The thermoelectric properties of XTe (X = Ge, Sn and Pb) monolayers from first-principles calculations

Thermoelectric (TE) materials are increasingly attracting the attention of researchers as new energy materials that are capable of converting thermal energy into electrical energy. In this work, combining first-principles calculations and the Boltzmann transport equation, the TE related properties of XTe (X = Ge, Sn and Pb) monolayers have been thoroughly studied. The calculated results show that XTe monolayers are indirect band gap semiconductors, and they possess small effective masses which lead to large carrier mobilities and high electrical conductivities. Except for p-type PbTe, the other XTe monolayers share extremely high PF, thanks to the high Seebeck coefficients and large electrical conductivity. Furthermore, owing to the low phonon group velocity and strong anharmonicity, the lattice thermal conductivities of SnTe and PbTe are quite low. At 500 K, the optimum figure of merit (ZT) values are calculated to be 1.26, 2.61 and 5.91 for GeTe, SnTe and PbTe respectively. The obtained ZT values of the XTe monolayers are larger than these of their bulk counterparts. These results qualify XTe monolayers as promising candidates for building outstanding TE devices.