Analytical estimation of emitter distribution in organic light-emitting diodes (OLEDs) from radiation pattern features

Ariel Epstein

Eleftheriades Group, EM

Abstract:

Organic light-emitting diodes (OLEDs) have been intensively investigated in recent years, holding promise for novel optoelectronic devices such as thin and flexible displays and efficient lighting instruments. Despite rapid technological progress in this area, device performance is still far from optimal, and great scientific efforts are being made to understand the fundamental physical processes determining the electrical and optical properties of the devices, to promote design of efficient OLEDs with wide viewing angles.

It is well recognized by now that the distribution of emitters (excitons) in the active layer, determined by the electrical properties of the device, has a crucial effect on the optical performance. As direct measurement of this distribution is difficult to achieve, numerous research groups have developed numerical techniques to evaluate this emission zone (EZ) profile from optical measurements, by fitting them using a stratified media optical simulation. Although at times producing highly resolved evaluations, these methods often rely on complicated fitting schemes and consume substantial computing power.

In this talk we shall present a different approach to this inverse problem, where we rigorously derive closed-form relations between two main features of measured radiation patterns (interference fringe position and prominence) and the two first moments of the spatial emitter distribution (mean position and width). These relations, based on Bragg's law, facilitate an analytical estimation method which is physically intuitive and computationally efficient. The method is applied successfully to simulated and experimental data, forming a novel set of engineering tools for OLED design and verification. Special emphasis would be given to key aspects of rigorous electromagnetic modeling of spontaneous emission devices such as OLEDs, in which radiation sources are of a statistical nature.

Biography:

Ariel Epstein received the B.A. degree in Computer Science from the Open University of Israel, and the B.A. degree in Physics and the B.Sc. degree in Electrical Engineering from the Technion – Israel Institute of Technology, Haifa, Israel, in 2000 and 2003, respectively. In 2013 he received his Ph.D. from the Technion for his thesis, titled "Rigorous Electromagnetic Analysis of Optical Emission of Organic Light-Emitting Diodes". His paper, "On the Relevance of Two-Dimensional Sources for Modeling Optical Emission from Layered Media" was the recipient of the Young Scientist Best Paper Award of the URSI Commission B International Symposium on Electromagnetic Theory (EMTS2013) held in Hiroshima, Japan, on May 2013. He is currently a Lyon Sachs Postdoctoral Fellow at the University of Toronto in the Electromagnetics group under the supervision of Professor Eleftheriades. His current research interests include utilization of electromagnetic theory, with emphasis on analytical techniques, for novel applications, e.g. electromagnetic metamaterials , nanoelectronic devices, etc.