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Title:
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Comparison of alkaline etches on multi-crystalline wafers
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Author(s):
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Published by:
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Publication date:
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ECN
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1995
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ECN report number:
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Document type:
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ECN-RX--95-061
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Other
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Number of pages:
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Full text:
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6
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Download PDF
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Abstract:
It is widely recognized that during further development of crystallinesilicon solar cell technology, reflection reduction and light trapping are
important issues. ECN and R and S Renewable Energy Systems developed low cost
technology for 16% encapsulated multi-crystalline Si (mc-Si) cells. Normally,
the surface morphology for mc-Si wafers is determined by a concentrated NaOH
or KOH saw damage etch. Within this project we have looked into reflection
reduction by texture etching with diluted NaOH and KOH solutions and found a
0.2% increase in efficiency for AR-coated un-encapsulated cells. The purpose
of the research described in this paper is to explore in detail how the
difference in macroscopic properties of the cell such as reflectance can be
related to the microscopic structure produced by saw damage and texture
etches. Cheap texturing methods based on alkaline etches produce faceted
surfaces. The texture varies from crystallite to crystallite depending on the
local crystal orientation. The composition and temperature of the specific
etchant used have a large influence on the shape of the texture. It has been
demonstrated elsewhere in ray-tracing studies that rather small tilt angles
of the facets (about 20 degrees) can give rise to very significant
encapsulated reflection reduction and light-trapping. This suggests that even
on multi-crystalline wafers with non-ideal crystallite orientations
significant reflection reduction can be achieved. To compare various textures
and explain their influence on cell properties it is important to
characterise the texture in detail. Multicrystalline neighbouring wafers
manufactured by Bayer were textured with different alkaline solutions.
Crystal orientations of individual crystallites were obtained by means of
Laue photography. Reflection measurements were made, both with the surface
bare and encapsulated. Both total and angularly resolved reflection
measurements were made. Optical, scanning electron and AFM microscopy were
used to study the surface morphology. We will first describe the experimental
techniques used. Next, results of the measurements will be presented and
discussed. 12 figs., 7 refs.
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