High-Temperature Thermoelectric Monolayer Bi 2 TeSe 2 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 Bi 2 TeSe 2, a new Janus Bi 2 Te 3 -based material, from the first-principles calculations. Compared with Bi 2 Se 3 /Bi 2 Te 3 monolayers and corresponding Janus materials, the Bi 2 TeSe 2 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/mK 2 at 900 K is obtained for the p-type Bi 2 TeSe 2 monolayer. The ultralow κ and enhanced SC of the Bi 2 TeSe 2 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 Bi 2 TeSe 2 monolayer and may open up an effective avenue for applying bismuth-based materials to a high-temperature TE field.