Self-passivation of Halide Interstitial Defects by Organic Cations in Hybrid Lead-Halide Perovskites: Ab Initio Quantum Dynamics

Halide interstitial defects severely hinder the optoelectronic performance of metal halide perovskites, making research on their passivation crucial. We demonstrate, using ab initio nonadiabatic molecular dynamics simulations, that hydrogen vacancies (H_v) at both N and C atoms of the methylammonium (MA) cation in MAPbI₃ efficiently passivate iodine interstitials (I_i), providing a self-passivation strategy for dealing with the H_v and I_i defects simultaneously. H_v at the N site (H_v-N) introduces a defect state into the valence band, while the state contributed by H_v at the C site (H_v-C) evolves from a shallow level at 0 K to a deep midgap state at ambient temperature, exhibiting a high environmental activity. Both H_v-N and H_v-C are strong Lewis bases, capable of capturing and passivating I_i defects. H_v-C is a stronger Lewis base, bonds with I_i better, and exhibits a more pronounced passivation effect. The charge carrier lifetimes in the passivated systems are significantly longer than in those containing either H_v or I_i, and even in pristine MAPbI₃. Our demonstration of the H_v and I_i defect self-passivation in MAPbI₃ suggests that systematic control of the relative concentrations of H_v and I_i can simultaneously eliminate both types of defects, thereby minimizing charge and energy losses. The demonstrated defect self-passivation strategy provides a promising means for defect control in organic-inorganic halide perovskites and related materials and deepens our atomistic understanding of defect chemistry and charge carrier dynamics in solar energy and optoelectronic materials.