Ultralow Lattice Thermal Conductivity and Extraordinary Thermoelectric Performance in Highly Disordered CuIn₇Se₁₁ Layered Compound

Abstract

Since the lattice thermal conductivity of thermoelectric materials is a relatively independent parameter, exploring semiconductor materials with intrinsically low lattice thermal conductivity is an important direction in the field of thermoelectric research. Herein, a high figure of merit ZT of 1.23 at 873 K and an exceptionally low lattice thermal conductivity of 0.18 W m−1 K−1 are realized in the n‐type CuIn7Se11 compound for the first time. The weak In─Se chemical bonds induce strong coupling between acoustic phonon and optical phonon with low frequency, leading to low sound velocity. The highly disordered configuration of Cu, In, and vacancies at In2, In3, and M sites, in conjunction with atomic‐scale slips and flips intensify phonon scattering. All these result in an intrinsically low thermal conductivity of the CuIn7Se11 compound. DFT calculation reveals that the density of states at the bottom of the conduction band is mainly contributed by the coupling between 4p orbitals of Se atoms and 5s orbitals of In atoms, featuring with a small effective mass. This small effective mass of charge carrier renders the CuIn7Se11 compound high carrier mobility of 435 cm2 V−1 s−1 at 300 K. Consequently, the CuIn7Se11 compound possesses an extraordinary thermoelectric performance