Preparation of Air Stable Lead-free CsSnI3 Perovskites: Synthesis Based on CsI and SnCl2 Solutions

Objective: This study focuses on the synthesis and analysis of the morphology of CsSnI3 crystals and films based on CsI (Cesium Iodide) and Tin(II) chloride (SnCl2) solutions. The aim of this approach is to synthesize air-stable perovskites and prevent phase transitions of tin-containing perovskite, where previous studies have often reported its rapid oxidation when dissolved in dimethyl sulfoxide. Methods: CsSnI3 crystalline films were obtained from CsI and SnCl2 solutions, in which deionized water and ultrapure ethanol were used for their dissolution. Dissolution and mixing were performed at room temperature. High-purity CsI (99.99%) and SnCl2 (99.99%) powders were used to obtain solutions. To obtain a homogeneous CsSnl3 solution, the SnCl2 solution was added dropwise to the CsI solution and stirred on a magnetic stirrer at 900rpm. The resulting solution was then applied to Fluorine-doped Tin Oxide (FTO) substrates heated on a hotplate without spin coating. The samples were heated to temperatures from 60℃ to 130℃, where, depending on the rate of evaporation of the liquid, the process of formation of crystalline and thin-film structures was controlled. Results: Stable CsSnI3 films were obtained. Scanning electron microscope (SEM) and X-ray diffraction analyses of the obtained cesium tin triiodide films deposited on conventional FTO glass substrates were performed. X-ray diffraction patterns of synthesized perovskite crystals and films were obtained. Conclusion: The synthesized CsSnI3 perovskite thin films retained their black perovskite phase for more than 4 months, indicating their long-term stability. Based on the results and long-term stability performance, it can be concluded that the black phases of CsSnI3 are suitable for various applications such as photovoltaic devices.