Screening of point defects in methylammonium lead halides: a Monte Carlo study

Abstract

We present a theoretical modeling of the point defect screening by the CH₃NH₃⁺ dipoles in CH₃NH₃PbX₃ (X = I, Br, Cl) perovskites. The organic sublattice of these materials is believed to be related to the exceptional performance of the perovskite solar cells. Our work is based on a statistical model with the short-range and dipolar interactions between the CH₃NH₃⁺ cations. We extend the model to account for the long-range charge–dipole interactions between the defects and organic cations. The model is studied by the Monte Carlo simulations on a three-dimensional lattice. We investigate the charge screening in different structural phases of CH₃NH₃PbI₃ perovskite for various values of the charge–dipole interaction energy. We demonstrate that a substantial interaction disturbs the antipolar long-range order of the CH₃NH₃⁺ cations giving rise to a multidomain phase with a small electric polarization. We also discuss the screening of two neighboring charges which might be important in a context of the photogenerated electron–hole pair separation.