Roll-to-Roll Fabrication of Large-Area Electrochromic WO3 Films via Slot-Die Coating and Intense Pulsed Light...

Electrochromic tungsten oxide (WO3) films are promising candidates for flexible smart window applications. However, realizing large-area WO3-based electrochromic devices fabricated by low-temperature solution processing remains challenging. Here, we report a roll-to-roll (R2R)-compatible strategy for the fast fabrication of electrochromic WO3 films by synergistically combining an ultrafast intense pulsed light (IPL) process with trace Pt additives acting as light absorbers. Pt-incorporated WO3 (WO3-Pt) films were coated onto flexible substrates and subsequently treated within 10 ms using intense broadband irradiation from a xenon flash lamp. Structural, optical and chemical analyses indicate that the IPL process promotes the photothermal modification of WO3, while the Pt additive significantly enhances photothermal heating efficiency and electronic conductivity of the WO3 films. When integrated into electrochromic devices, the IPL-treated WO3-Pt (WO3-Pt-IPL) films exhibit high optical contrast, accelerated switching kinetics, and enhanced cycling stability compared to bare and IPL-treated WO3 films without Pt. The electrochromic device based on WO3-Pt-IPL film exhibited the highest optical contrast of 61.5% at 550 nm and a coloration efficiency (CE) of 139 cm2 C-1, whereas the devices based on bare WO3, WO3-Pt, and WO3-IPL films showed lower optical contrast values of 55.5%, 59.7%, and 59.3%, respectively, with CE values of around 80 cm2 C-1. In addition, the WO3-Pt-IPL device maintained nearly constant bleached and colored transmittance over 1500 cycles, demonstrating markedly improved cycling stability compared with the other device configurations. We further demonstrate large-area fabrication of WO3 films via R2R slot-die coating combined with IPL processing, achieving excellent spatial uniformity. This approach enables energy-efficient and scalable production of flexible metal oxide films and provides a feasible pathway for tuning charge transport and electrochromic properties in electrochromic materials.