Stacked polymer cells set solar energy record

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LOS ANGELES (Feb. 14, 2:30 p.m. ET) — Scientists at the University of California, Los Angeles (UCLA) say they have significantly boosted the performance of polymer solar cells by building a new “tandem” device, stacking multiple cells which absorb different bands of the solar spectrum and convert them into electricity.

Independent verification comes from the US Department of Energy’s National Renewable Energy Laboratory, which has certified with a power conversion efficiency of 10.6 percent – a new record.

Tandem solar cells are an effective way to harvest a broader spectrum of solar radiation. However, conversion efficiency only increases when combining two cells if their materials are mutually compatible – hitherto making the performance of tandem devices lag behind that of single-layer solar cells.

The UCLA team’s breakthrough is a range of highly efficient single-layer and tandem polymer solar cells featuring a “low band gap conjugated” polymer designed specifically for the tandem structure. The band gap determines which part of the solar spectrum a polymer absorbs.

Professor Yang Yang of UCLA likens the configuration to a double-decker bus. He says: “The bus can carry a certain number of passengers on one deck, but if you were to add a second deck, you could hold many more people for the same amount of space. That’s what we’ve done here with the tandem polymer solar cell.”

He continues: “Everything is done by a very low-cost wet-coating process. As this is compatible with current manufacturing [techniques], I anticipate this technology will become commercially viable in the near future.”

The work is published in the peer-reviewed journal Nature Photonics.