Theoretical investigations of Janus WSeTe monolayer and related van der Waals heterostructures with promising thermoelectric performance

Recently, two-dimensional (2D) Janus MXY monolayers have received much attention due to their novel properties induced by the antisymmetric structures. In this work, the thermoelectric transport properties of the WSe2 and the Janus WSeTe monolayers are comparatively investigated based on first-principles calculations. The carriers of holes with higher mobility result in the better p-type power factor of WSeTe than WSe2. In addition, the broken of the mirror-asymmetry enhances the coupling strength between acoustic and optical branches and thus reduces the lattice thermal conductivity in WSeTe. The obtained ZT value of 1.53 is 5.9 times larger than that of WSe2 (0.26). Meanwhile, the thermoelectric performance of heterostructure MoSSe/WSeTe can be greatly enhanced by the biaxial compressive strain resulting from the band convergence. At the strain of -3%, the optimal ZT value of 1.62 is achieved for the p-type doped MoSSe/WSeTe at 300 K, which is 2.05 times higher than that of the unstrained structure. These results reveal that Janus monolayer WSeTe and its van der Waals heterostructure MoSSe/WSeTe are promising thermoelectric materials.