Thursday, 17 January 2013

New path to more efficient organic solar cells uncovered
7 Jan 2013

Why are efficient and affordable solar cells so highly coveted? Volume. The amount of solar power lighting up Earth's land mass every year is nearly 3,000 times the total amount of annual human energy use. But to compete with energy from fossil fuels, photovoltaic devices must convert sunlight to electricity with a certain measure of efficiency. For polymer-based organic photovoltaic cells, which are far less expensive to manufacture than silicon-based solar cells, scientists have long believed that the key to high efficiencies rests in the purity of the polymer/organic cell's two domains -- acceptor and donor. Now, however, an alternate and possibly easier route forward has been shown.

Working at Berkeley Lab's Advanced Light Source (ALS), a premier source of X-ray and ultraviolet light beams for research, an international team of scientists found that for highly efficient polymer/organic photovoltaic cells, size matters.

"We've shown that impure domains if made sufficiently small can also lead to improved performances in polymer-based organic photovoltaic cells," says Harald Ade, a physicist at North Carolina State University, who led this research. "There seems to be a happy medium, a sweet-spot of sorts, between purity and domain size that should be much easier to achieve than ultra-high purity."

Ade, a longtime user of the ALS, is the corresponding author of a paper describing this work in Advanced Energy Materials titled "Absolute Measurement of Domain Composition and Nanoscale Size Distribution Explains Performance in PTB7:PC71 BM Solar Cells." Co-authors are Brian Collins, Zhe Li, John Tumbleston, Eliot Gann and Christopher McNeill.

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