Researchers from the National Renewable Energy Laboratory of the US Department of Energy (NREL) have created a solar cell with a record efficiency of 39.5% under global illumination of 1 sun. This is the highest efficiency of solar cells of any type, measured using standard 1 sun conditions.
“The new cell is more efficient and has a simpler design that can be useful for a variety of new applications, such as applications with very limited space or space applications with low levels of radiation,” said Miles Steiner, senior NREL high efficiency scientist. Crystalline Photovoltaics Group (PV) and principal investigator of the project. He has worked with NREL colleagues Ryan France, John Hayes, Tao Song, Wald Olaware, Michelle Young and Alan Kibler.
Details of the development are set out in the article “Solar batteries with triple transitions with an efficiency of 39.5% terrestrial and 34.2% space efficiency due to thick superlattices of quantum wells”, which appears in the May issue of the magazine. Joule.
Earlier, NREL scientists set a record in 2020 with a 39.2% efficiency of six transitional solar cells using III-V materials.
Some of the best solar cells of recent times have been based on the inverted metamorphic multi-transition (IMM) architecture that was invented at NREL. This recently improved three-channel solar cell IMM has been added to the research cell’s best efficiency chart. The chart, which shows the success of experimental solar cells, includes a previous IMM record with three transitions of 37.9%, set in 2013 by Japanese corporation Sharp.
The increase in efficiency followed studies of solar cells with a “quantum well”, which use many very thin layers to change the properties of solar cells. Scientists have developed a quantum solar cell with unprecedented performance and implemented it in a device with three transitions with different gaps, where each transition is configured to capture and use a different piece of the solar spectrum.
Materials III-V, so named because they fall into the periodic table, cover a wide range of energy retardations, which allows them to navigate to different parts of the solar spectrum. The upper junction is made of gallium-indium phosphide (GaInP), the middle – of gallium arsenide (GaAs) with quantum wells, and the bottom – of gallium-indium arsenide (GaInAs) with an inappropriate lattice. Each material has been highly optimized over decades of research.
“The key element is that while GaAs is an excellent material and is commonly used in multi-junction cells III-V, it doesn’t have exactly the right width for a tri-junction cell, which means that the balance of photocurrents between the three cells is not with ‘is optimal. “Said Frans, a senior scientist and cell designer. “Here we have changed the width while maintaining the excellent quality of the material using quantum wells, which allows the use of this device and possibly other applications.”
The scientists used quantum wells in the middle layer to expand the band gap of the GaAs cell and increase the amount of light the cell can absorb. Importantly, they developed optically thick quantum wells without significant voltage losses. They also learned how to anneal the upper GaInAs cell during the growth process to improve its performance and how to minimize the density of thread dislocations in the inappropriate GaInAs lattice, which is discussed in separate publications. Together these three materials bring a new cell design.
Cells III-V are known for their high efficiency, but the production process has traditionally been expensive. Until now, cells III-V have been used to power applications such as space satellites, unmanned aerial vehicles and other niche applications. Researchers from NREL are working to drastically reduce the cost of producing III-V cells and provide alternative cell designs that will make these cells economical for a variety of new applications.
The new element III-V has also been tested for how effective it is in space applications, especially for solar-powered communications satellites and for which high cell efficiency is crucial, and was 34.2% for the start-dimension of life. The current cell design is suitable for low radiation environments, and a higher radiation application can be enabled by further developing the cell structure.