Study Of Deposition And Annealing Of CdTe Polycrystalline Thin Films

Owing to its optoelectronic and chemical properties, CdTe is an ideal absorber material for high-efficiency, lowcost thin film polycrystalline. However, a key factor of fabricating high-efficiency CdTe/CdS solar cells is gaining high-qulity polycrystalline CdTe thin films .Therefore, The thesis has investigated the structural and optoelectronic characteristics of CdTe polycrystalline thin films , the performance of CdTe solar cells, and the influence of their deposition and annealing process-.The deposition rate dependence of source temperature, substrate temperature and deposition pressure has been studied systematically. According to the results of XRD and AFM images, the structural changes of the CdTe thin films deposited in different pressure have been observed. Through the hall effect measurement, the temperature dependence of sheet resistivities, sheet carrier densities and hall mobilities have been calculated. We have concluded that the appropriate deposition conditions of CdTe thin film in comparatively high pressure are substrate temperature of 540-580 source temperature of 630 and the rate is 1-1.4m.min-1. The continuous, compact thin films have been achieved. The CdTe thin films with better quality deposited on the substrates with better crystal status. The crystal lattice constant of as-deposited CdTethin films increased with the deposition pressure raising. Hall effect measurement show that the resistivities of CdTe thin film monotonously decreased with the temperature increasing. From 20K to 80K the resistivities decrease rapidly and from 80K to 300K decrease slowly with temperature.The structural and optical properties changes of CdTe thin films have been studied, and the fuctions of O2 been discussed, after the CdCl2 treatment was used to CdTe thin film at different atmosphere (N2 O2), The AFM morphology images show that there are some continuesly distributing grains with diameter about 100nm in the CdCl2-treated CdTe thin flims, which was not observed in SEM images. SEM cross section of CdTe/CdS show that CdS layer was comsumed more greatly at 20% of atmosphere 0,(80% nitrogen and 20% oxygen) than N2(100% nitrogen). It indicated that the exist of O2 promoted the interdiffusion of CdTe/CdS. The optical energy gap of CdTe thin film is mainly due to it deposition process, and varies little after annealing at various ambience.The performance of solar cells depend on annealing ambiences have been studied. The J-V curve test illuminated : the performance of solar cells are better annealed at O2 atmosphere than those at N2, and changes little after annealed at different percent of 02 atmosphere.