JP2005353502A - Manufacturing method of organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance in-plane uniformity of affinity between an electrode acting as a grounding and an organic substance layer formed on it, and to prevent local and abnormal film deposition or uneven film deposition on the boundary of these. <P>SOLUTION: This manufacturing method of an organic electroluminescent element is to form at least an organic compound thin film containing a light emitting region on a first electrode, and to form a second electrode on the organic compound thin film. Before forming the organic compound thin film, surface treatment is applied to the surface of the first electrode by an organic solvent, and the organic compound thin film, a hole injection layer for example, is deposited by vacuum thin film forming technology with an organic solvent molecule remaining on the surface of the electrode. The organic solvent is, for example, at least one kind selected from cyclohexanone, p-xylene, o-xylene, m-xylene, tetrahydrofuran, toluene, ethylbenzene, cyclohexane, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a self-luminous organic electroluminescent element, and particularly relates to an improvement in a manufacturing technique of an organic electroluminescent element having a large area and used for illumination or the like.

  An organic electroluminescence element (hereinafter referred to as an organic EL element) is a self-luminous planar light source, has advantages such as a high response speed and no viewing angle dependency, and an increase in pixel size. Since it is relatively easy to make it flexible, etc., it is expected to be applied to a wide range of fields such as lighting devices and displays.

  As a configuration of the organic EL element, for example, a transparent electrode (anode) made of indium tin oxide (ITO) is formed on a transparent glass substrate, and a hole injection layer, a hole transport layer, a light emitting layer, A structure in which an electron transport layer, an electron injection layer, a cathode, and the like are formed by a vacuum deposition method or the like is known. In the organic EL element having such a configuration, when a DC voltage is applied between the transparent electrode as the anode and the cathode, holes injected from the transparent electrode through the hole injection layer are transferred to the hole transport layer. On the other hand, electrons injected from the cathode through the electron injection layer move to the light emitting layer through the electron transport layer, and recombination of these electron-hole pairs occurs in the light emitting layer. As a result, light having a predetermined wavelength is generated and observed from the transparent glass substrate side.

  By the way, in the production of this type of organic EL device, an organic compound thin film (hole injection layer, hole transport layer or light emitting layer, electron transport layer, electron injection layer, etc.) formed on the transparent electrode is uniformly formed. It is important to film. For example, if dirt or the like adheres to the surface of the transparent electrode on which these organic compound thin films are formed, it may cause defects in the organic compound thin film, for example, the hole injection layer. There is a risk of causing (part)).

Therefore, conventionally, prior to the formation of the organic compound thin film, the substrate and the transparent electrode are washed in advance to suppress contamination due to adhesion of the dirt (for example, Patent Document 1 and Patent Document 2). Etc.). For example, in Patent Document 1, for the purpose of surely preventing contamination of electrodes on the surface of a substrate, a cleaning chamber for cleaning the substrate, and a plasma provided in the cleaning chamber and in a cylindrical plasma generator are provided. And an organic EL element manufacturing apparatus including a plasma cleaning apparatus that generates a substrate and cleans a substrate therein. Further, in Patent Document 2, after the surface of the transparent conductive film of the transparent conductive substrate is ultrasonically cleaned in this order with a surfactant, water and an organic solvent, at least one of acid cleaning and plasma treatment is further performed. A method for producing an organic electroluminescence device is disclosed in which the contact angle of water on the surface of the transparent conductive film is less than 25 °, whereby the initial emission luminance is high and the emission luminance is disclosed. In addition, it is said that an organic electroluminescence device excellent in light emission life and stability can be produced.
Japanese Patent Laid-Open No. 10-255972 JP 7-220873 A

  However, although cleaning such as the plasma treatment can remove stains such as organic substances adhering to the surface of the transparent electrode, it is difficult to modify the surface of the transparent electrode itself. For example, the surface of the transparent electrode has an affinity for an organic compound thin film. Due to variations, there is a problem that it is difficult to form a uniform organic compound thin film thereon.

  When an organic substance is vapor-deposited on a transparent electrode subjected to wet cleaning, dry cleaning, or both, first, the organic substance to be deposited forms a weak electric double layer at the unit molecular layer level. At this time, since the surface of the transparent electrode is distributed with crystal structure variations, crystal orientation variations, and the like formed during film formation, local non-uniformity of charges is inherent. On the surface of the transparent electrode that has only been subjected to the wet cleaning or the dry cleaning, the local electric charge non-uniformity becomes apparent during the vacuum deposition of the organic substance, and the electric double layer formed on the surface is remarkably localized. It becomes disordered and causes local defects in the formed layer (for example, a hole injection layer formed of a low molecular amorphous material).

  This local defect in the hole injection layer or the like causes a so-called dark spot or light spot when the organic EL element emits light. In addition, as long as the organic EL element emits light by energization, the defect is a dark spot or light spot that gradually expands a defect that causes excessive current to flow locally or does not flow current locally. Is likely to be a causative factor in the growth, resulting in the growth of defects to a size that can be visually confirmed.

  The rate of occurrence of local defects as described above is not constant because it varies depending on the film forming method, film forming conditions, and the like of the formed transparent electrode. However, unlike an organic EL display having a pixel size of about 0.5 μm × 1.0 μm, the size of one pixel is 10 mm × 10 mm or more, and the area ratio is more than 1 million times that of the organic EL display. In the organic EL element, the probability of occurrence of a defect due to defective film formation is remarkably increased, and the above problem is remarkably revealed. In other words, even if a particularly noticeable defect is not observed when the light emitting area is small, as the light emitting area expands, the probability that an unfamiliar portion with an organic substance exists on the transparent electrode surface increases. The bonding property of the hole injection layer is deteriorated, and the light emission characteristics tend to be remarkably deteriorated. This is because the wet cleaning and the dry cleaning cannot eliminate the surface shape and surface potential distribution of the transparent electrode, and are affected by, for example, vacuum deposition of the hole injection layer.

  The present invention has been proposed in view of such a conventional situation, and an object of the present invention is to provide an electrode serving as a base such as a transparent electrode and an organic material layer (for example, a low molecular amorphous material) formed thereon. Improve the in-plane uniformity of affinity between layers with different physical properties, such as a hole injection layer, and prevent local abnormal or non-uniform film formation at these interfaces, It is to provide a method for producing an organic electroluminescence device capable of suppressing various light emission defects.

  The present inventors have made various studies over a long period of time to achieve the above-mentioned object. As a result, the inventors have found that it is effective to have organic solvent molecules on the electrode surface. The present invention has been completed on the basis of such knowledge, and an organic electroluminescence element in which an organic compound thin film including at least a light emitting region is formed on a first electrode, and a second electrode is formed on the organic compound thin film. The surface of the first electrode is surface-treated with an organic solvent before the organic compound thin film is formed, and the organic solvent molecules remain on the surface of the first electrode. The organic compound thin film is formed by, for example, a vacuum thin film forming technique.

  The function of the organic solvent molecules remaining on the surface of the first electrode by the surface treatment with the organic solvent is not necessarily clear, and details of the mechanism are unknown. However, the present inventors presume that this organic solvent molecule plays a role as a buffer material and prevents local abnormal film formation or non-uniform film formation on the surface of the first electrode. . For example, due to the surface shape of the first electrode and the distribution of the surface potential, the organic solvent molecules adhere to a portion where the adsorbing power (affinity) for the organic substance is higher than others. And when an organic compound thin film is vacuum-deposited, it adheres to the surface of a 1st electrode in the form which replaces with an organic solvent molecule | numerator, and formation of the nucleus by a hole injection material adhering locally is eased. As a result, it is considered that the formation of nuclei on the first electrode and the film growth around the nuclei are suppressed, and the film growth is performed uniformly.

  In any case, prior to forming the organic compound thin film on the first electrode, the surface of the first electrode is surface-treated with an organic solvent, and the organic solvent molecules remain on the surface of the first electrode. A compound thin film (when the organic compound thin film is composed of a plurality of organic layers, an organic layer in contact with the first electrode among the plurality of organic layers. For example, a hole injection layer) is formed by a vacuum thin film formation technique or the like. By forming the film, the in-plane uniformity of the affinity between the first electrode surface and the organic compound thin film formed thereon is improved, and the bonding property between the first electrode and the organic compound thin film is improved over the entire interface. It is made uniform with. As a result, the light emission luminance distribution unevenness is eliminated, and a laminated structure without light emission defects is reliably formed.

  According to the method of manufacturing an organic electroluminescence element of the present invention, local abnormal film formation when an organic material layer (for example, a hole injection layer made of a low molecular amorphous material) is formed on a first electrode serving as a base. Alternatively, non-uniform film formation can be prevented, and local light-emitting defects on the light-emitting surface of the manufactured organic electroluminescence element can be suppressed.

  Hereinafter, a method for producing an organic EL element to which the present invention is applied will be described in detail with reference to the drawings.

The present invention is particularly applicable to the manufacture of an organic EL element having a large area such as monochromatic light emission (for example, white light emission) and a light emission area exceeding 10 mm × 10 mm (= 100 mm ² ), such as an organic EL element for illumination. Is preferred. This is because in a large-area organic EL element, the probability of occurrence of a defect due to defective film formation is remarkably increased, a local light-emitting defect on the light-emitting surface is likely to occur, and the effect of the present invention is remarkable. Therefore, in the following embodiments, a description will be given assuming a method for manufacturing a large-area organic EL element for illumination or the like.

  The organic EL element to be manufactured in the manufacturing method of this embodiment is formed by sequentially laminating a transparent electrode 2, an organic compound thin film 3, and a cathode 4 functioning as an anode on a substrate 1, as shown in FIG. Thus, the element portion is configured.

  In addition to functioning as a support for supporting the element portion, the substrate 1 also functions as a barrier layer that prevents moisture, oxygen, and the like from entering the element portion. Although the constituent material of this board | substrate 1 is not specifically limited, For example, when it is a bottom emission type organic EL element, since light emission is taken out through the board | substrate 1, it is preferable that it is a transparent material. Therefore, for example, glass or plastic can be used. Glass is a preferable material because it is excellent in barrier properties such as moisture and oxygen. When plastic is used, the barrier property may be insufficient. In that case, it is preferable to form a barrier layer on the surface.

  An organic compound thin film 3 is formed on the transparent electrode 2, and as a configuration, it is sufficient that the light emitting layer is provided at a minimum. For example, the hole injection layer 5, the hole transport layer 6, the light emission A five-layer structure including the layer 7, the electron transport layer 8, and the electron injection layer 9 can be formed.

  As a material constituting each layer, any known organic EL element can be used and is not particularly limited. For example, the material of the hole injection layer 5 may be, for example, 4,4 ′, 4 ″ -tris [N- (1-naphthyl) -N-phenylamino] -triphenylamine (TNATA) or TDATA. Examples include arylamines, phthalocyanines such as copper phthalocyanine, Lewis acid-doped organic layers, etc. Examples of the material of the hole transport layer 6 include arylamines such as TPD, spiro TPD, NPD, and TPAC. Can be mentioned.

Examples of the material for the light emitting layer 7 include triarylamine derivatives, stilbene derivatives, polyarylenes, aromatic condensed polycyclic compounds, aromatic heterocyclic compounds, aromatic heterocyclic condensed compounds, and metal complex compounds. Alternatively, an aluminum complex (Alq ₃ ), a beryllium complex (Bebq ₂ ), or the like as a host material and a dopant dye doped thereto may be used. In this case, examples of the doping dye include perylene, Co-6, quinacridone (Qd), rubrene, and DCM.

  Examples of the material for the electron transport layer 8 include aluminum complexes, oxadiazoles, triazoles, and phenanthrolines. Examples of the material for the electron injection layer 9 include alkali metals such as lithium, lithium fluoride, lithium oxide, lithium complexes, and alkali metal-doped organic materials.

  The cathode 4 stacked on the organic compound thin film 3 is made of, for example, a metal material such as aluminum, or an alloy material such as an aluminum-lithium alloy or a magnesium-silver alloy. The cathode 4 is formed by depositing these metal materials and alloy materials by a vacuum thin film forming technique such as sputtering or vapor deposition.

  In order to manufacture the organic EL element having the above configuration, first, a substrate 1 having a transparent electrode 2 formed on the surface as shown in FIG. 2 is prepared. The substrate 1 is a glass substrate, for example, and the transparent electrode 2 is formed by depositing an inorganic transparent conductive material such as indium tin oxide (ITO) by vacuum vapor deposition or sputtering, and patterning it into a predetermined pattern by photolithography technology or the like. Form.

  The substrate 1 on which the transparent substrate 2 is formed is previously subjected to a cleaning process in a substrate cleaning process as necessary. In the substrate cleaning process, for example, after performing ultrasonic cleaning using a cleaning agent, a process of cleaning several times with ultrapure water is performed. Then, after washing with trichlorethylene, acetone, isopropyl alcohol, and ultrapure water, nitrogen blow drying is performed. After the substrate is baked to remove moisture, the substrate is further irradiated with ultraviolet-ozone to decompose and remove organic substances such as an organic solvent remaining on the surface, and then transferred to a processing chamber for vacuum deposition. The decomposition and removal of the organic matter is not limited to the ultraviolet-ozone irradiation but may be performed by, for example, plasma cleaning.

  Next, in the processing chamber, as shown in FIG. 3, the organic solvent 12 is dropped on the transparent electrode 2 using the coating apparatus 11 in the atmospheric pressure state, and the surface is surface-treated. At this time, the organic solvent 12 to be used is preferably not very polar and has a solubility parameter different from that of a low molecular compound (for example, a hole injection material or a hole transport material) formed on the transparent electrode 2. . Specific examples include at least one selected from cyclohexanenone, p-xylene, o-xylene, m-xylene, tetrahydrofuran, toluene, ethylbenzene, cyclohexane, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether. These can also be used as a mixed solution.

  As the surface treatment method of the transparent electrode 2 using the organic solvent 12, the organic solvent 12 may be applied to the surface of the transparent electrode 2 by a thin film forming method such as a spin coating method, a spray method, or a casting method, or a printing method. Examples of printing methods include letterpress printing, intaglio printing, offset printing, lithographic printing, letterpress reversal offset printing, screen printing, gravure printing, and ink jet methods.

  Alternatively, the surface treatment with the organic solvent 12 can be performed by exposing to a solvent vapor. In this case, for example, as shown in FIG. 4, the substrate 1 with the transparent electrode 2 is installed in the upper part of the processing chamber 13 so that the transparent electrode 2 is on the lower side, and the container containing the organic solvent 12 in the lower part. 14 is placed and heated by, for example, a hot plate 15. Thus, the inside of the processing chamber 13 is made an organic solvent atmosphere made of a gaseous organic solvent, and the surface of the transparent electrode 2 is exposed to the organic solvent atmosphere while keeping the concentration of the gaseous organic solvent in the processing chamber 13 constant. In the case of this method, the processing with the organic solvent 12 can be performed using the chamber of the vacuum vapor deposition machine, the processing chamber required in the case of coating or the like can be omitted, the apparatus configuration is simplified, and the productivity is improved. There is a merit that it can be improved.

  By performing the surface treatment with the organic solvent 12 by these methods, a thin layer of the organic solvent 12 is formed on the surface of the transparent electrode 2 as shown in FIG. The organic solvent 12 is not necessarily formed as a layer on the surface of the transparent electrode 2, and the organic solvent molecules are adsorbed only on the specifically strongly adsorbed portion of the surface of the transparent electrode 2. It is only necessary that the organic solvent molecules remain on the surface of 2.

  Here, after the surface of the transparent electrode 2 is surface-treated with the organic solvent 12, the entire substrate 1 on which the transparent electrode 2 is formed is heated before the low-molecular compound is deposited on the surface of the transparent electrode 2, You may make it improve the wettability of.

  As heating conditions in this case, for example, the heating temperature is preferably 40 ° C to 80 ° C. When the heating temperature is less than 40 ° C., it is difficult to effectively heat the entire substrate 1 including the surface of the transparent electrode 2, and it is difficult to improve the wettability of the surface of the transparent electrode 2. On the other hand, when the heating temperature exceeds 80 ° C., the entire substrate 1 is overheated, and the wettability tends to deteriorate due to excessive evaporation of the organic solvent. The heating time is preferably at least 30 seconds or more for uniform heating of the entire substrate 1. As the heating means, a hot plate, heated air, heated steam, or the like can be used.

  Alternatively, in the surface treatment of the transparent electrode 2 with the organic solvent 12, the organic solvent itself may be heated and used to obtain the same action. In this case, considering the boiling point of the organic solvent 12, the heating temperature is preferably 80 ° C. or lower.

  After the surface of the transparent electrode 2 is surface-treated with the organic solvent 12 as described above, a low molecular compound (here, a hole injection material) is vacuumed, for example, with the organic solvent molecules attached and remaining on the surface of the transparent electrode 2. The hole injection layer 5 is formed by vapor deposition. Vacuum deposition of the hole injection material may be performed by controlling the deposition conditions in a vacuum state in a vacuum deposition machine chamber.

  After the formation of the hole injection layer 5, the hole transport layer 6, the light emitting layer 7, the electron transport layer 8, and the electron injection layer (buffer layer) 9 are formed by the vacuum deposition method. A cathode 4 to be an electrode is formed. After forming each of these layers, patterning is performed to a predetermined size to form an organic EL element portion as shown in FIG. The hole injection layer 5 is not vacuum-deposited but spin-coated in solution, and then the substrate 1 is baked. Thereafter, the hole-transporting layer 6, light-emitting layer 7, electron-transporting layer 8, electron The injection layer 9 and the cathode 4 may be formed.

  Finally, as shown in FIG. 7, a cap structure 16 is placed on the cathode 4 and the periphery is sealed with, for example, an epoxy resin 17 to complete an organic EL element.

  In the manufacturing method described above, the uniformity of the film formation of the hole injection layer 6 formed on the transparent electrode 2 can be improved, the defects at the time of film formation can be suppressed, and a large light-emitting surface can be formed with high productivity. The organic EL flat illumination etc. which have can be produced. That is, when the hole injection layer 6 as the organic material layer is formed on the transparent electrode 2 as the first electrode, the organic material for uniformizing and improving the affinity for the organic substance on the surface of the transparent electrode 2 Since the surface treatment with the solvent is performed, the film forming property of the low molecular weight amorphous material constituting the hole injection layer 6 can be improved. As a result, the connectivity between the layers (hole injection layer 5 to cathode 4) formed thereon is improved, and local defects are suppressed. As a result, the film quality is improved, and further, the device is further improved. Suppression of short-circuiting, generation of dark spots, improvement of luminance half-life, suppression of uneven luminance of light emission, and the like are realized.

  As described above, in the manufacturing method according to the present embodiment, the organic compound thin film 3, particularly the hole injection layer 5, the hole transport layer 6, the light emitting layer 7, the electron transport layer 8, and the electrons formed thereon. Since the film formability of each layer of the injection layer 9 and the cathode 4 is improved by arranging the base, and the occurrence of local defects is suppressed, it becomes possible to provide a thin and large organic EL lighting panel, Its industrial value is great.

  In this example, in order to confirm the effect of the present invention, an organic EL element was actually manufactured, and the light emission defects and the light emission luminance were examined.

Preparation of organic EL element The glass substrate on which the ITO transparent electrode was patterned was wet washed and then irradiated with UV ozone. Next, an organic solvent was applied by spin coating on a UV ozone-cleaned ITO transparent electrode under conditions of a rotation speed of 3000 rpm and an application time of 10 seconds. The types of organic solvents used are as shown in Table 1.

  And after application | coating of this organic solvent, the board | substrate was moved to the vacuum evaporation machine in the state which evaporated the organic solvent. Next, a hole injecting layer, a hole transporting layer, and an electron transporting light emitting layer were formed by a vacuum vapor deposition machine. Further, lithium fluoride (LiF) was vacuum deposited to form a buffer layer (electron injection layer), and aluminum was vacuum deposited to a thickness of 6000 mm to form a cathode. The light emitting area was 30 mm × 25 mm. Finally, sealing was performed using an epoxy resin to produce an organic EL element.

Evaluation of Luminescent Characteristics With respect to each organic EL device produced by changing the type of organic solvent, the luminescent defect spots (dark spots and light spots) were observed and the number thereof was measured. The case where there are many light-emitting defect portions is “X”, the case where there are few light-emitting defects is “◯”, and the case where there are almost no defects is “◎”. Moreover, the light emission brightness | luminance of each produced organic EL element was measured. Each measurement was performed after emitting light for 3000 hours at a predetermined current value. The results are shown in Table 1 below. In the table, as a comparison, the measurement results of the sample in which the hole injection layer was formed without exposing the ITO transparent electrode to the organic solvent after the UV ozone irradiation were also shown.

  As is clear from Table 1, the number of light emitting defects is reduced by performing surface treatment with an organic solvent on the ITO transparent electrode as compared with the case where such treatment is not performed. Further, no change in light emission luminance due to the treatment was observed, and the light emitting surface showed good light emission characteristics.

It is a schematic sectional drawing which shows the structural example of the organic EL element to which the manufacturing method of this invention is applied. It is a schematic sectional drawing which shows the board | substrate with which the transparent electrode was formed. It is a schematic sectional drawing which shows the application | coating process of an organic solvent. It is a figure which shows the surface treatment process by exposing to an organic-solvent vapor | steam. It is a schematic sectional drawing which shows a mode that the organic-solvent layer was formed in the transparent electrode surface. It is a schematic sectional drawing which shows the state in which the organic compound thin film and the cathode were formed. It is a schematic sectional drawing which shows the attachment process of a cap structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate, 2 Transparent electrode, 3 Organic compound thin film, 4 Cathode, 5 Hole injection layer, 6 Hole transport layer, 7 Light emitting layer, 8 Electron transport layer, 9 Electron injection layer, 11 Coating device, 12 Organic solvent, 13 Processing chamber, 14 container, 15 hot plate, 16 cap structure

Claims (14)

An organic electroluminescent element manufacturing method comprising: forming an organic compound thin film including at least a light emitting region on a first electrode; and forming a second electrode on the organic compound thin film,
Before forming the organic compound thin film, the surface of the first electrode is surface-treated with an organic solvent, and the organic compound thin film is formed thereon with organic solvent molecules remaining on the surface of the first electrode. The manufacturing method of the organic electroluminescent element characterized by the above-mentioned.   2. The method of manufacturing an organic electroluminescent element according to claim 1, wherein the organic compound thin film is formed by a vacuum thin film forming technique.   The organic compound thin film is composed of a plurality of organic layers, and an organic layer in contact with the first electrode among the plurality of organic layers is formed in a state where the organic solvent molecules remain on the surface of the first electrode. The method for producing an organic electroluminescence element according to claim 1 or 2.   The method for producing an organic electroluminescent element according to claim 1, wherein the surface treatment with the organic solvent is performed by coating, spraying, or exposing to a solvent vapor.   The organic solvent is at least one selected from cyclohexanone, p-xylene, o-xylene, m-xylene, tetrahydrofuran, toluene, ethylbenzene, cyclohexane, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether. Item 5. A method for producing an organic electroluminescent element according to any one of Items 1 to 4.   6. The method of manufacturing an organic electroluminescent element according to claim 1, wherein the first electrode is an indium tin oxide electrode.   The method of manufacturing an organic electroluminescent element according to claim 1, wherein the first electrode is heated after the surface treatment with the organic solvent.   The method for producing an organic electroluminescent element according to claim 7, wherein the heating temperature is 40 ° C to 80 ° C.   The method for producing an organic electroluminescent element according to claim 1, wherein a heated organic solvent is used for the surface treatment.   The method for producing an organic electroluminescent element according to claim 9, wherein the heating temperature of the organic solvent is 80 ° C. or lower.   11. The method of manufacturing an organic electroluminescence element according to claim 1, wherein the surface of the first electrode is washed before the surface treatment with the organic solvent.   12. The method of manufacturing an organic electroluminescence element according to claim 11, wherein the cleaning includes a cleaning process with a solvent and a decomposition process of an organic substance. 13. The method of manufacturing an organic electrochromic element according to claim 1, wherein the size of one pixel of the organic electroluminescent element to be manufactured is 100 mm ² or more.   The method of manufacturing an organic electroluminescence element according to claim 13, wherein the organic electroluminescence element to be manufactured is for illumination.

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