Adhesive electrochromic WO3 thin films fabricated using a WO3 nanoparticle-based ink

• Aqueous WO 3 nanoparticle (NP)-based electrochromic inks are fabricated. • Polyvinyl alcohol (PVA) is added to WO 3 ink to improve its adhesion to substrates. • Contact angle of the WO 3 NP ink decreases with increasing PVA content. • WO 3 /PVA films exhibit electrochromic properties in visible and infrared ranges. • The WO 3 films with optimal PVA content show high optical switching speeds. Nanotechnology has advanced rapidly in recent years, mainly due to the unique properties of basic elements, which can be tuned by altering their chemical composition and size. Owing to their unique properties, nanoparticles (NPs) are applied in many fields, such as catalysis, electronics, and coatings. In this study, we synthesized a coatable WO 3 NP dispersed ink and aimed to highlight the importance of developing an appropriate design strategy for achieving optimal physicochemical properties of the inks. Polyvinyl alcohol (PVA) was added to the WO 3 NP ink to improve its adhesion to indium tin oxide-coated glass substrates. The contact angle of the inks on the substrate decreased with the addition of PVA, indicating their good wettability. Furthermore, the WO 3 NP films exhibited an excellent transmittance change of 77 % at 633 nm and a coloration efficiency of 35 cm 2 /C. Their optical transmittance in the visible and near-infrared regions varied with the applied voltage, indicating their potential for applications in electrochromic devices and smart windows. Effect of PVA addition on WO 3 film formation