Characterization of high quality Cu(In,Ga)Se2 thin films prepared by rf-magnetron sputtering

This paper reports the production of high quality polycrystalline thin layers of CuIn0.7Ga0.3Se2 (CIGS), using rf-magnetron sputtering, from a powder target. These films are designed to be used as absorbers in solar cells. The depositions were carried out at substrate temperatures below 250 degrees C and glass substrates was used. The influence of the substrate temperatures on the crystalline quality as well as structural, optical and electrical properties of thin layers obtained has been studied. X-ray diffraction showed that the films were highly orientated in the (112) and/or (204)/(220) direction. In2Se3 secondary phase was observed on the samples grown at lower substrate temperatures. The surface morphology of CIGS layers studied by Atomic Force Microscopy (AFM) and Scanning Electronic Microscopy (SEM) has been also discussed. The most surprising and exciting outcome of this study was that the as grown films were of near stoichiometric composition. Resistivity measurements were carried out using the four point probe method. The optical absorption showed that energy gap values are between 1.13 and 1.18 eV and rather sharp absorption fronts. Thin film resistivities are between 10.7 and 60.9 Omega.cm depending on the experimental growth conditions. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim