Hydrogen Vacancies Heal Pb-Dimer Deep Traps and Suppress Coupled Ionic-Electronic Losses in Hybrid Perovskites

Organic-inorganic hybrid perovskites combine strong optical absorption, long carrier lifetimes, and unusual defect tolerance, yet these favorable properties appear difficult to reconcile with the deep-level Pb-dimer defect reported in previous studies. Here, we demonstrate that hydrogen vacancies (VH) on A-site organic cations can actively destabilize Pb-dimer and simultaneously suppress both ionic migration and nonradiative carrier loss in methylammonium lead iodide. By combining machine learning force field with nonadiabatic molecular dynamics, we capture the coupled structural and electronic evolution over extended time scales inaccessible to conventional ab initio approaches. We find that VH energetically favors interaction with the Pb-dimer, increases the Pb-Pb distance, and ultimately drives the dimer dissociation. The microscopic mechanism depends on the vacancy site: VH on the N site disrupts the dimer through lone-pair-assisted Pb-N interaction, whereas VH at the C site exhibits a heterogeneous, Pb-Pb-distance-dependent behavior, leading to either complete deep-trap passivation or residual shallow trap formation through competing Pb-C covalent bond formation. This defect healing restores local lattice rigidity, reduces iodide diffusion by up to ∼1.5 orders of magnitude, removes or weakens Pb-dimer-derived trap states, and prolongs carrier lifetimes by up to ∼7.8-fold. These results uncover an overlooked defect-healing function of A-site organic cations, in which local inorganic-lattice reinforcement enables deep-trap passivation and suppresses nonradiative loss in hybrid perovskites. This finding suggests a microscopic mechanism by which dynamic organic-inorganic coupling can contribute to the remarkable defect tolerance of hybrid perovskites.