Surface Trap States Passivation for High-Performance Inorganic Perovskite Solar Cells

Cesium halide perovskite CsPbX3 has emerged to be a promising candidate for photovoltaic materials due to their componential and thermal stability. During the fabrication of CsPbX3 films, rich halide ions could cause deep trap states on the surface of the perovskite film, leading to much charge recombination. Herein, Pb2+ solution post-processing strategy is introduced to passivate the deep trap states of CsPbI2Br films. The dissociative Pb2+ in the solution effectively combines with the excess halide ions on the perovskite surface to reduce the deep trap states of Pb vacancy (VPb) and I interstitial (Ii). As a result, the average photoluminescence lifetimes τave of the perovskite film prolonged nearly double after passivation. The trap density of perovskite is effectively decreased from 8 × 1016 to 6.64 × 1016 cm−3. The CsPb2Br solar cell shows an open-circuit-voltage as high as 1.29 V and power conversion efficiency of 12.34% with small hysteresis. The postprocessing method would provide an avenue to improve further the efficiency of inorganic perovskite solar cells via reducing surface traps.