Display device

Abstract

A display device (100) comprises: a first light-emitting element (1-1) which has a first light-emitting layer (13-1) that contains first quantum dots (Q1); a second light-emitting element (1-2) which has a second light-emitting layer (13-2) that contains second quantum dots (Q2); and a charge functional layer (for example, an anode-side charge functional layer (12)) which is shared by the first light-emitting element (1-1) and the second light-emitting element (1-2). The core material of the first quantum dots (Q1) is the same as the core material of the second quantum dots (Q2). The number of shell layers of the first quantum dots (Q1) is greater than the number of shell layers of the second quantum dots (Q2). A first shell (SH1) of the first quantum dots (Q1) and a third shell (SH3) of the second quantum dots (Q2) each contain a metal element and a first group 16 element. A second shell (SH2) of the first quantum dots (Q1) contains the metal element and a second group 16 element that is different from the first group 16 element.

Description

display device

[0001] One aspect of this disclosure relates to a display device having a light-emitting element including quantum dots.

[0002] Various technologies have been proposed for light-emitting elements containing quantum dots and for display devices having said light-emitting elements. For example, Patent Document 1 below shows a quantum dot configuration that contributes to improving the luminous efficiency of a light-emitting element.

[0003] International release WO2015 / 056750

[0004] One object of this disclosure is to realize a display device having higher luminous efficiency than conventional devices.

[0005] A display device according to one aspect of the present disclosure comprises a first light-emitting element having at least one anode and at least one cathode, a first light-emitting element having a first light-emitting layer including a first quantum dot, a second light-emitting element having a second light-emitting layer including a second quantum dot, and a charge functional layer shared by the first light-emitting element and the second light-emitting element, wherein the first light-emitting element and the second light-emitting element are located between at least one anode and at least one cathode, the first quantum dot and the second quantum dot each have a core-shell structure, and the core material of the first quantum dot is the second quantum The core material of the child dot is the same as the first light-emitting layer, the emission peak wavelength of the first light-emitting layer is longer than that of the second light-emitting layer, the number of shell layers of the first quantum dot is greater than that of the second quantum dot, the first quantum dot has a first shell and a second shell located on the outer surface of the first shell, the second quantum dot has a third shell, the first shell and the third shell each contain a metallic element and a first group 16 element, and the second shell contains the metallic element and a second group 16 element different from the first group 16 element.

[0006] A display device according to one aspect of the present disclosure comprises a first light-emitting element having at least one anode and at least one cathode, a first light-emitting element having a first light-emitting layer including a first quantum dot, a second light-emitting element having a second light-emitting layer including a second quantum dot, and a charge function layer shared by the first light-emitting element and the second light-emitting element, wherein the first light-emitting element and the second light-emitting element are located between at least one anode and at least one cathode, the first quantum dot and the second quantum dot each have a core-shell structure, the core material of the first quantum dot is the same as the core material of the second quantum dot, the emission peak wavelength of the first light-emitting layer is longer than the emission peak wavelength of the second light-emitting layer, the shell of the first quantum dot contains a metal element, a first group 16 element, and a second group 16 element different from the first group 16 element, and the letter x1 indicates the composition ratio of the second group 16 element to the metal element in the shell of the first quantum dot. Let x2 be the letter representing the composition ratio of the second group 16 element to the metal element in the shell of the second quantum dot, let x1min be the minimum value of x1 in the first quantum dot, let x2min be the minimum value of x2 in the second quantum dot, let x1max be the maximum value of x1 in the first quantum dot, and let x2max be the maximum value of x2 in the second quantum dot, then x1max - x1min ≥ 0.5 and x2max - x2min < 0.5.

[0007] According to one aspect of this disclosure, a display device having higher luminous efficiency than conventional devices can be realized.

[0008] This shows one example configuration of the display device in Embodiment 1. This shows an example configuration of the display device as a comparative example. This shows a schematic energy band diagram of the display device in Figure 2. This shows a schematic energy band diagram of the display device in Figure 1. This shows an example of the luminescence efficiency of each quantum dot. This shows examples of the light emission patterns in the display device in Figure 2 and the display device in Figure 1, respectively. This is a diagram explaining xmin and xmax for single-shell type quantum dots and multi-shell type quantum dots, respectively. This shows one example configuration of the display device in Embodiment 2. This shows a schematic energy band diagram of the display device in Figure 8. This shows another example configuration of the display device in Embodiment 2. This shows one example configuration of the display device in Embodiment 3. This shows a schematic energy band diagram of the display device in Figure 11. This shows one example configuration of the display device in Embodiment 4. This shows a schematic energy band diagram of the display device in Figure 13. This shows another example configuration of the display device in Embodiment 4. This is a diagram explaining xmin and xmax for gradient-shell type quantum dots.

[0009] [Embodiment 1] Embodiment 1 will be described below. For the sake of convenience, components having the same function as those described in Embodiment 1 will be denoted by the same reference numerals in subsequent embodiments, and their descriptions will not be repeated. For the sake of simplicity, explanations of known technical matters will be omitted as appropriate.

[0010] In this specification, each component, each material, and each numerical value described herein are merely examples unless otherwise specified. Therefore, for example, unless otherwise specified, the positional relationships of each component are not limited to the examples in each figure. Also, each figure is not necessarily drawn to scale. In this specification, unless otherwise specified, the notation "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B".

[0011] (Example of the configuration of the display device 100) Figure 1 shows an example of the configuration of the display device 100 in Embodiment 1. Figure 1 schematically shows the stacked structure of the display device 100. In the example of Figure 1, the display device 100 is provided with an anode 11, an anode-side charge function layer 12, a light-emitting layer 13, a cathode-side charge function layer 14, and a cathode 15, in this order from the bottom.

[0012] In the example shown in Figure 1, each part of the display device 100 is supported by the substrate 90. Therefore, in the example shown in Figure 1, the distance between the anode 11 and the substrate 90 is smaller than the distance between the cathode 15 and the substrate 90. That is, in the example shown in Figure 1, the anode 11 is the lower electrode and the cathode 15 is the upper electrode.

[0013] The anode 11 and cathode 15 only need to be arranged facing each other. The display device 100 is configured to be able to extract light emitted from the light-emitting layer 13 to the outside of the display device 100. For this reason, in the display device 100, at least one of the anode 11 and cathode 15 needs to be a light-transmitting electrode. Either the anode 11 or the cathode 15 may be a light-reflecting electrode.

[0014] Examples of materials for light-transmitting electrodes include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO (zinc oxide), AZO (aluminum-doped zinc oxide, also called ZAO), BZO (boron-doped zinc oxide), or FTO (fluorine-doped tin oxide).

[0015] Examples of materials for light-reflecting electrodes include metallic materials that have a high reflectivity for visible light. Therefore, Al, Cu, Au, Ag, and Mg can be used. Alloys of these metallic materials can also be used as materials for light-reflecting electrodes.

[0016] The display device 100 has a plurality of light-emitting elements. In the example shown in Figure 1, the display device 100 has a first light-emitting element 1_1 and a second light-emitting element 1_2 as light-emitting elements. In the example shown in Figure 1, the display device 100 also has a first anode 11_1 and a second anode 11_2 as anodes 11.

[0017] In the example in Figure 1, the first anode 11_1 corresponds to the first light-emitting element 1_1. On the other hand, the second anode 11_2 corresponds to the second light-emitting element 1_2. Thus, Figure 1 illustrates a configuration in which separate anodes are provided for the first light-emitting element 1_1 and the second light-emitting element 1_2.

[0018] However, unlike the example in Figure 1, a common anode 11 may be provided for the first light-emitting element 1_1 and the second light-emitting element 1_2. In other words, the anode 11 may be shared by the first light-emitting element 1_1 and the second light-emitting element 1_2. As described above, a light-emitting element according to one aspect of the present disclosure only needs to have at least one anode.

[0019] Figure 1 illustrates a configuration in which a common cathode 15 is provided for the first light-emitting element 1_1 and the second light-emitting element 1_2. However, unlike the example in Figure 1, the first light-emitting element 1_1 and the second light-emitting element 1_2 may be provided with separate cathodes. As described above, a light-emitting element according to one aspect of the present disclosure only needs to have at least one cathode.

[0020] A plurality of light-emitting elements according to one aspect of this disclosure only need to be located between at least one anode and at least one cathode. Therefore, for example, the first light-emitting element 1_1 and the second light-emitting element 1_2 only need to be located between the anode 11 and the cathode 15.

[0021] The light-emitting layer 13 only needs to be located between the anode 11 and the cathode 15. In the example in Figure 1, the light-emitting layer 13 is located between the anode-side charge functional layer 12 and the cathode-side charge functional layer 14. The light-emitting layer 13 only needs to be configured to emit electro-luminescence (EL) light. Therefore, the light-emitting layer 13 may contain any EL material. As an example, the light-emitting layer 13 may contain a QD (Quantum Dot). A QD is an example of an inorganic EL material.

[0022] The QD in the light-emitting layer 13 emits electroluminescent (EL) light through the recombination of holes supplied from the anode 11 and electrons transported from the cathode 15. Therefore, by applying a forward voltage between the anode 11 and the cathode 15, EL light can be generated in the light-emitting layer 13.

[0023] In the example shown in Figure 1, the display device 100 has a first light-emitting layer 13_1 and a second light-emitting layer 13_2 as its light-emitting layer 13. In the example shown in Figure 1, the first light-emitting layer 13_1 is the light-emitting layer of the first light-emitting element 1_1. On the other hand, the second light-emitting layer 13_2 is the light-emitting layer of the second light-emitting element 1_2. Therefore, in the example shown in Figure 1, the first light-emitting element 1_1 has the first light-emitting layer 13_1, and the second light-emitting element 1_2 has the second light-emitting layer 13_2.

[0024] In the example shown in Figure 1, the first light-emitting layer 13_1 contains the first quantum dot Q1. On the other hand, the second light-emitting layer 13_2 contains the second quantum dot Q2. Thus, the first quantum dot Q1 is located inside the first light-emitting element 1_1, and the second quantum dot Q2 is located inside the second light-emitting element 1_2.

[0025] In Embodiment 1, the first quantum dot Q1 and the second quantum dot Q2 each have a core-shell structure. In Embodiment 1, the core material of the first quantum dot Q1 is the same as the core material of the second quantum dot Q2. That is, in Embodiment 1, the material of the first core CR1, which will be described later, is the same as the material of the second core CR2, which will be described later. Embodiment 1 mainly illustrates the case where the material of the first core CR1 and the material of the second core CR2 are InP.

[0026] In this specification, the statement "the material of one component (e.g., the first core) is the same as the material of another component (e.g., the second core)" means that the constituent elements of the first component are the same as the constituent elements of the other component. Therefore, in this specification, the statement "the material of one component is the same as the material of another component" does not necessarily mean that the composition ratio of the constituent elements of the first component is the same as the composition ratio of the constituent elements of the other component.

[0027] In Embodiment 1, the first light-emitting layer 13_1 and the second light-emitting layer 13_2 are designed such that the emission peak wavelength of the first light-emitting layer 13_1 is longer than the emission peak wavelength of the second light-emitting layer 13_2. Therefore, the first quantum dot Q1 and the second quantum dot Q2 are designed such that the emission peak wavelength of the first quantum dot Q1 is longer than the emission peak wavelength of the second quantum dot Q2.

[0028] In this specification, red light means, for example, light with an emission peak wavelength greater than 600 nm and less than or equal to 780 nm. In this specification, green light means, for example, light with an emission peak wavelength greater than 500 nm and less than or equal to 600 nm. In this specification, blue light means light with an emission peak wavelength of 380 nm or more and less than or equal to 500 nm.

[0029] Furthermore, the technical matter in this specification that "the emission peak wavelength of the first light-emitting layer is longer than the emission peak wavelength of the second light-emitting layer" typically falls under any of the following cases 1 to 3: • Case 1: The first light-emitting layer emits red light and the second light-emitting layer emits green light; • Case 2: The first light-emitting layer emits red light and the second light-emitting layer emits blue light; • Case 3: The first light-emitting layer emits green light and the second light-emitting layer emits blue light.

[0030] Embodiment 1 primarily illustrates Case 1. That is, Embodiment 1 primarily illustrates the case where the first light-emitting layer 13_1 emits red light and the second light-emitting layer 13_2 emits green light. Therefore, Embodiment 1 primarily illustrates the case where the first quantum dot Q1 emits red light and the second quantum dot Q2 emits green light. Thus, Embodiment 1 primarily illustrates the case where the first light-emitting element 1_1 is a red light-emitting element and the second light-emitting element 1_2 is a green light-emitting element.

[0031] In Embodiment 1, the display device 100 only needs to include at least one charge functional layer shared by the first light-emitting element 1_1 and the second light-emitting element 1_2. In the example of FIG. 1, the anode-side charge functional layer 12 and the cathode-side charge functional layer 14 are shared by the first light-emitting element 1_1 and the second light-emitting element 1_2. Therefore, in the example of FIG. 1, the display device 100 includes two charge functional layers shared by the first light-emitting element 1_1 and the second light-emitting element 1_2.

[0032] However, as can be understood from the above description, one of the anode-side charge functional layer 12 and the cathode-side charge functional layer 14 does not need to be shared by the first light-emitting element 1_1 and the second light-emitting element 1_2. As an example, the first light-emitting element 1_1 and the second light-emitting element 1_2 may each have separate cathode-side charge functional layers.

[0033] The anode-side charge functional layer 12 is a charge functional layer located on the anode 11 side. The anode-side charge functional layer 12 only needs to be located between the anode 11 and the light-emitting layer 13. As described above, the anode 11 in the example of FIG. 1 is a lower electrode. Accordingly, the anode-side charge functional layer 12 in the example of FIG. 1 may also be referred to as a lower charge functional layer.

[0034] As an example, the charge functional layer according to one aspect of the present disclosure may be a charge transport layer. Therefore, in Embodiment 1, a case where the anode-side charge functional layer 12 is a Hole Transport Layer (HTL) is exemplified as an example. The anode-side charge functional layer 12 as an HTL only needs to contain any hole transport material.

[0035] For example, the anode-side charge functional layer 12 as an HTL may contain at least one selected from the group consisting of polyvinylcarbazole (PVK), poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)] (TFB) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD) as a hole transport material.

[0036] The cathode-side charge functional layer 14 is a charge functional layer located on the cathode 15 side. The cathode-side charge functional layer 14 only needs to be located between the cathode 15 and the light-emitting layer 13. As described above, the cathode 15 in the example of FIG. 1 is a top electrode. Accordingly, the cathode-side charge functional layer 14 in the example of FIG. 1 may also be referred to as a top charge functional layer.

[0037] In Embodiment 1, a case where the cathode-side charge functional layer 14 is an Electron Transport Layer (ETL) is exemplified as an example. The cathode-side charge functional layer 14 as an ETL only needs to contain any electron transport material.

[0038] For example, the cathode-side charge functional layer 14 as an ETL may contain at least one selected from the group consisting of zinc oxide (ZnO), magnesium zinc oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO3) as an electron transport material. The cathode-side charge functional layer 14 as an ETL may also contain inorganic nanoparticle materials, which are nanoparticles of these inorganic materials, as an electron transport material. Inorganic materials are less likely to degrade than organic materials. Therefore, a long-life display device can be realized by using an inorganic material as the electron transport material.

[0039] Next, the first quantum dot Q1 will be described in more detail. The first quantum dot Q1 in the example of FIG. 1 includes a first core CR1, a first shell SH1, and a second shell SH2. The first core CR1 is the core of the first quantum dot Q1. The first shell SH1 and the second shell SH2 are each located on the outer surface of the first core CR1. However, the second shell SH2 is a shell located more outward than the first shell SH1. Therefore, the second shell SH2 is located on the outer surface of the first shell SH1.

[0040] FIG. 1 illustrates a configuration in which the second shell SH2 is located over the entire outer surface of the first shell SH1. That is, a configuration in which the second shell SH2 covers the entire first shell SH1 is exemplified. However, it should be noted that the second shell SH2 only needs to be located on at least a part of the outer surface of the first shell SH1.

[0041] Furthermore, Figure 1 illustrates a configuration in which the first shell SH1 is located on the entire outer surface of the first core CR1. That is, a configuration in which the first shell SH1 covers the entire first core CR1 is illustrated. However, it should be noted that the first shell SH1 only needs to be located on at least a portion of the outer surface of the first core CR1.

[0042] Please note that the above matters concerning the first shell SH1, the second shell SH2, and the first core CR1 also apply to the other shells and cores described later, to the extent that there are no contradictions in content.

[0043] In Figure 1, for the sake of clarity, an example is shown where the first quantum dot Q1 has two shell layers. Therefore, in Figure 1, an example is shown where the first shell SH1 is the innermost shell of the first quantum dot Q1. Consequently, in the example in Figure 1, the first shell SH1 is in direct contact with the first core CR1.

[0044] However, the number of shell layers in the first quantum dot Q1 is not limited to the example in Figure 1. As can be understood from this, the first shell SH1 does not have to be the innermost shell of the first quantum dot Q1. In other words, the first shell SH1 does not have to be in direct contact with the first core CR1.

[0045] The first shell SH1 and the second shell SH2 each contain different types of elements. In Embodiment 1, the first shell SH1 contains a metallic element and a first group 16 element. On the other hand, the second shell SH2 contains the same metallic element and a second group 16 element. The second group 16 element is a different element from the first group 16 element. Note that the first shell SH1 does not necessarily contain the second group 16 element. The second shell SH2 does not necessarily contain the first group 16 element.

[0046] According to the first shell SH1 and the second shell SH2, electrons can be confined in a stepwise manner due to the band structure of the first shell SH1 and the second shell SH2. As a result, the risk of Auger recombination can be reduced.

[0047] Embodiment 1 primarily illustrates the case where the atomic number of the first group 16 element is greater than the atomic number of the second group 16 element. More specifically, Embodiment 1 primarily illustrates the case where the first group 16 element is Se (selenium) and the second group 16 element is S (sulfur).

[0048] The aforementioned metal elements are not particularly limited, as long as they are metal elements that can bond with the first group 16 elements and the second group 16 elements, respectively. Embodiment 1 mainly illustrates the case where the metal element is Zn (zinc). Therefore, for example, an example of the material for the first shell SH1 in Embodiment 1 is ZnSe. Also, an example of the material for the second shell SH2 is ZnS.

[0049] Next, we will describe the second quantum dot Q2. In the example in Figure 1, the second quantum dot Q2 has a second core CR2 and a third shell SH3. The second core CR2 is the core of the second quantum dot Q2. The third shell SH3 is located on the outer surface of the second core CR2.

[0050] In Figure 1, for the sake of clarity, the case where the second quantum dot Q2 has one shell layer is illustrated. Therefore, in Figure 1, the case where the third shell SH3 is the innermost shell of the second quantum dot Q2 is illustrated. Consequently, in the example in Figure 1, the third shell SH3 is in direct contact with the second core CR2.

[0051] However, the number of shell layers in the second quantum dot Q2 is not limited to the example in Figure 1. As can be understood from this, the third shell SH3 does not have to be the innermost shell of the second quantum dot Q2. In other words, the third shell SH3 does not have to be in direct contact with the second core CR2.

[0052] In Embodiment 1, the material of the third shell SH3 is the same as the material of the first shell SH1 described above. Therefore, in Embodiment 1, the third shell SH3 contains the above-mentioned metal element and the first group 16 element. From this, for example, ZnSe can be given as an example of the material of the third shell SH3 in Embodiment 1.

[0053] (Display device 100R as a comparative example) Next, a display device 100R will be described as a comparative example of the display device 100. Figure 2 shows an example of the configuration of the display device 100R. Figure 2 is a counterpart to Figure 1. In this specification, the second light-emitting element in the display device 100R will be referred to as the second light-emitting element 1_2R. The second quantum dot in the second light-emitting element 1_2R will be referred to as the second quantum dot Q2R.

[0054] The second quantum dot Q2R in the comparative example differs from the second quantum dot Q2 in that it further has a shell SH_OUTER. Therefore, in the example in Figure 2, unlike the example in Figure 1, the number of shell layers in the second quantum dot is 2.

[0055] In the example in Figure 2, the shell SH_OUTER is an outer shell of the third shell SH3. Therefore, the shell SH_OUTER is located on the outer surface of the third shell SH3. In this specification, the shell SH_OUTER is assumed to contain the above-mentioned metallic elements and a second group 16 element. Therefore, an example of the material of SH_OUTER is ZnS. Thus, the material of SH_OUTER may be the same as the material of the first shell SH1.

[0056] (Comparison between Example and Comparative Example 1) Figure 3 shows a schematic energy band diagram of the display device 100R. The energy band diagram in Figure 3 corresponds to the configuration example in Figure 2. The left side of Figure 3 shows the energy band of the first light-emitting element 1_1 in the display device 100R, and the right side shows the energy band of the second light-emitting element 1_2R in the display device 100R.

[0057] In the example shown in Figure 3, the first light-emitting layer 13_1 and the second light-emitting layer 13_2 are designed such that the emission peak wavelength of the first light-emitting layer 13_1 is longer than the emission peak wavelength of the second light-emitting layer 13_2. As a result, the band gap of the second core CR2 is larger than the band gap of the first core CR1. Furthermore, the ionization potential of the second core CR2, which is the absolute value of the energy difference between the vacuum level of the second core CR2 and the upper edge of the valence band, is larger than the ionization potential of the first core CR1, which is the absolute value of the energy difference between the vacuum level of the first core CR1 and the upper edge of the valence band.

[0058] Therefore, in the display device 100R in which the first light-emitting element 1_1 and the second light-emitting element 1_2R have a common charge functional layer, hole injection into the second core CR2 may be more difficult than hole injection into the first core CR1. As a result, the carrier balance in the second core CR2 of the display device 100R is more likely to deteriorate compared to the first core CR1. Consequently, in the display device 100R, Auger recombination may occur due to the deterioration of the carrier balance in the second core CR2, which may lead to a decrease in luminous efficiency.

[0059] In light of these problems with the display device 100R, the inventor of the present application (hereinafter simply referred to as "the inventor") has newly created the display device 100 shown in Figure 1 above. Figure 4 shows a schematic energy band diagram of the display device 100. Figure 4 is a counterpart to Figure 3. The energy band diagram in Figure 4 corresponds to the configuration example in Figure 1.

[0060] As described above, the second quantum dot Q2 in the display device 100 differs from the second quantum dot Q2R in the display device 100R in that it does not have a shell SH_OUTER. Therefore, in the display device 100, unlike the display device 100R, holes traveling from the anode-side charge functional layer 12 (e.g., HTL) to the second core CR2 are not blocked by the shell SH_OUTER.

[0061] As a result, hole injection into the second core CR2 is promoted in the display device 100 compared to the display device 100R. Consequently, the carrier balance deterioration is less likely to occur in the second core CR2 of the display device 100 compared to the second core CR2 of the display device 100R. Therefore, the display device 100 can achieve higher luminous efficiency compared to the display device 100R.

[0062] (Comparison between Examples and Comparative Examples 2) Figure 5 shows examples of the luminescence efficiency of each quantum dot obtained by the inventor. Figure 5 shows examples of the luminescence efficiency of the first quantum dot Q1, the second quantum dot Q2 according to the Examples, and the second quantum dot Q2R according to the Comparative Examples. In the graph of Figure 5, the horizontal axis (J) represents the current density, and the vertical axis represents EQE (External Quantum Efficiency).

[0063] In the example shown in Figure 5, (i) the material of the first core CR1 and the material of the second core CR2 is InP, (ii) the material of the first shell SH1 and the material of the third shell SH3 is ZnSe, and (iii) the material of the second shell SH2 and the material of SH_OUTER is ZnS.

[0064] Therefore, the first quantum dot Q1 in the example of Figure 5 has a core-shell structure of "InP / ZnSe / ZnS". The second quantum dot Q2 in the example has a core-shell structure of "InP / ZnSe". On the other hand, the second quantum dot Q2R in the comparative example has a core-shell structure of "InP / ZnSe / ZnS". Thus, in the example of Figure 5, the second quantum dot Q2R in the comparative example has the same core-shell structure as the first quantum dot Q1.

[0065] In the example shown in Figure 5, ITO is used as the material for the anode 11, NiO (nickel oxide) nanoparticles as the material for the inorganic HIL (inorganic hole injection layer), TFB as the material for the anode-side charge function layer 12 (e.g., HTL), magnesium zinc oxide (ZnMgO) nanoparticles as the material for the cathode-side charge function layer 14, and silver (Ag) as the material for the cathode 15. However, as will be apparent to those skilled in the art, the combination of materials for each component in the display device 100 is not limited to this example.

[0066] In the example shown in Figure 5, the first quantum dot Q1 emits red light. On the other hand, the second quantum dot Q2 in the embodiment and the second quantum dot Q2R in the comparative example each emit green light.

[0067] In this specification, the maximum value of EQE in the example of Figure 5 is denoted as EQmax. In the example of Figure 5, the EQmax of the second quantum dot Q2 according to the example was 2.6%. On the other hand, the EQmax of the second quantum dot Q2R according to the comparative example was 4.4%. In both the second quantum dot Q2 according to the example and the second quantum dot Q2R according to the comparative example, the EQmax was 0 mA / cm². ２ ~2mA / cm ２ This has been achieved in a low current range.

[0068] As shown in Figure 5, in the range of J greater than that corresponding to EQEmax, EQE tends to decrease as J increases. In the example in Figure 5, the maximum value of J is J = 30 mA / cm². ２ Therefore, in this specification, J = 30 mA / cm in the example of Figure 5. ２ The EQE in this case is EQE (30 mA / cm²). ２ ) is written as .

[0069] In the example shown in Figure 5, the EQE (30 mA / cm²) in the second quantum dot Q2 according to the embodiment is shown. ２ The EQE (30 mA / cm²) in the second quantum dot Q2R of the comparative example was 1.4%. ２ The percentage was 0.3%.

[0070] In this specification, EQE (30 mA / cm²)２ a value obtained by dividing ) by EQEmax, that is, {EQE(30 mA / cm ２ )} / EQEmax is referred to as normalized EQE. Normalized EQE is EQE(30 mA / cm ２ ) which is a value normalized by EQEmax.

[0071] In the example of FIG. 5, the normalized EQE of the second quantum dot Q2 according to the example was 0.54. On the other hand, the normalized EQE of the second quantum dot Q2R according to the comparative example was 0.068.

[0072] It can be said that normalized EQE is one of index values indicating the degree of decrease in luminous efficiency caused by Auger recombination. Specifically, it can be said that the larger the normalized EQE, the smaller the degree of decrease in luminous efficiency caused by Auger recombination.

[0073] In the example of FIG. 5, the normalized EQE of the second quantum dot Q2 according to the example is approximately 10 times larger than the normalized EQE of the second quantum dot Q2R according to the comparative example. Such a remarkable difference in normalized EQE could not have been easily predicted by a person skilled in the art based on the common technical knowledge at the time of filing. From this, it can be said that the display device 100 is not an invention that could have been easily created by a person skilled in the art based on the common technical knowledge at the time of filing.

[0074] As described above, the example of FIG. 5 confirms that the use of the second quantum dot Q2 according to the example in place of the second quantum dot Q2R according to the comparative example can significantly improve the luminous efficiency of the light emitting device. Therefore, according to the display device 100, a display device having higher luminous efficiency than conventional ones (e.g., a display device having significantly higher luminous efficiency than the display device 100R) can be realized.

[0075] (Comparison 3 between Examples and Comparative Examples) Next, with reference to FIG. 6, examples and comparative examples are further compared. FIG. 6 shows examples of light emission modes in each of the display device 100R and the display device 100. Reference numeral 610 in FIG. 6 shows an example of a light emission mode in the display device 100R. On the other hand, reference numeral 620 shows an example of a light emission mode in the display device 100. The example denoted by reference numeral 620 is an example paired with the example denoted by reference numeral 610.

[0076] In the example shown in Figure 6, the light emitted by the first quantum dot is referred to as the first color light, and the light emitted by the second quantum dot is referred to as the second color light. The emission peak wavelength of the second color light only needs to be shorter than the emission peak wavelength of the first color light. Red light can be given as an example of the first color light. Green light can be given as an example of the second color light.

[0077] As mentioned above, the band gap of the second quantum dot is larger than that of the first quantum dot. Therefore, in the example in Figure 6, the emission threshold voltage of the second light-emitting element is larger than that of the first light-emitting element.

[0078] First, let's consider the example of reference numeral 610. As described above, the normalized EQE in the second quantum dot Q2R of the comparative example is significantly smaller than the normalized EQE in the second quantum dot Q2 of the embodiment. Therefore, in the display device 100R, in order to output second color light of a predetermined brightness from the second light-emitting element 1_2R, it is necessary to apply a relatively high voltage to the second light-emitting element 1_2R.

[0079] As a result, in the display device 100R, a relatively large current flows from the charge function layer (e.g., anode-side charge function layer 12) shared by the first light-emitting element 1_1 and the second light-emitting element 1_2R to the second light-emitting layer 13_2.

[0080] As a result, in the display device 100R, there is a risk that an unintended leakage current may flow from the charge function layer to the first light-emitting layer 13_1. This leakage current in the display device 100R may cause a voltage greater than the light emission threshold voltage of the first light-emitting element 1_1 in the portion of the first light-emitting layer 13_1 that is close to the second light-emitting layer 13_2.

[0081] Therefore, even though the display device 100R does not intend for the first light-emitting element 1_1 to output first-color light, there is a risk that first-color light may be emitted from the first light-emitting element 1_1. The unintended generation of first-color light causes crosstalk in the display device 100R. This crosstalk causes a decrease in the display quality of the display device 100R.

[0082] Next, an example of reference numeral 620 will be described. As described above, the normalized EQE in the second quantum dot Q2 according to the embodiment is significantly larger than the normalized EQE in the second quantum dot Q2 according to the comparative example. For this reason, unlike the display device 100R, the display device 100 does not require a very high voltage to be applied to the second light-emitting element 1_2 in order to output a second color light of a predetermined brightness.

[0083] Therefore, in the display device 100, the current flowing from the above-mentioned charge function layer (e.g., anode-side charge function layer 12) to the second light-emitting layer 13_2 is smaller than in the example of the display device 100R. Consequently, the risk of the above-mentioned leakage current occurring in the display device 100 is lower than in the example of the display device 100R.

[0084] Therefore, in the display device 100, the risk of unintended first light being generated from the first light-emitting element 1_1 is lower than in the example of the display device 100R. Consequently, in the display device 100, the risk of crosstalk is lower than in the example of the display device 100R. For this reason, the display device 100 can achieve a higher display quality compared to the display device 100R.

[0085] (Supplement 1) The charge function layer common to the first light-emitting element 1_1 and the second light-emitting element 1_2 is not limited to a charge transport layer. For example, the charge function layer may be a charge injection layer. Therefore, the anode-side charge function layer 12 may be a hole injection layer (HIL). Also, the cathode-side charge function layer 14 may be an electron injection layer (EIL).

[0086] As an example, the display device 100 may have an inorganic HIL (inorganic hole injection layer) as a common charge function layer for the first light-emitting element 1_1 and the second light-emitting element 1_2. The inventors have confirmed that the same effects as in Embodiment 1 can be obtained even when the charge function layer is an inorganic HIL. Therefore, for example, the display device 100 may have an inorganic HIL as the anode-side charge function layer 12.

[0087] Examples of inorganic HIL materials include molybdenum oxide (MoO2).３ ), nickel oxide (NiO), chromium oxide (Cr ２ O ３ ), magnesium oxide (MgO), lanthanum nickel oxide (LaNiO) ３ ), or tungsten oxide (WO ３ Examples of metal oxides include those listed above. These inorganic materials, which are nanoparticles of inorganic materials, can also be used as materials for inorganic HILs. Inorganic materials are less prone to degradation than organic materials. Therefore, by using inorganic materials as materials for inorganic HILs, long-life display devices can be realized.

[0088] (Supplement 2) As described above, the display device 100 has a common charge function layer for the first light-emitting element 1_1 and the second light-emitting element 1_2. By providing such a common charge function layer, the configuration of the display device can be simplified compared to the case where the first light-emitting element 1_1 and the second light-emitting element 1_2 have separate charge function layers.

[0089] Therefore, according to Embodiment 1, a display device having high luminous efficiency can be obtained through a simpler manufacturing process than in the conventional method.

[0090] (Supplement 3) The quantum dots in this specification may be coated with halogen. In this specification, the ratio of halogen coating to quantum dots is referred to as halogen coverage. In this specification, halogen coverage is denoted as CV_HALO.

[0091] For example, CV_HALO is proportional to the number of halogen atoms per quantum dot divided by the surface area of ​​the quantum dot. From this, CV_HALO can be determined according to the following equation (1), CV_HALO∝CON_HALO×V_QD / S_QD …(1).

[0092] In equation (1), CON_HALO represents the halogen concentration in the light-emitting layer containing quantum dots. For example, CON_HALO can be defined as the sum of the signal intensities of F (fluorine), Cl (chlorine), Br (bromine), and I (iodine), obtained when the cross-section of the light-emitting layer is observed using SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray spectrometer).

[0093] In equation (1), V_QD represents the volume of the quantum dot. S_QD represents the surface area of ​​the quantum dot. The value obtained by dividing V_QD by S_QD, i.e., V_QD / S_QD, is proportional to the particle size of the quantum dot (D_QD, described later). Therefore, CV_HALO, which appears in equation (1), is proportional to the product of CON_HALO and D_QD.

[0094] In this specification, D_QD may be defined as a value equal to the diameter of a circle having the same area as the cross-sectional area of ​​the quantum dot in a cross-sectional observation. In this case, the shape of the quantum dot does not necessarily have to be spherical.

[0095] As another example, D_QD may be determined by measuring the particle size of each of the 20 quantum dots in the cross-sectional observation described above. For example, D_QD may be determined as a value equal to the average value of the 20 particle sizes measured in the cross-sectional observation.

[0096] The higher the halogen coverage of a quantum dot, the more strongly the surface of that quantum dot is protected by halogen. On the other hand, as the halogen coverage of a quantum dot increases, it becomes more difficult for the quantum dot to be coated by organic ligands. Therefore, the higher the halogen coverage of a quantum dot, the easier it is for multiple quantum dots to condense together.

[0097] As described above, in Embodiment 1, the second shell SH2 of the first quantum dot Q1 contains a second group 16 element (e.g., S). On the other hand, the third shell SH3 of the second quantum dot Q2 contains a first group 16 element (e.g., Se).

[0098] In Embodiment 1, typically, the atomic number of the second group 16 element is smaller than that of the first group 16 element. Therefore, the atomic radius of the second group 16 element is smaller than that of the first group 16 element. Consequently, the bonding force of the second group 16 element is greater than that of the first group 16 element.

[0099] From this, for example, the first quantum dot Q1 in the example in Figure 1 readily bonds with the aforementioned metal element (e.g., Zn) in another first quantum dot Q1. For this reason, the first quantum dot Q1 has a property that makes it easier to condense compared to the second quantum dot Q2.

[0100] On the other hand, the number of shell layers in the second quantum dot Q2 in the example in Figure 1 is less than the number of shell layers in the first quantum dot Q1. This indicates that the quantum confinement effect is weaker in the second quantum dot Q2 compared to the first quantum dot Q1. Therefore, the second quantum dot Q2 is more susceptible to surface defects than the first quantum dot Q1. In other words, the second quantum dot Q2 is more likely to experience a decrease in luminescence efficiency compared to the first quantum dot Q1.

[0101] Therefore, it is preferable that the halogen coverage of the second quantum dot Q2 be set to be greater than that of the first quantum dot Q1. As described above, the halogen coverage is proportional to the product of CON_HALO and D_QD. For this reason, by confirming that CON_HALO × D_QD of the second quantum dot Q2 is greater than CON_HALO × D_QD of the first quantum dot Q1, it can be confirmed that the halogen coverage of the second quantum dot Q2 is greater than that of the first quantum dot Q1.

[0102] By setting the halogen coverage of the second quantum dot Q2 in this way, the surface of the second quantum dot Q2 can be strongly protected by halogen, thereby reducing the risk of a decrease in the luminous efficiency of the second quantum dot Q2. In addition, by setting the halogen coverage of the first quantum dot Q1 as described above, the risk of multiple first quantum dots Q1 condensing together can also be reduced.

[0103] (Supplement 4) As described above, the light-emitting layer according to one aspect of this disclosure may contain halogens. In this specification, the halogen with the highest concentration among the halogens contained in the first light-emitting layer 13_1 is referred to as the first halogen. The halogen with the highest concentration among the halogens contained in the second light-emitting layer 13_2 is referred to as the second halogen.

[0104] The atomic radius of halogens with smaller atomic numbers is smaller than that of halogens with larger atomic numbers. Furthermore, the bonding force of halogens with smaller atomic numbers is stronger than that of halogens with larger atomic numbers.

[0105] Therefore, it is preferable that the atomic number of the second halogen is smaller than that of the first halogen. In this case, the atomic radius of the first halogen is larger than that of the second halogen. Consequently, the risk of multiple first quantum dots Q1 condensing together can be reduced. Furthermore, in the above case, the binding force of the second halogen is greater than that of the first halogen. Consequently, the surface of the second quantum dot Q2 can be strongly protected by the second halogen. Therefore, the risk of a decrease in the luminescence efficiency of the second quantum dot Q2 can also be reduced.

[0106] An example of a first halogen is I (iodine). And an example of a second halogen is Cl (chlorine).

[0107] (Supplement 5) In this specification, a core-shell type quantum dot in which the number of shell layers is 1 is referred to as a single-shell type quantum dot. The second quantum dot Q2 in the example in Figure 1 is an example of a single-shell type quantum dot.

[0108] On the other hand, a core-shell type quantum dot with two or more shell layers is called a multi-shell type quantum dot. The first quantum dot Q1 in the example in Figure 1 is an example of a multi-shell type quantum dot. The second quantum dot Q2R in the comparative example in Figure 2 is another example of a multi-shell type quantum dot.

[0109] For example, whether a quantum dot is a single-shell type quantum dot or a multi-shell type quantum dot may be determined based on the composition ratio of a predetermined element to the aforementioned metal element in the shell of the quantum dot. Therefore, for example, whether a quantum dot is a single-shell type quantum dot or a multi-shell type quantum dot may be determined based on the composition ratio of a second group 16 element to the metal element in the shell of the quantum dot.

[0110] In this specification, the letter x represents the composition ratio of the second group 16 element to the aforementioned metal element in the shell of a given quantum dot. The minimum value of x1 in the quantum dot is represented as xmin, and the maximum value of x in the quantum dot is represented as xmax.

[0111] Figure 7 illustrates xmin and xmax in single-shell and multi-shell quantum dots, respectively. In Figure 7, reference numeral 710 indicates a single-shell quantum dot Q_SINGLE. The quantum dot Q_SINGLE has a core CR and a shell SHELL located on the outer surface of the core CR. In the example of reference numeral 710, the number of shell layers is 1.

[0112] In Figure 7, reference numeral 720 indicates a multi-shell type quantum dot Q_MULTI. The quantum dot Q_MULTI has, as shells, (i) shell SHELL1, which is the innermost shell, and (ii) shell SHELL2, which is located on the outer surface of shell SHELL1. Therefore, the number of shell layers in the example of reference numeral 720 is 2.

[0113] As an example, consider the case where the aforementioned metal element is Zn, the first group 16 element is Se, and the second group 16 element is S. In this case, the composition formula of SHELL in the example in Figure 7 is ZnSe １－ｘ S ｘ This can be generally expressed as follows.

[0114] In single-shell quantum dots, the distribution of x within the shell is not thought to be significantly biased. In other words, the discrepancy between xmin and xmax is not thought to be very pronounced in single-shell quantum dots.

[0115] Therefore, as an example, if the following equation (2), xmax - xmin < 0.5 ... (2) holds true in the shell of a certain quantum dot, then that quantum dot can be considered a single-shell type quantum dot.

[0116] On the other hand, if the following equation (3), xmax - xmin ≥ 0.5 …(3) holds in the shell of a quantum dot, then that quantum dot can be considered a multi-shell type quantum dot.

[0117] In the example of reference numeral 710 in Figure 7, xmin is located on the inner circumference of the shell, and xmax is located on the outer circumference of the shell. In the example of reference numeral 710, equation (2) above holds true.

[0118] On the other hand, in the example of reference numeral 720 in Figure 7, xmin is located on the inner circumference of shell SHELL1, and xmax is located on the outer circumference of shell SHELL2. In the example of reference numeral 720, equation (3) above holds true.

[0119] In this specification, the letter x1 represents the composition ratio of the second group 16 element to the aforementioned metal element in the shell of the first quantum dot Q1. The letter x2 represents the composition ratio of the second group 16 element to the said metal element in the shell of the second quantum dot Q2.

[0120] In this specification, the minimum value of x1 in the first quantum dot Q1 is represented as x1min, and the minimum value of x2 in the second quantum dot Q2 is represented as x2min. As described above, the first shell SH1 of the first quantum dot Q1 and the third shell SH of the second quantum dot Q2 each contain the aforementioned metal element and the first group 16 element. For this reason, it is considered that in most cases both x1min and x2min are small values.

[0121] Therefore, for example, in Embodiment 1, the following equations (4) and (5), x1min < 0.1 …(4) and x2min < 0.1 …(5) may hold true.

[0122] In this specification, the maximum value of x1 in the first quantum dot Q1 is represented as x1max, and the maximum value of x2 in the second quantum dot Q2 is represented as x2max. As described above, the second shell SH2 of the first quantum dot Q1 contains the aforementioned metal element and a second group 16 element. For this reason, x1max is generally greater than x2max.

[0123] Therefore, in Embodiment 1, the following equation (6), x1max > x2max ... (6) may hold true.

[0124] In the example shown in Figure 1 above, the first quantum dot Q1 is a multi-shell type quantum dot, and the second quantum dot Q2 is a single-shell type quantum dot. Therefore, as can be understood from equations (2) to (3) above, in Embodiment 1, the following equations (7) and (8), x1max - x1min ≥ 0.5 …(7) x2max - x2min < 0.5 …(8) may hold.

[0125] In this specification, the shell in a quantum dot may be defined as a region of the quantum dot in which elements specific to the core of the quantum dot do not exist.

[0126] However, the method for defining the shell in a quantum dot is not limited to the above example. For example, within the region of the quantum dot, the region whose distance from the outermost edge of the quantum dot is less than a predetermined shell thickness may be defined as the shell.

[0127] In this specification, the shell thickness is denoted as T_SHELL. For example, T_SHELL may be defined by the following formula (8): T_SHELL = (D_QD - D_CORE) / 2 ... (8).

[0128] In equation (8), D_QD represents the particle size of the quantum dot. D_QD may be determined according to any of the methods described above. In equation (8), D_CORE represents the diameter of the quantum dot core. For example, D_CORE may be calculated based on the material of the core and the wavelength of light emitted from the core.

[0129] (Supplement 6) As described above, in the display device 100 of Embodiment 1, the first light-emitting element 1_1 is designed as a light-emitting element that outputs a first color light (e.g., red light). On the other hand, the second light-emitting element 1_2 is designed as a light-emitting element that outputs a second color light (e.g., green light). Thus, in Embodiment 1, typically, the proportion of first quantum dots in the first light-emitting element 1_1 is set to be greater than the proportion of first quantum dots in the second light-emitting element 1_2. On the other hand, the proportion of second quantum dots in the second light-emitting element 1_2 is set to be greater than the proportion of second quantum dots in the first light-emitting element 1_1. Note that in the figures of Embodiment 1, for the sake of clarity of explanation and illustration, the second quantum dots in the first light-emitting element 1_1 and the first quantum dots in the second light-emitting element 1_2 are not shown.

[0130] As an example, it is preferable that the proportion of first quantum dots in the first light-emitting element 1_1 is 70% or more. It is even more preferable that the proportion of first quantum dots in the first light-emitting element 1_1 is 90% or more.

[0131] On the other hand, it is preferable that the proportion of second quantum dots in the second light-emitting element 1_2 be 70% or more. It is even more preferable that the proportion of second quantum dots in the second light-emitting element 1_2 be 90% or more.

[0132] In this specification, the phrase "all quantum dots" refers to all quantum dots in any cross-section of a given light-emitting layer with a length of approximately 100 nm along the planar direction. Therefore, it should be noted that the phrase "all quantum dots" in this specification does not necessarily refer to all quantum dots in the entire light-emitting layer.

[0133] Similarly, in this specification, the term "quantum dot ratio" refers to the ratio of quantum dots in any cross-section of a given light-emitting layer with a length of approximately 100 nm along the planar direction. Therefore, it should be noted that the term "quantum dot ratio" in this specification does not necessarily refer to the ratio of all quantum dots in the entire light-emitting layer.

[0134] The specific structure of each layer of a light-emitting element according to one aspect of this disclosure may be confirmed, for example, by performing cross-sectional observation of each layer of the light-emitting element and performing EDX (energy-dispersive X-ray spectroscopy) on the cross-section. For example, a scanning electron microscope (SEM) may be used for such cross-sectional observation. As another example, a transmission electron microscope (TEM) may be used for such cross-sectional observation.

[0135] When confirming the specific structure of each layer of a light-emitting element according to one aspect of this disclosure, if cross-sectional observation is performed using TEM and EDX is performed on the cross-section, FIB (integrated ion beam) processing may also be used in combination.

[0136] As a method for cross-sectional observation, SEM may be used in preference to TEM. Therefore, if the specific structure of each layer of the light-emitting element can be confirmed based on the results of cross-sectional observation by SEM, the confirmation of the specific structure of each layer of the light-emitting element based on the results of cross-sectional observation by TEM may be omitted.

[0137] [Embodiment 2] Figure 8 shows an example configuration of the display device 100 in Embodiment 2. In Embodiment 2, the second light-emitting layer 13_2 of the two light-emitting elements 1_2 further includes a first quantum dot in addition to the second quantum dot Q2. In Figure 8, the first quantum dot in the second light-emitting element 1_2 is indicated by the code Q1_2. As shown in Figure 8, in the second light-emitting element 1_2, the first quantum dot Q1_2 is located on the cathode 15 side compared to the second quantum dot Q2.

[0138] The configuration of the second quantum dot Q2 in the second light-emitting element 1_2 in Figure 8 is equivalent to that in the example in Figure 1. Therefore, in the example of the second light-emitting element 1_2 in Figure 8, the case in which the second quantum dot Q2 has one shell layer is also illustrated.

[0139] The first quantum dot Q1_2 in the second light-emitting element 1_2 has a core-shell structure. In Figure 8, the first core of the first quantum dot Q1_2 is indicated by the code CR1_2. Also in Figure 8, the first and second shells of the first quantum dot Q1_2 are indicated by the codes SH1_2 and SH2_2, respectively. Thus, the first quantum dot Q1_2 in the second light-emitting element 1_2 is also an example of the multi-shell type quantum dot described above.

[0140] In the second embodiment, the second light-emitting element 1_2 is assumed to have the same material as the second core CR1_2 of the first quantum dot Q1_2. Therefore, the first quantum dot Q1_2 also emits second-color light.

[0141] In the second embodiment of the second light-emitting element 1_2, the first shell SH1_2 and the second shell SH2_2 of the first quantum dot Q1_2 are located on the outer surface of the first core CR1_2 of the first quantum dot Q1_2, respectively. However, the second shell SH2_2 is an outer shell of the first shell SH1_2. The second shell SH2_2 only needs to be located on at least a portion of the outer surface of the first shell SH1_2. In the example of Figure 8, the second shell SH2_2 is located on the entire outer surface of the first shell SH1_2.

[0142] In Figure 8, for the sake of clarity, an example is shown where the shell of the first quantum dot Q1_2 in the second light-emitting element 1_2 has two layers. Therefore, in Figure 8, an example is shown where the first shell SH1_2 of the first quantum dot Q1_2 is the innermost shell of the first quantum dot Q1_2. Consequently, in the example in Figure 8, the first shell SH1_2 of the first quantum dot Q1_2 is in direct contact with the first core CR1_2 of the first quantum dot Q1_2.

[0143] However, the number of shell layers in the first quantum dot Q1_2 in the second light-emitting element 1_2 is not limited to the example in Figure 8. As can be understood from this, the first shell SH1_2 of the first quantum dot Q1_2 does not have to be the innermost shell of the first quantum dot Q1_2. In other words, the first shell SH1_2 of the first quantum dot Q1_2 does not have to be in direct contact with the first core CR1_2 of the first quantum dot Q1_2.

[0144] The first shell SH1_2 of the first quantum dot Q1_2 in the second light-emitting element 1_2 contains the aforementioned metal element and the first group 16 element. From this, it can be said that the first shell SH1_2 of the first quantum dot Q1_2 in the second light-emitting element 1_2 is a shell that corresponds to the first shell SH1 of the first quantum dot Q1 in the first light-emitting element 1_1.

[0145] On the other hand, the second shell SH2_2 of the first quantum dot Q1_2 in the second light-emitting element 1_2 contains the aforementioned metal element and a second group 16 element. From this, it can be said that the second shell SH2_2 of the first quantum dot Q1_2 in the second light-emitting element 1_2 is a shell that corresponds to the second shell SH2 of the first quantum dot Q1 in the first light-emitting element 1_1.

[0146] Figure 9 shows a schematic energy band diagram of the display device 100 in Embodiment 2. The energy band diagram in Figure 9 corresponds to the configuration example in Figure 8. As can be seen from Figure 9, according to the display device 100 in Embodiment 2, in the second light-emitting element 1_2, the second shell SH2_2 of the first quantum dot Q1_2 prevents excessive electron injection into the second quantum dot Q2.

[0147] Therefore, the display device 100 in Embodiment 2 reduces the risk of Auger recombination in the second light-emitting layer 13_2 of the second light-emitting element 1_2. In other words, the display device 100 in Embodiment 2 improves the carrier balance in the second light-emitting layer 13_2. Thus, Embodiment 2 also makes it possible to realize a display device with higher luminous efficiency than conventional devices.

[0148] Figure 10 shows another configuration example of the display device 100 in Embodiment 2. In the example of Figure 10, unlike the example in Figure 8, the second shell SH2_2 of the first quantum dot Q1_2 in the second light-emitting element 1_2 is located on a part of the outer surface of the first shell SH1_2 of the first quantum dot Q1_2. Even when the configuration example in Figure 10 is adopted, the schematic energy band diagram of the display device 100 is the same as that of the example in Figure 9. Therefore, even with the configuration example in Figure 10, a display device with higher luminous efficiency than conventional devices can be realized.

[0149] [Embodiment 3] Figure 11 shows an example configuration of the display device 100 in Embodiment 3. The second light-emitting element 1_2 in Embodiment 3 has an intervening layer KX. As shown in Figure 11, in the second light-emitting element 1_2, the intervening layer KX is located on the cathode 15 side. Furthermore, in the second light-emitting element 1_2, the second quantum dot Q2 is not located inside the intervening layer KX.

[0150] The intercalated layer KX only needs to contain the aforementioned metal elements and a second group 16 element. Therefore, as an example, the intercalated layer KX may contain Zn and S. From this, a ZnS layer can be given as an example of the intercalated layer KX. The ZnS layer as the intercalated layer KX may also be called the ZnS intercalated layer.

[0151] Figure 12 shows a schematic energy band diagram of the display device 100 in Embodiment 3. The energy band diagram in Figure 12 corresponds to the configuration example in Figure 11. As can be seen from Figure 11, the display device 100 in Embodiment 3 can prevent excessive electron injection into the second quantum dot Q2 by the intervening layer KX.

[0152] Furthermore, since the core diameter of the second quantum dot Q2 in the example of Figure 12 is small, electrons can be confined to a small region in the second quantum dot Q2. Therefore, in the second light-emitting element 1_2 in the example of Figure 11 described above, an intervening layer KX is provided above the second quantum dot Q2. According to the configuration example shown in Figure 11, a stepped band structure is obtained in the second light-emitting element 1_2 by the third shell SH3, which plays a role in confining electrons, and the intervening layer KX. As a result, the risk of Auger recombination can be reduced.

[0153] As described above, the display device 100 in Embodiment 3 can also reduce the risk of Auger recombination in the second light-emitting layer 13_2 of the second light-emitting element 1_2. In other words, the display device 100 in Embodiment 3 can also improve the carrier balance in the second light-emitting layer 13_2. Therefore, Embodiment 3 can also realize a display device with higher luminous efficiency than conventional devices.

[0154] Furthermore, if the intervening layer KX is too thin (e.g., if the thickness of the intervening layer KX is less than 1 nm), it becomes difficult to form the intervening layer KX. On the other hand, if the intervening layer KX is too thick (e.g., if the thickness of the intervening layer KX exceeds 3 nm), the tunneling effect will not occur in the intervening layer KX, and proper carrier injection into the second light-emitting layer 13_2 will be inhibited.

[0155] Therefore, there is a preferred numerical range for the thickness of the intervening layer KX. For example, the thickness of the intervening layer KX is preferably 1 nm to 3 nm.

[0156] [Embodiment 4] Figure 13 shows an example configuration of the display device 100 in Embodiment 4. Embodiment 4 describes another example configuration relating to the intervening layer KX. The intervening layer KX in the example in Figure 13 is also located on the cathode 15 side.

[0157] In Figure 11 above, an example is shown in which the intervening layer KX in the second light-emitting element 1_2 does not contain quantum dots. However, in the second light-emitting element 1_2, the intervening layer KX may contain a portion of the quantum dots. Alternatively, in the second light-emitting element 1_2, the intervening layer KX may contain the entire quantum dots.

[0158] Therefore, in the second light-emitting element 1_2, at least a portion of the second quantum dot Q2 located on the cathode 15 side may be located inside the intervening layer KX. In the example of Figure 13, in the second light-emitting element 1_2, the entire second quantum dot Q2 located on the cathode 15 side is located inside the intervening layer KX.

[0159] Figure 14 shows a schematic energy band diagram of the display device 100 in Embodiment 4. The energy band diagram in Figure 14 corresponds to the configuration example in Figure 13. As can be seen from Figure 14, according to the display device 100 in Embodiment 4, the intervening layer KX in the second light-emitting element 1_2 prevents excessive electron injection into the second quantum dot Q2.

[0160] In the example in Figure 14, as in the example in Figure 12, the core diameter of the second quantum dot Q2 is small, so electrons can be confined to a small region in the second quantum dot Q2. Therefore, an intervening layer KX is also provided in the second light-emitting element 1_2 in the example in Figure 13 described above. In the configuration example shown in Figure 11, a stepped band structure is obtained in the second light-emitting element 1_2 by the third shell SH3, which plays a role in confining electrons, and the intervening layer KX. As a result, the risk of Auger recombination can be reduced.

[0161] As described above, the display device 100 in Embodiment 4 can also reduce the risk of Auger recombination in the second light-emitting layer 13_2 of the second light-emitting element 1_2. In other words, the display device 100 in Embodiment 4 can also improve the carrier balance in the second light-emitting layer 13_2. Therefore, Embodiment 4 can also realize a display device with higher luminous efficiency than conventional devices.

[0162] Figure 15 shows another configuration example of the display device 100 in Embodiment 4. In the example of Figure 15, unlike the example in Figure 13, in the second light-emitting element 1_2, a portion of the second quantum dot Q2 located on the cathode 15 side is located inside the intervening layer KX. Even when the configuration example of Figure 15 is adopted, the schematic energy band diagram of the display device 100 is the same as in the example of Figure 14. Therefore, even with the configuration example of Figure 15, a display device with higher luminous efficiency than conventional devices can be realized.

[0163] [Embodiment 5] In this specification, a core-shell type quantum dot in which the above-mentioned x continuously changes in the radial direction of the quantum dot is referred to as a gradient-shell type quantum dot. In a gradient-shell type quantum dot, the band structure of the shell that confines electrons can be set in a stepwise and continuous manner. Therefore, even when using a gradient-shell type quantum dot, the risk of Auger recombination can be reduced.

[0164] Figure 16 illustrates xmin and xmax in a gradient shell type quantum dot. Figure 16 is a counterpart to Figure 7. Figure 16 shows a gradient shell type quantum dot Q_GRAD. As an example, consider the case where, similar to Embodiment 1, the above-mentioned metal element is Zn, the first group 16 element is Se, and the second group 16 element is S. In this case, the composition formula of the shell SHELL in the example of Figure 16 is also ZnSe １－ｘ S ｘ This can be generally expressed as follows.

[0165] In gradient-shell quantum dots, as in multi-shell quantum dots, it is thought that there is a certain degree of bias in the distribution of x inside the shell. Therefore, equation (3) above can also hold true for gradient-shell quantum dots.

[0166] In one embodiment of the present disclosure (e.g., the display device 100 in Figure 1), a gradient-shell type first quantum dot Q1 may be used instead of a multi-shell type first quantum dot Q1. On the other hand, the second quantum dot Q2 may be a single-shell type quantum dot.

[0167] Therefore, as an example, equations (7) and (8) above may also hold true in a display device 100 that employs a gradient-shell type first quantum dot Q1 and a single-shell type second quantum dot Q2.

[0168] [Embodiment 6] The embodiments described above mainly describe a light-emitting device having a first light-emitting element having a first light-emitting layer and a second light-emitting element having a second light-emitting layer. However, a light-emitting device according to one aspect of the present disclosure may further have a third light-emitting element having a third light-emitting layer. The charge function layer in the light-emitting device may be shared by the first light-emitting element, the second light-emitting element, and the third light-emitting element. The third light-emitting layer may include a third quantum dot. The third quantum dot may have a core-shell structure. The core material of the third quantum dot may be the same as the core material of the first quantum dot and the second quantum dot.

[0169] In this case, for example, the first to third light-emitting layers should be designed such that (i) the emission peak wavelength of the first light-emitting layer is longer than the emission peak wavelength of the second light-emitting layer, and (ii) the emission peak wavelength of the second light-emitting layer is longer than the emission peak wavelength of the third light-emitting layer. Therefore, the first, second, and third quantum dots should be designed such that (i) the emission peak wavelength of the first quantum dot is longer than the emission peak wavelength of the second quantum dot, and (ii) the emission peak wavelength of the second quantum dot is longer than the emission peak wavelength of the third quantum dot.

[0170] As an example, we will describe the case where the first light-emitting layer 1 emits red light, the second light-emitting layer emits green light, and the third light-emitting layer emits blue light. That is, we will describe the case where the first quantum dot emits red light, the second quantum dot emits green light, and the third quantum dot emits blue light. Thus, in the light-emitting device of Embodiment 6, the first light-emitting element may be a red light-emitting element, the second light-emitting element may be a green light-emitting element, and the third light-emitting element may be a blue light-emitting element.

[0171] As mainly described in the embodiments above, let's consider the case where the number of shell layers in the first quantum dot is set to be greater than the number of shell layers in the second quantum dot. In this case, for example, the number of shell layers in the second quantum dot may be set to be greater than the number of shell layers in the third quantum dot.

[0172] As an example, consider the case where the first quantum dot has 3 shell layers, the second quantum dot has 2 shell layers, and the third quantum dot has 1 shell layer. In this case, for example, the first quantum dot may have a core-shell structure of "InP / ZnSe / ZnSeS / ZnS", the second quantum dot may have a core-shell structure of "InP / ZnSe / ZnSeS", and the third quantum dot may have a core-shell structure of "InP / ZnSe".

[0173] In this specification, the letter x3 represents the composition ratio (e.g., S) of the second group 16 element to the aforementioned metal element (e.g., Zn) in the shell of the third quantum dot. In this specification, the minimum value of x3 in the third quantum dot is represented as x3min, and the maximum value of x3 in the third quantum dot is represented as x3max.

[0174] The explanation of the relationship between x1 and x2 described in Embodiment 1 above also applies to the relationship between x2 and x3. Therefore, typically, x1min, x2min, and x3min in Embodiment 6 are all small values. For this reason, in Embodiment 6, in addition to equations (4) and (5) above, the following equation (9), x3min < 0.1 ... (9) may also hold.

[0175] In addition, in Embodiment 6, the following equation (10), x1max > x2max > x3max ... (10) may hold true.

[0176] [Additional Notes] One aspect of this disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of one aspect of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0177] 1_1 First light-emitting element 1_2 Second light-emitting element 11 Anode 11_1 First anode (Anode corresponding to the first light-emitting element) 11_2 Second anode (Anode corresponding to the second light-emitting element) 12 Anode-side charge functional layer (Example of a charge functional layer shared by the first and second light-emitting elements) 13_1 First light-emitting layer 13_2 Second light-emitting layer 14 Cathode-side charge functional layer (Example of a charge functional layer shared by the first and second light-emitting elements) 15 Cathode 100 Display device Q1 First quantum dot in the first light-emitting element Q2 Second quantum dot in the first light-emitting element Q1_2 First quantum dot in the second light-emitting element SH1 First shell of the first quantum dot in the first light-emitting element SH2 Second shell of the first quantum dot in the first light-emitting element SH3 Third shell SH1_2 First shell of the first quantum dot in the second light-emitting element SH2_2 Second shell of the first quantum dot in the second light-emitting element KX intervening layer

Claims

1. A first light-emitting element having at least one anode and at least one cathode, a first light-emitting layer containing a first quantum dot, a second light-emitting element having a second light-emitting layer containing a second quantum dot, and a charge function layer shared by the first and second light-emitting elements, wherein the first and second light-emitting elements are located between at least one anode and at least one cathode, the first and second quantum dots each have a core-shell structure, the core material of the first quantum dot is the same as the core material of the second quantum dot, the emission peak wavelength of the first light-emitting layer is longer than the emission peak wavelength of the second light-emitting layer, the number of shell layers in the first quantum dot is greater than the number of shell layers in the second quantum dot, the first quantum dot has a first shell and a second shell located on the outer surface of the first shell, and the second quantum dot has a third shell. A display device wherein the first shell and the third shell each contain a metallic element and a first group 16 element, and the second shell contains the metallic element and a second group 16 element different from the first group 16 element.

2. The display device according to claim 1, wherein the proportion of the first quantum dots in the first light-emitting element is greater than the proportion of the first quantum dots in the second light-emitting element, and the proportion of the second quantum dots in the second light-emitting element is greater than the proportion of the second quantum dots in the first light-emitting element.

3. The display device according to claim 2, wherein the proportion of the first quantum dots in the first light-emitting element is 70% or more.

4. The display device according to claim 3, wherein the proportion of the first quantum dots in the first light-emitting element is 90% or more.

5. The display device according to any one of claims 2 to 4, wherein the proportion of the second quantum dots in the second light-emitting element is 70% or more.

6. The display device according to claim 5, wherein the proportion of the second quantum dots in the second light-emitting element is 90% or more.

7. The display device according to any one of claims 1 to 6, wherein the atomic number of the first group 16 element is greater than the atomic number of the second group 16 element.

8. A display device according to any one of claims 1 to 7, wherein x1 is a character indicating the composition ratio of the second group 16 element to the metal element in the shell of the first quantum dot, x2 is a character indicating the composition ratio of the second group 16 element to the metal element in the shell of the second quantum dot, the minimum value of x1 in the first quantum dot is represented as x1min, and the minimum value of x2 in the second quantum dot is represented as x2min, such that x1min < 0.1 and x2min < 0.

1.

9. The display device according to claim 8, wherein when the maximum value of x1 in the first quantum dot is represented as x1max and the maximum value of x2 in the second quantum dot is represented as x2max, x1max > x2max.

10. The display device according to claim 9, wherein x1max - x1min ≥ 0.5 and x2max - x2min < 0.

5.

11. The display device according to any one of claims 1 to 10, wherein the first shell of the first quantum dot in the first light-emitting element is the innermost shell of the first quantum dot.

12. The display device according to any one of claims 1 to 11, wherein the first quantum dot in the first light-emitting element has two shell layers, and the second quantum dot in the second light-emitting element has one shell layer.

13. The display device according to any one of claims 1 to 12, wherein the charge function layer comprises an inorganic hole injection layer.

14. The display device according to any one of claims 1 to 13, wherein the second light-emitting layer in the second light-emitting device further includes the first quantum dot in addition to the second quantum dot, the first quantum dot in the second light-emitting device has a core-shell structure, the core material of the first quantum dot in the second light-emitting device is the same as the core material of the second quantum dot in the second light-emitting device, the first quantum dot in the second light-emitting device has a first shell of the first quantum dot in the second light-emitting device and a second shell of the first quantum dot in the second light-emitting device located on the outer surface of the first shell, the first shell of the first quantum dot in the second light-emitting device contains the metal element and the first group 16 element, the second shell of the first quantum dot in the second light-emitting device contains the metal element and the second group 16 element, and the first quantum dot in the second light-emitting device is located on the cathode side compared to the second quantum dot in the second light-emitting device.

15. The display device according to claim 14, wherein the first shell of the first quantum dot in the second light-emitting element is the innermost shell of the first quantum dot.

16. The display device according to claim 14 or 15, wherein the second quantum dot in the second light-emitting element has one shell layer, and the first quantum dot in the second light-emitting element has two shell layers.

17. The display device according to any one of claims 1 to 13, wherein the second light-emitting element has an intervening layer located on the cathode side, and the intervening layer contains the metal element and the second group 16 element.

18. The display device according to claim 17, wherein the second quantum dot of the second light-emitting element is not located inside the intervening layer.

19. The display device according to any one of claims 17, wherein at least a portion of the second quantum dot of the second light-emitting element, which is located on the cathode side, is located inside the intervening layer.

20. The display device according to any one of claims 17 to 19, wherein the thickness of the intervening layer is 1 nm or more and 3 nm or less.

21. The display device according to any one of claims 1 to 20, wherein the metallic element is Zn, the first group 16 element is Se, and the second group 16 element is S.

22. The display device according to any one of claims 1 to 21, wherein the halogen coverage of the second quantum dot is greater than the halogen coverage of the first quantum dot.

23. The display device according to any one of claims 1 to 22, wherein the halogen with the highest concentration among the halogens contained in the first light-emitting layer is referred to as the first halogen, the halogen with the highest concentration among the halogens contained in the second light-emitting layer is referred to as the second halogen, and the atomic number of the second halogen is smaller than the atomic number of the first halogen.

24. The display device according to claim 23, wherein the first halogen is iodine and the second halogen is chlorine.

25. A first light-emitting element having at least one anode and at least one cathode, a first light-emitting layer containing a first quantum dot, a second light-emitting element having a second light-emitting layer containing a second quantum dot, and a charge function layer shared by the first and second light-emitting elements, wherein the first and second light-emitting elements are located between at least one anode and at least one cathode, the first and second quantum dots each have a core-shell structure, the core material of the first quantum dot is the same as the core material of the second quantum dot, the emission peak wavelength of the first light-emitting layer is longer than the emission peak wavelength of the second light-emitting layer, the shell of the first quantum dot contains a metal element, a first group 16 element, and a second group 16 element different from the first group 16 element, and x1 is the letter indicating the composition ratio of the second group 16 element to the metal element in the shell of the first quantum dot. A display device in which, when x2 represents the composition ratio of the second group 16 element to the metal element in the shell of the second quantum dot, the minimum value of x1 in the first quantum dot is represented as x1min, the minimum value of x2 in the second quantum dot is represented as x2min, the maximum value of x1 in the first quantum dot is represented as x1max, and the maximum value of x2 in the second quantum dot is represented as x2max, x1max - x1min ≥ 0.5 and x2max - x2min < 0.

5.

26. The display device according to any one of claims 1 to 25, wherein at least one of the anodes includes a first anode corresponding to the first light-emitting element and a second anode corresponding to the second light-emitting element, and at least one of the cathodes is shared by the first light-emitting element and the second light-emitting element.

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