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

Abstract

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.