Luminescent solar concentrators (LSCs) are a class of optical devices able to harvest, downshift, and concentrate sunlight, thanks to the presence of emitting materials embedded in a polymer matrix. Use of LSCs in combination with silicon-based photovoltaic (PV) devices has been proposed as a viable strategy to enhance their ability to harvest diffuse light and facilitate their integration in the built environment. LSC performances can be improved by employing organic fluorophores with strong light absorption in the center of the solar spectrum and intense, red-shifted emission. In this work, we present the design, synthesis, characterization, and application in LSCs of a series of orange/red organic emitters featuring a benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-tetraoxide central core as an acceptor (A) unit. The latter was connected to different donor (D) and acceptor (A′) moieties by means of Pd-catalyzed direct arylation reactions, yielding compounds with either symmetric (D–A–D) or non-symmetric (D–A–A′) structures. We found that upon light absorption, the compounds attained excited states with a strong intramolecular charge-transfer character, whose evolution was greatly influenced by the nature of the substituents. In general, symmetric structures showed better photophysical properties for the application in LSCs than their non-symmetric counterparts, and using a donor group of moderate strength such as triphenylamine was found preferable. The best LSC built with these compounds presented photonic (external quantum efficiency of 8.4 ± 0.1%) and PV (device efficiency of 0.94 ± 0.06%) performances close to the state-of-the-art, coupled with a sufficient stability in accelerated aging tests.
This study reports the use of waterborne acrylic resin as a polymer matrix for thin-film luminescent solar concentrators (LSC). A water dispersable lanthanide complex based on commercially available Eu 3+ chelate (Lumilux SDP Red, Lu Red) is utilized as the red-emitting pigment. The derived thin polymer films of about 100 μm show absorptions of the organic ligand comprised between 300 and 400 nm, flanked by scattering phenomena caused by the presence of the micro-sized pigment particles, whose dispersion is not adversely affected by concentration. The film's emission displays the typical fluorescence of Eu 3+ chelates around 600 nm with quantum yields between 20 and 36%. External quantum efficiencies (𝜼 ext ) are found to increase up to 4-4.5% with Lu Red content less than 10-15%, while dropping to about 3% at the highest content, possibly due to the adverse influence of the scattering phenomena within the waveguide. Maximum device efficiencies (𝜼 dev ) of 0.70% confirm the potentiality offered by the new LSC systems, thus definitely supporting the waterborne polymer matrices for the development of high-performance and water-based solar collectors.
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