May 24, 2013   //   by admin   //   Small Grants

Inkjet printing of graphene and 2D materials: a new platform for cheap, flexible and transparent electronics

Researchers at the University of Cambridge have developed solution processable graphene functional inks for printed and large area electronics applications.

The team, which includes Dr Tawfique Hasan, Felice Torrisi and Prof Andrea Ferrari of Cambridge Graphene Centre recently produced a graphene-based ink by liquid phase exfoliation of graphite in water and organic solvents.

As the active component of a next-generation ink, graphene has an interesting set of properties. The ink can be used to print thin film transistors (TFT) as well as transparent and conductive patterns with sufficient mobilities and conductivity to pave the way for all-printed, flexible and transparent graphene devices on low-cost substrates such as plastic film and paper. The aim is to develop a portfolio of graphene-based inks for printable electronics.

There are other graphene-like layered materials with equally interesting but complementary electronic and optoelectronic properties, for example molybdenum disulphide (MoS2), with high mobility yet controllable band gaps for high ON/OFF ratio TFTs. With Small Grant funds provided by CIKC Hasan’s research team invested in an inkjet printer to take the very first, yet crucial, steps in its effort to develop a portfolio of inks with semiconducting, metallic and insulating properties for next generation printable electronics. Local product designer and specialist printed electronics company Novalia Ltd is now working with the team to validate the inks by printing them using industrial printing machines.

‘We have been able to successfully create a fully operational early-stage demonstrator using the basic, dispersed graphene inks developed at the University of Cambridge, with the support of CIKC funding,’ confirms Chris Jones of Novalia. The demonstrator in question is a printed image of a piano that can create sound when the keys are touched.

The team has filed a patent through Cambridge Enterprise to protect its work in the field of graphene and other layered material inks and their printing processes, and is now discussing routes to commercialisation. ‘The process to make the ink is scalable and can be fine-tuned to adjust the properties according to application specific needs,’ explains Torrisi. By the end of this year the goal is to produce 3 litres per day for R&D work and standardization. The inks are cheap and have superior stability and electronic properties compared to existing organic polymers. The team is also focusing on large-area, economic coating of these inks and estimate that it will be possible to produce a flexible transparent conductive film of graphene flake on polyethylene terephthalate (PET) at below £10 per square metre using current technology with plenty of opportunity to reduce this further in the future.

Developing conductive inks based on graphene that are compatible with commercial print processes, such as flexo, gravure and offset litho will require further work. However, as graphene is made from a widely available raw material, it has the appealing potential to significantly reduce the cost of conductive inks, which are currently made from precious metals, such as silver, and therefore carry a high price tag, even in large volumes.

‘Such a potentially inexpensive graphene-based functional ink, would benefit both the large-area electronics industry and the conventional printing sector in the coming years as printed electronics finds its place in mainstream applications,’ explains Jones.

‘CIKC has helped to accelerate the pace of research in what is a very fast-moving field, globally. We already had the knowledge to make the inks but it was important to be able to get the printer to produce consistent results to standardize the ink production and printing process. It also enabled us to fabricate demonstrators,’ says Hasan, who is a Royal Academy of Engineering Research Fellow.