part3(section 2): two development directions of display technology in the future -- mled and ink jet printing OLED

Click 4 times Date:2020-11-24

3.2 OLED

The light-emitting principle of OLED is that the organic coating is energized and self-luminous, so there is no need for light source systems such as light-emitting devices, driving circuits, light guide plates, etc., which greatly reduces the size and power consumption, and through material optimization, it can also achieve softness and folding. OLED mainly has two paths: evaporation type and printing type.

Vapor-deposited OLEDs use electron beams or lasers in a vacuum to heat and evaporate light-emitting materials, and finally condense on the substrate. In the evaporation process, a metal mask is needed to realize the precise transfer of the drawing to the substrate. However, when the size is too big, the mask will be distorted to a certain extent under the action of gravity. For high-precision manufacturing, the slightest error will seriously affect the product quality.

What's more, the utilization rate of materials in the evaporation process is only about 70%, and the need for a vacuum environment will cause the cost to rise. Therefore, the vapor-deposited OLED is also facing a commercial bottleneck in the big size screen. At present, South Korea's top two are in a leading position in this technical field, and Samsung have advantages in the small size and medium size markets, LG have advantages in the big size markets respectively.

Printed OLED, also known as inkjet printing (IJP), is similar to inkjet printing text on paper. The organic light-emitting material is sprayed on the substrate and dried to form a light-emitting film.

Printed OLED does not require a vacuum environment and can be produced under normal pressure. In the actual process, only about 2% of the solution will be wasted, and the material utilization rate has been greatly improved. Compared with the evaporation process, it is really "good and easy to use". The entire process has small scale restrictions, so for big size screen fields, printed OLEDs can be described as extremely cost-effective.

Although the printing principle is simple, the technical difficulty is not low. Between laboratory technology and industrial production, there is a long period of know-how exploration. Just take the sprayed ink droplet as a sample, it needs to strictly control its size, viscosity, surface tension, speed, direction, inertia and other parameters. If the viscosity is high, the ink will be blocked at the nozzle; if the viscosity is low, it is difficult for the ink to adhere to the substrate in an ideal condition, and so on.

But even if there are so many difficulties, printing OLED has more commercial value in the field of big size screen under consideration of factors such as the use of primary technology, production technology, and demand scenarios, just like LCD replacing CRT. Moreover, printing technology can be used not only for OLEDs, but also for QLEDs. It is a general-purpose technology for a wider range of applications.

Compared with the folding screen, the Yunjuan screen is pulled up from the front to the back. When the folding screen is closed, the thickness will be doubled, and the volume will increase significantly, and the consumer experience is not really good. However, the thickness of the Yunjuan screen will not increase when it is folded, the area is reduced, and the portability is improved.

In the future, the development of OLED will move towards quantum dot technology, and after quantum dot technology, more new technologies will be born. Technological changes never stop.

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