Is it possible to make printed electronics without the use of harmful chemicals? This is what a group of researchers hopes to discover as they construct totally recyclable printed electronics made with water rather than toxic chemicals.
In terms of human health hazards and environmental implications, this study has the potential to open industrial doors to a cleaner future. Printed electronics have traditionally been made by stacking component-bearing layers, but getting them to stay together has proven difficult.
“If you’re making a peanut butter and jelly sandwich, one layer on either slice of bread is easy,” said Dr. Aaron Franklin, a co-author on the paper and an Addy Professor of Electrical and Computer Engineering at Duke University. “However, if you put the jelly down first and then spread the peanut butter on top, forget it; the jelly will not stay put and will mix with the peanut butter.” Putting layers on top of each other is more difficult than putting them down on their own, but it is necessary if you want to manufacture electronic devices using printing.”
This research builds on Dr. Franklin’s and his colleagues’ prior work on recyclable printed electronics. The researchers used insulating nanocellulose, conductive graphene, and semiconducting carbon nanotubes for that task, and it was the carbon nanotubes that proved the most difficult to replace chemicals with water.
While they were successful in preventing the carbon nanotubes from clumping together by using a detergent-like surface-active agent, they later discovered that the ink they created lacked the necessary layer of carbon nanotubes that provided the density to allow high current electrons to travel across them.
“You want the carbon nanotubes to look like al dente spaghetti strewn down on a flat surface,” Dr. Franklin explained. “However, with water-based ink, they appear to have been taken one by one and tossed on a wall to check for doneness.” If we were using chemicals, we could just print numerous passes until we have enough nanotubes. But water isn’t like that. We could repeat it 100 times and still have the same density as the first time.”
This impediment was caused by the surface-active chemical used to prevent clumping of the carbon nanotubes, but it also resulted in a lack of adhesion of supplemental layers on top of the first layer. Traditionally, these surface-active substances have been removed using either extremely high temperatures, which demand a lot of energy, or dangerous chemicals, which pose both human health concerns and environmental problems, but Dr. Franklin and his team wanted to avoid both.
The researchers created a recurrent process in which the printed electronics are rinsed in water, followed by a drying phase using moderately low heat, and then the electronics are printed on again. The crucial discovery was that lowering the supply of surface-active compounds used in inks resulted in fully recyclable, fully functioning, and entirely water-based transistors.
“The performance of our thin-film transistors doesn’t match the best currently being manufactured, but they’re competitive enough to show the research community that we should all be doing more work to make these processes more environmentally friendly,” Dr. Franklin said.
Dr. Franklin believes that the technologies employed in this work might be applied to common electronics such as displays and screens that utilise think-film transistors, as proven in this study. Because present production methods consume vast amounts of energy and dangerous chemicals, the United States Environmental Protection Agency has issued warnings about this practise, which can be seen here.
What new discoveries in printed electronics will researchers make in the coming years and decades, and how might these new approaches benefit both human health and the environment? Only time will tell, which is why we do science!