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.