Redox-Active Ion Gels with Light-Driven Photocatalytic Doping in Organic Electrolyte-Gated Transistors for Transconductance Enhancements

Abstract

Organic electrolyte-gated transistors (OEGTs) are an attractive platform for low-voltage organic electronics because their operation is governed by coupled ionic and electronic transport. However, introducing photoresponse into OEGTs through a controllable molecular mechanism remains a significant challenge. Here, we report a photoredox-active ion gel that enables light-driven photocatalytic doping in an OEGT. The ion gel was constructed by incorporating 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) into a poly(vinylidene fluoride-co-hexafluoropropylene) matrix, together with the photoredox catalyst 9-mesityl-10-methylacridinium perchlorate (mmAc+) and the molecular oxidant 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ). Under light irradiation, photoexcited mmAc+ extracts electrons from the poly(3-hexylthiophene-2,5-diyl) channel and mediates its oxidation in the presence of 2,6-DCBQ, generating positively charged polarons through a photocatalytic doping process, while the ion gel supplies mobile counterions to stabilize the photogenerated charges. Ultraviolet photoelectron spectroscopy reveals an increased work function and deeper HOMO levels after photocatalytic doping, while X-ray photoelectron spectroscopy demonstrates strong interfacial polarization of TFSI– anions, and Fourier-transform infrared spectroscopy is consistent with the chemical participation of 2,6-DCBQ during light irradiation. By optimizing the catalyst and oxidant compositions, the device exhibits a pronounced enhancement in channel conductivity and transconductance, reaching 0.184 S cm−1 and 1.65 mS, respectively, which are 3–5 orders of magnitude higher than those of the pristine P3HT device, with 0.35 mS cm−1 and 0.052 μS, respectively. While achieving these maximum conductivities and transconductance enhancements involves an inherent trade-off with the Ion/off ratio due to a positively shifted threshold voltage, the OEGT device retains a practically discernible current contrast, thereby ensuring its functional switching capability and operational fidelity. These results establish photoredox catalytic ion gels as an effective strategy for coupling ionic gating with light-driven chemical doping, providing a new route toward multifunctional organic optoelectronic devices.