High-performance electronic, optical, and thermoelectric properties of 2D Mg ₂ In ₂ S ₅ monolayer for energy applications

Two-dimensional (2D) chalcogenide materials have recently attracted significant research interest due to their exceptional anisotropic properties and tunable electronic structures, making them strong contenders for advanced thermoelectric and optoelectronic technologies. In this work, we conduct a detailed first-principles study to explore the structural, electronic, optical, and thermoelectric properties of the Mg₂In₂S₅ monolayer. Phonon dispersion and calculated elastic constants confirm the material's dynamic and mechanical stability. Electronic band structure analysis reveals a direct band gap semiconductor with a moderate band gap of 1.76 eV, making it suitable for visible light absorption. The partial density of states shows notable hybridization between In-5p and S-3p orbitals, which plays a key role in charge transport behavior. Optical simulations highlight strong anisotropy in the dielectric function and absorption spectra, with pronounced absorption in the UV-visible range, underscoring the material's potential in photonic and solar energy applications. Thermoelectric properties, evaluated using the Boltzmann transport formalism, display directional dependence, high Seebeck coefficients, and strong power factors. Remarkably, the figure of merit (<i>ZT</i>) reaches values as high as 1.0 in-plane and 1.2 out-of-plane at elevated temperatures, indicating excellent performance for high-temperature thermoelectric applications. Overall, the Mg₂In₂S₅ monolayer demonstrates outstanding optoelectronic and thermoelectric characteristics, positioning it as a highly promising 2D material for energy harvesting and future nanoelectronic technologies.