OLED large area coating technology

  1. Inkjet printing technology

Inkjet printing technology can repeatedly eject spherical droplets with a diameter of 25~100μm (10pl~0.5nl), the rate of a single droplet is 0~4000/s, and the frequency of continuous droplets is as high as 1MHz. Piezojet technology is widely used in jet dispensing of materials such as biomedical reagents, liquid metals, and optical polymers [12-17]. Figure 1 is a schematic diagram of inkjet printing. The era of miniaturized electronics/computers has begun by reducing costs and increasing the functionality of electronic and photonic devices.

The main advantages of inkjet printing are: ① no mask; ② very flexible; ③ almost no waste; ④ fine lines; ⑤ suitable for rigid boards and flexible substrates.

High-precision laboratory inkjet systems with multiple print heads can accurately print various layers of materials. Other advantages of inkjet printing are:

1) Multi-material layers and multiple print heads;

2) Very precise printing technology with low material consumption (cost saving);

3) Software/GUI with good control over all printing processes and parameters.
The advantages that the inkjet integrated in the glove box brings to the user are:

1) The work/process is completed in a controlled environment; external influences such as oxygen can be avoided;

2) For special applications, for example, the humidity control system can allow printing processing at controlled humidity 0%~60% (without oxygen);

3) To reduce particles on the substrate, the glove box is usually a class 100 clean room system.
In 2009, Seiko Epson of Japan Seiko Co., Ltd. (printer manufacturer) introduced a new inkjet printing technology for OLED, suitable for large-size panels. This is a polymer-based OLED made by printing technology and sealed by a metal plate. The company launched 37in (and above) inkjet printed OLED TVs in 2012 [9].

  1. Spin coating process

In recent years, low manufacturing cost and easy-to-implement process solutions during OLED fabrication have attracted increasing attention [120-126]. Recently, Merck reported that the gap between the dissolution and evaporation processes of the phosphorescent green light-emitting material has been almost completely bridged during spin coating. Spin coaters are equipment used to produce thin film materials on flat substrates. The solution is placed on the substrate manually or by a dispensing system, and then the liquid is spread out by centrifugal force of high-speed rotation, as shown in Figure 2. During rotation, the substrate is held in place by vacuum suction. The spin coater is integrated into the glove box so users can dispense liquid materials without contaminating moisture- and oxygen-sensitive materials. Spin coating is a wet process, therefore, a certain amount of solvent is required. In order to avoid solvent evaporation and contamination of the air in the glove box, the exhaust system of the spin coater must be connected to an air purification system.

  1. Roll-to-roll printing technology

The cost-effective roll-to-roll technology is a necessary technology when producing large-area OLED lighting devices. GE has successfully used roll-to-roll printing technology (in the style of newspaper printing) to make OLEDs. This technology is a state-of-the-art fabrication technique for the fabrication of high-performance, high-efficiency, and ultra-low-cost OLEDs [口7-133]. The technology can be arbitrarily applied to printing energy-saving lighting systems of various sizes.