Thin-film photovoltaic modules have several advantages over conventional crystalline solar cells. They are lighter, cheaper to manufacture, use far less raw material, and are flexible enough to be embedded in clothing or rolled up and transported to a new location. Thin-film solar panels have several disadvantages as well, not the least of which is that they are far less efficient than their crystalline silicon cousins.
Scientists at the Karlsruhe Institute of Technology in Germany have discovered a way to boost the solar absorption rate of thin-film solar by as much as 200%. The secret? Imitating the tiny nanoholes found in the wings of the Pachliopta aristolochiae butterfly. That particular species was selected for study because its wings are almost completely black.
“The butterfly studied by us is very dark black. 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.” Using an electron scanning microscope, the researchers found the wings were perforated by a series of nanoholes that varied between 133 to 343 nanometers. The variance in the size of the holes allowed the wings to absorb light at a variety of different angles.
Reproducing the pattern and size of the holes in a thin-film substrate also allowed for the enhanced absorption of light from varying angles. “The optimization potential when transferring these structures to photovoltaic systems was found to be much higher than expected,” says Dr. Hendrik Hölscher of KIT’s Institute of Microstructure Technology. The results of the research conducted by him and his peers has just been published in the journal Science Advances.
The scientists found that, compared to a smooth surface, the absorption rate of perpendicular light increased by 97% and rose continuously until it reached 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,” Dr. Hölscher says.
Laboratory research is always fun to read about but may or may not ever make the transition from the lab to commercial use. If the research can be applied at an industrial scale, thin film technology could begin to match the efficiency of traditional solar panels at significantly lower prices.