Light-emitting element, display device, and method for producing light-emitting element

Abstract

A light-emitting element (ED) is provided, in that order, with: a first light-emitting layer (E1); a first charge generating layer (CG1) including first nanoparticles (NP1) composed of one of a n-type semiconductor material and a p-type semiconductor material; a second charge generating layer (CG2) including second nanoparticles (NP2) composed of the other of the n-type semiconductor material and the p-type semiconductor material; and a second light-emitting layer (E2).

Description

Light-emitting element, display device, and method for manufacturing light-emitting element

[0001] The present disclosure relates to a light-emitting element, a display device, and a method for manufacturing a light-emitting element.

[0002] Patent Document 1 discloses a tandem light-emitting device having a charge generating layer between two light-emitting layers, the charge generating layer being a stack of a layer containing n-type nanoparticles and a layer containing a hole-injecting material.

[0003] US 2018 / 0122873 A1

[0004] However, when a film of hole injection material is formed on a layer containing n-type nanoparticles, the hole injection material randomly penetrates into the gaps between the n-type nanoparticles. As a result, the hole injection material penetrates deeply into some gaps and not into others. Furthermore, some of the hole injection material may pass through the layer containing n-type nanoparticles and reach the light-emitting layer below the layer containing n-type nanoparticles, causing poor light emission in the light-emitting layer.

[0005] A light-emitting element according to one aspect of the present disclosure includes a first light-emitting layer, a first charge-generating layer located above the first light-emitting layer and including first nanoparticles made of one of an n-type semiconductor material and a p-type semiconductor material, a second charge-generating layer located above the first charge-generating layer and including second nanoparticles made of the other of an n-type semiconductor material and a p-type semiconductor material, and a second light-emitting layer located above the second charge-generating layer.

[0006] A display device according to an aspect of the present disclosure includes a light-emitting element according to an aspect of the present disclosure.

[0007] A method for manufacturing a light-emitting element according to one aspect of the present disclosure includes the steps of forming a first light-emitting layer, forming a first charge-generation layer after the first light-emitting layer, the first charge-generation layer including first nanoparticles made of one of an n-type semiconductor material and a p-type semiconductor material, forming a second charge-generation layer after the first charge-generation layer, the second charge-generation layer including second nanoparticles made of the other of the n-type semiconductor material and the p-type semiconductor material, and forming a second light-emitting layer after the second charge-generation layer.

[0008] According to the configuration according to one aspect of the present disclosure, the reliability of the light-emitting element can be improved.

[0009] FIG. 1 is a cross-sectional view showing a configuration example of a light-emitting device according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view showing another configuration example of a light-emitting device according to an embodiment of the present disclosure. FIG. 3 is a diagram showing an example of a method for manufacturing the light-emitting device shown in FIG. 1. FIG. 4 is a cross-sectional view showing an example of a band structure in the light-emitting device shown in FIG. 4. FIG. 5 is a diagram showing an example of a method for manufacturing the light-emitting device according to an embodiment of the present disclosure. FIG. 6 is a cross-sectional view showing an example of a configuration example of a light-emitting device according to an embodiment of the present disclosure. FIG. 7 is a cross-sectional view showing an example of a configuration example of a light-emitting device according to an embodiment of the present disclosure. FIG. 8 is a schematic view showing an example of a configuration example of a display device according to an embodiment of the present disclosure.

[0010] In the present disclosure, a "lower layer" means a layer formed in an earlier process than the layer being compared, and an "upper layer" means a layer formed in a later process than the layer being compared. Furthermore, in the present disclosure, a "quantum dot" refers to a dot having a maximum width of 100 nm or less. The shape of the quantum dots is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). The shape of the quantum dots may be, for example, a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0011] In the present disclosure, "nanoparticle" refers to a particle having a maximum width of about 1 to several hundred nm. The shape of the nanoparticle is not particularly limited as long as it satisfies the above maximum width, 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 branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof. The nanoparticle may be monocrystalline or polycrystalline.

[0012] [Embodiment 1] (Configuration of Light-Emitting Element) Fig. 1 is a cross-sectional view showing an example configuration of a light-emitting element according to one aspect of the present disclosure. Fig. 2 is a cross-sectional view showing another example configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figs. 1 and 2, a light-emitting element ED according to the present disclosure includes a first electrode C1, a first light-emitting layer E1 located above the first electrode C1, a first charge generation layer CG1 located above the first light-emitting layer E1, a second charge generation layer CG2 located above the first charge generation layer CG1, a second light-emitting layer E2 located above the second charge generation layer CG2, and a second electrode C2 located above the second light-emitting layer E2.

[0013] The first charge generation layer CG1 includes first nanoparticles NP1 made of one of an n-type semiconductor material and a p-type semiconductor material, and the second charge generation layer CG2 includes second nanoparticles NP2 made of the other of an n-type semiconductor material and a p-type semiconductor material. 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 the holes to move through the p-type semiconductor material and the electrons to move through the n-type semiconductor material. In this manner, charges are generated between the first charge generation layer CG1 and the second charge generation layer CG2 due to the reverse bias voltage. Generally, the entire stack of the p-type semiconductor material layer and the n-type semiconductor material layer is referred to as a "charge generation layer." For convenience, in this disclosure, one of the p-type semiconductor material layer and the n-type semiconductor material layer will be referred to as the "first charge generation layer" and the other will be referred to as the "second charge generation layer."

[0014] According to the above configuration, a so-called "tandem" light-emitting element ED can be realized, which has a combination of a first charge generation layer CG1 and a second charge generation layer CG2 between a first light-emitting layer E1 and a second light-emitting layer E2. The light-emitting element ED may be a quantum dot light-emitting diode (QLED). The first light-emitting layer E1 may include first quantum dots QD1 having light-emitting properties, and the second light-emitting layer E2 may include second quantum dots QD2 having light-emitting properties.

[0015] According to the above configuration, the second charge generation layer CG2 contains second nanoparticles NP2. As mentioned above, "nanoparticles" are particles with a maximum width of approximately 1 to several hundred nm, so the size difference between the first nanoparticles NP1 and the second nanoparticles NP2 is at most several hundred times. Therefore, the second nanoparticles NP2 have difficulty passing through the gaps between the first nanoparticles NP1, reducing the risk of the second nanoparticles NP2 causing poor light emission in the first light-emitting layer E1. On the other hand, in the configuration disclosed in Patent Document 1 in which a film of hole injection material is formed on n-type nanoparticles, the hole injection material may pass through the gaps between the n-type nanoparticles and reach the light-emitting layer located below the n-type nanoparticles, causing poor light emission in the light-emitting layer.

[0016] That is, according to the configuration of the present disclosure, the reliability of the tandem-type light-emitting element ED can be improved.

[0017] The light-emitting element ED may optionally include one or more of a charge injection layer K1 and / or a charge transport layer K2 located between the first electrode C1 and the first light-emitting layer E1, a charge transport layer located between the first light-emitting layer E1 and the first charge generation layer CG1, a charge transport layer K4 located between the second charge generation layer CG2 and the second light-emitting layer E2, and a charge transport layer K5 and / or a charge injection layer located between the second light-emitting layer E2 and the second electrode C2.

[0018] The average particle size of the second nanoparticles NP2 may be 0.2 times or more the average particle size of the first nanoparticles NP1. The particle size of one nanoparticle can be obtained by calculating the diameter of a circle having an area equivalent to the cross-sectional area of ​​the nanoparticle. The average particle size of the first nanoparticles NP1 may be the average value of the particle sizes of some of the first nanoparticles NP1 contained in the first charge generation layer CG1. The average particle size of the second nanoparticles NP2 may be the average value of the particle sizes of some of the second nanoparticles NP2 contained in the second charge generation layer CG2.

[0019] According to the above configuration, the average particle size of the second nanoparticles NP2 is 0.2 times or more the average particle size of the first nanoparticles NP1. Therefore, it is difficult for the second nanoparticles NP2 to penetrate deeply into the gaps between the first nanoparticles NP1. Therefore, the contact area of ​​the second nanoparticles NP2 and the first nanoparticles NP1 can be uniformized, and the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2 can be uniformized. On the other hand, in the configuration of the comparative example in which a film of hole injection material is formed on n-type nanoparticles, the hole injection material randomly penetrates into the gaps between the n-type nanoparticles. As a result, the hole injection material penetrates deeply into some gaps and not into others, resulting in uneven charge generation efficiency.

[0020] The average particle size of the second nanoparticles NP2 may preferably be 0.5 times or more the average particle size of the first nanoparticles NP1. The larger the size of the second nanoparticles NP2 relative to the size of the first nanoparticles NP1, the more difficult it is for the second nanoparticles NP2 to penetrate into the gaps in the first charge generation layer CG1. Therefore, the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2 can be made more uniform.

[0021] The average particle size of the second nanoparticles NP2 may be 10 times or less the average particle size of the first nanoparticles NP1. With this configuration, the contact area of ​​the second nanoparticles NP2 with the first nanoparticles NP1 is large, thereby improving the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2. Additionally, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. This reduction in electrical resistance reduces the turn-on voltage of the light-emitting element ED. If the second nanoparticles NP2 were more than 10 times larger than the first nanoparticles NP1, the contact area of ​​the second nanoparticles NP2 with the first nanoparticles NP1 would be small, potentially reducing the charge generation efficiency and increasing the electrical resistance.

[0022] The average particle size of the second nanoparticles NP2 may preferably be five times or less the average particle size of the first nanoparticles NP1. The smaller the second nanoparticles NP2 relative to the size of the first nanoparticles NP1, the larger the contact area between the second nanoparticles NP2 and the first nanoparticles NP1. This can further improve the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2, and further reduce the electrical resistance.

[0023] As shown in FIG. 1 , the average particle size of the second nanoparticles NP2 may be smaller than that of the first nanoparticles NP1. This configuration allows the second nanoparticles NP2 to conform to the undulations on the top surface of the first charge generation layer CG1, resulting in a large contact area between the second nanoparticles NP2 and the first nanoparticles NP1. This improves the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2. Additionally, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced.

[0024] 2, the average particle size of the second nanoparticles NP2 may be larger than the average particle size of the first nanoparticles NP1. With this configuration, the second nanoparticles NP2 have difficulty entering the gaps between the first nanoparticles NP1. Therefore, the charge generation efficiency can be made uniform between the first charge generation layer CG1 and the second charge generation layer CG2.

[0025] The n-type semiconductor material constituting one of the first nanoparticles NP1 and the second nanoparticles NP2 may be an inorganic material or a metal oxide. The n-type semiconductor material may be selected from the group consisting of zinc oxide, zinc magnesium oxide, titanium oxide, and tin oxide, for example. The composition ratio of the metal oxide semiconductor may differ from the stoichiometric composition. Many metal oxide semiconductors exhibit n-type properties when there is a shortage of oxygen atoms compared to the stoichiometric composition. The n-type semiconductor material may be doped with a donor.

[0026] The p-type semiconductor material constituting the other of the first nanoparticle NP1 and the second nanoparticle NP2 may be an inorganic material or a metal oxide. The p-type semiconductor material may be nickel oxide, nickel magnesium oxide, or copper oxide. The composition ratio of the metal oxide semiconductor may differ from the stoichiometric composition. Many metal oxide semiconductors exhibit p-type properties when there is an excess of oxygen atoms compared to the stoichiometric composition. The p-type semiconductor material may be doped with an acceptor.

[0027] As shown in Figures 1 and 2, the second nanoparticles NP2 may be in direct contact with the first nanoparticles NP1, through which holes and electrons can transfer.

[0028] The color of light emitted by the second light-emitting layer E2 may be substantially the same as the color of light emitted by the first light-emitting layer E1. The color of the two lights being substantially the same simply requires that they are nearly identical within the range visible to the human eye; strictly speaking, it is not required that the peak wavelengths of the light be completely identical. For example, if two peaks are detected in the emission wavelength spectra of two types of quantum dots and each peak wavelength is within the wavelength range of the same color, namely, 430-500 nm for blue, 500-570 nm for green, and 610-780 nm for red, then they are considered to be identical. Naturally, they are also considered to be identical when no two peaks are detected. This increases the luminance per current density, enabling the light-emitting element ED to operate at a low current density. A tandem light-emitting element includes multiple light-emitting units connected in series between an anode and a cathode, and the luminance per current density of the tandem light-emitting element is approximately proportional to the number of light-emitting units connected in series. An example of the light-emitting unit includes a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer in this order, thereby improving the reliability of the light-emitting element ED.

[0029] The light-emitting element ED may have a sequential structure, in which the first electrode C1 is an anode and the second electrode C2 is a cathode. In this case, the light-emitting element ED includes a substrate SB, an anode, a first light-emitting layer E1, a first charge generation layer CG1, a second charge generation layer CG2, a second light-emitting layer E2, and a cathode, in this order, and the first nanoparticles NP1 are made of an n-type semiconductor material and the second nanoparticles NP2 are made of a p-type semiconductor material.

[0030] The light-emitting element ED may have an anode made of indium tin oxide, a hole injection layer containing nickel oxide nanoparticles, a hole transport layer containing TFB, a light-emitting layer, a first charge generation layer containing zinc magnesium oxide nanoparticles, a second charge generation layer containing nickel oxide nanoparticles, a hole transport layer containing TFB, a light-emitting layer, an electron transport layer containing zinc magnesium oxide nanoparticles, and a cathode made of silver stacked in this order.

[0031] The light-emitting element ED may have an inverted structure, in which the first electrode C1 is the cathode and the second electrode C2 is the anode. In this case, the light-emitting element ED includes a substrate SB, a cathode, a first light-emitting layer E1, a first charge generation layer CG1, a second charge generation layer CG2, a second light-emitting layer E2, and an anode, in this order, and the first nanoparticles NP1 are made of a p-type semiconductor material and the second nanoparticles NP2 are made of an n-type semiconductor material.

[0032] In the light-emitting element ED, for example, a cathode made of silver, an electron transport layer containing zinc magnesium oxide nanoparticles, a light-emitting layer, a hole transport layer containing TFB, a first charge generation layer containing nickel oxide nanoparticles, a second charge generation layer containing zinc magnesium oxide nanoparticles, a light-emitting layer, a hole transport layer containing TFB, a hole injection layer containing nickel oxide nanoparticles, and an anode made of indium tin oxide may be stacked in this order.

[0033] (Method for Manufacturing the Light-Emitting Element) An example of a method for manufacturing the light-emitting element ED shown in FIGS. 1 and 2 will be described below.

[0034] First, a substrate SB is prepared, and a first electrode C1 is formed on the substrate SB. The substrate SB may be a simple support substrate, or a circuit board on which wiring and / or circuits connected to the first electrode C1 are formed. Next, a charge injection layer K1 and / or a charge transport layer K2 are formed on the first electrode C1 as needed. Then, a first light-emitting layer E1 is formed, and a charge transport layer is formed on the first light-emitting layer E1 as needed.

[0035] 3 is a diagram showing an example of a method for manufacturing the light-emitting device shown in FIG. 3. As shown in FIG. 3, a first charge generation layer CG1 containing first nanoparticles NP1 made of one of an n-type semiconductor material and a p-type semiconductor material is formed on the first light-emitting layer E1 or the charge transport layer (step S40). Next, a second charge generation layer CG2 containing second nanoparticles NP2 made of the other of an n-type semiconductor material and a p-type semiconductor material is formed on the first charge generation layer CG1 (step S50). Then, a charge transport layer K4 is formed on the second charge generation layer CG2 as needed (step S52).

[0036] Next, the second light-emitting layer E2 is formed, and if necessary, a charge transport layer K5 and / or a charge injection layer is formed on the second light-emitting layer E2, and then the second electrode C2 is formed, and if necessary, a sealing layer is formed on the second electrode C2.

[0037] [Embodiment 2] Another embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0038] (Configuration of Light-Emitting Element) Fig. 4 is a partial cross-sectional view showing an example configuration of a light-emitting element according to one embodiment of the present disclosure. As shown in Fig. 4, the light-emitting element ED may further include a third charge generation layer CG3 made of a conductive material and located between the first charge generation layer CG1 and the second charge generation layer CG2. The work function of the conductive material making up the third charge generation layer CG3 is preferably greater than the electron affinity of the n-type semiconductor material making up either the first nanoparticles NP1 or the second nanoparticles NP2, and smaller than the ionization potential of the p-type semiconductor material making up the other of the first nanoparticles NP1 and the second nanoparticles NP2.

[0039] 5 is a cross-sectional view showing an example of the band structure of the light-emitting element shown in FIG. 4. In the example shown in FIG. 5, the light-emitting element ED has a forward structure, with the first nanoparticles NP1 made of an n-type semiconductor material and the second nanoparticles NP2 made of a p-type semiconductor material. In FIG. 4, the Fermi levels of the first electrode C1, the third charge generation layer CG3, and the second electrode C2 are shown with solid lines, and the band gaps of the charge injection layer K1, the charge transport layer K2, the first light-emitting layer E1, the first charge generation layer CG1, the second charge generation layer CG2, the charge transport layer K4, the second light-emitting layer E2, and the charge transport layer K5 are shown with rectangles. The band gap is the band gap between the valence band (VB) and the conduction band (CB). The bottom side of the rectangle indicates the valence band maximum (VBM), and the top side of the rectangle indicates the conduction band minimum (CBM). The work function corresponds to the Fermi level, the electron affinity corresponds to the CBM, and the ionization potential corresponds to the VBM.

[0040] As shown in Figure 5, with the above configuration, the Fermi level of the conductive material constituting the third charge generation layer CG3 is between the VBM of the p-type semiconductor material and the CBM of the n-type semiconductor material. Therefore, hole-electron pairs are generated in the conductive material, and the electrons move to the n-type semiconductor material, and the holes move to the p-type semiconductor material. Hole-electron pairs are more likely to be generated in the conductive material than in the semiconductor material. Therefore, the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2 can be improved.

[0041] In addition, the gap between the VBM of the p-type semiconductor material and the CBM of the n-type semiconductor material is divided by the Fermi level of the conductive material, which reduces the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2. This reduction in electrical resistance reduces the turn-on voltage of the light-emitting element ED.

[0042] The conductive material constituting the third charge generation layer CG3 may be a metal, for example, selected from the group consisting of 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 transmit 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, for example, selected from the group consisting of 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.

[0043] 4, the third charge generation layer CG3 may have a conductive material distributed in the form of multiple islands. In this case, the thickness of the third charge generation layer CG3 can be considered to be the average value of the thickness of the conductive material in a given range, including areas where there is no conductive material. The thickness of the conductive material in areas where there is no conductive material is zero.

[0044] According to the above configuration, an electric field is concentrated in the conductive material distributed in islands, which makes it easier for hole-electron pairs to be generated in the conductive material, thereby improving the charge generation efficiency 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 charge generation layer and the second charge generation layer CG2 can be reduced by the electric field concentration. Therefore, the turn-on 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.

[0045] The third charge generation layer CG3 may be formed by a method such as vapor deposition or sputtering, etc. The third charge generation layer CG3 may be in the form of a continuous film.

[0046] (Method of Manufacturing a Light-Emitting Element) FIG. 6 is a diagram illustrating an example of a method of manufacturing a light-emitting element according to one aspect of the present disclosure. As shown in FIG. 6, the steps up to the formation of the first charge generation layer CG1 (step S40) are performed in the same manner as in the first embodiment described above. Following step S40, a third charge generation layer CG3 made of a conductive material is formed (step S80). As described above, the work function of the conductive material used here is preferably greater than the electron affinity of the n-type semiconductor material and less than the ionization potential of the p-type semiconductor material. Following step S80, the steps after the formation of the second charge generation layer CG2 (step S50) are performed in the same manner as in the first embodiment described above.

[0047] [Embodiment 3] (Configuration of Light-Emitting Element) Figure 7 is a partial cross-sectional view showing an example configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 7, the first charge generation layer CG1 may include a first SAM (Self-Assembled Monolayer) film M1 formed on the surface of the first nanoparticles NP1. The molecules constituting the first SAM film M1 are selected so that the first SAM film M1 exhibits electron transport properties when the first nanoparticles NP1 are made of an n-type semiconductor material, and exhibits hole transport properties when the first nanoparticles NP1 are made of a p-type semiconductor material.

[0048] According to 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. The charge transport properties of the first SAM film M1 promote the movement of holes or electrons between the second nanoparticles NP2 and the first nanoparticles NP1. This improves the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2. Additionally, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. This reduces the turn-on voltage of the light-emitting element ED.

[0049] The first SAM film M1 includes an organic molecule T1 having a functional group capable of binding to the surface of the first nanoparticle NP1. For example, when the organic molecule T1 exhibits hole transport properties, the organic molecule T1 may be selected from the group consisting of MeO-2PACz, 2PACz, Me-4PACz, and Br-2PACz.

[0050] The configuration according to the present embodiment 3 can be combined with the configuration according to the above-described embodiment 2. For example, the light-emitting element ED may include a first charge generation layer CG1 including first nanoparticles NP1 and a first SAM film M1, a second charge generation layer CG2 including second nanoparticles NP2, and a third charge generation layer CG3.

[0051] (Method for Manufacturing 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 the first nanoparticle NP1, and then a first charge generation layer CG1 is formed, which includes the first nanoparticle NP1 to which the first SAM film M1 is attached. For example, the first SAM film M1 can be formed on the surface of the first nanoparticle NP1 by a simple method such as submerging the first nanoparticle NP1 in a solution in which the organic molecule T1 is dissolved in a solvent.

[0052] 8 is a partial cross-sectional view showing an example of the configuration of a light-emitting device according to one aspect of the present disclosure. As shown in Fig. 8, the first charge generation layer CG1 may include a first SAM (self-assembled monolayer) film M1 formed on the surface of the first nanoparticles NP1 in contact with the second nanoparticles NP2.

[0053] According to this configuration, the first SAM film M1 extends between the first charge generation layer CG1 and the second charge generation layer CG2. The charge transport properties of the first SAM film M1 promote the movement of holes or electrons between the second nanoparticles NP2 and the first nanoparticles NP1. This improves the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2. In addition, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. This reduces the turn-on voltage of the light-emitting element ED.

[0054] The first SAM film M1 includes an organic molecule T1 having a functional group capable of binding to the surface of the first nanoparticle NP1. For example, when the organic molecule T1 exhibits hole transport properties, the organic molecule T1 may be selected from the group consisting of MeO-2PACz, 2PACz, Me-4PACz, and Br-2PACz.

[0055] The configuration according to the present embodiment 4 can be combined with the configuration according to the above-described embodiment 2. For example, the light-emitting element ED may include a first charge generation layer CG1 including first nanoparticles NP1 and a first SAM film M1, a second charge generation layer CG2 including second nanoparticles NP2, and a third charge generation layer CG3.

[0056] (Method for Manufacturing Light-Emitting Element) In the method for manufacturing the light-emitting element ED according to this embodiment, a first charge generation layer CG1 including first nanoparticles NP1 to which no first SAM film is attached is formed, and then a first SAM film M1 is formed on the surface of the first nanoparticles NP1. For example, the first SAM film M1 can be formed on the surface of the first nanoparticles NP1 by a simple method such as applying a solution in which organic molecules T1 are dissolved in a solvent to the surface of the first charge generation layer CG1.

[0057] [Embodiment 5] (Configuration of Light-Emitting Element) Figure 9 is a partial cross-sectional view showing an example configuration of a light-emitting element according to one aspect of the present disclosure. As shown in Figure 9, the second charge generation layer CG2 may include a second SAM (Self-Assembled Monolayer) film M2 formed on the surface of the second nanoparticles NP2. The molecules constituting the second SAM film M2 are selected so that the second SAM film M2 exhibits hole transport properties when the second nanoparticles NP2 are made of a p-type semiconductor material, and exhibits electron transport properties when the second nanoparticles NP2 are made of an n-type semiconductor material.

[0058] According to this configuration, at least a portion of the second SAM film M2 extends between the first charge generation layer CG1 and the second charge generation layer CG2. The charge transport properties of the second SAM film M2 promote the movement of holes and electrons between the second nanoparticles NP2 and the first nanoparticles NP1. This improves the charge generation efficiency between the first charge generation layer CG1 and the second charge generation layer CG2. Additionally, the electrical resistance between the first charge generation layer CG1 and the second charge generation layer CG2 can be reduced. This reduces the turn-on voltage of the light-emitting element ED.

[0059] The second SAM film M2 includes organic molecules T2 having functional groups capable of binding to the surfaces of the second nanoparticles NP2. For example, when the organic molecules T2 exhibit hole transport properties, they may be selected from the group consisting of MeO-2PACz, 2PACz, Me-4PACz, and Br-2PACz.

[0060] The configuration of this embodiment 5 can be combined with any one or more of the configurations of the above-described embodiments 2 to 4. For example, the light-emitting element ED may include a first charge generation layer CG1 including first nanoparticles NP1, a second charge generation layer CG2 including second nanoparticles NP2 and a second SAM film M2, and a third charge generation layer CG3. For example, the light-emitting element ED may include a first charge generation layer CG1 including first nanoparticles NP1 and a first SAM film M1, and a second charge generation layer CG2 including second nanoparticles NP2 and a second SAM film M2. The light-emitting element ED may include a first charge generation layer CG1 including first nanoparticles NP1 and a first SAM film M1, a second charge generation layer CG2 including second nanoparticles NP2 and a second SAM film M2, and a third charge generation layer CG3.

[0061] (Method for Manufacturing 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 second nanoparticles NP2, and then a second charge generation layer CG2 is formed that includes the second nanoparticles NP2 to which the second SAM film M2 is attached. For example, the second SAM film M2 can be formed on the surface of the second nanoparticles NP2 by a simple method such as submerging the second nanoparticles NP2 in a solution in which the organic molecules T2 are dissolved in a solvent.

[0062] [Embodiment 6] (Configuration of Display Device) Fig. 10 is a schematic diagram showing a configuration example of a display device according to one aspect of the present disclosure. As shown in Fig. 10, a 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 includes a display area DA in which a plurality of sub-pixels PX are provided, and a frame area NA in which a drive circuit DC that drives the display area DA is provided, and at least one of the plurality of sub-pixels PX includes a light-emitting element ED.

[0063] The light emitting element ED may have a configuration according to any one of the above-described first to fifth embodiments, or may have a configuration that is a combination or modification of those embodiments.

[0064] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0065] C1 First electrode C2 Second electrode DP Display device E1 First light-emitting layer E2 Second light-emitting layer ED Light-emitting element CG1 First charge generation layer CG2 Second charge generation layer CG3 Third charge generation layer M1 First SAM film M2 Second SAM film NP1 First nanoparticle NP2 Second nanoparticle SB Substrate

Claims

1. A light-emitting element comprising: a first light-emitting layer; a first charge-generating layer located above the first light-emitting layer and including first nanoparticles made of one of an n-type semiconductor material and a p-type semiconductor material; a second charge-generating layer located above the first charge-generating layer and including second nanoparticles made of the other of an n-type semiconductor material and a p-type semiconductor material; and a second light-emitting layer located above the second charge-generating layer.

2. The light-emitting device according to claim 1, wherein the average particle size of the second nanoparticles is at least 0.2 times the average particle size of the first nanoparticles.

3. The light-emitting element according to claim 1 or 2, wherein the average particle size of the second nanoparticles is 10 times or less the average particle size of the first nanoparticles.

4. The light-emitting element according to any one of claims 1 to 3, wherein the average particle size of the second nanoparticles is smaller than the average particle size of the first nanoparticles.

5. The light-emitting device according to any one of claims 1 to 4, wherein the n-type semiconductor material is selected from the group consisting of zinc oxide, zinc magnesium oxide, titanium oxide, and tin oxide.

6. The light-emitting device according to any one of claims 1 to 5, wherein the p-type semiconductor material is selected from the group consisting of nickel oxide, nickel magnesium oxide, and copper oxide.

7. The light-emitting device according to any one of claims 1 to 6, wherein the second nanoparticles are in direct contact with the first nanoparticles.

8. The light-emitting device according to any one of claims 1 to 6, further comprising a third charge generation layer located between the first charge generation layer and the second charge generation layer and made of a conductive material, wherein the work function of the conductive material is greater than the electron affinity of the n-type semiconductor material and less than the ionization potential of the p-type semiconductor material.

9. The light-emitting device according to claim 8, wherein the conductive material is a metal and the third charge generating layer has a thickness of 5 nm or less.

10. The light-emitting device according to claim 8, wherein the conductive material is a light-transmitting metal oxide.

11. The light-emitting element according to any one of claims 8 to 10, wherein the third charge generation layer contains the conductive material distributed in the form of a plurality of islands.

12. A light-emitting element described in any one of claims 1 to 11, wherein the first charge generation layer includes a first SAM (Self-Assembled Monolayer) film formed on the surface of the first nanoparticles, and the first SAM film exhibits electron transport properties when the first nanoparticles are made of the n-type semiconductor material, and exhibits hole transport properties when the first nanoparticles are made of the p-type semiconductor material.

13. A light-emitting element described in any one of claims 1 to 12, wherein the second charge generation layer includes a second SAM film formed on the surface of the second nanoparticles, and the second SAM film exhibits hole transport properties when the second nanoparticles are made of the p-type semiconductor material, and exhibits electron transport properties when the second nanoparticles are made of the n-type semiconductor material.

14. The light-emitting element according to any one of claims 1 to 13, wherein the color of light emitted by the second light-emitting layer is the same as the color of light emitted by the first light-emitting layer.

15. A light-emitting element according to any one of claims 1 to 14, comprising, in this order, a substrate, an anode, the first light-emitting layer, the first charge-generating layer, the second charge-generating layer, the second light-emitting layer, and a cathode, wherein the first nanoparticles are made of the n-type semiconductor material, and the second nanoparticles are made of the p-type semiconductor material.

16. A light-emitting element according to any one of claims 1 to 14, comprising a substrate, a cathode, the first light-emitting layer, the first charge-generating layer, the second charge-generating layer, the second light-emitting layer, and an anode, in this order; the first nanoparticles being made of the p-type semiconductor material; and the second nanoparticles being made of the n-type semiconductor material.

17. A display device comprising the light-emitting element according to any one of claims 1 to 16.

18. A method for manufacturing a light-emitting element, comprising: forming a first light-emitting layer; forming a first charge-generating layer containing first nanoparticles made of one of an n-type semiconductor material and a p-type semiconductor material after the first light-emitting layer; forming a second charge-generating layer containing second nanoparticles made of the other of the n-type semiconductor material and the p-type semiconductor material after the first charge-generating layer; and forming a second light-emitting layer after the second charge-generating layer.

19. The method for manufacturing a light-emitting element described in claim 18, further comprising the step of forming a third charge generation layer made of a conductive material after the first charge generation layer and before the second charge generation layer, wherein the work function of the conductive material is greater than the electron affinity of the n-type semiconductor material and less than the ionization potential of the p-type semiconductor material.

20. A method for manufacturing a light-emitting element as described in claim 18 or 19, further comprising a step of forming a first SAM film on the surface of the first nanoparticles, wherein the first SAM film exhibits electron transport properties when the first nanoparticles are made of the n-type semiconductor material, and exhibits hole transport properties when the first nanoparticles are made of the p-type semiconductor material.

21. A method for manufacturing a light-emitting element according to any one of claims 18 to 20, further comprising the step of forming a second SAM film on the surface of the second nanoparticles, wherein the second SAM film exhibits hole transport properties when the second nanoparticles are made of the p-type semiconductor material, and exhibits electron transport properties when the second nanoparticles are made of the n-type semiconductor material.

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