The “big five” class of materials that make up OLED
Introduction: there are many kinds of OLED materials, including anode materials, cathode materials, buffer layer materials, carrier transport materials and luminous materials.
1. Anode materials
The anode material of OLED is mainly used as the anode of the device, and its work function is required to be as high as possible to improve the injection efficiency of the holes. OLED devices require one side of the electrode to be transparent, so transparent ITO conductive glass with high power function is usually used as the anode. ITO (indium tin oxide) glass has a transmittance of over 80% in the wavelength range of 400nm ~ 1000nm, and also has a high transmittance in the near-ultraviolet region.
ITO (indium tin oxide) manufacturing process editor
(1) electrochemical diffusion process: doped superconducting films can be obtained by electrochemical diffusion method on glass. In the electrochemical treatment device, glass contacts with the molten metal or compound. Under the action of certain electric field, the ions in the molten metal or compound will diffuse to the glass surface, and the monovalent alkali metal ions in the glass will dissociate and spread to the cathode surface in equal amounts, so that the chemical composition of the glass surface will change. Performance changes accordingly.
(2) high temperature spraying and plasma spraying process: this technology is to heat the powder metal or non-metal, inorganic materials to the melting or not melting state, and further heating to make it atomized, forming high temperature high-speed flame flow to the glass substrate to be sprayed. In this way, YBaGUOx coating can be prepared on the substrate first and become superconducting material after heat treatment.
2. Cathode materials
The cathode material of OLED is mainly used as the cathode of the device. In order to improve the efficiency of electron injection, the metal material with the lowest work function should be selected, because electron injection is more difficult than hole injection. The size of the metal work function seriously affects the luminous efficiency and service life of OLED devices. The lower the metal work function is, the easier the electron injection will be, and the higher the luminous efficiency will be. In addition, the lower the work function, the lower the organic/metal interface barrier, the less joule heat generated in the operation, and the greater the life of the device.
OLED cathode usually adopts the following types:
(1) single metal cathode. Such as Al, Mg, Ca, etc., but they are easy to be oxidized in the air, resulting in device instability and shortened service life, so choose alloy as the cathode or increase the buffer layer to avoid this problem.
(2) alloy cathode. In order to improve the luminescence efficiency of devices and obtain stable devices, metal alloys are usually used as cathodes. In the evaporation of a single metal cathode film, a large number of defects will be formed, resulting in poor oxidation resistance. When the alloy cathode is steamed, a small amount of metal will first diffuse into the defect, so that the whole organic layer becomes very stable.
(3) layered cathode. This cathode is a barrier layer between the luminescent layer and the metal electrode, such as LiF, CsF, RbF, etc., which forms a double electrode with Al. The barrier layer can greatly improve the performance of the device.
It is composed of a very thin insulating material such as LiF, Li2O, MgO, Al2O3 and an outer layer of thick Al. Its electron injection performance is higher than that of pure Al electrode, and higher luminous efficiency and better i-v characteristic curve can be obtained.
3. Buffer layer material
In OLED, the hole transmission rate is about twice that of the electron transmission rate. In order to prevent light quenching caused by the hole transmission to the organic/metal cathode interface, the buffer layer CuPc should be introduced in the device preparation.
Phthalein cyanide copper; Phthalocyanine copper; Phthalocyanine blue; Copper phthalocyanine. Phthalocyanine; Organic synthesis,
As a buffer layer, CuPc can not only reduce the interface barrier between ITO/ organic layer, but also increase the adhesion degree of ITO/ organic interface, increase the contact of hole injection, inhibit the injection of hole into HTL layer, and balance the injection of electron and hole.
4, carrier transmission materials
OLED devices require that the electron energy injected from the anode and cathode should be balanced in the luminescent layer. In other words, the injection rate of the holes and electrons should be basically the same. Therefore, it is necessary to select appropriate holes and electron transmission materials. In the working process of the device, due to the heat may cause crystallization of the transmission material, resulting in the attenuation of OLED device performance, so we should choose the material with higher glass transition temperature (Tg) as the transmission material. NPB is usually selected as the hole transport layer and Alq3 as the electron transport material.
5. Luminous materials
Luminous materials are the most important materials in OLED devices. Generally, luminescent materials should have high luminescence efficiency, preferably with electron or hole transmission performance or both, stable and uniform film can be made after vacuum evaporation, and their HOMO and LUMO energy should match with the corresponding electrode.
In the small molecule luminescent materials, Alq3 is directly used as the luminescent layer material. Moreover, some of them cannot be used as the luminescent layer by themselves, but can only emit light when doped in another matrix material, such as red dopant DCJTB, green dopant DMQA, blue dopant BH1, BD1, etc. Alq3 is an organic material that can be used as both luminescent layer material and electron transport layer material.
HTM is required to have high thermal stability, form a small potential barrier with the anode, and can form a pinhole free film by vacuum evaporation. The most commonly used HTM are aromatic polyamines, mainly derivatives of trianiline.
TPD: N, N ‘-bis (3-methyphenyl) -n, N’ -diphenyl-1, 1 ‘-diphenyl-4, 4’ -diamine
The vitrification temperature of TPD is only about 60 degrees, which is not stable
NPD: N, N ‘-bis (1-nyl) -n, N’ -diphenyl-1, 1 ‘-diphenyl-4, 4’ -diamine
NPB is currently the commercially available hole transport material
ETM generally adopts aromatic compounds with large conjugated planes, such as 8-hydroxyquinoline aluminum (AlQ), 1,2,4 Triazoles (1, 2, 4-triazoles, TAZ),PBD, Beq2, DPVBi, etc., which are also good luminescent materials.
According to the molecular structure of compounds, organic luminescent materials are generally divided into two categories:
(1) high polymer, molecular weight 10,000-100,000, usually conductive conjugated polymer or semiconductor conjugated polymer, can be used as a film by the method of spin coating, simple to produce, low cost, but its purity is not easy to improve, in durability, brightness and color than small molecule organic compounds.
(2) small molecular organic compounds, with molecular weight of 500-2000, can be formed into films by vacuum evaporation, which can be divided into two categories according to molecular structure:
Organic small molecule compounds and complexes.
1) red light material
Mainly include: rhodanine dyes, DCM, DCT, DCJT, DCJTB, DCJTI and TPBD, etc
(2) green light material
Some of them are: Coumarin6(Kodak’s first product), quinacridone (QA), Coronene, naphthalimide.
(3) blue light materials
The main ones are: n-aromatic benzimidazoles; 1, 2, 4-triazole derivative (TAZ) (also ETM material); OXD- (p-nme2), a derivative of 1, 3-4-oxadiazole (high brightness); 1000 CD/m2); Double stilbene class (Distyrylarylene); BPVBi(brightness up to 6000Cd/m2).
2) complex luminescent materials
Metal complexes, which are between organic and inorganic materials, have both high fluorescence quantum efficiency of organic materials and high stability of inorganic materials.
Commonly used metal ions are; Be2+ Zn2+ Al3+ Ca3+ In3+ Tb3+ Eu3+ Gd3+, etc
The main complexes are: 8-hydroxyquinoline, 10-hydroxybenzoquinoline, Schiff base, -hydroxybenzothiazole (oxazole) and hydroxyl flavonoids
Global inventory of major OLED material suppliers:
After several years of technological development, OLED has become a new focus of the industry. With the maturity of OLED production technology, the disadvantages restricting its development are gradually supplemented, the advantages are gradually highlighted, and the demand rises rapidly. At present, the market scale of OLED light-emitting materials is growing rapidly, while OLED raw material field has high barriers, good competition pattern and strong profitability. Moreover, due to high cost, it has a great impact on the profitability of panel factories. “International optoelectronics and display” makes a special inventory of global OLED material suppliers, the details are as follows:
Merck is a global leader in high-performance materials. High-performance materials have four business units: liquid crystal materials, effect materials, semiconductor materials and OLED materials.
Merck is a major supplier of liquid crystal materials to the LCD industry, with a market share of more than 50 percent in TFT liquid crystal displays, and has advanced its OLED business. Currently, Merck has a 27% market share in HTL materials and a 21% market share in phosphorescent green materials. Merck has produced new OLED materials based on evaporation and solution applications. At the same time, the company also teamed up with epson, hoping to solve the production bottleneck of large panel OLED through the new inkjet printable OLED technology.
Japan is booming
The light-emitting OLED business basically includes the upstream business of materials, including hole transport layer (HTL), hole injection layer (HIL), electronic transport layer (ETL) and organic luminescence layer (OLL). In the field of HTL, the market share of exo has reached 22%, and the market share of phosphorescent blue materials has reached 69%.
As downstream manufacturer LG Display expands OLED panel production, the company plans to increase South Korea’s annual production capacity to five tonnes in the near term, two-and-a-half times its current capacity.
Doosan, South Korea
Doosan electronic materials co., LTD is the holding company of doosan group, mainly developing and producing copper clad laminate (CCL) and OLED materials. OLED material business mainly produces and supplies organic light-emitting materials of various types of OLED organic thin film layers (hole injection layer, hole transmission layer, luminescent layer and electronic transmission layer), and its downstream is mainly samsung display company. Doosan currently has 20 per cent of the HTL market.
At the end of 2015, doosan signed a memorandum of understanding (mou) with migo to cooperate in OLED materials, including the mutual use of OLED material-related patents and planned manufacturing cooperation.
The company’s two main businesses are semiconductors and OLED materials. In 2015, DS hi-metal split off its OLED materials business to set up DS Neolux to focus on OLED business. Its products basically cover the upstream of OLED material, as well as red substrate and circular polarizer. HTL and HIL materials are mainly supplied to samsung Display. Currently, the company’s market share in HTL is 31%. In terms of luminescent materials, according to the research data of UBI, due to the change of samsung’s supply chain, the business scale of deshan company experienced a slight decline in 2015, which was about $40 million.
According to the patent jointly filed by the company with samsung, the hole transport materials used in the HTL materials supplied by the company have high HOMO value and excellent charge balance, so they have the characteristics of high luminous rate of components, low driving voltage, high heat resistance and high color purity.
Nippon iron chemistry
Nippon steel chemical is a chemical manufacturer of Nippon steel sumitomo metal group, whose business areas include coal chemical, petrochemicals, epoxy resins and functional materials. The company’s OLED business is mainly in phosphorescent EL LumiAce material, whose quadruple energy efficiency blue phosphorescent is the world’s first industrialized technology.
In 2006, the company cooperated with UDC to develop a phosphorescent green material with a service life of 60,000 hours, and its market share is 21%. Currently, it is still the main procurement target of this material for samsung.
Soil conservation valley chemistry
The main products of baotugu chemical are basic chemicals, fine chemicals and functional resins. The company has been engaged in OLED business since 2001, mainly producing HTL and HIL materials, and also developing ETL and other materials. The HTL material is a triarylamine derivative, which can improve the injection/transmission performance of holes and electrons. It currently includes two products, el-301 and el-022t, and is the main procurement target of LG Display.
Japan JNC corporation
JNC co., ltd. is a company established by Chisso after its reorganization in 2011. Its business mainly involves functional materials such as liquid crystal and electronics, energy, environment, processed products such as fiber and resin, and chemicals.
JNC is one of the three international suppliers of TFT mixed liquid crystal materials. At present, its OLED material products are mainly small molecule blue light emitting materials and electronic transmission materials. After increasing production in 2013, the current monthly production capacity is about 100KG, and the downstream manufacturers are LG Display.
The company operates globally in five business segments: agricultural sciences, consumer solutions, infrastructure solutions, performance materials and chemicals, and performance plastics. Consumer solutions business: global consumer health, dow automotive systems and electronic materials. The OLED materials business is mainly attributed to electronic materials, and the subdivision of OLED light-emitting materials leads the world in sales.
UDC is a leader in the field of organic light-emitting diodes, OLED technology and materials research, with an experienced team of management and scientific advisors and government support.
UDC Universal Display, which dominates the global OLED light-emitting materials market, saw its revenue drop 11 percent in 2015 compared with 2014. Despite the decline in revenue, it maintained its top position in the market. In particular, the company has a dopant materials division, in which UDC holds an 82% stake. The division holds phosphor based patents and is responsible for supplying phosphor red and green luminescent materials to samsung and LG displays.
Business scope: 1. Basic materials; 2. 2. Information electronic materials; 3. Display materials; 4. Battery materials; 5. Batteries. The company attaches great importance to the material field dominated by OLED display materials. As a business field to strengthen high value-added independent technical capability and cultivate new growth businesses in the future, it is about to grow into a new generation of growth power for LG chem.
The electronic materials business of the company produces and supplies all kinds of display materials such as polarizer, 3DFPR, photosensitive materials, printed circuit board materials, ITO films and related materials.
Samsung is mainly in OLED steaming materials and TFE(thin film packaging). In terms of evaporation materials, samsung SDI and Novaled, as professional enterprises of organic material and component technology, lead the development of OLED evaporation materials field and continuously research and develop three core technologies, including: 1. Organic chemistry: high performance