First Principle Study of Electronic, Optical and Thermoelectric Properties of CuInS 2 and CuInSe 2

We report the bandgap, thermoelectric and optical properties of CuInS₂ and CuInSe₂ ternary chalcopyrite compounds based on DFT calculations. Our calculations shows that both CuInS₂ and CuInse₂ have a direct bandgap which were at the Γ-points. The computed bandgap were 1.35 and 0.85 eV for CuInS₂ and CuInSe₂. The optical properties analysis shows that the fundamental edge of absorption arise at 0.82 eV and 0.35 eV along the perpendicular and parallel polarization for CuIns₂ , while it arise at 0.13 eV and 0.16 eV along the perpendicular and parallel polarization for CuInSe₂ . The static dielectric constant, static refractive index and birefringence were then calculated. The calculated birefringence was negative, which meets the non-critical phase matching (NCPM) requirement, which is beneficial for high-performing laser systems. The optical absorption threshold lies at 1.4 and 0.83 eV for CuInS₂ and CuInSe₂. These compounds show low reflectivity and high absorption in the visible region. Both compounds have high electrical conductivity and Seebeck coefficient, making them promising candidates for thermoelectric devices.