Ultralong Carrier Lifetime in Lead-Free Perovskites Enabled by Elimination of Electron-Phonon Coupling in Target...

Nonradiative electron-hole recombination driven by nonadiabatic coupling (NAC) between band-edge states is the primary bottleneck limiting carrier lifetime and thus the power conversion efficiency (PCE) of photovoltaic and photocatalytic materials. In this work, we demonstrate that NAC in lead-free Ruddlesden-Popper (RP) perovskites can be substantially reduced by identifying and suppressing the electron-phonon (e-ph) coupling in the specific atomic layer that contributes most strongly to carrier recombination, which we term the target layer. Taking Y₂Ti₂O₅S₂ as a model system, we show that its rock-salt [Y₂S₂]²⁺ layer is the dominant source of e-ph coupling. By tuning the spatial distribution of the band-edge states to eliminate their overlap within this target layer, the NAC of Ti-based (and Zr-based) RP perovskites is reduced to 0.18 meV, comparable to that of lead halide perovskites (0.16 meV). Time-dependent density functional theory (TDDFT) simulations yield a carrier lifetime of ∼0.8 μs for the designed material Ba₃Zr₂O₅S₂ at room temperature, surpassing that of c-CsPbI₃ (∼0.4 μs). This strategy of controlling NAC through target-layer engineering provides new insight into carrier dynamics and offers a practical guideline for designing lead-free perovskites with improved PCE.