Dip coating process. Silicon sheet growth development for the large-area silicon sheet task of the Low Cost Silicon Solar Array Project. Quarterly report No. 5, December 18, 1976--March 21, 1977

Description/Abstract

Ceramic substrates can be coated with a thin layer of large-grain polycrystalline silicon by a dip-coating process. The silicon-on-ceramic (SOC) material appears to be quite promising as a low-cost cell material but requires somewhat special fabrication procedure since the contacts to both the n- and p-layers are now made on the front surface. Solar cells have been made on SOC material and on single-crystal control samples. Photodiodes 0.01 to 0.1 cm/sup 2/ made on substrates coated with vitreous carbon prior to dip coating with silicon showed the best efficiency of SOC material to date, namely over 6 percent uncorrected and about 12 percent inherent efficiency. Etching procedures have indicated that the dislocation density varies from almost 10/sup 7/ cm/sup -2/ to almost dislocation-free material, assuming that all etch pits are due to dislocations. EBIC measurements procedures were also improved, and it was found that diodes appear to be fairly uniform in EBIC response. A new SOC coating facility is being designed which will coat larger substrates in a continuous manner. The purpose is to minimize the contamination problem by reducing the contact area of the substrate with molten silicon. By having much larger throughput, it will also demonstrate the scale-up potential of the silicon-on-ceramic process. Portions of the new facility are under construction. An attempt has been made to model the economics of a large-scale facility for coating ceramic panels with silicon. A first iteration based on available parameters estimates showed that major cost items were poly Si ($2.90 per square meter), labor and burden ($2.50 per square meter), and the ceramic substrate ($2.50 per square meter), for a total price of about $11 per square meter.