Using a Flexible Fountain Pen to Directly Write Organic Semiconductor Patterns with Crystallization Regulated by the Precursor Film

Abstract Organic semiconductor (OSC) films fabricated by meniscus‐guided coating (MGC) methods are suitable for cost‐effective and flexible electronics. However, achieving crystalline thin films by MGC methods is still challenging because the nucleation and crystal growth processes are influenced by the intertwined interactions among solvent evaporation, stochastic nucleation, and the fluid flow instabilities. Herein, a novel flexible fountain pen with active ink supply is designed and used to print OSCs. This direct‐write method allows the flexible pen tip to contact the substrate, maintaining a robust meniscus by eliminating the gap found in conventional MGCs. An in situ optical microscopy observation system shows that the precursor film plays a critical role on the crystallization and the formation of coffee rings and dendrites. The computational fluid dynamics simulations demonstrate that the microstructure of the pen promotes extensional flows, facilitating mass transport and crystal alignment. Highly‐aligned ribbon‐shaped crystals of a small organic molecule (TIPS‐pentacene), as well as a semiconducting polymer (N2200) with highly‐ordered orientations, have been successfully printed by the flexible fountain pen. Organic field‐effect transistors based on the flexible pen printed OSCs exhibit high performances and strong anisotropic mobility. In addition, the flexible fountain pen is expandable for printing multiple lines or large‐area films.