Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in both hybrid (CH3NH3PbBr3) and all-inorganic (CsPbBr3) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations show that head-to-head Cs motion coupled to Br face expansion, on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3.
@article{arxiv.1604.08107,
title = {Local polar fluctuations in lead halide perovskite crystals},
author = {Omer Yaffe and Yinsheng Guo and Liang Z. Tan and David A. Egger and Trevor Hull and Constantinos C. Stoumpos and Fan Zheng and Tony F. Heinz and Leeor Kronik and Mercouri G. Kanatzidis and Jonathan S Owen and Andrew M. Rappe and Marcos A. Pimenta and Louis E. Brus},
journal= {arXiv preprint arXiv:1604.08107},
year = {2017}
}