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Control of aggregate formation in poly(3-hexylthiophene) by solvent, molecular weight, and synthetic method

  • Aggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5%) that can be obtained, even for poor solvent quality. We showAggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5%) that can be obtained, even for poor solvent quality. We show that inducing aggregation in solution leads to control of aggregate properties in thin films. As expected, the field-effect mobility correlates with the propensity to aggregation. Correspondingly, we find that a well-defined synthetic approach, tailored to give a narrow molecular weight distribution, is needed to obtain high field effect mobilities of up to 0.01 cm2/Vs for low molecular weight samples (=11 kDa), while the influence of synthetic method is negligible for samples of higher molecular weight, if low molecular weight fractions are removed by extraction.show moreshow less

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Metadaten
Author:Christina Scharsich, Ruth H. Lohwasser, Michael Sommer, Udom Asawapirom, Ullrich Scherf, Mukundan Thelakkat, Dieter NeherORCiDGND, Anna Koehler
DOI:https://doi.org/10.1002/polb.23022
ISSN:0887-6266 (print)
Parent Title (English):Journal of polymer science : B, Polymer physics
Publisher:Wiley-Blackwell
Place of publication:Hoboken
Document Type:Article
Language:English
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Tag:UV-vis spectroscopy; conformational analysis; conjugated polymers; crystallization; films; interaction parameter; molar mass distribution; molecular weight distribution; nucleation; photophysics; structure
Volume:50
Issue:6
Pagenumber:12
First Page:442
Last Page:453
Funder:Deutsche Forschungsgemeinschaft [Graduiertenkolleg 1640, SPP 1635]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer Review:Referiert