Electronic, optical, and thermoelectric properties of Janus In-based monochalcogenides.

Inspired by the successfully experimental synthesis of Janus structures recently, we systematically study the electronic, optical, and electronic transport properties of Janus monolayers In$_2$XY (X/Y = S,~Se,~Te with X $\neq$ Y) in the presence of a biaxial strain and electric field using density functional theory. Monolayers In$_2$XY are dynamically and thermally stable at room temperature. At equilibrium, both In$_2$STe and In$_2$SeTe are direct semiconductors while In$_2$SSe exhibits an indirect semiconducting behavior. The strain significantly alters the electronic structure of In$_2$XY and their photocatalytic activity. Besides, the indirect--direct gap transitions can be found due to applied strain. The effect of the electric field on optical properties of In$_2$XY is negligible. Meanwhile, the optical absorbance intensity of the Janus In$_2$XY monolayers is remarkably increased by compressive strain. Also, In$_2$XY monolayers exhibit very low lattice thermal conductivities resulting in a high figure of merit $ZT$, which makes them potential candidates for room-temperature thermoelectric materials.