Effects of annealing on the structural properties of Cu(In,Ga)Se ₂ thin films prepared by RF sputtering

Cu(In,Ga)Se₂ (CIGS) thin films have been prepared by radio frequency (RF) magnetron sputtering from a CuIn_0.8Ga _0.2Se₂ 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 Cu _2-xSe secondary phase which is detrimental to CIGS solar cells.