Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tuning the energy levels of organic semiconductors

04.07.2019

Physicists from the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and the Center for Advancing Electronics Dresden (cfaed) at the TU Dresden, together with researchers from Tübingen, Potsdam and Mainz were able to demonstrate how electronic energies in organic semiconductor films can be tuned by electrostatic forces. A diverse set of experiments supported by simulations were able to rationalize the effect of specific electrostatic forces exerted by the molecular building blocks on charge carriers. The study was published recently in Nature Communications.

In electronic devices based on organic semiconductors such as solar cells, light-emitting diodes, photodetectors or transistors, electronic excitations and charge transport levels are important concepts to describe their operation principles and performances.


Examples of film structures used for the calculations of the charge - quadrupole interaction energy (EQ) of crystalline films in edge-on (a) and face-on orientation (b). The molecules are represented by discs for illustration purpose. The length scale is given in Å. EQ values are calculated for the red molecules at the film surface.

Author: Frank Ortmann


Dr. Frank Ortmann, cfaed Independent Research Group Leader

Photo: cfaed/Jürgen Lösel

The corresponding energetics, however, are more difficult to access and to tune than in conventional inorganic semiconductors like silicon chips, which stands as a general challenge. This applies both to the measurement and to the controlled influence from outside.

One tuning knob exploits the long-range Coulomb interactions, which is enhanced in organic materials. In the present study, the dependence of the energies of charge transport levels and of excitonic states on blend composition and molecular orientation in the organic material is explored.

Excitons are bound pairs of an electron and a hole that are formed in the semiconductor material by light absorption. Scientists refer to blend composition when the components consist of different organic semiconducting materials.

The findings demonstrate that the energetics in organic films can be tuned by adjusting a single molecular parameter, namely the molecular quadrupole moment in the pi-stacking direction of the molecules. An electric quadrupole can consist of two positive and two equally strong negative charges which form two oppositely equal dipoles. In the simplest case, the four charges are alternately arranged at the corners of a square.

The authors further link device parameters of organic solar cells such as the photovoltage or the photocurrent to this quadrupole moment. The results help to explain recent breakthroughs of device efficiency in organic solar cells, which are based on a new class of organic materials.

As the observed electrostatic effect is a general property of organic materials, including so-called “small molecules” and polymers, it can help to improve the performance of all types of organic devices.

Press picture:
1) Download from https://cfaed.tu-dresden.de/files/Images/dynamic/press_releases/2019/ortmann_edg...
Image caption: Examples of film structures used for the calculations of the charge - quadrupole interaction energy (EQ) of crystalline films in edge-on (a) and face-on orientation (b). The molecules are represented by discs for illustration purpose. The length scale is given in Å. EQ values are calculated for the red molecules at the film surface.
Author: Frank Ortmann

About the Computational Nanoelectronics Group:
The research group at the Center for Advancing Electronics Dresden (cfaed) headed by Dr. Frank Ortmann investigates electronic properties and charge transport properties of novel semiconductor materials. Here, organic semiconductors are currently an important focus of the work, which is funded by the German Research Foundation under the Emmy Noether Program. The group has been based at the cfaed since 2017.
Info: https://cfaed.tu-dresden.de/ortmann-home

Media inquiries:
Matthias Hahndorf
Center for Advancing Electronics Dresden (cfaed)
TU Dresden
Head of Communications
Tel.: +49 351 463-42847
E-mail: matthias.hahndorf@tu-dresden.de

cfaed
cfaed is a microelectronics research cluster funded by the German Excellence Initiative. It comprises 11 cooperating institutes in Saxony, host university is the Technische Universität Dresden (TUD). About 300 scientists from more than 20 countries investigate new technologies for electronic information processing. These technologies are inspired by innovative materials such as silicon nanowires, carbon nanotubes or polymers or based on completely new concepts such as the chemical chip or circuit fabrication methods by self-assembling structures such as DNA-Origami. The orchestration of these new devices into heterogeneous information processing systems with focus on their resilience and energy-efficiency is also part of cfaed’s research program which comprises nine different research paths.

www.cfaed.tu-dresden.de 

Wissenschaftliche Ansprechpartner:

Prof. Karl Leo
Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP)
TU Dresden
E-Mail: karl.leo@iapp.de

Dr. Frank Ortmann
Center for Advancing Electronics Dresden (cfaed)
TU Dresden,
Tel.: +49 351 463-43260
E-Mail: frank.ortmann@tu-dresden.de

Originalpublikation:

“Impact of molecular quadrupole moments on the energy levels at organic heterojunctions” (Nature Communications)
Web: https://www.nature.com/articles/s41467-019-10435-2
DOI: 10.1038/s41563-018-0030-8
Authors: M. Schwarze, K. S. Schellhammer, K. Ortstein, J. Benduhn, C. Gaul, A. Hinderhofer, L. Perdigón Toro, R. Scholz, J. Kublitski, S. Roland, M. Lau, C. Poelking, D. Andrienko, G. Cuniberti, F. Schreiber, D. Neher, K. Vandewal, F. Ortmann, Karl Leo

Kim-Astrid Magister | idw - Informationsdienst Wissenschaft

More articles from Physics and Astronomy:

nachricht Heat flow through single molecules detected
19.07.2019 | Okinawa Institute of Science and Technology (OIST) Graduate University

nachricht Better thermal conductivity by adjusting the arrangement of atoms
19.07.2019 | Universität Basel

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Better thermal conductivity by adjusting the arrangement of atoms

Adjusting the thermal conductivity of materials is one of the challenges nanoscience is currently facing. Together with colleagues from the Netherlands and Spain, researchers from the University of Basel have shown that the atomic vibrations that determine heat generation in nanowires can be controlled through the arrangement of atoms alone. The scientists will publish the results shortly in the journal Nano Letters.

In the electronics and computer industry, components are becoming ever smaller and more powerful. However, there are problems with the heat generation. It is...

Im Focus: First-ever visualizations of electrical gating effects on electronic structure

Scientists have visualised the electronic structure in a microelectronic device for the first time, opening up opportunities for finely-tuned high performance electronic devices.

Physicists from the University of Warwick and the University of Washington have developed a technique to measure the energy and momentum of electrons in...

Im Focus: Megakaryocytes act as „bouncers“ restraining cell migration in the bone marrow

Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.

Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...

Im Focus: Artificial neural network resolves puzzles from condensed matter physics: Which is the perfect quantum theory?

For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.

Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...

Im Focus: Extremely hard yet metallically conductive: Bayreuth researchers develop novel material with high-tech prospects

An international research group led by scientists from the University of Bayreuth has produced a previously unknown material: Rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications. Indeed, it is a super-hard metallic conductor that can withstand extremely high pressures like a diamond. A process now developed in Bayreuth opens up the possibility of producing rhenium nitride pernitride and other technologically interesting materials in sufficiently large quantity for their properties characterisation. The new findings are presented in "Nature Communications".

The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Heat flow through single molecules detected

19.07.2019 | Physics and Astronomy

Heat transport through single molecules

19.07.2019 | Physics and Astronomy

Welcome Committee for Comets

19.07.2019 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>