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High-Concentration III-V Multijunction Solar Cells

We develop advanced multijiunction cell technology and transfer the resulting intellectual property to industry. We have a distinguished record of accomplishment in the field, including the invention of the original gallium indium phosphide/gallium arsenide (GaInP/GaAs) multijunction cell and its transfer to the high-efficiency cell industry, and the invention and development of the inverted metamorphic multijunction (IMM) cell technology.

PV Research

Other Materials & Devices pages:

We address the full range of multijunction development issues including:

  • Design of new cell concepts
  • Science-based development of methods for practical implementation of these concepts
  • Proof of concept via demonstration of record-efficiency devices at the laboratory scale.
Graphic showing the layers that comprise IMM solar cells.

In the IMM cell, high-performance subcells are realized by: (1) inverting the usual growth order, growing mismatched cells last, (2) engineering a transparent buffer layer to mitigate dislocations, and (3) removing the primary substrate/attachment to the secondary "handle."

Our Expertise

We have expertise in the following:

  • Developing advanced III-V multijunction solar cell architectures for terrestrial and space applications
  • Epitaxial growth and processing of ultrahigh-efficiency III-V multijunction solar cells
  • Metamorphic materials science and engineering
  • Growth of challenging new III-V alloys
  • Characterizing and analyzing multijunction photovoltaics
  • Developing and applying experimentally grounded device physics models of multijunction cell performance
  • Numerical modeling of cell performance, including effects of luminescent coupling, inhomogeneous illumination, cell heating, and three-dimensional flow of electrical current
  • Developing III-V photovoltaics for high-temperature operation
  • Developing III-V multijunction structures for photoelectrochemical hydrogen production.

Current Research Areas

The efficiency and concentration of III-V multijunction solar cells can be highly leveraged to reduce the cost of high-concentration photovoltaic (HCPV) systems. We have demonstrated ~46% efficiency with a four-junction IMM solar cell. (A metamorphic solar cell uses a compositionally graded buffer to incorporate nearly perfect single-crystal layers with different crystal lattice parameters.) We are extending the concept to five- and six-junction IMM solar cell devices that have the potential to exceed 50% efficiency at high concentrations. By focusing on the underlying device physics and materials science of metamorphic multijunction solar cells, we aim to develop five- and six-junction cells with 50% efficiency and optimized energy production under real-world conditions, resulting in a significant advance for the HCPV market.

Schematic of a target 6-junction IMM solar cell structure that could have an efficiency > 50%.

The SunShot Initiative goals can be exceeded with HCPV by increasing both efficiency and concentration.

We are focusing on maximizing energy yield in HCPV systems through cell-level design to reduce the LCOE. We use realistic model-directed multijunction device design, materials research, light-management strategies, and series-resistance mitigation to develop the design. We are advancing the scientific understanding of dislocation nucleation and glide in III-V alloys to achieve low threading-dislocation densities in ternary and quaternary junctions. We are also studying techniques to grow metastable compositions of quaternary III-V alloys and to mitigate oxygen-related defects in aluminum-containing alloys. Our work improves the understanding of the physics of the complex optoelectronic multijunction solar cell devices concerning light emission, relatively high light-injection levels associated with high concentration, and small device sizes.

Tools and Capabilities

We use the following as we develop and transfer multijunction cell technology:

  • Cluster tool, which comprises a metal-organic vapor-phase epitaxy (MOVPE) growth system connected via load locks to a molecular-beam epitaxy (MBE) growth system and an analytical chamber
  • Two stand-alone MOVPE growth systems
  • Stand-alone MBE growth system
  • Cleanroom in which epitaxial wafers can be processed into full devices
  • Suite of cell testing techniques, including current-voltage and quantum efficiency testing of full multijunction cells
  • Numerical modeling of cell performance issues relevant for incorporation into real-world systems, including inhomogeneous illumination, cell heating, and three-dimensional flow of electrical current.

Projects

The current activities are funded by sources including:

A critical component of our work is transfer of our technology to industry partners.

We also conduct research on various approaches to III-V/silicon tandem cells. This work is funded by DOE EERE SuNLaMP (see "Mechanically Stacked Hybrid PV Tandems" and "Si-based Tandem Solar Cells") and DOE ARPA-E (see "Micro-Optical Tandem Luminescent Solar Concentrator").

Working with Us

Existing HCPV systems use ~40%-efficient three-junction solar cells. Increased efficiency and concentration could make them the most economical solar option in regions of high direct normal irradiance.

Visit Working with Us to learn more about NREL's PV partnership opportunities. Two of the primary mechanisms by which we transfer technology to industry partners are licensing of the intellectual property, and Cooperative Research and Development Agreements (CRADAs). In CRADAs, our NREL group works together with an industry partner to develop the innovations needed to commercialize our technology. We have had CRADA partnerships with virtually all the U.S. multijunction industry leaders.

Contact us for specific information on NREL's R&D in the area of high-efficiency III-V cells.

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