DOE supports photovoltaic (PV) research and development and facilities at its national laboratories to accelerate progress toward achieving the SunShot Initiative's technological and economic targets. The Solar Energy Technologies Office funds three-year projects based on a peer-reviewed proposal process that targets the challenges pertaining to various PV materials and technologies:
The research projects below are funded to the National Renewable Energy Laboratory (NREL) in Golden, Colorado. NREL is also performing supporting research with the potential for cross-cutting technology applications.
High-Efficiency Multijunction Solar Cells
$7,649,010 total over 3 years
III-V materials are often used in multijunction cells, in which several stacked cells each harvest a portion of the solar spectrum. Higher efficiencies can be reached with an increasing number of stacked cells, or junctions than achievable with a single junction PV cell. This three-part research effort focuses on developing a pathway to multijunction III-V efficiencies approaching 50%, advancing the basic materials science underpinnings of the PV materials, and building on foundational advancements in the understanding and quantification of the electro-optical device physics of extremely high-performance multijunction solar cells. NREL is using its inverted metamorphic multijunction (IMM) technology platform to serve as the basis for a four-junction structure with an efficiency target of 48%. Reaching this milestone provides a clear pathway to efficiencies approaching 50%. The researchers are also building on the literature and the 2012 discovery of a new material factor for dislocation energetics to gain a better understanding of and control over dislocation formation and glide in metamorphic materials appropriate for the development of the fourth junction. Under this award, the researchers are using new experimental and computational techniques to gain a better understanding of critical multijunction behaviors such as luminescent coupling that can impact cell performance as a function of cell temperature and light concentration.
For more information, visit the III-V materials page.
Low-Cost, High Efficiency Hydride Vapor Phase Epitaxy III-V Solar Cells
$1.5M total over 3 years
Although costs are typically too high to be competitive with Si or CdTe PV cells, single-junction solar cells made from III-V materials are among the most efficient one-sun panels made today. NREL proposes a new III-V, one-sun solar cell concept that has the potential to outperform silicon (Si) modules in both efficiency and cost. This technology is expected to reach grid parity cost points, along with favorable balance-of-system (BOS) efficiencies, by significantly lowering the cost of III-V material growth and by applying a simple, fast layer-transfer process to reuse an epitaxial template wafer. Almost all III-V solar cells are grown by metalorganic vapor phase epitaxy (MOVPE) today because of high material quality, interface control in multilayer devices, and the availability of highly purified metalorganic precursors, but this process is very expensive. A radically different growth process is needed for III-V solar cells to obtain one-sun grid parity, or to even compete with Si modules. That process is Hydride Vapor Phase Epitaxy (HVPE). NREL proposes to grow III-V materials by HVPE in a revolutionary, in-line reactor, rather than by expensive MOVPE in a traditional batch reactor. The many advantages of HVPE include much lower precursor costs (pure metals rather than organometallic engineered molecules, representing a 5–10x savings), higher deposition rates (1–5 µm/min or 10–50x faster), significantly better material utilization (much lower arsine overpressure), and inherent cost savings due to atmospheric-pressure, in-line growth.
An Integrated Approach to Organic Photovoltaics
$4,437,000 total over 3 years
Organic photovoltaics (OPV) hold the promise of extremely low-cost fabrication and easy integration into existing materials such as windows or fabrics. However, OPV technology is currently hampered by short lifetimes and low (typically <10%) efficiencies. This project is working to develop tools and understanding to advance organic OPV efficiency and device lifetime to meet the SunShot Initiative goals of 20% power conversion efficiency systems with a greater than 25-year lifetime, all at an installed cost of less than $0.50 per watt (W). To achieve these goals, the research team is structuring the project to have three integrated research tasks: 1) the design and development of new absorber materials through combinatorial computational methods coupled to their direct synthesis, characterization, and device optimization; 2) the development of charge-selective hole and electron contacts that optimize interface properties, performance, and stability for new active layer materials; 3) the investigation of device and materials degradation mechanisms and mitigation strategies to extend device lifetime. The overarching theme for this project is to integrate theory, computation, and characterization to discover and develop new materials that enable both synthesis and device optimization directly coupled with contact development and the evaluation of material and device stability.
For more information, visit the organic photovoltaics page.
CZTS – Next-Generation Earth-Abundant Thin Film CZTS Photovoltaics
$6,900,000 total over 3 years
Kesterites (i.e., "CZTS," Cu2ZnSnSxSe4-x, and related alloys) can contribute to SunShot goals by providing an earth-abundant, thin-film alternative to CuInxGa1-xSe2 (CIGS) and CdTe. However, kesterite device performance must reach at least 18% to be a viable candidate for meeting the SunShot modules $0.50/W goal and resulting terrawatt-scale production. To achieve the necessary performance increase, the fundamental understanding of kesterite materials must be improved and applied to the absorber deposition process. CZTS work at NREL aims to develop this basic understanding of how defects and interfaces in the kesterite materials system work and how to control them during film processing. The researchers will then minimize defect concentrations, optimize interfaces, and demonstrate associated improvements in device performance. If fundamental limitations to kesterite performance exist, this work strives to reveal them.
For more information, visit the CZTS thin-film photovoltaics page.
CIGS Thin-Film PV Technology: Overcoming Barriers to Increase Efficiency and Reduce Cost
$9,098,010 over 3 years
The objective of this project is to create knowledge that enables increases in efficiency, reliability, and reductions in cost for CIGS technology. The research team is targeting challenges with potential for significant impact by: 1) increasing the laboratory cell efficiency past the state-of-the-art of 20%, and toward the doable, but challenging, efficiency of 23%; 2) showing continuous improvement in deposition processes and alternative window layers that can potentially reduce cost per square meter; 3) contributing to the knowledge base from which industry and the community at large can benefit.
For more information, visit the CIGS thin-film photovoltaics page.
Rapid Development of Earth-Abundant Thin-Film Solar Cells
1,500,000 over 3 years
The materials base for inorganic thin-film solar cells must be diversified to achieve SunShot Initiative goals. This calls for an accelerated development of new PV technologies that have the potential to achieve very high efficiencies, yet use only inexpensive and abundant materials. The objective of this project is to establish and test a sustainable framework for rapid development of new earth-abundant thin-film solar cells. The approach iteratively combines predictive first principles theory and high-throughput experiments. It considers both individual materials and PV device prototypes to accelerate the development process. The research team plans to demonstrate the methodology for designing PV technologies materials and devices on the example of earth-abundant ternary copper sulfides. This project aims to benefit the domestic PV industry by expanding viable PV technology options.
Understanding How Defects in CdTe Limit the Performance of Solar Cells
$10,008,990 over 3 years
CdTe is currently the market leader in thin-film PV because cost-competitive and reliable cells can be fabricated. However, in order to advance CdTe technology, the industry must address fundamental material concerns such as higher than desired defect concentrations and recombination. The objective of the NREL 3-year CdTe SunShot project is to identify the primary mechanisms that limit the open-circuit voltage and fill factor of polycrystalline CdTe PV devices, and develop alternative materials synthesis processes and/or device designs that avoid these problems. The project relies heavily on model systems, such as single-crystal materials, where point and extended defects can be introduced sequentially. Studies on the model system are being designed to identify the likely sources of the dominating recombination processes in commercial polycrystalline CdTe materials and devices. Key goals of the project include producing a model CdTe PV device that demonstrates ≥20% conversion efficiency, while also improving our understanding of the process and materials capable of attaining the SunShot module cost goal of ≤$0.50/W.
For more information, visit the CdTe thin-film photovoltaics page.
Cell and Module Performance
$8,154,000 over 3 years
The Cell and Module Performance agreement supports the independent evaluation of cell and module contract deliverables, providing the U.S. PV industry with accurate and independent efficiency measurements and calibrations for all PV technologies and material systems. Since its inception in 1980, this partnership has developed a unique competency for the DOE Solar Program to fairly evaluate atypical cells in cases when the data are impacted by artifacts such as metastability, spurious photocurrents, bias rate, nonlinearity, and other issues such as contacting and area definitions. The NREL team supports commercial testing and module qualification labs by providing required ISO 17025-accredited calibrations. This agreement includes peak watt calibrations for primary terrestrial reference cells that are in the calibration chain from test laboratories to researchers to large-scale manufacturers. The team also supports domestic and international PV cell and module standards development.
Multifunctional Transparent Conducting Oxides
$1,500,000 over 3 years
Nearly all PV cells require the use of transparent conducting oxides (TCOs) to provide an electrical contact without blocking any useful photons from reaching the absorber. Improvements in TCOs will have ramifications across several PV technologies. The purpose of this research is to build a set of transparent conducting oxide solutions that can be employed to enhance both the efficiency and stability for a range of PV devices. Key objectives of this work include improving the interfacial performance, lowering materials costs, and improving both efficiency and reliability. These enhancements apply to existing PV systems where the currently used TCOs are or will be performance limiting, as well as to PV devices based on new absorbers with accordingly new transparent contact requirements. This activity focuses on building foundational capabilities and improving understanding for a number of key attributes identified by the PV community, including materials suitable for band-edge engineering, materials with tunable dielectric constants, materials with high performance at low process temperatures, and roll-to-roll compatible materials. This project integrates theory, synthesis, and characterization to develop new and/or improved materials specifically addressing performance in conductivity, band alignment, processing and stability.