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Black Silicon Can Increase Solar Efficiency

Researchers at Heinrich-Hertz-Institut (HHI) have found a way to boost solar cell efficiency by using black silicon, a material that can absorb virtually all sunlight that hits it, including infrared radiation.

Traditional silicon-based PV cells capture solar radiation and convert it to electricity, but not all types of solar radiation can be absorbed.

Almost 25 percent of the sun’s light spectrum is made up of infrared radiation, which cannot be converted to electricity by traditional PV cells. Using black silicon can overcome this inability to fully capture solar radiation.

“Black silicon is produced by irradiating standard silicon with femtosecond laser pulses under a sulfur containing atmosphere,” explains Dr. Stefan Kontermann, head of the research group working on the project at HHI.

“This structures the surface and integrates sulfur atoms into the silicon lattice, making the treated material appear black,” he added.


Black silicon irradiated with a laser. Photo Credit: Fraunhofer HHI


If manufacturers were to equip their solar cells with this black silicon, it would significantly improve solar cell efficiency.

The researchers changed the shape of the laser pulse used to irradiate the silicon, helping them solve a key issue of black silicon: In regular silicon, infrared light doesn’t have enough energy to excite the electrons into the conduction band and convert them to electricity.

However, the laser pulses can alter the sulfur incorporated into the black silicon to change its energy levels by controlling the flow of electrons.

Black silicon solar cell prototypes have been built successfully – the next step is to make them commercially available. The researchers are hoping to increase the efficiency of commercial solar cells, which is currently at around 17 percent, by one percent when black silicon is used.

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