Role of Meniscus Shape on Crystallization of Molecular Semiconductors and Fluid Dynamics During Meniscus-Guided Coating

Meniscus-guided coating (MGC) is a promising method that offers predictable fabrication of highly crystalline thin films. For the integration of molecular semiconductors into large-area electronic devices with high efficiency and reliability, homogeneous and highly ordered film morphologies are required. The solution processing of such defect-free film structures requires comprehensive understanding of the complex relationship between molecular crystallization, fluid dynamics, and meniscus shape. In this work, the role of the meniscus shape on fluid dynamics in the coating bead and the crystallization process of the low molecular weight semiconductor 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) during zone-casting is systematically investigated. Depending on meniscus shape and coating velocity, four morphological subregimes are found: stick-slip morphology, unidirectional homogenous crystal stripes, spherulitic morphology, and directional branched morphology; of which the second exhibits the highest crystallinity with a reduced trap density in the thin film, resulting in improved saturation and effective mobilities in field-effect transistors (FET). Numerical simulation of fluid dynamics explains the observed morphological trends, which are correlated with the electrical behavior of the devices. This work provides a fundamental basis for upscaling MGC methods for the application of functional thin films. Here, the role of meniscus shape on the morphology and charge transport behavior of organic semiconductors is investigated using meniscus-guided coating. By varying the height of the meniscus and the substrate velocity, four different morphologies are obtained: I) stick-slip, II) unidirectional, III) spherulite, and IV) directional branching morphologies. Among these, type II showed the highest performance in field-effect transistors.image