A Study of the Back Contacts on CdTe/CdS Solar cells

Conventional back contacts on CdTe/CdS solar cells are commonly made with Cu/Au or Cu/graphite. Often the contact limits the solar cells efficiency and the performance degrades because of Cu diffusion to the junction. In order to get stable and 'non-rectifying' back contacts Sb has been applied. Pre-deposition etching treatments, post-deposition annealing, influence of Sb layer thickness and stability issues have been studied. Different etchants not only clean the CdTe surface but they also produce a conducting Te layer on the grain boundaries. Using a mixture of nitric and phosphoric acid and Sb/Au as a back contact. 12.5% efficiency cells are obtained. The stability of solar cells depends on the etching solution. Stability tests under continues 1 sun illumination suggest that under optimum condition stable cells with Sb/Au contact can be developed. A comparative analysis of the photovoltaic properties of solar cells with different back contacts will be presented.