5 years ago

Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains

Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains
Tianren Fu, James W. E. Kneller, Ging-Ji Nathan Wang, Leo Shaw, Jaewan Mun, Tadanori Kurosawa, Zhenan Bao, Michael F. Toney, Xiaodan Gu, Bob C. Schroeder, Theo Kreouzis, Yu-Cheng Chiu
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. The solid state packing and morphology of semiconducting polymers play a key role in achieving high charge carrier mobilities in field effect transistors. In this work, the creation of 3D transport pathways in organic semiconductors is found to be beneficial for charge transport, and can be artificially engineered by blending polymers with different solid state packing motifs.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adfm.201701973

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