A Micron-Scale K₂V₆O₁₆·1.5H₂O-Based Aqueous Ink for Inkjet-Printed Large-Area Multicolor Electrochromic Displays

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 K₂V₆O₁₆·1.5H₂O (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 cm²) 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.