Influence of Disorder and Anharmonic Fluctuations on the Dynamical Rashba Effect in Purely Inorganic Lead-Halide Perovskites

Doping organic metal-halide perovskites with cesium could be the best solution to stabilize highly-efficient perovskite solar cells. The understanding of the respective roles of the organic molecule, on one hand, and the inorganic lattice, on the other hand, is thus crucial to be able to optimize the physical properties of the mixed cation structures. In particular, the study of the recombination mechanisms is thought to be one of the key challenges toward full comprehension of their working principles. Using molecular dynamics and frozen phonons, we evidence subpicosecond anharmonic fluctuations in the fully inorganic CsPbI₃ perovskite. We reveal the effect of these fluctuations, combined with spin–orbit coupling, on the electronic band structure, evidencing a dynamical Rashba effect. Our study shows that under certain conditions space disorder can quench the Rashba effect. As for time disorder, we evidence a dynamical Rashba effect which is similar to what was found for MAPbI₃ and which is still sizable despite temperature disorder, the large investigated supercell, and the absence of the organic cations’ motion. We show that the spin texture associated with the Rashba splitting cannot be deemed responsible for a consistent reduction of recombination rates, although the spin mismatch between the valence and conduction bands increases with the ferroelectric distortion causing the Rashba splitting.