Breakthrough inks powering next generation displays

As acronyms go, OLED is one we see fairly frequently – even if we don’t exactly know what it stands for. Organic Light Emitting Diode displays are pretty much everywhere. Your phone, for example, no doubt has an OLED screen and that’s because it needs to be thin, light and offer excellent image quality. But, like all technology, it has its limitations. And where there are limitations, there are smart people endeavouring to overcome them.

For OLED displays, the biggest challenge is lack of brightness. When you compare it with LED, for example, the difference in brightness is marked. When measured, OLED usually tops out at around 1000 nits (nits being the unit for luminance), but LED can be up to eight times higher. But what it lacks in brightness it makes up for in perfect blacks that create enough of a contrast to compensate. So, on the whole, it’s a great technology that everyone is happy with. Mostly.

Because brightness is important. It affects visibility. And colour accuracy. Greater brightness on a screen makes colours more vivid. Images are more realistic and lifelike, detail is maintained – even in extremes of light and dark. In short, it makes what you’re looking at a whole lot clearer. Which is essential if you’re in the business of creating images in the first place and using an OLED display to take photos or for filming. So, it stands to reason that Canon should have a more than passing interest. In fact, we’ve been in the business for some time, with Canon Tokki Corporation specialising in OLED manufacturing equipment.

We, of course, are also world leaders in research and development and have been in the top five of US patent rankings for 37 years, with up to 8% of our sales revenue invested in R&D every year. In short, creating and improving incredible tech is what we do. When you combine the two, it will be absolutely no surprise to learn that Canon is responsible for a recent huge development in OLED technology. But to understand why OLED isn’t perfect, how it was improved and, in turn, how we made it even better, it helps to explain the way it works in the first place and how the next generation – QD-OLED – is different.

OLED vs QD-OLED

So, it’s best to think about these as thin layers, one on top of the other. Traditional OLED uses a layer of blue pixels which are coated in a yellow phosphor to make white light. Over the top of this lies a colour filter, which creates the red, blue and green (RGB) that we’re all familiar with – and in combinations these make all the colours we could possibly need. However, it’s this filter that is reason why OLED isn’t as bright as we might like it to be and causes manufacturers to compensate by adding a white pixel to the RGB layer, just to brighten things up a bit.

However, it’s not the ideal solution, so a version of OLED called QD-OLED was developed. The blue pixels remain, but the yellow phosphor is no more. Instead, a ‘mesh’ of printed semiconductor nanocrystals (or ‘Quantum Dots’, hence the ‘QD’) is layered over the blue pixels. These measure only a few nanometres in diameter and can emit light with high brightness and high colour purity. When the blue light hits the quantum dots, they turn red and green – and we arrive at our RGB display with no colour filter.

Did someone say ‘print’?

Sure did! There’s no hiding from the world of print, even in complex display technology. It’s clear that these printed nanoparticles are the game changer here, and they were initially made from cadmium selenide, with a coating around them, like an M&M. This coating is important because it makes the dots more stable, and cadmium is toxic, so it also stops it from escaping from the dots. This clearly wasn’t an ideal or sustainable solution, so quantum dots made with indium have quickly overtaken cadmium. But there are also a couple of big problems with indium; it is rare and anything rare is naturally very expensive. To overcome this, Canon Inc. has developed a quantum-dot ink with a perovskite structure, showing it to be a practical alternative.

But what on earth is a perovskite structure?

It’s a kind of crystal that’s named after the mineral perovskite because of its structural similarity – and it’s actually pretty cool because the term overall describes a group of materials that have a structure of cuboid and diamond shapes. They’re extremely versatile too because they have a wide range of properties for QD-OLED, such as fluorescence, superconductivity and ferroelectricity. They are best known for their use in solar cells, again because they are also low cost. Up until now, however, durability has been an issue for perovskite quantum dots, which is why they have largely been indium-based.

By ‘durability’ we mean both the longevity and robustness of the dot. So, the ability to hold their shape and resist changes in heat, light or air moisture, for example, and also their ability to withstand the pressures of manufacturing processes. Given our vast experience in (and proprietary technologies for) the development of ink and toner for printers, it makes sense that we would be able to solve the elusive practical durability problem. But how? We’ve developed a unique method for forming a suitable protective shell on the perovskite quantum dots.

Achieving an ultra-high definition world

As a business, we’re pretty used to world firsts, but surely we can be forgiven for being really excited by this breakthrough because quantum-dot inks have so much potential? Firstly, without the reliance on a rare substance like indium, the cost comes down substantially and any issues of supply disappear too. This, in turn, should certainly have a material impact on technologies across industries. And finally? The quality. This has the potential to open up a world of next generation 8K quantum dot displays – something that hasn’t yet been achieved. Imagine the ultra-high definition? Phew. While this technology won’t be in mass production immediately (Canon Inc. estimates mid 2020s), there’s no doubt it’s going to be a game changer.

Learn more about perovskite quantum dot inks on the Canon Global Website.