KR20160064320A - Organic light emitting display - Google Patents

Abstract

An organic light emitting display device according to an embodiment of the present invention includes a first sub pixel, a second sub pixel and a third sub pixel. The organic light emitting display device includes: a first electrode including a reflection layer and a transparent conductive layer; a hole injection layer which is arranged on the first electrode, and includes a P-type dopant and a host; a hole transport layer arranged on the hole injection layer; an organic light emitting layer arranged on the hole transport layer; and a second electrode arranged on the organic light emitting layer. An LUMO level of the hole injection layer is equal to or greater than a work function of each of the reflection layer and the transparent conduction layer. Thus, the organic light emitting display device of the present invention can suppress a reddish phenomenon which can occur in a low gray scale driving or under a state where a voltage is not applied.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light emitting display, and more particularly, to an organic light emitting display capable of minimizing a red light phenomenon that may occur during a low gray scale driving.

The organic light emitting diode (OLED) is a self-emissive type display device, and unlike a liquid crystal display (LCD), a separate light source is not required, so that it can be manufactured in a light and thin shape. Further, the organic light emitting display device is not only advantageous from the viewpoint of power consumption by low voltage driving, but also excellent in color implementation, response speed, viewing angle, and contrast ratio (CR), and is being studied as a next generation display.

The organic light emitting display generally comprises a red organic light emitting layer for emitting red light, a green organic light emitting layer for emitting green light, and a blue organic light emitting layer for emitting blue light. In each of the red organic light emitting layer, the green organic light emitting layer and the blue organic light emitting layer, holes and electrons supplied through the electrodes are coupled to each other to emit light. Generally, a hole injection layer and a hole transport layer are disposed between the red organic emission layer, the green organic emission layer, and the blue organic emission layer and the anode in order to smoothly move the holes.

In recent years, a technique of adding a P-type dopant to a hole injection layer disposed between an anode and an organic light emitting layer has been introduced in order to further accelerate the movement of holes and lower the driving voltage to improve the light emitting efficiency of the device. When the P type dopant is added, holes can be more smoothly supplied to the organic light emitting layers, thereby improving the lifetime and efficiency of the OLED display.

However, when a hole injection layer containing a P-type dopant is disposed, the anode and the hole injection layer including the P-type dopant directly contact each other. At this time, when the organic light emitting display device is driven to display an image at a low gray level, a reddish phenomenon occurs in which red color is expressed. Specifically, when the red sub-pixel, the green sub-pixel and the blue sub-pixel are driven at the same low current density in order to realize a low-gradation white color, not only the red sub-pixel starts emitting light first, .

Also, even when the voltage is not applied, the red sub-pixel operates due to the residual current remaining in the thin film transistor or the driving unit in the organic light emitting display device, resulting in a redis phenomenon.

As a result, there arises a problem that optical compensation and CR defect are caused and the image quality reliability of the organic light emitting display is deteriorated.

The inventors of the present invention have found that the redis phenomenon occurring in a state in which no voltage is applied or driven at a low gray level as described above is related to the LUMO level of the hole injection layer containing the P type dopant. The inventors of the present invention invented an organic light emitting display device including a hole injection layer having a new LUMO level so as to minimize a redis phenomenon.

That is, an object of the present invention is to provide an organic light emitting display device capable of suppressing a red light phenomenon that may occur during low gray level driving of an organic light emitting display device.

Another object of the present invention is to provide an organic light emitting diode display capable of minimizing the occurrence of a redis phenomenon due to a residual current in a state in which no voltage is applied.

The problems of the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

An OLED display according to an embodiment of the present invention includes a first sub-pixel, a second sub-pixel, and a third sub-pixel, the first electrode including a reflective layer and a transparent conductive layer; A hole injection layer disposed on the first electrode and including a P-type dopant and a host; A hole transport layer disposed on the hole injection layer; An organic light emitting layer disposed on the hole transporting layer; And a second electrode disposed on the organic light emitting layer, wherein a LUMO level of the hole injection layer is equal to or greater than a work function of each of the reflective layer and the transparent conductive layer.

 In the organic light emitting diode display according to an embodiment of the present invention, a redis phenomenon that may occur in driving a low gray level at a low current density can be suppressed.

According to another aspect of the present invention, the work function of the reflective layer may be equal to or less than a work function of the transparent conductive layer.

According to another feature of the present invention, the work function of the reflective layer may be 4.5 eV to 5.0 eV, or may be an alloy containing silver (Ag) or silver.

According to another aspect of the present invention, the transparent conductive layer includes at least one of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, And an oxide (ZnO: Zinc Oxide).

According to another feature of the present invention, the work function of the transparent conductive layer may be from 5.2 eV to 5.6 eV.

According to another aspect of the present invention, the LUMO level of the hole injection layer may be lower than the HOMO level of the hole transport layer.

According to another aspect of the present invention, the LUMO level of the hole injection layer may be 5.4 eV to 5.8 eV.

According to another aspect of the present invention, the LUMO level of the hole injection layer can be controlled by changing the amount of the P-type dopant added to the hole injection layer.

According to another aspect of the present invention, the hole injection layer may include 1.0 wt% to 4.0 wt% of the P-type dopant.

According to another aspect of the present invention, the P-type dopant may include at least one selected from the group consisting of F4-TCNQ, 1,4-TCAQ, 6,3-TCPQ, TCAQ, TCNTHPQ and TCNPQ.

According to another feature of the present invention, the host is selected from the group consisting of N, N'-di (naphthalen-1-yl) -N, N-diphenyl-benzidine (NPB) (TPD), N, N ', N'-tetranaphthyl-benzidine (TNB), di (p- tolyl) aminophenyl] -1,3,4- (TPA), N, N'-bis (phenanthrene-9-yl) -N, N'-diphenyl-benzidine (PPD) and BFA-1T .

According to another aspect of the present invention, the hole injection layer may have a thickness ranging from 10 Å to 100 Å.

According to another aspect of the present invention, the hole transport layer may be composed of the same host as the host of the hole injection layer.

According to another aspect of the present invention, an electron transport layer may be further disposed between the organic emission layer and the second electrode.

According to another aspect of the present invention, in the first sub-pixel, the second sub-pixel, and the third sub-pixel, light of different colors is emitted, and any one of red light, green light, Can be emitted.

The details of other embodiments are included in the detailed description and drawings.

In the present invention, when the organic light emitting display is driven at a low current density for low gray scale driving, the red sub-pixel is driven before the blue sub-pixel and the green sub-pixel are driven, Can be minimized.

In addition, in the present invention, when a voltage is not applied to the organic light emitting display, a residual phenomenon that may be undesirably caused by a residual current can be minimized.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the specification.

1 is a schematic cross-sectional view for explaining a top emission type OLED display according to an embodiment of the present invention.
FIG. 2 is a diagram showing energy bands for a first electrode, a pumping layer including a P-type dopant, and a hole transporting layer in a conventional organic light emitting diode display.
FIG. 3 is a diagram showing a current density-voltage curve (JV curve) for a red sub-pixel, a green sub-pixel and a blue sub-pixel in a conventional organic light emitting display.
4 is a diagram illustrating energy bands for the first electrode, the hole injection layer, and the hole transport layer in the organic light emitting diode display according to the embodiment of the present invention.
FIG. 5 is a graph showing current density-voltage curves (JV curves) for red sub-pixels, green sub-pixels and blue sub-pixels in an organic light emitting display according to an embodiment of the present invention.
6 is a photographed surface photograph of the organic light emitting display according to the embodiment of the present invention when driven at 0 gradation.
7 is a photographed surface photograph of the organic light emitting diode display according to the comparative example of the present invention driven at 0 gradation.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, and the like disclosed in the drawings for describing the embodiments of the present invention are illustrative, and thus the present invention is not limited thereto. Like reference numerals refer to like elements throughout the specification. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Where the terms "comprises", "having", "done", and the like are used in this specification, other portions may be added unless "only" is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

In interpreting the constituent elements, it is construed to include the error range even if there is no separate description.

In the case of a description of the positional relationship, for example, if the positional relationship between two parts is described as 'on', 'on top', 'under', and 'next to' Or " direct " is not used, one or more other portions may be located between the two portions.

It is to be understood that an element or layer is referred to as being another element or layer " on ", including both intervening layers or other elements directly on or in between.

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

Like reference numerals refer to like elements throughout the specification.

The sizes and thicknesses of the individual components shown in the figures are shown for convenience of explanation and the present invention is not necessarily limited to the size and thickness of the components shown.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other, partially or wholly, technically various interlocking and driving, and that the embodiments may be practiced independently of each other, It is possible.

In this specification, the organic light emitting display is driven at a low gray level, which means that the organic light emitting display is driven with a current density for displaying white, red, green or blue with a low gray level. Further, the low gradation can mean, for example, 15 gradations when the gradation is represented by a value from 0 to 255. [

Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view for explaining a top emission type OLED display according to an embodiment of the present invention.

1, an organic light emitting diode display 100 according to an embodiment of the present invention includes a substrate 110, a first electrode 120, a hole injection layer 130, a hole transport layer 140, The second organic light emitting layer 160b, the third organic light emitting layer 160c, the electron transporting layer 170, the second electrode 180, and the second organic light emitting layer 160a, the second auxiliary transport layer 150a, the second auxiliary transport layer 150b, And an organic material layer 190.

The substrate 110 is formed of an insulating material for supporting various components of the OLED display 100. At this time, the substrate 110 may be made of a material having transparency and flexibility.

As shown in FIG. 1, the substrate 110 includes a first sub-pixel R, a second sub-pixel G, and a third sub-pixel B as regions for displaying one color. In the first sub-pixel R, the second sub-pixel G and the third sub-pixel B, light of different colors may be emitted. For example, red light may be emitted in the first sub-pixel R, green light may be emitted in the second sub-pixel G, and blue light may be emitted in the third sub-pixel B.

A first electrode (120) is disposed on a substrate (110). The first electrode 120 applies a voltage to each of the first organic light emitting layer 160a, the second organic light emitting layer 160b, and the third organic light emitting layer 160c. At this time, the first electrode 120 is disposed in each of the first sub-pixel R, the second sub-pixel G, and the third sub-pixel B, respectively. In other words, the first sub-pixel R, the second sub-pixel G, and the third sub-pixel B are separately arranged.

The first electrode 120 includes a reflective layer 121 and a transparent conductive layer 122, and may serve as an anode.

The reflective layer 121 reflects light emitted from the organic light emitting layer 160 to the top of the organic light emitting display device 100 and is formed of a conductive compound having a high reflectivity. The reflective layer 121 may be silver (Ag), palladium (Pd), copper (Cu), aluminum (Al), nickel (Ni) / Cu alloy).

It is preferable that the work function of the reflective layer 121 is equal to or less than the work function of the transparent conductive layer 122. [ Here, a work function is the minimum energy required to pull out one of the electrons in a material. Generally, in an organic light emitting diode display, a material having a small work function is used as a cathode and a material having a large work function is used as an anode.

The work function of the reflective layer 121 may be between 4.5 eV and 5.0 eV, and more preferably between 4.7 eV and 4.9 eV. For example, the work function of the reflective layer 121 may be about 4.8 eV.

On the other hand, a transparent conductive layer 122 is disposed on the reflective layer 121. The transparent conductive layer 122 is for supplying holes and is made of a conductive material having a larger work function than the second electrode 180. The transparent conductive layer 122 is made of a transparent conductive oxide (TCO), and includes, but not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), indium zinc oxide And may include at least one selected from the group consisting of indium oxide, tin oxide, and zinc oxide (ZnO).

At this time, the work function of the transparent conductive layer 122 may be from 5.2 eV to 5.6 eV, and more preferably from 5.2 eV to 5.4 eV. For example, in the present invention, the work function of the transparent conductive layer 122 may be about 5.4 eV. When the work function of the transparent conductive layer 122 satisfies the above range, since it has a sufficient work function difference with the second electrode, more smooth hole injection is possible.

A hole injection layer 130 including a P-type dopant and a host is disposed on the first electrode 120. The hole injection layer 130 serves to smoothly inject holes into the organic light emitting layer 160.

When the P type dopant is doped as described above, the mobility of the hole injection layer 130 is greatly improved. Therefore, the organic light emitting layer 160 ) Can be performed more smoothly.

The OLED display 100 according to an exemplary embodiment of the present invention is configured such that the LUMO level of the hole injection layer 130 is lower than the work function of each of the reflective layer 121 and the transparent conductive layer 122 constituting the first electrode 120, Or more.

2 is a diagram illustrating an energy band diagram of a conventional organic light emitting display device. FIG. 2 shows the relationship between the work function of the first electrode including ITO as a transparent conductive layer and the hole injection layer (PHIL) including the P-type dopant and the hole transport layer (HTL) LUMO (Lowest Unoccupied Molecular Orbitals) and HOMO (Highest Occupied Molecular Orbitals) levels.

FIG. 3 is a diagram showing a current density-voltage curve (J-V curve) for a red sub-pixel, a green sub-pixel and a blue sub-pixel in a conventional OLED display. In FIG. 3, the current density-voltage curve for the red sub-pixel is shown by the solid line, the current density-voltage curve for the green sub-pixel is shown by the dotted line, and the current density-voltage curve for the blue sub- Respectively.

2, which illustrates an energy band diagram of a conventional organic light emitting display, when the first electrode is composed of a reflective layer (Ag) and a transparent conductive layer (ITO), between silver (Ag) and a transparent conductive oxide It can be seen that there is a difference in work function and the LUMO level of the hole injection layer including the P type dopant is located between the work function of the reflective layer (Ag) of the first electrode and the ITO.

In general, in order for an organic light emitting display to display a color, holes are required to be injected into the organic light emitting layer through the transparent conductive layer by applying a specific voltage or higher to make the voltage built in the transparent conductive layer.

However, when the LUMO level of the hole injection layer including the P-type dopant is located between the reflective layer (Ag) of the first electrode and the work function of the transparent conductive layer (ITO) as shown in FIG. 2, A phenomenon occurs in which the voltage is preferentially built in the reflective layer (Ag) without being built in the layer (ITO).

That is, when the LUMO level of the hole injection layer including the P-type dopant is located between the work function of the reflective layer (Ag) and the transparent conductive layer (ITO) of the first electrode, the work function of the reflective layer and the energy barrier The holes are injected from the reflective layer to the organic light emitting layer through the LUMO level of the hole injection layer including the P type dopant. As a result, the voltage is built-in to the reflective layer Ag before the voltage is built-in to the transparent conductive layer, and the organic light emitting display device malfunctions.

Than looking together to Figure 3 for a detailed description, as a result, the red sub-pixel has a low current density, i.e., a lower turns at a current density of about 0.01 to 1 mA / cm ² than the green sub-pixel, and blue sub-pixels-on voltage (Turn-ON voltage).

In other words, when the LUMO level of the hole injection layer including the P-type dopant is located between the work function of the reflective layer (Ag) and the transparent conductive layer (ITO) of the first electrode, And a redis phenomenon occurs in which the red sub-pixel emits light earlier than the green sub-pixel and the blue sub-pixel.

Also, as in the above-described case, even when no voltage is applied, a voltage is first built in the reflective layer due to a minute residual current present in the OLED display, resulting in a redis phenomenon.

However, in the OLED display 100 according to an embodiment of the present invention, the LUMO level of the hole injection layer 130 including the P-type dopant and the host is lower than the LUMO level of the reflective layer 121 constituting the first electrode 120, And more than the work function of each transparent conductive layer 122. When the LUMO level of the hole injection layer 130 is adjusted as in the present invention, the work function of the reflection layer 121 and the energy barrier of the hole injection layer 130 are sufficiently large, the voltage is not built in the reflection layer 121, Since the voltage is normally built in the transparent conductive layer 122, it is possible to suppress the malfunction that the holes are first injected through the reflective layer 121.

In other words, in the organic light emitting diode display 100 according to an embodiment of the present invention, holes are injected from the reflective layer 121 to form the organic light emitting layer 160 through the LUMO level of the hole injection layer 130 including the P- Can be minimized.

The LUMO level of the hole injection layer 130 is preferably equal to or lower than the HOMO level of the hole transport layer 140. [ This is because, when the LUMO level of the hole injection layer 130 is larger than the HOMO level of the hole transport layer 140, the mobility of the holes is greatly lowered and the hole transport can be prevented.

The LUMO level of the hole injection layer 130 is preferably 5.4 eV to 5.8 eV, and more preferably 5.4 eV to 5.6 eV. In general, since the work function of the conductive compound constituting the transparent conductive layer 122 is 5.4 eV or less, when the above range is satisfied, the drawback can be remarkably reduced and the hole transporting ability is also excellent.

The LUMO level of the hole injection layer 130 can be adjusted by changing the amount of the P-type dopant added to the hole injection layer 130.

At this time, the hole injection layer 130 preferably includes 1.0 to 4.0% by weight of the P-type dopant, more preferably 1.0 to 2.0% by weight. When the content of the P-type dopant is less than the above range, the drive voltage of each sub-pixel increases, and the LUMO level of the hole injection layer 130 is lower than the work function of each of the reflection layer 121 and the transparent conductive layer 122 , And if it exceeds the above range, the efficiency of the display device may be lowered, or a residual image may be generated.

A method of controlling the P-type dopant content of the hole injection layer 130 may include, but is not limited to, a method of forming a hole injection layer 130 including a P-type dopant and a host on the first electrode 120 using a scanning method A method of vapor-depositing can be used.

More specifically, in a scanning apparatus having a guide rail, a first evaporation source, and a second evaporation source, the mixing ratio of the P-type dopant and the host can be adjusted by adjusting the release rate of the P-type dopant and the host. In general, a host is injected into a first evaporation source located at the front of the scan direction and a second evaporation source located at the rear, and then the P-type dopant and the host are discharged according to the progress direction, Layer 130 is formed.

The P-type dopant constituting the hole injection layer 130 may include, but is not limited to, tetrafluoro-tetracyanoquinodimethane (F ₄ -TCNQ), 1,4-TCAQ, 6,3-TCPQ, TCAQ, TCNTHPQ, and TCNPQ.

[Chemical Formula 1]

The host constituting the hole injection layer 130 is preferably a heteroaromatic ring compound or an aromatic amine compound although not limited thereto. More specifically, N, N'-di (naphthalen-1-yl) N, N'-bis (3-methylphenyl) -1,1-biphenyl-4,4'-diamine (TPD), N, N'- N, N ', N'-tetranaphthyl-benzidine (TNB), di (p- tolyl) aminophenyl] cyclohexane (TPAC) '-Diphenyl-benzidine (PPD) and BFA-1T.

In addition, the thickness of the hole injection layer 130 is preferably 10 to 100 angstroms, more preferably 10 to 60 angstroms. If the thickness of the hole injection layer 130 is less than 10 angstroms, it is difficult to expect reduction of the redis phenomenon. If the thickness of the hole injection layer 130 exceeds 100 angstroms, the lifetime of the organic light emitting display device may be shortened and the driving voltage may increase significantly.

Next, a hole transporting layer 140 is disposed on the hole injection layer 130. The hole transport layer 140 receives holes from the hole injection layer 130 and transports the holes to the first organic emission layer 160a, the second organic emission layer 160b, and the third organic emission layer 160c.

The hole transport layer 140 includes a host and is preferably a heteroaromatic ring compound or an aromatic amine compound such as a host used in the hole injection layer 130. More specifically, N, N'-di (naphthalene- (NPB), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1-biphenyl-4,4'-diamine TPD), N, N ', N'-tetranaphthylbenzidine (TNB), di (p- tolyl) aminophenyl] cyclohexane (TPAC) N, N'-diphenyl-benzidine (PPD) and BFA-1T. At this time, the hole transport layer 140 and the hole injection layer 130 may be formed of the same host material. In this case, the hole injection layer 130 and the hole transport layer 140 may be disposed together in a continuous process in one process equipment.

On the other hand, a sub-transport layer may be disposed on the hole transport layer 140 to control the distance between the first electrode 120 and the organic light-emitting layer for each sub-pixel. More specifically, a first sub-transporting layer 150a is disposed between the hole transport layer 140 of the first sub-pixel R and the first organic emission layer 160a, and a hole transport layer 140 of the second sub- And the second organic light emitting layer 160b may be disposed between the second organic light emitting layer 160b and the second organic light emitting layer 160b. The first auxiliary transport layer 150a and the second auxiliary transport layer 150b each function to transfer holes to the first organic emission layer 160a and the second organic emission layer 160b smoothly.

The thickness of each of the first and second auxiliary transport layers 150a and 150b may form a microcavity optical distance. Specifically, the thicknesses of the first auxiliary transport layer 150a and the second auxiliary transport layer 150b are determined such that the organic material layers disposed between the first electrode 120 and the second electrode 180 form a micro-cavity structure .

Since the first sub-pixel R and the second sub-pixel G emit light of different colors, the thicknesses of the first sub-transporting layer 150a and the second sub-transporting layer 150b may be different from each other. It is assumed in FIG. 1 that the first organic light emitting layer 160a is a red organic light emitting layer and the second organic light emitting layer 160b is a green organic light emitting layer and the thickness of the first auxiliary transport layer 150a is set to a thickness of the second auxiliary transport layer 150b Respectively.

The first auxiliary transport layer 150a and the second auxiliary transport layer 150b are preferably heteroaromatic cyclic compounds or aromatic amine compounds such as the host used in the hole injection layer 130 and the hole transport layer 140, (NPB), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1 (TPA), N, N ', N'-tetranaphthyl-benzidine (TNB), di (p- tolyl) aminophenyl] cyclohexane -Bis (phenanthrene-9-yl) -N, N'-diphenyl-benzidine (PPD) and BFA-1T.

The organic light emitting layer 160 may be disposed directly on the hole transporting layer 140 or on the first and second auxiliary transporting layers 150a and 150b. More specifically, as shown in FIG. 1, a first organic light emitting layer 160a is disposed on the first hole transport layer 150a in the first sub-pixel R and a second organic light emitting layer 160b is disposed on the second sub- The third organic light emitting layer 160b may be disposed on the hole transport layer 140 in the third sub pixel B.

The organic light emitting layer 160 is a layer in which electrons and holes are combined to emit light, and is composed of a host and a dopant. The host of the organic light emitting layer 160 serves to transfer energy to the dopant for improving the luminous efficiency and the color purity. The dopant is a dye organic material that participates in a small amount in the host. The host may be different depending on the type of the host and the dopant used Thereby emitting color light.

The first organic light emitting layer 160a, the second organic light emitting layer 160b, and the third organic light emitting layer 160c of FIG. 1 emit light of different colors. The first organic light emitting layer 160a and the second organic light emitting layer 160b may emit red light or green light and the third organic light emitting layer 160c may emit blue light. Specifically, red light may be emitted in the first organic light emitting layer 160a, green light may be emitted in the second organic light emitting layer 160b, and blue light may be emitted in the third organic light emitting layer 160c.

Although not shown in FIG. 1, an organic light-emitting layer capable of emitting blue light can be additionally provided on the organic light-emitting layer capable of emitting any one of red light and green light in the first sub-pixel and the second sub- .

An electron transport layer 170 is disposed on the first organic light emitting layer 160a, the second organic light emitting layer 160b, and the third organic light emitting layer 160c. The electron transport layer 170 serves to smooth the movement of electrons to the first organic emission layer 160a, the second organic emission layer 160b, and the third organic emission layer 160c. The electron transport layer 170 may include any material selected from the group consisting of Alq3, PBD, TAZ, spiro-PBD, BAlq, lithium quinolate, BMB-3T, PF-6P, TPBI, COT, Or more.

A second electrode 180 is disposed on the electron transport layer 170. The second electrode 180 is made of a conductive material having a low work function since it needs to supply electrons. For example, although not limited thereto, the second electrode 180 may be made of an alloy of magnesium (Mg) and silver (Ag). The work function of the second electrode 180 may be about 4.1 eV. The second electrode 180 is not usually patterned, but is formed as a single layer. That is, the second electrode 180 is formed as a single layer on the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B, respectively. Since the organic light emitting diode display 100 according to an embodiment of the present invention is a top emission organic light emitting diode display 100, the second electrode 180 is formed as a cathode with a very thin thickness and is substantially transparent .

The organic layer 190 is disposed on the second electrode 180. The organic material layer 190 may serve to flatten the stepped portion of the second electrode 180 and compensate for the foreign material. The organic material layer 190 may be formed of an acrylic resin or an epoxy resin, but is not limited thereto.

Though not shown in FIG. 1, a thin film transistor connected to the first electrode 120 may be further disposed on the substrate 110.

In order to examine the effects of the present invention, organic light emitting display devices of Examples and Comparative Examples in which the LUMO level of the hole injection layer was changed were manufactured. 1, the first organic light emitting layer is a red organic light emitting layer, the second organic light emitting layer is a green organic light emitting layer, and the second organic light emitting layer is a green organic light emitting layer. Emitting layer, and the third organic light-emitting layer was composed of a blue organic light-emitting layer.

Specifically, a hole injecting layer doped with 1.5 wt% of F4-TCNQ as a P-type dopant and a hole transporting layer containing the same host as the host used in the hole injecting layer are provided between the first electrode and the organic light emitting layer An example was prepared. At this time, the organic light emitting display of the embodiment has a structure composed of Ag-ITO / hole injection layer / hole transporting layer / organic light emitting layer / electron transporting layer / cathode (Ag-Mg).

On the other hand, an organic light emitting display was manufactured in the same manner as in Example except that a hole injection layer doped with 0.5 wt% of F4-TCNQ as a P-type dopant was included in the comparative example.

4 and 5 show experimental data for the organic light emitting display of the embodiment. 4 is a diagram illustrating an energy band diagram for an OLED display 100 according to an exemplary embodiment of the present invention. Referring to FIG. 4 illustrates the work function for the first electrode 120 including the reflective layer 121 and the transparent conductive layer 122 and the energy band for the hole injection layer 130 and the hole transport layer 140 including the P- The upper side of the rectangle means the LUMO level of each layer and the lower side means the HOMO level of each layer. 4, the LUMO level of the hole injection layer 130 including the P-type dopant and the host is 5.4 eV, which is greater than the work function of the reflective layer 121 and the transparent conductive layer 122, respectively. When the LUMO level of the electron injection layer 130 including the P-type dopant is equal to or greater than the work function of each of the reflective layer 121 and the transparent conductive layer 122, a phenomenon in which holes are injected from the reflective layer 121 at low gradation .

The effect of the OLED display 100 having the energy band diagram shown in FIG. 4 can be seen from FIG.

5 is a graph showing a current density-voltage curve (JV curve) for a red sub-pixel R, a green sub-pixel G and a blue sub-pixel B in the OLED display 100 according to an embodiment of the present invention. Fig. In FIG. 5, the current density-voltage curve for the red sub-pixel R is shown by the solid line, the current density-voltage curve for the green sub-pixel G is shown by the dotted line, The density-voltage curve is shown by the one-dot chain line.

In contrast to the current density-voltage curve for the conventional OLED display shown in FIG. 3, the current density-voltage curve for the OLED display 100 according to the embodiment of the present invention shown in FIG. It can be seen that the red sub-pixel R exhibits substantially the same turn-on voltage as the green sub-pixel G and the blue sub-pixel B at the low current density. Therefore, the redis phenomenon occurring when the red sub-pixel R operates earlier than the green sub-pixel G and the blue sub-pixel B at the low current density can be suppressed.

More specifically, the color coordinate values and the luminance values of the organic light emitting diode display 100 manufactured by the examples and the comparative examples were measured at the 0 gradation level using a color meter (CA-310). The results are shown in Table 1 below.

division Concentration (% by weight) of P-type dopant The LUMO level (eV) Color coordinates Luminance
(nit) Visual observation Example 1.5 5.4 Not measurable 0.0010 6 Comparative Example 0.5 5.1 0.6991, 0.3009 0.0030 7

As can be seen from Table 1, it was found that the LUMO level of the hole injection layer can be controlled according to the concentration of the P-type dopant. In addition, in the case of the embodiment where the LUMO level of the hole injection layer is higher than the work function of silver (Ag) and ITO, it can be confirmed that the black color can be realized without the redis phenomenon.

6 and 7 in which the organic light emitting display device of the embodiment and the comparative example driven at the 0 gradation level are taken as an example, unlike the comparative example in which the red color is shown in FIG. 7, Of the total population.

Although the embodiments of the present invention have been described in detail with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those embodiments and various changes and modifications may be made without departing from the scope of the present invention. . Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

110: substrate
120: first electrode
121: reflective layer
122: transparent conductive layer
130: Hole injection layer
140: hole transport layer
150a: first auxiliary transport layer
150b: second auxiliary transport layer
160a: a first organic light emitting layer
160b: a second organic light emitting layer
160c: a third organic light emitting layer
170: electron transport layer
180: second electrode
190: organic layer
R: red sub-pixel
G: green sub-pixel
B: blue sub-pixel

Claims (16)

A first sub-pixel, a second sub-pixel, and a third sub-pixel,
A first electrode including a reflective layer and a transparent conductive layer;
A hole injection layer disposed on the first electrode and including a P-type dopant and a host;
A hole transport layer disposed on the hole injection layer;
An organic light emitting layer disposed on the hole transporting layer; And
And a second electrode disposed on the organic light emitting layer,
Wherein the LUMO level of the hole injection layer is equal to or higher than a work function of each of the reflective layer and the transparent conductive layer. The method according to claim 1,
Wherein a work function of the reflective layer is equal to or less than a work function of the transparent conductive layer. The method according to claim 1,
Wherein the work function of the reflective layer is 4.5 eV to 5.0 eV. The method according to claim 1,
Wherein the reflective layer is an alloy including silver (Ag) or silver. The method according to claim 1,
The transparent conductive layer may be formed of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, and zinc oxide (ZnO) Wherein the organic electroluminescent display device comprises at least one selected from the group consisting of organic electroluminescent (EL) display devices. The method according to claim 1,
And the work function of the transparent conductive layer is from 5.2 eV to 5.6 eV. The method according to claim 1,
And the LUMO level of the hole injection layer is lower than the HOMO level of the hole transport layer. The method according to claim 1,
And the LUMO level of the hole injection layer is 5.4 eV to 5.8 eV. The method according to claim 1,
Wherein the LUMO level of the hole injection layer is controlled by changing the amount of the P-type dopant added to the hole injection layer. The method according to claim 1,
Wherein the hole injection layer comprises 1.0 wt% to 4.0 wt% of the P-type dopant. The method according to claim 1,
Wherein the P type dopant comprises at least one selected from the group consisting of F4-TCNQ, 1,4-TCAQ, 6,3-TCPQ, TCAQ, TCNTHPQ and TCNPQ. The method according to claim 1,
The host can be selected from the group consisting of N, N'-di (naphthalen-1-yl) -N, N-diphenyl- benzidine (NPB), N, N'- N, N'-tetranaphthyl-benzidine (TNB), di (p-tolyl) aminophenyl] cyclohexane (TPAC), N, N'-bis (phenanthrene-9-yl) -N, N'-diphenyl-benzidine (PPD) and BFA-1T. The method according to claim 1,
Wherein the hole injection layer has a thickness of 10 to 100 ANGSTROM. The method according to claim 1,
Wherein the hole transport layer is made of the same host as the host of the hole injection layer. The method according to claim 1,
And an electron transport layer disposed between the organic emission layer and the second electrode. The method according to claim 1,
Wherein the first sub-pixel, the second sub-pixel, and the third sub-pixel respectively emit light of different colors, and one of red light, green light, and blue light is emitted. Emitting display device.

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