Display Week: Self-luminous quantum dots for notebooks and monitors

LCDs and OLEDs are a thing of the past, now come self-luminous quantum dots. This is what TCL is promising at Display Week with an impressive prototype.

May 20, 2024 at 9:13 pm CEST

5 min. read

c't Magazin

By

Ulrike Kuhlmann

This article was originally published in German and has been automatically translated.

So far, LCDs and OLEDs have been battling it out to be the dominant display technology. The undoubtedly good micro-LEDs are too expensive, mini-LEDs merely improve the backlight in the LCD. But now a new display technology is emerging that has all the advantages of OLEDs. At the same time, like LCDs, it should be particularly inexpensive to produce, namely by printing: Self-illuminating quantum dots that are electrically excited instead of using light.

Researchers have been working on such EL-QD displays (also known as QDEL displays) for years, but until now there have been no demonstrable results. At Display Week in San Jose, the Chinese panel manufacturer TCL CSOT is now presenting an impressively colorful 14-inch display whose luminous layer consists of quantum dots that are controlled by electric current instead of light. The quantum dots in the backlight previously used for LCDs ensure richer colors; in Samsung's QD OLEDs, they convert the blue light of an organic light-emitting layer into green and red light, thus serving as a kind of color filter.

Menschengedränge an Messestand — Many visitors wanted to see the high-color EL-QD display from TCL.

(Image: Ulrike Kuhlmann, c't magazin)

EL-QD displays need neither a power-hungry backlight and light-absorbing color filters nor an expensive organic light-emitting layer. TCL prints the pixels from quantum dots onto a substrate using an inkjet printing process and therefore does not require a fine metal mask (FMM). A lot of organic material remains on such metal masks during production, which is expensive.

The display with electrically excited quantum dots shown in San Jose displays 2880 x 1800 pixels on a 14-inch diagonal. TCL states a color gamut of 85 percent BT2020, which initially only indicates that it is a high-color display. The switching time is specified as 1 millisecond, the pixel refresh as 30 to 120 Hertz, as the display is capable of variable refresh rates (VRR). However, the name QLEDs chosen by TCL for its new display technology is causing confusion, as Samsung markets its LCDs with conventional quantum dots under this name.

Positive aging

Although the EL-QDs do not react to light, they do react to moisture, which is why they have to be well encapsulated between the electrical layers. And they exhibit positive aging. Sounds good, but it's not: as their luminosity increases over time, frequently used green quantum dots, for example, produce a green cast in the image. As with OLEDs, TCL must therefore take countermeasures here. Another problem at present is the lifespan of the blue quantum dots in particular.

Aufgeklappter Laptop, dessen Bildschirm eine Picknick-Szene zeigt: Im grünen Gras stehen dunkelblaue Teller mit Essen darauf auf, sowie ein Getränkeglas in einer blauen Schale — The electroluminescent quantum dots contain the environmental toxin cadmium, but the quantity remains far below the permitted level according to TCL.

(Image: Ulrike Kuhlmann, c't magazin)

Another sticking point is the environmental toxin cadmium used for the quantum dots. For some time now, the EU has been limiting the use of cadmium to a concentration of 100 parts per million (100 ppm) and is calling on panel manufacturers to switch to cadmium-free indium phosphide (InP). This has been implemented for green and red, but blue quantum dots still contain a very low proportion of cadmium. This is also the case in TCL's electroluminescent quantum dots. At Display Week, TCL explained that the cadmium content remains well below the limit value and that the company is working on indium phosphide variants.

The EL-QD displays are currently produced in a Generation 4.5 factory; TCL CSOT also has a Gen 5.5 factory for printed OLEDs that could be converted. The company expects EL-QD technology to be ready for series production in around three years. TCL plans to show a 25-inch monitor with an EL-QD display at the end of 2024. TCL is not focusing on large television displays, which do not promise good growth rates, explained a spokesperson at the trade fair, adding that TCL is concentrating on IT products instead. The first devices are due to go on sale in five years' time.

Ein eingeschalteter Computermonitor, darüber die Aufschrift "Quantum Dot Light Emitting Diode Display" — Samsung also has EL-QD technology on its radar, as a small monitor on the stand shows.

(Image: Ulrike Kuhlmann, c't magazin)

So the new display technology is not quite there yet, but it looks very promising. So promising, in fact, that Samsung is also showing a small monitor with an EL-QD display at Display Week. Unlike TCL CSOT, it is located in a corner of the stand; Samsung is focusing on its organic displays with classic quantum dots (QD OLEDs) at Display Week.