KR20110056819A - Organic light emitting diode with black microcavity - Google Patents

Abstract

PURPOSE: An organic light emitting diode with black microcavity is provided to implement brightness increase and contrast improvement by forming a black film having a function of a microcavity and absorbing external light at the same time. CONSTITUTION: An organic light-emitting layer(402) is formed in the bottom of a reflective layer(401). A transparent electrode layer(403) is formed in the bottom of the organic light-emitting layer. A black micro cavity is formed in the bottom of the transparent electrode layer. The black micro cavity comprises a first metal layer(404), a dielectric layer(405), and the second metal layer(406). An external light is guided the inside through the substrate and is reflected from a reflective electrode layer, the first metal layer, and the second metal layer.

Description

Organic light emitting diode with black microcavity

The present invention relates to an organic light emitting diode, and more particularly, to an organic light emitting diode having increased brightness and improved contrast ratio.

Organic light emitting diodes are self-light emitting devices using organic light emitting materials that emit light when an electric field is applied. The organic light emitting diode includes a positive electrode and a negative electrode, and an organic light emitting layer formed therebetween. When a voltage is applied between the positive electrode and the negative electrode, holes are injected from the positive electrode into the organic light emitting layer, and electrons are injected from the negative electrode into the organic light emitting layer. Holes and electrons injected into the organic light emitting layer combine in the organic light emitting layer to generate excitons, and light is emitted as the excitons transition from the excited state to the ground state.

The front emission type organic light emitting diode uses a material that can reflect light to the positive electrode and a material that can transmit light to the negative electrode so that the light generated in the organic light emitting layer is effectively emitted to the front surface of the organic light emitting diode. However, when the positive electrode is composed of a material having excellent reflection characteristics, the problem of lowering the contrast ratio occurs. In other words, the external light flowing to the front surface is reflected from the positive electrode, and the contrast ratio is reduced. 1 is a view for explaining the reason why the contrast ratio is lower in the conventional front emission type organic light emitting diode. Referring to FIG. 1, a conventional front emission type organic light emitting diode includes a positive electrode 101 having excellent reflection characteristics, a negative electrode 103 having high light transmittance, an organic light emitting layer 102 and a glass substrate 104 formed between the positive electrode and the negative electrode. It includes. External light is introduced from the front surface of the front emission type organic light emitting diode, and the external light is reflected by the positive electrode 101 made of a material having excellent reflection characteristics and is emitted to the front surface again. 2 illustrates external light reflection characteristics of an organic light emitting diode including a positive electrode having excellent reflection characteristics. Referring to FIG. 2, in the case of the conventional front emission type organic light emitting diode, the reflectivity of light in the visible light region is nearly 60 to 70%. This externally reflected external light causes the pixels to be turned off to reflect a certain level of light, which lowers the contrast ratio and consequently degrades the performance of the display device.

One of the efforts to increase the contrast ratio in front emission organic light emitting diodes is the use of circular polarizers. 3 is a view for explaining a front emission type organic light emitting diode using a circular polarizer. Referring to FIG. 3A, the organic light emitting diode includes a positive electrode 101, a negative electrode 103, an organic light emitting layer 102, and a glass substrate 104, and a circular polarization layer on the entire surface of the glass substrate 104. 105 is formed. External light flowing from the front surface of the organic light emitting diode passes through the circular polarization layer 105 and is not reflected to the outside. Referring to FIGS. 3B and 3C, the circularly polarized layer 105 may include protective layers 105a and 105c, linearly polarized layer 105b, adhesive layers 105d and 105f, and quarter-wave layer 105e. ). In the process of passing the linear polarization layer, the external light passes only the polarization in a predetermined direction and does not pass through the polarization in the other direction. The polarized light passing through the linear polarized layer passes through the quarter wavelength layer and is reflected by the mirror. In the process, the direction of the polarized light is changed by 90 ° and thus cannot pass through the linear polarized layer. As such, the circularly polarized layer prevents external light from being reflected from the organic light emitting diode, thereby increasing the brightness and contrast ratio of the organic light emitting diode. However, since the organic light emitting diode using the circular polarizing layer has a transmittance of 40 to 45% of the linear polarizing layer, more than 50% of the light emitted from the organic light emitting layer is absorbed by the linear polarizing layer, and thus the luminance is lowered. Since the thickness of is also about 0.2mm thick to increase the overall thickness of the display device, there is a problem that it is difficult to fabricate the integrated device because an additional process is required.

Accordingly, an object of the present invention is to provide a front emission type organic light emitting diode capable of increasing the brightness of the organic light emitting diode and improving the contrast ratio.

The present invention includes a reflective electrode layer, an organic light emitting layer formed on the lower surface of the reflective electrode layer, a transparent electrode layer formed on the lower surface of the organic light emitting layer, and a black microcavity formed on the lower surface of the transparent electrode layer, the black The micro cavity provides an organic light emitting diode in which a first metal layer, a dielectric layer, and a second metal layer are sequentially stacked on a lower surface of the transparent electrode layer.

According to one embodiment of the invention, the reflectivity of the first metal layer is preferably higher than the reflectivity of the second metal layer.

According to another embodiment of the present invention, the absorbance of the first metal layer is preferably lower than the absorbance of the second metal layer.

According to another embodiment of the present invention, the first metal layer may be made of aluminum or silver, and the second metal layer may be made of chromium, molybdenum or titanium.

According to another embodiment of the present invention, the thicknesses of the first electrode layer, the dielectric layer, and the second electrode layer of the black microcavity may be set such that the light reflected from each of the first electrode layer, the dielectric layer, and the second electrode layer is caused to cancel each other. Can be.

According to another embodiment of the present invention, the thickness of the transparent electrode layer may be set so that light generated in the organic light emitting layer may resonate between the reflective electrode layer and the first metal layer.

According to another embodiment of the present invention, the reflective electrode layer may be made of aluminum or silver.

According to another embodiment of the present invention, the transparent electrode layer may be made of indium tin oxide.

In the organic light emitting diode of the present invention, since the light emitted from the organic light emitting layer resonates between the reflective electrode layer and the first metal layer, the intensity of light emitted to the front surface of the organic light emitting diode increases, thereby increasing the luminance. In addition, since the external light supplied to the front is canceled by the black micro-cavity to cancel the interference, the contrast ratio increases. As described above, the black microcavity applied to the present invention simultaneously implements the microcavity function of resonating the light emitted from the organic light emitting layer and the black film function of absorbing external light, thereby simultaneously achieving the effect of increasing the brightness and improving the contrast ratio. To help.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The organic light emitting diode of the present invention includes a reflective electrode layer, an organic light emitting layer formed on the lower surface of the reflective electrode layer, a transparent electrode layer formed on the lower surface of the organic light emitting layer, and a black microcavity formed on the lower surface of the transparent electrode layer, wherein the black microcavity is The first metal layer, the dielectric layer, and the second metal layer are sequentially stacked on the lower surface of the transparent electrode layer.

The organic light emitting diode of the present invention can implement a black film function that can improve the microcavity and the contrast contrast which can increase the luminance by the above structural features.

The microcavity traps light between the two reflective layers and causes repeated reflections to enhance the light intensity of a certain wavelength band and reduce the light intensity of another wavelength band. When the microcavity is applied to a front emission organic light emitting diode (OLED), luminance can improve luminous efficiency. That is, the light emitted from the organic light emitting layer of the organic light emitting diode is emitted to the outside of the display through the glass substrate without directivity. When two layers of highly reflective materials are formed on the both sides of the organic light emitting layer to form a microcavity structure, light resonance occurs and one side Intensified in the direction (front-facing of the display device). As a result, the luminance and luminous efficiency of the organic light emitting diode can be increased.

The black film is formed on the front surface of the organic light emitting diode to prevent external light from being reflected by the organic light emitting diode to lower the brightness and contrast ratio. In general, a factor that determines the contrast ratio of a display device is luminance reflectance. The clear contrast ratio is expressed by the following equation (1).

Equation 1

CR = (L _on + RdL _ambient ) / (L _off + RdL _ambient )

CR: Real contrast ratio

(L _on : brightness of full white

L _off : Luminance in black state

Rd: luminance reflectance

L _ambient : Luminance of external light)

According to Equation 1 above, in order to improve the contrast ratio, the luminance reflectance of the organic light emitting diode should be reduced. A front emission type organic light emitting diode is formed on the back of the organic light emitting layer with a material layer having excellent reflection properties to reflect the light generated from the organic light emitting layer to the front. When using a black film, the external light introduced into the organic light emitting diode is The contrast ratio is increased because it can be prevented from being reflected and emitted back to the front.

4 is a cross-sectional view of an organic light emitting diode of the present invention. Referring to FIG. 4, the organic light emitting diode includes a reflective electrode layer 401, an organic light emitting layer 402, a transparent electrode layer 403, a first metal layer 404, a dielectric layer 405, a second metal layer 406, and a substrate 407. ). When an electric field is applied between the reflective electrode layer 401 and the transparent electrode layer 403, light is generated in the organic light emitting layer 402, and a part of the generated light is emitted to the front surface without being reflected by the reflective electrode layer 401, and part of the reflection is reflected. Reflected by the electrode layer 401 is emitted to the front. In addition, external light is introduced into the inside through the substrate 407 and reflected by the reflective electrode layer 401, the first metal layer 404, and the second metal layer 406.

5 is a view for explaining the resonance of light caused by the microcavity and the extinction interference of external light by the black film in the organic light emitting diode of the present invention. Referring to FIG. 5A, light generated in the organic light emitting layer 402 is resonated by the reflective electrode layer 401 and the first metal layer 404. The light generated by the organic light emitting layer 402 is reflected by the reflective electrode layer 401 and the first metal layer 404 before being emitted to the front surface, and the light intensity of a specific wavelength band is enhanced and emitted to the front surface. At this time, in order for the light emitted from the organic light emitting layer 402 to be emitted to the front part of the organic light emitting diode as a result, the first metal layer should be formed in a relatively thin thickness so that the light can pass therethrough, and the reflective electrode layer has the light transmitted therethrough. It should be formed to a relatively thick thickness so as not to be possible. The reflective electrode layer may be made of a metal material such as aluminum or silver having excellent reflection characteristics. In the present invention, by adjusting the thickness of the transparent electrode layer 403 it is possible to adjust the wavelength band of the light intensity is enhanced. That is, by adjusting the thickness of the transparent electrode layer forming material having a constant refractive index, such as indium tin oxide, the wavelength band of the resonant light can be adjusted as desired. In addition, the color purity of the organic light emitting diode may be controlled by adjusting the thickness of the transparent electrode layer. Referring to FIG. 5B, the black microcavity of the present invention may be formed of the first metal layer 404, the dielectric layer 405, and the second metal layer 406, and may pass through a substrate made of a transparent material such as glass. One external light is reflected by the first metal layer 404 and the second metal layer 406. The thickness of the first electrode layer, the dielectric layer, and the second electrode layer may be adjusted such that external light reflected from the first metal layer 404 and the second metal layer 406 is extinguished and canceled out. As described above with reference to FIG. 4, most of the external light introduced into the organic light emitting diode is reflected by the first metal layer 404 and the second metal layer 406, and canceled by extinction interference, and up to the reflective electrode layer 401. Some supplied external light is also absorbed by the first metal layer and then disappears. Therefore, since the external light is hardly reflected by the organic light emitting diode, the brightness and contrast ratio is improved.

In order for the black microcavity applied to the organic light emitting diode of the present invention to simultaneously perform the functions of the microcavity and the black film, it is preferable that the physical properties of each layer constituting the black microcavity are controlled. First, in order to secure the microcavity function, it is advantageous that the first metal layer has a higher reflectance than the second metal layer. This is to cause the light generated in the organic light emitting layer to be reflected and resonate between the reflective electrode layer and the first metal layer. Next, looking at the physical properties of the first metal layer and the second metal layer for the function of the black film, it is advantageous that the absorbance of the first metal layer is relatively lower than the absorbance of the second metal layer. This is to effectively absorb the external light reflected from the inside of the organic light emitting diode in the second metal layer, and also relates to the light generated in the organic light emitting layer must effectively transmit the first metal layer. In consideration of the above characteristics, a metal material having high reflectivity and low absorbance, such as aluminum or silver, is preferably used as the first metal layer, and low reflectivity and high such as chromium, molybdenum or titanium are used as the second metal layer. Preferably, a metal material having absorbance is used. The dielectric layer disposed between the first metal layer and the second metal layer changes the phase of external light flowing into the organic light emitting diode to induce extinction interference. The first electrode layer, the dielectric layer, and the second layer of the black microcavity The material and thickness of the electrode layer should be set so that the light reflected from each of the first electrode layer, the dielectric layer, and the second electrode layer causes a destructive interference.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

Example 1-1

A 12 nm thick chromium (Cr) layer, a 40 nm thick silicon oxide (SiO ₂ ) layer, a 160 nm thick silver (Ag) layer, a 115 nm thick indium tin oxide layer, and an 140 nm thick organic light emitting layer And conditions for the organic light emitting diode on which an aluminum layer having a reflectance of 90% or more was formed, and simulations of wavelength versus luminance and external light reflectivity were performed.

Example 1-2

The simulation was performed under the same conditions as in Example 1-1 except that the thickness of the silver (Ag) layer was set to 18 nm.

Example 1-3

The simulation was performed under the same conditions as in Example 1-1 except that the thickness of the silver (Ag) layer was set to 20 nm.

Example 1-4

The simulation was performed under the same conditions as in Example 1-1 except that the thickness of the silver (Ag) layer was set to 22 nm.

Examples 1-5

The simulation was performed under the same conditions as in Example 1-1 except that the thickness of the silver (Ag) layer was set to 24 nm.

Example 1-6

The simulation was performed under the same conditions as in Example 1-1 except that the thickness of the silver (Ag) layer was set to 26 nm.

Example 1-7

The simulation was performed under the same conditions as in Example 1-3 except that the thickness of the chromium (Cr) layer was set to 10 nm.

Example 1-8

The simulation was performed under the same conditions as in Example 1-3 except that the thickness of the chromium (Cr) layer was set to 11 nm.

Example 1-9

The simulation was performed under the same conditions as in Example 1-3 except that the thickness of the chromium (Cr) layer was set to 13 nm.

Comparative Example 1-1

Except for applying the circularly polarized layer instead of the chromium (Cr) layer having a thickness of 12 nm, the silicon oxide (SiO ₂ ) layer having a thickness of 40 nm, the silver (Ag) layer having a thickness of 160 nm, and the indium tin oxide layer having a thickness of 115 nm. Then, the simulation was performed under the same conditions as in Example 1-1.

Comparative Example 1-2

Except that 12 nm chromium (Cr) layer, 40 nm thick silicon oxide (SiO ₂ ) layer, 160 nm thick silver (Ag) layer, and 115 nm thick indium tin oxide layer were not applied. The simulation was performed under the same conditions as in Example 1-1.

Evaluation example 1

The wavelength-to-luminance curves for Examples 1-1 to 1-4 and Comparative Example 1-1 were as shown in FIG. Referring to FIG. 6A, luminance of the organic light emitting diodes of Examples 1-1 to 1-4 was significantly increased as compared with the organic light emitting diode of Comparative Example 1-1. The numerical values in parentheses shown in the graph of FIG. 6A indicate relative luminance ratios or luminous efficiency ratios. In Examples 1-1 to 1-4, the thinner the thickness of the silver layer, the higher the luminance or the luminous efficiency. This result is because, in Comparative Example 1-1, much of the light generated in the organic light emitting layer is absorbed in the circularly polarized layer.

Evaluation example 2

Wavelength to external light reflectivity for Examples 1-2 to Examples 1-6 and Comparative Examples 1-2 were the same as in FIG. Referring to (b) of FIG. 6, the organic light emitting diodes of Examples 1-2 to 1-6 had significantly lower external light reflectance than the organic light emitting diode of Comparative Example, and the thicker the silver layer, the more external light reflectivity. Low.

Evaluation Example 3

The wavelength-to-luminance curves for Examples 1-3, Examples 1-7 to Examples 1-9, and Comparative Example 1-1 were as shown in FIG. Referring to (a) of FIG. 7, the organic light emitting diodes of Examples 1-3 and Examples 1-7 to 1-9 had a significantly higher luminance than the organic light emitting diodes of Comparative Example 1-1. The numerical values in parentheses shown in the graph of FIG. 7A indicate relative luminance ratios or luminous efficiency ratios. In Examples 1-3 and Examples 1-7 to 1-9, the thinner the chromium layer, the higher the luminance or the luminous efficiency. This result is because, in Comparative Example 1-1, much of the light generated in the organic light emitting layer is absorbed in the circularly polarized layer.

Evaluation example 4

Wavelength versus external light reflectivity for Examples 1-3, Examples 1-7 to Examples 1-9, and Comparative Examples 1-2 were as shown in FIG. Referring to FIG. 7B, the organic light emitting diodes of Examples 1-3 and Examples 1-7 to 1-9 had a significantly lower external light reflectivity than the organic light emitting diodes of Comparative Examples 1-2. The thicker the chromium layer, the lower the external light reflectivity.

Examining the simulation results as described above, the organic light emitting diode of the present invention can be seen that the luminance and luminous efficiency is significantly higher than when the circular polarization layer is applied, and the external light reflectivity is significantly lower than when the circular polarization layer is not applied. . As the thickness of the silver or chromium layer is thinner, the luminance increases and the thickness of the chromium layer tends to decrease the external light reflectivity. .

1 is a view for explaining the reason why the contrast ratio is lower in the conventional front emission type organic light emitting diode.

2 illustrates external light reflection characteristics of an organic light emitting diode including a positive electrode having excellent reflection characteristics.

3 is a view for explaining a front emission type organic light emitting diode using a circular polarizer.

4 is a cross-sectional view of an organic light emitting diode of the present invention.

5 is a view for explaining the resonance of light caused by the microcavity and the extinction interference of external light by the black film in the organic light emitting diode of the present invention.

6 shows wavelength versus luminance curves for Examples 1-1 to 1-4 and Comparative Example 1-1, and wavelengths versus external light for Examples 1-2 to Example 1-6 and Comparative Examples 1-2. The reflectance curve is shown.

7 shows wavelength versus luminance curves for Examples 1-3 and Examples 1-7 to 1-9 and Comparative Example 1-1, and Examples 1-3 and Examples 1-7 to 1- Wavelength versus external light reflectivity curves for 9 and Comparative Examples 1-2 are shown.

Claims (8)

Reflective electrode layer; An organic light emitting layer formed on a lower surface of the reflective electrode layer; A transparent electrode layer formed on a lower surface of the organic light emitting layer; And It includes a black micro cavity formed on the lower surface of the transparent electrode layer, The black microcavity is an organic light emitting diode formed by sequentially stacking a first metal layer, a dielectric layer, and a second metal layer on a lower surface of the transparent electrode layer. The method of claim 1, And the reflectivity of the first metal layer is higher than that of the second metal layer. The method of claim 1, The absorbance of the first metal layer is an organic light emitting diode, characterized in that lower than the absorbance of the second metal layer. The method of claim 1, The first metal layer is made of aluminum or silver, the second metal layer is an organic light emitting diode, characterized in that made of chromium, molybdenum or titanium. The method of claim 1, The thickness of the first electrode layer, the dielectric layer and the second electrode layer of the black micro-cavity is characterized in that the light reflected from each of the first electrode layer, the dielectric layer and the second electrode layer is set to cancel the interference. The method of claim 1, The thickness of the transparent electrode layer is an organic light emitting diode, characterized in that the light generated from the organic light emitting layer is set so as to resonate between the reflective electrode layer and the first metal layer. The method of claim 1, The reflective electrode layer is an organic light emitting diode, characterized in that made of aluminum or silver. The method of claim 1, The transparent electrode layer is an organic light emitting diode, characterized in that made of indium tin oxide.

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