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1. Epitaxial Growth of Lead‐Free Double Perovskite Shell for CsPbX 3 /Cs 2 SnX 6 (X = Cl, Br, and I) Core/Shell Perovskite Nanocrystals with Enhanced Photoelectric Properties and Stability

   https://doi.org/10.1002/adfm.202309480  

   Lin, Hanjie ; Li, Shuya ; Zhang, Yuchen ; Chu, Chun ; MacSwain, Walker ; Meulenberg, Robert W. ; Qiao, Quinn ; Zhao, Dong ; Zheng, Weiwei ( November 2023 , Advanced Functional Materials)

   All‐inorganic lead halide perovskite nanocrystals (NCs) have great optoelectronic properties with promising applications in light‐emitting diodes (LEDs), lasers, photodetectors, solar cells, and photocatalysis. However, the intrinsic toxicity of Pb and instability of the NCs impede their broad applications. Shell‐coating is an effective method for enhanced environmental stability while reducing toxicity by choosing non‐toxic shell materials such as metal oxides, polymers, silica, etc. However, multiple perovskite NCs can be encapsulated within the shell material and a uniform epitaxial‐type shell growth of well‐isolated NCs is still challenging. In this work, lead‐free vacancy‐ordered double perovskite Cs₂SnX₆(X = Cl, Br, and I) shells are epitaxially grown on the surface of CsPbX₃NCs by a hot‐injection method. The effectiveness of the non‐toxic double perovskite shell protection is demonstrated by the enhanced environmental and phase stability against UV illumination and water. In addition, the photoluminescence quantum yields (PL QYs) increase for the CsPbCl₃and CsPbBr₃NCs after shelling because of the type I band alignment of the core/shell materials, while enhanced charge transport properties obtained from CsPbI₃/Cs₂SnI₆core/shell NCs are due to the efficient charge separation in the type II core/shell band alignment.

    

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2. Composition‐Dependent Photoluminescence Properties and Anti‐Counterfeiting Applications of A 2 AgX 3 (A = Rb, Cs; X =  Cl, Br, I)

   https://doi.org/10.1002/adfm.202104941  

   Kumar, Pawan ; Creason, Tielyr D. ; Fattal, Hadiah ; Sharma, Manila ; Du, Mao‐Hua ; Saparov, Bayram ( September 2021 , Advanced Functional Materials)

   Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue‐emitting all‐inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A₂AgX₃(A = Rb, Cs; X = Cl, Br, I) through solid‐state synthesis is reported. In contrast to the Cu(I) analogs, A₂AgX₃are broad‐band emitters sensitive to A and X site substitutions. First‐principle calculations show that defect‐bound excitons are responsible for the observed main PL peaks in Rb₂AgX₃and that self‐trapped excitons (STEs) contribute to a minor PL peak in Rb₂AgBr₃. This is in sharp contrast to Rb₂CuX₃, in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A₂AgX₃significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A₂AgX₃are prepared and successfully used in anti‐counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A₂AgX₃suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.

    

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3. Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms

   https://doi.org/10.1364/PRJ.402411  

   Wang, Yutao ; Quintana, Xavier ; Kim, Jiyun ; Guan, Xinwei ; Hu, Long ; Lin, Chun-Ho ; Jones, Brendon Tyler ; Chen, Weijian ; Wen, Xiaoming ; Gao, Hanwei ; et al ( October 2020 , Photonics Research)

   Halide perovskites, such as methylammonium lead halide perovskites (${\mathrm{MAPbX}}_3$,$\mathrm{X}=\mathrm{I}$, Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskites${\mathrm{CsPbX}}_3$are attracting a lot of attention because replacing the organic cations with${\mathrm{Cs}}^{+}$enhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance.

    

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4. Room temperature synthesis of lead-free FASnI 3 perovskite nanocrystals with improved stability by SnF 2 additive

   https://doi.org/10.1063/5.0125100  

   Chen, Zeying ; Dhakal, Tara P. ( March 2023 , Applied Physics Reviews)

   Tin halide perovskites are among the candidates for replacing lead-based ones for less toxicity and comparable optical properties. However, stability remains a challenge due to the easier oxidation of Sn 2+ than Pb 2+ . Here, for the first time, we applied the ligand-assisted reprecipitation method to synthesize CH(NH 2 ) 2 SnI 3 (FASnI 3 ) orthorhombic perovskite nanocrystals with an average diameter of 7.7 nm and a photoluminescence emission at 825 [Formula: see text] 2 nm (1.5 eV). The influence of synthesis parameters, including precursor solvent, precipitation media, temperature, and time on optical properties of nanocrystals, was studied. By incorporating SnF 2 , the stability of the nanocrystals was improved, and the oxidation from FASnI 3 to FA 2 SnI 6 was significantly delayed, which was quantitively demonstrated and confirmed by observing the characteristic diffraction peaks of the perovskite phase using x-ray diffraction at various exposure time to air. The addition of SnF 2 is optimized to be 6%. The FASnI 3 nanocrystals stayed stable for at least 265 days under N 2 storage at room temperature and relative humidity of 20%. 

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5. Inorganic CsPb 1− x Sn x IBr 2 for Efficient Wide‐Bandgap Perovskite Solar Cells

   https://doi.org/10.1002/aenm.201800525  

   Li, Nan ; Zhu, Zonglong ; Li, Jiangwei ; Jen, Alex K. ‐Y. ; Wang, Liduo ( May 2018 , Advanced Energy Materials)

   Recently, the stability of organic–inorganic perovskite thin films under thermal, photo, and moisture stresses has become a major concern for further commercialization due to the high volatility of the organic cations in the prototype perovskite composition (CH₃NH₃PbI₃). All inorganic cesium (Cs) based perovskite is an alternative to avoid the release or decomposition of organic cations. Moreover, substituting Pb with Sn in the organic–inorganic lead halide perovskites has been demonstrated to narrow the bandgap to 1.2–1.4 eV for high‐performance perovskite solar cells. In this work, a series of CsPb_1−xSn_xIBr₂perovskite alloys via one‐step antisolvent method is demonstrated. These perovskite films present tunable bandgaps from 2.04 to 1.64 eV. Consequently, the CsPb_0.75Sn_0.25IBr₂with homogeneous and densely crystallized morphology shows a remarkable power conversion efficiency of 11.53% and a highV_ocof 1.21 V with a much improved phase stability and illumination stability. This work provides a possibility for designing and synthesizing novel inorganic halide perovskites as the next generation of photovoltaic materials.

    

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