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Spotlight on Optics


  • April 2013

Optics InfoBase > Spotlight on Optics > Geometric light trapping with a V-trap for efficient organic solar cells

Geometric light trapping with a V-trap for efficient organic solar cells

Published in Optics Express, Vol. 21 Issue S3, pp.A305-A312 (2013)
by Soo Jin Kim, George Y. Margulis, Seung-Bum Rim, Mark L. Brongersma, Michael D. McGehee, and Peter Peumans

Source article Abstract | Full Text: PDF

Spotlight summary: The goal of light trapping in a solar cell is to maximize the optical path length in the cell’s active layer, increasing the amount of light absorbed, and therefore improving the solar cell’s efficiency. When sunlight strikes a solar cell some of it is absorbed and converted into electrical power and some of it is reflected. In a flat geometry, this reflected light is lost energy. Trapping light in the cell to improve efficiency has been demonstrated in inorganic and organic photovoltaic cells using a variety of methods such as surface textures, interference coatings, micro lenses, and wave optics just to name a few. The V-trap is a geometric configuration that angles strips of solar cells toward each other, forming V shaped groves. In this configuration the reflected light can bounce back and forth between neighboring cells multiple times, increasing the amount of light absorbed with each bounce.

A recent Optics Express paper by Soo Jin Kim et al., shows that using a V-trap cell configuration for light trapping improves photon absorption in an optimized organic photovoltaic solar cell. The team explored both theoretically and experimentally what the benefits are for using a V-trap configuration for a thin film polymer cell that has already been optimized for maximum overall power conversion efficiency over a broad spectrum (400 to 700nm). The theoretical model analyzes both the angle of the V-grove and angle of incidence of the incoming light. They experimentally demonstrated the robustness of their model, and reached a 35% increase in the power conversion efficiency of a cell with a 30 degree V-trap configuration compared to a planar cell geometry.

The paper concludes that the V-trap configuration provides the most benefit by improving the absorption of photons that are normally only weakly absorbed. This broadens the effective absorption spectrum compared to the same cell used in a flat geometry. It also helps to explain how a V-trap configuration still provides a substantial efficiency boost for a solar cell that is already highly optimized for a broad absorption spectrum. The authors have presented a comprehensive analysis that illustrates the benefits light trapping independent of active materials used.

--Greg Schmidt

ToC Category: Photovoltaics
OCIS Codes: (350.0350) Other areas of optics : Other areas of optics
(350.6050) Other areas of optics : Solar energy

Posted on April 19, 2013

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