Funneling the Solar Energy

Energy Funnels Boost Solar Cell Performance: MIT engineers propose a new way of harnessing photons for electricity, with the potential for capturing a wider spectrum of solar energy.

The quest to harness a broader spectrum of sunlight’s energy to produce electricity has taken a radically new turn, with the proposal of a “solar energy funnel” that takes advantage of materials under elastic strain.
In this case, the “funnel” is a metaphor: Electrons and their counterparts, holes — which are split off from atoms by the energy of photons — are driven to the center of the structure by electronic forces, not by gravity as in a household funnel. And yet, as it happens, the material actually does assume the shape of a funnel: It is a stretched sheet of vanishingly thin material, poked down at its center by a microscopic needle that indents the surface and produces a curved, funnel-like shape. ...
Strain — defined as the pushing or pulling of a material into a different shape — can be either elastic or inelastic. Xiaofeng Qian, a postdoc in MIT’s Department of Nuclear Science and Engineering who was a co-author of the paper, explains that elastic strain corresponds to stretched atomic bonds, while inelastic, or plastic, strain corresponds to broken or switched atomic bonds. A spring that is stretched and released is an example of elastic strain, whereas a piece of crumpled tinfoil is a case of plastic strain.
The new solar-funnel work uses precisely controlled elastic strain to govern electrons’ potential in the material. The MIT team used computer modeling to determine the effects of the strain on a thin layer of molybdenum disulfide (MoS2), a material that can form a film just a single molecule (about six angstroms) thick. ...

“We’re trying to use elastic strains to produce unprecedented properties,” says Ju Li, an MIT professor and corresponding author of a paper describing the new solar-funnel concept that was published in the journal Nature Photonics.

Article: Strain-engineered artificial atom as a broad-spectrum solar energy funnel.



Source: MIT News.