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.

Prussian blue (PB) is an anodic coloring candidate in the wide area of electrochromic (EC) applications. However, the co-influence of weak adhesion and low electrical conductivity leads to the poor stability and slow switching speed. To tackle this bottleneck, a novel TiO₂/Au/PB nanorod array is designed through hydrothermal and electrodeposition approaches on fluorine-doped tin oxide (FTO) glass. Such a designed ternary array structure could not only increase reactive site and conductivity, but also improve ion storage capacity and promote charge transfer, attributed to the synergistic effect of TiO₂/Au/PB core–shell heterostructure and the localized surface plasmon resonance (LSPR) effect of Au nanoparticles. Besides, density functional theory (DFT) calculation confirms the strong interaction between rutile TiO₂ and FTO substrate, which contributes to the improvement of EC cycle stability. Benefiting from these effects, the TiO₂/Au/PB film shows a fast coloration/bleaching response of 1.08/2.01 s (2.17/4.48 s, PB film) and ultra-stable EC performance of 86.8% after 20,000 cycles (50% after 600 cycles, PB film). Furthermore, the high-intensity light source can be shot clearly by the designed and assembled EC iris device (ECID) with TiO₂/Au/PB film as an EC layer, while the photograph without an ECID is blurry, confirming the feasibility of the material in portable digital products.