The Return of the Hairy Solar Panel
The big brains at the California Institute of Technology (every time I hear about Caltech I think of Richard Feynman...) have figured out a way to create solar panels that have at least three very desirable characteristics: 1) They are very good at absorbing light, 2) they are mostly made of cheap plastic and only use a very small amount of expensive semiconductors, and 3) they are flexible. How do they do that?
At the microscopic scale, the surface of the solar cells resemble the "hairy" nanowire-based solar panels that we've covered in the past, except that instead of making the wires with exotic materials like "indium gallium phosphide", they make them mostly out of plastic with a bit of silicon (2% silicon, 98% is polymer).
This structure is very good at absorbing light (it has a huge surface area to catch photons):
"These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials," says Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science [...] The light-trapping limit of a material refers to how much sunlight it is able to absorb. The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight. "We've surpassed previous optical microstructures developed to trap light," he says.
Part of the reason why so much light is absorbed is shown on the image above. Each of the silicon wires (30 and 100 microns in length and only 1 micron in diameter) is a good solar cell on its own, and the light that isn't absorbed is scattered and then hits other wires.
The flexibility of the panels is also important because it means that they can be manufactured using roll-to-roll processes, reducing production costs compared to non-flexible panels.
Next Step: Scaling Up
So far only a few square centimeters of cells have been made, but the Caltech team is already working on making new demonstration panels that are as big as regular solar panels and that have higher operating voltage.
Maybe one day I'll have a hairy solar panel on my rooftop...
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