WO2014116008A1

WO2014116008A1 - Organic electroluminescent device and display device including the same

Info

Publication number: WO2014116008A1
Application number: PCT/KR2014/000590
Authority: WO
Inventors: Kyung-Hoon Choi; Young-Jun Cho; Hyuck-Joo Kwon; Bong-Ok Kim
Original assignee: Rohm And Haas Electronic Materials Korea Ltd.
Priority date: 2013-01-24
Filing date: 2014-01-21
Publication date: 2014-07-31
Also published as: TW201445726A; KR20140095354A

Abstract

The invention relates to an organic electroluminescent device and a display device including the same. The organic electroluminescent device according to the invention, comprises: a substrate with a first sub-pixel area, a second sub-pixel area, and a third sub-pixel area formed thereon; a first set of electrodes formed on the first sub-pixel area, the second sub-pixel area, and the third sub-pixel area; a second set of electrodes opposing the first set of electrodes; and an organic light-emitting layer interposed between the first set of electrodes and the second set of electrodes; wherein the light-emitting layer formed on a first light-emitting area of the first sub-pixel area is a phosphorescent light-emitting layer, and the light-emitting layer formed on a second light-emitting area of the first sub-pixel area is fluorescent light-emitting layer.

Description

ORGANIC ELECTROLUMINESCENT DEVICE AND DISPLAY DEVICE INCLUDING THE SAME

The present invention relates to an organic electroluminescent (EL) device and a display device including the same.

Organic EL devices, one of the new flat panel displays, (FPDs), have a better viewing angle, contrast, etc. than liquid crystal display devices because they are self-light-emitting, can be made light and thin because a backlight is not necessary, and are advantageous in terms of power consumption.

Furthermore, organic EL devices have advantages of a low DC driving voltage, a fast response speed, a strong shock resistance (because it is fully solid), a wide temperature range, and a low manufacturing cost. In 1987, Eastman Kodak first developed an organic EL device using aromatic diamine; that is, small molecules, and alumina complexes as materials for forming a light-emitting layer [Appl. Phys. Lett. 51, 913, 1987].

The most important factor in determining light-emitting efficiency in an organic EL device is the light-emitting material. Fluorescent light-emitting materials have been widely used as light-emitting materials until now. However, active research is being carried out on phosphorescent light-emitting materials because they have a light-emitting efficiency that can be theoretically be four times greater than that of fluorescent light-emitting materials. In particular, in the case of organic EL devices adopted in mobile devices, the power efficiency of the device is important due to a limited battery capacity. Phosphorescent light-emitting materials have also been in the spotlight in terms of power consumption of the device. So far, the iridium (III) complex series has been widely used as the phosphorescent light-emitting material. Materials, such as bis(2-(2'-benzothienyl)-pyridinato-N,C-3')iridium(acetylacetonate) [(acac)Ir(btp)₂], tris(2-phenylpyridine)iridium [Ir(ppy)₃] and bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (Firpic), have been used for the RGB pixels.

In order to implement a low-power and high-efficiency panel in an organic EL device as described above, a phosphorescent light-emitting material with excellent light-emitting efficiency is needed to replace the fluorescent light-emitting material adopted in the light-emitting layer of a device. A green phosphorescent material and a red phosphorescent material are being commercialized, but a blue phosphorescent material has not yet been commercialized. There is a problem in that the white balance is not maintained in a low luminous area due to a difference between the efficiency of the phosphorescent material and the efficiency of the fluorescent material.

Korean Patent Laid-open Publication No. 2003-0020034 discloses an organic EL device in which a light-emitting layer having relatively low light-emitting efficiency of R, G, and B light-emitting layers is made of a phosphorescent material and the remaining light-emitting layers having relatively high light-emitting efficiency of the R, G, and B light-emitting layers is made of a fluorescent material in order to solve the problem that consumption power is increased because the driving current is increased to adjust the white balance.

Accordingly, the present invention intends to solve the above problems occurring in the prior art, and to provide an organic EL device capable of improving light-emitting efficiency and maintaining the white balance.

Furthermore, the present invention is intended to provide a display device including the organic EL device.

Objects to be solved by the present invention are not limited to the aforementioned objects and may be extended in various ways without departing from the spirit and scope of the present invention.

According to an aspect of the present invention, there is provided an organic EL device, including a substrate, first electrodes, second electrodes, and an organic light-emitting layer. The substrate includes a first sub-pixel area, a second sub-pixel area, and a third sub-pixel area. The first electrodes are formed on the first sub-pixel area, the second sub-pixel area, and the third sub-pixel area of the substrate. The second electrodes are formed to face the first electrodes. The organic light-emitting layer is interposed between each of the first electrodes and each of the second electrodes. The organic light-emitting layer formed on a first part of the first sub-pixel area is a phosphorescent light-emitting layer, and the organic light-emitting layer formed on a second part of the first sub-pixel area is a fluorescent light-emitting layer.

In an embodiment, the organic light-emitting layer formed on the second sub-pixel area is a phosphorescent light-emitting layer, the organic light-emitting layer formed on the third sub-pixel area is a fluorescent light-emitting layer, the second sub-pixel area neighbors the first part of the first sub-pixel area, and the third sub-pixel area neighbors the second part of the first sub-pixel area.

In an embodiment, the first sub-pixel area is a green pixel area, the second sub-pixel area is a red pixel area, and the third sub-pixel area is a blue pixel area.

According to another aspect of the present invention, there is provided an organic EL device, including a substrate, a first electrode, a second electrode, a third electrode, a first light-emitting layer, a second light-emitting layer, a third light-emitting layer, a fourth electrode, a fifth electrode, and a sixth electrode. The substrate includes a first light-emitting area and a second light-emitting area. The first electrode is formed on the first light-emitting area. The second electrode is formed on the second light-emitting area. The third electrode is formed on the first and second light-emitting areas. The first light-emitting layer is formed on the first light-emitting area of the first and second electrodes. The second light-emitting layer is formed on the second light-emitting area of the second and third electrodes. The fourth electrode is formed on the first light-emitting layer and formed to face the first electrode. The fifth electrode is formed on the second light-emitting layer and formed to face the second electrode. The sixth electrode is formed on the first and second light-emitting layers and formed to face the third electrode.

In an embodiment, the first light-emitting area includes a light-emitting layer containing a phosphorescent material, and the second light-emitting area includes a light-emitting layer containing a fluorescent material.

According to yet another aspect of the present invention, there is provided a display device including the organic EL device.

The organic EL device and display device according to the embodiments of the present invention can improve both power efficiency and the white balance using a phosphorescent material.

FIG. 1 is an equivalent circuit diagram of an organic light-emitting device according to an embodiment of the present invention.

FIG. 2a is a diagram showing the pixel structure of an organic light-emitting device according to a conventional RGB method.

FIG. 2b is a diagram showing the pixel structure of an organic light-emitting device according to an embodiment of the present invention.

FIG. 3a is a diagram showing the pixel structure of an organic light-emitting device according to a conventional pentile method.

FIG. 3b is a diagram showing the pixel structure of an organic light-emitting device according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of an organic light-emitting device according to an embodiment of the present invention.

FIG. 5 is a graph showing the light-emitting efficiency of a fluorescent material and a light-emitting material.

Specific structural and functional descriptions of embodiments of the present invention disclosed in this specification have been merely illustrated to describe the embodiments of the present invention. The embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in this specification.

The embodiments of the present invention may be modified in various ways and may have multiple forms, and thus specific embodiments are illustrated in the drawings and are described in detail in this specification or the application. However, it is to be understood that the specific embodiments are not intended to limit the present invention to a specific disclosure and the embodiments includes all changes, equivalents, and substitutions that are included in the spirit and technical scope of the present invention.

Terms, such as the first and the second, may be used to describe a variety of elements, but the elements should not be limited by the terms. The terms are used to only distinguish one element from the other element. For example, a first element may be named a second element, and likewise a second element may be named a first element without departing from the scope of the present invention.

When it is said that one element is described as being “connected” to or “coupled” with the other element, the one element may be directly connected to or coupled with the other element, and a third element also may be interposed between the two elements. In contrast, when it is said that one element is described as being “directly connected” to or “directly coupled” with the other element, it should be understood that a third element is not present between the two elements. Meanwhile, the same principle applies to other expressions, such as “between” and “just between” or “adjacent to” and “neighboring”, which describe relations between elements.

Terms used in this application are used to describe only specific embodiments and are not intended to limit the present invention. An expression of the singular number should be understood to include plural expressions, unless clearly expressed otherwise in the context. Terms, such as “include” or “have”, should be understood to indicate the existence of a described characteristic, number, step, operation, element, part, or a combination of them and understood to not exclude the existence of one or more other characteristics, numbers, steps, operations, elements, parts, or a combination of them or additional possibilities of them.

All terms used herein, including technical or scientific terms, have the same meanings as those typically understood by those skilled in the art unless otherwise defined. Terms, such as ones defined in common dictionaries, should be construed as having the same meanings as those in the context of related technology and should not be construed as having ideal or excessively formal meanings unless clearly defined in this application.

Hereinafter, some exemplary embodiments of the present invention are described in more detail with reference to the accompanying drawings. In order to help general understanding, the same reference numerals are used to denote the same elements throughout the drawings, and redundant descriptions of the same elements are omitted.

Referring to FIG. 1, the organic light-emitting device according to an embodiment of the present invention may include a plurality of

signal lines

101, 111, and 121 and a plurality of pixels PX connected to the signal lines and arranged in a matrix form.

The signal lines 101, 111, and 121 include a plurality of gate lines 111 for transferring gate signals (or scan signals), a plurality of data lines 101 for transferring data signals, and a plurality of driving voltage lines 121 for transferring driving voltage. The gate lines 111 may be formed in parallel in a row direction, and the data lines 101 and the driving voltage lines 121 may be formed in parallel in a column direction.

Each of the pixels PX may include a switching thin film transistor Qs, a driving thin film transistor Qd, a storage capacitor Cst, and an organic light emitting diode (OLED) LD.

The switching thin film transistor Qs has a control terminal, an input terminal, and an output terminal. The control terminal may be connected to the gate line 111, the input terminal may be connected to the data line 101, and the output terminal may be connected to the driving thin film transistor Qd. The switching thin film transistor Qs may transfer a data signal, which is applied to the data line 101, to the driving thin film transistor Qd in response to a scan signal applied to the gate line 111.

The driving thin film transistor Qd also has a control terminal, an input terminal, and an output terminal. The control terminal may be connected to the switching thin film transistor Qs, the input terminal may be connected to the driving voltage line 121, and the output terminal may be connected to the OLED LD. The driving thin film transistor Qd runs output current ILD whose amount is varied depending on voltage applied between the control terminal and the output terminal of the driving thin film transistor Qd.

The storage capacitor Cst may be connected between the control terminal and the input terminal of the driving thin film transistor Qd. The storage capacitor Cst can charge a data signal applied to the control terminal of the driving thin film transistor Qd and maintain the charged data signal even after the switching thin film transistor Qs is turned off.

The OLED LD has an anode connected to the output terminal of the driving thin film transistor Qd and a cathode connected to a common voltage Vss. The OLED LD can display an image by emitting light having a different intensity depending on the output current ILD of the driving thin film transistor Qd.

Each of the switching thin film transistor Qs and the driving thin film transistor Qd may be an n-channel field effect transistor (FET). Furthermore, at least one of the switching thin film transistor Qs and the driving thin film transistor Qd may be a p-channel FET. Furthermore, the connection relation among the thin film transistors Qs and Qd, the storage capacitor Cst, and the OLED LD may be changed.

Referring to FIG. 2a, the pixel structure 20 according to the conventional RGB method includes three

sub-pixels

201, 202, and 203 in one pixel. In FIG. 2a, the sub-pixel 201 may indicate a red sub-pixel, the sub-pixel 202 may indicate a green sub-pixel, and the sub-pixel 203 may indicate a blue sub-pixel.

In order to implement a low-power and high-efficiency panel in an organic EL device, a phosphorescent light-emitting material having excellent light-emitting efficiency is adopted in the light-emitting layer of the device. A green phosphorescent material and a red phosphorescent material are being commercialized, but a blue phosphorescent material has not yet been commercialized.

There is a problem in that the white balance is not maintained in a low luminous area due to a difference between the efficiency of the phosphorescent material and the efficiency of the fluorescent material.

Referring to FIG. 2b, the pixel structure 21 of the organic light-emitting device according to an embodiment of the present invention includes three

sub-pixels

201, 202, and 203 in one pixel. In FIG. 2b, the sub-pixel 201 may indicate a red sub-pixel, the sub-pixel 202 may indicate a green sub-pixel, and the sub-pixel 203 may indicate a blue sub-pixel.

In an embodiment of the present invention, the sub-pixel 202 may be divided into two light-emitting

areas

202a and 202b. In another embodiment, the sub-pixel 201 may include a light-emitting layer made of a phosphorescent material, and the light-emitting area 202a of the sub-pixel 202 may include a light-emitting layer made of a phosphorescent material. In such a case, the light-emitting area 202b of the sub-pixel 202 may include a light-emitting layer made of a fluorescent material, and the sub-pixel 203 may include a light-emitting layer made of a fluorescent material. The green sub-pixel 202 is separated into the two light-emitting

areas

202a and 202b, the light-emitting layer made of a phosphorescent material is formed in the light-emitting area 202a, and the light-emitting layer made of a fluorescent material is formed in the light-emitting area 202b. Accordingly, the white balance can be improved depending on luminosity.

In the aforementioned embodiment, the red sub-pixel 201 and the light-emitting area 202a of the green sub-pixel 202 have been illustrated as neighboring each other and having the respective light-emitting layers made of phosphorescent materials. According to embodiments, however, the red sub-pixel may be formed to neighbor a light-emitting area of the green sub-pixel in which a light-emitting layer made of a fluorescent material is formed.

Furthermore, in the illustrated embodiment, only the green sub-pixel 202 has been illustrated as being separated into the two light-emitting

areas

202a and 202b and having the light-emitting layers made of the phosphorescent material and the fluorescent material formed in the respective light-emitting

areas

202a and 202b. According to embodiments, however, the red or blue sub-pixel may be divided into two light-emitting areas, and light-emitting layers made of a phosphorescent material and a fluorescent material may be formed in the respective light-emitting areas. Furthermore, each of the two or three sub-pixels as well as one of the two or three sub-pixels may be divided into two light-emitting areas, and light-emitting layers made of a phosphorescent material and a fluorescent material may be formed in the respective light-emitting areas.

In the embodiment illustrated in FIG. 2b, the light-emitting

areas

202a and 202b included in the green sub-pixel are illustrated as having the same area. According to embodiments, however, the light-emitting

areas

202a and 202b may have different areas depending on light efficiencies of a light-emitting material and phosphorescent material included in the light-emitting layer. That is, the light-emitting area 202a including phosphorescent materials may be wider than the light-emitting area 202b including fluorescent materials, and the light-emitting area 202b including fluorescent materials may be wider than the light-emitting area 202a including phosphorescent materials. In such a case, a ratio of relative areas may be determined by the light-emitting efficiency of the phosphorescent material and the fluorescent material or may be properly selected and determined in order to adjust the white balance in driving the device.

FIG. 3a is a diagram showing the pixel structure of an organic light-emitting device according to the conventional pentile method.

Referring to FIG. 3a, unlike in the pixel structures according to the RGB method shown in FIGS. 2a and 2b, in the pixel structure 30 according to the pentile method, the green sub-pixels 302 are formed to neighbor the red sub-pixel 301 and the blue sub-pixel 303, respectively, and the red sub-pixel 301 and the blue sub-pixel 303 have an area twice the area of the green sub-pixel 302. That is, the green sub-pixels 302 are formed to have a relatively narrow area between the red sub-pixels 301 and the blue sub-pixels 303 that are alternately formed. The pixel structure according to the pentile method is adopted in an active mode organic light-emitting diode (AMOLED).

Referring to FIG. 3b, an organic light-emitting layer may be formed as a light-emitting layer including a phosphorescent material, in the first light-emitting area 301a of a green sub-pixel formed in the right side of the red sub-pixel 301. An organic light-emitting layer may be formed as a light-emitting layer including a fluorescent material, in the second light-emitting area 301b of the green sub-pixel formed on a surface on the right side of a blue sub-pixel 303. Accordingly, the power efficiency and the white balance across the entire luminous area can be improved by using both a phosphorescent material and a fluorescent material in a sub-pixel indicative of one color.

Referring to FIG. 4, the organic light-emitting device 40 according to an embodiment of the present invention includes a first substrate 410 and a second substrate 420, which faces the first substrate 410 and is configured for encapsulation.

Driving thin film transistors DTr for respective pixel areas are formed over the first substrate 410, and first electrodes 440 are connected to the respective driving thin film transistors DTr. Organic light-emitting layers including light-emitting

material patterns

401, 402a and 402b, and 403, which emit red, green, and blue colored lights, respectively, are formed over the first electrodes 440. A second electrode 430 is formed over the entire surface of the organic light-emitting layers. The first and the

second electrodes

440 and 430 apply an electric field to the organic light-emitting layers, and the first and the

second electrodes

440 and 430, and the organic light-emitting layers interposed between the first and the

second electrodes

440 and 430 form an organic EL device 40. The first electrodes 440 and the driving thin film transistors DTr form the

respective sub-pixel areas

460, 450, and 470, together with the respective organic light-emitting layers including the light-emitting

material patterns

401, 402a and 402b, and 403. Second electrodes corresponding to the first electrodes of an organic light-emitting device may be independently formed, but may be formed of one second electrode 430 as shown in FIG. 4.

The second electrode 430 and the second substrate 420 formed over the first substrate 410 are spaced apart from each other in a specific interval.

In an embodiment, the sub-pixel area 450 may indicate a green sub-pixel area, the sub-pixel area 460 may indicate a red sub-pixel, and the sub-pixel area 470 may indicate a blue sub-pixel area. In such a case, the sub-pixel area 450 indicative of green may be divided into a first light-emitting area 451 and a second light-emitting area 453. In an embodiment, the organic light-emitting layer 402a corresponding to the first light-emitting area 451 may be formed to include a phosphorescent material, and the organic light-emitting layer 402b corresponding to the second light-emitting area 453 may be formed to include a fluorescent material.

As shown in FIG. 4, the organic EL device according to an embodiment of the present invention can improve both power efficiency and the white balance across the entire luminous area using both a phosphorescent material and a fluorescent material in a sub-pixel indicative of one color.

FIG. 5 shows the luminous efficiencies of fluorescent materials and the luminous efficiencies of phosphorescent materials. The graph shows that the efficiencies of the phosphorescent materials are higher than efficiencies of the fluorescent materials in a low luminous area, i.e., in an area of about 100 cd/m² or less, and the efficiencies of the fluorescent materials are higher than the efficiencies of the phosphorescent materials in an area of about 100 cd/m² or more. In accordance with the organic EL device according to the present invention, a sub-pixel area is divided into a first light-emitting area and a second light-emitting area, a light-emitting layer made of a phosphorescent material is formed in the first light-emitting area, and a light-emitting layer made of a fluorescent material is formed in the second light-emitting area. Accordingly, both power efficiency and the white balance across the entire luminous area can be improved by using both a phosphorescent material and a fluorescent material in a sub-pixel indicative of one color.

The present invention can be widely used in manufacturing organic EL elements and manufacturing display devices including the same.

Although some embodiments of the present invention have been described above, those skilled in the art will appreciate that the present invention may be modified and changed in various ways without departing from the technical spirit and scope of the present invention.

[Description of Reference Numerals]

101: data line 111: gate line

121: driving voltage line 20, 21: pixel structure

201, 202, 203: sub-pixel 202a, 202b: light-emitting area

30, 31:

pixel structure

301, 302, 303: sub-pixel

302a, 302b: light-emitting area 40: organic light-emitting device

401, 402a, 402b, 403: light-emitting material pattern

410: first substrate 420: second substrate

430: second electrode 440: first electrode

450, 460, 470: sub-pixel area 451: first light-emitting area

453: second light-emitting area

Claims

An organic electroluminescent device, comprising:

a substrate with a first sub-pixel area, a second sub-pixel area, and a third sub-pixel area formed thereon;

a first set of electrodes formed on the first sub-pixel area, the second sub-pixel area, and the third sub-pixel area;

a second set of electrodes opposing the first set of electrodes; and

an organic light-emitting layer interposed between the first set of electrodes and the second set of electrodes;

wherein the light-emitting layer formed on a first light-emitting area of the first sub-pixel area is a phosphorescent light-emitting layer, and the light-emitting layer formed on a second light-emitting area of the first sub-pixel area is fluorescent light-emitting layer.
The device of claim 1, wherein the organic light-emitting layer formed on a first light-emitting area of the second sub-pixel area is a phosphorescent light-emitting layer, and the organic light-emitting layer formed on a second light-emitting area of the second sub-pixel area is fluorescent light-emitting layer.
The device of claim 1, wherein the organic light-emitting layer formed on the second sub-pixel area is a phosphorescent light-emitting layer, the organic light-emitting layer formed on the third sub-pixel area is a fluorescent light-emitting layer, the second sub-pixel area is adjacent to the first light-emitting area of the first sub-pixel area, and the third sub-pixel area is adjacent to the second light-emitting area of the first sub-pixel area.
The device of claim 3, wherein the first sub-pixel area is a green pixel area, the second sub-pixel area is a red pixel area, and the third sub-pixel area is a blue pixel area.
An organic electroluminescent device, comprising:

a substrate with a first light-emitting area and a second light-emitting area formed thereon;

a first electrode formed on the first light-emitting area;

a second electrode formed on the second light-emitting area;

a third electrode formed on the first and second light-emitting areas;

a first light-emitting layer formed on the first light-emitting areas of the first and third electrodes;

a second light-emitting layer formed on the second light-emitting areas of the second and third electrodes;

a fourth electrode formed on the first light-emitting layer, opposing the first electrode;

a fifth electrode formed on the second light-emitting layer, opposing the second electrode; and

a sixth electrode formed on the first and second light-emitting layers, opposing the third electrode.
The device of claim 5, wherein the first light-emitting area has a light-emitting layer containing phosphorescent material, and the second light-emitting area has a light-emitting layer containing fluorescent material.
A display device comprising the device of any one of claims 1 to 6.