The regioregular highly head-to-tail-coupled poly(3-alkylthiophene) (HT-P3AT) films were prepared by a friction-transfer technique. Polarized UV−vis absorption spectroscopy and grazing incidence X-ray diffraction (GIXD) were used to study the polymer molecular arrangement in the friction-transferred HT-P3AT films, and scanning electron microscopy (SEM) was used to observe the film surface morphology. The polarized UV−vis absorption spectra show a large dichroism regarding the drawing direction of friction-transfer. The order parameter is evaluated close to unity, which is the ideal orientation state. GIXD measurements show that alkyl side chains lie in the film plane, and the polymer backbones are well-ordered along the drawing direction of friction-transfer within 10° for poly(3-hexylthiophene) and 13° for poly(3-dodecylthiophene) in the film plane. The polymer backbones form a layered structure with the stacking of thiophene rings normal to the film surface. The polymer molecules in the friction-transferred films are ideally arranged three-dimensionally.

This review summarizes recent advancements in various orientation techniques for conjugated polymers for use in high performance organic field effect transistors.

A liquid-crystalline polymer, poly(9,9-dioctylfluorene) (PFO), was found to form highly oriented films by a friction-transfer technique. The polarized UV−vis absorption and photoluminescence spectra of the films formed showed strong dichroism with a dichroic ratio of approximately 10 in the drawing direction of friction transfer. Subsequent thermal treatments of the friction-transferred PFO films were specifically effective for the improvement of the physical properties, structure, and morphology of the films. By rapid and slow cooling from the liquid-crystalline melted states of the friction-transferred films, liquid-crystalline and crystalline films were prepared, respectively. Both thermally treated films showed enhanced optical anisotropy with a dichroic ratio of approximately 25 in photoluminescence spectra. The electron diffraction pattern of the crystalline film showed a large number of sharp diffraction spots as seen in a single crystal. The liquid-crystalline polymer was found to form a single-crystal-like thin film by the friction-transfer technique with subsequent thermal treatments.

We report the performance of solution-processed n-type organic thin-film transistors (OTFTs) based on C60 derivatives. Long-chain alkyl-substituted C60, C60-fused N-methylpyrrolidine-meta-C12 phenyl (C60MC12), was used as a semiconducting layer. The C60MC12-thin-film transistor shows high electron mobility of 0.067cm2∕Vs in saturation regime. From the result of x-ray diffraction analysis, the C60MC12 active layer forms highly ordered crystalline film. We found that self-assemble ability of long alkyl chains plays an important role for fabrication of highly ordered crystalline film, leading to achievement of high electron mobility in solution-processed n-type OTFTs.