Wide-bandgap CuIn1−xAlxSe2 thin films deposited on transparent conducting oxides

The development of wide-bandgap materials deposited on transparent conducting oxides for high efficiency and low cost semitransparent photovoltaic devices or tandem cells is becoming important in the last few years. CuIn1−xAlxSe2 (CIAS) thin films with bandgap above 1.95 eV for 0.7≤x≤0.9 were deposited onto bare and two different (tin-doped indium oxide, ITO and aluminium-doped zinc oxide, AZO) coated glass substrates by a two stage process consisting of the selenization of metallic precursor layers. Polycrystalline CIAS thin films orientated preferentially along the (1 1 2) plane with chalcopyrite structure were obtained. The bandgap energy increased no linearly with the Al addition. X-ray diffractograms showed the coexistence of several CIAS phases. Optical, structural and composition analysis revealed that the ITO and AZO substrates promote not only the incorporation of Se, but also a more homogenous distribution in depth regarding the CIAS samples on bare glass, and acted like a barrier to the oxidation from the glass substrate.