Effect of quartic anharmonicity on the carrier transport of cubic halide perovskites CsSnI3 and CsPbI3

Recent years have witnessed the rising of halide perovskites for potential applications in photovoltaic and optoelectric devices. Due to the tilting motions of the octahedrons and rattling of the filling atoms, cubic halide perovskites show strong anharmonicity and imaginary frequencies in the phonon dispersion, which brings a great challenge to the prediction of carrier transports based on many-body theory. We have investigated the effect of quartic lattice anharmonicity on the carrier transports of cubic CsSnI3 and CsPbI3 in a comparative perspective by first-principles calculations. The hybrid functional of HSE06 was employed to get accurate band gaps and the self-consistent phonon method was used to renormalize interatomic force constants. Based on the electron-phonon Wannier interpolation and Boltzmann transport equation, the carrier mobilities and mode -resolved scattering rates were calculated and the dominant scattering channels were analyzed. Our results reveal that the mobility takes 595.9 and 84.5 cm2/Vs at room temperature for cubic CsSnI3 and CsPbI3, respectively, in good agreement with the experiment results. The longitudinal stretching mode of the Sn(Pb)-I bond with frequency of 120 cm-1 plays a dominant role in carrier scattering. In comparison, the acoustic modes and the rattling modes have a negligible effect on carrier scattering. Calculations of the band scattering rates show that deep valleys emerge at the band edges for both the highest valence band and the lowest conduction band, which is responsible for the slow relaxation of hot carriers. The strength of intraband electron-phonon coupling (EPC) between the band edge and the Sn(Pb)-I bond stretching mode is far larger than those of other modes, which leads to the dominant scattering in carrier transport. Compared with the harmonic approximation of atom interactions, the inclusion of quartic anharmonicity leads to the enhancement of atom interactions, which decreases the EPC strength and consequently increases the carrier mobilities.