New review article: In 2015, there still is no universal solution to light outcoupling in OLEDs

In a new review article (Recent advances in light outcoupling from white organic light-emitting diodes) in the Journal of Photonics for Energy, my colleague Malte C. Gather (University of St. Andrews) and I summarize the recent efforts on the development of concepts for light outcoupling in white organic light-emitting diodes (OLEDs). Especially with respect to the complementary inorganic LED technology, it is extremely important to unlock higher external quantum efficiencies in OLEDs to stay competitive. Here, improving the outcoupling efficiency by far offers the largest margin (standard structures are at 20-30% of the internal efficiency maximum). The current status reveals that a universal solution with satisfying enhancement still waits to be found.


White organic light-emitting diodes: Status and perspective – published!

The above mentioned paper has finally shaped to its final form. White organic light-emitting diodes: Status and perspective has been published today in Reviews of Modern Physics (RMP). It contains more than 40 pages of densely packed details on white OLEDs including the main concepts of realizing white emission (from both polymers and/or small molecules), in depth discussions of respective efficiency limits, and promising strategies for enhanced light outcoupling. Here is an editorial summary (source RMP):

The conversion of electricity into a photon flux with color quality resembling natural sunlight is desirable for artificial illumination. The ubiquitous incandescent light bulb, introduced in 1880 by Thomas Edison, satisfies this color quality requirement but suffers from a rather poor energy conversion efficiency of approximately 5%. This review focuses on device strategies to produce efficient organic white light-emitting diodes based on small molecular and polymeric semiconductors, which in the context of next generation lighting have a considerable technological promise.

If you like it, please spread the word. Here is an exciting side note: This paper is published in the same issue of RMP that also contains the great Nobel lectures of Serge Haroche and David J. Wineland, who share the 2012 Nobel Prize for Physics. Another good reason to check out the current issue of RMP.

New review article on white OLEDs for SSL

The lighting sector currently sees a major overhaul, mainly driven by the urge to install and use light sources with highest possible energy efficiency in all sectors of our life (industrial and residential). Solid state lighting is the key technology in this change of generations, where both inorganic and organic light-emitting diodes (OLEDs) aim to reduce our energy use. More importantly, they both offer to maintain or even improve the color quality of artificial light.

The research effort on developing OLEDs for general lighting has been started roughly 20 years ago by Professor Junji Kido (Japan) and since then, the field has seen tremendous progress and also a variety of approaches to realize white light. Tracking, to which extend white OLED research has broadened over the years and where the key technologies are, is a task of its own. Together with my colleagues at the TU Dresden, Germany (group of Prof. Karl Leo), I have been working on a review article focussing on white OLEDs for solid state lighting. It has recently been accepted and will be published in Reviews of Modern Physics later this year. To bridge the gap till final publication, we made it available as a preprint: White organic light-emitting diodes: status and perspective.