Letter pubs.acs.org/NanoLett
General Strategy for Self-Assembly of Highly Oriented Nanocrystalline Semiconducting Polymers with High Mobility Chan Luo,*,†,‡ Aung Ko Ko Kyaw,† Louis A. Perez,§ Shrayesh Patel,§ Ming Wang,†,‡ Bruno Grimm,† Guillermo C. Bazan,†,‡ Edward J. Kramer,‡,§ and Alan J. Heeger*,†,‡ †
Center for Polymers and Organic Solids, ‡Mitsubishi Chemical Centre for Advanced Materials, and §Department of Materials, University of California Santa Barbara, Santa Barbara, California 93106, United States S Supporting Information *
ABSTRACT: Solution processable semiconducting polymers with excellent film forming capacity and mechanical flexibility are considered among the most progressive alternatives to conventional inorganic semiconductors. However, the random packing of polymer chains and the disorder of the polymer matrix typically result in low charge transport mobilities (10−5−10−2 cm2 V−1 s−1). These low mobilities compromise their performance and development. Here, we present a strategy, by utilizing capillary action, to mediate polymer chain self-assembly and unidirectional alignment on nanogrooved substrates. We designed a sandwich tunnel system separated by functionalized glass spacers to induce capillary action for controlling the polymer nanostructure, crystallinity, and charge transport. Using capillary action, we demonstrate saturation mobilities with average values of 21.3 and 18.5 cm2 V−1 s−1 on two different semiconducting polymers at a transistor channel length of 80 μm. These values are limited by the source-drain contact resistance, Rc. Using a longer channel length of 140 μm where the contact resistance is less important, we measured μh = 36.3 cm2 v−1 s−1. Extrapolating to infinite channel length where Rc is unimportant, the intrinsic mobility for poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (Mn = 140 kDa) at this degree of chain alignment and structural order is μh ≈ 47 cm2 v−1 s−1. Our results create a promising pathway toward high performance, solution processable, and low-cost organic electronics. KEYWORDS: Self-assembly, nanocrystalline, unidirectional alignment, semiconducting polymers, high charge mobility
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coating,15 strain stretching,16 Langmuir−Blodgett deposition,17 or topographical patterning.18 Although these processing methods have demonstrated progress toward molecular assembly and chain alignment, the measured TFT mobilities have remained insufficient for most applications (typically
