JP2021145093A - Organic electroluminescent element, display unit and illumination device - Google Patents

Abstract

To provide an organic electroluminescent element with memory property without using a transistor and a capacitor.SOLUTION: An organic EL element 1 includes a first electrode 3, an inorganic oxide layer 4 with memory property, a luminous layer 7 and a second electrode 10 provided on a substrate 2 in this order. The inorganic oxide layer 4 with memory property contains a material showing hysteresis in current-voltage properties.SELECTED DRAWING: Figure 1

Description

The present invention relates to an organic electroluminescence element (hereinafter, electroluminescence (electroluminescence) may be referred to as "EL"), a display device, and a lighting device.

In anticipation of future flexibility (from glass to film, etc.), organic EL devices, which are self-luminous thin film devices, are being energetically studied.
As a study with an eye on flexibility, an inverted structure type organic EL device that does not use an unstable material in the atmosphere such as an alkali metal has been reported and is attracting attention (see, for example, Non-Patent Document 1 and Non-Patent Document 2). ). In this inverse structure type organic EL element, the cathode, the light emitting layer, and the anode are arranged in this order on the substrate, as opposed to the normal organic EL element in which the anode, the light emitting layer, and the cathode are arranged in this order on the substrate. The feature is that the stacking order of the electrodes is reversed. In this inverse structure type organic EL element, since the electron injection layer is formed before the organic layer, the electron injection layer can be formed by a method such as sputtering that can damage the organic layer. Therefore, as the material of the electron injection layer, it becomes possible to use a material such as an oxide that is stable in the atmosphere and can promote electron injection (see, for example, Patent Documents 1 and 2).

Similar to the liquid crystal display, a passive matrix drive method and an active matrix drive method can be used as the drive method of the organic EL display (lighting device) in which a large number of organic EL elements are arranged in a matrix. Although the former has a simple structure, it is difficult to realize a large-sized and high-definition display. Therefore, the active matrix drive method is the mainstream as the drive method of the organic EL display currently on the market.

Japanese Unexamined Patent Publication No. 2012-4492 Japanese Unexamined Patent Publication No. 2007-53286

APPLIED PHYSICS LETTERS Volume 89,183510 (2006) Advanced Materials Volume23, page1829-1845 (2011) APPLIED PHYSICS LETTERS 110, 073501 (2017)) APPLIED PHYSICS LETTERS 94, 033501 (2009) APPLIED PHYSICS LETTERS 104, 183501 (2014)) APPLIED PHYSICS LETTERS 101, 063501 (2012)) APPLIED PHYSICS LETTERS 104, 143502 (2014)) Ceramics International Vol. 43, 2017, Pages S481-S487) Journal of Alloys and Compounds Vol.693, Pages 1180-1184)

In the active matrix drive system, in order to impart memory to the light emitting state of the organic EL element, it is necessary to provide a switching TFT and a capacitor having a complicated structure for each pixel. Few methods have been proposed to simplify it. The problems with organic EL displays having a transistor and capacitor structure are that the process of making the transistor is complicated, so an increase in cost and a decrease in yield are unavoidable, and the transistor consists of a source / drain electrode and a gate electrode. Therefore, it is necessary to form a fine pattern, and there is a limit to ultra-high definition.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an organic electroluminescence device having a memory property without using a transistor and a capacitor.
Another object of the present invention is to provide a display device and a lighting device including the above-mentioned organic electroluminescence element.

The present inventor has studied various simplifications of the structure of an active matrix-driven organic EL display. We have found that an organic EL display having a simple structure that does not use a transistor can be realized at low cost, and have come up with the idea that the above problems can be solved, and have completed the present invention.

The present invention provides the following means for solving the above problems.

(1) The organic electroluminescence element according to one aspect of the present invention is provided with a first electrode, a memory inorganic oxide layer, a light emitting layer, and a second electrode in this order on a substrate, and the memory inorganic. The oxide layer is characterized by containing a material that exhibits hysteresis in the current-voltage characteristic.

(2) In the organic electroluminescence device according to (1) above, the first electrode may be a cathode and the second electrode may be an anode.

(3) In the organic electroluminescence device according to any one of (1) or (2) above, the memory inorganic oxide layer may contain a transition metal.

(4) In the display device according to one aspect of the present invention, the plurality of organic electroluminescence elements according to any one of (1) to (3) above form a plurality of rows and a plurality of columns on the substrate. A plurality of first electrode wires are arranged in a matrix, and a plurality of first electrode wires are provided corresponding to each row of the plurality of organic electroluminescence elements arranged in a matrix, and a plurality of electrodes are provided corresponding to each column. A second electrode wire, a first driver for selectively applying a potential to the plurality of first electrode wires, and a first driver for selectively applying a potential to the plurality of second electrode wires. It is characterized by including two drivers and a control device for controlling the potential of the first driver and the potential of the second driver.

(5) The lighting device according to one aspect of the present invention is characterized by including the organic electroluminescence device according to any one of (1) to (3) above.

According to the organic electroluminescence device of the present invention, it is possible to provide an organic electroluminescence device having a memory property without using a transistor and a capacitor.
Further, since the display device and the lighting device of the present invention include the organic EL element of the present invention, they can be used stably for a long period of time.

It is sectional drawing for demonstrating an example of the organic EL element of this embodiment. It is sectional drawing of the simple element which can be used to obtain the current-voltage characteristic of a memory inorganic oxide. (A) is a conceptual diagram of the memory property shown by the memory-like inorganic oxide material, and (b) is another conceptual diagram of the memory property shown by the memory-like inorganic oxide material. It is a circuit diagram of a part of the display device of this invention. It is a timing chart for demonstrating the driving method of the display device of this invention. It is a current-voltage characteristic curve shown by a memory inorganic oxide layer used for explaining the driving method of the display device of this invention.

Hereinafter, the organic EL element, the display device, and the lighting device of the present invention will be described in detail.
The organic EL element of the present invention includes a first electrode, a memory inorganic oxide layer, a light emitting layer, and a second electrode in this order on a substrate, and the memory inorganic oxide layer has current-voltage characteristics. It is characterized by containing a material exhibiting hysteresis in the above.
FIG. 1 is a schematic cross-sectional view for explaining an example of the organic EL device of the present invention.
In the following, a case where the first electrode is a cathode and the second electrode is an anode will be described as an example.

The organic EL element 1 shown in FIG. 1 has a cathode 3, a memory inorganic oxide layer 4, an electron injection layer 5, an electron transport layer 6, a light emitting layer 7, and a hole transport layer 8 on a substrate 2. And has a laminated structure in which the hole injection layer 9 and the anode 10 are formed in this order.

The organic EL element 1 shown in FIG. 1 is an organic EL element (iOLED element) having an inverted structure in which a cathode 3 is arranged between a substrate 2 and a light emitting layer 7.
The organic EL element 1 shown in FIG. 1 may be a top emission type that extracts light on the side opposite to the substrate 2, or may be a bottom emission type that extracts light on the substrate 2 side.
Further, in the present embodiment, the organic EL element 1 having an inverted structure in which the cathode 3 is arranged between the substrate 2 and the light emitting layer 7 will be described as an example. However, the organic EL element of the present invention emits light from the substrate. It may have a forward structure in which an anode is arranged between the layers.

"substrate"
Examples of the material of the substrate 2 include a resin material and a glass material.
Examples of the resin material used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyether sulfone, polymethylmethacrylate, polycarbonate, polyarylate and the like. When a resin material is used as the material of the substrate 2, the organic EL element 1 having excellent flexibility can be obtained, which is preferable.
Examples of the glass material used for the substrate 2 include quartz glass and soda glass.

When the organic EL element 1 is a bottom emission type, a transparent substrate is used as the material of the substrate 2.
When the organic EL element 1 is of the top emission type, not only a transparent substrate but also an opaque substrate may be used as the material of the substrate 2. Examples of the opaque substrate include a substrate made of a ceramic material such as alumina, a substrate having an oxide film (insulating film) formed on the surface of a metal plate such as stainless steel, and a substrate made of a resin material.

The average thickness of the substrate 2 can be determined according to the material of the substrate 2 and the like, and is preferably 0.1 to 30 mm, more preferably 0.1 to 10 mm. The average thickness of the substrate 2 can be measured with a digital multimeter and a caliper.

"cathode"
The cathode 3 is formed in direct contact with the substrate 2.
As the material of the cathode 3, in the case of a bottom emission type device, it contains ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine oxide), In ₃ O ₃ , SnO ₂ , and Sb, which are transparent electrodes. Examples thereof include conductive materials of oxides such as _{SnO 2 and Al-containing ZnO.} Among these, it is preferable to use ITO, IZO, and FTO as the material of the cathode 3. In the case of a top emission type device, it is preferable to use a reflective electrode such as an alloy using silver.
The average thickness of the cathode 3 is not particularly limited, but is preferably 10 to 500 nm, more preferably 100 to 200 nm.
The average thickness of the cathode 3 can be measured by a stylus type step meter and spectroscopic ellipsometry.

"Memory inorganic oxide layer"
The memory-based inorganic oxide layer 4 has a function as a memory (memory property).
The memory inorganic oxide layer 4 preferably has a function of promoting an electron injection layer (high electron injection property).

The configuration in which the memory inorganic oxide layer 4 is used in the inverse structure organic EL device has the following advantages.
(I) The memory inorganic oxide layer 4 is made of an inorganic oxide and can also play a role of electron injection.
(Ii) Memory materials are required to have high stability, uniformity, and long-term stability. TFTs using inorganic oxide materials have already been realized in large-screen organic EL displays, and inorganic oxides are organic EL. It is easy to secure the performance required for the element.
(Iii) When an organic substance is used as a memory material, there are concerns about stability, uniformity, and long-term stability in the atmosphere, but inorganic oxides tend to form a uniform film and are stable in the atmosphere (oxygen, (Resistant to moisture), high long-term stability.

The memory inorganic oxide layer will be described with reference to FIGS. 2 and 3.
The memory property of the memory-based inorganic oxide material constituting the memory-based inorganic oxide layer is that a simple element in which the memory-based inorganic oxide is sandwiched between electrodes as shown in FIG. 2 is manufactured and a voltage is applied to both electrodes. Then, the relationship between the current and the voltage shows a hysteresis curve as shown in FIG.

3A and 3B are conceptual diagrams of the memory property of the memory-based inorganic oxide material obtained when the current-voltage characteristic is measured using the simple element shown in FIG. 2.
FIG. 3A shows a case where the material has two resistance states, a high resistance state and a low resistance state, and the resistance value of each resistance state can be said to be substantially constant.
The current flows when the voltage is increased from the initial state A (the voltage V between the electrodes is V _A (= 0)) and the voltage V between the electrodes becomes V _B (the state at this time is called the state B). First, it will further increase the voltage V between the electrodes, when the voltage V between the electrodes becomes V _C current I in (the state is referred to the state C in this case) becomes maximum (current I at this time is I _{max ), The current maintains I max} even if the voltage V between the electrodes is lowered from here, and when the voltage V between the electrodes is further lowered, when the voltage V between the electrodes becomes V _D (at this time). state begins to fall the current I in) that the state D of the voltage V between the electrodes is returned to V _a, returns to the initial state a (voltage V V _a (= 0 between electrodes)).
In FIG. 3B, as compared with FIG. 3A, the resistance values in the two resistance states of the high resistance state and the low resistance state have a voltage dependence and have a width, but the width has a width in the high resistance state. This is a case where the resistance value is very small compared to the difference between the resistance values in the low resistance state and the low resistance state.

The material that can be used for the memory inorganic oxide layer that can be used for the organic EL element of the present invention may be a layer containing a material that exhibits hysteresis in the current-voltage characteristics, and hysteresis in the current-voltage characteristics. It may be a layer made of a material indicating. For example, the current-voltage characteristic curve (high resistance side current-voltage characteristic curve) from the initial state where the applied voltage is zero to the maximum applied voltage state where the applied voltage is the maximum, and the applied voltage is lowered from the maximum applied voltage state. If the material has a different current-voltage characteristic curve (low resistance side current-voltage characteristic curve), the high resistance state and low resistance as shown in FIGS. 3 (a) and 3 (b). The material is not limited to a material in which the two resistance states of the state are clear.

The memory inorganic oxide layer may be a material containing a transition metal. For example, examples of the material containing the transition metal include ZnO (see Non-Patent Document 3), MgZnO (see Non-Patent Document 4), ZrZnO (see Non-Patent Document 5), ZnFeO (see Non-Patent Document 6), and CoFeO (Non-Patent Document 6). Reference 7), NiFeO (see Non-Patent Document 8), and TiO (see Non-Patent Document 9).

The memory inorganic oxide layer 4 may be a single layer of an inorganic oxide such as a metal oxide, or may be a laminated film containing a layer of an inorganic oxide such as a metal oxide. For example, it may be a layer in which one or both of a layer in which two or more kinds of metal oxides are mixed and a layer made of a single metal oxide are laminated, or a layer in which two or more kinds of metal oxides are mixed. good.
The metal elements constituting the metal oxide forming the memory inorganic oxide layer 4 include hafnium, zinc, titanium, tantalum, nickel, cerium, silicon, gadolinium, tungsten, copper, aluminum, niobium, zirconium, germanium, and iron. Examples of the oxide include materials that can exhibit memorability. Alternatively, any one of a solid electrolyte such as GeS and CuS and a perovskite type oxide such as _{Pr 0.7} Ca _0.3 MnO ₃ (PCMO) and SrTiO _{3 (STO) may be used.}
In order to exhibit memory properties, it may be composed of a plurality of layers as required.

The average thickness of the memory inorganic oxide layer 4 is not particularly limited, but is preferably 1 to 1000 nm, more preferably 2 to 100 nm.
The average thickness of the oxide layer 4 can be measured by a stylus type step meter and spectroscopic ellipsometry.

"Electron injection layer"
The electron injection layer 5 improves the speed and electron transportability of electron injection from the cathode to the light emitting layer 7, and it is preferable to have the electron injection layer 5 for improving the characteristics of the inverse structure type organic EL device. You may.
As the electron injection layer 5, a material made of a known material can be used.

"Electronic transport layer"
As the material of the electron transport layer 6, any material that can be usually used as the material of the electron transport layer 6 can be used, and these may be mixed and used.
Examples of low molecular weight compounds that can be used as materials for the electron transport layer 6 include bis [2- (o-hydroxyphenyl) benzothiazole] zinc (II) (ZnBTZ2), boron-containing compounds, Tris-1,3, Pyridine derivatives such as 5- (3'-(pyridine-3''-yl) phenyl) benzene (TmPyPhB), quinoline derivatives such as (2- (3- (9-carbazolyl) phenyl) quinoline (mCQ)) , 2-Phenyl-4,6-bis (3,5-dipyridylphenyl) pyrimidine derivatives such as pyrimidin (BPyPPM), pyrazine derivatives, phenanthroline derivatives such as vasophenantroline (BPhen), 2,4-bis (4-bis) Biphenyl) -6- (4'-(2-pyridinyl) -4-biphenyl)-[1,3,5] Triazine derivatives such as triazine (MPT), 3-phenyl-4- (1'-naphthyl)- Triazole derivatives such as 5-phenyl-1,2,4-triazole (TAZ), oxazole derivatives, 2- (4-biphenylyl) -5- (4-tert-butylphenyl-1,3,4-oxadiazole) ) (PBD) oxadiazole derivatives, such as 2,2', 2''-(1,3,5-ventryyl) -tris (1-phenyl-1-H-benzimidazole) (TPBI) Arocyclic tetracarboxylic acid anhydrides such as imidazole derivatives, naphthalene and perylene, bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (Zn (BTZ) 2), tris (8-hydroxyquinolinato) aluminum (Alq3) and the like. Various metal complexes typified by, sylrole derivatives such as 2,5-bis (6'-(2', 2 ″ -bipyridyl)) -1,1-dimethyl-3,4-diphenylsilol (PyPySPyPy). Examples thereof include organic silane derivatives, and one or more of these can be used.
Among these, a metal complex such as Alq3 and a pyridine derivative such as TmPyPhB are preferable, but they may not be used when electrons are efficiently transported from the electrode or the electron injection layer to the light emitting layer.

The average thickness of the electron transport layer 6 is not particularly limited, but is preferably 10 to 150 nm, more preferably 40 to 100 nm.
The average thickness of the electron transport layer 6 can be measured at the time of film formation with a crystal oscillator film thickness meter.

"Light emitting layer"
The material forming the light emitting layer 7 may be a low molecular weight compound or a high molecular weight compound. In the present invention, the small molecule material means a material that is not a polymer material (polymer), and does not necessarily mean an organic compound having a low molecular weight.

As the light emitting material used for the light emitting layer 7, for example, a phosphorescent material such as an iridium complex or a platinum complex, a fluorescent material, a thermal activated delayed fluorescent material, or the like can be used. Further, the light emitting material is not limited to the organic material, and for example, a quantum dot material such as cadmium selenium, a perovskite material, or the like can also be used.

The average thickness of the light emitting layer 7 is not particularly limited, but is preferably 10 to 1000 nm, and more preferably 20 to 100 nm.
The average thickness of the light emitting layer 7 may be measured by a stylus type step meter or may be measured by a crystal oscillator film thickness meter at the time of film formation of the light emitting layer 7.

"Hole transport layer"
As the hole-transporting organic material used for the hole-transporting layer 8, any material that can be usually used as the material for the hole-transporting layer 8 can be used, and these may be mixed and used, and various p. A type of high molecular weight material (organic polymer) and various p-type low molecular weight materials can be used alone or in combination.
Specifically, as the material of the hole transport layer 8, for example, N, N'-di (1-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α). -NPD), N4, N4'-bis (dibenzo [b, d] thiophene-4-yl) -N4, N4'-diphenylbiphenyl-4,4'-diamine (DBTPB), polyarylamine, fluorene-arylamine Copolymers, Fluorene-Bithiophene Copolymers, Poly (N-vinylcarbazole), Polyvinylpyrene, Polyvinylanthracene, Polythiophene, Polyalkylthiophene, Polyhexylthiophene, Poly (p-phenylenebinylene), Polytinylene vinylene, Pyreneformaldehyde Examples thereof include resins, ethylcarbazole formaldehyde resins or derivatives thereof. The material of these hole transport layers 8 can also be used as a mixture with other compounds. As an example, as a mixture containing polythiophene used as a material for the hole transport layer 8, poly (3,4-ethylenedioxythiophene / styrenesulfonic acid) (PEDOT / PSS) and the like can be mentioned.

The average thickness of the hole transport layer 8 is not particularly limited, but is preferably 10 to 150 nm, more preferably 20 to 100 nm.
The average thickness of the hole transport layer 8 can be measured by, for example, a stylus type profilometer or spectroscopic ellipsometry.

"Hole injection layer"
The hole injection layer 9 may be made of an inorganic material or an organic material. Since the inorganic material is more stable than the organic material, it is easy to obtain high resistance to oxygen and water as compared with the case where the organic material is used.
The inorganic material is not particularly limited, and for example, one or more metal oxides such as _{vanadium oxide (V 2} O ₅ ), molybdenum oxide (MoO ₃ ), and ruthenium oxide (RuO _{2) may be used.} can.
Organic materials include dipyrazino [2,3-f: 2', 3'-h] quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 2,3,5. 6-Tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) and the like can be used.

The average thickness of the hole injection layer 9 is not particularly limited, but is preferably 1 to 1000 nm, more preferably 5 to 50 nm.
The average thickness of the hole injection layer 9 can be measured at the time of film formation with a crystal oscillator film thickness meter.

"anode"
Examples of the material used for the anode 10 include ITO, IZO, Au, Pt, Ag, Cu, Al, and alloys containing these. Among these, it is preferable to use ITO, IZO, Au, Ag, Al as the material of the anode 10.
The average thickness of the anode 10 is not particularly limited, but is preferably 10 to 1000 nm, more preferably 30 to 150 nm. Further, even when an opaque material is used as the material of the anode 10, for example, by setting the average thickness to about 10 to 30 nm, it can be used as a transparent anode in a top emission type organic EL element.
The average thickness of the anode 10 can be measured by a crystal oscillator film thickness meter at the time of film formation of the anode 10.

"Sealing"
The organic EL element 1 shown in FIG. 1 may be sealed if necessary.
For example, the organic EL element 1 shown in FIG. 1 is provided by a sealing container (not shown) having a concave space for accommodating the organic EL element 1 and an adhesive that adheres the edge of the sealing container to the substrate 2. It may be sealed. Alternatively, the organic EL element 1 may be housed in a sealing container and sealed by filling it with a sealing material made of an ultraviolet (UV) curable resin or the like. Further, for example, the organic EL element 1 shown in FIG. 1 includes a plate member (not shown) arranged on the anode 10 and a frame member (not shown) arranged along the edge of the plate member on the side facing the anode 10. The sealing member (not shown) may be sealed with an adhesive that adheres between the plate member and the frame member and between the frame member and the substrate 2.

When the organic EL element 1 is sealed using the sealing container or the sealing member, a desiccant that absorbs moisture may be arranged in the sealing container or inside the sealing member. Further, a material that absorbs moisture may be used as the sealing container or the sealing member. Further, a space may be formed in the sealed sealing container or inside the sealing member.

As the material of the sealing container or the sealing member used when sealing the organic EL element 1 shown in FIG. 1, a resin material, a glass material, or the like can be used. Examples of the resin material and the glass material used for the sealing container or the sealing member include the same materials as those used for the substrate 2.

"Manufacturing method of organic EL element"
Next, as an example of the method for manufacturing the organic EL element of the present invention, the method for manufacturing the organic EL element 1 shown in FIG. 1 will be described.
In order to manufacture the organic EL element 1 shown in FIG. 1, first, the cathode 3 is formed on the substrate 2.
The cathode 3 can be formed by a sputtering method, a vacuum vapor deposition method, a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, a vapor phase deposition method, a liquid phase film formation method, or the like. A method of joining metal foils may be used for forming the cathode 3.

Next, an inorganic memory inorganic oxide layer 4 is formed on the cathode 3.
The memory inorganic oxide layer 4 is formed by using, for example, a spray pyrolysis method, a sol-gel method, a sputtering method, a vacuum vapor deposition method, or the like. The surface of the oxide layer 4 thus formed may be uneven rather than smooth.

Next, the electron injection layer 5 is formed on the memory inorganic oxide layer 4.
The electron injection layer 5 can be formed by the method for producing an organic thin film described above.

Next, the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 are formed on the electron injection layer 5 in this order.
The method for forming the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 is not particularly limited, and conventionally, the method of forming the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 is matched to the characteristics of the materials used for each of the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8. Various known forming methods can be appropriately used.

Specifically, as a method for forming each layer of the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8, an organic compound solution containing an organic compound to be the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 is used. Examples thereof include a coating method for coating, a vacuum vapor deposition method, and an ESDUS (Evasorative Spray Depositionation from Ultra-dilute Solution) method. Among the methods for forming the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8, it is particularly preferable to use the coating method. When the solvent solubility of the organic compounds forming the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 is low, it is preferable to use the vacuum vapor deposition method or the ESDUS method.

When the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 are formed by the coating method, the organic compounds to be the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 are each dissolved in a solvent. As a result, an organic compound solution containing an organic compound serving as an electron transport layer 6, a light emitting layer 7, and a hole transport layer 8 is formed.

Examples of the solvent used for dissolving the organic compound forming the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 include fragrances such as xylene, toluene, cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene, and tetramethylbenzene. Group hydrocarbon solvents, aromatic heterocyclic compound solvents such as pyridine, pyrazine, furan, pyrrol, thiophene and methylpyrrolidone, aliphatic hydrocarbon solvents such as hexane, pentane, heptane and cyclohexane are preferable, and these alone are used alone. Alternatively, they can be mixed and used.

Examples of the method for applying the organic compound solution containing the organic compound to be the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8 include a spin coating method, a casting method, a micro gravure coating method, a gravure coating method, and a bar coating method. Various coating methods such as a roll coating method, a wire bar coating method, a dip coating method, a spray coating method, a screen printing method, a flexographic printing method, an offset printing method, and an inkjet printing method can be used. Among these coating methods, it is preferable to use the spin coating method or the slit coating method because the film thickness can be more easily controlled.

Next, the hole injection layer 9 and the anode 10 are formed on the hole transport layer 8 in this order.
When the hole injection layer 9 is made of an inorganic material, the hole injection layer 9 can be formed in the same manner as, for example, the memory inorganic oxide layer 4.
When the hole injection layer 9 is made of an organic material, the hole injection layer 9 can be formed in the same manner as, for example, the electron transport layer 6, the light emitting layer 7, and the hole transport layer 8.
The anode 10 can be formed in the same manner as the cathode 3, for example.
By the above steps, the organic EL element 1 shown in FIG. 1 is obtained.

"Seal method"
When the organic EL element 1 shown in FIG. 1 is sealed, it can be sealed by using the usual method used for sealing the organic EL element.

"Other examples"
The organic EL device of the present invention is not limited to the organic EL device described in the above-described embodiment.
In the organic EL element 1 shown in FIG. 1, the electron injection layer 5, the electron transport layer 6, the hole transport layer 8, and the hole injection layer 9 may be formed as needed and may not be provided. ..
Further, each layer of the cathode 3, the memory inorganic oxide layer 4, the electron injection layer 5, the electron transport layer 6, the light emitting layer 7, the hole transport layer 8, the hole injection layer 9, and the anode 10 is formed by one layer. It may be made up of two or more layers.

Further, in the organic EL element 1 shown in FIG. 1, another layer may be provided between the layers shown in FIG. Specifically, an electron blocking layer or the like may be provided, if necessary, for the purpose of further improving the characteristics of the organic EL element.

The organic EL device of the present invention can change the emission color by appropriately selecting a material such as a light emitting layer, and can also obtain a desired emission color by using a color filter or the like in combination. Therefore, it can be suitably used as a light emitting part of a display device or a lighting device.

"Display device"
The display device according to the embodiment of the present invention displays an image using an element array group in which a plurality of organic EL elements of the present invention are arranged. The display device of the present embodiment includes an organic EL element in which the light emitting characteristics are less likely to deteriorate even when continuously driven, and the light emitting brightness is less likely to be lowered. Therefore, it can be used stably for a long period of time.

FIG. 4 is a partial circuit diagram of the display device 100 of the present invention. In FIG. 4, as a plurality of organic electroluminescent devices,
The display device 100 shown in FIG. 4 has a matrix in which a plurality of organic electroluminescence elements 101 (101p, 101q, 101r, 101s, ...) Of the present invention form a plurality of rows and a plurality of columns on a substrate. A plurality of first electrode lines 102 (102A, 102B, ...) Arranged and provided corresponding to each row of the plurality of organic electroluminescence elements 101 arranged in a matrix, and corresponding to each column. A plurality of second electrode wires 103 (103c, 103d, ...) Provided, a first driver 104 for selectively applying a potential to the plurality of first electrode wires 102, and the plurality of first electrode wires 103. A second driver 105 for selectively applying a potential to the second electrode line, and a control device (not shown) for controlling the potential of the first driver 104 and the potential of the second driver 105 are provided.

Each of the first electrode wires 102 is electrically connected to the cathode of each organic EL element 101, and each second electrode wire 103 is electrically connected to the anode of each organic EL element 101. Further, each first electrode wire 102 is electrically connected to each second electrode wire 103 via each organic EL element 101. The first driver 104 selectively applies potentials to the plurality of first electrode lines 102, and the second driver 103 selectively applies potentials to the plurality of second electrode lines 103. Therefore, the voltage applied to each organic EL element 101 is controlled by the selective control of the first driver 104 and the second driver 105, and the light emission / non-emission of the organic EL element is controlled.
For the sake of simplicity, the connection between each driver and each electrode line is omitted.

FIG. 5 is a timing chart for explaining a driving method of the display device of the present invention. For convenience of explanation, it is assumed that the organic EL device of the present invention provided with the memory-like inorganic oxide layer having the current-voltage characteristic shown in FIG. 6 is used.
The voltage applied to the organic EL element is the sum of the voltage applied to the memory inorganic oxide layer itself and the voltage applied to a portion other than the memory inorganic oxide layer. Therefore, the voltage applied to the organic EL element will be described as being applied to the memory inorganic oxide layer itself, ignoring the voltage applied to the portion other than the memory inorganic oxide layer.

In FIG. 5, the graphs indicated by reference numerals 102A and 102B are the first electrode line 102A and the first electrode line 102A and the first electrode line electrically connected to the cathode of the organic EL element 101, which are controlled via the first driver 104, respectively. It shows the time course of the potential of 102B. Further, the graphs indicated by reference numerals 103c and 103d indicate changes in the potentials of the second electrode line 103c and the second electrode line 103d, respectively, controlled via the second driver 105 with time.

In the initial state (t = 0), the memory-like inorganic oxide layer of the organic EL element 101 is in a high resistance state.
First, a potential of -2V is applied to the first electrode wire 102A and the first electrode wire 102B, and the potentials of the second electrode wire 103c and the second electrode wire 103d are set to 0V. At this time, the applied voltage, that is, the potential difference between the electrodes of each organic EL element 101 is 2V, which is smaller than the threshold voltage of 10V at which the memory inorganic oxide layer changes to a low resistance state. Therefore, the memory inorganic oxide layer maintains a high resistance state, and the current flowing through the light emitting layer of the organic EL element 101 is very small. Therefore, the light emitting layer does not emit light.

Then, when t = T ₁ , the first electrode wire 102A is controlled by the first driver 104, and the potential of -8V is applied to the first electrode wire 102A, and the first electrode wire 102A is controlled by the second driver 105. A potential of + 2V is applied to the second electrode line 103c and the second electrode line 103d. On the other hand, the first electrode wire 102B is maintained at -2V.
As a result, the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101p and the organic EL element 101r is 10V, and then 10V is maintained until _{t = T 2.} Here, this 10V is equal to the threshold voltage 10V at which the memory inorganic oxide layer changes to a low resistance state (see FIG. 6). Therefore, the memory-like inorganic oxide layer of the organic EL element 101p and the organic EL element 101r changes to a low resistance state. _{As a result, a current I high} sufficient for the light emitting layer to emit light flows through the organic EL element 101p and the organic EL element 101r, and the organic EL element 101p and the organic EL element 101r emit light. The low resistance state of the memory inorganic oxide layer of the organic EL element 101p and the organic EL element 101r is maintained even when the applied voltage between the electrodes is lowered, and _{when t = T 2} , the potential of the first electrode line 102A is maintained. Continues even if the voltage is returned to -2V. _{That is, the I high} flowing through the organic EL element 101p and the organic EL element 101r is maintained even when t = T ₂ , and light emission of the same brightness is maintained.
On the other hand, the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101q and the organic EL element 101s is 4V, and the memory inorganic oxide layer of the organic EL element 101q and the organic EL element 101s is maintained in a high resistance state and is organic. Since the current flowing through the light emitting layer of the EL element 101q and the organic EL element 101s is very small, it does not emit light.

Then, when t = T ₂ , the potential of the first electrode line 102A is returned to -2V by being controlled via the first driver 104, and the second is controlled via the second driver 105. The potentials of the electrode wire 103c and the second electrode wire 103d are returned to 0V. On the other hand, the first electrode wire 102B is maintained at -2V.
As a result, the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101p and the organic EL element 101r becomes 2V, but the low resistance state of the memory inorganic oxide layer is maintained, and the organic EL element 101p and the organic EL _{The I high} flowing through the element 101r is maintained, and the light emission of the same brightness is maintained.
On the other hand, since the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101q and the organic EL element 101s is lowered to 2V, the memory inorganic oxide layer of the organic EL element 101q and the organic EL element 101s is maintained in a high resistance state. The current flowing through the light emitting layer of the organic EL element 101q and the organic EL element 101s is very small and does not emit light.

Then, when t = T ₃ , the first electrode wire 102B is controlled by the first driver 104, and the potential of -8V is applied to the first electrode wire 102B, and the first electrode wire 102B is controlled by the second driver 105. A potential of + 2V is applied to the second electrode line 103c and the second electrode line 103d. On the other hand, the first electrode wire 102A is maintained at -2V.
Thus, the applied voltage or potential difference between the electrodes of the organic EL element 101q and the organic EL element 101s is 10V, the subsequent, 10V is maintained until t = _{T 4.} Here, this 10V is equal to the threshold voltage 10V at which the memory inorganic oxide layer changes to a low resistance state. Therefore, the memory-like inorganic oxide layer of the organic EL element 101q and the organic EL element 101s changes to a low resistance state. _{As a result, a current I high} sufficient for the light emitting layer to emit light flows through the organic EL element 101q and the organic EL element 101s, and the organic EL element 101q and the organic EL element 101s emit light. The low resistance state of the memory inorganic oxide layer of the organic EL element 101q and the organic EL element 101s is maintained even when the applied voltage between the electrodes is lowered, and _{when t = T 4} , the potential of the first electrode line 102B is maintained. Continues even if the voltage is returned to -2V. That, I _high flowing through the organic EL element 101q and the organic EL element 101s can also be maintained when the t = _{T 4,} light emission of the same luminance is maintained.
On the other hand, the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101p and the organic EL element 101r is 4V, and the memory inorganic oxide layer of the organic EL element 101q and the organic EL element 101s is maintained in a low resistance state and is organic. The current flowing through the light emitting layer of the EL element 101p and the organic EL element 101r is _{maintained at I high} , and light emission of the same brightness is maintained.

As described above, when t = T _{4 , the same current I high} flows through all of the organic EL element 101p, the organic EL element 101q, the organic EL element 101r, and the organic EL element 101s, and emits light with the same brightness.

Next, when t = T ₅ , when the light emitting state of the organic EL element, for example, the organic EL element 101p is changed to the non-light emitting state, the second electrode wire 103c is controlled by the second driver 105. A potential of 2V is applied. As a result, the applied voltage, that is, the potential difference between the electrodes of the organic EL element 101q becomes 0V, and the memory inorganic oxide layer returns to the high resistance state. At this time, the current flowing through the light emitting layer of the organic EL element 101q becomes very small, and the state becomes non-light emitting.

As described above, the display device of the present invention has a circuit configuration similar to that of the passive matrix drive system, but can be driven by an active matrix.

"Lighting device"
The lighting device according to an embodiment of the present invention emits surface light using an element array group in which a plurality of organic EL elements of the present invention are arranged.

1,101 Organic EL element (organic electroluminescence element)
2 Substrate 3 Cathode 4 Memory inorganic oxide layer 5 Electron injection layer 6 Electron transport layer 7 Light emitting layer 8 Hole transport layer 9 Hole injection layer 10 Anode 100 Display device 102 1st electrode line 103 2nd electrode line 104 1st Driver 105 2nd driver

Claims (5)

A first electrode, a memory inorganic oxide layer, a light emitting layer, and a second electrode are provided on the substrate in this order.
The organic electroluminescence device, wherein the memory-based inorganic oxide layer contains a material that exhibits hysteresis in current-voltage characteristics. The organic electroluminescence device according to claim 1, wherein the first electrode is a cathode and the second electrode is an anode. The organic electroluminescence device according to claim 1 or 2, wherein the memory inorganic oxide layer contains a transition metal. The plurality of organic electroluminescent devices according to any one of claims 1 to 3 are arranged in a matrix so as to form a plurality of rows and a plurality of columns on a substrate.
A plurality of first electrode wires provided corresponding to each row of the plurality of organic electroluminescence elements arranged in a matrix, a plurality of second electrode wires provided corresponding to each column, and the plurality of first electrode wires. A first driver for selectively applying an electric potential to the first electrode wire, a second driver for selectively applying an electric potential to the plurality of second electrode wires, and the first driver. A display device including a control device for controlling an electric potential and the electric potential of the second driver. A lighting device comprising the organic electroluminescence device according to any one of claims 1 to 3.

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