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

Abstract

A light-emitting element (10) includes an anode (2), a cathode (6), a light-emitting layer (4) provided between the anode (2) and the cathode (6), and a hole functional layer (3) provided between the anode (2) and the light-emitting layer (4). The hole functional layer (3) is a mixture of a plurality of polymers (22P) including a hole transport molecular structure (22U), an ionic liquid (11), and a crosslinking part (23) connecting the plurality of polymers (22P).

Description

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

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

[0002] In recent years, various display devices equipped with light-emitting elements have been developed, and in particular, display devices equipped with QLEDs (Quantum dot Light Emitting Diodes) or OLEDs (Organic 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, Non-Patent Document 1 describes 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F), which is a low-molecular-weight neutral dopant. ４ Using a mixed solution of -TCNQ) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), a low-molecular-weight neutral dopant F was used without forming a hole transport layer (HTL). ４ - It is described that a dopant layer made of TCNQ and a hole transport layer (HTL) made of TFB are formed separately.

[0004] Optics Express 2019, 27, 16 Interlayer doping with p-type dopant for charge balance in indium phosphide (InP)-based quantum dot light-emitting diodes

[0005] In the solution-based manufacturing process for light-emitting elements such as QLEDs or OLEDs, there is a problem in that when multiple layers are stacked sequentially, the solution in the upper layer dissolves the components of the already stacked lower layer. As described in Non-Patent Document 1, a low-molecular-weight neutral dopant F ４ -When a dopant layer consisting of TCNQ is provided, the solution used in the process after the formation of the dopant layer, for example, in the process of forming the hole transport layer (HTL), contains the dopant F４ - A large amount of TCNQ dissolves, and F which is a dopant ４ - TCNQ will also be distributed in the hole transport layer (HTL) provided so as to contact the dopant layer. Then, in the process after forming the hole transport layer (HTL), for example, in the solution used in the process of forming the light-emitting layer, F which is a dopant contained in the hole transport layer (HTL) ４ - Since TCNQ dissolves again, F which is a dopant contained in the hole transport layer (HTL) ４ - Due to the decrease in the amount of TCNQ, there is a problem that the improvement of the hole transport property in the hole transport layer (HTL) cannot be achieved to a satisfactory extent. Also, F which is a low molecular material of the π-conjugated system ４ - TCNQ tends to aggregate in the solution used in the process after forming the dopant layer. Therefore, F ４ - In the hole transport layer (HTL) in contact with the dopant layer composed of TCNQ, F which is a dopant ４ - TCNQ exists in an aggregated state, and there is also a problem that the hole transport property in the hole transport layer (HTL) cannot be uniformly improved.

[0006] One aspect of the present disclosure aims to provide a light-emitting device including a hole functional layer with uniformly improved hole transport property in the layer, a method for manufacturing the same, and a display device including the light-emitting device.

[0007] The light-emitting device of the present disclosure includes, in order to solve the above problems, an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and a hole functional layer provided between the anode and the light-emitting layer. The hole functional layer is a mixture of a plurality of polymers including a hole transport molecular structure, an ionic liquid, and a cross-linking portion connecting between the plurality of polymers.

[0008] The display device of the present disclosure includes the light-emitting device in order to solve the above problems.

[0009] To solve the above problems, the present disclosure provides a method for manufacturing a light-emitting element, comprising: a step of forming an anode; a step of forming a cathode; a step of forming a light-emitting layer between the step of forming the anode and the step of forming the cathode; and a step of forming a hole functional layer between the step of forming the anode and the step of forming the light-emitting layer, wherein the step of forming the hole functional layer comprises: a step of applying a solution comprising a plurality of polymers including functional groups and hole-transporting molecular structures whose reaction is initiated by heating and light irradiation, and an ionic liquid; and a step of performing at least one of a heat treatment and a light irradiation treatment to react the functional groups.

[0010] To solve the above problems, the present disclosure provides a method for manufacturing a light-emitting element, comprising: a step of forming an anode; a step of forming a cathode; a step of forming a light-emitting layer between the step of forming the anode and the step of forming the cathode; and a step of forming a hole functional layer between the step of forming the anode and the step of forming the light-emitting layer, wherein the step of forming the hole functional layer comprises: a step of applying a solution comprising a polymer containing a hole-transporting molecular structure and not containing functional groups whose reaction is initiated by at least one of heating and light irradiation; a plurality of monomers containing two or more functional groups whose reaction is initiated by at least one of heating and light irradiation and a hole-transporting molecular structure; and an ionic liquid; and a step of performing at least one of a heat treatment and a light irradiation treatment to react the functional groups.

[0011] According to one aspect of this disclosure, it is possible to provide a light-emitting element having a hole functional layer in which hole transportability is uniformly improved within the layer, a method for manufacturing the same, and a display device having the light-emitting element.

[0012] This is a plan view showing the schematic configuration of the display device of Embodiment 1. This is a cross-sectional view showing the schematic configuration of the light-emitting element provided in the display device of Embodiment 1. This is a diagram showing an example of quantum dots provided in the light-emitting layer of the light-emitting element shown in Figure 2. This is a diagram showing another example of quantum dots provided in the light-emitting layer of the light-emitting element shown in Figure 2. This is a diagram showing an example of the light-emitting layer of the light-emitting element shown in Figure 2. This is a diagram to explain the problems of a light-emitting element that has a hole functional layer, which is a comparative example that does not contain a dopant. This is a diagram to explain why hole transportability is improved and carrier balance is improved in the light-emitting element shown in Figure 2. This is a diagram showing an example of an ionic liquid contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing an example of a cation of an ionic liquid that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing the schematic configuration of a plurality of polymers having a crosslinking portion and a hole-transporting molecular structure contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing an example of a polymer that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing another example of a polymer that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing yet another example of a polymer that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram illustrating the polymer formation process shown in Figure 14. This is a diagram showing yet another example of a polymer that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing yet another example of a polymer that can be contained in the hole functional layer of the light-emitting element shown in Figure 2. This is a diagram showing the change in absorbance before and after rinsing a comparative example hole functional layer containing multiple polymers that have a hole-transporting molecular structure and no crosslinking portion, and an ionic liquid, with chlorobenzene. This is a diagram showing the change in absorbance before and after rinsing the hole functional layer provided in the light-emitting element shown in Figure 2 with chlorobenzene.

[0013] The embodiments of this disclosure will be described below with reference to Figures 1 to 19. 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.

[0014] [Embodiment 1] Figure 1 is a plan view showing the schematic configuration of the display device 1 of Embodiment 1.

[0015] 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.

[0016] Figure 2 is a cross-sectional view showing a schematic configuration of a light-emitting element 10 provided in the display device 1 of Embodiment 1. Figure 3 is a diagram showing an example of a quantum dot QD provided on the light-emitting layer 4 of the light-emitting element 10 shown in Figure 2. Figure 4 is a diagram showing another example of a quantum dot QD provided on the light-emitting layer 4 of the light-emitting element 10 shown in Figure 2. Figure 5 is a diagram showing an example of the light-emitting layer 4 of the light-emitting element 10 shown in Figure 2. In this embodiment, as shown in Figures 3, 4, and 5, the case in which the quantum dot QD is composed of a core QDC and a shell QDS is given as an example, but the embodiment is not limited to this.

[0017] The red subpixel RSP provided in the display area DA of the display device 1 includes a red light-emitting element in the light-emitting element 10 shown in Figure 2, in which the light-emitting layer 4 is a red light-emitting layer; the green subpixel GSP provided in the display area DA of the display device 1 includes a green light-emitting element in the light-emitting element 10 shown in Figure 2, in which the light-emitting layer 4 is a green light-emitting layer; and the blue subpixel BSP provided in the display area DA of the display device 1 includes a blue light-emitting element in the light-emitting element 10 shown in Figure 2, in which the light-emitting layer 4 is a blue light-emitting layer.

[0018] The light-emitting element 10 includes an anode 2, a cathode 6, a light-emitting layer 4 provided between the anode 2 and the cathode 6, a hole functional layer 3 provided between the anode 2 and the light-emitting layer 4, and an electronic functional layer 5 provided between the cathode 6 and the light-emitting layer 4.

[0019] The light-emitting element 10 shown in Figure 2 may be either a top-emission type or a bottom-emission type. Since the light-emitting element 10 has a sequential stacking structure in which the cathode 6 is positioned above the anode 2, to make it a top-emission type, the anode 2 should be made of an electrode material that reflects visible light and the cathode 6 should be made of an electrode material that transmits visible light. To make it a bottom-emission type, the anode 2 should be made of an electrode material that transmits visible light and the cathode 6 should be made of an electrode material that reflects visible light.

[0020] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and is conductive, but examples include metallic materials such as Al, Mg, Li, and Ag, or alloys of the metallic materials, or laminates of the metallic material and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the alloy and the transparent metal oxide.

[0021] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and is conductive, but examples include 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 and Ag, or nanowires made of metal materials such as Al and Ag.

[0022] The electronic functional layer 5 may be composed only of an electron transport layer (ETL), or may be composed only of an electron injection layer (EIL), or may be a layer in which an electron transport layer (ETL) and an electron injection layer (EIL) are laminated in this order from the anode 2 side, and may be omitted as appropriate. The electron transport layer (ETL) is an electron transport material suitably used for forming the electron transport layer. For example, it may be formed using 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 oxide containing ZnO or Zn and Mg, or may be formed using nanoparticles having electron transport properties such as ZnO particles or particles of an oxide containing Zn and Mg. The electron injection layer (EIL) is an electron transport material suitably used for forming the electron injection layer. For example, it may be formed using an alkali metal or alkaline earth metal 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, sodium polymethylmethacrylate polystyrene sulfonate, an oxide of an alkali metal or alkaline earth metal, a fluoride of an alkali metal or alkaline earth metal, an organic complex of an alkali metal, etc. In the present embodiment, the case where the electronic functional layer 5 is composed only of the electron transport layer (ETL) and the electron transport layer (ETL) is formed using ZnO nanoparticles will be described as an example, but it is not limited thereto.

[0023] When the light-emitting layer 4 shown in FIG. 2 contains quantum dots QD as shown in FIGS. 3, 4, and 5, the light-emitting layer 4 may contain an adduct AD that covers the periphery of at least one quantum dot QD as shown in FIGS. 3 and 4, or may contain a matrix MR as an adduct that fills the space between at least two quantum dots QD as shown in FIG. 5. The adduct AD or the matrix MR as an adduct may have properties as a semiconductor or insulator, for example, and may contain any of metal oxides, semimetal oxides, and metal sulfides.

[0024] The adduct AD or matrix MR as an adduct is, for example, silicon oxide (SiO₂) ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ It may also contain at least one of the following: ), lead oxide (PbO), and copper oxide (CuO). Here, the adduct AD or matrix MR as an adduct may be formed as a polymer. For example, if the adduct AD or matrix MR as an adduct contains silicon oxide as an oxide, it may also contain the case that the adduct AD or matrix MR as an adduct is a siloxane compound having siloxane bonds. The adduct AD or matrix MR as an adduct may, for example, contain zinc sulfide (ZnS), magnesium zinc sulfide (ZnMgS, ZnMgS ２ ) Gallium sulfide (GaS, Ga ２ S ３ ), zinc telluride (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa ２ S ４ ), and magnesium sulfide (MgGa ２ S ４ ) may contain at least one of the following. Note that the chemical formula of the compound is a representative example, and the composition ratio indicated in the chemical formula may be stoichiometric, but is not necessarily required.

[0025] The adduct AD is, for example, mainly composed of silicon oxide and may be in contact with the surface of the quantum dot QD as shown in Figure 3, or the adduct AD and the quantum dot QD may be joined via an organic ligand OL as shown in Figure 4. Furthermore, in the case where the adduct AD covers the periphery of at least one quantum dot QD, if the adduct AD is located in more than 90% of the periphery of the quantum dot QD in the cross-section of the light-emitting layer 4 passing through the quantum dot QD, the quantum dot QD may be considered to be covered by the adduct AD, regardless of whether the adduct AD is in contact with the surface of the quantum dot QD or whether the adduct AD and the quantum dot QD are joined via an organic ligand OL.

[0026] As shown in Figure 5, when the matrix MR as an adduct is formed to fill the space between at least two quantum dots QD, the matrix MR as an adduct has a thickness of 1000 nm in a direction perpendicular to the film thickness direction at any position in the film thickness direction of the light-emitting layer 4. ２It may be formed as a continuous film having the above area. In addition, in the light-emitting layer 4, the quantum dots QD may be embedded in a continuous film of matrix MR as an adduct. For example, if 60% or more of the surface of 80% or more of the quantum dots QD constituting the light-emitting layer 4 is in contact with a continuous film of matrix MR as an adduct, the quantum dots QD included in the light-emitting layer 4 may be considered to be embedded in the matrix MR as an adduct. Furthermore, the statement that the matrix MR as an adduct fills the space between at least two quantum dots QD does not mean that the space between the two quantum dots QD consists solely of the matrix MR as an adduct. Between the two quantum dots QD, in addition to the matrix MR as an adduct, a material such as a ligand different from the matrix MR as an adduct may be included. The material such as a ligand may be an organic ligand that coordinates to the quantum dots QD, or it may be an organic ligand that is separated from the quantum dots QD. When the light-emitting layer 4 contains an organic ligand, for example, the weight ratio of the organic ligand to the total weight of the light-emitting layer 4 may be less than 5%. The weight ratio of the organic ligand can be measured, for example, using TOF-SIMS (time-of-flight secondary ion mass spectrometry). If the organic ligand is dispersed in the light-emitting layer 4, it may contribute to the injection of holes and electrons into the quantum dot.

[0027] As shown in Figures 3, 4, and 5, in the formation of the light-emitting layer 4 containing quantum dots QD, first, a quantum dot dispersion is prepared. The quantum dot dispersion is a dispersion in which quantum dots QD and a precursor of adduct AD or a precursor of matrix MR as an adduct are dispersed in a solvent. The precursor includes a material that is converted to adduct AD or matrix MR as an adduct through hydrolysis and dehydration condensation by performing a specific operation such as heating or light irradiation. The precursor may have a coordinating functional group that forms a coordination bond with the surface of the quantum dots QD in the quantum dot dispersion. In this case, the precursor may coordinate to the quantum dots QD in the quantum dot dispersion. The quantum dot dispersion may also contain a halide having a halogen atom (for example, zinc chloride (ZnCl)). ２It may contain )). By mixing a material having a halogen atom in the quantum dot dispersion liquid, the halogen atom covers the surface of the quantum dot QD independently of the adduct AD or the matrix MR as an adduct, and thus the defects on the surface of the quantum dot QD can be reduced. Therefore, since the adduct AD or the matrix MR as an adduct has a halogen atom, each light-emitting element can increase the coverage rate of the quantum dot QD in the light-emitting layer 4 and further improve the light-emitting characteristics.

[0028] The quantum dot dispersion liquid may be prepared, for example, by preparing a mixed liquid obtained by stirring a dispersion liquid in which the quantum dot QD is dispersed and a dispersion liquid in which the precursor is dispersed, and extracting a predetermined layer of the mixed liquid. Here, the dispersion liquid in which the quantum dot QD is dispersed may have an organic ligand coordinated to the quantum dot QD. In this case, for example, in the stirring for preparing the above mixed liquid, the ligand coordinated to the quantum dot QD may be substituted with a part of a precursor such as 3-(mercaptoethyl)trimethoxysilane (MPS) from the organic ligand.

[0029] For example, when the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor has a coordinating functional group, the precursor may contain 3-(mercaptoethyl)trimethoxysilane (MPS). Also, when the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor does not have a coordinating functional group, the precursor may contain tetramethyl orthosilicate (TMOS). Further, for example, when the adduct AD or the matrix MR as an adduct contains zinc sulfide, the precursor may contain zinc xanthate, zinc thiourea acid, zinc dithiocarboxylic acid, and the like.

[0030] Next, the quantum dot dispersion is applied to the lower layer of the light-emitting layer 4 to convert the precursor into an adduct AD or a matrix MR as an adduct. The conversion of the precursor into an adduct AD or a matrix MR as an adduct is carried out by, for example, heating the applied quantum dot dispersion to volatilize the solvent and convert the precursor into an adduct AD or a matrix MR as an adduct. For example, if the precursor contains tetramethyl orthosilicate (TMOS) and 3-(mercaptopropyl)trimethoxysilane (MPS), dehydration condensation occurs between TMOS molecules, between MPS molecules, and between TMOS and MPS molecules, etc., to form silicon oxide as an adduct AD or a matrix MR as an adduct. Alternatively, for example, if the precursor contains zinc xanthogenic acid, the zinc xanthogenic acid is decomposed to form zinc sulfide as an adduct AD or a matrix MR as an adduct. The conversion of the precursor into an adduct AD or a matrix MR as an adduct occurs sequentially around the quantum dots QD of the quantum dot dispersion. By this method, a light-emitting layer 4 having an adduct AD or a matrix MR as an adduct can be formed.

[0031] The light-emitting layer 4 may be a light-emitting layer containing quantum dots (QD), or it may be a light-emitting layer containing an organic light-emitting material. The organic light-emitting material can be formed, for example, by a vapor deposition method. In this embodiment, the case in which a light-emitting layer containing quantum dots (QD) is used as the light-emitting layer 4 will be described as an example, but the embodiment is not limited to this.

[0032] The hole functional layer 3 is a layer that includes at least a hole transport layer (HTL), and may consist only of a hole transport layer (HTL), or it may be a layer in which a hole injection layer (HIL) and a hole transport layer (HTL) are stacked in that order from the anode 2 side. Details of the hole functional layer 3 will be described later.

[0033] In the light-emitting element 10 shown in Figure 2, the anode 2 is provided as a lower layer to the cathode 6, and the light-emitting layer 4 is provided on the hole functional layer 3. Furthermore, although the case in which the light-emitting layer 4 is in contact with the hole functional layer 3 is given as one example, the explanation is not limited to this case.

[0034] Figure 6 illustrates the problems of a light-emitting element equipped with a hole functional layer 3', which is a comparative example that does not contain a dopant.

[0035] In light-emitting elements such as QLEDs or OLEDs, an electron transport layer (ETL) composed of ZnO or ZnO nanoparticles and a hole transport layer (HTL) composed of organic materials are often used in combination. In such cases, the carrier balance of the light-emitting element becomes electron-heavy, i.e., hole-deficient, leading to a decrease in luminous efficiency (EQE), and it is known that the luminous efficiency (EQE) tends to decrease particularly in the high-voltage region. One reason why the carrier balance of the light-emitting element tends to become electron-heavy, i.e., hole-deficient, is that, as shown in Figure 6, the hole functional layer 3', which is a comparative example that does not contain a dopant, has a low carrier density of holes h, and when voltage is applied, the holes h supplied from the anode 2 to the hole functional layer 3' are supplied to the light-emitting layer 4 by hopping conduction. Note that the hole functional layer 3', which is a comparative example, differs from the hole functional layer 3 described later only in that it does not contain the ionic liquid 11.

[0036] As mentioned above, to prevent the carrier balance of the light-emitting element from becoming electron-heavy, i.e., hole-deficient, due to hopping conduction of holes h in the hole functional layer 3', dopants may be added. Such dopants include low-molecular-weight neutral dopants, such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F). ４ Examples include TCNQ and tris(pentafluorophenyl)borane (BCF). When such dopants are added, the dopant extracts electrons from the hole functional layer, making a portion of the hole functional layer a radical cation state, i.e., a state where cations are originally present. This improves the hole carrier density in the hole functional layer, thereby greatly improving the transport capacity of holes h.

[0037] However, the aforementioned low-molecular-weight neutral dopants have the problem of readily dissolving in low-polarity solvents with a dielectric constant of less than 5 (e.g., octane, toluene, etc.) and medium-polarity solvents with a dielectric constant of 5 or more but less than 30 (e.g., acetone, ethanol, PGME, etc.). Solvents with a dielectric constant of 30 or more are classified as high-polarity solvents; for example, DMF is a high-polarity solvent.

[0038] For example, in the process of forming a light-emitting layer containing quantum dots (QDs) which follows the process of forming a hole functional layer, low-polarity solvents such as octane are commonly used. In the process of patterning the light-emitting layer containing quantum dots (QDs) which follows the process of forming the hole functional layer, low-polarity solvents such as toluene or medium-polarity solvents such as PGME are commonly used. Therefore, when the aforementioned low-molecular-weight neutral dopants are added, a problem arises in the process of forming the light-emitting layer containing quantum dots (QDs) and the process of patterning the light-emitting layer: the low-molecular-weight neutral dopants dissolve and elute. In addition, the aforementioned low-molecular-weight neutral dopants tend to form aggregates (organic crystals) on their own, which can lead to problems such as the inability to uniformly disperse the dopants and the deterioration of the morphology of the film containing the low-molecular-weight neutral dopants.

[0039] Therefore, the hole functional layer 3 provided in the light-emitting element 10 shown in Figure 2 contains an ionic liquid 11 instead of the low-molecular-weight neutral dopant described above. Since the ionic liquid 11 contains cations, it can improve the hole carrier density in the hole functional layer 3 and greatly improve the hole h transport capacity. In addition, since the ionic liquid 11 contains cations and anions, it is highly polar, poorly soluble in low-polarity or medium-polarity solvents, and difficult to elute. Furthermore, since the ionic liquid 11 is originally a liquid, it is less likely to form aggregates, and problems such as inability to uniformly disperse or deterioration of the film morphology, as seen when using the low-molecular-weight neutral dopant described above, are less likely to occur.

[0040] Figure 7 is a diagram illustrating the reason why hole transport is improved and carrier balance is improved in the light-emitting element 10 shown in Figure 2. Figure 8 is a diagram showing an example of the ionic liquid 11 contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2. Figure 9 is a diagram showing an example of the cations of the ionic liquid 11 that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2. Figure 10 is a diagram showing an example of the anions of the ionic liquid 11 that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2. Figure 11 is a diagram showing the schematic configuration of a plurality of polymers 22P having a crosslinking portion 23 and a hole-transporting molecular structure 22U contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2.

[0041] As shown in Figure 7, the hole functional layer 3 is a mixture 21 of a plurality of polymers 22P (shown in Figure 11) containing a hole-transporting molecular structure 22U, an ionic liquid 11, and crosslinking portions 23 (shown in Figure 11) that connect the plurality of polymers 22P. In the mixture 21 shown in Figure 11, the ionic liquid 11 is supported by the plurality of polymers 22P, so the problem of the ionic liquid 11 eluting into the solvent is unlikely to occur, and the ionic liquid 11 is not shown in Figure 11. Here, "supported" refers to the ionic liquid 11, which is a liquid, being immobilized by the plurality of polymers 22P and losing its fluidity, and the ionic liquid 11 integrates with the plurality of polymers 22P, which are hole-transporting polymers, to form the hole functional layer 3. Whether the plurality of polymers 22P contain the ionic liquid 11, that is, whether the plurality of polymers 22P support the ionic liquid 11, can be confirmed, for example, from the results of mass spectrometry or FTIR analysis. Furthermore, whether the hole functional layer 3, which is the mixture 21, contains crosslinking portions 23 that connect multiple polymers 22P can be confirmed, for example, from the results of FTIR analysis or the degree of poor solubility of the hole functional layer 3.

[0042] The hole functional layer 3, which is a mixture 21 of multiple polymers 22P (shown in Figure 11) supporting an ionic liquid 11 and crosslinking portions 23 (shown in Figure 11) connecting the multiple polymers 22P, has a high carrier density of holes h, as shown in Figure 7, and a high transport capacity for holes h supplied from the anode 2 to the hole functional layer 3 when a voltage is applied. The ionic liquid 11 refers to a salt composed of cations and anions with a melting point of 100°C or lower.

[0043] In this embodiment, as shown in Figure 8, we will describe an example in which an ionic liquid 11 containing 1-methyl-3-butyl imidazolium as cation 12 and Bis(trifluoromethanesulfonyl)imide as anion 13 is used, but we are not limited to this. The ionic liquid 11 may contain, for example, one or more selected from cation 12a having an imidazolium salt structure, cation 12b having a pyrrolidinium salt structure, cation 12c having a pyridinium salt structure, cation 12d having a piperidinium salt structure, cation 12e having an ammonium salt structure, and cation 12f having a phosphonium salt structure, as shown in Figure 9. １ , R ２ , R ３ and R ４ Each of these alkyl groups may be the same or different. The ionic liquid 11 may contain, for example, one or more selected from the following as shown in Figure 10: chloride ion (anion 13a), bromide ion (anion 13b), iodide ion (anion 13c), tetrafluoroborate (anion 13d), hexafluorophosphate (anion 13e), and bis(fluorosulfonyl)imide (anion 13f).

[0044] As shown in Figure 8, the ionic liquid 11 is composed of a cation 12 and anion 13, and the cation 12 and anion 13 are preferably present in an amount of 0.1% to 10% by weight of the plurality of polymers 22P contained in the hole functional layer 3, that is, the plurality of polymers 22P that do not support the ionic liquid 11, and more preferably in an amount of 1% to 5% by weight.

[0045] Figure 12 shows an example of a polymer that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2.

[0046] As shown in Figure 12, in the aggregate of multiple polymers 21a, each polymer (second polymer) may, for example, contain a triphenylamine structure as the hole-transporting molecular structure 22U, but is not limited to this. Each polymer (second polymer) in the aggregate of multiple polymers 21a may contain, for example, a phenylamine structure, a carbazole structure, or an acridine structure as the hole-transporting molecular structure 22U. Furthermore, the crosslinking portion 23 that connects the multiple polymers (second polymers) in the aggregate of multiple polymers 21a may be formed by bonding functional groups contained in each of the multiple polymers (second polymers) that initiate a reaction by heating and / or light irradiation, but here, as an example, the crosslinking portion 23 may be formed by bonding azide groups, which are groups that initiate a reaction by light irradiation, but is not limited to this. Note that light irradiation means, for example, irradiation with light in the ultraviolet region, for example, light having a peak wavelength of 365 nm.

[0047] Figure 13 shows another example of a polymer that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2.

[0048] As shown in Figure 13, in the aggregate of multiple polymers 21b, each polymer (second polymer) may, for example, contain a triphenylamine structure as the hole-transporting molecular structure 22U, but is not limited to this. Each polymer (second polymer) in the aggregate of multiple polymers 21b may contain, for example, a phenylamine structure, a carbazole structure, or an acridine structure as the hole-transporting molecular structure 22U. Furthermore, the crosslinking portion 23 that connects the multiple polymers (second polymers) in the aggregate of multiple polymers 21b may be formed by bonding functional groups contained in each of the multiple polymers (second polymers) that initiate a reaction by heating and / or light irradiation, but here, as an example, the crosslinking portion 23 may be formed by bonding vinyl groups, which initiate a reaction by heating, but is not limited to this. Note that heating means, for example, heat treatment at a temperature of 100°C or higher and 300°C or lower.

[0049] Figure 14 shows yet another example of a polymer that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2. Figure 15 is a diagram illustrating the polymer formation process shown in Figure 14.

[0050] As shown in Figure 14, in the aggregate of multiple polymers 21c, each polymer may, for example, contain a triphenylamine structure as the hole-transporting molecular structure 22U, but this is not the only example. Each polymer in the aggregate of multiple polymers 21c may contain, for example, a phenylamine structure, a carbazole structure, or an acridine structure as the hole-transporting molecular structure 22U. Furthermore, the crosslinking portion 23 that connects the multiple polymers in the aggregate of multiple polymers 21c is formed by a radical-generating crosslinking agent and hydrocarbon groups contained in each of the multiple polymers. The radical-generating crosslinking agent may be a benzophenone dimer (BPO).

[0051] As shown in Figures 14 and 15, each of the multiple polymers in the aggregate 21c of multiple polymers is poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) containing hydrocarbon groups. Therefore, when radicals are generated in the benzophenone dimer (BPO), which is a radical-generating crosslinking agent, by performing at least one of exposure and heat treatment, radicals are also generated in the hydrocarbon groups of the TFB. Furthermore, when at least one of exposure and heat treatment is performed, a crosslinked portion 23 is formed by the benzophenone dimer (BPO), which is a radical-generating crosslinking agent, and the hydrocarbon groups contained in each of the multiple polymers. Note that exposure has the same meaning as light irradiation described above, for example, it means irradiation with light in the ultraviolet region, for example, light having a peak wavelength of 365 nm. Similarly, heat treatment has the same meaning as heating described above, for example, it means heat treatment at a temperature of 100°C or higher and 300°C or lower.

[0052] Figures 16 and 17 show yet another example of a polymer that can be contained in the hole functional layer 3 of the light-emitting element 10 shown in Figure 2.

[0053] As shown in Figures 16 and 17, the hole functional layer 3 further includes poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) as a polymer (first polymer) that does not contain a functional group whose reaction is initiated by heating and / or light irradiation, along with a plurality of polymers (second polymer) containing a crosslinked portion 23. Here, the plurality of polymers (second polymer) containing a crosslinked portion 23 are formed by bonding monomers, each containing two or more functional groups whose reaction is initiated by heating and / or light irradiation, and a hole-transporting molecular structure. Examples of such monomers include CBP-V (9,9'-([1,1'-Biphenyl]-4,4'-diyl)bis(3-ethenyl-9H-carbazole)), which contains two vinyl groups as functional groups as shown in Figure 16 and a carbazole structure as a hole-transporting molecular structure, or FLTA-V (4,4'-(9,9-dimethyl-9H-fluorene-2,7-diyl)bis(N-phenyl-N-(4-vinylphenyl)aniline)), which contains two vinyl groups as functional groups as shown in Figure 17 and a triphenylamine structure as a hole-transporting molecular structure.

[0054] As shown in Figure 16, after heating and / or light irradiation, the multiple polymers (second polymers) including the crosslinked portion 23 form an interpenetrating polymer network structure and have an interpenetrating polymer network structure. Therefore, the aggregate 21d of multiple polymers contained in the hole functional layer 3 includes multiple polymers (second polymers) including the crosslinked portion 23 formed by the bonding of functional groups of CBP-V, and TFB, which is a polymer (first polymer) that contains a hole-transporting molecular structure and does not contain functional groups that initiate a reaction upon heating and / or light irradiation. Furthermore, in the aggregate 21d of multiple polymers contained in the hole functional layer 3, the multiple polymers (second polymer) containing crosslinked portions 23 formed by the bonding of functional groups of CBP-V, and the TFB, which is a polymer (first polymer) containing a hole-transporting molecular structure and not containing functional groups that initiate a reaction upon at least one of heating and light irradiation, form an interpenetrating polymer network structure. Ionic liquid 11 is supported on each of the multiple polymers (second polymer) containing the crosslinked portions 23 that form the interpenetrating polymer network structure and the polymer (first polymer) containing a hole-transporting molecular structure and not containing functional groups that initiate a reaction upon at least one of heating and light irradiation. Although not shown in the figures, by further heating and light irradiation, the degree of crosslinking of the aggregate 21d of multiple polymers contained in the hole functional layer 3 can be improved, and an even more shrunk aggregate of multiple polymers can be realized.

[0055] As shown in Figure 17, after heating and light irradiation, the aggregate 21e of multiple polymers contained in the hole functional layer 3 includes multiple polymers (second polymer) that include crosslinked portions 23 formed by the bonding of FLTA-V functional groups, and TFB, which is a polymer (first polymer) that contains a hole-transporting molecular structure and does not contain functional groups that initiate a reaction upon heating and light irradiation. In the aggregate 21e of multiple polymers contained in the hole functional layer 3, the multiple polymers (second polymer) containing crosslinked portions 23 formed by the bonding of FLTA-V functional groups, and the TFB, which is a polymer (first polymer) containing a hole-transporting molecular structure and not containing functional groups that initiate a reaction upon at least one of heating and light irradiation, form an interpenetrating polymer network structure. Ionic liquid 11 is supported on each of the multiple polymers (second polymer) containing the crosslinked portions 23 that form the interpenetrating polymer network structure and the polymer (first polymer) containing a hole-transporting molecular structure and not containing functional groups that initiate a reaction upon at least one of heating and light irradiation. As shown in Figure 17, by further heating and light irradiation, the degree of crosslinking of the aggregate 21e of multiple polymers contained in the hole functional layer 3 can be improved, and a further shrunk aggregate 21e' of multiple polymers can be realized.

[0056] As described above, the hole functional layer 3, which is a mixture 21 of a plurality of polymers 22P containing a hole-transporting molecular structure 22U, an ionic liquid 11, and crosslinking portions 23 connecting the plurality of polymers 22P, is insoluble in any of the low-polarity solvents, medium-polarity solvents, and high-polarity solvents mentioned above. Similarly, the hole functional layer 3, which is a mixture 21 of a plurality of polymer aggregates 21a, 21b, 21c, 21d, 21e, and 21e' containing the crosslinking portions 23 and the ionic liquid 11, is also insoluble in any of the low-polarity solvents, medium-polarity solvents, and high-polarity solvents mentioned above.

[0057] In this embodiment, the case in which the hole functional layer 3 is composed only of a hole transport layer (HTL) has been described as an example, but the invention is not limited to this, and the hole functional layer 3 may be a layer in which a hole injection layer (HIL) and a hole transport layer (HTL) are laminated in this order from the anode 2 side. As for the material used for the hole injection layer (HIL), for example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS) can be used.

[0058] Figure 18 shows the change in absorbance of a hole functional layer 103, a comparative example comprising a plurality of polymers containing a hole-transporting molecular structure 22U and without a crosslinking portion 23, and an ionic liquid 11, before and after rinsing with chlorobenzene. Figure 19 shows the change in absorbance of a hole functional layer 3 provided in the light-emitting element 10 shown in Figure 2, before and after rinsing with chlorobenzene. Here, the hole functional layer 3 comprises an ionic liquid 11 and an aggregate 21b of a plurality of polymers shown in Figure 13, and each polymer contains a fluorene unit in its main chain, a triphenylamine structure as a hole-transporting molecular structure 22U, and a vinyl group, which is a group whose reaction is initiated by heating.

[0059] As shown in Figure 18, the absorbance of the comparative example, hole functional layer 103, after rinsing with chlorobenzene, a low-polarity solvent, decreased significantly compared to the absorbance before rinsing. This is because the film thickness of the comparative example, hole functional layer 103, became thinner, resulting in a decrease in absorbance.

[0060] On the other hand, as shown in Figure 19, the absorbance of the hole functional layer 3 provided in the light-emitting element 10 shown in Figure 2 after rinsing with chlorobenzene, a low-polarity solvent, shows almost no change compared to the absorbance before rinsing. This is because, in the case of the hole functional layer 3 provided in the light-emitting element 10 shown in Figure 2, there is almost no change in film thickness before and after rinsing, and therefore no change in the degree of light absorption.

[0061] For the comparative examples, hole functional layer 103 and hole functional layer 3 were obtained by forming an 8 mg / ml mixed solution of multiple polymers, ionic liquid 11, and solvent on a glass substrate using a spin coating method, and then heat-treating it at 200°C. After measuring the absorbance, the glass substrates with the hole functional layers were immersed (dipped) in chlorobenzene for 5 minutes, dried, and then the absorbance was measured again.

[0062] As shown in Figure 19, if the absorbance at the wavelength showing the maximum absorbance of the hole functional layer 3 before rinsing with the solvent is defined as the first absorbance, and the absorbance at the wavelength showing the maximum absorbance of the hole functional layer 3 after rinsing with the solvent is defined as the second absorbance, then (the second absorbance / the first absorbance) × 100% is preferably 80% or more.

[0063] The manufacturing method for the light-emitting element 10 shown in Figure 2 includes the steps of forming an anode 2, forming a cathode 6, forming a light-emitting layer 4 between the steps of forming the anode 2 and the cathode 6, and forming a hole functional layer 3 between the steps of forming the anode 2 and the light-emitting layer 4. The step of forming the hole functional layer 3 may include the steps of applying a solution containing a plurality of polymers including a functional group whose reaction is initiated by heating and light irradiation and a hole-transporting molecular structure 22U, and an ionic liquid 11, and performing at least one of a heat treatment and a light irradiation treatment to react the functional group, or the step of forming the hole functional layer 3 may include the steps of applying a solution containing a polymer including a hole-transporting molecular structure 22U and not including a functional group whose reaction is initiated by heating and light irradiation, a plurality of monomers including two or more functional groups whose reaction is initiated by heating and light irradiation and a hole-transporting molecular structure 22U, and an ionic liquid, and performing at least one of a heat treatment and a light irradiation treatment to react the functional group.

[0064] Furthermore, the step of forming the anode 2 is performed before the step of forming the cathode 6, and the step of forming the light-emitting layer 4 is performed immediately after the step of forming the hole functional layer 3. In the step of forming the light-emitting layer 4, the light-emitting layer 4 may be formed using a quantum dot dispersion in which quantum dots are dispersed in a low-polarity solvent or a medium-polarity solvent.

[0065] As described above, it is possible to realize a light-emitting element 10 equipped with a hole functional layer 3 that uniformly improves hole transportability within the layer, a method for manufacturing the light-emitting element 10, and a display device 1 equipped with the light-emitting element 10.

[0066] [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.

[0067] This disclosure can be used for light-emitting elements, display devices, and methods for manufacturing light-emitting elements.

[0068] 1 Display device 2 Anode 3 Hole functional layer 4 Light-emitting layer 5 Electronic functional layer 6 Cathode 10 Light-emitting element 11 Ionic liquid 12, 12a-12f Cations 13, 13a-13f Anions 21 Mixture 21a-21e, 21e' Aggregate of multiple polymers 22U Hole-transporting molecular structure 22P Polymer 23 Crosslinking part QD Quantum dot QDC Core QDS Shell AD Adduct MR Matrix OL Organic ligand h Hole RSP Red subpixel GSP Green subpixel BSP Blue subpixel PIX Pixel DA Display area NDA Frame 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-functional layer provided between the anode and the light-emitting layer, wherein the hole-functional layer is a mixture of a plurality of polymers containing a hole-transporting molecular structure, an ionic liquid, and crosslinking portions connecting the plurality of polymers.

2. The light-emitting element according to claim 1, wherein the plurality of polymers include a first polymer that does not contain functional groups that initiate a reaction upon heating and / or light irradiation.

3. The light-emitting element according to claim 1 or 2, wherein the anode is provided as a lower layer to the cathode, and the light-emitting layer is provided on the hole functional layer.

4. The light-emitting element according to claim 3, wherein the light-emitting layer is in contact with the hole functional layer.

5. The light-emitting element according to any one of claims 1 to 4, wherein the light-emitting layer includes quantum dots.

6. The light-emitting element according to any one of claims 1 to 5, wherein the plurality of polymers comprises a plurality of second polymers containing functional groups that initiate a reaction upon heating and / or light irradiation, and the crosslinked portion is formed by bonding the functional groups contained in each of the plurality of second polymers together.

7. The light-emitting element according to any one of claims 1 to 5, wherein the mixture comprises the plurality of polymers and the crosslinking portion, and the plurality of second polymers comprising the crosslinking portion are formed by bonding monomers, each having two or more functional groups that initiate a reaction by heating and / or light irradiation, and the hole-transporting molecular structure.

8. The light-emitting element according to claim 7, wherein the plurality of second polymers including the crosslinked portion form an interpenetrating polymer network structure.

9. The light-emitting element according to claim 7, wherein the plurality of second polymers including the crosslinked portion and the first polymer that does not contain a functional group and whose reaction is initiated by heating and / or light irradiation form an interpenetrating polymer network structure, and the ionic liquid is supported on each of the first polymer and the second polymer that form the interpenetrating polymer network structure.

10. The light-emitting element according to any one of claims 6 to 9, wherein the functional group contained in the second polymer is an azide group.

11. The light-emitting element according to any one of claims 6 to 9, wherein the functional group contained in the second polymer is a vinyl group.

12. The light-emitting element according to any one of claims 1 to 5, wherein the crosslinked portion is formed by a radical-generating crosslinking agent and hydrocarbon groups contained in each of the plurality of polymers.

13. The light-emitting element according to claim 12, wherein the radical-generating crosslinking agent is a benzophenone dimer.

14. The light-emitting element according to any one of claims 1 to 13, wherein the ionic liquid comprises one or more structures selected from imidazolium salt structure, pyrrolidinium salt structure, pyridinium salt structure, piperidinium salt structure, ammonium salt structure, and phosphonium salt structure.

15. The light-emitting element according to any one of claims 1 to 14, wherein the ionic liquid is composed of cations and anions, and the cations and anions are contained in an amount of 0.1% by weight or more and 10% by weight or less of the plurality of polymers.

16. The light-emitting element according to claim 15, wherein the cation and the anion are contained in an amount of 1% by weight or more and 5% by weight or less of the plurality of polymers.

17. The light-emitting element according to any one of claims 1 to 16, wherein the hole-transporting molecular structure is a triphenylamine structure.

18. The light-emitting element according to any one of claims 1 to 17, wherein the absorbance at the wavelength showing the maximum absorbance of the hole functional layer before rinsing with the solvent is defined as the first absorbance, and the absorbance at the wavelength showing the maximum absorbance of the hole functional layer after rinsing with the solvent is defined as the second absorbance, and (the second absorbance / the first absorbance) × 100% is 80% or more.

19. A display device comprising a light-emitting element according to any one of claims 1 to 18.

20. A method for manufacturing an luminescent element, comprising: a step of forming an anode; a step of forming a cathode; a step of forming a light-emitting layer performed between the step of forming the anode and the step of forming the cathode; and a step of forming a hole functional layer performed between the step of forming the anode and the step of forming the light-emitting layer, wherein the step of forming the hole functional layer comprises: a step of applying a solution containing a plurality of polymers including functional groups and hole-transporting molecular structures whose reaction is initiated by heating and light irradiation, and an ionic liquid; and a step of performing at least one of a heat treatment and a light irradiation treatment to react the functional groups.

21. A method for manufacturing a light-emitting element, comprising: a step of forming an anode; a step of forming a cathode; a step of forming a light-emitting layer performed between the step of forming the anode and the step of forming the cathode; and a step of forming a hole functional layer performed between the step of forming the anode and the step of forming the light-emitting layer, wherein the step of forming the hole functional layer comprises: a step of applying a solution containing a polymer that includes a hole-transporting molecular structure and does not contain functional groups that are initiated to react by at least one of heating and light irradiation; a plurality of monomers containing two or more functional groups that are initiated to react by at least one of heating and light irradiation and a hole-transporting molecular structure; and a step of performing at least one of a heat treatment and a light irradiation treatment to react the functional groups.

22. The method for manufacturing an luminescent element according to claim 20 or 21, wherein the step of forming the anode is performed before the step of forming the cathode, the step of forming the light-emitting layer is performed immediately after the step of forming the hole functional layer, and in the step of forming the light-emitting layer, the light-emitting layer is formed using a quantum dot dispersion in which quantum dots are dispersed in a low-polarity solvent or a medium-polarity solvent.

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