Polymer can Boost Plastic Solar Cells

Wednesday, December 2, 2015 @ 12:12 PM gHale

As the world increasingly looks to alternative sources of energy, inexpensive and environmentally friendly polymer-based solar cells have attracted significant attention, but they still do not match the power garnered by their more expensive silicon-based counterparts.

However, a newly developed polymer can minimize energy loss as well as silicon-based solar cells when converting photon energy from sunlight to electricity, said researchers at the RIKEN Center for Emergent Matter Science and Kyoto University’s Department of Polymer Chemistry.

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Solar cells work because photons from the sun strike electrons and move them into a position where they can create an electric current. Photon energy loss — the amount of energy lost when converting photons energy from sunlight into electric power — was greater in polymer-based solar cells than in silicon-based ones.

“In polymer-based plastic solar cells, larger photon energy loss causes lower voltage. This has been one of the largest limiting factors for efficiency,” said Hideo Ohkita, one of the authors of a study on the subject. “The new polymer has the potential to lead to a breakthrough on this issue.”

The group began working with the new polymer, where oxygen rather than sulfur atoms end up located at key positions, and found the new material was able to overcome some of the key obstacles to extracting and utilizing greater energy from sunlight.

“Since this new polymer greatly reduces photon energy loss, it has allowed us to achieve a superb power conversion efficiency of nearly 9 percent with a very high open-circuit voltage in plastic solar cells,” said researcher Itaru Osaka.

An efficiency of 15 percent is a breakthrough level that will allow polymer-based cells to end up commercialized.

“By achieving both a high short-circuit current and a high open-circuit voltage,” he said, “achieving a power conversion efficiency of 15 percent in single-junction cells is a realistic goal. This would have huge implications for the solar energy sector.”