Combined First-Principles and Machine Learning Study of Thermal Transport and Thermoelectric Properties of p-type Halide Perovskite CsCdX₃ (X = Cl, Br)

The thermal transport and thermoelectric properties of CsCdX₃ (X = Cl, Br) were investigated using first-principles calculations and machine learning interatomic potentials. The lattice thermal conductivity was obtained including the effect of temperature on the phonon dispersion spectrum and the contribution of the diffuson-like phonons, based on the self-consistent phonon (SCP) and two-channel phonon transport theories. We found that diffuson-like phonons contribute significantly to the lattice thermal transport. The ultralow lattice thermal conductivities of CsCdCl₃ and CsCdBr₃ at 300 K are 0.95 W/mK and 0.57 W/mK, respectively. The large Seebeck coefficient of CsCdCl₃ and CsCdBr₃ is about 800 μV/K and 700 μV/K at 900 K, due to the multi-valley energy band structure. The calculated maximum ZT of p-type CsCdBr₃ is 1.16 at 900 K, larger than most of the reported halide perovskite materials. We suggest that CsCdBr₃ is a promising candidate for thermoelectric halide perovskite materials.