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

The silane self-assembled monolayer (SAM) modification of a SiO2 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 0.18cm2∕Vs (current on∕off ratio of 107) was obtained for OTFTs with a liquid-crystalline polythiophene semiconductor built on an octyltrichlorosilane-modified SiO2 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.