Technique for widespread solar power use

Researchers at Princeton envision mass-produced rolls of material that converts sunlight to electricity, using a new technique for making solar cells.

Solar cells, or photovoltaics, convert light to electricity and are used to power many devices, from calculators to satellites.

The new photovoltaics are made from organic materials, which consists of small carbon-containing molecules, as opposed to the conventional inorganic, silicon-based materials. The materials are ultra-thin and flexible and could be applied to large surfaces.

Organic solar cells could be manufactured in a process something like printing or spraying the materials onto a roll of plastic, said Peter Peumans, a graduate student in the lab of electrical engineering professor Stephen Forrest. "In the end, you would have a sheet of solar cells that you just unroll and put on a roof," he said

The cells also could be made in different colours, Peumans said. Or they could be transparent so they could be applied to windows. The cells would serve as tinting, letting half the light through and using the other half to generate power, he said.

Researchers are now planning to combine the new materials and techniques. Doing so could yield at least 5 % efficiency, which would make the technology attractive to commercial manufacturers.

By comparison, conventional silicon chip-based solar cells are about 24 % efficient. "Organic solar cells will be cheaper to make, so in the end the cost of a watt of electricity will be lower than that of conventional materials." said Peumans.

The technique also opens new areas of materials science that could be applied to other types of technology, the researchers said. Solar cells are made of two types of materials sandwiched together, one that gives up electrons and another that attracts them, allowing a flow of electricity. The researchers figured out how to make those two materials mesh together like interlocking fingers so there is more opportunity for the electrons to transfer.

The key to this advance was to apply a metal cap to the film of material as it is being made. The cap allowed the surface of the material to stay smooth and uniform while the internal microstructure change and meshed together, which was an unexpected result, said Forrest.