Fraunhofer Institute scientists boosts efficiency of black silicon solar cells

German researchers from the Fraunhofer Institute discovered a way to further improve black silicon solar cells. The team is now working on mass producing the process as well as creating a hybrid cell that combines black silicon with a conventional solar panel to further improve efficiency.

Black silicon is a material that can absorb almost the entire spectrum of light. This includes infrared radiation. In comparison, traditional silicon solar panels can only capture 75% of the spectrum for conversion into solar energy.

To create black silicon, a laser is used to irradiate regular silicon under sulfuric conditions. The laser pulse treatment causes the silicon to integrate the sulfur into its composition, which turns it black.

Infrared does not possess enough energy to excite the electrons in the conduction band of normal silicon. The sulfur added to black silicon forms an intermediate level in the atomic lattice. This additional level serves as a step for electrons, allowing them to jump to the conduction band and vice versa. This allows black silicon to convert infrared radiation into usable electrical energy.

However, the transfer is still inefficient. Energy is still wasted when electrons move backwards from the conduction band.

The Fraunhofer Institute research team changed the shape of the laser pulses to overcome this weakness.  According to Dr. Stefan Kontermann, the new laser treatment maximizes the number of electrons that can climb up while minimizing the number that can go back down. This effectively doubled the efficiency of black silicon.

Engineers are already producing prototypes of the improved black silicon cells. They are also testing a new, tandem solar cell design that replaces the black covering of a standard solar cell with black silicon. The hybrid design is expected to boost efficiency by at least one percent.

In addition, the Fraunhofer Institute is also preparing the modified pulse laser system for mass production. Solar panel manufacturers will be able to create black silicon by simply adding the laser to their assembly line.

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