WO2019128756A1 - 复合薄膜及其制备方法和应用 - Google Patents

复合薄膜及其制备方法和应用 Download PDF

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WO2019128756A1
WO2019128756A1 PCT/CN2018/121478 CN2018121478W WO2019128756A1 WO 2019128756 A1 WO2019128756 A1 WO 2019128756A1 CN 2018121478 W CN2018121478 W CN 2018121478W WO 2019128756 A1 WO2019128756 A1 WO 2019128756A1
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zinc oxide
layer
nano
film
light emitting
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PCT/CN2018/121478
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French (fr)
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吴龙佳
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Tcl集团股份有限公司
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Publication of WO2019128756A1 publication Critical patent/WO2019128756A1/zh
Priority to US16/909,152 priority Critical patent/US11355725B2/en

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/14—Carrier transporting layers
    • H10K50/16—Electron transporting layers
    • H10K50/166—Electron transporting layers comprising a multilayered structure
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/14—Carrier transporting layers
    • H10K50/16—Electron transporting layers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G9/00—Compounds of zinc
    • C01G9/02—Oxides; Hydroxides
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/125—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light
    • H10K50/13—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light comprising stacked EL layers within one EL unit
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/14—Carrier transporting layers
    • H10K50/15—Hole transporting layers
    • H10K50/156—Hole transporting layers comprising a multilayered structure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C01P2004/86—Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
    • H—ELECTRICITY
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/10—Transparent electrodes, e.g. using graphene
    • H10K2102/101—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO]
    • H10K2102/103—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO] comprising indium oxides, e.g. ITO
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/301—Details of OLEDs
    • H10K2102/331—Nanoparticles used in non-emissive layers, e.g. in packaging layer
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/301—Details of OLEDs
    • H10K2102/351—Thickness

Definitions

  • the invention belongs to the technical field of display, and in particular relates to a composite film and a preparation method and application thereof.
  • QLEDs quantum dot light-emitting diodes
  • the nano-zinc oxide electron transport layer prepared by depositing a zinc oxide colloid solution has gradually become the main electron transport layer scheme used in quantum dot light-emitting diodes.
  • the nano-zinc oxide electron transport layer has excellent electron transport capability, and its electron mobility is as high as 10 -3 cm 2 /V ⁇ S or more.
  • nano zinc oxide has a good energy level matching relationship with the cathode and the quantum dot emitting layer, especially the red quantum dot emitting layer, which significantly reduces the injection barrier of electrons from the cathode to the quantum dot emitting layer, and The deeper valence band level can also function to effectively block holes.
  • nano-zinc oxide materials bring excellent performance to quantum dot light-emitting diodes, there are still some problems in the practical application that need to be solved.
  • a quantum dot light emitting diode when used in the field of display technology, as a basic unit of color development, a quantum dot light emitting diode must be capable of emitting red, green, and blue colors. That is to say, in the display technology, three kinds of red, green and blue quantum dot light-emitting diodes composed of three kinds of red, green and blue quantum dot light-emitting layers are needed.
  • the electron injection efficiency of different color light-emitting diodes is also different.
  • the nano-zinc oxide electron transport layer and the red quantum dot light-emitting layer have a very good energy level matching relationship, and the conduction band levels of the two are very close, which makes the red quantum dot light-emitting diode have excellent electron injection. effectiveness.
  • the conduction band energy level of the quantum dot light-emitting layer is continuously increased, and an electron injection barrier between the nano-zinc oxide electron transport layer and the nano-zinc oxide electron transport layer It is also growing (see Figure 1).
  • the conduction band energy level of the blue quantum dot light-emitting layer is significantly higher than that of the nano-zinc oxide electron transport layer, which greatly increases the electron injection barrier in the QLED device. In turn, the electron injection efficiency in the QLED device is significantly reduced.
  • the method of doping zinc oxide with metal ions can increase the conduction band energy level of the zinc oxide electron transport layer, and can also make the valence band energy level of the zinc oxide electron transport layer shallow, thereby causing the loss of hole blocking. A function that severely disrupts the device performance of QLED devices.
  • the invention provides a composite film and a preparation method thereof, and a light-emitting device comprising the same, which aims to solve the problem between a nano-zinc oxide electron transport layer and a cathode and a quantum dot light-emitting layer in a blue or green quantum dot light-emitting diode.
  • the level matching relationship is poor, resulting in a problem of high electron injection barrier.
  • the present invention is achieved by the first aspect, and provides a composite film comprising a N-layer film laminated in sequence, the N-layer film being a nano-ZnO film, and from the first film to The N-th film, the particle size of the nano-zinc oxide in the nano-zinc oxide film is increased layer by layer, wherein the value range of the N satisfies: 3 ⁇ N ⁇ 9.
  • a method of preparing a composite film comprising the steps of:
  • N-layer nano zinc oxide film is increased layer by layer or layer by layer to obtain a composite film, wherein the value range of the N is satisfied: 3 ⁇ N ⁇ 9.
  • a light emitting device comprising an anode and a cathode, and a light emitting layer and an electron transport layer disposed in a laminated manner between the anode and the cathode, the electron transport layer being disposed adjacent to the cathode,
  • the luminescent layer is disposed adjacent to the anode, the electron transport layer is the composite film described above; or the electron transport layer is a composite film prepared by the above method, and along the direction of the luminescent layer to the cathode, The first layer of film to the Nth layer film, wherein the particle size of the nano zinc oxide in the composite film increases layer by layer.
  • the composite film provided by the invention adopts nanometer zinc oxide as a constituent material, and is formed by compounding an N-layer film whose particle size of nano-zinc oxide is increased layer by layer, and can be obtained without doping other metal ions in the nano zinc oxide.
  • the layers have good energy level matching relationship, which solves the problem of high electron injection barrier in blue or green quantum dot light emitting diode devices.
  • the valence band energy level of the composite film is gradually deepened, further enhancing the blocking effect of the zinc oxide electron transport layer on holes, and significantly improving the luminous efficiency and device performance of the QLED device.
  • the composite film provided by the present invention does not need to introduce any other organic compound or inorganic compound as a dopant of the zinc oxide material, so there is no risk of introducing impurities, and thus it is not required to be used as an electron transport layer of the light-emitting device. Any complicated process helps to simplify the process and reduce costs.
  • the preparation method of the composite film provided by the invention can be prepared by simply preparing a zinc oxide colloid solution having different particle diameters and depositing the film into a film by a simple low-temperature solution method, thereby gradually obtaining a conduction band energy level.
  • the film prepared by the method can simultaneously realize the two functions of improving the electron injection efficiency in the blue quantum dot light emitting diode or the green quantum dot light emitting diode device and enhancing the hole blocking effect of the zinc oxide electron transport layer, and has strong applicability. And practicality, can significantly improve the luminous efficiency and device performance of QLED devices.
  • the method requires less equipment, and when synthesizing the zinc oxide colloidal solution, it is not necessary to introduce any other organic compound or inorganic compound as a dopant of the zinc oxide material, so there is no risk of introducing impurities, and thus, as a luminescence
  • the electron transport layer of the device does not need to perform any complicated processing, the operation process is simple, the cost is low, and the repeatability is good, and the prepared zinc oxide colloid solution has excellent monodispersity and stability.
  • the light-emitting device provided by the present invention contains the above composite film, and therefore, the light-emitting efficiency and device performance of the light-emitting device can be remarkably improved.
  • 1 is a schematic diagram of energy levels of red, green and blue three-color quantum dot light-emitting diodes provided by the prior art
  • FIG. 2 is a schematic structural diagram of a quantum dot light emitting diode according to an embodiment of the present invention.
  • first and second are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated.
  • features defining “first” and “second” may include one or more of the features either explicitly or implicitly.
  • the meaning of "a plurality" is two or more unless specifically and specifically defined otherwise.
  • the change in the particle size of the nano zinc oxide particles directly leads to a change in the forbidden band width of the nano zinc oxide material.
  • the smaller the particle size the wider the forbidden band width of the nano zinc oxide material.
  • the widening of the forbidden band width will bring about an increase in the conduction band level of the nano zinc oxide material and a deepening of the valence band level. Therefore, the nano-zinc oxide electron transport layer whose particle size gradually changes has a gradually increasing conduction band energy level and a gradually deepening valence band energy level.
  • the embodiment of the present invention provides a composite film comprising a N-layer film laminated in sequence, wherein the N-layer film is a nano-ZnO film (ie, the composite film is a multi-layer nano-ZnO film) a composite nano-zinc oxide composite film), and from the first film to the N-th film, the particle size of the nano-zinc oxide in the nano-zinc oxide film increases layer by layer, wherein the range of the N is satisfied :3 ⁇ N ⁇ 9.
  • the composite film provided by the embodiment of the invention adopts nano zinc oxide as a constituent material, and is formed by compounding an N-layer film with a particle size increase of nano zinc oxide layer by layer, and does not need to dope other metal ions in the nano zinc oxide.
  • a composite film composed of nano zinc oxide having a conduction band energy level gradually increasing and a valence band energy level becoming deeper is obtained. Since the composite film has a gradually higher conduction band energy level, when the composite film is used as an electron transport layer of a blue quantum dot light emitting diode or a green quantum dot light emitting diode, the cathode and the blue quantum dot emit a second layer.
  • the green quantum dot luminescent layer has a good energy level matching relationship, which solves the problem of high electron injection barrier in blue or green quantum dot light emitting diode devices.
  • the valence band energy level of the composite film is gradually deepened, further enhancing the blocking effect of the zinc oxide electron transport layer on holes, and significantly improving the luminous efficiency and device performance of the QLED device.
  • the composite film provided by the embodiment of the present invention does not need to introduce any other organic compound or inorganic compound as a dopant of the zinc oxide material, so there is no risk of introducing impurities, and thus is not used as an electron transport layer of the light-emitting device. Any complicated processing is required to simplify the process and reduce costs.
  • the nano zinc oxide composite film has a particle size increasing layer by layer, and the maximum particle size of the nano zinc oxide is ensured between the nano zinc oxide material having the largest particle diameter and the cathode energy level.
  • the particle size of the largest nano zinc oxide is too small, the conduction band level of the nano zinc oxide having the largest particle diameter is excessively increased, and an electron injection barrier is generated between the cathode level and the cathode level.
  • the particle size of the largest nano zinc oxide is too large, the synthesis reaction temperature required to achieve this particle size is too high, resulting in poor dispersion of the obtained nanoparticles, serious agglomeration, and affecting the late formation of the zinc oxide colloidal solution.
  • the nano zinc oxide thin film having the largest particle diameter that is, the nano zinc oxide in the N-th thin film has a particle diameter of 8 to 10 nm, and the reaction temperature used at this time is 70 to 90 °C.
  • the minimum particle size of the nano zinc oxide is to ensure that the conduction band level of the nano zinc oxide material can be significantly increased to be close to the conduction band level of the blue quantum dot light emitting layer or the green quantum dot light emitting layer, and the maximum level is reduced. An electron injection barrier between the electron transport layer and the quantum dot light emitting layer.
  • the particle size of the minimum nano zinc oxide is too large, the conduction band level of the nano zinc oxide material having the smallest particle size is insufficiently improved, and the conduction band level of the blue quantum dot emitting layer or the green quantum dot emitting layer is caused.
  • the nano zinc oxide thin film having the smallest particle diameter, that is, the nano zinc oxide in the first thin film has a particle diameter of 2-3 nm; and the reaction temperature used at this time is 0-10 ° C.
  • the particle size of the nano zinc oxide in the nano zinc oxide film is gradually increased from the minimum particle diameter described above to the maximum particle diameter described above.
  • This method of gradually increasing the particle size minimizes the difference in the conduction band level between the film layer and the film layer, and facilitates the smooth migration of electrons in the nano zinc oxide composite film whose conduction band level is gradually increased.
  • the number of layers of the nano zinc oxide film is an important parameter determining whether electrons can smoothly migrate in the nano zinc oxide composite film.
  • the value range of the N satisfies: 3 ⁇ N ⁇ 9, and the particle size of the nano zinc oxide increases from the minimum particle size to the maximum particle size.
  • the difference in particle size of the nano zinc oxide particles between the film layer and the film layer is large, which means that the difference in the conduction band level between the film layer and the film layer is also It will be larger, which will cause a large electron migration barrier in the nano zinc oxide composite film, affecting the smooth transmission of electrons in the nano zinc oxide composite film; and when the number of layers of the nano zinc oxide film is too large Moreover, the thickness of the nano zinc oxide composite film is too thick, hindering the injection of electrons, and affecting the charge injection balance of the device. Further preferably, the value range of the N satisfies: 5 ⁇ N ⁇ 7, and the particle size of the nano zinc oxide increases from the minimum particle size to the maximum particle size.
  • the thickness of the single-layer nano zinc oxide is 10-20 nm, and the total thickness of the composite film is 30-180 nm.
  • the total thickness of the composite film is less than 30 nm, the film layer used as the electron transport layer is easily broken down by electrons, and the carrier injection performance cannot be ensured; when the total thickness of the composite film is greater than 180 nm, it is used as an electron. When the layer is transported, it will hinder the injection of electrons and affect the charge injection balance of the device. More preferably, when the number of layers of the composite film is 5-7 layers, the total thickness of the composite film is 50-140 nm.
  • the composite film provided by the embodiment of the present invention can be obtained by the following method.
  • a method for preparing a composite film comprises the following steps:
  • the preparation method of the composite film provided by the embodiment of the invention can be prepared by simply preparing a zinc oxide colloid solution having different particle diameters and depositing the film into a film by a simple low-temperature solution method, thereby obtaining a gradually increasing energy level of the conduction band.
  • the film prepared by the method can simultaneously realize the two functions of improving the electron injection efficiency in the blue quantum dot light emitting diode or the green quantum dot light emitting diode device and enhancing the hole blocking effect of the zinc oxide electron transport layer, and has strong applicability. And practicality, can significantly improve the luminous efficiency and device performance of QLED devices.
  • the method requires less equipment, and when synthesizing the zinc oxide colloidal solution, it is not necessary to introduce any other organic compound or inorganic compound as a dopant of the zinc oxide material, so there is no risk of introducing impurities, and thus, as a luminescence
  • the electron transport layer of the device does not need to perform any complicated processing, the operation process is simple, the cost is low, and the repeatability is good, and the prepared zinc oxide colloid solution has excellent monodispersity and stability.
  • the mixed solution of the zinc salt and the alkali is formed by dissolving a zinc salt or an alkali in a solvent.
  • the zinc salt is used as a zinc source to provide zinc for preparing a nano zinc oxide film
  • the zinc salt includes but is not limited to zinc acetate and its hydrate, zinc nitrate and its hydrate, zinc sulfate and hydrate thereof. At least one of a substance, zinc chloride, a hydrate thereof, and the like.
  • the reaction process of preparing a zinc oxide colloidal solution having different particle diameters of nano zinc oxide by using a mixed solution of zinc salt and alkali is: reacting a zinc salt solution with an alkali solution to form a zinc hydroxide intermediate, followed by hydrogen
  • the zinc oxide intermediate undergoes a polycondensation reaction to gradually form nano zinc oxide particles.
  • the base provides a hydroxide ion for the reaction and plays an indispensable role.
  • the base is at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, TMAH, aqueous ammonia, ethanolamine, and ethylenediamine.
  • the solvent for forming a mixed solution of a zinc salt and a base may be an organic solvent or an inorganic solvent, and may be specifically selected from the group consisting of water, methanol, ethanol, propanol, butanol, ethylene glycol, and ethylene glycol monomethyl ether. At least one of DMSO, but is not limited thereto.
  • the mixed solution of the zinc salt and the alkali in the embodiment of the invention can be prepared by adding a zinc salt and a base to a solvent.
  • the mixed solution of the zinc salt and the alkali is prepared by dissolving the zinc salt in a solvent to obtain a salt solution; dissolving the alkali in the same or different solvent to obtain an alkali solution; The solution and the alkali solution are mixed to obtain a mixed solution.
  • the above steps can be carried out at room temperature (10-30 ° C).
  • the molar ratio of hydroxide ions to metal ions in the mixed solution is 1.5:1 to 2.5:1 to ensure the formation of doped nano zinc oxide particles and reduce the formation of reaction by-products.
  • the metal salt is significantly excessive, resulting in a large amount of metal salt unable to form nano zinc oxide particles; and when the molar ratio of hydroxide ion to metal ion is greater than 2.5:1
  • the lye is significantly excessive, and the excess hydroxide ions form a stable complex with the hydroxide intermediate, and cannot be polycondensed to form nano zinc oxide particles.
  • the molar ratio of hydroxide ions to metal ions in the mixed solution is selected from 1.5:1 to 2:1.
  • the mixed solution is reacted to obtain a zinc oxide colloid solution containing a metal ion doped: the mixed solution is reacted at 0-90 ° C for 30-240 min to prepare a zinc oxide colloid solution.
  • the above temperatures ensure the formation of nano zinc oxide particles and achieve good particle dispersibility while providing a sufficient temperature range for significant changes in the particle size of the nano zinc oxide particles.
  • the reaction temperature is lower than 0 ° C, the reaction temperature is too low, which will significantly slow down the formation of nano zinc oxide particles, and even can not produce nano zinc oxide particles, but only the hydroxide intermediate; and when the reaction temperature is higher than 90 ° C The obtained nano zinc oxide particles have poor dispersibility and agglomeration, which affects the late film formation of the doped zinc oxide colloid solution. Further, the reaction time is 30-240 min to ensure the formation of doped nano zinc oxide particles and control the particle size of the nanoparticles.
  • the reaction time is less than 30 min, the reaction time is too short, the formation of nano zinc oxide particles is insufficient, and the obtained nanoparticles have poor crystallinity; and when the reaction time exceeds 4 h, the excessively long particles grow up to cause the generated nanometers.
  • the particles are too large and the particle size is not uniform, which affects the late film formation of the zinc oxide colloidal solution. More preferably, the reaction time is from 1 to 2 hours.
  • the volume ratio of the precipitating agent to the reaction system solution is 2:1 to 6:1, so as to ensure that the excessive precipitant is destroyed to destroy the doped zinc oxide under the premise of sufficiently precipitating the nano zinc oxide particles containing the doped metal ions.
  • the solubility of the particles More preferably, the volume ratio of the precipitating agent to the reaction system solution is selected from 3:1 to 5:1.
  • the precipitant is one of the less polar solvents including, but not limited to, ethyl acetate, n-hexane, n-heptane, acetone, and the like.
  • the white precipitate obtained after centrifugation is again dissolved in the reaction solvent, and the washing is repeated several times to remove the reactants not involved in the reaction, and the finally obtained white precipitate is collected, which is soluble in the solvent to obtain an unequal metal ion having a larger ionic radius.
  • a doped zinc oxide colloidal solution that is, a colloidal solution containing nano-zinc oxide particles doped with a metal.
  • the zinc oxide colloid solution is synthesized by the low temperature solution method, and the zinc salt reacts with the alkali solution to form a hydroxide intermediate in the whole process of the low temperature solution method, and then the polycondensation reaction of the hydroxide intermediate gradually forms nano-oxidation.
  • Zinc particles the formation of nano zinc oxide particles are carried out in the liquid phase.
  • the zinc oxide colloid solution prepared by the low temperature solution method is simple, the cost is low, the operation is easy, the equipment requirement is low, and the repeatability is good.
  • the low temperature solution may be a low temperature alcoholysis method (using an alcohol as a solvent) or a low temperature hydrolysis method (using water as a solvent).
  • the embodiment of the present invention needs to synthesize nano zinc oxide particles.
  • a plurality of zinc oxide colloidal solutions having a gradually changing particle size, and the adjustment of the particle size of the nanoparticles is achieved by controlling the temperature of the synthesis reaction of the low temperature solution method. That is, a step of preparing a zinc oxide colloid solution having different particle diameters of nano zinc oxide by providing a mixed solution of a zinc salt and an alkali, comprising:
  • the zinc oxide colloidal solution having different particle diameters of the nano zinc oxide is prepared by changing the reaction temperature of the mixed solution of the zinc salt and the alkali, wherein the reaction temperature ranges from 0 to 90 °C.
  • the particle size of the nano zinc oxide in the zinc oxide colloid solution having the smallest particle diameter is 2-3 nm; the zinc oxide having the largest particle diameter
  • the nano zinc oxide in the colloidal solution has a particle diameter of 8 to 10 nm.
  • the corresponding reaction temperature is 70 to 90 ° C; the minimum particle diameter of the nano zinc oxide particles used is 2 to 3 nm, corresponding to The reaction temperature is 0 ⁇ 10 °C. That is, the reaction temperature of the zinc oxide colloid solution having the smallest particle diameter is 0 to 10 ° C, and the reaction temperature of the zinc oxide colloid solution having the largest particle diameter is 70 to 90 ° C.
  • the particle size of the obtained nano zinc oxide particles is adjusted according to different reaction temperatures in the preparation process.
  • the fraction of the zinc oxide colloidal solution whose particle diameter needs to be gradually changed is preferably 3 to 9 parts, wherein the particle diameter of each of the zinc oxide colloidal solution is gradually increased from the minimum particle diameter described above to The maximum particle size mentioned above, the corresponding reaction temperature of each zinc oxide colloid solution is also gradually increased from the lowest reaction temperature (0 to 10 ° C) to the highest reaction temperature (70 to 90 ° C).
  • the zinc oxide colloid solution is deposited on the substrate, and the selection of the substrate is not strictly limited, and may be a common substrate for depositing a composite film, or may be deposited with other functional layers, and further needs to be further A functional substrate on which an electron transporting film is deposited, such as a functional substrate on which a laminated bonded anode and a light-emitting layer are deposited, the composite film being deposited on the light-emitting layer.
  • the deposition method is not strictly limited. Based on the colloidal properties of the nano zinc oxide colloidal solution, solution processing can be used. Specifically, it includes, but is not limited to, one of a spin coating method, a knife coating method, a printing method, a spray coating method, a roll coating method, and an electrodeposition method.
  • the zinc oxide colloidal solution having the smallest particle size of the nano zinc oxide particles is first deposited on the substrate, and then the particle size of the nano zinc oxide particles is gradually increased.
  • the zinc oxide colloid solution is deposited in turn, and finally the zinc oxide colloidal solution having the largest particle size of the nano zinc oxide particles is deposited.
  • the zinc oxide colloidal solution having the largest particle size of the nano zinc oxide particles is first deposited on the substrate, and then the particle size of the nano zinc oxide particles is gradually reduced.
  • the order of the zinc oxide colloidal solution is deposited in turn, and finally the zinc oxide colloidal solution having the smallest particle size of the nano zinc oxide particles is deposited.
  • the prepared composite film is used for a light emitting device, particularly a blue quantum dot light emitting diode or a green quantum dot light emitting diode device
  • the quantum dot light emitting diode device is a positive blue quantum dot light emitting diode or a green quantum dot light emitting diode
  • the zinc oxide colloid solution having the smallest particle size of the nano zinc oxide particles is first deposited on the anode, the hole transport layer, the blue or green quantum dots.
  • the zinc oxide colloid solution is sequentially deposited in the order of increasing the particle size of the nano zinc oxide particles, and finally the zinc oxide colloidal solution having the largest particle size of the nano zinc oxide particles is deposited.
  • the quantum dot light emitting diode device is an inverted blue quantum dot light emitting diode or a green quantum dot light emitting diode
  • the particle size of the nano zinc oxide particles is firstly The largest zinc oxide colloid solution is deposited on the substrate on which the cathode has been deposited, and then the zinc oxide colloid solution is sequentially deposited in the order of decreasing particle size of the nano zinc oxide particles, and finally the zinc oxide colloid solution having the smallest particle size of the nano zinc oxide particles is deposited.
  • a plurality of doped zinc oxide colloidal solutions having a gradually increasing band energy level and a gradual deepening of the valence band energy level are synthesized by a simple low temperature solution method.
  • a nano zinc oxide composite film with gradually increasing the conduction band energy level and gradually increasing the valence band energy level was prepared. Since the nano zinc oxide composite film has a gradually higher conduction band energy level, the electron transport layer has a good energy level matching relationship with the cathode and the blue or green quantum dot light emitting layer, thereby substantially solving the blue color.
  • the high electron injection barrier in the green quantum dot light-emitting diode device, and the valence band energy level will gradually deepen, ensuring the blocking effect of the zinc oxide electron transport layer on the hole after doping, thereby significantly improving the Luminous efficiency and device performance of QLED devices.
  • a light emitting device comprising an anode and a cathode, and a light emitting layer and an electron transport layer laminated and disposed between the anode and the cathode, the electron transport layer being disposed adjacent to the cathode, the light emitting layer being close to
  • the electron transport layer is the composite film described above; or the electron transport layer is a composite film prepared by the above method, and along the direction of the light emitting layer to the cathode, from the first film to the film
  • the light-emitting device provided by the embodiment of the invention contains the above composite film, and therefore, the luminous efficiency and device performance of the light-emitting device can be remarkably improved.
  • the illuminating layer may be an organic luminescent layer or a quantum dot luminescent layer.
  • the light emitting diode device is an organic light emitting diode (OLED) device; when the light emitting layer is a quantum dot light emitting layer, the light emitting diode is a quantum dot light emitting diode ( QLED) device.
  • the light emitting device is a blue quantum dot light emitting device or a green quantum dot light emitting device, and the light emitting device comprises a stacked combined blue or green quantum dot light emitting layer, an electron transport layer and a cathode, wherein the electron transport The layer is the composite film.
  • the end of the composite film in contact with the cathode has nano zinc oxide particles having the largest particle diameter, and thus the electron transport layer at the end has the lowest conduction band energy level substantially consistent with the cathode energy level.
  • the end of the composite film contacting the blue quantum dot light emitting layer or the green quantum dot emitting layer has the smallest particle size of the nano zinc oxide particles, so the electron transporting layer has the highest energy level compared with the quantum dot emitting layer. Closed conduction band energy level. Between the two ends of the composite film, the particle size of the nano zinc oxide particles gradually changes, which means that the conduction band energy level of the nano zinc oxide electron transport layer gradually changes, and the electrons are minimized in the transport layer. Barriers to internal migration.
  • Such an energy level structure simultaneously ensures a good energy level matching relationship between the electron transport layer and the cathode and between the electron transport layer and the blue quantum dot light emitting layer or the green quantum dot light emitting layer, and the nano zinc oxide electron transport layer
  • the internal continuous energy level changes ensure the smooth migration of electrons inside the transport layer, making the nano-zinc oxide electron transport layer with gradually increasing the conduction band level, which minimizes the blue quantum dot light-emitting diode or green quantum dot.
  • An electron injection barrier in the light emitting diode is an electron injection barrier in the light emitting diode.
  • the valence band energy level of the nano zinc oxide electron transport layer in the embodiment of the present invention is also gradually deepened, and has the deepest valence band energy level at the end of the blue quantum dot light emitting layer or the green quantum dot light emitting layer, and further strengthens The blocking effect of the zinc oxide electron transport layer on holes.
  • the nano-zinc oxide electron transport layer in which the conduction band energy level is gradually increased and the valence band energy level is gradually deepened in the embodiment of the present invention is applied to a blue or green quantum dot light-emitting diode device, which significantly improves the QLED. Luminous efficiency and device performance of the device.
  • the light emitting device includes an anode 2 laminated on the substrate 1, a hole transport layer 3, a blue or green quantum dot light emitting layer 4, an electron transport layer 5, and The cathode 6, wherein the electron transport layer 5 is the above composite film, and the particle diameter of the nano zinc oxide in the composite film is reduced layer by layer along the direction of the cathode 6 to the blue or green quantum dot light-emitting layer 4.
  • the substrate 1 may be a hard substrate or a flexible substrate.
  • a glass substrate may be selected.
  • the anode 2 may be ITO, but is not limited thereto.
  • the hole transport layer 3 may be made of a hole transporting material conventional in the art, including but not limited to TFB, PVK, Poly-TPD, TCTA, CBP, etc. or a mixture of any combination thereof, or other high performance air. Hole transport material.
  • the quantum dots of the blue or green quantum dot light-emitting layer 4 may be one of green and blue quantum dots, and specifically may be CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, GaAs, GaP, GaSb, HgS, HgSe. At least one of HgTe, InAs, InP, InSb, AlAs, AlP, CuInS, CuInSe, and various quantum-shell structure quantum dot or alloy structure quantum dots; or common green and blue quantum dots.
  • the quantum dots may or may not contain cadmium.
  • the thickness of the light-emitting layer is preferably from 20 to 60 nm.
  • the electron transport layer 5 employs the above composite film.
  • the cathode 6 is made of a metal cathode material, such as metallic silver or metallic aluminum, or a nano silver wire or a nano copper wire, and the nano silver wire or the nano copper wire is used, which has a smaller electrical resistance and facilitates the smooth injection of carriers.
  • the thickness of the cathode is preferably 15-30 nm.
  • the obtained light emitting device can be subjected to a packaging process.
  • the embodiment of the invention provides a method for preparing a light-emitting device tube, comprising the following steps:
  • the light-emitting layer material solution is deposited on the anode surface.
  • the luminescent layer material solution may be deposited into a film by spin coating. Specifically, the anode substrate is placed on a homogenizer, and a solution of a certain concentration of the luminescent layer material is spin-coated to form a film, and the thickness of the luminescent layer is controlled by adjusting the concentration of the solution, the spin coating speed, and the spin coating time, and then Thermal annealing at a suitable temperature.
  • the method before preparing the luminescent layer, the method further comprises preparing a hole transport layer on the anode.
  • the hole transport layer may be prepared by the same method as the light-emitting layer, preferably by a solution processing method such as spin coating, and further controlling the film thickness by adjusting the concentration of the solution, the spin coating speed, and the spin coating time, and then at a suitable temperature. Lower thermal annealing treatment.
  • an electron transport layer on the light-emitting layer which is prepared by the method of the above composite film, which will not be described herein. It is worth noting that when the composite film is prepared, the direction along the cathode to the light-emitting layer is prepared. The particle size of the nano zinc oxide in the composite film is reduced layer by layer.
  • a cathode is prepared on the electron transport layer.
  • the substrate on which the functional layers are deposited is placed in an evaporation chamber to thermally evaporate the cathode through a mask.
  • the device is packaged, and the encapsulation conditions are preferably performed under conditions of an oxygen content and a water content of less than 0.1 ppm to ensure the stability of the device.
  • the light-emitting diode can also be obtained by another method.
  • the method for preparing the light-emitting diode includes the following steps:
  • An anode is prepared on the light-emitting layer.
  • each layer refers to the same embodiment. It is noted that, when preparing the composite film, the particle size of the nano zinc oxide in the composite film is layer by layer along the direction from the cathode to the light emitting layer. Reduced.
  • a nano zinc oxide composite film comprising the following steps:
  • an appropriate amount of zinc acetate is added to 50 ml of ethanol solvent to form a zinc salt solution having a total concentration of 0.1 mol/L, and an appropriate amount of lithium hydroxide powder is dissolved in another 50 ml of ethanol solvent to form a concentration of 0.2 mol/L. Lye.
  • the zinc salt solution was then cooled to 0 ° C and the lithium hydroxide solution was added dropwise until the molar ratio of hydroxide ion to zinc ion was 1.7:1. After the completion of the dropwise addition of the lithium hydroxide solution, the mixed solution was further stirred at 0 ° C for 1 h to obtain a homogeneous transparent solution.
  • a heptane solvent having a volume ratio of 3:1 was added to the homogeneous transparent solution to produce a large amount of white precipitate in the transparent solution.
  • the cloudy solution was centrifuged at 7000 rpm, and the resulting white precipitate was again dissolved in an ethanol solvent. This cleaning process is repeated four times.
  • the finally obtained white precipitate was dissolved in an appropriate amount of ethanol solvent to obtain a zinc oxide colloidal solution having a solution concentration of 30 mg/ml and a nanoparticle diameter of 2.3 nm.
  • the above method for synthesizing the zinc oxide colloidal solution was repeated four times, wherein the synthesis reaction temperature was gradually increased to 10 ° C, 25 ° C, 50 ° C and 70 ° C, respectively, and the remaining synthesis parameters were all unchanged. Finally, four zinc oxide colloidal solutions having a solution concentration of 30 mg/ml and nanoparticle particle diameters of 2.8 nm, 3.5 nm, 5.8 nm, and 7.6 nm were obtained. The particle size of the nanoparticles of the above five zinc oxide colloidal solutions were statistically obtained from transmission electron microscopy (TEM) photographs.
  • TEM transmission electron microscopy
  • the conduction band level, the valence band level and the forbidden band width of each zinc oxide colloid solution are obtained by measuring each zinc oxide colloid solution by UV photoelectron spectroscopy (UPS).
  • the conduction band energy level, the valence band energy level and the forbidden band width of each zinc oxide colloid solution in this embodiment are shown in Table 1.
  • the above-mentioned total of five parts of the zinc oxide colloidal solution are sequentially deposited by spin coating on the substrate on which the anode, the hole transport layer and the blue or green quantum dot light-emitting layer have been deposited, in such a manner that the particle size of the zinc oxide particles is gradually increased.
  • the spin coating speed of the zinc oxide colloid solution is gradually increased to control the thickness of each layer of nano zinc oxide film to be about 20 nm.
  • the spin speeds of the five zinc oxide colloidal solutions were 3000 rpm, 3000 rpm, 3500 rpm, 4000 rpm, and 5000 rpm, respectively, and the spin coating time was 30 s.
  • the nano-zinc oxide electron transport layer with the conduction band energy level gradually increasing and the valence band energy level gradually becoming deeper was obtained.
  • the total thickness of the nano zinc oxide electron transport layer is about 100 nm.
  • a nano zinc oxide composite film comprising the following steps:
  • an appropriate amount of zinc nitrate is added to 50 ml of ethanol solvent to form a zinc salt solution with a total concentration of 0.1 mol/L, and an appropriate amount of sodium hydroxide powder is dissolved in another 50 ml of ethanol solvent to form a concentration of 0.3 mol/L. Lye.
  • the zinc salt solution was then cooled to 0 ° C and sodium hydroxide solution was added dropwise until the molar ratio of hydroxide ions to zinc ions was 2:1. After the completion of the dropwise addition of the sodium hydroxide solution, the mixed solution was further stirred at 0 ° C for 2 hours to obtain a homogeneous transparent solution.
  • a 4:1 volume ratio of ethyl acetate solvent was added to the homogeneous clear solution to produce a large amount of white precipitate in the clear solution.
  • the cloudy solution was centrifuged at 7000 rpm, and the resulting white precipitate was again dissolved in an ethanol solvent. This cleaning process is repeated four times.
  • the finally obtained white precipitate was dissolved in an appropriate amount of ethanol solvent to obtain a zinc oxide colloidal solution having a solution concentration of 30 mg/ml and a nanoparticle size of 2.7 nm.
  • the above method for synthesizing the zinc oxide colloidal solution was repeated six times, wherein the synthesis reaction temperature was gradually increased to 5 ° C, 10 ° C, 20 ° C, 30 ° C, 50 ° C and 70 ° C, respectively, and the remaining synthesis parameters were all unchanged. Finally, six parts of a zinc oxide colloidal solution having a solution concentration of 30 mg/ml and a particle diameter of 3.2 nm, 3.9 nm, 4.8 nm, 6.1 nm, 6.9 nm and 8.5 nm were obtained.
  • the particle size of the nanoparticles of the above seven zinc oxide colloidal solutions were statistically obtained from transmission electron microscopy (TEM) photographs.
  • the above-mentioned total of seven parts of the zinc oxide colloidal solution are sequentially deposited by spin coating on the substrate on which the anode, the hole transport layer and the blue or green quantum dot light-emitting layer have been deposited, in such a manner that the particle size of the zinc oxide particles is gradually increased.
  • the spin coating speed of the zinc oxide colloid solution is gradually increased to control the thickness of each layer of nano zinc oxide film to be about 20 nm.
  • the spin speeds of the seven zinc oxide colloidal solutions were 3000 rpm, 3000 rpm, 3500 rpm, 3500 rpm, 4000 rpm, 4000 rpm, and 5000 rpm, respectively, and the spin coating time was 30 s.
  • the nano-zinc oxide electron transport layer with the conduction band energy level gradually increasing and the valence band energy level gradually becoming deeper was obtained.
  • the total thickness of the nano zinc oxide electron transport layer is about 140 nm.
  • a nano zinc oxide composite film comprising the following steps:
  • n-hexane solvent was added to the homogeneous clear solution to produce a large amount of white precipitate in the clear solution.
  • the cloudy solution was centrifuged at 7000 rpm, and the resulting white precipitate was again dissolved in an ethanol solvent. This cleaning process is repeated four times.
  • the finally obtained white precipitate was dissolved in an appropriate amount of ethanol solvent to obtain a zinc oxide colloidal solution having a solution concentration of 30 mg/ml and a nanoparticle particle diameter of 3.6 nm.
  • the above method for synthesizing the zinc oxide colloidal solution was repeated three times, wherein the synthesis reaction temperature was gradually increased to 10 ° C, 25 ° C and 80 ° C, respectively, and the remaining synthesis parameters were all unchanged. Finally, three zinc oxide colloid solutions having a solution concentration of 30 mg/ml and a particle diameter of 4.5 nm, 5.9 nm and 9.3 nm were obtained. The particle size of the nanoparticles of the above four zinc oxide colloidal solutions were statistically obtained from transmission electron microscopy (TEM) photographs.
  • TEM transmission electron microscopy
  • the above-mentioned total of four parts of the zinc oxide colloidal solution are sequentially deposited by spin coating in the order in which the particle size of the zinc oxide particles is gradually increased on the substrate on which the anode, the hole transport layer and the blue or green quantum dot light-emitting layer have been deposited.
  • the spin coating speed of the zinc oxide colloid solution is gradually increased to control the thickness of each layer of nano zinc oxide film to be about 20 nm.
  • the spin-coating speeds of the four zinc oxide colloidal solutions were 3000 rpm, respectively. 3500 rpm, 4000 rpm and 5000 rpm, and the spin coating time was 30 s.
  • the nano-zinc oxide electron transport layer with the conduction band energy level gradually increasing and the valence band energy level gradually becoming deeper was obtained.
  • the total thickness of the nano zinc oxide electron transport layer is about 80 nm.
  • a blue quantum dot light emitting diode or a green quantum dot light emitting diode device comprises, in order from bottom to top, a substrate, a cathode, an electron transport layer, a blue or green quantum dot light emitting layer, a hole transport layer, and an anode.
  • the material of the substrate is a glass piece
  • the material of the cathode is an ITO substrate
  • the material of the electron transport layer is a nano zinc oxide material whose conduction band energy level is gradually increased and the valence band energy level is gradually deepened
  • the material of the hole transport layer is used.
  • the material of the TFB and the anode is Al
  • the electron transport layer is the above composite film, and the particle diameter of the nano zinc oxide in the composite film is reduced layer by layer along the direction of the cathode to the light emitting layer.
  • the method for preparing the above blue quantum dot light emitting diode or green quantum dot light emitting diode device comprises the following steps:
  • a nano zinc oxide electron transport layer having a gradually increasing band level and a gradual deepening of the valence band level is prepared on the cathode;
  • a hole transport layer is deposited on the blue or green quantum dot light-emitting layer, and the anode is vapor-deposited on the hole transport layer to obtain a blue or green quantum dot light-emitting diode.
  • a blue quantum dot light emitting diode or a green quantum dot light emitting diode device comprises, in order from bottom to top, a substrate, an anode, a hole transport layer, a blue or green quantum dot light emitting layer, an electron transport layer and a cathode.
  • the material of the substrate is a glass piece
  • the material of the cathode is an ITO substrate
  • the material of the electron transport layer is a nano zinc oxide material whose conduction band energy level is gradually increased continuously
  • the material of the hole transport layer is TFB and the material of the anode is Al
  • the electron transport layer is the above composite film
  • the particle diameter of the nano zinc oxide in the composite film is reduced layer by layer along the direction from the cathode to the light emitting layer.
  • the method for preparing the above blue quantum dot light emitting diode or green quantum dot light emitting diode device comprises the following steps:
  • a hole transport layer and a blue or green quantum dot light-emitting layer are sequentially prepared on the anode substrate;
  • nano-zinc oxide electron transport layer having a conduction band energy level gradually decreasing and a valence band energy level becoming shallower on a blue or green quantum dot light-emitting layer;
  • the cathode is evaporated on the electron transport layer to obtain a blue or green quantum dot light emitting diode.

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Abstract

一种复合薄膜，所述复合薄膜包括依次层叠结合的N层薄膜，所述N层薄膜均为纳米氧化锌薄膜，且从第一层薄膜到第N层薄膜，所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加，其中，所述N的取值范围满足：3≤N≤9。所述复合薄膜，无需引入任何其它有机化合物或者无机化合物作为氧化锌材料的掺杂物，因而不存在任何引入杂质的风险，进而在作为发光器件的电子传输层时也不需要进行任何复杂的处理过程，有利于简化工艺，降低成本。

Description

复合薄膜及其制备方法和应用 技术领域
本发明属于显示技术领域，尤其涉及一种复合薄膜及其制备方法和应用。
 背景技术
近来，随着显示技术的不断发展，以量子点材料作为发光层的量子点发光二极管（QLED）展现出了巨大的应用前景。由于其发光效率高、发光颜色可控、色纯度高、器件稳定性好、可用于柔性用途等特点，使QLED在显示技术、固态照明等领域受到了越来越多的关注。
近年来，通过沉积氧化锌胶体溶液制得的纳米氧化锌电子传输层逐渐成为了量子点发光二极管中主要采用的电子传输层方案。一方面，纳米氧化锌电子传输层具有优良的电子传输能力，其电子迁移率高达10 -3cm 2/V·S以上。另一方面，纳米氧化锌与阴极和量子点发光层，尤其是红色量子点发光层之间具有良好的能级匹配关系，显著降低了电子从阴极到量子点发光层的注入势垒，并且其较深的价带能级又可以起到有效阻挡空穴的功能。这些特性都使纳米氧化锌电子传输层成为了量子点发光二极管器件的首选，显著提升了器件的稳定性和发光效率。
虽然纳米氧化锌材料为量子点发光二极管带来了优良的性能，但是在实际应用中该材料仍有一些问题亟待解决。例如，当把量子点发光二极管应用在显示技术领域时，作为显色的基本单元，量子点发光二极管必须能够发出红、绿、蓝三种颜色。也就是说，显示技术中需要用到由红色绿色蓝色三种量子点发光层分别组成的红绿蓝三种量子点发光二极管。而当把纳米氧化锌电子传输层应用在红绿蓝三种量子点发光二极管中时，不同颜色的发光二极管其电子注入效率也是不同的。如前文所述，纳米氧化锌电子传输层与红色量子点发光层之间有着非常好的能级匹配关系，两者的导带能级非常接近，这使得红色量子点发光二极管具有优秀的电子注入效率。而在其它两个颜色的量子点发光二极管中，随着发光波长向着短波长方向移动，量子点发光层的导带能级在不断提高，与纳米氧化锌电子传输层之间的电子注入势垒也在不断增大（见图1）。尤其是蓝色量子点发光二极管，其蓝色量子点发光层的导带能级要明显高于纳米氧化锌电子传输层的导带能级，这大大增加了QLED器件中的电子注入势垒，进而明显降低了QLED器件中的电子注入效率。为了解决这一难题，越来越多的研究人员尝试使用金属离子掺杂纳米氧化锌的方式来提高纳米氧化锌电子传输层的导带能级，但是该方法也有其自身存在的问题。一方面，虽然掺杂金属离子可以提高纳米氧化锌电子传输层的导带能级，进而缩小纳米氧化锌电子传输层与量子点发光层之间的电子注入势垒，但是在导带能级提高后纳米氧化锌电子传输层与阴极之间又产生了新的注入势垒。这使得该方法很难从根本上改善QLED器件中的电子注入效率。除此以外，金属离子掺杂氧化锌的方法在提高氧化锌电子传输层导带能级的同时，还可能使氧化锌电子传输层的价带能级变浅，进而使其丧失空穴阻挡这一功能，严重破坏QLED器件的器件性能。
 技术问题
本发明提供一种复合薄膜及其制备方法、一种含有上述复合薄膜的发光器件，旨在解决蓝色或者绿色量子点发光二极管中纳米氧化锌电子传输层与阴极和量子点发光层之间能级匹配关系较差，导致电子注入势垒较高的问题。
 技术解决方案
本发明是这样实现的，第一方面，提供了一种复合薄膜，所述复合薄膜包括依次层叠结合的N层薄膜，所述N层薄膜均为纳米氧化锌薄膜，且从第一层薄膜到第N层薄膜，所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加，其中，所述N的取值范围满足：3≤N≤9。
第二方面，提供了一种复合薄膜的制备方法，包括以下步骤：
提供锌盐、碱的混合溶液，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液；
提供基板，按照所述氧化锌胶体溶液中纳米氧化锌的粒径由小到大或由大到小的顺序，在所述基板上依次沉积所述氧化锌胶体溶液，制备纳米氧化锌的粒径逐层增加或逐层减小的N层纳米氧化锌薄膜，得到复合薄膜，其中，所述N的取值范围满足：3≤N≤9。
第三方面，提供了一种发光器件，所述发光器件包括包括阳极和阴极，以及设置在阳极和阴极之间层叠结合的发光层和电子传输层，所述电子传输层靠近所述阴极设置，所述发光层靠近所述阳极设置，所述电子传输层为上述的复合薄膜；或所述电子传输层为上述方法制备的复合薄膜，且沿着所述发光层到所述阴极的方向，从第一层薄膜到第N层薄膜，所述复合薄膜中纳米氧化锌的粒径逐层增加。
 有益效果
本发明提供的复合薄膜，采用纳米氧化锌作为组成物质，由纳米氧化锌的粒径逐层增加的N层薄膜复合而成，不需要在纳米氧化锌中掺杂其他金属离子，便可得到导带能级逐渐变高、而价带能级逐渐变深的纳米氧化锌组成的复合薄膜。由于所述复合薄膜具有逐渐变高的导带能级，因此，所述复合薄膜用作蓝量子点发光二极管或绿量子点发光二极管的电子传输层是，与阴极和蓝色或绿色量子点发光层之间都具有良好的能级匹配关系，解决了蓝色或者绿色量子点发光二极管器件中电子注入势垒较高的难题。同时，所述复合薄膜的价带能级逐渐变深，进一步增强了氧化锌电子传输层对空穴的阻挡作用，显著提高了QLED器件的发光效率和器件性能。此外，本发明提供的复合薄膜，无需引入任何其它有机化合物或者无机化合物作为氧化锌材料的掺杂物，因而不存在任何引入杂质的风险，进而在作为发光器件的电子传输层时也不需要进行任何复杂的处理过程，有利于简化工艺，降低成本。
本发明提供的复合薄膜的制备方法，只需通过简单的低温溶液法，单纯制备具有不同粒径的氧化锌胶体溶液并将其依次沉积成膜，便能制备得到导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌复合薄膜。该方法制备的薄膜，可以同时实现改善蓝量子点发光二极管或绿量子点发光二极管器件中的电子注入效率以及增强氧化锌电子传输层的空穴阻挡作用这两大功能，具有很强的适用性和实用性，可显著提高QLED器件的发光效率和器件性能。此外，该方法对设备要求较低，且在合成氧化锌胶体溶液时，无需引入任何其它有机化合物或者无机化合物作为氧化锌材料的掺杂物，因而不存在任何引入杂质的风险，进而在作为发光器件的电子传输层时也不需要进行任何复杂的处理过程，操作过程简单，成本低廉，具有良好的可重复性，制备出的氧化锌胶体溶液具有优秀的单分散性和稳定性。
本发明提供的发光器件，含有上述复合薄膜，因此，能够显著提高了发光器件的发光效率和器件性能。
 附图说明
图1是现有技术提供的红绿蓝三色量子点发光二极管的能级示意图；
图2是本发明实施例提供的量子点发光二极管的结构示意图。
 本发明的实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
在本发明的描述中，需要理解的是，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。在本发明的描述中，“多个”的含义是两个或两个以上，除非另有明确具体的限定。
由于量子限域效应，纳米氧化锌颗粒粒径的变化会直接带来纳米氧化锌材料禁带宽度的变化。颗粒粒径越小，纳米氧化锌材料的禁带宽度就越宽。而禁带宽度的变宽会带来纳米氧化锌材料导带能级的升高和价带能级的变深。因此，纳米颗粒粒径逐渐变化的纳米氧化锌电子传输层也就具有了逐渐升高的导带能级和逐渐加深的价带能级。
有鉴于此，本发明实施例提供了一种复合薄膜，所述复合薄膜包括依次层叠结合的N层薄膜，所述N层薄膜均为纳米氧化锌薄膜（即复合薄膜为多层纳米氧化锌薄膜复合形成的纳米氧化锌复合薄膜），且从第一层薄膜到第N层薄膜，所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加，其中，所述N的取值范围满足：3≤N≤9。
本发明实施例提供的复合薄膜，采用纳米氧化锌作为组成物质，由纳米氧化锌的粒径逐层增加的N层薄膜复合而成，不需要在纳米氧化锌中掺杂其他金属离子，便可得到导带能级逐渐变高、而价带能级逐渐变深的纳米氧化锌组成的复合薄膜。由于所述复合薄膜具有逐渐变高的导带能级，因此，所述复合薄膜用作蓝量子点发光二极管或绿量子点发光二极管的电子传输层时，与阴极和蓝色量子点发光二层或绿色量子点发光层之间都具有良好的能级匹配关系，解决了蓝色或者绿色量子点发光二极管器件中电子注入势垒较高的难题。同时，所述复合薄膜的价带能级逐渐变深，进一步增强了氧化锌电子传输层对空穴的阻挡作用，显著提高了QLED器件的发光效率和器件性能。此外，本发明实施例提供的复合薄膜，无需引入任何其它有机化合物或者无机化合物作为氧化锌材料的掺杂物，因而不存在任何引入杂质的风险，进而在作为发光器件的电子传输层时也不需要进行任何复杂的处理过程，有利于简化工艺，降低成本。
具体的，本发明实施例中，纳米氧化锌的粒径逐层增加的纳米氧化锌复合薄膜，纳米氧化锌的最大粒径要保证具有最大颗粒粒径的纳米氧化锌材料与阴极能级之间有着良好的能级匹配关系。当最大纳米氧化锌的粒径过小时，会导致具有最大粒径的纳米氧化锌的导带能级提升过高，与阴极能级之间产生电子注入势垒。而当最大纳米氧化锌的粒径过大时，会因为实现这一粒径所需的合成反应温度过高，造成所得纳米颗粒的分散性较差，团聚严重，影响氧化锌胶体溶液的后期成膜。优选的，粒径最大的纳米氧化锌薄膜即所述第N层薄膜中的纳米氧化锌的粒径为8-10nm，此时所用的反应温度为70-90℃。
所述纳米氧化锌的最小粒径要确保能够显著提高纳米氧化锌材料的导带能级，使其接近蓝色量子点发光二层或绿色量子点发光层的导带能级，最大限度的降低电子传输层与量子点发光层之间的电子注入势垒。当最小纳米氧化锌的粒径过大时，会导致具有最小粒径的纳米氧化锌材料的导带能级提升不足，与蓝色量子点发光二层或绿色量子点发光层的导带能级之间仍有较大电子注入势垒，并不能从根本上改善蓝量子点发光二极管或绿量子点发光二极管器件的电子注入效率。而当最小纳米氧化锌的粒径过小时，会因为实现这一粒径所需的合成反应温度过低，显著减慢纳米氧化锌颗粒的生成，并且生成的纳米氧化锌颗粒的结晶性也较差。优选的，粒径最小的纳米氧化锌薄膜即所述第一层薄膜中的纳米氧化锌的粒径为2-3nm；此时所用的反应温度为0-10℃。
所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加的复合薄膜中，纳米氧化锌薄膜中的纳米氧化锌的粒径从上述的最小粒径逐步增加至上述的最大粒径。这种粒径逐步增加的方式最大限度的减小了膜层与膜层之间导带能级的差异，便于电子在导带能级逐步提高的纳米氧化锌复合薄膜中顺畅的迁移。
所述纳米氧化锌薄膜的层数是决定着电子在纳米氧化锌复合薄膜中能否顺利迁移的重要参数。所述N的取值范围满足：3≤N≤9，纳米氧化锌的粒径从最小粒径逐层增加至最大粒径。所述纳米氧化锌薄膜的层数过少时，膜层与膜层之间的纳米氧化锌颗粒粒径的差异会较大，也就意味着膜层与膜层之间的导带能级差异也会较大，这会造成所述纳米氧化锌复合薄膜内具有较大的电子迁移势垒，影响电子在纳米氧化锌复合薄膜中的顺利传输；而当所述纳米氧化锌薄膜的层数过多时，又会导致纳米氧化锌复合薄膜的厚度过厚，阻碍电子的注入，影响器件的电荷注入平衡。进一步优选的，所述N的取值范围满足：5≤N≤7，纳米氧化锌的粒径从最小粒径逐层增加至最大粒径。
进一步优选的，所述复合薄膜中，单层纳米氧化锌的厚度为10-20nm，所述复合薄膜的总厚度为30-180nm。所述复合薄膜的总厚度小于30nm时，用做电子传输层的膜层很容易被电子击穿，无法保证载流子的注入性能；当所述复合薄膜的总厚度大于180nm时，用做电子传输层时，则会阻碍电子的注入，影响器件的电荷注入平衡。更优的，当所述复合薄膜的层数为5-7层时，所述复合薄膜的总厚度相应为50~140nm。
本发明实施例提供的复合薄膜，可以通过下述方法制备获得。
相应的，一种复合薄膜的制备方法，包括以下步骤：
S01.提供锌盐、碱的混合溶液，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液；
S02.提供基板，按照所述氧化锌胶体溶液中纳米氧化锌的粒径由小到大或由大到小的顺序，在所述基板上依次沉积所述氧化锌胶体溶液，制备纳米氧化锌的粒径逐层增加或逐层减小的N层纳米氧化锌薄膜，得到复合薄膜，其中，所述N的取值范围满足：3≤N≤9。
本发明实施例提供的复合薄膜的制备方法，只需通过简单的低温溶液法，单纯制备具有不同粒径的氧化锌胶体溶液并将其依次沉积成膜，便能制备得到导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌复合薄膜。该方法制备的薄膜，可以同时实现改善蓝量子点发光二极管或绿量子点发光二极管器件中的电子注入效率以及增强氧化锌电子传输层的空穴阻挡作用这两大功能，具有很强的适用性和实用性，可显著提高QLED器件的发光效率和器件性能。此外，该方法对设备要求较低，且在合成氧化锌胶体溶液时，无需引入任何其它有机化合物或者无机化合物作为氧化锌材料的掺杂物，因而不存在任何引入杂质的风险，进而在作为发光器件的电子传输层时也不需要进行任何复杂的处理过程，操作过程简单，成本低廉，具有良好的可重复性，制备出的氧化锌胶体溶液具有优秀的单分散性和稳定性。
具体的，上述步骤S01中，具体的，所述锌盐、碱的混合溶液，由锌盐、碱溶于溶剂中形成。
其中，所述锌盐作为锌源，为制备纳米氧化锌薄膜提供锌，具体的，所述锌盐包括但不局限于醋酸锌及其水合物、硝酸锌及其水合物、硫酸锌及其水合物、氯化锌及其水合物等中的至少一种。
本发明实施例中，采用述锌盐、碱的混合溶液，制备纳米氧化锌的粒径不同的氧化锌胶体溶液的反应历程为：锌盐溶液与碱液反应生成氢氧化锌中间体，随后氢氧化锌中间体发生缩聚反应逐步生成纳米氧化锌颗粒。反应体系中，所述碱为反应提供氢氧根离子，发挥不可或缺的作用。具体的，所述碱选自氢氧化锂、氢氧化钠、氢氧化钾、TMAH、氨水、乙醇胺、乙二胺中的至少一种。
发明实施例用于形成锌盐、碱的混合溶液的溶剂，可以为有机溶剂或无机溶剂，具体可选自水、甲醇、乙醇、丙醇、丁醇、乙二醇、乙二醇单甲醚、DMSO中的至少一种，但不限于此。
本发明实施例所述锌盐、碱的混合溶液，可以将锌盐、碱加入溶剂中制备获得。作为一种优选方式，所述锌盐、碱的混合溶液的制备方法如下：将锌盐溶解在溶剂中，得到盐溶液；将碱溶解在相同或不同的溶剂中，得到碱溶液；然后将盐溶液和碱溶液混合，得到混合溶液。上述步骤在室温（10-30℃）条件下完成即可。
优选的，所述混合溶液中，氢氧根离子与金属离子的摩尔比为1.5:1~2.5:1，以确保掺杂纳米氧化锌颗粒的形成和减少反应副产物的生成。当氢氧根离子与金属离子的摩尔比小于1.5：1时，金属盐显著过量，导致大量金属盐无法生成纳米氧化锌颗粒；而当氢氧根离子与金属离子的摩尔比大于2.5：1时，碱液显著过量，过量的氢氧根离子与氢氧化物中间体形成稳定的络合物，无法缩聚生成纳米氧化锌颗粒。更优的，所述混合溶液中，氢氧根离子与金属离子的摩尔比选为1.5:1~2:1.。
本发明实施例中，将所述混合溶液反应得到含掺杂金属离子的氧化锌胶体溶液的方法为：将所述混合溶液在0-90℃条件下反应30-240min，制备氧化锌胶体溶液。上述温度可以确保纳米氧化锌颗粒的形成和获得良好的颗粒分散性，同时为纳米氧化锌颗粒粒径的显著改变提供足够的温度范围。当反应温度低于0℃时，反应温度过低会显著减缓纳米氧化锌颗粒的生成，甚至无法生成纳米氧化锌颗粒，而只能得到氢氧化物中间体；而当反应温度高于90℃时，所得纳米氧化锌颗粒的分散性较差，团聚严重，影响掺杂氧化锌胶体溶液的后期成膜。进一步的，反应时间为30-240min，以确保掺杂纳米氧化锌颗粒的形成和控制纳米颗粒的粒径。当反应时间少于30min时，反应时间过短，纳米氧化锌颗粒形成不充分，并且所得纳米颗粒的结晶性较差；而当反应时间超过4h时，过长的颗粒长大时间使生成的纳米颗粒过大并且粒径不均匀，影响氧化锌胶体溶液的后期成膜。更优选的，反应时间为1~2h。
进一步的，在反应结束后，还包括在反应后的反应液中加入沉淀剂，混合溶液中产生白色沉淀（沉淀过程），经离心处理，得到含有掺杂金属离子的纳米氧化锌颗粒。其中，沉淀剂与反应体系溶液的体积比为2：1~6：1，以确保在充分沉淀含有掺杂金属离子的纳米氧化锌颗粒的前提下，避免过多的沉淀剂破坏掺杂氧化锌颗粒的溶解性。更优的，沉淀剂与反应体系溶液的体积比选为3：1~5：1。所述沉淀剂是极性较弱的溶剂中的一种，包括但不局限于乙酸乙酯、正己烷、正庚烷、丙酮等。将离心处理后所得白色沉淀再次溶于反应溶剂中，重复清洗多次以去除没有参与反应的反应物，收集最终所得白色沉淀，可溶于溶剂中得到具有较大离子半径的不等价金属离子掺杂氧化锌胶体溶液，即含有掺杂金属的纳米氧化锌颗粒的胶体溶液。
本发明实施例利用低温溶液法合成氧化锌胶体溶液，在低温溶液法的整个反应历程中（锌盐与碱液反应生成氢氧化物中间体，随后氢氧化物中间体发生缩聚反应逐步生成纳米氧化锌颗粒），纳米氧化锌颗粒的生成都是在液相中进行。本发明实施例采用低温溶液法制备的氧化锌胶体溶液，方法非常简单，成本低廉，易于操作，对设备要求较低，且可重复性好。低温溶液发可以是低温醇解法（以醇作为溶剂），也可以是低温水解法（以水作为溶剂）。
在上述氧化锌胶体溶液制备方法的基础上，本发明实施例为了制备出导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌复合薄膜，本发明实施例需要合成纳米氧化锌颗粒粒径逐渐变化的多份氧化锌胶体溶液，而对纳米颗粒粒径的调整则通过控制低温溶液法的合成反应温度来实现。即提供锌盐、碱的混合溶液，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液的步骤，包括：
改变所述锌盐、碱的混合溶液的反应温度，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液，其中，所述反应温度的范围为0-90℃。
基于上述复合薄膜中，对纳米氧化锌的粒径的选择依据，本发明实施例中，粒径最小的氧化锌胶体溶液中的纳米氧化锌的粒径为2-3nm；粒径最大的氧化锌胶体溶液中的纳米氧化锌的粒径为8-10nm。具体而言，本发明实施例中，所用纳米氧化锌颗粒的最大粒径为8~10nm时，对应的反应温度为70~90℃；所用纳米氧化锌颗粒的最小粒径为2~3nm，对应的反应温度为0~10℃。即制备粒径最小的所述氧化锌胶体溶液的反应温度为0-10℃，制备粒径最大的所述氧化锌胶体溶液的反应温度为70-90℃。
为了获得导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌复合薄膜，制备过程中根据不同的反应温度，来调整得到的纳米氧化锌颗粒的粒径。本发明实施例需要合成的纳米颗粒粒径逐渐变化的氧化锌胶体溶液的份数优选为3~9份，其中，每份氧化锌胶体溶液的纳米颗粒粒径从上述的最小粒径逐步增加至上述的最大粒径，相对应的每份氧化锌胶体溶液的合成反应温度也从最低反应温度（0~10℃）逐步升高至最高反应温度（70~90℃）。
具体的，上述步骤S02中，在基板上沉积所述氧化锌胶体溶液，所述基板的选择没有严格限定，可以为用于沉积复合薄膜的普通基板，也可以是沉积好其他功能层，需要进一步沉积电子传输薄膜的功能基板，如沉积有层叠结合的阳极、发光层的功能基板，所述复合薄膜沉积在发光层上。
沉积方式没有严格限制，基于纳米氧化锌胶体溶液的胶体性质，采用溶液加工法即可。具体的，包括但不局限于旋涂法、刮涂法、印刷法、喷涂法、滚涂法、电沉积法等中的一种。
在沉积多份纳米氧化锌的粒径不同的氧化锌胶体溶液时，先将纳米氧化锌颗粒粒径最小的氧化锌胶体溶液沉积在基板上，随后按照纳米氧化锌颗粒粒径逐渐变大的顺序依次沉积氧化锌胶体溶液，最后沉积纳米氧化锌颗粒粒径最大的氧化锌胶体溶液。或者，在沉积多份纳米氧化锌的粒径不同的氧化锌胶体溶液时，先将纳米氧化锌颗粒粒径最大的氧化锌胶体溶液沉积在基板上，随后按照纳米氧化锌颗粒粒径逐渐变小的顺序依次沉积氧化锌胶体溶液，最后沉积纳米氧化锌颗粒粒径最小的氧化锌胶体溶液。当制备的复合薄膜用于发光器件，特别是蓝量子点发光二极管或绿量子点发光二极管器件时，当所述量子点发光二极管器件为正型蓝量子点发光二极管或绿量子点发光二极管时，在沉积多份纳米氧化锌的粒径不同的氧化锌胶体溶液时，先将纳米氧化锌颗粒粒径最小的氧化锌胶体溶液沉积在已沉积有阳极、空穴传输层、蓝色或者绿色量子点发光层的基板上，随后按照纳米氧化锌颗粒粒径逐渐变大的顺序依次沉积氧化锌胶体溶液，最后沉积纳米氧化锌颗粒粒径最大的氧化锌胶体溶液。当所述量子点发光二极管器件为反型蓝量子点发光二极管或绿量子点发光二极管时，在沉积多份纳米氧化锌的粒径不同的氧化锌胶体溶液时，先将纳米氧化锌颗粒粒径最大的氧化锌胶体溶液沉积在已沉积有阴极的基板上，随后按照纳米氧化锌颗粒粒径逐渐变小的顺序依次沉积氧化锌胶体溶液，最后沉积纳米氧化锌颗粒粒径最小的氧化锌胶体溶液。
本发明实施例通过简单的低温溶液法，合成出了导带能级逐渐升高而价带能级逐渐加深的多份掺杂氧化锌胶体溶液。随后通过依次沉积掺杂氧化锌胶体溶液于基板上并进行热处理，制备出了导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌复合薄膜。由于纳米氧化锌复合薄膜具有逐渐变高的导带能级，因此该电子传输层与阴极和蓝色或绿色量子点发光层之间都具有良好的能级匹配关系，从本质上解决了蓝色或者绿色量子点发光二极管器件中电子注入势垒较高的难题，再加之其价带能级也会逐渐加深，确保了掺杂后氧化锌电子传输层对空穴的阻挡作用，进而显著提高了QLED器件的发光效率和器件性能。
以及，一种发光器件，所述发光器件括阳极和阴极，以及设置在阳极和阴极之间层叠结合的发光层和电子传输层，所述电子传输层靠近所述阴极设置，所述发光层靠近所述阳极设置，所述电子传输层为上述的复合薄膜；或所述电子传输层为上述方法制备的复合薄膜，且沿着所述发光层到所述阴极的方向，从第一层薄膜到第N层薄膜，所述复合薄膜中纳米氧化锌的粒径逐层增加。
本发明实施例提供的发光器件，含有上述复合薄膜，因此，能够显著提高了发光器件的发光效率和器件性能。
具体的，所述发光成可以为有机发光层，也可以为量子点发光层。对应的，当所述发光层为有机发光层时，所述发光二极管器件为有机发光二极管（OLED）器件；当所述发光层为量子点发光层时，所述发光二极管为量子点发光二极管（QLED）器件。
优选的，所述发光器件为蓝色量子点发光器件或绿色量子点发光器件，所述发光器件包括层叠结合的蓝色或绿色量子点发光层、电子传输层和阴极，其中，所述电子传输层为所述复合薄膜。
所述复合薄膜与阴极接触的一端具有粒径最大的纳米氧化锌颗粒，因此该端电子传输层具有最低的与阴极能级基本一致的导带能级。而所述复合薄膜与蓝色量子点发光二层或绿色量子点发光层接触的一端则具有最小粒径的纳米氧化锌颗粒，因此该端电子传输层具有最高的与量子点发光层能级较为接近的导带能级。而在所述复合薄膜的两端之间，纳米氧化锌颗粒的粒径逐渐变化，也就意味着纳米氧化锌电子传输层的导带能级逐渐变化，最大限度的减小了电子在传输层内部迁移时的势垒。这样的能级结构同时确保了电子传输层和阴极之间以及电子传输层和蓝色量子点发光二层或绿色量子点发光层之间良好的能级匹配关系，再加之纳米氧化锌电子传输层内部连续的能级变化确保了电子在传输层内部迁移的顺畅，使得这种导带能级逐渐升高的纳米氧化锌电子传输层，在最大程度上降低了蓝量子点发光二极管或绿量子点发光二极管中的电子注入势垒。同理，本发明实施例中纳米氧化锌电子传输层的价带能级也是逐渐加深的，并且在蓝色量子点发光二层或绿色量子点发光层一端具有最深的价带能级，进一步加强了氧化锌电子传输层对空穴的阻挡作用。综上所述，将本发明实施例中的导带能级逐渐升高而价带能级逐渐加深的纳米氧化锌电子传输层应用在蓝色或者绿色量子点发光二极管器件中，显著提高了QLED器件的发光效率和器件性能。
作为一种具体实施例，如图2所示，所述发光器件包括层叠结合在衬底1上的阳极2、空穴传输层3、蓝色或绿色量子点发光层4、电子传输层5和阴极6，其中，电子传输层5为上述复合薄膜，且沿着阴极6到蓝色或绿色量子点发光层4的方向，所述复合薄膜中纳米氧化锌的粒径逐层减小。
具体的，衬底1可采用硬质衬底或柔性衬底，具体的，可选用玻璃衬底。
阳极2可以为ITO，但不限于此。
空穴传输层3可采用本领域常规的空穴传输材料制成，包括但不限于TFB、PVK、Poly-TPD、TCTA、CBP等或者为其任意组合的混合物，亦可以是其它高性能的空穴传输材料。
蓝色或绿色量子点发光层4的量子点可以为绿、蓝量子点中的一种，具体可以为CdS、CdSe、CdTe、ZnO、ZnS、ZnSe、ZnTe、GaAs、GaP、GaSb、HgS、HgSe、HgTe、InAs、InP、InSb、AlAs、AlP、CuInS、CuInSe、以及各种核壳结构量子点或合金结构量子点中的至少一种；也可以为常见的绿、蓝量子点。所述量子点可以含镉或者不含镉。所述发光层的厚度优选为20-60nm。
电子传输层5采用上述复合薄膜。
阴极6采用金属阴极材料，如金属银或金属铝，或纳米银线或纳米铜线、采用所述纳米银线或所述纳米铜线，具有更小的电阻，有利于载流子顺利注入。所述阴极的厚度优选为15-30nm。
进一步的，可对得到的发光器件进行封装处理。
相应的，本发明实施例提供了一种发光器件管的制备方法，包括以下步骤：
Q01.在阳极上制备发光层；
具体的，可以采用溶液法加工实现，即将发光层材料溶解成发光层材料溶液后，将发光层材料溶液沉积在阳极表面。进一步的，可以通过旋涂的方式将所述发光层材料溶液沉积成膜。具体的，将阳极基片置于匀胶机上，将配制好一定浓度的发光层材料溶液旋涂成膜，通过调节溶液的浓度、旋涂速度和旋涂时间来控制发光层的厚度，然后在适当温度下热退火处理。
优选的，在制备发光层之前，还包括在阳极上制备空穴传输层。
所述空穴传输层可以采用与发光层相同的方法制备，优选采用溶液加工法，如旋涂，并进一步通过调节溶液的浓度、旋涂速度和旋涂时间来控制膜厚，然后在适当温度下热退火处理。
Q02.在所述发光层上制备电子传输层；
在所述发光层上制备电子传输层，采用上述复合薄膜的方法制备获得，此处不再赘述，值得注意的是，制备所述复合薄膜时，沿着所述阴极到所述发光层的方向，所述复合薄膜中纳米氧化锌的粒径逐层减小。
Q03.在所述电子传输层上制备阴极。
具体的，将沉积完各功能层的衬底置于蒸镀仓中通过掩膜板热蒸镀阴极。
进一步的，对器件进行封装处理，封装条件优选在氧含量和水含量均低于0.1ppm的条件下进行，以保证器件的稳定性。
当然，所述发光二极管也可以采用另一种方法制备获得，具体的，所述发光二极管的制备方法，包括以下步骤：
Q01.在阴极上制备电子传输层；
Q02.在所述电子传输层上制备发光层；
Q03.在所述发光层上制备阳极。
各层的制备方法参照同上一种实施方式，值得注意的是，制备所述复合薄膜时，沿着所述阴极到所述发光层的方向，所述复合薄膜中纳米氧化锌的粒径逐层减小。
下面结合具体实施例进行说明。
实施例1
一种纳米氧化锌复合薄膜，其制备方法包括以下步骤：
首先将适量的醋酸锌加入到50ml乙醇溶剂中形成总浓度为0.1mol/L 的锌盐溶液，同时将适量的氢氧化锂粉末溶解到另一份50ml乙醇溶剂中形成浓度为0.2mol/L的碱液。随后将锌盐溶液降温至0℃，并逐滴加入氢氧化锂溶液直到氢氧根离子与锌离子的摩尔比为1.7:1时停止。氢氧化锂溶液滴注完成后，将混合溶液在0℃下继续搅拌1h，得到一均匀透明溶液。随后，向均匀透明溶液中加入体积比为3：1的庚烷溶剂，使透明溶液中产生大量白色沉淀。将浑浊溶液以7000rpm的速度进行离心，所得白色沉淀再次溶于乙醇溶剂中。此清洗过程重复进行四次。最终所得白色沉淀溶于适量乙醇溶剂中，得到溶液浓度为30mg/ml，纳米颗粒粒径为2.3nm的氧化锌胶体溶液。
将上述合成氧化锌胶体溶液的方法重复进行四次，其中合成反应温度逐渐升高，分别为10℃、25℃、50℃和70℃，而其余合成参数全部不变。最终得到了四份，溶液浓度为30mg/ml，纳米颗粒粒径分别为2.8nm、3.5nm、5.8nm和7.6nm的氧化锌胶体溶液。以上五份氧化锌胶体溶液的纳米颗粒粒径均从透射电镜（TEM）照片中统计得到。而每份氧化锌胶体溶液的导带能级，价带能级以及禁带宽度都会通过将每份氧化锌胶体溶液单独成膜后利用紫外光电子能谱（UPS）测量获得。本实施例中每份氧化锌胶体溶液的导带能级，价带能级以及禁带宽度见表1。
将上述总共五份氧化锌胶体溶液按照氧化锌颗粒粒径逐渐变大的顺序以旋涂的方法依次沉积在已沉积有阳极，空穴传输层和蓝色或者绿色量子点发光层的基片上。其中随着纳米颗粒粒径的增大，氧化锌胶体溶液的旋涂转速逐渐加快，以控制每层纳米氧化锌薄膜的厚度都在20nm左右。这五份氧化锌胶体溶液的旋涂转速分别为3000rpm、3000rpm、3500rpm、4000rpm和5000rpm，而旋涂时间都为30s。当所有氧化锌胶体溶液依次沉积完成后，即制得了导带能级逐渐升高而价带能级逐渐变深的纳米氧化锌电子传输层。该纳米氧化锌电子传输层的总厚度在100nm左右。
表1
颗粒粒径 (nm) 导带能级（eV） 价带能级（eV） 禁带宽度（eV）
2.3 -3.47 -7.62 4.15
2.8 -3.66 -7.55 3.89
3.5 -3.82 -7.50 3.68
5.8 -3.99 -7.44 3.45
7.6 -4.05 -7.42 3.37
实施例2
一种纳米氧化锌复合薄膜，其制备方法包括以下步骤：
首先将适量的硝酸锌加入到50ml乙醇溶剂中形成总浓度为0.1mol/L 的锌盐溶液，同时将适量的氢氧化钠粉末溶解到另一份50ml乙醇溶剂中形成浓度为0.3mol/L的碱液。随后将锌盐溶液降温至0℃，并逐滴加入氢氧化钠溶液直到氢氧根离子与锌离子的摩尔比为2:1时停止。氢氧化钠溶液滴注完成后，将混合溶液在0℃下继续搅拌2h，得到一均匀透明溶液。随后，向均匀透明溶液中加入体积比为4：1的乙酸乙酯溶剂，使透明溶液中产生大量白色沉淀。将浑浊溶液以7000rpm的速度进行离心，所得白色沉淀再次溶于乙醇溶剂中。此清洗过程重复进行四次。最终所得白色沉淀溶于适量乙醇溶剂中，得到溶液浓度为30mg/ml，纳米颗粒粒径为2.7nm的氧化锌胶体溶液。
将上述合成氧化锌胶体溶液的方法重复进行六次，其中合成反应温度逐渐升高，分别为5℃、10℃、20℃、30℃、50℃和70℃，而其余合成参数全部不变。最终得到了六份，溶液浓度为30mg/ml，纳米颗粒粒径分别为3.2nm，3.9nm，4.8nm，6.1nm，6.9nm和8.5nm的氧化锌胶体溶液。
以上七份氧化锌胶体溶液的纳米颗粒粒径均从透射电镜（TEM）照片中统计得到。
将上述总共七份氧化锌胶体溶液按照氧化锌颗粒粒径逐渐变大的顺序以旋涂的方法依次沉积在已沉积有阳极，空穴传输层和蓝色或者绿色量子点发光层的基片上。其中随着纳米颗粒粒径的增大，氧化锌胶体溶液的旋涂转速逐渐加快，以控制每层纳米氧化锌薄膜的厚度都在20nm左右。这七份氧化锌胶体溶液的旋涂转速分别为3000rpm、3000rpm、3500rpm、3500rpm、4000rpm、4000rpm和5000rpm，而旋涂时间都为30s。当所有氧化锌胶体溶液依次沉积完成后，即制得了导带能级逐渐升高而价带能级逐渐变深的纳米氧化锌电子传输层。该纳米氧化锌电子传输层的总厚度在140nm左右。
实施例3
一种纳米氧化锌复合薄膜，其制备方法包括以下步骤：
首先将适量的氯化锌加入到50ml DMSO溶剂中形成总浓度为0.1mol/L 的锌盐溶液，同时将适量的TMAH粉末溶解到另一份50ml乙醇溶剂中形成浓度为0.3mol/L的碱液。随后将锌盐溶液降温至5℃，并逐滴加入氢氧化钠溶液直到氢氧根离子与锌离子的摩尔比为1.5:1时停止。TMAH溶液滴注完成后，将混合溶液在5℃下继续搅拌2h，得到一均匀透明溶液。随后，向均匀透明溶液中加入体积比为4：1的正己烷溶剂，使透明溶液中产生大量白色沉淀。将浑浊溶液以7000rpm的速度进行离心，所得白色沉淀再次溶于乙醇溶剂中。此清洗过程重复进行四次。最终所得白色沉淀溶于适量乙醇溶剂中，得到溶液浓度为30mg/ml，纳米颗粒粒径为3.6nm的氧化锌胶体溶液。
将上述合成氧化锌胶体溶液的方法重复进行三次，其中合成反应温度逐渐升高，分别为10℃、25℃和80℃，而其余合成参数全部不变。最终得到了三份，溶液浓度为30mg/ml，纳米颗粒粒径分别为4.5nm，5.9nm和9.3nm的氧化锌胶体溶液。以上四份氧化锌胶体溶液的纳米颗粒粒径均从透射电镜（TEM）照片中统计得到。
将上述总共四份氧化锌胶体溶液按照氧化锌颗粒粒径逐渐变大的顺序以旋涂的方法依次沉积在已沉积有阳极，空穴传输层和蓝色或者绿色量子点发光层的基片上。其中随着纳米颗粒粒径的增大，氧化锌胶体溶液的旋涂转速逐渐加快，以控制每层纳米氧化锌薄膜的厚度都在20nm左右。这四份氧化锌胶体溶液的旋涂转速分别为3000rpm、 3500rpm、4000rpm和5000rpm，而旋涂时间都为30s。当所有氧化锌胶体溶液依次沉积完成后，即制得了导带能级逐渐升高而价带能级逐渐变深的纳米氧化锌电子传输层。该纳米氧化锌电子传输层的总厚度在80nm左右。
实施例4
一种蓝量子点发光二极管或绿量子点发光二极管器件，从下而上依次包括衬底、阴极、电子传输层、蓝色或者绿色量子点发光层、空穴传输层、阳极。其中，衬底的材料为玻璃片，阴极的材料为ITO基板，电子传输层的材料为导带能级逐渐升高而价带能级也逐渐加深的纳米氧化锌材料，空穴传输层的材料为TFB及阳极的材料为Al，电子传输层为上述复合薄膜，且沿着所述阴极到所述发光层的方向，所述复合薄膜中纳米氧化锌的粒径逐层减小。
上述蓝量子点发光二极管或绿量子点发光二极管器件的制备方法，包括以下步骤：
在阴极上制备导带能级逐渐升高而价带能级也逐渐加深的纳米氧化锌电子传输层；
然后在电子传输层上旋涂蓝色或者绿色量子点发光层；
最后沉积空穴传输层于蓝色或者绿色量子点发光层上，并蒸镀阳极于空穴传输层上，得到蓝色或者绿色量子点发光二极管。
实施例5
一种蓝量子点发光二极管或绿量子点发光二极管器件，从下而上依次包括衬底、阳极、空穴传输层、蓝色或绿色量子点发光层、电子传输层和阴极。其中，衬底的材料为玻璃片，阴极的材料为ITO基板，电子传输层的材料为导带能级逐渐连续升高的纳米氧化锌材料，空穴传输层的材料为TFB及阳极的材料为Al，电子传输层为上述复合薄膜，且沿着所述阴极到所述发光层的方向，所述复合薄膜中纳米氧化锌的粒径逐层减小。
上述蓝量子点发光二极管或绿量子点发光二极管器件的制备方法，包括以下步骤：
首先在阳极基板上依次制备空穴传输层和蓝色或者绿色量子点发光层；
在蓝色或者绿色量子点发光层上制备导带能级逐渐降低而价带能级也逐渐变浅的纳米氧化锌电子传输层；
在电子传输层上蒸镀阴极，得到蓝色或者绿色量子点发光二极管。
以上所述实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的精神和范围，均应包含在本发明的保护范围之内。

Claims (20)

  1. 一种复合薄膜，其特征在于，所述复合薄膜包括依次层叠结合的N层薄膜，所述N层薄膜均为纳米氧化锌薄膜，且从第一层薄膜到第N层薄膜，所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加，其中，所述N的取值范围满足：3≤N≤9。
  2. 如权利要求1所述的复合薄膜，其特征在于，所述N的取值范围满足：5≤N≤7。
  3. 如权利要求1所述的复合薄膜，其特征在于，所述第一层薄膜中的纳米氧化锌的粒径为2-3nm。
  4. 如权利要求1所述的复合薄膜，所述第N层薄膜中的纳米氧化锌的粒径为8-10nm。
  5. 如权利要求1所述的复合薄膜，其特征在于，所述复合薄膜中，单层纳米氧化锌的厚度为10-20nm。
  6. 如权利要求1所述的复合薄膜，所述复合薄膜的总厚度为30-180nm。
  7. 一种复合薄膜的制备方法，其特征在于，包括以下步骤：
    提供锌盐、碱的混合溶液，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液；
    提供基板，按照所述氧化锌胶体溶液中纳米氧化锌的粒径由小到大或由大到小的顺序，在所述基板上依次沉积所述氧化锌胶体溶液，制备纳米氧化锌的粒径逐层增加或逐层减小的N层纳米氧化锌薄膜，得到复合薄膜，其中，所述N的取值范围满足：3≤N≤9。
  8. 如权利要求7所述的复合薄膜的制备方法，其特征在于，其中，粒径最小的氧化锌胶体溶液中的纳米氧化锌的粒径为2-3nm；粒径最大的氧化锌胶体溶液中的纳米氧化锌的粒径为8-10nm。
  9. 如权利要求7所述的复合薄膜的制备方法，提供锌盐、碱的混合溶液，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液的步骤，包括：
    改变所述锌盐、碱的混合溶液的反应温度，分别制备纳米氧化锌的粒径不同的氧化锌胶体溶液，其中，所述反应温度的范围为0-90℃。
  10. 如权利要求9所述的复合薄膜的制备方法，其特征在于，制备粒径最小的所述氧化锌胶体溶液的反应温度为0-10℃，制备粒径最大的所述氧化锌胶体溶液的反应温度为70-90℃。
  11. 如权利要求7所述的复合薄膜的制备方法，其特征在于，所述混合溶液中，氢氧根离子与金属离子的摩尔比为1.5:1~2.5:1。
  12. 如权利要求7所述的复合薄膜的制备方法，其特征在于，所述碱选自氢氧化锂、氢氧化钠、氢氧化钾、TMAH、氨水、乙醇胺、乙二胺中的至少一种；和/或
    所述锌盐选自醋酸锌及其水合物、硝酸锌及其水合物、硫酸锌及其水合物、氯化锌及其水合物中的至少一种。
  13. 一种发光器件，包括阳极和阴极，以及设置在阳极和阴极之间层叠结合的发光层和电子传输层，所述电子传输层靠近所述阴极设置，所述发光层靠近所述阳极设置，其特征在于，所述电子传输层复合薄膜，所述复合薄膜包括依次层叠结合的N层薄膜，所述N层薄膜均为纳米氧化锌薄膜，且从第一层薄膜到第N层薄膜，所述纳米氧化锌薄膜中的纳米氧化锌的粒径逐层增加，其中，所述N的取值范围满足：3≤N≤9，且沿着所述发光层到所述阴极的方向，从第一层薄膜到第N层薄膜，所述复合薄膜中纳米氧化锌的粒径逐层增加。
  14. 如权利要求13所述的发光器件，其特征在于，所述N的取值范围满足：5≤N≤7。
  15. 如权利要求13所述的发光器件，其特征在于，所述第一层薄膜中的纳米氧化锌的粒径为2-3n。
  16. 如权利要求13所述的发光器件，其特征在于，所述第N层薄膜中的纳米氧化锌的粒径为8-10nm。
  17. 如权利要求13所述的发光器件，其特征在于，所述复合薄膜中，单层纳米氧化锌的厚度为10-20nm。
  18. 如权利要求13所述的发光器件，其特征在于，所述复合薄膜中，所述复合薄膜的总厚度为30-180nm。
  19. 如权利要求13所述的发光器件，其特征在于，所述发光层为蓝色量子点发光层或绿色量子点发光层。
  20. 如权利要求19所述的发光器件，其特征在于，所述发光层为蓝色量子点发光层，所述蓝色量子点发光层与所述电子传输层、所述阴极层叠结合；
    或者，所述发光层为绿色量子点发光层，所述绿色量子点发光层与所述电子传输层、所述阴极层叠结合。
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