Inorganic CsPbBr3 Perovskite Nanocrystals as Interfacial Ion Reservoirs to Stabilize FAPbI3 Perovskite for Efficient Photovoltaics

Abstract Bulk lead halide perovskite films with unique optoelectronic properties and facile low‐cost processing methods are promising for various optoelectronic applications including photovoltaics. Solution‐processed colloidal inorganic perovskite nanocrystals with higher crystallinity hold good potential for devices with better stability and optoelectronic properties. To address phase stability and defect passivation issues in black phase FAPbI 3 perovskite, all‐inorganic perovskite CsPbBr 3 nanocrystals (CPB NCs) are adapted as an effective modifier to form CPB NC‐treated FAPbI 3 perovskite films (noted as CPB NC‐FAPbI 3 ). It is identified in this study that, the incorporated CsPbBr 3 NCs not only act as surface additives for the bulk perovskite films, but can also serve as ion reservoirs to supply both cation and halide exchanges at the interface. This two‐way ion exchange in CPB NC‐FAPbI 3 samples leads to the formation of a compositional gradient as FA 1− x Cs x PbI 3− y Br y layers on the bulk perovskite film surface with vertically varied x and y values. Defects at interfaces and grain boundaries are therefore effectively passivated, leading to improved stability and charge carrier dynamics. As a result, the CPB NC‐FAPbI 3 perovskite based solar cells exhibit overall enhancements in device efficiency and operational stability.