Theoretical study of Lewis base passivation of <i>p-</i>type surface defects in I–Br mixed-halide tin perovskites

Perovskite-silicon tandem solar cells have attracted considerable attention owing to their high power conversion efficiency (PCE), which exceeds the limits of single-junction devices. This study focused on lead-free tin-based perovskites with iodine-bromine mixed anions. Bromide perovskites have a wide bandgap; therefore, they are promising light absorbers for perovskite-silicon tandem solar cells. However, surface defects generally affect the PCE of Sn-based perovskite solar cells because they serve as trapping and recombination sites for excitons (electron-hole pairs). In this study, density functional theory calculations were employed to investigate the molecular passivation of surface defects in Sn-based mixed-halide perovskites. The results showed that a Lewis base is effective for passivating p-type defects. In addition, we established a molecule-defect interaction model to explain the passivation mechanism.