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

Abstract

A light-emitting element (2) comprises a light-emitting layer (23) that is positioned between an anode (21) and a cathode (25). The light-emitting layer includes a first quantum dot (31) and an adduct (40). The first quantum dot is directly adjacent to a layer (22) that is adjacent to the anode side of the light-emitting layer, or is adjacent to said layer with an organic ligand (41) or a semiconductor interposed therebetween.

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 includes an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the light-emitting layer including first quantum dots and an additive, and the first quantum dots are in direct contact with a layer adjacent to the light-emitting layer on the anode side, or adjacent to the layer via an organic ligand or a semiconductor.

[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 and an additive, and the first quantum dots being in direct contact with a layer adjacent to the light-emitting layer on the anode side, or adjacent to the layer via an organic ligand or a semiconductor.

[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] 1 is a schematic side cross-sectional view of a display device according to embodiment 1. FIG. 1 is a schematic view of a display device according to embodiment 1. FIG. 2 is a schematic enlarged view of a cross section of an emitting layer and its vicinity according to embodiment 1. FIG. 3 is a schematic view showing an addition filling spaces between quantum dots according to embodiment 1. FIG. 2 is a schematic side cross-sectional view of a display device according to a comparative embodiment. FIG. 3 is a schematic enlarged view of a cross section of an emitting layer and its vicinity according to a comparative embodiment. FIG. 4 is a flowchart showing a method for manufacturing a display device according to embodiment 1. FIG. 5 is a flowchart showing a method for forming an emitting layer according to embodiment 1. FIG. 6 is a schematic view showing a quantum dot dispersion according to embodiment 1. FIG. 7 is a schematic view showing a first dispersion according to embodiment 1. FIG. 8 is a process cross-sectional view showing a part of a method for forming an emitting layer according to embodiment 1. FIG. 9 is a process side view showing a mixing step in a method for forming an emitting layer according to embodiment 2. FIG. 10 is a schematic view showing a first dispersion according to embodiment 2. FIG. 11 is a schematic side cross-sectional view of a display device according to embodiment 3. FIG. 12 is a schematic enlarged view of a cross section of an emitting layer and its vicinity according to embodiment 3. FIG. 13 is a flowchart showing a method for forming an emitting layer according to embodiment 3. FIG. 14 is a schematic view showing a second dispersion according to embodiment 3. FIG. 15 is a process cross-sectional view showing a part of a method for forming an emitting layer according to embodiment 3. FIG. 16 is a schematic side cross-sectional view of a display device according to embodiment 4. FIG. 17 is a schematic enlarged view of a cross section of an emitting layer and its vicinity according to embodiment 4. 10 is a flowchart showing a method for manufacturing a display device according to Embodiment 4. FIG. 11 is a flowchart showing a method for forming a light-emitting layer according to Embodiment 4. FIG. 12 is a cross-sectional view showing a process of a part of the method for forming a light-emitting layer according to Embodiment 4.

[0009] [Embodiment 1] <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 and may be hatched differently 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 adjacent to the anode 21 side of the light-emitting layer 23 and contains a hole transport material. The hole transport layer 22 transports holes from the anode 21 to the light-emitting layer 23. In the present 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. For example, in the present disclosure, "two components adjacent" may refer to the shortest distance between the two components being 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 may contain an organic material as a hole transport material. For example, the hole transport layer 22 may contain at least one of polyvinylcarbazole (PVK) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD).

[0018] However, this embodiment is not limited to this, and the material of the hole transport layer 22 can be an organic or inorganic material that has been conventionally used in light-emitting devices containing quantum dots. For example, the organic material of the hole transport layer 22 can be a conductive compound 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). The inorganic material of the hole transport layer 22 can be molybdenum oxide, NiO, Cr ２ O ３ , MgO, MgZnO, LaNiO ３ , MoO ３ , or W.O. ３ In 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 and an adduct 40. The light-emitting layer 23 according to this embodiment also includes an organic ligand 41.

[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. ２The 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: additive> The additive 40 has insulating properties. For example, the additive 40 may contain 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 additive 40 may contain at least one of silicon oxide, aluminum oxide, and silicon nitride. In this case, the 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 addition 40 is located around a portion of the quantum dot 30. In particular, the addition 40 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.

[0030] 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 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 diagrams showing sets P1 and P2, which are examples of sets of quantum dots 30A and 30B, respectively.

[0031] 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.

[0032] 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%.

[0033] Referring back to FIGS. 1 and 3 , the additive 40 is adjacent to the electron transport layer 24 on the cathode 25 side of the light-emitting layer 23. In particular, the additive 40 may constitute a portion of the outer edge of the light-emitting layer 23 adjacent to the lower surface 24U of the electron transport layer 24, or a portion of the outer edge of the light-emitting layer 23 may be in direct contact with at least a portion of the lower surface 24U of the electron transport layer 24. Therefore, the light-emitting layer 23 includes the additive 40 between the electron transport layer 24 and the second quantum dots 32. As shown in FIG. 3 , the thickness T1 of the additive 40 located between the electron transport layer 24 and the second quantum dots 32 may be 1 nm or more and 5 nm or less. Note that, in the present disclosure, "thickness" may refer to the length in any direction of a member. For example, when the additive 40 encapsulates the second quantum dots 32 as described below, the thickness T1 of the additive 40 may refer not only to the length in the stacking direction of the light-emitting element 2 but also to the length in the direction from the center of the second quantum dots 32 toward the periphery. In the present disclosure, the term "thickness" may refer to, for example, the average thickness of a member within an observed area when observing a cross section of the light-emitting element 2 in the stacking direction. In this case, the area of ​​the cross section observed is 5 nm ２ 500nm or more ２ It may be the following:

[0034] The second light-emitting layer 23B may include an additive 40. In particular, the additive 40 may be formed to a thickness of 1000 nm in a plane perpendicular to the thickness direction of the second light-emitting layer 23B at any position in the thickness direction of the second light-emitting layer 23B. ２In the second light-emitting layer 23B, the second quantum dots 32 may be encapsulated in the continuous film of the additive 40. In other words, the second quantum dots 32 may be encapsulated in the continuous film of the additive 40.

[0035] 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 additive 40, the second quantum dots 32 contained in the second light-emitting layer 23B can be said to be encapsulated in the additive 40. In this way, the second light-emitting layer 23B containing the second quantum dots 32 encapsulated in the additive 40 has improved light-emitting properties and a longer lifespan.

[0036] The addition 40 may be located, for example, around the entire periphery of the second quantum dot 32. For example, as shown in Fig. 3, in any cross section passing through any second quantum dot 32, the addition 40 may be located around the entire periphery of the second quantum dot 32. Here, "the addition 40 is located around the entire periphery of the second quantum dot 32" may mean that the addition 40 is located over 90% or more of the periphery of the second quantum dot 32. Furthermore, the addition 40 may be in contact with the surface of the second quantum dot 32, as shown in Fig. 3.

[0037] The band gap of the additive 40 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 gap of the additive 40 may be wider than the band gap of the constituent material of the shell.

[0038] <Light-Emitting Layer: Organic Ligand> The organic ligand 41 may be, for example, an organic ligand having a carbon chain and a coordinating functional group located at one end of the carbon chain, which is generally used as a ligand for quantum dots. The organic ligand 41 may be located near the first quantum dots 31, and may particularly be coordinated to the first quantum dots 31. In other words, the coordinating functional group of the organic ligand 41 may form a coordinate bond with the outermost peripheral surface of the first quantum dots 31. In the present disclosure, "the organic ligand 41 is located near the first quantum dots 31" may also mean that, when a cross-section of the light-emitting layer 23 is observed, the organic ligand 41 is located within a range of 3 nm or less around the first quantum dots 31.

[0039] When a cross-sectional observation of the light-emitting layer 23 according to this embodiment confirms that the distance between the first quantum dot 31 and the organic ligand 41 is 1 nm or less, the organic ligand 41 may be considered to be coordinated to the first quantum dot 31. Alternatively, when it is confirmed that the first quantum dot 31 and the organic ligand 41 are in contact with each other, the organic ligand 41 may be considered to be coordinated to the first quantum dot 31.

[0040] In this embodiment, the light-emitting layer 23 is adjacent to the upper surface 22T of the hole transport layer 22 on the anode 21 side. In particular, in this embodiment, the first quantum dots 31 are in direct contact with the hole transport layer 22 or are adjacent to the upper surface 22T of the hole transport layer 22 via the organic ligand 41. In other words, the first quantum dots 31 are in direct contact with the layer to which the light-emitting layer 23 is adjacent on the anode 21 side or are adjacent to the layer via the organic ligand 41. Note that in the present disclosure, the phrase "the first member and the second member are adjacent to each other via a third member" may refer to the third member being located between the first member and the second member and adjacent to both the first member and the second member. In other words, in the above case, the third member may be in direct contact with the first member or may be close to the first member. In the above case, the third member may be in direct contact with the second member on the side opposite to the first member, or may be adjacent to the second member on the side opposite to the first member.

[0041] For this reason, in this embodiment, the hole transport layer 22 may have a portion on the upper surface 22T that is not in contact with the additive 40, and in particular, the hole transport layer 22 may not have a portion adjacent to the additive 40. For example, as shown in FIG. 3 , the additive 40 may be formed from the outer edge of the light-emitting layer 23 on the electron transport layer 24 side to partway along the hole transport layer 22 side of the light-emitting layer 23. The additive 40 may be located in a portion of the first light-emitting layer 23A. In other words, the additive 40 may be in contact with a portion of the outer peripheral surface of the first quantum dots 31 included in the first light-emitting layer 23A on the cathode 25 side.

[0042] <Additional Notes> 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 achieved using the earlier method, confirmation using the later method may be omitted.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] <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.

[0047] 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.

[0048] 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.

[0049] The light-emitting layer 23C includes a plurality of quantum dots 30 and an adduct 40 encapsulating each of the quantum dots 30. In particular, in the comparative example, the adduct 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 quantum dots 30 are not adjacent to either the hole transport layer 22 or the electron transport layer 24 via a ligand such as an organic ligand.

[0050] 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.

[0051] 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 additive 40 is an insulator, while the quantum dots 30 contain a material, such as a semiconductor, that has at least a higher electrical conductivity than the 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 .

[0052] 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.

[0053] In particular, in the virtual circuit on the path R of the light-emitting layer 23C according to the comparative embodiment, the 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 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 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.

[0054] 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.

[0055] 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.

[0056] Furthermore, in light-emitting devices that generally contain quantum dots as a light-emitting material in the light-emitting layer, the recombination of holes and electrons injected into the light-emitting layer may occur more frequently on the anode side due to the high mobility of electrons relative to holes. In this case, the position of excitons generated by this recombination is closer to the anode.

[0057] Here, in a light-emitting layer containing quantum dots, energy transfer may occur, in which the energy of excitons generated by the recombination of holes and electrons in the quantum dots is transferred to another component close to the quantum dots. If the energy of the excitons is transferred to a component other than the quantum dots, such as the hole transport material of the hole transport layer 22, the component may be deactivated and not contribute to light emission. In general, the probability of energy transfer, such as Förster transition, in which the energy of an exciton is transferred to another material, tends to increase as the distance between the two components at which the energy transfer occurs becomes shorter.

[0058] The light-emitting element 2C facilitates a reduction in the distance between the quantum dots 30 in which excitons are generated in the light-emitting layer 23C and the hole transport layer 22. Therefore, the light-emitting element 2C facilitates an increase in the process of energy transfer of the energy possessed by the excitons to the hole transport material, etc., of the hole transport layer 22, further reducing the luminous efficiency.

[0059] <Effects of the Light-Emitting Element According to the Embodiment> Meanwhile, in the light-emitting layer 23 of the light-emitting element 2 according to the embodiment, the first quantum dots 31 located closer to the anode 21 than the second quantum dots 32 are in direct contact with the hole transport layer 22 or are adjacent to the hole transport layer 22 via an organic ligand 41. For example, when the first quantum dots 31 are in direct contact with the hole transport layer 22, the first quantum dots 31 and the hole transport layer 22 can be considered to be in an electrically short-circuited state if contact resistance is ignored, and the contact resistance is also very small. Furthermore, when the first quantum dots 31 are adjacent to the hole transport layer 22 via the organic ligand 41, hole transport from the hole transport layer 22 to the first quantum dots 31 is mainly achieved by hopping conduction via the organic ligand 41.

[0060] Therefore, in the light-emitting layer 23, it is possible to reduce the effective electrical resistance between the first quantum dots 31 and the hole transport layer 22, such as the electrical resistance of the above-described virtual diode D formed between the first quantum dots 31 and the hole transport layer 22. Therefore, when the light-emitting element 2 is driven, holes injected into the light-emitting layer 23 are efficiently injected into the first quantum dots 31 and are efficiently transported via the first quantum dots 31 to the center side in the film thickness direction of the light-emitting layer 23.

[0061] 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.

[0062] Furthermore, since the light-emitting element 2 transports holes toward the center in the film thickness direction of the light-emitting layer 23, recombination of holes and electrons in the light-emitting layer 23 occurs toward the center in the film thickness direction of the light-emitting layer 23. Therefore, by increasing the distance between the excitons generated by this recombination and the hole transport layer 22, the light-emitting element 2 reduces the transfer of energy of the excitons to the hole transport material of the hole transport layer 22, etc.

[0063] In addition, the light-emitting layer 23 of the light-emitting element 2 according to this embodiment includes an addition 40 located around a portion of the quantum dots 30, including the second quantum dots 32. Therefore, the light-emitting layer 23 can protect a portion of the quantum dots 30 from foreign substances such as moisture by the addition 40. Therefore, the light-emitting element 2 can reduce deterioration of a portion of the quantum dots 30 in the light-emitting layer 23 by the addition 40.

[0064] In particular, for the reasons described above, in the light-emitting layer 23, recombination of holes and electrons is more likely to occur in the quantum dots 30 including the second quantum dots 32 located closer to the cathode 25 than the first quantum dots 31. Therefore, the light-emitting element 2 can more efficiently protect the quantum dots 30 including the second quantum dots 32 in which exciton energy transfer is less likely to occur than in the first quantum dots 31, thereby improving the light-emitting efficiency.

[0065] 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 some of the quantum dots 30 due to the addition 40. The display device 1 including the light-emitting element 2 achieves reduced power consumption and a longer lifespan.

[0066] As described above, when the first quantum dots 31 are in direct contact with the hole transport layer 22, the electrical resistance between the first quantum dots 31 and the hole transport layer 22 is approximately equal to a very small contact resistance. Therefore, the light-emitting device 2 having the light-emitting layer 23 including the first quantum dots 31 in direct contact with the hole transport layer 22 reduces the overall electrical resistance and thereby improves the luminous efficiency.

[0067] Furthermore, the light-emitting layer 23, in which the first quantum dots 31 are adjacent to the hole transport layer 22 via the organic ligands 41, can be formed using a dispersion in which the first quantum dots 31 coordinated with the organic ligands 41 are dispersed, as described below. In the dispersion and in the portion of the light-emitting layer 23 formed from the dispersion, the steric hindrance of the organic ligands 41 reduces aggregation of the first quantum dots 31. Therefore, a light-emitting device 2 having a light-emitting layer 23 including first quantum dots 31 adjacent to the hole transport layer 22 via the organic ligands 41 reduces the overall electrical resistance while reducing aggregation of the first quantum dots 40, thereby reducing the probability of deactivation of the first quantum dots. Therefore, the light-emitting device 2 having the above configuration further improves luminous efficiency.

[0068] In particular, the light-emitting layer 23 includes the additive 40 between the electron transport layer 24 and the second quantum dots 32. Therefore, in the light-emitting device 2, the additive 40 more efficiently protects the second quantum dots 32 from foreign substances such as moisture that penetrate from the electron transport layer 24 side. In particular, since the additive 40 fills the space between at least two second quantum dots 32, the additive 40 more efficiently protects the second quantum dots 32 in the light-emitting device 2.

[0069] Furthermore, the light-emitting layer 23 includes the additive 40 between the electron transport layer 24 and the second quantum dots 32, thereby increasing the distance of the second quantum dots 32 from the interface between the light-emitting layer 23 and the electron transport layer 24, where excess electrons tend to accumulate. Therefore, the light-emitting element 2 reduces deterioration of the second quantum dots 32 due to Auger electrons and the like generated from excess electrons accumulated at the interface between the light-emitting layer 23 and the electron transport layer 24.

[0070] Furthermore, the light-emitting layer 23 includes the additive 40 between the electron transport layer 24 and the second quantum dot 32, thereby including the virtual diode D described above between the light-emitting layer 23 and the electron transport layer 24. Therefore, the light-emitting element 2 can reduce the electron excess in the light-emitting layer 23 by reducing the efficiency of electron transport from the electron transport layer 24 to the light-emitting layer 23. Therefore, the light-emitting element 2 improves the carrier balance in the light-emitting layer 23 and reduces the luminous efficiency of the light-emitting layer 23 and the deterioration of each layer between the anode 21 and the cathode 25.

[0071] In this embodiment, the thickness of the additive 40 between the electron transport layer 24 and the second quantum dots 32 may be 1 nm or more, or the additive 40 may have insulating properties as described above. The insulating additive 40 further reduces the penetration of foreign matter into the second quantum dots 32. In particular, the insulating additive 40 reduces the injection of excess electrons, such as Auger electrons, into the second quantum dots 32, which may deteriorate the quantum dots 30, or the propagation of energy from these electrons. Therefore, with the above configuration, the light-emitting device 2 more efficiently protects the second quantum dots 32, further reduces deterioration of the second quantum dots 32, and further improves the carrier balance of the light-emitting layer 23.

[0072] Furthermore, since the thickness of the additive 40 between the electron transport layer 24 and the second quantum dots 32 is 5 nm or less, electrons can be tunneled more efficiently from the electron transport layer 24 to the second quantum dots 32. Therefore, with the above configuration, the light-emitting element 2 can prevent an excessive decrease in the efficiency of electron transport from the electron transport layer 24 to the second quantum dots 32, thereby improving the luminous efficiency of the light-emitting layer 23.

[0073] The light-emitting element 2 includes a hole transport layer 22 between the anode 21 and the light-emitting layer 23, adjacent to the light-emitting layer 23 on the anode 21 side, thereby further improving the efficiency of hole transport from the anode 21 to the light-emitting layer 23. In particular, the hole transport layer 22 includes an organic material, particularly at least one of PVK and TPD, as a hole transport material, thereby further improving the efficiency of hole transport from the anode 21 to the light-emitting layer 23.

[0074] <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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Preparation of Dispersion> 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.

[0079] In the method for forming the light-emitting layer 23 according to this embodiment, a quantum dot dispersion liquid and a first dispersion liquid are first prepared (step S1). The quantum dot dispersion liquid and the first dispersion liquid will be described in more detail with reference to Figs. 9 and 10. Figs. 9 and 10 are schematic diagrams showing the quantum dot dispersion liquid LQ and the first dispersion liquid L1, respectively, poured into a container C.

[0080] 9 , the quantum dot dispersion liquid LQ includes quantum dots 30 dispersed in a solvent 50 and organic ligands 41 that coordinate with the quantum dots 30. The quantum dot dispersion liquid LQ may be prepared by synthesizing a plurality of quantum dots 30 in the solvent 50 by any method, including conventionally known methods, and then adding the organic ligands 41 to the solvent 50. Alternatively, the quantum dot dispersion liquid LQ may be prepared by extracting quantum dots 30 that have been separately synthesized and the organic ligands 41 that coordinate with the quantum dots 30, and adding them to the solvent 50. The solvent 50 may be toluene.

[0081] 10 , the first dispersion liquid L1 includes quantum dots 30 dispersed in a solvent 50, a precursor 51 as a first precursor, and a precursor ligand 52 as a first precursor that coordinates with the quantum dots 30. The precursor 51 is a precursor of the adduct 40 and is converted into the adduct 40 by a conversion step described below. The precursor ligand 52 has at least a portion of the precursor 51 and a coordinating functional group that is located at an end and forms a coordinate bond with the outer peripheral surface of the quantum dots 30. Therefore, the precursor ligand 52 coordinates with the quantum dots 30, and a portion of the side opposite the coordinating functional group is converted into the adduct 40 by a conversion step described below.

[0082] For example, when the adduct 40 is silicon oxide, the precursor 51 may include tetramethyl orthosilicate (TMOS) shown in the following formula (1): Also, when the adduct 40 is silicon oxide, the precursor ligand 52 may include 3-(mercaptopropyl)trimethoxysilane (MPS) shown in the following formula (2):

[0083] In this case, the first dispersion liquid L1 contains ZnCl ２ The halogen source 53 may also serve as a catalyst for the conversion of the precursor 51 and precursor ligand 52 to the adduct 40, as described below.

[0084] The first dispersion L1 may be prepared by synthesizing a plurality of quantum dots 30 in a solvent 50 by any method, including a conventionally known method, and then adding a precursor 51, a precursor ligand 52, and a halogen source 53 to the solvent 50. Alternatively, the first dispersion L1 may be prepared by extracting quantum dots 30 synthesized separately and precursor ligands 52 that coordinate to the quantum dots 30, and adding them to the solvent 50 together with the precursor 51 and the halogen source 53.

[0085] The quantum dots 30 coordinated with the precursor ligands 52 may be synthesized, for example, by stirring a dispersion liquid in which the quantum dots 30 coordinated with the organic ligands 41 are dispersed, and a dispersion liquid in which an excess amount of the precursor ligands 52 is dispersed. In other words, the ligands coordinated to the quantum dots 30 may be replaced by the precursor ligands 52 from the organic ligands 41 by the stirring.

[0086] It should be noted 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 quantum dot dispersion liquid LQ and the first dispersion liquid L1 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.

[0087] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Film-Deposition 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 quantum dot dispersion liquid LQ and the first dispersion liquid L1, a film-deposition step of the light-emitting layer 23 is carried out. The film-deposition step of the light-emitting layer 23 will be described in more detail with reference to Fig. 11 in addition to Fig. 8. Fig. 11 is a process cross-sectional view showing the film-deposition step of the light-emitting layer 23, which is part of the method of forming the light-emitting layer 23.

[0088] In the film formation process of the light-emitting layer 23, first, the quantum dot dispersion liquid LQ is applied to the substrate 3, which is a laminate including the layers on the substrate 3 (step S2). For example, as shown in step S2 in Fig. 11, the quantum dot dispersion liquid LQ is applied to the hole transport layer 22 by any method including a conventionally known application method such as spin coating.

[0089] Here, the quantum dots 30 in the applied quantum dot dispersion liquid LQ may accumulate due to their own weight on the side of the hole transport layer 22. In this case, at the time point when step S2 is completed, the quantum dots 30 in the quantum dot dispersion liquid LQ or the organic ligands 41 coordinated to the quantum dots 30 may come into contact with the hole transport layer 22.

[0090] Next, each portion of the substrate 3 containing the applied quantum dot dispersion liquid LQ is heated, for example, at 130° C. for 5 minutes to dry the quantum dot dispersion liquid LQ (step S3). Here, in step S3, the solvent 50 of the applied quantum dot dispersion liquid LQ volatilizes, so that the quantum dots 30 in the quantum dot dispersion liquid LQ or the organic ligands 41 coordinated to the quantum dots 30 are adjacent to the hole transport layer 22. Alternatively, as described above, at the start of step S3, the quantum dots 30 in the quantum dot dispersion liquid LQ or the organic ligands 41 coordinated to the quantum dots 30 may be in contact with the hole transport layer 22.

[0091] 11 , at least some of the quantum dots 30 contained in the quantum dot dispersion liquid LQ become first quantum dots 31 that are in direct contact with the hole transport layer 22 or are adjacent to the hole transport layer 22 via the organic ligands 41. Therefore, by performing step S3, a first light-emitting layer 23A is formed on the hole transport layer 22 as a first quantum dot layer that includes the first quantum dots 31.

[0092] Next, the first dispersion L1 is applied to the substrate 3 using the laminate including the layers as the substrate (step S4). For example, as shown in step S4 of Fig. 11 , the first dispersion L1 is applied to the first light-emitting layer 23A by any method including a conventionally known application method such as spin coating.

[0093] In step S4, the solvent 50 of the first dispersion liquid L1 may penetrate between the first quantum dots 31 of the first light-emitting layer 23A, as long as the first quantum dots 31 contained in the first light-emitting layer 23A are kept in contact with the hole transport layer 22 or adjacent to each other via the organic ligands 41. However, the precursor 51 of the first dispersion liquid L1 may be located above the first quantum dots 31.

[0094] Next, the precursor of the adduct 40 in the first dispersion L1, which contains the precursor 51 and the precursor ligand 52, is converted into the adduct 40 (step S5). For example, the portions of the substrate 3 containing the applied first dispersion L1 are heated at 100° C. for 30 minutes, for example, to cause the precursor 51 and the precursor ligand 52 in the first dispersion L1 to react with each other.

[0095] The details of the reaction will be described below when the precursor 51 contains TMOS and the precursor ligand 52 contains MPS. For example, the heating converts the methoxy groups of the TMOS precursor 51 and the MPS precursor ligand 52 into water (H ２ O), which is replaced by a hydroxyl group (OH-), and methanol is produced as a by-product. Next, two of the above-mentioned 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 S5, precursor 51 and precursor ligand 52 are converted into adduct 40 containing silicon oxide.

[0096] 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 in 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 adduct 40.

[0097] Here, in step S5, the precursors 51 in the applied first dispersion L1 are located around the quantum dots 30, and the precursor ligands 52 are coordinated to the quantum dots 30. Therefore, the precursors 51 and precursor ligands 52 converted in step S5 are converted into adducts 40 so as to fill the spaces between the quantum dots 30. Therefore, as shown in step S5 of Fig. 11 , a second light-emitting layer 23B including a plurality of second quantum dots 32 encapsulated in the adducts 40 is formed on the first light-emitting layer 23A. This completes the formation of the light-emitting layer 23.

[0098] 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.

[0099] 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.

[0100] According to the above method, as described above, it is possible to manufacture a display device 1 including 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 some of the quantum dots 30 by the additive 40. In particular, in this embodiment, the second light-emitting layer 23B is formed by a method that includes converting a precursor of the additive 40. According to the above method, it is possible to more simply form the second light-emitting layer 23B that includes the additive 40 that fills the space between two second quantum dots 32.

[0101] In this embodiment, the light-emitting element 2 included in the display device 1 has the anode 21 located closer to the substrate 3 than the light-emitting layer 23. According to the above configuration, when the light-emitting element 2 is manufactured by the above method, the quantum dots 30 or the organic ligands 41 in the quantum dot dispersion liquid LQ can be easily brought into contact with the hole transport layer 22 in steps S2 and S3. Therefore, the light-emitting element 2 included in the display device 1 has the anode 21 located closer to the substrate 3 than the light-emitting layer 23, which further simplifies the formation of the first light-emitting layer 23A in the manufacturing process of the display device 1.

[0102] Furthermore, in the manufacturing method of the display device 1 according to this embodiment, in the process of forming the electron transport layer 24 and the cathode 25, an additive 40 is formed on the upper surface side of the light-emitting layer 23. Therefore, in the process of forming the electron transport layer 24 and the cathode 25, the quantum dots 30 contained in the light-emitting layer 23 are protected by the additive 40. Therefore, in the light-emitting element 2 included in the display device 1, the anode 21 is located closer to the substrate 3 than the light-emitting layer 23, and therefore the display device 1 can reduce deterioration of the quantum dots 30 contained in the light-emitting layer 23 in the process of forming the electron transport layer 24 and the cathode 25.

[0103] In addition, in the above-described step of forming the first light-emitting layer 23A, the quantum dot dispersion liquid LQ applied onto the hole transport layer 22 does not contain a precursor of the additive 40. Therefore, in the step of forming the first light-emitting layer 23A, it is sufficient to heat the quantum dot dispersion liquid LQ only as much as necessary to volatilize the solvent 50 of the quantum dot dispersion liquid LQ applied onto the hole transport layer 22. In other words, the step of forming the first light-emitting layer 23A does not require heating to an extent necessary to convert the precursor of the additive 40. Therefore, in the light-emitting element 2, even if the hole transport layer 22 contains an organic material that has higher hole transport efficiency but lower heat resistance than inorganic materials, deterioration of the hole transport layer 22 in the step of forming the first light-emitting layer 23A can be reduced.

[0104] [Embodiment 2] <Manufacturing method using a mixing process> The display device 1 according to this embodiment has the same configuration as the display device 1 according to the previous embodiment, but differs only in some of the steps in the manufacturing method of the light-emitting element 2. The manufacturing method of the light-emitting element 2 according to this embodiment differs from the manufacturing method of the light-emitting element 2 according to the previous embodiment only in the method of forming the light-emitting layer 23.

[0105] The light-emitting layer 23 according to this embodiment is formed by the same formation method as the light-emitting layer 23 according to the previous embodiment, except for the content of step S1 and the configuration of the first dispersion liquid used in steps S4 and S5. The method for forming the light-emitting layer 23 according to this embodiment will be described in detail with reference to Figs. 12 and 13. Fig. 12 is a side view showing a mixing step in the method for forming the light-emitting layer 23 according to this embodiment. Fig. 13 is a schematic view showing the first dispersion liquid according to this embodiment.

[0106] In step S1 according to this embodiment, the quantum dot dispersion liquid LQ may be prepared by the same method as the method according to the previous embodiment. On the other hand, in step S1 according to this embodiment, the first dispersion liquid is prepared using a mixing step. This mixing step will be described with reference to FIG.

[0107] In the mixing step according to this embodiment, dispersion liquid LA and dispersion liquid LB shown in step S1-1 of FIG. 12 are prepared.

[0108] Dispersion LA is a dispersion in which a precursor 51 as a first precursor and a precursor ligand 52 are dispersed in a solvent 54. The solvent 54 is a polar solvent such as N,N-dimethylformamide (DMF). Dispersion LA may further contain a halogen source 53 in the solvent 54. Dispersion LA may be prepared by adding a precursor 51, a precursor ligand 52, and a halogen source 53, which have been separately synthesized, to the solvent 54.

[0109] Dispersion liquid LB is, for example, a dispersion liquid in which a plurality of quantum dots 30 coordinated with organic ligands 41 are dispersed in a solvent 55. In particular, dispersion liquid LB may be the same dispersion liquid as quantum dot dispersion liquid LQ, except that it contains solvent 55 instead of solvent 50, and may be prepared by the same method as quantum dot dispersion liquid LQ. Solvent 55 is a non-polar solvent such as octane. Because solvents 54 and 55 have different polarities, when dispersion liquid LA and dispersion liquid LB are allowed to stand in a container, the liquid in the container separates into a layer of dispersion liquid LA and a layer of dispersion liquid LB, as shown in FIG. 12 .

[0110] 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 41 coordinated to the quantum dots 30 are replaced by precursor ligands 52. This makes it easier for the quantum dots 30 to disperse in solvent 54 than in solvent 55, and the quantum dots 30 migrate from dispersion liquid LB to dispersion liquid LA, as shown in step S1-2 of FIG.

[0111] Furthermore, during the stirring process, the precursor 51 and the precursor ligand 52 react in the dispersion liquid LA according to the reaction process described above, and are converted into an adduct around the quantum dots 30. Therefore, as shown in step S1-2 of Fig. 12, a quantum dot structure 60 including the quantum dots 30 is synthesized by mixing the dispersion liquid LA and the dispersion liquid LB. For example, the quantum dot structure 60 has an adduct 61 that encapsulates the quantum dots 30. Note that in step S1-2, the quantum dot structure 60 may migrate to the interface between the dispersion liquid LA and the dispersion liquid LB.

[0112] Here, the adduct 61 formed in the mixing step may have the same composition as the above-mentioned adduct 40. In this specification, "two components have the same composition" does not mean that both components have completely the same composition. For example, when the adduct 40 and the adduct 61 both contain two types of atoms, if 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.

[0113] 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.

[0114] Next, the quantum dot structures 60 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 quantum dot structures 60. Next, the precipitate containing the quantum dot structures 60 is dispersed in a solvent 50 in a separate container. Here, a precursor 51 and a halogen source 53 are added to the dispersion liquid to prepare a first dispersion liquid L1A shown in FIG. 13 .

[0115] 13 , the first dispersion L1A prepared in this embodiment contains quantum dot structures 60, precursors 51, and a halogen source 53 dispersed in a solvent 50. In other words, the first dispersion L1A differs from the first dispersion L1 only in that it contains an adduct 61 encapsulating the quantum dots 30 instead of the precursor ligands 52 that coordinate to the quantum dots 30.

[0116] In the process of forming the light-emitting layer 23 according to this embodiment, steps S2 to S5 are performed in this order after step S1. Here, steps S2 to S5 of the light-emitting layer 23 according to this embodiment are each performed in the same manner as steps S2 to S5 of the light-emitting layer 23 according to the previous embodiment, except for the content of steps S4 and S5.

[0117] In particular, in step S4 according to this embodiment, the first dispersion L1A is applied onto the first light-emitting layer 23A. Then, in step S5 according to this embodiment, the applied first dispersion L1A is heated to convert the precursor 51 in the first dispersion L1A into the adduct 40.

[0118] Here, in the applied first dispersion liquid L1A, the precursor 51 is located around the quantum dot structure 60. Therefore, the adduct 40 returned from the precursor 51 in step S5 is formed around the adduct 61 of the quantum dot structure 60. As described above, the adduct 61 has the same composition as the adduct 40 described above.

[0119] As a result, for the same reasons as those explained in step S5 of the previous embodiment, in step S5 of this embodiment, the second light-emitting layer 23B is formed on the first light-emitting layer 23A, and the process of forming the light-emitting layer 23 is completed.

[0120] The method according to this embodiment also makes it 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 the degradation of some of the quantum dots 30 by the addition 40.

[0121] 14 is a schematic side cross-sectional view of a display device 4 according to this embodiment. Compared to the display device 1 according to the previous embodiment, the display device 4 according to this embodiment includes a light-emitting element 5 instead of the light-emitting element 2. Compared to the light-emitting element 2, the light-emitting element 5 includes a light-emitting layer 26 instead of the light-emitting layer 23. Except for the above points, the display device 4 has the same configuration as the display device 1.

[0122] The light-emitting layer 26 will be described in more detail with reference to Fig. 15 in addition to Fig. 14. Fig. 15 is an enlarged schematic diagram of the cross section shown in Fig. 14, illustrating the light-emitting layer 26 and the vicinity of the light-emitting layer 26 in the hole transport layer 22 and the electron transport layer 24, and in particular, illustrating an enlarged region E2 shown in Fig. 14.

[0123] The light-emitting layer 26 includes a first light-emitting layer 26A and a second light-emitting layer 26B stacked in this order from the hole transport layer 22 side.

[0124] The first light-emitting layer 26A includes a plurality of first quantum dots 31 and a semiconductor 42. In particular, in this embodiment, the first light-emitting layer 26A includes the semiconductor 42 in a layer adjacent to the light-emitting layer 26 on the anode 21 side, in other words, between the hole transport layer 22 and the first quantum dots 31. Therefore, the first quantum dots 31 are adjacent to a layer adjacent to the light-emitting layer 26 on the anode 21 side, in other words, between the hole transport layer 22 and the semiconductor 42 interposed therebetween. However, some of the first quantum dots 31 may be in direct contact with the hole transport layer 22.

[0125] The semiconductor 42 may encapsulate a plurality of first quantum dots 31, or may fill the space between at least two first quantum dots 31. The semiconductor 42 has a higher conductivity than at least the additive 40. The semiconductor 42 may contain 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 contact resistance between the semiconductor 42 and the first quantum dots 31, the semiconductor 42 may contain the same material as the material contained in the outermost periphery of the shell or the like of the first quantum dots 31.

[0126] The second light-emitting layer 26B includes second quantum dots 32 located closer to the cathode 25 than the first quantum dots 31, and an additive 40 filling the spaces between the second quantum dots 32. In other words, the second light-emitting layer 26B may have the same configuration as the second light-emitting layer 23B according to the previous embodiment.

[0127] In the light-emitting layer 26 of the light-emitting element 5 according to this embodiment, the first quantum dots 31 are adjacent to each other via the semiconductor 42. Therefore, the effective electrical resistance of the virtual diode D formed between the hole transport layer 22 and the first quantum dots 31 in the light-emitting element 5 according to this embodiment is lower than when an insulator such as the addition 40 is located between the hole transport layer 22 and the first quantum dots 31.

[0128] Therefore, in the light-emitting element 5 according to this embodiment, holes are more efficiently transported from the hole transport layer 22 to the first quantum dots 31. Therefore, when the light-emitting element 5 is driven, holes injected into the light-emitting layer 26 are efficiently injected into the first quantum dots 31 and are also efficiently transported via the first quantum dots 31 to the center of the light-emitting layer 26 in the film thickness direction.

[0129] Furthermore, the light-emitting layer 26 according to this embodiment includes a second light-emitting layer 26B having the same configuration as the second light-emitting layer 23B according to the previous embodiment. Therefore, the light-emitting element 2 can more efficiently protect the quantum dots 30, including the second quantum dots 32 in which exciton energy transfer is less likely to occur than in the first quantum dots 31, thereby improving the light-emitting efficiency.

[0130] Therefore, for the same reasons as those described in the previous embodiment, the light-emitting element 5 achieves improved luminous efficiency and improved reliability of each layer between the anode 21 and the cathode 25 while reducing deterioration of some of the quantum dots 30 due to the addition 40. A display device 4 including the light-emitting element 5 achieves reduced power consumption and a longer lifespan. In particular, in the light-emitting layer 26, the first quantum dots 31 are adjacent to the hole transport layer 22 via the semiconductor 42. This allows the light-emitting element 5 to protect the first quantum dots 31 with the semiconductor 42 from foreign substances such as moisture that penetrate from the hole transport layer 22 side, thereby further improving the reliability of the light-emitting layer 26.

[0131] Furthermore, the light-emitting layer 26 includes a semiconductor 42 that fills the spaces between at least two first quantum dots 31. Therefore, the light-emitting element 2 protects the first quantum dots 31 with the semiconductor 42 while improving the efficiency of hole injection into the first quantum dots 31. From the viewpoint of achieving both the effect of protecting the first quantum dots 31 with the semiconductor 42 and the efficiency of hole injection into the first quantum dots 31, the thickness T2 of the semiconductor 42 located between the hole transport layer 22 and the first quantum dots may be 6 nm or more and 12 nm or less.

[0132] <Method of Forming Light-Emitting Layer Including Semiconductor> The method of manufacturing the display device 4 according to this embodiment is realized by the same method as the method of manufacturing the display device 1 described above, except that the method of forming the light-emitting layer 23 is replaced with the method of forming the light-emitting layer 26. The method of forming the light-emitting layer 26 according to this embodiment will be described in detail with reference to FIGS. 16 to 18. FIG. 16 is a flowchart showing the method of forming the light-emitting layer 26 according to this embodiment. FIG. 17 is a schematic diagram showing a second dispersion liquid, described below, used in the method of forming the light-emitting layer 26 according to this embodiment. FIG. 18 is a cross-sectional view showing a process of a part of the method of forming the light-emitting layer 26 according to this embodiment.

[0133] In the method for forming the light-emitting layer 26 according to this embodiment, first, a first dispersion and a second dispersion are prepared (step S6). The first dispersion may be prepared by the same method as the method for preparing the first dispersion L1 or L1A described above.

[0134] The second dispersion liquid according to this embodiment will be described in detail with reference to Fig. 17. The second dispersion liquid L2 is a dispersion liquid in which a plurality of quantum dots 30 and a precursor 57, which is a second precursor, are dispersed in a solvent 56. The second dispersion liquid L2 may contain a ligand 58 that coordinates with the quantum dots 30. The second dispersion liquid L2 may also contain a catalyst that promotes the conversion of the precursor 57 into the semiconductor 42. The solvent 56 is a polar solvent and may contain, for example, DMF.

[0135] Precursor 57 is a precursor of semiconductor 42 and is converted into semiconductor 42 by a method described below. For example, when semiconductor 42 contains a metal atom, precursor 57 may contain a metal acetate, a metal nitrate, or a metal halide as a metal source. Furthermore, when semiconductor 42 contains a sulfur atom, precursor 57 may contain at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, and thioacetamide as a sulfur source. Alternatively, precursor 57 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.

[0136] The ligand 58 may contain halide ions and may function as a catalyst to promote the conversion of the precursor 57 into the semiconductor 42. The ligand 58 may have polarity so as to facilitate dispersion of the coordinated quantum dots 30 in the polar solvent 56. On the other hand, the ligand 58 may have the same structure as the organic ligand 41, in other words, may be a carbon chain having a coordinating functional group at one end.

[0137] The second dispersion L2 may be prepared by adding separately synthesized quantum dots 30, precursors 57, and ligands 58 to a solvent 56. Alternatively, the second dispersion L2 may be prepared by adding precursors 57 to a solvent 56 in which quantum dots 30 coordinated with ligands 58 are dispersed. The quantum dots 30 coordinated with ligands 58 may be obtained by stirring a dispersion in which quantum dots 30 coordinated with organic ligands 41 are dispersed and a dispersion in which ligands 58 are dispersed, and replacing the ligand coordinated to the quantum dots 30 from the organic ligand 41 with the ligand 58.

[0138] In the manufacturing method of the display device 4 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-forming step of the light-emitting layer 26 is carried out. The film-forming step of the light-emitting layer 26 will be described in more detail with reference to FIG. 18 in addition to FIG. 16 .

[0139] In the film formation process of the light-emitting layer 26, first, the second dispersion L2 is applied to the substrate 3, which is a laminate including the layers on the substrate 3 (step S7). For example, as shown in step S7 of Fig. 18, the second dispersion L2 is applied to the hole transport layer 22 by any method including a conventionally known application method such as spin coating.

[0140] Next, the precursors of the semiconductors 42 in the second dispersion liquid L2 containing the precursors 57 are converted into the semiconductors 42 (step S8). For example, the portions of the substrate 3 containing the applied second dispersion liquid L2 are heated at a temperature of 80° C. to 500° C. for 1 minute or more, thereby causing a reaction of the precursors 57 in the second dispersion liquid L2.

[0141] In step S8, the precursor 57 in the applied second dispersion L2 is positioned around the quantum dots 30. Therefore, the precursor 57 converted in step S8 is converted into the semiconductor 42 so as to fill the spaces between the quantum dots 30. Therefore, as shown in step S8 in Fig. 18 , a first light-emitting layer 26A including a plurality of first quantum dots 31 encapsulated in the semiconductor 42 is formed on the hole transport layer 22.

[0142] Next, the second light-emitting layer 26B is formed on the first light-emitting layer 26A. The second light-emitting layer 26B may be formed by the same method as in steps S4 and S5 described above, except that the first dispersion liquid L1 or the first dispersion liquid L1A is applied to the first light-emitting layer 26A. In this way, the light-emitting layer 26 is formed, as shown in step S5 of FIG. 18 .

[0143] The method according to this embodiment makes it possible to manufacture a display device 4 having a light-emitting element 5 that improves light-emitting efficiency while protecting the first quantum dots 31 with the semiconductor 42 and the second quantum dots 32 with the additive 40.

[0144] Additionally, in the above method, the first quantum dots 31 are protected by the semiconductor 42 in the process of forming the second light-emitting layer 26B and subsequent processes. Therefore, the above method can further reduce deterioration of the first quantum dots 31 during the manufacturing process of the display device 4. Furthermore, in the above method, the semiconductor 42 can be formed by converting the precursor 57. Therefore, the above method can form the first light-emitting layer 23A, which includes the semiconductor 42 filling the spaces between the multiple first quantum dots 31, by a simpler method.

[0145] [Embodiment 4] <Light-emitting element with inverted structure> Figure 19 is a schematic side cross-sectional view of a display device 6 according to this embodiment. Compared to the display device 1 described above, the display device 6 according to this embodiment includes a light-emitting element 7 instead of the light-emitting element 2. Compared to the light-emitting element 2, the light-emitting element 7 includes, in this order from the substrate 3 side, a cathode 25, an electron transport layer 24, a light-emitting layer 27, a hole transport layer 22, and an anode 21. In other words, compared to the light-emitting element 2, the light-emitting element 7 includes a light-emitting layer 27 instead of the light-emitting layer 23, and the stacking order of the layers from the anode 21 to the cathode 25 is reversed. In other words, in this embodiment, the cathode 25 is located closer to the substrate 3 than the light-emitting layer 27. Except for the above points, the display device 6 has the same configuration as the display device 1.

[0146] Therefore, in this embodiment, the cathode 25 may be formed in an island shape for each sub-pixel in a plan view, and may be electrically connected to each pixel circuit PC of the substrate 3. On the other hand, the anode 21 may be formed in common for a plurality of sub-pixels.

[0147] The light-emitting layer 27 will be described in more detail with reference to Fig. 20 in addition to Fig. 19. Fig. 20 is an enlarged schematic diagram showing the light-emitting layer 27 and the vicinity of the light-emitting layer 27 in the hole transport layer 22 and the electron transport layer 24 in the cross section shown in Fig. 19, and in particular, an enlarged view of region E3 shown in Fig. 19.

[0148] The light-emitting layer 27 includes a plurality of quantum dots 30 and an additive 40. The quantum dots 30 include a first quantum dot 31 and a second quantum dot 32 located closer to the cathode 25 than the first quantum dot 31.

[0149] The light-emitting layer 27 is adjacent to the lower surface 22U of the hole transport layer 22 on the anode 21 side. In particular, in this embodiment, at least some of the first quantum dots 31 are adjacent to the hole transport layer 22. In other words, the first quantum dots 31 are in direct contact with or adjacent to the layer to which the light-emitting layer 23 is adjacent on the anode 21 side.

[0150] The additive 40 may form a portion of the outer edge of the light-emitting layer 27 that is adjacent to the top surface 24T of the electron transport layer 24. Therefore, the light-emitting layer 27 includes the additive 40 between the electron transport layer 24 and the second quantum dots 32.

[0151] Furthermore, in the light-emitting layer 27, the additive 40 encapsulates a plurality of quantum dots 30. In particular, the additive 40 according to this embodiment not only fills the spaces between at least two second quantum dots 32 but also fills the spaces between at least two first quantum dots 31. Therefore, as long as at least some of the first quantum dots 31 are adjacent to the hole transport layer 22, some of the first quantum dots 31 may be encapsulated in the additive 40; in other words, the additive 40 may be located between the hole transport layer 22 and some of the first quantum dots 31.

[0152] In this embodiment, the light-emitting layer 27 includes the additive 40, and the first quantum dots 31 are adjacent to the hole transport layer 22. Therefore, for the same reasons as described above, the additive 40 reduces deterioration of some of the quantum dots 30 in the light-emitting element 7, while improving the light-emitting efficiency and the reliability of each layer between the anode 21 and the cathode 25. The display device 6 including the light-emitting element 7 achieves reduced power consumption and a longer lifespan.

[0153] In particular, the additive 40 of the light-emitting layer 27 according to this embodiment fills the spaces between at least two first quantum dots 31 in addition to the spaces between at least two second quantum dots 32. Therefore, in the light-emitting device 7, the additive 40 can more efficiently protect both the first quantum dots 31 and the second quantum dots 32.

[0154] <Method for Manufacturing Light-Emitting Device with Inverted Structure> A method for manufacturing the display device 6 according to this embodiment will be described with reference to Fig. 21. Fig. 21 is a flowchart showing the method for manufacturing the display device 6 according to this embodiment.

[0155] In the method for manufacturing the display device 6 according to this embodiment, first, the substrate 3 is prepared by the same method as in step S21 described above. Next, the cathode 25 and the electron transport layer 24 are formed on the substrate 3 in this order by performing steps S26 and S25 described above in this order.

[0156] Next, the light-emitting layer 27 is formed (step S27). The method for forming the light-emitting layer 27 will be described in more detail with reference to Fig. 22 and Fig. 23. Fig. 22 is a flowchart showing the method for forming the light-emitting layer 27 according to this embodiment. Fig. 23 is a process cross-sectional view showing the film formation step of the light-emitting layer 27, which is part of the method for forming the light-emitting layer 27 according to this embodiment.

[0157] In the process of forming the light-emitting layer 27 according to this embodiment, first, a third dispersion is prepared (step S9). The third dispersion may be prepared by the same method as the preparation of the first dispersion L1 or the first dispersion L1A described above. In other words, the third dispersion according to this embodiment may have the same composition as the first dispersion L1 or the first dispersion L1A described above. In this embodiment, an example will be described in which the third dispersion has the same composition as the first dispersion L1.

[0158] Next, a film formation step of the light-emitting layer 27 is performed. In the film formation step of the light-emitting layer 23, first, the third dispersion liquid L3 is applied onto the substrate 3, which is a laminate including each layer, as a substrate (step S10). For example, as shown in step S10 of Fig. 23 , the third dispersion liquid L3 is applied onto the electron transport layer 24 by any method including a conventionally known application method such as spin coating.

[0159] Next, the precursor of the adduct 40 in the third dispersion L3, which contains the precursor 51 and the precursor ligand 52, is converted into the adduct 40 (step S11). For example, the portions of the substrate 3 containing the applied third dispersion L3 are heated at 100° C. for 30 minutes, for example, to cause the precursor 51 and the precursor ligand 52 in the third dispersion L3 to react with each other.

[0160] Here, in the applied third dispersion L3, the precursors 51 and precursor ligands 52 are located around the quantum dots 30. Therefore, as shown in step S11 of Fig. 23 , a light-emitting layer 28 including an adduct 40 encapsulating a plurality of quantum dots 30 is formed on the electron transport layer 24.

[0161] An additive 40 is located between the electron transport layer 24 and one of the quantum dots 30 in the light-emitting layer 28 that is located on the electron transport layer 24 side. Therefore, the quantum dot 30 becomes a second quantum dot 32. Meanwhile, an additive 40 is located above the first quantum dot 31 that is located on the side of the quantum dots 30 in the light-emitting layer 28 opposite the electron transport layer 24 side, in other words, on the top surface 28T side of the light-emitting layer 28.

[0162] Next, a portion of the additive 40 on the light-emitting layer 28 is removed (step S12). In particular, in step S12, at least a portion of the additive 40 located on the side opposite the substrate 3 from the first quantum dots 31, in other words, on the upper surface 28T side of the light-emitting layer 28 from the first quantum dots 31, is removed.

[0163] In step S12, the additives 40 may be removed, for example, by exposing the upper surface 28T of the light-emitting layer 28 to diluted ammonium fluoride. In step S12, the additives 40 are removed until the outermost surfaces of the first quantum dots 31 on the upper surface 28T side of the light-emitting layer 28 are partially exposed. This results in the formation of a light-emitting layer 27 in which at least a portion of the first quantum dots 31 is exposed on the upper surface 27T, as shown in step S12 of FIG.

[0164] 21 , following the formation of the light-emitting layer 27, the hole transport layer 22 is formed on the light-emitting layer 27 by the same method as in step S23. Here, at least a portion of the first quantum dots 31 is exposed on the upper surface 27T of the light-emitting layer 27. Therefore, by forming the hole transport layer 22, the first quantum dots 31 exposed on the upper surface 27T of the light-emitting layer 27 are adjacent to the hole transport layer 22.

[0165] Next, by the same method as in step S22, the anode 21 is formed on the hole transport layer 22. In this way, the display device 6 according to this embodiment is manufactured.

[0166] The method according to this embodiment makes it possible to manufacture a display device 6 including a light-emitting element 7 that improves luminous efficiency while protecting both the first quantum dots 31 and the second quantum dots 32 with the additive 40. In particular, the light-emitting element 7 according to this embodiment has a cathode 25 located closer to the substrate 3 than the light-emitting layer 27. Therefore, the above method makes it possible to manufacture a light-emitting element 7 that includes a light-emitting layer 23 that can protect both the first quantum dots 31 and the second quantum dots 32 with the additive 40.

[0167] However, the manufacturing method of the display device 6 according to this embodiment is not limited to the above method. For example, in this embodiment, after completion of step S11, the third dispersion L3 may be applied again, and the precursor 51 and the like in the third dispersion L3 may then be converted into the additive 40. In this case, the reaction time of the precursor 51 and the like in the third dispersion L3 may be shortened to about one-tenth of that in step S11. This may form the light-emitting layer 27 in which the thickness of the additive 40 formed on the upper surface 27T side is smaller than the thickness of the additive 40 formed on the electron transport layer 24 side.

[0168] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0169] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 22 Hole transport layer 23 Light-emitting layer 25 Cathode 30 Quantum dots 31 First quantum dots 32 Second quantum dots 40 Additive 41 Organic ligand 42 Semiconductor 51 Precursor (first precursor) 52 Precursor ligand (first precursor) 57 Precursor (second precursor) L1 First dispersion L2 Second dispersion L3 Third 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 contains first quantum dots and an additive, and the first quantum dots are in direct contact with an adjacent layer on the anode side, or adjacent to the adjacent layer via an organic ligand or a semiconductor.

2. The light-emitting device according to claim 1, wherein the first quantum dots are in direct contact with the adjacent layer on the anode side of the light-emitting layer.

3. The light-emitting device according to claim 1, wherein the first quantum dots are adjacent to the layer adjacent to the light-emitting layer on the anode side, with the organic ligand interposed therebetween.

4. The light-emitting device according to claim 1, wherein the first quantum dot is adjacent to the layer adjacent to the light-emitting layer on the anode side, with the semiconductor interposed therebetween.

5. A light-emitting element according to any one of claims 1 to 4, wherein the light-emitting layer includes second quantum dots located closer to the cathode than the first quantum dots, and the light-emitting layer includes the additive between the second quantum dot and an adjacent layer of the light-emitting layer on the cathode side.

6. The light-emitting device according to claim 5, wherein the thickness of the additive located between the second quantum dot and the adjacent layer on the cathode side of the light-emitting layer is 1 nm or more and 5 nm or less.

7. The light-emitting element according to claim 5 or 6, wherein the light-emitting layer contains a plurality of the second quantum dots, and the additive fills the spaces between at least two of the second quantum dots.

8. A light-emitting device according to any one of claims 1 to 7, wherein the light-emitting layer includes the semiconductor between the first quantum dots and an adjacent layer on the anode side of the light-emitting layer.

9. The light-emitting device according to claim 8, wherein the light-emitting layer includes a plurality of the first quantum dots, and the semiconductor fills the spaces between at least two of the first quantum dots.

10. The light-emitting element according to claim 8 or 9, wherein the semiconductor contains at least one of zinc sulfide, gallium sulfide, magnesium sulfide, cadmium sulfide, tin sulfide, indium sulfide, and manganese sulfide.

11. The light-emitting device according to any one of claims 1 to 7, wherein the light-emitting layer contains a plurality of the first quantum dots, and the additive fills the space between at least two of the first quantum dots.

12. The light-emitting element according to any one of claims 1 to 11, wherein the additive has insulating properties.

13. The light-emitting device of claim 12, wherein the additive comprises at least one member 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.

14. The light-emitting device according to claim 13, wherein the additive comprises at least one of silicon oxide, aluminum oxide, and silicon nitride.

15. A light-emitting element according to any one of claims 1 to 14, further comprising a hole transport layer located between the anode and the light-emitting layer and adjacent to the anode side of the light-emitting layer.

16. The light-emitting device of claim 15, wherein the hole transport layer comprises an organic material.

17. The light-emitting device according to claim 16, wherein the hole transport layer contains at least one of PVK and TPD.

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. The display device according to claim 18, wherein the anode is located closer to the substrate than the light-emitting layer.

20. The display device according to claim 18, wherein the cathode is located closer to the substrate than the light-emitting layer.

21. 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 comprising forming the light-emitting layer, the light-emitting layer comprising first quantum dots and an additive, and the first quantum dots being in direct contact with an adjacent layer on the anode side, or adjacent to the adjacent layer via an organic ligand or a semiconductor.

22. The method for manufacturing a light-emitting element according to claim 21, wherein the formation of the light-emitting layer includes: forming a first quantum dot layer containing the first quantum dots; applying a first dispersion containing a first precursor that is a precursor of the additive to a substrate; and converting the first precursor in the applied first dispersion into the additive.

23. The method for manufacturing a light-emitting element according to claim 21, wherein the formation of the light-emitting layer includes: applying a second dispersion containing the first quantum dots and a second precursor that is a precursor of the semiconductor to the substrate; converting the second precursor in the applied second dispersion to the semiconductor; applying a first dispersion containing a first precursor that is a precursor of the additive to the substrate; and converting the first precursor in the applied first dispersion to the additive.

24. The method for manufacturing a light-emitting element according to claim 21, wherein the formation of the light-emitting layer includes: applying a third dispersion containing the first quantum dots and a first precursor that is a precursor of the additive to the substrate; converting the first precursor in the applied third dispersion into the additive; and removing at least a portion of the additive located on a side opposite the substrate from the first quantum dots.

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