March 27 2009 / by Garry Golden
Category: Energy Year: General Rating: 2
Researchers at the Georgia Institute of Technology have developed a unique super-'hydrophobic' (water repelling) surface coating that 'boosts the light absorption of silicon photovoltaic cells both by trapping light in three-dimensional structures, and by making the surfaces self-cleaning allowing rain or dew to wash away the dust and dirt that can accumulate on photovoltaic arrays'.
The 'self cleaning' design mimics the water repelling surface of a lotus leaf, 'which uses surface roughness at two different size scales to create high contact angles that encourage water from rain or (desert dew) condensation to bead up and run off. As the water runs off, it carries with it any surface dust or dirt – which also doesn't adhere because of the unique surface properties'.
"The more sunlight that goes into the photovoltaic cells and the less that reflects back, the higher the efficiency can be," said C.P. Wong, Regents' professor in Georgia Tech's School of Materials Science and Engineering. "Our simulations show that we can potentially increase the final efficiency of the cells by as much as two percent with this surface structure."
"A normal silicon surface reflects a lot of the light that comes in, but by doing this texturing, the reflection is reduced to less than five percent," said Dennis Hess, a professor in the Georgia Tech School of Chemical and Biomolecular Engineering. "As much as 10 percent of the light that hits the cells is scattered because of dust and dirt of the surface. If you can keep the cells clean, in principle you can increase the efficiency. Even if you only improve this by a few percent, that could make a big difference."
This image shows silicon pyramid structures etched for one minute using hydrogen fluoride/hydrogen peroxide/water solution. The resulting structure has roughness at the micro and nanometer scales.
Credit: Image courtesy of C.P. Wong