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Breakthrough could see cheaper solar energy

Researchers at an American university have made a breakthrough that could pave the way for cheap and efficient solar cells using organic semiconductors.

Scientists at Rutgers University discovered that energy-carrying particles known as 'excitons' can travel thousands of times further in carbon-based semiconductors than scientists had previously thought.

The paper, reported here and due to be published in an upcoming issue of scientific journal Nature Materials, boosts hopes that inorganic solar cells will one day overtake conventional silicon-based cells, making solar energy a more viable replacement for fossil fuels.

"Organic semiconductors are promising for solar cells and other uses, such as video displays, because they can be fabricated in large plastic sheets," said Vitaly Podzorov, assistant professor of Physics at Rutgers. "But their limited photo-voltaic conversion efficiency has held them back. We expect our discovery to stimulate further development and progress."

Podzorov and his team observed that excitons - particles that form when semiconducting materials absorb light particles or 'photons' - travel up to eight microns (millionths of a metre) through an extremely pure crystal organic semiconductor called rubrene.

Previous experiments have seen excitons travel distances of less than 20 nanometres through other organic semiconductors - thousands of times less than they do through rubrene.

The new research suggests that excitons that diffuse through rubrene behave more like those seen in inorganic cells using metals such as silicon and gallium.

If this proves to be the case, it could see a vast increase in the efficiency of organic cells, which currently waste around 99 per cent of the sunlight that shines upon them.