13 June 2012—Liquid crystal displays dominate today’s big, bright world of color TVs. They are inefficient, though, and don’t produce the vibrant, richly hued images of organic light-emitting diode (OLED) screens, which are expensive to make in large sizes.
But a handful of start-up companies have been plugging away at another display technology that could enhance LCDs and unseat OLEDs: quantum dots. These light-emitting semiconductor nanocrystals shine pure colors when excited by electric current or light and promise rich, beautiful displays that would be inexpensive and easy to manufacture.
At Display Week, an industry meeting run by the Society for Information Display, quantum-dot developer Nanosys announced that it is working with 3M to commercialize a quantum-dot film that could be integrated into the back of today’s LCD panels. The film could cut the display’s power consumption by half and enable LCDs to generate 50 percent more colors within the range set by the National Television System Committee. Nanosys’s CEO, Jason Hartlove, says that major LCD manufacturers are now testing the film, and a 17-inch notebook incorporating the technology should be on shelves within six months. “We’ve designed this technology to give LCD manufacturers a competitive counterweight to OLEDs,” he says.
New LCD TVs typically have a strip of white LED backlights along the panel’s edge. Light guides spread the illumination evenly across the panel; the light then passes through a series of optical films that colorize, polarize, and diffuse it. The resulting red, green, and blue hues are mixed at different intensities to produce the display’s color gamut. More pure, saturated red, green, and blue yield a wider range, rendering more-lifelike images. But with today’s technology, “the broad-spectrum white has a bunch of pinks, yellows, and oranges,” Hartlove says. “So when you create a red from a color filter, you let in a bunch of different reddish colors.”
The process is also extremely inefficient: More than 90 percent of the light from the white LEDs (which are really blue LEDs coated in yellow phosphor) is wasted as it passes through the optical film stack.
Nanosys’s quantum-dot film effectively acts as the phosphor that converts some of the light from highly efficient blue LEDs to spectrally pure red and green, resulting in a broad color gamut. And it shouldn’t add extra cost. “This technology just drops in and is compatible with existing LCD manufacturing methods,” Hartlove says. “And we only use blue LEDs, which are half the cost of white.”