Ionic liquids-filled patterned cavities improve transmittance of transparent and stretchable electronic polydimethylsiloxane films

Transparent electrodes for flexible and wearable devices require considerable stretchability and patterned conductive materials. Transparent and stretchable polydimethylsiloxane (PDMS) films with patterned cavities were prepared by laser processing and transfer printing. Transparent conductive ionic liquids (ILs) and aqueous solution (AS) were injected into the cavities, obtaining electrodes with transmittance in the visible range of 99.94% (relative to blank PDMS films) and 92.80% (relative to air). This transmittance was almost identical to that of a blank PDMS film. The maximum tensile strain applied to the electrodes was 117.23%, and the resistance of the electrodes with network patterns measured by the four-probe method was 3.20 kΩ. After 10,000 stretching/releasing cycles under strain of 0–50%, these electrodes still performed optimally. The ILs and AS showed various transmittance and electrical properties. The electrodes with ILs had higher transmittance, while those with AS showed increased conductivity. These electrodes with five patterns (serpentine, circle, straight line, fold line, and rhombus) were analyzed. The pattern containing curves with a large curvature would result in a severe local stress concentration in the stretching process. Patterns containing parallel curves could optimize electrical conductivity. And patterns containing complex curves had a certain effect on the transmittance. In addition, taking advantage of the fact that the elastomer and the liquid can deform at will, these electrodes were used to fabricate two pressure sensors and two strain sensors, which were employed to demonstrate their sensitivity stability during cycling.