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

Abstract

A light extraction substrate for an organic light emitting device. A light scattering layer 121 disposed on a base substrate 110 comprises a first material and includes a first surface facing the base substrate, a second surface opposite to the first surface, and a plurality of holes 121a extending between the first surface and the second surface. A planarization layer 123 is disposed on the light scattering layer 121 and comprises a second material. The refractive index of the first material and the second material is in the range of 1.8 to 2.6. When measured on a plane perpendicular to the thickness direction of the light scattering layer 121, the diameter of the hole 121a is in the range of 350nm to 450nm. The ratio of the area occupied by the plurality of holes in the first surface to the area of ​​the first surface is at least 40%. The thickness of the planarization layer is 200nm or less.

Description

background Technical Field

[0001] This application claims the benefit of priority to Korean Patent Application Serial No. 10-2018-0060322, filed on May 28, 2018, the contents of which are hereby relied upon and incorporated herein in their entirety as if fully set forth below.

[0002] The present disclosure relates to a light extraction substrate of an organic light emitting device and a method for manufacturing the same, and more particularly, to a light extraction substrate of an organic light emitting device that can significantly improve light extraction efficiency and a method for manufacturing the same.

[0003] Related technical notes

[0004] For a variety of reasons, light generated by an organic light-emitting device, including an organic light-emitting diode (OLED), may be trapped in the organic light-emitting device, thereby limiting the luminous efficiency of the organic light-emitting device to a range of 20% to 30%. The refractive index of the organic layer and / or the transparent electrode is 1.8 to 1.9, which is higher than the refractive index of the surrounding glass base substrate or air. Therefore, a portion of the light may be trapped in the organic layer. In addition, the "plasmon waveguide" occurring in the metal electrode may cause light loss. In addition, total internal reflection may cause light to be trapped in the glass base substrate, which is called a "substrate mode." As a method of improving light extraction efficiency by overcoming the optical waveguide, a light extraction layer that can scatter light is introduced between the transparent electrode and the glass base substrate. Generally speaking, the light extraction layer located between the transparent substrate and the OLED is called an internal light extraction layer.

[0005] The light extraction layer of the related art is a film in which light scattering elements (such as holes or particles) with a size of tens of nanometers to several microns arranged in three dimensions (3D) are distributed. For the light extraction layer of the related art, precise design may be required, and several complex steps must be taken to manufacture. Since the light scattering elements can be distributed in a 3D arrangement, the light extraction layer of the related art may have extremely low light scattering efficiency, or even worse, if the light scattering elements are distributed in a single layer, the height of the light extraction layer may be uneven. Considering the structure of the light extraction layer of the related art and the refractive index of the film, it may be difficult to significantly improve the light extraction efficiency. Summary of the invention

[0006] According to one aspect of the present disclosure, a light extraction substrate of an organic light-emitting device may include: a base substrate; a light scattering layer, which is disposed on the base substrate and includes a first material, the light scattering layer includes a first surface facing the base substrate, and a second surface opposite to the first surface, a plurality of holes are formed in the light scattering layer, each of the plurality of holes extends between the first surface and the second surface; and a planarization layer, which is disposed on the light scattering layer and includes a second material. The refractive index of the first material and the second material may be in the range of 1.8 to 2.6. When measured on a plane perpendicular to the thickness direction of the light scattering layer, the diameter of the plurality of holes may be in the range of 350nm to 450nm. The ratio of the area occupied by the plurality of holes in the first surface to the area of ​​the first surface may be at least 40%. The thickness of the planarization layer may be 200nm or less.

[0007] According to another aspect of the present disclosure, an organic light-emitting device may include: a base substrate; a light scattering layer, which is disposed on the base substrate and includes a first material, the light scattering layer includes a first surface facing the base substrate, and a second surface opposite to the first surface, a plurality of holes are formed in the light scattering layer, each of the plurality of holes extends between the first surface and the second surface; a planarization layer, which is disposed on the light scattering layer and includes a second material; an anode electrode layer disposed on the planarization layer; an organic layer disposed on the anode electrode layer; and a cathode electrode layer disposed on the organic layer. The refractive index of the first material and the second material may be in the range of 1.8 to 2.6. When measured on a plane perpendicular to the thickness direction of the light scattering layer, the diameter of the plurality of holes may be in the range of 350nm to 450nm. The ratio of the area occupied by the plurality of holes in the first surface to the area of ​​the first surface may be at least 40%. The thickness of the planarization layer may be 200nm or less.

[0008] According to another aspect of the present disclosure, a method for manufacturing a light extraction substrate for an organic light-emitting device may include: forming a light scattering layer on a base substrate to form a plurality of holes in the light scattering layer, the light scattering layer comprising a first material and comprising a first surface facing the base substrate, and a second surface opposite to the first surface, each of the plurality of holes extending between the first surface and the second surface; forming a planarization layer on a support, the planarization layer comprising a second material; combining the planarization layer with the light scattering layer; and removing the support from the planarization layer.

[0009] According to another aspect of the present disclosure, a method for manufacturing a light extraction substrate for an organic light-emitting device may include: forming a planarization layer on a support, the planarization layer comprising a second material; forming a light scattering layer on the planarization layer to form a plurality of holes in the light scattering layer, the light scattering layer comprising a first material, the light scattering layer comprising a first surface facing the planarization layer, and a second surface opposite to the first surface, each of the plurality of holes extending between the first surface and the second surface; combining a base substrate with the light scattering layer; and removing the support from the planarization layer.

[0010] The present disclosure can significantly improve the performance of an organic light-emitting device by optimizing the distribution of light scattering elements (holes), the refractive index and thickness of a light extraction layer, and the like.

[0011] The present disclosure may provide an ultra-thin, efficient light extraction layer having light scattering holes embedded therein.

[0012] The methods and apparatus of the present disclosure have other features and advantages that are apparent from or are set forth in greater detail in the accompanying drawings and the following detailed description incorporated herein, which together serve to explain certain principles of the present disclosure.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a cross-sectional view schematically illustrating a structure of an organic light-emitting device according to an exemplary embodiment;

[0015] Figure 2 Illustrated Figure 1 a first surface of a light scattering layer of an organic light emitting device;

[0016] Figure 3 According to an exemplary embodiment, a first surface of a light scattering layer of an organic light emitting device is illustrated;

[0017] Figure 4 It is an example Figure 1 A graph showing the relationship between the refractive index and the light extraction efficiency of the light extraction layer of the organic light emitting device shown;

[0018] Figure 5 It is an example Figure 1 A graph showing the relationship between the diameter of the holes of the organic light emitting device and the light extraction efficiency;

[0019] Figure 6 It is an example Figure 1 A graph showing the relationship between the length of the holes of the organic light emitting device in the thickness direction of the light extraction layer and the light extraction efficiency;

[0020] Figure 7 It is an example Figure 1A graph showing the relationship between the area density of holes and the light extraction efficiency of the organic light emitting device shown;

[0021] Figure 8 It is an example Figure 1 A graph showing the relationship between the thickness of a planarization layer and light extraction efficiency of an organic light emitting device;

[0022] Fig. 9 is a cross-sectional view schematically illustrating a structure of a light extraction substrate of an organic light emitting device according to an exemplary embodiment;

[0023] Fig.10 It is an example Fig. 9 A graph showing the relationship between the refractive index of a planarization layer and the light extraction efficiency of an organic light emitting device;

[0024] Fig.11 According to an exemplary embodiment, a method of manufacturing a light extraction substrate of an organic light emitting device is schematically illustrated; and

[0025] Fig.12 According to an exemplary embodiment, a method of manufacturing a light extraction substrate of an organic light emitting device is schematically illustrated. DETAILED DESCRIPTION

[0026] Hereinafter, reference will be made to the present disclosure in detail, embodiments of which are shown in the accompanying drawings and described below so that those having ordinary skill in the art to which the present disclosure pertains can easily practice the present disclosure.

[0027] Figure 1 is a cross-sectional view schematically illustrating a structure of an organic light-emitting device according to an exemplary embodiment, and Figure 2 Illustrated Figure 1 The first surface of the light scattering layer 121 of the organic light emitting device is shown.

[0028] The present disclosure relates to improving the light emission efficiency of an organic light emitting device. The organic light emitting device can be used in a display device, a lighting device, etc.

[0029] An organic light emitting device according to some embodiments may include a light extraction substrate 100 and an organic light emitting diode (OLED) 200 .

[0030] In OLED 200, an organic layer 220 including a light-emitting layer may be located between an anode electrode layer 210 and a cathode electrode layer 230. According to some embodiments, the thickness of the organic layer 220 may be several hundred nanometers. According to some embodiments, the anode electrode layer 210 may contain a transparent conductive oxide, such as indium tin oxide (ITO). The cathode electrode layer 230 may contain a metal, such as aluminum (Al) or silver (Ag). When a current is applied through the two electrode layers, electrons and holes are recombined in the light-emitting layer of the organic layer 220, thereby emitting light.

[0031] The light extraction substrate 100 may include a base substrate 110 and a light extraction layer 120 fabricated on the base substrate 110. The light extraction layer 120 may include a light scattering layer 121 fabricated on the base substrate 110 and a planarization layer 123 fabricated on the light scattering layer 121. According to some such embodiments, the thickness of the light extraction layer 120, i.e., the sum of the thickness of the light scattering layer 121 and the thickness of the planarization layer 123, may be as high as 1 μm. According to some embodiments, the base substrate 110 may be a glass substrate or a polymer substrate [formed of polyimide (PI), poly (methyl methacrylate) (PMMA), polyethylene terephthalate (PET), etc.]. The light scattering layer 121 may include a first material. The light scattering layer 121 may include a first surface facing the base substrate 110 and a second surface opposite to the first surface. The light scattering layer 121 may be configured to have a plurality of holes 121a arranged between the first surface and the second surface. Therefore, a single layer of a plurality of holes 121a may be provided in the light scattering layer 121. According to some embodiments, the heights of the plurality of holes 121a may be substantially the same, but according to some other embodiments, the heights of the plurality of holes 121a may be different. (That is, the second surface may not be a flat surface.) According to some embodiments, the plurality of holes 121a may have a cylindrical shape, such as Figure 2 As shown, however, according to some alternative embodiments, the plurality of holes 121a may have a non-cylindrical shape, such as a spherical or elliptical cross-section shape. The elliptical cross-section may be parallel or perpendicular to the first surface, or may be arranged at a predetermined angle relative to the first surface. Furthermore, according to some embodiments, the plurality of holes 121a may have substantially the same shape, but according to some other embodiments, the plurality of holes 121a may have different shapes. For example, some holes 121a may have a cylindrical shape, while other holes 121a may have a non-cylindrical shape. According to some embodiments, the plurality of holes 121a may define a dot pattern on the first surface. According to some embodiments, the dots in the dot pattern may be periodically arranged, such as Figure 2 As shown, however, according to some other embodiments, the dots in the dot pattern may be randomly arranged, such as Figure 3As shown. The planarization layer 123 may contain a second material. According to some embodiments, the first material and the second material may be the same material, such as Figure 1 In contrast, according to some alternative embodiments, the first material and the second material may be different materials, such as Fig. 9 According to some embodiments, the refractive index of the first material and the second material may be in the range of 1.8 to 2.6. According to some embodiments, the first material and the second material may each include at least one selected from the group consisting of: i) SiO2, ii) AlON, iii) SiON, iv) TiO2, v) Al2O3, vi) ZnO, viii) ZrO2, and ix) a composite of at least one of SiO2, AlON, SiON, TiO2, Al2O3, ZnO, and ZrO2 and a polymer (i.e., an oxide-polymer hybrid material).

[0032] Light emitted from the organic layer 220 exits through the anode electrode layer 210 and the light extraction substrate 100. The organic light emitting device having the above-described configuration is referred to as a bottom emission organic light emitting device, but the present disclosure is not limited to the bottom emission organic light emitting device.

[0033] Figure 4 It is an example Figure 1 FIG. 1 is a graph showing the relationship between the refractive index of the light extraction layer 120 and the light extraction efficiency of an organic light emitting device.

[0034] In the light extraction layer 120 in which the light scattering layer 121 and the planarization layer 123 are formed of the same material, light extraction efficiency may be significantly improved by manufacturing the light extraction layer 120 from a material having a refractive index of 2.0 to 2.6.

[0035] To verify this feature, Figure 1 The illustrative organic light emitting device was subjected to optical simulation, and the results were obtained, such as Figure 4 As shown in the graph. Hole 121a is formed using nanoimprint technology. Calculations were performed using wave optical numerical analysis based on the finite difference time domain (FDTD) method. In the simulation, a maximum efficiency of 2.5 times was obtained at a refractive index of about 2.1, which was evaluated as the optimal refractive index. The efficiency obtained at a refractive index of 2.0 to 2.6 was at least 2.3 times. In the simulation, a refractive index of 2.1 is the optimal refractive index. Since the refractive index of the anode electrode layer 210 and the organic layer 220 is about 1.8 to 1.9, the refractive index matching between the light extraction layer 120 and these layers reduces the light loss caused by the waveguide mode.

[0036] Figure 5 It is an example Figure 1FIG. 1 is a graph showing the relationship between the diameter of the hole 121a of the organic light emitting device and the light extraction efficiency. Figure 6 It is an example Figure 1 FIG. 1 is a graph showing the relationship between the length of the hole 121 a of the organic light emitting device in the thickness direction of the light extraction layer and the light extraction efficiency.

[0037] exist Figure 1 In the light extraction layer 120 shown, the light extraction efficiency can be significantly improved by manufacturing the hole 121a so that its diameter is 400±50nm when measured on a plane perpendicular to the thickness direction of the light scattering layer 121. In addition, the light extraction efficiency can be significantly improved by manufacturing the hole 121a so that its length is 400±100nm when measured in the thickness direction of the light scattering layer 121.

[0038] Simulations were performed to verify these features and obtain Figure 5 and 6 The result graph is shown. In these simulations, when the best efficiency is obtained, the diameter and length are both 400 nm. It is obvious that the light extraction efficiency is more sensitively affected by the diameter of the hole 121a than the length of the hole 121a.

[0039] Figure 7 It is an example Figure 1 FIG. 1 is a graph showing the relationship between the area density of the holes 121 a and the light extraction efficiency of an organic light emitting device.

[0040] As the area density of the holes 121a in the first surface area increases, the light scattering probability increases, thereby increasing the light extraction efficiency. The optimal area density is at least 40%.

[0041] Figure 8 It is an example Figure 1 FIG. 1 is a graph showing the relationship between the thickness of the planarization layer 123 and the light extraction efficiency of the organic light emitting device.

[0042] The lower the thickness of the planarization layer 123, the greater the scattering probability of the light waveguide mode, thereby improving the light extraction efficiency. Excellent light extraction efficiency can be obtained by a planarization layer 123 with a maximum thickness of 200nm. A planarization layer 123 thickness of 200nm is sufficient to achieve by nanoimprinting technology. Although the refractive index of the light extraction layer 120 is changed, the same trend is observed. It is obvious that the physical distance between the hole 121a used as a light scattering element and the OLED 200 can significantly affect the light extraction efficiency.

[0043] Fig. 9 is a cross-sectional view schematically illustrating a structure of a light extraction substrate 100 of an organic light emitting device according to an exemplary embodiment.

[0044] According to some embodiments, Fig. 9 As shown, the light scattering layer 121 and the planarization layer 123 may be formed of different materials.

[0045] Fig.10 It is an example Fig. 9 FIG. 1 is a graph showing the relationship between the refractive index of the planarization layer 123 and the light extraction efficiency of the organic light emitting device.

[0046] Fig.10 The modeling results of the change in light extraction efficiency obtained by fixing the refractive index of the first material at 2.1 and changing the refractive index of the second material are illustrated. According to the simulation results, when the refractive index of the second material is greater than or equal to 1.8, the efficiency does not change significantly. However, it is obvious that the light extraction efficiency decreases sharply when the refractive index of the planarization layer 123 is reduced to a level of about 1.5, which is close to the refractive index of the base substrate 110 formed of glass, even in the case where the planarization layer 123 has a low thickness of 200nm. This is because, since the refractive index matching between the planarization layer 123 and the OLED 200 is not satisfied, the light is waveguided in the organic layer 220.

[0047] Fig.11 According to an exemplary embodiment, a method of manufacturing a light extraction substrate 100 of an organic light emitting device is schematically illustrated.

[0048] According to example embodiments, the light extraction layer 120 may be subjected to a nano-patterning process, thereby providing excellent reliability.

[0049] According to some embodiments, in a method of manufacturing a light extraction substrate 100, a first material layer is formed on a base substrate 110, and then a light scattering layer 121 is manufactured by nano-imprinting a plurality of holes 121a, such as Fig.11 As shown. In addition, a planarization layer 123 formed of a second material is manufactured on the support 300. Subsequently, the planarization layer 123 is combined with the light scattering layer 121. For example, according to some embodiments, the planarization layer 123 may be chemically combined with the light scattering layer 121 by heating. Thereafter, the support 300 is removed from the planarization layer 123.

[0050] Fig.12 According to an exemplary embodiment, a method of manufacturing a light extraction substrate 100 of an organic light emitting device is schematically illustrated.

[0051] In the method of manufacturing a light extraction substrate according to some embodiments, a planarization layer 123 formed of a second material is first manufactured on a support 300. Thereafter, a first material layer is formed on the planarization layer 123, and then a plurality of holes 121a are nano-imprinted. Subsequently, the base substrate 110 is combined with the light scattering layer 121. For example, according to some embodiments, the base substrate 110 may be chemically combined with the light scattering layer 121 by heating. Thereafter, the support 300 is removed from the planarization layer 123.

[0052] When the first material and the second material are the same material, the light extraction layer 120 may be manufactured by forming a layer of the first material (second material) on the support 300 and then nano-imprinting the holes 121a to a depth corresponding to a partial thickness of the first material layer.

[0053] The foregoing description of specific exemplary embodiments of the disclosure has been presented with respect to the accompanying drawings and is not intended to be exhaustive or to limit the disclosure to the precise form disclosed herein, and obviously many modifications and variations may be made by one of ordinary skill in the art in light of the above teachings.

[0054] Therefore, the scope of the present disclosure is not intended to be limited to the foregoing embodiments, but is defined by the appended claims and their equivalents.

Claims

1. A light extraction substrate for an organic light-emitting device, comprising: Base substrate; A light scattering layer, which is disposed on the base substrate and comprises a first material, the light scattering layer comprising a first surface facing the base substrate and a second surface opposite to the first surface, a plurality of holes being formed in the light scattering layer, each of the plurality of holes extending between the first surface and the second surface; as well as a planarization layer disposed on the light scattering layer and comprising a second material, wherein the refractive index of the first material and the second material is in the range of 1.8 to 2.6, The diameter of the plurality of pores is in the range of 350 nm to 450 nm when measured on a plane perpendicular to the thickness direction of the light scattering layer, The ratio of the area occupied by the plurality of holes in the first surface to the area of ​​the first surface is at least 40%, and The thickness of the planarization layer is 200 nm or less.

2. The light extraction substrate according to claim 1, wherein The length of the plurality of holes in the thickness direction of the light scattering layer is in the range of 300 nm to 500 nm.

3. The light extraction substrate according to claim 1, wherein The sum of the thickness of the light scattering layer and the thickness of the planarizing layer is 1 μm or less.

4. The light extraction substrate according to claim 1, wherein The plurality of holes have a shape selected from the group consisting of a cylindrical shape, a spherical shape, and a shape having an elliptical cross-section.

5. The light extraction substrate according to claim 1, wherein The first material and the second material are the same material or different materials.

6. The light extraction substrate according to claim 5, wherein The first material and the second material are the same material, and the refractive index of the first material and the second material is in the range of 2.0 to 2.

6.

7. The light extraction substrate according to claim 5, wherein The first material and the second material are different materials, and the refractive index of the second material is at least 1.

8.

8. The light extraction substrate according to claim 1, wherein The plurality of holes defines a dot pattern in the first surface.

9. The light extraction substrate according to claim 1, wherein: The base substrate includes a glass substrate or a polymer substrate.

10. The light extraction substrate according to claim 1, wherein The first material and the second material include at least one selected from the following group: SiO2, AlON, SiON, TiO2, Al2O3, ZnO, ZrO2 and a composite material of at least one of SiO2, AlON, SiON, TiO2, Al2O3, ZnO and ZrO2 and a polymer.

11. An organic light-emitting device, comprising: Base substrate; A light scattering layer, which is disposed on the base substrate and comprises a first material, the light scattering layer comprising a first surface facing the base substrate and a second surface opposite to the first surface, a plurality of holes being formed in the light scattering layer, each of the plurality of holes extending between the first surface and the second surface; a planarization layer disposed on the light scattering layer and comprising a second material; an anode electrode layer disposed on the planarization layer; an organic layer disposed on the anode electrode layer; as well as a cathode electrode layer disposed on the organic layer, wherein the refractive index of the first material and the second material is in the range of 1.8 to 2.6, The diameter of the plurality of pores is in the range of 350 nm to 450 nm when measured on a plane perpendicular to the thickness direction of the light scattering layer, The ratio of the area occupied by the plurality of holes in the first surface to the area of ​​the first surface is at least 40%, and The thickness of the planarization layer is 200 nm or less.

12. A method for manufacturing the light extraction substrate of the organic light emitting device of claim 1, the method comprising: forming a light scattering layer on a base substrate to form a plurality of holes in the light scattering layer, the light scattering layer comprising a first material and including a first surface facing the base substrate and a second surface opposite to the first surface, each hole in the plurality of holes extending between the first surface and the second surface; forming a planarization layer on the support, the planarization layer comprising a second material; combining a planarizing layer with a light scattering layer; as well as The support is removed from the planarization layer.

13. The method of claim 12, wherein: Forming the light scattering layer includes nano-imprinting a plurality of holes in the light scattering layer.

14. A method for manufacturing the light extraction substrate of the organic light emitting device of claim 1, the method comprising: forming a planarization layer on the support, the planarization layer comprising a second material; forming a light scattering layer on the planarization layer to form a plurality of holes in the light scattering layer, the light scattering layer comprising a first material, the light scattering layer comprising a first surface facing the planarization layer, and a second surface opposite to the first surface, each hole in the plurality of holes extending between the first surface and the second surface; combining a base substrate with a light scattering layer; as well as The support is removed from the planarization layer.

15. The method of claim 14, wherein: Forming the light scattering layer includes nano-imprinting a plurality of holes in the light scattering layer.

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