• HOME
  • NEWS
  • EXPLORE
    • CAREER
      • Companies
      • Jobs
    • EVENTS
    • iGEM
      • News
      • Team
    • PHOTOS
    • VIDEO
    • WIKI
  • BLOG
  • COMMUNITY
    • FACEBOOK
    • INSTAGRAM
    • TWITTER
Saturday, August 30, 2025
BIOENGINEER.ORG
No Result
View All Result
  • Login
  • HOME
  • NEWS
  • EXPLORE
    • CAREER
      • Companies
      • Jobs
        • Lecturer
        • PhD Studentship
        • Postdoc
        • Research Assistant
    • EVENTS
    • iGEM
      • News
      • Team
    • PHOTOS
    • VIDEO
    • WIKI
  • BLOG
  • COMMUNITY
    • FACEBOOK
    • INSTAGRAM
    • TWITTER
  • HOME
  • NEWS
  • EXPLORE
    • CAREER
      • Companies
      • Jobs
        • Lecturer
        • PhD Studentship
        • Postdoc
        • Research Assistant
    • EVENTS
    • iGEM
      • News
      • Team
    • PHOTOS
    • VIDEO
    • WIKI
  • BLOG
  • COMMUNITY
    • FACEBOOK
    • INSTAGRAM
    • TWITTER
No Result
View All Result
Bioengineer.org
No Result
View All Result
Home NEWS Science News Chemistry

Hot OLEDs can ‘switch back’

Bioengineer by Bioengineer
January 15, 2020
in Chemistry
Reading Time: 4 mins read
0
Share on FacebookShare on TwitterShare on LinkedinShare on RedditShare on Telegram

IMAGE

Credit: Anton Kirch, Axel Fischer, Matthias Liero, Jurgen Fuhrmann, Annegret Glitzky, Sebastian Reineke


It is well-known that LEDs and transistors should not be connected in parallel as slight differences in resistance can lead to imbalanced current flow. This effect gets even stronger if the devices heat up as their resistance changes with temperature. For organic LEDs (OLEDs), this is a big issue: Every large-area OLED lighting panel can be understood as a parallel connection of numerous individual tiny OLEDs. As a consequence, these devices show inhomogeneous light emission if they heat up. A phenomenon that has been observed by researchers as well as industrial companies in the last couple of years, is a saturation of brightness that occurs even though the total applied current is continuously increased. Now a team of researchers from TU Dresden (Chair of organic semiconductors at IAPP/cfaed, Prof. Sebastian Reineke) and the Weierstrass Institute Berlin (WIAS, deputy head of research group Partial Differential Equations, Dr. Annegret Glitzky) experimentally prove that OLEDs do not only saturate, they even show regions that are switched-back in brightness: Suddenly the OLED gets darker in a certain area although the total applied current is increased – clearly a counter-intuitive result. This so-called “switched-back” effect is directly related to the presence of a strong nonlinear electrothermal feedback in OLEDs that takes place upon heating up and which in turn induces negative differential resistance that makes the device prone to unstable operation.

The results have a strong impact on understanding long-term stability in applications with high brightness e.g. as they are found in the automotive sector. Here, OLEDs are now considered to replace LED technology for tail lights, signal lights, or brake lights due to their new design possibilities. One problem OLEDs are still facing are sudden-death phenomena. They are rarely described in literature due to their unpredictable and seemingly random occurrence. However, it is likely that the now proven switched-back regions are strongly related to such sudden-death phenomena. A better understanding of the OLED as a complex electrothermal system will, therefore, be essential to forecast device breakdown and to develop new strategies for better brightness uniformity and device stability. In the future, novel applications with ultra-high light intensity such as organic lasers will also benefit from exact knowledge about self-heating effects.

The cooperation between the two groups at IAPP and WIAS dates back to 2011. Since then, several joint publications about electrothermal feedback in organic semiconductor devices have been published. “The prediction of the switched-back regions actually goes back to 2014 when we got some first hints by a rather rudimentary simulation,” said Dr. Axel Fischer who is the corresponding author of this work and continues with “We then focused on creating an improved setup that would allow us to measure the effect for our lab-scale samples.”. The term “switched-back” is actually related to the current density that locally decreases in the OLED in contrast to the total current that still increases. As it is difficult to measure the local current density, a camera was used to detect the emission that corresponds to the local current flow. If there would be a decreasing brightness before the OLED degrades, it would be the proof of switched-back regions. Indeed, the experimentalists suddenly observed a decreasing luminance in the expected region of the active area just after the first negative differential resistance occurred. These experiments have been carried out and evaluated by Anton Kirch, who is currently a Ph.D. student at IAPP: “First, a region of negative differential resistance occurs and propagates through the device for increasing the supply current. At a certain point, they switch back regions that are distant to the electrodes and which do not have a sufficiently high power dissipation. One can imagine that these switched-back regions only ‘see’ the decreasing voltage of the OLED parts operating in the regime of negative differential resistance and do not know that the externally applied voltage still increases.”

To confirm the experimental results, the complex interplay between current and heat flow was studied numerically in a highly nonlinear system, taking the different layers of the OLED into account. Therefore, the mathematicians from the Weierstrass Institute Berlin created a simulation tool for solving the derived system of partial differential equations. “We had to introduce an advanced path following algorithm”, explains Dr. Matthias Liero, “to capture the behavior of the device within the bistable regime, i.e. when parts of the OLED operate in the regime of negative differential resistance”. After this was implemented, the numerical simulation was able to reproduce the experimental finding based on reasonable assumptions and parameters. Liero further outlines: “Frankly, we have been astonished about the qualitative and the quantitative agreement between simulation and experiment. The shape and occurrence of the switched-back region were calculated as found in the experiment.”. The group is now looking for further partners from science as well as from industry to transfer the results from lab-scale OLEDs to larger thin-film lighting panels and more complicated geometries.

Both groups want to continue their joint work on electrothermal feedback. The next challenges are to create new strategies to prevent switched-back regions in order to homogenize the luminance even upon self-heating. It will be the aim to create non-trivial solutions that explicitly take the non-linear nature of the problem into account. Furthermore, in-depth studies exploring the interdependency between the appearance of switched-back regions and sudden-death scenarios have been started.

###

Media Contact
Axel Fischer
[email protected]

Related Journal Article

http://dx.doi.org/10.1038/s41377-019-0236-9

Tags: Chemistry/Physics/Materials SciencesOptics
Share12Tweet8Share2ShareShareShare2

Related Posts

blank

Innovative Pimple Patches Offer Effective Solution for Stubborn Acne

August 29, 2025

Revealing the Unseen: A Breakthrough Method to Enhance Nanoscale Light Emission

August 29, 2025

Fluorescent Smart Eye Patch Revolutionizes Monitoring of Eye Health

August 29, 2025

Protective Dual Shell Extends Lifespan of Lithium-Rich Batteries

August 29, 2025
Please login to join discussion

POPULAR NEWS

  • blank

    Breakthrough in Computer Hardware Advances Solves Complex Optimization Challenges

    151 shares
    Share 60 Tweet 38
  • Molecules in Focus: Capturing the Timeless Dance of Particles

    142 shares
    Share 57 Tweet 36
  • New Drug Formulation Transforms Intravenous Treatments into Rapid Injections

    116 shares
    Share 46 Tweet 29
  • Neuropsychiatric Risks Linked to COVID-19 Revealed

    82 shares
    Share 33 Tweet 21

About

We bring you the latest biotechnology news from best research centers and universities around the world. Check our website.

Follow us

Recent News

Metabolomic Changes in Children Post-VSD Repair Revealed

AI Insights Transform Kidney Transplantation Research Landscape

Gene Variants Linked to Antipsychotic Movement Disorders

  • Contact Us

Bioengineer.org © Copyright 2023 All Rights Reserved.

Welcome Back!

Login to your account below

Forgotten Password?

Retrieve your password

Please enter your username or email address to reset your password.

Log In
No Result
View All Result
  • Homepages
    • Home Page 1
    • Home Page 2
  • News
  • National
  • Business
  • Health
  • Lifestyle
  • Science

Bioengineer.org © Copyright 2023 All Rights Reserved.