Bifacial CdS/CdTe Solar Cell using Transparent Barium Copper Sulfide as a Hole Transport Layer

We report the properties of earth-abundant p-type transparent BaCu4S3 (BCS) thin films deposited by solution-based method. Our films of 100 nm thickness show transparency > 70% over the visible and near-infrared regions. We study the bifacial photovoltaic performance of CdTe solar cells using BCS as a hole transport layer. The BCS deposition etches the CdTe to leave a Te rich surface which can help to reduce the barrier height. Our best device, completed with ITO on the BCS, when illuminated from the glass side illumination (eta = 12.3 %) shows improved performance relative to our standard Cu/Au back contact, with increased V-oc and FF. For film side illumination, J(sc) is low and (eta reaches just 1%). Once optimized, this earth-abundant transparent BCS could serve as an effective, inexpensive, low-toxicity back contact layer for bifacial CdTe solar cell.