Prepolymers, crosslinking copolymers, quantum dot composites, methods of making the same, and quantum dot light emitting diodes

Abstract

This invention relates to a prepolymer, a crosslinked copolymer, a quantum dot composite material, a method for preparing the same, and a quantum dot light-emitting diode. The prepolymer comprises interconnected repeating units and terminal groups. The repeating units have the structure shown in formula (I). The terminal groups contain at least one of the following: cyano, hydroxyl, sulfonic acid, mercapto, disulfide, phosphoro, amino, carboxyl, thiocyanate, and halogen, which can coordinate with inorganic materials to improve stability. Ar1 is a large π-conjugated nitrogen-containing heteroaryl group, possessing excellent film-forming properties and hole transport capability, as well as a low LUMO energy level, hindering electron transport. R9 is a crosslinkable group, providing the basis for crosslinking. After crosslinking, a crosslinked copolymer is obtained, which can significantly improve the film uniformity of inorganic materials. L1 and L2 are independently selected from single bonds, aryl groups with 6 to 20 ring atoms, or heteroaryl groups with 5 to 20 ring atoms, respectively. m and n are independently positive integers, and m / n is 1 to 99.

Description

Technical Field

[0001] This invention relates to the field of electroluminescence technology, and in particular to a prepolymer, a crosslinked copolymer, a quantum dot composite material, a method for preparing the same, and a quantum dot light-emitting diode. Background Technology

[0002] Display technology has made one qualitative leap after another, from the early cathode ray tube (CRT) to liquid crystal display (LCD) and plasma flat panel display (PDP) in the late 1980s and now to the mainstream OLED / QLED display.

[0003] Organic light-emitting diodes (OLEDs) have become the mainstream technology in the display field due to their excellent display performance, including self-illumination, simple structure, ultra-thinness, fast response speed, wide viewing angle, low power consumption, and flexible display capabilities. Quantum dot light-emitting diodes (QLEDs), on the other hand, have the advantages of saturated emitted light color and tunable wavelength, and have high quantum yields in both photoluminescence and electroluminescence, making them a strong competitor to OLEDs in recent years.

[0004] Although quantum dots have many advantages, their efficiency is reduced because they are easily oxidized by moisture and oxygen. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a ligand.

[0006] The technical solution is as follows:

[0007] A prepolymer, characterized in that the prepolymer comprises linked repeating units and terminal groups, the repeating units having the structure shown in formula (I):

[0008]

[0009] * indicates a connection point;

[0010] Each time the terminal group appears, it independently contains at least one of the following: cyano, hydroxyl, sulfonic acid, mercapto, disulfide, phosphorus, amino, carboxyl, thiocyanate, and halogen.

[0011] Ar1 is a large π-conjugated nitrogen-containing heteroaromatic group;

[0012] R9 is a crosslinkable group;

[0013] L1 and L2 are each independently selected from aryl groups with a single bond, a ring number of 6 to 20, or heteroaryl groups with a ring number of 5 to 20.

[0014] m and n are independent positive integers, and m / n ranges from 1 to 99.

[0015] The present invention also provides a method for preparing the prepolymer as described above, comprising the following steps:

[0016] Provide a compound containing L1 and Ar1, react it with a vinyl compound to prepare... monomer;

[0017] supply monomer;

[0018] Will monomer, Monomers, initiators, and chain transfer agents containing end groups are mixed to undergo a copolymerization reaction.

[0019] The present invention also provides a crosslinked copolymer, the crosslinked copolymer comprising crosslinking points and polymer chains connected to the crosslinking points, the polymer chains comprising structural subunits shown in formula (I-1) and structural subunits shown in formula (I-2);

[0020]

[0021] The crosslinking points are generated by R9 through crosslinking.

[0022] The present invention also provides a quantum dot composite material, characterized in that it comprises quantum dots and a crosslinked copolymer as described above.

[0023] The present invention also provides a method for preparing the quantum dot composite material as described above, comprising the following steps:

[0024] A quantum dot solution is provided, wherein the surface of the quantum dots contains transition ligands;

[0025] The prepolymer described above is dissolved in a first solvent to prepare a premixed solution;

[0026] The first quantum dot solution and the premixed liquid are mixed, and the prepolymer forms an intermediate with the quantum dots;

[0027] The intermediate is dissolved in a second solvent, and the quantum dot composite material is obtained through a cross-linking reaction. The second solvent is photolytic.

[0028] The present invention also provides a quantum dot light-emitting diode, comprising a cathode, an anode, a quantum dot light-emitting layer disposed between the cathode and the anode, and an electron transport layer disposed between the quantum dot light-emitting layer and the cathode;

[0029] The electron transport layer comprises a metal oxide;

[0030] The quantum dot light-emitting layer comprises the quantum dot composite material described above.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The prepolymer provided by this invention comprises end groups, Ar1, and R9. The end groups have a strong affinity for the surface of inorganic materials (such as QD) and can be tightly bound to the surface layer of inorganic materials (such as QD) through coordination bonds, making them difficult to detach and increasing the stability of inorganic materials (such as QD). Ar1 is a large π-conjugated nitrogen-containing heteroaromatic group, which has excellent film-forming properties and hole transport capabilities, as well as a low LUMO energy level, hindering the transport of (anodic) electrons. R9 is a crosslinkable group, providing a basis for crosslinking and enabling further film formation of inorganic particles.

[0033] Furthermore, the prepolymer of the present invention is cross-linked to obtain a cross-linked copolymer, which is then used as a surface modifier for quantum dots to prepare quantum dot composite materials. Since the cross-linked molecular chains form a network, the film-forming properties of the quantum dots are significantly improved, the interfacial properties of the quantum dots are modified, and the high luminescence efficiency of the quantum dots is maintained. In addition, because the cross-linked copolymer contains groups capable of transporting holes, it promotes hole transport and improves carrier balance.

[0034] If the quantum dot composite material provided by this invention is used in the light-emitting layer of a QLED, and the QLED also contains an electron transport layer, then the crosslinked copolymer of this invention can significantly improve the film uniformity of quantum dots, modify the interfacial properties between the quantum dot light-emitting layer and the electron transport layer, greatly reduce the exciton quenching of the quantum dot light-emitting layer by the electron transport layer, maintain the high quantum luminescence efficiency of the quantum dot light-emitting layer, and at the same time, based on the groups in the quantum dot light-emitting layer that have the ability to transport holes, it can promote the transport and injection of holes, improve the balance of charge carriers, thereby improving the performance and stability of the device. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a positive QLED device according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the structure of an inverted QLED device according to an embodiment of the present invention;

[0037] Figure 3 This is the 1H NMR spectrum of a prepolymer obtained according to an embodiment of the present invention. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] In this invention, "substitution" means that the hydrogen atom in the substituent is replaced by the substituent. Furthermore, the term "substituted or unsubstituted" in this invention means that the event or situation described subsequently may, but does not necessarily, occur; this description includes situations where the event or situation occurs or does not occur. For example, "substituted or unsubstituted aryl" means that the hydrogen atom on the aryl group may or may not be substituted.

[0041] Furthermore, when the substituents of the present invention can be further substituted, they can be replaced by the following groups: C 1-10 Straight-chain alkyl or branched-chain alkyl, C 1-10 Alkoxy, aryl with 6 to 20 ring atoms, or heteroaryl with 5 to 20 ring atoms.

[0042] In this invention, "alkyl" refers to a saturated aliphatic hydrocarbon group, including straight-chain and branched groups. For example, C1-C... 10 Alkyl refers to an alkyl group containing 1 to 10 carbon atoms. Non-limiting examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, n-hexyl, 1-ethyl-2-methylpropyl, 1,1,2-trimethylpropyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1,3-dimethylbutyl, 2-ethylbutyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, and 2,3-dimethylbutyl.

[0043] "Cycloalkyl" refers to a saturated or partially unsaturated monocyclic or polycyclic cyclic hydrocarbon substituent. A 3-10 membered cycloalkyl group refers to a group comprising 3 to 10 carbon atoms. In one embodiment, a 3-10 membered monocyclic cycloalkyl group is cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cycloheptyl, cyclohepttrienyl, cyclooctyl, etc.

[0044] Alkoxy groups include -O- (alkyl) and -O- (cycloalkyl). The definitions of alkyl and cycloalkyl are as described above. In one embodiment, the C1-C4 alkoxy group is methoxy, ethoxy, propoxy, butoxy, cyclopropoxy, or cyclobutoxy. The alkoxy group may be optionally substituted or unsubstituted.

[0045] In this invention, "ring atom number" refers to the number of atoms in the ring itself of a structural compound (e.g., monocyclic compound, fused-ring compound, cross-linked compound, carbocyclic compound, heterocyclic compound) obtained by atomic bonding to form a ring. When the ring is substituted by a substituent, the atoms contained in the substituent are not included in the ring-forming atoms. The same applies to the "ring atom number" described below unless otherwise specified. For example, the benzene ring has 6 ring atoms, the naphthalene ring has 10 ring atoms, and the thiophene group has 5 ring atoms.

[0046] "Aryl, aromatic group, or aromatic group" refers to a hydrocarbon group containing at least one aromatic ring. "Heteroaromatic group or heteroaromatic group" refers to an aromatic hydrocarbon group containing at least one heteroatom. The heteroatom is preferably selected from N, O, and S, and particularly preferably from N. A fused-ring aromatic group refers to an aromatic group whose ring can have two or more rings, wherein two carbon atoms are shared by two adjacent rings, i.e., a fused ring. A fused-heterocyclic aromatic group refers to a fused-ring aromatic hydrocarbon group containing at least one heteroatom. For the purposes of this invention, aromatic groups or heteroaromatic groups include not only systems with aromatic rings but also non-aromatic ring systems. Therefore, systems such as pyridine, thiophene, pyrrole, pyrazole, triazole, imidazole, oxazole, oxadiazole, thiazole, tetraazole, pyrazine, pyridazine, pyrimidine, triazine, and carbene are also considered aromatic groups or heterocyclic aromatic groups.

[0047] Further, the aromatic ring in the aromatic group of the present invention is selected from: benzene, naphthalene, anthracene, phenanthrene, benzo[a]phenanthrene, pyrene, acenaphthene, fluorene, and their derivatives; the heteroaromatic ring in the heteroaromatic group is selected from triazine, pyridine, pyrimidine, imidazole, furan, thiophene, benzo[a]furan, benzo[a]thiophene, indole, carbazole, pyrrolo[a]imidazolium, pyrrolo[a]pyrrolo, thiophenolo[a]pyrrolo, thiophenolo[a]thiophene, furan[a]pyrrolo, furan[a]furan, thiophenolo[a]furan, benzo[a]imidazolium, quinoline, isoquinoline, dibenzo[a]thiophene, dibenzo[a]furan, carbazole, and their derivatives. Even further, the aromatic ring in the aromatic group is selected from benzene, naphthalene, or biphenyl; the heteroaromatic ring in the heteroaromatic group is selected from pyridine, pyrimidine, imidazole, triazine, carbazole, triphenylamine, or diphenylamine.

[0048] In this invention, "*" represents a connection site.

[0049] In this invention, the asterisk (*) lines intersecting the ring should be understood in the usual sense in the art, indicating that connectable positions on the ring can be used as connection points, for example: This indicates that any one of the connectable positions X1 to X6 on the ring can be selected as the connection point. This indicates that any two of the connectable positions X1 to X6 on the ring can be selected as connection points.

[0050] Crosslinking refers to the process by which linear or branched polymer chains are covalently linked to form a network or three-dimensional polymer. Preferably, in this invention, the crosslinking method is photocrosslinking, utilizing light... radiation Make linear polymer The process of cross-linking to form network or three-dimensional polymers.

[0051] The technical solution of the present invention is as follows:

[0052] A prepolymer, characterized in that the prepolymer comprises linked repeating units and terminal groups, the repeating units having the structure shown in formula (I):

[0053]

[0054] * indicates a connection point;

[0055] Each time the terminal group appears, it independently contains at least one of the following: cyano, hydroxy, sulfonic acid, mercapto, disulfide, phosphorus, amino, carboxyl, thiocyanate, and halogen; the terminal group can be combined with quantum dots.

[0056] Ar1 is a large π-conjugated nitrogen-containing heteroaromatic group;

[0057] R9 is a crosslinkable group;

[0058] L1 and L2 are each independently selected from aryl groups with a single bond, a ring number of 6 to 20, or heteroaryl groups with a ring number of 5 to 20.

[0059] m and n are independent positive integers, and m / n ranges from 1 to 99.

[0060] The prepolymer provided by this invention comprises end groups, Ar1, and R9. The end groups have a strong affinity for the surface of the inorganic material (QD) and can be tightly bound to the surface layer of the inorganic material through coordination bonds, making them difficult to detach and increasing the stability of the inorganic material. The Ar1 is a large π-conjugated nitrogen-containing heteroaromatic group, which has excellent film-forming properties and hole transport capabilities, as well as a low LUMO energy level, hindering the transport of (anodic) electrons. R9 is a crosslinkable group, providing a basis for crosslinking and enabling further film formation of inorganic particles.

[0061] In this invention, the m / n ratio is controlled to be 1 to 99. For example, m / n can be, but is not limited to, 1, 2, 5, 9, 10, 19, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99. Such ligands are more conducive to improving the stability of inorganic materials. In addition, if the inorganic particles are QDs, since the cross-linked groups are insulating and non-conductive, an excessive amount of cross-linked groups will reduce the QD's ability to transport charge carriers.

[0062] In one embodiment, the terminal group is selected from at least one of cyano, mercapto, alkyl mercapto, aryl mercapto, dithio, carboxyl, thiocyanate, amino, halogen, and phosphine. Such terminal groups have a stronger affinity for metal atoms on the surface of inorganic particles (such as QDs). Further, the terminal group is selected from at least one of thiophene, 1,2-thiophene, 1,3-thiophene, 1,4-thiophene, thiopropionic acid, amine thiocyanate, and halogen. Besides having a strong affinity for the QD surface, it can also reduce the Fermi level of the QD, thereby making the LUMO and HOMO levels of the QD shallower. The ability of aromatic thiols, carboxylic acids, thiocyanate ions, and halide ions to change the QD energy level decreases in that order. After binding with aromatic thiols, the LUMO and HOMO levels of the QD are the shallowest, which is beneficial for hole injection.

[0063] In one embodiment, the Ar1 is selected from any of the groups shown in (A-1)-(A-4):

[0064]

[0065] in:

[0066] X and Y1 are each independently either N or CR1;

[0067] Y2 is independently selected from NR2, O, S, and CR3R4;

[0068] R1-R4 are each independently selected from: hydrogen atom, deuterium atom, alkyl group having 1 to 10 carbon atoms, alkoxy group having 1 to 10 carbon atoms, aryl group having 6 to 20 ring atoms, or heteroaryl group having 5 to 20 ring atoms;

[0069] (A-1)-(A-4) contains at least one N.

[0070] The groups shown in (A-1)-(A-4) have a rigid structure, good thermal stability and film-forming properties, which can further enhance the film-forming properties and hole transport capabilities of the quantum dot composite material of the present invention.

[0071] In one embodiment, R1-R4 are each independently selected from: methyl, ethyl, tert-butyl, phenyl, biphenyl, terphenyl, naphthyl, pyridyl, triazinyl, pyrimidinyl, and pyrazinyl.

[0072] In one embodiment, the Ar1 is selected from one of the following groups:

[0073]

[0074] Using the aforementioned N-containing heteroaryl groups can increase the conjugation degree of the compound, reduce LUMO, and further enhance its hole transport capability.

[0075] Furthermore, the Ar1 is selected from any of the following groups:

[0076]

[0077] In one embodiment, R9 is selected from at least one of an azide group and a ketone carbonyl group. Using these photosensitive groups results in good crosslinking, which is beneficial for improving the film-forming properties of quantum dots. Understandably, thermal crosslinking requires higher temperatures, and the end groups are less heat-resistant, especially the thiol groups. Compared to thermal crosslinking, this invention uses photocrosslinking groups as the crosslinking basis, resulting in better stability of each group and a better effect on improving the film uniformity of quantum dots after crosslinking. Ultimately, this can significantly reduce the quenching of QD excitons by metal oxides (such as ZnO).

[0078] In one embodiment, the ketone carbonyl group is a benzophenone group.

[0079] In one embodiment, L1 and L2 are each independently selected from single bonds or any of the groups shown in (B-1)-(B-7):

[0080]

[0081] in:

[0082] X1 and Y3 are each independently either N or CR5;

[0083] Y4 is independently selected from NR6 and CR7R8;

[0084] R5-R8 are each independently selected from: hydrogen atoms, deuterium atoms, alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, aryl groups having 6 to 20 ring atoms, or heteroaryl groups having 5 to 20 ring atoms.

[0085] In one embodiment, L1 and L2 are each independently selected from single bonds or one of the following groups:

[0086]

[0087] The following lists the structures of the prepolymers according to the present invention, but are not limited thereto:

[0088]

[0089]

[0090] The present invention also provides a method for preparing the prepolymer as described above, comprising the following steps:

[0091] Provide a compound containing L1 and Ar1, react it with a vinyl compound to prepare... monomer;

[0092] supply monomer;

[0093] Will monomer, Monomers, initiators, and chain transfer agents containing end groups are mixed to undergo a copolymerization reaction.

[0094] Furthermore, current QLED devices use inorganic quantum dots (QDs) as the light-emitting layer. Since QDs are inorganic nanoparticles, they have poor film-forming properties and easily penetrate into the gaps between other functional layers in the light-emitting device, reducing its performance. The industry typically uses surface modifiers to modify quantum dots to improve their film-forming properties; however, traditional surface modifiers often reduce the luminous efficiency of quantum dots.

[0095] Accordingly, the present invention also provides a crosslinked copolymer, the crosslinked copolymer comprising crosslinking points and polymer chains connected to the crosslinking points, the polymer chains comprising structural subunits shown in formula (I-1) and structural subunits shown in formula (I-2);

[0096]

[0097] The crosslinking points are generated by R9 through crosslinking.

[0098] Crosslinked copolymers, due to the network structure formed by the crosslinked molecular chains, can significantly improve the film-forming properties of quantum dots, modify their interfacial properties, and maintain their high luminescence efficiency. Furthermore, the presence of hole-transporting groups in the crosslinked copolymers promotes hole transport and improves carrier balance.

[0099] Understandably, the crosslinked copolymer of the present invention includes crosslinking points (generated by R9 through crosslinking) and polymer chains connected to the crosslinking points. The polymer chains include structural subunits shown in formula (I-1) and structural subunits shown in formula (I-2). The crosslinking points may be connected to the C of -CH2 in (I-1), the C of -CH in (I-1), or L2. As the type of crosslinkable group R9 changes, the type and position of the crosslinking points will also change.

[0100] In one embodiment, the crosslinked copolymer comprises at least one structure represented by formula (II) or formula (III):

[0101]

[0102] Furthermore, each occurrence of the crosslinked copolymer independently comprises at least the structure shown in any one of formulas (C-1)-(C-4):

[0103]

[0104] In one embodiment, the degree of crosslinking of the crosslinked copolymer is 10–100. Further, the degree of crosslinking of the crosslinked copolymer is 10–30. A suitable degree of crosslinking can improve the uniformity of quantum dot film formation while maintaining a good level of carrier transport capability in the QD.

[0105] In one embodiment, the crosslinking reaction is a photocrosslinking reaction, and the wavelength of the light source used in the photocrosslinking reaction is 254 nm to 400 nm.

[0106] This invention also provides a quantum dot composite material, comprising quantum dots and the crosslinked copolymer as described above. The network-like molecular weight of the crosslinked copolymer significantly improves the film-forming properties of the quantum dots, modifies their interfacial properties, and maintains their high luminescence efficiency. Furthermore, the presence of hole-transporting groups in the crosslinked copolymer promotes hole transport, improves carrier balance, and endows the quantum dot composite material with excellent properties.

[0107] In one embodiment, the percentage content of the quantum dots is 60% to 80% and the percentage content of the crosslinked copolymer is 20% to 40% by mass percentage of the quantum dot composite material.

[0108] In one embodiment, the quantum dots and the end groups on the crosslinked copolymer are connected together by coordination bonds.

[0109] The present invention also provides a method for preparing the quantum dot composite material as described above, comprising the following steps:

[0110] A quantum dot solution is provided, wherein the surface of the quantum dots contains transition ligands;

[0111] The prepolymer described above is dissolved in a first solvent to prepare a premixed solution;

[0112] The first quantum dot solution and the premixed liquid are mixed, and the prepolymer forms an intermediate with the quantum dots;

[0113] The intermediate is dissolved in a second solvent, and the quantum dot composite material is obtained through a cross-linking reaction. The second solvent is photolytic.

[0114] The method for preparing quantum dot composite materials provided by this invention replaces the original ligands of quantum dots with prepolymer ligands containing three different groups through ligand exchange. The method is simple to operate, has a high yield, and can form stable metal-organic complexes, which significantly improves the stability of quantum dots.

[0115] In one embodiment, the transition ligand is at least one selected from oleic acid, octylthiol, and trioctylphosphine. Such a transition ligand process is mature and stable, resulting in QD with good performance.

[0116] The solvent used in this invention to dissolve the prepolymer has good solubility for the prepolymer, which is more conducive to ligand exchange reactions. In one embodiment, the solvent in the quantum dot solution and the first solvent are each independently selected from at least one of toluene, n-octane, n-hexane, dimethyl anisole, and dihydroindene. Further, the solvent in the quantum dot solution and the first solvent are selected from the same solvent.

[0117] The solvent used in this invention to disperse organometallic complexes (intermediates) is photodegradable, resulting in minimal swelling of the crosslinked copolymer obtained after photocrosslinking of the prepolymer, and eliminating the need for a subsequent solvent removal step after the photocrosslinking reaction. In one embodiment, the second solvent is chloroform.

[0118] In one embodiment, the method for preparing the quantum dot composite material includes the following steps:

[0119] The transition ligand and the quantum dot are dissolved in a first solvent to prepare a first mixture;

[0120] The prepolymer is dissolved in a first solvent to prepare a premixed solution;

[0121] The first mixture and the premix are mixed and stirred for 10-30 hours. Through ligand exchange, the prepolymer forms a metal-organic complex with the quantum dots. After standing, the upper clear liquid and the lower solid are separated. The lower solid is then dissolved with an organic solvent. The metal-organic complex is irradiated with light (e.g., vertical irradiation for 5-20 minutes) to induce a photocrosslinking reaction. After drying, the mixture is annealed at 80-120°C.

[0122] In one embodiment, the wavelength of the light is 254 nm to 400 nm. The choice of wavelength depends on the type of photocrosslinking groups.

[0123] Current QLED devices typically use inorganic quantum dots (QD) as the light-emitting layer, ZnO as the electron transport layer, and organic hole transport materials (HTM) as the hole transport layer. However, there are several issues. Firstly, because both the QD light-emitting layer and the ZnO electron transport layer are inorganic nanoparticles, their films are not perfectly smooth and can penetrate into the gaps between each other's films, forming exciton traps that quench them and further degrade device performance. Secondly, the electron mobility of ZnO is much higher than that of the hole transport layer, and in red-green QLED devices, the electron injection barrier from ZnO to the QD layer is lower than the hole injection barrier from the hole transport layer to the QD layer. This creates an imbalance of charge carriers in the QD layer, leading to Auger recombination and further reducing device performance. Similar problems exist with electron transport layers made from other inorganic oxides besides ZnO.

[0124] Accordingly, the present invention also provides a specific quantum dot light-emitting device. The technical solution is as follows:

[0125] A quantum dot light-emitting diode includes a cathode, an anode, a quantum dot light-emitting layer disposed between the cathode and the anode, and an electron transport layer disposed between the quantum dot light-emitting layer and the cathode;

[0126] The electron transport layer comprises a metal oxide;

[0127] The quantum dot light-emitting layer comprises the quantum dot composite material described above.

[0128] The quantum dot composite material according to the present invention can significantly improve the uniformity of quantum dot film formation, modify the interface performance of the quantum dot luminescent layer and the electron transport layer, greatly reduce the exciton quenching of the quantum dot luminescent layer by the electron transport layer, maintain the high quantum luminescence efficiency of the quantum dot luminescent layer, and at the same time, based on the groups in the quantum dot luminescent layer that have the ability to transport holes, it can promote the transport and injection of holes, improve the balance of charge carriers, thereby improving the performance and stability of the device.

[0129] In one embodiment, the anode material is a transparent conductive oxide, including but not limited to at least one of ITO, FTO, ATO, AZO, IZO, IZTO, and IGTO.

[0130] In one embodiment, the quantum dot in this invention is a quantum dot luminescent material with a core-shell structure, such as one or more of group II-VI compounds, group III-V compounds, group II-V compounds, group III-VI compounds, group IV-VI compounds, group I-III-VI compounds, group II-IV-VI compounds, or group IV elements. The core material may be, but is not limited to, at least one selected from CdSe, CdS, ZnSe, ZnS, CdTe, CdZnS, CdZnSe, ZnSeS, ZnSeTe, ZnTeS, CdSeS, CdSeTe, CdTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdSeSTe, ZnSeSTe, CdZnSeSTe, InP, InAs, and InAsP. The shell material may be, but is not limited to, at least one selected from CdS, ZnSe, ZnS, CdSeS, and ZnSeS. Using such quantum dots results in higher luminescence performance.

[0131] In one embodiment, the metal oxide is selected from at least one or more of ZnO, BaO, and TiO2. Such metal oxides have excellent electron transport capabilities, which is beneficial for improving device performance.

[0132] In one embodiment, the cathode material is at least one of conductive carbon material, metallic material, and transparent conductive oxide material, wherein the conductive carbon material includes, but is not limited to, doped or undoped carbon nanotubes, doped or undoped graphene, doped or undoped graphene oxide, C60, graphite, carbon fiber, and porous carbon; the metallic material includes, but is not limited to, aluminum, silver, gold, calcium, barium, magnesium, or alloys thereof; and the transparent conductive oxide includes, but is not limited to, ITO, FTO, ATO, AZO, IZO, IZTO, and IGTO.

[0133] In one embodiment, the thickness of the cathode is 50 nm to 200 nm.

[0134] In one embodiment, the quantum dot transport layer further includes a hole injection layer and a hole transport layer, wherein the hole injection layer is disposed between the anode and the quantum dot light-emitting layer, and the hole transport layer is disposed between the hole injection layer and the quantum dot light-emitting layer.

[0135] Depending on the structure of the QLED device, QLED devices can be divided into upright structure and inverted structure.

[0136] As one implementation method, when the QLED device is in an upright configuration, such as Figure 1As shown, the QLED device includes an anode 102, a hole injection layer 103, a hole transport layer 104, a quantum dot light-emitting layer 105, an electron transport layer 106, and a cathode 107 sequentially stacked on a substrate 101. The quantum dot light-emitting layer 105 comprises the quantum dot composite material described in this invention, which may be in the form of a thin film or solid particles.

[0137] As another implementation method, when the QLED device is an inverted structure, such as Figure 2 As shown, the QLED device includes a cathode 202, an electron transport layer 203, a quantum dot light-emitting layer 204, a hole transport layer 205, a hole injection layer 206, and an anode 207, which are sequentially stacked on a substrate 201. The quantum dot light-emitting layer 204 contains the quantum dot composite material described in this invention, which can be in the form of a thin film or solid particles.

[0138] In one embodiment, the materials used to prepare the hole injection layer include, but are not limited to: PEDOT:PSS, NiOx, WO3, CuPc, HATCN, m-MTDATA, F4-TCQN, and MoO3.

[0139] In one embodiment, the material used to prepare the hole transport layer includes, but is not limited to: TPD, poly-TPD, PVK, CBP, NPB, TCTA, mCP, TAPC, and TFB;

[0140] In one embodiment, the substrate in the upright and / or inverted QLED device is glass.

[0141] In one embodiment, the thickness of the anode of the upright and / or inverted QLED device is 10–200 nm.

[0142] In one embodiment, the thickness of the hole injection layer in the upright and / or inverted QLED device is 10–100 nm.

[0143] In one embodiment, the thickness of the hole transport layer in the upright and / or inverted QLED device is 10–100 nm.

[0144] In one embodiment, the thickness of the quantum dot light-emitting layer of the upright and / or inverted QLED device is 10–100 nm.

[0145] In one embodiment, the thickness of the electron transport layer of the upright and / or inverted QLED device is 10–100 nm.

[0146] In one embodiment, the thickness of the cathode of the upright and / or inverted QLED device is 50–200 nm.

[0147] This invention also provides a method for fabricating a quantum dot light-emitting diode, comprising fabricating a quantum dot light-emitting layer, wherein the method for fabricating the quantum dot light-emitting diode includes the following steps:

[0148] Quantum dot composite materials are prepared using the above-described method to form the quantum dot luminescent layer.

[0149] When the quantum dot light-emitting diode is a positively positioned QLED device, its fabrication method includes the following steps:

[0150] Provide a substrate, and fabricate an anode on the substrate;

[0151] A hole injection layer is prepared on the anode;

[0152] A hole transport layer is prepared on hole injection;

[0153] A quantum dot luminescent layer is prepared on the hole transport layer using the quantum dot composite material preparation method of the present invention;

[0154] An electron transport layer is fabricated on a quantum dot luminescent layer;

[0155] A cathode is fabricated on an electron transport layer.

[0156] In one embodiment, the anode is prepared by magnetron sputtering or by directly purchasing a substrate with ITO as the anode; the hole injection layer, hole transport layer, quantum dot light-emitting layer, and electron transport layer in the upright QLED device are prepared by solution method or vapor deposition method, the solution method including coating, spin coating, or inkjet printing, and the vapor deposition method is evaporation method; the cathode in the upright QLED device is prepared by vapor deposition method, such as evaporation method.

[0157] In one embodiment, the method for fabricating the upright QLED device includes the following steps:

[0158] Provide a substrate, and fabricate an anode on the substrate;

[0159] A hole injection layer was prepared on the anode by inkjet printing;

[0160] A hole transport layer was prepared on the hole injection layer by inkjet printing;

[0161] A quantum dot luminescent layer is prepared on the hole transport layer using the quantum dot composite material preparation method of the present invention;

[0162] An electron transport layer was fabricated on a quantum dot light-emitting layer by inkjet printing;

[0163] A cathode is prepared by vapor deposition on the electron transport layer to obtain an upright QLED device.

[0164] This invention also provides a method for fabricating an inverted QLED device, comprising the following steps:

[0165] Provide a substrate, and deposit a cathode on the substrate;

[0166] An electron transport layer was fabricated on the cathode by inkjet printing;

[0167] A quantum dot luminescent layer is prepared on the electron transport layer using the preparation method of the quantum dot composite material of the present invention;

[0168] A hole transport layer was fabricated on a quantum dot light-emitting layer by inkjet printing;

[0169] A hole injection layer was prepared on the hole transport layer by inkjet printing;

[0170] An anode is prepared on the hole injection layer.

[0171] In one embodiment, the hole injection layer, hole transport layer, quantum dot light-emitting layer, and electron transport layer in the inverted QLED device are prepared by solution method or vapor deposition method. Solution method includes coating, spin coating, or inkjet printing, while vapor deposition method is vapor deposition. The cathode in the inverted QLED device is prepared by vapor deposition method, such as vapor deposition.

[0172] In one embodiment, the method for fabricating the inverted QLED device includes the following steps:

[0173] Provide a substrate, and deposit a cathode on the substrate;

[0174] An electron transport layer was fabricated on the cathode by inkjet printing;

[0175] A quantum dot luminescent layer is prepared on the electron transport layer using the preparation method of the quantum dot composite material of the present invention;

[0176] A hole transport layer was fabricated on a quantum dot light-emitting layer by inkjet printing;

[0177] A hole injection layer was prepared on the hole transport layer by inkjet printing;

[0178] An inverted QLED device is obtained by inkjet printing an anode onto a hole injection layer. Specific Implementation

[0180] Example 1

[0181] This embodiment provides a prepolymer and its preparation method, a crosslinked copolymer and its preparation method, a quantum dot composite material and its preparation method, and an upright QLED and its preparation method. A schematic diagram of the upright QLED is shown below. Figure 1As shown: From bottom to top, the following components are arranged in sequence: substrate 101, anode 102, hole injection layer 103, hole transport layer 104, QD light emission layer 105, electron transport layer 106, and cathode 107.

[0182] (1) Preparation of the anode:

[0183] An ITO anode with a thickness of 150 nm was fabricated on a glass substrate.

[0184] (2) Preparation of the hole injection layer:

[0185] The water-soluble conductive polymer PEDOT was inkjet printed onto the anode, dried to form a film, and then annealed at 150°C for 20 min to obtain a hole injection layer with a thickness of 45 nm.

[0186] (3) Preparation of hole transport layer:

[0187] TFB ink was inkjet printed onto the hole injection layer, vacuum dried to form a film, and then annealed at 230℃ for 30 min to obtain a hole transport layer with a thickness of 25 nm.

[0188] (4) Fabrication of quantum dot light-emitting layer:

[0189] i) Synthesize the monomer TPA, whose Chinese name is 4-(N,N-diphenylamino)styrene, using the following reaction formula:

[0190]

[0191] The specific synthesis process is as follows: 15g of triphenylmethylphosphine iodide (Mepph3l) was dissolved in 100ml of anhydrous tetrahydrofuran in a nitrogen glove box, then poured into a flask, followed by the addition of 3g of potassium tert-butoxide (t-BuOK). After 10 minutes, 5g of 4-(N,N-diphenylamino)benzaldehyde was added. After reacting at room temperature for 24 hours, the mixture was filtered and washed with deionized water and dichloromethane at a ratio of 1:1 (volume ratio). The crude product TPA was then dried with anhydrous sodium sulfate, and subsequently purified by dichloromethane silica gel column chromatography to obtain purified TPA.

[0192] ii) Synthesize intermediate 1, the reaction formula is as follows:

[0193]

[0194] The specific synthesis process is as follows: 1g of monomer TPA and 28.12mg of monomer 4-chloromethylstyrene were added to a flask, and then 27.19mg of chain transfer agent 2-cyanopropyl-2-ol dithiobenzoate (CPBD), 1.97mg of initiator azobisisobutyronitrile (AIBN), and 3ml of solvent 1,4-dioxane were added to the flask. The reaction was carried out at 90℃ for 24h under an argon atmosphere. The mixture was filtered, the filter cake was washed with methanol, and dried to obtain intermediate 1, with m = 95 and n = 5.

[0195] iii) Synthesize intermediate 2, the reaction formula is as follows:

[0196]

[0197] The specific synthesis process is as follows: 6 mg of intermediate 1 is dissolved in 10 ml of n-octane, then 24 mg of hexylamine is added, the reaction is carried out at room temperature for 1 h, filtered, the filter cake is washed with methanol, and dried to obtain intermediate 2.

[0198] iv) Synthesize prepolymer 1, the reaction formula is as follows:

[0199]

[0200] The specific synthesis process is as follows: 6 mg of intermediate 2 was dissolved in 10 ml of n-octane, then 24 mg of NaN3 was added, and the mixture was reacted at room temperature for 1 h. After filtration, the filter cake was washed with methanol and dried to obtain prepolymer 1. Its proton NMR spectrum is shown below. Figure 3 As shown, by Figure 3 It can be seen that the present invention has successfully synthesized the target prepolymer.

[0201] v) Ligand exchange for the preparation of organometallic complex intermediates:

[0202] Oleic acid and CdSe@ZnS quantum dots were mixed in toluene to prepare a CdSe@ZnS green quantum dot solution with oleic acid ligands;

[0203] At room temperature, prepolymer 1 was dissolved in toluene, and a CdSe@ZnS green quantum dot solution with oleic acid ligands was added. The mixture was stirred for 24 hours to allow ligand exchange, and after standing and separating the layers, the upper clear liquid was separated from the lower solid to obtain a solid metal-organic complex intermediate.

[0204] vi) Photocrosslinking to prepare the quantum dot emitting layer:

[0205] Quantum dot ink was obtained by dissolving a solid metal-organic complex in chloroform. This ink was then applied to a hole transport layer via inkjet printing. Subsequently, the quantum dot ink was irradiated with 254nm ultraviolet light for 5 minutes to induce a photocrosslinking reaction. After vacuum drying to form a film, it was annealed at 100°C for 10 minutes to obtain a quantum dot composite material. This composite material served as the quantum dot emitting layer, with a thickness of 15nm. The mass percentage of quantum dots in the quantum dot composite material was 80%, and the mass percentage of the crosslinked copolymer was 20%. The photocrosslinking group was -N3, and the specific crosslinking reaction was as follows:

[0206]

[0207] (5) Fabrication of the electron transport layer:

[0208] ZnO ink was inkjet printed onto the quantum dot light-emitting layer, vacuum dried to form a film, and then annealed at 120°C for 15 min to obtain an electron transport layer with a thickness of 40 nm.

[0209] (6) Preparation of cathode:

[0210] A cathode with a thickness of 150 nm was fabricated by depositing Al onto an electron transport layer.

[0211] (7) Packaging to obtain an upright QLED device.

[0212] Comparative Example 1

[0213] This comparative example provides a quantum dot composite material and its preparation method, as well as an upright QLED and its preparation method. A schematic diagram of the upright QLED is shown below. Figure 1 As shown: From bottom to top, the following components are arranged in sequence: substrate 101, anode 102, hole injection layer 103, hole transport layer 104, QD light emission layer 105, electron transport layer 106, and cathode 107.

[0214] (1) Preparation of the anode:

[0215] An ITO anode with a thickness of 150 nm was fabricated on a glass substrate.

[0216] (2) Preparation of the hole injection layer:

[0217] The water-soluble conductive polymer PEDOT was inkjet printed onto the anode, dried to form a film, and then annealed at 150°C for 20 min to obtain a hole injection layer with a thickness of 45 nm.

[0218] (3) Preparation of hole transport layer:

[0219] TFB ink was inkjet printed onto the hole injection layer, vacuum dried to form a film, and then annealed at 230℃ for 30 min to obtain a hole transport layer with a thickness of 25 nm.

[0220] (4) Fabrication of quantum dot light-emitting layer:

[0221] Oleic acid and CdSe@ZnS quantum dots were mixed in toluene to prepare a CdSe@ZnS green quantum dot solution with oleic acid ligands;

[0222] The quantum dot light-emitting layer with a thickness of 15 nm was obtained by inkjet printing, applying it onto the hole transport layer, vacuum drying it into a film, and then annealing it at 100°C for 10 min.

[0223] (5) Fabrication of the electron transport layer:

[0224] ZnO ink was inkjet printed onto the quantum dot light-emitting layer, vacuum dried to form a film, and then annealed at 120°C for 15 min to obtain an electron transport layer with a thickness of 40 nm.

[0225] (6) Preparation of cathode:

[0226] A cathode with a thickness of 150 nm was fabricated by depositing Al onto an electron transport layer.

[0227] (7) Packaging to obtain an upright QLED device.

[0228] 2. Performance Testing:

[0229] Performance evaluation of QLED devices

[0230] The test device shows the brightness variation curve with current or voltage, as well as the device's lifespan, measured in T80@1000nit, which is the time it takes for the brightness of the device to decay to 800nit from an initial brightness of 1000nit.

[0231] The external quantum efficiency, current efficiency, and external quantum efficiency are shown in Table 1.

[0232] Table 1

[0233] Example 1 Comparative Example 1 External quantum efficiency (%) 14.2 6.8 Current efficiency (cd / A) 56.8 27.2 T80@1000nit(h) 339 139

[0234] As shown in Table 1, the crosslinked copolymer obtained after crosslinking in Example 1 can improve the film-forming properties of quantum dots, modify the quantum dot / ZnO interface, reduce defects at the quantum dot / ZnO interface, improve the quenching of excitons in the quantum dot light-emitting layer by ZnO, and thus improve the overall performance of the device.

[0235] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0236] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims and drawings.

Claims

1. A prepolymer, characterized in that, The prepolymer comprises linked repeating units and terminal groups, the repeating units having the structure shown in formula (I): （I） * indicates a connection point; Each time the terminal group appears, it independently contains at least one of the following: cyano, hydroxyl, sulfonic acid, mercapto, disulfide, phosphorus, amino, carboxyl, thiocyanate, and halogen. R9 is a crosslinkable group; L1 and L2 are each independently selected from aryl groups with a single bond, a ring number of 6 to 20, or heteroaryl groups with a ring number of 5 to 20. m and n are independent positive integers, and m / n ranges from 1 to 99; The Ar1 is selected from any of the groups shown in (A-1)-(A-4): in: X and Y1 are each independently either N or CR1; Y2 is independently selected from NR2, O, S, and CR3R4; R1-R4 are each independently selected from: hydrogen atom, deuterium atom, alkyl group having 1 to 10 carbon atoms, alkoxy group having 1 to 10 carbon atoms, aryl group having 6 to 20 ring atoms, or heteroaryl group having 5 to 20 ring atoms; Each of (A-1) to (A-4) contains at least one N.

2. The prepolymer according to claim 1, characterized in that, R1-R4 are each independently selected from: methyl, ethyl, tert-butyl, phenyl, biphenyl, terphenyl, naphthyl, pyridyl, triazinyl, pyrimidinyl, and pyrazinyl.

3. The prepolymer according to claim 2, characterized in that, The Ar1 is selected from one of the following groups: 。 4. The prepolymer according to claim 1, characterized in that, L1 and L2 are each independently selected from single bonds or any of the groups shown in (B-1)-(B-7): in: X1 and Y3 are each independently either N or CR5; Y4 is independently selected from NR6 and CR7R8; R5-R8 are each independently selected from: hydrogen atoms, deuterium atoms, alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, aryl groups having 6 to 20 ring atoms, or heteroaryl groups having 5 to 20 ring atoms.

5. The prepolymer according to claim 4, characterized in that, L1 and L2 are each independently selected from single bonds or one of the following groups: 。 6. The prepolymer according to any one of claims 1 to 5, characterized in that, R9 is selected from at least one of azide group and ketone carbonyl group.

7. The prepolymer according to claim 1, characterized in that, It has any of the following structures: 、 、 、 、 、 、 or .

8. A method for preparing the prepolymer according to any one of claims 1 to 7, characterized in that, Includes the following steps: Provide a compound containing L1 and Ar1, react it with a vinyl compound to prepare... monomer; supply monomer; Will monomer, Monomers, initiators, and chain transfer agents containing end groups are mixed to undergo a copolymerization reaction.

9. A crosslinked copolymer, characterized in that, The crosslinked copolymer includes crosslinking points, polymer chains connected to the crosslinking points, and end groups, wherein the polymer chains include structural subunits shown in formula (I-1) and structural subunits shown in formula (I-2); (I-1) (I-2) * indicates a connection point; The definitions of the terminal groups, Ar1, R9, L1, and L2 are the same as those in any one of claims 1 to 7; The crosslinking points are generated by R9 through crosslinking.

10. The crosslinked copolymer according to claim 9, characterized in that, The crosslinking reaction is a photocrosslinking reaction, and the wavelength of the light source used in the photocrosslinking reaction is 254nm to 400nm.

11. A quantum dot composite material, characterized in that, Includes quantum dots and crosslinked copolymers as described in any one of claims 9 to 10.

12. The quantum dot composite material according to claim 11, characterized in that, The percentage content of the quantum dots is 60% to 80% and the percentage content of the crosslinked copolymer is 20% to 40% by mass percentage of the quantum dot composite material.

13. The quantum dot composite material according to claim 11, characterized in that, The quantum dots and the end groups on the crosslinked copolymer are connected together by coordination bonds.

14. The method for preparing the quantum dot composite material according to any one of claims 11 to 13, characterized in that, Includes the following steps: A quantum dot solution is provided, wherein the surface of the quantum dots contains transition ligands; Dissolve the prepolymer according to any one of claims 1 to 7 in a first solvent to prepare a premix; The quantum dot solution and the premix are mixed, and the prepolymer forms an intermediate with the quantum dots; The intermediate is dissolved in a second solvent, and the quantum dot composite material is obtained through a crosslinking reaction.

15. The method for preparing the quantum dot composite material according to claim 14, characterized in that, The transition ligand is at least one of oleic acid, octylthiol, and trioctylphosphine; and / or The solvent in the quantum dot solution and the first solvent are each independently selected from at least one of toluene, n-octane, n-hexane, dimethyl anisole, and dihydroindene; and / or The second solvent is chloroform.

16. A quantum dot light-emitting diode, characterized in that, It includes a cathode, an anode, a quantum dot light-emitting layer disposed between the cathode and the anode, and an electron transport layer disposed between the quantum dot light-emitting layer and the cathode; The electron transport layer comprises a metal oxide; The quantum dot luminescent layer comprises the quantum dot composite material according to any one of claims 11 to 13.

17. The quantum dot light-emitting diode according to claim 16, characterized in that, The metal oxide is selected from at least one or more of ZnO, BaO, and TiO2; and / or The quantum dots in the quantum dot luminescent layer are selected from quantum dot luminescent materials with a core-shell structure, and the core material is selected from at least one of CdSe, CdS, ZnSe, ZnS, CdTe, CdZnS, CdZnSe, ZnSeS, ZnSeTe, ZnTeS, CdSeS, CdSeTe, CdTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdSeSTe, ZnSeSTe, CdZnSeSTe, InP, InAs, and InAsP, and the shell material is selected from at least one of CdS, ZnSe, ZnS, CdSeS, and ZnSeS.

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