First-principles study on the optoelectronic and photocatalytic properties of the C2h-Janus Al2XY(X/Y S, Se and Te) monolayers

Recently, two-dimensional (2D) new C2h phase of group III monochalcogenides have exhibited great potentials for applications in the field of photoelectric devices because of their outstanding optoelectronic properties. Here, we theoretically predict the C2h phase of aluminum monochalcogenide (C2h-Al2XY) (X/YS, Se and Te; X≠Y) compounds with Janus structure via first-principles calculations. Janus C2h-Al2XY monolayers are found to be thermodynamically, dynamically, energetically, and mechanically stable. The entire Janus C2h-Al2XY monolayers exhibit semiconducting properties, with a band gap ranging from 2.25 to 2.57 eV, as calculated using the HSE06 method. The obvious anisotropic mechanical and optical characteristics are observed. All Janus C2h-Al2XY monolayers present high optical absorption in the ultraviolet and visible regions, suggesting that these monolayers have a favorable efficiency for absorbing solar light. These significant results imply that Janus C2h-Al2XY monolayers can be used in the fields such as nano-electronics and optoelectronics. Specifically, it has been found that the band edge position of Janus C2h-Al2SSe is capable of meeting the redox potential requirements for photocatalytic water splitting. Furthermore, biaxial strain can significantly adjust the band gap of the C2h-Al2SSe and enhance its visible light absorption. Most importantly, within the biaxial strain range of −6%–6 %, the band edge positions of Janus C2h-Al2SSe consistently satisfy the redox potentials required for photocatalytic water splitting. These findings indicate that the Janus C2h-Al2SSe monolayer is promising for photocatalytic water splitting due to its moderate band gap and suitable band edge positions as well as good absorption in the visible region.