Subscribe free to our newsletters via your
. 24/7 Space News .

Subscribe free to our newsletters via your

Artificial control of exciplexes opens possibilities for new electronics
by Staff Writers
Fukuoka, Japan (SPX) Mar 08, 2016

This schematic shows the basic structure of an exciplex-based OLED with emission color and efficiency that can be controlled simply by changing the spacer thickness. An exciplex forms when a hole in the highest occupied molecular orbital (HOMO) of a donor molecule is attracted to an electron in the lowest unoccupied molecular orbital (LUMO) of an acceptor molecule. Light is emitted when the electron releases energy as light and transfers across the spacer layer to the donor molecule, thus replacing the missing electron represented by the hole. The thickness of the spacer can be used to modify the attraction between the hole and electron and tune the exciplex energy. Without changing any of the molecules, emission color could be varied from orange to yellowish green and the efficiency enhanced eight fold by increasing the spacer thickness to 5 nm. This device was first reported in the paper titled 'Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers' written by H. Nakanotani at Kyushu University's Center for Organic Photonics and Electronics Research (OPERA) in Fukuoka, Japan, and colleagues and published online Feb. 26, 2016 in the journal Science Advances. Image courtesy Hajime Nakanotani and William John Potscavage Jr. For a larger version of this image please go here.

Demonstrating a strategy that could form the basis for a new class of electronic devices with uniquely tunable properties, researchers at Kyushu University were able to widely vary the emission color and efficiency of organic light-emitting diodes based on exciplexes simply by changing the distance between key molecules in the devices by a few nanometers.

This new way to control electrical properties by slightly changing the device thickness instead of the materials could lead to new kinds of organic electronic devices with switching behavior or light emission that reacts to external factors.

Organic electronic devices such as OLEDs and organic solar cells use thin films of organic molecules for the electrically active materials, making flexible and low-cost devices possible.

A key factor determining the properties of organic devices is the behavior of packets of electrical energy called excitons. An exciton consists of a negative electron attracted to a positive hole, which can be thought of as a missing electron.

In OLEDs, the energy in these excitons is released as light when the electron loses energy and fills the vacancy of the hole. Varying the exciton energy, for example, will change the emission color.

However, excitons are commonly localized on a single organic molecule and tightly bound with binding energies of about 0.5 eV. Thus, entirely new molecules must usually be designed and synthesized to obtain different properties from these Frenkel-type excitons, such as red, green, or blue emission for displays.

Researchers at Kyushu University's Center for Organic Photonics and Electronics Research (OPERA) instead focused on a different type of exciton called an exciplex, which is formed by a hole and electron located on two different molecules instead of the same molecule.

By manipulating the molecular distance between the electron-donating molecule (donor) and the electron-accepting molecule (acceptor) that carry the exciplex's hole and electron, respectively, the researchers could modify the properties of these weakly bound excitons.

"What we did is similar to placing sheets of paper between a magnet and a refrigerator," said Associate Professor Hajime Nakanotani, lead author of the paper reporting these results published online February 26, 2016, in the journal Science Advances.

"By increasing the thickness of an extremely thin layer of organic molecules inserted as a spacer between the donor and acceptor, we could reduce the attraction between the hole and electron in the exciplex and thereby greatly influence the exciplex's energy, lifetime, and emission color and efficiency."

Indeed, the changes can be large: by inserting a spacer layer with a thickness of only 5 nm between a donor layer and an acceptor layer in an OLED, the emission color shifted from orange to yellowish green and the light emission efficiency increased 700%.

For this to work, the organic molecule used for the spacer layer must have an excitation energy higher than those of the donor and acceptor, but such materials are already widely available.

While the molecular distance is currently determined by the thickness of the vacuum-deposited spacer layer, the researchers are now looking into other ways to control the distance.

"This gives us a powerful way to greatly vary device properties without redesigning or changing any of the materials," said Professor Chihaya Adachi, director of OPERA. "In the future, we envision new types of exciton-based devices that respond to external forces like pressure to control the distance and electrical behavior."

In addition, the researchers found that the exciplexes were still formed when the spacer was 10 nm thick, which is long on a molecular scale.

"This is some of the first evidence that electrons and holes could still interact like this across such a long distance," commented Professor Adachi, "so this structure may also be a useful tool for studying and understanding the physics of excitons to design better OLEDs and organic solar cells in the future."

"From both scientific and applications standpoints, we are excited to see where this new path for exciton engineering takes us and hope to establish a new category of exciton-based electronics."


Related Links
Kyushu University, OPERA
Computer Chip Architecture, Technology and Manufacture
Nano Technology News From

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Previous Report
World's first parallel computer based on biomolecular motors
Dresden, Germany (SPX) Mar 03, 2016
A study published this week in Proceedings of the National Academy of Sciences reports a new parallel-computing approach based on a combination of nanotechnology and biology that can solve combinatorial problems. The approach is scalable, error-tolerant, energy-efficient, and can be implemented with existing technologies. The pioneering achievement was developed by researchers from the Tec ... read more

China to use data relay satellite to explore dark side of moon

NASA May Return to Moon, But Only After Cutting Off ISS

Lunar love: When science meets artistry

New Lunar Exhibit Features NASA's Lunar Reconnaissance Orbiter Imagery

Great tilt gave Mars a new face

Space simulation crew hits halfway mark til August re-entry

Proton-M carrier rocket assembled ahead of Mars Mission

Monster volcano gave Mars extreme makeover: study

First tomatoes, peas harvested from mock Martian farm

Sore, but no taller, astronaut Scott Kelly adjusts to Earth

Test Dummies to Help Assess Crew Safety in Orion

Commercial Crew: Building in Safety from the Ground Up in a Unique Way

Aim Higher: China Plans to Send Rover to Mars in 2020

China's lunar probe sets record for longest stay

China's ambition after space station

Sky is the limit for China's national strategy

International Space Station's '1-year crew' returns to Earth

Scott Kelly and Mikhail Kornienko return to Earth after One-Year Mission

Paragon wins NASA ISS water processor development contract

NASA's Science Command Post Supports Scott Kelly's Year In Space

SpaceX launches SES-9 satellite to GEO; but booster landing fails

US Space Company in Talks With India to Launch Satellite

Ariane 5 launch contributes to Ariane 6 development

At last second, SpaceX delays satellite launch again

Evidence found for unstable heavy element at solar system formation

Imaging Technique May Help Discover Earth-Like Planets Around Other Stars

Newly discovered planet in the Hyades cluster could shed light on planetary evolution

Imaging technique may help discover Earth-like planets

Electron-beam imaging can see elements that are 'invisible' to common methods

New radar system set for testing

Scaling up tissue engineering

UMass Amherst team offers new, simpler law of complex wrinkle patterns

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.