Electrochromism: Yellow Tungsten Oxide Film

When it comes to the phenomenon of electrochromism, many people think of yellow tungsten oxide film (WO3 film) - an earliest and most studied inorganic electrochromic film material. Well, do you know what the electrochromic mechanism of crystalline WO3 film is? And what is the electrochromic mechanism of amorphous WO3 film?

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Some experts have studied the coloring process of amorphous and crystalline yellow tungsten oxide film films under different voltages through ellipsometry, and explained the difference between the two electrochromic mechanisms. During the coloring of crystalline and amorphous WO3 films, the refractive index decreases and the extinction coefficient increases. The change rate of the refractive index and extinction coefficient of the crystalline WO3 film is significantly higher than that of the amorphous WO3 film. The absorption coefficient of amorphous WO3 increases almost linearly in the entire visible light band, while the absorption of crystalline WO3 is more significant in the long wave band. It means that the discoloration mechanism of amorphous WO3 is small-pole transition absorption, while crystalline WO3 is similar to the Drude free electron absorption of heavily doped semiconductor.

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