The economics of solar cells always involves striking a balance between conversion efficiency and manufacturing costs.
Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) believe that they have struck a balance between both of these factors by developing a nanotechnology-enabled silicon solar cell that boasts 18.2 percent conversion efficiency and that should be cheaper to produce.
The research, which was published in the journal Nature Nanotechnology (“An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructures”), was able to create a solar cell without the use of anti-reflective coatings that are typically required to reach that conversion efficiency.
The NREL team was able to achieve this high efficiency without anti-reflection coatings by making billions of nano-sized holes in silicon. Since the holes are actually smaller than the light wavelengths striking the silicon, there is no sudden change in the light density and the light doesn’t reflect back off the surface of the silicon.
While the NREL researchers had previously demonstrated that these nanostructures in silicon reflected less light off the surface, this latest research was the first time they were able to use the technique to achieve high conversion efficiency with the nanostructure silicon cells.
“This work can have a big impact on both conventional and emerging solar cell based on nanowires and nanospheres. For the first time it shows that really great solar cells can be made from nanostructured semiconductors,” Howard Branz, the principal investigator of the research says in an NREL press release.
While attaining high energy conversion efficiencies for an individual cell—and even doing it with a cheaper manufacturing process that eliminates the need for antireflective coating—is an achievement, a big obstacle remains getting those individual cells into a module without significant losses in efficiency.
This may be an area that will be addressed in further research. Branz adds: “The next challenges are to translate these results to common industrial practice and then get the efficiency over 20 percent. After that, I hope to see these kinds of nanostructuring techniques used on far thinner cells to use less semiconductor material.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.