Enhanced photon collection in leaf-inspired luminescent solar concentrators

Abstract

A leaf-like structure is formed by placing luminescent plates in the vicinity of a luminescent fiber with their side surfaces facing the fiber. Its optical efficiency is expressed in terms of collection efficiency and absorptance of each luminescent component. This model allows one to calculate its optical efficiency under an arbitrary incident spectral photon flux. A clear lightguide can connect multiple fibers to transfer the photons generated by each leaf-like structure to a single photovoltaic cell. Thus, one can divide the incident area of a luminescent solar concentrator (LSC) into small regions without sacrificing its geometric gain. Lateral size reduction enhances its optical efficiency by alleviating the losses during the photon collection process. Other techniques reported for the conventional planar LSCs, such as edge mirrors and tandem structures, can be combined for further enhancement. In experiments, off-the-shelf luminescent components (2.0 mm-thick plates and 1.5 mm-diameter fibers) were used to assemble samples with various shapes. For example, the efficiency of collecting photons generated in the plates of a square device increased from 0.0052 to 0.024 by decreasing its side length from 50 to 10 mm and attaching mirrors on their outer edges. In contrast, optical efficiency is weakly dependent on leaf geometry, increasing design freedom on leaf shapes. The use of advanced luminescent materials as well as optimizing the leaf-like structure design would increase its optical efficiency further.