Compared with liquid crystal display (LCD), organic light-emitting diode (OLED) screens are lighter, shorter response time and larger viewing angle, and have obvious advantages in mobile terminals, wearable devices, virtual reality / augmented reality (VR/AR) devices and other fields. Market demand for flexible display is an important thrust for OLED to replace LCD. Samsung Group (Samsung), LG group (referred to as "LG") and other mainstream manufacturers have been shutting down LCD production line, and expand the OLED production line, OLED gradually replaced the liquid crystal display (LCD) trend has been very obvious, flexible OLED screen is expected to become mainstream display in 2 years.
I. General Situation of major countries and regions
At present, the demand for global LCD has stagnated, and the LCD industry has begun to face the crisis of overcapacity. South Korea's main panel companies have shifted their focus to OLED technology to gain market share through the first mover advantage in the OLED field and to expand the share of the OLED panel market.OLED panel enterprises are mainly concentrated in Korea, Japan and Taiwan.
1. Korea
Korea has always shown that the industry is in the leading position of the world. The South Korean government listed OLED as one of the next generation of key projects, plans to reduce taxes and reduce tariffs, and provide various policy support for enterprises, and further enhance the leading position of Korean OLED industry in the global market. Samsung enterprises and LG led enterprises in the OLED technology and industry advantages are very obvious.
Samsung focuses on the active matrix organic light emitting diode (AMOLED) technology for mobile devices. It now occupies 95% of the global market share.Samsung's small and medium-sized OLED has accumulated a lot in patents, technology and production equipment. Among them, the small size OLED technology has been leading the industry for 2~3 years. In 2015, Samsung monitors put in an additional OLED production line of $3 billion 600 million, which mainly provides OLED panels for small and medium-sized consumer electronics products such as mobile phones and tablet computers. Samsung's large size OLED panel has only one 8.5 generation production line, providing 120 thousand OLED panels per year. The products are mainly for mass production and technical experiments of Samsung AMOLED TV and OLED panel. As Samsung has been using the "low temperature polysilicon Technology (LTPS) backplane +RGB OLED" technology route, resulting in large size OLED panel has been difficult to break through the technical bottleneck, low product yield, high cost, has suspended the OLED TV panel expansion plan.
LG has been the main force and has dominated the OLED TV panel market. LG has 2 8.5 generation OLED production lines: E3 and E4, each using different processes, mainly producing 55 inch and 65 inch OLED panels. Among them, the E3 production line was built earlier, and each piece of glass substrate can produce 2 65 inch panels. Each E4 substrate can produce 3 65 inch panels. In November 2015, more than 9 generation OLED panel production lines were built. At present, the OLED panel yield of LG has exceeded 80%, which is equivalent to that of LCD. In 2016, the OLED sales volume was about 1 million 500 thousand.
2. Japan
Japan's display industry has been declining in recent years, and has been fully surpassed by South Korea in terms of core panel capacity and market share. However, it still has advantages in the field of patent accumulation and materials and equipment in the upstream industry chain, and its overall strength in the display area is still ahead of the rest of the world.
SONY (Sony) Company (SONY) is the earliest OLED TV manufacturer. It has a large number of patents and mature technologies in the small and medium-sized OLED panels. Matsushita has the semiconductor display industry chain operation experience and technology, and has a deep accumulation in the OLED panel technology layout. Japan Tokki group and UlvacInc are the world's leading manufacturers of OLED deposition equipment. With these bases, the Japanese government began to integrate the industry's main attack on the OLED panel. In 2014, SONY, Panasonic (Panasonic) Electrical Industry Co., Japan Innovation Network Corporation (INCJ) and Japan display company (JDI) jointly established JOLED Inc. company, which mainly produces small and medium size OLED panels, providing 10~30 inch OLED panels for notebook computers, tablet computers and electronic billboards. JOLED integrated SONY, Panasonic and other enterprises in the membrane technology, flexible panel technology, oxide semiconductor technology, JDI panel related technology. In terms of production, JOLED adopted Panasonic's "printed" mass production technology and began trial production in the second half of 2016.
3. Taiwan area
China's Taiwan area Au Optronics Co group (Au Optronics Co group) and friends of Au Optronics Co (referred to as "optoelectronics") panel shipments in the global market share. Among them, the global shipments of optoelectronic notebooks and TV panels ranked second, and the second of the total shipments of the optoelectronic computer display panel were 2, accounting for 30% of the total global market. With the global LCD panel enterprises turning to OLED technology, Taiwan display panel enterprises have begun to develop OLED panels, but the capacity is far lower than that of Korean and Japanese enterprises. At present, only group photoelectricity in 2017 OLED panel trial production. The group is expanding a 6 generation LTPS production line, producing about 23000 substrates per month, and producing LCD and AMOLED panels. In March 2017, Hon Hai Group acquired SHARP, further accelerating the progress of Taiwan's OLED panel business.
Two. Research progress of OLED materials and technology
1. device fabrication technology
Chang et al. Of Taiwan National Chiao Tung University [2] made use of spin coating and scraping methods to prepare green light OLED. The hole injection layer of the device is poly (3,4- ethylene two oxy thiophene) - polystyrene sulfonic acid (PEDOT:PSS), and the hole transport layer is 1,2,4,5- four (three fluoromethyl) benzene (TFB). The 2 layers are prepared by spin coating process. The main luminescent materials are gamma chloropropyl methyl two methoxy silane (TBD), PBD and polyvinyl carbazole (PVK), the luminescent guest material is Ir (mppy) 3, and the electron transport layer is 1,3,5- three (1- phenyl -1H- benzimidazole -2-) benzene (TPBi), the 2 layers are prepared by scraping coating method. They point out that the polyethylene glycol / aluminum (PEG/Al) hybrid electrode device has the best performance and the efficiency can reach 25cd/A. Compared with the OLED with single Al clicks, the starting voltage has also been reduced.
Serpil T. et al., Germany, made flexible SMOLED by spin coating the mixture of intrinsic SM and SM and UHMW-PS (the ratio of 20:3 and 20:4) as the luminescent layer. By comparing the results, it is found that when the mixing ratio of SM and UHMW-PS is 20:3, the device achieves the best performance and the luminous efficiency is 7.7cd/A.
Choi K.J. and others of Korea University of science and Technology (Korea University of technology and education) have studied the effect of [4] on the device performance by separately coating SM and PVK, and mixed coating SM and PVK, and evaporating SM as HTL in 4 cases. The device area is 43mm * 29mm, and they have the highest luminescence efficiency of SM and PVK as the hole transport layer, reaching 28.7lm/W. This gas assisted solution technology is still under study. It is foreseeable that the application of evaporation and coating technology will be important.
Inkjet printing technology is the best technology to prepare OLED at present. It has the advantages of fast device preparation and 100% utilization of raw materials. At present, it has partially realized industrialization and received the attention of big factories such as Samsung, LG and JOLED. Michiel J.J. and Coenen of Holst center in Holland made use of halogenated solvent solvent to make ink. 3 functional layers were printed, and 2 colors of OLED were prepared to achieve very good uniformity and brightness. This process is also suitable for the production of large area flexible OLED by R2R process.
2.OLED material
Liang et al [6] used SUZUKI coupling reaction to synthesize SAFBI and SBFBI. This is the 2 new benzimidazole additive [spiro fluorene] derivative, and their optical and photochemical properties have been studied. The device gives bright blue light, and the device exhibits better performance. At high brightness, the fading and color changes are very small. The current efficiency of the device is 1.96cd/A, CIE chroma coordinates (0.15, 0.10), the luminous efficiency is 1.34lm/WSBFBI, and the SAFBI unit is the same. According to the electroluminescence results of the device, it is possible to deduce the composition of the core of the 2 benzimidazole units, which can change the luminescence from sky blue to dark blue. Their experiments gave the design and preparation method of dark blue emitting materials based on spiro Fluorene Derivatives. According to the literature, this is the world's first non doped deep blue emitting device based on spiro [benzopene] derivatives.
Most aromatic amine materials can be electrically conductive through electrons and holes. Therefore, aromatic amine materials have also become an important blue light emitting material. Denneval et al. Studied the photoelectric properties of a series of pyrimidine chromophores. Their peak absorption accuracy for the compounds is 18NM and the peak value of luminescence wavelength is + 39nm.The optical properties of related dyes can be tested by their methods, and the optimized chromophores can be found quickly. At the same time, this method is used to study the chromophores of other materials.
Ouyang et al. [8] pointed out that the use of charge and excitons in materials is an effective way to obtain OLED. According to their research results, distorted intramolecular charge transfer (TICT state), intramolecular charge transfer (ICT state) and localized excited state (LE state) have been proved to increase the single exciton generation probability in the fluorescence emission of benzimidazole and three aniline derivatives, thereby enhancing the fluorescence emission. They systematically studied the synthesis, optical properties and electroluminescent properties of the material under special TICT and ICT States, and reduced the efficiency in high brightness mode very little, and achieved stable blue light output.
3. flexible OLED
[9], Kim Woohyun of Korea advanced technology research institute, has produced the world's first OLED on soft fibers, which is suitable for wearable devices. Due to the ductility of polyurethane (PU) and poly (vinyl alcohol) (PVA) layers, the bending stiffness of bare fabrics is only slightly reduced, which is used as a planarization layer by simple manufacturing processes including lamination and spin coating.Therefore, many mechanical properties of bare fabric substrates are retained in flat fabric substrates. They designed the non inverted top emitting OLED by considering the optical microcavity effect, and prepared the device by thermal evaporation. After 1000 bending experiments with a radius of curvature of 5mm, the device still shows a reliable green light emission angle of 70 degrees. In their other research, flexible OLED was also prepared by dip coating (Dip-Coating), which also achieved better device performance.
The optical fiber shape PLEC is manufactured by the full solution and can enlarge the actual application. The design consists of a coaxial structure including a modified metal wire cathode and a conductive directional carbon nanotube sheet anode. The electroluminescent polymer layer is sandwiched between them. Fiber shape offers unique and promising advantages.
At present, the research and development of OLED devices are mainly in the direction of large size, flexibility and transparency. OLED has gradually replaced LCD, becoming a new display device with low consumption and environmental protection. At present, OLED technology has been commercialized in the field of small size display, and has been gradually expanding to the market of large-size display. The OLED structure is simple and the manufacturing cost is less than LCD theoretically. But at present, the price is high and the price is high. At the same time, for flexible and wearable OLED devices, flexible substrates, flexible TFT, ITO instead of anode and flexible packaging technology still need to be breakthroughs. All these factors limit the promotion of OLED in a large area. However, OLED manufacturing technology is constantly being mature, production capacity is constantly improving, manufacturing costs have also been greatly reduced, and the conditions for large-scale application of OLED have basically matured. As the upstream manufacturing industry of intelligent products, OLED has attracted much attention, and the market potential is very large. China's enterprises must grasp the OLED industry and occupy a favorable position in the new generation of display technology.
