Phase transition model of FA cation ordering in FAPbX3 (X = Br, I) hybrid perovskites

Abstract

A proper understanding of structural phase transitions and cation dynamics in hybrid lead halide perovskites is important for further enhancement of the photovoltaic properties of these materials. Here, we propose a model describing the FA cation ordering in FAPbX₃ (X = Br, I) hybrid perovskites. Our model is based on the available structural information of these compounds and involves short-range framework-mediated interactions between the FA cations. We solve the model using Monte Carlo simulations, which allows us to reproduce the cubic-tetragonal phase transition and the FA cation arrangement. We show that a spontaneous electric polarization does not appear during this transition, which is supported by the thermally stimulated depolarization current experiments. We also extend our model to describe the FA cation ordering and frustration in the mixed FA_1−xCs_xPbX₃ system, which reveals a frustrated dipole behavior at low temperature.