Cs-content-dependent organic cation exchange in FA1-Cs PbI3 perovskite

FA-Cs mixed-cation perovskite has been reported as a promising candidate for obtaining highly efficient and stable photovoltaic devices. Phenylethylamine iodide (PEAI) post-treatment is a widely used and effective method for surface passivation of FA-Cs perovskite layer in devices. However, it is still controversial whether the PEAI post-treatment would form two-dimensional (2D) perovskite PEA2PbI4 capping layer or just result in PEA+ terminated surface. Here in this work, the function of PEAI post-treatment on FA-Cs mixed-cation perovskite FA1-xCsxPbI3 (x = 0.1–0.9) with varied Cs contents is elucidated. With increased Cs content, the FA-Cs perovskite shows higher resistance to the cation exchange between FA+ and PEA+. This Cs-content-dependent cation exchange results in the different PEAI reaction preferences with FA-Cs mixed-cation perovskites. Furthermore, higher Cs content with stronger resistance to cation exchange reaction leads to a wider processing window for post-treatment and defect passivation, which is beneficial for the fabrication of large-scale photovoltaic devices.