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n-Type Conjugated Polymers Based on 3,3’-Dicyano-2,2’-Bithiophene: Synthesis and Semiconducting Properties

Abstract

Three new alternating copolymers containing 3,3-dicyano-2,2-bithiophene (BT2CN), i.e., DPPTh-BT2CN, DPPPy-BT2CN and 2FIID-BT2CN based on diketopyrrolopyrrole (DPP) and isoindigo (IID) derivatives, were synthesized. The properties of these three polymers were compared with those of the reference polymer without cyano (CN) group, DPPTh-BT. The introduction of CN groups dramatically lowered both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the polymers. DPPTh-BT2CN exhibited HOMO and LUMO energy levels of -5.41 and -3.67 eV, respectively, which are much lower than those of the analogue polymer DPPTh-BT comprising biothiophene (BT) segment. DPPPy-BT2CN and 2FIID-BT2CN showed even lower HOMO and LUMO levels, which are -5.83 and -3.75 eV for DPPPy-BT2CN and -6.15 and -3.92 eV for 2FIID-BT2CN. Organic thin-film transistors (OTFTs) were fabricated to evaluate the semiconducting properties of the polymers. DPPTh-BT2CN-based OTFTs exhibited electron-dominant transport characteristics, similar to the devices based on the benchmark n-type conjugated polymer N2200. By contrast, DPPPy-BT2CN and 2FIID-BT2CN-based devices displayed pure n-channel characteristics due to their lower HOMO and LUMO levels. All three polymers displayed electron mobility (ue) of ca. 0.3 cm2 V-1 s-1, which is comparable to that of N2200 when the same device structure and measurement conditions were adopted.

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Publication details

The article was received on 27 Jul 2018, accepted on 31 Oct 2018 and first published on 07 Nov 2018


Article type: Paper
DOI: 10.1039/C8TC03725F
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    n-Type Conjugated Polymers Based on 3,3’-Dicyano-2,2’-Bithiophene: Synthesis and Semiconducting Properties

    Y. Geng, Y. Sui, Y. Deng, Y. Han, J. Zhang and W. Hu, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC03725F

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