First principles study of SnX 2 (X = S, Se) and Janus SnSSe monolayer for thermoelectric applications.

Tin-based chalcogenides are of increasing interest for thermoelectric applications owing to their low-cost, earth-abundant, and environmentally friendly nature. This is especially true for 2D materials, in which breaking of the structural symmetry plays a crucial role in tuning the electronic properties. 2D materials present a unique opportunity to manipulate the electronic and thermal properties by transforming a monolayer into a Janus monolayer. In the present work, we have investigated the thermoelectric properties of hexagonal SnS 2 , SnSe 2 monolayer, and Janus SnSSe monolayer. Density functional theoretical calculations points out the hexagonal Janus SnSSe monolayer as a potential high-performing thermoelectric material. Results for the Janus SnSSe monolayer show an ultra-low thermal conductivity originating from the low group velocity of the low-lying optical modes, leading to superior zT values of 0.5 and 3 at 300 K and 700 K for the p- type doping, respectively.