One of the first working full-color quantum-dot displays was shown off at a conference this week by a startup company that is working to commercialize the technology.
Quantum dots are nanoparticles made of inorganic materials that very efficiently emit a specific color of light (depending on the size of the dot) when they’re excited either by a beam of light or by an electrical current. Quantum-dot displays promise low power consumption and rich, beautiful color, much like organic light-emitting diode displays (OLEDs). But QD Vision, the company that demonstrated the prototype display, believes they will also prove less expensive to make than OLEDs at the huge scales favored by display manufacturers.
This week, QD Vision demonstrated a four-inch quantum-dot light-emitting diode (QLED) display at the Society for Information Display’s Display Week conference in Los Angeles. The company’s cofounder and chief technology officer, Seth Coe-Sullivan, cautions that the display is an early prototype, but says it rivals the efficiency and quality of colors in an OLED display. He says there are some engineering hurdles that the company will have to clear before bringing the display to market, which will take three to five years. Reaction to the company’s demonstration was positive but cautious.
The hope is that QLED will provide a sharper, more power-efficient alternative to today’s dominant technology, liquid-crystal displays (LCDs), without being more expensive. The way LCDs work—by filtering light from a backlight to create colored subpixels—entails throwing out some light, thereby dimming the picture and wasting power. OLEDs, which use electrical current to excite materials that emit red, green, and blue light, have rich, bright colors and waste less power. But so far, OLEDs can’t compete on price. This is because the display industry makes LCDs on huge glass panels, sometimes as big as a garage door, and then slices them up into whatever size is needed, for economies of scale. OLEDs can’t be made at this scale—too much material gets wasted, and it’s too expensive.
Companies that make OLED materials and manufacturing equipment, including Dupont and Kateeva, are working on methods for printing these devices at large scales with less waste, but Coe-Sullivan hopes printed QLED displays will leapfrog over OLEDs.
Quantum dots have unique advantages. By changing the size of the quantum dots, it is possible to precisely control the colors these displays produce, and to tailor this to what the human eye can perceive best, to make the displays even more efficient. Other materials don’t offer this kind of flexibility. Quantum dots can also be made into inks that can be printed using relatively inexpensive, less wasteful techniques.
QD Vision is not the first company to demonstrate a display that uses electrically excited quantum dots as the light-emitting element. Researchers at Samsung did that this spring. But QD Vision is the only company that has publicly committed to using quantum dots as the light-emitting element in a commercial display. LG has partnered with QD Vision to help the company develop its QLED displays.
In the meantime, QD Vision and two other companies, Nanosys and Nanoco, have developed quantum-dot products designed to be added to liquid-crystal displays, in varying formats, in order to improve the efficiency of the conventional light-emitting diode backlight. All these systems use quantum dots to convert light from a blue LED backlight, which is more power efficient than a white one, to red and green light, resulting in white light that is then passed through all the usual filters and other layers in the LCD. The size of this market is about $2 billion a year, estimates Nanoco CEO Michael Edelman. So far, Nanoco is concentrating on this and other applications for quantum dots, including lighting.
The OLED business is not quaking in its boots. Janice Mahon, vice president of technology commercialization at OLED-materials company Universal Display Corporation, says that quantum dots still can’t beat the best OLED materials, particularly in terms of lifetime. But she notes that it’s a young technology and the materials will get better, just as OLED materials did.
Jae-Byung Park, principle engineer at Samsung’s LCD R&D Center in Korea, who has been involved with the company’s quantum-dot efforts, sees another key technical hurdle. “The main issue is cadmium,” he says. The most efficient quantum dots incorporate this toxic element, Park says. European safety standards do not permit the long-term use of cadmium, and the Japanese market is particularly averse to the material. Nanoco stopped using cadmium in its materials several years ago. QD Vision is working on cadmium-free materials, as is Nanosys; Nanoco’s materials have been cadmium-free for a few years.
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