Excimer laser annealing to fabricate low cost solar cells. Quarterly technical report No. 1, 26 March-30 June 1984

Abstract

The objective of this research is to show whether or not pulsed excimer laser annealing (PELA) of ion-implanted junctions is a cost effective replacement for diffused junctions in fabricating crystalline silicon solar cells. The preliminary economic analysis completed during the first quarter of this program shows that the use of PELA to fabricate both the front junction and back surface field (BSF) would cost approximately 35 cents per peak watt (Wp), compared to a cost of 15 cents/Wp for diffusion, aluminum BSF and an extra cleaning step in the baseline process described by JPL. The cost advantage of the PELA process depends on improving the average cell efficiency from 14% to 16%, which would lower the overall cost of the module by about 15 cents/Wp. The technical goal of this research is to develop an optimized PELA process compatible with commercial production, and to demonstrate increased cell efficiency with sufficient product for adequate statistical analysis. During the first quarter of this program an excimer laser annealing station was set-up and made operational. The first experiment used 248 nm radiation to anneal phosphorus implants in polished and texture-etched silicon. Preliminary results showed that the PELA processed cells had overall efficiencies comparable to furnace annealed ion implanted controls, and that texture-etched material requires lower fluence for annealing than polished silicon. Process optimization will be carried out in the second quarter.