(Invited) Optimizing Material Systems for All-Inkjet-Printed Organic Thin-Film Transistors

All-inkjet-printed organic thin-film transistors enjoy advantages of low-cost printability and mechanical flexibility, thereby enabling newly emerging application areas. Recent developments have shown devices with low operating voltages and steep subthreshold slopes, using a bottom-gate bottom-contact structure. However, it would be also interesting to understand the optimization of the underlying materials system. This study investigates the composition and associated solvents for semiconductor inks, as well as the necessity of encapsulation. Basically, we compare the semiconductor inks of 6,13-bis(triisopropylsilylethynyl)pentacene with and without polystyrene binder, and find the importance of the polymer binder in lowering trap state density. Comparing semiconductor inks of different boiling points, e.g. toluene (low) and anisole (high), suggests that using a solvent with a high boiling point can enhance semiconductor crystallization. Using encapsulation with a fluoropolymer CYTOP is essential to reduce the trap state density. These results are important for further development of novel all-inkjet-printed organic thin-film transistors.