Display device and method for manufacturing display device

Abstract

This display device comprises: a first sub-pixel (P1) provided with a first light-emitting layer (6F) including first quantum dots (Q1); and a second sub-pixel (P2) provided with a second light-emitting layer (6S) including second quantum dots (Q2). The first quantum dots and the second quantum dots have individual core-shell structures which are made of the same core material. The emission peak wavelength of the first light-emitting layer is greater than the emission peak wavelength of the second light-emitting layer. The first light-emitting layer (6F) includes a first inorganic medium (B1), and the second light-emitting layer (6S) includes a second inorganic medium (B2). The ratio of the particle diameter of the second quantum dots to the particle diameter of the first quantum dots is 0.7 or more.

Description

Display device and method for manufacturing the same

[0001] The present invention relates to a display device and a method for manufacturing a display device.

[0002] Patent Document 1 describes a light-emitting diode (LED) having a light-emitting layer containing quantum dots with a core-shell structure.

[0003] Special Publication No. 2010-526420

[0004] A display device having sub-pixels containing quantum dots has a problem in that color changes become significant when driven for a long period of time.

[0005] A display device according to the present disclosure comprises a first sub-pixel having a first light-emitting layer including first quantum dots, and a second sub-pixel having a second light-emitting layer including second quantum dots, wherein the first quantum dots and the second quantum dots have a core-shell structure in which the core material is the same, the emission peak wavelength of the first light-emitting layer is greater than the emission peak wavelength of the second light-emitting layer, the first light-emitting layer includes a first inorganic medium, the second light-emitting layer includes a second inorganic medium, and a ratio of the particle size of the second quantum dots to the particle size of the first quantum dots is 0.7 or greater.

[0006] In a display device having sub-pixels containing quantum dots, changes in color can be reduced.

[0007] 1 is a cross-sectional view showing the configuration of a display device according to the present embodiment; FIG. 2 is a cross-sectional view showing the configuration of a display device according to the present embodiment; FIG. 3 is a cross-sectional view showing the configuration of a display device according to the present embodiment; FIG. 4 is a flowchart showing an example of forming first and second light-emitting layers; FIG. 5 is a cross-sectional view showing an example of forming first and second light-emitting layers; FIG. 6 is a schematic view showing an example of forming an inorganic medium; FIG. 7 is a cross-sectional view showing a comparative example of light-emitting layer formation; FIG. 8 is a graph showing the effect of the present embodiment (change in luminance of the light-emitting layer); FIG. 9 is a graph showing change in luminance of the comparative example; FIG. 10 is a graph showing the ease of aggregation of quantum dots; FIG. 11 is a block diagram showing the configuration of a display device according to the present embodiment; FIG. 12 is a schematic cross-sectional view showing an example of a display device according to Example 1 of the present disclosure; FIG. 13 is a schematic view for explaining the configuration of red quantum dots and green quantum dots; FIG. 14 is a schematic view for explaining the configuration of red quantum dots and green quantum dots; FIG. 15 is a flowchart showing a method for manufacturing a display device; FIG. 16 is a schematic view for explaining a method for manufacturing a quantum dot dispersion liquid; FIG. 17 is a schematic view for explaining the configuration of quantum dots according to a first modified example; FIG. 18 is a schematic view for explaining the configuration of quantum dots according to a second modified example; FIG. 19 is a schematic cross-sectional view showing an example of a display device according to Example 2 of the present disclosure;

[0008] 1 to 3 are cross-sectional views showing the configuration of a display device according to this embodiment. As shown in FIGS. 1 to 3, the display device 1 according to this embodiment includes a first subpixel P1 having a first light-emitting layer 6F including a first quantum dot Q1, and a second subpixel P2 having a second light-emitting layer 6S including a second quantum dot Q2. Although not shown in FIGS. 1 to 3, the first light-emitting layer 6F and the second light-emitting layer 6S may be separated by a structure such as a bank. The first quantum dot Q1 and the second quantum dot Q2 have a core-shell structure with the same core material. That is, the first quantum dot Q1 has a core C1 and a shell K1, and the second quantum dot Q2 has a core C2 and a shell K2. Note that the materials being the same means that the constituent elements are the same, and it is not necessary that the composition ratios of the constituent elements are the same.

[0009] The peak emission wavelength of the first light-emitting layer 6F is longer than that of the second light-emitting layer 6S. The first light-emitting layer 6F includes a first inorganic medium B1, and the second light-emitting layer 6S includes a second inorganic medium B2. The ratio of the particle size of the second quantum dots Q2 to the particle size of the first quantum dots Q1 is 0.7 or greater.

[0010] This allows the surface conditions of the first and second quantum dots Q1 and Q2, which emit light of different colors, to be uniform within a certain range, thereby preventing large differences in the luminance degradation of the first and second light-emitting layers 6F and 6S, and thereby reducing changes in color due to aging (long-term operation).

[0011] The first and second light-emitting layers 6F and 6S may be located between an anode 4 and a cathode 8, respectively. The first and second light-emitting layers 6F and 6S may emit different primary colors. The particle size of the second quantum dots Q2 may be 8.0 nm to 50 nm. Hereinafter, the first and second quantum dots Q1 and Q2 may be collectively referred to as quantum dots Q, and the first and second inorganic media B1 and B2 may be collectively referred to as inorganic media B.

[0012] 1 to 3, in the first light-emitting layer 6F, at least a portion of the first inorganic medium B1 may be located between the quantum dots Q including the first quantum dot Q1. In the second light-emitting layer 6S, at least a portion of the second inorganic medium B2 may be located between the quantum dots Q including the second quantum dot Q2.

[0013] As shown in Figure 2, the ratio of the particle size of the second quantum dot Q2 to the particle size of the first quantum dot Q1 may be greater than 1.0. As shown in Figures 1 and 2, the thickness of the shell K2 of the second quantum dot Q2 may be greater than the thickness of the shell K1 of the first quantum dot Q1. The shell materials (K1 and K2 materials) of the first quantum dot Q1 and the second quantum dot Q2 may include the same material. This common shell material may be at least one of zinc sulfide, zinc selenide, or zinc sulfide selenide.

[0014] The first light-emitting layer 6F and the second light-emitting layer 6S may each contain an organic substance. The first light-emitting layer 6F and the second light-emitting layer 6S may each contain an organic ligand J, and the ratio of the number of carbon atoms per unit volume contained in the second light-emitting layer 6S to the number of carbon atoms per unit volume contained in the first light-emitting layer 6F may be 0.7 to 1.3. In the present disclosure, if the presence of the organic ligand J can be confirmed in the light-emitting layer 6, it can be considered that the organic ligand J is coordinated to the quantum dots Q.

[0015] The first inorganic medium B1 and the second inorganic medium B2 are silicon compounds, and the molar ratio of carbon atoms to silicon atoms X in the second light-emitting layer 6S divided by the molar ratio of carbon atoms to silicon atoms X in the first light-emitting layer 6F may be 0.7 to 1.3.

[0016] The first inorganic medium B1 and the second inorganic medium B2 are sulfur compounds, and the molar ratio of carbon atoms to sulfur atoms X in the second light-emitting layer 6S divided by the molar ratio of carbon atoms to sulfur atoms X in the first light-emitting layer 6F may be 0.7 to 1.3.

[0017] The first light-emitting layer 6F may include a coordination group Y located between the first quantum dot Q1 and the first inorganic medium B1, and the coordination group Y may coordinate to the first quantum dot Q1 and bond to the first inorganic medium B1. The coordination group Y may have a carbon chain bonding to the first inorganic medium B1. The first inorganic medium B1 may surround the first quantum dot Q1. For example, when the shell K1 includes zinc sulfide (ZnS), the coordination group Y may include a thiol group (—SH). The first quantum dot Q1 is protected by the coordination group Y and the first inorganic medium B1 located around it. The coordination group Y and the first inorganic medium B1 may be referred to as a first protective material.

[0018] The second light-emitting layer 6S may include a coordination group Y located between the second quantum dot Q2 and the second inorganic medium B2, and the coordination group Y may coordinate to the second quantum dot Q2 and bond to the second inorganic medium B2. The coordination group Y may have a carbon chain bonding to the second inorganic medium B2. The second inorganic medium B2 may surround the second quantum dot Q2. For example, when the shell K2 includes zinc sulfide (ZnS), the coordination group Y may include a thiol group (—SH). The second quantum dot Q2 is protected by the coordination group Y and the second inorganic medium B2 located around it. The coordination group Y and the second inorganic medium B2 may be referred to as a second protective material. In the present disclosure, if the presence of the coordination group Y or the thiol group can be confirmed in the light-emitting layer 6, it can be considered that the coordination group Y is coordinated to the quantum dot Q.

[0019] The inorganic medium B (B1, B2) may be composed of the same inorganic material, and the inorganic material of the inorganic medium B may be an oxide or a sulfide. The inorganic material of the inorganic medium B (B1, B2) may be silicon oxide, zinc sulfide, or magnesium zinc sulfide. The inorganic medium B is an inorganic film B surrounding the quantum dots Q, and the inorganic film B (B1, B2) may contain an organic substance such as a hydrocarbon on the surface or inside, or may contain a halogen (e.g., fluorine, chlorine) on the surface or inside.

[0020] 1 to 3, the first subpixel P1 and the second subpixel P2 may have a common functional layer, which may be the hole transport layer 5 or the electron transport layer 7. The common functional layer may also be a hole injection layer. The common functional layer may also be at least one of the electrodes (here, the cathode 8).

[0021] The diameter of the core C2 of the second quantum dot Q2 may be smaller than the diameter of the core C1 of the first quantum dot Q1. The first light-emitting layer 6F may emit red light, and the second light-emitting layer 6S may emit green light.

[0022] As shown in Figure 3, the second light-emitting layer 6S may be thinner than the first light-emitting layer 6F. Generally, the mobility of holes in semiconductors is lower than that of electrons. Therefore, if the shell K is made thicker, holes become less likely to be injected than electrons. Therefore, if the second light-emitting layer 6S is made thinner, the center of the second light-emitting layer 6S in the thickness direction becomes closer to the hole transport layer 5, thereby promoting hole injection. Therefore, even if the shell K2 of the second quantum dot Q2 is thicker than the shell K1 of the first quantum dot Q1, the carrier balance (electron and hole injection ratio) in the second light-emitting layer 6S can be improved.

[0023] The ratio of the diameter of the plurality of quantum dots Q in the second light-emitting layer 6S (e.g., a group of quantum dots including the second quantum dots Q2 appearing in a 200 nm, 500 nm, or 1 μm-wide cross section of the light-emitting layer) to the average diameter of the plurality of quantum dots Q in the first light-emitting layer 6F (e.g., a group of quantum dots including the first quantum dots Q1 appearing in a 200 nm, 500 nm, or 1 μm-wide cross section of the light-emitting layer) may be 0.7 to 1.3. The cross section of the light-emitting layer may be visualized using a TEM image, an SEM image, or the like. The diameter of the quantum dots Q may be considered to be the same as the diameter of a circle having the same area as the cross-sectional area of ​​the quantum dots. The diameters of approximately 20 quantum dots Q in the cross section of the light-emitting layer may be measured, and the average value thereof may be used as the average diameter.

[0024] Fig. 4 is a flowchart showing an example of forming the first and second light-emitting layers. Fig. 5 is a cross-sectional view showing an example of forming the first and second light-emitting layers. Fig. 6 is a schematic view showing an example of forming an inorganic medium. Fig. 7 is a cross-sectional view showing a comparative example of forming the light-emitting layer. Fig. 8 is a graph showing the effect of this embodiment (change in luminance of the light-emitting layer). Fig. 9 is a graph showing change in luminance of the comparative example.

[0025] As shown in Figures 4 to 6, the manufacturing method of the display device of this embodiment includes a step of forming a first light-emitting layer 6F using a first solution 51 containing first quantum dots Q1, and a step of forming a second light-emitting layer 6S using a second solution 52 containing second quantum dots Q2.

[0026] The first quantum dots Q1 and the second quantum dots Q2 have a core-shell structure with the same core material, and the peak emission wavelength of the first light-emitting layer 6F is greater than the peak emission wavelength of the second light-emitting layer 6S. The first solution 51 contains a plurality of organic ligands J coordinated to the first quantum dots Q1, and the second solution 52 contains a plurality of organic ligands J coordinated to the second quantum dots Q2. The ratio of the particle size of the second quantum dots Q2 to the particle size of the first quantum dots Q1 is 0.7 or greater.

[0027] 4 to 6 , a first solution 51 containing first quantum dots Q1 protected by a first inorganic medium B1 may be produced by mixing a first precursor Z with a solution containing first quantum dots Q1 and organic ligand J to perform ligand exchange (substituting a portion of the organic ligand J with the first precursor Z), followed by extracting the first quantum dots Q1 protected by a first inorganic medium B1 and adding a solvent (e.g., toluene). A second solution 52 containing second quantum dots Q2 protected by a second inorganic medium B2 may be produced by mixing a second precursor Z with a solution containing second quantum dots Q2 and organic ligand J to perform ligand exchange (substituting a portion of the organic ligand J with the second precursor Z), followed by extracting the second quantum dots Q2 protected by a second inorganic medium B2 and adding a solvent (e.g., toluene).

[0028] Here, the first solution 51 may be produced using a portion (e.g., a middle layer portion of the mixture) of a liquid containing first quantum dots Q1 coordinated with a plurality of organic ligands J and a nonpolar solvent, and a liquid containing a first precursor Z and a polar solvent. The second solution 52 may be produced using a portion (e.g., a middle layer portion of the mixture described below) of a liquid containing second quantum dots Q2 coordinated with a plurality of organic ligands J and a nonpolar solvent, and a liquid containing a second precursor Z and a polar solvent.

[0029] As shown in Figures 5 and 6, the first solution 51 may include a coordination group Y and a first inorganic medium B1 positioned around the first quantum dot Q1, and the second solution 52 may include a coordination group Y and a second inorganic medium B2 positioned around the second quantum dot Q2.

[0030] As shown in FIG. 6, the first and second precursors Z may have an alkoxysilane group. The first and second precursors Z may also have a coordinating group Y containing the aforementioned carbon chain. The first and second precursors Z are at least one compound selected from (3-mercaptopropyl)trimethoxysilane (MPTS), (3-mercaptopropyl)triethoxysilane, 3-aminopropyltrimethoxysilane (APS), 3-aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, and 4-aminobutyltriethoxysilane, and the inorganic medium B (B1 and B2) is silicon oxide (e.g., SiO ２ ) in FIG. １ ~R ３The first and second precursors Z may further include tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetraisopropyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, trimethoxymethylsilane, ne, Triethoxymethylsilane, Trimethoxy(propyl)silane, Triethoxy(propyl)silane, Butyltrimeth Oxysilane, Butyltriethoxysilane, Triethoxy(isobutyl)silane, Cyclopentyltrimethoxysilane, He xyltrimethoxysilane, Hexyltriethoxysilane, Decyltrimethoxysilane, Decyltriethoxysilane, He xadecyltrimethoxysilane, Hexadecyltriethoxysilane, Octadecyltriethoxysilane, Octadecyltrim The composition may contain at least one compound selected from the group consisting of ethoxysilane, trimethoxyphenylsilane, triethoxyphenylsilane, allyltrimethoxysilane, allyltriethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

[0031] 4 and 5, the manufacturing method of the display device may include a step of applying a first solution 51 to the underlayer UL and a step of applying a second solution 52 to the underlayer UL. The underlayer UL may be a hole injection layer or a hole transport layer.

[0032] 4 and 5, a first solution 51 (coating liquid) applied to the underlayer UL may be baked and patterned (e.g., photolithography and etching) to form the first light-emitting layer 6F. A second solution 52 (coating liquid) applied to the underlayer UL may be baked and patterned to form the second light-emitting layer 6S. The first and second solutions 51 and 52 may be inkjet coated, eliminating the need for patterning.

[0033] 5, the first and second quantum dots Q1 and Q2 have the same particle size (preferably, the particle size ratio of the second quantum dots Q2 to the first quantum dots Q1 is 0.7 or more, or 1.3 or less, or 0.7 to 1.3). Therefore, the difference between the organic ligand coverage of the first quantum dots Q1 after the ligand exchange and the organic ligand coverage of the second quantum dots Q2 after the ligand exchange falls within a certain range. Therefore, as shown in FIG. 8, the second light-emitting layer 6S has the same luminance characteristics as the first light-emitting layer 6F, and the change in color tone is reduced.

[0034] On the other hand, in the comparative example shown in Figure 7, the particle sizes of the first quantum dots Q1 and the comparative quantum dots QT are not uniform (e.g., the particle size ratio of the comparative quantum dots QT to the first quantum dots Q1 is less than 0.7), so the difference between the organic ligand coverage of the first quantum dots Q1 after ligand exchange and the organic ligand coverage of the comparative quantum dots QT after ligand exchange does not fall within a certain range. In other words, because the particle size of the quantum dots QT is small, the ratio of the surface area to the volume of the quantum dots QT is large, making them prone to aggregation. Therefore, unless the coverage of the QT is significantly increased, the quantum dots QT will aggregate, making it impossible to manufacture an emissive layer. Therefore, as shown in Figure 9, the comparative emissive layer 6T is more susceptible to (and lasts longer than) the detachment of organic ligands and deteriorates more quickly than the first emissive layer 6F. As a result, the color tone changes significantly.

[0035] Furthermore, as will be described later, the use of an inorganic medium can strongly protect the surface of the quantum dots Q, thereby suppressing the decrease in brightness over operating time compared to when only organic ligands J are coordinated to the first and second quantum dots Q1 and Q2.

[0036] When the display device 1 is driven, the first and second quantum dots Q1 and Q2 are degraded due to the desorption of the organic ligands, and then the first and second quantum dots Q1 and Q2 are degraded due to the desorption of the inorganic medium. In Figures 8 and 9, the transition times from the decrease in luminance of the light-emitting layer due to the desorption of the organic ligands to the decrease in luminance of the light-emitting layer due to the desorption of the inorganic medium are designated as PO1, PO2, and POT.

[0037] 8 , when the first and second quantum dots Q1 and Q2 have the same particle size (preferably, when the particle size ratio of the second quantum dot Q2 to the first quantum dot Q1 is 0.7 or more, 1.3 or less, or 0.7 to 1.3), the time difference between the transition times PO1 and PO2 falls within a certain range, so that the deterioration state of the second quantum dot Q2 due to the desorption of the organic ligand J can be made to be the same as the deterioration state of the first quantum dot Q1 due to the desorption of the organic ligand J. As a result, the second light-emitting layer 6S has the same luminance characteristics as the first light-emitting layer 6F.

[0038] 9 , in the case of the first quantum dots Q1 and the comparative quantum dots QT, which have non-uniform particle sizes, the transition timing POT is significantly delayed from the transition timing PO1. Furthermore, because the degree of deterioration of the quantum dots due to the detachment of the organic ligand J is greater than the degree of deterioration of the quantum dots Q due to the detachment of the inorganic medium, the degree of deterioration of the comparative quantum dots QT at the transition timing POT is greater than the degree of deterioration of the first quantum dots Q1 at the transition timing PO1. In other words, the comparative light-emitting layer 6T will have luminance characteristics significantly lower than those of the first light-emitting layer 6F over time (after long-term operation), resulting in noticeable changes in color.

[0039] FIG. 10 is a graph showing the relationship between quantum dot particle size and the likelihood of aggregation. As shown in FIG. 10, as the particle size of the quantum dots Q increases, the quantum dots Q become less likely to aggregate. The likelihood of aggregation of quantum dots Q is proportional to the surface area / volume of the quantum dots Q, i.e., it is inversely proportional to the particle size of the quantum dots Q. Experiments by the inventors have shown that, for quantum dots with a particle size of approximately 3 nm or greater, aggregation of quantum dots Q can be prevented by setting the organic ligand coverage of the quantum dots Q to 100%. To prevent aggregation of quantum dots Q with a particle size of K (nm), the organic ligand coverage should be set to 3 / K or greater. As mentioned above, a low organic ligand coverage is preferable to suppress brightness degradation over operating time, so the organic ligand coverage after ligand exchange is controlled to approximately 3 / K. For example, for quantum dots Q with a particle size of 6 nm, setting the organic ligand coverage to 0.5 (50%) can maximize device reliability while preventing aggregation of quantum dots Q. Quantum dots Q with different emission colors can be considered to have substantially the same organic ligand coverage, i.e., the effects on aggregation suppression and device reliability can be considered to be substantially the same, when the ratio of the organic ligand coverage of the second quantum dot Q2 after ligand exchange to the organic ligand coverage of the first quantum dot Q1 after ligand exchange is 0.7 or more, 1.3 or less, or 0.7 to 1.3. Since this organic ligand coverage after ligand exchange is controlled to be 3 / K as described above, when the ratio of the particle size of the second quantum dot Q2 to the particle size of the first quantum dot Q1 is 0.7 or more, 1.3 or less, or 0.7 to 1.3, it is possible to suppress aggregation between quantum dots while ensuring maximum device reliability. Similarly, if the molar ratio of carbon atoms to silicon atoms X in the second light-emitting layer 6S divided by the molar ratio of carbon atoms to silicon atoms X in the first light-emitting layer 6F is 0.7 to 1.3, it can be said that the protection states of the first quantum dots Q1 and the second quantum dots Q2 are consistent, and the effects of the present disclosure are achieved.

[0040] Conversely, if the ratio of the particle size of the second quantum dots Q2 to the particle size of the first quantum dots Q1 is less than 0.7, in order to suppress aggregation of the second quantum dots Q2, the ratio of the organic ligand coverage of the second quantum dots Q2 after ligand exchange to the organic ligand coverage of the first quantum dots Q1 after ligand exchange must be increased to more than 1.3 (the organic ligand coverage of the first quantum dots Q1 and the organic ligand coverage of the second quantum dots Q2 cannot be considered substantially equivalent). As a result, the change in color becomes noticeable as shown in FIG. 9 , and the effect of the present disclosure is not achieved.

[0041] 11 is a block diagram showing the configuration of a display device according to this embodiment. The display device 1 includes a display unit DA, a first driver circuit SD (e.g., a data signal line drive circuit) and a second driver circuit GD (e.g., a scanning signal line drive circuit, a light-emitting control line drive circuit) that drive the display unit DA, and a control circuit CL that controls the first driver circuit SD and the second driver circuit GD. The display unit DA may include a substrate (pixel circuit substrate) and a light-emitting element layer. The light-emitting element layer may include a first sub-pixel P1 (9R) that emits red light, a second sub-pixel P2 (9G) that emits green light, and a third sub-pixel P3 (9B) that emits blue light. Each of the first to third sub-pixels P1 to P3 may be connected to a pixel circuit PC formed in the pixel circuit layer.

[0042] The first subpixel P1 may be a first light-emitting element (e.g., a red light-emitting element), the second subpixel P2 may be a second light-emitting element (e.g., a green light-emitting element), and the third subpixel P3 may be a third light-emitting element (e.g., a blue light-emitting element).

[0043] 12 is a schematic cross-sectional view showing an example of a display device according to Example 1 of the present disclosure. Hereinafter, for configurations related to different colors among similar basic configurations, a symbol indicating the color is further added to the symbol of the basic configuration. For example, a symbol R is further added to a configuration related to red, a symbol G is further added to a configuration related to green, and a symbol B is further added to a configuration related to blue.

[0044] 12 , the display device 1 according to the first embodiment includes a light-emitting element 2 and an array substrate 3. The display device 1 has a structure in which each layer of the light-emitting element 2 is stacked on the array substrate 3 on which a TFT (Thin Film Transistor) (not shown) is formed. In this specification, the direction from the light-emitting element 2 of the display device 1 to the array substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0045] The light-emitting element 2 includes, in this order from bottom to top, an anode 4 as a first electrode, a hole transport layer 5, a light-emitting layer 6, an electron transport layer 7, and a cathode 8 as a second electrode. A sealing layer (not shown) may also be provided to prevent oxygen and moisture in the atmosphere from penetrating into the element. The anode 4 of the light-emitting element 2 formed on the upper layer of the array substrate 3 is electrically connected to the array substrate 3.

[0046] At least one of the anode 4 and the cathode 8 is a transparent electrode that transmits visible light. Examples of the transparent electrode include ITO (indium tin oxide) and IZO (indium zinc oxide), which may be formed by sputtering or the like. Alternatively, either the anode 4 or the cathode 8 may contain a metal material, and preferred metal materials are Al, Cu, Au, Ag, and Mg, each of which has a high reflectivity for visible light, or alloys of these metals.

[0047] The hole transport layer 5 transports holes from the anode 4 to the light-emitting layer 6. Examples of materials for the hole transport layer 5 include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "p-TPD"), and polyvinylcarbazole (abbreviated as "PVK"). These hole transport materials may be used alone or in combination of two or more types. In addition, a hole injection layer (not shown) may be formed. Examples include a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (abbreviated as "PEDOT:PSS"), NiO (nickel oxide), CuSCN (copper thiocyanate), etc. These materials may be used alone or in combination of two or more types.

[0048] The electron transport layer 7 transports electrons from the cathode 8 to the light-emitting layer 6. Examples of materials for the electron transport layer 7 include ZnO (zinc oxide) nanoparticles, MgZnO (magnesium zinc oxide) nanoparticles, and 2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (abbreviated as "TPBi"). These electron transport materials may be used alone or in combination of two or more.

[0049] In Example 1, the display device 1 includes a red subpixel 9R, a green subpixel 9G, and a blue subpixel 9B. The red subpixel 9R includes a red light-emitting layer 6R including red quantum dots 10R that emit red light. The green subpixel 9G includes a green light-emitting layer 6G including green quantum dots 10G that emit green light. The blue subpixel 9B includes a blue light-emitting layer 6B including blue quantum dots 10B that emit blue light. The red quantum dots 10R are an example of a first quantum dot, the red light-emitting layer 6R is an example of a first light-emitting layer, and the red subpixel 9R is an example of a first subpixel. The green quantum dots 10G are an example of a second quantum dot, the green light-emitting layer 6G is an example of a second light-emitting layer, and the green subpixel 9G is an example of a second subpixel.

[0050] Here, red light is light having a peak emission wavelength of, for example, 600 nm or more and 780 nm or less, green light is light having a peak emission wavelength of, for example, 500 nm or more and 600 nm or less, and blue light is light having a peak emission wavelength of, for example, 400 nm or more and 500 nm or less.

[0051] In the display device 1 according to the first embodiment, a group including one red sub-pixel 9R, one green sub-pixel 9G, and one blue sub-pixel 9B may be defined as one pixel in the display device 1. Although only one pixel is shown in Fig. 12, in the first embodiment, the display device 1 may also include a plurality of other pixels.

[0052] The red sub-pixel 9R has a red pixel anode 4R, a hole transport layer 5, a red light-emitting layer 6R, an electron transport layer 7, and a cathode 8. The green sub-pixel 9G has a green pixel anode 4G, a hole transport layer 5, a green light-emitting layer 6G, an electron transport layer 7, and a cathode 8. The blue sub-pixel 9B has a blue pixel anode 4B, a hole transport layer 5, a blue light-emitting layer 6B, an electron transport layer 7, and a cathode 8.

[0053] In Example 1, the anode 4 includes a red pixel anode 4R corresponding to the red sub-pixel 9R, a green pixel anode 4G corresponding to the green sub-pixel 9G, and a blue pixel anode 4B corresponding to the blue sub-pixel 9B. In Example 1, the red sub-pixel 9R, green sub-pixel 9G, and blue sub-pixel 9B have a common hole transport layer 5, electron transport layer 7, and cathode 8.

[0054] The hole transport layer 5 may be separated so as to correspond to the red subpixel 9R, the green subpixel 9G, and the blue subpixel 9B, respectively. The electron transport layer 7 may be separated so as to correspond to the red subpixel 9R, the green subpixel 9G, and the blue subpixel 9B, respectively.

[0055] In Example 1, the thickness TR of the red light-emitting layer 6R, the thickness TG of the green light-emitting layer 6G, and the thickness TB of the blue light-emitting layer 6B are the same. The thickness T of the light-emitting layer 6 is the thickness in the stacking direction. Note that the thickness TR, the thickness TG, and the thickness TB may be different from each other.

[0056] The red light-emitting layer 6R includes one or more red quantum dots 10R and a first inorganic medium 21. At least a portion of the first inorganic medium 21 is located around the red quantum dots 10R. The green light-emitting layer 6G includes one or more green quantum dots 10G and a second inorganic medium 22. At least a portion of the second inorganic medium 22 is located around the green quantum dots 10G.

[0057] The blue light-emitting layer 6B includes one or more blue quantum dots 10B and a third inorganic medium 23. At least a portion of the third inorganic medium 23 is located around the blue quantum dots 10B.

[0058] In this disclosure, "quantum dot" refers to a dot having a maximum width of 100 nm or less. The shape of the quantum dot 10 is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). The shape of the quantum dot 10 may be, for example, a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0059] The quantum dot 10 is typically made of a semiconductor. The semiconductor may have a certain band gap. The semiconductor may be any material capable of emitting light and may include at least the materials described below. The semiconductor may be capable of emitting red, green, and blue light, respectively. The semiconductor may include, for example, at least one selected from the group consisting of a II-VI compound, a III-V compound, a chalcogenide, and a perovskite compound. Note that a II-VI compound refers to a compound containing a II group element and a VI group element, and a III-V compound refers to a compound containing a III group element and a V group element. Furthermore, a II group element may include a 2 group element and a 12 group element, a III group element may include a 3 group element and a 13 group element, a V group element may include a 5 group element and a 15 group element, and a VI group element may include a 6 group element and a 16 group element.

[0060] The II-VI compound includes, for example, at least one selected from the group consisting of MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe. The III-V compound includes, for example, at least one selected from the group consisting of GaAs, GaP, InN, InAs, InP, and InSb. The chalcogenide is a compound containing a VI A(16) group element, for example, CdS or CdSe. The chalcogenide may also include a mixed crystal thereof. The perovskite compound has, for example, a composition represented by the general formula CsPbX3. The constituent element X includes at least one element selected from the group consisting of Cl, Br, and I, for example.

[0061] Here, the numbering of element groups using Roman numerals is based on the old IUPAC (International Union of Pure and Applied Chemistry) system or the old CAS (Chemical Abstracts Service) system, and the numbering of element groups using Arabic numerals is based on the current IUPAC system. Note that the chemical formulas of the compounds in the present disclosure are representative examples, and the composition ratios described in the chemical formulas may be stoichiometric, but are not necessarily stoichiometric.

[0062] The quantum dot 10 has a core-shell structure including a core and a shell formed around the core. In Example 1, the quantum dot 10 is a sphere. The shell may be formed on the surface of the core. It is desirable that the shell cover the entire core, but it is not necessary that the shell completely cover the core. The shell may be formed on a portion of the surface of the core. If it is found that the core is surrounded by observation of a cross section of the quantum dot 10, it can be said that the quantum dot 10 has a core-shell structure. It is sufficient to be able to determine that the shell covers the entire core by observation of a cross section of the quantum dot 10.

[0063] The first inorganic medium 21, the second inorganic medium 22, and the third inorganic medium 23 contain inorganic materials. The first inorganic medium 21, the second inorganic medium 22, and the third inorganic medium 23 hold red quantum dots 10R, green quantum dots 10G, and blue quantum dots 10B, respectively. The first inorganic medium 21 is located between adjacent red quantum dots 10R. The second inorganic medium 22 is located between adjacent green quantum dots 10G. The third inorganic medium 23 is located between adjacent blue quantum dots 10B.

[0064] Each of the inorganic media 21, 22, and 23 is an element that constitutes a light-emitting layer in which the quantum dots 10 are distributed.

[0065] The inorganic media 21, 22, and 23 may be made of the same material as the shell material of the quantum dot 10. In this case, the average distance between adjacent cores (core-to-core distance) is preferably 5 nm or more.

[0066] The inorganic material constituting each of the inorganic media 21, 22, and 23 preferably has a band gap wider than the band gap of the material constituting the quantum dots 10. The inorganic material constituting each of the inorganic media 21, 22, and 23 may be a semiconductor material or an insulating material. The inorganic material constituting each of the inorganic media 21, 22, and 23 may be a silicon compound or a sulfur compound. The inorganic material constituting each of the inorganic media 21, 22, and 23 may be a silicon compound or a silicon oxide. The inorganic material constituting each of the inorganic media 21, 22, and 23 may be zinc sulfide or magnesium zinc sulfide. Specific examples of the inorganic material constituting each of the inorganic media 21, 22, and 23 include silicon oxide (SiO ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ ), lead oxide (PbO), copper oxide (CuO), zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS ２ ), gallium sulfide (GaS, Ga ２ S ３ ), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa ２ S ４ ), magnesium sulfide (MgGa ２ S ４ ) can be mentioned.

[0067] The inorganic media 21, 22, and 23 may be made of the same inorganic material or different inorganic materials. Alternatively, the first inorganic material and the second inorganic material may be made of the same inorganic material, and only the third inorganic medium 23 may be made of a different inorganic material.

[0068] <Configuration of Red Quantum Dots and Green Quantum Dots> The configuration of the red quantum dots 10R and the green quantum dots 10G will be described with reference to Fig. 13 and Fig. 14. Fig. 13 and Fig. 14 are schematic diagrams for explaining the configuration of the red quantum dots 10R and the green quantum dots 10G. Fig. 13 and Fig. 14 show one of the red quantum dots 10R included in the red light-emitting layer 6R, and one of the green quantum dots 10G included in the green light-emitting layer 6G.

[0069] As shown in Fig. 13, the red quantum dot 10R includes a core 11R and a shell 12R. The green quantum dot 10G includes a core 11G and a shell 12G. The core 11R of the red quantum dot 10R and the core 11G of the green quantum dot 10G are made of the same core material. The shell 12R of the red quantum dot 10R and the shell 12G of the green quantum dot 10G may be made of the same shell material. The shell material of the shell 12R and the shell 12G may include zinc sulfide, zinc selenide, or zinc sulfide selenide. Note that the shell 12R and the shell 12G may be made of different shell materials.

[0070] The average core diameter of the green quantum dots 10G may be smaller than the average core diameter of the red quantum dots 10R. The average core diameter of the red quantum dots 10R is the average of the core diameters D1 of one or more red quantum dots 10R included in the red light-emitting layer 6R. For example, when the core material is InP, the average core diameter of the red quantum dots 10R is 4.0 nm to 4.2 nm. The average core diameter of the green quantum dots 10G is the average of the core diameters D3 of one or more green quantum dots 10G included in the green light-emitting layer 6G. For example, when the core material is InP, the average core diameter of the green quantum dots 10G is 2.4 nm to 2.6 nm. If the red quantum dots 10R and the green quantum dots 10G do not have a shell, or if they have a shell with a thickness proportional to the core diameter as shown in Figure 7, the ratio of the average particle size of the green quantum dots 10G to the average particle size of the red quantum dots 10R will be 0.57 to 0.65, which is less than 0.7 and therefore does not achieve the effects of the present disclosure.

[0071] By adding a thicker shell to the green quantum dots 10G than the red quantum dots 10R, the ratio of the average particle size of the green quantum dots 10G to the average particle size of the red quantum dots 10R can be set to 0.7 or more. The average particle size of the red quantum dots 10R is the average of the particle sizes D2 of one or more red quantum dots 10R included in the red light-emitting layer 6R. The particle size D2 of the red quantum dots 10R is the particle size including the core 11R and the shell 12R. The average particle size of the green quantum dots 10G is the average of the particle sizes D4 of one or more green quantum dots 10G included in the green light-emitting layer 6G. The particle size D4 of the green quantum dots 10G is the particle size including the core 11G and the shell 12G. In Example 1, the average particle size of the red quantum dots 10R and the average particle size of the green quantum dots 10G are approximately the same. The average particle size of the red quantum dots 10R is, for example, 8.0 nm to 50 nm. The green quantum dots 10G have an average particle size of, for example, 8.0 nm to 50 nm.

[0072] The average shell thickness of the green quantum dots 10G is greater than the average shell thickness of the red quantum dots 10R. The average shell thickness of the red quantum dots 10R is the average of the thicknesses T1 of the shells 12R of one or more red quantum dots 10R included in the red light-emitting layer 6R. Thickness T1 corresponds to the radius of the particle diameter D2 minus the radius of the core diameter D1. The average shell thickness of the green quantum dots 10G is the average of the thicknesses T2 of the shells 12G of one or more green quantum dots 10G included in the green light-emitting layer 6G. Thickness T2 corresponds to the radius of the particle diameter D4 minus the radius of the core diameter D3.

[0073] The core diameter of the quantum dot 10 can be calculated using effective mass approximation from the band gap calculated from the emission wavelength of the quantum dot 10. When the core is made of ZnSe, the core diameter (nm) is calculated as {6.1 / [(1240 / λp)-2.7]}, where λp (nm) is the PL peak wavelength of the quantum dot 10. ０．５ When the core is InP, if the PL peak wavelength of the quantum dot is λp (nm), the core diameter (nm) is {2.6 / [(1240 / λp)-1.45]} ０．８６２ This becomes:

[0074] Each of the red light-emitting layer 6R and the green light-emitting layer 6G contains an organic substance. Specifically, each of the red light-emitting layer 6R and the green light-emitting layer 6G contains an organic ligand 13. The organic ligand 13 is an organic chain having a carbon atom. A plurality of organic ligands 13 are coordinated to the surface (outer surface) of each of the shell 12R of the red quantum dot 10R and the shell 12G of the green quantum dot 10G. By coordinating the organic ligands 13 to the surface of the shell 12R and the shell 12G, it is possible to prevent aggregation of each of the red quantum dots 10R included in the red light-emitting layer 6R and the green quantum dots 10G included in the green light-emitting layer 6G.

[0075] A coordination group 14 is coordinated to a portion of the surface of the shell 12R of the red quantum dot 10R. As shown in FIG. 14 , a first inorganic medium 21 is formed to surround the red quantum dot 10R. A coordination group 14 including a carbon chain is located between the red quantum dot 10R and the first inorganic medium 21, and the coordination group 14 is bonded to the first inorganic medium 21. The first inorganic medium 21 may surround the red quantum dot 10R continuously or discontinuously. The coordination group 14 and the first inorganic medium 21 located around the red quantum dot 10R can protect the surface of the red quantum dot 10R. In other words, because the coordination group 14 is bonded to the first inorganic medium 21, unlike the organic ligand 13, it is less likely to detach from the red quantum dot 10R when electricity is applied, and is less likely to deteriorate the red quantum dot 10R. Furthermore, the first inorganic medium 21 prevents oxygen and moisture permeating from the outside from reaching the surface of the red quantum dots 10R, thereby preventing deterioration of the red quantum dots 10R.

[0076] As shown in Fig. 13 , a coordination group 15 is coordinated to a portion of the surface of a shell 12G of a green quantum dot 10G. As shown in Fig. 14 , a second inorganic medium 22 is formed to surround the green quantum dot 10G. A coordination group 15 including a carbon chain is located between the green quantum dot 10G and the second inorganic medium 22, and the coordination group 15 is bonded to the second inorganic medium 22. The second inorganic medium 22 may surround the green quantum dot 10G continuously or discontinuously.

[0077] The surface of the green quantum dot 10G can be protected by the coordination group 15 and the second inorganic medium 22 located around the green quantum dot 10G. That is, because the coordination group 15 is bonded to the second inorganic medium 22, it is less likely to be detached from the green quantum dot 10G when a current is applied, unlike the organic ligand 13, and is less likely to deteriorate the green quantum dot 10G. Furthermore, the second inorganic medium 22 prevents oxygen and moisture that penetrate from the outside from reaching the surface of the green quantum dot 10G, thereby preventing deterioration of the green quantum dot 10G.

[0078] When the first inorganic medium 21 and the second inorganic medium 22 are silicon compounds, the molar ratio of carbon atoms to silicon atoms in the green light-emitting layer 6G divided by the molar ratio of carbon atoms to silicon atoms in the red light-emitting layer 6R may be 0.7 to 1.3. Furthermore, when the first inorganic medium 21 and the second inorganic medium 22 are sulfur compounds, the molar ratio of carbon atoms to sulfur atoms in the green light-emitting layer 6G divided by the molar ratio of carbon atoms to sulfur atoms in the red light-emitting layer 6R may be 0.7 to 1.3. This configuration protects the surfaces of the red quantum dots 10R and the green quantum dots 10G, preventing aggregation of the red quantum dots 10R contained in the red light-emitting layer 6R and the green quantum dots 10G contained in the green light-emitting layer 6G, thereby realizing a display device with little decrease in brightness over long periods of operation.

[0079] <Method of Manufacturing Display Device> A method of manufacturing the display device 1 will be described with reference to Fig. 15 to Fig. 17. Fig. 15 is a flowchart showing a method of manufacturing the display device 1. Fig. 16 and Fig. 17 are schematic diagrams for explaining a method of manufacturing a quantum dot dispersion liquid.

[0080] First, in step S1, a process of forming the array substrate 3 is performed. In step S1, a plurality of TFTs corresponding to each sub-pixel 9 may be formed on the array substrate 3.

[0081] In step S2, a process of forming the anode 4 is performed on the array substrate 3. In step S2, the anode 4 is formed by depositing an anode material by sputtering. In step S2, the anode 4 may be formed for each sub-pixel 9, or may be formed commonly to all the sub-pixels 9.

[0082] In step S3, a step of forming a hole transport layer 5 on the anode 4 is performed. In step S3, the hole transport layer 5 is formed by depositing a hole transport material on the anode 4 by, for example, a vapor deposition method or an inkjet method. In step S3, the hole transport layer 5 may be formed in common to all the sub-pixels 9, or may be formed for each sub-pixel 9.

[0083] In step S4, a step of forming the light-emitting layer 6 on the hole transport layer 5 is performed. In step S4, the light-emitting layer 6 may be formed for each sub-pixel by, for example, separate application using an inkjet method. In step S4, the light-emitting layer 6 is formed by applying a quantum dot dispersion liquid containing the quantum dots 10.

[0084] 16 and 17, a method for manufacturing a quantum dot dispersion liquid will be described. In the following description, a method for manufacturing a quantum dot dispersion liquid in which red quantum dots 10R and green quantum dots 10G are dispersed will be described. Note that the quantum dot dispersion liquid of blue quantum dots 10B is manufactured by the same method as the quantum dot dispersion liquid of red quantum dots 10R and green quantum dots 10G.

[0085] First, as shown in step S41 of FIG. 16 , a first dispersion L10 including an upper layer L1 and a lower layer L2 is prepared. The upper layer L1 is a liquid including red quantum dots P10R (see reference numeral 100 in FIG. 17 ) coordinated with a plurality of organic ligands 13 and a nonpolar solvent. The lower layer L2 is a liquid including a first precursor and a polar solvent. Furthermore, as shown in step S45, a second dispersion L20 including upper layer L5 and a lower layer L6 is prepared in a separate container. The upper layer L5 is a liquid including green quantum dots P10G (see reference numeral 110 in FIG. 17 ) coordinated with a plurality of organic ligands 13 and a nonpolar solvent. The lower layer L6 is a liquid including a second precursor and a polar solvent. The red quantum dots 10R and the green quantum dots 10G have a core-shell structure in which the core material is the same.

[0086] The non-polar solvent used for the upper layer portion L1 and the upper layer portion L5 may be a solvent having a relative dielectric constant at room temperature of not more than 3. For example, it may be pentane, hexane, cyclohexane, isooctane, octane, benzene, toluene, dichlorodifluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, tetrachloroethylene, 1,4-dioxane, or a mixture of at least two of these solvents.

[0087] The polar solvent used for the lower layer portion L2 and the lower layer portion L6 may be a solvent having a relative dielectric constant at room temperature of 30 or more, such as methanol, ethylene glycol, propylene glycol, diethylene glycol, glycerin, furfural, formic acid, ethylene carbonate, propylene carbonate, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, succinonitrile, nitromethane, nitrobenzene, dimethyl sulfoxide, sulfolane, water, or a mixture of at least two of these solvents.

[0088] The first precursor and the second precursor may be a metal halide such as zinc fluoride, zinc chloride, zinc bromide, zinc iodide, indium fluoride, indium chloride, indium bromide, or indium iodide.

[0089] Next, as shown in steps S42 and S46, steps are performed in which the first dispersion L10 and the second dispersion L20 are stirred to produce a mixture. The mixture produced in steps S42 and S46 is contained in the middle layer portions L3 and L7 of the first dispersion L10 and the second dispersion L20. That is, the middle layer portions L3 and L7 are liquids containing the mixture produced by stirring the first dispersion L10 and the second dispersion L20.

[0090] When the first dispersion L10 is stirred, some of the organic ligands 13 coordinated to the red quantum dots 10R are replaced with a first precursor Z containing an inorganic atom (e.g., silicon Si, sulfur S), forming coordination groups 14 coordinated to the red quantum dots 10R and a first inorganic medium 21 bonded thereto. Similarly, when the second dispersion L20 is stirred, as shown by reference numeral 111 in FIG. 17 , some of the organic ligands 13 coordinated to the green quantum dots 10G are replaced with a second precursor Z, forming coordination groups 15 coordinated to the green quantum dots 10G and a second inorganic medium 22 bonded thereto. As shown in step S42 in FIG. 16 , the polarity of the red quantum dots 10R surrounded by the coordination groups 14 and the first inorganic medium 21 changes, and they no longer disperse in either the upper layer L1 or the lower layer L2. Therefore, a middle layer L3 in which the red quantum dots 10R coordinated with the coordination groups 14 are dispersed is generated between the upper layer L1 and the lower layer L2. Furthermore, as shown in step S46, the polarity of the green quantum dots 10G surrounded by the coordination groups 15 and the second inorganic medium 22 also changes in the same way. Therefore, a middle layer L7 in which the green quantum dots 10G coordinated with the coordination groups 15 are dispersed is generated between the upper layer L5 and the lower layer L6.

[0091] Next, as shown in steps S43 and S47, steps for producing a red quantum dot dispersion liquid L4 and a green quantum dot dispersion liquid L8 are performed. The red quantum dot dispersion liquid L4 is an example of a first solution, and the second dispersion liquid L20 is an example of a second solution. In steps S43 and S47, only the middle layer portions L3 and L7 are recovered from the first dispersion liquid L10 and the second dispersion liquid L20. In steps S43 and S47, a portion of the red quantum dots 10R and the green quantum dots 10G extracted from the recovered middle layer portions L3 and L7 by precipitation using a technique such as centrifugation is dispersed in a solvent such as toluene. This produces a red quantum dot dispersion liquid L4 (first solution) and a green quantum dot dispersion liquid L8 (second solution). The degree of exchange of the organic ligand 13 with the precursor Z can be controlled by the stirring time and the concentration of the precursor Z being mixed. The smaller the particle size of the quantum dots 10, the greater the ratio of surface area to volume, and the more likely they are to aggregate due to removal of the organic ligands, and therefore unless the degree of exchange of the organic ligands 13 with the precursor Z is reduced (unless the amount of remaining organic ligands 13 is increased), they will aggregate and will no longer be able to be dispersed in a solvent. In the present disclosure, even for quantum dots 10 that emit short-wavelength light and have a small core diameter, increasing the particle size can reduce the organic ligands 13 to the same level as quantum dots 10 that emit long-wavelength light, thereby suppressing a decrease in brightness due to driving of the display device 1.

[0092] Returning to FIG. 15, in step S4, the red quantum dot dispersion liquid L4 and the green quantum dot dispersion liquid L8 produced in steps S43 and S47 are applied onto the hole transport layer 5.

[0093] The red quantum dot dispersion L4 applied to the hole transport layer 5 is treated (e.g., baked and patterned) to form a red light-emitting layer 6R. The green quantum dot dispersion L8 applied to the hole transport layer 5 is treated (e.g., baked and patterned) to form a green light-emitting layer 6G.

[0094] In step S5, an electron transport layer 7 is formed on the light-emitting layer 6. In step S5, the electron transport layer 7 is formed by depositing an electron transport material on the light-emitting layer 6 by, for example, a vapor deposition method or an inkjet method. In step S5, the electron transport layer 7 may be formed in common to all the sub-pixels 9, or may be formed for each sub-pixel 9.

[0095] In step S6, a cathode 8 is formed on the electron transport layer 7. In step S6, the cathode 8 is formed by depositing a cathode material by sputtering. In step S6, the cathode 8 may be formed in common to all the sub-pixels 9, or may be formed for each sub-pixel 9.

[0096] According to the display device 1, the protected state of the surface of the red quantum dot 10R can be made uniform to the protected state of the surface of the green quantum dot 10G, thereby realizing a display device in which the luminance reduction due to long-term driving is small in the red sub-pixel 9R and the green sub-pixel 9G, and the color change between the two sub-pixels 9R and 9G is small.

[0097] Furthermore, even if the average core diameter of the red quantum dots 10R and the average core diameter of the green quantum dots 10G are different, the protection state of the surfaces of the red quantum dots 10R and the green quantum dots 10G is uniform, thereby realizing a display device 1 with little change in color between the sub-pixels 9R and 9G.

[0098] Furthermore, the protection states of the surfaces of the red quantum dots 10R contained in the red light-emitting layer 6R that emits red light and the green quantum dots 10G contained in the green light-emitting layer 6G that emits green light are uniform, thereby realizing a display device 1 that is less likely to display reddish images over time.

[0099] Furthermore, since the red light-emitting layer 6R and the green light-emitting layer 6G each contain an organic substance, the red quantum dots 10R contained in the red light-emitting layer 6R and the green quantum dots 10G contained in the green light-emitting layer 6G do not aggregate, thereby making it possible to flatten the red light-emitting layer 6R and the green light-emitting layer 6G.

[0100] Furthermore, by configuring the green quantum dots 10G to have an average particle size of 8.0 nm to 50 nm, even if the amount of carbon atoms contained in the green light-emitting layer 6G is reduced, that is, even if the organic ligands 13 are sufficiently replaced with the second precursor Z, aggregation of the green quantum dots 10G in the green light-emitting layer 6G can be prevented.

[0101] Furthermore, by using the same shell material for the red quantum dots 10R and the green quantum dots 10G, the protection state of the surfaces of the red quantum dots 10R and the green quantum dots 10G can be made uniform.

[0102] Furthermore, by using the same inorganic material for the first inorganic medium 21 and the second inorganic medium 22, the same inorganic material is positioned at least partially around the red quantum dots 10R and the green quantum dots 10G, thereby making it possible to align the protection state of the surfaces of the red quantum dots 10R and the green quantum dots 10G.

[0103] Furthermore, by configuring the red subpixel 9R and the green subpixel 9G to have a common charge transport layer (hole transport layer 5 and electron transport layer 7), it is possible to make the carriers transported to the red light-emitting layer 6R and the green light-emitting layer 6G uniform and to make the deterioration states of the charge transport layers uniform, thereby reducing changes in color over driving time between the subpixels 9R and 9G.

[0104] [First Modification] In the above-described embodiment, the red quantum dots 10R contained in the red light-emitting layer 6R and the green quantum dots 10G contained in the green light-emitting layer 6G have the same average particle size, but this is not limited to this configuration. In the first modification, the average particle size of the green quantum dots 10AG contained in the green light-emitting layer 6G is larger than the average particle size of the red quantum dots 10AR contained in the red light-emitting layer 6R. In the following explanation, only the differences from the red quantum dots 10R and green quantum dots 10G according to Example 1 will be described.

[0105] 18 is a schematic diagram illustrating the configuration of quantum dots 10A according to the first modification. As shown in FIG. 18, the particle diameter D4 of the green quantum dots 10AG is larger than the particle diameter D2 of the red quantum dots 10AR. The ratio of the average particle diameter of the green quantum dots 10AG included in the green light-emitting layer 6G to the average particle diameter of the red quantum dots 10AR included in the red light-emitting layer 6R may be 1.0 or greater.

[0106] According to the configuration of the first modification, the surface area of ​​the green quantum dots 10AG can be increased. This increases the ratio of the surface area to the volume of the green quantum dots 10AG, making them less likely to aggregate. This makes it easier to align the protected state of the surfaces of the red quantum dots 10AR and the green quantum dots 10AG. In other words, even if the organic ligands 13 of the green quantum dots 10AG are replaced with the precursor Z to the same extent as in the red quantum dots 10AR, aggregation of the green quantum dots 10AG can be prevented.

[0107] [Second Modification] In the above-described embodiment, the quantum dots 10 are spherical, but are not limited to such a configuration. In the second modification, the quantum dots 10C may be cubic or rectangular. In the following description, only the differences from the quantum dots 10 according to the first embodiment will be described.

[0108] 19 and 20 are schematic diagrams illustrating the configuration of a quantum dot 10C according to the second modification. As shown in FIG. 19, the red quantum dot 10CR and the green quantum dot 10CG according to the second modification may be cubic. The red quantum dot 10CR and the green quantum dot 10CG may be rectangular. Although not shown, the blue quantum dot 10CB may be cubic or rectangular, similar to the red quantum dot 10CR and the green quantum dot 10CG.

[0109] As shown in Figure 20, each of the red quantum dots 10CR and the green quantum dots 10CG includes a

[100] plane. The squareness is the area ratio of a cross section parallel to the

[100] plane of each of the red quantum dots 10CR and the green quantum dots 10CG to the smallest square including said cross section. The average squareness of the red quantum dots 10CR is 0.83 to 1.0, and the average squareness of the green quantum dots 10CG is 0.83 to 1.0. The average squareness of the red quantum dots 10CR is the average of the squareness of one or more red quantum dots 10CR included in the red light-emitting layer 6R. The average squareness of the green quantum dots 10CG is the average of the squareness of one or more green quantum dots 10CG included in the green light-emitting layer 6G.

[0110] By setting the average squareness of the red quantum dots 10CR and the green quantum dots 10CG to 0.83 to 1.0, the first quantum dots and the second quantum dots can be formed into shapes that facilitate surface protection, i.e., the area on the surface of the red quantum dots 10CR and the green quantum dots 10CG over which the organic ligands 13 can be coordinated can be increased.

[0111] The difference between the average squareness of the red quantum dots 10CR and the average squareness of the green quantum dots 10CG is preferably less than 0.1. With this configuration, the shapes of the red quantum dots 10CR and the green quantum dots 10CG are substantially the same. This allows the surfaces of the red quantum dots 10CR and the green quantum dots 10CG to be uniformly protected.

[0112] Example 2 FIG. 21 is a schematic cross-sectional view showing an example of a display device 1A according to Example 2. Compared to the display device 1 according to Example 1, the display device 1A according to Example 2 has a green light-emitting layer 6G whose thickness is thinner than the red light-emitting layer 6R. As shown in FIG. 21 , the red sub-pixel 9R and the green sub-pixel 9G in the display device 1A share a common charge transport layer (a hole transport layer 5 and an electron transport layer 7). In the display device 1A, the thickness TG of the green light-emitting layer 6G is thinner than the thickness TR of the red light-emitting layer 6R. This configuration can improve the carrier balance in the green light-emitting layer 6G. Note that the thickness TB of the blue light-emitting layer 6B may be thicker than the thickness TG of the green light-emitting layer 6G.

[0113] 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.

[0114] REFERENCE SIGNS LIST 1 display device 4 anode 5 hole transport layer (charge transport layer) 6F 6R red light-emitting layer (first light-emitting layer) 6S 6G green light-emitting layer (second light-emitting layer) 7 electron transport layer (charge transport layer) 8 cathode P1 9R red subpixel (first subpixel) P2 9G green subpixel (second subpixel) Q1 10R red quantum dot (first quantum dot) Q2 10G green quantum dot (second quantum dot) B1 21 first inorganic medium B2 22 second inorganic medium J 13 organic ligand Y 14 coordination group C1 C2 core K1 K2 shell

Claims

1. A display device comprising: a first sub-pixel having a first light-emitting layer including first quantum dots; and a second sub-pixel having a second light-emitting layer including second quantum dots, wherein the first quantum dots and the second quantum dots have a core-shell structure with the same core material; the emission peak wavelength of the first light-emitting layer is greater than the emission peak wavelength of the second light-emitting layer; the first light-emitting layer includes a first inorganic medium; and the second light-emitting layer includes a second inorganic medium; and the ratio of the particle size of the second quantum dots to the particle size of the first quantum dots is 0.7 or greater.

2. The display device according to claim 1, wherein at least a portion of the first inorganic medium is located between a plurality of quantum dots including the first quantum dot, and at least a portion of the second inorganic medium is located between a plurality of quantum dots including the second quantum dot.

3. The display device according to claim 1 or 2, wherein the value of the ratio is greater than 1.

0.

4. The display device according to any one of claims 1 to 3, wherein the shell thickness of the second quantum dots is greater than the shell thickness of the first quantum dots.

5. The display device according to any one of claims 1 to 4, wherein the first light-emitting layer and the second light-emitting layer each contain an organic material.

6. The display device according to claim 5, wherein the first inorganic medium and the second inorganic medium are silicon compounds, and the molar ratio of carbon atoms to silicon atoms in the second light-emitting layer divided by the molar ratio of carbon atoms to silicon atoms in the first light-emitting layer is 0.7 to 1.

3.

7. The display device according to claim 5, wherein the first inorganic medium and the second inorganic medium are sulfur compounds, and the molar ratio of carbon atoms to sulfur atoms in the second light-emitting layer divided by the molar ratio of carbon atoms to sulfur atoms in the first light-emitting layer is 0.7 to 1.

3.

8. The display device of claim 5, wherein the first light-emitting layer and the second light-emitting layer each include an organic ligand.

9. The display device of claim 5, wherein the second light-emitting layer includes a coordinating group located between the second quantum dots and the second inorganic medium.

10. The display device of claim 9, wherein said second inorganic medium and said coordinating group are bonded.

11. The display device of claim 9, wherein the second inorganic medium surrounds the second quantum dots.

12. The display device according to any one of claims 1 to 11, wherein the particle diameter of the second quantum dots is 8.0 nm to 50 nm.

13. The display device according to any one of claims 1 to 12, wherein the shell materials of the first quantum dots and the second quantum dots are the same.

14. The display device of claim 13, wherein the shell material comprises zinc sulfide or zinc sulfide selenide.

15. The display device according to any one of claims 1 to 14, wherein the first inorganic medium and the second inorganic medium are made of the same inorganic material.

16. The display device according to claim 15, wherein the inorganic material is an oxide or a sulfide.

17. The display device according to claim 16, wherein the inorganic material is silicon oxide.

18. The display device according to claim 16, wherein the inorganic material is zinc sulfide or zinc magnesium sulfide.

19. The display device according to any one of claims 1 to 18, wherein the first sub-pixel and the second sub-pixel have a common functional layer.

20. The display device according to claim 19, wherein the common functional layer is an electron transport layer or a hole transport layer.

21. The display device according to any one of claims 1 to 20, wherein the second light-emitting layer is thinner than the first light-emitting layer.

22. The display device according to any one of claims 1 to 21, wherein the first quantum dots and the second quantum dots each include a [100] plane, and the squareness is defined as the ratio of the area of ​​a cross section parallel to the [100] plane to a square including the cross section, and the squareness of the first quantum dots is 0.83 to 1.0, and the squareness of the second quantum dots is 0.83 to 1.

0.

23. The display device according to claim 22, wherein the difference between the squareness of the first quantum dots and the squareness of the second quantum dots is less than 0.

1.

24. The display device according to any one of claims 1 to 23, wherein the core diameter of the second quantum dots is smaller than the core diameter of the first quantum dots.

25. The display device according to any one of claims 1 to 24, wherein the first light-emitting layer emits red light and the second light-emitting layer emits green light.

26. A display device according to any one of claims 1 to 25, wherein the ratio of the average particle size of the plurality of quantum dots including the second quantum dots to the average particle size of the plurality of quantum dots including the first quantum dots is 0.7 or greater.

27. A method for manufacturing a display device, comprising: forming a first light-emitting layer using a first solution containing first quantum dots; and forming a second light-emitting layer using a second solution containing second quantum dots; wherein the peak emission wavelength of the first light-emitting layer is greater than the peak emission wavelength of the second light-emitting layer; the first quantum dots and the second quantum dots have a core-shell structure with the same core material; the first solution contains a plurality of organic ligands that coordinate to the first quantum dots; the second solution contains a plurality of organic ligands that coordinate to the second quantum dots; and the ratio of the particle size of the second quantum dots to the particle size of the first quantum dots is 0.7 or greater.

28. The method for manufacturing a display device according to claim 27, wherein the first solution includes a first inorganic medium positioned around the first quantum dots, and the second solution includes a second inorganic medium positioned around the second quantum dots.

29. The method for manufacturing a display device according to claim 28, comprising the steps of: applying a first solution to an underlayer; and applying a second solution to the underlayer.

30. A method for manufacturing a display device according to any one of claims 27 to 29, wherein the first solution is produced using a portion of a mixture of a liquid containing first quantum dots coordinated with a plurality of organic ligands and a nonpolar solvent, and a liquid containing a first precursor and a polar solvent; and the second solution is produced using a portion of a mixture of a liquid containing second quantum dots coordinated with a plurality of organic ligands and a nonpolar solvent, and a liquid containing a second precursor and a polar solvent.

31. The method for manufacturing a display device according to claim 29, wherein the underlayer is a hole injection layer or a hole transport layer.

32. The method for manufacturing a display device according to claim 30, wherein the part of the mixture is a middle layer part of the mixture.

33. The method for manufacturing a display device described in claim 30, wherein the first solution includes a first inorganic medium positioned around the first quantum dots, the second solution includes a second inorganic medium positioned around the second quantum dots, the first precursor and the second precursor have a methoxysilane group, and the first inorganic medium and the second inorganic medium are silicon oxide.

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