Photovoltaic from self-assembling supramolecular networks

Technical University Munich

The scanning tunneling microscope image is superimposed on the right image area by a model of the atomic structure. CA Palma / TUM
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Organic photovoltaics is considered by many as an entry into cheaper power generation. One of the challenges still to be solved is the low order of the thin layers on the electrodes. A team of scientists from the Technical University of Munich (TUM) now presents a new approach: They built photoactive layers of self-organizing molecular networks on graphene surfaces. Their research results open up interesting, new possibilities for producing optoelectronic components with molecular precision.

Nature is unsurpassed in building self-organizing, complex, molecular machinery. This can absorb light and thus separate charges and transfer electrons. Nanotechnologists have long dreamed of mimicking these biomolecular structures and using them for cost-effective power generation.

Researchers from the Faculties of Physics and Chemistry at the Technical University of Munich, the Max Planck Institute for Polymer Research (MPI-P) and the Université de Strasbourg (UdS) have now modified dye molecules so that they can be used as building blocks for self-organizing molecular networks.

On the atomically smooth surface of a graphene layer on diamond, the molecules form the target architecture by themselves, similar to proteins or in DNA nanotechnology. The only driving force is the built-in, supramolecular interactions based on hydrogen bonds. As expected, the finished networks produced electricity during exposure.

From art to application

"For a long time, self-organizing molecular architectures were considered more of an art, " says PD. Friedrich Esch, one of the authors of the work. "With this publication, we are presenting for the first time a serious practical application of this technology." Display

"For conventional organic photovoltaics, improving the molecular order is still a challenge. The nanotechnology toolkit, on the other hand, offers us the ability to predetermine the arrangement of the building blocks of the layer atomically, "says Dr. Carlos-Andres Palma, who supervised the experiments. "The physical-chemical control of the components gives us additional levers for optimizing the function."

Scientists are now working to be able to coat even larger areas and to reproduce the photovoltaic properties under standard conditions. "From self-assembling layers of dyes intercalated between two-dimensional graphene electrodes, we expect a simple scale-up towards more efficient photovoltaic elements, " Dr. Palma. "Our layers are becoming an option for solar technology."

Perfect interaction of chemistry and physics

As a photoactive dye molecule, the scientist uses terrylene diimide. The trivalent melamine links the elongated diimide molecules into networks. The exact structure of these architectures is determined by the chemists through the previously inserted side groups of the terrylene diimide.

"This work is an excellent example of the interdisciplinary collaboration that we envisioned in establishing the Catalysis Research Center, a perfect combination of chemistry and physics, " says Professor Ulrich Heiz, director of the Central Institute for Catalysis Research at TU M nchen.

Additional Information:

Nature Communications, 2016; doi: 10.1038 / ncomms10815

(TU Munich, 02.03.2016 - KSA)