Moth Eyes-Inspired Nanostructures May Help Improve Thin Film Solar Cells
Thanks to the optimized design and structure of moth’s eyes, researchers may be closer to improving the efficiency of thin-film solar cells, ScienceDaily reports.
Researchers from the North Carolina State University have used moth’s eye structure as inspiration to develop nanostructures that inhibit “thin film interference”. Thin film interference occurs when incident light waves form a new light wave due to the reflection of the upper and lower boundaries of a thin film against each other.
Regular thin-film solar cells more or less have completely flat layers between them. Their new test solar film layer though, has its bottom layer surface laden with lots of tiny cones. The cones represent the same structure that is found on moth eyes, and produces the same light-absorbing effect.
This phenomenon is also observed when gasoline causes thin film interference in the form of rainbow sheen. Gasoline is mostly transparent but some light still reflects off of its surface. Light that penetrated through the substance reflects off the underlying surface of the water where both surfaces meet. As it reflects off the water and passes back through the gasoline, it takes a somewhat different optical path than the original track. The mismatch of the optical path lengths causes the thin film interference in the form of rainbow sheen.
While thin-film interference is a harmless phenomenon in nature, it is an engineering challenge for devices that use multiple layers of thin films. One of these is the thin film solar cells. The goal of solar cells is to convert as much sunlight as possible into power. While mechanical efficiency is important, the success of solar cells depends in part on how much sunlight they capture in the first place. The more thin films a solar cell has, the more interfaces there are. This translates to more light being lost as it is reflected back.
The researchers built “interfacial” nanostructures into the thin film solar cells to limit the amount of light reflected off at the interface. The nanostructures resemble a thick forest of thin cones and are in reality an extension of the thin film underneath them. The research team found that an interface appended with the nanostructures reflected 100 times less light than those without the nanostructures.
As sunlight gets through the first layer and into the cone-laden nanostructure, very little to almost no sunlight is lost due to being reflected back. According to the report, the researchers have observed that the nanostructured layer was capable of lessening the light reflected by a factor of 100 (compared to a thin film layer on a regular thin-film solar cell). This means that if the added energy absorbed won’t dissipate away as heat, it could mean a very huge efficiency boost; at a level that might even trump current standard solar cells by an exponential degree.
Even though it is technically a good breakthrough concept however, it is still just in its test phase. The next step in their research is to actually create an entire solar cell that uses the nanostructure. They are going to add the nanostructure to a whole single thin-film cell to see if the decrease in reflected light would actually correspond to an increase in its absorption efficiency.
If the researchers prove that the concept is feasible after the next step though, the project would then move forward to the technology’s possible mass production and commercialization.
Thin-film solar cells, though very convenient to install and use, fails to become the common standard fundamentally because of its base (in)efficiency. We’re only talking about a 10-13% efficiency rate versus the standard 15-25% rate of crystalline-type solar cells. One of the key reasons for this low efficiency level is that light actually gets reflected back between the film units, and this lessens the total amount of light that the solar cell could absorb.
Dr. Chih-Hao Chang, assistant professor of mechanical and aerospace engineering at NC State and one of the co-authors of a paper in the research, said:
“We were inspired by the surface structure of a moth’s eye, which has evolved so that it doesn’t reflect light, By mimicking that concept, we’ve developed a nanostructure that significantly minimizes thin-film interference.”
The researchers’ work demonstrates how an open minded perspective can help solve modern day problems simply by being willing to learn from nature. Chang also said,
“Our next steps are to design a solar device that takes advantage of this concept and to determine how we can scale it up for commercial applications.”
Former North Carolina State graduate student Qiaoyin Yang was the lead author of the paper. Co-authors include North Carolina State Ph.D. students Xu A. Zhang, Abhijeet Bagal and Wei Guo as well as Dr. Chih-Hao Chang. The researchers’ work “Antireflection Effects at Nanostructured Material Interfaces and the Suppression of Thin-Film Interference” was published this month in the journal Nanotechnology. Their work was supported by a NASA Early Career Faculty Award and the National Science Foundation’s ASSIST Engineering Research Center at North Carolina State.
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