National Renewable Energy Lab sets world records with highly efficient solar cell

With a single product, scientists at the National Renewable Energy Laboratory (NREL) have smashed two world records, thanks to a fabricated solar cell with an efficiency of 47.1 percent.

It is the most efficient solar converter in the world, thanks to its six-junction construction. This record was earned under concentrated illumination, but a variation under one-sun illumination set a separate record, with a conversion efficiency of 39.2 percent. Details of the cells were published in Nature Energy, which went into detail on the six-junction III-V solar cells.

The cells are made of around 140 layers of various III-V materials — named for their positions on the periodic table — which have a wide range of light absorption capabilities. These materials help support the performance of the cell’s six junctions, which are designed to capture light from a specific part of the solar spectrum. Despite the sizable capability being shoved into the device, it’s three times narrower than a human hair.

“One way to reduce cost is to reduce the required area, and you can do that by using a mirror to capture the light and focus the light down to a point,” Ryan France, co-author and a scientist in NREL’s III-V Multijunctions Group, said. “Then you can get away with a hundredth or even a thousandth of the material, compared to a flat-plate silicon cell. You use a lot less semiconductor material by concentrating the light. An additional advantage is that the efficiency goes up as you concentrate the light.”

The device, added the paper’s lead author John Geisz, showcases the impressive potential of multijunction solar cells in general. While 100 percent efficiency could never be achieved — there are certain limits demanded by thermodynamics — the potential to reach higher than 50 percent is quite achievable, so long as scientists could find a way to reduce the resistive barriers inside the cell. These barriers impede the flow of current.

Just as important, Geisz notes that NREL is currently working to reduce the cost of III-V solar cells to open up new markets for them.