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 Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

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: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Switched-on DNA

20.02.2017 | Materials Sciences

Second cause of hidden hearing loss identified

20.02.2017 | Health and Medicine

Prospect for more effective treatment of nerve pain

20.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>