Nuclear Quantum Effects Suppress Nonradiative Recombination in Hybrid Perovskites beyond Isotope Mass Effects

Hydrogen nuclear quantum effects (NQEs) and H/D isotope substitution play competing roles in hybrid organic-inorganic perovskites, yet their impact on carrier recombination remains unclear. Here, we combine ab initio molecular dynamics, ring-polymer molecular dynamics, and nonadiabatic molecular dynamics to resolve excited-state recombination in CH3NH3PbI3 and CD3ND3PbI3 at 160 and 330 K. We find that NQEs dominate over isotope-mass effects, suppressing nonradiative electron-hole recombination in CD3ND3PbI3 at both temperatures. Mechanistically, NQEs enhance structural fluctuations, reduce electron-hole overlap, weaken nonadiabatic coupling, and simultaneously strengthen gap fluctuations that accelerate loss of coherence. The combined reduction in coupling efficiency slows nonradiative recombination and prolongs carrier lifetime. These findings establish quantum nuclear motion as an important design variable in hybrid perovskites and suggest isotope-based control of lattice dynamics as a route to improved optoelectronic functionality.