Meet the Super Efficient
by David Wogan
Okay, they aren't actually Legos, but if you pulled up a microscope and took a peek at one of these solar panels, you would see a familiar studded pattern. A problem with solar panels is that most of the light energy that hits a solar panel is not absorbed.
But by trapping light in a solar panel, researchers found they can increase the overall efficiency of a panel by up to 22%. These results are published in the October issue of Scientific Reports by researchers from Imperial College of London, Belgium, China, and Japan.
"In recent years both the efficiency and cost of commercial solar panels have improved but they remain expensive compared to fossil fuels. As the absorbing material alone can make up half the cost of a solar panel our aim has been to reduce to a minimum the amount that is needed," said Dr. Nicholas Hylton from the Department of Physics at Imperial College London.
"The success of our technology, in combination with modern anti-reflection coatings, will take us a long way down the path towards highly efficient and thin solar cells that could be available at a competitive price."
Dr. Hylton and his colleagues attached rows of aluminum cylinders just 100 nanometers across to the top of the solar panel - giving them a Lego-like appearance - where they interact with passing light, causing individual light rays to change course. More energy is extracted from the light as the rays become trapped inside the solar panel and travel for longer distances through its absorbing layer.
To make the "bricks", several layers of gallium arsenide (a semi-conductor) and silicon dioxide (a protective layer) were added on top of a base of semi-conductors. The aluminum was then deposited on top of the stack, and patterned into studs using electron beam lithography. Previous attempts have used silver and gold studs because those materials have strong interactions with light, but researchers found that they interact too well with light by absorbing the light before it enters the solar panel.
"The key to understanding these new results is in the way the internal structures of these metals interact with light. Gold and silver both have a strong effect on passing light rays, which can penetrate into the tiny studs and be absorbed, whereas aluminum has a different interaction and merely bends and scatters light as it travels past them into the solar cells."
It also helps that aluminum is cheaper and far more abundant than silver and gold.
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