Abstract : Water-enriched tungsten oxide (We-WO₃), synthesized via extended ultrasonication and electrochemical deposition, showed multifunctionality in electrochromic (EC) device and energy storage system. As an EC film, it achieved 73.6% optical contrast, 3.3 s coloration time, and 93.1 cm²/C coloration efficiency. Meanwhile, We-WO3 exhibited a charge transfer resistance of 20.5 Ω, a reasonable capacitance of 35.6 mF/cm², and capacitance retention of 78.4%. Water enrichment improved particle dispersion, altered its morphology, and intensified the Li⁺ ion activity. Integrated with a quantum-dot-sensitized solar cell (QDSSC), the We-WO₃ EC film functioned effectively without an external power source using the QDSSC’s 0.56 V open-circuit voltage.