The Department of NREL, National Renewable Energy Laboratory, has set a new solar cell efficiency record in normal sunlight at 39.5%. The triple-junction solar cell could achieve record efficiency by improving the cell’s middle layer and using new techniques to construct quantum wells.
NREL’s High-Efficiency Crystalline Photovoltaics (PV) Group created the solar cell using hundreds of layers of materials, each optimized based on previous versions of solar cell technology spanning decades of research and development in this product group.
The solar cell is made up of three different materials:
- gallium indium phosphide (GaInP) at the top
- gallium arsenide (GaAs) at the middle, which is surrounded by the aforementioned quantum wells
- lattice-mismatched gallium indium arsenide at the bottom (GaInAs)
These materials have previously been utilized in solar cells and currently dominate the market for space solar power.
The previous record for conventional sunlight solar cells was 39.2%, nearly as efficient as this new record, but that cell was a six junction unit. Using recent advances in quantum well layer research, this solar cell with identical materials was able to improve generation efficiency.
The key drawbacks of this product category are its high cost (10 USD per watt vs. 10 cents for normal solar cells) and its slow manufacture compared to conventional polysilicon solar cells. Furthermore, given the impending worldwide solar dominance, material availability is constrained.
For example, the quantum well portion of the solar cell takes 55 minutes to grow, and the complete cell takes four hours to grow. While this isn’t a fair comparison, a typical 250 MW/year polysilicon manufacturing line aims to move tens of thousands of solar cells every hour.
However, it holds promises for space solar and solar-powered automobiles. After all, its high costs mean that these cells are primarily used in expensive markets.
The most common market is space, as the ISS currently uses triple-junction cells with about 30% efficiency. Cells of this type have also been used in soon-to-be-released solar-powered vehicles.
“The new cell is more efficient and has a simpler design that could be effective for a range of new applications, such as highly area-constrained applications or low-radiation space applications,” said Myles Steiner, the project’s principal investigator and senior scientist in NREL’s High-Efficiency Crystalline Photovoltaics (PV) Group. Ryan France, John Geisz, Tao Song, Waldo Olavarria, Michelle Young, and Alan Kibbler worked with him at NREL.
To know more about the development, read the publication “Triple-junction solar cells with 39.5% terrestrial and 34.2% space efficiency enabled by thick quantum well superlattices,” which appeared in the May issue of the journal Joule.
As the cutout above from the NREL Research Cell Record Efficiency Chart shows, these are undoubtedly one of the most productive solar cells ever built. The red box indicates the current record solar cell efficiency. The class of solar cells above and to the left of the indicated cell set records by concentrating sunlight through mirrors and other methods.
Scientists previously discovered that an endless number of connectors could theoretically achieve an efficiency of 85% under maximum sunlight concentration. In contrast, conservative calculations imply that a 62% solar cell efficiency might be attained with 1,000 times concentrated sunlight utilizing several realistic assumptions.