Solution-Processable, Thin, and High-κ Dielectric Polyurea Gate Insulator with Strong Hydrogen Bonding for Low-Voltage Organic Thin-Film Transistors

We developed a solution-processable, thin, and high-dielectric polyurea-based organic gate insulator for low-voltage operation and high performance of organic thin-film transistors (OTFTs). A 60 nm-thick polyurea thin film exhibited a high dielectric constant of 5.82 and excellent electrical insulating properties owing to strong hydrogen bonding. The hydrogen bonding of the synthesized polyurea was confirmed using infrared spectroscopy and was quantitatively evaluated by measuring the interactive force using atomic force microscopy. Moreover, the effect of hydrogen bonding of polyurea on the insulating properties was systematically investigated through the combination of various monomers and control of the thickness of the polyurea film. The dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene-based OTFTs with the polyurea gate insulator showed excellent thin-film transistor (TFT) performance with a field-effect mobility of 1.390 cm2/V·s and an on/off ratio of ∼105 at a low operation voltage below 2 V. In addition, it is possible to fabricate flexible polymer organic semiconductor (OSC)-based TFT devices using a solution process, owing to excellent solvent stability in various organic solvents. We believe that the solution-processable polyurea gate insulator with a high dielectric constant and good insulation properties is a promising candidate for low-voltage-operated OTFTs using various OSCs.