KR20090105072A - Organic light emitting device - Google Patents

Abstract

PURPOSE: An organic light emitting device is provided to increase a transition speed of a hole and an electron by using a mixed host having a different property in at least one part of a plurality of sub light emitting layers. CONSTITUTION: An organic light emitting device includes a first electrode, a second electrode, and a light emitting layer(50). The second electrode is faced with the first electrode. The light emitting layer is positioned between the first electrode and the second electrode. The light emitting layer emits a white light. The light emitting layer includes a first sub light emitting layer(50a), a second sub light emitting layer(50b), and a third sub light emitting layer(50c). The first sub light emitting layer emits a light of a first color. The second sub light emitting layer emits a light of a second color. The third sub light emitting layer emits a light of a third color. At least one layer among the first sub light emitting layer, the second sub light emitting layer, and the third sub light emitting layer includes a host in which at least two kinds of hosts are mixed.

Description

Organic light emitting element {ORGANIC LIGHT EMITTING DEVICE}

The present invention relates to an organic light emitting device.

Recently, there is a demand for weight reduction and thinning of a monitor or a television, and according to such a demand, a cathode ray tube (CRT) has been replaced by a liquid crystal display (LCD).

However, the liquid crystal display device requires not only a separate backlight as a light emitting device, but also has limitations in response speed and viewing angle.

Recently, as a display device capable of overcoming this, an organic light emitting device (OLED) has attracted attention.

The organic light emitting device combines electrons injected from one electrode and holes injected from another electrode in a light emitting layer positioned between the two electrodes to generate excitons, and the excitons emit energy while emitting energy. do.

The organic light emitting device is self-luminous and does not need a separate light source, which is advantageous in terms of power consumption, and also has excellent response speed, viewing angle, and contrast ratio.

The organic light emitting device may include a plurality of pixels, such as a red pixel, a blue pixel, and a green pixel, each of which includes a red light emitting layer, a blue light emitting layer, and a green light emitting layer, and displays a unique color for each pixel. These can be combined to display full color.

On the other hand, recently, researches on white OLEDs that emit light of red, green, and blue wavelengths simultaneously from the light emitting layer of the organic light emitting diodes and combine them to produce white light have been actively conducted. The white organic light emitting diode may be effectively used for lighting as well as a display device.

Methods of implementing a white light emitting device include a method of doping a plurality of dopants in a single light emitting layer and a method of stacking a plurality of light emitting layers in sequence.

Among the single light emitting layer, since the red, green, and blue doping materials must be doped in a single layer, the process is very complicated and the light emission efficiency is largely changed according to the doping concentration, thereby making it difficult to implement a stable device.

In addition, in the case of a plurality of light emitting layers, it is difficult to control charge transfer between the layers, and particularly, when phosphorescent materials are included, efficiency may be reduced according to luminance.

Therefore, the problem to be solved by the present invention is to increase the luminous efficiency and to prevent the efficiency decrease according to the luminance.

An organic light emitting diode according to an embodiment of the present invention includes a first electrode, a second electrode facing the first electrode, and a light emitting layer positioned between the first electrode and the second electrode and emitting white light; The light emitting layer includes a first sub light emitting layer emitting light of the first color, a second sub light emitting layer emitting light of the second color, and a third sub light emitting layer emitting light of the third color. At least one layer of the first sub emitting layer, the second sub emitting layer, and the third sub emitting layer includes a mixed host in which at least two kinds of hosts are mixed.

The mixed host may include a hole transporting host and an electron transporting host.

The second sub emission layer may be positioned between the first sub emission layer and the third sub emission layer, and at least one of the first sub emission layer and the third sub emission layer may include the mixed host.

The first sub emission layer and the third sub emission layer include the mixed host, and the mixing host of the first sub emission layer and the mixing host of the third sub emission layer have a mixing ratio of the hole transport layer host and the electron transport host. It may be included differently.

One of the first sub emitting layer and the third sub emitting layer has a ratio of the hole transporting host to a ratio higher than that of the electron transporting host, and the other of the first sub emitting layer and the third sub emitting layer has a ratio of the electron transporting host. The ratio may be higher than the ratio of the hole transport host.

The first electrode is an anode, the second electrode is a cathode, and a layer positioned close to the first electrode among the first sub-emitting layer and the third sub-emitting layer has a ratio of the hole transporting host to a ratio of the electron transporting host. A higher ratio of the first sub-emitting layer and the third sub-emitting layer closer to the second electrode may have a higher ratio of the electron transporting host than a ratio of the hole transporting host.

The organic light emitting diode may further include at least one of a hole transport auxiliary layer positioned between the first electrode and the light emitting layer, and an electron transport auxiliary layer positioned between the second electrode and the light emitting layer.

The hole transport host is NPB (N, N'-bis- (1-naphtyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine), CBP (4,4-bis ( carbazol-9-yl) -biphenyl), TPD (N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine), PPD (p- phenylenediamine), phthalocyanine, CuPc, and at least one selected from m-MTDATA, and the electron transporting host is Alq ₃ (tris (8-hydroxyquinolino) aluminum), ADN, TAZ, TPBI (1,3,5- tris (N-phenylbenzimidazole-2-yl) benzene) may include at least one selected from.

The first color may be red, the second color may be blue, and the third color may be green.

According to an exemplary embodiment of the present invention, the movement speed of the holes and the electrons may be increased by using a mixed host having different characteristics in at least some of the plurality of sub emission layers.

In particular, holes are injected from the anode by using a mixed host including more hosts having hole transport characteristics in the sub emitting layer near the anode and a mixed host including more hosts having electron transport characteristics in the sub emitting layer near the cathode. And the electrons injected from the cathode can be more easily moved to increase the number of holes and electrons reaching the light emitting layer.

Therefore, the efficiency in which exciton is generated by recombination of holes and electrons in the emission layer may be increased, thereby improving quantum efficiency of the organic light emitting device.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

Next, an organic light emitting diode display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

1 is a plan view of a passive matrix OLED display according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view of the organic light emitting diode display of FIG. 1 taken along line II-II.

A plurality of anodes 20 and a plurality of cathodes 80 are formed to intersect on the insulating substrate 10 made of transparent glass or plastic.

The anode 20 is formed at predetermined intervals and extends along one direction of the insulating substrate 10. The anode 20 is an electrode into which holes are injected. The anode 20 is made of a transparent conductive material having a high work function and emitted light, and may be, for example, ITO or IZO.

The cathode 80 is also formed at predetermined intervals and extends along the other direction of the insulating substrate 10 to intersect the anode 20. The cathode 80 is an electrode into which electrons are injected. The cathode 80 is made of a conductive material having a low work function and does not affect organic materials. For example, the cathode 80 may be selected from aluminum (Al), calcium (Ca), and barium (Ba). Can be.

An organic light emitting member is formed between the anode 20 and the cathode 70.

The organic light emitting member includes an emission layer 50 and a plurality of auxiliary layers for enhancing the emission efficiency of the emission layer 50.

The light emitting layer 50 includes a first sub light emitting layer 50a, a second sub light emitting layer 50b, and a third sub light emitting layer 50c that emit light of different colors, and in the sub light emitting layers 50a, 50b, and 50c. The emitted light is combined to give white light.

For example, the white light may combine red, blue, and green light. In this case, the first, second, and third sub emission layers 50a, 50b, and 50c may emit light of one of red, blue, and green light, respectively. I can make it.

 The first, second, and third sub light emitting layers 50a, 50b, and 50c have a dopant doped with a host light emitting material.

The host luminescent material is made of an organic material or a mixture of organic and inorganic materials that uniquely emits light of any one of the primary colors, such as the three primary colors of red, green and blue, such as Alq ₃ (tris (8-hydroxyquinoline) aluminum), NPB (N, N'-bis- (1-naphtyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine), CBP (4,4-bis (carbazol-9-yl ) -biphenyl), TPBI (1,3,5-tris (N-phenylbenzimidazole-2-yl) benzene), TCTA (4,4 ', 4 "-tris (N-carbazolyl) trophenylamine), ADN, TAZ, TPBI It may be one selected from.

The dopant is mixed with the host luminescent material at a predetermined ratio to improve charge mobility, such as Ir (pq) 2acac (iridium (III) bis (1-phenylquinoline) acetylacetonate) and FIrpic (iridium (III) bis (4,6- (di-fluorophenyl) -pyridinato-N) picolinate) or Irppy3 (iridium (III) tris (1-phenylpyridine)).

At least one of the first, second, and third sub light emitting layers 50a, 50b, and 50c includes a mixed host in which two or more types of host light emitting materials having different characteristics are mixed.

In particular, among the first, second, and third sub light emitting layers 50a, 50b, and 50c, the first sub light emitting layer 50a and the third sub light emitting layer 50c which are located close to the anode 20 and the cathode 80 side. When each includes a mixed host, it is effective to increase the mobility of holes injected from the anode 20 and charges injected from the cathode 80.

In this case, since the blue light emitting host light emitting material may be limited due to material limitations, the second sub light emitting layer 50b may be a blue light emitting layer, and may be positioned above and below the anode 20 and the cathode 80. It is preferable that one of the first sub emission layer 50a and the third sub emission layer 50c is a red sub emission layer and the other is a green sub emission layer.

The mixed host includes a host light emitting material having hole transporting properties and a host light emitting material having electron transporting properties. Here, the host material having the hole transporting property is NPB (N, N'-bis- (1-naphtyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine), CBP (4 , 4-bis (carbazol-9-yl) -biphenyl), and the like, and host materials having electron transport properties include Alq ₃ (tris (8-hydroxyquinoline) aluminum), ADN, TAZ, TPBI, and the like. have.

At this time, the mixing host of the first sub emission layer 50a and the mixing host of the third sub emission layer 50c may have different mixing ratios of the hole transport layer host and the electron transport host.

Specifically, in order to facilitate the movement of holes, the first sub light emitting layer 50a close to the anode 20 preferably has a higher ratio of a host having hole transporting characteristics, and a third close to the cathode 80. In order to facilitate the movement of electrons, the sub light emitting layer 50c preferably has a higher ratio of hosts having electron transporting properties among the mixed hosts. For example, the first sub emission layer 50a may have a ratio of about 50 wt% to 95 wt% of a host having hole transport characteristics in the mixed host, and the second sub emission layer 50 c may include a ratio of a host having electron transport characteristics among the mixed hosts. About 50 to 95% by weight.

The auxiliary layer includes a hole injection layer 30, a hole transport layer 40, an electron transport layer 60, and an electron injection layer to balance electrons and holes. (electron injection layer) 70. The hole injection layer 30 and the hole transport layer 40 are positioned between the anode 20 and the light emitting layer 50 to increase the efficiency of hole injection and movement, and the electron transport layer 60 and the electron injection layer 70. Is positioned between the light emitting layer 50 and the cathode 80 to increase the efficiency of electron injection and movement.

In addition, a hole blocking layer (not shown) and / or an electron blocking layer (not shown) may be further included to appropriately control the movement speed of the holes and the electrons, and block the passage of the holes and the electrons.

As described above, according to an exemplary embodiment of the present invention, the speed of movement of holes and electrons can be increased by using a mixed host having different characteristics in at least some of the plurality of sub emission layers. In particular, holes are injected from the anode by using a mixed host including more hosts having hole transport characteristics in the sub emitting layer near the anode and a mixed host including more hosts having electron transport characteristics in the sub emitting layer near the cathode. And the electrons injected from the cathode can be more easily moved to increase the number of holes and electrons reaching the light emitting layer. Therefore, the efficiency in which exciton is generated by recombination of holes and electrons in the emission layer may be increased, thereby improving quantum efficiency of the organic light emitting device.

As described below, an organic light emitting device according to an embodiment of the present invention and an organic light emitting device according to a comparative example were manufactured to check quantum efficiency.

Example 1

In this embodiment, the organic light emitting device shown in FIGS. 1 and 2 was fabricated.

The anode 20 is formed by stacking ITO on the insulating substrate 10 by sputtering.

Subsequently, the substrate is placed in a chamber filled with acetone or isopropyl alcohol, and ultrasonically cleaned, followed by oxygen plasma treatment to improve the interfacial characteristics of the anode 20.

Next, NPD is vacuum-deposited about 60 nm on the anode 20 to form the hole injection layer 30. Next, TCTA is vacuum deposited about 30 nm on the hole injection layer 30 to form the hole transport layer 40.

First sub-emission layer 50a doped with Ir (pq) 2acac (dopant) to a mixed host containing about 50:50 of TCTA (host 1) and TPBI (host 2) on hole transport layer 40 ), Irppy3 (dopant) in a mixed host containing about 50:50 of the second sub-emission layer 50b doped with FIrpic (dopant) to mCP (host), TCTA (host 1) and TPBI (host 2) Light emitting layer 50 is formed by sequentially stacking the third sub light emitting layer 50c doped with about 5%.

Next, a BCP is vacuum-deposited on the light emitting layer 50 to form a hole blocking layer (not shown), and Alq3 and LiF are sequentially vacuum-deposited thereon to form an electron transfer layer 60 and an electron injection layer 70. .

Finally, aluminum 80 is deposited on the electron injection layer 70 to form the cathode 80.

Example 2

An organic light emitting device is manufactured in the same manner as in Example 1.

Unlike the first embodiment, the mixed host is used only for the first sub light emitting layer 50a and the single host is used for the third sub light emitting layer 50c.

First 10% doped Ir (pq) 2acac (dopant) to a mixed host containing about 50:50 of ITO / NPD / TCTA / TCTA (Host 1) and TPBI (Host 2) on insulating substrate 10 Third sub-emission layer / BCP / Alq3 / LiF / Al doped with sub-emission layer / mCP (host) about 15% FIrpic (dopant) and second sub-emission layer / TPBI (host) about 5% Irppy3 (dopant) In order to stack the organic light emitting device.

Example 3

An organic light emitting device is manufactured in the same manner as in Example 1.

Unlike the first embodiment, the mixing ratio of the two types of host light emitting materials is different in the mixed host of the first sub light emitting layer and the third sub light emitting layer.

10% doped Ir (pq) 2acac (dopant) to a mixed host containing about 75:25 of ITO / NPD / TCTA / TCTA (host 1) and TPBI (host 2) on the insulating substrate 10 Irppy3 in a mixed host containing about 25% of the second sub-emissive layer / TCTA (host 1) and TPBI (host 2) at about 15% doped FIrpic (dopant) to the first sub-emissive layer / mCP (host) An organic light emitting device was manufactured by sequentially stacking a third sub light emitting layer / BCP / Alq 3 / LiF / Al doped with (dopant) about 5%.

[Comparative Example]

An organic light emitting device is manufactured in the same manner as in Example 1.

However, in this comparative example, a single host was used for both the first sub emission layer and the third sub emission layer.

Doping about 15% FIrpic to the first sub-emissive layer / mCP (host) doped ITO / NPD / TCTA / TCTA (host) to Ir (pq) 2acac (dopant) on the insulating substrate 10 An organic light emitting device was manufactured by sequentially stacking a third sub light emitting layer / BCP / Alq 3 / LiF / Al doped with Irppy 3 (dopant) to one second sub light emitting layer / TCTA (host).

3 illustrates light emission efficiency of the organic light emitting diodes according to Examples 1 to 3 and Comparative Examples.

3 is a graph showing the light emission efficiency of the organic light emitting device according to the embodiment and the comparative example of the present invention.

In FIG. 3, A, B, C, and D show a change in quantum efficiency, which is an internal efficiency among luminous efficiencies, as the luminance of the organic light emitting diodes according to Examples 1, 2, 3, and Comparative Examples are changed.

Referring to FIG. 3, it can be seen that Examples (A, B, and C) of the present invention using a mixed host in at least one of the sub emitting layers have a significantly higher quantum efficiency than the comparative example (D) using a single host. have.

In particular, it can be seen that the use of the mixed dopant in both the first sub-emitting layer and the third sub-light emitting layer (A, C) is higher than that in the case of using the mixed dopant in only one sub-light emitting layer (B). In addition, even when the mixed dopant is used in both the first sub emission layer and the third sub emission layer, the mixing ratio of the two types of host emission materials is different in the mixing host of the first sub emission layer and the third sub emission layer (C). It can be seen that the quantum efficiency is higher than that in the same case (A).

From these results, the organic light emitting device according to the embodiment of the present invention can be seen that the luminous efficiency is improved.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

1 is a plan view of a passive matrix OLED display according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the organic light emitting diode display of FIG. 1 taken along the line II-II. FIG.

3 is a graph showing the light emission efficiency of the organic light emitting device according to the embodiment and the comparative example of the present invention.

Claims (9)

First electrode, A second electrode facing the first electrode, and An emission layer positioned between the first electrode and the second electrode and emitting white light Including, The light emitting layer is A first sub light emitting layer emitting light of the first color; A second sub light emitting layer emitting light of the second color, and A third sub light emitting layer emitting light of the third color Including; The at least one layer of the first sub light emitting layer, the second sub light emitting layer, and the third sub light emitting layer includes a mixed host in which at least two kinds of hosts are mixed. In claim 1, The mixed host includes a hole transporting host and an electron transporting host. In claim 2, The second sub light emitting layer is positioned between the first sub light emitting layer and the third sub light emitting layer. And at least one of the first sub emission layer and the third sub emission layer includes the mixed host. In claim 3, The first sub light emitting layer and the third sub light emitting layer include the mixed host, The mixed host of the first sub light emitting layer and the mixed host of the third sub light emitting layer have different mixing ratios of the hole transport layer host and the electron transport host. In claim 4, One of the first sub emitting layer and the third sub emitting layer has a ratio of the hole transporting host to a ratio higher than that of the electron transporting host, The other of the first sub emission layer and the third sub emission layer has a ratio of the electron transporting host higher than that of the hole transporting host. Organic light emitting device. In claim 5, The first electrode is an anode and the second electrode is a cathode, The layer of the first sub light emitting layer and the third sub light emitting layer located close to the first electrode has a higher ratio of the hole transporting host than a ratio of the electron transporting host, The layer of the first sub emission layer and the third sub emission layer that is located close to the second electrode has a higher ratio of the electron transport host than a ratio of the hole transport host. Organic light emitting device. In claim 6, A hole transport auxiliary layer positioned between the first electrode and the light emitting layer, and An electron transporting auxiliary layer positioned between the second electrode and the light emitting layer An organic light emitting device further comprising at least one of. In claim 4, The hole transport host is NPB (N, N'-bis- (1-naphtyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine), CBP (4,4-bis ( carbazol-9-yl) -biphenyl), TPD (N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine), PPD (p- phenylenediamine), phthalocyanine, CuPc, at least one selected from m-MTDATA, The electron transporting host is an organic light emitting device including at least one selected from Alq ₃ (tris (8-hydroxyquinolino) aluminum), ADN, TAZ, TPBI (1,3,5-tris (N-phenylbenzimidazole-2-yl) benzene) device. In claim 1, The first color is red, the second color is blue, and the third color is green.

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