III-V Multijunction Materials and Devices R&D
NREL has a strong research capability in III-V multijunction photovoltaic (PV) cells. The inverted metamorphic multijunction (IMM) technology, which is fundamentally a new technology path with breakthrough performance and cost advantages, is a particular focus.
We invented and first demonstrated the IMM solar cell and introduced it to the PV industry. Our scientists earlier invented and demonstrated the first-ever multijunction PV cell—and then worked with industry to develop the industry-standard GaInP/Ga(In)As/Ge) technology. III-V multijunction cells, which address both space and terrestrial power needs, have achieved the highest energy conversion efficiencies of all PV cells, with the current record exceeding 40%.
CPV systems leverage the high electrical output of III-V multijunction cells while minimizing the cell cost as a fraction of the system cost. The goal is low levelized cost of energy for installations at scales ranging from large rooftops to utilities.
Researchers within the National Center for Photovoltaics (NCPV) at NREL are responding to demand from the CPV and high-efficiency cell industries by continuing to develop the IMM technology. We partner with industry on robust operation and reliability in real-world operating environments.
- Inverted Metamorphic Multijunction Cells. We develop and implement new IMM device concepts for higher conversion efficiencies and lower fabrication costs.
- Cell Reliability. We study the characteristics of possible degradation mechanisms for IMM cells to identify which mechanisms may trigger unreliable performance. This understanding will lead to mitigating causes of efficiency reductions.
- Lattice-Mismatched Cell Science. We develop the scientific underpinnings required for major advances in controlling dislocations caused by the mismatch of crystal lattices from one subcell to another. Ultimately, these results feed back to device design, leading to improved cell performance and reliability.
- Advanced Modeling. We develop two- and three-dimensional models of cell operation to better understand key performance-related factors such as how current flows within the device—leading to optimizing cells under real-world operating conditions.
- 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
- Clean room 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.
Our researchers invented and transferred the IMM cell to industry, and we develop cells with improved performance, reliability, and cost effectiveness. Our interconnected research and development (R&D) tasks create a path toward the industry's requirements of higher-performance cells that are optimized for real-world concentrator systems.
We transfer our technological advances to major industrial players through licensing and high-value cooperative research and development agreements (CRADAs). Our basic criteria for CRADA projects are the following: (1) potential for a significant impact on the industry, (2) advancement of the technology, and (3) strong connection to our core competency of multijunction cells.
We work with numerous university and industry partners.