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Intra‐ and intermolecular ordering greatly impacts the electronic and optoelectronic properties of semiconducting polymers. The interrelationship between ordering of alkyl sidechains and conjugated backbones has yet to be fully detailed, despite much prior effort. Here, the discovery of a highly ordered alkyl sidechain phase in six representative semiconducting polymers, determined from distinct spectroscopic and diffraction signatures, is reported. The sidechain ordering exhibits unusually large coherence lengths (≥70 nm), induces torsional/twisting backbone disorder, and results in a vertically multilayered nanostructure with ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in situ variable temperature scattering measurements in a model system poly{4‐(5‐(4,8‐bis(3‐butylnonyl)‐6‐methylbenzo[1,2‐b:4,5‐b′]dithiophen‐2‐yl)thiophen‐2‐yl)‐2‐(2‐butyloctyl)‐5,6‐difluoro‐7‐(5‐methylthiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole} (PBnDT‐FTAZ) clearly delineate this competition of ordering that prevents simultaneous long‐range order of both moieties. The long‐range sidechain ordering can be exploited as a transient state to fabricate PBnDT‐FTAZ films with an atypical edge‐on texture and 2.5× improved field‐effect transistor mobility. The observed influence of ordering between the moieties implies that improved molecular design can produce synergistic rather than destructive ordering effects. Given the large sidechain coherence lengths observed, such synergistic ordering should greatly improve the coherence length of backbone ordering and thereby improve electronic and optoelectronic properties such as charge transport and exciton diffusion lengths.
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1806977 (1 of 13)
Competition between Exceptionally Long-Range
Alkyl Sidechain Ordering and Backbone Ordering in
Semiconducting Polymers and Its Impact on Electronic
and Optoelectronic Properties
Joshua H. Carpenter, Masoud Ghasemi, Eliot Gann, Indunil Angunawela, Samuel J. Stuard,
Jeromy James Rech, Earl Ritchie, Brendan T. O’Connor, Joanna Atkin, Wei You,
Dean M. DeLongchamp, and Harald Ade*
Intra- and intermolecular ordering greatly impacts the electronic and optoelectronic
properties of semiconducting polymers. The interrelationship between ordering
of alkyl sidechains and conjugated backbones has yet to be fully detailed, despite
much prior effort. Here, the discovery of a highly ordered alkyl sidechain phase
in six representative semiconducting polymers, determined from distinct spec-
troscopic and diffraction signatures, is reported. The sidechain ordering exhibits
unusually large coherence lengths (70 nm), induces torsional/twisting back-
bone disorder, and results in a vertically multilayered nanostructure with ordered
sidechain layers alternating with disordered backbone layers. Calorimetry and in
situ variable temperature scattering measurements in a model system poly{4-(5-
(4,8-bis(3-butylnonyl)-6-methylbenzo[1,2-b:4,5-b]dithiophen-2-yl)thiophen-2-yl)-
2-(2-butyloctyl)-5,6-difluoro-7-(5-methylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole}
(PBnDT-FTAZ) clearly delineate this competition of ordering that prevents simulta-
neous long-range order of both moieties. The long-range sidechain ordering can be
exploited as a transient state to fabricate PBnDT-FTAZ films with an atypical edge-
on texture and 2.5× improved field-effect transistor mobility. The observed influence
of ordering between the moieties implies that improved molecular design can pro-
duce synergistic rather than destructive ordering effects. Given the large sidechain
coherence lengths observed, such synergistic ordering should greatly improve the
coherence length of backbone ordering and thereby improve electronic and opto-
electronic properties such as charge transport and exciton diffusion lengths.
DOI: 10.1002/adfm.201806977
Dr. J. H. Carpenter, Dr. M. Ghasemi, I. Angunawela, S. J. Stuard,
Prof. H. Ade
Department of Physics and Organic and Carbon Electronics
Lab (ORaCEL)
North Carolina State University
Raleigh, NC 27695, USA
E-mail: harald_ade@ncsu.edu
Dr. E. Gann, Dr. D. M. DeLongchamp
Materials Science and Engineering Division
National Institute of Standards and Technology
100 Bureau Drive, Gaithersburg, MD 20899, USA
J. J. Rech, E. Ritchie, Prof. J. Atkin, Prof. W. You
Department of Chemistry
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599-3290, USA
Prof. B. T. O’Connor
Department of Mechanical and Aerospace Engineering and ORaCEL
North Carolina State University
Raleigh, NC 27695, USA
insulating alkyl sidechains, cause complex
and competing phenomena in terms of
material phase behavior,[1,2] morphology
formation,[3–6] and local ordering,[7–12] that
inherently affect material performance.
Results in the literature for SCPs that are
generally more crystalline and have sim-
pler backbone structures, such as poly-
akylthiophenes (PATs), demonstrate that
ordering in the backbone and
π
-stacking
directions are not necessarily strongly cor-
related with ordering in the alkyl stacking
direction or ordering between alkyl side-
chains, especially in materials having
sufficiently high molecular weight.[13,14]
More broadly, it has been shown that
phase separation between backbone and
alkyl sidechain is a rather general trait
among SCPs and that ordering within
the alkyl nanodomains can occur even
when the nanodomains of the more rigid
backbones are amorphous, e.g., in regio-
random PATs.[15,16] Whether sidechains
can readily order independently of the
aromatic backbones and form separate
nanophases when monomer structures
and sidechain attachments are highly
asymmetric, as is often the case for amorphous donor–acceptor
(D–A) copolymers, is currently an open question.
Studies of ordering in SCPs have shown correlations between
backbone ordering and both charge transport and spectroscopic
Organic Electronics
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201806977.
1. Introduction
The two dissimilar constituents of semiconducting polymers
(SCPs), the semiconducting conjugated backbone and
Adv. Funct. Mater. 2019, 29, 1806977
... In the ordered regions, transport may occur through extended electronic states whereas in the disordered regions charges are thought to move by hopping between localized sites 3,4 . The ability of high resolution transmission electron microscopy (HR-TEM) [5][6][7][8][9][10][11] and X-ray scattering methods [12][13][14] to reveal the detailed morphology of semiconducting polymers presents an opportunity to reveal how ordered and disordered regions impact charge transport. The challenge is to model how charge transport occurs between these two regions, which can guide the design of new polymers and processing routes to achieve higher carrier mobilities. ...
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