Thermal fluctuations and carrier localization induced by dynamic disorder in MAPbI3 described by a first-principles based tight-binding model

TL;DR

This paper develops a first-principles based tight-binding model to study how thermal fluctuations and dynamic disorder in MAPbI3 affect electronic structure, revealing temperature-dependent band gap changes and carrier localization at room temperature.

Contribution

It introduces a novel tight-binding model incorporating non-Coulombic interactions to accurately simulate finite-temperature electronic structures of MAPbI3 at large scales.

Findings

Thermal disorder increases band gap and carrier mass.

Carrier localization occurs at 300 K in large supercells.

Localization length scale identified as approximately 5 nm.

Abstract

Halide perovskites are strongly influenced by large amplitude anharmonic lattice fluctuations at room temperature. We develop a tight binding model for dynamically disordered MAPbI$_3$ based on density functional theory (DFT) calculations to calculate electronic structure for finite temperature crystal structures at the length scale of thermal disorder and carrier localization. The model predicts individual Hamiltonian matrix elements and band structures with high accuracy, owing to the inclusion of additional matrix elements and descriptors for non-Coulombic interactions. We apply this model to electronic structure at length and time scales inaccessible to first principles methods, finding an increase in band gap, carrier mass, and the sub-picosecond fluctuations in these quantities with increasing temperature as well as the onset of carrier localization in large supercells induced by thermal disorder at 300 K. We identify the length scale $L^*= 5$ nm as the onset of localization in the electronic structure, associated with associated with decreasing band edge fluctuations, increasing carrier mass, and Rashba splitting approaching zero.