Luminescent Solar Concentrators Improved by Microcavity Effects
The Center for Nanoscale Materials Nanophotonics Group, collaborating with researchers at Northwestern University, is investigating the use of fluorescent plastics called luminescent solar concentrators (LSCs) to lower the cost of electricity from solar cells. The way light is re-emitted and reabsorbed inside an LSC is altered by taking advantage of optical "microcavity" effects, which occur when the dimensions of a structure are similar to the wavelength of light.
Concentrating sunlight is one strategy to squeeze more power out of existing solar cells, which ultimately reduces the cost of the energy they produce. The question now is how best to gather as much sunlight as cheaply as possible. Although lenses and mirrors are one solution (analogous to burning a piece of paper with a magnifying glass on a sunny day), they must be continually aimed at the sun as it moves across the sky each day, which requires an expensive tracking system.
Luminescent solar concentrators are inexpensive alternatives that do not require solar tracking because they capture sunlight and change it to a different wavelength. The theoretical potential for this intensification can exceed the equivalent of one hundred "suns" - the measurement of solar radiation on one spot. However, actual implementation has failed to produce such high intensities until now.
The research focuses on altering the way light is re-emitted and reabsorbed inside an LSC by taking advantage of optical "microcavity" effects that occur when the dimensions of a structure are similar to the wavelength of light. A series of thin films with nanometer-scale changes in thickness produce a "resonance-shifting" effect, in which light fails to "recognize" the environment from which it is emitted, drastically reducing reabsorption.
N.C. Giebink, G.P. Wiederrecht, and M.R. Wasielewski, "Resonance-shifting to circumvent reabsorption loss in luminescent solar concentrators," Nat. Photon. , 5, 694 ( 2011). doi:10.1038/nphoton.2011.236 (online)
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