Obtaining this information is a critical step in the development of a new class of solar cells, which promise significant savings in production costs compared to conventional silicon-based cells. The new analytical technique, published as the cover story in this week's issue of the Journal of Physical Chemistry B, was developed by a team led by Penn State University researcher John B. Asbury, assistant professor of chemistry.
Organic photovoltaic devices (OPV) have become important because they are much less expensive to produce than silicon-based solar cells. The material consists of a film made of two different types of chemicals: a polymer that releases an electron when it is struck by a photon of light and a large molecule that accepts the freed electrons, which is based on the soccer-ball-shaped "buckminsterfullerene" carbon molecules popularly known as "buckyballs." Because the electrical interactions needed to produce an electric current occur at the interfaces of the two components of this polymer blend, materials scientists need to understand the arrangement of molecules in the film. Asbury's new analytical technique provides a closer look at this arrangement than the techniques that traditionally have been used. Previous studies, using atomic-force microscopy, supply general information about the packing of the molecules, but they provide very limited information about the interfaces where the molecules actually come together. IR spectroscopy, on the other hand, provides a more detailed picture of the interface by tracing the exchange of electrons between two molecules of the film.
"The problems with OPVs today are that they are not efficient enough and they tend to stop working over time," says Asbury. In order to develop a useful electric current, the flow between the two components must be optimized. "To improve performance, we need to understand what happens at the molecular level when light is converted to electrons," Asbury explains.
When the film is exposed to light, each photon excites an electron in the polymer. If an interface between the polymer molecule and the functionalized buckminsterfullerene exists, a current can be produced. However, in the materials developed to date, many of the electrons appear to become sidetracked. Asbury exposes the film to light using ultrashort laser pulses, which causes photons of light to be converted to electrons across the entire surface at the same time. Two-dimensional IR spectroscopy is used to monitor the vibration of the molecules within the film. "The vibrations of the molecules are strongly affected by the presence or absence of electrons," says Asbury. "We use these vibrations as a probe to track the movement of electrons. By varying the structures of the materials, we expect to identify the side paths that reduce efficiency and ultimately to use that information to guide material design." The ultimate goal is a solar cell that is sufficiently inexpensive and efficient that it can be used on a rooftop to provide the electrical energy needed in a building.
In addition to Asbury, the Penn State research team includes graduate students Larry W. Barbour and Maureen Hegadorn. The work was funded by the Camille and Henry Dreyfus Foundation, the Petroleum Research Fund, and Penn State.
Barbara K. Kennedy | EurekAlert!
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Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
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Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
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Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
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For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
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