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5 May 2008 Optimization of Rugate filters for ultra light-trapping in solar cells
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We present the optimization of coatings that can be applied on top of solar cells. The purpose of these coatings is to reduce the light acceptance cone only in the long wavelength range. This allows for high transmission of light into the solar cell independent on the angle of incidence in the short wavelength range where the solar cell material shows high absorption. Furthermore, it allows for enhanced absorption of the direct sunlight in the long wavelength range by trapping such light using total internal reflection. The coating for this purpose is based on a combination of various design strategies with well defined impacts on the reflection spectra. It provides a set of free parameters which describe the index profile of the filter. Realistic numerical procedures for calculating efficiencies for crystalline silicon solar cells are used to optimize the free parameters of the coating. We show that these filters can lift the efficiency of 10μm thick solar cells up to 30.1%. This is a factor of 1.05 above the ≈ 28% limit found for unconcentrated illumination by Kerr et al.
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Stephan Fahr, Carolin Ulbrich, Thomas Kirchartz, Uwe Rau, Carsten Rockstuhl, and Falk Lederer "Optimization of Rugate filters for ultra light-trapping in solar cells", Proc. SPIE 7002, Photonics for Solar Energy Systems II, 70020B (5 May 2008);

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