Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains |
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| Authors: | Bob C. Schroeder Tadanori Kurosawa Tianren Fu Yu‐Cheng Chiu Jaewan Mun Ging‐Ji Nathan Wang Xiaodan Gu Leo Shaw James W. E. Kneller Theo Kreouzis Michael F. Toney Zhenan Bao |
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| Affiliation: | 1. Department of Chemical Engineering, Stanford University, Stanford, CA, USA;2. Materials Research Institute and School of Biological and Chemical Sciences, Queen Mary University of London, London, UK;3. Department of Advanced Materials Science, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan;4. Department of Chemical Engineering and Materials Science, Yuan Ze University, Taoyuan City, Taiwan;5. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA;6. School of Polymers and High Performance Materials, University of Southern Mississippi, Hattiesburg, MS, USA;7. Materials Research Institute and School of Physics and Astronomy, Queen Mary University of London, London, UK |
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| Abstract: | The solid‐state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high‐performing diketopyrrolopyrrole‐based polymers. By synthesizing a series of DPP‐based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face‐on/edge‐on orientation, which allows the formation of 3D carrier channels in an otherwise edge‐on‐oriented polymer chain network. Time‐of‐flight measurements performed on the various polymer films support this hypothesis by showing higher out‐of‐plane carrier mobilities for the partially face‐on‐oriented polymers. Additionally, a favorable morphology is mimicked by blending a face‐on polymer into an exclusively edge‐on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices. |
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| Keywords: | alkyl side chains charge transport diketopyrrolopyrrole polymer orientation semiconducting polymers |
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