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Hybrid graphene films seek ITO replacement

Posted: 16 Aug 2011     Print Version  Bookmark and Share

Keywords:nanowire  hybrid graphene  transparent display 

Graphene combined with other flexible, transparent electronic components being developed at Rice University and elsewhere, could lead to computers that wrap around the wrist and solar cells that wrap around just about anything.

The lab of Rice University chemist James Tour has developed a hybrid graphene thin film by combining a single-layer sheet of highly inductive graphene, the highly touted single-atom-thick form of carbon, with a fine grid of metal nanowire. The researchers claim the material can easily replace indium tin oxide (ITO), product widely used as a transparent, conductive coating.

A transparent, conductive coating is an essential element in virtually all flat-panel displays, including touch screens on smart phones and iPads, and is part of organic light-emitting diodes and solar cells. ITO seems to work well in all of these applications, but has several disadvantages. The element indium is increasingly rare and expensive. It is also brittle, which heightens the risk of a screen cracking when a smart phone is dropped and further rules ITO out as the basis for flexible displays. The Tour Lab's hybrid graphene film is said to be a strong candidate to replace ITO.

"Many people are working on ITO replacements, especially as it relates to flexible substrates," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. "Other labs have looked at using pure graphene. It might work theoretically, but when you put it on a substrate, it doesn't have high enough conductivity at a high enough transparency. It has to be assisted in some way."

Conversely, said postdoctoral researcher Yu Zhu, lead author of the new paper, fine metal meshes show good conductivity, but gaps in the nanowires to keep them transparent make them unsuitable as stand-alone components in conductive electrodes.

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A hybrid material that combines a fine aluminium mesh with a single-atom-thick layer of graphene outperforms materials common to current touch screens and solar cells. The transparent, flexible electrodes were developed in the lab of Rice University chemist James Tour.
Source: Rice University.

But combining the materials works superbly, Zhu said. The metal grid strengthens the graphene, and the graphene fills all the empty spaces between the grid. The researchers found a grid of 5µm nanowires made of inexpensive, lightweight aluminium did not detract from the material's transparency. "5µm grid lines are about a 10th the size of a human hair, and a human hair is hard to see," Tour said. Tour said metal grids could be easily produced on a flexible substrate via standard techniques, including roll-to-roll and ink-jet printing. Techniques for making large sheets of graphene are also improving rapidly, he said; commercial labs have already developed a roll-to-roll graphene production technique. "This material is ready to scale right now," he said.

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