One-step synthesis of Cu(In,Ga)Se2 absorber layers by magnetron sputtering from a single quaternary target

A one-step route was developed to fabricate Cu(In,Ga)Se2 (CIGS) absorber layers by direct magnetron sputtering from a single quaternary target with the composition of CuIn0.75Ga0.25Se2. The effects of the substrate temperature, the working pressure and the sputtering power on the morphology and phase structure of the CIGS layers were studied using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The microstructure properties of the layers, including the crystallinity, grain size, compactness and the surface evenness, were found to be strongly dependent on the deposition parameters. CIGS absorbers with compact microstructure and large grains of micrometer size were obtained at 400 °C and 160 W, showing a very strong (220)/(204) orientation preference when sputtered at a higher working pressure. Raman spectra indicated no precipitation of the Cu–Se binary phases, but revealed a slight difference in the Ga/(Ga + In) ratio of different layers. The overall composition of the as-sputtered CIGS film was confirmed to be in agreement with the target composition through energy dispersive X-ray spectroscopy study. In comparison with the conventional co-evaporation or post-selenization synthesis for CIGS, the one-step sputtering route is more simplified and economical, which shows great potential to reduce the production cost of CIGS-based solar cells. - Highlights: ► One-step sputtering simplifies the fabrication of Cu(In,Ga)Se2 (CIGS) absorbers. ► Microstructure of CIGS films is tunable by merely adjusting sputtering parameters. ► High sputtering temperature, pressure, and RF power favor high quality CIGS film. ► Columnar CIGS film has expected stoichiometry and strong (220)/(204) orientation.