Nanostructures inspired by butterfly wings can be added to solar cells, enhancing their light absorption rate by up to 200 per cent.
A team from the Karlsruhe Institute of Technology (KIT) in Germany have found that the wings of the butterfly Pachliopta aristolochiae are drilled by nanostructures (nanoholes) that help absorbing light over a wide spectrum far better than smooth surfaces.
“The butterfly studied by us is very dark black," said Dr. Hendrik Hölscher of KIT’s Institute of Microstructure Technology.
"This signifies that it perfectly absorbs sunlight for optimum heat management. Even more fascinating than its appearance are the mechanisms that help reaching the high absorption. The optimisation potential when transferring these structures to photovoltaics (PV) systems was found to be much higher than expected.”
Hölscher's team reproduced the butterfly’s nanostructures in the silicon absorbing layer of a thin-film solar cell. Subsequent analysis of light absorption yielded promising results: Compared to a smooth surface, the absorption rate of perpendicular incident light increased by 97% rising continuously until it reached 207% at an angle of incidence of 50 degrees.
Prior to transferring the nanostructures to solar cells, the researchers determined the diameter and arrangement of the nanoholes on the wing of the butterfly by means of scanning electron microscopy. Then, they 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, with respect to periodically arranged monosized nanoholes. Hence, the researchers introduced disorderly positioned holes in a thin-film PV absorber, with diameters varying from 133 to 343 nm.
They demonstrated that light yield can be enhanced considerably by removing material. In the project, they worked with hydrogenated amorphous silicon. According to the researchers, however, any type of thin-film PV technology can be improved with such nanostructures, also on the industrial scale.
[Nanostructures of the wing of Pachliopta aristolochiae can be transferred to solar cells and enhance their absorption rates by up to 200 percent. Image: Radwanul Siddique, KIT/Caltech]