The electrochromic mechanism of yellow tungsten oxide thin film can be explained by the dual injection model currently accepted and applied by academics. The dual injection model, also known as the dual injection model of cations and electrons, the Faughnan model, was proposed by Faughnan in 1975.
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The dual injection model considers that when a negative voltage is added to the WO3 film, electrons e- and cation M+ are simultaneously injected from both sides into the defect position in the WO3 lattice, and tungsten bronze MxWO3was generates. When an opposite voltage is applied to the WO3 film, e- and M+ are simultaneously extracted from the film, the MxWO3 disappears, and the film changes from blue to colorless. The injected e- changes W6+ to W5+, resulting in two W lattice positions (M, N), and the electrons of the W atom transition between the W6+ and W5+ lattice positions, so that WO3 can be changed between blue and colorless. It can be seen that in tungsten bronze, W6+ and W5+ coexist, and the color change is derived from the transition of electrons between two different energy levels of W6+ and W5+.
