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Professor Donal Bradley, director, Imperial College London Centre for Plastic Electronics

Professor Donal Bradley, director, Imperial College London Centre for Plastic Electronics

Graham Pitcher talks to a researcher who was 'there at the start' of the plastic electronics industry.

Few people can reasonably claim to have been 'there at the start' of an industry; Professor Donal Bradley was. His PhD at the University of Cambridge's Cavendish Laboratory focused on conjugated polymers, work that would result in the establishment of Cambridge Display Technology (CDT) and a new industry – broadly categorised as 'plastic electronics'.

So what was the attraction? "If you wanted to work in solid state at that time," he said, "it was all about low dimension semiconductors and the use of molecular beam epitaxy to create intricate structures. But people were also beginning to think about using organic materials for semiconductors."

Prof Bradley explained that he had always been interested in chemistry, as well as physics. "The interface between the two seemed an interesting area in which to work, but I was coming at the problem from the organic semiconductor side, rather than from the III-V materials side."

Early work in organic materials research focused on the development and synthesis of conducting materials that might act as metal replacements. "We thought they would be better, lower weight and have better processability," he recalled. "But we were also thinking about making optical switches with non linear properties."

His PhD focused on how to process polymers in order to make 'interesting structures'. "I was looking to better understand physical properties," he explained, "understanding how charge was transported and some emission properties." But work by others had shown that organic materials could act as leds and that sent Prof Bradley off in a new direction, into an area in which, he said, there 'wasn't a lot going on'.

That new direction saw him working with CDT cofounders Richard Friend and Jeremy Burroughes. "Richard had been looking to do organic transistors," Prof Bradley noted, "and organic leds came out of a discovery that involved Richard, Jeremy and myself."

The resulting patent application described 'an electroluminescent device comprising a semiconductor layer in the form of a thin dense polymer film …'. Prof Bradley was the corresponding author for the 1990 paper, published in Nature, that reported the discovery of conjugated polymer electroluminescence. This paper – the most cited paper in molecular electronic materials history – is believed to have launched plastic electronics.

But plastic electronics has had a long gestation period. "The technology has only been shown to be commercial in the last couple of years," he said, "mostly through the use of an active matrix oled in the Samsung Galaxy phone."

Ironically, that technology derives from work originally performed by Kodak. "Our work has gone on in parallel, focusing on solution processed materials and conjugated polymers. There are a lot of similarities," he said, "but Samsung's success has shown there is real opportunity."

There has also been the awareness that plastic electronics technology could be used for things other than displays. "There has been a lot of work on transistors, for example by Plastic Logic," Prof Bradley pointed out. "And there has been an increase in interest in lighting applications, where the technology used to make displays can be applied to create larger area elements."

Prof Bradley admits that getting plastic electronics technology out of the lab remains a challenge. "Part of the reason is that the UK has lost a lot of the larger companies that would have had an interest in these developments."

He said it is easier for Japanese companies, such as Sony, to pull technology through. "But there's also the scale of investment needed to commercialise the technology," he added. "Samsung is spending billions of dollars to improve device performance, while LG is spending $3billion on an oled tv plant. The UK has seen start ups, but that is difficult to translate into major scale activity and those companies tend to be bought."

Attempts to bring scale to the problem are being made through the establishment of plastic electronics Centres of Excellence; Prof Bradley is director of one such centre located at Imperial College. "We also have hopes for Technology and Innovation Centres (TICs), but the level of investment and support doesn't look so encouraging in terms of them being able to make a major impact."

Nevertheless, Prof Bradley believes the UK remains a world leader in plastic electronics, at least for the moment. "There is exceptionally strong university activity, but other parts of the world are catching up. The UK is still well placed and is one of the nations that people mention as a leader. But we can't afford to be complacent because there are a lot of strong groups in other places who are forging ahead."

Looking forward, Prof Bradley is turning his attention to photonics. "I'm researching organic materials as gain media for lasers. I'm also doing a lot of work with metal oxide systems, using solution based approaches with a range of fabrication methods. Zinc oxide and GaInZnO are very attractive options for displays, where we're looking to repace polysilicon."

Prof Bradley believes UK science has had a good decade in terms of funding in a period of change. "But we are being asked to justify more directly the connection between investment in science and the impact of the work. I don't think that's a negative thing, but we have to be careful that we don't neglect the fundamental components of science in order to do more applied science. We need strong disciplines that can be built on and we need to preserve our strengths while looking for opportunities."

Professor Donal Bradley,
Prof Bradley graduated from Imperial College in 1983 with a first class BSc in Physics and received a PhD in 1987 from the University of Cambridge for his work on conjugated polymers.

In 1989, he played a central role in the discovery of conjugated polymer electroluminescence, a move that led to his cofounding Cambridge Display Technology in 1992.

He is director of the Imperial College London Centre for Plastic Electronics and cofounder and director of Molecular Vision. Prof Bradley also holds the Lee-Lucas Chair of Experimental Physics at Imperial College, is deputy principal of the Faculty of Natural Sciences and has just been named Pro Rector (Research) at Imperial College, with responsibility for determining strategic research investment priorities and for coordinating and developing the College's external research relationships.

Prof Bradley has published 500 papers to date and his papers have been cited more than 33,500 times.

In 2010, Prof Bradley was awarded the Faraday Medal at the IET's Achievement Awards.

Author
Graham Pitcher

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