Mechanics-Guided Layer-by-Layer Transfer of Molecular Bilayer Semiconductors

Layer-controlled organic thin films are essential components of organic electronic devices. Although layer-transfer methods are effective for device prototyping, managing crack formation during this process is challenging. In this study, we investigate the fracture mechanics of bilayer-type organic semiconductor (OSC) films as a model for developing a crack-suppressed transfer methodology. We find that crack formation is strongly dependent on film thickness and is suppressed when the film is reduced to a single molecular bilayer (SMB) thickness. The observed crack directionality in thick films is clearly correlated with the crystallographic orientation. These fracture behaviors can be qualitatively explained by combining a macroscopic elasticity model with calculations of intermolecular interaction energies. Based on this understanding, we successfully fabricate highly ordered multilayered artificial lattices through sequential SMB transfers. Furthermore, by expanding the π-electron core to tune intermolecular interactions, we achieve the direct patterning of OSC films, even on lyophobic substrates, providing a suitable interface for organic thin-film transistors (OTFTs). OTFTs incorporating crack-suppressed SMBs exhibit sharp on/off switching with a subthreshold swing of less than 150 mV dec-1 and a relatively high device mobility exceeding 5 cm2 V-1 s-1. These findings pave the way for molecular layer engineering for surface tailoring and organic device manufacturing.