Current status of research and development of organic electroluminescent products

As a new generation of flat panel display devices, organic electroluminescent devices (OLED) have broad application prospects in mobile phones, PDAs, digital cameras, car displays, laptops, wall-mounted TVs and military fields. They are a new type of flat panel display device that will replace liquid crystal displays (LCDs) in the future. For this reason, OLED has been a hot topic in the research and development of new materials and display technologies in recent years, and its industrialization momentum is very rapid. At present, domestic and foreign research on OLED mainly focuses on the research of luminescent materials, the production of devices and product development. This article introduces the development of OLED products and looks forward to the commercial prospects of OLED.

Classification of OLED OLED can be divided into two types according to the light-emitting material: small molecule OLED and polymer OLED (also known as PLED). The difference between small molecule OLED and polymer OLED is mainly reflected in the different preparation processes of the devices: small molecule devices mainly use vacuum thermal evaporation process, while polymer devices use spin coating or spray printing process. The main small molecule material manufacturers are: Eastman Kodak, Idemitsu Kosan, Toyo INK Manufacturing, Mitsubishi Chemical, etc.; the main polymer material manufacturers are: CDT, Covion, Dow Chemical, Sumitomo Chemical, etc. At present, there are more than 1,400 patents related to OLED in the world, of which there are three most basic patents. The basic patents of small molecule OLED are owned by Kodak in the United States, and the patents of polymer OLED are owned by CDT (Cambridge Display Technology) in the United Kingdom and Uniax in the United States.

OLED driving methods can be divided into active driving and passive driving. Passive driving applies voltage to the corresponding rows and columns to make current flow through the selected pixels. It has a simple structure and low price, and is suitable for low-power, small-screen display devices, such as character displays. Active driving OLED display screens equip each pixel with a constant current source, which enables it to meet the requirements of high resolution and high information content required for video images, but the price is more expensive.

Overview of OLED product development Among foreign OLED products, most of those investing in small-molecule OLED products are Japanese and Taiwanese companies, while those investing in polymer OLED products are mostly European and American companies. According to statistics, there are about 85 companies in the world that have invested in research and development, of which more than 60 companies mainly use small-molecule OLED material systems, and only about 25 companies use polymer OLED material systems.

The commercialization process of small molecule OLED is faster than that of high molecule OLED, but it is mainly passively driven. In 1996, Pioneer took the lead in launching 256×64 monochrome products, and in 1997, Idemitsu Kosan also released the first full-color 320×240 product. After that, Pioneer and other manufacturers successively released a variety of monochrome and multi-color products. For a long time, Pioneer has been the leading manufacturer of passively driven small molecules.

In terms of active drive small molecules, Eastman Kodak is the leader. Eastman Kodak currently holds most of the small molecule material patents, and through cooperation with Sanyo, it has applied TFT technology to launch active drive small molecule OLED products. However, in terms of commercialization progress, active drive small molecules are still significantly behind the development of passive drive small molecule OLED.

At present, the polymer OLED is led by CDT, which is famous for its active drive technology. Other manufacturers include Seiko-Epson and Philips, which have received technology transfer from CDT. Philips is the main manufacturer of passive drive polymer OLED. In the past, the manufacturing process of polymer OLED used spin coating technology. In order to achieve a more full-color effect, CDT cooperated with Seiko-Epson to produce it with inkjet technology. Although samples were published in 1999, polymer OLED still has many problems in material selection, control of light-emitting component life, and uneven film thickness and difficulty in inkjet, which cannot be effectively solved.

Since inkjet technology requires about 5 to 6 processes, it is easy to produce ink dripping and color confusion, affecting the luminous efficiency and life. The inkjet head used may also be clogged during the manufacturing process, affecting the yield rate. In addition, the length of the polymer conjugated frame varies, the spectrum is wide, and it is not as fine as small molecule OLED. Moreover, since all polymer processes must be completed in a clean room, the maintenance cost of the clean room and machinery and equipment will be higher than that of small molecule OLED. Therefore, there are still many difficulties in applying it in downstream products on a large scale.

However, inkjet technology also has many advantages, such as easy to achieve a larger screen area, higher resolution, can be designed by computer aided design, no need for masks, no waste of organic materials, fewer production processes, and reduced equipment investment and space requirements. Therefore, many companies are still engaged in research in this area.

The following is the progress made by several major international companies in the research, development and industrialization of OLED products in recent years and their representative products: In 2000, Philips and Taiwan's Ritec and other companies launched OLED displays for mobile phone displays.

Motorola has begun selling cell phones with OLED displays.

DuPont of the United States invested 15 million US dollars in the United States UNIAX company to build a 6-inch polymer color luminescence test line.

Philips invested 50 million US dollars to build a 14-inch test line; Siemens also established a test line of a certain scale in Malaysia.

In 2001, Sony launched an OLED display for televisions with a 13-inch screen, 800×600 pixels, 16.7 million display colors, and each pixel driven by 4 TFTs.

eMagin introduces the first full-color small molecule OLED microdisplay with a resolution of 600×3×852 and 16M colors.

Toshiba America Electronics announced the first full-color OLED prototype using polymer as the light emitter, 2.85 inches, 26,000 colors, 64 grayscale levels, and LTPS TFT drive.

In 2002, Samsung launched 15-inch full-color OLED PC and laptop samples, Toshiba Matsushita Display Technology Co., Ltd. developed a 17-inch LTPS TFT-driven OLED panel with a resolution of up to XGA (1280×768), and Pioneer also claimed that a 20-inch full-color OLED panel was ready.

Recently, Kodak announced that it will launch the world's first OLED display screen in the Chinese market, the EasyShare LS633 digital camera, which has a 2.2-inch OLED display screen.

At present, more than 40 universities and research institutes in my country are involved in OLED research, such as Jilin University, Shanghai University, Tsinghua University, Huazhong University of Science and Technology, Nankai University, etc. Many large enterprise groups, such as China Aerospace Science and Industry Corporation in the field of national defense and military industry, Shaanxi Rainbow, Shanxi Nanfeng, Shanghai Broadcasting and Television Electronics and other professional group companies in the field of civilian products have actively invested in and participated in the research and development of OLED. The first full-color OLED display screen in China was also successfully developed by Beijing Visionox and Tsinghua University recently, indicating that my country's level in OLED display technology has entered the ranks of international leaders.

Market Analysis and Forecast Currently, the application development of OLED by various manufacturers is mainly based on monochrome and multi-color displays, and the main targets are mobile phones, handheld video games, audio panels and PDA markets. In the future, it will develop in two directions: one is to focus on text and digital display, and seize the low-end display market, including the mobile phone and audio panel market; the other direction is small full-color display, the main application market is digital cameras, video cameras and video phones and other application products, and then try to enter the large-size full-color display market, focusing on notebook computers, monitors and TV products. At present, most of the OLED displays launched by various manufacturers are still prototypes, and there is still a lot of room for improvement in the future to achieve commercialization.

According to the Taiwan Industrial Technology Research Institute, as the technology of full-color displays improves, 2-4 inch displays will enter the market, and the market volume is expected to increase from 100,000 in 1999 to 7 million in 2005. 2-4 inch displays will become the largest application market for full-color displays. By 2005, large-sized wall-mounted color TVs and rollable color TVs may be produced. New portable devices such as electronic books and newspapers using OLED will also appear in the near future.

According to the forecast of Stanford Resources, the OLED market will reach 70 million US dollars in 2005 and 700 million US dollars in 2007. If the technology can achieve more significant breakthroughs, the future growth will be more impressive. DisplaySearch also predicts that the market volume of OLED passive drive display will reach 40 million pieces in 2003, and its main application products will be mobile phones, followed by game consoles; the market demand will reach 120 million pieces in 2005, and the main application scope will still be mobile phones. Active drive display is expected to grow to 50 million pieces in 2005, increasing exponentially every year.

In short, the emergence and development of OLED, as a competitor and possible substitute for LCD, provides a rare opportunity for people to develop flat-panel displays for mobile communication products, automotive and airborne products, and even computers and televisions.