Preface: OLED display technology is an OEL display technology over the past decade, the rapid development has made great achievements. A growing number of global manufacturers display their R & D investment, much of the impetus to the industrialization of OLED process. At present, OLED has come on the eve of a large-scale production. It is believed that in the near future OEL display is bound to have a breakthrough.

I, OLED production and development

OLED research have originated from an accidental discovery. In 1979 the night at the Kodak company engaged in research work of Chinese scientists, Dr. Deng Qingyun (Dr.CWTang) in the way home think of all of a sudden forget that there are things in the laboratory, to go back, he found the darkness there is a bright East and West. Dakai Deng found out that it is an experiment in organic light-emitting batteries. This is how going on? OLED research on this year, which Dr. Deng also known as the father of OLED.

In 1987, Kodak's first published the results of their research since then, many of the world's enterprises and research institutions dedicated to the beginning of small molecule OLED devices and related issues, specifically related to the patent literature and the number increases each year to hundreds. In the United States (other than Kodak Company) and the Council of Europe, the vast majority of organic EL research from the early start of 9O. Today, high-efficiency (> 15lm / w) and high stability (150nits for the luminous intensity, working life> 10,000 hours) of organic EL devices have been developed.

Polymer organic EL on research than on small molecule organic EL research, started much later. Until 1990, only by Burroughes and its research partners succeed the first polymer organic EL devices. Since then, for the development of polymer EL technology in the United States and Europe to carry out a great deal of research. It is generally for the team, the polymer material than the small molecule organic materials should be stable, it has become the driving force behind the development of polymer EL.

Currently, OLED products from the laboratory to the market. From 1997 ~ l999 years, OLED displays is the only market in the on-board display, in 2000, the product of a gradual expansion of the scope of application to the phone screen. OLED in mobile phone applications and give a strong impetus to the further development of its technology and application of the rapid expansion of the existing LCD, LED and VFD put forward a strong challenge.

Second, OLED display features and classification

Organic electroluminescent (OrganicElectroluminescentLight) referred to as OEL. It has two branches of technology, is a molecular weight of 500 to 2000 between the small molecule organic light-emitting diode (OrganicLightEmittingDiode) referred to as OLED, or SM-OLED; and the other is in the molecular weight of 10,000 to 100,000 between the polymer (also known as polymerization Material) organic light-emitting diode (PolymerLight-EmittingDiode) or PLED referred to as P-OLED.

OEL display with the active light-emitting, light-emitting more efficient, low-power, light, thin, no restrictions on the merits of perspective, was that the industry is most likely in the next display to occupy the market hegemony of a new generation of display devices . As a brand-new display technology, OLED will inevitably there are still many deficiencies, the material life of the device, such as the yield has to be further studied, the increase in applications also need to be further expanded, and this for future research to explore the provision of a The major space research.

OLED technology over the past decade, the rapid development has made great achievements. As the world's growing number of display manufacturers have invested research and development, much of the impetus to the industrialization of OLED process, making the OLED industry to grow at an alarming rate and has now been reached on the eve of a large-scale production. The person in the industry predicted that 2007 may become a large-scale OLED production of the first year. From 2000 to 2005 OLED panel shipments an average annual growth rate of more than 175 percent, with the future of OLED products gradually to the active and large-size full-color direction, OLED industry will maintain rapid growth. OLED products have been gradually recognized by downstream manufacturers, demand is also increasing significantly. OLED is currently the main applications, including communications products (mobile phone screen deputy), consumer electronics (MP3), and on-board instrumentation and other areas.

Compared with the OLED technology, PLED technology development slightly behind, mainly because of the limited involvement of the manufacturers, technology is relatively mature and less, difficult synthesis of raw materials, equipment manufacturers, such as the reasons for less. Nevertheless, the pace of development is very fast, has been on the market today can be seen with a lower grade of PLED. According to DisplaySearch predicts that by 2008 PLED market share will be quickly increased to 40% of the market OEL.

Third, OLED light-emitting structure and mechanism of brief

OLED display is based on the organic material of a current semiconductor devices. Its typical structure in the ITO glass on the production of dozens of nanometer-thick layer of organic light-emitting materials for light-emitting layer, light-emitting layer above the layer of low work function of metal electrodes. When the voltage electrodes are added, the light-emitting layer to produce light radiation.

The mechanism of light-emitting OLED and the process from the Yin, Yang poles were injected electron and hole, was injected into the electron and hole in the organic layer transmission, and light-emitting layer in the complex so as to stimulate light-emitting molecules have a single layer exciton states, Single-exciton and light-emitting radioactive decay.



For full-color OLED There are three ways:

1, using white light-emitting layer filter increases. This is the easiest to obtain full color display.

2, using red, green, blue organic light-emitting materials, the light-emitting layer for the three-tier structure.

3, using a blue light-emitting organic materials, colors and then convert the material to obtain full color.

Fourth, OLED Preparation

1, OLED Preparation

At present, mainland China, OLED display devices is still in the preparation of the laboratory stage, but has reached the edge of the pilot, so we will focus on the laboratory preparation of OLED technology.

Whether laboratory, pilot or mass production, OLED devices are basically the same process of preparation, the main difference is that the vacuum evaporation device device. General laboratory manual selection of vacuum evaporation equipment for a single sample evaporation in order to facilitate the production of different types of experimental samples; pilot-line general of the use of semi-automatic vacuum evaporation equipment for multi-chip sample evaporation, so that small The switch-volume product; production line in general the use of automatic vacuum evaporation equipment for water sample evaporation (or line with the evaporation process technology) in order to improve the yield, reduce product cost. It is reported that some institutions are trying to use in the production line technology spin-coating process for the production of OLED products.

OLED display, including the preparation: ITO glass cleaning → → lithography and then wash before handling → → vacuum evaporation of organic layer vacuum evaporation → → back electrode vacuum evaporation coating in packaging → → → cutting test module assembly → → Products Aging and test experimental procedures, such as more than 10, several of its key processes of the process as follows.

(1) ITO glass of clean and surface treatment

ITO as a very positive direct impact on the state of the surface of the hole and inject film and the organic layer interface between the state of electronic and organic material of the film. If ITO unclean surface, its surface free energy become smaller, resulting in the evaporation of the above hole transport material together, uneven film.

ITO on the surface of the process: washing detergent wash ethanol → → → acetone cleaning water cleaning, ultrasonic cleaning machines are used for cleaning, washing-per-use cleaning 5 minutes, 5 minutes to stop, were repeated 3 times. Infrared drying oven and then stand-by. The cleaned on the surface of ITO glass still needs to be activated to deal with in order to increase the oxygen content of the ITO layer on the surface and improve the surface of the work function of ITO. Can also be used for the ratio of water: hydrogen peroxide: = 5:1:1 mixture of ammonia, hydrogen peroxide solution to deal with ITO on the surface, so that the surface of ITO surplus to reduce the tin content and increase the proportion of oxygen in order to improve the work function of ITO surface to increase Hole injection risk, OLED devices can increase the brightness of an order of magnitude.

ITO glass before use should be through "UV - ozone" or "plasma" surface treatment, the main purpose is to remove the organic residues on the surface ITO, ITO to the surface oxidation, an increase of the ITO surface work function, improve the smoothness of the surface of ITO. Untreated ITO surface work function of about 4.6 eV, after ultraviolet - ozone, or plasma surface treatment, the work function of ITO surface for more than 5.0 eV, light-emitting efficiency and working life will be improved. ITO glass on the surface must be dealt with in a vacuum dry environment, dealt with the ITO glass can not be placed in the air too long, otherwise it will lose the surface of ITO activity.

(2) ITO of the lithography process

(3) organic thin film vacuum deposition process

OLED devices require a high vacuum chamber in the evaporation of organic multi-layer film, the film has a bearing on the quality of the device and the quality of life. In the high vacuum chamber in place a number of organic materials evaporation of a boat, boat heating evaporation deposition of organic materials and the use of quartz crystal oscillators to control the thickness. ITO glass can be placed in the heat of the rotating sample holder, placed below the metal mask evaporation control board designs.

We are in the vacuum evaporation deposition equipment to carry out the experiment, the experimental results show that the organic material in the general evaporation temperature 170 ℃ ~ 400 ℃ between, ITO substrate samples in the temperature 100 ℃ ~ 150 ℃, the speed of evaporation in a crystal point 10 points, Crystal / s (that is, about 0.1nm ~ 1nm / S), evaporation in the vacuum chamber of 5 × 10-4Pa ~ 3 × 10-4Pa better results when the Deposition.

However, the evaporation of organic materials are still effective usage of materials with low (<10%), the concentration of dopants difficult to precisely control, evaporation rate instability, a vacuum chamber, and so less vulnerable to pollution, leading to sample substrate The coating uniformity can not require the device.

(4) metal electrode vacuum evaporation process

Metal electrodes still conducted in a vacuum evaporation chamber. Metal electrode is commonly used by low work function of active metals, organic material in the film after the completion of the evaporation deposition. Used a metal electrode Mg / Ag, Mg: Ag / Ag, Li / Al, LiF / Al, and so on. For the deposition of metal electrode boat usually molybdenum, tungsten and tantalum, and other materials for use in a different deposition metallic electrodes (mainly to prevent the evaporation of metal and metal boat from a chemical reaction).

Metal electrode materials with the general evaporation of the current heating to that in our vacuum evaporation deposition equipment to carry out the experiment, the experimental results show that the evaporation of the metal electrode materials in the heating current general 70A ~ 100A between the (individual metal to more than 100A) , ITO substrate samples in the temperature around 80 ℃, the rate of evaporation in the crystal 5 points to 50 points, Crystal / s (that is, about 0.5nm ~ 5nm / S), the vacuum evaporation chamber in the 7 × 10-4Pa ~ 5 × 10 -4Pa better results when the Deposition.

(5) Packaging Technology

OLED devices of the organic film and metal thin film of air and water immediately after oxidation, so that the device performance of the rapid drop in pre-packaged and must not contact air and water. Therefore, OLED technology package must be in the water of oxygen, there are inert-gas (such as argon) to carry out in the glove box. Packaging materials, including materials, adhesives and coverage. The use of ultraviolet-curable epoxy adhesive curing agent, using covers materials are sealed glass, sealed in with the installation of desiccant to the residual moisture absorption.

V. Preparation of OLED materials and their role in

OLED preparation of many types of materials can be broadly divided into anode materials, cathode materials, a buffer layer materials, carrier transport materials and light-emitting materials and so on a few major categories.

1, anode materials

OLED's anode materials for the main components of the anode, its work function as much as possible, in order to improve the efficiency into the hole. OLED devices require side of the electrode must be transparent, and therefore often choose work function of the high-transparent material for ITO conductive glass anode. ITO (indium-tin oxide) glass in the 400nm ~ 1000nm wavelength range of more than 80% transmission, but also in the area near UV also has a high transmission.

2, the cathode material

OLED cathode materials for the main components of the cathode used in order to enhance the efficiency of electronic injection, it should choose the lowest possible work function metal materials, as the electronic injection into the hole than larger more difficult. Metal work function of the size of a serious impact on the light-emitting OLED device efficiency and service life, the lower the work function of metal, the easier it will be injected into the electronic, light-emitting efficiency of the higher; In addition, the lower the work function, organic / metal interface barrier more Low, the work of Joule heat generated will be less, the device life will be enhanced.

OLED cathode commonly used form of the following:

(1) single-layer metal cathode. Such as Al, Mg, Ca, and so on, but they are in the air can be easily oxidized, resulting in unstable device, shortening the life, so choose to do alloy cathode or increase the buffer to avoid this problem.

(2) cathode alloy. In order to enhance the efficiency of light-emitting devices, the device can be stable, usually metal alloys as a cathode. In the evaporation of a single metal cathode film, it will form a large number of defects caused by the deterioration of oxidation-resistant; evaporation and alloy cathode, a small amount of metal will give priority to the proliferation of defects in the whole stability of the organic layer is made.

(3) of layered cathode. This is a cathode in the light-emitting layer between the electrode and metal by adding a layer of barrier, such as LiF, CsF, RbF, and so on, and they form a two-Al electrode. Barrier can be substantially improved device performance.

3, buffer layer material

OLED in the hole in the transmission rate is about twice the rate of electronic transmission, in order to prevent the hole transport to the organic / metal interface cathode-ray cause of the quenching, in the preparation of the device when the introduction of a buffer layer CuPc. CuPc as a buffer layer, not only can reduce the ITO / organic layer interface between the barrier, but also can increase the ITO / organic interface bonding, increased access into the hole to check the hole into the HTL layer, so that the electronic and To strike a balance between into the hole.

4, carrier transport materials

OLED device from the hole and into the anode from the cathode can be injected into the electronic relatively balanced into the light-emitting layer, that is, the requirements of the hole and into the e-rate should be the same, it is necessary to choose the right hole and the electronic transmission Materials. In the device, due to the heat transfer materials may cause crystallization of the OLED device performance led to the decay, so we should choose glass transition temperature (Tg) higher as a material transfer materials. Trials are usually chosen as the NPB hole transport layer, and the selection of Alq3 as the electronic transmission of materials.

5, light-emitting materials

Light-emitting OLED materials, device is the most important materials. General light-emitting materials should have high-efficiency light-emitting, preferably with a hole or electronic transmission performance, or both, vacuum evaporation can be made stable and uniform film, their HOMO and LUMO energy should be matched to the corresponding electrode , And other characteristics.

In the small molecule light-emitting materials, Alq3 is used directly as a separate layer of light-emitting materials. There are not separate itself as a light-emitting layer, in another doping can be Luminescent matrix material, such as red dopant DCJTB, green dopant DMQA, Blu-ray doping agents BH1, BD1, and so on. Alq3 can be used as both a light-emitting layer material, but also offering electronic transport layer of organic material of a material.

Six, OLED technology development analysis

OLED's an endless stream of new technologies, development of fast, new technology has greatly promoted the OEL towards industrialization process.

1, the use of laser technology transfer high-resolution imaging OLED

Laser-induced thermal imaging (referred to as LITI) method is to use a donor film, a group of high-precision laser systems and exposure to the completion of a substrate. Laser imaging system by the laser, optical modulator, the calibration of optical components and beam expansion, attenuator, the current account and the f-θ lens scanning components.

LITI described the process as follows: First, the transfer of donor pressure in the matrix, the donor and receptor on the surface to be in close contact. Then, using a laser beam on the donor's imaging template exposure, the results of imaging patterns from the donor contact for the transport layer (light-emitting materials) release and transport layer attached to the receptor on the surface contact. Finally, will be used for stripping body, such exposure in the area of high-resolution streak was the transfer. In order to form a full-color display, using the order of red, green, blue 3-for film.

LITI transfer is a unique advantage of the laser method of addressing high-resolution graphics, for example, transfer of the film is extremely uniform thickness, multi-layered transfer of power and scalability with the large-size glass motherboard, and so on.

Since this is a dry process, so LITI transfer from the transfer-soluble substances. As a result, we are able to put lining the hole transport layer soluble solution and to enhance the performance of OLED. LITI imaging methods have provided excellent thickness uniformity of straight, smooth and uniform imaging stripes. Light-emitting materials through spin-coating, screen coating, or vacuum deposition methods such as coating for the body on film. LITI imaging accuracy than ± 2.5μm, the accuracy of this special technology transfer LITI is a unique advantages. LITI use of technology, access to more than a high-resolution images of 200ppi. Compared with traditional methods of precision sheet mask (the limit for the resolution of 150ppi), this is a significant performance characteristics.

2, using organic and doped films can improve the black cathode of OLED performance

Xerox Canada's Dr. ZoranPopovic study, OLED is not the main reason for the stability of the organic layer from the aging spots. It is due to the aging of the spots, making field devices to reduce the quantum efficiency, resulting electroluminescent light gradually decreased, shortening the life of the device, limited the application of the device in the field.

In order to solve this problem, ZoranPopovic Dr. organic film doped with the use of black cathode combination, which has effectively improved the performance of OLED. The results show that, in order to TPD: rubrene doping agent for the incorporation hole transport layer to extend the life of the device; CuPc to increase the buffer to buffer the material to extend the life of the device; to increase the use of NPB: AlQ3 mixed materials HTM / ETM mixed Layer device to extend the life span.

Xerox's use of black cathode, making OLED structure of the natural light to reduce reflectivity, the device performance can be improved. Based on organic mixed layer of metal cathode, to improve contrast and reduce the growth of black spot.

3, OLED research and development of new products, the situation

⑴ long-life OLED Display

OsramOptoSemiconductorsGmbh the company in January 2006 launched a long-lived 2.7 inches 128 × 64 pixels OLED display graphics, for the 180-degree viewing angle, 2000:1 contrast ratio for. OLED is usually in the service life of about 5000 hours, and this product has reached 55,000 hours. And the LCD screen compared to the same specifications, with the price advantages of its current price of 19.5 U.S. dollars per unit. The product of the power consumption of 0.05 milliwatts of sleep, operating temperature of -30 ℃ ~ 70% ℃.

⑵ polymer OLED

CDT Britain in January 2006 the company announced that its polymer OLED research breakthroughs, they developed a successful 14-inch full-color polymer OLED displays, from amorphous silicon active matrix backplane drive. The display uses ink-jet printing technology to achieve a resolution of 1280 × 768.

⑶ large-size OLED TV

In May 2005, Samsung announced a single-chip OLED panels using materials developed 40-inch WXGA TV and in the same period in the international display at the annual meeting of the SID. The TV's OLED panels from amorphous silicon (a-Si) active matrix (AM) backplane drive with a 1280 × 800 pixel wide-screen format, contrast ratio of 5000:1 and brightness of 600nits, as well as to make OEL panel products TV applications to take a crucial step.

Seven, OEL development issues and the prospects for international

1, facing the development of the subject

A large display screen and TV is the direction of development, OLED to achieve large-scale, the biggest issue is the substrate (Backplane) source. There are many manufacturers started to TFT-LCD substrates for OLED as the substrate, and the actual ship, but a lower yield, only 40%. In theory, low-temperature polysilicon (LTPS) than a silicon (a-Si) is more suitable for OLED as the substrate, in particular for the following three technologies: DepositedPolySi, NonLaserLTPS, NewLaserLTPS.

However, OLED light and LTPS-TFT, is bound to consider the current OLED deposition of the machine's status, there are currently No. 1 on behalf of the 3.5-generation machine, the 4th generation is still more than a limit, do not have the machine供应. Therefore, OLED Substrate LTPS through the large-scale will continue to be a big issue.

At present, the production of PLED basically using spin-coating and ink-jet printing method, but spin-coating on the resolution of certain restrictions on the limit, and ink-jet printing equipment and expensive, a limited number of suppliers, manufacturers of organic material is not , To a certain extent, impeded the development process of PLED. Therefore, to enhance the synthesis of organic materials and production, promote the use of ink-jet printing of PLED technology is a major development issue.

2, the development prospects

OLED is a very promising flat panel display technology, it has a very good display performance, especially since the light-emitting, simple structure, ultra-thin, fast response, wide viewing angle, low-power and can be flexible display characteristics, Hailed as "a fantastic display", together with its investment in production facilities is far smaller than the TFT-LCD, has been favored by the major display manufacturers have become the display technology in the field of third-generation display the main force.

Conclusion: At present, OLED is in large-scale production of Eve, it is believed that with further research, new technologies are emerging, OLED display is bound to have a breakthrough.


Reference link: http://www.17led.com/LEDdisplay/2008-04/70.html