Electronic and Optical Modeling of Solar Cell Compounds CuGaSe2 and CuInSe2

We present dielectric-function-related optical properties such as absorption coefficient, refractive index, and reflectivity of the semiconducting chalcopyrites CuGaSe2 and CuInSe2. The optical properties were calculated in the framework of density functional theory (DFT) using linear combination of atomic orbitals (LCAO) and full-potential linearized augmented plane wave (FP-LAPW) methods. The calculated spectral dependence of complex dielectric functions is interpreted in terms of interband transitions within energy bands of both chalcopyrites; for example, the lowest energy peak in the epsilon(2) (omega) spectra for CuGaSe2 corresponds to interband transitions from Ga/Se-4p -> Ga-4s while that for CuInSe2 emerges as due to transition between Se-4p -> In-5s bands. The calculated dielectric constant, epsilon(1) (0), for CuInSe2 is higher than that of CuGaSe2. The electronic structure of both compounds is reasonably interpreted by the LCAO (DFT) method. The optical properties computed using the FP-LAPW model (with scissor correction) are close to the spectroscopic ellipsometry data available in the literature.