New “spintronic” OLEDs join next-generation display technology mix
We’ve seen a number of next-generation display technologies emerge in recent years, such as Sony’s “Crystal LED,” Uni-Pixel’s time-multiplexed optical shutter (TMOS) technology, and quantum dot LED (QLED) display technology from LG and QD Vision, and now there’s another one to add to the mix. While displays based on the new “spintronic” OLED technology invented by physicists at the University of Utah are still some years off, the researchers say they should be brighter, cheaper and more environmentally friendly than the LEDs found in the current crop of TVs, computer displays, traffic lights and other electronic devices.
The new technology, developed by Z. Valy Vardeny, University of Utah distinguished professor of physics and Tho D. Nguyen, a research assistant professor of physics, is based on a new kind of LED (Light Emitting Diode) known as a spin-polarized organic LED or spin OLED. Like normal OLEDs, the new spin OLED uses an organic semiconductor to generate light. But instead of simply being an electronic device that stores information based on the electrical charges of electrons, the organic semiconductor is a “spintronic” device that stores information using the “spins” of electrons.
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The invention of the spin OLED was made possible by a device, previously reported by Vardeny and colleagues in the journal Nature in 2004, known as an “organic spin valve.” Spin valves are electrical switches that transmit information using the angular momentum – or spin – of an electron, which can be in one of two directions, up or down, which can correlate to the zeroes and ones of binary code. This device is comprised of three layers, with an organic semiconducting layer sandwiched between two metal electrodes that are ferromagnets.
While the original spin valve device could only regulate electrical flow, the researchers believed it could be modified to also emit light, turning the organic spin valve into a spin OLED. To accomplish this, the researchers first used deuterium instead of normal hydrogen in the organic layer of the spin valve. The organic polymer used in the prototype spin OLED device is a polymer known as deuterated-DOO-PPV, which emits orange light.
Secondly, they used an extremely thin layer of lithium fluoride deposited on the cobalt electrode (the other electrode is made of a compound called lanthanum strontium manganese oxide). This layer allows 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, making the spin valve bipolar. Injecting electrons and electron holes at the same time sees the two canceling each other out and energy is released in the form of light.
“When they meet each other, they form ‘excitons,’ and these excitons give you light,” Vardeny says.
While conventional OLEDs require more current to boost their light intensity, the intensity of the new spin OLED can be controlled with a magnetic field. Additionally, while the color of light produced by each OLED is based on the semiconductor used, Vardeny says that a single spin OLED device could potentially produce different colors via changes in a magnetic field.
While the prototype spin OLED created by the University of Utah researchers only produces an orange light, Vardeny expects it will be possible to produce red and blue colors within two years. He also expects to eventually be able to make white spin OLEDs. However, there is another problem that also needs to be overcome. At the moment, the spin OLEDs only operate at temperatures below around minus 28° F (-33° C), so the technology needs to be improved so they can run at room temperature.
Vardeny is the lead author of a study detailing the new spin OLEDs, which appears in the journal Science.
Source: University of Utah