Thermostable Ion Gels for High-Temperature Operation of Electrolyte-Gated Transistors

High-temperature durability is critical for application of organic materials in electronic devices that operate in harsh environments. In this work, thermostable physically cross-linked polymer electrolytes, or thermostable physical ion gels, were successfully developed using crystallization-induced phase separation of semicrystalline polyamides (PAs) in an ionic liquid (IL). In these ion gels, phase-separated PA crystals act as network junctions and enable the ion gels to maintain their mechanical integrity up to 180 degrees C. ILs and ion gels are suitable electrolyte candidates for thin-film devices operating at high temperatures because they outperform other electrolytes that use aqueous and organic solvents, owing to their superior thermal stability and nonvolatility. In addition to thermal stability, the PA gels exhibited high ionic conductivity (similar to 1 mS/cm) and specific capacitance similar to 10 mu F/cm(2) ) at room temperature; these values increased significantly with increasing temperature, while the gel retained its solidstate mechanical integrity. These thermostable ion gels were successfully used as an electrolyte gate dielectric in organic thin-film transistors that operate at high temperatures (ca. 150 degrees C) and low voltages (<1 V). The transistors gated with the dielectrics had a high on/off current ratio of (3.04 +/- 0.24) x 10(5) and a hole mobility of 2.83 +/- 0.20 cm(2)/V.s. By contrast, conventional physical ion gels based on semicrystalline polymers of poly(vinylidene fluoride-co-hexafluoropropylene) and polyvinylidene fluoride lost their mechanical integrity and dewetted from a semiconductor channel at lower temperatures. Therefore, these results demonstrate an effective method of generating thermally stable, mechanically robust, and highly conductive solid polymer electrolytes for electronic and electrochemical devices operating in a wide temperature range.