Electrical properties of highly ordered and amorphous thin films of pentacene doped with iodineStructural studies on highly conductive thin tlhns of pentacene (PEN) were carried out by x-ray and electron diffraction methods. The ultrathin film before and after doping with iodine was confirmed to consist of single crystalline domains, and the lattice parameters were determined. Drastic elongation along the c axis as a result of doping was observed, while the u-b plane did not change during doping. The intercalation of iodine molecules between molecular layers of PEN was confirmed. 5220

We have demonstrated the iodine doping of vacuum-deposited pentacene (PEN) film which showed characteristic changes in structure and electrical conductivity. The iodine-doped film exhibited a high electrical conductivity of 110 Ω−1 cm−1, which was 11 orders of magnitude larger than that of as-deposited film, and a high electrical anisotropy of 108. The structural changes by the iodine doping were studied by means of x-ray diffraction method, ultraviolet-VIS absorption spectroscopy, and FT-infrared spectroscopy. These results revealed that iodine molecules were intercalated between the layers of PEN molecules to form charge transfer complex of PEN-iodine with highly ordered structure.

We investigate the growth and field-effect transistor performance of aligned pentacene thin films deposited by zone-casting from a solution of unsubstituted pentacene molecules in a chlorinated solvent. Polarized optical microscopy shows that solution processed pentacene films grow as large crystalline domains with pronounced anisotropy in the substrate plane, in contrast to vacuum sublimed pentacene films, which consist of small crystalline grains with random in-plane orientation. The high structural alignment is confirmed by in-plane and out-of-plane X-ray diffraction analysis, with out-of-plane 00n reflections up to at least the seventh order, and a pronounced in-plane anisotropy with the a-axis of the triclinic unit cell predominantly aligned parallel to the zone-casting direction and the ab-plane parallel to the substrate. The average charge carrier mobility of the zone-cast pentacene devices depends strongly on the underlying dielectric. Divinylsiloxane-bis-benzocyclobutene (BCB) resin is found to be a suitable gate dielectric allowing reproducible film deposition and high field-effect mobilities up to 0.4−0.7 cm2/(V s) and on/off ratios of 106−107. A small mobility anisotropy is observed for devices with channels aligned along and perpendicular to the zone-casting direction.