The discoloration mechanism of the crystalline tungsten oxide thin film conforms to the Drude-like free electron scattering model. And the free electrons play an important role in the optical properties of the electrochromic performance of the crystalline tungsten oxide film.
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In this regard, experts explained that ions and electrons (M+/e-) are simultaneously injected into tungsten oxide under the action of an external electric field. When e- occupies in W5+ ions, M+ will remain at this position in order to maintain electrical neutrality. Finally, a tungsten bronze compound MxWO3 is formed. Among them, the injected electron can be regarded as a free electron gas, the ions play a role of maintaining electrical neutrality, and the tungsten oxide exhibits a metal-like property. Optical modulation that enhances reflection and reduces absorption can be achieved by reducing the scattering of free electrons in the crystal. The electrons enter an extended state in the tungsten oxide band structure and are scattered by impurities, resulting in high reflectance and low transmittance in the near-infrared region.
