TW202139498A - Organic EL device capable of reducing driving voltage and enhancing leakage resistance - Google Patents

Abstract

The present invention relates to an organic EL device (1), in which an organic EL element (3) having an anode (11), an organic EL material layer (12), and a cathode (13) is disposed on a substrate (2). One side of the organic EL material layer (12) near the anode (11) is provided with a layered structure sequentially arranged with a hole injection layer (21), a hole transport layer (22), a light emitting layer (23), a hole blocking layer (24), an electron transport layer (25), and an electron injection layer (26). The hole injection layer (21) includes a first hole injection layer (21A) made of a hole injection material containing a p-dopant, and a second hole injection layer (21B) inserted between the first hole injection layer (21A) and the anode (11) and made of an undoped hole injection material. By inserting the second hole injection layer (21B) between the first hole injection layer (21A) and the anode (11), the present invention may reduce the driving voltage and also enhance the leakage resistance.

Description

Organic EL device

The present invention relates to an organic EL device.

Conventionally, there has been known an organic EL device in which an organic EL element having an anode, an organic EL material layer, and a cathode is arranged on a substrate. The following Patent Document 1 discloses a technique of doping an acceptor material on the hole injection layer in order to reduce the driving voltage of the organic EL element.

[Patent Document 1] Japanese Patent Application Publication No. 2007-243044 [Patent Document 2] JP 2019-083086 A

However, when an acceptor material is doped on the hole injection layer, the driving voltage is reduced and the leakage resistance is also reduced, and it is difficult to realize an organic EL device with high insulation resistance.

After intensive research, the inventors have newly discovered a technology that can reduce the driving voltage while improving the leakage resistance.

The object of the present invention is to provide an organic EL device capable of reducing driving voltage and improving leakage resistance.

In an organic EL device of the present invention, an organic EL element having an anode, an organic EL material layer and a cathode is arranged on a substrate. In the aforementioned organic EL device, the organic EL material layer has A layered structure composed of a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer. The hole injection layer includes the first hole injection composed of a hole injection material containing a p-dopant A layer and a second hole injection layer inserted between the first hole injection layer and the anode and made of an undoped hole injection material.

The inventors newly discovered that a second hole injection layer made of an undoped hole injection material is inserted between a first hole injection layer made of a hole injection material containing a p-dopant and an anode. As a result, the driving voltage of the organic EL device can be reduced, and the leakage resistance can be improved.

In another type of organic EL device, the thickness of the second hole injection layer is thinner than the thickness of the first hole injection layer.

In another type of organic EL device, the thickness of the second hole injection layer is 20 nm or less. [Effects of the invention]

According to the present invention, there is provided an organic EL device capable of reducing driving voltage and improving leakage resistance.

Hereinafter, referring to the drawings, a suitable embodiment of the present invention will be described in detail. In addition, in the following description, the same reference numerals are used for the same elements or elements having the same function, and repeated descriptions are omitted.

In the embodiment, the organic EL device 1 used in the passive matrix type organic EL display panel is taken as an example for description. As the number of pixels of the passive matrix organic EL display, for example, it can be set to 256×16 dots.

As shown in FIGS. 1 to 3, the organic EL device 1 of this embodiment is configured to include a substrate 2, an organic EL element 3, a structure 5, an insulating layer 6, an inorganic layer 7, a protective resin 8, a protective film 9, and a wiring portion 10. . In addition, in FIG. 1, illustration of the protective resin 8 and the protective film 9 is omitted.

The substrate 2 is an element substrate provided with an organic EL element 3, a wiring portion 10, and the like. The substrate 2 is, for example, a glass substrate, a ceramic substrate, a metal substrate, or a flexible substrate (for example, a plastic substrate, etc.). The substrate 2 has translucency, for example. The substrate 2 is formed in, for example, a rectangular plate shape.

The organic EL element 3 is an element that generates light by supplying electric current. In this embodiment, the organic EL element 3 is arranged on the substrate 2 so as to directly contact the substrate 2.

As shown in FIG. 4, the organic EL element 3 has an anode 11, an organic EL material layer 12, and a cathode 13 laminated in this order from the substrate 2 side.

The anode 11 is composed of a transparent conductive layer. As a material constituting the anode 11, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide: Registered Trademark), and other conductive materials having translucency can be used. The anode 11 can be formed, for example, by patterning a transparent conductive film formed on the substrate 2 by a PVD method (physical vapor deposition method) such as a vacuum vapor deposition method or a sputtering method.

The organic EL material layer 12 has a laminated structure composed of a plurality of layers. Specifically, as shown in FIG. 5, the organic EL material layer 12 has a hole injection layer 21, a hole transport layer 22, a light emitting layer 23, a hole blocking layer 24, and an electron transport layer arranged in this order from the side close to the anode 11. 25. Laminated structure formed by the electron injection layer 26. The hole blocking layer 24 can also be used as a part of the electron transport layer 25. Each layer of the organic EL material layer 12 can be formed by a PVD method, for example.

The cathode 13 is, for example, a metal electrode film made of metal such as aluminum and silver. The metal material constituting the cathode 13 may include alkaline earth metals (magnesium, calcium, etc.), and may also include light-transmitting materials such as IZO and ITO. In addition, the cathode 13 may be formed by laminating these materials. The cathode 13 can be formed by, for example, a resistance heating vapor deposition method, an induction heating vapor deposition method, an electron beam heating vapor deposition method, or a PVD method.

The structure 5 is arranged between adjacent organic EL elements 3 and extends in a direction D perpendicular to the substrate 2. The structure 5 can also function as a cathode separator for separating the cathodes 13 of adjacent organic EL elements 3 from each other. In the structure 5, the top surface 5a is larger than the bottom surface 5b. The top surface 5 a is a surface on the side opposite to the substrate 2 of the structure 5, and the bottom surface 5 b is a surface on the substrate 2 side of the structure 5. Specifically, the structure 5 is formed in a reverse tapered shape with a cross section that tapers from the top surface 5a toward the bottom surface 5b. The structure 5 is formed by, for example, a photolithography method.

The insulating layer 6 is arranged between the substrate 2 and the structure 5. The insulating layer 6 is composed of an inorganic insulating film or an organic insulating film. When the insulating layer 6 is composed of an inorganic insulating film, the insulating layer 6 contains, for example, silicon oxide, silicon oxynitride, silicon nitride, or aluminum oxide as a main component. In this case, the insulating layer 6 can be formed by, for example, a sputtering method, an atomic layer deposition (Atomic Layer Deposition) method, or a plasma CVD (Plasma Enhanced Chemical Vapor Deposition) method. When the insulating layer 6 is made of an organic insulating film, the insulating layer 6 can be made of, for example, novolak resin, phenol resin, polyimide resin, or the like. In this case, the insulating layer 6 can be formed by, for example, a photolithography method. The material constituting the insulating layer 6 may be the same as the material constituting the substrate 2.

The inorganic layer 7 covers the organic EL element 3 and the structure 5. The inorganic layer 7 may have a single-layer structure or a multilayer structure. The inorganic layer 7 includes, for example, an inorganic material mainly composed of silicon oxide, silicon oxynitride, silicon nitride, aluminum oxide, titanium dioxide, or zirconium oxide. The inorganic layer 7 is formed by, for example, a sputtering method, a plasma CVD method, a photo CVD (Photo Chemical Vapor Deposition) method, a Cat-CVD (Catalytic Chemical Vapor Deposition) method, or an atomic layer deposition method.

The protective resin 8 is a resin disposed on the inorganic layer 7 and used to improve resistance to mechanical damage. As the protective resin 8, for example, silicone resin, acrylic resin, and epoxy resin can be used. Among them, silicone resins are particularly excellent in impact function, and have high resistance to mechanical damage, so they are preferred. The protective resin 8 is formed by, for example, an inkjet method or a dispensing method.

The protective film 9 is a film that is arranged on the inorganic layer 7 or the protective resin 8 and improves the resistance to mechanical damage. As the protective film 9, for example, resin films such as PET films, metal foils such as aluminum foil, copper foil, and stainless steel foil can be used.

The wiring portion 10 is a lead-out wiring drawn from the organic EL element 3. The wiring part 10 is formed of, for example, a laminated film formed by sequentially laminating a molybdenum alloy, an aluminum alloy, and a molybdenum alloy.

Among them, as shown in FIG. 5, the hole injection layer 21 of the organic EL material layer 12 is composed of a first hole injection layer 21A and a second hole injection layer 21B. The second hole injection layer 21B is inserted between the first hole injection layer and the anode 11 and directly contacts the anode 11.

The first hole injection layer 21A is made of a hole injection material made of an amine compound. The amine compound of the hole injection material is, for example, a starburst triphenylamine derivative (m-MTDADA, NATA, 1-TNATA, 2-TNATA) or copper phthalocyanine (CuPc). The amine compound of the hole injection material can be selected from the group consisting of N,N'-diphenyl-N,N'-bis(1-naphthyl)benzidine (NPB), triphenylamine derivatives (TPD, β-NPD) , MeO-TPD, TAPC), aniline tetramer (TPTE), starburst triphenylamine derivatives (m-MTDADA, NATA, 1-TNATA, 2-TNATA), spiro triphenylamine derivatives (Spiro-TPD, At least one of the group consisting of Spiro-NPD, Spiro-TAD), red fluorene, pentacene, copper phthalocyanine (CuPc), titanium oxide phthalocyanine (TiOPc) and α-hexafluorothiophene (α-6T) .

The hole injection material constituting the first hole injection layer 21A may be a hole transport material used in the hole transport layer. In this case, the first hole injection layer 21A is made of, for example, N,N'-diphenyl-N,N'-bis(1-naphthyl)benzidine (NPB) or triphenylamine derivatives (TPD, βNPD, MeOTPD). , TAPC) and other amine compounds.

The hole injection material constituting the first hole injection layer 21A is doped with a p-dopant acceptor material. The acceptor material includes, for example, F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), F4DCNQI (N,N'-dicyano-2 ,3,5,6-Tetrafluoro-1,4-quinone diimide), Cl2DCNQI (N,N'-dicyano-2,5-dichloro-1,4-quinone diimide), Cl2F2DCNQI ( N,N'-dicyano-2,5-dichloro-3,6-difluoro-1,4-quinodiimide), F6DCNNQI (N,N'-dicyano-2,3,5, 6,7,8-hexafluoro-1,4-naphthoquinone diimide), CN4TTAQ (1,4,5,8-tetrahydro-1,4,5,8-tetrathio-2,3,6 , 7-Tetracyanoanthraquinone) and so on.

As an example, 2 wt% of the acceptor material is added (co-evaporated) to 98 wt% of the hole injection material to obtain the first hole injection layer 21A. The film thickness of the first hole injection layer 21A may be 40 to 100 nm or 50 to 65 nm.

The second hole injection layer 21B can be formed of a hole injection material made of the same amine compound as the first hole injection layer 21A. The hole injection material constituting the second hole injection layer 21B may be the same as or different from the hole injection material constituting the first hole injection layer 21A.

The hole injection material constituting the second hole injection layer 21B is not doped with the p-dopant, and is a so-called undoped layer. The second hole injection layer 21B can be formed by a vacuum vapor deposition method, for example.

The film thickness of the second hole injection layer 21B can be designed to be thinner than the film thickness of the first hole injection layer 21A. The film thickness of the second hole injection layer 21B may be 5-20 nm, or may be 5-10 nm.

The hole transport layer 22 is composed of a hole transport material composed of an amine-based compound. When the hole injection layer 21 is composed of a hole transport material, the hole transport material constituting the hole transport layer 22 and the hole transport material constituting the hole injection layer 21 may be the same or different.

The light-emitting layer 23 is composed of two layers, a blue light-emitting layer 23A on the side of the cathode 13 and a yellow light-emitting layer 23B on the side of the anode 11. The blue light emitting layer 23A is configured to include an electron transport host material or a hole transport host material and a blue light emitting material. The yellow light emitting layer 23B is configured to include an electron transport host material or a hole transport host material and a yellow light emitting material. The light-emitting layer 23 may have a multiple-layer structure or a single-layer structure.

As described above, in the organic EL device 1, a plurality of organic EL elements 3 having an anode 11, an organic EL material layer 12 and a cathode 13 are arranged on the substrate 2. The organic EL material layer 12 of each organic EL element 3 has a stack of a hole injection layer 21, a hole transport layer 22, a light emitting layer 23, an electron transport layer 25, and an electron injection layer 26 arranged in order from the side close to the anode 11. structure. The hole injection layer 21 includes a first hole injection layer 21A composed of a hole injection material containing a p-dopant, and an undoped hole inserted between the first hole injection layer 21A and the anode 11 The second hole injection layer 21B made of material.

The inventors conducted intensive research on the driving voltage and leakage resistance of organic EL devices, and obtained the following knowledge: by inserting the second hole injection layer 21B between the first hole injection layer 21A and the anode 11, the driving voltage can be reduced While improving the leakage resistance.

Therefore, the inventors confirmed the driving voltage and leakage resistance when the second hole injection layer 21B is inserted between the first hole injection layer 21A and the anode 11, and thus completed the experiment shown below.

(Reverse bias application test) As a reverse bias application test, a reverse bias voltage was applied to the organic EL device before assembly, and the voltage at which the device was broken was measured. More specifically, the anode wiring and the cathode wiring of the organic EL device are shared by Ag paste and connected by a reverse bias circuit. The results of the experiment are shown in Tables 1, 2 and Fig. 6 below.

Table 1 shows the device breakdown voltage in each film thickness related to the film thickness of the hole injection layer composed of only the first hole injection layer. Table 2 shows the device breakdown voltage in each film thickness related to the film thickness of the hole injection layer including the first hole injection layer and the second hole injection layer. Figure 6 is a graph plotting the results of Table 1 and Table 2. In the graph of FIG. 6, the results of Table 1 are shown by square marks, and the results of Table 2 are shown by △ marks.

【Table 1】 Film thickness of the hole injection layer (only the first hole injection layer) [nm] Component breakdown voltage [V] Sample 1 10 twenty three Sample 2 30 26 Sample 3 50 28 Sample 4 70 28.3 Sample 5 90 28 Sample 6 110 28.5 【Table 2】 Film thickness of hole injection layer [nm] Film thickness of the second hole injection layer [nm] Component breakdown voltage [V] Sample 7 70 0 28 Sample 8 75 5 32 Sample 9 80 10 34.8 Sample 10 110 40 35.5 Sample 11 140 70 35.4

From Table 1, 2 and Figure 6, it is confirmed that in samples 1 to 7 in which the hole injection layer does not include the second hole injection layer, the device breakdown voltage is less than 30V, but the hole injection layer includes the second hole injection layer. In samples 8 to 11 of the layer, the device breakdown voltage exceeds 30V, and a sufficiently high device breakdown voltage can be obtained for practical use. In particular, it was confirmed that in samples 9 to 11, the device breakdown voltage increased to approximately 35V.

(Chromaticity measurement) In addition, a spectroradiometer SR3AR (manufactured by TOPCON CORPORATION) was used to measure the chromaticity when the panel was lit, and the driving voltage when the current value was 17 mA was measured. The measurement results are shown in Table 3 and Figure 7 below. Table 3 shows the chromaticity in each film thickness related to the film thickness of the second hole injection layer. Figure 7 is a graph plotting the results of Table 3.

【table 3】 Film thickness of the second hole injection layer [nm] CIEx CIEy Drive voltage [V] Sample 12 0 0.280 0.296 7.0 Sample 13 5 0.284 0.300 7.0 Sample 14 10 0.287 0.303 7.0 Sample 15 40 0.303 0.328 7.8

It was confirmed from Table 3 and FIG. 7 that the panels of Sample 12 in which the hole injection layer did not include the second hole injection layer and Samples 13 to 15 in which the hole injection layer included the second hole injection layer were all lit. In particular, in the samples 13 and 14 where the film thickness of the second hole injection layer is relatively thin (20 nm or less), the blue light-emitting layer on the cathode side is dominated by light emission, that is, light-emitting with blue light. In sample 15 with a thick hole injection layer (more than 20 nm), the yellow light emitting layer on the anode side is dominated by light emission, that is, light emission with yellow light. From this, it can be seen that the position of recombination of holes and electrons is shifted according to the film thickness of the second hole injection layer, and it can be seen that the color tone of light emission can be adjusted by adjusting the film thickness of the second hole injection layer. For example, when adjusting the light emission with blue light, the film thickness of the second hole injection layer is designed to be 20 nm or less. In addition, it was confirmed that in samples 13 and 14 in which the film thickness of the second hole injection layer was thinner, the hole injection layer had the same driving voltage as that of the sample 12 that did not include the second hole injection layer. In order to lower the voltage.

1: Organic EL device 2: substrate 3: Organic EL element 5: structure 5a: Top surface 5b: bottom surface 6: Insulation layer 7: Inorganic layer 8: Protective resin 9: Protective film 10: Wiring part 11: anode 12: Organic EL material layer 13: Cathode 21: Hole injection layer 21A: The first hole injection layer 21B: The second hole injection layer 22: Hole transport layer 23: luminescent layer 23A: blue light-emitting layer 23B: yellow light-emitting layer 24: Hole blocking layer 25: electron transport layer 26: Electron injection layer D: The direction perpendicular to the substrate

Fig. 1 is a schematic plan view showing the organic EL device of the embodiment. Fig. 2 is a cross-sectional view taken along the line II-II of the organic EL device shown in Fig. 1. Fig. 3 is a cross-sectional view taken along the line III-III of the organic EL device shown in Fig. 1. Fig. 4 is a schematic cross-sectional view of an enlarged part of the organic EL element. Fig. 5 is a diagram for explaining the layered structure of the organic EL element of Fig. 4. Fig. 6 is a graph showing the relationship between the device breakdown voltage and the film thickness of the hole injection layer. Fig. 7 is a graph showing the relationship between the film thickness of the second hole injection layer and the chromaticity.

2: substrate

11: anode

12: Organic EL material layer

13: Cathode

21: Hole injection layer

21A: The first hole injection layer

21B: The second hole injection layer

22: Hole transport layer

23: luminescent layer

23A: blue light-emitting layer

23B: yellow light-emitting layer

24: Hole blocking layer

25: electron transport layer

26: Electron injection layer

Claims (3)

An organic EL device, which is provided with an organic EL element having an anode, an organic EL material layer and a cathode on a substrate, wherein The organic EL material layer has a layered structure in which a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are arranged in order from the side close to the anode, and The hole injection layer includes a first hole injection layer composed of a hole injection material containing a p-dopant, and an undoped hole injection material inserted between the first hole injection layer and the anode The second hole injection layer is formed. The organic EL device according to claim 1, wherein The thickness of the second hole injection layer is thinner than the thickness of the first hole injection layer. The organic EL device as described in claim 1 or 2, wherein The thickness of the second hole injection layer is 20 nm or less.

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