Strong anharmonicity-assisted low lattice thermal conductivities and high thermoelectric performance in double-anion Mo₂AB₂ (A = S, Se, Te; B = Cl, Br, I) semiconductors

The thermoelectric properties of layered Mo₂AB₂ (A = S, Se, Te; B = Cl, Br, I) materials are systematically investigated by first-principles approach. Soft transverse acoustic modes and direct Mo d–Mo d couplings give rise to strong anharmonicities and low lattice thermal conductivities. The double anions with distinctly different electronegativities of Mo₂AB₂ monolayers can reduce the correlation between electron transport and phonon scattering, and further benefit much to their good thermoelectric properties. Thermoelectric properties of these Mo₂AB₂ monolayers exhibit obvious anisotropies due to the direction-dependent chemical bondings and transport properties. Furthermore, their thermoelectric properties strongly depend on carrier type (n-type or p-type), carrier concentration and temperature. It is found that n-type Mo₂AB₂ monolayers can be excellent thermoelectric materials with high electric conductivity, σ, and figures of merit, ZT. Choosing the types of A and B anions of Mo₂AB₂ is an effective strategy to optimize their thermoelectric performance. These results provide rigorous understanding on thermoelectric properties of double-anions compounds and important guidance for achieving high thermoelectric performance in multi-anion compounds.