- Category: Technology
08 Oct 2012
- Published on Monday, 08 October 2012 10:13
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Mixing it up might not be a bad thing when it comes to organic solar cells.
Organic or polymer based solar cells are so called because they use conductive organic polymers of small molecules to transform light into energy, usually consisting of two domains known as the acceptor and donor layers.
When light hits an organic solar cell, the photons of light create excitons which move through the domains, generating a charge that can be harnessed for electricity.
Researchers had believed that keeping the donor and acceptor domains pure – preventing the materials of the layers from mixing – was the best way to ensure a smooth path of travel for the excitons for maximum energy generation.
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However, a team of researchers from the United Kingdom, Australia and China, as well physicists from North Carolina State University, took a closer look at the physical structure of polymer solar cells and found that some mixing might not be a bad thing.
According to NC State physicist Harald Ade, some mixing is already inherent in the production of these types of solar cells, and the team wanted to see what effect this had on the solar cells.
“When you manufacture the cell, the relative rate of evaporation of the solvents and additives determines how the active layer forms and the donor and acceptor mix. Ideally, you want the solvent to evaporate slowly enough so that the materials have time to separate – otherwise the layers ‘gum up’ and lower the cell’s efficiency,” he explained.
“We utilized an additive that slowed evaporation. This controlled the mixing and domain size of the active layer, and the portions that mixed were small.”
The efficiency of the mixed layers were not significantly lower than the best efficiency organic solar cells, claim the scientists. They believe that some mixing of the donor and acceptor isn’t a problem as long as the domains are small.
On an average, the power conversion efficiency of polymer solar cells tends to be in the range of 8 percent. Silicone-based solar cells have an efficiency ranging from 14 percent to 22 percent.
Currently, the best efficiency for organic solar cells his held by the German company Heliatek, which has achieved an efficiency of 10.7 percent for their organic tandem solar cells in April.
Because of the organic nature of the materials used in polymer solar cells, they are considered by some to be more environmentally friendly than those which use semiconductor material such as silicon, cadmium telluride or others that may be slightly toxic. They are also lighter and more flexible than solar products made with silicon, giving them a wider range of applications. – EcoSeed Staff