Consecutive Study Of Back Contact Barrier Height and CdS Layer Thickness And Their Effect On CdTe Solar Cell Efficiency*

Favored for its low cost and relatively high efficiency (22.1% in 2016), Cadmium Telluride (CdTe) solar cells are popular among the thin film generation because they still have room for improvement. CdTe solar cells have a high electron affinity (about 4.5 eV) and as a result when metal contacts are used, a good ohmic contact is not created, and a Schottky barrier is formed at the back-contact junction. This barrier impedes current flow and lowers cell performance. The thickness ratio of Cadmium Sulfide (CdS) to CdTe is also important as increasing or decreasing the thickness of the [n-type] CdS layer will affect the production and recombination rate of charge carriers.
In this work, we show our studies on the effect of the back-contact barrier height and CdS layer thickness on the performance of CdTe solar cells. Using the turning point technique and a corresponding formula, we were able to obtain the barrier height at the back-contact junction of cells with different back-contact materials. We have also fabricated four CdTe samples using a pulsed-laser deposition process, each with a different CdS layer thickness, and have determined their efficiencies. Our results show us that barrier height and CdS layer thickness do have a direct effect on solar cell performance.