Semprius has manufactured a four-junction, four-terminal stacked solar cell in collaboration with scientists at the University of Illinois/Urbana-Champaign and researchers at Solar Junction. Initial trials yielded measured efficiencies up to 43.9 percent.
The stacked solar cell is comprised of a three-junction microcell that is stacked on top of a single-junction germanium microcell using Semprius’ high-speed micro transfer printing process, which enables the simultaneous formation of thousands of stacked microcells with very 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 this 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. This reduces the spectral dependence of the solar cell and increases the solar cell’s energy yield under normal operation in the field.