New York, Jan 20

 Here comes a novel approach to harvest solar energy that could improve efficiency by storing the energy for later use.

Researchers from Massachusetts Institute of Technology (MIT), used sunlight to heat a high-temperature material whose infrared radiation would then be collected by a conventional photo-voltaic cell.

A conventional silicon-based solar cell does not take advantage of all the photons.

“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,” said Evelyn Wang, associate professor of mechanical engineering at MIT.

To address this, the team inserted a two-layer absorber-emitter device - made of novel materials including carbon nanotubes and photonic crystals - between the sunlight and the PV cell.

This intermediate material collects energy from a broad spectrum of sunlight, heating up in the process. When it heats up, as with a piece of iron that glows red hot, it emits light of a particular wavelength, which in this case is tuned to match the bandgap of the PV cell mounted nearby, said the study published in the journal Nature Nanotechnology.

Adding the extra step improves performance, because it makes it possible to take advantage of wavelengths of light that ordinarily go to waste.

“The design of the two-layer absorber-emitter material is key to this improvement,” said physics professor Marin Soljacic.

By:IANS