Ambipolar organic thin-film transistors using C₆₀ /pentacene structure: Characterization of electronic structure and device property

We fabricated ambipolar organic thin-film transistors (OTFTs) using C60 and pentacene. The electronic structure of the interface was investigated by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitude of the interface dipole and the band bendings at the interface was determined, and the complete energy level diagram for C60 on pentacene (C60 /pentacene) was obtained. The lowered band offsets, due to the enhanced charge redistribution in C60 /pentacene relative to pentacene on C60, are favorable for the ambipolar OTFTs. The measured field-effect mobilities were 0.017 cm2 V s and 0.007 cm2 V s for the p -channel and the n -channel operations, respectively. The threshold voltages were -2 V for the p channel and 15.6 V for the n channel, comparable to those of unipolar OTFTs using C60 or pentacene.