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A general relationship between disorder, aggregation and charge transport in conjugated polymers

Abstract

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

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Figure 1: Microstructure of conjugated polymer films.
Figure 2: Photo-physical characterization of pre-aggregated P3HT fibril:amorphous-blend films.
Figure 3: Modelling of the electronic effects of energetic and structural disorder.
Figure 4: Chain length effects on paracrystallinity and charge transport.
Figure 5: Activation energy for transport in semiconducting polymers.

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Acknowledgements

We thank G. Rumbles for his comments in the preparation of this manuscript. We gratefully thank A. Facchetti and Z. Chen (Polyera, Skokie, IL), and I. McCulloch and M. Heeney (Imperial College, London) for supplying materials (P[NDI2OD-T2], P3HT, and PBTTT). This work is supported by the Center for Advanced Molecular Photovoltaics Award No. KUS-C1-015-21 made by King Abdullah University of Science and Technology (KAUST) (R.N., J.R., K.V., A.S.), and NSF (J.R., A.S.). N.S. acknowledges support by a European Research Council (ERC) Starting Independent Researcher Fellowship under the grant agreement No. 279587. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences.

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A.S., J.R. and R.N. conceived the research. J.R., R.N., K.V. and F.P.V.K. prepared samples for optoelectronic and structural measurements. J.R. and R.N. carried out the XRD experiments and analysed the data. R.N. and K.V. performed the electrical and optical measurements. R.N. performed the simulations. M.F.T., P.S. and N.S. assisted with data interpretation. R.N., J.R. and A.S. wrote the manuscript and all authors participated in manuscript preparation and editing.

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Correspondence to Alberto Salleo.

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Noriega, R., Rivnay, J., Vandewal, K. et al. A general relationship between disorder, aggregation and charge transport in conjugated polymers. Nature Mater 12, 1038–1044 (2013). https://doi.org/10.1038/nmat3722

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