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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.
  • 2014-02-03 13:00:00
  • Article ID: 613227

New Understanding Could Result in More Efficient Organic Solar Cells

  • Credit: Giebink, Penn State

    An electron wave function, indicated by orange shading, spreads across several nanocrystalline fullerene molecules in this representation of an organic solar cell heterojunction.

The goal of making cheap organic solar cells may have gotten a little more approachable with a new understanding of the basic science of charge separation presented in a paper published online today, February 3, in Nature Communications. Co-authored by Penn State electrical engineer Noel Giebink with lead author Bethany Bernardo, an undergraduate in his group, and colleagues at IMEC in Belgium, Argonne National Lab, Northwestern, and Princeton, the paper suggests design rules for making more efficient solar cells in the future.

Organic solar cells currently have a top efficiency of approximately 10 percent in the laboratory, much less than inorganic single crystal silicon. One of the challenges to realizing efficient organic cells lies in separating the strongly bound pairs made up of a negatively charged electron and its positively charged hole that result from light absorption, collectively referred to as an exciton. The electron and hole need to be separated in order to make a current.

The way this is done is by creating a heterojunction, which is two different organic semiconductors next to each other, one of which likes to give up an electron and the other which accepts the electron, thereby splitting the original exciton into an electron and hole residing on nearby molecules. A long-standing question in the field, however, is how the nearby electron and hole – still strongly attracted to each other at this stage – manage to separate completely in order to generate current with the efficiency observed in most solar cells.

Over the past few years, a new perspective has proposed that the high separation efficiency relies on a quantum effect – the electron or hole can exist in a wavelike state spread out over several nearby molecules at the same time. When the wave function of one of the carriers collapses at a location far enough away from its partner, the charges can separate more easily. Giebink and colleagues’ work provide compelling new evidence to support this interpretation and identify nanocrystallinity of the common acceptor material made of C60 molecules (also known as fullerenes or buckyballs) as the key that allows this delocalization effect to take place.

This local crystalline order appears to be critical to efficient photocurrent generation in organic solar cells, says Giebink. “A common view in the community is that it takes a bunch of excess energy to break apart the exciton, which meant that there had to be a large energy level difference between the donor and acceptor materials. But that big energy offset reduces the voltage of the solar cell. Our work dispels this perceived tradeoff in light of the impact that wavefunction delocalization and local crystallinity have on the charge separation process. This result should help people design new molecules and optimize donor and acceptor morphologies that help increase solar cell voltage without sacrificing current.”

The team used various luminescence and electroabsorption spectroscopic techniques together with X-ray diffraction to reach their conclusion. Their results, detailed in the paper titled “Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells,” will provide other groups with a better understanding of charge separation as they design and model more efficient organic solar cells.

Noel (Chris) Giebink is assistant professor of electrical engineering and a faculty member in the Materials Research Institute at Penn State. He can be contacted at ncg2@psu.edu.

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Microbe Mystery Solved: What Happened to the Deepwater Horizon Oil Plume

The Deepwater Horizon oil spill in the Gulf of Mexico in 2010 is one of the most studied spills in history, yet scientists haven't agreed on the role of microbes in eating up the oil. Now a research team at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has identified all of the principal oil-degrading bacteria as well as their mechanisms for chewing up the many different components that make up the released crude oil.

New Class of 'Soft' Semiconductors Could Transform HD Displays

New research by Berkeley Lab scientists could help usher in a new generation of high-definition displays, optoelectronic devices, photodetectors, and more. They have shown that a class of "soft" semiconductors can be used to emit multiple, bright colors from a single nanowire at resolutions as small as 500 nanometers. The work could challenge quantum dot displays that rely upon traditional semiconductor nanocrystals to emit light.

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The Electrochemical Society and Toyota North America Announce 2017-2018 Fellowship Winners for Projects in Green Energy Technology

The ECS Toyota Young Investigator Fellowship Selection Committee has chosen three winners who will receive $50,000 fellowship awards each for projects in green energy technology. The awardees are Dr. Ahmet Kusoglu, Lawrence Berkeley National Laboratory; Professor Julie Renner, Case Western Reserve University; and Professor Shuhui Sun, Institut National de la Rechersche Scientifique (INRS).

Chicago Quantum Exchange to Create Technologically Transformative Ecosystem

The University of Chicago is collaborating with the U.S. Department of Energy's Argonne National Laboratory and Fermi National Accelerator Laboratory to launch an intellectual hub for advancing academic, industrial and governmental efforts in the science and engineering of quantum information.

Department of Energy Awards Six Research Contracts Totaling $258 Million to Accelerate U.S. Supercomputing Technology

Today U.S. Secretary of Energy Rick Perry announced that six leading U.S. technology companies will receive funding from the Department of Energy's Exascale Computing Project (ECP) as part of its new PathForward program, accelerating the research necessary to deploy the nation's first exascale supercomputers.

Cynthia Jenks Named Director of Argonne's Chemical Sciences and Engineering Division

Argonne has named Cynthia Jenks the next director of the laboratory's Chemical Sciences and Engineering Division. Jenks currently serves as the assistant director for scientific planning and the director of the Chemical and Biological Sciences Division at Ames Laboratory.

Argonne-Developed Technology for Producing Graphene Wins TechConnect National Innovation Award

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Honeywell UOP and Argonne Seek Research Collaborations in Catalysis Under Technologist in Residence Program

Researchers at Argonne are collaborating with Honeywell UOP scientists to explore innovative energy and chemicals production.

Follow the Fantastic Voyage of the ICARUS Neutrino Detector

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JSA Awards Graduate Fellowships for Research at Jefferson Lab

Jefferson Sciences Associates announced today the award of eight JSA/Jefferson Lab graduate fellowships. The doctoral students will use the fellowships to support their advanced studies at their universities and conduct research at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) - a U.S. Department of Energy nuclear physics laboratory managed and operated by JSA, a joint venture between SURA and PAE Applied Technologies.

Muon Magnet's Moment Has Arrived

On May 31, the 50-foot-wide superconducting electromagnet at the center of the Muon g-2 experiment saw its first beam of muon particles from Fermilab's accelerators, kicking off a three-year effort to measure just what happens to those particles when placed in a stunningly precise magnetic field. The answer could rewrite scientists' picture of the universe and how it works.

Seven Small Businesses to Collaborate with Argonne to Solve Technical Challenges

Seven small businesses have been selected to collaborate with researchers at Argonne to address technical challenges as part of DOE's Small Business Vouchers Program.


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New Class of Porous Materials Better Separates Carbon Dioxide from Other Gases

Enhanced stability in the presence of water could help reduce smokestack emissions of greenhouse gases.

Manipulating Earth-Abundant Materials to Harness the Sun's Energy

New material based on common iron ore can help turn intermittent sunlight and water into long-lasting fuel.

Oxygen: The Jekyll and Hyde of Biofuels

Scientists are devising ways to protect plants, biofuels and, ultimately, the atmosphere itself from damage caused by an element that sustains life on earth.

The Rise of Giant Viruses

Research reveals that giant viruses acquire genes piecemeal from others, with implications for bioenergy production and environmental cleanup.

Grasses: The Secrets Behind Their Success

Researchers find a grass gene affecting how plants manage water and carbon dioxide that could be useful to growing biofuel crops on marginal land.

New Perspectives Into Arctic Cloud Phases

Teamwork provides insight into complicated cloud processes that are important to potential environmental changes in the Arctic.

Mountaintop Plants and Soils to Become Out of Sync

Plants and soil microbes may be altered by climate warming at different rates and in different ways, meaning vital nutrient patterns could be misaligned.

If a Tree Falls in the Amazon

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Department of Energy Awards Six Research Contracts Totaling $258 Million to Accelerate U.S. Supercomputing Technology

Today U.S. Secretary of Energy Rick Perry announced that six leading U.S. technology companies will receive funding from the Department of Energy's Exascale Computing Project (ECP) as part of its new PathForward program, accelerating the research necessary to deploy the nation's first exascale supercomputers.


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