Light-emitting element production method and light-emitting element

Abstract

Provided is a light-emitting element production method comprising: a step for forming a light-emitting layer having quantum dots; a step for forming an intermediate layer that comprises a metal halide having a solubility in water of 2.5 mg / 100 g or above at 25°C on top of the light-emitting layer; and a step for forming a carrier transport layer on top of the intermediate layer. The step for forming the carrier transport layer comprises a step for coating the intermediate layer with a carrier transporting material dispersion liquid including a carrier transporting material and a first solvent, and a step for removing the first solvent.

Description

Light-emitting device manufacturing method and light-emitting device

[0001] The present disclosure relates to a method for manufacturing a light-emitting device and a light-emitting device.

[0002] Ligands (modifying groups) are generally provided on the surfaces of quantum dots for the purposes of protecting the quantum dots and improving their dispersibility in solvents. Organic ligands are generally used as the ligands because they provide excellent dispersibility of quantum dots in quantum dot dispersions. However, organic ligands made of insulating organic materials can hinder carrier injection in charge (carrier) injection-type light-emitting devices containing quantum dots in the light-emitting layer.

[0003] For this reason, inorganic ligands have recently been attracting attention as alternatives to organic ligands. Inorganic ligands are more stable than organic ligands and have excellent carrier injection properties. For example, Patent Document 1 discloses a quantum dot and a ZnF bonded to the surface of the quantum dot by ligand substitution of the organic ligand on the surface of the quantum dot. ２ and a fluoride-containing ligand such as

[0004] Japanese Patent Publication No. 2020-180278

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

[0006] However, ZnF ２ Some metal halides such as ZnF have very low solubility in solvents such as alcohols that are used to form such carrier transport layers. ２ When quantum dots have Zn—F bonds on the surface, as in the case of using a ligand, the surface tension of the light-emitting layer surface containing the quantum dots is smaller than the surface tension of the solvent used to form the carrier transport layer laminated on the light-emitting layer. ２A light-emitting layer containing quantum dots ligand-substituted with fluorine ligands such as those described above has poor wettability with a carrier transport material dispersion used to form a carrier transport layer to be laminated on the light-emitting layer. As a result, the thickness of the carrier transport layer formed on the light-emitting layer becomes non-uniform, and the device characteristics or reliability of the light-emitting device deteriorate.

[0007] In particular, when attempting to obtain a sufficient fluorine substitution amount, a metal halide layer consisting of excess fluorine ligands (in other words, excess metal halide) further reduces the wettability of the carrier transport material dispersion liquid, which in turn makes the thickness of the carrier transport layer formed on the light-emitting layer more non-uniform, further deteriorating the device characteristics or reliability of the light-emitting device.

[0008] On the other hand, as mentioned above, organic ligands can hinder carrier injection. Therefore, if only ligand removal is performed instead of ligand substitution to facilitate carrier injection, the bulk physical properties of the quantum dots become apparent. Thus, if the surface of the ligand-less quantum dots comes into direct contact with the carrier transport material dispersion, issues may arise regarding the wettability of the carrier transport material dispersion to the light-emitting layer. Furthermore, if the surface of the ligand-less quantum dots is exposed, the light-emitting efficiency may decrease. Therefore, although it is desirable for the ligand to be present on the surface of the quantum dots, the above-mentioned problems arise when a carrier transport layer is stacked on a light-emitting layer containing quantum dots.

[0009] One aspect of the present disclosure has been made in consideration of the above-mentioned problems, and an object of the present disclosure is to provide a method for manufacturing a light-emitting element that can improve the wettability of a carrier transport material dispersion liquid to a light-emitting layer, and that can manufacture a light-emitting element with good layer thickness uniformity and excellent light-emitting characteristics and reliability, and to provide such a light-emitting element.

[0010] In order to solve the above-described problems, a method for manufacturing a light-emitting element according to one aspect of the present disclosure includes the steps of: forming a light-emitting layer; forming an intermediate layer on the light-emitting layer; and forming a carrier transport layer on the intermediate layer. The step of forming the carrier transport layer includes the steps of applying a carrier transport material dispersion liquid on the intermediate layer, the carrier transport material dispersion liquid including a carrier transport material and a first solvent; and removing the first solvent. In the step of forming the intermediate layer, an intermediate layer is formed that includes, as the first metal halide, a metal halide having a solubility in water at 25°C of 2.5 mg / 100 g or more. In the step of forming the light-emitting layer, either (1) a light-emitting layer is formed that includes quantum dots and a second metal halide having a solubility in water at 25°C of less than 2.5 mg / 100 g, or (2) a light-emitting layer that includes the quantum dots and is organic ligand-free is formed.

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

[0012] In order to solve the above problems, a light-emitting element according to one aspect of the present disclosure includes a light-emitting layer containing quantum dots and a first metal halide, and (1) an intermediate layer containing the first metal halide and a carrier transport layer containing 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 containing a carrier transport material and the first metal halide is provided on and adjacent to the light-emitting layer, and the first metal halide has a solubility in water at 25°C of 2.5 mg / 100 g or more.

[0013] According to one aspect of the present disclosure, it is possible to provide a method for manufacturing a light-emitting element that can improve the wettability of a carrier transport material dispersion liquid to a light-emitting layer, and that can manufacture a light-emitting element with good uniformity in layer thickness and excellent light-emitting characteristics and reliability, and to provide such a light-emitting element.

[0014] 1 is a flowchart showing an example of a manufacturing method of a light-emitting element according to embodiment 1. FIG. 2 is a cross-sectional view showing a schematic configuration of a light-emitting element according to embodiment 1. FIG. 3 is a cross-sectional view showing a schematic configuration of quantum dots in the light-emitting element shown in FIG. 2. FIG. 4 is another cross-sectional view showing a schematic configuration of quantum dots in the light-emitting element shown in FIG. 2. FIG. 5 is a flowchart showing an example of a light-emitting layer forming step shown in FIG. 1. FIG. 6 is a flowchart showing another example of the light-emitting layer forming step shown in FIG. 1. FIG. 7 is a cross-sectional view showing a schematic configuration of a main part in the intermediate layer forming step and the electron transport layer forming step shown in FIG. 1. FIG. 8 is an energy band diagram for explaining an electron injection barrier when no metal halide is present between the quantum dot shell and the electron transport layer. FIG. 9 is an energy band diagram for explaining an electron injection barrier when a metal halide is present between the quantum dot shell and the electron transport layer. FIG. 10 is a table showing the band gaps of main metal halides and their solubilities in water at 25° C. FIG. 11 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 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 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element according to modified example 1 of embodiment 1. FIG. 14 is a flowchart showing an example of a manufacturing method of a light-emitting element according to modified example 1 of embodiment 1. FIG. 1 is a flowchart showing an example of a method for manufacturing a light-emitting element according to Modification 2 of Embodiment 1. FIG. 2 is a flowchart showing another example of a light-emitting layer forming step according to Modification 2 of Embodiment 1. FIG. 3 is a flowchart showing an example of a method for manufacturing a light-emitting element according to Embodiment 2. FIG. 4 is a cross-sectional view showing a schematic configuration of a light-emitting element according to Embodiment 2. FIG. 5 is a flowchart showing an example of a method for manufacturing a light-emitting element according to Modification 1 of Embodiment 2. FIG. 6 is a flowchart showing an example of a method for manufacturing a light-emitting element according to Modification 2 of Embodiment 2.

[0015] An embodiment of the present disclosure will be described in detail below. Hereinafter, a layer formed in a process earlier than a comparison layer will be referred to as a "lower layer," and a layer formed in a process later than a comparison layer will be referred to as an "upper layer." In the following description, the expression "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B," unless otherwise specified.

[0016] [Embodiment 1] One embodiment of the present disclosure will be described below with reference to Figures 1 to 16. Note that this embodiment describes a method for manufacturing a light-emitting device in which an intermediate layer containing a metal halide (first metal halide) and a carrier transport layer containing a carrier transport material are provided adjacent to each other in this order from the light-emitting layer side (i.e., the lower layer side) on the light-emitting layer. The light-emitting device according to the present disclosure is a quantum dot light-emitting diode (QLED) in which quantum dots are used 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 the intermediate layer.

[0017] A method for manufacturing a light-emitting device according to this embodiment includes the steps of: forming a light-emitting layer; forming an intermediate layer on the light-emitting layer; and forming a carrier transport layer on the intermediate layer. The step of forming the carrier transport layer includes the steps of applying a carrier transport material dispersion containing a carrier transport material and a first solvent onto the intermediate layer; and removing the first solvent. The step of forming the intermediate layer includes forming an intermediate layer containing a metal halide as the first metal halide having a solubility in water at 25°C of 2.5 mg / 100 g or more. The step of forming the light-emitting layer includes forming, as the light-emitting layer, either (1) a light-emitting layer containing quantum dots and a second metal halide having a solubility in water at 25°C of less than 2.5 mg / 100 g, or (2) a light-emitting layer containing the quantum dots and no organic ligand. In the present disclosure, solubility refers to the saturated solubility weight of the metal halide alone at 25°C.

[0018] In the following, an example will be described in which a light-emitting layer containing quantum dots and the second metal halide is formed as the light-emitting layer in the step of forming the light-emitting layer. Also, in the following, an example will be described in which the carrier transport layer formed on the intermediate layer is an electron transport layer. Also, in the following, an example will be described in which the light-emitting element has a conventional structure in which an anode is a lower electrode and a cathode is an upper electrode, and functional layers between the anode and the cathode include a hole injection layer, a hole transport layer, a light-emitting layer, an intermediate layer, and an electron transport layer. In the present disclosure, layers between the anode and the cathode are collectively referred to as functional layers.

[0019] However, the light-emitting element according to this embodiment is not limited thereto, and may have, for example, an inverted structure in which a cathode is a lower electrode and an anode is an upper electrode. Furthermore, as described above, in the light-emitting element according to this embodiment, when the carrier transport layer formed on the intermediate layer is an electron transport layer, the intermediate layer and the electron transport layer may be provided adjacent to each other on the light-emitting layer in this order from the light-emitting layer side. Therefore, when the carrier transport layer formed on the intermediate layer is an electron transport layer, a hole injection layer and a hole transport layer may or may not be provided. Therefore, the 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, and may have a configuration in which a functional layer other than the 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 as "CTL", the electron transport layer as "ETL", the hole transport layer as "HTL", the hole injection layer as "HIL", and the intermediate layer as "IL". Quantum dots may be referred to as "QD".

[0021] Fig. 1 is a flowchart showing an example of a manufacturing method for the light-emitting element 1 according to this embodiment. Fig. 2 is a cross-sectional view showing a schematic configuration of the light-emitting element 1 according to this embodiment. Fig. 3 is a cross-sectional view showing a schematic configuration of the QD21 in the light-emitting element 1 shown in Fig. 2. Fig. 4 is another cross-sectional view showing a schematic configuration of the QD21 in the light-emitting element 1 shown in Fig. 2.

[0022] 2 , the light-emitting element 1 according to this embodiment has, for example, a configuration in which an anode 2, a HIL11, a HTL12, an EML13, an IL14, an ETL15, and a cathode 3 are provided in this order from the lower layer side (e.g., the side of a support such as a substrate, not shown). Each layer from the anode 2 to the cathode 3 is generally supported by a substrate serving as a support. Note that, although not shown and not described, the light-emitting element 1 may also have functional layers, not shown, in addition to the HIL11, the HTL12, the EML13, the IL14, and the ETL15 between the anode 2 and the cathode 3.

[0023] In the method for manufacturing the light-emitting element 1 according to this embodiment, as shown in FIGS. 1 and 2 , first, an anode 2 is formed as a lower electrode on a substrate (not shown) (step S1, lower electrode formation step, anode formation step). Next, an HIL 11 is formed (step S2, hole injection layer formation step). Next, an HTL 12 is formed (step S3, hole transport layer formation step). Next, an EML 13 is formed (step S4, light-emitting layer formation step) containing QDs 21 and a metal halide 22 (second metal halide, inorganic ligand) having a solubility in water of less than 2.5 mg / 100 g at 25° C. (step S4, light-emitting layer formation step). Next, an IL 14 is formed on the EML 13 (step S5, intermediate layer formation step) containing a metal halide 31 (first metal halide) having a solubility in water of 2.5 mg / 100 g or more at 25° C. (step S6, carrier transport layer formation step, electron transport layer formation step). In step S6, as shown in FIG. 1 , a carrier transport material dispersion containing a carrier transport material 41 and a solvent (first solvent) is first applied onto IL 14 to form a coating film of the carrier transport material dispersion (step S6a, carrier transport material dispersion application step). Next, the coating film is heated or otherwise removed to remove the solvent contained in the coating film, i.e., the solvent (first solvent) contained in the applied carrier transport material dispersion (step S6b, first solvent removal step). This results in an ETL 15 containing the carrier transport material 41 being formed on IL 14. Next, a cathode 3 is formed as an upper electrode on ETL 15 (step S7, upper layer electrode formation step, cathode formation step). This results in the light-emitting element 1 shown in FIG. 2 . This process will be described in more detail below.

[0024] The anode 2 is an electrode containing a conductive material that supplies holes to the EML 13 when a voltage is applied. The cathode 3 is an electrode containing a conductive material that supplies electrons to the EML 13 when a voltage is applied. At least one of the anode 2 and the cathode 3 is a light-transmitting electrode. Either the anode 2 or the cathode 3 may be a so-called reflective electrode that is light-reflective. The light-emitting element 1 can extract light from the light-transmitting electrode side.

[0025] For example, if the light-emitting element 1 is a top-emission type light-emitting element that emits light from the upper electrode side, a translucent electrode is used for the upper electrode and a reflective electrode is used for the lower electrode, whereas if the light-emitting element 1 is a bottom-emission type light-emitting element that emits light from the lower electrode side, a translucent electrode is used for the lower electrode and a reflective electrode is used for the lower electrode.

[0026] The translucent electrode is formed of a conductive translucent 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, or Cu, or an alloy containing these metals. The reflective electrode may be formed by laminating a layer made of the above-mentioned light-transmitting material and a layer made of the above-mentioned light-reflective material.

[0028] The anode 2 is formed in step S1 and the cathode 3 is formed in step S5 by, for example, vapor deposition, sputtering, or the like. The anode 2 can be formed, for example, by depositing the conductive material on a substrate (not shown) by vapor deposition, sputtering, or the like. Similarly, the cathode 3 can be formed by depositing the conductive material on the ETL 15 by vapor deposition, sputtering, or the like.

[0029] The HIL 11 is a layer that has hole transport properties and promotes the injection of holes from the anode 2 to the HTL 12. The HIL 11 is made of a hole transport material such as a composite (PEDOT:PSS) of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS). The HIL 11 can be formed by any suitable method, such as a spin coating method or an inkjet method.

[0030] The HTL 12 has hole transport properties and transports holes from the HIL 11 to the EML 13. Examples of materials for the HTL 12 include 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, and WO ３ , MoO ３ The hole transporting material may be any suitable method, such as a spin coating method or an ink jet method, for forming the HTL 12.

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

[0032] In the EML 13, holes transported from the anode 2 and electrons transported from the cathode 3 recombine, and the resulting excitons emit light during the transition from the conduction band level to the valence band level of the QD 21.

[0033] QD21s are dots with a maximum particle width of 100 nm or less. QD21s are generally sometimes referred to as semiconductor nanoparticles because their composition is derived from semiconductor materials. QD21s are generally sometimes referred to as inorganic nanoparticles because their composition is derived from inorganic materials. QD21s are also sometimes referred to as nanocrystals because their structure has, for example, a specific crystalline structure.

[0034] The shape of the QD21 is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, the shape may be a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0035] The QDs 21 may contain at least one metal element, such as Cd, Zn, In, Sb, Al, Si, Ga, Pb, Ge, or Mg. Alternatively, the QDs 21 may be a semiconductor material that combines at least one metal element with a nonmetal element, such as S, Te, Se, N, P, or As.

[0036] QD21 may be formed of only a core, or may be a two-component, three-component, or four-component core. Alternatively, QD21 may have a core-shell structure including a core 21a and a shell 21b, as shown in Figure 3, or may be a core-shell or core-multishell structure.

[0037] As shown in FIG. 3 , when QD21 includes a shell 21b, it is sufficient that the core 21a is located at the center and the shell 21b is provided on the surface of the core 21a. While it is desirable for the shell 21b to cover the entire core 21a, it is not necessary for the shell 21b to completely cover the core 21a. The shell 21b may be formed on a portion of the surface of the core 21a. A QD21 can be said to have a core-shell structure if, upon observing a cross-section of the QD21, it is clear that the shell 21b is formed on a portion of the surface of the core 21a, or if it is clear that the shell 21b surrounds the core 21a. Therefore, it is sufficient to determine from a cross-section of the QD21 that the shell 21b covers the entire core 21a. The cross-sectional observation can be performed, for example, using a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM).

[0038] The QDs 21 may also include doped nanoparticles or have a compositionally graded structure. The shell 21b may be formed as a solid solution on the surface of the core 21a. In Figure 3, the boundary between the core 21a and the shell 21b is shown by a dotted line, indicating that the boundary between the core 21a and the shell 21b may or may not be identifiable by analysis. The shell 21b may be formed in multiple layers.

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

[0040] The emission wavelength of QD21 can be varied by adjusting the 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 from the blue wavelength region to the red wavelength region.

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

[0042] As described above, when the ligand is removed from the surface of the QD21, the bulk properties of the QD21 become apparent. When the surface of the ligand-free QD21 (the surface of the core 21a or shell 21b) comes into direct contact with the carrier transport material dispersion, the wettability of the carrier transport material dispersion to the EML13 may be compromised. Furthermore, for example, in the case of QD21 having only the core 21a or a core-shell structure in which Zn atoms are present on the surface of the QD21, the Zn atoms exposed on the surface may cause exciton deactivation. Therefore, it is desirable for a ligand to be coordinated to the surface of the QD21.

[0043] In the present disclosure, "coordination" refers to an interaction between a ligand and the surface of QD21, for example, the adsorption of a ligand to the surface of QD21 (in other words, the modification of the surface of QD21 by a ligand). Here, "adsorption" refers to an increase in the concentration of the ligand on the surface of QD21 compared to the surrounding area. The adsorption may be chemical adsorption, in which a chemical bond exists between QD21 and the ligand, or physical or electrostatic adsorption.

[0044] Therefore, as long as the ligand can interact with the surface of QD21, it may be bound by a coordinate bond, a covalent bond, an ionic bond, a hydrogen bond, or the like, or it does not necessarily have to be bound. The interaction may be, for example, a coordinate bond, a covalent bond, an ionic bond, a hydrogen bond, a van der Waals interaction, or another molecular interaction. Thus, in the present disclosure, "ligand" refers to a molecule or ion capable of interacting with the surface of QD21. In the present disclosure, if it is confirmed that a molecule or ion capable of interacting with QD21 and the surface of QD21 exists in EML13, the molecule or ion can be referred to as a "ligand." Note that in the present disclosure, the term "ligand" refers not only to molecules or ions coordinated to the surface of QD21, but also to molecules or ions that can coordinate but are not coordinated.

[0045] In carrier injection light-emitting devices, the shorter the ligand length, the better. Therefore, in this embodiment, a metal halide is used as the ligand (inorganic ligand). Compared to organic ligands commonly used for stable dispersion, metal halides have a shorter ligand length and can bring the QDs closer together. Therefore, compared to organic ligands, metal halides can improve carrier injection properties and suppress a decrease in luminous efficiency due to defects on the surface of the QDs.

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

[0047] Similarly, metal halide 31 exists as anions 31a and cations 31b. Of these anions 31a and cations 31b, the halogen, which is anion 31a, is negatively charged and is therefore attracted to the positively charged surface of QD21 as a halogen ligand.

[0048] 2, the EML 13 may include QDs 21, metal halide 22 before or after coordination with QDs 21, and metal halide 31 before or after coordination with QDs 21. Here, the "pre-coordination state" refers to a state in which an anion and a cation serving as a counterion are bonded. For example, the state in which anion 22a and cation 22b are bonded, or the state in which anion 31a and cation 31b are bonded. Furthermore, the "coordinated state" refers to a state in which the halogen, which is anion 22a or anion 31a, interacts with the surface of QDs 21 (for example, a state in which the halogen is bonded to the surface of QDs 21 as a halogen ligand).

[0049] The anion 22a or the anion 31a may be, for example, F － , Cl － ,Br － , I －Examples of the cation 22b or the cation 31b include 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＋ The metal ions of the metal halide 22 and the metal halide 31 will be specifically described later.

[0050] As shown in FIG. 4, the EML 13 according to this embodiment may include organic ligands 23 in addition to QDs 21, metal halides 22, and metal halides 31, and the organic ligands 23 may be coordinated to the surface of QDs 21.

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

[0052] When EML 13 further includes organic ligand 23, EML 13 may include, as organic ligand 23, an organic compound in a state before or after coordination with QD21. Note that when organic ligand 23 has, for example, a thiol (—SH) group as a coordinating functional group, the organic ligand 23 coordinates to QD21 via a sulfide (—S—) bond after a hydrogen atom of the thiol group is released. Therefore, here, an organic compound "in a state before coordination" refers to, for example, an organic compound in a state in which a hydrogen atom that will be released by coordination is bonded.

[0053] Examples of the organic ligand 23 include amine compounds such as oleylamine and dodecylamine; phosphonic compounds such as (12-phosphonododecyl)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; and thiol compounds such as dodecanethiol and octanethiol.

[0054] However, to facilitate carrier injection, it is desirable that the proportion of organic ligands 23 in the total amount of ligands is small, or that EML13 is organic ligand-free, i.e., contains no or substantially no organic ligands 23. In view of the effect of the halogen ligand, the weight ratio of organic ligands 23 to QD21 in EML13 (weight ratio of organic ligands 23 to the weight of QD21) is desirably 30% or less, more desirably 20% or less, and particularly desirably 10% or less, although this depends on the type and size of QD21 and the molecular weight of organic ligand 23. The weight ratio of organic ligands 23 to QD21 in EML13 can be evaluated by differential thermal analysis (TG-DTA). When EML13 contains only organic ligands 23 as a ligand, the weight ratio of organic ligands 23 to QD21 in EML13 measured by TG-DTA is approximately 30%. By substituting 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. Furthermore, by performing an 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, the absorption spectrum attributable to the organic ligand is confirmed by Fourier transform infrared spectroscopy (FT-IR), and if it is confirmed that "the absorption spectrum attributable to the organic ligand cannot be detected by the FT-IR method, i.e., the measured intensity is equal to or less than the noise," the compound can be said to be "organic ligand-free."

[0056] The number of molecules of organic ligand 23 relative to the number of metal atoms can be calculated by measuring the amount of components released from organic ligand 23 during heating using TG-DTA. In EML 13 formed without the step of removing organic ligand 23, the number of molecules of organic ligand 23 relative to the number of metal atoms calculated from the size of QD21 is usually about 38%, and in a solution state it is approximately 100% or more.

[0057] In many cases, synthesized or commercially obtained QDs have organic ligands coordinated as ligands. Commercially available QDs are generally provided in the form of quantum dot dispersions (QD dispersions) containing organic ligands. The organic ligands are used as dispersants to improve the dispersibility of QDs in the QD dispersions, as well as to improve the surface stability and storage stability of QDs. Furthermore, QDs are synthesized, for example, by a wet method, and the particle size of the QDs is controlled by coordinating organic ligands to the surface of the QDs. Therefore, QD dispersions synthesized by a wet method contain the organic ligands used in the synthesis of the QDs.

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

[0059] Therefore, in order to form the EML 13 in which the metal halide 22 is coordinated on the surface of the QDs 21 in the light-emitting layer formation process (step S3), it is necessary to replace the organic ligand contained in the synthesized or commercially obtained QD dispersion with the metal halide 22. Note that, for example, an unsubstituted organic ligand contained in the synthesized or commercially obtained QD dispersion may be coordinated on the surface of the QDs 21 as the organic ligand 23. However, for various purposes, such as improving the dispersibility of the QDs 21, an organic ligand different from the organic ligand contained in the synthesized or commercially obtained QD dispersion may be used as the ligand. Therefore, the organic ligand 23 may be an organic compound different from the organic ligand contained in the synthesized or commercially obtained QD dispersion.

[0060] In any case, in order to form an EML 13 in which a metal halide 22 is coordinated to the surface of a QD 21, at least a portion of the organic ligands 23 present on the surface of the QD 21 must be replaced with the metal halide 22.

[0061] Therefore, the light-emitting layer formation step (step S4) may include a step of preparing a QD dispersion containing QDs 21 and organic ligands 23, and a step of substituting the organic ligands 23 with metal halide 22 before or after applying the QD dispersion. By substituting the organic ligands 23 with metal halide 22 in this manner, an EML containing QDs 21 and metal halide 22 can be formed as EML 13.

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

[0063] The light-emitting layer forming step (step S4) will be described in more detail below with reference to FIGS.

[0064] 5 is a flowchart illustrating an example of the light-emitting layer formation process. The following describes a case where the light-emitting layer formation process includes preparing a QD dispersion containing QDs 21 and organic ligands 23, and substituting the organic ligands 23 with metal halide 22 before applying the QD dispersion.

[0065] In this case, in the light-emitting layer formation process, a QD dispersion containing QDs 21, organic ligands 23, and a solvent (second solvent) (hereinafter referred to as the "first QD dispersion") is first prepared (step S11, first QD dispersion preparation process), as shown in FIG. 5 . Note that the first QD dispersion preparation process may be a QD synthesis process or a process of redispersing QDs obtained in the QD synthesis process in a solvent. Hereinafter, as an example, a case where the first QD dispersion is prepared using QDs 21 and organic ligands 23 contained in a QD dispersion containing QDs 21 and organic ligands 23 (hereinafter referred to as the "initial QD dispersion") that has been synthesized or obtained commercially will be described.

[0066] In the first QD dispersion preparation process, for example, first, QDs 21 with organic ligands 23 coordinated to their surfaces are separated from the initial QD dispersion. In the QD 21 separation process, for example, the initial QD dispersion is first collected in a reaction vessel such as a centrifuge tube. The initial QD dispersion contains QDs 21, organic ligands 23, and a solvent. A nonpolar solvent is used as the solvent. Examples of nonpolar solvents include cyclohexane, toluene, hexane, octane, and chlorobenzene.

[0067] Next, an excess amount of poor solvent is added dropwise to the initial QD dispersion in the reaction vessel to precipitate the QDs 21 contained in the initial QD dispersion and having the organic ligands 23 coordinated thereto. The poor solvent used is a solvent in which QDs 21 are not dispersed, such as ethanol.

[0068] Next, centrifugation is performed and the supernatant is removed. The precipitated QD21 is then washed to separate the precipitated QD21 (i.e., the QD21 coordinated with the organic ligands 23). The washing of the QD21 is performed by adding a nonpolar solvent to the precipitated QD21 again to redisperse the QD21, then adding a poor solvent again, performing centrifugation, and removing the supernatant. This process is repeated multiple times. This allows at least a portion of the excess organic ligands 23 contained in the initial QD dispersion that are not coordinated with the QD21 to be removed.

[0069] Next, a non-polar solvent is added again to the separated QDs in the reaction vessel as a solvent (second solvent) to redisperse the QDs in the non-polar solvent, thereby preparing a first QD dispersion containing the QDs, the organic ligands coordinated to the QDs, and the non-polar solvent as the second solvent.

[0070] Next, a ligand solution containing metal halide 22 and a trace amount of polar solvent (solvent for the ligand solution) is added to the first QD dispersion in the reaction vessel and stirred. As described above, a polar solvent in which metal halide 22 is easily dissolved is used as the solvent for the ligand solution. The nonpolar solvent (e.g., cyclohexane, toluene, etc., as described above) in which QDs 21 are dispersed and the polar solvent (e.g., ethanol) in which metal halide 22 is dissolved are miscible within an appropriate range. The reaction solution in the reaction vessel is then allowed to stand for a predetermined period of time. This results in ligand substitution of at least a portion of the organic ligand 23 contained in the first QD dispersion with metal halide 22 (step S12, ligand substitution process).

[0071] The conditions used for ligand substitution, such as the concentration of the metal halide 22 in the ligand solution, the amount of the ligand solution added, the time required for the stirring and standing, etc., are not particularly limited. These conditions may be appropriately set depending on the materials used, etc., so that the ratio of each ligand in the finally formed EML 13 is the desired ratio.

[0072] Next, an excess amount of poor solvent is dropped into the reaction vessel again. Then, the mixture is centrifuged and the supernatant is removed. This removes at least a portion of the excess metal halide 22 not coordinated to the QDs 21 and the solvent in the reaction vessel, separating the QD composition containing the QDs 21 and the metal halide 22 present on the surface of the QDs 21 (step S13, QD composition separation step).

[0073] A non-polar solvent is then added to the reaction vessel as a solvent (a solvent for a second QD dispersion, described later), and the QD composition is dispersed in the non-polar solvent to prepare a QD dispersion (hereinafter referred to as the "second QD dispersion") containing at least QDs 21, a metal halide 22, and the non-polar solvent (step S14, second QD dispersion preparation step).

[0074] The solvent for the first QD dispersion must be miscible with the polar solvent in which the metal halide 22 is dissolved (even if a small amount of polar solvent is added dropwise, the QDs 21 will disperse without precipitating), but this is not necessary for the solvent used for the second QD dispersion.

[0075] Next, the second QD dispersion is applied to the HTL 12 to form a coating of the second QD dispersion (step S15, second QD dispersion application step). The second QD dispersion can be applied by any suitable method, such as bar coating, spin coating, or inkjet printing. The coating is then heated and dried to remove the solvent contained in the applied second QD dispersion (step S16, solvent removal step). This allows the formation of the EML 13 shown in FIG. 2, which contains QDs 21 and metal halides 22 present on the surface of the QDs 21.

[0076] As mentioned above, the EML 13 may further contain organic ligand 23. However, as mentioned above, to facilitate carrier injection, it is desirable that the proportion of organic ligand 23 in the total amount of ligands is small, or that the EML 13 is organic ligand-less, i.e., contains no or substantially no organic ligand 23. Therefore, if the second QD dispersion contains organic ligand 23, additional ligand substitution may be performed after removing the solvent in step S15 to form a thin film containing the QD composition.

[0077] 6 is a flowchart showing another example of the light-emitting layer formation step (step S4). Hereinafter, the light-emitting layer formation step will be described, which includes the steps of preparing a QD dispersion containing QDs 21 and organic ligands 23, and then applying the QD dispersion and substituting the organic ligands 23 with metal halide 22.

[0078] In this case, in the light-emitting layer formation process, first, as shown in Fig. 6, step S11, which is the same as step S11 shown in Fig. 5, is performed to prepare a first QD dispersion containing QDs 21, organic ligands 23 coordinated to the QDs 21, and the nonpolar solvent as the second solvent (step S11, first QD dispersion preparation process).

[0079] Next, the first QD dispersion is applied to the HTL 12 to form a coating of the first QD dispersion (step S21, first QD dispersion application step). The first QD dispersion can be applied by any suitable method, such as bar coating, spin coating, or inkjet printing. The coating is then heated and dried to remove the solvent contained in the applied first QD dispersion (step S22, solvent removal step). This forms the EML 13, which contains QDs 21 and organic ligands 23 coordinated to the QDs 21.

[0080] Next, a ligand solution containing a metal halide 22 and a polar solvent (solvent for the ligand solution) is supplied onto the EML 13 containing the QDs 21 and the organic ligand 23, bringing the ligand solution into contact with the EML 13. The ligand solution may be supplied, for example, by an inkjet method or a mist spraying device. Alternatively, to ensure uniform contact of the ligand solution with the EML 13, a sufficient amount of the ligand solution may be supplied dropwise to the EML 13, and after allowing to stand for a predetermined period of time, the ligand solution may be applied to the EML 13 by, for example, spin coating. Examples of the polar solvent include alcohols such as ethanol.

[0081] By bringing the ligand solution into contact with the EML 13 in this manner, at least a part of the organic ligands 23 contained in the EML 13 is substituted with the metal halide 22 (step S23, ligand substitution step).

[0082] In this case, the conditions used for the ligand substitution, such as the concentration of the metal halide 22 in the ligand solution, the amount of the ligand solution added, the time required for the ligand substitution, etc., are not particularly limited. In this case, too, these conditions may be appropriately set depending on the materials used, etc., so that the ratio of each ligand in the finally formed EML 13 is the desired ratio.

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

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

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

[0086] The EML 13 is then heated and dried to remove the solvent contained in the EML 13, i.e., the cleaning solution (step S26, cleaning solution removal step). The cleaning solution is a polar solvent such as ethanol. This process allows the formation of the EML 13 shown in FIG. 2, which includes the QDs 21 and the metal halide 22 present on the surface of the QDs 21.

[0087] In this case, as described above, the EML 13 may further contain the organic ligand 23. However, in this case, as described above, in order to facilitate carrier injection, it is desirable that the proportion of the organic ligand 23 in the total amount of ligands is small, or that the EML 13 is organic ligand-less, i.e., does not contain or substantially does not contain the organic ligand 23.

[0088] 5 , when additional ligand substitution is performed after step S15 as described above, steps similar to steps S23 to S26 can be performed after step S15. By performing an additional ligand substitution process in this manner, the amount of ligand substitution can be increased and the organic ligand 23 can be removed. However, the above example is merely an example, and by appropriately adjusting the ligand substitution conditions in step S12 (ligand substitution step), it is also possible to form an organic ligand-less EML 13 that does not contain or substantially does not contain organic ligand 23.

[0089] As described above, the metal halide 22 used in the ligand solution has a solubility in water of less than 2.5 mg / 100 g at 25° C. Examples of the metal halide 22 having a solubility in water of less than 2.5 mg / 100 g at 25° C. include CaF ２ , ZnF ２ , and GaF ３ At least one selected from the group consisting of:

[0090] Among these exemplary metal halides 22, ZnF is a compound consisting of F, a halogen with a small ionic radius, and the same cation as Zn on the surface of the QD 21, for example, on the surface of the shell 21b. ２ is suitable for surface modification of QD21.

[0091] However, ZnF ２ Some metal halides such as ZnF, specifically metal halides 22 with a solubility in water of less than 2.5 mg / 100 g at 25° C., have very low solubility in polar solvents such as alcohols, which are used to form CTLs such as ETL15. ２ When the QD21 has, for example, a Zn—F bond on the surface, the surface tension of the EML13 surface containing the QD21 becomes smaller than the surface tension of the solvent (first solvent) used to form the CTL layer on the EML13. ２The EML 13 containing the QDs 21 ligand-substituted with the metal halide 22 such as ZnO has poor wettability with the carrier transport material dispersion liquid used to form the CTL to be laminated on the EML 13 .

[0092] Therefore, if a metal halide 22 is present on the surface of the EML 13, for example, by applying a ligand solution containing the metal halide 22 as described above to modify the surface of the QDs 21, the metal halide 22 repels the carrier transport material dispersion liquid used to form the CTL layer deposited on the EML 13. As a result, it becomes difficult to uniformly deposit the carrier transport material 41 on the EML 13, resulting in an uneven thickness of the CTL layer deposited on the EML 13. This reduced uniformity in the CTL layer thickness leads to uneven emission and poor emission characteristics of the resulting light-emitting element 1. This results in reduced device characteristics and reliability of the resulting light-emitting element 1.

[0093] Therefore, in this embodiment, as described above, in the intermediate layer formation step (step S5), the IL 14 containing the metal halide 31 (first metal halide) having a solubility in water of 2.5 mg / 100 g or more at 25° C. is formed on the EML 13. Then, in the electron transport layer formation step (step S6), the ETL 15 is formed as the CTL on the IL 14, for example, as described above. This improves the wettability of the carrier transport material dispersion liquid to the base.

[0094] FIG. 7 is a cross-sectional view showing a schematic configuration of a main part in the intermediate layer forming step (step S5) and the electron transport layer forming step (step S6) shown in FIG.

[0095] As shown in FIGS. 2 and 7, the IL 14 is a layer that contains a metal halide 31 and is located between the EML 13 and the CTL (between the EML 13 and the ETL 15 in the examples shown in FIGS. 2 and 7).

[0096] The ETL 15 is a CTL that contains an electron transporting material and has an electron transport function that increases the efficiency of electron transport to the EML 13. Examples of the electron transporting material include ZnO, SnO, and TiO. ２ and the like metal oxides.

[0097] 7 , the carrier transport material dispersion 43 used to form the ETL 15 contains a carrier transport material 41 and a solvent 42 (first solvent). The solvent 42 used in the carrier transport material dispersion 43 is, for example, a protic polar solvent such as alcohol. A metal halide 31 having a solubility in water at 25° C. of 2.5 mg / 100 g or more dissolves in the protic polar solvent such as alcohol used in the carrier transport material dispersion 43.

[0098] However, the solubility of metal halides varies depending on the solvent used. However, it is not easy and requires a lot of time to check the solubility of metal halides every time the solvent is changed. Therefore, in this embodiment, the solubility of metal halides is defined by the solubility in water, which is the most common polar solvent, has a higher solubility for metal halides than alcohol, and has a solubility tendency similar to that of protic polar solvents.

[0099] In the intermediate layer formation process (step S5), a metal halide-containing liquid 33 containing a metal halide 31 and a polar solvent as a solvent 32 (a solvent for forming an intermediate layer, a third solvent) is applied to the EML 13 containing the metal halide 22 substituted through the ligand substitution process described above, to form a coating film containing the metal halide 31. The coating film is then heated and dried, for example, to remove the solvent 32 contained in the applied metal halide-containing liquid 33. This replaces some of the ligands on the surface of the QDs 21 in the EML 13 (organic ligands 23, if the EML 13 contains the metal halide 22 and the organic ligand 23), and forms a metal halide layer containing the metal halide 31 as IL14 on the EML 13.

[0100] The metal halide-containing liquid 33 may be applied by immersing the substrate on which the EML 13 is formed in the metal halide-containing liquid 33, or by applying the metal halide-containing liquid 33 onto the EML 13 by a spin coating method, an inkjet method, or the like. In this case, in order to bring the metal halide-containing liquid 33 into uniform contact with the EML 13, a sufficient amount of the metal halide-containing liquid 33 may be supplied, for example, by dropping it onto the EML 13, and after leaving it to stand for a predetermined time, the metal halide-containing liquid 33 may be applied onto the EML 13 by, for example, spin coating. In this case, the polar solvent may also be, for example, an alcohol such as ethanol.

[0101] Examples of the metal halide 31 include LiF, NaF, KF, RbF, CsF, and BeF. ２ , MgF ２ , SrF ２ , BaF ２ , AlF ３ , InF ３ , PbF ２ , LiCl, NaCl, KCl, RbCl, CsCl, BeCl ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , AlCl ３ , GaCl ３ , LiBr, NaBr, KBr, RbBr, CsBr, BeBr ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , AlBr ３ , SnBr ２ , LiI, NaI, KI, RbI, CsI, BeI ２ , MgI ２ , CaI ２ , and SrI ２ At least one selected from the group consisting of:

[0102] According to this embodiment, when the IL 14 is formed on the EML 13, as shown in FIG. 7 , the ETL 15 can be formed by the carrier transport material dispersion 43 while dissolving a part of the IL 14 by coating the carrier transport material dispersion 43.

[0103] For example, QD 21 and ZnF as metal halide 22 ２ BaF as the metal halide 31 on the EML 13 containing ２ Or ZnCl ２ When IL14 containing these metal halides 31 (BaF ２ Or ZnCl ２ ) is dissolved to form the ETL 15. This improves the wettability of the carrier transport material dispersion liquid 43 to the underlayer.

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

[0105] For example, as described above, the metal halide 31 having a solubility in water of 2.5 mg / 100 g or more at 25° C. has good wettability with the carrier transport material dispersion liquid 43. Therefore, a part of the organic ligands in the initial QD dispersion liquid may be replaced with such a metal halide, for example, ZnCl ２ to form EML13, and then ZnCl ２ Further ligand substitution is performed by repeatedly applying and washing with the alcohol solution of ZnCl. ２ In this case, the wettability of the EML 13 with the carrier transport material dispersion liquid 43 is not deteriorated.

[0106] Therefore, it is conceivable to replace some of the halogen ligands on the surface of the QDs 21 with halogen ligands suitable for alcohol application, without forming an IL 14 between the EML 13 and the CTL. For example, an ethanol solution of a highly soluble metal halide is applied to a QD thin film in which the organic ligands 23 have been ligand-substituted with fluoride ligands. Alternatively, a substrate on which the QD thin film has been formed is immersed in an ethanol solution of such a metal halide and washed. This allows some of the fluoride ligands on the surface of the QDs 21 to be ligand-substituted with halogen ligands suitable for alcohol application, such as chloride ligands. This also makes it possible to improve the wettability of the carrier transport material dispersion 43.

[0107] However, it is difficult to completely replace the fluoride ligands on the surface of the QD21 with chloride ligands. ２ The metal halide 31 such as the above dissolves in the carrier transport material dispersion liquid 43 .

[0108] Therefore, in this embodiment, the IL 14 is formed on the EML 13. According to this embodiment, by forming the IL 14, which can improve the wettability of the carrier transport material dispersion liquid 43, on the EML 13 in this manner, it is possible to further improve the wettability of the carrier transport material dispersion liquid 43, and to provide a light-emitting element 1 having good uniformity in layer thickness and excellent light-emitting characteristics and reliability.

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

[0110] To form the IL 14, it is necessary to select a metal halide 31 corresponding to the metal halide 22 on the surface of the QD 21 in the underlying EML 13. For example, ZnF ２ When using the above, the metal halide 31 may be, for example, ZnCl ２However, from the viewpoint of ligand substitution on the surface of QD21 and formation of IL14, it is desirable to use metal halides having the same halogen as metal halide 22 and metal halide 31.

[0111] The metal halide 31 contains anions 31a and cations 31b. The metal halide 22 is, for example, ZnF ２ When using the above, the metal halide 31 is CsF or BaF ２ It is desirable to select a metal halide containing a fluoride ligand as the anion 31a, such as:

[0112] As mentioned above, the QD 21 and the ZnF as the metal halide 22 ２ On EML 13 containing ZnCl as metal halide 31 ２ Upon forming IL14 containing ZnCl ２ ETL15 is formed while dissolving a part of the

[0113] The metal halide has a size that allows it to pass through the gaps between the QDs 21 in the EML 13. Therefore, when the carrier transport material dispersion 43 is applied to the IL 14, as shown in FIG. 7 , a part of the IL 14 is dissolved by the solvent 42 contained in the carrier transport material dispersion 43, as described above, and the metal halide 31 contained in the IL 14 penetrates into the EML 13.

[0114] Therefore, as described above, when forming the EML 13 containing the metal halide 22, the EML 13 further contains the metal halide 31 in addition to the metal halide 22. Therefore, in this case, both the anion 22a and the anion 31a are present as ligands on the surface of the QD 21. Therefore, when the metal halide 22 is ZnF ２ When the metal halide 31 is ZnCl ２ When the carrier transporting material dispersion liquid is used, two types of halogen, F and Cl, are present in the EML13 after coating.

[0115] In contrast, by using metal halides having the same halogen for metal halide 22 and metal halide 31 as described above, even if metal halide 31 contained in metal halide-containing liquid 33 used to form IL14 penetrates into EML 13, the number of types of halide ions contained in EML 13 does not increase. Therefore, by using metal halides having the same halogen for EML 13 and IL14, the effect on QD21 is small, and deterioration of the luminescence characteristics can be suppressed.

[0116] Since the metal halide 31 is composed of ionic crystals, the IL 14 formed by drying the solution containing the metal halide 31 becomes a crystalline thin film. Therefore, the gaps present in the IL 14 are only in the grain boundary regions and are 1 nm or less. Therefore, there are almost no gaps in the IL 14. Therefore, the carrier transport material 41 does not pass through the IL 14.

[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. Metal halide 31 having a solubility in water of 2.5 mg / 100 g or more at 25° C. has high solubility in polar solvents such as water, and dissolves to a thickness of 2 nm or more by application of the carrier transport material dispersion. Therefore, in this embodiment, if the layer thickness of IL14 dissolved by solvent 42 contained in carrier transport material dispersion 43 is T nm, it is preferable to form IL14 having a layer thickness D of 2+T nm or more in the intermediate layer formation step, as shown in FIG. 7 .

[0118] In this embodiment, in the carrier transport material dispersion liquid application step (step S6a), the ETL 15 is formed while dissolving a portion of the IL 14 in the solvent 42 contained in the carrier transport material dispersion liquid 43. In the carrier transport material dispersion liquid application step, as described above, the IL 14 is dissolved by 2 nm or more in the solvent 42.

[0119] On the other hand, from the viewpoint of suppressing tunneling, the layer thickness F of IL14 is preferably 2 nm or more, where F is the layer thickness of IL14 finally formed in the light-emitting element 1. Therefore, by dissolving IL14 to a thickness of 2 nm or more in the solvent 42 in the carrier transport material dispersion coating step and forming IL14 having a layer thickness of 2+T nm (T≧2) or more in the intermediate layer forming step, it is possible to sufficiently improve the wettability of the carrier transport material dispersion 43 and suppress carrier injection due to tunneling.

[0120] In this embodiment, the thickness of IL14 after the electron transport layer formation step (step S6) is the thickness F of IL14 in the light-emitting element 1. Therefore, D-T=F, and it is preferable that T and F are each 2 nm or more (i.e., T≧2 nm and F≧2 nm). Therefore, it is preferable to form IL14 having a thickness D of 4 nm or more in the intermediate layer formation step.

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

[0122] Therefore, to avoid the above-mentioned problems, it is desirable to form the IL 14 in the intermediate layer formation step to a thickness that prevents the IL 14 from being completely dissolved in the carrier transport material dispersion liquid 43 (preferably a thickness such that F≧2 nm, as described above). Therefore, the higher the solubility of the metal halide 31, the thicker the IL 14 should be. Alternatively, it is desirable 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 as the metal halide 31. The above solubility is such that, when the IL 14 is left in water at 25°C until it is completely dissolved, the IL 14 dissolves to a depth of approximately 5 μm. Therefore, the metal halide 31 may 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 and adjusting the thickness of the IL 14, it is possible to suppress the excess of electrons, improve the carrier balance, and improve the luminous efficiency of the light-emitting element 1.

[0124] However, the present embodiment is not limited to this. Instead of selecting the material of the metal halide 31 or adjusting the thickness of the IL 14 as described above, the dissolution of the IL 14 may be controlled by, for example, shortening the time for dropping (supplying) the carrier transport material dispersion 43 during spinning in the spin coating method, thereby reducing the time for contact between the IL 14 and the carrier transport material dispersion 43.

[0125] As described above, the carrier transport material dispersion liquid 43 contains the carrier transport material 41 and the solvent 42. As described above, the carrier transport material 41 is preferably a metal oxide, and the isoelectric point of the carrier transport material dispersion liquid 43 is preferably equal to or higher than pH 7. The metal oxide is used as metal oxide nanoparticles.

[0126] The isoelectric point indicates the pH of a solution at which the zeta potential (charge) of the particle surface is zero. Light scattering during electrophoresis (laser Doppler spectroscopy) is widely used to measure the isoelectric point. An electric field is applied to nanoparticles, such as QD or ETL particles, dispersed in a solution, and the zeta potential is calculated from the electrophoretic velocity, which corresponds to the charge of the particles. The isoelectric point is also measured by changing the pH of the solution.

[0127] Many of the metal oxide nanoparticles in the carrier transport material dispersion liquid 43, which uses alcohol as the main solvent, are materials whose surface potential is positively charged due to their surface terminal groups. In general, the surfaces of metal oxide nanoparticles are covered with hydroxyl groups (-OH). In metal oxide nanoparticles with an isoelectric point higher than pH 7, the hydroxyl groups (surface hydroxyl groups) present on the surfaces of the metal oxide nanoparticles are positively charged under electrically neutral conditions (pH = 7). ＋ or M-OH ２ ＋ The particle surface is positively charged. ２ The isoelectric points of most metal oxides, except for those mentioned above, are higher than pH 7, and the surfaces of metal oxides tend to be positively charged.

[0128] Furthermore, the surface of the QD21 has a positive polarity due to, for example, exposed Zn atoms and a lack of S atoms. Thus, because the surfaces of the QD21 and metal oxide nanoparticles are both positively charged, they electrostatically repel each other in most combinations. Therefore, it is difficult to arrange metal oxide nanoparticles in an orderly manner on the QD21.

[0129] However, according to the present embodiment, as described above, the influence of the surface potential can be reduced by inserting the metal halide 22 and the metal halide 31 between the QDs 21 and the metal oxide nanoparticles to spatially separate the QDs 21 and the metal oxide nanoparticles. As a result, the electrostatic repulsion between the QDs 21 and the metal oxide nanoparticles can be suppressed, enabling the metal oxide nanoparticles to be arranged in an orderly manner. This improves the uniformity of the ETL 15 layer thickness.

[0130] Generally, in QLEDs, electron transport materials have a higher mobility than hole transport materials. Therefore, in QLEDs, the EML often has an excess of electrons. Therefore, when IL14 is formed between EML13 and ETL15 as described above, it is preferable that IL14 has a wide band gap.

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

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

[0133] In a carrier injection light-emitting device, when no metal halide is present between the shell 21b of QD21 and the ETL 15, the height of the electron injection barrier when electrons are injected from the ETL 15 into QD21 is represented by the absolute value ΔE1 of the energy level difference between the conduction band minimum (CBM) of the ETL 15 and the conduction band minimum (CBM) of the shell 21b, as shown in Fig. 8. On the other hand, when a metal halide with a band gap larger than that of the shell 21b is present between the shell 21b of QD21 and the ETL 15, the height of the electron injection barrier when electrons are injected from the metal halide into QD21 is ΔE2, as shown in Fig. 9, 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. 8, electron injection from the ETL 15 to the EML 13 can be suppressed more than in the case shown in FIG. 7.

[0135] In this embodiment, the metal halides between the shell 21b of the QD 21 and the ETL 15 are the metal halide 22 and the metal halide 31. Therefore, according to this 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, it is possible to suppress electron injection from the ETL 15 to the EML 13. As a result, the carrier balance is improved, and the luminous efficiency of the light-emitting element 1 can be improved.

[0136] As described above, the band gaps of the metal halide 22 and the metal halide 31 are not particularly limited as long as they are larger than the band gap of the shell 21b. However, for carrier injection, it is preferable that the band gaps of the metal halide 22 and the metal halide 31 be wider than, for example, 3.4 eV, which is the band gap value of ZnS used in the shell 21b.

[0137] FIG. 10 shows a summary of the band gaps and water solubilities at 25° C. of major metal halides.

[0138] 11 shows, as an example, the energy levels of each layer of a light-emitting device that uses blue QDs that emit blue light as QD21 and has a metal halide band gap of about 4.4 eV (strictly speaking, 4.4 eV or more). FIG. 12 shows, as an example, the energy levels of each layer of a light-emitting device that uses red QDs that emit red light as QD21 and has a metal halide band gap of about 5.2 eV (strictly speaking, 5.2 eV or more).

[0139] In addition, in order to compare the energy levels, in Figures 11 and 12, the Fermi level E ＦAs shown in Figures 11 and 12, the upper valence band (VBM) of red and blue QDs is almost the same, and it has been widely reported that the band gap tends to widen due to the large difference in effective mass between holes and electrons, which causes the CBM of red QDs to be lower than that of blue QDs.

[0140] In order to efficiently inject carriers, it is preferable that the VBM of the ETL is deeper than the VBM of the metal halide in order to prevent carrier leakage from the QD layer (EML 13).

[0141] From the viewpoint of band gap, for carrier injection, it is preferable that the band gap of the metal halide is 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, holes (h ＋ ) and electrons (e － Therefore, when the band gap of a metal halide that does not cause non-radiative recombination is calculated based on the energy levels of ETL15 and QD21, the band gap of the metal halide is preferably less than 5.2 eV, for example.

[0142] As described above, the light-emitting element 1 manufactured by the light-emitting element manufacturing method according to this embodiment has an EML 13 containing QD 21, metal halide 22 (second metal halide), and metal halide 31 (first metal halide), and also has a configuration in which an IL 14 containing the metal halide 31 and an ETL 15 containing a carrier transport material 41 as a CTL containing a carrier transport material are arranged adjacent to each other in this order from the EML 13 side.

[0143] According to this embodiment, the IL 14 containing the metal halide 31 and the ETL 15 containing the carrier transport material 41 are provided adjacent to each other in this order 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 43) to the EML 13 when forming the ETL 15. As a result, a light-emitting element 1 having good layer thickness uniformity and excellent light-emitting characteristics and reliability can be provided.

[0144] (Variation 1) In this embodiment, as shown in Fig. 1, the light-emitting element 1 has been described as having a conventional structure in which the anode 2 is the lower electrode. However, as described above, the light-emitting element 1 may have an inverted structure in which the cathode 3 is the lower electrode. In addition, the CTL formed on the IL 14 is not limited to the ETL, and may be an HTL.

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

[0146] 13 has an inverted structure in which the cathode 3 is a lower electrode and the anode 2 is an upper electrode, and as an example, the cathode 3, ETL 15, EML 13, HTL 12, and anode 2 are provided in this order from the lower layer side (e.g., the side of a support such as a substrate, not shown). Although not shown and described, the light-emitting element 1 in this modification may also have a functional layer, not shown, between the anode 2 and the cathode 3.

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

[0148] As shown in FIG. 14 , in this modification, a cathode 3 is first formed as a lower electrode on a substrate (not shown) (step S31, lower electrode formation step, cathode formation step). Next, an ETL 15 is formed (step S32, electron transport layer formation step). Next, an EML 13 is formed (step S4, emissive layer formation step) containing QDs 21 and a metal halide 22 (second metal halide, inorganic ligand) having a solubility in water of less than 2.5 mg / 100 g at 25° C. Next, an IL 14 is formed on the EML 13 (step S5, intermediate layer formation step) containing a metal halide 31 (first metal halide) having a solubility in water of 2.5 mg / 100 g or more at 25° C. Next, an HTL 12 is formed on the IL 14 (step S33, carrier transport layer formation step, hole transport layer formation step). In step S33, as shown in FIG. 14 , a carrier transport material dispersion containing a carrier transport material 41′ and a solvent (first solvent) is first applied onto the IL 14 to form a coating of the carrier transport material dispersion (step S33a, carrier transport material dispersion application step). Next, the coating is heated or otherwise removed to remove the solvent contained in the coating, i.e., the solvent (first solvent) contained in the applied carrier transport material dispersion (step S33b, first solvent removal step). This results in the formation of the HTL 12 containing the carrier transport material 41′ as the carrier transport material on the IL 14. Next, the anode 2 is formed as an upper layer electrode on the HTL 12 (step S34, upper layer electrode formation step, anode formation step).

[0149] In this case, the cathode 3 can be formed by depositing the conductive material on a substrate (not shown) by vapor deposition, sputtering, or the like. The anode 2 can be formed by depositing the conductive material on the HTL 12 by vapor deposition, sputtering, or the like. Except for the different underlying layers, step S31 can be performed in the same manner as step S6, and step S33 can be performed in the same manner as step S1. Also, except for the different underlying layers, step S32 can be performed in the same manner as step S7, and step S33 can be performed in the same manner as step S3.

[0150] In this modification, a HTL 12 containing a carrier transport material 41' is formed on an IL 14 instead of an ETL 15 containing a carrier transport material 41. Examples of the carrier transport material 41' include NiO, WO ３ , MoO ３ The hole transporting material may be any of the following.

[0151] Thus, in this modification as well, the carrier transport material 41′ is a metal oxide, and the isoelectric point of the carrier transport material dispersion liquid containing the carrier transport material 41′ is preferably equal to or higher than pH 7. Note that in this modification as well, the metal oxide is used as metal oxide nanoparticles.

[0152] In this embodiment, in the carrier transport material dispersion coating step (step S33a), the HTL 12 is formed by dissolving a portion of the IL 14 in a solvent contained in the carrier transport material dispersion. In this carrier transport material dispersion coating step, the IL 14 is dissolved to a thickness of 2 nm or more in the solvent. The solvent may be a polar solvent similar to the solvent 42. Thus, in step S33, the HTL 12 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 manner, the CTL formed on the IL 14 may be the HTL, and, except for the specific materials described above, the ETL in step S6 can be read as the HTL. Note that, in this modification, the EML 13 may also be formed by the method shown in FIG. 5 or the method shown in FIG. 6.

[0153] As described above, the light-emitting element 1 manufactured by the light-emitting element manufacturing method of this modified example has an EML 13 containing QD 21, metal halide 22 (second metal halide), and metal halide 31 (first metal halide), and has a configuration in which an IL 14 containing the metal halide 31 and a HTL 12 containing a carrier transport material 41′ as a CTL containing a carrier transport material are arranged adjacent to each other in this order from the EML 13 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 provided adjacent to each other in this order from the EML 13 side, which improves the wettability of the carrier transport material dispersion, which is a coating liquid containing the carrier transport material 41′, to the EML 13 when the HTL 12 is formed. As a result, a light-emitting element 1 having good layer thickness uniformity and excellent light-emitting characteristics and reliability can be provided.

[0155] In this modification, the band gaps of the metal halide 22 and the metal halide 31 are set larger than the band gap of the shell 21 b , thereby making it possible to suppress hole injection from the HTL 12 to the EML 13 .

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

[0157] The method for manufacturing the light-emitting element 1 according to this modification is the same as that for manufacturing the light-emitting element 1 shown in FIG. 1 , except that step S4′ is performed instead of step S4 shown in FIG. 1 . In step S4′, an EML containing QDs 21 and a metal halide 22 is formed as the EML 13. Therefore, in this modification, as shown in FIGS. 15 and 2 , steps S1 to S3 are first performed in the same manner as in FIG. 1 . Next, an EML 13 containing QDs 21 and free of organic ligands is formed (step S4′, light-emitting layer formation step). Next, steps S5 to S7 similar to steps S5 to S7 shown in FIG. 1 are performed. In step S4′, for example, as described above, the organic-ligand-free EML 13 can be formed by appropriately adjusting the ligand substitution conditions in step S12 (ligand substitution step) in the light-emitting layer formation step shown in FIG. 5 .

[0158] 5, additional ligand substitution may be performed by performing steps similar to steps S23 to S26 shown in Fig. 6. This increases the amount of ligand substitution, thereby removing the organic ligand 23, and forming an organic ligand-free EML 13.

[0159] FIG. 16 is a flowchart showing another example of the light emitting layer forming step according to this modified example.

[0160] In the light-emitting layer formation process shown in FIG. 16, steps S11 to S22 are first performed in the same manner as in FIG. 6. Specifically, in the light-emitting layer formation process, as shown in FIG. 16, step S11, similar to step S11 shown in FIGS. 5 and 6, is performed to prepare a first QD dispersion containing QDs 21, organic ligands 23 coordinated to the QDs 21, and the nonpolar solvent as the second solvent (step S11, first QD dispersion preparation step). Next, the first QD dispersion is applied to the HTL 12 to form a coating film of the first QD dispersion (step S21, first QD dispersion application step). The coating film is then heated and dried to remove the solvent contained in the applied first QD dispersion (step S22, solvent removal step). This forms an EML 13 containing QDs 21 and organic ligands 23 coordinated to the QDs 21. Thereafter, in the light-emitting layer forming step shown in FIG. 16, the EML 13 is washed with a washing liquid to remove the organic ligand 23 contained in the EML 13 (step S41, organic ligand removing step, washing step).

[0161] The removal rate of the organic ligand 23 can be adjusted by, for example, the cleaning time, the supply amount of cleaning liquid, etc. In this embodiment, in step S41, as described above, the absorption spectrum attributable to the organic ligand is confirmed by the FT-IR method, and cleaning of the EML 13 is continued until it is confirmed that "the absorption spectrum attributable to the organic ligand cannot be detected by the FT-IR method, i.e., the measured intensity is equal to or less than the noise level."

[0162] The cleaning liquid may be any solvent capable of removing the organic ligands 23 contained in the EML 13. More specifically, the cleaning liquid may be any solvent capable of dissolving the organic ligands 23 coordinated to the QDs 21 and the excess organic ligands 23 not coordinated to the QDs 21. Examples of the cleaning liquid include alcohols such as methanol and ethanol.

[0163] Thereafter, the EML 13 is heated and dried to remove the solvent contained in the EML 13, that is, the cleaning solution (step S42, cleaning solution removal step), thereby forming an organic ligand-free EML 13.

[0164] Next, a ligand solution containing a metal halide 22 and a polar solvent as a solvent (solvent for the ligand solution) is supplied onto the EML 13 from which the organic ligand 23 has been removed, and the ligand solution is brought into contact with the EML 13. The supply of the ligand solution can be performed, for example, in the same manner as in step S23. However, in this modification, the organic ligand 23 has been removed in advance as described above. Therefore, in step S42, ligand addition is performed rather than ligand substitution.

[0165] 6 are then performed, thereby forming an organic ligand-free EML 13 containing QDs 21 and metal halides 22 present on the surfaces of the QDs 21.

[0166] As described above, the light-emitting layer formation process may include a first QD dispersion preparation process (step S11) for preparing a QD dispersion (first QD dispersion) containing QDs 21, organic ligands 23, and a solvent (second solvent), and a process for removing the organic ligands 23 before or after applying the first QD dispersion. In this manner, by removing the organic ligands 23 before or after applying the first QD dispersion, an EML containing QDs 21 and free of organic ligands can be formed as EML 13.

[0167] 16 has been described as an example in which, after step S42, steps S43 to S26 are subsequently performed to form an organic ligand-free EML 13 containing a metal halide 22. However, this modification is not limited to this example. After step S42, step S6 shown in FIG. 15 may be performed to form an IL 14 on the organic ligand-free EML 13 obtained in step S42. In this case, it is possible to finally manufacture a light-emitting device 1 having an EML 13 containing only a metal halide 31 as a metal halide.

[0168] In any case, this modified example makes it possible to provide a light-emitting element 1 that includes an organic ligand-free EML 13 containing QD 21 and a metal halide 31 (first metal halide), and that includes an IL 14 containing the metal halide 31 and an ETL 15 containing a carrier transport material 41 as a CTL that contains a carrier transport material, arranged adjacent to each other in this order from the EML 13 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 provided adjacent to each other in this order from the EML 13 side, thereby improving the wettability of the carrier transport material dispersion liquid 43 when forming the ETL 15. As a result, a light-emitting element 1 having good layer thickness uniformity and excellent light-emitting characteristics and reliability can be provided.

[0170] As described above, in this modification, the EML 13 may further include a metal halide 22 (second metal halide) in addition to the QDs 21 and the metal halide 31. Also in this modification, similarly to the first modification, a HTL 12 including a carrier transport material 41′ may be formed on the IL 14 as a CTL including a carrier transport material.

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

[0172] The method for manufacturing a light-emitting device according to this embodiment includes forming an EML and forming a CTL on the EML, the CTL forming step including applying a carrier transport material dispersion containing a carrier transport material, a first solvent, and a first metal halide onto the EML, and removing the first solvent. In the applying the carrier transport material dispersion, a metal halide having a solubility in water at 25° C. of 2.5 mg / 100 g or more is used as the first metal halide, and in the forming the EML, either (1) an EML containing QDs 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) an EML containing the QDs and no organic ligand is formed.

[0173] The following description will be given by taking an example in which the EML is formed as an EML containing QDs and the second metal halide in the EML formation step. The following description will also be given by taking an example in which the CTL formed on the EML is an ETL. The following description will also be given by taking an example in which the light-emitting element has a conventional structure in which an anode is a lower electrode and a cathode is an upper electrode, and includes a HIL, a HTL, an EML, and an ETL as functional layers between the anode and the cathode.

[0174] A specific description will be given below with reference to the drawings. Fig. 17 is a flowchart showing an example of a method for manufacturing the light-emitting element 1 according to this embodiment. Fig. 18 is a cross-sectional view showing a schematic configuration of the light-emitting element 1 according to this embodiment. For the sake of convenience, the same reference numerals will be used below for components having the same functions as those described in embodiment 1, and their description will not be repeated. Furthermore, it goes without saying that modifications similar to those in embodiment 1 are possible even if there is no particular explanation.

[0175] 18 , the light-emitting element 1 according to this embodiment has a configuration in which, for example, an anode 2, a HIL 11, a HTL 12, an EML 13, an ETL 15, and a cathode 3 are provided in this order from the lower layer side (e.g., the side of a support such as a substrate, not shown). However, the ETL 15 according to this embodiment is stacked on and adjacent to the EML 13, and contains a carrier transport material 41 and a metal halide 31 (first metal halide). Note that, although not shown and not described in the figures, the light-emitting element 1 may also have functional layers, not shown, other than the HIL 11, the HTL 12, the EML 13, and the ETL 15 between the anode 2 and the cathode 3 in this embodiment.

[0176] 17 and 18, in the method for manufacturing the light-emitting element 1 according to this embodiment, for example, steps S1 to S4 are first performed in the same manner as in Fig. 1. Note that in this embodiment as well, in step S4, the EML 13 may be formed by the method shown in Fig. 5 or the method shown in Fig. 6.

[0177] In this embodiment, after step S4, an ETL 15 is formed on the EML 13 (step S51, carrier transport layer formation step, electron transport layer formation step). In step S51, as shown in FIG. 17 , a carrier transport material dispersion containing a carrier transport material 41, a solvent (first solvent), and a metal halide 31 is first applied to the EML 13 to form a coating film of the carrier transport material dispersion (step S51a, carrier transport material dispersion application step). Next, the coating film is heated or otherwise removed to remove the solvent contained in the coating film, i.e., the solvent (first solvent) contained in the applied carrier transport material dispersion (step S51b, first solvent removal step). This results in the formation of an ETL 15 containing the carrier transport material 41 and the metal halide 31 on the EML 13. Next, step S7, similar to step S7 shown in FIG. 1 , is performed to form a cathode 3 as an upper electrode on the ETL 15. This results in the formation of a light-emitting device 1 shown in FIG. 18 .

[0178] In this manner, in this embodiment, the ETL 15 containing the carrier transport material 41 and the metal halide 31 is formed by applying a carrier transport material dispersion containing the carrier transport material 41, a solvent (first solvent), and the metal halide 31 onto the EML 13. As described above, the metal halide has a size that allows it to pass through the gaps between the QDs 21 in the EML 13.

[0179] For this reason, in this embodiment, as described above, when the carrier transport material dispersion is applied onto the EML 13, the metal halide 31 contained in the carrier transport material dispersion penetrates into the EML 13. As a result, some of the ligands (metal halide 22 and, if organic ligand 23 is included, organic ligand 23) on the surfaces of the QDs 21 in the EML 13 are substituted with the metal halide 31. At the same time, in this embodiment, a coating of the carrier transport material dispersion is formed on the EML 13.

[0180] Therefore, according to this embodiment, by applying the carrier transport material dispersion liquid containing the carrier transport material 41, the solvent (first solvent), and the metal halide 31 onto the EML 13 as described above, it is possible to improve the wettability of the carrier transport material dispersion liquid with respect to the EML 13. As a result, it is possible to manufacture a light-emitting element 1 having a good uniformity in layer thickness and excellent light-emitting characteristics and reliability.

[0181] Furthermore, according to this embodiment, as described above, the EML 13 is coated with a carrier transport material dispersion liquid containing the carrier transport material 41, a solvent (first solvent), and the metal halide 31, thereby forming the ETL 15 directly on the EML 13. Therefore, the number of steps can be reduced compared to the first embodiment, the manufacturing process can be simplified, and the time and cost required for manufacturing can be reduced.

[0182] Moreover, in this embodiment, the carrier transport material dispersion liquid can be applied in a state in which the carrier transport material 41 is modified with the metal halide 31. This improves the dispersibility of the carrier transport material 41. From a process perspective, this embodiment is particularly effective when a CTL such as the ETL 15 is provided on the EML 13 as described above.

[0183] In this embodiment, since the ETL 15 contains the metal halide 31, the formation of the ETL 15 requires the selection of a metal halide 31 that corresponds to the metal halide 22 on the surface of the QDs 21 in the underlying EML 13. In this embodiment, by using metal halides having the same halogen for the metal halide 22 and the metal halide 31, even if the metal halide 31 contained in the metal halide-containing liquid used to form the ETL 15 penetrates into the EML 13, the number of types of halide ions contained in the EML 13 does not increase. Therefore, by using metal halides with the same halogen for the EML 13 and the ETL 15, the effect on the QDs 21 is small, and a decrease in the luminescence characteristics can be suppressed.

[0184] Furthermore, the light-emitting element 1 manufactured by the light-emitting element manufacturing method according to this embodiment has an EML 13 containing QD 21, metal halide 22 (second metal halide), and metal halide 31 (first metal halide), as described above, and has a configuration in which an ETL 15 containing a carrier transport material 41 and metal halide 31 is provided on and adjacent to the EML 13 as a CTL containing a carrier transport material and metal halide 31 (first metal halide).

[0185] According to this embodiment, as described above, the ETL 15 containing the carrier transport material 41 and the metal halide 31 is provided adjacent to the EML 13, which improves the wettability of the coating liquid (carrier transport material dispersion) containing the carrier transport material 41 to the EML 13 when forming the ETL 15. As a result, it is possible to provide a light-emitting element 1 having good layer thickness uniformity and excellent light-emitting characteristics and reliability.

[0186] In this embodiment, as described above, when the EML 13 containing the metal halide 22 is formed, the EML 13 further contains a metal halide 31 in addition to the metal halide 22, as shown in Fig. 18. Therefore, in this embodiment, both the anions 22a and the anions 31a are present as ligands on the surface of the QD 21.

[0187] Therefore, in this embodiment, by using metal halides having the same halogen for the EML 13 and the ETL 15 as described above, even if the metal halide 31 contained in the carrier transport material dispersion liquid used to form the ETL 15 penetrates into the EML 13, the number of types of halide ions contained in the EML 13 does not increase. Therefore, by using metal halides having the same halogen for the EML 13 and the ETL 15, the effect on the QDs 21 is small, and deterioration of the luminescence characteristics can be suppressed.

[0188] In this embodiment, the thickness of each layer of the light-emitting element 1 may be set in the same manner as in the conventional light-emitting element. 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 desirable to appropriately adjust the thickness of the ETL 15 as necessary.

[0189] Furthermore, as described above, even when the carrier transport material dispersion liquid contains the carrier transport material 41, a solvent (first solvent), and a metal halide 31, for the same reasons as those described in embodiment 1, it is preferable that the carrier transport material 41 is a metal oxide, and that the isoelectric point of the carrier transport material dispersion liquid is pH 7 or higher.

[0190] 17 and 18 have been described with reference to an example in which the light-emitting element 1 has a conventional structure in which the anode 2 is the lower electrode. However, in this embodiment, the light-emitting element 1 may also have an inverted structure in which the cathode 3 is the lower electrode. Furthermore, the CTL formed on the EML 13 is not limited to an ETL, and may also be an HTL.

[0191] Therefore, although not shown, the light-emitting element 1 according to this embodiment may have an inverted structure in which the cathode 3 is a lower electrode and the anode 2 is an upper electrode, and may have a configuration in which the cathode 3, ETL 15, EML 13, HTL 12, and anode 2 are provided in this order from the lower layer side (for example, the support side such as a substrate, not shown). Although not shown and described, the light-emitting element 1 in this modification may also have a functional layer, not shown, between the anode 2 and the cathode 3.

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

[0193] As shown in FIG. 19 , in this modification, steps S31, S32, and S4 are performed in this order, similarly to FIG. 14 . Also in this modification, the EML 13 may be formed by the method shown in FIG. 5 or the method shown in FIG. 6 . Next, the HTL 12 is formed on the EML 13 formed in step S4 (step S51′, carrier transport layer formation step, hole transport layer formation step). In step S51′, as shown in FIG. 19 , a carrier transport material dispersion containing the carrier transport material 41′, a solvent (first solvent), and a metal halide 31 is first applied onto the EML 13 to form a coating of the carrier transport material dispersion (step S51a′, carrier transport material dispersion application step). Next, the solvent contained in the coating, i.e., the solvent (first solvent) contained in the applied carrier transport material dispersion, is removed by, for example, heating the coating (step S51b′, first solvent removal step). As a result, the HTL 12 containing the carrier transport material 41′ and the metal halide 31 is formed on the EML 13. Next, step S34 similar to step S34 shown in Fig. 14 is performed to form the anode 2 as an upper electrode on the HTL 12. As a result, the light-emitting element 1 according to this modification is formed.

[0194] In this modification, a carrier transport material dispersion containing a carrier transport material 41′, a solvent (first solvent), and a metal halide 31 is applied onto the EML 13 to form the HTL 12 containing the carrier transport material 41′ and the metal halide 31. As described above, the metal halide has a size that allows it to pass through the gaps between the QDs 21 in the EML 13.

[0195] Therefore, in this modification, as described above, when the carrier transport material dispersion is applied onto the EML 13, the metal halide 31 contained in the carrier transport material dispersion penetrates into the EML 13. As a result, some of the ligands on the surfaces of the QDs 21 in the EML 13 (organic ligands 23 when the EML 13 contains metal halide 22 and organic ligand 23) are substituted with the metal halide 31. At the same time, in this modification, a coating of the carrier transport material dispersion is formed on the EML 13.

[0196] Therefore, according to this modification, by applying the carrier transport material dispersion liquid containing the carrier transport material 41′, the solvent (first solvent), and the metal halide 31 onto the EML 13 as described above, it is possible to improve the wettability of the carrier transport material dispersion liquid with respect to the EML 13. As a result, it is possible to manufacture a light-emitting element 1 having a good uniformity in layer thickness and excellent light-emitting characteristics and reliability.

[0197] Furthermore, according to this modification, as described above, the carrier transport material dispersion liquid containing the carrier transport material 41′, a solvent (first solvent), and the metal halide 31 is applied onto the EML 13, so that the HTL 12 can be formed directly on the EML 13. Therefore, the number of steps can be reduced compared to the first modification of the first embodiment, the manufacturing process can be simplified, and the time and cost required for manufacturing can be reduced.

[0198] Moreover, in this modification, the carrier transport material dispersion liquid can be applied in a state where the carrier transport material 41′ is modified with the metal halide 31. This improves the dispersibility of the carrier transport material 41′.

[0199] In this modification, for the same reasons as those described in embodiment 1, the carrier transport material 41′ is preferably a metal oxide, and the isoelectric point of the carrier transport material dispersion liquid containing the carrier transport material is preferably equal to or higher than pH 7. In this modification, the metal oxide is used as metal oxide nanoparticles.

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

[0201] As described above, the light-emitting element 1 manufactured by the light-emitting element manufacturing method of this modified example has an EML 13 containing QD 21, metal halide 22 (second metal halide), and metal halide 31 (first metal halide), and has a configuration in which a HTL 12 containing a carrier transport material 41' and metal halide 31 is provided on the EML 13 adjacent to the EML 13 as a CTL containing a carrier transport material and metal halide 31 (first metal halide).

[0202] According to this modification, as described above, the HTL 12 containing the carrier transport material 41′ and the metal halide 31 is provided adjacent to the EML 13, which improves the wettability of the coating liquid (carrier transport material dispersion) containing the carrier transport material 41′ to the EML 13 when forming the ETL 15, thereby making it possible to provide a light-emitting element 1 having good layer thickness uniformity and excellent light-emitting characteristics and reliability.

[0203] In this modification, the band gaps of the metal halide 22 and the metal halide 31 are set larger than the band gap of the shell 21 b , thereby making it possible to suppress hole injection from the HTL 12 to the EML 13 .

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

[0205] As shown in FIG. 20 , the method for manufacturing the light-emitting element 1 according to this modification is the same as the method for manufacturing the light-emitting element 1 shown in FIG. 17 , except that step S4′ similar to step S4′ shown in FIG. 15 is performed instead of step S4 shown in FIG. In this modification, an organic ligand-less EML 13 may also be formed in step S4′ by, for example, appropriately adjusting the ligand substitution conditions in step S12 (ligand substitution step) in the light-emitting layer formation step shown in FIG. 5 . Alternatively, an organic ligand-less EML 13 may be formed by additional ligand substitution, such as by performing steps similar to steps S23 to S26 shown in FIG. 6 after step S15 shown in FIG. 5 . Alternatively, an organic ligand-less EML 13 may be formed using the method shown in FIG. 16 .

[0206] As described above, in this modification, the light-emitting layer formation process may also include a first QD dispersion preparation process (step S11) for preparing a QD dispersion (first QD dispersion) containing QDs 21, organic ligands 23, and a solvent (second solvent), and a process for removing the organic ligands 23 before or after applying the first QD dispersion. By removing the organic ligands 23 before or after applying the first QD dispersion, an EML containing QDs 21 and free of organic ligands can be formed as EML 13.

[0207] In any case, according to this modified example, a light-emitting element 1 can be provided that includes an organic ligand-free EML 13 containing QDs 21 and a metal halide 31 (first metal halide), and that includes an ETL 15 containing a carrier transport material 41 and a metal halide 31 as a CTL containing a carrier transport material and a metal halide 31 (first metal halide) on and adjacent to the EML 13.

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

[0209] As described above, in this modification, the EML 13 may further include a metal halide 22 (second metal halide) in addition to the QDs 21 and the metal halide 31. Also in this modification, as in the first modification, a carrier transport layer 12 including a carrier transport material 41′ and a metal halide 31 may be formed on the EML 13 as a carrier transport layer.

[0210] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0211] REFERENCE SIGNS LIST 1 Light-emitting element 2 Anode 3 Cathode 12 HTL (carrier transport layer) 15 ETL (carrier transport layer) 13 EML (light-emitting layer) 14 IL (intermediate layer) 21 QD 21a Core 21b Shell 22 Metal halide (second metal halide) 23 Organic ligand 31 Metal halide (first metal halide) 41, 41' Carrier transport material 42 Solvent (first solvent) 43 Carrier transport material dispersion

Claims

1. A method of manufacturing a semiconductor device comprising the steps of: forming a light-emitting layer including quantum dots; forming an intermediate layer containing a first metal halide on the light-emitting layer; applying a carrier transport material dispersion liquid containing a carrier transport material and a first solvent onto the intermediate layer, and then removing the first solvent to form a carrier transport layer, The first metal halide has a solubility in water at 25° C. of 2.5 mg / 100 g or more; The method for manufacturing a light-emitting element is characterized in that it satisfies at least one of a first condition 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, and a second condition that the quantum dots in the light-emitting layer are organic ligand-less.

2. The method for manufacturing the light-emitting element described in claim 1, characterized in that the method for manufacturing the light-emitting element satisfies the first condition.

3. The step of forming the light emitting layer includes: preparing a quantum dot dispersion liquid containing the quantum dots, organic ligands of the quantum dots, and a second solvent; The method for manufacturing a light-emitting element according to claim 2, further comprising the step of substituting the organic ligand with the second metal halide before or after applying the quantum dot dispersion liquid.

4. 4. The method for manufacturing a light-emitting device according to claim 2, wherein the halogen of the first metal halide is the same as the halogen of the second metal halide.

5. The method for manufacturing the light-emitting element described in claim 1, characterized in that the method for manufacturing the light-emitting element satisfies the second condition.

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

7. In the step of applying the carrier transport material dispersion liquid, the intermediate layer is dissolved to a thickness of 2 nm or more in the first solvent, A method for manufacturing a light-emitting element described in any one of claims 1 to 3, 5 and 6, characterized in that, when the thickness of the intermediate layer dissolved by the first solvent is T nm (T≧2), in the process of forming the intermediate layer, the intermediate layer is formed to have a thickness of 2+T nm or more.

8. A step of forming a light-emitting layer including quantum dots; a carrier transport material dispersion liquid containing a carrier transport material, a first solvent, and a first metal halide is applied onto the light-emitting layer, and the first solvent is subsequently removed to form a carrier transport layer, The first metal halide has a solubility in water at 25° C. of 2.5 mg / 100 g or more; The method for manufacturing a light-emitting element is characterized in that it satisfies at least one of a first condition 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, and a second condition that the quantum dots in the light-emitting layer are organic ligand-less.

9. The method for manufacturing the light-emitting element described in claim 8, characterized in that the method for manufacturing the light-emitting element satisfies the first condition.

10. The step of forming the light emitting layer includes: preparing a quantum dot dispersion liquid containing the quantum dots, an organic ligand, and a second solvent; The method for manufacturing a light-emitting element according to claim 9, further comprising the step of substituting the organic ligand with the second metal halide before or after applying the quantum dot dispersion liquid.

11. 11. The method for manufacturing a light-emitting element according to claim 9, wherein the halogen of the first metal halide is the same as the halogen of the second metal halide.

12. The method for manufacturing the light-emitting element described in claim 8, characterized in that the method for manufacturing the light-emitting element satisfies the second condition.

13. The step of forming the light emitting layer includes: preparing a quantum dot dispersion liquid containing the quantum dots, organic ligands of the quantum dots, and a second solvent; The method for manufacturing a light-emitting element according to claim 12, further comprising the step of removing the organic ligand before or after applying the quantum dot dispersion liquid.

14. The quantum dot has a core and a shell, The method for manufacturing a light-emitting element according to any one of claims 1 to 3, 5, 6, 8 to 10, 12 and 13, characterized in that the band gap of the first metal halide and the band gap of the second metal halide are each larger than the band gap of the shell.

15. The first metal halide is LiF, NaF, KF, RbF, CsF, BeF ２ , MgF ２ , SrF ２ , BaF ２ , AlF ３ , InF ３ , PbF ２ , LiCl, NaCl, KCl, RbCl, CsCl, BeCl ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , AlCl ３ , GaCl ３ , LiBr, NaBr, KBr, RbBr, CsBr, BeBr ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , AlBr ３ , SnBr ２ , LiI, NaI, KI, RbI, CsI, BeI ２ , MgI ２ , CaI ２ , and SrI ２ 14. The method for producing a light-emitting device according to claim 1, wherein the organic layer is at least one selected from the group consisting of:

16. the carrier transport material is a metal oxide, 14. The method for producing a light-emitting element according to claim 1, wherein the carrier transporting material dispersion has an isoelectric point of pH 7 or higher.

17. A light-emitting device comprising a light-emitting layer including quantum dots and a first metal halide, The light-emitting element satisfies at least one of a first condition that an intermediate layer containing the first metal halide and a carrier transport layer containing a carrier transport material are provided on the light-emitting layer so as to be adjacent to each other in this order from the light-emitting layer side, or a second condition that a carrier transport layer containing a carrier transport material and the first metal halide is provided on the light-emitting layer; A light-emitting device, wherein the first metal halide has a solubility in water at 25° C. of 2.5 mg / 100 g or more.

18. The light-emitting device according to claim 17 , wherein the light-emitting layer further comprises 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 described in claim 17 or 18, characterized in that the manufacturing method of the light-emitting element satisfies the first condition.

20. The light-emitting device according to claim 19, wherein the intermediate layer has a thickness of 2 nm or more.

21. The light-emitting element described in claim 17 or 18, characterized in that the manufacturing method of the light-emitting element satisfies the second condition.