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Research outputs

As an application-oriented research organisation, Fraunhofer aims to conduct highly innovative and solution-oriented research - for the benefit of society and to strengthen the German and European economy.

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Projects

Fraunhofer is tackling the current challenges facing industry head on. By pooling their expertise and involving industrial partners at an early stage, the Fraunhofer Institutes involved in the projects aim to turn original scientific ideas into marketable products as quickly as possible.

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Researchers

Scientific achievement and practical relevance are not opposites - at Fraunhofer they are mutually dependent. Thanks to the close organisational links between Fraunhofer Institutes and universities, science at Fraunhofer is conducted at an internationally first-class level.

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Institutes

The Fraunhofer-Gesellschaft is the leading organisation for applied research in Europe. Institutes and research facilities work under its umbrella at various locations throughout Germany.

Recent Additions

  • Publication
    Effects of sub-picosecond direct laser interference patterning on the optoelectronic properties of fluorine-doped tin oxide thin films
    ( 2022)
    Heffner, Herman
    ;
    Soldera, Marcos
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    Deconinck, Marielle
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    Vaynzof, Yana
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    Mulko, Lucinda
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    Micropatterning of metal oxides is of high interest for structuring electrodes in optoelectronic devices. In this work, the impact of infrared (IR) sub-picosecond Direct Laser Interference Patterning (DLIP) on the surface morphology, surface chemistry, optical and electrical properties of Fluorine-doped Tin Oxide (FTO) is studied. The topography characterization reveals periodic microchannels with an average height between 15 and 600 nm, depending on the applied laser fluence, decorated with Laser-Induced Periodic Surface Structures (LIPSS). The doping by aliovalent Sn atoms induced by non-linear IR absorption were revealed by X-ray Photoemission Spectroscopy (XPS) analysis. An increase in the average diffuse optical transmittance up to 730% was obtained in the spectral range 400-1000 nm as a consequence of the interaction of white light with the periodic micro- and nanostructures. The one-dimensionality of the microstructures caused a significant anisotropic electrical behavior, and an enhancement of the conductivity of up to 50% was obtained following the direction of the microchannels of the patterned films as compared to the unstructured material. Our results demonstrate that DLIP is a powerful technique for future application in structuring electrodes for highly efficient optoelectronic devices and sensors.
  • Publication
    Synthesis and Characterization of Phosphorus-Containing Isocyclam Macrocycles and their Nickel Complexes
    ( 2022)
    Gerschel, Philipp
    ;
    Guseva, Tatiana
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    ;
    The tetradentate azamacrocycle cyclam (=1,4,8,11-tetraazacyclotetradecane) was studied profoundly for the coordination of transition metal ions, and the resulting complexes were investigated extensively for their catalytic performance in, e.g., O2 activation and electrocatalytic CO2 reduction. Although the successful synthesis of analogous P4 macrocycles was described earlier, no tetradentate N,P mixed 14-membered macrocycles have been prepared to date and their chemistry remains elusive. Thus, in this work, we showcase the synthesis of phospha-aza mixed cyclam-based macrocycles by selectively “exchanging” one or two secondary amines in the macrocycle isocyclam (=1,4,7,11-tetraazacyclotetradecane) with tertiary phosphines. In addition, we herein present the preparation of the corresponding nickel complexes along with their complex chemical and structural characterization to provide first coordination studies.
  • Publication
    Enabling short-term energy flexibility markets through Blockchain
    ( 2022) ; ;
    Tcholtchev, Nikolay Vassilev
    ;
    Climate change has put significant pressure on energy markets. Political decisions such as the plan of the German government to shut down coal power plants by 2038 are shifting electricity production towards renewable and distributed energy resources. The share of these resources will continue to grow significantly in the coming years. This trend changes the ways how energy markets work which mandates fundamental changes in the underlying IT infrastructure. In this paper, we propose a blockchain-based solution which enables an economically viable and grid-serving integration of distributed energy resources into the existing energy system. Our blockchain-based approach targets intraday and day-ahead operating reserve markets, on which energy grid operators and operators of distributed energy resources can trade flexibilities within the schedulable energy production and consumption of their resources. By utilizing these flexibilities as an operating reserve, renewable and climate-friendly technologies can contribute to maintaining the grid stability and security of supply while simultaneously creating economically interesting business models for their operators. We propose to define blockchain-based short-term energy markets by utilizing the concept of general-purpose smart contracts and cryptocurrencies. This enables direct and decentralized trading of energy flexibilities without any intermediary or central instance. We demonstrate the feasibility of our approach through an implementation of a prototype of the proposed markets based on the Ethereum blockchain and provide a detailed evaluation of its efficiency and scalability.
  • Publication
    Evidence of Sulfur Non‐Innocence in [CoII(dithiacyclam)]2+‐Mediated Catalytic Oxygen Reduction Reactions
    ( 2022)
    Battistella, Beatrice
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    Iffland-Mühlhaus, Linda
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    Schütze, Maximilian
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    Cula, Beatrice
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    Kuhlmann, Uwe
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    Dau, Holger
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    Hildebrandt, Peter
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    Lohmiller, Thomas
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    Mebs, Stefan
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    Ray, Kallol
    In many metalloenzymes sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated Oxygen Reduction Reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (cyclam = 1,5,8,11-tetraaza-cyclotetradecane) (1) and the S-containing analog [Co(S2N2-cyclam)]2+ (S2N2-cyclam = 1,8-dithia-5,11-diaza-cyclotetradecane, (2) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the Co(II) centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Most viewed

  • Publication
    LED-pumped whispering-gallery laser
    A low-cost light-emitting diode (LED) is sufficient to pump a quasi-continuous-wave bidirectional high-Q whispering-gallery resonator laser made of Nd:YVO4. This is remarkable because of the very limited spatial and spectral coherence of an LED. The LED, delivering up to 3.5 W, centered around 810 nm, is turned on in intervals of 100 µs duration, and for these periods a laser output exceeding 0.8 mW has been verified. Furthermore, 0.1-s-long laser pulses are demonstrated. To the best of our knowledge this is the first demonstration of an LED-pumped high-Q whispering-gallery laser. The concept can be extended easily to other laser active materials. A prospect is also to pump several of such lasers with a single LED.
  • Publication
    MobiNa - Die mobile Notfallassistenz und Kommunikationsplattform für Menschen im Alter
    ( 2013)
    King, Ralf Simon
    MobiNa ist die mobile Nofallassistenz für das häusliche Umfeld. Die Assistenz kann in Verbindung mit weiterer Sensorik Notfälle, wie beispielsweise den Sturz einer Person, erkennen und der dieser schnell Hilfe über die mobile Kommunikationseinrichtung bereitstellen. Das System lässt sich um Telepräsenz- und Komfortfunktionen erweitern und das nutzerzentrierte Design sowie die Verwendung von kostengünstiger Hardware demonstrieren das marktnahe Entwicklungsstadium.
  • Publication
    InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells
    ( 2014)
    Alonso-Álvarez, D.
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    Thomas, T.
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    Führer, M.
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    Hylton, N.P.
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    Ekins-Daukes, N.
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    Lackner, D.
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    Philipps, S.P.
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    Bett, A.W.
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    Sodabanlu, H.
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    Fujii, H.
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    Watanabe, K.
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    Sugiyama, M.
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    Nasi, L.
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    Campanini, M.
    Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 ms, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.