Heat exchanger method, ingot casting; fixed abrasive method, multi-wire slicing, phase 2. Silicon sheet growth development for the large area sheet task of the low cost silicon solar array project
A crack-free silicon ingot has been cast in a graded, semiconductor purity silica crucible. More than 90% single crystallinity has been achieved in 2.5 kg cast ingots. The impurities on the surface of the melt have been reduced with the use of a rapid heat-up cycle and absence of graphite retainers. Solar cells fabricated out of HEM cast material have shown conversion efficiency up to 14% under AM1 Xenon source illumination. Considerable progress has been achieved in casting square cross-section ingots. The growth in the corners has been obtained but the problem area is in fabricating a custom-made graded crucible. Kerf loss was reduced to 6.2 mil, 0.155 mm in slicing 4 cm x 4 cm cross-section with 100% yield. The abrasive life of plated impregnated blades was increased by hardening the electroless nickel layer. In an effort to prevent diamond pull-out and thereby improve the abrasive life, the plated layer was increased from 0.3 mil, 7.5 ..mu..m to 0.5 mil, 12.5 ..mu..m. The extra thickness buried the diamonds. A thinner copper sheath for impregnation and a thicker nickel coating to prevent diamond pull-out is expected to improve the abrasive life. Higher feed forces increased the cutting rates but resulted in deeper surface damage
