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 Tl 2 O [Ma, Y.; et al. J. Am. Chem. Soc . 2017, 139, 11694–11697], we present a theoretical analysis of thermoelectric properties for monolayer Tl 2 O 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 ( k l ) 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 k l, 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 Bi 2 O 2 Se monolayer. These results reveal the potential applications of metal-shrouded monolayer Tl 2 O as a 2D high-performance thermoelectric material.