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ECN publication
Industrial application of uncapped Al2O3 and firing-through Al-BSF in open rear passivated solar cells
Cesar, I.; Granneman, E.; Vermont, P.; Khatri, H.; Kerp, H.; Shaikh, A.; Manshanden, P.; Mewe, A.A.; Romijn, I.G.; Weeber, A.W.
Published by: Publication date:
ECN Solar Energy 20-6-2011
ECN report number: Document type:
ECN-M--11-073 Conference Paper
Number of pages: Full text:
6 Download PDF  

Current bottlenecks for industrial application of Al2O3 deposited by Atomic Layer Deposition (ALD) on open rear passivated solar cells are low growth rate, firing stability of thin and uncapped layers, and Firing-through BSF formation during co-firing. Long term stability results on the performance of a high throughput ALD proto-type, the Levitrack, are presented. Excellent passivation properties have been obtained after firing: for 12 nm thick films deposited on p-Fz (1.8 a teff of 2.2 ms (?n=3x1015 cm-3) was obtained that remained constant over a period of 20 weeks. Furthermore, we report on the passivation quality of the firing-through BSF and Al2O3 coating as function of wafer peak temperatures between 790 and 845°C. Bifacial cells covered for 50% Al contacts resulted in local BSF thicknesses of 5 to 7 µm and FF of 78% and 77% for the best mc and mono crystalline cell respectively. For this study 12 nm uncapped aluminum oxide layers are deposited on the rear of p-type mc and mono bifacial cells. LBIC measurements confirm literature reports that uncapped Al2O3 passivation in general is heavily dependent on the wafer peak temperatures during firing in the investigated range.

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