The Dynamic Rashba Effect Does Not Account for the Prolonged Charge Carrier Lifetime in Metal Halide Perovskites.

Abstract

Rashba spin-orbit splitting in metal halide perovskites has been widely associated with a direct-to-indirect bandgap transition, a mechanism often proposed to suppress nonradiative recombination and extend carrier lifetimes. To critically assess this hypothesis, we developed a nonadiabatic molecular dynamics framework in momentum space that explicitly incorporates spin-orbit coupling and goes beyond harmonic approximation. Using this approach, we investigated electron-hole recombination dynamics in the racemic (<i>rac</i>), <i>S</i>, and <i>R</i> configurations of the chiral 3BrMBA₂PbI₄ perovskites. The <i>rac</i> structure, which preserves inversion symmetry, exhibits weak Rashba splitting and retains a direct-like bandgap under thermal fluctuations, yielding ∼1 ns recombination times. In contrast, the chiral <i>S</i> and <i>R</i> configurations break inversion symmetry, display pronounced Rashba splitting, and exhibit an indirect bandgap but show only ∼20% slower recombination. These findings indicate that dynamic Rashba spin-orbit splitting alone does not significantly enhance carrier lifetimes, underscoring the importance of atomistic-level understanding of recombination processes in perovskites.