KR102206852B1 - Organic light emitting device - Google Patents

Abstract

The present specification is an anode; A cathode provided opposite to the anode; A light emitting layer provided between the anode and the cathode and including a host and a dopant; A first hole transport layer provided between the anode and the emission layer; And a second hole transport layer provided between the first hole transport layer and the emission layer, wherein the HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer, and the second The HOMO energy level difference (ΔD) between the hole transport layer and the dopant is smaller than the HOMO energy level difference (ΔH) between the second hole transport layer and the host (ΔD <ΔH).

Description

Organic light emitting device {ORGANIC LIGHT EMITTING DEVICE}

The present specification relates to an organic light emitting device.

The organic light emission phenomenon is an example in which current is converted into visible light by an internal process of a specific organic molecule. The principle of organic light emission is as follows. When an organic material layer is placed between the anode and the cathode, when a voltage is applied between the inside of a specific organic molecule through the two electrodes, electrons and holes are injected into the organic material layer from the cathode and the anode, respectively. The electrons and holes injected into the organic material layer recombine to form excitons, and the excitons fall back to the ground state to emit light. An organic light-emitting device using this principle may generally include an anode, a cathode, and an organic material layer positioned therebetween, for example, an organic material layer including a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer.

An organic light-emitting device refers to a self-emission type device using an electroluminescence phenomenon that emits light when a current flows through a light-emitting organic compound, and is attracting attention as a next-generation material in various industrial fields such as displays and lighting.

It is necessary to develop a technology for improving the lifespan of the organic light-emitting device and lowering the driving voltage to increase the luminous efficiency of the organic light-emitting device.

US Patent Application Publication No. 2004-0251816

The present specification provides an organic light emitting device.

An exemplary embodiment of the present specification is an anode; A cathode provided opposite to the anode; A light emitting layer provided between the anode and the cathode and including a host and a dopant; A first hole transport layer provided between the anode and the emission layer; And a second hole transport layer provided between the first hole transport layer and the emission layer, wherein the HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer, and the second The HOMO energy level difference (ΔD) between the hole transport layer and the dopant is smaller than the HOMO energy level difference (ΔH) between the second hole transport layer and the host (ΔD <ΔH).

In addition, another exemplary embodiment of the present specification provides a display device including the aforementioned organic light emitting device.

In the organic light-emitting device according to the exemplary embodiment of the present specification, the hole injection effect is improved and the turn-on voltage is decreased, thereby reducing the driving voltage of the organic light-emitting device. Accordingly, according to the effect of lowering the driving voltage of the organic light emitting device, power consumption of the display device including the same may be lowered.

1 illustrates HOMO energy levels of a first hole transport layer, a second hole transport layer, a host of the emission layer, and a dopant of the emission layer in an organic light emitting diode according to an exemplary embodiment of the present specification.
FIG. 2 shows HOMO energy levels of a first hole transport layer, a second hole transport layer, a host of the emission layer, and a dopant of the emission layer of a conventional organic light-emitting device.
3 is a graph showing the current density according to the voltage of the organic light emitting device manufactured in Example 1 and Comparative Example 1 of the present specification.
4 is a diagram showing an organic light emitting device of the present specification.

Hereinafter, the present specification will be described in more detail.

When a member is referred to herein as being “on” another member, this includes not only the case where a member is in contact with another member, but also the case where another member exists between the two members.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

The present specification is an anode; A cathode provided opposite to the anode; A light emitting layer provided between the anode and the cathode and including a host and a dopant; A first hole transport layer provided between the anode and the emission layer; And a second hole transport layer provided between the first hole transport layer and the emission layer, wherein the HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer, and the second The HOMO energy level difference (ΔD) between the hole transport layer and the dopant is smaller than the HOMO energy level difference (ΔH) between the second hole transport layer and the host (ΔD <ΔH).

According to FIG. 2 of the present specification, in a conventional organic light emitting diode, the HOMO energy level of the second hole transport layer is changed to the HOMO energy level of the first hole transport layer and the emission layer in order to facilitate hole injection from the first hole transport layer to the host of the light emitting layer. Although the HOMO energy level of the host is set to have an intermediate value of the HOMO energy level, the hole injection performance from the second hole transport layer to the host of the emission layer is improved, while holes are injected into the dopant through the host of the emission layer, so that the driving voltage of the device is increased. there was.

However, according to FIG. 1, which is the organic light emitting device of the present specification, the organic light emitting device includes a second hole transport layer other than the first hole transport layer, and the HOMO energy level of the second hole transport layer is the first hole transport layer. Is lower than the HOMO energy level of, and the HOMO energy level difference (ΔD) between the second hole transport layer and the dopant is smaller than the HOMO energy level difference (ΔH) between the second hole transport layer and the host (ΔD <ΔH), Holes do not pass through the host of the emission layer, and holes are injected directly from the second hole transport layer to the dopant of the emission layer, and the hole injection effect is improved to decrease the turn-on voltage, thereby lowering the driving voltage of the organic light emitting device. It works.

In the present specification, the energy level means the amount of energy. Therefore, even when the energy level is displayed in the negative (-) direction from the vacuum level, the energy level is interpreted to mean the absolute value of the energy value. For example, the HOMO energy level means the distance from the vacuum level to the highest occupied molecular orbital. In addition, the LUMO energy level refers to the distance from the vacuum level to the lowest unoccupied molecular orbital.

In the present specification, the HOMO energy level may be measured by UV photoelectron spectroscopy (UPS), which measures the ionization potential of the material by irradiating UV on the surface of the thin film, and detecting electrons that protrude at this time. Alternatively, the measurement of the HOMO energy level may use cyclic voltammetry (CV) in which a substance to be measured is dissolved in a solvent together with an electrolyte, and then the oxidation potential is measured through voltage sweep. In addition, the PYSA (Photoemission Yield Spectrometer in Air) method can be used to measure the ionization potentioal in the atmosphere using a machine made by AC-3 (RKI).

Specifically, the HOMO energy level of the present specification was measured through an AC-3 (RKI) measuring instrument after vacuum deposition of a target material to a thickness of 50 nm or more on an ITO substrate.

In addition, the HOMO energy level is measured before each of the first hole transport layer, the second hole transport layer, and the light emitting layer is stacked by the method described above, and the above-described method in which the first hole transport layer, the second hole transport layer, and the light emitting layer are stacked. The HOMO energy levels of the first hole transport layer, the second hole transport layer, and the light emitting layer in the organic light-emitting device are the same as the HOMO energy levels measured before lamination.

According to an exemplary embodiment of the present specification, the HOMO energy level of the first hole transport layer and the second hole transport layer is 4 eV to 6 eV, respectively, and the HOMO energy level of the second hole transport layer is the HOMO energy of the first hole transport layer. Lower than the level

According to an exemplary embodiment of the present specification, the HOMO energy level difference (ΔD) between the second hole transport layer and the dopant and the HOMO energy level difference (ΔH) between the second hole transport layer and the host are 0.1 eV to 1 eV, respectively. , The HOMO energy level difference (ΔD) between the second hole transport layer and the dopant is smaller than the HOMO energy level difference (ΔH) between the second hole transport layer and the host (ΔD <ΔH).

According to an exemplary embodiment of the present specification, the first hole transport layer is provided in contact with the second hole transport layer.

According to an exemplary embodiment of the present specification, the second hole transport layer is provided in contact with the emission layer.

According to the exemplary embodiment of the present specification, the maximum emission wavelength of the dopant is in the range of 420nm to 500nm.

According to the exemplary embodiment of the present specification, the host is a blue host, the dopant is a blue dopant, and the emission layer is a blue emission layer.

According to an exemplary embodiment of the present specification, the first hole transport layer is a common hole transport layer. The common hole transport layer refers to a layer that transports holes injected from the hole injection layer to the second hole transport layer regardless of the color (RGB) of the organic light emitting device.

According to an exemplary embodiment of the present specification, the second hole transport layer is a blue hole transport layer. The blue hole transport layer means a layer in which holes transported from the common hole transport layer are injected into the blue light emitting layer.

According to an exemplary embodiment of the present specification, the second hole transport layer includes a monoamine compound, and the monoamine compound includes a fluorene derivative as a substituent.

The fluorene derivative may be selected from the following structures.

는 다른 치환기 또는 화합물에 연결되는 부위를 의미한다.In the above structure,

Means a site connected to another substituent or compound.

According to an exemplary embodiment of the present specification, the monoamine compound may be selected from the following compounds.

According to the exemplary embodiment of the present specification, the organic light emitting device may further include an additional organic material layer such as a hole injection layer between the anode and the first hole transport layer, but is not limited thereto.

Further, according to the exemplary embodiment of the present specification, an organic material layer such as an electron injection layer, an electron transport layer, and a hole blocking layer may be further included between the emission layer and the cathode, but is not limited thereto.

The organic light-emitting device of the present specification includes an emission layer between the anode and the cathode, and includes a first hole transport layer provided between the anode and the emission layer, and a second hole transport layer provided between the first hole transport layer and the emission layer. And the HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer, and the difference in the HOMO energy level (ΔD) between the second hole transport layer and the dopant is the second hole transport layer and the host It can be manufactured by materials and methods known in the art, except that the HOMO energy level difference (ΔH) is less than (ΔD <ΔH).

4 is a diagram illustrating an organic light emitting device of the present specification, but is not limited thereto. Specifically, according to FIG. 4, the anode 1, the first hole transport layer 10, the second hole transport layer 20, the emission layer 30, and the cathode 2 may be sequentially stacked to be manufactured. The structure of the device is not limited to this.

For example, the organic light emitting device of the present specification can be manufactured by sequentially stacking an anode, a hole injection layer, a first hole transport layer, a second hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode on a substrate. At this time, by using a PVD (physical vapor deposition) method such as sputtering or e-beam evaporation, an anode is formed by depositing a metal or a conductive metal oxide or an alloy thereof on the substrate. And, after forming a hole injection layer, a first hole transport layer, a second hole transport layer, a light emitting layer, an electron transport layer and an electron injection layer thereon, it can be prepared by depositing a material that can be used as a cathode thereon. In addition to such a method, from a cathode material to an electron injection layer, an electron transport layer, a light emitting layer, and a second hole transport layer on the substrate. An organic light-emitting device may be manufactured by sequentially depositing a first hole transport layer, a hole injection layer, and an anode material.

The substrate may be a glass substrate or a transparent plastic substrate having excellent transparency, surface smoothness, ease of handling, and water resistance, but is not limited thereto, and any substrate commonly used in organic light emitting devices is not limited thereto.

As the anode material, a material having a large work function is preferable so that holes can be smoothly injected into the organic material layer. Specific examples of the cathode material that can be used in the present invention include metals such as vanadium, chromium, copper, zinc, and gold, or alloys thereof; Metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); A combination of a metal and an oxide such as ZnO:Al or SnO ₂ :Sb; Poly(3-methylthiophene), poly[3,4-(ethylene-1,2-dioxy)thiophene] (PEDOT), conductive polymers such as polypyrrole and polyaniline, and the like, but are not limited thereto.

The cathode material is generally preferably a material having a small work function to facilitate electron injection into the organic material layer. Specific examples of the negative electrode material include metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead, or alloys thereof; There are multi-layered materials such as LiF/Al or LiO ₂ /Al, but are not limited thereto.

The hole injection layer is a layer that injects holes from the electrode, and has the ability to transport holes as a hole injection material, so that it has a hole injection effect at the anode, an excellent hole injection effect for the light emitting layer or the light emitting material, A compound that prevents the movement of excitons to the electron injection layer or the electron injection material and has excellent ability to form a thin film is preferable. It is preferable that the HOMO (highest occupied molecular orbital) of the hole injection material is between the work function of the positive electrode material and the HOMO of the surrounding organic material layer. Specific examples of hole injection materials include metal porphyrin, oligothiophene, arylamine-based organic substances, hexanitrile hexaazatriphenylene-based organic substances, quinacridone-based organic substances, and perylene-based organic substances. Organic substances, anthraquinone, polyaniline, and polythiophene-based conductive polymers, etc., but are not limited thereto.

The first hole transport layer is a layer that receives holes from the hole injection layer and transports holes to the light emitting layer through the second hole transport layer.As a hole transport material, the hole is transported from the anode or the hole injection layer and passes through the second hole transport layer. As a material that can be transferred to the light emitting layer, a material having high mobility for holes is suitable. As a specific example, an arylamine-based organic material may be used. As the arylamine-based organic material, there are triamine-based, diamine-based, and monoamine-based organic materials, and benzidine-based compounds may be used. In addition, the monoamine-based compound may additionally be doped with a p-type dopant, and the p-type dopant may be NDP-9, but is not limited thereto.

The light-emitting layer of the present specification is a material capable of emitting visible light, specifically, blue light, by transporting and bonding holes and electrons from the second hole transport layer and the electron transport layer. Examples of the host of the light-emitting layer include Alq ₃ , CBP ( 4,4'-N,N'-dicarbazole-biphenyl), 9,10-dinaphthylanthracene (ADN), TCTA(4,4',4"-tris(N-carbazolyl)-triphenylamine), ADN , dmCBP, Liq, TPBI, Balq, BCP, etc. may be used, but are not limited thereto.

Examples of the dopant of the light emitting layer are, on the other hand, known blue dopants, such as F ₂ Irpic, (F ₂ ppy) ₂ Ir (tmd), Ir (dfppz) ₃ , ter-fluorene, 4,4'-bis (4-diphenylaminostaryl) biphenyl (DPAVBi), 2,5,8,11-tetra-ti-butyl perylene (TBP), etc. may be used, but the present invention is not limited thereto.

The electron transport material of the electron transport layer is a layer that receives electrons from the electron injection layer and transports electrons to the light emitting layer, and if an additional electron transport layer is included, electrons are well injected from the cathode as an electron transport material and transferred to the light emitting layer. As a material that can be given, a material having high mobility for electrons is suitable. Specific examples include an Al complex of 8-hydroxyquinoline; Complexes including Alq3; Organic radical compounds; Hydroxyflavone-metal complexes and the like, but are not limited thereto. The electron transport layer can be used with any desired cathode material as used according to the prior art. In particular, examples of suitable cathode materials are conventional materials that have a low work function and are followed by an aluminum layer or a silver layer. Specifically, they are cesium, barium, calcium, ytterbium, and samarium, and in each case an aluminum layer or a silver layer follows.

The electron injection layer is a layer that injects electrons from the electrode, has the ability to transport electrons, has an electron injection effect from the cathode, an excellent electron injection effect on the light emitting layer or light emitting material, and injects holes of excitons generated from the light emitting layer. A compound that prevents migration to the layer and has excellent thin film formation ability is preferable. Specifically, fluorenone, anthraquinodimethane, diphenoquinone, thiopyran dioxide, oxazole, oxadiazole, triazole, imidazole, perylene tetracarboxylic acid, preorenylidene methane, anthrone, etc. Complex compounds and nitrogen-containing 5-membered ring derivatives, but are not limited thereto.

Examples of the metal complex compound include lithium 8-hydroxyquinolinato, bis(8-hydroxyquinolinato)zinc, bis(8-hydroxyquinolinato)copper, bis(8-hydroxyquinolinato)manganese, Tris(8-hydroxyquinolinato)aluminum, tris(2-methyl-8-hydroxyquinolinato)aluminum, tris(8-hydroxyquinolinato)gallium, bis(10-hydroxybenzo[h] Quinolinato)beryllium, bis(10-hydroxybenzo[h]quinolinato)zinc, bis(2-methyl-8-quinolinato)chlorogallium, bis(2-methyl-8-quinolinato)( o-cresolato)gallium, bis(2-methyl-8-quinolinato)(1-naphtholato)aluminum, bis(2-methyl-8-quinolinato)(2-naphtholato)gallium, etc. It is not limited to this.

The organic light emitting device according to the present specification may be a top emission type, a bottom emission type, or a double-sided emission type depending on the material used.

According to the exemplary embodiment of the present specification, the organic light emitting device may be a flexible organic light emitting device. In this case, the substrate may include a flexible material. Specifically, the substrate may be a flexible thin film type glass, a plastic substrate, or a film type substrate.

The material of the plastic substrate is not particularly limited, but in general, films such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyetheretherketone (PEEK), and polyimide (PI) are used in the form of a single layer or a multilayer. It may be included.

The present specification provides a display device including the organic light emitting device. In the display device, the organic light emitting device may serve as a pixel or a backlight. In addition, the configuration of the display device can be applied to those known in the art.

Hereinafter, examples will be described in detail in order to describe the present specification in detail. However, the embodiments according to the present specification may be modified in various forms, and the scope of the present specification is not construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely describe the present specification to those of ordinary skill in the art.

Example 1

A glass substrate (corning 7059 glass) coated with a thin film of 1000 Å of ITO (indium tin oxide) was placed in distilled water dissolved in a detergent and washed with ultrasonic waves. At this time, a product of Fischer Co. was used as a detergent, and Millipore Co. Distilled water filtered secondarily with the product's filter was used. After washing the ITO for 30 minutes, ultrasonic washing was performed for 10 minutes by repeating twice with distilled water. After washing with distilled water, ultrasonic cleaning was performed with a solvent such as isopropyl alcohol, acetone, and methanol, dried, and transferred to a plasma cleaner. In addition, after dry cleaning the substrate for 5 minutes using oxygen plasma, the substrate was transferred to a vacuum evaporator.

The ITO transparent electrode prepared as described above was thermally vacuum deposited to a thickness of 100Å to form a compound of the following compound HT1 and the following compound HI1 in a ratio of 98:2 (molar ratio) to form a hole injection layer. A common hole transport layer (first hole transport layer) was formed by vacuum depositing a compound (1150Å) represented by the following compound HT1 on the hole injection layer. The following compound HT2 was vacuum-deposited on the common hole transport layer (first hole transport layer) to form a blue hole transport layer (second hole transport layer) with a thickness of 50 Å to 100 Å. Subsequently, on the blue hole transport layer (second hole transport layer), a light emitting layer was formed by vacuum depositing the following compound BH as a host of the light emitting layer with a film thickness of 200 Å and the following compound BD as a dopant of the light emitting layer at a weight ratio of 25:1. ET1 and the following compound LiQ were vacuum-deposited at a weight ratio of 1:1 to form an electron injection and transport layer with a thickness of 310Å. Lithium fluoride (LiF) at a thickness of 12 Å and aluminum at a thickness of 1,000 Å were sequentially deposited on the electron injection and transport layer to form a cathode.

Comparative Example 1

In Example 1, it was prepared in the same manner as the blue hole transport layer (the second hole transport layer) except that the compound HT3, which is a conventional compound, was used instead of the compound HT2.

Table 1 below shows the HOMO energy levels of the common hole transport layer (the first hole transport layer), the blue hole transport layer (the second hole transport layer), the host of the blue emission layer, and the dopant of the blue emission layer of Example 1 and Comparative Example 1. The HOMO energy level was measured by vacuum deposition of the compound used for each layer on the ITO substrate to a thickness of 50 nm or more, and then using an AC-3 (RKI) measuring device.

In addition, in Table 1 below, the difference in HOMO energy level (ΔD) between the blue hole transport layer (second hole transport layer) of the organic light emitting device of Example 1 and Comparative Example 1 and the dopant of the light emitting layer and the blue hole transport layer (second hole transport layer) ) And the HOMO energy level difference (ΔH) of the host of the emission layer, and the values in Table 1 are expressed as absolute values.

The HOMO energy level of the first hole transport layer, the second hole transport layer, and the light-emitting layer in the above-described organic light-emitting device in which the first hole transport layer, the second hole transport layer, and the blue light-emitting layer are stacked is the same as the HOMO energy level measured by the above method. Do.

HOMO(eV) ΔD ΔH Example 1 Common hole transport layer
(1st hole transport layer) 5.34 0.12 0.44 Blue hole transport layer
(2nd hole transport layer) 5.28 Blue light emitting layer
Host 5.72 Blue light emitting layer
Dopant 5.40 Comparative Example 1 Common hole transport layer
(1st hole transport layer) 5.34 0.11 0.21 Blue hole transport layer
(2nd hole transport layer) 5.51 Host of blue light emitting layer 5.72 Blue light emitting layer
Dopant 5.40

In addition, in order to check the difference in driving voltage of the organic light emitting diodes manufactured in Example 1 and Comparative Example 1, the driving voltage was measured using a voltage-current measuring device, and the results are shown in FIG. 3. 3 is a graph showing the current density according to the voltage of the organic light emitting device manufactured in Example 1 and Comparative Example 1.

According to Tables 1 and 3, Example 1 of the organic light-emitting device of the present specification uses the compound HT2 containing a monoamine compound containing the fluorene derivative as a substituent as the second hole transport layer, and thus Table 1 As described above, the HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer, and the difference in the HOMO energy level (ΔD) between the second hole transport layer and the dopant is the HOMO between the second hole transport layer and the host. Since it is smaller than the energy level difference (ΔH) (ΔD <ΔH), there is an effect that holes are directly injected from the second hole transport layer to the dopant of the emission layer without passing through the host of the emission layer, and the hole injection effect is improved and the turn As the -on voltage decreases, the driving voltage of the organic light emitting device decreases.

On the other hand, in the organic light-emitting device of Comparative Example 1, the HOMO energy level of the second hole transport layer was adjusted to the HOMO energy level of the first hole transport layer and the host of the light emitting layer in order to facilitate hole injection from the first hole transport layer to the host of the light emitting layer. The intermediate value of the HOMO energy level, that is, the HOMO energy level of the second hole transport layer is set to have a higher value than the HOMO energy level of the first hole transport layer, but since holes are injected into the dopant through the host of the emission layer, the driving voltage of the device is There is a disadvantage of increasing.

Accordingly, it can be seen that Example 1, which is an organic light-emitting device according to an exemplary embodiment of the present specification, has a lower driving voltage than Comparative Example 1, which is a conventional organic light-emitting device.

1: anode
2: cathode
10: first hole transport layer
20: second hole transport layer
30: light emitting layer
(1): HOMO energy level of the first hole transport layer
(2): HOMO energy level of the second hole transport layer
(3): HOMO energy level of the light-emitting layer dopant
(4): HOMO energy level of the emitting layer host

Claims (8)

Anode;
A cathode provided opposite to the anode;
A light emitting layer provided between the anode and the cathode and including a host and a dopant;
A first hole transport layer provided between the anode and the emission layer; And
An organic light-emitting device comprising a second hole transport layer provided between the first hole transport layer and the light emitting layer,
The second hole transport layer is provided in contact with the emission layer,
The second hole transport layer includes a monoamine compound, and the monoamine compound is any one selected from the following compounds,
The HOMO energy level of the second hole transport layer is lower than the HOMO energy level of the first hole transport layer,
An organic light-emitting device in which the difference in HOMO energy level (ΔD) between the second hole transport layer and the dopant is smaller than the difference in HOMO energy level (ΔH) between the second hole transport layer and the host (ΔD <ΔH):

. The organic light-emitting device of claim 1, wherein the first hole transport layer is provided in contact with the second hole transport layer. delete The organic light-emitting device of claim 1, wherein the dopant has a maximum emission wavelength in a range of 420 nm to 500 nm. The organic light-emitting device of claim 1, wherein the host is a blue host, the dopant is a blue dopant, and the emission layer is a blue emission layer. The organic light-emitting device of claim 1, wherein the first hole transport layer is a common hole transport layer. The organic light-emitting device of claim 1, wherein the second hole transport layer is a blue hole transport layer. A display device comprising the organic light emitting device according to any one of claims 1, 2 and 4 to 7.

Images