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Title:
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LPCVD polysilicon passivating contacts for crystalline silicon solar cells
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Author(s):
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Published by:
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Publication date:
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ECN
Solar Energy
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15-5-2016
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ECN report number:
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Document type:
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ECN-V--16-005
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Article
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Number of pages:
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Full text:
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10
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Download PDF
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Published in: Photovoltaics International (PV-Tech), , 2016, Vol.32, p.45-56.
Abstract:
Contact recombination has long been identified as one of the key challenges for achieving high efficiency of crystalline silicon (c-Si) solar cells. As well as having the ability to extract majority carriers effectively, a contact to a solar cell should ideally be passivating. The combination of a thin oxide and doped polysilicon to obtain low recombination junctions was demonstrated in the 1980s to be a viable candidate for creating passivating contacts to c-Si solar cells. In recent years variations and innovations of this technology have seen
intense development and rapid progress towards demonstrating very high (25%) cell efficiencies. This paper presents the progress made by ECN and Tempress in developing and integrating the processing of polysilicon passivating contacts aimed at use in low-cost industrial cell production. The polysilicon is deposited by lowpressure chemical vapour deposition (LPCVD), and the results are presented for in situ as well as ex situ doping processes. Synergy and compatibility with industrial cell processing is demonstrated – for example, the application of hydrogenation from silicon nitride coating layers, and metallization by screen-printed firethrough paste. This demonstrates the potential application of polysilicon passivating contacts to a variety of cell designs in production in the near future. The way in which the passivating and contact properties depend on the layer parameters and subsequent cell processes is analysed and explained. Results are presented for 6" screen-printed bifacial n-type cells with a diffused boron emitter and an n-type polysilicon (n-poly) back contact, with an efficiency of 20.7%, as an industrially relevant application of the polysilicon technology. Ways
to improve cell efficiency to > 22% are indicated.
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