A team of American and Swiss scientists have set a new world efficiency record in solar energy conversion for a dual-junction silicon solar cell.
The record conversion level of 29.8 percent was achieved by stacking a top cell made of gallium indium phosphide (GaInP), developed by researchers at the U.S. National Renewable Energy Laboratory (NREL), onto a highly efficient crystalline silicon bottom cell; which was developed separately by researchers at the Swiss Centre for Electronics and Microtechnology (CSEM).
The resulting dual-junction III-V/Si solar cell performed better than what the NREL team thought possible.
“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 record was published in the official ledger “Solar efficiency tables”. Young’s co-authored paper “Realization of GaInP/Si dual-junction solar cells with 29.8 percent one-sun efficiency,” detailing the path to his team’s breakthrough, has been submitted for publication in the IEEE Journal of Photovoltaics.
The NREL has attracted U.S. government Sunshot funding achieve even higher efficiencies in dual-junction solar devices, and it was previous work by team member Stephanie Essig that piqued the interest of scientists at Switzerland’s CSEM labs.
“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,” said Matthieu Despeisse, the manager of crystalline silicon activities at CSEM.
Silicon heterojunction solar cells are composed of a monocrystalline silicon wafer surrounded by very thin amorphous silicon layers. They can maintain efficiency levels of up to 25.6 percent – far above conventional crystalline silicon solar cells – and perform better under extreme heat.
“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.
The research centres believe that with further collaboration on individual technologies, even further efficiency gains can be made.