Theoretical Investigation of Metal-Shrouded Tl₂O Monolayers: Pudding-Mold-Type Band Structure and Thermoelectric Performance

Inspired by the recent prediction of high carrier mobility and moderate energy gap in the metal-shrouded 2D semiconductor Tl2O [Ma, Y.; et al. J. Am. Chem. Soc. 2017, 139, 11694–11697], we present a theoretical analysis of thermoelectric properties for monolayer Tl2O by semiclassical Boltzmann transport theory. The “pudding-mold-type” valence band structure brings about a high p-type power factor (PF). A low lattice thermal conductivity (kl) 2.4 W m–1 K–1 for T = 300 K is obtained because of the coupling among optical and acoustic vibration modes and the strong phonon scatterings. Upon combination of the superior PF with the low kl, high figure of merit (ZT) values 3.35 (n-type) and 4.20 (p-type) are achieved for T = 900 K, exceeding those of usual transition metal dichalcogenides monolayers and being comparable with that of the recently fabricated Bi2O2Se monolayer. These results reveal the potential applications of metal-shrouded monolayer Tl2O as a 2D high-performance thermoelectric material.