Fig. 1 A schematic representation of a Linearly Polarized Luminescent Solar Concentrator (LP-LSC) for energy harvesting in displays. Most displays employ purely absorptive linear polarizers to improve their contrast ratio. In this linearly polarized LSC, dichroic dye molecules are aligned in the plane of a thin, flat plate waveguide using a polymerized liquid crystal host or a stretched polymer as a scaffold. The absorption of the waveguide is linearly polarized – ambient light or light from the back-plane is absorbed very strongly for polarizations parallel to the dipole moment of the dye molecules. However, perpendicular polarized light is transmitted, leaving the entire front surface of the device available for the display.

Fig. 2 Chemical structures of the materials used for the linearly polarized LSC studies. The liquid crystal host material used is Paliocolor LC242. The dichroic dye molecules are 4-dicyanomethyl-6-dimethylaminostiryl-4H-pyran (DCM) and 3-(2-Benzothiazolyl)-N,N-diethylumbelliferylamine (Coumarin 6).

Fig. 3 Polarized absorption and photoluminescence of the linearly polarized LSCs used in this study. The absorption of light polarized parallel to the rubbing direction is depicted as a solid red line, and the blue dotted line is light polarized perpendicular to the rubbing direction. The photoluminescence is plotted as a dotted green line. The left panel depicts the absorption of liquid crystal host doped with 1% C6 (solid weight content), while the right panel shows the results for a sample co-doped with C6 and DCM (both at 1% solid weight content).

Fig. 4 (a) A schematic representation of the Optical Quantum Efficiency (OQE) measurement set-up. A linearly polarized LSC is positioned in an integrating sphere and excited with monochromatic light that is either polarized parallel or perpendicular to the long axis of the dye molecules. We discriminate between edge and face emission by selectively blocking the edge emission with a black marker. (b) The OQE for a linearly polarized LSC based on Coumarin 6 dye molecules (left panel) and a sample co-doped with Coumarin 6 and DCM.

Fig. 5 (a) The performance of linearly polarized LSCs based on Coumarin 6 dye molecules as a function of geometric gain is simulated by measuring the current coming out of a solar cell attached to the edge of the LSC while varying the distance, d, between the excitation spot and the solar cell. This measurement is performed on LP-LSCs for which the dye molecules are aligned parallel (left schematic) or perpendicular (right schematic) to the solar cell. (b) The external quantum efficiency versus geometric gain, G, of the LP-LSCs. The performance of the parallel dipole LSC drops off faster than the LP-LSC for which the dipoles are aligned perpendicular to the solar cell. This is the result of the larger self-absorption of the first geometry, since there is a larger overlap between the emissive dipole and the absorptive dipole or these photons travelling towards the solar cell. The blue curve represents the performance of a uniformly illuminated LSC and is the weighted average of the two curves.