Cast Polycrystalline Silicon Photovoltaic Module Manufacturing Technology Improvements: Semiannual Subcontract Report, 1 January 1995 - 30 June 1995

This report describes work performed by Solarex, the objective of which is to advance Solarex's cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance, and expand its commercial production capacities. Two specific objectives are to reduce the manufacturing cost for polycrystalline silicon PV modules to less than $1.20/W and to increasethe manufacturing capability by a factor of three. To achieve these objectives, Solarex is working in the following technical areas: (1) casting, (2) wire saws, (3) cell process, (4) module assembly, (5) frameless module development, and (6) automated cell handling. Accomplishments reported include: (1) Cast first successful larger ingot producing 73% larger volume of usable silicon. (2)Increased the size of the ingot even further and cast an ingot yielding nine 11.4-cm x 11.4-cm bricks, representing a 125% increase in usable silicon from a single casting. (3) Operated the wire-saw in a semi-operational mode, producing 459,000 wafers at 94.1% overall yield. (4) Reduced the cost of wire saw consumables, spare parts, and waste disposal. (5) Developed a cost-effective back surfacefield process that increases cell efficiency by 5% and began production trials. (6) Developed a plan for increasing the capacity in the module assembly area. (7) Completed qualification testing of modules built using Spire's automated tabbing and stringing machine. (8) Selected, tested, and qualified a low-cost electrical termination system. (9) Completed long-term UV testing of experimentalback sheets. (10) Qualified the structure and adhesive-tape system for mounting frameless modules. (11) ARRI completed a study of the fracture properties of cast polycrystalline silicon wafers and provided the information necessary to calculate the maximum stresses allowable during wafer handling.