Taking inspiration from moth eyes, researchers have come up with a way to improve efficiency in solar cells and sharpen views for image sensors, as well as produce the needed patterned lenses more easily.
In solar cells, antireflective coating are responsible for collecting as much sunlight as possible to generate the most power. However, they are best suited for preventing a specific light wavelength from being reflected. Different films may be layered together to achieve the highest level of absorption, but the method is expensive and cannot be achieved over big areas.
In nature, an alternative strategy for design is found in moth eyes. Nocturnal moths are able to travel at night, relying just on light from the moon and stars and this is possible because they have eyes comprised of arrays of ommatidia or microsized lenses. Patterned in a dome, the ommatidia allows for reduced reflection and water beading. Despite discovering this design alternative, however, recreating patterns in moth eyes proved to be incompatible with manufacturing process on a large scale.
To address the problem, researchers turned to nanoimprint lithography, a stamping method that lets nanoscale patterns be imprinted over large areas in high resolution. Two sets of molds made out of nickel were used, one with microlens patterns and another with 200-nanometer domes. The molds were used on polycarbonate films, first the nanodomes and then the microlens patterns.
The resulting polycarbonate array was tested by researchers, comparing it with microlens arrays that don't include nanodome patterns to determine how much light it can reflect. Researchers found that the polycarbonate array reflected only 4.8 percent of light while microlens arrays reflected 8.7 percent of light. Even changing angles at which the light hits the arrays resulted in the polycarbonate sample to outperform the microlens array by twice as much.
Having figured out the right pattern to boost efficiency in solar cells, researchers are now working on demonstrating that making the polycarbonate array can be scaled to produce coatings as big as square meters. They are in the process of adapting the nanoimprint lithography method they used to a roller printer, which they believe should be able to stamp patterns on large-sized materials at high speed.
Published in the journal ACS Nano, the research lists Hemant Kumar Raut, Seeram Ramakrishna, Saman Safari Dinachali, Mohammad S. M. Saifullah, V. Anand Ganesh, Yee Chong Loke, Eng Huat Khoo, Aleksander Gora, Ramakrishnan Ganesan and Kwando Konadu Ansah-Antwi as authors.
Photo: Michael Dorausch | Flickr
