We present a photovoltaic tandem system made of two stacked fluorescent collector plates and gallium-indium-arsenide
(GaInP), gallium-arsenide (GaAs) and silicon (Si) solar cells, utilizing the spectral selectivity of fluorescent conversion.
Fluorescent collectors use fluorescent dye molecules embedded in a dielectric material to collect solar radiation.
Incoming radiation is converted into radiation of lower energy, reduced by the Stokes shift energy ΔE. Total internal
reflection keeps part of the converted radiation inside the collectors and guides it to the edges of the collector plates,
where GaInP and GaAs solar cells are mounted. In order to make use of the spectral selectivity of each collector, the
band gap energies Eg of the solar cells at the edges match the energy of dye emission. Optical transmission, reflection
and photoluminescence measurements analyze the fluorescent collectors. A spectral transfer matrix formalism allows us
to calculate the emitted photon flux of each collector as a function of the absorption/emission properties of the dye and
the spectrum of incident radiation. By multiplying the transfer matrices tailored on each collector with the quantum
efficiencies of the solar cells, we obtain the particular quantum efficiencies of each collector-cell sub-system and the
overall quantum efficiency of the tandem system. The results show very good agreement in the shape of predicted and
measured quantum efficiency curves of the tandem system.
Fluorescent photovoltaic collectors are examined theoretically with the help of Monte-Carlo simulations. The classical
construction of mounting solar cells on each side surface of the collector is compared to alternative set-ups: solar cells
only partly cover the collector side surfaces or they are mounted on the collector back surface, respectively. We find that
the collection probability of photons in most situations is higher for systems with solar cells mounted on the sides of the
collector compared to systems with solar cells at the bottom. In all cases collection probabilities in excess of 90 % are
only achieved if a photonic band stop filter is applied to the top surface of the collector. This filter acts as an omni-directional
spectral band stop and prevents the light emitted by the dye from leaving the collector. The application of
such a filter allows a solar cell area reduction of 99 %. However, inclusion of non-radiative losses in the collector
deteriorates the photon collection probability in all cases. This effect is especially important in systems with band stop
Photonic structures can be used to eliminate the main loss mechanism in fluorescent concentrators. Simulation routines
have been established to investigate the optical characteristic of different photonic crystals. Especially two kinds of
structures with an appropriate characteristic have been examined closely. The first is the rugate filter, a one-dimensional
photonic structure. In the rugate filter the refractive index is varied sinusoidally over the thickness of the filter. The
second is the opal, a three-dimensional photonic crystals made of spheres that are arranged in a self organization process.
Filters from these structures have been designed and optimized for the application and fluorescent concentrators and
have been optimized. Additional aspects of the structures like angular effects have been examined.