Mimicking the nanostructures (nanoholes) present on the wings of the butterfly Pachliopta aristolochiae scientists have created nanostructures on solar cells that help increase the cells’ sunlight absorption rate by 200 per cent.
The nanostructures on the wings of the butterfly help the insect absorb light over a wider spectrum – far better than smooth surfaces. If we consider solar cells, their surface is relatively smooth and due to that quite a lot of sunlight is reflected and that all accounts for lost unused energy.
Researchers of Karlsruhe Institute of Technology (KIT) reproduced the butterfly’s nanostructures in the silicon absorbing layer of a thin-film solar cell. 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 analyzed 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 nanometers.
The scientists 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.
On testing it was revealed that compared to a smooth surface, the absorption rate of perpendicular incident light increases by 97 per cent and rises continuously until it reaches 207 per cent at an angle of incidence of 50 degrees. However, this does not automatically imply that efficiency of the complete PV system is enhanced by the same factor and more study is required to determine the overall increase in efficiency of the PV system.
The study is published in the journal Science Advances.