Entanglement of conjugated polymer chains influences molecular self-assembly and carrier transport
KAUST DepartmentKAUST Solar Center (KSC)
Material Science and Engineering Program
Office of the VP
Organic Electronics and Photovoltaics Group
Physical Science and Engineering (PSE) Division
Online Publication Date2013-06-26
Print Publication Date2013-12-23
Permanent link to this recordhttp://hdl.handle.net/10754/562825
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AbstractThe influence of polymer entanglement on the self-assembly, molecular packing structure, and microstructure of low-Mw (lightly entangled) and high-Mw (highly entangled) poly (3-hexylthiophene) (P3HT), and the carrier transport in thin-film transistors, are investigated. The polymer chains are gradually disentangled in a marginal solvent via ultrasonication of the polymer solution, and demonstrate improved diffusivity of precursor species (coils, aggregates, and microcrystallites), enhanced nucleation and crystallization of P3HT in solution, and self-assembly of well-ordered and highly textured fibrils at the solid-liquid interface. In low-Mw P3HT, reducing chain entanglement enhances interchain and intrachain ordering, but reduces the interconnectivity of ordered domains (tie molecules) due to the presence of short chains, thus deteriorating carrier transport even in the face of improving crystallinity. Reducing chain entanglement in high-Mw P3HT solutions increases carrier mobility up to ≈20-fold, by enhancing interchain and intrachain ordering while maintaining a sufficiently large number of tie molecules between ordered domains. These results indicate that charge carrier mobility is strongly governed by the balancing of intrachain and interchain ordering, on the one hand, and interconnectivity of ordered domains, on the other hand. In high-Mw P3HT, intrachain and interchain ordering appear to be the key bottlenecks to charge transport, whereas in low-Mw P3HT, the limited interconnectivity of the ordered domains acts as the primary bottleneck to charge transport. Conjugated polymer chains of poly(3-hexylthiophene) (P3HT) are gradually disentangled in solution and trends in carrier transport mechanisms in organic thin film transistors for low- and high-molecular weight P3HT are investigated. While intrachain and interchain ordering within ordered domains are the key bottlenecks to charge transport in high-Mw P3HT films, the limited interconnectivity of ordered domains acts as the primary bottleneck to carrier transport in low-Mw P3HT films. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
SponsorsThe authors would like to thank Dr. Detlef-M. Smilgies for help with acquisition of GIWAXS data at CHESS, Prof. Yu Han for help with acquisition of UV-Vis spectra at KAUST, and Dr. Misjudeen Raji for help with GPC experiments at KAUST. The authors acknowledge Prof. Carlos Silva, Dr. Natalie Stingelin, Prof. Alberto Salleo, and Dr. Neil Treat for helpful discussions. Part of this work was supported by KAUST's Office of Competitive Research Funds under FIC and AEA awards.
JournalAdvanced Functional Materials