Enhanced Moisture Stability of Cesium‐Containing Compositional Perovskites by a Feasible Interfacial Engineering

Abstract The compositional perovskites have attracted broad attention due to the improved photovoltaic performance and enhanced stability compared with the single cation perovskite, such as methylammonium lead iodide and formamidinium lead iodide. In this study, the moisture stability of the widely used cesium and bromide‐containing mixed perovskites is carefully studied by characterizing the morphology, crystallization, and device performance before and after the exposure to moisture. Though the mixed perovskites possess strong resistance to moisture in the ambient air, a rapid degradation is observed when the perovskites are exposed to a high relative humidity (RH) up to 70%. The degradation is evidenced by the obvious appearance of CsPbI 3 phase along with needle‐like morphology after several hours' storage in 70% RH. Moreover, to suppress the erosion of perovskites by the high‐level moisture, an interfacial engineering is introduced with phenylethylammonium iodide (PEAI). The PEAI passivation not only shows a retarded degradation but also delivers an enhanced photovoltaic performance from 13% to >17% with much improved stability under high‐level moisture. The results imply the efficacy of interfacial engineering in fabricating high‐efficiency and stable perovskite solar cells.