Journal article

Electrochemical aspects of display technology based on nanostructured titanium dioxide with attached viologen chromophores

Progress in recent years in the field of electrochromic displays based on viologen modified high-surface area TiO2 electrodes (Vio2+/TiO2) has moved the technol. towards commercialization. Viologen mols. (Vio2+), derivatized with phosphonic acid attachment groups can be chemisorbed on nanostructured TiO2 layers of thickness 2-10 μm. Characterization by cyclic voltammetry, spectroelectrochem. and impedance spectroscopy demonstrates that colorless Vio2+/TiO2 is reversibly reduced to the strongly colored cation radical species Vio+•TiO2. This system can constitute the working electrode of an electrochromic display with a capacitive doped SnO2 electrode as counter electrode, the latter coated by an electrochem. inert white light-reflecting layer. Such a device is stable upon repeated coloration-bleaching cycles with a bleached-to-colored state contrast ratio exceeding 5. Multicolor displays can be achieved by patterning different electrochromophores onto different areas of one working electrode.


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