Research from physicists at North Carolina State University (NCSU) and other places is challenging a once-held belief about polymer-based solar cells, and could help those power sources be more efficient.
Polymer-based solar cells use two domains, known as acceptor and donor layers. Energy particles, called excitons, must travel quickly between the layers so that they can be harnessed as an energy source. It was believed that for the excitons to travel the most efficiently between the two layers — and thus have the solar cells capture the most amount of energy — those layers had to be as pure as possible, reports Insciences Organisation.
But Harald Ade, a physicist from NCSU, and scientists from the United Kingdom, Australia, and China, found that this theory may no longer be true. Their research, published in Advanced Energy Materials and Advanced Materials, showed that some mixing of the two layers may not be detrimental to the energy-generation process. In fact, the researchers found, if the structure of the mixed domains is small, the solar cell works quite efficiently.
We had previously found that the domains in these solar cells weren’t pure. So we looked at how additives affected the production of these 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. 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.
Ade and his colleagues are trying to find the optimum proportion. “We’re looking for the perfect mix here, both in terms of the solvents and additives we might use in order to manufacture polymer-based solar cells, and in terms of the physical mixing of the domains and how that may affect efficiency,” Ade says.
A polymer solar cell is a flexible solar cell, made with polymers that convert sunlight into electricity using the photovoltaic effect. Most commercial solar cells are made from a purified silicon crystal, similar to what is used in integrated circuits and computer chips. But the high cost of the silicon solar cells and their complex production process has prompted researchers and manufacturers to search for alternate photovoltaic technologies. Polymer solar cells are lighter than silicon-based cells, potentially disposable, flexible, have less environmental impact, and are relatively inexpensive to build.
Source: “Researchers Reveal How Solvent Mixtures Affect Organic Solar Cell Structure,” Insciences, 10/5/12
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