Efficiency limits of photovoltaic fluorescent collectors
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(a) Schematic drawing of a fluorescent collector with a solar cells at its bottom. The fluorescent layer absorbs incoming photons (1) and emits them at lower photon energy. Without photonic band stop (PBS) some of these photons leave the collector (2a). The PBS reflects these photons back into the collector (2b). (b) Spectral dependence of the absorption and emission coefficients, and , of the ideal fluorescent dye with for photon energies, , in the range and for . The PBS has an omnidirectional reflectance for .
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(a) The simulated efficiencies for FC with PBS (open squares) follow the radiative efficiency limit (solid line) when calculated with reference to the photonic threshold energy . The efficiencies without PBS (open circles) are at about 0.88 (solid line) calculated with reference to the band gap energy of the underlying solar cell. (b) Efficiencies for a band gap energy and threshold energy for ideal (rad.) and nonideal (nonrad.) solar cells. Without photonic band stop (PBS), the efficiencies degrade rapidly with decreasing coverage fraction (full and open circles, for the radiative and the nonradiative case). With PBS the systems efficiency drops much slower with decreasing for an ideal solar cell (open squares) and achieves even an optimum at in the nonradiative case (full squares).
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