TY - JOUR
T1 - Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing
AU - Shaw, Leo
AU - Hayoz, Pascal
AU - Diao, Ying
AU - Reinspach, Julia Antonia
AU - To, John W.F.
AU - Toney, Michael F.
AU - Weitz, R. Thomas
AU - Bao, Zhenan
N1 - Funding Information:
L.S. gratefully acknowledges support from the Kodak Graduate Fellowship. The authors would also like to acknowledge support from the National Science Foundation (DMR-1303178) and BASF. M.T. and Z.B. acknowledge support from the National Science Foundation Materials Genome Program (Grant No. 1434799). Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. J.R. acknowledges support from the Swedish Knut and Alice Wallenberg Foundation.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/4/27
Y1 - 2016/4/27
N2 - The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used to tune polymer alignment in a one-step deposition process not requiring substrate patterning or any postdeposition treatment.
AB - The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used to tune polymer alignment in a one-step deposition process not requiring substrate patterning or any postdeposition treatment.
KW - donor-acceptor copolymers
KW - field-effect transistors
KW - organic semiconductors
KW - polymer alignment
KW - polymer semiconductors
KW - solution processing
KW - solution shearing
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U2 - 10.1021/acsami.6b01607
DO - 10.1021/acsami.6b01607
M3 - Article
AN - SCOPUS:84964901506
SN - 1944-8244
VL - 8
SP - 9285
EP - 9296
JO - ACS applied materials & interfaces
JF - ACS applied materials & interfaces
IS - 14
ER -