Photovoltaic Czochralski silicon manufacturing technology improvements. Annual subcontract report, 1 April 1993--31 March 1994

This report describes work performed under a 3-year, 3-phase, cost-share contract to demonstrate significant cost reductions and improvements in manufacturing technology. The objective of the program is to reduce costs in photovoltaic manufacturing by approximately 10% per year. The work was focused in three main areas: (1) silicon crystal growth and thin wafer technology; (2) silicon cell processing; and (3) silicon module fabrication and environmental, safety, and health issues. During this reporting period, several significant improvements were achieved. The crystal growing operation improved significantly with an increase in growth capacity due to larger crucibles, higher polysilicon packing density, and high pull speeds. Wafer processing with wire saws progressed rapidly, and the operation is completely converted to wire saw wafer processing. The wire saws yield almost 50% more wafers per inch in production, thus improving manufacturing volume by 50% without any additional expense in crystal growth. Cell processing improvements focused on better understanding the contact paste and firing processes. Module designs for lower material and labor costs began with the focus on a new junction box, larger modules with larger cells, and a less costly framing technique. In addition, chlorofluorocarbon (CFC) usage was completely eliminated in the Siemens manufacturing facility during this period, resulting in significant reductions in the cost of caustic waste treatment