The influence of stoichiometry and annealing temperature on the properties of CuIn0.7Ga0.3Se2 and CuIn0.7Ga0.3Te2 thin films

CuIn0.7Ga0.3Se2 and CuIn0.7Ga0.3Te2 thin films have been prepared by the electron beam evaporation technique and annealed at various temperatures (450 °C, 475 °C, 500 °C, 525 °C and 600 °C). Optical transmittance measurements have been carried out in the wavelength range 300-1200 nm. The films show high absorption in the solar radiation spectral range, and their optical band gaps range from 1.33 eV to 1.22 eV for CuIn0.7Ga0.3Se2 and from 1.13 eV to 1.06 eV for CuIn0.7Ga0.3Te2, depending on the annealing temperature. X-ray diffraction (XRD) indicates the films are crystallized in a single phase with the chalcopyrite structure and a preferred orientation along the (112) plane. The dependence of the lattice parameters on the composition of the films is investigated. Surface morphology has been determined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). These results are correlated with the XRD microstructural analysis.