Strain-induced enhancement in the thermoelectric performance of a ZrS2 monolayer

The increase of a thermoelectric material's figure of merit (ZT value) is limited by the interplay of the transport coefficients. Here we report the greatly enhanced thermoelectric performance of a ZrS2 monolayer by the biaxial tensile strain, due to the simultaneous increase of the Seebeck coefficient and decrease of the thermal conductivity. Based on first-principles calculations combined with the Boltzmann transport theory, we predict that the band structure of the ZrS2 monolayer can be effectively engineered by the strain, and the Seebeck coefficient is significantly increased. The thermal conductivity is reduced by the applied tensile strain due to the phonon softening. At the strain of 6%, the maximum ZT value of 2.4 is obtained for the p-type doped ZrS2 monolayer at 300 K, which is 4.3 times larger than that of the unstrained system. Moreover, the temperature dependence of the ZT values is investigated, and compared with the unstrained system, the ZT values of the p- and n-type doping are much more balanced by the applied strain.