Tunable Electronic and Optical Properties of Monolayer and Multilayer Janus MoSSe as a Photocatalyst for Solar Water Splitting: A First-Principles Study

Recently, novel two-dimensional materials for solar water splitting have drawn enormous research attention for the interesting tunable electronic and optical properties. We investigate the geometry, electronic, and optical properties of the monolayer (ML) and multilayer Janus MoSSe with the first-principles calculations. We find that the ML Janus MoSSe is a semiconductor with a direct band gap of 2.14 eV, which is suitable for absorbing visual light efficiently. It also holds an appropriate band edge alignment with the water redox potentials. The biaxial strain could effectively modulate the electronic and optical properties of the ML MoSSe, from a direct semiconductor to the indirect one, even to be metal. As for the bilayer (BL) MoSSe, the stacking order could effectively affect the electronic, optical, and redox properties. The most stable stacking order is the A'B type, followed by the AA', AA-SeSe, AA-SS, and AA-SSe stacking faults. For the BL MoSSe, they are all indirect semiconductors. The indirect band gap of the multilayer MoSSe decreases monotonously as the number of layers increases, maybe due to the quantum confinement effect and interaction between the layers. The appropriate optical and band alignment with the water redox potentials together with the rich modulation methods imply that MoSSe could be used as an efficient photocatalysist for the water splitting.