Hot Electrons Could Double Solar Cell Power Efficiency

Hot electron solar cell
Hot electrons could pass through an ultra-thin solar cell without cooling down, with the potential for doubling solar cell efficiency. Image credit: Michael Naughton.

Scientists have experimentally verified a theory suggesting that hot electrons could double the output of solar cells. The researchers, from Boston College, have built solar cells that successfully use hot electrons to increase the cells' power ouput. Although the power increase is small, the concept could lead to solar cells that break conventional efficiency limits.

Michael Naughton, a physics professor at Boston College, and others have designed an ultra-thin (15-nanometer-thick) solar cell, which hot electrons can quickly pass through before cooling. In conventional, thicker , only the "cooler" lower-energy electrons that have longer wavelengths can pass through.

When a conventional solar cell absorbs a high-energy photon, it produces a hot electron that quickly loses much of its energy as heat before it can pass through the cell and be used to generate electricity. Although solar cells can be designed to absorb high-energy photons and use hot electrons, they aren't able to absorb low-energy photons as well. The new solar cell design, however, can absorb both.

Theoretically, solar cells that can absorb hot and cool electrons could nearly double their . Conventional solar cells can convert at most about 35% of sunlight energy into electricity, and the rest is wasted as heat. By absorbing the hot electrons, solar cells could achieve efficiencies of up to 67%, according to an article in MIT's Technology Review. By doubling the efficiency, the cost of solar power could be cut in half.

There are still challenges with the new ultra-thin solar cells, however. Because they're so thin, most of the light passes through them, so they only convert about 3% of incoming light into electricity. But past research has shown that adding to the could allow them to absorb more light while still keeping a short travel distance for the electrons. In addition, the scientists are investigating incorporating into the to increase the number of electrons collected from the absorbed light.

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Dec 18, 2009
maybe capturing 100% of the photonic energy requires a non-blinking brewster prism array, hopefully some scientist will read this comment and build the patent for it :)

Dec 19, 2009
Actually, the trick is probably to create a stack of these ultra thin cells. Each layer absorbs some photons and passes the rest thru, until all the light is absorbed and converted into electricity. It would be essential of course to have a very inexpensive manufacturing process so that the stacks wouldn't have to be created one layer at a time, but I don't see why epitaxial growth processes along with diffusion sputtering used for normal silicon manufacturing couldn't be used.

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