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.