Multi-junction solar cells have been gaining attention due to their ability to capture and convert a broader range of the solar spectrum into electricity compared to single-junction cells. One of the most recent breakthroughs in this field has been achieved by researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), who created a solar cell with a record 39.5% efficiency under 1-sun global illumination. This article explores the advancements and techniques used to enhance the efficiency of multi-junction solar cells.
Quantum Well Solar Cells: The Key to Enhanced Efficiency
The NREL team developed a quantum well solar cell with unprecedented performance, focusing on modifying solar cell properties by utilizing many very thin layers. They implemented this technology into a device with three junctions, each with different bandgaps. These junctions were specifically designed to capture and utilize different slices of the solar spectrum, leading to higher overall efficiency.
III-V Materials: Expanding the Solar Spectrum Coverage
The new solar cell relies on III-V materials, known for their high efficiency and wide range of energy bandgaps. These materials, named after their positions on the periodic table, include gallium indium phosphide (GaInP), gallium arsenide (GaAs) with quantum wells, and lattice-mismatched gallium indium arsenide (GaInAs). Over decades of research, each material has been optimized to maximize its performance within multi-junction solar cells.
Optimizing Bandgaps with Quantum Wells
A crucial aspect of the NREL team’s work was their use of quantum wells in the middle layer of the solar cell to extend the bandgap of the GaAs cell. This innovation increased the amount of light the cell could absorb and further improved efficiency. The researchers developed optically thick quantum well devices without significant voltage loss, a critical step in optimizing the cell design.
Reducing Manufacturing Costs and Expanding Applications
Despite their high efficiency, III-V solar cells have been expensive to manufacture, limiting their use to niche applications like space satellites and unmanned aerial vehicles. NREL researchers have been working on reducing manufacturing costs and providing alternative cell designs to make these cells more economical for a broader range of applications.
Space Applications: Efficiency for Communications Satellites
The new III-V cell has also been tested for its suitability in space applications, particularly for communications satellites that rely on solar cells for power. The cell demonstrated a 34.2% efficiency for beginning-of-life measurements in low-radiation environments, making it a promising option for powering satellites and other space applications.
Conclusion
The development of the high-efficiency multi-junction solar cell by NREL researchers represents a significant step forward in solar cell technology. By incorporating quantum well solar cells, optimizing III-V materials, and extending bandgaps, the team achieved a record 39.5% efficiency under 1-sun global illumination. As researchers continue to refine manufacturing processes and reduce costs, multi-junction solar cells could become increasingly practical and attractive for a wider range of applications, both on Earth and in space.
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