Scientists have figured out why low-cost organic solar cells lose their efficiency over time

OptiSolar solar panels.

Like in other areas of electronics, silicon dominates the solar field. But researchers have pinpointed other promising materials that could someday lead to cheaper and/or more efficient solar cells.

Polymers are one of those materials. They are used in organic solar cells, which many say could someday help lower the cost of solar panels and help them compete more effectively with fossil fuel power. They are also physically flexible, which means they could be incorporated into many different types of surfaces to create new types of solar energy collection.

But organic cells have a flaw: They are less efficient at converting light energy into electricity than silicon cells, and their efficiency declines as they operate. Preventing that decline in efficiency is necessary if backers want to make them a cost-effective alternative to silicon cells.

Technical University of Munich researchers published a paper in Advanced Materials (subscription required) today describing the first observation of why the efficiency declines occurs. They found that when a key layer inside the cells absorbs light and releases electrons, its structure expands and spreads apart. This causes the areas that are actively converting light into electricity to shrink. The team observed that this caused the efficiency to drop by 25 percent over a seven hour period.

With that knowledge in hand, the researchers are now interested in developing cells that combat the forces that caused them to become less efficient. For example, the key layers could be built so that they readjust to their optimal size, instead of the less efficient size, once the cell starts operating. The researchers will also look into reducing or controlling the shift by adding other materials.

“The consequence of such measures could be that industrially produced cells finally cross the economically crucial efficiency threshold also for long-term operation,” co-author Stephan Roth said in a release.


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