Accumulated Structural Evolution under Diurnal Cycling Degrades Wide-Bandgap Perovskite Solar Cells

Mixed-halide wide-bandgap (WBG) perovskite thin films are prime candidate materials for next generation tandem perovskite photovoltaics. One major concern about this material class is the apparent halide phase segregation during operation, which reduces the operational lifetime. Here, we investigate the impact of phase segregation and crystallite orientation on the degradation of WBG perovskite films under a light/dark cycling mode. The photoluminescence of perovskite thin film presents a red-shift peak under illumination, then it exhibits a complete recovery to the initial position during storage in the dark, while operando structural evolution results reveal that light-induced lattice distortion, phase segregation, and phase reorientation only partially recover under the dark condition. These findings align with the observed partial recovery of the power conversion efficiency in the dark, demonstrating the accumulation of crystalline distortion and phase reorientation over light/dark operation is one of the significant causes for the performance loss in WBG perovskite solar cells.