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Electronics made of plastic

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When the concept was first proposed, it was dismissed as being unrealizable: “It’ll never work,” commented one expert assessor of an application for research funding. Today, 15 years later, the physicist Professor Karl Leo and two of his colleagues have been presented with the "Deutscher Zukunftspreis", one of Germany’s most prestigious research awards, for what was once a highly controversial idea. Leo, director of the Fraunhofer Institute for Photonic Microsystems IPMS in Dresden, has devoted most of his career to organic electronics. Until now, most electronic components have been made of inorganic silicon. The brittle material is a good semiconductor, but its manufacture requires a highly sophisticated process. It involves growing large crystals at high temperatures and then cutting them into thin slices known as wafers.

The more elegant solution is to use an organic material, a type of dye commonly used in the production of road signs. Such materials have the advantage that they can be applied as a coating on flexible films and other substrates. This gives rise to endless new possibilities, such as displays that can be rolled up and carried in a vest pocket or switchable window panes that light up at night to illuminate rooms while hardly consuming any electricity. On the other hand, organic dyes are poor electrical conductors. But this is where the once-mocked ingenious idea comes into play: their less-than-satisfactory conductivity can be increased by doping, i.e. adding a small amount of another chemical substance. After years of experiments, the researchers have succeeded in creating materials with an electrical conductivity a million and more times greater than the original dyes, with a doping ratio of no more than one percent.

The "Deutscher Zukunftspreis 2011", endowed with 250,000 euros, has been awarded by the President of the Federal Republic of Germany every year since 1997. It honors outstanding innovations that have made the transition from the research laboratory to industrial practice, thus helping to create jobs. Fraunhofer is a frequent winner of this prize, no doubt because it operates precisely at this interface between the world of research and the commercial market. This time, the jury chose to honor organic electronics, which Leo describes as a technology “that will revolutionize our lives”.

The ultrathin semiconductor coatings have already made their way into mass production. They are equally versatile as the silicon chips that preceded them, for instance converting electrical energy into light just as easily as they convert sunlight into electricity. Novaled AG has adopted the first approach, using the technology to produce materials for displays and lamps, while Heliatek GmbH has chosen to focus on photovoltaics. Both of these companies are spinoffs created by former members of Professor Leo’s research team. By now they employ a total of nearly 200 people, and work closely together with other Dresden-based companies in a technology network. This year’s Zukunftspreis is shared by the founders of these two spinoffs, Jan Blochwitz-Nimoth (Novaled) and Martin Pfeiffer (Heliatek), and their mentor Professor Leo. Novaled AG is slightly further ahead in terms of marketing: the company is already mass-producing materials for cellphone displays. In two or three years’ time, it intends to start supplying materials for ultraflat TV screens that display true-to-life colors and consume a minimum of energy. “OLED displays combine the best qualities of LED and plasma screens, the two technologies currently available,” says Blochwitz-Nimroth. They are more energy-efficient than plasma TVs and deliver sharper images than LED technology, because they don’t need backlighting.

Solar cells made of organic materials have not yet reached the mass market. Heliatek GmbH expects to start production sometime next year. The company’s latest prototypes have an efficiency of ten percent, which is not yet high enough to compete with conventional silicon cells. “But in the longer term we will reach efficiencies approaching 20 percent”, Professor Leo states. Moreover, organic cells have other advantages compared with silicon technology, foremost among them a simpler – and therefore cheaper – manufacturing process.

The method employed by Karl Leo and his prize-winning former colleagues involves depositing microscopically thin layers of the organic material on a substrate. These coatings have a thickness of no more than one fifth of a micrometer – one thousand times thinner than in conventional solar cells. Only about a gram of semiconductor material is needed to coat a surface area of one square meter – in a process that takes place at room temperature, not at the 1,000 or so degrees Celsius required to produce inorganic cells.

This not only saves energy but also allows PET films to be used as the substrate, instead of the heat-resistant glass that was previously the only option. PET is the same plastic used to make bottles for soft drinks. It is cheap, light and flexible. The prize-winners have developed a continuous process based on roll-to-roll technology that enables the solar cells to be manufactured cheaply in large numbers. The resulting lightweight modules can be installed on roofs too weak to support the weight of standard photovoltaic panels.

Before making its final choice, the jury had shortlisted three projects as potential winners of the "Deutscher Zukunftspreis". A second project rooted in Fraunhofer research was among this year’s finalists, competing alongside the organic electronics team. These researchers have developed an advanced photovoltaic technology, known as “concentrated photovoltaics (CPV)”, which consists of very-high-efficiency solar cells and sun-tracking concentrator modules. The nominated team comprised Andreas W. Bett, deputy director of the Fraunhofer Institute for Solar Energy Systems ISE, Hansjörg Lerchenmüller from Soitec Solar and Klaus-Dieter Rasch from AZUR SPACE Solar Power.

It was thus against such strong competitors that the organic electronics team led by Professor Leo won the "Deutscher Zukunftspreis 2011". German President Christian Wulff presented the award to Professor Karl Leo, Dr. Jan Blochwitz-Nimoth and Dr. Martin Pfeiffer in mid-December.

Prof. Karl Leo | Quelle: EurekAlert!
Weitere Informationen:
www.fraunhofer.de/en/press/research-news/2011/december/electronics-made-of-plastic.html

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