In CdS/CdTe solar cells it is necessary to determine the efficiency limitations related with the intermixing at the interface between the CdS window layer and CdTe absorber layer. So understanding the properties of the solid solution (CdSxTe1-x on the CdTe side which is CdTe rich and CdS1-yTey, on the CdS side which is CdS rich) that is always formed in this region is essential. We produced thin films of CdS1-yTey solid solution-which is CdS rich - by first producing CdS:In thin films on glass substrates by the spray pyrolysis technique and then annealing the films in nitrogen atmosphere at 400 degrees C in the presence of Te vapor. We are the first who produce this solid solution by this simple and low cost method. The composition and morphology of the films were determined by energy dispersive X-ray detection (EDAX) measurements and scanning electron microscopy (SEM) observations respectively. Eight values of y in the range 0 <= y <= 0.2845 were obtained. The transmittance was measured and used to investigate the optical bandgap energy by using the second derivative of the absorbance. It is found that the films show a single hexagonal phase for y <= 0.0852 and then a mixed (hexagonal and cubic) phase for 0.0997 <= y <= 0.2845. Bandgap energies in the range 2.259 <= E-g <= 2.528 eV were obtained. Urbach tailing in the bandgap was also investigated. (C) 2012 Elsevier Ltd. All rights reserved.