13th July 2012
A new spintronic OLED that produces an orange color holds promise for brighter, cheaper and more environmentally friendly LEDs than the traditional ones used in television and computer displays, lighting and electronic devices.
Traditional LEDs, introduced in the early 1960s, use conventional semiconductors to generate colored light. Newer OLEDs that contain an organic polymer semiconductor to generate light have become increasingly common in the past decade, particularly for displays in MP3 music players, digital cameras and cellular phones. OLED TVs are expected to hit the market later this year, and OLEDs may soon be used increasingly for 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 the electrons. This was enabled by the team’s previous creation of an organic spin valve, which they modified to emit light as well as to regulate current flow.
Organic spin valves comprise three layers: an organic layer that acts as a semiconductor and is sandwiched between two metal electrodes which are ferromagnets. In the new spin OLED, one of the ferromagnets is composed of cobolt 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 the semiconductor that emits the orange light.
Using deuterium instead of hydrogen made the device more efficient, the physicists said. The team also deposited a thin layer of lithium fluoride on the cobolt electrode which will allow negatively charged electrons to be injected through one side of the spin valve at the same time as 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 will have to be improved so they can run at room temperature. They currently operate at temperatures no warmer than −28 °F, Vardeny said.
The study appeared in today’s issue of Science.