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

Abstract

A light-emitting layer (23) provided to a light-emitting element (2) includes a light-emitting material (30) and a matrix material (40). In a direction along the lamination direction (LD) of the light-emitting element, the ionization potential of the matrix material is smaller or the electron affinity of the matrix material is larger toward the center of the light-emitting layer in comparison to both an end (23A) of the light-emitting layer toward an anode (21) and an end (23B) of the light-emitting layer toward a cathode (25).

Description

Light-emitting element, display device, and method for manufacturing the same

[0001] The present disclosure relates to a light-emitting device containing quantum dots as a light-emitting material, a display device including the light-emitting device, and a method for manufacturing the light-emitting device.

[0002] Patent Document 1 discloses that gradients are provided in the ionization potential and electron affinity of each part of the light-emitting layer of the light-emitting element in the direction along the stacking direction of the light-emitting element. The purpose of Patent Document 1 is to achieve a light-emitting element with high luminous efficiency and small fluctuation in chromaticity through the above configuration.

[0003] Japanese Patent Application Publication No. 2009-71188

[0004] As in the light-emitting element described in Patent Document 1, simply providing a gradient at the upper and lower end levels of the band gap of the light-emitting layer may result in insufficient improvement of the carrier balance in the light-emitting layer. In particular, the configuration described in Patent Document 1 only improves one of the hole excess and electron excess in the light-emitting layer, making it difficult to improve the concentration of both holes and electrons in the light-emitting layer, in other words, to resolve the carrier balance. This may result in a decrease in luminous efficiency or a shortened lifetime in the light-emitting element.

[0005] A light-emitting element according to one aspect of the present disclosure includes an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer includes a plurality of light-emitting materials and a matrix material that fills the space between at least two of the light-emitting materials and has a higher ionization potential or a lower electron affinity than the light-emitting materials, and the ionization potential of the matrix material is smaller or the electron affinity of the matrix material is larger at the center of the light-emitting layer than at the end of the light-emitting layer on the anode side and the end of the light-emitting layer on the cathode side, respectively, in the stacking direction.

[0006] 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 facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, wherein the light-emitting layer includes a plurality of light-emitting materials and a matrix material that fills a space between at least two of the light-emitting materials and has a larger ionization potential than the light-emitting materials or a smaller electron affinity than the light-emitting materials, and the ionization potential of the matrix material is smaller or the electron affinity of the matrix material is larger at the center of the light-emitting layer than at the end of the light-emitting layer on the anode side and the end of the light-emitting layer on the cathode side, respectively.

[0007] The carrier balance in the light-emitting layer of the light-emitting element is improved, thereby improving the light-emitting efficiency of the light-emitting element.

[0008] FIG. 1 is a schematic side cross-sectional view of a display device according to embodiment 1, and a band diagram of each layer of a functional layer of a light-emitting element. FIG. 2 is a schematic view of a display device according to embodiment 1. FIG. 3 is a schematic enlarged side cross-sectional view of a light-emitting layer according to embodiment 1. FIG. 4 is a schematic diagram for showing a matrix material filling spaces between quantum dots according to embodiment 1. FIG. 5 is a flowchart of a manufacturing method of a display device according to embodiment 1. FIG. 6 is a band diagram of each layer of a functional layer of a light-emitting element according to embodiment 2. FIG. 7 is a band diagram of each layer of a functional layer of a light-emitting element according to embodiment 3. FIG. 8 is a schematic enlarged side cross-sectional view of a light-emitting layer according to embodiment 4. FIG. 9 is a band diagram of each layer of a functional layer of a light-emitting element according to embodiment 4.

[0009] [Embodiment 1] <Display Device: Overview> Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in each drawing, similar configurations are assigned the same reference numerals, and their description will be omitted. Furthermore, in this disclosure, for simplicity of illustration, components assigned the same reference numerals may be drawn to different scales and may be hatched differently depending on the drawing. However, the components shown in each drawing of the present disclosure are merely examples, and the scales are not limited to those shown in the drawings. Furthermore, in this disclosure, components with different hatching have the same configuration as described above. Furthermore, in each drawing of the present disclosure, when two components have substantially the same shape but different compositions, etc., they may be assigned different reference numerals but the same hatching.

[0010] 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, a smartphone, or the like. 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 2 and a pixel circuit PC that drives the light-emitting element 2. The display device 1 performs display on the display unit DA by controlling light emission from each of the plurality of light-emitting elements 2 formed in the display unit DA via the driver circuit DR and the pixel circuit PC.

[0011] The structure of the display unit DA of the display device 1, particularly the structure of the light-emitting element 2, will be described in more detail with reference to Fig. 1. Fig. 1 is a diagram showing a schematic side cross-sectional view 101 of the display device 1 according to an embodiment of the present disclosure and a band diagram 102 of each layer of a functional layer (described later) of the light-emitting element 2. In particular, the schematic side cross-sectional view 101 shows a cross section perpendicular to the display surface of the display device 1 and passing through the light-emitting element 2. Note that all band diagrams in the present disclosure, including the band diagram 102, show a case where an energy level at infinity is located upward in the plane of the paper.

[0012] 1, the display device 1 according to this embodiment includes a display section DA that includes the above-described plurality of light-emitting elements 2 and a substrate 3, and in particular includes the plurality of light-emitting elements 2 on the substrate 3. The display device 1 has a structure in which the layers of the light-emitting elements 2 are stacked on the substrate 3 on which, for example, TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits PC. In this specification, the direction from the light-emitting elements 2 of the display device 1 to the substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0013] The light-emitting element 2 includes an anode 21, a hole transport layer 22, a light-emitting layer 23, an electron transport layer 24, and a cathode 25, in this order from the substrate 3 side. The anode 21 of the light-emitting element 2 is electrically connected to the TFT of the substrate 3. In this embodiment, as shown in FIG. 1 , the stacking direction of the layers of the light-emitting element 2 is defined as a stacking direction LD. The stacking direction LD may be, for example, substantially the same as the normal direction to the upper surface of the substrate 3, or may be substantially the same as the normal direction to the upper surface or lower surface of any layer of the light-emitting element 2.

[0014] Schematic cross-sectional side view 101 shows a schematic cross section of display device 1 with stacking direction LD as the up-down direction in the plane of the paper. In addition, all band diagrams in this disclosure, including band diagram 102, show the band gaps of each layer with stacking direction LD as the left-right direction in the plane of the paper, with the hole transport layer 22 side on the left side and the electron transport layer 24 side on the right side in the plane of the paper.

[0015] Note that, in this disclosure, there are sections where the magnitude of the ionization potential and electron affinity of each layer of the light-emitting element 2 is discussed with reference to each band diagram. Here, the "ionization potential" of a specific member in this disclosure refers to the absolute value of the magnitude of the ionization potential of the specific member based on the energy level at infinity. In other words, the "ionization potential" of a specific member in this disclosure refers to the absolute value of the energy difference between the energy level at infinity and the lower end level of the band gap of the specific member. For example, in this disclosure, "the ionization potential of a first member is greater than the ionization potential of a second member" means that, in the band diagram, the lower end level of the band gap of the first member is located below the lower end level of the band gap of the second member.

[0016] Furthermore, the "electron affinity" of a specific component in the present disclosure refers to the absolute value of the magnitude of the electron affinity of the specific component based on the energy level at infinity. In other words, the "electron affinity" of a specific component in the present disclosure refers to the absolute value of the energy difference between the energy level at infinity and the upper end level of the band gap of the specific component. For example, in the present disclosure, "the electron affinity of a first component is greater than the electron affinity of a second component" means that the upper end level of the band gap of the first component is located lower than the upper end level of the band gap of the second component in a band diagram.

[0017] The ionization potential of a predetermined component in the present disclosure may be confirmed by performing photoelectron spectroscopy on the component. Furthermore, the electron affinity of a predetermined component in the present disclosure may be confirmed by performing inverse photoelectron spectroscopy on the component. For example, in the present disclosure, after forming a thin film of the predetermined component, the thin film may be removed by sputtering, and at least one of photoelectron spectroscopy and inverse photoelectron spectroscopy may be performed on the removed portion of the thin film. In the present disclosure, photoelectron spectroscopy and inverse photoelectron spectroscopy may be performed simultaneously. The band gap of a predetermined component in the present disclosure may be confirmed by confirming the ionization potential and electron affinity of the component.

[0018] <Outline of Light-Emitting Element> The structure of each layer of the light-emitting element 2 will be described in more detail below.

[0019] The anode 21 and the cathode 25 comprise conductive materials and are electrically connected to the hole transport layer 22 and the electron transport layer 24, respectively.

[0020] At least one of the anode 21 and the cathode 25 is a transparent electrode that transmits visible light. Examples of transparent electrodes that can be used include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), and FTO (fluorine-doped tin oxide). The transparent electrode may be formed by a sputtering method or the like. Alternatively, either the anode 21 or the cathode 25 may contain a metal material, preferably Al, Cu, Au, Ag, or Mg, or an alloy thereof, which have high reflectivity for visible light.

[0021] The hole transport layer 22, the light-emitting layer 23, and the electron transport layer 24, which are located between the anode 21 and the cathode 25, are layers that have a light-emitting function or a function of transporting charges from each electrode. For this reason, in the present disclosure, each layer located between the anode 21 and the cathode 25, including the hole transport layer 22, the light-emitting layer 23, and the electron transport layer 24, may be referred to as a "functional layer."

[0022] The hole transport layer 22 is a layer containing a hole transport material that transports holes from the anode 21 to the light-emitting layer 23. In particular, in this embodiment, the hole transport layer 22 is in contact with the light-emitting layer 23. The material of the hole transport layer 22 can be an organic or inorganic material that has been conventionally used in light-emitting devices containing quantum dots. For example, the hole transport layer 22 may contain at least one of polyvinylcarbazole (PVK) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD) as the hole transport material. Examples of organic materials that can be used for the hole transport layer 22 include 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), conductive compounds such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB), polytriallylamine semiconductor (PTAA), and [dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile] (HAT-CN). Examples of inorganic materials that can be used for the hole transport layer 22 include MoO ３ Molybdenum oxides such as NiO, Cr ２ O ３ , MgO, LaNiO ３ , or W.O. ３ Metal oxides such as the above can be used.

[0023] The electron transport layer 24 is a layer containing an electron transport material that transports electrons from the cathode 25 to the light-emitting layer 23. In particular, in this embodiment, the electron transport layer 24 is in contact with the light-emitting layer 23. The material of the electron transport layer 24 can be an organic or inorganic material that has been conventionally used in light-emitting devices containing quantum dots. For example, the electron transport layer 24 can be made of an electron transport material such as zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO ３), or may contain an inorganic nanoparticle material that is nanoparticles of these inorganic materials. Alternatively, the electron transport layer 24 may contain an organic material as the electron transport material, such as tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), or (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Note that the inorganic material of the electron transport layer 24 may be a metal oxide, such as ZnO, ZAO, ITO, InGaZnO, or electride.

[0024] In this embodiment, the hole transport layer 22 and the electron transport layer 24 can be formed by vacuum deposition, sputtering, or a coating method using a colloidal solution using the above-mentioned materials. The light-emitting element 2 may also include a hole injection layer between the anode 21 and the hole transport layer 22, or an electron injection layer between the cathode 25 and the electron transport layer 24. The hole injection layer and the electron injection layer may both be formed by the same method as the hole transport layer 22 or the electron transport layer 24.

[0025] <Light-emitting layer: quantum dots> The light-emitting layer 23 according to this embodiment will be described in more detail with reference to Fig. 3 in addition to Fig. 1. Fig. 3 is a schematic diagram showing an enlarged view of a part of the side cross section of the light-emitting layer 23 in the cross section shown in Fig. 1, particularly of region E shown in Fig. 1.

[0026] The light-emitting layer 23 includes a plurality of quantum dots 30 as a light-emitting material, and also includes a matrix material 40 .

[0027] The quantum dots 30 may each have a core / shell structure, including a core and a shell surrounding the core. In this embodiment, the quantum dots 30 are, for example, luminescent semiconductor nanoparticles that emit light due to excitons generated by the recombination of injected electrons and holes. For example, the recombination of electrons and holes in the quantum dots 30 occurs primarily in the core. The core of the quantum dot 30 is a luminescent material that has a valence band level and a conduction band level and emits light due to the recombination of holes in the valence band level and electrons in the conduction band level. The quantum dots 30 emit light with a narrow spectrum due to the quantum confinement effect, enabling the production of light with a relatively deep chromaticity. Furthermore, the shell functions to suppress the occurrence of defects or dangling bonds in the core and reduce the recombination of carriers undergoing a deactivation process.

[0028] The core and shell materials of the quantum dots 30 may each contain materials used for the core and shell materials of conventionally known core / shell quantum dots. The quantum dots 30 may have a core / shell structure of, for example, InP / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or a I-III-V chalcopyrite-based material / ZnS, including CuInGaS (CIGS). Alternatively, the quantum dots 30 may contain InZnP, CdSeTe, or ZnSeTe. The core of the quantum dots 30 may also contain CuInZnS, CuInS, CuGaS, AgInS, or ZnAgInS. The shell may be formed from multiple layers containing multiple different materials.

[0029] In this embodiment, from the viewpoint of improving the efficiency of hole injection from the hole transport layer 22 to the quantum dots 30, the ionization potential may be smaller in the quantum dots 30 than in the hole transport layer 22. Furthermore, from the viewpoint of reducing the outflow of electrons from the quantum dots 30 to the hole transport layer 22, the electron affinity may be larger in the quantum dots 30 than in the hole transport layer 22. Furthermore, from the viewpoint of improving the efficiency of electron injection from the electron transport layer 24 to the quantum dots 30, the electron affinity may be larger in the quantum dots 30 than in the electron transport layer 24. In addition, from the viewpoint of reducing the outflow of holes from the quantum dots 30 to the electron transport layer 24, the ionization potential may be smaller in the quantum dots 30 than in the electron transport layer 24. The materials of the hole transport layer 22, the electron transport layer 24, and the quantum dots 30 may be determined so that the band gaps of the hole transport layer 22, the electron transport layer 24, and the quantum dots 30 respectively satisfy the above-described configuration.

[0030] The quantum dots 30 have a particle size of about 1 to 100 nm. The wavelength of light emitted from the quantum dots 30 can be controlled by the particle size. In particular, since the quantum dots 30 have a core / shell structure, the wavelength of light emitted from the quantum dots 30 can be controlled by controlling the particle size of the core. Therefore, by controlling the particle size of the quantum dots 30, the wavelength of light emitted by the display device 1 can be controlled.

[0031] <Light-emitting layer: matrix material: matrix material filling spaces between quantum dots> In this embodiment, the matrix material 40 fills the spaces between the quantum dots 30. The matrix material 40 filling the spaces between the quantum dots 30 will be described in more detail with further reference to FIG. 4. Schematic diagrams 401 and 402 in FIG. 4 are schematic diagrams showing the matrix material 40 filling the spaces between the quantum dots 30. In particular, schematic diagrams 401 and 402 are respectively diagrams showing two examples of a set P of two quantum dots 30 and the region (space) K between them shown in FIG. 3. In particular, schematic diagrams 401 and 402 are respectively diagrams showing sets P1 and P2, which are examples of sets of quantum dots 30A and 30B.

[0032] In this specification, the matrix material 40 filling the spaces between the quantum dots 30 means that the matrix material 40 fills at least the region K between the quantum dots 30A and 30B, as shown in the schematic diagram 401 of the set P1 in Fig. 4 . The region K is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of the quantum dots 30A and 30B and the opposing peripheries of the quantum dots 30A and 30B in the cross section of the light-emitting layer 23. Therefore, as shown in the schematic diagram 402 of the set P2 in Fig. 4 , the region K can exist even if the quantum dots 30A and 30B are close to each other, and the matrix material 40 fills the region K.

[0033] The matrix material 40 filling the spaces between the quantum dots 30 does not necessarily mean that the region K between the quantum dots 30A and 30B is entirely made of the matrix material 40. For example, the region K between the quantum dots 30A and 30B may contain a material, such as a ligand, different from the material of the matrix material 40. Specifically, the light-emitting layer 23 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 30 in the dispersion liquid used for coating and that coordinates to the outer surfaces of the quantum dots 30 in the dispersion liquid. In this case, in the light-emitting layer 23, from the viewpoint of improving the reliability of the light-emitting layer 23, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%, for example.

[0034] The matrix material 40 may have a continuous film. In the present disclosure, the term "the matrix material 40 has a continuous film" means that the matrix material 40 has a thickness of 1000 nm in a plane direction perpendicular to the film thickness direction of the light-emitting layer 23. ２ Alternatively, the term "quantum dots" may refer to a continuous portion having an area equal to or larger than that of the quantum dots 30. In the light-emitting layer 23, the quantum dots 30 may be encapsulated in a continuous film of the matrix material 40. In this case, the matrix material 40 protects the quantum dots 30 more firmly.

[0035] 1 and 3 , the matrix material 40 includes, in order from the anode 21 side, a first portion 41, a second portion 42, and a third portion 43. As particularly shown in FIG. 3 , an end portion 41A of the first portion 41 on the anode 21 side may form an end portion 23A of the light-emitting layer 23 on the anode 21 side. Furthermore, an end portion 43A of the third portion 43 on the cathode 25 side may form an end portion 23B of the light-emitting layer 23 on the cathode 25 side.

[0036] In other words, for example, the outer edge (upper and lower surfaces) of the light-emitting layer 23 may be covered with the matrix material 40. Alternatively, a portion of the matrix material 40 may extend from the outer edge of the light-emitting layer 23, with the quantum dots 30 positioned away from the outer edge. However, the outer edge of the light-emitting layer 23 may not be formed solely from the matrix material 40, and some of the quantum dots 30 may be exposed from the matrix material 40. The matrix material 40 may refer to the portion of the light-emitting layer 23 excluding the plurality of quantum dots 30.

[0037] The end of the first portion 41 on the cathode 25 side is not particularly limited as long as it is located closer to the anode 21 than the second portion 42. For example, as shown by the dotted line in FIG. 3 , the end of the first portion 41 on the cathode 25 side may be end 41B that contacts the anode 21-side end of the quantum dot 30 located closer to the anode 21 among the multiple quantum dots 30 included in the light-emitting layer 23. Furthermore, as shown by the dashed-dotted line in FIG. 3 , the end of the first portion 41 on the cathode 25 side may be end 41C, on an extension of which is located the center of the quantum dot 30 located closer to the anode 21 among the multiple quantum dots 30 included in the light-emitting layer 23. Furthermore, as shown by the two-dot-dash line in FIG. 3 , the end of the first portion 41 on the cathode 25 side may be end 41D that contacts the cathode 25-side end of the quantum dot 30 located closer to the anode 21 among the multiple quantum dots 30 included in the light-emitting layer 23.

[0038] In the present disclosure, the "edge" of each layer of the light-emitting element 2 may refer to a region in any region of the layer where the components of the layer account for, for example, 90% or less of the components of the other region, or a region including a boundary with another layer. Furthermore, in the present disclosure, "contact" between two layers of the light-emitting element 2 refers to the presence of a region that contains both of the components of the two layers. The position of the edge of each layer of the light-emitting element 2 and whether or not the two layers contact can be confirmed, for example, by observing the cross section of each layer of the light-emitting element 2 using a transmission electron microscope (TEM).

[0039] The end of the third portion 43 on the anode 21 side is not particularly limited as long as it is located closer to the cathode 25 than the second portion 42. For example, as shown by the dotted line in FIG. 3 , the end of the third portion 43 on the anode 21 side may be end 43B that contacts the cathode 25-side end of a quantum dot 30 located closer to the cathode 25 among the multiple quantum dots 30 included in the light-emitting layer 23. Furthermore, as shown by the dashed-dotted line in FIG. 3 , the end of the third portion 43 on the anode 21 side may be end 43C, the extension of which is located the center of a quantum dot 30 located closer to the cathode 25 among the multiple quantum dots 30 included in the light-emitting layer 23. Furthermore, as shown by the two-dot-dash line in FIG. 3 , the end of the third portion 43 on the anode 21 side may be end 43D that contacts the anode 21-side end of a quantum dot 30 located closer to the cathode 25 among the multiple quantum dots 30 included in the light-emitting layer 23.

[0040] In this embodiment, the first portion 41 may include at least a portion from the end 41A on the anode 21 side to the end on the cathode 25 side, excluding the quantum dots 30. The third portion 43 may include at least a portion from the end 43A on the cathode 25 side to the end on the anode 21 side, excluding the quantum dots 30. The second portion 42 may be in contact with the first portion 41 and the third portion 43. In this case, the second portion 42 may include at least a portion from the end of the first portion 41 on the cathode 25 side to the end of the third portion 43 on the anode 21 side, excluding the quantum dots 30.

[0041] <Light-emitting layer: matrix material: band gap> The ionization potential of the matrix material 40 is smaller in the second portion 42 than in the first portion 41 and the third portion 43. In particular, the ionization potential of the matrix material 40 gradually decreases from the first portion 41 to the second portion 42 and from the third portion 43 to the second portion 42. This corresponds to the fact that, in the band diagram 102, the lower end level of the band gap of the matrix material 40 gradually increases from the first portion 41 to the second portion 42 and from the third portion 43 to the second portion 42.

[0042] Furthermore, the electron affinity of the matrix material 40 is greater in the second portion 42 than in the first portion 41 and the third portion 43. In particular, the electron affinity of the matrix material 40 gradually increases from the first portion 41 to the second portion 42 and from the third portion 43 to the second portion 42. This corresponds to the fact that, in the band diagram 102, the upper end level of the band gap of the matrix material 40 gradually decreases from the first portion 41 to the second portion 42 and from the third portion 43 to the second portion 42.

[0043] For this reason, the ionization potential of the matrix material 40 is smaller in the direction along the stacking direction LD, closer to the center than the ends 23A and 23B of the light-emitting layer 23. Also, the electron affinity of the matrix material 40 is larger in the direction along the stacking direction LD, closer to the center than the ends 23A and 23B of the light-emitting layer 23. Furthermore, from the above configuration, the band gap of the matrix material 40 is smaller in the direction along the stacking direction LD, closer to the center than the ends 23A and 23B of the light-emitting layer 23.

[0044] Furthermore, the first portion 41, the second portion 42, and the third portion 43 may each have a different band gap depending on the position along the stacking direction LD. In particular, for example, the band gap of the second portion 42 may gradually decrease from each of the end portions on the first portion 41 side and the third portion 43 side toward the center of the light-emitting layer 23.

[0045] In this embodiment, each portion of the matrix material 40 has a higher ionization potential than the quantum dots 30 or a lower electron affinity than the quantum dots 30. In particular, in this embodiment, the matrix material 40 may have a higher ionization potential than the quantum dots 30 and a lower electron affinity than the quantum dots 30.

[0046] In addition, when the quantum dot 30 has the above-described core / shell structure, the ionization potential of the quantum dot 30 in the present disclosure may refer to the ionization potential of either the shell or the core of the quantum dot 30. Similarly, the electron affinity of the quantum dot 30 in the present disclosure may refer to the electron affinity of either the shell or the core of the quantum dot 30.

[0047] As described above, the matrix material 40 fills the space between at least two quantum dots 30, and in particular, the matrix material 40 may encapsulate the quantum dots 30. For this reason, holes from the hole transport layer 22 and electrons from the electron transport layer 24 are often injected into the quantum dots 30 via the matrix material 40. Therefore, the matrix material 40 has a larger ionization potential or a smaller electron affinity than the quantum dots 30, which improves the efficiency of charge injection from each electrode to the quantum dots 30 in the light-emitting layer 23.

[0048] In particular, from the viewpoint of improving the efficiency of injection of holes from the hole transport layer 22 and electrons from the electron transport layer 24 into the quantum dots 30 via the matrix material 40, the band gap of the quantum dots 30 may be smaller than the band gap of any part of the matrix material 40. In particular, any part of the matrix material 40 may have a band gap larger than the band gap of the quantum dots 30.

[0049] <Light-Emitting Layer: Matrix Material: Material> The matrix material 40 may include an organic material. In this case, the matrix material 40 may include at least one selected from the group including PVK, TFB, poly-TPD, PTAA, NPB, TPD, TCTA, Alq3, CBP, mCBP, DBP, CzSi, DPEPO, DPTPCz, MADN, PPT, Spiro-2CBP, SPPO13, TCPZ, TSPO1, TAZ, BCzPh, DPVBi, TPBi, OXD-7, and T2T, or a derivative of one of these materials. These materials often have a larger band gap than materials typically used for quantum dots, which can improve the efficiency of carrier injection from the matrix material 40 to the quantum dots 30. In this disclosure, the term "derivative" refers to a compound obtained by replacing some atoms or functional groups of a certain compound with other atoms or functional groups while maintaining the original skeleton of the compound.

[0050] The matrix material 40 may also contain an inorganic material. In general, inorganic materials are more resistant to deterioration due to contact with foreign substances such as water and air or due to heat than organic materials, thereby improving the reliability of the matrix material 40. In this case, the matrix material 40 may be any of MgO, MgS, MgSe, MgTe, MnS, MnSe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, BN, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, InP, Si, Ge, diamond, LiF, NaF, KF, RbF, CsF, and BeF. ２ , MgF ２ , CaF ２ , SrF ２ , BaF ２ , CuF, AgF, ZnF ２ , AlF ３ , GaF ３ , InF ３ , SnF ２ , PbF ２ , LiCl, NaCl, KCl, RbCl, CsCl, BeCl ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , CuCl, AgCl, ZnCl ２ , AlCl３ 、1aCl ３ 、ｩnCl ３ 、″nCl ２ 、PbCl ２ 、LiBr、ｮaBr、KBr、2b｢r、3s｢r、｢e｢r ２ 、gBr ２ 、CaBr ２ 、″rBr ２ 、BaBr ２ 、CuBr、|gBrrZn｢r ２ 、|lBr ３ 、1aBr ３ 、ｩnBr ３ 、″nBr ２ 、.bBr ２ The ２ 、gｩ ２ 、Caｩ ２ 、″rｩ ２ 、Baｩ ２ 、CuI、|ggI ２ 、|lｩ ３ 、1aｩ ３ 、ｩnｩ ３ 、″nｩ ２ 、.bｩ ２ 、4iｯ ｘ 、Zrｯ ｘ 、69 ｘ 、8bｯ ｘ 、oｯ ｘ 、O ｘ 、0eｯ ｘ 、CoO ｘ 、iｯO ｘ 、CuO ｘ 、｡gｯ ｘ 、|lO ｘ 、1a9 ｘ 、9nｯ ｘ 、′′iｯ ｘ 、1eｯ ｘ 、″nｯ ｘ 、.bｯ ｘ 、CuAlｳ ２ 、CuGaaｳ ２ 、CuInｳ ２ 、CuAlｳe ２ 、CuGaｳe ２ 、CuInｳe ２ 、AgAlｳ ２ 、AgGaaｳ ２ 、AgInｳ２ , AgAlSe ２ , AgGaSe ２ , and AgInSe ２ These materials often have a larger band gap than materials generally used for quantum dots, and can improve the efficiency of carrier injection from the matrix material 40 into the quantum dots 30. The matrix material 40 may include both at least one of the organic materials and at least one of the inorganic materials described above.

[0051] The materials contained in each of the first portion 41, the second portion 42, and the third portion 43 of the matrix material 40 may be determined so that the band gap of the matrix material 40 is as shown in the band diagram 102. In particular, the materials of each portion of the matrix material 40 may be determined so that the ionization potential of the matrix material 40 is smaller and the electron affinity is larger on the central side than on each side of the end 23A and the end 23B.

[0052] In particular, the first portion 41 and the third portion 43 may contain the same material. In this case, at least a part of the material can be common to the first portion 41 and the third portion 43, thereby reducing the manufacturing cost of the matrix material 40. In this case, the difference in band gap between the first portion 41 and the third portion 43 is also reduced, making it easier to design the band gap of each portion of the matrix material 40.

[0053] On the other hand, the first portion 41 and the third portion 43 may contain different materials. In this case, it becomes easy to provide a difference in band gap between the first portion 41 and the third portion 43, and thus it becomes easy to adjust the carrier balance in the light-emitting layer 23. For example, the first portion 41 and the third portion 43 may contain a part of a common material and may also contain different materials.

[0054] The second portion 42 may contain a material different from the materials of the first portion 41 and the third portion 43. In this case, it becomes easier to make the band gap of the second portion 42 different from the band gaps of the first portion 41 and the third portion 43, and it becomes easier to form the matrix material 40 having the above-described band gap structure.

[0055] Furthermore, the second portion 42 may contain a mixture of the material of the first portion 41 and the material of the third portion 43. For example, if the first portion 41 contains ZnSe and the third portion 43 contains ZnTe, where x is a real number satisfying 0<x<1, the second portion 42 may contain ZnSe. ｘ Te １－ｘ For example, when the first portion 41 contains CuI and the third portion 43 contains CuBr, the second portion 42 may contain CuBr, where x is a real number satisfying 0<x<1. ｘ I １－ｘ may include:

[0056] Among the materials of the matrix material 40 described above, depending on the combination of multiple materials, a mixture having a band gap smaller than the band gap of each material may be produced, resulting in band gap bowing. Band gap bowing may occur when materials containing metal elements and nonmetal elements with large differences in electronegativity are mixed. The material of the second portion 42 described above is an example of a mixture having a band gap smaller than the respective materials of the first portion 41 and the third portion 43, and is an example of a material in which the above-mentioned band gap bowing may occur.

[0057] In this case, it is easier to make the band gap of the second portion 42 different from the band gaps of the first portion 41 and the third portion 43, and it is also possible to use part of the material of the first portion 41 and part of the material of the third portion 43 in common with part of the material of the second portion 42. Therefore, with the above configuration, it becomes easier to form the matrix material 40 having the above-described band gap structure, and the cost of forming the matrix material 40 can be reduced.

[0058] The materials of each portion of the matrix material 40 and the quantum dots 30 may be determined so that each portion of the matrix material 40 has a larger ionization potential than the quantum dots 30 or a smaller electron affinity than the quantum dots 30. In particular, the band gap of the material of each portion of the matrix material 40 may be larger than the band gap of the material of each portion of the quantum dots 30.

[0059] In the present disclosure, the concentration and type of material of each layer of the light-emitting element 2 may not necessarily be uniform in a direction perpendicular to the stacking direction LD. For example, the concentration and type of material of each layer of the light-emitting element 2 may vary depending on the position in the direction perpendicular to the stacking direction LD. Accordingly, the ionization potential and electron affinity of each layer of the light-emitting element 2 may not necessarily be uniform in the direction perpendicular to the stacking direction LD. In other words, the ionization potential and electron affinity of each layer of the light-emitting element 2 may vary depending on the position of the light-emitting element 2 in the stacking direction LD.

[0060] Furthermore, in the present disclosure, the comparison of the magnitude of the ionization potential and the electron affinity in the direction along the stacking direction LD in each layer of the above-described light-emitting element 2 does not have to be a comparison of each layer on a straight line along the stacking direction LD. For example, the comparison may be a comparison at different positions in a direction perpendicular to the stacking direction LD, as long as it is a comparison in the direction along the stacking direction LD.

[0061] <Effects of Light-Emitting Element> In this embodiment, the light-emitting layer 23 of the light-emitting element 2 includes a plurality of quantum dots 30 as a light-emitting material and a matrix material 40 filling the spaces between at least two of the quantum dots. The ionization potential of the matrix material 40 is smaller at the center of the light-emitting layer 23 than at the end on the anode 21 side and the end on the cathode 25 side in the stacking direction LD. This configuration makes it easier for holes injected from the hole transport layer 22 into the matrix material 40 to be transported toward the center of the light-emitting layer 23 than toward the anode 21 side in the stacking direction LD. This configuration also reduces the outflow of the holes from the end on the cathode 25 side of the matrix material 40 toward the electron transport layer 24.

[0062] In particular, holes are more likely to be transported toward the center of the light-emitting layer 23 in the stacking direction LD in the light-emitting layer 23. Therefore, the light-emitting element 2 including the light-emitting layer 23 makes it easier to inject holes not only into the quantum dots 30 located closer to the anode 21, but also into the quantum dots 30 located closer to the cathode 25, among the multiple quantum dots included in the light-emitting layer 23.

[0063] Therefore, the light-emitting element 2 according to this embodiment improves the efficiency of hole injection in the light-emitting layer 23. Generally, light-emitting elements that include quantum dots as light-emitting materials in their light-emitting layers often have an excess of electrons. Therefore, the light-emitting element 2 can improve its luminous efficiency by increasing the concentration of holes in the light-emitting layer 23 and reducing the excess of electrons. Furthermore, the light-emitting element 2 efficiently injects holes into the quantum dots 30 regardless of their positions in the stacking direction LD of the quantum dots 30. Therefore, the light-emitting element 2 can inject holes into a larger number of quantum dots 30, thereby improving its luminous efficiency.

[0064] Furthermore, in this embodiment, the light-emitting layer 23 of the light-emitting element 2 includes a matrix material 40 having a larger electron affinity at the center of the light-emitting layer 23 compared to the end on the anode 21 side and the end on the cathode 25 side in the stacking direction LD. With this configuration, electrons injected from the electron transport layer 24 into the matrix material 40 are more easily transported toward the center of the light-emitting layer 23 than toward the cathode 25 side in the stacking direction LD. Furthermore, the above configuration reduces the outflow of the electrons from the end on the anode 21 side of the matrix material 40 to the hole transport layer 22 side.

[0065] In particular, electrons are more likely to be transported toward the center of the light-emitting layer 23 in the direction along the stacking direction LD in the light-emitting layer 23. Therefore, the light-emitting element 2 including the light-emitting layer 23 makes it easier to inject electrons not only into the quantum dots 30 located closer to the cathode 25 among the multiple quantum dots included in the light-emitting layer 23, but also into the quantum dots 30 located closer to the anode 21.

[0066] Therefore, the light-emitting element 2 according to this embodiment improves the efficiency of electron injection in the light-emitting layer 23. Generally, the carrier balance in the light-emitting layer of a light-emitting element varies depending on the band gap of each layer from the anode to the cathode, and therefore, depending on the light-emitting element, an excess of holes may occur in the light-emitting layer. Therefore, the light-emitting element 2 can improve its luminous efficiency by increasing the electron concentration in the light-emitting layer 23 and reducing the excess of holes. Furthermore, the light-emitting element 2 efficiently injects electrons into the quantum dots 30 regardless of their positions in the stacking direction LD of the quantum dots 30. Therefore, the light-emitting element 2 can inject electrons into a larger number of quantum dots 30, thereby improving its luminous efficiency.

[0067] As described above, the light-emitting element 2 according to this embodiment improves the carrier balance in the light-emitting layer 23, thereby improving the light-emitting efficiency. In particular, the light-emitting element 2 improves both the hole concentration and the electron concentration in the light-emitting layer 23, thereby further improving the light-emitting efficiency. The display device 1 including the light-emitting element 2 according to this embodiment achieves power saving.

[0068] Note that improving the carrier balance in the light-emitting layer 23 of the light-emitting element 2 reduces the probability of processes, such as the generation of Auger electrons, that can deteriorate the material of the light-emitting layer 23 and the materials around the light-emitting layer 23. This extends the life of the light-emitting element 2 and the display device 1 including the light-emitting element 2.

[0069] The band gap of the matrix material 40 is smaller at the center side than at the end on the anode 21 side and the end on the cathode 25 side in the stacking direction LD. This makes it easier for holes and electrons injected into the light-emitting layer 23 to move to the center of the light-emitting layer 23. This allows the light-emitting element 2 to inject holes and electrons into more quantum dots 30, thereby improving luminous efficiency.

[0070] The light-emitting layer 23 includes, in order from the anode 21 side, a first portion 41, a second portion 42, and a third portion 43. Therefore, in the light-emitting device 2, it is possible to individually set the band gaps of the first portion 41, the second portion 42, and the third portion 43 so that the band gap of the matrix material 40 satisfies the above-mentioned configuration. Therefore, in the light-emitting device 2, it is easier to design the band gap of the matrix material 40 and to form the matrix material 40.

[0071] In particular, in the matrix material 40, the ionization potential gradually decreases and the electron affinity gradually increases from the first portion 41 to the second portion 42 and from the third portion 43 to the second portion 42. Therefore, the light-emitting layer 23 reduces the barrier to the transport of holes and electrons in the matrix material 40, making it easier to transport holes and electrons toward the center in the stacking direction LD. This allows the light-emitting element 2 to inject holes and electrons into more quantum dots 30, thereby improving the luminous efficiency.

[0072] <Method of Manufacturing Display Device> An example of a method of manufacturing the display device 1 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing a method of manufacturing the display device 1 according to this embodiment.

[0073] In the manufacturing method of the display device 1 according to this embodiment, first, a substrate 3 is prepared (step S1). The preparation of the substrate 3 may be performed, for example, by forming a driver circuit DR and a pixel circuit PC such as a TFT on a substrate such as a rigid glass substrate or a flexible film substrate.

[0074] Next, the anode 21 is formed by the above-described method (step S2), and then the hole transport layer 22 is formed (step S3). The anode 21 may be formed, for example, by depositing a thin film of the above-described material and then patterning it for each subpixel. The hole transport layer 22 may be formed in common to multiple subpixels by a method such as coating or film formation, or may be further patterned.

[0075] Next, the first portion 41 is formed on the hole transport layer 22 (step S4). If the first portion 41 contains a low-molecular-weight organic material, the first portion 41 may be formed by a vapor deposition method. If the first portion 41 contains a high-molecular-weight organic material, the first portion 41 may be formed by a coating method such as spin coating. If the first portion 41 contains an inorganic material, the first portion 41 may be formed by a vacuum film formation method such as a sputtering method. Alternatively, if the first portion 41 contains an inorganic material, the first portion 41 may be formed by applying a dispersion in which a precursor or nanoparticles of the inorganic material are dispersed. If the dispersion contains a precursor of the inorganic material, the formation of the first portion 41 may include converting the precursor in the dispersion into the inorganic material by a process such as heating the applied dispersion.

[0076] Next, a layer containing quantum dots 30 is formed on the first portion 41. Specifically, for example, after step S4, a quantum dot dispersion liquid in which quantum dots 30 are dispersed is applied to the first portion 41 (step S5). The quantum dot dispersion liquid may be, for example, a dispersion liquid in which a plurality of quantum dots 30 each having a ligand coordinated thereto are dispersed. The application of the quantum dot dispersion liquid may be performed by various application methods such as spin coating. Next, the applied quantum dot dispersion liquid is dried (step S6). The quantum dot dispersion liquid may be dried, for example, by heating the quantum dot dispersion liquid. As a result, a layer containing quantum dots 30 is formed on the first portion 41.

[0077] In this embodiment, the formation of the first portion 41 and the formation of the layer including the quantum dots 30 are performed separately, but this is not limited to this. For example, instead of steps S4, S5, and S6, a dispersion liquid in which precursors or nanoparticles of the material of the first portion 41 and the plurality of quantum dots 30 are dispersed may be applied to the hole transport layer 22. The dispersion liquid may then be dried, so that the formation of the first portion 41 and the formation of the layer including the quantum dots 30 are performed approximately simultaneously. In this case, the first portion 41 is formed sequentially around the quantum dots 30, so that the first portion 41 filling the spaces between the plurality of quantum dots 30 can be formed more efficiently.

[0078] Furthermore, the formation of the layer containing the quantum dots 30 is not limited to the above-described method. For example, instead of steps S6 and S7, the quantum dot dispersion liquid in which the quantum dots 30 are dispersed may be sprayed by dry spray or the like. In this case, the spraying position or the size of the sprayed droplets may be adjusted so that the solvent of the quantum dot dispersion liquid evaporates before it reaches the first portion 41. This reduces the amount of solvent of the quantum dot dispersion liquid that comes into contact with the first portion 41, thereby reducing deterioration of the first portion 41.

[0079] Following step S6, the second portion 42 is formed above the first portion 41 (step S7). Step S7 may be performed by the same method as step S4, except that the band gap of the material to be formed is different. In particular, the material of the second portion 42 used in step S7 may have a smaller ionization potential or a larger electron affinity than the material of the first portion 41.

[0080] In step S7, the second portion 42 may be formed by sputtering two or more different materials. In this case, the deposition rate may be changed sequentially for each material depending on the deposition time. This may result in the formation of the second portion 42 in step S7, in which the ionization potential and electron affinity gradually change in the direction along the stacking direction LD.

[0081] Next, a quantum dot dispersion liquid in which quantum dots 30 are dispersed is applied onto the second portion 42 (step S8), and then the applied quantum dot dispersion liquid is dried (step S9). Step S8 may be performed by the same method as step S5, and step S9 may be performed by the same method as step S6.

[0082] Following step S9, a third portion 43 is formed above the second portion 42 (step S10). Step S10 may be performed by the same method as step S4 or step S7, except that the band gap of the material to be formed is different. In particular, the material of the third portion 43 used in step S10 may have a higher ionization potential or a lower electron affinity than the material of the second portion 42, or may be the same as the material of the first portion 41. In this way, the light-emitting layer 23 is formed, which includes the plurality of quantum dots 30 and the matrix material 40 filling the spaces between the plurality of quantum dots 30.

[0083] After the light-emitting layer 23 is formed, the electron transport layer 24 is formed on the light-emitting layer 23 by the method described above (step S11), and then the cathode 25 is formed (step S12). The electron transport layer 24 may be formed commonly to a plurality of sub-pixels by a method such as coating film formation, or may be further patterned. The cathode 25 may be formed, for example, by forming a thin film of the material described above commonly to a plurality of sub-pixels.

[0084] In this manner, the light-emitting element 2 is formed on the substrate 3, thereby completing the manufacture of the display device 1. The above method improves both the hole concentration and the electron concentration in the light-emitting layer 23, making it possible to manufacture a light-emitting element 2 with improved luminous efficiency, and also to manufacture a display device 1 that achieves power saving.

[0085] [Embodiment 2] <Matrix material differing only in ionization potential> The display device 1 according to this embodiment has the same configuration as the display device 1 according to the previous embodiment, except for the band gap of each portion of the matrix material 40 of the light-emitting element 2 included therein. The band gap of each layer of the functional layer of the light-emitting element 2 included in the display device 1 according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a band diagram of each layer of the functional layer of the light-emitting element 2 according to this embodiment.

[0086] In this embodiment, the electron affinity of the matrix material 40 may be substantially the same depending on the position along the stacking direction LD. In particular, the electron affinities of the first portion 41, the second portion 42, and the third portion 43 may be substantially the same. Note that, in this disclosure, "the electron affinities of the two components are substantially the same" does not necessarily mean that the electron affinities of the two components are completely the same. For example, the electron affinities of the matrix material 40 according to this embodiment may differ by, for example, 0.1 eV or less along the stacking direction LD.

[0087] Although the light-emitting element 2 according to this embodiment has been described as having substantially the same electron affinity in the direction along the stacking direction LD, this is not limiting. For example, in this embodiment, the electron affinity of the second portion 42 may be smaller than the electron affinity of the first portion 41 or the electron affinity of the third portion 43.

[0088] In the light-emitting element 2 according to this embodiment, the ionization potential of the matrix material 40 is also smaller at the center of the light-emitting layer 23 than at the end portions 23A and 23B in the direction along the stacking direction LD. Therefore, the light-emitting element 2 according to this embodiment improves the efficiency of hole injection from the anode 21 to the light-emitting layer 23, and reduces the electron excess. Therefore, for the same reason as described above, the light-emitting element 2 according to this embodiment can improve the carrier balance of the light-emitting layer 23.

[0089] The display device 1 according to this embodiment may be manufactured by the same method as the method for manufacturing the display device 1 according to the previous embodiment, except for the band gap of the material used to form the matrix material 40 .

[0090] [Embodiment 3] <Matrix material differing only in electron affinity> The display device 1 according to this embodiment has the same configuration as the display device 1 according to the above-described embodiment 1, except for the band gap of each portion of the matrix material 40 of the light-emitting element 2 included therein. The band gap of each layer of the functional layer of the light-emitting element 2 included in the display device 1 according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a band diagram of each layer of the functional layer of the light-emitting element 2 according to this embodiment.

[0091] In this embodiment, the ionization potential of the matrix material 40 may be substantially the same depending on the position along the stacking direction LD. In particular, the ionization potentials of the first portion 41, the second portion 42, and the third portion 43 may be substantially the same. Note that, in this disclosure, "the ionization potentials of the two members are substantially the same" does not necessarily mean that the ionization potentials of the two members are completely the same. For example, the ionization potentials of the matrix material 40 according to this embodiment may have some difference within a range that does not affect charge injection from each transport layer to the quantum dots 30 via the matrix material 40.

[0092] Although the light-emitting element 2 according to this embodiment has been described as having substantially the same ionization potential in the direction along the stacking direction LD, this is not limiting. For example, in this embodiment, the ionization potential of the second portion 42 may be greater than the ionization potential of the first portion 41 or the ionization potential of the third portion 43.

[0093] In the light-emitting element 2 according to this embodiment, the electron affinity of the matrix material 40 is also greater at the center of the light-emitting layer 23 than at the end portions 23A and 23B in the direction along the stacking direction LD. Therefore, the light-emitting element 2 according to this embodiment improves the efficiency of electron injection from the cathode 25 to the light-emitting layer 23, and reduces the excess of holes. Therefore, for the same reason as described above, the light-emitting element 2 according to this embodiment can improve the carrier balance of the light-emitting layer 23.

[0094] The display device 1 according to this embodiment may be manufactured by the same method as the method for manufacturing the display device 1 according to the previous embodiment, except for the band gap of the material used to form the matrix material 40 .

[0095] [Embodiment 4] <Modification of Matrix Material> The display device 1 according to this embodiment has the same configuration as the display device 1 according to the above-described embodiment 1, except for the structure of the light-emitting layer 23 of the light-emitting element 2 included therein and the band gap of each portion of the matrix material 40. The light-emitting layer 23 of the light-emitting element 2 included in the display device 1 according to this embodiment will be described with reference to Figures 8 and 9. Figure 8 is a side cross-sectional view of the light-emitting layer 23 according to this embodiment, and an enlarged side cross-sectional view of the light-emitting layer 23 at a position corresponding to the position shown in Figure 3. Figure 9 is a band diagram of each layer of the functional layer of the light-emitting element 2 according to this embodiment.

[0096] In this embodiment, the first portion 41 and the third portion 43 each surround the quantum dot 30. In addition, in this embodiment, the second portion 42 is located between the quantum dot 30 covered by the first portion 41 and the quantum dot 30 covered by the third portion 43.

[0097] 8 , the end of the first portion 41 on the cathode 25 side may be an end 41E that contacts the cathode 25 side end of the quantum dot 30 located on the anode 21 side among the multiple quantum dots 30 included in the light-emitting layer 23. Furthermore, the end of the third portion 43 on the anode 21 side may be an end 43D that contacts the anode 21 side end of the quantum dot 30 located on the cathode 25 side among the multiple quantum dots 30 included in the light-emitting layer 23. However, this is not limited to this embodiment, and the end 41E may be located further toward the cathode 25 than the cathode 25 side end of the quantum dot 30 located on the anode 21 side among the multiple quantum dots 30. Furthermore, the end 43E may be located further toward the anode 21 than the anode 21 side end of the quantum dot 30 located on the cathode 25 side among the multiple quantum dots 30.

[0098] 9 , in the present embodiment, the ionization potential of the matrix material 40 is smaller in the second portion 42 than in the first portion 41 or the third portion 43. Furthermore, the electron affinity of the matrix material 40 is larger in the second portion 42 than in the first portion 41 or the third portion 43. However, each of the first portion 41, the second portion 42, and the third portion 43 may have substantially the same ionization potential and electron affinity regardless of the position in the direction along the stacking direction LD.

[0099] For the same reasons as those described in the first embodiment, the light-emitting device 2 according to this embodiment improves both the hole concentration and the electron concentration in the light-emitting layer 23, thereby improving the luminous efficiency. In particular, the light-emitting layer 23 according to this embodiment includes a second portion 42 between a first portion 41 and a third portion 43, each of which covers a plurality of quantum dots 30. Therefore, the light-emitting layer 23 achieves the matrix material 40 that improves the luminous efficiency described above simply by adjusting the band gap between the first portion 41 and the third portion 43 and the second portion 42. Therefore, the light-emitting device 2 according to this embodiment can simplify the design of the light-emitting layer 23. Furthermore, the light-emitting device 2 according to this embodiment can simplify the manufacturing process or reduce manufacturing costs.

[0100] The manufacturing method of the display device 1 according to this embodiment may be the same as the above-described manufacturing method of the display device 1. For example, in the step of forming the light-emitting layer 23 according to this embodiment, first, a dispersion liquid in which a precursor of the material of the first portion 41 and the quantum dots 30 are dispersed may be applied, and the applied dispersion liquid may be heated to convert the precursor into the first portion 41. This allows the first portion 41 covering the multiple quantum dots 30 to be easily formed.

[0101] Next, the second portion 42 may be formed, followed by applying a dispersion liquid in which the precursor of the material of the third portion 43 and the quantum dots 30 are dispersed, and then heating the applied dispersion liquid to convert the precursor into the third portion 43. In this way, the third portion 43 covering the multiple quantum dots 30 can be easily formed.

[0102] Furthermore, in forming the second portion 42, the band gap does not need to be different depending on the position of the second portion 42. In other words, the second portion 42 may be formed by depositing a layer containing the same material regardless of the position. This makes it possible to form the second portion 42 more simply.

[0103] 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.

[0104] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 22 Hole transport layer 23 Light-emitting layer 24 Electron transport layer 25 Cathode 30 Quantum dots (light-emitting material) 40 Matrix material 41 Part 1 42 Part 2 43 Part 3

Claims

1. A light-emitting device comprising an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer contains a plurality of light-emitting materials and a matrix material that fills the space between at least two of the light-emitting materials and has a higher ionization potential or a lower electron affinity than the light-emitting materials, and wherein, in the stacking direction, the ionization potential of the matrix material is lower or the electron affinity of the matrix material is higher at the center of the light-emitting layer than at the end of the light-emitting layer on the anode side and the end of the light-emitting layer on the cathode side.

2. The light-emitting element according to claim 1, wherein, in the direction along the stacking direction, the ionization potential of the matrix material is smaller and the electron affinity of the matrix material is larger at the center of the light-emitting layer than at the end of the light-emitting layer on the anode side and the end of the light-emitting layer on the cathode side.

3. The light-emitting element according to claim 1 or 2, further comprising a hole transport layer located between the anode and the light-emitting layer and in contact with the light-emitting layer, wherein the light-emitting material has a smaller ionization potential or a larger electron affinity than the hole transport layer.

4. The light-emitting device according to any one of claims 1 to 3, further comprising an electron transport layer located between the cathode and the light-emitting layer and in contact with the light-emitting layer, wherein the light-emitting material has a smaller ionization potential or a larger electron affinity than the electron transport layer.

5. A light-emitting element according to any one of claims 1 to 4, wherein the band gap of the matrix material is smaller at a position closer to the center than the end on the anode side and the end on the cathode side in the direction along the stacking direction.

6. The light-emitting device according to any one of claims 1 to 5, wherein the band gap of the light-emitting material is smaller than the band gap of any of the matrix materials.

7. A light-emitting element according to any one of claims 1 to 6, wherein the matrix material includes, in order from the anode side, a first portion, a second portion, and a third portion, and the ionization potential of the matrix material is smaller in the second portion than in the first portion or the third portion, or the electron affinity of the matrix material is larger in the second portion than in the first portion or the third portion.

8. The light-emitting device of claim 7, wherein said first portion and said third portion comprise the same material.

9. The light-emitting device according to claim 7 or 8, wherein the first portion and the third portion comprise different materials.

10. A light-emitting device according to any one of claims 7 to 9, wherein the second portion comprises a material different from the material of each of the first portion and the third portion.

11. A light-emitting device according to any one of claims 7 to 10, wherein the second portion comprises a mixture of the material of the first portion and the material of the third portion.

12. A light-emitting element described in any one of claims 7 to 11, wherein each of the first and third parts surrounds the luminescent material, and the second part is located between the luminescent material covered by the first part and the luminescent material covered by the third part.

13. A light-emitting element described in any one of claims 7 to 12, wherein the ionization potential of the matrix material gradually decreases from the first portion to the second portion and from the third portion to the second portion, or the electron affinity of the matrix material gradually increases.

14. The light-emitting device according to any one of claims 1 to 13, wherein the matrix material includes an organic material.

15. The light-emitting device according to claim 14, wherein the matrix material comprises at least one member selected from the group consisting of PVK, TFB, poly-TPD, PTAA, NPB, TPD, TCTA, Alq3, CBP, mCBP, DBP, CzSi, DPEPO, DPTPCz, MADN, PPT, Spiro-2CBP, SPPO13, TCPZ, TSPO1, TAZ, BCzPh, DPVBi, TPBi, OXD-7, and T2T, or a derivative of one of said members.

16. The light-emitting device according to any one of claims 1 to 15, wherein the matrix material includes an inorganic material.

17. The matrix material is MgO, MgS, MgSe, MgTe, MnS, MnSe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, BN, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, InP, Si, Ge, diamond, LiF, NaF, KF, RbF, CsF, BeF ２ , MgF ２ , CaF ２ , SrF ２ , BaF ２ , CuF, AgF, ZnF ２ , AlF ３ , GaF ３ , InF ３ , SnF ２ , PbF ２ , LiCl, NaCl, KCl, RbCl, CsCl, BeCl ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , CuCl, AgCl, ZnCl ２ , AlCl ３ , GaCl ３ , InCl ３ , SnCl ２ , PbCl ２ , LiBr, NaBr, KBr, RbBr, CsBr, BeBr ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , CuBr, AgBr, ZnBr ２ , AlBr ３ , GaBr ３ , InBr ３ , SnBr ２ , PbBr ２ , LiI, NaI, KI, RbI, CsI, BeI ２ , MgI ２ , CaI ２ , SrI ２ , BaI ２ , CuI, AgI, ZnI ２ , AlI ３ , GaI ３ , InI ３ , SnI ２ , PbI ２ , TiO ｘ , ZrO ｘ , V.O. ｘ , NbO ｘ , MoO ｘ , W.O. ｘ , FeO ｘ , CoO ｘ , NiO ｘ , CuO ｘ , AgO ｘ , AlO ｘ , GaO ｘ , InO ｘ , SiO ｘ , GeO ｘ , SnO ｘ , PbO ｘ , CuAlS ２ , CuGaS ２ , CuInS ２ , CuAlSe ２ , CuGaSe ２ , CuInSe ２ , AgAlS ２ , AgGaS ２ , AgInS ２ , AgAlSe ２ , AgGaSe ２ , and AgInSe ２ The light-emitting device according to claim 16 , comprising at least one of the group comprising:

18. The light-emitting device according to any one of claims 1 to 17, wherein the light-emitting material is a quantum dot.

19. A display device comprising a substrate and a plurality of light-emitting elements according to any one of claims 1 to 18 on said substrate.

20. A method for manufacturing a light-emitting element comprising an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, wherein the light-emitting layer comprises a plurality of light-emitting materials and a matrix material that fills spaces between at least two of the light-emitting materials and has a higher ionization potential than the light-emitting materials or a lower electron affinity than the light-emitting materials, and wherein the ionization potential of the matrix material is lower or the electron affinity of the matrix material is higher at the center of the light-emitting layer than at the end of the light-emitting layer on the anode side and at the end of the light-emitting layer on the cathode side.

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