Silicon wire arrays enable development of highly absorbing and flexible solar cells

February 17th, 2010 - 2:08 pm ICT by ANI  

Washington, Feb 17 (ANI): A team of scientists from the California Institute of Technology (Caltech) has used arrays of long, thin silicon wires embedded in a polymer substrate created a new type of flexible solar cell that enhances the absorption of sunlight and efficiently converts its photons into electrons.

The solar cell does all this using only a fraction of the expensive semiconductor materials required by conventional solar cells.

“These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials,” said Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science, and director of Caltech’s Resnick Institute, which focuses on sustainability research.

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,” said Atwater.

Atwater noted that the solar cells’ enhanced absorption is “useful absorption.”

“Many materials can absorb light quite well but not generate electricity-like, for instance, black paint,” he explained.

“What’s most important in a solar cell is whether that absorption leads to the creation of charge carriers,” he said.

The silicon wire arrays created by Atwater and his colleagues are able to convert between 90 and 100 percent of the photons they absorb into electrons-in technical terms, the wires have a near-perfect internal quantum efficiency.

“High absorption plus good conversion makes for a high-quality solar cell. It’s an important advance,” said Atwater.

According to Atwater, the key to the success of these solar cells is their silicon wires, each of which, “is independently a high-efficiency, high-quality solar cell.”

When brought together in an array, however, they are even more effective, because they interact to increase the cell’s ability to absorb light.

“Light comes into each wire, and a portion is absorbed and another portion scatters. The collective scattering interactions between the wires makes the array very absorbing,” said Atwater.

While these arrays have the thickness of a conventional crystalline solar cell, their volume is equivalent to that of a two-micron-thick film.

Since the silicon material is an expensive component of a conventional solar cell, a cell that requires just one-fiftieth of the amount of this semiconductor will be much cheaper to produce.

The composite nature of these solar cells means that they are also flexible, Atwater added. (ANI)

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