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

Abstract

This light-emitting element (10) comprises an anode (2), a cathode (5), a light-emitting layer (EM) provided between the anode (2) and the cathode (5), and a hole injection layer (3HI) as a hole functional layer provided between the anode (2) and the light-emitting layer (EM) and containing an oxide semiconductor material. A hole-transporting material (SAMP) as a polymer having hole-transporting properties or an oligomer having hole-transporting properties is bonded to the surface of the hole injection layer (3HI) on the light-emitting layer (EM) side.

Description

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

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

[0002] In recent years, various display devices equipped with light-emitting elements have been developed, and in particular, display devices equipped with OLEDs (Organic Light Emitting Diodes) or QLEDs (Quantum Dot Light Emitting Diodes) have attracted considerable attention due to their ability to achieve low power consumption, thin design, and high image quality.

[0003] For example, Patent Document 1 describes bonding an organic monomer to the light-emitting layer side of a hole transport layer provided between the anode and the light-emitting layer of a light-emitting device.

[0004] International Public Publication "WO2020 / 174594 A1"

[0005] As described in Patent Document 1, by bonding an organic monomer to the light-emitting layer side surface of a hole transport layer provided between the anode and the light-emitting layer of a light-emitting element, the number of hydroxyl groups that may be contained in the hole transport layer can be reduced, and the quenching phenomenon that occurs in the light-emitting layer due to the hydroxyl groups contained in the hole transport layer can be suppressed. However, in the configuration described in Patent Document 1, the organic monomer bonded to the light-emitting layer side surface of the hole transport layer remains in the monomer state and does not have good hole transport properties. Therefore, the hole injection characteristics from the hole transport layer to the light-emitting layer via the organic monomer are poor, and there is a problem in that a light-emitting element with a satisfactory external quantum efficiency (EQE) cannot be realized.

[0006] One aspect of this disclosure aims to provide a light-emitting element and a method for manufacturing such an element, which can suppress quenching in the light-emitting layer caused by hydroxyl groups that may be contained in the hole functional layer and have good external quantum efficiency (EQE), as well as a display device equipped with such a light-emitting element.

[0007] To solve the above problems, the light-emitting element of the present disclosure includes an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole-transporting material provided between the anode and the light-emitting layer and comprising an oxide semiconductor material, wherein a hole-transporting material, which is a polymer or oligomer having hole-transporting properties, is bonded to the light-emitting layer side of the hole-transporting material.

[0008] The display device of this disclosure includes the light-emitting element in order to solve the aforementioned problems.

[0009] To solve the above problems, the method for manufacturing a light-emitting element of the present disclosure includes the steps of: forming an anode; forming a hole functional layer containing an oxide semiconductor material on the anode; forming a monomer on the surface of the hole functional layer having a group that can bond to the hole functional layer and a hole-transporting molecular skeleton; a monomer treatment step of treating the monomer with a crosslinking agent containing a conjugated system structure; oligomerizing or polymerizing the monomer treated with the crosslinking agent; forming a light-emitting layer; and forming a cathode.

[0010] According to one aspect of this disclosure, it is possible to provide a light-emitting element and a method for manufacturing such an element, which can suppress quenching in the light-emitting layer caused by hydroxyl groups that may be contained in the hole functional layer and have good external quantum efficiency (EQE), as well as a display device equipped with such a light-emitting element.

[0011] Figure 2 is a plan view showing the schematic configuration of a display device including the light-emitting element of Embodiment 1. Figure 2 is a cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 1. Figure 3 is a cross-sectional view showing the schematic configuration of the layer provided between the anode and the light-emitting layer of the light-emitting element of Embodiment 1. Figure 4 is a diagram showing the voltage-current density characteristics of the light-emitting element of Embodiment 1 and the light-emitting element of the comparative example, respectively. Figure 5 is a diagram showing the current density-external quantum efficiency (EQE) characteristics of the light-emitting element of Embodiment 1 and the light-emitting element of the comparative example, respectively. Figure 6 is a cross-sectional view showing the schematic configuration of a light-emitting element that is a modified example of Embodiment 1. Figure 7 is a diagram showing an example of the manufacturing process of the light-emitting element of Embodiment 1, shown in Figure 2. Figure 8 is a diagram showing the state of the layer provided between the anode and the light-emitting layer of the light-emitting element of the comparative example. Figure 8 is a diagram showing the results of analyzing the layer provided between the anode and the light-emitting layer of the light-emitting element of the comparative example using X-ray photoelectron spectroscopy (XPS). Figure 8 is a diagram showing the FT-IR results of the layer provided between the anode and the light-emitting layer of the light-emitting element of the comparative example, shown in Figure 8. Figure 3 is a diagram showing the results of analyzing the layer provided between the anode and the light-emitting layer of the light-emitting element of Embodiment 1, respectively using X-ray photoelectron spectroscopy (XPS). This figure shows the FT-IR results of the layer provided between the anode and the light-emitting layer of the light-emitting element of Embodiment 1 shown in Figure 3.

[0012] The embodiments of this disclosure will be described below with reference to Figures 1 to 12. For the sake of convenience, in the following description, components having the same function as those described in a particular embodiment will be denoted by the same reference numerals, and their descriptions may be omitted.

[0013] [Embodiment 1] Figure 1 is a plan view showing the schematic configuration of a display device 1 including the light-emitting element 10 of Embodiment 1 shown in Figure 2. Figure 2 is a cross-sectional view showing the schematic configuration of the light-emitting element 10 of Embodiment 1. Figure 3 is a cross-sectional view showing the schematic configuration of the layer 3 provided between the anode 2 and the light-emitting layer EM of the light-emitting element 10 of Embodiment 1 shown in Figure 2. Figure 4 is a diagram showing the voltage-current density characteristics of the light-emitting element 10 of Embodiment 1 and the comparative light-emitting element 100, respectively, shown in Figure 2. Figure 5 is a diagram showing the current density-external quantum efficiency (EQE) characteristics of the light-emitting element 10 of Embodiment 1 and the comparative light-emitting element 100, respectively, shown in Figure 2. Figure 6 is a cross-sectional view showing the schematic configuration of a light-emitting element 10a, which is a modified example of Embodiment 1.

[0014] As shown in Figure 1, the display device 1 comprises a frame area NDA and a display area DA. The display area DA of the display device 1 is provided with a plurality of pixels PIX, and each pixel PIX includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, the case in which one pixel PIX is composed of a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP is described as an example, but it is not limited to this. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, green subpixel GSP, and blue subpixel BSP.

[0015] Each of the red subpixels RSP, green subpixel GSP, and blue subpixel BSP provided in the display area DA of the display device 1 includes the light-emitting element 10 shown in Figure 2. Specifically, the red subpixel RSP includes a red light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a red light-emitting layer; the green subpixel GSP includes a green light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a green light-emitting layer; and the blue subpixel BSP includes a blue light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a blue light-emitting layer.

[0016] As shown in Figure 2, the light-emitting element 10 includes an anode 2, a cathode 5, a light-emitting layer EM provided between the anode 2 and the cathode 5, and a hole injection layer 3HI, which is a hole functional layer containing an oxide semiconductor material, provided between the anode 2 and the light-emitting layer EM. In this embodiment, the case in which the hole functional layer containing the oxide semiconductor material is the hole injection layer 3HI is described as an example, but the invention is not limited to this, and the hole transport layer may also be a hole transport layer as long as it contains an oxide semiconductor material. As the oxide semiconductor material, for example, nickel oxide can be used, and nickel oxide nanoparticles can be suitably used. In this embodiment, the hole functional layer containing the oxide semiconductor material is a hole injection layer 3HI containing nickel oxide, specifically a hole injection layer 3HI containing nickel oxide nanoparticles, but the invention is not limited to this. Furthermore, in this embodiment, the case in which the light-emitting element 10 further includes an electronic functional layer 4 between the cathode 5 and the light-emitting layer EM is described as an example, but the invention is not limited to this, and the electronic functional layer 4 may be omitted as appropriate.

[0017] In the case of a hole functional layer containing the oxide semiconductor material described above, for example, a hole injection layer 3HI containing nickel oxide nanoparticles, it is known that a relatively large number of residual hydroxyl groups are present, and that these residual hydroxyl groups cause quenching in the light-emitting layer EM. Therefore, in this embodiment, in order to reduce the number of residual hydroxyl groups contained in the hole injection layer 3HI, a hole-transporting material SAMP, which is a polymer or oligomer with hole-transporting properties, is bonded to the surface of the hole injection layer 3HI facing the light-emitting layer EM, as shown in Figures 2 and 3. In this embodiment, as shown in Figure 2, the case in which layer 3 provided between the anode 2 and the light-emitting layer EM is composed of a hole injection layer 3HI and a hole-transporting material SAMP bonded to the surface of the hole injection layer 3HI facing the light-emitting layer EM is described as an example, but the embodiment is not limited to this. For example, as shown in Figure 6, the light-emitting element 10a, the layer 3a provided between the anode 2 and the light-emitting layer EM may consist of a hole injection layer 3HI, a hole transport material SAMP bonded to the surface of the hole injection layer 3HI facing the light-emitting layer EM, and a hole transport layer 3HT, all stacked in this order from the anode 2 side. That is, a hole transport layer 3HT may be provided between the hole injection layer 3HI, on which the hole transport material SAMP is bonded to the surface facing the light-emitting layer EM, and the light-emitting layer EM.

[0018] As shown in Figure 3, the hole transport material SAMP is bonded to the EM-side surface of the hole injection layer 3HI. The hole transport material SAMP includes a plurality of hole transport units HTS bonded to the hole injection layer 3HI, which is a hole functional layer, via SCU groups that can bond to the hole injection layer 3HI, i.e., SCU groups that can bond to the residual hydroxyl groups of the hole injection layer 3HI, and a crosslinking unit CCLU that includes a conjugated system structure and connects two adjacent hole transport units HTS. The hole transport unit HTS is a part of the hole transport material SAMP, possessing hole transport properties and bonded to the hole injection layer 3HI via SCU groups that can bond to the residual hydroxyl groups of the hole injection layer 3HI. The hole-transporting material SAMP may be a polymer having hole-transporting properties, and the hole-transporting polymer includes five or more hole-transporting units HTS bonded to the hole-injection layer 3HI, and a crosslinking unit CCLU that includes a conjugated structure and connects two adjacent hole-transporting units HTS. However, the hole-transporting material SAMP is not limited thereto, and may be a hole-transporting oligomer, and the hole-transporting oligomer may include two to four hole-transporting units HTS bonded to the hole-injection layer 3HI, and a crosslinking unit CCLU that includes a conjugated structure and connects two adjacent hole-transporting units HTS. The hole transport material SAMP bonded to the light-emitting layer EM side of the hole injection layer 3HI shown in Figure 3 contains a crosslinked unit CCLU and a hole transport unit HTS with a conjugated structure, and is an oligomer or polymer, thus possessing good hole transport properties. Therefore, the hole injection characteristics from the hole injection layer 3HI to the light-emitting layer EM via the hole transport material SAMP are good, and a light-emitting element 10 with good external quantum efficiency (EQE) can be realized.

[0019] In this embodiment, we will explain, as an example, the case in which the hole transport material SAMP shown in Figure 3 has a carbazole skeleton as the hole transport unit HTS, which has an R1 group that is a SCU group capable of bonding to the hole injection layer 3HI, which is a hole functional layer, as shown in (Chemical Formula 1) below, but we are not limited to this. The carbazole skeleton refers to the portion in (Chemical Formula 1) below that consists of 12 carbon atoms and 1 nitrogen atom, excluding the R1 group. For example, the hole transport material SAMP shown in Figure 3 may have a diphenylamine skeleton as the hole transport unit HTS, which has an R1 group that is a SCU group capable of bonding to the hole injection layer 3HI, which is a hole functional layer, as shown in (Chemical Formula 2) below. The diphenylamine skeleton refers to the portion in (Chemical Formula 2) below that consists of 12 carbon atoms and 1 nitrogen atom, excluding the R1 group. The hole transport material SAMP shown in Figure 3 may have an acridine skeleton as the hole transport unit HTS, which includes an R1 group, an SCU group capable of bonding to the hole injection layer 3HI, a hole functional layer, as shown in (Chemical Formula 3) below. The acridine skeleton refers to the portion in (Chemical Formula 3) below that consists of 13 carbon atoms and 1 nitrogen atom, excluding the R1 group. The hole transport material SAMP shown in Figure 3 may also have a triphenylamine skeleton as the hole transport unit HTS, which includes an R1 group, an SCU group capable of bonding to the hole injection layer 3HI, a hole functional layer, as shown in (Chemical Formula 4) below. The triphenylamine skeleton refers to the portion in (Chemical Formula 4) below that consists of 18 carbon atoms and 1 nitrogen atom, excluding the R1 group. In (Chemical Formula 4) below, the case where the R1 group is positioned in the para position relative to the nitrogen atom is given as an example, but the explanation is not limited to this, and the R1 group may be positioned in the ortho or meta position relative to the nitrogen atom. The hole transport material SAMP shown in Figure 3 may have a phenoxazine skeleton as a hole transport unit HTS, which includes an R1 group, an SCU group capable of bonding with the hole injection layer 3HI, which is a hole functional layer, as shown in (Chemical Formula 5) below. The phenoxazine skeleton refers to the portion in (Chemical Formula 5) below that consists of 12 carbon atoms, 1 nitrogen atom, and 1 oxygen atom, excluding the R1 group.The hole-transporting material SAMP shown in Figure 3 may have a phenothiazine skeleton as a hole-transporting unit HTS, which is a phenothiazine skeleton equipped with an R1 group, an SCU group capable of bonding to the hole-injection layer 3HI, which is a hole-functional layer, as shown in (Chemical Formula 6) below. The phenothiazine skeleton refers to the portion in (Chemical Formula 6) below that consists of 12 carbon atoms, 1 nitrogen atom, and 1 sulfur atom, excluding the R1 group. The carbazole skeleton, diphenylamine skeleton, triphenylamine skeleton, acridine skeleton, phenoxazine skeleton, and phenothiazine skeleton, which are suitably used as the hole-transporting unit HTS described above, may have further substituents as long as they have the corresponding skeleton, and may have a portion in which these substituents condense to form a cyclic structure. For example, the molecular groups shown in (Chemical Formula 7), (Chemical Formula 8), and (Chemical Formula 9) below can be given as examples of a carbazole skeleton equipped with an R1 group that has further substituents, but are not limited thereto. Furthermore, as an example of a case where a diphenylamine skeleton having an R1 group has further substituents, the molecule shown below (Chemical Formula 10) can be cited, but is not limited to this.

[0020] In this embodiment, as shown in Figure 3, the hole transport material SAMP comprises a plurality of hole transport units HTS, and each of the plurality of hole transport units HTS has a carbazole skeleton equipped with an R1 group, which is a group SCU capable of binding to the hole injection layer 3HI, which is the hole functional layer shown in (Chemical Formula 1) above. However, the embodiment is not limited to this. The plurality of hole transport units HTS in the hole transport material SAMP include, for example, a first hole transport unit having a first skeleton and a second hole transport unit having a second skeleton different from the first skeleton, and the first skeleton and the second skeleton may be selected from a carbazole skeleton, a diphenylamine skeleton, a triphenylamine skeleton, an acridine skeleton, a phenoxazine skeleton, and a phenothiazine skeleton, respectively. Each of the multiple hole transport units HTS in the hole transport material SAMP is a part of the hole transport material SAMP, possessing hole transport properties and being bonded to the hole injection layer 3HI via a group SCU that can bond to the residual hydroxyl groups of the hole injection layer 3HI.

[0021] The R1 group, which is a group SCU that can bond to the hole implantation layer 3HI, which is the hole functional layer in the above chemical formulas (1 to 10), is, for example, a phosphonic acid group (-P(=O)(OH) ２ It is preferable that the R1 group has either a carboxyl group (-C(=O)(OH)) or a carboxyl group. Furthermore, it is preferable that the R1 group is bonded to a nitrogen atom in the molecular skeleton, as shown in (Chemical Formulas 1-3) and (Chemical Formulas 5-10) above, and is bonded to a site located in the para position relative to the nitrogen atom, as shown in (Chemical Formula 4) above.

[0022] In this embodiment, as shown in Figure 3, the hole transport unit HTS of the hole transport material SAMP is bonded to the hole injection layer 3HI, which is a hole functional layer, via -P(=O)(O-)(O-). That is, the phosphonic acid group (-P(=O)(OH)) possessed by the hole transport unit HTS ２The two hydroxyl groups (OH) in ) react with the residual hydroxyl groups (OH) contained in the hole injection layer 3HI, which is the hole functional layer, to form a bond. Note that the statement that the hole transport unit HTS of the hole transport material SAMP is bonded to the hole injection layer 3HI, which is the hole functional layer, via -P(=O)(O-)(O-) means that the hole transport unit HTS of the hole transport material SAMP is bonded to -C ｎ H ２ｎ This also includes the case where the hole transport unit HTS is bonded to the hole injection layer 3HI, which is a hole functional layer, via -P(=O)(O-)(O-). In this case, n may be 0 or a natural number, but it is preferably 2 or more and 4 or less. Figure 3 illustrates the case where n is 2. Furthermore, the hole transport unit HTS of the hole transport material SAMP may be bonded to the hole injection layer 3HI, which is a hole functional layer, via -C(=O)(O-). That is, one hydroxyl group (OH) in the carboxyl group (-C(=O)(OH)) of the hole transport unit HTS reacts with a residual hydroxyl group (OH) contained in the hole injection layer 3HI, which is a hole functional layer, to form a bond. Furthermore, the statement that the hole transport unit HTS of the hole transport material SAMP is bonded to the hole injection layer 3HI, which is a hole functional layer, via -C(=O)(O-) means that the hole transport unit HTS of the hole transport material SAMP is bonded to -C ｎ H ２ｎ This also includes the case where it is bonded to the hole injection layer 3HI, which is the hole functional layer, via -C(=O)(O-), in which case n may be 0 or a natural number, but it is preferably 2 or more and 4 or less. From the standpoint of reducing the residual hydroxyl groups (OH) contained in the hole injection layer 3HI, which is the hole functional layer, the R1 group, which is an SCU group that can bond to the hole injection layer 3HI, is preferable to a phosphonic acid group (-P(=O)(OH)) having two hydroxyl groups (OH) as the terminal functional group of each of the above-mentioned skeletons, rather than a carboxyl group (-C(=O)(OH)) having one hydroxyl group (OH). ２ It is preferable to have ).

[0023] In this embodiment, as shown in Figure 3, the case in which each of the multiple hole transport units HTS of the hole transport material SAMP is bonded to the hole injection layer 3HI, which is a hole functional layer, via -P(=O)(O-)(O-) was described as an example, but the embodiment is not limited to this. Some of the multiple hole transport units HTS of the hole transport material SAMP may be bonded to the hole injection layer 3HI, which is a hole functional layer, via -P(=O)(O-)(O-), while other parts of the multiple hole transport units HTS of the hole transport material SAMP may be bonded to the hole injection layer 3HI, which is a hole functional layer, via -C(=O)(O-).

[0024] As shown in Figure 3, the hole transport material SAMP includes a crosslinking unit CCLU. In this embodiment, we will describe, as an example, the case in which a crosslinking unit CCLU is used that includes three sulfur atoms and two conjugated molecule benzene rings, and in which the sulfur atoms and the conjugated molecule are alternately bonded, but we are not limited to this. The crosslinking unit CCLU is not particularly limited as long as it includes a conjugated structure (π-conjugated structure) and can link two adjacent hole transport units HTS.

[0025] The crosslinking unit CCLU comprises sulfur atoms at both ends, N (where N is a natural number) group 16 atoms and N+1 conjugated molecules located between the sulfur atoms at both ends, and is constructed by alternately bonding the group 16 atoms and the conjugated molecules. That is, conjugated molecules are located next to the sulfur atoms at both ends. The N group 16 atoms are one or more atoms selected from sulfur atoms and oxygen atoms, and may be, for example, sulfur atoms. To obtain such a crosslinked unit CCLU, for example, a raw material for a crosslinked unit CCLU may be used that contains three sulfur atoms and two conjugated benzene rings, and in which the sulfur atoms and the conjugated molecules are alternately bonded, such as 4-4'-thiobisbenzenethiol (see chemical formula 12) described later, or a raw material for a crosslinked unit CCLU may be used that contains five sulfur atoms and four conjugated benzene rings, and in which the sulfur atoms and the conjugated molecules are alternately bonded, such as 4-4'-thiotetrakisbenzenethiol (see chemical formula 13) described later.

[0026] The CCLU is not limited to this, and the N group 16 atoms contained in the CCLU may be oxygen atoms. In this case, the CCLU may be composed of, for example, sulfur atoms, benzene rings which are conjugated molecules, oxygen atoms, benzene rings which are conjugated molecules, and sulfur atoms bonded alternately.

[0027] The CCLU is not limited to this, and the N group 16 atoms contained in the CCLU may be two types of atoms selected from sulfur atoms and oxygen atoms. In this case, the CCLU may be composed of, for example, sulfur atoms and benzene rings which are conjugated molecules, sulfur atoms and benzene rings which are conjugated molecules, oxygen atoms and benzene rings which are conjugated molecules, and sulfur atoms bonded alternately.

[0028] As described above, the crosslinking unit CCLU includes a conjugated system structure (π-conjugated system structure) and can connect two adjacent hole transport units HTS. By using such a crosslinking unit CCLU, it is possible to realize an oligomerized or polymerized hole transport material SAMP with good hole transport properties.

[0029] The light-emitting element 10 shown in Figure 2 and the light-emitting element 10a shown in Figure 6 may be either a top-emission type or a bottom-emission type. In this embodiment, the case in which the light-emitting element 10 shown in Figure 2 and the light-emitting element 10a shown in Figure 6 are arranged in a forward-stacked structure with the cathode 5 above the anode 2 is given as an example, but the embodiment is not limited to this, and although not shown, the light-emitting element may have a configuration in which the light-emitting elements 10 and 10a are inverted, that is, an inverted-stacked structure with the anode 2 above the cathode 5. Even in the case of an inverted-stacked structure, the hole injection layer 3HI is located between the anode 2 and the light-emitting layer EM, the hole transport material SAMP faces the light-emitting layer EM side of the hole injection layer 3HI, and if an electronic functional layer 4 is present, the electronic functional layer 4 is located between the light-emitting layer EM and the cathode 5. As in this embodiment, in order to make the forward-stacked light-emitting elements 10 and 10a a top-emission type, the anode 2 should be formed from an electrode material that reflects visible light and the cathode 5 should be formed from an electrode material that transmits visible light. In order to make the forward-stacked light-emitting elements 10 and 10a a bottom-emission type, the anode 2 should be formed from an electrode material that transmits visible light and the cathode 5 should be formed from an electrode material that reflects visible light. On the other hand, in order to make the inverted-stacked light-emitting elements a top-emission type, the cathode 5 should be formed from an electrode material that reflects visible light and the anode 2 should be formed from an electrode material that transmits visible light. In order to make the inverted-stacked light-emitting elements a bottom-emission type, the cathode 5 should be formed from an electrode material that transmits visible light and the anode 2 should be formed from an electrode material that reflects visible light.

[0030] As the electrode material that reflects visible light, there is no particular limitation as long as it can reflect visible light and has conductivity. For example, metal materials such as Al, Mg, Li, Ag, alloys of the above metal materials, laminates of the above metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the above alloys and the above transparent metal oxides can be mentioned.

[0031] On the other hand, as the electrode material that transmits visible light, there is no particular limitation as long as it can transmit visible light and has conductivity. For example, transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al, Ag, or nano wires (Nano Wire) made of metal materials such as Al, Ag can be mentioned.

[0032] The light-emitting layer EM provided in the light-emitting element 10 shown in FIG. 2 and the light-emitting element 10a shown in FIG. 6 may be a light-emitting layer containing quantum dots or a light-emitting layer containing an organic light-emitting material. The light-emitting elements 10 and 10a provided with a light-emitting layer containing quantum dots are QLEDs (Quantum dot Light Emitting Diodes), and the light-emitting elements 10 and 10a provided with a light-emitting layer containing an organic light-emitting material are OLEDs (Organic Light Emitting Diodes).

[0033] Quantum dots such as the red-emitting quantum dots contained in the red-emitting layer, the green-emitting quantum dots contained in the green-emitting layer, and the blue-emitting quantum dots contained in the blue-emitting layer may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a core / shell structure with a continuously varying ratio. Note that the shell may cover a part of the core, but it is better if it completely covers the core. The core of the quantum dot may contain, for example, one or more selected from Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, and ZnSeTe. The shell of the quantum dot may contain, for example, one or more selected from CdS, ZnS, CdSSSe, CdTeSe, CdSTe, ZnSSSe, ZnSTe, ZnTeSe, and AgInP (AIP), and those with a lattice constant close to the core and a larger band gap than the core may be selected.

[0034] The electronic functional layer 4 provided in the light-emitting element 10 shown in FIG. 2 and the light-emitting element 10a shown in FIG. 6 only needs to include at least one of an electron transport layer and an electron injection layer. When both the electron transport layer and the electron injection layer are included, the electron injection layer and the electron transport layer are laminated in this order from the cathode 5 side.

[0035] The electron transport layer may be formed using, for example, an organic material such as 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or may be formed using an inorganic material such as ZnO nanoparticles or nanoparticles of an oxide containing Zn and Mg.

[0036] The electron injection layer can be formed using, for example, alkali metals or alkaline earth metals such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate, sodium polystyrene sulfonate, alkali metals or alkaline earth metals, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, or organic complexes of alkali metals.

[0037] The hole transport layer 3HT provided in the light-emitting element 10a shown in Figure 6 can be formed using, for example, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine (poly-TPD), or polyvinylcarbazole (PVK), but is not limited to these, and may also be formed using inorganic hole transport materials.

[0038] In this embodiment, in order to realize a top-emission type light-emitting element 10, the anode 2 is formed from a laminate of an indium tin oxide film, an Ag film, and another indium tin oxide film, which are electrode materials that reflect visible light, and the cathode 5 is formed from a nanowire made of Ag, which is an electrode material that transmits visible light. Furthermore, the hole injection layer 3HI of the light-emitting element 10 is formed using nickel oxide nanoparticles. In addition, the hole transport material SAMP bonded to the EM-side surface of the hole injection layer 3HI of the light-emitting element 10 is composed of a plurality of hole transport units HTS having a carbazole skeleton bonded to the EM-side surface of the hole injection layer 3HI via -P(=O)(O-)(O-), and a crosslinking unit CCLU which is composed of three sulfur atoms and two benzene rings alternately bonded and connects two adjacent hole transport units HTS. The hole transport material SAMP may be a polymer having five or more hole transport units HTS, or an oligomer having two to four hole transport units HTS. Multiple hole transport material SAMPs are bonded to the light-emitting layer EM side of the hole injection layer 3HI of the light-emitting element 10. Some of these SAMPs are polymers, while the remaining SAMPs are oligomers. Furthermore, the electronic functional layer 4 of the light-emitting element 10 consists solely of an electron transport layer, which is formed from ZnO nanoparticles.

[0039] On the other hand, the comparative example light-emitting element 100 is identical to the light-emitting element 10 described above in all other respects, except that the hole transport material bonded to the EM-side surface of the hole injection layer 3HI differs from the hole transport material SAMP bonded to the EM-side surface of the hole injection layer 3HI in the light-emitting element 10 described above. The hole transport material bonded to the EM-side surface of the hole injection layer 3HI in the comparative example light-emitting element 100 is a monomer HTSM (see Figure 8) composed of a single hole transport unit HTS having a carbazole skeleton bonded to the EM-side surface of the hole injection layer 3HI via -P(=O)(O-)(O-).

[0040] As can be seen from FIG. 4 showing the voltage-current density characteristics of the light-emitting element 10 of Embodiment 1 and the light-emitting element 100 of the comparative example described above, in the case of the light-emitting element 10, compared with the light-emitting element 100 of the comparative example, at a certain current density, for example, 5 mA / cm ２ or 10 mA / cm ２ can be realized at a lower voltage, and it can be confirmed that the hole transport ability has been improved.

[0041] Further, as can be seen from FIG. 5 showing the current density-external quantum efficiency (EQE) characteristics of the light-emitting element 10 of Embodiment 1 and the light-emitting element 100 of the comparative example described above, in the case of the light-emitting element 10, compared with the light-emitting element 100 of the comparative example, the normalized external quantum efficiency (EQE) is improved at any current density. In particular, in the high current density region of 10 mA / cm ２ or more, it can be confirmed that the normalized external quantum efficiency (EQE) is improved by about 2 times.

[0042] FIG. 7 is a diagram showing an example of the manufacturing process of the light-emitting element 10 of Embodiment 1 shown in FIG. 2. FIG. 8 is a diagram showing the state of the layer 103 provided between the anode and the light-emitting layer of the light-emitting element 100 of the comparative example. The layer 103 provided between the anode and the light-emitting layer is composed of a hole injection layer 3HI and a monomer HTSM bonded to the surface of the hole injection layer 3HI on the light-emitting layer EM side.

[0043] As shown in FIG. 7, the manufacturing process of the light-emitting element 10 of Embodiment 1 includes a step S1 of forming an anode 2, a step S2 of forming a hole injection layer 3HI, a step S3 of forming a monomer HTSM having a group SCU capable of bonding to a hydroxyl group (OH) and a hole-transporting molecular skeleton on the surface of the hole injection layer 3HI, a first heat treatment step S4, a first rinse step S5, a second heat treatment step S6, a step S7 of treating the monomer HTSM formed on the surface of the hole injection layer 3HI with a cross-linking agent and a reaction initiator containing a conjugated system structure, a third heat treatment step S8, a second rinse step S9, a fourth heat treatment step S10, a step S11 of forming a light-emitting layer EM, a step S12 of forming an electron functional layer 4, and a step S13 of forming a cathode 5.

[0044] In step S1, which is the process for forming anode 2, an anode 2, which is an electrode that reflects visible light, is formed by stacking an indium tin oxide film, an Ag film, and an indium tin oxide film in that order.

[0045] In step S2, which involves forming the hole injection layer 3HI, a dispersion of nickel oxide nanoparticles is applied to the anode 2 to form the hole injection layer 3HI consisting of nickel oxide nanoparticles.

[0046] In step S3, which involves forming monomer HTSM, monomer HTSM having a group SCU capable of binding to residual hydroxyl groups (OH) contained in the hole injection layer 3HI, which is made of nickel oxide nanoparticles, and a hole-transporting molecular skeleton was formed on the surface of the hole injection layer 3HI. As the monomer HTSM, Br-2PACz ([2-(3,6-dibromo-9H-carbazole-9-yl)ethyl]phosphonic acid) shown in the following chemical formula 11 was used. A solution of Br-2PACz shown in the following chemical formula 11 (Br-2PACz concentration 10 mM) was applied to the hole injection layer 3HI using spin coating to form monomer HTSM on the surface of the hole injection layer 3HI. The invention is not limited to this, and the monomer HTSM may be formed on the surface of the hole-injection layer 3HI by immersing the laminate of anode 2 and hole-injection layer 3HI in an ethanol solution of Br-2PACz shown below (chemical formula 11) (concentration of Br-2PACz is 10 mM). Here, the case in which 2PACz having bromine (Br) is used has been described as an example, but in the third heat treatment step S8 described later, 2PACz having halogen atoms other than bromine (Br) may be used as long as it can react with the thiol group (-SH group) of 4-4'-thiobisbenzenethiol.

[0047] In this embodiment, as an example, the case in which Br-2PACz shown below (Chemical Formula 11) is used as the monomer HTSM having a carbazole skeleton with an R1 group as shown above (Chemical Formula 1) will be described, but the embodiment is not limited thereto. As the monomer HTSM having a diphenylamine skeleton with an R1 group as shown above (Chemical Formula 2), molecules in which bromine (Br) is positioned in the para position relative to the nitrogen atom in each of the two benzene rings of the diphenylamine skeleton with an R1 group as shown above (Chemical Formula 2) can be suitably used. Furthermore, as the monomer HTSM having an acridine skeleton with an R1 group as shown above (Chemical Formula 3), molecules in which bromine (Br) is positioned in the para position relative to the nitrogen atom in each of the two benzene rings of the acridine skeleton with an R1 group as shown above (Chemical Formula 3) can be suitably used. Furthermore, as a monomer HTSM having a triphenylamine skeleton with an R1 group as shown in (Chemical Formula 4) above, a molecule in which bromine (Br) is positioned in the para position relative to the nitrogen atom in each of the two benzene rings of the triphenylamine skeleton with an R1 group as shown in (Chemical Formula 4) above that do not have an R1 group can be suitably used. Furthermore, as a monomer HTSM having a phenoxazine skeleton with an R1 group as shown in (Chemical Formula 5) above, a molecule in which bromine (Br) is positioned in the para position relative to the nitrogen atom in each of the two benzene rings of the phenoxazine skeleton with an R1 group as shown in (Chemical Formula 5) above can be suitably used. Furthermore, as a monomer HTSM having a phenothiazine skeleton with an R1 group as shown in (Chemical Formula 6) above, a molecule in which bromine (Br) is positioned in the para position relative to the nitrogen atom in each of the two benzene rings of the phenothiazine skeleton with an R1 group as shown in (Chemical Formula 6) above can be suitably used.

[0048] In the first heat treatment step S4, the residual hydroxyl groups (OH) contained in the hole injection layer 3HI and the phosphonic acid groups (-P(=O)(OH)) of Br-2PACz ２ The mixture was reacted with the solvent, ethanol, and then baked at 100°C using a hot plate to remove it.

[0049] In the first rinsing step S5, ethanol was used to wash away excess Br-2PACz. This step removes Br-2PACz that are not bonded to the surface of the hole injection layer 3HI, so that a self-assembled monolayer (SAM) is formed on the surface of the hole injection layer 3HI by the monomer HTSM.

[0050] In the second heat treatment step S6, in order to remove the ethanol remaining after the first rinsing step S5, the material was fired at 100°C using a hot plate. Figure 8 shows the state of the hole injection layer 3HI after the second heat treatment step S6, and a self-assembled monolayer (SAM) is formed on the surface of the hole injection layer 3HI by the monomer HTSM.

[0051] In step S7, which involves treating the monomer HTSM formed on the surface of the hole injection layer 3HI with a crosslinking agent containing a conjugated system structure and a reaction initiator, the monomer HTSM formed on the surface of the hole injection layer 3HI was treated with a treatment solution prepared by adding 4-4'-thiobisbenzenethiol (10 mM), shown in the following chemical formula 12, which is a crosslinking agent containing a conjugated system structure, and triethylamine (4 ml), which is a reaction initiator, to toluene (16 ml). The treatment of the monomer HTSM formed on the surface of the hole injection layer 3HI with the treatment solution may be carried out, for example, by immersing a laminate of anode 2, hole injection layer 3HI, and monomer HTSM formed on the surface of hole injection layer 3HI in the treatment solution for, for example, 1 hour. In addition, 4-4'-thiotetrakisbenzenethiol shown in the following chemical formula 13 may be used instead of 4-4'-thiobisbenzenethiol shown in the following chemical formula 12, which is a crosslinking agent containing a conjugated system structure. Furthermore, for example, in the 4-4'-thiobisbenzenethiol shown in (Chemical Formula 12) and the 4-4'-thiotetrakisbenzenethiol shown in (Chemical Formula 13) below, molecules in which oxygen atoms are incorporated in place of sulfur atoms at positions other than the terminal sulfur atoms may be used as crosslinking agents, or molecules in which oxygen atoms are incorporated in place of sulfur atoms at only some of the positions other than the terminal sulfur atoms may be used as crosslinking agents.

[0052] The third heat treatment step S8 is a step in which the thiol group (-SH group) of 4-4'-thiobisbenzenethiol and the bromine (Br) of Br-2PACz are subjected to a click reaction, as shown in (Chemical Formula 14) below, to polymerize or oligomerize, and the solvent toluene is removed. In this step, firing was performed at 120°C using a hot plate. Note that in (Chemical Formula 14) below, n is a natural number of 2 or more, and the phosphonic acid group (-P(=O)(OH)) shown in (Chemical Formula 14) below ２ As shown in Figure 8, the two hydroxyl groups of ) are already bonded to the residual hydroxyl groups of the hole-injection layer 3HI after the second heat treatment step S6 described above.

[0053] In the second rinsing step S9, washing was performed using toluene to remove excess 4-4'-thiobisbenzenethiol and triethylamine.

[0054] In the fourth heat treatment step S10, in order to remove the toluene remaining after the second rinsing step S9, a hole injection layer 3HI can be obtained in which a hole transporting material SAMP, which is a hole transporting polymer (poly-phenyl-S-2PACz) or a hole transporting oligomer (oligo-phenyl-S-2PACz), is bonded to the surface, as shown in Figure 3.

[0055] A hole-transporting polymer (poly-phenyl-S-2PACz) is a polymer that has repeating units of [-S-Ph-S-Ph-S-HTS]n (where n is a natural number greater than or equal to 5), where the hole-transporting unit shown in Figure 3 is denoted as HTS, the sulfur atom as S, and the benzene ring as Ph.

[0056] The hole-transporting oligomer (oligo-phenyl-S-2PACz) is a ring-opening oligomer represented as HS-Ph-S-Ph-S-[HTS-S-Ph-S-Ph]n-SH (where n is a natural number between 2 and 4) when the hole-transporting unit shown in Figure 3 is represented as HTS, the sulfur atom as S, the benzene ring as Ph, and the hydrogen atom as H. ＊ -Ph-S-Ph-S-[HTS-S-Ph-S-Ph]n-S ＊ (Here, n is a natural number between 2 and 4, and S ＊ A ring-bound oligomer can exist, represented as (where the two atoms are the same sulfur atom).

[0057] In step S11, which involves forming the light-emitting layer EM, the light-emitting layer EM can be formed by applying a dispersion of quantum dots (for example, quantum dots made of CdSe, InP, or ZnSe).

[0058] In step S12, which involves forming the electronic functional layer 4, an electronic functional layer 4 consisting solely of an electron transport layer was formed by applying a dispersion of ZnO nanoparticles.

[0059] In step S13, which involves forming the cathode 5, a nanowire made of Ag was used to form the cathode 5, which is an electrode that transmits visible light.

[0060] As described above, in the manufacturing process of the light-emitting element 10 shown in Figure 7, in both step S3, which forms the monomer HTSM, and step S7, which treats the monomer HTSM formed on the surface of the hole injection layer 3HI with a crosslinking agent and a reaction initiator containing a conjugated system structure, it is not necessary to dissolve the polymer or oligomer in a solvent. Therefore, the range of solvents that can be selected in each step S3 and S7 is broadened, and productivity can be improved. Since the solvents that can dissolve polymers and oligomers are limited, if it is necessary to dissolve the polymer or oligomer, the range of solvents that can be selected is narrowed, which may lead to a decrease in productivity.

[0061] In the manufacturing method of the light-emitting element 10 described with reference to Figure 7, in step S7, in which the monomer HTSM formed on the surface of the hole injection layer 3HI is treated with a crosslinking agent containing a conjugated system structure and a reaction initiator, the first heat treatment step S4, the first rinsing step S5, and the second heat treatment step S6 may be omitted as appropriate, as long as the monomer HTSM is not washed away. Also, the second rinsing step S9 and the fourth heat treatment step S10, which follow the third heat treatment step S8, a step in which the monomer HTSM treated with the crosslinking agent is oligomerized or polymerized, may be omitted as appropriate. Furthermore, in step S7, in which the monomer HTSM formed on the surface of the hole injection layer 3HI is treated with a crosslinking agent containing a conjugated system structure and a reaction initiator, the reaction initiator may be omitted, and the treatment may be carried out with only the crosslinking agent containing a conjugated system structure.

[0062] Figure 9 shows the results of analyzing the layer 103 provided between the anode and the light-emitting layer of the comparative example light-emitting element 100 shown in Figure 8 using X-ray photoelectron spectroscopy (XPS). Figure 10 shows the FT-IR results of the layer 103 provided between the anode and the light-emitting layer of the comparative example light-emitting element 100 shown in Figure 8. Figure 11 shows the results of analyzing the layer 3 provided between the anode 2 and the light-emitting layer EM of the light-emitting element 10 of Embodiment 1 shown in Figure 3 using X-ray photoelectron spectroscopy (XPS). Figure 12 shows the FT-IR results of the layer 3 provided between the anode 2 and the light-emitting layer EM of the light-emitting element 10 of Embodiment 1 shown in Figure 3.

[0063] As shown in Figure 9, when the layer 103 provided between the anode and the light-emitting layer of the comparative example light-emitting element 100 shown in Figure 8 was analyzed using X-ray photoelectron spectroscopy (XPS), no C-S bonds were confirmed. Also, as shown in Figure 10, when the FT-IR results of the layer 103 provided between the anode and the light-emitting layer of the comparative example light-emitting element 100 shown in Figure 8 were analyzed, no S-H bonds were confirmed. On the other hand, as shown in Figure 11, when the layer 3 provided between the anode 2 and the light-emitting layer EM of the light-emitting element 10 of Embodiment 1 shown in Figure 3 was analyzed using X-ray photoelectron spectroscopy (XPS), a C-S bond was confirmed. This C-S bond was formed in the third heat treatment step S8 described above by a click reaction between the thiol group (-SH group) of 4-4'-thiobisbenzenethiol and the bromine (Br) of Br-2PACz. As shown in Figure 12, no S-H bonds were detected in the FT-IR results of the layer 3 provided between the anode 2 and the light-emitting layer EM of the light-emitting element 10 of Embodiment 1 shown in Figure 3. Since there are almost no S-H bonds, it is presumed that the hole-transporting material SAMP shown in Figure 3 exists in the form of a polymer (poly-phenyl-S-2PACz) with hole-transporting properties or an oligomer (oligo-phenyl-S-2PACz) with ring-closed hole-transporting properties. Furthermore, if the amount of 4-4'-thiobisbenzenethiol is excessive relative to the amount of Br-2PACz, an oligomer (oligo-phenyl-S-2PACz) with ring-opened hole-transporting properties may also be formed.

[0064] [Additional Notes] 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.

[0065] This disclosure can be used in light-emitting elements, methods for manufacturing light-emitting elements, and display devices.

[0066] 1 Display device 2 Anode 3, 3a Layers provided between the anode and the light-emitting layer 3HI Hole injection layer 3HT Hole transport layer 4 Electronic functional layer 5 Cathode 10, 10a Light-emitting element EM Light-emitting layer SAMP Hole transport material HTS Hole transport unit CCLU Crosslinking unit SCU Bondable group HTSM Monomer PIX Pixel RSP Red subpixel GSP Green subpixel BSP Blue subpixel DA Display area NDA Border area

Claims

1. A light-emitting element comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and a hole-transporting material provided between the anode and the light-emitting layer and containing an oxide semiconductor material, wherein a hole-transporting material, which is a polymer or oligomer having hole-transporting properties, is bonded to the surface of the hole-transporting material of the hole-transporting layer facing the light-emitting layer.

2. The light-emitting element according to claim 1, wherein the hole-transporting material is a polymer having hole-transporting properties, and the polymer having hole-transporting properties comprises five or more hole-transporting units bonded to the hole-functional layer, and a crosslinking unit having a conjugated structure and connecting two adjacent hole-transporting units.

3. The light-emitting element according to claim 1, wherein the hole-transporting material is a hole-transporting oligomer, and the hole-transporting oligomer comprises two to four hole-transporting units bonded to the hole-functional layer, and a crosslinking unit that includes a conjugated structure and connects two adjacent hole-transporting units.

4. The light-emitting element according to claim 2 or 3, wherein the hole transporting unit has a carbazole skeleton, a diphenylamine skeleton, a triphenylamine skeleton, an acridine skeleton, a phenoxazine skeleton, or a phenothiazine skeleton.

5. The light-emitting element according to claim 2 or 3, wherein the plurality of hole-transporting units include a first hole-transporting unit having a first skeleton and a second hole-transporting unit having a second skeleton different from the first skeleton, and the first skeleton and the second skeleton are each selected from a carbazole skeleton, a diphenylamine skeleton, a triphenylamine skeleton, an acridine skeleton, a phenoxazine skeleton, and a phenothiazine skeleton.

6. The light-emitting element according to any one of claims 2 to 5, wherein the hole transporting unit is coupled to the hole functional layer via -P(=O)(O-)(O-).

7. The light-emitting element according to any one of claims 2 to 5, wherein the hole transporting unit is coupled to the hole functional layer via -C(=O)(O-).

8. The light-emitting element according to any one of claims 2 to 5, wherein some of the hole-transporting units of the plurality of hole-transporting units are coupled to the hole-functional layer via -P(=O)(O-)(O-), and other parts of the hole-transporting units of the plurality of hole-transporting units are coupled to the hole-functional layer via -C(=O)(O-).

9. The light-emitting element according to any one of claims 2 to 8, wherein the crosslinking unit comprises sulfur atoms at both ends, N (where N is a natural number) group 16 atoms and N+1 conjugated molecules located between the sulfur atoms at both ends, and the group 16 atoms and the conjugated molecules are alternately bonded, and the N group 16 atoms are one or more atoms selected from sulfur atoms and oxygen atoms.

10. The light-emitting element according to claim 9, wherein the N group 16 atoms are sulfur atoms.

11. The light-emitting element according to claim 9, wherein the N group 16 atoms are oxygen atoms.

12. The light-emitting element according to any one of claims 9 to 11, wherein the conjugated molecule is a benzene ring.

13. The light-emitting element according to any one of claims 1 to 12, wherein the hole functional layer is a hole injection layer containing nickel oxide.

14. The light-emitting element according to any one of claims 1 to 13, wherein the hole functional layer is a hole injection layer containing nickel oxide nanoparticles.

15. The light-emitting element according to claim 13 or 14, wherein a hole transport layer is provided between the hole injection layer and the light-emitting layer.

16. A display device including a light-emitting element according to any one of claims 1 to 15.

17. A method for manufacturing an optical element, comprising the steps of: forming an anode; forming a hole functional layer containing an oxide semiconductor material on the anode; forming a monomer on the surface of the hole functional layer having a group that can bond to the hole functional layer and a hole-transporting molecular skeleton; a monomer treatment step of treating the monomer with a crosslinking agent containing a conjugated system structure; oligomerizing or polymerizing the monomer treated with the crosslinking agent; forming an emissive layer; and forming a cathode.

18. The method for manufacturing a light-emitting element according to claim 17, wherein between the step of forming the monomer and the monomer processing step, the method includes a heat treatment step of bonding groups of the monomer that can bond to the hole functional layer to the surface of the hole functional layer, and a rinsing step of removing excess monomer.

19. The method for manufacturing a light-emitting element according to claim 17 or 18, wherein in the monomer treatment step, the monomer is treated with the crosslinking agent and the reaction initiator.

20. A method for manufacturing a light-emitting element according to any one of claims 17 to 19, wherein the monomer used in the step of forming the monomer comprises a plurality of halogen groups, the crosslinking agent used in the monomer processing step comprises a plurality of thiol groups, and in the step of oligomerizing or polymerizing the monomer, the halogen groups of the monomer and the thiol groups of the crosslinking agent are bonded together.

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