QD-OLED: the challenge of creating the perfect hybrid TV

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We are not talking about QLED

The new technology, natural evolution of Quantum Dot that combines them with OLEDs, it could soon be marketed by two big names in the sector such as Sony and Panasonic with the first QD-OLED TVs

Currently all OLED panels for TVs are supplied by LG and use a W-OLED technology, i.e. the organic substrate consists of white self-illuminating organic LEDs that are filtered with an RGB matrix to obtain the various colors. A pixel is actually left blank, in order to better control the peak brightness and this can limit the technology in terms of image quality: in fact, if you want a high brightness, the unfiltered white LED goes on and you lose in terms of chromatic fidelity, vice versa if you want a well saturated color you cannot reach good brightness peaks.

This aspect has represented for years the Achilles heel of OLED displays in favor of LCDs that today find their maximum determination in Quantum Dot displays. However, to date, OLED technology has remained a bit ahead due to the perfect contrasts and deep blacks and a wider viewing angle.. But if we combine the two technologies? The idea of ​​Samsung display is precisely to get to market the first QD-OLED TVs (Quantum Dot OLED), but perhaps the first customers could be unrelated to the Korean giant or Sony and Panasonic.

RGB OLED technology compared to LG's W-OLED

TV QD-OLED: the union of two worlds

Until now, Samsung Display had focused on the production of QLED panels, which is an evolution of normal LCD technology that however uses a Quantum Dot filter between the LED backlight and liquid crystals to obtain purer and more saturated colors, in this way it is possible to obtain wider gamuts, without losing maximum brightness. Unfortunately, however, there is a big limitation: when a liquid crystal cell "closes" to "turn off" a pixel on the display there is always some spurious light that filters and therefore the blacks are not perfect and the contrast is low. For this, technologies such as local dimming have been implemented, which allows you to modulate the backlight in different areas, in order to limit this effect. However, the pixel-wise precision of an OLED cannot be achieved.

Operation of LCD and OLED

If you can't defeat your enemy, then ally with him. QD-OLED TV technology replaces the W-RGB matrix of classic W-OLEDs with a Quantum Dot color filter. Quantum dots are particular nanostructures that absorb blue light and re-emit it with a different wavelength, typically red and green in practical applications. In practice we have obtained a control of the contrast at the pixel level, without the annoying problem of color fidelity in highlights. Furthermore, the structure of the panels for QD-OLED TVs is simpler than previous LCDs - no backlighting or LCD layer - and OLED too - because it is enough to produce only one color which is blue..

White OLED and QD-OLED are confronto. In the White OLED the red emissive layers, blue and green are sandwiched together to create white light (note that the emission takes place downwards where the color filters and the TFT matrix are located). To the right, two blue emissive layers are used to produce light of the same color which will excite the quantum dots to produce red and green.

All the large format OLED displays marketed today are of the White OLED type, in which to an OLED panel capable of reproducing white light, RGB color filters are applied (plus one transparent for “pumping” the brightness). The advantage is that each subpixel can be turned on or completely off, for the benefit of the contrast ratio and perfect black, while not having specific OLEDs for each color and in particular blue, guarantees superior longevity of the panel in terms of color uniformity. The disadvantages are those of a lower luminous efficiency due to the use of color filters, a less wide gamut than Quantum Dots and the tendency to wash out colors as brightness increases due to the white subpixel.

Operation diagram of a QD-OLED TV panel

In QD-OLED technology, as in the White OLED one, an OLED panel is used as a base, this time, however, in blue. Instead of a normal color filter to create red and green, in this technology a layer of Quantum Dots filters is added. Recall that Quantum Dots are essentially materials that absorb blue light and re-emit it, through a process of luminescence, converted to red and green. This hybrid technology offers the best of both worlds on paper: all the advantages of OLED, married with the wide gamut of Quantum Dots and better efficiency.

All the challenges that Samsung has to overcome

QD-OLED technology, in addition to the potential quality advantages, has on its side the fact of greatly simplifying the structure of the panel. Compared to a QLED, the backlight disappears, the LCD panel, the polarizer. However, an effective jet printing technique is required for the deposition of the various layers and Quantum Dots, that must be perfectly aligned with the millions of subpixels that we find on a 4K or even 8K screen. According to rumors, Samsung would have solved this problem thanks to its subsidiary SEMES, which will supply the machinery necessary for the production of the panels.

The main problem remains that of the blue light source. Samsung has already tried once to produce an OLED RGB TV, but at the time it was unable to start mass production precisely because of the problems with the blue emitter. Blue OLEDs have efficiency and longevity issues, that is, they tend to lose their peak brightness quickly. Samsung would have solved this problem by making a triple layer OLED panel, in such a way as to obtain the required brightness, but by reducing the stress on each blue OLED substrate. Since all the OLED panel, like the white one from LG, emits light of the same color, there shouldn't be the long-term color uniformity issues that plagued RGB OLEDs, but the unknown remains as to how much Samsung has really solved the problem of the longevity of the blue emitter of these panels in the long run.

Another glitch Samsung will face is that of spurious blue light. The red and green sub pixels, indeed, in order to offer the color range that is expected, they must be able to completely absorb the blue light produced by the OLED and transform it into their respective primaries. The complication is given by the fact that the materials used in the Quantum Dots have an absorption curve that usually has a minimum just in the vicinity of the blue wavelength. What materials will Samsung have identified? And how he solved the problem?

Quantum Dot emission spectra

Quantum dots are tiny particles that have excellent photon emitting properties and are widely used in many LCD displays today as QD photoluminescence capabilities allow for the conversion of blue LED light into red and green light to create better-than-white color displays- Backlit LCDs . QD particles can also be used to create emissive displays, where the QDs themselves emit light: this technology could prove to be the successor to OLEDs as QDs could prove to have higher efficiency and a wider color gamut (narrow spectrum emission).

Situation continuously updated

Obviously there is no shortage of problems. First of all you need a perfect alignment between the OLED matrix and that of the Quantum Dot. Furthermore, combining two different technologies can be dangerous. Have you wondered why LG doesn't just make RGB OLEDs, without the filtered white component? The white component helps reduce stress on high lights, increasing the longevity of the whole panel and moreover it is more efficient. In fact the colored OLEDs, especially the blue ones, present serious problems in this regard: they struggle to reach high brightness peaks and have a short life. QD-OLED TVs will have to cope with this problem, it is assumed that multilayer panels with different layers of OLED will be used to try to solve the problem. And then there remains the problem of spurious blue light: Quantum Dots don't have a perfect absorption curve, so something could still pass.

I primi TV QD-OLED

Mass production of QD-OLED TV panels is expected to start in 2021, with the first models on the market in the second half of the year. Probably the CES - or what remains of it due to the health emergency - or IFA 2021 could be excellent opportunities to show this new technology at work. It seems strange that Samsung Electronics - a division of the Korean giant that deals with consumer electronics - has not entered the game. Maybe he already has his hands in the dough or maybe he is focusing on other promising technologies such as MicroLED that is fascinating many, including Apple: the idea in this case is a simple LCD which miniaturizes the backlighting to reach a very high number of dimming areas (ideally equal to the number of pixels).

From reliable press sources we learn that after a few days, China has become the protagonist of two stories that refer to industrial espionage and the theft of intellectual property to the detriment of the Korean Samsung and seven Taiwanese chip companies.

If the espionage suffered by Samsung refers to only one Chinese company, the attack on Taiwan would bring in a group of "state" crackers directly linked to the Chinese government.

It is unthinkable that China is on the world stage, directly or not, is the only country to move according to spy schemes. But the two episodes become news for the temporal proximity of the two events, and because they concern a giant like Samsung and its "experimental" OLED panels, and an attack on the Taiwanese chip industry.

Spy on inkjet printing of Samsung OLEDs

Two researchers from Samsung Display and an official from a partner company of Samsung have been accused by Korean prosecutors of industrial espionage for the benefit of China, and then arrested. The damage inflicted on Samsung as a result of the espionage would be quantifiable in millions of dollars e concern the inkjet printing of OLED panels.

American strategies of Chinese boycott could not go without countermeasures!! In the long run, when China will be equipped to produce high-tech components on its own, the initial victory of this trade war will turn into a heavy defeat