Wear your electronics

An electronic revolution could be on the way with the development of a thin film of plastic that conducts electricity and produces solar power, changing the way we light our homes and design clothes.

An international research project has begun that could bring organic light emitting devices (OLEDs) to the mass market.

The devices are thin and flexible, which means that lighting and electronic display screens could be created on almost any material, so that clothes and packaging can display electronic information.

The devices' uses vary from lighting that is more efficient than current bulbs to clothes which change colour at the press of a button and beer cans that display the latest football results.

At present, the devices are used as displays in some mobile phones and MP3 players, but they are not reliable enough for larger screens such as TVs and computers as they stop working after a few months.

"Their use in large televisions, clothes, lighting etc is longer term: 1-3 years away for televisions; 2-5 years for clothes; maybe 5-10 years for lighting and large displays," Dr Alison Walker of the British University of Bath's Department of Physics said.

An international consortium of researchers, led by the university, has begun a three-year project to put the science behind the devices on a firmer basis, so helping make them efficient enough to be mass produced.

The consortium, called Modecom, consists of 13 groups from nine universities and two companies. Three groups are from Britain, six from the US and one each from China, Belgium, Italy and Denmark.

"The consortium is funded by the European Commission," Walker said.

"Modecom's output is primarily scientific and will be published in the open literature and presented at international conferences so will be accessible to Australian researchers."

The devices make use of a discovery made 15 years ago that some polymers have the property of either turning electricity into light, or light into electricity, depending on how the devices are made.

Because these polymers are thin and flexible, they could be used in a multiplicity of ways:

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As a transparent window. This is like a conventional window during the day, but when it gets dark a switch is turned on and the entire window area emits light in a more efficient way than conventional or energy-saving bulbs, promising huge savings;
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In clothing which displays strips of the polymer which run off solar power, allowing electronic messages to be displayed which can be updated. This could be useful for the emergency services;
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In packaging for common goods that could be made to display electronic messages such as health warnings and recipes or could emit light;
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As a source of solar power to top up mobile phone batteries;
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As lightweight, solar power sources that could be rolled up and stored and which would also be suitable for people requiring electricity in remote locations, such as field researchers, mountaineers, sailors and military personnel.

However, Walker doesn't think this technology will replace traditional solar power sources as they are very inefficient.

Their key advantage is cost: they are cheap and their energy cost in manufacture would also be low, so the devices themselves will cost a few cents. They are also portable and flexible so their main use would be to replace batteries that, according to Walker, could happen in 5-10 years.

Walker goes on to say, the main thing holding the technology back is efficiency and degradation for displays, lighting and clothing and for solar cells, efficiency, then degradation.

The polymer is made from chains of molecules, and is called organic because they contain carbon. Electrons and holes injected into the polymer film form bound states called excitons that break down under electrical current, emitting light as they do so.

Walker's part of the consortium's research uses a mathematical technique called Monte Carlo analysis in which computer-generated random numbers are used to plot the paths of electrons, holes and excitons as they move across the film.

The results from this can be used to calculate how the chemical structure and impurities affect the device's performance. Chemists can use this data to design more efficient materials.

The Modecom consortium will work on the molecular level and also look at the workings of the device as a whole. This research will aid the understanding of the polymer materials used in plastic electronics in applications such as electronic paper and intelligent labels on groceries.


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