Method for manufacturing light-emitting element and light-emitting element

Abstract

A method for manufacturing a light-emitting element includes: a step for forming a light-emitting layer containing quantum dots; forming an intermediate layer on the light-emitting layer, the intermediate layer containing a metal halide having a solubility in water at 25 DEG C of 2.5 mg / 100 g or more; and a step for forming a carrier transport layer on the intermediate layer. The step for forming the carrier transport layer includes: a step for applying a carrier transport material dispersion containing a carrier transport material and a first solvent on the intermediate layer; and a step for removing the first solvent.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a light emitting element and a light emitting element. Background Art

[0002] For the purpose of protecting the quantum dots and improving the dispersibility of the solvent, a ligand (modifying group) is usually provided on the surface of the quantum dots. As the above-mentioned ligand, organic ligands are usually used because the dispersibility of the quantum dots in the quantum dot dispersion is excellent. However, in the charge (carrier) injection type light-emitting element containing quantum dots in the light-emitting layer, the organic ligand of the insulating organic material used will become an obstacle to the carrier injection.

[0003] Therefore, in recent years, inorganic ligands have attracted attention as ligands to replace organic ligands. Inorganic ligands are more stable than organic ligands and have excellent carrier injection properties. For example, Patent Document 1 discloses a stable quantum dot composition, which includes quantum dots and fluoride ligands such as ZnF2 that are bound to the surface of the quantum dots by ligand replacement of organic ligands on the surface of the quantum dots. Prior art literature Patent Literature

[0004] Patent Document 1: Japanese International Publication No. 2020-180278 Summary of the invention Technical Problems to be Solved by the Invention

[0005] When an electron transport layer containing, for example, ZnO nanoparticles as a carrier transport material is stacked on a light-emitting layer containing quantum dots as a carrier transport layer, alcohol is used as a solvent in a carrier transport material dispersion liquid which is a coating liquid containing the above-mentioned carrier transport material and is used to form the carrier transport layer.

[0006] However, some metal halides such as ZnF2 have very low solubility in solvents such as alcohols used to form such carrier transport layers. When the quantum dots have Zn-F bonds on the surface, as in the case of using ZnF2 ligands as inorganic ligands, the surface tension of the surface of the light-emitting layer containing the quantum dots is less than the surface tension of the solvent used to form the carrier transport layer stacked on the light-emitting layer. Therefore, the light-emitting layer containing quantum dots in which fluorine ligands such as ZnF2 have been ligand-substituted has poor wettability with a dispersion of a carrier transport material used to form a carrier transport layer stacked on the light-emitting layer. As a result, the thickness of the carrier transport layer formed on the light-emitting layer becomes uneven, and the element characteristics or reliability of the light-emitting element are reduced.

[0007] In particular, if a sufficient amount of fluorine substitution is to be obtained, the wettability of the carrier transport material dispersion liquid is further reduced due to the metal halide layer composed of the remaining fluorine ligand (in other words, the remaining metal halide). In this case, the thickness of the carrier transport layer formed on the light-emitting layer becomes further non-uniform, and the device characteristics or reliability of the light-emitting element are further reduced.

[0008] On the other hand, as mentioned above, organic ligands may become an obstacle to carrier injection. Therefore, in order to facilitate carrier injection, if only ligand removal is performed to replace ligand replacement, the physical properties of the quantum dot are obvious. In this way, if the surface of the quantum dot without ligands is in direct contact with the dispersion of carrier transport material, the wettability of the dispersion of carrier transport material to the light-emitting layer may arise. In addition, if the surface of the quantum dot without ligands is exposed, the luminous efficiency may be reduced. Therefore, it is preferred that ligands exist on the surface of the quantum dot, but in the case of stacking a carrier transport layer on the light-emitting layer containing quantum dots, the above-mentioned problems exist.

[0009] One aspect of the present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a method for manufacturing a light-emitting element and such a light-emitting element, which can improve the wettability of the carrier transport material dispersion to the light-emitting layer, and can manufacture a light-emitting element with good layer thickness uniformity, excellent light-emitting characteristics and reliability. Technical solutions for solving technical problems

[0010] In order to solve the above-mentioned problems, a method for manufacturing a light-emitting element according to one embodiment of the present disclosure includes: a step of forming a light-emitting layer; a step of forming an intermediate layer on the light-emitting layer, the intermediate layer comprising a first metal halide; and a step of forming a carrier transport layer on the intermediate layer, the step of forming the carrier transport layer including: a step of coating a carrier transport material dispersion on the intermediate layer, the carrier transport material dispersion comprising a carrier transport material and a first solvent; and a step of removing the first solvent, in the step of forming the intermediate layer, an intermediate layer is formed, the intermediate layer comprising a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. as the first metal halide, and in the step of forming the light-emitting layer, as the light-emitting layer, (1) a light-emitting layer comprising quantum dots and a second metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. is formed, or (2) a light-emitting layer comprising the quantum dots and having no organic ligand is formed.

[0011] In order to solve the above-mentioned problems, a method for manufacturing a light-emitting element according to one embodiment of the present invention comprises: a step of forming a light-emitting layer; and a step of forming a carrier transport layer on the light-emitting layer, wherein the step of forming the carrier transport layer comprises: a step of applying a carrier transport material dispersion on the light-emitting layer, wherein the carrier transport material dispersion contains a carrier transport material, a first solvent and a first metal halide; and a step of removing the first solvent, wherein in the step of applying the carrier transport material dispersion, as the first metal halide, a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. is used, and in the step of forming the light-emitting layer, as the light-emitting layer, (1) a light-emitting layer containing quantum dots and a second metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. is formed, or (2) a light-emitting layer containing the quantum dots and having no organic ligand is formed.

[0012] In order to solve the above-mentioned problems, a light-emitting element of one embodiment of the present invention has a light-emitting layer, wherein the light-emitting layer includes quantum dots and a first metal halide, (1) an intermediate layer including the first metal halide and a carrier transport layer including a carrier transport material are arranged adjacent to each other in sequence from the light-emitting layer side, or (2) on the light-emitting layer, a carrier transport layer including a carrier transport material and the first metal halide is arranged adjacent to the light-emitting layer, and the solubility of the first metal halide in water at 25°C is not less than 2.5 mg / 100 g. Beneficial Effects

[0013] According to one embodiment of the present disclosure, a method for manufacturing a light-emitting element and such a light-emitting element can be provided, which can improve the wettability of a carrier transport material dispersion liquid to a light-emitting layer, and can manufacture a light-emitting element with good layer thickness uniformity, excellent light-emitting characteristics and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flowchart showing an example of a method for manufacturing the light emitting element according to the first embodiment. Figure 2 It is a cross-sectional view schematically showing the structure of the light emitting element according to the first embodiment. Figure 3 Yes means Figure 2 A cross-sectional view schematically showing the structure of a quantum dot in a light-emitting element. Figure 4 Yes means Figure 2 Another cross-sectional view schematically showing the structure of quantum dots in a light-emitting element. Figure 5 Yes means Figure 1 A flow chart showing an example of a light emitting layer forming process is shown. Figure 6 Yes means Figure 1 FIG. 1 is a flow chart of another example of the light emitting layer forming process shown in FIG. Figure 7 Yes means Figure 1 2 is a cross-sectional view schematically showing the configuration of the main parts in the intermediate layer forming step and the electron transport layer forming step. Figure 8 This is an energy band diagram for explaining the electron injection blocking layer when there is no metal halide between the shell of the quantum dot and the electron transport layer. Fig. 9 This is an energy band diagram for explaining the electron injection blocking layer when a metal halide is present between the shell of a quantum dot and the electron transport layer. Fig.10 This is a table showing the band gaps of major metal halides and their solubility in water at 25°C. Fig.11 This is a diagram showing the energy levels of each layer of a light-emitting element using blue quantum dots and having a metal halide band gap of about 4.4 eV. Fig.12 This is a diagram showing the energy levels of each layer of a light-emitting element using red quantum dots and having a metal halide band gap of about 5.2 eV. Fig.13 This is a cross-sectional view showing an example of a schematic configuration of a light emitting element according to Modification 1 of the first embodiment. Fig.14 This is a flowchart showing an example of a method for manufacturing a light emitting element according to Modification 1 of the first embodiment. Fig.15 This is a flowchart showing an example of a method for manufacturing a light emitting element according to Modification 2 of the first embodiment. Fig.16 This is a flowchart showing another example of the light emitting layer forming step according to Modification 2 of the first embodiment. Fig.17 This is a flowchart showing an example of a method for manufacturing the light emitting element according to the second embodiment. Fig.18 It is a cross-sectional view schematically showing the structure of a light emitting element according to the second embodiment. Fig.19 This is a flowchart showing an example of a method for manufacturing a light emitting element according to Modification 1 of the second embodiment. Fig. 20 This is a flowchart showing an example of a method for manufacturing a light emitting element according to Modification 2 of the second embodiment. DETAILED DESCRIPTION

[0015] Hereinafter, one embodiment of the present disclosure will be described in detail. Hereinafter, a layer formed by a process before the layer of the comparison object is referred to as a "lower layer", and a layer formed by a process after the layer of the comparison object is referred to as an "upper layer". In the following description, the description of "A to B" for two numbers A and B means "Above A and Below B" unless otherwise specified.

[0016] [First embodiment] based on Figure 1-Figure 16 An embodiment of the present invention is described as follows. In addition, in this embodiment, a method for manufacturing a light-emitting element is described, in which an intermediate layer containing a metal halide (first metal halide) and a carrier transport layer containing a carrier transport material are arranged adjacent to each other in sequence from the above-mentioned light-emitting layer side (i.e., the lower layer side) on the light-emitting layer. The light-emitting element disclosed in the present invention is a quantum dot light-emitting diode (QLED) using quantum dots as the light-emitting material in the light-emitting layer. In the present disclosure, the layer between the light-emitting layer and the carrier transport layer is referred to as an intermediate layer.

[0017] The method for manufacturing a light-emitting element of this embodiment includes: a step of forming a light-emitting layer; a step of forming an intermediate layer containing a first metal halide on the light-emitting layer; a step of forming a carrier transport layer on the intermediate layer, wherein the step of forming the carrier transport layer includes: a step of coating the intermediate layer with a carrier transport material dispersion containing a carrier transport material and a first solvent; and a step of removing the first solvent. In the step of forming the intermediate layer, an intermediate layer containing a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. is formed as the first metal halide, and in the step of forming the light-emitting layer, a light-emitting layer containing (1) quantum dots and a second metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. is formed as the light-emitting layer, or (2) a light-emitting layer containing the quantum dots and having no organic ligand is formed. In addition, in the present invention, solubility refers to the saturated dissolved weight of the metal halide monomer at 25° C.

[0018] Hereinafter, an example is given in which, in the process of forming the above-mentioned light-emitting layer, a light-emitting layer including quantum dots and the above-mentioned second metal halide is formed as the above-mentioned light-emitting layer. In addition, the following example is given in which the carrier transport layer formed on the intermediate layer is an electron transport layer. In addition, the following example is given as an example for explanation, and the above-mentioned light-emitting element has a conventional structure in which the anode is used as the lower electrode and the cathode is used as the upper electrode, and a hole injection layer, a hole transport layer, a light-emitting layer, an intermediate layer, and an electron transport layer are provided between the anode and the cathode as functional layers. In addition, in the present disclosure, the layers between the anode and the cathode are collectively referred to as functional layers.

[0019] However, the light-emitting element of the present embodiment is not limited thereto, and for example, may have an inverted structure in which the cathode is used as the lower electrode and the anode is used as the upper electrode. In addition, as described above, in the case where the carrier transport layer formed on the above-mentioned intermediate layer of the light-emitting element of the present embodiment is an electron transport layer, on the light-emitting layer, the above-mentioned intermediate layer and the above-mentioned electron transport layer are sequentially arranged adjacent to each other from the above-mentioned light-emitting layer side. Therefore, in the case where the carrier transport layer formed on the above-mentioned intermediate layer is an electron transport layer, a hole injection layer and a hole transport layer may be provided, or may not be provided. Therefore, the above-mentioned light-emitting element may have a configuration in which at least one of the hole injection layer and the hole transport layer is not provided, or may have a configuration in which a functional layer other than the above-mentioned functional layer is provided between the anode and the cathode.

[0020] Hereinafter, the light-emitting layer may be referred to as “EML”, the carrier transport layer may be referred to as “CTL”, the electron transport layer may be referred to as “ETL”, the hole transport layer may be referred to as “HTL”, the hole injection layer may be referred to as “HIL”, and the intermediate layer may be referred to as “IL”. In addition, the quantum dot may be referred to as “QD”.

[0021] Figure 1 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to the present embodiment. Figure 2 It is a cross-sectional view showing a schematic structure of the light emitting element 1 according to the present embodiment. Figure 3 Yes means Figure 2 A cross-sectional view schematically showing the structure of QD 21 in the light-emitting element 1 shown. Figure 4 Yes means Figure 2 Another cross-sectional view schematically showing the structure of QD 21 in light-emitting element 1 is shown.

[0022] like Figure 2 As shown, the light emitting element 1 of this embodiment has, as an example, a configuration in which an anode 2, HIL 11, HTL 12, EML 13, IL 14, ETL 15, and a cathode 3 are sequentially provided from the lower layer side (for example, the side of a support body not shown such as a substrate). Each layer from the anode 2 to the cathode 3 is usually supported by a substrate as a support body. In addition, although illustration and description are omitted, the light emitting element 1 may also include a functional layer not shown in the figure other than the HIL 11, HTL 12, EML 13, IL 14, and ETL 15 between the anode 2 and the cathode 3.

[0023] In the method for manufacturing the light emitting element 1 of this embodiment, Figure 1 as well as Figure 2As shown, first, an anode 2 is formed as a lower electrode on a substrate not shown in the figure (step S1, lower electrode forming step, anode forming step). Then, HIL11 is formed (step S2, hole injection layer forming step). Then, HTL12 is formed (step S3, hole transport layer forming step). Next, EML13 is formed containing QD21 and a metal halide 22 (second metal halide, inorganic ligand) having a solubility of less than 2.5 mg / 100 g in water at 25°C (step S4, light-emitting layer forming step). Next, IL14 of a metal halide 31 (first metal halide) having a solubility of more than 2.5 mg / 100 g in water at 25°C is formed on EML13 (step S5, intermediate layer forming step). Next, ETL15 is formed on IL14 (step S6, carrier transport layer forming step, electron transport layer forming step). In step S6, as Figure 1 As shown, first, a carrier transport material dispersion containing a carrier transport material 41 and a solvent (first solvent) is applied on IL14 to form a coating film of the carrier transport material dispersion (step S6a, carrier transport material dispersion coating step). Next, the coating film is heated to remove the solvent contained in the coating film, that is, the solvent (first solvent) contained in the applied carrier transport material dispersion (step S6b, first solvent removal step). Thus, ETL15 containing the carrier transport material 41 is formed on IL14. Next, a cathode 3 is formed on ETL15 as an upper electrode (step S7, upper electrode forming step, cathode forming step). Thus, Figure 2 The light emitting element 1 shown is described in more detail below.

[0024] The anode 2 is an electrode containing a conductive material and supplying holes (holes) to the EML 13 by applying a voltage. The cathode 3 is an electrode containing a conductive material and supplying electrons to the EML 13 by applying a voltage. At least one of the anode 2 and the cathode 3 is a light-transmitting electrode. In addition, either the anode 2 or the cathode 3 may be a so-called reflective electrode having light reflectivity. The light-emitting element 1 can extract light from the light-transmitting electrode side.

[0025] For example, when the light emitting element 1 is a top emission type light emitting element that radiates light from the upper electrode side, a light-transmitting electrode is used as the upper electrode, and a reflective electrode is used as the lower electrode. On the other hand, when the light emitting element 1 is a bottom emission type light emitting element that radiates light from the lower electrode side, a light-transmitting electrode is used as the lower electrode, and a reflective electrode is used as the lower electrode.

[0026] The light-transmitting electrode is formed of a conductive light-transmitting material such as ITO (indium tin oxide), IZO (indium zinc oxide), AgNW (silver nanowire), a thin film of MgAg (magnesium-silver) alloy, or a thin film of Ag.

[0027] On the other hand, the reflective electrode is formed of a conductive light reflective material such as a metal such as Ag, Al, Cu, or an alloy containing these metals. Alternatively, the reflective electrode may be formed by laminating a layer composed of the above light-transmitting material and a layer composed of the above light-reflective material.

[0028] In the formation of the anode 2 in step S1 and the formation of the cathode 3 in step S5, for example, a vapor deposition method, a sputtering method, etc. are used. The anode 2 can be formed by forming a film of the above-mentioned conductive material on a substrate (not shown) by a vapor deposition method or a sputtering method. Similarly, the cathode 3 can be formed by forming a film of the above-mentioned conductive material on the ETL 15 by a vapor deposition method or a sputtering method.

[0029] The HIL 11 is a layer having hole transport properties and promoting hole injection from the anode 2 to the HTL 12. The material of the HIL 11 uses a hole transport material such as a compound of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrenesulfonic acid (PSS) (PEDOT:PSS). In forming the HIL 11, any method such as a spin coating method or an ink jet method can be appropriately selected.

[0030] The HTL 12 is a layer having a hole transport property and transports holes from the HIL 11 to the EML 13 . The materials of HTL12 include, for example, TFB (Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)]), p-TPD (Poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine]), PVK (polyvinylcarbazole), NiO, WO, Mo3 and other hole transport materials. For the formation of HTL12, any method such as spin coating and inkjet can be appropriately selected.

[0031] As described above, the light emitting element 1 is a QLED, and the EML 13 is a QD light emitting layer including QD 21 as a light emitting material. The EML 13 includes QD 21, a metal halide 22 (a second metal halide) having a solubility of less than 2.5 mg / 100 g in water at 25°C, and a metal halide 31 (a first metal halide) having a solubility of 2.5 mg / 100 g or more in water at 25°C. The EML 13 includes nano-sized QD 21 as a light emitting material corresponding to the light emitting color.

[0032] In the EML 13 , holes transferred from the anode 2 and electrons transferred from the cathode 3 are recombined, and light is emitted in the process in which excitons generated thereby are transferred from the conduction band energy level to the valence band energy level of the QD 21 .

[0033] QD21 is a point where the maximum width of a particle is below 100 nm. Generally speaking, since the composition of QD21 is derived from a semiconductor material, it is sometimes referred to as a semiconductor nanoparticle. In addition, since QD21 is usually composed of an inorganic material, it is sometimes referred to as an inorganic nanoparticle. In addition, the structure of QD21, for example, has a specific crystal structure, and is therefore sometimes referred to as a nanocrystal.

[0034] The shape of QD21 is not particularly limited as long as it is within the range that satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). 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 surfaces, or a combination of these shapes.

[0035] QD21 may include at least one metal element. Examples of the metal element included in QD21 include Cd, Zn, In, Sb, Al, Si, Ga, Pb, Ge, and Mg. In addition, QD21 may also be a semiconductor material formed by combining at least one metal element with non-metal elements such as S, Te, Se, N, P, and As.

[0036] QD21 may be formed by only the nucleus, or may be a two-component nucleus, a three-component nucleus, or a four-component nucleus. Figure 3 The structure shown has a core-shell structure including a core 21a and a shell 21b, and may also be a core-shell type or a core-multi-shell type.

[0037] like Figure 3As shown, in the case where QD21 includes a shell 21b, there is a core 21a in the center, and the shell 21b only needs to be provided on the surface of the core 21a. The shell 21b preferably covers the entire core 21a, but the shell 21b does not need to completely cover the core 21a. The shell 21b may also be formed on a portion of the surface of the core 21a. QD21 can be said to have a core-shell structure as long as it is judged that the shell 21b is formed on a portion of the surface of the core 21a, or it is judged that the shell 21b wraps the core 21a, in the observation of a cross section of the QD21. Therefore, it is sufficient to judge that the shell 21b covers the entire core 21a by observing a cross section of QD21. In addition, the above-mentioned cross-sectional observation can be performed, for example, by a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM).

[0038] In addition, QD 21 may include doped nanoparticles, or may have a structure with a gradient composition. In addition, the shell 21b may be formed in a state of being solid-solution-coated on the surface of the core 21a. Figure 3 In the figure, the boundary between the core 21a and the shell 21b is indicated by a dotted line, which means that the boundary between the core 21a and the shell 21b may be confirmed by analysis or may not be confirmed. The shell 21b may also be formed into multiple layers.

[0039] The core 21a can be composed of, for example, Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, etc. The shell 21b can be composed of, for example, CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc. When QD21 has a core-shell structure, an example of the material of QD21 (combination of materials of core 21a / shell 21b) can include, for example, ZnSe / ZnS, InP / ZnS, CdSe / CdS, etc.

[0040] QD21 can change various emission wavelengths by particle size, composition, etc. QD21 is a QD that emits visible light, and by appropriately adjusting the particle size and composition of QD21, the emission wavelength can be controlled to be in the blue to red wavelength regions.

[0041] As described above, the metal halide 22 (second metal halide) is a metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. The metal halide 22 will be described together with the metal halide 31 (first metal halide) later.

[0042] As described above, when ligand removal is performed and no ligand is present on the surface of QD21, the physical properties of the main body of QD21 are significant. In this way, if the surface of QD21 without ligand (the surface of core 21a or shell 21b) is in direct contact with the dispersion of carrier transport material, the wettability of the dispersion of carrier transport material to EML13 may arise. In addition, for example, in QD21 having only core 21a or core-shell structure in which Zn atoms exist on the surface of QD21, the Zn atoms exposed on the surface can cause the deactivation of excitons. Therefore, it is preferred to coordinate ligands on the surface of QD21.

[0043] In addition, in the present disclosure, "coordination" means the surface interaction between the ligand and QD21, for example, the ligand is adsorbed on the surface of QD21 (in other words, the ligand modifies the surface of QD21). In addition, here, "adsorption" means that the concentration of the ligand on the surface of QD21 is increased compared to the surrounding. The above-mentioned adsorption can be chemical adsorption with chemical bonding between QD21 and the ligand, or it can be physical adsorption or electrostatic adsorption.

[0044] Therefore, as long as the ligand can interact with the surface of QD21, it may be bonded by coordination bonding, covalent bonding, ionic bonding, hydrogen bonding, etc., or it may not be necessary to bond. The above-mentioned interaction may be, for example, coordination bonding, covalent bonding, ionic bonding, hydrogen bonding, or van der Waals interaction or other molecular interaction. Thus, in the present disclosure, "ligand" means a molecule or ion that can interact with the surface of QD21. In the present disclosure in EML13, if it can be confirmed that there are molecules or ions that can interact with QD21 and the surface of QD21, then the molecule or ion may be referred to as a "ligand". In addition, in the present disclosure, not only molecules or ions coordinated on the surface of QD21, but also molecules or ions that can be coordinated but not coordinated are referred to as "ligands".

[0045] In a carrier injection type light-emitting element, the shorter the length of the ligand, the better. Therefore, in this embodiment, a metal halide is used as a ligand (inorganic ligand). Compared with organic ligands that are generally used for stable dispersion, the length of the metal halide ligand is short, which enables QD21 to be close to each other. Therefore, compared with organic ligands, metal halides can improve carrier injection and can suppress the reduction in luminous efficiency caused by defects on the surface of QD21.

[0046] The metal halide 22 exists as anions 22a and cations 22b. Of these anions 22a and cations 22b, the halogen in the anion 22a is negatively charged, and therefore is attracted to the positively charged surface of the QD 21 as a halogen ligand.

[0047] Similarly, the metal halide 31 exists as anions 31a and cations 31b. Of these anions 31a and cations 31b, the halogen as the anion 31a is negatively charged, and therefore is attracted to the positively charged surface of the QD 21 as a halogen ligand.

[0048] For example Figure 2 As shown, EML13 may include QD21, a metal halide 22 in a state before coordination with QD21 or in a coordinated state, and a metal halide 31 in a state before coordination with QD21 or in a coordinated state. Here, the "state before coordination" means a state in which an anion is combined with a cation that serves as a counter ion. For example, it means a state in which an anion 22a is combined with a cation 22b, or a state in which an anion 31a is combined with a cation 31b. In addition, the "coordinated state" means a state in which a halogen as an anion 22a or an anion 31a interacts with the surface of QD21 (for example, a state in which a halogen as a halogen ligand is combined with the surface of QD21).

[0049] Examples of the anion 22a or the anion 31a include F - , Cl - Br - ,I - As the cation 22b or the cation 31b, for example, Li + 、Na + , K + , Rb + , Cs + 、Be 2+ Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ 、Zn 2+ 、Al 3+ , Ga 3+ 、In 3+ Sn 2+ , Pb 2+ In addition, the specific metal halide 22 and the metal halide 31 will be described later.

[0050] like Figure 4 As shown in FIG. 1 , the EML 13 according to the present embodiment may include an organic ligand 23 in addition to the QD 21 , the metal halide 22 , and the metal halide 31 . The organic ligand 23 may be coordinated on the surface of the QD 21 .

[0051] The organic ligand 23 is an organic compound containing at least one coordinating functional group that can coordinate to the QD 21. Representative examples of the coordinating functional group include at least one functional group selected from the group consisting of an amino group, a phosphonic acid group, a phosphine group, a phosphine oxide group, a carboxyl group, and a thiol group.

[0052] When EML13 also contains an organic ligand 23, EML13 may contain an organic compound in a state before coordination with QD21 or in a coordinated state as the organic ligand 23. In addition, when the organic ligand 23 has, for example, a thiol (-SH) group as a coordinating functional group, the hydrogen atom of the thiol group of the organic ligand 23 is detached and coordinated with QD21 through a sulfide (-S-) bond. Therefore, here, the organic compound in the "state before coordination" means, for example, an organic compound in a state in which a hydrogen atom detached by coordination is bonded.

[0053] As the above-mentioned organic ligand 23, for example, there can be cited: amine compounds such as oleylamine and dodecylamine; phosphine compounds such as 12-phosphonyldodecyl)phosphonic acid and 11-mercaptoundecylphosphonic acid; phosphine compounds such as trioctylphosphine and tributylphosphine; phosphine oxide compounds such as trioctylphosphine oxide and tributylphosphine oxide; aliphatic compounds such as oleic acid and octanoic acid; thiol compounds such as dodecanethiol and octanethiol; and the like.

[0054] However, in order to facilitate carrier injection, it is preferred that the proportion of organic ligand 23 in the total amount of ligands is small, or EML13 is an organic ligand-free material that does not contain or substantially does not contain organic ligand 23. From the perspective of the effect of the halogen ligand, the weight ratio of organic ligand 23 in EML13 to QD21 (the weight ratio of organic ligand 23 to the weight of QD21) depends on the type and size of QD21 and the molecular weight of the organic ligand 23, but is preferably less than 30%, more preferably less than 20%, and particularly preferably less than 10%. The weight ratio of organic ligand 23 in EML13 to QD21 can be evaluated by differential thermal analysis (TG-DTA). In the case where EML13 only includes organic ligand 23 as a ligand, the weight ratio of organic ligand 23 in EML13 to QD21 measured by TG-DTA is about 30%. By replacing the organic ligand 23 with the metal halide 22, the weight ratio of the organic ligand 23 measured by TG-DTA can be reduced to, for example, 20% or less. In addition, by performing the organic ligand removal step described later, the weight ratio of the organic ligand 23 measured by TG-DTA can be reduced to 10% or less.

[0055] In the present disclosure, if the absorption spectrum from the organic ligand can be confirmed by Fourier transform infrared spectroscopy (FT-IR) and it is confirmed that "the absorption spectrum from the organic ligand cannot be detected by the FT-IR method, that is, the measurement intensity is below the noise", it can be said that "there is no organic ligand".

[0056] By measuring the amount of the detached component of the organic ligand 23 during heating by TG-DTA, the number of molecules of the organic ligand 23 relative to the above-mentioned metal atoms can be calculated. In addition, in the EML 13 formed without performing the process of removing the organic ligand 23, the number of molecules of the organic ligand 23 relative to the number of the above-mentioned metal atoms calculated based on the size of the QD 21 is usually about 38%, and is roughly 100% or more in the solution state.

[0057] In the QD obtained by synthesis or commercially, in most cases, the organic ligand is used as a ligand. Commercially available QD is generally provided in the state of a quantum dot dispersion (QD dispersion) containing an organic ligand. The organic ligand is used as a dispersant to improve the dispersibility of the QD in the QD dispersion, and is also used to improve the surface stability and storage stability of the QD. In addition, the synthesis of QD, for example, uses a wet method to control the particle size of the QD by making the organic ligand coordinate to the surface of the QD. Therefore, the organic ligand used in the synthesis of the QD is contained in the QD dispersion synthesized by the wet method.

[0058] In the present embodiment, as described above, in the light emitting layer forming step (step S3 ), first, the EML 13 including the QDs 21 and the metal halide 22 is formed.

[0059] Therefore, in the light-emitting layer forming process (step S3), in order to form EML13 coordinated with metal halide 22 on the surface of QD21, it is necessary to replace the organic ligand contained in the synthesized or commercially obtained QD dispersion with metal halide 22. In addition, on the surface of QD21, as an organic ligand 23, for example, an unsubstituted organic ligand contained in the synthesized or commercially obtained QD dispersion can also be coordinated. However, for various purposes such as improving the dispersibility of QD21, an organic ligand different from the organic ligand contained in the synthesized or commercially obtained QD dispersion can also be used as a ligand. Therefore, the organic ligand 23 can also be an organic compound different from the organic ligand contained in the synthesized or commercially obtained QD dispersion.

[0060] In short, in order to form the EML 13 in which the metal halide 22 is coordinated on the surface of the QD 21 , it is necessary to replace at least a part of the organic ligand 23 present on the surface of the QD 21 with the metal halide 22 .

[0061] Therefore, the light-emitting layer forming step (step S4) may also include: a step of preparing a QD dispersion liquid containing QDs 21 and an organic ligand 23; and a step of replacing the organic ligand 23 with a metal halide 22 before or after applying the QD dispersion liquid. By replacing the organic ligand 23 with a metal halide 22 in this way, an EML containing QDs 21 and a metal halide 22 can be formed as the EML 13.

[0062] In addition, the type of ligand contained in EML13 can be determined by combining multiple analytical methods such as MALDI (matrix-assisted laser desorption ionization) method, TOF-MS (time-of-flight mass spectrometry) method, LC-MS / MS (liquid chromatography mass spectrometry) method, TOF-SIMS (time-of-flight secondary ion mass spectrometry) method, ICP-AES (inductively coupled plasma atomic emission spectrometry) method, and NMR (nuclear magnetic resonance) method.

[0063] Below, refer to Figure 5 and Figure 6 , the above-mentioned light-emitting layer forming process (step S4) is explained in more detail.

[0064] Figure 5 1 is a flowchart showing an example of the light-emitting layer forming process. The light-emitting layer forming process includes: a step of preparing a QD dispersion liquid containing QDs 21 and an organic ligand 23; and a step of replacing the organic ligand 23 with a metal halide 22 before applying the QD dispersion liquid.

[0065] In this case, in the above-mentioned light-emitting layer forming step, first, as Figure 5 As shown, a QD dispersion liquid (hereinafter referred to as "first QD dispersion liquid") containing QD21, organic ligand 23 and a solvent (second solvent) is adjusted (step S11, first QD dispersion liquid adjustment process). In addition, the above-mentioned first QD dispersion liquid adjustment process can also be a process of redispersing the QDs obtained in the QD synthesis process or the QD synthesis process in a solvent. Below, as an example, the case of adjusting the above-mentioned first QD dispersion liquid using QD21 and organic ligand 23 contained in a QD dispersion liquid (hereinafter referred to as "initial QD dispersion liquid") obtained synthetically or commercially and containing QD21 and organic ligand 23 is cited as an example to illustrate.

[0066] In the first QD dispersion liquid preparation step, for example, first, QD21 having an organic ligand 23 coordinated on the surface is separated from the initial QD dispersion. In the QD21 separation step, for example, first, the initial QD dispersion is collected into a reaction container such as a remote sink tube. The initial QD dispersion contains QD21, an organic ligand 23 and a solvent. A non-polar solvent is used in the above-mentioned solvent. Examples of the non-polar solvent include cyclohexane, toluene, hexane, octane, chlorobenzene and the like.

[0067] Next, an excess amount of a poor solvent is added dropwise to the initial QD dispersion in the reaction vessel to precipitate QDs 21 coordinated with organic ligands 23 contained in the initial QD dispersion. As the poor solvent, a solvent that does not disperse QDs 21, such as ethanol, is used.

[0068] Next, centrifugal separation is performed to remove the supernatant. Next, the precipitated QD21 is washed and the precipitated QD21 (i.e., QD21 coordinated with the organic ligand 23) is separated. In addition, the washing of the QD21 is performed by repeatedly performing the following operation: a non-polar solvent is added again as a solvent to the precipitated QD21 to redisperse the QD21, and then a poor solvent is added again to perform centrifugal separation and remove the supernatant. In this way, at least a portion of the remaining organic ligand 23 not coordinated with QD21 contained in the initial QD dispersion can be removed.

[0069] Next, a non-polar solvent is added again as a solvent (second solvent) to the QD21 in the separated reaction container to redisperse the QD21 in the non-polar solvent. Thus, a first QD dispersion liquid including QD21, an organic ligand 23 coordinated to the QD21, and the non-polar solvent as the second solvent is adjusted.

[0070] Next, a ligand solution containing a metal halide 22 and a trace amount of a polar solvent as a solvent (solvent of the ligand solution) is added to the first QD dispersion in the above-mentioned reaction container and stirred. In the ligand solution, as described above, a polar solvent in which the metal halide 22 is easily soluble is used as a solvent. A non-polar solvent (as described above, such as cyclohexane, toluene, etc.) in which QD 21 is dispersed is mixed with a polar solvent (such as ethanol) in which the metal halide 22 is dissolved within an appropriate range. Then, the reaction solution in the above-mentioned reaction container is allowed to stand for a specified time. Thus, at least a portion of the organic ligand 23 contained in the above-mentioned first QD dispersion is replaced by the metal halide 22 (step S12, ligand replacement process).

[0071] In addition, the concentration of the metal halide 22 in the ligand solution, the amount of the ligand solution added, and the time required for the above stirring and standing are not particularly limited. These conditions can be appropriately set according to the materials used, so that the ratio of each ligand in the EML 13 finally formed becomes a desired ratio.

[0072] Next, an excess amount of poor solvent is added to the reaction vessel again. Then, centrifugation is performed to remove the supernatant. Thus, at least a portion of the remaining metal halide 22 not coordinated to QD21 contained in the supernatant and the solvent in the reaction vessel are removed, and the QD composition containing QD21 and the metal halide 22 present on the surface of the QD21 is separated (step S13, QD composition separation process).

[0073] Then, a non-polar solvent is added to the reaction vessel as a solvent (a solvent for the second QD dispersion described later) to disperse the QD composition in the non-polar solvent. Thus, a QD dispersion containing at least QD 21, metal halide 22 and the non-polar solvent (hereinafter referred to as "second QD dispersion") is adjusted (step S14, second QD dispersion adjustment step).

[0074] In addition, the solvent of the first QD dispersion liquid needs to be mixed with the polar solvent in which the metal halide 22 is dissolved (even if a small amount of the polar solvent is dropped, the QD 21 is dispersed without precipitation), but the solvent used in the second QD dispersion liquid does not need this.

[0075] Next, the second QD dispersion is coated on HTL12 to form a coating of the second QD dispersion (step S15, second QD dispersion coating process). In coating the second QD dispersion, any method such as rod coating, spin coating, inkjet, etc. can be appropriately selected. Next, the coating is heated and dried to remove the solvent contained in the coated second QD dispersion (step S16, solvent removal process). Thus, a QD21 and a metal halide 22 present on the surface of the QD21 can be formed. Figure 2 EML13 shown.

[0076] In addition, as described above, the EML 13 may also contain an organic ligand 23. However, as described above, in order to facilitate carrier injection, it is preferred that the proportion of the organic ligand 23 in the total amount of the ligand is small, or the EML 13 is an organic ligand-free ligand that does not contain or substantially does not contain the organic ligand 23. Therefore, in the case where the second QD dispersion liquid contains the organic ligand 23, the solvent may be removed in step S15 to form a thin film containing the QD composition, and then additional ligand replacement may be performed.

[0077] also, Figure 62 is a flowchart showing another example of the light-emitting layer forming step (step S4). Hereinafter, the light-emitting layer forming step includes a step of preparing a QD dispersion liquid containing QDs 21 and organic ligands 23 and a step of replacing the organic ligands 23 with a metal halide 22 after applying the QD dispersion liquid.

[0078] In this case, in the above-mentioned light-emitting layer forming step, first, as Figure 6 As shown, proceed with Figure 5 Thus, the first QD dispersion liquid containing the QD 21, the organic ligand 23 coordinated to the QD 21, and the nonpolar solvent as the second solvent is prepared (step S11, first QD dispersion liquid preparation step).

[0079] Next, by coating the first QD dispersion on HTL12, a coating film of the first QD dispersion is formed (step S21, first QD dispersion coating process). In the coating of the first QD dispersion, any method such as rod coating, spin coating, inkjet coating, etc. can be appropriately selected. Next, the coating film is heated and dried, etc., to temporarily remove the solvent contained in the coated first QD dispersion (step S22, solvent removal process). Thus, EML13 containing QD21 and an organic ligand 23 coordinated with the QD21 is formed.

[0080] Next, a ligand solution is supplied to the EML 13 containing the QD 21 and the organic ligand 23 so that the ligand solution is in contact with the EML 13. The ligand solution contains a metal halide 22 and a polar solvent as a solvent (solvent for the ligand solution). The ligand solution can be supplied by, for example, an inkjet method or a spray device. In addition, in order to make the ligand solution contact the EML 13 uniformly, a sufficient amount of the ligand solution can be supplied to the EML 13 by dripping, etc., and after standing for a predetermined time, the ligand solution can be applied to the EML 13 by, for example, spin coating. As the polar solvent, alcohols such as ethanol can be cited.

[0081] In this way, by bringing the ligand solution into contact with the EML 13 , at least a part of the organic ligand 23 included in the EML 13 is replaced with the metal halide 22 (step S23 , ligand replacement step).

[0082] In addition, in this case, the concentration of the metal halide 22 in the ligand solution, the amount of the ligand solution added, and the time required for the ligand replacement are not particularly limited. In this case, these conditions can be appropriately set according to the materials used, for example, the ratio of each ligand in the EML 13 finally formed becomes a desired ratio.

[0083] Alternatively, instead of supplying the ligand solution by spin coating or the like, the ligand solution may be supplied to the EML 13 by immersing the substrate on which the EML 13 including the QDs 21 and the organic ligand 23 is formed in the ligand solution.

[0084] Next, the EML 13 and the like after the ligand solution is supplied are heated and dried to remove the solvent contained in the supplied ligand solution (step S24 , solvent removal step).

[0085] Next, a sufficient amount of cleaning liquid is supplied to the EML 13, and the EML 13 is cleaned with the cleaning liquid, thereby removing at least a portion of the remaining metal halide 22 that is not coordinated to the QD 21 (step S25, cleaning step).

[0086] After that, the EML 13 is heated and dried to remove the solvent contained in the EML 13, that is, the cleaning solution (step S26, cleaning solution removal process). For example, a polar solvent such as ethanol is used as the cleaning solution. Thus, a QD 21 and a metal halide 22 present on the surface of the QD 21 can be formed. Figure 2 EML13 shown.

[0087] In this case, as described above, the EML 13 may further contain an organic ligand 23. However, in this case, as described above, in order to facilitate carrier injection, it is preferred that the ratio of the organic ligand 23 in the total amount of the ligand is small, or the EML 13 is free of organic ligands and does not contain or substantially contain organic ligands 23.

[0088] In addition, Figure 5 In the light-emitting layer forming process shown, when additional ligand replacement is further performed after step S15 as described above, the same steps as steps S23 to S26 can be performed after step S15. By performing additional ligand replacement treatment in this way, the ligand replacement amount can be increased and the organic ligand 23 can be removed. However, the above illustration is only an example, and in the above step S12 (ligand replacement process), by appropriately adjusting the ligand replacement conditions, an organic ligand-free EML 13 that does not contain or substantially does not contain the organic ligand 23 can also be formed.

[0089] As the metal halide 22 used in the ligand solution, as described above, a metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. is used. Thus, as the metal halide 22 having a solubility of less than 2.5 mg / 100 g in water at 25° C., for example, at least one selected from the group consisting of CaF2, ZnF2, and GaF3 can be cited.

[0090] Among these exemplified metal halides 22 , ZnF 2 composed of halogen F having a small ion radius and cations of the same type as Zn on the surface of the QD 21 , for example, the surface of the shell 21 b , is suitable for surface modification of the QD 21 .

[0091] However, for some metal halides such as ZnF2, specifically, metal halide 22 having a solubility of less than 2.5 mg / 100 g in water at 25°C, the solubility in polar solvents such as alcohols used in forming CTLs (e.g., ETL15) is very low. When QD21 has, for example, a Zn-F bond on its surface, as in the case of using ZnF2 as a ligand, the surface tension of the surface of the EML13 containing the QD21 is lower than the surface tension of the solvent (first solvent) used in the formation of the CTL stacked on the EML13. Therefore, as described above, the EML13 containing QD21 whose ligand is replaced by a metal halide 22 such as ZnF2 has poor wettability with the carrier transport material dispersion used in the formation of the CTL stacked on the EML13.

[0092] Therefore, in order to modify the surface of QD 21, as described above, for example, a ligand solution containing a metal halide 22 is applied. If such a metal halide 22 exists on the surface of EML 13, the carrier transport material dispersion used to form the CTL stacked on EML 13 can be bounced off by the metal halide 22. As a result, it is difficult to uniformly stack the carrier transport material 41 on EML 13, and the thickness of the CTL stacked on EML 13 becomes uneven. Such a decrease in the uniformity of the thickness of the CTL leads to uneven light emission and deterioration of the light emission characteristics of the obtained light-emitting element 1. As a result, the element characteristics of the obtained light-emitting element 1 are reduced and the reliability is reduced.

[0093] Therefore, in this embodiment, as described above, in the intermediate layer forming step (step S5), IL14 containing a metal halide 31 (first metal halide) having a solubility of 2.5 mg / 100 g or more in water at 25° C. is formed on EML13. Then, in the electron transport layer forming step (step S6), ETL15 as described above is formed on the IL14 as CTL. Thus, the wettability of the carrier transport material dispersion to the substrate is improved.

[0094] Figure 7 Yes means Figure 1 2 is a cross-sectional view schematically showing the configuration of the main parts in the intermediate layer forming step (step S5) and the electron transport layer forming step (step S6).

[0095] like Figure 2 and Figure 7 As shown, IL14 includes a metal halide 31 and is located between EML13 and CTL (in Figure 2 and Figure 7 In the example shown, this is a layer between EML 13 and ETL 15 .

[0096] The ETL 15 contains an electron transport material and is a CTL having an electron transport function for improving the efficiency of electron transport to the EML 13. Examples of the electron transport material include metal oxides such as ZnO, SnO, and TiO 2.

[0097] like Figure 7 As shown, the carrier transport material dispersion 43 for forming the ETL 15 includes a carrier transport material 41 and a solvent 42 (first solvent). For example, a protic polar solvent such as alcohol is used as the solvent 42 used in the above-mentioned carrier transport material dispersion 43. The metal halide 31 having a solubility of 2.5 mg / 100 g or more in water at 25° C. is dissolved in the protic polar solvent such as alcohol used in the carrier transport material dispersion 43.

[0098] However, the solubility of the metal halide varies depending on the solvent used. However, it is not easy to check the solubility of the metal halide every time the solvent is changed, and it is very troublesome. Therefore, in this embodiment, as the most common polar solvent, the solubility of the metal halide is greater than that of alcohol, and the solubility tends to be determined by the solubility relative to the solubility of water, which is a solvent similar to the protic polar solvent.

[0099] In the intermediate layer forming process (step S5), a metal halide-containing liquid 33 is applied on the EML 13 containing the metal halide 22 replaced by the above-mentioned ligand replacement process, and the metal halide-containing liquid 33 contains the metal halide 31 and a polar solvent as the solvent 32 (solvent for intermediate layer formation, third solvent), and forms a coating film containing the metal halide 31. Then, the coating film is heated and dried, etc. to remove the solvent 32 contained in the applied metal halide-containing liquid 33. As a result, when a part of the ligand on the surface of the QD 21 in the EML 13 (when the EML 13 contains the metal halide 22 and the organic ligand 23, the organic ligand 23) is replaced by the metal halide 31, a metal halide layer containing the metal halide 31 is formed on the EML 13 as the IL 14.

[0100] The coating of the metal halide-containing liquid 33 can be performed by immersing the substrate on which the EML 13 is formed in the metal halide-containing liquid 33, or by coating the metal halide-containing liquid 33 on the EML 13 by spin coating, ink jetting, etc. In this case, in order to make the metal halide-containing liquid 33 and the EML 13 uniformly contact, a sufficient amount of the metal halide-containing liquid 33 can be added dropwise to the EML 13, and after standing for a predetermined time, the metal halide-containing liquid 33 can be coated on the EML 13 by, for example, spin coating. In this case, as the polar solvent, alcohols such as ethanol can be cited.

[0101] As the above-mentioned metal halide 31, for example, at least one of LiF, NaF, KF, RbF, CsF, BeF2, MgF2, SrF2, BaF2, AlF3, InF3, PbF2, LiCl, NaCl, KCl, RbCl, CsCl, BeCl2, MgCl2, CaCl2, SrCl2, BaCl2, AlCl3, GaCl3, LiBr, NaBr, KBr, RbBr, CsBr, BeBr2, MgBr2, CaBr2, SrBr2, BaBr2, AlBr3, SnBr2, LiI, NaI, KI, RbI, CsI, BeI2, MgI2, CaI2 and SrI2 can be selected.

[0102] According to this embodiment, when the IL 14 is formed on the EML 13, as shown in FIG. Figure 7 As shown, by applying the carrier transport material dispersion 43 , a part of the IL 14 can be dissolved, and at the same time, the ETL 15 can be formed by the carrier transport material dispersion 43 .

[0103] For example, when IL14 containing BaF2 or ZnCl2 as metal halide 31 is formed on EML13 containing QD21 and ZnF2 as metal halide 22, ETL15 is formed while dissolving part of the metal halide 31 (BaF2 or ZnCl2). Thus, wettability of carrier transport material dispersion 43 to the substrate is improved.

[0104] The phenomena of coating, drying, and surface aggregation of nanoparticles of the carrier transport material dispersion 43 on the substrate involve physical properties such as solid-liquid interfacial tension, solubility, and solid surface potential. Therefore, based on these physical properties, the wettability of the carrier transport material dispersion 43 relative to the substrate is improved by improving the wettability of the ligands present on the surface of QD21 and the carrier transport material dispersion 43.

[0105] For example, as described above, the metal halide 31 having a solubility of 2.5 mg / 100 g or more in water at 25° C. has good wettability to the carrier transport material dispersion 43. Therefore, after a part of the organic ligand in the initial QD dispersion is replaced with such a metal halide, such as ZnCl2, to form EML13, the EML13 is repeatedly coated with and washed with an alcohol solution of ZnCl2, thereby performing additional ligand replacement. Thus, when the surface of QD21 is composed of ZnCl2, the wettability of the carrier transport material dispersion 43 to EML13 will not deteriorate.

[0106] Therefore, IL14 is not formed between EML13 and CTL, and it can be considered to replace part of the halogen ligands on the surface of QD21 with, for example, halogen ligands suitable for alcohol coating. For example, an ethanol solution of a metal halide with high solubility is applied to the QD film in which the organic ligand 23 is replaced by a fluoride ligand. Alternatively, the substrate formed with the above-mentioned QD film is immersed in such an ethanol solution of a metal halide for cleaning. In this way, part of the fluoride ligands on the surface of QD21 can be replaced by halogen ligands such as chloride ligands suitable for alcohol coating. In this case, the wettability of the carrier transport material dispersion 43 can also be improved.

[0107] However, it is difficult to completely replace, for example, fluoride ligands on the surface of the QD 21 with chloride ligands. In addition, as described above, the metal halide 31 such as ZnCl 2 is dissolved in the carrier transport material dispersion 43 .

[0108] Therefore, in this embodiment, the above-mentioned IL14 is formed on the EML13. According to this embodiment, by forming the IL14 that can improve the wettability of the carrier transport material dispersion 43 on the EML13, the wettability of the carrier transport material dispersion 43 can be further improved, and the light-emitting element 1 with good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0109] As described above, when CTL such as ETL 15 is provided on EML 13, IL 14 is particularly effective in processing.

[0110] In addition, when forming IL14, it is necessary to select a metal halide 31 corresponding to the metal halide 22 on the surface of QD21 in EML13 as the base. When ZnF2 is used as the metal halide 22, as described above, ZnCl2 may be used as the metal halide 31. However, from the viewpoint of ligand substitution on the surface of QD21 and formation of IL14, it is desirable that the metal halide 22 and the metal halide 31 use metal halides having the same halogen.

[0111] The metal halide 31 includes anions 31a and cations 31b. When ZnF2 is used as the metal halide 22, for example, CsF or BaF2 is preferably selected as the metal halide 31, and a metal halide containing a fluoride ligand is preferably selected as the anion 31a.

[0112] As described above, when the IL 14 including ZnCl 2 as the metal halide 31 is formed on the EML 13 including the QD 21 and ZnF 2 as the metal halide 22 , the ETL 15 is formed while a part of the ZnCl 2 is dissolved.

[0113] The metal halide has a size that passes through the gaps between the QDs 21 in the EML 13. Therefore, as Figure 7 As shown, when the carrier transport material dispersion 43 is applied on the IL 14 , the solvent 42 contained in the carrier transport material dispersion 43 partially dissolves the IL 14 as described above, and the metal halide 31 contained in the IL 14 intrudes into the EML 13 .

[0114] Therefore, as described above, when the EML 13 including the metal halide 22 is formed, the EML 13 includes the metal halide 31 in addition to the metal halide 22. Therefore, in this case, both the anion 22a and the anion 31a exist as ligands on the surface of the QD 21. Therefore, when the metal halide 22 is ZnF2, if ZnCl2 is used as the metal halide 31, two halogens, F and Cl, exist in the EML 13 after the carrier transport dispersion is applied.

[0115] In contrast, as described above, by using metal halides having the same halogen as the metal halide 22 and the metal halide 31, even if the metal halide 31 contained in the metal halide-containing liquid 33 for forming the IL14 intrudes into the EML13, the types of halide ions contained in the EML13 do not increase. Therefore, by using metal halides having the same halogen type as the EML13 and the IL14, the influence on the QD21 is small, and the reduction in the light-emitting characteristics can be suppressed.

[0116] In addition, since the metal halide 31 is composed of ionic crystals, the IL14 formed by drying the solution in which the metal halide 31 is dissolved becomes a crystalline thin film. Therefore, the gaps existing in the IL14 are only in the region of the grain boundary, which is less than 1 nm. Therefore, the IL14 has almost no gaps. Therefore, the carrier transport material 41 does not pass through the IL14.

[0117] In order to improve the wettability of the carrier transport material dispersion, it is preferable to dissolve IL14 to a thickness of 2 nm or more. The metal halide 31 having a solubility of 2.5 mg / 100 g or more in water at 25°C has a high solubility in polar solvents represented by water, and dissolves to a thickness of 2 nm or more by coating the carrier transport material dispersion. Therefore, in this embodiment, when the thickness of IL14 dissolved by the solvent 42 contained in the carrier transport material dispersion 43 is set to T nm, in the intermediate layer forming step, as shown in FIG. Figure 7 As shown, it is preferred to form IL14 having a layer thickness D of 2+T nm or more.

[0118] In this embodiment, in the carrier transport material dispersion liquid coating step (step S6a), the solvent 42 contained in the carrier transport material dispersion liquid 43 dissolves part of the IL 14 and simultaneously forms the ETL 15. In this carrier transport material dispersion liquid coating step, the solvent 42 dissolves the IL 14 of 2 nm or more as described above.

[0119] On the other hand, if the thickness of IL14 of the finally formed light-emitting element 1 is F, the thickness F of IL14 is preferably 2 nm or more from the viewpoint of suppressing tunneling. Therefore, in the above-mentioned carrier transport material dispersion liquid coating step, IL14 with a thickness of 2 nm or more is dissolved by the above-mentioned solvent 42, and in the above-mentioned intermediate layer forming step, IL14 with a thickness of 2+T nm (T≥2) or more is formed, so that the wettability of the above-mentioned carrier transport material dispersion liquid 43 can be sufficiently improved, and carrier injection caused by tunneling can be suppressed.

[0120] In addition, in this embodiment, the thickness of IL14 after the electron transport layer forming step (step S6) becomes the thickness F of IL14 in the light emitting element 1. Therefore, DT=F, and T and F are preferably 2 nm or more (that is, T≥2 nm and F≥2 nm). Therefore, in the intermediate layer forming step, it is preferable to form IL14 having a thickness D of 4 nm or more.

[0121] In this embodiment, as described above, the solubility of the metal halide 22 in water at 25° C. is 2.5 mg / 100 g or more. However, if the solubility of the metal halide 31 is too high, when the carrier transport material dispersion 43 is applied, the IL 14 is completely dissolved, and the metal halide 22 with low solubility in the EML 13 directly contacts the carrier transport material dispersion 43, which may cause a problem in the wettability of the carrier transport material dispersion 43.

[0122] Therefore, in order to avoid the above-mentioned problem, it is preferred that in the above-mentioned intermediate layer forming step, IL14 is formed to a thickness at which IL14 is not completely dissolved in the carrier transport material dispersion 43 (preferably a thickness of F ≥ 2 nm as described above). Therefore, the higher the solubility of the metal halide 31, the thicker IL14 is preferably formed. Alternatively, as the metal halide 31, it is preferred to use a metal halide having the above-mentioned solubility (i.e., solubility in water at 25°C) of 10,000 mg (= 10 g) / 100 g or less. The above-mentioned solubility is a solubility that can dissolve the IL14 to about 5 μm when the above-mentioned IL14 is placed in water at 25°C and completely dissolved. Therefore, the metal halide 31 may also be a metal halide having a solubility in water at 25°C of 2.5 mg / 100 g or more and 10,000 mg (= 10 g) / 100 g or less.

[0123] As described above, according to this embodiment, by selecting the material of the metal halide 31 or adjusting the thickness of the IL 14 , it is possible to suppress excess electrons, improve carrier balance, and improve the light emission efficiency of the light emitting element 1 .

[0124] However, the present embodiment is not limited thereto. As described above, instead of selecting the material of the metal halide 31 or adjusting the thickness of the IL14, the dissolution of the IL14 may be controlled by reducing the contact time between the IL14 and the carrier transport material dispersion 43, for example, by shortening the dripping time (supply time) of the carrier transport material dispersion 43 during the rotation in the spin coating method.

[0125] As described above, the carrier transport material dispersion 43 includes the carrier transport material 41 and the solvent 42. The carrier transport material 41 is preferably a metal oxide as described above, and the isoelectric point of the carrier transport material dispersion 43 is preferably not less than pH 7. In addition, the metal oxide is used as metal oxide nanoparticles.

[0126] The isoelectric point indicates the pH of the solution at which the zeta potential (charge) of the particle surface is 0. In the measurement of the isoelectric point, light scattering during electrophoresis (laser Doppler method) is widely used, and an electric field is applied to nanoparticles such as QD or ETL particles dispersed in the solution, and the zeta potential is calculated based on the electrophoretic velocity corresponding to the charge of the particles. In addition, the isoelectric point is measured by changing the pH of the solution at this time.

[0127] The metal oxide nanoparticles in the carrier transport material dispersion 43 with alcohol as the main solvent are mostly materials with positive surface potential due to their surface terminal groups. Generally speaking, the surface of the metal oxide nanoparticles is covered with hydroxyl groups (-OH). In the metal oxide nanoparticles with an isoelectric point greater than pH 7, the hydroxyl groups (surface hydroxyl groups) existing on the surface of the metal oxide nanoparticles become M under the condition of electroneutrality (pH = 7). + or M - OH 2+ Therefore, the isoelectric point of most metal oxides except SiO2 is greater than pH 7, and the surface of metal oxides is prone to positive charge.

[0128] In addition, the surface of QD21 is, for example, in a state where Zn atoms are exposed and S atoms are insufficient, and thus the polarity is +. Thus, since the surfaces of QD21 and metal oxide nanoparticles are both positively charged, most combinations electrostatically repel each other. Therefore, it is difficult to neatly arrange metal oxide nanoparticles on QD21.

[0129] However, according to the present embodiment, as described above, by inserting the metal halide 22 and the metal halide 31 between the QD 21 and the metal oxide nanoparticles, the QD 21 and the metal oxide nanoparticles are spatially separated, thereby reducing the influence of the surface potential. As a result, the electrostatic repulsion between the QD 21 and the metal oxide nanoparticles can be suppressed, and the metal oxide nanoparticles can be neatly arranged. Therefore, the uniformity of the layer thickness of the ETL 15 can be improved.

[0130] Generally speaking, in QLED, the mobility of electron transport material is greater than that of hole transport material. Therefore, in QLED, there are many cases where there are too many electrons in EML. Therefore, as described above, when IL14 is formed between EML13 and ETL15, IL14 is preferably a wide bandgap.

[0131] Specifically, as described above, when QD 21 has a core 21a and a shell 21b, the band gap of the metal halide 22 and the band gap of the metal halide 31 are preferably larger than the band gap of the shell 21b. In this way, by making the band gaps of the metal halide 22 and the metal halide 31 larger than the band gap of the shell 21b, the carriers injected from the CTL into the EML 13 can be confined within the QD 21.

[0132] Figure 8 This is an energy band diagram for explaining the electron injection barrier when no metal halide exists between the shell 21 b of the QD 21 and the ETL 15 . Fig. 9 This is an energy band diagram for explaining the electron injection barrier when a metal halide is present between the shell 21 b of the QD 21 and the ETL 15 .

[0133] In a carrier injection type light emitting element, when there is no metal halide between the shell 21b of QD21 and ETL115, the height of the electron injection barrier when electrons are injected from ETL115 to QD21 is as follows: Figure 8 As shown in FIG. 1 , the absolute value ΔE1 of the difference in energy level between the lower end (CBM) of the conduction band of ETL 115 and the lower end (CBM) of the conduction band of shell 21b is used. Fig. 9 As shown, when a metal halide having a band gap larger than that of the shell 21 b exists between the shell 21 b of the QD 21 and the ETL 15 , the height of the electron injection barrier when electrons are injected from the metal halide into the QD 21 is ΔE2, which is larger than ΔE1.

[0134] Therefore, by making the band gap of the metal halide between the shell 21b of the QD 21 and the ETL 15 larger than the band gap of the shell 21b, as shown in FIG. Figure 8 As shown, Figure 7 Compared with the case shown in FIG. 1 , electron injection from the ETL 15 to the EML 13 can be suppressed.

[0135] In addition, in the present embodiment, the metal halide between the shell 21b of the QD 21 and the ETL 15 is the metal halide 22 and the metal halide 31. Therefore, according to the present embodiment, by making the band gaps of the metal halide 22 and the metal halide 31 larger than the band gap of the shell 21b, the electron injection from the ETL 15 to the EML 13 can be suppressed. As a result, the carrier balance can be improved, and the light emission efficiency of the light emitting element 1 can be improved.

[0136] The band gap of the metal halide 22 and the metal halide 31 may be larger than the band gap of the shell 21b as described above, and the specific value thereof is not particularly limited. However, as a preferred value of the band gap of the metal halide 22 and the metal halide 31, for example, for carrier injection, it is preferred that the band gap be wider than the band gap value of ZnS used in the shell 21b, i.e., 3.4 eV.

[0137] Fig.10 The band gaps and solubility in water at 25°C of the main metal halides are summarized.

[0138] also, Fig.11 The diagram shows the energy levels of each layer of a light-emitting element having a band gap of about 4.4 eV (strictly speaking, 4.4 eV or more) of a metal halide, using a blue QD that emits blue light as QD21 as an example. Fig.12 This diagram shows the energy levels of each layer of a light-emitting element in which red QDs emitting red light are used as QDs 21 and the band gap of a metal halide is about 5.2 eV (strictly speaking, 5.2 eV or more).

[0139] In addition, Fig.11 and Fig.12 In order to compare the energy levels, the height of the Fermi level EF of the metal halide and QD21 is made consistent. Fig.11 and Fig.12 As shown, it is reported that in red QDs and blue QDs, the upper end of the valence band (VBM) is almost unchanged, and the effective mass difference between holes and electrons is large. Therefore, the CBM of red QD is lower than that of blue QD, resulting in a greater tendency for the band gap to widen.

[0140] In order to efficiently perform carrier injection and prevent carrier leakage from the QD layer (EML 13), the VBM of the ETL is preferably deeper than the VBM of the metal halide.

[0141] In addition, from the perspective of band gap, for carrier injection, as described above, the band gap of the metal halide is preferably larger than the band gap of the shell 21b, for example, the band gap of ZnS as described above. However, if the band gap of the metal halide is too large, it is easy to cause holes (h + ) and electron (e - ) will cause non-luminescent recombination, and the luminescence efficiency will decrease. Therefore, if the band gap of the metal halide that does not cause non-luminescent recombination is calculated based on the energy levels of ETL15 and QD21, the band gap of the metal halide is preferably lower than, for example, 5.2 eV.

[0142] The light-emitting element 1 manufactured by the manufacturing method of the light-emitting element of the present embodiment has the following structure as described above: it has EML13, which includes QD21, metal halide 22 (second metal halide) and metal halide 31 (first metal halide), and at the same time, ML14 including the above-mentioned metal halide 31 and ETL15 including carrier transport material 41 as CTL including carrier transport material are arranged adjacent to each other in sequence from the above-mentioned EML13 side.

[0143] According to the present embodiment, the IL 14 including the metal halide 31 and the ETL 15 including the carrier transport material 41 are disposed adjacent to each other in sequence from the EML 13 side, thereby improving the wettability of the coating liquid (i.e., the carrier transport material dispersion liquid 43) including the carrier transport material 41 with respect to the EML 13 when forming the ETL 15. As a result, the light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0144] (Variant 1) In this embodiment, if Figure 1As shown, the case where the light emitting element 1 has a normal structure with the anode 2 as the lower electrode is exemplified. However, as described above, the light emitting element 1 may also have an inverted structure with the cathode 3 as the lower electrode. In addition, the CTL formed on the IL 14 is not limited to the ETL, but may also be the HTL.

[0145] Fig.13 It is a cross-sectional view showing an example of a schematic configuration of the light emitting element 1 according to the present modification.

[0146] Fig.13 The light-emitting element 1 shown has an inverted structure with a cathode 3 as a lower electrode and an anode 2 as an upper electrode, and as an example, has a structure in which the cathode 3, ETL 15, EML 13, HTL 12 and anode 2 are sequentially arranged from the lower side (for example, the side of a support body not shown such as a substrate). In addition, although illustration and description are omitted, in this modified example, the light-emitting element 1 may also have a functional layer not shown between the anode 2 and the cathode 3.

[0147] Fig.14 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to this modification.

[0148] like Fig.14 As shown, in this variation, first, a cathode 3 is formed as a lower electrode on a substrate not shown in the figure (step S31, lower electrode forming step, cathode forming step). Then, ETL15 is formed (step S32, electron transport layer forming step). Next, EML13 is formed containing QD21 and a metal halide 22 (second metal halide, inorganic ligand) having a solubility of less than 2.5 mg / 100 g in water at 25°C (step S4, light-emitting layer forming step). Next, IL14 containing a metal halide 31 (first metal halide) having a solubility of more than 2.5 mg / 100 g in water at 25°C is formed on EML13 (step S5, intermediate layer forming step). Next, HTL12 is formed on IL14 (step S33, carrier transport layer forming step, hole transport layer forming step). In step S33, as Fig.14As shown, first, a carrier transport material dispersion containing a carrier transport material 41' and a solvent (first solvent) is applied on IL14 to form a coating of the carrier transport material dispersion (step S33a, carrier transport material dispersion coating step). Next, the coating is heated to remove the solvent contained in the coating, that is, the solvent (first solvent) contained in the applied carrier transport material dispersion (step S33b, first solvent removal step). Thus, HTL12 is formed on IL14, and HTL12 contains a carrier transport material 41' as a carrier transport material. Next, an anode 2 is formed on HTL12 as an upper electrode (step S34, upper electrode forming step, anode forming step).

[0149] In this case, the cathode 3 can be formed, for example, by forming a film of the conductive material on a substrate not shown by a vapor deposition method or a sputtering method. The anode 2 can be formed by forming a film of the conductive material on the HTL 12 by a vapor deposition method or a sputtering method. Except that the layer serving as the base is different, step S31 can be implemented in the same manner as step S6, and step S33 can be implemented in the same manner as step S1. In addition, except that the layer serving as the base is different, step S32 can be implemented in the same manner as step S7, and step S33 can be implemented in the same manner as step S3.

[0150] In this modification, HTL 12 including carrier transport material 41' is formed on IL 14 instead of ETL 15 including carrier transport material 41. As the carrier transport material 41', hole transport materials such as NiO, WO3, and MoO3 can be used.

[0151] Thus, in this modification, the carrier transport material 41' is a metal oxide, and the isoelectric point of the carrier transport material dispersion containing the carrier transport material 41' is preferably not less than pH 7. In this modification, the metal oxide is also used as metal oxide nanoparticles.

[0152] In this embodiment, in the carrier transport material dispersion coating step (step S33a), a part of IL14 is dissolved by using a solvent contained in the carrier transport material dispersion, and HTL12 is formed at the same time. In this carrier transport material dispersion coating step, IL14 of more than 2 nm is dissolved by using the above-mentioned solvent. Among the above-mentioned solvents, the same polar solvent as solvent 42 can be used. In this way, in step S33, HTL12 is formed in the same manner as step S6, except that a carrier transport material dispersion containing a carrier transport material 41' is used instead of the carrier transport material dispersion 43 containing the carrier transport material 41 in step S6. In this way, the CTL formed on the IL14 can be an HTL. As described above, in addition to the specific material, in step S6, the ETL can be replaced with the HTL. In addition, in this modification, EML13 can be formed by Figure 5 The method shown can also be formed by Figure 6 The method shown is formed.

[0153] The light-emitting element 1 manufactured by the manufacturing method of the light-emitting element of this variant example has the following structure as described above: it has EML13, which includes QD21, metal halide 22 (second metal halide) and metal halide 31 (first metal halide), and at the same time, IL14 including the above-mentioned metal halide 31 and HTL12 including carrier transport material 41' as CTL including carrier transport material are arranged adjacent to each other in sequence from the above-mentioned EML13 side.

[0154] According to this modification, as described above, the IL 14 containing the metal halide 31 and the HTL 12 containing the carrier transport material 41' are disposed adjacent to each other in sequence from the EML 13 side, thereby improving the wettability of the coating liquid containing the carrier transport material 41', i.e., the carrier transport material dispersion liquid, with respect to the EML 13 when forming the HTL 12. As a result, a light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0155] In the present modification, by making the band gaps of the metal halide 22 and the metal halide 31 larger than the band gap of the shell 21 b , hole injection from the HTL 12 to the EML 13 can be suppressed.

[0156] (Variant 2) Fig.15 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to this modification.

[0157] like Fig.15 As shown, the manufacturing method of the light emitting element 1 of this modification example is to replace Figure 1In addition to the step S4 shown in the figure, the step S4' is performed. Figure 1 The manufacturing method of the light emitting element 1 shown in FIG. 1 is the same as that of the light emitting element 1 shown in FIG. 1 . In step S4′, an EML including QD 21 and metal halide 22 is formed as EML 13. Fig.15 as well as Figure 2 As shown, first, with Figure 1 Similarly, steps S1 to S3 are performed. Next, an EML 13 containing QDs 21 and having no organic ligand is formed (step S4', light-emitting layer forming step). Figure 1 The steps S5 to S7 shown in the figure are the same as the steps S5 to S7. In step S4', for example, as described above, Figure 5 In the step S12 (ligand replacement step) in the light-emitting layer forming step shown above, the ligand replacement conditions are appropriately adjusted to form the EML 13 without an organic ligand.

[0158] In addition, as mentioned above, it is also possible to Figure 5 After step S15 shown in FIG. Figure 6 The same steps as steps S23 to S26 are performed to further perform additional ligand substitution. Thus, the ligand substitution amount can be increased to remove the organic ligand 23 and form an EML 13 without an organic ligand.

[0159] also, Fig.16 This is a flowchart showing another example of the light emitting layer forming step according to this modification.

[0160] exist Fig.16 In the light emitting layer forming process shown in FIG. Figure 6 Similarly, step S11 to step S22 are performed. That is, in the above-mentioned light-emitting layer forming process, first, as Fig.16 As shown, by Figure 5 as well as Figure 6 The same step S11 as shown is to prepare the first QD dispersion, wherein the first QD dispersion contains QD21, an organic ligand 23 coordinated with the QD21, and the non-polar solvent as the second solvent (step S11, first QD dispersion preparation process). Next, the first QD dispersion is applied on the HTL12 to form a coating of the first QD dispersion (step S21, first QD dispersion coating process). Next, the coating is heated and dried to temporarily remove the solvent contained in the applied first QD dispersion (step S22, solvent removal process). Thus, an EML13 containing QD21 and an organic ligand 23 coordinated with the QD21 is formed. Afterwards, in Fig.16In the light emitting layer forming step shown, the EML 13 is cleaned with a cleaning solution to remove the organic ligand 23 included in the EML 13 (step S41 , organic ligand removing step, cleaning step).

[0161] The removal rate of the organic ligand 23 can be adjusted, for example, by the cleaning time, the supply amount of the cleaning liquid, etc. In the present embodiment, in step S41, as described above, the absorption spectrum from the organic ligand is confirmed by the FT-IR method, and the EML 13 is cleaned until it can be confirmed that "the absorption spectrum from the organic ligand cannot be detected by the FT-IR method, that is, the measurement intensity is below the noise".

[0162] The cleaning liquid may be any solvent that can remove the organic ligand 23 included in the EML 13. More specifically, the cleaning liquid may be any solvent that can dissolve the organic ligand 23 coordinated to the QD 21 and the remaining organic ligand 23 that is not coordinated to the QD 21. Examples of the cleaning liquid include alcohols such as methanol and ethanol.

[0163] Thereafter, the solvent contained in the EML 13 , that is, the cleaning liquid is removed by heating and drying the EML 13 (step S42 , cleaning liquid removing step). Thus, the EML 13 without organic ligands is formed.

[0164] Next, a ligand solution is supplied to the EML 13 from which the organic ligand 23 has been removed, the ligand solution containing the metal halide 22 and a polar solvent as a solvent (solvent for the ligand solution), so that the ligand solution is brought into contact with the EML 13. The supply of the ligand solution can be performed in the same manner as in step S23. However, in this modification, as described above, the organic ligand 23 is removed in advance. Therefore, in step S42, ligand replacement is not performed, but ligand addition is performed.

[0165] Next, proceed with Figure 6 Steps S24 to S26 shown in FIG. 1 are the same as steps S24 to S26. Thus, an EML 13 containing the QDs 21 and the metal halide 22 present on the surface of the QDs 21 and having no organic ligand can be formed.

[0166] As described above, the light-emitting layer forming process may also include: a first QD dispersion liquid adjustment process (step S11), adjusting the QD dispersion liquid (first QD dispersion liquid), the QD dispersion liquid (first QD dispersion liquid) containing QD21, organic ligand 23 and solvent (second solvent); and a removal process, before or after applying the first QD dispersion liquid, removing the organic ligand 23. In this way, before or after applying the first QD dispersion liquid, by removing the organic ligand 23, an EML containing QD21 and no organic ligand can be formed as EML13.

[0167] In addition, Fig.16 In the light emitting layer forming process shown in the figure, as described above, the case where steps S43 to S26 are performed after step S42 to form the EML 13 containing the metal halide 22 and having no organic ligand is described as an example. However, this modification is not limited to this, and steps S43 to S26 may be performed after step S42. Fig.15 The step S6 shown in the figure is performed to form the IL 14 on the EM 13 without organic ligand obtained in the step S42. In this case, the light-emitting element 1 having the EML 13 containing only the metal halide 31 as the metal halide can be finally manufactured.

[0168] In summary, according to this variation, a light-emitting element 1 can be provided, which has an EML13 without organic ligands, wherein the EML13 contains QD21 and a metal halide 31 (first metal halide), and an IL14 containing the above-mentioned metal halide 31 and an ETL15 containing a carrier transport material 41 which serves as a CTL containing the above-mentioned carrier transport material are arranged adjacent to each other in sequence from the above-mentioned EML13 side.

[0169] As described above, in this modification, the IL 14 containing the metal halide 31 and the ETL 15 containing the carrier transport material 41 are disposed adjacent to each other in sequence from the EML 13 side, thereby improving the wettability of the carrier transport material dispersion 43 when forming the ETL 15. As a result, a light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0170] In addition, as described above, in this modification, the EML 13 may further include a metal halide 22 (second metal halide) in addition to the QD 21 and the metal halide 31. In addition, in this modification, as in the modification 1, an HTL 12 including a carrier transport material 41' as a CTL including a carrier transport material may be formed on the IL 14.

[0171] [Second Embodiment] In this embodiment, points different from the first embodiment will be described.

[0172] The method for manufacturing a light-emitting element of the present embodiment includes a step of forming an EML and a step of forming a CTL on the EML, and the step of forming the CTL includes: a step of coating a carrier transport material dispersion containing a carrier transport material, a first solvent, and a first metal halide on the EML; and a step of removing the first solvent. In the step of coating the carrier transport material dispersion, a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. is used as the first metal halide, and in the step of forming the EML, as the EML, (1) an EML containing QDs and a second metal halide having a solubility of less than 2.5 mg / 100 g in water at 25° C. is formed, or (2) an EML containing the QDs and having no organic ligands is formed.

[0173] Hereinafter, in the process of forming the EML, an EML including QDs and the second metal halide is formed as the EML. In addition, an example is given below in which the CTL formed on the EML is an ETL. In addition, the following example is given below in which the light-emitting element has a conventional structure in which the anode is used as a lower electrode and the cathode is used as an upper electrode, and a HIL, HTL, EML, and ETL are provided between the anode and the cathode as functional layers.

[0174] Hereinafter, the invention will be described in detail with reference to the accompanying drawings. Fig.17 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to the present embodiment. Fig.18 1 is a cross-sectional view showing a schematic structure of the light emitting element 1 of the present embodiment. In addition, for the sake of convenience, the same reference numerals are used for components having the same functions as those described in the first embodiment, and their description is not repeated. In addition, unless otherwise specified, the same modifications as those in the first embodiment can of course be made.

[0175] like Fig.18 As shown, as an example, the light-emitting element 1 of this embodiment has a structure in which an anode 2, HIL 11, HTL 12, EML 13, ETL 15, and a cathode 3 are sequentially provided from the lower layer side (for example, the support body side of a substrate, etc., which is not shown in the figure). However, the ETL 15 of this embodiment is stacked on the EML 13 adjacent to the EML 13, and includes a carrier transport material 41 and a metal halide 31 (first metal halide). In addition, in this embodiment, although illustration and description are omitted, the light-emitting element 1 may also have a functional layer other than the HIL 11, HTL 12, EML 13, and ETL 15, which is not shown in the figure, between the anode 2 and the cathode 3.

[0176] In the method for manufacturing the light emitting element 1 of this embodiment, Fig.17 and Fig.18 As shown, for example, first, with Figure 1 Similarly, steps S1 to S4 are performed. In addition, in the present embodiment, in step S4, EML13 can be Figure 5 The method shown can also be formed by Figure 6 The method shown is formed.

[0177] In this embodiment, after the above step 4, the ETL 15 is then formed on the above EML 13 (step S51, carrier transport layer forming step, electron transport layer forming step). Fig.17 As shown, first, a carrier transport material dispersion containing a carrier transport material 41, a solvent (first solvent) and a metal halide 31 is coated on EML13 to form a coating of the carrier transport material dispersion (step S51a, carrier transport material dispersion coating step). Next, the coating is heated to remove the solvent contained in the coating, that is, the solvent (first solvent) contained in the coated carrier transport material dispersion (step S51b, first solvent removal step). Thus, ETL15 containing a carrier transport material 41 and a metal halide 31 is formed on EML13. Next, the coating is heated to remove the solvent (first solvent) contained in the coated carrier transport material dispersion. Figure 1 In step S7, which is the same as step S7 shown in FIG. 1 , a cathode 3 is formed on the ETL 15 as an upper electrode. Fig.18 The light-emitting element 1 is shown.

[0178] Thus, in this embodiment, a carrier transport material dispersion liquid including a carrier transport material 41, a solvent (first solvent), and a metal halide 31 is applied on the EML 13, thereby forming the ETL 15 including the carrier transport material 41 and the metal halide 31. As described above, the metal halide has a size that passes through the gaps between the QDs 21 in the EML 13.

[0179] Therefore, in the present embodiment, as described above, when the carrier transport material dispersion is applied on the EML 13, the metal halide 31 contained in the carrier transport material dispersion invades the EML 13. As a result, part of the ligands (when the metal halide 22 and the organic ligand 23 are included, the organic ligand 23) on the surface of the QD 21 in the EML 13 is replaced by the metal halide 31. At the same time, in the present embodiment, a coating film of the carrier transport material dispersion is formed on the EML 13.

[0180] Therefore, according to the present embodiment, as described above, by coating the carrier transport material dispersion containing the carrier transport material 41, the solvent (first solvent) and the metal halide 31 on the EML 13, the wettability of the carrier transport material dispersion to the EML 13 can be improved. As a result, the light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be manufactured.

[0181] Furthermore, according to the present embodiment, as described above, by coating the carrier transport material dispersion liquid including the carrier transport material 41, the solvent (first solvent) and the metal halide 31 on the EML 13, the ETL 15 can be directly formed on the EML 13. Therefore, compared with the first embodiment, the number of steps can be reduced, the manufacturing steps can be simplified, and the time and cost spent on manufacturing can be reduced.

[0182] Furthermore, in this embodiment, the carrier transport material dispersion can be applied in a state where the carrier transport material 41 is modified by the metal halide 31. Therefore, it is possible to improve the dispersibility of the carrier transport material 41. This embodiment is particularly effective in the case where a CTL such as the ETL 15 is provided on the EML 13 as described above.

[0183] In addition, in the present embodiment, since the ETL 15 includes the metal halide 31, it is necessary to select the metal halide 31 corresponding to the metal halide 22 on the surface of the QD 21 in the EML 13 as the base in the formation of the ETL 15. In the present embodiment, by using the metal halide 22 and the metal halide 31 having the same halogen, even if the metal halide 31 contained in the metal halide-containing liquid used to form the ETL 15 intrudes into the EML 13, the types of halide ions contained in the EML 13 will not increase. Therefore, by using the metal halide having the same halogen type in the EML 13 and the ETL 15, the influence on the QD 21 is small, and the reduction of the light-emitting characteristics can be suppressed.

[0184] In addition, as described above, the light-emitting element 1 manufactured by the manufacturing method of the light-emitting element of the present embodiment has the following structure: it has an EML13, which includes a QD21, a metal halide 22 (a second metal halide) and a metal halide 31 (a first metal halide), and an ETL15 including a carrier transport material 41 and a metal halide 31 is arranged on the above-mentioned EML13 adjacent to the EML13 as a CTL including a carrier transport material and the metal halide 31 (a first metal halide).

[0185] According to the present embodiment, as described above, by providing the ETL 15 including the carrier transport material 41 and the metal halide 31 adjacent to the EML 13, the wettability of the coating liquid (carrier transport material dispersion liquid) including the carrier transport material 41 to the EML 13 when forming the ETL 15 can be improved. As a result, the light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0186] In addition, in this embodiment, as described above, when the EML 13 including the metal halide 22 is formed, Fig.18 As shown, the EML 13 includes the metal halide 22 and the metal halide 31. Therefore, in the present embodiment, both the anion 22a and the anion 31a exist as ligands on the surface of the QD 21.

[0187] Therefore, in this embodiment, as described above, by using metal halide having the same halogen in EML13 and ETL15, even if the metal halide 31 contained in the carrier transport material dispersion liquid used to form the above-mentioned ETL15 invades into EML13, the types of halide ions contained in EML13 will not increase. Therefore, by using metal halide having the same halogen type in EML13 and ETL15, the influence on QD21 is small, and the reduction of light-emitting characteristics can be suppressed.

[0188] In this embodiment, the thickness of each layer of the light emitting element 1 can be set in the same manner as in the prior art. However, when a wide-gap metal halide is used as the metal halide 31, carrier injection from the ETL 15 is suppressed. Therefore, it is preferable to appropriately adjust the thickness of the ETL 15 as needed.

[0189] In addition, as described above, even in the case where the carrier transport material dispersion contains the carrier transport material 41, a solvent (first solvent) and a metal halide 31, the carrier transport material 41 is preferably a metal oxide, and the isoelectric point of the above-mentioned carrier transport material dispersion is preferably above pH 7 for the same reasons as described in the first embodiment.

[0190] (Variant 1) exist Fig.17 as well as Fig.18 In the embodiment, the case where the light emitting element 1 has a conventional structure in which the anode 2 is set as the lower electrode is described as an example. However, in this embodiment, the light emitting element 1 may also have an inverted structure in which the cathode 3 is the lower electrode. In addition, the CTL formed on the EML 13 is not limited to the ETL, and may be an HTL.

[0191] Therefore, although not shown in the figure, the light-emitting element 1 of this embodiment has an inverted structure in which the cathode 3 is used as the lower electrode and the anode 2 is used as the upper electrode. As an example, the cathode 3, ETL 15, EML 13, HTL 12 and anode 2 may be sequentially arranged from the lower side (for example, the side of a support body such as a substrate not shown). In addition, although the figure and description are omitted, in this modified example, the light-emitting element 1 may also have a functional layer not shown between the anode 2 and the cathode 3.

[0192] Fig.19 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to this modification.

[0193] like Fig.19 As shown, in this variation, first, Fig.14 Similarly, step S31, step S32, and step S4 are performed in sequence. In addition, in this variant, EML13 can be Figure 5 The method of expression can also be formed by Figure 6 Next, HTL 12 is formed on EML 13 formed in step S4 (step S51', carrier transport layer forming step, hole transport layer forming step). In step S51', as shown in FIG. Fig.19 As shown, first, a carrier transport material dispersion containing the carrier transport material 41', a solvent (first solvent) and a metal halide 31 is coated on EML13 to form a coating film of the carrier transport material dispersion (step S51a', carrier transport material dispersion coating process). Next, the coating film is heated to remove the solvent contained in the coating film, that is, the solvent (first solvent) contained in the coated carrier transport material dispersion (step S51b', first solvent removal process). Thus, HTL12 containing the carrier transport material 41' and the metal halide 31 is formed on EML13. Next, the same Fig.14 In step S34 shown in FIG. 1 , an anode 2 is formed as an upper electrode on the HTL 12 . Thus, the light emitting element 1 of this modification is formed.

[0194] Thus, in this modification, a carrier transport material dispersion liquid including a carrier transport material 41', a solvent (first solvent), and a metal halide 31 is coated on the EML 13, thereby forming the HTL 12 including the carrier transport material 41' and the metal halide 31. As described above, the metal halide has a size that passes through the gaps between the QDs 21 in the EML 13.

[0195] Therefore, even in this modification, as described above, if the carrier transport material dispersion is coated on the EML 13, the metal halide 31 contained in the carrier transport material dispersion invades the EML 13. As a result, part of the ligands on the surface of the QD 21 in the EML 13 (when the EML 13 contains the metal halide 22 and the organic ligand 23, the organic ligand 23) is replaced by the metal halide 31. At the same time, in this modification, a coating film of the carrier transport material dispersion is formed on the EML 13.

[0196] Therefore, according to this modification, as described above, by coating the carrier transport material dispersion containing the carrier transport material 41', the solvent (first solvent) and the metal halide 31 on the EML 13, the wettability of the carrier transport material dispersion to the EML 13 can be improved. As a result, the light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be manufactured.

[0197] Furthermore, according to this modification, as described above, by coating a carrier transport material dispersion liquid including a carrier transport material 41', a solvent (first solvent) and a metal halide 31 on the EML 13, the HTL 12 can be directly formed on the EML 13. Therefore, compared with the modification 1 of the first embodiment, the number of steps can be reduced, the manufacturing steps can be simplified, and the time and cost spent on manufacturing can be reduced.

[0198] Furthermore, in this modification, the carrier transport material dispersion can be applied in a state where the carrier transport material 41 ′ is modified by the metal halide 31 . Therefore, the dispersibility of the carrier transport material 41 ′ can be improved.

[0199] In this modification, for the same reason as described in the first embodiment, the carrier transport material 41' is a metal oxide, and the isoelectric point of the carrier transport material dispersion containing the carrier transport material is preferably above pH 7. In this modification, the metal oxide is also used as metal oxide nanoparticles.

[0200] In this modification, if the carrier transport material 41' is used as the carrier transport material in step S51', the HTL 12 is formed on the EML 13 in the same manner as step S51. As described above, the CTL formed on the EML 13 may be the HTL, and in step S51, the ETL may be replaced with the HTL except for the specific materials described above.

[0201] As described above, the light-emitting element 1 manufactured by the manufacturing method of the light-emitting element of this variant example has the following features: it has EML13, EML13 includes QD21, metal halide 22 (second metal halide) and metal halide 31 (first metal halide), and HTL12 including carrier transport material 41' and metal halide 31 is arranged on the above-mentioned EML13 adjacent to the EML13 as CTL including carrier transport material and metal halide 31 (first metal halide).

[0202] According to this variation, as described above, by arranging the HTL12 containing the carrier transport material 41' and the metal halide 31 adjacent to the EML13, the wettability of the coating liquid (carrier transport material dispersion liquid) containing the carrier transport material 41' to the EML13 when forming the ETL15 can be improved, and a light-emitting element 1 with good uniformity of layer thickness, excellent luminescent characteristics and reliability can be provided.

[0203] In the present modification, by making the band gaps of the metal halide 22 and the metal halide 31 larger than the band gap of the shell 21 b , hole injection from the HTL 12 to the EML 13 can be suppressed.

[0204] (Variant 2) Fig. 20 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to this modification.

[0205] like Fig. 20 As shown, the manufacturing method of the light emitting element 1 of this modification example is to replace Fig.17 Step S4 shown in FIG. Fig.15 The step S4' shown is the same as the step S4' except that Fig.17 The manufacturing method of the light emitting element 1 shown in FIG. 1 is the same as that of the light emitting element 1 shown in FIG. Figure 5 In the above-mentioned step S12 (ligand replacement step) in the light-emitting layer formation step shown in FIG. 1 , the ligand replacement conditions are appropriately adjusted to form the EML 13 without organic ligands. Figure 5 After step S15, the Figure 6 By performing additional ligand replacement in the same steps as steps S23 to S26 shown in the figure, an EML 13 without an organic ligand is formed. Fig.16 The method shown forms EML13 without organic ligand.

[0206] As described above, in this modification, the light-emitting layer forming process may also include: a first QD dispersion liquid preparation process (step S11), preparing a QD dispersion liquid (first QD dispersion liquid) containing QD21, an organic ligand 23, and a solvent (second solvent); and a removal process, before or after applying the first QD dispersion liquid, removing the organic ligand 23. In this way, before or after applying the first QD dispersion liquid, by removing the organic ligand 23, an EML containing QD21 and having no organic ligand can be formed as EML13.

[0207] In summary, according to this variation, a light-emitting element 1 can be provided, which has an organic ligand-free EML13 containing QD21 and a metal halide 31 (first metal halide), and an ETL15 containing a carrier transporting material 41 and a metal halide 31 is arranged on the above-mentioned EML13 adjacent to the EML13 as a CTL containing a carrier transporting material and the metal halide 31 (first metal halide).

[0208] As described above, in this modification, by providing the ETL 15 including the carrier transport material 41 and the metal halide 31 adjacent to the EML 13, the wettability of the coating liquid (carrier transport material dispersion liquid) including the carrier transport material 41 to the EML 13 when forming the ETL 15 can be improved. As a result, the light-emitting element 1 having good uniformity of layer thickness, excellent light-emitting characteristics and reliability can be provided.

[0209] In addition, as described above, in this modification, the EML 13 may further include a metal halide 22 (second metal halide) in addition to the QD 21 and the metal halide 31. In addition, in this modification, as in the modification 1, an HTL 12 including a carrier transport material 41' and a metal halide 31 may be formed on the EML 13 as a CTL.

[0210] The present disclosure is not limited to the above-mentioned embodiments, and various changes can be made within the scope of the claims. The embodiments obtained by appropriately combining the technical solutions disclosed in different embodiments are also included in the technical scope of the present disclosure. Moreover, by combining the technical means disclosed in each embodiment, new technical features can be formed. Description of Reference Numerals

[0211] 1: Light-emitting element 2: Anode 3: Cathode 12: HTL (Carrier Transport Layer) 15: ETL (Carrier Transport Layer) 13: EML (Emitting Layer) 14: IL (intermediate layer) 21: QD 21a: Nuclear 21b: Shell 22: Metal halide (second metal halide) 23: Organic ligands 31: Metal halide (first metal halide) 41, 41': Carrier transport materials 42: solvent (first solvent) 43: Carrier transport material dispersion

Claims

1. A method for manufacturing a light emitting element, characterized in that: The method for manufacturing the light emitting element comprises: A step of forming a light-emitting layer; forming an intermediate layer on the light-emitting layer, wherein the intermediate layer comprises a first metal halide; and forming a carrier transport layer on the intermediate layer, The process of forming the carrier transport layer comprises: a step of coating a carrier transport material dispersion on the intermediate layer, wherein the carrier transport material dispersion contains a carrier transport material and a first solvent; and a step of removing the first solvent, In the step of forming the intermediate layer, the intermediate layer is formed, the intermediate layer containing a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. as the first metal halide, In the process of forming the light-emitting layer, as the light-emitting layer, (1) a light-emitting layer comprising quantum dots and a second metal halide having a solubility in water at 25° C. of less than 2.5 mg / 100 g is formed, or (2) a light-emitting layer comprising the quantum dots and having no organic ligands is formed.

2. The method for manufacturing a light emitting element according to claim 1, wherein: In the step of forming the light-emitting layer, a light-emitting layer including the quantum dots and the second metal halide is formed as the light-emitting layer.

3. The method for manufacturing a light emitting element according to claim 2, wherein: The process of forming the light-emitting layer includes: A step of preparing a quantum dot dispersion, wherein the quantum dot dispersion comprises the quantum dots, an organic ligand and a second solvent; and A process of replacing the organic ligand with the second metal halide before or after applying the quantum dot dispersion.

4. The method for manufacturing a light emitting element according to claim 2 or 3, characterized in that: As the first metal halide, a metal halide having the same halogen as that of the second metal halide is used.

5. The method for manufacturing a light emitting element according to claim 1, wherein: In the step of forming the light-emitting layer, a light-emitting layer containing the quantum dots and having no organic ligand is formed as the light-emitting layer.

6. The method for manufacturing a light emitting element according to claim 5, characterized in that: The process of forming the light-emitting layer includes: A step of preparing a quantum dot dispersion liquid comprising the quantum dots, an organic ligand and a second solvent; A step of removing the organic ligand before or after applying the quantum dot dispersion.

7. The method for manufacturing a light emitting element according to any one of claims 1 to 6, characterized in that: In the step of applying the carrier transport material dispersion, the intermediate layer is dissolved by the first solvent to a thickness of 2 nm or more. When the thickness of the intermediate layer dissolved by the first solvent is set to Tnm, wherein T≥2, in the step of forming the intermediate layer, the intermediate layer having a thickness of 2+Tnm or more is formed.

8. A method for manufacturing a light emitting element, characterized in that: The method for manufacturing the light emitting element comprises: a step of forming a light emitting layer; and forming a carrier transport layer on the light-emitting layer, The process of forming the carrier transport layer comprises: A step of coating a carrier transport material dispersion on the light emitting layer, wherein the carrier transport material dispersion contains a carrier transport material, a first solvent, and a first metal halide; and a step of removing the first solvent, In the step of applying the carrier transport material dispersion, a metal halide having a solubility of 2.5 mg / 100 g or more in water at 25° C. is used as the first metal halide. In the process of forming the light-emitting layer, as the light-emitting layer, (1) a light-emitting layer comprising quantum dots and a second metal halide having a solubility in water at 25° C. of less than 2.5 mg / 100 g is formed, or (2) a light-emitting layer comprising the quantum dots and having no organic ligands is formed.

9. The method for manufacturing a light emitting element according to claim 8, characterized in that: In the step of forming the light-emitting layer, a light-emitting layer including the quantum dots and the second metal halide is formed as the light-emitting layer.

10. The method for manufacturing a light emitting element according to claim 9, characterized in that: The process of forming the light-emitting layer includes: A step of preparing a quantum dot dispersion, wherein the quantum dot dispersion comprises the quantum dots, an organic ligand and a second solvent; A process of replacing the organic ligand with the second metal halide before or after applying the quantum dot dispersion.

11. The method for manufacturing a light emitting element according to claim 9 or 10, characterized in that: The first metal halide uses a metal halide having the same halogen as that of the second metal halide.

12. The method for manufacturing a light emitting element according to claim 8, wherein: In the step of forming the light-emitting layer, a light-emitting layer containing the quantum dots and having no organic ligand is formed as the light-emitting layer.

13. The method for manufacturing a light emitting element according to claim 12, characterized in that: The process of forming the light-emitting layer includes: A step of preparing a quantum dot dispersion, wherein the quantum dot dispersion comprises the quantum dots, an organic ligand and a second solvent; and A step of removing the organic ligand before or after applying the quantum dot dispersion.

14. The method for manufacturing a light emitting element according to any one of claims 1 to 13, characterized in that: The quantum dot has a core and a shell, A band gap of the first metal halide and a band gap of the second metal halide are respectively larger than a band gap of the shell.

15. The method for manufacturing a light emitting element according to any one of claims 1 to 14, characterized in that: The first metal halide is at least one selected from the group consisting of LiF, NaF, KF, RbF, CsF, BeF2, MgF2, SrF2, BaF2, AlF3, InF3, PbF2, LiCl, NaCl, KCl, RbCl, CsCl, BeCl2, MgCl2, CaCl2, SrCl2, BaCl2, AlCl3, GaCl3, LiBr, NaBr, KBr, RbBr, CsBr, BeBr2, MgBr2, CaBr2, SrBr2, BaBr2, AlBr3, SnBr2, LiI, NaI, KI, RbI, CsI, BeI2, MgI2, CaI2 and SrI2.

16. The method for manufacturing a light emitting element according to any one of claims 1 to 15, characterized in that: The carrier transport material is a metal oxide, The isoelectric point of the carrier transport material dispersion is pH 7 or higher.

17. A light emitting element, characterized in that: The light-emitting element has a light-emitting layer, and the light-emitting layer includes quantum dots and a first metal halide. (1) an intermediate layer including the first metal halide and a carrier transport layer including a carrier transport material are provided adjacent to each other in this order from the light-emitting layer side, or (2) a carrier transport layer including a carrier transport material and the first metal halide is provided adjacent to the light-emitting layer on the light-emitting layer, The solubility of the first metal halide in water at 25° C. is greater than 2.5 mg / 100 g.

18. The light emitting element according to claim 17, characterized in that The light-emitting layer further contains a second metal halide having a solubility in water at 25° C. of less than 2.5 mg / 100 g.

19. The light emitting element according to claim 17 or 18, characterized in that: The light-emitting layer, the intermediate layer, and the carrier transport layer including the carrier transport material are disposed adjacent to each other in this order from the lower layer side.

20. The light emitting element according to claim 19, characterized in that The intermediate layer has a layer thickness of 2 nm or more.

21. The light emitting element according to claim 17 or 18, characterized in that: The carrier transport layer is provided on the light-emitting layer and adjacent to the light-emitting layer, and the carrier transport layer includes the carrier transport material and the first metal halide.

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