TY - JOUR
T1 - Role of Postdeposition Thermal Annealing on Intracrystallite and Intercrystallite Structuring and Charge Transport in Poly(3-hexylthiophene)
AU - Gu, Kaichen
AU - Wang, Yucheng
AU - Li, Ruipeng
AU - Tsai, Esther
AU - Onorato, Jonathan W.
AU - Luscombe, Christine K.
AU - Priestley, Rodney D.
AU - Loo, Yueh Lin
N1 - Funding Information:
This work was supported by ExxonMobil through its membership in the Princeton E-filliates Partnership of the Andlinger Center for Energy and the Environment. K.G. and Y.-L.L. acknowledge support from the National Science Foundation (NSF) through grant CMMI-1824674. Y.W. and R.D.P. acknowledge support from the NSF Materials Research Science and Engineering Center Program through the Princeton Center for Complex Materials (DMR-1420541). C.K.L. acknowledges NSF DMR-1708317. The P3HT samples were synthesized in part upon work supported by the State of Washington through the University of Washington Clean Energy Institute and via funding from the Washington Research Foundation. X-ray scattering measurements were conducted at the Center for Functional Nanomaterials (CFN) and the Complex Materials Scattering (CMS) beamline of the National Synchrotron Light Source II (NSLS-II), both of which are U.S. DOE Office of Science Facilities, at Brookhaven National Laboratory, under Contract No. DE-SC0012704.
Publisher Copyright:
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PY - 2021/1/13
Y1 - 2021/1/13
N2 - The performance of electronic devices comprising conjugated polymers as the active layer depends not only on the intrinsic characteristics of the materials but also on the details of the extrinsic processing conditions. In this study, we examine the effect of postdeposition thermal treatments on the microstructure of poly(3-hexylthiophene) (P3HT) thin films and its impact on their electrical properties. Unsurprisingly, we find thermal annealing of P3HT thin films to generally increase their crystallinity and crystallite coherence length while retaining the same crystal structure. Despite such favorable structural improvements of the polymer active layers, however, thermal annealing at high temperatures can lead to a net reduction in the mobility of transistors, implicating structural changes in the intercrystallite amorphous regions of these semicrystalline active layers take place on annealing, and the simplistic picture that crystallinity governs charge transport is not always valid. Our results instead suggest tie-chain pullout, which occurs during crystal growth and perfection upon thermal annealing to govern charge transport, particularly in low-molecular-weight systems in which the tie-chain fraction is low. By demonstrating the interplay between intracrystallite and intercrystallite structuring in determining the macroscopic charge transport, we shed light on how structural evolution and charge-transport properties of nominally the same polymer can vary depending on the details of processing.
AB - The performance of electronic devices comprising conjugated polymers as the active layer depends not only on the intrinsic characteristics of the materials but also on the details of the extrinsic processing conditions. In this study, we examine the effect of postdeposition thermal treatments on the microstructure of poly(3-hexylthiophene) (P3HT) thin films and its impact on their electrical properties. Unsurprisingly, we find thermal annealing of P3HT thin films to generally increase their crystallinity and crystallite coherence length while retaining the same crystal structure. Despite such favorable structural improvements of the polymer active layers, however, thermal annealing at high temperatures can lead to a net reduction in the mobility of transistors, implicating structural changes in the intercrystallite amorphous regions of these semicrystalline active layers take place on annealing, and the simplistic picture that crystallinity governs charge transport is not always valid. Our results instead suggest tie-chain pullout, which occurs during crystal growth and perfection upon thermal annealing to govern charge transport, particularly in low-molecular-weight systems in which the tie-chain fraction is low. By demonstrating the interplay between intracrystallite and intercrystallite structuring in determining the macroscopic charge transport, we shed light on how structural evolution and charge-transport properties of nominally the same polymer can vary depending on the details of processing.
KW - charge transport
KW - conjugated polymers
KW - field-effect transistors
KW - organic electronics
KW - polymer tie chains
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U2 - 10.1021/acsami.0c16676
DO - 10.1021/acsami.0c16676
M3 - Article
C2 - 33372509
AN - SCOPUS:85099085511
SN - 1944-8244
VL - 13
SP - 999
EP - 1007
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 1
ER -