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Unraveling Interfacial Photoinduced Charge Transfer and Localization in CsPbBr3 Nanocrystals/Naphthalenediimide
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  • Eliane A. Morais
    Eliane A. Morais
    Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
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  • Maykon A. Lemes
    Maykon A. Lemes
    Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
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  • Natalilian R. S. Souza
    Natalilian R. S. Souza
    Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
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  • Amando Siuiti Ito
    Amando Siuiti Ito
    Engineering, Modeling and Applied Social Sciences Center, Federal University of ABC, Santo André 09280-560, Brazil
    Institute of Physics, University of São Paulo, São Paulo 05508-060, Brazil
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  • Evandro L. Duarte
    Evandro L. Duarte
    Institute of Physics, University of São Paulo, São Paulo 05508-060, Brazil
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    Orcidhttps://orcid.org/0000-0001-5550-6541
  • Ronaldo S. Silva
    Ronaldo S. Silva
    Federal University of Sergipe, São Cristóvão 49100-000, SE, Brazil
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    Orcidhttps://orcid.org/0000-0001-6983-110X
  • Sergio Brochsztain
    Sergio Brochsztain
    Engineering, Modeling and Applied Social Sciences Center, Federal University of ABC, Santo André 09280-560, Brazil
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    Orcidhttps://orcid.org/0000-0002-1129-8039
  • Jose A. Souza*
    Jose A. Souza
    Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-6832-3581
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ACS Omega

Cite this: ACS Omega 2024, 9, 20, 22296–22304
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https://doi.org/10.1021/acsomega.4c01651
Published May 9, 2024

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Abstract

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Halide perovskites have attracted much attention for energy conversion. However, efficient charge carrier generation, separation, and mobility remain the most important issues limiting the higher efficiency of solar cells. An efficient interfacial charge transfer process associated with exciton dynamics between all-inorganic CsPbBr3 nanocrystals and organic electron acceptors has been suggested. We observed a strong PL quenching of 78% in thin films when silane-functionalized naphthalenediimides (SNDI), used as electron-acceptors, are anchored on CsPbBr3 nanocrystals. Optical and structural characterizations confirm the charge transfer process without QDs degradation. The issue of whether these transferred charges are indeed available for utilization in solar cells remains uncertain. Our results reveal that the CsPbBr3 nanocrystals capped with these electron-acceptor SNDI molecules show a drastic increase in the electrical resistance and the absence of a photoconductivity effect. The results suggest charge transfer followed by strong localization of the charge carriers, preventing their extraction toward the electrodes of solar cell devices. We hope that this crucial aspect to attract attention and unveil a potential mechanism for charge delocalization, which could, in turn, lead to a groundbreaking enhancement in solar cell efficiency.

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Introduction

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Semiconducting materials are of great interest for technological applications due to their optoelectronic properties involving the creation of exciton through light absorption and its dissociation, followed by separation into free charge carriers. (1) Controlling the electrical transport properties involving the creation, transfer, and mobility of charge carriers can be applied in several areas, going from energy generation to catalysis. However, poor visible light harvesting, a short carrier lifetime, and mainly high carrier exciton recombination effects can hinder its practical applications. (2) An important strategy to overcome these drawbacks is the combination of different semiconducting nanomaterials, which can be tailored to induce energy or electron transfer processes. Such hybrid-engineered interface materials can join the advantageous physical and chemical properties of each constituent, and they can convert light absorption into electrical or chemical energy. Besides tailoring the band gap energy, (3) the key to improving efficiency in solar cells and photocatalytic activity is to suppress charge recombination and improve separation and mobility. For example, a well-defined interface in heterojunctions effectively facilitates charge transfer and suppresses the recombination of photogenerated electrons and holes, leading to higher activity and stability. (4)
Halide perovskite semiconducting materials have shown improved optical and electronic properties such as a wide absorption spectrum, tunable band gap energy, low charge recombination rates, and high charge carrier mobility, which are essential for a diversity of applications. In particular, all-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, and I) nanocrystals, with high photoluminescence (PL) quantum yields and stability, have received great attention in perovskite-based photovoltaic systems. (5−7) As mentioned above, the conversion efficiency of their photovoltaic devices is related to the charge-transfer (CT) rate between light harvesting and hole-/electron-transporting materials. Electron-donating, -accepting, and charge-transporting sandwiched materials play an important role in the extraction of charge carriers from the active layer and decrease exciton recombination. (8) To achieve a higher photovoltaic conversion efficiency, besides understanding the CT process across the interface, an ideal matching of interfacial engineering involving energy-level alignment is necessary. This positive synergy between materials improving photophysical properties is not easily commonly found. (9) Nevertheless, the interfacial CT process and exciton dynamics between all-inorganic CsPbX3 NCs and molecular acceptors have not been fully investigated. (10) Indeed, all-inorganic CsPbX3 NCs can be very important in optoelectronic devices and photocatalytic applications if an ideal counterpart is found and their interfacial charge-transfer dynamics are fully understood. (11)
The growth of a heterojunction where there is charge transfer from one part to another is a relevant matter from both technological and fundamental bases by itself due to the exciting physics and chemistry at the interface. For this reason, we have taken advantage of the electronic synergy between all-inorganic semiconductors and molecular acceptors to investigate the optoelectronic properties of QDs and a novel naphthalenediimide-based molecule in an effort to pursue highly efficient charge carrier separation materials. These naphthalenediimides (NDIs) are n-type organic semiconductors with great importance in electronic devices such as solar cells due to their electron affinity. (12−15) They are rated among the best nonfullerene materials as electron-transport layers in solar cells. (16) Moreover, NDIs can be easily reduced to stable organic radicals (17) due to their electron-deficient nature in the aromatic nucleus, allowing the creation of a variety of hybrid materials to be used in organic electronics. (18) Here, we report the synthesis of colloidal perovskite quantum dots decorated with an NDI derivative functionalized with silane groups, N,N′-bis(3-triethoxysilylpropyl)-1,4,5,8 naphthalenediimides (SNDI), to create local heterojunctions. SNDI features hydrolyzable silane groups, resulting in strong binding to the surface of CsPbX3 nanocrystals. As mentioned, it has been demonstrated that attaching electron-acceptor molecules to the surface of perovskites may facilitate charge transfer, ultimately enhancing the separation of charges into free carriers. (19) However, the question of whether these transferred charges, driven by these molecules, are indeed available for utilization in either catalysis or solar cells remains uncertain. Here, we shed light on this issue. We have combined these electron-acceptor molecules with CsPbBr3 nanocrystals in the form of colloidal solutions and thin films and observed a strong PL quenching, suggesting a charge transfer process. However, DC and AC electrical transport measurements reveal a drastic increase in electrical resistance and the absence of a photoconductivity effect when the molecules are anchored. The results suggest charge transfer followed by a strong localization of the charge carriers preventing their extraction toward the metallic electrodes.

Results and Discussion

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We have synthesized the colloidal quantum dot solution of CsPbBr3 perovskites by the hot injection method. Besides the facile technique, this synthetic method allows fast growth and nucleation of nanosized particles. The synthesis of aromatic molecules was obtained via an established procedure as mentioned above. Figure 1a,b displays the absorption and PL spectra of SNDI and CsPbBr3 QDs in toluene. The solution of SNDI under UV light (365 nm) is shown in the inset of Figure 1a, while a colloidal solution of CsPbBr3 QDs under UV (365 nm─revealing a green color) is displayed in the inset of Figure 1b. The absorption spectrum of SNDI (Figure 1a) shows the typical vibrational structure of NDI derivatives, with the most intense absorption peaking at 382 nm, a secondary maximum at 362 nm, and a shoulder at 344 nm. The structure of the SNDI is shown in the inset of Figure 1a. The PL spectrum of SNDI shows an excimer-like broad band with a maximum at 470 nm and a shoulder at 412 nm, which can be attributed to monomeric SNDI. The HOMO–LUMO energy gap of organic molecules is usually assigned at the crossing point between absorption and emission spectra, which is at 393 nm for SNDI in toluene (Figure 1a), giving Eg = 3.15 eV. The synthesized CsPbBr3 QDs exhibit a photoluminescent emission centered at 513 nm (E = 2.41 eV) with a fwhm of ∼13 nm. The UV–visible spectroscopy for the same sample exhibits a maximum absorption band at 508 nm (E = 2.44 eV).

Figure 1

Figure 1. Photoluminescence and UV–visible absorption spectra of toluene solutions of (a) SNDI (λex = 320 nm) and (b) CsPbBr3 QDs (λex = 425 nm). The insets show the structure of SNDI along with its solution and the QDs colloidal solution under UV light─365 nm.

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As mentioned earlier, 1,4,5,8 naphthalenediimide (NDI) aromatic molecules are an important class of electron-accepting organic semiconductors. In order to study the synergy of SNDI and CsPbBr3 QDs, we have prepared solutions by titrating the QDs (2.5 μL) solution with SNDI (2.5 μL) in toluene (3 mL) placed in a quartz cuvette. Here, UV–vis absorption measurements were used to calculate the concentration of quantum dots in the solution, which was performed using Beer’s law described by the equation A = εbc, where A is the absorbance (dimensionless), b is the optical path (cm), c is the concentration (mol L–1), and ε is the molar absorptivity (mol–1·L·cm–1). The latter is characteristic of each substance in each λ; the concentration formula used to substitute in the previous equation was c = (c0·V)/V0. (20) For this calculation, we used ε = 2.42 × 10–2 × d3, which is the absorptivity value of the QDs of CsPbBr3 in toluene at a wavelength of 400 nm. (21) Thus, the calculated concentration of the QDs in the solution was found to be 20.2 nM. After that, we performed photoluminescence analysis (Figure 2), where aliquots of 2.5 μL from the SNDI solution were added, and the PL spectrum was collected after each addition until a total of 15 μL of SNDI was reached.

Figure 2

Figure 2. (a) PL emission measurements of CsPbBr3 QDs with the addition of SNDI up to 15 μL. The inset indicates a linear relationship of I0/I vs [SNDI] (excitation of 425 nm). (b) Absorption spectrum of the QDs of CsPbBr3 with the addition of 15 μL of SNDI. The inset shows a Tauc plot estimating the band gap energy of both systems. The concentrations for each measurement are SNDI (mol/L): 8.33 × 10–7 (2.5 μL); 1.66 × 10–6 (5.0 μL); 2.49 × 10–6 (7.5 μL); 3.32 × 10–6 (10.0 μL); 4.15 × 10–6 (12.5 μL); and 4.98 × 10–6 (15.0 μL).

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As can be seen in Figure 2a, when 2.5 μL of SNDI was added to the colloidal solution of the QDs, quenching of the emission was observed. Nevertheless, a significant quenching of 54% is observed when 15 μL of SNDI is added. In the PL emission measurements, we used the excitation wavelength of 425 nm to avoid the absorption of SNDI. Such an observation suggests the presence of NDI molecules anchored on the surface of CsPbBr3 QDs. A quantitative analysis of PL quenching was done using the Stern–Volmer equation, I0/I = 1 + KSV.[SNDI], where I0 and I are the PL intensities before and after the addition of NDI, respectively, KSV is the SV quenching constant, and [SNDI] is the concentration of the SNDI quencher. The linear behavior shown in the inset of Figure 2a produces a slope of 1.7 × 105 M–1. This KSV value indicates a strong interaction of SNDI with the surface of the QDs. The presence of such an interaction is anticipated to lead to photoinduced charge separation, as already observed with other electronic acceptors. (10,22,23)
As the quenching of emission in the PL of CsPbBr3 QDs is significant, we perform UV–vis measurements to evaluate the possible degradation of the QDs. Figure 2b shows absorption measurements of both pure CsPbBr3 quantum dots and CsPbBr3 QDs with 15.0 μL of SNDI (54% quenching of PL). The purification of the QDs solution may affect the interaction with the SNDI molecules. Usually, the purification is done by centrifugation, the solution─supernatant is discarded, and the nanoparticles are redispersed in toluene. As can be seen in Figure 2b, both samples present a narrow absorption band at 508 nm, indicating the absence of QDs degradation. The extent of emission from CsPbBr3 QDs at low SNDI concentrations indicates that the interaction with the quantum dots is static in nature, as observed with the Ferrocene redox couple (24) and CdSe semiconductor colloidal solutions that interact with electron acceptors and induce photocatalytic reduction. (25,26) According to these studies, surface electron transfer can provide insights into the photovoltaic role of semiconductor nanocrystals in solar fuel generation. As there is no efficient spectral overlap between the SNDI absorption spectrum and the CsPbBr3 QDs emission spectrum, we will disregard the possibility of the energy transfer process. (27) In order to estimate the band gap energies (Eg) of the samples, we use the Tauc plot method. (28) The results are displayed in the inset of Figure 2b. The band gap energy of CsPbBr3 NCs was estimated to be Eg = 2.32 eV, which is consistent with the previously reported values, (29) and for SNDI, we observe a value close to the expected around ∼3 eV.
Figure 3a–d displays TEM images showing the same morphology for CsPbBr3 QDs and CsPbBr3/SNDI QDs. The particles can be depicted as cuboid-like shape with a mean size distribution (the edge dimension) of 15(2) nm for the QDs and 17(2) nm for the QDs/SNDI. Notable is that the synthesized CsPbBr3 nanocrystals are larger than their Bohr exciton radii, exhibiting a weak quantum confinement effect. (30) In short, from the optical analysis and TEM results, the combination of SNDI and CsPbBr3 QDs brings about a quenching in the photoluminescence emission, while the quencher molecules adsorbed on the surface led to a slight increase in the average size of the QDs. We have also probed the interaction of the SNDI with the QDs surface through FTIR spectroscopy (Figure S4). The characteristic bands of the oleic acid (OA) (908 and 1641 cm–1) and OAm (719, 991, and 1463 cm–1) ligands are barely seen in the SNDI/QD sample. Instead, most of the bands due to the SNDI molecule are present in SNDI/QD (marked with black stars in Figure S4), suggesting that the original ligands were replaced by SNDI. Furthermore, the band due to Si–O–C in SNDI (1058 cm–1) was replaced by the Si–O–Si (1118 cm–1) in SNDI/QD (pink stars in Figure S4), indicating hydrolysis and condensation of the triethoxysilane groups in the presence of the QDs. (31)

Figure 3

Figure 3. TEM images showing the morphology and size of the CsPbBr3 QDs (a,b) and CsPbBr3/SNDI (d,e). The graphics (c,f) show the particle size distribution for both samples.

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Since the potential applications of this observed charge transfer phenomenon are most likely in solid-state devices, we performed a study of the quenching of PL emission in thin films. We also discuss this effect in more detail, including time-resolved PL and charge transport through electrical resistivity characterizations. To carry out these experiments, we prepared three different solutions as mentioned in the Experimental Section. The PL measurements for the three films (pure CsPbBr3 QDs, with 2.5 μL, and with 15.0 μL of SNDI) are shown in Figure 4. A very strong quenching of PL is observed, suggesting complete exciton dissociation. For example, PL for the film with 2.5 μL of SNDI decreases by 78%. The inset of Figure 4 shows a pronounced absorption band at 508 nm for the hybrid sample, indicating that the QDs in the thin film with 15.0 μL SNDI are chemically stable, thus confirming that even with the complete quenching of the exciton recombination, the quantum dots remain stable. A schematic diagram showing electron affinity and ionization energy, (13) considering the charge carrier transfer at the interface of CsPbBr3 and SNDI, is displayed in Figure 4b. To further verify the possible degradation of the quantum dots in the solid state after the formation of the film, we have measured X-ray diffraction, as shown in Figure S1 of the Supporting Information. We have observed that all Bragg reflections belong to the expected orthorhombic crystal phase, indicating stabilization of the CsPbBr3 QDs in the form of thin films and also the QDs with organic molecules, CsPbBr3 QDs/SNDI film.

Figure 4

Figure 4. (a) Photoluminescence spectra collected in a thin film for the CsPbBr3 QDs pure (black), with 2.5 μL (red) and 15.0 μL (blue) of SNDI (excitation = 425 nm). The inset shows UV–vis measurements showing the absorption band at 508 nm of the QDs/SNDI thin film and (b) energy-level scheme summarizing the band structure of CsPbBr3 and the electronic structure of SNDI upon irradiation. The concentrations for each measurement are SNDI (mol/L): 8.33 × 10–7 (2.5 μL) and 4.98 × 10–6 (15.0 μL).

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When we compare the PL emission of colloidal solution and solid state as SNDI is added, a much more drastic decay is observed for the samples as a thin film. Accordingly, the distance between the semiconductor and the molecular acceptors is crucial for both electron and energy transfer. Our results are closely related to the fact that the motion degree of freedom of SNDI molecules is lower in a thin film than in a colloidal solution. Therefore, this physical state allows a massive amount of acceptor molecules anchored on the QDs surfaces and more effective contact with the CsPbBr3, thereby ensuring a better charge/electron transfer. The above-mentioned process suggests that the SNDI acceptors are anchored to the surface of the semiconductor. It results in a lowering of the energy levels of the molecules that facilitate the energy/charge transfer. (32) As can be seen in Figure 4b, the estimated energy levels indicate that the SNDI LUMO is −0.45 eV lower than the conductive band and the HOMO is −1.15 eV below the valence band (VB). Such results indicate significant synergy between the perovskite semiconductor and the molecular acceptors.
Time-resolved PL analysis was employed to unravel the change in exciton recombination/dissociation and charge carrier dynamics due to the interaction between QDs and NDI molecules, as shown in Figure S2 of the Supporting Information. The PL decay intensity for the samples was fitted with a three-exponential decay function assigned to (trap-assisted) (τ1), exciton (τ2), and free charge carriers (τ3) recombination lifetimes. (33) The results from the fit, along with the exponential equation, are presented in SM (see Table S1), which shows the lifetimes as well as their respective contributions (A). The results suggest that the main contributions of the charge dynamics among the three decay curves are attributed to the charge trapping centers (traps) (A1) and exciton recombination (A2). The average decay time decreases with the addition of the SNDI from τm = 4.3 ns to τm = 1.33 ns. This difference is associated with a change in exciton dissociation and charge dynamics, i.e., dissociation leading to charge carrier separation.
To further understand the charge transfer and photo carrier-induced dynamics in the thin films of the QDs and QDs/SNDI, electrical transport characterization was performed using direct current (DC) and impedance spectroscopy measurements. (34) For this experiment, we set up two devices: (1) the first 40 μL of CsPbBr3 QDs stock solution was drop-cast five times into the FTO substrate. For each layer, the FTO substrate with the thin film of the sample was annealed at 90 °C for solvent evaporation; (2) for the second device, it was performed using the same drop casting method, however using 40 μL of the CsPbBr3 QDs suspension mixed with SNDI molecules. On top of the prepared thin film, another metallic glass FTO was placed, thus forming a capacitor with the sample as a dielectric sandwiched between them. The insets of Figure 5a,b show images of both devices, revealing a very bright color for the concentrated and pure CsPbBr3 QDs and a more shadowed film for a mixture of CsPbBr3 QDs/SNDI due to emission quenching. A four-probe method was used to measure the electrical resistance, which is obtained by using Ohm’s law (V = R·I), where I is a constant electrical current, V is the voltage drop between both substrates, and R is the electrical resistance of the sample measured out of the plane of the substrate. The geometric factor of all fabricated devices is very similar. Figure 5a,b shows the current–voltage (I–V) measurements for both samples in the dark and in the presence of light (1 sun) by using a solar simulator. The plot displays a very linear dependence, Figure 5a, in the I–V curves for the QDs device. The slope indicates the electrical resistance of the sample, which was found to be R = 1.9 kΩ. A significant drop in the slope (R = 0.6 kΩ) is also observed when the same sample is irradiated due to the presence of photoinduced charge carriers, showing that the charge carriers are extracted and collected toward the electrodes. For the hybrid sample, QDs with SNDI molecules, we observed a significant increase in the electrical resistivity to 0.9 MΩ, as shown in Figure 5b. These results suggest that the charge carriers are not being collected at the metallic electrodes after exciton dissociation. Furthermore, the electrical resistivity in the presence of light is slightly lower ∼0.8 MΩ, i.e., the photoelectric effect is almost absent. These results are very important and reveal that, even though we have observed a local charge transfer process, the photoinduced charge carriers are strongly localized when SNDI molecules are present. These results suggest that photoinduced electrons involve charge carrier transfer from CsPbBr3 to metallic glass (FTO) and their absence when SNDI is present.

Figure 5

Figure 5. Current–voltage (I–V) curves under dark and light (1 sun from a solar simulator) for two samples: CsPbBr3 QDs (a) and CsPbBr3 QDs/SNDI (b). The inset shows a photograph of devices under UV light at 365 nm. Energy-level scheme and charge separation for the Nyquist impedance spectroscopy for the samples under conditions of dark and light illumination of 1 sun from the solar simulator for (c) CsPbBr3 QDs and (d) CsPbBr3/SNDI.

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The impedance spectroscopy measurements were also measured simultaneously with DC resistivity to evaluate the capacitance and relaxation dynamics of charge carriers. Figure 5c,d shows the Nyquist plots for CsPbBr3 QDs and CsPbBr3/SNDI in dark and under light illumination. The Nyquist plots for CsPbBr3 QDs reveal the presence of a single semicircle with a characteristic frequency of ω0 = 538 Hz, which is attributed predominantly to relaxation arising from the electronic transport of the particles. The imaginary part as a function of frequency is shown in Figure S3 of the SM for both samples. This characteristic frequency increases to ω0 = 673 Hz when the light is turned on, i.e., the charge transport is faster. The DC electrical resistance can also be found at the low-frequency limit ω ≈ 0, where the curves intercept the real axis (Z′). We observe a drastic variation in both imaginary and real contributions when the pure QDs are illuminated due to the photogenerated charges in the system from exciton dissociation. On the other hand, one can observe the starting of a second semicircle at low frequencies when SNDI molecules are present. It can be associated with high-resistance interparticle contribution due to the presence of molecules on the surface of the nanoparticles. This result can suggest that the presence of the molecules decorating the QDs increases the grain boundary resistance contribution. Intergrain contributions are observed to be very important in the transport properties of these halide perovskites. (35) The electrical resistance for these hybrid samples is higher, as observed in DC results. A small variation is also observed for CsPbBr3/SNDI when comparing dark and under light irradiation. The characteristic frequency changes from ω0 = 300 to 378 Hz when the light is turned on. All of the parameters from impedance spectroscopy measurements are displayed in Table S2 of Supporting Information. A more detailed study involving the capacitance and dielectric constant of these two devices will be published elsewhere.
To achieve high charge separation and mobility, a detailed understanding of the charge transfer process across the interface and favorable interfacial energy-level alignment is necessary. The interfacial dynamic process and exciton dynamics between all-inorganic CsPbX3 NCs and molecular acceptors have not been fully understood so far. The sequential achievement of light absorption by the perovskites, exciton formation and dissociation, charge extraction, and collection of free carriers at the metallic electrodes ultimately decides the successful performance of a photovoltaic device. Figure 6 shows a schematic illustration of the energy-level diagram of QDs, SNDI, and FTO, along with the transfer/recombination pathways. It is suggested that when the hybrid sample (CsPbBr3/SNDI) is irradiated with 425 nm, the electrons from the VB are promoted to the conduction band of the QDs, afterward, to the LUMO of SNDI molecules. In the sequence, even though there is a favorable interfacial energy-level alignment with FTO, the photoinduced charges are not transferred to the FTO electrode. Therefore, our results indicate that this state is strongly localized, and the photoinduced electrons cannot be collected at the FTO metallic substrate. Eventually, the electrons are transferred back to the VB of the quantum dots in nonradiative recombination, as illustrated in Figure 6.

Figure 6

Figure 6. Schematic illustration of the energy-level diagram of QDs, SNDI, and FTO, along with transfer and recombination pathways upon irradiation.

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Conclusions

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Electron-accepting molecules used as charge-separating materials can play an important role in the extraction of charge carriers, opening the possibility to increase solar cell efficiency. In our study, we have successfully synthesized both CsPbBr3 QDs and SNDI molecules. The interaction of SNDI with QDs proved to be highly effective in quenching the luminescence in both colloidal solutions and thin films. Notably, in the latter, the PL quenching was particularly more pronounced, with a reduction in intensity of 78% without degradation of the QDs. The CsPbBr3 QDs and CsPbBr3 QDs/SNDI samples exhibited a uniform size distribution, 15(2) nm for the former and 17(2) nm for the latter, featuring a cubic-shaped particle morphology. The time-resolved PL analyses showed that the major contributions of charge dynamics among the three decays are attributed to the charge trapping centers and exciton recombinations. The DC and AC transport measurements showed a significant increase in the electrical resistivity in hybrid samples (comprising CsPbBr3 quantum dots and SNDI). Additionally, no clear evidence of enhanced photoconductivity effects was observed, implying a robust localization of the photoinduced charge carriers. Upon irradiation, the electrons in the conduction band of the QDs are transferred to the LUMO energy level of SNDI molecules, but despite the favorable alignment of interfacial energy levels, our findings indicate that the photoinduced charges do not undergo transfer to the FTO metallic electrodes. Consequently, our results suggest that these transferred charges are strongly localized and unable to be collected by the FTO metallic substrate. We have proposed a mechanism to elucidate the charge transfer process and the factors contributing to their localization, which hinder their extraction toward the electrodes. We expect that this vital aspect will draw attention and reveal potential pathways for charge delocalization, ultimately paving the way for a groundbreaking improvement in solar cell efficiency.

Materials and Methods

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Chemicals

All chemicals were purchased from Sigma-Aldrich and Synth and were used without further purification. Cesium carbonate (Cs2CO3, Sigma-Aldrich, 99.9%), OA (Sigma-Aldrich, 90%), 1-octatdecene (ODE, Sigma-Aldrich, 90%), oleylamine (OAm, Sigma-Aldrich, 70%), lead bromide (PbBr2, Alfa Aesar, 99.99%), and toluene (Sigma-Aldrich, 99.8%). SNDI was synthesized through the reaction between 1,4,5,8-naphthalenetetracarboxylic dianhydride and 3-aminopropyltriethoxysilane according to the reported procedure. (36,37)

Preparation of Cs-Oleate

To prepare lead halide perovskite QDs via the hot injection method, a previous step, including preparation of the Cs source, was performed. Thus, Cs-oleate was prepared by transferring Cs2CO3 (0.407 g), OA (1.25 mL), and ODE (20 mL) into a 25 mL 3-neck round-bottom flask under vacuum and at a temperature of 120 °C for 1 h. The solution was then heated to 150 °C under an argon atmosphere until all Cs2CO3 reacted with OA. Because the Cs-oleate precipitates out of the ODE at room temperature, the solution must be preheated to 90 °C before use in the synthesis of QDs.

Synthesis of CsPbBr3 QDs

This synthesis was prepared via the hot injection method in accordance with a literature procedure. (38−40) 5 mL of ODE and 0.188 mmol of PbBr2 (0.069 g) for CsPbBr3 QDs were added into a 25 mL 3-neck round-bottom flask at 125 °C, under vacuum, for 1 h. After that, 0.5 mL of OA and 0.5 mL of OAm were injected at 120 °C under argon for 1 h. With the complete solubilization of PbBr2 salt, the temperature was then raised to 190 °C, and 0.4 mL of Cs-oleate solution was quickly injected. Immediately after 1 min, the mixture was cooled down in a water bath. After reacting all the precursors, the solution was instantly cooled down to 0° using an ice bath where the QDs were immediately formed. The resultant aggregated QDs were separated by centrifugation, and the supernatant was discarded. The precipitate was redispersed in dried toluene for all solutions.

Preparation of SNDI Stock Solution

A 1 mM NDI stock solution was prepared by dissolving 6.7 mg of SNDI in 10 mL of toluene.

PL Quenching of a QD Colloidal Solution with SNDI

2.5 μL of the QDs stock solution was added to 3 mL of toluene in a quartz cuvette, and the initial PL spectrum was registered. Aliquots of 2.5 μL from the SNDI stock solution were then added (up to 15 μL), and the PL was measured again after each addition.

Preparation of QDs/SNDI Thin Films

To produce thin films, three solutions were separately prepared and dropwise added in quartz substrates; the first solution was prepared by combining 3 mL of toluene and 2.5 μL of QDs. The second one combines 3 mL of toluene, 2.5 μL of QDs, and 2.5 μL of SNDI. And for the third solution, a mix of 3 mL of toluene, 2.5 μL of QDs, and 15 μL of SNDI. The dry thin films were obtained after complete solvent evaporation.

Experimental Characterization

Powder X-ray diffraction data were obtained using a diffractometer STADI-P model of Stoe with CuKα1 radiation whose wavelength is λ = 1.5406 Å CuKα, operating in the 40 kV/40 mA regime in a scanning interval of 2θ between 3 and 60° with a speed of 2°/min. To analyze the sample surface morphology and topography, transmission electron microscopy (TEM) images were obtained from a JEM1400 plus equipment from Jeol Thermo Scientific operating at 120 kV. Optical analysis was performed through UV–visible spectroscopy using an Evolution 220 Thermo Fisher spectrophotometer and photoluminescence using a static PL-spectrophotometer (Horiba fluorescence). For the time-resolved fluorescence measurements, the excitation source used was a titanium-sapphire laser Tsunami 3950 Spectra Physics, pumped by a solid-state laser Millenia Pro model 10sJS Spectra Physics. The repetition rate was set to 8.0 MHz using a pulse picker (Spectra Physics, model 3980-25). The Tsunami was set to give an output of 840 nm, and a second harmonic generator BBO crystal (GWN-23PL Spectra Physics) was used to generate the excitation beam at 422 nm. This beam was directed to a spectrofluorometer, model FL900CDT (UK). The emitted light was detected by a refrigerated microchannel plate photomultiplier (Hamamatsu R3809U) at 90° from the excitation beam. The emission wavelength of 516 nm was selected by a monochromator. The electrical transport (Keithley 2410 Sourcemeter) and impedance spectroscopy (SOLARTRON Impedance Analyze SI1260 coupled to a dielectric interface) measurements were performed by using a four-probe method carried out with an LED Solar Simulator (LSH-7320) in the 400–1100 nm wavelength range. The maximum output power is 110 mW/cm2, which is equivalent to 1.1 sun.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c01651.

  • Additional XRD patterns, photoluminescence lifetime, values of lifetimes, the Nyquist impedance spectroscopy, and FTIR spectra for all samples (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Eliane A. Morais - Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
    • Maykon A. Lemes - Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
    • Natalilian R. S. Souza - Center for Human and Natural Sciences, Federal University of ABC, Santo André 09210-580, São Paulo, Brazil
    • Amando Siuiti Ito - Engineering, Modeling and Applied Social Sciences Center, Federal University of ABC, Santo André 09280-560, Brazil;  Institute of Physics, University of São Paulo, São Paulo 05508-060, Brazil
    • Evandro L. Duarte - Institute of Physics, University of São Paulo, São Paulo 05508-060, Brazil;  Orcidhttps://orcid.org/0000-0001-5550-6541
    • Ronaldo S. Silva - Federal University of Sergipe, São Cristóvão 49100-000, SE, Brazil;  Orcidhttps://orcid.org/0000-0001-6983-110X
    • Sergio Brochsztain - Engineering, Modeling and Applied Social Sciences Center, Federal University of ABC, Santo André 09280-560, Brazil;  Orcidhttps://orcid.org/0000-0002-1129-8039
  • Author Contributions

    All authors contributed equally to the work. The student’s names are in alphabetical order.

  • Funding

    Open access funded by CAPES.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors would like to acknowledge the financial support from Brazilian agencies CAPES (CAPES-Pandemics 88881.504639/2020-01), FAPESP under grant nos. 2017/02317-2, 2021/14422-0, 2023/01316-3, 2023/10982-7, and CNPq (grants: 305229/2020-6). The authors are also grateful for the support from the Experimental Multiuser Center Facilities (UFABC).

References

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    Wang, Daizhe; Ye, Tengling; Zhang, Yong
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (40), 20819-20848CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A review. In perovskite solar cells (PerSCs), the electron transport layer (ETL) exts. and transports electrons from the perovskite light absorption layer (PAL) to the cathode, which plays an important role in improving the performance and long-term stability of the devices. Compared with fullerene derivs., non-fullerene n-type org. semiconductors have some unique advantages, such as mol. structure diversity, ease of modification, adjustable frontier MOs, and good stability. Recently, non-fullerene electron transport materials (ETMs) have attracted more and more attention as efficient ETLs in PerSCs. A variety of non-fullerene ETMs have been reported. Herein, we summarized the latest developments of non-fullerene org. ETMs in PerSCs, including small mol. org. ETMs and polymer ETMs. Esp., the common effects of substituents and design strategies of mol. configuration on the properties of non-fullerene ETMs were systematically summarized. At the same time, the remaining challenges and promising future trends of PerSCs based on non-fullerene org. ETMs are discussed.
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  17. 17
    Song, Q.; Li, F.; Wang, Z.; Zhang, X. A supramolecular strategy for tuning the energy level of naphthalenediimide: Promoted formation of radical anions with extraordinary stability. Chem. Sci. 2015, 6, 3342– 3346,  DOI: 10.1039/C5SC00862J
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    17
    A supramolecular strategy for tuning the energy level of naphthalenediimide: Promoted formation of radical anions with extraordinary stability
    Song, Qiao; Li, Fei; Wang, Zhiqiang; Zhang, Xi
    Chemical Science (2015), 6 (6), 3342-3346CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The authors report a supramol. strategy to promote and stabilize the formation of naphthalenediimide (NDI) radical anions. The LUMO and HOMO energy of NDI are lowered significantly by introducing cucurbit[7]uril (CB[7]) to each side of a designed NDI mol. through supramol. complexation. This promotes efficiently the photo-induced electron transfer process between NDI and bromide anions in aq. soln. The resulting NDI supramol. radical anions are of outstanding stability. They are even stable in aq. soln. at higher temps. of 40 °C and 60 °C. It is anticipated that this supramol. strategy may provide a facile method for stabilizing radicals towards the development of novel materials with spin-based properties and optical properties in the visible and near-IR regions.
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  18. 18
    Nakano, M.; Takimiya, K. Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials. Chem. Mater. 2017, 29, 256– 264,  DOI: 10.1021/acs.chemmater.6b03413
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    18
    Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials
    Nakano, Masahiro; Takimiya, Kazuo
    Chemistry of Materials (2017), 29 (1), 256-264CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The authors describe herein facile thiophene annulation reactions promoted by sodium sulfide hydrate (Na2S·9H2O) for the synthesis of acene(di)thiophenes that can be further utilized as org. semiconductors or building blocks for the elaboration of semiconducting oligomers and polymers. Sodium sulfide hydrate is an efficient source of sulfur for both the arom. nucleophilic substitution (SNAr) reaction and the nucleophilic hydrogen substitution (SNH) reaction to give a range of electron-donating acene(di)thiophenes and an electron-deficient naphtho[2,3-b:6,7-b']dithiophene diimide (NDTI), resp. Also are described org. semiconducting materials on the basis of these acene(di)thiophenes and their use in org. devices, such as org. field-effect transistors and org. photovoltaics, and demonstrate that synthetic evolution is one of the keys to promoting the field of org. semiconducting materials.
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  19. 19
    DuBose, T.; Kamat, V. Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal–Molecular Hybrids: Focus Review. Chem. Rev. 2022, 122, 12475– 12494,  DOI: 10.1021/acs.chemrev.2c00172
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    19
    Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal-Molecular Hybrids
    DuBose, Jeffrey T.; Kamat, Prashant V.
    Chemical Reviews (Washington, DC, United States) (2022), 122 (15), 12475-12494CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Energy and electron transfer processes in light harvesting assemblies dictate the outcome of the overall light energy conversion process. Halide perovskite nanocrystals such as CsPbBr3 with relatively high emission yield and strong light absorption can transfer singlet and triplet energy to surface-bound acceptor mols. They can also induce photocatalytic redn. and oxidn. by selectively transferring electrons and holes across the nanocrystal interface. This perspective discusses key factors dictating these excited-state pathways in perovskite nanocrystals and the fundamental differences between energy and electron transfer processes. Spectroscopic methods to decipher between these complex photoinduced pathways are presented. A basic understanding of the fundamental differences between the two excited deactivation processes (charge and energy transfer) and ways to modulate them should enable design of more efficient light harvesting assemblies with semiconductor and mol. systems.
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  20. 20
    Li, M.; Valandro, R.; He, R.; Zhao, Y.; Yang, P.; Schanze, S. Charge-Transfer Dynamics between Cesium Lead Halide Perovskite Nanocrystals and Surface-Anchored Naphthalimide Acceptors. J. Phys. Chem. C 2021, 125, 14778– 14785,  DOI: 10.1021/acs.jpcc.1c02622
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    20
    Charge-Transfer Dynamics between Cesium Lead Halide Perovskite Nanocrystals and Surface-Anchored Naphthalimide Acceptors
    Li, Meng; Valandro, Silvano R.; He, Ru; Zhao, Yan; Yang, Ping; Schanze, Kirk S.
    Journal of Physical Chemistry C (2021), 125 (27), 14778-14785CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    A series of 1,8-naphthalimide (NI) electron acceptors with a primary amine functional group linked to the N-position of the imide by -(CH2)n- linkers with varying lengths are found to quench the photoluminescence (PL) of CsPbBr3 nanocrystals (NC). Three NI-based quenchers were explored, NI-1, NI-2, and NI-3, with n = 2, 8, and 12, resp. The PL quenching is attributed to photoinduced electron transfer from the exciton state of the CsPbBr3 NCs to the naphthylimide acceptor. An NI acceptor that lacks the NH2 group does not quench the PL, which reveals that the amino group serves to anchor the acceptors to the surface of the NC. The photoinduced charge-transfer mechanism is supported by picosecond transient absorption (TA), which finds a long-lifetime bleach (>7 ns) for the CsPbBr3 NCs with surface-anchored NI-1 acceptors. Steady-state and time-resolved PL quenching was subjected to Stern-Volmer (SV) anal. The results show that the quenching efficiency varies in the order NI-1 » NI-2 > NI-3, with KSV ranging from ~ 106 M-1 for NI-1 to ~ 105 M-1 for NI-3. The quenching efficiency is approx. the same for steady-state and dynamic quenching. The results are interpreted by a mechanism where the exciton quenching dynamics is controlled by the rate of interfacial electron transfer. Diffusion and/or detrapping of the CsPbBr3 exciton may also play a role in detg. the rate of quenching.
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  21. 21
    Maes, J.; Balcaen, L.; Drijvers, E.; Zhao, Q.; De Roo, J.; Vantomme, A.; Vanhaecke, F.; Geiregat, P.; Hens, Z. Light Absorption Coefficient of CsPbBr3 Perovskite Nanocrystals. J. Phys. Chem. Lett. 2018, 9 (11), 3093– 3097,  DOI: 10.1021/acs.jpclett.8b01065
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    21
    Light Absorption Coefficient of CsPbBr3 Perovskite Nanocrystals
    Maes, Jorick; Balcaen, Lieve; Drijvers, Emile; Zhao, Qiang; De Roo, Jonathan; Vantomme, Andre; Vanhaecke, Frank; Geiregat, Pieter; Hens, Zeger
    Journal of Physical Chemistry Letters (2018), 9 (11), 3093-3097CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Inductively coupled plasma mass spectrometry (ICP-MS) was combined with UV-visible absorption spectroscopy and TEM to det. the size, compn., and intrinsic absorption coeff. μi of 4 to 11 nm sized colloidal CsPbBr3 nanocrystals (NCs). The ICP-MS measurements demonstrate the nonstoichiometric nature of the NCs, with a systematic excess of lead for all samples studied. Rutherford backscattering measurements indicate that this enrichment in lead concurs with a relative increase in the bromide content. At high photon energies, μi is independent of the nanocrystal size. This allows the nanocrystal concn. in CsPbBr3 nanocolloids to be readily obtained by a combination of absorption spectroscopy and the CsPbBr3 sizing curve.
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  22. 22
    Mishra, L.; Panigrahi, A.; Dubey, P.; Sarangi, K. Photo-induced charge transfer in composition-tuned halide perovskite nanocrystals with quinone and its impact on conduction current. J. Appl. Phys. 2022, 132, 195702,  DOI: 10.1063/5.0123558
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    22
    Photo-induced charge transfer in composition-tuned halide perovskite nanocrystals with quinone and its impact on conduction current
    Mishra, Leepsa; Panigrahi, Aradhana; Dubey, Priyanka; Sarangi, Manas Kumar
    Journal of Applied Physics (Melville, NY, United States) (2022), 132 (19), 195702CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
    A facile interfacial charge transfer (CT) with a reduced inter-layer energy band regulates the charge transport mechanism in any optoelectronic device. The enhancement in semiconductor-based device performance often demands improved CT dynamics and collection of free carriers with reduced charge recombination. In this work, we present a detailed inspection of the photo-induced CT between inorg. lead halide perovskite nanocrystals (PNCs) with varied compns. and their consequence on the charge transport process. The superior CT rate in mixed halide CsPbBr2Cl PNCs with naphthoquinone (NPQ) is revealed when compared with the parent CsPbBr3 PNCs and its anion-exchanged counterpart CsPbCl3. The glimpses of hole transfer contribution along with electron transfer are detected for CsPbBr2Cl with superior CT efficiency. The enhanced conduction current after the insertion of NPQ into the PNCs with a reduced hysteresis suggests an improved charge transport in the fabricated device compared to the pristine PNCs. These findings can contribute to a better understanding of multiple ways of engineering optoelectronic devices to boost performance and efficiencies and the concurrent role of the CT process in the conduction mechanism. (c) 2022 American Institute of Physics.
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  23. 23
    Mandal, S.; George, L.; Tkachenko, V. Charge transfer dynamics in CsPbBr3 perovskite quantum dots–anthraquinone/fullerene (C60) hybrids. Nanoscale 2019, 11, 862– 869,  DOI: 10.1039/C8NR08445A
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    23
    Charge transfer dynamics in CsPbBr3 perovskite quantum dots-anthraquinone/fullerene (C60) hybrids
    Mandal, Sadananda; George, Lijo; Tkachenko, Nikolai V.
    Nanoscale (2019), 11 (3), 862-869CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    An advantage of colloidal quantum dots, particularly perovskite quantum dots (PQDs), as photoactive components is that they easily form complexes with functional org. mols., which results in hybrids with enriched photophys. properties. Herein, we demonstrate the formation of stable ground state complexes of CsPbBr3 PQD with two widely used mol. electron acceptors, fullerene (C60) and anthraquinone, (AQ) which contain carboxylic anchor groups. Dynamics of the photo-induced electron transfer in the hybrids were compared. The use of carboxylic groups for binding results in stable complex formation and their photophys. properties depend on the ratio of components but not the abs. concns. (up to micromolar concns.). Time-resolved transient absorption (TA) spectroscopy shows that in both cases, a charge sepd. (CS) state is formed. Data anal. was aimed to evaluate the CS time const. in ideal one-to-one complexes and was found to be in the range of 30-190 ps. The CS state of PQD-AQ complexes recombines directly to the ground state in roughly one microsecond. Recombination of the CS state of PQD-C60 is more complex and points to strong inhomogeneity of these complexes. Majority of the CS states relax by first forming the C60 triplet state.
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  24. 24
    DuBose, T.; Kamat, V. Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr3 and Ferrocene Redox Couple. J. Phys. Chem. Lett. 2019, 10, 6074– 6080,  DOI: 10.1021/acs.jpclett.9b02294
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    24
    Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr3 and Ferrocene Redox Couple
    DuBose, Jeffrey T.; Kamat, Prashant V.
    Journal of Physical Chemistry Letters (2019), 10 (20), 6074-6080CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Interfacial charge transfer between a semiconductor nanocrystal and a mol. relay is an important step in nanomaterial photocatalysis. The ferrocene redox couple (Fc+/Fc0, E0 = -4.9 eV vs. vacuum) has now been used as a model redox relay system to study photocatalytic properties of CsPbBr3 perovskite nanocrystals. The photocatalytic redn. of ferrocenium (Fc+) to ferrocene (Fc0) with CsPbBr3 nanocrystals was dictated by the surface interactions. Whereas a rapid quenching and subsequent recovery of CsPbBr3 emission is seen at low Fc+ concns., the quenched emission was sustained at higher Fc+ concns. The photoinduced interfacial electron transfer between CsPbBr3 and ferrocenium (Fc+) studied using transient absorption spectroscopy occurred with a rate const. of 1.64 × 1010 s-1. Better understanding of interfacial processes using redox probes can lead to the improvement in photocatalytic performance of perovskite nanocrystals.
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    Bridewell, L.; Alam, R.; Karwacki, J.; Kamat, V. CdSe/CdS Nanorod Photocatalysts: Tuning the Interfacial Charge Transfer Process through Shell Length. Chem. Mater. 2015, 27, 5064– 5071,  DOI: 10.1021/acs.chemmater.5b01689
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    25
    CdSe/CdS Nanorod Photocatalysts: Tuning the Interfacial Charge Transfer Process through Shell Length
    Bridewell, Victoria L.; Alam, Rabeka; Karwacki, Christopher J.; Kamat, Prashant V.
    Chemistry of Materials (2015), 27 (14), 5064-5071CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    CdSe/CdS core/shell semiconductor nanorods (NR) with rod-in-rod morphol. offer new strategies for designing highly emissive nanostructures. The interplay between energetically matched semiconductors results in enhanced emission from the CdSe core. In order to further evaluate the cooperative role of these two semiconductors in a core/shell geometry, we have probed the photoinduced charge transfer between CdSe/CdS core/shell semiconductor NR and Me viologen (MV2+). The quenching of the emission by the electron acceptor, MV2+, as well as the prodn. of electron transfer product MV•+ depends on the aspect ratio (l/w) of the NR thus pointing out the role of CdS shell in detg. the overall photocatalytic efficiency. Transient absorption measurements show that the presence of MV2+ influences only the bleaching recovery of the CdS shell and not of the CdSe core recovery. Thus, optimization of shell aspect ratio plays a crucial role in maximizing the efficiency of this photocatalytic system.
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    Harris, C.; Kamat, V. Photocatalytic Events of CdSe Quantum Dots in Confined Media. Electrodic Behavior of Coupled Platinum Nanoparticles. ACS Nano 2010, 4 (12), 7321– 7330,  DOI: 10.1021/nn102564x
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    26
    Photocatalytic Events of CdSe Quantum Dots in Confined Media. Electrodic Behavior of Coupled Platinum Nanoparticles
    Harris, Clifton; Kamat, Prashant V.
    ACS Nano (2010), 4 (12), 7321-7330CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The electrodic behavior of platinum nanoparticles (2.8 nm diam.) and their role in influencing the photocatalytic behavior of CdSe quantum dots (3.4 nm diam.) was evaluated by confining both nanoparticles together in heptane/dioctyl sulfosuccinate/water reverse micelles. The particles spontaneously couple together within the micelles via micellar exchange processes and thus facilitate exptl. observation of electron transfer reactions inside the water pools. Electron transfer from CdSe to Pt occurs with a rate const. of 1.22 × 109 s-1. Using Me viologen (MV2+) as a probe mol., the role of Pt in the photocatalytic process is established. Ultrafast oxidn. of the photogenerated MV+· radicals indicates that Pt acts as an electron sink, scavenging electrons from MV+· with a rate const. of 3.1 × 109 s-1. The electron transfer between MV+· and Pt, and a drastically lower yield of MV+· under steady state irradn., confirms the ability of Pt nanoparticles to discharge electrons quickly. The kinetic details of photoinduced processes in CdSe-Pt assemblies and the electrodic behavior of Pt nanoparticles provide important information for the development of light energy conversion devices.
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    Marjit, K.; Ghosh, G.; Ghosh, S.; Ghosh, D.; Medda, A.; Patra, A. Electron Transfer Dynamics from CsPbBr3 Nanocrystals to Au144 Clusters. ACS Phys. Chem. Au 2023, 3 (4), 348– 357,  DOI: 10.1021/acsphyschemau.2c00070
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    Viezbicke, D.; Patel, S.; Davis, E.; Birnie, P. Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system. Phys. Status Solidi B 2015, 252, 1700– 1710,  DOI: 10.1002/pssb.201552007
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    28
    Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system
    Viezbicke, Brian D.; Patel, Shane; Davis, Benjamin E.; Birnie, Dunbar P., III
    Physica Status Solidi B: Basic Solid State Physics (2015), 252 (8), 1700-1710CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)
    One of the most frequently used methods for characterizing thin films is UV-Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called "Tauc" plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large no. of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examn. of the band gap values and their distribution leads to a discussion of some exptl. factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single cryst. material.
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    Xie, Y.; Yu, Y.; Gong, J.; Yang, C.; Zeng, P.; Dong, Y.; Yang, B.; Liang, R.; Ou, Q.; Zhang, S. Encapsulated room-temperature synthesized CsPbX3 perovskite quantum dots with high stability and wide color gamut for display. Opt. Mater. Express 2018, 8 (11), 3494– 3505,  DOI: 10.1364/ome.8.003494
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    Butkus, J.; Vashishtha, P.; Chen, K.; Gallaher, K.; Prasad, K.; Metin, Z.; Laufersky, G.; Gaston, N.; Halpert, J.; Hodgkiss, J. The Evolution of Quantum Confinement in CsPbBr3 Perovskite Nanocrystals. Chem. Mater. 2017, 29, 3644– 3652,  DOI: 10.1021/acs.chemmater.7b00478
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    The Evolution of Quantum Confinement in CsPbBr3 Perovskite Nanocrystals
    Butkus, Justinas; Vashishtha, Parth; Chen, Kai; Gallaher, Joseph K.; Prasad, Shyamal K. K.; Metin, Dani Z.; Laufersky, Geoffry; Gaston, Nicola; Halpert, Jonathan E.; Hodgkiss, Justin M.
    Chemistry of Materials (2017), 29 (8), 3644-3652CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Colloidal nanocrystals (NCs) of lead halide perovskites are considered highly promising materials that combine the exceptional optoelectronic properties of lead halide perovskites with tunability from quantum confinement. But can we assume that these materials are in the strong confinement regime. Here, we report an ultrafast transient absorption study of cubic CsPbBr3 NCs as a function of size, compared with the bulk material. For NCs above ∼7 nm edge length, spectral signatures are similar to the bulk material-characterized by state-filling with uncorrelated charges-but discrete new kinetic components emerge at high fluence due to bimol. recombination occurring in a discrete vol. Only for the smallest NCs (∼4 nm edge length) are strong quantum confinement effects manifest in TA spectral dynamics; focusing toward discrete energy states, enhanced bandgap renormalization energy, and departure from a Boltzmann statistical carrier cooling. At high fluence, we find that a hot-phonon bottleneck effect slows carrier cooling, but this appears to be intrinsic to the material, rather than size dependent. Overall, we find that the smallest NCs are understood in the framework of quantum confinement, however for the widely used NCs with edge lengths >7 nm the photophysics of bulk lead halide perovskites are a better point of ref.
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    Meng, C.; Yang, D.; Wu, Y.; Zhang, X.; Zeng, H.; Li, X. Synthesis of single CsPbBr3@SiO2 core–shell particles via surface activation. J. Mater. Chem. C 2020, 8, 17403– 17409,  DOI: 10.1039/D0TC03932B
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    Synthesis of single CsPbBr3@SiO2 core-shell particles via surface activation
    Meng, Cuifang; Yang, Dandan; Wu, Ye; Zhang, Xuejia; Zeng, Haibo; Li, Xiaoming
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2020), 8 (48), 17403-17409CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    Encapsulating Cs lead halide (CsPbX3, X = Cl, Br, and I) perovskite quantum dots (PQDs) into stable shells is an effective strategy for improving their stability, which however usually forms agglomerated particles or alters PQDs' original morphol. and optical properties. A surface activation strategy to prep. single CsPbBr3@SiO2 core-shell particles is proposed. (3-Aminopropyl)triethoxysilane (APTES) is used as a bifunctional surface ligand, which not only effectively passivates the surface defects of PQDs, but also provides -SiOMe and -SiOH groups for the formation of Si-O-Si covalent bonds with the subsequently introduced silanes. By controlling the hydrolysis rate of silanes, the prepn. of single CsPbBr3@SiO2 core-shell particles with an av. shell thickness of 1-2.7 nm was realized, and the PQDs maintained their initial cubic morphol. and optical properties after coating. The stability of CsPbBr3@SiO2 in harsh environments was effectively improved owing to the complete encapsulation of the SiO2 shell. The emission peak of CsPbBr3@SiO2 remains const. at 515 nm after being heated at 60° for 84 h, and the luminescence (PL) intensity still remains 90% after storage for 6 h in a high humidity environment. This work not only enhances the stability of PQDs for practical applications but also provides a reliable method to synthesize single core-shell particles, which can be instructive to other PQD systems.
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    Valero, S.; Cabrera-Espinoza, A.; Collavini, S.; Pascual, J.; Marinova, N.; Kosta, I.; Delgado, J. L. Naphthalene Diimide-Based Molecules for Efficient and Stable Perovskite Solar Cells. Eur. J. Org Chem. 2020, 2020, 5329– 5339,  DOI: 10.1002/ejoc.202000287
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    Huang, H.; Yuan, H.; Janssen, K.; Solís-Fernández, G.; Wang, Y.; Tan, C.; Jonckheere, D.; Debroye, E.; Long, J.; Hendrix, J.; Hofkens, J.; Steele, J.; Roeffaers, M. Efficient and Selective Photocatalytic Oxidation of Benzylic Alcohols with Hybrid Organic–Inorganic Perovskite Materials. ACS Energy Lett. 2018, 3, 755– 759,  DOI: 10.1021/acsenergylett.8b00131
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    Efficient and Selective Photocatalytic Oxidation of Benzylic Alcohols with Hybrid Organic-Inorganic Perovskite Materials
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  • Abstract

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    Figure 1

    Figure 1. Photoluminescence and UV–visible absorption spectra of toluene solutions of (a) SNDI (λex = 320 nm) and (b) CsPbBr3 QDs (λex = 425 nm). The insets show the structure of SNDI along with its solution and the QDs colloidal solution under UV light─365 nm.

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    Figure 2

    Figure 2. (a) PL emission measurements of CsPbBr3 QDs with the addition of SNDI up to 15 μL. The inset indicates a linear relationship of I0/I vs [SNDI] (excitation of 425 nm). (b) Absorption spectrum of the QDs of CsPbBr3 with the addition of 15 μL of SNDI. The inset shows a Tauc plot estimating the band gap energy of both systems. The concentrations for each measurement are SNDI (mol/L): 8.33 × 10–7 (2.5 μL); 1.66 × 10–6 (5.0 μL); 2.49 × 10–6 (7.5 μL); 3.32 × 10–6 (10.0 μL); 4.15 × 10–6 (12.5 μL); and 4.98 × 10–6 (15.0 μL).

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    Figure 3

    Figure 3. TEM images showing the morphology and size of the CsPbBr3 QDs (a,b) and CsPbBr3/SNDI (d,e). The graphics (c,f) show the particle size distribution for both samples.

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    Figure 4

    Figure 4. (a) Photoluminescence spectra collected in a thin film for the CsPbBr3 QDs pure (black), with 2.5 μL (red) and 15.0 μL (blue) of SNDI (excitation = 425 nm). The inset shows UV–vis measurements showing the absorption band at 508 nm of the QDs/SNDI thin film and (b) energy-level scheme summarizing the band structure of CsPbBr3 and the electronic structure of SNDI upon irradiation. The concentrations for each measurement are SNDI (mol/L): 8.33 × 10–7 (2.5 μL) and 4.98 × 10–6 (15.0 μL).

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    Figure 5

    Figure 5. Current–voltage (I–V) curves under dark and light (1 sun from a solar simulator) for two samples: CsPbBr3 QDs (a) and CsPbBr3 QDs/SNDI (b). The inset shows a photograph of devices under UV light at 365 nm. Energy-level scheme and charge separation for the Nyquist impedance spectroscopy for the samples under conditions of dark and light illumination of 1 sun from the solar simulator for (c) CsPbBr3 QDs and (d) CsPbBr3/SNDI.

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    Figure 6

    Figure 6. Schematic illustration of the energy-level diagram of QDs, SNDI, and FTO, along with transfer and recombination pathways upon irradiation.

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      Donor/Acceptor Charge-Transfer States at Two-Dimensional Metal Halide Perovskite and Organic Semiconductor Interfaces
      Zhao, Lianfeng; Lin, YunHui L.; Kim, Hoyeon; Giebink, Noel C.; Rand, Barry P.
      ACS Energy Letters (2018), 3 (11), 2708-2712CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Metal halide perovskite semiconductors with small exciton binding energy were widely used in perovskite solar cells and achieved rapid progress in terms of device performance. However, the strong excitonic nature of two-dimensional (2D) perovskites with small n values remains under-exploited (n represents the no. of inorg. monolayer sheets sandwiched between bulky org. cation layers). The authors report exptl. evidence of donor/acceptor charge-transfer (CT) states formed at 2-dimensional metal halide perovskite/org. semiconductor heterojunctions, with a corresponding increase in photocurrent prodn. for these excitonic materials. Also, the size of the org. cation in the 2-dimensional perovskite layer plays a crit. role in the CT process. The ability to dissoc. excitons in 2-dimensional perovskites by interfacing with an org. semiconductor in a donor/acceptor configuration opens up new opportunities for exploiting the excitonic nature of low-dimensional perovskites in applications such as solar cells, photodetectors, light-emitting devices, and light-matter interactions.
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    9. 9
      Zhu, R.; Gao, C.; Sun, T.; Shen, L.; Sun, D.; Li, X. Surface Decorating of CH3NH3PbBr3 Nanoparticles with the Chemically Adsorbed Perylenetetracarboxylic Diimide. Langmuir 2016, 32, 3294– 3299,  DOI: 10.1021/acs.langmuir.5b04221
      9
      Surface Decorating of CH3NH3PbBr3 Nanoparticles with the Chemically Adsorbed Perylenetetracarboxylic Diimide
      Zhu, Ruimin; Gao, Chengguang; Sun, Tingting; Shen, Li; Sun, Dejun; Li, Xiyou
      Langmuir (2016), 32 (13), 3294-3299CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      An org. dye-modified organolead halide CH3NH3PbBr3 nanoparticle (cubic) is prepd. successfully by using a perylenetetracarboxylic diimide (PDI) bearing an -NH3+ headgroup as the capping ligand. The nanoparticles are homogeneous with high crystallinity. The photoluminescence of perovskite is quenched completely by the chem. adsorbed PDI mols. This efficient fluorescence quenching has confirmed that the PDI mols. are anchored on the surface of CH3NH3PbBr3 nanoparticle. The resulting nanoparticles can be dispersed in org. solvents, and the resulting dispersion remains stable for days. This result provides a general guideline for surface engineering of organolead halide CH3NH3PbBr3 nanoparticles.
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    10. 10
      Kobosko, M.; DuBose, T.; Kamat, V. Perovskite Photocatalysis. Methyl Viologen Induces Unusually Long-Lived Charge Carrier Separation in CsPbBr3 Nanocrystals. ACS Energy Lett. 2020, 5, 221– 223,  DOI: 10.1021/acsenergylett.9b02573
      10
      Perovskite Photocatalysis. Methyl Viologen Induces Unusually Long-Lived Charge Carrier Separation in CsPbBr3 Nanocrystals
      Kobosko, Steven M.; DuBose, Jeffrey T.; Kamat, Prashant V.
      ACS Energy Letters (2020), 5 (1), 221-223CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      The strong binding between CsPbBr3 nanocrystals and Me viologen induces a long-lived charge-sepd. state following band gap excitation with important implications in photocatalytic processes. The unusually long-lived bleaching of the CsPbBr3 excitonic peak in this case arises from the creation of a dipole with the hole residing in CsPbBr3 and the electron in the surface-bound Me viologen moiety.
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    11. 11
      Ou, M.; Tu, W.; Yin, S.; Xing, W.; Wu, S.; Wang, H.; Wan, S.; Zhong, Q.; Xu, R. Amino-Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g-C3N4 for Enhanced Photocatalytic CO2 Reduction. Angew. Chem., Int. Ed. 2018, 57, 13570– 13574,  DOI: 10.1002/anie.201808930
      11
      Amino-Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g-C3N4 for Enhanced Photocatalytic CO2 Reduction
      Ou, Man; Tu, Wenguang; Yin, Shengming; Xing, Weinan; Wu, Shuyang; Wang, Haojing; Wan, Shipeng; Zhong, Qin; Xu, Rong
      Angewandte Chemie, International Edition (2018), 57 (41), 13570-13574CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chem. instability can be overcome. To circumvent these obstacles, we anchored CsPbBr3 QDs (CPB) on NHx-rich porous g-C3N4 nanosheets (PCN) to construct the composite photocatalysts via N-Br chem. bonding. The 20 CPB-PCN (20 wt. % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h-1 g-1 in acetonitrile/water for photocatalytic redn. of CO2 to CO under visible light irradn., which is around 15 times higher than that of CsPbBr3 QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.
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    12. 12
      Al Kobaisi, M.; Bhosale, V.; Latham, K.; Raynor, M.; Bhosale, V. Functional Naphthalene Diimides: Synthesis, Properties, and Applications. Chem. Rev. 2016, 116, 11685– 11796,  DOI: 10.1021/acs.chemrev.6b00160
      There is no corresponding record for this reference.
    13. 13
      Kumar, S.; Shukla, J.; Kumar, Y.; Mukhopadhyay, P. Electron-poor arylenediimides. Org. Chem. Front. 2018, 5, 2254– 2276,  DOI: 10.1039/C8QO00256H
      13
      Electron-poor arylenediimides
      Kumar, Sharvan; Shukla, Jyoti; Kumar, Yogendra; Mukhopadhyay, Pritam
      Organic Chemistry Frontiers (2018), 5 (14), 2254-2276CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
      A review. Arylenediimides are inherently electron deficient and provide enormous opportunities to conjugate electron withdrawing substituents in different regions of the π-scaffold. This review article highlights the gradual emergence of diverse mol. design principles to realize exceptionally electron deficient arylenediimide mols. Interestingly, non-conventional electron withdrawing substituents allow the realization of some of the strongest electron acceptors known from this class of mols. Thus, an enthralling and exceptionally close race to garner the top position within the electron deficient mols. unfolds, which has immense implications with regard to stability and potential applications.
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    14. 14
      Katz, E.; Lovinger, J.; Johnson, J.; Kloc, C.; Siegrist, T.; Li, W.; Lin, Y.; Dodabalapur, A. A soluble and air-stable organic semiconductor with high electron Mobility. Nature 2000, 404, 478– 481,  DOI: 10.1038/35006603
      14
      A soluble and air-stable organic semiconductor with high electron mobility
      Katz, H. E.; Lovinger, A. J.; Johnson, J.; Kloc, C.; Slegrist, T.; Li, W.; Lin, Y.-Y.; Dodabalapur, A.
      Nature (London) (2000), 404 (6777), 478-481CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      We report a crystallog. engineered naphthalenetetracarboxylic diimide deriv. that allows us to fabricate soln.-cast n-channel FETs with promising performance at ambient conditions. By integrating our n-channel FETs with soln.-deposited p-channel FETs, we are able to produce a complementary inverter circuit whose active layers are deposited entirely from the liq. phase. We expect that other complementary circuit designs can be realized by this approach as well.
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    15. 15
      Zhan, X.; Facchetti, A.; Barlow, S.; Marks, J.; Ratner, A.; Wasielewski, R.; Marder, R. Rylene and related diimides for organic electronics. Adv. Mater. 2011, 23, 268– 284,  DOI: 10.1002/adma.201001402
      15
      Rylene and Related Diimides for Organic Electronics
      Zhan, Xiaowei; Facchetti, Antonio; Barlow, Stephen; Marks, Tobin J.; Ratner, Mark A.; Wasielewski, Michael R.; Marder, Seth R.
      Advanced Materials (Weinheim, Germany) (2011), 23 (2), 268-284CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review with 85 refs. Org. electron-transporting materials are essential for the fabrication of org. p-n junctions, photovoltaic cells, n-channel field-effect transistors, and complementary logic circuits. Rylene diimides are a robust, versatile class of polycyclic arom. electron-transport materials with excellent thermal and oxidative stability, high electron affinities, and, in many cases, high electron mobilities; they are, therefore, promising candidates for a variety of org. electronics applications. In this review, recent developments in the area of high-electron-mobility diimides based on rylenes and related arom. cores, particularly perylene- and naphthalene-diimide-based small mols. and polymers, for application in high-performance org. field-effect transistors and photovoltaic cells are summarized and analyzed.
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    16. 16
      Wang, D.; Ye, T.; Zhang, Y. Recent advances of non-fullerene organic electron transport materials in perovskite solar cells. J. Mater. Chem. A 2020, 8, 20819– 20848,  DOI: 10.1039/D0TA06500E
      16
      Recent advances of non-fullerene organic electron transport materials in perovskite solar cells
      Wang, Daizhe; Ye, Tengling; Zhang, Yong
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (40), 20819-20848CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A review. In perovskite solar cells (PerSCs), the electron transport layer (ETL) exts. and transports electrons from the perovskite light absorption layer (PAL) to the cathode, which plays an important role in improving the performance and long-term stability of the devices. Compared with fullerene derivs., non-fullerene n-type org. semiconductors have some unique advantages, such as mol. structure diversity, ease of modification, adjustable frontier MOs, and good stability. Recently, non-fullerene electron transport materials (ETMs) have attracted more and more attention as efficient ETLs in PerSCs. A variety of non-fullerene ETMs have been reported. Herein, we summarized the latest developments of non-fullerene org. ETMs in PerSCs, including small mol. org. ETMs and polymer ETMs. Esp., the common effects of substituents and design strategies of mol. configuration on the properties of non-fullerene ETMs were systematically summarized. At the same time, the remaining challenges and promising future trends of PerSCs based on non-fullerene org. ETMs are discussed.
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    17. 17
      Song, Q.; Li, F.; Wang, Z.; Zhang, X. A supramolecular strategy for tuning the energy level of naphthalenediimide: Promoted formation of radical anions with extraordinary stability. Chem. Sci. 2015, 6, 3342– 3346,  DOI: 10.1039/C5SC00862J
      17
      A supramolecular strategy for tuning the energy level of naphthalenediimide: Promoted formation of radical anions with extraordinary stability
      Song, Qiao; Li, Fei; Wang, Zhiqiang; Zhang, Xi
      Chemical Science (2015), 6 (6), 3342-3346CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The authors report a supramol. strategy to promote and stabilize the formation of naphthalenediimide (NDI) radical anions. The LUMO and HOMO energy of NDI are lowered significantly by introducing cucurbit[7]uril (CB[7]) to each side of a designed NDI mol. through supramol. complexation. This promotes efficiently the photo-induced electron transfer process between NDI and bromide anions in aq. soln. The resulting NDI supramol. radical anions are of outstanding stability. They are even stable in aq. soln. at higher temps. of 40 °C and 60 °C. It is anticipated that this supramol. strategy may provide a facile method for stabilizing radicals towards the development of novel materials with spin-based properties and optical properties in the visible and near-IR regions.
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    18. 18
      Nakano, M.; Takimiya, K. Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials. Chem. Mater. 2017, 29, 256– 264,  DOI: 10.1021/acs.chemmater.6b03413
      18
      Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials
      Nakano, Masahiro; Takimiya, Kazuo
      Chemistry of Materials (2017), 29 (1), 256-264CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The authors describe herein facile thiophene annulation reactions promoted by sodium sulfide hydrate (Na2S·9H2O) for the synthesis of acene(di)thiophenes that can be further utilized as org. semiconductors or building blocks for the elaboration of semiconducting oligomers and polymers. Sodium sulfide hydrate is an efficient source of sulfur for both the arom. nucleophilic substitution (SNAr) reaction and the nucleophilic hydrogen substitution (SNH) reaction to give a range of electron-donating acene(di)thiophenes and an electron-deficient naphtho[2,3-b:6,7-b']dithiophene diimide (NDTI), resp. Also are described org. semiconducting materials on the basis of these acene(di)thiophenes and their use in org. devices, such as org. field-effect transistors and org. photovoltaics, and demonstrate that synthetic evolution is one of the keys to promoting the field of org. semiconducting materials.
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    19. 19
      DuBose, T.; Kamat, V. Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal–Molecular Hybrids: Focus Review. Chem. Rev. 2022, 122, 12475– 12494,  DOI: 10.1021/acs.chemrev.2c00172
      19
      Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal-Molecular Hybrids
      DuBose, Jeffrey T.; Kamat, Prashant V.
      Chemical Reviews (Washington, DC, United States) (2022), 122 (15), 12475-12494CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Energy and electron transfer processes in light harvesting assemblies dictate the outcome of the overall light energy conversion process. Halide perovskite nanocrystals such as CsPbBr3 with relatively high emission yield and strong light absorption can transfer singlet and triplet energy to surface-bound acceptor mols. They can also induce photocatalytic redn. and oxidn. by selectively transferring electrons and holes across the nanocrystal interface. This perspective discusses key factors dictating these excited-state pathways in perovskite nanocrystals and the fundamental differences between energy and electron transfer processes. Spectroscopic methods to decipher between these complex photoinduced pathways are presented. A basic understanding of the fundamental differences between the two excited deactivation processes (charge and energy transfer) and ways to modulate them should enable design of more efficient light harvesting assemblies with semiconductor and mol. systems.
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    20. 20
      Li, M.; Valandro, R.; He, R.; Zhao, Y.; Yang, P.; Schanze, S. Charge-Transfer Dynamics between Cesium Lead Halide Perovskite Nanocrystals and Surface-Anchored Naphthalimide Acceptors. J. Phys. Chem. C 2021, 125, 14778– 14785,  DOI: 10.1021/acs.jpcc.1c02622
      20
      Charge-Transfer Dynamics between Cesium Lead Halide Perovskite Nanocrystals and Surface-Anchored Naphthalimide Acceptors
      Li, Meng; Valandro, Silvano R.; He, Ru; Zhao, Yan; Yang, Ping; Schanze, Kirk S.
      Journal of Physical Chemistry C (2021), 125 (27), 14778-14785CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A series of 1,8-naphthalimide (NI) electron acceptors with a primary amine functional group linked to the N-position of the imide by -(CH2)n- linkers with varying lengths are found to quench the photoluminescence (PL) of CsPbBr3 nanocrystals (NC). Three NI-based quenchers were explored, NI-1, NI-2, and NI-3, with n = 2, 8, and 12, resp. The PL quenching is attributed to photoinduced electron transfer from the exciton state of the CsPbBr3 NCs to the naphthylimide acceptor. An NI acceptor that lacks the NH2 group does not quench the PL, which reveals that the amino group serves to anchor the acceptors to the surface of the NC. The photoinduced charge-transfer mechanism is supported by picosecond transient absorption (TA), which finds a long-lifetime bleach (>7 ns) for the CsPbBr3 NCs with surface-anchored NI-1 acceptors. Steady-state and time-resolved PL quenching was subjected to Stern-Volmer (SV) anal. The results show that the quenching efficiency varies in the order NI-1 » NI-2 > NI-3, with KSV ranging from ~ 106 M-1 for NI-1 to ~ 105 M-1 for NI-3. The quenching efficiency is approx. the same for steady-state and dynamic quenching. The results are interpreted by a mechanism where the exciton quenching dynamics is controlled by the rate of interfacial electron transfer. Diffusion and/or detrapping of the CsPbBr3 exciton may also play a role in detg. the rate of quenching.
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    21. 21
      Maes, J.; Balcaen, L.; Drijvers, E.; Zhao, Q.; De Roo, J.; Vantomme, A.; Vanhaecke, F.; Geiregat, P.; Hens, Z. Light Absorption Coefficient of CsPbBr3 Perovskite Nanocrystals. J. Phys. Chem. Lett. 2018, 9 (11), 3093– 3097,  DOI: 10.1021/acs.jpclett.8b01065
      21
      Light Absorption Coefficient of CsPbBr3 Perovskite Nanocrystals
      Maes, Jorick; Balcaen, Lieve; Drijvers, Emile; Zhao, Qiang; De Roo, Jonathan; Vantomme, Andre; Vanhaecke, Frank; Geiregat, Pieter; Hens, Zeger
      Journal of Physical Chemistry Letters (2018), 9 (11), 3093-3097CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Inductively coupled plasma mass spectrometry (ICP-MS) was combined with UV-visible absorption spectroscopy and TEM to det. the size, compn., and intrinsic absorption coeff. μi of 4 to 11 nm sized colloidal CsPbBr3 nanocrystals (NCs). The ICP-MS measurements demonstrate the nonstoichiometric nature of the NCs, with a systematic excess of lead for all samples studied. Rutherford backscattering measurements indicate that this enrichment in lead concurs with a relative increase in the bromide content. At high photon energies, μi is independent of the nanocrystal size. This allows the nanocrystal concn. in CsPbBr3 nanocolloids to be readily obtained by a combination of absorption spectroscopy and the CsPbBr3 sizing curve.
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    22. 22
      Mishra, L.; Panigrahi, A.; Dubey, P.; Sarangi, K. Photo-induced charge transfer in composition-tuned halide perovskite nanocrystals with quinone and its impact on conduction current. J. Appl. Phys. 2022, 132, 195702,  DOI: 10.1063/5.0123558
      22
      Photo-induced charge transfer in composition-tuned halide perovskite nanocrystals with quinone and its impact on conduction current
      Mishra, Leepsa; Panigrahi, Aradhana; Dubey, Priyanka; Sarangi, Manas Kumar
      Journal of Applied Physics (Melville, NY, United States) (2022), 132 (19), 195702CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      A facile interfacial charge transfer (CT) with a reduced inter-layer energy band regulates the charge transport mechanism in any optoelectronic device. The enhancement in semiconductor-based device performance often demands improved CT dynamics and collection of free carriers with reduced charge recombination. In this work, we present a detailed inspection of the photo-induced CT between inorg. lead halide perovskite nanocrystals (PNCs) with varied compns. and their consequence on the charge transport process. The superior CT rate in mixed halide CsPbBr2Cl PNCs with naphthoquinone (NPQ) is revealed when compared with the parent CsPbBr3 PNCs and its anion-exchanged counterpart CsPbCl3. The glimpses of hole transfer contribution along with electron transfer are detected for CsPbBr2Cl with superior CT efficiency. The enhanced conduction current after the insertion of NPQ into the PNCs with a reduced hysteresis suggests an improved charge transport in the fabricated device compared to the pristine PNCs. These findings can contribute to a better understanding of multiple ways of engineering optoelectronic devices to boost performance and efficiencies and the concurrent role of the CT process in the conduction mechanism. (c) 2022 American Institute of Physics.
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    23. 23
      Mandal, S.; George, L.; Tkachenko, V. Charge transfer dynamics in CsPbBr3 perovskite quantum dots–anthraquinone/fullerene (C60) hybrids. Nanoscale 2019, 11, 862– 869,  DOI: 10.1039/C8NR08445A
      23
      Charge transfer dynamics in CsPbBr3 perovskite quantum dots-anthraquinone/fullerene (C60) hybrids
      Mandal, Sadananda; George, Lijo; Tkachenko, Nikolai V.
      Nanoscale (2019), 11 (3), 862-869CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      An advantage of colloidal quantum dots, particularly perovskite quantum dots (PQDs), as photoactive components is that they easily form complexes with functional org. mols., which results in hybrids with enriched photophys. properties. Herein, we demonstrate the formation of stable ground state complexes of CsPbBr3 PQD with two widely used mol. electron acceptors, fullerene (C60) and anthraquinone, (AQ) which contain carboxylic anchor groups. Dynamics of the photo-induced electron transfer in the hybrids were compared. The use of carboxylic groups for binding results in stable complex formation and their photophys. properties depend on the ratio of components but not the abs. concns. (up to micromolar concns.). Time-resolved transient absorption (TA) spectroscopy shows that in both cases, a charge sepd. (CS) state is formed. Data anal. was aimed to evaluate the CS time const. in ideal one-to-one complexes and was found to be in the range of 30-190 ps. The CS state of PQD-AQ complexes recombines directly to the ground state in roughly one microsecond. Recombination of the CS state of PQD-C60 is more complex and points to strong inhomogeneity of these complexes. Majority of the CS states relax by first forming the C60 triplet state.
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    24. 24
      DuBose, T.; Kamat, V. Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr3 and Ferrocene Redox Couple. J. Phys. Chem. Lett. 2019, 10, 6074– 6080,  DOI: 10.1021/acs.jpclett.9b02294
      24
      Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr3 and Ferrocene Redox Couple
      DuBose, Jeffrey T.; Kamat, Prashant V.
      Journal of Physical Chemistry Letters (2019), 10 (20), 6074-6080CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Interfacial charge transfer between a semiconductor nanocrystal and a mol. relay is an important step in nanomaterial photocatalysis. The ferrocene redox couple (Fc+/Fc0, E0 = -4.9 eV vs. vacuum) has now been used as a model redox relay system to study photocatalytic properties of CsPbBr3 perovskite nanocrystals. The photocatalytic redn. of ferrocenium (Fc+) to ferrocene (Fc0) with CsPbBr3 nanocrystals was dictated by the surface interactions. Whereas a rapid quenching and subsequent recovery of CsPbBr3 emission is seen at low Fc+ concns., the quenched emission was sustained at higher Fc+ concns. The photoinduced interfacial electron transfer between CsPbBr3 and ferrocenium (Fc+) studied using transient absorption spectroscopy occurred with a rate const. of 1.64 × 1010 s-1. Better understanding of interfacial processes using redox probes can lead to the improvement in photocatalytic performance of perovskite nanocrystals.
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    25. 25
      Bridewell, L.; Alam, R.; Karwacki, J.; Kamat, V. CdSe/CdS Nanorod Photocatalysts: Tuning the Interfacial Charge Transfer Process through Shell Length. Chem. Mater. 2015, 27, 5064– 5071,  DOI: 10.1021/acs.chemmater.5b01689
      25
      CdSe/CdS Nanorod Photocatalysts: Tuning the Interfacial Charge Transfer Process through Shell Length
      Bridewell, Victoria L.; Alam, Rabeka; Karwacki, Christopher J.; Kamat, Prashant V.
      Chemistry of Materials (2015), 27 (14), 5064-5071CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      CdSe/CdS core/shell semiconductor nanorods (NR) with rod-in-rod morphol. offer new strategies for designing highly emissive nanostructures. The interplay between energetically matched semiconductors results in enhanced emission from the CdSe core. In order to further evaluate the cooperative role of these two semiconductors in a core/shell geometry, we have probed the photoinduced charge transfer between CdSe/CdS core/shell semiconductor NR and Me viologen (MV2+). The quenching of the emission by the electron acceptor, MV2+, as well as the prodn. of electron transfer product MV•+ depends on the aspect ratio (l/w) of the NR thus pointing out the role of CdS shell in detg. the overall photocatalytic efficiency. Transient absorption measurements show that the presence of MV2+ influences only the bleaching recovery of the CdS shell and not of the CdSe core recovery. Thus, optimization of shell aspect ratio plays a crucial role in maximizing the efficiency of this photocatalytic system.
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    26. 26
      Harris, C.; Kamat, V. Photocatalytic Events of CdSe Quantum Dots in Confined Media. Electrodic Behavior of Coupled Platinum Nanoparticles. ACS Nano 2010, 4 (12), 7321– 7330,  DOI: 10.1021/nn102564x
      26
      Photocatalytic Events of CdSe Quantum Dots in Confined Media. Electrodic Behavior of Coupled Platinum Nanoparticles
      Harris, Clifton; Kamat, Prashant V.
      ACS Nano (2010), 4 (12), 7321-7330CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The electrodic behavior of platinum nanoparticles (2.8 nm diam.) and their role in influencing the photocatalytic behavior of CdSe quantum dots (3.4 nm diam.) was evaluated by confining both nanoparticles together in heptane/dioctyl sulfosuccinate/water reverse micelles. The particles spontaneously couple together within the micelles via micellar exchange processes and thus facilitate exptl. observation of electron transfer reactions inside the water pools. Electron transfer from CdSe to Pt occurs with a rate const. of 1.22 × 109 s-1. Using Me viologen (MV2+) as a probe mol., the role of Pt in the photocatalytic process is established. Ultrafast oxidn. of the photogenerated MV+· radicals indicates that Pt acts as an electron sink, scavenging electrons from MV+· with a rate const. of 3.1 × 109 s-1. The electron transfer between MV+· and Pt, and a drastically lower yield of MV+· under steady state irradn., confirms the ability of Pt nanoparticles to discharge electrons quickly. The kinetic details of photoinduced processes in CdSe-Pt assemblies and the electrodic behavior of Pt nanoparticles provide important information for the development of light energy conversion devices.
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    27. 27
      Marjit, K.; Ghosh, G.; Ghosh, S.; Ghosh, D.; Medda, A.; Patra, A. Electron Transfer Dynamics from CsPbBr3 Nanocrystals to Au144 Clusters. ACS Phys. Chem. Au 2023, 3 (4), 348– 357,  DOI: 10.1021/acsphyschemau.2c00070
      There is no corresponding record for this reference.
    28. 28
      Viezbicke, D.; Patel, S.; Davis, E.; Birnie, P. Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system. Phys. Status Solidi B 2015, 252, 1700– 1710,  DOI: 10.1002/pssb.201552007
      28
      Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system
      Viezbicke, Brian D.; Patel, Shane; Davis, Benjamin E.; Birnie, Dunbar P., III
      Physica Status Solidi B: Basic Solid State Physics (2015), 252 (8), 1700-1710CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)
      One of the most frequently used methods for characterizing thin films is UV-Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called "Tauc" plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large no. of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examn. of the band gap values and their distribution leads to a discussion of some exptl. factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single cryst. material.
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    29. 29
      Xie, Y.; Yu, Y.; Gong, J.; Yang, C.; Zeng, P.; Dong, Y.; Yang, B.; Liang, R.; Ou, Q.; Zhang, S. Encapsulated room-temperature synthesized CsPbX3 perovskite quantum dots with high stability and wide color gamut for display. Opt. Mater. Express 2018, 8 (11), 3494– 3505,  DOI: 10.1364/ome.8.003494
      There is no corresponding record for this reference.
    30. 30
      Butkus, J.; Vashishtha, P.; Chen, K.; Gallaher, K.; Prasad, K.; Metin, Z.; Laufersky, G.; Gaston, N.; Halpert, J.; Hodgkiss, J. The Evolution of Quantum Confinement in CsPbBr3 Perovskite Nanocrystals. Chem. Mater. 2017, 29, 3644– 3652,  DOI: 10.1021/acs.chemmater.7b00478
      30
      The Evolution of Quantum Confinement in CsPbBr3 Perovskite Nanocrystals
      Butkus, Justinas; Vashishtha, Parth; Chen, Kai; Gallaher, Joseph K.; Prasad, Shyamal K. K.; Metin, Dani Z.; Laufersky, Geoffry; Gaston, Nicola; Halpert, Jonathan E.; Hodgkiss, Justin M.
      Chemistry of Materials (2017), 29 (8), 3644-3652CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Colloidal nanocrystals (NCs) of lead halide perovskites are considered highly promising materials that combine the exceptional optoelectronic properties of lead halide perovskites with tunability from quantum confinement. But can we assume that these materials are in the strong confinement regime. Here, we report an ultrafast transient absorption study of cubic CsPbBr3 NCs as a function of size, compared with the bulk material. For NCs above ∼7 nm edge length, spectral signatures are similar to the bulk material-characterized by state-filling with uncorrelated charges-but discrete new kinetic components emerge at high fluence due to bimol. recombination occurring in a discrete vol. Only for the smallest NCs (∼4 nm edge length) are strong quantum confinement effects manifest in TA spectral dynamics; focusing toward discrete energy states, enhanced bandgap renormalization energy, and departure from a Boltzmann statistical carrier cooling. At high fluence, we find that a hot-phonon bottleneck effect slows carrier cooling, but this appears to be intrinsic to the material, rather than size dependent. Overall, we find that the smallest NCs are understood in the framework of quantum confinement, however for the widely used NCs with edge lengths >7 nm the photophysics of bulk lead halide perovskites are a better point of ref.
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    31. 31
      Meng, C.; Yang, D.; Wu, Y.; Zhang, X.; Zeng, H.; Li, X. Synthesis of single CsPbBr3@SiO2 core–shell particles via surface activation. J. Mater. Chem. C 2020, 8, 17403– 17409,  DOI: 10.1039/D0TC03932B
      31
      Synthesis of single CsPbBr3@SiO2 core-shell particles via surface activation
      Meng, Cuifang; Yang, Dandan; Wu, Ye; Zhang, Xuejia; Zeng, Haibo; Li, Xiaoming
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2020), 8 (48), 17403-17409CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      Encapsulating Cs lead halide (CsPbX3, X = Cl, Br, and I) perovskite quantum dots (PQDs) into stable shells is an effective strategy for improving their stability, which however usually forms agglomerated particles or alters PQDs' original morphol. and optical properties. A surface activation strategy to prep. single CsPbBr3@SiO2 core-shell particles is proposed. (3-Aminopropyl)triethoxysilane (APTES) is used as a bifunctional surface ligand, which not only effectively passivates the surface defects of PQDs, but also provides -SiOMe and -SiOH groups for the formation of Si-O-Si covalent bonds with the subsequently introduced silanes. By controlling the hydrolysis rate of silanes, the prepn. of single CsPbBr3@SiO2 core-shell particles with an av. shell thickness of 1-2.7 nm was realized, and the PQDs maintained their initial cubic morphol. and optical properties after coating. The stability of CsPbBr3@SiO2 in harsh environments was effectively improved owing to the complete encapsulation of the SiO2 shell. The emission peak of CsPbBr3@SiO2 remains const. at 515 nm after being heated at 60° for 84 h, and the luminescence (PL) intensity still remains 90% after storage for 6 h in a high humidity environment. This work not only enhances the stability of PQDs for practical applications but also provides a reliable method to synthesize single core-shell particles, which can be instructive to other PQD systems.
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    32. 32
      Valero, S.; Cabrera-Espinoza, A.; Collavini, S.; Pascual, J.; Marinova, N.; Kosta, I.; Delgado, J. L. Naphthalene Diimide-Based Molecules for Efficient and Stable Perovskite Solar Cells. Eur. J. Org Chem. 2020, 2020, 5329– 5339,  DOI: 10.1002/ejoc.202000287
      There is no corresponding record for this reference.
    33. 33
      Huang, H.; Yuan, H.; Janssen, K.; Solís-Fernández, G.; Wang, Y.; Tan, C.; Jonckheere, D.; Debroye, E.; Long, J.; Hendrix, J.; Hofkens, J.; Steele, J.; Roeffaers, M. Efficient and Selective Photocatalytic Oxidation of Benzylic Alcohols with Hybrid Organic–Inorganic Perovskite Materials. ACS Energy Lett. 2018, 3, 755– 759,  DOI: 10.1021/acsenergylett.8b00131
      33
      Efficient and Selective Photocatalytic Oxidation of Benzylic Alcohols with Hybrid Organic-Inorganic Perovskite Materials
      Huang, Haowei; Yuan, Haifeng; Janssen, Kris P. F.; Solis-Fernandez, Guillermo; Wang, Ying; Tan, Collin Y. X.; Jonckheere, Dries; Debroye, Elke; Long, Jinlin; Hendrix, Jelle; Hofkens, Johan; Steele, Julian A.; Roeffaers, Maarten B. J.
      ACS Energy Letters (2018), 3 (4), 755-759CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      The impressive optoelectronic performance and low prodn. cost of metal halide perovskites have inspired applications well beyond efficient solar cells. Here, we widen the materials engineering options available for the efficient and selective photocatalytic oxidn. of benzylic alcs., an industrially significant reaction, using formamidinium Pb bromide (FAPbBr3) and other perovskite-based materials. The best performance was obtained using a FAPbBr3/TiO2 hybrid photocatalyst under simulated solar illumination. Detailed optical studies reveal the synergetic photophys. pathways arising in FAPbBr3/TiO2 composites. An exptl. supported model rationalizing the large conversion enhancement over the pure constituents shows that this strategy offers new prospects for metal halide perovskites in photocatalytic applications.
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    34. 34
      Souza, J. A.; Jardim, R. F. Magnetoresistivity in the clustered state of La0.7–xYxCa0.3MnO3 manganites. Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 71, 054404,  DOI: 10.1103/PhysRevB.71.054404
      There is no corresponding record for this reference.
    35. 35
      Sombrio, G.; Zhang, Z.; Bonadio, A.; de Oliveira, L. S.; de Queiroz, T. B.; Ferreira, F.; Janotti, A.; Souza, J. Charge Transportin MAPbI3 Pellets across the Tetragonal-to-Cubic Phase Transition: The Role of Grain Boundaries from Structural, Electrical, and Optical Characterizations. J. Phys. Chem. C 2020, 124, 10793– 10803,  DOI: 10.1021/acs.jpcc.0c00887
      There is no corresponding record for this reference.
    36. 36
      Moraes, T. B.; Schimidt, M. F.; Bacani, R.; Weber, G.; Politi, J.; Castanheira, B.; Brochsztain, S.; Silva, F. d. A.; Demets, F.; Triboni, R. Polysilsesquioxane naphthalenediimide thermo and photochromic gels. J. Lumin. 2018, 204, 685– 691,  DOI: 10.1016/j.jlumin.2018.08.036
      36
      Polysilsesquioxane naphthalenediimide thermo and photochromic gels
      Moraes, Thaisa B. F.; Schimidt, Marcos F. R. A.; Bacani, Rebeca; Weber, Gabriel; Politi, Mario J.; Castanheira, Bruna; Brochsztain, Sergio; Silva, Francisco de A.; Demets, Gregoire J.-F.; Triboni, Eduardo R.
      Journal of Luminescence (2018), 204 (), 685-691CODEN: JLUMA8; ISSN:0022-2313. (Elsevier B.V.)
      N,N'-Propyltriethoxysilane-bis-naphthalenediimide was used to obtain a thermo and photo-active bridged organo polysilsesquioxane gel in DMF. Photophys. and electrochem. measurements revealed a dense diimide π-stacked structure that favors electron-delocalized states and facilitates high yield inherent thermo and photo-generation of radical anions that may be used for photocatalytic purposes, or energy conversion.
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    37. 37
      Castanheira, B.; Triboni, E. R.; Andrade, L. D. S.; Trindade, F. D. J.; Otubo, L.; Teixeira, A. C. S. C.; Politi, M. J.; de Queiroz, T. B.; Brochsztain, S. Synthesis of Novel Periodic Mesoporous Organosilicas Containing 1,4,5,8-Naphthalenediimides within the Pore Walls and Their Reduction To Generate Wall-Embedded Free Radicals. Langmuir 2018, 34, 8195– 8204,  DOI: 10.1021/acs.langmuir.8b00220
      37
      Synthesis of Novel Periodic Mesoporous Organosilicas Containing 1,4,5,8-Naphthalenediimides within the Pore Walls and Their Reduction To Generate Wall-Embedded Free Radicals
      Castanheira, Bruna; Triboni, Eduardo Resende; Andrade, Luana dos Santos; Trindade, Fabiane de Jesus; Otubo, Larissa; Teixeira, Antonio Carlos Silva Costa; Politi, Mario Jose; de Queiroz, Thiago Branquinho; Brochsztain, Sergio
      Langmuir (2018), 34 (28), 8195-8204CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Novel periodic mesoporous organosilicas (PMOs) contg. 1,4,5,8-Naphthalenediimide (NDI) chromophores as an integral part of the pore walls were synthesized in acidic conditions, in the presence of inorg. tetra-Et orthosilicate, using triblock copolymer surfactant Pluronic P-123 as a template. The NDI precursor, the bridged silsesquioxane N,N'-bis(3-triethoxysilylpropyl)-1,4,5,8-naphthalenediimide, was synthesized by reaction of 1,4,5,8-naphthalenetetracarboxylic dianhydride with excess 3-aminopropyltriethoxysilane. A series of samples contg. up to 19% (wt. %) of NDI were prepd. (the materials were labeled PMONDIs). 13C and 29Si solid-state NMR revealed that the NDI moiety was intact in the PMONDIs and efficiently grafted to the silica network. Samples with up to 16% NDI load presented an ordered two-dimensional-hexagonal mesoscopic structure, according to small-angle X-ray scattering, transmission electron microscopy, and nitrogen adsorption isotherms. Fluorescence spectra of the PMONDIs showed excimer formation upon excitation, suggesting high flexibility of the org. moieties. Redn. of PMONDIs with aq. sodium dithionite led to the formation of wall-embedded NDI anion radicals, as obsd. by the appearance of new visible/near-IR absorption bands. The PMONDIs were also shown to be efficient photocatalysts in the degrdn. of sulfadiazine, an antibiotic selected here as a model pollutant, which is usually present in water bodies and wastewater.
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    38. 38
      Wang, S.; Yousefi Amin, A. A.; Wu, L.; Cao, M.; Zhang, Q.; Ameri, T. Perovskite Nanocrystals: Synthesis, Stability, and Optoelectronic Applications. Small Struct. 2021, 2, 2000124,  DOI: 10.1002/sstr.202170009
      There is no corresponding record for this reference.
    39. 39
      Protesescu, L.; Yakunin, S.; Bodnarchuk, M.; Krieg, F.; Caputo, R.; Hendon, C.; Yang, R.; Walsh, A.; Kovalenko, M. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15, 3692– 3696,  DOI: 10.1021/nl5048779
      39
      Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut
      Protesescu, Loredana; Yakunin, Sergii; Bodnarchuk, Maryna I.; Krieg, Franziska; Caputo, Riccarda; Hendon, Christopher H.; Yang, Ruo Xi; Walsh, Aron; Kovalenko, Maksym V.
      Nano Letters (2015), 15 (6), 3692-3696CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Metal halides perovskites, such as hybrid org.-inorg. MeNH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as soln.-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. A new avenue for halide perovskites was demonstrated by designing highly luminescent perovskite-based colloidal quantum dot materials. Monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorg. perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) were synthesized using inexpensive com. precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The luminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color std., high quantum yields of ≤90%, and radiative lifetimes at 1-29 ns. The compelling combination of enhanced optical properties and chem. robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegrdn.
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    40. 40
      Protesescu, L.; Yakunin, S.; Kumar, S.; Bär, J.; Bertolotti, F.; Masciocchi, N.; Guagliardi, A.; Grotevent, M.; Shorubalko, I.; Bodnarchuk, M. I.; Shih, C. J.; Kovalenko, M. V. Dismantling the “Red Wall” of Colloidal Perovskites: Highly Luminescent Formamidinium and Formamidinium–Cesium Lead Iodide Nanocrystals. ACS Nano 2017, 11, 3119– 3134,  DOI: 10.1021/acsnano.7b00116
      40
      Dismantling the "Red Wall" of Colloidal Perovskites: Highly Luminescent Formamidinium and Formamidinium-Cesium Lead Iodide Nanocrystals
      Protesescu, Loredana; Yakunin, Sergii; Kumar, Sudhir; Bar, Janine; Bertolotti, Federica; Masciocchi, Norberto; Guagliardi, Antonietta; Grotevent, Matthias; Shorubalko, Ivan; Bodnarchuk, Maryna I.; Shih, Chih-Jen; Kovalenko, Maksym V.
      ACS Nano (2017), 11 (3), 3119-3134CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A facile colloidal synthesis method is reported for obtaining FAPbI3 and FA-doped CsPbI3 NCs that are uniform in size (10-15 nm) and nearly cubic in shape and exhibit drastically higher robustness than their MA- or Cs-only cousins with similar sizes and morphologies. Detailed structural anal. indicated that the FAPbI3 NCs had a cubic crystal structure, while the FA0.1Cs0.9PbI3 NCs had a 3D orthorhombic structure that was isostructural to the structure of CsPbBr3 NCs. Bright luminescence (PL) with high quantum yield (QY > 70%) spanning red (690 nm, FA0.1Cs0.9PbI3 NCs) and near-IR (near-IR, ∼780 nm, FAPbI3 NCs) regions was sustained for several months or more in both the colloidal state and in films. The peak PL wavelengths can be fine-tuned by using postsynthetic cation- and anion-exchange reactions. Amplified spontaneous emissions with low thresholds of 28 and 7.5 μJ cm-2 were obtained from the films deposited from FA0.1Cs0.9PbI3 and FAPbI3 NCs, resp. Light-emitting diodes with a high external quantum efficiency of 2.3% were obtained by using FAPbI3 NCs.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c01651.

    • Additional XRD patterns, photoluminescence lifetime, values of lifetimes, the Nyquist impedance spectroscopy, and FTIR spectra for all samples (PDF)


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