JPH04357694A - Thin organic film el element - Google Patents

Abstract

PURPOSE:To conduct low voltage drive and enhance durability by providing at least one inclined structure layer having a concentration gradient in a component between respective layers of an EL element provided with organic compound layers between two electrodes. CONSTITUTION:A transparent positive electrode 2 comprising a vapor deposition thin film of a metal such as gold, platinum, palladium and the like or an oxide film of tin, indium-tin and the like is formed on a glass substrate 1. Between a compound layer 3 having an electron hole transport function and an electron transporting organic compound layer 4 having a light emission function both formed thereon, an inclined structure layer 8 having a concentration gradient wherein components of both the layers are continuously varied is provided. A negative electrode 7 is formed by vapor deposition of a metal having a little work function or of this metal together with another stable metal. Between the layer 4 and the negative electrode 7 an inclined structure layer 9 of components of both layers can be provided.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to electrical light emitting, that is, EL.
Regarding EL elements using (electroluminescence),
For more details, see EL with an organic compound layer between two electrodes.
The present invention relates to an organic thin film EL device that has at least one graded structure layer in which components have a concentration gradient between each layer of the device, thereby realizing low voltage driving and improved durability.

0002

[Prior Art] EL elements differ in their light emitting mechanisms (
1) An intrinsic EL light-emitting element that excites a light emitter through local movement of electrons and holes within the light-emitting layer and emits light only in an alternating current electric field; (2) Injection of electrons and holes from electrodes and their There are two types of EL devices: carrier injection type EL devices, which excite a luminescent material and emit light by recombination within a light emitting layer. (1) Intrinsic EL type light emitting devices generally use inorganic compounds as light emitters, but they require a high AC electric field of 100 V or more for driving, are expensive to manufacture, and have insufficient brightness and durability. It has many problems such as In the carrier injection type EL light emitting device (2), after the development of a technology using a thin organic compound as a light emitting layer, a high brightness light emitting device can be obtained by driving at a low voltage. These EL elements are disclosed in, for example, Japanese Patent Application Laid-Open No. 59-194393, US Pat. No. 4,720,43, Jpn. Journal
of Physics, vol. 27, p713
- 715, and is usually an element in which a hole injection transport layer or an electron injection layer is provided on one or both sides of a light emitting layer, and emits light with high brightness in a DC electric field of 50 V or less. However, the conventional carrier injection type EL light emitting device is
Since each layer of the multilayer structure is formed by laminating them, there are problems with poor physical and electrical connectivity between the layers, resulting in an increase in driving voltage and poor durability. (A, B in Figure 2)

0003

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned actual state of the prior art, and its purpose is to provide an organic thin film EL element that can reduce driving voltage and has excellent durability. . In order to solve the above-mentioned object, the present inventors have carefully studied the interlayer structure and found that each component forming the interlayer has a concentration gradient and does not have a clear interface as if the layers were simply laminated. The inventors have discovered that the above problems can be solved by using a so-called inclined structure, and have completed the present invention.

0004

[Means for Solving the Problems] That is, the present invention has the following features:
．． In an organic thin film EL device in which a compound layer having a hole transporting ability and an electron transporting organic compound layer having a light emitting function are laminated between two electrodes, at least one of which is a metal electrode,
2. An organic thin film EL device characterized in that a gradient structure layer is formed in at least one between each layer constituting the EL device, in which a concentration gradient is provided for each component forming the interlayer.
An organic thin film EL device in which a compound layer having a hole transporting ability, an organic compound layer having a light emitting function, and an organic compound layer having an electron transporting ability are laminated between two electrodes, at least one of which is a metal electrode. This organic thin film EL device is characterized in that a gradient structure layer is formed in at least one of the constituent layers in which a concentration gradient is provided for each component forming the interlayer.

[0005] The gradient structure layer of the present invention is produced by adjusting the evaporation rate using a vacuum evaporation apparatus having an evaporation boat each having an independent power supply circuit when laminating each organic compound layer and electrode layer of the device. Accordingly, there is provided an organic thin film EL device characterized in that a gradient structure layer is formed between each of the organic compound layers and between the organic compound layer and the metal electrode. The organic thin film EL device of the present invention is a device having the following configuration, in which at least one graded structure layer in which each component has a concentration gradient is laminated between the layers, such as (1) anode/positive layer. Compound layer with hole transport ability/electron transport organic compound layer with light emitting function/cathode (2) anode/compound layer with hole transport ability/organic compound layer with light emitting function/organic compound layer with electron transport ability / cathode.

Further, the present invention will be explained in detail below with reference to the drawings. FIGS. 1A and 1C are cross-sectional views of the organic thin film EL device of the present invention. 1 is a glass substrate, and 2 is a transparent anode formed on the substrate. The transparent anode 2 is a vapor-deposited thin film of metal such as gold, platinum, or palladium, or an oxide film such as tin or indium-tin, and is preferably transparent to visible light in order to extract luminescence. 3 is a compound layer having a hole transporting ability, and 4 is an electron transporting organic compound layer having a light emitting function. Reference numeral 8 denotes a so-called gradient structure layer where a concentration gradient is provided in which the components of layer 3 and the components of layer 4 change continuously. Further, 7 is a cathode, which is formed by vacuum evaporation of metal. As the metal used for the cathode 7, any solid metal that can be vacuum-deposited may be used, but it is particularly desirable to use a metal with a small work function or a co-deposition of a metal with a small work function and a stable metal. Reference numeral 9 denotes a portion of the graded structure layer consisting of the components of layer 4 and the components of layer 7. In addition, B and D in FIG. 1 show other organic thin films E of the present invention.
It is a sectional view of the L element, and layers 1 to 3 to be formed are the A
and C. 5 is an organic compound layer having a light-emitting function, and 10 is a portion of a gradient structure layer consisting of the components of layer 3 and the components of layer 5. Reference numeral 6 is an organic compound layer having an electron transport ability, and reference numeral 11 is a portion of a gradient structure layer consisting of the components of layer 5 and the components of layer 6. 7 is a cathode, which is made of the same metal as A and C, and 12 is a portion of a graded structure layer consisting of the components of layer 6 and the component of layer 7. Note that the EL element of the present invention requires EL to further improve the hole transport efficiency.
A gradient structure layer may be provided between the element anode 2 and the compound layer 3 having hole transport ability.

[0007] Compounds with hole transporting ability used in the present invention include compounds with excellent hole transporting ability such as polyvinylcarbazole oligomers that can be vacuum deposited and condensates of N,N-diphenyltoluidine and ketones. Examples include substances. Furthermore, examples of single organic compounds include triphenylamine derivatives, stilbene derivatives, oxadiazole derivatives, etc., but the organic compounds used in the present invention are not limited to these. Furthermore, organic compounds may be used in combination for the purpose of improving hole transport ability, prevention of crystallization, and stability.

On the other hand, examples of organic compounds having a light-emitting function used in the present invention include oxine metal complexes, perylene derivatives, polyphenylcyclopentadiene, phthaloperinone derivatives, triphenylamine derivatives, and many other organic compounds. However, the present invention is not limited to these.

The thickness of the compound layer 3 having the above-mentioned hole transporting ability alone is less than 1000 Å, preferably 10 Å to 50 Å.
0 Å, and if it exceeds 1000 Å, the driving voltage becomes significantly high, which is contrary to the purpose of the present invention. Also, a gradient structure layer 8 formed between a compound layer 3 having a hole transporting ability and an electron transporting organic compound layer 4 having a light emitting function, or a compound layer 3 having a hole transporting ability and an organic compound layer having a light emitting function. 5
The thickness of the gradient structure layer 10 formed between the layers is 5 Å.
~1000 Å, preferably 10 Å to 500 Å. If the thickness is less than 5 Å, the physical strength is poor, and if it exceeds 1000 Å, the driving voltage becomes significantly high, which is contrary to the purpose of the present invention.

Further, the thickness of the electron-transporting organic compound layer 4 having a light-emitting function or the organic compound layer 5 having a light-emitting function alone is less than 1000 Å, preferably 50 Å to 500 Å, and if it exceeds 1000 Å, the driving voltage becomes significantly high. Become,
This is contrary to the purpose of the present invention. Further, the organic compound layer 6 having electron transport ability of the present invention has a thickness of less than 1000 Å, preferably 50 Å.
Å to 500 Å. If the thickness exceeds 1000 Å, the driving voltage becomes significantly high, which is contrary to the purpose of the present invention. The thickness of the gradient structure layer 11 formed by the organic compound layer 5 having a light emitting function and the organic compound layer 6 having an electron transporting ability is determined from the gradient structure layer 8 or 10 in terms of physical strength and driving voltage. Preferably, they are the same. Note that when the thickness of the organic compound layer 6 having electron transport ability is 100 Å or less, the thickness of the gradient structure layer 11 portion is 200 Å to 500 Å.
It is preferable that it is Å. The gradient structure layer 9 formed between the electron-transporting organic compound layer 4 having a light-emitting function and the cathode 7, or the gradient structure layer 12 portion formed between the organic compound layer 6 having an electron-transporting ability and the cathode 7. Thickness is 5 Å ~
500 Å, preferably 10 Å to 100 Å. If the thickness is less than 5 Å, the adhesion effect between the layers is poor;
Even if the thickness exceeds 0.00 Å, there is no significant advantage.

[0011] The graded structure layer of the present invention is a layer in which each component forming a gap between the electrodes has a concentration gradient that continuously changes, and has a clear boundary as if the layers were simply laminated. It's something you don't have. Continuously changing concentration gradient means that the concentration of a component in one layer is constant and the concentration of a component in the other layer increases or decreases continuously, or that the concentration of a component in one layer is constant and the concentration of a component in the other layer increases or decreases continuously, or that the concentration of a component in one layer is constant and the concentration of a component in the other layer increases or decreases continuously, or The component concentration may increase or decrease. As a method for obtaining the gradient structure layer of the present invention, the components of one layer are deposited for a fixed time in vacuum, while the deposition time of the components of the other layer is continuously changed. Alternatively, the deposition time of the components of both layers may be continuously changed.

Furthermore, since the thickness of each organic compound layer directly affects the drive voltage, it is preferable to make it as thin as possible because the drive voltage will be lower, but on the other hand, the dielectric breakdown voltage also tends to decrease, and the overall The total thickness of the organic compound layer may be selected depending on the purpose and is not limited. Next, the cathode 7 of the present invention is preferably formed into a transparent cathode by vacuum deposition, and the thickness is not particularly limited.

The EL element obtained by the present invention is mainly used in flat panels, liquid crystal displays, backlights for LCDs, large screen displays, televisions, and the like.

[0014]

[Examples] The present invention will be explained in more detail with reference to Examples below. Example 1 As an anode, a glass coated with indium-tin oxide (manufactured by Matsuzaki Vacuum Co., Ltd., hereinafter referred to as ITO) was ultrasonically cleaned in acetone for 10 minutes. Next, it was boiled in ethanol for 5 minutes, taken out, dried by blowing dry nitrogen gas, and then set in a vacuum device. Next, N,N'-diphenyl-N,N'-
(3-methylphenyl)-1,1'-biphenyl-4,
4'-diamine (hereinafter referred to as TPD), an aluminum complex of oxine (hereinafter referred to as Alq3) as an electron-transporting organic compound with a light-emitting function, and magnesium and silver as cathode materials were used in separate power supply circuits in a vacuum apparatus. The vacuum level inside the vacuum device was set to 3 x 10-6 torr
And so. First, a TPD boat was heated on the ITO surface and TPD was deposited at a constant deposition rate of 1.0 Å/Sec.
0 Å was deposited to form an organic compound layer having hole transport ability. Furthermore, TPD started the deposition of Alq3 while continuing the deposition at a constant deposition rate of 1.0 Å/Sec. The deposition rate of Alq3 was gradually increased from 0 Å/Sec.
The deposition rate was 10 Å/Sec. At this point T.P.
By reducing the heating of D, the graded structure layer becomes 200 Å.
The TPD deposition was stopped when the film was formed. Continue Alq3
By continuing vapor deposition alone, a layer of an electron-transporting organic compound having a light-emitting function was formed with a thickness of 200 Å. Next, magnesium and silver were co-deposited to form a 2000 Å cathode. The obtained device emitted green light when a direct current voltage was applied to the ITO side as the anode and the above-mentioned cathode. Also, driving voltage 15V, current density 110 mA/cm2
showed a luminance of 945 cd/m2. Additionally, this device could be operated in the atmosphere. Furthermore, this element was heated at a current density of 6 mA/in sufficiently dry air.
It was driven under the conditions of cm2 and brightness of 50 cd/m2,
No decrease in brightness was observed after 48 hours.

Example 2 Using the same materials and performing the same operations as in Example 1, I
TO The glass surface has an organic compound layer with a hole transporting ability of 200 Å, a gradient structure layer of 100 Å, an electron transporting organic compound layer with a light emitting function of 200 Å, and a cathode of 200 Å.
00 Å to form an organic thin film EL device. The obtained device emitted green light when a direct current voltage was applied to the ITO side as the anode and the above-mentioned cathode. In addition, the driving voltage is 21V,
Current density 100mA/cm2 is 1000cd/m2
It showed a luminance of . Additionally, this device could be operated in the atmosphere. Furthermore, this element was heated to a luminance of 50 c at a current density of 5 mA/cm2 in sufficiently dry nitrogen.
Although the device was driven under the condition of d/m2, no decrease in brightness was observed after 48 hours.

Comparative Example 1 Using the same material as in Example 1, an organic compound layer having a hole transporting ability was formed on the surface of the ITO glass at a thickness of 250 Å.
An electron transporting organic compound layer with a light emitting function is formed at a thickness of 250 Å.
Then, a cathode of 2000 Å was vacuum deposited to produce an organic thin film EL device. This device emitted green light at 13 V, but the electrodes were destroyed within a few seconds.

Comparative Example 2 Using the same material as in Example 1, a 500 Å layer of an organic compound having a hole transporting ability was formed on the ITO glass surface, an 800 Å layer of an electron transporting organic compound having a light emitting function, and a cathode. An organic thin film EL device was fabricated by vacuum deposition of 2000 Å. This device has a driving voltage of 46V and a current density of 110V.
It exhibited green light emission with a brightness of 925 cd/m2 at mA/cm2. However, at 21 V, the luminance was less than 2 cd/m2. In addition, in order to draw out the cathode terminal, silver paste was applied to the cathode metal surface, and during the work of joining the cathode terminal,
The deposited cathode metal easily peeled off from the electron-transporting organic compound layer having a light-emitting function.

Example 3 Using the same material as in Example 1, a 400 Å layer of an organic compound having a hole-transporting ability and a 600 Å layer of an electron-transporting organic compound having a light-emitting function were deposited on the surface of an ITO glass. Thereafter, a 100 Å gradient structure layer was formed between the Alq3 and cathode metal layers, and then a 2000 Å cathode was vacuum deposited to produce an organic thin film EL device. This device has a brightness of 950c at a driving voltage of 30V and a current density of 100 mA/cm2.
It exhibited green luminescence of d/m2. In this element, when cellophane tape was applied to the surface of the cathode metal and peeled off, the organic compound layer portion was found to be attached to the cathode metal. Furthermore, no peeling occurred when the cathode terminal was drawn out during silver paste bonding.

Example 4 In the same manner as in Example 1, a gradient structure layer of 200 Å and 50 Å of an organic compound layer having a hole transporting ability was formed on the surface of an ITO glass, and an electron transporting organic compound layer having a light emitting function was further formed. After depositing 200 Å, a 50 Å graded structure layer was formed between the Alq3 and cathode metal layers, and then the cathode metal 20
00 Å was vacuum deposited to form an organic thin film EL device. The obtained device emitted green light when a direct current voltage was applied to the ITO side as the anode and the above-mentioned cathode. Drive voltage 19V, current density 100mA/cm2: 1050cd/m2
It showed a luminance of . Additionally, this device could be operated in the atmosphere. Furthermore, this element was heated to a luminance of 50 cd at a current density of 5 mA/cm2 in sufficiently dry nitrogen.
/m2, but no decrease in brightness was observed after 48 hours. Furthermore, this element did not cause peeling at the cathode portion when the cathode terminal was drawn out by silver paste bonding.

[0020]

Effects of the Invention The organic thin film EL device of the present invention has a so-called graded structure layer that does not have a clear interface between at least one of the multiple layers constituting the device.
The bonding properties between each layer are improved, and the injectability of carriers such as electrons is improved due to the enlarged bonding area. Furthermore, it has advantages such as low voltage driving and improved durability.

[Brief explanation of the drawing]

1A, B, C, and D of FIG. 1 are cross-sectional views showing an example of an organic thin film EL element according to the present invention.

FIGS. 2A and 2B are cross-sectional views showing an example of a conventional organic thin film EL element.

[Explanation of symbols]

1 Glass substrate 2 Anode 3 Compound layer having hole transporting ability 4 Electron transporting organic compound layer having light emitting function 5
Organic compound layer with a light-emitting function 6 Organic compound layer with an electron-transporting ability 7 Cathode 8 Gradient structure layer of a compound layer with a hole-transporting ability and an electron-transporting organic compound layer with a light-emitting function 9 Electron-transporting organic compound with a light-emitting function Gradient structure layer 10 of compound layer and cathode Gradient structure layer 11 of compound layer having hole transport ability and organic compound layer having light emitting function Gradient structure layer of organic compound layer having light emitting function and organic compound layer having electron transport ability 12 Organic compound layer with electron transport ability and graded structure layer of cathode

Claims (2)

[Claims] Claim 1: An organic thin film EL in which a compound layer having a hole transporting ability and an electron transporting organic compound layer having a light emitting function are laminated between two electrodes, at least one of which is a metal electrode.
An organic thin film EL device, characterized in that a gradient structure layer is formed in at least one of the layers constituting the EL device, in which a concentration gradient is provided for each component forming the interlayer. Claim 2: An organic thin film EL device in which a compound layer having a hole transporting ability, an organic compound layer having a light emitting function, and an organic compound layer having an electron transporting ability are laminated between two electrodes, at least one of which is a metal electrode. . An organic thin film EL device, characterized in that a gradient structure layer is formed in at least one space between each layer constituting the EL device, in which a concentration gradient is provided for each component forming the space between the layers.