Sir Richard Friend on organic solar-cell technologyby Rebecca Priestley
Plastic solar cells are the way of the future, says a visiting Cambridge physics professor.
A video screen you can roll up and put in your pocket! “Wallpaper” you can watch a movie on! These sorts of products are often touted as the future of organic light-emitting diodes, or LEDs, but when I asked Sir Richard Friend – who is lecturing to New Zealand audiences this month – if this was what he was working on, he laughed. On the phone from Cambridge, where he is Cavendish Professor of Physics – a role once held by Sir Ernest Rutherford – Friend said that although such products might be available in the future, there are other, more practical, applications of organic LEDs that he is more enthusiastic about. Organic LEDs using technology developed by Friend and his companies are already used in some smartphones, but he’s looking to apply the technology to much larger displays like solar cells and highly efficient lighting panels. The “organic” in organic semiconductors and LEDs simply refers to the use of carbon, which we know as the building-block of life, in place of silicon, which has driven the development of electronic products for decades.
Although solar cells have been available for many years, cost has limited their uptake. That’s because conventional solar cells use silicon to absorb and convert light energy into electricity, and processing silicon into a working solar cell is very expensive. One problem with silicon, says Friend, is that it’s very hard, “and the way you handle it is to literally cut wafers out of large single crystals. What we’re using are carbon-based molecules. We use plastics, or polymers, because they’re relatively easy to process onto thin, flexible films by printing them or painting them.” Friend has spent much of the past 25 years “showing how you can get silicon-like properties in organic semiconductors”. As well as trying to emulate silicon, he has drawn inspiration from biology. The operation of solar cells made with organic semiconductors, he says, is a bit like “what goes on in photosynthesis in green plants”, whereby carbon-based molecules in plants create chemical energy from carbon dioxide, water and sunlight. In the solar cell, the sunlight is translated into electrical energy.
One of the challenges in making efficient organic solar cells is making them as thin as possible. “Thinner is very good. If you want to make a thin solar cell, you’d really like to make it as thin as a leaf. Nature doesn’t need to make them any thicker, so why should we? And if you can make them thin, you use less materials so they cost less – and that’s a very straightforward proposition. “I’d like to see solar cells really take off, because the energy challenge we face is so serious. Dropping the cost of solar cells is essential and our plastic solar cells have a very good shot. But we’re not there yet.”
Sir Richard Friend, the Royal Society of New Zealand’s 2012 Distinguished Speaker, will lecture in Auckland, Hamilton, Wellington, Christchurch and Dunedin from October 10-16 (goo.gl/7S2Pj).
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