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Plastic solar cell reduces photon energy loss

Posted: 09 Dec 2015     Print Version  Bookmark and Share

Keywords:Kyoto University  solar cell  photon energy  silicon  polymer 

The holy grail of alternative energy sources remains elusive despite the attention given to cheaper and environmentally-friendly polymer-based solar cells. Although there has been significant progress in developing these technologies, they are still behind their more expensive silicon-based counterparts in terms of power harvesting performance.

Now, researchers at the RIKEN Centre for Emergent Matter Science and Kyoto University's department of polymer chemistry have shown that a newly developed polymer can reduce energy loss as well as silicon-based solar cells when converting photon energy from sunlight to electricity.

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," noted Hideo Ohkita, one of the authors of the study, which was published in the December 2 issue of Nature Communications. "The new polymer has the potential to lead to a breakthrough on this issue."

Solar energy conversion

A Japanese research team revealed an unusual way to achieve more efficient and robust conversion of solar energy into electricity (Photo credit: Kyoto University)

The group began working with the new polymer, where oxygen rather than sulfur atoms are located at key positions, and found that the new material was able to overcome some of the key obstacles to extracting and using 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 nine per cent with a very high open-circuit voltage in plastic solar cells," said Itaru Osaka, one of the authors of the study.

An efficiency of 15 per cent is usually seen as a breakthrough level that will allow polymer-based cells to be commercialised.

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

Plastic solar cell

(a) Chemical structures of PNTz4T and PNOz4T. (b) UV-visible absorption spectra of PNTz4T and PNOz4T in the thin film spin-coated from chlorobenzene solution. (c) Cyclic voltammogrammes of PNTz4T, PNOz4T (in the thin film), PC61BM and PC71BM (in the solution). (d) Energy diagrams of PNTz4T, PNOz4T, PC61BM and PC71BM, where the values were estimated by cyclic voltammetry. a.u., arbitrary unit.

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