Improved Cu/Mo back contact for CdS/CdTe solar cells

The simple back contact Cu (10 nm)/Mo (500 nm) gives low series resistance when the CdTe surface is both smooth and grain size is up to 5 μm, for this case the solar cell efficiency is typically around 8-12%. There are cases where the CdTe surface have an opposite characteristics, in these cases the series resistance is too high, it produces poor fill factor and efficiency. It can be drastically improved at 11.0% by using multilayer Cu/Mo/Cu/Mo without degrading the Jsc and Voc values. The improved efficiency is due to an important change in the fill factor via lowering the series resistance. The solar cells were fabricated using ITO/ZnO/CdS/CdTe layers. The ZnO, CdS, Cu and Mo films were deposited by rf-sputtering. The CdTe film was grown by conventional CSS technique. The cells were activated by using CHClF₂-argon-oxygen gases.