Ultrafast photo-induced carrier dynamics of perovskite films being degraded by atmospheric exposure

Perovskites have garnered significant attention as promising materials for photovoltaic applications due to their exceptional opto-electronic properties. Despite their excellent properties, perovskites face a significant challenge in terms of their poor stabilities. Perovskite materials are susceptible to the formation of defects within crystal lattices and/or grain boundaries when exposed to environmental factors, including oxygen and moisture. In this study, we intended to understand the degradation process of perovskite films on an ultrafast timescale and at the carrier level. Photo-induced carrier dynamics of perovskite films were investigated using ultrafast time-resolved transient absorption spectroscopy. Perovskite films were exposed to an atmospheric environment during entire experiments to induce degradation. Three decay modes (carrier trapping, carrier extraction, and carrier recombination) were proposed to explain the change in carrier dynamics, and the impact of atmospheric exposure on each decay mode was examined with increasing exposure time. Our findings demonstrate that atmospheric exposure causes a slowdown and reduction in carrier extraction, resulting in diminished light-harvesting properties. Nevertheless, it's worth noting that increasing carrier density within perovskite films recovers the decreased decay rate of the carrier extraction mode.