A Micron‐Scale K 2 V 6 O 16 ·1.5H 2 O‐Based Aqueous Ink for Inkjet‐Printed Large‐Area Multicolor Electrochromic Displays

ABSTRACT Inkjet printing offers a promising non‐contact route toward high‐throughput, large‐area manufacturing of functional films for next‐generation optoelectronic devices. However, the broader adoption in continuous production lines is hindered by the coffee‐ring effect that compromises film uniformity. Additionally, existing printable inks rely predominantly on nanoscale particles (<100 nm), which constrains material selection. Herein, we developed a green aqueous ink based on microscale K 2 V 6 O 16 ·1.5H 2 O (KVO) and a water/1,2‐propylene glycol (1,2‐PG) cosolvent system. The optimized ink exhibits excellent rheological properties for stable ejection, even with micron‐sized particles. Critically, the 1,2‐PG effectively inhibits the coffee‐ring effect by reducing the surface tension, allowing uniform deposition of large particles without the use of insulating surfactants. Therefore, a continuously patterned electrochromic film can be directly printed, which exhibits reversible multicolor transitions and remarkable cycling stability. Furthermore, we assembled a large‐scale electrochromic device (21.0 × 29.7 cm 2 ) with a complex pattern based on the printed KVO film, which demonstrates uniform and reversible color changes across the active area. Our ink formulation offers a green, surfactant‐free alternative to traditional electrochromic inks and demonstrates that large‐sized functional particles can be uniformly printed via synergistic Marangoni flow and viscosity control, expanding the material scope for inkjet‐printed electrochromic devices.