First Principle Study of Electronic, Optical and Thermoelectric Properties of CuInS2 and CuInSe2

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 shows 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.