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Polymers 2018, 10(8), 815;

Understanding the Intrinsic Carrier Transport in Highly Oriented Poly(3-hexylthiophene): Effect of Side Chain Regioregularity

State Key Laboratory of High Performance Ceramics and Superfine Microstructure and CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore
University of Chinese Academy of Sciences, Beijing 100049, China
Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA
Shanghai Institute of Materials Genome, Shanghai 200050, China
Authors to whom correspondence should be addressed.
Received: 1 July 2018 / Revised: 14 July 2018 / Accepted: 18 July 2018 / Published: 25 July 2018
(This article belongs to the Special Issue Polymers for Thermoelectric Application)
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The fundamental understanding of the influence of molecular structure on the carrier transport properties in the field of organic thermoelectrics (OTEs) is a big challenge since the carrier transport behavior in conducting polymers reveals average properties contributed from all carrier transport channels, including those through intra-chain, inter-chain, inter-grain, and hopping between disordered localized sites. Here, combining molecular dynamics simulations and experiments, we investigated the carrier transport properties of doped highly oriented poly(3-hexylthiophene) (P3HT) films with different side-chain regioregularity. It is demonstrated that the substitution of side chains can not only take effect on the carrier transport edge, but also on the dimensionality of the transport paths and as a result, on the carrier mobility. Conductive atomic force microscopy (C-AFM) study as well as temperature-dependent measurements of the electrical conductivity clearly showed ordered local current paths in the regular side chain P3HT films, while random paths prevailed in the irregular sample. Regular side chain substitution can be activated more easily and favors one-dimensional transport along the backbone chain direction, while the irregular sample presents the three-dimensional electron hopping behavior. As a consequence, the regular side chain P3HT samples demonstrated high carrier mobility of 2.9 ± 0.3 cm2/V·s, which is more than one order of magnitude higher than that in irregular side chain P3HT films, resulting in a maximum thermoelectric (TE) power factor of 39.1 ± 2.5 μW/mK2 at room temperature. These findings would formulate design rules for organic semiconductors based on these complex systems, and especially assist in the design of high performance OTE polymers. View Full-Text
Keywords: organic thermoelectric; poly(3-hexylthiophene); regioregularity; carrier transport organic thermoelectric; poly(3-hexylthiophene); regioregularity; carrier transport

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Qu, S.; Ming, C.; Yao, Q.; Lu, W.; Zeng, K.; Shi, W.; Shi, X.; Uher, C.; Chen, L. Understanding the Intrinsic Carrier Transport in Highly Oriented Poly(3-hexylthiophene): Effect of Side Chain Regioregularity. Polymers 2018, 10, 815.

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