Peculiar Defects Behavior in Charge Recombination of Metal Halide Perovskites

Defects are inevitably introduced in the near room-temperature and solution-based growth of metal halide perovskites (MHPs) thin films for solar cell devices. However, the astonishing improvements in the efficiency of the corresponding solar cells indicate that MHPs have a strong defect tolerance. Motivated by the recent experimental demonstration of a new state-of-art β phase CsPbI₃ with a stable and impressive efficiency reaching 18.4% at ambient conditions, we investigate the non-radiative recombination processes in CsPbI₃ using ab initio non-adiabatic molecular dynamics within real-time time-dependent Kohn-Sham formalism and surface-hopping framework. Regardless of their nature, we find that the native defects in CsPbI₃ do not accelerate the charge recombination process. We show that the strong tolerance of electron-hole recombination against defects is explained due to the combination of having low-frequency lattice phonons and weakly overlapping electron and hole states. The deep-level defect becomes tolerant owing to the strong covalency, which contrary to predictions from SRH theory in previous work. Considering similar results found in MAPbI₃, we propose that the strong defect tolerance is general to the metal halide perovskites.