Published: 1978
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Development effort has been applied to front junction and back surface field region formation and to high speed application of AR coatings to ribbon material. Effects on cell performance of various surface preparation procedures for web silicon material have also been studied. Ultrasonic seam bonding of foil interconnects to cell metallization has been identified as a potentially higher throughput, lower cost method of interconnection than producing discrete bonds. Collecting junctions have been made in wafer cells using reagent grade POCl3, containing titanium at the 20 ppMa level, and in such material doped with Ti to the 100 and 500 ppMa levels using TiCl4. No electrical effect of Ti doping was detected. Cells with boron diffusions made from boron-doped glasses deposited in a Silox reactor have shown back surface field action to that in cells using glasses formed in a cold wall horizontal reactor. Antireflection coatings of TiO2 in the 600 A range of thickness have been prepared by pulling from liquid precursor solutions at speeds ranging to 40 ft/min. Speeds above 10 ft/min are considered necessary for high throughput processing of continuous ribbon silicon. At 25 ft/min, the contribution to selling price of this process is estimated to be about $0.009/peak watt, with the cost of unrecovered alcohol being the major price component. Several methods of preparation of the web silicon surface have been considered with regard to ultimate cell performance.