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

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 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 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.

Formation and Composition-Dependent Properties of Alloys of Cubic Halide Perovskites

“…MAPbI 3 transforming into MAI+PbI 2 ), 1 being prone to oxidation (i.e. 2CsSnI 3 converting to the Sn-vacancy compound Cs 2 SnI 6 ), [2][3][4] or loss of Halogen, 5 possible phonon (dynamic) instability, [6][7][8] and often not having the ideal band gaps for tandem solar applications. 9 Because the properties P(x) of an alloy can deviate significantly from the composition (x)-weighted linear average of the respective properties of the constituents ('alloy bowing' 10,11 ), this raises the possibility that alloying might solve the problems with respect to instabilities to the above noted defficiencies.…”