TWI673898B - Light extraction substrate for organic light-emitting diode, method of fabricating the same, and organic light-emitting diode device including the same - Google Patents

Abstract

Provided are a light extraction substrate for an OLED, a method for manufacturing the same, and an organic light emitting diode device including the same. The light extraction substrate includes a base substrate and a scattering layer disposed on the base substrate. The scattering layer includes a mixture of a first metal oxide and a second metal oxide. The specific surface area of the second metal oxide is larger than that of the first metal oxide. The light extraction substrate significantly reduces the thickness of the planarization layer to improve the light extraction efficiency of the OLED device.

Description

Light extraction substrate for organic light emitting diode, method for manufacturing the same, and organic light emitting diode device including the same

The present disclosure relates to a light extraction substrate for an organic light-emitting diode (OLED), a method for manufacturing the same, and an organic light-emitting diode device including the same. More specifically, the present disclosure relates to a light extraction substrate for an OLED, a method of manufacturing the same, and an OLED device including the same, wherein the light extraction substrate may allow the thickness of a planarization layer to be significantly reduced, thereby improving the OLED device. Light extraction efficiency.

Generally speaking, light emitting diode devices can be generally classified into organic light emitting diode devices in which a light emitting layer is formed of an organic substance and inorganic light emitting diode devices in which a light emitting layer is formed of an inorganic substance. An organic light-emitting diode (OLED) in an organic light-emitting diode device is a self-light-emitting element that generates light using energy emitted by recombination of electrons injected from a cathode and holes injected from an anode. Such OLEDs have many advantages, such as driving with low voltage, self-emission, wide viewing angle, high resolution, natural color development, and low response time.

Recently, research has been actively applied to the application of OLEDs to various devices such as portable information devices, cameras, watches, office equipment, information display windows for vehicles, televisions (TVs), display devices, lighting devices, and the like.

A method for improving the light emitting efficiency of an OLED device includes a method of improving the light emitting efficiency of a material constituting the light emitting layer, and a method of improving the efficiency of extracting light generated by the light emitting layer.

Here, the light extraction efficiency is affected by the reflectivity of the layer forming the OLED device. In a conventional OLED, when a light beam generated by a light emitting layer is emitted at an angle greater than a critical angle, the light beam is between a higher refractive index layer that can be a transparent electrode layer and a lower refractive index layer that can be a substrate. The interface is totally reflected. This result reduces the light extraction efficiency, which in turn reduces the overall luminous efficiency of the OLED, thus causing problems.

Specifically, only about 20% of the light emitted by the OLED is emitted, and 80% of the light is due to the glass substrate and the OLED including the anode, the hole injection layer, the hole transport layer, the emission layer, the electron transport layer, and the electron injection layer. Waveguide effect caused by the difference in refractive index between them, and total reflection caused by the difference in refractive index between the glass substrate and the ambient atmosphere are lost. In addition, the refractive index of the internal organic light-emitting layer is in the range of 1.7 to 1.8, and the reflectance of indium tin oxide (ITO) commonly used in the anode is about 1.9. Since the two layers have a very small thickness ranging from 200 to 400 nm and the refractive index of the glass used for the substrate is about 1.5, a planar waveguide will be induced in the OLED device. The light loss ratio of the inner waveguide mode due to the above reasons is estimated to be 45%. In addition, since the refractive index of the glass substrate is 1.5 and the refractive index of the ambient atmosphere is 1, when light is directed outward from the inside of the glass substrate, a light beam having an incident angle greater than a critical angle will be totally reflected and trapped on the glass substrate internal. The proportion of trapped light is about 35%. Therefore, only about 20% of the generated light is emitted.

To solve the above problems, research is actively working on a light extraction layer that can extract 80% of the light, otherwise this light will be lost. The light extraction layer is generally divided into an internal light extraction layer and an external light extraction layer. As for the external light extraction layer, the light extraction efficiency can be improved by providing a film containing microlenses on the outer surface of the substrate, and the microlenses can have various shapes. In addition, since the internal light extraction layer can directly extract light lost in the light waveguide mode, the possibility of using the internal light extraction layer to improve the light extraction efficiency is greater than using the external light extraction layer. In this case, the light scattering effect of the inner light extraction layer can be maximized by mixing materials having different refractive indices, and then the inner light extraction layer is formed by using the mixed materials. However, the size of the scattering elements is therefore optically recognizable, and it is also necessary to mix these materials. In addition, for the life of the OLED, the surface of the internal light extraction layer on which the transparent electrode is disposed must be flat. Specifically, a scattering layer as an internal light extraction layer is inserted between the substrate and the transparent electrode, and the reliability of the transparent electrode is very important for the OLED. The unevenness of the transparent electrode, such as uneven sheet resistance, uneven thickness, or the presence of peaks due to the surface roughness of the internal light extraction layer, directly reduces the lifetime of the OLED. Therefore, the surface roughness of the internal light extraction layer is a factor that must be considered most carefully before forming a transparent electrode on the internal light extraction layer. Especially when the OLED is applied to a lighting device, the surface area of the OLED is an important factor. When the flatness of the transparent electrode cannot be ensured, the OLED may be deteriorated in a short time. Therefore, when an internal light extraction layer is used, a planarization layer needs to be provided between the internal light extraction layer and the transparent electrode. However, the conventional planarization layer is formed of a material having no scattering function. The planarization layer increases the distance from the light emitting layer to the internal light extraction layer. Therefore, the light transmitted by the dipole emission in the form of an evanescent wave will hardly reach the internal light extraction layer, thereby reducing the light extraction efficiency of the OLED device including the OLED.

FIG. 10 is a graph plotting a simulation result of the effect of the thickness of the planarization layer on the light extraction efficiency. The planarization layer is usually formed to have a thickness of 500 mm or more to obtain a desired flatness. In this case, the light extraction efficiency is reduced by an amount equivalent to 0.2 times or more compared to the case without a planarization layer. It should be noted that the simulation in FIG. 10 is performed by forming a planarization layer on the optimized internal light extraction layer. Under normal conditions, the reduction in light extraction efficiency caused by the thick planarization layer will be more serious.

The information disclosed in this background section only provides a better understanding of the background and should not be taken as an acknowledgement or any form of suggestion that this information constitutes prior art that is conventional to those skilled in the art.

Related patent documents

Patent Document 1: Korean Patent No. 10-0338332 (May 15, 2002)

Various embodiments of the present disclosure provide a light extraction substrate for an organic light emitting diode (OLED), a method of manufacturing the same, and an OLED device including the same, wherein the light extraction substrate may allow the thickness of the planarization layer to be significantly reduced, Then the light extraction efficiency of the OLED device is improved.

According to one aspect, a light extraction substrate for an OLED includes: a base substrate; and a scattering layer disposed on the base substrate. The scattering layer includes a mixture of a first metal oxide and a second metal oxide, and the specific surface area of the second metal oxide is larger than that of the first metal oxide.

The light extraction substrate may further include a capping layer disposed on the scattering layer, so that the capping layer is disposed between the scattering layer and the organic light emitting diode (OLED). The capping layer includes a third metal oxide, and its ratio is The surface area is greater than the specific surface area of the mixture of the first metal oxide and the second metal oxide.

The first to third metal oxides may have the same chemical composition.

Each of the first to third metal oxides may include rutile or anatase titanium dioxide.

The first metal oxide may include a first aggregate, the second metal oxide may include a second aggregate, and the third metal oxide may include a third aggregate. The crystal habit of the first polymer may be different from the second polymer and the third polymer, and the second polymer and the third polymer may have the same crystal habit.

According to another aspect, a method of manufacturing a light extraction substrate for an OLED includes: preparing a mixture by mixing a first metal oxide and a second metal oxide, and a specific surface area of the second metal oxide is greater than that of the first metal oxide Specific surface area of the object; and forming a scattering layer by coating the base substrate with the mixture.

According to yet another aspect, an OLED device includes the above-mentioned light extraction substrate on a path along which light generated by the OLED exits.

According to the disclosure, the cover layer is disposed between the scattering layer and the planarization layer to compensate the surface roughness of the scattering layer, thereby significantly reducing the thickness of the planarization layer. Therefore, this can minimize the distance between the OLED and the scattering layer, and then improve the light extraction efficiency of the OLED device.

In addition, since the cover layer is disposed between the scattering layer and the planarization layer, the flatness of the planarization layer can be improved, and the reliability of the OLED device can be obtained.

In addition, since the scattering layer is formed of titanium dioxide (TiO ₂ ) having a dendritic habit, a plurality of irregular holes capable of scattering light can be formed in the light scattering layer.

In addition, the light-scattering particles may be contained in a light-scattering layer and have a core-shell structure, where each core has a different refractive index from the shell. In particular, the core can be formed as a hollow, which can further improve the light extraction efficiency of the OLED device.

The methods and other features or advantages of the device disclosed in this disclosure will be obvious or explained in detail in the accompanying drawings and the following embodiments of the disclosure which are used to explain the specific principles of the disclosure.

Reference will now be made in detail to a light extraction substrate for an organic light emitting diode (OLED), a method of manufacturing the same, and an organic light emitting diode device including the same in accordance with this disclosure. An embodiment is shown in the drawings and described in detail The following is to enable those with ordinary knowledge in the technical field to which this disclosure belongs to easily implement this disclosure.

Throughout this document, reference is made to the accompanying drawings, in which the same component symbols will be used to identify the same or similar parts in different drawings. In the following description, a detailed description of conventional functions and components incorporated herein will be omitted when it is unclear which may make the subject matter of the present disclosure.

As shown in FIG. 1, a light extraction substrate 100 for an OLED according to an exemplary embodiment is a substrate disposed along a path where light emitted by the OLED 10 exits to enhance an OLED device including the OLED 10 Light extraction efficiency. The light extraction substrate 100 has a function of protecting the OLED 10 from an external environment. The OLED 10 can be used as a light source of a lighting device.

Although not specifically drawn, the OLED 10 has a multilayer structure of a transparent anode, an organic light emitting layer, and a cathode. The OLED 10 may be sandwiched between the light extraction substrate 100 and the back substrate facing the light extraction substrate 100 according to the present embodiment to encapsulate the OLED 10. The anode may be formed of a metal such as gold (Au), indium (In), or tin (Sn), or a metal oxide such as indium tin oxide (ITO), which has a large work function to facilitate hole injection into the organic light emitting layer. In addition, the cathode may be a metal thin film formed of aluminum (Al), aluminum: lithium (Al: Li), or magnesium: silver (Mg: Ag) with a smaller work function to promote electron injection into the organic light emitting layer. The organic light emitting layer may include a hole injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron injection layer sequentially stacked on the anode. When the OLED 10 is a white OLED for a lighting device, the emission layer may have a multilayer structure including, for example, a polymer emission layer that emits blue light and a low molecular emission layer that emits orange-red light. The emission layer may also have various other structures to emit white light. In addition, the OLED 10 may have a tandem structure. Specifically, when the OLEDs 10 are connected in series, a plurality of organic light-emitting layers may overlap with an interconnecting layer formed as a charge generation layer.

With this structure, when a forward voltage is applied between the anode and the cathode, electrons from the cathode migrate to the emission layer through the electron injection layer and the electron transport layer, and holes from the anode pass through the hole injection layer and the hole transport layer. Migration to the emission layer. The electrons and holes that migrate to the emission layer recombine with each other, thereby generating excitons. Light is emitted when an exciton transitions from an excited state to a ground state. The emitted light is proportional to the amount of current between the cathode and anode.

The light extraction substrate 100 for improving the light extraction efficiency of the OLED device may include a base substrate 110, a scattering layer 120, a cover layer 130, and a planarization layer 140. When the light extraction substrate 100 is disposed along the path of light emitted by the OLED 10, the scattering layer 120, the cover layer 130, and the planarization layer 140 form an internal light extraction layer (ILEL) for the OLED 10, and thus act To increase light extraction. This will be described in more detail below.

The base substrate 110 is a substrate on one surface of which the scattering layer 120, the cover layer 130, and the planarization layer 140 are supported. In addition, the base substrate 110 can also be used as a packaging substrate disposed along a path of light emitted by the OLED 10 to allow the generated light to exit therefrom and protect the OLED 10 from external environmental influences.

Any transparent substrate having excellent light transmittance and mechanical properties can be used as the base substrate 110. For example, the substrate 110 may be formed of a polymer material, such as a thermal or ultraviolet (UV) curable organic film. Alternatively, a chemically strengthened glass substrate formed of, for example, soda lime glass (SiO ₂ -CaO-Na ₂ O) or aluminosilicate glass (SiO ₂ -Al ₂ O ₃ -Na ₂ O) may be used as the base substrate 110. When the OLED device including the light extraction substrate 100 according to the present embodiment is applied to a lighting device, the base substrate 110 may be formed of soda lime glass. In addition, a substrate formed of a metal oxide or a metal nitride can be used as the base substrate 110. As the base substrate 110, a flexible substrate, more specifically, a thin glass substrate having a thickness of 1.5 mm or less can be used. A thin glass substrate can be manufactured using a fusion process or a floating process.

The scattering layer 120 scatters the light emitted by the OLED 10 to interfere with the optical waveguide mode, that is, to change the path of the light generated by the OLED 10, thereby improving the light extraction efficiency of the OLED device. The scattering layer 120 is formed on the base substrate 110. The thickness of the scattering layer 120 may range from 0.4 ㎛ to 5 ㎛. When the light extraction substrate 100 is applied to the OLED 10, the scattering layer 120 is disposed between the OLED 10 and the base substrate 110.

The scattering layer 120 includes a mixture of a first metal oxide and a second metal oxide. The first and second metal oxides may have the same chemical composition, such as titanium dioxide (TiO2). In addition, the first metal oxide and the second metal oxide may be titanium dioxide (TiO ₂ ) in a rutile phase or an anatase phase. Preferably, the first and second metal oxides are both rutile TiO ₂ . The first metal oxide has a smaller specific surface area than the second metal oxide. The first metal oxide may include a first polymer, and the second metal oxide may include a second polymer. Even when the first polymer and the second polymer have the same chemical composition and the same crystal phase, the specific surface areas of the first polymer and the second polymer are different. This is because the crystal habit of the first polymer is different from that of the second polymer. For example, the first metal oxide may include a first polymer having a dendritic habit and have a specific surface area of about 30.4 m ² / g. The second metal oxide may include a second polymer having a rod-like crystal habit, and have a specific surface area of about 92.8 m ² / g. In this case the specific surface area, the scattering layer 120 is formed of a mixture according to the ratio of the first metal oxide and second metal oxide may be greater than 30.4m ² / g and less than 92.8m ² / g. The specific surface area was measured using a gas adsorption analyzer (Macsorb HM Model-1208).

Titanium dioxide nano particles having a size of 30 to 50 nm can be polymerized to form a first polymer, and titanium dioxide nano particles having a size of 30 to 50 nm can be polymerized to form a second polymer. Referring to the dimensional analysis result shown in FIG. 6, the size of the first polymer may be 0.04 ㎛ to 2.7 ㎛. Referring to the size analysis result shown in FIG. 7, the size of the second polymer may be 0.035 ㎛ to 2.7 ㎛. The size of the first polymer and the second polymer was measured using a particle size analyzer (Malvern Mastersizer 2000). However, as described above, the polymerization processes of the first polymer and the second polymer are different, so the shapes of the first polymer and the second polymer are also different.

When the materials of the first polymer and the second polymer, that is, the scattering layer 120 have different shapes as described above, the light scattering effect of the scattering layer 120 can be maximized.

Although not specifically shown, the scattering layer 120 may include a plurality of holes as the first light scattering element. The scattering layer 120 contains dendritic titanium dioxide and therefore has a porous structure. That is, the scattering layer has a plurality of holes having a size capable of scattering light. During firing of the scattering layer 120 containing dendritic titanium dioxide, holes having a refractive index of 1 are formed in the scattering layer without any additional hole forming process. That is, dendritic titanium dioxide induces the formation of a plurality of holes. Because the titanium dioxide polymers of the first metal oxide and the second metal oxide have different shapes, that is, dendritic and rod-shaped, respectively, the holes occupying the space between the polymers can be formed into different shapes, so that the light The scattering effect is maximized.

In addition, the scattering layer 120 may further include a plurality of light scattering particles as the second light scattering element. The size of the primary particles of the plurality of light scattering particles may be in a range of 10 to 500 nm. In addition, a plurality of light scattering particles may be provided in a lower portion of the inside of the scattering layer 120 facing the base substrate 110. The plurality of light scattering particles coordinate with the plurality of holes to form a relatively complex light scattering structure. The plurality of light scattering particles may be mixed with the rutile titanium dioxide of the scattering layer 120, and then the mixture may be applied to the base substrate 110 so that the plurality of light scattering particles are arranged or disposed on the base substrate 110. Alternatively, before the scattering layer 120 is formed, a plurality of light scattering particles may be disposed on the base substrate 110 separately from the formation of the scattering layer 120, and then the scattering layer 120 may be covered.

The light scattering particles may be selected from a candidate group of metal oxides, such as one or two of silicon dioxide (SiO ₂ ), titanium dioxide (TiO ₂ ), zinc oxide (ZnO), and tin dioxide (SnO ₂ ), or A combination of two or more. In addition, the light scattering particles may include at least two portions having different refractive indexes. For example, light scattering particles may have a core-shell structure, where the core and the shell have different refractive indices. The core may be formed as a hollow, and the shell may be formed of a material having a refractive index of 1.5 to 2.7. When light-scattering particles are formed into such a core-shell structure, the refractive index difference between the core and the shell can further improve the ability to extract light generated by the OLED.

In addition, the plurality of light scattering particles may include a mixture of this core-shell structure particle and a simple particle having a single overall refractive index.

The rutile titanium dioxide of the scattering layer 120 is a high-refractive index metal oxide, and its refractive index ranges from 2.5 to 2.7. When a plurality of holes having a refractive index of 1 and a plurality of light scattering particles having a refractive index different from the pores are mixed with the rutile titanium dioxide in the scattering layer 120, a complex refractive index structure can be formed, such as high / low refractive index Structure or high / low / high refractive index structure. When such a complex refractive index structure is provided along a path where light generated by the OLED 10 is extracted, light generated by the OLED 10 can be extracted through a variety of paths, thereby maximizing the extraction of light generated by the OLED 10 ability.

The cover layer 130 is disposed on the scattering layer 120. In addition, the cover layer 130 is disposed between the scattering layer 120 and the planarization layer 140. The cover layer 130 may be formed of a third metal oxide, and the specific surface area of the third metal oxide is larger than that of the mixture of the first metal oxide and the second metal oxide of the scattering layer 120. The first to third metal oxides may have the same chemical composition. The third metal oxide contains a third polymer. The crystal habit of the third polymer may be different from the crystal habit of the first polymer, and may be the same as the crystal habit of the second polymer. That is, the cover layer 130 may be formed of a rod-shaped polymer of titanium dioxide of rutile or anatase. Therefore, the third aggregate filled in the cover layer 130 is denser than the mixture of the first polymer and the second polymer filled in the scattering layer 120, and thus the porosity of the cover layer 130 is smaller than that of the scattering layer 120. . The size of the pores is 10 to 500 nm, and the scattering layer 120 and the cover layer 130 have a porosity of 1 to 40%. The porosity can be measured using FIB (Focused Ion Beam), and the size of the hole indicates the length of the longest diameter of the hole. The third polymer forming the cover layer 130 may have a size similar to that of the second polymer of 0.035 to 2.7 ㎛. In addition, the cover layer 130 may be formed on the scattering layer 120 to have a thickness ranging from 50 nm to 200 nm. When the scattering layer 120 is coated with a cover layer 130 formed of the same type of titanium dioxide as the scattering layer 120, that is, rutile or anatase titanium dioxide, preferably rutile titanium dioxide, the advantage of good coating performance can be achieved. In addition, when the cover layer 130 is formed of the same rutile titanium dioxide as the scattering layer 120, both layers have the same refractive index. Due to the additional scattering at the interface between the cover layer 130 and the scattering layer 120, variables may be removed to make prediction of the optical path difficult. If the cover layer 130 is formed of anatase titanium dioxide, its refractive index may be different from that of the scattering layer 120. Therefore, when it is necessary to predict the optical path, it is preferable that the cover layer 130 is formed of rutile titanium dioxide so that its refractive index is the same as that of the scattering layer 120.

According to the present embodiment, the cover layer 130 is disposed between the scattering layer 120 and the planarization layer 140 to reduce the thickness of the planarization layer 140. In the conventional technique, the thickness of the planarization layer is usually set to 500 nm or more to obtain a desired flatness. In this case, as shown in FIG. 10, the light extraction efficiency is reduced to an amount equivalent to 0.2 times the degree of light extraction efficiency obtained without the planarization layer 140. This means that the thinner the planarization layer 140 is, the higher the light extraction efficiency is. Since the thickness of the planarizing layer 140 is determined by the surface roughness of the scattering layer 120, in order to reduce the thickness of the planarizing layer 140, the surface of the scattering layer 120 must be less rough than when the thickness of the planarizing layer is 500 nm or more. According to the present embodiment, the cover layer 130 is used to reduce the surface roughness of the scattering layer 120. Since the surface roughness of the cover layer 130 is lower than that of the scattering layer 120, the thickness of the planarization layer 140 can be significantly reduced.

The planarization layer 140 is disposed on the cover layer 130. The planarizing layer 140 functions in coordination with the scattering layer 120 and the cover layer 130 to form an internal light extraction layer for the OLED 10. The surface of the planarization layer 140 is adjacent to the OLED 10, and more specifically, is adjacent to the anode of the OLED 10. When the surface of the planarization layer 140 is adjacent to the anode of the OLED, the surface of the planarization layer 140 must have a high degree of flatness to prevent the electrical characteristics of the OLED 10 from being deteriorated. In this regard, the cover layer 130 can make the planarization layer 140 thin, while the conventional planarization layer requires a thickness of 500 nm or more or 800 nm or more. According to the present embodiment, since the cover layer 130 is disposed on the scattering layer 120 in a thickness range of 50 nm to 200 nm, the thickness of the planarization layer 140 may be in a range of 100 nm to 300 nm. As shown in FIG. 10, when the thickness of the planarization layer 140 is reduced to this range, it can be observed that the light extraction efficiency of the OLED device is improved by an amount equivalent to 0.2 times or more.

In order to maximize the light extraction efficiency of the OLED device, the planarization layer 140 may be formed of a material having a refractive index different from that of the cover layer 130. In addition, when the cover layer 130 and the scattering layer 120 are formed of the same rutile titanium dioxide, the cover layer 130 and the scattering layer 120 have the same refractive index. In this case, there is also a difference in refractive index between the planarizing layer 140 and the scattering layer 120 due to the same amount between the planarizing layer 140 and the cover layer 130. The planarization layer 140 may be formed of an organic material, an inorganic material, or a mixed material of organic and inorganic materials. Polydimethylsiloxane (PDMS) having a refractive index of 1.3 to 1.5 can be used as an organic material. The planarization layer 140 may also be selected from metal oxides having a refractive index of 1.7 to 2.7, such as magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium dioxide (ZrO ₂ ), and tin dioxide (SnO ₂ ), Zinc oxide (ZnO), silicon dioxide (SiO ₂ ) or titanium dioxide (TiO ₂ ), and a high refractive index polymer, but since the scattering layer 120 and the cover layer 130 are made of titanium dioxide (TiO ₂ ), So the refractive index of the material must be lower than that of titanium dioxide (TiO ₂ ). When the inner light extraction layer of a multilayer structure in which layers having different refractive index layers are stacked on each other is provided along a path in which light generated by the OLED 10 is emitted, different refractive indexes of the inner light extraction layer can improve the OLED device. Light extraction efficiency.

As described above, the light extraction substrate 100 for OLED according to the present embodiment includes the cover layer 130 between the scattering layer and the planarization layer 140, and the cover layer 130 can significantly reduce the thickness of the planarization layer 140.

Table 1 below shows the measurement results of the surface roughness of the flattening layer using an atomic force microscope (AFM) based on the presence of the cover layer and the thickness of the cover layer.

Table 1

As shown in the electron microscope image in FIG. 2, Comparative Example 1 shows the surface roughness of a flattened layer having a thickness of 0.86 形成 on a scattering layer having a thickness of 1.21 ㎛. As shown in the electron microscope image in FIG. 3, Example 1 of the present invention shows the surface roughness of a flattening layer having a thickness of 100 nm formed on a scattering layer having a thickness of 1.02 ㎛ and a cover layer having a thickness of 100 nm. As shown in the electron microscope image in FIG. 4, Example 2 of the present invention shows the surface roughness of a flattening layer having a thickness of 200 nm formed on a scattering layer having a thickness of 1.2 ㎛ and a cover layer having a thickness of 100 nm.

Referring to Table 1 described above, in Comparative Example 1, the surface roughness Rmax of the planarization layer was measured to be 139.1. In Example 1 of the present invention, the thickness of the planarization layer was reduced to 1/8 of Comparative Example 1, and the surface roughness Rmax of the planarization layer was measured to be 162.5 nm. Although the thickness of Example 1 of the present invention was significantly reduced, it was observed that the surface roughness Rmax of the planarization layer was not significantly different from the surface roughness Rmax of Comparative Example 1. In Example 2 of the present invention, the planarization layer was reduced to 1/4 of Comparative Example 1, and the surface roughness Rmax of the planarization layer was measured to be 79.4 nm. As can be seen from Examples 1 and 2 of the present invention, when a cover layer is formed between the scattering layer and the planarization layer, an excellent surface roughness can be obtained even in the case of forming a thin planarization layer. It is obvious that the cover layer can significantly reduce the thickness of the planarization layer. When the thickness of the planarization layer is reduced, the distance between the OLED and the scattering layer can also be reduced, thereby further improving the light extraction efficiency of the OLED device. In fact, in the case where the internal light extraction layer having a multilayer structure of a scattering layer and a planarization layer is disposed in front of the OLED, the measured amount of improved light extraction efficiency is equivalent to 1.5 times that in the case where no internal light extraction layer is provided . In addition, in the case where the internal light extraction layer having a multilayer structure including a scattering layer, a cover layer, and a planarization layer is provided in front of the OLED, and thus the distance between the scattering layer and the OLED is reduced, the improved light extraction efficiency is measured The amount is equivalent to 1.8 times in the case where an internal light extraction layer is not provided.

In addition, it can be observed that when the cover layer is disposed between the scattering layer and the planarization layer, in some cases, better flatness can be obtained than in the case where a thicker planarization layer is provided without the cover layer. The greater the flatness of the planarization layer, the higher the reliability of the OLED may be.

Hereinafter, a method of manufacturing a light extraction substrate for an OLED according to an exemplary embodiment will be described with reference to FIG. 5. Regarding the component symbols of the components of the light extraction substrate, reference will be made to the component symbols in FIG. 1.

FIG. 5 is a flowchart illustrating a method of manufacturing a light extraction substrate for an OLED according to an exemplary embodiment.

As shown in FIG. 5, the method for manufacturing a light extraction substrate for OLED according to this embodiment includes a hybrid preparation step S1, a scattering layer formation step S2, a cover layer formation step S3, and a planarization layer formation step S4.

Two types of titanium oxide (TiO ₂₎ mixture is first prepared, the mixture prepared at step S1, by mixing with different specific surface areas of dispersed liquid. For example, the first dispersion liquid is prepared by dispersing rutile or anatase titanium dioxide (TiO ₂ ), preferably rutile titanium dioxide (TiO ₂ ) having a dendritic habit in a first organic solvent. Preferably, the rutile titanium dioxide (TiO ₂ ) is dispersed in the first organic solvent in an amount of 5% to 60% by weight. Preferably, H ₂ O is used as the first organic solvent. As shown in the electron microscope image of FIG. 8, a dendritic titanium dioxide (TiO ₂ ) polymer is present in the first dispersion liquid produced through the operation of preparing the first dispersion liquid. In addition, in the mixture preparation step S1, by dispersing rutile or anatase titanium dioxide (TiO ₂ ), preferably rutile titanium dioxide (TiO ₂ ) having a rod-shaped crystal habit is dispersed in the second organic solvent. A second dispersion is prepared, and the specific surface area of the redstone titanium dioxide (TiO ₂ ) dispersed in the second organic solvent is larger than that of the rutile titanium dioxide (TiO ₂ ) dispersed in the first organic solvent. Preferably, the rutile titanium dioxide (TiO ₂ ) is dispersed in the second organic solvent in an amount of 5% to 60% by weight. Preferably, ethanol (EtOH) is used as the second organic solvent. As shown in the electron microscope image of FIG. 9, a rod-shaped titanium dioxide (TiO ₂ ) polymer is present in the second dispersion liquid produced by the operation of preparing the second dispersion liquid. As described above, the mixture preparation step S1 can prepare the mixture dispersion by mixing the first dispersion liquid produced by the operation of preparing the first dispersion liquid and the second dispersion liquid produced by the operation of preparing the second dispersion liquid. In the mixture preparation step S1, a plurality of light scattering particles may be mixed in the mixture dispersion.

Then, in the scattering layer forming step S2, the scattering layer 120 is formed by applying the mixture dispersion liquid to the base substrate 110. In the scattering layer forming step S2, the scattering layer 120 may be formed by a coating method, such as bar coating, slit die coating, spin coating, or dipping. The scattering layer 120 may be formed to have a thickness ranging from 0.4 ㎛ to 5 ㎛. A plurality of holes are formed in the inside of the scattering layer 120 without any additional operation, and the plurality of light scattering particles mixed in the mixed dispersion liquid in the mixing preparation step S1 are preferably disposed at the bottom of the scattering layer 120.

Next, in the cover layer forming step S3, the cover layer 130 is formed by coating the scattering layer 120 with a third dispersion liquid produced by dispersing titanium dioxide (TiO ₂ ) having a relatively large specific surface area in an organic solvent, for example, The second dispersion liquid produced by the operation of preparing the second dispersion liquid (that is, the second dispersion liquid can be used as the third dispersion liquid). In the cover layer forming step S3, the cover layer 130 may be formed by a coating method, such as bar coating, slit die coating, spin coating, or dipping. The cover layer 130 may be formed to have a thickness ranging from 50 nm to 200 nm.

Finally, in the planarization layer forming step S4, a planarization layer 140 is formed on the cover layer 130. The planarization layer 140 may be formed by a coating method, such as a bar coating, a slit die coating, a spin coating, or a dipping. Since the cover layer 130 is formed on the scattering layer 120, the planarization layer 140 may be formed to have a thin thickness ranging from 100 nm to 300 nm.

When the planarization layer forming step S4 is completed, a light extraction substrate 100 for an OLED is manufactured, wherein the distance between the OLED 10 and the scattering layer 120 is minimized due to a significant reduction in the thickness of the planarization layer 140.

The foregoing descriptions of specific exemplary embodiments of the present disclosure have been presented in conjunction with the accompanying drawings. It is not intended to be exhaustive or to limit the precise form disclosed in this disclosure, and it is obvious that many modifications and changes may be made by those having ordinary knowledge in the technical field to which this disclosure pertains in light of the above teachings.

Therefore, the scope of this disclosure is not limited to the foregoing embodiments, but is defined by the scope of the attached patent applications and their equivalents.

10‧‧‧OLED

100‧‧‧light extraction substrate

110‧‧‧ base substrate

120‧‧‧ scattering layer

130‧‧‧ Overlay

140‧‧‧ flattening layer

S1‧‧‧ Mixture preparation steps

S2‧‧‧Scattering layer formation steps

S3‧‧‧ Overlay formation step

S4‧‧‧Plane formation step

FIG. 1 is a cross-sectional view of an OLED device including a light extraction substrate disposed along a path where light generated by the OLED is emitted according to an exemplary embodiment; FIG.

FIG. 2 is an electron microscope image of a cross section of a light extraction substrate for OLED according to Comparative Example 1;

FIG. 3 is an electron microscope image of a cross section of a light extraction substrate for an OLED according to Example 1;

FIG. 4 is an electron microscope image of a cross section of a light extraction substrate for an OLED according to Example 2;

FIG. 5 is a flowchart illustrating a method of manufacturing a light extraction substrate for an OLED according to an exemplary embodiment; FIG.

Figure 6 is a graph plotting the results of analyzing the size of the polymer of the first metal oxide;

FIG. 7 is a graph plotting the results of analyzing the sizes of the polymer of the second metal oxide and the third metal oxide;

FIG. 8 is an electron microscope image of a first dispersion liquid used in a method for manufacturing a light extraction substrate for an OLED;

FIG. 9 is an electron microscope image of a second dispersion liquid used in a method for manufacturing a light extraction substrate for an OLED;

FIG. 10 is a graph plotting simulation results of the effect of the thickness of the planarization layer on the light extraction efficiency.

Claims (40)

A light extraction substrate for an organic light emitting diode includes: a base substrate; and a scattering layer disposed on the base substrate. The scattering layer includes a first metal oxide and a second metal oxide. A mixture, the specific surface area of the second metal oxide is greater than the specific surface area of the first metal oxide, wherein the first metal oxide includes a first polymer, and the second metal oxide includes a second polymer, The first polymer is different from the second polymer, wherein the first polymer has a dendritic crystal habit and the second polymer has a rod crystal habit. The light extraction substrate according to item 1 of the patent application scope further includes a cover layer disposed on the scattering layer, so that the cover layer is disposed between the scattering layer and an organic light emitting diode, and the cover The layer includes a third metal oxide having a specific surface area larger than the mixture of the first metal oxide and the second metal oxide. The light extraction substrate according to item 2 of the scope of the patent application, wherein the first metal oxide to the third metal oxide have the same chemical composition. The light extraction substrate according to item 3 of the scope of patent application, wherein the first metal oxide to the third metal oxide have the same refractive index. The light extraction substrate according to item 3 of the scope of the patent application, wherein the first metal oxide to the third metal oxide have the same crystal phase. The light extraction substrate according to item 3 of the scope of the patent application, wherein each of the first metal oxide to the third metal oxide includes titanium dioxide in a rutile phase or an anatase phase. The light extraction substrate according to item 3 of the scope of patent application, wherein the third metal oxide includes a third polymer, and the first polymer and the third polymer have different crystal habit, and the second polymer And this third polymer has the same crystal habit. The light extraction substrate according to item 1 of the scope of patent application, wherein the size of the first polymer is between 0.04 μm and 2.7 μm. The light extraction substrate according to item 7 of the patent application scope, wherein the third polymer has a rod crystal habit. The light extraction substrate according to item 9 of the scope of the patent application, wherein the size of the second polymer and the third polymer is between 0.035 μm and 2.7 μm. The light extraction substrate according to item 7 of the scope of the patent application, wherein the first polymer and the second polymer are filled in the scattering layer, so that the scattering layer generates pores; and the third polymer is filled in the The cover layer makes the cover layer porous. The light extraction substrate according to item 11 of the application, wherein the porosity of the scattering layer and the cover layer is between 1% and 40%. The light extraction substrate according to item 11 of the application, wherein the size of the pores generated in the scattering layer and the size of the pores generated in the cover layer are between 10 nm and 500 nm. The light extraction substrate according to item 11 of the scope of patent application, wherein the third polymer filled in the cover layer is more densely packed than the first polymer and the second polymer filled in the scattering layer, so the The porosity of the scattering layer is greater than the porosity of the cover layer. The light extraction substrate according to item 11 of the patent application scope, wherein the scattering layer is more Contains a number of light scattering particles. The light extraction substrate according to item 15 of the scope of the patent application, wherein each of the plurality of light scattering particles includes at least two parts, and the at least two parts have different refractive indexes. The light extraction substrate according to item 16 of the scope of the patent application, wherein the at least two parts include a core and a shell surrounding the core, and the shell has a different refractive index from the core. The light extraction substrate according to item 17 of the scope of the patent application, wherein the core is hollow. The light extraction substrate according to item 17 of the scope of patent application, wherein the refractive index of the shell is between 1.5 and 2.7. The light extraction substrate according to item 2 of the patent application range, wherein the thickness of the cover layer is between 50 nm and 200 nm. The light extraction substrate according to item 2 of the patent application scope, further comprising a planarization layer disposed on the cover layer, so that the planarization layer is disposed between the cover layer and the organic light emitting diode. The light extraction substrate according to item 21 of the patent application scope, wherein a surface roughness (Ra) of the planarization layer is smaller than a surface roughness (Ra) of each of the scattering layer and the cover layer. The light extraction substrate according to item 21 of the scope of patent application, wherein the thickness of the planarization layer is between 100 nm and 300 nm. The light extraction substrate according to item 21 of the application, wherein the refractive index of the planarization layer is different from the refractive index of the cover layer. The light extraction substrate as described in claim 24, wherein the planarization layer includes one of an organic material, an inorganic material, and a mixed material of organic and inorganic materials. The light extraction substrate according to item 24 of the application, wherein the planarization layer is formed of a material having a refractive index between 1.3 and 2.7. The light extraction substrate according to item 21 of the patent application scope, wherein the scattering layer, the cover layer, and the planarization layer are disposed between the base substrate and the organic light emitting diode to form the organic light emitting diode. An internal light extraction layer of the polar body. The light extraction substrate according to item 1 of the scope of patent application, wherein the thickness of the scattering layer is between 0.4 μm and 5 μm. The light extraction substrate according to item 1 of the patent application scope, wherein the base substrate comprises a flexible substrate. The light extraction substrate according to item 29 of the patent application scope, wherein the base substrate comprises a thin glass plate having a thickness of 1.5 mm or less. An organic light-emitting diode device including a light extraction substrate according to any one of the first to the thirtieth of the patent application scope along the path of light emitted by the organic light-emitting diode. A method for manufacturing a light extraction substrate for an organic light emitting diode, comprising: preparing a mixture by mixing a first metal oxide and a second metal oxide, wherein a specific surface area of the second metal oxide is greater than the A first metal oxide; and coating a base substrate with the mixture to form a scattering layer, wherein the first metal oxide includes a first polymer, and the second metal oxide includes a second polymer, the first The polymer is different from this second polymer, Wherein the first polymer has a dendritic crystal habit and the second polymer has a rod crystal habit. The method according to item 32 of the scope of patent application, wherein the first metal oxide and the second metal oxide have the same chemical composition. The method according to item 32 of the scope of patent application, wherein the preparing step of the mixture comprises: preparing a first dispersion liquid by dispersing the first metal oxide into a first organic solvent; and Dispersing the second metal oxide into a second organic solvent to prepare a second dispersion; and mixing the first dispersion and the second dispersion to prepare the mixture. The method as described in claim 34, wherein in the operation for preparing the first dispersion, the first metal oxide is dispersed in the first organic solvent in an amount of 5 to 60% by weight, and In the operation of preparing the second dispersion liquid, the second metal oxide is dispersed in the second organic solvent in an amount of 5 to 60% by weight. The method as described in claim 34, wherein each of the first metal oxide and the second metal oxide comprises rutile or anatase titanium dioxide, the first organic solvent comprises H ₂ O, and The second organic solvent contains EtOH. The method as described in claim 32, wherein during the step of forming the scattering layer, the base substrate is coated with the mixture so that the thickness of the scattering layer is between 0.4 μm and 5 μm. The method according to item 32 of the patent application scope, further comprising a step of dispersing the second metal oxide in an organic solvent after the step of forming the scattering layer. The dispersion liquid coats the scattering layer to form a cover layer. The method of claim 38, wherein during the step of forming the cover layer, the scattering layer is coated with the dispersion so that the thickness of the cover layer is between 50 nm and 200 nm. The method according to item 38 of the patent application scope, further comprising, after the step of forming the cover layer, forming a planarization layer on the cover layer so that the thickness of the planarization layer is between 100 nm and 300 nm.