Light-emitting element and display device

Abstract

A light-emitting element (ES) comprises: a positive electrode (51); a negative electrode (56); an EML (54) disposed between the positive electrode and the negative electrode; and an HIL (52) disposed between the positive electrode (51) and the EML (54). The HIL (52) contains NiO-NP (52a) and PVP (52b).

Description

[Technical Field]

[0001] The present disclosure relates to a light-emitting element, a method for manufacturing the same, a display device, and a nickel oxide nanoparticle dispersion. [Background technology]

[0002] In self-luminous light-emitting devices, a hole injection layer is often provided between the anode and the light-emitting layer to promote the injection of holes from the anode to the light-emitting layer. A composite of PEDOT (poly(3,4-ethylenedioxythiophene)) and PSS (poly(4-styrenesulfonic acid)), known as PEDOT:PSS, has been commonly used for the hole injection layer. PEDOT:PSS has excellent hole injection properties and is highly soluble in aqueous solvents, allowing it to be easily formed into a layer by liquid-phase film deposition.

[0003] However, PEDOT:PSS causes degradation of luminescence properties such as external quantum efficiency (EQE) over time.

[0004] Therefore, in recent years, it has been proposed to use nickel oxide nanoparticles in the hole injection layer instead of PEDOT:PSS (see, for example, Patent Document 1). Nickel oxide is a P-type oxide semiconductor material and has hole injection properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 001372 Summary of the Invention [Problem to be solved by the invention]

[0006] However, nickel oxide nanoparticles are prone to aggregation due to their small size, and solvents and additives suitable for nickel oxide nanoparticles have not yet been found, resulting in poor dispersibility in solvents. Therefore, when a hole injection layer is formed by, for example, spin coating (spinner application) of a nickel oxide nanoparticle dispersion containing nickel oxide nanoparticles, the film formation of the hole injection layer is poor, resulting in a non-uniform hole injection layer with poor flatness. As a result, biased hole migration in the hole injection layer is observed, and there is a high possibility that light emission will not be uniform.

[0007] The work function of the nickel oxide thin film is larger than that of, for example, ITO (indium tin oxide), which is used for the anode, but is smaller than the absolute value of the HOMO (highest occupied molecular orbital) or the energy level at the top of the valence band of most organic hole transport materials.

[0008] Therefore, in Patent Document 1, organic molecules having an electron-withdrawing group, such as trifluoromethylbenzoic acid, trifluoromethylphenylacetic acid, or trifluorobutyric acid, are bonded to the surface of the nickel oxide thin film to improve the hole injection properties of the hole injection layer.

[0009] To this end, Patent Document 1 discloses that a nickel oxide precursor liquid or a pre-prepared nickel oxide liquid containing, for example, lithium stearate as a ligand (dispersant) is first applied to a substrate provided with a conductive film. This is followed by annealing at 130 to 300°C for 10 to 90 minutes to form a nickel oxide thin film. Subsequently, an organic molecule solution, prepared by dissolving organic molecules having electron-withdrawing groups in a solvent, is applied to the surface of the nickel oxide thin film, and annealing is then performed at 80 to 180°C for 1 to 60 minutes to form a hole injection layer in which the organic molecules are bonded to the surface of the nickel oxide thin film. Preferably, to promote chemical bonding between the organic molecules and nickel atoms, the ligand is removed and the nickel atoms are exposed, for example, by ultraviolet ozone treatment, prior to application of the organic molecule solution. Therefore, the method described in Patent Document 1 requires complex and time-consuming processes.

[0010] One aspect of the present disclosure has been made in view of the above-described problems, and an object of the present disclosure is to provide a light-emitting element and a manufacturing method thereof, a display device, and a nickel oxide nanoparticle dispersion liquid capable of forming such a hole injection layer, which have good film-forming properties, improved hole injection properties, and a highly flat and robust hole injection layer, and which can be easily formed. [Means for solving the problem]

[0011] In order to solve the above problems, a light-emitting element according to one aspect of the present disclosure includes an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole injection layer provided between the anode and the light-emitting layer, wherein the hole injection layer contains nickel oxide nanoparticles and polyvinylpyrrolidone.

[0012] In order to solve the above problem, a display device according to an aspect of the present disclosure includes a plurality of the light-emitting elements according to an aspect of the present disclosure.

[0013] In order to solve the above problems, a nickel oxide nanoparticle dispersion according to one embodiment of the present disclosure contains nickel oxide nanoparticles, polyvinylpyrrolidone, and a solvent.

[0014] In order to solve the above problems, a method for manufacturing a light-emitting element according to one aspect of the present disclosure is a method for manufacturing a light-emitting element including an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole injection layer provided between the anode and the light-emitting layer, the method including a hole injection layer forming step of forming the hole injection layer, the hole injection layer forming step including a step of applying a nickel oxide nanoparticle dispersion liquid containing nickel oxide nanoparticles, polyvinylpyrrolidone, and a solvent, and a step of removing the solvent contained in the nickel oxide nanoparticle dispersion liquid. [Effects of the Invention]

[0015] According to one aspect of the present disclosure, it is possible to provide a light-emitting element and a manufacturing method thereof, a display device, and a nickel oxide nanoparticle dispersion liquid capable of forming such a hole injection layer, which have good film-forming properties, improved hole injection properties, and a highly flat and robust hole injection layer, and which can easily form such a hole injection layer. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element according to an embodiment. [Figure 2] 1 is a schematic diagram illustrating an example of a nickel oxide nanoparticle dispersion liquid according to an embodiment. [Figure 3] 1 is a flowchart illustrating an example of a method for manufacturing a light-emitting element according to an embodiment. [Figure 4] FIG. 10 is a cross-sectional view schematically illustrating the structure of a hole injection layer on an anode in a comparative light-emitting element in which the hole injection layer does not contain polyvinylpyrrolidone. [Figure 5] 1 is a cross-sectional view showing an example of a schematic configuration of a display device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described below with reference to Figures 1 to 4. In the following, a layer formed in a process earlier than a comparison layer will be referred to as a "lower layer," and a layer formed in a process later than a comparison layer will be referred to as an "upper layer." Furthermore, in the following description, the expression "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B," unless otherwise specified.

[0018] The light-emitting element according to this embodiment includes an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole injection layer provided between the anode and the light-emitting layer. The light-emitting element according to this embodiment is a quantum dot light-emitting diode (QLED) having a quantum dot light-emitting layer containing quantum dots as the light-emitting layer.

[0019] In this embodiment, the layers between the anode and cathode are collectively referred to as functional layers. As functional layers other than the hole injection layer and the light-emitting layer, for example, a hole transport layer may be provided between the hole injection layer and the light-emitting layer, and an electron transport layer may be provided between the light-emitting layer and the cathode. Although not described here, other functional layers may also be provided between the anode and the cathode. Hereinafter, quantum dots are referred to as "QDs," the light-emitting layer is referred to as "EML," and the hole injection layer is referred to as "HIL." The hole transport layer is referred to as "HTL," and the electron transport layer is referred to as "ETL."

[0020] FIG. 1 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element ES according to this embodiment.

[0021] The light-emitting element ES shown in FIG. 1 has a configuration in which an anode 51, an HIL 52, an HTL 53, an EML 54, an ETL 55, and a cathode 56 are provided in this order from the bottom.

[0022] 1 illustrates, as an example, a case where the light-emitting element ES has a conventional structure in which the anode 51 is a lower electrode and the cathode 56 is an upper electrode. However, the light-emitting element ES according to this embodiment is not limited to this structure and may have an inverted structure in which the cathode 56 is a lower electrode and the anode 51 is an upper electrode. In this case, the stacking order of the functional layers is reversed from that shown in FIG. 1. That is, the light-emitting element ES may have the cathode 56, ETL 55, EML 54, HTL 53, HIL 52, and anode 51 stacked in this order from the bottom up.

[0023] The anode 51 is formed on a substrate (not shown). The substrate is a support that supports each layer from the anode 51 to the cathode 56, and each layer from the anode 51 to the cathode 56 is generally formed on the substrate that serves as a support. Therefore, the light-emitting element ES may include a substrate as a support.

[0024] The substrate may be, for example, a rigid inorganic substrate such as a glass substrate, or a flexible substrate mainly composed of a resin such as polyimide. The substrate may be provided with a TFT (thin film transistor), a capacitive element, etc. (not shown).

[0025] The anode 51 is an electrode that supplies holes to the EML 54 when a voltage is applied thereto. The cathode 56 is an electrode that supplies electrons to the EML 54 when a voltage is applied thereto. The anode 51 and the cathode 56 each contain a conductive material and are connected to a power supply (not shown) so that a voltage is applied between them.

[0026] Of the anode 51 and the cathode 56, the electrode on the light extraction surface side of the light-emitting element ES must be light-transmitting. Each of the anode 51 and the cathode 56 may be a single layer or may have a multilayer structure.

[0027] When the light-emitting element ES is a top-emission type display element that extracts light from the upper electrode side provided on the opposite side of the substrate, a translucent electrode having light-transmitting properties is used for the upper electrode, and a so-called reflective electrode having light-reflecting properties is used for the lower electrode.

[0028] On the other hand, when the light emitting element ES is a bottom emission type display element that extracts light from the lower electrode side provided on the substrate side, a translucent electrode is used for the lower electrode and a reflective electrode is used for the upper electrode.

[0029] The translucent electrode is formed of a translucent material such as ITO, IZO (indium zinc oxide), AgNW (silver nanowire), a thin film of MgAg (magnesium-silver) alloy, or a thin film of Ag (silver).

[0030] The reflective electrode may be formed of a light-reflective material, such as a metal such as Ag or Al (aluminum), or an alloy containing such a metal, or may be formed by laminating a light-transmitting material and a light-reflective material. Thus, the reflective electrode may have a laminated structure such as ITO / Ag alloy / ITO, ITO / Ag / ITO, or Al / IZO.

[0031] The EML 54 is a layer that contains a light-emitting material and emits light by recombination of holes transported from the anode 51 and electrons transported from the cathode 56. As described above, the EML 54 is a QD light-emitting layer, and contains nano-sized QDs 54a corresponding to the emission color as the light-emitting material.

[0032] QD54a is a nanoparticle dot with a maximum width of 100 nm or less. QDs are generally referred to as semiconductor nanoparticles because their composition is derived from semiconductor materials. QDs are also sometimes referred to as nanocrystals because their structure, for example, has a specific crystalline structure.

[0033] The shape of the QD54a is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, it may have a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0034] QD54a may be a core type, or a core-shell type or core-multishell type containing a core and a shell. When QD54a contains a shell, the core is located at the center and the shell is provided on the surface of the core. While it is desirable for the shell to cover the entire core, it is not necessary for the shell to completely cover the core. QD54a may also be a two-component core type, a three-component core type, or a four-component core type. QD54a may also contain doped nanoparticles or have a compositionally graded structure.

[0035] The core can be made of, for example, Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, etc. The shell can be made of, for example, CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc.

[0036] The emission wavelength of QD54a can be varied by adjusting the particle size, composition, etc. QD54a is a QD that emits visible light, and by appropriately adjusting the particle size and composition of QD54a, it is possible to realize, for example, red light, green light, or blue light.

[0037] Before describing the HIL 52, the ETL 55 and the HTL 53 will be described. The HIL 52 will be described in detail later.

[0038] The ETL 55 is a charge transport layer that contains an electron transport material and has an electron transport function that increases the efficiency of electron transport to the EML 54. Examples of the electron transport material include N-type oxide semiconductor nanoparticles such as ZnO nanoparticles and MgZnO nanoparticles. Because these N-type oxide semiconductor nanoparticles have excellent electron injection properties, the electron injection layer is often omitted, as shown in Figure 1.

[0039] HTL 53 is a charge transport layer containing a hole transport material and having a hole transport function that enhances the efficiency of hole transport to EML 54. Examples of the hole transport material include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)] known as TFB, poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] known as p-TPD, and polyvinylcarbazole known as PVK.

[0040] (HIL52) Next, the HIL52 will be described in detail.

[0041] The HIL 52 is a charge injection layer that contains a hole transport material and has a hole injection function that promotes the injection of holes from the anode 51 to the EML 54. The HIL 52 contains nickel oxide nanoparticles (hereinafter referred to as "NiO-NPs") 52a and polyvinylpyrrolidone (hereinafter referred to as "PVP") 52b.

[0042] However, in the present disclosure, the molar ratio of nickel atoms to oxygen atoms in nickel oxide is not limited to 1:1, and nickel oxide is not limited to NiO. The nickel oxide used in the present disclosure may be nickel oxide composed of various molar ratios, and the nickel oxide represents nickel oxide nanocrystals.

[0043] NiO-NP52a is a hole-transporting material that enhances the efficiency of hole injection from the anode 51 to the HTL 53. PVP52b functions as a binder resin that binds the NiO-NP52a together. NiO-NP52a and PVP52b are integrated as the HTL 52. PVP52b also functions as a dispersant, penetrating between the NiO-NP52a particles and enhancing the dispersibility of the NiO-NP52a. Therefore, the NiO-NP52a is dispersed in the PVP52b.

[0044] As described above, QLEDs generally use n-type oxide semiconductor nanoparticles, such as ZnO nanoparticles and MgZnO nanoparticles, which have excellent electron injection properties in the ETL. Therefore, QLEDs generally tend to have poor hole injection properties compared to electron injection properties. Therefore, the amount of electron injection in the EML is generally greater than the amount of hole injection, resulting in problems of excessive electron supply and hole shortage. A large difference between the amount of hole injection and the amount of electron injection in the EML reduces luminous efficiency.

[0045] Furthermore, as mentioned above, the work function of nickel oxide thin films in QLEDs is smaller than the absolute value of the energy level at the top of the valence band of most organic hole transport materials. Furthermore, when using ITO as an anode, holes must be injected through a relatively high barrier. Therefore, improvements in hole injection are desirable.

[0046] In this context, as mentioned above, it would normally be unthinkable to mix PVP, an insulating polymer, into HIL52. However, as a result of studies by the present inventors, it was found that when HIL52 contains NiO-NP52a and PVP52b, the film-forming properties of HIL52 are improved, a highly flat and robust HIL52 can be obtained, and the EQE (external quantum efficiency) is improved. Furthermore, such HIL52 does not require the complicated and time-consuming process treatment described in Patent Document 1.

[0047] As described above, HIL52 contains NiO-NP52a and PVP52b, which allows it to achieve the aforementioned effects. However, as described above, PVP52b is an insulator. Therefore, in HIL52, hole movement occurs due to hole hopping conduction caused by the tunneling effect. Tunneling current between NiO-NP52a covered with an insulator such as PVP52b is more likely to occur as the distance between the NiO-NP52a is shorter. Tunneling current occurs when the distance between the NiO-NP52a is 3 nm or less. Tunneling current is more likely to occur when the distance between the NiO-NP52a is 2 nm or less, and particularly when it is 1.5 nm or less.

[0048] NiO-NP52a and PVP52b need only be mixed so that a tunneling current can be generated. In particular, by mixing NiO-NP52a and PVP52b so that the average distance between NiO-NP52a per unit volume falls within the above-mentioned range, sufficient tunneling current can be passed. As a result, the increase in voltage due to the addition of PVP52b, an insulator, can be sufficiently suppressed.

[0049] However, if the amount of PVP contained in HIL52 is too small, the effect of adding PVP may not be fully achieved.Also, even if a tunneling current can flow, if the amount of NiO-NP52a contained in HIL52 is too small, it will result in a decrease in the hole-transport external quantum efficiency (EQE).

[0050] Therefore, the volume ratio of NiO-NP52a to PVP52b in HIL52 (NiO-NP / PVP) is preferably 40 / 60 or more and 95 / 5 or less. In other words, the volume ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in HIL52 is preferably 40 vol% or more and 95 vol% or less. When the NiO-NP / PVP volume ratio is 40 / 60 or more, an external quantum efficiency (EQE) of 5.0% or more can be obtained, as shown in the examples described below. Furthermore, to fully obtain the effect of adding PVP, the volume ratio of NiO-NP / PVP is preferably 95 / 5 or less.

[0051] Furthermore, from the viewpoint of film-forming properties, the volume ratio of NiO-NP / PVP is more preferably 80 / 20 or less. Therefore, the volume ratio of NiO-NP / PVP is more preferably 40 / 60 or more and 80 / 20 or less. In other words, the volume ratio of NiO-NP52a relative to the total amount of NiO-NP52a and PVP52b in HIL52 is preferably 40 vol% or more and 80 vol% or less. As mentioned above, unevenness on the HIL surface leads to non-uniform light emission from the light-emitting device. By setting the volume ratio of NiO-NP / PVP to 80 / 20 or less, the film-forming properties of HIL52 can be improved, as shown in the examples described below, and a light-emitting device ES with a higher flatness of HIL52 and uniform light emission can be obtained.

[0052] From the viewpoint of EQE, the volume ratio of NiO-NP / PVP is more preferably 60 / 40 or more and 95 / 5 or less, and particularly preferably 60 / 40 or more and 80 / 20 or less. In other words, the volume ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in HIL52 is more preferably 60 vol% or more and 95 vol% or less, and particularly preferably 60 vol% or more and 80 vol% or less.

[0053] By setting the volume ratio of NiO-NP / PVP to 60 / 40 or more and 95 / 5 or less in this way, it is surprisingly possible to obtain a higher EQE than when HIL52 consists of only NiO-NP, as will be shown in the Examples described later, even though HIL52 contains PVP, which is an insulating polymer.

[0054] Even more surprisingly, the EQE can be further improved by adjusting the volume ratio of NiO-NP / PVP to 60 / 40 or more and 80 / 20 or less. Moreover, by adjusting the NiO-NP / PVP ratio to 60 / 40 or more and 80 / 20 or less, as described above, the film-forming properties of HIL52 can be improved, and the flatness of HIL52 can be improved, resulting in a light-emitting element ES that emits light uniformly.

[0055] In this embodiment, the term "nanoparticles" refers to particles with a volume median diameter (D50) of nano-size (i.e., less than 1 μm). The particle size of NiO-NP52a is not particularly limited as long as it is nano-size, but it is preferable that the volume median diameter (D50) is within the range of 8 nm or more and 20 nm or less, for example.

[0056] As the particle size (volume median diameter) of NiO-NP52a decreases, it becomes more prone to condensation and its dispersibility in solvents decreases, while the band gap increases, facilitating hole injection into the luminescent material. Therefore, it is preferable that the particle size (volume median diameter) of NiO-NP52a be within the above range. Here, the volume median diameter (D50) refers to the particle size (cumulative average diameter) when the cumulative percentage in the volume-based cumulative particle size distribution is 50%.

[0057] Furthermore, it is more desirable that NiO-NP52a has a volume median diameter (D50) that corresponds to the luminescent color (luminescent wavelength) of the luminescent material.

[0058] For example, when the light-emitting element ES is a red light-emitting element that emits red light and red QDs that emit red light are used as the light-emitting material, the volume median diameter (D50) of NiO-NP52a is preferably in the range of 12 nm to 20 nm. Furthermore, when the light-emitting element ES is a green light-emitting element that emits green light and green QDs that emit green light are used as the light-emitting material, the volume median diameter (D50) of NiO-NP52a is preferably in the range of 10 nm to 16 nm. When the light-emitting element ES is a blue light-emitting element that emits blue light and blue QDs that emit blue light are used as the light-emitting material, the volume median diameter (D50) of NiO-NP52a is preferably in the range of 8 nm to 14 nm.

[0059] Thus, the particle size of NiO-NP52a has a particle size suitable for the emission color of the luminescent material of EML54.

[0060] The thickness of each layer in the light-emitting element ES is not particularly limited and can be set in the same way as in the past. Therefore, the thickness of the HIL 52 is not particularly limited, but is preferably in the range of 20 nm to 30 nm, for example. This prevents pinholes from occurring and changes in the chromaticity (hue) of the emitted light.

[0061] In this embodiment, a nanoparticle size measurement device (model number: "Nanotrac Wave II-UT151") manufactured by Microtrac-Bell was used to measure the volume median diameter (D50). Pure water containing 30 mg / mL of NiO-NP52a was used as the measurement sample. A frequency analysis method using dynamic light scattering (DLS) was used for the analysis. The particle size was measured by extracting an electrical signal from a photodetector that mixes weak scattered light with a reference wave (heterodyne method), and then calculating an FFT (fast Fourier transform) power spectrum from this signal.

[0062] The HIL 52 is formed by spin-coating (spinner coating) a NiO-NP dispersion liquid obtained by dispersing NiO-NP 52a and PVP 52b in a solvent onto the anode 51, which is the underlying layer (base layer).

[0063] (NiO-NP dispersion) FIG. 2 is a schematic diagram showing an example of a NiO-NP dispersion 71 (nickel oxide nanoparticle dispersion) according to this embodiment.

[0064] As shown in FIG. 2, the NiO-NP dispersion liquid 71 according to this embodiment contains NiO-NPs 52a, PVP 52b, and a solvent 72 as a dispersion medium.

[0065] The NiO-NP dispersion 71 is a dispersion (dispersion for forming a hole transport layer) for forming the HIL 52. The NiO-NP dispersion 71 is a so-called colloidal solution in which NiO-NPs 52a and PVP 52b are dispersed in a solvent 72 until they become colloidal.

[0066] The NiO-NP dispersion 71 can be dispersed into both aqueous and organic solvents until it becomes colloidal, and therefore, the NiO-NP dispersion 71 can also be dispersed into, for example, an ink solvent for an inkjet coating device until it becomes colloidal.

[0067] Therefore, the solvent 72 may be either an aqueous solvent or an organic solvent. For example, amphoteric solvents such as water, alcohols such as methoxyethanol, glycols such as ethylene glycol, and glycol ethers such as diethylene glycol monobutyl ether (butyl carbitol) are preferably used as the solvent 72. This allows dispersion.

[0068] The volume ratio of NiO-NP 52a to PVP 52b (NiO-NP / PVP) in HIL52 depends on the volume ratio of NiO-NP 52a to PVP 52b (NiO-NP / PVP) in the NiO-NP dispersion 71.

[0069] Therefore, for the same reasons as for the volume ratio of NiO-NP / PVP in HIL52, the volume ratio of NiO-NP / PVP in the NiO-NP dispersion 71 is preferably 40 / 60 or more and 95 / 5 or less. Similarly, from the viewpoint of the above-mentioned film-forming property, the volume ratio of NiO-NP / PVP in the NiO-NP dispersion 71 is more preferably 80 / 20 or less. Therefore, the volume ratio of NiO-NP / PVP in the NiO-NP dispersion 71 is more preferably 40 / 60 or more and 80 / 20 or less. Furthermore, from the viewpoint of the above-mentioned EQE, the volume ratio of NiO-NP / PVP in the NiO-NP dispersion 71 is more preferably 60 / 40 or more and 95 / 5 or less, and particularly preferably 60 / 40 or more and 80 / 20 or less.

[0070] Furthermore, the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 is preferably 78.9 wt% or more and 99.1 wt% or less. As a result, as shown in the examples described later, the volume ratio of NiO-NP / PVP in the HIL52 can be set to 40 / 60 or more and 95 / 5 or less. Furthermore, as shown in the examples described later, by setting the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 to 78.9 wt% or more and 96.4 wt% or less, the volume ratio of NiO-NP / PVP in the HIL52 can be set to 40 / 60 or more and 80 / 20 or less.

[0071] Furthermore, as shown in the examples described later, the volume ratio of NiO-NP / PVP in HIL52 can be set to 60 / 40 or more and 95 / 5 or less by setting the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in NiO-NP dispersion 71 to 90.9 wt% or more and 99.1 wt% or less. Furthermore, the volume ratio of NiO-NP / PVP in HIL52 can be set to 60 / 40 or more and 80 / 20 or less by setting the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in NiO-NP dispersion 71 to 90.9 wt% or more and 96.4 wt% or less.

[0072] The weight ratio of NiO-NP / PVP in the NiO-NP dispersion 71 is maintained unchanged in HIL 52. Therefore, the weight ratio of NiO-NP 52a to PVP 52b (NiO-NP / PVP) in HIL 52 is the same as the weight ratio of NiO-NP / PVP in the NiO-NP dispersion 71.

[0073] Thus, in order to control the volume ratio of NiO and PVP in HIL52 (membrane), it is necessary to prepare a mixture solution at the above weight ratio in order to achieve that volume ratio.

[0074] The concentration (weight percent concentration) of NiO-NP 52a in the NiO-NP dispersion 71 is not particularly limited as long as it is set so as to obtain a desired thickness of HIL 52. However, from the viewpoint of controlling the thickness of HIL 52, the concentration of NiO-NP 52a in the NiO-NP dispersion 71 is preferably in the range of 5 mg / ml or more and 50 mg / ml or less.

[0075] The volume median diameter (D50) of the NiO-NPs 52a in the NiO-NP dispersion 71 is the same as the volume median diameter (D50) of the NiO-NPs 52a in the HIL52.

[0076] (Method of manufacturing the light-emitting element ES) Next, a method for manufacturing the light emitting element ES will be described.

[0077] A method for manufacturing a light-emitting device according to one embodiment of the present disclosure includes a step of forming the HIL 52 (HIL formation step). The HIL formation step includes a step of applying a NiO-NP dispersion 71 containing NiO-NP 52a, PVP 52b, and a solvent 72, and a step of removing the solvent 72 contained in the NiO-NP dispersion 71. The method for manufacturing a light-emitting device according to one embodiment of the present disclosure also includes a step of preparing the NiO-NP dispersion 71 as a method for manufacturing the NiO-NP dispersion 71, prior to the step of applying the NiO-NP dispersion 71.

[0078] Hereinafter, a method for manufacturing a light-emitting element according to one embodiment of the present disclosure will be described, taking the method for manufacturing the light-emitting element ES shown in FIG. 1 as an example.

[0079] FIG. 3 is a flowchart showing an example of a method for manufacturing the light-emitting element ES according to this embodiment.

[0080] In the method for manufacturing the light-emitting element ES according to this embodiment, as shown in FIG. 3, an anode 51 is formed on a substrate (not shown) (step S1, anode formation step). Meanwhile, a NiO-NP dispersion 71 shown in FIG. 2 is prepared (manufactured) (step S11, NiO-NP dispersion preparation step). Next, the HIL 52 is formed using the NiO-NP dispersion 71 (step S2, HIL formation step). Note that step S11 only needs to be performed before step S2, and may be performed in parallel with step S1, between step S1 and step S2 (i.e., after step S1 and before step S2), or before step S1.

[0081] In step S11, it is desirable to mix NiO-NP52a with PVP52b so that the volume ratio of NiO-NP52a to PVP52b (NiO-NP / PVP) in the NiO-NP dispersion 71 is the above-mentioned volume ratio. Specifically, in step S11, it is desirable to mix NiO-NP52a with PVP52b so that the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 is the above-mentioned weight ratio.

[0082] In step S2, first, the NiO-NP dispersion liquid 71 is applied onto the anode 51 (step S2a, NiO-NP dispersion liquid application step). This forms a coating film of the NiO-NP dispersion liquid 71. Next, the coating film is heated or the like to remove the solvent 72 contained in the coating film (i.e., the applied NiO-NP dispersion liquid 71), and the coating film is dried (step S2b, solvent removal step).

[0083] As described above, spin coating (spinner coating) is used to apply the NiO-NP dispersion 71. The spin rotation speed is not particularly limited and may be appropriately set depending on the concentration of NiO-NP 52a in the NiO-NP dispersion 71. For example, in the examples described later, the NiO-NP dispersion 71 was applied at a spin rotation speed of 1200 rpm / 30 sec.

[0084] The solvent 72 contained in the coating film can be removed by baking the coating film. Drying conditions such as the baking temperature and baking time may be appropriately set depending on the type of solvent 72 contained in the NiO-NP dispersion liquid 71, the concentration of NiO-NP 52a in the NiO-NP dispersion liquid 71, and the like, and are not particularly limited. For example, in the examples described below, the coating film was dried by baking at 200°C for 15 minutes.

[0085] Next, the HTL 53 is formed (step S3), the EML 54 is formed (step S4), the ETL 55 is formed (step S5), and the cathode 56 is formed (step S6).

[0086] The layers other than the HIL 52 (anode 51, HTL 53, EML 54, ETL 55, and cathode 56) are formed by the same method as conventional methods. The anode 51 and cathode 56 can be formed by, for example, film deposition, sputtering, or inkjet printing. The HTL 53 can be formed by, for example, vacuum deposition, spin coating, or inkjet printing. The ETL 55 can be formed by, for example, spin coating or inkjet printing. The EML 54 can be formed by applying a QD dispersion containing QDs 54a and a solvent, followed by drying the QD dispersion. The QD dispersion may contain a known ligand as a dispersant.

[0087] (effect) Next, the above-described light-emitting element ES, its manufacturing method, and the effects of the NiO-NP dispersion liquid 71 will be described in more detail.

[0088] FIG. 4 is a cross-sectional view schematically showing the structure of the HIL 52 on the anode 51 in a comparative light-emitting device in which the HIL 52 does not contain PVP 52b.

[0089] As mentioned above, NiO-NP52a particles are small and therefore prone to aggregation. Furthermore, no suitable solvents or additives have been found for NiO-NP52a, resulting in poor dispersibility in solvents. For this reason, NiO-NP dispersions that do not contain PVP52b experience NiO-NP52a settling over time, resulting in separation into two layers. Therefore, when forming HILs using NiO-NP dispersions that do not contain PVP52b, the NiO-NP dispersion must be prepared just before spin coating and must be spin coated before the NiO-NP52a settles.

[0090] Furthermore, as described above, when PVP52b is not used, NiO-NP52a tends to aggregate and has low dispersibility in a solvent, making it impossible to form a stable film, resulting in unevenness on the surface of HIL52, as shown in Figure 4. If the surface of HIL52 has unevenness, is non-uniform, and has poor flatness, the movement of holes in HIL52 becomes biased, resulting in non-uniform light emission from the light-emitting element.

[0091] However, as mentioned above, PVP functions as a dispersant, and therefore, by including PVP 52b in the NiO-NP dispersion 71, NiO-NP 52a does not settle, and the NiO-NP dispersion 71 can be prepared in advance and stored.

[0092] Therefore, as shown in the examples described later, the inclusion of PVP 52b in the NiO-NP dispersion 71 can improve the film-forming properties of the HIL 52. This improves the flatness of the HIL 52, allows the light-emitting element ES to emit light uniformly, and improves the hole injection properties of the HIL 52.

[0093] Furthermore, PVP52b does not adversely affect the luminescence properties, and therefore not only can it suppress the decrease in EQE, but depending on the amount added, it can also improve the EQE compared to when HIL52 is composed of NiO-NP alone.

[0094] As mentioned above, PVP52b functions as a binder resin. PVP52b has high thermal stability, and the inclusion of PVP52b in HIL52 results in a stronger and more stable HIL52 film than when HIL52 is made solely of NiO-NPs.

[0095] In contrast, vinyl polymers such as polyvinyl alcohol, which are similar to PVP52b, are not suitable as binder resins for HIL 52. HILs using polyvinyl alcohol as a binder resin have low thermal stability and low reliability.

[0096] Furthermore, as mentioned above, the method described in Patent Document 1 requires complicated and time-consuming processes. Furthermore, as mentioned above, Patent Document 1 describes a method for forming a NiO thin film by applying a NiO precursor solution or a pre-prepared NiO solution containing a ligand as a dispersant to a substrate provided with a conductive film, followed by annealing. To promote chemical bonding between the organic molecules and the Ni atoms, the ligand is removed and the nickel atoms are exposed, for example, by ultraviolet ozone treatment before applying the organic molecule solution. Therefore, while Patent Document 1 suggests that the ozone treatment may strengthen the film quality of the hole transport layer by promoting bonding between the organic molecules and the nickel atoms, if the substrate has a bank made of an organic insulator, the ozone treatment is likely to deform the bank shape.

[0097] However, according to this embodiment, as described above, the HIL 52 can be formed by applying the NiO-NP dispersion 71 containing PVP 52b and then baking it once. Furthermore, ozone treatment is not required. This simplifies the manufacturing process of the HIL 52. It is also possible to use a substrate having a bank, such as an edge cover, that covers the edges of the lower electrode. That is, the light-emitting element ES may have a bank, such as an edge cover, that covers the lower electrode of the anode 51 or the cathode 56.

[0098] Moreover, as described above, PVP dissolves in both aqueous and organic solvents, as well as in ink solvents used in inkjet coating devices. Therefore, according to this embodiment, the HIL 52 can be easily formed.

[0099] Therefore, according to this embodiment, it is possible to provide a light-emitting device ES having a highly flat and robust HIL 52 with good film-forming properties and improved hole injection properties, and a method for manufacturing the same, which can easily form such an HIL 52. This also makes it possible to provide a light-emitting device with a high EQE in which the decrease in EQE is suppressed, and further to provide a light-emitting device with an improved EQE and a higher EQE than conventional light-emitting devices, and a method for manufacturing the same. Furthermore, according to this embodiment, it is possible to provide a NiO-NP dispersion 71 capable of forming the above-described HIL 52.

[0100] The light-emitting element ES may be used as a light source for a light-emitting device such as a display device or a lighting device. Therefore, a light-emitting device according to one embodiment of the present disclosure may include the light-emitting element ES. This makes it possible to provide a light-emitting device that has a highly flat and robust HIL 52 with good film-forming properties and improved hole injection properties, and that can easily form such a HIL 52. A substrate having a bank may also be used as the substrate for the light-emitting device. For example, when the light-emitting device is a display device, the display device may have a configuration in which a plurality of pixels are provided with the light-emitting element ES in each pixel, and a bank is provided between each adjacent pixel. In this case, the bank is used as a pixel separation film that separates adjacent pixels.

[0101] These edge covers, banks for pixel separation films, etc. can be formed from a coatable photosensitive organic material such as polyimide resin, acrylic resin, etc.

[0102] Next, a display device according to this embodiment will be described. As described above, the light-emitting element ES may be used as a light source of the display device. The display device according to this embodiment includes a plurality of the light-emitting elements ES according to this embodiment.

[0103] FIG. 5 is a cross-sectional view showing an example of a schematic configuration of a main part of the display device 1 according to this embodiment.

[0104] As shown in Fig. 5, the display device 1 has pixels P. Each pixel P is provided with a light-emitting element ES. The display device 1 shown in Fig. 5 includes an array substrate on which a driving element layer is formed as a substrate 2, and has a configuration in which a light-emitting element layer 5 including a plurality of light-emitting elements ES with different emission wavelengths and a sealing layer 6 covering the light-emitting element layer 5 are stacked in this order on the substrate 2.

[0105] 5 includes, for example, a pixel RP (red pixel) that emits red light, a pixel GP (green pixel) that emits green light, and a pixel BP (blue pixel) that emits blue light as pixels P. An insulating bank BK is provided between each pixel SP as a pixel separation film that separates adjacent pixels P.

[0106] The display device 1 includes a plurality of light-emitting elements ES with different emission wavelengths, including a light-emitting element RES (red light-emitting element) that emits red light, a light-emitting element GES (green light-emitting element) that emits green light, and a light-emitting element BES (blue light-emitting element). The pixel RP includes a light-emitting element RES as the light-emitting element ES. The pixel GP includes a light-emitting element GES as the light-emitting element ES. The pixel BP includes a light-emitting element BES as the light-emitting element ES.

[0107] The light emitting element layer 5 includes the plurality of light emitting elements ES provided for each pixel P, and has a structure in which the layers of these light emitting elements ES are stacked on the substrate 2.

[0108] Therefore, as described above, when the light-emitting element ES has, for example, a conventional structure, the anode 51, HIL 52, HTL 53, EML 54, ETL 55, and cathode 56 of each light-emitting element ES are stacked on the substrate 2 in this order, for example, from the bottom side.

[0109] Although not shown, when the light emitting element ES has an inverted structure, the cathode 56, ETL 55, EML 54, HTL 53, HIL 52, and anode 51 are stacked in this order from the bottom as described above.

[0110] The substrate 2 functions as a support for forming each layer of these light-emitting elements ES. A driving element layer, for example, a TFT (thin film transistor) layer, is formed on the substrate 2. The TFT layer is provided with a driving circuit, which includes a driving element such as a TFT, as a pixel circuit for driving each light-emitting element ES.

[0111] As shown in FIG. 5 , the anode 51, HIL 52, HTL 53, EML 54, and ETL 55 in each pixel P are each separated into an island shape by a bank BK for each pixel P. On the other hand, the cathode 56, which is an upper layer electrode, is not separated by the bank BK but is formed as a common layer shared by each pixel P. Therefore, in this embodiment, the anode 51 is a patterned anode formed in an island pattern. The anode 51 in each pixel P is electrically connected to each of the multiple TFTs in the TFT layer. On the other hand, the cathode 56 is a common cathode provided in common to all pixels P.

[0112] The light-emitting element RES shown in Fig. 5 includes HIL52R as the HIL52, HTL53R as the HTL53, EML54R as the EML54, and ETL55R as the ETL55. The light-emitting element GES shown in Fig. 5 includes HIL52G as the HIL52, HTL53G as the HTL53, EML54G as the EML54, and ETL55G as the ETL55. The light-emitting element BES shown in Fig. 5 includes HIL52B as the HIL52, HTL53B as the HTL53, EML54B as the EML54, and ETL55B as the ETL55.

[0113] 5 has a configuration in which the anode 51, HIL52R, HTL53R, EML54R, ETL55R, and cathode 56 are stacked in this order from the substrate 2 side. The light-emitting element GES shown in Fig. 5 has a configuration in which the anode 51, HIL52G, HTL53G, EML54G, ETL55G, and cathode 56 are stacked in this order from the substrate 2 side. The light-emitting element BES shown in Fig. 5 has a configuration in which the anode 51, HIL52B, HTL53, EML54, ETL55, and cathode 56 are stacked in this order from the substrate 2 side.

[0114] As mentioned above, the particle size of NiO-NP52a exists, and the particle size is suitable for the emission color of the light-emitting material of EML54. Therefore, in the display device 1, the volume-based median diameter (D50) of NiO-NP52a in HIL52B of the light-emitting element RES is preferably within a range of 12 nm to 20 nm. Furthermore, the volume-based median diameter (D50) of NiO-NP52a in HIL52G of the light-emitting element GES is preferably within a range of 10 nm to 16 nm. Furthermore, the volume-based median diameter (D50) of NiO-NP52a in HIL52B of the light-emitting element BES is preferably within a range of 8 nm to 14 nm.

[0115] As described above, the bank BK is used as a pixel separation film and also as an edge cover that covers the edges of the patterned lower layer electrodes. Therefore, as shown in FIG. 5, the edges of the anode 51 are covered by the bank BK.

[0116] The bank BK is formed by applying the above-mentioned coatable photosensitive organic material and then patterning it by photolithography.

[0117] The light-emitting element layer 5 is covered with a sealing layer 6. The sealing layer 6 is light-transmitting and, for example, includes, in order from the lower layer side (i.e., the light-emitting element layer 5 side), a first inorganic sealing film, an organic sealing film, and a second inorganic sealing film. However, without being limited thereto, the sealing layer 6 may be formed of a single layer of inorganic sealing film or a laminate of five or more layers of organic sealing film and inorganic sealing film. The sealing layer 6 may also be, for example, sealing glass. By sealing each light-emitting element ES with the sealing layer 6, it is possible to prevent penetration of water, oxygen, etc. into the light-emitting elements ES.

[0118] The inorganic sealing film is a light-transmitting inorganic insulating film, and can be composed of, for example, a silicon oxide (SiOx) film, a silicon nitride (SiNx) film, a silicon oxynitride (SiNO) film, or a laminated film of these, formed by a CVD (chemical vapor deposition) method.

[0119] The organic sealing layer is a light-transmitting organic film having a planarizing effect, and can be made of a coatable organic material such as acrylic resin. The organic sealing layer can be formed by, for example, inkjet coating, and a bank (not shown) for stopping droplets may be provided in a non-display area called a frame area that surrounds the pixel area (display area) in which the plurality of pixels P are provided.

[0120] Furthermore, a functional film appropriately selected depending on the application may be formed on the sealing layer 6. Examples of the functional film include a functional film having at least one of an optical compensation function, a touch sensor function, and a protection function. Note that when the display device 1 is a solid display device (i.e., a non-flexible display device), a glass substrate such as a touch panel, a polarizing plate, or a cover glass may be provided instead of the functional film.

[0121] As described above, the display device 1 according to this embodiment includes the light-emitting element ES according to this embodiment. Therefore, according to this embodiment, it is possible to provide a display device 1 that is a light-emitting device and has a highly flat and strong hole injection layer with good film-forming properties and improved hole injection properties, and that can easily form such a hole injection layer.

[0122] [Example] Next, the effects of the light-emitting device ES according to this embodiment will be described with reference to examples and comparative examples. Note that the light-emitting device ES according to this embodiment is not limited to the following examples.

[0123] (EQE) In the following examples and comparative examples, EQE(N φ(exe) ) was evaluated as the number of photons (Np) extracted per unit area of ​​a cell fabricated as a light emitting device for evaluation relative to the number of carriers (Ne) injected into the cell, as shown in the following formula.

[0124] Np = λ / hc × P × 1 / S(1 / m 2 ) Ne = I / e × 1 / S(1 / m 2 ) N φ(exe) =Np / Ne×100=(P×λ×e) / (hc×I)×100(%) In the formula, I represents the current (A), P represents the light intensity (measured light amount (W)), and S represents the cell area (element area (m 2)), λ is the emission peak wavelength (m), e is the elementary electron quantity (A s), h is Planck's constant (J s), and c is the speed of light (m s -1 )

[0125] The current (I) was measured using a Keithley Instruments 2400 source meter. The light intensity (P) was measured using a Topcon House light intensity meter (model number: BM-5A). The cell area was 4 × 10 -6 (m 2 The emission peak wavelength (λ) was set to 536 (nm). Planck's constant was 6.626 × 10 -34 The elementary electron mass (e) is 1.602×10 -19 A·s. The speed of light (c) is 2.998×10 8 (m·s -1 ) was decided.

[0126] (Volume ratio of PVP and NiO-NPs in HIL) To control the volume ratio of ZnO-NP to PVP in the HIL at any desired ratio, a NiO-NP dispersion was prepared at that desired ratio, and a cell was fabricated using the dispersion, as shown in the following Examples and Comparative Examples. The volume ratio of PVP to NiO-NP in the HIL was adjusted to a value that would allow the density of NiO-NP to be 6.67 g / cm. 3 ], and the density of PVP is 1.2 [g / cm 3 ] was calculated as follows.

[0127] (Film forming property) The film-forming properties of the HIL were evaluated by measuring the layer thickness using atomic force microscopy (AFM) and judging the root mean square height (Rq), which represents the root mean square over a reference length and indicates the standard deviation of surface roughness.

[0128] In Table 1 described later, the film-formability rating "◎" indicates that Rq is less than 3.5 nm. The film-formability rating "◯" indicates that Rq is 3.5 nm or more and less than 5.5 nm. The film-formability rating "△" indicates that Rq is 5.5 nm or more.

[0129] Example 1 First, an ITO substrate with ITO formed on it was prepared as an anode and washed. Meanwhile, NiO-NPs with a median diameter (D50) of 14 nm, PVP, and water as a solvent were mixed at room temperature in a ratio of 30 mg of NiO-NPs, 0.28 mg of PVP, and 3 mL of water. The NiO-NPs and PVP were dispersed in the water to prepare a NiO-NP dispersion with a concentration of 90.91 wt%.

[0130] Next, 100 μL of the NiO-NP dispersion was applied to the ITO substrate at a spin speed of 1200 rpm / 30 sec, and then baked at 200°C for 15 minutes to evaporate the water. This resulted in a HIL with a layer thickness (design value) of 20 nm. The film formability was visually confirmed.

[0131] Next, a solution of TFB dissolved (dispersed) in chlorobenzene at 8 mg / mL was spin-coated onto the HIL, and the chlorobenzene was evaporated by baking at 110°C for 30 minutes, forming a HTL with a layer thickness (design value) of 30 nm.

[0132] Next, a QD colloidal solution of red QDs with a Cd / Se core / shell structure dispersed in octane at 20 mg / mL was spin-coated onto the HTL, followed by baking at 110 °C for 10 min to evaporate the solvent, forming an EML with a design thickness of 20 nm.

[0133] Next, a ZnO-NP dispersion (2.5 wt% ZnO nanoparticles (hereinafter referred to as "ZnO-NP") with a median diameter (D50) of 15 nm in ethanol) was spin-coated onto the EML, and the ethanol was evaporated by baking at 110°C for 10 minutes, forming an ETL with a layer thickness (design value) of 50 nm.

[0134] Next, Al was vapor-deposited on the ETL to form a cathode having a layer thickness (design value) of 100 nm.

[0135] Thereafter, the laminate in which the HIL to the cathode were formed on the ITO substrate was sealed with a cover glass. In this way, a cell was fabricated as a light-emitting device for evaluation. Next, the EQE of the fabricated cell was determined.

[0136] Examples 2 to 8 The same operation as in Example 1 was carried out, except that the blending amounts of NiO-NP, PVP, and water were changed as shown in Table 1 below. After a cell was fabricated as a light-emitting device for evaluation in this manner, the EQE of the fabricated cell was determined.

[0137] (Comparative Example 1) Except for not adding PVP to NiO-NP, the same operation as in Example 1 was carried out. In this way, a cell was produced as a light-emitting device for evaluation, and then the EQE of the produced cell was determined.

[0138] Table 1 summarizes the volume ratio of NiO-NP and PVP in the HIL, the blending amounts of NiO-NP, PVP, and water in the NiO-NP dispersion, the concentration (weight percent concentration) of NiO-NP in the NiO-NP dispersion, the weight ratio of NiO-NP to the total amount of NiO-NP and PVP in the NiO-NP dispersion, the film-forming properties of the HIL, and the EQE of the fabricated cells in Examples 1 to 8 and Comparative Example 1.

[0139] [Table 1] As can be seen from Table 1, adding PVP to NiO-NP improves the film-forming properties of the HIL. It was confirmed that all of the cells obtained in Examples 1 to 8 emitted uniform light. Furthermore, according to Examples 1 to 8, it was confirmed that by including PVP in the HIL, a HIL with strong and stable film quality could be obtained in any case.

[0140] Furthermore, from the results shown in Table 1, it can be seen that the volume ratio of NiO-NP 52a to PVP 52b (NiO-NP / PVP) in HIL52 is preferably 40 / 60 or more and 95 / 5 or less. Furthermore, from the viewpoint of film-forming properties, it can be seen that the above volume ratio of NiO-NP / PVP in HIL52 is more preferably 80 / 20 or less. Furthermore, from the viewpoint of EQE, it can be seen that the above volume ratio of NiO-NP / PVP in HIL52 is more preferably 60 / 40 or more and 95 / 5 or less, and particularly preferably 60 / 40 or more and 80 / 20 or less.

[0141] The volume ratio of NiO-NP52a to PVP52b (NiO-NP / PVP) in HIL52 is the same as the volume ratio of NiO-NP52a to PVP52b (NiO-NP / PVP) in NiO-NP dispersion 71. Therefore, the results shown in Table 1 indicate that the volume ratio of NiO-NP52a to PVP52b (NiO-NP / PVP) in NiO-NP dispersion 71 is preferably 40 / 60 or more and 95 / 5 or less. Furthermore, from the viewpoint of film-forming properties, the volume ratio of NiO-NP / PVP in NiO-NP dispersion 71 is more preferably 80 / 20 or less. Furthermore, from the viewpoint of EQE, the volume ratio of NiO-NP / PVP in NiO-NP dispersion 71 is more preferably 60 / 40 or more and 95 / 5 or less, and particularly preferably 60 / 40 or more and 80 / 20 or less.

[0142] Furthermore, from the results shown in Table 1, it can be seen that the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 is preferably 78.9 wt% or more and 99.1 wt% or less. Furthermore, from the viewpoint of film-forming properties, it can be seen that the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 is more preferably 96.4 wt% or less. Furthermore, from the viewpoint of EQE, it can be seen that the weight ratio of NiO-NP52a to the total amount of NiO-NP52a and PVP52b in the NiO-NP dispersion 71 is more preferably 90.9 wt% or more and 99.1 wt% or less, and particularly preferably 90.9 wt% or more and 96.4 wt% or less.

[0143] 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. [Explanation of symbols]

[0144] 51 Anode 52 HIL (Hole Injection Layer) 52a NiO-NP (nickel oxide nanoparticles) 52b PVP (Polyvinylpyrrolidone) 54 EML (Emitting Layer) 54a QD 56 Cathode 71 NiO-NP dispersion (nickel oxide nanoparticle dispersion) 72 Solvents

Claims

1. an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole injection layer provided between the anode and the light-emitting layer; the hole injection layer comprises nickel oxide nanoparticles and polyvinylpyrrolidone; the light-emitting layer contains quantum dots that emit red light, A light-emitting device characterized in that the volume-based median diameter (D50) of the nickel oxide nanoparticles is in the range of 12 nm or more and 20 nm or less.

2. A device comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and a hole injection layer provided between the anode and the light-emitting layer; the hole injection layer comprises nickel oxide nanoparticles and polyvinylpyrrolidone; the light-emitting layer contains quantum dots that emit green light, A light-emitting device characterized in that the volume-based median diameter (D50) of the nickel oxide nanoparticles is in the range of 10 nm or more and 16 nm or less.

3. A device comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and a hole injection layer provided between the anode and the light-emitting layer; the hole injection layer comprises nickel oxide nanoparticles and polyvinylpyrrolidone; the light-emitting layer contains quantum dots that emit blue light, A light-emitting device characterized in that the volume-based median diameter (D50) of the nickel oxide nanoparticles is in the range of 8 nm or more and 14 nm or less.

4. A display device comprising a plurality of light-emitting elements according to claim 1 .

5. A device comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and a hole injection layer provided between the anode and the light-emitting layer; The hole injection layer comprises nickel oxide nanoparticles and polyvinylpyrrolidone. A plurality of light emitting elements are provided, The plurality of light-emitting elements include a red light emitting element in which the light emitting layer contains quantum dots that emit red light; a green light-emitting element in which the light-emitting layer contains quantum dots that emit green light; the light-emitting layer includes a blue light-emitting element including quantum dots that emit blue light, the nickel oxide nanoparticles in the red light-emitting element have a volume-based median diameter (D50) in the range of 12 nm or more and 20 nm or less; the nickel oxide nanoparticles in the green light-emitting element have a volume-based median diameter (D50) in the range of 10 nm or more and 16 nm or less; A display device characterized in that the volume-based median diameter (D50) of the nickel oxide nanoparticles in the blue light-emitting element is in the range of 8 nm or more and 14 nm or less.

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