Unipolar Polymerized Ionic Liquid Copolymers as High-Capacitance Electrolyte Gates for n-Type Transistors

A series of well-defined polymerized ionic liquid (PIL) statistical and block copolymers consisting of ionic liquid monomer, 1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide, and a nonionic monomer, methyl methacrylate (MMA), were synthesized by nitroxide-mediated polymerization (NMP) with the goal of understanding the influence of polymer structure on the thin film capacitance. Copolymer compositions were varied from 8 to 54 wt % for both statistical and block copolymers and were characterized by predictable changes in glass transition temperature (75 °C > Tg > 45 °C). When integrated into thin film capacitors, block copolymers exhibited the formation of electrical double layer (EDL) at lower frequencies compared to the statistical copolymers of similar comonomer compositions. The materials that formed an EDL all produced a similar maximum double layer capacitance value, with the only difference being the frequency at which the EDL was formed. Finally, the PIL-containing materials that were utilized in organic thin-film transistors (OTFTs) showed a significant reduction in operating voltage compared to the poly(MMA) baseline. These results indicate that not only composition but also polymer architecture plays a vital role in the formation of an EDL and determines at which frequency the resulting OTFTs can be operated.