NanoGraphInk is a Marie-Curie project focused on graphene-based inks/pastes for printed electronics.

The market of printed electronics is based on Ag inks/pastes. However, Ag can be expensive. Ag nanoparticles have poor adhesion, while other Ag forms, such as nanowires or flakes have further processing difficulties and surface roughness. Printed Cu develops an insulating oxide layer, while other metals, carbon or polymers have average conductivity. Graphene has good conductivity and is emerging as potential Ag substitute for printed electronics, to be used in wearable devices, e-paper, roll-up portable or/and transparent displays, etc.

The overall objective of NanoGraphInk was the development of fully applicable and viable conductive nano-hybrid graphene-based inks and pastes for printable applications and device fabrication.

NanoGraphInk focused on two main methods, i.e. sonication and microfluidization, to develop stable graphene-based inks and pastes. Graphite was used as precursor, aiming at highly conductive inks by limiting non-conductive additives and stabilizers. Sonication was used to produce inks with polyhydroxylated fullerenes (fullerenols) as stabilizers, enabling over 6 months stability. These inks were used for inkjet printing and spray coating. Printed patterns were produced with sheet resistance down to 15 Ohm/sq for few hundred nm films. Microfluidization was used to prepare pastes stable for at least 20 months. These were used to print highly conductive patterns by screen and flexo printing or blade coating, with sheet resistance values of as low as 2-3 Ohm/sq for 20-25 micrometer films, at room temperature, avoiding heat treatments. This, along with the compatibility of the paste with perovskites, enabled their use in perovskite solar cells with good stability and cell efficiency.

The advantages of the graphene paste include scalability of production, low-cost compared to Ag, ease of applicability on large areas, stability, high conductivity without annealing, environmental friendliness, and compatibility with perovskites. These were used in stable perovskite solar cells with good efficiency, and low-cost compared to Si-based solar cells. This makes such inks ideally suited for exploitation, with potential for commercialization of the graphene-based paste or devices. This may create new jobs, promote innovation and entrepreneurship and open new markets for printed electronics.