Organic electronics: a novel semiconductor from the family of carbon nitrides

Research teams from the Humboldt-Universität and the Helmholtz Zentrum Berlin (HZB) have investigated a new material from the family of carbon nitrides. Triazine-based graphitic carbon nitride (TGCN) is a semiconductor that is useful in optoelectronic applications. Its structure is two-dimensional and layered, and it resembles that of graphene. Unlike graphene, its conductivity between the layers is 65-times higher than in-plane.

Some organic materials can be used in optoelectronics just like silicon-based semiconductors. Whether in solar cells, light-emitting diodes, or as transistors – the important property is the bandgap, i.e. the energy-difference of the electrons in the valence band and the conduction band. The basic principle underlying all electronic components is that electrons can be promoted by light or by voltage between the valence and the conduction band. Here, bandgaps between 1 and 2 eV are ideal.

A team led by the chemist Dr. Michael J. Bojdys from the chemistry department and IRIS Adlershof of the Humboldt-Universität zu Berlin, has recently synthesized an organic semiconductor from the family of carbon nitrides. This triazine-based graphitic carbon nitride (TGCN) consists exclusively from carbon and nitrogen atoms and can be grown as a brown film on quartz glass substrates. The C- and N-atoms connect in hexagonal, honeycomb patterns like carbon atoms in graphene. Just like in graphene, the crystal structure of TGCN is based on layered, two-dimensional sheets. In graphene, in-plane conductivity is excellent, however, it is much lower through the planes. In the case of TGCN, the opposite is observed: through-plane conductivity is 65-times higher than in-plane. With a bandgap of 1.7 eV TGCN is a good candidate for optoelectronic applications.

The HZB-physicist Dr. Christoph Merschjann has examined the charge carrier transport in samples of TGCN using time-resolved absorption measurements in the femto- to nanosecond regime at the laser lab JULiq – a joint lab between the HZB and the Freie Universität Berlin. Such laser experiments offer a unique way to correlate macroscopic conductivity and microscopic transport models. From his measurements, he was able to deduce how the charge carriers diffuse throughout the material. “Electrons do not exit the hexagonal honeycombs of triazine units horizontally, but they move at a slope to the nearest triazine-unit in the neighboring layer. The crystal structure of the material leads to a preferred movement of charge carriers along tube-like channels.” This mechanism could explain why the conductivity of TGCN is fundamentally higher through-plane than in-plane. “TGCN is the hitherto best candidate to replace silicon semiconductors and the critical, rare-earth dopants used in their manufacture”, says Michael Bojdys. “The production method for TGCN that we developed in my group at the Humboldt-Universität zu Berlin yields flat layers of semiconducting TGCN on insulating quartz glass. This enables relatively easy upscaling and device production.”

These results were recently published in the international edition of the renowned journal "Angewandte Chemie".


New scientific management at the Helmholtz-Zentrum Berlin

As of 1 June 2019, Prof. Dr. Bernd Rech and Prof. Dr. Jan Lüning are the new scientific directors of Helmholtz-Zentrum Berlin für Materialien und Energie. Bernd Rech is responsible for the “Energy and Information” department and Jan Lüning heads the “Matter” department. Thus the HZB Supervisory Board has appointed two internationally recognised experts at the top of HZB.

IRIS Adlershof congratulates and looks forward to the continuation of the close scientific collaboration.




14th International Symposium on Functional π-Electron Systems in the Berlin-Adlershof Science and Technology park

The “14th International Symposium on Functional π-Electron Systems” is part of a regular international conference series that began in 1989 in Osaka, Japan. The 14th edition of this series is jointly organized by the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) and IRIS Adlershof of Humboldt-Universität zu Berlin. It takes place 2nd - 7th June 2019 in the Berlin-Adlershof Science and Technology park, with over 400 participants. The scientific program is co-organized by Prof. Stefan Hecht (Department of Chemistry of HU) and Prof. Norbert Koch (Department of Physics of HU). Both are members of IRIS Adlershof.

The symposium focuses on:
- design and synthesis of new π-conjugated molecules and polymers,
- organic and polymeric semiconducting materials for thin film transistors,
- organic and polymeric photovoltaic and photo-responsive materials and devices,
- organic light-emitting materials for display and lighting application,
- hybrid and perovskite materials and devices,
- conjugated polymers and oligomers in chemo/bio-sensors, and
- bioelectronics.



CRC 951 “Hybrid Inorganic/Organic Systems for Opto-Electronics (HIOS)” successful to launch third funding period

The Collaborative Research Centre 951 "Hybrid Inorganic / Organic Systems for Opto-Electronics" (HIOS) will receive funding for another four years. This was decided by the German Research Foundation (DFG) at this years’ spring meeting in Bonn.
Since its establishment in 2011, the development and investigation of innovative hybrid systems has been the scientific focus of the CRC 951. These hybrid systems combine inorganic semiconductors, conjugated organic materials, and metal nanostructures with long-term goal to realize novel and superior opto-electronic functions in the meso- or nanoscopic range not achievable with any of the individual material classes alone. These functionscould be used, for example, in high-frequency and multi-colored light sources and sensors, as well as electronic and optical multifunctional devices of future generations of information technology.
In the past years, the CRC elucidated the fundamental chemical, electronic, photonic, and plasmonic interactions arising from the different nature of the components combined in HIOS. As one of many results, novel hybridized quantum states and coupled excitations at the inorganic/organic interfaces were uncovered. These impressive results laid the foundation for the next four years of exciting HIOS-research.
The German Research Foundation (DFG) has now acknowledged the achievements of the CRC 951 by granting a third funding period for 2019 – 2023. The CRC's spokesperson and deputy spokesperson, Norbert Koch and Oliver Benson (both members of IRIS Adlershof) look forward to the joint work with 21 principal investigators from physics and chemistry of Humboldt-Universität zu Berlin (coordinating university), Technische Universität Berlin, Freie Universität Berlin, Universität Potsdam, Helmholtz-Zentrum Berlin für Materialien und Energie, and Fritz-Haber-Institut der Max-Planck-Gesellschaft.


Berlin's cluster of excellence MATH+ established

you can find more information about the cluster of excellence MATH+ here.


Qiankun Wang receives 2018 Chinese Government Award

Congratulations! Qiankun Wang, doctoral student in the group of Norbert Koch, received the “2018 Chinese Government Award for
Outstanding Self-financed Students Abroad” of the China Scholarship Council.
Well deserved, Qiankun!


Dr. Valentina Forini was awarded an Einstein Junior Fellowship

Valentina Forini is a theoretical physicist who conducts research in the field of mathematical physics with a focus on string and quantum field theory. She specializes in the Anti-de-Sitter/Conformal Field Theory correspondence, hence the study of space-time-matter. Her contributions to string and gauge field theory are internationally recognised. From 2012 to 2017 Valentina Forini was group leader of an Emmy Noether Research Group at the Department of Physics of Humboldt-Universität zu Berlin.

Since then, Forini has been engaged in several research projects at IRIS Adlershof. Meanwhile Valentina Forini has been awarded a 2018/19 Simons Emmy Noether Fellowship at Perimeter Institute for Theoretical Physics in Canada. At IRIS she is also project leader for the European Marie-Curie ITN network Europlex. Moreover, Forini is a lecturer in Mathematics at City University London.

Now, Ms Forini has been awarded an Einstein Junior Fellowship by the Einstein Foundation Berlin IRIS Adlershof congratulates Ms. Forini warmly and looks forward to further cooperation.