Near-perfect antireflection coatingfor silicon solar energy utilization

Weijian Yang

Department of Electrical Engineering and Computer Sciences

University of California, Berkeley, CA, 94720, USA

UC Berkeley 2EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009

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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UC Berkeley 5EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009

Graded index

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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.

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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.

UC Berkeley 11EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009

Thank you!

Thank you!