Yesterday (Jan. 5) scientists at the National Renewable Energy Laboratory (NREL) and at the Swiss Center for Electronics and Microtechnology (CSEM) announced a new world record for converting sunlight into electricity using a dual-junction photovoltaic cell. The new test cell reached 29.4 percent efficiency without concentrating the power of the sun on the cell.
Moreover, "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.”
The new cell consists of two photovoltaic layers, a top cell made of gallium indium phosphide developed by NREL, and a bottom cell made of crystalline silicon heterojunction cell developed by CSEM. NREL stacked the two cells together to create the dual-junction device. Multi-junction solar cells can absorb more of the sun’s light, producing more electricity. However, most have been made out of more expensive materials, making them too expensive for use in conventional solar panels.
NREL researcher Stephanie Essig previously presented "Progress Towards a 30 percent Efficient GaInP/Si Tandem Solar Cell," to the 5th International Conference on Silicon Photovoltaics, in Germany in March. That attracted interest from CSEM. "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.
"CSEM partnered with the NREL scientists with the objective to demonstrate that 30 percent efficient tandem cells can be realized using silicon heterojunction bottom cells, thanks to the combination with high performance top cells such as those developed by NREL," added Matthieu Despeisse, manager of crystalline silicon activities at CSEM.
The researchers created a new design for the dual-junction solar cell. They said that and the contributions from CSEM were key to setting the record.
The researchers have submitted the research paper "Realization of GaInP/Si dual-junction solar cells with 29.8 percent one-sun efficiency," for publication in the IEEE Journal of Photovoltaics. The paper, co-authored by Young, Essig, Myles Steiner, John Geisz, Scott Ward, Tom Moriarty, Vincenzo LaSalvia, and Pauls Stradins, details how they broke the previous record. The researchers believe that greater efficiency can be achieved by the combination of NREL and CSEM cells.Tweet