Light emitting device with improved luminous efficiency and display device including the same

Abstract

To provide a light-emitting element with improved luminous efficiency, and a display device including the same.SOLUTION: A light-emitting element includes a reflection layer, a first electrode disposed on the reflection layer, a second electrode disposed opposite to the first electrode, a partial transmissive mirror disposed between the first electrode and the second electrode, a first light-emitting layer disposed between the first electrode and the partial transmissive mirror, and a second light-emitting layer disposed between the partial transmissive mirror and the second electrode. The partial transmissive mirror is disposed so that a resonance mode of primary or greater is formed between the reflection layer and the partial transmissive mirror and a resonance mode of secondary or greater is formed between the reflection layer and the second electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light emitting device and a display device including the same, and more particularly to an organic light emitting device and an organic light emitting display device having improved light emitting efficiency. [Background technology]

[0002] An organic light emitting device (OLED) is a display device that forms an image by emitting light when holes supplied from an anode and electrons supplied from a cathode combine in an organic light emitting layer. Such organic light emitting devices can exhibit excellent display properties such as a wide viewing angle, fast response time, thinness, low manufacturing cost, and high contrast.

[0003] Furthermore, the organic light emitting device can emit light of a desired color by selecting an appropriate material for the organic light emitting layer. Based on this principle, a color display device can be realized using the organic light emitting device. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION An object of the present invention is to provide an organic light emitting device and an organic light emitting display device having improved luminous efficiency. [Means for solving the problem]

[0005] According to one embodiment, a light-emitting element includes a reflective layer, a first electrode disposed on the reflective layer, a second electrode disposed opposite the first electrode, a partially reflective mirror disposed between the first electrode and the second electrode, a first light-emitting layer disposed between the first electrode and the partially reflective mirror, and a second light-emitting layer disposed between the partially reflective mirror and the second electrode, and the partially reflective mirror may be disposed such that a first-order or higher resonance mode is formed between the reflective layer and the partially reflective mirror, and a second-order or higher resonance mode is formed between the reflective layer and the second electrode.

[0006] The first electrode is a transparent electrode, and the second electrode is a partially transmissive electrode that reflects part of light and transmits part of it.

[0007] The reflective layer and the second electrode may define a microcavity having a resonant wavelength, and the partially transmitting mirror may be located at a node of an optical wave resonating within the microcavity.

[0008] For example, the partially transmitting mirror may comprise silver (Ag), aluminum (Al), a silver alloy, or an aluminum alloy.

[0009] For example, the thickness of the partially transmitting mirror is 5 nm to 30 nm.

[0010] The thickness of the second electrode and the thickness of the partially transmitting mirror may be different.

[0011] The first light-emitting layer may include a first hole transport layer disposed on the first electrode, a first organic light-emitting material layer disposed on the first hole transport layer, and a first electron transport layer disposed on the first organic light-emitting material layer, and the second light-emitting layer may include a second hole transport layer disposed on the partially transmitting mirror, a second organic light-emitting material layer disposed on the second hole transport layer, and a second electron transport layer disposed on the second organic light-emitting material layer.

[0012] The light-emitting element may further include a transparent conductor layer disposed on the partially transmitting mirror so as to face the second electrode.

[0013] The light emitting element may further include a charge generating layer disposed between the first light emitting layer and the second light emitting layer.

[0014] The light-emitting element may further include a third light-emitting layer arranged between the second light-emitting layer and the second electrode, and the partially transmitting mirror may include a first partially transmitting mirror arranged between the first light-emitting layer and the second light-emitting layer, and a second partially transmitting mirror arranged between the second light-emitting layer and the third light-emitting layer.

[0015] The first partially transmitting mirror and the second partially transmitting mirror may be arranged such that a first-order resonant mode is formed between the reflective layer and the first partially transmitting mirror, a second-order resonant mode is formed between the reflective layer and the second partially transmitting mirror, and a third-order resonant mode is formed between the reflective layer and the second electrode.

[0016] The reflective layer and the second electrode may form a microcavity having a resonant wavelength, the first partially transmitting mirror may be located at a first node of an optical wave resonating within the microcavity, and the second partially transmitting mirror may be located at a second node of an optical wave resonating within the microcavity.

[0017] A light-emitting element according to another embodiment includes a reflective layer, a first electrode arranged on the reflective layer, a second electrode arranged opposite the first electrode, a phase correction layer arranged between the first electrode and the second electrode, a first light-emitting layer arranged between the first electrode and the phase correction layer, a second light-emitting layer arranged between the phase correction layer and the second electrode, a first partially transmitting mirror arranged between the phase correction layer and the first light-emitting layer, and a second partially transmitting mirror arranged between the phase correction layer and the second light-emitting layer, and the first partially transmitting mirror and the second partially transmitting mirror may be arranged so that a first-order or higher resonance mode is formed between the reflective layer and the first partially transmitting mirror, and a second-order or higher resonance mode is formed between the reflective layer and the second electrode.

[0018] The reflective layer and the second electrode may define a microcavity having a resonant wavelength, and the phase correction layer may be located at a node of an optical wave resonating within the microcavity.

[0019] The reflective layer, the second electrode, the first partially transmitting mirror, and the second partially transmitting mirror can cause a phase modulation of greater than 180° to the reflected light.

[0020] For example, the phase correction layer may include a transparent conductive material.

[0021] For example, the thickness of the phase correction layer is 5 nm to 150 nm.

[0022] The optical distance between the reflective layer and the first partially transmitting mirror may be selected so that a first-order resonant mode or a second-order resonant mode is formed between the reflective layer and the first partially transmitting mirror, and the optical distance between the second partially transmitting mirror and the second electrode may be selected so that a first-order resonant mode or a second-order resonant mode is formed between the second partially transmitting mirror and the second electrode.

[0023] The first light-emitting layer may include a first hole transport layer disposed on the first electrode, a first organic light-emitting material layer disposed on the first hole transport layer, and a first electron transport layer disposed on the first organic light-emitting material layer, and the second light-emitting layer may include a second hole transport layer disposed on the second partially transmitting mirror, a second organic light-emitting material layer disposed on the second hole transport layer, and a second electron transport layer disposed on the second organic light-emitting material layer.

[0024] The first organic light-emitting material layer and the second organic light-emitting material layer can generate light of the same wavelength.

[0025] The optical distance between the reflective layer and the first partially transmitting mirror and the optical distance between the second partially transmitting mirror and the second electrode can be selected so that a resonant mode is formed for the wavelength of light generated from the first organic light-emitting material layer and the second organic light-emitting material layer.

[0026] The first organic light emitting material layer is capable of producing light at a first wavelength, and the second organic light emitting material layer is capable of producing light at a second wavelength different from the first wavelength.

[0027] The optical distance between the reflective layer and the first partially transmitting mirror may be selected so that a resonant mode is formed for a first wavelength, and the optical distance between the second partially transmitting mirror and the second electrode may be selected so that a resonant mode is formed for a second wavelength.

[0028] A display device according to yet another embodiment includes a plurality of pixels, each pixel including a reflective layer, a first electrode arranged on the reflective layer, a second electrode arranged opposite the first electrode, a partially reflective mirror arranged between the first electrode and the second electrode, and a light-emitting layer arranged between the first electrode and the partially reflective mirror and between the partially reflective mirror and the second electrode, wherein the partially reflective mirror may be arranged such that a first-order or higher resonance mode is formed between the reflective layer and the partially reflective mirror, and a second-order or higher resonance mode is formed between the reflective layer and the second electrode. [Effects of the Invention]

[0029] According to the present invention, even when a light-emitting element on a microcavity substrate has a thick light-emitting layer and a second-order, third-order, or higher-order resonance mode is formed, by disposing a partially transmitting mirror inside the microcavity and satisfying the first-order resonance condition, it is possible to suppress the physical phenomenon that reduces the Purcell effect in higher-order resonance modes, and ultimately improve the light-emitting efficiency and operating life of the light-emitting element.

[0030] Furthermore, by taking into consideration the phase delay caused by the metal that constitutes the reflective layer and providing a phase correction layer, it is possible to satisfy all of the first-order or higher resonance conditions and improve the luminous efficiency of the light-emitting element even when the phase delay in the reflective layer is greater than 180°. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view schematically illustrating a structure of a light-emitting device according to an embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing a microcavity structure of the light-emitting element shown in FIG. [Figure 3A] 2 is a diagram illustrating an example of a resonant mode of a microcavity of the light-emitting device shown in FIG. 1. FIG. [Figure 3B] 2 is a diagram illustrating an example of a resonant mode of a microcavity of the light-emitting device shown in FIG. 1. FIG. [Figure 4] 10 is a cross-sectional view schematically illustrating a structure of a light-emitting device according to another embodiment. [Figure 5] 10 is a cross-sectional view schematically illustrating a structure of a light emitting device according to yet another embodiment. [Figure 6] FIG. 6 is a conceptual diagram showing a microcavity structure of the light-emitting element shown in FIG. [Figure 7A] 6 is a diagram illustrating an example of a resonant mode of a microcavity of the light-emitting device shown in FIG. 5. FIG. [Figure 7B] 6 is a diagram illustrating an example of a resonant mode of a microcavity of the light-emitting device shown in FIG. 5. FIG. [Figure 7C]6 is a diagram illustrating an example of a resonant mode of a microcavity of the light-emitting device shown in FIG. 5. FIG. [Figure 8] 6 is a graph illustrating an example of a change in light emission characteristics of a light emitter depending on the resonance order in the light emitting device shown in FIG. 5, in comparison with a comparative example. [Figure 9] 6 is a graph illustrating an example of a change in light emission characteristics of the light emitting device according to the resonance order in the light emitting device shown in FIG. 5, in comparison with a comparative example. [Figure 10] 10 is a cross-sectional view schematically illustrating a structure of a light emitting device according to yet another embodiment. [Figure 11] 10 is a cross-sectional view schematically illustrating a structure of a light emitting device according to yet another embodiment. [Figure 12A] 12 is a diagram illustrating an example of a resonant mode of the microcavity of the light-emitting device shown in FIG. 11. FIG. [Figure 12B] 12 is a diagram illustrating an example of a resonant mode of the microcavity of the light-emitting device shown in FIG. 11. FIG. [Figure 12C] 12 is a diagram illustrating an example of a resonant mode of the microcavity of the light-emitting device shown in FIG. 11. FIG. [Figure 13] 12 is a diagram illustrating an example of a change in the resonant wavelength of a second-order resonator due to a change in the thickness of a phase correction layer in the light emitting device shown in FIG. 11. FIG. [Figure 14] 12 is a graph illustrating an example of a change in light emission characteristics of a light emitter depending on the resonance order in the light emitting device shown in FIG. 11, in comparison with a comparative example. [Figure 15] 10 is a conceptual diagram showing a microcavity structure of a light-emitting device according to yet another embodiment. [Figure 16] 10 is a cross-sectional view schematically illustrating a structure of a light emitting device according to yet another embodiment. [Figure 17] 1 is a cross-sectional view schematically illustrating a structure of a display device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, a light emitting device having improved luminous efficiency and a display device including the same will be described in detail with reference to the accompanying drawings. In the following drawings, the same reference numerals refer to the same components, and the size of each component may be exaggerated in the drawings for clarity and convenience. Furthermore, the embodiments described below are merely examples, and various modifications are possible from such embodiments.

[0033] Hereinafter, the term "upper" or "on" may include not only something that is directly on top in contact with something, but also something that is on top without contacting something. The singular expression includes the plural expression unless the context clearly indicates otherwise. Furthermore, when a part "comprises" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified to the contrary.

[0034] Use of the term "said" and similar directives can refer to both the singular and the plural. Unless an explicit order is stated for method steps or a statement to the contrary, such steps may be performed in any suitable order and are not necessarily limited to the order stated.

[0035] Furthermore, terms such as "unit" and "module" used in the specification refer to a unit that processes at least one function or operation, and may be realized by hardware or software, or by a combination of hardware and software.

[0036] The line connections or connecting members between components shown in the drawings are illustrative of functional connections and / or physical or circuit connections, and in an actual device, various alternative or additional functional connections, physical connections, or circuit connections may be shown.

[0037] The use of any examples or exemplary terms is merely for the purpose of illustrating in detail the technical idea, and the scope is not limited by such examples or exemplary terms, except as limited by the claims.

[0038] 1 is a cross-sectional view schematically illustrating a structure of a light-emitting device according to an embodiment. Referring to FIG. 1, a light-emitting device 200 according to an embodiment may include a reflective layer 110, a first electrode 120 disposed on the reflective layer 110, a second electrode 150 disposed opposite the first electrode 120, a partially transmitting mirror 140 disposed between the first electrode 120 and the second electrode 150, a first light-emitting layer 130a disposed between the first electrode 120 and the partially transmitting mirror 140, and a second light-emitting layer 130b disposed between the partially transmitting mirror 140 and the second electrode 150. The light-emitting device 200 may further include a transparent passivation layer 160 disposed on the second electrode 150 to protect the second electrode 150.

[0039] The light-emitting element 200 may also be an organic light-emitting element, also known as an organic light-emitting diode (OLED), and the first light-emitting layer 130a and the second light-emitting layer 130b may also be organic light-emitting layers containing organic light-emitting materials. For example, the first light-emitting layer 130a may include a first hole transfer layer 132a disposed on the first electrode 120, a first organic light-emitting material layer 131a disposed on the first hole transport layer 132a, and a first electron transfer layer 133a disposed on the first organic light-emitting material layer 131a. The second light-emitting layer 130b may include a second hole transport layer 132b disposed on the partially transmitting mirror 140, a second organic light-emitting material layer 131b disposed on the second hole transport layer 132b, and a second electron transport layer 133b disposed on the second organic light-emitting material layer 131b.

[0040] The first hole transport layer 132a and the second hole transport layer 132b may further function as hole injection layers, and the first electron transport layer 133a and the second electron transport layer 133b may further function as electron injection layers. Alternatively, additional hole injection layers may be disposed between the first electrode 120 and the first hole transport layer 132a and between the partially transmitting mirror 140 and the second hole transport layer 132b, respectively, and additional electron injection layers may be disposed between the first electron transport layer 133a and the partially transmitting mirror 140 and between the second electron transport layer 133b and the second electrode 150, respectively. Although not shown, the first light-emitting layer 130a and the second light-emitting layer 130b may further include various additional layers as necessary. For example, the first light-emitting layer 130a and the second light-emitting layer 130b may further include an electron blocking layer, a hole blocking layer, and the like.

[0041] In this structure, holes provided through the first hole transport layer 132a and the second hole transport layer 132b and electrons provided through the first electron transport layer 133a and the second electron transport layer 133b combine in the first organic light emitting material layer 131a and the second organic light emitting material layer 131b to generate light. The first organic light emitting material layer 131a and the second organic light emitting material layer 131b can also be formed by doping an organic host with a dopant material. The wavelength of the light generated from the first organic light emitting material layer 131a and the second organic light emitting material layer 131b is also determined by the properties of the organic host material and the organic dopant material.

[0042] The first electrode 120 may act as a positive electrode that provides holes to the first light emitting layer 130 a and the second light emitting layer 130 b, and the second electrode 150 may act as a negative electrode that provides electrons to the first light emitting layer 130 a and the second light emitting layer 130 b. To this end, the first electrode 120 may be made of a material having a relatively high work function, and the second electrode 150 may be made of a material having a relatively low work function.

[0043] The first electrode 120 may also be a transparent electrode that transmits color (e.g., visible light). For example, the first electrode 120 may include a transparent conductive oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), or aluminum zinc oxide (AZO).

[0044] The second electrode 150 can also function as a partially transparent electrode that reflects part of the light and transmits part of it. To achieve this, the second electrode 150 includes a very thin reflective metal. For example, the second electrode 150 may include silver (Ag), aluminum (Al), a silver alloy, or an aluminum alloy. For example, the silver alloy may be a mixed layer of silver (Ag) and magnesium (Mg), and the aluminum alloy may be a mixed layer of aluminum (Al) and lithium (Li). The total thickness of such a second electrode 150 is approximately 5 nm to 30 nm. Because the thickness of the second electrode 150 is very thin, part of the light can pass through the reflective metal.

[0045] The reflective layer 110 is also configured to reflect light generated by the first light-emitting layer 130a and the second light-emitting layer 130b and transmitted through the first electrode 120. To that end, the reflective layer 110 may contain silver (Ag), gold (Au), aluminum (Al), or an alloy containing these. However, the reflective layer 110 is not necessarily limited thereto, and may also contain other reflective materials.

[0046] The reflective layer 110 functions to form a microcavity together with the second electrode 150. In other words, a microcavity is formed between the reflective layer 110 and the second electrode 150 of the light emitting device 200. For example, light generated from the first light emitting layer 130a and the second light emitting layer 130b travels back and forth between the reflective layer 110 and the second electrode 150 and resonates, and then light corresponding to the resonant wavelength of the microcavity is emitted to the outside through the second electrode 150.

[0047] The resonant wavelength of the microcavity formed between the reflective layer 110 and the second electrode 150 is also determined by the optical length L of the microcavity. For example, when the resonant wavelength of the microcavity is λ, the optical length L of the microcavity is also nλ / 2 (n is a natural number). The optical length L of such a microcavity is also determined by the sum of the optical thicknesses of the layers forming the microcavity between the reflective layer 110 and the second electrode 150, the phase retardation due to the second electrode 150, and the phase retardation due to the reflective layer 110. Here, the optical thicknesses of the layers forming the microcavity between the reflective layer 110 and the second electrode 150 are not simply physical thicknesses, but are thicknesses that take into account the refractive index of the materials of the layers forming the microcavity. For example, the optical thickness of the layers forming the microcavity is the sum of the optical thicknesses of all the layers between the reflective layer 110 and the second electrode 150.

[0048] To improve the light-emitting efficiency of the light-emitting device 200, the optical length L of the microcavity is also determined to match the resonant wavelength of the microcavity to the emission wavelength of the first light-emitting layer 130a and the second light-emitting layer 130b. In other words, the resonant wavelength λ of the microcavity is also the same as the emission wavelength of the first light-emitting layer 130a and the second light-emitting layer 130b. To achieve this, the optical thickness of the layers disposed between the reflective layer 110 and the second electrode 150 can be adjusted taking into account the emission wavelengths of the first light-emitting layer 130a and the second light-emitting layer 130b. By using such a microcavity, light emitted from the light-emitting device 200 can be made to travel in a straight line, and only light within a narrow wavelength band can be selectively extracted, thereby improving the color purity of the light emitted from the light-emitting device 200.

[0049] Meanwhile, in a microcavity structure, the radiative decay rate of a light source within the microcavity changes depending on the Q factor and mode volume of the microcavity. This is called the Purcell effect. Enhancing the Purcell effect increases the radiative decay rate of the light source, thereby improving the spontaneous emission rate. In the case of organic light-emitting devices, the light source refers to the emitting dopant, and the Purcell effect increases the dopant's photoluminescence quantum yield (PLQY), further improving the device's luminous efficiency. Even if the dopant's PLQY is close to 1, the increased radiative decay rate due to the microcavity-induced Purcell effect can be expected to extend the light-emitting device's lifetime.

[0050] The Purcell effect is generally strong in the first-order resonant mode where n = 1, i.e., the optical length L of the microcavity is λ / 2. It rapidly decreases as n increases and the resonant order increases. This is because the longer the resonant length, the narrower the free spectral range, reducing the optical density of states (ODOS) formed by the microcavity and decreasing the efficiency of the light emitter inside the microcavity. Therefore, a microcavity with a first-order resonant mode is most effective for light-emitting devices. However, higher-order resonant modes can be applied when the thickness of the hole transport layer or light-emitting layer must be increased for the driving stability of the light-emitting device, or when multiple light-emitting layers or a tandem structure in which multiple light-emitting devices are stacked is used.

[0051] According to this embodiment, the partially transmitting mirror 140 within the microcavity enhances the Purcell effect so that a microcavity with a second-order, third-order, or higher-order resonant mode can have a first-order resonant mode. For example, FIG. 2 is a conceptual diagram showing the microcavity structure of the light-emitting device shown in FIG. 1. Referring to FIG. 2, a microcavity with a second-order resonant mode is formed by the reflective layer 110 and the second electrode 150. The partially transmitting mirror 140 is disposed in a region where the electric field strength of the light wave resonating within the microcavity is weakest, in other words, at a node of the light wave resonating within the microcavity. As a result, a portion of the light incident on the partially transmitting mirror 140 is reflected by the partially transmitting mirror 140, forming a new mini-resonator. Therefore, multiple resonant modes can be formed within the microcavity.

[0052] 3A and 3B exemplarily illustrate resonant modes of the microcavity of the light-emitting device shown in FIG. 1. First, referring to FIG. 3A, a resonator having a first-order resonant mode may be formed by the reflective layer 110 and the partially transmitting mirror 140. Also, as shown in FIG. 3B, a resonator having a second-order resonant mode may be formed by the reflective layer 110 and the second electrode 150. By further disposing the partially transmitting mirror 140 within the microcavity, the microcavity may further have a first-order resonant mode, thereby increasing the optical density of states. Although not shown, a first-order resonator having a first-order resonant mode may also be formed by the partially transmitting mirror 140 and the second electrode 150. Therefore, two first-order resonators having a first-order resonant mode may be connected to form one second-order resonator having a second-order resonant mode.

[0053] The partially transmitting mirror 140 may include the same material as the second electrode 150. In other words, the partially transmitting mirror 140 may include a reflective and conductive metal material, such as silver (Ag), aluminum (Al), a silver alloy, or an aluminum alloy. The partially transmitting mirror 140 may be formed to have a small thickness so that it can transmit a portion of light. For example, the partially transmitting mirror 140 may have a thickness of approximately 5 nm to 30 nm. If necessary, the thickness of the partially transmitting mirror 140 may be selected to be different from the thickness of the second electrode 150, which emits light to the outside of the light-emitting element 200. In other words, the reflectivity of the partially transmitting mirror 140 may be selected to be different from the reflectivity of the second electrode 150.

[0054] Furthermore, the first light-emitting layer 130a disposed between the reflective layer 110 and the partially transmitting mirror 140 may be located in a region where the electric field strength of the light wave resonating within the microcavity is at its maximum, in other words, at the antinode of the light wave resonating within the microcavity. The thickness and materials of the electron transport layer and hole transport layer can be selected to efficiently generate excitons in the light-emitting layer using holes and electrons injected from the electrodes. Positioning the light-emitting layer at the antinode of the microcavity is also optically advantageous. The second light-emitting layer 130b disposed between the partially transmitting mirror 140 and the second electrode 150 may also be located at the antinode of the light wave resonating within the microcavity.

[0055] 4 is a cross-sectional view schematically illustrating the structure of a light-emitting device according to another embodiment. Referring to FIG. 4, the light-emitting device 210 may further include a transparent conductor layer 141 disposed on the upper surface of the partially transmitting mirror 140 to face the second electrode 150. The transparent conductor layer 141 may perform a function similar to that of the first electrode 120. The transparent conductor layer 141, located between the partially transmitting mirror 140 and the second light-emitting layer 130b, is made of a material having a high work function to provide holes to the second light-emitting layer 130b. For example, the transparent conductor layer 141 may include ITO, IZO, AZO, etc.

[0056] The light emitting element 210 may further include a charge generation layer 142 disposed between the first light emitting layer 130a and the second light emitting layer 130b. The charge generation layer 142 may improve charge transfer between the first organic light emitting material layer 131a and the second organic light emitting material layer 131b. While FIG. 4 illustrates the charge generation layer 142 as being disposed between the lower surface of the partially transmitting mirror 140 and the upper surface of the first light emitting layer 130a, the charge generation layer 142 may be located anywhere between the first light emitting layer 130a and the second light emitting layer 130b.

[0057] The remaining configuration of the light emitting device 210 is the same as that of the light emitting device 200 shown in Fig. 1. Therefore, detailed description of the light emitting device 210 shown in Fig. 4 will be omitted.

[0058] 5 is a cross-sectional view schematically illustrating the structure of a light-emitting device according to yet another embodiment. Referring to FIG. 5, a light-emitting device 220 may include a reflective layer 110, a transparent first electrode 120 disposed on the reflective layer 110, a first light-emitting layer 130a disposed on the first electrode 120, a first partially transmitting mirror 140a disposed on the first light-emitting layer 130a, a second light-emitting layer 130b disposed on the first partially transmitting mirror 140a, a second light-emitting layer 130b disposed on the first partially transmitting mirror 140a, a second partially transmitting mirror 140b disposed on the second light-emitting layer 130b, a third light-emitting layer 130c disposed on the second partially transmitting mirror 140b, and a second electrode 150 disposed on the third light-emitting layer 130c. The light-emitting device 220 may further include a protective layer 160 disposed on the second electrode 150.

[0059] 1 and 4, the light emitting device 220 further includes a third light emitting layer 130c disposed between the second light emitting layer 130b and the second electrode 150, and a second partially transmitting mirror 140b disposed between the second light emitting layer 130b and the third light emitting layer 130c. While the light emitting devices 200 and 210 shown in FIGS. 1 and 4 are configured so that the microcavity has a second-order resonance mode, the microcavity of the light emitting device 220 shown in FIG. 5 has a third-order resonance mode. Furthermore, the resonance order of the microcavity is not limited thereto, and the microcavity may also be formed so as to have a fourth-order or higher-order resonance mode.

[0060] FIG. 6 is a conceptual diagram illustrating the microcavity structure of the light emitting device 220 shown in FIG. 5. Referring to FIG. 6, a microcavity having a third-order resonant mode is formed between the reflective layer 110 and the second electrode 150. The first partially transmitting mirror 140a disposed between the first light emitting layer 130a and the second light emitting layer 130b may be located in a first node region of the light wave resonating within the microcavity, and the second partially transmitting mirror 140b disposed between the second light emitting layer 130b and the third light emitting layer 130c may be located in a second node region of the light wave resonating within the microcavity. In this case, the first light emitting layer 130a may be located in a first antinode region of the light wave resonating within the microcavity, the second light emitting layer 130b may be located in a second antinode region of the light wave resonating within the microcavity, and the third light emitting layer 130c may be located in a third antinode region of the light wave resonating within the microcavity.

[0061] 7A to 7C exemplarily illustrate resonant modes of the microcavity of the light emitting device 220 shown in FIG. 7A to 7C, a first-order resonant mode may be formed between the reflective layer 110 and the first partially transmitting mirror 140a, a second-order resonant mode may be formed between the reflective layer 110 and the second partially transmitting mirror 140b, and a third-order resonant mode may be formed between the reflective layer 110 and the second electrode 150. Such multiple resonant modes are formed by positioning the first partially transmitting mirror 140a and the second partially transmitting mirror 140b in different node regions of the light wave resonating within the microcavity, as shown in FIG.

[0062] In this manner, multiple small resonators can be formed within one large microcavity, and these multiple small resonators can be optically coupled. This allows for optical effects to be achieved through interactions between first-order, second-order, and third-order resonances. For example, FIG. 8 is a graph illustrating, in comparison with a comparative example, the change in light-emitting characteristics of the light emitter according to the resonance order in the light-emitting device 220 shown in FIG. 5 . FIG. 9 is a graph illustrating, in comparison with a comparative example, the change in light-emitting characteristics of the light-emitting device 220 according to the resonance order in the light-emitting device 220 shown in FIG. 5 . In other words, the graph of FIG. 8 illustrates the intensity of light generated by the light emitter located within the microcavity, compared with a comparative example. The graph of FIG. 9 illustrates the intensity of light output from the light-emitting device 220 via the second electrode 150, which is generated by light resonating within the microcavity, compared with a comparative example.

[0063] Referring to FIG. 8, it can be seen that the intensity of light generated by the light emitter decreases as the resonance order increases, from the first resonance mode to the second resonance mode and then to the third resonance mode. This can be interpreted as a result of the Purcell effect described above. Meanwhile, it can be seen that when the first and second resonance modes are further generated within the microcavity using the first and second partially transmitting mirrors 140a and 140b, as in this embodiment, the light emission characteristics of the light emitter are further improved compared to when only the first resonance mode is present. This is believed to be the result of reinforcement characteristics being strengthened due to the mutually reinforcing interference of the various resonance modes. Furthermore, referring to FIG. 9, it can be predicted that the intensity of light output from the light emitting device 220 according to this embodiment is approximately twice as high as when only the first resonance mode is present, and therefore the light extraction efficiency is also improved.

[0064] As described above, the partial transmission mirrors 140, 140a, and 140b can be arranged so that a first-order or higher resonance mode is formed between the reflective layer 110 and the partial transmission mirrors 140, 140a, and 140b, and a second-order or higher resonance mode is formed between the reflective layer 110 and the second electrode 150. This allows the partial transmission mirrors to satisfy the first-order resonance condition within the microcavity, even when the light-emitting device on the microcavity substrate includes multiple light-emitting layers or has thick organic layers, resulting in the formation of second-order or higher-order resonance modes. As a result, the Purcell effect can be enhanced, which can further improve efficiency or extend the operating life of the light-emitting device.

[0065] FIG. 10 is a cross-sectional view schematically illustrating the structure of a light-emitting device according to yet another embodiment. Referring to FIG. 10, the light-emitting device 230 may further include a first transparent conductive layer 141a disposed between the upper surface of the first partially transmitting mirror 140a and the second light-emitting layer 130b, and a second transparent conductive layer 141b disposed between the upper surface of the second partially transmitting mirror 140b and the third light-emitting layer 130c. The light-emitting device 230 may also include a first charge generation layer 142a disposed between the first light-emitting layer 130a and the second light-emitting layer 130b, and a second charge generation layer 142b disposed between the second light-emitting layer 130b and the third light-emitting layer 130c. The remaining configuration of the light-emitting device 230 illustrated in FIG. 10 is the same as that of the light-emitting device 220 illustrated in FIG. 5, and therefore detailed description thereof will be omitted.

[0066] 11 is a cross-sectional view schematically illustrating the structure of a light-emitting device according to yet another embodiment. Referring to FIG. 11, light-emitting device 240 may include a reflective layer 110, a transparent first electrode 120 disposed on reflective layer 110, a partially transmissive second electrode 150 disposed opposite first electrode 120, a phase correction layer 144 disposed between first electrode 120 and second electrode 150, a first light-emitting layer 130a disposed between first electrode 120 and phase correction layer 144, a second light-emitting layer 130b disposed between phase correction layer 144 and second electrode 150, a first partially transmissive mirror 145 disposed between phase correction layer 144 and first light-emitting layer 130a, and a second partially transmissive mirror 146 disposed between phase correction layer 144 and second light-emitting layer 130b. Light-emitting device 240 may further include a protective layer 160 disposed on second electrode 150.

[0067] 1 through 10 , it is assumed that the phase of light reflected by the reflective layer 110, the second electrode 150, and the partially transmitting mirrors 140, 140a, and 140b is shifted by 180° (i.e., π). However, in the case of metal mirrors, the phase modulation is actually approximately 1.1 to 1.3 times larger due to the evanescent wave effect. For example, a silver (Ag) mirror experiences a phase modulation of 1.3×180°. This results in the optical length of the primary resonator actually being shorter than λ / 2. For example, when the resonant wavelength is 450 nm, the actual optical length of the primary resonator is approximately 170 nm, not 225 nm. The reason the resonator length is shortened by approximately 55 nm is because the reflective phase modulation by the silver thin film is 1.3π, not π.

[0068] Thus, phase modulation greater than π occurring in a metal mirror makes it difficult to serially connect multiple first-order resonators. When two first-order resonators designed for phase modulation greater than π are serially connected, the resulting resonator length is shorter than the length required to satisfy the second-order resonance condition, and the resulting actual resonant wavelength is shorter than the target resonant wavelength. For example, when two first-order resonators with a resonant wavelength of 450 nm are serially connected, the resulting second-order resonator can have a resonant wavelength of approximately 420 nm. When three first-order resonators designed for phase modulation greater than π are serially connected, the resulting resonator length is even shorter than the length required to satisfy the third-order resonance condition. This prevents constructive interference between the various resonant modes that satisfy the resonance conditions of multiple resonators.

[0069] The light-emitting device 240 shown in FIG. 11 may further include an additional cavity for phase correction within the microcavity to prevent the length of the second-order or higher resonators from becoming too short. The phase correction layer 144 does not directly contribute to light emission but can serve as such an additional cavity for phase correction. The phase correction layer 144 can match the final resonant wavelength of the second-order or higher resonators to a target resonant wavelength while connecting the first-order resonators arranged on both sides of the phase correction layer 144 in series. In other words, the final resonant wavelength of the second-order or higher resonators is also determined by the thickness D ( FIG. 12C ) of the phase correction layer 144. The exact thickness D of the phase correction layer 144 that matches the final resonant wavelength of the second-order or higher resonators to a target resonant wavelength can be calculated using, for example, a finite-differential time-domain simulator.

[0070] 12A to 12C exemplarily illustrate resonant modes of the microcavity of the light emitting device 240 shown in FIG. 11. Referring to FIG. 12A, a primary resonator is formed by the reflective layer 110 and a first partially transmitting mirror 145. Referring to FIG. 12B, another primary resonator is formed by the second partially transmitting mirror 146 and a second electrode 150. Referring to FIG. 12C, a secondary resonator is formed by connecting two primary resonators between the reflective layer 110 and the second electrode 150. A phase correction layer 144 is disposed between the first partially transmitting mirror 145 and the second partially transmitting mirror 146 to prevent the resonant wavelength of the secondary resonator from becoming shorter. The phase correction layer 144 may be located at a node of the light wave resonating in the microcavity between the reflective layer 110 and the second electrode 150 or in the secondary resonator. First partially transmitting mirror 145 and second partially transmitting mirror 146 are also disposed in direct contact with opposite surfaces of phase correction layer 144 .

[0071] The reflective layer 110, the second electrode 150, the first partially transmitting mirror 145, and the second partially transmitting mirror 146 can cause a phase modulation of more than 180° to the reflected light. The thickness D of the phase correction layer 144 is determined taking into account the phase modulation of more than 180° of the reflective layer 110, the second electrode 150, the first partially transmitting mirror 145, and the second partially transmitting mirror 146. In particular, the thickness D of the phase correction layer 144 can be determined so that the resonant wavelengths of the two primary resonators and the secondary resonator coincide with each other. For example, the thickness D of the phase correction layer 144 can be determined within a range of approximately 5 nm to 150 nm. Such a phase correction layer 144 may include a transparent conductive material having a high refractive index.

[0072] FIG. 13 illustrates the change in the resonant wavelength of the secondary resonators with the thickness of the phase correction layer 144 in the light-emitting device 240 shown in FIG. 11 . The two primary resonators are designed to have a resonant wavelength of approximately 450 nm. The reflective layer 110 includes a silver thin film approximately 200 nm thick, the first and second partially transmitting mirrors 145 and 146 each have a thickness of approximately 10 nm, and the second electrode 150 has a thickness of approximately 20 nm. The distance between the reflective layer 110 and the first partially transmitting mirror 145 and the distance between the second partially transmitting mirror 146 and the second electrode 150 are fixed at approximately 168 nm. The resonant characteristics of the secondary resonators were calculated while the phase correction distance, i.e., the thickness of the phase correction layer 144, was varied from 10 nm to 150 nm. Referring to FIG. 13 , it can be seen that when the thickness of the phase correction layer 144 is approximately 10 nm, the resonant wavelength is approximately 410 nm. As the thickness of phase correction layer 144 increases, the resonant wavelength gradually increases, and when the thickness of phase correction layer 144 is about 90 nm, a resonant wavelength of about 450 nm is formed.

[0073] FIG. 14 is a graph illustrating an example of a change in the light-emitting characteristics of the light emitter depending on the resonance order in the light-emitting device 240 shown in FIG. 11 , compared with a comparative example. The graph in FIG. 14 illustrates the intensity of light generated by the light emitter located in the microcavity, compared with a comparative example. Referring to FIG. 14 , it can be seen that the intensity of light generated by the light emitter decreases as the resonance order increases from the first-order resonance mode to the second-order resonance mode and the third-order resonance mode. Meanwhile, according to this embodiment, it can be confirmed that the light-emitting characteristics of the light emitter are further improved compared to a case where only the first-order resonance mode is present. As described above, by providing the phase correction layer 144 in consideration of the phase delay due to the metals constituting the reflective layer 110, the second electrode 150, the first partially transmitting mirror 145, and the second partially transmitting mirror 146, all of the first-order and higher resonance conditions can be satisfied even when the phase delay in the reflective layer 110, the second electrode 150, the first partially transmitting mirror 145, and the second partially transmitting mirror 146 is greater than 180°, thereby improving the light-emitting efficiency of the light-emitting device 240.

[0074] 12A to 12C, two first-order resonators are connected to form a final microcavity having a second-order resonant mode. However, this is not necessarily limited to this. For example, FIG. 15 is a conceptual diagram showing a microcavity structure of a light emitting device 250 according to another embodiment. Referring to FIG. 15, the resonator formed between the reflective layer 110 and the first partially transmitting mirror 145 is a second-order resonator having a second-order resonant mode. In addition, the resonator formed between the second partially transmitting mirror 146 and the second electrode 150 is also a second-order resonator having a second-order resonant mode. As a result, the resonator formed between the reflective layer 110 and the second electrode 150 is a fourth-order resonator having a fourth-order resonant mode. In this case, the phase correction layer 144 may be located at a second node of the light wave resonating in the fourth-order resonator.

[0075] As described above, the first partially transmitting mirror 145 and the second partially transmitting mirror 146 are arranged so that a first-order or higher resonance mode is formed between the reflective layer 110 and the first partially transmitting mirror 145, and a second-order or higher resonance mode is formed between the reflective layer 110 and the second electrode 150. For phase correction, a phase correction layer 144 having a predetermined thickness may be arranged between the first partially transmitting mirror 145 and the second partially transmitting mirror 146. Furthermore, the optical distance L1 between the reflective layer 110 and the first partially transmitting mirror 145 is selected so that a first-order or second-order resonance mode is formed between the reflective layer 110 and the first partially transmitting mirror 145, and the optical distance L2 between the second partially transmitting mirror 146 and the second electrode 150 is also selected so that a first-order or second-order resonance mode is formed between the second partially transmitting mirror 146 and the second electrode 150.

[0076] Meanwhile, the first light-emitting layer 130a and the second light-emitting layer 130b may have the same configuration as the first light-emitting layer 130a and the second light-emitting layer 130b already described in FIG. 1. For example, the first light-emitting layer 130a may include a first hole transport layer disposed on the first electrode 120, a first organic light-emitting material layer disposed on the first hole transport layer, and a first electron transport layer disposed on the first organic light-emitting material layer. Furthermore, the second light-emitting layer 130b may include a second hole transport layer disposed on the second partially transmitting mirror 146, a second organic light-emitting material layer disposed on the second hole transport layer, and a second electron transport layer disposed on the second organic light-emitting material layer.

[0077] The first organic light-emitting material layer in the first light-emitting layer 130a and the second organic light-emitting material layer in the second light-emitting layer 130b may contain organic materials that produce light of the same wavelength. The optical distance L1 between the reflective layer 110 and the first partially transmitting mirror 145 and the optical distance L2 between the second partially transmitting mirror 146 and the second electrode 150 are the same and are selected so that a resonant mode is formed for the wavelength of light produced in the first organic light-emitting material layer and the second organic light-emitting material layer.

[0078] In another example, the first organic light-emitting material layer in the first light-emitting layer 130a may include an organic material that emits light at a first wavelength, and the second organic light-emitting material layer in the second light-emitting layer 130b may include an organic material that emits light at a second wavelength different from the first wavelength. In this case, the optical distance L1 between the reflective layer 110 and the first partially transmitting mirror 145 may be selected so that a resonant mode is formed for the first wavelength, and the optical distance L2 between the second partially transmitting mirror 146 and the second electrode 150 may be selected so that a resonant mode is formed for the second wavelength. Furthermore, by adjusting the thickness of the phase correction layer 144, the optical distance L between the reflective layer 110 and the second electrode 150 can be selected so that a resonant mode is formed for one wavelength selected from the first and second wavelengths. Alternatively, the thickness of the correction layer 144 can be adjusted so that a resonant mode is formed for a third wavelength different from the first and second wavelengths. In this case, the light-emitting element 240 can emit multicolor light.

[0079] 11 shows two light-emitting layers, a first partially transmitting mirror, a phase correction layer, a second partially transmitting mirror, and a light-emitting layer may be further disposed between the second light-emitting layer 130b and the second electrode 150. In this case, the three light-emitting layers may emit light of different wavelengths. Alternatively, the three light-emitting layers may emit light of the same wavelength.

[0080] 16 is a cross-sectional view schematically illustrating the structure of a light emitting device according to yet another embodiment. Referring to FIG. 16, the light emitting device 250 may further include a transparent conductive layer 141 disposed between the upper surface of the second partially transmitting mirror 146 and the second light emitting layer 130b. The light emitting device 250 may also include a charge generation layer 142 disposed between the first light emitting layer 130a and the second light emitting layer 130b. The remaining configuration of the light emitting device 250 shown in FIG. 16 is the same as the configuration of the light emitting device 240 shown in FIG. 11, and therefore detailed description thereof will be omitted.

[0081] The light-emitting element described above can also be applied to a plurality of pixels of a display device. FIG. 17 is a cross-sectional view schematically illustrating the structure of a display device according to an embodiment. Referring to FIG. 17, a display device 1000 includes a plurality of pixels emitting light of different hues. Here, the plurality of pixels may include a red pixel 1100, a green pixel 1200, and a blue pixel 1300 arranged adjacent to each other on the same plane of a substrate 1001. For convenience, FIG. 17 shows only one unit pixel composed of a red pixel 1100, a green pixel 1200, and a blue pixel 1300. However, in reality, a large number of red pixels 1100, green pixels 1200, and blue pixels 1300 are repeatedly arranged on the substrate 1001.

[0082] The red pixel 1100 may include a reflective layer 110 arranged on a substrate 1001, a first electrode 120 arranged on the reflective layer 110, a second electrode 150 arranged opposite the first electrode 120, a partially transmitting mirror 140 arranged between the first electrode 120 and the second electrode 150, a first red light-emitting layer 130Ra arranged between the first electrode 120 and the partially transmitting mirror 140, a second red light-emitting layer 130Rb arranged between the partially transmitting mirror 140 and the second electrode 150, and a protective layer 160 arranged on the second electrode 150. The optical distances between the first electrode 120 and the partially transmitting mirror 140 and the optical distances between the partially transmitting mirror 140 and the second electrode 150 are determined so as to have a first-order or higher resonance mode for red light, and the optical distance between the first electrode 120 and the second electrode 150 is determined so as to have a second-order or higher resonance mode for red light.

[0083] The green pixel 1200 and the blue pixel 1300 have structures similar to the red pixel 1100. The green pixel 1200 includes a first green light-emitting layer 130Ga and a second green light-emitting layer 130Gb instead of the red light-emitting layers 130Ra and 130Rb, and the blue pixel 1300 includes a first blue light-emitting layer 130Ba and a second blue light-emitting layer 130Bb instead of the red light-emitting layers 130Ra and 130Rb. In the green pixel 1200, the optical distances between the first electrode 120 and the partially transmitting mirror 140 and between the partially transmitting mirror 140 and the second electrode 150 are determined so as to have a first-order or higher resonance mode for green light, and the optical distance between the first electrode 120 and the second electrode 150 is determined so as to have a second-order or higher resonance mode for green light. Furthermore, in the blue pixel 1300, the optical distance between the first electrode 120 and the partially transmitting mirror 140 and the optical distance between the partially transmitting mirror 140 and the second electrode 150 are determined so as to have a first-order or higher resonance mode for blue light, and the optical distance between the first electrode 120 and the second electrode 150 is determined so as to have a second-order or higher resonance mode for blue light.

[0084] 17, the red pixel 1100, the green pixel 1200, and the blue pixel 1300 are shown to have the same structure as the light emitting element 200 shown in FIG. 1, but are not necessarily limited to this. The display device 1000 may also apply light emitting elements 210, 220, 230, 240, and 250 according to other embodiments to the red pixel 1100, the green pixel 1200, and the blue pixel 1300, in addition to the light emitting element 200 shown in FIG.

[0085] The light emitting device and display device described above may be applied to devices of various sizes and various applications without limitation, for example, the light emitting device and display device described above may be applied to display panels of mobile phones or smartphones, tablets or smart tablets, laptops, televisions, smart televisions, or small display panels used in head-mounted displays, eyeglass displays, goggle displays, etc.

[0086] Although the light-emitting device having improved luminous efficiency and a display device including the same have been described with reference to the embodiments shown in the drawings, these are merely illustrative, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the disclosed embodiments should be considered from an illustrative rather than a restrictive perspective. The scope of the claims is set forth in the appended claims, not the foregoing description, and all differences within the scope of the claims should be construed as being within the scope of the claims. [Explanation of symbols]

[0087] 110 Reflective layer 120 1st electrode 130a, 130b light-emitting layer 140,145,146 Partially Passing Mirror 141 Transparent conductor layer 142 Charge generation layer 144 Phase correction layer 150 2nd electrode 160 protective layer 200,210,220,230,240,250 Light-emitting element 1000 display devices 1001 board 1100 red pixels 1200 green pixels 1300 blue pixels

Claims

1. A reflective layer; a first electrode disposed on the reflective layer; a second electrode disposed opposite the first electrode; a phase correction layer disposed between the first electrode and the second electrode; a first light-emitting layer disposed between the first electrode and the phase correction layer; a second light-emitting layer disposed between the phase correction layer and the second electrode; a first partially transmitting mirror disposed between the phase correction layer and the first light emitting layer; a second partially transmitting mirror disposed between the phase correction layer and the second light-emitting layer, a first or higher resonance mode is formed between the reflective layer and the first partially transmitting mirror, and a second or higher resonance mode is formed between the reflective layer and the second electrode.

2. The light-emitting element according to claim 1 , wherein the first electrode is a transparent electrode, and the second electrode is a partially transmissive electrode that reflects part of light and transmits part of light.

3. 3. The light-emitting device according to claim 1, wherein the reflective layer and the second electrode form a microcavity having a resonant wavelength, and the phase correction layer is located at a node of an optical wave resonating within the microcavity.

4. 4. The light-emitting element according to claim 1, wherein the reflective layer, the second electrode, the first partially transmitting mirror, and the second partially transmitting mirror cause a phase modulation of greater than 180° for light reflected by the reflective layer, the second electrode, the first partially transmitting mirror, and the second partially transmitting mirror.

5. 5. The light-emitting device according to claim 1, wherein the phase correction layer is made of a transparent conductive material.

6. The light-emitting device according to claim 5 , wherein the phase correction layer has a thickness of 5 nm to 150 nm.

7. 7. The light-emitting device according to claim 1, wherein the first partially transmitting mirror and the second partially transmitting mirror contain silver (Ag), aluminum (Al), a silver alloy, or an aluminum alloy.

8. The light-emitting device according to claim 7 , wherein the first partially transmitting mirror and the second partially transmitting mirror have a thickness of 5 nm to 30 nm.

9. an optical distance between the reflective layer and the first partially transmitting mirror is selected so that a first-order resonant mode or a second-order resonant mode is formed between the reflective layer and the first partially transmitting mirror; 9. The light-emitting element according to claim 1, wherein an optical distance between the second partially transmitting mirror and the second electrode is selected so that a first-order resonance mode or a second-order resonance mode is formed between the second partially transmitting mirror and the second electrode.

10. The first light-emitting layer is a first hole transport layer disposed on the first electrode; a first organic light-emitting material layer disposed on the first hole transport layer; a first electron transport layer disposed on the first organic light-emitting material layer; The second light-emitting layer is a second hole transport layer disposed on the second partially transmitting mirror; a second organic light-emitting material layer disposed on the second hole transport layer; 10. The light-emitting device according to claim 1, further comprising: a second electron transport layer disposed on the second organic light-emitting material layer.

11. 11. The light-emitting device of claim 10, wherein the first layer of organic light-emitting material and the second layer of organic light-emitting material produce light of the same wavelength.

12. 12. The light-emitting element according to claim 11, wherein an optical distance between the reflective layer and the first partially transmitting mirror and an optical distance between the second partially transmitting mirror and the second electrode are selected so that a resonant mode is formed for the wavelength of light generated from the first organic light-emitting material layer and the second organic light-emitting material layer.

13. 11. The light-emitting element of claim 10, wherein the first organic light-emitting material layer produces light at a first wavelength, and the second organic light-emitting material layer produces light at a second wavelength different from the first wavelength.

14. an optical distance between the reflective layer and the first partially transmitting mirror is selected so that a resonant mode is formed for a first wavelength; The light-emitting device according to claim 13 , wherein an optical distance between the second partially transmitting mirror and the second electrode is selected so that a resonant mode is formed for the second wavelength.

15. It includes a plurality of pixels, A display device, wherein each pixel comprises a light-emitting element according to any one of claims 1 to 14.

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