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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2013-10-25 14:00:00
  • Article ID: 609468

ASU, Georgia Tech Create Breakthrough for Solar Cell Efficiency

New atomic layer-by-layer InGaN technology offers perfect crystal

  • Credit: Arizona State University

    The atomic arrangement at a relaxed InGaN/GaN interface. Research at Arizona State University and Georgia Tech show layer-by-layer crystal growth may lead to recording breaking efficiencies in photovoltaic solar cell technology.

Margaret Coulombe

480-727-8934

Margaret.coulombe@asu.edu

Did you know that crystals form the basis for the penetrating icy blue glare of car headlights and could be fundamental to the future in solar energy technology?

Crystals are at the heart of diodes. Not the kind you might find in quartz, formed naturally, but manufactured to form alloys, such as indium gallium nitride or InGaN. This alloy forms the light emitting region of LEDs, for illumination in the visible range, and of laser diodes (LDs) in the blue-UV range.

Research into making better crystals, with high crystalline quality, light emission efficiency and luminosity, is also at the heart of studies being done at Arizona State University by Research Scientist Alec Fischer and Doctoral Candidate Yong Wei in Professor Fernando Ponce’s group in the Department of Physics.

In an article recently published in the journal Applied Physics Letters, the ASU group, in collaboration with a scientific team led by Professor Alan Doolittle at the Georgia Institute of Technology, has just revealed the fundamental aspect of a new approach to growing InGaN crystals for diodes, which promises to move photovoltaic solar cell technology toward record-breaking efficiencies.

Solar energy crystallizes

The InGaN crystals are grown as layers in a sandwich-like arrangement on sapphire substrates. Typically, researchers have found that the atomic separation of the layers varies; a condition that can lead to high levels of strain, breakdowns in growth, and fluctuations in the alloy’s chemical composition.

“Being able to ease the strain and increase the uniformity in the composition of InGaN is very desirable,” says Ponce, “but difficult to achieve. Growth of these layers is similar to trying to smoothly fit together two honeycombs with different cell sizes, where size difference disrupts a periodic arrangement of the cells.”

As outlined in their publication, the authors developed an approach where pulses of molecules were introduced to achieve the desired alloy composition. The method, developed by Doolittle, is called metal-modulated epitaxy. “This technique allows an atomic layer-by-layer growth of the material,” says Ponce.

Analysis of the atomic arrangement and the luminosity at the nanoscale level was performed by Fischer, the lead author of the study, and Wei. Their results showed that the films grown with the epitaxy technique had almost ideal characteristics and revealed that the unexpected results came from the strain relaxation at the first atomic layer of crystal growth.

“Doolittle’s group was able to assemble a final crystal that is more uniform and whose lattice structures match up…resulting in a film that resembles a perfect crystal,” says Ponce. “The luminosity was also like that of a perfect crystal. Something that no one in our field thought was possible.”

The perfect solar cell?

The ASU and Georgia Tech team’s elimination of these two seemingly insurmountable defects (non-uniform composition and mismatched lattice alignment) ultimately means that LEDs and solar photovoltaic products can now be developed that have much higher, efficient performance.

“While we are still a ways off from record-setting solar cells, this breakthrough could have immediate and lasting impact on light emitting devices and could potentially make the second most abundant semiconductor family, III-Nitrides, a real player in the solar cell field,” says Doolittle. Doolittle’s team at Georgia Tech's School of Electrical and Computer Engineering also included Michael Moseley and Brendan Gunning. A patent is pending for the new technology.

The collaboration was made possible by ASU’s Engineering Research Center for Quantum Energy and Sustainable Solar Technologies (QESST) funded by National Science Foundation and U.S. Department of Energy. The center, which brought the two research groups together, is directed by ASU Professor Christiana Honsberg of the Ira A. Fulton Schools of Engineering. Designed to increase photovoltaic electricity and help create devices that are scalable to commercial production, the center has built partnerships with leading solar energy companies and fueled collaborations between many of the notable universities in the U.S., Asia, Europe and Australia. The center also serves as a platform for educational opportunities for students including new college courses, partnerships with local elementary schools and public engagement events to raise awareness of the exciting challenges of harnessing the sun to power our world.

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Kentucky Researchers First to Produce High Grade Rare Earths From Coal

University of Kentucky researchers have produced nearly pure rare earth concentrates from Kentucky coal using an environmentally-conscious and cost-effective process, a groundbreaking accomplishment in the energy industry.

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Jefferson Lab Scientist Selected to Receive Francis Slack Award

Dr. Hari Areti, has been selected to receive the Francis G. Slack Award, established by the Southeastern Section of the American Physical Society, to honor excellence in service to Physics in the Southeastern U.S.

ORNL Wins Nine R&D 100 Awards

Researchers at the Department of Energy's Oak Ridge National Laboratory have received nine R&D 100 Awards in recognition of their significant advancements in science and technology.

Argonne Scientists Capture Several R&D 100 Awards

Innovative technologies developed by researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory recently earned several R&D 100 Awards.

Eight Los Alamos innovations win R&D 100 Awards

Eight Los Alamos National Laboratory technologies won R&D 100 Awards last week at R&D Magazine's annual ceremony in Orlando, Florida.

Physicist David Gates Named Editor-in-Chief of Plasma, a New Online Journal

Article announces David Gates' appointment as editor-in-chief of Plasma magazine

Argonne to Install Comanche System to Explore ARM Technology for High-Performance Computing

Argonne National Laboratory is collaborating with Hewlett Packard Enterprise (HPE) to provide system software expertise and a development ecosystem for a future high-performance computing (HPC) system based on 64-bit ARM processors.

CANDLE Shines in 2017 HPCwire Readers' and Editors' Choice Awards

Argonne National Laboratory has been recognized in the annual <em>HPCwire</em> Readers' and Editors' Choice Awards, presented at the 2017 International Conference for High Performance Computing, Networking, Storage and Analysis (SC17), in Denver, Colorado.

SLAC's Helen Quinn Honored with 2018 Benjamin Franklin Medal in Physics

Helen Quinn, a professor emerita at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University, will receive the 2018 Benjamin Franklin Medal in Physics - one of eight prestigious Franklin Institute Awards that will be handed out in Philadelphia next April.

PPPL Honors Grierson and Greenough for Distinguished Research and Engineering Achievements

Article describes PPPL's presentation of 2017 Kaul Prize and Distinguished Engineering Fellow awards.

INCITE Grants of 5.95 Billion Hours Awarded to 55 Computational Research Projects

The U.S. Department of Energy's Office of Science announced 55 projects with high potential for accelerating discovery through its Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. The projects will share 5.95 billion core-hours on three of America's most powerful supercomputers dedicated to capability-limited open science and support a broad range of large-scale research campaigns from infectious disease treatment to next-generation materials development.


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The Challenge of Estimating Alaska's Soil Carbon Stocks

A geospatial analysis determined the optimal distribution of sites needed to reliably estimate Alaska's vast soil carbon.

Unplugging the Cellulose Biofuel Bottleneck

Molecular-level understanding of cellulose structure reveals why it resists degradation and could lead to cost-effective biofuels.

How Fungal Enzymes Break Down Plant Cell Walls

Lignocellulose-degrading enzyme complexes could improve biofuel production.

Stretching to Perfection of 2-D Semiconductors

Scientists use heat and mismatched surfaces to stretch films that can potentially improve the efficient operation of devices.

Simple is Beautiful in Quantum Computing

Defect spins in diamond were controlled with a simpler, geometric method, leading to faster computing.

The Effect of Hurricanes on Puerto Rico's Dry Forests

More frequent storms turn forests from carbon source to sink.

A Chemical Thermometer for Tropical Forests

Monoterpene measures how certain forests respond to heat stress.

Where a Leaf Lands and Lies Influences Carbon Levels in Soil for Years to Come

Whether carbon comes from leaves or needles affects how fast it decomposes, but where it ends up determines how long it's available.

Twisting Molecule Wrings More Power from Solar Cells

Readily rotating molecules let electrons last, resulting in higher solar cell efficiency.

Rules Are Only Suggestions in Heavy Elements

The arrangement of electrons in an exotic human-made element shows that certain properties of heavy elements cannot be predicted using lighter ones.


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