Ink-jet printing of organic semiconductor for fabricating organic thin-film transistors: Film uniformity control by ink composition

We have investigated the influence of solvent chemistry on ink-jet printed semiconductor patterns. Our research focuses on improving the uniformity of an ink-jet printed single dot semiconductor by adjusting the solvent mixture combination. Use of a solvent mixture with one solvent of a lower boiling point and a higher solubility with respect to the semiconductor molecules and another of a higher boiling point and a lower solubility allows us to produce a uniform single dot pattern by ink-jet printing. It was observed that the film uniformity of the semiconductor layer plays an important role in determining the electrical parameters of the transistor. In comparison with uncontrolled ink composition, the OTFT fabricated from the well-controlled ink exhibited better device performance, including a carrier mobility of 8.5 × 10−3 cm2 V−1 s−1 in the saturation regime, an on/off current ratio of 103, and a threshold voltage of 0.39 V with subthreshold slopes of 0.95 V dec−1.