AALTO UNIVERSITY, HELSINKI, FINLAND & FRAUNHOFER INSTITUTE FOR SOLAR ENERGY SYSTEMS ISE, FREIBURG, GERMANY. A team of researchers developed black silicon solar cells that have higher efficiencies. Black silicon cells are designed to get anything from the infrared spectrum that typical solar cells cannot absorb. Being able to integrate black silicon cells with conventional solar cells can boost the total solar cell efficiency by about 1%.

Assistant Professor Hele Savin of Aalto University and researchers from Fraunhofer ISE improved the efficiency of black silicon solar cell to 18.7%. This new efficiency record broke the existing 18.2% record held by the US Department of Energy’s National Renewable Energy Laboratory (NREL) that utilized thermal oxidation as a passivating layer.

Black silicon is acquired by irradiating conventional silicon under sulfur atmosphere with a femtosecond laser. Then the surface is roughened and individual sulfur atoms in the silicon lattice are installed. The material is apparently black. The team developed a new “Passivation” method that set a new record for efficiency.

The researchers applied a boron diffusion in order to create a pn-junction, maintaining the excellent optical properties of the black silicone structure. Then, by applying atomic layer deposited AI203, an effective passivation of the nanostructured surface was achieved. Their study reveals that the nano structured front surface has a high electrical quality comparable to a pyramidal textured surface. Currently, the team is looking for ways that will still improve the process to achieve efficiencies more than 20%.