Gel‐Switchable Droplet Front for Large‐Scale Uniformity of Inkjet Printed Silver Patterns

Abstract Attempts at achieving uniform deposits by drop drying are crucial in inkjet printed electronics, since homogeneous surface profiles of solution processed films are frustrated by the ubiquitous coffee ring effect. However, the majority of research on the final shape has been conducted for only dots and narrow lines, as it remains a big challenge to regulate the flows between droplets. Here, a facile and green way to achieve excellent uniformity of inkjet printed film on large scale (8 cm × 8 cm) is shown, by developing a simple but novel gel ink, which contains only small molecule components, but boasts advantages in printability, filming, and low‐temperature processing properties. Fast evaporation, high‐concentration metal coordination, and enhanced Marangoni flow all contribute to rapid sol (printing) to gel (filming) transition process, leading to the formation of gel‐switchable front of each droplet (≈10 pL) within the deposition delay, which suppresses flows during droplet coalescence with eliminated boundaries. The resulting silver nanoparticle film is optimized (140 °C, 30 min) to have a low resistivity of 6.42 × 10⁻⁸ Ω m and a surface fluctuation of 15 nm, which is extremely flat with respect to each undulation span of 35 µm (Δh/ΔL ≈ 3/7000).