Stacked solar cell reaches 43.9% efficiency

April 29, 2014 // By Paul Buckley
Stacked solar cell reaches 43.9% efficiency
Semprius Inc. has manufactured the first four-junction, four-terminal stacked solar cell which is capable of achieving a efficiency level of 43.9 percent by using the company's proprietary micro transfer printing process.

To achieve the world-class efficiency perfomance Semprius collaborated with Professor John Rogers and his team at the Frederick Seitz Materials Research Laboratory at the University of Illinois art Urbana-Champaign and researchers at Solar Junction , a leading III-V high-efficiency solar cell manufacturer and important Semprius partner.

Initial trials yielded solar cells with measured efficiencies up to 43.9 percent. The company claims the process is capable of achieving solar cell efficiencies greater than 50 percent in the near future.

The stacked solar cell is comprised of a three-junction microcell that is stacked on top of a single-junction germanium microcell using the Semprius’ micro transfer printing process, which enables the simultaneous formation of thousands of stacked microcells with high yields. By using four junctions, the stacked cell is able to capture light across a broader portion of the solar spectrum and therefore achieve efficiencies much higher than conventional silicon and thin-film single-junction solar cells.

A key achievement of the project was the development of a new interfacial material that is placed between the top and bottom cell to minimize optical losses within the stack and thereby optimize overall conversion efficiency. In addition, the new stacked cell has four terminals, rather than the standard two to reduce the spectral dependence of the solar cell and increase the solar cell’s energy yield under normal operation in the field.

In 2012, Semprius announced the first mass-produced photovoltaic module that exceeded 33 percent efficiency. In September 2013, Semprius increased this record to 35.5 percent, as confirmed by the Fraunhofer Institute for Solar Energy Systems ISE in Germany

Scott Burroughs, vice president of Technology at Semprius, said: “Because the process we used is fully compatible with our current production processes, we believe this demonstration can be easily transferred to manufacturing.”

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