Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Optoelectronic materials: Optimum solution

09.08.2011
Highly efficient organic light-emitting diodes are created by optimizing the molecular structure and device configuration

Organic light-emitting diodes (OLEDs) are seen as a promising replacement for the liquid-crystal displays (LCDs) used in many flat-screen televisions because they are cheaper to mass-produce. Zhikuan Chen at the A*STAR Institute of Materials Research and Engineering and co-workers have now shown how meticulous engineering of fluorescent molecules can dramatically increase OLED efficiency.

Conventional light-emitting diodes are made of inorganic crystals such as gallium arsenide. OLEDS, on the other hand, utilize carbon-based materials that can be made flexible. Today, OLED technology is commonly used to make large-area outdoor displays and wearable displays. However, further improvements in operation efficiency are required if OLEDs are to become truly competitive against the alternative options.

Chen and his co-workers have now reported blue light-emitting devices that reach an external quantum efficiency (EQE) of as high as 9.4%—almost double the classical upper limit of 5% for fluorescence-based OLEDs. “This improvement is important because higher efficiency means a lower driving voltage and thus lower power consumption and increased device lifetime,” explains Chen.

EQE is an important measure of LED operation as it determines what fraction of the charge carriers injected into the device are converted into photons that can be emitted. EQE takes into account the chance that the two types of charge carriers—negatively charged electrons and positively charged holes—recombine with each other, as well as the intrinsic probability that this results in the creation of a photon and the chance that this photon will escape from the device. Chen and his team have now used computer models to optimize these various processes.

Simulations enabled the researchers to find a structure for their active molecule—an oligofluorene—that best balanced charge carrier injection into the material and charge transport through it to enhance device emission efficiency. Further improvements were made by selecting the best emitting-layer thickness and by doping the emitter in an appropriate organic host material to minimize efficiency loss.

The OLEDs emitted blue light centered at a wavelength of 450 nanometers. Chen and his co-workers found that the high EQE was possible because the fraction of charge carriers that recombine without emitting light was negligible. Importantly, the light output was stable during operation, making it more amenable to use in practical situations. “Soon we hope to develop these materials further for lighting and displays applications,” says Chen.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering

References
Zhen, C. G. et al. Achieving highly efficient fluorescent blue organic light-emitting diodes through optimizing molecular structures and device configuration. Advanced Functional Materials 21, 699–707 (2011).

Lee Swee Heng | Research asia research news
Further information:
http://www.imre.a-star.edu.sg/
http://www.researchsea.com

More articles from Materials Sciences:

nachricht The stacked colour sensor
16.11.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

nachricht Counterfeits and product piracy can be prevented by security features, such as printed 3-D microstructures
16.11.2017 | Karlsruher Institut für Technologie (KIT)

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>