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Stanford Tech Makes Solar Cells Less Reflective, More Efficient


military cell coverA Stanford University team of scientists has recently found a new way of allowing more sunlight to be absorbed by solar cells.

In traditional cells, the energy is carried through a metal wire grid. The downfall is the grid also blocks the light from being used as energy. The findings of Vihay Narasimhan, Ruby Lais and Thomas Hymel could certainly lead to a breakthrough in technology.

Metal contacts are, of course, what is used to transfer electricity back and forth. The problem is that metal is not transparent. The lead study author, Narasimhan performed the work when he was a graduate student, “Using nanotechnology, we have developed a novel way to make the upper metal contact nearly invisible to incoming light.”

To the naked eye, the surface looked like a flat and shiny gold-mirror, but the gold was filled with an abundance of square, nano sized holes. When analyzed, the gold surface was seen to reflect 50% of the sunlight that they want to absorb. “The more metal you have on the surface, the more light you block. That light, is then lost and cannot be converted into electricity,” says Yi Cui, co-author. The team figured that hiding the reflective surface, somehow, may give them the opportunity to absorb more light with the semi-conductor.

To fix this one sided trade-off, the team immersed perforated gold film with silicon in a solution of hydrofluoric acid, with hydrogen peroxide. This process helped the team develop a nanopillar tower of silicon that would rise above the metal surface to redirect the light. The gold film sank into the silicon, and nanopillars popped up from holes that were in the film.

The outcome was that the gold surface turned a dark red color which indicated the metal was no longer reflecting the light. “As soon as the silicon nanopillars began to emerge, they started funneling light around the metal grid and into the silicon substrate underneath,” said Narasimhan.

These three very bright graduate students, Narasimhan, Hymel and Lai may have discovered a significant breakthrough in solar technology. It all started with the solar cell taking a dip.

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