Gating effects of conductive polymeric ionic liquids

Abstract

Poly(ionic liquid)s (POILs) belong to one of the most promising materials class in electrochemistry. In this study, we investigate POILs as a gating material within a field-effect transistor, additionally describing their glassy dynamics and charge transport properties. Four different imidazolium-based POILs have been investigated, ranging from homopolymers with varied counterions, i.e. POIL 1: P(APMIN(Tf)₂) poly(1-[2-acryloylpropyl]-3-methylimidazolium bis(trifluoromethane)sulfonamide) and POIL 2: P(APMIPF₆) poly(1-[2-acryloylpropyl]-3-methylimidazolium hexafluorophosphate, to semifluorinated random copolymers, i.e. POIL 3: P(APMIN(Tf)₂-co-TFEA) (TFEA: 2,2,2-trifluoroethyl acrylate), and finally to semifluorinated triblock copolymers, POIL 4: P(APMIN(Tf)₂-co-TFEA)-b-PPFS-b-P(APMIN(Tf)₂-co-TFEA) (PPFS: polypentafluorostyrene). Their glassy dynamics and charge transport mechanism are investigated by broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and alternating current chip-calorimetry (ACC). The gating effects of these POILs are studied in detail, showing for the first time a reversible phase transition between thin films formed from the brownmillertite phase SrCoO_2.5 and the perovskite phase SrCoO₃ by use of such POILs, being especially pronounced for POIL 1: P(APMIN(Tf)₂) homopolymer displaying gate voltages (V_G) of 3–4 V and a gating time of ∼4 h. In the case of the POIL 3, P(APMIN(Tf)₂-co-TFEA) as a random copolymer, higher V_G (−8/+5 V) and a longer gating time (∼16 h) are revealed. Phase transition between SrCoO_2.5 and SrCoO₃ could not be observed from POILs 2 & 4 even using very large gate voltages (−10/+8 V) for a much longer time (48 h), indicating that primarily charge density and charge-carrier mobility are decisive in ionic liquid gating.