Transparent nanopaper could make foldable smartphones

Conductive, transparent paper could soon be used for foldable computers, transparent touchscreens, or digital camouflage clothing, according to a paper published today.

The review, which appears in the journal Science and Technology of Advanced Materials, notes the promising field of cellulose-based electronics. “With widespread and intensive efforts, low-cost and light-weight ‘green’ electronics fabricated on transparent nanopaper substrate will provide new technologies impacting our daily life,” write the authors, from Nanyang Technological University in Singapore.

Unlike the plastic and silicon that make most electronics, cellulose is renewable and biodegradable, so it won’t sit in landfills. It’s also strong and lightweight, and scientists are making significant progress in using ‘nanocellulose’ for electronics.

Researchers at Nanyang Technological University created cellulose ‘nanopaper’ out of cellulose and silver wires. It conducted electricity even after being folded in half 500 times. Nanopaper can also be transparent, as much as 90%, so could be used for smartphone screens or displays.

“The proof of concept is there,” Koon-Yang Lee, a materials scientist at Imperial College London, told Professional Engineering. “Studies have shown that you can actually do this by impregnating these nanopapers with the right component or polymers. You can actually make very thin and flexible OLED screens.”

The authors note that there are still a number of challenges to overcome, including reducing the cost of manufacturing. Another challenge is making sure that the nanopaper only starts degrading when you want it to, and not when the device is still within its operation life. Lee said this could be achieved by encasing the nanopaper away from the elements in a polymer which could then be removed during the recycling process.

The bigger challenge – and one of the major drawbacks of cellulose nanopaper compared to silicon – is what Lee calls “batch to batch variability”. “You can imagine trees grown in Scandinavia would have different cellulose content compared to trees grown in China, for example,” he explains. “Even within the same forest the tree on the left is going to be different from the tree on the right. That batch to batch variability is going to be a major challenge if you want to build consumer electronics that are the same for everybody.”

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