Single-layer group-III monochalcogenide photocatalysts for water splitting

The recent synthesis of single-layer GaS and GaSe opens the question of stability for other single-layer group-III monochalcogenides (MX, M = Ga and In, X = S, Se, and Te) and how the dimension reduction affects the properties of these materials. Using a first-principles design approach, we determine that the single-layer group-III monochalcogenides exhibit low formation energies and are suitable for photocatalytic water splitting. First, density-functional calculations using a van der Waals functional reveal that the monochalcogenides have formation energies similar to that of single-layer MoS₂, implying the ease of mechanically extracting single-layer monochalcogenides from their layered bulk counterparts. Next, calculations using a hybrid density functional and the quasiparticle many-body G₀W₀ approximation determine the conduction and valence band edge positions. Comparing the band edge positions with the redox potentials of water shows that single-layer monochalcogenides are potential photocatalysts for water splitting. Moreover, the bandgaps, band edge positions, and optical absorption of the single-layer monochalcogenides can be tuned by biaxial strain to increase the efficiency of solar energy conversion. Finally, calculations of the enthalpy of solvation of the single-layer monochalcogenides suggest their stability in aqueous solution.