V-doping-induced oxygen vacancy in WO3 inverse opal film for improved electrochromic response in NIR region

2D vanadium-doped tungsten oxide (V-doped WO3) inverse opal (IO) monolayer film was successfully fabricated on ITO glass by simply doping vanadium ions within pre-synthesized 2D WO3 IO. The new material exhibited a large-area highly ordered porous array with featured structural colors. The obtained 2D V-doped WO3 IO film showed an improved electrochromic response in near infrared (NIR) region with a high optical contrast as 24.2% at 1100 nm wavelength, much higher than that of crystallized m-WO3 IO film (18.1%), or amorphous WO3 IO composite film (6.4%). Such advanced property could be attributed to the successful doping of vanadium, resulting in enhanced absorption owing to oxygen vacancies defect-inductive effect, and greatly improved the electrochromic response in the NIR region. Further, the V-doped WO3 IO film also featured with an excellent cyclic stability with the capacity retention of (75.2%) after 30 cycles, comparable to crystallized m-WO3 IO film (78.0%). As contrast to it, the amorphous WO3 IO film was found destroyed even after 10 cycles.