Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Breakthrough in OLED Technology

02.03.2015

Scientists break a barrier in the fabrication of ultra-bright OLEDs that may enable electrically-driven organic lasers and thin, flexible, low-power -- even wearable -- display technologies

Organic light emitting diodes (OLEDs), which are made from carbon-containing materials, have the potential to revolutionize future display technologies, making low-power displays so thin they'll wrap or fold around other structures, for instance.

Conventional LCD displays must be backlit by either fluorescent light bulbs or conventional LEDs whereas OLEDs don’t require back lighting. An even greater technological breakthrough will be OLED-based laser diodes, and researchers have long dreamed of building organic lasers, but they have been hindered by the organic materials' tendency to operate inefficiently at the high currents required for lasing.

Now a new study from a team of researchers in California and Japan shows that OLEDs made with finely patterned structures can produce bright, low-power light sources, a key step toward making organic lasers. The results are reported in a paper appearing this week on the cover of the journal Applied Physics Letters, from AIP Publishing.

The key finding, the researchers say, is to confine charge transport and recombination to nanoscale areas, which extends electroluminescent efficiency roll off the current density at which the efficiency of the OLEDs dramatically decreases -- by almost two orders of magnitude. The new device structures do this by suppressing heating and preventing charge recombination.

“An important effect of suppressing roll-off is an increase in the efficiency of devices at high brightness,” said Chihaya Adachi of Kyushu University, who is a co-author of the paper. “This results in lower power to obtain the same brightness.”

“For years scientists working in organic semiconductors have dreamed of making electrically-driven organic lasers,” said Thuc-Quyen Nguyen of the University of California, Santa Barbara, another co-author. “Lasers operate in extreme conditions with electric currents that are significantly higher than those used in common displays and lighting. At these high currents, energy loss processes become stronger and make lasing difficult.

"We see this work, which reduces some loss processes, as one step on the road toward realizing organic lasers,” Nguyen added.

How OLEDs Work

OLEDs operate through the interaction of electrons and holes. “As a simple visualization,” Adachi said, “one can think of an organic semiconductor as a subway train with someone sitting in every seat. The seats represent molecules and the people represent energetic particles, i.e., electrons. When people board the train from one end, they have extra energy and want to go to the relaxed state of sitting. As people board, some of the seated people rise and exit the train at the other end leaving empty seats, or ‘holes,’ for the standing people to fill. When a standing person sits, the person goes to a relaxed state and releases energy. In the case of OLEDs, the person releases the energy as light.”

Production of OLED-based lasers requires current densities of thousands of amperes per square centimeter (kA/cm2), but until now, current densities have been limited by heating. “At high current densities, brightness is limited by annihilation processes,” Adachi said. “Think of large numbers of people on the train colliding into each other and losing energy in ways other than by sitting and releasing light.”

In previous work, Adachi and colleagues showed OLED performance at current densities over 1 kA/cm2 but without the necessary efficiency required for lasers and bright lighting. In their current paper, they show that the efficiency problem can be solved by using electron-beam lithography to produce finely-patterned OLED structures. The small device area supports charge density injection of 2.8 kA/cm2 while maintaining 100 times higher luminescent efficiency than previously observed. “In our device structure, we have effectively confined the entrance and exit to the middle of the train. People diffuse to the two less crowded ends of the train and reduce collisions and annihilation.”

The article, “Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm,” is authored by Kyohei Hayashi, Hajime Nakanotani, Munetomo Inoue, Kou Yoshida, Oleksandr Mikhnenko, Thuc-Quyen Nguyen and Chihaya Adachi. It will be published in then journal Applied Physics Letters on March 2, 2015 (DOI: 10.1063/1.4913461). After that date it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/106/9/10.1063/1.4913461 .

Researchers on this paper are affiliated with University of California, Santa Barbara and Kyushu University.

ABOUT THE JOURNAL

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org

Contact Information
Jason Socrates Bardi, AIP
jbardi@aip.org

240-535-4954

@jasonbardi

Jason Socrates Bardi, AIP | newswise

Further reports about: AIP Applied Applied Physics Applied Physics Letters OLED diodes heating lasers physics

More articles from Physics and Astronomy:

nachricht Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa

nachricht Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>