Amorphous Silicon Alloy Photovoltaic Technology - From R&D to Production

The key requirements for photovoltaic modules to be accepted for large-scale terrestrial applications are (i) low material cost, (ii) high efficiency with good stability, (iii) low manufacturing cost with good yield and (iv) environmental safety. Thin films of amorphous silicon alloy are inexpensive; the products are also environmentally benign. The challenge has been to improve the stable efficiency of these modules and transfer the R&D results into production. Using a multijunction, multi-bandgap approach to capture the solar spectrum more efficiently, we have developed one-square-foot modules with initial efficiency of 11.8% After 1000 h of one-sun light soaking, a stable efficiency of 10.2% was obtained. Both the efficiency values were confirmed by National Renewable Energy Laboratory. The technology has been transferred to production using an automated roll-to-roll process in which different layers of the cell structure are deposited in a continuous manner onto stainless steel rolls, 14′ wide and half a mile long. The rolls are next processed into modules of different sizes. This inexpensive manufacturing process produces high efficiency modules with subcell yields greater than 99% The key features of the technology transfer and future scope for improvement are discussed.