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ECN publication
High power n-type Metal-Wrap-Through cells and modules using industrial processes
Guillevin, N.; Heurtault, Benoit; Geerligs, L.J.; Aken, B.B. van; Bennett, I.J.; Jansen, M.J.; Weeber, A.W.; Bultman, J.H.; Jianming, Wang; Ziqian, Wang; Zhai, jinye; Zhiliang, Wan; Shuquan, Tian; Wenchao, Zhao; Zhiyan, Hu ; Gaofei, Li ; Jingfeng, Xiong
Published by: Publication date:
ECN Solar Energy 30-9-2013
ECN report number: Document type:
ECN-M--13-028 Conference Paper
Number of pages: Full text:
7 Download PDF  

This paper reviews our recent progress in the development of metal wrap through (MWT) cells and modules, produced from n-type Czochralski silicon wafers. The use of n-type silicon as base material allows for high efficiencies: for front emitter-contacted industrial cells, efficiencies above 20% have been reported. N-type MWT (n-MWT) cells produced by industrial process technologies allow even higher efficiency due to reduced front metal coverage. Based on the same industrial technology, the efficiency of the bifacial n-MWT cells exceeds the efficiency of the n-type front-and-rear contact and bifacial “Pasha” technology (n-Pasha) by 0.1-0.2% absolute, with a maximum n-MWT efficiency of 20.1% so far. Additionally, full back-contacting of the MWT cells in a module results in reduced cell to module (CTM) fill factor losses. In a direct 60-cell module performance comparison, the n-MWT module, based on integrated backfoil, produced 3% higher power output than the comparable tabbed front emitter-contacted n-Pasha module. Thanks to reduced resistive losses in copper circuitry on the backfoil compared to traditional tabs, the CTM FF loss of the MWT module was reduced by about 2.2%abs. compared to the tabbed front emitter contact module. A full-size module made using MWT cells of 19.6% average efficiency resulted in a power output close to 280W. Latest results of the development of the n-MWT technology at cell and module level are discussed in this paper, including a recent direct comparison run between n-MWT and n-Pasha cells and results of n-MWT cells from 140µm thin mono-crystalline wafers, with only very slight loss (1% of Isc) for the thin cells. Also reverse characteristics and effects of reverse bias for extended time at cell and module level are reported, where we find a higher tolerance of MWT modules than tabbed front contact modules for hotspots.

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