Amorphous and Crystalline Ti-Doped WO₃·2H₂O for Dual-Band Electrochromic Smart Windows

The dual-band electrochromic smart windows (DESW) can selectively modulate visible (VIS) and near-infrared (NIR) transmittance, which is expected to effectively reduce building energy consumption. However, the complex preparation of dual-band electrochromic materials has restricted the further development of DESW. In this work, amorphous and crystalline Ti-doped WO3·2H2O (TiWH) were synthesized by a simple precipitation method, which does not require strict control of the oxygen content and temperature. Ti doping reduced the crystallinity of WO3·2H2O and increased the specific surface area. 3% TiWH films exhibited excellent dual-band electrochromism with high transmittance modulation (633 nm: 83.8%, 1050 nm: 72.5%), fast response time (bleached/colored time: 14.9/15.3 s at 633 nm, 16.0/3.5 s at 1050 nm), good coloration efficiency (633 nm: 22.8 cm2 C–1, 1050 nm: 90.8 cm2 C–1), and high capacitance of 47.1 mF cm–2 at 0.1 mA cm–2. The electrochromic device can still maintain good dual-band electrochromism (bright, cool, and dark modes). The excellent dual-band electrochromism and energy storage make TiWH have a good application prospect in green buildings.