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

Abstract

Recently, two-dimensional (2D) new C_2h 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 C_2h phase of aluminum monochalcogenide (C_2h-Al₂XY) (X/YS, Se and Te; X≠Y) compounds with Janus structure via first-principles calculations. Janus C_2h-Al₂XY monolayers are found to be thermodynamically, dynamically, energetically, and mechanically stable. The entire Janus C_2h-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 C_2h-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 C_2h-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 C_2h-Al₂SSe is capable of meeting the redox potential requirements for photocatalytic water splitting. Furthermore, biaxial strain can significantly adjust the band gap of the C_2h-Al₂SSe and enhance its visible light absorption. Most importantly, within the biaxial strain range of −6%–6 %, the band edge positions of Janus C_2h-Al₂SSe consistently satisfy the redox potentials required for photocatalytic water splitting. These findings indicate that the Janus C_2h-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.