18-20%* will be required. Ref. A4 reports that efforts are underway at NASA and COMSAT to improve tne efficiency of silicon solar cells for space applications and that new developments have resulted in a demonstrated efficiency of 15% in the laboratory. Ref. All states that the efficiency goal can be achieved through increases in fill factor, short-circuit current and open circuit voltage. Since lower resistivity gives higher open circuit voltage, Ref. All points out the desirability of decreasing the resistivity of bulk silicon to 0.025 ohm/in (0.01 ohm/cm). It also states that increased short-circuit current could be achieved by anti-reflective coatings that match across the cell spectrum, and concludes that the major issue is to achieve these improvements in a mass produced, light weight solar cell blanket. Ref. A4 reports that many researchers in the field doubt that the efficiency goal will be met. b. Solar Cell Thickness The solar photovoltaic SPS concept is based heavily on the availability of a solar cell blanket with a cell thickness of 2 mils (50 microns). Also included would be a 1 mil (25 micron) thick FEP plastic cover, 0.25 mil (6 micron) thick metal contacts, 1 mil (25 micron) thick metal interconnects, 0.5 mil (13 micron) FEP plastic base layer and a 0.5 mil (13 micron) Kapton plastic substrate (Ref. All). Current cell thicknesses are 8-10 mils (200-250 microns) for the best production cells available for flight use, and for geosynchronous orbit, these cells use 6 mil (150 micron) thick shields (Ref. A5). Ref. A4 reports that some effort has been expended on 6 mil (150 micron) cells and that 4 mil (100 micron) cells have been built in experimental laboratories. Ref All states that work is currently in process on 4 mil (100 micron) thick silicon ribbons. Ref. A4 concludes that "the extension to 2 mils (50 microns) without increasing handling costs is going to be very difficult at best."
RkJQdWJsaXNoZXIy MTU5NjU0Mg==