In this work, the influence of the variation of chemical bath thiourea concentration in the solution for depositing Us layers upon the spectral response of chemical bath deposition (CBD)-CdS/CdTe solar cells is studied. Although changes in the short and long wavelength range for the spectral response of the cells were observed in dependence of the thiourea concentration, no significant changes were observed in the diffusion length of minority carriers in the CdTe layer, as determined from the constant photocurrent method, when the thiourea concentration is increased in the Us deposition solution. (c) 2006 Elsevier B.V. All rights reserved.