How to tap the sun’s energy through heat as well as light


By David L. Chandler – A conventional silicon-based solar cell “doesn’t take advantage of all the photons,” Evelyn Wang explains. That’s because converting the energy of a photon into electricity requires that the photon’s energy level match that of a characteristic of the photovoltaic (PV) material called a bandgap. Silicon’s bandgap responds to many wavelengths of light, but misses many others.

The design of the two-layer absorber-emitter material is key to this improvement. Its outer layer, facing the sunlight, is an array of multi-walled carbon nanotubes, which very efficiently absorbs the light’s energy and turns it to heat. This layer is bonded tightly to a layer of a photonic crystal, which is precisely engineered so that when it is heated by the attached layer of nanotubes, it “glows” with light whose peak intensity is mostly above the bandgap of the adjacent PV, ensuring that most of the energy collected by the absorber is then turned into electricity. more> http://tinyurl.com/la28mm7

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