The OLED screen can be "printed" unexpectedly. The liquid crystal represents a high degree of panic. OLED panels can be produced by "inkjet printing"? You read that right, if OLED wants to conquer the mainstream market, it may have to rely on this technology.
At the end of November 2018, BOE announced the successful development of China's first 55-inch 4K OLED display using inkjet printing technology, which is expected to break the monopoly of Korean companies in the field of large-size OLEDs.
The mainstream OLED production generally uses the evaporation process. This technology mainly faces the problem of yield and cost. Compared with the evaporation process, the OLED panel manufacturing process of inkjet printing technology is a feasible method to reduce the production cost.
In fact, many panel manufacturers at home and abroad have begun to develop inkjet printing technology very early, including Samsung, LG, BOE, CSOT and so on. As early as the end of last year, JOLED, an affiliate of Japan Display Corporation (JDI), announced that the 21.6-inch OLED panels produced by the world's first "printing production method" had begun to be supplied, and in the early days they were mainly used for medical device displays.
What is the difference between vapor deposition and inkjet printing?
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Vacuum evaporation
The most common method for forming an organic layer is "evaporation." Evaporation is similar to evaporation. When the water is boiled in the pot, the steam acts as dew on the lid of the pot. The difference is that evaporation uses organic materials instead of water, and heating is performed in a vacuum state instead of under normal atmospheric pressure.
Evaporation must first be carried out in a vacuum, that is, in a device called a vacuum chamber. The manufactured large-scale LTPS backplane is color patterned in a vacuum chamber.
Once the LTPS is manufactured and placed in the evaporation vacuum chamber, then a precision metal mask (FMM) is placed under the LTPS substrate. The mask is a device with small holes engraved on the thin steel plate, so when the organic material is vapor-deposited, it can only be deposited in a specific position. When the mask is ready, place the evaporation source under it and heat it to an appropriate temperature. When the heating starts, the small organic molecules in the molecular unit pass through the mask and deposit to the desired position.
inkjet printing
Inkjet printing technology is like inkjet printing on paper, injecting less than tens of pl (one trillionth of a liter) of OLED ink for mass production of display screens. Compared with the vapor deposition method that vaporizes organic matter in a vacuum state, inkjet printing technology has the advantages of being able to produce under normal pressure, less ink dripping onto the outside of the substrate, and improving the efficiency of material usage.
In order to perform inkjet printing, the OLED material must first be melted in a solvent to make it into an ink shape. The ink containing the OLED material passes through the nozzles of the inkjet head and prints between the barriers of the substrate. Then, the solvent is removed through a drying process, and the OLED material printing can be completed. Inkjet printing technology can be used in various types of display screen manufacturing processes, and its application prospects in the field of large-size OLEDs are particularly exciting. This is because the substrate required to make large-size display panels should be higher than the eighth generation. Compared with the vacuum evaporation method, the inkjet method has more advantages in the production of large-area equipment.
What are the advantages of inkjet printing compared to evaporation process?
The craft is simpler. Organic light-emitting materials have higher evaporation efficiency and material utilization rate. During evaporation, organic material gas is deposited on the glass substrate without difference, and the material utilization rate is low.
As a large-size fine metal mask, the process cannot be applied to the manufacture of large-size panels. The manufacturing cost is lower. In the use of raw materials for OLED panels, printing OLED saves about 90 percent compared with evaporation technology.
What are the difficulties of inkjet printing?
Ink: The stability of the ink is a key factor in the printing process, and in addition to its own property changes, the larger factor that affects the stability of the ink is air bubbles. Assuming that existing manufacturers can provide stable and large quantities of ink-free ink, air bubbles will be introduced during the transportation and filling of the ink, and there is no good solution for how to remove air bubbles for the time being.
Nozzle: In addition to the single nozzle single nozzle system used on small RD machines, single nozzle multiple nozzle nozzle systems are generally used on medium platforms and above. The nozzle can use multiple nozzles for printing during the printing process, so that the ink volume in each pixel can be evened under the premise of improving production efficiency.
Film formation: Film formation is also one of the difficulties of solution printing. The ink already evaporates on the surface when it is printed. Generally, the edge of the ink evaporates faster, and the coffee ring phenomenon will appear.
