All-solution-processed bottom-gate organic thin-film transistor with improved subthreshold behaviour using functionalized pentacene active layer

Abstract

We report organic thin-film transistors (OTFTs) made by simple solution processes in an
\nambient air environment. Inkjet-printed silver electrodes were used for bottom-gate and
\nbottom-contacted source/drain electrodes. A spin-coated cross-linked poly(4-vinylphenol)
\n(PVP) and a spin-coated 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were
\nused as a gate dielectric layer and an active layer, respectively. A high-boiling-point solvent
\nwas used for TIPS-pentacene and the resulting film showed stem-like morphology. X-ray
\ndiffraction (XRD) measurement showed the spin-coated active layer was well crystallized,
\nshowing the (0 0 1) plane. The reasonable mobility, on/off ratio and threshold voltage of the
\nfabricated device, which are comparable to those of the previously reported TIPS-pentacene
\nOTFT with gold electrodes, show that the printed silver electrodes worked successfully as gate
\nand source/drain electrodes. Furthermore, the device showed a subthreshold slope of
\n0.61 V/dec in the linear region (VDS = −5 V), which is the lowest value for spin-coated
\nTIPS-pentacene TFT ever reported, and much lower than that of the thermally evaporated
\npentacene OTFTs. It is thought that the surface energy of the PVP dielectric layer is well
\nmatched with that of a well-ordered TIPS-pentacene (0 0 1) surface when a high-boiling-point
\nsolvent and a low-temperature drying process are used, thereby making good interface
\nproperties, and showing higher performances than those for pentacene TFT with the same
\nstructure.