QD-OLED (Quantum Dot OLED) and QNED (Quantum Nano Emitting Diode) are two screen technologies under investigation by Samsung Display. QD-OLED televisions could become a reality in 2022. But how do these two new techniques work?
The versatility of quantum dots
Which quantum dots can be incorporated into screen technology in many ways, we have known that for some time now. Current QLED TVs use a QD film in the backlight.
So essentially they still are LCD TVs, but they enjoy it very spacious color gamut that quantum dots provide. The sacred quantum dot grail is a micro-LED quantum dot screen. Such a screen is emissive, each pixel itself emits light, and the quantum dots are stimulated electrically, instead of with blue light as is currently the case. Color filters would be unnecessary.
But we are far from that yet. However, the quantum dot roadmap contains a very interesting intermediate step. The QDCC, or quantum dot color converter.
QDCC: replace the color filter with quantum dots
Quantum dots create very pure colors, and the color can be determined relatively accurately based on the size of the quantum dot crystal. Why then do we use the quantum dots to make white light for which we then have to apply a color filter? Isn’t there a way to use the pure light from the quantum dots directly? Yes, that is indeed possible, and for that we look at the QDCC, or Quantum Dot Color Converter. The color filter (which filters out light) is replaced by a layer with quantum dots in the same pattern as the color filter. Instead of filtering out light, the quantum dots convert the incident light to the desired color. Since the background lighting uses blue LEDs (as with current QLED TVs), the light is simply passed through for the blue pixel.
You may also see QDCC appear under the name QDCF (Quantum Dot Color Filter). However, we prefer QDCC because it better illustrates that it is explicitly not a color filter.
With the help of a QDCC you also create an emissive screen instead of a transmissive screen. After all, it is the quantum dots in the pixels themselves that emit light. Then you can expect a greatly improved contrast, viewing angle and greater energy efficiency. That concept was first explored in conjunction with an LCD panel, as illustrated below.
However, this solution proved unfeasible for several reasons. But that does not mean that the concept has to be discarded.
QD-OLED: the unexpected combination
All that has to be found is a new solution to create blue light that can be switched on and off at pixel level. The QDCC layer can remain unchanged. The first solution put forward is QD-OLED. Yes, you read that correctly, a combination of quantum dots and OLED in one screen.
The operation of a QD-OLED TV is very similar to that of WOLED TV as we can now. Just like with a WOLED TV the OLED layer is applied over the entire screen, the main difference is that the OLED layer does not produce white light but blue light. In the QDCC layer, the blue light is converted to red and green using quantum dots. The light may continue for the blue pixel.
QD-OLED could potentially hit the market as early as 2022.
QNED: Quantum Nano Emitting Diode
QNED, Quantum Nano Emitting Diode is very similar to QD-OLED, but should be more energy efficient, with higher brightness, longer lifespan and free from burn-in hazards. By replacing the blue OLED layer with small blue LEDs, all these improvements are obtained. These LEDs are very small and have the shape of rods, which is why they are called nanorods (nano rods). The active material is Gallium Nitride (GaN).
Those are strong promises that it must of course still fulfill. The technology would already be in a fairly advanced phase, but it would not be the first time that a technology has subsequently been put on hold, for technical or commercial reasons.
Not to be confused with LG QNED
Wait a minute, before we continue we need to clarify something. In 2021 launched LG are models with QNED. At LG, the marketing term QNED stands for Quantum Dot + NanoCell + miniLED. In other words, these are LCD TVs that use one mini-LED backlight, quantum dot technology and LG’s NanoCell technology. Those TVs are in no way comparable to the Samsung QNED technology that we explain in this article.
In other words, LG has somewhat hijacked the term QNED. It also wanted to trade the term QNED, but the US Patent and Trademark Office has refused. Precisely because QNED stands for Quantum Nano Emitting Diode, and is a generic name for a screen technology. Despite the refused trademark, LG may use the term as a marketing term. So watch out for confusion.
QD-OLED relies on an OLED layer to produce light. The organic material is subject to aging and there is a risk of burn-in. Samsung is therefore investigating another solution that uses very small, inorganic GaN LEDs. They would be barely 2 µm high and 0.62 µm wide. This makes it possible to cover the entire substrate with it, such as with QD-OLED. The size of the pixel itself is then determined by the driving transistors (TFT).
With that, we make it seem much simpler than it really is. The manufacture and use of those nanorod LEDs is very complex. They are first separately manufactured and harvested. To then apply them to the screen, one will probably rely on inkjet printing. The nanorods are mixed in a medium that is printed. The distribution of the nanorods in the medium should be quite uniform, and it should also dry uniformly. The surface to be covered is large, so that is a challenge.
According to UBI research Samsung Display uses 10 to 20 nanorods per pixel. They must be properly aligned so that they do not short circuit the circuit. The driver is equipped with extra transistors to ensure this and an extra transistor to restore the circuit in the event of a defect. This control is much more complex than for other TVs. The pixels could possibly be round in shape, instead of the usual rectangular shape.
QNED technology has made significant strides since its first patents in 2016. It still has some way to go, but analysts say it could potentially hit the market around 2025.
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