Influence of aluminum doping in CuInS2 prepared by spray pyrolysis on different substrates

The structural and optical properties of the CuInS2 semiconductor thin films doped with aluminum ([Al]/[In] = 1‰ and 2‰) are reported. Films are deposited using the spray pyrolysis technique on various substrates: glass, In2S3/glass, ZnO/glass, as well as SnO2/glass, In2S3 and ZnO are used as optical windows in photovoltaic system, CuInS2 as the absorber material and SnO2 as ohmic contact. In2S3, ZnO and SnO2 are grown by spray pyrolysis. During CuInS2 thin layer deposition, the substrate temperature is 340 °C. The deposition run lasts for 5 min.X-ray diffraction is used to characterize CuInS2 film cristallinity. The effect of aluminum inclusions as well as of the substrate material on the CuInS2 film is investigated.The optical absorption coefficient α for the Al-doped CuInS2 compounds is obtained from reflection and transmission spectra. It is in the range of [3.69–4.37] × 106 cm−1 ([9.55–12.31] × 106 cm−1, respectively) for 1‰ aluminum content in the spray solution (2‰, respectively).The direct band gap value is in the order of 1.44 eV for the 1‰ Al-doped CuInS2 thin layers and 1.48 eV for 2‰ Al content.