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Title:
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Limiting light escape angle in silicon photovoltaics: ideal and realistic cells
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Author(s):
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Kosten, E.D.; Newman, B.K.; Lloyd, J.V.; Polman, A.; Atwater, H.A.
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Published by:
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Publication date:
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ECN
Solar Energy
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2-1-2015
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ECN report number:
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Document type:
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ECN-W--15-011
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Article (scientific)
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Number of pages:
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9
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Published in: IEEE Journal of Photovoltaics (IEEE), , 2015, Vol.5, p.61-69.
Abstract:
Restricting the light escape angle within a solar cell significantly enhances light trapping, resulting in potentially higher efficiency in thinner cells. Using an improved detailed balance model for silicon and neglecting diffuse light, we calculate an efficiency gain of 3%abs for an ideal Si cell of 3-µm thickness and the escape angle restricted to 2.767° under AM1.5 direct illumination. Applying the model to current high-efficiency cell technologies, we find that a heterojunction-type device with better surface and contact passivation is better suited to escape angle restriction than a homojunction type device. In these more realistic cell models, we also find that there is little benefit gained by restricting the escape angle to less than 10°. The benefits of combining moderate escape angle restriction with low to moderate concentration offers further efficiency gains. Finally, we consider two potential
structures for escape angle restriction: a narrowband graded index optical multilayer and a
broadband ray optical structure. The broadband structure, which provides greater angle
restriction, allows for higher efficiencies and much thinner cells than the narrowband structure.
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