Slurry painted CuInS₂ and CuIn₅S₈ layers: Preparation and photoelectrochemical characterization

Layers of CuInS₂, and CuIn₅S₈ were prepared by the slurry painting method from powders of the respective semiconductors, followed by annealing in Ar and then in H₂S. The layers were characterized by X-ray powder diffraction, electron microprobe and surface analyses and, for their photovoltaic behaviour, by photoelectrochemical methods using a liquid polysulfide electrolyte as the junction-forming phase. For the CuInS₂ layers, large spatial variations in the photocurrent were found using laser scanning techniques, and these were correlated roughly with the In:Cu ratio, which was found to be > 1 for areas of good photoactivity. Incorporation of the flux metal (Zn or Cd from ZnCl₂ or CdCl₂) into the layers was not found to be detrimental to the photoactivity, and possibly even beneficial. A steep increase in the dark reverse saturation current under small (< 0.1 V) reverse bias occurred, also on slurry painted In₂S₃ layers (which were also photoactive), and was connected with a layer of In₂O₃ or In₂S₃ at the surface of all films. Surface analyses (AES and XPS) showed that strong Cu depletion occurred at the surface of both CuInS₂ and CuIn₅S₈. The surface of the former was found to be predominantly In₂O₃, while the latter was mainly In₂S₃, with possibly very localized surface oxide patches.