| Thin film solar cells have been studied by many research groups. Among the solar cells, solar cell of CdS/CdTe polycrystalline thin films are one of the most important ones, attention has been received intensively due to the price, easy making technology and its stability. The CdS thin films in CdS/CdTe solar cells are used not only for n-type materials but also for window materials, the quality of thin films deposited will limit the efficiency and lifetime of solar cells.CdS thin films have been prepared by a wide rang of methods including electrodeposition(ED), close-space sublimation(CSS), screen printing(SP), molecular chemical expitaxy(MBE), physical vapour deposition(PVD), sputtering and chemical bath deposition(CBD). Among them, chemical bath deposition method is one of the simple and inexpensive techniques that have widely applied to the fabrication of semiconductor layers for photovoltaic applications. This thesis presented the deposition process of CdS thin films by chemical bath deposition (CBD) and heat-treatment after preparation, which concentrated on low temperature preparation. For completeness, CdS thin films before and after heat-treatment were characterized using X-ray Diffraction, Optical Transmission, Atomic Force Microscopy, and Capacitance-Voltage Measurements. It was found that the properties of the annealed CdS thin films changed partially in this paper. After annealing, the crystal structure didn't change,the transmittance of the films decreased from 80% to 75% so as to the band gap which also decreased from 2.70eV to 2.55eV. AFM measurement indicated that CdS thin films obtained were uniform and adhesive with the stoichiometric ration and less defects. The average size of the annealed CdS thin films was 0.3 in diameter while the one of the as-deposited one was 0.2μm. It showed from Mott–Schottky plots that the doping density increased after annealing with the order of 1016-1018 cm-3. The optical transmittance decreased as the temperature of annealing increased. It also presented the measured values of the optical transmittance and doping density of CdS thin films heat-treated with and without CdCl2 treatment. It was found as supposed that the doping density in the annealed CdS thin films increased after the CdCl2 treatment.According to my results, brief summarization was taken as follows:1. As-deposited CdS thin films, which is of cubic crystalline structure with (111) preferential orientation, are transparent, homogeneous, uniform and compact as the deposition conditions and concentrations of the reaction reagents were varied. The crystal structure had less change after annealing, which probably indicated CdS particles were recrystallized partially.2. The thickness of the CdS thin films didn't change when the deposition time was more than 15 minutes due to the whole reaction completion within 15 min.3. The best conditions were obtained to deposit CdS thin films by CBD. They were: pH of 9.5, temperature of 65℃, the ratio of CdCl2 to thiourea and NH4Cl was 1:5:15, and the deposition time of 15 min.4. The heat treatment influence on CdS thin films from CBD was investigated briefly, but the results showed the conditions weren't optimized.
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