Cadmium chloride treatment of CdTe solar cells

The picture at right shows a cross-sectional micrograph of a CdS/CdTe solar cell that was deposited on glass. The large grains on top are the CdTe layer which is about 10 microns thick. The fine grain material at the bottom is 1 micron of transparent conducting oxide. In between is a 100 nm layer of CdS which cannot be distinguished at this level of detail. In order to achieve maximum efficiency it has been found that is it necessary to treat this structure with CdCl₂ at elevated temperatures. Originally this process was performed by boiling the device in a saturated methanol solution. The student on this project, Yoxa Mahathongdy, has developed an alternative vapor phase treatment for this processing step. Using statistical experimental designs she identified an opitimum processing window. Cells processed using the vapor phase technique are more reproducible and demonstrate superior performance compared to solution-treated cells. Current studies are directed at determing the diffusion coefficient of chlorine in these cells, and developing a better understanding of the role chlorine plays.

This project is supported by the National Renewable Energy Laboratory