Continuous and highly ordered organic semiconductor thin films via dip-coating: the critical role of meniscus angle

Dip-coating is a low-cost, high-throughput technique for the deposition of organic semiconductors over large area on various substrates. Tremendous studies have been done and many parameters such as withdrawal speed, solvent type and solution concentration have been investigated. However, most of the depositions were ribbons or dendritic crystals with low coverage of the substrate due to the ignorance of the critical role of dynamic solution-substrate interactions during dip-coating. In this study, meniscus angle (MA) was proposed to quantify the real-time in-situ solution-substrate interactions during dip-coating. By proper surface treatment of the substrate, the value of MA can be tuned and centimeter-sized, continuous and highly ordered organic semiconductor thin films were achieved. The charge transport properties of the continuous thin films were investigated by the construction of organic field-effect transistors. Maximum (average) hole mobility up to 11.9(5.1) cm2 V−1s−1 was obtained. The average mobility was 82% higher than that of ribbon crystals, indicating the high crystallinity of the thin films. Our work reveals the critical role of dynamic solution-substrate interactions during dip-coating. The ability to produce large-area, continuous and highly ordered organic semiconductor thin films by dip-coating could revival the old technique for the application in various optoelectronics.