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

Abstract

A light-emitting element (5R) is provided with a first electrode (22), a second electrode (25), and a light-emitting layer (24REM) provided between the first electrode (22) and the second electrode (25). The light-emitting layer (24REM) contains quantum dots (RQD) and a metal halide (MHa) having a melting point of 200 DEG C or less.

Description

Technical Field

[0001] The present disclosure relates to a light emitting element, a display device, a method for manufacturing a light emitting element, and a method for recovering the light emitting characteristics of a light emitting element. Background Art

[0002] In recent years, QLED (Quantum dot Light Emitting Diode) display devices, which are light-emitting elements containing quantum dots, have attracted much attention due to their ability to achieve low power consumption, thinness, and high image quality.

[0003] For example, Patent Document 1 describes fluorine-containing nanocrystals, that is, quantum dots containing fluorine in at least a part of the core and the shell. Prior art literature Patent Literature

[0004] Patent Document 1: Japanese Patent Publication No. 2015-147726 Summary of the invention Technical Problems to be Solved by the Invention

[0005] It is known that quantum dots containing ligands partially detach from the quantum dots over time. Although there are differences in the degree of such ligand detachment, such ligand detachment occurs in the same manner regardless of whether the ligand is an organic ligand or a halogen ligand such as fluorine.

[0006] Therefore, in the case of the light-emitting element having fluorine-containing quantum dots as a light-emitting layer and the display device having the light-emitting element described in Patent Document 1, there is a problem that it is difficult to ensure the long-term reliability of the light-emitting layer containing quantum dots, and it is impossible to avoid the reduction in the light-emitting characteristics (light-emitting efficiency) of the light-emitting layer containing quantum dots over time.

[0007] One aspect of the present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a light-emitting element, a display device, a method for manufacturing a light-emitting element, and a method for restoring the light-emitting characteristics of a light-emitting element, which can improve the long-term reliability of a light-emitting layer containing quantum dots and restore reduced light-emitting characteristics (light-emitting efficiency). Technical solutions for solving technical problems

[0008] In order to solve the above problems, the light-emitting element disclosed in the present invention includes: a first electrode; a second electrode; and a light-emitting layer, which is arranged between the first electrode and the second electrode, and the light-emitting layer contains quantum dots and a metal halide with a melting point below 200°C.

[0009] In order to solve the above-mentioned problem, the display device disclosed in the present invention includes a display panel including the light-emitting element and a driving circuit. The driving circuit passes a current at a current density selected within a first current density range between the first electrode and the second electrode based on an image signal input from the outside, so that the light-emitting layer emits light at a brightness corresponding to the selected current density, and the melting point of the metal halide is higher than the temperature of the light-emitting element when the current passes between the first electrode and the second electrode at the selected current density.

[0010] In order to solve the above-mentioned problem, the display device disclosed in the present invention includes: a display panel including the light-emitting element; and a heating unit to make the temperature of the light-emitting element higher than the melting point of the metal halide.

[0011] In order to solve the above problems, the method for manufacturing a light-emitting element disclosed herein includes a step of forming a light-emitting layer containing quantum dots and a metal halide having a melting point of 200° C. or less.

[0012] In order to solve the above-mentioned problems, in a method for recovering light emission characteristics of a light emitting element disclosed herein, the light emitting element is manufactured by the above-mentioned method for manufacturing a light emitting element, and the recovery method includes a step of melting the metal halide. Beneficial Effects

[0013] According to one aspect of the present disclosure, a light-emitting element, a display device, a method for manufacturing a light-emitting element, and a method for restoring the light-emitting characteristics of a light-emitting element are provided, which are capable of improving the long-term reliability of a light-emitting layer containing quantum dots and restoring reduced light-emitting characteristics (light-emitting efficiency). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a plan view showing a schematic configuration of a display device according to Embodiment 1. Figure 2 This is a cross-sectional view schematically showing the structure of a display region of a display panel included in the display device according to Embodiment 1. Figure 3 This is a cross-sectional view schematically showing the structure of a red light-emitting element included in the display device of Embodiment 1. Figure 4 Yes means Figure 3 The diagram shows energy band levels of the hole transport layer, electron transport layer, quantum dots, and metal halide included in the red light-emitting element. Figure 5 Yes means Figure 3 The graph shown is a graph showing the temporal change of the light-emitting layer of a red light-emitting element after being driven for a predetermined period of time. Figure 6This is a diagram showing the relationship between the current density of a current flowing between the first electrode and the second electrode included in each of the plurality of light-emitting elements of the display device according to Embodiment 1 and the temperature of the light-emitting element. Figure 7 It means for Figure 5 The light-emitting layer of the red light-emitting element shown in the figure changes with time, and the metal halide contained in the light-emitting layer is melted to restore the light-emitting characteristics (light-emitting efficiency) of the red light-emitting element. Figure 8 This is a cross-sectional view schematically showing the structure of another red light-emitting element that the display device of embodiment 1 can have. Fig. 9 A diagram showing energy band levels of a hole transport layer, an electron transport layer, quantum dots, and a metal halide included in the green light-emitting element of the display device of Embodiment 1. Fig.10 A diagram showing energy band levels of a hole transport layer, an electron transport layer, quantum dots, and a metal halide included in the blue light-emitting element of the display device of Embodiment 1. Fig.11 This is a diagram showing an example of a material that can be used as a metal halide contained in a light-emitting layer of a light-emitting element of each color included in the display device of Embodiment 1. Fig.12 This is a cross-sectional view showing a schematic structure of a red light-emitting element included in the display device of embodiment 2. Fig.13 To express Fig.12 The diagram shows energy bands of a hole transport layer, an electron transport layer, quantum dots, and two metal halide layers included in a red light-emitting element. Fig.14 It is shown Fig.12 The graph shown is a graph showing the temporal change of the light-emitting layer of the red light-emitting element after being driven for a predetermined period of time. Fig.15 It means relative to Fig.14 The light-emitting layer of the red light-emitting element shown in the figure changes with time, and the metal halide layer contained in the light-emitting layer is melted to restore the light-emitting characteristics (light-emitting efficiency) of the red light-emitting element. Fig.16 This is a plan view showing a schematic configuration of a display device according to a third embodiment. Fig.17 It is shown Fig.16 A diagram showing a heating unit included in a display device according to Embodiment 3. DETAILED DESCRIPTION

[0015] based on Figures 1 to 17, the embodiments of the present disclosure are described as follows. In the following, for the sake of convenience, the same reference numerals are sometimes used to indicate the same functions as the components described in the specific embodiments, and the description thereof is omitted.

[0016] [Implementation Method 1] Figure 1 This is a plan view showing a schematic configuration of a display device 1 according to Embodiment 1.

[0017] like Figure 1 As shown, the display device 1 includes a display panel 30, and the display panel 30 includes a frame area NDA and a display area DA. In the display area DA of the display panel 30, a plurality of pixels PIX are provided, and each pixel PIX includes a red sub-pixel RSUB, a green sub-pixel GSUB, and a blue sub-pixel BSUB. In the present embodiment, a case where a pixel PIX is composed of a red sub-pixel RSUB, a green sub-pixel GSUB, and a blue sub-pixel BSUB is taken as an example for explanation, but it is not limited to this. For example, in addition to the red sub-pixel RSUB, the green sub-pixel GSUB, and the blue sub-pixel BSUB, a pixel PIX may also include sub-pixels of other colors. In addition, in the present embodiment, an example is given in which a scanning side driving circuit 31 and a data side driving circuit 32 are provided in the frame area NDA of the display panel 30, but it is not limited to this, and at least one of the scanning side driving circuit 31 and the data side driving circuit 32 may also be externally mounted on the display panel 30.

[0018] Figure 2 1 is a cross-sectional view schematically showing the configuration of a display area DA of a display panel 30 included in the display device 1 according to the first embodiment.

[0019] like Figure 2 As shown, in the display area DA of the display panel 30 of the display device 1, on the substrate 12, there are, in order from the substrate 12 side: a blocking 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 dam 23, a sealing layer 6 and a functional film 39.

[0020] The red sub-pixel RSUB in the display area DA of the display panel 30 includes a red light-emitting element 5R, the green sub-pixel GSUB in the display area DA of the display panel 30 includes a green light-emitting element 5G, and the blue sub-pixel BSUB in the display area DA of the display device 30 includes a blue light-emitting element 5B.

[0021] The substrate 12 may be a resin substrate made of a resin material such as polyimide, or a glass substrate. In this embodiment, in order to set the display device 1 as a flexible display device, the case where a resin substrate made of a resin material such as polyimide is used as the substrate 12 is cited as an example for description, but the present invention is not limited thereto. In the case where the display device 1 is a non-flexible display device, a glass substrate can be used as the substrate 12.

[0022] The barrier layer 3 is a layer that prevents foreign matter such as water and oxygen from invading the thin film transistor TR, the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B. For example, it can be composed of a silicon oxide film, a silicon nitride film, an oxynitride silicon film, or a stacked film of these layers formed by a CVD method.

[0023] The transistor TR portion of the thin film transistor layer 4 including the transistor TR includes a semiconductor film SEM and a doped semiconductor film SEM'·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 other than the transistor TR portion of the thin film transistor layer 4 including the transistor TR includes the inorganic insulating film 16, the inorganic insulating film 18, the inorganic insulating film 20 and the planarization film 21.

[0024] The semiconductor film SEM·SEM'·SEM" may also be composed of, for example, low-temperature polycrystalline silicon (LTPS) or an oxide semiconductor (for example, an In-Ga-Zn-O type semiconductor). In this embodiment, an example is given in which the transistor TR has a top-gate structure, but the present invention is not limited thereto, and the transistor TR may also have a bottom-gate structure.

[0025] The gate electrode G, the source electrode S, and the drain electrode D are formed of a single-layer film or a stacked film of a metal including at least one of aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper, for example.

[0026] The inorganic insulating films 16 , 18 , and 20 may be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon nitride oxide film, or a stacked film thereof formed by a CVD method.

[0027] The planarizing film 21 can be made of a coatable organic material such as polyimide or acrylic, or can be formed of an inorganic film.

[0028] The red light emitting element 5R included in the red sub-pixel RSUB includes a first electrode 22 on a higher layer than the planarization film 21, a functional layer 24R including a red light emitting layer, and a second electrode 25. The green light emitting element 5G included in the green sub-pixel GSUB includes a first electrode 22 on a higher layer than the planarization film 21, a functional layer 24G including a green light emitting layer, and a second electrode 25. The blue light emitting element 5B included in the blue sub-pixel BSUB includes a first electrode 22 on a higher layer than the planarization film 21, a functional layer 24B including a blue light emitting layer, and a second electrode 25. In addition, the insulating bank 23 covering the edge of the first electrode 22 can be formed by, for example, applying an organic material such as polyimide or acrylic and then patterning it by photolithography, or can be formed of an inorganic film.

[0029] In this embodiment, the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B are described as a forward stacking structure, but the present invention is not limited thereto. The red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B may also be a reverse stacking structure. Figure 3) includes a first electrode 22 as an anode and a second electrode 25 as a cathode that is higher than the first electrode 22. The functional layer 24R including the red light-emitting layer 24REM between the first electrode 22 as the anode and the second electrode 25 as the cathode can be formed by, for example, stacking a hole injection layer, a hole transport layer, a red light-emitting layer, an electron transport layer, and an electron injection layer in sequence from the first electrode 22 side. In the functional layer 24R including the red light-emitting layer 24REM, one or more of the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer other than the red light-emitting layer 24REM can also be appropriately omitted. In the present embodiment, the case where the functional layer 24R including the red light-emitting layer REM is formed by stacking a hole injection layer 24HI, a hole transport layer 24HT, a red light-emitting layer 24REM, and an electron transport layer 24ET in sequence from the anode side of the first electrode 22 is cited as an example for explanation, but it is not limited to this. The green light emitting element 5G as a forward stacked structure includes a first electrode 22 as an anode and a second electrode 25 as a cathode on an upper layer than the first electrode 22. The functional layer 24G including the green light emitting layer provided between the first electrode 22 as an anode and the second electrode 25 as a cathode can be formed by, for example, stacking a hole injection layer, a hole transport layer, a green light emitting layer, an electron transport layer, and an electron injection layer in sequence from the first electrode 22 side. In the functional layer 24G including the green light emitting layer, one or more of the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer other than the green light emitting layer may be appropriately omitted. In the present embodiment, the case where the functional layer 24G including the green light emitting layer is formed by stacking a hole injection layer, a hole transport layer, a green light emitting layer, and an electron transport layer in sequence from the anode side of the first electrode 22 is cited as an example for explanation, but it is not limited to this. The blue light-emitting element 5B as a forward stacked structure includes a first electrode 22 as an anode and a second electrode 25 as a cathode on an upper layer than the first electrode 22. The functional layer 24B including a blue light-emitting layer provided between the first electrode 22 as an anode and the second electrode 25 as a cathode can be formed by, for example, stacking a hole injection layer, a hole transport layer, a blue light-emitting layer, an electron transport layer, and an electron injection layer in sequence from the first electrode 22 side. In the functional layer 24B including a blue light-emitting layer, one or more of the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer of the blue light-emitting layer may be appropriately omitted. In the present embodiment, the case where the functional layer 24B including a blue light-emitting layer is formed by stacking a hole injection layer, a hole transport layer, a blue light-emitting layer, and an electron transport layer in sequence from the anode side of the first electrode 22 is cited as an example for explanation, but it is not limited to this.

[0030] As a red light emitting element 5R' (refer to Figure 8) has a first electrode 22 as a cathode and a second electrode 25 as an anode which is higher than the first electrode 22, and includes a functional layer 24R' including a red light-emitting layer 24REM which is disposed between the first electrode 22 as a cathode and the second electrode 25 as an anode, which can be formed by, for example, stacking an electron injection layer, an electron transport layer, a red light-emitting layer, a hole transport layer, and a hole injection layer in sequence from the first electrode 22 side. In the functional layer 24R' including the red light-emitting layer 24REM, one or more of the electron injection layer, the electron transport layer, the hole transport layer, and the hole injection layer other than the red light-emitting layer 24REM can also be appropriately omitted. The green light-emitting element which is not shown in the figure as a reverse stacking structure has a first electrode as a cathode and a second electrode as an anode which is higher than the first electrode, and includes a functional layer including a green light-emitting layer which is disposed between the first electrode as a cathode and the second electrode as an anode, which can be formed by, for example, stacking an electron injection layer, an electron transport layer, a green light-emitting layer, a hole transport layer, and a hole injection layer in sequence from the first electrode side. In the functional layer including the green light-emitting layer, one or more of the electron injection layer, electron transport layer, hole transport layer and hole injection layer other than the green light-emitting layer may be appropriately omitted. The blue light-emitting element as a reverse stacking structure not shown in the figure has a first electrode as a cathode and a second electrode as an anode on an upper layer than the first electrode, and the functional layer including the blue light-emitting layer arranged between the first electrode as a cathode and the second electrode as an anode can be formed by, for example, stacking an electron injection layer, an electron transport layer, a blue light-emitting layer, a hole transport layer and a hole injection layer in sequence from the first electrode side. In the functional layer including the blue light-emitting layer, one or more of the hole injection layer, hole transport layer and electron injection layer other than the blue light-emitting layer may be appropriately omitted.

[0031] The material used for the hole injection layer is not particularly limited as long as it is a hole injecting material that can stabilize the injection of holes into the light emitting layer, and for example, PEDOT:PSS or the like can be used.

[0032] Materials used for the hole transport layer include, for example, organic materials such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine))] (TFB), (poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine]) (poly-TPD) or polyvinylcarbazole (PVK). Nanoparticles with hole transport properties such as NiO particles may also be used.

[0033] As a material for the electron transport layer, for example, an organic material such as 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) can be used, or nanoparticles having electron transport properties such as ZnO particles can be used.

[0034] The material used for the electron injection layer 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, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, organic complexes of alkali metals, and the like can be used, 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 sodium polystyrene sulfonate, etc.

[0035] In addition, in the present embodiment, the following case is taken as an example for explanation, the functional layer 24R including the red light emitting layer, the functional layer 24G including the green light emitting layer, and the functional layer 24B including the blue light emitting layer respectively have a hole injection layer formed in the same process using the same material, a hole transport layer formed in the same process using the same material, and an electron transport layer formed in the same process using the same material, but it is not limited to this. For example, each hole injection layer included in each functional layer 24R, 24G, and 24B can also be formed with mutually different materials. For example, the hole injection layers included in two functional layers of the functional layers 24R, 24G, and 24B are formed in the same process using the same material, and the hole injection layer included in only the remaining one functional layer is formed in other processes using different materials. In addition, for example, each hole transport layer included in each functional layer 24R, 24G, and 24B may also be formed of different materials. For example, the hole transport layer included in each of the two functional layers of the functional layers 24R, 24G, and 24B may also be formed using the same material in the same process, and the hole transport layer included in only the remaining one functional layer may be formed using a different material in another process. In addition, for example, each electron transport layer included in each functional layer 24R, 24G, and 24B may be formed of different materials. For example, the electron transport layer included in each of the two functional layers of the functional layers 24R, 24G, and 24B may be formed using the same material through the same process, and the electron transport layer included in only the remaining one functional layer may be formed using a different material in another process.

[0036] In the present embodiment, the case where the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B are all QLED (quantum dot light emitting diode) is used as an example for explanation, but it is not limited to this. At least one of the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B can be QLED. For example, when one of the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B is QLED, the remaining two can also be OLED (organic light emitting diode). For example, when two of the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B are QLED, the remaining one can also be OLED.

[0037] As in the present embodiment, when the red light emitting element 5R, the green light emitting element 5G and the blue light emitting element 5B are respectively QLEDs, the light emitting layers of the light emitting elements of each color are composed of quantum dots. The quantum dots may also have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure that continuously changes the core / shell ratio. In addition, although the shell can completely cover the core, it may also cover a portion of the core. In the case where the core is a mono-element system, for example, it may be composed of Si, C, etc., in the case of a binary system, for example, it may be composed of CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, etc., in the case of a ternary system, for example, it may be composed of CdSeTe, GaInP, ZnSeTe, etc., and in the case of a quaternary system, for example, it may be composed of AIGS, etc. When the shell part is a binary system, for example, it can be composed of CdS, CdTe, CdSe, ZnS, ZnSe, ZnTe, etc. When it is a ternary system, for example, it can be composed of CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc.

[0038] Here, the quantum dot refers to a quantum dot including an organic ligand or an inorganic ligand (for example, a halogen ligand) arranged on the surface of the quantum dot or in the vicinity of the surface of the quantum dot.

[0039] In addition, in the quantum dot, the maximum width of the ligand portion is omitted is less than 100 nm. In addition, in the quantum dot, the shape of the ligand portion is omitted as long as it satisfies the range of the above-mentioned maximum width, and is not limited to a sphere (circular cross section). For example, it can be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branch-shaped three-dimensional shape, a three-dimensional shape with concave and convex on the surface, or a combination of these shapes.

[0040] A control circuit including transistors TR for controlling the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B, respectively, is provided in the thin film transistor layer 4 including the transistor TR for each of the red sub-pixel RSUB, the green sub-pixel GSUB, and the blue sub-pixel BSUB. In addition, the control circuit including the transistor TR provided for each of the red sub-pixel RSUB, the green sub-pixel GSUB, and the blue sub-pixel BSUB and the light emitting element are collectively referred to as a sub-pixel circuit.

[0041] Figure 2 The red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B shown can be either a top emission type or a bottom emission type. Since the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B are in a forward stacked structure in which the second electrode 25 as the cathode is configured as an upper layer compared to the first electrode 22 as the anode, in order to become a top emission type, the first electrode 22 as the anode is formed of an electrode material that reflects visible light, and the second electrode 25 as the cathode is formed of an electrode material that transmits visible light. In order to become a bottom emission type, the first electrode 22 as the anode is formed of an electrode material that transmits visible light, and the second electrode 25 as the cathode is formed of an electrode material that reflects visible light. On the other hand, in the red light emitting element 5R' (refer to Figure 8 ), the green light emitting element and the blue light emitting element are in the case of a reverse stacking structure in which the first electrode 22 as the cathode is arranged as the upper layer compared to the second electrode 25 as the anode. In order to become a top emission type, the first electrode 22 as the cathode is formed of an electrode material that reflects visible light, and the second electrode 25 as the anode is formed of an electrode material that transmits visible light. In order to become a bottom emission type, the first electrode 22 as the cathode is formed of an electrode material that transmits visible light, and the second electrode 25 as the anode is formed of an electrode material that reflects visible light.

[0042] Electrode materials that reflect visible light are not particularly limited as long as they are conductive and can reflect visible light. Examples include metal materials such as Al, Mg, Li, Ag, or alloys of the metal materials, or stacks of the metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or stacks of the alloys and the transparent metal oxides.

[0043] The electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and has conductivity. Examples thereof include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.) or thin films made of metal materials such as Al and Ag, or nanowires made of metal materials such as Al and Ag.

[0044] The first electrode 22 and the second electrode 25 can be formed by a general electrode forming method, for example, physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, EB deposition, and ion plating, or chemical vapor deposition (CVD) methods, etc. In addition, the patterning method of the first electrode 22 and the second electrode 25 is not particularly limited as long as it can be formed into a desired pattern with good accuracy, and specifically, photolithography, inkjet method, etc. can be cited.

[0045] The sealing layer 6 is a light-transmitting film, and may be composed of, for example, an inorganic sealing film 26 covering the second electrode 25, an organic film 27 on the upper layer of the inorganic sealing film 26, and an inorganic sealing film 28 on the upper layer of the organic film 27. The sealing layer 6 prevents foreign matter 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.

[0046] The inorganic sealing layer 26 and the inorganic sealing layer 28 are respectively inorganic films, and can be composed of, for example, a silicon oxide film, a silicon nitride film or a silicon oxynitride film formed by a CVD method, or a stacked film of these layers. The organic sealing film 27 is a light-transmitting organic film with a flattening effect, and can be composed of a coatable organic material such as acrylic acid. The organic film 27 can be formed by, for example, an inkjet method. In this embodiment, an example is given of a case where the sealing layer 6 is formed by two layers of inorganic films and a layer of organic film disposed between the two layers of inorganic films, but the stacking order of the two layers of inorganic films and the one layer of organic film is not limited to this. In addition, the sealing layer 6 can be composed of only an inorganic film, only an organic film, one layer of an inorganic film and two layers of organic films, or more than two layers of inorganic films and more than two layers of organic films.

[0047] The functional film 39 is a film having at least one of an optical compensation function, a touch sensor function, and a protective function, for example.

[0048] Figure 3 This is a diagram showing a schematic configuration of a red light emitting element 5R included in the display device 1 according to the first embodiment. Figure 3 The red light emitting element 5R shown is a red light emitting element in an initial state before being driven or in which the driving time is relatively short.

[0049] like Figure 3 As shown, the functional layer 24R including the red light-emitting layer 24REM provided between the first electrode 22 as the anode and the second electrode 25 as the cathode can be formed by stacking a hole injection layer 24HI, a hole transport layer 24HT, a red light-emitting layer 24REM and an electron transport layer 24ET in sequence starting from the first electrode 22 side.

[0050] The red light emitting layer 24REM includes red light emitting quantum dots RQD containing ligands L1, ligands L2, and metal halide MHa.

[0051] In this embodiment, the case where an organic ligand is used as a ligand for eliminating surface defects existing on the surface of the red light-emitting quantum dot RQD is described as an example, but the present invention is not limited to this, and for example, a halogen ligand may also be used. Figure 3 The ligand L1 shown is a ligand disposed on the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD. Figure 3 The ligand L2 shown is located slightly away from the surface of the red light-emitting quantum dot RQD and is a remaining ligand that compensates for the ligand L1.

[0052] In this embodiment, as ligand L1 and ligand L2, the case of using trioctylphosphine (TOP) which is an organic ligand with a melting point of 30°C and a boiling point of 234°C is taken as an example for explanation, but it is not limited to this. Organic ligands with a melting point below 50°C may also be used. For example, oleic acid (OA) which is an organic ligand with a melting point of 13°C and a boiling point of 360°C, or dodecanethiol (DDT) which is an organic ligand with a melting point of -7°C and a boiling point of 277°C may also be used.

[0053] In this embodiment, as ligand L1 and ligand L2, the case of using one organic ligand is cited as an example for explanation, but it is not limited to this, and two or more organic ligands can also be used. For example, as ligand L1 and ligand L2, two or more of trioctylphosphine (TOP), oleic acid (OA) and dodecanethiol (DDT) can be used.

[0054] Figure 6 The graph shows the relationship between the current density of the current flowing between the first electrode 22 and the second electrode 25 of each of the plurality of light emitting elements 5R, 5G, and 5B of the display device 1 according to the first embodiment and the temperature of the light emitting elements 5R, 5G, and 5B.

[0055] like Figure 6 As shown, the current density of the current flowing between the first electrode 22 and the second electrode 25 of each of the plurality of light emitting elements 5R, 5G, and 5B of the display device 1 is, for example, 10 mA / cm 2Under a normal driving condition of the light emitting element (driving voltage of, for example, 5 V) of about 10 000 , the temperature of the light emitting elements 5R, 5G, and 5B including the light emitting layer rises to about 50°C.

[0056] As described above, in this embodiment, trioctylphosphine (TOP) having a melting point of 30° C. is used as the ligand L1 and the ligand L2, and therefore, under the above-mentioned driving conditions of the usual light-emitting element in which the temperature of the light-emitting elements 5R, 5G, and 5B including the light-emitting layer rises to about 50° C., the ligand L1 and the ligand L2 exist in the light-emitting layer in a liquid state. Therefore, the ligand L1 and the ligand L2 existing in a liquid state, especially the ligand L2 located slightly away from the surface of the quantum dot, are easily volatilized.

[0057] Figure 5 It is shown Figure 3 The graph shown is a graph showing the temporal change of the red light emitting layer 24REM after the red light emitting element 5R is driven for a predetermined time.

[0058] and Figure 3 Compared with the red light emitting layer 24REM of the red light emitting element 5R in the initial state shown in FIG. Figure 5 In the red light-emitting layer 24REM of the red light-emitting element 5R shown after being driven for a predetermined time, the ligand L1 arranged on the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD is detached with the passage of time and the current driving pressure, so the number of ligands L1 of each red light-emitting quantum dot RQD is reduced. Originally, the ligand L2 plays a role in compensating for the ligand L1 detached from the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD. As mentioned above, under the normal driving conditions of the light-emitting element, the ligand L2 exists in the light-emitting layer in a liquid state. Therefore, with the passage of time, Figure 5The ligand L2 shown gradually volatilizes, and the remaining ligand L2 to compensate for the detached ligand L1 is insufficient. Therefore, the deactivation of the red light-emitting quantum dots RQD caused by surface defects occurs, it is difficult to ensure the long-term reliability of the red light-emitting element 5R, and it is inevitable that the luminescence characteristics (luminous efficiency) of the red light-emitting layer 24REM containing the red light-emitting quantum dots RQD will decrease over time. Considering the amount of gradual volatilization over time, it is also considered that the red light-emitting layer 24REM initially contains a large amount of residual ligands that compensate for the ligand L1, namely, ligand L2, but the organic ligands used as ligands L1 and ligand L2, such as trioctylphosphine (TOP), oleic acid (OA) and dodecyl mercaptan (DDT) are insulating. When they are contained in large quantities in the red light-emitting layer 24REM, it becomes difficult to inject holes from the hole transport layer 24HT and inject electrons from the electron transport layer 24ET, resulting in an increase in the driving voltage of the red light-emitting element 5R and a deterioration in the electrical characteristics of the red light-emitting element 5R. For such reasons, the amount of the ligand L2 contained in the red light-emitting layer 24REM is preferably appropriately determined within a range capable of maintaining good hole injection characteristics from the hole transport layer 24HT and electron injection characteristics from the electron transport layer 24ET.

[0059] In addition, as ligands L1 and L2, for example, when oleic acid (OA) with a melting point of 13°C or dodecyl mercaptan (DDT) with a melting point of -7°C is used, not only under the above-mentioned normal driving conditions of the light-emitting element, but also when the light-emitting element is not driven, for example, when stored at room temperature (25°C), since ligands L1 and L2 are present in the light-emitting layer in a liquid state, the volatilization amount of ligand L2 is further increased, making it difficult to ensure the long-term reliability of the light-emitting element, and inevitably reducing the light-emitting characteristics (light-emitting efficiency) of the light-emitting layer containing quantum dots over time.

[0060] In this embodiment, if Figure 3 As shown, the red light-emitting layer 24REM of the red light-emitting element 5R includes: red light-emitting quantum dots RQD including ligand L1, ligand L2, and metal halide MHa. That is, the red light-emitting layer 24REM is a layer obtained by mixing the red light-emitting quantum dots RQD including ligand L1, ligand L2, and metal halide MHa.

[0061] In this embodiment, the case where the red light-emitting layer 24REM includes the ligand L2 is described as an example, but the present invention is not limited thereto. The red light-emitting layer 24REM may not include the ligand L2 but include red light-emitting quantum dots RQD including the ligand L1 and the metal halide MHa.

[0062] Figure 4 It shows that Figure 3The diagram shows the energy band levels of the hole transport layer 24HT, the electron transport layer 24ET, the red light-emitting quantum dots RQD of the ligand L1, and the metal halide MHa included in the red light-emitting element 5R.

[0063] like Figure 4 As shown, it is preferred to use a metal halide MHa whose difference between the upper end of the valence band of the metal halide MHa (MHa(VBM)) and the lower end of the conduction band of the metal halide MHa (MHa(CBM)), that is, the band gap (MHa(Bg)) of the metal halide MHa is greater than the difference between the upper end of the valence band of the red light-emitting quantum dot RQD (RQD(VBM)) and the lower end of the conduction band of the red light-emitting quantum dot RQD (RQD(CBM)), that is, the band gap (RQD(Bg)) of the red light-emitting quantum dot RQD. In this embodiment, an example is given in which the upper end of the valence band of the metal halide MHa (MHa(VBM)) is deeper than the upper end of the valence band of the red light-emitting quantum dot RQD (RQD(VBM)) and the lower end of the conduction band of the metal halide MHa (MHa(CBM)) is shallower than the lower end of the conduction band of the red light-emitting quantum dot RQD (RQD(CBM)), but it is not limited to this.

[0064] As described above, by using a metal halide MHa having a band gap greater than the band gap of the red light-emitting quantum dot RQD (RQD(Bg)), current leakage between multiple light-emitting elements generated by the metal halide MHa can be suppressed. In this embodiment, a red light-emitting quantum dot RQD having an upper end of the valence band (RQD(VBM)) of -5.6 eV, a lower end of the conduction band (RQD(CBM)) of -3.6 eV, and a band gap (RQD(Bg)) of 2 eV is used, but it is not limited to this.

[0065] Fig.11 1 is a diagram showing an example of a material that can be used as the metal halide MHa contained in the light-emitting layers of the light-emitting elements 5R, 5G, and 5B of each color included in the display device 1 of the first embodiment.

[0066] In consideration of suppressing the current leakage between the plurality of light emitting elements via the metal halide MHa, the metal halide MHa included in the red light emitting layer 24REM of the red light emitting element 5R is preferably selected from Fig.11 Among the various metal halides shown, namely fluoride, chloride, bromide and iodide, a metal halide MHa having a band gap (MHa(Bg)) greater than the band gap of the red light-emitting quantum dot RQD (eg, RQD(Bg) = 2 eV) is selected.

[0067] As the metal halide MHa included in the red light emitting layer 24REM of the red light emitting element 5R of this embodiment, it is more preferable to use, for example, Fig.11Among the various metal halides shown, a metal halide MHa having a band gap (MHa(Bg)) greater than the band gap of the red light-emitting quantum dot RQD (e.g., RQD(Bg)=2eV) and a value smaller than 3 times (e.g., 6eV) greater than the band gap of the red light-emitting quantum dot RQD (e.g., RQD(Bg)=2eV) is selected. By making the band gap of the red light-emitting quantum dot RQD (RQD(Bg)) and the band gap of the halide MHa (MHa(Bg)) within a range of less than 3 times, the deterioration of the electrical characteristics of the red light-emitting element 5R can be suppressed.

[0068] When using a metal halide MHa having a band gap greater than the band gap of the red light-emitting quantum dot RQD (RQD(Bg)), the amount of the metal halide MHa contained in the red light-emitting layer 24REM is preferably appropriately determined within a range capable of well maintaining the injection characteristics of holes from the hole transport layer 24HT and the injection characteristics of electrons from the electron transport layer 24ET.

[0069] In addition, the process temperature of the metal halide MHa melting process described later is preferably such that it does not affect Figure 3 and Figure 5 The hole injection layer 24H1 , the hole transport layer 24HT, the ligands L1 and L2 contained in the red light emitting layer 24REM, and the electron transport layer 24ET are shown to be at a temperature at which they are thermally damaged.

[0070] For example, Figure 3 and Figure 5 When the ligands L1 and L2 contained in the hole injection layer 24H1, the hole transport layer 24HT, the red light emitting layer 24REM and the electron transport layer 24ET are respectively organic materials, the process temperature of the metal halide MHa melting process is preferably set to 200°C or less so as not to cause thermal damage to these organic materials. In order to set the process temperature of the metal halide MHa melting process to 200°C or less, Fig.11 From among the various metal halides shown, namely, fluoride, chloride, bromide, and iodide, a metal halide MHa having a melting point of 200° C. or less may be selected. As the metal halide MHa having a melting point of 200° C. or less contained in the red light emitting layer 24REM, for example, GaCl3 having a melting point of 78° C., AlBr3 having a melting point of 98° C., GaBr3 having a melting point of 122° C., AlI3 having a melting point of 191° C., and AlCl3 having a melting point of 192° C. can be preferably used.

[0071] The metal halide MHa contained in the red light-emitting layer 24REM of the red light-emitting element 5R of the present embodiment has a band gap greater than the band gap of the red light-emitting quantum dot RQD (for example, RQD (Bg) = 2 eV). In order to be applicable also when the hole injection layer 24HI, the hole transport layer 24HT, the ligands L1 and L2 contained in the red light-emitting layer 24REM and the electron transport layer 24ET are respectively organic materials, the process temperature of the process of melting the metal halide MHa is achieved below 200°C. For example, it is preferred to use GaCl3 with a melting point of 78°C and a band gap Bg of 4.3 eV, AlBr3 with a melting point of 98°C and a band gap Bg of 4.1 eV, GaBr3 with a melting point of 122°C and a band gap Bg of 3.4 eV, AlI3 with a melting point of 191°C and a band gap Bg of 3.3 eV, and AlCl3 with a melting point of 192°C and a band gap Bg of 5.3 eV.

[0072] In addition, in the case where the red light-emitting quantum dot RQD has a core and a shell, and the shell is composed of cubic ZnS (band gap Bg is 3.4 eV), it is preferred to Fig.11 Among the various metal halides shown, a metal halide having a band gap Bg of 3.4 eV or more and 5.3 eV or less is selected. For example, GaCl3 having a melting point of 78°C and a band gap Bg of 4.3 eV, AlBr3 having a melting point of 98°C and a band gap Bg of 4.1 eV, GaBr3 having a melting point of 122°C and a band gap Bg of 3.4 eV, and AlC3 having a melting point of 192°C and a band gap Bg of 5.3 eV can be preferably used. As described above, when the band gap (MHa(Bg)) of the metal halide MHa is 3.4 eV or more and 5.3 eV or less, it is close to the band gap Bg (3.4 eV) of the cubic ZnS constituting the shell of the red light-emitting quantum dot RQD, so that the deterioration of the electrical characteristics of the red light-emitting element 5R can be suppressed to a minimum.

[0073] In this embodiment, GaCl 3 having a melting point of 78° C. and a band gap Bg of 4.3 eV is used as the metal halide MHa contained in the red light emitting layer 24REM, but the present invention is not limited thereto.

[0074] Figure 7 is shown relative to Figure 5 The red light emitting layer 24REM of the red light emitting element 5R shown in the figure changes with time, and the light emitting characteristics (light emitting efficiency) of the red light emitting element 5R are restored by melting the metal halide MHa included in the red light emitting layer 24REM.

[0075] The melting point of the metal halide MHa contained in the red light-emitting layer 24REM is preferably higher than 50°C. In this case, when the temperature of the light-emitting elements 5R, 5G, and 5B including the light-emitting layer rises to about 50°C during the driving of the above-mentioned normal light-emitting element and when the light-emitting element is not driven, for example, when stored at room temperature (25°C), the metal halide MHa contained in the red light-emitting layer 24REM exists in a solid state, and therefore the vapor pressure of the metal halide MHa is as low as possible, so that the volatilization of the metal halide MHa contained in the red light-emitting layer 24REM can be ignored. In this embodiment, for such reasons, GaCl3 with a melting point of 78°C and a band gap Bg of 4.3 eV is used as the metal halide MHa contained in the red light-emitting layer 24REM.

[0076] On the other hand, Figure 7 In the red light-emitting layer 24REM of the red light-emitting element 5R shown after being driven for a specified time, the ligand L1 arranged on the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD is detached due to the passage of time and the current driving stress, so the number of ligands L1 of each red light-emitting quantum dot RQD is reduced. In addition, under the driving conditions of the normal light-emitting element, since the ligand L2 exists in the light-emitting layer in a liquid state, the ligand L2 gradually evaporates over time, and the remaining ligand L2 to compensate for the detached ligand L1 is insufficient. Therefore, the deactivation of the red light-emitting quantum dot RQD caused by the surface defects occurs, it is difficult to ensure the long-term reliability of the red light-emitting element 5R, and it is impossible to avoid the reduction of the luminous characteristics (luminous efficiency) of the red light-emitting layer 24REM containing the red light-emitting quantum dot RQD over time.

[0077] Therefore, if Figure 7 As shown, a process of melting the metal halide MHa contained in the red light-emitting layer 24REM of the red light-emitting element 5R after being driven for a predetermined time is performed. That is, a method for recovering the luminescent characteristics (luminescent efficiency) of the red light-emitting element 5R including the process of melting the metal halide MHa is implemented. In the state of the metal halide MHa in a solid state, the movement of the metal ions M+ and the halogen ions Ha- constituting the metal halide MHa is also small, and the halogen ions Ha- are associated with the surface defects of the red light-emitting quantum dots RQD generated by the detachment of the ligand L1, and the probability of eliminating the surface defects of the red light-emitting quantum dots RQD by the halogen ions Ha- is also low. For such reasons, a process of melting the metal halide MHa contained in the red light-emitting layer 24REM is temporarily performed, and by melting the metal halide MHa and ionizing it, the movement of the halogen ions Ha- is increased, and the surface defects of the red light-emitting quantum dots RQD can be eliminated by the halogen ions Ha-.

[0078] In addition, by performing a process of melting the metal halide MHa contained in the red light-emitting layer 24REM, the ligand L2 contained in the red light-emitting layer 24REM can also be made into a liquid state. Since the metal ions M+ and halogen ions Ha- constituting the metal halide MHa move in the liquid, the probability of eliminating the surface defects of the red light-emitting quantum dots RQD can be further increased.

[0079] Furthermore, when an organic ligand such as oleylamine having a melting point of 50° C. is used as the ligand L1 and the ligand L2, if the temperature of the red light-emitting layer 24REM is increased to melt the oleylamine, the metal halide MHa can be dissolved in the liquid oleylamine (melted), and the metal ions M+ and halogen ions Ha- constituting the metal halide MHa move in the liquid, thereby further increasing the probability of terminating the surface defects of the red light-emitting quantum dots RQD. In addition, the metal halide MHa can be dissolved in the liquid oleylamine without increasing the temperature of the red light-emitting layer 24REM to a temperature at which the metal halide MHa melts.

[0080] In this embodiment, GaCl3 having a melting point of 78°C and a band gap Bg of 4.3 eV is used as the metal halide MHa. Therefore, GaCl3 as the metal halide MHa can be melted at a relatively low temperature of 78°C. Therefore, in the process of melting the metal halide MHa, there is no Figure 7 The hole injection layer 24HI, the hole transport layer 24HT, the ligands L1 and L2 contained in the red light emitting layer 24REM, and the electron transport layer 24ET are thermally damaged.

[0081] In the process of melting the metal halide MHa, the metal halide MHa in a liquid state is ionized into metal ions M+ and halogen ions Ha. - In this embodiment, the metal ion M+ is Ga 3+ , halogen ion Ha - C1 - .

[0082] In addition, the metal halide MHa contained in the red light emitting layer 24REM may also contain Fig.11 Among the various metal halides shown, for example, two or more different metal halides selected from GaCl3, AlBr3, GaBr3, AlI3 and AlCl3. A mixture of two or more metal halides can melt at a lower temperature due to a decrease in the freezing point.

[0083] like Figure 6As shown, the current density of the current flowing between the first electrode 22 and the second electrode 25 respectively provided in the plurality of light emitting elements 5R, 5G, and 5B of the display device 1 is, for example, 100 mA / cm 2 Under the driving condition (driving voltage is, for example, 5 V), the temperature of the light-emitting elements 5R, 5G, and 5B including the light-emitting layer rises to approximately 200°C.

[0084] Figure 1 The scanning-side driving circuit 31 and the data-side driving circuit 32 included in the display device 1 of the present embodiment shown have a mode of performing a step of melting the metal halide MHa.

[0085] The data side driving circuit 32 flows a current at a current density selected within a first current density range between the first electrode 22 and the second electrode 25 of each of the plurality of light emitting elements 5R, 5G, and 5B based on a video signal input from the outside, so that the light emitting layer of each of the plurality of light emitting elements 5R, 5G, and 5B emits light at a brightness corresponding to the selected current density. Furthermore, the melting point of the metal halide MHa is higher than the temperature of the plurality of light emitting elements 5R, 5G, and 5B when the current flows between the first electrode 22 and the second electrode 25 at the selected current density.

[0086] In this embodiment, GaCl3 having a melting point of 78° C. and a band gap Bg of 4.3 eV is used as the metal halide MHa·MHa′·MHa″ contained in the light emitting layer 24 of each color. Figure 6 The relationship between the current density and the temperature of the light emitting element 5R, 5G, 5B is shown in FIG. 1 , and the first current density range is set to a maximum temperature of less than 78° C. Therefore, in the data side driving circuit 32, the first current density range is set to, for example, 0 mA / cm 2 Above and 20mA / cm 2 Next, in the first current density range under the driving conditions (driving voltage is, for example, 5V) of the light-emitting elements for normal display in the display device 1, the maximum temperature of the light-emitting elements 5R, 5G, and 5B is set to be 70° C. or less. Therefore, under the driving conditions of the light-emitting elements for normal display in the display device 1, since the metal halide MHa, MHa', MHa" contained in the light-emitting layer 24 of each color exists in a solid state, the vapor pressure is lowered compared to the liquid state, thereby being able to suppress volatilization.

[0087] Figure 1The data side driving circuit 32 of the display device 1 of the present embodiment shown in the figure further includes a mode for performing the following process: a current is passed between the first electrode 22 and the second electrode 25 respectively provided in the plurality of light emitting elements 5R, 5G, 5B at a current density selected within a second current density range having a value larger than the first current density range, so that the metal halide MHa·MHa'·MHa" of the plurality of light emitting elements 5R, 5G, 5B is melted at a temperature higher than the melting point of the metal halide MHa·MHa'·MHa".

[0088] In this embodiment, GaCl3 having a melting point of 78° C. and a band gap Bg of 4.3 eV is used as the metal halide MHa·MHa′·MHa″ contained in the light emitting layer 24 of each color. Figure 6 The relationship between the current density and the temperature of the light emitting elements 5R, 5G, and 5B is shown in FIG. 1 , and the second current density range is set to a minimum temperature of 78° C. or above. Therefore, in the data side driving circuit 32, the second current density range is set to, for example, 30 mA / cm 2 Above and 100mA / cm 2 Therefore, when the data side driving circuit 32 of the display device 1 is driven in a mode of performing a melting process of the metal halide MHa, MHa', MHa", that is, between the first electrode 22 and the second electrode 25 of each of the plurality of light emitting elements 5R, 5G, 5B, 30 mA / cm 2 When a current having the above current density flows, the metal halides MHa, MHa', and MHa" included in the light-emitting layers of each color can be melted and ionized.

[0089] The setting of the first current density range and the second current density range described above is an example and is not limited thereto, and can be appropriately set in consideration of the melting point of the metal halide MHa·MHa'·MHa" used.

[0090] The above-mentioned mode of melting the metal halides MHa·MHa'·MHa" may be performed once or multiple times during the manufacturing process of the display device 1 or after the user starts using the display device 1.

[0091] As described above, in the present embodiment, the case where a separate process of melting the metal halide MHa·MHa'·MHa" is performed is described as an example, but the present invention is not limited to this. For example, a leakage path is formed in the light-emitting layer in each color light-emitting element of the display device, and even when a large current flows locally in the leakage path, the temperature of the light-emitting layer may rise. It is reported that in the case where silver, which is widely used as a cathode of the light-emitting element, and indium in ITO, which is widely used as an anode, are used as electrode materials, metals such as silver and indium reach the light-emitting layer by diffusion, and a filamentary conduction path formed by the silver, indium, and other metals reaching the light-emitting layer sometimes becomes a leakage path for the light-emitting layer in the light-emitting elements of various colors. In this way, when a filamentary leakage path is formed by the silver, indium, and other metals reaching the light-emitting layer, the filamentary leakage path is melted and interrupted due to the Joule heat of the leakage conduction, and the leakage path of the light-emitting layer disappears. Even in such a case, the metal halide MHa·MHa'·MHa" around the leakage path in the light-emitting layer melts, eliminating the surface defects of the quantum dots QD.

[0092] In the display device, even without performing a separate step of melting the metal halide MHa·MHa'·MHa", as described above, it is sometimes possible to melt the metal halide MHa·MHa'·MHa" around the leakage path in the light-emitting layer to eliminate the surface defects of the quantum dots QD.

[0093] Figure 3 and Figure 5 The manufacturing method of the red light-emitting element 5R shown includes the step of forming a red light-emitting quantum dot RQD containing a ligand L1, a ligand L2, and a red light-emitting layer 24REM of a metal halide MHa. As described above, the red light-emitting layer 24REM may not contain the ligand L2. As described above, as the metal halide MHa, a metal halide having a melting point of 200° C. or less can be suitably used. In the present embodiment, GaCl3 having a melting point of 78° C. and a band gap Bg of 4.3 eV is used.

[0094] In the process of forming the red light-emitting layer 24REM, a quantum dot solution containing red light-emitting quantum dots RQD containing ligand L1, ligand L2, metal halide MHa and solvent is used. For example, the red light-emitting layer 24REM can be formed by dripping the quantum dot solution on the hole transport layer 24HT using a coating or inkjet method. In addition, the red light-emitting quantum dots RQD containing the ligand L1 can be obtained by preparing a quantum dot solution containing quantum dots not containing ligand L1, ligand L1·L2, metal halide MHa and solvent. In addition, the red light-emitting quantum dots RQD containing the ligand L1 can also be obtained by treating quantum dots not containing ligand L1 with the ligand L1 before preparing the above-mentioned quantum dot solution.

[0095] As the solvent, the red light-emitting quantum dots RQD and the metal halide MHa containing the ligand L1 can be dispersed, and the ligand L2 can be dissolved or dispersed. For example, toluene, hexane, octane, etc. can be preferably used. In addition, when the ligands L1 and L2 are organic materials, due to the mixing of the ligand L2 and the metal halide MHa, there may be a situation where both the ligand L2 and the metal halide MHa are dissolved in the solvent.

[0096] Figure 8 This is a cross-sectional view schematically showing the structure of another red light emitting element 5R′ that the display device 1 according to the first embodiment may include.

[0097] Figure 8 The red light emitting element 5R' shown as a reverse stacking structure has a first electrode 22 as a cathode and a second electrode 25 as an anode which is higher than the first electrode 22. The functional layer 24R' including the red light emitting layer 24REM provided between the first electrode 22 as a cathode and the second electrode 25 as an anode can be formed by, for example, sequentially stacking an electron transport layer 24ET, a red light emitting layer 24REM, a hole transport layer 24HT, and a hole injection layer 24H1 from the side of the first electrode 22. In the case of the red light emitting element 5R' as a reverse stacking structure, since it also has a red light emitting layer 24REM including a metal halide MHa, the metal halide MHa is melted and ionized in the same manner as the red light emitting element 5R as the forward stacking structure described above, thereby increasing the movement of the halogen ions Ha-, and the surface defects of the red light emitting quantum dots RQD can be eliminated by the halogen ions Ha-.

[0098] Fig. 9 The diagram shows the energy band levels of the hole transport layer 24HT, the electron transport layer 24ET, the green light-emitting quantum dots GQD, and the metal halide MHa′ included in the green light-emitting element 5G of the display device 1 according to the first embodiment.

[0099] The green light-emitting layer of the green light-emitting element 5G of the display device 1 of the embodiment 1 (not shown) includes: green light-emitting quantum dots GQD containing ligands L1, ligands L2, and metal halide MHa'.

[0100] In this embodiment, the case where the green light-emitting layer includes the ligand L2 is illustrated, but the present invention is not limited thereto. The green light-emitting layer may not include the ligand L2 but include green light-emitting quantum dots GQD including the ligand L1 and the metal halide MHa.

[0101] like Fig. 9As shown, it is preferred to use a metal halide MHa' whose difference between the upper end of the valence band of the metal halide MHa (MHa'(VBM)) and the lower end of the conduction band of the metal halide MHa (MHa'(CBM)), that is, the band gap (MHa'(Bg)) of the metal halide MHa' is greater than the difference between the upper end of the valence band of the green light-emitting quantum dot GQD (GQD(VBM)) and the lower end of the conduction band of the green light-emitting quantum dot GQD (GQD(CBM)), that is, the band gap (GQD(Bg)) of the green light-emitting quantum dot GQD. In this embodiment, an example is given in which the upper end of the valence band of the metal halide MHa' (MHa'(VBM)) is deeper than the upper end of the valence band of the green light-emitting quantum dot GQD (GQD(VBM)), and the lower end of the conduction band of the metal halide MHa (MHa'(CBM)) is shallower than the lower end of the conduction band of the green light-emitting quantum dot GQD (GQD(CBM)), but it is not limited to this. As described above, by using a metal halide MHa' having a band gap greater than the band gap of the green light-emitting quantum dot GQD (GQD(Bg)), current leakage between multiple light-emitting elements generated by the metal halide MHa' can be suppressed. In this embodiment, a green light-emitting quantum dot GQD having an upper end of the valence band (GQD(VBM)) of -5.6 eV, a lower end of the conduction band (GQD(CBM)) of -3.3 eV, and a band gap (GQD(Bg)) of 2.3 eV is used, but it is not limited to this.

[0102] In addition, the metal halide MHa contained in the green light-emitting layer of the green light-emitting element 5G is preferably selected from, for example Fig.11 Among the various metal halides shown, a metal halide MHa' having a band gap (MHa'(Bg)) greater than the band gap of the green light-emitting quantum dot GQD (e.g., GQD(Bg)=2.3eV) and a value smaller than 3 times (e.g., 6.9eV) is selected. By making the band gap of the green light-emitting quantum dot GQD (GQD(Bg)) and the band gap of the halide MHa' (MHa'(Bg)) within a range of less than 3 times, the deterioration of the electrical characteristics of the green light-emitting element 5G can be suppressed.

[0103] In addition, in the present embodiment, as the metal halide MHa' included in the green light-emitting layer of the green light-emitting element 5G, GaCl3 with a melting point of 78°C and a band gap Bg of 4.3 eV is used, which is the same as the metal halide MHa included in the red light-emitting layer 24REM of the red light-emitting element 5R, but it is not limited to this, and it may also be a metal halide different from the metal halide MHa' included in the green light-emitting layer of the green light-emitting element 5G and the metal halide MHa included in the red light-emitting layer 24REM of the red light-emitting element 5R.

[0104] Fig.10 1 is a diagram showing the energy band levels of the hole transport layer 24HT, the electron transport layer 24ET, the blue light-emitting quantum dots BQD, and the metal halide MHa" included in the blue light-emitting element 5B of the display device 1 according to the first embodiment.

[0105] The blue light-emitting layer of the blue light-emitting element 5B of the display device 1 of the embodiment 1 (not shown) includes: blue light-emitting quantum dots BQD containing ligand L1, ligand L2, and metal halide MHa.

[0106] In this embodiment, the case where the blue light-emitting layer includes the ligand L2 is illustrated, but the present invention is not limited thereto. The blue light-emitting layer may not include the ligand L2 but may include blue light-emitting quantum dots BQD including the ligand L1 and the metal halide MHa.

[0107] like Fig.10 As shown, it is preferred to use a metal halide MHa whose band gap (MHa) (Bg) is greater than the difference between the valence band upper end (MHa) (VBM) of the metal halide MHa and the conduction band lower end (MHa) (CBM) of the blue light-emitting quantum dot BQD. In this embodiment, an example is given in which the valence band upper end (MHa) (VBM) of the metal halide MHa is deeper than the valence band upper end (BQD (VBM)) of the blue light-emitting quantum dot BQD, and the metal halide MHa is greater than the band gap (BQD (Bg)) of the blue light-emitting quantum dot BQD. The lower end of the conduction band of the metal halide MHa" (MHa" (CBM)) is shallower than the lower end of the conduction band of the blue light-emitting quantum dot BQD (BQD (CBM)), but it is not limited to this. As described above, by using a metal halide MHa" having a band gap greater than the band gap of the blue light-emitting quantum dot BQD (BQD (Bg)), the current leakage between multiple light-emitting elements generated by the metal halide MHa" can be suppressed. In the present embodiment, a blue light-emitting quantum dot BQD having an upper end of the valence band (BQD (VBM)) of -5.6 eV, a lower end of the conduction band (BQD (CBM)) of -2.8 eV, and a band gap (BQD (Bg)) of 2.8 eV is used, but it is not limited to this.

[0108] As the metal halide MHa" contained in the blue light-emitting layer of the blue light-emitting element 5B of this embodiment, it is more preferable to select from, for example Fig.11Among the various metal halides shown, a metal halide MHa" is selected whose band gap (MHa" (Bg)) is greater than the band gap of the red light-emitting quantum dot BQD (for example, BQD (Bg) = 2.8 eV) and is smaller than 3 times the band gap of the red light-emitting quantum dot BQD (for example, BQD (Bg) = 2.8 eV) (for example, 8.4 eV). By making the band gap of the blue light-emitting quantum dot BQD (BQD (Bg)) and the band gap of the halide MHa" (MHa' (Bg)) within a range of less than 3 times, the deterioration of the electrical characteristics of the blue light-emitting element 5B can be suppressed.

[0109] In addition, in the present embodiment, as the metal halide MHa" included in the blue light-emitting layer of the blue light-emitting element 5B, GaCl3 having the same melting point of 78°C and band gap Bg of 4.3 eV as the metal halide MHa included in the red light-emitting layer 24REM of the red light-emitting element 5R and the metal halide MHa' included in the green light-emitting layer of the green light-emitting element 5G is used, but the present invention is not limited to this, and the metal halide MHa" included in the blue light-emitting layer of the blue light-emitting element 5B, the metal halide MHa included in the red light-emitting layer 24REM of the red light-emitting element 5R, and the metal halide MHa' included in the green light-emitting layer of the green light-emitting element 5G may also be different metal halides.

[0110] In the above-mentioned present embodiment, the case where each color light-emitting layer possessed by each color light-emitting element 5R, 5G, and 5B of the display device 1 respectively includes the corresponding quantum dots containing the ligand L1, the ligand L2, and the metal halide is illustrated as an example, but it is not limited to this. It can also be set as a light-emitting layer of a specific color among the various color light-emitting layers possessed by the various color light-emitting elements 5R, 5G, and 5B of the display device 1. For example, only the red light-emitting layer includes the corresponding quantum dots containing the ligand L1, the ligand L2, and the metal halide, and the remaining green light-emitting layer and the blue light-emitting layer do not contain metal halides, but contain the corresponding quantum dots of the ligand L1 and the ligand L2.

[0111] According to the above-mentioned light-emitting elements 5R, 5R'·5G·5B, display device 1, manufacturing method of light-emitting elements 5R·5R'5G·5B, and method of restoring the light-emitting characteristics of light-emitting elements 5R·5R'·5G·5B, it is possible to improve the long-term reliability of the light-emitting layer containing quantum dots and restore the reduced light-emitting characteristics (light-emitting efficiency).

[0112] [Implementation method 2] Next, based on Figures 12 to 15Embodiment 2 of the present disclosure is described. In the red light-emitting element 5R" included in the display device of the present embodiment, the red light-emitting layer 24REM' is different from the light-emitting elements of each color included in the display device 1 described in Embodiment 1 in that it includes a quantum dot layer and a metal halide layer MHa1·MHa2, wherein the quantum dot layer includes red light-emitting quantum dots RQD containing ligands L1 and ligands L2, and the metal halide layer MHa1 includes one or more layers of metal halide MHa. Other than that, it is as described in Embodiment 1. For the sake of convenience of description, components having the same functions as those shown in the drawings of Embodiment 1 are marked with the same figure marks, and their descriptions are omitted.

[0113] Fig.12 This is a cross-sectional view showing a schematic structure of a red light emitting element 5R" included in the display device of Embodiment 2. Fig.12 The red light emitting element 5R" shown represents a red light emitting element in an initial state before being driven or after a relatively short driving time.

[0114] like Fig.12 As shown, the red light-emitting layer 24REM' of the red light-emitting element 5R" includes: a quantum dot layer, including red light-emitting quantum dots RQD containing ligands L1 and ligands L2; ​​a metal halide layer MHa1, including a metal halide MHa arranged as a lower layer of the quantum dot layer; and a metal halide layer MHa2, including a metal halide MHa arranged as an upper layer of the quantum dot layer.

[0115] In this embodiment, the case where the quantum dot layer of the red light emitting layer 24REM' includes the ligand L2 is taken as an example for description, but the present invention is not limited thereto, and the quantum dot layer of the red light emitting layer 24REM' may not include the ligand L2.

[0116] In addition, in this embodiment, the case where the red light-emitting layer 24REM' includes two metal halide layers MHa1 and metal halide layers MHa2 is illustrated, but it is not limited to this. It may also include only one of the two metal halide layers MHa1 and the metal halide layer MHa2, or more than two metal halide layers including metal halide MHa may be stacked on at least one of the upper layer and the lower layer of the quantum dot layer.

[0117] In addition, in this embodiment, an example is given in which the metal halide MHa contained in the metal halide layer MHa1 and the metal halide MHa contained in the metal halide layer MHa2 are the same metal halide, but the present invention is not limited to this. The metal halide MHa contained in the metal halide layer MHa1 and the metal halide MHa contained in the metal halide layer MHa2 may also be different metal halides.

[0118] In this embodiment, similar to the above-mentioned embodiment 1, the case of using GaCl3 with a melting point of 78°C and a band gap Bg of 4.3 eV as the metal halide MHa, and using trioctylphosphine (TOP) with a melting point of 30°C and a boiling point of 234°C as the ligand L1 and the ligand L2 is taken as an example for explanation, but is not limited to this.

[0119] Fig.13 It shows that Fig.12 1 is a diagram showing energy band levels of the hole transport layer 24HT, the electron transport layer 24ET, the red light-emitting quantum dots RQD of the ligand L1, and the metal halide layers MHa1·MHa2 containing the metal halide MHa, which are included in the red light-emitting element 5R″ shown in FIG.

[0120] like Fig.13 As shown, it is preferred to use a metal halide MHa1·MHa2 whose difference between the upper end of the valence band (MHa1(VBM)·MHa2(VBM)) of the metal halide MHa1·MHa2 and the lower end of the conduction band (MHa1(CBM)·MHa2(CBM)) of the metal halide MHa, that is, the band gap (MHa1(Bg)·MHa2(Bg)) of the metal halide MHa is greater than the difference between the upper end of the valence band (RQD(VBM)) of the red light-emitting quantum dot RQD and the lower end of the conduction band (RQD(CBM)) of the red light-emitting quantum dot RQD, that is, the band gap (MHa2(Bg)) of the red light-emitting quantum dot RQD. In this embodiment, an example is given in which the upper end of the valence band of the metal halide MHa1·MHa2 (MHa1(VBM)·MHa2(VBM)) is deeper than the upper end of the valence band of the red light-emitting quantum dot RQD (RQD(VBM)), and the lower end of the conduction band of the metal halide MHa1·MHa2 (MHa1(CBM)·MHa2(CBM)) is shallower than the lower end of the conduction band of the red light-emitting quantum dot RQD (RQD(CBM)), but it is not limited to this. As described above, by using a metal halide MHa1·MHa2 having a band gap greater than the band gap of the red light-emitting quantum dot RQD (RQD(Bg)), current leakage between multiple light-emitting elements generated by the metal halide MHa1·MHa2 can be suppressed.

[0121] Fig.14 It is shown Fig.12 4 is a graph showing the temporal change of the red light emitting layer 24REM' after the red light emitting element 5R" is driven for a predetermined time.

[0122] and Fig.12 Compared with the red light emitting layer 24REM' of the red light emitting element 5R" in the initial state shown in FIG. Fig.14In the red light-emitting layer 24REM' of the red light-emitting element 5R" shown after being driven for a predetermined time, as time passes and the current driving pressure increases, the ligand L1 arranged on the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD is detached, so the number of ligands L1 per red light-emitting quantum dot RQD decreases. Originally, the ligand L2 plays a role in compensating for the ligand L1 detached from the surface of the red light-emitting quantum dot RQD or near the surface of the red light-emitting quantum dot RQD. As described above, under the normal driving conditions of the light-emitting element, the ligand L2 exists in the light-emitting layer in a liquid state. Therefore, as time passes, Fig.12 The ligand L2 shown gradually volatilizes, and the remaining ligand L2 is insufficient to compensate for the detached ligand L1. Therefore, the deactivation of the red light-emitting quantum dots RQD due to surface defects occurs, making it difficult to ensure the long-term reliability of the red light-emitting element 5R", and it is unavoidable that the luminescent properties (luminescent efficiency) of the quantum dot layer 24 containing the red light-emitting quantum dots RQD decrease over time.

[0123] Fig.15 is shown relative to Fig.14 The red light emitting layer 24REM' of the red light emitting element 5R" shown in the figure shows a state where the light emitting characteristics (light emitting efficiency) of the red light emitting element 5R" are restored by melting the metal halide MHa1 and the metal halide MHa2 contained in the red light emitting layer 24REM'.

[0124] Therefore, if Fig.15 As shown, a process is performed to melt the metal halide MHa1 and the metal halide MHa2 contained in the red light-emitting layer 24REM' of the red light-emitting element 5R" after being driven for a specified time. That is, a method for recovering the luminous characteristics (luminous efficiency) of the red light-emitting element 5R" is implemented, including the process of melting the metal halide MHa. The process of melting the metal halide layer MHa1 and the metal halide layer MHa2 is the same as the process of melting the above-mentioned metal halide MHa in embodiment 1, and therefore its description is omitted here.

[0125] form Fig.12 The process of forming the red light-emitting layer 24REM' shown includes: forming a quantum dot layer of red light-emitting quantum dots RQD containing ligand L1 and ligand L2; and forming a metal halide layer MHal·MHa2 containing metal halide MHa using a metal halide solution containing metal halide MHa and a solvent.

[0126] In this embodiment, for example, after a metal halide layer MHa1 containing metal halide MHa is formed on the hole transport layer 24HT, a quantum dot layer containing red light-emitting quantum dots RQD of ligand L1 and ligand L2 is formed, and then a metal halide layer MHa2 containing metal halide MHa is formed to form a red light-emitting layer 24REM'.

[0127] According to the above-mentioned light-emitting element 5R", the display device including the light-emitting element 5R", the manufacturing method of the light-emitting element 5R" and the method of recovering the light-emitting characteristics of the light-emitting element 5R", it is possible to improve the long-term reliability of the light-emitting layer including quantum dots and recover the reduced light-emitting characteristics (light-emitting efficiency).

[0128] [Implementation method 3] Next, based on Fig.16 and Fig.17 Embodiment 3 of the present invention will be described. The display device 1a of this embodiment is different from the display devices described in Embodiments 1 and 2 in that it includes a heating unit 33 for the process of melting the metal halide MHa. Other than that, it is the same as described in Embodiments 1 and 2. For the sake of convenience, components having the same functions as those shown in the drawings of Embodiments 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0129] Fig.16 It is a plan view showing a schematic configuration of a display device 1 a according to a third embodiment.

[0130] Fig.17 It is shown Fig.16 FIG. 2 is a diagram showing a heating unit 33 included in a display device 1 a according to a third embodiment.

[0131] like Fig.17 As shown, the display device 1a includes a heating unit 33 for performing a step of melting the metal halide MHa.

[0132] In this embodiment, since the display device 1a also has a heating unit 33 for performing a process of melting the metal halide MHa, the case where the scanning side driving circuit 31a and the data side driving circuit 32a do not have a process mode for melting the metal halide MHa is taken as an example for explanation, but it is not limited to this and may also have a mode for performing the process of melting the metal halide MHa in the same way as in embodiments 1 and 2.

[0133] like Fig.17 As shown, the heating unit 33 only needs to heat the region including the metal halide MHa, and therefore, may be provided to overlap only the display region DA of the display panel 30 , but the present invention is not limited thereto.

[0134] When the heating unit 33 is additionally provided as in the display device 1a, the temperature of the light emitting element can be easily raised to a relatively high temperature compared to the method of controlling the temperature of the light emitting element by changing the current density in the first and second embodiments.

[0135] In addition, when a heating unit 33 is separately provided as in the display device 1a, the step of melting the metal halide MHa can be performed even before forming the second electrode 25 of the light emitting element. Figure 3 After the electron transport layer 24ET is formed on the red light emitting layer 24REM included in the red light emitting element 5R shown, the step of melting the metal halide MHa can be performed. That is, the step of melting the metal halide MHa can be performed in the manufacturing process of the light emitting element.

[0136] In addition, when a heating unit 33 for performing a step of melting the metal halide MHa is separately provided as in the display device 1a, the display panel 30 may be used as long as the heat resistance of the display panel 30 can be ensured. Fig.11 Among the various metal halides shown, those having a melting point exceeding 200°C.

[0137] For example, by changing the organic layer included in the display panel 30 to an inorganic layer and omitting the organic layer that can be omitted, the heat resistance of the display panel 30 can be ensured. For example, the hole injection layer 24HI included in the light-emitting element is omitted, the hole transport layer 24HT is formed of NiO particles, the electron transport layer 24ET is formed of ZnO particles, and the ligand L1 included in the quantum dot is an inorganic ligand (such as a halogen ligand). By omitting the ligand L2, the heat resistance of the light-emitting element can be ensured.

[0138] On the other hand, as the metal halide MHa·MHa'·MHa", it is preferred to use a metal halide having a melting point of 130°C or less, and it is further preferred to use a metal halide having a melting point of 100°C or less. When using a metal halide MHa·MHa'·MHa" having a melting point of 130°C or less, the process of melting the metal halide MHa·MHa'·MHa" can be performed at a temperature below 130°C. Usually, the highest temperature reached in the element formation process is mostly below the boiling point of an organic solvent (for example, octane, chlorobenzene, toluene, etc.), that is, 130°C, and the process of melting the metal halide MHa·MHa'·MHa" is also performed at a temperature below 130°C, thereby suppressing adverse effects on various elements of the display device. In addition, when using a metal halide MHa·MHa'·MHa" having a melting point of 100°C or less, the process of melting the metal halide MHa·MHa'·MHa" can be performed at a temperature below 100°C. Therefore, when the step of melting the metal halide MHa·MHa'·MHa" can be performed at 100° C. or lower, adverse effects on other electronic components and the like included in the display device can be suppressed.

[0139] [Additional Notes] The present disclosure is not limited to the above-mentioned embodiments, and various changes can be made within the scope indicated by the claims. The embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical methods disclosed in each embodiment. Industrial Applicability

[0140] The present invention discloses a light emitting element, a display device, a method for manufacturing a light emitting element, and a method for recovering the light emitting characteristics of a light emitting element. Description of Reference Numerals

[0141] 1.1a Display device 3 Barrier layer 4 Thin Film Transistor Layer 5R, 5R', 5R" red light emitting element (light emitting element) 5G green light emitting element (light emitting element) 5B blue light emitting element (light emitting element) 12 substrates 221 first electrode 24R, 24R', 24R" including functional layers of red light emitting layer 24G contains the functional layer of green light emitting layer 24B Functional layer including blue light emitting layer 24HI hole injection layer 24HT hole transport layer 24REM, 24REM' red luminous layer (luminous layer) 24ET electron transport layer 25 second electrode 30 Display Panel 31. 31a Scanning side driving circuit 32, 32a Data side driving circuit (driving circuit) 33 Heating unit PIX RSUB second red sub-pixel GSUB second green subpixel BSUB second blue sub-pixel DA display area NDA border area RQD Red Luminescent Quantum Dots (Quantum Dots) GQD Green Luminescent Quantum Dots (Quantum Dots) BQD Blue Luminescent Quantum Dots (Quantum Dots) L1, L2 ligands MHa, MHa', MHa" Metal Halide Mha1 metal halide layer Mha2 metal halide layer M+, Ha- molten metal halide Bg band gap Lower end of CBM conduction band Upper end of VBM valence band

Claims

1. A light emitting element, characterized in that: include: a first electrode; a second electrode; as well as a light-emitting layer disposed between the first electrode and the second electrode, The light-emitting layer includes quantum dots and a metal halide with a melting point of 200° C. or less.

2. The light emitting element according to claim 1, characterized in that The light emitting layer is a layer in which the quantum dots and the metal halide are mixed in one layer.

3. The light emitting element according to claim 1, wherein: The light-emitting layer comprises: a quantum dot layer comprising the quantum dots; and The metal halide layer contains more than one layer of the metal halide.

4. The light emitting element according to any one of claims 1 to 3, characterized in that: The light-emitting layer contains an organic ligand having a melting point of 50° C. or less.

5. The light emitting element according to any one of claims 1 to 4, characterized in that: The band gap of the metal halide is greater than the band gap of the quantum dot.

6. The light emitting element according to claim 5, characterized in that The band gap of the metal halide is less than 3 times the band gap of the quantum dot.

7. The light emitting element according to any one of claims 1 to 6, characterized in that: The metal halide has a band gap of 3.4 eV or more and 5.3 eV or less.

8. The light emitting element according to any one of claims 1 to 7, characterized in that: The melting point of the metal halide is higher than 50°C.

9. The light emitting element according to any one of claims 1 to 8, characterized in that: The light emitting layer includes the metal halide and a second metal halide of a different type from the metal halide.

10. The light emitting element according to any one of claims 1 to 9, characterized in that: Between the first electrode and the second electrode, 30 mA / cm 2 Current flows at a current density above 100%.

11. A display device, characterized in that: A display panel and a driving circuit are included, wherein the display panel includes the light-emitting element according to any one of claims 1 to 9, The driving circuit flows a current at a current density selected within a first current density range between the first electrode and the second electrode based on an image signal input from the outside, so that the light-emitting layer emits light at a brightness corresponding to the selected current density. The melting point of the metal halide is higher than the temperature of the light emitting element when a current flows between the first electrode and the second electrode at the selected current density.

12. The display device according to claim 11, characterized in that: The driving circuit causes a current to flow between the first electrode and the second electrode at a current density selected in a second current density range, wherein the second current density range has a value greater than the first current density range, so that the temperature of the light-emitting element is higher than the melting point of the metal halide.

13. A display device, comprising: A display panel comprising the light emitting element according to any one of claims 1 to 9; as well as A heating unit that makes the temperature of the light emitting element higher than the melting point of the metal halide.

14. A method for manufacturing a light-emitting element, comprising the step of forming a light-emitting layer, wherein the light-emitting layer contains quantum dots and a metal halide having a melting point of 200°C or less.

15. The method for manufacturing a light emitting element according to claim 14, characterized in that: In the step of forming the light-emitting layer, the light-emitting layer is formed using a quantum dot solution including the quantum dots, the metal halide, and a solvent.

16. The method for manufacturing a light emitting element according to claim 14, wherein: The process of forming the light-emitting layer includes: A process of forming a quantum dot layer containing the quantum dots; and A step of forming a metal halide layer containing the metal halide using a metal halide solution containing the metal halide and a solvent.

17. The method for manufacturing a light emitting element according to any one of claims 14 to 16, characterized in that: The method further includes the step of melting the metal halide. 18 . A method for recovering the light emitting characteristics of a light emitting element, the light emitting element being a light emitting element manufactured by the method for manufacturing a light emitting element according to any one of claims 14 to 17, the recovery method comprising a step of melting the metal halide.

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