Light-emitting element, display device, and light-emitting element manufacturing method

Abstract

A light-emitting element (2) comprises an emissive layer (23) located between an anode (21) and a cathode (25). The emissive layer includes a first quantum dot (31), a second quantum dot (32), a first adduct (40), and a second adduct (42). The first adduct is positioned between the first quantum dot and a layer (22) that the emissive layer is adjacent to on the anode side. The second adduct is positioned between the second quantum dot and a layer (24) that the emissive layer is adjacent to on the cathode side. The thickness (T1) of the first adduct is smaller than the thickness (T2) of the second adduct.

Description

Light-emitting element, display device, and method for manufacturing the same

[0001] The present disclosure relates to a light-emitting element, a display device including the light-emitting element, and a method for manufacturing the light-emitting element.

[0002] Non-Patent Document 1 discloses a quantum dot structure having quantum dots (semiconductor nanoparticles) and an additive containing silicon oxide (silica) located around the quantum dots as a light emitter used in a light-emitting device. The structure having the additive around the quantum dots protects the quantum dots with the additive, improving the reliability of the quantum dots.

[0003] Cong Shen, Yanqing Zhu et al. Blue-Emitting InP / GaP / ZnS Quantum Dots with Enhanced Stability by Siloxane Capping: Implication for Electroluminescent Devices. ACS Appl. Nano Mater. 2022.5.2, pp. 2801-2811.

[0004] In a light-emitting device having a light-emitting layer with a structure such as that described in Non-Patent Document 1, the injection of charges from each electrode into the quantum dots is hindered by the additive, which may increase the resistance of the light-emitting device or reduce the light-emitting efficiency of the light-emitting device. In particular, in the above-mentioned light-emitting device, the problem of reduced efficiency of charge injection into each quantum dot in the light-emitting layer due to low electron mobility tends to become more pronounced when holes are injected into the quantum dots.

[0005] A light-emitting element according to one aspect of the present disclosure comprises an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer includes first quantum dots, second quantum dots located closer to the cathode than the first quantum dots, a first additive located between the first quantum dots and a layer adjacent to the light-emitting layer on the anode side, and a second additive located between the second quantum dots and a layer adjacent to the light-emitting layer on the cathode side, wherein the thickness of the first additive is smaller than the thickness of the second additive.

[0006] A method for manufacturing a light-emitting element according to one aspect of the present disclosure is a method for manufacturing a light-emitting element including an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, the light-emitting layer including first quantum dots, second quantum dots located closer to the cathode than the first quantum dots, a first additive located between the first quantum dots and a layer adjacent to the light-emitting layer on the anode side, and a second additive located between the second quantum dots and a layer adjacent to the light-emitting layer on the cathode side, the thickness of the first additive being smaller than the thickness of the second additive.

[0007] According to a configuration according to one aspect of the present disclosure, in a light-emitting element, the efficiency of hole injection into quantum dots located on the anode side in the light-emitting layer is improved while at least some of the quantum dots are protected by an additive.

[0008] FIG. 1 is a schematic side cross-sectional view of a display device according to an embodiment. FIG. 2 is a schematic view of a display device according to an embodiment. FIG. 3 is a schematic enlarged view of a cross section of a light-emitting layer according to an embodiment and its vicinity. FIG. 4 is a schematic view showing an addition filling spaces between quantum dots according to an embodiment. FIG. 5 is a schematic side cross-sectional view of a display device according to a comparative embodiment. FIG. 6 is a schematic enlarged view of a cross section of a light-emitting layer according to a comparative embodiment. FIG. 7 is a flowchart showing a method for manufacturing a display device according to an embodiment. FIG. 8 is a flowchart showing a method for forming a light-emitting layer according to an embodiment. FIG. 9 is a process side view showing a mixing process in the method for forming a light-emitting layer according to an embodiment. FIG. 10 is a schematic view showing a first dispersion according to an embodiment. FIG. 11 is a schematic view showing a second dispersion according to an embodiment. FIG. 12 is a process cross-sectional view showing a part of a method for forming a light-emitting layer according to an embodiment.

[0009] [Embodiments] <Display Device: Overview> Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in each drawing, similar configurations are assigned the same reference numerals, and their description will be omitted. Furthermore, in this disclosure, for simplicity of illustration, components assigned the same reference numerals may be shown at different scales or with different hatching depending on the drawing. However, the components shown in each drawing of the present disclosure are merely examples, and the scales are not limited to those shown in the drawings. Furthermore, in this disclosure, even for components with different hatching, components assigned the same reference numerals have similar configurations as described above.

[0010] 2 is a schematic diagram of a display device 1 according to this embodiment. The display device 1 is a device that can be used, for example, as a display for a television, a smartphone, or the like. The display device 1 includes a display unit DA including a plurality of sub-pixels X, and a driver circuit DR that drives the plurality of sub-pixels X. Each of the plurality of sub-pixels X includes a light-emitting element 2 and a pixel circuit PC that drives the light-emitting element 2. The display device 1 performs display on the display unit DA by controlling light emission from each of the plurality of light-emitting elements 2 formed in the display unit DA via the driver circuit DR and the pixel circuit PC.

[0011] The structure of the display unit DA of the display device 1, particularly the structure of the light-emitting element 2, will be described in more detail with reference to Fig. 1. Fig. 1 is a schematic side cross-sectional view of the display device 1 according to an embodiment of the present disclosure, particularly showing a cross section perpendicular to the display surface of the display device 1 and passing through the light-emitting element 2. Note that each schematic cross-sectional view and each process cross-sectional view of the display device in the present disclosure shows a cross section corresponding to the cross section of the display device 1 shown in Fig. 1.

[0012] 1, the display device 1 according to this embodiment includes a display section DA that includes the above-described plurality of light-emitting elements 2 and a substrate 3, and in particular includes the plurality of light-emitting elements 2 on the substrate 3. The display device 1 has a structure in which the layers of the light-emitting elements 2 are stacked on the substrate 3 on which, for example, TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits PC. In this specification, the direction from the light-emitting elements 2 of the display device 1 to the substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0013] The light-emitting element 2 includes an anode 21, a hole transport layer 22, a light-emitting layer 23, an electron transport layer 24, and a cathode 25, in this order from the substrate 3 side. The anode 21 is electrically connected to the TFT of the substrate 3.

[0014] <Outline of Light-Emitting Element> The structure of each layer of the light-emitting element 2 will be described in more detail below.

[0015] The anode 21 and the cathode 25 comprise conductive materials and are electrically connected to the hole transport layer 22 and the electron transport layer 24, respectively.

[0016] At least one of the anode 21 and the cathode 25 is a transparent electrode that transmits visible light. Examples of transparent electrodes include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), and FTO (fluorine-doped tin oxide). Either the anode 21 or the cathode 25 may contain a metal material. As the metal material, Al, Cu, Au, Ag, or Mg, or an alloy thereof, which have high visible light reflectance, are preferred. The anode 21 and the cathode 25 may be formed by sputtering or the like, or may be patterned by dry etching or the like.

[0017] The hole transport layer 22 is a layer containing a hole transport material that is adjacent to the anode 21 side of the light-emitting layer 23 and transports holes from the anode 21 to the light-emitting layer 23. In this disclosure, "two components adjacent" may refer to the two components being in direct contact with each other, or may refer to the two components being in close proximity to each other. In particular, "two components adjacent" in this disclosure may refer to the two components being in close proximity to each other via another component. For example, when "two components adjacent" in this disclosure refers to the two components being adjacent to each other, the shortest distance between the two components may be 4 nm or less, or a component having a size of 4 nm or less may be located between the two components. In this embodiment, the hole transport layer 22, in other words, the layer adjacent to the light-emitting layer 23 on the anode 21 side, may contain an inorganic substance. In particular, the hole transport layer 22 may contain an inorganic material as a hole transport material. For example, the hole transport layer may contain an oxide of Ni or Cr. The hole transport layer 22 may also contain zinc sulfide or zinc sulfide selenide. Furthermore, the hole transport layer 22 may also contain a p-type semiconductor. The hole transport layer 22 containing the above-described materials further improves the efficiency of hole injection from the anode 21 to the light-emitting layer 23.

[0018] However, this embodiment is not limited to this, and organic or inorganic materials conventionally employed in light-emitting elements containing quantum dots can be used as the material for the hole transport layer 22. For example, conductive compounds such as polyvinylcarbazole (PVK), [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD), 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylenevinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB) can be used as the organic material for the hole transport layer 22. Other inorganic materials for the hole transport layer 22 include molybdenum oxide, MgO, MgZnO, and LaNiO. ３ , MoO ３ , or W.O. ３In particular, as the material for the hole transport layer 22, a material having a large electron affinity and ionization potential is suitable.

[0019] The electron transport layer 24 is a layer containing an electron transport material that transports electrons from the cathode 25 to the light-emitting layer 23. The material of the electron transport layer 24 can be an organic or inorganic material that has been conventionally used in light-emitting devices containing quantum dots. For example, the electron transport layer 24 can be made of zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO ３ ), or may contain an inorganic nanoparticle material that is a nanoparticle of these inorganic materials. Alternatively, the electron transport layer 24 may contain an organic material as the electron transport material, such as tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), or (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Note that, as the inorganic material of the electron transport layer 24, metal oxides such as ZnO, ZAO, ITO, InGaZnO, or electride may be used. In particular, a material with a small electron affinity is suitable as the material of the electron transport layer 24.

[0020] In this embodiment, the hole transport layer 22 and the electron transport layer 24 can be formed by vacuum deposition, sputtering, or a coating method using a colloidal solution using the above-mentioned materials. The light-emitting element 2 may also include a hole injection layer between the anode 21 and the hole transport layer 22, or an electron injection layer between the cathode 25 and the electron transport layer 24. The light-emitting element 2 may also include an intermediate layer between the hole transport layer 22 and the light-emitting layer 23, or between the electron transport layer 24 and the light-emitting layer 23. The hole injection layer, electron injection layer, and intermediate layer may all be formed by the same method as the hole transport layer 22 or the electron transport layer 24.

[0021] <Light-emitting layer: quantum dots> The light-emitting layer 23 according to this embodiment will be described in more detail with reference to Fig. 3 in addition to Fig. 1. Fig. 3 is an enlarged schematic diagram of the cross section shown in Fig. 1, illustrating the light-emitting layer 23 and the vicinity of the light-emitting layer 23 among the hole transport layer 22 and the electron transport layer 24, and in particular, illustrating an enlarged region E1 shown in Fig. 1.

[0022] The light-emitting layer 23 according to this embodiment includes a plurality of quantum dots 30, a first additive 40, a semiconductor 41, and a second additive 42.

[0023] The quantum dots 30 may each have a core / shell structure, including a core and a shell surrounding the core. In this embodiment, the quantum dots 30 are, for example, luminescent semiconductor nanoparticles that emit light due to excitons generated by the recombination of injected electrons and holes. For example, the recombination of electrons and holes in the quantum dots 30 occurs primarily in the core. The core of the quantum dot 30 is a luminescent material that has a valence band level and a conduction band level and emits light due to the recombination of holes in the valence band level and electrons in the conduction band level. The quantum dots 30 emit light with a narrow spectrum due to the quantum confinement effect, enabling the production of light with a relatively deep chromaticity. Furthermore, the shell functions to suppress the occurrence of defects or dangling bonds in the core and reduce the recombination of carriers undergoing a deactivation process.

[0024] The core and shell materials of the quantum dots 30 may each contain materials used for the core and shell materials of conventionally known core / shell quantum dots. The quantum dots 30 may have a core / shell structure such as InP / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or CIGS / ZnS. The shell may be formed of multiple layers containing multiple different materials.

[0025] The quantum dots 30 have a particle size of about 1 to 100 nm. The wavelength of light emitted from the quantum dots 30 can be controlled by the particle size. In particular, since the quantum dots 30 have a core / shell structure, the wavelength of light emitted from the quantum dots 30 can be controlled by controlling the particle size of the core. Therefore, by controlling the particle size of the quantum dots 30, the wavelength of light emitted by the display device 1 can be controlled.

[0026] The light-emitting layer 23 has a thickness of 1000 nm or less in a plane direction perpendicular to the thickness direction at any position in the thickness direction. ２ The light-emitting layer 23 may contain one or more quantum dots 30 per layer. In this case, the light-emitting layer 23 generally contains quantum dots 30 at a concentration sufficient to function as a light-emitting layer of a light-emitting element.

[0027] In this embodiment, the quantum dots 30 include first quantum dots 31 and second quantum dots 32. In particular, the second quantum dots 32 are located closer to the cathode 25 than the first quantum dots 31. For example, as shown in FIGS. 1 and 3 , the light-emitting layer 23 may include a first light-emitting layer 23A and a second light-emitting layer 23B located closer to the cathode 25 than the first light-emitting layer 23A. In this case, the first light-emitting layer 23A may include the first quantum dots 31 of the quantum dots 30, and the second light-emitting layer 23B may include the second quantum dots 32 of the quantum dots 30. Note that the first light-emitting layer 23A and the second light-emitting layer 23B in this disclosure are merely components provided for convenience in order to more clearly explain the configuration of the light-emitting layer 23 in this disclosure. In other words, the light-emitting layer 23 does not need to include a clearly distinguishable first light-emitting layer 23A and second light-emitting layer 23B. As described above, in the present disclosure, the specific configuration of the light-emitting layer 23 is not particularly limited as long as the positional relationship of each part of the light-emitting layer 23, for example, the quantum dots as well as the adducts and organic ligands described below, can be confirmed, for example, by observing a cross section of the light-emitting layer 23.

[0028] <Light-Emitting Layer: First Additive> The first light-emitting layer 23A includes a first additive 40. The first additive 40 has insulating properties. For example, the first additive 40 may include at least one selected from the group including silicon oxide, boron oxide, phosphorus oxide, germanium oxide, beryllium fluoride, arsenic sulfide, silicon selenide, germanium sulfide, titanium oxide, tellurium oxide, aluminum oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, and silicon nitride. In particular, the first additive 40 may include at least one of silicon oxide, aluminum oxide, and silicon nitride. In this case, the first additive 40 becomes denser, thereby further improving the effect of protecting the quantum dots 30 (described later) from foreign substances such as moisture.

[0029] The first addition 40 is located between the layer adjacent to the light-emitting layer 23 on the anode 21 side, in other words, between the hole transport layer 22 and the first quantum dots 31. As shown in FIG. 3 , the thickness T1 of the first addition 40 between the upper surface 22T of the hole transport layer 22 and the first quantum dots 31 may be 1 nm or more and 3 nm or less. In the present disclosure, "thickness" refers to the dimension in a direction perpendicular to the in-plane direction of a layered member. As will be described later, when the first addition 40 covers the first quantum dots 31, the "thickness" of the first addition 40 in the present disclosure refers to the length in the direction from the center of the first quantum dots 31 to the periphery. When observing a cross section of the light-emitting element 2 in the stacking direction, the "thickness" refers to the average thickness of the members within the observed range. In this case, the area of ​​the cross section observed is 5 nm ２ 500nm or more ２ The following is the result.

[0030] In particular, the first additives 40 may be located around the first quantum dots 31, or may be located all around the first quantum dots 31 and cover the first quantum dots 31. In this case, the first light-emitting layer 23A can be considered to include a plurality of first quantum dot structures 33, each including a first quantum dot 31 and a first additive 40 encapsulating the first quantum dots 31.

[0031] 3 , in any cross section passing through any first quantum dot 31, the first addition 40 may be located around the entire periphery of the first quantum dot 31. Here, "the first addition 40 is located around the entire periphery of the first quantum dot 31" may mean that the first addition 40 is located over 90% or more of the periphery of the first quantum dot 31. Furthermore, the surface of the first quantum dot 31 and the first addition 40 may be in contact with each other.

[0032] <Light-Emitting Layer: Semiconductor> The first light-emitting layer 23A includes a semiconductor 41. The semiconductor 41 has a higher conductivity than at least the first additive 40. The semiconductor 41 may include at least one of zinc sulfide, gallium sulfide, magnesium sulfide, cadmium sulfide, tin sulfide, indium sulfide, and manganese sulfide. In particular, from the viewpoint of reducing the contact resistance between the semiconductor 41 and the first quantum dots 31, the semiconductor 41 may include the same material as the material included in the outermost periphery of the shell or the like of the first quantum dots 31.

[0033] In particular, the semiconductor 41 may contain the plurality of first quantum dot structures 33 contained in the first light-emitting layer 23A, and the semiconductor 41 may also form the outer edge where the light-emitting layer 23 contacts the upper surface 22T of the hole transport layer 22.

[0034] In this embodiment, the space between at least two first quantum dots 31 may be filled with the semiconductor 41, or may be filled with both the first additive 40 and the semiconductor 41. For example, when the first additive 40 is located only partially around each first quantum dot 31, the space between at least two first quantum dots 31 may be filled with only the semiconductor 41. Alternatively, when the first additive 40 is located entirely around each first quantum dot 31, the space between at least two first quantum dots 31 may be filled with both the first additive 40 and the semiconductor 41.

[0035] Here, the material filling the spaces between the quantum dots 30 will be described in more detail with further reference to Fig. 4. Schematic diagrams 401 and 402 in Fig. 4 are schematic diagrams showing the material filling the spaces between the quantum dots 30. In particular, schematic diagrams 401 and 402 are respectively diagrams showing two examples of a set P of two quantum dots 30 and the region (space) K between them, as shown in Fig. 3. In particular, schematic diagrams 401 and 402 are respectively diagrams showing set P1 and set P2, which are examples of sets of quantum dots 30A and 30B.

[0036] In this specification, "a member filling the spaces between the quantum dots 30" means that the member fills at least the region K between the quantum dots 30A and 30B, as shown in the schematic diagram 401 of the set P1 in Fig. 4. Region K is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of the quantum dots 30A and 30B and the opposing peripheries of the quantum dots 30A and 30B in the cross section of the light-emitting layer 23. Therefore, as shown in the schematic diagram 402 of the set P2 in Fig. 4, region K can exist even if the quantum dots 30A and 30B are close to each other, and the member fills region K.

[0037] The phrase "a material fills the spaces between the quantum dots 30" does not necessarily mean that the region K between the quantum dots 30A and 30B is entirely made of the material. For example, the region K between the quantum dots 30A and 30B may contain a material, such as a ligand, that is different from the material of the material. Specifically, for example, the light-emitting layer 23 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 30 in the dispersion liquid used for coating and that coordinates to the outer surfaces of the quantum dots 30 in the dispersion liquid. In this case, in the light-emitting layer 23, from the viewpoint of improving the reliability of the light-emitting layer 23, for example, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%.

[0038] <Light-Emitting Layer: Second Additive> The second light-emitting layer 23B includes a second additive 42. The second additive 42 has insulating properties. For example, the second additive 42 may include the same material as the first additive 40, and in particular, may have the same composition. In other words, at least one of the first additive 40 and the second additive 42 may include the above-mentioned material. Note that, in this specification, "the two components have the same composition" does not mean that both components have completely the same composition. For example, if the first additive 40 and the second additive 42 both include two types of atoms, and the difference in the ratio of one atom to the other atom is 1% or less, the two may be considered to have the same composition.

[0039] In particular, the second additive 42 may contain at least one of silicon oxide, aluminum oxide, and silicon nitride. In this case, the second additive 42 becomes denser, thereby further improving the effect of protecting the quantum dots 30, which will be described later, from foreign substances such as moisture. The first additive 40 may contain at least one of silicon oxide, aluminum oxide, and silicon nitride, and the second additive 42 may contain at least one of silicon oxide, aluminum oxide, and silicon nitride. In this case, the first additive 40 and the second additive 42 can more effectively protect the quantum dots 30.

[0040] Furthermore, in this disclosure, "atom" does not only mean that it exists as a single atom. In this disclosure, "atom" also includes those that exist in the form of a molecule having two or more atoms, including the atom in question and another atom, those that exist in the form of a complex, those that exist in the form of a compound, or those that exist in the form of an ion. However, in this disclosure, "atom" does not limit the form of existence of other atoms. In other words, a metal atom includes those that exist in the form of a compound containing a metal atom, and those that exist in the form of a metal ion. Regardless of the form of existence of a metal atom, if its presence in a substance can be identified by analysis, the substance may be considered to contain the metal atom.

[0041] The second additive 42 is adjacent to the electron transport layer 24 on the cathode 25 side of the light-emitting layer 23. In particular, the second additive 42 may form a portion of the outer edge of the light-emitting layer 23 that is adjacent to the lower surface 24U of the electron transport layer 24. Therefore, the light-emitting layer 23 includes the second additive 42 between the electron transport layer 24 and the second quantum dots 32.

[0042] The thickness T1 is smaller than the thickness T2 of the second additive 42 located between the electron transport layer 24 and the second quantum dots 32 shown in Fig. 3. In particular, the thickness T2 may be 3 nm or more and 6 nm or less. The second additive 42 may be located between at least two second quantum dots 32 of the quantum dots 30, and may further fill the space between the two second quantum dots 32.

[0043] The second addition 42 is formed at a position in the thickness direction of the second light-emitting layer 23B, and has a thickness of 1000 nm in a plane direction perpendicular to the thickness direction. ２ In the second light-emitting layer 23B, the second quantum dots 32 may be encapsulated in the continuous film of the second additive 42. In other words, the second quantum dots 32 may be encapsulated in the continuous film of the second additive 42.

[0044] For example, when 60% or more of the surface of 80% or more of the second quantum dots 32 constituting the second light-emitting layer 23B is in contact with the continuous film of the second additive 42, the second quantum dots 32 contained in the second light-emitting layer 23B can be said to be encapsulated in the second additive 42. In this way, the second light-emitting layer 23B including the second quantum dots 32 encapsulated in the second additive 42 has improved light-emitting properties and a longer lifespan.

[0045] The second addition 42 may be located, for example, over the entire periphery of the second quantum dot 32. For example, as shown in Fig. 3 , the second addition 42 may be located over the entire periphery of any second quantum dot 32 in any cross section passing through any second quantum dot 32. Here, "the second addition 42 is located over the entire periphery of the second quantum dot 32" may mean that the second addition 42 is located over 90% or more of the periphery of the second quantum dot 32. Furthermore, the surface of the second quantum dot 32 and the second addition 42 may be in contact with each other, as shown in Fig. 3 .

[0046] The band gaps of the first additive 40 and the second additive 42 may be wider than the band gap of the constituent material of the quantum dot 30. When the quantum dot 30 has a core and a shell surrounding the core, the band gaps of the first additive 40 and the second additive 42 may be wider than the band gap of the constituent material of the shell.

[0047] <Additional Note> The first light-emitting layer 23A may include a first additive 40 and a semiconductor 41 between the upper surface 22T of the hole transport layer 22 and the first quantum dots 31. In this case, the distance between the upper surface 22T of the hole transport layer 22 and the first quantum dots 31 in the film thickness direction of the light-emitting layer 23, in other words, the thickness T3 between the first additive 40 and the semiconductor 41, may be 6 nm or more and 12 nm or less.

[0048] The specific structure of each layer of the light-emitting device 2 according to this embodiment may be confirmed by confirming the composition at the interface of each layer and its position in the film thickness direction. This confirmation may be performed, for example, by Method 1: EDX (Energy Dispersive X-ray Spectroscopy) of the cross section of each layer of the light-emitting device 2 using a TEM (Transmission Electron Microscope). In particular, Method 1 may also be performed in conjunction with FIB (Focused Ion Beam) processing. Furthermore, a more detailed method for performing the confirmation may include, for example, Method 2: Dynamic SIMS (Secondary Ion Mass Spectroscopy) is used to confirm the distribution of elements or molecules in the film thickness direction of each layer of the light-emitting device 2. Furthermore, Method 3: In Method 2, dynamic SIMS may be replaced with TOF (Time Of Flight)-SIMS (Static SIMS). The confirmation methods are prioritized in the order of Methods 1 to 3 described above. If confirmation is successful using the earlier method, confirmation using the later method may be omitted.

[0049] The light-emitting element 2 according to this embodiment is not limited to the above-described layer structure. For example, the light-emitting element 2 may include at least one of a hole injection layer located between the anode 21 and the hole transport layer 22 and an electron injection layer located between the cathode 25 and the electron transport layer 24.

[0050] The light-emitting element 2 may also include at least one of an electron blocking layer located between the hole transport layer 22 and the light-emitting layer 23, and a hole blocking layer located between the electron transport layer 24 and the light-emitting layer 23. Therefore, the layer adjacent to the light-emitting layer 23 on the anode 21 side may be an electron blocking layer, or the layer adjacent to the light-emitting layer 23 on the cathode 25 side may be a hole blocking layer. In addition, the light-emitting element 2 may also include a protective layer or intermediate layer located at least either between the hole transport layer 22 and the light-emitting layer 23 or between the electron transport layer 24 and the light-emitting layer 23. Therefore, at least one of the layer adjacent to the light-emitting layer 23 on the anode 21 side and the layer adjacent to the light-emitting layer 23 on the cathode 25 side may be a protective layer or intermediate layer.

[0051] Furthermore, the light-emitting element 2 may include only the light-emitting layer 23 between the anode 21 and the cathode 25, in other words, it may not include a charge transport layer between the anode 21 and the cathode 25. In this case, the layer adjacent to the light-emitting layer 23 on the anode 21 side may be the anode 21, or the layer adjacent to the light-emitting layer 23 on the cathode 25 side may be the cathode 25.

[0052] In addition, the light-emitting element 2 may include, from the substrate 3 side, the cathode 25, the electron transport layer 24, the light-emitting layer 23, the hole transport layer 22, and the anode 21, in this order. In other words, the stacking order of the layers from the anode 21 to the cathode 25 of the light-emitting element 2 may be reversed. When the light-emitting element 2 includes the cathode 25 on the substrate 3 side of the light-emitting layer 23, the light-emitting layer 23 includes, on the electron transport layer 24, the second light-emitting layer 23B and the first light-emitting layer 23A, in this order.

[0053] <Light-emitting layer according to comparative example> The effects of the light-emitting element and display device according to this embodiment will be described by comparing them with the light-emitting element and display device according to comparative examples. Figure 5 is a schematic side cross-sectional view of a display device 1C according to comparative example.

[0054] Compared to the display device 1 according to this embodiment, the display device 1C according to the comparative embodiment includes a light-emitting element 2C instead of the light-emitting element 2. Compared to the light-emitting element 2, the light-emitting element 2C has a light-emitting layer 23C instead of the light-emitting layer 23.

[0055] 6 is an enlarged schematic diagram showing the light-emitting layer 23C and the vicinity of the light-emitting layer 23C in the hole transport layer 22 and the electron transport layer 24 in the cross section shown in FIG. 5, and in particular showing an enlarged region EC shown in FIG.

[0056] The light-emitting layer 23C includes a plurality of quantum dots 30 and a first additive 40 encapsulating each of the quantum dots 30. In particular, in the comparative example, the first additive 40 is adjacent to both the hole transport layer 22 and the electron transport layer 24, and none of the quantum dots 30 is adjacent to either the hole transport layer 22 or the electron transport layer 24. Furthermore, the light-emitting layer 23C does not include a semiconductor 41; in other words, the semiconductor 41 is not included between the quantum dots 30 and the hole transport layer 22.

[0057] The thickness of the first addition 40 located between the quantum dots 30 included in the light-emitting layer 23C that are located on the hole transport layer 22 side and the upper surface 22T of the hole transport layer 22 is defined as thickness T4. The thickness of the first addition 40 located between the quantum dots 30 included in the light-emitting layer 23C that are located on the electron transport layer 24 side and the lower surface 24U of the electron transport layer 24 is defined as thickness T5. In this case, in the comparative example, thickness T4 is equal to or greater than thickness T5.

[0058] Except for the above points, the display device 1C according to the comparative embodiment has the same configuration as the display device 1 according to this embodiment.

[0059] Here, the path of charges flowing through the light-emitting layer 23C when the light-emitting element 2C according to the comparative example is driven will be considered. In the comparative example, the first additive 40 is an insulator, while the quantum dots 30 contain a material, such as a semiconductor, that has at least higher electrical conductivity than the first additive 40. Therefore, when the light-emitting element 2C is driven, charges are thought to be transported mainly along the path R that connects the hole transport layer 22 and the electron transport layer 24 via the quantum dots 30, as shown in FIG. 6 .

[0060] Under the above assumptions, the light-emitting layer 23C on the path R when the light-emitting element 2C is driven is regarded as a circuit that connects the hole transport layer 22 and the electron transport layer 24 and transports charges. In this case, the circuit can be regarded as a circuit in which, in addition to the resistance between the hole transport layer 22 and the electron transport layer 24, each quantum dot 30 and each first addition 40 on the path R behaves as a virtual diode D. In the example shown in Figure 6, the virtual circuit formed along the path R can be regarded as including a total of five diodes D in addition to the resistance between the hole transport layer 22 and the electron transport layer 24.

[0061] In particular, in the virtual circuit on the path R of the light-emitting layer 23C according to the comparative embodiment, the first addition 40 is located not only between the electron transport layer 24 and the quantum dots 30, but also between the hole transport layer 22 and the quantum dots 30. Therefore, when the light-emitting element 2C including the light-emitting layer 23C is driven, the first addition 40 formed between the hole transport layer 22 and the quantum dots 30 behaves as a virtual diode D. Therefore, in the light-emitting element 2C according to the comparative embodiment, the first addition 40 between the hole transport layer 22 and the quantum dots 30, which behaves as a virtual diode D, reduces the efficiency of hole injection from the hole transport layer 22 to the quantum dots 30.

[0062] In general, in light-emitting devices that include quantum dots as light-emitting materials in their light-emitting layers, electron excess, in which the electron concentration in the light-emitting layer exceeds the hole concentration, can occur due to differences in the charge injection efficiency into the light-emitting layer and differences in charge mobility. The electron excess in the light-emitting layer not only increases the deactivation process in the quantum dots and reduces the luminous efficiency of the light-emitting device, but can also be a contributing factor to the generation of Auger electrons by the excess electrons. Auger electrons do not contribute to the luminescence of the quantum dots and can cause degradation of the quantum dots and materials in their vicinity.

[0063] Therefore, the light-emitting element 2C reduces the light-emitting efficiency of the light-emitting layer 23C, increases the excess electrons in the light-emitting layer 23C, and increases the deterioration of the quantum dots 30 in the light-emitting layer 23C or the transport material of each transport layer due to Auger electrons generated from the excess electrons.

[0064] In particular, in the comparative embodiment, the thickness T4 is equal to or greater than the thickness T5. In the light-emitting layer 23C of the light-emitting element 2C, the effective electrical resistance of the virtual diode D described above between the hole transport layer 22 and the quantum dots 30 is equal to or greater than the effective electrical resistance between the electron transport layer 24 and the quantum dots 30. Therefore, due to the above circumstances, an excess of electrons is likely to occur in the light-emitting layer 23C of the light-emitting element 2C according to the comparative embodiment.

[0065] <Effects of the Light-Emitting Element According to the Embodiment> Meanwhile, the thickness T1 of the first addition 40 between the hole transport layer 22 and the first quantum dot 31 is smaller than the thickness T2 of the second addition 42 between the electron transport layer 24 and the second quantum dot 32. Therefore, the effective electrical resistance of the above-described virtual diode D in the light-emitting layer 23 of the light-emitting element 2 is lower between the hole transport layer 22 and the first quantum dot 31 than between the electron transport layer 24 and the second quantum dot 32. Therefore, the light-emitting element 2 according to the present embodiment improves the efficiency of hole injection from the anode 21 to the light-emitting layer 23 via the hole transport layer 22 compared to the efficiency of electron injection from the cathode 25 to the light-emitting layer 23 via the electron transport layer 24.

[0066] Furthermore, in the light-emitting layer 23 of the light-emitting element 2 according to this embodiment, the first quantum dots 31 located closer to the anode 21 than the second quantum dots 32 include not only the first additives 40 but also the semiconductors 41 between them and the hole transport layer 22. Therefore, the light-emitting element 2 according to this embodiment further reduces the effective electrical resistance of the virtual diodes D formed between the hole transport layer 22 and the first quantum dots 31, compared to the light-emitting element 2C according to the comparative embodiment. Therefore, in the light-emitting element 2 according to this embodiment, the transport of holes from the hole transport layer 22 to the first quantum dots 31 is more efficiently achieved.

[0067] This improves the efficiency of hole injection from the hole transport layer 22 to the first quantum dots 31 in the light-emitting element 2, and reduces the deterioration of the luminous efficiency in the light-emitting layer 23 and the layers between the anode 21 and the cathode 25.

[0068] In addition, the light-emitting layer 23 of the light-emitting element 2 according to this embodiment includes a first additive 40 located around the first quantum dot 31 and a second additive 42 located around the second quantum dot 32. Therefore, the light-emitting layer 23 can protect the quantum dots 30 including the first quantum dot 31 and the second quantum dot 32 from foreign substances such as moisture by the first additive 40 and the second additive 42. Therefore, the light-emitting element 2 can reduce deterioration of the quantum dots 30 in the light-emitting layer 23 by the first additive 40 and the second additive 42.

[0069] Therefore, the light-emitting element 2 achieves improved luminous efficiency and improved reliability of each layer between the anode 21 and the cathode 25 while reducing deterioration of the quantum dots 30 due to the first and second additives 40 and 42. The display device 1 including the light-emitting element 2 achieves reduced power consumption and a longer lifespan.

[0070] The thickness T1 may be 1 nm or more, and the thickness T3 may be 6 nm or more, from the viewpoint of further improving the effect of protecting the first quantum dots 31. Furthermore, from the viewpoint of further improving the efficiency of hole injection from the anode 21 to the light-emitting layer 23 via the hole transport layer 22, the thickness T1 may be 3 nm or less, and the thickness T3 may be 12 nm or less.

[0071] The first addition 40 is positioned around the entire periphery of the first quantum dots 31, covering the first quantum dots 31, thereby further improving the protective effect of the first addition 40 on the first quantum dots 31 in the light-emitting device 2. Furthermore, the spaces between the multiple first quantum dots are filled with the semiconductor 41, thereby further improving the protective effect of the semiconductor 41 on the first quantum dots 31 in the light-emitting device 2. In addition, the spaces between the multiple first quantum dots are filled with the first addition 40 and the semiconductor 41, thereby further improving the protective effect of the first quantum dots 31 in the light-emitting device 2.

[0072] By including a semiconductor 41 between the multiple first quantum dots 31, the efficiency of hole injection from the hole transport layer 22 to the first quantum dots 31 is improved compared to when only the first additive is located between the multiple first quantum dots 31.

[0073] From the viewpoint of further improving the protective effect of the second quantum dots 32, the thickness T2 may be 3 nm or more, or, as described above, the second additive 42 may fill the space between at least two second quantum dots 32. Furthermore, from the viewpoint of reducing the retention of excess electrons on the cathode 25 side of the light-emitting layer 23 and reducing the overall electrical resistance of the light-emitting element 2, the thickness T2 may be 6 nm or less.

[0074] As described above, the first additive 40 or the second additive 42 may have insulating properties. The insulating first additive 40 or the second additive 42 further reduces the penetration of foreign substances into the quantum dots 30. In particular, the insulating first additive 40 or the second additive 42 reduces the injection of excess electrons, such as Auger electrons, into the quantum dots 30, which may deteriorate the quantum dots 30, or the propagation of energy from these electrons. Therefore, with the above configuration, the light-emitting element 2 more efficiently protects the quantum dots 30, further reduces deterioration of the quantum dots 30, and further improves the carrier balance of the light-emitting layer 23.

[0075] <Method of Manufacturing Display Device: Up to Formation of Hole Transport Layer> A method of manufacturing the display device 1 according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart showing a method of manufacturing the display device 1 according to this embodiment.

[0076] In the manufacturing method of the display device 1 according to this embodiment, first, the substrate 3 is prepared (step S21). The substrate 3 may be manufactured by forming a plurality of the pixel circuits PC described above on a glass substrate, for example.

[0077] Next, the light-emitting element 2 is formed on the substrate 3. In the process of forming the light-emitting element 2, for example, first, the anode 21 is formed on the substrate 3 by any of the methods described above (step S22). For example, if the substrate 3 has a plurality of pixel circuits PC, the anode 21 may be formed in an island shape for each pixel circuit PC.

[0078] Next, by any of the methods described above, the hole transport layer 22 is formed on the anode 21 (step S23). The hole transport layer 22 may be formed in common for the plurality of anodes 21, or may be formed in an island shape for each anode 21. When the hole transport layer 22 is formed in an island shape, the material of the hole transport layer 22 may differ depending on the emission color of the sub-pixel.

[0079] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Mixing Step> Next, the light-emitting layer 23 is formed (step S24). The method for forming the light-emitting layer 23 will be described in more detail with reference to Fig. 8. Fig. 8 is a flowchart showing the method for forming the light-emitting layer 23 according to this embodiment.

[0080] In the method for forming the light-emitting layer 23 according to this embodiment, first, a first dispersion and a second dispersion are prepared (step S1). In step S1 according to this embodiment, the first dispersion and the second dispersion are prepared using a mixing step. Hereinafter, the mixing step in the preparation of the first dispersion will be described with reference to FIG. 9. FIG. 9 is a side view illustrating the mixing step in the method for forming the light-emitting layer 23 according to this embodiment.

[0081] In the mixing step according to this embodiment, dispersion liquid LA and dispersion liquid LB shown in step S1-1 of FIG. 9 are prepared.

[0082] The dispersion liquid LA is a dispersion liquid in which a precursor 51 as a first precursor and a precursor ligand 52 are dispersed in a solvent 50. The solvent 50 is a polar solvent such as N,N-dimethylformamide (DMF). The precursor 51 and the precursor ligand 52 are first precursors that are precursors of the first adduct 40, and are converted to the first adduct 40 by a reaction or the like described below. For example, when the first adduct 40 and the second adduct 42 are silicon oxide, the precursor 51 may contain tetramethyl orthosilicate (TMOS) shown in the following formula (1). Furthermore, when the first adduct 40 and the second adduct 42 are silicon oxide, the precursor ligand 52 may contain 3-(mercaptopropyl)trimethoxysilane (MPS) shown in the following formula (2).

[0083] In this case, dispersion LA may further include a halogen source 53 in solvent 50. The halogen source 53 may function as a catalyst for the conversion of precursor 51 and precursor ligand 52 to first adduct 40, as described below.

[0084] Dispersion LA may be prepared by adding separately synthesized precursor 51 , precursor ligand 52 , and halogen source 53 to solvent 50 .

[0085] The dispersion liquid LB is, for example, a dispersion liquid in which a plurality of quantum dots 30, each coordinated with an organic ligand 55, is dispersed in a solvent 54. The solvent 54 is a non-polar solvent such as octane. The organic ligand 55 may include a carbon chain having a coordinating functional group at one end capable of forming a coordinate bond with the outermost surface of the quantum dots 30.

[0086] The dispersion liquid LB may be prepared by synthesizing a plurality of quantum dots 30 in a solvent 54 by any method, including a conventionally known method, and then adding the organic ligands 55 to the solvent 54. Alternatively, the dispersion liquid LB may be prepared by extracting quantum dots 30 that have been separately synthesized and the organic ligands 55 that coordinate to the quantum dots 30, and adding the extracted quantum dots 30 to the solvent 54.

[0087] Since solvent 50 and solvent 54 have different polarities, when dispersion LA and dispersion LB are left to stand in a container, the liquid in the container separates into a layer of dispersion LA and a layer of dispersion LB, as shown in FIG. 9 .

[0088] Next, the dispersion liquid LA and the dispersion liquid LB are thoroughly stirred and mixed in the container. During the stirring process, some of the organic ligands 55 coordinated to the quantum dots 30 are replaced by precursor ligands 52. This makes it easier for the quantum dots 30 to disperse in the solvent 50 than in the solvent 54, and the quantum dots 30 migrate from the dispersion liquid LB to the dispersion liquid LA, as shown in step S1-2 of FIG.

[0089] Furthermore, during the stirring process, the precursor 51 and the precursor ligand 52 react in the dispersion liquid LA and are converted into an adduct around the quantum dots 30 .

[0090] The details of the reaction when the precursor 51 contains TMOS and the precursor ligand 52 contains MPS will be described. For example, in the mixing process, the methoxy groups of the TMOS precursor 51 and the MPS precursor ligand 52 are converted into water (H ２ O), which is replaced by a hydroxyl group (OH-), and methanol is produced as a by-product. Next, the two hydroxyl groups undergo dehydration condensation with each other, resulting in dehydration condensation between TMOS and MPS, between two TMOSs, and between two MPSs. As a result, in step S1, the precursor 51 and the precursor ligand 52 are converted into a first adduct 40 containing silicon oxide.

[0091] The reaction between precursor 51 and precursor ligand 52 may proceed using a halogen source 53 as a catalyst. In step S5, some of the methoxy groups of TMOS of precursor 51 and MPS of precursor ligand 52 may react through the reaction. In other words, methoxy groups or hydroxyl groups may remain in first adduct 40.

[0092] In the mixed solution of the dispersion liquid LA and the dispersion liquid LB, the precursor 51 and the precursor ligand 52 are located around the quantum dots 30. Therefore, as shown in step S1-2 of Fig. 9, by mixing the dispersion liquid LA and the dispersion liquid LB, a first quantum dot structure 33 including the quantum dots 30 and the first adduct 40 covering the quantum dots 30 is synthesized. Note that in step S1-2, the first quantum dot structure 33 may migrate to the interface between the dispersion liquid LA and the dispersion liquid LB.

[0093] Next, the first quantum dot structures 33 are extracted from the dispersion liquid LA, for example, by centrifuging the dispersion liquid LA at 4000 rpm for 5 minutes. When centrifuging the dispersion liquid LA, a poor solvent such as ethyl acetate or acetone may be added to the dispersion liquid LA to precipitate the first quantum dot structures 33. Next, the precipitate containing the first quantum dot structures 33 is dispersed in a solvent 50 in a separate container together with a precursor of the semiconductor 41. In this manner, the first dispersion liquid is prepared.

[0094] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: First Dispersion> The first dispersion prepared by the above-described mixing step will be described with reference to Fig. 10. Fig. 10 is a schematic diagram showing the first dispersion L1 according to the present embodiment poured into a container C.

[0095] 10 , the first dispersion liquid L1 is a dispersion liquid in which a plurality of first quantum dot structures 33 and a precursor 56 of a semiconductor 41 are dispersed in a solvent 50. For example, when the semiconductor 41 contains a metal atom, the precursor 56 may contain a metal acetate, a metal nitrate, or a metal halide as a metal source. When the semiconductor 41 contains a sulfur atom, the precursor 56 may contain at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea, and thioacetamide as a sulfur source. Alternatively, the precursor 56 may contain a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to a metal atom.

[0096] The first dispersion liquid L1 may contain a polar ligand that is coordinated to the outermost peripheral surface of the first quantum dot structure 33 in order to improve the dispersibility of the first quantum dot structure 33 in the solvent 50. The ligand may contain a halide ion so that the ligand functions as a catalyst that promotes the conversion of the precursor 56 into the semiconductor 41.

[0097] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Second Dispersion> The mixing step in preparing the second dispersion differs from the mixing step in preparing the first dispersion in that precursor 51 and precursor ligand 52 are second precursors that are precursors of second adduct 42, and are converted into second adduct 42 by the reaction described above or the like. However, except for the above, in the mixing step in preparing the second dispersion, the respective configurations of dispersion LA and dispersion LB, and the method of stirring dispersion LA and dispersion LB may be the same as in the mixing step in preparing the first dispersion.

[0098] In the following, as described above, a case will be described where the first adduct 40 and the second adduct 42 are the same as each other. In other words, in the following description, the first precursor, which is the precursor of the first adduct 40, and the second precursor, which is the precursor of the second adduct 42, are both the precursor 51 and the precursor ligand 52.

[0099] As a result, in the mixing step of preparing the second dispersion, a second quantum dot structure is synthesized that includes the quantum dots 30 and the second adduct 42 that covers the quantum dots 30. Thereafter, in the mixing step of preparing the second dispersion, the second quantum dot structure is extracted, and the second quantum dot structure, the precursor 51, and the halogen source 53 are dispersed in a solvent in a separate container. In this way, the second dispersion is prepared.

[0100] The second dispersion liquid prepared by the above-described mixing step will be described with reference to Fig. 11. Fig. 11 is a schematic diagram showing the second dispersion liquid L2 according to this embodiment poured into a container C.

[0101] 11 , the second dispersion L2 is a dispersion in which a plurality of second quantum dot structures 34, each including quantum dots 30 and a second adduct 42 covering the quantum dots 30, are dispersed in a solvent 57. The second dispersion also includes a precursor 51 and a halogen source 53 dispersed in the solvent 57. The solvent 57 may include, for example, toluene.

[0102] Note that step S1 does not have to be performed after step S23, in other words, it does not have to be performed after the formation of the hole transport layer 22. In particular, the preparation of the first dispersion L1 and the second dispersion L2 may be completed by the time step S23 is completed, in other words, by the time the formation of the hole transport layer 22 is completed.

[0103] <Manufacturing Method of Display Device: Formation of Light-Emitting Layer: Film-Depositing Step> In the manufacturing method of the display device 1 according to this embodiment, after the formation of the hole transport layer 22 and the preparation of the first dispersion L1 and the second dispersion L2, a film-depositing step of the light-emitting layer 23 is carried out. The film-depositing step of the light-emitting layer 23 will be described in more detail with reference to Fig. 12 in addition to Fig. 8. Fig. 12 is a process cross-sectional view showing the film-depositing step of the light-emitting layer 23, which is part of the method of forming the light-emitting layer 23.

[0104] In the film formation process of the light-emitting layer 23, first, a laminate including each layer on the substrate 3 is used as a substrate, and the first dispersion L1 is applied to the substrate (step S2). For example, as shown in step S2 of Fig. 12, the first dispersion L1 is applied to the hole transport layer 22 by any method including a conventionally known application method such as spin coating.

[0105] Next, the precursor of the semiconductor 41 in the first dispersion liquid L1 containing the precursor 56 is converted into the semiconductor 41 (step S3). For example, the precursor 56 in the first dispersion liquid L1 is reacted by heating each portion of the substrate 3 containing the applied first dispersion liquid L1 at a temperature of, for example, 80° C. to 500° C. for 1 minute or more.

[0106] In step S3, the precursor 56 in the applied first dispersion liquid L1 is located around the first quantum dot structures 33. Therefore, the precursor 56 converted in step S3 is converted into the semiconductor 41 so as to fill the spaces between the first quantum dot structures 33. Therefore, as shown in step S3 in Fig. 12 , a first light-emitting layer 23A including a plurality of first quantum dot structures 33 encapsulated in the semiconductor 41 is formed on the hole transport layer 22.

[0107] Next, the second dispersion L2 is applied onto the substrate 3, which is a laminate including the layers on the substrate 3 (step S4). For example, as shown in step S4 in Fig. 12, the second dispersion L2 is applied onto the first light-emitting layer 23A by any method including a conventionally known application method such as spin coating.

[0108] Next, the precursor of the second adduct 42 in the second dispersion liquid L2, which contains the precursor 51, is converted into the second adduct 42 (step S5). For example, each portion of the substrate 3 containing the applied second dispersion liquid L2 is heated at 100° C. for 30 minutes, for example, to cause a reaction of the precursor 51 in the second dispersion liquid L2. The reaction of the precursor 51 may proceed using a halogen source 53 as a catalyst.

[0109] Here, in step S5, the precursor 51 in the applied second dispersion L2 is located around the second quantum dot structures 34. Therefore, the precursor 51 converted in step S5 is converted into the second adduct 42 so as to fill the spaces between the second quantum dot structures 34. Therefore, as shown in step S5 of Fig. 12, a second light-emitting layer 23B including a plurality of second quantum dots 32 encapsulated in the second adduct 42 is formed on the first light-emitting layer 23A. This completes the formation of the light-emitting layer 23.

[0110] 7 , after the light-emitting layer 23 is formed, the electron transport layer 24 is formed on the light-emitting layer 23 by any of the methods described above (step S25). The electron transport layer 24 may be formed by the same method as the hole transport layer 22, except for the formation position and the material used.

[0111] Next, the cathode 25 is formed on the electron transport layer 24 by the various methods described above (step S26). The cathode 25 may be formed in common for a plurality of anodes 21. In this manner, the display device 1 including the light-emitting element 2 on the substrate 3 is manufactured.

[0112] According to the above method, as described above, it is possible to manufacture a display device 1 having a light-emitting element 2 that achieves improved luminous efficiency and improved reliability of each layer between the anode 21 and the cathode 25 while reducing deterioration of the quantum dots 30 by the first additive 40 and the second additive 42.

[0113] In particular, in this embodiment, the first light-emitting layer 23A is formed by a method including conversion of a first precursor that is a precursor of the first adduct 40. Also, in this embodiment, the second light-emitting layer 23B is formed by a method including conversion of a second precursor that is a precursor of the second adduct 42. According to the above method, it is possible to more simply form the first light-emitting layer 23A including the first adduct 40 that covers the first quantum dots 31, and the second light-emitting layer 23B including the second adduct 42 that fills the spaces between the second quantum dots 32.

[0114] In particular, the reaction time of the first precursor in the conversion of the first precursor may be shorter than the reaction time of the second precursor in the conversion of the second precursor. According to the above configuration, the light-emitting layer 23 having a thickness T1 smaller than the thickness T2 can be more simply formed. The reaction time of the first precursor in the conversion of the first precursor may be, for example, the time it takes for the precursor 51 and the precursor ligand 52 to react in the preparation of the first dispersion L1. The reaction time of the second precursor in the conversion of the second precursor may be, for example, the sum of the time it takes for the precursor 51 and the precursor ligand 52 to react in the preparation of the second dispersion L2 and the reaction time of the precursor 51 in the applied second dispersion L2.

[0115] In this embodiment, the method for forming the light-emitting layer 23 is not limited to the above. For example, in the step of forming the first light-emitting layer 23A, a dispersion liquid in which quantum dots 30 and a first precursor are dispersed may first be applied to the hole transport layer 22, and the first precursor in the dispersion liquid may be converted into the first adduct 40 to form a layer including the first quantum dot structure 33. Next, a dispersion liquid in which a precursor 56 is dispersed may be applied to the layer including the first quantum dot structure 33, and the precursor 56 in the dispersion liquid may be converted into the semiconductor 41 to form the first light-emitting layer 23A.

[0116] In addition, in the process of forming the second light-emitting layer 23B, a dispersion liquid in which quantum dots 30 and the second precursor are dispersed may be applied to the first light-emitting layer 23A, and the second precursor may be converted into the second adduct 42 in the dispersion liquid to form the second light-emitting layer 23B.

[0117] In other words, the conversion of the first precursor to the first adduct 40 may occur before or after the application of the first dispersion, and the conversion of the second precursor to the second adduct 42 may occur before or after the application of the second dispersion, or may occur both before and after the application of the second dispersion.

[0118] In the manufacturing method of the display device 1 according to this embodiment, after the hole transport layer 22 is formed, the applied first dispersion L1 or the applied second dispersion L2 may be heated. In particular, since the first dispersion L1 is applied on the hole transport layer 22, heat generated by heating the first dispersion L1 is likely to propagate to the hole transport layer 22. Therefore, since the hole transport layer 22 according to this embodiment contains an inorganic substance, deterioration of the hole transport layer 22 in the manufacturing process of the light-emitting element 2 is reduced.

[0119] 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 different technical means disclosed in the 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 the embodiments.

[0120] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 22 Hole transport layer 23 Light-emitting layer 24 Electron transport layer 25 Cathode 30 Quantum dots 31 First quantum dots 32 Second quantum dots 40 First adduct 41 Semiconductor 42 Second adduct 51 Precursor (first precursor, second precursor) 52 Precursor ligand (first precursor, second precursor) L1 First dispersion L2 Second dispersion

Claims

1. A light-emitting device comprising: an anode; a cathode facing the anode; and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer includes first quantum dots and second quantum dots located closer to the cathode than the first quantum dots; a first additive located between the first quantum dots and an adjacent layer on the anode side of the light-emitting layer; and a second additive located between the second quantum dots and an adjacent layer on the cathode side of the light-emitting layer, wherein the thickness of the first additive is smaller than the thickness of the second additive.

2. The light-emitting device according to claim 1, wherein the thickness of the first additive is 1 nm or more and 3 nm or less.

3. The light-emitting device according to claim 1 or 2, wherein the distance between the adjacent layer of the light-emitting layer on the anode side and the first quantum dot is 6 nm or more and 12 nm or less.

4. The light-emitting element according to any one of claims 1 to 3, wherein the thickness of the second additive is 3 nm or more and 6 nm or less.

5. The light-emitting element according to any one of claims 1 to 4, wherein the layer adjacent to the light-emitting layer on the anode side contains an inorganic material.

6. The light-emitting device according to claim 5, further comprising a hole transport layer containing the inorganic material between the anode and the light-emitting layer.

7. The light-emitting device according to claim 5 or 6, wherein the inorganic material contains an oxide of Ni or Cr.

8. The light-emitting element according to any one of claims 5 to 7, wherein the inorganic material includes zinc sulfide or zinc sulfide selenide.

9. The light-emitting device according to any one of claims 5 to 8, wherein the inorganic material contains a p-type semiconductor.

10. A light-emitting device according to any one of claims 1 to 9, wherein the first additive covers the first quantum dot.

11. The light-emitting device according to any one of claims 1 to 10, wherein the light-emitting layer contains a plurality of the second quantum dots, and the second additive fills the spaces between at least two of the second quantum dots.

12. A light-emitting element according to any one of claims 1 to 11, wherein the light-emitting layer contains a plurality of the first quantum dots and a semiconductor, and the space between at least two of the first quantum dots is filled with the semiconductor, or is filled with the first additive and the semiconductor.

13. The light-emitting element according to claim 12, wherein the semiconductor includes at least one of zinc sulfide, gallium sulfide, magnesium sulfide, cadmium sulfide, tin sulfide, indium sulfide, and manganese sulfide.

14. The light-emitting element according to any one of claims 1 to 13, wherein the first attachment or the second attachment has insulating properties.

15. The light-emitting device according to claim 14, wherein at least one of the first additive and the second additive comprises at least one selected from the group consisting of silicon oxide, boron oxide, phosphorus oxide, germanium oxide, beryllium fluoride, arsenic sulfide, silicon selenide, germanium sulfide, titanium oxide, tellurium oxide, aluminum oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, and silicon nitride.

16. The light-emitting device according to claim 15, wherein at least one of the first additive and the second additive includes at least one of silicon oxide, aluminum oxide, and silicon nitride.

17. The light-emitting device according to claim 16, wherein the first additive comprises at least one of silicon oxide, aluminum oxide, and silicon nitride, and the second additive comprises at least one of silicon oxide, aluminum oxide, and silicon nitride.

18. A display device comprising a substrate and a plurality of light-emitting elements according to any one of claims 1 to 17 on said substrate.

19. A method for manufacturing a light-emitting device comprising an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, wherein the light-emitting layer comprises first quantum dots and second quantum dots located closer to the cathode than the first quantum dots, a first additive located between the first quantum dots and an adjacent layer on the anode side of the light-emitting layer, and a second additive located between the second quantum dots and an adjacent layer on the cathode side of the light-emitting layer, wherein the thickness of the first additive is smaller than the thickness of the second additive.

20. A method for manufacturing a light-emitting element according to claim 19, wherein the formation of the light-emitting layer comprises: applying a first dispersion containing the first quantum dots to a substrate; converting a first precursor that is a precursor of the first adduct into the first adduct; applying a second dispersion containing the second quantum dots and a second precursor that is a precursor of the second adduct to a substrate; and converting the second precursor into the second adduct.

21. The method for producing a light-emitting element according to claim 20, wherein the reaction time of the first precursor during the conversion of the first precursor is shorter than the reaction time of the second precursor during the conversion of the second precursor.

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