WO3 film for preparing large area electrochromic device is a typical representative of the earliest and the most studied cathode electrochromic materials. However, due to the complexity of the electrochromic process of tungsten trioxide, its mechanism remains controversial. Currently, the widely accepted and applied electrochromic model is the dual injection model, which is also known as the Fanghnan model.
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Fanghnan model considers that the electrochromic mechanism of tungsten trioxide electrochromic thin film is: In the process of electrochromism, due to the action of external electric field, after the double injection of cation and electron into WO3 lattice gap, MxWO3 (tungsten bronze) structure containing W5+ is produced, and WO3 film is changed from the original transparent state to the colored state - blue. When a reverse voltage is applied, the cation and electron are extracted, and the WO3 film new_s to the original transparent state. The production of W5+ is considered to be the cause of discoloration of the WO3 film.
