Growth and structural properties of reactively co-sputtered CIGS films and their solar cell applications

Abstract

Using reactive sputtering, we fabricated stoichiometric CuIn1−xGaxSe2 (CIGS) thin films. Both Cu0.6Ga0.4 (CuGa) and Cu0.4In0.6 (CuIn) alloy targets were simultaneously sputtered under the delivery of elemental Se produced from a thermal cracker. By changing the sputtering rates of the CuGa and the CuIn, we were able to obtain the composition ratios of Cu/(Ga+In) and Ga/(Ga+In) in the range of 0.71–0.95 and 0.10–0.30, respectively. Both the grain size and the surface roughness of the CIGS film increased as the Cu/(Ga+In) ratio increased. In the X-ray diffraction analysis on CIGS films of 0.9 m, preferential growth with a [112] orientation was found, and reflections from the (211), (220)/(204), (301), (312)/(116), (400)/(008), and (332)/(316) planes were observed. The CIGS films showed the existence of Cu2−xSe phases in the Cu-rich samples and ordered defect compound (ODC) phases in the Cu-poor films, as confirmed in the Raman measurements. A best device performance of η = 8.1%, Voc = 0.442 V, Jsc = 34.3 mA/cm2, and FF = 53.4% was obtained from a cell fabricated with a CIGS layer (t = 0.9 µm) with the Cu/(Ga+In) ratio = 0.71 and the Ga/(Ga+In) ratio = 0.10.