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Organic light‐emitting diodes (OLEDs) have been established as a mature display pixel technology. While introducing the same technology in a large‐area form factor to general lighting and signage applications, some key questions remain unanswered. Under high‐brightness conditions, OLED panels were reported to exhibit nonlinear electrothermal behavior causing lateral brightness inhomogeneities and even regions of switched‐back luminance. Also, the physical understanding of sudden device failure and burn‐ins is still rudimentary. A safe and stable operation of lighting tiles, therefore, requires an in‐depth understanding of these physical phenomena. Here, it is shown that the electrothermal treatment of thin‐film devices allows grasping the underlying physics. Configurations of OLEDs with different lateral dimensions are studied as a role model and it is reported that devices exceeding a certain panel size develop three stable, self heating‐induced operating branches. Switching between them causes the sudden formation of dark spots in devices without any preexisting inhomogeneities. A current‐stabilized operation mode is commonly used in the lighting industry, as it ensures degradation‐induced voltage adjustments. Here, it is demonstrated that a tristable operation always leads to destructive switching, independent of applying constant currents or voltages. With this new understanding of the effects at high operation brightness, it will be possible to adjust driving schemes accordingly, design more resilient system integrations, and develop additional failure mitigation strategies. [ABSTRACT FROM AUTHOR]

We study the convergence of two generalized marker-and-cell covolume schemes for the incompressible Stokes and Navier-Stokes equations introduced by Cavendish, Hall, Nicolaides, and Porsching. The schemes are defined on unstructured triangular Delaunay meshes and exploit the Delaunay-Voronoi duality. The study is motivated by the fact that the related discrete incompressibility condition allows to obtain a discrete maximum principle for the finite volume solution of an advection-diffusion problem coupled to the flow. The convergence theory uses discrete functional analysis and compactness arguments based on recent results for finite volume discretizations for the biharmonic equation. For both schemes, we prove the strong convergence in L2 for the velocities and the discrete rotations of the velocities for the Stokes and the Navier-Stokes problem. Further, for one of the schemes, we also prove the strong convergence of the pressure in L2. These predictions are confirmed by numerical examples presented in the article. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 1397-1424, 2014 [ABSTRACT FROM AUTHOR]

Abstract: We consider a p(x)‐Laplace thermistor model for electrothermal effects in organic semiconductor devices and propose a hybrid finite‐volume/finite‐element scheme which is combined with path‐following methods to find a numerical solution. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]