In situ Investigation of Water Interaction with Lead-Free All Inorganic Perovskite (Cs₂SnI_xCl_6–x)

Hybrid halide perovskites display a great tunability of optoelectronic properties and environmental stability by controlling the halogen anions (e.g., I, Cl, and Br). However, their water interaction and degradation mechanisms are not fully elucidated. In this work, the interaction of Cs₂SnCl₆ and Cl-enriched solid solution Cs₂SnI_0.9Cl_5.1 with water was systematically studied by in situ synchrotron X-ray diffraction and micro-Raman spectra and compared with the isostructural Cs₂SnI₆. Unlike Cs₂SnI₆, which experiences a direct dissolution in water, Cs₂SnCl₆ displays an enhanced stability and the dissolution of the Cs₂SnCl₆ accompanies with the formation of an amorphous alteration phase.  Under controlled dehydration conditions, two-dimensional Cs₂SnCl₆ flakes can be precipitated out from water solution. Furthermore, the mixed halide perovskite (Cs₂SnI_0.9Cl_5.1) experiences fast iodide dissolution in water solution and transforms to a more chloride-enriched perovskite which shows a behavior similar to Cs₂SnCl₆. The mechanistic understanding of the dissolution–precipitation process of Cs₂SnI_xCl_6–x perovskites is useful for developing new perovskites with varied halogen and controlled environmental stability.