1 research outputs found
Control of Polymer-Packing Orientation in Thin Films through Synthetic Tailoring of Backbone Coplanarity
Controlling solid-state order of
π-conjugated polymers through
macromolecular design is essential for achieving high electronic device
performance; yet, it remains a challenge, especially with respect
to polymer-packing orientation. Our work investigates the influence
of backbone coplanarity on a polymer’s preference to pack face-on
or edge-on relative to the substrate. Isoindigo-based polymers were
synthesized with increasing planarity by systematically substituting
thiophenes for phenyl rings in the acceptor comonomer. This increasing
backbone coplanarity, supported by density functional theory (DFT)
calculations of representative trimers, leads to the narrowing of
polymer band gaps as characterized by ultraviolet-visible-near infrared
(UV-vis-NIR) spectroscopy and cyclic voltammetry. Among the polymers
studied, regiosymmetric II and TII polymers exhibited the highest
hole mobilities in organic field-effect transistors (OFETs), while
in organic photovoltaics (OPVs), TBII polymers that display intermediate
levels of planarity provided the highest power conversion efficiencies.
Upon thin-film analysis by atomic force microscropy (AFM) and grazing-incidence
X-ray diffraction (GIXD), we discovered that polymer-packing orientation
could be controlled by tuning polymer planarity and solubility. Highly
soluble, planar polymers favor face-on orientation in thin films while
the less soluble, nonplanar polymers favor an edge-on orientation.
This study advances our fundamental understanding of how polymer structure
influences nanostructural order and reveals a new synthetic strategy
for the design of semiconducting materials with rationally engineered
solid-state properties