Abstarct: In this thesis, the physical properties of CdS and CdTe thin films also the heterostructure junction properties of CdS/CdTe solar cells were investigated In this research for samples characterizations the field emission scanning electron microscope (FESEM), Energy Dispersive X-ray (EDX), X-ray diffraction (XRD), Raman Spectroscopy, UV-Vis. Spectroscopy, Photoluminescence (PL), Seebeck effect and current-voltage (in dark and illumination conditions) characterizations were used. In the first section, thin films of CdS were fabricated by the cost effective chemical bath deposition (CBD) method. The effects of time duration, temperture deposition, type of the substrate (glass and FTO) and finally annealing effect on the physical properties were studied. The results showed all the grown samples have n-type nature and sample with the lowest growth time has the lowest electrical sheet resistance (3.6 MΩ/sq). In the second section, thin films of CdTe were successfully grown by RF magnetron sputtering. In this study we investigated various parameters including: the deposition time duration, temperature of the substate and finally annealing effect on physical properties of the samples. The results show that all samples have p-type conductivity and the electrical properties of the grown samples are very sensitive to the CdCl2 treatment. At the end, we tried to fabricate a number of CdTe/CdS solar cells and studied the effect of various parameters such as: annealing, the thickness of CdTe laxyer, and CdCl2 concentration on I-V characteristics in of these devices the dark and light conditions. In this research, we achieved an efficiency of 2.23% in our optimized solar cell.