Scientists at the US National Renewable Energy Laboratory (NREL) have developed a new solar cell. The six-junction cell has the highest solar conversion efficiency of 47.1%. A variant of the same cell also broke an efficiency record under ‘one-sun illumination’ at 39.2%.
John Geisz, a principal scientist at NREL and lead author of a new paper on the record-setting cell, stated that the device demonstrated the extraordinary potential of multijunction solar cells. The work appears in Nature Energy.
To construct the device, the NREL researcher team worked with III-V materials. The materials are so-named because of their position on the periodic table. Each of the cell’s six junctions (i.e., the photoactive layers) is designed to capture light from a specific part of the solar spectrum. The device that is three times narrower than a human hair contains about 140 total layers of various III-V materials, which support the performance of these junctions. The new solar cells are used to power satellites due to their highly-efficient nature and the cost associated with making them.
Ryan France, co-author and a scientist in the III-V Multijunction Group at NREL stated that on Earth, the six-junction solar cell is well-suited for use in concentrator photovoltaics. He added that the way to cut costs is to reduce the required area. France stated that this could be done by using a mirror to capture the light and focus the light down to a point. According to the co-author, you could get away with even a thousandth of the material, compared to a flat-plate silicon cell. He stated that one could use a lot less semiconductor material by concentrating the light. The bonus is that the efficiency would go up as you concentrate the light. He described the potential for the solar cell to exceed 50% efficiency, which is very achievable. However, 100% efficiency cannot be reached due to the fundamental limits imposed by thermodynamics.
Geisz said that currently, the main obstacle in the research to top 50% efficiency is to reduce the resistive barriers inside the cell that impede the flow of current. He noted that NREL is also heavily engaged in reducing the cost of III-V solar cells, enabling new markets for these highly efficient devices.