Schematic diagram of the light-trapping elements used to optimize absorption within a polymer-embedded silicon wire array
A new way of making solar cells promises a cheaper way to generate electricity from the sun and new ways to integrate solar power into other products.
Solar cells, or photovoltaics, are widely made using wafers of silicon that are stiff and brittle. California Institute of Technology physics professor Harry Atwater is making photovoltaics differently.
"Our technology uses 50-100 times less silicon," he said, "in the form of a sparse array of wires. And that sparse array of wires has exactly the same light absorption and electricity-collection properties as the conventional silicon wafer cell."
Photomicrograph of a silicon wire array embedded within a transparent, flexible polymer film
The tiny silicon wires stick up from the base, or substrate, looking something like a microscopic hair brush. And because the key component of solar cells is an expensive, highly purified form of silicon, there's a real economic benefit to this design.
"So what that means is, in terms of cost, is you can use 100 times less silicon. And that's potentially very significant."
But the silicon is what converts light into electricity, so you might think using so much less silicon would reduce the electrical output, but Atwater says that's not the case.
"The light comes in and is both directly absorbed by the wires, and some of the light bounces around in between the wires. And that bouncing around or multiple scattering in between the wires results in dramatically enhanced absorption," Atwater explained. "In fact, the absorption enhancement that we see is in the range of 20 to 50 times the single-pass absorbance."
Atwater and his colleagues have made prototypes of the design in the lab, and the product doesn't look like the typical solar panels you might see on top of a building.
"What we do with our wire arrays is grow them on a supporting substrate, and we peel them off inside a plastic sheet, so that the material has exactly the optical and electrical properties of a silicon wafer, but instead it basically has the mechanical properties of a flexible plastic sheet."
That flexibility opens the door to potential new applications, such as what Atwater calls "integrated photovoltaics." For example, the solar cell could be built into roofing material, saving money on installation. Other ideas for new uses come from the physical form of Atwater's novel design.
"Well, one of the things that's interesting about these flexible sheets is that they can be curved, so you could imagine putting them in unconventional forms, like on the surface of a vehicle or something like that, where you don't have a flat surface."
The Caltech professor says he's optimistic about commercializing his new solar cell design because the manufacturing process should not require development of any new technologies. And he stresses that it should reduce the cost of generating power from the sun.
"The wonderful thing about solar energy is that it's accessible and available everywhere in the world, from the cloudiest place in northern Europe to the sunniest place in north-central Africa to the Outback of Australia to South Asia. And in fact [the use of solar energy is] growing worldwide for that reason."
Harry Atwater's description of his new design for solar cells is published in the journal Nature Materials.