Friday, 6 November 2009

Light down a wire for solar power
4 November 2009

Solar energy could be produced cheaply in specially designed optical fibres, say researchers. The work, published in the journal Angewandte Chemie, makes use of nanometre-scale wires built around optical fibres like bristles. Those wires give the light much more surface area to interact with, leading to higher overall efficiencies.

However, only the ends of the fibres must be exposed - they funnel the light elsewhere for power generation. Instead of roof-sized panels, small collectors could be used on the roof, with the real machinery of solar energy generation tucked away, for example, between a home's walls. "Using this technology, we can make photovoltaic generators that are foldable, concealed and mobile," said Zhong Lin Wang of the Georgia Institute of Technology in the US.

Dye job
The most efficient - and the most familiar - solar cells are those based on silicon, which absorbs light, generates electrons, and shuttles them around to create a current. Recent years have seen leaps and bounds in the use of so-called Dye-Sensitised Solar Cells, in which the electrons are released from special dye molecules designed to absorb sunlight. While dye-sensitised cells are promising because they make use of cheap and robust materials, they are comparatively inefficient.

The new method starts with commercial optical fibre, like that used in telecommunications, with the outer layer stripped off. The team then creates a "forest" of zinc oxide nanowires around the fibre, and deposits the dye molecules over them. This creates a much larger effective surface area that helps to boost the cells' efficiency. What is more, the light needs enter only at the ends of the fibres, so a large-scale implementation could see just small collectors on a roof, with the bulk of the power-generating materials tucked away.

"Optical fibre could conduct sunlight into a building's walls where the nanostructures would convert it to electricity. This is truly a three-dimensional solar cell," Professor Wang said. Professor Wang said that future modifications to the surfaces of the nanowires could boost the devices' efficiency. "It's really nice, elegant work," said Saif Haque, a solar cell researcher from Imperial College London. "It's a clever way to make better use of the light."