Light-emitting element and display device

Abstract

A light-emitting element (ED) according to the present disclosure comprises, between a first light-emitting layer (E1) and a second light-emitting layer (E2), a first charge generation layer (CG1) that contains a first n-type material (N1) and a second charge generation layer (CG2) that contains a first p-type material (P1), wherein (i) the first charge generation layer (CG1) further contains, mixed therein, a second n-type material (N2) different from the first n-type material (N1) and / or (ii) the second charge generation layer (CG2) further contains, mixed therein, a second p-type material (P2) different from the first p-type material (P1).

Description

Light-emitting element and display device

[0001] This disclosure relates to a light-emitting element and a display device.

[0002] Patent Document 1 discloses a tandem-type light-emitting device.

[0003] US2018 / 0122873A1

[0004] Tandem-type light-emitting diodes require a higher drive voltage than non-tandem-type diodes, roughly twice as high. Higher drive voltages necessitate higher operating voltage and withstand voltage ratings for the drive circuit, leading to increased manufacturing costs and lower yield for the diodes. Therefore, reducing the drive voltage of tandem-type diodes is desirable.

[0005] To solve the above problems, a light-emitting element according to one aspect of the present disclosure comprises a first light-emitting layer and a second light-emitting layer, a first charge generation layer located between the first light-emitting layer and the second light-emitting layer and containing a first n-type material, and a second charge generation layer located between the first charge generation layer and the second light-emitting layer and containing a first p-type material, wherein at least one of the following is the configuration: (i) the first charge generation layer further contains a second n-type material different from the first n-type material by mixing, or (ii) the second charge generation layer further contains a second p-type material different from the first p-type material by mixing.

[0006] To solve the above problems, a display device according to one aspect of the present disclosure has a configuration that includes a light-emitting element according to one aspect of the present disclosure.

[0007] According to one aspect of this disclosure, the driving voltage of a tandem-type light-emitting element can be reduced.

[0008] This is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a cross-sectional view showing an example of a quantum dot adduct provided in the first light-emitting layer shown in Figure 1. This is a cross-sectional view showing an example of a quantum dot adduct provided in the first light-emitting layer shown in Figure 1. This is a cross-sectional view showing an example of the first light-emitting layer provided in Figure 1. This is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 1. This shows an example of the mixing ratio of n-type semiconductor material in the first charge generation layer. This shows an example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This shows another example of the process for forming the first charge generation layer. This is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 13. This shows an example of the mixing ratio of p-type semiconductor material in the second charge generation layer. This is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 16. This is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 18. This is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. This is a schematic diagram showing an example of the configuration of a display device according to one aspect of the present disclosure.

[0009] [Embodiment 1] (Configuration of a light-emitting element) Figure 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 1, the light-emitting element ED according to the present disclosure comprises a first electrode C1 and a second electrode C2, a first light-emitting layer E1 located between the first electrode C1 and the second electrode C2, a second light-emitting layer E2 located between the first light-emitting layer E1 and the second electrode C2, a first charge generation layer CG1 located between the first light-emitting layer E1 and the second light-emitting layer E2 and containing at least a first n-type material N1, and a second charge generation layer CG2 located between the first charge generation layer CG1 and the second light-emitting layer E2 and containing at least a first p-type material P1. In the light-emitting element ED according to this disclosure, at least one of the following is true: (i) the first charge generation layer CG1 contains a mixture of a first n-type material N1 and a second n-type material N2 different from that material; or (ii) the second charge generation layer CG2 contains a mixture of a first p-type material P1 and a second p-type material P2 (see Figure 13, etc.).

[0010] The first n-type material N1 and the second n-type material N2 are n-type semiconductor materials, and the first p-type material P1 and the second p-type material P2 are p-type semiconductor materials. When a reverse bias voltage is applied to the n-type semiconductor material and the p-type semiconductor material, hole-electron pairs are generated at the interface between the n-type semiconductor material and the p-type semiconductor material, allowing holes to move through the p-type semiconductor material and electrons to move through the n-type semiconductor material. In this way, a charge is generated between the first charge generation layer CG1 and the second charge generation layer CG2 by the reverse bias voltage. Generally, the entire stack of layers of n-type semiconductor material and p-type semiconductor material is referred to as a "charge generation layer". For convenience, in this disclosure, the layer of n-type semiconductor material is referred to as the "first charge generation layer," and the layer of p-type semiconductor material is referred to as the "second charge generation layer."

[0011] The first n-type material N1, the second n-type material N2, the first p-type material P1, and the second p-type material P2 are inorganic materials. Because inorganic materials are less prone to degradation than organic materials, the first charge generation layer CG1 and the second charge generation layer CG2 have excellent reliability.

[0012] As shown in Fig. 1, in the configuration according to Embodiment 1, the first charge generation layer CG1 contains a mixture of the first n-type material N1 and the second n-type material N2. In the present disclosure, for the sake of simplicity of explanation, among the two n-type semiconductor materials, the one with a larger electron affinity is referred to as the "first n-type material", and the one with a smaller electron affinity is referred to as the "second n-type material". Therefore, the electron affinity of the second n-type material N2 is smaller than the electron affinity of the first n-type material N1. Further, the second charge generation layer CG2 contains the first p-type material P1 but does not contain the second p-type material P2.

[0013] In the present disclosure, when a certain layer X contains a mixture of a certain material Y and another certain material Z, it includes the following seven cases. First, material Z may be dissolved in the continuous film of material Y. Second, material Z may be precipitated in the continuous film of material Y. Third, nanoparticles of material Z may be embedded in the continuous film of material Y. Fourth, material Y may be dissolved in the continuous film of material Z. Fifth, material Y may be precipitated in the continuous film of material Z. Sixth, nanoparticles of material Y may be embedded in the continuous film of material Z. Seventh, nanoparticles of material Y and nanoparticles of material Z may be mixed.

[0014] Fig. 1 shows an example in which the first n-type material N1 is the first nanoparticle NP1, the second n-type material N2 is the second nanoparticle NP2, the first p-type material P1 is the third nanoparticle NP3, and the first nanoparticle NP1 and the second nanoparticle NP2 are mixed.

[0015] In the present disclosure, the "nanoparticle" means a particle with a maximum width of about 1 to several hundred nm. The shape of the nanoparticle may be within the range that satisfies the above maximum width and is not particularly limited, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). The shape of the nanoparticle may be, for example, a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branched three-dimensional shape, a three-dimensional shape having irregularities on the surface, or a combination thereof. The nanoparticle may be a single crystal or a polycrystal.

[0016] The light-emitting element ED may optionally include one or more of the following: a hole injection layer K1 and / or a hole transport layer K2 located between the first electrode C1 and the first light-emitting layer E1; an electron transport layer located between the first light-emitting layer E1 and the first charge generation layer CG1; a hole transport layer K4 located between the second charge generation layer CG2 and the second light-emitting layer E2; and an electron transport layer K5 and / or an electron injection layer located between the second light-emitting layer E2 and the second electrode C2.

[0017] (Emitting Layer) The first emitting layer E1 may include a first quantum dot QD1, and the second emitting layer E2 may include a second quantum dot QD2. The light-emitting element ED may be a tandem type quantum dot light-emitting diode (QLED). The first emitting layer E1 and the second emitting layer E2 may emit light of the same color. Here, same-color emission means that the colors are approximately the same within the range visible to the human eye, and it is not required that the peaks of the light wavelengths be exactly the same in a strict sense. For example, if two peaks are detected in the emission wavelength spectra of the first emitting layer E1 and the second emitting layer E2, and the wavelengths of each peak fall within the wavelength ranges of the same color, namely 430-500 nm for blue, 500-570 nm for green, and 610-780 nm for red, then their emission colors are considered to be the same. Also, if the respective peaks overlap and are detected as a single peak, then the emission colors are considered to be the same.

[0018] The first light-emitting layer E1 may include adducts formed around the first quantum dots QD1 and / or adducts filling the spaces between at least two first quantum dots QD1. In addition, / or the second light-emitting layer E2 may include adducts formed around the second quantum dots QD2 and / or adducts filling the spaces between at least two second quantum dots QD2. The adducts may have properties such as semiconductors or insulators. The adducts may include one or more of metal oxides, metalloid oxides, and metal sulfides.

[0019] The adduct is an oxide, for example, silicon oxide (SiO₂). ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ ), lead oxide (PbO), and copper oxide (CuO). Here, the adduct may be formed as a polymer. For example, when the adduct contains silicon oxide as an oxide, it may include the case where the adduct is a siloxane compound having a siloxane bond. Also, the adduct may be a sulfide, for example, zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS ２ ), gallium sulfide (GaS, Ga ２ S ３ ), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa ２ S ４ ), and magnesium gallium sulfide (MgGa ２ S ４ ). Note that the chemical formulas of the compounds are merely representative examples. The composition ratio of the compounds contained in the adduct may be stoichiometric (stoichiometric composition ratio) or non-stoichiometric.

[0020] Figures 2 and 3 are cross-sectional views showing examples of quantum dot adducts provided in the first light-emitting layer shown in Figure 1. As shown in Figures 2 and 3, in the first light-emitting layer E1, the adduct AD1 may be formed so as to surround at least one first quantum dot QD1. The adduct AD1 is mainly composed of silicon oxide, for example. In the quantum dot adducts 100A and 100B shown in Figures 2 and 3, the adduct AD1 is shown as being located around the entire periphery of the first quantum dot QD1 in a cross-section passing through the first quantum dot QD1. However, it is not limited to this, and if the adduct AD1 is located around 90% or more of the periphery of the first quantum dot QD1, it may be considered that the adduct AD1 is formed to surround the first quantum dot QD1. The adduct AD1 may be in direct contact with the surface of the first quantum dot QD1, as shown in Figure 2, or it may be linked to the surface of the first quantum dot QD1 via an organic ligand OL1, as shown in Figure 3.

[0021] Similarly, in the second light-emitting layer E2, adducts may be formed around at least one second quantum dot QD2. If adducts are located in more than 90% of the area around the second quantum dot QD2, it may be considered that the adducts are formed to cover the second quantum dot QD2. The adducts may be in direct contact with the surface of the second quantum dot QD2, or they may be linked to the surface of the second quantum dot QD2 via organic ligands.

[0022] Figure 4 is a cross-sectional view showing an example in which the first light-emitting layer shown in Figure 1 is equipped with an adduct. As shown in Figure 4, an adduct AD1 may be formed in the first light-emitting layer E1 so as to fill the space between at least two first quantum dots QD1. In this case, the adduct AD1 is 1000 nm in a direction perpendicular to the film thickness direction at any position in the film thickness direction of the first light-emitting layer E1. ２It may be formed as a continuous film having the above area. Furthermore, the first quantum dot QD1 may be embedded within the continuous film of the adduct AD1. For example, if 60% or more of the surface of 80% or more of the first quantum dot QD1 constituting the first light-emitting layer E1 is in contact with the continuous film of the adduct AD1, then the first quantum dot QD1 contained in the first light-emitting layer E1 can be said to be embedded within the continuous film of the adduct AD1. Also, for the adduct AD1 to fill the space between at least two first quantum dot QD1 of the first light-emitting layer E1 means either the adduct AD1 filling the space between the two first quantum dot QD1 by itself, or the adduct AD1 filling the space together with other materials. For example, an additional material such as a ligand different from the adduct AD1 may be included between the two first quantum dot QD1. The ligand and other materials may be an organic ligand OL1 that coordinates to the first quantum dot QD1, or an organic ligand OL1 that is free from the first quantum dot QD1. The free organic ligand OL1 may be contained in the adduct AD1. When the first light-emitting layer E1 contains the organic ligand OL1, for example, the weight ratio of the organic ligand OL1 to the total weight of the first light-emitting layer E1 may be less than 5%. The weight ratio of the organic ligand OL1 can be measured, for example, using TOF-SIMS (time-of-flight secondary ion mass spectrometry). When the organic ligand OL1 is dispersed in the first light-emitting layer E1, the organic ligand OL1 may contribute to the injection of holes and / or electrons into the first light-emitting layer E1.

[0023] Similarly, in the second light-emitting layer E2, an adduct may be formed such that it fills the space between at least two second quantum dots QD2. Alternatively, the second quantum dots QD2 may be embedded in a continuous film of adducts. The space between two second quantum dots QD2 may be filled by the adduct alone, or by the adduct in combination with other materials. For example, a material such as a ligand different from the adduct may be additionally included between two second quantum dots QD2. This material such as a ligand may be an organic ligand that coordinates to the second quantum dots QD2, or it may be an organic ligand that is free from the second quantum dots QD2. The free organic ligand may be included in the adduct. When the second light-emitting layer E2 contains an organic ligand, for example, the weight ratio of the organic ligand to the total weight of the second light-emitting layer E2 may be less than 5%. The weight ratio of the organic ligand can be measured, for example, using TOF-SIMS (time-of-flight secondary ion mass spectrometry). If an organic ligand is dispersed in the second light-emitting layer E2, the organic ligand may contribute to the injection of holes and / or electrons into the second light-emitting layer E2.

[0024] (Band Structure of the Light-Emitting Device) Figure 5 is a band diagram showing an example of the band structure of the light-emitting device shown in Figure 1. In Figure 5, the Fermi levels of the first electrode C1 and the second electrode C2 are shown by solid lines. The band gaps of the hole injection layer K1, the hole transport layer K2, the first quantum dot QD1 of the first light-emitting layer E1, the first n-type material N1 and the second n-type material N2 contained in the first charge generation layer CG1, the first p-type material P1 contained in the second charge generation layer CG2, the hole transport layer K4, the second quantum dot QD2 of the second light-emitting layer E2, and the electron transport layer K5 are shown by rectangles. The band gap is the energy difference between the valence band (VB) and the conduction band (CB). The bottom edge of the rectangle indicates the highest part of the valence band (valence band maximum: VBM), and the top edge of the rectangle indicates the lowest part of the conduction band (conduction band minimum: CBM). The work function corresponds to the energy difference (absolute value) between the Fermi level and the vacuum level at absolute zero, the electron affinity corresponds to the energy difference (absolute value) between the CBM and the vacuum level, and the ionization potential corresponds to the energy difference (absolute value) between the VBM and the vacuum level.

[0025] As shown in Figure 5, according to the configuration of this embodiment 1, the first charge generation layer CG1 has both electron affinity in the first n-type material N1 and electron affinity in the second n-type material N2. Therefore, by determining the first n-type material N1 such that its electron affinity is close to that of the first p-type material P1, the voltage required for charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. At the same time, by determining the second n-type material N2 such that its electron affinity is close to that of the first light-emitting layer E1, the voltage required for electron injection from the first charge generation layer CG1 to the first light-emitting layer E1 can be reduced. Both of these reduce the driving voltage of the light-emitting element ED.

[0026] It was known that combining an electron-transporting material with high electron affinity and a hole-transporting material with low ionization potential would reduce the voltage required for charge generation. However, electron-transporting materials with high electron affinity require a higher voltage for electron injection into the light-emitting layer. Similarly, hole-transporting materials with low ionization potential require a higher voltage for hole injection into the light-emitting layer. Therefore, even when combining an electron-transporting material with high electron affinity and a hole-transporting material with low ionization potential, it was not possible to reduce the overall driving voltage of a tandem-type light-emitting element.

[0027] In contrast, according to the configuration of Embodiment 1 of the present disclosure, the voltage required for both charge generation and electron injection into the first light-emitting layer E1 can be reduced, and the overall driving voltage of the light-emitting element ED can be reduced.

[0028] The difference between the electron affinity of the second-type n material N2 and the electron affinity of the first-type n material N1 may be 0.1 eV or more, preferably 0.3 eV or more. Since the ease of electron injection differs by about 50 times for every 0.1 eV difference in electron affinity, the reduction in the driving voltage of the light-emitting element ED becomes significant.

[0029] The difference between the electron affinity of the first n-type material N1 and the ionization potential of the first p-type material P1 may be 1.5 eV or less, preferably 1.0 eV or less. The smaller the difference between the electron affinity of the first n-type material N1 and the ionization potential of the first p-type material P1, the lower the voltage required for charge generation.

[0030] (Differences in n-type semiconductor materials) In this disclosure, the statement that the second n-type material N2 is different from the first n-type material N1 includes the following three cases:

[0031] Firstly, the constituent elements of the second-type n material N2 may differ from those of the first-type n material N1. Due to the difference in constituent elements, the electron affinity of the second-type n material N2 may differ from that of the first-type n material N1. For example, a combination of the first-type n material N1 and the second-type n material N2 may include titanium oxide (TiO2). ２), zinc oxide (ZnO), magnesium zinc oxide (ZnMgO), zinc sulfide (ZnS), zirconium oxide (ZrO) ２ ), tin oxide (SnO ２ It may be a combination of two compounds selected from the group consisting of ) etc.

[0032] Secondly, the constituent elements of the second-type n material N2 may be the same as those of the first-type n material N1, and the composition ratio of the second-type n material N2 may differ from that of the first-type n material N1. Due to the difference in composition ratio, the electron affinity of the second-type n material N2 may differ from that of the first-type n material N1. For example, if the first-type n material N1 is Zn （１－ｘ） Mg ｘ O(0 < x < 1), and the second n-type material N2 is Zn （１－ｙ） Mg ｙ It is acceptable for the expression to be O(0 < y < 1, x ≠ y). Zn （１－ｘ） Mg ｘ O and Zn （１－ｙ） Mg ｙ Both O and N2 have composition ratios that conform to stoichiometry, and their composition ratios are different from each other since x ≠ y. In this case, the combination of x and y may be a combination of two numerical values ​​selected from the group consisting of 0.05, 0.1, 0.15, 0.2, etc. It is not limited to the case where both the first n-type material N1 and the second n-type material N2 satisfy stoichiometry; one or both may deviate from stoichiometry.

[0033] Thirdly, when the first n-type material N1 is the first nanoparticle NP1 and the second n-type material N2 is the second nanoparticle NP2, the average particle size of the second nanoparticle NP2 may differ from the average particle size of the first nanoparticle NP1. This is regardless of whether the constituent elements and / or composition ratio of the second nanoparticle NP2 are different from or the same as the constituent elements and / or composition ratio of the first nanoparticle NP1. The average particle sizes of the first nanoparticle NP1 and the second nanoparticle NP2 may differ even if their constituent elements are different, even if their constituent elements are the same but their composition ratios are different, or even if their constituent elements are the same and their composition ratios are the same. Due to the difference in average particle size, the electron affinity of the second nanoparticle NP2 may differ from that of the first nanoparticle NP1. For example, if both the first n-type material N1 and the second n-type material N2 are Zn ０．８５ Mg ０．１５ In the case of nanoparticles of O, the combination of the average particle sizes of both may be a combination of two particle sizes selected from the group consisting of 4 nm, 6 nm, 8 nm, 12 nm, etc. For example, one of the first n-type material N1 and the second n-type material N2 is ZnO nanoparticles, and the other is Zn （１－ｘ） Mg ｘ The nanoparticles may be of type O (0 < x < 1).

[0034] The smaller the particle size of the nanoparticles, the larger the band gap tends to be. Therefore, the smaller the particle size of the nanoparticles, the smaller the electron affinity tends to be. Note that if the constituent elements of the first nanoparticle NP1 and the second nanoparticle NP2 are different, or if the constituent elements of both are the same but the composition ratio is different, the average particle size of both may be the same.

[0035] (Ratio of n-type semiconductor material) In this disclosure, the ratio of the first n-type material N1 to the second n-type material N2 in the first charge generation layer CG1 may be substantially constant even if it fluctuates in the thickness direction (Z direction in Figure 1) of the first charge generation layer CG1. The ratio of one material Y to another material Z in a certain layer X may be a volume ratio. The volume ratio can be measured using a scanning electron microscope energy-dispersive X-ray fluorescence spectrometer (SEM-EDX) or a scanning transmission electron microscope energy-dispersive X-ray fluorescence spectrometer (STEM-EDX). Other methods may be used as appropriate. This measurement is performed not on the entire layer X, but on a part of layer X, for example, a volume of 10,000 nm. ３ The above observations are sufficient. When nanoparticles of material Y and nanoparticles of material Z are mixed, the ratio of material Y to material Z in a certain layer X may be the relative ratio of the number of nanoparticles of material Z to the number of nanoparticles of material Y when observing the cross-section of layer X. This cross-sectional observation is not of the entire layer X, but of a part of layer X, for example, a cross-sectional area of ​​1000 nm. ２ Observe the above points.

[0036] Referring again to Figure 1, when the ratio of the second n-type material N2 to the first n-type material N1 in the first portion H1 of the first charge generation layer CG1 closer to the second charge generation layer CG2 is different from the ratio of the second n-type material N2 to the first n-type material N1 in the second portion H2 of the first charge generation layer CG1 further from the second charge generation layer CG2, the ratio fluctuates in the thickness direction of the first charge generation layer CG1 (the Z direction in Figure 1). The first charge generation layer CG1 can be divided into two parts at its central plane in the thickness direction, with the first portion H1 being the half closer to the second charge generation layer CG2 (or a further part of that half). The second portion H2 can be the half further from the second charge generation layer CG2 (or a further part of that half).

[0037] Figure 6 shows an example of the mixing ratio of n-type semiconductor material in the first charge generation layer. As shown in Figure 6, it is beneficial for further reducing the driving voltage of the light-emitting element ED if the ratio of the second n-type material N2 to the first n-type material N1 in the first portion H1 closer to the second charge generation layer CG2 is smaller than the ratio of the second n-type material N2 to the first n-type material N1 in the second portion H2 further away from the second charge generation layer CG2. This is because, as mentioned above, the first n-type material N1 contributes to lowering the voltage of charge generation between the first charge generation layer CG1 and the second charge generation layer CG2, and the second n-type material N2 contributes to lowering the voltage of electron injection from the first charge generation layer CG1 to the first light-emitting layer E1.

[0038] The total ratio of the first n-type material N1 and the second n-type material N2 to the first charge generation layer CG1 is set to 100%. In this case, the average ratio of the second n-type material N2 in the entire first charge generation layer CG1 may be 10% to 90%, preferably 30% to 70%, and more preferably about 50%. Having an average of 10% or more of the first n-type material N1 significantly reduces the voltage of charge generation, and having an average of 10% or more of the second n-type material N2 significantly reduces the voltage of electron injection into the first light-emitting layer E1. Having an average of 30% or more of each material allows for greater utilization of both effects, and having an average of about 50% of each material maximizes both effects. Near the interface on the second charge generation layer CG2 side, it is preferable that the first n-type material N1 accounts for more than 50%, and it is more beneficial the closer it is to 100%. Similarly, it is preferable that the amount of the second n-type material N2 near the interface on the first light-emitting layer E1 side is greater than 50%, and it is more beneficial if it is closer to 100%.

[0039] If the first n-type material N1 is a first nanoparticle NP1 and the second n-type material N2 is a second nanoparticle NP2, then the ratio of the second nanoparticle NP2 to the first nanoparticle NP1 in the first portion H1 may be smaller than the ratio of the second nanoparticle NP2 to the first nanoparticle NP1 in the second portion H2.

[0040] (Method for Manufacturing a Light-Emitting Device) Referring again to Figure 1, one example of a method for manufacturing a light-emitting device ED according to the present disclosure is: a step of preparing a substrate SB; a step of forming a first electrode C1 on the substrate SB; a step of optionally forming a hole injection layer K1 and / or a hole transport layer K2 on the first electrode C1; a step of forming a first light-emitting layer E1 on the first electrode C1 or the hole injection layer K1 or the hole transport layer K2; a step of optionally forming an electron transport layer on the first light-emitting layer E1; and a step of forming a first charge generation layer C on the first light-emitting layer E1 or the electron transport layer. The process includes, in this order: forming G1; forming a second charge generation layer CG2 on a first charge generation layer CG1; optionally forming a hole transport layer K4 on a second charge generation layer CG2; forming a second light-emitting layer E2 on a second charge generation layer CG2 or a hole transport layer K4; optionally forming an electron transport layer K5 and / or an electron injection layer on a second light-emitting layer E2; and forming a second electrode C2 on a second light-emitting layer E2, an electron transport layer K5, or an electron injection layer.

[0041] Alternatively, another example of a method for manufacturing a light-emitting element ED according to the present disclosure is a step of preparing a substrate, a step of forming a second electrode C2 on the substrate, an optional step of forming an electron transport layer K5 and / or an electron injection layer on the second electrode C2, a step of forming a second light-emitting layer E2 on the second electrode C2 or the electron transport layer K5 or the electron injection layer, an optional step of forming a hole transport layer K4 on the second light-emitting layer E2, and a second charge generation layer CG2 on the second light-emitting layer E2 or the hole transport layer K4. The process includes, in this order: forming a layer; forming a first charge generation layer CG1 on a second charge generation layer CG2; optionally forming an electron transport layer on the first charge generation layer CG1; forming a first light-emitting layer E1 on the first charge generation layer CG1 or the electron transport layer; optionally forming a hole injection layer K1 and / or a hole transport layer K2 on the first light-emitting layer E1; and forming a first electrode C1 on the first light-emitting layer E1 or the hole injection layer K1 or the hole transport layer K2.

[0042] (Steps for forming a charge generation layer) Figure 7 shows an example of the steps for forming a first charge generation layer. As shown in Figure 7, a solution L1 in which a precursor V1 of the first type n material N1 and a precursor V2 of the second type n material N2 are dissolved is applied to a base layer, for example, a first light-emitting layer E1, an electron transport layer, or a second charge generation layer CG2. The first charge generation layer CG1 may then be formed by firing the coating of the solution L1. In this first charge generation layer CG1, the second type n material N2 is solid-dissolved or precipitated in a continuous film of the first type n material N1, or the first type n material N1 is solid-dissolved or precipitated in a continuous film of the second type n material N2. The first type n material N1 and the second type n material N2 may be selected from the group consisting of, for example, titanium oxide, zinc oxide, magnesium zinc oxide, zinc sulfide, zirconium oxide, and tin oxide, as described above. For example, titanium nitrate can be used as a precursor of titanium dioxide, zinc acetate as a precursor of zinc oxide, and zinc xanthogenic acid as a precursor of zinc sulfide.

[0043] When varying the ratio of the first n-type material N1 and the second n-type material N2 in the first charge generation layer CG1 in the thickness direction, the coating and firing of a solution L1 in which at least one of the precursors V1 and V2 has a different concentration is repeated.

[0044] Figure 8 shows another example of the process for forming the first charge generation layer. As shown in Figure 8, a solution L2 containing a precursor V1 of the first n-type material N1 is applied to the base layer. Then, before firing, a solution L3 containing a precursor V2 of the second n-type material N2 is applied on top of the film of solution L2. Alternatively, a solution L3 containing a precursor V2 of the second n-type material N2 is applied to the base layer, and then a solution L2 containing a precursor V1 of the first n-type material N1 is applied on top of the film of solution L3. The first charge generation layer CG1 may then be formed by firing the film containing solutions L2 and L3.

[0045] Figure 9 shows another example of the process for forming the first charge generation layer. As shown in Figure 9, a solution L4 containing dissolved precursor V1 of the first n-type material N1 and dispersed second nanoparticles NP2 of the second n-type material N2 is applied to a substrate layer. The first charge generation layer CG1 may then be formed by firing the coating of solution L4. In this first charge generation layer CG1, the second nanoparticles NP2 of the second n-type material N2 are embedded within a continuous film of the first n-type material N1. By repeatedly applying and firing solutions L4 with different concentrations of at least one of the precursor V1 and the second nanoparticles NP2, the ratio of the first n-type material N1 to the second n-type material N2 in the first charge generation layer CG1 can be varied in the thickness direction.

[0046] Alternatively, a solution in which first nanoparticles NP1 of the first type n material N1 are dispersed and a precursor V2 of the second type n material N2 is dissolved is applied to the substrate layer. Then, the coating film of the solution is fired to form a first charge generation layer CG1. In this first charge generation layer CG1, the first nanoparticles NP1 of the first type n material N1 are embedded in a continuous film of the second type n material N2. By repeatedly applying and firing solutions with different concentrations of at least one of the first nanoparticles NP1 and the precursor V2, the ratio of the first type n material N1 to the second type n material N2 in the first charge generation layer CG1 can be varied in the thickness direction.

[0047] Figure 10 shows another example of the process for forming the first charge generation layer. As shown in Figure 10, a solution L2 in which the precursor V1 of the first n-type material N1 is dissolved is applied to the substrate layer. Then, before firing, a solution L5 in which the second nanoparticles NP2 of the second n-type material N2 are dispersed is applied on top of the solution L2 coating. Alternatively, a solution L5 in which the second nanoparticles NP2 of the second n-type material N2 are dispersed is applied to the substrate layer, and then a solution L2 in which the precursor V1 of the first n-type material N1 is dissolved is applied on top of the solution L5 coating. Then, the coating containing solutions L2 and L5 is fired to form the first charge generation layer CG1.

[0048] Alternatively, a solution L3 containing the precursor V2 of the second type n material N2 may be applied to the substrate layer, and a solution L7 (see Figure 12) containing the first nanoparticle NP1 of the first type n material N1 dispersed on top of the solution L3 coating may be applied. Alternatively, a solution L7 containing the first nanoparticle NP1 of the first type n material N1 dispersed on top of the substrate layer may be applied, and a solution L3 containing the precursor V2 of the second type n material N2 may be applied on top of the solution L7 coating. Then, the coating containing solutions L3 and L7 may be fired to form the first charge generation layer CG1.

[0049] Figure 11 shows another example of the process for forming the first charge generation layer. As shown in Figure 11, a solution L6 in which first nanoparticles NP1 of the first n-type material N1 and second nanoparticles NP2 of the second n-type material N2 are dispersed is applied to a substrate layer. The first charge generation layer CG1 may be formed by firing the coating film of solution L6. In this first charge generation layer CG1, the first nanoparticles NP1 and the second nanoparticles NP2 are mixed. By repeatedly applying and firing solution L6 with different concentrations of at least one of the first nanoparticles NP1 and the second nanoparticles NP2, the ratio of the first n-type material N1 and the second n-type material N2 in the first charge generation layer CG1 can be varied in the thickness direction.

[0050] Figure 12 shows another example of the process for forming the first charge generation layer. As shown in Figure 12, a solution L7 in which first nanoparticles NP1 of the first n-type material N1 are dispersed is applied to the substrate layer. Then, before firing, a solution L5 in which second nanoparticles NP2 of the second n-type material N2 are dispersed is applied on top of the solution L7 coating. Alternatively, a solution L5 in which second nanoparticles NP2 of the second n-type material N2 are dispersed is applied to the substrate layer, and then a solution L7 in which first nanoparticles NP1 of the first n-type material N1 are dispersed is applied on top of the solution L5 coating. Then, the coating containing solutions L5 and L7 is fired to form the first charge generation layer CG1.

[0051] (Steps for forming the light-emitting layer) In the step of forming the first light-emitting layer E1, first, a first quantum dot dispersion is prepared. The first quantum dot dispersion is a dispersion in which at least first quantum dots QD1 are dispersed in a solvent. If the first light-emitting layer E1 contains an adduct AD1, the first quantum dot dispersion is a dispersion in which the first quantum dots QD1 and a precursor of the adduct AD1 are dispersed in a solvent. The precursor includes a material that is converted to the adduct AD1 through hydrolysis and dehydration condensation by performing a specific operation such as heating or light irradiation. The precursor may have a coordinating functional group that forms a coordination bond with the surface of the first quantum dots QD1 in the first quantum dot dispersion. In this case, the precursor may coordinate to the first quantum dots QD1 in the first quantum dot dispersion. The first quantum dot dispersion also contains a halide having a halogen atom (for example, zinc chloride (ZnCl)). ２ The material may also contain halogen atoms. By mixing a material having halogen atoms into the first quantum dot dispersion, the halogen atoms can coat the surface of the first quantum dot QD1 independently of the adduct AD1, thereby reducing defects on the surface of the first quantum dot QD1. Therefore, by having halogen atoms in the adduct AD1, the light-emitting element ED increases the coverage of the first quantum dot QD1 in the first light-emitting layer E1, thereby improving its light-emitting properties.

[0052] The first quantum dot dispersion may be prepared, for example, by stirring a dispersion containing the first quantum dot QD1 and a dispersion containing a precursor of the adduct AD1 to prepare a mixture, and then extracting a predetermined layer from the mixture. Here, the dispersion containing the first quantum dot QD1 may contain an organic ligand that coordinates to the first quantum dot QD1. In this case, for example, during stirring for the preparation of the mixture, the ligand that coordinates to the first quantum dot QD1 may be replaced from an organic ligand to a part of the precursor of the adduct AD1, such as MPS.

[0053] For example, if adduct AD1 contains silicon oxide and the precursor of adduct AD1 has a coordination functional group, the precursor may contain 3-(mercaptopropyl)trimethoxysilane (MPS). Also, if adduct AD1 contains silicon oxide and the precursor of adduct AD1 does not have a coordination functional group, the precursor may contain tetramethyl orthosilicate (TMOS). Furthermore, for example, if adduct AD1 contains zinc sulfide, the precursor of adduct AD1 may contain zinc xanthogenic acid, zinc thioureate, and zinc dithiocarboxylate, etc.

[0054] Next, the first quantum dot dispersion is applied to the lower layer of the first light-emitting layer E1 to convert the precursor into adduct AD1. The conversion of the precursor into adduct AD1 is carried out by, for example, heating the applied first quantum dot dispersion to volatilize the solvent and convert the precursor into adduct AD1. For example, if the precursor contains TMOS and MPS, dehydration condensation occurs between TMOS molecules, between MPS molecules, and between TMOS and MPS molecules to form silicon oxide as adduct AD1. Alternatively, for example, if the precursor contains zinc xanthogenic acid, the zinc xanthogenic acid is decomposed to form zinc sulfide as adduct AD1. The conversion of the precursor into adduct AD1 occurs sequentially around the first quantum dots QD1 of the first quantum dot dispersion. By this method, the first light-emitting layer E1 having adduct AD1 can be formed.

[0055] Similarly, in the process of forming the second light-emitting layer E2, first, a second quantum dot dispersion is prepared in which at least the second quantum dots QD2 are dispersed in the solvent. If the second light-emitting layer E2 contains an adduct, the second quantum dot dispersion is a dispersion in which the second quantum dots QD2 and the precursor of the adduct are dispersed in the solvent. Next, the second quantum dot dispersion is applied onto the lower layer of the second light-emitting layer E2 to convert the precursor into an adduct. By this method, a second light-emitting layer E2 having an adduct can be formed.

[0056] [Embodiment 2] (Configuration of a light-emitting element) Figure 13 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 13, the light-emitting element ED according to the present disclosure comprises a first electrode C1 and a second electrode C2, a first light-emitting layer E1 located between the first electrode and the second electrode C2, a second light-emitting layer E2 located between the first light-emitting layer E1 and the second electrode C2, a first charge generation layer CG1 located between the first light-emitting layer and the second light-emitting layer and containing at least a first n-type material N1, and a second charge generation layer CG2 located between the first charge generation layer CG1 and the second light-emitting layer E2 and containing at least a first p-type material P1. In the light-emitting element ED according to this disclosure, at least one of the following is true: (i) the first charge generation layer CG1 contains a mixture of a first n-type material N1 and a second n-type material N2 different from that material; or (ii) the second charge generation layer CG2 contains a mixture of a first p-type material P1 and a second p-type material P2 different from that material.

[0057] As shown in Figure 13, in the configuration according to this second embodiment, the first charge generation layer CG1 contains the first n-type material N1 but does not contain the second n-type material N2 (see Figure 1, etc.). Furthermore, the second charge generation layer CG2 contains a mixture of the first p-type material P1 and the second p-type material P2. In this disclosure, for the sake of simplicity, of the two p-type semiconductor materials, the one with the smaller ionization potential is referred to as the "first p-type material," and the one with the larger ionization potential is referred to as the "second p-type material." Therefore, the ionization potential of the second p-type material P2 is greater than the ionization potential of the first p-type material P1.

[0058] Figure 13 shows an example in which the first n-type material N1 is the first nanoparticle NP1, the first p-type material P1 is the third nanoparticle NP3, the second p-type material P2 is the fourth nanoparticle NP4, and the third nanoparticle NP3 and the fourth nanoparticle NP4 are mixed.

[0059] (Band structure of the light-emitting element) Figure 14 is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 13. In Figure 14, the Fermi levels of the first electrode C1 and the second electrode C2 are shown by solid lines. The band gaps of the hole injection layer K1, the hole transport layer K2, the first quantum dot QD1 of the first light-emitting layer E1, the first n-type material N1 contained in the first charge generation layer CG1, the first p-type material P1 and the second p-type material P2 contained in the second charge generation layer CG2, the hole transport layer K4, the second quantum dot QD2 of the second light-emitting layer E2, and the electron transport layer K5 are shown by rectangles.

[0060] As shown in Figure 14, according to the configuration of this second embodiment, the second charge generation layer CG2 has both the ionization potential of the first p-type material P1 and the ionization potential of the second p-type material P2. Therefore, by determining the first p-type material P1 such that the electron affinity of the first n-type material N1 is close to the ionization potential of the first p-type material P1, the voltage required for charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. At the same time, by determining the second p-type material P2 such that the ionization potential of the second p-type material P2 is close to the ionization potential of the second light-emitting layer E2, the voltage required for hole injection from the second charge generation layer CG2 to the second light-emitting layer E2 can be reduced. Both of these reduce the driving voltage of the light-emitting element ED.

[0061] The difference between the ionization potential of the second p-type material P2 and the ionization potential of the first p-type material P1 may be 0.1 eV or more, preferably 0.3 eV or more. Since the ease of hole injection differs by about 50 times for every 0.1 eV difference in ionization potential, the reduction in the driving voltage of the light-emitting element ED becomes significant.

[0062] (Differences in p-type semiconductor materials) In this disclosure, the statement that the second p-type material P2 is different from the first p-type material P1 includes the following three cases:

[0063] Firstly, the constituent elements of the second p-type material P2 may differ from those of the first p-type material P1. Due to the difference in constituent elements, the ionization potential of the second p-type material P2 may differ from that of the first p-type material P1. For example, the combination of the first p-type material P1 and the second p-type material P2 is copper oxide (Cu ２ O), nickel oxide (NiO), magnesium nickel oxide (NiMgO), nickel lanthanum oxide (LaNiO) ３ It may be a combination of two compounds selected from the group consisting of ) etc.

[0064] Secondly, the constituent elements of the second p-type material P2 may be the same as those of the first p-type material P1, and the composition ratio of the second p-type material P2 may differ from that of the first p-type material P1. Due to the difference in composition ratio, the ionization potential of the second p-type material P2 may differ from that of the first p-type material P1. For example, if the first p-type material P1 is Ni （１－ｘ） Mg ｘ O (0 < x < 1), and the second p-type material P2 is Ni （１－ｙ） Mg ｙ It is acceptable for the expression to be O(0 < y < 1, x ≠ y). （１－ｘ） Mg ｘ O and Ni （１－ｙ） Mg ｙ Both O and P2 have composition ratios that conform to stoichiometry, and their composition ratios are different from each other since x ≠ y. In this case, the combination of x and y may be a combination of two numerical values ​​selected from the group consisting of 0.05, 0.1, 0.15, 0.2, etc. It is not limited to the case where both the first p-type material P1 and the second p-type material P2 satisfy stoichiometry; one or both may deviate from stoichiometry.

[0065] Thirdly, when the first p-type material P1 is the third nanoparticle NP3 and the second p-type material P2 is the fourth nanoparticle NP4, the average particle size of the fourth nanoparticle NP4 may differ from that of the third nanoparticle NP3. This is regardless of whether the constituent elements and / or composition ratio of the fourth nanoparticle NP4 are different from or the same as those of the third nanoparticle NP3. The average particle sizes of the third nanoparticle NP3 and the fourth nanoparticle NP4 may differ whether their constituent elements are different, whether their constituent elements are the same but their composition ratios are different, or whether their constituent elements are the same and their composition ratios are the same. Due to the difference in average particle size, the ionization potential of the fourth nanoparticle NP4 may differ from that of the third nanoparticle NP3. For example, if both the first p-type material P1 and the second p-type material P2 are Ni ０．８５ Mg ０．１５ In the case of nanoparticles of O, the combination of the average particle sizes of both may be a combination of two particle sizes selected from the group consisting of 4 nm, 6 nm, 8 nm, 12 nm, etc. For example, if one of the first p-type material P1 and the second p-type material P2 is NiO nanoparticles, and the other is Ni （１－ｘ） Mg ｘ The nanoparticles may be of type O (0 < x < 1).

[0066] The smaller the particle size of the nanoparticles, the larger the band gap tends to be. Therefore, the smaller the particle size of the nanoparticles, the larger the ionization potential tends to be. Note that if the constituent elements of the third nanoparticle NP3 and the fourth nanoparticle NP4 are different, or if the constituent elements of both are the same but the composition ratio is different, the average particle size of both may be the same.

[0067] (Proportion of p-type semiconductor material) In this disclosure, the proportion of the first p-type material P1 and the second p-type material P2 in the second charge generation layer CG2 may remain substantially constant even if it varies in the thickness direction of the second charge generation layer CG2 (Z direction in Figure 13).

[0068] When the ratio of the second p-type material P2 to the first p-type material P1 in the third portion H3 of the second charge generation layer CG2, which is farther from the first charge generation layer CG1, differs from the ratio of the second p-type material P2 to the first p-type material P1 in the fourth portion H4 of the second charge generation layer CG2, which is closer to the first charge generation layer CG1, this ratio fluctuates in the thickness direction of the second charge generation layer CG2 (the Z direction in Figure 13). The second charge generation layer CG2 may be divided into two halves along its central plane in the thickness direction, with the third portion H3 being the half farther from the first charge generation layer CG1 (or a further part of that half). The fourth portion H4 may be the half closer to the first charge generation layer CG1 (or a further part of that half).

[0069] Figure 15 shows an example of the mixing ratio of p-type semiconductor materials in the second charge generation layer. As shown in Figure 15, a larger ratio of the second p-type material P2 to the first p-type material P1 in the third portion H3 than the ratio of the second p-type material P2 to the first p-type material P1 in the fourth portion H4 is beneficial for further reducing the driving voltage of the light-emitting element ED. This is because, as mentioned above, the first p-type material P1 contributes to lowering the voltage of charge generation between the first charge generation layer CG1 and the second charge generation layer CG2, and the second p-type material P2 contributes to lowering the voltage of hole injection from the second charge generation layer CG2 to the second light-emitting layer E2.

[0070] The total ratio of the first p-type material P1 and the second p-type material P2 to the second charge generation layer CG2 is set to 100%. In this case, the average proportion of the second p-type material P2 in the entire second charge generation layer CG2 may be 10% to 90%, preferably 30% to 70%, and more preferably about 50%. Having an average of 10% or more of the first p-type material P1 significantly reduces the voltage for charge generation, and having an average of 10% or more of the second p-type material P2 significantly reduces the voltage for hole injection into the second light-emitting layer E2. Having an average of 30% or more of each material allows for greater utilization of both effects, and having an average of about 50% of each material maximizes both effects. Furthermore, near the interface on the first charge generation layer CG1 side, it is preferable that the first p-type material P1 is greater than 50%, and it is more beneficial the closer it is to 100%. Similarly, near the interface on the second light-emitting layer E2 side, it is preferable that the second p-type material P2 makes up more than 50%, and it is more beneficial as it approaches 100%.

[0071] If the first p-type material P1 is a third nanoparticle NP3 and the second p-type material P2 is a fourth nanoparticle NP4, then the ratio of the fourth nanoparticle NP4 to the third nanoparticle NP3 in the third portion H3 may be greater than the ratio of the fourth nanoparticle NP4 to the third nanoparticle NP3 in the fourth portion H4.

[0072] (Method for manufacturing a light-emitting element) The light-emitting element ED according to this second embodiment can be manufactured by the same manufacturing method as the light-emitting element ED according to the first embodiment described above. The second charge generation layer CG2 according to this second embodiment can be formed by various processes, similar to the first charge generation layer CG1 according to the second embodiment described above.

[0073] [Embodiment 3] (Configuration of a light-emitting element) Figure 16 is a cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 16, the light-emitting element ED according to the present disclosure comprises a first electrode C1 and a second electrode C2, a first light-emitting layer E1 located between the first electrode and the second electrode C2, a second light-emitting layer E2 located between the first light-emitting layer E1 and the second electrode C2, a first charge generation layer CG1 located between the first light-emitting layer and the second light-emitting layer and containing a first n-type material N1, and a second charge generation layer CG2 located between the first charge generation layer CG1 and the second light-emitting layer E2 and containing a first p-type material P1. In the light-emitting element ED according to the present disclosure, at least one of the following is true: (i) the first charge generation layer CG1 contains a mixture of a second n-type material N2 different from the first n-type material N1, or (ii) the second charge generation layer CG2 contains a mixture of a second p-type material P2 different from the first p-type material P1.

[0074] In the configuration according to this third embodiment, the first charge generation layer CG1 contains a mixture of a first n-type material N1 and a second n-type material N2, and the second charge generation layer CG2 contains a mixture of a first p-type material P1 and a second p-type material P2. In this disclosure, as described above, the electron affinity of the second n-type material N2 is smaller than the electron affinity of the first n-type material N1, and the ionization potential of the second p-type material P2 is larger than the ionization potential of the first p-type material P1.

[0075] (Band structure of the light-emitting element) Figure 17 is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 16. In Figure 17, the Fermi levels of the first electrode C1 and the second electrode C2 are shown by solid lines. The band gaps of the hole injection layer K1, the hole transport layer K2, the first quantum dot QD1 of the first light-emitting layer E1, the first n-type material N1 and the second n-type material N2 contained in the first charge generation layer CG1, the first p-type material P1 and the second p-type material P2 contained in the second charge generation layer CG2, the hole transport layer K4, the second quantum dot QD2 of the second light-emitting layer E2, and the electron transport layer K5 are shown by rectangles.

[0076] As shown in Figure 17, according to the configuration of this embodiment 3, by determining the first n-type material N1 and the first p-type material P1 such that the electron affinity of the first n-type material N1 and the ionization potential of the first p-type material P1 are close, the charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced to a low voltage. At the same time, by determining the second n-type material N2 such that the electron affinity of the second n-type material N2 and the first light-emitting layer E1 are close, the electron injection from the first charge generation layer CG1 to the first light-emitting layer E1 can be reduced to a low voltage. Furthermore, by determining the second p-type material P2 such that the ionization potential of the second p-type material P2 and the second light-emitting layer E2 are close, the hole injection from the second charge generation layer CG2 to the second light-emitting layer E2 can be reduced to a low voltage. These three factors reduce the driving voltage of the light-emitting element ED.

[0077] The configuration according to this third embodiment corresponds to a combination of the above-described embodiments 1 and 2. Compared to the above-described embodiments 1 and 2, the configuration according to this third embodiment can further reduce the driving voltage of the light-emitting element ED.

[0078] [Embodiment 4] (Configuration of a light-emitting element) Figure 18 is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 18, the light-emitting element ED may further include a third charge-generating layer CG3 made of a conductive material, located between the first charge-generating layer CG1 and the second charge-generating layer CG2. It is desirable that the work function of the conductive material constituting the third charge-generating layer CG3 is greater than the electron affinity of the first n-type material N1 and less than the ionization potential of the first p-type material P1.

[0079] (Band structure of the light-emitting element) Figure 19 is a band diagram showing an example of the band structure of the light-emitting element shown in Figure 18. In Figure 19, the Fermi levels of the first electrode C1, the second electrode C2, and the third charge generation layer CG3 are shown by solid lines. The band gaps of the hole injection layer K1, the hole transport layer K2, the first quantum dot QD1 of the first light-emitting layer E1, the first n-type material N1 and the second n-type material N2 contained in the first charge generation layer CG1, the first p-type material P1 contained in the second charge generation layer CG2, the hole transport layer K4, the second quantum dot QD2 of the second light-emitting layer E2, and the electron transport layer K5 are shown by rectangles.

[0080] As shown in Figure 19, with the above configuration, the Fermi level of the conductive material constituting the third charge generation layer CG3 is between the VBM of the first p-type material P1 and the CBM of the first n-type material N1. Therefore, hole pairs are generated in the conductive material, electrons can move to the first n-type material N1, and holes can move to the first p-type material P1. Hole pairs are more easily generated in conductive materials than in semiconductor materials. Consequently, the charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced to a lower voltage, and the driving voltage of the light-emitting element ED can be further reduced.

[0081] The conductive material constituting the third charge generation layer CG3 may be a metal, and may be selected from the group consisting of, for example, aluminum and silver. When the conductive material is a metal, the third charge generation layer CG3 may have a thickness of 5 nm or less. Visible light can generally pass through a thin metal film with a thickness of 5 nm or less. Alternatively, the conductive material constituting the third charge generation layer CG3 may be a light-transmitting metal oxide, and may be selected from the group consisting of, for example, indium tin oxide, indium zinc oxide, and fluorine-doped tin oxide. Whether the conductive material is a metal or a light-transmitting metal oxide, the third charge generation layer CG3 may have a thickness of 0.5 nm or more.

[0082] The third charge generation layer CG3 may be in a form in which the conductive material is distributed in multiple island-like structures. In this case, the thickness of the third charge generation layer CG3 can be considered as the average value of the thickness of the conductive material in a given range, including the areas where no conductive material is present. The thickness of the conductive material in the areas where no conductive material is present is 0.

[0083] According to the above configuration, the electric field is concentrated on the island-like distributed conductive material, making it easier for hole pairs to be generated in the conductive material, and allowing for lower voltage charge generation between the first charge generation layer CG1 and the second charge generation layer CG2. In addition, the voltage required for charge generation between the first and second charge generation layers can be reduced by electric field concentration. Therefore, the rise voltage of the light-emitting element can be reduced. Furthermore, since light passes between the islands of conductive material, the light transmittance of the third charge generation layer CG3 can be improved.

[0084] The third charge generation layer CG3 may be formed by methods such as vapor deposition or sputtering. The third charge generation layer CG3 may also be in the form of a continuous film.

[0085] (Method for manufacturing a light-emitting element) The steps prior to the formation of the first charge generation layer CG1 are carried out in the same manner as in Embodiment 1 described above. Next, a third charge generation layer CG3 made of a conductive material is formed. The work function of the conductive material used here is preferably greater than the electron affinity of the n-type semiconductor material and smaller than the ionization potential of the p-type semiconductor material, as described above. Next, the steps after the formation of the second charge generation layer CG2 are carried out in the same manner as in Embodiment 1 described above.

[0086] The configuration according to this fourth embodiment corresponds to the configuration according to the first embodiment described above, with the addition of a third charge generation layer CG3. The third charge generation layer CG3 may be added to the configurations according to the second and third embodiments described above, and these configurations are also included in the scope of this disclosure.

[0087] [Embodiment 5] (Configuration of a light-emitting element) Figure 20 is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 20, the first charge generation layer CG1 may include a first SAM (Self-Assembled Monolayer) film M1 formed on at least one surface of the first nanoparticle NP1 and the second nanoparticle NP2. The molecules constituting the first SAM film M1 are selected so that the first SAM film M1 exhibits electron transport properties. The first SAM film M1 includes an organic molecule T1 having a functional group that can bond to the surface of the first nanoparticle NP1.

[0088] The first SAM film M1 may be formed only on the first nanoparticle NP1, on both the first nanoparticle NP1 and the second nanoparticle NP2, or on only the second nanoparticle NP2.

[0089] In this configuration, at least a portion of the first SAM film M1 extends between the first charge generation layer CG1 and the second charge generation layer CG2. When the first SAM film M1 is formed on the surface of the first nanoparticle NP1, the electron transport properties of the first SAM film M1 promote the movement of electrons between the first nanoparticle NP1 and the second charge generation layer CG2. When the first SAM film M1 is formed on the surface of the second nanoparticle NP2, the electron transport properties of the first SAM film M1 promote the movement of electrons between the second nanoparticle NP2 and the second charge generation layer CG2. Therefore, the voltage required for charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. In addition, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. Therefore, the rise voltage and drive voltage of the light-emitting element ED can be reduced.

[0090] (Method for manufacturing a light-emitting element) In the method for manufacturing the light-emitting element ED according to this embodiment, a first SAM film M1 is formed on the surface of a first nanoparticle NP1 and / or a second nanoparticle NP2. Next, with the first SAM film M1 attached to at least one of the first nanoparticle NP1 and the second nanoparticle NP2, a first charge generation layer CG1 containing the first nanoparticle NP1 and the second nanoparticle NP2 is formed. For example, the first SAM film M1 can be formed on the surface of the first nanoparticle NP1 by a simple method such as mixing the first nanoparticle NP1 into a solution in which an organic molecule T1 is dissolved in a solvent. The second charge generation layer CG2 may be formed on or below the first charge generation layer CG1.

[0091] The configuration according to this embodiment 5 corresponds to the configuration according to embodiment 1 described above, with the addition of a first SAM film M1. The first SAM film M1 may be added to the configurations according to embodiments 2 to 4 described above, and these configurations are also included in the scope of this disclosure.

[0092] [Embodiment 6] (Configuration of a light-emitting element) Figure 21 is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 21, the first charge generation layer CG1 may include a first SAM (Self-Assembled Monolayer) film M1 formed on the surface of the portion of the first nanoparticles NP1 and the second nanoparticles NP2 that are in contact with the second charge generation layer CG2.

[0093] In this configuration, the first SAM film M1 spreads between the first charge generation layer CG1 and the second charge generation layer CG2. The electron transport properties of the first SAM film M1 promote the movement of electrons between the first charge generation layer CG1 and the second charge generation layer CG2. Therefore, charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be performed at a lower voltage. In addition, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. Therefore, the rise voltage and drive voltage of the light-emitting element ED can be reduced.

[0094] (Method for manufacturing a light-emitting element) In the method for manufacturing the light-emitting element ED according to this embodiment, a first charge generation layer CG1 containing the first nanoparticle NP1 and the second nanoparticle NP2 is formed in a state where the first SAM film M1 is not attached to either the first nanoparticle NP1 or the second nanoparticle NP2. Next, the first SAM film M1 is formed on the surface of the first nanoparticle NP1 and the second nanoparticle NP2. For example, the first SAM film M1 can be formed on the surface of the first nanoparticle NP1 and the second nanoparticle NP2 by a simple method such as coating the surface of the first charge generation layer CG1 with a solution of organic molecule T1 dissolved in a solvent. Then, the second charge generation layer CG2 is formed on top of the first charge generation layer CG1.

[0095] The configuration according to this embodiment 6 corresponds to the configuration according to embodiment 1 described above, with the addition of a first SAM film M1. The first SAM film M1 may be added to the configurations according to embodiments 2 to 4 described above, and these configurations are also included in the scope of this disclosure.

[0096] [Embodiment 7] (Configuration of a light-emitting element) Figure 22 is a partial cross-sectional view showing an example of the configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 22, the second charge generation layer CG2 may include a second SAM (Self-Assembled Monolayer) film M2 formed on at least one surface of the third nanoparticle NP3 and the fourth nanoparticle NP4. The molecules constituting the second SAM film M2 are selected so that the second SAM film M2 exhibits hole transport properties. The second SAM film M2 includes an organic molecule T2 having a functional group that can bind to the surface of the third nanoparticle NP3. Organic molecule T2 is, for example, [2-(3,6-dimethoxy-9H-carbazole-9-yl)ethyl]phosphonic acid, [2-(3,6-dimethyl-9H-carbazole-9-yl)ethyl]phosphonic acid, [2-(9H-carbazole-9-yl)ethyl]phosphonic acid, [2-(3,6-dibromo-9H-carbazole-9-yl)ethyl]phosphonic acid, [2-(3,6-dichloro-9H-carbazole-9-yl)ethyl]phosphonic acid, [2-(3,6-difluoro-9H-carbazole [-9-yl)ethyl]phosphonic acid, [2-(3,6-diiodo-9H-carbazole-9-yl)ethyl]phosphonic acid, [4-(3,6-dimethoxy-9H-carbazole-9-yl)butyl]phosphonic acid, [4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid, [4-(9H-carbazole-9-yl)butyl]phosphonic acid, and [4-(3,6-dibromo-9H-carbazole-9-yl)butyl]phosphonic acid may be selected from the group consisting of [-9-yl)ethyl]phosphonic acid, [2-(3,6-diiodo-9H-carbazole-9-yl)ethyl]phosphonic acid, [4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid].

[0097] The second SAM film M2 may be formed only on the third nanoparticle NP3, on both the third nanoparticle NP3 and the fourth nanoparticle NP4, or on only the fourth nanoparticle NP4.

[0098] In this configuration, at least a portion of the second SAM film M2 spreads between the first charge generation layer CG1 and the second charge generation layer CG2. When the second SAM film M2 is formed on the surface of the third nanoparticle NP3, the hole transport properties of the second SAM film M2 promote the movement of holes between the third nanoparticle NP3 and the first charge generation layer CG1. When the second SAM film M2 is formed on the surface of the fourth nanoparticle NP4, the hole transport properties of the second SAM film M2 promote the movement of holes between the fourth nanoparticle NP4 and the first charge generation layer CG1. Therefore, the charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced in voltage. In addition, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. Therefore, the rise voltage and drive voltage of the light-emitting element ED can be reduced.

[0099] (Method for manufacturing a light-emitting element) In the method for manufacturing the light-emitting element ED according to this embodiment, a second SAM film M2 is formed on the surface of the third nanoparticle NP3 and / or the fourth nanoparticle NP4. Next, with the second SAM film M2 attached to at least one of the third nanoparticle NP3 and the fourth nanoparticle NP4, a second charge generation layer CG2 containing the third nanoparticle NP3 and the fourth nanoparticle NP4 is formed. For example, the second SAM film M2 can be formed on the surface of the third nanoparticle NP3 by a simple method such as mixing the third nanoparticle NP3 into a solution in which an organic molecule T2 is dissolved in a solvent. The first charge generation layer CG1 may be formed on or below the second charge generation layer CG2.

[0100] The configuration according to this embodiment 7 corresponds to the configuration according to embodiment 3 described above, with the addition of a second SAM film M2. The second SAM film M2 may be added to the configurations according to embodiments 1 to 2 and 4 to 6 described above, and these configurations are also included in the scope of this disclosure.

[0101] [Embodiment 8] (Configuration of light-emitting element) The second charge generation layer CG2 may include a second SAM (Self-Assembled Monolayer) film M2 formed on the surface of the portion of the third nanoparticle NP3 and the fourth nanoparticle NP4 that is in contact with the first charge generation layer CG1.

[0102] In this configuration, the second SAM film M2 spreads between the first charge generation layer CG1 and the second charge generation layer CG2. The hole transport properties of the second SAM film M2 promote hole movement between the first charge generation layer CG1 and the second charge generation layer CG2. Therefore, charge generation between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced to a lower voltage. In addition, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. Therefore, the rise voltage and drive voltage of the light-emitting element ED can be reduced.

[0103] (Method for manufacturing a light-emitting element) In the method for manufacturing the light-emitting element ED according to this embodiment, a second charge generation layer CG2 containing the third nanoparticle NP3 and the fourth nanoparticle NP4 is formed without the second SAM film M2 adhering to either the third nanoparticle NP3 or the fourth nanoparticle NP4. Next, the second SAM film M2 is formed on the surfaces of the third nanoparticle NP3 and the fourth nanoparticle NP4. For example, the second SAM film M2 can be formed on the surfaces of the third nanoparticle NP3 and the fourth nanoparticle NP4 by a simple method such as coating the surface of the second charge generation layer CG2 with a solution of organic molecule T2 dissolved in a solvent. Then, the first charge generation layer CG1 is formed on top of the second charge generation layer CG2.

[0104] The configuration according to this embodiment 8 corresponds to the configuration according to embodiment 3 described above, with the addition of a second SAM film M2. The second SAM film M2 may be added to the configurations according to embodiments 1 to 2 and 4 to 6 described above, and these configurations are also included in the scope of this disclosure.

[0105] [Embodiment 9] (Configuration of Display Device) Figure 23 is a schematic diagram showing an example of the configuration of a display device according to one aspect of the present disclosure. As shown in Figure 23, the display device DP according to the present disclosure includes a light-emitting element ED according to the present disclosure. For example, the display device DP comprises a display area DA provided with a plurality of subpixels PX and a frame area NA provided with a drive circuit DC that drives the display area DA, wherein at least one of the plurality of subpixels PX includes a light-emitting element ED.

[0106] The light-emitting element ED may have a configuration according to any of the embodiments 1 to 8 described above, or it may be a combination or modification thereof.

[0107] 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 in the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0108] AD1 Adductor CG1 First charge generation layer CG2 Second charge generation layer CG3 Third charge generation layer DP Display device E1 First light-emitting layer E2 Second light-emitting layer ED Light-emitting element H1 Part of the first charge generation layer closer to the second charge generation layer H2 Part of the first charge generation layer further from the second charge generation layer H3 Part of the second charge generation layer further from the first charge generation layer H4 Part of the second charge generation layer closer to the first charge generation layer N1 First n-type material N2 Second n-type material M1 First SAM film M2 Second SAM film NP1 First nanoparticle NP2 Second nanoparticle NP3 Third nanoparticle NP4 Fourth nanoparticle OL1 Organic ligand P1 First p-type material P2 Second p-type material

Claims

1. A light-emitting element comprising: a first light-emitting layer and a second light-emitting layer; a first charge generation layer located between the first light-emitting layer and the second light-emitting layer and containing a first n-type material; and a second charge generation layer located between the first charge generation layer and the second light-emitting layer and containing a first p-type material, wherein at least one of the following is true: (i) the first charge generation layer further comprises a mixture of a second n-type material different from the first n-type material; or (ii) the second charge generation layer further comprises a mixture of a second p-type material different from the first p-type material.

2. The light-emitting element according to claim 1, wherein the first charge generation layer comprises a mixture of the first n-type material and the second n-type material, and the electron affinity of the second n-type material is smaller than the electron affinity of the first n-type material.

3. The light-emitting element according to claim 1, wherein the second charge generation layer comprises a mixture of the first p-type material and the second p-type material, and the ionization potential in the second p-type material is greater than the ionization potential in the first p-type material.

4. The light-emitting element according to claim 1, wherein the first charge generation layer comprises a mixture of the first n-type material and the second n-type material, and the second charge generation layer comprises a mixture of the first p-type material and the second p-type material, wherein the electron affinity of the second n-type material is smaller than the electron affinity of the first n-type material, and the ionization potential of the second p-type material is larger than the ionization potential of the first p-type material.

5. The light-emitting element according to claim 2 or 4, wherein the difference between the electron affinity of the second n-type material and the electron affinity of the first n-type material is 0.1 eV or more.

6. The light-emitting element according to claim 3 or 4, wherein the difference between the ionization potential of the second p-type material and the ionization potential of the first p-type material is 0.1 eV or more.

7. The light-emitting element according to any one of claims 1 to 6, wherein the difference between the electron affinity of the first n-type material and the ionization potential of the first p-type material is 1.5 eV or less.

8. The light-emitting element according to any one of claims 2, 4, and 5, wherein the first n-type material is a first nanoparticle and the second n-type material is a second nanoparticle.

9. The light-emitting element according to any one of claims 3, 4, and 6, wherein the first p-type material is a third nanoparticle and the second p-type material is a fourth nanoparticle.

10. The light-emitting element according to any one of claims 2, 4, 5, and 8, wherein the constituent elements of the second n-type material are different from the constituent elements of the first n-type material.

11. The light-emitting element according to any one of claims 2, 4, 5, and 8, wherein the constituent elements of the second n-type material are the same as those of the first n-type material, and the composition ratio of the second n-type material is different from that of the first n-type material.

12. The light-emitting element according to claim 8, wherein the average particle size of the second nanoparticle is different from the average particle size of the first nanoparticle.

13. The light-emitting element according to any one of claims 2, 4, 5, 8 and 10 to 12, wherein the ratio of the second n-type material to the first n-type material in the portion of the first charge generation layer closer to the second charge generation layer is smaller than the ratio of the second n-type material to the first n-type material in the portion of the first charge generation layer further from the second charge generation layer.

14. The light-emitting element according to any one of claims 3, 4, 6, and 9, wherein the constituent elements of the second p-type material are different from the constituent elements of the first p-type material.

15. The light-emitting element according to any one of claims 3, 4, 6, and 9, wherein the constituent elements of the second p-type material are the same as those of the first p-type material, and the composition ratio of the second p-type material is different from that of the first p-type material.

16. The light-emitting element according to claim 9, wherein the average particle size of the fourth nanoparticle is different from the average particle size of the third nanoparticle.

17. The light-emitting element according to any one of claims 3, 4, 6, 9 and 14 to 16, wherein the ratio of the second p-type material to the first p-type material in the portion of the second charge generation layer furthest from the first charge generation layer is greater than the ratio of the second p-type material to the first p-type material in the portion of the second charge generation layer closer to the first charge generation layer.

18. The light-emitting element according to any one of claims 1 to 17, further comprising a third charge-generating layer made of a conductive material, located between the first charge-generating layer and the second charge-generating layer, wherein the work function of the conductive material is greater than the electron affinity of the first n-type material and less than the ionization potential of the first p-type material.

19. The light-emitting element according to claim 8 or 12, wherein the first charge generation layer comprises a first SAM (Self-Assembled Monolayer) film formed on at least one of the first nanoparticles and the second nanoparticles.

20. The light-emitting element according to claim 9 or 16, wherein the second charge generation layer comprises a second SAM film formed on at least one of the third nanoparticles and the fourth nanoparticles.

21. The light-emitting element according to any one of claims 1 to 20, wherein the first light-emitting layer includes a first quantum dot.

22. The light-emitting element according to claim 21, wherein the first light-emitting layer includes either (i) an adduct formed around at least one of the first quantum dots, or (ii) an adduct filling the space between at least two of the first quantum dots.

23. The light-emitting element according to claim 22, wherein the first light-emitting layer contains an organic ligand released from the first quantum dot.

24. The light-emitting element according to any one of claims 1 to 20, wherein the second light-emitting layer includes a second quantum dot.

25. The light-emitting element according to claim 24, wherein the second light-emitting layer includes either (i) an adduct formed around at least one of the second quantum dots, or (ii) an adduct filling the space between at least two of the second quantum dots.

26. The light-emitting element according to claim 25, wherein the second light-emitting layer contains an organic ligand released from the second quantum dot.

27. A display device comprising a light-emitting element according to any one of claims 1 to 26.

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