The investigation of the charge carrier energy states in CdS/CdTe solar cells was based on the studies of absorption and photoconductivity spectral dependencies, quantum efficiency, photoconductivity kinetics measurements at 78 and 300 K. The analysis of the absorption spectra of cadmium telluride (CdTe) films used as a component of SnO2/CdS/CdTe/Ni solar cells, had shown that its heat treatment in CdCl2 leads to the formation of an impurity level localized at similar to 20 meV from the top of CdTe valence band. The high photovoltaic properties of the SnO2/ CdS/CdTe/Ni solar cells are determined by the presence of the recombination level with a lifetime equal to 180 mu s. The heterojunctions heat treatment in CdCl2 leads to the structure defects removal in the semiconductor layers, recrystallization of US film and to the formation of CdSxTex-1, (x similar to 0.95) solutions at the interface. (c) 2004 Elsevier B.V. All rights reserved.