News in Science

New twist on solar cell design

Scientists in the US have developed a new flexible and lightweight solar cell, which uses a fraction the amount of silicon used in conventional cells, while still achieving high light conversion rates.

Reporting in journal Nature Materials Professor Harry Atwater of the Caltech and colleagues believe their new design could be used in applications ranging from car sun roofs to devices in clothing.

The key is to the cells high efficiency is its use of small micrometre sized rods of silicon instead of traditional silicon wafers.

Incoming light bounces back and forth multiple times between the rods in the panel until it's absorbed.

Small alumina nano-particle reflectors are placed between the rods to ensure the light is guided as efficiently as possible.

The scientists claim up to 85% of usable sunlight is absorbed by the new panels, compared to approximately 17% efficiency with current commerically available solar cells.

Atwater says the silicon wire arrays offer a mechanically flexible alternative to conventional silicon wafer photovoltaics, and are much better at absorping in the near-infrared spectrum.

This allows overall sunlight absorption to exceed that of an equivalent volume of randomly textured silicon panels over a wide range of sunlight angles.

'Interesting' result

Professor Martin Green of the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales says "the good absorption demonstrated using the sparse array of silicon wires is interesting."

""The challenge with silicon wires has been getting good voltage output, because surface areas are large and this ultimately limits voltage," says Green.

"However, the sparse array's total surface area need not be a lot more than a thin conventional cell of the same volume, and that gives some hope here."

But Green believes thinner versions of current solar cell technology could prove to be just as effective.

"Although volume is a reasonable metric to compare devices, low volume is of interest not only to reduce material costs, but also manufacturing time," he says. "It is not obvious that you would get much benefit in the latter area with this sparse array approach.

"I imagine a thin conventional cell could have been deposited much more quickly with the techniques used."