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Bright prospects for organic-LED lighting

Bjorn Lussem
2009 SPIE Newsroom  
Author Information Björn Lüssem, Sebastian Reineke, Thomas Rosenow, Gregor Schwartz, and Karl Leo Institut für Angewandte Photophysik Technical University Dresden Dresden, Germany  ... 
doi:10.1117/2.1200912.002522 fatcat:3hpcwnwd45d43kejeter56tlkm

Vertical organic transistors

Björn Lüssem, Alrun Günther, Axel Fischer, Daniel Kasemann, Karl Leo
2015 Journal of Physics: Condensed Matter  
Vertical organic transistors Björn Lüssem, Alrun Günther, Axel Fischer et al.  ... 
doi:10.1088/0953-8984/27/44/443003 pmid:26466388 fatcat:sgwmetote5a5bigsfod7hf423y

Flexo-Ionic Effect of Ionic Liquid Crystal Elastomers

C. P. Hemantha Rajapaksha, M. D. Tharindupriya Gunathilaka, Suresh Narute, Hamad Albehaijan, Camilo Piedrahita, Pushpa Paudel, Chenrun Feng, Björn Lüssem, Thein Kyu, Antal Jákli
2021 Molecules  
The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The
more » ... test response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in sensors and wearable micropower generators.
doi:10.3390/molecules26144234 fatcat:zek2gbj2brdqviqfrmowlzpgwu

Doped organic transistors operating in the inversion and depletion regime

Björn Lüssem, Max L. Tietze, Hans Kleemann, Christoph Hoßbach, Johann W. Bartha, Alexander Zakhidov, Karl Leo
2013 Nature Communications  
The inversion field-effect transistor is the basic device of modern microelectronics and is nowadays used more than a billion times on every state-of-the-art computer chip. In the future, this rigid technology will be complemented by flexible electronics produced at extremely low cost. Organic field-effect transistors have the potential to be the basic device for flexible electronics, but still need much improvement. In particular, despite more than 20 years of research, organic inversion mode
more » ... ransistors have not been reported so far. Here we discuss the first realization of organic inversion transistors and the optimization of organic depletion transistors by our organic doping technology. We show that the transistor parameters-in particular, the threshold voltage and the ON/OFF ratio-can be controlled by the doping concentration and the thickness of the transistor channel. Injection of minority carriers into the doped transistor channel is achieved by doped contacts, which allows forming an inversion layer.
doi:10.1038/ncomms3775 pmid:24225722 pmcid:PMC3868197 fatcat:oo3edanw75dx3aqhzsc7cedzya

Resistive switching of rose bengal devices: A molecular effect?

Silvia Karthäuser, Björn Lüssem, Martin Weides, Manuela Alba, Astrid Besmehn, Robert Oligschlaeger, Rainer Waser
2006 Journal of Applied Physics  
The resistive switching behavior of devices consisting of aluminum top electrode, molecular layer ͑rose bengal͒, and bottom electrode ͑zinc oxide and indium tin oxide͒ is examined. By measuring the current versus voltage dependence of these devices for various frequencies and by systematically varying the composition of the device, we show that the switching is an extrinsic effect that is not primarily dependent on the molecular layer. It is shown that the molecular layer is short circuited by
more » ... ilaments of either zinc oxide or aluminum and that the switching effect is due to a thin layer of aluminum oxide at the zinc oxide/aluminum interface.
doi:10.1063/1.2364036 fatcat:4zmesfecmbawbhbdvuxmriu3ya

White organic light-emitting diodes: Status and perspective

Sebastian Reineke, Michael Thomschke, Björn Lüssem, Karl Leo
2013 Reviews of Modern Physics  
White organic light-emitting diodes (OLEDs) are ultra-thin, large-area light sources made from organic semiconductor materials. Over the last decades, much research has been spent on finding the suitable materials to realize highly efficient monochrome and white OLEDs. With their high efficiency, color-tunability, and color-quality, white OLEDs are emerging to become one of the next generation light sources. In this review, we discuss the physics of a variety of device concepts that are
more » ... ed to realize white OLEDs based on both polymer and small molecule organic materi als. Owing to the fact that about 80 % of the internally generated photons are trapped within the thin-film layer structure, we put a second focus on reviewing promising concepts for improved light outcoupling.
doi:10.1103/revmodphys.85.1245 fatcat:x54lxhev5bh7jimkh3irdksrm4

Self Assembly of Mixed Monolayers of Mercaptoundecylferrocene and Undecanethiol studied by STM

Lars Müller-Meskamp, Björn Lüssem, Silvia Karthäuser, Melanie Homberger, Ulrich Simon, Rainer Waser
2007 Journal of Physics, Conference Series  
doi:10.1088/1742-6596/61/1/170 fatcat:lzaw7wo4hnbyzapjsh7ye6kgze

Feel the Heat: Nonlinear Electrothermal Feedback in Organic LEDs

Axel Fischer, Thomas Koprucki, Klaus Gärtner, Max L. Tietze, Jacqueline Brückner, Björn Lüssem, Karl Leo, Annegret Glitzky, Reinhard Scholz
2014 Advanced Functional Materials  
Björn Lüssem, ehem.  ...  Björn Lüssem, Paul Pahner, Dr. Torben Menke, Alrun A. Günther, Dr. Christian Körner und Prof. Dr. Karl Leo, speziell aber meinem 1. Korrekturleser "bis zur letzten Minute vor Abgabe" Tobias Mönch.  ... 
doi:10.1002/adfm.201303066 fatcat:a3zio5wwnjc57dyglxdvplp5vy

Molecular doping for control of gate bias stress in organic thin film transistors

Moritz P. Hein, Alexander A. Zakhidov, Björn Lüssem, Jens Jankowski, Max L. Tietze, Moritz K. Riede, Karl Leo
2014 Applied Physics Letters  
doi:10.1063/1.4861168 fatcat:i4o4j6zjmzb5jhtgqatlmkfoua

Enhanced and balanced efficiency of white bi-directional organic light-emitting diodes

Jonghee Lee, Hyunsu Cho, Tae-Wook Koh, Changhun Yun, Simone Hofmann, Jae-Hyun Lee, Yong Hyun Kim, Björn Lüssem, Jeong-Ik Lee, Karl Leo, Malte C. Gather, Seunghyup Yoo
2013 Optics Express  
We report on the characteristics of enhanced and balanced whitelight emission from bi-directional organic light-emitting diodes (BiOLEDs) enabled by the introduction of micro-cavity effects. The insertion of an additional metal layer between the indium tin oxide anode and the hole transporting layer results in similar light output of our BiOLEDs in both top and bottom direction and in reduced distortion of the electroluminescence spectrum. Furthermore, we find that by utilizing MC effects, the
more » ... verall current efficiency can be improved by 26.2% compared to that of a conventional device.
doi:10.1364/oe.21.028040 pmid:24514317 fatcat:67bquwgjq5hzfibptlmbb6x5ha

Color-stable, ITO-free white organic light-emitting diodes with enhanced efficiency using solution-processed transparent electrodes and optical outcoupling layers

Hong-Wei Chang, Yong Hyun Kim, Jonghee Lee, Simone Hofmann, Björn Lüssem, Lars Müller-Meskamp, Malte C. Gather, Karl Leo, Chung-Chih Wu
2014 Organic electronics  
Lussem, K. Leo, Highly efficient white organic light-emitting diodes based on fluorescent blue emitters, Journal of Applied Physics, 108 (2010) 113113-113113-113115.  ... 
doi:10.1016/j.orgel.2014.02.017 fatcat:5ocwvorajjasrarjjbppi5r7iy

Tuning charge carrier transport and optical birefringence in liquid-crystalline thin films: A new design space for organic light-emitting diodes

Chang-Min Keum, Shiyi Liu, Akram Al-Shadeedi, Vikash Kaphle, Michiel Koen Callens, Lu Han, Kristiaan Neyts, Hongping Zhao, Malte C. Gather, Scott D. Bunge, Robert J. Twieg, Antal Jakli (+1 others)
2018 Scientific Reports  
Liquid-crystalline organic semiconductors exhibit unique properties that make them highly interesting for organic optoelectronic applications. Their optical and electrical anisotropies and the possibility to control the alignment of the liquid-crystalline semiconductor allow not only to optimize charge carrier transport, but to tune the optical property of organic thin-film devices as well. In this study, the molecular orientation in a liquid-crystalline semiconductor film is tuned by a novel
more » ... ading process as well as by different annealing protocols. The altered alignment is verified by cross-polarized optical microscopy and spectroscopic ellipsometry. It is shown that a change in alignment of the liquidcrystalline semiconductor improves charge transport in single charge carrier devices profoundly. Comparing the current-voltage characteristics of single charge carrier devices with simulations shows an excellent agreement and from this an in-depth understanding of single charge carrier transport in two-terminal devices is obtained. Finally, p-i-n type organic light-emitting diodes (OLEDs) compatible with vacuum processing techniques used in state-of-the-art OLEDs are demonstrated employing liquidcrystalline host matrix in the emission layer. Controlling the order in thin films of organic semiconductors down to the molecular level has been recognized as a key to improving the performance of organic electronic devices 1-4 . Several techniques to influence crystal structure and molecular alignment have been introduced, in particular for solution-processed organic semiconductors. For wet-chemical processes, the complex interaction of the semiconductor material with the solvent presents an additional means to influence the molecular orientation. For example, it was demonstrated that a simple off-centre spin-coating method enables the formation of highly aligned molecular packing structure of the organic semiconductor 5 ; a solution shearing method alters the π-π stacking distance between co-facially stacked molecules and introduces lattice strain 6 ; and chemically tailoring of the organic/metal contact interface was shown to influence the microstructure of solution-cast organic thin films 7 . These processes resulted in molecular structures in organic field-effect transistors with high charge carrier mobility. However, solution processing is still highly challenging for highly-efficient organic light-emitting diodes (OLEDs) or solar cells consisting of a multitude of functional layers 8, 9 . Chemically orthogonal solvents have to be found that are not harmful to pre-deposited films, which significantly restricts the choice of materials and possible number of layers. Although it has been reported recently that OLEDs with even a single organic layer hold Published: xx xx xxxx OPEN 2 ScIEntIfIc RepoRTs | (2018) 8:699 |
doi:10.1038/s41598-018-19157-9 pmid:29335503 pmcid:PMC5768873 fatcat:mnglvmobtzat3ob5bbdojjdrn4

Mathematics Subject Classification. 82D37, 80A20

Axel Fischer, Thomas Koprucki, Klaus Gärtner, Max Tietze, Jacqueline Brückner, Björn Lüssem, Karl Leo, Annegret Glitzky, Reinhard Scholz
2010 unpublished
For lighting applications, Organic light-emitting diodes (OLED) need much higher brightness than for displays, leading to self-heating. Due to the temperature-activated transport in organic semiconductors, this can result in brightness inhomogeneities and catastrophic failure. Here, we show that due to the strong electrothermal feedback of OLEDs, the common spatial current and voltage distribution is completely changed, requiring advanced device modeling and operation concepts. Our study
more » ... demonstrates the effect of negative differential resistance (NDR) in OLEDs induced by self-heating. As a consequence, for increasing voltage, regions with declining voltages are propagating through the device, and even more interestingly, a part of these regions show even decreasing currents, leading to strong local variation in luminance. The expected breakthrough of OLED lighting technology will require an improved price performance ratio, and the realization of modules with very high brightness but untainted appearance is considered to be an essential step into this direction. Thus, a deeper understanding of the control of electrothermal feedback will help to make OLEDs in lighting more competitive.

Weierstraß-Institut für Angewandte Analysis und Stochastik Self-heating effects in organic semiconductor devices enhanced by positive temperature feedback

Axel Fischer, Paul Pahner, Björn Lüssem, Karl Leo, Reinhard Scholz, Thomas Koprucki, Jürgen Fuhrmann, Klaus Gärtner, Annegret Glitzky
2010 Mathematics Subject Classification. 80A20, 35K05, 35C05   unpublished
We studied the influence of heating effects in an organic device containing a layer sequence of n-doped / intrinsic / n-doped C 60 between crossbar metal electrodes. A strong positive feedback between current and temperature occurs at high current densities beyond 100 A/cm 2 , as predicted by the extended Gaussian disorder model (EGDM) applicable to organic semiconductors. These devices give a perfect setting for studying the heat transport at high power densities because C 60 can withstand
more » ... eratures above 200 • C. Infrared images of the device and detailed numerical simulations of the heat transport demonstrate that the electrical circuit produces a superposition of a homogeneous power dissipation in the active volume and strong heat sources localized at the contact edges. Hence, close to the contact edges, the current density is significantly enhanced with respect to the central region of the device , demonstrating that three-dimensional effects have a strong impact on a device with seemingly one-dimensional transport.

Controlling energy levels and Fermi level en route to fully tailored energetics in organic semiconductors

Ross Warren, Alberto Privitera, Pascal Kaienburg, Andreas E. Lauritzen, Oliver Thimm, Jenny Nelson, Moritz K. Riede
2019 Nature Communications  
Peer review information Nature Communications thanks Bjorn Lussem and the other, anonymous, reviewers for their contribution to the peer review of this work. Peer reviewer reports are available.  ... 
doi:10.1038/s41467-019-13563-x pmid:31804495 pmcid:PMC6895164 fatcat:kchhuzrwhvcbtpkri5xqji6wju
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