A dual-junction semiconductor solar cell has overcome a theoretical limit to take a world record for efficiency — 29.8 percent. The device consists of a GaInP top cell developed at the National Renewable Energy Laboratory (NREL) and a crystalline silicon bottom cell developed at the Swiss Center for Electronics and Microtechnology (CSEM). "It's a record within this mechanically stacked category," said David Young, a senior researcher at NREL. "The performance of the dual-junction device exceeded the theoretical limit of 29.4 percent for crystalline silicon solar cells." Created separately and stacked by NREL, the two cells work in concert using silicon heterojunction technology. "We believe that the silicon heterojunction technology is today the most efficient silicon technology for application in tandem solar cells" said Christophe Ballif, head of photovoltaic activities at CSEM. The result indicates that even greater efficiencies can be achieved through combining cells, the researchers said. Funding for the project came from the U.S. Department of Energy, Swiss Confederation and Nano-Tera.ch initiative. The record was published in Progress in Photovoltaics (doi: 10.1002/pip.2728) along with efficiency ratings for multiple cell and module types.