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Highly Transparent Tunnel Junction for High Concentration III-V Multijunction Solar Cells

National Renewable Energy Laboratory

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Technology Marketing Summary

The most efficient commercially available solar panels use three or four sub-cells stacked one on top of the other, each capturing a distinct wavelength of light. When multiple cells are used in a solar configuration they are separated by tunnel junctions, which act like diodes to allow electrons to pass through in one direction and also prevent the formation of undesirable electric fields between junctions. In order for lower bandgap sub-cells to function effectively, the tunnel junctions placed between higher bandgap sub-cells also need to be sufficiently transparent; this is especially important for the upper tunnel junctions as every sub-cell below will be affected by the wavelengths of light passing through.

In order to capture even more of the solar spectrum and continue to push the boundaries of solar efficiency forward, the next generation of multijunction solar cells will have architectures incorporating five or six sub-cells. Current tunnel junction solutions utilize heavily-doped InGaP (Eg=~1.7 eV) to separate the top InGaP cell and the middle GaAs (Eg = ~1.4 eV) sub-cell, as the 1.7 eV bandgap is higher than that of the sub-cell. However, as more sub-cells are added tunnel junctions that are optically transparent at higher bandgaps will be required.

Description

Researchers at NREL have created an AlGaAs/GaAs/AlGaAs quantum well tunnel junction (QWTJ) that is optically transparent above 1.7 eV and has been demonstrated to act as an effective diode between a 2.1 eV AlGaInP top cell and 1.7 eV AlGaAs sub-cell. The researchers used high aluminum content in the outer junction layers and an extremely thin GaAs layer, thereby increasing transparency while maintaining the quantum well which allows electron transmission. This invention makes it possible for new advanced multijunction solar cell architectures to maximize the efficiency of individual sub-cells.

Benefits
  • Optically transparent above 1.7 eV
  • Higher efficiency
  • Lower cost
  • Enables new solar panel architectures
Applications and Industries
  • Multijunction solar cells
  • Aerospace
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
ROI 17-60, Provisional Patent 62/491,061PrototypeAvailable05/02/201705/02/2017

Contact NREL About This Technology

To: Bill Hadley<bill.hadley@nrel.gov>