Ionic Gel Fillers Enable Transparent and High‐ k Elastomer Composites for Flexible Electronics

Abstract Next‐generation flexible electronics, such as flexible sensors and stretchable displays, have propelled the crucial dielectric elastomers to feature highly comprehensive properties, including superior stretchability, dielectric constant, and transparency. Although incorporating fillers effectively enhances the dielectric constant, traditional solid fillers often introduce issues of rigidity and opacity. Recently, liquid fillers are reported to circumvent these challenges due to their inherent softness and transparency. However, concerns regarding leakage due to the fluid nature of liquids persist. Herein, an ionic gel filler embedded in an elastomer (IGBDE) is introduced, which achieves a high dielectric constant of 14.3. The gel fillers retain the softness and transparency of liquids, thereby enabling IGBDE to achieve a high transmittance of 90% and elongation of 788%. Moreover, the solid form avoids the leakage issue. The resulting alternating current electroluminescent (ACEL) devices show an 11.5‐fold enhancement in luminance compared to commercial elastomer‐based devices, achieving a luminance of 547.5 cd m ⁻² with an elongation up to 500%. Furthermore, IGBDE can also serve as a sensor to monitor strain changes. The use of ionic gel fillers merges the advantages of solid and liquid states, offering significant potential to advance the development of flexible electronic devices.