High-efficiency solar cells are demanded by all applications of photovoltaics. Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have created a solar cell with a record 39.5% efficiency under 1-sun global illumination. This is the highest efficiency recorded for any type of solar cell, measured using standard 1-sun condition, which gives a better indication of how well they might perform in the real world.
NREL scientists previously set a record in 2020 with a 39.2% efficient six-junction solar cell using III-V materials.
The improvement in efficiency followed research into “quantum well” solar cells, which utilize many very thin layers to modify solar cell properties. The new solar cell is based on the inverted metamorphic multijunction (IMM) architecture that was invented at NREL. It contains three junctions with different bandgaps, where each junction is tuned to capture and utilize a different slice of the solar spectrum.
The top junction is made of gallium indium phosphide (GaInP), the middle of gallium arsenide (GaAs) with quantum wells, and the bottom of lattice-mismatched gallium indium arsenide (GaInAs).
“A key element is that while GaAs is an excellent material and generally used in III-V multijunction cells, it does not have quite the correct bandgap for a three-junction cell, meaning that the balance of photocurrents between the three cells is not optimal,” said Ryan France, senior scientist, and cell designer. “Here, we have modified the bandgap while maintaining excellent material quality by using quantum wells, which enables this device and potentially other applications.”
The team used quantum wells in the middle layer to extend the bandgap of the GaAs cell and increase the amount of light that the cell can absorb. The middle layer of this solar cell contained up to 300 quantum wells, boosting the overall efficiency to new heights. They developed optically thick quantum well devices without major voltage loss.
NREL researchers have been working toward drastically reducing the manufacturing cost of III-V cells and providing alternate cell designs, which will make these cells economic for a variety of new applications. The new III-V cell was also tested for how efficient it would be in space applications, especially for communication satellites, which are powered by solar cells and for which high cell efficiency is crucial, and came in at 34.2% for a beginning-of-life measurement. The present design of the cell is suitable for low-radiation environments, and higher-radiation applications may be enabled by further development of the cell structure.