Is it time to move away from silicon-based solar? | Alternative Energy | Forums

Anyone heard of Gallium before?

CHICAGO—Currently, the world has the capacity to manufacture over 40 Gigawatts of solar panels each year, the vast majority of them silicon-based. And it's easy to see why: our expertise with processing the material has led to a staggering drop in costs, making photovoltaics (PVs) much more cost-competitive than just about anyone had predicted.

But that manufacturing innovation hasn't been matched on the basic research side; it's been over a decade since the last time anyone set a new efficiency record for silicon cells. And, even as manufacturing costs have dropped, the cost of support equipment and installation has remained stubbornly high and is an ever-increasing slice of the total price of PV systems.

That's got people thinking that it might be time that we get more power out of each installation. At the meeting of the American Association for the Advancement of Science, two researchers spelled out how they were finding ways to take an expensive material and make it cheap enough to be deployed on the same scale as silicon.

The material in question is gallium arsenide, which can be fashioned into solar cells with efficiencies twice those of silicon. The high cost of the material, however, has limited its use to applications like satellites. But two research groups have come up with ways to get much more out of GaAs, and the lab heads presented their latest work at the meeting of the American Association for the Advancement of Science.

Gallium goes thin

Both teams have figured out how to make extremely thin layers of GaAs. Harry Atwater's group at Caltech has developed a process that allows them to peel hundreds of thin layers off a large aggregate of the material, much like individual graphene sheets can be peeled off a block of graphite. The end result is an extremely thin film of GaAs (he passed some samples around to the audience).

John Rodgers, who works at the University of Illinois at Urbana-Champaign, grows thin layers of GaAs separated by a thin sacrificial layer. When the sacrificial layer is etched away, you're left with a collection of thin GaAs chips; the silicon wafer they were grown on can then be recycled, cutting down on the costs significantly. A plastic stamp can then pick up the chips and "print" them onto just about any surface, including one pre-patterned with wiring.

In the rare cases where GaAs chips are used here on Earth, they're typically used in what's called a concentrated solar system, where lenses pump as many photons into the chips as they can manage without melting. But these tracking and focusing systems add significantly to the cost of these systems. Both groups are thinking of doing some focusing, but going about it in different ways.

Rodgers, who can print large arrays of tiny GaAs chips, is managing costs by keeping things simple: his team's process simply involves dropping a plastic sphere that acts as a lens on top of the chip. There are some ideas about how to manufacture more specialized spheres that focus the light more efficiently, but, for now, simplicity is the selling point.

http://arstechnica.c.....sed-solar/