Butterfly wing design doubles solar cell absorption

Technology News |
By Nick Flaherty

The wings of the butterfly Pachliopta aristolochiae have nanoholes that absorb light over a wide spectrum far better than smooth surfaces, and the team at KIT has been able to transfer these nanostructures to solar cells, enhancing the light absorption rate by up to 200 percent.

“The butterfly we studied is very dark black. This signifies that it perfectly absorbs sunlight for optimum heat management,” said Dr Hendrik Hölscher of KIT’s Institute of Microstructure Technology (IMT). “Even more fascinating than its appearance are the mechanisms that help reaching the high absorption. The optimization potential when transferring these structures to photovoltaics (PV) systems was found to be much higher than expected,”

The researchers measured the diameter and arrangement of the nanoholes on the wing of the butterfly via scanning electron microscopy and analysed the rates of light absorption for various hole patterns in a computer simulation. They found that disordered holes of varying diameters, such as those found in the black butterfly, produced most stable absorption rates over the complete spectrum at variable angles of incidence.

The team then built a layer of disorderly positioned holes in a thin-film PV absorber, with diameters varying from 133 to 343 nm. This showed the absorption rate of perpendicular incident light increases by 97% and rises continuously until it reaches 207% at an angle of incidence of 50 degrees. “This is particularly interesting under European conditions. Frequently, we have diffuse light that hardly falls on solar cells at a vertical angle,” said Hölscher.

However, this does not automatically imply that efficiency of the complete PV system is enhanced by the same factor, says Guillaume Gomard of IMT. “Other components also play a role, so the 200 percent are to be considered a theoretical limit for efficiency enhancement,” he said.

The scientists demonstrated that light yield can be enhanced considerably by removing material. In the project, they worked with hydrogenated amorphous silicon, but any type of thin-film PV technology can be improved with such nanostructures, also on the industrial scale.

The scientists report their results in the journal Science Advances. DOI: 10.1126/sciadv.1700232.

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