This review highlights the state-of-the-art catalytic methods for the direct asymmetric synthesis of α-chiral primary amines and demonstrates their utility in the construction of molecular complexities.
Perovskite materials and their optoelectronic devices have attracted intensive attentions in recent years. However, it is difficult to further improve the performance of perovskite devices due to the poor stability and the intrinsic deep level trap states (DLTS), which are caused by surface dangling bonds and grain boundaries. Herein, the CH 3 NH 3 PbBr 3 perovskite microcrystal is encapsulated by a dense Al 2 O 3 layer to form a microenvironment. Through optical measurement, it is found that the structure of perovskite can be healed by itself even under high temperature and long-time laser illumination. The DLTS density decreases nearly an order of magnitude, which results in 4-14 times enhancement of light emission. The observation is ascribed to the micron-level environment, which serves as a self-sufficient high-vacuum growth chamber, where the components of the perovskite are completely retained when sublimated and the decomposed atoms can re-arrange after thermal treatment. The modified structure showing high thermal stability is able to maintain excellent optical and lasing stability up to 2 years. This discovery provides a new idea and perspective for improving the stability of perovskite and can be of practical interest for perovskite device application.
photovoltaic devices (23.3%), showing great potential toward practical applications. [1] However, thermal instability of organic components (e.g., methylammonium (MA) and formamidinium (FA)) and high toxicity of heavy metal lead (Pb) pose challenges for practical applications. [2][3][4][5] To address these issues, a new perovskite family of organic-free and lead-free cesium tin tri-iodide (CsSnI 3 ) has been proposed and attracted considerable attention. [6][7][8] One of the potential candidates within the new perovskite family is the inorganic CsSnI 3 . This kind of perovskite possesses favorable direct bandgap (around 1.3 eV), high optical absorption coefficient (about 10 4 cm −1 in the visible range), and ultralow exciton binding energy (18 meV), making it very promising as a photoactive layer for PSCs' construction. [9][10][11] Since the first report in 2014 by Kumar et al., the efficiency of CsSnI 3based perovskite solar cells has witnessed steady improvement from 2.02% to 10.1% in 2021. [12,13] Such development has mainly been attributed to addressing the factors that affect the performance of the devices, such as annealing temperature, [14] film fabrication method, [15] and interface regulation. [16,17] However, little efforts have been made to Organic-free and lead-free CsSnI 3 perovskite solar cells (PSCs) have recently gained growing attention as a promising template to mitigate the thermal instability and lead toxicity of hybrid lead-based PSCs. However, the relatively low device efficiency due to the high content of Sn(II)-related defects hinders its further development. Herein, highly performed CsSnI 3−x Br x compositional perovskite-based PSCs are achieved by using dimethyl ketoxime (C 3 H 7 NO, DMKO) as a multifunctional additive. As a commercially used deoxidant, DMKO can effectively neutralize the oxygen molecule and reduce Sn 4+ back to Sn 2+ , enhancing the oxidation resistance of the film. Besides, the electron-rich oxime group (NOH) in DMKO tends to interact with Sn 2+ ions with extremely low adsorption energy less than −15 eV and inhibits defect formation, resulting in films with low defect density. The corresponding PSCs deliver a considerable open-circuit voltage (V oc ) of 0.75 V with a record efficiency as high as 11.2%, which represents the highest reported efficiency for lead-free all-inorganic PSCs thus far. More importantly, the grain surface distributed DMKO provides an in situ encapsulation of the perovskite, which results in greatly enhanced ambient stability of the un-encapsulated devices.
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