Cesium Moderation and Structural Transformation on α-CsPbI2Br Perovskite Durability via Cation Retarding Migration: A Combined Simulation and Experimental Study

Preliminary density functional theory studies suggest that cesium-ion (Cs⁺) migration possesses a low energy barrier at defective surfaces, which potentially induces lattice distortion of α-CsPbI₂Br perovskites. Herein, we introduced surface design via mixed-cation and mixed-halide methods to enhance the durability and functionality of all-inorganic CsPbI₂Br solar cells. The adsorption and adhesion energies indicate that formamidinium bromide (FABr) passivation creates a nonbonding surface with resistance to water molecules and induces lattice reconstruction at the surface into a cubic-like structure. Experimental validation in solar cell applications reveals that nonencapsulated formamidinium bromide − based devices can retain 84 % of the initial efficiency (13.29 %) after 336 h of use with 40 %–43 % of relative humidity, outperforming the reference cell that retained 20 % of the original efficiency (10.31 %) after 144 h. This findings highlight the dual role of FABr passivation in stabilizing the surface and reorganizing the lattice structure, contributing to significantly enhanced durability and performance CsPbI₂Br solar cells.