Solid-state electrochromic device consisting of amorphous WO3 and Cr2O3

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Abstract
The electrochromic (EC) characteristics were investigated on a solid‐state EC device In2O3/a‐WO3//Cr2O3/Au which was prepared by vacuum deposition. Besides the color change caused by passage of current in the WO3 layer, the color of the Cr2O3 layer was also changed as a result of electrochemical reaction at the interface. In the open‐circuit condition after the coloration, rapid spontaneous discoloration was found due to bimolecular recombination of the colored species in both layers at the interface. The existence of adsorbed water molecules in the respective layers is essential for the solid‐state ECD. The ECD in this study was scarcely affected by the ambient condition and was able to operate in the high vacuum (e.g., 10—6 Torr) since the Cr2O3 layer adsorbed water tightly. Positive polarization of the Cr2O3 layer in an electrolyte solution (Na2SO4 aqueous solution) caused change in the color as a result of electrochemical reaction, whereas the coloration of a‐WO3 was taken place by negative polarization of the a‐WO3. We have confirmed that this ECD could be operated without any conspicuous deterioration after the reversible switching cycles more than 5×106 times.