Design Of Luminescent Solar Concentrators Research Articles

Environmental Effects on the Performance of Quantum Dot Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are all-photonic, semitransparent solar devices with great potential in the emerging fields of building-integrated photovoltaics and agrivoltaics. Over the past decade, particularly with the advent of quantum dot (QD) LSCs, tremendous progress has been made in terms of photovoltaic efficiency and device size by increasing solar spectral coverage and suppressing reabsorption losses. Despite these advances in LSC design, the effects of environmental conditions such as rain, dust, and dirt deposits, which are ubiquitous in both urban and agricultural environments, on LSC performance have been largely overlooked. Here, we address these issues by systematically investigating the environmental effects on the solar harvesting and waveguiding capability of state-of-the-art QD-LSCs, namely, the presence of airborne pollutants (dust), water droplets, and dried deposits. Our results show that dust is unexpectedly insignificant for the waveguiding of the concentrated luminescence and only reduces the LSC efficiency through a shadowing effect when deposited on the outer surface, while dust accumulation on the inner LSC side increases the output power due to backscattering of transmitted sunlight. Water droplets, on the other hand, do not dim the incident sunlight, but are detrimental to waveguiding by forming an optical interface with the LSC. Finally, dried deposits, which mimic the evaporation residues of heavy rain or humidity, have the worst effect of all, combining shading and waveguide losses. These results are relevant for the design of application-specific surface functionalization/protection strategies real LSC modules.

Spatially Resolved Optical Efficiency Measurements of Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are able to concentrate both direct and diffuse solar radiation, and this ability has led to great interest in using them to improve solar energy capture when coupled to traditional photovoltaics (PV). In principle, a large-area LSC could concentrate light onto a much smaller area of PV, thus reducing costs or enabling new architectures. However, LSCs suffer from various optical losses which are hard to quantify using simple measurements of power conversion efficiency. Here, we show that spatially resolved photoluminescence quantum efficiency measurements on large-area LSCs can be used to resolve various loss processes such as out-coupling, self-absorption via emitters, and self-absorption from the LSC matrix. Further, these measurements allow for the extrapolation of device performance to arbitrarily large LSCs. Our results provide insight into the optimization of optical properties and guide the design of future LSCs for improved solar energy capture.

Minimizing Scaling Losses in High-Performance Quantum Dot Luminescent Solar Concentrators for Large-Area Solar Windows.

While luminescent solar concentrators (LSCs) have been researched for several decades, there is still a lack of commercially available systems, mostly due to scalability, performance, aesthetics, or some combination of these challenges. These obstacles can be overcome by the systematic optimization of a laminated glass LSC design, demonstrated herein. In particular, we first show that it is possible to improve optical and electrical efficiencies of an LSC by fine-tuned optimization of the constituent fluorophore-containing interlayer resin. Further still, an increased understanding of commercially available solar cells allows us to establish a direct correlation between the device's optical and electrical efficiency. Next, optical characterization of LSCs of varying sizes allows us to elucidate the main loss mechanisms in our LSCs, as well as ways to mitigate them. Altogether these optimization steps create opportunities for high-performance multi-interlayer LSC devices with demonstrated electrical power conversion efficiency as high as 1.1% to 4.9% at visual light transmission of 74% to 5%. Furthermore, careful examination of different blue-color (red-band absorbing) dyes provides a path for color-tunability of LSC windows toward neutral regimes. Design iterations of multiple device form factors enabled a color-neutral prototype without significant performance losses by separating color-neutralizing and LSC layers into different panes of an insulated glass unit. This work demonstrates the importance of LSC design optimization in achieving high-performance solar window technology with commercially acceptable aesthetics.

Visible to infrared down conversion of Er3+ doped tellurite glass for luminescent solar converters

A series of tellurite glasses having the composition70TeO2–20ZnO–(10-x)Nb2O5 (in mol%) doped with Er3+ ion (x = 0.5, 1.0, 1.5, 2.5, 3, 3.5 and 4 mol% respectively) was synthesized using the melt quenching route. Based on the Raman analysis and Differential Scanning Calorimetry, the produced glasses exhibited low-phonon (772 cm−1) energy and good thermal stability (147 °C), respectively. The X-ray (XR) diffraction proved the amorphous state of the synthesized glasses, which highlights the high quality of the obtained glass materials. The impact of Er2O3 content on the local structure around erbium ions was investigated via Judd-Ofelt theory. Various radiative parameters such as the quality factors (χ), the branching ratios (β), the quantum efficiencies (η) and radiative lifetimes (τR) have been reported and discussed. The Down-conversion (DC) energy-process in the Er3+ ions was analyzed using an excitation wavelength of 488 nm and the different mechanisms involved in the 1.53 µm emission are discussed. The effect of erbium content on the measured lifetime of the 4I13/2state was analyzed according the M. Inokuti and F. Hirayama (I-H) model. For high concentrations of Er2O3 oxide, the obtained results showed an efficient energy transfer between Er3+ ions, which may cause the luminescence quenching and the reduction in radiative parameters of the 4I13/2 → 4I15/2 transition at 1.53 µm. While the addition of Er2O3 oxide at low content up to a concentration of 4.211020 cm−3 showed that this glass possessed high quantum efficiency (91%), large emission cross section of about 9.1 10−21 cm2 and effective bandwidth exceeding 100 nm attributed to the 1.53 µm emission, which makes the proposed tellurite glass highly promising in many photonic applications, especially for the design of luminescent solar concentrators (LSC) for bandgap solar cells in the range of 0.7–0.9 eV.

Singlet Exciton Dynamics of Perylene Diimide- and Tetracene-Based Hetero/Homogeneous Substrates via an Ab Initio Kinetic Monte Carlo Model

Luminescent solar concentrators (LSCs) are devices that trap a portion of the solar spectrum and funnel it toward photon-harvesting devices. The modeling of LSCs at a quantum chemical level, however, remains a challenge due to the complexity of exciton and photon dynamic modeling. This study examines singlet exciton dynamics occurring within a typical LSC device. To do this, we use a rejection-free kinetic Monte Carlo method to predict diffusion lengths, diffusion coefficients, substrate anisotropy, and average exciton lifetimes of perylene diimide (PDI)- and tetracene-based substrates in the low-concentration scheme. Ab initio rate constants are computed using time-dependent density functional theory-based methods. PDI-type substrates are observed to display enhanced singlet exciton transport properties compared to tetracene. Simulations show that substrates with dipole-aligned chromophores are characterized by anisotropic exciton diffusion, with slightly improved transport properties. Finally, a PDI–tetracene substrate is simulated for both disordered and dipole-aligned chromophore configurations. In this multidopant substrate, transport is predominantly mediated by PDI due to the asymmetry in the transport rates between the two dyes considered. We conclude by discussing the properties of multidopant substrates and how they can impact the design of next-generation LSCs.

Solar Pumping of Fiber Lasers with Solid‐State Luminescent Concentrators: Design Optimization by Ray Tracing

AbstractSolar‐pumped lasers (SPLs) typically couple sunlight into the laser cavity using focusing optics and solar tracking. Luminescent solar concentrators (LSC) are an alternative, fully planar, scalable pump source that can concentrate diffuse light. For liquid LSC‐based SPLs, reflective cavities have been used to trap light and pump a Nd3+‐doped silica fiber. Here, three solid‐state LSC‐based SPL designs, in addition to the reflective cavity making use of total internal reflection, are analyzed by ray‐tracing simulations. Results are compared to a liquid LSC reference, also used for validating simulations. Substituting the liquid‐state LSC for a solid‐state LSC (with the fiber placed inside) allows a 7‐fold enhancement of the gain coefficient, corresponding to a 30‐fold enhancement of the laser output power. An additional 4‐fold increase of the output power is possible with a fiber of kilometers length. These results show a roadmap for realizing SPLs with output powers on the order of 2.8 W m−2 under terrestrial sunlight, while keeping an identical reflective cavity used for the liquid LSC design. In addition, room‐temperature operation should be possible with certain solid LSC designs, and the necessity for a reflective cavity comprised of costly dielectric mirrors may be relieved.

Luminescent Solar Concentrators Based on Energy Transfer from an Aggregation-Induced Emitter Conjugated Polymer.

Luminescent solar concentrators (LSCs) are solar-harvesting devices fabricated from a transparent waveguide that is doped or coated with lumophores. Despite their potential for architectural integration, the optical efficiency of LSCs is often limited by incomplete harvesting of solar radiation and aggregation-caused quenching (ACQ) of lumophores in the solid state. Here, we demonstrate a multilumophore LSC design that circumvents these challenges through a combination of nonradiative Förster resonance energy transfer (FRET) and aggregation-induced emission (AIE). The LSC incorporates a green-emitting poly(tetraphenylethylene), p-O-TPE, as an energy donor and a red-emitting perylene bisimide molecular dye (PDI-Sil) as the energy acceptor, within an organic–inorganic hybrid diureasil waveguide. Steady-state photoluminescence studies demonstrate the diureasil host induced AIE from the p-O-PTE donor polymer, leading to a high photoluminescence quantum yield (PLQY) of ∼45% and a large Stokes shift of ∼150 nm. Covalent grafting of the PDI-Sil acceptor to the siliceous domains of the diureasil waveguide also inhibits nonradiative losses by preventing molecular aggregation. Due to the excellent spectral overlap, FRET was shown to occur from p-O-TPE to PDI-Sil, which increased with acceptor concentration. As a result, the final LSC (4.5 cm × 4.5 cm × 0.3 cm) with an optimized donor–acceptor ratio (1:1 by wt %) exhibited an internal photon efficiency of 20%, demonstrating a viable design for LSCs utilizing an AIE-based FRET approach to improve the solar-harvesting performance.

Impact of the Edges of a Backside Diffusive Reflector on the External Quantum Efficiency of Luminescent Solar Concentrators: Experimental and Computational Approach

Luminescent Solar Concentrators (LSCs) have been proposed in the 1970s as cheap planar concentrators for residential applications and nowadays represent a novel idea with excellent perspectives for building integration photovoltaics. The interest in LSCs has increased in the last years, due to improved stability of luminescent dyes, the introduction of quantum dots and nanorods and the overall reported increase in module efficiency. Computational methods have been suddenly applied as an important tool for the description of light dynamics in LSCs. With “raytracing methods” light is described as particle-like (photons) and each particle is tracked. It is precious tool for the description of absorption/reemission events, refraction and internal reflection in LSCs. It is also a very useful approach for the description of LSC edge effects, which may be well described by means of basic geometrical optics and are the subject of this work. The impact of scattering layers on the backside of LSCs is analysed in detail both experimentally and computationally. Results give evidence of the non-wavelength dependent impact of backside diffusers to the external quantum efficiency of LSCs and thus to their overall performance. A possible design of LSC as smart windows in photovoltaic facades is also suggested, where the benefits of the edge effects described are taken into account.

Design and Response of High‐Efficiency, Planar, Doped Luminescent Solar Concentrators Using Organic–Inorganic Di‐Ureasil Waveguides

Luminescent solar concentrators (LSCs) offer significant potential for solar energy capture in the urban environment. Here, the first example of a planar, doped LSC using Lumogen Red (LR305) as the luminophore and a di‐ureasil organic–inorganic hybrid as the waveguide is reported. The di‐ureasil waveguide offers several advantages over organic polymer waveguides including facile solution‐processing from benign solvents and extension of the absorption window through energy transfer. Spectral evaluation using absorption and photoluminescence spectroscopies is used to optimize the LSC composition, yielding optical efficiencies as high as 14.5% (300–800 nm). A power conversion efficiency (PCE) of 0.54% is obtained for the champion LSC coupled to a c‐Si PV cell using the di‐ureasil precursor as an optical glue to minimize interfacial losses. Finally, a simple figure of merit to evaluate the performance of LSC‐solar cell composite systems is proposed that enables comparison of the actual improvement in the efficiency of solar cells due to the attachment of the LSC, irrespective of the LSC design, architecture or materials. A PCE of 17.4% for the solar cell in the emission region of the LSC is obtained, which is a remarkable improvement of ≈40% over its AM 1.5G value.

Asymptotic solution of light transport problems in optically thick luminescent media

We study light transport in optically thick luminescent random media. Using radiative transport theory for luminescent media and applying asymptotic and computational methods, a corrected diffusion approximation is derived with the associated boundary conditions and boundary layer solution. The accuracy of this approach is verified for a plane-parallel slab problem. In particular, the reduced system models accurately the effect of reabsorption. The impacts of varying the Stokes shift and using experimentally measured luminescence data are explored in detail. The results of this study have application to the design of luminescent solar concentrators, fluorescence medical imaging, and optical cooling using anti-Stokes fluorescence.

Luminescent solar concentrators: From experimental validation of 3D ray-tracing simulations to coloured stained-glass windows for BIPV

Luminescent solar concentrators (LSC) are a promising technology for building integrated photovoltaics (BIPV) given the wide variety of forms and colours that can be realised. Given the flexibility of the technology, the use of ray-trace modelling is indispensable in the design, performance evaluation, and optimisation of LSCs. This work begins by comparing a three dimensional (3D) ray-trace model of an LSC with experimental results. The study includes 70 samples – both square and circular LSCs, containing five different fluorescent organic dyes (BASF Lumogen) each at seven different concentrations. The figure-of-merit used for performance evaluation was the average power density determined at the LSC edge sheet, measured using an optical fibre connected to a spectrometer. The results demonstrate that 3D ray-trace results gives good agreement with the experimental measurements, to within around ±5% within a wide concentration range (optical density=0.05–8) and a maximum difference of ±13%. The wide range of colours achieved is presented in a CIE chart. Overall, the validated experimental results give confidence in the use of modelling for future larger LSCs for BIPV. Therefore, based on these results and the colours achievable, a model of a stained-glass window is constructed and its performance throughout a solar day is simulated.

Size- and structure-dependent efficiency enhancement for luminescent solar concentrators

Size- and structure-dependent efficiency enhancement methods are studied for luminescent solar concentrators (LSCs) fabricated by casting organic laser dyes into PMMA matrixes. The enhancement are achieved mainly by attaching a white diffuser with an airgap at the bottom of the LSC and adding refractive index matched optical gel between the LSC's edges and the attached photovoltaic cells. The size-dependent efficiency enhancement is studied for a single layer by changing the size up to 120 cm. The results show that the enhancement from the white diffuser drops and then tends to plateau at a certain size of LSC. This also applies to multilayer LSCs. Together with optical gel, the efficiency enhancement is higher for multilayer structures than that for single layers. We also demonstrate the optimal length for the design of LSCs due to reabsorption of dyes. These results could be applied to optimize the design of other LSCs.

A new design of luminescent solar concentrator and its trial run

Normal luminescent solar concentrators (LSC) have a great limitation in their light transportation because the light produced by the recently reported LSCs is not a point light source. In order to enable LSCs to use optical fibers as the effective remote light transport media, a new design of LSC, which uses three color luminescent fibers for solar absorption and uses clear optical fiber bundles to transport the absorbed sunlight into a remote place, is fabricated and tested. Radiation flux ratios with a mean value of 5.7%, the luminous flux up to 114.1 lumens, and the light efficiency of 0.56% have been achieved during the trial run. The luminous efficacy as 0.643 lm W−1 is higher than that of combusting candles (0.3 lm W−1) but lower than that of the incandescent light bulbs (16–40 lm W−1). Further, since the sun light is free, different from electrical light sources, the luminous efficacy of the new LSC does not result in any electricity consumption when it is under operation. A color analysis and spectrum test proves that the light produced by the new LSC performs a great match to the direct sun light in color. Copyright © 2010 John Wiley & Sons, Ltd.