Highly conductive, binary ionic liquid–solvent mixture ion gels for effective switching of electrolyte-gated transistors

Ionic liquid-based solid polymer electrolytes, or ion gels, have attracted great research attention recently as nonvolatile electrolytes for thin film electronic/electrochemical devices due to their outstanding electrochemical properties, such as thermal/electrochemical stability, ionic conductivity, and specific capacitance. Although the polymer host provides solid-state mechanical integrity to the liquid electrolytes, it simultaneously causes sluggish ion transport and ion polarization, which leads to slow response of the ion gel-based devices to an applied bias. To address this issue and enhance the ion motion in the ion gels, we blended the aprotic solvent propylene carbonate (PC) with the ion gels and investigated the effect of the blend composition on the electrical, thermal, and mechanical properties of the solid electrolytes. Both the ionic conductivity and specific capacitance of the blended ion gels were significantly increased compared to the neat ion gel, exhibiting maximum values of ∼6 mS cm−1 and ∼15 μF cm−2, respectively, at a PC mole fraction of 81%. When these mixed ion gels were applied in transistor gating experiments, the mixed ion gel-gated devices showed superior device performance to the neat ion gel without added PC, namely, larger channel current and smaller subthreshold swing. These results demonstrate that the solvent-blending strategy provides an effective pathway to improve ion transport and also the operational performance of ion gel-based thin-film devices.