Black silicon in one step
Science continues to progress when it comes to increasing solar cell efficiency. Black silicon production is one example. Current research brings black silicon closer to mass production.
Researchers at Rice University in Houston, Texas, have developed a simpler method for producing black silicon. An advantage of the material is that it catches more sunlight, and thus converts more sunlight into electricity; the more light that is absorbed through the active elements of the solar cell, the more energy that is generated. The material looks black since it reflects hardly any light. This antireflection is achieved by using very small nano-needles to process the surface of the wafer. These needles need to be smaller than the wavelength of the light that is being trapped. Andrew Barron, project leader and chemist at Rice University, says, “Such surface structures efficiently absorb sunlight independently of irradiation angle – from sunrise to sunset. Previous strategies have reduced the reflection of sunlight off of the solar cells to about six percent, but antireflection is limited to a specific spectrum of sunlight and also dependent on angle of incidence and wavelength.”
Production reduced to one step
Until now, it took either a lot of time or energy to produce black silicon wafers. Texan researchers just reduced the process to one step that even takes place at room temperature. The researchers take a mixture of copper nitrate, phosphoric acid, hydrogen fluoride, and water. When this mixture is applied to a crystalline silicon wafer, the phosphoric acid reduces the copper ions to copper nanoparticles. These nanoparticles excite the electrons on the surface of the silicone, oxidize the silicon, and thus enable the hydrogen fluoride to burn an inverted pyramid structure into the silicon surface.
By refining this process, scientists succeeded in generating nanopores smaller than 590 nanometers. Researchers claim that these nanopores can catch ninety-nine percent of light. In contrast, pure, non-etched silicon reflects nearly one hundred percent of sunlight. Research is not yet complete and there is still a long way to go before mass production. “The needles still need a protective layer to guard them from exposure to weather conditions,” says Barron. Barron and his colleagues are also working to reduce production time farther; the etching process still lasts eight hours. “However, simplifying black silicon production to one step makes the process much more feasible than previous methods,” says Barron. (Sven Ullrich/ Craig Morris/ Michelle Hardy)