J. Mater. Chem. C
Field effect transistors (FETs) were fabricated using a new type of phenacene molecule, 3,12-ditetradecyl[7]phenacene ((C14H29)2-[7]phenacene), and solid gate dielectrics or an electric double layer (EDL) capacitor with an (1-butyl-3-methylimidazolium hexafluorophosphate (bmim[PF6])). The new molecule, (C14H29)2-[7]phenacene, was efficiently synthesized via the Mallory photoreaction. Its crystal structure and electronic properties were determined, using X-ray diffraction, scanning tunneling microscopy / spectroscopy (STM and STS), absorption spectroscopy, and photoelectron yield spectroscopy, which showed a monoclinic crystal lattice (space group P21 (No. 4)) and an energy gap of ~3.0 eV. The STM image clearly showed the molecular structure of (C14H29)2-[7]phenacene, as well as the closed molecular stacking indicative of a strong fastener effect between alkyl chains. The X-ray diffraction pattern of thin films of (C14H29)2-[7]phenacene formed on an SiO2/Si substrate suggested that the molecule stood on the surface with an inclined angle of 30° with respect to the normal axis of the surface. The FET properties were recorded in two-terminal measurement mode, showing p-channel normally-off characteristics. The averaged values of field-effect mobility, m, were 1.6(3) cm2 V-1 s-1 for a (C14H29)2-[7]phenacene thin-film FET with SiO2 gate dielectric and 1.0(2) cm2 V-1 s-1 for a (C14H29)2-[7]phenacene thin-film EDL FET with bmim[PF6]. Thus, the good FET performance was obtained with an FET using a thin film of (C14H29)2-[7]phenacene, and the effects of adding alkyl chains to a phenacene molecule on its FET properties are fully discussed. This study could pioneer an avenue for the realization of high-performance FETs through the addition of alkyl chains to phenacene molecules.
