Two
kinds of dumbbell-shaped acceptor–donor–acceptor
(A–D–A)-type triad single-component (SC) photovoltaic
molecules based on a benzodithiophene-rhodanine (BDTRh) core and [6,6]-phenyl-C61 butyric acid (PC61BA) termini, BDTRh–C2–PC61BA and BDTRh–C10–PC61BA, were synthesized by modulating the alkyl (C2 and C10)
spacer lengths. Both SC photovoltaic structures had similar UV–vis
spectra in solution, but BDTRh–C10–PC61BA showed a significantly higher absorption coefficient as
a thin film. In films, a more facile intermolecular photo-induced
charge transfer was observed for BDTRh–C10–PC61BA in the broad-band transient absorption measurements. BDTRh–C10–PC61BA also exhibited a higher hole mobility
(by 25 times) and less bimolecular recombination than BDTRh–C2–PC61BA. By plotting the normalized external
quantum efficiency data, a higher charge-transfer state was measured
for BDTRh–C10–PC61BA, reducing
its voltage loss. A higher power conversion efficiency of ∼2%
was obtained for BDTRh–C10–PC61BA, showing higher open-circuit voltage, short-circuit current density,
and fill factor than those of BDTRh–C2–PC61BA devices. The different carrier dynamics, voltage loss,
and optical and photoelectrical characteristics depending on the spacer
length were interpreted in terms of the film morphology. The longer
decyl spacer in BDTRh–C10–PC61BA afforded a significantly enhanced intermolecular ordering of the
p-type core compared to BDTRh–C2–PC61BA, suggesting that the alkyl spacer length plays a critical role
in controlling the intermolecular packing interaction.
A new benzodithiophene (BDT) building block, 4,8-bis(5-(2-ethylhexyl)-3-fluoro-4-hexylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (3-FBDT), was designed by tailoring the positions and numbers of alkyl and F substituents by adjusting the torsional energy barrier. The incorporation of...
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