Inkjet-printed graphene electrodes may lead to low-cost, large-area, possibly foldable devices

Apr 24, 2013 by Lisa Zyga feature
A vial of the new graphene ink, which contains nanometer-sized graphene flakes. The ink is highly conductive and has excellent morphology, enabling it to be used to print electrodes. Credit: Ethan B. Secor, et al. ©2013 American Chemical Society

(Phys.org) —Using an ink containing tiny graphene flakes, scientists have inkjet-printed graphene patterns that can be used for printing finely detailed, highly conductive electrodes. Although inkjet-printed graphene has been previously demonstrated, the graphene patterns printed in the new study are about 250 times more conductive than previous patterns. The printed graphene ink is also highly tolerant to bending stresses, with the ability to withstand folding with only a slight decrease in conductivity.

The researchers, Ethan B. Secor, et al., at Northwestern University in Evanston, Illinois, have published their study on inkjet-printing graphene patterns in a recent issue of The Journal of Physical Chemistry Letters.

As the researchers explain, inkjet printing is an attractive method for printing because it is low-cost, can print large areas, and can print on . Researchers have previously used inkjet printing to fabricate a variety of components such as , , , and . However, printing highly conductive electrodes is still a challenge because of the requirement for very fine resolution. Recently, researchers have turned to graphene due to its high conductivity, , and intrinsic flexibility compared to other inks, hoping that graphene-based inks could be used for printing electrodes.

One of the most important steps in printing with graphene ink is obtaining a large amount of graphene. There are several methods for mass-producing graphene, but the one with advantages for inkjet printing is exfoliation—or the breaking apart—of other materials such as or reduced graphene oxide (RGO) to produce graphene flakes. Previous studies have demonstrated inkjet printing of exfoliated RGO flakes for electrodes, sensors, and other applications. However, the of RGO flakes, which contain carbon, oxygen, and , are inferior to the properties of pristine graphene flakes, which contain only carbon atoms.

The methods currently used to produce pristine graphene through exfoliation have encountered a few challenges. The process typically requires solvents and surfactants that leave residues on the graphene, which decreases its conductivity. Another problem is that, while small graphene flakes are necessary for stable printing, they increase the number of flake-to-flake junctions, which also decreases conductivity.

Inkjet-printed graphene electrodes may lead to low-cost, large-area, possibly foldable devices
A flexible substrate printed with graphene ink in (top) the unfolded state and (bottom) the folded state. The device can be folded with only a slight decrease in conductivity. Credit: Ethan B. Secor, et al. ©2013 American Chemical Society

In the new study, the scientists developed a new approach that overcomes these problems. The new room-temperature process uses ethanol as a solvent and ethyl cellulose as a stabilizing polymer, neither of which leaves a residue. This method produces high yields of a black powder with a graphene content of 15%, which is higher than most previous methods. The graphene flakes in the powder have thicknesses of about 2 nm and areas of about 50 x 50 nm2. Although such a small flake size results in numerous flake-to-flake junctions, the ethyl cellulose stabilizing polymer reduces the resistance between flakes better than other surfactants.

The researchers then dispersed the black powder into a solvent to create a fluid ink that can be used for printing. They demonstrated inkjet printing with the graphene-based ink and found that the ink's excellent morphology and conductivity enabled printing of precise patterns suitable for printing . The researchers could also print multiple layers of ink while maintaining uniform patterns, with each layer adding about 14 nm to the thickness.

The researchers assessed the printed ink's mechanical properties by printing lines on flexible polyimide substrates. They found that the ink's conductivity remained virtually unchanged even at high bending radiuses of less than 1 mm, even though the substrate began to crack. Even when the researchers folded a substrate with printed features, the ink showed only a 5% decrease in conductivity that can likely be attributed to substrate cracking rather than damage to the ink itself. The mechanical tests suggest that graphene inks may be used to create foldable electronic devices in the future.

"Essentially all electronic devices and circuits required high- and high-resolution electrical contacts and interconnects," coauthor Mark Hersam, a professor of Materials Science and Engineering at Northwestern University, told Phys.org. "Therefore, our graphene inks have the potential to impact a wide range of applications, especially printed electronics, flexible electronics, and foldable electronics. Example downstream applications for these types of electronic devices include smartphones, tablets, flat panel displays, and photovoltaics."

In the future, the researchers plan to work on applying the new graphene ink to these kinds of applications.

"Thus far, we have achieved the graphen ink development and characterization," Hersam said. "On the other hand, our future research will focus on integrating our printed graphene inks into fully fabricated electronic devices and circuits including the downstream applications listed above. In this manner, we can fully exploit our fundamental research advances for real-world technology."

Explore further: Mirror-image forms of corannulene molecules could lead to exciting new possibilities in nanotechnology

More information: Ethan B. Secor, et al. "Inkjet Printing of High Conductivity, Flexible Graphene Patterns." The Journal of Physical Chemistry Letters. DOI: 10.1021/jz400644c

Journal reference: Journal of Physical Chemistry Letters search and more info website

4.3 /5 (17 votes)

Related Stories

Scientists produce graphene using microorganisms

Mar 22, 2012

The Graphene Research Group at Toyohashi University of Technology (Japan) reports on the synthesis of graphene by reducing graphene oxide using microorganisms extracted from a local river.

New generation of flexible graphene transistors

Mar 15, 2012

Making electronic components using graphene, a material composed of a single layer of carbon atoms, is one of today's major technological challenges. Researchers hope to harness the outstanding electron mobility ...

Recommended for you

Tiny graphene drum could form future quantum memory

Aug 28, 2014

Scientists from TU Delft's Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential ...

Graphene reinvents the future

Aug 27, 2014

For many scientists, the discovery of one-atom-thick sheets of graphene is hugely significant, something with the potential to affect just about every aspect of human activity and endeavour.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

FastEddy
1 / 5 (6) Apr 25, 2013
What might seem at first glance to be inherently obvious, still a worthy article/information. And the processes are clearly outlined. It would be nice to know the details of the results: Thick-by-wide printed pathways = resistance per meter? Two layers = half resistance? ... Still searching for the "Perfect Conductor".