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, ${\mathrm{CsSnBr}}_3$. At room temperature, the electron (hole) Hall mobilities in ${\mathrm{CsSnBr}}_3$ are 106 (256) ${\mathrm{cm}}^2/\left(\mathrm{Vs}\right)$ when neglecting anharmonic effects and 59 (145) ${\mathrm{cm}}^2/\left(\mathrm{Vs}\right)$ 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.

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• Anharmonic lattice dynamics
• Electron-phonon coupling
• First-principles calculations
• Perovskites