Transparent and Colorless Polyimides Containing Multiple Trifluoromethyl Groups as Gate Insulators for Flexible Organic Transistors with Superior Electrical Stability

A suitable insulating polymer material that is compatible with the fabrication process of organic transistors and has excellent electrical properties is critically required for the next-generation flexible organic electronics. In this study, using a one-step polymerization method, we synthesized two different solution-processable polyimides (PIs) incorporated with abundant trifluoromethyl groups. Not only were the two resulting PIs - termed 6FDA-6FDAM-PI and 6FDA-TFMB-PI - well soluble in organic solvents, but also they showed transparent and colorless optical properties. The fluorinated PI films showed smooth surface topographies and surface energy values that were appropriate for their use in bottom-gate organic transistors. Organic transistors separately fabricated with 6FDA-6FDAM-PI and 6FDA-TFMB-PI as the gate insulators showed excellent device performance and electrical stability under various testing conditions, especially for pentacene-based devices. The excellent performance of the devices with fluorinated PIs was attributed to the enhanced microstructure of the organic semiconductor and the fluorine-rich characteristic of the underlying gate insulator. Furthermore, organic complementary circuits including the basic logic gates of NOT, NOR, and NAND were demonstrated using these devices.