Excimer Laser Annealing to Fabricate Low Cost Solar Cells. Quarterly Technical Report No. 3, October 1-December 31, 1984

摘要

The objective of this program is to determine whether or not pulsed excimer laser annealing (PELA) of ion-implanted junctions is a cost effective replacement for diffused junctions in the fabrication of crystalline silicon solar cells. The preliminary economic analysis completed during the first quarter of this program showed that the use of ion implantation and PELA to fabricate both the front junction and back surface field (BSF) was more expensive, per wafer, than a hypothetical baseline diffusion process. However, a cost advantage may be attained if the implant-PELA process yields an improvement in the average cell efficiency from 14%, as assumed for the baseline diffusion process, to 16%. This improvement in cell efficiency 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 third quarter of this program it was shown that a KrF based excimer laser, which would be the most economical to operate, can produce results equal to those seen with a XeCl laser, which was used for most experiments reported in the literature. Also during this quarter it was shown that the PELA junction can probably be improved by the time-temperature cycles typically used to sinter screen printed contacts. It was also shown that a PELA process with minimum overlap (pulsing each surface area once) is preferred for both technical as well as economic reasons. PELA of ion implanted junctions on texture-etched silicon did not yield good cells when screen printed contacts were applied. Work planned during the fourth quarter includes optimization of the PELA process parameters for use with screen printed contacts on polished wafers, completion of the 300 wafer process demonstration task, and completion of the economic analysis. (ERA citation 10:020206)