February 18, 2010

Caltech Silicon Wire Arrays Surpass Conventional Light Trapping Limits

This is a schematic diagram of the light-trapping elements used to optimize absorption within a polymer-embedded silicon wire array.
[Credit: Caltech/Michael Kelzenberg]

Using arrays of long, thin silicon wires embedded in a polymer substrate, a team of scientists from the California Institute of Technology (Caltech) has 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
* The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight
* the wires have a near-perfect internal quantum efficiency.
* Each wire measures between 30 and 100 microns in length and only 1 micron in diameter. “The entire thickness of the array is the length of the wire,” notes Atwater. “But in terms of area or volume, just 2 percent of it is silicon, and 98 percent is polymer.”

The next steps, Atwater says, are to increase the operating voltage and the overall size of the solar cell. "The structures we've made are square centimeters in size," he explains. "We're now scaling up to make cells that will be hundreds of square centimeters—the size of a normal cell."

Atwater says that the team is already "on its way" to showing that large-area cells work just as well as these smaller versions.

Nature Materials paper, "Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications"

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