Orange/Red Benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-Tetraoxide-Based Emitters for Luminescent Solar Concentrators: Effect of Structures on Fluorescence Properties and Device Performances

Abstract

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.

Luminescent Solar Concentrators from Food Substances: A Safe and Simple Experiment to Approach Sunlight Energy Harvesting

“…As shown in Figure , curcumin in isomalt displays much higher emission intensities than riboflavin, with broad peaks from 450 to 600 nm. We believe that other more specific effects observed, such as the red-shift of the emission peaks with concentration and its change in shape in the case of riboflavin, are of a higher level of detail and thus beyond the educational scope of the experiment ,− (see SI).…”

“…30 Nonetheless, these materials may suffer limited performances when compared to the state-of-the-art devices. 31 To investigate whether the combination of isomalt with riboflavin or curcumin is suitable to prepare functioning slab LSCs, we fabricated several samples comprising various quantities of fluorophores to isomalt. Given its long-known emission properties, we have also tried quinine as an edible fluorophore during preliminary tests.…”

“…η dev assesses the LSC performances in the light-to-electricity conversion (Figure 3b). For this system, it reached a maximum value of 0.65, lower than other state-ofthe-art devices 46 and data gathered from our lab comprising PMMA-based LSC (∼1−1.2), 31 but representative of the light collecting ability of the isomalt LSC devices and still comparable to other recently published devices that were not optimized for η dev . 47 A complete characterization of photonic efficiencies is available in the SI (Figure S6).…”