Optical properties of Al-doped CuInSe2 from the first principle calculation

Two kinds of exchange-correlation functional GGA-PBE and HSE06 were used in the first principle method to calculate the complex dielectric function of CuInSe2 and CuAlSe2. Compared with experimental data, GGA-PBE functional cannot properly predict dielectric function, while calculated results by HSE06 quantitatively agree with experimental data. With HSE06 functional, optical properties of CuIn1−xAlxSe2 (x=0, 0.25, 0.5, 0.75 and 1) were calculated. As x increases from 0 to 1, within the solar spectrum, the real and the imaginary parts of the dielectric functions reduce, the static dielectric constant decreases from 7 to 5, the absorption coefficient and refractive indices decrease, while the optical band gap increases from 1.07 to 2.61 eV.