AN ALL GEL ELECTROCHROMIC DEVICE

The project was to build an electrochromic device in which all active layers could be deposited from gels. Transparent conducting electrodes (ITO) and amorphous WO3 coatings have already been made via the gel route. Therefore an electrolyte gel was looked for. A mixed organic-inorganic electrolyte was made through the reaction of a polyol (glycerol) and a carboxylic acid (acetic acid) onto an alkoxide (Ti(OBun)4). A gel is obtained upon hydrolysis in which Ti-O-Ti polymeric species are linked through organic bridges. Layers deposited from these gels exhibit high protonic conductivity at room temperature (σ=10-5Ω-1cm-1). These gels are able to dissolve large amounts of lithium salts, giving rise to higher ionic conductivities (σ=10-4Ω-1 cm-1 at 300 K). Display devices can be easily made when layers of these gels are deposited onto transparent conducting electrodes. A typical electrochromic cell is made of: conducting electrode |WO3gel|electrolyte gel|conducting electrode. Such cells exhibit response times of about 40 s under an applied voltage of ±2.5 v. Open-circuit memory can be as large as six months. They have already been cycled more than 4×105 times without failure.