KR20150078395A - Organic light emitting diode display device - Google Patents

Abstract

The present invention is to disclose an organic electroluminescent display device. The disclosed organic electroluminescent display device comprises: a substrate including a plurality of unit pixels which are formed of a red sub pixel, a green sub pixel, and a blue sub pixel; a first electrode formed on the substrate; an organic light emitting layer which is formed on the first electrode and includes a first light emitting layer and a second light emitting layer; and a second electrode formed on the organic light emitting layer. The first light emitting layer includes a first dopant. The second light emitting layer includes a second dopant. A wavelength value having the maximum intensity of an intrinsic photoluminescence (PL) spectrum by the first dopant and an intrinsic PL spectrum by the second dopant is different. The organic electroluminescent display device according to the present invention improves the viewing angle over a single wavelength dopant or when only a long wavelength dopant is applied or improves service life or efficiency. Moreover, the present invention has an advantage by having a simple process because a light emitting layer is formed with a double layer including two dopants having different wavelengths and it doesn′t need to consider the content ratio of the two dopants having different wavelengths.

Description

[0001] The present invention relates to an organic light emitting diode display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device capable of improving a color gamut while preventing a viewing angle problem and improving lifetime.

In recent years, as the information age has come to a full-fledged information age, a display field for visually expressing electrical information signals has been rapidly developed. In response to this, various flat panel display devices having excellent performance of thinning, light weight, Flat Display Device) has been developed to replace CRT (Cathode Ray Tube).

Specific examples of such flat panel display devices include a liquid crystal display device (LCD), an organic light emitting display (OLED), an electrophoretic display (EPD) A plasma display panel (PDP), a field emission display (FED), an electroluminescence display (ELD), and an electro-wetting display (EWD) And the like. In general, a flat panel display panel, which realizes images, is an essential component. The flat panel display panel includes a pair of substrates bonded together with an intrinsic light emitting material or a polarizing material layer therebetween.

Since an organic light emitting diode (OLED) display device, which is one of such flat panel display devices, includes an organic light emitting element that is a self light emitting element, a separate light source used in a liquid crystal display It is lightweight and thin. In addition, it has superior viewing angle and contrast ratio compared with liquid crystal display devices, is advantageous in terms of power consumption, can be driven by DC low voltage, has a quick response speed, is resistant to external impacts due to its solid internal components, It has advantages.

The organic light emitting device is a device for emitting light by applying an electric field by depositing an organic light emitting layer formed of an organic material between a cathode made of ITO or the like and a cathode made of aluminum (Al) or the like on a glass substrate. When a voltage is applied between the anode and the cathode of the organic light emitting diode, holes are injected from the anode, electrons are injected from the cathode, and then excitons are generated in the light emitting layer through migration. The organic light emitting display may use light emitted when the generated excitons fall to a ground state.

At this time, the conventional organic light emitting display device has a structure in which a reflection plate is formed in a substrate including electrodes or transistors of each device for each of red (R), green (G) and blue (B) Images can be implemented. (R), green (G), and blue (B) colors by controlling the optical distance, reflectance, transmittance, and refractive index for each of the red (R), green (B) light can be emitted. By this micro cavity effect, the maximum luminous efficiency can be obtained for each pixel, and color purity can be improved.

However, such conventional organic light emitting display devices are highly dependent on luminescent dopants, and there is a high possibility that a problem of a viewing angle occurs when a color is changed.

When the organic light emitting display device uses a short wavelength dopant in a red (R) pixel, the organic light emitting display device exhibits better characteristics than the long wavelength dopant in terms of efficiency and lifetime, but may cause a problem in the viewing angle. Particularly, in the case of using a short wavelength dopant in a red (R) pixel, there is a problem of reduction in luminance depending on the viewing angle. Further, when the conventional organic light emitting display uses a long wavelength dopant in green (G) and blue (B) pixels, the organic light emitting display exhibits better characteristics than the short wavelength dopant in terms of efficiency and lifetime, but may cause problems in the viewing angle.

In addition, when the conventional organic light emitting display device uses a long wavelength dopant in a red (R) pixel, the viewing angle is not a problem, but the efficiency is lower than that of the short wavelength dopant, and in particular, the lifetime is short. Further, when the conventional organic light emitting display device uses a short wavelength dopant in green (G) and blue (B) pixels, the viewing angle is not a problem, but the efficiency is lower than that of the long wavelength dopant, .

It is an object of the present invention to provide an organic electroluminescent display device having a viewing angle improved, a lifetime and an efficiency improved compared with a case of applying only a short wavelength dopant or a long wavelength dopant.

Another object of the present invention is to provide an organic electroluminescence display device in which the light emitting layer is formed as a double layer containing two dopants having different wavelengths and the process is simple without considering the content ratio of two dopants having different wavelengths.

According to an aspect of the present invention, there is provided an organic light emitting display including: a substrate including a plurality of unit pixels each including a red sub-pixel, a green sub-pixel, and a blue sub-pixel; A first electrode formed on the substrate; An organic light emitting layer formed on the first electrode, the organic light emitting layer including a first light emitting layer and a second light emitting layer; And a second electrode formed on the organic light emitting layer, wherein the first light emitting layer includes a first dopant, the second light emitting layer includes a second dopant, and a unique photoluminescence (PL) Spectrum and the intrinsic PL (photoluminescence) spectrum due to the second dopant are characterized in that the wavelength values having the maximum intensity are different from each other.

The organic electroluminescent display device according to the present invention has the first effect that the viewing angle is improved, the lifetime and the efficiency are improved as compared with the case where only the short-wavelength dopant or the long-wavelength dopant is applied.

In addition, the organic electroluminescent display device according to the present invention has a second effect in which the light emitting layer is formed of a double layer containing two dopants having different wavelengths, and the process is simple without considering the content ratio of two dopants having different wavelengths.

1 is a view illustrating an organic light emitting display device according to the present invention.
FIG. 2 is a diagram illustrating a color coordinate change amount for a viewing angle in a red sub-pixel of an organic light emitting display according to the present invention.
FIG. 3 is a diagram illustrating lifetime of a red sub-pixel of an organic light emitting display according to the present invention.
FIG. 4 is a diagram illustrating a color coordinate change amount for a viewing angle in a green sub-pixel of an organic light emitting display according to the present invention.
FIG. 5 is a diagram showing the lifetime of a green sub-pixel of an organic light emitting display according to the present invention.
FIG. 6 is a diagram illustrating the amount of color coordinate change with respect to a viewing angle in a blue sub-pixel of an organic light emitting display according to the present invention.
FIG. 7 is a diagram illustrating lifetime of the blue sub-pixel of the organic light emitting display according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the size and thickness of the device may be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

1 is a view illustrating an organic light emitting display device according to the present invention.

1, an organic light emitting display according to an embodiment of the present invention includes an element substrate 50 (FIG. 1) divided into a plurality of unit pixels including a red sub-pixel R, a green sub-pixel G, and a blue sub- The organic light emitting device 100 is formed. A capping layer 140 is formed on the organic light emitting device 100.

The organic light emitting device 100 includes a first electrode 110, an organic light emitting layer 120, and a second electrode 130. Although not shown in the drawing, a bank pattern may be formed on the first electrode 110 to expose the first electrode 110 only in the light emitting region. That is, the light emitting region and the non-light emitting region of the unit pixel can be defined through the bank pattern.

The first electrode 110 may be an anode. At this time, the first electrode 110 serves as a reflective electrode, and may further include a reflective layer. The reflective layer may be formed of a metal material having a high reflectance such as aluminum (Al). In addition, the first electrode 110 may be formed of a transparent conductive material such as ITO. However, the material is not limited to the above material, and a material that can serve as the first electrode 110 in the organic light emitting diode 100 is generally sufficient.

The organic light emitting layer 120 may be formed on the first electrode 110 exposed through the bank pattern. The organic light emitting layer 120 may include a hole injection layer 121, a hole transporting layer 122, an emitting material layer 200, and an electron transporting layer 124 . At this time, although not shown in the figure, an electron injection layer may be further formed on the electron transport layer 124.

The light emitting layer 200 may include a first light emitting layer 201 and a second light emitting layer 202. The first light emitting layer 201 and the second light emitting layer 202 may include a host different from the dopant. That is, the first light emitting layer 201 may include a first dopant and a first host. In addition, the second light emitting layer 202 may include a second dopant and a second host.

The first dopant and the second dopant may respectively emit light having a PL (photoluminescence) spectrum of the first and second light emitting layers 201 and 202 themselves. That is, the PL spectrum may be formed differently depending on the dopant, and the intrinsic PL (photoluminescence) spectrum due to the first dopant and the intrinsic PL (photoluminescence) spectrum due to the second dopant have a wavelength value Can be formed to be different from each other.

A dopant for realizing a PL spectrum having a relatively large peak intensity value can be defined as a long wavelength dopant and a dopant for realizing a PL spectrum having a relatively small peak intensity value can be defined as a short wavelength dopant. Therefore, the PL spectrum formed when the short wavelength dopant is used and the PL spectrum formed when the long wavelength dopant is used are different from each other.

For example, the light emitting layer adjacent to the anode includes a short wavelength dopant, and the light emitting layer adjacent to the cathode includes a long wavelength dopant. When the first electrode 110 is an anode, the first light emitting layer 201 includes a short wavelength dopant, and the second light emitting layer 202 includes a long wavelength dopant. At this time, either the fluorescent material or the phosphorescent material may be applied to the long wavelength and short wavelength dopants, respectively.

That is, when the first electrode 110 is an anode, a wavelength value having a maximum intensity of an intrinsic PL spectrum due to the first dopant of the first emitting layer 201 is higher than a wavelength value of the second dopant of the second emitting layer 202 The intensity of the PL spectrum can be reduced.

In order to emit light at the interface between the first light emitting layer 201 and the second light emitting layer 202, the light emitting layer of either the first light emitting layer 201 or the second light emitting layer 202 may be a hole type host ) And the other light emitting layer is formed including an electron type host.

For example, the light emitting layer adjacent to the anode includes a hole host, and the light emitting layer adjacent to the cathode is formed including an electron host. When the first electrode 110 is an anode, the first light emitting layer 201 includes a hole host, and the second light emitting layer 202 includes an electronic host. That is, when the first electrode 110 is an anode, the first host of the first light emitting layer 201 is a hole host and the second host of the second light emitting layer 202 is an electronic host. Accordingly, the first light emitting layer 201 may include a hole host and a long wavelength dopant, and the second light emitting layer 202 may include an electron host and a short wavelength dopant.

In the conventional organic light emitting display, the light emitting layer 200 is formed as a single layer, and the light emitting layer includes a short wavelength dopant or a long wavelength dopant. In this case, when the light emitting layer 200 includes only a short wavelength dopant or a long wavelength dopant, the efficiency and lifetime are excellent, but there is a problem in the viewing angle or a viewing angle is not a problem, but the efficiency and lifetime are poor. For example, when only a short-wavelength dopant is used in a red pixel, efficiency and lifetime are excellent. However, there is a problem in view angle, and when only a long-wavelength dopant is used, the viewing angle is not a problem but efficiency and lifetime are poor. In the case of using green and blue pixels, only long wavelength dopant exhibits excellent efficiency and long lifetime, but has a large viewing angle problem. When only a short wavelength dopant is used, the viewing angle is not a problem but its efficiency and lifetime are poor .

In order to improve the organic electroluminescence display device according to the present invention, the light emitting layer 200 is formed of the first light emitting layer 201 and the second light emitting layer 202. One of the light emitting layers of the first and second light emitting layers 201 and 202 includes a long wavelength dopant and the other light emitting layer includes a short wavelength dopant.

The results of comparison experiments between the organic light emitting display of the present invention and the conventional organic light emitting display will be described in detail as follows.

FIG. 2 is a view showing the amount of color coordinate change with respect to the viewing angle in the red sub-pixel of the organic light emitting display of the present invention.

Referring to FIG. 2, when the organic light emitting display device includes a light emitting layer (Dopant B) including a long wavelength dopant, the viewing angle is about 0.06 at a viewing angle of 60 deg. . However, it has been confirmed that when the light emitting layer (Dopant A) including a short wavelength dopant is included, a high color coordinate change amount (? U'v ') of about 0.13 occurs.

The organic electroluminescent display device according to the present invention includes a light emitting layer (2EML) composed of a first light emitting layer including a short wavelength dopant and a second light emitting layer including a long wavelength dopant, and having a color coordinate change amount? U'v 'of about 0.085 Respectively. That is, the organic light emitting display according to the present invention has improved viewing angle as compared with an organic light emitting display including a light emitting layer (Dopant A) including a conventional short wavelength dopant. Further, as the viewing angle is improved, the problem of poor drop in brightness can be improved.

FIG. 3 is a diagram illustrating lifetime of a red sub-pixel of an organic light emitting display according to the present invention.

Referring to FIG. 3, when the organic electroluminescent display device includes a light emitting layer (Dopant A) including a short wavelength dopant, the lifetime is about 800 hours. However, when the light emitting layer (Dopant B) containing a long wavelength dopant is included, it is confirmed that the lifetime is relatively short as compared with the case where the light emitting layer (Dopant A) containing a short wavelength dopant is included within a lifetime of about 300 hours .

The organic electroluminescent display device according to the present invention has a lifetime of 800 hours or longer including a first emission layer including a short wavelength dopant and a second emission layer including a second emission layer including a long wavelength dopant. By using two kinds of dopants, it can be seen that the life span is improved by dispersing the stress.

That is, the organic light emitting display device according to the present invention has improved lifetime compared with an organic light emitting display device including a light emitting layer (Dopant A) including a conventional short wavelength dopant. Further, it was confirmed that the lifetime could be improved as compared with the case of including the light emitting layer (Dopant B) containing the long wavelength dopant.

4 is a graph showing the amount of change in color coordinates with respect to a viewing angle in a green sub-pixel of an organic light emitting display according to the present invention.

Referring to FIG. 4, when a conventional organic light emitting display includes a light emitting layer (Dopant A) including a short wavelength dopant, the viewing angle is not affected by a change in color coordinate (? U'v ') of about 0.023 at a viewing angle of 60 degrees . However, it has been confirmed that a relatively high chromaticity coordinate change (? U'v ') of about 0.066 occurs when the light emitting layer (Dopant B) including the long wavelength dopant is included.

The organic electroluminescent display device according to the present invention includes a light emitting layer (2EML) composed of a first light emitting layer including a short wavelength dopant and a second light emitting layer including a long wavelength dopant and having a color coordinate change amount? U'v 'of about 0.039 Respectively. That is, the organic light emitting display device according to the present invention has improved viewing angle compared to an organic light emitting display device including a light emitting layer (Dopant B) including a long wavelength dopant.

FIG. 5 is a diagram showing the lifetime of a green sub-pixel of an organic light emitting display according to the present invention.

Referring to FIG. 5, when the organic light emitting display device includes a light emitting layer (Dopant B) including a long wavelength dopant, the lifetime is about 360 hours. However, it has been confirmed that when the light emitting layer (Dopant A) including a short wavelength dopant is included, the lifetime is extremely short as compared with the case where the light emitting layer (Dopant B) containing a long wavelength dopant is included at a lifetime of about 150 hours .

The organic electroluminescent display device according to the present invention has a lifetime of about 300 hours including a first emission layer including a short wavelength dopant and a second emission layer including a second emission layer including a long wavelength dopant. That is, the organic light emitting display device according to the present invention has improved lifetime compared to an organic light emitting display device including a light emitting layer (Dopant B) including a long wavelength dopant.

FIG. 6 is a graph showing the amount of color coordinate change with respect to a viewing angle in a blue sub-pixel of an organic light emitting display according to the present invention.

Referring to FIG. 6, when a conventional organic light emitting display includes a light emitting layer (Dopant A) including a short wavelength dopant, the viewing angle is not affected by the color coordinate variation (? U'v ') of about 0.018 at a viewing angle of 60 degrees . However, it has been confirmed that a relatively high chromaticity coordinate variation (? U'v ') of about 0.076 occurs when the light emitting layer (Dopant B) including the long wavelength dopant is included.

The organic electroluminescent display device according to the present invention includes a light emitting layer (2EML) composed of a first light emitting layer including a short wavelength dopant and a second light emitting layer including a long wavelength dopant, and has a color coordinate change amount? U'v 'of about 0.042 Respectively. That is, the organic light emitting display device according to the present invention has improved viewing angle compared to an organic light emitting display device including a light emitting layer (Dopant B) including a long wavelength dopant.

FIG. 7 is a diagram illustrating lifetime of the blue sub-pixel of the organic light emitting display according to the present invention.

Referring to FIG. 7, when the organic light emitting display device includes a light emitting layer (Dopant B) including a long wavelength dopant, the lifetime is about 550 hours. However, when the light emitting layer (Dopant A) containing a short wavelength dopant is included, it has been found that the lifetime is extremely short as compared with the case where the light emitting layer (Dopant B) containing a long wavelength dopant is included at a lifetime of about 200 hours .

The organic electroluminescent display device according to the present invention has a lifetime of about 450 hours including a light emitting layer (2EML) comprising a first light emitting layer including a short wavelength dopant and a second light emitting layer including a long wavelength dopant. That is, the organic light emitting display device according to the present invention has improved lifetime compared to an organic light emitting display device including a light emitting layer (Dopant B) including a long wavelength dopant.

Therefore, it can be seen that the organic light emitting display according to the present invention can be formed with satisfactory lifetime and viewing angle in red (R), green (G) and blue sub-pixels (B). In addition, since a light emitting layer including a long wavelength dopant and a light emitting layer including a short wavelength dopant are included in a separate process, the process has a simple effect.

The light emitted from the organic light emitting diode 100 of the organic light emitting display according to the present invention has a unique photoluminescence (PL) spectrum of the light emitting layer itself different for each of the red (R), green (G) and blue . In addition, the organic light emitting layer 120 may emit light including an EL spectrum due to a micro-cavity effect in addition to the PL spectrum. That is, the light emitted from the organic light emitting diode 100 may be light that is amplified by overlapping the EL spectrum and the PL spectrum. The light thus amplified can further increase the efficiency.

Referring to FIG. 1, the organic light emitting layer 120 may further include an organic layer other than the layers as needed. For example, it may further include an optical adjustment layer 123 for an optimized thickness for each sub-pixel. The optical adjustment layer 123 may be formed of the same material as the hole transport layer 122. The optical control layer 123 may be omitted for each sub-pixel or may have a different thickness.

That is, in the organic light emitting display according to the present invention, the thickness of the organic light emitting layer 120 is different in consideration of the emission wavelength for each of red (R), green (G) and blue (B) Can be adjusted. As a result, a color image due to a micro-cavity effect can be realized.

The micro cavity effect can improve the color purity and improve the light emission efficiently by using the optical resonance effect. In addition, unnecessary optical components can be reduced. Using such a micro cavity effect, the light emitted from the organic light emitting diode 100 includes an electroluminescence (EL) spectrum in which red (R), green (G) and blue (B) .

At this time, the PL spectrum may be formed differently depending on the dopant. That is, the PL spectrum formed when the short wavelength dopant is used and the PL spectrum formed when the long wavelength dopant is used are different from each other. Therefore, the PL spectrum formed when the dopant of the first emitting layer 201 is used and the PL spectrum formed when the dopant of the second emitting layer 202 is used are different from each other.

Here, the EL spectrum of the organic light emitting display according to the present invention may include a difference between the wavelength of the PL spectrum due to the dopant of the first light emitting layer 201 and the wavelength of the PL spectrum due to the dopant of the second light emitting layer 202 The wavelengths of the light can be adjusted. For example, a wavelength value having the maximum intensity of the EL spectrum is a wavelength value having a maximum intensity of the PL spectrum due to the dopant of the first light emitting layer 201 and a maximum value of the maximum value of the PL spectrum due to the dopant of the second light emitting layer 202 May be adjusted so as to have an intermediate value of the wavelength value having the intensity.

As a result, the overlap between the EL spectrum and the two PL spectra is increased, and the efficiency can be further increased. In particular, when only a short-wavelength dopant of a conventional organic light emitting display device was used in a red sub-pixel, the organic light emitting display device according to the present invention had an emission efficiency of 41.0 cd / A and a long wavelength dopant only 35.8 cd / cd / A.

The EL spectrum may control the wavelength by controlling the thickness of the organic light emitting layer 120. For example, the EL spectrum can adjust the wavelength value by adjusting the thickness of the optical control layer 123 of the organic light emitting layer 120.

A second electrode 130 is formed on the organic light emitting layer 120. When the first electrode 110 is an anode, the second electrode 130 may be a cathode. The second electrode 130 may be formed as a translucent electrode to emit light toward the front surface.

The element substrate 50 includes a thin film transistor Tr that drives each sub-pixel formed on an insulating substrate 10 formed of a material such as glass or plastic. The thin film transistor Tr includes a gate electrode formed on an insulating substrate 10, a gate insulating film covering the gate electrode, a semiconductor layer overlapping the gate electrode with the gate insulating film interposed therebetween to form a channel, And may be composed of a source electrode and a drain electrode opposed to each other. A planarizing film 20 is formed on the thin film transistor Tr. The thin film transistor (Tr) drain electrode formed on the element substrate 50 is connected to the organic light emitting diode first electrode 110.

A capping layer 140 is formed on the organic light emitting device 100. The capping layer 140 may be formed of an organic material or an inorganic material on the second electrode 130 of the organic light emitting diode 100. At this time, the capping layer 140 may also serve as one optical control layer. The capping layer 140 may increase the reflectance at the interface between the capping layer and the exterior by controlling the refractive index difference with the external. This increased reflectivity allows the capping layer 140 to exhibit a micro-cavity effect at a particular wavelength. At this time, the capping layer 140 may have a different thickness for each sub-pixel.

Therefore, the organic electroluminescent display device according to the present invention can improve the viewing angle, the lifetime and the efficiency, as compared with the case where only the short-wavelength dopant or the long-wavelength dopant is applied. In addition, the light emitting layer is formed as a double layer containing two dopants having different wavelengths, and the process is simple without considering the content ratio of the two dopants having different wavelengths.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

50: element substrate
100: Organic light emitting device
110: first electrode
120: organic light emitting layer
130: second electrode
140: capping layer
200: light emitting layer
201: First light emitting layer
202: second light emitting layer

Claims (8)

A substrate having a plurality of unit pixels each comprising a red sub-pixel, a green sub-pixel and a blue sub-pixel;
A first electrode formed on the substrate;
An organic light emitting layer formed on the first electrode, the organic light emitting layer including a first light emitting layer and a second light emitting layer; And
And a second electrode formed on the organic light emitting layer,
Wherein the first light emitting layer comprises a first dopant, the second light emitting layer comprises a second dopant,
Wherein the intrinsic PL (photoluminescence) spectrum due to the first dopant and the intrinsic PL (photoluminescence) spectrum due to the second dopant are different from each other in wavelength value having the maximum intensity.
The method according to claim 1,
Wherein a wavelength value having a maximum intensity of an intrinsic PL (photoluminescence) spectrum due to the first dopant is smaller than a wavelength value having a maximum intensity of an intrinsic PL (photoluminescence) spectrum due to a second dopant. Device.
The method according to claim 1,
Wherein the first light emitting layer includes a hole type host and the second light emitting layer comprises an electron type host.
The method according to claim 1,
And an EL (electroluminescence) spectrum in which light emitted from the organic light emitting layer passes through a resonance structure for each of red, green, and blue sub-pixels.
5. The method of claim 4,
The wavelength value having the maximum intensity of the EL spectrum is,
And a wavelength value between a wavelength value having the maximum intensity of the PL spectrum due to the first dopant and a wavelength value having the maximum intensity of the PL spectrum due to the second dopant.
6. The method of claim 5,
Wherein a wavelength value having the maximum intensity of the EL spectrum is adjusted by changing a thickness of the organic light emitting layer of the organic light emitting device.
The method according to claim 6,
Wherein the thickness of the organic light emitting layer is changed by omitting the optical control layer or by adjusting the thickness of the optical control layer.
8. The method of claim 7,
Wherein the optical control layer is formed of the same material as the hole transport layer of the organic light emitting layer.

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