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Issue 37, 2017
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Dithienylbenzodiimide: a new electron-deficient unit for n-type polymer semiconductors

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Inspired by the excellent device performance of imide-functionalized polymer semiconductors in organic electronics, a novel imide-based building block, dithienylbenzodiimide (TBDI), with fused backbone is designed and synthesized. Single-crystal structure analysis reveals that the TBDI unit features non-planar backbone conformation but with a tight π-stacking distance of 3.36 Å. By copolymerizing with various electron-rich co-units, a series of TBDI-based polymer semiconductors is synthesized and the optoelectronic, thermal, electrochemical and charge transport properties of the semiconductors are characterized. Attributed to the non-planar backbone and intrinsic electrical property of TBDI, all polymers exhibit wide bandgaps (∼2.0 eV) with low-lying HOMOs (<−5.5 eV). Organic thin-film transistors are fabricated by incorporating the TBDI-based polymers as the active layer to investigate their charge transport properties. The dithienylbenzodiimide-bithiophene copolymer shows ambipolar transport characteristics with an electron and hole mobility of 0.15 and 0.015 cm2 V−1 s−1, respectively. By incorporating weaker electron donor co-units, the dithienylbenzodiimide–thiophene and dithienylbenzodiimide–difluorobithiophene copolymers exhibit unipolar n-channel transistor performance with electron mobility up to 0.11 and 0.34 cm2 V−1 s−1, respectively. Most high-performance n-channel polymer semiconductors reported to date typically show narrow bandgaps with high-lying HOMOs, resulting in substantial p-channel performance. The new TBDI-based wide bandgap polymers with low-lying HOMOs greatly suppress p-channel performance and lead to improved Ion/Ioff ratios. The excellent n-channel performance is attributed to the strong electron-withdrawing capability of imide groups, low-lying frontier molecular orbitals, compact π-stacking distance, and a high degree of film crystallinity as confirmed by GIWAXS analysis with distinct interlamellar and π-stacking diffraction patterns. The result reveals that a building block with non-planar backbone can be utilized for constructing high crystalline polymer semiconductors with substantial charge carrier mobility. The study indicates that dithienylbenzodiimide is a promising unit for synthesizing wide bandgap polymeric semiconductors with unipolar n-channel performance.

Graphical abstract: Dithienylbenzodiimide: a new electron-deficient unit for n-type polymer semiconductors

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Publication details

The article was received on 28 Jun 2017, accepted on 18 Jul 2017 and first published on 18 Jul 2017

Article type: Paper
DOI: 10.1039/C7TC02903A
Citation: J. Mater. Chem. C, 2017,5, 9559-9569
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    Dithienylbenzodiimide: a new electron-deficient unit for n-type polymer semiconductors

    J. Chen, X. Zhang, G. Wang, M. A. Uddin, Y. Tang, Y. Wang, Q. Liao, A. Facchetti, T. J. Marks and X. Guo, J. Mater. Chem. C, 2017, 5, 9559
    DOI: 10.1039/C7TC02903A

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