Two-dimensional ternary chalcogenides FeX2Y4 (X=Ga, In; Y= S, Se, Te): Promising materials for sustainable energy

Two-dimensional layered materials, particularly ternary chalcogenides, are promising for technological applications, as they exhibit tunable electronic, optical, and magnetic properties. Here we present detailed first-principles calculations of electronic, optical, and thermal transport properties of FeX2Y4 (X=Ga, In; Y=S, Se, Te) ternary layered chalcogenides, relevant for sustainable energy applications. We show that the monolayers, similar to bulk, are dynamically and thermally stable, as demonstrated by phonon dispersion and molecular dynamics simulations. The exfoliation energy of monolayers is comparable to graphene and transition-metal dichalcogenides, suggesting possible synthesis of monolayers by mechanical exfoliation. In the hexagonal crystal structure, these materials are nonmagnetic semiconductors with varied band-gap values, that are interesting for photocatalysis, photovoltaics, and thermoelectric applications. FeGa2S4 and FeIn2S4 monolayers exhibit suitable band gaps and band-edge positions for photocatalytic water splitting and CO2 reduction. FeGa2Se4 and FeIn2Se4 monolayers are promising photocatalysts for hydrogen evolution reaction. The calculated optical absorption spectra indicate that FeIn2Te4, FeIn2Se4, and FeGa2Se4 are promising photovoltaic absorbers with high spectroscopic limited maximum efficiencies of ∼ 30%, 27%, and 24.5%, respectively, comparable to existing high-performance thin-film absorber materials, such as CdTe (∼31.5%) and CuInSe2 (∼28%). The narrow band gaps and relatively low room-temperature lattice thermal conductivity of FeGa2Te4 (11.00 W/mK) and FeIn2Te4 (8.84 W/mK) monolayers suggest potential applications in thermoelectrics. We thereby propose FeX2Y4 ternary layered chalcogenides as promising materials for sustainable energy applications due to their suitable electronic, optical, and thermal properties.