Novel CdSe-based PV structure for high efficiency CdSe/CIGS tandem solar cells

One of the key challenges for CIGS-based PV technologies is to achieve efficiencies in the -20% range and higher, in order to compete with c-Si efficiencies and to reduce $/Watt manufacturing costs. A tandem device structure is one path to achieving these high efficiencies. CIGS has an ideal bandgap (-1.1 eV) for the bottom cell of a tandem structure and CdSe is an ideal material for the top cell, given its favorable optical properties and -1.75 eV bandgap. While theoretical efficiencies for a CdSe/CIGS-based tandem PV structure exceed 36%, prior attempts at CdSe-based PV devices have failed to achieve high efficiencies. We propose an innovative device structure to solve previously encountered issues by inserting an engineered graded blocking layer in the top CdSe-based cell. We present the proposed device structure and simulations showing robust device performance over for a broad range of defect densities, including comparisons to a conventional structure lacking the graded blocking layer.