Water‐Surface Drag Coating: A New Route Toward High‐Quality Conjugated Small‐Molecule Thin Films with Enhanced Charge Transport Properties

Abstract Electronic properties of organic semiconductor (OSC) thin films are largely determined by their morphologies and crystallinities. However, solution‐processed conjugated small‐molecule OSC thin films usually exhibit abundant grain boundaries and impure grain orientations because of complex fluid dynamics during solution coating. Here, a novel methodology, water‐surface drag coating, is demonstrated to fabricate high‐quality OSC thin films with greatly enhanced charge transport properties. This method utilizes the water surface to alter the evaporation dynamics of solution to enlarge the grain size, and a unique drag‐coating process to achieve the unidirectional growth of organic crystals. Using 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene (Dif‐TES‐ADT) as an example, thin films with millimeter‐sized single‐crystal domains and pure crystallographic orientations are achieved, revealing a significant enhancement (4.7 times) of carrier mobility. More importantly, the resulting film can be directly transferred onto any desired flexible substrates, and flexible transistors based on the Dif‐TES‐ADT thin films show a mobility as high as 16.1 cm² V⁻¹ s⁻¹, which represents the highest mobility value for the flexible transistors reported thus far. The method is general for the growth of various high‐quality OSC thin films, thus opening up opportunities for high‐performance organic flexible electronics.