Thermally and Mechanically Stable Polyimides as Flexible Substrates for Organic Field-Effect Transistors

Highly thermal-mechanical stable polymers have attracted extensive research interest as substrates for flexible or wearable electronic devices, such as polyimides (PIs). Here, we report a class of PIs as substrates for flexible organic field-effect transistors (OFETs), prepared by the polycondensation of pyromellitic dianhydride (PMDA) or 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) with three kinds of heterocyclic diamines, including 2,6-diaminothianthrene (SSDA), 2,6-diaminophenoxathiin (SODA), and 2,6-diaminodibenzo-p-dioxin (OODA). Flexible and tough PI films were obtained with a very low coefficient of thermal expansion (CTE) down to 7.3 ppm K–1. Furthermore, the copolymers of PI(OODA–PmBn) prepared from PMDA and BPDA with OODA could exhibit an extremely low CTE of 5.5 ppm K–1 (PI(OODA–P5B5)) without an observed Tg up to 400 °C, which was attributed to the suitable polymer chain rigidity and packing resulting in better in-plane orientation. Finally, this superheat-resistant PI(OODA–P5B5) was applied as the substrate in flexible OFETs, showing compatible and stable device performance even after being baked at 200 °C for 2 h or bended for 1000 cycles. These results indicate that the designed super-thermal-mechanically stable polyimides have potential applications as substrates for flexible electronics.