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2. The influence of impurities on the charge carrier mobility of small molecule organic semiconductors

Author

Friederich, Pascal, Fediai, Artem, Li, Jing, Mondal, Anirban, Kotadiya, Naresh B., Symalla, Franz, Wetzelaer, Gert-Jan A. H., Andrienko, Denis, Blase, Xavier, Beljonne, David, Blom, Paul W. M., Brédas, Jean-Luc, and Wenzel, Wolfgang

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

Amorphous organic semiconductors based on small molecules and polymers are used in many applications, most prominently organic light emitting diodes (OLEDs) and organic solar cells. Impurities and charge traps are omnipresent in most currently available organic semiconductors and limit charge transport and thus device efficiency. The microscopic cause as well as the chemical nature of these traps are presently not well understood. Using a multiscale model we characterize the influence of impurities on the density of states and charge transport in small-molecule amorphous organic semiconductors. We use the model to quantitatively describe the influence of water molecules and water-oxygen complexes on the electron and hole mobilities. These species are seen to impact the shape of the density of states and to act as explicit charge traps within the energy gap. Our results show that trap states introduced by molecular oxygen can be deep enough to limit the electron mobility in widely used materials., Comment: 13 pages + SI, 7 figures + TOC-graphic + 2 figures in SI

Published
2019

3. 45‐4: Late‐News Paper: On the Determination of Ionization Potentials.

Author

Symalla, Franz, Fediai, Artem, Neumann, Tobias, and Strunk, Timo

Subjects
ENERGY levels (Quantum mechanics), IONIZATION energy, DIGITAL twins, ELECTRON affinity
Abstract

OLED device performance is intricately linked to microscopic processes influenced by molecular properties, creating a complex interdependence. Two key material properties in the design of balanced devices are ionization potential (IP) and electron affinities (EA). In this work we discuss how measured quantities relate to relevant energy levels in OLEDs. We present a simulation approach to compute IP and EA, benchmarked against experimental data, to shed light on the complexity of these properties. The thereby derived understanding has the potential to improve material alignment in OLED devices, ultimately improving efficiency. [ABSTRACT FROM AUTHOR]

Published
2024
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4. 37‐3: Donor‐Acceptor Alignment and Charge Separation in Small Molecule Organic Semiconductors.

Author

Fediai, Artem, Neumann, Tobias, Symalla, Franz, and Strunk, Timo

Subjects
CHARGE transfer, MOLECULAR interactions, BINDING energy, ENERGY transfer, SMALL molecules, ORGANIC semiconductors
Abstract

Understanding complex molecular interactions in OLED materials such as donor‐acceptor charge transfer are crucial for device efficiency. Utilizing simulation tools as a virtual microscope, we investigate how fundamental molecular properties, especially Coulomb interactions, impact charge transfer dynamics and overall device performance. Our findings reveal that molecular packing and microelectrostatic environments significantly influence charge transfer binding energy, underscoring the importance of molecular arrangement in material design. These insights, difficult to obtain experimentally, are pivotal in formulating design guidelines for high‐performance organic compounds, thereby advancing our understanding of OLED molecular interactions and aiding in the development of more efficient and durable devices. [ABSTRACT FROM AUTHOR]

Published
2024
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5. 45‐4: Late‐News Paper:On the Determination of Ionization Potentials

Author

Symalla, Franz, Fediai, Artem, Neumann, Tobias, and Strunk, Timo

Abstract

OLED device performance is intricately linked to microscopic processes influenced by molecular properties, creating a complex interdependence. Two key material properties in the design of balanced devices are ionization potential (IP) and electron affinities (EA). In this work we discuss how measured quantities relate to relevant energy levels in OLEDs. We present a simulation approach to compute IP and EA, benchmarked against experimental data, to shed light on the complexity of these properties. The thereby derived understanding has the potential to improve material alignment in OLED devices, ultimately improving efficiency.

Published
2024
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17. (Invited) The Interplay of Conformation and Electronic Structure in Metal Organic Frameworks

Author

Pramudya, Yohanes, primary, Kozlowska, Mariana, additional, Heidrich, Shahriar, additional, Krstić, Marjan, additional, Haldar, Ritesh, additional, Neumann, Tobias, additional, Schlöder, Tobias, additional, Zhang, Qiang, additional, Symalla, Franz, additional, Hassan, Zeinab Mohamed, additional, Liu, Xiaojing, additional, Heinke, Lars, additional, Woell, Christof, additional, and Wenzel, Wolfgang, additional

Published
2020
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21. 28‐1: Invited Paper:Bottom‐Up OLED Development by Virtual Design: Systematic Elimination of Performance Bottlenecks Using a Microscopic Simulation Approach

Author

Neumann, Tobias, Symalla, Franz, Strunk, Timo, Feidai, Artem, Kaiser, Simon, Friederich, Pascal, and Wenzel, Wolfgang

Abstract

The gap between computational chemistry and parametric device simulations limits the potentially immense impact of computer models on OLED R&D. We present a review on a bottom‐up multiscale modeling approach to bridge this gap and systematically eliminate performance bottlenecks by virtual design. In several case studies we demonstrate how microscopic simulations can support experimental R&D by identifying fundamental reasons for performance bottlenecks, and by deriving strategies for their elimination.

Published
2022
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23. Modellierung von Ladungs- und Exzitondynamik in amorphen organischen Halbleitern = Modeling of charge and exciton dynamics in amorphous organic semiconductors

Author

Symalla, Franz and Wenzel, W.

Subjects
Technology, Organic electronics, multi-scale modeling, ddc:600
Abstract

Organische Halbleiter finden Anwendungen in vielen Technolgien, wie organischen Leuchtdioden, organischen Solarzellen oder organischen Transistoren. Die Effizienz der Bauteile wird hierbei maßgeblich von den elektronischen Transporteigenschaften der zugrundeliegenden organischen Halbleiter bestimmt, deren oft amorphe Struktur zu Ladungsperkolationseffekten auf einer Größenordnung von 100nm führen kann. In dieser Arbeit werden Methoden vorgestellt, die es ermöglichen mesoskopischen Ladungstransport in amorphen organischen Halbleitern, auf der Basis zugrundeliegender quantenchemischer Rechnungen, effizient zu simulieren. Dabei werden Methoden zur effizienten Auswertung der Coulomb-Wechselwirkung zwischen Ladungsträgern in kinetischen Monte-Carlo Verfahren (KMC), sowie Algorithmen zur Beschleuningung von Vielteilchen-KMC-Verfahren vorgestellt. Die Methoden werden gegen den prototypischen organischen Halbleiter alpha-NPD validiert. Es wird gezeigt, dass Ladungstransport in gemischten Emissions-Transport Materialien, wie sie in organischen Leuchtdioden Einsatz finden, durch Hüpftransport zwischen Emittermolekülen stattfindet, indem räumliche Distanzen zwischen End- und Anfangszustand durch virtuelle Zustände auf Transportmolekülen überbrückt werden. Desweitern wird gezeigt, dass Ladungsträgerinjektion an metallisch-organischen Grenzflächen bei hohen elektrischen Feldern durch virtuelle Übergangszustände auf organischen Molekülen in der Nähe der Grenzfläche um mehrere Größenordnungen verstärkt wird.

Published
2018
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32. Superexchange Charge Transport in Loaded Metal Organic Frameworks

Author

Neumann, Tobias, primary, Liu, Jianxi, additional, Wächter, Tobias, additional, Friederich, Pascal, additional, Symalla, Franz, additional, Welle, Alexander, additional, Mugnaini, Veronica, additional, Meded, Velimir, additional, Zharnikov, Michael, additional, Wöll, Christof, additional, and Wenzel, Wolfgang, additional

Published
2016
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33. Molecular Origin of the Charge Carrier Mobility in Small Molecule Organic Semiconductors

Author

Friederich, Pascal, primary, Meded, Velimir, additional, Poschlad, Angela, additional, Neumann, Tobias, additional, Rodin, Vadim, additional, Stehr, Vera, additional, Symalla, Franz, additional, Danilov, Denis, additional, Lüdemann, Gesa, additional, Fink, Reinhold F., additional, Kondov, Ivan, additional, von Wrochem, Florian, additional, and Wenzel, Wolfgang, additional

Published
2016
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44. Disorder compensation controls doping efficiency in organic semiconductors

Author

Fediai, Artem, Symalla, Franz, Friederich, Pascal, and Wenzel, Wolfgang

Subjects
Technology, Science, Computational science, technology, industry, and agriculture, Article, Condensed Matter::Materials Science, Semiconductors, Condensed Matter::Superconductivity, Electronic devices, Computational methods, lcsh:Q, Condensed Matter::Strongly Correlated Electrons, lcsh:Science, human activities, ddc:600
Abstract

Conductivity doping of inorganic and organic semiconductors enables a fantastic variety of highly-efficient electronic devices. While well understood for inorganic materials, the mechanism of doping-induced conductivity and Fermi level shift in organic semiconductors remains elusive. In microscopic simulations with full treatment of many-body Coulomb effects, we reproduce the Fermi level shift in agreement with experimental observations. We find that the additional disorder introduced by doping can actually compensate the intrinsic disorder of the material, such that the total disorder remains constant or is even reduced at doping molar ratios relevant to experiment. In addition to the established dependence of the doping-induced states on the Coulomb interaction in the ionized host-dopant pair, we find that the position of the Fermi level and electrical conductivity is controlled by disorder compensation. By providing a quantitative model for doping in organic semiconductors we enable the predictive design of more efficient redox pairs., Though conductivity doping in organic semiconductors has been widely studied in organic electronics, a clear mechanistic picture that explains the phenomenon is still lacking. Here, the authors report a theoretical approach to elucidate the role of disorder compensation in doped organic materials.

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45. Rational In Silico Design of an Organic Semiconductor with Improved Electron Mobility

Author

Friederich, Pascal, Gómez, Verónica, Sprau, Christian, Meded, Velimir, Strunk, Timo, Jenne, Michael, Magri, Andrea, Symalla, Franz, Colsmann, Alexander, Ruben, Mario, and Wenzel, Wolfgang

Subjects
7. Clean energy
Abstract

Organic semiconductors find a wide range of applications, such as in organic light emitting diodes, organic solar cells, and organic field effect transistors. One of their most striking disadvantages in comparison to crystalline inorganic semiconductors is their low charge-carrier mobility, which manifests itself in major device constraints such as limited photoactive layer thicknesses. Trial-and-error attempts to increase charge-carrier mobility are impeded by the complex interplay of the molecular and electronic structure of the material with its morphology. Here, the viability of a multiscale simulation approach to rationally design materials with improved electron mobility is demonstrated. Starting from one of the most widely used electron conducting materials (Alq3), novel organic semiconductors with tailored electronic properties are designed for which an improvement of the electron mobility by three orders of magnitude is predicted and experimentally confirmed.

46. Ab initio charge-carrier mobility model for amorphous molecular semiconductors.

Author

Massé, Andrea, Friederich, Pascal, Symalla, Franz, Feilong Liu, Nitsche, Robert, Coehoorn, Reinder, Wenzel, Wolfgang, and Bobbert, Peter A.

Subjects
*CHARGE carrier mobility, *ORGANIC semiconductors, *CHARGE transfer
Abstract

Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α-NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α-NPD. We apply our mobility model to two types of hole-only α-NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength. [ABSTRACT FROM AUTHOR]

Published
2016
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