Near-perfect antireflection coating for silicon solar energy utilization

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Near-perfect antireflection coatingfor silicon
solar energy utilization

• Weijian Yang
• Department of Electrical Engineering and Computer
  Sciences
• University of California, Berkeley, CA, 94720,
  USA

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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.

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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.

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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.

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Graded index
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Moths eye

• Graded effective medium can reduce index mismatch
  at the interface and eliminate reflection.
• Change air/material ratio gradually.

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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.

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Graded index AR coating
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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
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References

• 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.

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Thank you!

• Thank you!