NREL hits 18.2% efficiency with black silicon solar cell

Oct 16, 2012 - The US National Renewable Energy Laboratory (NREL) on Friday said it had reached 18.2% efficiency with black silicon solar cells using nanotechnology techniques.

NREL achieved that result after optimising the surface area and the doping concentration of its nanotechnology process.

One of the key features of the cells is that the black silicon material does not reflect light. NREL explains that the technology will allow manufacturers to cut solar cell production costs as it eliminates the need to add an anti-reflection layer, or two. Minimum reflectivity in solar cells is crucial as all reflected light is actually wasted.

“The next challenges are to translate these results to common industrial practice and then get the efficiency over 20%,” commented Howard Branz, part of the NREL scientist team that worked on the black silicon cells. The US Energy Department backed the research with a grant under the American Recovery and Reinvestment Act.

NREL's process involves nano-islands of silver on a silicon wafer that are immersed briefly in liquids to make billions of nano-sized holes on the wafer surface. The holes and silicon walls are smaller than the light wavelengths hitting them, so the light does not recognize any sudden change in density at the surface and, thus, do not reflect back into the atmosphere.

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