High Efficiency Mono-Crystalline Solar Cells with Simple Manufacturable Technology
Upadhyaya, A. D.
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This paper describes the analysis and optimization of phosphorus-doped n(+) emitters for Si solar cells with screen-printed contacts to improve the uniformity of contact formation. Analysis of the simulated emitters showed that J(oe) increases with the increase in phosphorus surface concentration. Cells fabricated on emitter having a higher surface concentration and shallower junction depth, were on an average 0.3% (absolute) higher in efficiency and 0.5 mA/cm (2) higher in J(sc) values. Internal quantum efficiency analysis showed that the J(sc) enhancement was due to better short wavelength response in these cells. In addition the fill factors were also slightly higher in the cells with higher surface concentration and shallower junction depth. SEM analysis showed larger (~1.5μm) and more uniformly distributed Ag crystallites on the surface of cells with emitter that had higher surface concentration. This may lead to a more tolerant contact firing process and result in a higher yield of high-efficiency cells. Furthermore, use of emitters with higher phosphorus surface concentration and shallower junction depth reduces the cell processing time appreciably leading to high throughput and cost savings in cell manufacturing. We were able to tailor the emitter profile and the firing conditions of a commercially available front silver paste to obtain good average FF’s of 77.7% in conjunction with short circuit current (J(sc)) of 34.8 mA/cm (2) and an open circuit (V(oc)) of 619 mV and efficiency of ~17% on 149 cm (2) Czochralski silicon wafers.