WO2015139480A1 - Inkjet-printing organic electroluminescent display and method for manufacturing same - Google Patents

Abstract

Provided are an inkjet-printing organic electroluminescent display and a method for manufacturing the same. The display structure comprises a transparent substrate, a patterned transparent anode layer, a hole injection layer, a hole transport layer, a light-emitting layer, and a metal cathode that are sequentially stacked. The light-emitting layer comprises a material mixed by dissolvable organic small molecules and polymer. The dissolvable organic small molecules and the polymer are mixed and used as a printing solution to manufacture a light-emitting layer. A phase crystallization phenomenon that an organic small molecule solution is dried to form a film is inhibited. Under a common effect of a high boiling point solvent, a process that a solution is naturally dried to form a film in a sub-pixel can be effectively controlled, so as to obtain a uniform film of a light-emitting layer, thereby effectively improving performance of an inkjet-printing display screen.

Description

Ink jet printing organic electroluminescent display and preparation method thereof

Technical field

 The invention relates to the technical field of preparing an organic electroluminescent display by an inkjet printing technology, in particular to an inkjet printing organic electroluminescent display and a preparation method thereof.

Background technique

 After nearly two decades of development, all-solid-state organic electroluminescent display (OLED) characterized by thinness, low consumption, high response, and high resolution is displayed in liquid crystal ( LCD) is the mainstream of the flat panel display field, and its potential market prospects are optimistic about the industry. At present, OLED products entering the market are small molecule OLEDs prepared by vacuum evaporation technology. . This technology has high product cost due to its complicated preparation process and high equipment cost, and is increasingly mature in LCD technology. It is difficult to win in the competition. Solution-processed wet-processed thin-film technology has attracted widespread attention in the industry due to its low cost equipment, simple preparation process, and obvious low-cost advantages. Preparation of OLED in wet process In the technology, the full-color display screen technology is prepared by spraying the desired functional materials on the desired pattern substrate through the printing nozzle, which not only improves the material utilization rate, but also has simple preparation process, low equipment cost and large size. The high-resolution and even flexible display area is considered to be the most promising in the field of flat panel display and can drive polymer displays ( PLED) A low-cost thin film patterning preparation technology industrialized.

 In order to occupy this new market with potential low cost, South Korea's Samsung Electronics, LG Many display companies, such as Sony in Japan and DuPont in the United States, are actively studying the transfer of flat panel display preparation technology from evaporation technology to inkjet printing technology. Since 1999, Epson Corporation of Japan (Seiko Epson) ) Cooperated with Cambridge Display Technology (CDT) for the first time in the International Flat Panel Display Conference (SID) after the inkjet printing full color PLED display, inkjet printing PLED Display prototype products continue to emerge, and displays have made great strides in terms of product size, pixel resolution, and illuminance purity. However, so far, inkjet printing PLEDs exhibited at home and abroad The displays are just prototypes and have not yet entered the market for commercialization.

 Inkjet printing PLED It is difficult to form mature products into the market mainly due to various factors such as the performance of polymer materials to be improved and the inkjet printing preparation process of polymer solutions are not mature enough and stable. It is well known that the purification of polymer materials is difficult, and the luminous efficiency and lifetime of materials are far less than those of small molecular materials. For example, polymer blue materials are highly susceptible to photo-oxidation and other intrinsic factors leading to inkjet printing. PLED The display life is not effectively broken. In inkjet printing to prepare full-color displays, the quality of the functional layer film in the sub-pixel is a key factor affecting device performance. The mass of the solution injected into the pixel pit determines the thickness of the film in the sub-pixel, and the process of controlling the drying of the solution into a film is the key to forming a uniform high-performance device without the pinhole film. However, the polymer solution generally has a large viscosity, and the liquid column has a long rupture length, and it is difficult to form a droplet of a satellite droplet to obtain a stable droplet. This not only affects the precise positioning of the droplets, but also limits the resolution and the production of large-size products. At the same time, it also affects the uniformity of the film in the pixel, which results in low product yield, high production cost, and masks inkjet. The low cost advantage of printing technology.

 The development of soluble small molecule luminescent materials has opened up a new way for inkjet printing to prepare OLED displays. Seiko Epson of Japan The company, Fujimi and DuPont Display have developed soluble small molecule luminescent materials, which have made breakthroughs in luminous efficiency, brightness and longevity [ Kim M. N., Cho I. S., Park B., et al. Highly Efficient Ink-jet Printed Small Molecular Phosphorescent OLED. SID 09 Digest, 2009: 1734-1736; Mackenzie D., Shin J. H., Zhang J., et al. Printed, Doped Flexible P-OLED Displays and Lighting. SID 09 Digest, 2009: 20-24 ] . However, since the small molecule solution generally has a small viscosity and a small surface tension, the droplets ejected by the ink jet printing are easily dried in the pixel pit to form a film, which is difficult to obtain a uniform film, and inkjet printing of these high-performance small molecules. The performance of the display for material preparation is not satisfactory.

Summary of the invention

It is an object of the present invention to provide an ink jet printed organic electroluminescent display in view of the problems and difficulties of the prior art. By adjusting the ratio of materials, the interaction between organic small molecules and polymer molecules is utilized to improve the short-chain pinholes of the polymer, and the fracture length of the solution column can be appropriately shortened to improve the printability of the solution. It is easy to obtain stable droplets during inkjet printing. At the same time, by regulating the aggregation state of molecules in the film formation process, the crystallization and phase separation of organic small molecules during film formation are effectively suppressed, thereby preparing uniform high quality functions. Layer film. In addition, the invention can also blend high-performance organic small molecule and polymer hybrid electroluminescent display screen by blending soluble small molecule with polymer solution and making full use of the high efficiency and long life of the small molecule material.

 The above display has a structure consisting of a transparent substrate (Substrate), a patterned transparent anode layer (ITO) and polyimide ( PI) pixel edge, hole injection layer (HIL), hole transport layer (HTL), light-emitting layer (EML), metal cathode (Cathode) (see Figure 1).

 In the above display, the transparent substrate is glass (Glass) Hard materials such as quartz, or flexible materials such as plastic film and paper fiber.

In the above display, the transparent electrode layer is a metal or metal oxide layer, and the specific composition includes aluminum metal, gold, silver, or metal oxide. The best implementation material may be indium tin oxide (ITO), tin oxide (SnO). ).

In the above display, the metal cathode layer is a metal lithium, boron, sodium, calcium, magnesium, barium, strontium, potassium, aluminum, gold, silver, or a metal oxide, or an alloy of two or more of them.

In the above display, the hole injecting layer is a film composed of a conjugated or non-conjugated high conductance system having carbon or silicon as a main chain; the most preferred material may be polyaniline, polythiophene, polypyrrole, or polyparaphenylene acetylene. film.

 Above display The hole transport layer may be an aromatic triamine compound or a carbazole compound having a low ionization energy and a film of an organometallic complex, and the best implementation material may be a polyvinylcarbazole film.

In the above display, the luminescent layer comprises a blue luminescent layer film, a red luminescent layer film and a green luminescent layer film; the blue luminescent layer film may be a polymer film, or may be two or three organic polymers, organic a small molecule blending film; the blue light emitting layer film, the red light emitting layer film and the green light emitting layer film are sprayed by an inkjet printing technology comprising a soluble organic small molecule and a polymer blending solution, and the red light emitting material can be It is an organic small molecule dendritic fluorescent compound G0 (structure shown in Figure 2) and polyparaphenylene vinylene derivative (MEH-PPV, structure shown in Figure 2) blended in proportion (mass ratio 10:1), or it may be small organic The complex of the molecular dendritic fluorescent compound G0 and ruthenium phosphorescent small molecule Ir(piq) ₂ acac (structure shown in Figure 2) and MEH-PPV blended in proportion (mass ratio 10:1:2), or may be organic small The complex of the molecular dendritic fluorescent compound G0 and ruthenium phosphorescent small molecule Ir(piq) ₂ acac and polystyrene (PS, structure shown in Figure 2) are blended in proportion (mass ratio 100:10:1); green light-emitting material It may be an organic small molecule dendritic fluorescent compound G0 and a polyparaphenylene acetylene derivative (P-PPV, structure shown in Figure 2) blended in proportion (mass ratio 10:1), or may be an organic small molecule dendritic fluorescent compound The complex of G0 and ruthenium is a small phosphorescent molecule Ir(mppy) ₃ (see Figure 2 for structure) and P-PPV is blended in proportion (mass ratio 10:1:2), or it may be an organic small molecule dendritic fluorescent compound G0. The phosphorescent small molecule Ir(mppy) ₃ and polystyrene (PS) are blended with ruthenium in proportion (mass ratio: 100:10:1).

The above display, the blue, red and green luminescent materials, the solvent thereof may be a single aromatic solvent such as toluene, xylene or chlorobenzene or a high boiling point ether thereof (eg, isophthalic acid, dimethyl Blended composite solvent such as anisole).

In the above display, the blue light-emitting layer film may be a film prepared by a wet technique such as a spin coating technique, a slit coating, a curtain coating, a screen printing, a pulling technique, or an inkjet printing technique.

 In the above display, the blue, red, and green light-emitting layer films may be films that are color-patterned by inkjet printing technology.

 A method for preparing an inkjet printed organic electroluminescent display comprises the following steps:

 (1) using a patterned transparent conductive glass as a substrate, and performing surface modification after cleaning; the patterned transparent conductive glass is composed of The transparent substrate is composed of a patterned transparent anode layer;

 (2) spin-coating to prepare a hole injection layer, spin coating a hole transport layer, and then spin coating blue soluble organic small molecules and polymers The material is blended to obtain a blue light-emitting layer film, and after removing the residual solvent, the red and green soluble organic small molecule and the polymer blend material are sprayed to obtain a red light-emitting layer film and a green light-emitting layer film, and finally evaporated. Metal cathode, finally paste the glass encapsulant with epoxy resin and UV-curing to obtain an inkjet printed organic electroluminescent display, the hole injection layer has a thickness of 40-80 nm; and the hole transport layer has a thickness of 20-40nm.

Advantages and Effects of the Invention: The present invention proposes to blend a soluble organic small molecule with a polymer to form an inkjet printing solution, which shortens the liquid column fracture length and improves the function of the small chain between the organic small molecule and the polymer. The long chain of polymer is easy to block the pinhole, thereby regulating the stability of the inkjet printing droplets, so that the droplets can be accurately injected into the corresponding sub-pixel pits; at the same time, the organic small molecule solution is dried and crystallized during the film formation process. The phase is also effectively inhibited by the interference of the long-chain polymer, and is blended by high-low-boiling solvent, which can effectively adjust the film drying process to obtain a uniform film, high-efficiency and long-life organic small molecule material for inkjet printing. The performance of organic small molecule polymer hybrid display screens has been significantly improved. Therefore, the method for ink-jet printing organic small molecule polymer hybrid display screen proposed by the invention may provide an effective way to enable the inkjet printing full color display screen to enter the market to realize productization.

DRAWINGS

 Figure 1 is a schematic diagram of the structure of an OLED full color display prepared by inkjet printing.

 Figure 2 is a structural formula of the material used in the present invention.

 Figure 3 is a photograph of an organic small molecule polymer flat panel display prepared by inkjet printing.

detailed description

 Example 1

The ink-jet printing display structure shown in Figure 1 was used, and the patterned ITO transparent conductive glass was used as the substrate. The surface contaminants were washed with deionized water, dried by high-pressure nitrogen gas, and irradiated with ultraviolet light. Modified, then spin-coated on a 100-stage clean bench to prepare PEDOT:PSS (polyaniline derivative) hole injection layer, thickness 40-80nm, heated at 200 degrees Celsius for 10 minutes under nitrogen atmosphere, after cooling it in nitrogen The hole transport layer was spin-coated with PVK (polyvinylcarbazole, structure shown in Figure 2) in a glove box. The solvent was chlorobenzene and the film thickness was about 40 nm. Then, a blue light-emitting layer film is spray-coated, and the buffer layer material is selected from a dendritic compound G0 and a blue-light polyfluorene PFO (see FIG. 2). The mass ratio is G0:PFO=3:1. The solvent is p -xylene and the film thickness is 60-80 nm. Since the PVK layer has a very low solubility in p -xylene, it is not dissolved or damaged when the blue buffer layer is spin-coated. Then, it was heated at 140 ° C for 30 minutes in a nitrogen atmosphere to remove residual solvent. After cooling, the red and green organic small molecule polymer blend was inkjet printed in air. The ratio of the red luminescent solution was G0: Ir(piq) ₂ Acac:MEH-PPV=10:1:2 (mass ratio), green luminescent solution, so the ratio is G0: Ir(mppy) ₃ :P-PPV=10:1:2 (mass ratio), the solvent used for the phosphorescent material is Chlorobenzene, the rest is p -xylene, and then into the vacuum evaporation chamber. When the vacuum is less than 3×10 ^-4 Pa, the Ba/Al cathode is vapor-deposited. Finally, the glass encapsulant is pasted with epoxy resin and UV-cured. . Figure 3 is a photo of an organic small molecule polymer flat panel display prepared by inkjet printing. Using a blending solution of small organic molecules and a polymer, an inkjet printing process is used to realize the preparation of an organic small molecule polymer by a solution method. Screen.

 Example 2

Example 1 was repeated, and the ratio of the inkjet printed red luminescent solution was G0: Ir(piq) ₂ acac:PS=100:10:1 (mass ratio), and the ratio of the green luminescent solution was G0: Ir(mppy) ₃ : PS=100:10:1 (mass ratio), other conditions are unchanged.

 Example 3

 Repeat Example 1 for inkjet printing. The red luminescent solution used is G0: MEH-PPV=10:1 (mass ratio) The green luminescent solution is G0: P-PPV=10:1 (mass ratio), and other conditions are unchanged.

 Example 4

 Example 1 was repeated, and the blue buffer layer was selected from dendrimer G0 and blue light polyfluorene PFO and polystyrene PS. G0: PFO: PS = 3:1: 0.03 (mass ratio) Blend solution, other conditions are unchanged.

 Example 5

Example 4 was repeated, and the ratio of the inkjet printed red luminescent solution was G0: Ir(piq) ₂ acac:PS=100:10:1 (mass ratio), and the ratio of the green luminescent solution was G0: Ir(mppy) ₃ : PS=100:10:1 (mass ratio), other conditions are unchanged.

 Example 6

 Repeat Example 4, the red luminescent solution used for inkjet printing is G0: MEH-PPV=10:1 (mass ratio) The green luminescent solution is G0: P-PPV=10:1 (mass ratio), and other conditions are unchanged.

 Example 7

 Example 1 was repeated. Inkjet printing The solvent used for the red-green luminescent solution was added with 3,4-dimethylanisole in a volume ratio of 1:1. DMA), other conditions are unchanged.

 Example 8

 Example 2, inkjet printing The solvent used for the red-green luminescent solution was added with 3,4-dimethylanisole in a volume ratio of 1:1. DMA), other conditions are unchanged.

 Example 9

 Example 3, inkjet printing The solvent used for the red-green luminescent solution was added with 3,4-dimethylanisole in a volume ratio of 1:1. DMA), other conditions are unchanged.

 Example 10

 Example 4, inkjet printing The solvent used for the red-green luminescent solution was added with 3,4-dimethylanisole in a volume ratio of 1:1. DMA), other conditions are unchanged.

 Example 11

 Example 5, inkjet printing The solvent used for the red-green luminescent solution was added with 3,4-dimethylanisole in a volume ratio of 1:1. DMA), other conditions are unchanged.

 Example 12

 Example 6 was repeated, and the solvent used for inkjet printing of the red-green luminescent solution was added with 3,4-dimethylanisole (DMA) at a volume ratio of 1:1. ), other conditions remain unchanged.

Claims (7)

1. An inkjet printed organic electroluminescent display, characterized in that The display structure comprises a transparent substrate, a patterned transparent anode layer, a hole injection layer, a hole transport layer, a light-emitting layer and a gold cathode, which are sequentially stacked, and the light-emitting layer comprises a soluble organic small molecule and a polymer blend. material.
2. An ink-jet printing organic electroluminescent display according to claim 1, wherein the light-emitting layer comprises a blue light-emitting layer film, a red light-emitting layer film, and a green light-emitting layer film; and the blue light-emitting layer film The red light-emitting layer film and the green light-emitting layer film are sprayed by an inkjet printing technique comprising a soluble organic small molecule and a polymer blend solution.
3. An ink-jet printing organic electroluminescent display according to claim 2, wherein the solvent of the blending solution is a single solvent of an aromatic hydrocarbon such as toluene, xylene or chlorobenzene or a total of the same as the high-boiling ether Mixed compound solvent; the ethers include m-xylylene ether or dimethyl anisole.
4. A method of fabricating an ink-jet printing organic electroluminescent display according to claim 1, comprising the steps of:

   (1) using a patterned transparent conductive glass as a substrate, and performing surface modification after cleaning; the patterned transparent conductive glass is composed of a transparent substrate and a patterned transparent anode layer;

   (2) spin-coating to prepare a hole injecting layer, spin-coating the hole transporting layer, and then spin-coating the blue soluble organic small molecule and the polymer blending material to obtain a blue light-emitting layer film, after removing the residual solvent, Spraying and printing red and green soluble organic small molecules and polymer blending materials, that is, obtaining a red light emitting layer film and a green light emitting layer film, finally evaporating a metal cathode, and finally bonding the glass encapsulating sheet with epoxy resin and performing ultraviolet curing to obtain An inkjet printed organic electroluminescent display.
5. The method of fabricating an ink-jet printing organic electroluminescent display according to claim 4, wherein the hole injecting layer has a thickness of 40 to 80 nm; and the hole transporting layer has a thickness of 20 to 40 nm.
6. The method of fabricating an ink-jet printing organic electroluminescent display according to claim 4, wherein the transparent substrate comprises a hard material or a flexible material in the step (1); the hard material comprises glass or Quartz; the flexible material comprises a plastic film or a paper fiber; the patterned transparent anode layer is a metal layer or a metal oxide layer.
7. The method for preparing an ink-jet printing organic electroluminescent display according to claim 4, wherein the organic small molecule in the step (2) comprises Ir(mppy)3, Ir(piq)2acac or G0; The polymer comprises PFO, P-PPV or MEH-PPV; the mass ratio of the small molecule to the polymer is: blue luminescent material by mass ratio G0: PFO = 3:1, red luminescent material by mass ratio G0:

   Ir(piq) ₂ acac:MEH-PPV=10:1:2 , green luminescent material by mass ratio G0: Ir(mppy) ₃ :P-PPV=10:1:2; the metal cathode includes metal, metal alloy Or a metal oxide, wherein the metal comprises lithium, boron, sodium, calcium, magnesium, lanthanum, cerium, potassium, aluminum, gold or silver; the hole injecting layer is conjugated or non-conjugated with carbon or silicon as a main chain A film composed of a high conductivity system; the hole transport layer is an aromatic triamine compound or a carbazole compound having a low ionization energy and an organic metal complex film.