Interface-Mediated Self-Assembly in Inkjet Printing of Single-Crystal Organic Semiconductor Films

Abstract

Recent reports have demonstrated that printing processes are more suitable for producing high-performance organic thin-film transistors (OTFTs) than vacuum processes, although the formation mechanism of solution-based films is not yet understood. Here, we use molecular dynamics simulations to show that prototypical solution-processable organic semiconductors (OSCs) form a temporal lyotropic liquid-crystalline (LLC) molecular layer at the air–liquid interface of the semiconductor solution, which subsequently serves as a versatile precursor to the growth of a single-crystalline film. The molecules exhibit spontaneous alignments of the molecular long axes to form a molecular layer that is parallel to the air–liquid interface, whereas alignment with the short axes is not observed and the molecules move diffusively within the layer. The onset of short-axis orientational and positional ordering was observed in the later stage of film growth. Our findings provide evidence that unique way of film growth occurs via stepwise order formation in solution-processed OSCs allowing the nonepitaxial growth of extremely large-area single-crystal films.