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

Cesium halide perovskite CsPbX 3 has emerged to be a promising candidate for photovoltaic materials due to their componential and thermal stability. During the fabrication of CsPbX 3 films, rich halide ions could cause deep trap states on the surface of the perovskite film, leading to much charge recombination. Herein, Pb 2+ solution post‐processing strategy is introduced to passivate the deep trap states of CsPbI 2 Br films. The dissociative Pb 2+ in the solution effectively combines with the excess halide ions on the perovskite surface to reduce the deep trap states of Pb vacancy ( V Pb ) and I interstitial ( I i ). As a result, the average photoluminescence lifetimes τ ave of the perovskite film prolonged nearly double after passivation. The trap density of perovskite is effectively decreased from 8 × 10 16 to 6.64 × 10 16 cm −3 . The CsPb 2 Br 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.