WO3 Films Based on Porous ITO Electrodes: Preparation and Electrochromic Property

doi:10.15541/jim20240531

Abstract

Abstract:

Electrochromic smart windows can regulate indoor light through modulating optical transmittance of electrochromic materials to realize energy-saving buildings. Amorphous tungsten oxide (WO₃) film fabricated by magnetron sputtering technology is the most likely to be industrialized due to its advantages of large-area and uniform deposition. However, electrochromic characteristics of the sputtered WO₃ film lag behind those of the solution-process approach due to inefficient ion transport arising from its intrinsically dense atomic structure. In this work, a strategy to develop microstructured magnetron-sputtered WO₃ films by introducing the buried porous electrodes to improve the optical modulation and response time was proposed. The results demonstrate that the porous sputtered WO₃ films prepared by this method exhibit significantly enhanced electrochromic characteristics compared with the dense WO₃ films. When thickness of the porous WO₃ increased to 300 nm, the optimized electrochromic characteristics were achieved, with a remarkable optical modulation of up to 79.08%, coloring and bleaching times of only 2.6 and 2.0 s, and a high coloring efficiency of 52.5 cm²/C. The improved performance is mainly attributed to synergistic effect of the porous indium tin oxide (ITO) electrode and the porous WO₃ film. The porous ITO electrode can increase the surface area with the increased WO₃ component and then increase electronic charges, facilitating the redox reaction process. Moreover, the porous WO₃ film offers a larger surface area for the electrolyte, increases reactive active sites and shortens ion diffusion pathway, which accelerates the ion diffusion and migration process, realizing efficient redox reactions and fast ion transport. This work provides an effective method for preparing high-performance micro- and nano-structured sputtered electrochromic films.

Key words: electrochromism, magnetron sputtering, ITO electrode, porous WO₃

CLC Number:

TQ174

YANG Guang, ZHANG Nan, CHEN Shujin, WANG Yi, XIE An, YAN Yujie. WO₃ Films Based on Porous ITO Electrodes: Preparation and Electrochromic Property[J]. Journal of Inorganic Materials, 2025, 40(7): 781-789.

Figures/Tables 6

Fig. 1 Preparation process flow chart of WO3 films based on porous ITO electrodes

Fig. 2 SEM images of the porous ITO film and porous and dense WO3 film (a) SEM image of porous ITO film; (b, c) SEM-EDS images of In and Sn elements in ITO film; (d) SEM image of porous WO3 film; (e, f) SEM-EDS images of W and O elements in WO3 film; (g) SEM image of porous WO3 film; (h) Cross-sectional SEM image of FTO/ITO/WO3; (i) SEM image of dense WO3 film

Fig. 3 Electrochemical and electrochromic properties of the porous and dense WO3 films (a) CV curves at 50 mV/s; (b) Transmittance spectra at the colored and bleached states; (c) In-situ transmittance spectra at 700 nm; (d) Optical density (ΔOD) variations with respect to the charge density at 700 nm

Fig. 4 Electrochemical and electrochromic properties of the porous WO3 films with different thicknesses (a) CV curves at 50 mV/s; (b) Transmittance spectra at the colored and bleached states; (c) In-situ transmittance spectra at 700 nm; (d) ΔOD variations with respect to the charge density at 700 nm; (e) Digital photos of the coloring and bleaching states. Colorful figures are available on website

Fig. 5 Electrochemical and electrochromic properties of the porous WO3 films prepared from PS microspheres with different diameters (a) CV curves at 50 mV/s; (b) Transmittance spectra at the colored and bleached states; (c) In-situ transmittance spectra at 700 nm; (d) ΔOD variations with respect to the charge density at 700 nm. Colorful figures are available on website

Fig. 6 Schematic diagrams of ion and charge transport in dense bulk and porous WO3 films and related EIS curves (a) Dense bulk WO3 film; (b) Porous WO3 film; (c) EIS curves of dense bulk and porous WO3 films. Colorful figures are available on website

References 33

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WO₃ Films Based on Porous ITO Electrodes: Preparation and Electrochromic Property

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