The NREL laboratory achieves the new world record for multi-junction photovoltaics, both in concentrated light and in “natural lighting”.
NREL’s new “six-junction” solar cell is made of 140 layers of material, but it’s thinner than hair.
New world record for multi-junction photovoltaics.
A group of researchers from the National Renewable Energy Laboratory (NREL) of the US Department of Energy have developed a six-connection solar cell with unprecedented conversion efficiency. It is able to transform 47.1% of incident light into electricity under optical concentration. A unique value which, although more contained, remains a record even with simple lighting.
Part of the extraordinary result is linked to the technological approach. Multi-junction cells are created for the specific purpose of exceeding the efficiency limits of standard photovoltaics. These are units with pn interfaces made with different semiconductors. The pn junction of each material produces an electric current in response to different wavelengths of light. Therefore, the more photoactive layers used in its production, the more it is – in theory – possible to increase the range of wavelengths to be absorbed, thus improving the production.
To build their six-junction solar cell, the NREL team relied on III-V materials, named for their position on the periodic table. Each of the six interfaces is specially designed to capture light from a specific part of the solar spectrum. The device contains around 140 total layers of various III-V materials to support the performance of these bonds, but it is three times thinner than a human hair.
This device truly demonstrates the extraordinary potential of multi-junction solar cells.
John Geisz, NREL Group Scientist and Senior Research Author.
Due to the high costs of PV III-V, this technology is mainly used to power satellites and space vehicles. But that doesn’t mean it can’t have applications on earth.
“One way to cut costs is to reduce the area requiredGeisz explains,And you can do this by using a mirror to catch the light and focus it on a point. So you can get by with a dime or even a thousandth of material, compared to a traditional silicon cell. You use much less semiconductor material by focusing the light. An additional benefit is that the efficiency increases as the light is focused.“
The first laboratory tests showed that the new six-junction cell achieves 47.1% efficiency with a concentration of only 143%. The value drops to 39.2% with natural light.
It is very difficult to increase the efficiency of this architecture due to internal resistance barriers. For this reason, the team is now focusing on the economic aspect. The next target? To reduce production costs.