| For the present, the researches and production of thin film solar cells are the focus in the photovoltaic field. Among the solar cells, CdS/CdTe polycrystalline thin film ones are the most important because they could be cheapest, much easy to produce and stable to work. There are some key problems about CdS/CdTe solar cells have not been understood for long time, which results from the basic characteristics: polycrystalline, compound heterojunction devices. Related Compound Semi-conductive solar cells are the fields in which are being mainly investigated.In this thesis, the several important steps of preparing CdS/CdTe solar cells have been deeply investigated. The steps include the deposition and post treatment of polycrystalline CdS, CdTe thin films and ZnTe/ZnTe:Cu complex back contact layers that are the function layers in CdS/CdTe solar cells. The main factors to limit conversion efficiency of CdS/CdTe solar cells have been analyzed after measuring the device characteristics. The effects to influence the performance of the cells have been studied by theoretical calculation. From the researches, high efficiency of CdS/CdTe polycrystalline solar cells fabricated by us has been demonstrated. The main creative results ofthe thesis have been achieved as follows,1. CdS polycrystalline thin films are fabricated on the different substrata of three kinds by chemical bath deposition and vacuum evaporation. Specially, the effects of solution concentrations with three different ranges on the structural properties have been investigated. SEM and XRD observations have showed that the polycrystalline thin films fabricated by chemical bath deposition in a low concentration are more continuous, homogeneous and compact than that prepared by vacuum evaporation.2. In the many factors that influence the quality of CdS deposition, the surface roughness of substrata is the important one. Exactly, SnO2/glass substrata are the best, the glass substrata are the better, and ITO/glass substrata are not good for deposition of CdS polycrystalline thin films. It is interesting that CdS polycrystalline thin films prepared by CBD show the hexagonal phase on ITO/glass substrates, the cubic phase on ITO/glass substrates; however, all CdS films deposited by vacuum evaporation show hexagonal phase on the substrata of three kinds.3. From above results, the SnO2/glass substrates were chosen to be fabricated CdS thin films by CBD. The thickness of CdS thin films was about 80(Tl500A.4. The post-deposition treatment for CdS polycrystalline thin films was a step in the fabrication of polycrystalline CdS/CdTe solar cells. The effects of CdCl2 vapor treatment on CdS films have been investigated. A comparison between the'structure of CdS films with and without CdCL. treatment was presented. With the increase of annealing temperature and annealing time, the cubic phases of CdS films are destroyed and the transparency of CdS films decreases. Thus, the annealing process with CdCL treatment has been canceled in our fabrication procedure ofCdS/CdTe solar cells.5. The thick CdTe films on quartz glass as the source was often used in close-spaced sublimation (CSS). However, it is better to change the substrata of the source for fabrication and production of large area solar cell, and the high pure graphite plank could be the best substitute. Therefore, the deposition conditions of CSS have been investigated when using graphite plank as the source substrate. The continuous, homogeneous CdTe thin films have been obtained, and it has been demonstrated that the efficiency of CdS/CdTe solar cells is higher than 12. 3%.6. The deposition of CdTe polycrystalline thin films by the CSS technique is based on the reversible dissolution and combination process of CdTe at high temperatures. The temperature of CdTe beginning to dissociate has been observed to be about 470癈 under the pressure of around 2 kpa. The results has become an important foundation that determines the CSS procedure.7. As the same, the temperature of CdS beginning to dissociate under the same pressu...
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