Rubicene: a molecular fragment of C70 for use in organic field-effect transistors

Abstract

Rubicene, a molecular fragment of C₇₀, is a promising organic semiconductor material that displays excellent electronic characteristics for use in organic field-effect transistors (OFETs). Bottom-gate/bottom-contact polycrystalline thin-film OFETs using rubicene exhibit a saturation hole mobility of 0.20 cm² V⁻¹ s⁻¹ and a current on/off ratio (I_on/I_off) of 1.0 × 10⁴. In addition, the device performance can be improved with a mobility of 0.32 cm² V⁻¹ s⁻¹ and I_on/I_off of 2.5 × 10⁴ with pentafluorobenzenethiol (PFBT) self-assembled monolayer (SAM) treatment on Au electrodes. To characterize the interfacial electronic structure and morphology of rubicene on Au and PFBT/Au, ultraviolet photoelectron spectroscopy (UPS), theoretical calculation with density functional theory (DFT) and grazing incidence X-ray diffraction (GIXD) were performed. With PFBT SAM treatment, the hole injection barrier from Au to rubicene is significantly decreased from 1.15 to 0.48 eV due to the formation of a large interface dipole on Au that increased its work function from 4.33 to 5.67 eV. Furthermore, PFBT SAM treatment also induces an “edge-on” configuration of rubicene, which can lead to the increase in carrier mobility. These results indicate that rubicene can serve as a benchmark organic semiconductor for model charge transport studies and in various organic electronic devices.