In situ carbothermal reduction of oxygen vacancies in monoclinic WO3-x film for dual-band electrochromic windows

Dual-band electrochromic windows have emerged as a promising approach to reduce building energy consumption. However, developing facile and effective method for preparing single-component dual-band electrochromic material remains a challenge. Herein, an in situ carbothermal reduction strategy was utilized to fabricate monoclinic oxygen-deficient tungsten oxide (WO3-x) for high-performance dual-band electrochromism. Polyvinylpyrrolidone (PVP–K90) underwent transformation into amorphous carbon at high temperature, serving as the reducing agent embedded in the tungsten oxide film, and in situ inducing the formation of oxygen vacancies during annealing treatment. Lastly, the amorphous carbon was gasified without weakening the transmittance of WO3-x film. The content of oxygen vacancies in WO3-x could be modulated by controlling the added amount of PVP-K90. The intrinsic generation of oxygen vacancies not only obtained a strong local surface plasmon resonance (LSPR) absorption in near-infrared (NIR) range, but also improved lithium ion (Li+) diffusion in WO3-x film. The WO3-x electrochromic film exhibited excellent dual-band electrochromic performance in optical modulation, switching time, coloring efficiency, bistability, and cycle stability. Furthermore, the WO3-x film was applied to electrochromic window to verify its available regulation in solar illumination and heat, indicating that the designed modification strategy has potential for developing a single-component dual-band electrochromic window with outstanding performance.