Synergistic Self-Passivation of Vacancy Complexes in Metal Halide Perovskites

Intrinsic defects like iodine (VI) and hydrogen (VH) vacancies severely weaken the optoelectronic stability of metal halide perovskites. However, their coupled evolution and collective impact on nonradiative loss remain poorly understood. Using first-principles calculations and nonadiabatic molecular dynamics, we reveal that the thermodynamically prevalent VI strongly promotes VH formation, driving the favorable formation of highly stable VI·VH defect complexes. These complexes trigger a synergistic self-passivation: the VI·VH-C (iodine and carbon-site hydrogen vacancies) complex forms a rigid Pb-Pb-CH2NH3 complex driven by a robust Pb-C coordinate bond ("hard anchoring") that simultaneously immobilizes VI migration and eliminates deep trap states, while the VI·VH-N (iodine and nitrogen-site hydrogen vacancies) complex achieves electronic passivation through dynamic Pb-N interactions within a fluxional Pb-CH3NH2···Pb configuration ("soft anchoring"). Both pathways strongly suppress lattice anharmonicity, nonadiabatic coupling, and electron-phonon interactions, extending carrier lifetime by up to 3 orders of magnitude. Our findings establish that defect coupling in perovskites can drive favorable structural and electronic reconstructions that intrinsically passivate deep traps and suppress ion migration, revealing synergistic self-passivation as an intrinsic defect tolerance mechanism in halide photovoltaics.