The NREL laboratory achieves the new world record in multi-junction photovoltaics, both with concentrated light and under “natural lighting”.
NREL’s new “six junction” solar cell consists of 140 layers of materials, but is thinner than hair.
New world record in multi-junction photovoltaics.
A group of researchers from the US Department of Energy’s National Renewable Energy Laboratory (NREL) has developed a six-connection solar cell with unprecedented conversion efficiency. It is capable of transforming 47.1% of the incident light into electricity under optical concentration. A unique value that, although more contained, remains a record even with simple lighting.
Part of the extraordinary result is related to the technological approach. Multiple junction cells are created with the precise goal of exceeding the efficiency limits of standard photovoltaics. They 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 – in theory – it is possible to increase the range of wavelengths to be absorbed, improving 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 portion of the solar spectrum. The device contains approximately 140 total layers of various III-V materials to support the performance of these bonds, yet 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 lead author of the research.
Due to the high costs of PV III-V, this technology is mainly used to power satellites and space vehicles. But this does not mean that it cannot have applications on land.
“ One way to cut costs is to reduce the required area ,” explains Geisz, “ and you can do this by using a mirror to capture the light and focus it on one point. So you can get away with a penny or even a thousandth of the material, compared to a traditional silicon cell. You use much less semiconductor material by concentrating the light. An added benefit is that the efficiency increases as the light is concentrated. “
The first laboratory tests have shown that the new six junction cell achieves an efficiency of 47.1% with a concentration of only 143%. The value drops to 39.2% with natural lighting.
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.
More information: www.nrel.gov – www.nature.com