Relative Impression Displacement Governs Morphology and Conductivity in Flexographically Printed Graphite/Carbon Dot Layers on Paper

Owing to its distinctive advantages, roll-to-roll flexographic printing has been widely used for food packaging, newspapers, and magazine production. In recent decades, this mass-production technique has also been utilized for printing electrodes on different substrates for biosensors, transistors, batteries, supercapacitors, and solar cells. The printing process relies on several parameters to achieve well-defined printed features, including printing speed, separation between the printing plate and the substrate, and the rheological properties of the ink. Herein, we investigated the effect of impression roller displacement on the physical and electrical properties of printed graphite/carbon dot layers. Relative impression displacement (RID) describes the displacement of the impression roller from a reference position. It influences the distance between the printing plate cylinder and the impression roller but does not directly represent the distance between them. Interestingly, deteriorated print quality did not necessarily result in poorer electrical conductivity. At small impression displacement (i.e., 48 μm), printing defects such as halo effects, viscous fingering, and ink accumulation in unwanted regions were pronounced, with an average sheet resistance of 168 ± 62 Ω/sq. As the impression displacement increased to 500 μm, the definition and morphological uniformity of the printed layers improved. However, the average sheet resistance increased to 596 ± 116 Ω/sq. This study establishes the relationships between impression displacement, coating morphology, and electrical performance, highlighting the trade-off between improved feature definition and electrical conductivity in flexographically printed conductive layers on paper substrates.