Solution processable, electrochromic ion gels for sub-1 V, flexible displays on plastic

The functionality of ion gels can be enhanced by incorporating different types of redox-active species. Here, we have expanded the functionality of ion gels composed of polystyrene-block-poly(methyl methacrylate)-block-polystyrene and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to include electrochromism by adding an electrochromic (EC) redox molecule, methyl viologen. Ferrocene was also added to the EC gel as an anodic species. The EC gel was inserted between two indium-tin oxide-coated glass slides (or plastic sheets) to make a simple two-terminal electrochromic device (ECD). The ECD changed color upon application of 0.7 V. The coloration efficiency (η) was 105 cm²/C, and the ECD exhibited good operational stability over 24 h even in air. Because the EC gel is processed from common solvents (acetone) at room temperature, it can be coated onto plastic straightforwardly, and we demonstrated a patterned flexible ECD. Overall, the results demonstrate that sub-1 V, flexible ECDs based on EC ion gels can be prepared by simple solution processing, and thus, they are potentially attractive components for printed electronics.