Thin-film Luminescent Solar Concentrators Research Articles

Semi-Transparent Luminescent Solar Concentrators Based on Intramolecular Energy Transfer in Polyurethane Matrices.

Luminescent solar concentrators (LSCs) are spectral conversion devices offering interesting opportunities for the integration of photovoltaics into the built environment and portable systems. The Förster-resonance energy transfer (FRET) process can boost the optical response of LSCs by reducing energy losses typically associated to non-radiative processes occurring within the device under operation. In this work, a new class of FRET-based thin-film LSC devices is presented, in which the synthetic versatility of linear polyurethanes (PU) is exploited to control the photophysical properties and the device performance of the resulting LSCs. A series of luminescent linear PUs are synthesized in the presence of two novel bis-hydroxyl-functionalized luminophores of suitable optical properties, used as chain extenders during the step-growth polyaddition reaction for the formation of the linear macromolecular network. By synthetically tuning their composition, the obtained luminescent PUs can achieve a high energy transfer efficiency (≈90%) between the covalently linked luminophores. The corresponding LSC devices exhibit excellent photonic response, with external and internal photon efficiencies as high as ≈4% and ≈37%, respectively. Furthermore, their optimized power conversion efficiency combined with their enhanced average visible-light transmittance highlight their suitability for potential use as transparent solar energy devices.

Constructing highly efficient and ultra-stable (against Temperature, Humidity and Sunlight) luminescent solar concentrators by using dendritic CsPbBr3@SiO2 particles

Conventional perovskite quantum dots (PQDs) suffer long-term stability, further limiting practical application of luminescent solar concentrators (LSCs). In this work, novel dendritic CsPbBr3@SiO2 particles with bright solid-state green light emission and 46 % of photoluminescence quantum yield (PLQY) have first been synthesized via one-step solid-phase calcination method. The dendritic CsPbBr3@SiO2 particles have then been used as fluorescent material for construction of LSCs along with using organosilicon polymers with better compatibility as waveguide materials. Single-layer thin film LSCs and overall curing LSCs are easily prepared by the casting and curing method, exhibiting high external optical efficiency (ηopt) of 7.88 % and 10.92 %, respectively. The maximum internal quantum efficiency (ηint) of thin film LSCs and overall curing LSCs reach 45.09 % and 44.07 %, respectively, while their maximum external quantum efficiency (ηext) of 29.42 % and 34.07 % are obtained, respectively. Importantly, both types of LSCs show excellent stability, maintaining above 92 % of the initial ηopt under high-relative-humidity (RH = 90 %), high-temperature (60 °C) and sunlight exposure conditions for two weeks or room temperature environment for twenty weeks. Moreover, both types of LSCs at optimal conditions have good transparency (>40 % over 515 nm of light wavelength). Otherwise, both types of LSCs have higher ηopt than that of the previous related work.

High-loading of organosilane-grafted carbon dots in high-performance luminescent solar concentrators with ultrahigh transparency

Carbon dots (CDs) generally suffer from aggregation-induced fluorescence quenching effect in solid-state, which significantly limits their application in photoelectric devices. Due to this effect, it is a great challenge to achieve high-transparency and high-performance luminescent solar concentrators (LSCs) based on CDs. Here, the synthesis of organosilane-grafted carbon dots (Si-CDs) is rationally designed by hydrothermal method using anhydrous citric acid, ethanolamine and KH-792 as the reaction precursors. The obtained Si-CDs can be uniformly dispersed in the polyvinyl alcohol (PVA) matrix through the dehydration condensation reaction and hydrogen bonding between the silicon hydroxyl group of Si-CDs and the hydroxyl group of PVA. Based on this property, Si-CDs/PVA thin-film LSCs (5 ×5 ×0.2 cm3) with ultrahigh CD loading (25 wt%) and high transparency can be fabricated, exhibiting excellent absorption in the UV spectral region and about 90 % transmission in the visible range. Furthermore, the power conversion efficiency (PCE) of the LSCs can reach 2.09 % under a standard solar light and shows excellent stability even over 12 weeks. This synthetic design is expected to be beneficial for future development of CD synthesis and paves the way for the development of CDs-based photoelectric devices.

Highly efficient sandwich design thin film luminescent solar concentrators based on blue and green emissive MAPbBr3 perovskites nanostructures

This study deals with the optimally designed blue and green emissive MAPbBr3 perovskite nanostructures (PNSs). Later PNSs were utilized as fluorescent material in a sandwich-design thin film luminescent solar concentrator (SD-TLSC). The fabricated SD-TLSC exhibits high performance with an impressive optical efficiency of 5.75% and a high average visible transmission (AVT) of 85.7%, which is the two-fold enhancement of the conventional single thin film LSC configuration. The high performance of the SD-TLC is induced by effective solar radiation absorption in the entire wavelength ranges, which is attributed to its unique morphology that exhibit different PL emission. These ground-breaking results pave the way for the potential practical use of perovskite-based SD-TLSC as solar windows, marking a major advancement in the field of building-integrated photovoltaic (BIPV).

Modeling and comparison of bulk and thin-film luminescent solar concentrators based on colloidal perovskite quantum dots.

Photovoltaic integrated luminescent solar concentrators (LSCs) can be embedded in modern buildings to serve as power-generation units. In this Letter, we demonstrate and develop a Monte Carlo ray-tracing model and a numerical description for the performance and loss evaluation of LSCs based on colloidal quantum dots. The performance differences between bulk and thin-film LSCs are systematically analyzed at different sizes and concentrations. It is found that large-area thin-film LSCs generally perform better, which is attributed to the suppression of scattering and the retention of quantum yield by this structure with twice the performance of bulk LSCs.

Performance of Luminescent Solar Concentrators Integrated with Negative Replica Layers of Leaf Surface Microstructures.

In this study, a negative replica layer of leaf surface microstructures was used to cover the top surfaces of semitransparent thin-film luminescent solar concentrators (LSCs) to enhance the concentrators’ performance. With low reflection on the air–glass interface of the glass plate in a thin-film LSC, a negative replica layer enables the scattering of incident sunlight and increases the path of light transmitted into the LSC and the thin phosphor layer at the bottom surface of the LSC. The incident sunlight is therefore more likely to interact with the phosphor particles in the thin-film phosphor layer, thereby enhancing the performance of the LSC. In this study, semitransparent thin-film LSCs with different inorganic phosphors were examined. The experimental results revealed that the optical collection efficiency of semitransparent thin-film LSCs covered with negative replica layers of leaf surface microstructures was higher than that of the semitransparent thin-film LSCs without negative replica layers. Furthermore, the LSCs with negative replica layers with high haze ratios exhibited high optical collection efficiency. Integrating negative replica layers of leaf surface microstructures as semitransparent layers in thin-film LSCs may optimize the application of LSCs in building-integrated photovoltaics (BIPVs).

Y-shaped alkynylimidazoles as effective push-pull fluorescent dyes for luminescent solar concentrators (LSCs)

The synthesis of three 2-arylalkynyl-4,5-diarylimidazoles endcapped with typical electron-donating (ED) and electron-withdrawing (EW) groups (push-pull system) and their evaluation as fluorescent dyes for thin-film luminescent solar concentrators (LSCs) is described. These novel Y-shaped imidazole-based fluorophores were easily assembled in good chemical yields through a three-step synthetic sequence involving a double Suzuki arylation, followed by a dehydrogenative alkynylation, and a Knoevenagel condensation. Their optical and spectroscopic properties were analyzed both in solution and in poly(methyl methacrylate) (PMMA) films. All the molecules in PMMA films showed an intense, red-shifted emission between 540 and 575 nm with large Stokes shift (>120 nm), moderate-to-good fluorescence quantum yields (QY) and good device efficiencies (ηdev), especially for compound 3.

Thin-Film Luminescent Solar Concentrator Based on Intramolecular Charge Transfer Fluorophore and Effect of Polymer Matrix on Device Efficiency.

Luminescent solar concentrators (LSCs) provide a transformative approach to integrating photovoltaics into a built environment. In this paper, we report thin-film LSCs composed of intramolecular charge transfer fluorophore (DACT-II) and discuss the effect of two polymers, polymethyl methacrylate (PMMA), and poly (benzyl methacrylate) (PBzMA) on the performance of large-area LSCs. As observed experimentally, DACT-II with the charge-donating diphenylaminocarbazole and charge-accepting triphenyltriazine moieties shows a large Stokes shift and limited re-absorption losses in both polymers. Our results show that thin-film LSC (10 × 10 × 0.3 cm3) with optimized concentration (0.9 wt%) of DACT-II in PBzMA gives better performance than that in the PMMA matrix. In particular, optical conversion efficiency (ηopt) and power-conversion efficiency (ηPCE) of DACT-II/PBzMA LSC are 2.32% and 0.33%, respectively, almost 1.2 times higher than for DACT-II/PMMA LSC.

Reducing reabsorption in luminescent solar concentrators with a self-assembling polymer matrix

Reabsorption in luminescent solar concentrators (LSC) is a major factor hindering their commercialisation. This issue is caused by the inherently small Stokes shift of luminophores which creates a large spectral overlap between absorption and emission, leading to reabsorption of waveguided photons. As reabsorption events amplify loss mechanisms such as escape cone losses and non-radiative emission, they are the most detrimental to photon output. Reducing reabsorption can be achieved by decreasing the amount of luminophore-doped waveguide compared to the overall LSC, resulting in an increase in research of both thin film LSCs, and new methods of templating or etching polymer thin films to reduce lateral reabsorption. Here we use self-assembly to alter the structure of a common host matrix, poly (methylmethacrylate) (PMMA) by the addition of a co-polymer, polystyrene-block-poly (acrylic acid) (PS-b-PAA); when in a 1:1 PMMA:PS-b-PAA ratio this creates holes of ~1.6 μm circumference within the polymer matrix, thus providing a simple way to reduce the volume of the luminophore doped host matrix. While quantifying the trade-offs associated with different LSC fabrications and surface effects, we show that the alteration of the host matrix with the PS-b-PAA results in a close to halving of the total number of reabsorption events (PS-b-PAA = 4.4; PMMA = 4.0; 1:1 = 1.8). Device photoluminescence efficiency increases by 10% compared to single component polymer matrices (PS-b-PAA = 76%; PMMA = 77%; 1:1 = 87%), though there is an increase in detrimental outcoupling also linked to this. We also investigated the following polymer ratios of PMMA:PS-b 1:1, 1:2, 1:3, 3:1, 2:1 and found that the ideal ratio to maximise LSC performance is the 1:1 ratio. These trade-offs and new design strategy will aid future efforts in device optimisation.

Benzo[1,2-d:4,5-d′]bisthiazole fluorophores for luminescent solar concentrators: synthesis, optical properties and effect of the polymer matrix on the device performances

Three new fluorophores (BBT2-4) with a D-A-D structure, characterised by the common benzo[1,2-d:4,5-d′]bisthiazole (BBT) as acceptor core (A) and different donor groups (D), were designed and synthesised for use in thin-film luminescent solar concentrators (LSC). The optical and spectroscopic properties of the new dyes were analysed both in solution (toluene) and in polymeric films, using static and time-resolved techniques. All the prepared molecules showed intense emissions between 460 and 550 nm with large Stokes shift (>50 nm), moderate-to-good fluorescence quantum yields (Φf) both in toluene solution (18–73%) and in poly(methyl methacrylate) (PMMA) films (10–52%) and good optical efficiencies (5.8–7.5%) as LSC. Transient absorption spectroscopy (TAS) studies highlighted that higher Φf were related to long excited-state lifetimes and that such properties were critically dependent on the polarity of the surrounding environment. Notably, homogeneous BBT4 dispersions into the less polar poly(benzyl methacrylate) (PBzMA) and poly(cyclohexyl methacrylate) (PCMA) polymeric matrices showed higher Φf (52.6% and 65.6%, respectively) than those gathered from PMMA films. Accordingly, BBT4/PCMA films revealed significant optical efficiency of 9.0% as LSC, which was comparable to that provided by the state-of-art fluorophore Lumogen Red 305 (10.1%).

Sustainable by design, large Stokes shift benzothiadiazole derivatives for efficient luminescent solar concentrators

The combination of a de novo design approach and micellar catalysis enables the preparation of innovative luminophores connecting efficiency and sustainability for the preparation of thin film luminescent solar concentrators.

Highly emissive fluorescent silica-based core/shell nanoparticles for efficient and stable luminescent solar concentrators

Luminescent solar concentrators (LSCs) represent a viable spectral conversion technology to maximize sunlight harvesting while promising to reduce the current gap for integration of solar cells into the built environment. In this work, novel highly emissive and photostable core-shell nanostructured luminescent species were synthesized and used in LSC devices. Such systems were obtained by entrapping Lumogen F Red 305 in silica-based shells by means of the sol-gel process using a combination of hydrophilic (tetraethyl orthosilicate) and hydrophobic (phenyltriethoxysilane) silica precursors. By tuning their relative proportions during the synthetic process, fine control over the characteristic dimensions and morphology of the obtained dye-doped core-shell nanoparticles could be achieved, leading to a maximum concentration of non-covalently entrapped fluorescent dye of ~ 1 wt%. Optical characterization showed that the newly synthetized nanoparticles displayed markedly improved photoluminescence quantum yield in solid state (~ 95%) with respect to the non-encapsulated dye (~ 2%), as a result of an effective suppression of dye aggregation and fluorescence quenching phenomena. In addition, their excellent photostability under harsh UV light exposure was demonstrated, resulting from the protective action of the encapsulating hybrid silica-based shell, which can effectively limit photobleaching of the luminescent core. Their incorporation in thin-film LSCs led to a maximum internal photon efficiency as high as ~ 29%, thus providing evidence of their suitability as highly performing luminescent species with superior optical response and excellent photostability. Also, a maximum external photon efficiency as high as 2.12% was achieved. This work provides the first demonstration of silica-based encapsulation of Lumogen F Red 305 and of the application of silica-based core-shell nanoparticles in LSCs, thus paving the path to the development of a new class of highly efficient and stable nanostructured luminophores for the photovoltaic field. The first demonstration of silica-based encapsulation of Lumogen F Red 305 and of the application of silica-based core-shell luminescent species in LSCs is given, thus opening the path to the development of highly efficient and stable nanostructured luminophores for the photovoltaic field. • Novel nanostructured luminescent species are synthetized. • The nanostructured luminophores are based on hybrid core-shell silica nanoparticles. • Such nanoparticles exhibit enhanced luminescence quantum yield and photostability. • Their use as luminophores in luminescent solar concentrators (LSCs) is demonstrated. • The obtained LSCs exhibit high efficiency and prolonged stability.

Efficient and Stable Thin‐Film Luminescent Solar Concentrators Enabled by Near‐Infrared Emission Perovskite Nanocrystals

A novel triphenylphosphine (TPP) treatment strategy was developed to prepare the near-infrared emission CsPbI3 nanocrystal (NC)-polymer composite thin-film luminescent solar concentrators (LSCs) featured with high absolute photoluminescence quantum yield (PLQY), low reabsorption, and high stability. The PL emission of the LSCs is centered at ~700 nm with 99.4±0.4% PLQY and narrow full width at half maximum (FWHM) of 75 meV, (i.e., 30 nm). Compared with LSCs prepared with classic CsPbI3 NCs, the stability of the LSCs after TPP treatments has been greatly improved, even after long-term (30 days) immersion in water and strong mercury lamp irradiation (50 mW/cm2). Due to the presence of lone pair electrons on the phosphorus atom, TPP is also used as a photoinitiator, with higher efficiency than other common photoinitiators. A large-area (~75 cm2) infrared LSCs were achieved with a high optical conversion efficiency of 3.1% at the geometric factor of 10.

CdSe/CdS–poly(cyclohexylethylene) thin film luminescent solar concentrators

Thin film luminescent solar concentrators are promising components of distributed power generation systems for building integrated photovoltaic applications. However, thin film geometries require high luminophore loading fractions to achieve sufficient absorption of sunlight, which, in the case of nanocrystal luminophores, can lead to aggregation and light scattering. In this work, we integrate CdSe/CdS nanocrystals into thin films of poly(cyclohexylethylene) at a range of loading fractions and characterize the composites with a combination of spectroscopic and simulation tools. We find that increased incident sunlight scattering is observed for the increasing luminophore loading fraction, but that the scattering is mostly limited to higher energy sunlight such that visible transmittance and haze of the samples are all greater than 89.7% and less than 8.3%, respectively. We then analyze the refractive index of the composite and show that the increase in loading fraction also affects the propagation of photoluminescence in the film, especially if the refractive index of the film is greater than that of the substrate. These studies show the importance of understanding the optical transport within thin films and provide design criteria to fabricate thin films for future implementation into building integrated photovoltaic applications.

Thin-Film Luminescent Solar Concentrators Using Inorganic Phosphors

Because of the predicted shortage of fossil fuels in the future, public interest in utilizing solar energy for photovoltaic (PV) electricity has exponentially increased in recent years. In particular, interest in the building integration of PVs is growing worldwide, and the use of building-integrated PVs (BIPVs) is one of the fastest growing segments of the PV industry. Luminescent solar concentrators (LSCs) are one of the possible approaches for BIPVs. However, the high cost and poor stability of the dyes or quantum dots used in conventional LSCs prevent the widespread adoption of electricity generation through the LSC-based solar energy. Therefore, inorganic phosphors with long lifetime and photostability under ultraviolet (UV) excitation and moisture are favorable luminescent materials for LSCs. In this paper, thin-film LSCs using commercial inorganic phosphors are proposed. The thin-film LSCs with different inorganic phosphors were examined. The phosphor concentration and relative position of the thin phosphor layer were investigated to determine the suitable structure of a thin-film LSC. This paper aimed to achieve an understanding of thin-film LSCs by using inorganic phosphors and to provide useful guidelines for future commercialization.

The potential of scalability in high efficiency hybrid perovskite thin film luminescent solar concentrators

Hybrid metal-halide perovskite (PVSK) thin films have recently demonstrated exciting potential as candidates for broadband luminescent solar concentrators (LSCs). Here, we examine the correlation between film thickness, lead halide sources in the precursors, and film morphology, with the optical efficiency of planar PVSK LSCs with a view to optimizing device performance. After synthesizing and testing sixteen different types of PVSK samples, we report a maximum optical efficiency of 34.7% in CH3NH3PbI3 LSC made with Pb(Ac)2 precursor, and with optimal thickness in the 150–300 nm range. Using 3D Monte Carlo simulations that incorporate experimental results, we accurately estimate self-absorption and surface losses, and most importantly, demonstrate the possibility of scaling these LSCs up to almost 100 cm, thereby providing a route toward optimizing thin film PVSK materials for these and other optoelectronic and photovoltaic applications.

Absorption coefficient dependent non-linear properties of thin film luminescent solar concentrators

This research article studied absorption coefficient dependent losses and efficiency of thin film luminescent solar concentrator (LSC). The optimum absorption coefficient was determined by fabricating red dye doped thin film LSCs with varying absorption coefficients of 24–202 cm-1. The optical, electrical, and ray-trace model predicted results were compared to establish the optimum absorption coefficient for fabricated thin film LSCs. The optical and electrical efficiencies of thin film LSCs are a function of absorption coefficient; follow linearly at lower values, gradually becoming non- linear at higher values of absorption coefficient which restricts the overall efficiency. The multi layered ray–trace model predicted results deviated from the experimental results at high absorption coefficient. Non-linearity was introduced by losses mechanism of re-absorption, resonant energy transfer (RET), and scattering in thin film LSCs. Re-absorption losses were found to be dependent on optical path-length and absorption coefficient of thin film. They were identified and quantified through locally collected emission and optical path-length in thin film LSCs. Re-absorption losses caused a red shift in emission peak by ≈ 20 nm as the absorption coefficient increased from 24 to 202 cm-1. RET decreased fluorescence life time of dye from 5 ns to 2 ns for the absorption coefficient increased from 24–202 cm-1. These absorption coefficient dependent losses limit the optical and electrical efficiency of thin film LSC devices, and compared with bulk LSC.

Colloidal carbon dots based highly stable luminescent solar concentrators

Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for photovoltaic (PV) cells, reducing the cost of PV generated power. Typical LSCs consist of optical waveguides doped with highly emissive fluorophores e.g. quantum dots (QDs) or dyes/polymers which are required to exhibit high optical efficiency and long-term stability. Compared to conventional fluorophores, carbon dots (C-dots) have superior advantages of non-toxicity, environmental friendliness, low-cost and simple preparation using abundant carbon based feedstock. Here, we demonstrate large-area LSCs (up to 100cm2) using colloidal C-dots. Two types of LSCs were fabricated by either incorporating oil-soluble oleylamine-treated C-dots into photo-polymerized poly(lauryl methacrylate) (PLMA) or spin-coating the water-soluble C-dots/polyvinylpyrrolidone (PVP) mixture on the glass substrate. LSCs based on C-dots/PLMA exhibit a quantum efficiency of 4% (geometric (G) factor of 38) and an optical efficiency of 1.1% (100cm2, G factor of 12.5) of tandem thin-film LSCs based on C-dots/PVP was achieved under one sun illumination. This performance is comparable to those of LSCs based on inorganic QDs with similar G factor. The LSCs based on C-dots are highly air-stable without any noticeable variation in photoluminescence under ultraviolet illumination (1.3W/cm2) for over 12h.

UV-curable fluoropolymers crosslinked with functional fluorescent dyes: the way to multifunctional thin-film luminescent solar concentrators

Co-crosslinking a luminescent dye with a photo-curable fluorinated polymer allows highly stable multifunctional thin-film luminescent solar concentrators to be obtained.

Enhancing optical efficiency of thin-film luminescent solar concentrators by combining energy transfer and stacked design

We report on a new approach aimed at enhancing the optical efficiency of luminescent solar concentrators (LSCs) based on poly(methyl methacrylate) (PMMA) thin-films doped with highly emissive fluorophores. In detail, a series of high-energy absorbing fluorophores (HEF) and perylene bisimides (PBI) red-emitting dyes were utilized in order to favor the collection of a large number of incident photons by the thin-film LSCs. The use of two fluorescent PMMA layers coated on the opposite surfaces of a glass slab was found to effectively increase the light concentration. The worthwhile combination of the appropriate HEF and PBI fluorophores within the secondary (bottom) PMMA layer assured optically efficiencies 10–14% greater than the maximum value of single-dye LSCs.