Polymers
with an abundant amorphous domain should facilitate energy
dissipation upon stretching, making near amorphous π-conjugated
polymers have immense potential in realizing intrinsically stretchable
field-effect transistor (FET) devices. In this study, high mobility
preservation under the stretched state is attempted by replacing typical
alkyl-monothienyl (T-R) on a benzo[1,2-b:4,5-b’]dithiophene-difluorobenzothiadiazole
backbone with three other biaxially extended side-chains, including
alkyl-dithienyl (2T-R), branching alkyl-trithienyl (3T-R), and alkyl-benzotrithienyl
(B3T-R) groups. Despite showing near amorphous features, the semi-2D
BDT-based polymers with bulkier biaxially extended side chains (PBDT-2T,
PBDT-3T, and PBDT-B3T) still present comparable mobility to the reference
semicrystalline polymer (PBDT-T). Although these four polymers yield
comparable mobility, they show distinctly different mobility retention
in the stretched state. From the study of their mobility-stretchability
relationship, the interdigitating and/or entanglement of these biaxially
extended conjugated side chains are shown to play a nontrivial role
in the resultant mechanical robustness against the stretching force.
Owing to the proper spatial mobility and geometry, the branched 3T-R
side chain possesses a more intense interdigitating and/or entanglement
capability than the linear 2T-R one and the fused B3T-R one, providing
better mechanical strength under stretched states. Meanwhile, it maintains
sufficient interchain connectivity for intermittent interchain hopping
to compensate for the 1D charge transport along the backbone, ensuring
good charge transport even in the stretched state. As a result, the
printed PBDT-3T film is demonstrated to deliver a high mobility retention
of 73% at a 60% strain exerted parallel to the charge-transporting
direction and a very stable mobility retention of 88% after 1000 stretching-releasing
cycles at a 60% strain, being one of the best stretchable near amorphous
conjugated polymers reported thus far. Our result underlines the effectiveness
of using biaxially extended conjugated side chains to realize high-performance
stretchable polymers.
Intrinsically stretchable isoindigo–bithiophene conjugated copolymers for organic field-effect transistors with high carrier mobility were achieved using hydrogen-bonded poly(acrylate amide) side chains.
To
date, few studies of the mobility–stretchability properties
of N-type semiconductors, including naphthalenediimide (NDI)-based
polymers, have been conducted, and the preparation of intrinsically
stretchable N-type semiconducting polymers is very important in the
construction of stretchable electronics. In this study, three NDI-based
random terpolymers are synthesized by introducing functionalized conjugation
break spacers (CBSs) with ester, sulfone, and amide groups. N-type
semiconducting polymers with ester and amide-based CBSs undergo conformational
reorganization during stretching, as evidenced by the progressive
evolution of mixed edge-on and face-on orientations, as well as the
increased UV–vis dichroic ratio. This phenomenon is attributed
to the improved chain conformability and ductility from the randomized
distribution of the CBSs along the polymer backbone with more planar
CBSs. Therefore, polymers with ester-based CBSs achieve superior orthogonal
electron mobility (μe) >0.005 cm2 V–1 s–1 and an average μe retention of 61% after 400 cyclic stretching at 60% strain.
To the best of our knowledge, this study is the first to decipher
the mobility–stretchability properties of N-type semiconducting
polymers that warrant further investigation for constructing intrinsically
stretchable and wearable electronics.
Conjugated
polymers synthesized through random terpolymerization
have recently attracted great research interest due to the synergetic
effect on the polymer’s crystallinity and semiconducting properties.
Several studies have demonstrated the efficacy of random terpolymerization
in fine-tuning the aggregation behavior and optoelectronic property
of conjugated polymers to yield enhanced device performance. However,
as an influential approach of backbone engineering, its efficacy in
modulating the mobility–stretchability property of high-performance
conjugated polymers has not been fuller explored to date. Herein,
a series of random terpolymers based on the diketopyrrolopyrrole-bithiophene
(DPP-2T) backbone incorporating different amounts of isoindigo (IID)
unit are synthesized, and their structure–mobility–stretchability
correlation is thoroughly investigated. Our results reveal that random
terpolymers containing a low IID content (DPP95 and DPP90) show enhanced
interchain packing and solid-state aggregation to result in improved
charge-transporting performance (can reach 4 order higher) compared
to the parent polymer DPP100. In addition, owing to the enriched amorphous
feature, DPP95 and DPP90 deliver an improved orthogonal mobility (μh) of >0.01 cm2 V–1 s–1 under a 100% strain, higher than the value (∼0.002 cm2 V–1 s–1) of DPP100. Moreover,
DPP95 even yields 20% enhanced orthogonal μh retention
after 800 stretching–releasing cycles with 60% strain. As concluded
from a series of analyses, the improved mobility–stretchability
property exerted by random terpolymerization arises from the enriched
amorphous feature and enhanced aggregation behavior imposed by the
geometry mismatch between different acceptors (DPP and IID). This
study demonstrates that backbone engineering through rational random
terpolymerization not only enhances the mobility–stretchability
of a conjugated polymer but also realizes a better mechanical endurance,
providing a new perspective for the design of high-performance stretchable
conjugated polymers.
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