Marangoni Flow Control Framework for Uniform Thin-Film Formation in Inkjet-Printed Light-Emitting Devices

Uniform thin-film formation in solution-processed materials is governed by evaporation-driven internal flow during drying. Among these flows, capillary-driven coffee-ring formation is relatively well understood, whereas Marangoni flow remains difficult to control and insufficiently understood. In inkjet-printed light-emitting devices, where film uniformity directly determines pixel-level optical performance, uncontrolled internal flow poses a critical challenge. Here, we present an integrated ink-process framework that enables guided control of solutal Marangoni flow tendency through the combined design of ternary solvent systems and vacuum drying. A simplified analytical model based on Raoult's law and the ideal gas law was developed to estimate solvent evaporation dynamics and surface tension evolution. By systematically exploring combinations of boiling points and surface tensions, four representative Marangoni flow modes are identified: strong inward flow, strong outward flow, inward-to-outward transition, and outward-to-inward transition. Pixel morphology exhibited clear correlations with these estimated flow tendencies, consistent with the simplified analytical estimation and supported by interferometric surface profiling. Optimized ink design exhibiting an outward-to-inward Marangoni flow tendency produced highly uniform emission layers, resulting in a 22-fold enhancement in current efficiency and external quantum efficiency compared to uncontrolled devices. These findings demonstrate that rational regulation of Marangoni-driven film formation through solvent system design under vacuum drying enables high-performance inkjet-printed optoelectronic devices.