Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

From molecules to organic light emitting diodes

08.04.2015

Scientists at the MPI-P Mainz, BASF Ludwigshafen, the University of Ulm, and Innovation Lab Heidelberg have developed a simulation toolkit for evaluating properties of organic light emitting diodes (OLEDs) based solely on their chemical composition. The package is integrated in the free software VOTCA and helps to pre-select suitable organic molecules for lighting and display applications.

The research group headed by Dr. Denis Andrienko, project leader at the Max Planck Institute for Polymer Research (Theory department, director Prof. Kurt Kremer) has developed a set of multiscale simulation techniques which predict macroscopic properties of an organic light emitting diode (OLED) from its chemical composition.


Possible workflows of parameter-free OLED simulations: polarizable force-fields and electronic properties of isolated molecules obtained from first principles are used to generate amorphous morphologies and evaluate charge transfer rates in small systems (microscopic models). Coarse-grained models are parametrized either by matching macroscopic observables, e.g., charge mobility, of the microscopic and coarse-grained (lattice) models. The resulting analytical expressions for mobility are then used to solve drift-diffusion equations for the entire device, after incorporating long-range electrostatic effects and electrodes. Alternatively, off-lattice models can be developed by matching distributions and correlations of site energies, electronic couplings, and positions of molecules. The master equations for this model can be solved using the kinetic Monte Carlo algorithm, yielding macroscopic characteristics of a device.

© AFM

The link between the molecular and mesoscopic scales became possible by combining advanced coarse-graining techniques with efficient simulation algorithms (see Figure). Implemented, among others, by the PhD candidate Pascal Kordt and postdoctoral fellow Dr. Jeroen van der Holst, this development facilitated computer simulations of electron and exciton motion in about 100 nanometer-thick OLED layers, i.e. macroscopically large, yet microscopically-resolved systems.

The developed methods are reviewed in the feature article “Modeling of Organic Light Emitting Diodes: From Molecular to Device Properties” of Advanced Functional Materials, and highlighted as a cover page.

Denis Andrienko explains how useful the software is to the organic semiconductors industry: “Modern mobile phones already use OLED (AMOLED), and large OLED-based TV screens are entering the market. Yet, the materials design for these applications often progresses via the trial-and-error strategy”, he explains.

“In our approach both atomistic morphologies of amorphous OLED layers and charge motion are predicted solely from molecular structures. In contrast to experiments, OLED properties are then directly linked to the underlying chemistry and material morphology.”

The expectation, backed up by the European Research Council and financially supported by the German Ministry for Education and Research (grant MESOMERIE, FKZ 13N10723), is that the computer-based design will rapidly grow in the coming years, allowing companies to save money on synthesis and characterization of new materials.

Interestingly, the 2014 Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for the invention of efficient blue light-emitting diodes, or LEDs. LEDs are by now used as signal lights in alarm clocks, entertainment devices, flashlights, and more recently in large-area displays, where tiny red, green, and blue LEDs form a pixel. Millions of pixels are employed to display an image.

In every pixel electrons constantly recombine with their counterparts (holes) and form photons, the elementary particle of light. Depending on the material, these photons have different energy, or wavelength, which then determines the light color. LEDs are made of inorganic materials and are therefore exceptionally stable. Recent developments in organic semiconductors illustrated that organic semiconductors can provide complementary material properties, e.g. high contrast ratios, curved shapes, or mechanical flexibility (bendable and foldable displays).

The task of computer simulations is to help designing new materials for OLEDs. Even with modern supercomputers, however, it is impossible to simulate an OLED with the full atomistic detail. To remedy the situation, multiscale schemes are employed: properties of a single molecule are evaluated using first principle methods.

Subsequently, a classical molecular model is parameterized and used to study systems of thousands molecules. OLED layers, however, consist of 100 nanometer thick layers (millions of molecules). In VOTCA, an intermediate stochastic model is introduced, which reproduces distributions of important microscopic properties (e.g. distances between molecules), and is then employed to simulate an entire OLED device.

In spite of the clear roadmap in designing new materials for OLEDs, the methods and code development are always “under construction”, which makes it an interesting and exciting research topic.

Weitere Informationen:

http://www.mpip-mainz.mpg.de/molecules_to_OLED - Press release and original publication
http://www2.mpip-mainz.mpg.de/~andrienk/ - Information about Dr. Andrienko and his research
http://www.mpip-mainz.mpg.de/home/en - Max Planck Institute for Polymer Research

Natacha Bouvier | Max-Planck-Institut für Polymerforschung

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

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: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>