Phys.org  September 26, 2023
Dual-band electrochromism, the independent modulation of visible and near-infrared light by a single material, is highly desirable for smart windows to enhance the energy efficiency of buildings. Tungsten oxides are commercially important electrochromic materials, exhibiting reversible visible and near-infrared absorption when electrochemically reduced in an electrolyte containing small cations or protons. The presence of structural water in tungsten oxides has been associated with faster electrochromic switching speeds. A team of researchers in the US (North Carolina State University, UT Austin, Vanderbilt University) found that WO3·H2O, a crystalline hydrate, exhibited dual-band electrochromism unlike the anhydrous WO3. Making use of this property they tuned the electrochromic response of tungsten oxides demonstrated absorption of near-infrared light at low Li+/e– injection, followed by the absorption of visible light at higher Li+/e– injection because of an electrochemically induced phase transition. The dual-band modulation was possible due to the more open structure of WO3·H2O compared to WO3, which facilitated a more extended solid-solution Li+ insertion regime that benefited the modulation of near-infrared radiation via plasmon absorption. Higher degrees of Li+/e– insertion led to polaronic absorption associated with localized charge storage. According to the researchers their results show how structural factors influence the electrochemically induced spectral response of transition-metal oxides and the important role of structural water beyond optical switching speed… read more. TECHNICAL ARTICLE
Graphical abstract. Credit: ACS Photonics 2023, 10, 9, 3409–3418, September 1, 2023