Effects of annealing on the structural properties of Cu(In,Ga)Se2 thin films prepared by RF sputtering

Cu(In,Ga)Se2 (CIGS) thin films have been prepared by radio frequency (RF) magnetron sputtering from a CuIn0.8Ga0.2Se2 target. The effects of in-situ annealing in Ar atmosphere on phase structure, composition and surface morphology of the films have been investigated by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX), atomic force microscopy (AFM) and Raman spectroscopy. XRD patterns show that both as-deposited and annealed films have a chalcopyrite structure with strong (112) preferred orientation. The annealed films display a higher degree of crystallinity and smoother surface, while there is little difference in grain size for films annealed at temperatures ranging from 300°C to 500°C. Results of EDAX reveal that the films are near to stoichiometry. Raman spectrum of the films annealed at 300°C shows only the CIGS A1 mode peak indicating the formation of single-phase chalcopyrite with enhanced crystalline ordering. The films annealed at higher temperatures exhibit a non-chalcopyrite mode at around 260 cm-1 assigned to Cu2-xSe secondary phase which is detrimental to CIGS solar cells.