To get a jump on our CES coverage, we decided to have a call with Jason Hartlove, CEO of quantum dot supplier, Nanosys, to learn more about their activities, what they will show at CES and their expectations for quantum dot development.
One of the key demos Nanosys will be showcasing in their suite in the Westgate will be a color volume demo. Many are now coming around to the notion that using color volume to describe an HDR display’s color performance as a function of luminance is a much better way that simply showing a two-dimensional CIE color gamut chart. This discussion gets more complicated when considering OLED HDR displays which use a RGBW pixel structure. Using the white subpixel allows the OLED panel to reach higher luminance levels, but it compromises the color performance, effectively shrinking the color volume when the white sub-pixel is used.
Hartlove said that they plan to show a side-by-side demo of an OLED HDR TV with a quantum dot-based LCD HDR TV. Data on the color volume was gathered using a third party expert who followed industry accepted metrology as defined by the International Committee on Display Metrology (ICDM). The demo will feature content driven from an xBox to show a gaming application. I will be most interested to see this demo along with the accompanying color volume data.
We next turned to discussing some of the development projects the company has been working on and their status. For example, last summer, Nanosys showed some advanced air-stable quantum dot materials. Quantum dots are very sensitive to air and humidity, so creating air-stable materials offers huge advantages – the biggest being lower cost. Hartlove explained that having air-stable materials relaxes the requirements for how you handle the materials during production and packaging into films. “Our goal is to reach zero added cost to the manufacturing and packaging process by eliminating the need to control moisture and humidity to high levels,” said Hartlove. He didn’t say they were quite there yet, but implied they were getting close.
Nanosys has also been working on new ways to use the quantum dots in display devices. One architecture they are focusing on is embedding the air-stable quantum dots into the color filter part of an LCD display. This configuration offers huge efficiency savings if it can be implemented.
For example, today’s quantum-dot TVs using a film architecture start with blue light in the backlight that is converted to white light via the red and green quantum dots in the film. This white light is modulated by the LCD then filtered at the sub-pixel level to pass only the red, green or blue component. In other words, two-thirds of the light is still wasted in this approach.
If the quantum dots are embedded at the sub-pixel level in the color filters, then LCD-modulated blue light can now pass thru the clear blue sub-pixel while converting to red or green light in those sub-pixels. This might reduce the energy use of the LCD by 50% to 66%. Such saving might be used for lower power consumption or to boost light out.
Putting the quantum dots in the color filter also requires them to be in a microns-thin layer. That is not much volume for the blue-light-to-green or red conversion, so the density of the quantum dots needs to be increased significantly without inducing quenching (too much emission reduces efficiency and light output). Developing this high density packing in inks and photoresist is the crux of the efforts that Nanosys is working on.
Hartlove explained they have been supplying materials to panel partners who are trying to develop displays using this capability. But there is a complication. The polarizer, which normally sits on the outside of the liquid crystal cell, needs to move inside the cell. This has to happen for two reasons. For one, quantum dot generation is a homogenous process, which means light generated in the green subpixel will emit forward and backward. If this generation takes place in the location of current color filters – outside of the LC cell – the distance is long enough to allow some leakage into adjacent sub-pixels, compromising color purity and color volume. In addition, this generated light is unpolarized, so the back-generated light would interfere with the polarized light coming from the back light. Therefore, the polarizer needs to move inside the cell.
Nanosys is not working on the methods to create an in-cell polarizer, but it is clear one can’t use the polymer-based polarizers used today on the outside on the inside of the cell. What companies are doing here is a story for another day.
Hartlove is also excited about the idea of a microLED panel fabricated with quantum dots. Here, the idea is to fabricate wafer-scale arrays of micron-sized blue LEDs, then sub-pattern each microLED with a clear, red QD and green QD elements. One or more of these might form a pixel in the display. He likes this idea because the devices are small and the light flux is modest, so not too challenging for current quantum dot materials. In addition, red, green and blue light is emitting from a single semiconductor system, which is a lot more cost effective, stable and consistent over time compared to current RGB LEDs, which are based upon two different material systems.
While Hartlove says they would like to also use this architecture for higher power blue LEDs to use in conventional edge or direct backlight architectures, the optical flux power densities are much higher, so a more difficult problem to solve.
The company is also working on electrically-activated quantum dot materials, but this remains in the research phase as they are shifting their efforts from Cd-based to Cd-free materials, with a focus on the blue material to start.
At CES, Hartlove expects Hisense and TCL to have new quantum dot TV announcements and a new player will be entering the TV space with a quantum dot solution we will have to wait to CES to know about. The brands using quantum dots for monitors are expanding beyond Samsung and Philips with Asus and BenQ getting in the game, but he was unsure if they will be at CES.
Overall, Hartlove is very optimistic as their cost reduction efforts should allow quantum dot solutions to migrate from flagship products into mainstream solutions in 2017.
This article first published on www.displaydaily.com