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Thin-films boost solar cell efficiency

10 May 2007

Polymer solar cells could soon rival silicon panels thanks to scientists in the US and Korea, who have increased the efficiency of thin film photovoltaics to more than 6.1%.

Flexible polymer photovoltaics now have an efficiency of 6.1% thanks to work being carried out by a team from Wake Forest University, US, and the Korea Institute of Science and Technology. What's more, the researchers believe that they can reach the 10% mark by next year (Applied Physics Letters 90 163511).

To put things into perspective, traditional solar panels convert about 12-15% of the light that hits them into useful electrical power. As polymers close in on this crucial figure, they become a viable technology for commercial use, in the residential market right through to being a mobile power supply for the military.

The team used thermal annealing to modify the charge transport pathways. "We have learned how to control charge mobility and balance in a thin conducting plastic film using meso-structuring of nanoscale materials," David Carroll from Wake Forest University told optics.org.

Carroll believes the costs of this new technology will be comparable with that reported by companies such as Konarka. "We hope this approach will be very cheap. We are not there yet but we hope to get from dollars per KW to pennies per KW," he said.

The group is now trying to improve the absorption characteristics of its solar cell. "Today's commonly used materials have relatively narrow absorption bands so many groups are trying to integrate frequency converters with thin films," explained Carroll. "The trouble with thin films is that light is lost to reflection so they are not appropriate for use with frequency converters."

To overcome these issues, Carroll and his colleagues have developed what they call the "Fiber cell". "Our Fiber cell approach combines the optical properties of a fiber optic with our new high efficiency thin film technology," he said. "When combined, the performance (not yet reported) is astonishing and the geometry is ideal for frequency conversion. We have been granted patents and are trying to commercialize Fiber cell.

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