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Researchers at MIT have created a “quantum-dot” organic light-emitting device (QD-OLED) that may one day replace LCDs as the flat-panel display of choice for consumer electronics.
The QD-OLED device combines organic materials and high-performing inorganic nanocrystals to create a hybrid optoelectronic structure, the so-called quantum dot. Also called artificial atoms, quantum dots are nanometer scale “boxes” that selectively hold or release electrons. Unlike traditional LCDs, which must be lit from behind, quantum dots generate their own light. Depending on their size, the dots can be “tuned” to emit any colour in the visible spectrum. In addition, the colours of light they produce are much more “saturated” than that from other sources. The QD-OLED contains only a single layer of quantum dots sandwiched between two organic thin films, where previous QD-OLEDs used 10 to 20 layers. The researchers have demonstrated organized assemblies over 1 cm2 in size and the same principle could be used to make bigger components. The MIT team’s method of combining organic and inorganic materials may pave the way for new technologies and enhance understanding of the physics of the materials.
In addition to being used for very thin, bright flat-panel displays, the QD-OLEDs may also be used in a variety of other applications, including scientific wavelength calibration, robotic vision and miniaturisation. The QD-OLEDs created in the MIT study have a 2500 percent improvement in luminescent power efficiency over previous QD-OLEDs. “One of the goals is to demonstrate a display that’s stable, simple to produce, flat, high-resolution and uses minimal power,” explains Vladimir Bulovic, QD-OLED co-developer and assistant professor of electrical engineering and computer science at MIT. The researchers go on to note that in time, the devices may be made even more efficient and achieve even higher colour saturation.
When using nanotechnology, manufacturers are faced with fabricating large-scale components out of building blocks invisible to the naked eye. Creating hybrid optoelectronic devices depends on the precise positioning of these functionally distinct materials. This was one of the major hurdles facing the project according to Moungi Bawendi, QD-OLED co-developer and professor of chemistry at MIT. “The challenge is how to efficiently transport electrical charges to an active area of a hybrid device that’s only a single layer of quantum dots,” says Bawendi.
The solution comes from recent advances in traditional organic-LED (OLED) technology, used to create TVs or computer screens only a fraction of an inch thick with the same brightness as LCDs. Bulovic and Bawendi use organic molecules currently used in OLEDs as an organic semiconductor to deliver an electrical charge to the quantum dots. In two parallel processes, which are already widely applicable in industry, separate but layered structures are created out of nanoscale materials.
MIT envisions QD-OLEDs becoming complementary to OLEDs because they can be built with compatible manufacturing methods.