Dependence of CdS/CdTe thin film solar cell characteristics on the processing conditions

The effects of post deposition heat treatment on the electrical and structural properties of thin film glass/ITO/CdS/CdTe/Au solar cells have been investigated. The results of three types of cells: as-deposited, annealed in air at 400 degrees C for 30 min and CdCl2 treated cells are compared. XRD studies of the CdTe layer showed some preferred orientation along the {311} direction in as-deposited material, but heat and CdCl2 treatments resulted in increased randomisation. Temperature dependent J-V characteristics indicated that in the as-deposited and heat treated specimens current transport was dominated by tunnelling recombination processes. In contrast, in the CdCl2 treated cells, which showed much improved electrical characteristics, current transport was limited by thermal emission across the junction suggesting a reduction in the interfacial recombination rates. Spectral response measurements under reverse bias confirmed the improvement in junction characteristics following CdCl2 treatment.