Organic-inorganic perovskite materials are revolutionizing photovoltaics with high power conversion efficiencies, but experience significant environmental degradation and instability. In this work, the phase stability and decomposition mechanisms of lead-free all inorganic Cs₂SnI₆ perovskite upon water and moisture exposure were systematically investigated via in situ synchrotron X-ray diffraction, environmental SEM, and micro-Raman spectroscopy. A critical relative humidity (80%) is identified below which Cs₂SnI₆ perovskite is stable without decomposition. Under higher humidity or aqueous environment, Cs₂SnI₆ perovskite decomposes into SnI₄ and CsI through etch pits formation and stepwave propagation, leading to rapid crystal dissolution. A partial reversibility of the Cs₂SnI₆ perovskite upon dissolution and re-precipitation with subsequent dehydration was identified, suggesting a self-healing capability of Cs₂SnI₆ and thus enhanced air stability. Mechanistic understanding of the Cs₂SnI₆ degradation behavior can be a vital step towards developing new perovskites with enhanced environmental stability and materials performance.

有机-无机钙钛矿材料正在以高功率转换效率为光伏技术带来革命性的变化，但是却经历了严重的环境退化和不稳定性。在这项工作中，通过原位同步加速器X射线衍射，环境SEM和显微拉曼光谱系统地研究了无铅所有无机Cs ₂ SnI ₆钙钛矿在水和湿气中暴露后的相稳定性和分解机理。鉴定出临界相对湿度（80％），低于该临界湿度，Cs ₂ SnI ₆钙钛矿稳定而不会分解。在较高湿度或水性环境下，Cs ₂ SnI ₆钙钛矿分解为SnI ₄通过刻蚀坑的形成和阶跃波传播实现CsI和CsI，从而导致晶体快速溶解。溶解后Cs ₂ SnI ₆钙钛矿具有部分可逆性，再沉淀并随后脱水，这表明Cs ₂ SnI ₆具有自我修复能力，因此增强了空气稳定性。对Cs ₂ SnI ₆降解行为的机械理解可能是开发具有增强的环境稳定性和材料性能的新型钙钛矿的重要一步。