In this paper, concentrating structures of plasmonic luminescent downshifting composite layers (c-pLDS) containing lumogen yellow dye and silver nanoparticles (Ag NPs) to increase the efficiency of Photovoltaic (PV) devices were investigated. The c-pLDS structures allowed for a wider absorption range of both wavelength shifting and light concentration with a strong energy transfer that red shifts photons to wavelengths which gives greater spectral response of solar cells. The optimum dye concentration in a poly(methyl,methacrylate) polymer of a thin layer ~10μm spin coated on glass substrate was established. Subsequently, plasmonic coupling with Ag NPs was introduced for the c-pLDS composite structures. Plasmonic coupling has been observed to produce fluorescence emission enhancement of up to 20% for the dye c-pLDS layer. The c-pLDS layer was modelled for CdTe mini modules (15x15 cm) and compared with a blank PMMA/GLASS and dye c-LDS structure. It has been demonstrated that the addition of c-pLDS layers containing lumogen yellow dye increases the optical efficiency and the Short circuit current (Jsc) of CdTe solar cells. An increase of 7.3% in the optical efficiency has been achieved and a 30% in the Jsc was obtained when a c-pLDS composite layer is used.
The quantum dot solar concentrator optical efficiency is undermined by the parameters of re-absorption, scattering, and escape cone losses. These losses can be address through enhancing quantum dot (QDs) absorption and emission. This have been achieved through plasmonic coupling between QDs and gold nanoparticles (Au NPs). The plasmonic composite of various concertation of QDs and Au NPs were studied. The spacing between QDs and Au NPs is controlled through concentration distribution of both QD and Au NPs in the plasmonic composite, and it showed a significant increase in absorption and which is more pronounced for higher spectral overlap of QDs and surface plasmon resonance (SPR) frequency. The optimum plasmonic coupling showed a 17 % increase in the fluorescence emission for QDs in plasmonic composite. The results have shown significant enhancement in absorption, fluorescence emission for the p-QDSC.
A Quantum Dot Solar Concentrator (QDSC) is based on the Luminescent Solar Concentrator (LSC), a concept first
introduced in the 1960s. LSCs consist of a flat plate of polymer material doped with a luminescent dye. A percentage of
incident insolation, absorbed and re-emitted by the dye molecules is trapped inside the plate by total internal reflection.
Reflective material situated on three of the edges and the back surface increases the trapping efficiency of the plate.
Through successive reflection events light is concentrated onto a photovoltaic (PV) cell positioned on the fourth edge of
the plate. Degradation of luminescent dyes prevented LSCs from being fully developed. A QDSC replaces luminescent
dyes with semiconductor nanocrystals known as quantum dots (QDs). Passivation of QD cores with shells of higher
band gap material is expected to provide increased stability. QDs offer further advantages such as broad absorption
spectra to utilize more of the solar spectrum and size tunability that allows spectral matching of the QDs emission to the
peak efficiency of PV cells.
Small-scale QDSCs have been fabricated using QDs bought commercially. The QDs have an emission wavelength of
600nm, close to the peak efficiency of a typical silicon PV cell. The systems were electrically characterized using a 4 cm
monocrystalline PV cell optically matched to the QDSC edge with silicon oil. To investigate the effect of shape and size
on concentrator efficiency, four different sized quadratic, two triangular and three circular QDSCs of various diameters
were fabricated.
KEYWORDS: Reflectors, Solar concentrators, Reflection, Absorption, Photovoltaics, Quantum dots, Modeling, Solar cells, Reflectivity, Signal attenuation
Quantum Dot Solar Concentrators (QDSCs) are static, non-imaging concentrators which do not require expensive solar
tracking and concentrate both direct and diffuse light. Optical efficiencies (ηopt) and concentration ratios (C) of a single
plate QDSC were calculated by Monte-Carlo ray-trace modelling. Consideration of reflection, refraction, quantum dot
(QD) photon emission and absorption and light attenuation in the device matrix were included in the analysis. In this
paper, the effect of placing plane and diffuse reflectors at the rear surface was analyzed. Mirrors with a structured surface
(saw-tooth shaped) were also modelled and the effect of each reflector type on C was determined, for direct and diffuse
incident light. The diffuse and structured reflectors perform better than the plane reflector under direct light, but there is
no significant difference under diffuse light. A spectrally selective reflector, placed at the top surface, reflects light
emitted by QDs inside the escape cone back into the concentrator. For a particular set of model parameters, the model
results show an increase in C of 13% due to the inclusion of a spectrally selective reflector.
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