Light-emitting element and display device

Abstract

The present disclosure provides a light-emitting element capable of achieving both sufficient injection of a current to quantum dots and reduction of a reactive current in a light-emitting layer. A display device (1) includes a light-emitting element (20), said light-emitting element (20) including an anode (21), a light-emitting layer (23), and a cathode (25). The light-emitting layer (23) includes quantum dots (31, 32), and includes a matrix layer (232) made of a metal oxide or the like in the thickness direction, and a non-matrix region (231) other than the matrix layer (232).

Description

Light-emitting element and display device

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

[0002] A light-emitting layer containing semiconductor nanocrystalline particles such as quantum dots emits light when a current is injected into the semiconductor nanocrystalline particles. A known technique for increasing the luminous efficiency of such a light-emitting layer containing semiconductor nanocrystalline particles is to fill the gaps between the semiconductor nanocrystalline particles in the light-emitting layer with a sintered body of a conductive semiconductor material (see, for example, Patent Document 1). Another known technique for increasing the durability of fluorescent microparticles containing quantum dots is to form a silica shell around the quantum dots (see, for example, Patent Document 2).

[0003] Japanese Patent Publication No. 2010-526420 International Publication No. 2012 / 161065

[0004] In the technology described in Patent Document 1, reactive current is generated that passes through the light-emitting layer without being injected into the semiconductor nanocrystal particles, making it difficult to inject current into the semiconductor nanocrystal particles, and the improvement in the luminous efficiency of the light-emitting layer may be insufficient. In the technology described in Patent Document 2, although a shell is provided, current is easily injected into the quantum dots, but reactive current is also easily generated, which may result in an insufficient improvement in the luminous efficiency of the light-emitting layer containing the fluorescent fine particles. As such, the conventional technology leaves room for further study from the perspective of achieving both sufficient current injection into the quantum dots and reduced reactive current in the light-emitting layer.

[0005] An object of one aspect of the present disclosure is to provide a light-emitting element that can achieve both sufficient injection of current into quantum dots and reduction of reactive current in the light-emitting layer.

[0006] In order to solve the above problems, a light-emitting element according to one embodiment of the present disclosure includes a first electrode, a quantum dot-containing light-emitting layer, and a second electrode stacked in this order, the light-emitting layer including at least one matrix layer containing one or more oxides selected from the group consisting of metal oxides and semi-metal oxides, and the total thickness of the matrix layer is smaller than the thickness of the light-emitting layer.

[0007] In order to solve the above problem, a display device according to an aspect of the present disclosure includes the above light-emitting element.

[0008] According to one aspect of the present disclosure, it is possible to provide a light-emitting device that can achieve both sufficient injection of current into quantum dots and reduction of reactive current in the light-emitting layer.

[0009] FIG. 5 is a diagram schematically illustrating an example of a layer configuration in a display device according to embodiment 1 of the present disclosure. FIG. 6 is a diagram schematically illustrating a configuration of an example of a display device according to embodiment 1 of the present disclosure. FIG. 7 is a first diagram for explaining the relationship between quantum dots and a matrix layer according to the present disclosure. FIG. 8 is a second diagram for explaining the relationship between quantum dots and a matrix layer according to embodiment 1 of the present disclosure. FIG. 9 is a diagram schematically illustrating an example of a structure of a matrix layer according to embodiment 1 of the present disclosure. FIG. 10 is a diagram for explaining a reaction process of a precursor of a metal oxide constituting the matrix layer of FIG. 5. FIG. 11 is a diagram schematically illustrating a first example of a metal oxide constituting the matrix layer according to embodiment 1 of the present disclosure. FIG. 12 is a diagram schematically illustrating a second example of a metal oxide constituting the matrix layer according to embodiment 1 of the present disclosure. FIG. 13 is a diagram for explaining current injection in the light-emitting layer of the light-emitting device according to embodiment 1 of the present disclosure. FIG. 14 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 2 of the present disclosure. FIG. 15 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 3 of the present disclosure. FIG. 16 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 4 of the present disclosure. FIG. 17 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 5 of the present disclosure. FIG. 18 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 6 of the present disclosure. FIG. 1 is a diagram schematically illustrating the layer configuration of a light-emitting layer in embodiment 7 of the present disclosure. FIG. 2 is a diagram schematically illustrating the layer configuration of a light-emitting device of comparative example 1. FIG. 3 is a diagram schematically illustrating the layer configuration of a light-emitting device of comparative example 2. FIG. 4 is a diagram illustrating an example of an equivalent circuit diagram of current density in a light-emitting device. FIG. 5 is a diagram illustrating the current-voltage (J-V) characteristics of light-emitting devices of example, comparative example 1, and comparative example 2. FIG. 6 is a diagram illustrating the luminous efficiency of light-emitting devices of example, comparative example 1, and comparative example 2.

[0010] In the present disclosure, an emissive layer containing quantum dots is provided with an inorganic matrix layer and a non-matrix layer, thereby achieving both current injection into the quantum dots and reduced reactive current in the emissive layer. In this specification, the symbol "to" denotes a range inclusive of both the numerical values ​​at both ends. One embodiment of the present disclosure is further described below.

[0011] [Embodiment 1] [Display Device] A display device according to the present disclosure includes a light-emitting element according to the present disclosure, which will be described later. The display device according to the present disclosure can have the same configuration as a known display device including a light-emitting element, except that it includes the light-emitting element described above. Examples of the display device include a television set and a smartphone.

[0012] The display device of the present disclosure can also be applied to a device that adjusts and outputs two or more luminous colors, for example, the display device of the present disclosure can also be applied to a lighting device, and the display device of the present disclosure is also suitable for a lighting device that can output any light, for example, from warm light to cool light, by appropriately adjusting the output of two or more luminous colors.

[0013] [Light-emitting element] <Electrode> In the light-emitting element according to the present disclosure, a first electrode, a light-emitting layer containing quantum dots, and a second electrode are arranged in this order. In this embodiment, the first electrode will be described as an anode and the second electrode as a cathode. In the present disclosure, the first electrode may be the cathode and the second electrode may be the anode. In this manner, in the present disclosure, one of the first electrode and the second electrode will be the anode, and the other will be the cathode, depending on the configuration of the light-emitting element.

[0014] The anode is an electrode for supplying holes to each layer constituting the light-emitting element, and the cathode is an electrode for supplying electrons to each layer constituting the light-emitting element. Both the anode and the cathode are electrically conductive.

[0015] To enhance hole injection properties, a material with a relatively high work function (e.g., a material with a work function of 4.5 eV or more) is preferably used as the anode material. Examples of electrode materials with a high work function include Pt (5.65 eV), Ir (5.25 eV), Ni (5.2 eV), Au (5.15 eV), and Pd (5.15 eV), as well as indium tin oxide (In—Sn—O).

[0016] The anode has optical properties such as reflecting a portion of visible light and transmitting the remainder, and typically includes both an electrode material that reflects visible light and an electrode material that transmits visible light.

[0017] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, Ag, Pd, and Cu, as well as alloys of these metal materials (such as APC (Ag-Pd-Cu) alloy).

[0018] Examples of electrode materials that transmit visible light include thin films of transparent metal oxides (e.g., indium tin oxide, indium zinc oxide (In—Zn—O), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), FTO (fluorine-doped tin oxide), and indium gallium zinc oxide (In—Ga—Zn—O)), thin films made of metal materials such as Al, Mg, and Ag, or alloys of these metal materials (e.g., Mg—Ag alloy), and nanowires (NW) made of these metal materials. Transparent electrodes can be formed by sputtering or the like.

[0019] Among transparent metal oxides, indium tin oxide has a relatively high work function of 4.6 to 5.0 eV and is therefore suitable for use as an anode material. Furthermore, for the anode, a laminate (e.g., indium tin oxide / Ag) in which an indium tin oxide layer is formed on the surface of a metal material can be used for the purpose of improving the conductivity as an electrode layer or adding the function of reflecting visible light.

[0020] The cathode has, for example, electrical conductivity and visible light transparency. A material with a relatively small work function is preferably used as the cathode material, for example, from the viewpoint of enhancing electron injection properties. Examples of electrode materials constituting the cathode include metal materials such as alkali metals, alkaline earth metals, and Al, alloys containing these, and nanowires (e.g., Ag nanowires). Examples of alloys include alloys of Mg and Ag, and Al doped with a small amount of Li.

[0021] <Light-emitting layer> (Quantum dots) The light-emitting layer contains quantum dots. The light-emitting layer containing quantum dots is a light-emitting diode (QLED) element that uses quantum dots in the light-emitting layer.

[0022] Quantum dots are semiconductor particles with a particle size of approximately 100 nm or less (e.g., several nm to several tens of nm), and emit light due to excitons generated by the recombination of injected electrons and holes. Quantum dots are also called (luminescent) semiconductor nanoparticles because their composition is derived from semiconductor materials.

[0023] The wavelength of light emitted from quantum dots can be controlled by their particle size. In quantum dots with a core-shell structure, which will be described later, the wavelength of light emitted from the quantum dots can be controlled by controlling the particle size of the core. In this way, by controlling the particle size or composition of the quantum dots, the wavelength of light emitted by the display device can be controlled.

[0024] The shape of the quantum dots is not limited. For example, the shape of the quantum dots may be a spherical three-dimensional shape (with a circular cross section), a polygonal three-dimensional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, or a three-dimensional shape with an uneven surface, or a combination thereof.

[0025] The quantum dots may be formed of only a core, or may have a core-shell structure including a core and a shell. The shell may be formed in a solid solution state on the surface of the core. The quantum dots may also include doped nanoparticles.

[0026] For example, the recombination of electrons and holes in quantum dots occurs primarily in the core. The core of a quantum dot has a valence band level and a conduction band level, and light is emitted by the recombination of holes in the valence band level and electrons in the conduction band level. Because the light emitted from quantum dots has a narrow spectrum due to the quantum confinement effect, it is possible to obtain light with a relatively deep chromaticity. Furthermore, the shell has the function of suppressing the occurrence of defects or dangling bonds in the core and reducing the recombination of carriers that undergo a deactivation process.

[0027] Examples of quantum dot core materials include Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, and ZnSeTe. Examples of quantum dot shell materials include CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AIP.

[0028] Examples of combinations of quantum dot core and shell materials include CdSe / CdS, InP / ZnS, ZnSe / ZnS, and CIGS / ZnS.

[0029] In the light-emitting layer, the quantum dots may have a shell made of the same material as the matrix layer in the portion exposed from the matrix layer. In this specification, a shell made of substantially the same material as the matrix layer of the quantum dots in the light-emitting layer is also referred to as a "matrix shell." The above shell and the "matrix shell" can be distinguished by the difference in material. For example, if the quantum dots have a shell of ZnS and the matrix layer is made of silicon oxide, the shell and the matrix shell can be distinguished by whether they are a sulfide or an oxide.

[0030] Furthermore, a matrix shell can be added to the quantum dots in the light-emitting layer, as described below. Therefore, a shell made of substantially the same material as the matrix layer present on the surface of the quantum dots, or a shell made of substantially the same material as the matrix layer present between the quantum dots and the matrix layer via an organic material, can be considered a matrix shell. Note that "substantially the same material" includes not only materials whose composition is completely identical, but also materials whose main constituent elements (e.g., oxygen and silicon in the case of silicon oxide) are the same. The composition of the matrix shell material does not have to be completely identical to that of the matrix layer material, as long as it can function as a matrix shell in the present disclosure.

[0031] If the thickness of the shell or matrix shell is too thin, the protection of the core particle may be insufficient, and if the thickness of the shell or matrix shell is too thick, current injection into the core particle due to the tunneling effect may not occur. From the viewpoint of protecting the core particle and sufficiently injecting current into the core particle, the thickness of the shell or matrix shell is preferably 1 to 3 nm. Note that the thickness of the shell or matrix shell can be determined by measuring the minimum length of the shell region in the direction from the center point of the region in the image of the quantum dot to the periphery for any 10 quantum dots extracted from an image of the cross section of the light-emitting element taken with a scanning electron microscope (SEM), and averaging the values ​​for the 10 quantum dots.

[0032] The quantum dots described above are quantum dots that emit visible light, and by appropriately adjusting the particle size and composition of the quantum dots, it is possible to control the emission wavelength to any wavelength range, for example, from the blue wavelength range to the red wavelength range.

[0033] A ligand may be coordinated to the surface of the quantum dot as long as the effects of the present disclosure are obtained. Various known ligands can be used as the ligand. The ligand may be an organic ligand or an inorganic ligand.

[0034] The light-emitting layer containing quantum dots can arbitrarily set the emitted color by adjusting the size of the quantum dots. Furthermore, as will be described in detail later, the light-emitting layer containing quantum dots can be easily and precisely fabricated by a coating method, and the thickness of the fabricated light-emitting layer can be sufficiently controlled. Furthermore, layers other than the light-emitting layer containing quantum dots are not thermally damaged by the manufacturing conditions of the light-emitting layer. Therefore, a light-emitting device including a light-emitting layer containing quantum dots is suitable from the viewpoint of increasing the reliability of the light-emitting device.

[0035] (Matrix Layer) The light-emitting layer includes at least one matrix layer containing one or more oxides selected from the group consisting of metal oxides and semi-metal oxides. A "semi-metal" is generally a substance that exhibits properties intermediate between those of metals and non-metals. Examples of semi-metals include boron, silicon, arsenic, and tellurium.

[0036] Examples of the metal oxides include titanium oxide, aluminum oxide, phosphorus oxide, germanium oxide, hafnium oxide, zirconium oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, and copper oxide. Examples of the metalloid oxides include silicon oxide, boron oxide, and tellurium oxide. The metalloid oxide preferably contains silicon oxide because it allows the use of a material that bonds to the quantum dot surface and to the matrix layer material, such as mercaptoalkylalkoxysilane, which will be described later, and thus enables the quantum dot surface to be strongly protected.

[0037] The metal oxide and the metalloid oxide have a band gap larger than that of the quantum dots. In the present disclosure, in the light-emitting layer, the material having such a larger band gap fills the spaces between the quantum dots in a portion of the thickness direction of the light-emitting layer.

[0038] The matrix layer may extend over substantially the entire light-emitting layer in a direction perpendicular to the thickness direction of the light-emitting layer (hereinafter also referred to as the "plane direction"). For example, the matrix layer may fill the spaces between adjacent quantum dots in 80% or more of the quantum dots contained in the light-emitting layer. Alternatively, the matrix layer may be positioned over substantially the entire periphery of the quantum dots. For example, the matrix layer may be positioned over 90% or more of the entire periphery of the cross section of the quantum dot.

[0039] The light-emitting layer has a thickness of 1000 nm in the surface direction. ２ It is sufficient that the quantum dot contains one or more quantum dots.

[0040] In the matrix layer, the band gap of the metal oxide and metalloid oxide is preferably 2.8 eV or more, which is the band gap of the core of the blue quantum dot, more preferably 5.0 eV or more, and even more preferably 7.0 eV or more. This prevents reactive current from flowing through the matrix layer at a voltage sufficient for injecting current into the quantum dots (e.g., 2.8 V, 5.0 V, or 7.0 V). The band gap may be, for example, 10 eV or less so that current can be injected into the quantum dots by tunneling through the matrix material. The band gap can be determined appropriately depending on the type of metal oxide and metalloid oxide.

[0041] It is preferable that the thickness of the light-emitting layer is sufficiently large relative to the particle size of the quantum dots, so that a sufficient number of quantum dots are present in the thickness direction of the light-emitting layer and the brightness of the light-emitting layer is increased. From this perspective, the thickness of the light-emitting layer is preferably at least twice the particle size of the quantum dots. On the other hand, if the thickness of the light-emitting layer is too thick, the resistance of the light-emitting layer may increase, resulting in a high driving voltage of the device, so the thickness may be no more than five times the particle size of the quantum dots. The film thickness of the light-emitting layer 23 can be specifically determined based on the above-mentioned perspective, and may be, for example, approximately 5 to 100 nm.

[0042] In the present disclosure, the thickness of the light-emitting layer is expressed as the maximum thickness in a region of about 100 nm at any position on the cross section of the light-emitting element photographed with a scanning electron microscope (SEM). Furthermore, in the present disclosure, the particle size of the quantum dots is expressed as the diameter of a circle having an area equal to the average area of ​​10 quantum dots extracted from the image of the cross section of the light-emitting element photographed with a scanning electron microscope (SEM). For example, when the quantum dots have a core-shell structure, the particle size of the quantum dots is the particle size of the quantum dots including the shell (excluding the matrix shell).

[0043] The light-emitting layer has one or more matrix layers. The total thickness of the matrix layers is smaller than the thickness of the light-emitting layer. When the light-emitting layer has multiple matrix layers, the total thickness of the matrix layers is expressed as the sum of the thicknesses of all the matrix layers in the light-emitting layer. The thickness of the matrix layers is expressed in the same way as the thickness of the light-emitting layer.

[0044] From the viewpoint of sufficiently reducing reactive current and sufficiently protecting the quantum dots with the matrix layer, the thickness of each matrix layer is preferably 0.3 times or more, more preferably 0.5 times or more, and even more preferably 1 time or more, the particle size of the quantum dots. From the viewpoint of increasing the luminous efficiency of the light-emitting layer, the thickness of each matrix layer is preferably 2 times or less, more preferably 1.5 times or less, and even more preferably 1.3 times or less. Considering these viewpoints and the particle size of the quantum dots, the thickness of each matrix layer is preferably 3 to 20 nm.

[0045] In the present disclosure, since the total thickness of the matrix layer is smaller than the thickness of the light-emitting layer, the light-emitting layer includes the matrix layer and a region other than the matrix layer (also referred to as a "non-matrix region") in the thickness direction of the light-emitting layer. Thus, in the present disclosure, the matrix layer is located at any position in the thickness direction. More preferably, the quantum dots have a matrix shell made of the same material as the matrix layer, and the quantum dots have the matrix shell in the non-matrix region. The matrix or matrix shell can prevent foreign substances such as water or oxygen that have penetrated slightly through the sealing layer from reaching the quantum dots and deteriorating the quantum dots.

[0046] The non-matrix region does not necessarily have a matrix layer, and may be a region that does not substantially contain any matrix layer material other than the matrix shell. A region that does not substantially contain any matrix layer material may be, for example, a region in which the matrix layer material is not continuous between adjacent quantum dots. The non-matrix region may contain organic ligands derived from the quantum dots, may contain other components as a medium other than the matrix layer material, may contain a binder component such as a resin that binds the quantum dots together, or may contain essentially nothing other than the quantum dots.

[0047] <Functional Layers Other Than the Light-Emitting Layer> In the present disclosure, the light-emitting element may further include layers other than the first electrode, second electrode, and light-emitting layer described above, as long as the effects of the present disclosure are obtained. Examples of such layers include functional layers that contribute to at least one of the injection, movement, and blocking of carriers (electrons or holes). Examples of such functional layers include a hole injection layer, an electron injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, and an electron transport layer.

[0048] The hole injection layer is disposed adjacent to, for example, the anode. The hole injection layer may be composed of a hole transport material that transports holes from the anode to the light-emitting layer. The hole transport material may be an organic or inorganic material that has been conventionally used in light-emitting devices including quantum dots. For example, the hole transport material may include at least one of polyvinylcarbazole (PVK) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD). Examples of organic hole transport materials include conductive compounds such as 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB). Examples of inorganic hole transport materials include molybdenum oxide, NiO, Cr ２ O ３ , MgO, MgZnO, LaNiO ３ , MoO ３ , or W.O. ３ The hole transport material is particularly preferably a material having a large electron affinity and ionization potential.

[0049] The electron injection layer is disposed adjacent to, for example, the cathode. The electron injection layer may be composed of an electron transport material that transports electrons from the cathode to the light-emitting layer. The electron transport material may be an organic or inorganic material that has been conventionally used in light-emitting devices including quantum dots. For example, the electron transport material may be zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO ３), or may include inorganic nanoparticle materials that are nanoparticles of these inorganic materials. Examples of organic electron transport materials include tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), and (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Examples of inorganic electron transport materials include metal oxides such as ZnO, ZAO, ITO, InGaZnO, or electride. It is particularly preferable that the electron transport material be a material with a small electron affinity.

[0050] The hole transport layer and the electron blocking layer may be composed of the hole transport material described above. The materials of the hole injection layer, the hole transport layer, and the electron blocking layer may be the same or different.

[0051] The hole blocking layer and the electron transporting layer may be composed of the electron transporting materials described above. The materials of the electron injection layer, the electron transporting layer, and the hole blocking layer may be the same or different.

[0052] [Specific Examples] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, similar components are denoted by the same reference numerals, and their description will be omitted. Furthermore, depending on the content of the illustration, the display or scale of components denoted by the same reference numerals may differ between drawings, but unless otherwise specified, such differences in display do not mean differences in the components.

[0053] 2 is a schematic diagram of a display device 1 according to this embodiment. The display device 1 is a device that can be used, for example, as a display for a television or a smartphone. The display device 1 includes a display unit DA including a plurality of sub-pixels X, and a driver circuit DR that drives the plurality of sub-pixels X. Each of the plurality of sub-pixels X includes a light-emitting element 20 and a pixel circuit PC that drives the light-emitting element 20. The display device 1 performs display on the display unit DA by controlling light emission from each of the plurality of light-emitting elements 20 formed in the display unit DA via the driver circuit DR and the pixel circuit PC.

[0054] The structure of the display unit DA of the display device 1, particularly the structure of the light-emitting element 20, will be described in more detail with reference to Fig. 1. Fig. 1 is a schematic side cross-sectional view of the display device 1 according to an embodiment of the present disclosure, and particularly shows a cross section perpendicular to the display surface of the display device 1 and passing through the light-emitting element 20.

[0055] 1, the display device 1 according to this embodiment includes, in a display section DA, the above-described plurality of light-emitting elements 20 and a substrate 10, and in particular, the plurality of light-emitting elements 20 on the substrate 10. The display device 1 has a structure in which, for example, layers of the light-emitting elements 20 are stacked on the substrate 10 on which TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits PC.

[0056] 1 , the light-emitting element 20 has a configuration in which an anode 21, a hole transport layer 22, a light-emitting layer 23, an electron transport layer 24, and a cathode 25 are stacked in this order from the substrate 10 side. The anode 21 is electrically connected to the TFT of the substrate 10.

[0057] The light-emitting layer 23 has a non-matrix region 231 on the substrate 10 side and a matrix layer 232 on the opposite side. The light-emitting layer 23 also includes quantum dots 31 and 32. The quantum dot 31 is composed of a quantum dot structure 311, which is a quantum dot having a core particle or a core-shell structure, and a matrix shell 312, and is disposed in the non-matrix region 231. The quantum dot 32 is composed of a quantum dot structure (a quantum dot having a core particle or a core-shell structure) and is disposed in the matrix layer 232.

[0058] Here, the space between quantum dots filled with a matrix layer in the present disclosure will be described with reference to FIGS. 3 and 4 . In the present disclosure, "space between quantum dots filled with a matrix layer" means that there is a region between adjacent quantum dots where the material of the matrix layer is continuously present between the quantum dots. The region K between the quantum dots is indicated by a shaded area in FIGS. 3 and 4 . In FIG. 3 , region K is a region in the cross section of the light-emitting layer that is surrounded by two straight lines (common circumstantial lines) tangent to the outer peripheries of quantum dot 32A and quantum dot 32B and the opposing outer peripheries of quantum dot 32A and quantum dot 32B. Region K is also a substantially triangular region surrounded by two straight lines (common circumstantial lines) tangent to the outer peripheries of adjacent quantum dots 32B and 32C and the opposing outer peripheries of quantum dot 32B and quantum dot 32C. In the present disclosure, "having a region between adjacent quantum dots where the material of the matrix layer is present continuously between the quantum dots" refers to a state in which at least a portion of region K is filled with the material of the matrix layer, as shown in Figure 3 or Figure 4.

[0059] In the present disclosure, as long as the matrix layer 232 is present continuously between adjacent quantum dots, it may fill the entire region K as shown in Fig. 3 or may not fill the entire region K as shown in Fig. 4. That is, the quantum dots 32 may be exposed from the matrix layer 232 as shown in Fig. 4. Furthermore, the matrix layer 232 may or may not cover the outer edge (either the upper or lower surface) of the light-emitting layer.

[0060] The matrix layer 232 in region K may contain components other than the material of the matrix layer 232. For example, the matrix layer 232 in region K may contain other materials, such as a ligand, that are different from the material of the matrix layer 232. More specifically, the matrix layer 232 in region K may contain an organic ligand that is added to improve the dispersibility of the quantum dots 30 or 31 in the dispersion liquid used to coat and form the light-emitting layer 23, and that coordinates to the surfaces of the quantum dots in the dispersion liquid. In this case, from the viewpoint of improving the reliability of the light-emitting layer 23, it is preferable that the content of the organic ligand in the matrix layer 232 in region K be less than 5%, for example.

[0061] The matrix layer 232 is formed at a position in the thickness direction of the light-emitting layer 23 so as to have a thickness of 1000 nm in the in-plane direction. ２ It may have a continuous film with an area of ​​more than 1000 nm.

[0062] The light-emitting layer 23 generally has to have a sufficient concentration of quantum dots 31, 32 to function as a light-emitting layer of a light-emitting element. For example, the light-emitting layer 23 has a thickness of 1000 nm or more in a plane direction perpendicular to the thickness direction at any position in the thickness direction. ２ It is sufficient that one or more quantum dots 30 are contained per one.

[0063] The matrix layer 232 may be positioned substantially over the entire periphery of the quantum dot 32. For example, the matrix layer 232 may be positioned over 90% or more of the periphery of the quantum dot 32.

[0064] The band gap of the matrix layer 232 may be wider than the band gap of the constituent material of the quantum dots 32. In the case where the quantum dots 32 have a core-shell structure, the band gap of the matrix layer 232 may be wider than the band gap of the constituent material of the shell.

[0065] <Microscopic Structure> Here, the microscopic structure of a matrix layer will be described with reference to FIGS. 5 to 8 , using a silicon oxide matrix layer as an example. FIG. 5 is a diagram schematically illustrating an example of the structure of a matrix layer according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating a reaction process of a metal oxide precursor constituting the matrix layer of FIG. 5 . FIG. 7 is a diagram schematically illustrating a first example of a metal oxide constituting the matrix layer according to the first embodiment of the present disclosure. FIG. 8 is a diagram schematically illustrating a second example of a metal oxide constituting the matrix layer according to the first embodiment of the present disclosure. Hereinafter, a case where a matrix layer is formed from a precursor containing tetramethyl orthosilicate (TMOS) will be described as an example.

[0066] 5, the matrix layer 232 has a three-dimensional network structure having Si—O—Si bonds. In addition, in the silicon oxide constituting the matrix layer 232, some of the Si—O—Si bonds are substituted with methoxy groups (CH ３ In this way, the silicon oxide may contain a portion in which a methoxy group exists between Si atoms that are not bonded to each other by a Si—O—Si bond.

[0067] The silicon oxide shown in FIG. 5 can be formed, for example, as follows: Two TMOS 61 shown in the schematic diagram 601 of FIG. 6 are mixed with water (H ２ By reacting with hydroxyl groups (OH), the methoxy groups of each TMOS 61 are reacted and replaced with hydroxyl groups (OH-) to form derivatives 62, as shown in schematic diagram 602. This reaction proceeds using halogens such as fluorine, chlorine, bromine, and iodine as catalysts, and methanol is produced as a by-product of the reaction.

[0068] Furthermore, the hydroxyl groups of the two derivatives 62 shown in the schematic diagram 602 of FIG. 6 react with each other to form a condensate 63 having an Si—O—Si bond by dehydration condensation, as shown in the schematic diagram 603.

[0069] As the above reaction progresses, a compound having the chemical formula [SiO ３ ・(2CH ３ )] ｎHere, n is an integer representing the degree of condensation. The condensation product 64 has a structure that is one-dimensionally extended by the Si-O-Si bond. Furthermore, as the above reaction progresses, the substitution of methoxy groups with hydroxyl groups and dehydration condensation between the hydroxyl groups also progresses within the condensation product 64. Finally, silicon oxide 65 (SiO ２ The silicon oxide 65 has a three-dimensional network structure formed by Si—O—Si bonds.

[0070] If the above reaction is stopped after the condensate 64 is produced but before the silicon oxide 65 is produced, a three-dimensional network structure formed by Si—O—Si bonds may be formed, while some methoxy groups may remain in the condensate 64. The silicon oxide in this embodiment may contain such an intermediate reaction structure as long as the effects of the present disclosure can be obtained.

[0071] [Manufacturing Method] <Manufacturing Method of Display Device> The display device 1 according to this embodiment can be manufactured by forming multiple light-emitting elements 20 on a substrate 10 on which a driver circuit DR, a pixel circuit PC, and the like are separately formed. In the manufacturing method of the light-emitting element 20 according to this embodiment, the layers other than the light-emitting layer 23 may be formed by any method. For example, the layers other than the light-emitting layer 23 may be formed using common materials and a common film-forming process. For example, the layers can be formed by applying a solution containing the materials of each layer to the substrate 10 or a layer formed thereon by spin coating, slit coating, or the like, and then drying the solution. Alternatively, the layers can be formed by preparing a solution in which the materials of each layer are mixed with a solvent for viscosity control, and printing the solution on the substrate 10 or a layer formed thereon by inkjet printing, screen printing, or the like. Printing methods are suitable for manufacturing light-emitting panels and display panels because they enable uniform deposition of each layer over a large area.

[0072] <Method for manufacturing light-emitting layer> The first electrode, the second electrode, and the functional layer in the light-emitting element can be manufactured by known methods. The light-emitting layer in the present disclosure can be manufactured using a known method for manufacturing a light-emitting layer containing quantum dots.

[0073] For example, the light-emitting layer 23 is formed by forming the anode 21, which is a first electrode, on the substrate 10. For example, the anode 21 is formed by forming an Ag layer and an indium tin oxide layer in this order on the surface of the substrate 10 using a sputtering method.

[0074] Next, the hole transport layer 22 is formed on the anode 21. For example, the hole transport layer 22 is formed by depositing a hole transport material on the surface of the anode 21 at a specific deposition rate with or without a common mask.

[0075] Next, the light-emitting layer 23 is formed on the hole-transporting layer 22. The light-emitting layer 23 of the present disclosure can be formed by the below-described fabrication method A or fabrication method B.

[0076] Next, the electron transport layer 24 is formed on the matrix layer 232 of the light emitting layer 23. For example, a magnesium-silver alloy thin film is formed on the surface of the electron transport layer 24 by using a vapor deposition method.

[0077] (Method A for Producing a Light-Emitting Layer) First, a first dispersion liquid is prepared that substantially contains quantum dots 31 as a dispersoid and a solvent as a dispersion medium. The quantum dots 31 have a matrix shell of, for example, silicon oxide. Also, a first solution is prepared that substantially contains a material for the matrix layer as a solute and a solvent as a solvent. The material for the matrix layer is a component that can react with each other to form silicon oxide, for example, upon firing, and more specifically, can be one compound selected from the following compound group A and compound group B, or a mixture of two or more compounds. The solvent of the first solution has a polarity substantially opposite to that of the solvent of the first dispersion liquid.

[0078] Compound group A: TetraethylOrthosilicate (TEOS), TetramethylOrthosilicate (TMOS), TetraisopropylOrtho silicate, TetrapropylOrthosilicate, TetrabutylOrthosilicate, Trimethoxymethylsilane, Triethoxymethylsilane, Trimethoxy(propyl)silane, Triethoxy(propyl)silane, Butyltrime thoxysilane, Butyltriethoxysilane, Triethoxy(isobutyl)silane, Cyclopentyltrimethoxys ilane, Hexyltrimethoxysilane, Hexyltriethoxysilane, Decyltrimethoxysilane, Decyltriet Hoxysilane, Hexadecyltrimethoxysilane, Hexadecyltriethoxysilane, Octadecyltriethoxys Ally ltrimethoxysilane, Allyltriethoxysilane, Vinyltrimethoxysilane, Vinyltriethoxysilane

[0079] Compound group B: (3-Mercaptopropyl)trimethoxysilane (MPS), (3-Mercaptopropyl)triethoxysilane, 3-Aminopropyltrimethoxy silane (APS), 3-Aminopropyltriethoxysilane, 4-Aminobutyltrimethoxysilane, 4-Aminobutyltriethoxysilane

[0080] Then, the first dispersion liquid is applied twice by a known application method to the surface of the hole transport layer 22. In this way, a coating film in which the quantum dots 31 are essentially two-layered is produced.

[0081] Next, the first solution is applied to the surface of the coating of the first dispersion once, or multiple times as necessary, by a known coating method, and the coating of the first solution is baked. By this baking, the matrix layer material in the coating of the first solution bonds to the matrix shell or to each other to form the matrix layer 232. In this way, the light-emitting layer 23 can be produced on the hole transport layer 22, having a non-matrix region 231 substantially having quantum dots 31 with a layer of matrix shell, and a matrix layer 232 thereon substantially having a layer of quantum dots 32.

[0082] (Method B for Producing a Light-Emitting Layer) First, the first dispersion liquid described above is prepared. In addition, a second dispersion liquid is prepared that substantially contains the quantum dots 31 as a dispersoid, the material of the matrix layer as a solute, and a solvent as a dispersion medium and a solvent.

[0083] Then, the first dispersion is applied once to the surface of the hole transport layer 22 by a known application method to prepare a coating film in which the layer of quantum dots 31 is substantially a single layer.

[0084] Next, the second dispersion is applied once onto the surface of the coating of the first dispersion to produce a coating of the second dispersion in which the quantum dots 31 are substantially a single layer and the material of the matrix layer is interposed between the quantum dots 31. The coating is then baked. By this baking, the matrix layer materials in the coating of the second dispersion bond to the matrix shells or to each other to form a matrix layer 232. In this way, a light-emitting layer 23 can be produced on the hole transport layer 22, which has a non-matrix region 231 substantially having quantum dots 31 with a single layer of matrix shell, and a matrix layer 232 thereon substantially having a single layer of quantum dots 32.

[0085] (Example of Dispersion Preparation) The first dispersion and the second dispersion can be prepared by the following method. First, a dispersion a1 is prepared, in which quantum dots having ligands are used as dispersoids and a polar or nonpolar solvent is used as a dispersion medium. A solution a2 is prepared, in which materials for the matrix layer and the matrix shell are used as solutes and a nonpolar or polar solvent is used as a solvent. The polar solvent may be a solvent having a relative dielectric constant of 30 or more at room temperature. Examples include methanol, ethylene glycol, propylene glycol, diethylene glycol, glycerin, furfural, formic acid, ethylene carbonate, propylene carbonate, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, succinonitrile, nitromethane, nitrobenzene, dimethyl sulfoxide, sulfolane, water, and a mixture of at least two of these solvents. The nonpolar solvent may be a solvent having a relative dielectric constant of 3 or less at room temperature. Examples include pentane, hexane, cyclohexane, isooctane, octane, benzene, toluene, dichlorodifluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, tetrachloroethylene, 1,4-dioxane, or a mixture of at least two of these solvents.

[0086] The matrix shell material is, for example, a component having a first binding group that binds to the surface of the quantum dots 32 and a second binding group that binds to the material of the matrix layer. When the matrix layer is made of silicon oxide, it is, for example, a mercaptoalkylalkoxysilane or an aminoalkylalkoxysilane. In this case, the mercapto group or amino group corresponds to the first binding group, and the alkoxy group corresponds to the second binding group. More specifically, the matrix shell material may be a compound selected from the above-mentioned compound group B, or a mixture of two or more compounds. By using a material that binds to both the quantum dot surface and the matrix layer material, the quantum dot surface can be strongly protected because it is less likely to detach than organic ligands that bind only to the quantum dot surface.

[0087] To promote the substitution reaction between the ligand and the matrix shell material, solution a2 may further contain a halogen source such as zinc fluoride, zinc chloride, zinc bromide, zinc iodide, indium fluoride, indium chloride, indium bromide, or indium iodide. The halogen may be appropriately selected within a range that can promote the substitution reaction in the dispersion.

[0088] The contents of the various components in the preparation of the dispersion may be appropriately determined depending on various conditions, such as the dispersibility or solubility of the various components. For example, the content of quantum dots in dispersion a1 may be 1 to 100 mg / mL. The content of the matrix layer material in solution a2 may be 0.01 to 1 M. The content of the matrix shell material in solution a2 may be 0.01 to 1 M. Furthermore, the content of halogen in solution a2 may be 0.01 to 1 M.

[0089] Next, dispersion a1 and solution a2 are stirred and allowed to stand. By standing, an intermediate layer containing quantum dots 31, whose ligands have been replaced with the matrix shell material, and the matrix layer material is formed between the nonpolar solvent layer and the polar solvent layer. The second dispersion is obtained by extracting the intermediate layer through a separation or extraction procedure such as centrifugation. The first dispersion is obtained by preparing solution a2 without adding the matrix layer material.

[0090] When the concentration of the matrix layer material in the second dispersion is reduced, the reaction of forming the matrix shell (e.g., Si—O—Si formation reaction) by bonding of the matrix shell material coordinated to the quantum dots 32 becomes dominant, and an extremely thin layer (e.g., SiO ２A matrix shell (such as a matrix shell of the above-mentioned mercaptoalkylalkoxysilane or aminoalkylalkoxysilane) can be formed. This matrix shell is bonded to the quantum dots 32 via the mercapto group or amino group in the mercaptoalkylalkoxysilane or aminoalkylalkoxysilane, and therefore the mercapto group or amino group and carbon chain are present between the matrix shell and the quantum dots. In other words, the matrix shell is present between the quantum dots and the matrix dots via an organic substance. When the concentration of the matrix layer material in the second dispersion is increased, in addition to the reaction of forming the matrix shell, reactions of forming bonds (e.g., Si—O—Si bonds) between the matrix shell material and the matrix layer material and between the matrix layer materials themselves proceed, and a matrix layer that is substantially integrated with the matrix shell can be formed even in regions distant from the quantum dots 32.

[0091] According to the above manufacturing method, the matrix layer can be produced without using a method in which the thickness and position are determined depending on the lamination position, such as sputtering, and therefore the thickness of the matrix layer and the position of the matrix layer in the light-emitting layer can be easily and accurately controlled.

[0092] (Features of the Light-Emitting Layer) The light-emitting layer 23 in FIG. 1 has a non-matrix region 231 on the anode 21 side, which is the first electrode, and a matrix layer 232 on the cathode 25 side, which is the second electrode. That is, in the non-matrix region 231 and the matrix layer 232, both of which are formed by a coating method, the matrix layer 232 is located higher than the non-matrix region 231 at the time of formation. Generally, when forming a matrix layer by sputtering or vapor deposition, it is relatively easy to form the matrix layer only on the side of the light-emitting layer closer to the substrate, even when controlling the thickness of the matrix layer. However, with such methods as sputtering, it is not easy to form a matrix layer on the side of the light-emitting layer farther from the substrate. When forming a light-emitting layer 23 including a matrix layer 232 located on the opposite side of the non-matrix region 231 on the substrate 10 side, both of the above-described fabrication methods A and B are suitable because they can easily form such a light-emitting layer 23.

[0093] Furthermore, the light-emitting layer 23 produced by the above-described production method A or production method B has a characteristic that the number of carbon atoms per unit area in the matrix layer 232 in its cross section is smaller than the number of carbon atoms per unit area in the non-matrix region 231. This is because, while quantum dots usually have ligands, the ligands are replaced with the material of the matrix shell in the above-described production method A or production method B. This characteristic may be confirmed by observing an area of ​​about 100 nm at any position on the cross section of the light-emitting element using energy dispersive X-ray spectroscopy (SEM-EDX), determining the magnitude of the signal intensities derived from the carbon atoms in the non-matrix region 231 and the matrix layer 232, and converting these values ​​into values ​​per specific unit area as necessary, and checking the magnitude of the signal intensities.

[0094] In the present disclosure, the matrix layer is one or both of a metal oxide and a metalloid oxide, as described above, and the material of the matrix shell is a component that can react with and bond to such a material of the matrix layer. Thus, in the light-emitting layer 23, the quantum dots in the present disclosure are bonded to components that do not contain or have fewer carbon atoms, such as metal oxides and metalloid oxides. Therefore, the light-emitting layer 23 fabricated by the above-described fabrication method A or fabrication method B has the above-described characteristics. Therefore, light-emitting devices and display devices including the light-emitting layer 23 having the above-described characteristics are preferable in terms of ease of fabrication compared to light-emitting devices and display devices having a matrix layer fabricated by methods such as sputtering.

[0095] Furthermore, in the light-emitting layer 23 having the above characteristics, the organic ligands originally attached to the quantum dots are encapsulated in the matrix or matrix shell material, preventing them from being released into the light-emitting layer due to foreign matter such as water or oxygen that has penetrated the sealing layer slightly or due to device operation. The organic ligands released into the light-emitting layer can form a path for reactive current. Therefore, the light-emitting layer 23 having the above characteristics is advantageous from the perspective of further suppressing reactive current. Furthermore, it is possible to prevent the organic ligands from being released from the quantum dots, which could result in the quantum dot surface being unprotected and reducing brightness.

[0096] In this embodiment, the light-emitting element 20 having the light-emitting layer 23 as described above is suitable for suppressing the generation of electrons and improving the carrier balance, and is more suitable for cases where electrons are likely to become excessive, such as red light-emitting elements.

[0097] The above-described structure of the light-emitting layer in the present disclosure can be confirmed by measuring a cross section of the light-emitting layer by energy dispersive X-ray spectroscopy (SEM-EDX) and examining the element distribution of the light-emitting layer.

[0098] (Major Effects) When a voltage is applied to the light-emitting element 20, a current is injected from the hole transport layer 22 into the light-emitting layer 23. Quantum dots 31 having a matrix shell are distributed in a generally layered manner in the non-matrix region 231 of the light-emitting layer 23. Because the matrix shell 312 of the quantum dots 31 is sufficiently thin, the current injected from the hole transport layer 22 is injected into the quantum dots 31 by the tunneling effect, as shown by the solid arrow in FIG.

[0099] Furthermore, the quantum dots 32 are distributed in a generally layered pattern in the matrix layer 232. The matrix layer 232 has a thickness greater than the particle size of the quantum dots 32, but the shortest distance in the thickness direction of the light-emitting layer 23 from the quantum dots 32 to the non-matrix region 231 and the shortest distance from the quantum dots 32 to the electron transport layer 24 are both sufficiently short to allow current injection. Therefore, as shown by the solid arrows in Figure 9, a current injected into the quantum dots 31 is easily injected by the quantum dots 32 in the matrix layer 232, and a current injected into the quantum dots 32 is easily injected by the electron transport layer 24.

[0100] On the other hand, the matrix layer 232 is composed of one or both of a metal oxide and a metalloid oxide and has a thickness greater than the particle size of the quantum dots 32. Therefore, reactive current, i.e., current injected into portions of the matrix layer 232 other than the quantum dots 32, is sufficiently prevented from passing through the matrix layer 232, as indicated by the dashed arrows in FIG. 9 . Furthermore, because current is less likely to flow through portions of the matrix layer 232 other than the quantum dots 32, current injected from the non-matrix region 231 toward the matrix layer 232 is more likely to be injected into the quantum dots 32, through which current flows more easily. Therefore, the matrix layer 232 prevents the generation of reactive current that reaches the electron transport layer 24 from the hole transport layer 22 without being injected into the quantum dots 31 and 32 in the light-emitting layer 23. This also makes it easier for current to be injected into the quantum dots 32, thereby further enhancing the luminous efficiency of the quantum dots 32. In this way, the light-emitting element 20 can achieve both sufficient current injection into the quantum dots 31 and 32 in the light-emitting layer 23 and reduced reactive current in the light-emitting layer 23.

[0101] As described above, in this embodiment, the display device 1 includes the light-emitting element 20, and in the light-emitting element 20, the anode 21 as a first electrode, the light-emitting layer 23 containing quantum dots, and the cathode 25 as a second electrode are arranged in this order, and the light-emitting layer 23 includes at least one matrix layer 232 containing one or more oxides selected from the group consisting of metal oxides and semi-metal oxides, and the total thickness of the matrix layer 232 is smaller than the thickness of the light-emitting layer 23. Therefore, in the light-emitting element 20, it is possible to sufficiently inject current into the quantum dots 31, 32 of the light-emitting layer 23 and sufficiently reduce reactive current in the light-emitting layer 23.

[0102] Furthermore, the matrix layer 232 is located in a portion of the light-emitting layer 23 on the second electrode (cathode) side in the thickness direction of the light-emitting layer 23. Therefore, even if a reactive current is generated in the non-matrix region 231 among the currents injected from the anode 21 into the light-emitting layer 23, the reactive current is prevented by the matrix layer 232 and is easily injected into the quantum dots 32. Therefore, the above configuration is even more effective from the viewpoint of preventing the injection of a reactive current from the light-emitting layer 23 into the electron transport layer 24.

[0103] In addition, the anode 21, which is a first electrode, is formed on the substrate 10. Since the light-emitting layer 23 can be produced by the above-described production method A or production method B, even if the light-emitting layer 23 has a configuration in which the matrix layer 232 is located on the second electrode (cathode) side of the light-emitting layer 23 in the thickness direction of the light-emitting layer 23, this is more effective in terms of ease of production of the light-emitting layer 23 compared to when the matrix layer is produced by a method such as sputtering or vapor deposition.

[0104] The thickness of each matrix layer 232 is 3 to 20 nm, which is equal to or greater than the particle diameter of the quantum dots 31 and 32. This configuration is even more effective in terms of preventing the generation of reactive current in the light-emitting layer 23 by the matrix layer 232.

[0105] Furthermore, the band gap of the metal oxide and semi-metal oxide constituting the matrix layer 232 is 2.8 eV or more. The matrix layer 232 that satisfies this band gap is even more effective from the viewpoint of preventing the generation of reactive current in the light-emitting layer 23. Furthermore, it is even more effective from the viewpoint of facilitating the construction of the matrix layer 232 if the semi-metal oxide contains silicon oxide.

[0106] Furthermore, the number of carbon atoms per unit area of ​​the matrix layer 232 in the cross section of the light-emitting layer 23 is smaller than the number of carbon atoms per unit area of ​​the non-matrix region 231 in the light-emitting layer 23. The matrix layer 232 generally tends to be less conductive to current than general ligands associated with quantum dots. Therefore, the above configuration is even more effective in preventing the generation of reactive current in the matrix layer 232.

[0107] The thickness of the matrix shell 312 in the quantum dot 31 is 1 to 3 nm. This configuration is even more effective in terms of enabling sufficient current injection into the quantum dot structure 311 of the quantum dot 31 by the tunnel effect.

[0108] The thickness of the light-emitting layer 23 is at least twice the particle diameter of the quantum dots 31 and 32. This configuration is suitable for distributing the quantum dots 31 and 32 in two or more layers in the light-emitting layer, and is even more effective from the viewpoint of increasing the light-emitting efficiency of the light-emitting layer 23.

[0109] Other embodiments of the present disclosure will be described below. For ease of explanation, in the following embodiments, components having the same functions as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0110] [Embodiment 2] Fig. 10 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to embodiment 2 of the present disclosure. As shown in Fig. 10, light-emitting element 200 has the same configuration as light-emitting element 20 according to embodiment 1, except that light-emitting layer 223 is included instead of light-emitting layer 23.

[0111] The light-emitting layer 223 has a matrix layer 224 on the substrate 10 side and quantum dots 32 distributed in approximately one layer in the matrix layer 224, and has a non-matrix region 225 on the opposite side from the substrate 10 and quantum dots 31 distributed in approximately one layer in the non-matrix region 225.

[0112] The light-emitting layer 223 can be produced, for example, by the following method: First, the second dispersion (quantum dots with a matrix shell, a material for the matrix layer, and a solvent) is applied once to the surface of the hole transport layer 22 by a known application method and baked. Next, the first dispersion (quantum dots with a matrix shell and a solvent) is applied once to the surface of the coating of the second dispersion.

[0113] In this embodiment, the matrix layer 224 is located on the first electrode (anode 21) side of the light-emitting layer 223 in the thickness direction of the light-emitting layer 223. This configuration is suitable for suppressing hole generation to improve carrier balance, and is suitable from the viewpoint of improving carrier balance in light-emitting elements that are prone to electron deficiency, such as blue light-emitting elements.

[0114] 11 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to a third embodiment of the present disclosure. As shown in FIG. 11 , light-emitting element 300 has the same configuration as light-emitting element 20 according to the first embodiment, except that light-emitting layer 323 is included instead of light-emitting layer 23.

[0115] The light-emitting layer 323 has a matrix layer 324 on the substrate 10 side and quantum dots 33 distributed in approximately one layer in the matrix layer 324, and has a non-matrix region 325 on the opposite side from the substrate 10 and quantum dots 31 distributed in approximately one layer in the non-matrix region 325.

[0116] The thickness of the matrix layer 324 is less than the particle diameter of the quantum dots 31 (for example, slightly more than half), and some of the quantum dots 33 distributed in the matrix layer 324 are exposed from the matrix layer 324 to the non-matrix region 325. The exposed parts of the quantum dots 33 are covered with a matrix shell 331. The matrix shell 331 covers the surfaces of the quantum dots 33 and is made of the same material as the matrix layer 324, and is integrated with the matrix layer 324.

[0117] The light-emitting layer 323 can be produced, for example, by the following method. First, a first dispersion is applied once to the surface of the hole transport layer 22 by a known coating method. Next, a first solution (matrix layer material and solvent) is applied once to the surface of the coating of the first dispersion, and then baked. In this case, the concentration of the matrix layer material in the first solution is adjusted to a concentration such that the thickness of the matrix layer 324 to be produced is a desired thickness less than the particle diameter of the quantum dots 33. Next, the first dispersion is applied once to the surface of the produced matrix layer 324 by a known coating method. Note that the quantum dots 33 may be the same as the quantum dots 31 having a matrix shell, or may be the same as the quantum dots 32 (quantum dot structure).

[0118] In this embodiment, the quantum dots 33 in the matrix layer 324 have a matrix shell 331 made of the same material as the matrix layer 324 in the portion exposed from the matrix layer 324. The matrix layer 324 is located in the portion of the light-emitting layer 323 on the first electrode (anode 21) side. This configuration in which the matrix layer 324 is only partially present relative to the quantum dots 33 in the thickness direction of the light-emitting layer 323 is preferable from the viewpoint of improving current injection into the quantum dots 33 on the matrix layer 324 side. Furthermore, as described above, having the matrix shell 331 in the portion of the quantum dots 33 exposed from the matrix layer 324 is preferable from the viewpoint of preventing foreign substances such as water or oxygen from reaching the quantum dots 33 and further preventing detachment of organic ligands and thereby preventing deterioration of the quantum dots 33.

[0119] 12 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to a fourth embodiment of the present disclosure. As shown in Fig. 12, light-emitting element 400 has the same configuration as light-emitting element 20 according to the first embodiment, except that light-emitting layer 423 is included instead of light-emitting layer 23.

[0120] The light-emitting layer 423 has a non-matrix region 424 on the substrate 10 side and quantum dots 31 distributed in approximately one layer in the non-matrix region 424, and has a matrix layer 425 on the opposite side from the substrate 10 and quantum dots 33 distributed in approximately one layer in the matrix layer 425.

[0121] The configuration of the light-emitting layer 423 is reversed in the thickness direction of the light-emitting layer 423 from that of the light-emitting layer 323 of Embodiment 3. That is, the thickness of the matrix layer 425 is less than the particle diameter of the quantum dots 33 (for example, slightly more than half), and some of the quantum dots 33 distributed in the matrix layer 425 are exposed from the matrix layer 425 to the non-matrix region 424 side. The exposed parts of the quantum dots 33 are covered with a matrix shell 331. The matrix shell 331 is integrated with the matrix layer 425.

[0122] The light-emitting layer 423 can be produced, for example, by the following method. First, a first dispersion is applied twice to the surface of the hole transport layer 22 by a known coating method. Next, a first solution (matrix layer material and solvent) is applied once to the surface of the coating of the first dispersion, followed by baking. In this case, the concentration of the matrix layer material in the first solution is adjusted to a concentration such that the thickness of the matrix layer 425 to be produced is a desired thickness that is less than the particle diameter of the quantum dots 33.

[0123] The position of the matrix layer 425 in the thickness direction of the light-emitting layer 423 can be adjusted by the polarity of the solvents of the first dispersion liquid and the first solution. For example, when the hole transport layer is made of a non-polar organic material, a non-polar solvent is used as the solvent for the first dispersion liquid, and a polar solvent is used as the solvent for the first solution.

[0124] In this embodiment, the quantum dots 33 in the matrix layer 425 have a matrix shell 331 made of the same material as the matrix layer 425 in the portion exposed from the matrix layer 425. The matrix layer 425 is located in the portion of the light-emitting layer 423 on the second electrode (cathode 25) side. This configuration in which the matrix layer 425 is only partially present relative to the quantum dots 33 in the thickness direction of the light-emitting layer 423 is preferable from the viewpoint of improving current injection into the quantum dots 33 on the matrix layer 425 side. Furthermore, as described above, having the matrix shell 331 in the portion of the quantum dots 33 exposed from the matrix layer 324 is preferable from the viewpoint of preventing foreign substances such as water or oxygen from reaching the quantum dots 33 and further preventing detachment of organic ligands and thereby preventing deterioration of the quantum dots 33.

[0125] 13 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to a fifth embodiment of the present disclosure. As shown in Fig. 13, a light-emitting element 500 has the same configuration as the light-emitting element 20 according to the first embodiment, except that the light-emitting element 500 has a light-emitting layer 523 instead of the light-emitting layer 23.

[0126] The light-emitting layer 523 has, from the substrate 10 side, a first matrix layer 524, a non-matrix region 525, and a second matrix layer 526, and has quantum dots 33 distributed in approximately one layer in the first matrix layer 524 and the non-matrix region 525, and quantum dots 32 distributed in approximately one layer in the second matrix layer 526.

[0127] A part of the quantum dots 33 distributed in the first matrix layer 524 and the non-matrix region 525 is exposed from the first matrix layer 524 to the non-matrix region 525. The exposed part of the quantum dots 33 is covered with a matrix shell 331. The matrix shell 331 is integrated with the first matrix layer 524.

[0128] The light-emitting layer 523 can be produced, for example, by the following method. First, a first dispersion is applied once to the surface of the hole transport layer 22 by a known coating method. Next, a first solution (matrix layer material and solvent) is applied once to the surface of the coating of the first dispersion, followed by baking. In this case, the concentration of the matrix layer material in the first solution is adjusted to a concentration such that the thickness of the produced first matrix layer 524 is a desired thickness less than the particle diameter of the quantum dots 33. Next, a second dispersion is applied once to the surface of the produced first matrix layer 524 by a known coating method, followed by baking.

[0129] In this embodiment, the light-emitting layer 523 includes a first matrix layer 524 located on the first electrode (anode 21) side of the light-emitting layer 523 in the thickness direction of the light-emitting layer 523, and a second matrix layer 526 located on the second electrode (cathode 25) side. Such a configuration in which matrix layers are provided on both electrode sides of the light-emitting layer 523 is preferable from the viewpoint of preventing impurities from penetrating into the light-emitting layer 523 from both electrode sides and protecting the quantum dots 32, 33 against such impurity penetration. Furthermore, this embodiment is preferable from the viewpoint of improving current injection into the quantum dots 33 on the first matrix layer 524 side, since the quantum dots 33 have a matrix shell 331 made of the same material as the first matrix layer 524 in the portion exposed from the first matrix layer 524. Furthermore, having the matrix shell 331 in the portion of the quantum dots 33 exposed from the matrix layer 324 is preferable from the viewpoint of preventing foreign substances such as water or oxygen from reaching the quantum dots 33 and further preventing detachment of organic ligands and thereby preventing deterioration of the quantum dots 33, as described above.

[0130] 14 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to a sixth embodiment of the present disclosure. As shown in Fig. 14, light-emitting element 600 has the same configuration as light-emitting element 20 according to the first embodiment, except that light-emitting layer 623 is included instead of light-emitting layer 23.

[0131] The light-emitting layer 623 has quantum dots 31 and 32 distributed in approximately three layers. That is, the light-emitting layer 623 has, from the substrate 10 side, a first non-matrix region 624, a matrix layer 625, and a second non-matrix region 626, and has quantum dots 31 distributed in approximately one layer in the first non-matrix region 624, quantum dots 32 distributed in approximately one layer in the matrix layer 625, and quantum dots 31 distributed in approximately one layer in the second non-matrix region 626.

[0132] The light-emitting layer 623 can be produced, for example, by the following method. First, a first dispersion is applied once to the surface of the hole transport layer 22 by a known coating method. Next, a second dispersion is applied once to the surface of the coating of the first dispersion, followed by baking. Next, the first dispersion is applied once to the surface of the produced matrix layer 625.

[0133] In this embodiment, the matrix layer 625 is located in the middle of the light-emitting layer 623 in the thickness direction of the light-emitting layer 623. This configuration is preferable from the viewpoint of reducing the reactive current without changing the carrier balance, and is preferable from the viewpoint of reducing the reactive current in a light-emitting element that serves as a reference among multiple types of light-emitting elements, such as a green light-emitting element in an RGB light-emitting device.

[0134] 15 is a diagram schematically illustrating the layer configuration of a light-emitting layer according to a seventh embodiment of the present disclosure. As shown in Fig. 15, a light-emitting element 700 has the same configuration as the light-emitting element 20 according to the first embodiment, except that the light-emitting element 700 has a light-emitting layer 723 instead of the light-emitting layer 23.

[0135] The light-emitting layer 723 has quantum dots 31 and 32 distributed in approximately three layers. That is, the light-emitting layer 723 has, from the substrate 10 side, a first matrix layer 724, a non-matrix region 725, and a second matrix layer 726, and has quantum dots 32 distributed in approximately one layer in the first matrix layer 724, quantum dots 31 distributed in approximately one layer in the non-matrix region 725, and quantum dots 32 distributed in approximately one layer in the second matrix layer 726.

[0136] The light-emitting layer 723 can be produced, for example, by the following method. First, the second dispersion is applied once to the surface of the hole transport layer 22 by a known application method, followed by baking. Next, the first dispersion is applied once to the surface of the produced first matrix layer 724. Next, the second dispersion is applied once to the surface of the coating of the first dispersion, followed by baking.

[0137] In this embodiment, the light-emitting layer 723 has approximately three layers of quantum dots 31 and 32, but has matrix layers on both electrode sides of the light-emitting layer 723, as in embodiment 5. This is therefore preferable from the viewpoint of preventing impurities from entering the light-emitting layer 523 from both electrode sides, and is preferable from the viewpoint of protecting the quantum dots 31 and 32 against the intrusion of such impurities.

[0138] [Other Aspects] The light-emitting element according to the present disclosure may further include a light-emitting layer other than the above-described light-emitting layer including the matrix layer. For example, the light-emitting element may further include a light-emitting layer that does not include a matrix layer, or may further include an organic light-emitting layer instead of quantum dots.

[0139] 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.

[0140] An embodiment of the present disclosure is described below.

[0141] [Preparation of Light-Emitting Element] As an example of the present disclosure, a light-emitting element 20 having a light-emitting layer 23 as shown in FIG. 1 was prepared.

[0142] Furthermore, as Comparative Example 1, a light-emitting element 1100 having a light-emitting layer 1123 as shown in Fig. 16 was set. The light-emitting element 1100 has the same configuration as the light-emitting element 20 of the example, except that it has a light-emitting layer 1123 instead of the light-emitting layer 23 of the example. The light-emitting layer 1123 has the same configuration as the light-emitting layer 23, except that it does not have a matrix layer 232 and has quantum dots 31 instead of the quantum dots 32. The entire area of ​​the light-emitting layer 1123 in the thickness direction is a non-matrix region 1124. The light-emitting layer 1123 can be produced by applying the first dispersion twice.

[0143] Furthermore, as Comparative Example 2, a light-emitting device 1200 having a light-emitting layer 1223 as shown in Fig. 17 was set up. The light-emitting device 1200 has the same configuration as the light-emitting device 20 of the Example, except that it has the light-emitting layer 1223 instead of the light-emitting layer 23 of the Example. The light-emitting layer 1223 has the same configuration as the light-emitting layer 23 of the Example, except that it does not have the non-matrix region 231 and has quantum dots 31 instead of the quantum dots 32. The entire area of ​​the light-emitting layer 1223 in the thickness direction is the matrix layer 1224. The light-emitting layer 1223 can be produced by repeatedly applying and baking the second dispersion twice.

[0144] [Evaluation] The reactive current and luminous efficiency of the light-emitting layer were determined for each of the light-emitting device 20 of Example, the light-emitting device 1100 of Comparative Example 1, and the light-emitting device 1200 of Comparative Example 2 as follows.

[0145] First, an example of an equivalent circuit diagram of the current density in a light-emitting device is shown in Fig. 18. As shown in Fig. 18, the current J flowing through the light-emitting device is divided into the diode current J injected into the quantum dots and contributing to light emission. ｄｉｏｄｅ and reactive current J that does not contribute to light emission. ｌｅａｋ It is modeled as the sum of

[0146] Diode current J flowing through the diode ｄｉｏｄｅ is V ｄｉｏｄｅ is the voltage across the diode, e is the elementary charge, k is the Boltzmann constant, T is the temperature, and J ０ is given by the following equation, where is a constant.

[0147]

[0148] n is called the diode coefficient, and the easier it is to inject current into the quantum dots, the smaller it becomes, and ideally it is 2. Here, based on the results of fitting the experimental data, n was set to 4 for light-emitting element 1100 of Comparative Example 1, which has the best current injection into the quantum dots, n was set to 8 for light-emitting element 20 of the example with the next best current injection, and n was set to 12 for light-emitting element 1200 of Comparative Example 2, which has the least current injection (see Table 1 below).

[0149] Reactive current J ｌｅａｋis the current flowing through organic substances such as organic ligands in the light-emitting layer, and can be modeled as a space charge-limited current (SCLC) that is proportional to the power of the voltage. Here, it is assumed to be proportional to the square of the voltage, A is a constant, and the reactive current J ｌｅａｋ is given by the following equation:

[0150]

[0151] The voltage V applied to the light emitting element is V ｄｉｏｄｅ The voltage across the series resistor V ｓ However, V ｓ According to Ohm's law, the series resistance is expressed by the following equation:

[0152]

[0153] The luminance L of the light-emitting element is J ｄｉｏｄｅ , and the luminous efficiency (EQE) of the light-emitting element is proportional to L / J, and the EQE for each current density (J) was calculated for the light-emitting elements of Example, Comparative Example 1, and Comparative Example 2. FIG. 19 shows the calculation results of the current-voltage (J-V) characteristics of each light-emitting element. FIG. 20 shows the calculation results of the luminous efficiency of each light-emitting element. The parameters used in the calculations are shown in the table below. In FIGS. 19 and 20, the solid line indicates Example, the dashed line indicates Comparative Example 1, and the dashed two-dot line indicates Comparative Example 2. In FIG. 19, the dashed line indicates the diode current of Comparative Example 1, and the dotted line indicates the reactive current of Comparative Example 1.

[0154]

[0155] The ease of current injection into the quantum dots is in the order of Comparative Example 1 > Example > Comparative Example 2. Therefore, n is in the order of Comparative Example 1 < Example < Comparative Example 2, and the luminous efficiency EQE when there is no reactive current is ０ The order is Comparative Example 1 > Example > Comparative Example 2.

[0156] Parameter A, which indicates the magnitude of the reactive current, has a value only in Comparative Example 1, and is set to 0 in the Example and Comparative Example 2. That is, all of the current flowing through the light-emitting element is diode current in the Example and Comparative Example 2. In Fig. 19, both the diode current and the reactive current are shown only in Comparative Example 1, and only the diode current is shown in each of the Example and Comparative Example 2.

[0157] In Example and Comparative Example 2, no reactive current flows. Therefore, the EQE does not decrease at low current densities, and the EQE is constant across the entire current range. In contrast, in Comparative Example 1, a reactive current that does not contribute to light emission flows. Therefore, the EQE decreases in the low current range where the ratio of the reactive current to the diode current becomes relatively large. The current (J = 10 mA / cm) used in an actual display device ２ The luminous efficiency (EQE) of the light-emitting element in the above test was 7% in Comparative Example 1 and 5% in Comparative Example 2, but was 10% in the example, which was the highest (FIG. 20).

[0158] In Comparative Example 1, in addition to the diode current, a reactive current that does not contribute to light emission flows. At high voltages, the reactive current is small relative to the diode current. On the other hand, at low voltages, the reactive current is large relative to the diode current, and the EQE decreases significantly, especially at low currents ( FIG. 20 ). In Example and Comparative Example 2, no reactive current flows and all current is diode current, so the EQE does not decrease at low currents.

[0159] Thus, the light-emitting element 20 of the example exhibits good results in terms of luminous efficiency, charge injection into the quantum dots, and prevention of reactive current. This is thought to be because current injection into the quantum dots is improved by forming only a portion of the light-emitting layer in the thickness direction as a matrix layer, reactive current is less likely to flow due to the matrix layer in series, and the organic ligands are less likely to detach from the quantum dots in the light-emitting layer because they are capped by the matrix layer.

[0160] The light-emitting device 1100 of Comparative Example 1 excels in injecting current into the quantum dots. This is thought to be because the light-emitting layer does not have a matrix layer, making it easy to inject current into the quantum dots. On the other hand, the light-emitting device 1100 of Comparative Example 1 is insufficient in terms of luminous efficiency and prevention of reactive current. This is thought to be because reactive current flows in the light-emitting layer due to organic ligands, etc., that have detached from the quantum dots, which reduces the luminous efficiency of the light-emitting layer.

[0161] The light-emitting device 1200 of Comparative Example 2 exhibits good results in preventing reactive current. This is thought to be because the matrix layer in the light-emitting layer makes it difficult for reactive current to flow, and because the organic ligands are capped by the matrix layer and therefore are difficult to desorb into the light-emitting layer. On the other hand, the light-emitting device 1200 of Comparative Example 2 has insufficient luminous efficiency. This is thought to be because the matrix layer is present throughout the entire thickness of the light-emitting layer, making it difficult for current to be injected into the quantum dots.

[0162] 1 Display device 10 Substrate 20, 200, 300, 400, 500, 600, 700, 1100, 1200 Light-emitting element 21 Anode (first electrode) 22 Hole transport layer 23, 223, 323, 423, 523, 623, 723, 1123, 1223 Light-emitting layer 24 Electron transport layer 25 Cathode (second electrode) 31, 32, 33 Quantum dots 225, 231, 325, 424, 525, 725, 1124 Non-matrix region 224, 232, 324, 425, 625, 1224 Matrix layer 311 Quantum dot structure 312, 331 Matrix shell 524, 724 First matrix layer 526, 726 Second matrix layer 624 First non-matrix region 626 Second non-matrix region DA Display section DR Driver circuit K Region PC Pixel circuit X Sub-pixel

Claims

1. A light-emitting device comprising a first electrode, a quantum dot-containing light-emitting layer, and a second electrode, stacked in this order; the light-emitting layer comprises at least one matrix layer containing one or more oxides selected from the group consisting of metal oxides and semi-metal oxides; and the total thickness of the matrix layers is smaller than the thickness of the light-emitting layer.

2. The light-emitting element according to claim 1, wherein the matrix layer is located on a portion of the light-emitting layer on the first electrode side in the thickness direction of the light-emitting layer.

3. The light-emitting element according to claim 1, wherein the matrix layer is located on a portion of the light-emitting layer on the second electrode side in the thickness direction of the light-emitting layer.

4. The light-emitting element described in claim 1, wherein the matrix layer includes a first matrix layer located on a portion of the light-emitting layer on the first electrode side in the thickness direction of the light-emitting layer, and a second matrix layer located on a portion of the light-emitting layer on the second electrode side in the thickness direction of the light-emitting layer.

5. The light-emitting device according to any one of claims 1 to 4, wherein the matrix layer is located at a middle portion of the light-emitting layer in the thickness direction of the light-emitting layer.

6. The light-emitting device according to any one of claims 1 to 5, wherein the thickness of each of said matrix layers is at least one time the particle diameter of said quantum dots.

7. The light-emitting device according to any one of claims 1 to 6, wherein the thickness of each of the matrix layers is 3 to 20 nm.

8. The light-emitting device according to any one of claims 1 to 7, wherein the band gap of the metal oxide and the semi-metal oxide is 2.8 eV or more.

9. The light-emitting device according to any one of claims 1 to 8, wherein the semi-metal oxide comprises silicon oxide.

10. A light-emitting element according to any one of claims 1 to 9, wherein the number of carbon atoms per unit area of ​​the matrix layer in the cross section of the light-emitting layer is smaller than the number of carbon atoms per unit area of ​​the portion of the light-emitting layer other than the matrix layer.

11. The light-emitting device according to any one of claims 1 to 10, wherein the quantum dots have a matrix shell made of the same material as the matrix layer in the portion exposed from the matrix layer.

12. The light-emitting device according to claim 11, wherein the matrix shell has a thickness of 1 to 3 nm.

13. The light-emitting device according to any one of claims 1 to 12, wherein the thickness of the light-emitting layer is at least twice the particle diameter of the quantum dots.

14. The light-emitting device according to any one of claims 1 to 13, wherein the first electrode is an anode and the second electrode is a cathode.

15. The light-emitting device according to any one of claims 1 to 14, wherein the first electrode is formed on a substrate.

16. A display device comprising a light-emitting element according to any one of claims 1 to 15.

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