What About Adding QDs to OLEDs?

I’m writing this week’s editorial from my hotel room in Las Vegas, just before the last day of Infocomm. It’s been a fascinating three weeks for me, with SID, Infocomm and AWE Expo. I’ve really looked at so many displays and technologies. What’s clear is that most display technologies can find a niche to exist, even if they don’t dominate like LCD or OLED or projection.

I wrote in my SID report about the development of QDs that can replace the colour filter, effectively announced by Nanosys at SID. The more I think about this, the more I think it could be a very big deal. To briefly explain…

To date, QDs have been put in the backlight of the system, to convert some of the the blue light from the LEDs to red and green. Then the light goes through the LC cell and the colour filter. That means that you are throwing away (in the filter), most of the light that you just created, which is kind of crazy. Why not put the QDs where the filter is and simply deal with blue light in the backlight and cell? I had this idea in 2012 and had correspondence with Nanosys in 2013 about the concept. At the time, they explained that it was too difficult because the QDs are sensitive to oxygen, so display manufacturing and encapsulation would be difficult.

However, the company has been working on the encapsulation, and has a formula, now, that encapsulates each individual QD. The dots can then be put in a photoresist for photolithography, to allow air-exposed manufacture exploiting the processes already used for filter production in TV-sized LCDs. Filters for smaller panels are often made by inkjet processes and Nanosys believes it can also develop materials for that process.

It has been pointed out, also, that because the QD would emit non-polarised light, it has to be placed on top of the polariser, rather than between the polarisers, as current filters are. That would mean putting the polariser in the cell, another engineering challenge and meaning a change in processing.

Now, that is going to be tricky, as processes and equipment are very fussy and difficult to optimise for high yield (one specialist I discussed this with said ‘Good luck with that!’ when he thought about the chemistry), but Nanosys is working with potential customers and believes it can succeed. If it does, the technique has the potential to dramatically boost the efficiency of LCDs, which has implications for all applications, including HDR in TV, where high brightness (2,000 cd/m²?) TVs will be feasible without breaking energy regulations, or using much more power than current high end sets. Public displays could have really high brightness and mobile devices have longer life and brighter displays.

It occurred to me this week, that the same logic could apply to OLEDs. If you used the LG approach, but made the base a blue OLED (maybe the new TADF materials we talked about in our SID report) and then put QDs on the front, instead of a filter, you could keep the manufacturing process that LG has, but boost the efficiency, brightness and lifetimes of OLEDs, again significantly. And that’s another big deal.

Remember, you read it here first!

Meanwhile, the LED and projection companies are making dramatic improvements (as Chris’s Display Daily points out for LED). All this competition to provide, bigger, brighter, lower power displays is really going to improve things for display users and buyers.


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