Light-emitting element and display device

Abstract

A light-emitting element (2) comprises a light-emitting layer (23) positioned between an anode (21) and a cathode (25). The light-emitting layer contains quantum dots (30) and an adduct (40) containing a metal oxide. In a cross-section parallel to the film thickness direction (DT) of the light-emitting layer, the ratio of the cross-sectional area of one quantum dot to the minimum value of the area of a square that contains therein the entirety of the cross-section of that quantum dot is referred to as the first ratio of that quantum dot. In said cross-section, the ratio of the cross-sectional area of one quantum dot to the minimum value of the area of an equilateral triangle that contains therein the entirety of the cross-section of that quantum dot is referred to as the second ratio of that quantum dot. Of quantum dots in said cross-section, the total of the proportion of first quantum dots (31) for which the first ratio is not less than 0.83 and the proportion of second quantum dots for which the second ratio is not less than 0.73 is not less than 50%.

Description

Light-emitting element, display device

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

[0002] Non-Patent Document 1 discloses a quantum dot structure having quantum dots (semiconductor nanoparticles) in a matrix containing silicon oxide (silica) as a light emitter used in a light-emitting device. The structure having quantum dots in a matrix protects the quantum dots with the matrix, 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] Even in the quantum dot structure described in Non-Patent Document 1, it is conceivable to improve the reliability of the quantum dots by disposing a ligand that coordinates to the quantum dots between the quantum dots and the matrix. However, the quantum dots described in Non-Patent Document 1 have an approximately spherical shape, and polar and non-polar surfaces are formed on the outermost periphery of the quantum dots. Since the coordinating functional group of the ligand may have difficulty forming a coordinate bond with the non-polar surface, it is difficult to efficiently coordinate the ligand to the quantum dots described in Non-Patent Document 1.

[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, wherein the light-emitting layer includes quantum dots and an additive containing a metal oxide, wherein in any cross-section of the light-emitting layer, a ratio of the cross-sectional area of ​​one quantum dot to the minimum area of ​​a square that contains the entire cross-section of the quantum dot is defined as a first ratio of the quantum dot, and a ratio of the cross-sectional area of ​​one quantum dot to the minimum area of ​​an equilateral triangle that contains the entire cross-section of the quantum dot is defined as a second ratio of the quantum dot, and 50% or more of the quantum dots in any cross-section of the light-emitting layer are at least one of first quantum dots having the first ratio of 0.83 or more and second quantum dots having the second ratio of 0.73 or more.

[0006] According to the configuration of one aspect of the present disclosure, the reliability of the quantum dots is improved by further increasing the number of ligands coordinated to the quantum dots contained in the light-emitting layer of the light-emitting device.

[0007] 1 is a schematic cross-sectional side view of a display device according to embodiment 1. FIG. 2 is a schematic diagram of a display device according to embodiment 1. FIG. 3 is a schematic enlarged view of a light-emitting layer in the cross section of the display device according to embodiment 1. FIG. 4 is a schematic diagram illustrating the crystal structure and crystal planes of a quantum dot material in embodiment 1. FIG. 5 is a schematic perspective view showing a first quantum dot in embodiment 1. FIG. 6 is a schematic diagram showing an example of a cross section of a first quantum dot in embodiment 1. FIG. 7 is a schematic diagram showing an addition filling a space between quantum dots in embodiment 1. FIG. 8 is a schematic enlarged view of a quantum dot and the vicinity of the quantum dot in the cross section of the display device according to embodiment 1. FIG. 9 is a schematic cross-sectional side view of a display device according to embodiment 2. FIG. 10 is a schematic enlarged view of a light-emitting layer in the cross section of the display device according to embodiment 2. FIG. 11 is a schematic perspective view showing a second quantum dot in embodiment 2. FIG. 12 is a schematic diagram showing an example of a cross section of the second quantum dot in embodiment 2. FIG. 13 is a schematic cross-sectional side view of a display device according to embodiment 3. FIG. 14 is a schematic enlarged view of a light-emitting layer in the cross section of the display device according to embodiment 3.

[0008] [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 drawn to 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, components with different hatching have the same configuration as described above. Furthermore, in each drawing of the present disclosure, when two components have substantially the same shape but different compositions, etc., they may be assigned different reference numerals but the same hatching.

[0009] 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.

[0010] 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. In other words, the cross section shown in Fig. 1 is a cross section parallel to the film thickness direction DT of the light-emitting layer 23, which will be described later. 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.

[0011] 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 a 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."

[0012] The light-emitting element 2 includes an anode 21 as a first electrode, a hole transport layer 22, a light-emitting layer 23, an electron transport layer 24, and a cathode 25 as a second electrode, in this order from the substrate 3 side. The anode 21 is electrically connected to the TFT of the substrate 3.

[0013] <Outline of Light-Emitting Element> The structure of each layer of the light-emitting element 2 will be described in more detail below.

[0014] 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.

[0015] 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.

[0016] The hole transport layer 22 is a layer containing a hole transport material that transports holes from the anode 21 to the light-emitting layer 23. In this embodiment, the material of the hole transport layer 22 can be an organic or inorganic material that has been conventionally used in light-emitting devices including quantum dots. For example, conductive compounds such as polyvinylcarbazole (PVK), [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD), 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylenevinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB) can be used as organic materials for the hole transport layer 22. Examples of inorganic materials for the hole transport layer 22 include molybdenum oxide, NiO, and 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.

[0017] 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.

[0018] 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 an intermediate layer, which may be, for example, an electron blocking layer between the hole transport layer 22 and the light-emitting layer 23, or a hole blocking layer 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.

[0019] <Light-Emitting Layer: Overview> 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 light-emitting layer 23 in the cross section shown in Fig. 1, and in particular, an enlarged schematic diagram of region E1 shown in Fig. 1. In other words, Fig. 3 is an enlarged schematic diagram of a cross section parallel to the thickness direction DT of the light-emitting layer 23.

[0020] Note that the "thickness direction DT of the light-emitting layer 23" in the present disclosure may be, for example, the normal direction of the lower surface 23U, which is the end surface of the light-emitting layer 23 on the anode 21 side, or the normal direction of the upper surface 23T, which is the end surface of the light-emitting layer 23 on the cathode 25 side. In this embodiment, the lower surface 23U and the upper surface 23T of the light-emitting layer 23 are parallel to the in-plane direction of the substrate 3. However, this is not limiting, and the lower surface 23U and the upper surface 23T of the light-emitting layer 23 do not have to be parallel.

[0021] Furthermore, in the present disclosure, the term "cross section parallel to the thickness direction DT of the light-emitting layer 23" does not refer only to a cross section that is completely parallel to the thickness direction DT. For example, in the present disclosure, the term "cross section parallel to the thickness direction DT of the light-emitting layer 23" may include a cross section of the light-emitting layer 23 obtained using a processing device for observing the cross section of the light-emitting layer 23. In other words, the difference between the cross section and the thickness direction DT may be included in the range of error in the angle of the cross section of the light-emitting layer 23 obtained using the processing device in settings for obtaining a cross section of the light-emitting layer 23 parallel to the thickness direction DT. Specifically, when the cross section of the light-emitting layer 23 deviates from the thickness direction DT by approximately ±5°, the cross section may be considered to be a cross section parallel to the thickness direction DT.

[0022] As shown in FIGS. 1 and 3, the light-emitting layer 23 according to this embodiment includes a plurality of quantum dots 30 and an additive 40 .

[0023] <Light-Emitting Layer: Quantum Dots> 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 light emitted from the quantum dots 30 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain 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 material of the quantum dots 30 will be described in detail with reference to Fig. 4. Fig. 4 is a schematic diagram illustrating the crystal structure and crystal planes of the material of the quantum dots 30.

[0025] The material of the quantum dot 30 according to this embodiment, particularly the material on the outermost surface side of the quantum dot 30, includes a crystal C having a zincblende-type structure as a crystal structure. The crystal C has atoms A1 and A2 that are different from each other. Furthermore, as shown in the schematic diagram 401 of FIG. 4, for example, the crystal C has a structure in which atoms A1 and A2 having a face-centered cubic structure are combined. In particular, when the lattice constant of the crystal C is 1 in the xyz space, the crystal C has atoms A1 having a face-centered cubic structure and atoms A2 having a face-centered cubic structure whose coordinates are shifted by (1 / 4, 1 / 4, 1 / 4) relative to each atom A1.

[0026] In this disclosure, "atom" does not only mean that an atom exists as a single atom. In this disclosure, "atom" also includes an atom that exists in the form of a molecule having two or more atoms, including the atom in question and another atom, an atom that exists in the form of a complex, an atom that exists in the form of a compound, or an atom that exists in the form of an ion. However, in this disclosure, "atom" does not limit the form of existence of other atoms.

[0027] The crystal C may have a specific crystal plane on its outermost surface, and may also grow on a specific crystal plane during the growth of the crystal C. Hereinafter, in this disclosure, the orientation of a crystal plane is represented by Miller indices (hkl) using integers h, k, and l. In particular, in this disclosure, a crystal plane oriented according to the Miller indices (hkl) is referred to as an (hkl) plane.

[0028] For example, as shown in the schematic diagram 402 of FIG. 4 , the crystal C may have a crystal plane K of the (100) plane. An atom A1 is located on the crystal plane K. Hereinafter, a crystal plane K is defined as a crystal plane that is equivalent to the crystal plane K of the (100) plane and on which only one of the atoms A1 and A2 is located. In other words, the crystal plane K also includes the (010) plane, the (001) plane, the (−100) plane, the (0-10) plane, and the (00-1) plane.

[0029] For example, as shown in the schematic diagram 403 of FIG. 4 , the crystal C may have a crystal plane L of the (111) plane. An atom A1 is located on the crystal plane L. Hereinafter, a crystal plane L is defined as a crystal plane that is equivalent to the crystal plane L of the (111) plane and on which only one of the atoms A1 and A2 is located. In other words, the crystal plane L also includes the (-111) plane, the (1-11) plane, the (1-1-1) plane, the (-11-1) plane, the (-1-11) plane, the (-1-1-1) plane, and the (-1-1-1) plane.

[0030] For example, as shown in the schematic diagram 404 of FIG. 4 , the crystal C may have a crystal plane M of the (110) plane. Atoms A1 and A2 are located on the crystal plane M. Hereinafter, a crystal plane that is equivalent to the crystal plane M of the (110) plane and on which both atoms A1 and A2 are located will be referred to as the crystal plane M. In other words, the crystal plane M also includes the (-110) plane, the (1-10) plane, the (-1-10) plane, the (011) plane, the (01-1) plane, the (0-11) plane, the (0-1-1) plane, the (101) plane, the (-101) plane, the (10-1) plane, and the (-10-1) plane.

[0031] The quantum dots 30 may have conventionally known materials and structures, as long as they have zincblende crystals located on the outermost surface as described above. For example, the quantum dots 30 may contain materials used for the core and shell 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 from multiple layers containing multiple different materials.

[0032] 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.

[0033] The light-emitting layer 23 has a thickness of 1000 nm or less in a plane direction perpendicular to the thickness direction at any position in the thickness direction. ２ The light-emitting layer 23 may contain one or more quantum dots 30 per layer. In this case, the light-emitting layer 23 generally contains quantum dots 30 at a concentration sufficient to function as a light-emitting layer of a light-emitting element.

[0034] <Light-emitting layer: first quantum dot: crystal plane> The light-emitting layer 23 according to this embodiment includes at least one first quantum dot 31 as the quantum dot 30. In particular, the proportion of the first quantum dot 31 among the quantum dots 30 in a cross section parallel to the thickness direction DT of the light-emitting layer 23 is 50% or more. The structure of the first quantum dot 31 will be described in more detail with reference to Fig. 5 . Fig. 5 is a schematic perspective view of the first quantum dot 31 according to this embodiment.

[0035] For example, as shown in the first quantum dot 31A in FIG. 5 , the first quantum dot 31 is a cubic quantum dot having a crystal face K having a (100) plane and a crystal face equivalent to the crystal face K on its outermost surface. Specifically, the first quantum dot 31A may have the crystal face K on its outermost surface, which may be a (100) plane, a (−100) plane, a (010) plane, a (0-10) plane, a (001) plane, or a (00-1) plane. Alternatively, as shown in the first quantum dot 31B in FIG. 5 , the first quantum dot 31 may have a crystal face L and a crystal face M in addition to the crystal face K. However, even in this case, the ratio of the total area of ​​the crystal faces K to the total area of ​​the outermost surface of the first quantum dot 31B is relatively high. Note that FIG. 5 indicates some of the crystal faces on the outermost surface of the first quantum dot 31 with symbols, and the crystal face K located on the back side of the first quantum dot 31 is also shown.

[0036] As described above, since only one of the two types of atoms is located on crystal face K, a bias in the electron cloud occurs on crystal face K, and thus a substantial local charge occurs on crystal face K. Therefore, crystal face K is a polar face having polarity. On the other hand, since both types of atoms are located on crystal face M, the bias in the electron cloud on crystal face M is reduced, and thus crystal face M becomes closer to electrical neutrality. Therefore, crystal face M is a non-polar face with less polarity than crystal face K.

[0037] <Light-Emitting Layer:First Quantum Dots:First Ratio> Here, as shown in Fig. 3 , in a cross section parallel to the thickness direction DT of the light-emitting layer 23, the square SQ is defined as the square with the smallest area that contains all of the cross sections of the first quantum dots 31. In this case, the area of ​​the square SQ is the same as the smallest value of the area of ​​the squares that contain all of the cross sections of the first quantum dots 31. The relationship between the cross sections of the first quantum dots 31 and the square SQ in this embodiment will be described in detail with reference to Fig. 6 as well. Fig. 6 is a schematic diagram showing an example of the cross section of the first quantum dots 31.

[0038] 6 shows an example of a cross section of the first quantum dot 31 in a cross section that is parallel to the film thickness direction DT of the light-emitting layer 23 and approximately parallel to one of the crystal planes K. The first quantum dot 31 shown in FIG. 6 has a crystal plane K and a crystal plane M, and the cross section shown in FIG. 6 passes through the crystal plane K and the crystal plane M of the first quantum dot 31.

[0039] In this case, the higher the ratio of the length of the crystal plane K to the perimeter of the cross section of the first quantum dot 31, the higher the ratio of the total area of ​​the crystal plane K to the total area of ​​the outermost surface of the first quantum dot 31. Furthermore, the higher the ratio of the length of the crystal plane K to the perimeter of the cross section of the first quantum dot 31, the closer the outer shape of the first quantum dot 31 becomes to a square; in other words, the higher the ratio of the cross-sectional area of ​​the first quantum dot 31 to the area of ​​the square SQ. Therefore, the higher the ratio of the total area of ​​the crystal plane K to the total area of ​​the outermost surface of the first quantum dot 31, the higher the ratio of the cross-sectional area of ​​the first quantum dot 31 to the area of ​​the square SQ.

[0040] A first ratio is the ratio of the cross-sectional area of ​​the quantum dots 30 to the area of ​​the square SQ in a cross section parallel to the thickness direction DT of the light-emitting layer 23. In the present disclosure, the first ratio of the first quantum dots 31 in a cross section parallel to the thickness direction DT of the light-emitting layer 23 is 0.83 or more.

[0041] 6 , assume that the cross section of the first quantum dot 31 is substantially parallel to any one of the crystal planes K and that the first ratio of the first quantum dot 31 is 0.83 or more. In this case, the total length of the crystal planes K is equal to or greater than the total length of the crystal planes M around the periphery of the first quantum dot 31 in the cross section.

[0042] Therefore, in a cross section parallel to the thickness direction DT of the light-emitting layer 23, the first ratio of the first quantum dots 31 is 0.83 or more, and therefore the ratio of the total area of ​​the crystal planes K to the total area of ​​the outermost surface of the first quantum dots 31 becomes high. In other words, the ratio of the area of ​​the polar planes to the area of ​​the nonpolar planes on the outermost surface of the first quantum dots 31 becomes high.

[0043] Therefore, when it is confirmed that the first ratio of quantum dots 30 is 0.83 or more in a cross section of light-emitting layer 23 parallel to the thickness direction DT, the quantum dots 30 may be considered to be first quantum dots 31. Note that light-emitting layer 23 may include quantum dots 30C whose first ratio is less than 0.83 in a cross section of light-emitting layer 23 parallel to the thickness direction DT.

[0044] Note that the above discussion is based on a cross section parallel to the crystal plane K of the first quantum dots 31, and the first ratio may decrease depending on the angle of the cross section relative to the crystal plane K of the first quantum dots 31. However, even in this case, the tendency remains that the ratio of the cross-sectional area of ​​the first quantum dots 31 to the area of ​​the square SQ increases as the ratio of the total area of ​​the crystal planes K to the total area of ​​the outermost surfaces of the first quantum dots 31 increases. Therefore, based on the above, if 50% or more of the first quantum dots 31 among the identified quantum dots 30 are confirmed to have a first ratio of 0.83 or more, it can be considered that at least 50% of the quantum dots 30 in the light-emitting layer 23 are first quantum dots 31.

[0045] The first proportion of quantum dots 30 in a cross section parallel to the thickness direction DT of the light-emitting layer 23 may be confirmed, for example, as follows. First, the light-emitting layer 23 is processed to expose a cross section parallel to the thickness direction DT, and then the cross section is observed by EDX (energy dispersive X-ray spectroscopy) using an electron microscope such as a TEM (transmission electron microscope). Next, approximately 10 to 20 quantum dots 30 are identified from the obtained electron image, and then the outer shape of each quantum dot 30 is identified. In this way, the first proportion of each quantum dot 30 can be calculated based on the outer shape of each identified quantum dot 30.

[0046] <Light-Emitting Layer: Additive> Returning to FIGS. 1 and 3 , the additive 40 is located around the quantum dots 30. In particular, the additive 40 may be located between at least two quantum dots 30. In the present disclosure, the term "surrounding" refers to a region extending around an object (here, the quantum dots 30), and the distance from the object is not particularly limited. However, in the present disclosure, the term "surrounding" may refer to a region extending outward from the surface of the object to a given width, or may refer to a region from the quantum dots 30 having a width approximately within the distance between adjacent quantum dots 30. In addition, in the present disclosure, "disposed around" does not necessarily mean continuously surrounding the object, but also includes cases where the additive is intermittently surrounding the object and cases where the additive is disposed in only a portion of the region extending around the object.

[0047] The additive 40 has, for example, insulating properties. The additive 40 includes, for example, a metal oxide, and in particular, the metal oxide included in the additive 40 includes a metal atom and an oxygen atom. In the present disclosure, the metal atoms included in the metal oxide of the additive 40 include oxides having atoms that may generally be referred to as semimetal atoms, including silicon (Si), boron (B), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te).

[0048] For example, the additive 40 may comprise, for example, silicon oxide; in other words, assuming x such that 0<x, the additive 40 may comprise, for example, SiO ｘ In particular, the additive 40 may include silica (SiO ２ SiO, which has insulating properties and in which silicon atoms and oxygen atoms are strongly bonded, may be included.ｘ By including the additive 40, the light-emitting element 2 can improve the protective effect of the additive 40 on the quantum dots 30. ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), beryllium fluoride (BeF ２ ), arsenic sulfide (As ２ S ３ ), silicon selenide (SiSe ２ ), germanium sulfide (GeS), titanium oxide (TiO ２ ), tellurium oxide (TeO ２ ), aluminum oxide (Al ２ O ３ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ ), lead oxide (PbO), silicon nitride (Si ３ N ４ ) may contain one or more selected from the group consisting of. The chemical formulas written in parentheses after the compound names are representative examples. The composition ratios written in the chemical formulas may be stoichiometric, but do not necessarily have to be stoichiometric.

[0049] In particular, the additive 40 according to this embodiment may fill the space between at least two quantum dots 30. In this case, the additive 40 can be considered to include an inorganic matrix filling the space between at least two quantum dots 30. The material filling the spaces between the quantum dots 30 will be described in more detail with further reference to FIG. 7. Schematic diagrams 701 and 702 in FIG. 7 are schematic diagrams showing the material filling the spaces between the quantum dots 30. In particular, the schematic diagrams 701 and 702 respectively show two examples of a set P of two first quantum dots 31 and the region (space) R between them shown in FIG. 3. In particular, the schematic diagrams 701 and 702 respectively show a set P1 and a set P2, which are examples of sets of a first quantum dot 31A and a first quantum dot 31B.

[0050] In this specification, "a member filling the spaces between the first quantum dots 31" means that the member fills at least the region R between the first quantum dots 31A and 31B, as shown in the schematic diagram 701 of the set P1 in Fig. 7. The region R is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of the first quantum dots 31A and 31B and the opposing peripheries of the first quantum dots 31A and 31B in the cross section of the light-emitting layer 23. Therefore, as shown in the schematic diagram 702 of the set P2 in Fig. 7, the region R can exist even if the first quantum dots 31A and 31B are close to each other, and the member fills the region R.

[0051] The expression "a material fills the spaces between the plurality of first quantum dots 31" does not necessarily mean that the region R between the first quantum dots 31A and 31B is made entirely of a material. For example, the region R between the first quantum dots 31A and 31B may contain a material such as a ligand (described later) which is not shown in FIG. 3. 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 ligand (described later) to the total weight including the region R may be less than 5%.

[0052] 7 has been described with reference to an example in which the addition 40 fills the space between two first quantum dots 31, but the configuration of the addition 40 is not limited to this. For example, the addition 40 may fill the space between a first quantum dot and a quantum dot 30 other than the first quantum dot 31, or the space between two quantum dots 30 other than the first quantum dot 31.

[0053] Referring back to FIG. 3, the addition 40 is formed at any position in the thickness direction DT of the light-emitting layer 23 by 1000 nm in a direction perpendicular to the thickness direction DT of the light-emitting layer 23. ２ In the light-emitting layer 23, the quantum dots 30 may be encapsulated in the continuous film of the additive 40. In other words, the quantum dots 30 may be encapsulated in the continuous film of the additive 40.

[0054] For example, when 60% or more of the surface of 80% or more of the quantum dots 30 constituting the light-emitting layer 23 is in contact with the continuous film of the additive 40, the quantum dots 30 contained in the light-emitting layer 23 can be said to be encapsulated in the additive 40. Thus, the light-emitting layer 23 containing quantum dots 30 encapsulated in the additive 40 can prevent impurities such as water or oxygen from penetrating to the surface of the quantum dots 30, which could cause the surface of the quantum dots 30 to oxidize. Furthermore, when the light-emitting layer 23 containing quantum dots 30 encapsulated in the additive 40 contains a ligand, the additive 40 encapsulates the quantum dots 30 containing the ligand, thereby fixing the position of the ligand in the light-emitting layer 23. Therefore, the light-emitting layer 23 can prevent the ligand from being detached from the quantum dots 30, thereby reducing the protective effect on the surface of the quantum dots 30. As a result, the light-emitting device 2 including the light-emitting layer 23 containing quantum dots 30 encapsulated in the additive 40 has improved light-emitting characteristics and a longer lifespan.

[0055] The addition 40 may be located, for example, all around the quantum dot 30. For example, as shown in Fig. 3, in any cross section passing through any quantum dot 30, the addition 40 may be located all around the quantum dot 30. Here, "the addition 40 is located all around the quantum dot 30" may mean that the addition 40 is located over 90% or more of the periphery of the quantum dot 30. Furthermore, as shown in Fig. 3, the surface of the quantum dot 30 and the addition 40 may come into contact with each other.

[0056] However, the additions 40 are not limited to the above and may be formed only on a portion of the periphery of the quantum dots 30. For example, the additions 40 may be discontinuous, typically having discontinuities of 8 nm or more. The light-emitting layer 23 may include, for example, a plurality of discontinuous additions 40 around one quantum dot 30. In this case, the thickness of the additions 40 may be 1 nm or more in order to improve the protective effect of the additions 40 on the quantum dots 30. Furthermore, the thickness of the additions 40 may be 3 nm or less so that carriers can tunnel through the additions 40 and be efficiently injected from the periphery of the quantum dots 30 into the interior of the quantum dots 30. This allows the light-emitting layer 23 to both improve the protective effect on the surfaces of the quantum dots 30 and improve the efficiency of current injection into the quantum dots 30, thereby achieving both high light-emitting efficiency and a long lifespan for the light-emitting element 2.

[0057] <Light-Emitting Layer: Ligand> The light-emitting layer 23 may further include a ligand. The ligand will be described in more detail with reference to Fig. 8. Fig. 8 is a schematic diagram showing an enlarged view of one first quantum dot 31 and the vicinity of the first quantum dot 31 in a cross section parallel to the thickness direction DT of the light-emitting layer 23. In particular, Fig. 8 shows an enlarged view of region E2 shown in Fig. 3.

[0058] 8, the light-emitting layer 23 may include a ligand 41, which is not shown in FIG. 3. The ligand 41 is located near the quantum dots 30 including the first quantum dots 31 or near the adduct 40.

[0059] The ligand 41 may be an organic ligand containing carbon and may further contain one or more of hydrogen, nitrogen, and oxygen. In other words, the light-emitting layer 23 may have a carbon atom between the first quantum dot 31 and the adduct 40. The ligand 41 may have, for example, a carbon chain and a coordinating functional group located at one end of the carbon chain. In this case, the coordinating functional group of the ligand 41 may have polarity, and may form a coordinate bond with the outermost surface of the quantum dot 30 due to the polarity.

[0060] When a cross-sectional observation of the light-emitting layer 23 according to this embodiment confirms that the distance between the quantum dots 30 and the ligands 41 is 3 nm or less, the ligands 41 may be considered to be coordinated to the quantum dots 30. Alternatively, when it is confirmed that the quantum dots 30 and the ligands 41 are in contact with each other, the ligands 41 may be considered to be coordinated to the quantum dots 30.

[0061] The end of the ligand 41 opposite to the coordination functional group may be located in the vicinity of the adduct 40, and further, the ligand 41 may be chemically bonded to the adduct 40. When it is confirmed that the distance between the adduct 40 and the ligand 41 is 3 nm or less in cross-sectional observation of the light-emitting layer 23 according to this embodiment, the ligand 41 may be considered to be bonded to the adduct 40. Alternatively, when it is confirmed that the adduct 40 and the ligand 41 are in contact with each other, the ligand 41 may be considered to be bonded to the adduct 40.

[0062] <Effects of Polar Surfaces of First Quantum Dots> As described above, the first quantum dots 31 have a high ratio of the area of ​​polar surfaces to the area of ​​nonpolar surfaces on their outermost surfaces. In addition, because the coordination functional group of the ligand 41 has polarity, the ligand 41 is more likely to form a coordination bond with the polar crystal surface K than with the nonpolar crystal surface M. Therefore, the ligand 41 is more efficiently coordinated to the first quantum dots 31, which have a high ratio of the total area of ​​the crystal surfaces K to the total area of ​​their outermost surfaces.

[0063] As will be described later, the method of forming the light-emitting layer 23 may include, for example, applying a dispersion liquid in which a plurality of quantum dots 30 are dispersed in a solvent. In this case, the ligands 41 are coordinated to each quantum dot 30, thereby improving the dispersibility of each quantum dot 30 in the dispersion liquid and reducing aggregation of the quantum dots 30. By forming the light-emitting layer 23 using a dispersion liquid in which aggregation of the quantum dots 30 is reduced, aggregation of the quantum dots 30 is also reduced in the light-emitting layer 23.

[0064] The reduction in aggregation of the quantum dots 30 in the light-emitting layer 23 reduces the deactivation of the quantum dots 30 and reduces the energy transfer of excitons between the quantum dots 30, which is a contributing factor to the deactivation process, thereby improving the luminous efficiency of the light-emitting layer 23. Furthermore, the reduction in aggregation of the quantum dots 30 in the light-emitting layer 23 reduces cracks in the light-emitting layer 23 caused by stress concentrated near the aggregated quantum dots 30, thereby improving the reliability of the light-emitting layer 23.

[0065] In this embodiment, the light-emitting layer 23 includes the first quantum dots 31 having a high ratio of the total area of ​​the crystal planes K to the total area of ​​the outermost surface. Therefore, the light-emitting element 2 including the light-emitting layer 23 has improved luminous efficiency.

[0066] Furthermore, since the crystal face K of the first quantum dot 31 and the ligand 41 form a stronger coordinate bond, the light-emitting layer 23 reduces the separation of the ligand 41 from the first quantum dot 31 between the first quantum dot 31 and the adduct 40. This reduces the deterioration of the first quantum dots 31 contained in the light-emitting layer 23 of the light-emitting element 2, improving the reliability of the light-emitting layer 23.

[0067] In addition, the light-emitting layer 23 according to this embodiment includes an additive 40 positioned between the quantum dots 30. Therefore, the additive 40 in the light-emitting element 2 can reduce the penetration of foreign substances such as moisture into the quantum dots 30 in the light-emitting layer 23, thereby reducing deterioration of the quantum dots 30. Furthermore, the additive 40 according to this embodiment has insulating properties. Therefore, the light-emitting element 2 can more efficiently reduce the transfer of energy of excess electrons to the quantum dots 30, as described above, thereby further reducing deterioration of the quantum dots 30. Because the additive 40 is positioned between the quantum dots, the light-emitting element 2 further improves the protective effect of the additive 40 on each quantum dot 30. Furthermore, because the additive 40 fills the spaces between the quantum dots, the light-emitting element 2 further improves the protective effect of the additive 40 on each quantum dot 30.

[0068] The first quantum dots 31 and the additives 40 may be in direct contact with each other without the ligands 41. Even in this case, the ratio of the total area of ​​the crystal faces K to the total area of ​​the outermost surfaces of the first quantum dots 31 is high, thereby improving the intimate contact between the first quantum dots 31 and the additives 40. As a result, even in the above case, the additives 40 contained in the light-emitting layer 23 of the light-emitting element 2 improve the protective effect of the first quantum dots 31, thereby improving the reliability of the light-emitting layer 23.

[0069] Therefore, the light-emitting element 2 according to this embodiment improves the luminous efficiency of the light-emitting layer 23 while reducing deterioration of the quantum dots 30 in the light-emitting layer 23. The display device 1 including the light-emitting element 2 achieves a longer lifespan and reduced power consumption.

[0070] In a cross section parallel to the thickness direction DT of the light-emitting layer 23, the average value of the first ratio of each quantum dot 30 may be 0.83 or more. In this case, the ratio of the first quantum dots 31 to the quantum dots 30 contained in the light-emitting layer 23 becomes higher. Alternatively, in this case, the ratio of the area of ​​the crystal plane K to the area of ​​the crystal plane M on the outermost surface of the first quantum dots 31 contained in the light-emitting layer 23 increases. Therefore, with the above configuration, the light-emitting element 2 further improves the luminous efficiency of the light-emitting layer 23 while reducing deterioration of the quantum dots 30 in the light-emitting layer 23.

[0071] 1 and 3, the light-emitting layer 23 according to this embodiment may have a first portion 23A and a second portion 23B located closer to the cathode 25 than the first portion 23A. The first portion 23A and the second portion 23B of the light-emitting layer 23 will be described in more detail with reference to Fig. 3. Note that the cross section shown in Fig. 3 is a cross section passing through both the first portion 23A and the second portion 23B.

[0072] As shown by the dotted line in Fig. 3, a line segment 23S is assumed to be parallel to the film thickness direction DT of the light-emitting layer 23 and to connect the lower surface 23U to the upper surface 23T of the light-emitting layer 23. Also, as shown by the dashed line in Fig. 3, a perpendicular bisector 23L is assumed to be perpendicular to the line segment 23S. The perpendicular bisector 23L is also shown by the dashed line in Fig. 1.

[0073] In this case, the first portion 23A is located on the anode 21 side of the perpendicular bisecting plane 23L in the light-emitting layer 23, and the second portion 23B is located on the cathode 25 side of the perpendicular bisecting plane 23L in the light-emitting layer 23. The first portion 23A and the second portion 23B may be continuous at the perpendicular bisecting plane 23L.

[0074] In this embodiment, each of the first portion 23A and the second portion 23B includes a quantum dot 30 including at least one first quantum dot 31, and an additive 40. For example, the first quantum dot 31 and the like included in the first portion 23A and the second portion 23B may be confirmed by observing, by the above-described method, a cross section that is parallel to the thickness direction DT of the light-emitting layer 23 and passes through the first portion 23A and the second portion 23B.

[0075] In the above cross section, the perpendicular bisector 23L may cross some of the quantum dots 30, in other words, some of the quantum dots 30 may be located across the first portion 23A and the second portion 23B. In this case, the quantum dot 30 may be considered to be included in both the first portion 23A and the second portion 23B, or may be considered to be included in whichever of the first portion 23A and the second portion 23B the center of the quantum dot 30 is located.

[0076] Here, in a cross section parallel to the thickness direction DT of the light-emitting layer 23, the average value of the first proportion of the quantum dots 30 in the second portion 23B may be higher than the average value of the first proportion of the quantum dots 30 in the first portion 23A. Alternatively, in a cross section parallel to the thickness direction DT of the light-emitting layer 23, the ratio of the total number of first quantum dots 31 to the total number of quantum dots 30 may be higher in the second portion 23B than in the first portion 23A.

[0077] In this case, the ratio of the first quantum dots 31 to the quantum dots 30 contained in the light-emitting layer 23 is higher in the second portion 23B than in the first portion 23A. Alternatively, in this case, the ratio of the area of ​​crystal planes K to the area of ​​crystal planes M on the outermost surfaces of the first quantum dots 31 contained in the light-emitting layer 23 is larger in the second portion 23B than in the first portion 23A.

[0078] Generally, in a light-emitting element whose light-emitting layer contains quantum dots as a light-emitting material, an excess of electrons may occur in the light-emitting layer, where the concentration of electrons is higher than the concentration of holes, due to factors such as differences in charge mobility and differences in the efficiency of charge injection from each electrode to the light-emitting layer.

[0079] The excess electrons reduce the efficiency of exciton generation due to hole-electron recombination in quantum dots, and the excess electrons may also increase the efficiency of generating high-energy electrons such as Auger electrons. The excess high-energy electrons, such as Auger electrons, increase the degradation of the light-emitting layer or layers adjacent to the light-emitting layer, and also promote the occurrence of deactivation processes in materials such as quantum dots that do not contribute to light emission.

[0080] Since the second portion 23B is located closer to the cathode 25 than the first portion 23A, electrons are more easily injected into holes in the second portion 23B than in the first portion 23A. Therefore, the above-mentioned excess electrons are more likely to occur in the second portion 23B than in the first portion 23A.

[0081] In this embodiment, due to the above-described configuration, the second portion 23B further reduces deterioration of the included quantum dots 30 and improves the luminous efficiency more than the first portion 23A. Therefore, even when an excess of electrons occurs in the light-emitting layer 23, the light-emitting element 2 can suppress a decrease in luminous efficiency or a decrease in reliability.

[0082] <Additional Note> The light-emitting element 2 according to this embodiment is not limited to the layer structure described above. 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. 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.

[0083] Furthermore, in this embodiment, the display device 1 includes the light-emitting element 2 having the anode 21 closer to the substrate 3 than the light-emitting layer 23, but is not limited to this. For example, the light-emitting element 2 may include, in order from the substrate 3 side, the cathode 25, the electron transport layer 24, the light-emitting layer 23, the hole transport layer 22, and the anode 21. In this case, the second portion 23B may be located closer to the anode 21 than the first portion 23A, or may be located closer to the cathode 25.

[0084] <Manufacturing Method: Overview> The display device 1 according to this embodiment may be manufactured by forming multiple light-emitting elements 2 on a substrate 3 on which a driver circuit DR, pixel circuits PC, and the like are separately formed. In the manufacturing method of the light-emitting element 2 according to this embodiment, the layers other than the light-emitting layer 23 may be formed by any method, using common materials and common film-forming processes. For example, each layer can be formed by applying a solution containing the materials for each layer by a spin coating method, a slit coating method, or the like, and then drying the solution. For example, each layer can be formed by preparing a solution in which the materials for each layer are mixed with a solvent for viscosity control, and printing the solution by an inkjet method, a screen printing method, or the like. The printing method is suitable for producing light-emitting panels and display panels because it allows each layer to be uniformly formed over a large area.

[0085] <Manufacturing Method: Synthesis of Quantum Dots> The light-emitting layer 23 may be formed, for example, by applying a first dispersion liquid in which quantum dots 30 synthesized separately are dispersed, and then drying the first dispersion liquid.

[0086] The quantum dots 30 can be synthesized by, for example, a heating method, a hot injection method, a microwave-assisted method, or a continuous flow method. Each of these synthesis methods will be described below.

[0087] The heating method is a technique for synthesizing quantum dots 30 by mixing materials in an organic solvent and heating the materials to thermally decompose and react them. In the heating method, TOP (trioctylphosphine) or TOPO (trioctylphosphine oxide) is used as the organic solvent, dimethylcadmium is used as the Group II raw material, and a desired element, such as a TOP complex of S, Se, or Te, or an organometallic compound bonded with a methyl group or an ethyl group, is used as the Group VI raw material. The Group II and Group VI raw materials are mixed in the organic solvent and heated to about 300°C to thermally decompose the raw materials. By maintaining a high degree of supersaturation of the Group II and Group VI elements in the organic solvent, the reaction to form a Group II-VI compound is promoted, and quantum dots 30 can be synthesized.

[0088] Hot injection is a technique for generating uniform crystal growth nuclei at a high density by rapidly injecting raw materials into a heated organic solvent, utilizing the supersaturation near the injection region. In hot injection, TOP or T-TOPO is used as the organic solvent for the raw materials. The raw materials are heated to approximately 300°C, and Group II and VI raw materials are rapidly injected into the organic solvent. This rapidly increases the supersaturation level locally around the injection region, generating uniform crystal growth nuclei at a high density. Because high supersaturation is localized near the injection region, raw materials consumed in the growth of the growth nuclei are constantly supplied by diffusion from the surrounding low-supersaturation region due to the concentration gradient, thereby continuing the growth of quantum dots 30. This technique involves adding a surfactant or a ligand-containing material to the raw materials to prevent the aggregation of quantum dots 30 due to the high density of nucleation. Examples of such materials include alkylphosphines and alkylphosphine oxides such as trioctylphosphine or trioctylphosphine oxide, long-chain carboxylic acids such as oleic acid, and long-chain amines such as oleylamine.

[0089] The microwave-assisted method is a technique that uses microwaves to selectively heat the growth raw material. This method allows for good reaction control due to the selective heating, and allows the temperature to be raised to the required reaction temperature range in a short time. Furthermore, compared to the injection method, this method is simpler and allows quantum dots 30 to be synthesized even in air. Microwaves are selectively resonantly absorbed by molecules with polarization. Therefore, if a chalcogenide compatible with the microwave wavelength is used as the raw material, selective raw material heating is possible, allowing for controlled growth of quantum dots 30. Due to this characteristic, the raw material must have polarization, and raw materials different from those used in the heating method or hot injection may be used. One example of a raw material is a mixed solution of cadmium stearate, an alkane solvent, and a group VI powder.

[0090] The continuous flow method is a technique in which the nucleation reaction and the growth reaction occur in separate reactors by reacting the raw materials while flowing an organic solvent containing the raw materials. Because the nucleation reaction and the growth reaction occur in separate reactors, an appropriate temperature gradient can be precisely set, allowing for precise control of each reaction. This method is suitable for mass production because it is relatively easy to control crystal growth. As explained in the three previous manufacturing methods, quantum dots 30 can be grown in either an organic solution or a gas phase containing the vapor of an organic solution using the continuous flow method. In the continuous flow method, an organic solvent and Group II and Group VI raw materials are mixed, and the raw materials are transported along the liquid or gas flow. Furthermore, appropriate temperature gradients are set for the nucleation stage, which is the starting point for the growth of the quantum dots 30, and the crystal growth stage. This allows for precise control of the nucleation and growth reactions in separate reactors. By separating the nucleation and crystal growth reactions into separate containers and transporting them between the containers using the liquid or gas flow, the conditions appropriate for each stage can be precisely and independently controlled.

[0091] In crystal growth, it is important to maintain a high degree of supersaturation of the raw material, which is the driving force for nucleation and crystal growth. The four types of production methods mentioned above, for example, have been developed based on differences in the means for realizing and maintaining this condition.

[0092] In this embodiment, by controlling the synthesis conditions when synthesizing the quantum dots 30, the quantum dots 30 to be synthesized can be the first quantum dots 31. In particular, when synthesizing the first quantum dots 31, the quantum dots 30 should be synthesized under conditions such that the (100) equivalent plane appears preferentially on the outermost surface.

[0093] One method for selectively revealing a specific crystal plane is to control the pH (hydrogen ion concentration) of the solvent in which the materials are mixed to a specific range. For example, it has been experimentally found that in order for the outermost surface of the quantum dot 30 to have a zincblende crystal structure and to have a shape that terminates in polar (100) equivalent planes and (111) equivalent planes, it is sufficient to maintain the pH of the solvent in the range of 9 to 11. In this pH range, the pH is higher than the neutral condition of pH = 7, and the pH of the solvent is higher than the neutral condition of pH = 7. ＋ Because it is a weak base with a high concentration, H ＋ It is thought that the intermediate reaction between the raw material species and the crystalline planes is involved in the mechanism of preferential formation of specific crystal planes.

[0094] As an alternative, it has been found that adding an organic ligand that strongly binds to the desired crystal plane to the organic solvent containing the raw materials stabilizes the desired crystal plane, allowing crystal growth to occur preferentially on other crystal planes. As a result, the desired crystal plane can occupy 80% or more of the surface of the quantum dot 30. For example, if the surface of the quantum dot 30 has a zincblende crystal structure, it is possible to add a ligand that strongly binds to polar planes to the material. This allows crystal growth to occur preferentially on the (110) equivalent plane, which is a nonpolar plane, and makes it easier for the (111) equivalent plane and the (100) equivalent plane, which are polar planes, to appear.

[0095] The binding between the surface of the quantum dots 30 and the ligands during growth is temporary, and it is believed that the organic solvent is in an equilibrium state where the ligands repeatedly detach and attach. Therefore, increasing the solution temperature increases the rate of detachment and attachment, making it easier for raw materials to access the entire surface of the quantum dots 30. As a result, atoms preferentially deposit on crystal faces with many dangling bonds and high surface energy. For example, when the CdS shell of the quantum dots 30 is synthesized at temperatures above 275°C, atoms preferentially deposit on (111)-equivalent faces with a high dangling bond density, resulting in the appearance of (100)-equivalent faces on the surface of the quantum dots 30.

[0096] <Manufacturing Method: Formation of Light-Emitting Layer> The first dispersion used to form the light-emitting layer 23 may be prepared by dispersing quantum dots 30, which have been synthesized by the method described above so that the (100) equivalent plane, in other words, the crystal plane K, appears preferentially on the surface, in a solvent. Therefore, in this embodiment, the first dispersion contains a large amount of first quantum dots 31 as the quantum dots 30. Formation of the light-emitting layer 23 may include applying the first dispersion to a substrate and volatilizing the solvent by heating the first dispersion.

[0097] Here, the first dispersion may further contain a precursor of the adduct 40, and the formation of the light-emitting layer 23 may include conversion of the precursor to the adduct 40. The conversion of the precursor to the adduct 40 may be achieved by heating the first dispersion after application as described above, thereby causing the precursors in the first dispersion to react with each other.

[0098] For example, the first dispersion may contain, in addition to the quantum dots 30, tetramethyl orthosilicate (TMOS) represented by the following formula (1) dispersed in a solvent as a precursor of the adduct 40. Furthermore, the first dispersion may contain 3-(mercaptopropyl)trimethoxysilane (MPS) represented by the following formula (2) dispersed in a solvent.

[0099] In this case, the first dispersion contains F, which catalyzes the reaction of TMOS and MPS. － , Cl － ,Br － , I －In this embodiment, a metal halide such as zinc fluoride, zinc chloride, zinc bromide, zinc iodide, indium fluoride, indium chloride, indium bromide, or indium iodide may be used as the halogen source. In addition, the thiol group of MPS may function as a coordinating functional group that forms a coordinate bond with the quantum dots 30; in other words, MPS may be a ligand that coordinates to the quantum dots 30.

[0100] For example, by heating the first dispersion, the methoxy groups of TMOS and MPS are converted 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.

[0101] As described above, in the formation of the light-emitting layer 23, at least a portion of the TMOS and MPS is converted into silicon oxide, which is the adduct 40. In particular, the conversion of the TMOS and MPS into the adduct 40 occurs around the quantum dots 30. Therefore, in the formation of the light-emitting layer 23, the adduct 40 is formed so as to fill the spaces between the multiple quantum dots 30.

[0102] The conversion of the precursor of the adduct 40 may be carried out during the preparation of the first dispersion. The preparation of the first dispersion may include, for example, a step of replacing the ligand coordinated to the quantum dots 30 with MPS.

[0103] For example, first, a second dispersion liquid is prepared in which quantum dots 30 coordinated with organic ligands are dispersed in a solvent with low polarity. － , Cl － ,Br － , I － A third dispersion liquid is prepared in which ions of halogen atoms such as those mentioned above are dispersed in a solvent with high polarity.

[0104] In the present disclosure, a "highly polar solvent" may be a solvent having a relative dielectric constant at room temperature of 30 or more. For example, the "highly polar solvent" in the present disclosure may be 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.

[0105] In the present disclosure, a "low-polarity solvent" may be a solvent having a relative dielectric constant at room temperature of not more than 3. For example, the "low-polarity solvent" in the present disclosure 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.

[0106] Next, the second dispersion and the third dispersion are poured into the same container. Because the solvents of the second dispersion and the third dispersion have different polarities, the mixture in the container separates into a liquid layer of the second dispersion and a liquid layer of the third dispersion.

[0107] Next, the second dispersion and the third dispersion are mixed by stirring. As a result, some of the organic ligands coordinated to the quantum dots 30 are replaced with MPS. As a result, the quantum dots 30 become more easily dispersible in the solvent of the third dispersion than in the solvent of the second dispersion, and some of the quantum dots 30 migrate to the third dispersion. Some of the quantum dots 30 may be exposed between the liquid layer of the second dispersion and the liquid layer of the third dispersion.

[0108] Furthermore, by the above-mentioned mixing, at least a portion of the TMOS and MPS is converted into the adduct 40 by the above-mentioned reaction. In this case, some of the MPS forms coordinate bonds with the quantum dots 30 on the thiol group side, while reacting with other MPS or TMOS on the methoxy group side. As a result, around the quantum dots 30, ligands 41 that form coordinate bonds with the surfaces of the quantum dots 30 and adducts 40 that bond to the ligands 41 are formed. By bonding the adducts 40 to the ligands 41, the adducts 40 can strongly fix the position of the ligands 41 relative to the quantum dots 30. Therefore, a dispersion containing the adducts 40 that bond to the ligands 41 can prevent the ligands 41 from detaching from the surfaces of the quantum dots 30 and can strongly protect the quantum dots 30.

[0109] Next, the third dispersion is extracted from the container, and the quantum dots 30, as well as the adducts 40 and the ligands 41 located around the quantum dots 30, are extracted from the third dispersion by centrifuging the third dispersion, etc. When centrifuging the third dispersion, a poor solvent such as ethyl acetate or acetone may be added to the third dispersion to precipitate the quantum dots 30.

[0110] Thereafter, the extracted quantum dots 30, adduct 40, and ligand 41 may be dispersed in a solvent to prepare a first dispersion. A precursor of the adduct 40 and a halogen source may be further added to the first dispersion. According to the above method, a structure in which the ligand 41 is located between the quantum dots 30 and the adduct 40 and is coordinated to the quantum dots 30 can be easily formed.

[0111] The first portion 23A and the second portion 23B may be formed by preparing two types of first dispersions, applying and drying one of the first dispersions to form the first portion 23A, and then applying and drying the other first dispersion to form the second portion 23B. In this case, the quantum dots 30 contained in the first dispersion used to form the second portion 23B may be synthesized under conditions that make it easier for the (100) equivalent plane to appear on the outermost surface, compared to the quantum dots 30 contained in the first dispersion used to form the first portion 23A.

[0112] 9 is a schematic side cross-sectional view of a display device 4 according to this embodiment. The display device 4 according to this embodiment differs in configuration from the display device 1 according to the previous embodiment only in that it includes a light-emitting element 5 instead of the light-emitting element 2. The light-emitting element 5 according to this embodiment differs in configuration from the light-emitting element 2 according to the previous embodiment only in that it includes a light-emitting layer 26 instead of the light-emitting layer 23.

[0113] Fig. 10 is an enlarged schematic diagram of the light-emitting layer 26 in the cross section shown in Fig. 9, particularly an enlarged schematic diagram of a region E3 shown in Fig. 9. In other words, Fig. 10 is an enlarged schematic diagram of a cross section parallel to the thickness direction DT of the light-emitting layer 26.

[0114] The light-emitting layer 26 according to this embodiment includes a plurality of quantum dots 30 and an additive 40. In particular, the light-emitting layer 26 includes at least one second quantum dot 32 as the quantum dot 30. Furthermore, the proportion of the second quantum dot 32 among the quantum dots 30 in a cross section parallel to the thickness direction DT of the light-emitting layer 26 is 50% or more. The structure of the second quantum dot 32 will be described in more detail with reference to FIG. 11 . FIG. 11 is a schematic perspective view of the second quantum dot 32 according to this embodiment.

[0115] For example, as shown in second quantum dot 32A in Fig. 11 , second quantum dot 32 is a quantum dot having a regular tetrahedron shape with crystal plane L including the (111) plane on the outermost surface. Alternatively, second quantum dot 32 may have crystal plane M in addition to crystal plane L, as shown in second quantum dot 32B in Fig. 11 . However, even in this case, second quantum dot 32B has crystal plane L on its outermost surface with an area equal to or greater than the area of ​​crystal plane M. Note that in Fig. 11 , some of the crystal planes that second quantum dot 32 has on its outermost surface are indicated by symbols.

[0116] As described above, since only one of the two types of atoms is located on the crystal plane L, the crystal plane L is a polar plane having polarity for the same reason that the crystal plane K is a polar plane.

[0117] 10 , in a cross section parallel to the thickness direction DT of the light-emitting layer 26, the equilateral triangle TR is defined as the triangle with the smallest area that contains all of the cross sections of the second quantum dots 32. In this case, the area of ​​the equilateral triangle TR is the same as the smallest value of the areas of the equilateral triangles TR that contain all of the cross sections of the second quantum dots 32. The relationship between the cross sections of the second quantum dots 32 and the equilateral triangle TR in this embodiment will be described in detail with reference to FIG. 12 . FIG. 12 is a schematic diagram showing an example of a cross section of the second quantum dots 32.

[0118] 12 shows an example of a cross section of the second quantum dot 32 in a cross section that is parallel to the film thickness direction DT of the light-emitting layer 26 and approximately parallel to one of the crystal planes L. The second quantum dot 32 shown in FIG. 12 has a crystal plane L and a crystal plane M, and the cross section shown in FIG. 12 passes through the crystal plane L and the crystal plane M of the second quantum dot 32.

[0119] In this case, the higher the ratio of the length of the crystal plane L to the perimeter of the cross section of the second quantum dot 32, the higher the ratio of the total area of ​​the crystal plane L to the total area of ​​the outermost surface of the second quantum dot 32. Furthermore, the higher the ratio of the length of the crystal plane L to the perimeter of the cross section of the second quantum dot 32, the closer the outer shape of the second quantum dot 32 becomes to an equilateral triangle; in other words, the higher the ratio of the cross-sectional area of ​​the second quantum dot 32 to the area of ​​the equilateral triangle TR. Therefore, the higher the ratio of the total area of ​​the crystal plane L to the total area of ​​the outermost surface of the second quantum dot 32, the higher the ratio of the cross-sectional area of ​​the second quantum dot 32 to the area of ​​the equilateral triangle TR.

[0120] The second ratio is the ratio of the cross-sectional area of ​​the quantum dots 30 to the area of ​​the equilateral triangle TR in a cross section parallel to the thickness direction DT of the light-emitting layer 26. In the present disclosure, the second ratio of the second quantum dots 32 in a cross section parallel to the thickness direction DT of the light-emitting layer 26 is 0.73 or more.

[0121] 12 , assume that the cross section of the second quantum dot 32 is substantially parallel to any one of the crystal planes L and that the second ratio of the second quantum dot 32 is 0.73 or more. In this case, the total length of the crystal planes L is equal to or greater than the total length of the crystal planes M around the periphery of the second quantum dot 32 in the cross section.

[0122] Therefore, in a cross section parallel to the thickness direction DT of the light-emitting layer 26, the second ratio of the second quantum dots 32 is 0.73 or more, and therefore the ratio of the total area of ​​the crystal planes L to the total area of ​​the outermost surfaces of the second quantum dots 32 becomes high. In other words, the ratio of the area of ​​the polar planes to the area of ​​the nonpolar planes on the outermost surfaces of the second quantum dots 32 becomes high.

[0123] Therefore, when it is confirmed that the second ratio of the quantum dots 30 is 0.73 or more in a cross section of the light-emitting layer 26 parallel to the thickness direction DT, the quantum dots 30 may be considered to be second quantum dots 32. Note that the light-emitting layer 26 may include quantum dots 30C whose second ratio is less than 0.73 in a cross section of the light-emitting layer 26 parallel to the thickness direction DT.

[0124] Note that the above discussion is based on a cross section parallel to the crystal plane L of the second quantum dots 32, and the second ratio may decrease depending on the angle of the cross section relative to the crystal plane L of the second quantum dots 32. However, even in this case, the tendency remains that the ratio of the cross-sectional area of ​​the second quantum dots 32 to the area of ​​the equilateral triangle TR increases as the ratio of the total area of ​​the crystal planes L to the total area of ​​the outermost surfaces of the second quantum dots 32 increases. Therefore, based on the above, if 50% or more of the second quantum dots 32 among the identified quantum dots 30 are confirmed to have a second ratio of 0.73 or more, it can be considered that the light-emitting layer 26 contains at least 50% of the quantum dots 30 that are second quantum dots 32.

[0125] The method for confirming the second proportion of quantum dots 30 in a cross section parallel to the film thickness direction DT of the light-emitting layer 26 may be a method in which the first proportion in the method for confirming the first proportion of quantum dots 30 according to the previous embodiment is replaced with the second proportion.

[0126] Except for the above, the light-emitting layer 26 has the same configuration as the light-emitting layer 23. For example, the light-emitting layer 26 may include an adduct 40 filling the spaces between the quantum dots 30, including the second quantum dots 32. Furthermore, although not shown in Figures 9 and 10, the light-emitting layer 26 may also include a ligand 41 located between the quantum dots 30 and the adduct 40. Furthermore, some of the quantum dots 30 included in the light-emitting layer 26 may be quantum dots 30C that are not the second quantum dots 32.

[0127] The second quantum dots 32 have, on their outermost surfaces, crystal faces L that are polar faces and have an area equal to or greater than that of the crystal faces M. Therefore, for the same reasons as those described in the previous embodiment, the light-emitting layer 26 reduces aggregation of the quantum dots 30 while protecting the quantum dots 30 with the additives 40. Therefore, the light-emitting element 5 including the light-emitting layer 26 reduces deterioration of the quantum dots 30 in the light-emitting layer 26 while improving the luminous efficiency of the light-emitting layer 26. The display device 4 including the light-emitting element 5 achieves a longer lifespan and reduced power consumption.

[0128] In a cross section of the light-emitting layer 26 parallel to the thickness direction DT, the average value of the second ratio of each quantum dot 30 may be 0.73 or more. In this case, the ratio of the second quantum dots 32 to the quantum dots 30 contained in the light-emitting layer 26 becomes higher. Alternatively, in this case, the ratio of the area of ​​the crystal plane L to the area of ​​the crystal plane M on the outermost surface of the second quantum dots 32 contained in the light-emitting layer 26 increases. Therefore, with the above configuration, the light-emitting element 5 further improves the luminous efficiency of the light-emitting layer 26 while reducing deterioration of the quantum dots 30 in the light-emitting layer 26.

[0129] As shown by the dotted line in Fig. 10, a line segment 26S is assumed to be parallel to the film thickness direction DT of the light-emitting layer 26 and to connect the lower surface 26U to the upper surface 26T of the light-emitting layer 26. Also, as shown by the dashed line in Fig. 10, a perpendicular bisector 26L is assumed to be perpendicular to the line segment 26S. The perpendicular bisector 26L is also shown by the dashed line in Fig. 9.

[0130] In this case, light-emitting layer 26 may include first portion 26A located closer to anode 21 than perpendicular bisecting plane 26L, and second portion 26B located closer to cathode 25 than perpendicular bisecting plane 26L. Each of first portion 26A and second portion 26B may have the same configuration as first portion 23A and second portion 23B, respectively, except that first portion 26A and second portion 26B include second quantum dots 32 instead of first quantum dots 31.

[0131] Here, in a cross section parallel to the thickness direction DT of the light-emitting layer 26, the average value of the second proportion of the quantum dots 30 in the second portion 26B may be higher than the average value of the second proportion of the quantum dots 30 in the first portion 26A. Alternatively, in a cross section parallel to the thickness direction DT of the light-emitting layer 26, the ratio of the total number of second quantum dots 32 to the total number of quantum dots 30 may be higher in the second portion 26B than in the first portion 26A.

[0132] In this case, the ratio of the second quantum dots 32 to the quantum dots 30 contained in the light-emitting layer 26 is higher in the second portion 26B than in the first portion 26A. Alternatively, in this case, the ratio of the area of ​​the crystal planes L to the area of ​​the crystal planes M on the outermost surfaces of the second quantum dots 32 contained in the light-emitting layer 26 is larger in the second portion 26B than in the first portion 26A.

[0133] In this embodiment, due to the above-described configuration, the second portion 26B further reduces deterioration of the included quantum dots 30 and improves the luminous efficiency more than the first portion 26A. Therefore, even when an excess of electrons occurs in the light-emitting layer 26, the light-emitting element 5 can suppress a decrease in luminous efficiency or a decrease in reliability.

[0134] The manufacturing method of the display device 4 according to this embodiment may be the same as the manufacturing method of the display device 1 according to the previous embodiment, except for the method of synthesizing the quantum dots 30. The manufacturing method of the quantum dots 30 according to this embodiment may be the same as the manufacturing method of the quantum dots 30 according to the previous embodiment, except for the point that the crystalline material of the quantum dots 30 is grown so that the (111) equivalent plane is more likely to appear on the outermost surface than the (110) equivalent plane. Therefore, in this embodiment, the first dispersion contains a large amount of second quantum dots 32 as the quantum dots 30.

[0135] For example, when using II-VI group crystals such as ZnS and CdS, or III-V group crystals such as InN and InP, it is known that a (111) equivalent plane appears when the Group VI or Group V raw material is relatively reduced. This is because the reduction in the Group V or Group VI raw material relatively increases the number of dangling orbitals in the (111) equivalent plane, which has a high areal density of bonding orbitals.

[0136] The first portion 26A and the second portion 26B may be formed by preparing two types of first dispersions, applying and drying one of the first dispersions to form the first portion 26A, and then applying and drying the other first dispersion to form the second portion 26B. In this case, the quantum dots 30 contained in the first dispersion used to form the second portion 26B may be synthesized under conditions that make it easier for the (111) equivalent plane to appear on the outermost surface, compared to the quantum dots 30 contained in the first dispersion used to form the first portion 26A.

[0137] 13 is a schematic side cross-sectional view of a display device 6 according to this embodiment. The display device 6 according to this embodiment differs in configuration from the display device 4 according to the previous embodiment only in that it includes a light-emitting element 7 instead of the light-emitting element 5. The light-emitting element 7 according to this embodiment differs in configuration from the light-emitting element 5 according to the previous embodiment only in that it includes a light-emitting layer 27 instead of the light-emitting layer 26.

[0138] Fig. 14 is an enlarged schematic view of the light-emitting layer 27 in the cross section shown in Fig. 13, particularly an enlarged schematic view of a region E4 shown in Fig. 13. In other words, Fig. 14 is an enlarged schematic view of a cross section parallel to the thickness direction DT of the light-emitting layer 27.

[0139] The light-emitting layer 27 according to this embodiment has a plurality of quantum dots 30 and an additive 40. In particular, the light-emitting layer 27 includes, as the quantum dots 30, at least one first quantum dot 31 and at least one second quantum dot 32. The first quantum dot 31 according to this embodiment has the same configuration as the first quantum dot 31 according to the first embodiment, and the second quantum dot 32 according to this embodiment has the same configuration as the second quantum dot 32 according to the previous embodiment. In particular, the sum of the proportion of the first quantum dots 31 and the proportion of the second quantum dots among the quantum dots 30 in a cross section parallel to the thickness direction DT of the light-emitting layer 27 is 50% or more.

[0140] For example, suppose the shapes of the quantum dots 30 in a cross section parallel to the thickness direction DT of the light-emitting layer 27 are identified by the above-described method, and the first ratio and the second ratio are calculated for each quantum dot 30. In this case, in this embodiment, among the identified quantum dots 30, the total of the first quantum dots 31 having a first ratio of 0.83 or more and the second quantum dots 32 having a second ratio of 0.73 or more is confirmed to be 50% or more of the quantum dots 30 in the cross section.

[0141] Except for the above, light-emitting layer 27 has the same configuration as light-emitting layer 23 or light-emitting layer 26. For example, light-emitting layer 27 may include an adduct 40 filling the space between quantum dots 30 including first quantum dots 31 and second quantum dots 32. Furthermore, light-emitting layer 27 may include a ligand 41 located between the quantum dots 30 and the adduct 40, although this is not shown in Figures 13 and 14. Furthermore, some of the quantum dots 30 included in light-emitting layer 26 may be quantum dots 30C that are neither the first quantum dots 31 nor the second quantum dots 32.

[0142] The light-emitting layer 27 includes first quantum dots 31 and second quantum dots 32, each having a polar surface on its outermost surface that is larger than the area of ​​the non-polar surface. For the same reasons as described above, the light-emitting layer 27 reduces aggregation of the quantum dots 30 while protecting the quantum dots 30 with the additives 40. Therefore, the light-emitting device 7 including the light-emitting layer 27 improves the luminous efficiency of the light-emitting layer 27 while reducing deterioration of the quantum dots 30 in the light-emitting layer 27. The display device 6 including the light-emitting device 7 achieves a longer lifespan and reduced power consumption.

[0143] In particular, the light-emitting layer 27 according to this embodiment includes both the first quantum dots 31 and the second quantum dots 32 as at least a portion of the quantum dots 30. Therefore, the light-emitting layer 27 includes quantum dots 30 having different shapes, namely, the first quantum dots 31 whose outer shape is close to a cube and the second quantum dots 32 whose outer shape is close to a regular tetrahedron. Therefore, in the light-emitting layer 27 according to this embodiment, when two adjacent quantum dots 30 are the first quantum dot 31 and the second quantum dot 32, the crystal planes that are most prevalent on the outermost surfaces of the two quantum dots have different orientations.

[0144] With the above configuration, the distance between two adjacent first quantum dots 31 and second quantum dots 32 is greater than when the two adjacent quantum dots 30 consist only of first quantum dots 31 or only of second quantum dots 32. Therefore, the light-emitting device 7 according to this embodiment further reduces the aggregation of the quantum dots 30 in the light-emitting layer 27. From the viewpoint of further reducing the aggregation of the quantum dots 30 in the light-emitting layer 27, the ratio of the second quantum dots 32 to the first quantum dots 31 contained in the light-emitting layer 27 may be 1 / 3 or more and 3 / 10 or less. The "ratio of the second quantum dots 32 to the first quantum dots 31" may refer to the ratio of the number of the first quantum dots 31, the weight ratio, or the volume ratio, and is particularly preferably the ratio of the number of the first quantum dots 31 and the second quantum dots 32.

[0145] The light-emitting layer 27 may include quantum dots 30 in which the first ratio is 0.83 or more and the second ratio is 0.73 or more in a cross section parallel to the thickness direction DT of the light-emitting layer 27. The quantum dots 30 may be considered to be both first quantum dots 31 and second quantum dots 32. In this case, the quantum dots 30 can be considered to have a large amount of both the crystal plane K and the crystal plane L on their outermost surfaces, and therefore the distance between the quantum dots 30 and other quantum dots 30 becomes larger. Therefore, the light-emitting element 7 having the above configuration also exhibits the effect of further reducing the aggregation of the quantum dots 30 described above.

[0146] However, the light-emitting layer 27 may separately include, in the cross section, first quantum dots 31 having a first ratio of 0.83 or more and a second ratio of less than 0.73, and second quantum dots 32 having a first ratio of less than 0.83 and a second ratio of 0.73 or more. In this case, the distance between the first quantum dots 31 and the second quantum dots 32 is more efficiently increased. Therefore, the light-emitting device 7 having the above configuration exhibits the effect of further reducing the aggregation of the quantum dots 30.

[0147] In a cross section of the light-emitting layer 27 parallel to the thickness direction DT, the average value of the first ratio of the quantum dots 30 may be 0.83 or more, or the average value of the second ratio may be 0.73 or more. In this case, the ratio of the first quantum dots 31 or the second quantum dots 32 to the quantum dots 30 contained in the light-emitting layer 27 becomes higher. Alternatively, in this case, the ratio of the area of ​​polar faces to the area of ​​nonpolar faces on the outermost surfaces of the quantum dots 30 contained in the light-emitting layer 27 increases. Therefore, with the above configuration, the light-emitting element 7 further improves the luminous efficiency of the light-emitting layer 27 while reducing deterioration of the quantum dots 30 in the light-emitting layer 27.

[0148] As shown by the dotted line in Fig. 14, a line segment 27S is assumed to be parallel to the film thickness direction DT of the light-emitting layer 27 and to connect the lower surface 27U to the upper surface 27T of the light-emitting layer 27. Also, as shown by the dashed line in Fig. 14, a perpendicular bisector 27L is assumed to be perpendicular to the line segment 27S. The perpendicular bisector 27L is also shown by the dashed line in Fig. 13.

[0149] In this case, light-emitting layer 27 may include first portion 27A located closer to anode 21 than perpendicular bisecting plane 27L, and second portion 27B located closer to cathode 25 than perpendicular bisecting plane 27L. Each of first portion 27A and second portion 27B may have the same configuration as each of first portion 23A and second portion 23B, or each of first portion 26A and second portion 26B, except that first portion 27A and second portion 27B include at least one of first quantum dots 31 and second quantum dots 32.

[0150] Here, in a cross section parallel to the thickness direction DT of the light-emitting layer 27, the average value of the first proportion or the average value of the second proportion of the quantum dots 30 in the second portion 27B may be higher than the average value of the first proportion or the average value of the second proportion of the quantum dots 30 in the first portion 27A. Alternatively, in a cross section parallel to the thickness direction DT of the light-emitting layer 27, the ratio of the total number of the first quantum dots 31 and the second quantum dots 32 to the total number of quantum dots 30 may be higher in the second portion 27B than in the first portion 27A.

[0151] In this case, the ratio of the first quantum dots 31 and the second quantum dots 32 to the quantum dots 30 contained in the light-emitting layer 27 is higher in the second portion 27B than in the first portion 27A. Alternatively, in this case, the ratio of the area of ​​polar faces to the area of ​​nonpolar faces on the outermost surfaces of the quantum dots 30 contained in the light-emitting layer 27 is higher in the second portion 27B than in the first portion 27A.

[0152] In this embodiment, due to the above-described configuration, the second portion 27B further reduces deterioration of the included quantum dots 30 and improves the luminous efficiency more than the first portion 27A. Therefore, even when an excess of electrons occurs in the light-emitting layer 27, the light-emitting element 7 can suppress a decrease in luminous efficiency or a decrease in reliability.

[0153] The manufacturing method of the display device 6 according to this embodiment may be the same as the manufacturing method of the display device 4 according to the previous embodiment, except that both the first quantum dots 31 and the second quantum dots 32 are dispersed in the first dispersion. The first dispersion according to this embodiment may be prepared by adding the first quantum dots 31 and the second quantum dots 32, which have been individually synthesized by the above-described method, to a solvent.

[0154] The first portion 27A and the second portion 27B may be formed by preparing two types of first dispersions, applying and drying one of the first dispersions to form the first portion 27A, and then applying and drying the other first dispersion to form the second portion 27B. In this case, the quantum dots 30 contained in the first dispersion used to form the second portion 27B may be synthesized under conditions that make it easier for polar faces to appear on the outermost surface, compared to the quantum dots 30 contained in the first dispersion used to form the first portion 27A.

[0155] 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.

[0156] REFERENCE SIGNS LIST 1 display device 2 light-emitting element 3 substrate 21 anode 23 light-emitting layer 23S line segment 23L perpendicular bisector 23A first part 23B second part 25 cathode 30 quantum dot 31 first quantum dot 32 second quantum dot 40 appendage SQ square TR equilateral triangle

Claims

1. An anode, a cathode facing the anode, and a light-emitting layer positioned between the anode and the cathode, wherein the light-emitting layer includes quantum dots and an additive containing a metal oxide. In a cross-section parallel to the film thickness direction of the light-emitting layer, the ratio of the cross-sectional area of one of the quantum dots to the minimum value of the area of a square that entirely encloses the cross-section of the quantum dot is defined as the first ratio of the quantum dot, and the ratio of the cross-sectional area of one of the quantum dots to the minimum value of the area of an equilateral triangle that entirely encloses the cross-section of the quantum dot is defined as the second ratio of the quantum dot. Among the quantum dots in the cross-section parallel to the film thickness direction of the light-emitting layer, the sum of the ratio of the first quantum dots with the first ratio of 0.83 or more and the ratio of the second quantum dots with the second ratio of 0.73 or more is 50% or more. A light-emitting device.

2. The light-emitting device according to claim 1, wherein the light-emitting layer includes at least one of the first quantum dots and at least one of the second quantum dots.

3. The light-emitting device according to claim 2, wherein the ratio of the number of the second quantum dots to the number of the first quantum dots included in the light-emitting layer is 1 / 3 or more and 3 or less.

4. The metal oxide contains SiO ｘ The light-emitting element according to any one of claims 1 to 3, which contains 5. The light-emitting device according to any one of claims 1 to 4, wherein the light-emitting layer contains carbon atoms between the first quantum dots and the additive or between the second quantum dots and the additive.

6. The light-emitting device according to any one of claims 1 to 5, wherein in a cross-section parallel to the film thickness direction of the light-emitting layer, the average value of the first ratio is 0.83 or more.

7. The light-emitting device according to any one of claims 1 to 6, wherein in a cross-section parallel to the film thickness direction of the light-emitting layer, the average value of the second ratio is 0.73 or more.

8. The light-emitting device according to any one of claims 1 to 7, wherein the light-emitting layer includes a first part positioned on the anode side with respect to a perpendicular bisecting plane of any line segment along the film thickness direction of the light-emitting layer from the end face on the anode side to the end face on the cathode side, and a second part positioned on the cathode side with respect to the perpendicular bisecting plane.

9. The light-emitting device according to claim 8, wherein in a cross-section parallel to the film thickness direction of the light-emitting layer and passing through the first part and the second part, the average value of the first ratio in the second part is higher than the average value of the first ratio in the first part.

10. The light-emitting device according to claim 8 or 9, wherein, in a cross section parallel to the film thickness direction of the light-emitting layer and passing through the first part and the second part, the average value of the second ratio in the second part is higher than the average value of the second ratio in the first part.

11. The light-emitting device according to any one of claims 8 to 10, wherein, in a cross section parallel to the film thickness direction of the light-emitting layer and passing through the first part and the second part, the ratio of the total number of the first quantum dots and the second quantum dots to the total number of the quantum dots is higher in the second part than in the first part.

12. The light-emitting device according to any one of claims 1 to 11, wherein the additive is located between at least two of the quantum dots.

13. The light-emitting device according to any one of claims 1 to 12, wherein the additive includes an inorganic matrix filling between at least two of the quantum dots.

14. A display device including a substrate and a plurality of the light-emitting devices according to any one of claims 1 to 13 provided on the substrate.

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