In previous papers we have reported the improvement of the efficiency of CdS/CdTe solar cells by varying the thiourea/CdCl2 ratio (R-tc) in the chemical bath solution used for the deposition of the CdS layers. In this work, a more complete study concerning the physical properties of Chemical Bath Deposited (CBD) CdS layers studied by photoluminescence, X-ray diffraction and optical spectroscopy are correlated to the I-V characteristics under AM 1.5 sunlight and the spectral response of CdS/CdTe solar cells. It is confirmed that the optimum R-tc for the CBD CdS films is R-tc=5, since in this case the best solar cells were obtained and these films show the better optical and structural characteristics. (C) 2006 Elsevier B.V. All rights reserved.