Low Cost Thin-Film CdS-Based Solar Cells—Progress and Promise

The direct conversion of sunlight to electricity using thin film solar cells is potentially a low cost renewable source of energy. A major factor contributing to the low projected costs is the very small quantities of materials required as the active layers of the cells can be as little as 2 μm thick. The efficiency of solar cells will have to exceed ten percent to achieve economic power generation. Until 1976 no thin film solar cells with above seven percent efficiency in sunlight had been reported, but since then the Institute of Energy Conversion has successively reported 7.8, 8.55 and 9.15 percent. This paper will describe the loss minimization methodology utilized to achieve these increases in performance. Analysis shows that efficiencies as high as 14–16 percent for CdS-based solar cells are achievable. The research and development necessary to achieve these high efficiencies will be described. The feasibility of an extremely low cost manufacturing process capable of producing solar cells costing 250 dollars/kWatt will be discussed. Recent progress in development of low-cost thin-film devices shows great promise that direct conversion of sunlight to electricity can make a measurable contribution to the electrical energy supply both nationally and internationally.