Light-emitting element and display device

Abstract

The present disclosure provides a light-emitting element for which there is a reduced possibility of a decrease in brightness which occurs as a consequence of being driven over a long period of time. A light-emitting element (1) comprises a light-emitting layer (13) including quantum dots (133) and a halogen. The light-emitting layer (13) includes at least one auxiliary layer (132) including at least one oxide selected from the group consisting of metal oxides, metalloid oxides, and precursors thereof. The metal oxides and the metalloid oxides have a number of oxygen atoms greater than half the valence of the metal atoms or metalloid atoms.

Description

Light-emitting element and display device

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

[0002] A light-emitting layer containing semiconductor nanocrystalline particles such as quantum dots emits light when energy such as an electric current is injected into the semiconductor nanocrystalline particles. For example, a technique for increasing the luminous efficiency of a light-emitting layer containing such semiconductor nanocrystalline particles is known in which the gaps between the semiconductor nanocrystalline particles in the light-emitting layer are filled with a sintered body of a conductive semiconductor material (see, for example, Patent Document 1).

[0003] Japan Special Table No. 2010-526420

[0004] On the other hand, in a light-emitting device having a light-emitting layer containing the above-described semiconductor nanocrystalline particles, the luminance of the light-emitting layer may decrease when driven for a long period of time.

[0005] An object of one embodiment of the present disclosure is to provide a light-emitting element in which a decrease in luminance due to long-term driving is suppressed.

[0006] In order to solve the above problems, a light-emitting element according to one embodiment of the present disclosure has an emission layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semimetal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the semimetal atoms, and precursors thereof, and the emission layer contains at least the oxide as an auxiliary layer.

[0007] In order to solve the above problem, a display device according to an aspect of the present disclosure includes the above light-emitting element.

[0008] According to one embodiment of the present disclosure, a light-emitting element in which a decrease in luminance due to long-term driving is suppressed can be realized.

[0009] FIG. 1 is a diagram schematically showing a layer configuration of a light-emitting device according to a first embodiment of the present disclosure. FIG. 2 is a diagram for explaining an example of a manufacturing process for quantum dots according to the present disclosure. FIG. 3 is a diagram for explaining an example of a manufacturing method for quantum dots according to the present disclosure. FIG. 4 is a diagram schematically showing a configuration of a display device according to a first embodiment of the present disclosure. FIG. 5 is a diagram schematically showing a layer configuration in a display device according to a first embodiment of the present disclosure. FIG. 6 is a diagram for explaining a reaction state of an example of a semi-metal oxide according to the present disclosure. FIG. 7 is a diagram for explaining the oxygen number of an example of a semi-metal oxide according to the present disclosure. FIG. 8 is a diagram for explaining changes in quantum dots in a light-emitting device according to a first embodiment of the present disclosure. FIG. 9 is a diagram for explaining changes in quantum dots in a light-emitting device having no auxiliary layer. FIG. 10 is a diagram schematically showing a layer configuration of a light-emitting device according to a second embodiment of the present disclosure. FIG. 11 is a diagram schematically showing a layer configuration of a light-emitting device according to a third embodiment of the present disclosure. FIG. 12 is a diagram schematically showing a layer configuration of a light-emitting device according to a fourth embodiment of the present disclosure. FIG. 13 is a diagram schematically showing a layer configuration of a light-emitting device according to a fifth embodiment of the present disclosure. FIG. 14 is a diagram schematically showing a layer configuration in a display device according to a sixth embodiment of the present disclosure.

[0010] In this specification, the symbol "to" means a range including both the numerical values ​​at both ends.

[0011] [First embodiment] [Light-emitting element] A first embodiment of the present disclosure will be described using a light-emitting element that emits light by application of a voltage as an example. The layer structure of the light-emitting element according to the first embodiment is schematically shown in Fig. 1. As shown in Fig. 1, the light-emitting element 1 has a first electrode 11, a hole transport layer 12, a light-emitting layer 13, an electron transport layer 14, and a second electrode 15.

[0012] In this embodiment, the first electrode 11 serves as an anode and the second electrode 15 serves as a cathode depending on the configuration of the light-emitting element. The anode is an electrode for supplying holes to each layer constituting the light-emitting element. The cathode is an electrode for supplying electrons to each layer constituting the light-emitting element. Both the anode and the cathode are conductive.

[0013] To enhance hole injection properties, a material with a relatively high work function (e.g., a material with a work function of 4.5 eV or more) is preferably used as the anode material. Examples of electrode materials with a high work function include Pt (5.65 eV), Ir (5.25 eV), Ni (5.2 eV), Au (5.15 eV), and Pd (5.15 eV), as well as indium tin oxide (In—Sn—O).

[0014] The anode has optical properties such as reflecting a portion of visible light and transmitting the remainder, and typically includes both an electrode material that reflects visible light and an electrode material that transmits visible light.

[0015] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, Ag, Pd, and Cu, as well as alloys of these metal materials (such as APC (Ag-Pd-Cu) alloy).

[0016] Examples of electrode materials that transmit visible light include thin films of transparent metal oxides (e.g., indium tin oxide, indium zinc oxide (In—Zn—O), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), FTO (fluorine-doped tin oxide), and indium gallium zinc oxide (In—Ga—Zn—O)), thin films made of metal materials such as Al, Mg, and Ag, or alloys of these metal materials (e.g., Mg—Ag alloy), and nanowires (NW) made of these metal materials. Transparent electrodes can be formed by sputtering or the like.

[0017] Among transparent metal oxides, indium tin oxide has a relatively high work function of 4.6 to 5.0 eV and is therefore suitable for use as an anode material. Furthermore, for the anode, a laminate (e.g., indium tin oxide / Ag) in which an indium tin oxide layer is formed on the surface of a metal material can be used for the purpose of improving the conductivity as an electrode layer or adding the function of reflecting visible light.

[0018] The cathode has, for example, electrical conductivity and visible light transparency. A material with a relatively small work function is preferably used as the cathode material, for example, from the viewpoint of enhancing electron injection properties. Examples of electrode materials constituting the cathode include metal materials such as alkali metals, alkaline earth metals, and Al, alloys containing these, and nanowires (e.g., Ag nanowires). Examples of alloys include alloys of Mg and Ag, and Al doped with a small amount of Li.

[0019] The hole transport layer 12 may be composed of the hole transport material described above. It may be composed of a hole transport material that transports holes from the anode to the light-emitting layer. The hole transport material may be an organic or inorganic material that has been conventionally used in light-emitting devices including quantum dots. For example, the hole transport material may include at least one of polyvinylcarbazole (PVK) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD). Examples of organic hole transport materials include conductive compounds such as 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB). Examples of inorganic hole transport materials include molybdenum oxide, NiO, Cr ２ O ３ , MgO, MgZnO, LaNiO ３ , MoO ３ , or W.O. ３ The hole transport material is particularly preferably a material having a large electron affinity and ionization potential.

[0020] The light-emitting layer 13 contains quantum dots and will be described in detail later.

[0021] The electron transport layer 14 may be composed of an electron transport material that transports electrons from the cathode to the light-emitting layer. The electron transport material may be an organic or inorganic material that has been conventionally employed in light-emitting devices, such as quantum dot-containing light-emitting devices. For example, the electron transport material may be zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO ３ ), or may include inorganic nanoparticle materials that are nanoparticles of these inorganic materials. Examples of organic electron transport materials include tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), and (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Examples of inorganic electron transport materials include metal oxides such as ZnO, ZAO, ITO, InGaZnO, or electride. It is particularly preferable that the electron transport material be a material with a small electron affinity.

[0022] As described above, in the light-emitting element 1 of this embodiment, the first electrode, the light-emitting layer, and the second electrode are arranged in this order.

[0023] [Light-Emitting Layer] The light-emitting layer 13 includes a QD layer 131 and an auxiliary layer 132. The QD layer 131 is a layer containing quantum dots (QDs) 133. The auxiliary layer 132 is a layer adjacent to the QD layer 131 in the stacking direction and contains one or more compounds selected from the group consisting of metal oxides, semi-metal oxides, and precursors thereof, which will be described later. The light-emitting layer 13 also contains a halogen in one or both of the QD layer 131 and the auxiliary layer 132. Thus, the light-emitting element 1 has a light-emitting layer 13 containing quantum dots and a halogen.

[0024] It is preferable that the thickness of the QD layer 131 be sufficiently large relative to the particle size of the quantum dots 133, so that a sufficient number of quantum dots 133 are present in the thickness direction of the QD layer 131 and the brightness of the light-emitting layer 13 is increased. From this perspective, the thickness of the QD layer 131 is preferably at least twice the particle size of the quantum dots 133. On the other hand, if the thickness of the QD layer 131 is too thick, the resistance of the QD layer 131 may increase, resulting in a high driving voltage for the light-emitting device. Therefore, the thickness of the QD layer 131 may be no more than five times the particle size of the quantum dots 133. The film thickness of the QD layer 131 can be specifically determined from the above perspective and may be, for example, approximately 5 to 100 nm.

[0025] In the present disclosure, the thickness of the QD layer 131 is expressed as the maximum thickness in a region of about 100 nm at any position on the cross section of the light-emitting element 1 photographed with a scanning electron microscope (SEM). Furthermore, in the present disclosure, the particle size of the quantum dots 133 is expressed as the diameter of a circle having an area equal to the average area of ​​10 quantum dots 133 extracted from the image of the cross section of the light-emitting element 1 photographed with a scanning electron microscope (SEM). Note that, for example, if the quantum dots 133 have a core-shell structure, the particle size of the quantum dots 133 is the particle size of the quantum dots 133 including the shell.

[0026] The QD layer 131 has a thickness of 1000 nm in a direction perpendicular to the thickness direction of the QD layer 131 (hereinafter also referred to as the "plane direction"). ２ It is sufficient that one or more quantum dots 133 are included per one.

[0027] [Quantum Dots] The quantum dots 133 include a dot body 134 and a ligand 135 coordinated to its surface. The dot body 134 is a semiconductor particle with a particle size of approximately 100 nm or less (for example, several nm to several tens of nm), and emits light, for example, due to excitons generated by the recombination of injected electrons and holes. Because the composition of the dot body 134 is derived from a semiconductor material, it is also called a (luminescent) semiconductor nanoparticle.

[0028] The wavelength of light emitted from the quantum dots 133 can be controlled by the particle size of the dot body 134. In quantum dots 133 having a core-shell structure described below, the wavelength of light emitted from the quantum dots 133 can be controlled by controlling the particle size of the core. In this way, by controlling the particle size or composition of the dot body 134, the wavelength of light emitted from the light-emitting layer 13 can be controlled.

[0029] There are no limitations on the shape of the dot body 134. For example, the shape of the dot body 134 may be a spherical three-dimensional shape (with a circular cross section), or may be a polygonal three-dimensional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, or a three-dimensional shape with an uneven surface, or a combination thereof.

[0030] The dot body 134 may be formed of only a core, or may have a core-shell structure including a core and a shell. The shell may be formed in a solid solution state on the surface of the core. The dot body 134 may also include doped nanoparticles.

[0031] For example, recombination of electrons and holes in the dot body 134 occurs mainly in the core. The core of the dot body 134 has a valence band level and a conduction band level, and emits light by recombination of holes in the valence band level and electrons in the conduction band level. Light emitted from the quantum dot 133 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain light with a relatively deep chromaticity. Furthermore, the shell has the function of suppressing the occurrence of defects or dangling bonds in the core and reducing the recombination of carriers that undergo a deactivation process.

[0032] Examples of materials for the core of the dot body 134 include Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, and ZnSeTe. Examples of materials for the shell of the dot body 134 include CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AIP.

[0033] Examples of combinations of core and shell materials for the dot body 134 include CdSe / CdS, InP / ZnS, ZnSe / ZnS, and CIGS / ZnS.

[0034] Various known ligands can be used as the ligand 135. The ligand 135 may be an organic ligand, an inorganic ligand, or may contain both.

[0035] As shown in Figures 1 and 2, the ligand 135 includes both an organic ligand 135a and an inorganic ligand 135c. The organic ligand 135a does not include a metal oxide or a semi-metal oxide but includes a carbon atom. The inorganic ligand 135c includes a metal oxide or a semi-metal oxide and may further include a carbon atom. The inorganic ligand 135c includes an inorganic ligand 135b and a linking portion connected to the inorganic ligand 135b. The linking portion, which will be described in detail later, is a portion configured by bonding the inorganic ligand 135b to a metal oxide or semi-metal oxide in the auxiliary layer 132. In this way, the quantum dot 133 may include an organic ligand 135a as part of the ligand. Bonding the inorganic ligands 135b to each other via a linking portion is preferable because the inorganic ligand 135c is less likely to detach from the quantum dot and the quantum dot surface can be strongly protected. In addition, oxygen or moisture that penetrates into the QD layer of the light-emitting element is blocked by the connecting portion and does not reach the quantum dots, so the quantum dots are less likely to deteriorate.

[0036] If the amount (coordination amount) of the organic ligands 135a coordinated to the quantum dots 133 in the light-emitting layer 13 is too large, the organic ligands 135a may be detached from the dot bodies 134, resulting in a decrease in the brightness of the light-emitting layer 13. If the amount is too small, the quantum dots 133 may be aggregated and present in the QD layer 131. From the viewpoint of suppressing a decrease in the brightness of the light-emitting layer 13, the coordination amount is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. Furthermore, from the viewpoint of ensuring that the quantum dots 133 are sufficiently dispersed and present in the QD layer 131, the coordination amount of the organic ligands 135a in the quantum dots 133 is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more.

[0037] The coordination amount of the organic ligand 135a can be determined by the following method. For example, the amount of the organic ligand 135a in the entire light-emitting layer 13 is represented by the number A of carbon atoms in a specific region (e.g., a region approximately 100 nm square) in the cross section of the light-emitting layer 13. The amount of the organic ligand 135a coordinated to the quantum dot 133 is represented by the number B of carbon atoms detected at substantially the same position as the element specific to the quantum dot 133 (a region within 2 nm around the quantum dot 133). Therefore, the coordination amount (%) of the organic ligand 135a can be determined by B / A×100.

[0038] If the ratio of the amount of organic ligand (here, the number of carbon atoms) to the amount of inorganic ligand 135c in quantum dots 133 (here, the number of metal atoms or metalloid atoms in the metal oxide or metalloid oxide) is too small, quantum dots 133 may exist in an aggregated state in QD layer 131. From the viewpoint of ensuring that quantum dots 133 exist in a sufficiently dispersed state in QD layer 131, this ratio is preferably 5 or more, more preferably 10 or more, and even more preferably 15 or more.

[0039] In the present disclosure, the organic ligand may be replaced with a metal oxide or semi-metal oxide as the light-emitting device is used (light emission), and therefore the above ratio may decrease with use over time.

[0040] The amount of organic ligand in the quantum dot 133 is represented by the number of carbon atoms B described above. The amount of inorganic ligand 135c in the quantum dot 133 is represented by the number of metal atoms or metalloid atoms C of the metal oxide or metalloid oxide detected at substantially the same position as the element specific to the quantum dot 133 (a region within 2 nm around the quantum dot 133). Therefore, the ratio of the amount of inorganic ligand 135c to the amount of organic ligand in the quantum dot 133 can be calculated as B / C.

[0041] [Auxiliary Layer] The light-emitting layer 13 further includes at least one auxiliary layer 132 containing one or more compounds selected from the group consisting of metal oxides, semi-metal oxides, and precursors thereof (hereinafter also referred to as "auxiliary layer compounds"). Thus, in the present disclosure, the auxiliary layer 132 constitutes a part of the light-emitting layer 13 in the thickness direction.

[0042] The metal oxide is an oxide of a metal having a number of oxygen atoms greater than half the valence of the metal atom. Examples of the metal oxide include titanium oxide, aluminum oxide, phosphorus oxide, germanium oxide, hafnium oxide, zirconium oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, and copper oxide.

[0043] The metalloid oxides are oxides of metalloids with a number of oxygen atoms greater than half the valence of the metalloid atom. "Metalloids" are generally substances that exhibit properties intermediate between metals and nonmetals. Examples of metalloids include boron, silicon, arsenic, and tellurium. Examples of metalloid oxides include silicon oxide, boron oxide, and tellurium oxide.

[0044] In the auxiliary layer 132, the metal oxides and metalloid oxides have a number of oxygen atoms greater than half the valence of the metal or metalloid atoms. The "valence of a metal atom" refers to the valence of a metal atom in a metal oxide having the most stable composition ratio, and the "valence of a metalloid atom" refers to the valence of a metalloid atom in a metalloid oxide having the most stable composition ratio. Examples of the valences of such metal atoms and metalloid atoms are listed below: Si: tetravalent, Ti: tetravalent, Al: trivalent, B: trivalent, P: pentavalent, Ge: tetravalent, Hf: tetravalent, Zn: divalent, Zr: tetravalent, Te: tetravalent, Bi: trivalent, V: pentavalent, Sb: pentavalent, Pb: divalent, Cu: divalent, Cd: divalent, Fe: divalent, Mn: divalent, Ni: divalent, W: hexavalent, and Mg: divalent.

[0045] The inclusion of the auxiliary layer 132 containing the metal oxide or semi-metal oxide having the above-described valence in the light-emitting layer 13 is effective in suppressing deterioration over time of the quantum dots 133 in the QD layer 131. The mechanism by which the metal oxide or semi-metal oxide in the auxiliary layer 132 protects the quantum dots 133 will be described later.

[0046] The semi-metal oxide is silicon oxide because it contains a functional group (-SH or -NH) capable of coordinating with quantum dots, such as compounds represented by the following formulas 1 and 2: ２ 7) and a material in which a part that causes a reaction to form Si—O—Si is bonded via a strong covalent bond as shown in FIG. 7, which is preferable from the viewpoint that the functional group is unlikely to be detached from the quantum dot and the quantum dot surface can be strongly protected. In this case, the quantum dot 133 has the inorganic ligand body 135c described above, and a part of the inorganic ligand body 135c has SiO Ｘ and auxiliary layer 132 may include SiO Ｙ where X<Y and Y>2. Such a configuration may include SiO ２ This is preferable from the viewpoint of increasing the coverage rate of the QD layer and is preferable from the viewpoint of more strongly protecting the quantum dots in the QD layer.

[0047] The semi-metal oxide may include, for example, one or both of a compound represented by the following formula 1 and a compound represented by the following formula 2.

[0048]

[0049] In the above formula, R １ , R ２ and R ３ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 10.

[0050] The compound of formula 1 and the compound of formula 2 each contain a functional group (-SH or -NH) capable of coordinating to a quantum dot. ２ In addition, the ratio of the number of oxygen atoms to the number of silicon atoms (O / Si) is 3 in all cases, and the number of oxygen atoms is 3, which is greater than half (2) of the valence of Si (4). １ , R ２ and R ３ In order to promote the Si—O—Si forming reaction described later, it is preferable that the number of carbon atoms contained is small, and it is more preferable that the group is a hydrogen atom, methyl or ethyl.

[0051] Examples of the compounds of formula 1 and formula 2 include (3-mercaptopropyl)trimethoxysilane (MPTS), (3-mercaptopropyl)triethoxysilane, 3-aminopropyltrimethoxysilane (APS), 3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane, and 4-aminobutyltriethoxysilane (these are referred to as compound group C1).

[0052] The compounds of formula 1 and formula 2 each contain -SH or -NH ２ The compound can be further bonded to the quantum dot via a siloxane bond to form the inorganic ligand 135c. Therefore, the semimetal oxide can be one or both of the compound of Formula 1 and the compound of Formula 2, and the SiO ２The structure prevents the structures (inorganic ligands and inorganic ligand bodies) derived from the compound from being detached from the quantum dots, and the SiO ２ This is preferable from the viewpoint of blocking by the structure.

[0053] Alternatively, the metalloid oxide may include one or both of a compound represented by the following formula 3 and a compound represented by the following formula 4:

[0054]

[0055] In the above formula, R １ , R ２ , R ３ and R ４ each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ５ represents a hydrocarbon group having 1 to 20 carbon atoms.

[0056] The O / Si ratio of the compound of formula 3 is 4, and the O / Si ratio of the compound of formula 4 is 3. Thus, both compounds have a number of oxygen atoms greater than half the valence of Si. １ , R ２ , R ３ and R ４ R preferably contains a small number of carbon atoms, and more preferably is a hydrogen atom, methyl, or ethyl, in order to promote the Si—O—Si forming reaction described below. ５ The hydrocarbon group is preferably a saturated or unsaturated hydrocarbon group having 1 to 4 carbon atoms, so as not to prevent current injection into the quantum dots.

[0057] Examples of the compounds of formula 3 and formula 4 include tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetraisopropyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, tetraiso ... Orthosilicate, Trimethoxymethylsilane, Triethoxymethylsilane, Trimethox y(propyl)silane, Triethoxy(propyl)silane, Butyltrimethoxysilane, Butylt riethoxysilane, triethoxy(isobutyl)silane, cyclopentyltrimethoxysilane , Hexyltrimethoxysilane, Hexyltriethoxysilane, Decyltrimethoxysilane, Dec Examples of the silanes include hexadecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltriethoxysilane, octadecyltriethoxysilane, trimethoxyphenylsilane, triethoxyphenylsilane, allyltrimethoxysilane, allyltriethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane (these are designated as compound group C2).

[0058] Both the compound of Formula 3 and the compound of Formula 4 can be further bonded to the compound coordinated to the quantum dots via a siloxane bond to form the inorganic ligand 135c. Therefore, when the semimetal oxide is one or both of the compound of Formula 3 and the compound of Formula 4, the oxygen and moisture reaching the QD layer can be prevented from reaching the quantum dots by the SiO ２ This is preferable from the viewpoint of blocking by the structure.

[0059] In the present disclosure, the number of atoms, such as carbon atoms, silicon atoms, and oxygen atoms, near the quantum dot surface in the cross section of the auxiliary layer or QD layer can be determined by Auger electron spectroscopy (AES).Furthermore, in the present disclosure, the structure of the metal oxide or metalloid oxide in the light-emitting layer can be determined by gas chromatography mass spectrometry (GCMS).

[0060] The precursor is a compound that changes into a metal oxide or semi-metal oxide at least under the conditions of use of the light-emitting device (or unconditionally in the auxiliary layer). Therefore, the auxiliary layer may contain a precursor thereof instead of the metal oxide or semi-metal oxide. Examples of the precursor include acids, sulfates, nitrates, and acetates of the metal or semi-metal oxide in the metal oxide or semi-metal oxide.

[0061] If the thickness of each auxiliary layer 132 is too thick, it may be difficult to inject current into the quantum dots in the QD layer, and if it is too thin, the protection of the quantum dots in the QD layer may become insufficient over time. From the viewpoint of long-term stability of the luminous efficiency of the QD layer, the thickness of each auxiliary layer 132 is preferably 1 nm or more and 3 nm or less. In an embodiment in which multiple auxiliary layers 132 exist in one emitting layer, or in an embodiment in which multiple emitting layers exist in one light-emitting device, the above-mentioned thickness of the auxiliary layer 132 is the thickness per layer. It is preferable that the auxiliary layer 132 has the above-mentioned thickness from the viewpoints of enabling a current applied to the light-emitting element to tunnel through the auxiliary layer and of allowing sufficient current to be passed through the quantum dots in the emitting layer.

[0062] The auxiliary layer compound may include a compound that is liquid at the operating temperature of the light-emitting device of the present disclosure. Therefore, in the present disclosure, the auxiliary layer may be liquid. In the present disclosure, the auxiliary layer may be such that the auxiliary layer compound is unevenly distributed along the surface direction of the light-emitting layer, partially distributed in the thickness direction of the light-emitting layer, and substantially continuously distributed along the surface direction of the light-emitting layer. The auxiliary layer may be a layer that is substantially adjacent to the QD layer in the thickness direction of the light-emitting layer, as described above, or may be a layer that overlaps a portion of the QD layer (i.e., some of the QDs in the QD layer are included in the auxiliary layer).

[0063] Such an auxiliary layer can be specified based on the specific gravity of the portion of the light-emitting layer that contains the auxiliary layer compound that constitutes the auxiliary layer.

[0064] For example, the above-mentioned auxiliary layer can be specified as a portion of the light-emitting layer containing the auxiliary layer compound, the specific gravity of which is 0.7 times or more that of the auxiliary layer compound. The specific gravity can be determined from the amount of the auxiliary layer compound present per unit volume of the light-emitting layer. Taking TMOS as an example, the specific gravity of TMOS alone is 1.03 and its molecular weight is 152. Therefore, the number of TMOS molecules per given volume can be calculated by multiplying the specific gravity by the volume / molecular weight by the Avogadro constant, and is given as follows: ３ The number of particles per atom is approximately 4. Here, Avogadro's constant is 6.02 × 10 ２３ mol －１ Since one TMOS molecule contains one Si atom, ３ The amount of Si atoms present per unit volume in an actual device was measured, and the value was found to be the same as that of the TMOS alone (1 nm ３ The portion that is 0.7 times or more of the number of particles (approximately 4 particles per particle) can be considered as the auxiliary layer.

[0065] The thickness of the auxiliary layer is expressed as the length of a portion on the top of the quantum dot in the thickness direction of the light-emitting layer, the portion having a specific gravity of 0.7 times or more that of the auxiliary layer compound. More specifically, the thickness of the auxiliary layer is expressed as the average value of the lengths of the portions on the top of the quantum dot, measured at 10 random points within an arbitrary range of about 100 nm in length in the cross section of the light-emitting layer. The identification of the auxiliary layer is suitable for identifying an auxiliary layer that includes a portion of the quantum dot in the thickness direction.

[0066] Alternatively, in the present disclosure, the auxiliary layer is a portion in which the auxiliary layer compound is present continuously along the surface direction of the light-emitting layer without substantially containing quantum dots, and is unevenly distributed in a portion in the thickness direction of the light-emitting layer.

[0067] Such an auxiliary layer can be identified by the presence of an auxiliary layer compound that constitutes the auxiliary layer in the light-emitting layer, which can be identified by the ratio of specific elements that constitute the auxiliary layer compound, for example, the ratio of metal or metalloid elements to oxygen elements in a cross section of the light-emitting layer if the auxiliary layer compound is a metal oxide or metalloid oxide.

[0068] The thickness of the auxiliary layer is expressed as the length of the portion above the quantum dots in the thickness direction of the light-emitting layer, in the region where the auxiliary layer compound is present, in the portion that does not contain quantum dots along the surface direction of the light-emitting layer. More specifically, the thickness of the auxiliary layer is expressed as the average value of the length of the portion above the quantum dots measured at 10 random points within an arbitrary range of about 100 nm in length in the cross section of the light-emitting layer. The identification of the auxiliary layer is suitable for identifying an auxiliary layer that does not substantially overlap with the quantum dots in the thickness direction. As will be described in detail later, the thickness or position of the auxiliary layer may change over time. The auxiliary layer of the present disclosure may be identified by at least one of the methods described above.

[0069] The auxiliary layer is located on one side of the light-emitting layer in the thickness direction of the light-emitting layer. This arrangement of the auxiliary layer is preferable from the viewpoint of simplifying the manufacturing process by adding only one additional step of forming the auxiliary layer. In particular, the auxiliary layer is located on the cathode (second electrode) side of the light-emitting layer in the thickness direction of the light-emitting layer. With this arrangement of the auxiliary layer, it is expected that the metal oxide or metalloid oxide having oxygen atoms in the auxiliary layer with more than half the valence of the oxygen atoms in the stable state in the auxiliary layer will diffuse to the anode side (i.e., the light-emitting layer) due to the electric field of the light-emitting layer when a current is applied. Therefore, this is preferable from the viewpoint of further promoting protection of the quantum dots in the light-emitting layer by the metal oxide or metalloid oxide in the auxiliary layer.

[0070] If the ratio B / D of the amount B (the number of carbon atoms) of the organic ligands contained in the quantum dots to the amount D of the auxiliary layer compound contained in the auxiliary layer is too high, the protection of the quantum dots may become insufficient over time, and if it is too low, it may have an adverse effect on the current efficiency of the light-emitting element. From the viewpoint of sufficiently increasing the current efficiency of the light-emitting element, B / D is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more. From the viewpoint of ensuring sufficient protection of the quantum dots over a long period of time, B / D is preferably 100 or less, more preferably 50 or less, and even more preferably 20 or less.

[0071] The amount D of the auxiliary layer compound is expressed as the number of metal atoms or metalloid atoms in the metal oxide, metalloid oxide, and precursors thereof.

[0072] [Halogen] The light-emitting layer contains a halogen. The halogen acts as a catalyst for the condensation reaction when the auxiliary layer compound in the auxiliary layer forms an inorganic ligand. Thus, in the present disclosure, the light-emitting layer contains a halogen as an initiator for the reaction to form the inorganic ligand. The halogen may be in any form as long as it exhibits this function, and may be included in the light-emitting layer as a halogen compound. The type of halogen can also be appropriately selected from fluorine, chlorine, bromine, and iodine as long as it exhibits the above-mentioned catalytic function. Examples of the halogen compound include zinc fluoride, zinc chloride, zinc bromide, zinc iodide, indium fluoride, indium chloride, indium bromide, and indium iodide.

[0073] The halogen content in the light-emitting layer may be an amount sufficient to catalyze the reaction in the QD layer in which the auxiliary layer compound reaches the QD layer and forms an inorganic ligand with respect to the inorganic ligand coordinated to the quantum dots. For example, the halogen content in the light-emitting layer may be in a molar ratio of 0.3 to 3, expressed as a molar ratio of halogen to metal and metalloid elements in the auxiliary layer compound of the auxiliary layer.

[0074] The halogen may be present in the QD layer, the auxiliary layer, or both layers. When the halogen is present in the QD layer, the halogen may be carried by the quantum dots or may be included independently of the quantum dots. When the halogen is present in the auxiliary layer, the halogen may be carried by the auxiliary layer compound or may be included independently of the auxiliary layer compound.

[0075] The inclusion of a halogen in the QD layer of the light-emitting layer, i.e., the light-emitting layer including an auxiliary layer containing an auxiliary layer compound and a layer containing quantum dots and a halogen, is preferred from the viewpoint of preferentially forming an inorganic ligand body, and is suitable when the auxiliary layer compound is a metalloid oxide represented by the aforementioned formula (3) or formula (4). Furthermore, the inclusion of a halogen in the QD layer allows at least a portion of the halogen to be coordinated to the QDs, and is therefore preferred from the viewpoint of protecting the QDs through the presence of such a halogen. The inclusion of a halogen in the auxiliary layer of the light-emitting layer is preferred from the viewpoint of allowing the auxiliary layer compound capable of coordinating with the quantum dots to act on the quantum dots according to the state of the quantum dots in the QD layer, and is suitable, for example, when the auxiliary layer compound is a metalloid oxide represented by the aforementioned formula (1) or formula (2).

[0076] [Example of Quantum Dot Preparation] Quantum dots can usually be stably protected and stored in a solution state dispersed in a non-polar solvent by a long-chain organic ligand. The quantum dots of the present disclosure can be prepared, for example, by replacing some of the organic ligands that the quantum dots already have with inorganic ligands that can coordinate to QDs, such as compounds selected from compound group C1, and then growing the inorganic ligand body.

[0077] In the ligand replacement, the non-polar solvent layer 31 and the polar solvent layer 32 are placed in the same container, and quantum dots having an organic ligand, a precursor of an inorganic ligand (metalloid oxide) (e.g., at least one of the compounds of compound group C1 and compound group C2), and a halogen source (e.g., a metal halide described later) are dispersed in the above-mentioned solvent.

[0078] The quantum dots having organic ligands are dispersed in the non-polar solvent layer 31, but not in the polar solvent layer 32. Therefore, they exist only in the upper layer. In contrast, the precursors of inorganic ligands and halogens are dispersed in the polar solvent layer 32, but not in the non-polar solvent layer 31. Therefore, they exist only in the lower layer.

[0079] Next, the two solvents in the container are stirred for an appropriate period (e.g., several hours to a day). This stirring causes the organic ligands to be desorbed from the quantum dots, and the precursors of the inorganic ligands are coordinated to the quantum dots. As a result, the polarity of the quantum dots changes, and they no longer disperse in either the nonpolar solvent layer 31 or the polar solvent layer 32. Therefore, they precipitate between the two solvents to form the intermediate layer 36.

[0080] Furthermore, as the stirring proceeds, a precursor of another inorganic ligand further binds to the inorganic ligand coordinated to the quantum dot, for example, through a condensation reaction, and the inorganic ligand body grows. Thus, quantum dots having both an inorganic ligand body and an organic ligand are produced. If the stirring time is too long, the organic ligand is further desorbed, further increasing the polarity of the ligand and making the quantum dots more likely to aggregate. Therefore, the stirring conditions, including the stirring time, are set to a level that prevents such aggregation (to the extent that some of the organic ligand remains). In this way, the content of the organic ligand (content of the inorganic ligand body) in the quantum dots can be appropriately adjusted by the stirring conditions during ligand replacement.

[0081] Next, the generated quantum dots are precipitated by a method such as centrifugation, and the solvents such as the non-polar solvent layer 31 and the polar solvent layer 32 are removed, and the generated quantum dots are collected.

[0082] The polar solvent may be a solvent having a relative dielectric constant at room temperature of 30 or more. Examples of polar solvents include methanol, ethylene glycol, propylene glycol, diethylene glycol, glycerin, furfural, formic acid, ethylene carbonate, propylene carbonate, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, succinonitrile, nitromethane, nitrobenzene, dimethyl sulfoxide, sulfolane, water, and mixtures of two or more of these.

[0083] The non-polar solvent may be a solvent having a relative dielectric constant at room temperature of not more than 3. Examples of the non-polar solvent include pentane, hexane, cyclohexane, isooctane, octane, benzene, toluene, dichlorodifluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, tetrachloroethylene, 1,4-dioxane, and a mixture of two or more of these.

[0084] The halogen source may be a component that contains a halogen and acts as a catalyst for the reaction to form the aforementioned inorganic ligand body. Examples of halogen sources include metal halides, examples of which include zinc fluoride, zinc chloride, zinc bromide, zinc iodide, indium fluoride, indium chloride, indium bromide, and indium iodide.

[0085] [Example of Manufacturing the Light-Emitting Device] The light-emitting device can be manufactured by a known method for manufacturing a QLED light-emitting device, except for the light-emitting layer. The light-emitting layer in the present disclosure can be manufactured using a known method for manufacturing a QLED light-emitting layer. For example, the light-emitting device can be manufactured by the following method.

[0086] First, the first electrode 11, which is an anode, is formed on a substrate (e.g., reference numeral 103 in FIG. 5 ). For example, the first electrode 11 is formed by sequentially forming an Ag layer and an indium tin oxide layer on the surface of the substrate using a sputtering method.

[0087] Next, the hole transport layer 12 is formed on the first electrode 11. For example, the hole transport layer 12 is formed by depositing a hole transport material on the surface of the first electrode 11 at a specific deposition rate through a common mask or without a mask.

[0088] Next, the light-emitting layer 13 is formed on the hole-transporting layer 12. A manufacturing example of the light-emitting layer 13 will be described later.

[0089] Next, the electron transport layer 14 is formed on the light-emitting layer 13. For example, the electron transport layer 14 is formed by depositing an electron transport material on the surface of the light-emitting layer 13 at a specific deposition rate, either through a common mask or without a mask. Next, the second electrode 15, which is a cathode, is formed on the electron transport layer 14. For example, a magnesium-silver alloy thin film is formed on the surface of the electron transport layer 14 by deposition.

[0090] [Example of Manufacturing the Light-Emitting Layer] The quantum dots prepared in the above-mentioned preparation example are dispersed in a solvent such as toluene as needed to adjust the concentration. In this way, a paint for the QD layer in which the quantum dots are dispersed is prepared. The paint for the QD layer may further contain a halogen, and the halogen concentration may be adjusted in this way.

[0091] In addition, a coating material for the auxiliary layer is prepared containing an auxiliary layer compound and a polar solvent. The coating material for the auxiliary layer may further contain a halogen, or the halogen concentration may be adjusted in this way.

[0092] Next, the coating material for the QD layer is applied to the surface of the hole transport layer 12 by a known coating method such as an inkjet method. For example, if the quantum dots are configured as two layers stacked in the thickness direction of the light-emitting layer, a single layer of quantum dots is formed by one coating, and this process is repeated twice. In this way, a coating film consisting essentially of two layers of quantum dots 133 stacked on top of each other is produced. The produced coating film is then baked as necessary. In this way, a QD layer is produced on the surface of the hole transport layer 12.

[0093] Next, a coating material for the auxiliary layer is applied to the surface of the QD layer by a known coating method such as an inkjet method to form a coating film of the auxiliary layer compound. The coating film is then dried or baked as necessary. In this way, the auxiliary layer is formed on the surface of the QD layer, and an emissive layer including the QD layer and the auxiliary layer is formed on the surface of the hole transport layer 12.

[0094] [Display Device] The display device according to the present disclosure includes the above-described light-emitting element. The display device according to the present disclosure may be configured similarly to a known display device having a known light-emitting element, except for the above-described light-emitting element. Examples of display devices include television sets and smartphones. In the following description, for similar configurations that differ only in the emitted light color, a symbol indicating the color is added to the symbol of the configuration. For example, a symbol R is added to a configuration related to red, a symbol G is added to a configuration related to green, and a symbol B is added to a configuration related to blue.

[0095] FIG. 4 is a plan view schematically illustrating a configuration of a display device 100 according to an embodiment of the present disclosure. FIG. 4 illustrates a smartphone, which is an example of a display device. As illustrated in FIG. 4, the display device 100 includes a display area 101 and a frame area 102 surrounding the display area 101. The display area 101 includes a plurality of pixels 10, and for example, the plurality of pixels 10 are regularly arranged within the display area 101. Each pixel 10 includes, for example, a red light-emitting element 1R, a green light-emitting element 1G, and a blue light-emitting element 1B arranged side by side. The red light-emitting element 1R, the green light-emitting element 1G, and the blue light-emitting element 1B each correspond to a sub-pixel in the pixel 10.

[0096] Fig. 5 is a diagram schematically illustrating the layer configuration of a pixel 10 of the display device 100 of Fig. 4. In one pixel 10, a red light-emitting element 1R, a green light-emitting element 1G, and a blue light-emitting element 1B are each configured between a substrate 103 and an outer functional layer 104.

[0097] The substrate 103 is a glass substrate or a flexible substrate whose main component is a resin such as polyimide, or may have a laminated structure including, for example, two polyimide films and an inorganic film sandwiched between them.

[0098] Banks 105 are arranged at appropriate intervals on the surface of the substrate 103, and light-emitting elements 1 of each color are configured between adjacent banks 105. The red light-emitting element 1R is configured by stacking a red first electrode (anode) 11R, a red hole transport layer 12R, a red QD layer 131R, a red auxiliary layer 132R, a red electron transport layer 14R, and a red second electrode 15R in this order. Similarly, the green light-emitting element 1G is configured by stacking a green first electrode (anode) 11G, a green hole transport layer 12G, a green QD layer 131G, a green auxiliary layer 132G, a green electron transport layer 14G, and a green second electrode 15G in this order. The blue light-emitting element 1B is configured by stacking a blue first electrode (anode) 11B, a blue hole transport layer 12B, a blue QD layer 131B, a blue auxiliary layer 132B, a blue electron transport layer 14B, and a blue second electrode 15B in this order. Each of these layers may be a common layer integrally formed across adjacent light emitting elements, or may be an independent layer formed for each light emitting element.

[0099] The external functional layer 104 is a layer that adds various functions to the display device 100, such as optical control, a touch sensor, or surface protection.

[0100] [Mechanism for Reinforcing Quantum Dots] First, the reaction mechanism of the metalloid oxide in the present disclosure will be explained using silicon oxide as an example.

[0101] As shown in FIG. 6, two TMOSs were hydrolyzed to form methanol (CH ３ The hydrolysis is carried out by the elimination of halogens (F － , Cl － ,Br － and I － The presence of catalysis is promoted by the presence of catalysis.

[0102] The relationship between the progress of the silicon oxide reaction and the O / Si ratio in this disclosure is shown in Figure 7. When TMOS is unreacted, four oxygen atoms are bonded to one silicon atom (SiO ＸSince X is 4, the ratio of the number of oxygen atoms to the number of silicon atoms (O / Si ratio) is 4. When TMOS is one-dimensionally bonded by the above hydrolysis, three oxygen atoms are bonded to one silicon atom (SiO Ｘ Since X is 3 (X = 1 × 2 + 1 / 2 × 2), the O / Si ratio is 3. When TMOS is further hydrolyzed into a two-dimensional bonded state, two oxygen atoms are bonded to one silicon atom (SiO Ｘ Since X is 2 (X=1 / 2×4), the O / Si ratio is 2. In this way, the more the reaction of TMOS proceeds, the smaller the O / Si ratio becomes.

[0103] In the present disclosure, since metal oxides and metalloid oxides have the above-described reactivity, the metal oxides and metalloid oxides contained in the auxiliary layer have a number of oxygen atoms that is greater than half the valence of the metal atom or metalloid atom.

[0104] Examples of metal oxides or semi-metal oxides in which the ratio of oxygen atoms to metal atoms or semi-metal atoms decreases with the reaction due to such a mechanism include SiO ２ In addition to CuO (CuSO ４ ), ZnO (Zn(NO ３ ) ２ ), CdO(Cd(CH ３ COO) ２ , Cd(NO ３ ) ２ )), FeO (FeSO ４ ), Mn ３ O ４ (Mn ２ SO ４ ), NiO(Ni(NO ３ ) ２ ), W.O. ３ (H ２ O ４ W), Bi ２ O ３ (Bi(NO ３ ) ２ ) and MgO (Mg(NO ３ ) ２ ) The parentheses indicate the precursor of the metal oxide or semi-metal oxide.

[0105] The mechanism by which the auxiliary layer compound reinforces the quantum dots in the light-emitting device will be described with reference to Fig. 8. In Fig. 8, 8A to 8D respectively show the initial state of the light-emitting device and specific states that change over time.

[0106] As shown in FIG. 8A, the QD layer 131 includes quantum dots each having a dot body 134 and a ligand 135 coordinated thereto, and a halogen (not shown) is included as a metal halide. As described above, the ligand 135 includes an organic ligand 135a and an inorganic ligand 135c. Here, the inorganic ligand 135c is a silicon oxide condensate. The auxiliary layer 132 includes a silicon oxide, such as TMOS, as a semi-metal oxide.

[0107] When a voltage is applied to the light-emitting element, the quantum dots in the QD layer 131 emit light. As the light-emitting element continues to be energized, organic ligands 135a may be detached from the quantum dots, as shown in 8B of FIG. 8. Meanwhile, as the light-emitting element is energized, semi-metal oxide (here, TMOS) 132a diffuses from the auxiliary layer 132 toward the anode (first electrode 11) and is supplied to the QD layer 131.

[0108] When the semi-metal oxide 132a is present in the QD layer 131, the semi-metal oxide 132a reacts with the inorganic ligand 135c in the presence of the metal halide and is bonded to the inorganic ligand 135b as shown in FIG. 8C due to the heat generated by the application of current. This reaction replaces the organic ligand 135a with the inorganic ligand 135b in the ligand 135. In this way, the semi-metal oxide 132a in the auxiliary layer 132 reinforces the inorganic ligand 135c of the quantum dots in the QD layer 131 when the light-emitting device is energized (heated).

[0109] 8D, the quantum dots in the QD layer 131 become reinforcing ligands 135d to which inorganic ligands have been added, and the loss of ligands 135 due to the application of current is replenished by other ligands. As a result, the quantum dots in the QD layer 131 can continue to retain sufficient ligands over time.

[0110] Thus, in the light-emitting element of the present disclosure, the ligands of the quantum dots in the QD layer 131 are reinforced by reaction with an auxiliary layer compound, such as a semi-metal oxide, so that oxygen or moisture that penetrates into the QD layer of the light-emitting element is blocked by the ligands reinforced by reaction with the auxiliary layer compound and does not reach the dot body 134.

[0111] Therefore, in the light-emitting element of the present disclosure, the quantum dots 133 can be protected by bonding a metal oxide or a metalloid oxide to the site where the organic ligand 135a has been released from the quantum dots 133. Furthermore, since the quantum dots 133 are protected by becoming the reinforcing ligands 135d, the function of the ligands of the quantum dots 133 is fully restored, and thereafter, the ligands do not deteriorate, further improving the reliability of the quantum dots. Therefore, the quantum dots are more strongly protected after the organic ligands of the quantum dots are released, and as a result, high reliability of the light-emitting element can be achieved.

[0112] In addition, as the quantum dots are protected by the above-mentioned mechanism, at least a portion of the auxiliary layer compounds diffused from the auxiliary layer is fixed to the quantum dots as a metal oxide or semi-metal oxide, and the auxiliary layer compounds in the auxiliary layer decrease as the light-emitting device is used.

[0113] [Without Auxiliary Layer] For reference, the state of a light-emitting device without an auxiliary layer will be described with reference to Fig. 9. In Fig. 9, 9A to 9D respectively show the initial state of the light-emitting device and specific states that change over time. As shown in 9A of Fig. 9, the initial state of the light-emitting device is the same as the embodiment of Fig. 8 described above, except that it does not have an auxiliary layer.

[0114] As shown in 9B of FIG. 9, as the power supply to the light-emitting element continues, the organic ligands 135a are detached from the quantum dots, which is the same as the embodiment shown in 8B of FIG. 8. If the power supply to the light-emitting element is stopped at this point, some of the detached organic ligands 135a may re-coordinate with the dot body 134. Although not mentioned above, this point is also the same in the embodiment shown in 8B of FIG. 8. The function of the quantum dot is restored by the re-coordination of the organic ligands 135a. Normally, not all of the detached organic ligands 135a can be re-coordinated, so the recovery of the quantum dot function by the re-coordination of the organic ligands 135a is not complete.

[0115] Therefore, as shown in 9C of Fig. 9, as the light-emitting element continues to be energized, the number of quantum dots from which the organic ligands 135a have been released increases, and eventually, as shown in 9D of Fig. 9, the quantum dots in the light-emitting layer 73 become quantum dots from which the organic ligands 135a have been released. As a result, the function of the quantum dots decreases, and the quantum dots may deteriorate starting from the parts where the ligands are missing.

[0116] [Major Effects of the Present Embodiment] The light-emitting element 1 of the present embodiment includes a light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semimetal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the semimetal atoms, and precursors thereof, and the light-emitting layer contains at least the compound as an auxiliary layer. The metal oxides and semimetal oxides having the above numbers of oxygen atoms have the reactivity of a condensation reaction that reinforces the ligand. Therefore, according to the present embodiment, a light-emitting element can be realized that is less likely to experience a decrease in brightness over long periods of operation.

[0117] In this embodiment, the semi-metal oxide is silicon oxide, and the quantum dot has an inorganic ligand and a linking portion that links to the inorganic ligand, and the linking portion has SiO Ｘ and the auxiliary layer comprises SiO Ｙwhere X<Y and Y>2. This configuration is even more effective in terms of providing stronger protection for the quantum dots in the QD layer.

[0118] In this embodiment, the light-emitting device has a first electrode, a light-emitting layer, and a second electrode stacked in this order. This configuration allows for the use of heat generated by passing current to protect the quantum dots in the QD layer, which is more effective in protecting the quantum dots in the QD layer as the light-emitting device is used.

[0119] In this embodiment, the auxiliary layer is located on one side of the light-emitting layer in the thickness direction of the light-emitting layer, which is more effective from the viewpoint of easily configuring a light-emitting device that can protect the quantum dots in the QD layer.

[0120] In this embodiment, the auxiliary layer is located on the second electrode side of the light-emitting layer in the thickness direction of the light-emitting layer. This configuration is more effective from the viewpoint of realizing migration and diffusion of the metal oxide or metalloid oxide toward the second electrode (anode) side by utilizing the electron cathode, since the metal oxide or metalloid oxide used in the reaction for protecting the quantum dots in the QD layer has a higher ratio of oxygen atoms to metal atoms.

[0121] In this embodiment, the amount of organic ligands coordinated to the quantum dots in the light-emitting layer 13 is 50% or less, which is more effective in preventing the quantum dots 133 from forming an aggregated structure in the QD layer 131 and in suppressing a decrease in the brightness of the light-emitting layer 13.

[0122] In this embodiment, the thickness of each auxiliary layer is 1 nm to 3 nm, which is more effective in terms of allowing current to tunnel through the auxiliary layer and in terms of long-term stability of the luminous efficiency of the QD layer.

[0123] In this embodiment, the metalloid oxide may contain one or both of the compound represented by the above formula 1 and the compound represented by the following formula 2. This configuration is even more effective from the viewpoints of suppressing detachment from the quantum dots after the binding reaction and sufficiently enhancing the barrier function of the quantum dots in the QD layer against oxygen and moisture.

[0124] In this embodiment, the semi-metal oxide may include one or both of the compound represented by the above formula 3 and the compound represented by the following formula 4. This configuration is even more effective in terms of sufficiently enhancing the barrier function of the quantum dots in the QD layer against oxygen and moisture.

[0125] In this embodiment, the light-emitting layer may include an auxiliary layer containing an auxiliary layer compound and a layer containing quantum dots and a halogen. This configuration is more effective in terms of preferentially forming inorganic ligands and protecting the QDs by the presence of the halogen.

[0126] Other embodiments of the present disclosure will be described below. For ease of explanation, in the following embodiments, components having the same functions as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0127] Second Embodiment The layer structure of a light-emitting device according to a second embodiment of the present disclosure is shown schematically in Fig. 10. As shown in Fig. 10, the light-emitting device 2 has the same structure as the light-emitting device 1 of the first embodiment described above, except that the auxiliary layer 132 is disposed on the first electrode 11 side of the QD layer 131. The auxiliary layer 132 is in contact with the hole transport layer 12 adjacent to the light-emitting layer 33 on the first electrode 11 side, but is not in contact with the electron transport layer 14 adjacent to the light-emitting layer 33 on the second electrode 15 side.

[0128] This embodiment has the same effects as the first embodiment described above, and is even more effective in terms of increasing diffusivity into the QD layer 131 when the auxiliary layer contains a metal oxide or semi-metal oxide with a larger positive charge.

[0129] [Third Embodiment] The layer structure of a light-emitting device according to a third embodiment of the present disclosure is schematically shown in Fig. 11. As shown in Fig. 11, the light-emitting device 3 has the same structure as the light-emitting device 1 of the first embodiment described above, except that the light-emitting device 3 has a light-emitting layer 33 instead of the light-emitting layer 13.

[0130] The light-emitting layer 33 has a first QD layer 331, an auxiliary layer 332, and a second QD layer 333, in this order from the first electrode 11 side. The first QD layer 331 and the second QD layer 333 each have the same configuration as the light-emitting layer 13 of the first embodiment, except that they each include a substantially single layer of quantum dots 133. The auxiliary layer 332 has the same configuration as the light-emitting layer 13 of the first embodiment, except that it is located between the first QD layer 331 and the second QD layer 333 in the stacking direction. Thus, in the light-emitting element 3, the auxiliary layer 332 is located in the middle portion of the light-emitting layer 33 in the thickness direction of the light-emitting layer 33. Thus, in the present disclosure, the auxiliary layer 332 does not need to be in contact with the electron transport layer 14 adjacent to the light-emitting layer 33 on the second electrode 15 side.

[0131] This embodiment also has the same effects as the above-described embodiment, but is even more effective in terms of shortening the distance between the auxiliary layer 332 and the quantum dots 133 in each QD layer.

[0132] [Fourth embodiment] The layer structure of a light-emitting device according to a fourth embodiment of the present disclosure is schematically shown in Fig. 12. As shown in Fig. 12, the light-emitting device 4 has the same structure as the light-emitting device 1 of the first embodiment described above, except that the light-emitting device 4 has a light-emitting layer 43 instead of the light-emitting layer 13.

[0133] The light-emitting layer 43 has a first QD layer 431, a first auxiliary layer 432, a second QD layer 433, and a second auxiliary layer 434, in this order from the first electrode 11 side. The first QD layer 431 and the second QD layer 433 each have the same configuration as the light-emitting layer 13 of the first embodiment, except that they each include a substantially single layer of quantum dots 133. The first auxiliary layer 432 and the second auxiliary layer 434 have the same configuration as the light-emitting layer 13 of the first embodiment, except that they are arranged on the second electrode 15 side with respect to the first QD layer 331 and the second QD layer 333, respectively.

[0134] This embodiment also provides the same advantages as the previous embodiment, but is more effective in terms of promoting the migration and diffusion of metal oxides or semi-metal oxides toward the second electrode (anode) by utilizing the electron cathode property of the metal oxide or semi-metal oxide, and in terms of shortening the distance between the auxiliary layer and each QD layer.

[0135] Fifth Embodiment The layer structure of a light-emitting device according to a fifth embodiment of the present disclosure is schematically shown in Fig. 13. As shown in Fig. 13, the light-emitting device 5 has the same structure as the light-emitting device 1 of the first embodiment described above, except that it has a light-emitting layer 53 instead of the light-emitting layer 13.

[0136] The light-emitting layer 53 has the same configuration as the light-emitting layer 23 of the second embodiment described above, except for the relative position of the auxiliary layer 532 in the stacking direction to the QD layer 531. The auxiliary layer 532 is disposed at a position overlapping the second layer of quantum dots 133 in the QD layer 531 in the stacking direction. That is, the light-emitting layer 53 includes two layers of quantum dots 133, and the auxiliary layer 532 is formed on the second electrode 15 side of the QD layer 531 with a thickness thicker than 0.5 layers of quantum dots 133.

[0137] This embodiment also has the same effects as the above-described embodiment, but is even more effective in terms of further shortening the distance between the auxiliary layer and the quantum dots 133 in each QD layer.

[0138] Sixth Embodiment The layer configuration of a display device according to a sixth embodiment of the present disclosure is schematically shown in Fig. 14. As shown in Fig. 14, a pixel 60 includes a first transparent substrate 203, a bank 204 that partitions one surface of the first transparent substrate 203, a light-emitting layer 63 formed in each partition partitioned by the bank 204, a sealing layer 207 that covers the bank 204 and the light-emitting layer 63 in the stacking direction, a light source 206 that corresponds to each partition of the bank 204 and is arranged opposite each light-emitting layer 63, and a second substrate 205 that supports the light source 206 on its surface.

[0139] The light-emitting layer 63 has a QD layer 631 and an auxiliary layer 632, and the QD layer 631 and the auxiliary layer 632 are configured in the same manner as the QD layer 131 and the auxiliary layer 132 in the first embodiment described above.

[0140] The light source 206 emits excitation light that excites the quantum dots in the QD layer 631. The excitation light is, for example, ultraviolet light or blue light. The light source 206 is, for example, an organic EL element. The sealing layer 207 is a light-transmitting layer and is made of, for example, a curable resin.

[0141] The pixel 60 can be manufactured, for example, by bonding a light source substrate having a light source 206 on a second substrate 205 and an emitting substrate having a bank 204 and an emitting layer 63 on a first transparent substrate 203 together via a light-transmitting adhesive, and then curing the adhesive to form a sealing layer 207.

[0142] When excitation light is irradiated from the light source 206, the quantum dots in the QD layer 631 emit light, causing the light-emitting layer 63 to emit light of a desired color. The light from the light-emitting layer 63 is emitted downward in FIG. 14 as indicated by the arrow in the figure.

[0143] The auxiliary layer compound is supplied from the auxiliary layer 632 to the QD layer 631. Furthermore, upon irradiation with excitation light, the QD layer 631 emits light and generates heat. Thus, similar to the first embodiment, quantum dots are reinforced by a metal oxide or semi-metal oxide.

[0144] As described above, this embodiment also achieves the same effects as the above-described embodiment. That is, even if the organic ligands 135 a are released over time due to photoexcitation of the quantum dots in the QD layer 631, the quantum dots 133 can be protected by bonding a metal oxide or semi-metal oxide to the sites where the organic ligands 135 a have been released from the quantum dots 133. Furthermore, if the QD layer 631 contains a halogen, the quantum dots 133 in the QD layer 631 can be protected by the halogen.

[0145] [Other Embodiments] In the embodiments of the present disclosure, one of the first electrode and the second electrode may be an anode and the other may be a cathode depending on the configuration of the light-emitting element. For example, in the first embodiment, the first electrode may be a cathode and the second electrode may be an anode.

[0146] In an embodiment of the present disclosure, the light-emitting element may further include layers other than the first electrode, second electrode, and light-emitting layer described above, as long as the effects of the present disclosure are obtained. Examples of such layers include functional layers that contribute to at least one of the injection, movement, and blocking of carriers (electrons or holes). Examples of such functional layers include a hole injection layer, an electron injection layer, an electron blocking layer, and a hole blocking layer, in addition to the hole transport layer and electron transport layer described above.

[0147] The hole injection layer is disposed adjacent to the anode, for example. The electron blocking layer is disposed between the hole transport layer and the light-emitting layer, for example. The hole injection layer and the electron blocking layer may be made of the hole transport material described above. The materials of the hole injection layer, the hole transport layer, and the electron blocking layer may be the same or different.

[0148] The electron injection layer is disposed adjacent to the cathode, for example. The hole blocking layer is disposed between the electron transport layer and the light-emitting layer, for example. The electron injection layer and the hole blocking layer may be composed of the above-mentioned electron transport material. The materials of the electron injection layer, the electron transport layer, and the hole blocking layer may be the same or different.

[0149] In embodiments of the present disclosure, the composition of the quantum dot ligand changes appropriately with time as reinforcement progresses. For example, initially, the ligand contains some organic ligands and the other inorganic ligands. As reinforcement progresses, the proportion of inorganic components in the ligand tends to increase, and the amount of organic ligands in the ligand tends to decrease.

[0150] Therefore, a light-emitting device according to the present disclosure can be confirmed or estimated by the fact that the quantum dots initially have organic ligands, or by the fact that the light-emitting layer has a structure supporting this. Examples of such supporting structures include the presence of organic ligands desorbed from the quantum dots in the light-emitting layer (QD layer), the fact that the quantum dots have inorganic ligands in place of the desorbed organic ligands, the presence in the light-emitting layer of a catalyst that sufficiently promotes the ligand reinforcement reaction within a feasible temperature range, and the inclusion of a layer of (excess) auxiliary layer compound in the light-emitting layer. A light-emitting device that includes some or all of these supporting structures can be reasonably estimated to be a light-emitting device according to the present disclosure.

[0151] In the embodiments of the present disclosure, the auxiliary layer may be continuously disposed in its plane direction, may have island-shaped voids, or may be arranged in an island-like manner, as long as the effects of the present disclosure are exhibited. Similarly, the QD layer may be continuously disposed in its plane direction, may have island-shaped voids, or may be arranged in an island-like manner, as long as the effects of the present disclosure are exhibited.

[0152] In some embodiments of the present disclosure, the ratio of oxygen atoms to metal or metalloid atoms in the metal oxide or metalloid oxide in the auxiliary layer need not be the lowest value for that oxide within the range that provides the effects of the present disclosure (i.e., the range that can react with the quantum dot ligands in the QD layer). For example, in the first embodiment described above, the O / Si ratio of the metal oxide or metalloid oxide in the auxiliary layer may be greater than 2 and less than 4 (e.g., 3).

[0153] In embodiments of the present disclosure, a pixel in a display device may further include sub-pixels of other colors, and the sub-pixels may be arranged in a configuration other than parallel, for example, the sub-pixels may be arranged in a Pentile array.

[0154] In an embodiment of the present disclosure, the display device may further include a device for heating the light-emitting layer to restore the quantum dots. Examples of such a heating device include a planar heater. The inclusion of such a heating device is more effective in terms of optimizing the reinforcement of the quantum dots (restoring the function of the ligands).

[0155] In addition to display devices, the light-emitting element of the present disclosure can be applied to light sources that emit monochromatic light or light sources for devices that adjust and output two or more emitted colors. For example, the light-emitting element of the present disclosure can also be applied to lighting devices. More specifically, the light-emitting element of the present disclosure can also be applied to lighting devices that can output any light, for example, from warm light to cool light, by appropriately adjusting the output of two or more emitted colors.

[0156] 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.

[0157] For example, a light-emitting device according to the present disclosure has a light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semi-metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the semi-metal atoms, and precursors thereof, the light-emitting layer containing at least the semi-metal oxide as an auxiliary layer, the semi-metal oxide being silicon oxide, the quantum dots having inorganic ligands and linking portions linking to the inorganic ligands, and the linking portions having SiO Ｘ and the auxiliary layer is SiO Ｙ and may be a light-emitting element that includes the light-emitting layer and is located at a middle portion of the light-emitting layer in the thickness direction of the light-emitting layer, with the proviso that X<Y and Y>2 are satisfied.

[0158] Alternatively, the light-emitting device according to the present disclosure has a light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semi-metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the semi-metal atoms, and precursors thereof, the light-emitting layer containing at least the semi-metal oxide as an auxiliary layer, the semi-metal oxide being silicon oxide, the quantum dots having inorganic ligands and linking portions linking to the inorganic ligands, and the linking portions having SiO Ｘ and the auxiliary layer is SiO Ｙ and the thickness of each auxiliary layer is 1 nm to 3 nm, provided that X<Y and Y>2 are satisfied.

[0159] Alternatively, the light-emitting device according to the present disclosure is a light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atom, metalloid oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metalloid atom, and precursors thereof, the light-emitting layer containing at least the metalloid oxide as an auxiliary layer, the metalloid oxide being silicon oxide and including one or more compounds selected from the group consisting of compounds represented by the above-mentioned formulas 1 to 4, the quantum dots having inorganic ligands and linking portions linking to the inorganic ligands, and the linking portions having SiO in at least a portion thereof. Ｘ and the auxiliary layer is SiO Ｙ However, X<Y and Y>2 are satisfied.

[0160] Furthermore, in the present disclosure, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0161] 1 to 5 Light-emitting element 10, 60 Pixel 11 First electrode 12 Hole transport layer 13, 23, 33, 43, 53, 63, 73 Light-emitting layer 14 Electron transport layer 15 Second electrode 31 Non-polar solvent layer 32 Polar solvent layer 36 Intermediate layer 100 Display device 101 Display area 102 Frame area 103 Substrate 104 External functional layer 105, 204 Bank 131, 531 QD layer 132, 332, 532, 632 Auxiliary layer 132a Semimetal oxide 133 Quantum dot 134 Dot body 135 Ligand 135a Organic ligand 135b Inorganic ligand 135c Inorganic ligand body 135d Reinforcing ligand 203 First transparent substrate 205 Second substrate 206 Light source 207 Sealing layer 331, 431 First QD layer 333, 433 Second QD layer 432 First auxiliary layer 434 Second auxiliary layer

Claims

1. A light-emitting device having a light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semimetal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the semimetal atoms, and precursors thereof, wherein the light-emitting layer contains at least the compound as an auxiliary layer.

2. The semi-metal oxide is silicon oxide, and the quantum dot has an inorganic ligand and a connecting portion that connects to the inorganic ligand, and the connecting portion has SiO Ｘ The auxiliary layer comprises SiO Ｙ 10. The light-emitting device of claim 1, comprising: where X<Y and Y>2.

3. The light-emitting device according to claim 1 or 2, wherein the auxiliary layer is located on one side of the light-emitting layer in the thickness direction of the light-emitting layer.

4. The light-emitting device according to any one of claims 1 to 3, wherein the auxiliary layer is located at a middle portion of the light-emitting layer in the thickness direction of the light-emitting layer.

5. The light-emitting device according to any one of claims 1 to 4, wherein the amount of organic ligands coordinated to the quantum dots in the light-emitting layer is 50% or less.

6. The light-emitting device according to any one of claims 1 to 5, wherein the thickness of each of the auxiliary layers is 1 nm or more and 3 nm or less.

7. The light-emitting device according to any one of claims 1 to 6, wherein the semi-metal oxide includes one or both of a compound represented by the following formula 1 and a compound represented by the following formula 2: In the above formula, R １ , R ２ and R ３ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 10.

8. The light-emitting device according to any one of claims 1 to 7, wherein the semi-metal oxide includes one or both of a compound represented by the following formula 3 and a compound represented by the following formula 4: In the above formula, R １ , R ２、 R ３ and R ４ each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ５ represents a hydrocarbon group having 1 to 20 carbon atoms.

9. The light-emitting device according to any one of claims 1 to 8, wherein the light-emitting layer comprises the auxiliary layer containing the compound and a layer containing the quantum dots and the halogen.

10. The light-emitting device according to any one of claims 1 to 9, wherein a first electrode, the light-emitting layer, and a second electrode are arranged in this order.

11. The light-emitting device according to claim 10, wherein the auxiliary layer is located on a portion of the light-emitting layer on the second electrode side in the thickness direction of the light-emitting layer.

12. A light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semi-metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, and precursors thereof, wherein the light-emitting layer contains at least the semi-metal oxide as an auxiliary layer, the semi-metal oxide being silicon oxide, the quantum dots having inorganic ligands and connecting portions connecting to the inorganic ligands, and the connecting portions having SiO Ｘ The auxiliary layer comprises SiO Ｙ (where X<Y and Y>2), and is located at an intermediate portion of the light-emitting layer in a thickness direction of the light-emitting layer.

13. A light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semi-metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, and precursors thereof, wherein the light-emitting layer contains at least the semi-metal oxide as an auxiliary layer, the semi-metal oxide being silicon oxide, the quantum dots having inorganic ligands and connecting portions connecting to the inorganic ligands, and the connecting portions having SiO Ｘ The auxiliary layer comprises SiO Ｙ (where X<Y and Y>2), wherein each of the auxiliary layers has a thickness of 1 nm or more and 3 nm or less.

14. A light-emitting layer containing quantum dots, a halogen, and one or more compounds selected from the group consisting of metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, semi-metal oxides, which are oxides of metals having a number of oxygen atoms greater than half the valence of the metal atoms, and precursors thereof, wherein the light-emitting layer contains at least the semi-metal oxide as an auxiliary layer, the semi-metal oxide is silicon oxide and includes one or more compounds selected from the group consisting of compounds represented by the following formulas 1 to 4, the quantum dots have inorganic ligands and linking portions linked to the inorganic ligands, and the linking portions have SiO in at least a portion thereof. Ｘ The auxiliary layer comprises SiO Ｙ a light-emitting element including: (where X<Y and Y>2); In the above formula, R １ , R ２、 R ３ and R ４ each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ５ represents a hydrocarbon group having 1 to 20 carbon atoms, and n represents an integer of 1 to 10.

15. A display device comprising the light-emitting element according to any one of claims 1 to 14.

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