posted on 2022-01-10, 19:04authored byJames F. Ponder, Shawn A. Gregory, Amalie Atassi, Akanksha K. Menon, Augustus W. Lang, Lisa R. Savagian, John R. Reynolds, Shannon K. Yee
The
processability and electronic properties of conjugated polymers
(CPs) have become increasingly important due to the potential of these
materials in redox and solid-state devices for a broad range of applications.
To solubilize CPs, side chains are needed, but such side chains reduce
the relative fraction of electroactive material in the film, potentially
obstructing π–π intermolecular interactions, localizing
charge carriers, and compromising desirable optoelectronic properties.
To reduce the deleterious effects of side chains, we demonstrate that
post-processing side chain removal, exemplified here via ester hydrolysis,
significantly increases the electrical conductivity of chemically
doped CP films. Beginning with a model system consisting of an ester
functionalized ProDOT copolymerized with a dimethylProDOT, we used
a variety of methods to assess the changes in polymer film volume
and morphology upon hydrolysis and resulting active material densification.
Via a combination of electrochemistry, X-ray photoelectron spectroscopy,
and charge transport models, we demonstrate that this increase in
electrical conductivity is not due to an increase in degree of doping
but an increase in charge carrier density and reduction in carrier
localization that occurs due to side chain removal. With this improved
understanding of side chain hydrolysis, we then apply this method
to high-performance ProDOT-alt-EDOTx copolymers. After hydrolysis, these ProDOT-alt-EDOTx copolymers yield exceptional electrical
conductivities (∼700 S/cm), outperforming all previously reported
oligoether-/glycol-based CP systems. Ultimately, this methodology
advances the ability to solution process highly electrically conductive
CP films.