Charge localization induced by reorientation of FA cations greatly suppresses nonradiative electron-hole recombination in FAPbI₃ perovskites: A time-domain Ab Initio study^†

Recent experiments report the rotation of FA (FA=HC[NH₂]₂⁺) cations significantly influence the excited-state lifetime of FAPbI₃. However, the underlying mechanism remains unclear. Using ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional simulations, we have demonstrated that reorientation of partial FA cations significantly inhibits nonradiative electron-hole recombination with respect to the pristine FAPbI3 due to the decreased NA coupling by localizing electron and hole in different positions and the suppressed atomic motions. Slow nuclear motions simultaneously increase the decoherence time, which is overcome by the reduced NA coupling, extending electron-hole recombination time scales to several nanoseconds and being about 3.9 times longer than that in pristine FAPbI₃, which occurs within sub-nanosecond and agrees with experiment. Our study established the mechanism for the experimentally reported prolonged excited-state lifetime, providing a rational strategy for design of high performance of perovskite solar cells and optoelectronic devices.