High-Temperature Thermoelectric Monolayer Bi₂TeSe₂ with High Power Factor and Ultralow Thermal Conductivity

Because of the quantum confinement effect and the interface/surface effect, the band gap of 0.8–1.5 eV for two-dimensional (2D) bismuth-based material is significantly enlarged relative to that of bulk phase materials (∼0.2 eV), which removes the inhibition effect caused by bipolar transport for the Seebeck coefficients of bulk-phase bismuth-based materials at high temperature. Therefore, the 2D bismuth-based materials exhibit huge application prospects in high-temperature thermoelectric (TE) devices, whereas their figure of merits (ZT) need to be further improved. This work reports the thermal and electrical transport properties of 2D Bi2TeSe2, a new Janus Bi2Te3-based material, from the first-principles calculations. Compared with Bi2Se3/Bi2Te3 monolayers and corresponding Janus materials, the Bi2TeSe2 monolayer exhibits a much lower lattice thermal conductivity (κ) of 0.27 W/mK at 900 K because of stronger phonon anharmonicity and higher frequency phonon scattering. In addition, because the energy pockets around the valence band maximum show convergence character, the Seebeck coefficient (SC) of the p-type system is effectively enhanced. Combined with its intrinsic high electron transport properties, a high power factor of 3.48 mW/mK2 at 900 K is obtained for the p-type Bi2TeSe2 monolayer. The ultralow κ and enhanced SC of the Bi2TeSe2 monolayer eventually result in a significant optimal ZT value of 3.45 at 900 K. Thus, our study provides insights into the thermoelectric properties of the Bi2TeSe2 monolayer and may open up an effective avenue for applying bismuth-based materials to a high-temperature TE field.