First-principles investigation of VCu3X4 (X = S, Se, Te) chalcogenides for high-performance optoelectronic and thermoelectric devices

In this study, the thermoelectric potential of sulvanite compounds VCu 3 X 4 (X = S, Se and Te) is investigated using density functional theory (DFT). The exchange-correlation potential was determined using the generalized gradient approximation for solids (GGA-PBEsol). Analysis of the band structures reveals the semiconducting nature with direct band gaps for all the compounds investigated. The analysis of the band structures indicates that all compounds exhibit a semiconducting nature, characterized by a narrow energy gap between the conduction and valence bands, suggesting a pseudo-metallic behavior. Optical properties, such as absorption, dispersion, dielectric functions, energy loss function, refractive index, extinction coefficient, reflectivity, and optical conductivity, were studied within the energy range of 0 to 14 eV. Anisotropic polarization is observed in all compounds, accompanied by strong absorption in the visible and lower ultraviolet spectra, making these materials suitable for optoelectronic applications. Thermoelectric analysis indicates that these compounds exhibit promising performance, at 300 K, the Seebeck coefficients reach approximately 250 μV/K, the power factors lie in the range of 7.5–10.12 × 10 11 W/m·K 2 ·s, and the calculated figure of merit (ZT) values are 0.75–0.76. At 800 K, the Seebeck coefficients remain high (∼237–244 μV/K), power factors increase significantly, and ZT values rise to 0.78–0.79, highlighting their potential for efficient energy conversion. The effective masses of holes and electrons were also calculated from the band dispersions. These findings demonstrate the dual application potential of VCu 3 X 4 (X = S, Se, Te), compounds in both thermoelectric and optoelectronic devices, opening avenues for multifunctional energy-efficient technologies, including waste-heat recovery and renewable energy applications.