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

Abstract

Conspectus Electrochromic 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.

Advanced inorganic nanomaterials for high-performance electrochromic applications

“…1,2 The mechanism of electrochromism can be attributed to the ions and electrons that are injected/extracted into/from the EC materials under an applied voltage, resulting in the redox reaction of materials and reversible changes in optical properties. [20][21][22][23][24] The optical modulation, switching time, coloration efficiency, bistability, cycling stability, and energy consumption are the main evaluating parameters of EC materials and devices.…”

“…Generally, EC materials can be divided into organic materials and inorganic materials. [20][21][22] Organic EC materials mainly include organic small molecules (viologen and its derivatives) 25 and conducting polymers (e.g., polyaniline, polythiophene, polypyrrole, and their derivatives). 17,[26][27][28] The organic EC materials stand out due to their multicolor tunability, fast response, flexibility, structural modifiability, and easy processing, which endow them wide potential applications, especially in displays and wearable devices.…”

“…Generally, EC materials can be divided into organic materials and inorganic materials. 20–22 Organic EC materials mainly include organic small molecules (viologen and its derivatives) 25 and conducting polymers ( e.g. , polyaniline, polythiophene, polypyrrole, and their derivatives).…”

Deposition of Nanostructured Tungsten Oxide Layers by a New Method: Periodic Modulation of the Deposition Angle

“…Tungsten oxide electrochromic layers can be prepared using various methods, such as electrodeposition, sol–gel, spray pyrolysis, chemical vapor deposition (CVD), thermal evaporation deposition, sputtering, and nanoparticle deposition. , Chemical techniques (e.g., sol–gel synthesis) require simple equipment and can provide layers with a highly developed surface; however, they are difficult for scaling up and include a stage of high-temperature processing that makes their application with flexible polymer substrates impossible. On the contrary, physical methods are free of these shortcomings.…”

Amorphous bismuth and GO co-doped WO3 electrochromic film with fast-switching time and long-term stability

“…Electrochromic devices (ECDs) usually consist of five layers: transparent conductive layer, electrochromic layer, electrolyte layer, ion storage layer, and transparent conductive layer. 9 The electrochromic layer is the key component determining overall electrochromic performance. 3 Tungsten trioxide (WO 3 ) is a widely researched transition metal oxide and typical cathode electrochromic material, which results in changes of coloration when the ions are inserted/extracted into/out of the materials.…”