Low-Cost III-V Solar Cells

At present, the cost of III-V solar cells is very high, which limits their use to high-concentration and space applications. We develop technologies to drastically lower the cost of these devices, while maintaining their conversion efficiency, thus enabling their use in conventional flat-plate and low-concentration applications. We address the two major costs in the production of high-efficiency III-V devices: the cost of the epitaxy and the single-crystal substrates used for growth.

Our Expertise

We have expertise in the following:

• Growth of III-V device structures using advanced hydride vapor-phase epitaxy (HVPE)
• Computational fluid dynamics and thermodynamic/kinetic reaction modeling
• Advanced semiconductor growth reactor design
• Processing, characterizing, and analyzing III-V materials and devices.

Schematic of an in-line HVPE reactor with continual substrate reuse that eliminates metal-organic sources and uses cheap elemental metals. The bar charts show the relative materials costs for each layer.

Current Research Areas

It is critical to lower the deposition costs of today's industry standard metal-organic vapor-phase epitaxy MOVPE) growth process for the economic viability of III-V devices in one-sun applications. The major costs in MOVPE growth stem from high costs of source material and relatively low throughput. HVPE growth uses low-cost elemental source materials and has demonstrated high-quality III-V growth at rates at least an order of magnitude higher than typical MOVPE growth. Techno-economic analysis indicates that combining high-throughput, low-cost HVPE with effective wafer reuse—while maintaining high efficiency—can lower III-V energy costs to levels suitable for one-sun and low-concentration markets.

In pursuit of this goal, our work addresses the costs of both the epitaxial growth of the III-V device layers and the substrates on which these layers are grown, to lay the foundation for a competitive, impactful, U.S.-led III-V PV industry.

Schematic of the operation of our HVPE system, indicated by steps 1 through 7.

HVPE Growth of III-V Solar Cells. We are developing low-cost III-V PV using our innovative dual-chamber HVPE growth reactor that mimics an in-line production tool. We are able to create very abrupt doping and composition interfaces in our system, a capability that was previously quite difficult using HVPE growth. Utilizing this system, we have demonstrated single-junction GaAs solar cells with >20% conversion efficiency grown and > 1 micron per minute. We are currently developing monolithic two-junction devices with target efficiencies >30%, with three-junction devices being planned for the future. In addition, we are pursuing high-quality top cells for integration with high-efficiency crystalline Si solar cells with an expected tandem cell efficiency >30%.

Current research involves understanding and improving the HVPE growth of these multi-layer structures using robust experimental methods and computation fluid dynamics models coupled to kinetic descriptions of the growth reactions. We also study the effect of particular device structures on overall performance using the quality of the HVPE-grown materials as inputs. Contact us for specific information on the National Center for Photovoltaics (NCPV) R&D in the area of HVPE growth.

Schematic of our transfer technique using two-dimensional materials.

2-D Materials. We are also developing strategies to harness two-dimensional (2-D) materials as low-cost templates for the epitaxy of III-V semiconductors for high-efficiency PV. Contact us for specific information on the NCPV's R&D in the area of 2-D materials.

Tools and Capabilities

We use the following as we develop low-cost III-V device technology:

• Custom, dual chamber HVPE system capable of high spatial uniformity, sharp interfaces, very high growth rates, and high material utilization
• 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
• Computational fluid dynamics modeling software for understanding and improving growth systems, as well as developing next-generation growth reactors.

Projects

The current activities are funded by sources that include:

• DOE Energy Efficiency and Renewable Energy (EERE) SuNLaMP, "High-efficiency, low-cost, one-sun, III-V photovoltaics"
• DOE EERE Next Gen III, "Optimized, low-cost, >30% efficient InGaAsP/Si tandem solar cells"
• ARPA-E OPEN, "Ultrahigh Efficiency Photovoltaics at Ultralow Costs"

Working with Us

Visit Working with Us to learn more about NREL's PV partnership opportunities.