Solar CIGS reach 18.7 percent efficiency

Swiss lab improves efficiency for CIGS cells using plastic substrate, beating its own record and U.S. December announcement of 15.7 percent.

Empa and Flisom's flexible CIGS solar cell made on a polymer substrate. Empa

Swiss scientists have broken an energy conversion efficiency record for flexible thin-film CIGS solar cells, Empa, the Swiss Federal Laboratories for Materials Science and Technology, announced last week.

In collaboration with the Swiss solar start-up Flisom, Empa has achieved an 18.7 percent efficiency for CIGS (copper indium gallium selenide) flexible solar cells, which the lab says was made possible by mounting them on a polymer substrate. This breaks Empa's record of 17.6 percent when mounting the CIGS on steel foil substrates, according to the Swiss lab.

Solar efficiency is the amount of electricity per square inch that can be gleaned from a solar cell. While traditional silicon cells are generally more efficient that CIGS cells, CIGS cells have some advantages.

Flexible CIGS can be made via roll-to-roll processing in which the cells are "printed" or patterned on giant rolls of flexible material, which makes them less expensive to manufacture than traditional cells. Because CIGS can be made flexible and are generally lighter than silicon panels, they offer more options on how they can be installed and what kind of frames or supports are needed, and can be less expensive to ship.

"The latest improvements in cell efficiency were made possible through a reduction in recombination losses by improving the structural properties of the CIGS layer and the proprietary low-temperature deposition process for growing the layers as well as in situ doping with Na during the final stage. With these results, polymer films have for the first time proven to be superior to metal foils as a carrier substrate for achieving highest efficiency," Empa said in a statement.

The breakthrough is significant.

In December 2010, the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) confirmed that start-up MiaSole had achieved 15.7 percent efficiency for its CIGS solar cells. Those cells are also made via roll-to-roll manufacturing.

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