Self-Healing of Photocurrent Degradation in Perovskite Solar Cells: The Role of Defect-Trapped Excitons

Solution-processed lead halide perovskites have emerged as one of the most promising materials in optoelectronic applications. However, the perovskites are not stable over prolonged solar illumination. A recent experimental study has revealed light-activated photocurrent degradation and self-healing in lead halide perovskites, which has important implications in tackling the photostability problems of the perovskites. Unfortunately, the physical origin of the experimental observations is unclear. In this work, we propose a first-principles theory that can elucidate all key experimental observations. By focusing on defect-trapped excitons, the theory can rationalize both fast and slow time scales of self-healing, contrasting dynamics of the photocurrent degradation and its recovery, and the steep temperature dependence of the two competing processes. We further predict that the same phenomenon of self-healing could also be observed in other lead halide perovskites with even faster time scales of recovery. The work provides a general framework for elucidating defect-controlled excitation dynamics in perovskites.