Effect of CdCl2 heat treatment on ZnTe back electron reflector layer in thin film CdTe solar cells

The effect of CdCl2 heat treatment on the ZnTe layer used as the back electron reflector layer in polycrystalline CdTe solar cells was investigated. A thin film of ZnTe was grown on top of polycrystalline CdTe layer using metalorganic vapor phase epitaxy, which was then subjected to CdCl2 heat treatment. The effect was examined using various characterization techniques such as X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscope images and it was found that the ZnTe layer transformed into CdTe and ZnO due to the treatment. This was verified by performing CdCl2 heat treatment on pure ZnTe thin layer directly grown on glass which also showed the conversion of ZnTe to CdTe and ZnO. To study the effect of this transformation on final device performance, thin film CdTe solar cell structures were fabricated with ZnTe electron reflector layer with and without the CdCl2 heat treatment. The device without the ZnTe layer seemed to perform better than the devices with ZnTe layer and the CdCl2 heat treatment.