Scientists around the world are regularly setting new world records in solar cell efficiency, and a team from the National Renewable Energy Laboratory (NREL) has just achieved 47.1%. The new solar conversion efficiency record was achieved with a six-junction solar cell and was measured under concentrated illumination. The team said a variation of the same cell also “set the efficiency record under one-sun illumination at 39.2%.”
The paper is titled “Six-junction III-V solar cells with 47.1% conversion efficiency under 143 Suns concentration” recently appeared in the Nature Energy journal. Lead author and principal scientist in the High-Efficiency Crystalline Photovoltaic Group at NREL, John Geisz said, “This device really demonstrates the extraordinary potential of multijunction solar cells.”
The six-junction solar cell is constructed using six different types of photoactive layers. The III-V materials the NREL researchers used were based upon their position on the periodic table, each one having a wide range of light absorption properties. Each one collects energy from different parts of the solar spectrum. Amazingly, there are more than 140 layers in a solar cell that is 3x thinner than a human hair.
III-V solar cells are mainly used to power satellites in space, where they achieve unmatched performance. Co-author of the study, and scientist in the III-V Multijunctions Group at NREL, Ryan France, explains how these could be used in concentrator photovoltaics:
One way to reduce cost is to reduce the required area. 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.
The team thinks the potential for these solar cells to exceed 50% efficiency is “actually very achievable” as France points out, but 100% is not possible as thermodynamics has certain fundamental limits that simply cannot be reached.
The official release by NREL states they are heavily engaged in bringing down the cost of III-V solar cells, which would enable entirely new markets for the “highly efficient devices.” Geisz said the team will now focus on achieving more than 50% efficiency. To do so, they will need to “reduce the resistive barriers inside the cell that impede the flow of current.”
The paper concludes by saying:
To develop these junctions, it was necessary to minimize threading dislocations in lattice-mismatched III–V alloys, prevent phase segregation in metastable quaternary III–V alloys and understand dopant diffusion in complex structures. Further reduction of the series resistance within this structure could realistically enable efficiencies over 50%.
This research was funded by the U.S. Department of Energy’s Solar Energy Technologies Office. “NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development.”
