OPEN HOUSE 2021
VR display using flexible OLEDs and QD device were introduced as the next generation display

NHK is holding "OPEN HOUSE 2021" by the online method at June 1 - 30, 2021. In this here, topics of display are close up base on the official HP (https://www.nhk.or.jp/strl/english/open2021/index.html).

As immersive type VR display of the future, 51.3-inch curved monitor using 3 30-inch 4K flexible OLEDs was introduced. As picture 1, highly immersive feeling was obtained by curvature of OLED panels because of covering image against almost view angle. Its resolution was 6480 × 3840. For this reason, viewer can't view almost each pixel in fact.

Picture.2 30-inch 4K flexible OLED

Picture.1 immersive VR display (HP of NHK)

30-inch 4K OLED has been jointly developed with Sharp Display Technology. This panel is composed of reflection anode, hole injection layer, hole transporting layer, R/G/B emission layer, electron transporting layer, electron injection layer, and transparent cathode. In short, it's a top emission structure. It can be bended and rolled by making use of two plastic film substrates (base substrate and encapsulation substrate). Its thickness and weight are 0.5 �o and 100 g respectively. It's pilot-produced by making the conventional technology, which was adopted for OLED of smartphone. By the way, IGZO (In-Ga-ZnO) -TFT was used as active-matrix transistor.

QD-LED without Cd was developed and disclosed

And also, quantum dot light-emitting diodes (QD-LEDs) with vibrant colors were appealed as the next generation display, too. QD materials are small particle-shaped semiconductor crystals. Their structure is composed of a ligand for coloring using and ink solution around a core and shell, which are responsible for the luminescence. The core diameter is small, and ranges from 1 to 10 nm. One feature of QD materials is that the color of the emitted light varies depending on the size of the core, changing to red as the size becomes larger, and to green and blue as the size becomes smaller. If the sizes of the particles are kept the same for each color, luminescence of vibrant colors with high color purity can be obtained. Therefore, R,G,B independently full-color display is obtained by patterning of each sub-pixel, for example, the ink-jet printing method.

As you know, Cd series materials have been mainly developed as QD material. By contrast, NHK succeeded to find Cd-free materials in accordance with all colors (InP, SeZn). This makes it possible to reproduce around 80% of the color range defined by the Rec. ITU-R BT.2020 international standard for 4K/8K.

Figure.1 QD-LED and its color reproducibility

Picture.3 Emission of QD-LED

By the way, pilot-produced device is composed of anode/hole injection layer/QD layer/electron transporting layer/cathode. In short, its structure is almost same as that of OLED except for emission layer. Of course, QD layer can be formed by various wet-coating methods, such as the ink-jet printing method.