J. Doran

Modelling the Effect of Device Geometry on Concentration Ratios of Quantum Dot Solar Concentrators

Quantum dot solar concentrators (QDSCs) are static, non-imaging concentrators which concentrate both direct and diffuse light. Using Monte-Carlo ray-trace modelling, concentration ratios (C) were predicted for QDSCs of different 2-D geometries. The optimum shape and size were determined, for given system parameters, by calculating the relative cost per unit power output. Devices with different 3-D geometry were also compared. The thickness of the plate was varied and devices with tapered thickness were modelled to investigate the effect on C.

Quantum dot solar concentrators: an investigation of various geometries

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.

Down shifting in poly(vinyl alcohol) gels doped with terbium complex.

Novel poly(vinyl alcohol) (PVA) based soft gels with luminescent properties are detailed in this contribution. Lanthanide complex of terbium ions with anthranilic acid, Tb(ant)3·2H2O, was synthesized and incorporated into a DMSO/water solution, followed by addition of PVA, to attain soft gels at room temperature. Morphological and thermal analyses revealed homogeneous distribution of Tb(ant)3·2H2O into the PVOH/DMSO/water gel, and that incorporation of the terbium complex does not alter the thermal properties of the gels. The gels are transparent and luminescent, as they exhibit Large Stokes shift down shifting (LSS DS) up to 400nm, with very high emission quantum yield, that was found to be function of Tb complex concentration.

External Quantum Efficiency Improvement with Luminescent Downshifting Layers: Experimental and Modelling

Core-shell quantum dots CdSe/ZnS and lumogen yellow organic dye are characterized by their inclusion in luminescent downshifting (LDS) layers. Layers were deposited on top of crystalline silicon cell (c-Si), dye synthesized solar cell (DSSC), and cadmium telluride (CdTe) minimodules. External quantum efficiency measurements for the solar cell/LDS devices are discussed. Experimental results were compared with an optical model developed by Rothemund, 2014.

Thermoreversible luminescent organogels doped with Eu(TTA)3phen complex

This manuscript details the preparation and characterization of luminescent organogels in toluene. Gels were prepared by using 12-hydroxystearic acid (12HSA) as gelator and different amounts of thenoyltrifluoroacetonato 1,10-phenanthroline europium(III) complex (Eu(TTA)3phen). The gelation properties and the thermoreversible behavior from solid-like to liquid systems were investigated by differential scanning calorimetry. At higher concentration, an interaction of Eu complex with the polar group of the gelator was revealed by DSC and FTIR analyses. The spectroscopic behavior of the complex was investigated in toluene solution and in the gel state. TEM analysis revealed that 12HSA is able to solvate the Eu diketonate complex inducing a remarkable increase in the Eu-Eu distance. The Eu(TTA)3phen in the gel state exhibits a very high emission quantum yield, Φ, which was found to be independent of Eu complex concentration, at least for the composition range analyzed. These results indicate that 12HSA organogels containing Eu(TTA)3phen are promising materials for optical applications.

Ray-trace modelling of reflectors for quantum dot solar concentrators

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.

Two step continuous method to synthesize colloidal spheroid gold nanorods.

This research investigated a two-step continuous process to synthesize colloidal suspension of spheroid gold nanorods. In the first step; gold precursor was reduced to seed-like particles in the presence of polyvinylpyrrolidone and ascorbic acid. In continuous second step; silver nitrate and alkaline sodium hydroxide produced various shape and size Au nanoparticles. The shape was manipulated through weight ratio of ascorbic acid to silver nitrate by varying silver nitrate concentration. The specific weight ratio of 1.35-1.75 grew spheroid gold nanorods of aspect ratio ∼1.85 to ∼2.2. Lower weight ratio of 0.5-1.1 formed spherical nanoparticle. The alkaline medium increased the yield of gold nanorods and reduced reaction time at room temperature. The synthesized gold nanorods retained their shape and size in ethanol. The surface plasmon resonance was red shifted by ∼5 nm due to higher refractive index of ethanol than water.

Spectroscopic characterisation of a quantum dot solar concentrator

Spectroscopic measurements have been undertaken for a range of different quantum dot (QD) types and transparent host materials for use in a novel solar energy-concentrating device, a Quantum Dot Solar Concentrator1 (QDSC). A QDSC comprises QDs seeded in materials such as plastics and glasses that are suitable for incorporation into buildings where photovoltaic cells attached to the edges convert direct and diffuse solar energy into electricity for use in the building. High transparency in the matrix material and QDs with a large Stokes shift are essential for an efficient QDSC. An optimum matrix material for a QDSC has been determined based on absorption characteristics and an optimum commercially available QD type has been chosen using steady-state absorption, photoluminescence and photoluminescence excitation spectroscopy of QDs in solution and solid matrices.

Plasmonic quantum dot solar concentrator

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.

Preparation and luminescence properties of organogel doped with Eu(TTA)3phen complex

In this contribution we report the preparation and the luminescence property of Eu(TTA)3phen complex doped toluene gels. Gels were prepared by using either a low molecular weight gelator, 12-hydroxystearic acid (HSA), or a macromolecular gelator, syndiotactic polymethylmethacrylate (s-PMMA). The gelation properties and their reversible behavior from solid-like to liquid systems have been investigated. In addition, photophysical investigations, as well as morphology, thermal properties and ageing behavior of the gels were analyzed as a function of composition of the gels.