Light-emitting element

Abstract

The light-emitting layer (3) of the light-emitting element includes: quantum dots (31); a plurality of first ligands (32) having a first functional group (34) and a positively charged portion (35); a plurality of second ligands (33) having a second functional group (41) and a negatively charged portion (42); and an ionic liquid (34) for dispersing the quantum dots (31).

Description

Technical Field

[0001] The present invention relates to a light-emitting element having a light-emitting layer in which quantum dots are dispersed in a liquid, and a method for manufacturing the light-emitting element. Background Art

[0002] There has been proposed an organic EL (Electro-Luminescence) element (OLED (Organic Light Emitting Diode)) having a liquid light-emitting layer. Since the light-emitting layer of this OLED is liquid, it is difficult to cause peeling between the light-emitting layer and the carrier injection layer even when the organic EL element is bent, and thus it is expected to be suitable for a flexible display.

[0003] In the liquid (medium) of this light-emitting layer, a molten salt called an ionic liquid that melts at room temperature is often used. This molten salt has an extremely low vapor pressure and does not evaporate, and has conductivity through ionic conduction.

[0004] An organic electroluminescent element having a light-emitting layer containing this molten salt and a light-emitting substance is known (Patent Document 1).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Invention Specification "Patent No. 5441308 (registered on December 27, 2013)" Summary of the Invention

[0008] Technical Problem to be Solved by the Invention

[0009] However, when the above ionic liquid is to be applied to a QLED (Quantum dot Light Emitting Diode), since the size of the quantum dots is larger than the organic molecules of the ionic liquid, there is a problem that aggregation is likely to occur in the ionic liquid.

[0010] Solution to the Problem

[0011] The light-emitting element according to the present invention is a light-emitting element including an anode, a cathode, and a light-emitting layer provided between the anode and the cathode, the light-emitting layer including: quantum dots; a plurality of first ligands having a first functional group coordinated to the quantum dots and a positively charged portion; a plurality of second ligands having a second functional group coordinated to the quantum dots coordinated with the first ligands and a negatively charged portion; and a room-temperature molten salt that disperses the quantum dots.

[0012] The manufacturing method of the light-emitting element according to the present invention is a manufacturing method of a light-emitting element including a step of forming an anode, a step of forming a cathode, and a step of forming a light-emitting layer. The step of forming the light-emitting layer includes: a first step of forming a frame-shaped resin material on either the anode or the cathode; and a second step of forming the following structure inside the frame-shaped resin material: quantum dots; a plurality of first ligands having a first functional group coordinated to the quantum dots and a positively charged portion; a plurality of second ligands having a second functional group coordinated to the quantum dots coordinated with the first ligands and a negatively charged portion; and a liquid room-temperature molten salt in which the quantum dots are dispersed.

[0013] Another manufacturing method of the light-emitting element according to the present invention is a manufacturing method of a light-emitting element including a step of forming an anode, a step of forming a cathode, a step of bonding the anode and the cathode, and a step of forming a light-emitting layer. The step of bonding the anode and the cathode includes: a first step of forming a frame-shaped resin material on either the anode or the cathode, with the portion other than the liquid injection hole formed in a frame shape; and a second step of bonding the anode and the cathode via the resin material. The step of forming the light-emitting layer includes: a liquid injection step of injecting the following composition between the bonded anode and cathode through the liquid injection hole: quantum dots; a plurality of first ligands having a first functional group coordinated to the quantum dots and a positively charged portion; a plurality of second ligands having a second functional group coordinated to the quantum dots coordinated with the first ligands and a negatively charged portion; a room-temperature molten salt in which the quantum dots are dispersed; and a step of sealing the liquid injection hole after the liquid injection step.

[0014] Advantages of the Invention

[0015] According to one aspect of the present invention, a light-emitting element and a manufacturing method of a light-emitting element in which aggregation of quantum dots in an ionic liquid is difficult to occur can be realized. Description of the Drawings

[0016] Figure 1 is a cross-sectional view of the light-emitting element according to the first embodiment.

[0017] Figure 2 is along Figure 1 the cross-sectional view taken along the line AA shown.

[0018] Figure 3 is a conceptual diagram of the light-emitting layer provided in the above light-emitting element.

[0019] Figure 4 is a diagram showing the general formula of candidates for the first ligand provided in the above light-emitting layer.

[0020] Figure 5 is a diagram showing the general formula of another candidate for the first ligand.

[0021] Figure 6 It is a diagram showing the general formula of another candidate of the above-mentioned first ligand.

[0022] Figure 7 It is a diagram showing the general formula of another candidate of the above-mentioned first ligand.

[0023] Figure 8 It is a diagram showing the structure of the above-mentioned first ligand.

[0024] Figure 9 It is a diagram showing another structure of the above-mentioned first ligand.

[0025] Figure 10 It is a diagram showing the general formula of a candidate of the second ligand provided in the above-mentioned light-emitting layer.

[0026] Figure 11 It is a diagram showing another general formula of a candidate of the above-mentioned second ligand.

[0027] Figure 12 It is a diagram showing yet another general formula of a candidate of the above-mentioned second ligand.

[0028] Figure 13 It is a diagram showing the structure of the above-mentioned second ligand.

[0029] Figure 14 It is a diagram showing another structure of the above-mentioned second ligand.

[0030] Figure 15 It is a diagram for explaining ligand exchange.

[0031] Figure 16 It is a diagram for explaining ligand exchange.

[0032] Figure 17 It is a diagram for explaining ligand exchange.

[0033] Figure 18 It is a diagram for explaining ligand exchange.

[0034] Figure 19 It is a diagram for explaining graft modification.

[0035] Figure 20 It is a diagram for explaining graft modification.

[0036] Figure 21 It is a diagram for explaining graft modification.

[0037] Figure 22 It is a diagram for explaining graft modification.

[0038] Figure 23 It is a diagram for explaining graft modification.

[0039] Figure 24 This is a diagram for explaining graft modification.

[0040] Figure 25 This is a conceptual diagram of the light-emitting layer of a light-emitting element related to a comparative example.

[0041] Figure 26 This is a conceptual diagram of the light-emitting layer of a light-emitting element related to another comparative example.

[0042] Figure 27 This is a flowchart showing the manufacturing method of the light-emitting element related to the first embodiment.

[0043] Figure 28 This is a flowchart showing another manufacturing method of the above light-emitting element.

[0044] Figure 29 This is a cross-sectional view of the light-emitting element related to the second embodiment.

[0045] Figure 30 This is a conceptual diagram of quantum dots provided on the light-emitting layer of the light-emitting element related to the third embodiment.

[0046] Figure 31 This is a conceptual diagram of another quantum dot provided on the above light-emitting layer.

[0047] Figure 32 This is a conceptual diagram of yet another quantum dot provided on the above light-emitting layer.

[0048] Figure 33 This is a conceptual diagram of yet another quantum dot provided on the above light-emitting layer.

[0049] Figure 34 This is a conceptual diagram of yet another quantum dot provided on the above light-emitting layer.

[0050] Figure 35 This is a diagram showing the method of modifying the above quantum dots by ligand exchange.

[0051] Figure 36 This is a diagram showing the method of modifying the above quantum dots by graft modification.

[0052] Figure 37 This is a diagram showing another method of modifying the above quantum dots by graft modification.

[0053] Figure 38 This is a diagram showing another method of modifying the above quantum dots by graft modification.

[0054] Figure 39 This is a diagram showing another method of modifying the above quantum dots by graft modification.

[0055] Figure 40It is a diagram showing another method of modifying the above-mentioned quantum dots by graft modification.

[0056] Figure 41 It is a diagram for explaining an example of an ionic liquid.

[0057] Figure 42 It is a diagram for explaining another example of an ionic liquid.

[0058] Figure 43 It is a diagram for explaining yet another example of an ionic liquid. Detailed implementation mode

[0059] (First implementation mode)

[0060] Figure 1 It is a cross-sectional view of the light-emitting element 10A related to the first implementation mode. Figure 2 It is along Figure 1 The cross-sectional view taken along the line AA shown. Figure 3 It is a conceptual diagram of the light-emitting layer 3 provided in the light-emitting element 10A.

[0061] The light-emitting element 10A sequentially includes on a glass substrate 8: an anode 1 (anode) containing ITO (Indium Tin Oxide), a hole transportation layer (HTL) 2 containing PEDOT:PSS, a light-emitting layer 3, an electron transportation layer (ETL) 4 containing CsCO3, and a cathode 5 (cathode) containing ITO.

[0062] The light-emitting layer 3 contains an ionic liquid 47 (liquid room-temperature molten salt) and a spacer 7 (frame-shaped resin material) provided between the hole transportation layer 2 and the electron transportation layer 4 to seal the ionic liquid 47. The ionic liquid 47 in which quantum dots 31 are dispersed is sealed inside the spacer 7.

[0063] As the spacer 7, a sealing material used in this field such as a resin material can be used. The material of the spacer 7 is not particularly limited, and acrylic resin, epoxy resin, fluororesin, silicone resin, rubber resin, ester resin, etc. can be used. Among them, from the aspect of waterproof function, epoxy resin is preferred. Among the epoxy resins, thermosetting epoxy resin or photocuring epoxy resin is preferred.

[0064] The liquid injection hole 71 can be preset on a part of the spacer 7, and the ionic liquid 47 in which the quantum dots 31 are dispersed is injected. The liquid injection method of the ionic liquid 47 can use the same method as the liquid injection method of liquid crystal. In this way, the spacer 7 can also have the liquid injection hole 71 that is sealed after injecting the ionic liquid 47 in which the quantum dots 31 are dispersed. In addition, the liquid injection method of the ionic liquid 47 can also be that the liquid injection hole 71 is not preset on a part of the spacer 7, but the ionic liquid 47 is coated on the hole transport layer 2 by inkjet or the like, and then the electron transport layer 4 is laminated.

[0065] The wavelength conversion layer 63 that converts the light emitted from the light-emitting layer 3 into red light, the wavelength conversion layer 62 that converts the above light into green light, and the wavelength conversion layer 61 that converts the above light into blue light are provided on the cathode 5. A substrate 9 made of glass is provided on the wavelength conversion layers 61, 62, and 63.

[0066] The materials of the anode 1, the hole transport layer 2, the electron transport layer 4, and the cathode 5 can be selected from the conventionally known materials.

[0067] From the viewpoint of holding the ionic liquid 47, the hole transport layer 2 and the electron transport layer 4 preferably have small voids. Therefore, the hole transport layer 2 is preferably composed of a thin film of the material of the hole transport layer 2, and the electron transport layer 4 is preferably composed of a thin film of the material of the electron transport layer 4.

[0068] The light-emitting layer 3 includes a plurality of quantum dots 31, a plurality of first ligands 32 coordinated on each quantum dot 31, a plurality of second ligands 33 coordinated on the quantum dots 31 coordinated with a plurality of first ligands 32, and an ionic liquid 47 in which the quantum dots 31 are dispersed. The material of the quantum dots 31 is not particularly limited, and conventionally known materials can be appropriately used.

[0069] A part of the plurality of quantum dots 31 is a quantum dot that emits light in the red wavelength region (640 nm to 770 nm, hereinafter sometimes referred to as red light), another part of the plurality of quantum dots 31 is a quantum dot that emits light in the green wavelength region (490 nm to 550 nm, hereinafter sometimes referred to as green light), and still another part of the plurality of quantum dots 31 is a quantum dot that emits light in the blue wavelength region (430 nm to 490 nm, hereinafter sometimes referred to as blue light). The light emitted from the light-emitting layer 3 is preferably white light.

[0070] The ionic liquid 47 contains a molten salt. The molten salt refers to a salt that exhibits liquid characteristics at normal temperature. The molten salt is usually composed of an inorganic or organic cation and an inorganic or organic anion, and has a high evaporation temperature, high ionic conductivity, heat resistance, and flame retardancy.

[0071] For example, the molten salt can use a polymer compound represented by the following chemical formula 1.

[0072] [Chemical Formula 1]

[0073]

[0074] In the formula, X1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroalkylene group having 1 to 20 carbon atoms, or a substituted or unsubstituted heteroarylene group having 4 to 30 carbon atoms.

[0075] X2 - is a sulfonate anion or a carboxylate anion.

[0076] R3, R4, R5, and R6 are each independently a hydrogen atom, a halogen atom, a carboxyl group, an amino group, a nitro group, a cyano group, a hydroxyl group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted silicon-containing group having 1 to 20 carbon atoms, a substituted or unsubstituted fluorine-containing group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, or a substituted or unsubstituted heteroarylalkyl group having 3 to 30 carbon atoms.

[0077] n is an integer from 50 to 500.

[0078] The total content of the quantum dots for red light, the quantum dots for green light, and the quantum dots for blue light relative to the ionic liquid 47 is preferably 0.5% by weight to 10% by weight.

[0079] The ratio between the first ligand 32 and the second ligand 33 is preferably 35:65 to 65:35 as a theoretical value.

[0080] The thickness of the light-emitting layer 3 containing the ionic liquid 47 is preferably 50 nm or more and 1000 nm or less.

[0081] At least a positively charged first ligand 32 and at least a negatively charged second ligand 33 are coordinated on the quantum dots 31.

[0082] The light-emitting layer 3 may further contain a porous resin (such as an olefin resin) for holding the ionic liquid 47 containing a room-temperature molten salt.

[0083] Figure 4 It is a diagram showing a general formula that is a candidate for the first ligand 32 provided in the light-emitting layer 3. Figure 5 It is a diagram showing another general formula of the above candidate.Figure 6 and Figure 7 is a diagram showing another general formula of the above candidates. Figure 8 is a diagram showing the constitution of the first ligand 32. Figure 9 is a diagram showing another constitution of the first ligand 32.

[0084] The first ligand 32 is specifically selected from Figure 4 the general formula of the pyridinium group 37 shown, Figure 5 the general formula of the imidazolium group 38 shown, Figure 6 the general formula of the ammonium group 39 shown, and Figure 7 the general formula of the phosphonium group 40 shown. As Figures 4 to 7 shown, the candidate pyridinium group 37, imidazolium group 38, ammonium group 39, and phosphonium group 40 of the first ligand 32 have a positively charged part 35 containing a cation.

[0085] As Figure 8 and Figure 9 shown, the first ligand 32 has: a first functional group 34 coordinated to the quantum dot 31, a positively charged part 35, a first main chain 36 disposed between the first functional group 34 and the positively charged part 35 and composed of a saturated or unsaturated hydrocarbon having 3 to 20 carbon atoms, and an alkyl group 56. The part of the positively charged part 35 that is far from the quantum dot 31 can more effectively inhibit the aggregation between quantum dots 31. Therefore, the positively charged part 35 is included in the functional group (pyridinium group 37) bonded to the carbon 53 that is farthest from the carbon 52 bonded to the first functional group 34 in the first main chain 36.

[0086] In the general formula as Figures 4 to 7 shown, one of the plurality of Rs, as Figure 8 and Figure 9 shown, has a first functional group 34 coordinated to the quantum dot 31 at its end. Specifically, R has an alkyl chain having 2 to 20 carbon atoms and has a thiol group, a carboxyl group, an amino group, etc. at the end. The R that does not have a functional group is an alkyl group 56 having 1 to 5 carbon atoms or an H atom.

[0087] The ionic liquid 47 contains a counter anion for the cation shown in Figures 4 to 7 for the first ligand 32. This counter anion is, for example, selected from Li + , Na + , K + , Rb + , Cs + , etc.

[0088] Thus, when there is a distance of 5 or more carbon atoms via the first main chain 36 between the first functional group 34 contained in the first ligand 32 and the positively charged portion 35, the distance between the plurality of quantum dots 31 can be sufficiently maintained. Therefore, the dispersibility of the quantum dots 31 with respect to the ionic liquid 47 is further improved.

[0089] Figure 10 It is a diagram showing a general formula of a candidate for the second ligand 33 provided in the light-emitting layer 3. Figure 11 It is a diagram showing another general formula of the above candidate. Figure 12 It is a diagram showing still another general formula of the above candidate. Figure 13 It is a diagram showing the structure of the second ligand 33. Figure 14 It is a diagram showing another structure of the second ligand 33.

[0090] The second ligand 33 is specifically selected from Figure 10 the general formula of the carboxyl group 44 shown, Figure 11 the general formula of the sulfonate group 45 shown, and Figure 12 the general formula of the imide sulfonate group 46 shown. As Figures 10 to 12 shown, the carboxyl group 44, the sulfonate group 45, and the imide sulfonate group 46 of the candidate for the second ligand 33 have a negatively charged portion 42 containing an anion.

[0091] In Figures 10 to 12 the general formula shown, one of the Rs of the carboxyl group 44, the Rs of the sulfonate group 45, and the multiple Rs of the imide sulfonate group 46 is as Figure 13 and Figure 14 shown, and has a second functional group 41 coordinated to the quantum dot 31 at its end. Specifically, R has an alkyl chain with 2 to 20 carbon atoms and has a thiol group, a carboxyl group, an amino group, etc. at the end. R that does not have the second functional group 41 can be an alkyl group with 1 to 5 carbon atoms or an H atom.

[0092] The ionic liquid 47 includes a counter cation for the Figures 10 to 12 anion shown. This counter cation is selected from, for example, BF4 - , PF6 - , Cl - , Br - , I - etc.

[0093] As Figure 13As shown, the second ligand 33 has: a second functional group 41 coordinated to the quantum dots 31, a negatively charged portion 42, a second main chain 43 disposed between the second functional group 41 and the negatively charged portion 42 and composed of a saturated or unsaturated hydrocarbon having 3 to 20 carbon atoms, and an alkyl group 60. The portion of the negatively charged portion 42 that is farther from the quantum dots 31 can more effectively inhibit the direct aggregation of the quantum dots 31 with each other. Therefore, the negatively charged portion 42 is included in a functional group (imide sulfonate group 46) bonded to the carbon 55 that is farthest from the carbon 54 to which the second functional group 41 is bonded in the second main chain 43.

[0094] As Figure 14 shown, the second ligand 33 has a second functional group 41 coordinated to the quantum dots 31, a negatively charged portion 42, and a second main chain 43 disposed between the second functional group 41 and the negatively charged portion 42 and composed of a saturated or unsaturated hydrocarbon having 3 to 20 carbon atoms. The negatively charged portion 42 is included in a functional group (sulfonate group 45) bonded to the carbon 55 that is farthest from the carbon 54 to which the second functional group 41 is bonded in the second main chain 43.

[0095] In this way, when there is a distance of 3 or more carbon atoms via the second main chain 43 between the second functional group 41 and the negatively charged portion 42 included in the second ligand 33, the distance between multiple quantum dots 31 can be sufficiently maintained. Therefore, the dispersibility of the quantum dots 31 in the ionic liquid 47 is further improved.

[0096] In addition to the multiple quantum dots 31 coordinated by the first ligand 32 and the second ligand 33, multiple quantum dots 31 not coordinated by the first ligand 32 and the second ligand 33 can also be dispersed in the ionic liquid 47.

[0097] For the quantum dots 31 having multiple first ligands 32 and multiple second ligands 33, the closer the number of positively charged portions 35 is to the same number as the number of negatively charged portions 42, the more effectively the aggregation of the quantum dots 31 can be inhibited. Therefore, for the quantum dots 31 having multiple first ligands 32 and multiple second ligands 33, it is preferable that the number of positively charged portions 35 is in the range of 0.8 times or more and 1.2 times or less the number of negatively charged portions 42.

[0098] Figures 15 to 18 is a diagram for explaining ligand exchange. A nonpolar solvent 11 such as toluene or octane is separated from a polar solvent 12 such as water or acetonitrile. Then, as Figure 15As shown, quantum dots 31 with ligands 15 are dispersed in a non-polar solvent 11. In a polar solvent 12, a first ligand 32 containing a first functional group 34 and a positively charged portion 35 and a second ligand 33 containing a second functional group 41 and a negatively charged portion 42 are dispersed. Then, if the reaction is carried out while stirring at 0 °C to 100 °C for 1 hour to 1 day in a state where it is separated into two layers of a polar solvent 12 and a non-polar solvent 11, as Figure 16 shown, the quantum dots 31 move from the non-polar solvent 11 to the polar solvent 12 while exchanging the ligand 15 for the first ligand 32 and the second ligand 33. At this time, the first ligand 32 and the second ligand 33 contained in the polar solvent 12 preferably have a higher concentration than the ligand 15 contained in the non-polar solvent 11.

[0099] Next, as Figure 17 shown, when the polar solvent 12 is taken out, an ionic liquid 47 is mixed, and the polar solvent 12 is dried by heating or the like, as Figure 18 shown, quantum dots 31 having the first ligand 32, the second ligand 33, and the ligand 15 dispersed in the ionic liquid 47 are obtained.

[0100] The quantum dots 31 having the first ligand 32, the second ligand 33, and the ligand 15 can be coated on the light-emitting element 10A in a state where the polar solvent 12 and the ionic liquid 47 are mixed, and then the polar solvent 12 is dried and evaporated, or can be coated on the light-emitting element 10A after the polar solvent 12 mixed with the ionic liquid 47 is dried and evaporated.

[0101] Figures 19 to 24 is a diagram for explaining graft modification. If the ligand has, in addition to the functional group at the site bonded to the quantum dots 31, other functional groups including reactivity, then as Figure 16 described in, without exchanging the ligand, another functional group including an ionic group can be attached to the other functional group.

[0102] The quantum dots 31 include a graft-modified ligand 64. The graft-modified ligand 64 includes a functional group 65 disposed at the site bonded to the quantum dots 31, a functional group 66 disposed on the side opposite to the quantum dots 31, and a main chain 67 disposed between the functional groups 65 and 66.

[0103] At this time, if a thiol-ene reaction is used, no by-products are generated, so it is particularly preferred. First, quantum dots modified with a ligand having two thiol groups, vinyl, a molecule including a functional group having an ion, a radical generator such as a dihalogen or an azo compound, are mixed and dispersed in an amphiphilic solvent such as ethyl acetate. Then, when radicals are generated by light irradiation or heating, a functional group 72 having a positively charged portion 68 or a functional group 70 having a negatively charged portion 69 is attached to the functional group 66 at the end of the graft-modified ligand 64 of the quantum dots 31.

[0104] Next, an ionic liquid is mixed in a solvent, and a polar solvent is dried by heating or the like to obtain quantum dots having ionic functional groups dispersed in the ionic liquid.

[0105] It can be coated on the light-emitting element 10A in a state of being mixed with a polar solvent and then the polar solvent is dried and evaporated, or it can be coated on the light-emitting element 10A after the polar solvent mixed with the ionic liquid is dried and evaporated.

[0106] Figure 25 It is a conceptual diagram of the light-emitting layer provided in the light-emitting element related to the comparative example. Figure 25 It is a conceptual diagram of the light-emitting layer provided in the light-emitting element related to another comparative example.

[0107] As the ligand 98 of the quantum dot 31, a long-chain alkyl group with low polarity is usually used. In this way, even if the quantum dot 31 including the ligand 98 with low polarity is dispersed in the ionic liquid 47, as Figure 25 shown, due to the different polarities of the ionic liquid 47 of the solvent and the quantum dot 31, aggregation between the quantum dots 31 is likely to occur. In this way, if aggregation between the quantum dots 31 occurs, the problem of reduced luminous efficiency of the light-emitting layer occurs.

[0108] When only one polarity of electricity is carried in the ionic part of the ligand 97 provided for the quantum dot 31, for example, as Figure 26 shown, when only a positive charge is carried in the ionic part of the ligand 97, the dispersibility of the quantum dot 31 in the ionic liquid 47 is not a problem, but in the ionic liquid 47 of the light-emitting layer of the light-emitting element as an electroluminescent element, it is biased toward the anode 1 side or the cathode 5 side due to electrophoresis. Therefore, aggregation of the quantum dots 31 and the interaction between the anode 1 and the cathode 5 and the quantum dots 31 are likely to occur, and the problem of reduced luminous efficiency of the light-emitting layer occurs.

[0109] In contrast, in the light-emitting element 10A according to the first embodiment, the quantum dot 31 coordinated with the first ligand 32 including the positively charged positive charge part 35 and the second ligand 33 including the negatively charged negative charge part 42 is dispersed in the ionic liquid 47. Since the ionic liquid 47 has conductivity, the dispersibility of the quantum dot 31 coordinated with the first ligand 32 including the positively charged positive charge part 35 and the second ligand 33 including the negatively charged negative charge part 42 is improved. And the shift of the quantum dot 31 toward the anode 1 side or the cathode 5 side caused by electrophoresis is suppressed. As a result, aggregation of the quantum dots 31 is difficult to occur even over time, so the luminous efficiency of the light-emitting layer 3 is difficult to decrease, and the problems of the Figure 25 , Figure 26 comparative example are solved.

[0110] Figure 27 This is a flowchart showing the manufacturing method of the light-emitting element 10A according to the first embodiment. First, an anode 1 of a transparent electrode is formed on a substrate 8 (step S1). Then, a hole transport layer 2 is laminated on the anode 1 (step S2). Next, a spacer 7 containing an ultraviolet curable resin is formed on the hole transport layer 2 by photolithography or the like (step S3).

[0111] In addition, the ligand 15 of the quantum dot 31 is pre-modified by graft modification of ionic functional groups, for example (step S5). Then, the quantum dot 31 with the modified ligand 15 is dispersed in an ionic liquid 47 (step S6).

[0112] Next, the quantum dot 31 with the modified ligand 15 is coated on the hole transport layer 2 on which the spacer 7 is formed (step S4).

[0113] In addition, a cathode 5 of a transparent electrode is pre-formed (step S7). Then, an electron transport layer 4 is laminated on the cathode 5 (step S8).

[0114] After that, the anode 1 and the cathode 5 are bonded together with the hole transport layer 2 and the electron transport layer 4 facing each other (step S9).

[0115] The hole transport layer 2 and the electron transport layer 4 can be formed by existing well-known methods.

[0116] In addition, a light-emitting layer 3 can be formed by laminating a porous resin (polyolefin) on the hole transport layer 2 and impregnating the ionic liquid 47.

[0117] Figure 28 This is a flowchart showing another manufacturing method of the light-emitting element 10A. The same reference numerals are assigned to the same components as those described above, and their detailed descriptions are not repeated.

[0118] First, an anode 1 of a transparent electrode is formed on a substrate 8 (step S1). Then, a spacer 7 having an injection hole 71 is formed on the anode 1 of the transparent electrode (step S10).

[0119] In addition, a cathode 5 of a transparent electrode is pre-formed (step S7). Then, the anode 1 on which the cathode 5 and the spacer 7 having the injection hole 71 are formed is bonded (step S11).

[0120] In addition, the ligand 15 of the quantum dot 31 is pre-modified by graft modification of ionic functional groups, for example (step S5). Then, the quantum dot 31 with the modified ligand 15 is dispersed in an ionic liquid 47 (step S6).

[0121] Next, the ionic liquid 47 in which the modified quantum dots 31 of the ligand 15 are dispersed is injected through the liquid injection hole 71 formed in the spacer 7 (step S12). Then, after spin coating and baking treatment at 100 °C for 1 hour, the solvent is completely removed in a vacuum oven to form a light-emitting layer with a thickness of 80 nm. After that, the liquid injection hole 71 is sealed (step S13).

[0122] In addition, a hole transport layer 2 can be laminated on the anode 1, and a spacer 7 having a liquid injection hole 71 can be formed on the hole transport layer 2.

[0123] (Second Embodiment)

[0124] Figure 29 It is a cross-sectional view of the light-emitting element 10C according to the second embodiment. The same reference numerals are assigned to the same components as those described above, and the detailed description thereof will not be repeated.

[0125] The light-emitting element 10C is provided with quantum dots 31R, 31G, and 31B for each of a red light-emitting layer 3R that emits red light, a green light-emitting layer 3G that emits green light, and a blue light-emitting layer 3B that emits blue light. And the ionic liquids 47 containing the quantum dots 31R, 31G, and 31B of each color are separated from each other by the spacer 7.

[0126] The light-emitting element 10C includes a glass substrate 8. Anodes 1R corresponding to red light, 1G corresponding to green light, and 1B corresponding to blue light are formed on the substrate 8. A hole transport layer 2C containing PEDOT:PSS is formed on the substrate 8 so as to cover the anodes 1R, 1G, and 1B. And an electron transport layer 4C containing CsCO3 is formed on the red light-emitting layer 3R, the green light-emitting layer 3G, and the blue light-emitting layer 3B. Cathodes 5R corresponding to the anode 1R, 5G corresponding to the anode 1G, and 5B corresponding to the anode 1B are formed to be embedded in the electron transport layer 4C. A glass substrate 9 is disposed on the electron transport layer 4C.

[0127] The light-emitting layer 3C includes an ionic liquid 47 containing quantum dots 31R, an ionic liquid 47 containing quantum dots 31G, an ionic liquid 47 containing quantum dots 31B, and a spacer 7 provided between the hole transport layer 2C and the electron transport layer 4C to separate these ionic liquids 47 from each other.

[0128] (Third Embodiment)

[0129] Figure 30 It is a conceptual diagram of the quantum dots 31 provided on the light-emitting layer of the light-emitting element according to the third embodiment. The same reference numerals are assigned to the same components as those described above, and the detailed description thereof is omitted.

[0130] A first ligand 32 and a second ligand 33 are coordinated on the quantum dot 31. The first ligand 32 has a first functional group 34 and a positively charged portion 35. The second ligand 33 has a second functional group 41 and a negatively charged portion 42. Thus, the first ligand 32 has the first functional group 34 and a portion that is only positively charged, and the second ligand 33 has the second functional group 41 and a portion that is only negatively charged.

[0131] Figure 31 It is a conceptual diagram of another quantum dot 31B. The same reference numerals are assigned to the components that are the same as those described above, and their detailed descriptions are omitted.

[0132] A first ligand 32B and a second ligand 33B are coordinated on the quantum dot 31B. The first ligand 32B has a first functional group 34, a positively charged portion 35, and a negatively charged portion 42. The positively charged portion 35 and the negatively charged portion 42 are arranged in parallel with respect to the first functional group 34. The second ligand 33B has a second functional group 41, a negatively charged portion 42, and a positively charged portion 35. The negatively charged portion 42 and the positively charged portion 35 are arranged in parallel with respect to the second functional group 41.

[0133] Figure 32 It is a conceptual diagram of another quantum dot 31C. The same reference numerals are assigned to the components that are the same as those described above, and their detailed descriptions are omitted.

[0134] A first ligand 32C and a second ligand 33C are coordinated on the quantum dot 31C. The first ligand 32C has a first functional group 34, a positively charged portion 35, and a negatively charged portion 42. The positively charged portion 35 and the negatively charged portion 42 are arranged in series with respect to the first functional group 34. The second ligand 33C has a second functional group 41, a negatively charged portion 42, and a positively charged portion 35. The negatively charged portion 42 and the positively charged portion 35 are arranged in series with respect to the second functional group 41. For both the first ligand 32C and the second ligand 33C, the distance between the negatively charged portion 42 and the quantum dot 31C is greater than the distance between the positively charged portion 35 and the quantum dot 31C.

[0135] Figure 33 It is a conceptual diagram of another quantum dot 31D. The same reference numerals are assigned to the components that are the same as those described above, and their detailed descriptions are omitted.

[0136] The quantum dot 31D is coordinated with a first ligand 32D and a second ligand 33D. The first ligand 32D has a first functional group 34, a positively charged portion 35, and a negatively charged portion 42. The positively charged portion 35 and the negatively charged portion 42 are arranged in series with respect to the first functional group 34. The second ligand 33D has a second functional group 41, a negatively charged portion 42, and a positively charged portion 35. The negatively charged portion 42 and the positively charged portion 35 are arranged in series with respect to the second functional group 41. For both the first ligand 32D and the second ligand 33D, the distance between the negatively charged portion 35 and the quantum dot 31D is greater than the distance between the positively charged portion 42 and the quantum dot 31D.

[0137] Figure 34 It is a conceptual diagram of another quantum dot 31E. The same reference numerals are given to the same components as those described above, and their detailed descriptions are omitted.

[0138] The quantum dot 31E is coordinated with a first ligand 32C and a second ligand 33D. For the first ligand 32C, the distance between the negatively charged portion 42 and the quantum dot 31E is greater than the distance between the positively charged portion 35 and the quantum dot 31E. Also, for the second ligand 33D, the distance between the positively charged portion 35 and the quantum dot 31E is greater than the distance between the negatively charged portion 42 and the quantum dot 31E.

[0139] Thus, the first ligands 32B, 32C, 32D and the second ligands 33B, 33C, 33D provided on the quantum dots 31B, 31C, 31D, 31E have zwitterions containing a positively charged portion 35 and a negatively charged portion 42.

[0140] The quantum dots 31B, 31C, 31D, 31E only need to have at least one pair of ionic functional groups selected from cationic functional groups and anionic functional groups, but the more equal the amounts of the cationic functional group and the anionic functional group are, the more preferable.

[0141] Figure 35 It is a diagram showing a method of modifying the quantum dot 31 by modification group exchange. The same reference numerals are given to the same components as those described above, and their detailed descriptions are omitted.

[0142] It is also possible to modify the first ligand 32 and the second ligand 33 to the quantum dot 31 by modification group exchange in which the ligand 97 coordinated to the quantum dot 31 is exchanged for the first ligand 32 and the second ligand 33.

[0143] Figure 36 It is a diagram showing a method of modifying the quantum dot 31 by graft modification. The same reference numerals are given to the same components as those described above, and their detailed descriptions are omitted.

[0144] The reactive functional group 16 coordinated to the quantum dot 31 can also be converted into the first ligand 32 by graft modification, and then the quantum dot 31 is modified. Examples of the functional group 16 capable of graft modification include an amino group, a halogen group, a hydroxyl group, a vinyl group, etc.

[0145] It is also possible to combine and use methods of exchanging and graft-modifying multiple such modifying groups.

[0146] Figures 37 to 40 It is a diagram showing another method of modifying a quantum dot by graft modification. The same reference numerals are given to the same components as those described above, and the detailed description thereof is omitted.

[0147] First, diamine 100 is further mixed in the quantum dot 31 coordinated with the ligand 99 containing an amino acid. The quantum dot 31 includes CdSe. For example, it is prepared by coordinating hexamethylenediamine to the quantum dot 31. Then, the quantum dot 31 is mixed with the following materials at 80 °C for 48 hours to obtain a sulfonic acid - amide salt.

[0148] · 1 - propylene 1,3 - sultone (8.0 mmL, 0.1 mmol)

[0149] · dimethylformamide (DMF, 120)

[0150] In this way, the quantum dot 31 modified by the first ligand 32C containing the positively charged part 35 and the negatively charged part 42 is obtained.

[0151] Figure 41 It is a diagram for explaining an example of the ionic liquid 47. The same reference numerals are given to the same components as those described above, and the detailed description thereof is omitted.

[0152] The ionic liquid 47 can also be a liquid in which either the cation 50 or the anion 51 is a polymer. Figure 41 An example where the cation 50 is a polymer is shown.

[0153] Figure 42 It is a diagram for explaining another example of the ionic liquid 47. The same reference numerals are given to the same components as those described above, and the detailed description thereof is omitted.

[0154] The ionic liquid 47 can also be a liquid of a zwitterion in which the cation 50 and the anion 51 are paired within the molecule.

[0155] Figure 43 It is a diagram for explaining yet another example of the ionic liquid 47. The same reference numerals are given to the same components as those described above, and the detailed description thereof is omitted.

[0156] The ionic liquid 47 may contain other types of ionic liquids, solvents, and charge carrier transport materials.

[0157] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope defined by the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical methods disclosed in each embodiment.

[0158] Description of Reference Numerals

[0159] 1 Anode

[0160] 2 Hole Transport Layer

[0161] 4 Electron Transport Layer

[0162] 3 Light-Emitting Layer

[0163] 5 Cathode

[0164] 7 Spacer (frame-shaped resin material)

[0165] 10A Light-Emitting Element

[0166] 31 Quantum Dots

[0167] 31R Quantum Dots (third quantum dots)

[0168] 31G Quantum Dots (second quantum dots)

[0169] 31B Quantum Dots (first quantum dots)

[0170] 32 First Ligand

[0171] 33 Second Ligand

[0172] 34 First Functional Group

[0173] 35 Positively Charged Portion (positively charged part)

[0174] 36 First Main Chain

[0175] 41 Second Functional Group

[0176] 42 Negatively Charged Portion (negatively charged part)

[0177] 43 Second Main Chain

[0178] 47 Ionic Liquid (room temperature molten salt)

[0179] 71 Liquid Injection Hole

Claims

1. A light-emitting element, which includes an anode, a cathode, and a light-emitting layer disposed between the anode and the cathode, wherein the light-emitting element is characterized in that, the light-emitting layer includes: quantum dots; a plurality of first ligands, having a first functional group coordinated to the quantum dots and a positively charged portion; a plurality of second ligands, having a second functional group coordinated to the quantum dots coordinated with the first ligands and a negatively charged portion; and a room-temperature molten salt, which disperses the quantum dots, the first ligand further has a negatively charged portion, the second ligand further has a positively charged portion, the first ligand includes a first main chain composed of a saturated or unsaturated hydrocarbon having 3 to 20 carbon atoms between the first functional group and the positively charged portion, the second ligand includes a second main chain composed of a saturated or unsaturated hydrocarbon having 3 to 20 carbon atoms between the second functional group and the negatively charged portion, a distance of 5 or more carbon atoms exists between the first functional group contained in the first ligand and the positively charged portion across the first main chain, a distance of 3 or more carbon atoms exists between the second functional group contained in the second ligand and the negatively charged portion across the second main chain.

2. The light-emitting element according to claim 1, wherein the positively charged portion is included in a functional group bonded to a carbon farthest from the carbon bonded to the first functional group in the first main chain.

3. The light-emitting element according to claim 1, wherein the negatively charged portion is included in a functional group bonded to a carbon farthest from the carbon bonded to the first functional group in the second main chain.

4. The light-emitting element according to claim 1, wherein the distance between the quantum dots of the first ligand and the negatively charged portion is greater than the distance between the quantum dots and the positively charged portion, the distance between the quantum dots of the second ligand and the positively charged portion is greater than the distance between the quantum dots and the negatively charged portion.

5. The light-emitting element according to any one of claims 1 to 4, wherein for the quantum dots having the plurality of first ligands and the plurality of second ligands, the number of the positively charged portions is in the range of 0.8 times or more and 1.2 times or less of the number of the negatively charged portions.

6. The light-emitting element according to any one of claims 1 to 4, wherein a frame-shaped resin material is formed on either the anode or the cathode, the light-emitting layer is formed inside the frame-shaped resin material.

7. The light-emitting element according to any one of claims 1 to 4, wherein a hole transport layer is included between the anode and the light-emitting layer, an electron transport layer is included between the cathode and the light-emitting layer, a frame-shaped resin material is formed on either the hole transport layer or the electron transport layer, the light-emitting layer is formed inside the frame-shaped resin material.

8. The light-emitting element according to any one of claims 1 to 4, wherein the quantum dots are a plurality of quantum dots, the light-emitting layer further contains a porous resin, The room-temperature molten salt that disperses the plurality of quantum dots is in a liquid state. The room-temperature molten salt is held by the porous resin.

9. The light-emitting element according to any one of claims 1 to 4, wherein the positively charged portion includes any one of a pyridinium group, an imidazolium group, an ammonium group, and a phosphonium group.

10. The light-emitting element according to any one of claims 1 to 4, wherein the negatively charged portion includes any one of a carboxyl group, a sulfonate group, and an imide sulfonate group.

11. The light-emitting element according to any one of claims 1 to 4, wherein the quantum dots are a plurality of quantum dots, the content of the plurality of quantum dots is 0.5% by weight or more and 10% by weight or less relative to the room-temperature molten salt.

12. The light-emitting element according to any one of claims 1 to 4, wherein the quantum dots are a plurality of quantum dots, the plurality of quantum dots are composed of any one of a first quantum dot that emits light in a blue wavelength region, a second quantum dot that emits light in a green wavelength region, and a third quantum dot that emits light in a red wavelength region.

13. The light-emitting element according to any one of claims 1 to 4, wherein the quantum dots are a plurality of quantum dots, the plurality of quantum dots include a first quantum dot that emits light in a blue wavelength region, a second quantum dot that emits light in a green wavelength region, and a third quantum dot that emits light in a red wavelength region, and the light-emitting layer emits white light.

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