Nonclassical Growth of Atomically Flat Two-Dimensional Organic Single Crystals on a Liquid Surface through Fusion

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 cm(2) 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.