20 February 2012 A photo-aligned self-assembled monolayer for polymer transistors
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Abstract
There is a continuing interest in improving electrical characteristics of an organic thin-film transistor (OTFT). One can accomplish this by controlling molecular orientations of semiconductor materials in the vicinities of an insulating layer as well as an electrode material. First, it is widely known that a self-assembled monolayer (SAM) is effective for this purpose. Second, a thin structured layer underneath an organic semiconductor material is effective for aligning the organic molecules in a specific direction. Irradiating azobenzene compounds with ultraviolet light converts trans isomers into cis-forms. When exposed to linearly-polarized ultraviolet light, the difference in the absorbance between the two isomers leads to a state where the azobenzene molecules are aligned perpendicular to the polarization direction of the ultraviolet light. Such a photo-alignment layer results in anisotropic charge transport in an OTFT and the current flow along the channel direction is enhanced. In principle, we expect that combination of these two technologies (SAM and photo-alignment) would further improve the current flow in OTFTs. In experiment, we synthesized a compound 4-(3- (trichlorosilyl)propoxy)azobenzene (Azo-SAM) and used this material to align an organic semiconductor poly(3- hexylthiophene) (P3HT). We formed the Azo-SAM on a glass substrate, spin-coated a P3HT/1, 2, 4-trichlorobenzene solution, annealed in nitrogen atmosphere and exposed it to linearly-polarized ultraviolet light. Absorbance spectroscopy in the visible range revealed anisotropy in the two samples exposed to the two polarization directions orthogonal to each other. Fabrication of organic transistors with this photo-alignment SAM is under way.
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Tatsuhiko Kawaguchi, Takehiro Okura, Yuusuke Suenaga, Tomonori Hanasaki, Ichiro Fujieda, "A photo-aligned self-assembled monolayer for polymer transistors", Proc. SPIE 8258, Organic Photonic Materials and Devices XIV, 825819 (20 February 2012); doi: 10.1117/12.906559; https://doi.org/10.1117/12.906559
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