Graphene–organic optoelectronics

Graphene, a one-atom–thick form of graphite, has been hailed as a wonder material. Surging at a strong pace, cost-effective printing techniques have already been exploiting graphene phenomenal properties to ultimately develop more complex electronic devices. But for all its promise as a material for well-miniaturised, flexible and transparent devices, further studies into graphene-based hybrid structures with tailor-made properties are required.

Against this backdrop, scientists initiated the EU-funded project 'Graphene supramolecular electronics: A life-long training career development project' (GREAT). The project team sought to tune graphene properties by functionalising them with organic molecules. Compared to pure graphene, such graphene–organic hybrid structures have superior properties, including improved conductivity, charge mobility and mechanical strength.

Scientists designed and optimised low-cost and scalable processes to obtain liquid-phase exfoliated graphene dispersions. Different organic molecules that acted as functional groups were studied and characterised, with alkanes and long aliphatic chain molecules resulting in high-yield production of single-layer graphene.

GREAT employed wet processing techniques to produce dispersions of functionalised graphene, thus obtaining thin hybrid films of approximately 100 nm. By varying the end-groups of the organic molecules used in the exfoliation process, scientists could obtain stimuli-responsive graphene–organic hybrid materials that hold potential for multifunctional electronics.

In particular, photochromic molecules were found to have a great impact on graphene-based optoelectronic switches. Furthermore, in two-terminal device configurations, the electrical properties of thin graphene–azobenzene hybrid films could be reversibly modulated by alternating ultraviolet and visible light irradiation cycles.

GREAT significantly contributed to a molecular-scale understanding of innovating technologies based on organic electronics that could replace those we use today. The developed graphene–organic hybrid systems also hold great promise for light-activated memory switches and high-sensitivity photosensors.