Solar Cell Breaks Efficiency Record—Recycling photons raises the energy output

[OKIsItJustMe]

http://spectrum.ieee.org/green-tech/solar/solar-cell-breaks-efficiency-record

NEWS

Solar Cell Breaks Efficiency Record

Recycling photons raises the energy output

By Neil Savage / June 2011

24 June 2011—A photovoltaic cell that reaches record-breaking efficiency could make http://spectrum.ieee.org/green-tech/solar">solar energy competitive with fossil fuels, says the company that created the cell.

https://www.altadevices.com/">Alta Devices, a start-up in Santa Clara, Calif., presented research at the http://www.ieee-pvsc.org/PVSC37/">37th IEEE Photovoltaic Specialist Conference, in Seattle, this week that claims its thin-film gallium-arsenide cell can convert 27.6 percent of the sunlight striking the cell into electricity, under standardized conditions. Since the paper was submitted, the company says it has upped the efficiency to 28.2 percent. That beats the previous record of 26.4 percent for a solar cell with a single p-n junction, which was the first improvement in years over 26.1 percent. Both numbers, according to Alta, were http://spectrum.ieee.org/energy/renewables/solarcell-squabble">independently confirmed by the http://www.nrel.gov/">National Renewable Energy Laboratory.

The efficiency was measured on a laboratory-made solar cell. Efficiency tends to decrease once the cells are packaged into usable modules. "We assume we will ultimately be able to achieve modules that are around 26 percent, and that’s plenty to be competitive with fossil fuels," says Christopher Norris, CEO of Alta.

The key to achieving the record was photon recycling. When the photons in sunlight are absorbed in a photovoltaic material, they split into an electron and a hole. The electrons that pass out of the cell can be used as electricity, but many of them are lost in the semiconductor when they recombine with a hole to produce either waste heat or a new photon. By carefully growing a high-quality single crystal of gallium arsenide, the company managed to ensure that more than 99 percent of the recombinations would result in new photons. Those photons could then create a new electron-hole pair and give the electron another chance to be captured as electricity. The Alta team also improved the reflectivity of the metal contacts on the back of the solar cell, so that any photons that exited the cell would be sent back in for possible reabsorption.

…

[Gregorian]

1. Some interesting stuff in that article. Epitaxial Liftoff

And maximum photovoltaic efficiency maximum with this method being a little over 30%.

So we're now at nearly 30% efficient. That ends up being something around 100 Watts per meter by the time it's converted, I think.