KR102430339B1 - Organic light emitting display - Google Patents

Abstract

According to an embodiment of the present invention, an organic light emitting display device includes a first sub-pixel, a second sub-pixel, and a third sub-pixel, comprising: 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 transport layer; and a second electrode disposed on the organic light emitting layer, wherein the LUMO level of the hole injection layer is greater than or equal to the work function of each of the reflective layer and the transparent conductive layer. It is possible to suppress the redish phenomenon that may occur in the state in which is not applied.

Description

Organic light emitting display device {ORGANIC LIGHT EMITTING DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 that may occur during low grayscale driving.

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

An organic light emitting diode display generally includes 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 combined with each other to emit light. In general, a hole injection layer and a hole transport layer are disposed between the red organic light emitting layer, the green organic light emitting layer, and the blue organic light emitting layer and the anode to facilitate the movement of holes.

Recently, a technique of adding a P-type dopant to the hole injection layer disposed between the anode and the organic light emitting layer has been introduced in order to further accelerate the hole movement and lower the driving voltage to improve the luminous efficiency of the device. As such, when the P-type dopant is added, holes can be more smoothly supplied to the organic light emitting layers, thereby improving the lifespan and efficiency of the organic light emitting display device.

However, when the hole injection layer including the P-type dopant is disposed, the anode and the hole injection layer including the P-type dopant are in direct contact. In this case, when the organic light emitting diode display is driven to display an image in a low grayscale, a reddish phenomenon occurs in which a red color is expressed. Specifically, when all of the red sub-pixel, the green sub-pixel, and the blue sub-pixel are driven with the same low current density to realize low-gray white, the red sub-pixel not only starts to emit light first, but also emits the brightest light. make it

Also, even in a state where no voltage is applied, the red sub-pixel is operated by the residual current remaining in the thin film transistor or the driving unit inside the organic light emitting diode display, and a reddish phenomenon occurs.

As a result, there is a problem in that image quality reliability of the organic light emitting diode display is deteriorated due to optical compensation and CR failure.

As described above, the inventors of the present invention have understood that the redish phenomenon occurring in a state in which a low grayscale is driven or a voltage is not applied is related to the LUMO level of the hole injection layer including the P-type dopant. Accordingly, the inventors of the present invention have invented an organic light emitting diode display including a hole injection layer having a new LUMO level to minimize the redish phenomenon.

That is, an object of the present invention is to provide an organic light emitting diode display capable of suppressing a reddish phenomenon that may occur when the organic light emitting diode display is driven with a low gray scale.

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

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

According to an embodiment of the present invention, an organic light emitting display device includes a first sub-pixel, a second sub-pixel, and a third sub-pixel, comprising: 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 transport layer; and a second electrode disposed on the organic light emitting layer, wherein the LUMO level of the hole injection layer is greater than or equal to 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, it is possible to suppress a reddish phenomenon that may occur during low grayscale driving at a low current density.

According to another feature of the present invention, the work function of the reflective layer may be less than or equal to the 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, and may be silver (Ag) or an alloy containing silver.

According to another feature of the present invention, the transparent conductive layer is indium tin oxide (ITO: Indium Tin Oxide), indium zinc oxide (IZO: Indium Zinc Oxide), indium oxide (Indium Oxide), tin oxide (Tin Oxide) and zinc It may include any one or more selected from the group consisting of oxides (ZnO: Zinc Oxide).

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

According to another feature of the present invention, the LUMO level of the hole injection layer may be less than or equal to the HOMO level of the hole transport layer.

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

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

According to another feature 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 feature 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 N,N'-di(naphthalen-1-yl)-N,N-diphenyl-benzidine (NPB), N,N'-diphenyl-N,N'- bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine (TPD), N,N',N'-tetranaphthyl-benzidine (TNB), di(p-tolyl)aminophenyl] It may include any one or more selected from the group consisting of cyclohexane (TPAC), N,N'-bis(phenanthren-9-yl)-N,N'-diphenyl-benzidine (PPD), and BFA-1T. .

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

According to another feature 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 feature of the present invention, an electron transport layer disposed between the organic light emitting layer and the second electrode may be further included.

According to another feature of the present invention, light of different colors is emitted from each of the first sub-pixel, the second sub-pixel, and the third sub-pixel, and any one of red light, green light, and blue light is emitted. can be illuminated.

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

According to the present invention, when the organic light emitting diode display is driven at a low current density for low grayscale driving, the red sub-pixel is first driven before the blue sub-pixel and the green sub-pixel are driven, so that a reddish phenomenon occurs in the organic light emitting diode display. can be minimized

Also, according to the present invention, when no voltage is applied to the organic light emitting diode display, a reddish phenomenon that may be undesirably generated due to a residual current can be minimized.

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

1 is a schematic cross-sectional view illustrating a top emission type organic light emitting display device according to an exemplary embodiment.
FIG. 2 is a diagram illustrating an energy band diagram of a first electrode, a hole injection layer including a P-type dopant, and a hole transport layer in a conventional organic light emitting diode display.
3 is a diagram illustrating 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 diode display.
4 is a diagram illustrating an energy band diagram of a first electrode, a hole injection layer, and a hole transport layer in an organic light emitting diode display according to an exemplary embodiment of the present invention.
5 is a diagram illustrating a current density-voltage curve (JV curve) 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 a surface photograph taken when the organic light emitting diode display according to an exemplary embodiment of the present invention is driven at 0 gray level.
7 is a surface photograph taken when the organic light emitting diode display according to the comparative example of the present invention is driven at 0 gray scale.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative and the present invention is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, the case in which the plural is included is included unless specifically stated otherwise.

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

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'beside', etc., 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

When a device or layer is referred to as 'on' another device or layer, it includes any other layer or layer interposed therebetween or directly on the other device.

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

Like reference numerals refer to like elements throughout.

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

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

In the present specification, when the organic light emitting diode display is driven with a low gray scale, it means that the organic light emitting diode display is driven with a current density for displaying white, red, green, or blue colors with a low gray scale. Also, the low grayscale may mean 15 grayscales, for example, when the grayscale is expressed as a value of 0 to 255.

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

1 is a schematic cross-sectional view illustrating a top emission type organic light emitting display device according to an exemplary embodiment.

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

The substrate 110 is used to support various components of the organic light emitting diode display 100 and is formed of an insulating material. In this case, 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 an area for displaying one color. Lights of different colors may be emitted from each of the first sub-pixel R, the second sub-pixel G, and the third sub-pixel B. For example, red light may be emitted from the first sub-pixel R, green light may be emitted from the second sub-pixel G, and blue light may be emitted from the third sub-pixel B.

The first electrode 120 is disposed on the substrate 110 . The first electrode 120 serves to apply a voltage to each of the first organic emission layer 160a, the second organic emission layer 160b, and the third organic emission layer 160c. In this case, 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. In other words, the first sub-pixel R, the second sub-pixel G, and the third sub-pixel B are separately disposed.

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 the light emitted from the organic light emitting layer 160 to the upper portion of the organic light emitting display device 100 , and is made of a conductive compound having excellent reflectance. The reflective layer 121 may be silver (Ag), palladium (Pd), copper (Cu), aluminum (Al), nickel (Ni), or an alloy including these, for example, silver or APC (Ag/Pd). /Cu alloy).

The work function of the reflective layer 121 is preferably equal to or less than the work function of the transparent conductive layer 122 . Here, the work function means the minimum energy required to pull out one electron in a material. In general, 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 4.5 eV to 5.0 eV, more preferably 4.7 eV to 4.9 eV, and for example, the work function of the reflective layer 121 may be about 4.8 eV.

Meanwhile, the 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), but is not limited thereto, but is not limited thereto, but is not limited thereto, but is not limited thereto, but is not limited to indium tin oxide (ITO), indium zinc oxide (IZO), and indium. It may include any one or more selected from the group consisting of oxide (Indium Oxide), tin oxide (Tin Oxide), and zinc oxide (ZnO: Zinc Oxide).

In this case, the work function of the transparent conductive layer 122 may be 5.2 eV to 5.6 eV, more preferably 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 from 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 .

At this time, the hole injection layer 130 is formed by doping a P-type dopant into a certain host. When the P-type dopant is doped as described above, the mobility of the hole injection layer 130 is greatly improved, so that the organic light emitting layer 160 . ) can be more smoothly injected into the hole.

In the organic light emitting diode display 100 according to an embodiment of the present invention, the LUMO level of the hole injection layer 130 is a work function of each of the reflective layer 121 and the transparent conductive layer 122 constituting the first electrode 120 . It is characterized by more than one.

2 is a diagram exemplarily illustrating an energy band diagram of a conventional organic light emitting diode display. 2 shows the lowest unoccupied molecular (LUMO) of the hole injection layer (PHIL) and the hole transport layer (HTL) including the work function of the first electrode including silver (Ag) as the reflective layer and ITO as the transparent conductive layer and the P-type dopant. Orbitals) levels and Highest Occupied Molecular Orbitals (HOMO) levels are shown.

3 is a diagram illustrating 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 organic light emitting diode display. In FIG. 3 , the current density-voltage curve for the red sub-pixel is indicated by a solid line, the current density-voltage curve for the green sub-pixel is indicated by a dotted line, and the current density-voltage curve for the blue sub-pixel is indicated by a dashed-dotted line. shown.

Referring to FIG. 2 showing an energy band diagram of a conventional organic light emitting diode display, when the first electrode is formed of a reflective layer (Ag) and a transparent conductive layer (ITO), between silver (Ag) and a transparent conductive oxide of the organic light emitting display device 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 transparent conductive layer (ITO).

In general, in order for an organic light emitting diode display to display colors, a voltage greater than a certain level is applied so that the voltage is built-in in the transparent conductive layer, so that holes must be injected into the organic light emitting layer through the transparent conductive layer.

However, as shown in FIG. 2 , 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) of the first electrode and the transparent conductive layer (ITO), transparent conduction at a low current density A phenomenon in which the voltage is preferentially built-in to the reflective layer Ag instead of being built-in to the layer ITO occurs.

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) of the first electrode and the work function of the transparent conductive layer (ITO), the work function of the reflective layer and the energy barrier of the hole injection layer is not large enough, holes are injected from the reflective layer to move 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 diode display malfunctions.

Referring to FIG. 3 together for a more detailed description, as a result, the red sub-pixel has a lower turn-on voltage than the green sub-pixel and the blue sub-pixel at a low current density, that is, a current density of about 0.01 to 1 mA/cm ² . (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) of the first electrode and the transparent conductive layer (ITO), holes first pass through the reflective layer rather than the transparent conductive layer. This injection causes a fine current to flow, and a reddish phenomenon occurs in which the red sub-pixel emits light before the green sub-pixel and the blue sub-pixel.

Also, as described above, even when no voltage is applied, a voltage is first built into the reflective layer due to a minute residual current existing inside the organic light emitting diode display device, so that a reddish phenomenon occurs.

However, in the organic light emitting diode 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 the reflective layer 121 constituting the first electrode 120 and It is greater than or equal to the work function of each of the transparent conductive layers 122 . When the LUMO level of the hole injection layer 130 is adjusted as in the present invention, the work function of the reflective layer 121 and the energy barrier of the hole injection layer 130 are sufficiently large, and the voltage is not built-in to the reflective layer 121, Since the voltage is normally built-in to the transparent conductive layer 122 , a malfunction in which holes are first injected through the reflective layer 121 can be suppressed.

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 the organic light emitting layer 160 through the LUMO level of the hole injection layer 130 including the P-type dopant. It is possible to minimize the phenomenon of moving to

The LUMO level of the hole injection layer 130 is preferably equal to or less than the HOMO level of the hole transport layer 140 . This is because, when the LUMO level of the hole injection layer 130 is greater than the HOMO level of the hole transport layer 140 , the mobility of holes is greatly reduced, which may prevent hole transport.

The LUMO level of the hole injection layer 130 is preferably 5.4 eV to 5.8 eV, 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 redish phenomenon can be significantly reduced and the hole transport ability is also excellent.

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

In this case, the hole injection layer 130 preferably contains 1.0 wt% to 4.0 wt% of the P-type dopant, and more preferably 1.0 wt% to 2.0 wt%. When the content of the P-type dopant is less than the above range, the driving voltage of each sub-pixel is all increased, and the LUMO level of the hole injection layer 130 is higher than the work function of each of the reflective layer 121 and the transparent conductive layer 122 . is not easy to adjust, and when the above range is exceeded, problems such as reduced efficiency of the display device or an afterimage may occur.

As a method of adjusting the P-type dopant content of the hole injection layer 130, but is not limited thereto, the hole injection layer 130 including the P-type dopant and the host in the first electrode 120 using a scan method. A deposition method may be used.

More specifically, in a scanning device including a guide rail, a first deposition source, and a second deposition source, a mixing ratio of the P-type dopant and the host may be adjusted by controlling the release rates of the P-type dopant and the host. In general, after injecting the P-type dopant into the first deposition source located at the front of the scan and the host into the second deposition source located at the rear of the scan, the P-type dopant and the host are emitted along the direction of the scan to inject holes. A layer 130 is formed.

The P-type dopant constituting the hole injection layer 130 includes, but is not limited to, tetrafluoro-tetracyano-quinodimethane (F ₄ -TCNQ), 1,4-TCAQ, It is preferable to include any one or more selected from the group consisting of 6,3-TCPQ, TCAQ, TCNTHPQ and TCNPQ.

[Formula 1]

On the other hand, the host constituting the hole injection layer 130, but is not limited thereto, is preferably a heteroaromatic ring compound or an aromatic amine compound, more specifically, N,N'-di(naphthalen-1-yl) -N,N-diphenyl-benzidine (NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine (TPD), N,N',N'-tetranaphthyl-benzidine (TNB), di(p-tolyl)aminophenyl]cyclohexane (TPAC), N,N'-bis(phenanthren-9-yl)-N,N It is more preferable to include at least one selected from the group consisting of '-diphenyl-benzidine (PPD) and BFA-1T.

In addition, the hole injection layer 130 preferably has a thickness of 10 Å to 100 Å, more preferably 10 Å to 60 Å. When the thickness of the hole injection layer 130 is less than 10 Å, it is difficult to expect a reduction in the redish phenomenon, and when the thickness is greater than 100 Å, the lifespan of the organic light emitting diode display may decrease and the driving voltage may increase significantly.

Next, the hole transport 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 them 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 like the host used in the hole injection layer 130 , it is preferably a heteroaromatic ring compound or an aromatic amine compound, and more specifically, N,N'-di(naphthalene-1). -yl)-N,N-diphenyl-benzidine (NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine ( TPD), N,N',N'-tetranaphthyl-benzidine (TNB), di(p-tolyl)aminophenyl]cyclohexane (TPAC), N,N'-bis(phenanthren-9-yl)- It may include any one or more selected from the group consisting of N,N'-diphenyl-benzidine (PPD) and BFA-1T. In this case, 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.

Meanwhile, an auxiliary transport layer may be disposed on the hole transport layer 140 to adjust the distance between the first electrode 120 and the organic emission layer for each sub-pixel. More specifically, the first auxiliary transport layer 150a is disposed between the hole transport layer 140 of the first sub-pixel R and the first organic emission layer 160a, and the hole transport layer 140 of the second sub-pixel G is disposed. ) and a second auxiliary transport layer 150b may be disposed between the second organic emission layer 160b. Each of the first auxiliary transport layer 150a and the second auxiliary transport layer 150b serves to smoothly transfer holes to the first organic light emitting layer 160a and the second organic light emitting layer 160b, respectively.

A thickness of each of the first auxiliary transport layer 150a and the second auxiliary transport layer 150b may form an optical distance of a microcavity. Specifically, the thickness of each of the first auxiliary transport layer 150a and the second auxiliary transport layer 150b is determined such that the organic material layers disposed between the first electrode 120 and the second electrode 180 form a microcavity structure. can

Since light of different colors is emitted from the first sub-pixel R and the second sub-pixel G, the thickness of each of the first auxiliary transport layer 150a and the second auxiliary transport layer 150b may be different from each other. In FIG. 1 , it is assumed that the first organic emission layer 160a is a red organic emission layer and the second organic emission layer 160b is a green organic emission layer, and the thickness of the first auxiliary transport layer 150a is the thickness of the second auxiliary transport layer 150b. expressed more thickly.

The first auxiliary transport layer 150a and the second auxiliary transport layer 150b are preferably a heteroaromatic ring compound or an aromatic amine compound, like the host used in the hole injection layer 130 and the hole transport layer 140 , more specifically , N,N'-di(naphthalen-1-yl)-N,N-diphenyl-benzidine (NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1 -biphenyl-4,4'-diamine (TPD), N,N',N'-tetranaphthyl-benzidine (TNB), di(p-tolyl)aminophenyl]cyclohexane (TPAC), N,N' -bis(phenanthren-9-yl)-N,N'-diphenyl-benzidine (PPD) and may include any one or more selected from the group consisting of BFA-1T.

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

The organic emission layer 160 is a layer that emits light by combining electrons and holes, and includes a host and a dopant. The host of the organic light emitting layer 160 is a material that transfers energy to the dopant to improve luminous efficiency and color purity, and the dopant is a dye-based organic material that participates in a small amount in the host. It emits colored light.

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

Meanwhile, although not shown in FIG. 1 , in the first sub-pixel and the second sub-pixel, an organic emission layer capable of emitting blue light is additionally formed on the organic emission layer capable of emitting any one of red light and green light. can be placed.

An electron transport layer 170 is disposed on the first organic emission layer 160a, the second organic emission layer 160b, and the third organic emission layer 160c. The electron transport layer 170 serves to smoothly move 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 is not limited thereto, but any one selected from the group consisting of Alq3, PBD, TAZ, spiro-PBD, BAlq, Liq (lithium quinolate), BMB-3T, PF-6P, TPBI, COT and SAlq It is preferable to include the above.

The second electrode 180 is disposed on the electron transport layer 170 . Since the second electrode 180 needs to supply electrons, it is made of a conductive material having a low work function. Although not limited thereto, for example, the second electrode 180 may be formed 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 normally patterned and is formed as a single layer. That is, the second electrode 180 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 embodiment of the present invention is the top emission type organic light emitting display device 100 , the second electrode 180 is a cathode and is formed to have a very thin thickness to be substantially transparent. can be

An organic material layer 190 is disposed on the second electrode 180 . The organic material layer 190 may serve to planarize the step of the second electrode 180 and compensate for foreign matter. The organic material layer 190 may be formed of an acrylic-based resin or an epoxy-based resin, but is not necessarily limited thereto.

Although 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. In this case, the organic light emitting display devices of Examples and Comparative Examples were all manufactured to have the same structure as the organic light emitting display device as shown in FIG. 1 , and the first organic light emitting layer was a red organic light emitting layer, and the second organic light emitting layer was a green organic light emitting layer. As the light emitting layer, the third organic light emitting layer was composed of a blue organic light emitting layer.

Specifically, between the first electrode and the organic light emitting layer, a hole injection layer doped with 1.5 wt% of F4-TCNQ as a P-type dopant and a hole transport layer containing the same host as the host used in the hole injection layer. An example was prepared. In this case, the organic light emitting diode display according to the embodiment has a structure of Ag-ITO/hole injection layer/hole transport layer/organic emission layer/electron transport layer/cathode (Ag-Mg).

Meanwhile, in Comparative Example, an organic light emitting diode display was manufactured in the same manner as in Example, except that the hole injection layer doped with F4-TCNQ in an amount of 0.5 wt% as a P-type dopant was included.

4 and 5 show experimental data for the organic light emitting diode display according to the embodiment. Specifically, FIG. 4 is a diagram illustrating an energy band diagram of the organic light emitting diode display 100 according to an embodiment of the present invention. In FIG. 4 , the energy band for the hole injection layer 130 and the hole transport layer 140 including the P-type dopant together with the work function for the first electrode 120 including the reflective layer 121 and the transparent conductive layer 122 . is shown in the form of a rectangle, the upper side of the rectangle means the LUMO level of each layer, and the lower side means the HOMO level of each layer. Referring to FIG. 4 , it can be seen that 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 or equal to the work functions of the reflective layer 121 and the transparent conductive layer 122 . When the LUMO level of the hole 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, holes are injected from the reflective layer 121 in a low grayscale to emit light is suppressed

The effect of the organic light emitting diode display 100 of the present invention having the energy band diagram shown in FIG. 4 can be confirmed through FIG. 5 .

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 diode display 100 according to an exemplary embodiment of the present invention. It is a drawing showing In FIG. 5 , the current density-voltage curve for the red sub-pixel R is shown by a solid line, the current density-voltage curve for the green sub-pixel G is shown by a dotted line, and the current for the blue sub-pixel B is shown in FIG. 5 . Density-voltage curves are shown with dashed-dotted lines.

In comparison with the current density-voltage curve for the conventional organic light emitting diode display shown in FIG. 3 , the current density-voltage curve for the organic light emitting diode display 100 according to the exemplary embodiment shown in FIG. 5 . 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 a low current density. Accordingly, it is possible to suppress a reddish phenomenon that occurs when the red sub-pixel R operates before the green sub-pixel G and the blue sub-pixel B at a low current density.

More specifically, the color coordinate values and luminance values of the organic light emitting diode display 100 manufactured according to the Examples and Comparative Examples were measured at 0 gray level using a color meter CA-310. The results are shown in [Table 1] below.

division Concentration of P-type dopant (wt%) LUMO level (eV) of the hole injection layer color coordinates luminance
(nit) visual observation Example 1.5 5.4 Measurable 0.0010 Fig. 6 comparative example 0.5 5.1 0.6991, 0.3009 0.0030 Fig. 7

As can be seen from [Table 1], it was found that the LUMO level of the hole injection layer could be adjusted according to the concentration of the P-type dopant. In addition, in the case of an embodiment in which the LUMO level of the hole injection layer is higher than the work function of silver (Ag) and ITO, the color coordinates are not displayed, and thus it can be confirmed that a black color can be implemented without a reddish phenomenon.

6 and 7, in which the organic light emitting diode display of the embodiment and the comparative example driven at 0 gray level are photographed, unlike the comparative example in which the red color shown in FIG. 7 is expressed, the embodiment shown in FIG. It was confirmed that this did not happen.

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 various modifications may be made within the scope 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 spirit of the present invention, but to illustrate, and the scope of the technical spirit 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 interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in 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: first organic light emitting layer
160b: second organic light emitting layer
160c: 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)

An organic light emitting diode display including a first sub-pixel, a second sub-pixel, and a third sub-pixel, the organic light emitting diode display comprising:
a first electrode comprising 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;
first, second, and third organic light emitting layers disposed on the hole transport layer for each of the first, second, and third sub-pixels;
a first auxiliary transport layer disposed between the hole transport layer and the first organic light emitting layer;
a second auxiliary transport layer disposed between the hole transport layer and the second organic light emitting layer; and
a second electrode disposed on the organic light emitting layer;
The thickness of the first auxiliary transport layer and the second auxiliary transport layer are different from each other,
The work function of the reflective layer is less than or equal to the work function of the transparent conductive layer,
The LUMO level of the hole injection layer is 5.4 eV to 5.8 eV, which is the same as the work function of the transparent conductive layer,
The hole injection layer comprises 1.0 wt% to 4.0 wt% of the P-type dopant. delete The method of claim 1,
The reflective layer has a work function of 4.5 eV to 5.0 eV. 4. The method of claim 3,
The reflective layer is silver (Ag) or an alloy containing silver. The method of claim 1,
The transparent conductive layer is made of Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), Indium Oxide, Tin Oxide, and Zinc Oxide (ZnO). An organic light emitting display device comprising at least one selected from the group consisting of: 6. The method of claim 5,
The work function of the transparent conductive layer is 5.2 eV to 5.6 eV. The method of claim 1,
The LUMO level of the hole injection layer is equal to or less than the HOMO level of the hole transport layer. delete delete delete The method of claim 1,
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 of claim 1,
The host is N,N'-di(naphthalen-1-yl)-N,N-diphenyl-benzidine (NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1 ,1-biphenyl-4,4'-diamine (TPD), N,N',N'-tetranaphthyl-benzidine (TNB), di(p-tolyl)aminophenyl]cyclohexane (TPAC), N, An organic light emitting diode display comprising at least one selected from the group consisting of N'-bis(phenanthren-9-yl)-N,N'-diphenyl-benzidine (PPD) and BFA-1T. The method of claim 1,
and the hole injection layer has a thickness of 10 Å to 100 Å. The method of claim 1,
The organic light emitting display device, characterized in that the hole transport layer is composed of the same host as the host of the hole injection layer. The method of claim 1,
The organic light emitting display device of claim 1, further comprising an electron transport layer disposed between the organic light emitting layer and the second electrode. The method of claim 1,
The first sub-pixel is a red sub-pixel, the second sub-pixel is a green sub-pixel, and the third sub-pixel is a blue sub-pixel.

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