on mixed org.-inorg. halide perovskite. Grain boundaries are present in polycryst. thin film solar cell, and they play an important role that could be benign or detrimental to solar-cell performance. Here we present efficient charge sepn. and collection at the grain boundaries measured by KPFM and c-AFM in CH3NH3PbI3 film in a CH3NH3PbI3/TiO2/FTO/glass heterojunction structure. We observe the presence of a potential barrier along the grain boundaries under dark conditions and higher photovoltage along the grain boundaries compare to grain interior under the illumination. Also, c-AFM measurement presents higher short-circuit current collection near grain boundaries, confirming the beneficial roles grain boundaries play in collecting carriers efficiently.
25. 25
  Shao, Y.; Fang, Y.; Li, T.; Wang, Q.; Dong, Q.; Deng, Y.; Yuan, Y.; Wei, H.; Wang, M.; Gruverman, A.; Shield, J.; Huang, J. Grain boundary dominated ion migration in polycrystalline organic–inorganic halide perovskite films Energy Environ. Sci. 2016, 9, 1752– 1759 DOI: 10.1039/C6EE00413J
  25
  Grain boundary dominated ion migration in polycrystalline organic-inorganic halide perovskite films
  Shao, Yuchuan; Fang, Yanjun; Li, Tao; Wang, Qi; Dong, Qingfeng; Deng, Yehao; Yuan, Yongbo; Wei, Haotong; Wang, Meiyu; Gruverman, Alexei; Shield, Jeffery; Huang, Jinsong
  Energy & Environmental Science (2016), 9 (5), 1752-1759CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
  The efficiency of perovskite solar cells is approaching that of single-cryst. silicon solar cells despite the presence of a large grain boundary (GB) area in the polycryst. thin films. Here, by using a combination of nanoscopic and macroscopic level measurements, we show that ion migration in polycryst. perovskites dominates through GBs. Atomic force microscopy measurements reveal much stronger hysteresis both for photocurrent and dark-current at the GBs than on the grain interiors, which can be explained by faster ion migration at the GBs. The dramatically enhanced ion migration results in the redistribution of ions along the GBs after elec. poling, in contrast to the intact grain area. The perovskite single-crystal devices without GBs show negligible current hysteresis and no ion-migration signal. The discovery of dominating ion migration through GBs in perovskites can lead to broad applications in many types of devices including photovoltaics, memristors, and ion batteries.
26. 26
  González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Organometal halide perovskites: bulk low-dimension materials and nanoparticles Part. Part. Syst. Charact. 2015, 32, 709– 720 DOI: 10.1002/ppsc.201400214
  26
  Organometal Halide Perovskites: Bulk Low-Dimension Materials and Nanoparticles
  Gonzalez-Carrero, Soranyel; Galian, Raquel E.; Perez-Prieto, Julia
  Particle & Particle Systems Characterization (2015), 32 (7), 709-720CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Organometal halide perovskites (hybrid perovskites) contain an anionic metal-halogen-semiconducting framework and charge-compensating org. cations. As hybrid materials, they combine useful properties of both org. and inorg. materials, such as plastic mech. properties and good electronic mobility related to org. and inorg. material, resp. They are prepd. from abundant and low cost starting compds. The perovskite stoichiometry is assocd. with the dimensionality of its inorg. framework, which can vary from three to zero, 3D consisting of corner-sharing MX6 octahedra, and 0D consisting of isolated octahedra. Small-sized org. cations can fit into the MX6 octahedra of the 3D framework and in all dimensions org. cations surround the inorg. framework. Regarding the low dimensionality in the material, this refers to at least one of its dimensions being shorter than approx. 100 nm. These materials should be considered as genuine nanomaterials or as bulk materials depending on whether they have three or less than three dimensions on the nanoscale, resp. In principle, hybrid perovskite nanoparticles can be prepd. with different shapes and with inorg. framework dimensionalities varying from 0D to 3D, and this also applies to the bulk material. This report is mainly focused on the unique properties of organometal halide perovskite nanoparticles.
27. 27
  González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Organic–inorganic and all-inorganic lead halide nanoparticles Opt. Express 2016, 24, A285– A301 DOI: 10.1364/oe.24.00a285
  There is no corresponding record for this reference.
28. 28
  Schmidt, L. C.; Pertegás, A.; González-Carrero, S.; Malinkiewicz, O.; Agouram, S.; Espallargas, G. M.; Bolink, H. J.; Galian, R. E.; Pérez-Prieto, J. Nontemplate synthesis of CH₃NH₃PbBr₃ perovskite nanoparticles J. Am. Chem. Soc. 2014, 136, 850– 853 DOI: 10.1021/ja4109209
  28
  Nontemplate Synthesis of CH3NH3PbBr3 Perovskite Nanoparticles
  Schmidt, Luciana C.; Pertegas, Antonio; Gonzalez-Carrero, Soranyel; Malinkiewicz, Olga; Agouram, Said; Minguez Espallargas, Guillermo; Bolink, Henk J.; Galian, Raquel E.; Perez-Prieto, Julia
  Journal of the American Chemical Society (2014), 136 (3), 850-853CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  To date, there is no example in the literature of free, nm-sized, organo-Pb halide MeNH3PbBr3 perovskites. The prepn. is reported of 6 nm-sized nanoparticles of this type by a simple and fast method based on the use of an NH4Br with a medium-sized chain that keeps the nanoparticles dispersed in a wide range of org. solvents. These nanoparticles can be maintained stable in the solid state and in concd. solns. for >3 mo, without requiring a mesoporous material. This makes it possible to prep. homogeneous thin films of these nanoparticles by spin-coating on a SiO2 substrate. Both the colloidal soln. and the thin film emit light within a narrow bandwidth of the visible spectrum and with a high quantum yield (∼20%); this could be advantageous in the design of optoelectronic devices.
29. 29
  Zhu, H.; Fu, Y.; Meng, F.; Wu, X.; Gong, Z.; Ding, Q.; Gustafsson, M. V.; Trinh, M. T.; Jin, S.; Zhu, X.-Y. Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors Nat. Mater. 2015, 14, 636– 642 DOI: 10.1038/nmat4271
  29
  Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors
  Zhu, Haiming; Fu, Yongping; Meng, Fei; Wu, Xiaoxi; Gong, Zizhou; Ding, Qi; Gustafsson, Martin V.; Trinh, M. Tuan; Jin, Song; Zhu, X.-Y.
  Nature Materials (2015), 14 (6), 636-642CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
  The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same phys. properties that are ideal for semiconductor lasers. Here, we show room-temp. and wavelength-tunable lasing from single-crystal lead halide perovskite nanowires with very low lasing thresholds (220 nJ cm-2) and high quality factors (Q ∼ 3,600). The lasing threshold corresponds to a charge carrier d. as low as 1.5 × 1016 cm-3. Kinetic anal. based on time-resolved fluorescence reveals little charge carrier trapping in these single-crystal nanowires and gives estd. lasing quantum yields approaching 100%. Such lasing performance, coupled with the facile soln. growth of single-crystal nanowires and the broad stoichiometry-dependent tunability of emission color, makes lead halide perovskites ideal materials for the development of nanophotonics, in parallel with the rapid development in photovoltaics from the same materials.
30. 30
  Fu, Y.; Meng, F.; Rowley, M. B.; Thompson, B. J.; Shearer, M. J.; Ma, D.; Hamers, R. J.; Wright, J. C.; Jin, S. Solution growth of single crystal methylammonium lead halide perovskite nanostructures for optoelectronic and photovoltaic applications J. Am. Chem. Soc. 2015, 137, 5810– 5818 DOI: 10.1021/jacs.5b02651
  30
  Solution Growth of Single Crystal Methylammonium Lead Halide Perovskite Nanostructures for Optoelectronic and Photovoltaic Applications
  Fu, Yongping; Meng, Fei; Rowley, Matthew B.; Thompson, Blaise J.; Shearer, Melinda J.; Ma, Dewei; Hamers, Robert J.; Wright, John C.; Jin, Song
  Journal of the American Chemical Society (2015), 137 (17), 5810-5818CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Understanding crystal growth and improving material quality is important for improving semiconductors for electronic, optoelectronic, and photovoltaic applications. Amidst the surging interest in solar cells based on hybrid org.-inorg. lead halide perovskites and the exciting progress in device performance, improved understanding and better control of the crystal growth of these perovskites could further boost their optoelectronic and photovoltaic performance. Here, new insights are reported on the crystal growth of the perovskite materials, esp. cryst. nanostructures. Specifically, single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide perovskites (CH3NH3PbI3 and CH3NH3PbBr3) are successfully grown via a dissoln.-recrystn. pathway in a soln. synthesis from lead iodide (or lead acetate) films coated on substrates. These single crystal nanostructures display strong room-temp. photoluminescence and long carrier lifetime. It is also reported that a solid-liq. interfacial conversion reaction can create a highly cryst., nanostructured MAPbI3 film with micrometer grain size and high surface coverage that enables photovoltaic devices with a power conversion efficiency of 10.6%. These results suggest that single-crystal perovskite nanostructures provide improved photophys. properties that are important for fundamental studies and future applications in nanoscale optoelectronic and photonic devices.
31. 31
  Zhu, F.; Men, L.; Guo, Y.; Zhu, Q.; Bhattacharjee, U.; Goodwin, P. M.; Petrich, J. W.; Smith, E. A.; Vela, J. Shape evolution and single particle luminescence of organometal halide perovskite nanocrystals ACS Nano 2015, 9, 2948– 2959 DOI: 10.1021/nn507020s
  31
  Shape Evolution and Single Particle Luminescence of Organometal Halide Perovskite Nanocrystals
  Zhu, Feng; Men, Long; Guo, Yijun; Zhu, Qiaochu; Bhattacharjee, Ujjal; Goodwin, Peter M.; Petrich, Jacob W.; Smith, Emily A.; Vela, Javier
  ACS Nano (2015), 9 (3), 2948-2959CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Organometallic halide perovskites MeNH3PbX3 (X = I, Br, Cl) have quickly become 1 of the most promising semiconductors for solar cells, with photovoltaics made of these materials reaching power conversion efficiencies of ∼20%. Improving the ability to harness the full potential of organometal halide perovskites will require more controllable syntheses that permit a detailed understanding of their fundamental chem. and photophysics. MeNH3PbX3 (X = I, Br) nanocrystals with different morphols. (dots, rods, plates, or sheets) were systematically synthesized by using different solvents and capping ligands. MeNH3PbX3 nanowires and nanorods capped with octylammonium halides show relatively higher luminescence (PL) quantum yields and long PL lifetimes. MeNH3PbI3 nanowires monitored at the single particle level show shape-correlated PL emission across whole particles, with little photobleaching obsd. and very few off periods. This work highlights the potential of low-dimensional organometal halide perovskite semiconductors in constructing new porous and nanostructured solar cell architectures, as well as in applying these materials to other fields such as light-emitting devices and single particle imaging and tracking.
32. 32
  Aharon, S.; Etgar, L. Two dimensional organometal halide perovskite nanorods with tunable optical properties Nano Lett. 2016, 16, 3230– 3235 DOI: 10.1021/acs.nanolett.6b00665
  32
  Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties
  Aharon, Sigalit; Etgar, Lioz
  Nano Letters (2016), 16 (5), 3230-3235CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Facile low-temp. synthesis of 2-dimensional (2D) Pb halide perovskite nanorods (NRs) is presented. These NRs show a shift to higher energies in the absorbance and in the luminescence compared to the bulk material, which supports their 2D structure. XRD anal. of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. By alternating the halide compn., the authors were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, the authors were able to provide the formation mechanism of these novel 2D perovskite NRs.
33. 33
  González-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Maximizing the emissive properties of CH₃NH₃PbBr₃ perovskite nanoparticles J. Mater. Chem. A 2015, 3, 9187– 9193 DOI: 10.1039/c4ta05878j
  33
  Maximizing the emissive properties of CH3NH3PbBr3 perovskite nanoparticles
  Gonzalez-Carrero, Soranyel; Galian, Raquel E.; Perez-Prieto, Julia
  Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (17), 9187-9193CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
  Highly luminescent and photostable MeNH3PbBr3 nanoparticles were prepd. by fine-tuning the molar ratio between MeNH3Br, PbBr2, a medium-size alkyl-chain NH4+ salt, and 1-octadecene. The nanoparticles exhibit an excellent photoluminescence quantum yield (∼83%) and av. recombination lifetime (∼600 ns) in toluene dispersion.
34. 34
  Huang, B.; Bates, M.; Zhuang, X. Super-resolution fluorescence microscopy Annu. Rev. Biochem. 2009, 78, 993– 1016 DOI: 10.1146/annurev.biochem.77.061906.092014
  34
  Super-resolution fluorescence microscopy
  Huang, Bo; Bates, Mark; Zhuang, Xiaowei
  Annual Review of Biochemistry (2009), 78 (), 993-1016CODEN: ARBOAW; ISSN:0066-4154. (Annual Reviews Inc.)
  A review. Achieving a spatial resoln. that is not limited by the diffraction of light, recent developments of super-resoln. fluorescence microscopy techniques allow the observation of many biol. structures not resolvable in conventional fluorescence microscopy. New advances in these techniques now give them the ability to image three-dimensional (3D) structures, measure interactions by multicolor colocalization, and record dynamic processes in living cells at the nanometer scale. It is anticipated that super-resoln. fluorescence microscopy will become a widely used tool for cell and tissue imaging to provide previously unobserved details of biol. structures and processes.
35. 35
  Habuchi, S. Super-resolution molecular and functional imaging of nanoscale architectures in life and materials science Front. Bioeng. Biotechnol. 2014, 2, 20 DOI: 10.3389/fbioe.2014.00020
  35
  Super-resolution molecular and functional imaging of nanoscale architectures in life and materials science
  Habuchi Satoshi
  Frontiers in bioengineering and biotechnology (2014), 2 (), 20 ISSN:.
  Super-resolution (SR) fluorescence microscopy has been revolutionizing the way in which we investigate the structures, dynamics, and functions of a wide range of nanoscale systems. In this review, I describe the current state of various SR fluorescence microscopy techniques along with the latest developments of fluorophores and labeling for the SR microscopy. I discuss the applications of SR microscopy in the fields of life science and materials science with a special emphasis on quantitative molecular imaging and nanoscale functional imaging. These studies open new opportunities for unraveling the physical, chemical, and optical properties of a wide range of nanoscale architectures together with their nanostructures and will enable the development of new (bio-)nanotechnology.
36. 36
  Neely, R. K.; Dedecker, P.; Hotta, J.-i.; Urbanavičiu̅tė, G.; Klimašauskas, S.; Hofkens, J. DNA fluorocode: a single molecule, optical map of DNA with nanometre resolution Chem. Sci. 2010, 1, 453– 460 DOI: 10.1039/c0sc00277a
  36
  DNA fluorocode: A single molecule, optical map of DNA with nanometre resolution
  Neely, Robert K.; Dedecker, Peter; Hotta, Jun-ichi; Urbanaviciute, Giedre; Klimasauskas, Saulius; Hofkens, Johan
  Chemical Science (2010), 1 (4), 453-460CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  We present a new method for single-mol. optical DNA mapping using an exceptionally dense, yet sequence-specific coverage of DNA with a fluorescent probe. The method employs a DNA methyltransferase enzyme to direct the DNA labeling, followed by mol. combing of the DNA onto a polymer-coated surface and subsequent sub-diffraction limit localization of the fluorophores. The result is a 'DNA fluorocode'; a simple description of the DNA sequence, with a max. achievable resoln. of less than 20 bases, which can be read and analyzed like a barcode. We demonstrate the generation of a fluorocode for genomic DNA from the lambda bacteriophage using a DNA methyltransferase, M.HhaI, to direct fluorescent labels to four-base sequences reading 5'-GCGC-3'. A consensus fluorocode that allows the study of the DNA sequence at the level of an individual labeling site can be generated from a handful of mols.
37. 37
  Chen, Y.; He, M.; Peng, J.; Sun, Y.; Liang, Z. Structure and growth control of organic–inorganic halide perovskites for optoelectronics: From polycrystalline films to single crystals Adv. Sci. 2016, 3, 1500392 DOI: 10.1002/advs.201500392
  37
  Structure and Growth Control of Organic-Inorganic Halide Perovskites for Optoelectronics: From Polycrystalline Films to Single Crystals
  Chen Yani; He Minhong; Peng Jiajun; Sun Yong; Liang Ziqi
  Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2016), 3 (4), 1500392 ISSN:2198-3844.
  Recently, organic-inorganic halide perovskites have sparked tremendous research interest because of their ground-breaking photovoltaic performance. The crystallization process and crystal shape of perovskites have striking impacts on their optoelectronic properties. Polycrystalline films and single crystals are two main forms of perovskites. Currently, perovskite thin films have been under intensive investigation while studies of perovskite single crystals are just in their infancy. This review article is concentrated upon the control of perovskite structures and growth, which are intimately correlated for improvements of not only solar cells but also light-emitting diodes, lasers, and photodetectors. We begin with the survey of the film formation process of perovskites including deposition methods and morphological optimization avenues. Strategies such as the use of additives, thermal annealing, solvent annealing, atmospheric control, and solvent engineering have been successfully employed to yield high-quality perovskite films. Next, we turn to summarize the shape evolution of perovskites single crystals from three-dimensional large sized single crystals, two-dimensional nanoplates, one-dimensional nanowires, to zero-dimensional quantum dots. Siginificant functions of perovskites single crystals are highlighted, which benefit fundamental studies of intrinsic photophysics. Then, the growth mechanisms of the previously mentioned perovskite crystals are unveiled. Lastly, perspectives for structure and growth control of perovskites are outlined towards high-performance (opto)electronic devices.
38. 38
  De Roo, J.; Ibáñez, M.; Geiregat, P.; Nedelcu, G.; Walravens, W.; Maes, J.; Martins, J. C.; Van Driessche, I.; Kovalenko, M. V.; Hens, Z. Highly dynamic ligand binding and light absorption coefficient of cesium lead bromide perovskite nanocrystals ACS Nano 2016, 10, 2071– 2081 DOI: 10.1021/acsnano.5b06295
  38
  Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals
  De Roo, Jonathan; Ibanez, Maria; Geiregat, Pieter; Nedelcu, Georgian; Walravens, Willem; Maes, Jorick; Martins, Jose C.; Van Driessche, Isabel; Kovalenko, Maksym V.; Hens, Zeger
  ACS Nano (2016), 10 (2), 2071-2081CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects of their chem. and photophysics such as surface chem. and quant. light absorption. Here, we elaborate on the synthesis of CsPbBr3 NCs and their surface chem. In addn., the intrinsic absorption coeff. was detd. exptl. by combining elemental anal. with accurate optical absorption measurements. 1H soln. NMR spectroscopy was used to characterize sample purity, elucidate the surface chem., and evaluate the influence of purifn. methods on the surface compn. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purifn. procedures. However, when a small amt. of both oleic acid and oleylamine is added, the NCs can be purified, maintaining optical, colloidal, and material integrity. In addn., we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid.
39. 39
  Ma, Q.; Mimura, K. i.; Kato, K. Tuning shape of barium titanate nanocubes by combination of oleic acid/tert-butylamine through hydrothermal process J. Alloys Compd. 2016, 655, 71– 78 DOI: 10.1016/j.jallcom.2015.09.156
  39
  Tuning shape of barium titanate nanocubes by combination of oleic acid/tert-butylamine through hydrothermal process
  Ma, Qiang; Mimura, Ken-ichi; Kato, Kazumi
  Journal of Alloys and Compounds (2016), 655 (), 71-78CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
  The shape and surface morphol. of mono-dispersed barium titanate (BaTiO3) nanocrystals were controlled by tuning the compn. of hydrothermal reaction system. High-quality BaTiO3 nanocubes with the smooth surface and 90° std. corner angle were synthesized by the hydrothermal method using a relatively low concn. of oleic acid and tert-butylamine, which were used as surfactant and additive, resp. The av. size of BaTiO3 nanocubes was ∼25 nm and the size distribution was relatively narrow. As a large amt. of surfactant and additive was employed, BaTiO3 nanocrystals with convex structure were synthesized. The terrace structure were developed at the {100} surface of the nanocrystals. Here, we analyzed systematically the role of oleic acid and tert-butylamine on the surface morphol. of BaTiO3 nanocrystals. Our study demonstrates the possibility of synthesizing high-quality BaTiO3 nanocubes for com. application. These findings can be applied on other perovskite nanomaterials.
40. 40
  Tian, Y.; Peter, M.; Unger, E.; Abdellah, M.; Zheng, K.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold Phys. Chem. Chem. Phys. 2015, 17, 24978– 24987 DOI: 10.1039/C5CP04410C
  40
  Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold
  Tian, Yuxi; Peter, Maximilian; Unger, Eva; Abdellah, Mohamed; Zheng, Kaibo; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
  Physical Chemistry Chemical Physics (2015), 17 (38), 24978-24987CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  A light-induced luminescence (PL) enhancement in surface-deposited methylammonium lead iodide (MeNH3PbI3) perovskites was studied using time-resolved luminescence microscopy. The authors found the PL intensity to increase up to 3 orders of magnitude upon light illumination with an excitation power d. of 0.01-1 W cm-2. The PL enhancement is accompanied by an increase of the PL lifetime from several nanoseconds to several hundred nanoseconds and also by an increase of the initial amplitude of the PL decay. The latter suggests excited state quenching at the sub-ps timescale. A model is proposed where the trapping sites responsible for nonradiative charge recombination can be de-activated by a photochem. reaction involving O. The reaction zone is spatially limited by the excitation light-penetration depth and diffusion length of the charge carriers. The latter increases in the light-curing process making the reaction zone spreading from the surface towards the interior of the crystal. The PL enhancement can be reversed by switching on/off the excitation light or switching the atm. between O and N. Slow diffusion of the reactants and products and equil. between the active and cured trapping sites probably are the reasons for peculiar responses of PL to such varied exptl. conditions.
41. 41
  Kim, B. J.; Kim, D. H.; Lee, Y.-Y.; Shin, H.-W.; Han, G. S.; Hong, J. S.; Mahmood, K.; Ahn, T. K.; Joo, Y.-C.; Hong, K. S.; Park, N.-G.; Lee, S.; Jung, H. S. Highly efficient and bending durable perovskite solar cells: toward a wearable power source Energy Environ. Sci. 2015, 8, 916– 921 DOI: 10.1039/C4EE02441A
  41
  Highly efficient and bending durable perovskite solar cells: toward a wearable power source
  Kim, Byeong Jo; Kim, Dong Hoe; Lee, Yoo-Yong; Shin, Hee-Won; Han, Gill Sang; Hong, Jung Sug; Mahmood, Khalid; Ahn, Tae Kyu; Joo, Young-Chang; Hong, Kug Sun; Park, Nam-Gyu; Lee, Sangwook; Jung, Hyun Suk
  Energy & Environmental Science (2015), 8 (3), 916-921CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
  Perovskite solar cells are promising candidates for realizing an efficient, flexible, and lightwt. energy supply system for wearable electronic devices. For flexible perovskite solar cells, achieving high power conversion efficiency (PCE) while using a low-temp. technol. for the fabrication of a compact charge collection layer is a crit. issue. Herein, we report on a flexible perovskite solar cell exhibiting 12.2% PCE as a result of the employment of an annealing-free, 20 nm thick, amorphous, compact TiOx layer deposited by at. layer deposition. The excellent performance of the cell was attributed to fast electron transport, verified by time-resolved photoluminescence and impedance studies. The PCE remained the same down to 0.4 sun illumination, as well as to a 45° tilt to incident light. Mech. bending of the devices worsened device performance by only 7% when a bending radius of 1 mm was used. The devices maintained 95% of the initial PCE after 1000 bending cycles for a bending radius of 10 mm. Degrdn. of the device performance by the bending was the result of crack formation from the transparent conducting oxide layer, demonstrating the potential of the low-temp.-processed TiOx layer to achieve more efficient and bendable perovskite solar cells, which becomes closer to a practical wearable power source.
42. 42
  Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals Science 2015, 347, 519– 522 DOI: 10.1126/science.aaa2725
  42
  Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals
  Shi, Dong; Adinolfi, Valerio; Comin, Riccardo; Yuan, Mingjian; Alarousu, Erkki; Buin, Andrei; Chen, Yin; Hoogland, Sjoerd; Rothenberger, Alexander; Katsiev, Khabiboulakh; Losovyj, Yaroslav; Zhang, Xin; Dowben, Peter A.; Mohammed, Omar F.; Sargent, Edward H.; Bakr, Osman M.
  Science (Washington, DC, United States) (2015), 347 (6221), 519-522CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  The fundamental properties and ultimate performance limits of organolead trihalide MAPbX3 (MA = CH3NH3+; X = Br- or I-) perovskites remain obscured by extensive disorder in polycryst. MAPbX3 films. The authors report an antisolvent vapor-assisted crystn. approach that enables the authors to create sizable crack-free MAPbX3 single crystals with vols. exceeding 100 cubic millimeters. These large single crystals enabled a detailed characterization of their optical and charge transport characteristics. The authors obsd. exceptionally low trap-state densities ∼109 to 1010 per cubic centimeter in MAPbX3 single crystals (comparable to the best photovoltaic-quality silicon) and charge carrier diffusion lengths exceeding 10 μm. These results were validated with d. functional theory calcns.
43. 43
  Ponseca, C. S., Jr.; Tian, Y.; Sundström, V.; Scheblykin, I. G. Excited state and charge-carrier dynamics in perovskite solar cell materials Nanotechnology 2016, 27, 082001 DOI: 10.1088/0957-4484/27/8/082001
  43
  Excited state and charge-carrier dynamics in perovskite solar cell materials
  Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundstrom, Villy; Scheblykin, Ivan G.
  Nanotechnology (2016), 27 (8), 082001/1-082001/16CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
  Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technol. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved cond., transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.
44. 44
  Wen, X.; Feng, Y.; Huang, S.; Huang, F.; Cheng, Y.-B.; Green, M.; Ho-Baillie, A. Defect trapping states and charge carrier recombination in organic–inorganic halide perovskites J. Mater. Chem. C 2016, 4, 793– 800 DOI: 10.1039/C5TC03109E
  44
  Defect trapping states and charge carrier recombination in organic-inorganic halide perovskites
  Wen, Xiaoming; Feng, Yu; Huang, Shujuan; Huang, Fuzhi; Cheng, Yi-Bing; Green, Martin; Ho-Baillie, Anita
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (4), 793-800CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  Org.-inorg. perovskite solar cells have attracted huge research interest due to rapid improvement in device performance showing great potential to be the next generation flexible solar cells. Unique defect properties in perovskite have been considered as the possible mechanism for the superior performance, and closely relevant to the effects of hysteresis and light soaking. To date, the quant. correlation and in-depth understanding of defects in org.-inorg. perovskite are still lacking although extensive investigation have been undertaken. Here we study defect trapping states and carrier recombination dynamics in org.-inorg. halide perovskites. At low excitation the photoluminescence (PL) intensity exhibits a super-linear increase with increasing excitation, due to the slow depopulation rate of the defect states. The steady state and time-resolved photoluminescence (PL) carried out in this work reveal that the carrier recombination dynamics is ultimately correlated with both the defect d. and the relaxation rate of the carriers in defects. A model is established for the relationship between the properties of the defect trapping state and steady state PL intensity. Two key parameters, (i) the ratio of the trap-state d. to the depopulation rate of trapped states and (ii) ratio of the max. d. of covalence band electrons to the trapping rate, can be extd. from the model based on the excitation dependent steady state PL. This work demonstrates that the properties of defect trapping states are closely related to the fabrication technique, and suggests that the org.-inorg. halide perovskite is partly defect-tolerant.
45. 45
  Merdasa, A.; Bag, M.; Tian, Y.; Källman, E.; Dobrovolsky, A.; Scheblykin, I. G. Super-resolution luminescence micro-spectroscopy reveals mechanism of photoinduced degradation in CH₃NH₃PbI₃ perovskite nanocrystals J. Phys. Chem. C 2016, 120, 10711– 10719 DOI: 10.1021/acs.jpcc.6b03512
  45
  Super-Resolution Luminescence Microspectroscopy Reveals the Mechanism of Photoinduced Degradation in CH3NH3PbI3 Perovskite Nanocrystals
  Merdasa, Aboma; Bag, Monojit; Tian, Yuxi; Kaellman, Elin; Dobrovolsky, Alexander; Scheblykin, Ivan G.
  Journal of Physical Chemistry C (2016), 120 (19), 10711-10719CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Photoinduced degrdn. of individual methylammonium lead triiodide (MAPbI3) perovskite nanocrystals was studied using super-resoln. luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degrdn. process, indicating that the degrdn. needs a high concn. of mobile photogenerated charges to occur. Probably the mechanistic process of degrdn. occurs as the three-dimensional MAPbI3 crystal structure smoothly collapses to the two-dimensional layered PbI2 structure. The degrdn. starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA+), which distorts the lattice structure causing alterations to the Pb-I-Pb bond angle and in turn changes the effective band gap.
46. 46
  Kong, W.; Rahimi-Iman, A.; Bi, G.; Dai, X.; Wu, H. Oxygen intercalation induced by photocatalysis on the surface of hybrid lead halide perovskites J. Phys. Chem. C 2016, 120, 7606– 7611 DOI: 10.1021/acs.jpcc.6b00496
  46
  Oxygen Intercalation Induced by Photocatalysis on the Surface of Hybrid Lead Halide Perovskites
  Kong, Weiguang; Rahimi-Iman, Arash; Bi, Gang; Dai, Xusheng; Wu, Huizhen
  Journal of Physical Chemistry C (2016), 120 (14), 7606-7611CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Methylammonium lead iodide (MAPbI3) perovskite has emerged as a dazzling nova in the solar cell realm. However, the robustness or stability of the material exposed to different ambiences is a key issue. In this paper, resonance Raman spectroscopy is combined with surface and bulk crystal characterizations to interpret the oxygen intercalation phenomenon on the surface of MAPbI3. We observe that oxygen can intercalate into the frameworks of MAPbI3 with the assistance of laser radiation excitation. By lowering down the pressure in the exptl. chamber, the intercalated oxygen can be readily removed. XPS and X-ray diffraction characterizations suggest that Pb-O bonds are mainly formed on the surface of MAPbI3 but are constrained to avoid the formation of PbO compd. The quantum chem. calcn. based on d. functional theory supports the above conclusions. The understanding of oxygen intercalation in MAPbI3 shall benefit the improvement of stability of the important solar cell materials.
47. 47
  Aristidou, N.; Sanchez-Molina, I.; Chotchuangchutchaval, T.; Brown, M.; Martinez, L.; Rath, T.; Haque, S. A. The role of oxygen in the degradation of methylammonium lead trihalide perovskite photoactive layers Angew. Chem., Int. Ed. 2015, 54, 8208– 8212 DOI: 10.1002/anie.201503153
  47
  The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers
  Aristidou, Nicholas; Sanchez-Molina, Irene; Chotchuangchutchaval, Thana; Brown, Michael; Martinez, Luis; Rath, Thomas; Haque, Saif A.
  Angewandte Chemie, International Edition (2015), 54 (28), 8208-8212CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  In this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2O3/CH3NH3PbI3 photoactive layers rapidly decomp. yielding methylamine, PbI2, and I2 as products. We show that this degrdn. is initiated by the reaction of superoxide (O2-) with the methylammonium moiety of the perovskite absorber. Fluorescent mol. probe studies indicate that the O2- species is generated by the reaction of photoexcited electrons in the perovskite and mol. oxygen. We show that the yield of O2- generation is significantly reduced when the mp-Al2O3 film is replaced with an mp-TiO2 electron extn. and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.
48. 48
  Müller, C.; Glaser, T.; Plogmeyer, M.; Sendner, M.; Döring, S.; Bakulin, A. A.; Brzuska, C.; Scheer, R.; Pshenichnikov, M. S.; Kowalsky, W.; Pucci, A.; Lovrinčić, R. Water infiltration in methylammonium lead iodide perovskite: fast and inconspicuous Chem. Mat. 2015, 27, 7835– 7841 DOI: 10.1021/acs.chemmater.5b03883
  48
  Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous
  Mueller, Christian; Glaser, Tobias; Plogmeyer, Marcel; Sendner, Michael; Doering, Sebastian; Bakulin, Artem A.; Brzuska, Carlo; Scheer, Roland; Pshenichnikov, Maxim S.; Kowalsky, Wolfgang; Pucci, Annemarie; Lovrincic, Robert
  Chemistry of Materials (2015), 27 (22), 7835-7841CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  While the susceptibility of CH3NH3PbI3 to water is well-documented, the influence of water on device performance is not well-understood. Herein, the authors use IR spectroscopy to show that water infiltration into CH3NH3PbI3 occurs much faster and at a humidity much lower than previously thought. The authors propose a mol. model in which water mols. have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb-I cage. Also, the exposure of CH3NH3PbI3 to the ambient environment increases the photocurrent of films in lateral devices by >1 order of magnitude. The obsd. slow component in the photocurrent buildup indicates that the effect is assocd. with enhanced proton conduction when light is combined with water and oxygen exposure.
49. 49
  Mosconi, E.; Azpiroz, J. M.; De Angelis, F. Ab initio molecular dynamics simulations of methylammonium lead iodide perovskite degradation by water Chem. Mat. 2015, 27, 4885– 4892 DOI: 10.1021/acs.chemmater.5b01991
  49
  Ab Initio Molecular Dynamics Simulations of Methylammonium Lead Iodide Perovskite Degradation by Water
  Mosconi, Edoardo; Azpiroz, Jon M.; De Angelis, Filippo
  Chemistry of Materials (2015), 27 (13), 4885-4892CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  Protecting organohalide perovskite thin films from H2O and ambient humidity represents a paramount challenge for the com. uptake of perovskite solar cells and, in general, of related optoelectronic devices. Therefore, understanding the perovskite/H2O interface is of crucial importance. As a step in this direction, here the authors present ab initio mol. dynamics simulations aimed at unraveling the atomistic details of the interaction between the methylammonium lead iodide (MAPbI3) perovskite surfaces and a liq. H2O environment. According to the calcns., MAI-terminated surfaces undergo a rapid solvation process, driven by the interaction of H2O mols. with Pb atoms, which prompts the release of I atoms. PbI2-terminated surfaces, instead, seem to be more robust to degrdn., by virtue of the stronger (shorter) Pb-I bonds formed on these facets. The authors also observe the incorporation of a H2O mol. into the PbI2-terminated slab, which could represent the 1st step in the formation of an intermediate hydrated phase. PbI2 defects on the PbI2-terminated surface promote the rapid dissoln. of the exposed facet. Surface hydration, which is spontaneous for both MAI- and PbI2-terminated slabs, does not modify the electronic landscape of the former, while the local band gap of the PbI2-exposing model widens by ∼0.3 eV in the interfacial region. Finally, H2O incorporation into bulk MAPbI3 produces almost no changes in the tetragonal structure of the perovskite crystal (∼1% vol. expansion) but slightly opens the band gap. Probably this work, unraveling some of the atomistic details of the perovskite/H2O interface, may inspire new interfacial modifications and device architectures with increased stabilities, which could in turn assist the com. uptake of perovskite solar cells and optoelectronic devices.
50. 50
  Tian, Y.; Merdasa, A.; Unger, E.; Abdellah, M.; Zheng, K.; McKibbin, S.; Mikkelsen, A.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Enhanced organo-metal halide perovskite photoluminescence from nanosized defect-free crystallites and emitting sites J. Phys. Chem. Lett. 2015, 6, 4171– 4177 DOI: 10.1021/acs.jpclett.5b02033
  50
  Enhanced Organo-Metal Halide Perovskite Photoluminescence from Nanosized Defect-Free Crystallites and Emitting Sites
  Tian, Yuxi; Merdasa, Aboma; Unger, Eva; Abdellah, Mohamed; Zheng, Kaibo; McKibbin, Sarah; Mikkelsen, Anders; Pullerits, Tonu; Yartsev, Arkady; Sundstroem, Villy; Scheblykin, Ivan G.
  Journal of Physical Chemistry Letters (2015), 6 (20), 4171-4177CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Luminescence (PL) of organo-metal halide perovskite semiconductors can be enhanced by several orders of magnitude by exposure to visible light. PL microscopy and super-resoln. optical imaging were applied to study this phenomenon with spatial resoln. better than 10 nm using films of MeNH3PbI3 prepd. by the equimolar soln.-deposition method, resulting in crystals of different sizes. PL of ∼100 nm crystals enhances much faster than that of larger, μm-sized ones. This crystal-size dependence of the photochem. light passivation of charge traps responsible for PL quenching allowed concluding that traps are present in the entire crystal vol. rather than at the surface only. Because of this effect, dark μm-sized perovskite crystals can be converted into highly luminescent smaller ones just by mech. grinding. Super-resoln. optical imaging shows spatial inhomogeneity of the PL intensity within perovskite crystals and the existence of <100 nm-sized localized emitting sites. The possible origin of these sites is discussed.
51. 51
  Cichos, F.; von Borczyskowski, C.; Orrit, M. Power-law intermittency of single emitters Curr. Opin. Colloid Interface Sci. 2007, 12, 272– 284 DOI: 10.1016/j.cocis.2007.07.012
  51
  Power-law intermittency of single emitters
  Cichos, F.; von Borczyskowski, C.; Orrit, M.
  Current Opinion in Colloid & Interface Science (2007), 12 (6), 272-284CODEN: COCSFL; ISSN:1359-0294. (Elsevier B.V.)
  A review. We summarize exptl. observations of fluorescence intermittency of single semiconductor nanocrystals and single mols. We review the main models proposed earlier to explain the broad power-law distributions of on- and off-blinking times. We argue that a self-trapping model with a distribution of trapping distances can account for most, if not all, observations to date. We propose possible scenarios for photo-ionization, the switching to states with long on-times and the influence of disorder and surfaces on the trapping dynamics.
52. 52
  Frantsuzov, P.; Kuno, M.; Janko, B.; Marcus, R. A. Universal emission intermittency in quantum dots, nanorods and nanowires Nat. Phys. 2008, 4, 519– 522 DOI: 10.1038/nphys1001
  There is no corresponding record for this reference.
53. 53
  Clifford, J. N.; Bell, T. D. M.; Tinnefeld, P.; Heilemann, M.; Melnikov, S. M.; Hotta, J.-i.; Sliwa, M.; Dedecker, P.; Sauer, M.; Hofkens, J.; Yeow, E. K. L. Fluorescence of single molecules in polymer films: sensitivity of blinking to local environment J. Phys. Chem. B 2007, 111, 6987– 6991 DOI: 10.1021/jp072864d
  53
  Fluorescence of Single Molecules in Polymer Films: Sensitivity of Blinking to Local Environment
  Clifford, John N.; Bell, Toby D. M.; Tinnefeld, Philip; Heilemann, Mike; Melnikov, Sergey M.; Hotta, Jun-Ichi; Sliwa, Michel; Dedecker, Peter; Sauer, Markus; Hofkens, Johan; Yeow, Edwin K. L.
  Journal of Physical Chemistry B (2007), 111 (25), 6987-6991CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
  The single-mol. fluorescence blinking behavior of the org. dye Atto 647N in various polymer matrixes such as Zeonex, PVK, and PVA and aq. media was studied. Fluorescence blinking with off-times in the millisecond to second time range is assigned to dye radical ions formed by photoinduced electron transfer reactions from or to the environment. In Zeonex and PVK, the measured off-time distributions show power law dependence, whereas, in PVA, no such dependence is obsd. Rather, in this polymer, off-time distributions can be best fitted to monoexponential or stretched exponential functions. Furthermore, treatment of PVA samples to mild heating and low pressure greatly reduces the frequency of blinking events. We tentatively ascribe this to the removal of water pockets within the polymer film itself. Measurements of the dye immobilized in water in the presence of methylviologen, a strongly oxidizing agent, reveal simple exponential on- and off-time distributions. Thus, our data suggest that the blinking behavior of single org. mols. is sensitive to their immediate environment and, moreover, that fluorescence blinking on- and off-time distributions do not inherently and uniquely obey a power law.
54. 54
  Hoogenboom, J. P.; Hernando, J.; van Dijk, E. M. H. P.; van Hulst, N. F.; García-Parajó, M. F. Power-law blinking in the fluorescence of single organic molecules ChemPhysChem 2007, 8, 823– 833 DOI: 10.1002/cphc.200600783
  54
  Power-law blinking in the fluorescence of single organic molecules
  Hoogenboom, Jacob P.; Hernando, Jordi; van Dijk, Erik M. H. P.; van Hulst, Niek F.; Garcia-Parajo, Maria F.
  ChemPhysChem (2007), 8 (6), 823-833CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The blinking behavior of perylene diimide mols. is investigated at the single-mol. level. We observe long-time scale blinking of individual multi-chromophoric complexes embedded in a poly(methylmethacrylate) matrix, as well as for the monomeric dye absorbed on a glass substrate at ambient conditions. In both these different systems, the blinking of single mols. is found to obey analogous power-law statistics for both the on and off periods. The obsd. range for single-mol. power-law blinking extends over the full exptl. time window, covering four orders of magnitude in time and six orders of magnitude in probability d. From mol. to mol., we observe a large spread in off-time power-law exponents. The distributions of off-exponents in both systems are markedly different whereas both on-exponent distributions appear similar. Our results are consistent with models that ascribe the power-law behavior to charge sepn. and (environment-dependent) recombination by electron tunneling to a dynamic distribution of charge acceptors. As a consequence of power-law statistics, single mol. properties like the total no. of emitted photons display non-ergodicity.
55. 55
  Kuno, M.; Fromm, D. P.; Hamann, H. F.; Gallagher, A.; Nesbitt, D. J. Nonexponential “blinking” kinetics of single CdSe quantum dots: a universal power law behavior J. Chem. Phys. 2000, 112, 3117– 3120 DOI: 10.1063/1.480896
  55
  Nonexponential "blinking" kinetics of single CdSe quantum dots: A universal power law behavior
  Kuno, M.; Fromm, D. P.; Hamann, H. F.; Gallagher, A.; Nesbitt, D. J.
  Journal of Chemical Physics (2000), 112 (7), 3117-3120CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  Single mol. confocal microscopy is used to study fluorescence intermittency of individual ZnS overcoated CdSe quantum dots (QDs) excited at 488 nm. The confocal app. permits the distribution of on and off times (i.e., periods of sustained fluorescence emission and darkness) to be measured over an unprecedentedly large dynamic range (109) of probability densities, with nonexponential behavior in τoff over a 105 range in time scales. In dramatic contrast, these same τoff distributions in all QDs are described with remarkable simplicity over this 109-fold dynamic range by a simple inverse power law, i.e., P(τoff).varies.1/τoff1+α. Such inverse power law behavior is a clear signature of distributed kinetics, such as predicted for (i) an exponential distribution of trap depths or (ii) a distribution of tunneling distances between QD core/interface states. This has important statistical implications for all previous studies of fluorescence intermittency in semiconductor QDs and may have broader implications for other systems such as single polymer mols.
56. 56
  Peterson, J. J.; Nesbitt, D. J. Modified power law behavior in quantum dot blinking: a novel role for biexcitons and Auger ionization Nano Lett. 2009, 9, 338– 345 DOI: 10.1021/nl803108p
  56
  Modified Power Law Behavior in Quantum Dot Blinking: A Novel Role for Biexcitons and Auger Ionization
  Peterson, Jeffrey J.; Nesbitt, David J.
  Nano Letters (2009), 9 (1), 338-345CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Single photon detection methods are used to acquire fluorescence trajectories from single CdSe/ZnS colloidal quantum dots (QDs) and analyze their blinking behavior. Although the "off-time" distributions follow ideal power law behavior at all wavelengths and intensities, significant deviations from power law behavior are obsd. for the "on-times". Specifically, with improved time resoln., trajectory durations, and photon statistics, we report a near-exponential falloff of on-time probability distributions at long times. Investigation of this falloff behavior as a function of laser wavelength and power demonstrate that these deviations originate from multiexciton dynamics, whose formation probabilities can be very low on a "per laser pulse" basis, but become nearly unity on the time scales of the longest on-times. The near quadratic, power-dependent results indicate the predominant role of biexcitons in the long time on-to-off blinking dynamics, which can be interpreted in terms of an Auger ionization event. In conjunction with Poisson modeling of the photon statistics, the data is consistent with QD ionization efficiencies of order ≈10-5 and highlight a novel role for biexcitons and Auger ionization in QD blinking.
57. 57
  Hu, F.; Zhang, H.; Sun, C.; Yin, C.; Lv, B.; Zhang, C.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Superior optical properties of perovskite nanocrystals as single photon emitters ACS Nano 2015, 9, 12410– 12416 DOI: 10.1021/acsnano.5b05769
  57
  Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters
  Hu, Fengrui; Zhang, Huichao; Sun, Chun; Yin, Chunyang; Lv, Bihu; Zhang, Chunfeng; Yu, William W.; Wang, Xiaoyong; Zhang, Yu; Xiao, Min
  ACS Nano (2015), 9 (12), 12410-12416CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Single photon emission was obsd. from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. The radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temps. to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.
58. 58
  Park, Y.-S.; Guo, S.; Makarov, N. S.; Klimov, V. I. Room temperature single-photon emission from individual perovskite quantum dots ACS Nano 2015, 9, 10386– 10393 DOI: 10.1021/acsnano.5b04584
  58
  Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots
  Park, Young-Shin; Guo, Shaojun; Makarov, Nikolay S.; Klimov, Victor I.
  ACS Nano (2015), 9 (10), 10386-10393CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Lead-halide-based perovskites have been the subject of numerous recent studies largely motivated by their exceptional performance in solar cells. Electronic and optical properties of these materials have been commonly controlled by varying the compn. (e.g., the halide component) and/or crystal structure. Use of nanostructured forms of perovskites can provide addnl. means for tailoring their functionalities via effects of quantum confinement and wave function engineering. Furthermore, it may enable applications that explicitly rely on the quantum nature of electronic excitations. Here, we demonstrate that CsPbX3 quantum dots (X = I, Br) can serve as room-temp. sources of quantum light, as indicated by strong photon antibunching detected in single-dot photoluminescence measurements. We explain this observation by the presence of fast nonradiative Auger recombination, which renders multiexciton states virtually nonemissive and limits the fraction of photon coincidence events to ∼6% on av. We analyze limitations of these quantum dots assocd. with irreversible photodegrdn. and fluctuations ("blinking") of the photoluminescence intensity. On the basis of emission intensity-lifetime correlations, we assign the "blinking" behavior to random charging/discharging of the quantum dot driven by photoassisted ionization. This study suggests that perovskite quantum dots hold significant promise for applications such as quantum emitters; however, to realize this goal, one must resolve the problems of photochem. stability and photocharging. These problems are largely similar to those of more traditional quantum dots and, hopefully, can be successfully resolved using advanced methodologies developed over the years in the field of colloidal nanostructures.
59. 59
  Verberk, R.; van Oijen, A. M.; Orrit, M. Simple model for the power-law blinking of single semiconductor nanocrystals Phys. Rev. B 2002, 66, 233202 DOI: 10.1103/PhysRevB.66.233202
  59
  Simple model for the power-law blinking of single semiconductor nanocrystals
  Verberk, Rogier; van Oijen, Antoine M.; Orrit, Michel
  Physical Review B: Condensed Matter and Materials Physics (2002), 66 (23), 233202/1-233202/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  We assign the blinking of nanocrystals to electron tunneling towards a uniform spatial distribution of traps. This naturally explains the power-law distribution of off times, and the power-law correlation function we measured on uncapped CdS dots. Capped dots, on the other hand, present extended on times leading to a radically different correlation function. This is readily described in our model by involving two different, dark and bright, charged states. Coulomb blockade prevents further ionization of the charged dot, thus giving rise to long, power-law distributed off and on times.
60. 60
  Galland, C.; Ghosh, Y.; Steinbruck, A.; Sykora, M.; Hollingsworth, J. A.; Klimov, V. I.; Htoon, H. Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots Nature 2011, 479, 203– 207 DOI: 10.1038/nature10569
  60
  Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots
  Galland, Christophe; Ghosh, Yagnaseni; Steinbrueck, Andrea; Sykora, Milan; Hollingsworth, Jennifer A.; Klimov, Victor I.; Htoon, Han
  Nature (London, United Kingdom) (2011), 479 (7372), 203-207CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Luminescence blinking - random switching between states of high (ON) and low (OFF) emissivities - is a universal property of mol. emitters found in dyes, polymers, biol. mols. and artificial nanostructures such as nanocrystal quantum dots, C nanotubes and nanowires. For the past 15 years, colloidal nanocrystals were used as a model system to study this phenomenon. The occurrence of OFF periods in nanocrystal emission was commonly attributed to the presence of an addnl. charge, which leads to luminescence quenching by nonradiative recombination (the Auger mechanism). This charging model was recently challenged in several reports. Time-resolved luminescence studies of individual nanocrystal quantum dots were performed while electrochem. controlling the degree of their charging, with the goal of clarifying the role of charging in blinking. Two distinct types of blinking are possible: conventional (A-type) blinking due to charging and discharging of the nanocrystal core, in which lower luminescence intensities correlate with shorter luminescence lifetimes; and a 2nd sort (B-type), in which large changes in the emission intensity are not accompanied by significant changes in emission dynamics. B-type blinking is attributed to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept hot electrons before they relax into emitting core states. Both blinking mechanisms can be electrochem. controlled and completely suppressed by application of an appropriate potential.
61. 61
  Rabouw, F. T.; Kamp, M.; van Dijk-Moes, R. J. A.; Gamelin, D. R.; Koenderink, A. F.; Meijerink, A.; Vanmaekelbergh, D. Delayed exciton emission and its relation to blinking in CdSe quantum dots Nano Lett. 2015, 15, 7718– 7725 DOI: 10.1021/acs.nanolett.5b03818
  61
  Delayed Exciton Emission and Its Relation to Blinking in CdSe Quantum Dots
  Rabouw, Freddy T.; Kamp, Marko; van Dijk-Moes, Relinde J. A.; Gamelin, Daniel R.; Koenderink, A. Femius; Meijerink, Andries; Vanmaekelbergh, Daniel
  Nano Letters (2015), 15 (11), 7718-7725CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  The efficiency and stability of emission from semiconductor nanocrystal quantum dots (QDs) is neg. affected by blinking on the single-nanocrystal level, i.e., random alternation of bright and dark periods. The time scales of these fluctuations can be as long as many seconds, orders of magnitude longer than typical lifetimes of exciton states in QDs. The authors study luminescence from QDs delayed over microseconds to milliseconds. The results prove the existence of long-lived charge-sepd. states in QDs. The authors study the properties of delayed emission as a direct way to learn about charge carrier sepn. and recovery of the exciton state. A new microscopic model is developed to connect delayed emission to exciton recombination and blinking from which bright periods in blinking are in fact not characterized by uninterrupted optical cycling as often assumed.
62. 62
  Rosen, S.; Schwartz, O.; Oron, D. Transient fluorescence of the off state in blinking CdSe/CdS/ZnS semiconductor nanocrystals is not governed by Auger recombination Phys. Rev. Lett. 2010, 104, 157404 DOI: 10.1103/PhysRevLett.104.157404
  62
  Transient Fluorescence of the Off State in Blinking CdSe/CdS/ZnS Semiconductor Nanocrystals Is Not Governed by Auger Recombination
  Rosen, Shamir; Schwartz, Osip; Oron, Dan
  Physical Review Letters (2010), 104 (15), 157404/1-157404/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  The obsd. intermittent light emission from colloidal semiconductor nanocrystals has long been assocd. with Auger recombination assisted quenching. The authors test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the obsd. decay dynamics seem inconsistent with those expected from Auger processes. Rather, the data suggest that in the off state the quantum dot cycles in a 3-step process: photoexcitation, rapid trapping, and subsequent slow nonradiative decay.
63. 63
  Cordones, A. A.; Bixby, T. J.; Leone, S. R. Direct measurement of off-state trapping rate fluctuations in single quantum dot fluorescence Nano Lett. 2011, 11, 3366– 3369 DOI: 10.1021/nl2017674
  63
  Direct Measurement of Off-State Trapping Rate Fluctuations in Single Quantum Dot Fluorescence
  Cordones, Amy A.; Bixby, Teresa J.; Leone, Stephen R.
  Nano Letters (2011), 11 (8), 3366-3369CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Fluorescence decay times measured during the off-state of single CdSe/ZnS quantum dot blinking decrease with increasing off-state duration, contradicting the charging model widely considered to explain the blinking phenomenon. The change in the nonradiative process of a short off-state duration compared to a long one was studied here through simultaneous measurement of fluorescence decay and blinking behavior. The results were studied in the framework of two models based on fluctuating trapping rates.
64. 64
  Bronson, J. E.; Fei, J.; Hofman, J. M.; Gonzalez, R. L., Jr.; Wiggins, C. H. Learning rates and states from biophysical time series: a Bayesian approach to model selection and single-molecule FRET data Biophys. J. 2009, 97, 3196– 3205 DOI: 10.1016/j.bpj.2009.09.031
  64
  Learning rates and states from biophysical time series: a Bayesian approach to model selection and single-molecule FRET data
  Bronson, Jonathan E.; Fei, Jingyi; Hofman, Jake M.; Gonzalez, Ruben L., Jr.; Wiggins, Chris H.
  Biophysical Journal (2009), 97 (12), 3196-3205CODEN: BIOJAU; ISSN:0006-3495. (Cell Press)
  Time series data provided by single-mol. Forster resonance energy transfer (smFRET) expts. offer the opportunity to infer not only model parameters describing mol. complexes, e.g., rate consts., but also information about the model itself, e.g., the no. of conformational states. Resolving whether such states exist or how many of them exist requires a careful approach to the problem of model selection, here meaning discrimination among models with differing nos. of states. The most straightforward approach to model selection generalizes the common idea of max. likelihood-selecting the most likely parameter values-to max. evidence: selecting the most likely model. In either case, such an inference presents a tremendous computational challenge, which we here address by exploiting an approxn. technique termed variational Bayesian expectation maximization. We demonstrate how this technique can be applied to temporal data such as smFRET time series; show superior statistical consistency relative to the max. likelihood approach; compare its performance on smFRET data generated from expts. on the ribosome; and illustrate how model selection in such probabilistic or generative modeling can facilitate anal. of closely related temporal data currently prevalent in biophysics.
65. 65
  Wu, B.; Nguyen, H. T.; Ku, Z.; Han, G.; Giovanni, D.; Mathews, N.; Fan, H. J.; Sum, T. C. Discerning the surface and bulk recombination kinetics of organic–inorganic halide perovskite single crystals Adv. Energy Mater. 2016, 6, 1600551 DOI: 10.1002/aenm.201600551
  There is no corresponding record for this reference.
66. 66
  Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. Enhanced photoluminescence and solar cell performance via Lewis base passivation of organic–inorganic lead halide perovskites ACS Nano 2014, 8, 9815– 9821 DOI: 10.1021/nn5036476
  66
  Enhanced Photoluminescence and Solar Cell Performance via Lewis Base Passivation of Organic-Inorganic Lead Halide Perovskites
  Noel, Nakita K.; Abate, Antonio; Stranks, Samuel D.; Parrott, Elizabeth S.; Burlakov, Victor M.; Goriely, Alain; Snaith, Henry J.
  ACS Nano (2014), 8 (10), 9815-9821CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Org.-inorg. metal halide perovskites have recently emerged as a top contender to be used as an absorber material in highly efficient, low-cost photovoltaic devices. Soln.-processed semiconductors tend to have a high d. of defect states and exhibit a large degree of electronic disorder. Perovskites appear to go against this trend, and despite relatively little knowledge of the impact of electronic defects, certified solar-to-elec. power conversion efficiencies of up to 17.9% have been achieved. Here, through treatment of the crystal surfaces with the Lewis bases thiophene and pyridine, the authors demonstrate significantly reduced nonradiative electron-hole recombination within the MeNH3PbI3-xClx perovskite, achieving photoluminescence lifetimes which are enhanced by nearly an order of magnitude, up to 2 μs. Probably this is due to the electronic passivation of under-coordinated Pb atoms within the crystal. Through this method of Lewis base passivation, the authors achieve power conversion efficiencies for soln.-processed planar heterojunction solar cells enhanced from 13% for the untreated solar cells to 15.3% and 16.5% for the thiophene and pyridine-treated solar cells, resp.
67. 67
  Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic transport in hybrid lead iodide perovskite solar cells Nat. Commun. 2015, 6, 7497 DOI: 10.1038/ncomms8497
  67
  Ionic transport in hybrid lead iodide perovskite solar cells
  Eames, Christopher; Frost, Jarvist M.; Barnes, Piers R. F.; O'Regan, Brian C.; Walsh, Aron; Islam, M. Saiful
  Nature Communications (2015), 6 (), 7497CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  Solar cells based on org.-inorg. halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behavior such as current-voltage hysteresis and a low-frequency giant dielec. response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chem. origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extd. from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and exptl. study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.
68. 68
  Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F. Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation Energy Environ. Sci. 2015, 8, 2118– 2127 DOI: 10.1039/C5EE01265A
  68
  Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation
  Azpiroz, Jon M.; Mosconi, Edoardo; Bisquert, Juan; De Angelis, Filippo
  Energy & Environmental Science (2015), 8 (7), 2118-2127CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
  In spite of the unprecedented advance of organohalide lead perovskites in the photovoltaics scenario, many of the characteristics of this class of materials, including their slow photocond. response, solar cell hysteresis, and switchable photocurrent, remain poorly understood. Many exptl. hints point to defect migration as a plausible mechanism underlying these anomalous properties. By means of state-of-the-art first-principles computational analyses carried out on the tetragonal MAPbI3 (MA = methylammonium) perovskite and on its interface with TiO2, we demonstrate that iodine vacancies and interstitials may easily diffuse across the perovskite crystal, with migration activation energies as low as ∼0.1 eV. Under working conditions, iodine-related defects are predicted to migrate at the electrodes on very short time scales (<1 μs). MA and Pb vacancies, with calcd. activation barriers of ∼0.5 and 0.8 eV, resp., could be responsible for the slow response inherent to perovskites, with typical calcd. migration times of the order of tens of ms to minutes. By investigating realistic models of the perovskite/TiO2 interface we show that neg. charged defects, e.g. MA vacancies, close to the electron transport layer (TiO2 in our case) modify the perovskite electronic state landscape, hampering charge extn. at selective contacts, thus possibly contributing to the obsd. solar cell hysteresis. We further demonstrate the role of the electron transport layer in affecting the initial concn. of defects close to the selective contacts, highlighting how charge sepn. at the perovskite/TiO2 interface may further change the defect distribution. We believe that this work, identifying the mobile species in perovskite solar cells, their migration across the perovskite material, and their effect on the operational mechanism of the device, may pave the way for the development of new materials and solar cell architectures with improved and stabilized efficiencies.
69. 69
  Klein-Kedem, N.; Cahen, D.; Hodes, G. Effects of light and electron beam irradiation on halide perovskites and their solar cells Acc. Chem. Res. 2016, 49, 347– 354 DOI: 10.1021/acs.accounts.5b00469
  69
  Effects of Light and Electron Beam Irradiation on Halide Perovskites and Their Solar Cells
  Klein-Kedem, Nir; Cahen, David; Hodes, Gary
  Accounts of Chemical Research (2016), 49 (2), 347-354CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review is presented. Hybrid alkylammonium lead halide perovskite solar cells have, in a very few years of research, exceeded a light-to-electricity conversion efficiency of 20%, not far behind cryst. silicon cells. These perovskites do not contain any rare element, the amt. of toxic lead used is very small, and the cells can be made with a low energy input. They therefore already conform to two of the three requirements for viable, com. solar cells-efficient and cheap. The potential deal-breaker is their long-term stability. While reasonable short-term (hours) and even medium term (months) stability has been demonstrated, there is concern whether they will be stable for the two decades or more expected from com. cells in view of the intrinsically unstable nature of these materials. In particular, they have a tendency to be sensitive to various types of irradn., including sunlight, under certain conditions. This Account focuses on the effect of irradn. on the hybrid (and to a small degree, all-inorg.) lead halide perovskites and their solar cells. It is split up into two main sections. First, we look at the effect of electron beams on the materials. This is important, since such beams are used for characterization of both the perovskites themselves and cells made from them (electron microscopy for morphol. and compositional characterization; electron beam-induced current to study cell operation mechanism; cathodoluminescence for charge carrier recombination studies). Since the perovskites are sensitive to electron beam irradn., it is important to minimize beam damage to draw valid conclusions from such measurements. The second section treats the effect of visible and solar UV irradn. on the perovskites and their cells. As we show, there are many such effects. However, those affecting the perovskite directly need not necessarily always be detrimental to the cells, while those affecting the solar cells, which are composed of several other phases as well as the perovskite light absorber, are not always due to the perovskite itself. While we cannot yet say whether perovskite solar cells will or will not be stable over the long-term, the information in this Account should be a useful source to help achieve this goal.
70. 70
  Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A. Atomistic origins of CH₃NH₃PbI₃ degradation to PbI₂ in vacuum Appl. Phys. Lett. 2015, 106, 131904 DOI: 10.1063/1.4916821
  70
  Atomistic origins of CH3NH3PbI3 degradation to PbI2 in vacuum
  Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A.
  Applied Physics Letters (2015), 106 (13), 131904/1-131904/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  We study the mechanisms of CH3NH3PbI3 degrdn. and its transformation to PbI2 by means of X-ray diffraction and the d. functional theory. The exptl. anal. shows that the material can degrade in both air and vacuum conditions, with humidity and temp.-annealing strongly accelerating such process. Based on ab initio calcns., we argue that even in the absence of humidity, a decompn. of the perovskite structure can take place through the statistical formation of mol. defects with a non-ionic character, whose volatility at surfaces should break the thermodn. defect equil. We finally discuss the strategies that can limit such phenomenon and subsequently prolong the lifetime of the material. (c) 2015 American Institute of Physics.
71. 71
  Zhang, L.; Sit, P. H.-L. Ab initio study of interaction of water, hydroxyl radicals, and hydroxide ions with CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ surfaces J. Phys. Chem. C 2015, 119, 22370– 22378 DOI: 10.1021/acs.jpcc.5b07000
  71
  Ab Initio Study of Interaction of Water, Hydroxyl Radicals, and Hydroxide Ions with CH3NH3PbI3 and CH3NH3PbBr3 Surfaces
  Zhang, Linghai; Sit, Patrick H.-L.
  Journal of Physical Chemistry C (2015), 119 (39), 22370-22378CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Although there have been tremendous breakthroughs in perovskite solar cells over the past few years, degrdn. of perovskite has been a huge problem. Recently, a no. of exptl. studies have demonstrated that org.-inorg. halide perovskite materials are sensitive to humid air, and several degrdn. mechanisms have been proposed. However, the decompn. process of perovskites is only partially known and controversial. In this paper, we theor. study the structures of the tetragonal CH3NH3PbI3 and CH3NH3PbBr3 (110) surfaces and the degrdn. mechanism using d. functional theory calcns. both with and without the van der Waals correction. The computed results indicate that the CH3NH3+ (MA) cations preferentially orient with the NH3 group pointing into the surface. This allows the formation of more hydrogen···halide hydrogen bonds between the MA cations and the halides. Moreover, the interactions of water mols., hydroxyl radicals, and hydroxide ions with the perovskite surfaces are investigated. It has been suggested that the deprotonation of the MA cations followed by the desorption of the CH3NH2 mols. is a key step in the degrdn. mechanism. We found that the hydroxyl radicals and hydroxide ions facilitate this desorption process while water mols. have little effect on it. These present findings are pertinent to revealing the decompn. mechanisms of perovskite materials.
72. 72
  Bryant, D.; Aristidou, N.; Pont, S.; Sanchez-Molina, I.; Chotchunangatchaval, T.; Wheeler, S.; Durrant, J. R.; Haque, S. A. Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells Energy Environ. Sci. 2016, 9, 1655– 1660 DOI: 10.1039/C6EE00409A
  72
  Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells
  Bryant, Daniel; Aristidou, Nicholas; Pont, Sebastian; Sanchez-Molina, Irene; Chotchunangatchaval, Thana; Wheeler, Scot; Durrant, James R.; Haque, Saif A.
  Energy & Environmental Science (2016), 9 (5), 1655-1660CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
  Here, we demonstrate that light and oxygen-induced degrdn. is the main reason for the low operational stability of methylammonium lead triiodide (MeNH3PbI3) perovskite solar cells exposed to ambient conditions. When exposed to both light and dry air, unencapsulated MeNH3PbI3 solar cells rapidly degrade on timescales of minutes to a few hours. This rapid degrdn. is also obsd. under elec. bias driven current flow in the dark in the presence of O2. In contrast, significantly slower degrdn. is obsd. when the MeNH3PbI3 devices are exposed to moisture alone (e.g. 85% relative humidity in N2). We show that this light and oxygen induced degrdn. can be slowed down by the use of interlayers that are able to remove electrons from the perovskite film before they can react with oxygen to form O2-. These observations demonstrate that the operational stability of electronic and optoelectronic devices that exploit the electron transporting properties of MeNH3PbI3 will be critically dependent upon the use of suitable barrier layers and device configurations to mitigate the oxygen sensitivity of this remarkable material.
73. 73
  Su, L.; Lu, G.; Kenens, B.; Rocha, S.; Fron, E.; Yuan, H.; Chen, C.; Van Dorpe, P.; Roeffaers, M. B. J.; Mizuno, H.; Hofkens, J.; Hutchison, J. A.; Uji-i, H. Visualization of molecular fluorescence point spread functions via remote excitation switching fluorescence microscopy Nat. Commun. 2015, 6, 6287 DOI: 10.1038/ncomms7287
  73
  Visualization of molecular fluorescence point spread functions via remote excitation switching fluorescence microscopy
  Su, Liang; Lu, Gang; Kenens, Bart; Rocha, Susana; Fron, Eduard; Yuan, Haifeng; Chen, Chang; Van Dorpe, Pol; Roeffaers, Maarten B. J.; Mizuno, Hideaki; Hofkens, Johan; Hutchison, James A.; Uji-i, Hiroshi
  Nature Communications (2015), 6 (), 6287CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  The enhancement of mol. absorption, emission and scattering processes by coupling to surface plasmon polaritons on metallic nanoparticles is a key issue in plasmonics for applications in (bio)chem. sensing, light harvesting and photocatalysis. Nevertheless, the point spread functions for single-mol. emission near metallic nanoparticles remain difficult to characterize due to fluorophore photodegrdn., background emission and scattering from the plasmonic structure. Here, we overcome this problem by exciting fluorophores remotely using plasmons propagating along metallic nanowires. The expts. reveal a complex array of single-mol. fluorescence point spread functions that depend not only on nanowire dimensions but also on the position and orientation of the mol. transition dipole. This work has consequences for both single-mol. regime-sensing and super-resoln. imaging involving metallic nanoparticles and opens the possibilities for fast size sorting of metallic nanoparticles, and for predicting mol. orientation and binding position on metallic nanoparticles via far-field optical imaging.
74. 74
  Su, L.; Yuan, H.; Lu, G.; Rocha, S.; Orrit, M.; Hofkens, J.; Uji-i, H. Super-resolution localization and defocused fluorescence microscopy on resonantly coupled single-molecule, single-nanorod hybrids ACS Nano 2016, 10, 2455– 2466 DOI: 10.1021/acsnano.5b07294
  74
  Super-resolution Localization and Defocused Fluorescence Microscopy on Resonantly Coupled Single-Molecule, Single-Nanorod Hybrids
  Su, Liang; Yuan, Haifeng; Lu, Gang; Rocha, Susana; Orrit, Michel; Hofkens, Johan; Uji-i, Hiroshi
  ACS Nano (2016), 10 (2), 2455-2466CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Optical antennas made of metallic nanostructures dramatically enhance single-mol. fluorescence to boost the detection sensitivity. Moreover, emission properties detected at the optical far field are dictated by the antenna. Here we study the emission from mol.-antenna hybrids by means of super-resoln. localization and defocused imaging. Whereas gold nanorods make single-crystal violet mols. in the tip's vicinity visible in fluorescence, super-resoln. localization on the enhanced mol. fluorescence reveals geometrical centers of the nanorod antenna instead. Furthermore, emission angular distributions of dyes linked to the nanorod surface resemble that of nanorods in defocused imaging. The exptl. observations are consistent with numerical calcns. using the finite-difference time-domain method.
Supporting Information
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.6b00107.
- PL intensity correlated super-resolution localization mapping on a single-crystal MAPbI₃ nanorod, Gaussian fitting widths time evolution during PL blinking of a single-crystal nanorod and a cluster of several nanorods, super-resolution localization mapping on polycrystalline deposits, and PL decays of nanorods and polycrystalline films (PDF)
- ao6b00107_si_001.pdf (671.31 kb)
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Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface TrapsClick to copy article linkArticle link copied!

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Abstract

Introduction

Results and Discussion

MAPbI3 Nanorods

Figure 1

Figure 2

PL of Individual MAPbI3 Nanorods under Ambient Conditions

Super-Resolution Localization Microscopy on Individual Nanorods and Nanorod Clusters

Figure 3

Power-Law Distributions of the ON and OFF Times

Figure 4

Correlation between PL Decay Time and Intensity of Individual Nanorods

Figure 5

PL of MAPbI3 Nanorods in Different Atmospheres

Figure 6

Discussion on the Possible Nature of Charge Traps

Conclusions

Experimental Section

Materials

Preparation of Methylammonium Iodide (CH3NH3I)

Polycrystalline Perovskite Crystals

Synthesis of Perovskite Nanorods

XRD

AFM

Integrated Optical and Electron Microscope (iLEM)

Confocal Optical Microscope for Time-Resolved Measurements

Sample Preparation

Supporting Information

Terms & Conditions

Author Information

Acknowledgment

References

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Abstract

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

References

Supporting Information

Supporting Information

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Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface Traps
Click to copy article linkArticle link copied!

MAPbI₃ Nanorods

PL of Individual MAPbI₃ Nanorods under Ambient Conditions

PL of MAPbI₃ Nanorods in Different Atmospheres

Preparation of Methylammonium Iodide (CH₃NH₃I)