CdTe/CdS solar cells are thin film solar cells made of several different materials. As front contact sen es a TCO, the p-n junction is an intermixed CdS/CdTe heterojunction and the metallization on the CdTe layer, which is needed for the back contact, usually shows a Schottky diode behaviour. Therefore the optoelectrical properties of the cells are complex and can often not be explained straight forward like in silicon solar cells. In order to determine the: physical cell parameters like the Schottky barrier height and the minority carrier diffusion length in the absorber layer. we investigated the temperature dependence of the dark I-V characteristics and the spectral response. By modelling the temperature and wavelength dependence of the cell parameters, physical quantities such as the barrier height of the Schottky contact can be determined.