Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Toward a truly white organic LED

13.09.2013
Utah physicists develop polymer with tunable colors

By inserting platinum atoms into an organic semiconductor, University of Utah physicists were able to "tune" the plastic-like polymer to emit light of different colors – a step toward more efficient, less expensive and truly white organic LEDs for light bulbs of the future.


A sample of the yellowish-colored, platinum-rich polymer known as Pt-1, emits light as a laser beam hits it at a University of Utah physics laboratory. The light appears white because the polymer emits a combination of broad-spectrum violet and yellow, which combine to appear white. The polymer and its relatives hold promise for use in a new generation of organic light-emitting diodes, or OLEDs, which could produce white light for more efficient LED light bulbs of the future.

Credit: Tek Basel, University of Utah.

"These new, platinum-rich polymers hold promise for white organic light-emitting diodes and new kinds of more efficient solar cells," says University of Utah physicist Z. Valy Vardeny, who led a study of the polymers published online Friday, Sept. 13 in the journal Scientific Reports.

Certain existing white light bulbs use LEDs, or light-emitting diodes, and some phone displays use organic LEDs, or OLEDs. Neither are truly white LEDs, but instead use LEDs made of different materials that each emit a different color, then combine or convert those colors to create white light, Vardeny says.

In the new study, Vardeny and colleagues report how they inserted platinum metal atoms at different intervals along a chain-like organic polymer, and thus were able to adjust or tune the colors emitted. That is a step toward a truly white OLED generated by multiple colors from a single polymer.

Existing white OLED displays – like those in recent cell phones – use different organic polymers that emit different colors, which are arranged in pixels of red, green and blue and then combined to make white light, says Vardeny, a distinguished professor of physics. "This new polymer has all those colors simultaneously, so no need for small pixels and complicated engineering to create them."

"This polymer emits light in the blue and red spectral range, and can be tuned to cover the whole visible spectrum," he adds. "As such, it can serve as the active [or working] layer in white OLEDs that are predicted to replace regular light bulbs."

Vardeny says the new polymer also could be used in a new type of solar power cell in which the platinum would help the polymer convert sunlight to electricity more efficiently. And because the platinum-rich polymer would allow physicists to "read" the information stored in electrons' "spins" or intrinsic angular momentum, the new polymers also have potential uses for computer memory.

Not Quite Yet an OLED

In the new study, the researchers made the new platinum-rich polymers and then used various optical methods to characterize their properties and show how they light up when stimulated by light.

The polymers in the new study aren't quite OLEDs because they emit light when stimulated by other light. An OLED is a polymer that emits light when stimulated by electrical current.

"We haven't yet fabricated an OLED with it," Vardeny says. "The paper shows we get multiple colors simultaneously from one polymer," making it possible to develop an OLED in which single pixels emit white light.

Vardeny predicts about one year until design of a "platinum-rich pi-conjugated polymer" that is tuned to emit white light when stimulated by light, and about two years until development of true white organic LEDs.

"The whole project is supported by the U.S. Department of Energy for replacing white light from regular [incandescent] bulbs," he says.

The University of Utah conducted the research with the department's Los Alamos National Laboratory. Additional funding came from the National Science Foundation's Materials Research Science and Engineering Center program at the University of Utah, the National Natural Science Foundation of China, and China's Fundamental Research Funds for the Central Universities.

Using Platinum to Tune Polymer Color Emissions

Inorganic semiconductors were used to generate colors in the original LEDs, introduced in the 1960s. Organic LEDs, or OLEDs, generate light with organic polymers which are "plastic" semiconductors and are used in many of the latest cell phones, digital camera displays and big-screen televisions.

Existing white LEDs are not truly white. White results from combining colors of the entire spectrum, but light from blue, green and red LEDs can be combined to create white light, as is the case with many cell phone displays. Other "white" LEDs use blue LEDs, "down-convert" some of the blue to yellow, and then mix the blue and yellow to produce light that appears white.

The new platinum-doped polymers hold promise for making white OLEDs, but can convert more energy to light than other OLEDs now under development, Vardeny says. That is because the addition of platinum to the polymer makes accessible more energy stored within the polymer molecules.

Polymers have two kinds of electronic states:

A "singlet" state that can be stimulated by light or electricity to emit higher energy, fluorescent blue light. Until now, OLEDs derived their light only from this state, allowing them to convert only 25 percent of energy into light – better than incandescent bulbs but far from perfect.

A normally inaccessible "triplet" state that theoretically could emit lower energy phosphorescent red light, but normally does not, leaving 75 percent of electrical energy that goes into the polymer inaccessible for conversion to light.

Vardeny says he and his colleagues decided to add platinum atoms to a polymer because it already was known that "if you put a heavy atom in molecules in general, it can make the triplet state more accessible to being stimulated by light and emitting light."

Ideally, a new generation of white OLEDs would not only produce true white light, but also be much more energy efficient because they would use both fluorescence and phosphorescence, he adds.

For the study, the researchers used two versions of the same polymer. One version, Pt-1, had a platinum atom in every unit or link in the chain-like semiconducting polymer. Pt-1 emitted violet and yellow light. The other version, Pt-3, had a platinum atom every third unit, and emitted blue and orange light.

By varying the amount of platinum in the polymer, the physicists could create and adjust emissions of fluorescent and phosphorescent light, and adjust the relative intensity of one color over another.

"What is new here is that we can tune the colors the polymer emits and the relative intensities of those colors by changing the abundance of this heavy atom in the polymer," Vardeny says. "The idea, ultimately, is to mix this polymer with different platinum units so we can cover the whole spectrum easily and produce white light."

Vardeny conducted the new study with former University of Utah postdoctoral researcher Chuanxiang Sheng, now at Nanjing University of Science and Technology in China; Sergei Tretiak of Los Alamos National Laboratory; and with University of Utah graduate students Sanjeev Singh, Alessio Gambetta, Tomer Drori and Minghong Tong. The physicists hired chemist Leonard Wojcik to synthesize the platinum-rich polymers.

University of Utah Communications
75 Fort Douglas Boulevard
Salt Lake City, UT 84113
801-581-6773 fax: 801-585-3350

Lee J. Siegel | EurekAlert!
Further information:
http://www.utah.edu

More articles from Physics and Astronomy:

nachricht Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie

nachricht Seeing the quantum future... literally
16.01.2017 | University of Sydney

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: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>