Biphase Nanocrystalline WO3 Thin Films for Dual-Functional Electrochromic Smart Windows with Long-Term Stability

Electrochromic energy storage devices (EESDs) integrating optical modulation and energy storage are gaining attention for smart building applications. The WO3 thin films with a biphasic nanocrystalline structure were prepared using a facile solution-based method and a low-temperature scalable blade-coating technology. Combined with zinc as the counter electrode, the WO3–Zn EESDs utilizes the redox reactions of WO3 and Zn to achieve dual functionality of energy storage and electrochromism. The structure with biphasic nanocrystals embedded in the amorphous WO3 matrix strengthens the electrochemical activity and structural stability of the film, thereby improving the optical performance and cycling stability of the device. The device exhibits a 76% optical modulation at 633 nm, a high areal capacity of 106.8 mAh m–2 at 0.1 A m–2, and exceptional cycling stability, retaining 90.8% of optical modulation after 5000 cycles. These findings highlight the potential of WO3–Zn EESDs for sustainable energy systems and multifunctional smart window applications.