Quantum dot light-emitting diode and method for preparing the same

Abstract

The present invention discloses a quantum dot light-emitting diode and a preparation method thereof. The quantum dot light-emitting diode includes: a quantum dot layer; an anion polymer layer formed on the surface of the quantum dot layer; and an electron transport layer formed on the surface of the anion polymer layer. In the quantum dot layer of the quantum dot light-emitting diode of the present invention, the surface in contact with the electron transport layer is coordinated with an anion polymer, and the remaining regions of the quantum dot layer still retain the original ligands. According to the principle of like charge repulsion and opposite charge attraction, when the surface ligand on the side of the quantum dot layer close to the electron transport layer is replaced with an anion polymer, the electron injection with the same charge as the functional group of this anion polymer can be hindered to a certain extent, thereby contributing to improving the effective recombination of carriers in the entire quantum dot layer and enhancing the device performance.

Description

Technical Field

[0001] The present invention relates to the field of quantum dot light-emitting devices, and particularly to a quantum dot light-emitting diode and a preparation method thereof. Background Art

[0002] Quantum dots (QDs) are usually composed of dozens to millions of atoms, with geometric sizes similar to exciton sizes. They not only inherit some characteristics of bulk semiconductors but also exhibit unique optoelectronic properties, specifically including: high color purity, continuously adjustable emission spectra with size and composition, narrow full-width at half-maximum, high fluorescence efficiency, long lifetime, excellent monodispersity and photothermal stability, and also excellent solution processability. They have broad application prospects in the fields of display, laser, photovoltaics, biological labeling, etc. Among them, the application of QDs in the display field, especially the QD-LCD TVs vigorously promoted by manufacturers such as TCL and Samsung, also indicates that their initial commercialization has emerged.

[0003] With the continuous improvement of quantum dot synthesis technology, the continuous optimization of device structures, and the continuous in-depth theoretical research on the lifetime problem of QLED (quantum dot light-emitting diode) devices, the efficiency and lifetime of the devices have been greatly improved. In particular, the device performances of red and green QLEDs have been able to rival those of existing widely used OLEDs (organic light-emitting diodes), marking a solid step towards the true commercialization of QLEDs. Existing high-performance QLEDs usually use ZnO with high electron mobility as the electron transport layer. Due to the fact that the electron mobility in the existing QLED device structure is much higher than the hole mobility, the interfacial charge accumulation between the quantum dot layer and the electron transport layer is very serious, which not only causes excessive heat generation in the device but also leads to an increase in voltage and a significant decrease in lifetime and efficiency.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies of the existing technology, the purpose of the present invention is to provide a quantum dot light-emitting diode and a preparation method thereof, aiming to solve the problem that the electron mobility in existing QLED devices is much higher than the hole mobility, resulting in very serious interfacial charge accumulation between the quantum dot layer and the electron transport layer.

[0006] The technical solution of the present invention is as follows:

[0007] A quantum dot light-emitting diode, which includes:

[0008] A quantum dot layer;

[0009] An anion polymer layer, which is formed on the surface of the quantum dot layer;

[0010] An electron transport layer is formed on the surface of the anion polymer layer.

[0011] In the quantum dot layer of the quantum dot light-emitting diode of the present invention, the surface in contact with the electron transport layer is coordinated with an anion polymer, and the remaining regions of the quantum dot layer still retain the original ligands. According to the principle of like charges repelling and opposite charges attracting, when the surface ligand on the side of the quantum dot layer close to the electron transport layer is replaced with an anion polymer, the injection of electrons with the same charge as the functional groups of this anion polymer can be hindered to a certain extent, thereby contributing to the effective recombination of carriers in the entire quantum dot layer and improving the device performance.

[0012] In a second aspect of the present invention, there is provided a method for manufacturing a quantum dot light-emitting diode, which includes the following steps:

[0013] Form an anion polymer layer on the surface of the quantum dot layer;

[0014] Form an electron transport layer on the surface of the anion polymer layer.

[0015] In the present invention, the surface of the quantum dot layer on the side where the electron transport layer is located is coordinated with an anion polymer, while the remaining regions of the quantum dot layer still remain as the original ligands of the quantum dots. According to the principle of like charges repelling and opposite charges attracting, when the surface ligand on the side of the quantum dot layer close to the electron transport layer is replaced with an anion polymer, the injection of electrons with the same charge as the functional groups of this anion polymer can be hindered to a certain extent, thereby contributing to the effective recombination of carriers in the entire quantum dot layer and improving the device performance. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of a quantum dot light-emitting diode provided in an embodiment of the present invention.

[0017] Figure 2 It is a schematic flow diagram of a method for manufacturing a quantum dot light-emitting diode provided in an embodiment of the present invention.

[0018] Figure 3 It is a schematic diagram before and after ligand exchange of the quantum dot layer in an embodiment of the present invention. Detailed Embodiments

[0019] The present invention provides a quantum dot light-emitting diode and a method for manufacturing the same. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] An embodiment of the present invention provides a quantum dot light-emitting diode, which includes:

[0021] A quantum dot layer;

[0022] An anion polymer layer, which is formed on the surface of the quantum dot layer;

[0023] An electron transport layer, which is formed on the surface of the anion polymer layer.

[0024] In the existing quantum dot light-emitting diodes, the surface of the entire quantum dot layer is usually coordinated with original ligands. In the quantum dot layer of the quantum dot light-emitting diode of this embodiment, the surface in contact with the electron transport layer is coordinated with an anion polymer, and the remaining regions of the quantum dot layer still retain the original ligands. According to the principle of like charge repulsion and opposite charge attraction, when the original ligands on the surface of the quantum dot layer close to the side where the electron transport layer is located are replaced with an anion polymer, it can to a certain extent hinder the injection of electrons with the same charge as the functional groups of this anion polymer, thereby contributing to improving the effective recombination of carriers in the entire quantum dot layer and enhancing the device performance.

[0025] In addition, in the existing quantum dot light-emitting diodes, the original ligands coordinated with the quantum dots are usually non-polar ligands, and the entire surface of the quantum dot layer is in a non-polar state, while the surface of the electron transport layer in contact with the quantum dot layer is in a polar state. In this way, due to the large polarity difference between the quantum dot layer and the electron transport layer, the connection between the quantum dot layer and the electron transport layer is not tight, there are a large number of defects, electron injection is difficult, non-radiative recombination is serious, and the light-emitting performance of the device is low. To solve this technical problem, the existing method is to first perform ligand exchange in the form of a quantum dot solution, and then deposit the quantum dot solution after ligand exchange to form a quantum dot layer, so as to improve the compatibility between the quantum dot layer and the electron transport layer by this method. Although this method can achieve effective ligand exchange, the ligand exchange occurs on the surfaces of all quantum dots, which results in a significant reduction in the fluorescence efficiency of the quantum dots themselves.

[0026] In the quantum dot light-emitting diode of this embodiment, by coordinating the region of the quantum dot layer close to the electron transport layer with an anion polymer, while the remaining regions of the quantum dot layer still remain as non-polar ligands of the quantum dots, ligand exchange in some regions of the quantum dot layer is achieved on the premise of not losing the original fluorescence efficiency of the quantum dots. At the same time, this anion polymer can not only form a dense protective layer on the surface of the quantum dot layer to prevent the surface ligands from falling off due to the polarity difference during the subsequent deposition of the electron transport layer, reduce the defects on the surface of the quantum dots, and thus improve the light-emitting efficiency of the quantum dots.

[0027] In one embodiment, the original ligand is selected from one or more of organic carboxylic acids having 8 or more carbon atoms, primary amines having 8 or more carbon atoms, secondary or tertiary amines having 4 or more branched-chain carbon atoms, and organic phosphines having 4 or more branched-chain carbon atoms, etc.

[0028] In one embodiment, the original ligand is selected from one or more of organic carboxylic acids having 8 to 20 carbon atoms, primary amines having 8 to 20 carbon atoms, secondary or tertiary amines having 4 to 20 branched-chain carbon atoms, and organic phosphines having 4 to 20 branched-chain carbon atoms, etc.

[0029] By way of example, the organic carboxylic acids having 8 to 20 carbon atoms are selected from one or more of octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecenoic acid, and octadecenoic acid, etc.

[0030] By way of example, the primary amines having 8 to 20 carbon atoms are selected from one or more of octylamine, nonylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine, etc.

[0031] By way of example, the secondary or tertiary amines having 4 to 20 branched-chain carbon atoms are selected from one or more of tributylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, and tridecylamine, etc.

[0032] By way of example, the organic phosphines having 4 to 20 branched-chain carbon atoms are selected from one or more of tributylphosphine, trihexylphosphine, triheptylphosphine, trioctylphosphine, trinonylphosphine, and tridecylphosphine, etc.

[0033] In this example, the anionic polymer is a polymer formed by crosslinking polymerization of anionic polymer monomers. Among them, the structural formula of the anionic polymer monomer is X-R, where X is a functional group and R is a carbon chain with a chain length of 4 to 30, and at least one of a double bond and an alkyne bond is present in the R chain. The carbon chain can be a straight chain or a branched chain, etc.

[0034] In one embodiment, the anionic polymer layer is bonded to the surface of the quantum dot layer through an ionic bond, and this ionic bond is formed by the interaction between the functional group in the anionic polymer and the cation in the quantum dot.

[0035] In one embodiment, X is selected from one of sulfonic acid group, carboxyl group, thiol group, etc., but is not limited thereto.

[0036] In one embodiment, the anionic polymer monomer is selected from one or more of sodium styrene sulfonate, sodium vinyl sulfonate, arachidonic acid, docosahexaenoic acid, etc., but is not limited thereto.

[0037] In one embodiment, the anionic polymer is selected from one or more of polystyrene sulfonic acid polymers, vinyl sulfonic acid polymers, arachidonic acid polymers, docosahexaenoic acid polymers, etc., but is not limited thereto.

[0038] In this embodiment, the quantum dot light-emitting diode is divided into two types: a normal structure and an inverted structure, and each structure of the quantum dot light-emitting diode can have various forms. The following takes Figure 1 the quantum dot light-emitting diode with the normal structure shown as an example to introduce the structure and material selection of the quantum dot light-emitting diode in this embodiment. As Figure 1 shown, the quantum dot light-emitting diode sequentially includes a substrate, an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode from bottom to top; wherein, a layer of anionic polymer is formed on the surface of the quantum dot layer on the side where the electron transport layer is located.

[0039] In one embodiment, the substrate can be a rigid substrate or a flexible substrate, and the specific substrate is selected from glass, silicon wafers, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyethersulfone, or a combination thereof, etc.

[0040] In one embodiment, the material of the anode can be selected from nickel, platinum, vanadium, chromium, copper, zinc, gold, or their alloys; the material of the anode can also be selected from one or more of zinc oxide, indium oxide, tin oxide, indium zinc oxide, indium-doped tin oxide, fluorine-doped tin oxide, antimony-doped tin oxide, and aluminum-doped zinc oxide, etc.; the material of the anode can also be any combination of the above two or more.

[0041] In one embodiment, the material of the hole injection layer can be selected from materials with good hole injection performance, for example, but not limited to poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS), copper phthalocyanine (CuPc), 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane (F4-TCNQ), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HATCN), doped or undoped transition metal oxides, doped or undoped metal chalcogenides, etc.; wherein, the transition metal oxides include but are not limited to one or more of MoO3, VO2, WO3, CuO; the metal chalcogenides include but are not limited to one or more of MoS2, MoSe2, WS2, WSe2, CuS. In one embodiment, the thickness of the hole injection layer is 10-150 nm.

[0042] In one embodiment, the material of the hole transport layer may be selected from organic materials with good hole transport ability, such as, but not limited to, poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB), polyvinylcarbazole (PVK), poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (Poly-TPD), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine) (PFB), 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), 4,4'-bis(9-carbazolyl)biphenyl (CBP), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), doped graphene, undoped graphene, C60, or one or more of them. In one embodiment, the thickness of the hole transport layer is 10 - 150 nm.

[0043] In one embodiment, the quantum dots can be selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe of Group II-VI; or GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb of Group III-V; or SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe of Group IV-VI; or a combination of any one or more of the above.

[0044] In one embodiment, the electron transport layer can be selected from one or more of ZnO, TiO2, Alq3, SnO, ZrO, AlZnO, ZnSnO, BCP, TAZ, PBD, TPBI, Bphen, CsCO3. In one embodiment, the thickness of the electron transport layer is 5 to 100 nm.

[0045] In one embodiment, the cathode can be selected from metals or their alloys, such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, lead, cesium, barium, or their alloys; the cathode can also be composed of a multi-layer structural material, for example, composed of a first layer and a second layer located on the first layer, the material of the first layer is an alkali metal halide, an alkaline earth metal halide, an alkali metal oxide, or a combination thereof, and the material of the second layer is an alkaline earth metal, a Group 13 metal, or a combination thereof. For example, the cathode is LiF / Al, LiO2 / Al, LiF / Ca, Liq / Al, and BaF2 / Ca, but not limited thereto.

[0046] An embodiment of the present invention provides a method for preparing a quantum dot light-emitting diode, as Figure 2 shown, including the steps:

[0047] S10. Form an anion polymer layer on the surface of the quantum dot layer;

[0048] S20. Form an electron transport layer on the surface of the anion polymer layer.

[0049] In this embodiment, the surface of the quantum dot layer on the side where the electron transport layer is located is coordinated with an anion polymer, while the remaining regions of the quantum dot layer still remain the original ligands of the quantum dots. According to the principle of like charge repulsion and unlike charge attraction, when the surface ligand of the quantum dot layer close to the side where the electron transport layer is located is replaced with an anion polymer, it can to a certain extent hinder the electron injection with the same charge as the functional group of this anion polymer, thereby contributing to enhancing the effective recombination of carriers in the entire quantum dot layer and improving the device performance.

[0050] In step S10, in one embodiment, the method for forming an anion polymer layer on the surface of the quantum dot layer includes the following steps:

[0051] S11. Provide a quantum dot layer, and the two surfaces (for example, Figure 3 the upper surface and the lower surface in

[0052] are both bound with the original ligands; -4 Under a vacuum condition of <5×10 Figure 3 Pa, ligand exchange is carried out between the anion polymer monomer and the original ligand on one of the two surfaces of the quantum dot layer (for example,

[0053] the upper surface in

[0054] In this embodiment, when an anionic polymer monomer is added to the surface of the quantum dot layer with the original ligand, under the dual induction of the ligand concentration difference and the interaction between the cations on the surface of the quantum dots and the functional groups of the anionic polymer monomer, the anionic polymer monomer will directly diffuse along the quantum dot layer from top to bottom, thereby inducing ligand exchange of the ligand on the surface of the quantum dot layer (the surface in contact with the electron transport layer). At the same time, in order to prevent the entire quantum dot film layer from undergoing ligand exchange due to an excessive concentration difference, vacuum treatment is performed above the quantum dot film layer (the vacuum condition is preferably 5×10 -4 Pa). Under the condition of vacuum pumping, an upward pulling force is generated on the ligand to be exchanged, so as to better balance the ligand exchange that occurs in the entire quantum dot film layer due to an excessive concentration difference of the ligand to be exchanged. Ligand exchange does not occur in the remaining regions of the quantum dot layer, and the remaining regions still have the original ligand of the quantum dots. As Figure 3 shown, the surfaces of all the quantum dots in the quantum dot layer 1 before ligand exchange are coordinated with the original ligand, and the surface on the side close to the electron transport layer in the quantum dot layer 2 after ligand exchange is coordinated with the anionic polymer monomer, while the remaining regions all maintain the original ligand. Then, the anionic polymer monomer on the surface of the quantum dot layer undergoes cross-linking polymerization to generate an anionic polymer. When the ligand on the side of the quantum dot layer close to the electron transport layer is replaced with an anionic polymer, it can to a certain extent hinder the electron injection with the same charge as the functional group of this anionic polymer, thereby contributing to improving the effective recombination of carriers in the entire quantum dot layer and enhancing the device performance.

[0055] In addition, in the existing ligand exchange, it occurs on the surfaces of all quantum dots, which results in a significant reduction in the fluorescence efficiency of the quantum dots themselves. Different from the existing ligand exchange, this embodiment effectively avoids the problem of a significant reduction in the fluorescence efficiency of the quantum dots themselves caused by the existing ligand exchange while maintaining the fluorescence of the original quantum dots without loss, and realizes ligand exchange in some regions on the surface of the quantum dot layer. At the same time, the anionic polymer can not only form a dense protective layer on the surface of the quantum dot layer to prevent the surface ligand from falling off due to polarity differences during the subsequent deposition of the electron transport layer, reduce the defects on the surface of the quantum dots, and thus improve the luminescence efficiency of the quantum dots. In addition, this embodiment has the advantages of simple, mild, effective, fast method and strong universality, and is very suitable for the future large-scale application of quantum dots.

[0056] In this embodiment, the detailed details of the anionic polymer monomer and the anionic polymer are as described above and will not be elaborated here.

[0057] In step S11, the surface of the quantum dot layer is bound with original ligands, that is to say, the quantum dots in the original quantum dot layer are all coordinated with original ligands. For the specific types of the original ligands, please refer to the above, and will not be elaborated here. It should be noted that in this step, in the quantum dot layer, the surfaces of all quantum dots are bound with the original ligands, so the surface of the entire quantum dot layer presents a non-polar state.

[0058] In one embodiment, a method for preparing a quantum dot layer includes the following steps: spin-coating a prepared quantum dot solution, and then performing thermal annealing treatment to obtain a quantum dot layer. Among them, the film thickness can be controlled by adjusting the concentration of the solution, the spin-coating speed, and the spin-coating time. Among them, the quantum dots are quantum dots with original ligands bound to their surfaces. In one embodiment, the thickness of the quantum dot layer can be 20-60 nm, such as 30 nm.

[0059] In one embodiment, the concentration of the quantum dot solution is 10-30 mg / ml. In one embodiment, the solvent used to disperse the quantum dots is selected from at least one of n-octane, n-hexane, cyclohexane, cyclooctane, etc., but is not limited thereto.

[0060] In one embodiment, step S12 includes: adding an anionic polymer monomer to one surface of the quantum dot layer, and then placing it under a vacuum of <5×10 -4 Pa, performing spin-coating to cause ligand exchange between the anionic polymer monomer and the original ligand. After the ligand exchange is completed, the surface of the quantum dot layer is washed, and finally dried to obtain a quantum dot layer with an anionic polymer monomer bound to its surface.

[0061] In one embodiment, step S12 specifically includes: dropping an anionic polymer monomer onto one surface of the quantum dot layer, and then placing it under a vacuum of <5×10 -4 Pa, performing spin-coating, the spin-coating speed is 100-2000 rpm, and the spin-coating time is 10 s-2 min, to cause ligand exchange between the anionic polymer monomer and the original ligand. After the ligand exchange is completed, a small amount of isopropanol is added to wash the surface of the quantum dot layer, and finally dried at 50-120 °C for 30 min-4 h to obtain a quantum dot layer with an anionic polymer monomer bound to its surface. In one embodiment, the volume ratio of isopropanol to the anionic polymer monomer is 1-20:1.

[0062] In one embodiment, according to the mass ratio of the anionic polymer monomer to the quantum dots of 5-30%:1, the anionic polymer monomer is added to one surface of the quantum dot layer, and placed under a vacuum of <5×10 -4 Pa, and ligand exchange is carried out between the anionic polymer monomer and the original ligand located on one surface of the quantum dot layer.

[0063] In this embodiment, when an anionic polymer monomer is added to one surface of the quantum dot layer, under the dual induction of the ligand concentration difference and the interaction between the cations on the quantum dot surface and the functional groups of the anionic polymer monomer, the anionic polymer monomer will directly diffuse along the direction from top to bottom of the quantum dot layer, thereby inducing ligand exchange of the ligands on the surface of the quantum dot layer (the surface in contact with the electron transport layer). At the same time, in order to prevent the entire quantum dot film layer from undergoing ligand exchange due to an excessive concentration difference, vacuum treatment is performed above the quantum dot film layer (the vacuum condition is preferably <5×10 -4 Pa). Under the condition of vacuum pumping, an upward pulling force is generated on the ligands to be exchanged, so as to better balance the problem that the ligand exchange occurs in the entire quantum dot film layer due to an excessive concentration difference of the ligands to be exchanged. In the remaining areas, no ligand exchange occurs, and the remaining areas still have the original ligands of the quantum dots. By using the above ligand exchange method, on the premise of maintaining the fluorescence of the original quantum dots without loss, the problem of a significant reduction in the fluorescence efficiency of the quantum dots caused by the existing ligand exchange is effectively avoided, and ligand exchange occurs in some areas on the surface of the quantum dot layer.

[0064] In step S13, in one embodiment, the conditions for polymerizing the anionic polymer monomer: under the action of an initiator, ultraviolet light curing is performed on the anionic polymer monomer. Under ultraviolet light conditions, under the action of an initiator, the double bonds between the anionic polymer monomers can undergo crosslinking polymerization to obtain an anionic polymer layer. The initiator includes but is not limited to one of phosphine oxide, α-amino ketone, phenyl glyoxylate, monoacyl phosphine, benzyl methyl ketal, hydroxy ketone, etc. It should be noted that this embodiment is not limited to the method of ultraviolet light irradiation, and other conditions can also be used to initiate the crosslinking polymerization of the double bonds between the anionic polymer monomers.

[0065] In one embodiment, the working parameters of ultraviolet light irradiation: the light wavelength is 365 nm, the temperature is 25 - 120 °C, and the light irradiation time is 1 - 60 min. The mass ratio of the initiator to the anionic polymer monomer is 0.001 - 0.1.

[0066] In this embodiment, the obtained quantum dot light-emitting diode can be encapsulated. The encapsulation process can use common machine encapsulation or manual encapsulation. In one embodiment, in the environment of the encapsulation process, the oxygen content and water content are both lower than 0.1 ppm to ensure the stability of the device.

[0067] The present invention will be described in detail below through examples.

[0068] Example 1:

[0069] 1. Ligand exchange was carried out on the CdZnSe / ZnSe / ZnS quantum dot layer with sodium p-styrenesulfonate, and then polymerization was carried out to obtain a quantum dot layer with sodium p-styrenesulfonate polymer in some areas.

[0070] (1) First, deposit the CdZnSe / ZnSe / ZnS quantum dot layer on the hole transport layer. The concentration of the quantum dots is 20 mg / ml, the solvent is n-octane, and the volume is 40 μl.

[0071] (2) Then, 300 μl of sodium p-styrenesulfonate was dropped onto the surface of the quantum dot layer, and then spin coating was carried out under a vacuum condition of 6×10 -4 Pa (the speed is 1000 rpm and the time is 2 min). After completion, 1.5 ml of isopropanol was added to rinse the surface of the quantum dot layer.

[0072] (3) The obtained substrate was dried at 60 °C for 40 min to obtain a quantum dot layer with sodium p-styrenesulfonate in some areas.

[0073] (4) After the exchange was completed, an alcoholic solution of benzil was added, and the mass ratio of benzil to sodium p-styrenesulfonate was 0.02:1. Then, it was placed under UV light for photopolymerization. The working parameters of the UV light: the light wavelength is 365 nm, the temperature is 25 °C, and the light time is 30 min, to obtain a quantum dot layer with sodium p-styrenesulfonate polymer in some areas.

[0074] 2. Preparation of quantum dot light-emitting diodes:

[0075] The quantum dot light-emitting diode of this embodiment includes, from bottom to top in sequence: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are sequentially deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 110 nm; the hole injection layer is PEDOT:PSS with a thickness of 90 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in step 1 above with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 50 nm; the cathode is Al with a thickness of 60 nm.

[0076] Comparative Example 1:

[0077] It is the same as Example 1, except that the quantum dot layer does not go through the ligand exchange and polymerization processes in step 1 above.

[0078] Example 2:

[0079] 1. Ligand exchange was carried out on the CdZnSe / ZnSe / ZnS quantum dot layer with sodium vinylsulfonate, and then polymerization was carried out to obtain a quantum dot layer with vinylsulfonic acid polymer in some areas.

[0080] (1) First, deposit a CdZnSe / ZnSe / ZnS quantum dot layer on the hole transport layer. The concentration of the quantum dots is 20 mg / ml, the solvent is n - octane, and the volume is 40 μl.

[0081] (2) Then, drop 200 μl of sodium vinyl sulfonate onto the surface of the quantum dot layer, and then perform spin - coating (at a speed of 1000 rpm for 1 min) under a vacuum condition of 6×10 -4 Pa. After completion, add 1.5 ml of isopropanol to rinse the surface of the quantum dot layer.

[0082] (3) Place the obtained substrate at 60 °C and dry it for 30 min to obtain a quantum dot layer with sodium vinyl sulfonate in some areas.

[0083] (4) After the exchange is completed, add an alcoholic solution of benzophenone, where the mass ratio of benzophenone to sodium vinyl sulfonate is 0.02:1. Then, place it under UV light for photopolymerization. The working parameters of the UV light: the light wavelength is 365 nm, the temperature is 60 °C, and the light time is 10 min, to obtain a quantum dot layer with vinyl sulfonic acid polymer in some areas.

[0084] 2. Preparation of quantum dot light - emitting diodes:

[0085] The quantum dot light - emitting diode in this embodiment includes, from bottom to top in sequence: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are sequentially deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 110 nm; the hole injection layer is PEDOT:PSS with a thickness of 80 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in Step 1 above with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 40 nm; the cathode is Al with a thickness of 60 nm.

[0086] Comparative Example 2:

[0087] It is the same as Example 2, except that the quantum dot layer does not go through the ligand exchange and polymerization processes in Step 1 above.

[0088] Example 3:

[0089] 1. Perform ligand exchange on the CdZnSe / ZnSe / ZnS quantum dot layer with arachidonic acid, and then polymerize to obtain a quantum dot layer with arachidonic acid polymer in some areas.

[0090] ((1) First, deposit a CdZnSe / ZnSe / ZnS quantum dot layer on the hole transport layer. The concentration of the quantum dots is 20 mg / ml, the solvent is n - octane, and the volume is 40 μl.

[0091] (2) Then, 230 μL of arachidonic acid was dropped onto the surface of the quantum dot layer, and then spin coating was carried out under a vacuum condition of 6×10 - 4 Pa (speed: 1000 rpm, time: 3 min). After completion, 1.8 mL of isopropanol was added to rinse the surface of the quantum dot layer.

[0092] (3) The obtained substrate was dried at 70 °C for 40 min to obtain a quantum dot layer with arachidonic acid in some regions.

[0093] (4) After the exchange was completed, an alcoholic solution of benzophenone was added, where the mass ratio of benzophenone to arachidonic acid was 0.02:1. Then, it was placed under UV light for photopolymerization, where the working parameters of the UV light: light wavelength was 365 nm, temperature was 80 °C, and light exposure time was 50 min, to obtain a quantum dot layer with arachidonic acid polymer in some regions.

[0094] 2. Preparation of quantum dot light-emitting diodes:

[0095] The quantum dot light-emitting diode of this embodiment includes, from bottom to top in sequence: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are sequentially deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 120 nm; the hole injection layer is PEDOT:PSS with a thickness of 100 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in step 1 above with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 40 nm; the cathode is Al with a thickness of 60 nm.

[0096] Comparative Example 3:

[0097] It is the same as Example 3, except that the quantum dot layer does not go through the ligand exchange and polymerization processes in step 1 above.

[0098] Example 4:

[0099] 1. For Cd x Zn 1-x Se / Cd y Zn 1-y Se / ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer was subjected to ligand exchange with sodium p-styrenesulfonate and then polymerized to obtain a quantum dot layer with p-styrenesulfonic acid polymer in some regions.

[0100] (1) First, Cd x Zn 1-x Se / Cdy Zn 1-y A ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer. The quantum dot concentration is 20 mg / ml, the solvent is n-octane, and the volume is 40 μl.

[0101] (2) Then, 300 μl of sodium p-styrenesulfonate was dropped onto the surface of the quantum dot layer, and then spin coating was carried out under a vacuum condition of 6×10 -4 Pa (spin coating speed: 1000 rpm, time: 2 min). After completion, 1.5 ml of isopropanol was added to rinse the surface of the quantum dot layer.

[0102] (3) The obtained substrate was dried at 60 °C for 40 min to obtain a quantum dot layer with sodium p-styrenesulfonate in some regions.

[0103] (4) After the exchange was completed, an alcoholic solution of benzil was added, where the mass ratio of benzil to sodium p-styrenesulfonate was 0.02:1. Then, it was placed under UV light for photopolymerization. The working parameters of the UV light: light wavelength was 365 nm, temperature was 25 °C, and light exposure time was 20 min, to obtain a quantum dot layer with p-styrene sulfonic acid polymer in some regions.

[0104] 2. Preparation of quantum dot light-emitting diodes:

[0105] The quantum dot light-emitting diode of this example, from bottom to top, successively includes: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are successively deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 110 nm; the hole injection layer is PEDOT:PSS with a thickness of 90 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in Step 1 above, with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 50 nm; the cathode is Al with a thickness of 60 nm.

[0106] Comparative Example 4:

[0107] It is the same as Example 1, except that the quantum dot layer does not undergo the ligand exchange and polymerization processes in Step 1 above.

[0108] Example 5:

[0109] 1. For Cd x Zn 1-x Se / Cd y Zn 1-yThe Se / ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer is subjected to ligand exchange with sodium vinyl sulfonate, and then polymerized to obtain a quantum dot layer with vinyl sulfonic acid polymer in some regions.

[0110] (1) First, deposit Cd x Zn 1-x Se / Cd y Zn 1-y Se / ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer. The quantum dot concentration is 20 mg / ml, the solvent is n-octane, and the volume is 40 microliters.

[0111] (2) Then, drop 200 microliters of sodium vinyl sulfonate onto the surface of the quantum dot layer, and then spin-coat it (speed: 1000 rpm, time: 1 min) under a vacuum condition of 6×10 -4 Pa. After completion, add 1.5 ml of isopropanol to rinse the surface of the quantum dot layer.

[0112] (3) Place the obtained substrate in an oven at 60 °C for 30 min to obtain a quantum dot layer with sodium vinyl sulfonate in some regions.

[0113] (4) After the exchange is completed, add an alcoholic solution of benzophenone, where the mass ratio of benzophenone to sodium vinyl sulfonate is 0.02:1. Then, place it under UV light for photopolymerization. The working parameters of the UV light: light wavelength is 365 nm, temperature is 120 °C, and light exposure time is 25 min, to obtain a quantum dot layer with vinyl sulfonic acid polymer in some regions.

[0114] 2. Preparation of quantum dot light-emitting diodes:

[0115] The quantum dot light-emitting diode in this example includes, from bottom to top in sequence: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are sequentially deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 110 nm; the hole injection layer is PEDOT:PSS with a thickness of 80 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in step 1 above with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 40 nm; the cathode is Al with a thickness of 60 nm.

[0116] Comparative Example 5:

[0117] It is the same as Example 5, except that the quantum dot layer does not undergo the ligand exchange and polymerization processes in step 1 above.

[0118] Example 6:

[0119] 1. For Cd x Zn 1-x Se / Cd y Zn 1-y Se / ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer is subjected to ligand exchange with arachidonic acid, and then polymerized to obtain a quantum dot layer with arachidonic acid polymer in some regions.

[0120] (1) First, deposit Cd x Zn 1-x Se / Cd y Zn 1-y Se / ZnSe / CdZnS (0 < x < 1, 0 < y < 1, and x < y) quantum dot layer on the hole transport layer. The quantum dot concentration is 20 mg / ml, the solvent is n - octane, and the volume is 40 μl.

[0121] (2) Then, drop 230 μl of arachidonic acid onto the surface of the quantum dot layer, and then perform spin - coating (speed: 1000 rpm, time: 3 min) under a vacuum condition of 6×10 - 4 Pa. After completion, add 1.8 ml of isopropanol to rinse the surface of the quantum dot layer.

[0122] (3) Place the obtained substrate in an oven at 70 °C and dry for 40 min to obtain a quantum dot layer with arachidonic acid in some regions.

[0123] (4) After the exchange is completed, add an alcohol solution of benzil, where the mass ratio of benzil to arachidonic acid is 0.02:1. Then, place it under UV light for photo - polymerization. The working parameters of the UV light: light wavelength is 365 nm, temperature is 30 °C, and light exposure time is 30 min to obtain a quantum dot layer with arachidonic acid polymer in some regions.

[0124] 2. Preparation of quantum dot light - emitting diode:

[0125] The quantum dot light - emitting diode in this embodiment includes, from bottom to top in sequence: an anode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a cathode, which are sequentially deposited on a substrate. Among them, the substrate is a glass substrate; the anode is ITO with a thickness of 120 nm; the hole injection layer is PEDOT:PSS with a thickness of 100 nm; the hole transport layer is TFB with a thickness of 70 nm. The quantum dot layer is the quantum dot layer prepared in step 1 above with a thickness of 60 nm. The electron transport layer is ZnO with a thickness of 40 nm; the cathode is Al with a thickness of 60 nm.

[0126] Comparative Example 6:

[0127] Consistent with Example 6, except that the quantum dot layer does not undergo the ligand exchange and polymerization processes in Step 1 above.

[0128] Table 1. EQE (%) of the devices prepared in the comparative example and Examples 1-6

[0129]

[0130] The performance of the quantum dot layers and quantum dot light-emitting diodes prepared in the comparative example and Examples 1-6 was tested as follows:

[0131] External quantum dot efficiency:

[0132] The ratio of the number of electron-hole pairs injected into the quantum dots converted into the number of emitted photons, with the unit of %, is an important parameter to measure the quality of electroluminescent devices and can be obtained by measuring with an EQE optical test instrument. The specific calculation formula is as follows:

[0133]

[0134] In the formula, ηe is the optical output coupling efficiency, ηr is the ratio of the number of recombined carriers to the number of injected carriers, χ is the ratio of the number of excitons generating photons to the total number of excitons, and K R is the radiation process rate, and K NR is the non-radiation process rate.

[0135] In summary, the present invention provides a quantum dot light-emitting diode and a preparation method thereof. By coordinating the surface of the quantum dot layer on the side where the electron transport layer is located with an anionic polymer, while the remaining regions of the quantum dot layer still remain the original ligands of the quantum dots. According to the principle of like charge repulsion and unlike charge attraction, when the surface ligand of the quantum dot layer close to the side where the electron transport layer is located is replaced with an anionic polymer, it can to a certain extent hinder the injection of electrons with the same charge as the functional groups of this anionic polymer, thereby contributing to improving the effective recombination of carriers in the entire quantum dot layer and enhancing the device performance. In addition, by coordinating the region of the quantum dot layer close to the electron transport layer with an anionic polymer, while the remaining regions of the quantum dot layer still remain the original ligands of the quantum dots, in this way, on the premise of not losing the original fluorescence of the quantum dots, the problem of a significant reduction in the fluorescence efficiency of the quantum dots caused by the existing ligand exchange is effectively avoided, and ligand exchange occurs in some regions on the surface of the quantum dot layer.

[0136] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a quantum dot light-emitting diode, characterized in that, It includes the following steps: Form an anionic polymer layer on the surface of the quantum dot layer; Form an electron transport layer on the surface of the anionic polymer layer; The preparation method for forming the anionic polymer layer on the surface of the quantum dot layer includes the following steps: Provide a quantum dot layer, and original ligands are bonded to both surfaces of the quantum dot layer; Under a vacuum condition of <5x10 -4 Pa, ligand exchange is carried out using an anionic polymer monomer and the original ligand located on only one surface close to the electron transport layer among the two surfaces of the quantum dot layer, to obtain a quantum dot layer with an anionic polymer monomer bound to the surface; Cause the anionic polymer monomer to undergo a polymerization reaction to obtain the anionic polymer layer.

2. The preparation method of the quantum dot light-emitting diode according to claim 1, wherein, The structural formula of the anionic polymer monomer is X-R, where X is a functional group and R is a carbon chain with a chain length greater than or equal to 4 and less than or equal to 30, and at least one of a double bond and an alkyne bond is present in the R chain.

3. The preparation method of the quantum dot light-emitting diode according to claim 2, wherein The X is selected from one of a sulfonic acid group, a carboxyl group, and a thiol group.

4. The method for preparing a quantum dot light-emitting diode according to claim 2, wherein The anionic polymer monomer is selected from one or more of sodium p-styrenesulfonate, sodium vinylsulfonate, arachidonic acid, and docosahexaenoic acid.

5. The preparation method of the quantum dot light-emitting diode according to claim 1, wherein The mass ratio of the anionic polymer monomer to the quantum dots is 5-30%:

1.

6. The preparation method of the quantum dot light-emitting diode according to claim 1, wherein, The conditions for causing the anionic polymer monomer to undergo a polymerization reaction: ultraviolet light irradiation is performed on the anionic polymer monomer.

7. A quantum dot light emitting diode, characterized in that, The quantum dot light-emitting diode is prepared by using the preparation method according to any one of claims 1-6.

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