Light-emitting element, display device, method for manufacturing light-emitting element, and method for manufacturing display device

Abstract

A light-emitting element (1) according to the present disclosure comprises, in the following order: a circuit board (2) including a control circuit (PC); a first electrode (3) electrically connected to the control circuit (PC); an active layer (4) including a light-emitting layer (EML); a light-transmissive second electrode (5); a light-transmissive transparent layer (6); and an optical functional layer (7). One of the first electrode (3) and the optical functional layer (7) is a light semi-transmissive layer, and the other is a light-reflective layer.

Description

Light-emitting element, display device, method for manufacturing a light-emitting element, and method for manufacturing a display device

[0001] The present disclosure relates to a light-emitting element, a display device, a method for manufacturing a light-emitting element, and a method for manufacturing a display device.

[0002] Patent Document 1 discloses a laminated structure including a reflective layer, an optical path length adjustment layer, a light extraction layer, an electrode, a light-emitting layer, an electrode, and a protective layer in this order from the substrate side toward the light emission direction for the purpose of improving the light extraction efficiency.

[0003] Japanese Patent Application Laid-Open No. 2011-60549 (published on March 24, 2011)

[0004] However, in the configuration disclosed in Patent Document 1, since there are a reflective layer, an optical path length adjustment layer, and a light extraction layer between the substrate and the electrode, it has been difficult to connect the electrode to the circuit provided on the substrate. There is a demand for a light-emitting element that is easy to connect an electrode to the substrate and has excellent light extraction efficiency and internal quantum efficiency.

[0005] A light-emitting element according to one aspect of the present disclosure includes a circuit board including a control circuit, an optical function layer, a first electrode located between the circuit board and the optical function layer and electrically connected to the control circuit, an active layer located between the first electrode and the optical function layer and including a light-emitting layer, a second electrode located between the active layer and the optical function layer and having light transmissivity, and a transparent layer located between the second electrode and the optical function layer and having light transmissivity, and either the first electrode or the optical function layer is a light semi-transmissive layer and the other is a light reflective layer.

[0006] A display device according to one aspect of the present disclosure has a configuration including a light-emitting element according to one aspect of the present disclosure.

[0007] A method for manufacturing a light-emitting element according to one aspect of the present disclosure includes the steps of: preparing a circuit board including a control circuit; forming a first electrode electrically connected to the control circuit on the circuit board; forming an active layer including a light-emitting layer on the first electrode; forming a second electrode having light transmittance on the active layer; forming a transparent layer having light transmittance on the second electrode; and forming an optical functional layer on the transparent layer, wherein either the first electrode or the optical functional layer is a light semitransmitting layer and the other is a light reflective layer.

[0008] A display device according to one aspect of this disclosure is a method including a method for manufacturing a light-emitting element according to one aspect of this disclosure.

[0009] According to one aspect of this disclosure, it is possible to realize a light-emitting element that is easy to connect to a control circuit and has excellent light extraction efficiency and internal quantum efficiency.

[0010] This is a cross-sectional view showing an example of the configuration of a light-emitting element according to one embodiment of the present disclosure. This is a flowchart showing an example of a method for manufacturing a light-emitting element according to one embodiment of the present disclosure. This is a cross-sectional view showing an example of the configuration of display device according to one embodiment of the present disclosure. This is a cross-sectional view showing an example of a method for manufacturing a display device according to one embodiment of the present disclosure.

[0011] [Embodiment 1] (Configuration of a light-emitting element) Figure 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one embodiment of the present disclosure. As shown in Figure 1, the light-emitting element 1 according to the present disclosure comprises a circuit board 2 including a control circuit PC, an optical functional layer 7, a first electrode 3 located between the circuit board 2 and the optical functional layer 7 and electrically connected to the control circuit PC, an active layer 4 located between the first electrode 3 and the optical functional layer 7 and including a light-emitting layer EML, a second electrode 5 located between the active layer 4 and the optical functional layer 7 and having light transmittance, and a transparent layer 6 located between the second electrode 5 and the optical functional layer and having light transmittance. Either the first electrode 3 or the optical functional layer 7 is a light semitransmitting layer having light semitransmission and light semireflection, and the other is a light reflective layer having only light reflectance.

[0012] According to the above configuration, the first electrode 3, the active layer 4, and the second electrode 5 influence the current-voltage characteristics and internal quantum efficiency of the light-emitting element 1. Therefore, the material and thickness of the transparent layer 6 and the optical functional layer 7 can be determined to optimize the optical path length inside the light-emitting element 1, independently of the current-voltage characteristics and internal quantum efficiency. Furthermore, the material and thickness of the first electrode 3, the active layer 4, and the second electrode 5 can be determined to optimize the current-voltage characteristics and internal quantum efficiency, independently of the optical path length inside the light-emitting element. Consequently, the light extraction efficiency and internal quantum efficiency of the light-emitting element 1 can be improved. In addition, the transparent layer 6 and the optical functional layer 7 are located on the opposite side of the circuit board 2 from the first electrode 3. Therefore, it is easy to connect the first electrode 3 to the control circuit PC provided on the circuit board 2.

[0013] The active layer 4 may optionally include one or more charge-functional layers such as a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer, another hole blocking layer, an electron transport layer (ETL), and an electron injection layer. The control circuit PC controls the current or voltage applied to the first electrode 3, thereby controlling the emission of light from the light-emitting layer (EML). The control circuit PC is also referred to as the "pixel circuit" in a display device DP (see Figure 5) equipped with pixels having light-emitting elements 1.

[0014] In this disclosure, when a layer or a material constituting that layer has a high light transmittance and a low light reflectance, the layer is said to have "light transmittance" or "light transmittance only". When a layer or a material constituting that layer has a low light transmittance and a high light reflectance, the layer is said to have "light reflectance" or "light reflectance only". When a layer or a material constituting that layer has both a high light transmittance and a high light reflectance, the layer is said to have "light semi-transmittance and light semi-reflectance". For example, a layer having a light transmittance of more than 70% and a light reflectance of less than 30% can be said to have "light transmittance", a layer having a light transmittance of less than 40% and a light reflectance of more than 60% can be said to have "light reflectance", and a layer having a light transmittance of 40% or more and 70% or less and a light reflectance of 30% or more and 60% or less can be said to have "light semi-transmittance and light semi-reflectance". For example, a layer having a light transmittance of 80% or more and a light reflectance of 20% or less may be described as having "light transmittance," a layer having a light transmittance of 20% or less and a light reflectance of 80% or more may be described as having "light reflectance," and a layer having a light transmittance of more than 20% but less than 80% and a light reflectance of more than 20% but less than 80% may be described as having "light semi-transmitting and light semi-reflective properties." The light transmittance and light reflectance may be the light transmittance and light reflectance at the emission peak wavelength of the light-emitting layer EML.

[0015] It is beneficial to have an optical resonator formed between the optical functional layer 7 and the first electrode 3 that enhances light having wavelengths within ±10% of the peak wavelength of the light-emitting layer EML. For example, when the peak wavelength of the light-emitting layer EML is 650 nm, an optical resonator that enhances light with wavelengths between 585 nm and 715 nm is preferred. For example, when the peak wavelength of the light-emitting layer EML is 460 nm, an optical resonator that enhances light with wavelengths between 414 nm and 506 nm is preferred. This optical resonator in the light-emitting layer EML improves the light extraction efficiency of the light-emitting element 1 and further improves the color purity of the light-emitting element 1.

[0016] It is advantageous that the optical functional layer 7 is a metal film. Unlike reflection by multilayer films, light reflection by a metal film occurs on the surface of the metal film. Therefore, the optical path length between the optical functional layer 7 and the first electrode 3 can be precisely set, making it easier to form an optical resonator that amplifies light of a desired wavelength. For the same reasons as the optical functional layer 7, it is also advantageous that the first electrode 3 is a metal film.

[0017] It is beneficial for the transparent layer 6 to include a transparent organic film 6a. The organic film has excellent "self-leveling ability," which is the ability to flatten its own upper surface regardless of whether the substrate is uneven or flat. Because the upper surface of the transparent layer 6 is flattened by the self-leveling ability of the transparent organic film 6a, the optical functional layer 7 can be easily formed as a flat reflective film by forming the optical functional layer 7 on top of it. As a result, the optical path length between the optical functional layer 7 and the first electrode 3 can be precisely set, making it easy to form an optical resonator that amplifies light of a desired wavelength. In addition, even if the upper surface of the active layer 4 is uneven, it does not significantly affect the optical functional layer 7, making it suitable for using an active layer 4 formed by methods that easily result in an uneven upper surface, such as printing technology and photolithography technology.

[0018] The transparent organic film 6a may be, for example, an acrylic resin and a polyimide resin. The transparent organic film 6a may contain a photosensitive resin, for example, an acrylic resin to which a photosensitive agent has been added may be used.

[0019] The light-emitting element 1 may be a top-emission type that emits light in the direction from the circuit board 2 toward the optical functional layer 7. In this case, the optical functional layer 7 is a semi-transparent layer having semi-transparent and semi-reflective properties, and the first electrode 3 is a light-reflecting layer having only light reflectivity. Alternatively, the light-emitting element 1 may be a bottom-emission type that emits light in the direction from the optical functional layer 7 toward the circuit board 2. In this case, the first electrode 3 is a semi-transparent layer having semi-transparent and semi-reflective properties, and the optical functional layer 7 is a light-reflecting layer having only light reflectivity.

[0020] (Method for Manufacturing a Light-Emitting Device) Figure 2 is a flowchart showing an example of a method for manufacturing a light-emitting device according to one embodiment of the present disclosure. As shown in Figure 2, first, a circuit board 2 including a control circuit PC is prepared (step S10). Then, a first electrode 3 electrically connected to the control circuit PC is formed on the circuit board 2 (step S20), an active layer 4 including a light-emitting layer EML is formed on the first electrode 3 (step S30), and a second electrode 5 having light transmittance is formed on the active layer 4 (step S40).

[0021] Next, a transparent layer 6 having light-transmitting properties is formed above the second electrode 5 (step S50), and an optical functional layer 7 is formed above the transparent layer 6 (step S60). In steps 20 and S60, the first electrode 3 and the optical functional layer 7 are formed such that one of them is a semi-transparent layer having both semi-transparent and semi-reflective properties, and the other is a reflective layer having only reflective properties.

[0022] Regarding step S60, the optical functional layer 7 may consist of a metal film. For example, the optical functional layer 7 may be formed by depositing a metal onto the upper surface of the transparent layer 6.

[0023] Step S30 includes at least a step of forming an emissive layer (EML) (Step S33). Step S30 may optionally include one or more steps of forming charge functional layers, such as a step of forming a hole injection layer (HIL) (Step S31), a step of forming a hole transport layer (HTL) (Step S32), a step of forming an electron blocking layer, a step of forming a hole blocking layer, a step of forming an electron transport layer (ETL) (Step S34), and a step of forming an electron injection layer.

[0024] [Embodiment 2] Figure 3 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one embodiment of the present disclosure. As shown in Figure 3, in the light-emitting element 1 according to the present disclosure, the transparent layer 6 may include a transparent organic film 6a and a transparent inorganic film 6b located between the transparent organic film 6a and the optical functional layer 7. The transparent inorganic film 6b can reduce the ingress and / or penetration of water, oxygen, and impurities into the interior of the light-emitting element 1, thereby reducing the degradation of the active layer 4 and the control circuit PC.

[0025] The transparent inorganic film may contain, for example, silicon dioxide and silicon nitride.

[0026] [Embodiment 3] Figure 4 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one embodiment of the present disclosure. As shown in Figure 4, the transparent layer 6 in the light-emitting element 1 according to the present disclosure may include a transparent inorganic film 6b. In this case, it is preferable to form the active layer 4 such that the upper surface of the active layer 4 is flat. Therefore, it is preferable to form each layer included in the active layer 4 by a method that facilitates the formation of a flat film, such as vapor deposition.

[0027] [Embodiment 4] Figure 5 is a cross-sectional view showing an example of the configuration of a display device according to one embodiment of the present disclosure. As shown in Figure 5, the display device DP according to the present disclosure comprises at least one light-emitting element 1 according to the present disclosure.

[0028] The display device DP may include a plurality of light-emitting elements 1. The plurality of light-emitting elements 1 may include, for example, a first light-emitting element 1R and a second light-emitting element 1G having a different emission wavelength from the first light-emitting element 1R, and the thickness of the transparent layer 6R of the first light-emitting element 1R and the thickness of the transparent layer 6G of the second light-emitting element 1G may be different. With this configuration, the thickness of the transparent layers 6R and 6G can be set according to the emission wavelengths of the first light-emitting element 1R and the second light-emitting element 1G, and the light extraction efficiency and internal quantum efficiency of the first light-emitting element 1R and the second light-emitting element 1G can be improved.

[0029] The display device DP may further include a third light-emitting element 1B having a different emission wavelength from both the first and second light-emitting elements 1R and 1G, and the thickness of the transparent layer 6B of the third light-emitting element 1B may differ from the thickness of the transparent layers 6R and 6G of the first and second light-emitting elements 1R and 1G.

[0030] The first to third light-emitting elements 1R, 1G, and 1B may share one or more components. For example, the control circuits PC for each of the first to third light-emitting elements 1R, 1G, and 1B may be provided on a single circuit board 2 shared by the first to third light-emitting elements 1R, 1G, and 1B. For example, if the active layer 4 includes a charge function layer, the charge function layer may be continuous across the first to third light-emitting elements 1R, 1G, and 1B. For example, the second electrode 5 may be continuous across the first to third light-emitting elements 1R, 1G, and 1B. For example, the transparent layers 6R, 6G, and 6B for each of the first to third light-emitting elements 1R, 1G, and 1B may be formed integrally. For example, the optical function layer 7 may be continuous across the first to third light-emitting elements 1R, 1G, and 1B.

[0031] (Method for manufacturing a display device) The method for manufacturing the display device DP according to this disclosure includes the method for manufacturing the light-emitting element 1 according to this disclosure.

[0032] Figure 6 is a cross-sectional view showing an example of a method for manufacturing a display device according to one embodiment of the present disclosure. As shown in Figure 6, transparent layers 6R, 6G, and 6B of different thicknesses can be formed simultaneously and integrally using a photosensitive resin. First, steps S10, S20, S30, and S40 are performed for each of the first to third light-emitting elements 1R, 1G, and 1B to form the second electrode 5. Then, a liquid 6X containing a photosensitive resin is applied to the second electrode 5 over the regions corresponding to each of the first to third light-emitting elements 1R, 1G, and 1B (step S51), and the coating of liquid 6X is exposed using a gray tone mask or half tone mask 10 (step S52). Here, the photosensitive resin contained in the liquid 6X is preferably a photocurable resin. Subsequently, the liquid 6X that has not solidified is removed by washing. Since the exposure amount can be made different in the regions corresponding to each of the first to third light-emitting elements 1R, 1G, and 1B using the gray tone mask or half tone mask 10, the thickness of the solidified photosensitive resin can be made different. Therefore, transparent layers 6R, 6G, and 6B of different thicknesses are simultaneously formed integrally from the coating film of liquid 6. Steps S51 and S52 are included in step S50.

[0033] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0034] 1. Light-emitting element 2. Circuit board 3. First electrode 4. Active layer 5. Second electrode 6, 6R, 6G, 6B. Transparent layer 6a. Transparent organic film 6b. Transparent inorganic film 7. Optical functional layer DP: Display device EML: Light-emitting layer PC: Control circuit

Claims

1. A light-emitting element comprising: a circuit board including a control circuit; an optical functional layer; a first electrode located between the circuit board and the optical functional layer and electrically connected to the control circuit; an active layer located between the first electrode and the optical functional layer and including a light-emitting layer; a second electrode located between the active layer and the optical functional layer and having light transmittance; and a transparent layer located between the second electrode and the optical functional layer and having light transmittance, wherein either the first electrode or the optical functional layer is a light-semitransparent layer and the other is a light-reflecting layer.

2. The light-emitting element according to claim 1, wherein an optical resonator is formed between the optical functional layer and the first electrode, which enhances light having wavelengths in the range of ±10% of the peak wavelength of the light-emitting layer.

3. The light-emitting element according to claim 1 or 2, wherein the optical functional layer is a metal film, and the first electrode includes a metal film.

4. The light-emitting element according to any one of claims 1 to 3, wherein the transparent layer includes a transparent organic film.

5. The light-emitting element according to any one of claims 1 to 3, wherein the transparent layer comprises a transparent organic film and a transparent inorganic film located between the transparent organic film and the optical functional layer.

6. The light-emitting element according to claim 4 or 5, wherein the transparent organic film comprises a photosensitive resin.

7. The light-emitting element according to any one of claims 1 to 3, wherein the transparent layer includes a transparent inorganic film.

8. The light-emitting element according to any one of claims 1 to 7, wherein the optical functional layer is a light semitransmitting layer and the first electrode is a light reflective layer.

9. The light-emitting element according to any one of claims 1 to 7, wherein the optical functional layer is a light-reflecting layer and the first electrode is a light-semitransparent layer.

10. A display device comprising a light-emitting element according to any one of claims 1 to 9.

11. The display device according to claim 10, wherein the light-emitting element comprises a first light-emitting element and a second light-emitting element having a different emission wavelength from the first light-emitting element, and the thickness of the transparent layer of the first light-emitting element is different from the thickness of the transparent layer of the second light-emitting element.

12. A method for manufacturing a light-emitting element, comprising the steps of: preparing a circuit board including a control circuit; forming a first electrode electrically connected to the control circuit on the circuit board; forming an active layer including a light-emitting layer on the first electrode; forming a second electrode having light transmittance on the active layer; forming a transparent layer having light transmittance on the second electrode; and forming an optical functional layer on the transparent layer, wherein either the first electrode or the optical functional layer is a light semitransmitting layer and the other is a light reflective layer.

13. The method for manufacturing a light-emitting element according to claim 12, wherein the optical functional layer is made of a metal film.

14. A method for manufacturing a display device, including the method for manufacturing a light-emitting element according to claim 12 or 13.

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