<p>This study investigates the structural, mechanical, electronic, optical, photovoltaic, and thermoelectric properties of tetragonal Al₂HgSe₄ material using density functional theory (DFT) calculations. The structural and Mechanical analysis confirms the material’s stability in the tetragonal phase with the lattice constants of a₀ = 5.811 Å and c₀ = 10.848 Å. On the other hand, the electronic structure calculations reveal a semiconductor behavior with a direct bandgap of 2.410 eV at the Γ point, indicating promising potential for photovoltaic applications. Additionally, the optical properties, including the dielectric function, optical conductivity, refractive index, and reflectivity, exhibit strong anisotropy and significant absorption in the visible and near-ultraviolet regions. Furthermore, the thermoelectric properties of Al₂HgSe₄ were also systematically investigated using Boltzmann transport theory, revealing the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and the thermoelectric figure of merit (ZT). Our results show that the Seebeck coefficient increases with temperature up to 200 K, enhancing the thermoelectric response, but decreases at higher temperatures due to increased carrier scattering. Electronic thermal conductivity increases rapidly with temperature, reflecting the role of electron–phonon interactions that may limit thermoelectric performance. The increase of (ZT) indicated improved efficiency related to the Seebeck coefficient and electrical conductivity.</p>