A-Site Cation Segregation in Alloyed Perovskite Solar Cells

Organic–inorganic lead halide perovskites have emerged as a dominant candidate for third-generation photovoltaics technologies. Further improvement of both the photovoltaic power conversion efficiency and the long-term operational stability is crucial for the deployment of this technology. However, within the perovskite layer, the labile nature of the A-site alloyed composition can initiate cation segregation during crystallization and device operation, which potentially leads to device failure and hinders commercialization. In this Review, we provide a mechanistic overview of the underlying origins of cation segregation and summarize the characterization techniques and the implications of cation segregation on perovskite films and devices. By assessing the nature and effect of cation segregation, we further discuss the ongoing studies for mitigating the segregation, including the modified crystallization process, optimized thin-film fabrication, suppressed cation migration, and monitor external stress conditions. Finally, we outline challenges and potential methods in constructing homogeneous A-site alloyed perovskites for photovoltaic applications.