Silicon web process development. Low Cost Solar Array Project: Large Area Silicon Test Task. Annual report, April 1978-April 1979

Abstract

A total of 154 experimental silicon web growth runs were performed during the first year of this program. Each of the web crystals grown was characterized dimensionally, showing that the average width per run had increased by 60% as compared to the start of the program. Maximum width reach 3.5 cm for longer web crystals, and 4.1 cm for short crystals. Web lengths greater than 3 meters were grown. Growth speeds of 10 cm/minute were attained for short periods of growth. The maximum combined width and speed resulted in a throughput area rate of 8 square centimeters per minute. The thickness of web crystals grown during this period commonly occurred within the range of 100 to 200 ..mu..m (4 to 8 mils). Selected samples of web were further characterized as appropriate. Electrical characterization included bulk resistivity, minority carrier lifetime by the open circuit decay method, and a variety of other solar cell properties. Web solar cells fabricated for web characterization purposes reached 14.5% AM1 efficiency and averaged 12%. Development of solar cell fabrication techniques included boron and aluminum back surface fields, impurity gettering during cell fabrication, web surface preparation prior to cell fabrication, and tailoring of the cell fabrication processmore » for web. During the first year of this program 46 solar cell fabrication runs were made, comprising a total of over 750 solar cells.« less