A simple dip-coating approach to enhance the electrochromic performance of WO3 thin film by doping carbon quantum dots

As a typical electrochromic material, WO 3 has been extensively studied due to its exceptional photoelectric properties. However, like most transition metal oxides, it suffers from intrinsic limitations, including low conductivity and slow response kinetics. Since conventional carbon quantum dots (CQDs) doping methods often alter the surface and internal structure of WO 3 films, this study employs an impregnation method to introduce CQDs into WO 3 films by post-treatment method, thereby avoiding the structural damage caused by traditional doping approaches. This method not only preserves the original microstructure of WO 3 but also significantly enhances the electrochromic performance (e.g., response speed, optical contrast, and cycling stability) by leveraging the high conductivity and unique optical properties of CQDs. This mild and efficient doping strategy offers new insights for optimizing the performance of other transition metal oxide materials. By precisely controlling the CQDs doping concentration (0.05 wt%), a high-performance WO 3 -CQDs-2 composite film was successfully fabricated. This film exhibits outstanding performance across multiple key metrics: a high areal charge capacity (39.8 mC cm −2 ), a remarkable optical modulation range (ΔT = 72.7 %), fast response times (2.3 s/3.4 s), and excellent cycling stability (retaining 93.2 % of initial performance after 2000 cycles). Additionally, the film's bandgap was narrowed by 0.21 eV, further confirming improved charge transport properties. This comprehensive performance enhancement provides a reliable material foundation for the practical application of electrochromic devices.