Quantum Dot Displays Start to Shine
Unlike OLEDs, they may soon be practical for larger displays, such as computer screens and televisions.
Few display technologies rival the visual brilliance and energy-saving potential of organic light-emitting diodes (OLEDs). Yet OLED displays are mostly found in smaller applications like mobile phones. The manufacturing technology for OLEDs has struggled to scale up for mass producing computer monitors or televisions.
Now QD Vision, an MIT spinoff, has announced a display technology based on quantum dots that could not only be easier to manufacture than OLEDs, but also be even brighter and more energy-efficient.
Last week, the Massachusetts company announced a partnership with major manufacturer LG Display to develop displays that use quantum-dot light-emitting diodes (QLEDs) as their pixels. In early November, QD Vision also partnered with Solvay, a Belgium-based chemical company, to build a platform for printing QLEDs.
Quantum dots are nanometer-sized semiconducting crystals that can shine a bright, spectrally pure color when exposed to either light (photoluminescence) or electrical current (electroluminescence). QD Vision’s first product, a quantum dot optic that warms the normally harsh glow produced by LED lamps, relies on photoluminescence; the quantum dots emit color when light from the LEDs excites them.
Silicon Valley-based Nanosys, another company working with quantum dots, expects to have its own product available in early 2011. Nanosys adds a strip of quantum dots to a liquid-crystal display’s backlight to improve color quality and energy efficiency. QD Vision is developing a similar product.
To use quantum dots as the main element in a display, the crystals need to be excited by electrons, not photons. “[Electroluminescence of quantum dots is] something we’ve been working on a very long time, and now it’s getting to this point of commercial traction,” says Seth Coe-Sullivan, QD Vision’s chief technology officer.
The target is the OLED market. “Small OLED displays are getting very good market traction,” says Coe-Sullivan, “but there are still some unresolved challenges with OLEDs, and we see QLEDs as a way to solve them.” The main benefit of QLEDs over OLEDs, he says, is in manufacturing. “There’s been lots of proposals for manufacturing OLEDs at a larger scale, but none of them have worked out.”
OLEDs need to be patterned as they are deposited, something that’s traditionally been done with something called a shadow mask. But due to the chemical properties of OLEDs, the shadow mask technique isn’t accurate at larger sizes. QLEDS, in contrast, don’t need a shadow mask. They can be suspended in a liquid solution, which allows them to be deposited using any number of scalable techniques, including ink-jet printing.
The intrinsic physical properties of QLEDs, which can be made of cadmium selenide as well as cadmium-free semiconductors, make them a compelling replacement for OLEDs.
While some OLED displays still require color filters to produce pure colors, QLEDS emit pure, bright color from the start, Coe-Sullivan says. Additionally, QLEDs are fundamentally superior to OLEDs in the way that they convert electrons to photons, which means that a quantum-dot display operates at lower voltages.
“If they can make this electroluminescence technology work, then we think that’s a good thing for the industry,” says Jason Hartlove, president of Nanosys, which is also developing electroluminescent quantum dots. “My personal view, which goes against what some folks in the industry are betting on, is that OLED displays will never really gain full traction,” he says. “Then there will be a new tech that will emerge, and we hope that’ll be emissive quantum dots.”
“QLEDs are still in the early stage,” says Jennifer Colegrove, analyst at DisplaySearch, a market research firm. “I do think it has a very promising future, and I hope we can see a full color demo by next year.”
Coe-Sullivan is hesitant to provide a solid time line for QLED manufacturing. Since QD Vision was founded, the company has made strides, thanks to tweaks in chemistry and engineering, that have improved the length of time that electroluminescent quantum dots can shine. But currently, the best QLEDs have a lifetime of 10,000 hours—not long enough for a large display. Other challenges for display developers, says Coe-Sullivan, include ensuring uniform color performance across the spectrum and making sure the other parts of a display do not require too much power.
“QD Vision has made an awful lot of progress,” Coe-Sullivan says. “We’re just getting to that point where you can see commercialization on the horizon.”
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