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

2. UC Berkeley2EE 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.

3. UC Berkeley3EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 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.

4. UC Berkeley4EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 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.

5. UC Berkeley5EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Graded index

6. UC Berkeley6EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Moth’s eye  Graded effective medium can reduce index mismatch at the interface and eliminate reflection.  Change air/material ratio gradually.

7. UC Berkeley7EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Oblique-angle deposition  A random growth fluctuation in the substrate produces a shadow region that the subsequent incident vapor flux cannot reach.

8. UC Berkeley8EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Graded index AR coating

9. UC Berkeley9EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Comparison StructureAve. ReflectionAve. Transmission Si32.6%67.4% Single layer quarter wavelength 18.8%81.2% Graded index3.79%96.12

10. UC Berkeley10EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 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.

11. UC Berkeley11EE 235 Solar Cell Presentation Weijian Yang Mar. 2, 2009 Thank you!