Quantum Dot Solar Concentrators Research Articles

Quantum dot solar concentrator: Optical transportation and doping concentration optimization

This research investigated optical transport properties, quantum dot doping, and size optimization for Quantum Dot Solar Concentrators (QDSCs) through correlating spectroscopic and electrical characterization, and model predictions. QDSC plates of 60×40×2mm containing; 0.005, 0.01, 0.03, 0.05, and 0.07wt% of CdSe/ZnS quantum dot were fabricated by a drop casting technique and the edges were optically smoothed by polishing. QD fluorescence emission transport properties in QDSC plates were examined with varying optical path-length using laser lines 405, 488 and 532nm, and white light with a cut-off wavelength of 600nm. Emerging fluorescence emission falls off as the optical path-length increases and the rate of fall-off is increased for higher QD concentration; the emission is nearly negligible above the 25mm optical path-length for 0.05 and 0.07wt% QDSC plates. Re-absorption is mainly responsible for reduced emission in lower QD concentration QDSCs for fixed optical path-lengths. In higher concentration QDSCs, scattering and re-absorption both contribute to the reduced emission, which is verified through the white light scattering profile of QDSCs. Emission is reduced by up to 70% for >20mm optical path-length where emission is lost before reaching the edge. The optimum concentration of QD doping has been found while balancing the QDSC device dimensions, and also ensuring sufficient absorption of the incident light.

Enhanced quantum dot emission for luminescent solar concentrators using plasmonic interaction

Plasmonic excitation enhanced fluorescence of CdSe/ZnS core-shell quantum dots (QDs) in the presence of Au nanoparticles (NPs) has been studied for application in quantum dot solar concentrator (QDSC) devices. We observe that there is an optimal concentration of Au NPs that gives a maximum 53% fluorescence emission enhancement for the particular QD/Au NP composite studied. The optimal concentration depends on the coupling and spacing between neighboring QDs and Au NPs. We show the continuous transition from fluorescence enhancement to quenching, depending on Au NP concentration. The locally enhanced electromagnetic field induced by the surface plasmon resonance in the Au NPs leads to an increased excitation rate for the QDs. This is evidenced by excitation wavelength dependent fluorescence enhancement, where the locally enhanced field around the Au NPs is more pronounced close to the surface plasmon resonance (SPR) wavelength. However, at higher concentrations of Au NPs non-radiative energy transfer from the QDs to the Au NPs particles leads to a decrease of the emission, which is confirmed by detection of both a double exponential lifetime decay in, and a decrease in the lifetime of the QDs. The overall fluorescence emission enhancement depends on these competing effects; increased excitation rate and non-radiative energy transfer.

Improving the optical efficiency and concentration of a single-plate quantum dot solar concentrator using near infra-red emitting quantum dots

Low luminescent quantum yields and large overlap between quantum dot (QD) emission and absorption spectra of present commercially-available visible-emitting QDs have led to low optical efficiencies for single-plate quantum dot solar concentrators (QDSCs). It is shown that using near infra-red (NIR) emitting QDs, re-absorption of QD emitted photons can be reduced greatly, thereby diminishing escape cone losses thus improving optical efficiencies and concentration ratios. Using Monte-Carlo ray-trace modelling, escape cone losses are quantified for different types of QD. A minimum 25% escape cone loss would be expected for a plate with refractive index of 1.5 containing QDs with no spectral overlap. It is shown that escape cone losses account for ∼57% of incident photons absorbed in QDSCs containing commercially-available visible-emitting QDs.

Synthesis and optical properties of CdS quantum dots embedded in silica matrix thin films and their applications as luminescent solar concentrators

CdS quantum dot (QD) solar concentrators were prepared by a sol–gel spin coating method. Thin films were prepared at different annealing temperatures and characterized by X-ray diffraction and spectroscopic techniques. The effect of temperature on the optical properties of CdS QDs embedded in silica matrix was assessed before and after exposure of the samples to sunlight for up to 4 weeks. The results show that as the annealing temperature increases, the fluorescent intensity and Stokes shift decrease. Therefore lower temperatures are preferable for the preparation of highly efficient QD solar concentrator systems.

Quantum dot solar concentrators: Electrical conversion efficiencies and comparative concentrating factors of fabricated devices

A novel, non-tracking concentrator is described, which uses nano-scale quantum dot technology to render the concept of a fluorescent dye solar concentrator (FSC) a practical proposition. The quantum dot solar concentrator (QDSC) comprises quantum dots (QDs) seeded in materials such as plastics and glasses that are suitable for incorporation into building façades. Photovoltaic (PV) cells attached to the edges convert direct and diffuse solar energy collected into electricity for use in the building. Small scale QDSC devices were fabricated. Devices have been characterised to determine current, voltage and power readings. Electrical conversion efficiencies, fill factors and comparative concentrating factors are reported.

Quantum dot solar concentrator: Device optimisation using spectroscopic techniques

The quantum dot solar concentrator (QDSC) is a novel non-tracking solar concentrator comprising quantum dots (QDs) seeded in materials such as plastics and glasses, that concentrates both direct and diffuse solar energy on attached photovoltaic cells. Spectroscopic measurements have been undertaken for a range of different quantum dot (QD) types and transparent host materials. High transparency in the matrix material and QDs with high quantum efficiency 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.

Quantum dot solar concentrator behaviour, predicted using a ray trace approach

SYNOPSIS Using a three-dimensional raytrace technique, a model to optimise the design of Quantum Dot Solar Concentrators for photovoltaic applications has been developed. The model includes reflection, refraction and absorption of solar radiation allowing the prediction of the optical efficiency. The optical efficiency is defined as the energy emitted from the selected edge or edges divided by the solar energy incident on the material. Using the model, a parametric analysis was performed and the optical properties of a selected system optimised. Details of the model and predictions of concentrator efficiency and ray path lengths for a range of quantum dot seeding levels are shown. The effects of path length on energy absorbed in the carrier material and that reaching the photovoltaic material are presented.