Impact of Ionic Liquid Gels on the Mixed Ionic‐Electronic Transport in Solid‐State Organic Electrochemical Transistors

Abstract Solid‐state organic electrochemical transistors (SSOECT) offer promising advantages for dense integration in flexible and wearable platforms. However, the thermodynamics and underlying physics of these devices have not been extensively investigated. In this study, four ionic liquids including EMIMTFSI, EMIMPF₆, HMIMTFSI, and HMIMPF₆, combined with a polymer matrix, are employed as solid‐state electrolytes for SSOECTs. It is revealed that a larger ion size may contribute to a slightly higher transconductance at room temperature. Furthermore, the temperature‐dependent electrical measurements are also conducted. Intriguingly, SSOECTs incorporating HMIMTFSI and HMIMPF₆ exhibit a double‐slope behavior, characterized by a low activation energy (≈10 meV) at higher temperatures and a higher activation energy (≈330 meV) at lower temperatures. In sharp contrast, a single activation energy of ≈30 meV is achieved for EMIM⁺ based devices. This phenomenon is associated with the glass transition of HMIM⁺ based electrolytes, as confirmed by differential scanning calorimetry characterizations. Additionally, studies on temperature‐dependent transient behavior show that a decrease in temperature leads to prolonged rise and decay times, with devices using EMIMTFSI exhibiting the fastest switching speeds and reduced temperature sensitivity. These findings provide new insights into mixed ionic–electronic transport mechanisms and offer potential strategies for enhancing the performance of SSOECT devices.