Fast electrochromic response and high coloration efficiency of al-doped WO3 thin films for smart window applications

Abstract

Herein, vertically aligned Al:WO3 nanoplate arrays were directly grown on ITO glass by a facile electrodeposition method and annealed in an argon atmosphere at 450 degrees C for 2h. Besides, this study reports the influence of Al doping on the electrochromic properties of WO3 film in detail. Electrochromic properties such as cyclic voltammetry, chronoamperometry and optical transmittance were analyzed by protonic insertion/extraction in the 1 M LiClO4/propylene carbonate as an electrolyte. The noticeable reversible color changing from transparent to the blue can be realized under the potential bias of +/- 1.0 V. XRD studies show that the produces films have highly crystalline structure. The EDS results clearly confirm the incorporation of Al element into the WO3 network. From the optical absorption measurement, direct band gap energies are calculated as 3.62 and 3.34 eV for the WO3 and the Al:WO3, respectively. Compared to the as-prepared WO3, the Al:WO3 film exhibits outstanding electrochromic performance, including wide optical modulation (55.9%), high coloration efficiency (148.1 cm(2)C(-1)), quick reaction kinetics (1.23 s and 1.01 s for colored and bleaching times, respectively), good rate capability and cycle durability at a wavelength of 632.8 nm. EIS measurements based on a charge-transfer resistance reveal that the dramatic improvement in the electrochemically active surface is achieved in the Al:WO3 film. The increase of active surface facilitates transport kinetics for electron and ion intercalation/deintercalation within the porous metal oxide to enhance coloration efficiency. Comparatively energy levels of the WO3 and the Al:WO3 electrochromic films are also represented. From the Mott-Schottky studies, it is estimated that the donor concentration of the films is of the order of 1020 cm(-3). Taken together, these results not only provide important insight into a promising electrode for electrochromic displays applications, but also offer an economic and effective strategy for manufacturing of other doped metal oxide films.