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Organic single crystals with low defect density are key functional materials for next‐generation electronics. Classical crystallization commonly results in a high density of molecular steps, which are defects that can trap charge carriers and reduce the mobility of organic semiconductors. Herein, a novel nonclassical crystallization mechanism involving nucleation, fusion, and growth is designed. The introduction of the fusion stage changes the crystal growth mode from three‐dimensional island growth to two‐dimensional layer‐by‐layer growth and leads to large‐area two‐dimensional molecular crystals with almost no molecular steps. Therefore, the average mobility is observed to improve from 1.26 to 2.07 cm2 V−1 s−1. The nonclassical crystallization mechanism paves the way for atomically flat single crystals to probe the intrinsic optoelectronic properties of organic semiconductors. [ABSTRACT FROM AUTHOR]

A novel strategy for the growth of molecularly thin two-dimensional molecular crystals (2DMCs) of organic semiconductors with poor solubility was developed. Large-area bilayer 2DMCs were grown on a liquid surface at elevated temperatures, with record mobility and superior photoresponse. [ABSTRACT FROM AUTHOR]

Two‐dimensional molecular crystals (2DMCs) open a new door for the controllable growth of 2D materials by molecular design with a energy gap and solution processability. However, the growth of 2DMCs with defined molecular layers remains full of challenges. Herein, we report a novel method to produce various 2DMCs with a defined number of molecular layers. When the surface tension and viscosity are tuned to control the spreading of the solution on the liquid surface, large‐area quasi‐freestanding 2DMCs from bulk size down to the monolayer limit are obtained, which makes it possible to probe the intrinsic layer‐dependent optoelectronic properties of organic semiconductors down to the physical limit, and paves the way for the application of 2DMCs in new optoelectronic devices and technologies. [ABSTRACT FROM AUTHOR]

Innenrücktitelbild: Layer-Defining Strategy to Grow Two-Dimensional Molecular Crystals on a Liquid Surface down to the Monolayer Limit (Angew. Chem. 45/2019) Keywords: Grenzflächen; Organische Elektronik; Organische Halbleiter; Organische Kristalle; Photodetektoren. [Extracted from the article]