Improvement of Characteristics of Complementary Elactrochromic Devices by the Use of Various Transition-Metal-Oxide Films

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Coloration efficiency and contrast of WO_3-based electrochromic (EC) cells are not enough for the application of display devices. This investigation aims to improve characteristics of EC devices by the combination of various transition-metal-oxide films, such as WO_3, WO_3/MoO_3, NiO and Ta_2O_5 films. Followings are the main results of this investigation.1. Preparation of WO_3, NiO and WO_3/MoO_3 filmsWO_3 films as cathodic EC films were prepared by rf sputtering. Examining the conditions for film preparation, coloration efficiency was improved about 20% compared with the conventional evaporated films. NiO films were prepared by rf sputtering, and were found to be anodic EC ones with high contrast. Mixed films of WO_3/MoO_3 were also prepared, whose coloration efficiency was high in viside wavelength range, and was about twice of WO_3 evaporated films.2. EC cells with liquid electrolyteEC characteristics were investigated with EC cells containing electrolyte of anodic, neutral and alkaline solutions. Construction of complementary EC cells was found to be difficult when both WO_3 and NiO films were used as EC materials.3. Measurements of characteristics of EC cellsOptical absorption spectra of colored films of WO_3 and NiO were measured. From the results, absorptance of complementary EC cell is expected to be wavelength independent in near-infrared and visible regions.4. Preparation of EC half cells with solid electrolyteSolid electrolyte layers were prepared by rf sputtering of Ta_2O_5 target, and were confirmed to be ionic conductors. EC cells composed of a solid electrolyte layer and an EC layer of WO_3 or NiO showed stable color-bleach characteristics.5. Preparation of all-solid-state complementary EC cellsComplementary EC cells consisting of WO_3/Ta_2O_5/NiO structure were prepared. The EC characteristics of the cells are now under investigation.