Controlled orientation of liquid-crystalline polythiophene semiconductors for high-performance organic thin-film transistors

The silane self-assembled monolayer (SAM) modification of a $\mathrm{Si}{\mathrm{O}}_2$ gate dielectric surface improved the molecular ordering of organic channel semiconductor in organic thin-film transistors (OTFTs), leading to a significant improvement in transistor performance. Mobility of up to $0.18{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ (current on∕off ratio of ${10}^7$ ) was obtained for OTFTs with a liquid-crystalline polythiophene semiconductor built on an octyltrichlorosilane-modified $\mathrm{Si}{\mathrm{O}}_2$ gate dielectric layer, a 450 times improvement over those built on a nonmodified dielectric layer. The mobility enhancement was attributed to the edge-on orientation of the polythiophene molecules induced by the silane SAM layer as deduced from the crystal domain structures in the atomic force microscopic images.