Thermoelectric properties of the Janus PtSTe monolayer compared with its parent structures

We use ab initio calculations to study phonon and charge-carrier transport in the Janus $\mathrm{PtSTe}$ monolayer, a lower-symmetry derivative of quasi-two-dimensional transition metal chalcogenides, with a view to characterizing its thermoelectric performance. For the sake of comparison, we also perform the same study on its parent structures, ${\mathrm{PtTe}}_{2}$ and ${\mathrm{PtS}}_{2}$. We find a significantly increased thermoelectric figure of merit, driven by modest increases in the Seebeck coefficient but, most importantly, by a drastic reduction in the thermal conductivity. We show that this decrease cannot be explained by a simple inspection of the phonon band structure; instead, it has its roots in a relaxation of the selection rules for three-phonon scattering as a result of the broken symmetry of the Janus structure. This suggests that Janus monolayers have a significant intrinsic advantage and untapped potential for thermoelectric applications among quasi-two-dimensional systems.