Improving CdS/CdTe thin film solar cell efficiency by optimizing the physical properties of CdS with the application of thermal and chemical treatments

CdS polycrystalline thin films have been used as a window layer in CdTe, Cu(In,Ga)Se2 and Cu2ZnSnS4 solar cells; the specific optical and electrical properties of the CdS-partner play an important role in the photovoltaic device performance, so that one of the problems to be solved is to reduce the pin-hole density and intergrain cavities on the CdS surface. SnO2:F/soda-lime glass substrates (FTO) were treated with HCl, Ar and O2. CdS films were deposited on FTO substrates by using the chemical bath deposition technique and then CdS thin films were thermally annealed on CdCl2, Ar atmospheres and muffle at atmospheric ambient. Optical and morphological measurements revealed that the HCl treatment improves the CdS growth because the defect levels were reduced while the grain size is increased. The processed CdS-thin films were applied on CdTe solar cells and the photovoltaic efficiency was about 12% when the CdS thin films were thermally annealed in muffle at atmospheric ambient.