Energy researchers set new record for solar cell efficiency
January 7, 2016
Scientists at the US Energy Department's National Renewable Energy Laboratory (NREL) and at the Swiss Center for Electronics & Microtechnology (CSEM) have jointly set a new world record for converting non-concentrated sunlight into electricity using a dual-junction III-V/Si solar cell.
The newly certified record conversion efficiency of 29.8 per cent was set using a top cell made of gallium indium phosphide developed by NREL, and a bottom cell made of crystalline silicon developed by CSEM using silicon heterojunction technology. The two cells were made separately and then stacked by NREL.
"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 per cent for crystalline silicon solar cells."
Young is co-author of a paper – "Realisation of GaInP/Si dual-junction solar cells with 29.8 per cent one-sun efficiency" – which details the steps taken to break the previous record. His co-authors from NREL are Stephanie Essig, Myles Steiner, John Geisz, Scott Ward, Tom Moriarty, Vincenzo LaSalvia and Pauls Stradins. The paper has been submitted for publication in the IEEE Journal of Photovoltaics.
Essig attracted interest from CSEM when she presented a paper – "Progress towards a 30 per cent efficient GaInP/Si randem solar cell" – to the Fifth International Conference on Silicon Photovoltaics, in Germany in March 2015.
"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 PV activities at CSEM.
A new design for the dual-junction solar cell and the contributions from CSEM were key to setting the record. These first collaboration results further indicate that even greater efficiency can be achieved by the combination of NREL and CSEM cells.
"CSEM partnered with the NREL scientists with the objective to demonstrate that 30 per cent efficient tandem cells can be realised using silicon heterojunction bottom cells, thanks to the combination with high performance top cells such as those developed by NREL," said Matthieu Despeisse, manager of crystalline silicon activities at CSEM.
The funding for the research came from the Energy Department's Office of Energy Efficiency and Renewable Energy SunShot Initiative, which aims to make solar energy fully cost-competitive with traditional energy sources, and from the Swiss Confederation and the Nano-Tera initiative.
NREL is the US Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by the Alliance for Sustainable Energy.