Flexible and Transparent Electrochromic Displays with Simultaneously Implementable Subpixelated Ion Gel-Based Viologens by Multiple Patterning

Electrochromic materials reversibly change colors by redox reactions depending on the oxidation states. To utilize electrochromic materials for active-matrix display applications, an electrochromic display (ECD) requires simultaneous implementation of various colors and a fine-pixelation process. Herein, flexible and transparent ECDs with simultaneously implementable subpixelated EC gels by sequential multiple patterning are successfully demonstrated. Ionic liquid-based EC gels of monoheptyl-viologen, diheptyl-viologen (DHV), and diphenyl-viologen (DPV) are used to create the colors of ECDs: magenta, blue, and green, respectively. Especially, to realize an improved green color, DHV–DPV composite gels are synthesized. Three EC gels exhibit stable properties without degradation during repetitive operation. Moreover, a transmittance greater than 90% is maintained in a bleached state, which is sufficient for application as a transparent display. The subpixelation process for multicolored-flexible ECDs is designed to facilitate both easy fabrication and rapid operation with various patterns at low cost. The subpixelated EC gels using a film mask can be implemented to a minimum size of 200 µm. Furthermore, the subpixelated flexible ECDs exhibit high durability even after 1000 cycles of mechanical bending tests at a bending radius of 10 mm. Therefore, these EC materials can be used directly for flexible and transparent active-matrix displays.