All posts by Matthias Liero

WIAS at FVCA9

Uncategorized, ,

The Weierstrass Institute is represented with five contributions at this year’s conference “Finite Volumes for Complex Applications IX“ taking place virtually from the 15th until the 19th of June, 2020. From the conference home page:

“The goal of the symposium is to bring together mathematicians, physicists, and engineers interested in physically motivated discretizations and their application. Contributions to the further advancement of the theoretical understanding of suitable finite volume, finite element, discontinuous Galerkin and other discretization schemes, and the exploration of new application fields for them including software related improvements are also welcome. “

WIAS contributions:

  • Non-isothermal Scharfetter-Gummel scheme for electro-thermal transport simulation in degenerate semiconductors (Markus Kantner and Thomas Koprucki)
  • Challenges in drift-diffusion semiconductor simulations
    (Patricio Farrell and Dirk Peschka)
  • Unipolar Drift-Diffusion Simulation of S-shaped Current-Voltage Relations for Organic Semiconductor Devices (Duy-Hai Doan, Jürgen Fuhrmann, Annegret Glitzky, Matthias Liero, and Grigor Nika)
  • Well-balanced discretisation for the compressible Stokes problem by gradient-robustness (Alexander Link and Christian Merdon)
  • On the significance of pressure-robustness for the space discretization of incompressible high Reynolds number flows (Christian Merdon and Alexander Linke)

Moreover, the FVCA9 book has just been published and can be found here .

AMaSiS 2020 workshop postponed to 2021

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Due to the current situation, the international workshop AMaSiS 2020, 5-9 October 2020 at WIAS Berlin, is called off. However, it is planned to run  AMaSiS – “Applied Mathematics and Simulation for semiconductor heterostructures and electrochemical Systems” – next year, presumably early in September 2021. Any contribution to the workshop in 2021 is greatly appreciated! 

The organizers:

Jürgen Fuhrmann (WIAS Berlin)
Annegret Glitzky (WIAS Berlin)
Ansgar Jüngel (TU Wien)
Hans-Christoph Kaiser (WIAS Berlin)
Markus Kantner (WIAS Berlin)
Manuel Landstorfer (WIAS Berlin)
Oliver Marquardt (WIAS Berlin)

Email: amasis2020@wias-berlin.de

S-shaped IV-curves in organic semiconductors

Organic electronics, Self-heating
Simulated Joule heat density [W/cm^3] in an organic thin-film transistor

Simulated current–voltage characteristics using the electrothermal drift–diffusion model for different reference mobilities

Organic semiconductors show a complex interplay between charge-carrier and heat flow. In particular, due to Joule self-heating the temperature in an organic device increases, which in turn leads to an increase in conductivity due to temperature activated hopping transport. A positive feedback loop arises. In recent publications by our colleagues from the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), S-shaped current-voltage characteristics of organic devices have been observed in experiments. In previous work, we have modeled this interplay via a coarse thermistor model for the net current and heat flow (see here).

In order to give a more detailed description of the processes, we extended our drift-diffusion simulation tool ddfermi to take self-heating and the positive feedback in the mobility laws, that are usually used for organic materials, into account. The details can be found in a recently published paper with out partners from the IAPP and the company m4sim GmbH in the Journal of Computational Electronics.

In the paper, an electrothermal drift–diffusion model for organic semiconductor devices with Gauss–Fermi statistics and positive temperature feedback for the charge carrier mobilities is introduced. We apply temperature-dependent Ohmic contact boundary conditions for the electrostatic potential and discretize the system by a finite volume based generalized Scharfetter–Gummel scheme. Using path-following techniques, we demonstrate that the model exhibits S-shaped current–voltage curves with regions of negative differential resistance.

Drift–diffusion simulation of S-shaped current–voltage relations for organic semiconductor devices
Duy Hai Doan, Axel Fischer, Jürgen Fuhrmann, Annegret Glitzky & Matthias Liero
Journal of Computational Electronics (2020)
https://doi.org/10.1007/s10825-020-01505-6

Open Access funding provided by Projekt DEAL. The work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy—The Berlin Mathematics Research Center MATH+ (EXC-2046/1, Project ID: 390685689) in transition project SE18, Project AA2-1 and AA2-6 and the DFG Project EFOD (Grant No. RE 3198/6-1).

Hot OLEDs can “switch back”

Organic electronics, ,
OLED
Luminance in a large-area OLED. Due to the interplay of current flow and self-heating, regions with negative differential resistance and “switched back” behavior are forming in the OLED (luminance decreases despite increasing supplied currents).

Due to their fascinating properties, organic light-emitting diodes (OLEDs) are increasingly used in devices such as smartphone displays or television screens. Large-area OLEDs are also becoming increasingly interesting for new lighting concepts. For the design of such components, the non-linear effect of the self-heating of the materials as well as a resulting switch-back effect must be considered appropriately. Researchers from the TU Dresden and the Weierstrass Institute recently published a paper on Experimental proof of Joule heating-induced switched-back regions in OLEDs in the renowned scientific journal nature research – Light: Science & Applications (2-year impact factor: 14.000, 5-year impact factor: 15.132).

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – The Berlin Mathematics Research Center MATH+ (EXC-2046/1, project ID: 390685689).

www.mathplus.de

http://www.wias-berlin.de/projects/mathplus-AA2-1/