Water‐Resistant Lead‐Free Perovskitoid Single Crystal for Efficient X‐Ray Detection

Abstract Despite the rapid progress of hybrid organic–inorganic halide perovskites in optoelectronic applications, their water resistance is still limited because of the interaction of both the organic and inorganic components with water molecules. In this study, a cation engineering protocol to obtain a material with inherent high water resistance by incorporating benzamidinium (BAH) cations into the bismuth halide framework is developed. Analysis of the crystal structure indicates that (BAH)BiI₄ exhibits a molecular 1D perovskitoid structure with an edge‐sharing mode and strong noncovalent interactions within the crystal, including I•••I interaction, hydrogen bonding, and π–π stacking between adjacent BAH cations. Such strong noncovalent interactions provide excellent water resistance, with negligible decomposition of crystals during water soaking for two months. The feasibility of the (BAH)BiI₄ crystal for X‐ray detection, with a sensitivity as high as 1181.8 µC Gy_air⁻¹ cm⁻² and a detection limit below 77 nGy_air s⁻¹ under 50 V bias is further demonstrated. Such good values are due mainly to efficient charge transport along the π–π stacking between neighboring BAH cations and I•••I interactions between adjacent inorganic chains. These findings provide a new approach to improve the water resistance of perovskite/perovskitoid optoelectronic devices.