Controllable Sign Reversal of the Seebeck Coefficient and Thermoelectric Performance of the Janus MoSH Monolayer

The Janus MoSH monolayer has attracted extensive attention from researchers; however, to our knowledge, there is no work yet to investigate the thermoelectric properties governed by electron-phonon (e-ph) interactions of the Janus MoSH monolayer in detail, either experimentally or theoretically. In this work, we carry out first-principles calculations on the thermoelectric performance of the MoSH monolayer in the presence of e-ph scattering by solving the Boltzmann transport equation iteratively. We find that by adjusting the Fermi level to the nearby band edge which corresponds to the van Hove singularity (VHS), the sign of the Seebeck coefficient of MoSH can be inverted and the ZT value (figure of merit) increases about 13 times (from 0.0011 to 0.0145). This sizable enhancement of ZT value requires not only the existence of the VHS at Fermi level, but also a constant Fermi surface. Such a case is expected to occur often in realistic materials, not limited only to the MoSH monolayer. In view of the nature of two-dimensional (2D) materials, the Fermi level of the Janus MoSH monolayer can be readily controlled by applying a gate voltage instead of chemical carrier doping. As such, our study proposes a feasible way to control the thermoelectric performance in a 2D structure.