2D Single-Crystalline Molecular Semiconductors with Precise Layer Definition Achieved by Floating-Coffee-Ring-Driven Assembly

2D organic materials with in‐plane van der Waals forces among molecules have unique characteristics that ensure a brilliant future for multifunctional applications. Soluble organic semiconductors can be used to achieve low‐cost and high‐throughput manufacturing of electronic devices. However, achieving solution‐processed 2D single‐crystalline semiconductors with uniform morphology remains a substantial challenge. Here, the fabrication of 2D molecular single‐crystal semiconductors with precise layer definition by using a floating‐coffee‐ring‐driven assembly is presented. In particular, bilayer molecular films exhibit single‐crystalline features with atomic smoothness and high film uniformity over a large area; field‐effect transistors yield average and maximum carrier mobilities of 4.8 and 13.0 cm2 V−1 s−1, respectively. This work demonstrates the strong potential of 2D molecular crystals for low‐cost, large‐area, and high‐performance electronics. The floating‐coffee‐ring‐driven assembly of 2D single‐crystalline molecular semiconductors with precise layer definition is presented. Typical single‐crystalline features, atomic smoothness, and high morphologic uniformity over a large area are achieved. Field‐effect transistors devices yield a maximum carrier mobility of 13.0 cm2 V−1 s−1 and thus show promise for low‐cost, large‐area, and high‐performance electronics.