KR101730554B1 - Organic electroluminescent device - Google Patents

Abstract

The present invention provides a plasma display panel comprising: a first electrode on a substrate; A hole transport layer on the first electrode;
A light emitting material layer made of a host material and a dopant material, which are phosphorescent materials, on the hole transport layer; An electron transport layer on the light emitting material layer; An electron injection layer on the electron transport layer; And a second electrode over the electron injection layer, wherein the light emitting material layer includes a host layer, a host dopant mixed layer, and a dopant layer.

Description

[0001] The present invention relates to an organic electroluminescent device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device capable of improving luminous efficiency and decreasing the concentration of a dopant.

2. Description of the Related Art Flat panel displays having excellent characteristics such as thinning, lightening, and low power consumption have been widely developed and applied to various fields.

An organic electroluminescent display device or an organic electroluminescent display device, also referred to as an organic light emitting diode (OLED), is an organic electroluminescent display device in which charges are injected into a light emitting layer formed between a cathode serving as an electron injecting electrode and a cathode serving as a hole injecting electrode So that the electron and the hole are paired to form an exciton, and then the exciton extinguishes to emit light.

Such an organic electroluminescent device can be formed not only on a flexible substrate such as a plastic but also has excellent color sensitivity due to self-luminescence and is low in plasma display panel (Plasma Display Panel) or inorganic electroluminescence It has the advantage of being able to drive (less than 10V) voltage and relatively low power consumption.

In general, an organic electroluminescent device includes an emitting material layer (EML) disposed between an anode electrode, which is an anode, and a cathode electrode, which is a cathode, on a substrate.

In order to inject holes from the anode electrode and electrons from the cathode electrode into the light emitting material layer, a hole transporting layer (HTL) is formed between the anode electrode and the light emitting material layer, and an electron transporting layer electron transporting layer (ETL).

In order to inject holes and electrons more efficiently, a hole injecting layer (HIL) is formed between the anode electrode and the hole transporting layer, and an electron injecting layer (EIL) is formed between the electron transporting layer and the cathode electrode. .

In the organic electroluminescent device having such a structure, holes injected from the anode electrode to the light emitting material layer through the hole injecting layer and the hole transporting layer, and electrons injected from the cathode to the light emitting material layer through the electron injecting layer and the electron transporting layer are recombined the excitons are formed through recombination, and light of a color corresponding to the band gap of the light emitting material layer is emitted from the excitons.

In recent years, phosphorescent materials have been used more frequently than fluorescent materials in the luminescent material layer.

In the case of fluorescent materials, only about 25% of the excitons formed in the emissive material layer are used to make this light, while 75% of the triplet is mostly lost to heat, whereas phosphorescent materials emit light that converts both singlet and triplet light into light It has a mechanism.

Phosphorescent dopants generally contain heavy atoms such as Ir, Pt, and Eu in the center of organic matter, and have a high probability of electron transition from triplet to singlet.

However, such a dopant can not constitute a light emitting material layer alone because a rapid efficiency reduction occurs due to a concentration extinction phenomenon.

Thus, a luminescent layer is formed together with the host material having higher thermal stability and higher triplet energy than the dopant.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing a dopant distribution in an organic light emitting layer in a conventional organic electroluminescent device. FIG.

As shown in the figure, the host material 12 is formed of the light emitting material layer 10 as a main material, and the dopant 14 on the host 12 has a concentration ratio of 8% to 12% And the host 12 and the dopant 14 are uniformly mixed over the entire surface of the organic light emitting layer 10.

However, when the luminescent material layer 10 has such a structure, there is no barrier region capable of accumulating an exciton in the luminescent material layer 10, whereby the exciton is formed concentrically in a specific region The luminescent region has a Gaussian distribution characteristic.

Therefore, it is impossible to expect such effects as improvement of luminous efficiency due to accumulation of excitons and reduction of doping amount of dopant.

An object of the present invention is to provide an organic electroluminescent device capable of improving the luminous efficiency and reducing the concentration of the dopant by having a barrier region capable of accumulating an exciton in the luminous material layer.

In order to solve the above problems, an organic electroluminescent device according to the present invention includes: a first electrode on a substrate; A hole transport layer on the first electrode; A light emitting material layer made of a host material and a dopant material, which are phosphorescent materials, on the hole transport layer; An electron transport layer on the light emitting material layer; An electron injection layer on the electron transport layer; And a second electrode on the electron injection layer. The light emitting material layer includes a host layer, a host dopant mixed layer, and a dopant layer.

At this time, the host material is BeBq2 represented by the following formula (1), and the dopant material is Btp2lr (acac) represented by the following formula (2).

Formula 1

(2)

The light emitting material layer may include a first host layer, a first host dopant mixed layer, a first dopant layer, a second host dopant mixed layer, a second host layer, a third host layer, a third host dopant mixed layer , A second dopant layer, a fourth host dopant mixed layer, and a fourth host layer.

The first, second, third, and fourth host layers each have a first thickness, the first, second, third, and fourth host dopant mixed layers have a second thickness that is thicker than the first thickness, 2 dopant layer has a third thickness less than the second thickness, the second thickness is 1.5 to 2.5 times the first thickness, and the third thickness is 1 to 10 ANGSTROM.

In the light emitting material layer, the concentration ratio of the host material and the dopant material is 99: 1 to 98: 2.

The organic electroluminescent device according to the present invention has a barrier capable of accumulating excitons composed only of a dopant in the light emitting material layer to accumulate the excitons, thereby improving the luminous efficiency and lowering the concentration of the dopant.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing a dopant distribution in an organic light emitting layer in a conventional organic electroluminescent device. FIG.
2 is a sectional view of an organic electroluminescent device according to an embodiment of the present invention.
3 is an enlarged view of an organic light emitting layer in an organic electroluminescent device according to an embodiment of the present invention.
4 is an enlarged view of only a hole transporting layer and an electron transporting layer provided on both sides of the light emitting material layer in the organic electroluminescent device according to the embodiment of the present invention.
5 is a view schematically illustrating a deposition apparatus for manufacturing an organic electroluminescent device according to an embodiment of the present invention.
FIG. 6 is a graph illustrating the luminous efficiency of a conventional organic electroluminescent device according to changes in luminance per unit area of the organic electroluminescent device according to an embodiment of the present invention and a conventional organic electroluminescent device.

Hereinafter, an organic electroluminescent device according to an embodiment of the present invention will be described.

FIG. 2 is a cross-sectional view of an organic electroluminescent device according to an embodiment of the present invention, FIG. 3 is an enlarged view of an organic electroluminescent device in an organic electroluminescent device according to an embodiment of the present invention, FIG. Only the hole transporting layer and the electron transporting layer provided on both sides of the light emitting material layer in the organic electroluminescent device according to the example are enlarged.

2 and 3, an organic electroluminescent device according to an embodiment of the present invention includes a hole injection layer 120, a hole transport layer 130, and a light emitting layer 130 on an anode electrode 110, And a material layer 140 are sequentially formed.

An electron transport layer 150 and an electron injection layer 160 are sequentially formed on the light emitting material layer 140. A cathode electrode 170 is formed on the electron injection layer 160.

Here, the anode electrode 110 is made of a transparent conductive material such as indium tin oxide (ITO), which is a relatively high work function value.

In addition, the hole injection layer 120 may be formed of N, N'-diphenyl-N, N'-bis- [4- (phenylmetholylamino) -phenyl] And the hole transport layer 130 is made of 4,4'-bis [N- (1-naphthyl) -N-phenylamino] -biphenyl (NPD).

Meanwhile, in the embodiment according to the present invention, the light emitting material layer 140 is composed of a host and a dopant as shown in FIG. In this case, the light emitting material layer 140 may be formed of a host only layer (hereinafter referred to as a host layer), a host layer and a dopant layer (not shown) such that the host and the dopant are not uniformly mixed on the entire surface, (Hereinafter referred to as a host dopant mixed layer) and a dopant-only region (hereinafter referred to as a dopant layer).

Here, the host material is made of BeBq2 and the dopant material is made of Btp2lr (acac). In this case, the concentration of the dopant material relative to the host material is 1 to 2% in the entire luminescent material layer 140. [

In the organic electroluminescent device according to an embodiment of the present invention, BeBq2, which is a host material of the light emitting material layer 140, is represented by the following Chemical Formula 1 and Btp2lr (acac) which is a dopant substance is represented by Chemical Formula 2 below.

Formula 1

(2)

The host material and the dopant material of Formulas 1 and 2 substantially become red phosphors. The light emitting material layer 140 formed of the host material and the dopant material represented by Formulas 1 and 2 has hole (h ⁺ ) and hole The electron (e ^- ) combines to form an exciton and then disappears and emits red light.

Meanwhile, the electron injection layer (160 in FIG. 3) is made of Alq3 or DAlq3, and the electron transport layer 150 is made of LiF or Liq.

Also, the cathode electrode (170 in FIG. 3) is made of any one of metal materials MgAg, Al, and MgAl having a low work function value.

More specifically, the cross-sectional structure of the light emitting material layer, which is the most characteristic structure in the organic electroluminescent device according to the embodiment of the present invention, will be described with reference to FIG. Although the hole transport layer 130 and the electron transport layer 150 are located on the left and right sides and the light emitting material layer 140 is formed between the two material layers 130 and 150, Emitting material layer 140 and the electron transporting layer 150 are stacked on a substrate (not shown), the hole transporting layer 130, the light emitting material layer 140, and the electron transporting layer 140 are formed on a substrate (160).

A first host layer 141a is formed on the hole transport layer 130 and has a first thickness and is made of only a host material in contact with the hole transport layer 130. A first host layer 141a is formed on the first host layer 141a, A first host dopant mixed layer 143a doped with a dopant is formed having a second thickness larger than the first thickness.

A first dopant layer ECA1 having a third thickness smaller than the first thickness is formed on the first host dopant mixed layer 141a and a second host dopant mixed layer 143b having the second thickness is formed on the other portion. Are formed.

Second and third host layers 141b and 141c having a first thickness are successively formed on the second host dopant mixed layer 143b, and a third host dopant mixed layer 143b having a second thickness is formed on the second host dopant mixed layer 143b. (143c) are formed.

A second dopant layer (ECA2) having a third thickness is formed on the third host dopant mixed layer (143c), and a fourth host dopant mixed layer (143c) having a second thickness and a second dopant layer And a fourth host layer 141d are sequentially formed.

Here, the second thickness is 1.5 to 2.5 times the first thickness. For example, the first thickness may be 30 ANGSTROM and the second thickness may be 60 ANGSTROM. In this case, the third thickness is 1 to 10 angstroms.

Particularly, in the case where the first and second dopant layers ECA1 and ECA2 have a value larger than 10 angstroms, rapid efficiency reduction occurs due to the concentration quenching phenomenon of the dopant itself. When the first and second dopant layers ECA1 and ECA2 are smaller than 1 angstrom, The effect of increasing the luminous efficiency can not be realized. Therefore, the third thickness of the first and second dopant layers ECA1 and ECA2 is preferably at least 1 ANGSTROM to at most 10 ANGSTROM

The light emitting material layer 140 formed to have such a structure has a remarkably excellent effect in terms of luminous efficiency compared to the organic electroluminescent device 10 of FIG. 1 in which the conventional host material and the dopant material have a constant concentration ratio and are mixed to form one layer And the like.

Hereinafter, a method of forming the light emitting material layer having the above-described structure will be described.

5 is a view illustrating a deposition apparatus for fabricating an organic electroluminescent device according to an embodiment of the present invention.

The deposition apparatus 200 for fabricating an organic electroluminescent device according to an embodiment of the present invention includes a vacuum chamber 210, first and second evaporation paths 230a and 230b for discharging the evaporation source gas, an angle limiting plate 240, And a stage 220, as shown in FIG.

At this time, the vacuum chamber 210 is divided into the first region A1 and the second region A2 by the angle restricting plate 212. In the first region A1, And the second evaporation passage 230b is disposed in the second region A2 as an evaporation source of an organic material forming a dopant.

The evaporation apparatus 200 for fabricating an organic electroluminescence device according to the present invention has a structure in which the first evaporation path 230a is formed in the vacuum chamber 210 by adjusting the height h of the angle limiting plate 240, A first section B1 through which a host material gas (hereinafter referred to as a host gas) 271 is discharged through the second evaporation path 230 and only a host material is deposited through the second evaporation path 230b and a dopant material gas A second section B2 in which only the dopant material is discharged and a host gas 271 discharged through the first evaporation path 230a and the second evaporation path 230b The dopant gas 274 having an appropriate concentration ratio has a mixed gas atmosphere to form a third section B3 in which the host and the dopant material are simultaneously deposited.

At this time, the first, second and third sections B1, B2, and third sections are formed by adjusting the height of the angle limiting plate 240 and adjusting the distance between the first evaporating furnace 230a and the second evaporating furnace 230b. B3 can be adjusted.

That is, if the height h of the angle limiting plate 240 is increased, the width of the third section B3 where the mixed gas containing the host material and the dopant material is evaporated is reduced, and the widths of the first and second When the height h of the angle limiting plate 240 is lowered, the width of the third section B3 becomes larger and the widths of the first and second sections B3 and B3 located on both sides of the third section B3 become larger. B1, and B2 are small.

The distance between the first evaporation passage 230a and the angle limiting plate 240 is set to a first distance d1 and the distance between the second evaporation passage 230b and the angle limiting plate 240 is set to be When the angle limiting plate 240 is positioned such that the first distance d1 is greater than the second distance d2 when the distance d2 is 2, the width of the first section B1 becomes smaller, When the angle limiting plate 240 is positioned so that the second distance d2 is larger than the first distance, the width of the second section B2 becomes small.

A substrate 200 on which a shadow mask 250 having an opening oa corresponding to a portion where a light emitting material layer is to be formed is placed on the bottom surface of the vacuum chamber 210 using the deposition apparatus 200 having the above- 260 at a constant moving speed so as to sequentially pass through the first section B1, the third section B3 and the second section B2, and then the moving direction is changed to the opposite direction, Corresponding to the opening oa of the shadow mask 250 by moving the substrate 260 through the first section B2, B3, and B1, that is, by moving the substrate 260 once through the vacuum chamber 210, A first host dopant mixed layer (143a in FIG. 4) / a first dopant layer (ECA1 in FIG. 4) / a second host dopant mixed layer (143b in FIG. 4) / Second host layer (141b in Fig. 4).

Accordingly, the substrate 260, on which the shadow mask 250 is mounted on the bottom surface of the vacuum chamber 210, is divided into the first, third, and second sections B1, B3, and B2 through the deposition apparatus 200, The first host layer 141a / the first host dopant mixed layer 143a / the first dopant layer ECA1 / the second host dopant mixed layer 143b / the second host dopant mixed layer 143b / The host layer 141b, the third host layer 141c, the third host dopant mixed layer 143c, the second dopant layer ECA2, the fourth host dopant mixed layer 143d, and the fourth host layer 141d. Emitting layer 140 may be formed.

5, the deposition apparatus 200 for fabricating an organic electroluminescent device according to an embodiment of the present invention includes a vacuum chamber 210 in which the first and second evaporation paths 230a and 230b The substrate 260 and the shadow mask 250 are fixed and the first and second evaporation paths 230a and 230b and the prepared substrate 240 are placed on the substrate 260. However, So that the stage 220 is reciprocated linearly.

(Or reciprocal number of stages) of the substrate 260 passing through the first, third, and second sections B1, B3, and B2 within the vacuum chamber 210 through the deposition apparatus 200 described above The number of dopant layers (ECA1, ECA2 in Fig. 4) in which only the pure dopant in the luminescent material layer (140 in Fig. 4) is deposited can be adjusted.

On the other hand, the dopant layer (ECA1, ECA2 in FIG. 4) formed with a thickness of about 1 to 10 angstroms with only such a dopant material has a region for accumulating excitons in which holes and electrons are combined by the HOMO LUMO level And the excitons accumulated in the dopant layer (ECA1 and ECA2 of FIG. 4) are emitted almost at the same time when the density reaches an appropriate level to generate light, thereby improving the luminous efficiency. In addition, The dopant concentration in the host can be lowered compared to the conventional organic electroluminescent device forming the host dopant mixed layer.

In the case of the dopant, it is possible to cause a rapid efficiency reduction due to the concentration quenching phenomenon, and since the thermal stability is lower than that of the host, considering the lifetime of the device, the lower the dopant concentration in the host, the better the device life.

Therefore, in this aspect, the organic electroluminescent device according to the embodiment of the present invention having a light emitting material layer having a dopant concentration of about 1% to 2% has a light emitting material layer having a dopant concentration of about 8% to 12% The organic electroluminescent device of the present invention is superior in terms of stability and longevity of an organic light emitting layer compared to a conventional organic electroluminescent device.

FIG. 6 is a graph illustrating the luminous efficiency of a conventional organic electroluminescent device according to variation of luminous intensity per unit area of the organic electroluminescent device according to an embodiment of the present invention and a conventional organic electroluminescent device.

As shown in the figure, in the comparative example, the luminous efficiency is greatly reduced from 41 to 34 as the luminous intensity per unit area increases. On the other hand, in the embodiment of the present invention, the luminous efficiency is reduced to about 42 to 41 .

Therefore, it can be seen that the embodiment of the present invention has an advantage that the stable luminous efficiency can be maintained even when the luminous intensity per unit area is changed.

The present invention is not limited to the above-described embodiments, and various changes and modifications may be made without departing from the spirit of the present invention.

130: hole transport layer 140: light emitting material layer
141a, 141b, 141c, 141d: first, second, third and fourth host layers
143a, 143b, 143c and 143d: first, second, third and fourth host dopant mixed layers
150: electron transport layer
ECA1, ECA2: First and second dopant layers

Claims (6)

A first electrode on the substrate;
A hole transport layer on the first electrode;
A light emitting material layer made of a host material and a dopant material, which are phosphorescent materials, on the hole transport layer;
An electron transport layer on the light emitting material layer;
An electron injection layer on the electron transport layer;
And a second electrode
/ RTI >
Wherein the host material is BeBq2 represented by the following formula (1)
Wherein the dopant material is Btp2lr (acac) represented by the following formula (2)
Formula 1

(2)

Wherein the light emitting material layer comprises a first host layer consisting of only the host material sequentially on the hole transport layer,
A first host dopant mixed layer in which the host material and the dopant material are mixed,
A first dopant layer made of only the dopant material,
A second host dopant mixed layer in which the host material and the dopant material are mixed,
A second host layer and a third host layer made of only the host material,
A third host dopant mixed layer in which the host material and the dopant material are mixed,
A second dopant layer made of only the dopant material,
A fourth host dopant mixed layer in which the host material and the dopant material are mixed,
Having a laminated structure of a fourth host layer made of only the host material
Organic electroluminescent device.





delete delete The method according to claim 1,
The first, second, third, and fourth host layers each have a first thickness, the first, second, third, and fourth host dopant mixed layers have a second thickness greater than the first thickness, Layer has a third thickness that is less than the second thickness.
5. The method of claim 4,
The second thickness being 1.5 to 2.5 times the first thickness,
And the third thickness is 1 to 10 ANGSTROM.
The method according to claim 1,
Wherein the light emitting material layer has a concentration ratio of the host material and the dopant material of 99: 1 to 98: 2.

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