Projects

Luminescent solar concentrators (LSC) are able to concentrate sunlight on solar cells, which can reduce costs in harvesting solar energy. In contrast to mirror and lens based systems LSCs can concentrate not only direct but also diffuse radiation, enabling their use in regions far from the equator like Central Europe. Conventional LSCs consist of transparent glass or plastic plates which are doped with luminescent materials such as organic dyes. Thus incoming radiation is absorbed by these materials and emitted again inside the plate as light with longer wavelength. Most of the emitted light is trapped by total internal reflection within the concentrator and it is guided to the edges, where solar cells are attached. This way of concentrating light, however, is not lossless: As total internal reflection occurs only for certain angles, 26% of the emitted light cannot be capture and it is lost in the escape cone. Another major loss mechanism is reabsorption, which currently limits the size of such devices. State of the art systems efficiencies of up to 7% are too still low for commercial use. In cooperation with Fraunhofer ISE and the Freiburg Materials Research Center this PhD project investigates the novel concept of a photonic luminescent solar concentrator that aims at reducing the losses while increasing the efficiency. By means of embedding the luminescent material in a photonic crystal the emission characteristics can be modified: first, emission should be restricted to directions that are efficiently guided to the solar cells to circumvent the escape cone. Second, the emission spectrum can be altered due to spectral redistribution, which can help to reduce reabsorption losses. In this project, we investigate the influence of the photonic crystal on an embedded emitter theoretically and quantify the effects using wave-optical calculations. Further, photonic luminescent solar concentrators with different structure are being fabricated and characterized.