The oxygen vacancy modulated a-WO _{3− x} enables independent control of VIS and NIR light and has great application potential in high-performance smart windows.

A high performance ECD with a structure of glass/ITO/WO ₃ /LiF/NiO/ITO has been prepared by electron beam and resistance evaporation methods.

In this report, W⁶⁺ doping as a defect engineering strategy has been proposed to improve the electrochromic properties of NiO film. Further research was conducted to explore the electrochromic properties and the modified mechanism of W-doped NiO film. Compared to the pure NiO, W-doped NiO film exhibits improved electrochromic properties with significant optical modulation (61.56% at 550 nm), fast switching speed (4.42 s/1.40 s for coloring/bleaching), high coloration efficiency (45.41 cm²·C⁻¹) and outstanding cycling stability (no significant attenuation after 2000 cycles) in Li-based electrolytes. Density functional theory (DFT) calculations combined with the experimental results indicate that the improved electrochromic properties were due to enhanced the electronic conductivity and ion conductivity after the introduction of W⁶⁺. The charge capacity of W-doped NiO has also been improved, and it can function with WO₃ to achieve a high performance black electrochromic smart window (ECSW) by balancing charge. This work could advance the fundamental understanding of defect engineering as an effective strategy to boost the electrochromic properties of NiO anodic material, manifesting a significant development as a candidate counter electrode in high-performance black smart windows.

All-solid-state electrochromic devices with the structure of glass/ITO/WO₃/Ta₂O₅/Li/V₂O₅/ITO were prepared by an evaporation method. Because of the use of a V₂O₅ complementary layer, the ECD can achieve obvious color change between yellow-green and emerald green with superior cycling performance up to 5000 cycles, indicating the great potential in smart window applications.