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    • 2018-11-07 01:05:03
    • Article ID: 703508

    Dancing atoms in perovskite materials provide insight into how solar cells work

    A new study is a step forward in understanding why perovskite materials work so well in energy devices and potentially leads the way toward a theorized "hot" technology that would significantly improve the efficiency of today's solar cells.

    • Credit: Greg Stewart/SLAC National Accelerator Laboratory

      When the researchers scattered neutrons off the perovskite material (red beam) they were able to measure the energy the neutrons lost or gained (white and blue lines). Using this information, they were able to see the structure and motion of the atoms and molecules within the material (arrangement of blue and purple spheres).

    A closer look at materials that make up conventional solar cells reveals a nearly rigid arrangement of atoms with little movement. But in hybrid perovskites, a promising class of solar cell materials, the arrangements are more flexible and atoms dance wildly around, an effect that impacts the performance of the solar cells but has been difficult to measure.

    In a paper published in the Proceedings of the National Academy of Sciences, an international team of researchers led by the U.S. Department of Energy’s SLAC National Accelerator Laboratory has developed a new understanding of those wild dances and how they affect the functioning of perovskite materials. The results could explain why perovskite solar cells are so efficient and aid the quest to design hot-carrier solar cells, a theorized technology that would almost double the efficiency limits of conventional solar cells by converting more sunlight into usable electrical energy.

    Piece of the puzzle

    Perovskite solar cells, which can be produced at room temperature, offer a less expensive and potentially better performing alternative to conventional solar cell materials like silicon, which have to be manufactured at extremely high temperatures to eliminate defects. But a lack of understanding about what makes perovskite materials so efficient at converting sunlight into electricity has been a major hurdle to producing even higher efficiency perovskite solar cells.

    “It’s really only been over the last five or six years that people have developed this intense interest in solar perovskite materials,” says Mike Toney, a distinguished staff scientist at SLAC’s Stanford Synchrotron Radiation Light Source (SSRL) who led the study. “As a consequence, a lot of the foundational knowledge about what makes the materials work is missing. In this research, we provided an important piece of this puzzle by showing what sets them apart from more conventional solar cell materials. This provides us with scientific underpinnings that will allow us to start engineering these materials in a rational way.”

    Keeping it hot

    When sunlight hits a solar cell, some of the energy can be used to kick electrons in the material up to higher energy states. These higher-energy electrons are funneled out of the material, producing electricity.

    But before this happens, a majority of the sun’s energy is lost to heat with some fraction also lost during the extraction of usable energy or due to inefficient light collection. In many conventional solar cells, such as those made with silicon, acoustic phonons – a sort of sound wave that propagates through material – are the primary way that this heat is carried through the material. The energy lost by the electron as heat limits the efficiency of the solar cell.

    In this study, theorists from the United Kingdom, led by Imperial College Professor Aron Walsh and electronic structure theorists Jonathan Skelton and Jarvist Frost, provided a theoretical framework for interpreting the experimental results. They predicted that acoustic phonons traveling through perovskites would have short lifetimes as a result of the flexible arrangements of dancing atoms and molecules in the material.

    Stanford chemists Hema Karunadasa and Ian Smith were able to grow the large, specialized single crystals that were essential for this work. With the help of Peter Gehring, a physicist at the NIST Center for Neutron Research, the team scattered neutrons off these perovskite single crystals in a way that allowed them to retrace the motion of the atoms and molecules within the material. This allowed them to precisely measure the lifetime of the acoustic phonons.

    The research team found that in perovskites, acoustic phonons are incredibly short-lived, surviving for only 10 to 20 trillionths of a second. Without these phonons trucking heat through the material, the electrons might stay hot and hold onto their energy as they’re pulled out of the material. Harnessing this effect could potentially lead to hot-carrier solar cells with efficiencies that are nearly twice as high as conventional solar cells.

    In addition, this phenomenon could explain how perovskite solar cells work so well despite the material being riddled with defects that would trap electrons and dampen performance in other materials.

    “Since phonons in perovskites don’t travel very far, they end up heating the area surrounding the electrons, which might provide the boost the electrons need to escape the traps and continue on their merry way,” Toney says.

    Transforming energy production

    To follow up on this study, researchers at the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory will investigate this phenomenon in more complicated perovskite materials that are shown to be more efficient in energy devices. They would like to figure out how changing the chemical make-up of the material affects acoustic phonon lifetimes.

    “We need to fundamentally transform our energy system as quickly as possible,” says Aryeh Gold-Parker, who co-led the study as a PhD student at Stanford University and SLAC. “As we move toward a low-carbon future, a very important piece is having cheap and efficient solar cells. The hope in perovskites is that they'll lead to commercial solar panels that are more efficient and cheaper than the ones on the market today.”

    The research team also included scientists from NIST; the University of Bath and Kings College London, both in the UK; and Yonsei University in Korea.

    SSRL is a DOE Office of Science user facility. This work was supported by the DOE’s Office of Science and the Solar Energy Technologies Office; the Engineering and Physical Sciences Research Council; the Royal Society; and the Leverhulme Trust.


    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, Calif., SLAC is operated by Stanford University for the U.S. Department of Energy's Office of Science. For more information, please visit slac.stanford.edu.

    SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

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    Microbes Eat the Same in Labs and the Desert

    Analyses of natural communities forming soil crusts agree with laboratory studies of isolated microbe-metabolite relationships.

    Scientists Produce 3-D Chemical Maps of Single Bacteria

    Scientists at the National Synchrotron Light Source II (NSLS-II)--a U.S. Department of Energy (DOE) Office of Science User Facility at DOE's Brookhaven National Laboratory--have used ultrabright x-rays to image single bacteria with higher spatial resolution than ever before. Their work, published in Scientific Reports, demonstrates an x-ray imaging technique, called x-ray fluorescence microscopy (XRF), as an effective approach to produce 3-D images of small biological samples.

    Self-Sensing Materials Are Here

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    New design coats molecular components and dramatically improves stability under tough, oxidizing conditions.

    X-Rays Show How Periods of Stress Changed an Ice Age Hyena to the Bone

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    Turning Wood Scraps into Tape

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    Argonne's Min Si receives early career award from IEEE Computer Society

    Argonne's Min Si wins Award for Excellence for Early Career Researchers in High Performance Computing through the Institute of Electrical and Electronics Engineers.

    Jefferson Lab Director Appointed to Distinguished Professorship

    Stuart Henderson, director of the Department of Energy's Thomas Jefferson National Accelerator Facility, has been appointed the Governor's Distinguished CEBAF professor at Old Dominion University. The position is supported by the Commonwealth of Virginia and is named for the Continuous Electron Beam Accelerator Facility, which is the main research facility located at Jefferson Lab.

    DOE issues call for HPC for Energy Innovation proposals

    The U.S. Department of Energy's (DOE) High Performance Computing for Energy Innovation (HPC4EI) Initiative today issued its first joint solicitation for the High Performance Computing for Manufacturing Program (HPC4Mfg) and the High Performance Computing for Materials Program (HPC4Mtls).

    DOE funding advances project to turn captured CO2 into key chemicals

    The U.S. Department of Energy has selected Southern Research for an award of up to $1.5 million to advance technology for carbon dioxide utilization.

    Sierra Reaches Higher Altitudes, Takes Number Two Spot on List of Fastest Supercomputers

    Sierra, Lawrence Livermore National Laboratory's newest supercomputer, rose to second place on the list of the world's fastest computing systems, TOP500 List representatives announced Monday at the International Conference for High Performance Computing, Networking, Storage and Analysis conference (SC18) in Dallas.

    Green energy: Wind energy agreement will provide savings, 50 percent of electricity needs for Kansas State University Manhattan campus

    Kansas State University has signed an agreement with Westar Energy to provide approximately 50 percent of the energy needs for the university's main Manhattan campus from a wind farm in Nemaha County and save the university nearly $200,000 annually.

    INCITE grants awarded to 62 computational research projects

    The U.S. Department of Energy announced new projects for 2019 through its Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program.

    Argonne's Raj Kettimuthu Named ACM Distinguished Member

    Argonne computer scientist Raj Kettimuthu recently was named a Distinguished Member of the Association for Computing Machinery for his development of tools to analyze and enhance end-to-end data transfer performance.

    Jefferson Lab-Affiliated Researchers Honored as APS Fellows

    The Department of Energy's Thomas Jefferson National Accelerator Facility now has a few more fellows on campus. The American Physical Society, a professional membership society that works on behalf of the physics community, recently announced its list of 2018 fellowships.

    Jefferson Lab Receives DOE Award for Energy Efficient Upgrade

    On Oct. 23, a team from the Department of Energy's Thomas Jefferson National Accelerator Facility was honored at the 2018 Federal Energy and Water Management Award Ceremony for upgrades made to the lab's data center, ultimately improving its energy efficiency.


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    Microbes Eat the Same in Labs and the Desert

    Analyses of natural communities forming soil crusts agree with laboratory studies of isolated microbe-metabolite relationships.

    Diverse Biofeedstocks Have High Ethanol Yields and Offer Biorefineries Flexibility

    Evidence suggests that biorefineries can accept various feedstocks without negatively impacting the amount of ethanol produced per acre.

    Opening Access to Explore the Synthetic Chemistry of Neptunium

    New, easily prepared starting material opens access to learning more about a difficult-to-control element in nuclear waste.

    Tiny Titanium Barrier Halts Big Problem in Fuel-Producing Solar Cells

    New design coats molecular components and dramatically improves stability under tough, oxidizing conditions.

    Turning Wood Scraps into Tape

    A new chemical process converts a component of wasted wood pulp and other biomass into high-value pressure-sensitive adhesives.

    Very Heavy Elements Deliver More Electrons

    Scientists revise understanding of the limits of bonding for very electron-rich heavy elements.

    Probing Water's "No-Man's Land" Temperature Region

    Measuring the physical properties of water at previously unexplored temperatures offers insights into one of the world's essential liquids.

    Novel Soil Bacteria with Unusual Genes Synthesize Unique Antibiotic Precursors

    A large-scale soil project uncovered genetic information from bacteria with the capacity to make specialized molecules that could lead to new pharmaceuticals.

    Warmer Temperatures Lengthen Growing Season, Increase Plants' Vulnerability to Frost

    Experimental warming treatments show how peatland forests may respond to future environmental change.

    Rising Stars Seek to Learn from the Master: Mother Nature

    A trio of scientists was recognized for their early career successes in uncovering how microbes produce fuel, insights that could change our energy portfolio


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