Solvent Effect on the Electrical Properties of Triisopropylsilylethynyl (TIPS) Pentacene Organic Thin-Film Transistors

We investigated the electrical properties of triisopropylsilylethynyl (TIPS) pentacene organic thin-film transistor (OTFT) depending on solvent type. TIPS pentacene was spin coated by using chlorobenzene, p-xylene, chloroform, and toluene as solvents. A broad spectrum of electrical properties was affected by the solvent choice. Fabricated OTFT with chlorobenzene shows field-effect mobility of 1.0 ?? 1^0-2 cm²/V ?? s, on/off ratio of 4.3 ?? 10³, and threshold voltage of 5.5 V. In contrast, with chloroform, the mobility is 5.8 ?? 10^-7 cm²/V ?? s, on/off ratio of 1.1 ?? 10², and threshold voltage of 1.7 V. Further investigation by measurement of the grain size of TIPS thin films by atomic force microscopy (AFM) and X-ray diffraction spectroscopy showed that solvents with higher boiling points resulted in larger grain sizes and improved crystallinity. The higher performance electrical characteristics are explained by large grain size and high crystallinity of the TIPS pentacene layer in films spin coated with higher boiling point such as chlorobenzene.