Abstract
Experiment shows that solar cells based on FA0.75Cs0.25Pb0.5Sn0.5I3 carry a lower charge recombination rate and higher power conversion efficiency than those of FAPbI3 despite the fact that the former has a smaller band gap. However, the underlying mechanism remains unclear. Using nonadiabatic (NA) molecular dynamics, we demonstrate that low-frequency vibrations drive electron-hole recombination in pristine FAPbI3 occurring in about 1 ns, showing excellent agreement with experiment. Cs/Sn substitution to FA/Pb not only narrows its band gap by 0.3 eV but also delocalizes the electron wave function significantly, leading to enhancement of NA coupling. Importantly, doping accelerates quantum decoherence caused by increased atomic fluctuations. As a result, rapid decoherence prevails a small band gap and strong NA coupling, slowing charge recombination and extending the charge carriers' lifetime to several nanoseconds. Our study reveals the importance of quantum coherence on quantum dynamics in perovskite materials and suggests a rational strategy to design high-performance perovskite solar cells.
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