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4. Critical Evaluation of Organic Thin-Film Transistor Models

Author

Krammer, Markus, Borchert, James W., Petritz, Andreas, Karner-Petritz, Esther, Schider, Gerburg, Stadlober, Barbara, Klauk, Hagen, and Zojer, Karin

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Thin-film transistors (TFTs) represent a wide-spread tool to determine the charge-carrier mobility of materials. Mobilities and further transistor parameters like contact resistances are commonly extracted from the electrical characteristics. However, the trust in such extracted parameters is limited, because their values depend on the extraction technique and on the underlying transistor model. We propose a technique to establish whether a chosen model is adequate to represent the transistor operation. This two-step technique analyzes the electrical measurements of a series of TFTs with different channel lengths. The first step extracts the parameters for each individual transistor by fitting the full output and transfer characteristics to the transistor model. The second step checks whether the channel-length dependence of the extracted parameters is consistent with the model. We demonstrate the merit of the technique for distinct sets of organic TFTs that differ in the semiconductor, the contacts, and the geometry. Independent of the transistor set, our technique consistently reveals that state-of-the-art transistor models fail to reproduce the correct channel-length dependence. Our technique suggests that contemporary transistor models require improvements in terms of charge-carrier-density dependence of the mobility and/or the consideration of uncompensated charges in the transistor channel., Comment: 20 pages, 10 figures

Published
2018

6. Impact of thermal transport parameters on the operating temperature of OLEDs

Author

Krikun, Georgii and Zojer, Karin

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Excess heat in organic light emitting diodes (OLEDs) that is produced during their operation may accelerate their degradation and may cause an inhomogeneous brightness distribution, in particular in large area OLEDs. Assessing the quantitative impact of heat excess is difficult, because all decisive processes related to charge transport and emission via charge recombination are thermally activated. For example, electric currents that are elevated due to larger temperatures cause additional Joule heating and increase, hence, the device temperature even further. Here we establish how parameters responsible for heat transport, i.e., the thermal conductivity of the organic layers and the heat transfer coefficient between the device surface and the environment govern the temperature inside the OLED. We establish, relying on three-dimensional drift-diffusion simulations that self-consistently couple thermally-activated charge transport and heat transport, that the thermal conductivity of organic layers is not a bottleneck for heat transport, because the encountered layer thicknesses in realistic device geometries prevent heat accumulation. The heat transfer to the ambient environment is the key parameter to dissipate excess heat from the device. Intentionally elevated operating temperatures, that may improve the OLEDs electric performance, are not necessarily beneficial, as any increase in operating temperature decreases the device stability. The thermal effects being decisive for the OLED temperature occur in device layers beyond the electrically active region. We propose analytical expressions that relate the temperature in the device for a given point of operation to the heat transfer to the environment and the substrate., Comment: 19 pages, 5 figures

Published
2018
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8. R‐Vine Copulas for Data‐Driven Quantification of Descriptor Relationships in Porous Materials.

Author

Neumann, Matthias, Gräfensteiner, Phillip, Machado Charry, Eduardo, Hirn, Ulrich, Hilger, André, Manke, Ingo, Schennach, Robert, Schmidt, Volker, and Zojer, Karin

Subjects
MULTIVARIATE analysis, POROUS materials, INHOMOGENEOUS materials, MATERIALS analysis, PARAMETRIC modeling
Abstract

Local variations in the 3D microstructure can control the macroscopic behavior of heterogeneous porous materials. For example, the permittivity through porous sheets or membranes is governed by local high‐volume pathways or bottlenecks. Due to local variations, unfeasibly large amounts of microstructure data may be needed to reliably predict such material properties directly from image data. Here it is demonstrated that a vine copula approach provides parametric models for local microstructure descriptors that compactly capture the 3D microstructure including its local variations and efficiently probe it with respect to selected, measurable properties. In contrast to common methods of complexity reduction, the proposed approach creates parametric models for the multivariate probability distribution of high‐dimensional descriptor vectors that inherently contain the complex, nonlinear dependencies between these descriptors. Therein, material properties are offered in physically motivated distributions of microstructure descriptors rather than as normally distributed data. Applied to porous fiber networks (paper) before and after unidirectional compression, it is shown that the copula‐based models reveal material‐characteristic relationships between two or more microstructure descriptors. In this way, the presented modeling approach can provide deeper insight into the microscopic origin of effective macroscopic properties of heterogeneous porous materials. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Advancing Green Hydrogen Purity with Iron-Based Self-Cleaning Oxygen Carriers in Chemical Looping Hydrogen.

Author

Blaschke, Fabio, Prasad, Biswal Prabhu, Charry, Eduardo Machado, Halper, Katharina, Fuchs, Maximilian, Resel, Roland, Zojer, Karin, Lammer, Michael, Hasso, Richard, and Hacker, Viktor

Subjects
GREEN fuels, OXYGEN carriers, HYDROGEN production, CLEAN energy, ZIRCONIUM oxide
Abstract

Green hydrogen is central to the energy transition, but its production often requires expensive materials and poses environmental risks due to the perfluorinated substances used in electrolysis. This study introduces a transformative approach to green hydrogen production via chemical looping, utilizing an iron-based oxygen carrier with yttrium-stabilized zirconium oxide (YSZ). A significant innovation is the replacement of Al2O3 with SiO2 as an inert support pellet, enhancing process efficiency and reducing CO2 contamination by minimizing carbon deposition by up to 700%. The major findings include achieving a remarkable hydrogen purity of 99.994% without the need for additional purification methods. The Fe-YSZ oxygen carrier possesses a significantly higher pore volume of 323 mm³/g and pore surface area of 18.3 m²/g, increasing the pore volume in the iron matrix by up to 50%, further improving efficiency. The catalytic system exhibits a unique self-cleaning effect, substantially reducing CO2 contamination. Fe-YSZ-SiO2 demonstrated CO2 contamination levels below 100 ppm, which is particularly noteworthy. This research advances our understanding of chemical looping mechanisms and offers practical, sustainable solutions for green hydrogen production, highlighting the crucial synergy between support pellets and oxygen carriers. These findings underscore the potential of chemical looping hydrogen (CLH) technology for use in efficient and environmentally friendly hydrogen production, contributing to the transition to cleaner energy sources. [ABSTRACT FROM AUTHOR]

Published
2024
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18. 2D Semiconductors: Interfacial Band Engineering of MoS 2 /Gold Interfaces Using Pyrimidine‐Containing Self‐Assembled Monolayers: Toward Contact‐Resistance‐Free Bottom‐Contacts (Adv. Electron. Mater. 5/2020)

Author

Matković, Aleksandar, primary, Petritz, Andreas, additional, Schider, Gerburg, additional, Krammer, Markus, additional, Kratzer, Markus, additional, Karner‐Petritz, Esther, additional, Fian, Alexander, additional, Gold, Herbert, additional, Gärtner, Michael, additional, Terfort, Andreas, additional, Teichert, Christian, additional, Zojer, Egbert, additional, Zojer, Karin, additional, and Stadlober, Barbara, additional

Published
2020
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19. Interfacial Band Engineering of MoS2/Gold Interfaces Using Pyrimidine‐Containing Self‐Assembled Monolayers: Toward Contact‐Resistance‐Free Bottom‐Contacts

Author

Matković, Aleksandar, primary, Petritz, Andreas, additional, Schider, Gerburg, additional, Krammer, Markus, additional, Kratzer, Markus, additional, Karner‐Petritz, Esther, additional, Fian, Alexander, additional, Gold, Herbert, additional, Gärtner, Michael, additional, Terfort, Andreas, additional, Teichert, Christian, additional, Zojer, Egbert, additional, Zojer, Karin, additional, and Stadlober, Barbara, additional

Published
2020
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23. Interfacial Band Engineering of MoS2/Gold Interfaces Using Pyrimidine‐Containing Self‐Assembled Monolayers: Toward Contact‐Resistance‐Free Bottom‐Contacts.

Author

Matković, Aleksandar, Petritz, Andreas, Schider, Gerburg, Krammer, Markus, Kratzer, Markus, Karner‐Petritz, Esther, Fian, Alexander, Gold, Herbert, Gärtner, Michael, Terfort, Andreas, Teichert, Christian, Zojer, Egbert, Zojer, Karin, and Stadlober, Barbara

Subjects
KELVIN probe force microscopy, OHMIC contacts, MONOMOLECULAR films, GOLD electrodes, SEMICONDUCTOR devices, ELECTRON work function
Abstract

Bottom‐contact architectures with common electrode materials such as gold are crucial for the integration of 2D semiconductors into existing device concepts. The high contact resistance to gold—especially for bottom contacts—is, however, a general problem in 2D semiconductor thin‐film transistors. Pyrimidine‐containing self‐assembled monolayers on gold electrodes are investigated for tuning the electrode work functions in order to minimize that contact resistance. Their frequently ignored asymmetric and bias‐dependent nature is recorded by Kelvin probe force microscopy through a direct mapping of the potential drop across the channel during device operation. A reduction of the contact resistances exceeding two orders of magnitude is achieved via a suitable self‐assembled monolayer, which vastly improves the overall device performance. [ABSTRACT FROM AUTHOR]

Published
2020
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25. Embedded Dipole Self‐Assembled Monolayers for Contact Resistance Tuning in p‐Type and n‐Type Organic Thin Film Transistors and Flexible Electronic Circuits

Author

Petritz, Andreas, primary, Krammer, Markus, additional, Sauter, Eric, additional, Gärtner, Michael, additional, Nascimbeni, Giulia, additional, Schrode, Benedikt, additional, Fian, Alexander, additional, Gold, Herbert, additional, Cojocaru, Andreea, additional, Karner‐Petritz, Esther, additional, Resel, Roland, additional, Terfort, Andreas, additional, Zojer, Egbert, additional, Zharnikov, Michael, additional, Zojer, Karin, additional, and Stadlober, Barbara, additional

Published
2018
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30. Role of the Charge-Transfer State in Reduced Langevin Recombination in Organic Solar Cells:A Theoretical Study

Author

Liu, Yiming, Zojer, Karin, Lassen, Benny, Kjelstrup-Hansen, Jakob, Rubahn, Horst-Guenter, and Madsen, Morten

Abstract

Reduced Langevin recombination has been observed in organic solar cells (OSCs) for many years, but its origin is still unclear. A recent work by Burke et al. (Adv. Energy Mater. 2015, 5, 1500123-1) was inspired by this reduced Langevin recombination, and they proposed an equilibrium model of charge-transfer (CT) states that correlates the open-circuit voltage of OSCs with experimentally available device parameters. In this work, we extend Burke et al.'s CT model further and for the first time directly correlate the reduced Langevin recombination with the energetic and dynamic behavior of the CT state. Recombination through CT states leads in a straightforward manner to a decrease in the Langevin reduction factor with increasing temperature, without explicit consideration of the temperature dependence of the mobility. To verify the correlation between the CT states and reduced Langevin recombination, we incorporated this CT model and the reduced Langevin model into drift-diffusion simulations of a bilayer OSC. The simulations not only successfully reproduced realistic current-voltage (J-V) characteristics of the bilayer OSC, but also demonstrate that the two models consistently lead to same value of the apparent Langevin reduction factor.

Published
2015

33. Influence of morphology and polymer:nanoparticle ratio on device performance of hybrid solar cells—an approach in experiment and simulation

Author

Arar, Mario, primary, Gruber, Manfred, additional, Edler, Michael, additional, Haas, Wernfried, additional, Hofer, Ferdinand, additional, Bansal, Neha, additional, Reynolds, Luke X, additional, Haque, Saif A, additional, Zojer, Karin, additional, Trimmel, Gregor, additional, and Rath, Thomas, additional

Published
2013
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35. Mechanism of surface proton transfer doping in pentacene based organic thin‐film transistors

Author

Ausserlechner, Simon J., primary, Gruber, Manfred, additional, Hetzel, Reinhold, additional, Flesch, Heinz‐Georg, additional, Ladinig, Lukas, additional, Hauser, Lucas, additional, Haase, Anja, additional, Buchner, Michael, additional, Resel, Roland, additional, Schürrer, Ferdinand, additional, Stadlober, Barbara, additional, Trimmel, Gregor, additional, Zojer, Karin, additional, and Zojer, Egbert, additional

Published
2011
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