Light-bending algae boost organic solar cell efficiency

[USA] No matter how useful a certain human innovation may be, nature has usually beaten us to it by millions of years, and more often than not done a better job of it too. A Yale team has looked to nature to help solve a design problem, using tiny fossilized creatures called diatoms to improve the light absorption rate of organic solar cells.

Diatoms are a group of phytoplankton, often called the “jewels of the sea” because of their glassy silica shells that warp light. Better yet, they’re extremely common in oceans and fresh water around the world, making them perfect candidates for improving photovoltaics.

“It’s really amazing that these things exist in nature,” says Lyndsey McMillon-Brown, lead author of the study. “They help trap and scatter light for the algae to photosynthesize, so we’re able to use something directly from nature and put it in a solar cell.”

Organic photovoltaic solar cells have an active layer made of organic polymers, which means they can be cheaper than conventional solar cells but not quite as efficient. The main issue is that the active layer needs to be very thin, less than 300 nanometers, which puts an upper limit on the conversion efficiency. To counter that, in the past engineers have embedded nanostructures that can trap light more effectively, but these materials begin to blow out the budget again.

The diatoms were added to the thin active layer in the organic solar cell

So the Yale team turned to nature. Diatoms can already scatter light effectively, so the researchers wanted to see if they could act as a cheaper, readily-available stand-in for those scattering materials. And, it turns out, they can. By embedding ground-up fossilized diatoms into the active layer of the cell, the researchers found they could reduce the amount of other materials needed while still producing the same amount of electricity.

“We were able to see what the right concentration was and how much of this material we needed to put into our solar cells to get enhancement,” says McMillon-Brown. “It’s really beneficial because the active layer materials we use are expensive and very rare. It didn’t interrupt our existing processing steps, so it doesn’t add any complexities or challenges, and can definitely be an easy addition to existing commercialized organic solar cells.”

The results have been promising, but the researchers say that they could be even better with some additional tweaking. Different species of diatoms may be better than others at scattering light, and these could be combined with different polymers in the active layer of the cell to find just the right combination for better efficiency.

The research was published in the journal Organic Electronics.

Photo: Yale researchers have used light-manipulating algae called diatoms to improve the efficiency of organic solar cells(Credit: Depositphotos/sciencepics)

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