Influence of Solute Concentration on Meniscus-Guided Coating of Highly Crystalline Organic Thin Films

Meniscus-guided coating methods are a successful approach to precipitate highly crystalline organic thin films at the tip of a receding meniscus. Their optimization nevertheless requires better understanding of the underlying fluid- and thermodynamics. Here, the systematic investigation of the impact of solute concentration is reported on the morphology and electrical characteristics of highly crystalline films of two benchmark organic semiconductors: C-8-BTBT and TIPS-Pentacene. Building on the previous model that predicts the ideal coating speed by balancing substrate motion with solvent evaporation, the approach combines a complete fluid dynamics simulation, including solute transport and precipitation, with a broad set of experimental results. The fluid dynamics modeling confirms that precipitation is strongly enhanced at the tip of the meniscus, regardless of the solute concentration in the bulk of solution. This relative independence explains why the film morphology is little affected by the solute concentration. On the other hand, a rise in concentration results in thicker films. This is rationalized by the mass balance during precipitation. Furthermore, a rise in concentration generally results in films with better electrical characteristics, while the presence of the solute has limited impact on the optimal coating speed that remains close to the ideal balanced speed.