Scientists at the US National Renewable Energy Laboratory (NREL) have published findings to Nature Energy on a new solar cell concept with enormous potential. The six-junction cell achieved a solar conversion efficiency of 47.1pc under concentrated illumination, creating a new world record. A second record was also achieved with efficiency of 39.2pc under one-sun illumination.
To construct the device, researchers used so-called III-V materials, which have a wide range of light absorption properties. The name is derived from their position on the periodic table.
Each of the cells’ six photoactive layers – referred to as junctions – are designed to capture light from a specific part of the solar spectrum. In total, the device contains 140 layers of various III-V materials, each three times narrower than a human hair.
Due to their highly efficient nature and the cost associated with making them, III-V solar cells are most often used to power satellites. However, according to the paper’s co-author, Ryan France, this powerful cell design could be well-suited for use in concentrator photovoltaics.
Use a lot less semiconductor material
“One way to reduce cost is to reduce the required area,” he said. “And you can do that by using a mirror to capture the light and focus the light down to a point.
“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.”
France added that it is “very achievable” to soon exceed 50pc efficiency. However, 100pc efficiency can never be reached due to the fundamental limits imposed by thermodynamics.
According to the lead author of the paper, John Geisz, in order to surpass 50pc efficiency the restrictive barriers inside the cell that impede the flow of current will need to be reduced.
Earlier this year, researchers in Japan found that a recently discovered molecule, important in a plant’s ability to photosynthesise sunlight, could also reap rewards for solar cells. The discovery could allow us to better mimic the process of photosynthesis in an artificial system to capture solar energy.