Perhaps you have been putting on some old blues records to get you through this turbulent time. It’s a normal thing to feel a little down about the world right now. And some days I feel the same way about blue emitters for next-generation display technology.
Sure, blue LED technology has seemingly advanced light years in the past two decades to reach where it is today. And there is no doubt it is a success story of optoelectronics impacting our daily lives. I urge you, just try to count the number of blue LEDs you interact with on a daily basis.
As we all know, blue LEDs have enabled the LCDs we love(hate) today. They have their drawbacks though. LCDs with blue LED light engines are really a brute force approach to getting colored light to our eyes in a well-controlled fashion. The future of flexible, light weight, efficient displays will require new ways of generating red, green, and blue light.
Of course, OLED has become a key enabling technology when it comes to these future displays, but OLED is not without its drawbacks.
OLED has struggled with blue materials for some time now. They exist, but never quite meet the mark, seemingly always requiring a sacrifice of color, efficiency, or stability. The lack of a satisfactory blue material is one of the reasons OLED TVs are actually white OLED with color filters.
It seems like good blue emitters are just really, really hard to make. The same holds true for blue EL-QLED.
It’s fun to talk about all the progress being made in the world of EL-QLEDs, but the elephant in the room is still blue. WE NEED A GOOD BLUE DEVICE! If blue EL-QLED can advance, it would compete directly with blue OLED (and could provide the blue for QD color filter technology), possibly enabling devices we have only dreamt of. So here I’ll highlight recent progress in Cd-free EL devices that provides a glimmer of hope and a healthy dose of reality on why I’m still singing the blues about blue EL-QLED.
Two of the most recognizable brands when it comes to quantum dots (Samsung and Nanosys) have both reported on their blue EL-QLED progress in the past year. Nanosys presented impressive numbers at SID Display week 2019 with >12% efficiency of a ZnTeSe EL-QLED device with a T50 of about 100 hours at 100 nits. That’s 50% emission after only a few days! And we are celebrating this as a success since most blue QD-OLED devices are far worse than that!
One great feature about ZnSe-based QDs is that they have very pure color emission, with a peak width (FWHM) of around 20 nm. Samsung has also reported they are working on a ZnTeSe alloyed QD with similar properties (narrow peak width, high quantum yield) but have not yet reported any device performance other than to say it is >10% efficient.
Of course I have over simplified the by providing only three metrics, as there are many other important factors like manufacturability, toxicity (non-Cd would be ideal), and the need/desires of the consumer (cue marketing to make that happen). Regardless, I hope this gives you a view from where I sit… at home… for the foreseeable future.
Here’s to the day we stop singing the blues about blue EL-QLED, and instead sing the triumphant songs of success.