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Crystals 2019, 9(3), 144; https://doi.org/10.3390/cryst9030144

Study on Correlation between Structural and Electronic Properties of Fluorinated Oligothiophenes Transistors by Controlling Film Thickness

1
Department of Optics and Photonics, National Central University, Zhongli 320, Taiwan
2
National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
3
Department of Chemistry, National Tsing-Hua University, Hsinchu 300, Taiwan
*
Author to whom correspondence should be addressed.
Received: 1 February 2019 / Revised: 5 March 2019 / Accepted: 7 March 2019 / Published: 12 March 2019
(This article belongs to the Special Issue Thin Film Transistor)
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Abstract

α,ω-diperfluorohexylquaterthiophene (DFH-4T) has been an attractive n-type material employed in the development of high-mobility organic field-effect transistors. This paper presents a systematic study of the relationship between DFH-4T transistor performance and film structure properties as controlled by deposited thickness. When the DFH-4T thickness increases from 8 nm to 80 nm, the room-temperature field-effect mobility increases monotonically from 0.01 to 1 cm2·V−1·s−1, while the threshold voltage shows a different trend of first decrease then increase. The morphology of thin films revealed by atomic force microscopy shows a dramatic change from multilayered terrace to stacked rod like structures as the film thickness is increased. Yet the crystallite structure and the orientation of molecular constituent, as determined by X-ray diffraction and near-edge X-ray absorption fine structure respectively, do not differ much with respect to film thickness increase. Further analyses of low-temperature transport measurements with mobility-edge model demonstrate that the electronic states of DFH-4T transistors are mainly determined by the film continuity and crystallinity of the bottom multilayered terrace. Moreover, the capacitance-voltage measurements of DFH-4T metal-insulator-semiconductor diodes demonstrate a morphological dependence of charge injection from top contacts, which well explains the variation of threshold voltage with thickness. The overall study provides a deeper understanding of microstructural and molecular growth of DFH-4T film and clarify the structural effects on charge transport and injection for implementation of high-mobility top-contact transistors. View Full-Text
Keywords: organic film growth; organic transistor; charge transport and injection mechanisms organic film growth; organic transistor; charge transport and injection mechanisms
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Chang, J.-F.; Shie, H.-S.; Yang, Y.-W.; Wang, C.-H. Study on Correlation between Structural and Electronic Properties of Fluorinated Oligothiophenes Transistors by Controlling Film Thickness. Crystals 2019, 9, 144.

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