The Effect of Dyes Aligned by Liquid Crystals on Luminescent Solar Concentrator Performance

Abstract

Luminescent solar concentrators suffer from a high loss of emitted photons through the surfaces. Previous measurements on filled waveguides showed 40-50% of all the absorbed energy and 50-60% of all absorbed photons were lost through the top and bottom of the waveguide. Aligning the dye molecules in a preferred direction can be beneficial to the light output, since fluorescent dyes tend to be dichroic in absorption and emission. Planar alignment of the dye molecules leads to an increase in surface losses, while the total edge output of these planar arrays is similar to the total output of an isotropic dye array. Homeotropic aligned waveguides show a decrease in surface-loss compared to an isotropic waveguide. Emitted photons are directed more towards the edges in this alignment and so surface losses are greatly reduced. However, edge output does not increase, likely a result of increased re-absorption of an emitted photon by other dye molecules. These internal losses are related to the small Stokes-shift of the dye molecules, non-unity quantum efficiency and trapping of photons in the thin dye layer.