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With distinct ion insertion-induced tinting behavior, tungsten oxide (WO 3 ) has been intensively studied as a representative electrochromic (EC) material for many years. To enhance its EC properties, strategies including nanostructuring, plasmonic engineering, and metal ion doping have been adopted. Here, we show that rare earth element of gadolinium (Gd) doping can effectively improve the coloration efficiency ( η ) of a sputtered amorphous WO 3 (∼30% enhancement at the maximum of eye-sensitive wavelength of 520 nm for 0.57 wt% doping). By combining the film structural characterization and electrochemical analysis, such an increment can be attributed to the monoclinic Gd 2 O 3 nanoislands formed on WO 3 surface which enhanced charge capacity and reaction kinetics of the film. The large transmittance modulation (76% at 800 nm), high coloration efficiency (68.3 cm 2  C −1 at 633 nm) and fast switching speed (7.8 and 10.4 s for coloration and bleach time, respectively) were achieved for the modest Gd-doped WO 3 film (0.9%). However, further increasing of Gd doping results in decreasing of η , which could be attributed to the excess amount of Gd 2 O 3 that inhibits the penetration of electrolyte into the active material. We believe that the understanding of the Gd-doping effect on the electrochemical behaviours of WO 3 may shed light on selecting the proper doping elements and their concentration for energy-saving smart windows. [ABSTRACT FROM AUTHOR]

Nanostructured WO 3 films prepared by an industry compatible method with large surface area and strong adhesive force to the substrate are highly desired for electrochromic (EC) applications. Here, we report the preparation of a kind of WO 3 nanoisland films on indium-doped tin oxide (ITO)-coated glass substrates by Ag-induced reactive sputtering deposition combined with a post-etching treatment. Our study demonstrates that compared with the bare WO 3 film, the nanoisland film exhibits apparently enhanced EC performance, including high luminous transmittance (92.8%) in a bleached state, high luminous coloration efficiency (126.4 cm2/C), relatively fast color-switching time (7.1 s for coloring and 12.1 s for bleaching), decent long-term cycling stability (2000 cycles) and improved self-bleaching ability. Electrochemical kinetics analysis indicates that such enhanced EC performance relies on large lithium-ion diffusion coefficient (2.37 × 10−10 cm2/s), a good ability of charge storage (10.82 mF/cm2), and low charge-transfer resistance (196 Ω) of the nanoisland microstructure. The results shed light on exploring a novel method to prepare high EC performance WO 3 film. Image 1 • WO 3 nanoisland films can be fabricated by Ag-induced magnetron sputter deposition combined with a post-etching treatment, which significantly increases the contact interface between the electrolyte and materials. • The special nanostructure promotes the electrochromic performance eminently: higher optical transmittance (92.8%), coloration efficiency (126.4 cm2/C) and fast response time (7.1 s for coloring and 12.1 s for bleaching). • The electrochemical performance was analyzed to explain the internal cause relying on large ion diffusion coefficient (2.37 × 10−10 cm2/s), good charge storage (10.82 mF/cm2), and low charge-transfer resistance (196 Ω). [ABSTRACT FROM AUTHOR]