Light-emitting element and display device

Abstract

A red light-emitting element (5R) comprises: an anode (22); a cathode (25) that is a higher layer than the anode (22); and a red light-emitting layer (24L) that includes quantum dots (QD) and a matrix (MR) and is disposed between the anode (22) and the cathode (25), wherein a surface treatment agent (DPS) that forms a dipole is distributed in at least a portion of the matrix (MR) located on the side of a first surface (S1) on the side of the cathode (25) of the red light-emitting layer (24L).

Description

Light-emitting element and display device

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

[0002] In recent years, display devices equipped with quantum dot light-emitting diodes (QLEDs), which are light-emitting elements containing quantum dots, have attracted considerable attention because of their ability to achieve low power consumption, thinness, and high image quality.

[0003] For example, Patent Document 1 describes a light-emitting device having a light-emitting layer containing quantum dots in a matrix.

[0004] Japanese Patent Publication "Patent Publication No. 2011-502333"

[0005] In the case of the light-emitting element described in Patent Document 1, generally, the number of electrons in the carriers injected into the quantum dots is more than the number of holes, which is likely to cause an electron excess state, resulting in a deterioration in the light-emitting characteristics and reliability of the light-emitting element.

[0006] Furthermore, defects may also occur in the matrix contained in the light-emitting layer of the light-emitting element described in Patent Document 1. When defects occur in the matrix, there is a problem that the light-emitting characteristics and reliability of the light-emitting element are deteriorated.

[0007] An object of one embodiment of the present disclosure is to provide a light-emitting element and a display device that can reduce the possibility of deterioration in light-emitting characteristics and reliability and can improve carrier balance.

[0008] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure comprises an anode, a cathode that is a layer above the anode, and a light-emitting layer that includes quantum dots and a matrix and is disposed between the anode and the cathode, wherein a surface treatment agent that forms a dipole is distributed in at least a portion of the matrix located on the first surface side of the light-emitting layer that is closer to the cathode.

[0009] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure includes an anode; a cathode that is a layer above the anode; a light-emitting layer that includes quantum dots and a matrix and is disposed between the anode and the cathode; and a surface treatment agent in the matrix, in a region that is 3 nm or more away from the second surface of the light-emitting layer on the anode side toward the first surface on the cathode side, where the value N of (number of groups that can coordinate to the matrix / number of carbon atoms C) is 0.1 or more.

[0010] In order to solve the above-mentioned problems, the display device of the present disclosure includes the light-emitting element.

[0011] According to one embodiment of the present disclosure, it is possible to provide a light-emitting element and a display device in which the possibility of deterioration in light-emitting characteristics and reliability can be reduced and carrier balance can be improved.

[0012] 1 is a plan view showing a schematic configuration of a display device of Embodiment 1. FIG. 2 is a cross-sectional view showing a schematic configuration of a display region of the display device of Embodiment 1. FIG. 3 is a cross-sectional view showing a schematic configuration of a red light-emitting element provided in the display device of Embodiment 1. FIG. 4 is a cross-sectional view showing a schematic configuration of another red light-emitting element that can be provided in the display device of Embodiment 1. FIG. 5 is a schematic view for explaining a matrix of a red light-emitting layer provided in the red light-emitting element shown in FIGS. 3 and 4. FIG. 6 is another schematic view for explaining a matrix of a red light-emitting layer provided in the red light-emitting element shown in FIGS. 3 and 4. FIG. 7 is a diagram showing the band levels of each of the hole transport layer, red light-emitting layer, and electron transport layer in a red light-emitting element of Comparative Example 1 having a red light-emitting layer composed only of quantum dots, and a red light-emitting element of Comparative Example 2 having a red light-emitting layer composed of quantum dots and a surface treatment agent that forms a dipole. FIG. 8 is a diagram showing the band levels of each of the hole transport layer, red light-emitting layer, and electron transport layer in a red light-emitting element of Comparative Example 3 having a red light-emitting layer composed of quantum dots and a matrix, and a red light-emitting element provided in the display device of Embodiment 1.

[0013] The following describes an embodiment of the present disclosure with reference to Figures 1 to 8. For the sake of convenience, components having the same functions as those described in a specific embodiment will be denoted by the same reference numerals, and their description may be omitted.

[0014] FIG. 1 is a plan view showing a schematic configuration of a display device 1 according to the first embodiment.

[0015] As shown in Fig. 1, the display device 1 includes a frame area NDA and a display area DA. The display area DA of the display device 1 includes a plurality of pixels PIX, each of which includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, a case in which one pixel PIX is configured with a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP will be described as an example, but this is not limiting. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP.

[0016] FIG. 2 is a cross-sectional view showing a schematic configuration of the display area DA of the display device 1 of the first embodiment.

[0017] As shown in Figure 2, in the display area DA of the display device 1, a barrier layer 3, a thin film transistor layer 4 including a transistor TR, a red light-emitting element 5R, a green light-emitting element 5G, a blue light-emitting element 5B and a bank 23, a sealing layer 6, and a functional film 39 are provided on a substrate 12 in this order from the substrate 12 side.

[0018] The red subpixel RSP provided in the display area DA of the display device 1 includes a red light-emitting element 5R (light-emitting element), the green subpixel GSP provided in the display area DA of the display device 1 includes a green light-emitting element 5G (light-emitting element), and the blue subpixel BSP provided in the display area DA of the display device 1 includes a blue light-emitting element 5B (light-emitting element). The red light-emitting element 5R included in the red subpixel RSP includes an anode 22, a functional layer 24R including a red light-emitting layer, and a cathode 25. The green light-emitting element 5G included in the green subpixel GSP includes an anode 22, a functional layer 24G including a green light-emitting layer, and a cathode 25. The blue light-emitting element 5B included in the blue subpixel BSP includes an anode 22, a functional layer 24B including a blue light-emitting layer, and a cathode 25.

[0019] The substrate 12 may be, for example, a resin substrate made of a resin material such as polyimide, or a glass substrate. In this embodiment, since the display device 1 is a flexible display device, a case where a resin substrate made of a resin material such as polyimide is used as the substrate 12 will be described as an example, but this is not limiting. If the display device 1 is a non-flexible display device, a glass substrate can be used as the substrate 12.

[0020] The barrier layer 3 is a layer that prevents foreign substances such as water and oxygen from penetrating into the transistor TR, the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B, and can be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these, formed by the CVD method.

[0021] The transistor TR portion of the thin film transistor layer 4 including the transistor TR includes the semiconductor film SEM and doped semiconductor films SEM′ and SEM″, an inorganic insulating film 16, a gate electrode G, an inorganic insulating film 18, an inorganic insulating film 20, a source electrode S and a drain electrode D, and a planarization film 21, and the portion of the thin film transistor layer 4 including the transistor TR other than the transistor TR portion includes the inorganic insulating film 16, the inorganic insulating film 18, the inorganic insulating film 20, and the planarization film 21.

[0022] The semiconductor films SEM, SEM', and SEM'' may be made of, for example, low-temperature polysilicon (LTPS) or an oxide semiconductor (for example, an In-Ga-Zn-O based semiconductor). In this embodiment, the case where the transistor TR has a top-gate structure will be described as an example, but the present invention is not limited to this, and the transistor TR may also have a bottom-gate structure.

[0023] The gate electrode G and the source electrode S and drain electrode D can be formed of a single layer or a multilayer film of a metal containing at least one of aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper, for example.

[0024] The inorganic insulating films 16, 18 and 20 can be formed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these films, which are formed by the CVD method.

[0025] The planarizing film 21 can be made of a coatable organic material such as polyimide or acrylic.

[0026] The red light-emitting element 5R includes an anode 22 above the planarization film 21, a functional layer 24R including a red light-emitting layer, and a cathode 25 above the anode 22. The green light-emitting element 5G includes an anode 22 above the planarization film 21, a functional layer 24G including a green light-emitting layer, and a cathode 25 above the anode 22. The blue light-emitting element 5B includes an anode 22 above the planarization film 21, a functional layer 24B including a blue light-emitting layer, and a cathode 25 above the anode 22. The insulating bank 23 covering the edge of the anode 22 can be formed by applying an organic material such as polyimide or acrylic and then patterning it by photolithography.

[0027] The sealing layer 6 is a light-transmitting film, and can be composed of, for example, an inorganic sealing film 26 that covers the cathode 25, an organic film 27 that is above the inorganic sealing film 26, and an inorganic sealing film 28 that is above the organic film 27. The sealing layer 6 prevents foreign substances such as water and oxygen from penetrating into the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B.

[0028] The inorganic sealing films 26 and 28 are each an inorganic film, and may be formed, for example, by a CVD method using a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof. The organic film 27 is a light-transmitting organic film with a planarizing effect, and may be formed, for example, using a coatable organic material such as acrylic. The organic film 27 may also be formed, for example, by an inkjet method. In this embodiment, the sealing layer 6 is formed of two inorganic films and one organic film disposed between the two inorganic films. However, the stacking order of the two inorganic films and one organic film is not limited to this. Furthermore, the sealing layer 6 may be formed solely of an inorganic film, solely of an organic film, one inorganic film and two organic films, or two or more inorganic films and two or more organic films.

[0029] The functional film 39 is a film having at least one of an optical compensation function, a touch sensor function, and a protection function, for example.

[0030] Fig. 3 is a cross-sectional view showing a schematic configuration of the red light-emitting element 5R provided in the display device 1 of Embodiment 1. Fig. 4 is a cross-sectional view showing a schematic configuration of another red light-emitting element 5R that can be provided in the display device 1 of Embodiment 1. As shown in Fig. 2, the red light-emitting element 5R is provided on the substrate 12, and therefore, although not shown in Figs. 3 and 4, it is assumed that the substrate 12 is present below the anode 22.

[0031] 3 and 4 , the red light-emitting element 5R includes an anode 22, a cathode 25, and a functional layer 24R including a red light-emitting layer 24L disposed between the anode 22 and the cathode 25. The red light-emitting layer 24L includes quantum dots QD and a matrix MR, and has a first surface S1 on the cathode 25 side and a second surface S2 on the anode 22 side. In this embodiment, the first surface S1, which has no thickness, is the boundary surface with the adjacent second charge transport layer 24E, and the second surface S2, which has no thickness, is the boundary surface with the adjacent first charge transport layer 24H. Note that each of the first surface S1 and the second surface S2 may be formed of the quantum dots QD and the matrix MR, or may be formed of only the matrix MR.

[0032] As shown in FIGS. 3 and 4 , in the red light-emitting element 5R of this embodiment, the surface treatment agent DPS that forms a dipole moment, i.e., a dipole, is distributed in at least a part of the matrix MR located on the first surface S1 side of the red light-emitting layer 24L, which is closer to the cathode 25.

[0033] In the present disclosure, the dipole-forming surface treatment agent DPS refers to a surface treatment agent DPS that, when coordinated to, bonded to, or adjacent to the surface of any material, causes a change in the electronic level (work function) of the surface of the material by 0.01 eV or more compared to before the surface was coordinated to, bonded to, or adjacent to the surface. A change in the electronic level of 0.05 eV or more is preferable, 0.1 eV or more is even more preferable, and 1 eV or more is even more preferable. The electronic level (work function) may be measured, for example, using PYS (photoelectron yield spectroscopy). If measurement using PYS (photoelectron yield spectroscopy) is difficult, measurement may be performed using UPS (ultraviolet photoelectron spectroscopy). If measurement using UPS (ultraviolet photoelectron spectroscopy) is difficult, the surface energy of the surface treatment agent may be measured and analyzed by contacting a probe with the cross section of the element using a measurement such as SKPM (Kelvin Probe Atomic Force Microscope, also abbreviated as KFM or KPFM).

[0034] Furthermore, in the present disclosure, the dipole-forming surface treatment agent DPS can be considered to be a dipole-forming surface treatment agent if the value N (number of groups capable of coordinating to the matrix / number of carbon atoms) is 0.1 or greater. Furthermore, the value N is more preferably 0.25 or greater, and even more preferably 0.5 or greater. The value N (number of groups capable of coordinating to the matrix / number of carbon atoms) may be a value within one molecule, within the repeating skeleton of a polymer, or within one unit. Furthermore, the dipole-forming surface treatment agent DPS may be a monomer, oligomer, or polymer, as long as the value N (number of groups capable of coordinating to the matrix / number of carbon atoms) is within the above-mentioned range.

[0035] The value N can be measured using TOF-SIMS (time-of-flight secondary ion mass spectrometry). For example, if the device is measured from the upper layer (e.g., electron transport layer) to the lower layer (e.g., hole transport layer) using TOF-SIMS, and there is a region where the value N is 0.1 or greater, and this region is 3 nm or greater away from the second surface on the anode side toward the first surface on the cathode side, then it can be assumed that the surface treatment agent DPS that forms the dipole is present on the matrix MR. Measurements can be performed in the same way even if the top and bottom are reversed. Furthermore, the material used in the surface treatment agent that forms the dipole can also be similarly determined using TOF-SIMS.

[0036] Note that the phrase "the dipole-forming surface treatment agent DPS is distributed in at least a portion of the matrix MR located on the first surface S1 side" refers not only to the case where the dipole-forming surface treatment agent DPS is distributed in at least a portion of the matrix MR located on the first surface S1 side, but also to the case where the dipole-forming surface treatment agent DPS is formed so as to be in contact with the first surface S1 formed by the matrix MR, or the case where the dipole-forming surface treatment agent DPS is formed on the first surface S1 formed by the matrix MR with a film thickness of, for example, 0.01 nm or more and 10 nm or less. In the red light-emitting element 5R, the first surface S1 is the upper surface that is located farther from the substrate 12 (not shown) than the second surface S2, i.e., is located on the upper side, and the dipole-forming surface treatment agent DPS is distributed in at least a portion of the matrix MR located on the upper surface side. Here, the matrix MR located on the first surface S1 side (upper surface side) refers to a portion of the matrix MR that does not include the second surface S2 but includes the first surface S1, and may be, for example, when the matrix MR is divided into N equal parts in the thickness direction (N is a natural number of 2 or more), the portion may be the portion of the matrix MR that is located farthest from the anode 22. Note that the red light-emitting layer 24L may be formed first, followed by a heat treatment and then a treatment using the surface treatment agent DPS that forms a dipole, or the red light-emitting layer 24L may be formed first, followed by a treatment using the surface treatment agent DPS that forms a dipole, and then a heat treatment.

[0037] The first surface S1 of the red light-emitting layer 24L included in the red light-emitting element 5R shown in Fig. 3 is formed to be substantially flat, whereas the first surface S1 of the red light-emitting layer 24L included in the red light-emitting element 5R shown in Fig. 4 is formed to be uneven or curved. In a region where the amount of matrix MR is sufficiently large relative to the amount of quantum dots QD, the first surface S1 of the red light-emitting layer 24L is likely to have a shape like that shown in Fig. 3, while in a region where the amount of matrix MR is not sufficiently large relative to the amount of quantum dots QD, the first surface S1 of the red light-emitting layer 24L is likely to have a shape like that shown in Fig. 4. Therefore, the first surface S1 of the red light-emitting layer 24L included in one red light-emitting element 5R may have both the shape of the first surface S1 shown in Fig. 3 and the shape of the first surface S1 shown in Fig. 4.

[0038] 2 may be of either a top-emission type or a bottom-emission type. The red light-emitting element 5R, green light-emitting element 5G, and blue light-emitting element 5B have a forward-laid structure in which the cathode 25 is disposed above the anode 22. To form the red light-emitting element 5R, green light-emitting element 5G, and blue light-emitting element 5B as a top-emission type, the anode 22 may be formed of an electrode material that reflects visible light, and the cathode 25 may be formed of an electrode material that transmits visible light. To form the bottom-emission type, the anode 22 may be formed of an electrode material that transmits visible light, and the cathode 25 may be formed of an electrode material that reflects visible light.

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

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

[0041] 2 , the functional layer 24R including the red light-emitting layer 24L included in the red light-emitting element 5R, the functional layer 24G including the green light-emitting layer included in the green light-emitting element 5G, and the functional layer 24B including the blue light-emitting layer included in the blue light-emitting element 5B may be, for example, a laminate in which a first charge transport layer 24H, a red light-emitting layer 24L, any one of a green light-emitting layer and a blue light-emitting layer, and a second charge transport layer 24E are stacked in this order from the anode 22 side. The first charge transport layer 24H may include at least one of a hole injection layer (HIL) and a hole transport layer (HTL), and the second charge transport layer 24E may include at least one of an electron injection layer (EIL) and an electron transport layer (ETL).

[0042] The material used for the hole injection layer (HIL) is not particularly limited as long as it is a hole injection material that can stabilize the injection of holes into the light emitting layer. For example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS) can be used. In addition, NiO particles or MoO ３ Nanoparticles having hole transport properties, such as particles, may also be used.

[0043] Examples of materials used for the hole transport layer (HTL) include organic materials such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine (poly-TPD), and polyvinylcarbazole (PVK), and nanoparticles having hole transport properties such as NiO particles.

[0044] The material used for the electron transport layer (ETL) may be, for example, an organic material such as 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or nanoparticles having electron transport properties such as ZnO particles or particles of an oxide containing Zn and Mg.

[0045] The material used for the electron injection layer (EIL) is not particularly limited as long as it is an electron-injecting material that can stabilize the injection of electrons into the light-emitting layer. For example, alkali metals or alkaline earth metals such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate polystyrene sodium sulfonate, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, organic complexes of alkali metals, etc. may be used.

[0046] 2, the red light-emitting layer 24L of the red light-emitting element 5R, the green light-emitting layer of the green light-emitting element 5G, and the blue light-emitting layer of the blue light-emitting element 5B contain quantum dots QDs, and the quantum dots QDs may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure in which the core / shell ratio is continuously changed. Note that the shell may cover only a portion of the core, but it is more preferable for the shell to completely cover the core. The core material of the quantum dot QD is, for example, a crystal of a II-VI group semiconductor such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, PbS, PbSe, HgS, HgSe, HgTe, a crystal of a III-V group semiconductor such as GaAs, GaP, InN, InAs, InP, InSb, Ga ３ S ２ , Ga ２ Se ３ , In ２ S ３ , In２ Se ３ Crystals of III-VI group semiconductors such as CuInGaS, AgInGaS, CuInGaS, AgInGaZnS, CuInGaSe, AgInGaSe, etc., crystals of I-III-VI group semiconductors such as C and Si, crystals of IV group semiconductors such as CsPbI ３ , CsPbBr ３ , CsPbCl ３ The shell material can be made of a semiconductor crystal with a perovskite structure such as the above. The shell material is selected from the same material group as the core material, and is preferably one that has a lattice constant close to that of the core material and a larger band gap than the core material.

[0047] 2, the red light-emitting layer 24L of the red light-emitting element 5R, the green light-emitting layer of the green light-emitting element 5G, and the blue light-emitting layer of the blue light-emitting element 5B each include a matrix MR. The matrix MR may include, for example, a metal sulfide or an oxide containing a metal element or a metalloid element. Examples of metalloid elements include B, Si, Ge, As, Sb, and Te. The metal sulfide may include one or more metal elements selected from Zn, Mg, and Ga, and may be, for example, zinc sulfide, magnesium zinc sulfide, gallium sulfide, tellurium zinc sulfide, magnesium sulfide, or gallium zinc sulfide. Examples of oxides containing a metal element or a metalloid element include, but are not limited to, silicon oxide, beryllium oxide, boron oxide, magnesium oxide, aluminum oxide, calcium oxide, scandium oxide, titanium oxide, manganese oxide, nickel oxide, gallium oxide, germanium oxide, arsenic oxide, strontium oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, indium oxide, tin oxide, antimony oxide, barium oxide, cerium oxide, europium oxide, hafnium oxide, tantalum oxide, and thorium oxide.

[0048] The matrix MR refers to a component that contains and holds quantum dots QDs, for example, having a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure with a continuously changing core / shell ratio, and can be referred to as a substrate, a base material, or a filler. The matrix MR may be solid at room temperature. Note that the quantum dots QDs do not necessarily have to be distributed evenly throughout the matrix MR. Furthermore, certain regions of the matrix MR that do not contain quantum dots QDs are also permitted. Note that even if only a portion of the quantum dots QDs are covered by the matrix MR, the matrix MR is a component that contains and holds the quantum dots QDs.

[0049] Fig. 5 is a schematic diagram illustrating the matrix MR of the red light-emitting layer 24L provided in the red light-emitting element 5R shown in Fig. 3 and Fig. 4. Fig. 6 is another schematic diagram illustrating the matrix MR of the red light-emitting layer 24L provided in the red light-emitting element 5R shown in Fig. 3 and Fig. 4.

[0050] In this specification, "the matrix fills the spaces between the quantum dots QD" means that the matrix fills at least the region K between the quantum dots QDA and QDB, as shown in the set P1 in Fig. 5. Region K is a region surrounded by two straight lines (common circumstantial lines) tangent to the peripheries of the quantum dots QDA and QDB and the opposing peripheries of the quantum dots QDA and QDB in the cross section of the light-emitting layer. Therefore, as shown in the set P2 in Fig. 6, region K can exist even if the quantum dots QDA and QDB are close to each other, and the matrix fills region K.

[0051] The matrix MR filling the spaces between the quantum dots QD does not necessarily mean that the region K between the quantum dots QDA and QDB is entirely composed of the matrix MR. For example, the region K between the quantum dots QDA and QDB may contain a material, such as a ligand, different from the material of the matrix MR. Specifically, for example, the light-emitting layer 24L may contain an organic ligand that is added to improve the dispersibility of the quantum dots QD in the dispersion liquid used for coating and that coordinates to the outer surfaces of the quantum dots QD in the dispersion liquid. In this case, in the light-emitting layer 24L, from the viewpoint of improving the reliability of the light-emitting layer 24L, for example, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%.

[0052] The matrix MR may fill the region of the light-emitting layer 24L other than the region where the quantum dots QDs are present. For example, the outer edge (top and bottom surfaces) of the light-emitting layer 24L may be covered with the matrix MR. Alternatively, the light-emitting layer 24L may be configured such that a portion of the matrix MR extends from the outer edge thereof, and the quantum dots QDs are positioned away from the outer edge. The outer edge of the light-emitting layer 24L may not be formed solely by the matrix MR, and some of the quantum dots QDs may be exposed from the matrix MR. The matrix MR may refer to the portion of the light-emitting layer 24L excluding the quantum dots QDs.

[0053] The matrix MR is formed at a position in the thickness direction of the light-emitting layer 24L, and has a thickness of 1000 nm in a plane direction perpendicular to the thickness direction. ２ In the light-emitting layer 24L, the quantum dots QD may be encapsulated in a continuous film of the matrix MR, in other words, the quantum dots QD may be encapsulated in a continuous film of the matrix MR.

[0054] For example, when 60% or more of the surface of 80% or more of the quantum dots QDs constituting the light-emitting layer 24L is in contact with the continuous film of the matrix MR, the quantum dots QDs contained in the light-emitting layer 24L can be said to be encapsulated in the matrix MR. In this way, the light-emitting layer 24L containing the quantum dots QDs encapsulated in the matrix MR improves the light-emitting properties and extends the lifetime.

[0055] The light-emitting layer 24L has a thickness of 1000 nm or more in a plane direction perpendicular to the film thickness direction at any position in the film thickness direction. ２ In this case, the light-emitting layer 24L generally contains a sufficient concentration of quantum dots QD to function as a light-emitting layer of a light-emitting element.

[0056] The matrix MR may be positioned, for example, over the entire periphery of the quantum dot QD. For example, as shown in the figure, in any cross section passing through any quantum dot QD, the matrix MR may be positioned over the entire periphery of the quantum dot QD. Here, "the matrix MR is positioned over the entire periphery of the quantum dot QD" may mean that the matrix MR is positioned over 90% or more of the periphery of the quantum dot QD. Furthermore, as shown in FIG. 3, the surface of the quantum dot QD and the matrix MR may be in contact with each other.

[0057] The band gap of the matrix MR may be wider than the band gap of the material constituting the quantum dot QD. When the quantum dot QD has a core and a shell surrounding the core, the band gap of the matrix MR may be wider than the band gap of the material constituting the shell.

[0058] In this embodiment, as described below, a case where a matrix MR made of zinc sulfide is a component that contains and holds quantum dots QDs will be described as an example, but the present invention is not limited to this. For example, a matrix MR composed of a mixture of a first matrix (e.g., zinc sulfide) and a second matrix (e.g., silicon oxide) that are different materials may be used as a component that contains and holds quantum dots QDs. Furthermore, for example, although not shown, the first matrix and the second matrix, which are different materials, may cover different portions of the same quantum dots QDs, such as when at least some of the quantum dots QDs are only partially covered by the first matrix and the remaining portions are covered by the second matrix. Note that even when only a portion of the quantum dots QDs are covered by the first matrix or the second matrix, the first matrix or the second matrix is ​​a component that contains and holds quantum dots QDs.

[0059] A matrix MR may be filled between multiple quantum dots QDs. "A matrix MR is filled between multiple quantum dots QDs" means that a matrix MR is filled between at least two quantum dots QDs. Note that "a matrix MR is filled between two quantum dots QDs" means that a region formed between two adjacent quantum dots QDs is filled or filled with a matrix MR, or that the two adjacent quantum dots QDs are held together by the presence of a matrix MR in this region.

[0060] Unless otherwise specified or contradictory, the structure of the matrix MR may be determined as described above by observing a cross section of the light-emitting layer, for example, the red light-emitting layer 24L, with a width of about 100 nm, and it is not necessary to observe the above-described structure throughout the entire light-emitting layer, for example, the red light-emitting layer 24L. The matrix MR may contain a substance different from the main material (for example, an inorganic substance such as an inorganic semiconductor) as, for example, an additive.

[0061] In this embodiment, the red light-emitting element 5R shown in Figures 3 and 4 has the following configuration, but this is merely an example and is not intended to be limiting. The red light-emitting element 5R shown in Figures 3 and 4 is a top-emission type, so that the anode 22 is a laminate in which an Al layer and an ITO (indium tin oxide) layer are laminated in this order from the substrate 12 side (not shown), thereby realizing an electrode that reflects visible light, and the cathode 25 is a thin film made of Al, thereby realizing an electrode that transmits visible light. The first charge transport layer 24H is composed of a laminate in which a hole injection layer (HIL) and a hole transport layer (HTL) are laminated in this order from the anode 22 side. The hole injection layer (HIL) is formed using nickel oxide particles to a thickness of 50 nm, and the hole transport layer (HTL) is formed using poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) to a thickness of 30 nm. Note that the hole injection layer (HIL) is formed using, for example, MoO instead of nickel oxide particles. ３The quantum dots (QD) may be formed to a thickness of 10 nm using particles. The quantum dots (QD) used had a core material made of InP and a shell material made of ZnS. The matrix (MR) used a matrix made of ZnS. The dipole-forming surface treatment agent (DPS) used polyethyleneimine (PEI) shown in the following (Chemical Formula 1), which is a polymer containing 100 or more groups capable of coordinating to the matrix, was used. When polyethyleneimine (PEI) or polyethyleneimine ethoxylate (PEIE), which will be described later, is distributed, attached, or laminated on an inorganic semiconductor such as ZnS, which is the matrix (MR), a dipole moment is formed, and the conduction band minimum (CBM) and valence band maximum (VBM) levels of ZnS shift toward the vacuum level, i.e., become shallower. Furthermore, compared to when polyethyleneimine (PEI) or polyethyleneimine ethoxylate (PEIE) is formed with a thickness of 0.01 nm or more and 10 nm or less in the direction perpendicular to the first surface S1, the amount of shift of the conduction band minimum (CBM) and valence band maximum (VBM) of ZnS toward the vacuum level can be increased when the polyethyleneimine (PEI) or polyethyleneimine ethoxylate (PEIE) is distributed, attached, or laminated on a metal or conductive polymer in addition to the inorganic semiconductors described above. The second charge transport layer 24E is composed of an electron transport layer (ETL), and the electron transport layer (ETL) is formed with a thickness of 50 nm using zinc oxide particles. Furthermore, the band gap of the matrix MR, that is, the band gap of ZnS, is larger than the band gap of the core of the quantum dot QD, that is, the band gap of InP.

[0062] 3 and 4 , a red light-emitting device 5R including quantum dots QD and a matrix MR is first formed, and then the exposed surface of the red light-emitting layer 24L, i.e., the first surface S1 side, is treated with a dipole-forming surface treatment agent DPS. This allows the dipole-forming surface treatment agent DPS to be distributed in at least a portion of the matrix MR located on the first surface S1 side of the red light-emitting layer 24L, which faces the cathode 25. This distribution of the dipole-forming surface treatment agent DPS shifts the conduction band minimum (CBM) and valence band maximum (VBM) of the matrix MR toward the vacuum level, thereby increasing the barrier for electron injection from the cathode 25 to the matrix MR of the red light-emitting layer 24L. This suppresses electron injection from the cathode 25 to the matrix MR of the red light-emitting layer 24L, i.e., improves carrier balance, thereby reducing the possibility of the light-emitting device entering an electron-excess state and deteriorating the light-emitting characteristics and reliability of the light-emitting device. Furthermore, in the case of the red light-emitting element 5R, since the red light-emitting element 5R contains the dipole-forming surface treatment agent DPS, it is possible to reduce the possibility of defects occurring in the matrix MR and to reduce the possibility of deterioration in the light-emitting characteristics and reliability. Note that the red light-emitting layer 24L may be formed first, followed by a heat treatment, and then a treatment using the dipole-forming surface treatment agent DPS, or the red light-emitting layer 24L may be formed first, followed by a treatment using the dipole-forming surface treatment agent DPS, and then a heat treatment.

[0063] Here, of the red light-emitting element 5R, green light-emitting element 5G, and blue light-emitting element 5B provided in the display device 1 shown in Figure 2, the red light-emitting element 5R has been described as an example, but like the red light-emitting element 5R, the green light-emitting element 5G and blue light-emitting element 5B can also be configured to include a surface treatment agent DPS that forms a dipole.

[0064] In this embodiment, an example will be described in which the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B provided in the display device 1 shown in Figure 2 are all configured to contain a surface treatment agent DPS that forms a dipole, but this is not limited to this. For example, of the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B provided in the display device 1 shown in Figure 2, only the light-emitting elements of a specific color may be configured to contain a surface treatment agent DPS that forms a dipole, or only the light-emitting elements of two specific colors may be configured to contain a surface treatment agent DPS that forms a dipole.

[0065] As in the red light-emitting element 5R shown in FIGS. 3 and 4 , an electron transport layer (ETL) may be provided as the second charge transport layer 24E between the first surface S1 of the red light-emitting layer 24L and the cathode 25, which is a layer above the first surface S1.

[0066] Furthermore, as shown in FIGS. 3 and 4, at least a portion of the surface treatment agent DPS forming the distributed dipoles may be in contact with both the first surface S1 and the electron transport layer (ETL), which is the second charge transport layer 24E.

[0067] Note that, for example, as shown in FIG. 4 , when the first surface S1 of the red light-emitting layer 24L is formed in an uneven or curved shape or when the matrix MR is made of a porous material, the dipole-forming surface treatment agent DPS may penetrate to the inside of the matrix MR, modify the inside of the matrix MR, and reduce the possibility of defects occurring in the matrix MR.

[0068] Furthermore, in the case where the red light-emitting layer 24L is formed first, and then the treatment using the dipole-forming surface treatment agent DPS is performed, followed by a heat treatment to decompose the precursor material of the matrix MR (e.g., zinc xanthate), the dipole-forming surface treatment agent DPS is applied from above the quantum dots QD and matrix MR contained in the red light-emitting layer 24L. Therefore, the dipole-forming surface treatment agent DPS is distributed in at least a portion of the matrix MR located on the first surface S1 side of the red light-emitting layer 24L, which is the cathode side. Then, during the decomposition of the precursor material of the matrix MR by the heat treatment, the precursor material sinks to the anode 22 side in this state. Therefore, the dipole-forming surface treatment agent DPS is unlikely to be distributed in the matrix MR in a region less than 3 nm away from the second surface S2 of the red light-emitting layer 24L in the direction toward the first surface S1. This makes it possible to realize a red light-emitting element in which the dipole-forming surface treatment agent DPS is present in a region 3 nm or more away from the second surface S2 of the red light-emitting layer 24L in the direction toward the first surface S1.

[0069] As described above, in the case of the red light-emitting device 5R of this embodiment, the red light-emitting layer 24L containing the quantum dots QD and the matrix MR is first formed, and then treatment is performed using the dipole-forming surface treatment agent DPS from the exposed surface side of the red light-emitting layer 24L, i.e., the first surface S1 side. Therefore, if the amount of the surface treatment agent DPS that forms the dipole in the region of the matrix MR that is 3 nm or more away from the second surface S2 in the first surface S1 direction is X moles, and the amount of the surface treatment agent DPS that forms the dipole in the region of the matrix MR that is less than 3 nm away from the second surface S2 in the first surface S1 direction is Y moles, then (X / (X+Y))×100% is often 50% or more. Furthermore, when the dipole-forming surface treatment agent DPS is an oligomer or polymer, the amount of the surface treatment agent DPS that forms the dipole in the region of the matrix MR that is 3 nm or more away from the second surface S2 in the first surface S1 direction is X moles. 3 The amount of surface treatment agent DPS that forms a dipole in the region of less than 3 nm from the second surface S2 to the first surface S1 is defined as Ym 3 In this case, (X / (X+Y))×100% is often 50% or more.

[0070] The dipole-forming surface treatment agent DPS can be formed to a thickness of a single molecule to a few molecules that is sufficient to form a dipole moment. For example, it is preferable that the surface treatment agent DPS be formed to a thickness of 0.01 nm or more and 10 nm or less in the direction perpendicular to the first surface S1. In the case of the above-mentioned electron transport layer (ETL) or hole transport layer (HTL), generally, when formed to a thickness greater than 10 nm, electrons or holes pass directly through due to the tunneling effect. Therefore, when formed to a thickness of 10 nm or less, the electron transport properties of the electron transport layer (ETL) or the hole transport properties of the hole transport layer (HTL) are not utilized. On the other hand, when the dipole-forming surface treatment agent DPS modifies the matrix MR, as in this embodiment, even if the dipole-forming surface treatment agent DPS is formed to a thickness of a single molecule to a few molecules, it is sufficient because it can increase the barrier to electron injection into the matrix MR.

[0071] In this embodiment, the dipole-forming surface treatment agent DPS has been described using, as an example, a polymer containing 100 or more amines as groups capable of coordinating to the matrix MR, such as polyethyleneimine (PEI) shown in the above (Chemical Formula 1). However, the present invention is not limited to this. For example, the dipole-forming surface treatment agent DPS may be a monomer, oligomer, or polymer containing 10 or more groups capable of coordinating to the matrix MR. Note that n in the above (Chemical Formula 1) is not particularly limited as long as it is a natural number containing a predetermined number or more of amines capable of coordinating to the matrix MR, for example, 10 or more or 100 or more. The dipole-forming surface treatment agent DPS preferably has a value of (number of groups capable of coordinating to the matrix / number of carbon atoms C) per molecule of 0.1 or more, more preferably 0.25 or more, and even more preferably 0.5 or more. Furthermore, the dipole-forming surface treatment agent DPS may be a monomer, oligomer, or polymer, as long as the value of (number of groups capable of coordinating to the matrix / number of carbon atoms) in one molecule is within the above-mentioned range. It is preferable that the dipole-forming surface treatment agent DPS contains a larger number of coordinating functional groups (e.g., amines) in one molecule in order to coordinate the dipole-forming surface treatment agent DPS to the matrix MR at high density. The number of amines and carbon atoms in one unit of polyethyleneimine (PEI) shown in the above (Chemical Formula 1) is 11:22, i.e., number of primary to tertiary amines:number of carbon atoms = 1:2, and the value of (number of primary to tertiary amines) / [(number of primary to tertiary amines) + (number of carbon atoms)] is 0.33, and the value of (number of primary to tertiary amines) / (number of carbon atoms) is 0.5.

[0072] Furthermore, in consideration of affinity with the upper layer, the surface treatment agent DPS that forms the dipole may appropriately incorporate any of the following: a hydrophobic skeleton containing an alkyl chain; a hydrophilic skeleton containing, for example, an ether group, an ester group, or a polyethylene glycol (PEG)-based skeleton; and a water-repellent skeleton such as a fluorous skeleton containing many C—F groups.

[0073] In the present disclosure, a group capable of coordinating to a matrix refers to a group having a bond capable of coordinating to an inorganic substance, but does not necessarily have to actually be coordinated. When the matrix MR contains a metal sulfide such as ZnS, as in this embodiment, the dipole-forming surface treatment agent DPS preferably contains at least one functional group capable of coordinating to the matrix MR selected from amine, carboxylic acid, thiol, phosphine, and halogen. As described above, when the matrix MR contains a metal sulfide such as ZnS, the functional group capable of coordinating to the matrix MR contained in the dipole-forming surface treatment agent DPS is preferably an amine. In this manner, by using a dipole-forming surface treatment agent DPS that has a functional group capable of coordinating to the matrix MR and is capable of forming a dipole, the dipole-forming process can be more efficiently performed on the first surface S1 of the red light-emitting layer 24L. In this embodiment, quantum dots QDs whose shell material is made of ZnS, a metal sulfide, are used, so the dipole-forming surface treatment agent DPS can coordinate not only to the matrix MR but also to the shell of the quantum dots QDs. In addition, if the number of functional groups capable of coordinating to the matrix MR contained in the surface treatment agent DPS that forms the dipole is too large, the coverage rate and coordination density of the red light-emitting layer 24L on the first surface S1 will decrease, so it is preferable to adjust the number appropriately.

[0074] When the matrix MR contains an oxide containing a metal element or a semimetal element, such as silicon oxide or aluminum oxide, the surface treatment agent DPS that forms a dipole preferably contains at least one functional group selected from phosphonic acid and disulfide as a functional group capable of coordinating to the matrix MR.

[0075] As the surface treatment agent DPS that forms a dipole, for example, a polymer such as polyethyleneimine ethoxylate (PEIE) shown in the following (Chemical Formula 2) may be used. Note that x, y, and z in the following (Chemical Formula 2) are not particularly limited as long as they are natural numbers sufficient to form a dipole, and may be different or the same. It is preferable that the surface treatment agent DPS that forms a dipole contains a large number of coordinating functional groups (e.g., amines) per molecule in order to coordinate the dipole-forming surface treatment agent DPS to the matrix MR at high density. Hydroxy groups (OH groups) also have weak but coordinating properties to the matrix MR. Therefore, x, y, and z in the following (Chemical Formula 2) may be determined so that the ratio of (number of primary to tertiary amines + number of hydroxyl groups):number of carbon atoms (C) is approximately 1:2. The surface treatment agent DPS that forms a dipole may be a monomer, oligomer, or polymer. The polyethyleneimine ethoxylate (PEIE) shown in the following (Chemical Formula 2) is an example of polyethyleneimine ethoxylate (PEIE), and therefore polyethyleneimine ethoxylate (PEIE) is not limited to the structural formula shown in the following (Chemical Formula 2). Furthermore, as the surface treatment agent DPS that forms a dipole, for example, Alq3 (tris-8-quinolinolatoaluminum complex) shown in the following (Chemical Formula 3), in which the value in one molecule of (number of groups that can coordinate to the matrix / number of carbon atoms) is 1 / 9, i.e., 0.1 or more, may be used. The surface treatment agent DPS that forms a dipole preferably has a value in one molecule of (number of groups that can coordinate to the matrix / number of carbon atoms) of 0.1 or more, more preferably 0.25 or more, and even more preferably 0.5 or more.

[0076] 7 is a diagram showing the band levels of the hole transport layer, the red light-emitting layer, and the electron transport layer, which is the second charge transport layer 24E, in a red light-emitting device 50R of Comparative Example 1 having a red light-emitting layer composed only of quantum dots QD, and a red light-emitting device 51R of Comparative Example 2 having a red light-emitting layer composed of quantum dots QD and a surface treatment agent DPS that forms a dipole. Fig. 8 is a diagram showing the band levels of the hole transport layer, the red light-emitting layer, and the electron transport layer, which is the second charge transport layer 24E, in a red light-emitting device 52R of Comparative Example 3 having a red light-emitting layer composed of quantum dots QD and a matrix MR, and a red light-emitting device 5R provided in the display device 1 of embodiment 1.

[0077] As shown in Figure 7, in the case of the red light-emitting element 51R of Comparative Example 2, by treating the quantum dot QDs with the surface treatment agent DPS that forms a dipole, the level at the bottom of the conduction band of the quantum dot QDs (QD(CBM)) and the level at the top of the valence band of the quantum dot QDs (QD(VBM)) are shifted toward the vacuum level, i.e., become shallower, compared to the level at the bottom of the conduction band of the quantum dot QDs (QD(CBM)) and the level at the top of the valence band of the quantum dot QDs (QD(VBM)) of the red light-emitting element 50R of Comparative Example 1, respectively.

[0078] On the other hand, as shown in FIG. 8, in the case of the red light-emitting element 5R provided in the display device 1 of embodiment 1, as described above, the surface treatment agent DPS that forms a dipole moment, i.e., a dipole, is distributed in at least a part of the matrix MR located on the first surface S1 side of the red light-emitting layer 24L on the cathode 25 side. Therefore, in the case of the red light-emitting element 5R, the level of the bottom of the conduction band of the matrix MR (MR(CBM)) and the level of the top of the valence band of the matrix MR (MR(VBM)) in the red light-emitting element 52R of Comparative Example 3, which was not treated with the dipole-forming surface treatment agent DPS, are shifted toward the vacuum level by treatment with the dipole-forming surface treatment agent DPS, while the level of the bottom of the conduction band of the matrix MR (MR'(CBM)) and the level of the top of the valence band of the matrix MR (MR'(VBM)) in the red light-emitting element 52R of Comparative Example 3, which was not treated with the dipole-forming surface treatment agent DPS, maintains their original levels.

[0079] The band level of the red light-emitting element 5R shown in the center of Figure 8 is the band level when the surface treatment agent DPS that forms a dipole penetrates to the inside of the matrix MR, and the band level of the red light-emitting element 5R shown on the far right of Figure 8 is the band level when the surface treatment agent DPS that forms a dipole is distributed only in the vicinity of the first surface S1 of the red light-emitting layer.

[0080] As can be seen from the band level of the red light-emitting element 5R shown in the middle of FIG. 8 , the shift toward the vacuum level suppresses the injection of electrons from the cathode 25 side to the level at the bottom of the conduction band of the matrix MR (MR′(CBM)), but the shift toward the vacuum level promotes the injection of holes from the anode 22 side to the level at the top of the valence band of the matrix MR (MR′(VBM)). This reduces the possibility that the red light-emitting element 5R will enter an electron excess state, which will deteriorate the light-emitting characteristics and reliability.

[0081] As can be seen from the band level of the red light-emitting element 5R shown on the right side of FIG. 8 , the injection of electrons from the cathode 25 side to the level at the bottom of the conduction band of the matrix MR (MR′(CBM)) is suppressed by the shift to the vacuum level side, but the injection of holes from the anode 22 side occurs via the level at the top of the valence band of the matrix MR (MR(VBM)), where no shift to the vacuum level side has occurred, and is therefore not suppressed. Therefore, the red light-emitting element 5R can be brought into an electron excess state, which can reduce the possibility of deterioration in light-emitting characteristics and reliability.

[0082] [Additional Notes] 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.

[0083] The present disclosure can be used in light-emitting devices and display devices.

[0084] DESCRIPTION OF SYMBOLS 1 Display device 3 Barrier layer 4 Thin film transistor layer 5R Red light emitting element (light emitting element) 5G Green light emitting element (light emitting element) 5B Blue light emitting element (light emitting element) 6 Sealing layer 12 Substrate 16, 18, 20 Inorganic insulating film 21 Planarization film 22 Anode 24R Functional layer including red light emitting layer 24G Functional layer including green light emitting layer 24B Functional layer including blue light emitting layer 24L Red light emitting layer (light emitting layer) 24H First charge transport layer 24E Second charge transport layer 25 Cathode 26, 28 Inorganic sealing film 27 Organic film 39 Functional film S1 First surface S2 Second surface DPS Surface treatment agent forming a dipole QD Quantum dot MR Matrix PIX Pixel RSP Red subpixel GSP Green subpixel BSP Blue subpixel DA Display area NDA Frame area CBM: Conduction band bottom level VBM: Valence band top level

Claims

1. A light-emitting device comprising: an anode; a cathode that is a layer above the anode; and a light-emitting layer that includes quantum dots and a matrix and is disposed between the anode and the cathode, wherein a surface treatment agent that forms a dipole is distributed in at least a portion of the matrix located on a first surface side of the light-emitting layer that faces the cathode.

2. A light-emitting element comprising: an anode; a cathode that is a layer above the anode; a light-emitting layer that includes quantum dots and a matrix and is disposed between the anode and the cathode; and a surface treatment agent in the matrix, in a region that is 3 nm or more away from the second surface of the light-emitting layer on the anode side toward the first surface on the cathode side, where the value N of (number of groups that can coordinate to the matrix / number of carbon atoms C) is 0.1 or more.

3. The light-emitting element according to claim 2, wherein the value N is 0.25 or greater.

4. The light-emitting element according to claim 2, wherein the value N is 0.5 or greater.

5. The light-emitting element according to claim 1, wherein the dipole-forming surface treatment agent is present in the matrix in a region 3 nm or more away from the second surface of the light-emitting layer on the anode side toward the first surface on the cathode side.

6. The light-emitting element according to claim 1, wherein, in the matrix, when the amount of surface treatment agent present that forms the dipole in a region 3 nm or more away from the second surface on the anode side of the light-emitting layer toward the first surface on the cathode side is X moles, and the amount of surface treatment agent present that forms the dipole in a region less than 3 nm from the second surface is Y moles, (X / (X+Y))×100% is 50% or more.

7. In the matrix, the amount of the surface treatment agent that forms the dipole in a region that is 3 nm or more away from the second surface of the light-emitting layer on the anode side toward the first surface of the light-emitting layer on the cathode side is set to Xm 3 and the amount of the surface treatment agent forming the dipole in the region less than 3 nm from the second surface is Ym 3 2. The light-emitting element according to claim 1, wherein (X / (X+Y))×100% is 50% or more.

8. The light-emitting device according to any one of claims 1 and 5 to 7, wherein an electron transport layer is provided between the first surface and the cathode.

9. The light-emitting device according to claim 8, wherein at least a portion of the distributed surface treatment agent forming the dipole is in contact with both the first surface and the electron transport layer.

10. A light-emitting element according to any one of claims 1, 5 to 9, wherein the surface treatment agent that forms the dipole is formed to a film thickness of 0.01 nm or more and 10 nm or less in the direction perpendicular to the first surface.

11. A light-emitting element described in any one of claims 1, 5 to 10, wherein the surface treatment agent that forms the dipole has a value of 0.1 or more in one molecule (number of groups that can coordinate to the matrix / number of carbon atoms C).

12. The light-emitting device according to claim 11, wherein the dipole-forming surface treatment agent has a value of (number of groups capable of coordinating to the matrix / number of carbon atoms) in one molecule of 0.25 or more.

13. The light-emitting device according to claim 12, wherein the dipole-forming surface treatment agent has a value of (number of groups capable of coordinating to the matrix / number of carbon atoms) in one molecule of 0.5 or more.

14. The light-emitting device according to any one of claims 1, 5 to 13, wherein the surface treatment agent forming the dipole is any one of a monomer, an oligomer, and a polymer.

15. The light-emitting device according to claim 14, wherein the dipole-forming surface treatment agent is a monomer.

16. The light-emitting device according to claim 14, wherein the dipole-forming surface treatment agent is an oligomer.

17. The light-emitting device according to claim 14, wherein the dipole-forming surface treatment agent is a polymer.

18. A light-emitting element according to any one of claims 1, 5 to 17, wherein the matrix contains a metal sulfide, and the surface treatment agent that forms the dipole contains at least one group selected from the group consisting of amine, carboxylic acid, thiol, phosphine, halogen, and hydroxy group as a group that can coordinate to the matrix.

19. A light-emitting device according to any one of claims 1, 5 to 17, wherein the matrix contains an oxide containing a metal element or a semi-metal element, and the surface treatment agent that forms the dipole contains at least one group selected from the group consisting of phosphonic acid and disulfide as a group capable of coordinating to the matrix.

20. The light-emitting device according to claim 18, wherein the group capable of coordinating to the matrix contained in the surface treatment agent that forms the dipole is an amine.

21. The light-emitting device according to any one of claims 1, 5 to 13, and 17, wherein the surface treatment agent for forming the dipole is polyethyleneimine (PEI).

22. The light-emitting device according to any one of claims 1, 5 to 13, and 17, wherein the surface treatment agent for forming the dipole is polyethyleneimine ethoxylate (PEIE).

23. The light-emitting device according to any one of claims 1, 5 to 13, and 15, wherein the surface treatment agent for forming the dipole is Alq3.

24. A light-emitting device according to any one of claims 1 to 23, wherein the band gap of the matrix is ​​larger than the band gap of the core of the quantum dot.

25. A display device comprising a light-emitting element according to any one of claims 1 to 24.

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