High-Efficiency Crystalline Photovoltaics
Within the National Center for Photovoltaics (NCPV), we are working to increase cell efficiency and reduce manufacturing costs for the highest-efficiency photovoltaic devices involving single-crystal silicon and III-Vs. We are key players in developing low-cost, manufacturable techniques for further increasing the efficiency of advanced silicon cells, and continue to be at the forefront of developing the highest-efficiency III-V multijunction cells for both space and high-concentration terrestrial applications. We are also a driving force in two industry-relevant areas: low-cost III-V photovoltaic cells for 1-sun and low-concentration terrestrial applications, and very high-efficiency silicon-based tandem cells.
We are developing a >23%-efficiency, low-cost industrial-size cell on n-Cz wafer by 2018.
Silicon Solar Cells
We are focusing on high-efficiency, low-cost silicon photovoltaics, considering the urgent need to develop high-throughput, low-cost, robust processes and device architectures that enable highly efficient n-type Czochralski (Cz) wafer silicon cells. We address technology bottlenecks—from the silicon crystal/wafers all the way to finished 23% interdigitated back-contact cells with passivated contacts.
4-junction cell with "engineered" buffers has ~46% conversion efficiency.
III-V Multijunction Solar Cells
The efficiency and concentration of III-V multijunction solar cells can be highly leveraged to reduce the cost of high-concentration photovoltaic systems. We are recognized for the invention, development, and technology transfer of a range of key device architectures, most recently including the inverted metamorphic multijunction (IMM) solar cell. In this device architecture, a metamorphic solar cell uses a compositionally graded buffer to incorporate nearly perfect single-crystal layers with different crystal lattice parameters. With this architecture, we have demonstrated ~46% efficiency with a four-junction IMM cell. 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.
Schematic of in-line HVPE reactor with continual substrate reuse that eliminates metal-organic sources and uses cheap elemental metals.
Low-Cost III-V Solar Cells
We are developing methods to greatly reduce the cost of manufacturing III-V solar cells. We address the cost of epitaxial growth by developing low-cost hydride vapor-phase epitaxy (HVPE) growth, and the cost of the substrates by several substrate-reuse approaches. This work aims at single-junction cells with efficiencies >25% and tandems with efficiencies >30%, for one-sun and low-concentration applications.
(a) Bonded GaInP on silicon cell. (b) High-efficiency four-terminal design gives good energy yield under real-world conditions.
Hybrid Tandem Solar Cells
We are developing high-efficiency III-V/silicon tandem solar cells by both epitaxial and stacking/bonding approaches. Our present work in epitaxial III-V/Si uses an approach based on selective-area growth enabled by patterning via nanoimprint lithography. In the stacking/bonding approach, we are developing a novel cell structure using transparent, conductive adhesives for cell stacking to enable inexpensive stacked tandem cells. By combining device modeling and cell fabrication, we will understand the impact of device geometry on energy yield.