Application of locational CdCl2 treatment to CdS thin films grown on an ultra-thin MgZnO for CdTe solar cells

In this study, the impact of locational CdCl2 treatment on the MgZnO/CdS stacks was investigated. In the stack structure with an ultra-thin MgZnO layer, the samples with CdCl2 applied to the inter-face, the top-surface, and both the inter-face and top-surface were grown by chemical bath deposition. The application of CdCl2 to the inter-face and to the inter-face and top-surface caused the CdS to change from cubic to hexagonal phase and the formation a cubic CdO phase. However, the MgZnO phase disappeared in the stacks, due to the applied experimental conditions. CdCl2 treatment only to the inter-face or only to the top-surface improved the grain structure of the stacks, but CdCl2 applied to both surfaces led to a porous structure. In addition, it was observed the presence of CdS and MgZnO absorption edges in all stacks. Besides, similar emission bands revealed for defect transitions relating to the MgZnO and CdS layers in all samples. The refractive index values decreased with the effect of CdCl2 treatment. In addition, the application of CdCl2 only to the top-surface appeared the inter-band transition of both MgZnO and CdS, while CdCl2 treatment to both surfaces caused the sharp band transition to disappear. According to the analysis results, it can be said that local CdCl2 treatment has a clear effect on the structural and optical properties of MgZnO/CdS stacks, and that CdTe can potentially improve cell performance with optimization processes.