3. The development of improved production processes, 4. Improvements in collection efficiency, and optimization of temperatures reached with solar concentrators, 5. The use of multijunction cell designs, 6. The use of lithium doping, 7. Improved antireflection coatings, 8. Methods of decreasing surface recombination velocity, 9. Methods of improving high-temperature and high solar intensity performance, and 10. New methods for environmentally testing devices to provide more reliable and better designed parts. b. Key Issue No. 2 — Solar Cell Cost Reduction The need for reducing the cost of solar cells is a critical factor for the SSPS and has been recognized as the prime item not only for SSPS, but also for terrestrial applications of photovoltaic energy conversion techniques. Solar cells used in the space program presently cost about $80 per watt, while the SSPS requires a cost of about $0.40 per watt. Although it is known that a major portion of this reduction in cost will be possible as a result of mass production, there still are several approaches that need to be studied. Solar cell cost reduction will be accomplished by developing: 1. New silicon material sources, 2. New crystal-growing processes, 3. New solar cell fabrication processes, 4. Ways of minimizing the heat or power input to the processes, 5. New mass production and automated processing techniques. c. Key Issue No. 3 — Solar Cell Array Blanket Improvement The SSPS will utilize very large area solar cell arrays that will be able to be effectively handled, only if large integrated submodules or blankets of cells can be developed. Presently, solar cell arrays are made much like an art mosaic where individual cells are fitted, interconnected, and bonded to substrates. Power-to-weight ratios of about 60 W/lb could presently be achieved, but ultra lightweight blankets of over 400 W/lb are required for the SSPS. This can be accomplished by developing:
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