Light-emitting element, display device, method for producing light-emitting element, nanoparticle, and method for producing nanoparticle

Abstract

The light-emitting element according to the present disclosure comprises an anode and a cathode, a light-emitting layer disposed between the anode and the cathode, and an oxide layer (HFL) that is disposed between the anode and the light-emitting layer. The oxide layer has hole transportability and contains trivalent nickel.

Description

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

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

[0002] Patent Document 1 discloses a configuration in which a buffer layer containing nanoparticles containing a metal oxide such as nickel oxide is any layer selected from a hole transport layer, a hole injection layer, a hole extraction layer, an electron transport layer, an electron injection layer, and an electron extraction layer.

[0003] Japan Special Publication No. 2018-506857

[0004] The carrier balance in the light-emitting layer of the light-emitting device tends to fall into an electron excess state, which reduces the external quantum efficiency (EQE) of the light-emitting device.

[0005] A light-emitting element according to one aspect of the present disclosure includes an anode and a cathode, a light-emitting layer located between the anode and the cathode, and an oxide layer located between the anode and the light-emitting layer, the oxide layer having hole transport properties and containing trivalent nickel.

[0006] A display device according to an aspect of the present disclosure includes a light-emitting element according to an 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 forming an anode, forming a cathode, forming a light-emitting layer between the steps of forming the anode and forming the cathode, and forming an oxide layer having hole-transporting properties between the steps of forming the anode and forming the light-emitting layer, such that the oxide layer contains trivalent nickel.

[0008] The nanoparticles according to one embodiment of the present disclosure contain trivalent nickel and an oxide.

[0009] A method for producing nanoparticles according to one embodiment of the present disclosure includes a step of obtaining a second liquid in which second nanoparticles containing trivalent nickel are dispersed by mixing a first liquid in which first nanoparticles containing nickel oxide are dispersed with an oxidation treatment solution.

[0010] According to one aspect of the present disclosure, the external quantum efficiency (EQE) of a light-emitting device can be improved.

[0011] 1 is a schematic cross-sectional view showing an example of the configuration of a light-emitting element according to an embodiment of the present disclosure. FIG. 1 is a schematic cross-sectional view showing an example of the composition of nanoparticles according to an aspect of the present disclosure. FIG. 1 is a schematic cross-sectional view showing a modified example of the configuration of a light-emitting element according to an embodiment of the present disclosure. FIG. 2 is a schematic flow diagram showing an example of a first manufacturing method of a light-emitting element according to an embodiment of the present disclosure. FIG. 3 is a schematic cross-sectional view showing an example of a process for forming the oxide layer shown in FIG. 4. FIG. 4 is a diagram showing a roughness curve showing the surface roughness of an oxide layer according to an example of the present disclosure. FIG. 5 is a diagram showing a roughness curve showing the surface roughness of a hole injection layer according to a comparative example. FIG. 6 is a diagram showing curves showing the photoelectric characteristics of light-emitting elements according to an example and a comparative example. FIG. 7 is a diagram for explaining arithmetic mean roughness and ten-point mean roughness. FIG. 8 is a schematic flow diagram showing an example of a second manufacturing method of a light-emitting element according to an embodiment of the present disclosure. FIG. 9 is a schematic diagram showing an example of a process for preparing the second liquid shown in FIG. 10. FIG. 11 is a schematic cross-sectional view showing an example of a process for forming an oxide layer in the second manufacturing method of a light-emitting element according to an embodiment of the present disclosure. FIG. 12 is a schematic cross-sectional view showing an example of a configuration of a display device according to an aspect of the present disclosure.

[0012] [Embodiment 1] (Configuration of Light-Emitting Element) Fig. 1 is a schematic cross-sectional view showing an example of the configuration of a light-emitting element according to an embodiment of the present disclosure. As shown in Fig. 1 and Fig. 2, a light-emitting element ED according to the present disclosure includes an anode AD, a cathode CD, an emitting layer EML located between the anode AD and the cathode CD, and an oxide layer HFL located between the anode AD and the emitting layer EML, having hole transport properties, and containing trivalent nickel (Ni(III)). In the example shown in Fig. 1, the oxide layer HFL is used as a hole injection layer.

[0013] In the past, nickel oxide (NiO) containing divalent nickel has been used for the oxide layer having hole transport properties, but trivalent nickel has not been used. Furthermore, the carrier balance in the light-emitting layer of the light-emitting element tends to fall into an electron excess, which reduces the external quantum efficiency (EQE) of the light-emitting element.

[0014] According to the above configuration of the present disclosure, the oxide layer HFL contains trivalent nickel. Trivalent nickel is superior to divalent nickel in terms of hole mobility. Therefore, the oxide layer HFL according to the present disclosure has high hole mobility and improves the carry balance in the emitting layer EML. As a result, the internal quantum efficiency (IQE) and external quantum efficiency (EQE) of the light-emitting element ED are improved.

[0015] The oxide layer HFL may contain hydroxide and / or oxyhydroxide in addition to oxide. The oxide layer HFL may contain nanoparticles NP, and the nanoparticles NP may contain trivalent nickel (Ni(III)) and hydroxyl groups (—OH). Trivalent nickel and hydroxyl groups coexist in the nanoparticles NP. The hydroxyl groups allow trivalent nickel to exist. Here, the hydroxyl groups may be chemically bonded to the trivalent nickel or may be covalently bonded. In the form of nickel oxyhydroxide (NiO(OH)), the trivalent nickel and hydroxyl groups can stably exist. In addition to nanoparticles NP containing trivalent nickel, the oxide layer HFL may also contain nanoparticles not containing trivalent nickel, and / or a matrix material located between the nanoparticles NP, and / or a ligand material capable of coordinating with the nanoparticles NP. For example, as shown in the bottom row of Figure 5 described below, the oxide layer HFL may contain first nanoparticles NP1 not containing trivalent nickel and second nanoparticles NP2 containing trivalent nickel.

[0016] 2 is a schematic diagram showing an example of the composition of the oxide layer HFL according to one embodiment of the present disclosure. In FIG. 2, m and n are natural numbers and represent the abundance ratio of nickel oxide (NiO) and nickel oxyhydroxide (NiO(OH)). In the nanoparticles NP, the distribution of nickel oxide and nickel oxyhydroxide is arbitrary and is not limited.

[0017] When the oxide layer HFL according to the present disclosure is subjected to an analysis using an X-ray photoelectron spectrometer (XPS) or an energy dispersive X-ray fluorescence analyzer (EDX), at least trivalent nickel is detected. Furthermore, hydroxyl groups can also be expected to be detected.

[0018] Referring again to FIG. 1 , the light-emitting device ED may be a quantum dot light-emitting diode (QLED) in which the emission layer EML contains quantum dots QDs. The quantum dots QDs may include one or more compounds selected from the group consisting of cadmium selenium (CdSe), indium phosphide (InP), zinc selenium (ZnSe), etc. The quantum dots QDs may have a core structure, a core-shell structure, or a multi-shell structure. Alternatively, the light-emitting device ED may be an organic light-emitting diode (OLED) in which the emission layer EML contains an organic light-emitting material.

[0019] The anode AD may be formed by vapor deposition or sputtering and may have a single-layer structure or a multi-layer structure. For example, the anode AD may be formed by sequentially vapor-depositing indium tin oxide (ITO), silver (Ag), and ITO, and then patterning a film consisting of three layers of ITO / Ag / ITO.

[0020] The cathode CD may be formed by vapor deposition or sputtering and may have a single layer structure or a multi-layer structure. The cathode CD may include, for example, an ITO film or silver nanowires.

[0021] The light-emitting element ED may include additional components. For example, the light-emitting element ED may include an electron transport layer ETL and / or an electron injection layer (EIL) located between the emitting layer EML and the cathode CD. For example, the light-emitting element ED may include a hole transport layer HTL located between the oxide layer HFL and the emitting layer EML.

[0022] The electron transport layer ETL may include an inorganic continuous film, an organic continuous film, or nanoparticles. The electron transport layer ETL may include a metal oxide such as zinc oxide (ZnO) and magnesium zinc oxide (MgZnO).

[0023] The hole transport layer HTL may include an inorganic continuous film or an organic continuous film, and may include a hole transporting organic material such as TFB and poly-TPD.

[0024] 3 is a schematic cross-sectional view showing a modified example of the configuration of a light-emitting element according to an embodiment of the present disclosure. As shown in FIG. 3, the oxide layer HFL may serve as both a hole injection layer and a hole transport layer. Alternatively, a separate hole injection layer may be provided between the oxide layer HFL and the anode AD, and the oxide layer HFL may be used as a hole transport layer.

[0025] (First Manufacturing Method of Light-Emitting Device) Fig. 4 is a schematic flow diagram showing an example of a first manufacturing method of a light-emitting device according to an embodiment of the present disclosure. As shown in Fig. 4, the first manufacturing method of a light-emitting device ED according to the present disclosure includes the steps of preparing a substrate SB such as a support substrate or a circuit board (step S10), forming an anode AD (step S20), forming a cathode CD (step S30), forming an emitting layer EML between the steps of forming the anode AD and the cathode CD (step S40), and forming an oxide layer HFL having hole transport properties between the steps of forming the anode AD and the step of forming the emitting layer EML so that the oxide layer HFL contains trivalent nickel (Ni(III)) (step S50). This allows the light-emitting device ED according to the present disclosure to be manufactured.

[0026] The light-emitting element ED may be manufactured in the order of steps S10, S20, S50, S40, and S30. That is, the anode AD may be formed on the substrate SB, the oxide layer HFL may be formed on the anode AD, the emitting layer EML may be formed on the oxide layer HFL, and the cathode CD may be formed on the emitting layer EML. It should be understood that the light-emitting element ED may alternatively be manufactured in the order of steps S10, S30, S40, S50, and S20. That is, the cathode CD may be formed on the substrate SB, the emitting layer EML may be formed on the cathode CD, the oxide layer HFL may be formed on the emitting layer EML, and the anode AD may be formed on the oxide layer HFL. Hereinafter, for simplicity of explanation, a case where the anode AD is formed in order will be described. In the present disclosure, "forming component X on component Y" encompasses a case where component X is in direct contact with component Y, and a case where another component Z is sandwiched between component X and component Y, so that component X is not in contact with component Y.

[0027] The method for manufacturing the light-emitting element ED according to the present disclosure may include steps of forming additional components, such as a step of forming a hole transport layer HTL (step S60) and a step of forming an electron transport layer ETL (step S70).

[0028] 5 is a schematic cross-sectional view showing an example of the process for forming the oxide layer shown in FIG. 4. As shown in FIGS. 4 and 5, the process for forming the oxide layer HFL (step S50) in the first manufacturing method includes the steps of: applying a first liquid DL1 containing a plurality of first nanoparticles NP1 dispersed therein, onto the anode AD (step S52a), and drying the liquid (step S52b) to form a nanoparticle layer NPL containing a plurality of first nanoparticles NP1 (step S52); and contacting the nanoparticle layer NPL with an oxidation treatment solution OPL to convert some or all of the plurality of first nanoparticles NP1 into one or more second nanoparticles NP2 containing trivalent nickel (Ni(III)). This forms an oxide layer HFL containing one or more second nanoparticles NP2 (and, in some cases, one or more first nanoparticles NP1). The oxide layer HFL may then be washed and dried (step S56). The second nanoparticles NP2 correspond to the nanoparticles NP shown in Figures 1 and 3. The second nanoparticles NP2 may contain nickel oxide containing divalent nickel and nickel oxyhydroxide containing trivalent nickel, as shown in Figure 2.

[0029] According to the first manufacturing method, it has been experimentally confirmed that the surface roughness of the oxide layer HFL is reduced more than that of the nanoparticle layer NPL. By reducing the surface roughness, it is possible to reduce the leakage current and in-plane luminance unevenness of the light-emitting element ED. Therefore, the EQE and reliability of the light-emitting element ED are improved.

[0030] In step S54, the nanoparticle layer NPL may be brought into contact with the oxidation treatment solution OPL by immersing the nanoparticle layer NPL in the oxidation treatment solution OPL. The nanoparticle layer NPL may be brought into contact with the oxidation treatment solution OPL by other methods, such as applying or spraying the oxidation treatment solution OPL onto the nanoparticle layer NPL. The oxidation treatment solution OPL penetrates into the nanoparticle layer NPL and oxidizes some or all of the first nanoparticles NP1, resulting in some or all of the divalent nickel (III) becoming trivalent nickel (Ni(III)). Immersion is preferred in order to supply a sufficient amount of the oxidation treatment solution OPL to the entire nanoparticle layer NPL.

[0031] The oxidation treatment solution OPL is an aqueous solution of hydrogen peroxide (H ２ O ２ aq.) Part or all of nickel oxide (NiO) may be hydrogen peroxide (H ２ O ２ ) and becomes nickel oxyhydroxide (NiO(OH)). For step S54, the inventors recommend that the oxidation treatment solution OPL be an aqueous hydrogen peroxide solution, that the concentration of the aqueous hydrogen peroxide solution be 1 to 55 mol%, and that the immersion time be 1 to 60 minutes. For step S56, the inventors recommend that the drying temperature be 100 to 200°C and the drying time be 1 to 60 minutes.

[0032] Example 1 A light-emitting element ED according to Example 1 of the present disclosure was manufactured using the method shown in FIGS. 4 and 5. A planarization film was formed on a substrate SB using an insulating material, an anode AD was formed on the planarization film, and an edge cover was formed to cover the edge of the anode AD. Then, a nanoparticle layer NPL including first nanoparticles NP1 containing nickel oxide was formed on the anode AD and the edge cover. Subsequently, the nanoparticle layer NPL together with the substrate SB was immersed in an oxidation treatment solution OPL for 5 minutes. The oxidation treatment solution OPL was a hydrogen peroxide aqueous solution with a concentration of 40 mol%. The oxide layer HFL was then washed with water and dried at 200° C. for 15 minutes.

[0033] Next, the surface roughness of the oxide layer HFL was measured using an atomic force microscope (AFM). After the measurement, a hole transport layer HTL, an emission layer EML, an electron transport layer ETL, and a cathode CD were formed. The hole transport layer HTL was formed and dried using TFB to a target thickness of 25 nm after drying. The quantum dots QD were luminescent quantum dots with cadmium selenium (CdSe) as the core material, and the emission layer EML was formed and dried to a target thickness of 30 nm after drying. The electron transport layer ETL was formed and dried using zinc oxide (ZnO) to a target thickness of 50 nm after drying. After the light-emitting device ED was completed, the electrical characteristics of the light-emitting device ED were measured.

[0034] Comparative Example 1 A light-emitting device according to Comparative Example 1 of the present disclosure was manufactured and measured in the same manner as the light-emitting device ED according to Example 1 described above, except that the nanoparticle layer NPL was used as the hole injection layer.

[0035] Fig. 6 is a diagram showing a roughness curve illustrating the surface roughness of an oxide layer according to an example of the present disclosure. Fig. 7 is a diagram showing a roughness curve illustrating the surface roughness of a hole injection layer according to a comparative example. Fig. 8 is a diagram showing curves illustrating the photoelectric characteristics of light-emitting devices according to examples and comparative examples. In Fig. 8, the curve according to Example 1 is shown by a solid line, and the curve according to Comparative Example 1 is shown by a dashed line. The vertical axis of Fig. 8 represents the EQE of the light-emitting device, and the horizontal axis represents the current density applied to the light-emitting device.

[0036] Compared with the roughness curve of the hole injection layer according to Comparative Example 1 shown in FIG. 6 , the roughness curve of the oxide layer HFL according to Example 1 shown in FIG. 7 had smaller fluctuations in the height direction of the surface. Therefore, the oxide layer HFL had a smaller surface roughness than the nanoparticle layer NPL. More specifically, the nanoparticle layer NPL according to Comparative Example 1 had an arithmetic mean roughness of 3.0 nm and a ten-point mean roughness of 17.5 nm. In contrast, the oxide layer HFL according to Example 1 had an arithmetic mean roughness of 2.3 nm and a ten-point mean roughness of 14.0 nm. Furthermore, as shown in FIG. 7 , the EQE according to Example 1 was consistently greater than the EQE according to Comparative Example 1.

[0037] FIG. 9 is a diagram illustrating arithmetic mean roughness and ten-point mean roughness. As shown in FIG. 9 , a reference length L is extracted from the roughness curve of the surface to be measured in the direction of the mean line. The x-axis is taken in the direction of the mean line of this extracted portion, and the y-axis is taken in the direction of the longitudinal magnification. The roughness curve is expressed by the function y = f(x). The value m of the mean line y = m of this extracted portion is expressed by the following formula (1), and the arithmetic mean roughness Ra of this extracted portion is expressed by the following formula (2). Furthermore, the ten-point mean roughness Rz of this extracted portion is the sum of the average value of the absolute values ​​of the elevations (Yp1 to Yp5) of the highest to fifth highest peaks and the average value of the absolute values ​​of the elevations (Yv1 to Yv5) of the lowest to fifth lowest valley bottoms, measured from the mean line y = m in the longitudinal magnification direction. That is, the ten-point mean roughness Rz of the extracted portion is expressed by the following formula (3).

[0038] 10 is a schematic flow diagram showing an example of a second manufacturing method of a light-emitting element according to an embodiment of the present disclosure. As shown in FIG. 10, the second manufacturing method of the light-emitting element ED according to the present disclosure includes steps S10, S20, S50, S60, S40, S70, and S30, and further includes a step (step S80) of preparing a second liquid DL2 in which second nanoparticles NP2 containing trivalent nickel are dispersed.

[0039] Fig. 11 is a schematic diagram showing an example of the step of preparing the second liquid shown in Fig. 10. As shown in Fig. 11, the step of preparing the second liquid DL2 (step S80) may include a step of obtaining the second liquid DL2 in which one or more second nanoparticles NP2 containing trivalent nickel (and in some cases one or more first nanoparticles NP1) are dispersed by mixing the first liquid DL1 in which a plurality of first nanoparticles NP1 containing nickel oxide (Ni(II)O) are dispersed with an oxidation treatment solution OPL.

[0040] 12 is a schematic cross-sectional view illustrating an example of a step of forming an oxide layer in the second manufacturing method of the light-emitting element according to the embodiment of the present disclosure. As shown in FIG. 10 and FIG. 12, in the step of forming the oxide layer HFL (step S50) in the second manufacturing method, the second liquid DL2 is applied onto the anode AD (step S58a) and dried (step S58b), thereby forming the oxide layer HFL (step S58).

[0041] According to the second manufacturing method, the first liquid DL1 containing the first nanoparticles NP1 is mixed with the oxidation treatment solution OPL. Therefore, when the amount and concentration of the oxidation treatment solution OPL are sufficient, all of the first nanoparticles NP1 can meet with the oxidation treatment solution OPL and become second nanoparticles NP2. On the other hand, according to the first manufacturing method described above, the nanoparticle layer NPL comes into contact with the oxidation treatment solution OPL. Therefore, even if the amount and concentration of the oxidation treatment solution OPL are sufficient, the oxidation treatment solution OPL may not completely penetrate the nanoparticle layer NPL, and some of the first nanoparticles NP1 may not meet with the oxidation treatment solution OPL.

[0042] Therefore, according to the second manufacturing method, the proportion of trivalent nickel in the nickel contained in the oxide layer HFL can be increased, and the hole mobility of the oxide layer HFL can be further improved.

[0043] 11 again, in step S80, it is preferable to mix the first liquid DL1 with the oxidation treatment solution OPL using a flow method. The reaction between nickel oxide and an oxidizing agent is an exothermic reaction. Compared to the batch method, the flow method allows the reaction to proceed little by little, reducing the amount of heat generated per unit time and allowing the reaction to proceed mildly. Furthermore, by controlling the concentrations and flow rates of the first liquid DL1 and the oxidation treatment solution OPL, respectively, it is possible to control the proportion of trivalent nickel in the nickel contained in the oxide layer HFL.

[0044] The mixer 10 may be used to combine the first liquid DL1 with the oxidizing treatment solution OPL and to generate turbulent flow within the mixer 10 and the pipe 20. The turbulent flow stirs and mixes the first liquid DL1 and the oxidizing treatment solution OPL. The mixer 10 may be T-shaped, V-shaped, or of another type.

[0045] The oxidation treatment solution OPL may be an aqueous hydrogen peroxide solution. Regarding step S80, the inventors recommend that the concentration of the first nanoparticles NP1 in the first liquid DL1 be 1 to 60 mg / ml, that the oxidation treatment solution OPL be an aqueous hydrogen peroxide solution, and that the concentration of the aqueous hydrogen peroxide solution be 1 to 55 mol%. The inventors recommend that the flow rate of the first liquid DL1 at the first inlet 12 of the mixer 10 be 1 to 10 ml / h, and that the flow rate of the aqueous hydrogen peroxide solution at the second inlet 14 of the mixer 10 be 1 to 10 ml / h. Furthermore, the inventors recommend that the synthesis time, i.e., the residence time required for the first nanoparticles NP1 to flow from the junction 16 of the mixer 10 to the outlet 22 of the tube 20, be 30 seconds to 5 minutes.

[0046] It should be understood that the process of preparing the second liquid DL2 (step S80) may be a process of externally procuring the first nanoparticles NP1 to prepare the first liquid DL1 and reacting the first liquid DL1 with the oxidation treatment solution OPL to prepare the second liquid DL2, a process of externally procuring the second nanoparticles NP2 to prepare the second liquid DL2, or a process of externally procuring the second liquid DL2.

[0047] [Embodiment 2] Fig. 13 is a schematic diagram showing a configuration example of a display device according to one aspect of the present disclosure. As shown in Fig. 13, a display device DP according to the present disclosure includes one or more light-emitting elements ED according to the present disclosure. For example, the display device DP includes a display area DA in which a plurality of sub-pixels PX are provided, and a frame area NA in which a drive circuit DC that drives the display area DA is provided, and at least one of the plurality of sub-pixels PX includes a pixel circuit PC and a light-emitting element ED. The light-emitting element ED may have the configuration according to the above-described embodiment 1 or a modified configuration thereof.

[0048] [Embodiment 3] Referring again to Figure 2, the nanoparticles NP according to the present disclosure contain trivalent nickel and an oxide. The nanoparticles NP may further contain hydroxyl groups. When the nanoparticles NP according to the present disclosure are subjected to analytical devices such as XPS and EDX, at least trivalent nickel is detected. Furthermore, hydroxyl groups can be detected.

[0049] 11 , the method for producing nanoparticles according to the present disclosure may include a step of mixing a first liquid DL1 containing a plurality of first nanoparticles NP1 containing nickel oxide dispersed therein with an oxidation treatment solution OPL to obtain a second liquid DL2 containing one or more second nanoparticles NP2 containing trivalent nickel (and optionally one or more first nanoparticles NP1) dispersed therein. It is preferable to mix the first liquid DL1 with the oxidation treatment solution OPL using a flow method. The oxidation treatment solution OPL may be an aqueous hydrogen peroxide solution.

[0050] The inventors recommend that the concentration of the first nanoparticles NP1 in the first liquid DL1 be 1 to 60 mg / ml, that the oxidation treatment solution OPL be an aqueous hydrogen peroxide solution, and that the concentration of the aqueous hydrogen peroxide solution be 1 to 55 mol%. The inventors recommend that the flow rate of the first liquid DL1 at the first inlet 12 of the mixer 10 be 1 to 10 ml / h, and that the flow rate of the aqueous hydrogen peroxide solution at the second inlet 14 of the mixer 10 be 1 to 10 ml / h. Furthermore, the inventors recommend that the synthesis time, i.e., the residence time required for the first nanoparticles NP1 to flow from the junction 16 of the mixer 10 to the outlet 22 of the tube 20, be 30 seconds to 5 minutes.

[0051] Example 2 Nanoparticles NP according to Example 2 of the present disclosure were produced using the method shown in Figure 11. A first liquid DL1 was prepared so that the concentration of the first nanoparticles NP1 was 30 mg / ml, and an oxidation treatment solution OPL was prepared so that the concentration of an aqueous hydrogen peroxide solution was 10 mol%. The first liquid DL1 and the aqueous hydrogen peroxide solution were then injected into the mixer 10 using a piston so that the flow rate of the first liquid DL1 at the first inlet 12 of the mixer 10 was 6 ml / h, and the flow rate of the aqueous hydrogen peroxide solution at the second inlet 14 of the mixer 10 was 3 ml / h. The synthesis time was 1 minute.

[0052] The second nanoparticles NP2 (or a mixture of the first nanoparticles NP1 and the second nanoparticles NP2) were separated from the resulting second liquid DL, and the second nanoparticles NP2 (or the mixture) were analyzed by XPS. As a result of the analysis, divalent nickel and trivalent nickel were detected. From this detection result, it can be inferred that a portion of the divalent nickel in the nickel oxide became trivalent nickel. Furthermore, since hydroxyl groups were also detected, it can be inferred that a portion of the nickel oxide became nickel oxyhydroxide.

[0053] The present disclosure is not limited to the above-described embodiments, 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 the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0054] AD Anode CD Cathode DL1 First liquid DL2 Second liquid DP Display device EML Emitting layer HFL Oxide layer NP Nanoparticle NP1 First nanoparticle NP2 Second nanoparticle NPL Nanoparticle layer OPL Oxidation treatment solution QD Quantum dot

Claims

1. A light-emitting element comprising: an anode and a cathode; a light-emitting layer located between the anode and the cathode; and an oxide layer located between the anode and the light-emitting layer, the oxide layer having hole transport properties and containing trivalent nickel.

2. The light-emitting element according to claim 1, wherein the oxide layer contains nanoparticles, and the nanoparticles contain the trivalent nickel and hydroxyl groups.

3. The light-emitting element according to claim 2, wherein the hydroxyl group is covalently bonded to the trivalent nickel.

4. The light-emitting device according to any one of claims 1 to 3, wherein the light-emitting layer contains quantum dots.

5. The light-emitting device according to any one of claims 1 to 3, wherein the light-emitting layer comprises an organic light-emitting material.

6. A display device comprising the light-emitting element according to any one of claims 1 to 5.

7. A method for manufacturing a light-emitting element, comprising: a step of forming an anode; a step of forming a cathode; a step of forming a light-emitting layer between the step of forming the anode and the step of forming the cathode; and a step of forming an oxide layer having hole transport properties between the step of forming the anode and the step of forming the light-emitting layer, such that the oxide layer contains trivalent nickel.

8. The method for manufacturing a light-emitting element according to claim 7, wherein the step of forming the oxide layer comprises the steps of: applying a first liquid, in which first nanoparticles containing nickel oxide are dispersed, onto the anode and drying the liquid to form a nanoparticle layer containing the first nanoparticles; and bringing the nanoparticle layer into contact with an oxidation treatment solution to convert some or all of the first nanoparticles into second nanoparticles containing trivalent nickel.

9. The method for producing a light-emitting element according to claim 8, wherein the nanoparticle layer is immersed in the oxidation treatment solution.

10. A method for manufacturing a light-emitting element according to claim 7, further comprising the step of obtaining a second liquid in which second nanoparticles containing trivalent nickel are dispersed by mixing a first liquid in which first nanoparticles containing nickel oxide are dispersed with an oxidation treatment solution, and forming the oxide layer by applying the second liquid onto the anode and drying it.

11. The method for manufacturing a light-emitting element according to claim 10, wherein the first liquid is mixed with the oxidation treatment solution by a flow method.

12. The method for manufacturing a light-emitting element according to any one of claims 8 to 11, wherein the oxidation treatment solution is an aqueous solution of hydrogen peroxide.

13. Nanoparticles containing trivalent nickel and oxide.

14. The nanoparticles of claim 13, further comprising hydroxyl groups.

15. A method for producing nanoparticles, comprising a step of mixing a first liquid in which first nanoparticles containing nickel oxide are dispersed with an oxidation treatment solution to obtain a second liquid in which second nanoparticles containing trivalent nickel are dispersed.

16. The method for producing nanoparticles according to claim 15, wherein the first liquid is mixed with the oxidation treatment solution by a flow method.

17. The method for producing nanoparticles according to claim 15 or 16, wherein the oxidation treatment solution is an aqueous hydrogen peroxide solution.

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