DESIGN AND FABRICATION OF HIGH-EFFICIENCY THIN-FILM CDS-CU2S SOLAR-CELLS

Thin film photovoltaic cells of CdS/Cu2S which exhibit conversion efficiencies in excess of 9% have been designed and fabricated. Specific cell designs are prepared from an analysis of optical and electronic loss mechanisms operative in the cell. Material and engineering modifications to the fabrication process are then made to minimize specific energy conversion losses. The present cell design consists of five thin film layers which are sequentially prepared on a copper substrate 35 μm thick. In addition to the material control required for each component layer, the electrical, chemical, mechanical and topological compatibilities at the interfaces between each adjoining layer must be assured to achieve the desired cell performance. Our present analysis shows that a fully optimized solar cell based on a CdS/Cu2S junction will have a practical conversion efficiency limit of about 11%. It is anticipated that practical conversion efficiencies of 14-15% can be achieved utilizing a (CdZn)S/Cu2S junction designed to produce the maximum open-circuit voltage possible using Cu2S as the absorbing layer. Present cell results which incorporate this design are presented. © 1979.