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“Spintronic” OLED promises brighter displays

Photonics Spectra
Sep 2012
SALT LAKE CITY – A new “spintronic” OLED that produces an orange color holds promise for brighter, cheaper and more environmentally friendly LEDs than the ones typically used in television and computer displays, lighting and electronic devices.

Traditional LEDs, introduced in the early 1960s, use conventional semiconductors to generate colored light. OLEDs with an organic polymer semiconductor that generates light have become increasingly common in the past decade, particularly for displays in consumer electronics such as MP3 players, digital cameras and cell phones. OLED TVs are expected to hit the market later this year, and OLEDs soon may become more common in room lighting.

Physicists at the University of Utah have developed a prototype of the new spin-polarized OLED, or spin OLED.

“It’s a completely different technology,” said Z. Valy Vardeny, distinguished professor of physics and senior author of the study. “These new organic LEDs can be brighter than regular organic LEDs.”

Vardeny expects that it will be possible within two years to use the new OLED to produce red and blue, and eventually white as well.

The spintronic device uses an organic semiconductor and stores information using the spins of electrons. This was enabled by the researchers’ previous creation of an organic spin valve, which they modified to emit light and to regulate current flow.


A new “spintronic” organic LED glows orangish (center) when the device, chilled well below freezing, is exposed to a magnetic field from the two poles of an electromagnet on either side of it. University of Utah physicists have reported a prototype of this new kind of LED.


Organic spin valves comprise three layers: An organic layer, sandwiched between two metal electrode ferromagnets, acts as a semiconductor. In the new spin OLED, one ferromagnet is composed of cobalt, and the other is made of a lanthanum strontium manganese oxide compound. The organic layer is a polymer known as deuterated-DOO-PPV, which is a semiconductor that emits orange light.

Using deuterium instead of hydrogen made the device more efficient, the physicists said.

They also deposited a thin layer of lithium fluoride on the cobalt electrode, which allows negatively charged electrons to be injected through one side of the spin valve while at the same time positively charged electron holes are injected through the opposite side.

“When they meet each other, they form excitons, and these give you light,” Vardeny said.

This also means that the spintronic OLEDs can be controlled with a magnetic field rather than requiring more electrical current to boost intensity.

Current OLEDs produce a particular color of light – such as red, green or blue – based on the semiconductor used. The new spin OLEDs could be a step toward creating a single device that can produce different colors when controlled by changes in magnetic field.

Before the devices hit the market, they must be able to run at room temperature. They currently operate at temperatures no warmer than 228 °F, Vardeny said.

The study appeared in Science (doi: 10.1126/science.1223444).


GLOSSARY
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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