Thin Film as a Back Contact layer*

We report the properties of earth-abundant p-type transparent conducting nanocomposite (NC) thin film (CuS)_x (ZnS)_1-x, deposited by a facile and low-cost chemical bath deposition method. Our films of ~45 nm thickness show transparency ~80 % in the visible spectral region (at 550 nm) with compact grains of size < 15 nm. The purpose of fabricating of these wide band gap (~ 2.70 eV) (CuS)_x (ZnS)_1-x partially transparent thin films was to utilize them as back contacts to CdTe thin film solar cells. Since critical avenues to increased energy yield for CdTe PV technology, such as bifacial cell or tandem cell designs, rely on the need to develop transparent back contact approaches that enable high efficiency and high transparency. Further, when finished with a conductive transparent indium tin oxide (ITO) layer, the high transparency of the NC thin film interface layer enables back illuminated operation of the solar cell. Once optimized, and with an improved interface and bulk CdTe carrier lifetimes, this NC earth-abundant transparent conductor based on Cu, Zn, and S may serve as an effective, inexpensive, low-toxicity back contact layer for a bifacial CdTe solar cell.