Impact of anharmonicity on the carrier mobility of the Pb-free CsSnBr$_3$ perovskite

TL;DR

This paper investigates how anharmonic lattice vibrations affect carrier mobility in lead-free CsSnBr3 perovskite, revealing that anharmonic effects significantly reduce mobility estimates and proposing a workflow for accurate first-principles calculations.

Contribution

It introduces a combined approach using temperature-dependent effective potentials and Boltzmann transport equations to accurately compute carrier mobilities in anharmonic perovskites.

Findings

Anharmonic effects lower electron/hole mobilities by about 45-50%.

Harmonic approximation overestimates mobilities due to neglecting soft mode scattering.

Provides a workflow for first-principles mobility calculations in anharmonic materials.

Abstract

Charge carrier mobilities are critical parameters in halide perovskite solar cells, governing their average carrier velocity under an applied electric field and overall efficiency. Recent advances in first-principles calculations of electron-phonon interactions and carrier mobilities have enabled predictive computations for perovskite solar cells. However, the flexible octahedral frameworks and cationic displacements in these materials challenge the harmonic approximation, leading to significant difficulties in accurately calculating transport properties. To address these issues, we combine temperature-dependent effective potentials with the ab initio Boltzmann transport equations to compute carrier mobilities in a representative lead-free perovskite, CsSnBr$_3$. At room temperature, the electron/hole Hall mobilities in CsSnBr$_3$ are 106/256 cm$^2$/Vs when neglecting anharmonic effects and 59/145 cm$^2$/Vs when included. This overestimation of the harmonic approximation arises from the neglect of scattering coming from soft modes. We provide a workflow for performing first-principles carrier mobility calculations in anharmonic systems, advancing the predictive modeling of perovskite solar cells.