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ECN publication
Benchmark of open rear side solar cell with improved AL-BSF process at ECN
Published by: Publication date:
ECN Solar Energy 4-2-2008
ECN report number: Document type:
ECN-M--08-002 Conference Paper
Number of pages: Full text:
6 Download PDF  

Presented at: 23rd European Photovoltaic Solar Energy Conference and Exhibition, Valencia, Spain, 1-5 september 2008.

In search of methods that allow processing of thinner multi-crystalline silicon solar cells (<<200µm) without bowing, an open rear side concept, the PASHA cell (Passivated on All Sides H-patterned cell), was developed in our laboratories based on an H-patterned rear metallization design combined with a industrial silicon nitride rear side passivation layer. We report on the performance of this method compared to an improved full Al-BSF reference process on thin 6 inch mc-Si wafers (<210µm, 156x156 mm). Evaluating the average performance of both processes, the product of Jsc and Voc for the PASHA cell with opened silicon nitride is 20.3 mW/cm2, which is 2% lower than for the reference. When the rear side fingers of the PASHA cell are short-circuited, equal fill factors of 77% are obtained as for the reference. The maximum efficiency obtained for the short-circuited PASHA cell and the reference is 15.8% and 16.1% respectively. The key factors that explain these results are: an improved front side passivation of the reference due to an additional PASHA clean step that precedes the SiNx deposition; poor passivation under and high series resistance in the rear fingers of the PASHA cell; an internal rear reflection gain that does not sufficiently compensate these effects. Further, a strong bias illumination dependence of spectral response for the PASHA cell is found which is attributed to the recombination behavior of the SiNx layer on the rear side of the cell.

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