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Secondary growth of CsPbI 3 inorganic perovskite film with an in-situ 3D-to-0D phase transformation induced by organic cation is demonstrated. Functional quaternary alkylammonium, benzyldodecyldimethylammonium (BDA+), could react with the surficial layers of CsPbI 3 film for targeted defect passivation. Such surface reconstruction as 0D/3D perovskites can greatly improve both film stability and photovoltaic performance. [Display omitted] Efficiency and stability are the main research focuses for perovskite solar cells. Inorganic perovskites like CsPbI 3 possess higher chemical stability than those with organic A-site cations, while they also exhibit higher defect density. Nonetheless, it is highly challenging to induce orderly secondary arrangement or reconstruction of inorganic perovskites with reduced defects because of their unique chemical properties. In this work, in-situ three-dimension-to-zero-dimension (3D-to-0D) phase transformation and surface reconstruction on CsPbI 3 film is achieved as induced by a functional organic cation, benzyldodecyldimethylammonium (BDA), a process of which that is similar to phase-transfer catalysis. With the help of BDABr salt treatment, 0D Cs 4 PbI 6 perovskites are secondarily formed along CsPbI 3 grain boundaries with Cs-related cationic defects passivated, yielding structures of higher stability. The BDA-CsPbI 3 films exhibit reduced non-radiative recombination and promoted charge transfer, leading to inorganic perovskite solar cells with a high power conversion efficiency of 20.63% and good operational stability. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskites have attracted increasing attention for applications in perovskite solar cells (PSCs) and optoelectronics, including light‐emitting devices (LEDs). Cesium lead halide perovskites with tunable I/Br ratios and a band gap aligning with the sunlight region are promising candidates for PSCs. Although impressive progress has been made to improve device efficiency from the initial 2.9 % with low phase stability to over 20 % with high stability, there are still questions regarding the perovskite crystal growth mechanism, especially at low temperatures. In this Minireview, we summarize recent developments in using an organic matrix, including the addition and use of organic ions, polymers, and solvent molecules, for the crystallization of black phase inorganic perovskites at temperatures lower than the phase transition point. We also discuss possible mechanisms for this low‐temperature crystallization and their effect on the stability of black phase perovskites. We conclude with an outlook and perspective for further fabrication of large‐scale inorganic perovskites for optoelectronic applications. [ABSTRACT FROM AUTHOR]