Reduction of escape cone losses in luminescent solar concentrators with cholesteric mirrors

The Luminescent Solar Concentrator (LSC) consists of a transparent polymer plate containing luminescent particles. Solar cells are connected to one or more sides of the polymer plate. Part of the light emitted by the luminescent particles is guided towards the solar cells by total internal reflection. About 25% of the dye emission is typically emitted within the optical escape cone of the matrix material and is lost due to emission from the top. We study the application of selectively-reflective cholesteric layers to reduce these losses. We have implemented these mirrors in the ray-tracing model for the LSC. The simulations show that an optimum in performance can be obtained by selecting an appropriate centre wavelength of the cholesteric mirror. External Quantum Efficiency measurements were performed on LSC devices with a mc-Si, GaAs or InGaP cell and a dichroic mirror. This mirror shows a similar behavior as the cholesteric mirror. The results show that for a 5x5 cm2 LSC the mirror does improve the EQE in the absorption range of the dye