We have established the effect of copper dopant concentration (Cu/Sn = 0–30 at.%) on the structural, morphological and optical properties of SnO2 : S films grown on glass substrate using a spray pyrolysis technique. According to the experimental evidence and data analysis, we found that the polycrystalline layers in undoped condition mainly consist of mixed phases such as SnS2 and SnO2, whilst in doped ones, Cu2SnS3 and Cu4SnS4 phases are dominant. With increasing Cu concentration, a decrease in the grain size with a change in the shape of the grains is observed. Optical measurement analysis showed that these films have a direct band gap energy of about 2.98–3.59 eV.
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