Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Novel LEDs pave the way to cheaper displays

08.11.2013
Applications in smart phones or luminescent bathroom tiles conceivable / Collaboration of Bonn University, Regensburg University, the University of Utah and MIT

Researchers from the universities of Bonn and Regensburg have developed a novel type of organic light-emitting diode (OLED). These lights are suitable for the design of particularly energy-efficient cheap displays, which find applications in smart phones, tablet PCs or TVs.


Novel molecules for OLEDs. The synthetic design promotes random changes in orientation of the molecular "compass needle", increasing overall brightness.

John Lupton

Applications in lighting such as in luminescent tiles are also conceivable. The scientists have now reported their findings in the journal “Angewandte Chemie” (DOI: 10.1002/anie.201307601).

OLEDs are already used in the displays of smart phones or digital cameras today. They offer an especially bright image with high contrast, but come with a serious drawback: typically, only one quarter of the electrical energy invested in running the device is actually converted into light. This ratio can be raised by adding traces of noble metals such as platinum or iridium to the active material, but these elements are rare and very expensive. Making high-quality OLEDs is therefore a rather costly business.

This could change in the near future. The scientists from Bonn, Regensburg and the US have demonstrated a novel type of OLED, which shows potential for high conversion efficiencies without having to resort to noble metals. OLED displays could well get quite a bit cheaper soon.

OLEDs aren’t really “organic”

OLEDs are called so because, ideally, they are made up of organic molecules, which consist solely of carbon and hydrogen. The operating principle of an OLED is rather simple: a thin film of the molecules is contacted by electrodes, which are connected to a battery so that an electrical current can flow. This current is made up of positive and negative charges. When the charges meet, they annihilate, destroying each other in a flash of light.

Since positive and negative charges attract each other, generating light from electricity should be a pretty efficient business. The problem lies in the intricate quantum-mechanical nature of charges, which also posses a magnetic moment – scientists call this the “spin”. Charges with like spin repel each other, much as the north poles of two bar magnets do. This repulsion outweighs the attraction between positive and negative charges, so that different charges with like spin cannot generate light. Instead, they convert electrical energy into heat – a rather exotic and not overly useful way of electrical heating.

In conventional OLEDs this loss of energy occurs frequently: three quarters of all charges carry the same spin. Much like the needle of a compass, they point in the same direction but cannot touch each other, effectively lowering the yield of useful light. OLED manufacturers have come up with a clever trick to raise the yield: they twirl the compass needles around with an even stronger magnet, allowing the charges to generate light after all. To do this requires heavy metals such as platinum or iridium, which allow virtually all of the electrical energy to be converted into light. Strictly speaking, conventional materials in OLEDs are not organic compounds at all, but metal-organic substances. This distinction is more than semantic in nature, since noble metals are extremely expensive.

Useful spin flip flops

“We can also raise the efficiency using a different mechanism”, Dr. John Lupton, Professor of Physics at the University of Regensburg, explains. “Charges can flip the orientation of their spins spontaneously – you just have to wait for long enough for this to occur.” In conventional OLEDs, however, there is not enough time to do this since the electrical energy is not stored for long enough in the molecular architecture. Instead, the molecules give up and simply convert the energy to heat.

“It appears that, in our OLEDs, the molecules can store electrical energy for significantly longer than is conventionally assumed”, notes chemists Professor Sigurd Höger of the University of Bonn. “Our molecules can therefore exploit the spontaneous jumps in spin orientation in order to generate light.” The new compounds therefore hold potential to minimize electrical generation of heat in OLEDs without having to resort to any “metal-organic tricks”, thereby converting the electrical energy very effectively into light.

The study was supported by the Volkswagen Foundation and the German Science Foundation (DFG), with collaborators based at the University of Utah and the Massachusetts Institute of Technology (M.I.T.).

Publication: Metal-free OLED triplet emitters by side-stepping Kasha’s rule; D. Chaudhuri, E. Sigmund, A. Meyer, L. Röck, P. Klemm, S. Lautenschlager, A. Schmid, S. R. Yost, T. Van Voorhis, S. Bange, S. Höger und J. M. Lupton; Angewandte Chemie (DOI: 10.1002/anie.201307601)

Contact:

Prof. Dr. Sigurd Höger
Universität Bonn
Kekulé-Institut für Organische Chemie und Biochemie
Tel.: 0228 73-6127
E-mail: hoeger@uni-bonn.de
Prof. Dr. John Lupton
Universität Regensburg
Institut für Experimentelle und Angewandte Physik
Tel.: 0941 943-2081
E-mail: John.Lupton@ur.de

Alexander Schlaak | idw
Further information:
http://www.ur.de

More articles from Power and Electrical Engineering:

nachricht Waste from paper and pulp industry supplies raw material for development of new redox flow batteries
12.10.2017 | Johannes Gutenberg-Universität Mainz

nachricht Low-cost battery from waste graphite
11.10.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>