Impact of the Ink Formulation and Coating Speed on the Polymorphism and Morphology of a Solution-Sheared Thin Film of a Blended Organic Semiconductor

Despite the recent encouraging advances in achieving high-performance organic field effect transistors employing meniscus-guided processing techniques compatible with roll-to-roll manufacturing, there is still a very limited knowledge about how all the coating parameters influence the thin film electrical characteristics. Here, the polymorphism and morphology of thin films of the organic semiconductor dibenzo-tetrathiafulvalene blended with polystyrene deposited by bar-assisted meniscus shearing (BAMS) are investigated in-depth by modifying the coating speed and ink formulation. It is found that all these parameters significantly affect the crystallization process and the resulting thin film characteristics. Remarkably, pure polymorphs with optimized field-effect mobilities can be achieved only within a narrow range of conditions. The precise control of the film morphology and crystal structure is of paramount importance in order to move toward real applications achieving high device-to-device reproducibility.