Microstructured Ultrathin Organic Semiconductor Film via Dip-Coating: Precise Assembly and Diverse Applications

ConspectusOrganic semiconductors (OSCs) have led to considerable progress in various fields owing to their intrinsic flexibility, adjustable chemical structures, multifunctionalities, and low processing cost. The optoelectronic properties of OSCs greatly depend on their aggregation state in molecular assemblies. To obtain ideal and reliable optoelectronic performances, a highly controlled assembly method for modulating OSC packing structures is indispensable. In particular, ultrathin OSC microstructures consisting of one to several molecular layers, known as microstructured ultrathin organic semiconductor films (MUOSFs), are of great importance for both fundamental research and applications of OSCs. However, most reported film thicknesses or molecular layer numbers of ultrathin OSC films/microstructures are "average values" rather than "real values" and are not molecularly precise. The lack of an effective and general assembly strategy seriously hinders the progress of MUOSFs. In this Account, we summarize our recent progress in exploring the assembly strategy, the underlying mechanism, and diverse applications of MUOSFs prepared via dip-coating under optimized conditions.Dip-coating, with an intrinsic three-phase contact line, has a great advantage to precisely assemble ultrathin OSC films/microstructures. As an evaporation-controlled method, the assembly processes used in dip-coating are susceptible to multiple factors, such as pulling speed, molecular structures, and solution properties. Under the guidance of our proposed "Balance Principle" for adjusting these factors, uniform and continuous MUOSFs can be obtained over a large area. Under optimized conditions, the number of molecular layers of MUOSFs can be customized with monolayer precision, which is significant for investigating the charge transport mechanism of OSCs. At the same time, the ultrathin and partial coverage characteristics of MUOSFs are beneficial to fabricate flexible and transparent devices for wearable electronics. Notably, the morphologies and coverage of ultrathin microstripes can be well tuned by the pulling speed, which is highly desired for high-performance bio/chemical sensors, because the large specific surface area provides abundant reactive sites.The feasibility and generality of our assembly method demonstrate that dip-coated MUOSFs have excellent advantages for fundamental research and applications of OSC materials, based on which many promising future works around MUOSFs can be extended to more related fields by engineering molecular orientations, packing structures, film morphologies, coverage, etc. The work on the assembly and applications of MUOSFs might offer the potential to promote the progress of organic electronics.