A new ‘spintronic’ organic light-emitting diode promises to be brighter, lower-cost and more environmentally friendly than those currently used in lighting, television and computer displays and other electronic devices.
“It’s a completely different technology,” says Z. Valy Vardeny of theUniversity of Utah. “These new organic LEDs can be brighter than regular organic LEDs.”
So far, the team’s produced only an orange version of the new LED – known technically as a spin-polarized organic LED or spin OLED. But within two years, they say, they expect to have red and blue versions as well, and eventually white spin OLEDs.
Unnfortunately, though, the LEDs can only operate at temperatures belowminus 28 degrees Fahrenheit, and it could take five years to get them working at room temperature.
OLEDs use an organic polymer or ‘plastic’ semiconductor to generate light, and have become increasingly common in MP3 music players, cellular phones and digital cameras. They’re also expected to be used increasingly for room lighting, and in large-screen TVs.
The Utah OLED also uses an organic semiconductor, but doesn’t just store information based on the electrical charges of electrons. Instead, it’s a spintronic device, storing information using the ‘spins’ of the electrons as well.
It does this thanks to an ‘organic spin valve’, modified to emit light as well as electric current.
Organic spin valves are composed of three layers: an organic layer that acts as a semiconductor, sandwiched between two metal electrodes that are ferromagnets. In the new spin OLED, one of the ferromagnet metal electrodes is made of cobalt and the other one of a compound called lanthanum strontium manganese oxide. The organic layer in the new OLED is a polymer known as deuterated-DOO-PPV, which is a semiconductor that emits orange-colored light.
The whole device is 300 microns wide and long, and just 40 nanometers thick.
One big advance from the Utah team was to use deuterium instead of hydrogen in the organic layer of the spin valve, making the production of light more efficient.
The other was the use of an extremely thin layer of lithium fluoride deposited on the cobalt electrode. This allows negatively charged electrons to be injected through one side of the spin valve while positively charged electron holes are injected through the other. This allows light to be generated, and means more current can be generated.
Existing OLEDs each produce a particular color of light, based on the semiconductor used. Vardeny says the beauty of the new spin OLEDs is that, in the future, a single device could produce different colors when controlled by changes in magnetic field.
