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June 27, 2006

nanoscale tech: Boosting solar cell efficiency by making silicon black

Silicon surfaces rendered black by pits and bumps only nanometers or billionths of a meter large could in the future help make solar power cells 15-20 percent more efficient. Koynov and his colleagues instead developed a simple and fast technique that creates these textures using wet chemical processes. Their method works regardless of the crystalline structure of the silicon, its thickness, or what extra chemical additives it possesses.

Scientists want to minimize reflection as much as possible when it comes to solar power cells made of silicon, because the more light they reflect, the less they convert to electricity. Often, anti-reflective coatings are used, which reduce the amount of average reflection in the wavelengths of light solar power cells use by 85 percent to 92 percent. The novel treatment developed by researchers at the Technical University of Munich can cut the surface reflection silicon experiences by 95 percent to 98 percent across the wavelengths of light solar power cells use, making them black.

Steps:
1) Deposit grains of gold only nanometers large onto a flat silicon surface.
2) Next the silicon between the areas covered by the clusters is etched away with a solution of hydrogen peroxide and hydrofluoric acid. The gold nanoparticles exhibit catalytic action drilling into the surface.
3)The areas covered by the gold form 50-to-100-nanometer-high pits on the surface while the silicon between the gold makes up the bumps.
4)The nanoparticles are then removed with a solution of iodine and potassium iodide.

Gold could react badly with semiconductors, so other metals have also been analyzed with some success.

Related solar articles:
Daystar reaches milestones in efficiency

Prior article on competing solar firm, nanosolar

Solar energy survey and prior info on Daystar

the Energy blog's summary of a solar industry forecast Solar Production will reach at least 10 GW/yr by 2010 (530% growth versus 2005).

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