The effects of interstitial iodine in hybrid perovskite hot carrier cooling: A non-adiabatic molecular dynamics study

Understanding the defect chemistry of lead-halide perovskites and its effects on the hot-carrier lifetime is of significance for both fundamental understanding and applications as solar cell light absorbing materials. In this study, the mechanistic details of hot carrier decay in hybrid perovskites are investigated using a newly developed non-adiabatic molecular dynamics method. In this approach, the nuclear trajectory is based on Born-Oppenheimer ground state molecular dynamics, which is then followed by the evolution of carrier wave function including the detailed balance and decoherence effects. We found the longer decay time for hot electrons due to the incorporation of interstitial iodine in the hybrid lead-halide perovskites (MAPbI₃), while the hot hole decay time is not affected significantly by the interstitial iodine. The underlying mechanism for such modulation of hot carrier dynamics is attributed to the changes of carrier density of states and the electron-phonon coupling strength. Hence, iodine interstitial is the necessary condition to create long-lived hot electrons in perovskites, which is further demonstrated by the comparative analysis with the pure MAPbI₃.