Fast-Switching WO3-Based Electrochromic Devices: Design, Fabrication, and Applications

ConspectusElectrochromic devices (ECDs) can reversibly regulate their optical properties (transmittance, reflectance, and color) via internal ion migration under applied voltage, thus exhibiting advantages such as controllable switching, high contrast ratio between bleached and colored states, and low power consumption. Based on these features, ECDs have been studied in the fields of photothermal modulation, dynamic display, energy storage, and camouflage. Recently, remarkable breakthroughs have been made in ECDs with respect to the contrast ratio, coloration efficiency, cycle stability, and scale-up fabrication. Nevertheless, the response speed, which is related to the efficiency and power consumption of devices, especially in application scenarios with strict requirements on switching rate, remains a major restricting parameter.Typically, the modulation strategies for the response speed of ECDs can be divided based on three aspects, i.e., electrodes, electrochromic materials, and electrolytes. The basic method for improving the response speed of ECDs involves expediting the migration of ions in the electrolyte to ensure that they getting into and out of the electrochromic layer more quickly and conveniently. By optimizing the electrode layer for improving electron transport, ion migration can be favored in this layer. The structure of the electrolyte layer, ion type, and structure of the electrochromic layer are equally crucial parameters influencing the entry of ions into the electrochromic layer. These directions can provide abundant opportunities for the basic research and practical applications of ECDs.In this Account, we highlighted the recent progress on modulation strategies related to improving the response of WO3-based ECDs, primarily the progress made by our group. First, we discussed various modulation strategies of electrolyte in detail, including multivalent ions, tandem proton transport, and hybrid ion synergy. Then, we presented two additional modulation strategies for electrodes and electrochromic materials to improve the response speed of ECDs. Accordingly, we discussed various examples of our previous works on fast-switching WO3-based ECDs to demonstrate their application prospects. Finally, we summarized the current challenges involved in fast-switching WO3-based ECDs and identified some possible prospects for their future design.