Multicolor, Dual-Image, Printed Electrochromic Displays Based on Tandem Configuration

We prepared multicolor, dual-image, printed electrochromic displays (ECDs) based on three hybrid electrodes containing mesoporous titanium dioxide (TiO₂) functionalized with various phosphonated viologens. When the hybrid electrodes are employed in ECDs, diverse colors (e.g., cyan, green, magenta, emerald, and yellow) are obtained depending on the electron affinity of the <i>N</i>-substituents of the viologen. The devices show fast switching speed (e.g., coloration ~2.0 s, bleaching ~1.5 s) and high coloration efficiency (~328.8 cm²/C), which is attributed to the large surface area of the hybrid electrode. We also introduced a tandem configuration by inserting double-sided fluorine-doped tin oxide electrode (dsFTO) between two hybrid electrodes to overcome the limitation of the achievable colors (one or maximum two) in a single cell. The dsFTO can serve as a counter electrode of both hybrid electrodes, allowing independent or simultaneous operation of each hybrid electrode through adjusting applied voltage. To extend the functionality of tandem ECDs, the patterned hybrid electrodes are fabricated using electrostatic-force-assisted dispensing printing and applied to ECDs. The resulting devices alternately exhibit two pieces of information in a variety of colors, in which the device operation is controllable in accordance with the direction of applied voltage and the combination of hybrid electrodes. The printed, tandem structured ECDs are expected to have high potential for next-generation transparent displays.