Molecular orientation dependence of hole-injection barrier in pentacene thin film on the Au surface in organic thin film transistor

We have investigated the effects of a buffer layer insertion on the performance of the pentacene based thin film transistor with a bottom contact structure. When the pentacene molecules have a standing up coordination on the Au surface that is modified by the benzenethiol or methanethiol, the transition region in the pentacene thin film is removed along the boundary between the Au and silicon oxide region, and the hole-injection barrier decreases by 0.4 eV. Pentacene on various surfaces showed that the highly occupied molecular level is 0.2-0.4 eV lower in the standing up coordination than in the lying down coordination.