Light-emitting element and display device

Abstract

A light-emitting element (1a) is provided with a positive electrode (2), a negative electrode (6), a light-emitting layer (4a) provided between the positive electrode (2) and the negative electrode (6), and an electron transport layer (5) as a carrier transport layer provided between the negative electrode (6) and the light-emitting layer (4a), and the light-emitting layer (4a) contains a plurality of quantum dots (QDa) and a matrix (MR) provided at least partially between each of the plurality of quantum dots (QDa). The electron transport layer (5) includes a layer in which at least a first material (5a) and a second material (5b) are mixed, the first material (5a) being a material different from the second material (5b).

Description

Technical Field

[0001] This disclosure relates to light-emitting elements and display devices. Background Technology

[0002] In recent years, quantum dot light-emitting elements, namely QLED (Quantum dot Light Emitting Diode), and display devices equipped with QLED have attracted much attention due to their ability to achieve low power consumption, thinness, and high image quality.

[0003] For example, Patent Document 1 discloses quantum dots with fluoride ligands or fluoride anions bonded to their surface.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2020-180278 (published on November 5, 2020) Summary of the Invention The technical problem this disclosure aims to solve The invention described in Patent Document 1 has problems such as low durability of the light-emitting element and low luminous efficiency.

[0005] One aspect of this disclosure is to provide light-emitting elements and display devices that can improve durability and luminous efficiency.

[0006] Technical solutions for solving technical problems To solve the above-mentioned technical problems, the light-emitting element disclosed herein comprises: an anode; a cathode; a light-emitting layer disposed between the anode and the cathode; and a carrier transport layer disposed between one of the anode and the cathode and the light-emitting layer, the light-emitting layer comprising a plurality of quantum dots and a matrix, the matrix being disposed in at least a portion between each of the plurality of quantum dots, and the carrier transport layer comprising at least a layer mixed with a first material and a second material, wherein the first material is a material different from the second material.

[0007] To address the aforementioned technical problems, the display device disclosed herein includes a plurality of light-emitting elements, comprising: a first light-emitting element; and a second light-emitting element that emits light of a different wavelength than the first light-emitting element. The first light-emitting element has a first quantum dot as the quantum dot, and the second light-emitting element has a second quantum dot as the quantum dot. Each of the first and second light-emitting elements has a common electron transport layer between the cathode and the light-emitting layer as the carrier transport layer. The common electron transport layer includes a layer at least mixed with the first material, the second material, and a third material. The third material is different from the first and second materials. The electron affinity of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the first material, the second material, and the third material is such that the matrix ≤ the second material < the core portion of the second quantum dot ≤ the third material < the core portion of the first quantum dot ≤ the first material.

[0008] To solve the above-mentioned technical problems, the display device disclosed herein includes a plurality of light-emitting elements, the plurality of light-emitting elements including: a first light-emitting element; and a second light-emitting element that emits light of a different wavelength than the first light-emitting element. The first light-emitting element has a first quantum dot as the quantum dot, and the second light-emitting element has a second quantum dot as the quantum dot. The first light-emitting element and the second light-emitting element each have a common hole transport layer as the carrier transport layer between the anode and the light-emitting layer. The common hole transport layer includes a layer that is at least mixed with the first material, the second material, and the third material. The third material is different from the first material and the second material. The ionization potential of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the first material, the second material, and the third material is such that the magnitude of the ionization potential is: matrix ≥ second material > core portion of the second quantum dot ≥ third material > core portion of the first quantum dot ≥ first material.

[0009] To address the aforementioned technical problems, the display device disclosed herein includes a plurality of light-emitting elements, comprising: a first light-emitting element; and a second light-emitting element emitting light of a different wavelength than the first light-emitting element. The first light-emitting element comprises: a first quantum dot; and a first carrier transport layer. The second light-emitting element comprises: a second quantum dot; and a second carrier transport layer. The first carrier transport layer includes a layer comprising a mixture of the first material and the second material. The second carrier transport layer includes a layer comprising a mixture of the first material, the second material, and a third material, wherein the third material is a material different from the first material and the second material.

[0010] Beneficial effects According to one aspect of this disclosure, light-emitting elements and display devices that can improve durability and luminous efficiency can be provided. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view showing the schematic configuration of the light-emitting element in the first embodiment.

[0012] Figure 2 It is used to explain in Figure 1 The diagram shows a region formed between two adjacent quantum dots in the light-emitting layer of the light-emitting element of the first embodiment, where the quantum dots are arranged close together.

[0013] Figure 3 It is used to explain in Figure 1 The diagram shows the region formed between the quantum dots in the light-emitting layer of the light-emitting element of the first embodiment, where two adjacent quantum dots are arranged slightly apart.

[0014] Figure 4 It is a general representation Figure 1 A diagram showing the energy band levels of the light-emitting layer of the light-emitting element in the first embodiment.

[0015] Figure 5 It is a general representation Figure 1 The diagram shows the energy levels of the hole transport layer, the light-emitting layer, and the electron transport layer of the light-emitting element in the first embodiment.

[0016] Figure 6 This is a graph showing the relationship between the particle radius of ZnO and its band gap and electron affinity.

[0017] Figure 7 It represents Zn 1-x Mg xA graph showing the relationship between the x value in O and electron affinity.

[0018] Figure 8 It means Figure 1 A diagram showing the electron injection mechanism in the light-emitting element of the first embodiment.

[0019] Figure 9 This is a diagram showing the general configuration of the light-emitting element as a modified example of the first embodiment and the preferred mixing ratio of the first material and the second material in the electron transport layer.

[0020] Figure 10 This is a cross-sectional view showing a schematic configuration of the light-emitting element in the second exemplary embodiment.

[0021] Figure 11 It is a general representation Figure 10 The diagram shows the energy levels of the hole transport layer, the light-emitting layer, and the electron transport layer of the light-emitting element in the second embodiment.

[0022] Figure 12 This is a diagram showing the schematic configuration of the light-emitting element as a modified example of the second embodiment and the preferred mixing ratio of the first and second materials in the hole transport layer.

[0023] Figure 13 This is a cross-sectional view showing the schematic configuration of the display device according to the third embodiment.

[0024] Figure 14 It means Figure 13 The diagram shows the electron injection mechanism in the light-emitting element of the display device according to the third embodiment.

[0025] Figure 15 This is a cross-sectional view showing the schematic configuration of the display device according to the fourth embodiment.

[0026] Figure 16 It means Figure 15 The diagram shows the electron injection mechanism in the light-emitting element of the display device according to the fourth embodiment.

[0027] Figure 17 This is a cross-sectional view showing the schematic configuration of the display device according to the fifth embodiment.

[0028] Figure 18 It means Figure 17 The diagram shows the hole injection mechanism in the light-emitting element of the display device according to the fifth embodiment.

[0029] Figure 19 This is a cross-sectional view showing the schematic configuration of the display device according to the sixth embodiment.

[0030] Figure 20 This is a cross-sectional view showing the schematic configuration of the display device according to the seventh embodiment. Detailed Implementation

[0031] based on Figures 1 to 20 Embodiments of this disclosure will be described below. For ease of explanation, configurations having the same function as those described in specific embodiments will sometimes be marked with the same reference numerals and their descriptions will be omitted.

[0032] (First Implementation) Figure 1 This is a cross-sectional view showing the schematic configuration of the light-emitting element 1a in the first embodiment.

[0033] like Figure 1 As shown, the light-emitting element 1a includes an anode 2, a cathode 6, a light-emitting layer 4a disposed between the anode 2 and the cathode 6, an electron transport layer 5 serving as a carrier transport layer disposed between the cathode 6 and the light-emitting layer 4a, and a hole transport layer 3 serving as a carrier transport layer disposed between the anode 2 and the light-emitting layer 4a. The light-emitting layer 4a includes a plurality of quantum dots QDa and a matrix MR disposed between each of the plurality of quantum dots QDa. The electron transport layer 5, serving as a carrier transport layer, includes a layer that at least mixes a first material 5a and a second material 5b, wherein the first material 5a is a material different from the second material 5b. In this embodiment, the case where the electron transport layer 5 is composed of a layer formed by mixing the first material 5a and the second material 5b is illustrated as an example, but it is not limited to this; the electron transport layer 5 may simply include a layer formed by mixing the first material 5a and the second material 5b. Furthermore, the statement that the first material 5a and the second material 5b are different materials refers to any one of the following three situations: First, the constituent elements of the first material 5a and the second material 5b are different; second, the constituent elements of the first material 5a and the second material 5b are the same, but the composition ratio of the first material 5a and the second material 5b is different; and third, the first material 5a and the second material 5b are both nanoparticles, that is, the first material 5a and the second material 5b are each composed of the same element and have the same composition ratio, but the particle size distribution of the first material 5a and the second material 5b are different.

[0034] In this embodiment, the example given is that an electron transport layer 5 is provided between the cathode 6 and the light-emitting layer 4a as a carrier transport layer, and a hole transport layer 3 is provided between the anode 2 and the light-emitting layer 4a as a carrier transport layer. However, this is not a limitation. The carrier transport layer may also be provided between the cathode 6 and the light-emitting layer 4a and between the anode 2 and the light-emitting layer 4a at least one. The cathode 6 and the light-emitting layer 4a may have at least one of an electron transport layer and an electron injection layer as a carrier transport layer, and the anode 2 and the light-emitting layer 4a may have at least one of a hole transport layer and a hole injection layer as a carrier transport layer.

[0035] In the light-emitting element 1a, the anode 2 is made of a conductive material and is connected to the hole transport layer 3, and the cathode 6 is made of a conductive material and is connected to the electron transport layer 5.

[0036] At least one of the anode 2 and the cathode 6 is composed of a transparent conductive film. Examples of transparent conductive films include ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ZnO, AZO (Aluminum-doped Zinc Oxide), BZO (Boron-doped Zinc Oxide), as well as thin-layered, nano-particle-sized, or nanowire-sized Ag, Al, Cu, Au, etc. The transparent conductive film can be formed by sputtering, vapor deposition, coating, etc.

[0037] Either the anode 2 or the cathode 6 can be made of metal. The metal is preferably Al, Cu, Au, or Ag, which have high reflectivity to visible light.

[0038] The hole transport layer 3 is formed, for example, from p-type oxide semiconductors (e.g., NiO, MgNiO, Cu2O) or organic materials such as PEDOT (polyvinyl dioxythiophene), PSS (polystyrene sulfonate), or PVK (poly-N-vinylcarbazole). The hole transport layer 3 can be formed by coating, sputtering, evaporation, or other methods.

[0039] The luminescent layer 4a comprises quantum dots QDa and a matrix MR. For example, core / shell quantum dots with structures such as CdSe / CdS, CdSe / ZnS, InP / ZnS, ZnSe / ZnS, and CIGS / ZnS can be used as the quantum dots QDa. Furthermore, the quantum dots QDa can also contain organic or inorganic ligands (e.g., halogen ligands).

[0040] Here, a quantum dot refers to a dot with a maximum width of less than 100 nm. The shape of a quantum dot is not particularly limited as long as it meets the above maximum width requirement, and it is not limited to a spherical three-dimensional shape (a circular cross-sectional shape). For example, it can be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a dendritic three-dimensional shape, a three-dimensional shape with uneven surfaces, or a combination of these shapes.

[0041] In the light-emitting layer 4a of the light-emitting element 1a in this embodiment, such as Figure 1 As shown, the example illustrates the case where multiple quantum dots QDa are filled with matrix MR, but it is not limited to this. In the light-emitting layer 4a, the matrix MR can also be disposed in at least a portion between the multiple quantum dots QDa.

[0042] In this embodiment, an example is given of using a material for the shell of the quantum dot QDa, namely a metal sulfide (e.g., ZnS (ionization potential: 7.2 eV, electron affinity: 3.2 eV)), to form the matrix MR, but it is not limited to this.

[0043] When the matrix MR contains metal sulfides, as described later, the matrix MR can be formed by coating a solution containing a precursor of metal sulfides and then sintering. Furthermore, the luminescent layer containing the matrix MR containing metal sulfides is relatively stable relative to oxygen and water, resulting in high reliability.

[0044] Figure 2 It is used to explain in Figure 1 The diagram shows the region R formed between quantum dots QD1 and QD2 when two adjacent quantum dots QD1 and QD2 are arranged close together in the light-emitting layer 4a of the light-emitting element 1a.

[0045] Figure 3 It is used to explain in Figure 1 The diagram shows the region R formed between quantum dots QD1 and QD2 when two adjacent quantum dots QD1 and QD2 are arranged slightly apart in the light-emitting layer 4a of the light-emitting element 1a.

[0046] Figure 2 and Figure 3 The region R shown is enclosed by two straight lines (common external tangents) that connect to the outer peripheries of two adjacent quantum dots QD1 and QD2, and the opposite outer peripheries of the two adjacent quantum dots QD1 and QD2. For example... Figure 2 As shown, even when two adjacent quantum dots QD1 and QD2 are configured close together, such as Figure 3As shown, even when two adjacent quantum dots QD1 and QD2 are configured slightly apart, there exists a region R filled with matrix MR. "Matrix MR fills the space between two adjacent quantum dots QD1 and QD2" means that... Figure 2 as well as Figure 3 The region R shown is filled or filled with matrix MR. Furthermore, in this disclosure, two adjacent quantum dots QD1 and QD2 can be maintained by the presence of matrix MR in region R; for example, at least a portion of region R can also be filled with matrix MR.

[0047] In this embodiment, examples are given as follows: Figure 2 and Figure 3 The example shown illustrates the case where the region R formed between two adjacent quantum dots QD1 and QD2, i.e., the space between multiple quantum dots QDa, is filled with the matrix MR, but it is not limited to this.

[0048] Furthermore, maintaining quantum dots QD1 and QD2 by the matrix MR present in the region R formed between two adjacent quantum dots QD1 and QD2 means that at least a portion of the region R is filled by the matrix MR, including both the case where the entire region R is filled by the matrix MR and the case where a portion of the region R is filled by the matrix MR.

[0049] The matrix MR can also be formed to fill the region (space) outside the multiple quantum dots QDa of the luminescent layer 4a. Additionally, as... Figure 1 As shown, the light-emitting layer 4a can also be configured such that the matrix MR forms the outer edge of the light-emitting layer 4a, with multiple quantum dots QDa located away from the outer edge. That is, the matrix MR can contain multiple quantum dots QDa. Furthermore, at least a portion of the outer edge of the light-emitting layer 4a can also be composed of the matrix MR and quantum dots QDa. In addition, the multiple quantum dots QDa can each be embedded in the matrix MR at intervals. Furthermore, here, the outer edge refers to the first surface of the light-emitting layer 4a (e.g., Figure 1 The surface of the light-emitting layer 4a that contacts the electron transport layer 5 (as shown) and the second surface of the light-emitting layer (e.g., Figure 1 The surface of the light-emitting layer 4a that contacts the hole transport layer 3 (shown).

[0050] Matrix MR can also comprise continuous films. A continuous film is a film that is not interrupted by materials other than those constituting the continuous film. A continuous film can also be an integral film continuously connected by chemical bonds of compounds contained in the matrix MR. For example, such a continuous film can be formed with a planar direction orthogonal to the thickness direction of 1000 nm. 2 The membrane with the area above.

[0051] "A matrix is ​​disposed in at least a portion between each of the multiple quantum dots" is sufficient as long as it can be determined that the matrix MR is filled between at least two quantum dots QDa or is in contact with the quantum dots QDa. In addition, the composition of the matrix MR can be determined by analyzing the material of the matrix MR located in the middle between two quantum dots QDa. In the case where there is a void in the middle between two quantum dots QDa, the composition of the matrix MR can be determined by analyzing the material of the inner wall of the void.

[0052] Figure 1 The luminescent layer 4a shown, comprising quantum dots QDa and a matrix MR, can be formed, for example, by coating a quantum dot solution containing multiple quantum dots QDa, a metal sulfide precursor as a precursor to the matrix MR, and a solvent. For example, zinc ethyl xanthate, which forms ZnS, can be used as the precursor of the aforementioned metal sulfide, and N,N-dimethylformamide or dimethyl sulfoxide can be used as the solvent.

[0053] Figure 4 It is a general representation Figure 1 The diagram shows the energy band levels of the light-emitting layer 4a in the light-emitting element 1a of the first embodiment. The light-emitting element 1a having the light-emitting layer 4a is, for example, a red light-emitting element having a red light-emitting layer.

[0054] In this embodiment, CdSe(Red) is used as the core portion of the quantum dot QDa, and ZnS is used as the matrix MR. Therefore, as Figure 4 As shown, the band level at the lower end of the conduction band of the core portion of the quantum dot QDa (QDa(CBM)) is 3.6 eV, the band level at the upper end of the valence band of the core portion of the quantum dot QDa (QDa(VBM)) is 5.6 eV, the band level at the lower end of the conduction band of the matrix MR (MR(CBM)) is 3.2 eV, and the band level at the upper end of the valence band of the matrix MR (MR(VBM)) is 7.2 eV. Furthermore, as described above, in this embodiment, since the shell portion of the quantum dot QDa and the matrix MR are formed of ZnS, the diagrams of the band levels at the lower end of the conduction band of the shell portion of the quantum dot QDa (which have the same band level as the lower end of the conduction band of the matrix MR (CBM)) and the band levels at the upper end of the valence band of the shell portion of the quantum dot QDa (which have the same band level as the upper end of the valence band of the matrix MR (VBM)) are omitted here.

[0055] Furthermore, the absolute value of the energy difference between the vacuum level and the upper valence band level (VBM) is the same as the value of the ionization potential, and the absolute value of the energy difference between the vacuum level and the lower conduction band level (CBM) is the same as the value of the electron affinity.

[0056] Figure 5 It is a general representation Figure 1The diagram shows the band levels of the hole transport layer 3, the light-emitting layer 4a, and the electron transport layer 5 of the light-emitting element 1a in the first embodiment.

[0057] like Figure 5 As shown, the electron transport layer 5, which serves as the charge carrier transport layer, includes at least a layer that mixes a first material 5a and a second material 5b. The first material 5a is a different material from the second material 5b. Therefore, the electron affinity of the first material 5a (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the first material 5a (5a (CBM))) and the electron affinity of the second material 5b (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the second material 5b (5b (CBM))) are different.

[0058] As described above, by using an electron transport layer 5 comprising a layer of first material 5a and second material 5b of different materials, compared to the case of using an electron transport layer composed of a single material, by injecting electrons e from the cathode 6 into the light-emitting layer 4a containing the matrix MR, appropriate band levels can be adjusted, and it is easy to realize the injection of electrons e from the cathode 6 into the electron transport layer 5 and from the electron transport layer 5 into the light-emitting layer 4a containing the matrix MR, thereby achieving low voltage.

[0059] That is, by using an electron transport layer 5 comprising a layer of different materials, namely a first material 5a and a second material 5b, the electron affinity of the first material 5a is different from that of the second material 5b, thereby making it easier to inject electrons e into the light-emitting layer 4a, which has different energy levels due to the quantum dot QDa and the matrix MR.

[0060] Furthermore, by using an electron transport layer 5 comprising a layer formed by mixing a first material 5a and a second material 5b, which are different materials, it is possible to enable multiple band levels (electron affinities) from which electrons e are injected into the light-emitting layer 4a from the electron transport layer 5. Within the electron transport layer 5, electrons e can also be easily moved from the material with a deeper energy level, i.e., the first material 5a, to the material with a shallower energy level, the second material 5b. As a result, electrons e can be efficiently injected from the first material 5a and the second material 5b into the quantum dot QDa and the matrix MR, which have different energy levels.

[0061] In addition, Figure 5 The diagram illustrates the case where the energy level of the lower end of the conduction band of the core portion of the quantum dot QDa (QDa(CBM)) is shallower than the energy level of the lower end of the conduction band of the first material 5a (5a(CBM)). However, the same effect can be obtained even when the energy level of the lower end of the conduction band of the core portion of the quantum dot QDa (QDa(CBM)) is deeper than the energy level of the lower end of the conduction band of the first material 5a (5a(CBM)).

[0062] The surface of the light-emitting layer 4a is composed of two different materials: quantum dots (QDa) and a matrix (MR). The electron transport layer 5 also comprises a layer composed of two different materials: a first material 5a and a second material 5b. This improves the adhesion between the light-emitting layer 4a and the electron transport layer 5, as well as the conductivity and mechanical stress resistance at their interface. Furthermore, the light-emitting layer 4a and the electron transport layer 5 are easily planarized, resulting in good in-plane uniformity of light emission.

[0063] like Figure 5 As shown, preferably, the electron affinity of the second material 5b (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the second material 5b (5b(CBM))) is less than the electron affinity of the first material 5a (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the first material 5a (5a(CBM))), and the electron affinity of the core portion of the quantum dot QDa (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the core portion of the quantum dot QDa (QDa(CBM))) is less than or equal to the electron affinity of the first material 5a.

[0064] According to this configuration, the electron affinity decreases in the order of cathode 6, first material 5a, and the core portion of quantum dot QDa. Therefore, electrons e can be injected into the core portion of quantum dot QDa at a low voltage, and the driving voltage of light-emitting element 1a becomes lower.

[0065] The electron affinity of the matrix MR (the absolute value of the difference between the vacuum energy level and the band level at the lower end of the conduction band of the matrix MR (MR(CBM))) is preferably less than or equal to the electron affinity of the second material 5b.

[0066] Based on this configuration, the electron affinity decreases in the order of cathode 6, first material 5a, second material 5b, and matrix MR, thus allowing electrons (e) to be injected into the matrix MR at a low voltage. Specifically, based on... Figure 8 As described later, electrons (e) injected into the matrix MR migrate to quantum dots (QDa) located far from the electron transport layer 5 and recombine to emit light. Therefore, quantum dots (QDa) far from the electron transport layer 5 can emit light at a relatively low voltage, resulting in high brightness. The higher the voltage, the more quantum dots (QDa) far from the electron transport layer 5 will emit light, thus reducing roll-off. That is, the current dependence and voltage dependence of luminous efficiency can be improved, and the decrease in luminous efficiency in the high-current region can be particularly reduced.

[0067] The preferred second material 5b has a lower electron affinity than the core portion of the quantum dot QDa.

[0068] With this configuration, electrons e can be easily injected from the core portion of the quantum point QDa from the first material 5a, and electrons e can be easily injected from the second material 5b into the matrix MR, both of which can be injected at low voltage.

[0069] On the other hand, if the electron affinity of the second material 5b is greater than that of the core portion of the quantum dot QDa, then electrons e are simultaneously injected from the second material 5b into both the core portion and the matrix MR of the quantum dot QDa.

[0070] Preferably, the electron affinity of the first material 5a differs from that of the second material 5b by more than 0.1 eV.

[0071] Since a difference of 0.1 eV in electron affinity results in a difference of approximately 50 times in the ease of current injection, it is possible to preferentially direct current to materials with suitable electron affinity.

[0072] The preferred first material 5a and the second material 5b are each composed of an inorganic compound.

[0073] With this configuration, the reliability of the light-emitting element 1a can be improved.

[0074] The first material 5a and the second material 5b are nanoparticles, preferably in order of increasing electron affinity, with the electron transport layer 5 containing a large volume ratio. In this embodiment, preferably, the volume ratio of the second material 5b in the electron transport layer 5 is greater than the volume ratio of the first material 5a in the electron transport layer 5. This facilitates the injection of electrons (e) into nanoparticles with low electron affinity, improving the injection efficiency of electrons into the matrix MR, which has low injection efficiency.

[0075] Preferably, the first material 5a and the second material 5b are nanoparticles. Near the interface with the cathode 6, the volume ratio of the electron transport layer 5 increases sequentially according to their electron affinity, from highest to lowest. In this embodiment, preferably, the volume ratio of the first material 5a in the electron transport layer 5 is greater than the volume ratio of the second material 5b in the electron transport layer 5. This facilitates the injection of electrons (e) from the cathode 6 into the electron transport layer 5. Furthermore, "near the interface" refers to the portion within 30 nm of the interface.

[0076] Preferably, the first material 5a and the second material 5b are nanoparticles. Near the interface with the light-emitting layer 4a, the volume ratio of the electron transport layer 5 increases sequentially according to their electron affinity. In this embodiment, preferably, the volume ratio of the second material 5b in the electron transport layer 5 is greater than the volume ratio of the first material 5a in the electron transport layer 5. This facilitates the injection of electrons (e) from the electron transport layer 5 into the matrix MR.

[0077] Preferably, the first material 5a and the second material 5b are nanoparticles, with the first material 5a decreasing in size from the cathode 6 side towards the light-emitting layer 4a side. This prevents electrons e from being sequentially injected into the first material 5a and the second material 5b according to their flow direction, thus minimizing the voltage within the electron transport layer 5. Preferably, the second material 5b increases in size from the cathode 6 side towards the light-emitting layer 4a side. This also prevents electrons e from being sequentially injected into the first material 5a and the second material 5b according to their flow direction, further minimizing the voltage within the electron transport layer 5.

[0078] In this embodiment, CdSe(Red) is used as the core of the quantum dot QDa, and ZnS is used as the matrix MR. Therefore, the band level at the lower end of the conduction band (QDa(CBM)) of the quantum dot QDa and the electron affinity of the core of the quantum dot QDa are 3.6 eV, and the band level at the lower end of the conduction band (MR(CBM)) of the matrix MR and the electron affinity of the matrix MR are 3.2 eV. Therefore, the electron affinity of the first material 5a is preferably 3.6 eV or more, and the electron affinity of the second material 5b is preferably 3.2 eV or more and less than 3.6 eV.

[0079] For example, at least one selected from TiO2 and SnO2 can be used as the first material 5a, and at least one selected from GaP, AlSb, ZrO2, GaN, ZnS and ZnTe can be used as the second material 5b.

[0080] Here, the electron affinity and ionization potential of each material are treated as the figures recorded in Table 1 below.

[0081] [Table 1] ( ) represents the emission color of the quantum dot.

[0082] Figure 6 This is a graph showing the relationship between the particle radius of ZnO and its band gap and electron affinity.

[0083] Preferably, the first material 5a and the second material 5b contained in the electron transport layer 5 are nanoparticles, for example, preferably ZnO nanoparticles.

[0084] The smaller the particle size of ZnO nanoparticles, the wider the band gap and the smaller the electron affinity due to quantum effects. Therefore, by changing the particle size of the first material 5a and the second material 5b, an electron transport layer 5 with two electron affinities can be achieved.

[0085] In this embodiment, CdSe(Red) is used as the core part of the quantum dot QDa and ZnS is used as the matrix MR. Therefore, it is preferable that the electron affinity of the first material 5a is 3.6 eV or more, and it is preferable that the electron affinity of the second material 5b is 3.2 eV or more and less than 3.6 eV.

[0086] Therefore, as the first material 5a and the second material 5b, when using ZnO nanoparticles, such as Figure 6 As shown, ZnO nanoparticles with an average particle size of 4.5 nm or more and a radius of 2.25 nm or more can be used as the first material 5a, and ZnO nanoparticles with an average particle size of 3.2 nm or more and less than 4.5 nm and a radius of 1.6 nm or more and less than 2.25 nm can be used as the second material 5b.

[0087] The first material 5a and the second material 5b can each be composed of the same element and have the same composition ratio, but the particle size distribution of the first material 5a and the particle size distribution of the second material 5b are different.

[0088] The electron transport layer 5 includes a first material 5a having a first particle size distribution and a second material 5b having a second particle size distribution different from the first particle size distribution. For example, the electron transport layer 5 includes a first material 5a having a particle size distribution within approximately ±15% centered at a particle size of 12 nm and a second material 5b having a particle size distribution within approximately ±15% centered at a particle size of 4 nm.

[0089] Here, "particle size" refers to the diameter of a circle with an area equivalent to that of a particle, as confirmed in cross-sectional observation of the layer containing the particles. "Different particle size distributions" means that the two particle size distributions do not need to be completely separated and can have overlapping particle size ranges. If at least two particle size peaks can be confirmed in cross-sectional observation of the electron transport layer 5 containing the first material 5a and the second material 5b, then the electron transport layer 5 is considered to contain particles with two different particle size distributions.

[0090] Figure 7 It represents Zn 1-x Mg x A graph showing the relationship between the x value in O and electron affinity.

[0091] The first material 5a and the second material 5b contained in the electron transport layer 5 can be configured such that the constituent elements of the first material 5a and the constituent elements of the second material 5b are the same, but the composition ratio of the first material 5a and the composition ratio of the second material 5b are different.

[0092] For example, the first material 5a and the second material 5b can each be Zn with an average particle size of 12 nm. 1-x Mg x O nanoparticles. For example... Figure 7 As shown, when Zn 1-x Mg x When the x value in O changes, the electron affinity changes. Therefore, by making the x values ​​of the first material 5a and the second material 5b different, it is possible to realize an electron transport layer 5 with two electron affinities.

[0093] As described above, the electron affinity of the first material 5a is preferably 3.6 eV or higher, and the electron affinity of the second material 5b is preferably 3.2 eV or higher and less than 3.6 eV.

[0094] Therefore, it is preferable that the x value of the first material 5a is 0 or more and 0.15 or less, and it is preferable that the x value of the second material 5b is greater than 0.15 and 0.35 or less.

[0095] Figure 8 It means Figure 1 A diagram illustrating the electron injection mechanism in the light-emitting element 1a of the first embodiment is shown. Furthermore, in Figure 8 In the process, the second applied voltage is higher than the first applied voltage, the third applied voltage is higher than the second applied voltage, and the fourth applied voltage is higher than the third applied voltage.

[0096] like Figure 8 As shown, under the first applied voltage and the second applied voltage, electrons e can be injected from the cathode 6 through the first material 5a into the quantum dot QDa, which is in contact with the electron transport layer 5, at a relatively low voltage, so that it recombines with the hole h and emits light.

[0097] like Figure 8 As shown, under the third and fourth applied voltages, electrons e can be injected from the cathode 6 into the matrix MR via the first material 5a and the second material 5b at a relatively low voltage. Then, the injected electrons e are injected into quantum dots QDa in the light-emitting layer 4a, and recombine with holes h to emit light.

[0098] In particular, for quantum dots QDa that are not in contact with the electron transport layer 5, electrons e need to be injected via the matrix MR. By actively injecting electrons e into the matrix MR at a low voltage, quantum dots QDa that are far from the electron transport layer 5 can emit light at a relatively low voltage, thereby obtaining high brightness.

[0099] Therefore, based on the light-emitting element 1a, it is possible to drive it at a low voltage without reducing luminous efficiency. Furthermore, the higher the voltage, the more the quantum dot QDa, which is farther from the electron transport layer 5, emits light, thus reducing roll-off. That is, the current dependence and voltage dependence of luminous efficiency can be improved, particularly reducing the decrease in luminous efficiency in high-current regions. Since the light-emitting element 1a possesses a matrix MR, its durability can be improved, and for the reasons mentioned above, its luminous efficiency can also be improved. Therefore, the display device including the light-emitting element 1a can also improve both durability and luminous efficiency.

[0100] Figure 9 This is a diagram showing the schematic configuration of the light-emitting element 1a' as a modified example of the first embodiment and the preferred mixing ratio of the first material 5a and the second material 5b in the electron transport layer 5.

[0101] like Figure 9 As shown, the preferred light-emitting element 1a' includes an electron transport layer 5 comprising a first electron transport layer 5' and a second electron transport layer 5''. The first electron transport layer 5' is positioned closer to the light-emitting layer 4a than the second electron transport layer 5''. The first electron transport layer 5' is a layer that at least mixes a first material 5a and a second material 5b. The amount of first material 5a contained in a unit volume of the second electron transport layer 5'' is greater than the amount of first material 5a contained in a unit volume of the first electron transport layer 5'.

[0102] At the interface between the electron transport layer 5 and the cathode 6 in the light-emitting element 1a', it is preferable that the first material 5a is more abundant than the second material 5b, and more preferably, it is composed only of the first material 5a. Therefore, for example, the first electron transport layer 5' is a layer that at least mixes the first material 5a and the second material 5b, and the second electron transport layer 5" can also be a layer composed only of the first material 5a. As a result, it will not become an obstacle to the sequential injection of electrons e into the second electron transport layer 5" and the first electron transport layer 5' in accordance with the direction of electron e flow, and the voltage within the electron transport layer 5 can be minimized.

[0103] On the other hand, at the interface between the electron transport layer 5 and the light-emitting layer 4a in the light-emitting element 1a', the second material 5b is preferably more abundant than the first material 5a. Therefore, by distributing a large amount of the second material 5b, which facilitates the injection of electrons e into the matrix MR, near the matrix MR where electrons e are difficult to inject, the luminous efficiency can be improved.

[0104] Furthermore, as described above, when the electron transport layer 5 is composed of a layer mixed with a first material 5a and a second material 5b, the second material 5b can gradually increase and the first material 5a can gradually decrease as the cathode 6 gets closer to the light-emitting layer 4a. This prevents the electrons e from becoming an obstacle to the sequential injection of the first material 5a and the second material 5b according to the electron e flow direction, thus minimizing the voltage within the electron transport layer 5.

[0105] Figure 9 The electron transport layer 5 shown can be formed, for example, by spin-coating a solution of nanoparticles as the second material 5b and spin-coating a solution of nanoparticles as the first material 5a before drying. Alternatively, it can be formed by preparing multiple solutions with different mixing ratios (mixing concentrations) of nanoparticles as the first material 5a and nanoparticles as the second material 5b, and coating and stacking them in sequence from solutions with low mixing ratios (mixing concentrations) of the first material 5a to solutions with high mixing concentrations, thereby forming a concentration distribution in the layer thickness direction.

[0106] Furthermore, in this embodiment, an example is formed by first forming the light-emitting layer 4a, followed by forming... Figure 9 The case of electron transport layer 5 shown is illustrated as an example, but it is not limited to this. For example, after forming cathode 6, it can be formed... Figure 9 In the case where the electron transport layer 5 is shown and then the light-emitting layer 4a is formed, a solution of nanoparticles as the first material 5a can be spin-coated, and a solution of nanoparticles as the second material 5b can be spin-coated before drying. Alternatively, multiple solutions with different mixing ratios (mixing concentrations) of nanoparticles as the first material 5a and nanoparticles as the second material 5b can be prepared, and the solutions can be coated and stacked multiple times in sequence from solutions with high mixing ratios (mixing concentrations) of the first material 5a to solutions with low mixing concentrations, thereby forming a concentration distribution in the layer thickness direction.

[0107] (Second Implementation) Figure 10 This is a cross-sectional view showing the schematic configuration of the light-emitting element 10a according to the second embodiment. In the first embodiment, the same reference numerals are used to label the same constituent elements as described above, and their detailed descriptions are not repeated.

[0108] Figure 10The light-emitting element 10a shown includes: an anode 2, a cathode 6, a light-emitting layer 4a disposed between the anode 2 and the cathode 6, an electron transport layer 15 disposed between the cathode 6 and the light-emitting layer 4a as a carrier transport layer, and a hole transport layer 13 disposed between the anode 2 and the light-emitting layer 4a as a carrier transport layer. The hole transport layer 13, as a carrier transport layer, at least includes a layer formed by mixing a first material 13a and a second material 13b, wherein the first material 13a is a material different from the second material 13b. In this embodiment, the example shown is that the hole transport layer 13 is composed of a layer mixed with the first material 13a and the second material 13b, but it is not limited thereto; the hole transport layer 13 may contain any layer mixed with the first material 13a and the second material 13b. Furthermore, the statement that the first material 13a and the second material 13b are different materials refers to any one of the following three situations: First, the constituent elements of the first material 13a and the second material 13b are different; second, even if the constituent elements of the first material 13a and the second material 13b are the same, the composition ratio of the first material 13a and the composition ratio of the second material 13b are different; and third, when the first material 13a and the second material 13b are both nanoparticles, the first material 13a and the second material 13b are composed of the same elements and have the same composition ratio, but the particle size distribution of the first material 13a and the particle size distribution of the second material 13b are different.

[0109] Electron transport layer 15 is, for example, made of n-type oxide semiconductor (e.g., ZnO, Zn 1-x Mg x The electron transport layer 15 is formed using O (0≤x<1), TiO2, and SnO2. It can be either nanoparticles or a continuous film. The electron transport layer 15 can be formed through coating, sputtering, evaporation, or other methods.

[0110] Figure 11 It is a general representation Figure 10 The diagram shows the band levels of the hole transport layer 13, the light-emitting layer 4a, and the electron transport layer 15 of the light-emitting element 10a in the second embodiment.

[0111] Furthermore, in this embodiment, since the shell portion of the quantum dot QDa and the matrix MR are formed of ZnS, the diagrams of the lower conduction band level of the shell portion of the quantum dot QDa, which is the same as the lower conduction band level (MR(CBM)) of the matrix MR, and the upper valence band level of the shell portion of the quantum dot QDa, which is the same as the upper valence band level (MR(VBM)) of the matrix MR, are omitted here.

[0112] like Figure 11As shown, the hole transport layer 13, which serves as the carrier transport layer, comprises at least a layer that mixes a first material 13a and a second material 13b. The first material 13a is a different material from the second material 13b, so the ionization potential of the first material 13a (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the first material 13a (13a (VBM))) and the ionization potential of the second material 13b (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the second material 13b (13b (VBM))) are different.

[0113] As described above, by using a hole transport layer 13 comprising a mixture of different materials, namely a first material 13a and a second material 13b, compared to the case of using a hole transport layer made of a single material, the appropriate energy level can be adjusted by injecting holes h from the anode 2 into the light-emitting layer 4a comprising the matrix MR. This allows for easy injection of holes h from the anode 2 into the hole transport layer 13 and from the hole transport layer 13 into the light-emitting layer 4a comprising the matrix MR, thereby achieving low voltage.

[0114] That is, by using a hole transport layer 13 that is composed of a mixture of different materials, namely a first material 13a and a second material 13b, the ionization potential of the first material 13a is different from that of the second material 5b, thereby making it easier to inject holes h into the light-emitting layer 4a, which has different energy levels due to the quantum dot QDa and the matrix MR.

[0115] Furthermore, by using a hole transport layer 13 comprising a mixture of different materials, namely a first material 13a and a second material 13b, it is possible to have multiple energy levels (ionization potentials) from which holes h are injected into the light-emitting layer 4a from the hole transport layer 13. Within the hole transport layer 13, holes h can also be easily moved from the first material 13a, which is a shallower energy level, to the second material 13b, which is a deeper energy level. As a result, holes h can be efficiently injected from the first material 13a and the second material 13b into quantum dots QDa and the matrix MR, which have different energy levels.

[0116] In addition, Figure 11 The diagram illustrates the case where the energy level of the upper valence band of the core portion of the quantum dot QDa (QDa(VBM)) is deeper than that of the upper valence band of the first material 13a (13a(VBM)). However, the same effect can be achieved even when the energy level of the upper valence band of the core portion of the quantum dot QDa (QDa(VBM)) is shallower than that of the upper valence band of the first material 13a (13a(VBM)).

[0117] The surface of the light-emitting layer 4a is composed of two different materials: quantum dots (QDa) and a matrix (MR). The hole transport layer 13 also comprises a layer of two different materials, namely a mixture of the first material 13a and the second material 13b. This improves the adhesion between the light-emitting layer 4a and the hole transport layer 13, as well as the conductivity and mechanical stress resistance at their interface. Furthermore, the light-emitting layer 4a and the hole transport layer 13 are easily planarized, resulting in good in-plane uniformity of light emission.

[0118] like Figure 11 As shown, preferably, the ionization potential of the second material 13b (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the second material 13b (13b(VBM))) is greater than the ionization potential of the first material 13a (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the first material 13a (13a(VBM))), and the ionization potential of the core portion of the quantum dot QDa (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the core portion of the quantum dot QDa (QDa(VBM))) is greater than the ionization potential of the first material 13a.

[0119] According to this configuration, since the ionization potential increases in the order of anode 2, first material 13a, and the core portion of quantum dot QDa, holes h can be injected into the core portion of quantum dot QDa with a low voltage, thus reducing the driving voltage of light-emitting element 10a.

[0120] The preferred ionization potential of the matrix MR (the absolute value of the difference between the vacuum energy level and the band level at the upper end of the valence electron band of the matrix MR (MR(VBM))) is greater than or equal to the ionization potential of the second material 13b.

[0121] With this configuration, since the ionization potential increases in the order of anode 2, first material 13a, second material 13b, and matrix MR, holes h can be injected into the matrix MR at a low voltage. The holes h injected into the matrix MR migrate to quantum dots QDa located away from the hole transport layer 13 and recombine to emit light. Therefore, quantum dots QDa located away from the hole transport layer 13 can emit light at a lower voltage, resulting in high brightness. The higher the voltage, the more quantum dots QDa located away from the hole transport layer 13 will emit light, thus reducing roll-off. In other words, the current dependence and voltage dependence of luminescence efficiency can be improved, particularly reducing the decrease in luminescence efficiency in high-current regions.

[0122] The ionization potential of the preferred second material 13b is greater than that of the core portion of the quantum dot QDa.

[0123] With this configuration, holes h can be easily injected from the first material 13a into the core portion of the quantum dot QDa, and holes h can be easily injected from the second material 13b into the matrix MR, both of which can be injected at low voltage.

[0124] On the other hand, when the ionization potential of the second material 13b is smaller than the ionization potential of the core portion of the quantum dot QDa, holes h are simultaneously injected from the second material 13b into both the core portion of the quantum dot QDa and the matrix MR.

[0125] Preferably, the difference between the ionization potential of the first material 13a and the ionization potential of the second material 13b is 0.1 eV or more.

[0126] For every 0.1 eV difference in ionization potential, the ease of hole injection will differ by about 50 times, thus enabling holes h to be preferentially injected into materials with suitable ionization potentials.

[0127] The first material 13a and the second material 13b are preferably composed of inorganic compounds.

[0128] With this configuration, the reliability of the light-emitting element 10a can be improved.

[0129] The first material 13a and the second material 13b are nanoparticles, and preferably, the volume ratio of the hole transport layer 13 containing them is large, in descending order of their ionization potential. In this embodiment, it is preferable that the volume ratio of the second material 13b contained in the hole transport layer 13 is larger than the volume ratio of the first material 13a contained in the hole transport layer 13. This facilitates the injection of holes h into nanoparticles with high ionization potential, and improves the injection efficiency of holes h into the matrix MR, which has low injection efficiency.

[0130] Preferably, the first material 13a and the second material 13b are nanoparticles, and near the interface with the anode 2, the hole transport layer 13 contains a large volume ratio of these nanoparticles in order of increasing ionization potential. In this embodiment, it is preferable that the volume ratio of the first material 13a in the hole transport layer 13 is larger than the volume ratio of the second material 13b in the hole transport layer 13. This facilitates the injection of holes h from the anode 2 into the hole transport layer 13.

[0131] Preferably, the first material 13a and the second material 13b are nanoparticles, and near the interface with the light-emitting layer 4a, the hole transport layer 13 contains a large volume fraction of these nanoparticles in descending order of their ionization potential. In this embodiment, it is preferable that the volume fraction of the second material 13b contained in the hole transport layer 13 is larger than the volume fraction of the first material 13a contained in the hole transport layer 13. This facilitates the injection of holes h from the hole transport layer 13 into the matrix MR.

[0132] The first material 13a and the second material 13b are nanoparticles. Preferably, the first material 13a decreases from the anode 2 side towards the light-emitting layer 4a side. This prevents it from hindering the sequential injection of holes h into the first material 13a and the second material 13b in the direction of hole h flow, thus minimizing the voltage within the hole transport layer 13. Preferably, the second material 13b increases from the anode 2 side towards the light-emitting layer 4a side. This also prevents it from hindering the sequential injection of holes h into the first material 13a and the second material 13b in the direction of hole h flow, thus minimizing the voltage within the hole transport layer 13.

[0133] In this embodiment, CdSe(Red) is used as the core of the quantum dot QDa, and ZnS is used as the matrix MR. Therefore, the band level at the upper valence band (QDa(VBM)) of the quantum dot QDa and the ionization potential of the core of the quantum dot QDa are 5.6 eV, and the band level at the upper valence band (MR(VBM)) of the matrix MR and the ionization potential of the matrix MR are 7.2 eV. Therefore, it is preferable that the ionization potential of the first material 13a is 5.6 eV or less, and it is preferable that the ionization potential of the second material 13b is greater than 5.6 eV and less than 7.2 eV.

[0134] For example, as the first material 13a, at least one selected from AlSb, Cu2O and NiO can be used appropriately, and as the second material 13b, at least one selected from GaP, GaN, ZnS, ZnTe and LaNiO3 can be used appropriately.

[0135] Here, the electron affinity and ionization potential of each material are treated as the figures recorded in Table 1 above.

[0136] The first material 13a and the second material 13b can be composed of the same element and have the same composition ratio, but the particle size distribution of the first material 13a and the particle size distribution of the second material 13b are different.

[0137] For example, if the particle size of NiO or Cu2O nanoparticles is reduced, the band gap widens due to quantum effects and the ionization potential increases. Therefore, by changing the particle size of the first material 13a and the second material 13b, a hole transport layer 13 with two ionization potentials can be realized.

[0138] Each of the first material 13a and the second material 13b contained in the hole transport layer 13 is the same as the constituent elements of the first material 13a and the second material 13b, and the composition ratio of the first material 13a and the composition ratio of the second material 13b may be different.

[0139] For example, it could also be nanoparticles with an average particle size of 12 nm, i.e., Ni. 1-x Mg xO (0≤x<1), a material with an ionization potential of 5.6eV and x=0.25 is used as the first material 13a, and a material with an ionization potential of 5.8eV and x=0.5 is used as the second material 13b.

[0140] Furthermore, to enable the hole transport layer 13 to have different ionization potentials, Cu2O, NiO, or NiO can also be used in the hole transport layer 13. 1-x (LaNiO3) x Different materials. Nanoparticles of various materials are fabricated using known techniques, and hole transport layers 13 are formed using a mixture of nanoparticles with organic solvents such as ethanol and spin coating, inkjet coating, etc.

[0141] Figure 12 This is a diagram showing the schematic configuration of the light-emitting element 10a' as a modified example of the second embodiment and the preferred mixing ratio of the first material 13a and the second material 13b in the hole transport layer 13.

[0142] like Figure 12 As shown, the hole transport layer 13 of the preferred light-emitting element 10a' includes a first hole transport layer 13' and a second hole transport layer 13'". The second hole transport layer 13' is positioned closer to the light-emitting layer 4a than the first hole transport layer 13'. The second hole transport layer 13' is a layer that mixes at least a first material 13a and a second material 13b. The amount of first material 13a contained in a unit volume of the first hole transport layer 13' is greater than the amount of first material 13a contained in a unit volume of the second hole transport layer 13'.

[0143] At the interface between the hole transport layer 13 of the light-emitting element 10a' and the anode 2, it is preferable that the first material 13a is more abundant than the second material 13b, and more preferably, it is composed only of the first material 13a. Therefore, for example, the second hole transport layer 13” is a layer that at least mixes the first material 13a and the second material 13b, and the first hole transport layer 13” can also be a layer composed only of the first material 13a. As a result, it will not become an obstacle to the sequential injection of holes h into the first hole transport layer 13' and the second hole transport layer 13” in the direction of hole h flow, and the voltage in the hole transport layer 13 can be minimized.

[0144] On the other hand, at the interface between the hole transport layer 13 and the light-emitting layer 4a in the light-emitting element 10a', the second material 13b is preferably more abundant than the first material 13a. Therefore, by distributing a greater amount of the second material 13b, which facilitates the injection of holes h into the matrix MR, near the matrix MR where it is difficult to inject holes h, the luminous efficiency can be improved.

[0145] Furthermore, as described above, when the hole transport layer 13 is composed of a layer that mixes a first material 13a and a second material 13b, the second material 13b can be gradually increased and the first material 13a can be gradually decreased as the hole transport layer 13 approaches the light-emitting layer 4a from the anode 2. This prevents the holes h from being injected sequentially into the first material 13a and the second material 13b in the direction of hole h flow, thus minimizing the voltage within the hole transport layer 13.

[0146] Figure 12 The hole transport layer 13 shown can be formed, for example, by spin-coating a solution of nanoparticles as the first material 13a and spin-coating a solution of nanoparticles as the second material 13b before drying. Alternatively, multiple solutions with different mixing ratios (mixing concentrations) of nanoparticles as the first material 13a and nanoparticles as the second material 13b can be prepared and coated and stacked in sequence from solutions with high mixing ratios (mixing concentrations) of the first material 13a to solutions with low mixing concentrations, thereby forming a concentration distribution in the layer thickness direction.

[0147] Furthermore, in this embodiment, examples of those formed first are listed. Figure 12 The example shown is of a hole transport layer 13 followed by a light-emitting layer 4a, but it is not limited to this case. For example, the light-emitting layer 4a may be formed first, followed by the formation of the light-emitting layer 4a. Figure 12 When the hole transport layer 13 shown is subsequently formed into an anode 2, a solution of nanoparticles as the second material 13b can be spin-coated, and a solution of nanoparticles as the first material 13a can be spin-coated before drying. Alternatively, multiple solutions with different mixing ratios (mixing concentrations) of nanoparticles as the first material 13a and nanoparticles as the second material 13b can be prepared, and the solutions can be coated and stacked in sequence from solutions with low mixing ratios (mixing concentrations) of the first material 13a to solutions with high mixing concentrations, thereby forming a concentration distribution in the layer thickness direction.

[0148] (Third Implementation) Figure 13 This is a cross-sectional view showing the schematic configuration of the display device 20 according to the third embodiment.

[0149] like Figure 13As shown, the display device 20 includes a light-emitting element (first light-emitting element) 1a” and a light-emitting element (second light-emitting element) 1b that emits light of a different wavelength than the light-emitting element 1a”. For example, the light-emitting element 1a” may be a red light-emitting element with a red light-emitting layer, and the light-emitting element 1b may be a green light-emitting element with a green light-emitting layer. The light-emitting element 1a” has a quantum dot (first quantum dot) QDa, and the light-emitting element 1b has a quantum dot (second quantum dot) QDb. Furthermore, both the light-emitting element 1a” and the light-emitting element 1b have an electron transport layer (common electron transport layer) 25 between the cathode 6 and the light-emitting layers 4a and 4b as a carrier transport layer.

[0150] The electron transport layer (common electron transport layer) 25 includes a layer formed by mixing a first material 5a, a second material 5b, and a third material 5c that is different from the first material 5a and the second material 5b. In this embodiment, the electron transport layer 25 is illustrated as being composed of a layer formed by mixing the first material 5a, the second material 5b, and the third material 5c, but it is not limited to this. The electron transport layer 25 may contain any layer formed by mixing the first material 5a, the second material 5b, and the third material 5c.

[0151] Furthermore, in light-emitting elements 1a” and 1b, the portion other than the electron transport layer (common electron transport layer) 25 (which serves as a common layer) and the cathode 6 is separated by the partition wall 8.

[0152] Figure 14 It means Figure 13 The diagram shows the electron injection mechanism in the light-emitting elements 1a” and 1b of the display device 20 of the third embodiment.

[0153] In this embodiment, CdSe(Red) is used as the core portion of quantum dot QDa, CdSe(Green) is used as the core portion of quantum dot QDb, and ZnMgS is used as the matrix MR. Therefore, as Figure 14 As shown, the band level at the lower end of the conduction band of the core region of quantum dot QDa (QDa(CBM)) is 3.6 eV, the band level at the lower end of the conduction band of the core region of quantum dot QDb (QDb(CBM)) is 3.3 eV, and the band level at the lower end of the conduction band of matrix MR (MR(CBM)) is 2.8 eV.

[0154] If the band levels at the lower end of the conduction band of the core region of quantum dot QDa (QDa(CBM)), the band levels at the lower end of the conduction band of the core region of quantum dot QDb (QDb(CBM)), and the band levels at the lower end of the conduction band of the matrix MR (MR(CBM)) are... Figure 14For the energy levels shown, the band level at the lower end of the conduction band of the first material 5a (5a(CBM)) only needs to be 3.6 eV or higher; the band level at the lower end of the conduction band of the second material 5b (5b(CBM)) only needs to be 2.8 eV or higher and less than 3.3 eV; and the band level at the lower end of the conduction band of the third material 5c (5c(CBM)) only needs to be 3.3 eV or higher and less than 3.6 eV. In other words, the electron affinity of the first material 5a only needs to be 3.6 eV or higher; the electron affinity of the second material 5b only needs to be 2.8 eV or higher and less than 3.3 eV; and the electron affinity of the third material 5c only needs to be 3.3 eV or higher and less than 3.6 eV.

[0155] Therefore, in the display device 20 of this embodiment, the magnitudes of the electron affinity of the matrix MR, the core portion of the quantum dot (first quantum dot) QDa, the core portion of the quantum dot (second quantum dot) QDb, the first material 5a, the second material 5b, and the third material 5c are as follows: matrix MR (2.8 eV) ≤ second material 5b (2.8 eV or more and less than 3.3 eV) < core portion of the quantum dot (second quantum dot) QDb (3.3 eV) ≤ third material 5c (3.3 eV or more and less than 3.6 eV) < core portion of the quantum dot (first quantum dot) QDa (3.6 eV) ≤ first material 5a (3.6 eV or more).

[0156] As the first material 5a, at least one selected from TiO2 and SnO2 may be used; as the second material 5b, at least one selected from GaN, ZnS, ZnTe, Ca2SnO4 and CaSnO3 may be used; and as the third material 5c, at least one selected from GaP, AlSb, ZrO2 and CuO2 may be used.

[0157] Furthermore, when ZnO nanoparticles are used as the first material 5a, the second material 5b, and the third material 5c, ZnO nanoparticles with an average particle size of 4.5 nm or more and a radius of 2.25 nm or more can be used as the first material 5a; ZnO nanoparticles with an average particle size of 2.5 nm or more and less than 3.5 nm and a radius of 1.25 nm or more and less than 1.75 nm can be used as the second material 5b; and ZnO nanoparticles with an average particle size of 3.5 nm or more and less than 4.5 nm and a radius of 1.75 nm or more and less than 2.25 nm can be used as the third material 5c.

[0158] The first material 5a, the second material 5b, and the third material 5c are each composed of the same element and have the same composition ratio. The particle size distribution of the first material 5a, the second material 5b, and the third material 5c can be different.

[0159] Furthermore, Zn with an average particle size of 12 nm is used as the first material 5a, the second material 5b, and the third material 5c. 1-x Mg x In the case of O nanoparticles, for example, as the first material 5a, a material with x ≤ 0.15 can be used; as the second material 5b, a material with 0.3 < x ≤ 0.55 can be used; and as the third material 5c, a material with 0.15 < x ≤ 0.3 can be used.

[0160] In this embodiment, the example shown is that the light-emitting element 1a” and the light-emitting element 1b each have a matrix MR made of the same material, but it is not limited to this, and the matrix may also be made of different materials. In addition, as long as the electron transport layer (common electron transport layer) 25 of each of the light-emitting elements 1a” and 1b, which serves as a common layer, is made of the same material, it may also be separated by the partition wall 8.

[0161] According to the display device 20, such as Figure 14 As shown, electrons e are injected in descending order of electron affinity as voltage is applied. That is, at the lowest first applied voltage, electrons e are injected from the first material 5a into the core portion of quantum dot (first quantum dot) QDa; at a second applied voltage higher than the first applied voltage, electrons e are injected from the third material 5c into the core portion of quantum dot (second quantum dot) QDb; and at a third applied voltage higher than the second applied voltage, electrons e are injected from the second material 5b via the matrix MR into the core portions of quantum dot (first quantum dot) QDa and quantum dot (second quantum dot) QDb located away from the electron transport layer (common electron transport layer) 25, and luminescence occurs.

[0162] According to the display device 20, light-emitting elements 1a” and 1b that emit light of different wavelengths can emit light efficiently with low voltage. Furthermore, the electron transport layer 25 is a common electron transport layer for each of the light-emitting elements 1a” and 1b. Therefore, the number of manufacturing steps of the display device 20 can be reduced.

[0163] (Fourth Implementation) Figure 15 This is a cross-sectional view showing the schematic configuration of the display device 30 according to the fourth embodiment.

[0164] Figure 15The display device 30 shown includes: a first light-emitting element 1a”', a second light-emitting element 1b', and a third light-emitting element 1c that emits light of a different wavelength than the first light-emitting element 1a”' and the second light-emitting element 1b'. Additionally, the electron transport layer (common electron transport layer) 25' comprises a layer formed by mixing a first material 5a, a second material 5b, a third material 5c, and a fourth material 5d different from the first material 5a, the second material 5b, and the third material 5c. The first light-emitting element 1a”', the second light-emitting element 1b', and the third light-emitting element 1c each possess the common electron transport layer (common electron transport layer) 25'. For example, the light-emitting element 1a”' can be a red light-emitting element including a red light-emitting layer, the light-emitting element 1b' can be a green light-emitting element including a green light-emitting layer, and the third light-emitting element 1c can be a blue light-emitting element including a blue light-emitting layer.

[0165] Figure 16 It means Figure 15 The diagram shows the electron injection mechanism in the light-emitting elements 1a”', 1b’ and 1c of the display device 30 of the fourth embodiment.

[0166] In this embodiment, CdSe(Red) is used as the core portion of quantum dot QDa, CdSe(Green) is used as the core portion of quantum dot QDb, CdSe(Blue) is used as the core portion of quantum dot QDc, ​​and ZnMgS is used as the matrix MR. Therefore, as Figure 16 As shown, the band level at the lower end of the conduction band of the core region of quantum dot QDa (QDa(CBM)) is 3.6 eV, the band level at the lower end of the conduction band of the core region of quantum dot QDb (QDb(CBM)) is 3.3 eV, the band level at the lower end of the conduction band of the core region of quantum dot QDc (QDc(CBM)) is 2.9 eV, and the band level at the lower end of the conduction band of matrix MR (MR(CBM)) is 2.8 eV.

[0167] The band levels at the lower end of the conduction band of the core region of quantum dot QDa (QDa(CBM)), the band levels at the lower end of the conduction band of the core region of quantum dot QDb (QDb(CBM)), the band levels at the lower end of the conduction band of the core region of quantum dot QDc (QDc(CBM)), and the band levels at the lower end of the conduction band of the matrix MR (MR(CBM)) are... Figure 16As shown, the band level at the lower end of the conduction band of the first material 5a (5a(CBM)) can be above 3.6 eV; the band level at the lower end of the conduction band of the second material 5b (5b(CBM)) only needs to be above 2.8 eV and below 2.9 eV; the band level at the lower end of the conduction band of the third material 5c (5c(CBM)) only needs to be above 3.3 eV and below 3.6 eV; and the band level at the lower end of the conduction band of the fourth material 5d (5d(CBM)) only needs to be above 2.9 eV and below 3.3 eV. That is, the electron affinity of the first material 5a only needs to be above 3.6 eV, the electron affinity of the second material 5b only needs to be above 2.8 eV and less than 2.9 eV, the electron affinity of the third material 5c only needs to be above 3.3 eV and less than 3.6 eV, and the electron affinity of the fourth material 5d only needs to be above 2.9 eV and less than 3.3 eV.

[0168] Therefore, in the display device 30 of this embodiment, the electron affinity of the matrix MR, the core portion of the first quantum dot QDa, the core portion of the second quantum dot QDb, the core portion of the third quantum dot QDc, ​​the first material 5a, the second material 5b, the third material 5c, and the fourth material 5d is in the following order: matrix MR (2.8 eV) ≤ second material 5b (2.8 eV or more and less than 2.9 eV) < core portion of the third quantum dot QDb (2.9 eV) ≤ fourth material 5d (2.9 eV or more and less than 3.3 eV) < core portion of the second quantum dot QDb (3.3 eV) ≤ third material 5c (3.3 eV or more and less than 3.6 eV) < core portion of the first quantum dot QDa (3.6 eV) ≤ first material 5a (3.6 eV or more).

[0169] In this embodiment, the example shown is that the light-emitting elements 1a”', 1b’, and 1c each have a matrix MR made of the same material, but it is not limited to this and may also have matrices made of different materials. In addition, the electron transport layer (common electron transport layer) 25' of each of the light-emitting elements 1a”', 1b’, and 1c as a common layer may also be separated by the partition wall 8 as long as they are made of the same material.

[0170] According to the display device 30, light-emitting elements 1a”’, 1b’ and 1c that emit light of different wavelengths can emit light efficiently with low voltage. Furthermore, the electron transport layer 25 is a common electron transport layer for each of the light-emitting elements 1a”’, 1b’ and 1c. Therefore, the number of manufacturing steps of the display device 30 can be reduced.

[0171] (Fifth Implementation) Figure 17This is a cross-sectional view showing the schematic configuration of the display device 40 according to the fifth embodiment.

[0172] like Figure 17 As shown, the display device 40 includes a light-emitting element (first light-emitting element) 10a” and a light-emitting element (second light-emitting element) 10b that emits light of a different wavelength than the light-emitting element 10a”. For example, the light-emitting element 10a” may be a red light-emitting element including a red light-emitting layer, and the light-emitting element 10b may be a green light-emitting element including a green light-emitting layer. The light-emitting element 10a” has a quantum dot (first quantum dot) QDa, and the light-emitting element 10b has a quantum dot (second quantum dot) QDb'. Furthermore, each of the light-emitting elements 10a” and 10b has a hole transport layer (common hole transport layer) 23 between the anode 2 and the light-emitting layers 4a and 4b as a carrier transport layer.

[0173] The hole transport layer (common hole transport layer) 23 includes a layer composed of a first material 13a, a second material 13b, and a third material 13c, which is different from the first material 13a and the second material 13b. In this embodiment, the hole transport layer 23 is illustrated as a layer composed of a mixture of the first material 13a, the second material 13b, and the third material 13c, but it is not limited to this. The hole transport layer 23 may simply include a layer composed of a mixture of the first material 13a, the second material 13b, and the third material 13c.

[0174] Furthermore, in light-emitting elements 10a” and 10b, the portion other than the hole transport layer (common hole transport layer) 23, the electron transport layer 15, and the cathode 6, which serve as common layers, is separated by partition walls 8a and 8b.

[0175] Figure 18 It means Figure 17 The diagram shows the hole injection mechanism in the light-emitting element 10a” and the light-emitting element 10b of the display device 40 of the fifth embodiment.

[0176] In this embodiment, CdSe (Red) is used as the core of quantum dot QDa, ZnSe (Blue) is used as the core of quantum dot QDb', and ZnS is used as the matrix MR. Therefore, the band level at the upper valence band (QDa(VBM)) of the core of quantum dot QDa and the ionization potential of the core of quantum dot QDa are 5.6 eV, the band level at the upper valence band (QDb'(VBM)) of the core of quantum dot QDb' and the ionization potential of the core of quantum dot QDb' are 5.8 eV, and the band level at the upper valence band (MR(VBM)) of the matrix MR and the ionization potential of the matrix MR are 7.2 eV. Therefore, it is preferable that the ionization potential of the first material 13a is 5.6 eV or less, it is preferable that the ionization potential of the second material 13b is greater than 5.8 eV and less than 7.2 eV, and it is preferable that the ionization potential of the third material 13c is greater than 5.6 eV and less than 5.8 eV.

[0177] Therefore, in the display device 40 of this embodiment, the magnitudes of the ionization potentials of the matrix MR, the core portion of the first quantum dot QDa, the core portion of the second quantum dot QDb', the first material 13a, the second material 13b, and the third material 13c are as follows: matrix MR (7.2 eV) ≥ second material 13b (greater than 5.8 eV and less than 7.2 eV) > core portion of the second quantum dot QDb' (5.8 eV) ≥ third material 13c (greater than 5.6 eV and less than 5.8 eV) > core portion of the first quantum dot QDa (5.6 eV) ≥ first material 13a (5.6 eV and less than 5.6 eV).

[0178] In addition, ZnTe can be used as a third material 13c.

[0179] In this embodiment, it is illustrated that the light-emitting element 10a” and the light-emitting element 10b each have a matrix MR made of the same material, but it is not limited to this and may also have a matrix made of different materials. In the light-emitting element 10a” and the light-emitting element 10b, the hole transport layer (common hole transport layer) 23, which serves as a common layer, may be made of the same material or may be separated by the partition walls 8a and 8b.

[0180] According to the display device 40, such as Figure 18As shown, at the lowest first applied voltage, holes h are injected from the first material 13a into the core portion of quantum dot (first quantum dot) QDa. At the second applied voltage, which is higher than the first applied voltage, holes h are injected from the third material 13c into the core portion of quantum dot (second quantum dot) QDb'. At the third applied voltage, which is higher than the second applied voltage, holes h are injected from the second material 13b through the matrix MR into the core portions of quantum dot (first quantum dot) QDa and quantum dot (second quantum dot) QDb' located away from the hole transport layer (common hole transport layer) 23, and light is emitted.

[0181] According to the display device 40, light-emitting elements 10a” and 10b that emit light of different wavelengths can emit light efficiently with low voltage. Furthermore, the hole transport layer 23 is a common hole transport layer for each of the light-emitting elements 10a” and 10b. Therefore, the number of manufacturing steps of the display device 40 can be reduced.

[0182] Although not illustrated, the display device 40 may also include a light-emitting element (third light-emitting element) that emits light of a different wavelength than light-emitting elements 10a” and 10b. The light-emitting element (third light-emitting element) has a third quantum dot as a quantum dot, and each of the light-emitting elements (10a”, 10b, and the third light-emitting element) has a common hole transport layer as a carrier transport layer between the anode 2 and the light-emitting layer. The aforementioned common hole transport layer includes a mixture of a first material 13a, a second material 13b, a third material 13c, and a mixture of the first material 13a and the second material 13b. 3a. A layer of a fourth material different from the second material 13b and the third material 13c. In this case, the magnitudes of the ionization potentials of the matrix MR, the core portion of the first quantum dot QDa, the core portion of the second quantum dot QDb', the core portion of the third quantum dot, the first material 13a, the second material 13b, the third material 13c, and the fourth material are as follows: matrix MR ≥ second material 13b > core portion of the third quantum dot ≥ fourth material > core portion of the second quantum dot QDb' ≥ third material 13c > core portion of the first quantum dot QDa ≥ first material 13a.

[0183] (Sixth Implementation Method) Figure 19 This is a cross-sectional view showing the schematic configuration of the display device 50 according to the sixth embodiment.

[0184] like Figure 19As shown, the display device 50 includes a light-emitting element (first light-emitting element) 1a and a light-emitting element 1b (second light-emitting element) that emits light of a different wavelength than the light-emitting element (first light-emitting element) 1a. The light-emitting element 1a has a quantum dot (first quantum dot) QDa and an electron transport layer 5 serving as a carrier transport layer. The light-emitting element 1b has a quantum dot (second quantum dot) QDb and an electron transport layer 25 serving as a carrier transport layer. The electron transport layer 5 includes a layer formed by mixing a first material 5a and a second material 5b. The electron transport layer 25 includes a layer formed by mixing the first material 5a, the second material 5b, and a third material 5c, which is different from the first material 5a and the second material 5b.

[0185] Although not illustrated, the display device 50 may also include a light-emitting element (third light-emitting element) that emits light at a different wavelength than the light-emitting elements (first light-emitting element) 1a and 1b (second light-emitting element). The light-emitting element (third light-emitting element) has quantum dots (third quantum dots) and an electron transport layer as a charge carrier transport layer. The electron transport layer of the light-emitting element (third light-emitting element) comprises a layer made of a mixture of a first material 5a, a second material 5b, a third material 5c, and a fourth material that is different from the first material 5a, the second material 5b, and the third material 5c.

[0186] Furthermore, in the display device 50, the portion other than the cathode 6, which is a common layer, is separated by the partition wall 8c.

[0187] According to the display device 50, by using multiple electron transport layers made of different materials, by injecting electrons e from the cathode 6 into the light-emitting layer containing the matrix MR, the appropriate energy level can be adjusted, and electrons e can be easily injected from the cathode 6 into the electron transport layer and from the electron transport layer into the light-emitting layer containing the matrix MR, thereby achieving low voltage.

[0188] (Seventh Implementation) Figure 20 This is a cross-sectional view showing the schematic configuration of the display device 60 according to the seventh embodiment.

[0189] like Figure 20As shown, the display device 60 includes a light-emitting element (first light-emitting element) 10a and a light-emitting element 10b (second light-emitting element) that emits light of a different wavelength than the light-emitting element (first light-emitting element) 10a. The light-emitting element 10a has a quantum dot (first quantum dot) QDa and a hole transport layer 13 as a carrier transport layer, and the light-emitting element 10b has a quantum dot (second quantum dot) QDb' and a hole transport layer 23 as a carrier transport layer. The hole transport layer 13 includes a layer formed by mixing a first material 13a and a second material 13b, and the hole transport layer 23 includes a layer formed by mixing the first material 13a, the second material 13b, and a third material 13c that is different from the first material 13a and the second material 13b.

[0190] Although not illustrated, the display device 60 may also include a light-emitting element (third light-emitting element) that emits light of a different wavelength than that of the light-emitting element (first light-emitting element) 10a and the light-emitting element 10b (second light-emitting element). The light-emitting element (third light-emitting element) has a quantum dot (third quantum dot) and a hole transport layer as a carrier transport layer. The hole transport layer of the light-emitting element (third light-emitting element) includes a layer formed by mixing a first material 13a, a second material 13b, a third material 13c, and a fourth material that is different from the first material 13a, the second material 13b, and the third material 13c.

[0191] Furthermore, in the display device 60, the portion other than the electron transport layer 15, which serves as a common layer, and the cathode 6 is separated by the partition wall 8c.

[0192] According to the display device 60, by using multiple hole transport layers made of different materials, and by injecting holes h from the anode 2 into the light-emitting layer containing the matrix MR, an appropriate energy level can be adjusted, and holes h can be easily injected from the anode 2 into the hole transport layer and from the hole transport layer into the light-emitting layer containing the matrix MR, thereby achieving low voltage.

[0193] [Additional Notes] This disclosure is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical solutions disclosed in different embodiments are also included in the technical scope of this disclosure. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0194] Industrial availability This disclosure can be used in light-emitting elements and display devices.

[0195] Explanation of reference numerals in the attached figures 1a, 1a', 1a”, 1a”': Light-emitting elements; 1b, 1b', 1c: Light-emitting elements; 2: Anode; 3: Hole transport layer; 4a, 4b, 4b', 4c: Emissive layers; 5: Electron transport layer (carrier transport layer); 5': First electron transport layer; 5”: Second electron transport layer; 5a: First material; 5b: Second material; 5c: Third material; 5d: Fourth material; 6: Cathode; 8, 8a, 8b, 8c: partition walls; 10a, 10a', 10a”, 10b: Light-emitting elements; 13: Hole transport layer (carrier transport layer); 13': First hole transport layer; 13”: Second hole transport layer; 13a: First Material; 13b: Second material; 13c: Tertiary material; 15: Electron transport layer; 20, 30, 40, 50, 60: Display devices; 23: Hole transport layer (carrier transport layer); 25, 25': Electron transport layer (carrier transport layer); QDa, QDb, QDb', QDc: Quantum dots; MR: matrix; CBM: Energy level at the lower end of the conduction band; VBM: The energy level at the upper end of the valence electron band; h: Hole; e: electron.

Claims

1. A light-emitting element, characterized in that, It possesses: anode; cathode; A light-emitting layer disposed between the anode and the cathode; and A carrier transport layer is disposed between one of the anode and the cathode and the light-emitting layer. The light-emitting layer comprises a plurality of quantum dots and a matrix, wherein the matrix is ​​disposed at least in a portion between each of the plurality of quantum dots. The carrier transport layer includes a layer that is at least mixed with a first material and a second material. The first material is a different material from the second material.

2. The light-emitting element according to claim 1, characterized in that, In the light-emitting layer, the matrix fills the spaces between each of the plurality of quantum dots.

3. The light-emitting element according to claim 1 or 2, characterized in that, The first material and the second material are both nanoparticles.

4. The light-emitting element according to any one of claims 1 to 3, characterized in that, The constituent elements of the first material are different from those of the second material.

5. The light-emitting element according to any one of claims 1 to 3, characterized in that, The constituent elements of the first material are the same as those of the second material. The composition ratio of the first material is different from that of the second material.

6. The light-emitting element according to claim 3, characterized in that, The first material and the second material are each composed of the same element and have the same composition ratio. The particle size distribution of the first material is different from that of the second material.

7. The light-emitting element according to any one of claims 1 to 6, characterized in that, The carrier transport layer is an electron transport layer disposed between the cathode and the light-emitting layer. The electron affinity of the first material is different from that of the second material.

8. The light-emitting element according to claim 7, characterized in that, The electron affinity of the second material is less than that of the first material. The electron affinity of the core portion of the quantum dot is less than that of the first material.

9. The light-emitting element according to claim 8, characterized in that, The electron affinity of the matrix is ​​less than that of the second material.

10. The light-emitting element according to claim 8 or 9, characterized in that, The electron affinity of the second material is less than that of the core portion of the quantum dot.

11. The light-emitting element according to any one of claims 8 to 10, characterized in that, The electron affinity of the first material differs from that of the second material by more than 0.1 eV.

12. The light-emitting element according to any one of claims 8 to 11, characterized in that, The electron transport layer includes a first electron transport layer and a second electron transport layer. The first electron transport layer is positioned closer to the light-emitting layer than the second electron transport layer. The first electron transport layer is the layer that is at least mixed with a first material and a second material. The amount of the first material contained per unit volume of the second electron transport layer is greater than the amount of the first material contained per unit volume of the first electron transport layer.

13. The light-emitting element according to any one of claims 1 to 6, characterized in that, The carrier transport layer is a hole transport layer disposed between the anode and the light-emitting layer. The ionization potential of the first material is different from that of the second material.

14. The light-emitting element according to claim 13, characterized in that, The ionization potential of the second material is greater than that of the first material. The ionization potential of the core portion of the quantum dot is greater than the ionization potential of the first material.

15. The light-emitting element according to claim 14, characterized in that, The ionization potential of the matrix is ​​greater than or equal to the ionization potential of the second material.

16. The light-emitting element according to claim 14 or 15, characterized in that, The ionization potential of the second material is greater than the ionization potential of the core portion of the quantum dot.

17. The light-emitting element according to any one of claims 13 to 16, characterized in that, The ionization potential of the first material differs from that of the second material by more than 0.1 eV.

18. The light-emitting element according to any one of claims 14 to 17, characterized in that, The hole transport layer includes a first hole transport layer and a second hole transport layer. The second hole transport layer is configured to be closer to the light-emitting layer than the first hole transport layer. The second hole transport layer is the layer that is at least mixed with the first material and the second material. The amount of the first material contained per unit volume of the first hole transport layer is greater than the amount of the first material contained per unit volume of the second hole transport layer.

19. The light-emitting element according to any one of claims 1 to 18, characterized in that, The first material and the second material are each composed of inorganic compounds.

20. The light-emitting element according to any one of claims 1 to 19, characterized in that, The matrix contains metal sulfides.

21. A display device, characterized in that, The display device includes a plurality of light-emitting elements as described in any one of claims 1 to 6. The plurality of light-emitting elements includes: a first light-emitting element; and a second light-emitting element that emits light of a different wavelength than the first light-emitting element. The first light-emitting element has a first quantum dot as the quantum dot. The second light-emitting element has a second quantum dot as the quantum dot. The first light-emitting element and the second light-emitting element each have a common electron transport layer between the cathode and the light-emitting layer as the charge carrier transport layer. The common electron transport layer includes a layer containing at least a mixture of the first material, the second material, and a third material, wherein the third material is different from the first material and the second material. The electron affinity of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the first material, the second material, and the third material is such that the matrix ≤ the second material < the core portion of the second quantum dot ≤ the third material < the core portion of the first quantum dot ≤ the first material.

22. The display device according to claim 21, characterized in that, The plurality of light-emitting elements includes a third light-emitting element, which emits light of a different wavelength than the first and second light-emitting elements. The third light-emitting element has a third quantum dot as the quantum dot. Each of the first, second, and third light-emitting elements has a common electron transport layer as the carrier transport layer between the cathode and the light-emitting layer. The common electron transport layer includes a layer at least composed of a mixture of the first material, the second material, the third material, and a fourth material, wherein the fourth material is different from the first, second, and third materials. The electron affinity of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the core portion of the third quantum dot, the first material, the second material, the third material, and the fourth material is such that the matrix ≤ the second material < the core portion of the third quantum dot ≤ the fourth material < the core portion of the second quantum dot ≤ the third material < the core portion of the first quantum dot ≤ the first material.

23. A display device, characterized in that, The display device includes a plurality of light-emitting elements as described in any one of claims 1 to 6. The plurality of light-emitting elements includes: a first light-emitting element; and a second light-emitting element that emits light of a different wavelength than the first light-emitting element. The first light-emitting element has a first quantum dot as the quantum dot. The second light-emitting element has a second quantum dot as the quantum dot. The first light-emitting element and the second light-emitting element each have a common hole transport layer between the anode and the light-emitting layer as the carrier transport layer. The common hole transport layer includes a layer containing at least a mixture of the first material, the second material, and a third material, wherein the third material is different from the first material and the second material. The ionization potentials of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the first material, the second material, and the third material are respectively: matrix ≥ second material > core portion of the second quantum dot ≥ third material > core portion of the first quantum dot ≥ first material.

24. The display device according to claim 23, characterized in that, The plurality of light-emitting elements includes a third light-emitting element, which emits light of a different wavelength than the first and second light-emitting elements. The third light-emitting element has a third quantum dot as the quantum dot. Each of the first, second, and third light-emitting elements has a common hole transport layer between the anode and the light-emitting layer as a carrier transport layer. The common hole transport layer includes a layer at least composed of a mixture of the first material, the second material, the third material, and a fourth material, wherein the fourth material is different from the first, second, and third materials. The ionization potentials of the matrix, the core portion of the first quantum dot, the core portion of the second quantum dot, the core portion of the third quantum dot, the first material, the second material, the third material, and the fourth material are respectively: matrix ≥ second material > core portion of the third quantum dot ≥ fourth material > core portion of the second quantum dot ≥ third material > core portion of the first quantum dot ≥ first material.

25. A display device, characterized in that, The display device includes a plurality of light-emitting elements as described in any one of claims 1 to 6. The plurality of light-emitting elements includes: a first light-emitting element; and a second light-emitting element that emits light of a different wavelength than the first light-emitting element. The first light-emitting element comprises: a first quantum dot, which serves as the quantum dot; and a first carrier transport layer, which serves as the carrier transport layer. The second light-emitting element comprises: a second quantum dot, which serves as the quantum dot; and a second carrier transport layer, which serves as the carrier transport layer, wherein the first carrier transport layer comprises a layer mixed with the first material and the second material. The second carrier transport layer includes a layer containing a mixture of the first material, the second material, and a third material, wherein the third material is a material different from the first material and the second material.

26. The display device according to claim 25, characterized in that, The plurality of light-emitting elements includes a third light-emitting element, which emits light different from that of the first and second light-emitting elements. The third light-emitting element comprises: a third quantum dot, which serves as the quantum dot; and a third carrier transport layer, which serves as the carrier transport layer. The third carrier transport layer includes a layer containing a mixture of the first material, the second material, the third material, and a fourth material, wherein the fourth material is a material different from the first material, the second material, and the third material.

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