Highest Efficiency in Black Solar Cells Ever: 18.7%

Scientists at Aalto University (Finland) and Fraunhofer Institute for Solar Energy Systems (Germany) reported at the 3rd International Conference on Crystalline Silicon Photovoltaics (25-27 March 2013, Hamelin, Germany) an efficiency of 18.7% for black silicon solar cells, the highest efficiency reported so far for a black silicon solar cell.

The previous efficiency record of 18.2% was held by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) using thermal oxidation as a passivating layer.

Solar panels convert into electricity only three quarters of the energy of sunlight due to the loss of all the infrared part of the spectrum. One way of overcoming this problem is to use black silicon, a material that absorbs and converts the most of the sunshine.

Black silicon is produced by irradiation of conventional silicon by femtosecond laser pulses in a gaseous medium, usually containing sulfur. During this process the intermediate levels are generated, which facilitate the electrons “jumping”.

The researchers were able to apply a boron diffusion to create a pn-junction, maintaining the excellent optical properties of the black silicon structure. By applying atomic layer deposited Al2O3, an effective passivation of the nanostructured surfaces was achieved.

Routes for improving the cell efficiency are already identified, and efficiencies clearly above 20% should be within reach.