Can OLED panels be produced in an "inkjet printing" way? You are not mistaken, OLED may have to rely on this technology in order to conquer the mainstream market.
At the end of November, BOE announced the successful development of China's first 55-inch 4K OLED display with inkjet printing technology, which is expected to break the monopoly of Korean companies in the large-size OLED field.
The mainstream OLED production generally adopts the evaporation process. This technology is mainly faced with problems of yield and cost. The OLED panel manufacturing process of inkjet printing technology is a feasible method to reduce the production cost compared to the evaporation process.
In fact, many panel manufacturers at home and abroad have long started to develop inkjet printing technology, including Samsung, LG, BOE, CSOT and so on. As early as the end of last year, Japan Display Corporation (JDI) affiliate JOLED announced that the world's first "printing production mode of production of 21.6 吋 OLED panels, has begun to supply, early is mainly used for medical device displays.
What is the difference between evaporation and inkjet printing?
The principle of OLED illumination is to make a layer of tens of nanometers thick luminescent material on ITO glass - that is, the material of the OLED screen pixel self-luminous, there is a metal electrode above the luminescent layer, the electrode is applied with voltage, and the luminescent layer is generated. Optical radiation; electrons and holes are injected from the yin and yang respectively, and the injected electrons and holes are transported in the organic layer, and are combined in the light-emitting layer to excite the light-emitting layer molecules to generate singlet excitons, and the singlet exciton radiation attenuates the light. Thereby forming one pixel points.
The most common method of forming an organic layer is "evaporation." Evaporation is similar to evaporation. When boiled in the pot, the steam turns into dew on the lid. The difference is that the evaporation uses an organic material instead of water and is heated under vacuum rather than at normal atmospheric pressure.
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The evaporation must first be carried out in a vacuum, that is to say in a device called a vacuum chamber. A large LTPS backsheet was fabricated and color patterned in a vacuum chamber.
Once the LTPS is fabricated and placed in the evaporation vacuum chamber, then a precision metal mask (FMM) is placed under the LTPS substrate. The reticle is a device having a small hole in the thin steel plate, so that when the organic material is evaporated, it can only be deposited at a specific position. When the mask is ready, place the evaporation source underneath and heat it to the appropriate temperature. When heating begins, small organic molecules in the molecular unit pass through the mask and accumulate to the desired location.
Inkjet printing technology is a technique for producing OLED inks of less than tens of pl (one trillionth of a liter) for mass production of screens, like inkjet printing on paper. Compared with the vapor deposition method in which the organic matter is vaporized under vacuum, the inkjet printing technology has the advantages of being able to produce at a normal pressure, dropping less ink to the outside of the substrate, and improving material use efficiency.
In order to perform inkjet printing, the OLED material is first melted in a solvent to make it into an ink shape. The ink containing the OLED material is printed between the grids of the substrate through the nozzles of the ink jet head. The OLED material is then printed by removing the solvent through a drying process. Inkjet printing technology can be used in various types of display processes, and the application prospects in the large-size OLED field are particularly promising. This is because the substrate required to make a large-sized display panel should be higher than the 8th generation, and the inkjet method has an advantage in producing a large-area device as compared with the vacuum evaporation method.
What are the advantages of inkjet printing compared to the evaporation process?
The process is simpler. The organic light-emitting material has higher evaporation efficiency, and the material utilization rate is deposited on the glass substrate without any difference in vapor deposition, and the material utilization rate is low.
As a large-sized fine metal mask, the process cannot be applied to the manufacture of large-sized panels. The manufacturing cost is lower, and in the use of raw materials for OLED panels, printing OLEDs saves about 90% compared to evaporation technology.
What are the difficulties in inkjet printing?
Ink: The stability of the ink is a key factor in the printing process, and in addition to its own property change factors, the larger factor affecting the stability of the ink is the bubble. Assuming that the existing manufacturers can provide stable and large quantities of non-impurity inks, the ink will introduce bubbles during transportation and filling, and there is no good solution for how to remove the bubbles.
Nozzle: In addition to the single-nozzle single-nozzle system on the small-scale R&D machine, the single-nozzle multi-nozzle system is generally used above the medium-sized platform. The nozzle can be printed by multiple nozzles during the printing process, thereby achieving the effect of homogenizing the volume of ink in each pixel under the premise of improving production efficiency.
Film formation: Film formation is also one of the difficulties in solution printing. When the ink is printed, it already starts to volatilize on the surface. Generally, the edge of the ink evaporates faster, and a coffee ring phenomenon occurs.
Summary: Our lives are inseparable from a variety of screens, and the variety of data that surrounds the screen is becoming more and more valuable. The three screens on TV, mobile phones and cars have become the most important entrances for information competition in the future, and the most basic screen technology will continue to develop and continue to usher in new breakthroughs.