Enhanced solid-state order and field-effect hole mobility through control of nanoscale polymer aggregation

M.S. Chen, O.P. Lee, J.R. Niskala, A.T. Yiu, Ch. J. Tassone, K. Schmidt, P.M. Beaujuge, S.S. Onishi, M.F. Toney, A. Zettl, J.M.J. Fréchet
Journal of the American Chemical Society, 135(51), 19229-19236, (2013)

Enhanced solid-state order and field-effect hole mobility through control of nanoscale polymer aggregation

Keywords

Organic field-effect transistors

Abstract

​Efficient charge carrier transport in organic field-effect transistors (OFETs) often requires thin films that display long-range order and close π–π packing that is oriented in-plane with the substrate. Although some polymers have achieved high field-effect mobility with such solid-state properties, there are currently few general strategies for controlling the orientation of π-stacking within polymer films. In order to probe structural effects on polymer-packing alignment, furan-containing diketopyrrolopyrrole (DPP) polymers with similar optoelectronic properties were synthesized with either linear hexadecyl or branched 2-butyloctyl side chains. Differences in polymer solubility were observed and attributed to variation in side-chain shape and polymer backbone curvature. Averaged field-effect hole mobilities of the polymers range from 0.19 to 1.82 cm2/V·s, where PDPP3F-C16 is the least soluble polymer and provides the highest maximum mobility of 2.25 cm2/V·s. Analysis of the films by AFM and GIXD reveal that less soluble polymers with linear side chains exhibit larger crystalline domains, pack considerably more closely, and align with a greater preference for in-plane π–π packing. Characterization of the polymer solutions prior to spin-coating shows a correlation between early onset nanoscale aggregation and the formation of films with highly oriented in-plane π-stacking. This effect is further observed when nonsolvent is added to PDPP3F-BO solutions to induce aggregation, which results in films with increased nanostructural order, in-plane π–π orientation, and field-effect hole mobilities. Since nearly all π-conjugated materials may be coaxed to aggregate, this strategy for enhancing solid-state properties and OFET performance has applicability to a wide variety of organic electronic materials.

Code

DOI: 10.1021/ja4088665

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