Templating Highly Crystalline Organic Semiconductors Using Atomic Membranes of Graphene at the Anode/Organic...

Charge and energy transport in organic semiconductors is highly anisotropic and dependent on crystalline ordering. Here, we demonstrate a novel approach for ordering crystalline organic semiconductors, with orientations optimized for optoelectronics applications, by using a single monolayer of graphene as a molecular template. We show, in particular, that large-area graphene can be integrated on metals and oxides to modify their surface energies and used to template copper phthalocyanine (CuPc), a prototypical organic semiconductor. On unmodified substrates, thermally evaporated films of CuPc are small-grained, and the molecules are in the "standing-up" (100) orientation. On graphene modified substrates, CuPc is templated in favorable "lying-down" (112̅) and (012̅) orientations with drastically larger crystal sizes. This results in an 86% increase in the absorption coefficient at 700 nm and should furthermore result in enhanced energy and charge transport. The use of highly conductive and transparent (>95%) graphene membranes as templates is expected to be a foundation for developing future planar and nanostructured organic light-emitting diodes and organic photovoltaics with improved performance.