Black silicon lets maximum amount of sunlight reach a solar cell. It is simply silicon with a highly textured surface of nano-scale spikes or pores that are smaller than the wavelength of light. The texture allows efficient collection of light from any angle - from sunrise to sunset.

Andrew Barron and Yen-Tien Lu from Rice University in US replaced a two-step process that involved metal deposition and electro-less chemical etching with a single step process that works at room temperature.

The chemical stew that made it possible was a mix of copper nitrate, phosphorous acid, hydrogen fluoride and water.

When applied to a silicon wafer, the phosphorous acid reduces the copper ions to copper nanoparticles. The nanoparticles attract electrons from the silicon wafer's surface, oxidising it and allowing hydrogen fluoride to burn inverted pyramid-shaped nanopores into the silicon.

Fine-tuning the process resulted in a black silicon layer with pores as small as 590 nanometres (billionths of a metre) that let through more than 99 percent of light. By comparison, a clean, un-etched silicon wafer reflects nearly 100 percent of light.

The findings appeared in Journal of Materials Chemistry.


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