Bismuth-Doped Crystalline/Amorphous WO₃ Composite Film: Superior Electrochromic Performance and Structure Evolution

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• Tungsten trioxide (WO₃) is a key material for electrochromic smart glass.
• Improving the performance and stability of WO₃-based devices is crucial for practical applications.

Purpose of the Study:

• To synthesize and characterize bismuth-doped WO₃ (Bi-WO₃) nanoparticle composite films using a two-step sol-gel method.
• To investigate the electrochromic properties and long-term stability of the designed composite films.
• To understand the phase transformation and morphological evolution during electrochromic cycling and its impact on performance.

Main Methods:

• Two-step sol-gel synthesis of crystalline/amorphous Bi-WO₃ nanoparticle composite films.
• Characterization of electrochromic performance, including optical modulation, switching times, and coloration efficiency.
• Analysis of structural and morphological changes during continuous electrochromic cycling.

Main Results:

• The Bi-WO₃ composite films exhibited high optical modulation (82.7%), rapid switching (2.1s coloring, 2.0s bleaching), and excellent coloration efficiency (102.23 cm²/C).
• Remarkable cycling stability was achieved, retaining 84.5% of initial modulation after 10,200 cycles.
• Phase transformation from amorphous to orthorhombic WO₃·H₂O and morphological changes to anisotropic nanosheets were observed during degradation, but reversible proton behavior in amorphous Bi-WO₃ mitigated irreversible trapping.

Conclusions:

• The synergistic effect between amorphous and crystalline Bi-WO₃ layers and their interface engineering significantly enhances electrochromic performance and stability.
• The study provides an effective strategy for developing high-performance WO₃-based electrochromic materials.
• Insights into degradation mechanisms offer guidance for designing next-generation smart optical devices.