To reduce surface loss in luminescent solar concentrators (LSCs), we systematically apply organic wavelength-selective mirrors, chiral nematic (cholesteric) liquid crystals, onto the LSCs with an air gap and determine their effect on waveguide output. The highest output is achieved using a scattering background and cholesteric mirror with a reflection band significantly redshifted (approximately 150 nm) from the emission peak of the fluorescent dye. The use of an air gap results in light bending away from the waveguide surface normal and, consequently, a redshift of the cholesteric mirrors is required. Up to 35% more dye-emitted light energy exits the waveguide edge after application of the cholesteric, and an increase in absolute edge power of 12% was found for a waveguide using a separate scatterer.
The molecular order in a smectic monomer is utilized to create a photoreactive material that is highly polarization-selective during its photo-crosslinking polymerization. A dichroic photoinitiator adapts the molecular orientation of its aligned smectic B host monomer which reaches a degree of orientation larger than 0.9. This value correlates to a dichroic ratio, defined as the absorbance ratio of light with its polarization respectively parallel and perpendicular to the orientation axis, of 32. This is substantially higher than the dichroic ratio of similar dichroic initiators previously studied in nematic host monomers which considerably improves the polymerization contrast. The presence of an inhibitor, such as a hydroquinone, in the monomeric mixture enhances the polymerization contrast further. The effect of the inhibitor is due to the close to zero monomer to polymer conversion for the polarization perpendicular to the alignment in the initial stages of polymerization. It is argued that the high polarization-selectivity of the above-described system is potentially useful in nano and/or microstructuring techniques without the use of masks such as polarization holography.
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