Designer Conjugation-Break Spacer That Boosts Charge Transport in Semiconducting Terpolymers

Conjugated polymers (CPs) are pivotal
for high-mobility
applications,
typically avoiding nonconjugated units due to their perceived negative
impact on charge transport. Contrary to this belief, our study introduces
a nonconjugated unit, DKPDO, which when employed as a conjugation-break
spacer (CBS), significantly enhances charge transport. DKPDO was obtained
as a center-modified isoindigo variant featuring strongly electron-withdrawing
amide groups that diminish the electron density and foster multiple
hydrogen-bonding interactions. This results in enhanced electron deficiency
and reinforced coplanarity relative to isoindigo. DKPDO was incorporated
into a polymer backbone, comprising isoindigo and bithiophene, to
create a series of terpolymers with varied molar ratios, allowing
systematic evaluation of their solubilities, interchain interactions,
crystallinities, and energy levels. Notably, incorporating DKPDO into
the terpolymers results in a universal improvement of hole mobilities
and operational stabilities over the DKPDO-free counterpart. Remarkably,
the terpolymer containing 2.5% DKPDO achieves a high hole mobility
of 4.12 cm2 V–1 s–1, approximately 6-fold higher than that of the parent CP and among
the highest for CPs based on center-inserted isoindigo units. The
study not only, for the first time, realizes charge transport enhancement
with CBS in polymer backbones but also sets a precedent for the strategic
use of nonconjugated units in developing high-performing CPs.