Effects of heat treatment of vacuum evaporated CdCl₂ layer on the properties of CdS/CdTe solar cells

In this work, CdTe films were prepared by r.f. magnetron sputtering. Influence of dry CdCl₂ treatments on the structural and optical properties of CdTe films was investigated by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and UV-Visible spectrophotometer. Also, CdS/CdTe thin film solar cells were fabricated by all sputtering process and the cell characteristics were studied. The as-deposited CdTe thin films had a zincblende structure highly oriented with the (111) direction parallel to the substrate surface. The CdTe films lose their preferred orientation and become polycrystalline by heat treatment with dry CdCl₂ treatment. The wet CdCl₂ treatment exhibited a similar trend, but is less effective for grain growth than dry CdCl₂ treatment. The photovoltaic properties of the CdS/CdTe solar cell were considerably improved with the increase in the annealing temperature, which was caused by the increase of grain size in CdTe films. However, the wet CdCl₂ process was not suitable for reproducible fabrication.