Optimization of front metal contact firing scheme to achieve high fill factors on screen printed silicon solar cells

For widespread implementation of silicon PV, the module cost must be reduced by a factor of 2–4. This can be accomplished by lowering the cost of solar cell materials and processing without sacrificing cell efficiency. A combination of high throughput belt line processing, SP contacts and mc-Si material offers an opportunity for significant cost reduction. However, most cell manufacturers who use the above combination are only able to achieve fill factors in the range of 0.68–0.75 with cell efficiencies in the range of 10–14%. Thus throughput gains are attained at the expense of device performance. In addition, there is considerable scatter in the fill factor of the SP cells in the literature with no clear guidelines for achieving high fill factors. This paper shows that proper understanding of loss mechanisms and optimization of SP paste and firing cycle can lead to fill factors approaching 0.77 and 0.79 on mc-Si and single crystal silicon, respectively, on a 45 Ω/□ rapidly formed belt line emitter with a shallow junction depth of ∼0.27 μm. It was observed that deep and shallow emitters on mc-Si could lead to the same values of fill factors ∼0.77 when the proper combination of paste and firing cycle is applied. The peak firing temperature for deep emitter is higher than the shallow ones with superior value of junction leakage current.