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article imageHighly flexible lights made from graphene

By Tim Sandle     Jun 7, 2016 in Technology
Graphene has been successfully used as the basis of a new generation of flexible organic light-emitting diodes (OLEDs). These lights are flexible, being based on a plastic material.
While technologists continue to develop the first thin, flexible fold-away computer, a breakthrough has been made with the light-emitting diodes required to power such a device. The basis of both technological strands is graphene.
Graphene is a highly conductive material; and one that is lightweight, transparent and very strong. It seen by many scientists as the basis for a new generation of electronics, not only due to its power but also because it can be crumpled and folded.
Success with the flexible organic light-emitting diodes has come from South Korea. Here, research led by Professor Seunghyup Yoo from the School of Electrical Engineering, KAIST and Professor Tae-Woo Lee from the Department of Materials Science and Engineering, Pohang University of Science and Technology.
The lights use graphene as a transparent electrode, according to This is positioned between titanium dioxide and conducting polymer layers. The lights are positioned in a stack formation, within layers of glass or plastic. The layers are ultra-thin and multi-layers of organic compounds are sandwiched between two electrodes (cathode and anode).
The lights work by a voltage being applied across the electrodes. Here, electrons from the cathode are pulled toward the holes (positive charges) from the anode. The electrons meet the holes in the emissive layer, where light is produced through the release of energy as a photon. Different lighting effects can be achieved, depending upon whether the LED emits from the top or the bottom.
While graphene light-emitting diodes have been developed previously, the efficiencies of these have been limited. This is due to photon loss, a phenomenon called ‘loss from surface plasmon polariton.’ The newly developed devices have overcome this through having a transparent structure within which a titanium oxide layer with a high refractive index together with a hole-injection layer of conducting polymers with a low refractive is sandwiched between the graphene electrodes.
The technology has created interest on Twitter, with tweets from EDN-Europe; Carl Johnson, who said: "OLED ramp is on. Research is ongoing. Flexible here we come"; and Graphene Guide, who declared: "World Beholds KAIST Made Graphene OLEDs."
The research outcomes are published in the journal Nature Communications. The research paper is titled “Synergetic electrode architecture for efficient graphene-based flexible organic light-emitting diodes.”
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