Light-emitting element, display device, and quantum dot-containing liquid

Abstract

The present invention is provided with a first electrode (E1), a second electrode (E2), a quantum dot layer (6) positioned between the first electrode and the second electrode, and a light scattering part (7) positioned between the quantum dot layer and the second electrode. The quantum dot layer (6) includes a plurality of light-emitting quantum dots (Q) and a matrix material (MX) located between the plurality of quantum dots. The light scattering part (7) and the matrix material (MX) are formed of the same material.

Description

Light-emitting element, display device, and quantum dot-containing liquid

[0001] This disclosure relates to light-emitting elements, etc.

[0002] Patent Document 1 discloses a method for coating quantum dots with silica.

[0003] Japanese Patent No. 6592504

[0004] Light-emitting devices containing quantum dots and matrix materials have the challenge of low light extraction efficiency.

[0005] The light-emitting element according to this disclosure comprises a first electrode and a second electrode, a quantum dot layer located between the first electrode and the second electrode, and a light-scattering portion located between the quantum dot layer and the second electrode, wherein the quantum dot layer includes a plurality of luminescent quantum dots and a matrix material located between the plurality of quantum dots, and the light-scattering portion and the matrix material are made of the same material.

[0006] The light extraction efficiency of light-emitting devices, including quantum dots and matrix materials, is improved.

[0007] This is a cross-sectional view showing an example of the configuration of a light-emitting element according to this embodiment. These are images and graphs showing the surface state of the light-scattering part. These are images and graphs showing the surface state of the light-scattering part. These are images and graphs showing the surface state of the light-scattering part. These are images and graphs showing the surface state of the light-scattering part. These are images and graphs showing the surface state of the light-scattering part. These are images and graphs showing the surface state of the light-scattering part. This is a schematic diagram showing an example of the configuration of a quantum dot layer. This is a flowchart showing an example of the formation of a quantum dot layer and a light-scattering part. This is a schematic diagram showing an example of the preparation of a quantum dot-containing liquid. This is a schematic diagram showing an example of the configuration of a quantum dot-containing liquid. This is a flowchart showing a method for manufacturing a light-emitting element. This is a graph showing the voltage-current density characteristics of the mixed solution of the first and second liquids in Figure 10 when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). This graph shows the current density-EQE (external quantum efficiency) characteristics of a mixture of the first and second solutions when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). This graph shows the voltage-luminance characteristics of a mixture of the first and second solutions in Figure 10 when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). This graph shows the current density-luminance characteristics of a mixture of the first and second solutions when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). Figure 10 shows graphs of FTIR measurements for a mixture of the first and second solutions, with zinc chloride concentrations of 0.02 mol / L (Example), 0.2 mol / L (Comparative Example 1), and 0.1 mol / L (Comparative Example 2).Figure 10 is a graph showing the results of level measurements by photoelectron yield spectroscopy for a mixture of the first and second solutions in Figure 10, when the zinc chloride concentration is 0.02 mol / L (Example) and when the zinc chloride concentration is 0.2 mol / L (Comparative Example). Figure 10 is an image showing the state of the light scattering area for a mixture of the first and second solutions in Figure 10, when the zinc chloride concentration is 0.02 mol / L (Example), when the zinc chloride concentration is 0.2 mol / L (Comparative Example 1), and when the zinc chloride concentration is 0.05 mol / L (Comparative Example 2). This is a schematic diagram showing an example of the configuration of the display device according to this embodiment.

[0008] Figure 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to this embodiment. As shown in Figure 1, the light-emitting element 10 comprises, in order from the bottom layer side (pixel circuit board 1 side), a first electrode E1, a functional layer 4, a quantum dot layer 6, a light scattering section 7, a functional layer 8, and a second electrode E2. The quantum dot layer 6 is a light-emitting layer and emits light through the recombination of holes supplied from one of the first and second electrodes E1 and E2 (anode) and electrons supplied from the other (cathode). The light generated in the quantum dot layer 6 is extracted to the top of the light-emitting element 10 through the light scattering section 7 and the second electrode E2.

[0009] The light scattering section 7 is located between the quantum dot layer 6 and the second electrode E2. The quantum dot layer 6 includes a plurality of luminescent quantum dots Q and a matrix material MX located between the plurality of quantum dots Q, and the light scattering section 7 and the matrix material MX are made of the same material.

[0010] "Same material" means that at least the main components are common. In other words, the light scattering section 7 and the matrix material MX only need to have common main components, and the elemental composition between the light scattering section 7 and the matrix material MX does not need to be perfectly identical. For example, if the compositional analysis of the light scattering section 7 and the matrix material MX shows that the common elemental composition accounts for more than 50% of the composition ratio, then the main components can be considered to be common.

[0011] Since the light-emitting element 10 includes a light-scattering section 7 made of the same material as the matrix material MX of the quantum dot layer 6 (light-emitting layer), the light extraction efficiency is increased.

[0012] The light scattering section 7 may be in contact with the light extraction side surface of the quantum dot layer 6, and the matrix material MX and the light scattering section 7 may be connected (continuous). The light-emitting element 10 may be of the top-emission type. In this case, since the light scattering section 7 is located between the light extraction surface and the quantum dot layer 6, the effect of improving the light extraction efficiency due to light scattering in the light scattering section 7 is significant.

[0013] The first electrode E1 may be the anode, and the functional layer 4 may be the hole transport layer (HTL). The functional layer 8 may be the electron transport layer (ETL), and the second electrode E2 may be the cathode.

[0014] The light-scattering portion 7 located on the quantum dot layer 6 may have surface irregularities (upper surface roughness with light-scattering properties). The matrix material MX may contain at least one of oxides, sulfides, selenides, and tellurides as its main component.

[0015] The light-emitting element 10 includes a functional layer 8 (e.g., ETL) located on the light-scattering portion 7, and the refractive index of the light-scattering portion 7 may be lower than that of the functional layer 8. This improves the light-scattering characteristics of the light-scattering portion 7. The refractive index of the light-scattering portion 7 may be less than 0.95 times, less than 0.9 times, or less than 0.85 times the refractive index of the functional layer 8.

[0016] The matrix material MX may have an amorphous (non-crystalline) structure or a polycrystalline structure. The amorphous or polycrystalline structure can be detected by electron diffraction, X-ray diffraction, etc. The matrix material MX may contain halogens (e.g., chlorine, iodine, fluorine). The matrix material MX may contain oxides containing group 14 elements, and the group 14 elements may be Si or Ge.

[0017] The difference between the lowest and highest positions on the surface (top surface) of the light scattering portion 7 may be 5.0 to 30 nm. In cross-sectional observation of the surface of the light scattering portion 7, there may be multiple protrusions that are 10 nm or more higher than the surrounding area per 1.0 μm, and the main component of the protrusions may be an oxide (for example, silicon oxide). Silicon oxide has a low refractive index, and the difference in refractive index is large when compared to general ETL materials, so the Rayleigh scattering effect is greater. In the quantum dot layer 6, the atomic ratio of halogens to group 14 elements may be 0.1 to 0.35 (described later). This makes it less likely for cracks to occur in the quantum dot layer 6 and reduces leakage current.

[0018] Figures 2 to 7 are images and graphs showing the surface state of the light scattering area. Figures 2 to 7 show the results of inspecting the surface topography of the light scattering area 7 (a region of 1.0 [μm] × 1.0 [μm]) using an atomic force microscope (Dimension Icon, Bruker). Here, the height data on the white line drawn in the upper AFM image (including height data of the two-dimensional region) is extracted to the lower graph, and in the lower graph, the average height of the observation area (observation field) is used as the reference (0 nm). When cross-sectional TEM and cross-sectional SEM measurements are taken, images corresponding to the lower graph can be obtained.

[0019] Figures 2 to 7 show that the difference between the lowest and highest positions on the surface (top surface) of the light scattering portion 7 is in the range of 5.0 to 30 nm. In this case, the effect of improving light extraction efficiency due to light scattering (especially Rayleigh scattering) is sufficiently obtained. Since the intensity of Rayleigh scattering is proportional to the sixth power of the size of the scatterer, if the roughness is less than 5 nm, the scattering intensity decreases rapidly, and it becomes difficult to obtain the effect of improving extraction efficiency. Also, if the roughness exceeds 30 nm, the quantum dot layer 6 becomes thinner, the leakage current due to the proximity of the functional layer 4 (HTL) and functional layer 8 (ETL) increases, and the EQE decreases. Figures 2 to 7 also show that the surface of the light scattering portion 7 has multiple peaks (convexities) with a height of 10 nm or more per 1.0 μm in width.

[0020] Figure 8 is a schematic diagram showing an example of the configuration of a quantum dot layer. As shown in Figure 8, in the quantum dot layer 6, a coordinating group Y may be located between the quantum dot Q and the matrix material MX, and the coordinating group Y may bond to the matrix material MX. The coordinating group Y may coordinate to the quantum dot Q. By coordinating the quantum dot Q with the coordinating group Y, the quantum dot Q can be effectively protected, improving EQE and reliability. On the other hand, because the coordination of the coordinating group Y with the quantum dot Q reduces the degree of freedom of the spatial position in which the matrix material MX can exist, cracking is more likely to occur during the formation of the matrix material MX. Therefore, by setting the atomic ratio of halogens to group 14 elements in the quantum dot layer 6 to 0.1 to 0.35, cracking of the quantum dot layer 6 can be effectively suppressed.

[0021] The matrix material MX contains silicon oxide, and the coordinating group Y may contain a carbon chain. The coordinating group Y may contain a thiol group (HS). The quantum dot layer 6 may contain an organic ligand J. The coordination of the organic ligand J to the quantum dot Q improves dispersibility in liquid, but reduces the degree of freedom of the spatial position in which the matrix material MX may exist. Therefore, by setting the atomic ratio of halogens to group 14 elements in the quantum dot layer 6 to 0.1 to 0.35, cracking of the quantum dot layer 6 can be effectively suppressed. If a ligand material corresponding to the coordinating group Y is confirmed in the quantum dot layer 6, it may be considered that the coordinating group Y is coordinated to the quantum dot Q. The matrix material MX may contain a polymer (for example, a polymer containing siloxane bonds). For example, if the matrix material MX contains silicon oxide as an oxide, it may include the case where the matrix material MX is a siloxane compound having siloxane bonds.

[0022] When the quantum dot layer 6 is measured by FTIR, the peak value originating from the OH group may be 0.65 times or less the peak value originating from silicon oxide (see below). The HOMO level of the quantum dot Q may be -5.5 [eV] or higher (see below).

[0023] Quantum dots Q (Q1 to Q3) may be dots (particles) with a maximum width of 100 nm or less. The shape of the quantum dots Q is not particularly restricted as long as it satisfies the above maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, it may be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branch-shaped three-dimensional shape, a three-dimensional shape with irregularities on the surface, or a combination thereof. The quantum dots may be semiconductor single crystals, and their particle size may be 1.0 nm to 50 nm. A quantum dot may have at least one of the following: crystals of group II-VI semiconductor compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe; crystals of group III-V semiconductor compounds such as GaAs, GaP, InN, InAs, InP, InSb; and crystals of group IV semiconductor compounds such as Si and Ge. A quantum dot Q may be, for example, a core-shell type in which the above crystal is used as a core and the core is overcoated with a shell material with a high band gap, or a shell-less type composed only of a core.

[0024] The matrix material MX of the quantum dot layer 6 can be described as a base material, inorganic medium, or filler. The elemental proportion of carbon in the matrix material MX may be 10% or less. It is desirable that the matrix material MX has a wider band gap than the core material of the quantum dot Q. A semiconductor or an insulator can be used as the matrix material MX.

[0025] One of the first and second electrodes E1 and E2 (for example, the cathode) may be formed of a light-transmitting material. As the light-transmitting material, for example, a transparent conductive material can be used. Examples of transparent conductive materials include ITO (indium tin oxide), IZO (indium zinc oxide), and SnO. ２ (Tin oxide), FTO (fluorine-doped tin oxide), etc. can be used.

[0026] The other of the first and second electrodes E1 and E2 (for example, the anode) may be formed of a light-reflective material. As the light-reflective material, for example, a metallic material can be used. As the metallic material, for example, Al (aluminum), Ag (silver), Cu (copper), Au (gold), etc. can be used.

[0027] Examples of materials for the functional layer 4 (hole transport layer or hole injection layer) include metal oxides such as nickel oxide (NiO), as well as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "Poly-TPD"), polyvinylcarbazole (abbreviated as "PVK"), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviated as "PTAA"). These materials may be used individually or in combination of two or more. Inorganic materials such as metal oxides may be used for the HIL in contact with the first electrode E1, and organic materials may be used for the HTL in contact with the light scattering section 7. Nanoparticles of metal oxides such as nickel oxide may be used in the functional layer 4 (hole transport layer or hole injection layer).

[0028] The materials for functional layer 8 (electron transport layer) include zinc oxide (ZnO), magnesium zinc oxide (MgZnO), and titanium oxide (TiO ２ Examples of metal oxides include those listed above, as well as compounds or complexes containing one or more nitrogen-containing heterocycles such as oxadiazole rings, triazole rings, triazine rings, quinoline rings, phenanthroline rings, pyrimidine rings, pyridine rings, imidazole rings, and carbazole rings. Nanoparticles of metal oxides such as zinc oxide may be used in the electron transport layer (ETL).

[0029] FIG. 9 is a flowchart showing an example of forming a quantum dot layer and a light scattering portion. FIG. 10 is a schematic diagram showing an example of preparing a quantum dot-containing liquid. FIG. 11 is a schematic diagram showing a configuration example of the quantum dot-containing liquid. Here, as shown in FIGS. 9 to 11, a quantum dot-containing liquid QL was prepared using a first liquid A1 and a second liquid A2. For example, the first liquid A1 is a liquid (2 mg / mL) in which blue quantum dots are dispersed in a nonpolar solvent (e.g., octane), and TMSPT: 3-Trimethoxysilylpropanethiol, trimethoxysilylpropanethiol, C ６ H １６ O ３ SSi) is added so as to be 0.4 mol / L, and further, DPSD: diphenylsilanediol, diphenylsilanediol, C1 ２ H1 ２ O[[ID=ll]] ２ Si) may be a liquid added so as to be 0.4 mol / L. For example, the second liquid A2 may be a liquid in which a halogen source (e.g., zinc chloride) is dissolved at 0.04 mol / L in a polar solvent such as N,N-dimethylformamide (DMF). The above-mentioned halogen source may be, for example, a halogen compound other than chloride, and the halogen compound may be another metal halide or ammonium halide. For example, ZnBr ２ , ZnI ２ , NH ４ Cl, NH ４ Br, NH ４ I may be used.

[0030] 0.4 mg of barium hydroxide (Ba(OH) ２ ) is added as a reaction catalyst to a mixed solution (concentration of zinc chloride: 0.02 mol / L) obtained by mixing the first liquid A1 and the second liquid A2 in equal amounts, and a stir bar is added, and the mixed solution is vigorously stirred for about 12 hours. As a result, the blue quantum dots moved from the layer of the first liquid A1 to the interface AK (intermediate layer) between the first and second liquids A1 and A2. Here, as shown in FIG. 11, a part of the organic ligand J coordinated to the quantum dot Q is replaced by the precursor Z (TMSPT). Halogens HA such as Cl, F, and Br may be coordinated to the quantum dot Q

[0031] Thereafter, when centrifuged at 4000 rpm for 5 minutes, the quantum dots Q present in the interface AK (intermediate layer) precipitated to the bottom of the container. After removing all the solvents, they were dispersed in a nonpolar solvent such as toluene to obtain a quantum dot-containing liquid QL with a desired concentration.

[0032] The quantum dot-containing liquid QL contains a nonpolar solvent (e.g., toluene), a plurality of quantum dots Q dispersed in the nonpolar solvent, an organic ligand J, a precursor Z of an oxide of Group 14 elements (e.g., TMSPT), and a metal halide X (e.g., zinc chloride), and the atomic ratio of halogen to Group 14 elements (e.g., Si) may be 0.1 to 0.35. The precursor Z of the oxide of Group 14 elements (e.g., TMSPT) contains a ligand Y having a thiol group (HS) at the end, and the ligand Y may be bonded to Group 14 elements (Si). The thiol group of the ligand Y may be coordinated to the quantum dots Q. Since the thiol group has a strong coordination force to the quantum dot surface, it effectively protects defects and improves the EQE and reliability during energization. R in FIG. 11 １ ~R ３ is a hydrocarbon group. R １ ~R ３ may be, for example, a methyl group.

[0033] The quantum dot-containing liquid QL is applied to an underlayer such as HTL, and by performing treatment of the coating solution (baking, etc.), the quantum dot layer 6 and the light scattering portion 7 are formed. For example, a quantum dot layer 6 containing a matrix material MX filling the spaces between the quantum dots Q is formed by a hydrolysis reaction and a dehydration condensation reaction that occur during baking of the coating solution, and a light scattering portion 7 as a surface layer is formed by a volume change during the formation process of the matrix material MX.

[0034] (Fabrication of Light-Emitting Device) FIG. 12 is a flowchart showing a method for manufacturing a light-emitting device. In step S10, a first electrode E1, which is a reflective electrode (in the case of a top emission type) or a transmissive electrode (in the case of a bottom emission type), is formed on a substrate 1. For example, using a sputtering method or a vapor deposition method, etc., ITO with a film thickness of 20 nm, silver with a film thickness of 100 nm, and ITO with a film thickness of 50 nm are laminated in this order to form an anode. An ITO film with a film thickness of 30 nm may also be used as the anode.

[0035] In step S20, a functional layer 4 is formed on the first electrode E1. A nickel oxide nanoparticle dispersion (for example, a liquid in which nickel oxide nanoparticles are dispersed at 15 mg / mL in a solvent obtained by mixing water and 2-methoxyethanol in equal volumes) is applied by spin coating under the atmosphere and fired at 200° C. to form a hole injection layer (HIL) (this process may be repeated 1 to 5 times). In step S20, a SAM layer (self-assembled monolayer) may be formed on the hole injection layer. For example, an ethanol solution of 0.01 M such as [2-(3,6-Dimethyl-9H-carbazol-9-yl)ethyl]phosphonic Acid (Me-2PACz), [2-(3,6-Dibromo-9H-carbazol-9-yl)ethyl]phosphonic Acid (Br-2PACz), etc. is applied to the nickel oxide layer by spin coating under a nitrogen atmosphere, and then the solvent is volatilized by firing to form a SAM layer. In step S20, further, a hole transport layer (HTL) is formed on the HIL or the SAM layer 4. For example, a solution in which poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (abbreviation "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviation "Poly-TPD"), polyvinylcarbazole (abbreviation "PVK"), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviation "PTAA"), etc. are dispersed in a chlorobenzene solvent is applied by spin coating under a nitrogen atmosphere to form a hole transport layer (HTL). A TFB film with a film thickness of 30 nm may be used as the HTL.

[0036] In step S30, a quantum dot layer 6 and a light scattering part 7 are formed on the functional layer 4 (on the HTL). For example, the prepared quantum dot-containing liquid QL is applied on the functional layer 4, and the coating liquid is fired at 100° C. (see FIGS. 9 to 11).

[0037] In step S40, a functional layer 8 is formed. For example, a liquid in which MgZnO nanoparticles are dispersed in a solvent (such as ethanol) is applied by spin coating under a nitrogen atmosphere to form an electron transport layer (ETL). Mg ０．１５ Zn０．８５ A ZnO nanoparticle film with a thickness of 60 nm may be formed using O nanoparticles. The doping material for ZnO is not limited to Mg as described above. ZnO may be doped with at least one of Li, Al, Ti, Ga, and Zr, or it may be undoped. As the functional layer 8 (ETL), TiO ２ membrane or ZrO ２ A film may be formed.

[0038] In step S50, a second electrode E2 is formed on the functional layer 8. For example, the cathode is made of ITO formed to a thickness of about 100 nm using the sputtering method, or silver (Ag) or gold (Au) formed to a thickness of about 20 nm using the vapor deposition method. An Ag film with a thickness of 50 nm may also be formed.

[0039] Figure 13 is a graph showing the voltage-current density characteristics of the mixture of the first and second solutions from Figure 10 when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). Figure 14 is a graph showing the current density-EQE (external quantum efficiency) characteristics of the mixture of the first and second solutions when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). From Figures 13 and 14, it can be seen that by setting the zinc chloride concentration to 0.02 mol / L, both the voltage-current density characteristics and the current density-EQE characteristics are significantly improved.

[0040] Figure 15 is a graph showing the voltage-luminance characteristics of the mixture of the first and second solutions from Figure 10 when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). Figure 16 is a graph showing the current density-luminance characteristics of the mixture of the first and second solutions when the zinc chloride concentration is 0.02 mol / L (gray line) and when the zinc chloride concentration is 0.2 mol / L (black line). From Figures 15 and 16, it can be seen that by setting the zinc chloride concentration to 0.02 mol / L, both the voltage-luminance characteristics and the current density-luminance characteristics are significantly improved.

[0041] Figures 17 and 18 are graphs showing the FTIR measurement results for the mixture of the first and second solutions from Figure 10 when the zinc chloride concentration was 0.02 mol / L (Example), when the zinc chloride concentration was 0.2 mol / L (Comparative Example 1), and when the zinc chloride concentration was 0.1 mol / L (Comparative Example 2). From Figures 17 and 18, it can be seen that by setting the zinc chloride concentration to 0.02 mol / L, the unreacted hydroxyl groups (wavenumber 3400 cm) －１ It is understood that residues (at the point of contact) are less likely to remain, and the protective effect of the matrix material MX is enhanced. As a result, the resistance to exposure to oxygen and moisture and the reliability during electrical conduction are improved. Thus, when the quantum dot layer 6 is measured by FTIR, the peak value originating from the OH group may be 0.65 times or less the peak value originating from silicon oxide.

[0042] Figure 19 is a graph showing the results of energy level measurements by atmospheric photoelectron yield spectroscopy (AC-3, RIKEN KEKI Co., Ltd.) for a mixture of the first and second solutions from Figure 10, with a zinc chloride concentration of 0.02 mol / L (Example) and a zinc chloride concentration of 0.2 mol / L (Comparative Example). From Figure 19, it can be seen that the HOMO of the Example is -5.5 [eV] and the HOMO of the Comparative Example is -5.9 [eV]. It can be seen that if the amount of zinc chloride added is small, the depth of the HOMO deepen is small, and the carrier balance of quantum dot light-emitting devices, which generally have an excess of electrons, is improved.

[0043] Figure 20 shows images (images of the surface of the light-scattering area) of the mixed solution of the first and second solutions from Figure 10 when the zinc chloride concentration is 0.02 mol / L (Example), when the zinc chloride concentration is 0.2 mol / L (Comparative Example 1), and when the zinc chloride concentration is 0.05 mol / L (Comparative Example 2). From Figure 20, it can be seen that when the zinc chloride concentration is 0.02 mol / L, the surface irregularities are formed uniformly, and the light diffusion effect is enhanced.

[0044] Furthermore, it was revealed that when the zinc chloride concentration was 0.05 mol / L (Comparative Example 2) or 0.2 mol / L (Comparative Example 1), and there was a large amount of chlorine coordination to the quantum dot Q, cracks were likely to occur on the surface of the quantum dot layer 6. This cracking phenomenon causes leakage current that does not contribute to light emission. As shown in Figure 13, the light-emitting element obtained with a zinc chloride concentration of 0.2 mol / L showed an increased leakage current in the low-voltage region before light emission started, and a decrease in EQE. Therefore, a zinc chloride concentration of 0.035 mol / L or less is preferable. On the other hand, if the zinc chloride concentration is low and there is little chlorine coordination to the quantum dot, the protective effect of the quantum dot Q is weakened, which adversely affects EQE and reliability during energization. Therefore, a zinc chloride concentration of 0.01 mol / L or higher is preferable.

[0045] In the mixture of the first and second solutions shown in Figure 10, when the zinc chloride concentration was 0.2 mol / L, the Cl / Si (atomic ratio) contained in the quantum dot layer 6 was 2.0. The preferred atomic ratio in the quantum dot layer 6 (expected to be Cl / Si = 0.2) was achieved when the zinc chloride concentration was 0.02 mol / L, but not when the zinc chloride concentration was 0.05 mol / L. Therefore, the range of the Cl / Si (atomic ratio) contained in the film (quantum dot layer 6) is preferably 10% to 35%.

[0046] Figure 21 is a schematic diagram showing an example configuration of a display device according to this embodiment. The display device 20 includes a display unit DA, a first driver circuit D1 (e.g., a data signal line drive circuit) and a second driver circuit D2 (e.g., a scan signal line drive circuit and a light emission control line drive circuit) that drive the display unit DA, and a control circuit CL that controls the first driver circuit D1 and the second driver circuit D2. The display unit DA may include a substrate (pixel circuit board 1) and a light-emitting element layer. The light-emitting element layer may include a red light-emitting element 10R (10), a green light-emitting element 10G (10), and a blue light-emitting element 10B (10), and each of the light-emitting elements 10R, 10G, and 10B may be connected to a pixel circuit PC formed in the pixel circuit layer.

[0047] [Additional Notes] The embodiments described above are for illustrative and explanatory purposes only, and not for limiting purposes. It will be apparent to those skilled in the art that many variations are possible based on these examples and descriptions.

[0048] 1 Substrate (pixel circuit board) 4 Functional layer 6 Quantum dot layer 7 Light scattering section 8 Functional layer 9 Second electrode 10 Light-emitting element 20 Display device Q Quantum dot E1 First electrode E2 Second electrode MX Matrix material

Claims

1. A light-emitting element comprising: a first electrode and a second electrode; a quantum dot layer located between the first electrode and the second electrode; and a light-scattering portion located between the quantum dot layer and the second electrode, wherein the quantum dot layer includes a plurality of luminescent quantum dots and a matrix material located between the plurality of quantum dots, and the light-scattering portion and the matrix material are made of the same material.

2. The light-emitting element according to claim 1, wherein the light-scattering portion is located on the quantum dot layer and has surface irregularities.

3. The light-emitting element according to claim 1 or 2, wherein the light-scattering portion and the matrix material are connected.

4. The light-emitting element according to any one of claims 1 to 3, wherein the material comprises at least one of an oxide, a sulfide, a selenide, and a telluride.

5. The light-emitting element according to claim 2, further comprising a functional layer located on the light-scattering portion, wherein the light-scattering portion has a refractive index smaller than that of the functional layer.

6. The light-emitting element according to any one of claims 1 to 5, wherein the material has an amorphous structure.

7. The light-emitting element according to any one of claims 1 to 6, wherein the material contains a halogen.

8. The light-emitting element according to any one of claims 1 to 7, wherein the material includes an oxide containing a group 14 element.

9. The light-emitting element according to claim 8, wherein the group 14 element is Si or Ge.

10. The light-emitting element according to any one of claims 1 to 9, wherein the difference between the lowest and highest positions on the surface of the light-scattering element is 5 to 20 nm.

11. The light-emitting element according to any one of claims 1 to 10, wherein, in cross-sectional observation of the surface of the light-scattering element, there are three or more protrusions that are 10 nm or more higher than the surrounding area per 1.0 μm.

12. The light-emitting element according to claim 11, wherein the main component of the protrusion is an oxide.

13. The light-emitting element according to claim 7, wherein the material contains a group 14 element, and the atomic ratio of halogens to group 14 elements in the quantum dot layer is 0.1 to 0.

35.

14. The light-emitting element according to any one of claims 1 to 13, wherein a coordination group is located between each quantum dot and the matrix material.

15. The light-emitting element according to claim 14, wherein the coordinating group is bonded to the matrix material.

16. The light-emitting element according to claim 14 or 15, wherein the matrix material contains silicon oxide and the coordinating group is an organic substance.

17. The light-emitting element according to claim 16, wherein when the quantum dot layer is measured by FTIR, the peak value originating from the OH group is 0.65 times or less the peak value originating from silicon oxide.

18. The light-emitting element according to any one of claims 1 to 17, wherein the HOMO level of each quantum dot is -5.5 [eV] or higher.

19. The light-emitting element according to any one of claims 1 to 18, wherein it is a top-emission type, the first electrode is an anode, and the second electrode is a cathode.

20. A display device comprising a light-emitting element according to any one of claims 1 to 19.

21. A quantum dot-containing liquid comprising a nonpolar solvent, a plurality of quantum dots dispersed in the nonpolar solvent, an organic ligand, a precursor of an oxide of a group 14 element, and a metal halide, wherein the atomic ratio of halogen to group 14 elements is 0.1 to 0.

35.

22. The quantum dot-containing liquid according to claim 21, wherein the precursor comprises a coordinating group having a thiol group at its terminus, and the coordinating group is bonded to a group 14 element.

Images