2 research outputs found
Unique Reversible Crystal-to-Crystal Phase Transitionî—¸Structural and Functional Properties of Fused Ladder Thienoarenes
Donor–acceptor
type molecules based on fused ladder thienoarenes,
indacenodithiophene (IDT), and dithienocyclopenta–thienothiophene
(DTCTT), coupled with benzothiadiazole, are prepared, and their solid-state
structures are investigated. They display a rich variety of solid
phases ranging from amorphous glass states to crystalline states,
upon changes in the central aromatic core and side group structures.
Most notably, the DTCTT-based derivatives showed reversible crystal-to-crystal
phase transitions in heating and cooling cycles. Unlike what has been
seen in π-conjugated molecules, variable temperature XRD revealed
that structural change occurs continuously during the transition.
A columnar self-assembled structure with slip-stacked π–π
interaction is proposed to be involved in the solid state. This research
provides the evidence of unique structural behavior of the DTCTT-based
molecules through the detailed structural analysis. This unique structural
transition paves the way for these materials to have self-healing
of crystal defects, leading to improved optoelectronic properties
Mixing Behavior in Small Molecule:Fullerene Organic Photovoltaics
We
report a novel method to determine the amount of pure, aggregated
phase of donor and acceptor in organic photovoltaic (OPV) bulk heterojunctions.
By determination of the diffraction intensity per unit volume for
both donor and acceptor, the volume content of pure, aggregated donor
and acceptor in the blend can be determined. We find that for the
small molecule X2:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)
system, in contrast to most polymer systems, all the PCBM is aggregated,
indicating there is negligible miscibility of PCBM with X2. This provides
an explanation why the performance of OPV devices of X2:PCBM are high
over a large range of PCBM concentrations. This is in contrast to
many other OPV blends, where PCBM forms a mixed phase with the donor
and does not provide sufficient transport for electrons when the PCBM
concentration is low. This study demonstrates that a mixed phase is
not necessarily a requirement for good OPV device performance