Luminescent Concentrators Research Articles

Nonimaging Optical Gain in Luminescent Concentration through Photonic Control of Emission Étendue

Luminescent and nonimaging optical concentration constitute two fundamentally different ways of collecting and intensifying light. Whereas nonimaging concentrators based on reflective, refractive, or diffractive optics operate most effectively for collimated light, luminescent concentrators (LCs) rely on absorption, re-emission, and waveguiding to concentrate diffuse light incident from any direction. LCs have been explored in many different shapes and sizes but have so far been unable to exploit the power of nonimaging optics to further increase their concentration ratio because their emission is angularly isotropic. Here, we use a luminescent thin film bilayer to create sharply directed conical emission in an LC and derive a nonimaging optical solution to leverage this directionality for secondary geometric gain ranging up to an order of magnitude or higher. We demonstrate this concept experimentally using a custom compound parabolic optical element index-matched to the LC surface and show that it delivers three times more luminescent power to an opposing GaAs photovoltaic cell when the emission profile is conically directed than when it is isotropic or the nonimaging optic is absent. These results open up a significant and general opportunity to improve LC performance for a variety of applications including photovoltaics, photobioreactors, and scintillator-based radiation detection.

A transparent thin-film sensor for multi-focal image reconstruction and depth estimation.

We present a fully transparent and flexible light-sensing film that, based on a single thin-film luminescent concentrator layer, supports simultaneous multi-focal image reconstruction and depth estimation without additional optics. Together with the sampling of two-dimensional light fields propagated inside the film layer under various focal conditions, it allows entire focal image stacks to be computed after only one recording that can be used for depth estimation. The transparency and flexibility of our sensor unlock the potential of lensless multilayer imaging and depth sensing with arbitrary sensor shapes--enabling novel human-computer interfaces.

Luminescent Solar Concentration with Semiconductor Nanorods and Transfer-Printed Micro-Silicon Solar Cells

We utilize CdSe/CdS seeded nanorods as a tunable lumophore for luminescent concentration. Transfer-printed, ultrathin crystalline Si solar cells are embedded directly into the luminescent concentrator, allowing the study of luminescent concentrators with an area over 5000 times the area of the solar cell. By increasing the size of the CdS rod with respect to the luminescent CdSe seed, the reabsorption of propagating photons is dramatically reduced. At long luminescence propagation distances, this reduced reabsorption can overcome the diminished quantum yield inherent to the larger semiconductor structures, which is studied with lifetime spectroscopy. A Monte Carlo ray tracing model is developed to explain the performance of the luminescent concentrator and is then used as a design tool to determine the effect of luminescence trapping on the concentration of light using both CdSe/CdS nanorods and a model organic dye. We design an efficient luminescence trapping structure that should allow the luminescent concentrator based on CdSe/CdS nanorods to operate in the high-concentration regime.

Condensation and salt-induced decondensation of DNA upon incorporation of a V-shaped luminescent [Ru2(bpy)4(mbpibH2)]4 +

This paper first reports on the condensation of DNA to a tightly packed state induced by a V-shaped di-ruthenium(II) complex [Ru2(bpy)4(mbpibH2)]Cl4 (bpy=2,2′-bipyridine and mbpibH2=1,3-bis([1,10]phenanthroline[5,6-d]imidazol-2-yl)benzene), which binds to the groove of herring sperm DNA (hsDNA) with the binding constant of 2.0×107M−1 (0.05M NaCl, pH7.2). The di-Ru(II) complex is found to induce the condensation of both hsDNA to long chain-like particle clusters and originally circular plasmid pBR322 DNA to particulate structure under neutral conditions. More interestingly, the presence of NaCl has a significant impact on the condensation and decondensation of DNA upon incorporation of [Ru2(bpy)4(mbpibH2)]4+, representing tunable luminescence characteristics by NaCl. High salt concentration facilitates the decondensation of DNA-[Ru2(bpy)4(mbpibH2)]4+ adducts. The results from this study offer an effective method to control the condensation and decondensation of DNA upon incorporation of luminescent concentrators.

Towards a transparent, flexible, scalable and disposable image sensor using thin-film luminescent concentrators

Most image sensors are planar, opaque, and inflexible. We present a novel image sensor that is based on a luminescent concentrator (LC) film which absorbs light from a specific portion of the spectrum. The absorbed light is re-emitted at a lower frequency and transported to the edges of the LC by total internal reflection. The light transport is measured at the border of the film by line scan cameras. With these measurements, images that are focused onto the LC surface can be reconstructed. Thus, our image sensor is fully transparent, flexible, scalable and, due to its low cost, potentially disposable.

The effect of perylene diimide aggregation on the light collection efficiency of luminescent concentrators

The effect of dye concentration on the efficiency of a luminescent concentrator based on a perylene diimide (PDI) derivative incorporated in poly(methyl methacrylate) films cast on glass substrates is described. The predictions of ray-trace modelling are compared to experimental data from integrating sphere luminescence measurements. Increasing the PDI concentration leads to aggregation of the dye and an associated shift in the emission spectrum. The larger Stokes shift between emission and absorption spectra of the aggregated form reduces luminescence re-absorption and increases collection efficiency. However, the lower fluorescence quantum yield of the PDI aggregates restricts overall absorbed light to luminescence conversion. The relevance of the results to optimize organic molecule based luminescent solar concentrators is discussed.

Progress in phosphors and filters for luminescent solar concentrators

Luminescent solar concentrators would allow for high concentration if losses by reabsorption and escape could be minimized. We introduce a phosphor with close-to-optimal luminescent properties and hardly any reabsorption. A problem for use in a luminescent concentrator is the large scattering of this material; we discuss possible solutions for this. Furthermore, the use of broad-band cholesteric filters to prevent escape of luminescent radiation from this phosphor is investigated both experimentally and using simulations. Simulations are also used to predict the ultimate performance of luminescent concentrators.

Flexible concentrator photovoltaics based on microscale silicon solar cells embedded in luminescent waveguides

Unconventional methods to exploit monocrystalline silicon and other established materials in photovoltaic (PV) systems can create new engineering opportunities, device capabilities and cost structures. Here we show a type of composite luminescent concentrator PV system that embeds large scale, interconnected arrays of microscale silicon solar cells in thin matrix layers doped with luminophores. Photons that strike cells directly generate power in the usual manner; those incident on the matrix launch wavelength-downconverted photons that reflect and waveguide into the sides and bottom surfaces of the cells to increase further their power output, by more than 300% in examples reported here. Unlike conventional luminescent photovoltaics, this unusual design can be implemented in ultrathin, mechanically bendable formats. Detailed studies of design considerations and fabrication aspects for such devices, using both experimental and computational approaches, provide quantitative descriptions of the underlying materials science and optics.

Hybrid(Luminescent and Fresnel ) Concentrators to Improve Solar Panel Conversion Efficiency

The spectral response of the Si solar cell does not coincidence with the sun irradiance spectrum, so the efficiency of the Si solar cell is not high. To improve the Si solar cell one try to make use of most region of the sun spectrum by using dyes which absorb un useful wavelengths and radiate at useful region of spectrum (by stock shift). Fluorescence's dye is used as luminescent concentrator to increase the efficiency of the solar cell. The results show that the performance efficiency and out power for crystalline silicon solar cells are improved.

Hybrid(Luminescent and Fresnel ) Concentrators to Improve Solar Panel Conversion Efficiency

The spectral response of the Si solar cell does not coincidence with the sun irradiance spectrum, so the efficiency of the Si solar cell is not high. To improve the Si solar cell one try to make use of most region of the sun spectrum by using dyes which absorb un useful wavelengths and radiate at useful region of spectrum (by stock shift). Fluorescence's dye is used as luminescent concentrator to increase the efficiency of the solar cell. The results show that the performance efficiency and out power for crystalline silicon solar cells are improved.

Operating regimes for second generation luminescent solar concentrators

ABSTRACTIn this paper, we introduce the concept of first and second generation luminescent solar concentrators. Traditional, first generation devices are characterised by their randomly oriented molecules that absorb sunlight and emit luminescence isotropically. By applying detailed balance to the absorbed and emitted photon fluxes we derive the Shockley–Queisser limit for these devices. It is found that they have inherently low efficiency due to optical losses (the well known reabsorption problem) and also that device performance is strongly affected by the areal ratio between the top and edge surfaces. This latter property makes it very difficult to achieve significant cost reductions because as the edge area is reduced (to lessen the amount of expensive photovoltaic material required for conversion), the efficiency of the system diminishes. First generation concentrators have now approached the fundamental limits which we predict here, thus to achieve a stand‐alone luminescent concentrator that enables significant cost reductions, second generation approaches are now needed. New, second generation devices are characterised by either directional emitters or photonic filters which enhance the waveguiding mechanism, allowing high efficiency and large sizes to be achieved simultaneously. Here we define the fundamental operating regime in which second generation technology must reach to surpass the limit of first generation devices. Copyright © 2011 John Wiley & Sons, Ltd.

New developments in luminescence for solar energy utilization

As our fossil sources of energy diminish constantly search for alternative energy solutions becomes vital. The interest in exploiting solar energy for photovoltaic electricity has grown exponentially in recent decade, however, its high cost is still a limiting factor for massive uses. Static luminescent concentrator could provide a partial solution if properly designed. The paper summarizes the requirements for efficient and photostable luminescent concentrators, provides the latest results and ideas and shows how they can be materialized. It is demonstrated how the plate efficiency can be improved by applying a thin film with optical contact to transparent plate, silver plasmons that increase the transition probability of the colorants, photonic systems preventing the escape of the luminescence from the plate when traveling to the cell, creating fluorescence in the UV and visible part of the spectrum, using materials in which the absorption and emission from different electronic levels prevent self-absorption.

Outdoor characterisation of High Efficiency Luminescent Solar Concentrators

AbstractThis work presents recent results on outdoor characterisation of high efficiency luminescent solar concentrators. Outdoor measurements at 25�C and corrected to 1000 W/m2 have been compared with indoor characterization according to the international standards for conventional photovoltaic devices. Dependence of electrical parameters with temperature is also shown, together with results of various 1-day monitoring campaigns of luminescent concentrators performance under varying irradiance conditions. Results highlight the importance of those devices as potentially cheap, residential concentrating systems.

Enhancing photon harvesting in organic solar cells with luminescent concentrators

The authors report on the application of luminescent concentrators on organic solar cells fabricated zinc-phthalocyanine and C60. These solar cells have their main absorption in the wavelength range between 600 and 800nm. Below 600nm, the low absorption limits the quantum efficiency. Luminescence concentrators are used to overcome this limitation by spectrally shifting blue and green light towards the red and waveguiding it to the solar cell. With a second solar cell harvesting the red light transmitted through the concentrator, the photocurrent density is increased compared to a single solar cell of equal active area from about 8.5 up to 10mA∕cm2.

I-V Performance and Stability Study of Dyes for Luminescent Plate Concentrators

In this paper, both the performance and stability of luminescent flat plate concentrator (LFPC) plates in combination with mc-Si photovoltaic cells are studied. It is shown that the electrical current of a silicon solar cell attached to the luminescent plate is improved by a factor 1.5 using a LFPC containing a single dye. It is also shown that most of the dyes are not stable in the polymer plates that are currently used. Screening of the stability of several other dyes indicates that the stability is strongly dependent on the type of dye and the polymer matrix, e.g., additives or the monomer residues.

Molecular-based concepts in PV towards full spectrum utilization

Molecular-based concepts offer the potential of low materials and processing costs in photovoltaics (PV), which is especially interesting if high efficiencies can be obtained. To accomplish high efficiencies, a better utilization of the solar spectrum is of high importance. The concept of two-photon absorption in dye-sensitized solar cells and full spectrum aspects of luminescent flat plates concentrators are discussed in this paper. The two-photon dye cell can be compared to a tandem solar cell on the molecular level. The luminescent concentrator offers the potential to employ full spectrum utilization in combination with static concentration of both direct and diffuse light.

Physicochemical aspects of the creation of modern light-sensitive materials based on polymethine dyes

Features of the photophysical and photochemical characteristics of polymethine dyes that determine their use as light-sensitive materials (luminescent light concentrators, fluorescent probes and markers for the intercalation of DNA, laser media, polymerization photoinitiators, electroluminescent media) are analyzed. The main paths of the degradation of the electronic excitation energy (photoisomerization, intercombination and internal conversion, electron phototransfer in ion pairs, interaction of chromophores, like and mixed association) are discussed. The relation between these factors and the structure of the dyes and the nature of the medium is examined. Special attention is paid to methods of creating and optimizing colored light-sensitive polymeric materials.

Thin-film luminescent concentrators for position-sensitive devices

The output emittance at the edge of a luminescent concentrator (LC) depends on the physical properties of the dye and matrix used, the spectral intensity of the incident light, and the geometric parameters of the LC. If a projection of the light source on a LC is smaller than its aperture, the LC's output signal will also depend on the position of the projection. This LC feature opens the possibility of determining the position of the light spot and thus building a new type of position-sensitive device. The advantage of LC position-sensitive devices compared with CCD-based sensors is their greater simplicity; LC detection devices have larger linear range than conventional position-sensitive sensors based on discrete photodetectors. Here we describe our study of LC's as two-dimensional position-sensitive elements and analyze, by ray-tracing simulation, different LC designs to get improved linear response. In addition, we discuss experimental results showing real characteristics of position-sensitive devices based on the integration of LC's with photodetectors. We found that spatial resolution of a 12-mm-radius LC-based sensor is of the order of 13 mum within the linear range +/-5 mm.

Thin-film luminescent concentrators for integrated devices

A luminescent concentrator (LC) is a nonimaging optical device used for collecting light energy. As a result of its unique properties, a LC also offers the possibility of separating different portions of the spectrum and concentrating them at the same time. LC’s can be applied to a whole range of problems requiring the collection, manipulation, and distribution or measurement of light. We present the theory of LC’s as spectral elements, describe the design of LC devices in general, and show how a LC can be modeled by the use of a simple ray-optic algorithm. We also discuss how thin-film LC elements that use a photopolymer material can be integrated with electronics on a semiconductor substrate, and as a final contribution we give experimental results for several prototype integrated LC photodetectors as proof of concept.

Thin-film luminescent concentrators for integrated devices: a cookbook

A luminescent concentrator (LC) is a nonimaging optical device used for collecting light energy. As a result of its unique properties, a LC also offers the possibility of separating different portions of the spectrum and concentrating them at the same time. Hence, LC's can be applied to a whole range of problems requiring the collection, manipulation, and distribution or measurement of light. Further-more, as described in our previous research, thin-film LC elements can be deposited directly over sensor and processing electronics in the form of integrated LC devices. As an aid to further research, the materials and technology required to fabricate these thin-film LC elements through the use of an ultraviolet-curable photopolymer are documented in detail.