WO2024005436A2 - Organic electroluminescent device including light extraction layer - Google Patents

Abstract

Disclosed is an organic electroluminescent device including a light extraction layer. The organic electroluminescent device including a light extraction layer comprises a substrate, a first electrode, at least one organic layer including a blue light emitting layer, a second electrode, and the light extraction layer in this order, wherein the light extraction layer may contain a material that satisfies the following conditions (1) to (3). Condition (1): n(@450nm) ≥ 2.00, condition (2): k@420nm ≥ 0.10, and condition (3) k@450nm ≤ 0.01 (where n represents the refractive index at a defined wavelength, and k represents the extinction coefficient at a defined wavelength). Accordingly, the organic electroluminescent device may have improved light emission efficiency outside the light extraction layer, and improved color purity.

Description

Organic electroluminescent device including light extraction layer

The present invention relates to organic electroluminescent devices, and particularly to organic electroluminescent devices including a light extraction layer.

The luminous efficiency of organic electroluminescent devices is divided into internal luminous efficiency and external luminous efficiency. In the case of external luminous efficiency, internal luminescence generated from the organic material layer interposed between the first and second electrodes is reduced by about 20% through an optical process. It is emitted to the outside at a low level, and about 80% is destroyed in the optical process.

In order to prevent light from being extinguished during the optical process and improve external luminous efficiency, various organic compounds with high refractive index have been applied as materials for the optical extraction layer. Even to this day, even external luminous materials have improved external luminous efficiency. Efforts are continuing to develop stable organic compounds with a high refractive index that can be increased, but in the case of organic electroluminescent devices, blue light emits light in the region of 440nm to 510nm, so the light extraction layer with a high refractive index has a wavelength of 440nm. As part of the light in the -450 nm range is absorbed, efficiency decreases and color purity decreases.

In addition, UV light existing in the natural world or UV light generated during the film encapsulation process (TFE: Thin Film Encapsulation) causes denaturation of the light emitting layer and functional layer.

Efforts are being made to develop high refractive index organic compounds to expand light extraction ability, and at the same time, to develop organic compounds that are stable against UV light, which is a factor in reducing the lifespan of instruments that occurs during the manufacturing and use of instruments.

<Prior art literature>

Korean Patent Publication No. 10-2004-0098238

The purpose of the present invention is to achieve better device service life in RGB image display devices.

Generally, in order to improve light extraction, a high refractive light extraction layer is laminated. In Patent Document 1, an organic light extraction layer with a refractive index of 1.7 or more and a film thickness of 60 nm is deposited on the upper electrode of an organic EL device, and red light emission and green light emission are obtained. This resulted in an improvement in luminous efficiency of the device by approximately 1.5 times.

Here, in the RGB image display device, the improvement in lifespan is achieved by ensuring that the wavelength of light generated from the light emitting layer falls within the absorption band region of the light extraction layer, thereby not reducing efficiency due to its own light absorption, and by using the UV light present in natural light. This is to prevent the lifespan of the device from being reduced and to extend the lifespan of the device by absorbing UV light sources that may occur during the device manufacturing process.

However, the purpose of the present invention is not limited to this, and of course, even if not explicitly mentioned, purposes or effects that can be understood from the means of solving the problem or the embodiment are also included.

The present invention for achieving the above object includes a substrate, a first electrode, at least one organic layer including a blue light-emitting layer, a second electrode, and a light extraction layer in this order, and the light extraction layer satisfies the following conditions (1) to It may be composed of an organic electroluminescent device containing a material that satisfies condition (3).

Here, condition (1) n(@450nm) ≥ 2.00

Condition (2) k@420nm ≥ 0.10

Condition (3) k@450nm ≤ 0.01

(At this time, n represents the refractive index at a defined wavelength, and k represents the extinction coefficient at a defined wavelength).

The second electrode may be made of an organic electroluminescent device containing metal.

The light extraction layer may be composed of an organic electroluminescent device having a film thickness of 200 nm or less.

It may be comprised of an organic electroluminescent device in which the peak wavelength of the PL spectrum of the light emitting material included in the blue light emitting layer is 430 nm or more and 500 nm or less.

The organic layer may be composed of an organic electroluminescent device that further includes a red light-emitting layer and a green light-emitting layer.

It may be composed of a light extraction layer for an organic electroluminescent device having a refractive index of 2.20 or more at a wavelength of 450 nm under condition (1).

The organic electroluminescent device according to the present invention can have high efficiency by having a light extraction layer containing a light extraction layer compound having a refractive index (n) of 2.0 or more at a wavelength of 450 nm.

Specifically, by forming the light extraction layer, both blue devices, green devices, and red devices can have high efficiency.

In addition, the organic light-emitting device according to the present invention forms a light extraction layer using a compound for a light extraction layer that has an extinction coefficient (k) of 0.1 or more at 420 nm and an extinction coefficient (k) of 0.01 or less at 450 nm, thereby preventing the absorption of visible light in the visible region. It can help maintain the long life of devices made of organic electroluminescent devices by reducing the possibility of reduced efficiency and color change, and by absorbing UV light that may be exposed during the manufacturing process and use of the device.

The above effects and additional effects will be described in detail below.

In addition, the various and beneficial advantages and effects of the present invention are not limited to the above-described content, and may be more easily understood in the process of explaining specific embodiments of the present invention.

1 is a cross-sectional view schematically showing an organic light-emitting device according to an embodiment of the present invention.

Figure 2 is a graph showing the spectrum of blue wavelengths generated from organic electroluminescent devices and the extinction coefficient within the range of 380 nm to 530 nm for each comparative compound.

Since the present invention can be subject to various changes and have various forms, specific embodiments will be illustrated in the drawings and described in detail in the text.

However, this is not intended to limit the present invention to a specific disclosed form, and all technical and scientific terms used in this specification have the same meaning as generally understood by those skilled in the art unless otherwise specified. .

The present invention will be described in more detail below.

The light extraction layer for an organic electroluminescent device according to an embodiment of the present invention may satisfy the following conditions.

Condition (1) n(@450nm) ≥ 2.00

Condition (2) k@420nm ≥ 0.10

Condition (3) k@450nm ≤ 0.01

At this time, n represents the refractive index at a defined wavelength.

The k represents the extinction coefficient at a defined wavelength.

The organic electroluminescent device according to the present invention has a refractive index of 2.25 or more at a wavelength of 450 nm, an extinction coefficient of 0.10 or more at 420 nm, and a light extraction layer containing a light extraction layer compound with an extinction coefficient of 0.01 or less at 450 nm, and has high efficiency and You can have a long life.

Specifically, the light extraction layer for an organic electroluminescent device according to the present invention can be used in the device process if it has an extinction coefficient of 0.10 or more at 420 nm among light extraction materials with a high refractive index of 2.0 or more at the 450 nm wavelength under condition (1). It can contribute to improving the service life of organic electroluminescent devices by minimizing damage to organic substances inside the organic electroluminescent devices by effectively absorbing high energy in the UV region during use.

In addition, if it has an extinction coefficient of 0.01 or less at 450 nm, it does not absorb the internal light emission of the organic electroluminescent device, contributing to improving efficiency and color purity.

Below, the organic electroluminescent device according to the present invention will be described in more detail.

1 is a cross-sectional view schematically showing an organic light-emitting device according to an embodiment of the present invention. Referring to FIG. 1, an organic light emitting device according to an embodiment includes a first electrode 110, a hole injection layer 210, a charge generation layer 215, a light emitting layer 220, and a first electrode 110 sequentially stacked on a substrate 100. It may include an electron transport layer 230, an electron injection layer 235, a second electrode 120, and a light extraction layer 300.

The first electrode 110 and the second electrode 120 are disposed to face each other, and an organic material layer 200 may be disposed between the first electrode 110 and the second electrode 120. The organic material layer 200 may include a hole injection layer 210, a charge generation layer 215, a light emitting layer 220, an electron transport layer 230, and an electron injection layer 235.

Meanwhile, the light extraction layer 300 presented in the present invention may be disposed on the outside of any one or more of the first electrode and the second electrode.

Specifically, among both sides of the first electrode or the second electrode, the side adjacent to the organic material layer interposed between the first electrode and the second electrode is called the inner side, and the side not adjacent to the organic material layer is called the outer side. That is, when the light extraction layer is disposed on the outside of the first electrode, the first electrode is interposed between the light extraction layer and the organic material layer, and when the light extraction layer is disposed on the outside of the second electrode, the first electrode is interposed between the light extraction layer and the organic material layer. 2 electrodes are interposed.

In addition, according to one embodiment of the present invention, the organic light emitting device may have one or more various organic material layers interposed on the inside of the first electrode and the second electrode, and on the outside of at least one of the first electrode and the second electrode. A light extraction layer may be formed. That is, the light extraction layer may be formed on both the outside of the first electrode and the outside of the second electrode, or may be formed only on the outside of the first electrode or the outside of the second electrode.

At this time, the light extraction layer may have a refractive index of 2.0 or more, specifically 2.2 or more at a wavelength of 450 nm, and an extinction coefficient of 0.10 or more at 420 nm and 0.01 or less at 450 nm.

In the organic light emitting device of one embodiment shown in FIG. 1, the first electrode 110 is conductive. The first electrode 110 may be formed of a metal alloy or a conductive compound. The first electrode 110 is generally an anode, but its function as an electrode is not limited.

The first electrode 110 may be formed on the substrate 100 using an electrode material deposition method, electron beam evaporation, or sputtering method. The material of the first electrode 110 may be selected from materials with a high work function to facilitate injection of holes into the organic light emitting device.

The light extraction layer 300 proposed in the present invention is applied when the light emission direction of the organic light emitting device is top emission, and therefore the first electrode 110 uses a reflective electrode. These materials include Mg (magnesium), Al (aluminum), Al-Li (aluminum-lithium), Ca (calcium), Mg-In (magnesium-indium), and Mg-Ag (magnesium-silver), which are not oxides. It can also be manufactured using the same metal. Recently, carbon substrate flexible electrode materials such as CNT (carbon nanotube) and graphene may be used.

The organic material layer 200 may be formed of multiple layers. When the organic material layer 200 is a plurality of layers, the organic material layer 200 includes a hole transport region 210 to 215 disposed on the first electrode 110, a light-emitting layer 220 disposed on the hole transport region, and the light-emitting layer. It may include an electron transport region (230-235) disposed on (220).

In addition, the hole injection layer 210 is formed by depositing a hole injection layer material on the top of the first electrode 110 by a method such as vacuum deposition, spin coating, casting, or LB (Langmuir-Blodgett) method. It can be. When forming the hole injection layer 210 by the vacuum deposition method, the deposition conditions vary depending on the compound used as the material for the hole injection layer 210, the structure and thermal characteristics of the desired hole injection layer 210, etc. In general, a deposition temperature of 50-500°C, a vacuum degree of 10-8 to 10-3 torr, a deposition rate of 0.01 to 100 Å/sec, and a layer thickness of 10 Å to 5 ㎛ can be appropriately selected. Meanwhile, a charge generation layer 215 may be additionally deposited on the surface of the hole injection layer 210 as needed. Common materials can be used as the charge generation layer material, and HATCN is an example.

In addition, the light-emitting layer 220 may be formed by depositing a light-emitting layer material on the hole transport layer 210 or the charge generation layer 215 by a method such as vacuum deposition, spin coating, casting, or LB method. . When forming the light emitting layer 220 by the vacuum deposition method, the deposition conditions vary depending on the compound used, but it is generally recommended to select conditions within the same range as those for forming the hole injection layer 210.

The light emitting layer material may use a known compound as a host or dopant.

Here, when a phosphorescent dopant is used together with the light emitting layer material, a hole blocking material (HBL) is added to the top of the light emitting layer 220 to prevent the diffusion of triplet excitons or holes into the electron transport layer 230 by vacuum deposition or It can be laminated through spin coating. The hole blocking material that can be used is not particularly limited, and known materials can be arbitrarily selected and used. For example, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, or hole blocking materials described in Japanese Patent Application Laid-Open No. 11-329734 (A1), etc., representative examples include Balq (bis (8-hyde) Roxy-2-methylquinolinolnato)-aluminum biphenoxide), phenanthrolines-based compounds (e.g., UDC's BCP (bassocuproin)), etc. can be used. The light emitting layer 220 of the present invention may include one or more layers or two or more blue light emitting layers.

Additionally, the electron transport layer 230 is formed on top of the light emitting layer 220, and may be formed by a method such as vacuum deposition, spin coating, or casting. The deposition conditions for the electron transport layer 230 vary depending on the compound used, but it is generally recommended to select conditions that are approximately the same as those for forming the hole injection layer 210.

Furthermore, the electron injection layer 235 may be formed by depositing an electron injection layer material on top of the electron transport layer 230, and may be formed by methods such as vacuum deposition, spin coating, and casting.

In addition, the second electrode 120 is used as an electron injection electrode, and may be formed on the electron injection layer 235 by a method such as vacuum deposition or sputtering. Various metals may be used as materials for the second electrode 120. Specific examples include materials such as aluminum, gold, silver, and magnesium, but are not limited thereto.

The organic light emitting device of the present invention includes the light extraction layer 300, the first electrode 100, the hole injection layer 210, the charge generation layer 215, the light emitting layer 220, the electron transport layer 230, and the electron injection layer described above. In addition to the organic electroluminescent device having a structure including the layer 235, the second electrode 120, and the light extraction layer 300, organic electroluminescent devices of various structures are possible, and, if necessary, one or two layers. It is also possible to additionally include an intermediate layer.

Meanwhile, the thickness of each organic layer formed according to the present invention can be adjusted according to the required degree, and may be specifically 1 to 1,000 nm, and more specifically 1 to 150 nm. The light extraction layer 300 may be formed on both sides of the first electrode 110 on the outer side where the hole injection layer 210 is not formed. Additionally, the electron injection layer 235 may be formed on both sides of the second electrode 120 on the outer side where the electron injection layer 235 is not formed, but is not limited thereto. The light extraction layer 300 may be formed through a deposition process, and the thickness of the light extraction layer 300 may be 100 to 2,000 Å, and more specifically, 300 to 1,000 Å. Through such thickness adjustment, the transmittance of the light extraction layer 300 can be prevented from decreasing.

In addition, although not shown in FIG. 1, according to one embodiment of the present invention, between the light extraction layer 300 and the first electrode 110 or between the light extraction layer 300 and the second electrode 120 Organic layers with various functions may be additionally formed. Alternatively, an organic material layer performing various functions may be additionally formed on the top (outer surface) of the light extraction layer 300, but is not limited thereto.

In an organic light emitting device, as voltage is applied to the first electrode 110 and the second electrode 120, holes injected from the first electrode 110 pass through the hole transport regions 210 to 215 and then pass through the light emitting layer. 220, and the electrons injected from the second electrode 120 move to the light emitting layer 220 through the electron transport regions 230 to 235. Electrons and holes recombine in the light emitting layer 220 to generate excitons, and the excitons emit light as they fall from the excited state to the ground state.

The optical path generated in the light emitting layer 220 may exhibit very different trends depending on the refractive index of the organic and inorganic materials that make up the organic light emitting device. Light passing through the second electrode 120 can only pass through at an angle smaller than the critical angle of the second electrode 120. Other lights that contact the second electrode 120 at a angle greater than the critical angle are totally reflected or reflected and are not emitted outside the organic light emitting device.

If the light extraction layer 300 has a high refractive index, it contributes to improving luminous efficiency by reducing total reflection or reflection phenomenon, and if it has an appropriate thickness, it contributes to high efficiency and color purity by maximizing the micro-cavity phenomenon. do.

The light extraction layer 300 is located on the outermost side of the organic light emitting device and has a significant influence on the device characteristics without affecting the operation of the device at all. Therefore, the light extraction layer 300 is important from both the viewpoints of protecting the interior of the organic light emitting device and improving device characteristics. Organic materials absorb light energy in a specific wavelength range and this depends on the energy band gap. If this energy band gap is adjusted for the purpose of absorbing the UV region, which can affect the organic materials inside the organic light-emitting device, the light extraction layer 300 can be used for the purpose of protecting the organic light-emitting device, including improving optical properties. You can.

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

Hereinafter, the present specification will be described in detail using examples. However, the embodiments according to the present specification may be modified into various other forms, and the scope of the present application is not to be construed as being limited to the embodiments described in detail below. The embodiments of this application are provided to more completely explain the present specification to those with average knowledge in the art.

<Experimental Example 1>

Methods for measuring refractive index and extinction coefficient

Regarding the compound for the light extraction layer prepared in <Experimental Example 2>, J.A. Measure the refractive index (n) and extinction coefficient (k) using WOOLLAM's Ellipsometer device.

Preparation of specimens for measurement:

To measure the optical properties of the compound, the silicon substrate was washed in Ethanol, DI Water, and Acetone using Ultrasonic for 20 minutes each, and then the washed silicon substrate was

A specimen is produced by forming a 50nm thick layered film using the compound prepared above at a vacuum level of 2.0x10-7 Torr at a speed of 1Å/sec.

The refractive index and extinction coefficient of the manufactured specimen were measured in the wavelength range of 380 nm to 530 nm using the ellipsometer device.

<Experimental Example 2>

Manufacturing of organic electroluminescent devices

Table 1 shows the structure of a general organic light-emitting device. The organic light-emitting device manufactured as an example of the present invention has the following structure from below: first electrode 110) / hole injection layer 210 / charge generation layer 215 / light emitting layer They are laminated in the following order: (220) / electron transport layer (230) / electron injection layer (235) / second electrode (120)) / light extraction layer (300).

The materials listed in Table 1 below were used for the hole injection layer 210, charge generation layer 215, light emitting layer 220, electron transport layer 230, and electron injection layer 235.

A second electrode 120 for electron injection was formed on the electron injection layer 235. Various metals can be used as the cathode.

Additionally, a light extraction layer 300 was formed on the second electrode 120.

HIL-1	HIL-2	BH01
BD01	ET01	Liq

Table 2 below shows the structural formulas of the materials used in the light extraction layer in Comparative Example 1 and Examples 1 to 4.

Alq3	k-Test1
k-Test2	k-Test3
k-Test4

<Comparative Example 1>

A glass substrate was provided, a reflective layer containing Ag was formed on the upper part of the substrate as a reflective film of the first electrode, and ITO was deposited on the upper part of the reflective film formed of Ag. Subsequently, 100 nm of HIL-1 was deposited on the hole injection layer as an organic layer on top of the ITO, and a 10 nm fmf layer of a mixture of HIL-1 and HIL-2 (9:1, wt./wt.) was deposited on the host BH01 as a dopant BD01. was doped at 2% by weight to form a 25 nm light-emitting layer. The electron transport layer was formed with a mixture of ET01 and Liq (1:1, wt./wt.) to a thickness of 30 nm, and then 1 nm of LiF was deposited to form an electron injection layer. Subsequently, MgAg was deposited to a thickness of 15 nm as a second electrode, and Alq3 shown in Figure 2 was deposited to a thickness of 60 nm as a light extraction layer on the second electrode. A blue organic light-emitting device was manufactured by encapsulating the device manufactured in this way in a glove box.

<Example 1> to <Example 4>

An organic electroluminescent device was manufactured in the same manner as in Comparative Example 1, except that the k-Test1, k-Test2, k-Test3, and k-Test4 compounds shown in Table 2 were used to form a light extraction layer.

<Experimental Example 3>

Performance evaluation of organic electroluminescent devices

In evaluating efficiency and color coordinates, voltage is applied to a Keithley 2400 source measurement unit to inject electrons and holes, and light is measured using a Konica Minolta spectroradiometer (Konica Minolta CS-2000). The luminance and color coordinates when emitted were measured.

In the case of life evaluation, the change in luminance at 10 mA/cm2 was measured using the same equipment, and life evaluation was conducted with the LED light source evenly illuminated on the specimen in the measurement room to reproduce the everyday use situation (lighting room). (When measuring, measure in a dark room after turning off the lights)

In order to evaluate the lifespan of the material itself, a darkroom was implemented and lifespan evaluation was conducted, and the lifespan change during daily use was measured and compared with the lifespan change during the lifespan evaluation of the material itself. The results are shown in Table 3. indicated.

	n	k@420	k@450	Cd/A	CIE_y	B.I.	Life (Lighting room)	Life (Darkroom)
Alq3	1.82	0.04	0.00	5.35	0.046	116	118	203
k-Test1	2.00	0.01	0.00	6.25	0.047	133	120	199
k-Test2	2.31	0.08	0.00	7.07	0.047	150	145	205
k-Test3	2.34	0.34	0.01	7.16	0.049	146	175	211
k-Test4	2.43	1.00	0.26	8.95	0.116	77	197	205

In the results of Experimental Example 1 and Experiment 3, the extinction coefficient according to the wavelength of each material and the emission spectrum according to the wavelength are shown in Figure 2.

As shown in Figure 2, looking at the absorption coefficient according to the wavelength of each light extraction material, it can be seen that light generated in the light emitting layer (EML) can be absorbed, and UV generated during the production of natural or organic electroluminescent devices can be absorbed. You can.

From the results of Comparative Example 1 and Examples 1 to 4, it was confirmed that there was a significant increase in efficiency when a material satisfying condition (1) in claim 1 was used as a light extraction layer.

In addition, although the lifespan of all materials was the same in a darkroom, it was confirmed that the lifespan was improved in a lighted room when a material that satisfied condition (2) was used as a light extraction layer.

In the case of materials outside of condition (3), an increase in efficiency was achieved due to high refraction, but CIE_y was seen to increase sharply and BI to decrease. As a result, the light extraction layer itself absorbed some of the light generated from the light emitting layer. It was found that it was due to absorption.

From the above results, it can be seen that the greater the refractive index of the light extraction layer, the greater the efficiency. In the case of materials with an extinction coefficient of k@420nm≥0.10, actual service life can be improved when the device is actually used in a natural environment. In the case of a material with k@450nm≤0.01, it was confirmed that absorption of light generated in the light-emitting layer could be avoided, making it possible to implement an organic electroluminescent device with high efficiency, long lifespan, and high color purity.

Although the present invention has been shown and described in connection with preferred embodiments for illustrating the principles of the present invention, the present invention is not limited to the configuration and operation as shown and described. Rather, those skilled in the art will be able to understand that many changes and modifications can be made to the present invention without departing from the spirit and scope of the appended claims. Accordingly, all such appropriate changes, modifications and equivalents shall be considered to fall within the scope of the present invention.

The present invention as described above can be widely used in the organic electroluminescent device industry.

100...substrate

110...first electrode

200...organic layer

210...hole injection layer

215...charge generation layer

220...light emitting layer

230...electron transport layer

235...electron injection layer

120...second electrode

300...light extraction layer

Claims (6)

1. A substrate, a first electrode, one or more organic layers including a blue light-emitting layer, a second electrode, and a light extraction layer are provided in this order, and the light extraction layer includes a material that satisfies the following conditions (1) to (3). Organic electroluminescent device.

   Condition (1) n(@450nm) ≥ 2.00

   Condition (2) k(@420nm) ≥ 0.10

   Condition (3) k(@450nm) ≤ 0.01

   (At this time, n represents the refractive index at a defined wavelength, and k represents the extinction coefficient at a defined wavelength).
2. According to claim 1,

   An organic electroluminescent device in which the second electrode includes metal.
3. According to claim 1,

   An organic electroluminescent device wherein the light extraction layer has a film thickness of 200 nm or less.
4. According to claim 1,

   An organic electroluminescent device in which the peak wavelength of the PL spectrum of the light-emitting material included in the blue light-emitting layer is 430 nm or more and 500 nm or less.
5. The method according to any one of claims 1 to 4,

   An organic electroluminescent device wherein the organic layer further includes a red light-emitting layer and a green light-emitting layer.
6. According to claim 1,

   A light extraction layer for an organic electroluminescent device having a refractive index of 2.20 or more at a wavelength of 450 nm under condition (1).

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