Light-emitting element and light-emitting device

Abstract

A light-emitting element (30) includes: an anode (4); a cathode (8); a light-emitting layer (6) provided between the anode (4) and the cathode (8); a hole transport layer (5) provided between the anode (4) and the light-emitting layer (6); and a control electrode (9) provided inside the hole transport layer (5) so as to be separated from the anode (4) and having an opening (9K).

Description

Light-emitting element and light-emitting device

[0001] The present disclosure relates to a light-emitting element and a light-emitting device.

[0002] In recent years, various display devices have been developed as light-emitting devices including light-emitting elements. In particular, display devices including OLED (Organic Light Emitting Diode) or QLED (Quantum dot Light Emitting Diode) have received high attention because they can achieve low power consumption, thinning, and high image quality.

[0003] For example, Patent Document 1 describes a light-emitting element including an organic hole transport layer made of polyvinylcarbazole.

[0004] Japanese Patent Application Laid-Open No. 2011-61028

[0005] However, in a light-emitting element including an organic hole transport layer and a light-emitting device including such a light-emitting element, the relatively low hole transport ability of the organic hole transport layer, which is an organic substance, strongly affects the element characteristics, and there is a problem that a satisfactory external quantum efficiency (EQE) cannot be obtained.

[0006] An aspect of the present disclosure aims to provide a light-emitting element capable of improving the external quantum efficiency (EQE) and a light-emitting device including such a light-emitting element.

[0007] The light-emitting element of the present disclosure includes, in order to solve the above problems, an anode, a cathode, a light-emitting layer provided between the anode and the cathode, a hole transport layer provided between the anode and the light-emitting layer, and a control electrode provided inside the hole transport layer and spaced apart from the anode and having an opening.

[0008] The light-emitting device of the present disclosure includes a plurality of the above light-emitting elements in order to solve the above problems.

[0009] According to an aspect of the present disclosure, a light-emitting element capable of improving the external quantum efficiency (EQE) and a light-emitting device including such a light-emitting element can be provided.

[0010] This figure shows the typical device characteristics of a light-emitting element comprising an electron transport layer, an emissive layer containing quantum dots, and an organic hole transport layer. This figure shows the equivalent circuit of a light-emitting element showing the typical device characteristics shown in Figure 1. This figure shows a simplified equivalent circuit of the equivalent circuit shown in Figure 2. This figure shows the equivalent circuit of a bipolar transistor which is essentially the same as the simplified equivalent circuit shown in Figure 3. In the simplified equivalent circuit shown in Figure 3, the V-I characteristics of the diode corresponding to ETL / QD and the V-I characteristics of the diode corresponding to HTL are separated, and the current density (J)-external quantum efficiency (EQE) characteristics are superimposed, showing that the peak of the external quantum efficiency (EQE) is near the intersection of the diode current and the diode current, and that the external quantum efficiency (EQE) of the light-emitting element can be improved by improving the V-I characteristics of the diode. This figure shows a schematic cross-sectional view of the configuration of a light-emitting element of Embodiment 1, which is provided inside the hole transport layer. This is a plan view showing an example of a control electrode provided in the light-emitting element of Embodiment 1 shown in Figure 6. This is a plan view showing an example of a control electrode that can be provided in the light-emitting element of Embodiment 1 shown in Figure 6. This is a plan view showing another example of a control electrode that can be provided to the light-emitting element of Embodiment 1 shown in Figure 6. This is a plan view showing yet another example of a control electrode that can be provided to the light-emitting element of Embodiment 1 shown in Figure 6. This is a diagram for explaining the driving method of the light-emitting element of Embodiment 1 shown in Figure 6. This is a diagram showing the V-I characteristics of the light-emitting element of Embodiment 1 shown in Figure 6. This is a diagram showing the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element of Embodiment 1 shown in Figure 6. This is a diagram showing part of the manufacturing process of the light-emitting element of Embodiment 1 shown in Figure 6. This is a diagram showing a process after the manufacturing process of the light-emitting element of Embodiment 1 shown in Figure 14. This is a diagram showing a process after the manufacturing process of the light-emitting element of Embodiment 1 shown in Figure 15. This is a diagram showing the manufacturing process of a light-emitting element that is a modified example of Embodiment 1 shown in Figure 6. This is a cross-sectional view showing the schematic configuration of a light-emitting element that is yet another modified example of Embodiment 1. This is a diagram showing an example of the material constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. This is a diagram showing another example of the material constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. This is a diagram showing yet another example of the material constituting the light-emitting layer provided in the light-emitting element of Embodiment 1.This is a plan view showing the schematic configuration of a display device, which is an example of a light-emitting device including a plurality of light-emitting elements of Embodiment 1. This is a plan view showing the schematic configuration of a display device shown in Figure 22, in which light-emitting elements with control electrodes are provided in each subpixel. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 2, which has control electrodes provided inside a hole transport layer. This is a diagram for explaining the driving method of the light-emitting element of Embodiment 2 shown in Figure 24. This is a diagram showing the V-I characteristics of the light-emitting element of Embodiment 2 shown in Figure 24. This is a diagram showing the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element of Embodiment 2 shown in Figure 24. This is a diagram showing a part of the manufacturing process of the light-emitting element of Embodiment 2 shown in Figure 24. This is a diagram showing a process after the manufacturing process of the light-emitting element of Embodiment 2 shown in Figure 28. This is a diagram showing a process after the manufacturing process of the light-emitting element of Embodiment 2 shown in Figure 29. This is a partial enlarged view of the Z portion shown in Figure 30.

[0011] The embodiments of this disclosure will be described below with reference to Figures 1 to 31. For the sake of convenience, in the following description, components having the same function as those described in a particular embodiment will be denoted by the same reference numerals, and their descriptions may be omitted.

[0012] [Embodiment 1] Figure 1 shows the typical device characteristics of a light-emitting element comprising a light-emitting layer containing quantum dots, an electron transport layer, and an organic hole transport layer. Figure 2 shows the equivalent circuit EQC1 of the light-emitting element showing the typical device characteristics shown in Figure 1. Figure 3 shows the equivalent circuit EQC2, which is a simplified version of the equivalent circuit EQC1 shown in Figure 2. Figure 4 shows the equivalent circuits BEQC1 and BEQC2 of a bipolar transistor, which are essentially the same as the simplified equivalent circuit EQC2 shown in Figure 3. Figure 5 is a diagram illustrating that by separating the V-I characteristics of the diode corresponding to ETL / QD and the V-I characteristics of the diode corresponding to HTL in the simplified equivalent circuit EQC2 shown in Figure 3, and superimposing the current density (J) - external quantum efficiency (EQE) characteristics, the peak of the external quantum efficiency (EQE) is near the intersection of the diode current and the diode current, and that the external quantum efficiency (EQE) of the light-emitting element can be improved by improving the V-I characteristics of the diode.

[0013] The typical device characteristics (V-I characteristics) of a light-emitting element (LED) equipped with a light-emitting layer containing quantum dots, an electron transport layer, and an organic hole transport layer, as shown in Figure 1, have the following two features compared to the device characteristics (V-I characteristics) of a light-emitting element (LED) made entirely of inorganic semiconductors. The first feature is that the current exhibits nonlinearity in the region from 0V to approximately 3V, and the second feature is that the current suppression in the region near 10V is considerably large due to the series resistance caused by the wiring, and shows a dependence of approximately the square to cube of the voltage. The first feature mentioned above is due to ligands being coordinated to the quantum dots contained in the light-emitting layer, and the second feature mentioned above is due to the presence of an organic hole transport layer, which is an organic material. In Figure 1, only the V-I characteristics shown by the thick solid line in the range of approximately 1.2V to 6V are measured values, while the other V-I characteristics shown by the dotted lines are calculated results. In Figure 1, the typical element characteristics (V-I characteristics) of the light-emitting element shown by the dotted and thick solid lines represent the V-I characteristics of the equivalent circuit EQC1 shown in Figure 2. The thick dotted line Id in Figure 1 represents the element characteristics (V-I characteristics) of the diode corresponding to the quantum dot QD and electron transport layer ETL shown in Figure 2. The solid line Isclc in Figure 1 represents the element characteristics (V-I characteristics) of the diode corresponding to the ligand coordinated to the quantum dot QD shown in Figure 2. The dashed line Ip in Figure 1 represents the element characteristics (V-I characteristics) of the shunt (shunt resistor) corresponding to the part of the light-emitting layer other than the quantum dot QD and ligand shown in Figure 2.

[0014] The reason why a light-emitting element comprising an electron transport layer, a light-emitting layer containing quantum dots, and an organic hole transport layer exhibits the unique element characteristics shown in Figure 1 can be explained by the equivalent circuit EQC1 shown in Figure 2. As shown in Figure 2, the equivalent circuit EQC1 of a light-emitting element comprising a light-emitting layer containing quantum dots, an electron transport layer, and an organic hole transport layer is a circuit in which a diode corresponding to the quantum dot QD and the electron transport layer ETL, a shunt (shunt resistor) corresponding to the part of the light-emitting layer other than the quantum dot QD and the ligand, and a diode corresponding to the ligand coordinated to the quantum dot QD are connected in parallel, and a diode corresponding to the organic hole transport layer and a series resistor corresponding to the wiring are connected in series.

[0015] Analysis using the equivalent circuit EQC1 shown in Figure 2 revealed that, as shown in Figure 1, the current flowing through the diode corresponding to the ligand coordinated to the quantum dot QD is less than 1 / 10000 of the current flowing through the diode corresponding to the quantum dot QD and the electron transport layer ETL. Therefore, in the equivalent circuit of a light-emitting device comprising a light-emitting layer containing quantum dots, an electron transport layer, and an organic hole transport layer, the diode corresponding to the ligand coordinated to the quantum dot QD can be ignored. For similar reasons, the shunt (shunt resistor) corresponding to the part of the light-emitting layer other than the quantum dot QD and ligand can also be ignored in the equivalent circuit of a light-emitting device comprising a light-emitting layer containing quantum dots, an electron transport layer, and an organic hole transport layer.

[0016] For the reasons stated above, the equivalent circuit EQC1 shown in Figure 2 can be simplified to the equivalent circuit EQC2 shown in Figure 3. As shown in Figure 3, the equivalent circuit EQC2 is a circuit in which a diode corresponding to the organic hole transport layer, a diode corresponding to the quantum dot QD and electron transport layer ETL, and a series resistor corresponding to the wiring are connected in series.

[0017] The equivalent circuit EQC2 shown in Figure 3 is essentially the same as the equivalent circuit BEQC1 and the equivalent circuit BEQC2 of the bipolar transistor shown in Figure 4 (more precisely, the same operation as when the base current is 0).

[0018] As shown in Figure 5, the inventors of this disclosure have found that by separating the V-I characteristics of the diode corresponding to ETL / QD and the V-I characteristics of the diode corresponding to HTL in the simplified equivalent circuit EQC2 shown in Figure 3, and superimposing the current density (J)-external quantum efficiency (EQE) characteristics, the peak of the external quantum efficiency (EQE) is near the intersection of the diode current and the diode current. They also found that by improving the hole transport characteristics of the HTL represented by the diode in the direction of the arrow shown in Figure 5, the external quantum efficiency (EQE) of the light-emitting element can be improved. Here, the hole transport characteristics of the HTL are the V-I characteristics of the HTL represented by the diode, and it is sufficient if a large current can be passed with a small voltage drop.

[0019] As shown in Figure 5, shifting the intersection point of the diode current and the diode current upwards in the figure, i.e., towards the high-current side, can improve the external quantum efficiency (EQE) of the light-emitting element, and increasing the change in current in response to voltage changes in the diode can suppress the roll-off of the light-emitting element. Such changes in the characteristics of the HTL correspond to an improvement in the hole transportability of the HTL.

[0020] However, as mentioned above, in order to change the V-I characteristics of a diode, one might consider changing the material that makes up the organic hole transport layer. However, since the material that makes up the organic hole transport layer basically needs to be a material that has hole transport capability, it is difficult to significantly change the V-I characteristics even if that material is changed.

[0021] Therefore, the inventors of this disclosure have found that, as will be described in detail later, by providing a control electrode inside the hole transport layer and driving the control electrode in conjunction with the light-emitting drive of the light-emitting element, it is possible to increase the injection of holes into the light-emitting layer by actively attracting and accelerating holes in the hole transport layer, thereby greatly improving the V-I characteristics of the light-emitting element. Furthermore, they have also found that the position of the control electrode in this case is important because if it is adjacent to the anode, the hole density that can be injected into the light-emitting layer will be low, and if it is located below the hole transport layer, the effect of promoting hole movement in the hole transport layer will be low. Therefore, as described above, it is desirable for the control electrode to be located inside the hole transport layer.

[0022] Figure 6 is a cross-sectional view showing a schematic configuration of the light-emitting element 30 of Embodiment 1, which is equipped with a control electrode 9 provided inside the hole transport layer 5.

[0023] As shown in Figure 6, the light-emitting element 30 includes an anode 4, a cathode 8, a light-emitting layer 6 provided between the anode 4 and the cathode 8, a hole transport layer 5 provided between the anode 4 and the light-emitting layer 6, and a control electrode 9 spaced apart from the anode 4 and provided inside the hole transport layer 5, and having multiple apertures 9K. In this embodiment, the case in which the control electrode 9 has multiple apertures 9K is described as an example, but the invention is not limited to this, and the control electrode 9 may have only one aperture 9K. Also, in this embodiment, the case in which the light-emitting element 30 includes a bank 3 that defines the light-emitting region of the light-emitting element and an electron transport layer 7 between the light-emitting layer 6 and the cathode 8 is described as an example, but the invention is not limited to this. The substrate 2 including the thin-film transistor shown in Figure 6 will be described in detail later.

[0024] In this embodiment, the case in which the control electrode 9 is composed of a conductor will be described as an example, but the embodiment is not limited to this, and the control electrode 9 may be composed of a conductor and an insulator, as in Embodiment 2 described later. When the control electrode 9 is composed of a conductor and an insulator, this also includes the case in which the insulator covers at least a part of the conductor. In these cases, the conductor constituting the control electrode 9 can be considered to be in contact with the hole transport layer 5 via the insulator. When the control electrode 9 is composed of a conductor, if a voltage is applied such that the control electrode 9 is at a low potential relative to the anode 4, some of the holes transported in the thickness direction of the hole transport layer 5 will be captured by the control electrode 9, and a current will flow through the control electrode 9. In other words, the current flowing through the control electrode 9 can control the holes transported in the thickness direction of the hole transport layer 5.

[0025] The control electrode 9 can be made of any conductive material, but if the light-emitting element 30 is a bottom-emission type light-emitting element that extracts light in the direction of the lower layer of the light-emitting layer 6, and the cathode 8 is positioned above the anode 4 in a forward-facing structure, the extraction efficiency will decrease if there is a layer that absorbs or reflects light between the light-emitting layer 6 and the anode 4, so it is preferable to use a transparent electrode for the control electrode 9. If the anode 4 is positioned above the cathode 8 in an inverted-facing structure, the control electrode 9 is positioned above the light-emitting layer 6, so if there is a reflective layer between the light-emitting layer 6 and the anode 4, the light that is moving in the opposite direction to the light extraction direction will be returned to the light extraction direction, improving light extraction, so it is preferable to use a reflective electrode for the control electrode 9. When using the transmissive electrodes described above, the conductor constituting the control electrode 9 is preferably a transparent electrode material that transmits visible light. For example, fluorinated tin oxide (FTO), indium tin oxide (ITO), zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), and indium gallium zinc oxide can be suitably used. When using the reflective electrodes described above, the conductor constituting the control electrode 9 is preferably a material that reflects visible light. For example, metallic materials such as Al and Ag can be suitably used.

[0026] On the other hand, if the light-emitting element 30 is a top-emission type light-emitting element that extracts light in the direction of the upper layer of the light-emitting layer 6, and has a forward-facing structure in which the cathode 8 is positioned above the anode 4, it is preferable to use a reflective electrode for the control electrode 9 because if there is a reflective layer between the light-emitting layer 6 and the anode 4, the light extraction can be improved by returning light that is moving in the opposite direction to the light extraction direction. In contrast, if there is an inverse-facing structure in which the anode 4 is positioned above the cathode 8, the control electrode 9 is positioned above the light-emitting layer 6, so if there is a layer that absorbs or reflects light between the light-emitting layer 6 and the anode 4, the extraction efficiency will decrease, so it is preferable to use a transmissive electrode for the control electrode 9.

[0027] There is a trade-off relationship between the contact area, which is the area where the surface of the control electrode 9 is in contact with the hole transport layer 5, and the area of ​​the opening 9K of the control electrode 9. That is, as the contact area increases, the area of ​​the opening 9K of the control electrode 9 decreases, and as the contact area decreases, the area of ​​the opening 9K of the control electrode 9 increases. The larger the contact area, the greater the area of ​​the hole transport layer 5 that can be controlled by the control electrode 9. The larger the area of ​​the opening 9K of the control electrode 9, the more accelerated holes can pass through the opening 9K. Therefore, the contact area and the area of ​​the opening 9K of the control electrode 9 can be appropriately determined by considering both the amount of holes accelerated in the hole transport layer 5 and the amount of accelerated holes that pass through the opening 9K. As shown in Figure 6, in this embodiment, the control electrode 9 is made of a conductor and the entire surface of the control electrode 9 is in contact with the hole transport layer 5, as an example, but it is not limited to this.

[0028] The control electrode 9, located inside the hole transport layer 5, is not particularly limited in its position within the hole transport layer 5 as long as it is spaced apart from the anode 4, that is, electrically isolated from the anode 4. However, in order to further enhance the hole injection effect into the light-emitting layer 6, it is preferable that the control electrode 9 be located closer to the surface of the hole transport layer 5 facing the light-emitting layer 6 (the fourth surface), which is closer to the surface of the hole transport layer 5 facing the light-emitting layer 6, anode 4, which is closer to the surface of the hole transport layer 5 facing the anode 4, which is closer to the surface of the hole transport layer 5, which is closer to the surface of the hole transport layer 5, which is closer to the surface of the hole transport layer 5, which is closer to the surface of the hole transport layer 5, which is closer to the surface of the hole transport layer 5, which is closer to the surface of the anode 4, that is, while insulating so that it does not conduct electricity.

[0029] As shown in Figure 6, in this embodiment, we will explain using the example where the light-emitting element 30 is a forward-stacked light-emitting element, the anode 4 is a lower electrode provided below the light-emitting layer 6, and the cathode 8 is an upper electrode provided above the light-emitting layer 6, but we are not limited to this. The light-emitting element 30 may also be an inverted-stacked light-emitting element, in which case the cathode 8 is a lower electrode provided below the light-emitting layer 6, and the anode 4 is an upper electrode provided above the light-emitting layer 6.

[0030] Figure 7 is a plan view showing an example of a control electrode 9 provided on the light-emitting element 30 of Embodiment 1 shown in Figure 6. Figure 8 is a plan view showing an example of a control electrode 9 that can be provided on the light-emitting element 30 of Embodiment 1 shown in Figure 6. Figure 9 is a plan view showing another example of a control electrode 9 that can be provided on the light-emitting element 30 of Embodiment 1 shown in Figure 6. Figure 10 is a plan view showing yet another example of a control electrode 9 that can be provided on the light-emitting element 30 of Embodiment 1 shown in Figure 6. Note that in Figures 7, 8, 9 and 10, only the lower part of the hole transport layer 5 provided on the anode 4 side of the control electrode 9 is shown, and the upper part of the hole transport layer 5 provided on the cathode 8 side of the control electrode 9 is not shown.

[0031] As shown in Figures 7 and 8, in this embodiment, the control electrode 9 is described as being provided in a mesh shape consisting of 20 or more openings 9K, but it is not limited to this, and in a plan view, the control electrode 9 may have multiple openings 9K only in the region near the center of the hole transport layer 5, or conversely, multiple openings 9K may be provided only in the peripheral region of the hole transport layer 5. With such a configuration, in the portion of the control electrode 9 provided with openings 9K, accelerated holes can pass through the openings 9K.

[0032] Although not shown in the diagram, the control electrode 9 may be arranged in a stripe shape in a plan view, at least in the region near the center of the hole transport layer 5. The entire control electrode 9 may be arranged in a stripe shape, or the control electrode 9 may be arranged in a stripe shape only in the region near the center of the hole transport layer 5 in a plan view, or only in the peripheral region of the hole transport layer 5. With such a configuration, accelerated holes can pass through the portion of the control electrode 9 that is arranged in a stripe shape. When the entire control electrode 9 is arranged in a stripe shape, the control electrode 9 is composed of multiple conductors spaced apart from each other, so these multiple conductors may be electrically connected using wiring or the like.

[0033] As shown in Figure 9, the control electrode 9 includes a plurality of first apertures 9K1 and a plurality of second apertures 9K2 provided outside the plurality of first apertures 9K1. The plurality of second apertures 9K2 are provided along the edge 5E of the hole transport layer 5 in a plan view, and the average area of ​​the plurality of second apertures 9K2 may be smaller than the average area of ​​the plurality of first apertures 9K1. In a plan view, the edge 5E of the hole transport layer 5 is the edge of the effective light-emitting region of the light-emitting element 30. With this configuration, more holes accelerated can pass through the region near the center of the effective light-emitting region of the light-emitting element 30 than in the region near the edge of the effective light-emitting region. Therefore, even if the hole transport layer 5 and the light-emitting layer 6 are formed thicker around the edge of the effective light-emitting region, and the area around the edge of the effective light-emitting region shines brightly, the uniformity of the brightness of the entire effective light-emitting region can be improved.

[0034] As shown in Figure 10, the control electrode 9 may have multiple openings, for example, a plurality of first openings 9K1, a plurality of second openings 9K2 located outside the plurality of first openings 9K1 and smaller than the plurality of first openings 9K1, and a plurality of third openings 9K3 located outside the plurality of second openings 9K2 and smaller than the plurality of second openings 9K2. Here, we will explain using the example of a case where the size of the multiple openings of the control electrode 9 decreases in three stages as it approaches the end of the control electrode 9, but we are not limited to this, and the size of the multiple openings of the control electrode 9 may decrease in N stages (where N is a natural number of 3 or more) as it approaches the end of the control electrode 9. With such a configuration, as you approach the area near the center from the end of the control electrode 9, more accelerated holes pass through the control electrode 9, so even when the hole transport layer 5 and the light-emitting layer 6 are formed thicker around the edge of the effective light-emitting region and the area around the edge of the effective light-emitting region glows brightly, the uniformity of the brightness of the entire effective light-emitting region can be improved.

[0035] For example, in the control electrodes 9 shown in Figures 7, 8, 9, and 10, and in the control electrodes 9 arranged in a stripe shape (not shown), if Sg is the sum of the areas A of each of the multiple openings when the control electrode 9 is viewed from above, and S is the area of ​​the region where the light-emitting layer 6 and the hole transport layer 5 overlap in a plan view of the light-emitting element 30 shown in Figure 6, then the value of Sg / S is preferably 0.2 or more, and the value of the area A of each of the multiple openings of the control electrode 9 is preferably 0.09 square μm or more and 0.9 square μm or less. With such a configuration, it is possible to achieve a good balance between the acceleration of holes by the control electrode 9 and the passage of the accelerated holes through the control electrode 9. Here, the opening of the control electrode 9 means a through hole that penetrates the control electrode 9, but in cases where the control electrode 9 is arranged in a stripe shape, it may mean the region between the conductors. Note that the area S of the region where the light-emitting layer 6 and the hole transport layer 5 overlap in a plan view of the light-emitting element 30 shown in Figure 6 is included in the effective light-emitting region of the light-emitting element 30.

[0036] Furthermore, as shown in Figures 7, 9, and 10, the control electrode 9 may be provided such that, in a plan view, its end coincides with the end 5E of the hole transport layer 5. However, as shown in Figure 8, the control electrode 9 may be provided only in an inner region spaced apart from the end 5E of the hole transport layer 5 in a plan view, and the distance between the end 5E of the hole transport layer 5 and the inner region may be 0.3 μm or more and 0.95 μm or less. With such a configuration, more holes are accelerated as the distance from the end 5E of the hole transport layer 5 approaches the central region. Therefore, even when the hole transport layer 5 and the light-emitting layer 6 are formed thicker around the edges of the effective light-emitting region, and the edges of the effective light-emitting region glow brightly, the uniformity of the brightness of the entire effective light-emitting region can be improved.

[0037] The light-emitting element 30 shown in Figure 6 may be either a top-emission type or a bottom-emission type. The light-emitting element 30 shown in Figure 6 is a light-emitting element with a sequential structure in which the cathode 8 is positioned above the anode 4. In order to make such a sequential structure light-emitting element a top-emission type, the anode 4 should be formed from an electrode material that reflects visible light and the cathode 8 should be formed from an electrode material that transmits visible light. In order to make such a sequential structure light-emitting element a bottom-emission type, the anode 4 should be formed from an electrode material that transmits visible light and the cathode 8 should be formed from an electrode material that reflects visible light.

[0038] Furthermore, the light-emitting element 30 shown in Figure 6 may be a light-emitting element with an inverted stack structure in which the anode 4 is positioned above the cathode 8. To make such an inverted stack structure light-emitting element a top-emission type, the cathode 8 should be formed from an electrode material that reflects visible light and the anode 4 should be formed from an electrode material that transmits visible light. To make such an inverted stack structure light-emitting element a bottom-emission type, the cathode 8 should be formed from an electrode material that transmits visible light and the anode 4 should be formed from an electrode material that reflects visible light.

[0039] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and is conductive, but examples include metallic materials such as Al, Mg, Li, and Ag, or alloys of the metallic materials, or laminates of the metallic material and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the alloy and the transparent metal oxide.

[0040] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and is conductive, but examples include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al and Ag, or nanowires made of metal materials such as Al and Ag.

[0041] The hole transport material contained in the hole transport layer 5 provided in the light-emitting element 30 shown in Figure 6 may be an organic material such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine (poly-TPD), or polyvinylcarbazole (PVK), or an inorganic material such as nickel oxide (NiO) nanoparticles. In this embodiment, for example, the hole transport layer 5 was formed by coating a solution containing crosslinkable TFB, but the invention is not limited to this, and the hole transport layer 5 may also be formed using an inkjet method with a solution containing crosslinkable TFB. Organic materials are generally preferred as hole transport materials. The TFB, poly-TPD, and PVK mentioned above have HOMO (highest occupied orbital) levels close to the valence band upper edge (VBM) of the light-emitting layer 6, or, if the light-emitting layer 6 is composed of quantum dots, close to the valence band upper edge (VBM) of the quantum dots, thus enabling relatively efficient hole injection.

[0042] The light-emitting element 30 shown in Figure 6 may include a hole injection layer (HIL) between the anode 4 and the hole transport layer 5. If the light-emitting element 30 shown in Figure 6 includes a hole injection layer (HIL), the material used to form the hole injection layer (HIL) is not particularly limited as long as it is a hole injection material that can stabilize the injection of holes into the light-emitting layer 6. For example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS) can be used.

[0043] As shown in Figure 6, in this embodiment, the case in which the light-emitting element 30 is equipped with an electron transport layer 7 is described as an example, but the invention is not limited to this, and the light-emitting element 30 may further be equipped with an electron injection layer between the electron transport layer 7 and the cathode 8. Alternatively, the light-emitting element 30 may be equipped with only an electron injection layer between the light-emitting layer 6 and the cathode 8.

[0044] The electron transport material contained in the electron transport layer 7 provided in the light-emitting element 30 shown in Figure 6 may be an organic material such as 2,2',2"-(1,3,5-benzintriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or it may be an electron-transporting nanoparticle such as ZnO particles or oxide particles containing Zn and Mg.

[0045] If the light-emitting element 30 shown in Figure 6 is equipped with an electron injection layer (EIL), the material used to form the electron injection layer (EIL) is not particularly limited as long as it is an electron injection material that can stabilize the injection of electrons into the light-emitting layer 6. For example, alkali metals or alkaline earth metals such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate, sodium polystyrene sulfonate, alkali metals or alkaline earth metals, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, or organic complexes of alkali metals can be used.

[0046] In each embodiment of this disclosure, the light-emitting layer 6 of the light-emitting device is described as an example in which the light-emitting device is a QLED (Quantum dot Light Emitting Diode), but the invention is not limited thereto. For example, the light-emitting device may be an OLED (Organic Light Emitting Diode) equipped with a light-emitting layer containing an organic light-emitting material instead of a light-emitting layer containing quantum dots. A quantum dot is a semiconductor nanoparticle that emits light by the recombination of electrons and holes as the excitons lose energy, after which excitons are generated by injected electrons and holes. A quantum dot may have a core / shell structure, for example, which includes a core and a shell that covers at least a portion of the surface of the core. The shell may be a single layer, a multi-shell consisting of multiple layers containing different materials, or a giant shell with a thickness of 2 nm or more. In this case, the recombination of electrons and holes in the quantum dot mainly occurs in the core. The core of the quantum dot has a valence band level and a conduction band level, and emits light by the recombination of holes in the valence band level and electrons in the conduction band level. Because the emission from quantum dots has a narrow spectrum due to the quantum confinement effect, it is possible to obtain emission with relatively deep chromaticity. Furthermore, the shell has the function of suppressing the generation of defects or dangling bonds in the core and reducing the recombination of carriers that undergo the deactivation process. From the viewpoint of efficiently obtaining the quantum confinement effect in quantum dots, the particle size of the quantum dot core may be about twice or less the exciton Bohr radius of the core material.

[0047] The quantum dot may include materials used for conventionally known core and shell materials in the core and shell materials, respectively. For example, the quantum dot may have a core / shell structure of a group I-III-V chalcopyrite material / ZnS including InP / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or CuInGaS (CIGS). In addition, the quantum dot may contain InZnP, CdSeTe, or ZnSeTe. Furthermore, the core of the quantum dot may contain CuInZnS, CuInS, CuGaS, AgInS, or ZnAgInS. The shell may be formed from multiple layers containing multiple different materials.

[0048] The particle size of the quantum dots is approximately 1 to 100 nm. The quantum dots may be spherical or non-spherical in shape. In this disclosure, the particle size of the quantum dots may be measured by performing cross-sectional observation of the light-emitting layer 6 in the film thickness direction. In this cross-sectional observation, the particle size of each quantum dot may be considered to be the same as the diameter of a circle having the same area as its cross-sectional area. The particle size of the quantum dots may also be measured by measuring the particle size of 20 quantum dots in the cross-sectional observation and calculating the average. The cross-sectional observation may also be performed by analyzing images obtained by capturing cross-sectional images of each layer using a transmission electron microscope (TEM).

[0049] Figure 11 is a diagram illustrating the driving method of the light-emitting element 30 of Embodiment 1 shown in Figure 6.

[0050] As shown in Figure 11, a first voltage V is present between the anode 4 and the cathode 8. Ｄ A second voltage V is applied, and a second voltage V is applied between the control electrode 9 and the anode 4. Ｇ The light-emitting element 30 can be driven by applying this force.

[0051] In this embodiment, as shown in Figure 11, the second voltage V Ｇ The electrode was applied so that anode 4 was positive and control electrode 9 was negative.

[0052] As shown in FIG. 11, by driving the light-emitting element 30, holes injected into the hole transport layer 5 are accelerated by the control electrode 9, and light emission of the light-emitting element 30 can be performed in a state where the hole transport ability of the hole transport layer 5 is improved. Further, when driving the light-emitting element 30 as shown in FIG. 11, some holes are captured by the control electrode 9 and become the current captured by the control electrode 9, but the remaining holes pass through the control electrode 9, so the hole injection into the light-emitting layer 6 is improved and the external quantum efficiency (EQE) is improved. This behavior corresponds to the broken line in FIG. 5 described above (parallel movement of the current of the diode to the high-current side). As a result, the intersection with the diode current also moves to the high-current side and the external quantum efficiency (EQE) is improved.

[0053] Generally, in the light-emitting layer provided in the light-emitting element, a state where the supply amount of electrons is larger than the supply amount of holes is likely to occur. As shown in FIG. 11, the second voltage V Ｇ is preferably applied such that the anode 4 is positive and the control electrode 9 is negative. However, in the light-emitting layer provided in the light-emitting element, when a state where the supply amount of holes is larger than the supply amount of electrons occurs, the second voltage V Ｇ may be applied such that the anode 4 is negative and the control electrode 9 is positive to suppress the injection of holes into the light-emitting layer.

[0054] FIG. 12 is a diagram showing the V-I characteristics of the light-emitting element 30 of Embodiment 1 shown in FIG. 6. FIG. 13 is a diagram showing the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30 of Embodiment 1 shown in FIG. 6.

[0055] As shown in FIG. 12, as the control voltage (second voltage V Ｇ ) is more negative and its absolute value is larger, the control current I Ｄ increases, so the hole injection is improved. -V' shown in FIG. 12 Ｇ and -V Ｇ are negative second voltages V Ｇ , and the absolute value of -V' Ｇ is larger than that of -V Ｇ . On the other hand, when the control voltage (second voltage V Ｇ ) is positive, the control current I Ｄ decreases, so the hole injection is restricted. +V shown in FIG. 12 Ｇ is a positive second voltage V ＧIt is. Also, the control voltage (second voltage V Ｇ Regardless of the magnitude or polarity (positive or negative), the first voltage V Ｄ In the high injection region where the control current I Ｄ The control current I increases Ｄ The signal saturates. The solid line shown in Figure 12 represents the V-I characteristics of the light-emitting element 30 measured without driving the control electrode 9.

[0056] As shown in Figure 13, the second voltage V Ｇ As shown in Figure 12, -V Ｇ From a comparison of the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30 measured with the second voltage V applied, and the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30 measured without driving the control electrode 9 shown by the solid line in Figure 13, the second voltage V Ｇ as -V Ｇ It can be confirmed that the external quantum efficiency (EQE) of the light-emitting element 30 to which the applied voltage is applied is greatly improved.

[0057] Figure 14 shows a part of the manufacturing process of the light-emitting element 30 of Embodiment 1 shown in Figure 6. Figure 15 shows a process following the manufacturing process of the light-emitting element 30 of Embodiment 1 shown in Figure 14. Figure 16 shows a process following the manufacturing process of the light-emitting element of Embodiment 1 shown in Figure 15. In Figures 14, 15, and 16, at least one of a cross-sectional view and a plan view of each process is shown.

[0058] In the process of forming bank 3 on the substrate 2 shown in Figure 14, for example, bank 3 defining the light-emitting region of the light-emitting element 30 can be formed by coating an organic material such as polyimide or acrylic and then patterning it using photolithography (morphology S1). The substrate 2 is a substrate containing a thin-film transistor. The substrate 2 is provided with exposed connection wiring SH, which is electrically connected to the control electrode 9 via control wiring (not shown), and anode connection wiring AH. In the process of forming bank 3 on the substrate 2, bank 3 is formed in such a way that the exposed state of connection wiring SH and anode connection wiring AH is maintained. The substrate 2 containing the thin-film transistor may be formed using materials similar to those used in the past.

[0059] Next, in the step of forming the anode 4 shown in Figure 14, the anode 4 is formed so that it is electrically connected to the anode connection wiring AH and electrically isolated from the control electrode 9 connection wiring SH. In this case, the anode 4 must be located at least above the region of the anode connection wiring AH and not in electrical contact with the control electrode 9 connection wiring SH (morphology S2). Note that this step is unnecessary if the anode connection wiring AH itself can perform the role of an anode. Hereafter, the explanation will assume that the anode 4 has been formed, including this case.

[0060] Next, in the step of forming the first resist layer RS1 shown in Figure 14, the first resist layer RS1 was formed on the connecting wiring SH, on the entire surface of the anode 4, on the region between the connecting wiring SH and the anode 4, and on at least the inclined surface of the bank 3 (morphology S3).

[0061] Next, in the process of patterning the first resist layer RS1 shown in Figure 15, exposure and development were performed so as to leave only the first resist layer RS1 provided on the connecting wiring SH (Form S4).

[0062] Next, in the step of forming the lower part 5b of the hole transport layer 5 shown in Figure 15, a solution containing crosslinkable TFB was applied to deposit the lower part 5b of the hole transport layer 5 with a thickness of approximately 5 nm on the first resist layer RS1, on the anode 4, and in the region between the first resist layer RS1 and the anode 4 (morphology S5).

[0063] Next, in the step of peeling off the first resist layer RS1 shown in Figure 15, a lift-off step was performed to peel off the lower part 5b of the hole transport layer 5 located on the first resist layer RS1 along with the first resist layer RS1, thereby forming a through hole 5bK in the lower part 5b of the hole transport layer 5 that exposes the connection wiring SH of the control electrode 9 (morphology S6).

[0064] Next, in the step of forming the layer 9O that will form the control electrode 9 shown in Figure 16, the metal layer 9O that will form the control electrode 9 was formed on the connection wiring SH of the control electrode 9 and on the lower part 5b of the hole transport layer 5 (morphology S7). As a result, the connection wiring SH of the control electrode 9 and the metal layer 9O that will form the control electrode 9 come into contact in the vertical direction and are electrically connected. The entire metal layer 9O that will form the control electrode 9 is electrically connected. Furthermore, for example, the thickness of the metal layer 9O that will form the control electrode 9 can be formed to be between 1 nm and 5 nm.

[0065] Next, in the process of forming the control electrode 9 shown in Figure 16, a resist layer (not shown) is formed on the metal layer 9O that will form the control electrode 9, and after patterning the resist layer into a predetermined shape, the metal layer 9O that will form the control electrode 9 is patterned using the resist layer as a mask, thereby forming a control electrode 9 having multiple openings 9K (Module S8).

[0066] Next, in the step of forming the upper part 5t of the hole transport layer 5 shown in Figure 16, a solution containing crosslinkable TFB was applied or printed onto the lower part 5b of the hole transport layer 5 and the control electrode 9, and then the upper part 5t of the hole transport layer 5 with a film thickness of approximately 40 nm was formed by thermal curing at a temperature of, for example, 80°C to 100°C (morphology S9).

[0067] Next, although not shown in the diagram, the process of forming the light-emitting layer 6, the process of forming the electron transport layer 7, and the process of forming the cathode 8 are carried out in this order to manufacture the light-emitting element 30 shown in Figure 6.

[0068] Furthermore, by appropriately adjusting the film thickness of the lower part 5b of the hole transport layer 5 in the process of forming the lower part 5b of the hole transport layer 5 shown in Figure 15 (morphology S5) and the film thickness of the upper part 5t of the hole transport layer 5 in the process of forming the upper part 5t of the hole transport layer 5 shown in Figure 16 (morphology S9), the vertical position of the control electrode 9 in the hole transport layer 5 can be adjusted.

[0069] Figure 17 shows a manufacturing process for a light-emitting element, which is a modified example of Embodiment 1 shown in Figure 6.

[0070] In the light-emitting element manufactured by the process shown in Figure 17 (forms S1 to S8), the connection wiring SH provided on the substrate 2 is arranged so as to be surrounded by the anode connection wiring AH, and the shape of the control electrode 9 obtained in the process of forming the control electrode 9 (form S8) is different from the shape of the control electrode 9 provided in the light-emitting element 30 described above. Furthermore, the light-emitting element manufactured by the process shown in Figure 17 (forms S1 to S8) also differs from the light-emitting element 30 described above in that the control electrode 9 is provided spaced apart from the end of the lower part 5b of the hole transport layer 5. Note that each of the processes shown in Figure 17 (forms S1 to S8) is the same as each of the processes shown in Figures 14, 15 and 16 (forms S1 to S8) described above, so their explanation is omitted.

[0071] As described above, the light-emitting element 30 shown in Figure 6 and the light-emitting element which is a modified example of Embodiment 1 shown in Figure 6 may include control wiring (not shown) connected to the control electrode 9, and connecting wiring SH which is electrically connected to the control electrode 9 via the control wiring. The connecting wiring SH is preferably made of a conductor. The connecting wiring SH is preferably provided on the side of the anode 4 opposite to the hole transport layer 5, i.e., on the substrate 2. The connecting wiring SH may also be electrically connected to the control electrode 9 via the control wiring which is located in a first contact hole provided in the anode 4 and in a through hole (second contact hole) 5bK provided in a part of the hole transport layer 5 (lower part 5b of the hole transport layer 5). The control electrode 9 and the control wiring may also be made of the same material.

[0072] Figure 18 is a cross-sectional view showing a schematic configuration of a light-emitting element 30a, which is yet another modification of Embodiment 1.

[0073] In the case of the light-emitting element 30 shown in Figure 6, as described above, the bank 3 was formed first and then the anode 4 was formed during manufacturing. However, as shown in the light-emitting element 30a in Figure 18, the anode 4 may be formed first and then the bank 3 may be formed. The light-emitting element 30a has the same effects as the light-emitting element 30 described above.

[0074] Figure 19 shows an example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1. Figure 20 shows another example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1. Figure 21 shows yet another example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1.

[0075] The light-emitting layer 6 provided in the light-emitting elements 30 and 30a of Embodiment 1 may include an adduct AD surrounding at least one quantum dot BQD, as shown in Figures 19 and 20, or a matrix MR as an adduct filling the space between at least two quantum dot BQDs, as shown in Figure 21. In other words, in the light-emitting layer 6, an adduct may exist around the quantum dot BQD. The adduct AD or the matrix MR as an adduct may have properties such as semiconductor or insulator. The adduct AD or the matrix MR as an adduct may include any of metal oxides, metalloid oxides, and metal sulfides. Note that, as shown in Figures 19, 20, and 21, the quantum dot BQD includes a core BQDC and a shell BQDS.

[0076] The adduct AD or matrix MR as an adduct is, for example, silicon oxide (SiO₂) ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５It may also contain at least one of the following: ), lead oxide (PbO), and copper oxide (CuO). Here, the adduct AD or matrix MR as an adduct may be formed as a polymer. For example, if the adduct AD or matrix MR as an adduct contains silicon oxide as an oxide, it may also be a siloxane compound having siloxane bonds. Furthermore, the adduct AD or matrix MR as an adduct may contain, for example, zinc sulfide (ZnS) and magnesium zinc sulfide (ZnMgS, ZnMgS ２ ) may contain at least one of the following. Note that the chemical formula of the compound is a representative example, and the composition ratio indicated in the chemical formula may or may not be stoichiometric.

[0077] As shown in Figures 19 and 20, in the case where the adduct AD surrounds at least one quantum dot BQD, if the adduct AD occupies more than 90% of the periphery of the quantum dot BQD in the cross-section of the light-emitting layer 6 passing through the quantum dot BQD, then the quantum dot BQD may be considered to be covered by the adduct AD. The adduct AD is, for example, mainly composed of silicon oxide and may be arranged in contact with the surface of the quantum dot BQD, or with an organic ligand OL between the adduct AD and the quantum dot BQD.

[0078] As shown in Figure 21, when the matrix MR as an adduct is formed to fill the space between at least two quantum dots BQD, the matrix MR as an adduct has a thickness of 1000 nm in a direction perpendicular to the film thickness direction at any position in the film thickness direction of the light-emitting layer 6. ２It may be formed as a continuous film having the above area. In addition, in the light-emitting layer 6, the quantum dots BQD may be embedded in a continuous film of matrix MR as an adduct. For example, if 60% or more of the surface of 80% or more of the quantum dots BQD constituting the light-emitting layer 6 is in contact with a continuous film of matrix MR as an adduct, then the quantum dots BQD contained in the light-emitting layer 6 can be said to be embedded in matrix MR as an adduct. Furthermore, when we say that matrix MR as an adduct fills the space between at least two quantum dots BQD, the space between the two quantum dots BQD may be filled only with matrix MR as an adduct, or it may be filled with matrix MR as an adduct and other materials. In addition to matrix MR as an adduct, a material such as a ligand different from matrix MR as an adduct may be included between the two quantum dots BQD. The material such as ligand may be an organic ligand that coordinates to the quantum dots BQD, or it may be an organic ligand that is separated from the quantum dots BQD. If the light-emitting layer 6 contains an organic ligand, for example, the weight ratio of the organic ligand to the total weight of the light-emitting layer 6 may be less than 5%. The weight ratio of the organic ligand can be measured, for example, using TOF-SIMS (time-of-flight secondary ion mass spectrometry). If the organic ligand is dispersed in the light-emitting layer 6, the organic ligand may contribute to the injection of holes and electrons into the quantum dot BQD.

[0079] In forming the light-emitting layer 6, first, a quantum dot dispersion is prepared. The quantum dot dispersion is a dispersion in which quantum dots BQD and a precursor of adduct AD or a precursor of matrix MR as an adduct are dispersed in a solvent. The precursor includes a material that is converted to adduct AD or matrix MR as an adduct through hydrolysis and dehydration condensation by performing a specific operation such as heating or light irradiation. The precursor may have a coordinating functional group that forms a coordination bond with the surface of the quantum dot BQD in the quantum dot dispersion. In this case, the precursor may coordinate to the quantum dot BQD in the quantum dot dispersion. The quantum dot dispersion may also contain a halide having a halogen atom (for example, zinc chloride (ZnCl)). ２The material may also contain halogen atoms. By mixing a material having halogen atoms into the quantum dot dispersion, the halogen atoms can coat the surface of the quantum dot BQD independently of the adduct or the matrix MR as an adduct, thereby reducing defects on the surface of the quantum dot BQD. Therefore, by having halogen atoms in the adduct AD or the matrix MR as an adduct, each light-emitting device increases the coverage of the quantum dot BQD in the light-emitting layer 6, thereby improving the light-emitting properties.

[0080] A quantum dot dispersion may be prepared, for example, by stirring a dispersion containing quantum dots BQD and a dispersion containing a precursor to prepare a mixture, and then extracting a predetermined layer from the mixture. Here, the dispersion containing quantum dots BQD may contain an organic ligand that coordinates to the quantum dots BQD. In this case, for example, during the stirring for the preparation of the mixture, the ligand that coordinates to the quantum dots BQD may be replaced from the organic ligand with a part of a precursor such as 3-(mercaptopropyl)trimethoxysilane (MPS).

[0081] For example, if the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor has a coordination functional group, the precursor may contain 3-(trimethoxysilyl-1-propanechiol (TMSPT)). Also, if the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor does not have a coordination functional group, the precursor may contain diphenylsilanediol (DPSD). Furthermore, barium hydroxide (Ba(OH)) may be used as a catalyst. ２ ) may also be included. Furthermore, for example, if the adduct AD or the matrix MR as an adduct contains zinc sulfide, the precursor may also contain zinc xanthogenic acid, zinc thioureate, and zinc dithiocarboxylate, etc.

[0082] Next, the quantum dot dispersion is coated onto the lower layer of the light-emitting layer 6 to convert the precursor into an adduct AD or a matrix MR as an adduct. The conversion of the precursor into an adduct AD or a matrix MR as an adduct is carried out, for example, by heating the coated quantum dot dispersion to volatilize the solvent and convert the precursor into an adduct AD or a matrix MR as an adduct. For example, if the precursor contains diphenylsilanediol (DPSD) and 3-(trimethoxysilyl-1-propanediol (TMSPT), barium hydroxide (Ba(OH)) is used between diphenylsilanediol (DPSD) molecules, between 3-(trimethoxysilyl-1-propanediol (TMSPT) molecules, and between diphenylsilanediol (DPSD) and 3-(trimethoxysilyl-1-propanediol (TMSPT) molecules. ２ Dehydration condensation occurs using catalysts such as , thereby forming silicon oxide as adduct AD or matrix MR as an adduct. Alternatively, for example, if the precursor contains zinc xanthogenic acid, the zinc xanthogenic acid is decomposed to form zinc sulfide as adduct AD or matrix MR as an adduct. The conversion of the precursor to adduct AD or matrix MR as an adduct occurs sequentially around the quantum dots BQD in the quantum dot dispersion. By this method, a light-emitting layer 6 having adduct AD or matrix MR as an adduct can be formed.

[0083] Figure 22 is a plan view showing a schematic configuration of a display device 1, which is an example of a light-emitting device including a plurality of light-emitting elements 30 and 30a of Embodiment 1. Figure 23 is a plan view showing a schematic configuration of the display device 1 shown in Figure 22, in which light-emitting elements 30 and 30a equipped with control electrodes 9 are provided for each sub-pixel RSP, GSP, and BSP.

[0084] As shown in Figure 22, the display device 1 comprises a frame area NDA and a display area DA. The display area DA of the display device 1 is provided with a plurality of pixels PIX, and each pixel PIX includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, the case in which one pixel PIX is composed of a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP is described as an example, but it is not limited to this. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, green subpixel GSP, and blue subpixel BSP. In this embodiment, the display device 1 is provided with a red light-emitting element 30 / 30a, which is a red light-emitting element with a red light-emitting layer 6, in its red subpixel RSP, the display device 1 is provided with a green light-emitting element 30 / 30a, which is a green light-emitting element with a green light-emitting layer 6, in its green subpixel GSP, and the display device 1 is provided with a blue light-emitting element 30 / 30a, which is a blue light-emitting element with a blue light-emitting layer 6, as an example, but the embodiment is not limited to this. In this embodiment, the display device 1 is used as an example to describe a light-emitting device that includes a plurality of light-emitting elements 30 / 30a of Embodiment 1, but the light-emitting device that includes a plurality of light-emitting elements 30 / 30a of Embodiment 1 may be, for example, a lighting device.

[0085] As shown in Figure 23, in this embodiment, we will explain using the example of a case where each subpixel of the light-emitting device, the display device 1, is equipped with a light-emitting element 30, 30a having a control electrode 9. However, we are not limited to this, and for example, if each subpixel of each color is equipped with a light-emitting element with different materials for the hole transport layer 5 and electron transport layer 7, then only the subpixels of a specific color may be equipped with a light-emitting element 30, 30a having a control electrode 9, and the subpixels other than the specific color may be equipped with a light-emitting element without a control electrode 9.

[0086] According to this embodiment, it is possible to realize a light-emitting element 30 or 30a that can improve external quantum efficiency (EQE), and a display device 1 which is a light-emitting device equipped with the light-emitting elements 30 or 30a.

[0087] [Embodiment 2] The light-emitting element 30b of this embodiment differs from the light-emitting elements 30 and 30a of Embodiment 1, which have a control electrode 9 made of a conductor, in that it has a control electrode 9 made of a conductor 9M and an insulator 10.

[0088] Figure 24 is a cross-sectional view showing a schematic configuration of the light-emitting element 30b of Embodiment 2, which is equipped with a control electrode 9 provided inside the hole transport layer 5.

[0089] As shown in Figure 24, the light-emitting element 30b includes an anode 4, a cathode 8, a light-emitting layer 6 provided between the anode 4 and the cathode 8, a hole transport layer 5 provided between the anode 4 and the light-emitting layer 6, and a control electrode 9 spaced apart from the anode 4 and provided inside the hole transport layer 5, and having multiple apertures 9K. In this embodiment, the case in which the control electrode 9 has multiple apertures 9K is described as an example, but it is not limited to this, and the control electrode 9 may have only one aperture 9K.

[0090] As shown in Figure 24, the control electrode 9 may be composed of a conductor 9M and an insulator 10 covering at least a part of the conductor 9M. In this embodiment, the case in which the control electrode 9 is composed of a conductor 9M and an insulator 10 covering the entire conductor 9M will be described as an example. As shown in Figure 24, the control electrode 9 is composed of a conductor 9M and an insulator 10, and it is preferable that the control electrode 9 is in contact with the hole transport layer 5 via the insulator 10. With such a configuration, the hole transport capability of the hole transport layer 5 can be controlled by voltage. Furthermore, with such a configuration, the presence of the insulator 10 can suppress unnecessary leakage current, so the power consumption when driving the control electrode 9 can be suppressed, and this effect is particularly high during high-brightness operation.

[0091] As the conductor 9M, the material used to form the control electrode 9 composed of the conductor described above in Embodiment 1 can be used.

[0092] As shown in Figure 24, the control electrode 9 may be composed of a conductor 9M having a first surface facing the anode 4, a second surface facing the light-emitting layer 6, and a side surface connecting the first surface and the second surface, and an insulator 10 covering the first surface, the second surface, and the side surface, respectively. Alternatively, the control electrode 9 may be composed of a conductor 9M having a first surface facing the anode 4, a second surface facing the light-emitting layer 6, and a side surface connecting the first surface and the second surface, and an insulator 10 covering the first surface and the second surface, respectively. The insulator 10 may contain any of the following: an oxide of Si or Ge, a nitride of Si or Ge, an oxide of a metal element, and a nitride of a metal element, for example, silicon oxide, aluminum oxide, and titanium oxide. When the conductor 9M is made of a metal element, the insulator 10 may be a surface oxide film obtained by heat-treating the surface of the conductor 9M, or a surface oxide film obtained by spontaneous oxidation.

[0093] Figure 25 is a diagram illustrating the driving method of the light-emitting element 30b of Embodiment 2 shown in Figure 24.

[0094] As shown in Figure 25, a first voltage V is present between the anode 4 and the cathode 8. Ｄ A second voltage V is applied, and a second voltage V is applied between the control electrode 9 and the anode 4. Ｇ The light-emitting element 30b can be driven by applying this.

[0095] In this embodiment, as shown in Figure 25, the second voltage V Ｇ The electrode was applied so that anode 4 was positive and control electrode 9 was negative.

[0096] As shown in Figure 25, by driving the light-emitting element 30b, holes injected into the hole transport layer 5 are accelerated by the control electrode 9, thereby improving the hole transport capability of the hole transport layer 5 and enabling the light-emitting element 30b to emit light. Since the control electrode 9 provided on the light-emitting element 30b is composed of a conductor 9M and an insulator 10 covering at least a part of the conductor 9M, when the light-emitting element 30b is driven as shown in Figure 25, it is possible to suppress the trapping of holes by the control electrode 9 and reduce the current trapped by the control electrode 9. Therefore, more holes pass through the control electrode 9, further improving hole injection into the light-emitting layer 6 and further improving the external quantum efficiency (EQE). In addition, there is no hole loss, especially in the high injection region, and roll-off is also improved.

[0097] Figure 26 shows the V-I characteristics of the light-emitting element 30b of Embodiment 2 shown in Figure 24. Figure 27 shows the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30b of Embodiment 2 shown in Figure 24.

[0098] As shown in Figure 26, the control voltage (second voltage V Ｇ The more negative and larger the absolute value of ) the control current I Ｄ As this increases, hole injection improves. -V' shown in Figure 26. Ｇ and -V Ｇ This is the negative second voltage V Ｇ And, -V Ｇ Rather than -V' Ｇ The absolute value is large. On the other hand, the control voltage (second voltage V Ｇ If ) is positive, the control current I Ｄ As the amount decreases, hole injection is restricted. (See Figure 26 for +V) Ｇ This is the positive second voltage V Ｇ Furthermore, as described above, the control electrode 9 provided on the light-emitting element 30b is composed of a conductor 9M and an insulator 10 that covers at least a part of the conductor 9M, so the first voltage V Ｄ Even in the high injection region where the control current I is high, Ｄ The voltage does not saturate, and hole loss can be suppressed. The solid line shown in Figure 26 represents the V-I characteristics of the light-emitting element 30b measured without driving the control electrode 9.

[0099] As shown in Figure 27, the second voltage V Ｇ As shown in Figure 26, -V' Ｇ The current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30b, measured with the applied voltage, and the -V shown in Figure 26 are shown. Ｇ By comparing the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30b measured with the applied voltage, and the current density (J)-external quantum efficiency (EQE) characteristics of the light-emitting element 30b measured without driving the control electrode 9 shown by the solid line in Figure 26, the control voltage (second voltage V) can be determined. Ｇ It can be confirmed that the more negative and larger the absolute value of ), the greater the improvement in the external quantum efficiency (EQE) of the light-emitting element 30b.

[0100] Figure 28 shows a part of the manufacturing process of the light-emitting element 30b of Embodiment 2 shown in Figure 24. Figure 29 shows a process following the manufacturing process of the light-emitting element 30b of Embodiment 2 shown in Figure 28. Figure 30 shows a process following the manufacturing process of the light-emitting element 30b of Embodiment 2 shown in Figure 29. Figure 31 is a partially enlarged view of the Z portion shown in Figure 30. Note that in Figures 28, 29, and 30, at least one of a cross-sectional view and a plan view of each process is shown.

[0101] The manufacturing process for the light-emitting element 30b includes the steps described above in Embodiment 1 (forms S1 to S6), and form S6 shown in Figure 28 is the same as form S6 shown in Figure 15. Therefore, the explanation of the steps described above in Embodiment 1 (forms S1 to S6) is omitted.

[0102] In the process of forming the metal layer 9O that will form the control electrode 9 shown in Figure 28, the metal layer 9O that will form the control electrode 9 was formed on the connecting wiring SH and on the lower part 5b of the hole transport layer 5 (morphology S7'). For example, the thickness of the metal layer 9O that will form the control electrode 9 can be set so that the thickness of the metal layer 9O after oxidation is, for example, 5 nm or more. In this embodiment, an Al layer was formed as the metal layer 9O that will form the control electrode 9, but it is not limited to this, and for example, a Cr layer or a Ni layer may be formed. Note that the metal layer 9O that will form the control electrode 9 formed in the process of forming the metal layer 9O that will form the control electrode 9 shown in Figure 28 (morphology S7') becomes part of the insulator 10, so its thickness is different from the metal layer 9O that will form the control electrode 9 formed in the process shown in Figure 16 (morphology S7).

[0103] Next, in the process of forming the second resist layer RS2 shown in Figure 28, the second resist layer RS2 was formed over the entire surface of the metal layer 9O that would become the control electrode 9 and the bank 3. Then, exposure and development were performed so that, in a plan view, the second resist layer RS2 remained only on the metal layer 9O that would become the control electrode 9, which overlaps with the connecting wiring SH (morphology S8').

[0104] Next, in the step of forming the insulating layer 10Ob shown in Figure 29, the Al layer, which is the metal layer 9O that will form the control electrode 9 not covered by the second resist layer RS2, was oxidized (morphology S9'). In this embodiment, the metal layer 9O that will form the control electrode 9 not covered by the second resist layer RS2 was oxidized, for example, by heat treatment at a high temperature of about 500°C for about 30 minutes in dry air, and Al ２ O ３ We were able to obtain a layer.

[0105] In addition, as a means of forming a lower insulator other than those described above, instead of insulating the metal layer by heat treatment at high temperatures, it is also possible to deposit materials such as silicon oxide, aluminum oxide, and titanium oxide to a predetermined thickness. The thickness of this insulating layer only needs to be a few nanometers.

[0106] Next, in the step of peeling off the second resist layer RS2 shown in Figure 29, by peeling off the second resist layer RS2, it is possible to expose the Al layer, which is part of the metal layer 9O that will form the control electrode 9, only in the region that overlaps with the connecting wiring SH in a plan view, and whose surface is not oxidized (morphology S10').

[0107] Next, in the step of forming the metal layer 9O' that will form the control electrode 9 shown in Figure 29, the metal layer 9O' that will form the control electrode 9 was formed over the entire surface of the metal layer 9O that will form the control electrode 9 and the layer 10Ob that will form the insulator below it (morphology S11'). The thickness of the metal layer 9O' that will form the control electrode 9 can be, for example, 10 nm or more and 20 nm or less.

[0108] Next, in the process of oxidizing the metal layer 9O' that will form the control electrode 9 shown in Figure 30, a portion of the cathode 8 side of the metal layer 9O' that will form the control electrode 9 is oxidized, and the Al layer which is the metal layer 9O'b that will form the control electrode 9 and the Al layer 10Ot which is the insulator on top of the oxidized metal layer 9O' that will form the control electrode 9 are oxidized. ２ O ３ A laminate can be obtained in which layers are stacked (morphology S12'). The thickness of the layer 10Ot forming the upper insulator can be made to be, for example, about 5 nm, similar to the thickness of the layer 10Ob forming the lower insulator. The metal layer 9O' that will form the control electrode 9 can be oxidized only on its upper surface by heat treatment, for example, in dry air at a high temperature of about 500°C for a predetermined time. The time (minutes) for the heat treatment can be, for example, if it is known that oxidation to a thickness of d nm can be achieved in t minutes, then the time (minutes) required for oxidation to x nm is (x / d). ２ This can be determined. Furthermore, as a means of forming an insulator on the upper part of the control electrode 9, instead of forming an oxide layer by heat treatment at high temperatures as described above, other options include natural oxidation of the surface, or depositing silicon oxide, aluminum oxide, titanium oxide, etc., to a predetermined thickness.

[0109] Next, in the process of forming the control electrode 9 shown in Figure 30, a resist layer (not shown) is formed on the upper insulator layer 10Ot, and after patterning the resist layer into a predetermined shape, the resist layer is used as a mask to form the lower insulator layer 10Ob, which is Al ２ O ３ The Al layer is the base metal layer 9O'b that forms the layer and the control electrode 9, and the Al layer 10Ot that forms the upper insulator. ２ O ３ By patterning a laminate formed by stacking layers, a control electrode 9 having multiple openings 9K can be formed (morphology S13'). In the process of forming the control electrode 9 shown in Figure 30 (morphology S13'), as a result of the formation of multiple openings 9K, at least a portion of the side surface of the conductor 9M, including the side surface of the opening 9K formed on the conductor 9M, is naturally oxidized, and Al ２ O ３ This forms a layer. Therefore, as shown in Figure 31, in this embodiment, a control electrode 9 can be realized that is composed of a conductor 9M and an insulator 10 that covers the entire conductor 9M.

[0110] Next, although not shown in the diagram, the process of forming the upper part 5t of the hole transport layer 5 shown in Figure 16 (morphology S9), the process of forming the light-emitting layer 6, the process of forming the electron transport layer 7, and the process of forming the cathode 8 are carried out in this order to manufacture the light-emitting element 30b shown in Figure 24.

[0111] According to this embodiment, a light-emitting element 30b capable of improving external quantum efficiency (EQE), and a light-emitting device equipped with the light-emitting element 30b can be realized.

[0112] [Additional Notes] 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.

[0113] This disclosure can be used in light-emitting elements and light-emitting devices.

[0114] 1 Display device 2 Substrate 3 Bank 4 Anode 5 Hole transport layer 5E Edge of hole transport layer 5b Lower part of hole transport layer 5bK Through hole at the bottom of hole transport layer 5t Upper part of hole transport layer 6 Light-emitting layer 7 Electron transport layer 8 Cathode 9 Control electrode 9O, 9O', 9O'b Metal layer that forms the basis of the control electrode 9K Aperture of the control electrode 9K1 First aperture of the control electrode 9K2 Second aperture of the control electrode 9K3 Third aperture of the control electrode 9M Conductor 10 Insulator 10Ob Layer forming the lower insulator 10Ot Layer forming the upper insulator 30, 30a, 30b Light-emitting element SH Connection wiring for the control electrode AH Connection wiring for the anode BQD Quantum dot BQDC Quantum dot core BQDS Quantum dot shell AD Adductor OL Organic ligand MR Matrix RS1 First resist layer RS2 Second resist layer PIX Pixel RSP Red subpixel GSP Green subpixel BSP Blue subpixel DA Display area NDA Border area

Claims

1. A light-emitting element comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; a hole transport layer provided between the anode and the light-emitting layer; and a control electrode spaced apart from the anode and provided inside the hole transport layer, and having an opening.

2. The light-emitting element according to claim 1, wherein the control electrode has a plurality of apertures.

3. The light-emitting element according to claim 1 or 2, wherein the control electrode is made of a conductor.

4. The light-emitting element according to claim 1 or 2, wherein the control electrode is composed of a conductor and an insulator covering at least a portion of the conductor.

5. The light-emitting element according to claim 1 or 2, wherein the control electrode is composed of a conductor and an insulator, and the control electrode is in contact with the hole transport layer via the insulator.

6. The light-emitting element according to claim 1 or 2, wherein the control electrode comprises a conductor having a first surface facing the anode, a second surface facing the light-emitting layer, and a side surface connecting the first surface and the second surface, and an insulator covering the first surface and the second surface, respectively.

7. The light-emitting element according to claim 1 or 2, wherein the control electrode comprises a conductor having a first surface facing the anode, a second surface facing the light-emitting layer, and a side surface connecting the first surface and the second surface, and an insulator covering the first surface, the second surface, and the side surface, respectively.

8. The light-emitting element according to any one of claims 4 to 7, wherein the insulator comprises an oxide of Si or Ge, a nitride of Si or Ge, an oxide of a metal element, and a nitride of a metal element.

9. The light-emitting element according to any one of claims 4 to 7, wherein the insulator is one of silicon oxide, aluminum oxide, and titanium oxide.

10. The light-emitting element according to any one of claims 1 to 9, wherein the control electrode is provided closer to the fourth surface facing the light-emitting layer than to the third surface facing the anode of the hole transport layer.

11. The light-emitting element according to any one of claims 1 to 10, wherein the control electrode is arranged in a mesh shape in a plan view, at least in the region near the center of the hole transport layer.

12. The light-emitting element according to any one of claims 1 to 10, wherein the control electrodes are arranged in a stripe shape in a plan view, at least in the region near the center of the hole transport layer.

13. The light-emitting element according to any one of claims 1 to 12, wherein the control electrode has a plurality of apertures, and when the control electrode is viewed from above, the sum of the areas A of each of the plurality of apertures is Sg, and when the area of ​​the region where the light-emitting layer and the hole transport layer overlap in a plan view is S, the value of Sg / S is 0.2 or more, and the value of the area A of each of the plurality of apertures is 0.09 square μm or more and 0.9 square μm or less.

14. The light-emitting element according to any one of claims 1 to 13, wherein the control electrode is provided only in an inner region spaced apart from the edge of the hole transport layer in a plan view.

15. The light-emitting element according to claim 14, wherein the distance between the end of the hole transport layer and the inner region is 0.3 μm or more and 0.95 μm or less.

16. The light-emitting element according to any one of claims 1 to 13, wherein the control electrode has a plurality of openings, the plurality of openings includes a plurality of first openings and a plurality of second openings provided outside the plurality of first openings, the plurality of second openings are provided along the edge of the hole transport layer in a plan view, and the average area of ​​the plurality of second openings is smaller than the average area of ​​the plurality of first openings.

17. The light-emitting element according to any one of claims 1 to 13, wherein the control electrode has a plurality of apertures, and the size of the plurality of apertures decreases in N steps (where N is a natural number of 3 or more) as they approach the end of the control electrode.

18. The light-emitting element according to any one of claims 1 to 17, wherein a first voltage is applied between the anode and the cathode, and a second voltage is applied between the control electrode and the anode.

19. The light-emitting element according to claim 18, wherein the second voltage is applied such that the anode is positive and the control electrode is negative.

20. A light-emitting element according to any one of claims 1 to 19, comprising: a control wiring connected to the control electrode; and a connecting wiring electrically connected to the control electrode via the control wiring.

21. The light-emitting element according to claim 20, wherein the connecting wiring is made of a conductor.

22. The light-emitting element according to claim 20 or 21, wherein the connecting wiring is provided on the side of the anode opposite to the hole transport layer side.

23. The light-emitting element according to any one of claims 20 to 22, wherein the connecting wiring is electrically connected to the control electrode via the control wiring disposed in a first contact hole provided in the anode and a second contact hole provided in the hole transport layer.

24. The light-emitting element according to any one of claims 20 to 23, wherein the control electrode and the control wiring are made of the same material.

25. The light-emitting element according to any one of claims 1 to 24, wherein the anode is a lower electrode provided as a layer below the light-emitting layer, and the cathode is an upper electrode provided as a layer above the light-emitting layer.

26. The light-emitting element according to any one of claims 1 to 25, wherein the light-emitting layer includes a plurality of quantum dots.

27. The light-emitting element according to claim 26, wherein an adduct exists around the quantum dot in the light-emitting layer.

28. The light-emitting element according to claim 27, wherein the adduct fills the space between at least two of the quantum dots, and the adduct contains a ligand.

29. A light-emitting device comprising a plurality of light-emitting elements according to any one of claims 1 to 28.

Images