Transcript Slide 1

Near-perfect antireflection coating
for silicon solar energy utilization
Weijian Yang
Department of Electrical Engineering and Computer Sciences
University of California, Berkeley, CA, 94720, USA
Motivation
 AR coating can improve solar collection efficiency.
 Solar radiation
 Broadband spectrum.
 Incident angle changes within a day.
 An idea AR coating should maintain a low
reflectance for a broadband spectrum and all
angles of incidence.
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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AR coating
 Fresnel reflection
 Traditional quarter-wave AR coating suffers from a small
range of optical spectrum and incident angle.
 Grade index nanorod thin film structure.
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Graded Index
 Reflectance of the AR coating depends on
smoothness of the index profile.
 Minimize the differential reflectance at each
interface of the multilayer structure.
n  ni  ( ns  ni ) z
n  ni  ( ns  ni )(3 z 2  2 z 3 )
n  ni  ( ns  ni )(10z 3  15z 4  6 z 5 )
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Graded index
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Moth’s eye
 Graded effective medium can reduce index
mismatch at the interface and eliminate reflection.
 Change air/material ratio gradually.
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Oblique-angle deposition
 A random growth fluctuation
in the substrate produces a
shadow region that the
subsequent incident vapor
flux cannot reach.
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Graded index AR coating
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Comparison
Structure
Ave. Reflection Ave. Transmission
Si
32.6%
67.4%
Single layer quarter
wavelength
18.8%
81.2%
Graded index
3.79%
96.12
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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References
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M. Kuo, et.al., Opt. Lett., 33, 2527, 2008.
J. Xi, et.al., Nature Photonics, 1, 176, 2007.
J. Xi, et.al., Opt. Lett., 5, 601, 2006.
S. Kennedy, et.al., Appl. Opt., 42, 4573, 2003.
 www.physorg.com.
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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Thank you!
Thank you!
UC Berkeley
EE 235 Solar Cell Presentation Weijian Yang
Mar. 2, 2009
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