Mechanism of Crystallization and Implications for Charge Transport in Poly(3-ethylhexylthiophene) Thin Films

Duc T. Duong, Victor Ho, Zhengrong Shang, Sonya Mollinger, Stefan C.B. Mannsfeld, Javier Dacuña, Michael F. Toney, Rachel Segalman, Alberto Salleo

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Abstract

In this work, crystallization kinetics and aggregate growth of poly(3-ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X-ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time-dependent, field-effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2-3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter-aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics. Recrystallization kinetics and its relationship to charge transport in poly(3-ethylhexylthiophene) (P3EHT) thin films are investigated using a combination of grazing incidence X-ray diffraction, optical absorption, and field-effect transistor measurements. These results show that thin film crystallization kinetics is limited by polymer chain reorganization and that charge percolation depends strongly on the edge-to-edge distance between aggregates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Original languageEnglish (US)
Pages (from-to)4515-4521
Number of pages7
JournalAdvanced Functional Materials
Volume24
Issue number28
DOIs
StatePublished - Apr 9 2014
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-015-21
Acknowledgements: A.S. gratefully acknowledges financial support from the National Science Foundation (DMR 1205752 award). D.T.D. is supported by a Stanford Graduate Fellowship and the National Science Foundation Graduate Research Fellowship. S. M. is supported by a Stanford Graduate Fellowship. J.D. was supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST). A portion of this research was carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

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