Effects of the annealing temperature and CdCl2 treatment of CdTe films prepared by vacuum evaporation on structural properties of the CdTe films and photovoltaic properties of thin film CdS/CdTe solar cells were investigated. The crystal structure of as-deposited CdTe films was zincblende type with preferential orientation of the (111) plane parallel to the substrate. The preferential orientation of the (111) plane in CdTe films decreased, and the grain size of CdTe films increased with the increase of the annealing temperature and the CdCl2 treatment. As increasing annealing temperature, the conversion efficiency of the CdS/CdTe solar cells without and with CdCl2 was increased due to increasing grain size and improving crystalline of CdTe films. However, the efficiency of cells annealed at the temperature of higher than 500°C for cells without CdCl2 treatment and 450°C for cells with CdCl2 treatment was reduced because of increasing reverse saturation current density and series resistance.

CdTe films for solar cell application were prepared at various growth temperatures by a vacuum evaporation system having close spacing between the source and substrate. The CdTe thin films had a cubic structure highly oriented with the (111) direction perpendicular to the substrate surface, regardless of the growth temperature. The crystallites are of random shape and reach up to about 2 µm in size with increasing growth temperature. The higher growth temperature contributed to the reduction of dark resistivity from 6 × 10 7 ·cm at room temperature to 45.4 × 10 6 ·cm at 300 • C. The photovoltaic properties of the CdS/CdTe solar cell were considerably improved with the increase in the growth temperature, which was caused by the increase of (111) texture and grain size in CdTe films.

The degradation process of silicone rubber was investigated by leakage current monitoring in the inclined-plane method. A data acquisition system (DAS) with 12-bit, 8-channel analogi digital (AD) converter was prepared. The maximum erosion depth was measured for use as the degradation indicator. The result suggests that the discharge duration and current waveform are well corresponding with the degradation process. And fast Fourier transform (FFT) analysis from the stored wavefonn shows that the harmonic ratio 13111 corresponds with the initial sur face transition from hydrophobic to hydrophilic, and with further progressive degradation. In addition, it may be possible to use cumulative charge and peak pulses as quantitative indica tors of failure. Furthermore, the contact angle was adopted for assessing surface degradation.These results indicate that the surfaces are divided into top and bottom areas depending on the degree of exposure to dry band arcing. It seems that the bottom area subjected to most of the dry band arcing contains very short chains of silicone rubber as well as alumina lrihydrate fillers, while the top area shows the loss of filler particles.

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