KR102550746B1 - Organic light emitting display device - Google Patents

Abstract

An organic light emitting diode display according to an exemplary embodiment of the present invention includes a plurality of sub-pixels including a red sub-pixel, a green sub-pixel, and a blue sub-pixel. One sub-pixel of the plurality of sub-pixels includes an organic light emitting layer made of a host and a dopant, and a hole transport layer disposed under the organic light emitting layer. It is characterized in that the difference between the LUMO level of the organic light emitting layer and the LUMO level of the hole transport layer is 0.6 to 0.9 eV. The organic light emitting diode display according to an exemplary embodiment of the present invention prevents the redish phenomenon caused by the leakage current of the thin film transistor, which may occur due to driving of adjacent pixels, and the redish phenomenon, which may occur when the organic light emitting display device is driven at a low gray level. It can be prevented. In addition, lifespan characteristics of the organic light emitting display device may be improved by improving hole injection characteristics into the organic light emitting layer through the hole transport layer including the second hole transport layer region and the fourth hole transport layer region including the P-type dopant.

Description

Organic light emitting display device {ORGANIC LIGHT EMITTING DISPLAY DEVICE}

The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display capable of minimizing a reddish phenomenon caused by a leakage current of a thin film transistor and a reddish phenomenon that may occur during low grayscale driving. .

An organic light emitting display (OLED) is a self-emissive display device, and unlike a liquid crystal display (LCD), it does not require a separate light source and can be manufactured to be lightweight and thin. In addition, the organic light emitting display device is advantageous in terms of power consumption due to low voltage driving, and is being studied as a next-generation display because it is excellent in color implementation, response speed, viewing angle, and contrast ratio (CR).

1 is a diagram illustrating an energy band diagram of an organic light emitting stack of a conventional organic light emitting display device. 2 is a diagram illustrating current density-voltage curves (J-V curves) for a red sub-pixel, a green sub-pixel, and a blue sub-pixel in a conventional organic light emitting display device. FIG. 1 exemplarily illustrates an energy band diagram of a red organic light emitting stack of a conventional organic light emitting display device, and includes a hole transport layer (HTL), an electron blocking layer (EBL), and a red organic light emitting layer included in the red organic light emitting stack. The LUMO (Lowest Unoccupied Molecular Orbitals) level and HOMO (Highest Occupied Molecular Orbitals) level of the host (RED HOST) and the electron transport layer (ETL) are shown. In FIG. 2, the current density-voltage curve for the red sub-pixel is shown as a solid line, the current density-voltage curve for the green sub-pixel is shown as a dotted line, and the current density-voltage curve for the blue sub-pixel is shown as a dotted line. shown

In an organic light emitting display device including a conventional red organic light emitting stack showing an energy band diagram as shown in FIG. 1 , when driving a blue organic light emitting stack or a green organic light emitting stack around the red organic light emitting stack, the thin film transistor There was a problem of leakage current. This problem is a difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron blocking layer used in the conventional red organic light emitting stack, and the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron transport layer. It occurs because it is quite small, about 0.1 to 0.3 eV.

Referring to FIG. 2 together for a more detailed explanation, the red organic light emitting stack disposed in the red sub-pixel has a lower current density, that is, a current density of about 0.01 to 1 mA/cm 2 than the green organic light emitting stack and the blue organic light emitting stack. It has a lower turn-on voltage. In other words, the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron blocking layer and the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron transport layer are the LUMO levels of the host of the other color organic light emitting layer. Since the difference between the LUMO level of the organic light emitting layer and the LUMO level of the organic light emitting layer of a different color is smaller than the difference between the LUMO level of the host and the electron transport layer, the red organic light emitting stack emits first when a small leakage current of the same magnitude flows. Start the action. Therefore, in a conventional organic light emitting display device using a red organic light emitting stack, when driving a blue sub-pixel or a green sub-pixel, a redish phenomenon occurs due to a leakage current in which the red sub-pixel is also driven.

In addition, when a conventional organic light emitting display device using the above-described red organic light emitting stack is driven to display an image of a low grayscale level, the redish phenomenon occurs. Specifically, when all of the red sub-pixel, the green sub-pixel, and the blue sub-pixel are driven at a low current density in order to implement low-gradation white, the red organic light emitting stack is a green organic light emitting stack and a blue organic light emitting stack, as described above. Since it has a lower turn-on voltage, the red organic light emitting stack not only starts the light emitting operation first but also emits the brightest light when a low current of the same magnitude flows. Therefore, when a low-gradation white color is implemented in an organic light emitting display device using a conventional red organic light emitting stack, a reddish phenomenon occurs in which reddish white color is implemented instead of pure white color.

[Related technical literature]

1. White organic light emitting device (Patent Application No. 10-2011-0094916)

The inventors of the present invention found that the redish phenomenon of the organic light emitting diode display as described above is related to the LUMO level of the host of the red organic light emitting layer included in the red organic light emitting stack. In addition, the inventors of the present invention found that when the anode is made of a transparent conductive oxide and silver (Ag), the voltage is reduced due to the difference in work function between the transparent conductive oxide and silver when the organic light emitting display device is driven at low gradations and at high gradations. It was found that the built-in part is different, and thereby a reddish phenomenon may occur. Accordingly, the inventors of the present invention invented a host of a red organic light emitting layer having a new LUMO level capable of minimizing the reddish phenomenon and an organic light emitting display device including the same.

An object to be solved by the present invention is to provide an organic light emitting display device in which redish phenomenon caused by leakage current of a thin film transistor, which may occur due to driving of an adjacent pixel, is prevented.

Another object to be solved by the present invention is to provide an organic light emitting display device in which redish phenomenon that may occur during low grayscale driving of the organic light emitting display device is prevented.

Another problem to be solved by the present invention is to provide an organic light emitting display device having an improved lifetime by improving hole injection characteristics into an organic light emitting layer.

Solved problems according to embodiments of the present invention are not limited to the above-mentioned problems, and other problems not mentioned above will be clearly understood by those skilled in the art from the description below.

An organic light emitting diode display according to an exemplary embodiment includes a plurality of sub-pixels including a red sub-pixel, a green sub-pixel, and a blue sub-pixel. One sub-pixel of the plurality of sub-pixels includes an organic light emitting layer made of a host and a dopant, and a hole transport layer disposed under the organic light emitting layer. It is characterized in that the difference between the LUMO level of the organic light emitting layer and the LUMO level of the hole transport layer is 0.6 to 0.9 eV. The organic light emitting diode display according to an exemplary embodiment of the present invention prevents the redish phenomenon caused by the leakage current of the thin film transistor, which may occur due to driving of adjacent pixels, and the redish phenomenon, which may occur when the organic light emitting display device is driven at a low gray level. It can be prevented.

According to another feature of the present invention, one sub-pixel is a red sub-pixel.

According to another feature of the present invention, an electron blocking layer is further included between the organic light emitting layer and the hole transport layer.

According to another feature of the present invention, the difference between the LUMO level of the host of the organic light emitting layer and the LUMO level of the electron blocking layer is characterized in that 0.6 to 0.9 eV.

According to another feature of the present invention, the difference between the LUMO level of the host of the organic light emitting layer and the LUMO level of the hole transport layer is determined based on electron mobility in a low gray level and a driving voltage for driving the organic light emitting layer.

According to another feature of the present invention, the host of the organic light emitting layer is characterized in that it consists of a beryllium-based complex (beryllium complex).

The hole transport layer of the organic light emitting diode display according to another embodiment of the present invention includes first to third hole transport layer regions, the second hole transport layer region includes a P-type dopant, and the first hole transport layer region and the third hole transport layer region contain a p-type dopant. It may be disposed between the transport layer regions.

According to another feature of the present invention, the P-type dopant may be F4-TCNQ (tetrafluoro-tetracyanoquinodimethane).

According to another feature of the present invention, the thickness of the second hole transport layer region may be 10% or less of the total thickness of the hole transport layer.

According to another feature of the present invention, a fourth hole transport layer region including a P-type dopant may be further included under the first hole transport layer region.

An organic light emitting diode display according to another embodiment of the present invention includes a substrate including red sub-pixels, green sub-pixels, and blue sub-pixels, a thin film transistor formed on the substrate, an anode formed to be electrically connected to the thin film transistor, and an anode formed on the anode. and an organic light emitting stack formed thereon and a cathode formed on the organic light emitting stack. The organic light emitting stack includes a red organic light emitting stack disposed in a red sub-pixel. The red organic light emitting stack includes a red organic light emitting layer including a host and a dopant and a hole transport layer disposed under the red organic light emitting layer. The difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the hole transport layer is 0.6 to 0.9 eV. In the organic light emitting diode display according to another exemplary embodiment of the present invention, reddish phenomenon in the organic light emitting display device is minimized when the red sub-pixel is driven by the leakage current of the thin film transistor that may be generated by driving other sub-pixels. In addition, when the organic light emitting diode display is driven at a current density for implementing low-grayscale white, the reddish phenomenon that may occur undesirably can be minimized.

According to another feature of the present invention, the organic light emitting stack further includes a green organic light emitting stack disposed on a green sub-pixel and including a green organic light emitting layer and a blue organic light emitting stack disposed on a blue sub pixel and including a blue organic light emitting layer. characterized by

According to another feature of the present invention, the difference between the maximum value and the minimum value of the LUMO level of the host of the red organic light emitting layer, the LUMO level of the host of the green organic light emitting layer, and the LUMO level of the host of the blue organic light emitting layer is 0.2 eV. .

According to another feature of the present invention, the LUMO level of the host of the red organic light emitting layer is 3.04 eV, the LUMO level of the host of the green organic light emitting layer is 2.9 eV, and the LUMO level of the host of the blue organic light emitting layer is 3.0 eV. do.

According to another feature of the present invention, an electron blocking layer is further included between the red organic light emitting layer and the hole transport layer, and the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron blocking layer is 0.6 to 0.9 eV. to be

According to another feature of the present invention, the anode is characterized in that it includes a reflective layer and a transparent conductive layer formed on the reflective layer.

According to another feature of the present invention, the reflective layer is characterized in that silver (Ag) or an alloy containing silver.

According to another feature of the present invention, a difference in vacuum level between the reflective layer and the transparent conductive layer is 0.2 eV or more.

According to another feature of the present invention, the host of the red organic light emitting layer is characterized in that it consists of a beryllium-based complex (beryllium complex).

Other embodiment specifics are included in the detailed description and drawings.

According to the present invention, it is possible to minimize redish phenomenon in an organic light emitting diode display when a red sub-pixel is driven by a leakage current of a thin film transistor that may be generated by driving a blue sub-pixel or a green sub-pixel.

In addition, the present invention can minimize the reddish phenomenon that may occur undesirably when the organic light emitting diode display is driven at a current density for implementing low-grayscale white.

In addition, the present invention can improve lifespan characteristics of the organic light emitting display device by improving hole injection characteristics into the organic light emitting layer in the organic light emitting display device.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

Since the content of the invention described in the problem to be solved, the means for solving the problem, and the effect above does not specify the essential features of the claim, the scope of the claim is not limited by the matters described in the content of the invention.

1 is a diagram illustrating an energy band diagram of an organic light emitting stack of a conventional organic light emitting display device.
2 is a diagram illustrating current density-voltage curves (JV curves) for a red sub-pixel, a green sub-pixel, and a blue sub-pixel in a conventional organic light emitting display device.
3A is a schematic cross-sectional view illustrating an organic light emitting display device according to an exemplary embodiment of the present invention.
FIG. 3B is an enlarged view of region X of FIG. 3A.
4 is an energy band diagram of an organic light emitting stack of an organic light emitting display device according to an exemplary embodiment of the present invention.
5 is a diagram illustrating current density-voltage curves (JV curves) for a red sub-pixel, a green sub-pixel, and a blue sub-pixel in an organic light emitting diode display according to an exemplary embodiment of the present invention.
6 is an enlarged view for explaining an organic light emitting display device according to another exemplary embodiment of the present invention.
7A and 7B are enlarged views illustrating an organic light emitting display device according to another exemplary embodiment of the present invention.
8 is a diagram illustrating current density-voltage curves (JV curves) for a red sub-pixel, a green sub-pixel, and a blue sub-pixel in an organic light emitting diode display according to another exemplary embodiment of the present invention.
9A to 9D are diagrams illustrating comparative evaluation results of lifespan characteristics of a comparative example and an organic light emitting display device according to another exemplary embodiment of the present invention.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative, so the present invention is not limited to the details shown. Like reference numbers designate like elements throughout the specification. In addition, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. When 'includes', 'has', 'consists of', etc. mentioned in this specification is used, other parts may be added unless 'only' is used. In the case where a component is expressed in the singular, the case including the plural is included unless otherwise explicitly stated.

In interpreting the components, even if there is no separate explicit description, it is interpreted as including the error range.

In the case of a description of a positional relationship, for example, 'on top of', 'on top of', 'at the bottom of', 'next to', etc. Or, unless 'directly' is used, one or more other parts may be located between the two parts.

When an element or layer is referred to as “on” another element or layer, it includes all cases where another element or layer is directly on top of another element or another layer or other element intervenes therebetween.

Although first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below may also be the second component within the technical spirit of the present invention.

Like reference numbers designate like elements throughout the specification.

The size and thickness of each component shown in the drawings are shown for convenience of description, and the present invention is not necessarily limited to the size and thickness of the illustrated components.

Each feature of the various embodiments of the present invention can be partially or entirely combined or combined with each other, technically various interlocking and driving are possible, and each embodiment can be implemented independently of each other or can be implemented together in a related relationship. may be

In this specification, the fact that the organic light emitting diode display is driven at a low gradation means that the organic light emitting diode display is driven at a current density for displaying white, red, green, or blue in a low gradation. Also, low grayscale may mean 31 grayscales, for example, when grayscales are expressed as values of 0 to 255.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3A is a schematic cross-sectional view illustrating an organic light emitting display device according to an exemplary embodiment of the present invention. FIG. 3B is an enlarged view of region X of FIG. 3A. Referring to FIGS. 3A and 3B , the organic light emitting diode display 100 includes a substrate 110 , a thin film transistor 120 , an anode 140 , an organic light emitting stack 150 and a cathode 160 . In FIG. 3A , only one red sub-pixel R, one green sub-pixel G, and one blue sub-pixel B among a plurality of sub-pixels of the organic light emitting diode display 100 are illustrated for convenience of explanation. . 3A and 3 illustrate that the organic light emitting display device 100 according to an exemplary embodiment of the present invention is a top emission type organic light emitting display device 100 .

The substrate 110 for supporting various components of the organic light emitting display device 100 is formed of an insulating material. A buffer layer 131 is formed on the substrate 110 to protect various components of the organic light emitting diode display 100 from permeation of moisture and oxygen from the outside of the substrate 110 .

A thin film transistor 120 including a gate electrode 121 , an active layer 122 , a source electrode 123 and a drain electrode 124 is formed on the buffer layer 131 . Specifically, an active layer 122 is formed on the substrate 110, and a gate insulating layer 132 for insulating the active layer 122 and the gate electrode 121 is formed on the active layer 122, An interlayer insulating layer 133 is formed to insulate the gate electrode 121 from the source electrode 123 and the drain electrode 124, and on the interlayer insulating layer 133, the source electrodes in contact with the active layer 122 ( 123) and a drain electrode 124 are formed. The thin film transistor 120 is formed in each of the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B. In this specification, only the driving thin film transistor among various thin film transistors that may be included in the organic light emitting display device 100 is illustrated for convenience of description. Also, in this specification, the thin film transistor 120 is described as having a coplanar structure, but a thin film transistor having an inverted staggered structure may also be used.

An overcoating layer 134 is formed on the thin film transistor 120 . The over-coating layer 134 functions as a planarization layer for planarizing the upper portion of the substrate 110 . The overcoating layer 134 includes a contact hole for electrically connecting the thin film transistor 120 and the anode 140 of the organic light emitting stack 150 .

An anode 140 is formed on the overcoating layer 134 . The anode 140 includes a transparent conductive layer 141 and a reflective layer 142 . The anode 140 is formed in each of the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B, and the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B The anodes 140 formed on each are electrically isolated from each other.

A reflective layer 142 is formed on the overcoating layer 134 . The reflective layer 142 reflects light emitted from the organic light emitting stack 150 toward the top of the organic light emitting display device 100 and is formed of a conductive layer having excellent reflectivity. The reflective layer 142 may be silver (Ag) or an alloy containing silver, for example, silver or APC (Ag/Pd/Cu). The reflective layer 142 may be electrically connected to the thin film transistor 120 through the contact hole of the overcoating layer 134 and, for example, electrically connected to the source electrode 123 of the thin film transistor 120 . The work function of the reflective layer 142 may be about 4.8 eV.

A transparent conductive layer 141 is formed on the reflective layer 142 . The transparent conductive layer 141 is for supplying holes to the organic light emitting layer of the organic light emitting stack 150 and is formed of a conductive material having a high work function. The transparent conductive layer 141 is formed of transparent conductive oxide (TCO), and may be formed of, for example, ITO, IZO, or the like. The work function of the transparent conductive layer 141 may be about 5.4 eV. A difference in vacuum level between the reflective layer 142 and the transparent conductive layer 141 may be greater than or equal to 0.2 eV.

A bank 135 is formed on the anode 140 and the overcoating layer 134 . The bank 135 divides adjacent sub-pixel areas. Also, the bank 135 may divide a pixel area composed of a plurality of sub-pixel areas.

A cathode 160 is formed over the anode 140 . Since the cathode 160 needs to supply electrons, it is formed of a conductive material having a low work function. For example, the cathode 160 may be formed of an alloy of magnesium (Mg) and silver (Ag). The work function of cathode 160 may be about 4.1 eV. Cathode 160 is not patterned, but is formed as one layer over anode 140 . That is, the cathode 160 is formed as a single layer in the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B. Since the organic light emitting diode display 100 according to an exemplary embodiment of the present invention is a top emission organic light emitting diode display 100, the cathode 160 may be formed with a very thin thickness and may be substantially transparent.

An organic light emitting stack 150 is formed between the anode 140 and the cathode 160 . The organic light emitting stack 150 includes a red organic light emitting stack 150R formed on a red sub-pixel R, a green organic light emitting stack 150G formed on a green sub-pixel G, and a blue organic light emitting stack 150G formed on a blue sub-pixel B. and a stack 150B. The red organic light emitting stack 150R, the green organic light emitting stack 150G, and the blue organic light emitting stack 150B are formed to be separated from each other.

Hereinafter, the red organic light emitting stack 150R among the red organic light emitting stack 150R, the green organic light emitting stack 150G, and the blue organic light emitting stack 150B will be described in detail with reference to FIG. 3B .

FIG. 3B is an enlarged view of region X of FIG. 3A.

Referring to FIG. 3B , the red organic light emitting stack 150R includes a hole transport layer (HTL; 151R) formed on the anode 140, an electron blocking layer (EBL; 154R) formed on the hole transport layer 151R, and an electron blocking layer ( 154R) and an electron transport layer (ETL) 153R formed on the red organic light emitting layer 152R. Hereinafter, FIG. 4 is also referred to for a detailed description of the hole transport layer 151R, the electron blocking layer 154R, the red organic light emitting layer 152R, and the electron transport layer 153R of the red organic light emitting stack 150R.

4 is a diagram illustrating an energy band diagram of an organic light emitting stack 150 of an organic light emitting display device according to an exemplary embodiment of the present invention. In FIG. 4 , the hole transport layer 151R of the red organic light emitting stack 150R, the electron blocking layer 154R, and the host and electron transport layers of the red organic light emitting layer 152R together with work functions for the anode 140 and the cathode 160 The energy band for (153R) is shown in the form of a rectangle, and the upper side of the rectangle means the LUMO level of each layer, and the lower side means the HOMO level of each layer.

The hole transport layer 151R formed on the anode 140 is a layer that accelerates and transports holes to the red organic light emitting layer 152R. The LUMO level of the hole transport layer 151R may be about 2.38 eV, and the HOMO level may be about 5.38 eV. The hole transport layer 151R is an organic material layer, and is formed of an organic material that satisfies the above-described LUMO level and HOMO level, for example, NPD (4.4'-bis[N-(1-naphthy1)-N-pheny1-amino]bipheny1 ) and the like.

An electron blocking layer 154R is formed on the hole transporting layer 151R. The electron blocking layer 154R has a lower electron affinity than the electron transport layer 153R, thereby blocking the flow of electrons, and maximizes the staying time of electrons in the red organic light emitting layer 152R, thereby improving light emitting efficiency. The LUMO level of the electron blocking layer 154R may be about 2.2 eV and the HOMO level may be about 5.4 eV. The electron blocking layer 154R is an organic material layer and may be formed of a material that satisfies the above-described LUMO level and HOMO level.

A red organic light emitting layer 152R is formed on the electron blocking layer 154R. The red organic emission layer 152R is a layer that emits red light by combining electrons and holes. The red organic emission layer 152R includes a host and a dopant. The host of the red organic light emitting layer 152R is a material serving to transfer energy to a dopant to improve luminous efficiency and color purity, and the dopant of the red organic light emitting layer 152R is a dye organic material added in a small amount to the host.

The difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the hole transport layer 151R and the difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the electron blocking layer 154R are low. It is determined based on the electron mobility and driving voltage in the gray level. Specifically, the difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the hole transport layer 151R is 0.6 to 0.9 eV.

Further, when the electron blocking layer 154R is used as shown in FIG. 3B, the difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the electron blocking layer 154R is 0.6 to 0.9 eV. . A difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the hole transport layer 151R and a difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the electron blocking layer 154R are 0.9 When it is greater than eV or 0.2 to 0.3 eV, a driving voltage for driving the red organic light emitting stack 150R increases, and accordingly, a problem in that the lifespan of the red organic light emitting stack 150R is reduced may occur.

In addition, the difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the hole transport layer 151R and the difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the electron blocking layer 154R When is less than 0.6 eV, since the electron mobility increases, the Reddish phenomenon caused by the leakage current and the Reddish phenomenon occur during low gradation driving, as in the prior art, so that the organic light emitting display device 100 may have a color defect. there is.

Accordingly, the host of the red organic light emitting layer 152R of the organic light emitting display device 100 of the present invention is formed of an organic material that can satisfy the above-described LUMO level condition, for example, a beryllium-based complex. material can be formed. In this case, the LUMO level of the host of the red organic light emitting layer 152R may be about 3.04 eV, and the HOMO level may be about 5.75 eV.

An electron transport layer 153R is formed on the red organic emission layer 152R. The electron transport layer 153R is a layer that accelerates and transports electrons to the red organic light emitting layer 152R. The LUMO level of the electron transport layer 153R may be about 2.8 eV, and the HOMO level may be about 5.8 eV. The electron transport layer 153R is an organic material layer and is formed of an organic material that satisfies the above-described LUMO level and HOMO level, and may be formed of, for example, Alq3.

The green organic light emitting stack 150G and the blue organic light emitting stack 150B may also be formed of a material similar to that of the red organic light emitting stack 150R. However, since the colors of the emitted light are different from each other, the materials constituting the green organic emission layer of the green organic emission stack 150G and the blue organic emission layer of the blue organic emission stack 150B are different from the materials constituting the red organic emission layer 152R. can be different However, the difference between the LUMO level of the host of the green organic light emitting layer and the blue organic light emitting layer and the LUMO level of the hole transport layer 151R, and the LUMO level of the host of the green organic light emitting layer and the blue organic light emitting layer and the LUMO level of the electron blocking layer 154R The difference between them is also preferably 0.6 to 0.9 eV.

A difference between a maximum value and a minimum value among the LUMO level of the host of the red organic light emitting layer 152R, the LUMO level of the host of the green organic light emitting layer, and the LUMO level of the host of the blue organic light emitting layer may be 0.2 eV. That is, the LUMO level of the host of the red organic light emitting layer 152R, the LUMO level of the host of the green organic light emitting layer, and the LUMO level of the host of the blue organic light emitting layer may be determined to be balanced. For example, the LUMO level of the host of the green organic light emitting layer may be 2.9 eV, and the LUMO level of the host of the blue organic light emitting layer may be 3.0 eV.

Hereinafter, FIG. 5 will also be referred to for a more detailed description of driving and effects of the organic light emitting display device 100 according to an exemplary embodiment of the present invention.

5 is a current density-voltage curve (J-V curve) for a red sub-pixel R, a green sub-pixel G, and a blue sub-pixel B in the organic light emitting display device 100 according to an exemplary embodiment of the present invention. ) is a drawing showing. In FIG. 5, the current density-voltage curve for the red sub-pixel (R) is shown as a solid line, the current density-voltage curve for the green sub-pixel (G) is shown as a dotted line, and the blue sub-pixel (B) The current density-voltage curve for is shown as a dotted line.

When compared with the current density-voltage curve of the conventional organic light emitting diode display shown in FIG. The red organic light emitting stack 150R disposed in the red sub-pixel R of R has substantially the same turn-on voltage as the green organic light emitting stack 150G and the blue organic light emitting stack 150B at a low current density.

In other words, in the organic light emitting display device 100 according to an embodiment of the present invention, the LUMO level of the host of the red organic light emitting layer 152R is equal to the LUMO level of the hole transport layer 151R and the LUMO level of the electron blocking layer 154R. Since the LUMO levels of the material of the red organic light emitting layer 152R and the host are determined to have a difference of 0.6 to 0.9 eV, the mobility of electrons moving from the red organic light emitting layer 152R to the anode 140 may be reduced.

In addition, in the conventional organic light emitting diode display shown in FIG. 1, since the difference between the LUMO level of the host of the red organic light emitting layer, the LUMO level of the hole transport layer, and the LUMO level of the electron blocking layer is small, the green sub-pixel and the blue sub-pixel and Unlike, in the red sub-pixel, the voltage is directly built into the transparent conductive layer of the anode, and the redish phenomenon occurs during low-grayscale driving of the organic light emitting display device.

However, in the organic light emitting display device 100 according to an embodiment of the present invention, as shown in FIG. 4 , the LUMO level of the host of the red organic light emitting layer 152R, the LUMO level of the hole transport layer 151R, and the electron blocking layer ( Since the difference between the LUMO levels of 154R) is sufficient, the anode 140 in all of the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B when the organic light emitting display device 100 is driven at low gray levels A voltage may be built-in to the reflective layer 142, and then a voltage may be built-in to the transparent conductive layer 141 as the gray level increases.

Accordingly, the organic light emitting diode display 100 according to an exemplary embodiment of the present invention prevents the redish phenomenon due to leakage current that occurs in the conventional organic light emitting display and the redish phenomenon that may occur when driving at a low current density. can do.

6 is an enlarged view for explaining an organic light emitting display device according to another exemplary embodiment of the present invention, and is an enlarged view of region X of FIG. 3A .

Referring to FIG. 6 , compared to the organic light emitting diode display 100 according to the exemplary embodiment illustrated in FIGS. 3A and 3B , the electron blocking layer 154R is omitted. When the electron blocking layer is not used, the red organic light emitting layer 152R is directly formed on the hole transport layer 151R. In this case, a difference between the LUMO level of the host of the red organic light emitting layer 152R and the LUMO level of the hole transport layer 151R is 0.6 to 0.9 eV. Since no electron blocking layer is used, the LUMO level of the host of the red organic light emitting layer 152R can be determined without considering the LUMO level of the electron blocking layer.

7A and 7B are enlarged views for explaining an organic light emitting display device according to another exemplary embodiment of the present invention, and are enlarged views of an X region of the organic light emitting display device according to an exemplary embodiment described in FIG. 3A .

Referring to FIG. 7A , the hole transport layer 151R of the organic light emitting diode display 100 according to another exemplary embodiment of the present invention may be formed of a multiple layer including a plurality of hole transport layer regions instead of a single layer.

That is, the hole transport layer 151R may include a first hole transport layer region 155R, a second hole transport layer region 156R, and a third hole transport layer region 157R sequentially stacked in one process. In addition, the second hole transport layer region 156R disposed between the first hole transport layer region 155R and the third hole transport layer region 157R may include a P-type dopant. The second hole transport layer region 156R including the P-type dopant may function as a hole injection layer that facilitates hole injection and may improve hole injection characteristics into the red organic emission layer 152R.

The P-type dopant doped in the second hole transport layer region 156R may be, for example, F ₄ -TCNQ (tetrafluoro-tetracyanoquinodimethane), but is not limited thereto.

In addition, the thickness of the second hole transport layer region 156R including the P-type dopant may be formed to a thickness of 10% or less of the total thickness of the hole transport layer 151R in consideration of hole injection characteristics into the red organic light emitting layer 152R. can For example, when the entire thickness of the hole transport layer 151R is 1000 Å, the thickness of the second hole transport layer region 156R including the P-type dopant may be formed to a thickness of 100 Å or less.

Referring to FIG. 7B , the hole transport layer 151R of the organic light emitting diode display 100 according to another embodiment of the present invention includes the first hole transport layer region 155R and the second hole transport layer region described with reference to FIG. 7A . In addition to 156R and the third hole transport layer region 157R, a fourth hole transport layer region 158R disposed below the first hole transport layer region 155R may be further included.

Also, the fourth hole transport layer region 158R may include a P-type dopant like the second hole transport layer region 156R. Hole injection characteristics into the red organic light emitting layer 152R may be further improved through the fourth hole transport layer region 158R including the P-type dopant additionally formed in the second hole transport layer region 156R including the P-type dopant. can Similar to the aforementioned second hole transport layer region 156R, the thickness of the fourth hole transport layer region 158R may be less than 10% of the total thickness of the hole transport layer 151R in consideration of hole injection characteristics.

8 is a diagram illustrating current density-voltage curves (J-V curves) of a red sub-pixel, a green sub-pixel, and a blue sub-pixel in an organic light emitting diode display according to another exemplary embodiment described with reference to FIG. 7B. . In FIG. 8 , the current density-voltage curve for the red sub-pixel (R) is shown as a solid line, the current density-voltage curve for the green sub-pixel (G) is shown as a dashed-dot line, and for the blue sub-pixel (B) The current density-voltage curve for is shown as a dotted line.

When compared with the current density-voltage curve of the conventional organic light emitting display shown in FIG. 2 , the current density-voltage curve of the organic light emitting display device 100 according to another exemplary embodiment shown in FIG. 8 The red organic light emitting stack 150R disposed in the red sub-pixel R in R has substantially the same turn-on voltage as the green organic light emitting stack 150G and the blue organic light emitting stack 150B at a low current density.

In other words, the organic light emitting display device 100 according to another embodiment of the present invention includes a hole transport layer 151R including a second hole transport layer region 156R and a fourth hole transport layer region 158R including a P-type dopant. ), and the LUMO level of the host of the red organic light emitting layer 152R is different from the LUMO level of the hole transport layer 151R and the LUMO level of the electron blocking layer 154R by 0.6 to 0.9 eV. Since the LUMO level of the material and the host is determined, the mobility of electrons moving from the red organic emission layer 152R to the anode 140 may be reduced.

That is, the organic light emitting display device 100 according to another embodiment of the present invention is applied with the hole transport layer 151R including the second hole transport layer region 156R and the fourth hole transport layer region 158R including a P-type dopant. ), the Reddish phenomenon due to leakage current occurring in a conventional organic light emitting display device and the Reddish phenomenon that may occur when driving at a low current density can be suppressed.

9A to 9D are diagrams illustrating comparative evaluation results of lifespan characteristics of a comparative example and an organic light emitting display device according to another exemplary embodiment of the present invention.

More specifically, FIGS. 9A to 9D show a comparative example including a single-layer hole transport layer and an organic light emitting display device 100 including a hole transport layer composed of multiple layers according to another embodiment of the present invention, respectively. , the results of comparative evaluation of life characteristics during red, green, and blue light emission are shown.

First, referring to FIG. 9A , life characteristics from 100% luminance to 95% luminance of organic light emitting display devices according to comparative examples and embodiments in white light emission are compared, and organic light emitting display according to another embodiment of the present invention is compared. The life of the device showed an improved result to about 100% level when compared to the comparative example.

9B, 9C, and 9D , life characteristics from 100% luminance to 95% luminance of the organic light emitting display device according to Comparative Examples and Examples when emitting red, green, and blue light are compared, In the organic light emitting diode display according to another exemplary embodiment of the present invention, lifespans were improved by 67%, 78%, and 140%, respectively, compared to the comparative example.

That is, in the case of the organic light emitting diode display according to another embodiment of the present invention, the hole transport layer including the second hole transport layer region and the fourth hole transport layer region including the P-type dopant is applied, so that holes in the organic light emitting layer Injection characteristics may be further improved, and lifespan of the organic light emitting display may be improved by about 1.5 times compared to an organic light emitting display having a single hole transport layer.

In addition, in the case of an organic light emitting display device according to another embodiment of the present invention including a hole transport layer made of a composite layer including a p-type dopant, the driving voltage and light emitting efficiency were equivalent to those of the comparative example, and the organic light emitting display It is possible to obtain the effect of improving the lifetime while satisfying the electro-optical characteristics required for the device.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and may be variously modified and implemented without departing from the technical spirit of the present invention. . Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be construed according to the claims below, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

110: substrate
120: thin film transistor
121: gate electrode
122: active layer
123: source electrode
124: drain electrode
131: buffer layer
132: gate insulating layer
133: interlayer insulating layer
134: over coating layer
135: bank
140: anode
141: transparent conductive layer
142: reflective layer
150: organic light emitting stack
150R: red organic light emitting stack
150G: green organic light emitting stack
150B: blue organic light emitting stack
151R: hole transport layer of red organic light emitting stack
152R: red organic light emitting layer of the red organic light emitting stack
153R: electron transport layer of red organic light emitting stack
154R: electron blocking layer of the red organic light emitting stack
155R: first hole transport layer region of the red organic light emitting stack
156R: second hole transport layer region of the red organic light emitting stack
157R: third hole transport layer region of red organic light emitting stack
158R: 4th hole transport layer region of the red organic light emitting stack
160: cathode
100: organic light emitting display device
R: red sub-pixel
G: green sub-pixel
B: blue sub-pixel

Claims (20)

An organic light emitting display device including a plurality of sub-pixels including a red sub-pixel, a green sub-pixel, and a blue sub-pixel, comprising:
One sub-pixel of the plurality of sub-pixels,
An active layer, a gate electrode disposed on the active layer, a gate insulating layer disposed to insulate the gate electrode and the active layer, an interlayer insulating layer disposed on the gate electrode, and the active layer and the active layer on the interlayer insulating layer. thin film transistors each including a source electrode and a drain electrode in contact with each other;
an overcoating layer disposed on the thin film transistor and including a contact hole exposing the source electrode of the thin film transistor;
an anode including a reflective layer electrically connected to the exposed source electrode of the thin film transistor through a contact hole of the overcoating layer and a transparent conductive layer disposed on the reflective layer and electrically connected to the source electrode through the reflective layer;
a bank disposed to distinguish between adjacent sub-pixels among the plurality of sub-pixels and overlapping an end of the anode and the contact hole of the overcoating layer on the anode;
an organic light emitting stack disposed between the banks on the anode; and
a transparent cathode disposed on the organic light emitting stack;
The organic light emitting stack includes a red organic light emitting stack disposed in the red sub-pixel;
The red organic light emitting stack,
a red organic light emitting layer comprising a host and a dopant;
a hole transport layer disposed under the red organic light emitting layer; and
An electron blocking layer disposed between the red organic light emitting layer and the hole transport layer;
The difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the hole transport layer is 0.6 to 0.9 eV,
The organic light emitting display device, characterized in that the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron blocking layer is 0.6 to 0.9 eV.
delete delete According to claim 1,
The organic light emitting display device, characterized in that the difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the hole transport layer is determined based on electron mobility in a low gradation and a driving voltage for driving the organic light emitting layer.
According to claim 1,
The host of the red organic light emitting layer is characterized in that made of a beryllium complex (beryllium complex), organic light emitting display device.
According to claim 1,
The hole transport layer includes first to third hole transport layer regions;
The third hole transport layer region is disposed under the electron blocking layer,
The organic light emitting display device of claim 1 , wherein the second hole transport layer region includes a p-type dopant and is disposed between the first hole transport layer region and the third hole transport layer region.
According to claim 6,
The organic light emitting display device, characterized in that the P-type dopant is F4-TCNQ (tetrafluoro-tetracyanoquinodimethane).
According to claim 6,
A thickness of the second hole transport layer region is 10% or less of a total thickness of the hole transport layer.
According to claim 6,
and a fourth hole transport layer region including the P-type dopant under the first hole transport layer region.
According to claim 9,
the fourth hole transport layer region is disposed between the anode and the first hole transport layer;
The organic light emitting display device of claim 1 , wherein a thickness of the fourth hole transport layer region is 10% or less of a total thickness of the hole transport layer.
a substrate including a red sub-pixel, a green sub-pixel, and a blue sub-pixel;
An active layer disposed on the substrate, a gate electrode disposed on the active layer, a gate insulating layer disposed to insulate the gate electrode and the active layer, an interlayer insulating layer disposed on the gate electrode, and an interlayer insulating layer disposed on the gate electrode. a thin film transistor including a source electrode and a drain electrode respectively in contact with the active layer;
an overcoating layer disposed on the thin film transistor and including a contact hole exposing the source electrode of the thin film transistor;
an anode including a reflective layer electrically connected to the exposed source electrode of the thin film transistor through a contact hole of the overcoating layer and a transparent conductive layer disposed on the reflective layer and electrically connected to the source electrode through the reflective layer;
a bank disposed to distinguish between adjacent sub-pixels among the plurality of sub-pixels and overlapping an end of the anode and the contact hole of the overcoating layer on the anode;
an organic light emitting stack disposed between the banks on the anode; and
a transparent cathode disposed over the organic light emitting stack;
The organic light emitting stack includes a red organic light emitting stack disposed in the red sub-pixel;
The red organic light emitting stack,
a red organic light emitting layer comprising a host and a dopant;
a hole transport layer disposed under the red organic light emitting layer; and
An electron blocking layer disposed between the red organic light emitting layer and the hole transport layer;
The difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the hole transport layer is 0.6 to 0.9 eV,
A difference between the LUMO level of the host of the red organic light emitting layer and the LUMO level of the electron blocking layer is 0.6 to 0.9 eV, the organic light emitting display device.
According to claim 11,
The organic light emitting stack may further include a green organic light emitting stack disposed on the green sub-pixel and including a green organic light emitting layer and a blue organic light emitting stack disposed on the blue sub pixel and including a blue organic light emitting layer. light-emitting display device.
delete According to claim 12,
The LUMO level of the host of the red organic light emitting layer is 3.04 eV,
The LUMO level of the host of the green organic light emitting layer is 2.9 eV,
The organic light emitting display device, characterized in that the LUMO level of the host of the blue organic light emitting layer is 3.0 eV.
delete delete According to claim 11,
The organic light emitting display device, characterized in that the reflective layer is silver (Ag) or an alloy containing silver.
According to claim 11,
An organic light emitting display device, characterized in that a difference in vacuum level between the reflective layer and the transparent conductive layer is 0.2 eV or more.
According to claim 11,
The host of the red organic light emitting layer is characterized in that made of a beryllium complex (beryllium complex), organic light emitting display device. According to claim 11,
The hole transport layer includes first to fourth hole transport layer regions;
The third hole transport layer region is disposed under the electron blocking layer,
the second hole transport layer region includes a p-type dopant and is disposed between the first hole transport layer region and the third hole transport layer region;
the fourth hole transport layer region includes a p-type dopant and is disposed between the anode and the first hole transport layer;
and a thickness of the second hole transport layer region and a thickness of the fourth hole transport layer region are each less than 10% of a total thickness of the hole transport layer.

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