First-principles study on electronic and optical properties of van der Waals heterostructures stacked by g-ZnO and Janus-WSSe monolayers

In this paper, we designed van der Waals heterostructures by stacking g-ZnO and Janus WSSe monlayers with each other, and selected two most stable structures of them for in-depth study. The AA-stacking g-ZnO/Janus-WSeS heterostructure shows a type-I band arrangement. Staggered gap of AB-stacking g-ZnO/Janus-WSS het-erostructure indicates it exhibits a typical type-II band arrangement. Further investigations show that the band alignment of AB-stacking g-ZnO/Janus-WSS heterostructure meets the requirement of water redox potentials at PH = 7. To explore the regulation effect on these two heterostructures, a biaxial strain parallel to the stacking layers from-6 to 8 % is applied. Results show the type-I AA-stacking g-ZnO/Janus-WSeS vdW heterostructure can be transformed to type-II under a moderate negative biaxial strain. For AB-stacking g-ZnO/Janus-WSSe vdW heterostructure, a suitable strain can be applied to tune the band gap and the band alignment to meet the requirement of photoelectric devices. In addition, the absorption coefficients of these two heterostructures at different strains were calculated. Results show negative strain will enhance the absorption of UV light and weaken the absorption of visible light. The favorable band edge positions and strong absorption in visible light and UV light make the AB-stacking g-ZnO/Janus-WSSe vdW heterostructure as a potential UV irradiation catalyst for water splitting.