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

TL;DR

This study investigates how disorder and anharmonic fluctuations influence the dynamical Rashba effect in inorganic lead-halide perovskites, revealing conditions under which the effect is quenched or persists, impacting recombination mechanisms.

Contribution

It demonstrates the role of anharmonic fluctuations and disorder in modulating the dynamical Rashba effect in CsPbI3 perovskites using molecular dynamics and phonon analysis.

Findings

Anharmonic fluctuations occur on sub-picosecond timescales in CsPbI3.

Disorder can quench the Rashba effect under certain conditions.

A sizable dynamical Rashba effect persists despite temperature disorder and absence of organic cation motion.

Abstract

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, is thus crucial in order 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 towards full comprehension of their working principles. Using molecular dynamics and frozen phonons, we evidence sub-picosecond anharmonic fluctuations in the fully inorganic $CsPbI_3$ 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 show 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 $MAPbI_3$ 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 to the Rashba splitting cannot be deemed responsible for a consistent reduction of recombination rates, although the spin mismatch between valence and conduction band increases with the ferroelectric distortion causing the Rashba splitting.