Researchers Create Solar Cell With Record Efficiency Rate

GOLDEN, Colo. — Researchers at the National Renewable Energy Laboratory have created the most efficient solar cell ever made, the numbers coming in at a record 39.5% efficiency under 1-sun global illumination.

Details of the research appear in the May issue of the journal Joule.

According to the NREL, the jump in efficiency was a byproduct of research into so-called “quantum well” solar cells to which researchers add or subtract very thin layers of solar cell material to modify their properties.

Realizing they’d come up with a solar cell with unprecedented performance, they then loaded it into a device they could tune to capture and analyze a different slice of the solar spectrum.

In a press release the laboratory explained the materials used in the test — called III-V materials because of where they fall on the periodic table — span a wide range of energy band gaps that allow them to target different parts of the solar spectrum.

The lab went on to explain the top junction is made of gallium indium phosphide (GaInP), the middle of gallium arsenide (GaAs) with quantum wells, and the bottom of lattice-mismatched gallium indium arsenide (GaInAs). Each material has been highly optimized over decades of research.

“A key element is that while GaAs is an excellent material and generally used in III-V multijunction cells, it does not have quite the correct bandgap for a three-junction cell, meaning that the balance of photocurrents between the three cells is not optimal,” said Ryan France, senior scientist and cell designer, in a written statement. 

“Here, we have modified the bandgap while maintaining excellent material quality by using quantum wells, which enables this device and potentially other applications,” he said.

The researchers used quantum wells in the middle layer to extend the bandgap of the GaAs cell and increase the amount of light that the cell can absorb.

At the same time, they developed optically thick quantum well devices without major voltage loss. They also learned how to anneal the GaInP top cell during the growth process in order to improve its performance and how to minimize the threading dislocation density in lattice-mismatched GaInAs, discussed in separate publications. Altogether, these three materials inform the novel cell design.

III-V cells are known for their high efficiency, but the manufacturing process has traditionally been expensive. 

To date, III-V cells have generally been used to power applications such as space satellites, unmanned aerial vehicles and other niche applications. 

Myles Steiner, a senior scientist in NREL’s High Efficiency Crystalline Photovoltaics Group and principal investigator on the project, said given its efficiency and its simpler design, the new solar cell may be useful for a variety of new applications.

Joining Steiner and France on the project were researchers John Geisz, Tao Song, Waldo Olavarria, Michelle Young, and Alan Kibbler.

NREL scientists previously set a record in 2020 with a 39.2% efficient six-junction solar cell using III-V materials.

The new III-V cell was also tested for how efficient it would be in space applications, especially for communications satellites, which are powered by solar cells and for which high cell efficiency is crucial, and came in at 34.2% for a beginning-of-life measurement. 

The present design of the cell is suitable for low-radiation environments, and higher-radiation applications may be enabled by further development of the cell structure, the laboratory said.

Dan can be reached at [email protected] and @DanMcCue