Charge-Transfer-Controlled Growth of Organic Semiconductor Crystals on Graphene

Controlling the growth behavior of organic semiconductors (OSCs) is essential because it determines their optoelectronic properties. In order to accomplish this, graphene templates with electronic-state tunability are used to affect the growth of OSCs by controlling the van der Waals interaction between OSC ad-molecules and graphene. However, in many graphene-molecule systems, the charge transfer between an ad-molecule and a graphene template causes another important interaction. This charge-transfer-induced interaction is never considered in the growth scheme of OSCs. Here, the effects of charge transfer on the formation of graphene-OSC heterostructures are investigated, using fullerene (C₆₀) as a model compound. By in situ electrical doping of a graphene template to suppress the charge transfer between C₆₀ ad-molecules and graphene, the layer-by-layer growth of a C₆₀ film on graphene can be achieved. Under this condition, the graphene-C₆₀ interface is free of Fermi-level pinning; thus, barristors fabricated on the graphene-C₆₀ interface show a nearly ideal Schottky-Mott limit with efficient modulation of the charge-injection barrier. Moreover, the optimized C₆₀ film exhibits a high field-effect electron mobility of 2.5 cm² V^-1 s^-1. These results provide an efficient route to engineering highly efficient optoelectronic graphene-OSC hybrid material applications.