The performance of organic semiconductor thin films in electronic devices is related to their crystal structure and morphology, with charge transport mobility dependent on the degree of crystallinity and on the crystallographic orientation. Here organic molecular beam deposition of vanadyl phthalocyanine is studied on graphene and it is shown that crystalline grains up to several micrometers across can be formed at substrate temperatures of 155 °C, compared to room temperature grain sizes of ≈30 nm. The effect on charge transport is probed by conducting atomic force microscopy, with the high temperature films on graphene showing increased mobility and uniformity and decreased trap density. These results illustrate an important advantage for the integration of graphene electrodes with organic semiconductor devices: the homogeneous surface of graphene results in high diffusion and low nucleation rates for thin film growth, encouraging the formation of highly crystalline films even with nonepitaxial growth.

"Growth of large crystalline grains of vanadyl-phthalocyanine without epitaxy on graphene"

A. J. Marsden, L. A. Rochford, D. Wood, A. J. Ramadan, Z. P. L Laker, T. S. Jones and N. R Wilson

http://onlinelibrary.wiley.com/doi/10.1002/adfm.201503594/full