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Title:
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Alkaline etching for reflectance reduction in multicrystalline 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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1-6-2004
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ECN report number:
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Document type:
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ECN-RX--04-075
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Article (scientific)
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Number of pages:
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20
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Published in: Journal of the Electrochemical Society (ECS), , 2004, Vol.151, p.408-427.
Abstract:
The reflection reducing properties of alkaline-etched multicrystallinewafers are investigated experimentally for high concentration saw-damage
etching and low concentration texture etching. Saw-damage etch textures
are too flat for multiple bounce reflectance in air, with only 1.6%
of the multicrystalline wafer surface calculated to have facet tilt
angles above 45degrees whereby double-bounce reflectance is guaranteed.
Texture etching yields 3% lower reflectance in air, due to high angled
(up to 54.7degrees) pyramidal structures on near (100) orientations,
whereby 13% of the multicrystalline etch surface has tilt angles above
45degrees. However, under encapsulation, light is coupled more effectively
into the silicon; reflectances for the saw-damage and texture-etched
wafers compare only 7 and 5.5% higher, respectively, than upright pyramid
textures on monocrystalline silicon(100), compared to 18 and 15% higher
in air. This is because a far larger proportion of the multicrystalline
wafer (around 40% for the two etches) has tilt angles above 20.9degrees
whereby escaping light is totally internally reflected at the glass-air
interface. For texture etching, not only {111} planes are stable to
etching but the whole range of {XXY} crystallographic planes between
these and {110} orientations, contrary to the accepted texture etching
theory.
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