(78b) Fluence (fluid-enhanced crystal engineering) for Controlled Molecular Packing and Morphology in Organic Electronics

Solution coating of organic semiconductors has a great potential for achieving low cost manufacturing of large area and flexible electronics. During the coating process, crystalline thin films of organic semiconductors are usually formed under kinetic conditions driven by the rapid solvent evaporation needed for high-throughput industrial-scale production. Yet, fast crystallization poses challenges to the control of thin film morphology. Two commonly encountered problems are mass-transport-limited crystal growth and uncontrolled nucleation. Both phenomena severely limit the electrical performance of organic semiconductors by introducing randomly distributed grain boundaries and structural defects. To address these challenges, we introduce a new approach, FLUENCE (fluid-enhanced crystal engineering) for controlling morphology of solution printed thin films, wherein both nucleation and crystal growth are controlled by designing the fluid flow of the ink. Specifically, crystal growth is enhanced using micropillar-patterned printing blade to induce recirculation in the ink, and nucleation is controlled by engineering the curvature of the ink meniscus. With FLUENCE, we demonstrate for the first time a fast direct coating of patterned, millimeter-wide, centimeter-long, highly-aligned single-crystalline organic semiconductor thin films. Such a film morphology enabled an unprecedented charge transport behavior.