Understanding the microstructures
of semiconducting polymers is
critical for improving the charge transport properties of polymer
field-effect transistors (PFETs). A series of diketopyrrolopyrrole-based
copolymers designed by implementing the concept of intramolecular
noncovalent conformational locks through the functionalization of
polymer backbones with fluorine atoms or methoxy groups were synthesized
and compared with their unfunctionalized analogue. In contrast to
the bimodal texture of the unfunctionalized polymer, the thin films
of the polymer with fluorine atoms exhibit predominantly edge-on texture
with much improved crystalline ordering. The thin films of the polymer
modified with methoxy groups have a principally face-on texture. These
dramatic differences in thin-film texture can be correlated with the
polymers’ solubilities. Furthermore, the improved crystalline
ordering of these semiconductor polymers enables the fabrication of
high-performance PFETs: the hole mobility of the methoxy-modified
polymer is reduced by half with respect to that of the unmodified
polymer, whereas the hole mobility values of the fluorine-modified
polymer are up to ∼6 times higher, approximately 1.32 cm2 V–1 s–1, and exhibit
pronounced thermal stability. These results provide new guidelines
for the molecular design of semiconducting polymers with noncovalent
conformational locks.
A new 3D nonfullerene small-molecule acceptor is reported. The 3D interlocking geometry of the small-molecule acceptor enables uniform molecular conformation and strong intermolecular connectivity, facilitating favorable nanoscale phase separation and electron charge transfer. By employing both a novel polymer donor and a nonfullerene small-molecule acceptor in the solution-processed organic solar cells, a high-power conversion efficiency of close to 6% is demonstrated.
One-dimensional low bandgap polymer nanowires successfully incorporated into bulk-heterojunction organic solar cells, yielding a high PCE exceeding 10% with thick films.
A donor-acceptor conjugated copolymer enables the formation of nanowire systems that can be successfully introduced into bulk-heterojunction organic solar cells. A simple binary solvent mixture that makes polarity control possible allows kinetic control over the self-assembly of the crystalline polymer into a nanowire structure during the film-forming process. The enhanced photoconductivity of the nanowire-embedded photoactive layer efficiently facilitates photon harvesting in the solar cells. The resultant maximum power conversion efficiency is 8.2% in a conventional single-cell structure, revealing a 60% higher performance than in devices without nanowires.
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