Anharmonic phonon renormalization and thermoelectric properties of CsPbX (X = Cl, Br, and I): first-principles calculations.

Halide perovskites with ultralow thermal conductivity have emerged as promising candidates for thermoelectric materials. We study the lattice dynamics and thermoelectric properties of cubic all-inorganic lead halide perovskites CsPbX (X = Cl, Br, and I) through first-principles calculations. Combined with self-consistent phonon theory, we have successfully renormalized the phonon frequency using a quartic anharmonic term, allowing us to accurately reproduce the phonon dispersion of the high-temperature cubic phase of CsPbX without any imaginary frequencies. Cubic CsPbX exhibit ultralow lattice thermal conductivities (0.61-1.71 Wm K) at room temperature. Because of the strong quartic anharmonic renormalization and hardening of the soft modes, the lattice thermal conductivities of cubic CsPbX all exhibit weak temperature dependence. Notably, CsPbCl exhibits remarkably high thermal conductivity and a long phonon lifetime. This can be attributed to the smallest atomic mean square displacement and the weakest tilting and distortions of PbCl octahedra, resulting from the strongest Pb-Cl covalent bonding. Furthermore, the maximum value of 0.63 at 900 K is obtained for the n-type CsPbBr.