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Improvement of Photophysical Properties of CsPbBr3 and Mn2+:CsPb(Br,Cl)3 Perovskite Nanocrystals by Sr2+ Doping for White Light-Emitting Diodes
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Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Phys. Chem. C 2022, 126, 27, 11277-11284
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C: Physical Properties of Materials and Interfaces

Improvement of Photophysical Properties of CsPbBr3 and Mn2+:CsPb(Br,Cl)3 Perovskite Nanocrystals by Sr2+ Doping for White Light-Emitting Diodes
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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2022, 126, 27, 11277–11284
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https://doi.org/10.1021/acs.jpcc.2c01244
Published June 28, 2022

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Abstract

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All-inorganic metal halide perovskite nanocrystals (NCs) having the general formula ABX3, where A is a monovalent cation, for example, Cs+, B is a divalent cation, typically Pb2+, and X is Cl–, Br–, I–, or their binary mixture, show potential in optoelectronic devices. In this work, we explore the effect of B-site doping on the optoelectronic properties of CsPbX3 NCs (X = Br, Cl). First, the Pb2+ ions in the pristine CsPbBr3 NC are partially substituted by Mn2+ ions. The alkaline earth metal strontium is then doped on both pristine and the Mn2+-substituted NCs. We found that a small percentage of Sr2+ doping remarkably improves the photoluminescence quantum yield of CsPbBr3 and Mn2+-state emission in Mn2+:CsPb(Br,Cl)3 NCs. Perovskite NC film/poly(methyl methacrylate) composites with all four NC variants were used in a white light-emitting diode (WLED), where Sr2+ doping increased the luminous efficiency of the WLED by ∼4.7%. We attribute this performance enhancement to a reduced defect density and an attenuated microstrain in the local NC structure.

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Introduction

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All-inorganic lead halide perovskite nanocrystals (NCs), for example, CsPbX3 (X = Cl–, Br–, I–), have attracted remarkable attention owing to their high photoluminescence quantum yield (PLQY), defect tolerance, adjustable band gaps, narrow PL linewidth, and low-cost fabrication. (1−3) These features make perovskite NCs a good candidate for optoelectronic applications, such as light-emitting diodes (LEDs), (4−6) solar cells, (7,8) lasers, (9,10) and photodetectors. (11,12) In perovskite-based white LEDs (WLEDs), CsPbX3 perovskite NCs can be used as PL converters either by using a combination of red-/green-/blue-emitting perovskites and exciting them using a UV LED (13) or by using the combinations of red-/green-emitting perovskites excited using a blue LED. (14) Conveniently, in CsPbX3 perovskite NCs, the halogen content X– can be tuned to alter the emission color, for example, the CsPbI3, CsPbBr3, and CsPbCl3 NCs can be deployed as the red (∼1.7 eV), green (∼2.4 eV), and blue (∼3.0 eV) emitters, respectively. (1) However, these perovskite NCs under ambient conditions often suffer from low stability, while the presence of surface defects promotes non-radiative recombinations and deteriorates optical properties. (15,16)
Compositional engineering is a promising method to counter these problems. Homovalent M2+ ions (M = Zn, (17,18) Cd, (17,19) Sr, (20,21) Mn, (22,23) and Sn (17,24)) or heterovalent N3+ dopants (N = Ce, (25) Bi, (26) Sb, (27) and Al (28)) can increase stability and reduce defect density in perovskite NCs. (16,29,30) Among these dopants, Mn2+ incorporation into the CsPbX3 (X = Br, Cl) perovskite lattice gives rise to a characteristic emission around ∼2.1 eV (31) due to the d–d transition between the 4T1 and 6A1 configurations. (32,33) Therefore, Mn2+:CsPbX3 (X = Br,Cl) perovskite NCs can serve as a viable alternative to CsPbI3 NCs for harnessing emission in the red region in perovskite-based WLEDs, (34−36) given that Mn2+:CsPbX3 (X = Br, Cl) NCs have better phase stability than CsPbI3 NCs. (37) Nevertheless, low PLQY of the Mn state emission is still an issue, which can be improved by co-doping Mn2+:CsPbX3 NCs with bivalent Co2+, (38) Ni2+, (39) and Cu2+ (40) or trivalent Bi3+ (41) and Yb3+ (42) ions.
In this work, we present improved photophysical properties of CsPbBr3 and Mn2+:CsPb(Br,Cl)3 perovskite NCs achieved by Sr2+ doping. We utilized scanning transmission electron microscopy (STEM) to show that Sr2+ doping leads to a more uniform size distribution of the perovskite NCs. Microstrain calculations were performed by using the Williamson–Hall (W–H) method extracted from X-ray diffraction (XRD) analyses, which revealed that Sr2+ doping decreases defect density in the perovskite NCs. Consequently, a remarkable increase in the PLQY with longer PL lifetimes was observed for both Sr2+-doped NCs, Sr2+:CsPbBr3 and Sr2+:Mn2+:CsPb(Br,Cl)3.
Finally, perovskite-based WLEDs were constructed by using CsPbBr3/PMMA [PMMA = poly(methyl methacrylate)] and Mn2+:CsPb(Br,Cl)3/PMMA NCs as PL converters excited using a UV LED. WLEDs fabricated with Sr2+-doped perovskite NCs, that is, Sr2+:CsPbBr3 and Sr2+:Mn2+:CsPb(Br,Cl)3, exhibit a higher PL intensity, higher luminescence efficiency, and slightly higher color rendering index (CRI) than those fabricated with pristine CsPbBr3 and Mn2+:CsPb(Br,Cl)3 perovskite NCs. The results presented here provide a good platform to enhance the photophysical properties of CsPbBr3 and Mn2+:CsPb(Br,Cl)3 perovskite NCs using the Sr2+ doping strategy.

Experimental Procedure

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Materials

Lead(II) bromide (PbBr2, ≥98%), strontium bromide (SrBr2, 99.99% trace metal basis), manganese(II) chloride tetrahydrate (MnCl2·4H2O, ≥98%), cesium carbonate (Cs2CO3, 99.9%, Sigma-Aldrich), 1-octadecene (ODE, 90%), oleylamine (OLAM, 70%), and oleic acid (OA, 90%) were purchased from Sigma-Aldrich. Toluene (≥99%, Merck) was purchased and used without any further purification. PMMA with an average Mw of 15,000 (GPC) was purchased from Aldrich Chemical Company, Inc.

Synthesis of Cs-Oleate for CsPbBr3 NCs

203.5 mg (266.67 mg) of Cs2CO3, 625 μL (1,167 μL) of OA, and 10 mL of ODE were put into a round bottom flask and dried under vacuum at 120 °C while stirring for 1 h. After drying, the temperature was increased to 150 °C under a nitrogen atmosphere. The solution was kept at 150 °C overnight to make sure that all Cs2CO3 reacted with OA. The values given in parentheses are for Cs-oleate synthesis of pristine and Sr2+:Mn2+:CsPb(Br,Cl)3 NCs.

Synthesis of Pristine and Sr2+:CsPbBr3 NCs

For the synthesis of pristine CsPbBr3 NCs, first, 17.2 mg of PbBr2 was put into a glass tube along with 1.25 mL of ODE, 125 μL of OA, and 125 μL of OLAM and dissolved/degassed at 120 °C for 30 min under vacuum. After degassing, the temperature was increased to 180 °C under nitrogen, and then, 100 μL of Cs-oleate was injected. After injection, the solution was immediately cooled down using an ice bath and then centrifuged for 15 min at 6000 rpm. Later, the supernatant was discarded, and the NCs were dispersed in toluene. For the synthesis of Sr2+:CsPbBr3 NCs, the same procedure was followed except that 1, 2, 5, and 10% SrBr2 was added to the solution, while the same molar amount of PbBr2 was excluded.

Synthesis of Mn2+:CsPb(Br,Cl)3 and Sr2+:Mn2+:CsPb(Br,Cl)3 NCs

For the synthesis of Mn2+:CsPb(Br,Cl)3 NCs, first, 9.175 mg of PbBr2 and 4.95 mg of MnCl2·4H2O were put into a glass tube along with 1.25 mL of ODE, 125 μL of OA, and 125 μL of OLAM and dissolved/degassed at 120 °C for 30 min under vacuum. After degassing, the temperature was increased to 180 °C where 100 μL of Cs-oleate was injected under nitrogen. After injection, the solution was immediately cooled down using an ice bath and then centrifuged for 15 min at 6000 rpm. The supernatant was then discarded, and the perovskite NCs were dispersed in toluene. For the synthesis of Sr2+:Mn2+:CsPb(Br,Cl)3 NCs, the same process was followed except that 2% SrBr2 was added to the solution, while the same molar amount of PbBr2 was excluded.

Fabrication of the WLED

0.5 g of PMMA was dissolved in 10 mL of toluene. For each film of CsPbBr3, drop-cast films were prepared with the mixture of 40 μL of PMMA and 120 μL of the perovskite, while Mn2+:CsPb(Br,Cl)3 drop-cast films were prepared with the mixture of 40 μL of PMMA and 240 μL of perovskite dispersion on 1.5 cm × 1.5 cm glass substrates. Then, these CsPbBr3 and Mn2+:CsPb(Br,Cl)3 (for 0 and 2% Sr2+ series, respectively) were placed on the LED laterally. The emission spectra were taken from the perovskite layers excited with UV light (366 nm of wavelength, 12 V, and 8 W power), and the International Commission on Illumination (CIE) chromaticity diagram was extracted from the OSRAM ColorCalculator program.

Characterization

STEM images for all perovskite NCs were taken by using scanning electron microscopy (SEM) with STEM mode: Quanta 250, FEI, Hillsboro, OR. Perovskite dispersions were dropped onto 300 mesh holey carbon-Cu (50 μm) for STEM images. XRD analyses were done by using X’Pert Pro, Philips, Eindhoven, the Netherlands. Optical measurements including absorption, PL, PL lifetime, and PLQY were carried out on an FS5 spectrofluorometer (Edinburgh Instruments, U.K.). For PL and PLQY measurements, excitation wavelengths of CsPbBr3 and Mn2+:CsPb(Br,Cl)3 samples were 400 nm and 390 nm, respectively. For lifetime measurements, CsPbBr3 and Mn2+:CsPb(Br,Cl)3 samples were excited with 442 nm and 307 nm lasers, respectively. Trace metal analysis was carried out using an inductively coupled plasma-mass spectrometer on an Agilent 7500ce Octopole Reaction System.

Results and Discussion

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Inductively coupled plasma mass spectrometry (ICP–MS) measurements were carried out to determine the actual doping ratios of Sr2+/Pb2+ in Sr2+-doped Sr2+:CsPbBr3 (Table 1 and Figure S1) and Sr2+:Mn2+:CsPb(Br,Cl)3 NCs (Table S1). The ICP–MS analysis shows that Sr2+ was successfully doped into perovskite NCs. The Sr2+/Pb2+ ratio was systematically increased by increasing the SrBr2 concentration in the perovskite solution. The Sr2+ doping concentrations measured against their addition amounts agreed with the report by Chen et al. on Sr2+:CsPbI3 NCs. (20) Since MnCl2 was used for incorporating Mn2+ ions into the pristine CsPbBr3 particle, a fraction of bromide ions were replaced by chloride ions. Ion chromatography (IC) analysis revealed Br–/Cl– ratios in Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 samples to be 72.34 and 75.26%, respectively (Table S1).
Table 1. Actual Sr2+/Pb2+ mol Ratio, NC Size, PLQY, and PL Lifetime of Various CsPbBr3 NC Samples Having Different %Sr2+ Dopings
% Sr2+ amount in Sr2+:CsPbBr3Actual Sr2+/Pb2+ mol ratio (%)Average NC Size (nm)PLQY (%)PL lifetime (ns)
0% Sr2+ 20.384.77.62
1% Sr2+0.04716.888.88.42
2% Sr2+0.09917.392.610.39
5% Sr2+0.23816.083.07.30
10% Sr2+1.05117.070.06.84
The relative propensity for the formation of a given NC was explored computationally employing density functional theory (DFT). We first constructed three cubic NCs of size ∼3 nm (Figure S10). Their cohesive energy (Ecohesive), which quantifies the energy required to dissociate the atoms constituting the NC into a collection of neutral free atoms, was calculated using eq S5 (see the Supporting Information). For the pristine CsPbBr3, Sr2+-doped Sr2+:CsPbBr3, and Sr2+/Mn2+ co-doped Sr2+:Mn2+:CsPb(Br,Cl)3 NCs, Ecohesive was computed to be 3.04, 3.05, and 3.17 eV/atom, respectively. Hence, the Sr2+ doping replacing two Pb2+ ions is marginally favorable (ΔEcohesive ∼ 0.01 eV/atom), whereas the Cl– anions from MnCl2 drive the formation of Sr2+:Mn2+:CsPb(Br,Cl)3, which has ΔEcohesive ∼ 0.13 eV/atom when compared with the pristine NC.
Perovskites doped with Mn2+ have been reported in the literature to have a marginally increased Ecohesive (43) and a generally improved robustness. (16,44) Consequently, two additional models were examined to investigate the effects of Mn doping on Ecohesive, Mn2+:CsPbBr3 and Sr2+:CsPb(Br,Cl)3. In our simulations, however, the calculated Ecohesive was not affected by Mn doping. Ecohesive was maintained at 3.04 eV/atom in the Mn2+:CsPbBr3 model, which substitutes two Mn2+ ions for two Pb2+ ions in the pristine NC. Ecohesive was again unchanged at 3.17 eV/atom for the Sr2+:CsPb(Br,Cl)3 model, where two Mn2+ dopants from the Sr2+:Mn2+:CsPb(Br,Cl)3 particle have been replaced with the original Pb2+ ions. Accordingly, Mn2+ doping seems to have a less pronounced effect on Ecohesive, and hence on stability, for bromide nanoparticles than it does for the iodide nanoparticles, for which it is hypothesized that the smaller Mn2+ ion partially releases the strain imposed by the larger iodide ions. (16)
The morphology and size distribution of CsPbBr3 NCs upon Sr2+ doping were monitored via the STEM mode in SEM. The incorporation of Sr2+ ions into the perovskite lattice does not significantly affect the structure and morphology (Figure S2). The reason for the decrease in NC size upon Sr2+ doping (Figure S2) could be the effect of the impurity (i.e., the dopant) on crystallization dynamics. (45) We argue that the Sr2+ impurities lead to a reduction of the energy threshold for nucleation and cause more nuclei to form, resulting in a smaller NC size. The uniformity of NC size distribution is improved upon Sr2+ doping until the 2% Sr2+ concentration; however, higher Sr2+ concentrations beyond 2% adversely affect NC homogeneity (Figure S2a–e insets).
Figure 1a shows the XRD patterns of pristine and Sr2+:CsPbBr3 NC samples having various Sr2+ concentrations. XRD reflections of all samples confirm the orthorhombic Pnma crystal structure of CsPbBr3. (46) The incorporation of Sr2+ ions into the perovskite lattice does not cause any additional XRD reflection, confirming no phase transition upon doping. Furthermore, due to the similar ionic radii of Pb2+ (119 pm) and Sr2+ (118 pm) ions, (47) no systematic shift in XRD reflections was observed upon Sr2+ doping.

Figure 1

Figure 1. (a) XRD patterns, (b) microstrain values, (c) lattice parameters obtained by the W–H plot, (d) PL spectra, (e) time-resolved PL (TRPL) plot, and (f) PLQY distribution of pristine and Sr2+:CsPbBr3 NCs.

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The absence of a systematic shift in the XRD patterns (Figure 1a) motivated us to investigate the influence of the Sr2+-doping concentration on microstrain, which describes local distortions of a crystal lattice. (48,49) Microstrain in the studied NCs was calculated from the slope of the WH plot (Figure S4 and Table S3). Figure 1b shows that microstrain decreases upon Sr2+ additive until the 2% concentration and then systematically increases at higher concentrations. This suggests that until the 2% Sr2+ concentration, the defect density in the NCs and concomitantly defect-related lattice distortions are reduced, resulting in a smaller microstrain in the crystal structure.
Variation of three cell-length lattice constants (a0, b0, and c0) as a function of the Sr2+concentration is summarized in Table S2, and their trend is shown in Figure 1c. We observe that the b0 parameter reaches a minimum at the 2% Sr2+ concentration and then increases as the Sr2+ concentration exceeds 2%, whereas the a0 and c0 parameters follow the opposite trend. These results indicate that the octahedral tilt angle changes upon Sr2+ doping. Recalling the trend in microstrain with the Sr2+-doping concentration, which reaches a minimum for the 2% Sr2+ sample, we argue that the reduced defect-related lattice distortions in the perovskite NCs are the reason for the change in lattice parameters, peaking at 2% Sr2+.
To understand the doping effect further, we have carried out optical measurements as shown in Figure 1d–f. The PL spectra of pristine and Sr2+:CsPbBr3 NCs are shown in Figure 1d. Despite the changes in the NC size upon doping (Table 1), the PL emission energy (Figure 1d) and absorption edges (Figure S5) of all samples are strikingly similar. We rationalize this by considering that the studied CsPbBr3 NCs are within the intermediate-to-weak quantum confinement regime, (50) and the incorporation of Sr2+ ions into the lattice does not affect the band gap energy of CsPbBr3.
From Tauc’s plot (Figure S5), the band gap energies of both pristine CsPbBr3 and Sr2+:CsPbBr3 NC samples are calculated to be ∼2.39 eV. PL signals were centered at 2.41 eV. Furthermore, the full width half-maxima of PL peaks were reduced upon Sr2+ doping, in line with the NC size distribution (Figure S2).
To better understand the effect of Sr2+ doping on the optoelectronic properties of the NCs, 2D periodic slab models were constructed for the pristine CsPbBr3 and 5% Sr2+-doped Sr2+:CsPbBr3 NCs (Figure 2a, top) and analyzed using DFT. Inspection of the projected densities of states (pDOS; Figure 2b, top) and the band structures (Figure S11) of the pristine and Sr2+-doped models suggests that both NCs are a direct-bandgap material, with the valence band maximum (VBM) and conduction band minimum (CBM) located at the Γ-point. In line with the experimental observations, Figure 2b shows that Sr2+ inclusion into CsPbBr3 NCs had no significant effect on the DOS, where the VBM consists mainly of filled Br(p) orbitals, while the CBM is made up mainly of empty Pb(p) orbitals.

Figure 2

Figure 2. (a) Four periodic slab models considered for the computational study: pristine CsPbBr3, Sr2+-doped Sr2+:CsPbBr3, Mn2+-doped Mn2+:CsPb(Br,Cl)3, and Sr2+/Mn2+ co-doped Sr2+:Mn2+:CsPb(Br,Cl)3 and (b) their corresponding pDOS.

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Figure 1e shows time-resolved PL (TRPL) results for CsPbBr3 NCs with varied Sr2+ contents. The average PL lifetimes (τavg) of the samples, calculated using eq S4, systematically increase upon the incorporation of Sr2+ ions into the perovskite NCs until the 2% concentration. At higher Sr2+ concentrations (>2%), however, the PL lifetime gradually decreases (Table 1). Considering that PL lifetimes are inversely proportional to the defect concentration, (51,52) the trend in PL lifetimes agrees with that of the calculated microstrain data. The PLQY results in Figure 1f demonstrate a trend analogous to that of the PL lifetime and microstrain. The PLQY of the pristine CsPbBr3 NC was found to be 84.7%. Sr2+ doping increased the PLQY to 88.8% for 1% Sr2+ and 92.6% for 2% Sr2+. As Sr2+ concentrations increased, PLQY dropped to 83% for 5% Sr2+ and then to 70% for 10% Sr2+.
According to the microstrain calculations (Figure 1b), defect-related distortions are reduced when Sr2+ ions are incorporated into the CsPbBr3 lattice until the 2% concentration. The minimum microstrain originating from fewer defects was also determined for the same 2% Sr2+ sample. Since defect sites serve as potential non-radiative recombination centers for this class of material, the reduced defect density at low Sr2+-doping concentrations should eliminate non-radiative recombination pathways, resulting in a higher PLQY and longer PL lifetime. (53) Beyond 2% Sr2+ addition, we argue that the added dopants may trigger the formation of new defects, (21) which would cause an increased microstrain and may lead to a reduction in PL lifetimes and PLQY.
The STEM images of Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 NCs are given in Figure S3. 2% Sr2+ incorporation into the Mn2+:CsPb(Br,Cl)3 lattice does not change the shape of NCs but decreases the particle size and improves monodispersity, similar to the Sr2+:CsPbBr3 case (Figure S2).
To quantify the impact of the 2% Sr2+ additive on the NCs, XRD of Mn2+:CsPb(Br,Cl)3 NCs was carried out. The XRD patterns shown in Figure 3a correspond to the orthorhombic perovskite phase. (54) Since Mn2+ ions have a smaller radius (67 pm) than Pb2+ ions (119 pm), (47) the XRD signal for Mn2+-doped perovskite NCs shifts to higher angles, indicating that Mn2+ ions were successfully incorporated into the perovskite lattice. (55) However, this shift in the XRD signal in Mn2+:CsPb(Br,Cl)3 is not exclusively due to Mn2+ ions substituting for Pb2+ ions. The overall lattice shrinking can also be attributed to Cl–/Br– substitutions (Figure 3b). (37) Subsequent doping of the Sr2+ ions into the Mn2+:CsPb(Br,Cl)3 NCs does not cause any peak shift, indicating that the Sr2+ ions are substituted with the Pb2+ ions instead of the Mn2+ ions. Microstrain calculations of both Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 samples again confirmed that Sr2+ doping reduces microstrain (Figure 3c). Regarding variations in the cell-length lattice constants of the Sr2+/Mn2+ co-doped samples, we found that the lattice parameter b0 increases, while c0 decreases, and a0 stays constant at 8.13 Å, as shown in Figure 3c and Table S2.

Figure 3

Figure 3. (a) XRD patterns: NCs show reflections at 15.4, 22.0, 31.1, 35.0, 38.4, and 44.6°, (b) comparisons of XRD signal positions for CsPbBr3, Mn2+:CsPb(Br,Cl)3, and Sr2+:Mn2+:CsPb(Br,Cl)3 perovskite NCs, (c) microstrain and lattice constant parameters, (d) PL/absorption spectra, (e) TRPL plot, and (f) PLQY comparisons of Mn2+:CsPb(Br,Cl)3 and 2%Sr2:Mn2+:CsPb(Br,Cl)3 NCs.

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The UV–vis and PL spectra of the Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 samples are shown in Figure 3d, both of which demonstrate very similar absorption behavior. Comparison of these spectra (Figure S6) reveals the appearance of the characteristic PL peak at around 2.1 eV due to the Mn state. Indeed, DFT calculations on both Mn-doped systems reveal (Figure 2b, bottom) Mn d-states just below the empty Pb(p) states resulting in a midgap state. Tauc’s plots (Figure S7) yield band gaps of 2.70 and 2.69 eV for these two samples, respectively. This slight change in the band gap energies between the samples was also observed in PL peak positions, with the Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 NCs exhibiting exciton PL signals at 2.72 and 2.71 eV, respectively (Figure 3d). Considering that Sr2+ doping at low concentrations (≤1% actual doping) does not affect the band gap energy (Figure S5), the slight change in band gap and PL emission energies observed herein can be attributed to small differences in Br–/Cl– ratios in the perovskite structures; see Table S1.
Interestingly, PL emission due to the Mn state in Mn2+:CsPb(Br,Cl)3 perovskite NCs increases upon Sr2+ doping. TRPL measurements of these samples (Figure 3e) reveal that the average PL lifetime of the Mn2+:CsPb(Br,Cl)3 NCs increases from 9.39 to 10.10 ns as a result of the 2% Sr2+ additive, attributable to a lower defect density in the 2% Sr2+ sample.
PLQY measurements were performed on the Mn2+:CsPb(Br,Cl)3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 NCs in the 2.38–1.59 eV (521–780 nm) and 3.02–2.38 eV (410–521 nm) ranges, relevant for the Mn state and perovskite emission, respectively. The PLQY of the Mn-state emission increases from 7.6% in Mn2+:CsPb(Br,Cl)3 to 14.2% in 2%Sr2+:Mn2+:CsPb(Br,Cl)3, as can be seen in Figure 3f, highlighting the beneficial effect of Sr2+ co-doping along with Mn2+. In addition, the perovskite PLQY increases from 43.4 to 49.1% due to Sr2+ doping. These optical improvements with better exciton-to-Mn2+ energy transfer upon Sr2+ incorporation are a direct consequence of a lowered defect density.
Finally, two sets of UV-pumped tricolor WLEDs were fabricated using perovskite/PMMA composite films via the drop-casting method (Figures S8 and S9). Under UV light, CsPbBr3/PMMA works as a green emitter, while Mn2+:CsPb(Br,Cl)3/PMMA is a red–blue emitter, and these two combinations were used together to construct the 0%Sr2+:WLED. The 2%Sr2+:WLED, on the other hand, was fabricated using 2%Sr2+:CsPbBr3/PMMA (green emitter) and 2%Sr2+:Mn2+:CsPb(Br,Cl)3/PMMA (red–blue emitter) layers.
The PL spectra (Figure 4a) and the CIE coordinates (Figure 4b) of both the 0% and 2%Sr2+:WLED show that the 2%Sr2+:WLED has a higher luminescence efficiency (290 lm/W under a UV light) than the pristine WLED (277 lm/W). Sr2+ doping is observed to decrease the computed work function for both pristine and Mn-doped particles (Table 2), which may improve device efficiency and enhance charge extraction in heterojunction-layered devices. (56) Furthermore, the CRI increases from 80 in the pristine 0% Sr2+:WLED system to 83 in the 2% Sr2+:WLED system. We surmise that the deficiency of red emission for the pristine 0% Sr2+:WLED system is partly compensated by the increased PL emission of the Mn state in the Sr2+:WLED system.

Figure 4

Figure 4. (a) PL spectra of the pristine WLED and 2%Sr2+:WLED and (b) corresponding CIE coordinates.

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Table 2. Computed Work Function and Band Gapsa of Four Slab Models (Figure 2a) Considered in This Studyb
NC particlework function (eV)band gap (eV)
CsPbBr34.431.89 (2.39)
Sr2+:CsPbBr34.381.98 (2.39)
Mn2+:CsPb(Br,Cl)34.282.06 (2.70)
Sr2+:Mn2+:CsPb(Br,Cl)34.192.11 (2.69)
a

The overestimation of the computed band gap widening upon Sr2+ doping can be attributed to possible structural changes when Sr2+ is doped since ca 5% Sr2+ concentration is used in simulations rather than <1% in experiments.

b

Experimentally obtained band gaps are added in the parenthesis for comparison. The systematic underestimation of the calculated band gaps (with respect to the experiment) can be attributed to the presence of (57) (i) the unphysical electron self-Coulomb repulsion, (ii) derivative discontinuity of the energy with respect to the number of electrons, and (iii) the nonlinear dependence of energy on the number of electrons in the Perdew–Burke–Ernzerhof functional. (58,59)

Conclusions

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We have presented a detailed study on the effect of Sr2+ doping into CsPbBr3 and Mn2+:CsPb(Br,Cl)3 perovskite NCs. The STEM images showed a decrease in perovskite NC size after Sr2+ doping. The changes in the lattice parameters and microstrains were calculated from XRD signals; microstrain decreased and reached a minimum at the 2% Sr2+ concentration, possibly due to the elimination of defects. In addition, the optical properties of the NCs improved, with the PLQY of the CsPbBr3 NCs increasing from 84.7% in the pristine sample to 92.6% in the Sr2+:CsPbBr3 NCs, caused by reduced non-radiative recombination pathways with fewer defects in the sample. Inspired by the optical property enhancements of CsPbBr3 NCs due to Sr2+ doping, we have applied the same doping strategy to enhance the optical properties of Mn2+:CsPb(Br,Cl)3 NCs. As a result of 2% Sr2+ addition, the PLQY of the Mn2+-state emission increased from 7.6 to 14.2%. Finally, the 2%Sr2+:CsPbBr3 and 2%Sr2+:Mn2+:CsPb(Br,Cl)3 NCs were used to construct a WLED that provided improved white light compared to WLEDs constructed with their undoped counterparts. Our study shows that adding Sr2+ to pristine perovskite materials can be a successful strategy for improving their optical properties.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.2c01244.

  • STEM images, WH plot calculations, Tauc plots, ICP–MS and IC analysis results, TRPL parameters, and DFT computational details (PDF)

  • DFT-computed structures: slab models and non-periodic clusters (ZIP)

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Author Information

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  • Corresponding Author
  • Authors
    • Hurriyet Yuce - Department of Materials Science and Engineering, Izmir Institute of Technology, Urla, 35430 Izmir, Turkey
    • Mukunda Mandal - Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany;  Orcidhttps://orcid.org/0000-0002-5984-465X
    • Yenal Yalcinkaya - Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
    • Denis Andrienko - Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany;  Orcidhttps://orcid.org/0000-0002-1541-1377
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was partially supported by the IZTECH Scientific Research Project with the number 2021IYTE-1-0036. D.A. acknowledges support from the Deutsche Forschungsgemeinschaft (DFG) within the Priority Program SPP2196 (“Perovskite Semiconductors: From Fundamental Properties to Devices”) under project no. 424708673. Y.Y. acknowledges the SPP2196 project (Deutsche Forschungsgemeinschaft) for funding. M.M. acknowledges postdoctoral support from the Alexander von Humboldt Foundation.

References

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This article references 59 other publications.

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    Blue-emitting materials and their light-emitting diodes (LEDs) are always challenging in lighting and display applications. Recently, perovskite LEDs (PeLEDs) with efficient and stable green/red emission have made great progress, where external quantum efficiency (EQE) over 20% has been reached. However, it is still a big challenge to realize stable blue PeLEDs with high efficiency mainly because of the poor film quality and unreasonable device structure. Herein, a cocktail strategy, i.e., multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3, is demonstrated to improve both the efficiency and stability of blue PeLEDs. Combined with the "insulator-perovskite-insulator" structure, PeLEDs based on a multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3 perovskite film show max. EQE of 2.01% and max. luminance of 4015 cd/m2 at 484 nm. More importantly, the device exhibits robust durability, and its half-lifetime is over 300 min under continuous operation. The multication strategy could open up a new avenue for the design of new blue-emitting materials for high-performing PeLEDs.
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    Quantum dots are replacing conventional phosphors as down-conversion materials for white light-emitting devices (LEDs). The authors synthesized Cs Pb halide (CsPbX3) perovskite nanocrystals, whose luminescence emission wavelength could be easily tuned throughout the visible spectrum by changing their chem. compn. (X = Br- or I-) and/or shape (nanocubes -NC-, nanoplatelets -NPL- or nanosheets -NS-). By taking advantage of these 2 characteristics, the authors were able to form thin films of inorg. quantum dots that down-convert a com. UV LED (365 nm) to a white light with tunable color correlated temp. (CCT). Starting from a mixt. of CsPbBr3 NPLs and NCs (blue and green emitting), the emission spectrum could be completed in the orange/red region either by CsPbI3 nanocrystals (all-perovskite approach) or by different chalcogenides (hybrid approach), including Cu-In-Zn-S (CIZS) or giant-shell (GS) CdSe/CdS nanocrystals. X-ray-induced stabilization of the ligand shell coating the nanocrystals inhibited anion-exchange between bromide and iodide-based perovskite nanocrystals in the 1st approach, as well as enhancing the overall film stability. The 2nd approach allowed an easier tuning of the emission spectrum since the particles could be pre-mixed in soln.
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    Li, X.; Wu, Y.; Zhang, S.; Cai, B.; Gu, Y.; Song, J.; Zeng, H. CsPbX3 Quantum Dots for Lighting and Displays: Roomerature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26, 2435– 2445,  DOI: 10.1002/adfm.201600109
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    CsPbX3 quantum dots for lighting and displays: Room-temperature synthesis, photoluminescence superiorities, underlying origins and white light-emitting diodes
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    Recently, Kovalenko and Li developed CsPbX3 (X = Cl, Br, I) inorg. perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temp., inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temp. (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersatd. recrystn. (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the obsd. 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temp. and wide color gamut.
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    A review. Defects have always been an integral part of semiconductor crystals, controlling their optical and electronic properties. Even though growing popularity of the CsPbX3 (X = Cl, Br, I, and their mixt.) nanocrystals (NCs) in various applications stems from their defect-tolerant nature, the properties, stability, and practical utility of these substances are still very much governed by the defects. A variety of methods, which are halide-specific, were developed to regulate the activities of the defects for enhancing the luminescence and stability of these NCs. In this Perspective, the authors trace the origin and manifestation of different types of defects in luminescence properties and stability of the CsPbX3 NCs, critically examine the rationale of various passivation strategies to obtain an in-depth understanding of the problem, and recommend the most effective strategy to be followed for tackling defects under any given condition.
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    Highly Emissive Divalent-Ion-Doped Colloidal CsPb1-xMxBr3 Perovskite Nanocrystals through Cation Exchange
    van der Stam, Ward; Geuchies, Jaco J.; Altantzis, Thomas; van den Bos, Karel H. W.; Meeldijk, Johannes D.; Van Aert, Sandra; Bals, Sara; Vanmaekelbergh, Daniel; de Mello Donega, Celso
    Journal of the American Chemical Society (2017), 139 (11), 4087-4097CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A method is presented that allows partial cation exchange in colloidal CsPbBr3 nanocrystals (NCs), whereby Pb2+ is exchanged for several isovalent cations, resulting in doped CsPb1-xMxBr3 NCs (M = Sn2+, Cd2+, and Zn2+; 0 < x ≤ 0.1), with preservation of the original NC shape. The size of the parent NCs is also preserved in the product NCs, apart from a small (few %) contraction of the unit cells upon incorporation of the guest cations. The partial Pb2+ for M2+ exchange leads to a blue-shift of the optical spectra, while maintaining the high luminescence quantum yields (>50%), sharp absorption features, and narrow emission of the parent CsPbBr3 NCs. The blue-shift in the optical spectra is attributed to the lattice contraction that accompanies the Pb2+ for M2+ cation exchange and is obsd. to scale linearly with the lattice contraction. This work opens up new possibilities to engineer the properties of halide perovskite NCs, which to date are the only known system where cation and anion exchange reactions can be sequentially combined while preserving the original NC shape, resulting in compositionally diverse perovskite NCs.
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  18. 18
    Vashishtha, P. Performance Enhanced Light-Emitting Diodes Fabricated from Nanocrystalline CsPbBr3 with in Situ Zn2+ Addition. ACS Appl. Electron. Mater. 2020, 2, 4002– 4011,  DOI: 10.1021/acsaelm.0c00827
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    18
    Performance Enhanced Light-Emitting Diodes Fabricated from Nanocrystalline CsPbBr3 with In Situ Zn2+ Addition
    Vashishtha, Parth; Griffith, Benjamin E.; Brown, Alasdair A. M.; Hooper, Thomas J. N.; Fang, Yanan; Ansari, Mohammed S.; Bruno, Annalisa; Pu, Suan Hui; Mhaisalkar, Subodh G.; White, Tim; Hanna, John V.
    ACS Applied Electronic Materials (2020), 2 (12), 4002-4011CODEN: AAEMBP; ISSN:2637-6113. (American Chemical Society)
    Inorg. cesium lead halide perovskite nanocrystals are promising materials for optoelectronic applications as they exhibit high thermal stability alongside precise color tunability and high color purity; however, their optical properties are degraded by surface defects. This work demonstrates a room temp. synthesis of CsPbBr3 nanocrystals facilitating in situ surface passivation via the incorporation of Zn2+ cations. The facile incorporation ZnBr2 into the precursor soln. facilitates Zn2+ and Br- substitution into the nanocrystal surface/subsurface layers to induce passivation of existing Pb2+ and Br- vacancies and increase the photoluminescence quantum yield from ~ 48 to 86%. The XPS and solid-state 1H MAS NMR techniques show that the key modification is a redn. of the octylamine:oleic acid ratio leading to a near-neutral surface charge; this is accompanied by the appearance of larger nanosheets and nanowires obsd. by quant. powder XRD and HR-TEM. The suitability of these perovskite nanocrystals for elec. driven applications was confirmed by the fabrication of light-emitting diodes, which demonstrate that the in situ Zn2+ passivation strategy enhanced the external quantum efficiency by ~ 60%.
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  19. 19
    Imran, M. Alloy CsCdXPb1-XBr3 Perovskite Nanocrystals: The Role of Surface Passivation in Preserving Composition and Blue Emission. Chem. Mater. 2020, 32, 10641– 10652,  DOI: 10.1021/acs.chemmater.0c03825
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    19
    Alloy CsCdxPb1-xBr3 perovskite nanocrystals: role of surface passivation in preserving composition and blue emission
    Imran, Muhammad; Ramade, Julien; Di Stasio, Francesco; De Franco, Manuela; Buha, Joka; Van Aert, Sandra; Goldoni, Luca; Lauciello, Simone; Prato, Mirko; Infante, Ivan; Bals, Sara; Manna, Liberato
    Chemistry of Materials (2020), 32 (24), 10641-10652CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and compn. and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX3 perovskite NCs composed of two different M2+ cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCdxPb1-xBr3 NCs, which exhibit a cubic perovskite phase contg. Cd-rich domains of Ruddlesden-Popper phases (RP phases). The RP domains spontaneously transform into pure orthorhombic perovskite ones upon NC aging, and the emission color of the NCs shifts from blue to green over days. On the other hand, postsynthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocryst. NCs with cubic phase, highlighting the metastability of RP domains. When NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd2+ ions are expelled from NCs upon aging, and the NCs phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when NCs are coated with ammonium bromides, the loss of Cd2+ ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in the latter cases is ascribed to the satn. of surface vacancies, which may act as channels for the expulsion of Cd2+ ions from NCs.
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  20. 20
    Chen, C.; Xuan, T.; Bai, W.; Zhou, T.; Huang, F.; Xie, A.; Wang, L.; Xie, R. J. Highly Stable CsPbI3:Sr2+ Nanocrystals with near-Unity Quantum Yield Enabling Perovskite Light-Emitting Diodes with an External Quantum Efficiency of 17.1%. Nano Energy 2021, 85, 106033,  DOI: 10.1016/j.nanoen.2021.106033
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    20
    Highly stable CsPbI3:Sr2+ nanocrystals with near-unity quantum yield enabling perovskite light-emitting diodes with an external quantum efficiency of 17.1%
    Chen, Cheng; Xuan, Tongtong; Bai, Wenhao; Zhou, Tianliang; Huang, Fan; Xie, An; Wang, Le; Xie, Rong-Jun
    Nano Energy (2021), 85 (), 106033CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
    Removing long-chain ligands on the surface of perovskite nanocrystals (NCs) is a promising strategy to facilitate charge transport toward a high-performance perovskite light-emitting diode (PeLED). However, perovskite NCs, esp. CsPbI3 NCs, tend to decomp. in the ligand removal procedure due to their poor stability of perovskite NCs and high polarity of solvents. Here, we report Sr2+-doped CsPbI3 NCs that were synthesized by a modified hot injection method. These NCs show enhanced stability and near-unity photoluminescence quantum yield (PLQY, 99.8%). More importantly, the CsPbI3:Sr2+ NCs still maintain a high PLQY (97.5%) after removing surface ligands by a polar solvent (Et acetate, EA). Furthermore, a mixt. of EA and octane was used to prep. smooth and dense CsPbI3:Sr2+ NC films with an exceedingly high PLQY of 73.2% and a high stability under ambient conditions. Finally, the red-emitting CsPbI3:1.8% Sr2+ PeLEDs demonstrate a world-record peak external quantum efficiency (EQE) of 17.1%.
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  21. 21
    Lu, M.; Zhang, X.; Zhang, Y.; Guo, J.; Shen, X.; Yu, W. W.; Rogach, A. L. Simultaneous Strontium Doping and Chlorine Surface Passivation Improve Luminescence Intensity and Stability of CsPbI3 Nanocrystals Enabling Efficient Light-Emitting Devices. Adv. Mater. 2018, 30, e1804691  DOI: 10.1002/adma.201804691
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    There is no corresponding record for this reference.
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    Liu, W.; Lin, Q.; Li, H.; Wu, K.; Robel, I.; Pietryga, J. M.; Klimov, V. I. Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content. J. Am. Chem. Soc. 2016, 138, 14954– 14961,  DOI: 10.1021/jacs.6b08085
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    22
    Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content
    Liu, Wenyong; Lin, Qianglu; Li, Hongbo; Wu, Kaifeng; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.
    Journal of the American Chemical Society (2016), 138 (45), 14954-14961CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A new family of doped semiconductor nanocrystals (NCs) is introduced, offering unique insights into the chem. mechanism of doping, as well as into the fundamental interactions between the dopant and the semiconductor host. By elucidating the role of relative bond strengths within the precursor and the host lattice, an effective approach was developed for incorporating Mn ions into nanocrystals of Pb halide perovskites (CsPbX3, where X = Cl, Br, or I). In a key enabling step not possible in, e.g., II-VI nanocrystals, gentle chem. means were used to finely and reversibly tune the NC band gap over a wide range of energies (1.8-3.1 eV) via post-synthetic anion exchange. A dramatic effect was obsd. of halide identity on relative intensities of intrinsic band-edge and Mn emission bands, which the authors ascribe to the influence of the energy difference between the corresponding transitions on the rate of reverse energy transfer from the Mn ion to the semiconductor host.
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  23. 23
    Parobek, D.; Dong, Y.; Qiao, T.; Son, D. H. Direct Hot-Injection Synthesis of Mn-Doped CsPbBr3 Nanocrystals. Chem. Mater. 2018, 30, 2939– 2944,  DOI: 10.1021/acs.chemmater.8b00310
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    23
    Direct Hot-Injection Synthesis of Mn-Doped CsPbBr3 Nanocrystals
    Parobek, David; Dong, Yitong; Qiao, Tian; Son, Dong Hee
    Chemistry of Materials (2018), 30 (9), 2939-2944CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    We report the direct hot-injection synthesis of Mn-doped cesium lead bromide (CsPbBr3) perovskite nanocrystals. In contrast to Mn-doped CsPbCl3 nanocrystals, where doping of Mn under typical hot-injection synthesis condition has been relatively straightforward, extending the same approach to CsPbBr3 has been very difficult. Here, we achieved the synthesis of Mn-doped CsPbBr3 nanocrystals via the formation of an intermediate structure (L2[Pb1-xMnx]Br4, L = ligand) before the hot-injection of the Cs precursor, which contains the same Mn-Br coordination present in Mn-doped CsPbBr3 nanocrystals. A strong correlation was obsd. between the Mn luminescence intensities of L2[Pb1-xMnx]Br4 and Mn-doped CsPbBr3 nanocrystals, suggesting the possible role of L2[Pb1-xMnx]Br4 as the structural precursor to Mn-doped CsPbBr3 nanocrystals. The successful Mn doping in CsPbBr3 nanocrystal host, which has significantly better optical characteristics than CsPbCl3 nanocrystals, will expand the range of useful properties of Mn-doped cesium lead halide perovskite nanocrystals resulting from the coupling of exciton and Mn.
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  24. 24
    Li, M.; Zhang, X.; Matras-Postolek, K.; Chen, H.-S.; Yang, P. An Anion-Driven Sn2+ Exchange Reaction in CsPbBr3 Nanocrystals towards Tunable and High Photoluminescence. J. Mater. Chem. C 2018, 6, 5506– 5513,  DOI: 10.1039/c8tc00990b
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    24
    An anion-driven Sn2+ exchange reaction in CsPbBr3 nanocrystals towards tunable and high photoluminescence
    Li, Meng; Zhang, Xiao; Matras-Postolek, Katarzyna; Chen, Hsueh-Shih; Yang, Ping
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2018), 6 (20), 5506-5513CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    Fast and efficient ion-exchange reactions endow CsPbX3 nanocrystals (NCs) with superior photoluminescence (PL) properties. In this study, SnX2 (X = I, Cl) was used as a Sn precursor to conduct the cation exchange reaction, which was promoted by anion exchange between the parent CsPbBr3 NCs and the guest X in SnX2. The anion-driven cation exchange reaction occurred efficiently (10 min). CsSnI3 NCs were created by ion-exchange reactions between CsPbBr3 NCs and the SnI2 precursor. The CsSnI3 NCs retained the initial morphol. of CsPbBr3 NCs and revealed a high PL efficiency (59%) and prolonged PL lifetime. In contrast, the exchange reaction of Sn2+ ions in CsPbBr3 NCs did not occur in a short time using SnBr2 as a precursor. After the cation exchange reaction, the 4f peaks of Pb ions in XPS spectra shifted to low binding energies as compared to those of the parent CsPbX3 NCs. This is ascribed to the increase in the no. of Pb-oleate (Pb-OA) species. Contrary to the hot-injection method used to synthesize CsSnI3 NCs, the kinetically controlled ion exchange reactions lead to the synthesis of CsSnI3 NCs with a high structural stability. Thus, an anion-exchange-promoted cation exchange reaction is a particularly efficient versatile tool to dope Sn2+ into CsPbX3 NCs.
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    Yao, J.-S. Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals Based Light-Emitting Diodes. J. Am. Chem. Soc. 2018, 140, 3626– 3634,  DOI: 10.1021/jacs.7b11955
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    25
    Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals Based Light-Emitting Diodes
    Yao, Ji-Song; Ge, Jing; Han, Bo-Ning; Wang, Kun-Hua; Yao, Hong-Bin; Yu, Hao-Lei; Li, Jian-Hai; Zhu, Bai-Sheng; Song, Ji-Zhong; Chen, Chen; Zhang, Qun; Zeng, Hai-Bo; Luo, Yi; Yu, Shu-Hong
    Journal of the American Chemical Society (2018), 140 (10), 3626-3634CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A novel strategy to enhance the photo/electroluminescence efficiency of CsPbBr3 perovskite nanocrystals (NCs) through doping of heterovalent Ce3+ via a facile hot-injection method is proposed. The Ce3+ was chosen as the dopant for CsPbBr3 NCs by virtue of its similar ion radius and formation of higher energy level of conduction band with Br in comparison with the Pb2+ cation to maintain the integrity of perovskite structure without introducing addnl. trap states. By increasing the doping amt. of Ce3+ in CsPbBr3 NCs to 2.88% (at. percentage of Ce compared to Pb), the luminescence quantum yield (PLQY) of CsPbBr3 NCs reached up to 89%, a factor of 2 increase in comparison with the native, undoped ones. The ultrafast transient absorption and time-resolved luminescence (PL) spectroscopy unraveled that the Ce3+-doping can significantly modulate the PL kinetics to enhance the PL efficiency of doped CsPbBr3 NCs. The LED device fabricated by adopting Ce3+-doped CsPbBr3 NCs as the emitting layers exhibited a pronounced improvement of electroluminescence with external quantum efficiency (EQE) from 1.6% to 4.4% via the Ce3+-doping.
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  26. 26
    Begum, R.; Parida, M. R.; Abdelhady, A. L.; Murali, B.; Alyami, N. M.; Ahmed, G. H.; Hedhili, M. N.; Bakr, O. M.; Mohammed, O. F. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping. J. Am. Chem. Soc. 2017, 139, 731– 737,  DOI: 10.1021/jacs.6b09575
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    26
    Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping
    Begum, Raihana; Parida, Manas R.; Abdelhady, Ahmed L.; Murali, Banavoth; Alyami, Noktan M.; Ahmed, Ghada H.; Hedhili, Mohamed Nejib; Bakr, Osman M.; Mohammed, Omar F.
    Journal of the American Chemical Society (2017), 139 (2), 731-737CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Since compelling device efficiencies of perovskite solar cells were achieved, investigative efforts have turned to understand other key challenges in these systems, such as engineering interfacial energy-level alignment and charge transfer (CT). However, these types of studies on perovskite thin-film devices are impeded by the morphol. and compositional heterogeneity of the films and their ill-defined surfaces. Here, we use well-defined ligand-protected perovskite nanocrystals (NCs) as model systems to elucidate the role of heterovalent doping on charge-carrier dynamics and energy level alignment at the interface of perovskite NCs with mol. acceptors. More specifically, we develop an in situ doping approach for colloidal CsPbBr3 perovskite NCs with heterovalent Bi3+ ions by hot injection to precisely tune their band structure and excited-state dynamics. This synthetic method allowed us to map the impact of doping on CT from the NCs to different mol. acceptors. Using time-resolved spectroscopy with broadband capability, we clearly demonstrate that CT at the interface of NCs can be tuned and promoted by metal ion doping. We found that doping increases the energy difference between states of the mol. acceptor and the donor moieties, subsequently facilitating the interfacial CT process. This work highlights the key variable components not only for promoting interfacial CT in perovskites, but also for establishing a higher degree of precision and control over the surface and the interface of perovskite mol. acceptors.
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    Zhang, X.; Wang, H.; Hu, Y.; Pei, Y.; Wang, S.; Shi, Z.; Colvin, V. L.; Wang, S.; Zhang, Y.; Yu, W. W. Strong Blue Emission from Sb3+ -Doped Super Small CsPbBr3 Nanocrystals. J. Phys. Chem. Lett. 2019, 10, 1750– 1756,  DOI: 10.1021/acs.jpclett.9b00790
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    27
    Strong Blue Emission from Sb3+-Doped Super Small CsPbBr3 Nanocrystals
    Zhang, Xiangtong; Wang, Hua; Hu, Yue; Pei, Yixian; Wang, Shixun; Shi, Zhifeng; Colvin, Vicki L.; Wang, Shengnian; Zhang, Yu; Yu, William W.
    Journal of Physical Chemistry Letters (2019), 10 (8), 1750-1756CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Colloidal lead halide perovskite nanocrystals (NCs) have high tunability in the visible light region and high photoluminescence quantum yields (PL QYs) for green and red emissions, but bright blue emission is still a challenge. Super small CsPbBr3 perovskite NCs emit blue light around 460 nm with a narrow peak width, and they do not have the problem of phase sepn. like their Cl-Br counterparts. However, the blue emission from super small CsPbBr3 NCs easily becomes green over time, and their PL QY is still low. The doping of Sb3+ ions successfully reduced the surface energy, improved the lattice energy, passivated the defect states below the band gap, eventually boosted the PL QY of blue emission to 73.8%, and resulted in better spectral stability even at elevated temps. in soln. (40-100 °C). Its CIE coordinates were (0.14, 0.06), which are close to the primary blue color (0.155, 0.070) according to the NTSC TV color std.
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  28. 28
    Liu, M.; Zhong, G.; Yin, Y.; Miao, J.; Li, K.; Wang, C.; Xu, X.; Shen, C.; Meng, H. Aluminum-Doped Cesium Lead Bromide Perovskite Nanocrystals with Stable Blue Photoluminescence Used for Display Backlight. Adv. Sci. 2017, 4, 1700335,  DOI: 10.1002/advs.201700335
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    Aluminum-Doped Cesium Lead Bromide Perovskite Nanocrystals with Stable Blue Photoluminescence Used for Display Backlight
    Liu Ming; Yin Yongming; Miao Jingsheng; Li Ke; Wang Chengqun; Xu Xiuru; Shen Clifton; Meng Hong; Zhong Guohua
    Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2017), 4 (11), 1700335 ISSN:2198-3844.
    Bright and stable blue emitters with narrow full-width at half-maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al(3+)) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead-halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion-exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red-emitting CdSe@ZnS NCs result in UV-pumped white light-emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU-R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low-cost, earth-abundant, solution-processable Al-doped perovskite NCs can be promising candidate materials for blue down-conversion layer in backlit displays.
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    Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L. Genesis, Challenges and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater. 2018, 17, 394– 405,  DOI: 10.1038/s41563-018-0018-4
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    Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals
    Akkerman, Quinten A.; Raino, Gabriele; Kovalenko, Maksym V.; Manna, Liberato
    Nature Materials (2018), 17 (5), 394-405CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
    A review. Lead halide perovskites (LHPs) in the form of nanometer-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same exptl. mindset and theor. framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.
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    Ng, C. K.; Wang, C.; Jasieniak, J. J. Synthetic Evolution of Colloidal Metal Halide Perovskite Nanocrystals. Langmuir 2019, 35, 11609,  DOI: 10.1021/acs.langmuir.9b00855
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    Synthetic Evolution of Colloidal Metal Halide Perovskite Nanocrystals
    Ng, Chun Kiu; Wang, Chujie; Jasieniak, Jacek J.
    Langmuir (2019), 35 (36), 11609-11628CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A review. Metal halide perovskite semiconductor nanocrystals have emerged as a lucrative class of materials for many optoelectronic applications. By leveraging the synthetic toolboxes developed from decades of research into more traditional semiconductor nanocrystals, remarkable progress has been made across these materials in terms of their structural, compositional, and optoelectronic control. Here, we review this progress in terms of their underlying formation stages, synthetic approaches, and postsynthetic treatment steps. This assessment highlights the rapidly maturing nature of the perovskite nanocrystal field, particularly with regard to their lead-based derivs. It further demonstrates that significant challenges remain around precisely controlling their nucleation and growth processes. In going forward, a deeper understanding of the role of precursors and ligands will significantly bolster the versatility in the size, shape, compn., and functional properties of these exciting materials.
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    Huang, G.; Wang, C.; Xu, S.; Zong, S.; Lu, J.; Wang, Z.; Lu, C.; Cui, Y. Postsynthetic Doping of MnCl2 Molecules into Preformed CsPbBr3 Perovskite Nanocrystals via a Halide Exchange-Driven Cation Exchange. Adv. Mater. 2017, 29, 1700095,  DOI: 10.1002/adma.201700095
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    Pradeep, K. R.; Viswanatha, R. Mechanism of Mn Emission: Energy Transfer vs Charge Transfer Dynamics in Mn-Doped Quantum Dots. APL Mater. 2020, 8, 020901,  DOI: 10.1063/1.5140888
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    Mechanism of Mn emission: Energy transfer vs charge transfer dynamics in Mn-doped quantum dots
    Pradeep, K. R.; Viswanatha, Ranjani
    APL Materials (2020), 8 (2), 020901CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
    A review. In the quest for new functional materials, transition metal doping in semiconductors has attracted significant attention, wherein introduction of dopant atoms alters a range of phys. properties of the host such as its optical, magnetic, and electronic properties. Hence, the choice of appropriate dopants to meet the current challenges makes semiconductor doping a highly versatile field. In the past, Mn doping in II-VI semiconductors has been extensively studied. The interest in these systems arises from a prominent orange emission from an optically forbidden state. An extended debate in the literature spanning the last three decades has so far shed light on various anomalous properties of Mn emission, specifically in quantum-confined systems leading to more questions. In this perspective, we review the literature with specific emphasis on the mechanism of Mn emission and an understanding of the electron-hole pathway during the excitation and de-excitation process in doped quantum dots. We explore various phenomena of energy and charge transfer mechanisms along with expts. in support of these phenomena which can eventually lead to a better understanding of spin driven optoelectronics. (c) 2020 American Institute of Physics.
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  33. 33
    Meinardi, F.; Akkerman, Q. A.; Bruni, F.; Park, S.; Mauri, M.; Dang, Z.; Manna, L.; Brovelli, S. Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators. ACS Energy Lett. 2017, 2, 2368– 2377,  DOI: 10.1021/acsenergylett.7b00701
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    Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators
    Meinardi, Francesco; Akkerman, Quinten A.; Bruni, Francesco; Park, Sungwook; Mauri, Michele; Dang, Zhiya; Manna, Liberato; Brovelli, Sergio
    ACS Energy Letters (2017), 2 (10), 2368-2377CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    Halide perovskite nanocrystals (NCs) are promising soln.-processed emitters for low-cost optoelectronics and photonics. Doping adds a degree of freedom for their design and enables us to fully decouple their absorption and emission functions. This is paramount for luminescent solar concentrators (LSCs) that enable fabrication of electrode-less solar windows for building-integrated photovoltaic applications. Here, we demonstrate the suitability of manganese-doped CsPbCl3 NCs as reabsorption-free emitters for large-area LSCs. Light propagation measurements and Monte Carlo simulations indicate that the dopant emission is unaffected by reabsorption. Nanocomposite LSCs were fabricated via mass copolymn. of acrylate monomers, ensuring thermal and mech. stability and optimal compatibility of the NCs, with fully preserved emission efficiency. As a result, perovskite LSCs behave closely to ideal devices, in which all portions of the illuminated area contribute equally to the total optical power. These results demonstrate the potential of doped perovskite NCs for LSCs, as well as for other photonic technologies relying on low-attenuation long-range optical wave guiding.
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    Chen, W.; Shi, T.; Du, J.; Zang, Z.; Yao, Z.; Li, M.; Sun, K.; Hu, W.; Leng, Y.; Tang, X. Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices. ACS Appl. Interfaces 2018, 10, 43978– 43986,  DOI: 10.1021/acsami.8b14046
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    34
    Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices
    Chen, Weiwei; Shi, Tongchao; Du, Juan; Zang, Zhigang; Yao, Zhiqiang; Li, Meng; Sun, Kuan; Hu, Wei; Leng, Yuxin; Tang, Xiaosheng
    ACS Applied Materials & Interfaces (2018), 10 (50), 43978-43986CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    As an outstanding less-Pb candidate, doping Mn2+ ions into perovskite quantum dots (QDs) has received significant interest in the application of light-emitting diodes (LEDs). However, their further applications are impeded by poor chem. instability. Here, the silica-wrapped Mn-doped CsPbCl3 QDs are fabricated via hydrolyzing (3-aminopropyl) triethoxysilane with improved operational stability. Also, the photoluminescence quantum yield as high as 55.4% for the CsPbMnCl3@SiO2 composite is achieved. Silica wrapping can protect the perovskite QDs from damage by temp. and humidity as well as anion exchange. Furthermore, white LED devices are prepd. by employing the mixt. of green CsPbBr3 QDs and orange-red CsPbMnCl3@SiO2 composites. The as-obtained white LED device operated at a forward current of 20 mA exhibits bright natural light with a high luminous efficiency of 77.59 lm/W, and the corresponding color rendering index of 82 and color temp. (CCT) of 3950 K are obtained. Addnl., the electroluminescence spectrum shows nearly no variation after 24 h operation. This work will promote the Mn-doped CsPbCl3 QDs material to the practical application in solid-state LEDs.
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    Chen, Z. Highly Efficient Mn-Doped CsPb(Br/Cl)3 Mixed-Halide Perovskite via a Simple Large-Scale Synthesis Method. Mater. Sci. Eng. B 2021, 273, 115426,  DOI: 10.1016/j.mseb.2021.115426
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    Highly efficient Mn-doped CsPb(Br/Cl)3 mixed-halide perovskite via a simple large-scale synthesis method
    Chen, Zhihao; He, Haiyang; Wen, Zhuoqi; Cui, Zhongjie; Mei, Shiliang; Yang, Dan; Wei, Xian; Zhang, Wanlu; Xie, Fengxian; Yang, Bobo; Guo, Ruiqian
    Materials Science & Engineering, B: Advanced Functional Solid-State Materials (2021), 273 (), 115426CODEN: MSBTEK; ISSN:0921-5107. (Elsevier B.V.)
    Broadband emission Mn2+ doped lead halide perovskites are deemed as promising phosphor materials for solid state white light-emitting-diodes (WLEDs). Herein, we report a facile gram-scale synthesis of Mn-doped CsPb(Br/Cl)3 phosphors by doping MnCl2 into CsPbBr3 perovskite nanocrystals at room temp. The obtained phosphors present dual-color emission with blue emission at 463 nm and red emission at 602 nm. Increasing MnCl2 doping amt. can enhance the red emission while more 3-Aminopropyltrimethoxysilane (APTMS) ligands can repress Mn related impurity and provide high stability. Further, two kinds of WLEDs (monocomponnet and two-component) are demonstrated. The monocomponent WLED exhibits warm white light under various driving currents (30 mA-150 mA), and the two-component WLED shows good chromatic performance close to ideal white light (0.33, 0.33), demonstrating their potential applications in WLED devices.
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  36. 36
    Zheng, Y.; Yuan, X.; Yang, J.; Li, Q.; Yang, X.; Fan, Y.; Li, H.; Liu, H.; Zhao, J. Cu Doping-Enhanced Emission Efficiency of Mn2+ in Cesium Lead Halide Perovskite Nanocrystals for Efficient White Light-Emitting Diodes. J. Lumin. 2020, 227, 117586,  DOI: 10.1016/j.jlumin.2020.117586
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    Cu doping-enhanced emission efficiency of Mn2+ in cesium lead halide perovskite nanocrystals for efficient white light-emitting diodes
    Zheng, Yuzhu; Yuan, Xi; Yang, Jian; Li, Qiuyan; Yang, Xinxuan; Fan, Yi; Li, Haibo; Liu, Huilian; Zhao, Jialong
    Journal of Luminescence (2020), 227 (), 117586CODEN: JLUMA8; ISSN:0022-2313. (Elsevier B.V.)
    Enhancing emission efficiency of Mn2+ in blue-orange dual-emitting Mn doped cesium lead halide perovskite nanocrystals (NCs) with high photoluminescence quantum yields (PL QYs) is important to fabricate high efficiency white light emitting diodes for solid state lighting. The synthesis and luminescent properties of Mn doped CsPbCl3-xBrx NCs through anion exchange of Mn and Cu co-doped CsPbCl3 NCs with PbBr2 at room temp. were studied by means of steady-state and time-resolved PL spectroscopy. The high Mn2+ PL QYs of 52-63% were obtained in the initial Mn and Cu co-doped CsPbCl3 NCs synthesized under various Mn/Pb/Cu molar ratios at 190 °C by hot injection method. A record Mn2+ PL QY up to 53% was achieved in the blue (450 nm) -orange (600 nm) dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs through anion exchange. The enhancement of Mn emission efficiencies was attributed to reduced defect states in the doped NCs due to the incorporation of Cu ions. The efficient warm white light emitting diodes with color rendering index of 85 and luminous efficacy of 69 lm/W were fabricated by combination of the blue-orange dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs and green emissive CsPbBr3@Cs4PbBr6 core/shell NCs. The improved color rendering index was demonstrated with increasing Mn content.
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    Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. 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
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    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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    Cao, Z.; Li, J.; Wang, L.; Xing, K.; Yuan, X.; Zhao, J.; Gao, X.; Li, H. Enhancing Luminescence of Intrinsic and Mn Doped CsPbCl3 Perovskite Nanocrystals through Co2+ Doping. Mater. Res. Bull. 2020, 121, 110608,  DOI: 10.1016/j.materresbull.2019.110608
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    Enhancing luminescence of intrinsic and Mn doped CsPbCl3 perovskite nanocrystals through Co2+ doping
    Cao, Zhen; Li, Ji; Wang, Li; Xing, Ke; Yuan, Xi; Zhao, Jialong; Gao, Xin; Li, Haibo
    Materials Research Bulletin (2020), 121 (), 110608CODEN: MRBUAC; ISSN:0025-5408. (Elsevier Ltd.)
    In this work, the effects of Co2+ ions on the structural and luminescent properties of intrinsic and Mn doped CsPbCl3 NCs were studied by using photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) spectroscopy, and transmission electron microscopy (TEM). The undoped and Mn doped CsPbCl3 NCs with various Co/Pb molar ratios were synthesized at 190°C. It was found that the quantum yields of purple emissions in these CsPbCl3 NCs were greatly enhanced up to 30% after Co2+ ions were doped. The diffraction peaks in XRD patterns shifted to a large angle with the increase of Co/Pb molar ratio, indicating Co doping in Pb-site. Further both intrinsic and Mn doped CsPbCl3 NCs exhibited uniform cubes with av. sizes of 8-10 nm and good crystallinity after Co doping. The enhancement of purple emissions from excitons in the CsPbCl3 NCs was related to the redn. of nonradiative defects in these NCs through Co2+ doping.
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    Xing, K.; Yuan, X.; Wang, Y.; Li, J.; Wang, Y.; Fan, Y.; Yuan, L.; Li, K.; Wu, Z.; Li, H.; Zhao, J. Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride. J. Phys. Chem. Lett. 2019, 10, 4177– 4184,  DOI: 10.1021/acs.jpclett.9b01588
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    Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride
    Xing, Ke; Yuan, Xi; Wang, Yu; Li, Ji; Wang, Yunjun; Fan, Yi; Yuan, Long; Li, Kai; Wu, Zhijian; Li, Haibo; Zhao, Jialong
    Journal of Physical Chemistry Letters (2019), 10 (15), 4177-4184CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    It is challenging to improve the emission efficiency of Mn-doped CsPbCl3 (Mn:CsPbCl3) nanocrystals (NCs) because the excellent optical performances are dependent on high doping efficiency and few defects and traps. Steady-state and time-resolved luminescence (PL) spectroscopies were used to study the luminescence properties of Mn:CsPbCl3 NCs with different Mn doping levels synthesized in the presence of Ni chloride. The doping efficiency of Mn ions in Mn:CsPbCl3 NCs was greatly enhanced in the presence of NiCl2, and the PL wavelength of Mn2+ ions was tuned from 594 to 638 nm by varying the concn. of dopant Mn from 0.11% to 15.25%. The high emission quantum yields of Mn:CsPbCl3 NCs with orange and red emissions peaked at 600 and 620 nm in hexane were 70% and 39%, resp. The improvement in doping and emission efficiencies of Mn2+ was attributed to the enhanced formation energies of the Mn doping under the Mn and Ni codoped configuration and the resulting redn. of defects and traps in Mn:CsPbCl3 NCs with incorporation of Ni2+ ions.
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    Zhang, J.; Zheng, Y.; Liu, G.; Ma, Y.; Gong, L.; Guan, R.; Cui, X.; Yan, J.; Zhao, J.; Yang, J. Pressure-Engineered Optical and Charge Transport Properties of Mn2+/Cu2+ Codoped CsPbCl3 Perovskite Nanocrystals via Structural Progression. ACS Appl. Mater. Interfaces 2020, 12, 48225– 48236,  DOI: 10.1021/acsami.0c15068
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    Pressure-Engineered Optical and Charge Transport Properties of Mn2+/Cu2+ Codoped CsPbCl3 Perovskite Nanocrystals via Structural Progression
    Zhang, Junkai; Zheng, Yuzhu; Liu, Guangtao; Ma, Yanzhang; Gong, Lei; Guan, Renquan; Cui, Xiaoyan; Yan, Jiejuan; Zhao, Jialong; Yang, Jinghai
    ACS Applied Materials & Interfaces (2020), 12 (42), 48225-48236CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    In this work, compared with the corresponding pure CsPbCl3 nanocrystals (NCs) and Mn2+-doped CsPbCl3 NCs, Mn2+/Cu2+-codoped CsPbCl3 NCs exhibited improved photoluminescence (PL) and photoluminescence quantum yields (PL QYs) (57.6%), prolonged PL lifetimes (1.78 ms), and enhanced thermal endurance (523 K) as a result of efficient Mn2+ doping (3.66%) induced by the addn. of CuCl2. Furthermore, we applied pressure on Mn2+/Cu2+-codoped CsPbCl3 NCs to reveal that a red shift of photoluminescence followed by a blue shift was caused by band gap evolution and related to the structural phase transition from cubic to orthorhombic. Moreover, we also found that under the preheating condition of 523 K, such phase transition exhibited obvious morphol. invariance, accompanied by significantly enhanced cond. The pressure applied to the products treated with high temp. enlarged the elec. difference and easily intensified the interface by closer packaging. Interestingly, defect-triggered mixed ionic and electronic conducting (MIEC) was obsd. in annealed NCs when the applied pressure was 2.9 GPa. The pressure-dependent ionic conduction was closely related to local nanocrystal amorphization and increased deviatoric stress, as clearly described by in situ impedance spectra. Finally, retrieved products exhibited better cond. (improved by 5-6 times) and enhanced photoelec. response than those when pressure was not applied. Our findings not only reveal the pressure-tuned optical and elec. properties via structural progression but also open up the promising exploration of more amorphous all-inorg. CsPbX3-based photoelec. applications.
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    Shao, H.; Bai, X.; Cui, H.; Pan, G.; Jing, P.; Qu, S.; Zhu, J.; Zhai, Y.; Dong, B.; Song, H. White Light Emission in Bi3+/Mn2+ Ion Co-Doped CsPbCl3 Perovskite Nanocrystals. Nanoscale 2018, 10, 1023– 1029,  DOI: 10.1039/c7nr08136g
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    White light emission in Bi3+/Mn2+ ion co-doped CsPbCl3 perovskite nanocrystals
    Shao, He; Bai, Xue; Cui, Haining; Pan, Gencai; Jing, Pengtao; Qu, Songnan; Zhu, Jinyang; Zhai, Yue; Dong, Biao; Song, Hongwei
    Nanoscale (2018), 10 (3), 1023-1029CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Colloidal perovskite nanocrystals (NCs), esp. the fully inorg. cesium lead halide (CsPbX3, X = Cl, Br, I) NCs, have been considered as promising candidates for lighting and display applications due to their narrow band emission, tunable band gap and high photoluminescence quantum yields (QYs). However, owing to the anion exchange in the CsPbX3 NCs, stable multi-color and white light emissions are difficult to achieve, thus limiting their practical optoelectronic applications. In this work, dual ion Bi3+/Mn2+ codoped CsPbCl3 perovskite NCs were prepd. through the hot injection method for the first time to the best of our knowledge. Through simply adjusting the doping ion concns., the codoped NCs exhibited tunable emissions spanning the wide range of correlated color temp. (CCT) from 19 000 K to 4250 K under UV excitation. This interesting spectroscopic behavior benefits from efficient energy transfer from the perovskite NC host to the intrinsic energy levels of Bi3+ or Mn2+ doping ions. Finally, taking advantage of the cooperation between the excitonic transition of the CsPbCl3 perovskite NC host and the intrinsic emissions from Bi3+ and Mn2+ ions, white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.29) was developed in the codoped CsPbCl3 NCs.
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    Cai, T.; Wang, J.; Li, W.; Hills-Kimball, K.; Yang, H.; Nagaoka, Y.; Yuan, Y.; Zia, R.; Chen, O. Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators. Adv. Sci. 2020, 7, 2001317,  DOI: 10.1002/advs.202001317
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    Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators
    Cai, Tong; Wang, Junyu; Li, Wenhao; Hills-Kimball, Katie; Yang, Hanjun; Nagaoka, Yasutaka; Yuan, Yucheng; Zia, Rashid; Chen, Ou
    Advanced Science (Weinheim, Germany) (2020), 7 (18), 2001317CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot-injection technique is reported. The resulting NCs show a unique triple-wavelength emission covering UV/blue, visible, and near-IR regions. By optimizing the dopant concns., the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter-dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chem. studies and future applications of perovskite NCs.
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    Akkerman, Q. A.; Meggiolaro, D.; Dang, Z.; De Angelis, F.; Manna, L. Fluorescent Alloy CsPbxMn1-XI3 Perovskite Nanocrystals with High Structural and Optical Stability. ACS Energy Lett. 2017, 2, 2183– 2186,  DOI: 10.1021/acsenergylett.7b00707
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    Fluorescent Alloy CsPbxMn1-xI3 Perovskite Nanocrystals with High Structural and Optical Stability
    Akkerman, Quinten A.; Meggiolaro, Daniele; Dang, Zhiya; De Angelis, Filippo; Manna, Liberato
    ACS Energy Letters (2017), 2 (9), 2183-2186CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    CsPbI3 nanocrystals are still limited in their use because of their phase instability as they degrade into the yellow nonemitting δ-CsPbI3 phase within a few days. We show that alloyed CsPbxMn1-xI3 nanocrystals have essentially the same optical features and crystal structure as the parent α-CsPbI3 system, but they are stable in films and in soln. for periods over a month. The stabilization stems from a small decrease in the lattice parameters slightly increasing the Goldsmith tolerance factor, combined with an increase in the cohesive energy. Finally, hybrid d. functional calcns. confirm that the Mn2+ levels fall within the conduction band, thus not strongly altering the optical properties.
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    Wang, Y.; Chen, Y.; Zhang, T.; Wang, X.; Zhao, Y. Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics. Adv. Mater. 2020, 32, 2001025,  DOI: 10.1002/adma.202001025
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    Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics
    Wang, Yong; Chen, Yuetian; Zhang, Taiyang; Wang, Xingtao; Zhao, Yixin
    Advanced Materials (Weinheim, Germany) (2020), 32 (45), 2001025CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Research on chem. stable inorg. perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorg. perovskites, CsPbI3 with good chem. components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells. Comparing to the anisotropic org. cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI3 exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI3 induces the challenges of different crystal phase competition and room temp. phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI3 perovskite are presented. The development of various soln. chem. approaches for depositing high-quality phase-pure CsPbI3 perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI3 are discussed. The latest exptl. and theor. studies on the fundamental phys. properties of photoactive phase CsPbI3 have deepened the understanding of inorg. perovskites. The future development and research directions toward achieving highly stable CsPbI3 materials will further advance inorg. perovskite for highly stable and efficient photovoltaics.
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    Thanh, N. T. K.; Maclean, N.; Mahiddine, S. Mechanisms of Nucleation and Growth of Nanoparticles in Solution. Chem. Rev. 2014, 114, 7610– 7630,  DOI: 10.1021/cr400544s
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    Mechanisms of Nucleation and Growth of Nanoparticles in Solution
    Thanh, Nguyen T. K.; MacLean, N.; Mahiddine, S.
    Chemical Reviews (Washington, DC, United States) (2014), 114 (15), 7610-7630CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. This work covers the area of crystal growth of nanoparticles in soln. The authors first discuss classical crystal growth and crystal nucleation and the formation of particle size distribution. They then continue the discussion of crystal growth with the coverage of the theories of the LaMer Mechanism, Ostwald Ripening, Digestive Ripening, Finke-Watzky two step mechanism, coalescence and orientated attachment, and intraparticle growth. They then discuss literature examples of nanoparticle formation of copper, silver, and gold noble metals, and metal oxides. The use of nanoparticle formation for the formation of quantum dots are also given.
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    Stoumpos, C. C. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Cryst. Growth Des. 2013, 13, 2722– 2727,  DOI: 10.1021/cg400645t
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    Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection
    Stoumpos, Constantinos C.; Malliakas, Christos D.; Peters, John A.; Liu, Zhifu; Sebastian, Maria; Im, Jino; Chasapis, Thomas C.; Wibowo, Arief C.; Chung, Duck Young; Freeman, Arthur J.; Wessels, Bruce W.; Kanatzidis, Mercouri G.
    Crystal Growth & Design (2013), 13 (7), 2722-2727CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    The synthesis, crystal growth, and structural and optoelectronic characterization was carried out for the perovskite compd. CsPbBr3. This compd. is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photocond. response, with detector resoln. comparable to that of com., state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temp. does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approx. equal. The μτ product for electrons is comparable to Cd Zn telluride (CZT) and that for holes is 10 times higher than CZT.
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    High performance CsPbBr3 nanocrystals (NCs) were synthesized via a hot injection method followed by a room-temp. ligand exchange modification using 3-mercaptopropyltrimethoxysilane (MPTMS). The ligand exchange promotes crystal growth and enhances the photoluminescence quantum yield (PLQY) of the NCs to near unity. The oscillator strength of the interband transition based on UV-vis absorption was surprisingly amplified by a factor of 2.5. The NC's surface was passivated via S-Pb polar covalent bonding, which shifts the thermodn. equil. and favors NC growth with a higher Br-to-Pb at. ratio on the surface. Moreover, the perovskite lattice was strained by a cross-linked polymeric network of self-condensed siloxane. The strain within CsPbBr3 NCs was modulated by mixing at room temp. with Cs3PrCl6 NCs for controlled halide exchange and Pr doping; thereby blue emission from the Pr-doped CsPb(Cl/Br)3 NCs was achieved with optimized brightness (PLQY = 88%) at 464 nm.
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    Ahmed, G. H.; El-Demellawi, J. K.; Yin, J.; Pan, J.; Velusamy, D. B.; Hedhili, M. N.; Alarousu, E.; Bakr, O. M.; Alshareef, H. N.; Mohammed, O. F. Giant Photoluminescence Enhancement in CsPbCl3 Perovskite Nanocrystals by Simultaneous Dual-Surface Passivation. ACS Energy Lett. 2018, 3, 2301– 2307,  DOI: 10.1021/acsenergylett.8b01441
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    The presence of localized trap states on the surface of CsPbCl3 perovskite nanocrystals (NCs) is one of the greatest challenges precluding the development of optoelectronic applications of these NCs. Passivation of these defect sites provides a promising pathway to remediating their electronic and optical properties, such as the photoluminescence quantum yield (PLQY). Herein, we demonstrate a postsynthetic dual-surface treatment using trivalent metal ion salts, i.e., YCl3, as a new passivation approach that enhances the PLQY up to 60% while preserving the NC size and crystal structure. Such remarkable enhancement of the PLQY along with prolongation of the av. PL lifetimes of treated NCs samples indicates effective passivation of the surface defects and subsequent suppression of the formation of surface nonradiative recombination centers. As a segue toward optoelectronic applications, we probed the photoelec. performance of the NCs using ultraflexible devices; we found that YCl3-treated CsPbCl3 NC films exhibit an order of magnitude larger photocurrent compared to their nontreated counterparts. Our exptl. and theor. results provide an insightful understanding of the effective passivating roles of Y3+ and Cl- ions on the surface of CsPbCl3 NCs, as well as offering a new path to synthesize high-quality NCs for UV light conversion applications.
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    Chemistry of Materials (2018), 30 (11), 3633-3637CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    While the Cs lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) are in limelight for their promising optical and opto-electronic properties, the trapping of charge carriers by the defect states greatly diminishes their photoluminescence quantum yield (PLQY). Herein a simple treatment with Na or NH4+ tetra-fluoroborate salt can dramatically improve the PL properties of CsPbX3 NCs emitting in the blue-yellow region. The authors have achieved near-unity PLQY for CsPbBr3 and CsPbBrxCl3-x and substantially high PLQY for CsPbCl3 and CsPbBrxI3-x NCs by this method. The effect of this treatment is also reflected from much-improved PL decay profiles of the NCs. The findings, which demonstrate the effectiveness of tetrafluoroborate ion in producing high quality photo-luminescent perovskite NCs by removing excess Pb from the surface, are expected to boost the utility of these materials in practical applications.
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    The easily tunable emission of halide perovskite nanocrystals throughout the visible spectrum makes them an extremely promising material for light-emitting applications. Whereas high quantum yields and long-term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields, broad emission profiles, and insufficient colloidal stability. In this work, we present a facile synthetic approach for obtaining two-dimensional CsPbBr3 nanoplatelets with monolayer-precise control over their thickness, resulting in sharp photoluminescence and electroluminescence peaks with a tunable emission wavelength between 432 and 497 nm due to quantum confinement. Subsequent addn. of a PbBr2-ligand soln. repairs surface defects likely stemming from bromide and lead vacancies in a subensemble of weakly emissive nanoplatelets. The overall photoluminescence quantum yield of the blue-emissive colloidal dispersions is consequently enhanced up to a value of 73 ± 2%. Transient optical spectroscopy measurements focusing on the excitonic resonances further confirm the proposed repair process. Addnl., the high stability of these nanoplatelets in films and to prolonged UV light exposure is shown.
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    Nano Letters (2016), 16 (12), 7376-7380CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX3) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl3 and CsPb(Cl/Br)3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concns. and no signature of phase sepn. The strong sensitized luminescence from d-d transition of Mn2+ ions upon band-edge excitation of the CsPbX3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 nanocrystals and well-defined ESR spectra of Mn2+ in host CsPbX3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb2+. These observations indicate that CsPbX3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.
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    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (36), 9281-9287CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    The emission colors of cesium lead halide perovskite nanocrystals (NCs) can be controlled by dynamic ion exchange and Mn2+ doping. Herein the authors report a novel strategy for the synthesis of Cs(PbxMn1-x)(ClyBr1-y)3 NCs via a post-synthetic cation-anion cosubstitution exchange reaction to tailor their optical properties in a wide range. Colloidal CsPbBr3 and CsPb1-xMnxCl3 NCs are first prepd., sep., and then mixed together in hexane soln. The Pb2+ and Br- ions in the CsPbBr3 NCs are simultaneously exchanged for the Mn2+ and Cl- ions in the CsPb1-xMnxCl3 NCs, resulting in homogeneous Cs(PbxMn1-x)(ClyBr1-y)3, with preservation of the shape and crystal structure of the initial NCs. This in situ ion exchange method avoids the degrdn. of photoluminescence originating from the addnl. purifn. process of the NCs, and in situ Mn2+ substitution also greatly enhances the emission intensity and quantum yield of the as-obtained NCs, which is related to the bound exciton effect.
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  1. Shuanglong Wang, Mukunda Mandal, Heng Zhang, Dag W. Breiby, Okan Yildiz, Zhitian Ling, George Floudas, Mischa Bonn, Denis Andrienko, Hai I. Wang, Paul W. M. Blom, Wojciech Pisula, Tomasz Marszalek. Odd–Even Alkyl Chain Effects on the Structure and Charge Carrier Transport of Two-Dimensional Sn-Based Perovskite Semiconductors. Journal of the American Chemical Society 2024, 146 (28) , 19128-19136. https://doi.org/10.1021/jacs.4c03936
  2. Deyin Wang, Zifang Hong, Jiacheng Sun, Yuhua Wang. High-Performance In3+-Doped CsPbBr3 Quantum Dots for Wide Color Gamut Backlighting. ACS Applied Nano Materials 2024, 7 (1) , 323-330. https://doi.org/10.1021/acsanm.3c04511
  3. Jing Zhang, Xiong Shen, Siyu Ma, Jianhui Sun, Fengjiao Chen, Haoxiang Ma, Limin An, Kai Pan. Temperature-dependent photoluminescence and third-order nonlinear optical properties of Mn2+ doped CsPbCl3 nanocrystals. Optical Materials 2023, 136 , 113362. https://doi.org/10.1016/j.optmat.2022.113362
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  • Abstract

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    Figure 1

    Figure 1. (a) XRD patterns, (b) microstrain values, (c) lattice parameters obtained by the W–H plot, (d) PL spectra, (e) time-resolved PL (TRPL) plot, and (f) PLQY distribution of pristine and Sr2+:CsPbBr3 NCs.

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    Figure 2

    Figure 2. (a) Four periodic slab models considered for the computational study: pristine CsPbBr3, Sr2+-doped Sr2+:CsPbBr3, Mn2+-doped Mn2+:CsPb(Br,Cl)3, and Sr2+/Mn2+ co-doped Sr2+:Mn2+:CsPb(Br,Cl)3 and (b) their corresponding pDOS.

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    Figure 3

    Figure 3. (a) XRD patterns: NCs show reflections at 15.4, 22.0, 31.1, 35.0, 38.4, and 44.6°, (b) comparisons of XRD signal positions for CsPbBr3, Mn2+:CsPb(Br,Cl)3, and Sr2+:Mn2+:CsPb(Br,Cl)3 perovskite NCs, (c) microstrain and lattice constant parameters, (d) PL/absorption spectra, (e) TRPL plot, and (f) PLQY comparisons of Mn2+:CsPb(Br,Cl)3 and 2%Sr2:Mn2+:CsPb(Br,Cl)3 NCs.

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    Figure 4

    Figure 4. (a) PL spectra of the pristine WLED and 2%Sr2+:WLED and (b) corresponding CIE coordinates.

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      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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    2. 2
      Akkerman, Q. A.; D’Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.; Prato, M.; Manna, L. Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions. J. Am. Chem. Soc. 2015, 137, 10276– 10281,  DOI: 10.1021/jacs.5b05602
      2
      Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions
      Akkerman, Quinten A.; D'Innocenzo, Valerio; Accornero, Sara; Scarpellini, Alice; Petrozza, Annamaria; Prato, Mirko; Manna, Liberato
      Journal of the American Chemical Society (2015), 137 (32), 10276-10281CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Via controlled anion exchange reactions using a range of different halide precursors, the chem. compn. and the optical properties of pre-synthesized colloidal Cs Pb halide perovskite nanocrystals (NCs) can be finely tuned, from green emitting CsPbBr3 to bright emitters in any other region of the visible spectrum, and back, by displacement of Cl- or I- ions and reinsertion of Br- ions. This approach gives access to perovskite semiconductor NCs with both structural and optical qualities comparable to those of directly synthesized NCs. Anion exchange is a dynamic process that takes place in soln. between NCs. By mixing solns. contg. perovskite NCs emitting in different spectral ranges (due to different halide compns.) their mutual fast exchange dynamics leads to homogenization in their compn., resulting in NCs emitting in a narrow spectral region that is intermediate between those of the parent nanoparticles.
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    3. 3
      Brown, A. A. M.; Damodaran, B.; Jiang, L.; Tey, J. N.; Pu, S. H.; Mathews, N.; Mhaisalkar, S. G. Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability. Adv. Energy Mater. 2020, 10, 2001349,  DOI: 10.1002/aenm.202001349
      3
      Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability
      Brown, Alasdair A. M.; Damodaran, Bahulayan; Jiang, Liudi; Tey, Ju Nie; Pu, Suan Hui; Mathews, Nripan; Mhaisalkar, Subodh G.
      Advanced Energy Materials (2020), 10 (34), 2001349CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
      A review. In this progress report, recent improvements to the room temperaturesyntheses of lead halide perovskite nanocrystals (APbX3, X = Cl, Br, I) are assessed, focusing on various aspects which influence the com. viability of the technol. Perovskite nanocrystals can be prepd. easily from low-cost precursors under ambient conditions, yet they have displayed near-unity photoluminescence quantum yield with narrow, highly tunable emission peaks. In addn. to their impressive ambipolar charge carrier mobilities, these properties make lead halide perovskite nanocrystals very attractive for light-emitting diode (LED) applications. However, there are still many practical hurdles preventing commercialization. Recent developments in room temp. synthesis and purifn. protocols are ed, closely evaluating the suitability of particular techniques for industry. This is followed by an assessment of the wide range of ligands deployed on perovskite nanocrystal surfaces, analyzing their impact on colloidal stability, as well as LED efficiency. Based on these observations, a perspective on important future research directions that can expedite the industrial adoption of perovskite nanocrystals is provided.
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    4. 4
      Yuan, F.; Ran, C.; Zhang, L.; Dong, H.; Jiao, B.; Hou, X.; Li, J.; Wu, Z. A Cocktail of Multiple Cations in Inorganic Halide Perovskite toward Efficient and Highly Stable Blue Light-Emitting Diodes. ACS Energy Lett. 2020, 5, 1062– 1069,  DOI: 10.1021/acsenergylett.9b02562
      4
      A Cocktail of Multiple Cations in Inorganic Halide Perovskite toward Efficient and Highly Stable Blue Light-Emitting Diodes
      Yuan, Fang; Ran, Chenxin; Zhang, Lin; Dong, Hua; Jiao, Bo; Hou, Xun; Li, Jingrui; Wu, Zhaoxin
      ACS Energy Letters (2020), 5 (4), 1062-1069CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Blue-emitting materials and their light-emitting diodes (LEDs) are always challenging in lighting and display applications. Recently, perovskite LEDs (PeLEDs) with efficient and stable green/red emission have made great progress, where external quantum efficiency (EQE) over 20% has been reached. However, it is still a big challenge to realize stable blue PeLEDs with high efficiency mainly because of the poor film quality and unreasonable device structure. Herein, a cocktail strategy, i.e., multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3, is demonstrated to improve both the efficiency and stability of blue PeLEDs. Combined with the "insulator-perovskite-insulator" structure, PeLEDs based on a multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3 perovskite film show max. EQE of 2.01% and max. luminance of 4015 cd/m2 at 484 nm. More importantly, the device exhibits robust durability, and its half-lifetime is over 300 min under continuous operation. The multication strategy could open up a new avenue for the design of new blue-emitting materials for high-performing PeLEDs.
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    5. 5
      De Marco, N.; Zhou, H.; Chen, Q.; Sun, P.; Liu, Z.; Meng, L.; Yao, E.-P.; Liu, Y.; Schiffer, A.; Yang, Y. Guanidinium: A Route to Enhanced Carrier Lifetime and Open-Circuit Voltage in Hybrid Perovskite Solar Cells. Nano Lett. 2016, 16, 1009– 1016,  DOI: 10.1021/acs.nanolett.5b04060
      5
      Guanidinium: A Route to Enhanced Carrier Lifetime and Open-Circuit Voltage in Hybrid Perovskite Solar Cells
      De Marco Nicholas; Zhou Huanping; Chen Qi; Sun Pengyu; Liu Zonghao; Meng Lei; Yao En-Ping; Liu Yongsheng; Schiffer Andy; Yang Yang
      Nano letters (2016), 16 (2), 1009-16 ISSN:.
      Hybrid perovskites have shown astonishing power conversion efficiencies owed to their remarkable absorber characteristics including long carrier lifetimes, and a relatively substantial defect tolerance for solution-processed polycrystalline films. However, nonradiative charge carrier recombination at grain boundaries limits open circuit voltages and consequent performance improvements of perovskite solar cells. Here we address such recombination pathways and demonstrate a passivation effect through guanidinium-based additives to achieve extraordinarily enhanced carrier lifetimes and higher obtainable open circuit voltages. Time-resolved photoluminescence measurements yield carrier lifetimes in guanidinium-based films an order of magnitude greater than pure-methylammonium counterparts, giving rise to higher device open circuit voltages and power conversion efficiencies exceeding 17%. A reduction in defect activation energy of over 30% calculated via admittance spectroscopy and confocal fluorescence intensity mapping indicates successful passivation of recombination/trap centers at grain boundaries. We speculate that guanidinium ions serve to suppress formation of iodide vacancies and passivate under-coordinated iodine species at grain boundaries and within the bulk through their hydrogen bonding capability. These results present a simple method for suppressing nonradiative carrier loss in hybrid perovskites to further improve performances toward highly efficient solar cells.
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    6. 6
      Guner, T.; Demir, M. M. A Review on Halide Perovskites as Color Conversion Layers in White Light Emitting Diode Applications. Phys. Status Solidi A 2018, 215, 1800120,  DOI: 10.1002/pssa.201800120
      There is no corresponding record for this reference.
    7. 7
      Chen, K. High Efficiency Mesoscopic Solar Cells Using CsPbI3 Perovskite Quantum Dots Enabled by Chemical Interface Engineering. J. Am. Chem. Soc. 2020, 142, 3775– 3783,  DOI: 10.1021/jacs.9b10700
      7
      High Efficiency Mesoscopic Solar Cells Using CsPbI3 Perovskite Quantum Dots Enabled by Chemical Interface Engineering
      Chen, Keqiang; Jin, Wei; Zhang, Yupeng; Yang, Tingqiang; Reiss, Peter; Zhong, Qiaohui; Bach, Udo; Li, Qitao; Wang, Yingwei; Zhang, Han; Bao, Qiaoliang; Liu, Yueli
      Journal of the American Chemical Society (2020), 142 (8), 3775-3783CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      All-inorg. α-CsPbI3 perovskite quantum dots (QDs) are attracting great interest as solar cell absorbers due to their appealing light harvesting properties and enhanced stability due to the absence of volatile org. constituents. Moreover, ex situ synthesized QDs significantly reduce the variability of the perovskite layer deposition process. However, the incorporation of α-CsPbI3 QDs into mesoporous TiO2 (m-TiO2) is highly challenging, but these constitute the best performing electron transport materials in state-of-the-art perovskite solar cells. Herein, the m-TiO2 surface is engineered using an electron-rich cesium-ion contg. Me acetate soln. As one effect of this treatment, the solid-liq. interfacial tension at the TiO2 surface is reduced and the wettability is improved, facilitating the migration of the QDs into m-TiO2. As a second effect, Cs+ ions passivate the QD surface and promote the charge transfer at the m-TiO2/QD interface, leading to an enhancement of the electron injection rate by a factor of 3. In combination with an ethanol-environment smoothing route that significantly reduces the surface roughness of the m-TiO2/QD layer, optimized devices exhibit highly reproducible power conversion efficiencies exceeding 13%. The best cell with an efficiency of 14.32% (reverse scan) reaches a short-circuit c.d. of 17.77 mA cm-2, which is an outstanding value for QD-based perovskite solar cells.
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    8. 8
      Zhang, X. Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells. Adv. Energy Mater. 2018, 8, 1702049,  DOI: 10.1002/aenm.201702049
      There is no corresponding record for this reference.
    9. 9
      Yakunin, S.; Protesescu, L.; Krieg, F.; Bodnarchuk, M. I.; Nedelcu, G.; Humer, M.; De Luca, G.; Fiebig, M.; Heiss, W.; Kovalenko, M. V. Low-Threshold Amplified Spontaneous Emission and Lasing from Colloidal Nanocrystals of Caesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056,  DOI: 10.1038/ncomms9056
      9
      Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites
      Yakunin, Sergii; Protesescu, Loredana; Krieg, Franziska; Bodnarchuk, Maryna I.; Nedelcu, Georgian; Humer, Markus; De Luca, Gabriele; Fiebig, Manfred; Heiss, Wolfgang; Kovalenko, Maksym V.
      Nature Communications (2015), 6 (), 8056CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcryst., thin-film and bulk single-cryst. metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temp. optical amplification can be obtained in the entire visible spectral range (440-700 nm) with low pump thresholds down to 5±1 μJ cm-2 and high values of modal net gain of at least 450±30 cm-1. Two kinds of lasing modes are successfully obsd.: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals.
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    10. 10
      Huang, X.; Guo, Q.; Yang, D.; Xiao, X.; Liu, X.; Xia, Z.; Fan, F.; Qiu, J.; Dong, G. Reversible 3D Laser Printing of Perovskite Quantum Dots inside a Transparent Medium. Nat. Photonics 2020, 14, 82– 88,  DOI: 10.1038/s41566-019-0538-8
      10
      Reversible 3D laser printing of perovskite quantum dots inside a transparent medium
      Huang, Xiongjian; Guo, Qianyi; Yang, Dandan; Xiao, Xiudi; Liu, Xiaofeng; Xia, Zhiguo; Fan, Fengjia; Qiu, Jianrong; Dong, Guoping
      Nature Photonics (2020), 14 (2), 82-88CODEN: NPAHBY; ISSN:1749-4885. (Nature Research)
      The three-dimensional (3D) patterning of semiconductors is potentially important for exploring new functionalities and applications in optoelectronics1,2. Here, we show that it is possible to write on demand 3D patterns of perovskite quantum dots (QDs) inside a transparent glass material using a femtosecond laser. By utilizing the inherent ionic nature and low formation energy of perovskite, highly luminescent CsPbBr3 QDs can be reversibly fabricated in situ and decompd. through femtosecond laser irradn. and thermal annealing. This pattern of writing and erasing can be repeated for many cycles, and the luminescent QDs are well protected by the inorg. glass matrix, resulting in stable perovskite QDs with potential applications such as high-capacity optical data storage, information encryption and 3D artwork.
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    11. 11
      Bao, C.; Yang, J.; Bai, S.; Xu, W.; Yan, Z.; Xu, Q.; Liu, J.; Zhang, W.; Gao, F. High Performance and Stable All-Inorganic Metal Halide Perovskite-Based Photodetectors for Optical Communication Applications. Adv. Mater. 2018, 30, 1870288,  DOI: 10.1002/adma.201870288
      There is no corresponding record for this reference.
    12. 12
      Wu, D. Welding Perovskite Nanowires for Stable, Sensitive, Flexible Photodetectors. ACS Nano 2020, 14, 2777– 2787,  DOI: 10.1021/acsnano.9b09315
      12
      Welding Perovskite Nanowires for Stable, Sensitive, Flexible Photodetectors
      Wu, Dingjun; Zhou, Hai; Song, Zehao; Zheng, Meng; Liu, Ronghuan; Pan, Xiyan; Wan, Houzhao; Zhang, Jun; Wang, Hao; Li, Xiaoming; Zeng, Haibo
      ACS Nano (2020), 14 (3), 2777-2787CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Compared with a single nanowire (NW) or NW array, the simpler prepn. process of an NW network (NWN) enables it to be fabricated in large-scale, flexible, and wearable applications of photodetectors (PDs). However, the NWN behaves many microinterfaces (MIs) between NWs, seriously limiting the device performance and stability. Here, we demonstrate a welding strategy for an MAPbI3 NWN, which enhances the crystallinity of the NWN and enhances the radial transmission of photogenerated carriers, leading to a better device performance with ultrahigh stability. Our NWN PDs fabricated by using the welding strategy showed ultrahigh performance with an on/off ratio and detectivity of 2.8 × 104 and 4.16 × 1012 Jones, resp., which are the best performance for reported metal-semiconductor-metal (MSM) perovskite NWN PDs and are comparable to those of single-NW or NW array PDs. More importantly, our unpackaged NWN PDs show ultrahigh storage stability in air with a humidity of 55-65%, and the flexible NWN PDs can enable 250 bending cycles at different bending radii and 1000 bending cycles at fixed bending radii with no performance degrdn. being obsd. These results indicate our welding strategy is very powerful for improving the performance of the NW device with applications in the wearable field.
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    13. 13
      Palazon, F.; Di Stasio, F.; Akkerman, Q. A.; Krahne, R.; Prato, M.; Manna, L. Polymer-Free Films of Inorganic Halide Perovskite Nanocrystals as UV-to-White Color-Conversion Layers in LEDs. Chem. Mater. 2016, 28, 2902– 2906,  DOI: 10.1021/acs.chemmater.6b00954
      13
      Polymer-Free Films of Inorganic Halide Perovskite Nanocrystals as UV-to-White Color-Conversion Layers in LEDs
      Palazon, Francisco; Di Stasio, Francesco; Akkerman, Quinten A.; Krahne, Roman; Prato, Mirko; Manna, Liberato
      Chemistry of Materials (2016), 28 (9), 2902-2906CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Quantum dots are replacing conventional phosphors as down-conversion materials for white light-emitting devices (LEDs). The authors synthesized Cs Pb halide (CsPbX3) perovskite nanocrystals, whose luminescence emission wavelength could be easily tuned throughout the visible spectrum by changing their chem. compn. (X = Br- or I-) and/or shape (nanocubes -NC-, nanoplatelets -NPL- or nanosheets -NS-). By taking advantage of these 2 characteristics, the authors were able to form thin films of inorg. quantum dots that down-convert a com. UV LED (365 nm) to a white light with tunable color correlated temp. (CCT). Starting from a mixt. of CsPbBr3 NPLs and NCs (blue and green emitting), the emission spectrum could be completed in the orange/red region either by CsPbI3 nanocrystals (all-perovskite approach) or by different chalcogenides (hybrid approach), including Cu-In-Zn-S (CIZS) or giant-shell (GS) CdSe/CdS nanocrystals. X-ray-induced stabilization of the ligand shell coating the nanocrystals inhibited anion-exchange between bromide and iodide-based perovskite nanocrystals in the 1st approach, as well as enhancing the overall film stability. The 2nd approach allowed an easier tuning of the emission spectrum since the particles could be pre-mixed in soln.
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    14. 14
      Li, X.; Wu, Y.; Zhang, S.; Cai, B.; Gu, Y.; Song, J.; Zeng, H. CsPbX3 Quantum Dots for Lighting and Displays: Roomerature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26, 2435– 2445,  DOI: 10.1002/adfm.201600109
      14
      CsPbX3 quantum dots for lighting and displays: Room-temperature synthesis, photoluminescence superiorities, underlying origins and white light-emitting diodes
      Li, Xiaoming; Wu, Ye; Zhang, Shengli; Cai, Bo; Gu, Yu; Song, Jizhong; Zeng, Haibo
      Advanced Functional Materials (2016), 26 (15), 2435-2445CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Recently, Kovalenko and Li developed CsPbX3 (X = Cl, Br, I) inorg. perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temp., inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temp. (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersatd. recrystn. (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the obsd. 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temp. and wide color gamut.
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    15. 15
      Yang, D.; Li, X.; Zhou, W.; Zhang, S.; Meng, C.; Wu, Y.; Wang, Y.; Zeng, H. CsPbBr3 Quantum Dots 2.0: Benzenesulfonic Acid Equivalent Ligand Awakens Complete Purification. Adv. Mater. 2019, 31, 1970049,  DOI: 10.1002/adma.201970049
      There is no corresponding record for this reference.
    16. 16
      Seth, S.; Ahmed, T.; De, A.; Samanta, A. Tackling the Defects, Stability, and Photoluminescence of CsPbX3 Perovskite Nanocrystals. ACS Energy Lett. 2019, 4, 1610– 1618,  DOI: 10.1021/acsenergylett.9b00849
      16
      Tackling the Defects, Stability, and Photoluminescence of CsPbX3 Perovskite Nanocrystals
      Seth, Sudipta; Ahmed, Tasnim; De, Apurba; Samanta, Anunay
      ACS Energy Letters (2019), 4 (7), 1610-1618CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      A review. Defects have always been an integral part of semiconductor crystals, controlling their optical and electronic properties. Even though growing popularity of the CsPbX3 (X = Cl, Br, I, and their mixt.) nanocrystals (NCs) in various applications stems from their defect-tolerant nature, the properties, stability, and practical utility of these substances are still very much governed by the defects. A variety of methods, which are halide-specific, were developed to regulate the activities of the defects for enhancing the luminescence and stability of these NCs. In this Perspective, the authors trace the origin and manifestation of different types of defects in luminescence properties and stability of the CsPbX3 NCs, critically examine the rationale of various passivation strategies to obtain an in-depth understanding of the problem, and recommend the most effective strategy to be followed for tackling defects under any given condition.
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    17. 17
      Van der Stam, W.; Geuchies, J. J.; Altantzis, T.; Van Den Bos, K. H. W.; Meeldijk, J. D.; Van Aert, S.; Bals, S.; Vanmaekelbergh, D.; De Mello Donega, C. Highly Emissive Divalent-Ion-Doped Colloidal CsPb1-xMxBr3 Perovskite Nanocrystals through Cation Exchange. J. Am. Chem. Soc. 2017, 139, 4087– 4097,  DOI: 10.1021/jacs.6b13079
      17
      Highly Emissive Divalent-Ion-Doped Colloidal CsPb1-xMxBr3 Perovskite Nanocrystals through Cation Exchange
      van der Stam, Ward; Geuchies, Jaco J.; Altantzis, Thomas; van den Bos, Karel H. W.; Meeldijk, Johannes D.; Van Aert, Sandra; Bals, Sara; Vanmaekelbergh, Daniel; de Mello Donega, Celso
      Journal of the American Chemical Society (2017), 139 (11), 4087-4097CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A method is presented that allows partial cation exchange in colloidal CsPbBr3 nanocrystals (NCs), whereby Pb2+ is exchanged for several isovalent cations, resulting in doped CsPb1-xMxBr3 NCs (M = Sn2+, Cd2+, and Zn2+; 0 < x ≤ 0.1), with preservation of the original NC shape. The size of the parent NCs is also preserved in the product NCs, apart from a small (few %) contraction of the unit cells upon incorporation of the guest cations. The partial Pb2+ for M2+ exchange leads to a blue-shift of the optical spectra, while maintaining the high luminescence quantum yields (>50%), sharp absorption features, and narrow emission of the parent CsPbBr3 NCs. The blue-shift in the optical spectra is attributed to the lattice contraction that accompanies the Pb2+ for M2+ cation exchange and is obsd. to scale linearly with the lattice contraction. This work opens up new possibilities to engineer the properties of halide perovskite NCs, which to date are the only known system where cation and anion exchange reactions can be sequentially combined while preserving the original NC shape, resulting in compositionally diverse perovskite NCs.
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    18. 18
      Vashishtha, P. Performance Enhanced Light-Emitting Diodes Fabricated from Nanocrystalline CsPbBr3 with in Situ Zn2+ Addition. ACS Appl. Electron. Mater. 2020, 2, 4002– 4011,  DOI: 10.1021/acsaelm.0c00827
      18
      Performance Enhanced Light-Emitting Diodes Fabricated from Nanocrystalline CsPbBr3 with In Situ Zn2+ Addition
      Vashishtha, Parth; Griffith, Benjamin E.; Brown, Alasdair A. M.; Hooper, Thomas J. N.; Fang, Yanan; Ansari, Mohammed S.; Bruno, Annalisa; Pu, Suan Hui; Mhaisalkar, Subodh G.; White, Tim; Hanna, John V.
      ACS Applied Electronic Materials (2020), 2 (12), 4002-4011CODEN: AAEMBP; ISSN:2637-6113. (American Chemical Society)
      Inorg. cesium lead halide perovskite nanocrystals are promising materials for optoelectronic applications as they exhibit high thermal stability alongside precise color tunability and high color purity; however, their optical properties are degraded by surface defects. This work demonstrates a room temp. synthesis of CsPbBr3 nanocrystals facilitating in situ surface passivation via the incorporation of Zn2+ cations. The facile incorporation ZnBr2 into the precursor soln. facilitates Zn2+ and Br- substitution into the nanocrystal surface/subsurface layers to induce passivation of existing Pb2+ and Br- vacancies and increase the photoluminescence quantum yield from ~ 48 to 86%. The XPS and solid-state 1H MAS NMR techniques show that the key modification is a redn. of the octylamine:oleic acid ratio leading to a near-neutral surface charge; this is accompanied by the appearance of larger nanosheets and nanowires obsd. by quant. powder XRD and HR-TEM. The suitability of these perovskite nanocrystals for elec. driven applications was confirmed by the fabrication of light-emitting diodes, which demonstrate that the in situ Zn2+ passivation strategy enhanced the external quantum efficiency by ~ 60%.
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    19. 19
      Imran, M. Alloy CsCdXPb1-XBr3 Perovskite Nanocrystals: The Role of Surface Passivation in Preserving Composition and Blue Emission. Chem. Mater. 2020, 32, 10641– 10652,  DOI: 10.1021/acs.chemmater.0c03825
      19
      Alloy CsCdxPb1-xBr3 perovskite nanocrystals: role of surface passivation in preserving composition and blue emission
      Imran, Muhammad; Ramade, Julien; Di Stasio, Francesco; De Franco, Manuela; Buha, Joka; Van Aert, Sandra; Goldoni, Luca; Lauciello, Simone; Prato, Mirko; Infante, Ivan; Bals, Sara; Manna, Liberato
      Chemistry of Materials (2020), 32 (24), 10641-10652CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and compn. and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX3 perovskite NCs composed of two different M2+ cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCdxPb1-xBr3 NCs, which exhibit a cubic perovskite phase contg. Cd-rich domains of Ruddlesden-Popper phases (RP phases). The RP domains spontaneously transform into pure orthorhombic perovskite ones upon NC aging, and the emission color of the NCs shifts from blue to green over days. On the other hand, postsynthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocryst. NCs with cubic phase, highlighting the metastability of RP domains. When NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd2+ ions are expelled from NCs upon aging, and the NCs phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when NCs are coated with ammonium bromides, the loss of Cd2+ ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in the latter cases is ascribed to the satn. of surface vacancies, which may act as channels for the expulsion of Cd2+ ions from NCs.
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    20. 20
      Chen, C.; Xuan, T.; Bai, W.; Zhou, T.; Huang, F.; Xie, A.; Wang, L.; Xie, R. J. Highly Stable CsPbI3:Sr2+ Nanocrystals with near-Unity Quantum Yield Enabling Perovskite Light-Emitting Diodes with an External Quantum Efficiency of 17.1%. Nano Energy 2021, 85, 106033,  DOI: 10.1016/j.nanoen.2021.106033
      20
      Highly stable CsPbI3:Sr2+ nanocrystals with near-unity quantum yield enabling perovskite light-emitting diodes with an external quantum efficiency of 17.1%
      Chen, Cheng; Xuan, Tongtong; Bai, Wenhao; Zhou, Tianliang; Huang, Fan; Xie, An; Wang, Le; Xie, Rong-Jun
      Nano Energy (2021), 85 (), 106033CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
      Removing long-chain ligands on the surface of perovskite nanocrystals (NCs) is a promising strategy to facilitate charge transport toward a high-performance perovskite light-emitting diode (PeLED). However, perovskite NCs, esp. CsPbI3 NCs, tend to decomp. in the ligand removal procedure due to their poor stability of perovskite NCs and high polarity of solvents. Here, we report Sr2+-doped CsPbI3 NCs that were synthesized by a modified hot injection method. These NCs show enhanced stability and near-unity photoluminescence quantum yield (PLQY, 99.8%). More importantly, the CsPbI3:Sr2+ NCs still maintain a high PLQY (97.5%) after removing surface ligands by a polar solvent (Et acetate, EA). Furthermore, a mixt. of EA and octane was used to prep. smooth and dense CsPbI3:Sr2+ NC films with an exceedingly high PLQY of 73.2% and a high stability under ambient conditions. Finally, the red-emitting CsPbI3:1.8% Sr2+ PeLEDs demonstrate a world-record peak external quantum efficiency (EQE) of 17.1%.
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    21. 21
      Lu, M.; Zhang, X.; Zhang, Y.; Guo, J.; Shen, X.; Yu, W. W.; Rogach, A. L. Simultaneous Strontium Doping and Chlorine Surface Passivation Improve Luminescence Intensity and Stability of CsPbI3 Nanocrystals Enabling Efficient Light-Emitting Devices. Adv. Mater. 2018, 30, e1804691  DOI: 10.1002/adma.201804691
      There is no corresponding record for this reference.
    22. 22
      Liu, W.; Lin, Q.; Li, H.; Wu, K.; Robel, I.; Pietryga, J. M.; Klimov, V. I. Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content. J. Am. Chem. Soc. 2016, 138, 14954– 14961,  DOI: 10.1021/jacs.6b08085
      22
      Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content
      Liu, Wenyong; Lin, Qianglu; Li, Hongbo; Wu, Kaifeng; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.
      Journal of the American Chemical Society (2016), 138 (45), 14954-14961CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A new family of doped semiconductor nanocrystals (NCs) is introduced, offering unique insights into the chem. mechanism of doping, as well as into the fundamental interactions between the dopant and the semiconductor host. By elucidating the role of relative bond strengths within the precursor and the host lattice, an effective approach was developed for incorporating Mn ions into nanocrystals of Pb halide perovskites (CsPbX3, where X = Cl, Br, or I). In a key enabling step not possible in, e.g., II-VI nanocrystals, gentle chem. means were used to finely and reversibly tune the NC band gap over a wide range of energies (1.8-3.1 eV) via post-synthetic anion exchange. A dramatic effect was obsd. of halide identity on relative intensities of intrinsic band-edge and Mn emission bands, which the authors ascribe to the influence of the energy difference between the corresponding transitions on the rate of reverse energy transfer from the Mn ion to the semiconductor host.
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    23. 23
      Parobek, D.; Dong, Y.; Qiao, T.; Son, D. H. Direct Hot-Injection Synthesis of Mn-Doped CsPbBr3 Nanocrystals. Chem. Mater. 2018, 30, 2939– 2944,  DOI: 10.1021/acs.chemmater.8b00310
      23
      Direct Hot-Injection Synthesis of Mn-Doped CsPbBr3 Nanocrystals
      Parobek, David; Dong, Yitong; Qiao, Tian; Son, Dong Hee
      Chemistry of Materials (2018), 30 (9), 2939-2944CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      We report the direct hot-injection synthesis of Mn-doped cesium lead bromide (CsPbBr3) perovskite nanocrystals. In contrast to Mn-doped CsPbCl3 nanocrystals, where doping of Mn under typical hot-injection synthesis condition has been relatively straightforward, extending the same approach to CsPbBr3 has been very difficult. Here, we achieved the synthesis of Mn-doped CsPbBr3 nanocrystals via the formation of an intermediate structure (L2[Pb1-xMnx]Br4, L = ligand) before the hot-injection of the Cs precursor, which contains the same Mn-Br coordination present in Mn-doped CsPbBr3 nanocrystals. A strong correlation was obsd. between the Mn luminescence intensities of L2[Pb1-xMnx]Br4 and Mn-doped CsPbBr3 nanocrystals, suggesting the possible role of L2[Pb1-xMnx]Br4 as the structural precursor to Mn-doped CsPbBr3 nanocrystals. The successful Mn doping in CsPbBr3 nanocrystal host, which has significantly better optical characteristics than CsPbCl3 nanocrystals, will expand the range of useful properties of Mn-doped cesium lead halide perovskite nanocrystals resulting from the coupling of exciton and Mn.
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    24. 24
      Li, M.; Zhang, X.; Matras-Postolek, K.; Chen, H.-S.; Yang, P. An Anion-Driven Sn2+ Exchange Reaction in CsPbBr3 Nanocrystals towards Tunable and High Photoluminescence. J. Mater. Chem. C 2018, 6, 5506– 5513,  DOI: 10.1039/c8tc00990b
      24
      An anion-driven Sn2+ exchange reaction in CsPbBr3 nanocrystals towards tunable and high photoluminescence
      Li, Meng; Zhang, Xiao; Matras-Postolek, Katarzyna; Chen, Hsueh-Shih; Yang, Ping
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2018), 6 (20), 5506-5513CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      Fast and efficient ion-exchange reactions endow CsPbX3 nanocrystals (NCs) with superior photoluminescence (PL) properties. In this study, SnX2 (X = I, Cl) was used as a Sn precursor to conduct the cation exchange reaction, which was promoted by anion exchange between the parent CsPbBr3 NCs and the guest X in SnX2. The anion-driven cation exchange reaction occurred efficiently (10 min). CsSnI3 NCs were created by ion-exchange reactions between CsPbBr3 NCs and the SnI2 precursor. The CsSnI3 NCs retained the initial morphol. of CsPbBr3 NCs and revealed a high PL efficiency (59%) and prolonged PL lifetime. In contrast, the exchange reaction of Sn2+ ions in CsPbBr3 NCs did not occur in a short time using SnBr2 as a precursor. After the cation exchange reaction, the 4f peaks of Pb ions in XPS spectra shifted to low binding energies as compared to those of the parent CsPbX3 NCs. This is ascribed to the increase in the no. of Pb-oleate (Pb-OA) species. Contrary to the hot-injection method used to synthesize CsSnI3 NCs, the kinetically controlled ion exchange reactions lead to the synthesis of CsSnI3 NCs with a high structural stability. Thus, an anion-exchange-promoted cation exchange reaction is a particularly efficient versatile tool to dope Sn2+ into CsPbX3 NCs.
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    25. 25
      Yao, J.-S. Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals Based Light-Emitting Diodes. J. Am. Chem. Soc. 2018, 140, 3626– 3634,  DOI: 10.1021/jacs.7b11955
      25
      Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals Based Light-Emitting Diodes
      Yao, Ji-Song; Ge, Jing; Han, Bo-Ning; Wang, Kun-Hua; Yao, Hong-Bin; Yu, Hao-Lei; Li, Jian-Hai; Zhu, Bai-Sheng; Song, Ji-Zhong; Chen, Chen; Zhang, Qun; Zeng, Hai-Bo; Luo, Yi; Yu, Shu-Hong
      Journal of the American Chemical Society (2018), 140 (10), 3626-3634CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A novel strategy to enhance the photo/electroluminescence efficiency of CsPbBr3 perovskite nanocrystals (NCs) through doping of heterovalent Ce3+ via a facile hot-injection method is proposed. The Ce3+ was chosen as the dopant for CsPbBr3 NCs by virtue of its similar ion radius and formation of higher energy level of conduction band with Br in comparison with the Pb2+ cation to maintain the integrity of perovskite structure without introducing addnl. trap states. By increasing the doping amt. of Ce3+ in CsPbBr3 NCs to 2.88% (at. percentage of Ce compared to Pb), the luminescence quantum yield (PLQY) of CsPbBr3 NCs reached up to 89%, a factor of 2 increase in comparison with the native, undoped ones. The ultrafast transient absorption and time-resolved luminescence (PL) spectroscopy unraveled that the Ce3+-doping can significantly modulate the PL kinetics to enhance the PL efficiency of doped CsPbBr3 NCs. The LED device fabricated by adopting Ce3+-doped CsPbBr3 NCs as the emitting layers exhibited a pronounced improvement of electroluminescence with external quantum efficiency (EQE) from 1.6% to 4.4% via the Ce3+-doping.
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    26. 26
      Begum, R.; Parida, M. R.; Abdelhady, A. L.; Murali, B.; Alyami, N. M.; Ahmed, G. H.; Hedhili, M. N.; Bakr, O. M.; Mohammed, O. F. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping. J. Am. Chem. Soc. 2017, 139, 731– 737,  DOI: 10.1021/jacs.6b09575
      26
      Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping
      Begum, Raihana; Parida, Manas R.; Abdelhady, Ahmed L.; Murali, Banavoth; Alyami, Noktan M.; Ahmed, Ghada H.; Hedhili, Mohamed Nejib; Bakr, Osman M.; Mohammed, Omar F.
      Journal of the American Chemical Society (2017), 139 (2), 731-737CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Since compelling device efficiencies of perovskite solar cells were achieved, investigative efforts have turned to understand other key challenges in these systems, such as engineering interfacial energy-level alignment and charge transfer (CT). However, these types of studies on perovskite thin-film devices are impeded by the morphol. and compositional heterogeneity of the films and their ill-defined surfaces. Here, we use well-defined ligand-protected perovskite nanocrystals (NCs) as model systems to elucidate the role of heterovalent doping on charge-carrier dynamics and energy level alignment at the interface of perovskite NCs with mol. acceptors. More specifically, we develop an in situ doping approach for colloidal CsPbBr3 perovskite NCs with heterovalent Bi3+ ions by hot injection to precisely tune their band structure and excited-state dynamics. This synthetic method allowed us to map the impact of doping on CT from the NCs to different mol. acceptors. Using time-resolved spectroscopy with broadband capability, we clearly demonstrate that CT at the interface of NCs can be tuned and promoted by metal ion doping. We found that doping increases the energy difference between states of the mol. acceptor and the donor moieties, subsequently facilitating the interfacial CT process. This work highlights the key variable components not only for promoting interfacial CT in perovskites, but also for establishing a higher degree of precision and control over the surface and the interface of perovskite mol. acceptors.
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    27. 27
      Zhang, X.; Wang, H.; Hu, Y.; Pei, Y.; Wang, S.; Shi, Z.; Colvin, V. L.; Wang, S.; Zhang, Y.; Yu, W. W. Strong Blue Emission from Sb3+ -Doped Super Small CsPbBr3 Nanocrystals. J. Phys. Chem. Lett. 2019, 10, 1750– 1756,  DOI: 10.1021/acs.jpclett.9b00790
      27
      Strong Blue Emission from Sb3+-Doped Super Small CsPbBr3 Nanocrystals
      Zhang, Xiangtong; Wang, Hua; Hu, Yue; Pei, Yixian; Wang, Shixun; Shi, Zhifeng; Colvin, Vicki L.; Wang, Shengnian; Zhang, Yu; Yu, William W.
      Journal of Physical Chemistry Letters (2019), 10 (8), 1750-1756CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Colloidal lead halide perovskite nanocrystals (NCs) have high tunability in the visible light region and high photoluminescence quantum yields (PL QYs) for green and red emissions, but bright blue emission is still a challenge. Super small CsPbBr3 perovskite NCs emit blue light around 460 nm with a narrow peak width, and they do not have the problem of phase sepn. like their Cl-Br counterparts. However, the blue emission from super small CsPbBr3 NCs easily becomes green over time, and their PL QY is still low. The doping of Sb3+ ions successfully reduced the surface energy, improved the lattice energy, passivated the defect states below the band gap, eventually boosted the PL QY of blue emission to 73.8%, and resulted in better spectral stability even at elevated temps. in soln. (40-100 °C). Its CIE coordinates were (0.14, 0.06), which are close to the primary blue color (0.155, 0.070) according to the NTSC TV color std.
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    28. 28
      Liu, M.; Zhong, G.; Yin, Y.; Miao, J.; Li, K.; Wang, C.; Xu, X.; Shen, C.; Meng, H. Aluminum-Doped Cesium Lead Bromide Perovskite Nanocrystals with Stable Blue Photoluminescence Used for Display Backlight. Adv. Sci. 2017, 4, 1700335,  DOI: 10.1002/advs.201700335
      28
      Aluminum-Doped Cesium Lead Bromide Perovskite Nanocrystals with Stable Blue Photoluminescence Used for Display Backlight
      Liu Ming; Yin Yongming; Miao Jingsheng; Li Ke; Wang Chengqun; Xu Xiuru; Shen Clifton; Meng Hong; Zhong Guohua
      Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2017), 4 (11), 1700335 ISSN:2198-3844.
      Bright and stable blue emitters with narrow full-width at half-maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al(3+)) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead-halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion-exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red-emitting CdSe@ZnS NCs result in UV-pumped white light-emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU-R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low-cost, earth-abundant, solution-processable Al-doped perovskite NCs can be promising candidate materials for blue down-conversion layer in backlit displays.
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    29. 29
      Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L. Genesis, Challenges and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater. 2018, 17, 394– 405,  DOI: 10.1038/s41563-018-0018-4
      29
      Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals
      Akkerman, Quinten A.; Raino, Gabriele; Kovalenko, Maksym V.; Manna, Liberato
      Nature Materials (2018), 17 (5), 394-405CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
      A review. Lead halide perovskites (LHPs) in the form of nanometer-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same exptl. mindset and theor. framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.
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    30. 30
      Ng, C. K.; Wang, C.; Jasieniak, J. J. Synthetic Evolution of Colloidal Metal Halide Perovskite Nanocrystals. Langmuir 2019, 35, 11609,  DOI: 10.1021/acs.langmuir.9b00855
      30
      Synthetic Evolution of Colloidal Metal Halide Perovskite Nanocrystals
      Ng, Chun Kiu; Wang, Chujie; Jasieniak, Jacek J.
      Langmuir (2019), 35 (36), 11609-11628CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A review. Metal halide perovskite semiconductor nanocrystals have emerged as a lucrative class of materials for many optoelectronic applications. By leveraging the synthetic toolboxes developed from decades of research into more traditional semiconductor nanocrystals, remarkable progress has been made across these materials in terms of their structural, compositional, and optoelectronic control. Here, we review this progress in terms of their underlying formation stages, synthetic approaches, and postsynthetic treatment steps. This assessment highlights the rapidly maturing nature of the perovskite nanocrystal field, particularly with regard to their lead-based derivs. It further demonstrates that significant challenges remain around precisely controlling their nucleation and growth processes. In going forward, a deeper understanding of the role of precursors and ligands will significantly bolster the versatility in the size, shape, compn., and functional properties of these exciting materials.
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    31. 31
      Huang, G.; Wang, C.; Xu, S.; Zong, S.; Lu, J.; Wang, Z.; Lu, C.; Cui, Y. Postsynthetic Doping of MnCl2 Molecules into Preformed CsPbBr3 Perovskite Nanocrystals via a Halide Exchange-Driven Cation Exchange. Adv. Mater. 2017, 29, 1700095,  DOI: 10.1002/adma.201700095
      There is no corresponding record for this reference.
    32. 32
      Pradeep, K. R.; Viswanatha, R. Mechanism of Mn Emission: Energy Transfer vs Charge Transfer Dynamics in Mn-Doped Quantum Dots. APL Mater. 2020, 8, 020901,  DOI: 10.1063/1.5140888
      32
      Mechanism of Mn emission: Energy transfer vs charge transfer dynamics in Mn-doped quantum dots
      Pradeep, K. R.; Viswanatha, Ranjani
      APL Materials (2020), 8 (2), 020901CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
      A review. In the quest for new functional materials, transition metal doping in semiconductors has attracted significant attention, wherein introduction of dopant atoms alters a range of phys. properties of the host such as its optical, magnetic, and electronic properties. Hence, the choice of appropriate dopants to meet the current challenges makes semiconductor doping a highly versatile field. In the past, Mn doping in II-VI semiconductors has been extensively studied. The interest in these systems arises from a prominent orange emission from an optically forbidden state. An extended debate in the literature spanning the last three decades has so far shed light on various anomalous properties of Mn emission, specifically in quantum-confined systems leading to more questions. In this perspective, we review the literature with specific emphasis on the mechanism of Mn emission and an understanding of the electron-hole pathway during the excitation and de-excitation process in doped quantum dots. We explore various phenomena of energy and charge transfer mechanisms along with expts. in support of these phenomena which can eventually lead to a better understanding of spin driven optoelectronics. (c) 2020 American Institute of Physics.
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    33. 33
      Meinardi, F.; Akkerman, Q. A.; Bruni, F.; Park, S.; Mauri, M.; Dang, Z.; Manna, L.; Brovelli, S. Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators. ACS Energy Lett. 2017, 2, 2368– 2377,  DOI: 10.1021/acsenergylett.7b00701
      33
      Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators
      Meinardi, Francesco; Akkerman, Quinten A.; Bruni, Francesco; Park, Sungwook; Mauri, Michele; Dang, Zhiya; Manna, Liberato; Brovelli, Sergio
      ACS Energy Letters (2017), 2 (10), 2368-2377CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Halide perovskite nanocrystals (NCs) are promising soln.-processed emitters for low-cost optoelectronics and photonics. Doping adds a degree of freedom for their design and enables us to fully decouple their absorption and emission functions. This is paramount for luminescent solar concentrators (LSCs) that enable fabrication of electrode-less solar windows for building-integrated photovoltaic applications. Here, we demonstrate the suitability of manganese-doped CsPbCl3 NCs as reabsorption-free emitters for large-area LSCs. Light propagation measurements and Monte Carlo simulations indicate that the dopant emission is unaffected by reabsorption. Nanocomposite LSCs were fabricated via mass copolymn. of acrylate monomers, ensuring thermal and mech. stability and optimal compatibility of the NCs, with fully preserved emission efficiency. As a result, perovskite LSCs behave closely to ideal devices, in which all portions of the illuminated area contribute equally to the total optical power. These results demonstrate the potential of doped perovskite NCs for LSCs, as well as for other photonic technologies relying on low-attenuation long-range optical wave guiding.
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    34. 34
      Chen, W.; Shi, T.; Du, J.; Zang, Z.; Yao, Z.; Li, M.; Sun, K.; Hu, W.; Leng, Y.; Tang, X. Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices. ACS Appl. Interfaces 2018, 10, 43978– 43986,  DOI: 10.1021/acsami.8b14046
      34
      Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices
      Chen, Weiwei; Shi, Tongchao; Du, Juan; Zang, Zhigang; Yao, Zhiqiang; Li, Meng; Sun, Kuan; Hu, Wei; Leng, Yuxin; Tang, Xiaosheng
      ACS Applied Materials & Interfaces (2018), 10 (50), 43978-43986CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      As an outstanding less-Pb candidate, doping Mn2+ ions into perovskite quantum dots (QDs) has received significant interest in the application of light-emitting diodes (LEDs). However, their further applications are impeded by poor chem. instability. Here, the silica-wrapped Mn-doped CsPbCl3 QDs are fabricated via hydrolyzing (3-aminopropyl) triethoxysilane with improved operational stability. Also, the photoluminescence quantum yield as high as 55.4% for the CsPbMnCl3@SiO2 composite is achieved. Silica wrapping can protect the perovskite QDs from damage by temp. and humidity as well as anion exchange. Furthermore, white LED devices are prepd. by employing the mixt. of green CsPbBr3 QDs and orange-red CsPbMnCl3@SiO2 composites. The as-obtained white LED device operated at a forward current of 20 mA exhibits bright natural light with a high luminous efficiency of 77.59 lm/W, and the corresponding color rendering index of 82 and color temp. (CCT) of 3950 K are obtained. Addnl., the electroluminescence spectrum shows nearly no variation after 24 h operation. This work will promote the Mn-doped CsPbCl3 QDs material to the practical application in solid-state LEDs.
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    35. 35
      Chen, Z. Highly Efficient Mn-Doped CsPb(Br/Cl)3 Mixed-Halide Perovskite via a Simple Large-Scale Synthesis Method. Mater. Sci. Eng. B 2021, 273, 115426,  DOI: 10.1016/j.mseb.2021.115426
      35
      Highly efficient Mn-doped CsPb(Br/Cl)3 mixed-halide perovskite via a simple large-scale synthesis method
      Chen, Zhihao; He, Haiyang; Wen, Zhuoqi; Cui, Zhongjie; Mei, Shiliang; Yang, Dan; Wei, Xian; Zhang, Wanlu; Xie, Fengxian; Yang, Bobo; Guo, Ruiqian
      Materials Science & Engineering, B: Advanced Functional Solid-State Materials (2021), 273 (), 115426CODEN: MSBTEK; ISSN:0921-5107. (Elsevier B.V.)
      Broadband emission Mn2+ doped lead halide perovskites are deemed as promising phosphor materials for solid state white light-emitting-diodes (WLEDs). Herein, we report a facile gram-scale synthesis of Mn-doped CsPb(Br/Cl)3 phosphors by doping MnCl2 into CsPbBr3 perovskite nanocrystals at room temp. The obtained phosphors present dual-color emission with blue emission at 463 nm and red emission at 602 nm. Increasing MnCl2 doping amt. can enhance the red emission while more 3-Aminopropyltrimethoxysilane (APTMS) ligands can repress Mn related impurity and provide high stability. Further, two kinds of WLEDs (monocomponnet and two-component) are demonstrated. The monocomponent WLED exhibits warm white light under various driving currents (30 mA-150 mA), and the two-component WLED shows good chromatic performance close to ideal white light (0.33, 0.33), demonstrating their potential applications in WLED devices.
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    36. 36
      Zheng, Y.; Yuan, X.; Yang, J.; Li, Q.; Yang, X.; Fan, Y.; Li, H.; Liu, H.; Zhao, J. Cu Doping-Enhanced Emission Efficiency of Mn2+ in Cesium Lead Halide Perovskite Nanocrystals for Efficient White Light-Emitting Diodes. J. Lumin. 2020, 227, 117586,  DOI: 10.1016/j.jlumin.2020.117586
      36
      Cu doping-enhanced emission efficiency of Mn2+ in cesium lead halide perovskite nanocrystals for efficient white light-emitting diodes
      Zheng, Yuzhu; Yuan, Xi; Yang, Jian; Li, Qiuyan; Yang, Xinxuan; Fan, Yi; Li, Haibo; Liu, Huilian; Zhao, Jialong
      Journal of Luminescence (2020), 227 (), 117586CODEN: JLUMA8; ISSN:0022-2313. (Elsevier B.V.)
      Enhancing emission efficiency of Mn2+ in blue-orange dual-emitting Mn doped cesium lead halide perovskite nanocrystals (NCs) with high photoluminescence quantum yields (PL QYs) is important to fabricate high efficiency white light emitting diodes for solid state lighting. The synthesis and luminescent properties of Mn doped CsPbCl3-xBrx NCs through anion exchange of Mn and Cu co-doped CsPbCl3 NCs with PbBr2 at room temp. were studied by means of steady-state and time-resolved PL spectroscopy. The high Mn2+ PL QYs of 52-63% were obtained in the initial Mn and Cu co-doped CsPbCl3 NCs synthesized under various Mn/Pb/Cu molar ratios at 190 °C by hot injection method. A record Mn2+ PL QY up to 53% was achieved in the blue (450 nm) -orange (600 nm) dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs through anion exchange. The enhancement of Mn emission efficiencies was attributed to reduced defect states in the doped NCs due to the incorporation of Cu ions. The efficient warm white light emitting diodes with color rendering index of 85 and luminous efficacy of 69 lm/W were fabricated by combination of the blue-orange dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs and green emissive CsPbBr3@Cs4PbBr6 core/shell NCs. The improved color rendering index was demonstrated with increasing Mn content.
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    37. 37
      Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. 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
      37
      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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    38. 38
      Cao, Z.; Li, J.; Wang, L.; Xing, K.; Yuan, X.; Zhao, J.; Gao, X.; Li, H. Enhancing Luminescence of Intrinsic and Mn Doped CsPbCl3 Perovskite Nanocrystals through Co2+ Doping. Mater. Res. Bull. 2020, 121, 110608,  DOI: 10.1016/j.materresbull.2019.110608
      38
      Enhancing luminescence of intrinsic and Mn doped CsPbCl3 perovskite nanocrystals through Co2+ doping
      Cao, Zhen; Li, Ji; Wang, Li; Xing, Ke; Yuan, Xi; Zhao, Jialong; Gao, Xin; Li, Haibo
      Materials Research Bulletin (2020), 121 (), 110608CODEN: MRBUAC; ISSN:0025-5408. (Elsevier Ltd.)
      In this work, the effects of Co2+ ions on the structural and luminescent properties of intrinsic and Mn doped CsPbCl3 NCs were studied by using photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) spectroscopy, and transmission electron microscopy (TEM). The undoped and Mn doped CsPbCl3 NCs with various Co/Pb molar ratios were synthesized at 190°C. It was found that the quantum yields of purple emissions in these CsPbCl3 NCs were greatly enhanced up to 30% after Co2+ ions were doped. The diffraction peaks in XRD patterns shifted to a large angle with the increase of Co/Pb molar ratio, indicating Co doping in Pb-site. Further both intrinsic and Mn doped CsPbCl3 NCs exhibited uniform cubes with av. sizes of 8-10 nm and good crystallinity after Co doping. The enhancement of purple emissions from excitons in the CsPbCl3 NCs was related to the redn. of nonradiative defects in these NCs through Co2+ doping.
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    39. 39
      Xing, K.; Yuan, X.; Wang, Y.; Li, J.; Wang, Y.; Fan, Y.; Yuan, L.; Li, K.; Wu, Z.; Li, H.; Zhao, J. Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride. J. Phys. Chem. Lett. 2019, 10, 4177– 4184,  DOI: 10.1021/acs.jpclett.9b01588
      39
      Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride
      Xing, Ke; Yuan, Xi; Wang, Yu; Li, Ji; Wang, Yunjun; Fan, Yi; Yuan, Long; Li, Kai; Wu, Zhijian; Li, Haibo; Zhao, Jialong
      Journal of Physical Chemistry Letters (2019), 10 (15), 4177-4184CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      It is challenging to improve the emission efficiency of Mn-doped CsPbCl3 (Mn:CsPbCl3) nanocrystals (NCs) because the excellent optical performances are dependent on high doping efficiency and few defects and traps. Steady-state and time-resolved luminescence (PL) spectroscopies were used to study the luminescence properties of Mn:CsPbCl3 NCs with different Mn doping levels synthesized in the presence of Ni chloride. The doping efficiency of Mn ions in Mn:CsPbCl3 NCs was greatly enhanced in the presence of NiCl2, and the PL wavelength of Mn2+ ions was tuned from 594 to 638 nm by varying the concn. of dopant Mn from 0.11% to 15.25%. The high emission quantum yields of Mn:CsPbCl3 NCs with orange and red emissions peaked at 600 and 620 nm in hexane were 70% and 39%, resp. The improvement in doping and emission efficiencies of Mn2+ was attributed to the enhanced formation energies of the Mn doping under the Mn and Ni codoped configuration and the resulting redn. of defects and traps in Mn:CsPbCl3 NCs with incorporation of Ni2+ ions.
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    40. 40
      Zhang, J.; Zheng, Y.; Liu, G.; Ma, Y.; Gong, L.; Guan, R.; Cui, X.; Yan, J.; Zhao, J.; Yang, J. Pressure-Engineered Optical and Charge Transport Properties of Mn2+/Cu2+ Codoped CsPbCl3 Perovskite Nanocrystals via Structural Progression. ACS Appl. Mater. Interfaces 2020, 12, 48225– 48236,  DOI: 10.1021/acsami.0c15068
      40
      Pressure-Engineered Optical and Charge Transport Properties of Mn2+/Cu2+ Codoped CsPbCl3 Perovskite Nanocrystals via Structural Progression
      Zhang, Junkai; Zheng, Yuzhu; Liu, Guangtao; Ma, Yanzhang; Gong, Lei; Guan, Renquan; Cui, Xiaoyan; Yan, Jiejuan; Zhao, Jialong; Yang, Jinghai
      ACS Applied Materials & Interfaces (2020), 12 (42), 48225-48236CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      In this work, compared with the corresponding pure CsPbCl3 nanocrystals (NCs) and Mn2+-doped CsPbCl3 NCs, Mn2+/Cu2+-codoped CsPbCl3 NCs exhibited improved photoluminescence (PL) and photoluminescence quantum yields (PL QYs) (57.6%), prolonged PL lifetimes (1.78 ms), and enhanced thermal endurance (523 K) as a result of efficient Mn2+ doping (3.66%) induced by the addn. of CuCl2. Furthermore, we applied pressure on Mn2+/Cu2+-codoped CsPbCl3 NCs to reveal that a red shift of photoluminescence followed by a blue shift was caused by band gap evolution and related to the structural phase transition from cubic to orthorhombic. Moreover, we also found that under the preheating condition of 523 K, such phase transition exhibited obvious morphol. invariance, accompanied by significantly enhanced cond. The pressure applied to the products treated with high temp. enlarged the elec. difference and easily intensified the interface by closer packaging. Interestingly, defect-triggered mixed ionic and electronic conducting (MIEC) was obsd. in annealed NCs when the applied pressure was 2.9 GPa. The pressure-dependent ionic conduction was closely related to local nanocrystal amorphization and increased deviatoric stress, as clearly described by in situ impedance spectra. Finally, retrieved products exhibited better cond. (improved by 5-6 times) and enhanced photoelec. response than those when pressure was not applied. Our findings not only reveal the pressure-tuned optical and elec. properties via structural progression but also open up the promising exploration of more amorphous all-inorg. CsPbX3-based photoelec. applications.
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    41. 41
      Shao, H.; Bai, X.; Cui, H.; Pan, G.; Jing, P.; Qu, S.; Zhu, J.; Zhai, Y.; Dong, B.; Song, H. White Light Emission in Bi3+/Mn2+ Ion Co-Doped CsPbCl3 Perovskite Nanocrystals. Nanoscale 2018, 10, 1023– 1029,  DOI: 10.1039/c7nr08136g
      41
      White light emission in Bi3+/Mn2+ ion co-doped CsPbCl3 perovskite nanocrystals
      Shao, He; Bai, Xue; Cui, Haining; Pan, Gencai; Jing, Pengtao; Qu, Songnan; Zhu, Jinyang; Zhai, Yue; Dong, Biao; Song, Hongwei
      Nanoscale (2018), 10 (3), 1023-1029CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Colloidal perovskite nanocrystals (NCs), esp. the fully inorg. cesium lead halide (CsPbX3, X = Cl, Br, I) NCs, have been considered as promising candidates for lighting and display applications due to their narrow band emission, tunable band gap and high photoluminescence quantum yields (QYs). However, owing to the anion exchange in the CsPbX3 NCs, stable multi-color and white light emissions are difficult to achieve, thus limiting their practical optoelectronic applications. In this work, dual ion Bi3+/Mn2+ codoped CsPbCl3 perovskite NCs were prepd. through the hot injection method for the first time to the best of our knowledge. Through simply adjusting the doping ion concns., the codoped NCs exhibited tunable emissions spanning the wide range of correlated color temp. (CCT) from 19 000 K to 4250 K under UV excitation. This interesting spectroscopic behavior benefits from efficient energy transfer from the perovskite NC host to the intrinsic energy levels of Bi3+ or Mn2+ doping ions. Finally, taking advantage of the cooperation between the excitonic transition of the CsPbCl3 perovskite NC host and the intrinsic emissions from Bi3+ and Mn2+ ions, white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.29) was developed in the codoped CsPbCl3 NCs.
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    42. 42
      Cai, T.; Wang, J.; Li, W.; Hills-Kimball, K.; Yang, H.; Nagaoka, Y.; Yuan, Y.; Zia, R.; Chen, O. Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators. Adv. Sci. 2020, 7, 2001317,  DOI: 10.1002/advs.202001317
      42
      Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators
      Cai, Tong; Wang, Junyu; Li, Wenhao; Hills-Kimball, Katie; Yang, Hanjun; Nagaoka, Yasutaka; Yuan, Yucheng; Zia, Rashid; Chen, Ou
      Advanced Science (Weinheim, Germany) (2020), 7 (18), 2001317CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot-injection technique is reported. The resulting NCs show a unique triple-wavelength emission covering UV/blue, visible, and near-IR regions. By optimizing the dopant concns., the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter-dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chem. studies and future applications of perovskite NCs.
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    43. 43
      Akkerman, Q. A.; Meggiolaro, D.; Dang, Z.; De Angelis, F.; Manna, L. Fluorescent Alloy CsPbxMn1-XI3 Perovskite Nanocrystals with High Structural and Optical Stability. ACS Energy Lett. 2017, 2, 2183– 2186,  DOI: 10.1021/acsenergylett.7b00707
      43
      Fluorescent Alloy CsPbxMn1-xI3 Perovskite Nanocrystals with High Structural and Optical Stability
      Akkerman, Quinten A.; Meggiolaro, Daniele; Dang, Zhiya; De Angelis, Filippo; Manna, Liberato
      ACS Energy Letters (2017), 2 (9), 2183-2186CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      CsPbI3 nanocrystals are still limited in their use because of their phase instability as they degrade into the yellow nonemitting δ-CsPbI3 phase within a few days. We show that alloyed CsPbxMn1-xI3 nanocrystals have essentially the same optical features and crystal structure as the parent α-CsPbI3 system, but they are stable in films and in soln. for periods over a month. The stabilization stems from a small decrease in the lattice parameters slightly increasing the Goldsmith tolerance factor, combined with an increase in the cohesive energy. Finally, hybrid d. functional calcns. confirm that the Mn2+ levels fall within the conduction band, thus not strongly altering the optical properties.
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    44. 44
      Wang, Y.; Chen, Y.; Zhang, T.; Wang, X.; Zhao, Y. Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics. Adv. Mater. 2020, 32, 2001025,  DOI: 10.1002/adma.202001025
      44
      Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics
      Wang, Yong; Chen, Yuetian; Zhang, Taiyang; Wang, Xingtao; Zhao, Yixin
      Advanced Materials (Weinheim, Germany) (2020), 32 (45), 2001025CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Research on chem. stable inorg. perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorg. perovskites, CsPbI3 with good chem. components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells. Comparing to the anisotropic org. cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI3 exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI3 induces the challenges of different crystal phase competition and room temp. phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI3 perovskite are presented. The development of various soln. chem. approaches for depositing high-quality phase-pure CsPbI3 perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI3 are discussed. The latest exptl. and theor. studies on the fundamental phys. properties of photoactive phase CsPbI3 have deepened the understanding of inorg. perovskites. The future development and research directions toward achieving highly stable CsPbI3 materials will further advance inorg. perovskite for highly stable and efficient photovoltaics.
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    45. 45
      Thanh, N. T. K.; Maclean, N.; Mahiddine, S. Mechanisms of Nucleation and Growth of Nanoparticles in Solution. Chem. Rev. 2014, 114, 7610– 7630,  DOI: 10.1021/cr400544s
      45
      Mechanisms of Nucleation and Growth of Nanoparticles in Solution
      Thanh, Nguyen T. K.; MacLean, N.; Mahiddine, S.
      Chemical Reviews (Washington, DC, United States) (2014), 114 (15), 7610-7630CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. This work covers the area of crystal growth of nanoparticles in soln. The authors first discuss classical crystal growth and crystal nucleation and the formation of particle size distribution. They then continue the discussion of crystal growth with the coverage of the theories of the LaMer Mechanism, Ostwald Ripening, Digestive Ripening, Finke-Watzky two step mechanism, coalescence and orientated attachment, and intraparticle growth. They then discuss literature examples of nanoparticle formation of copper, silver, and gold noble metals, and metal oxides. The use of nanoparticle formation for the formation of quantum dots are also given.
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    46. 46
      Stoumpos, C. C. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Cryst. Growth Des. 2013, 13, 2722– 2727,  DOI: 10.1021/cg400645t
      46
      Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection
      Stoumpos, Constantinos C.; Malliakas, Christos D.; Peters, John A.; Liu, Zhifu; Sebastian, Maria; Im, Jino; Chasapis, Thomas C.; Wibowo, Arief C.; Chung, Duck Young; Freeman, Arthur J.; Wessels, Bruce W.; Kanatzidis, Mercouri G.
      Crystal Growth & Design (2013), 13 (7), 2722-2727CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      The synthesis, crystal growth, and structural and optoelectronic characterization was carried out for the perovskite compd. CsPbBr3. This compd. is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photocond. response, with detector resoln. comparable to that of com., state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temp. does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approx. equal. The μτ product for electrons is comparable to Cd Zn telluride (CZT) and that for holes is 10 times higher than CZT.
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    47. 47
      Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr., Sect. A 1976, 32, 751– 767,  DOI: 10.1107/s0567739476001551
      There is no corresponding record for this reference.
    48. 48
      Wang, X.; Xu, Z.; Zhuo, S.; Hu, P.; Yang, Y.; Zhou, B.; Zhang, W.-H. Strain Modulation for High Brightness Blue Luminescence of Pr3+-Doped Perovskite Nanocrystals via Siloxane Passivation. ACS Appl. Electron. Mater. 2021, 3, 3815– 3823,  DOI: 10.1021/acsaelm.1c00422
      48
      Strain Modulation for High Brightness Blue Luminescence of Pr3+-Doped Perovskite Nanocrystals via Siloxane Passivation
      Wang, Xianghua; Xu, Zhiliang; Zhuo, Shaoqi; Hu, Peng; Yang, Yong; Zhou, Bin; Zhang, Wen-Hua
      ACS Applied Electronic Materials (2021), 3 (9), 3815-3823CODEN: AAEMBP; ISSN:2637-6113. (American Chemical Society)
      High performance CsPbBr3 nanocrystals (NCs) were synthesized via a hot injection method followed by a room-temp. ligand exchange modification using 3-mercaptopropyltrimethoxysilane (MPTMS). The ligand exchange promotes crystal growth and enhances the photoluminescence quantum yield (PLQY) of the NCs to near unity. The oscillator strength of the interband transition based on UV-vis absorption was surprisingly amplified by a factor of 2.5. The NC's surface was passivated via S-Pb polar covalent bonding, which shifts the thermodn. equil. and favors NC growth with a higher Br-to-Pb at. ratio on the surface. Moreover, the perovskite lattice was strained by a cross-linked polymeric network of self-condensed siloxane. The strain within CsPbBr3 NCs was modulated by mixing at room temp. with Cs3PrCl6 NCs for controlled halide exchange and Pr doping; thereby blue emission from the Pr-doped CsPb(Cl/Br)3 NCs was achieved with optimized brightness (PLQY = 88%) at 464 nm.
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    49. 49
      Yuce, H. Understanding the Impact of SrI2 Additive on the Properties of Sn-Based Halide Perovskites. Opt. Mater. 2021, 123, 111806,  DOI: 10.1016/j.optmat.2021.111806
      There is no corresponding record for this reference.
    50. 50
      Becker, M. A. Bright Triplet Excitons in Caesium Lead Halide Perovskites. Nature 2018, 553, 189– 193,  DOI: 10.1038/nature25147
      50
      Bright triplet excitons in caesium lead halide perovskites
      Becker, Michael A.; Vaxenburg, Roman; Nedelcu, Georgian; Sercel, Peter C.; Shabaev, Andrew; Mehl, Michael J.; Michopoulos, John G.; Lambrakos, Samuel G.; Bernstein, Noam; Lyons, John L.; Stoferle, Thilo; Mahrt, Rainer F.; Kovalenko, Maksym V.; Norris, David J.; Raino, Gabriele; Efros, Alexander L.
      Nature (London, United Kingdom) (2018), 553 (7687), 189-193CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
      Nanostructured semiconductors emit light from electronic states known as excitons. For org. materials, Hund's rules state that the lowest-energy exciton is a poorly emitting triplet state. For inorg. semiconductors, similar rules predict an analog of this triplet state known as the 'dark exciton'. Because dark excitons release photons slowly, hindering emission from inorg. nanostructures, materials that disobey these rules have been sought. However, despite considerable exptl. and theor. efforts, no inorg. semiconductors have been identified in which the lowest exciton is bright. Here we show that the lowest exciton in caesium lead halide perovskites (CsPbX3, with X = Cl, Br or I) involves a highly emissive triplet state. We first use an effective-mass model and group theory to demonstrate the possibility of such a state existing, which can occur when the strong spin-orbit coupling in the conduction band of a perovskite is combined with the Rashba effect. We then apply our model to CsPbX3 nanocrystals, and measure size- and compn.-dependent fluorescence at the single-nanocrystal level. The bright triplet character of the lowest exciton explains the anomalous photon-emission rates of these materials, which emit about 20 and 1,000 times faster than any other semiconductor nanocrystal at room and cryogenic temps., resp. The existence of this bright triplet exciton is further confirmed by anal. of the fine structure in low-temp. fluorescence spectra. For semiconductor nanocrystals, which are already used in lighting, lasers and displays, these excitons could lead to materials with brighter emission. More generally, our results provide criteria for identifying other semiconductors that exhibit bright excitons, with potential implications for optoelectronic devices.
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    51. 51
      Ahmed, G. H.; El-Demellawi, J. K.; Yin, J.; Pan, J.; Velusamy, D. B.; Hedhili, M. N.; Alarousu, E.; Bakr, O. M.; Alshareef, H. N.; Mohammed, O. F. Giant Photoluminescence Enhancement in CsPbCl3 Perovskite Nanocrystals by Simultaneous Dual-Surface Passivation. ACS Energy Lett. 2018, 3, 2301– 2307,  DOI: 10.1021/acsenergylett.8b01441
      51
      Giant Photoluminescence Enhancement in CsPbCl3 Perovskite Nanocrystals by Simultaneous Dual-Surface Passivation
      Ahmed, Ghada H.; El-Demellawi, Jehad K.; Yin, Jun; Pan, Jun; Velusamy, Dhinesh Babu; Hedhili, Mohamed Nejib; Alarousu, Erkki; Bakr, Osman M.; Alshareef, Husam N.; Mohammed, Omar F.
      ACS Energy Letters (2018), 3 (10), 2301-2307CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      The presence of localized trap states on the surface of CsPbCl3 perovskite nanocrystals (NCs) is one of the greatest challenges precluding the development of optoelectronic applications of these NCs. Passivation of these defect sites provides a promising pathway to remediating their electronic and optical properties, such as the photoluminescence quantum yield (PLQY). Herein, we demonstrate a postsynthetic dual-surface treatment using trivalent metal ion salts, i.e., YCl3, as a new passivation approach that enhances the PLQY up to 60% while preserving the NC size and crystal structure. Such remarkable enhancement of the PLQY along with prolongation of the av. PL lifetimes of treated NCs samples indicates effective passivation of the surface defects and subsequent suppression of the formation of surface nonradiative recombination centers. As a segue toward optoelectronic applications, we probed the photoelec. performance of the NCs using ultraflexible devices; we found that YCl3-treated CsPbCl3 NC films exhibit an order of magnitude larger photocurrent compared to their nontreated counterparts. Our exptl. and theor. results provide an insightful understanding of the effective passivating roles of Y3+ and Cl- ions on the surface of CsPbCl3 NCs, as well as offering a new path to synthesize high-quality NCs for UV light conversion applications.
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    52. 52
      Ahmed, T.; Seth, S.; Samanta, A. Boosting the Photoluminescence of CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals Covering a Wide Wavelength Range by Postsynthetic Treatment with Tetrafluoroborate Salts. Chem. Mater. 2018, 30, 3633– 3637,  DOI: 10.1021/acs.chemmater.8b01235
      52
      Boosting the Photoluminescence of CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals Covering a Wide Wavelength Range by Postsynthetic Treatment with Tetrafluoroborate Salts
      Ahmed, Tasnim; Seth, Sudipta; Samanta, Anunay
      Chemistry of Materials (2018), 30 (11), 3633-3637CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      While the Cs lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) are in limelight for their promising optical and opto-electronic properties, the trapping of charge carriers by the defect states greatly diminishes their photoluminescence quantum yield (PLQY). Herein a simple treatment with Na or NH4+ tetra-fluoroborate salt can dramatically improve the PL properties of CsPbX3 NCs emitting in the blue-yellow region. The authors have achieved near-unity PLQY for CsPbBr3 and CsPbBrxCl3-x and substantially high PLQY for CsPbCl3 and CsPbBrxI3-x NCs by this method. The effect of this treatment is also reflected from much-improved PL decay profiles of the NCs. The findings, which demonstrate the effectiveness of tetrafluoroborate ion in producing high quality photo-luminescent perovskite NCs by removing excess Pb from the surface, are expected to boost the utility of these materials in practical applications.
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    53. 53
      Bohn, B. J. Boosting Tunable Blue Luminescence of Halide Perovskite Nanoplatelets through Postsynthetic Surface Trap Repair. Nano Lett. 2018, 18, 5231– 5238,  DOI: 10.1021/acs.nanolett.8b02190
      53
      Boosting Tunable Blue Luminescence of Halide Perovskite Nanoplatelets through Postsynthetic Surface Trap Repair
      Bohn, Bernhard J.; Tong, Yu; Gramlich, Moritz; Lai, May Ling; Doeblinger, Markus; Wang, Kun; Hoye, Robert L. Z.; Mueller-Buschbaum, Peter; Stranks, Samuel D.; Urban, Alexander S.; Polavarapu, Lakshminarayana; Feldmann, Jochen
      Nano Letters (2018), 18 (8), 5231-5238CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The easily tunable emission of halide perovskite nanocrystals throughout the visible spectrum makes them an extremely promising material for light-emitting applications. Whereas high quantum yields and long-term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields, broad emission profiles, and insufficient colloidal stability. In this work, we present a facile synthetic approach for obtaining two-dimensional CsPbBr3 nanoplatelets with monolayer-precise control over their thickness, resulting in sharp photoluminescence and electroluminescence peaks with a tunable emission wavelength between 432 and 497 nm due to quantum confinement. Subsequent addn. of a PbBr2-ligand soln. repairs surface defects likely stemming from bromide and lead vacancies in a subensemble of weakly emissive nanoplatelets. The overall photoluminescence quantum yield of the blue-emissive colloidal dispersions is consequently enhanced up to a value of 73 ± 2%. Transient optical spectroscopy measurements focusing on the excitonic resonances further confirm the proposed repair process. Addnl., the high stability of these nanoplatelets in films and to prolonged UV light exposure is shown.
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    54. 54
      Parobek, D.; Roman, B. J.; Dong, Y.; Jin, H.; Lee, E.; Sheldon, M.; Son, D. H. Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals. Nano Lett. 2016, 16, 7376– 7380,  DOI: 10.1021/acs.nanolett.6b02772
      54
      Exciton-to-dopant energy transfer in Mn-doped cesium lead halide perovskite nanocrystals
      Parobek, David; Roman, Benjamin J.; Dong, Yitong; Jin, Ho; Lee, Elbert; Sheldon, Matthew; Son, Dong Hee
      Nano Letters (2016), 16 (12), 7376-7380CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX3) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl3 and CsPb(Cl/Br)3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concns. and no signature of phase sepn. The strong sensitized luminescence from d-d transition of Mn2+ ions upon band-edge excitation of the CsPbX3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 nanocrystals and well-defined ESR spectra of Mn2+ in host CsPbX3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb2+. These observations indicate that CsPbX3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.
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    55. 55
      Li, F.; Xia, Z.; Gong, Y.; Gu, L.; Liu, Q. Optical Properties of Mn2+ Doped Cesium Lead Halide Perovskite Nanocrystals via a Cation-Anion Co-Substitution Exchange Reaction. J. Mater. Chem. C 2017, 5, 9281,  DOI: 10.1039/c7tc03575f
      55
      Optical properties of Mn2+ doped cesium lead halide perovskite nanocrystals via a cation-anion co-substitution exchange reaction
      Li, Fei; Xia, Zhiguo; Gong, Yue; Gu, Lin; Liu, Quanlin
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (36), 9281-9287CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      The emission colors of cesium lead halide perovskite nanocrystals (NCs) can be controlled by dynamic ion exchange and Mn2+ doping. Herein the authors report a novel strategy for the synthesis of Cs(PbxMn1-x)(ClyBr1-y)3 NCs via a post-synthetic cation-anion cosubstitution exchange reaction to tailor their optical properties in a wide range. Colloidal CsPbBr3 and CsPb1-xMnxCl3 NCs are first prepd., sep., and then mixed together in hexane soln. The Pb2+ and Br- ions in the CsPbBr3 NCs are simultaneously exchanged for the Mn2+ and Cl- ions in the CsPb1-xMnxCl3 NCs, resulting in homogeneous Cs(PbxMn1-x)(ClyBr1-y)3, with preservation of the shape and crystal structure of the initial NCs. This in situ ion exchange method avoids the degrdn. of photoluminescence originating from the addnl. purifn. process of the NCs, and in situ Mn2+ substitution also greatly enhances the emission intensity and quantum yield of the as-obtained NCs, which is related to the bound exciton effect.
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    56. 56
      Canil, L. Tuning Halide Perovskite Energy Levels. Energy Environ. Sci. 2021, 14, 1429– 1438,  DOI: 10.1039/d0ee02216k
      56
      Tuning halide perovskite energy levels
      Canil, Laura; Cramer, Tobias; Fraboni, Beatrice; Ricciarelli, Damiano; Meggiolaro, Daniele; Singh, Ajay; Liu, Maning; Rusu, Marin; Wolff, Christian M.; Phung, Nga; Wang, Qiong; Neher, Dieter; Unold, Thomas; Vivo, Paola; Gagliardi, Alessio; De Angelis, Filippo; Abate, Antonio
      Energy & Environmental Science (2021), 14 (3), 1429-1438CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      The ability to control the energy levels in semiconductors is compelling for optoelectronic applications. In this study, we managed to tune the work function (WF) of halide perovskite semiconductors using self-assembled monolayers of small mols. to induce stable dipoles at the surface. The direction and intensity of the surface dipoles rely on specific mol.-to-surface interactions. Electron acceptor or donor mols. result in the pos. or neg. WF shifts up to several hundreds of meV. Our approach provides a versatile tool to control the WF of halide perovskite and adjust the energy level alignment at the interface with charge transport materials in perovskite-based optoelectronics. The impact on perovskite solar cells is reported and discussed in detail with the support of modeling.
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    57. 57
      Crowley, J. M.; Tahir-Kheli, J.; Goddard, W. A. Accurate Ab Initio Quantum Mechanics Simulations of Bi2Se3 and Bi2Te3 Topological Insulator Surfaces. J. Phys. Chem. Lett. 2015, 6, 3792– 3796,  DOI: 10.1021/acs.jpclett.5b01586
      57
      Accurate Ab Initio Quantum Mechanics Simulations of Bi2Se3 and Bi2Te3 Topological Insulator Surfaces
      Crowley, Jason M.; Tahir-Kheli, Jamil; Goddard, William A.
      Journal of Physical Chemistry Letters (2015), 6 (19), 3792-3796CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      It has been established exptl. that Bi2Te3 and Bi2Se3 are topol. insulators, with zero band gap surface states exhibiting linear dispersion at the Fermi energy. Std. d. functional theory (DFT) methods such as PBE lead to large errors in the band gaps for such strongly correlated systems, while more accurate GW methods are too expensive computationally to apply to the thin films studied exptl. We show here that the hybrid B3PW91 d. functional yields GW-quality results for these systems at a computational cost comparable to PBE. The efficiency of our approach stems from the use of Gaussian basis functions instead of plane waves or augmented plane waves. This remarkable success without empirical corrections of any kind opens the door to computational studies of real chem. involving the topol. surface state, and our approach is expected to be applicable to other semiconductors with strong spin-orbit coupling.
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    58. 58
      Perdew, J. P.; Levy, M. Physical Content of the Exact Kohn-Sham Orbital Energies: Band Gaps and Derivative Discontinuities. Phys. Rev. Lett. 1983, 51, 1884,  DOI: 10.1103/physrevlett.51.1884
      58
      Physical content of the exact Kohn-Sham orbital energies: band gaps and derivative discontinuities
      Perdew, John P.; Levy, Mel
      Physical Review Letters (1983), 51 (20), 1884-7CODEN: PRLTAO; ISSN:0031-9007.
      The local d. approxn. for the exchange correlation potential underestimates the fundamental band gaps of semiconductors and insulators by about 40%. It is argued that underestn. of the gap width is also to be expected from the unknown exact potential of Kohn-Sham d.-functional theory, because of deriv. discontinuities of the exchange-correlation energy. The need for an energy-dependent potential in band theory is emphasized. The center of the gap, however, is predicted exactly by the Kohn-Sham band structure.
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    59. 59
      Mori-Sánchez, P.; Cohen, A. J.; Yang, W. Localization and Delocalization Errors in Density Functional Theory and Implications for Band-Gap Prediction. Phys. Rev. Lett. 2008, 100, 146401,  DOI: 10.1103/PhysRevLett.100.146401
      59
      Localization and Delocalization Errors in Density Functional Theory and Implications for Band-Gap Prediction
      Mori-Sanchez, Paula; Cohen, Aron J.; Yang, Weitao
      Physical Review Letters (2008), 100 (14), 146401/1-146401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The band-gap problem and other systematic failures of approx. exchange-correlation functionals are explained from an anal. of total energy for fractional charges. The deviation from the correct intrinsic linear behavior in finite systems leads to delocalization and localization errors in large and bulk systems. Functionals whose energy is convex for fractional charges such as the local d. approxn. display an incorrect apparent linearity in the bulk limit, due to the delocalization error. Concave functionals also have an incorrect apparent linearity in the bulk calcn., due to the localization error and imposed symmetry. This resolves an apparent paradox and identifies the phys. nature of the error to be addressed to obtain accurate band gaps from d. functional theory.
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