High Efficiency CdTe/CdS Thin Film Solar Cells Prepared by Treating CdTe Films with a Freon Gas in Substitution of CdCl2

CdTe/CdS thin film solar cells have reached a sufficient conversion efficiency to be considered for an industrial application. The fabrication process is quite fast and it is one of the easiest to be transferred to a large-scale production. In the past, we have simplified the fabrication process by eliminating the etching step by making a completely dry process. A further simplification has been done by substituting the CdCl2 step by treating CdTe films in an atmosphere containing a non toxic gas that is inert at room temperature, namely HCFCl2. This belongs to the Freon© family. The best treatment conditions are as follows. Treatment temperature is typically 400°C. Time of treatment is on the order of a few minutes and the atmosphere containing Cl is typically 100 mbar of Ar containing 15% of HCFCl2. The change in the morphology of CdTe films after treatment is very similar to that obtained with CdCl2 treatment and an increase in the size of small grains is always observed. Solar cell efficiency obtained with this treatment, close to 16%, is comparable if not larger than that reached with CdCl2 treatment. The Cl2-treatment can be made with any gas of the Freon family and the only need is that the gas contains chlorine. This method is very effective in producing high efficiency cells. It avoids the use of CdCl2 that could be dangerous and instead it uses a gas that is stable, inert and not toxic at room temperature. Besides it eliminates the step of CdCl2 evaporation and, as a consequence, it is much more suitable for an industrial production. This process has been patented