Molecular Polarization Switching for Improved Light Coupling in Luminescent Solar Concentrators

Luminescent solar concentrators (LSCS) are nontracking light-concentrating devices employing luminophore-doped waveguides. The use of a homeotropic-aligned dye with the emissive transition dipole moment parallel to the alignment axis can improve the coupling of luminescence to waveguide modes in an LSC. However, this configuration leads to weaker absorption of normal incidence radiation by the transition, potentially reducing the LSC external quantum efficiency. We demonstrate a mechanism for overcoming this problem by employing a square-symmetric porphyrin sensitizer that can effectively absorb radiation at normal incidence and transfer energy to an emitter species. The rapid loss of electronic anisotropy in an excited porphyrin leads to excitation of two degenerate states, yielding an energized dipole favorably oriented to undergo fast resonance energy transfer to a nearby homeotropic-aligned emitter. This mechanism is demonstrated in a proof-of-principle device utilizing a homeotropic-aligned liquid crystal host.