Non-Janus WSSe/MoSSeHeterobilayer and Its PhotocatalyticBand Offset

We propose two non-Janus configurations, i.e., S2Se1 and S2Se2, of MoSSe and WSSe monolayers, which are appreciably more stable than their parent Janus configuration by proper exchanges of equivalent S and Se atoms. Specifically, S2Se1 is not only the most stable in the energetic sense but also dynamically stable. Our HSE06+SOC band structure calculation shows that the monolayers exhibit band gaps in the visible region comparable to those of the Janus configuration. S2Se1 WSSe exhibits a direct gap for the spin-up component, while it displays an indirect gap for the spin-down component due to the strong spin–orbit interaction. Our calculation of the activation barrier indicates that the Janus configuration can be converted to S2Se1 by a 15% uniaxial strain. Due to the absence of vertical polarization, we finally show that a S2Se1 WSSe/MoSSe heterobilayer can be much more advantageous than a Janus heterobilayer for the photocatalytic reduction of CO2 to CO or HCOOH in almost the entire pH range.