Soluble poly(4-fluorostyrene): a high-performance dielectric electret for organic transistors and memories†
Electrets, referring to an insulating dielectric material carrying quasi-permanent neat charges, are attracting interest for their potential wide applications in electronic devices, filtration fabrics and biological/medical sterilization. Here we report a high-performance, optical transparent and solution-processible polymer electret, atactic poly(4-fluorostyrene) (FPS), synthesized by radical polymerization. The deep bulk traps of FPS could stably accommodate charges, and the hydrophobicity of this material prevents moisture invasion in ambient environments, both of which contribute to the high environmental-stability. Subsequently, the solution processed FPS film with a high sheet charge density of 6.8 × 1012 cm−2, high dielectric strength, good thermal stability and decreased leakage current is introduced as a gate dielectric for organic field effect transistors (OFETs) and non-volatile memories. Using FPS-coated SiO2 as the gate dielectric and 2,7-didodecylbenzothieno[3,2-b]benzothiophene (C12-BTBT) as the semiconductor, OFETs can work with a high mobility of 11.2 cm2 V−1 s−1 and on/off ratio of 107, along with a large memory window of 108 V, and enhanced memory stability over one month during direct exposure to ambient air. Finally, we use a conjugated polymer blended with FPS to show the general improvement of OFET performance by our FPS electret.