H X Moo3 nanoparticle solution, method of preparing and use thereof, and quantum dot light emitting diode

Abstract

The application belongs to the technical field of semiconductor display and illumination materials, and particularly relates to a kind of H X MoO3 nanoparticle solution, preparation method and application thereof, and quantum dot light emitting diode. The H X MoO3 nanoparticle solution of the application is prepared by oxidation reaction of molybdenum powder and hydrogen peroxide in the presence of alcohol solvent, and the purification process of filtering, evaporating, dispersing and centrifuging the reaction system can eliminate the residual molybdenum powder and hydrogen peroxide, and realize the H X MoO3 nanoparticle solution. The H X MoO3 nanoparticle film has excellent photoelectric performance and high stability, and when used as the hole injection layer of quantum dot light emitting diode, the brightness and external quantum efficiency of the device are high, and the service life is greatly improved, which is suitable for quantum dot light emitting diode.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor display and lighting materials, and specifically relates to a H X MoO3 nanoparticle solution, preparation method and application thereof, and quantum dot light-emitting diodes. Background Art

[0002] Quantum dot light emitting diodes (QLEDs), as emerging electroluminescent display devices, are considered to be the most promising technology in the display and lighting fields due to their advantages such as high fluorescence quantum yield, narrow and tunable emission spectrum, and solution processability.

[0003] Currently, the structure of standard QLEDs generally consists of a substrate, an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode. The hole injection layer is often made of a highly conductive organic semiconductor polymer, such as poly(ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS). However, a study (Jia W, Tchoudakov R, Segal E, et al. Synthetic Metals, 2003, 132(3):269-278) reports that the inherent acidity of PEDOT:PSS can damage the anode electrode, and its hygroscopicity can make it unstable, significantly reducing the lifespan of QLEDs.

[0004] To improve the stability of QLEDs, hole-injection materials with high conductivity and excellent stability are generally used to replace PEDOT:PSS. Molybdenum oxide (MoO3), a solution-processable transition metal oxide with well-matched energy levels, has become a leading choice for replacing PEDOT:PSS due to its extremely high stability and unique hole-injection mechanism as a hole-injection layer.

[0005] At present, among the common MoO3 preparation methods, the MoO3 film prepared by the ammonium molybdate sol-gel method has poor conductivity and cannot meet actual needs. X MoO3 nanoparticle films have poor stability due to the presence of oxidant residues and large particle agglomerates during the preparation process, and are still unable to be effectively applied in quantum dot light-emitting diodes.

[0006] Based on this, we explore an improved H X The preparation method of MoO3 nanoparticles, which can enhance the hole injection and conductivity of the material and achieve high efficiency and long life of QLEDs, has become a technical problem that needs to be solved urgently. Summary of the Invention

[0007] Based on the above problems, the first object of the present application is to provide an H X The preparation method of the MoO3 nanoparticle solution can eliminate residual molybdenum powder and hydrogen peroxide in the oxidation reaction, and realize uniform particle size and distribution, and high conductivity and high transmittance of the H X The preparation method of the MoO3 nanoparticle solution.

[0008] The second object of the present application is also to provide an H X The MoO3 nanoparticle solution has uniform particle size and distribution, and the prepared H X The MoO3 nanoparticle film has excellent photoelectric performance and extremely high stability, and when used as a hole injection layer of a quantum dot light emitting diode, the brightness and external quantum efficiency of the device are high, and the service life is greatly improved.

[0009] The third object of the present application is to provide the above H X The application of the MoO3 nanoparticle solution.

[0010] The fourth object of the present application is to provide a quantum dot light emitting diode with high brightness and external quantum efficiency, and long service life.

[0011] In order to achieve the above objects, the H X The preparation method of the MoO3 nanoparticle solution adopts the technical scheme of:

[0012] An H X The preparation method of the MoO3 nanoparticle solution comprises the following steps:

[0013] (1) uniformly dispersing molybdenum powder in an alcohol solvent to obtain a dispersion liquid of the molybdenum powder; under stirring, adding a hydrogen peroxide solution to the dispersion liquid of the molybdenum powder, and stirring to obtain a composite system containing H X MoO3 and unreacted raw materials;

[0014] (2) filtering the composite system obtained in step (1), and evaporating to dryness to obtain H X MoO3 powder material;

[0015] (3) stirring and dispersing the H X MoO3 powder material obtained in step (2) in an alcohol solvent, and then centrifuging, and the obtained supernatant is a H X MoO3 nanoparticle solution with uniform dispersion and uniform particle size.

[0016] The H XThe preparation method of MoO3 nanoparticle solution is based on the oxidation reaction of molybdenum powder and hydrogen peroxide. Under the premise of using alcohol solvent as a buffer to control the overly violent reaction process and promote the uniform dispersion of nanoparticles, an innovative purification process of filtering, evaporating, dispersing and centrifuging the system after the reaction is proposed. Not only is the process simple, but it also completely eliminates the residue of hydrogen peroxide and molybdenum powder, ensuring the uniformity of the particle size of the nanoparticles to the greatest extent, and obtaining uniformly dispersed and uniformly sized H2O3 nanoparticles. X MoO3 nanoparticle solution system, the solution was used to prepare the obtained H X MoO3 nanoparticle film has excellent photoelectric properties and extremely high stability. When used as the hole injection layer of quantum dot light-emitting diodes, the device has high brightness and external quantum efficiency, and its service life is greatly improved.

[0017] Preferably, in step (1), the alcohol solvent is ethanol, ethylene glycol or isopropanol; and the particle size of the molybdenum powder is 10-150 μm.

[0018] More preferably, the alcohol solvent is ethanol. The present invention uses ethanol in the ethanol dispersion of molybdenum powder. Ethanol is not only non-toxic and harmless, cheap and easily available, but also has two functions: one is to act as a buffer to control the excessively violent oxidation reaction process, and the other is to provide H for the reaction product. + , effectively promoting the uniform dispersion of nanoparticles.

[0019] The present invention uses molybdenum powder and hydrogen peroxide to react, and no other impurities are introduced during the reaction process, which facilitates the separation and purification of subsequent products. Preferably, in step (1), the ratio of molybdenum powder to alcohol solvent is 1g: (50-200) mL; the ratio of molybdenum powder to hydrogen peroxide is 1g: (1-4) mL; the concentration of the hydrogen peroxide is 30%; and the stirring reaction time is 24-30h. The present invention has been verified by preliminary experiments that the ratio of molybdenum powder to hydrogen peroxide is 1g: (1-4) mL to prepare nanoparticles with uniform particle size. When the ratio of molybdenum powder to hydrogen peroxide is 1g: 5mL, H x MoO3 nanoparticles are too large to meet the application requirements in QLED.

[0020] Preferably, in step (2), the filtration is performed using a filter head with a fineness of 0.2 μm. The use of a filter head with such fineness can effectively filter out unreacted molybdenum powder and nanoparticles with a particle size greater than 200 nm, thereby avoiding the formation of molybdenum powder and large particles of H x Effect of MoO3 on QLED device performance.

[0021] Preferably, the evaporation to dryness operation is performed at 100-120° C. The evaporation to dryness operation is provided in the present invention to further eliminate the incompletely reacted H 2 O 2 remaining after the reaction.

[0022] Further, in step (3), the alcohol solvent is ethanol, ethylene glycol or isopropyl alcohol; H X The concentration of the MoO3 powder material after stirring and dispersing in the alcohol solvent is 10-20 mg / mL; the stirring and dispersing time is 3-5 h.

[0023] Further, the centrifugal speed is 10000-15000 rpm, and the centrifugal time is 10-20 min. The system after stirring and dispersing is subjected to high-speed centrifugation to remove the agglomerated large particles H X MoO3 nanoparticles, obtaining MoO3 nanoparticles with uniform particle size and uniform dispersion H X MoO3 nanoparticle solution.

[0024] The present application provides H X MoO3 nanoparticle solution, using the above-mentioned H X MoO3 nanoparticle solution is prepared by the preparation method.

[0025] The present application provides H X MoO3 nanoparticle solution is a deep blue solution system, H X MoO3 nanoparticle material exhibits amorphous structure in terms of crystallinity, and is a uniform size nanoparticle in terms of substance form, with a particle size of about 26 nm. H X MoO3 nanoparticle material exhibits coexistence of MoO3 and MoO2 in terms of substance composition, wherein Mo exists in the form of Mo 4+ , Mo 5+ , Mo 6+ In addition, H X MoO3 nanoparticle semiconductor is a typical n-type semiconductor material, with a conduction band bottom energy level of 4.85 eV, a valence band top energy level of 8.17 eV, and a work function of 5.35 eV. After being used as a hole injection layer in QLEDs, H X The low conduction band bottom energy level of the MoO3 thin film can effectively promote the injection of holes from the anode to the hole injection layer, and the n-type semiconductor property can form a p-n junction with the adjacent p-type hole transport layer material, further promoting the transport of holes from the hole injection layer to the hole transport layer, suitable for use as a hole injection layer material in QLEDs.

[0026] The present application provides H X The application of the MoO3 nanoparticle solution is specifically the application of the preparation material of the hole injection layer in a quantum dot light emitting diode.

[0027] Compared with the existing oxidation method for preparing H X MoO3 nanoparticles, the MoO3 nanoparticles prepared by the present application after purification improvement H XThe MoO3 nanoparticle solution completely eliminates the residues of hydrogen peroxide and molybdenum powder in the former, and ensures the uniform particle size of the nanoparticles to the maximum extent, realizes the H X MoO3 nanoparticle material, and successfully realizes the H X MoO3 nanoparticle material as a hole injection layer to construct a quantum dot light emitting diode.

[0028] The quantum dot light emitting diode of the present application comprises a hole injection layer, a hole transport layer, a quantum dot light emitting layer and an electron transport layer; the hole injection layer adopts the H X MoO3 nanoparticle solution is prepared.

[0029] Further, the preparation method of the hole injection layer comprises the following steps: mixing the H X The MoO3 nanoparticle solution is spin-coated on an anode ITO substrate, and then low-temperature annealing treatment is performed; the spin-coating speed is 4000-6000 rpm; the temperature of the low-temperature annealing treatment is 80-120 DEG C, and the time is 10-20 min.

[0030] The quantum dots of different structures and types are different in energy level, and based on the consideration of effectively improving the brightness and service life of the light emitting diode, preferably, the quantum dots used in the quantum dot light emitting layer are ZnCdSe / ZnS quantum dots.

[0031] The present application uses the H X The MoO3 nanoparticle solution is used as a hole injection layer to construct a quantum dot light emitting diode device, and the obtained H X The MoO3 nanoparticle film has excellent photoelectric performance and extremely high stability, and when used as a hole injection layer of a quantum dot light emitting diode, the brightness and external quantum efficiency of the device can reach 44100 cd / m 2 and 14.50%, while the T 95 life of the device under the initial brightness of 100 cd / m 2 is 5749.97 h, which is 109 times of the service life of a standard device, and the service life is greatly improved, and the present application has a wide application prospect in the preparation field of quantum dot light emitting diodes. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The preparation process flow chart of the H X MoO3 nanoparticle solution in the present application embodiment 1 is shown in the figure;

[0033] Figure 2 The preparation process flow chart of the H XDevice structure and energy level structure diagram of QLEDs using a thin film prepared from a MoO3 nanoparticle solution as a hole injection layer;

[0034] Figure 3 H in Example 1 of the present invention X Transmission electron microscopy (TEM) characterization of MoO3 nanoparticles in solution and H2O prepared by spin coating on glass substrates X Scanning probe microscopy (AFM) morphology characterization of MoO3 nanoparticle film;

[0035] Figure 4 H in Example 1 of the present invention X AFM topography characterization of the film prepared by MoO3 nanoparticle solution on ITO substrate and glass substrate;

[0036] Figure 5 H in Example 1 of the present invention X Conductive atomic force microscopy (C-AFM) current image of a film prepared from a MoO3 nanoparticle solution;

[0037] Figure 6 H in Example 1 of the present invention X X-ray diffraction (XRD) patterns of MoO3 nanoparticles in solution after annealing at different temperatures;

[0038] Figure 7 H in Example 1 of the present invention X X-ray photon spectroscopy (XPS) spectrum of the nanoparticles in the MoO3 nanoparticle solution;

[0039] Figure 8 H in Example 1 of the present invention X The relationship between the absorption coefficient of nanoparticles and photon energy in MoO3 nanoparticle solution;

[0040] Figure 9 H in Example 1 of the present invention X Ultraviolet photoelectron spectroscopy (UPS) graph of MoO3 nanoparticles in solution;

[0041] Figure 10 H in Example 2 of the present invention X Photoelectric performance test diagram of red QLEDs using a thin film prepared from a MoO3 nanoparticle solution as a hole injection layer;

[0042] Figure 11 H in Example 2 of the present invention X Comparison of the lifespan of red light QLEDs using a thin film prepared from MoO3 nanoparticle solution as a hole injection layer and the standard structure red light QLEDs based on PEDOT:PSS as a hole injection layer in comparative example 1. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and effects of the present invention clearer and more specific, the present invention is described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the materials used in the present invention are all conventional commercial products in the art.

[0044] In the following embodiments, the anode involved is indium tin oxide (ITO), purchased from Tinwell Technology Ltd; the hole transport layer is poly [9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine] (TFB) purchased from Amerian DyeSource; quantum dots (QDs) are ZnCdSe / ZnS red light quantum dots, which are obtained in the laboratory according to the existing method; zinc magnesium oxide (ZnMgO) solution is also prepared in the laboratory; the aluminum electrode is made of a density of 2.702 g / cm 3 Aluminum particles with a boiling point of 2467°C, a melting point of 660.4°C, and a purity of 99.99% were prepared by vapor deposition. The aluminum particles were purchased from Kurt J. Lesker. UV-curable resin was purchased from Norland, USA, with a specification of NOA61. Detergent was purchased from Alconox, USA.

[0045] In other embodiments, ZnCdSe / ZnS red light quantum dots can also be obtained through commercial channels, which can achieve technical effects equivalent to those of the present invention.

[0046] In the following examples and test examples, the conductive atomic force microscope and Kelvin probe microscope used were Dimension Icon models; the transmission electron microscope was JEM-2100; the UV-visible-near-infrared spectrophotometer was PELambda 950; the X-ray diffraction analyzer was Bruker D8 Advance; the X-ray / UV photoelectron spectrometer was AXIS-ULTRA; the spectroradiometer was PR-735, M-75Lens, standard SD card, and power adapter (AC-730-6). The hot plate model was 11-100-49H. The UV photoelectron spectrometer (ESCALAB 250XI) and device lifetime test system were Newport Keithley N6705B. The spin coater model was WS-650MZ-23NPP / LITE.

[0047] Example 1

[0048] This embodiment is H X An embodiment of a MoO3 nanoparticle solution and a method for preparing the same. XPreparation method of MoO3 nanoparticle solution, preparation process flow chart is as follows Figure 1 The specific steps are as follows:

[0049] (1) Take 0.1g platinum powder and add it to a small bottle filled with 10mL chromatography grade ethanol, place it on a stirring platform and stir, so that the platinum powder deposited at the bottom of the small bottle is evenly dispersed in ethanol, and obtain an ethanol dispersion of platinum powder;

[0050] Under stirring, 0.3 mL of 30% hydrogen peroxide solution was added to the ethanol dispersion of molybdenum powder for stirring reaction. The stirring process was continued for 24 h to obtain a dark blue system with a precipitate at the bottom, which contained H X A composite system of MoO3 and unreacted raw materials (hydrogen peroxide and molybdenum powder);

[0051] (2) The composite system obtained in step (1) was filtered through a 0.2 μm filter head, and the dark blue solution obtained by filtration was placed on a constant temperature heating table at 110°C and heated until the solvent was evaporated to dryness to obtain H X MoO3 powder material;

[0052] (3) using chromatographic grade ethanol to obtain H X The MoO3 powder material was diluted to a concentration of 16 mg / mL, and then stirred and dispersed for 4 hours. The resulting solution was then centrifuged at 12000 rpm for 15 minutes, and the upper dark blue solution was taken to obtain the H in Example 1. X MoO3 nanoparticle solution.

[0053] Example 2

[0054] This embodiment is H X Application of MoO3 nanoparticle solution and examples of quantum dot light-emitting diodes.

[0055] H in this embodiment X Application of MoO3 nanoparticle solution, specifically H X Application of MoO3 nanoparticle solution as preparation material for hole injection layer in quantum dot light-emitting diodes.

[0056] The quantum dot light-emitting diode of this embodiment includes a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, and an electron transport layer; the hole injection layer is prepared by using the H prepared in Example 1. X MoO3 nanoparticle solution was prepared.

[0057] The specific device structure (a) and energy level structure (b) of the quantum dot light emitting diode of this embodiment are as follows: Figure 2 As shown. The structural material of quantum dot light emitting diode is ITO / H XMoO3 / TFB / QDs / ZnMgO / Al, where ITO is used as the anode electrode of QLEDs, H X The MoO3 nanoparticle film serves as the hole injection layer, TFB, QDs, and ZnMgO serve as the hole transport layer, quantum dot light-emitting layer, and electron transport layer of the QLEDs, respectively. Al serves as the cathode electrode of the QLEDs. The device preparation and construction methods are as follows:

[0058] (1) Preparation of the anode ITO substrate: A glass substrate with a fixed pattern ITO electrode layer deposited thereon was ultrasonically cleaned in detergent, water, acetone, and isopropyl alcohol, and then subjected to UV-ozone treatment for 15 minutes to increase the surface wettability, thereby obtaining the anode ITO substrate;

[0059] (2) Preparation of hole injection layer: 50 μL of H2O2 prepared in Example 1 was measured with a pipette. X The MoO3 nanoparticle solution was spin-coated onto the above-mentioned anode ITO substrate at a rotation speed of 5000 rpm, and was placed on a constant temperature heating table at 100°C for annealing for 15 minutes, and then quickly transferred to a nitrogen-filled glove box to isolate the air to obtain a substrate containing a hole injection layer.

[0060] (3) Preparation of hole transport layer: Using a pipette, a chlorobenzene solution of TFB (8 mg / mL) was spin-coated at 3000 rpm on the hole injection layer surface of the substrate obtained in step (2) to form a film, and annealed at 150°C for 30 min to obtain a substrate containing a hole transport layer;

[0061] (4) Preparation of quantum dot light-emitting layer and electron transport layer: After the annealing in step (3) is completed, wait for the substrate to cool to room temperature, measure an n-octane solution (18 mg / mL) of red light-emitting ZnCdSe / ZnS quantum dots (QDs) and spin-coat it on the hole transport layer surface of the substrate obtained in step (3) at a speed of 3000 rpm to form a quantum dot light-emitting layer, then continue to measure an ethanol solution (30 mg / mL) of ZnMgO and spin-coat it on the surface of the quantum dot light-emitting layer at a speed of 2000 rpm to form a film, and place it on a constant temperature heating table for annealing at 60°C for 30 minutes;

[0062] (5) Preparation of cathode electrode: The substrate obtained after step (4) was placed in a thermal evaporation coating machine under high vacuum (1×10 -6 mbar) in the deposition chamber. An Al cathode was deposited at a thermal deposition rate of 100 nm / s to a thickness of 100 nm. After the aluminum plating was completed, the device was encapsulated with UV-curable resin and a cover glass to complete the construction of the quantum dot light-emitting diode device.

[0063] Comparative Example 1

[0064] The quantum dot light-emitting diode of this comparative example includes a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, and an electron transport layer; the hole injection layer is prepared using a PEDOT:PSS solution. The specific preparation method of the quantum dot light-emitting diode is the same as that of Example 2, except for the difference in the hole injection layer material.

[0065] Comparative Example 2

[0066] The quantum dot light-emitting diode of this comparative example includes a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, and an electron transport layer; the hole injection layer is prepared by the following method: X The specific preparation method of the quantum dot light emitting diode is the same as that of Example 2 except that the hole injection layer material is different.

[0067] H of Comparative Example 2 X The preparation steps of MoO3 nanoparticle solution are as follows:

[0068] (1) Take 0.1g platinum powder and add it to a small bottle filled with 10mL chromatography grade ethanol, place it on a stirring platform and stir, so that the platinum powder deposited at the bottom of the small bottle is evenly dispersed in ethanol, and obtain an ethanol dispersion of platinum powder;

[0069] Under stirring, 0.3 mL of 30% hydrogen peroxide solution was added to the ethanol dispersion of molybdenum powder for stirring reaction. The stirring process was continued for 24 h to obtain a dark blue system with a precipitate at the bottom, which contained H X A composite system of MoO3 and unreacted raw materials (hydrogen peroxide and molybdenum powder);

[0070] (2) After the composite system obtained in step (1) was allowed to stand for 1 hour, the solvent was removed in a vacuum drying oven, and the remaining dark blue powder was redispersed in ethanol and ultrasonically treated for 10 minutes to obtain H of comparative example 2. X MoO3 nanoparticle solution.

[0071] Comparative Example 3

[0072] The quantum dot light-emitting diode of this comparative example includes a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, and an electron transport layer; the hole injection layer is prepared by the following method: X The specific preparation method of the quantum dot light emitting diode is the same as that of Example 2 except that the hole injection layer material is different.

[0073] H of Comparative Example 3 X The preparation steps of MoO3 nanoparticle solution are as follows:

[0074] (1) Take 0.1g platinum powder and add it to a small bottle filled with 10mL chromatography grade ethanol, place it on a stirring platform and stir, so that the platinum powder deposited at the bottom of the small bottle is evenly dispersed in ethanol, and obtain an ethanol dispersion of platinum powder;

[0075] Under stirring, 0.3 mL of 30% hydrogen peroxide solution was added to the ethanol dispersion of molybdenum powder for stirring reaction. The stirring process was continued for 24 h to obtain a dark blue system with a precipitate at the bottom, which contained H X A composite system of MoO3 and unreacted raw materials (hydrogen peroxide and molybdenum powder);

[0076] (2) After the composite system obtained in step (1) was allowed to stand for 1 hour, the solvent was removed in a vacuum drying oven, and the remaining dark blue powder was redispersed in ethanol and ultrasonically treated for 10 minutes. The solution system obtained after ultrasonication was centrifuged at 4000 rpm, and the supernatant was taken to obtain H of Comparative Example 3. X MoO3 nanoparticle solution.

[0077] Comparative Example 4

[0078] The quantum dot light-emitting diode of this comparative example includes a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, and an electron transport layer; the hole injection layer is prepared by the following method: X The specific preparation method of the quantum dot light emitting diode is the same as that of Example 2 except that the hole injection layer material is different.

[0079] H of Comparative Example 4 X The preparation steps of MoO3 nanoparticle solution are as follows:

[0080] (1) Take 0.1g platinum powder and add it to a small bottle filled with 10mL chromatography grade ethanol, place it on a stirring platform and stir, so that the platinum powder deposited at the bottom of the small bottle is evenly dispersed in ethanol, and obtain an ethanol dispersion of platinum powder;

[0081] Under stirring, 0.3 mL of 30% hydrogen peroxide solution was added to the ethanol dispersion of molybdenum powder for stirring reaction. The stirring process was continued for 24 h to obtain a dark blue system with a precipitate at the bottom, which contained H X A composite system of MoO3 and unreacted raw materials (hydrogen peroxide and molybdenum powder);

[0082] (2) After the composite system obtained in step (1) was allowed to stand for 1 hour, the solvent was removed in a vacuum drying oven, and the remaining dark blue powder was redispersed in ethanol, ultrasonically treated for 30 minutes, and filtered with a 0.45 μm organic phase filter to obtain H of Comparative Example 4. X MoO3 nanoparticle solution.

[0083] Test Example 1

[0084] In this test example, the H X The basic morphology of MoO3 nanoparticle solution was characterized. X Transmission electron microscopy (TEM) characterization of MoO3 nanoparticle solution and spin-coated H on glass substrate X Scanning probe microscopy (AFM) morphology characterization of the film obtained from MoO3 nanoparticle solution is shown in the figure Figure 3 shown.

[0085] in, Figure 3 (a) shows H X TEM image of MoO3 nanoparticle solution, the inset is the particle size statistical histogram. Figure 3 (a) It can be seen that H X The particle size of MoO3 nanoparticles is uniform and the dispersion is good. Figure 3 (b) shows H X Small-scale AFM image of a thin film prepared by spin-coating a MoO3 nanoparticle solution onto a glass substrate at 5000 rpm. Nanoparticle-shaped H X MoO3, thus proving that the present invention successfully achieves H X Preparation of MoO3 nanoparticle solution.

[0086] Test Example 2

[0087] In order to further verify the H X The properties of the film formed by spin coating of MoO3 nanoparticle solution were investigated. X The MoO3 nanoparticle films were characterized as follows.

[0088] like Figure 4 The H prepared in Example 1 is shown. X AFM morphology characterization of the film obtained from MoO3 nanoparticle solution on ITO substrate and glass substrate. Figure 4 As shown in (a), H X The root mean square roughness of the MoO3 nanoparticle film on the ITO substrate is 0.40nm, compared with Figure 4 (b) shows that the root mean square roughness of the HxMoO3 nanoparticle film on the glass substrate is 0.16nm. The smaller root mean square roughness value confirms that the HxMoO3 nanoparticle film prepared by spin coating has a good roughness. X The surface of the MoO3 nanoparticle film is smooth.

[0089] like Figure 5 Shown is H XThe C-AFM current image of the MoO3 nanoparticle film confirms that the current in the film micro-area reaches the nanoampere level under a bias of 2V. X MoO3 nanoparticle films have excellent electrical conductivity and are feasible for application.

[0090] Test Example 3

[0091] This test example is for the H of Example 1 X The crystallinity and material composition of the nanoparticles in the MoO3 nanoparticle solution were characterized.

[0092] like Figure 6 Shown are the H X XRD pattern of MoO3 nanoparticles. Figure 6 It can be seen that H X MoO3 nanoparticles are amorphous within the range of 300℃, and the protrusions in the figure are caused by the quartz substrate.

[0093] like Figure 7 Shown is H X XPS characterization data of MoO3 nanoparticles. Figure 7 (a) is the fine spectrum of Mo 3d, which shows that 5 / 2 In the electron orbital, the Mo valence state corresponding to the peak position of 232.55eV is Mo 5+ / Mo 6+ , the Mo valence state corresponding to the 231.33 eV peak is Mo 4+ . Further combine Figure 7 The O1s fine spectrum shown in (b) shows that H X Mo in MoO3 nanoparticles 4+ It exists in the form of MoO2, corresponding to the 531.92eV peak position, Mo 5+ 、Mo 6+ It exists in the form of MoO3, corresponding to the peak position of 530.34eV. 4+ The presence of H X The conductivity of MoO3 nanoparticle films, 5+ The presence of a large number of H X The oxygen vacancies in MoO3 further enhance the conductivity of the film.

[0094] Test Example 4

[0095] This test example is to test the H prepared in Example 1 X The semiconductor properties of the nanoparticles in the MoO3 nanoparticle solution were characterized.

[0096] like Figure 8 Shown is H XRelationship between the absorption coefficient of MoO3 nanoparticles and photon energy. Figure 8 The characterization results confirmed that H X The band gap of MoO3 semiconductor material is 3.32eV.

[0097] like Figure 9 Shown is H X UPS characterization of MoO3 nanoparticles. Figure 9 As shown in the secondary electron cutoff spectrum of (a), H x The secondary electron cutoff edge (E cut off ) value is 15.87eV. Figure 9 (b) As shown in the spectrum of the valence band edge region, the energy between the valence band energy level and the Fermi level of the material is called the Fermi edge (E Fermi ), its value is 2.82eV. According to the principle of Einstein's photoelectric effect, the work function (WF) of the material itself can be calculated according to WF=21.22-E cut off The valence band top energy level (VBM) of the material can be calculated based on VBM=21.22-(E cut off -E Fermi ) is determined, the conduction band bottom energy level (CBM) of the material can be determined according to CBM=E g -VBM is used for calculation. The calculation results and data show that H X The conduction band bottom energy level of MoO3 semiconductor material film is 4.85eV, the valence band top energy level is 8.17eV, the work function is 5.35eV, and the band gap is 3.32eV, which proves that the nanomaterial is a typical n-type semiconductor material. After being used as a hole injection layer in QLEDs, H X The lower conduction band bottom energy level of MoO3 film can effectively promote the injection of holes from the anode into the hole injection layer. At the same time, its n-type semiconductor properties can form a pn junction with the adjacent p-type hole transport layer material, further promoting the transport of holes from the hole injection layer to the hole transport layer.

[0098] Test Example 5

[0099] In order to verify H X The performance of red light QLEDs constructed with MoO3 nanoparticle film as the hole injection layer was tested on the QLEDs prepared in Example 2.

[0100] like Figure 10 H X The current density-voltage-luminance curve (JVL, Figure (a)) and current efficiency-luminance-external quantum efficiency curve (CE-L-EQE, Figure (b)) of red QLEDs constructed with MoO3 nanoparticle-based hole injection layer. Figure 10 It can be seen that based on H X The maximum brightness of red QLEDs devices with MoO3 as the hole injection layer can reach 44100cd / m 2 , the maximum current efficiency can reach 11.54cd / A, and the maximum external quantum efficiency can reach 14.50%.

[0101] Test Example 6

[0102] In order to verify H X The device life of the red QLEDs constructed with MoO3 nanoparticle film as the hole injection layer is compared with the red QLEDs standard device of Comparative Example 1 based on the standard structure of the existing material PEDOT:PSS as the hole injection layer, and the H prepared by conventional methods in Comparative Examples 2 to 4. X MoO3 nanoparticles as the hole injection layer of the red QLEDs device, and the H-based embodiment of the present invention X The lifespan of red QLEDs devices with MoO3 as hole injection layer was tested.

[0103] Among them, due to the preparation method of Comparative Examples 2 to 4, H X The red QLEDs device constructed with MoO3 nanoparticles as the hole injection layer has the problem of not lighting up or having low brightness, and there are a lot of black spots that cannot be tested, so the device life cannot be effectively tested. The device life test results of Comparative Examples 2 to 4 are not shown here. Figure 11 Shown are the comparative results of the life test of Example 2 of the present invention and Comparative Example 1.

[0104] The device life test of the present invention is carried out in accordance with the following specifications. In the constant current mode, the aging process of the device is accelerated according to the electrical aging mechanism existing inside the device. The life of the device can be calculated by the formula L0 n ×T=K (where K is a constant, the acceleration factor is 1 <n<2)得出,本文中取加速系数n=1.5。由于基于H X The performance difference between the red light device with MoO3 as HIL and the standard device is shown in Figure 1. The constant current applied to the standard device of Comparative Example 1 is 15000 cd / m 2 The current value under H X The constant current applied to the MoO3-based device was at an initial luminance of 10,000 cd / m 2 The current value when .

[0105] Figure 11 Finally, the standard device of comparative example 1 and H X The initial brightness of MoO3-based devices is 100 cd / m 2 T of the lower device 95Lifespan (the time it takes for the brightness to decay to 95% of the initial brightness is defined as T 95 The lifetimes of H are 52.81h and 5749.97h respectively. X MoO3 as a hole injection layer can greatly improve the device life, which is about 108 times, which fully proves that the H X MoO3 nanoparticles have an advantage in the stability of quantum dot light-emitting diode devices.

[0106] Furthermore, in practical applications, the initial brightness is often 1000 cd / m 2 The lighting and display devices are evaluated under the lifespan, and the H of Example 2 of the present invention X The initial brightness of MoO3-based devices is 1000 cd / m 2 T of the lower device 95 The lifespan of the long-life quantum dot light-emitting diode can reach 181.83h. Based on this data, it is fully confirmed that H X MoO3-based semiconductor materials have great application prospects in the fields of display and lighting.

Claims

1. A quantum dot light emitting diode, characterized in that: It includes a hole injection layer, a hole transport layer, a quantum dot light emitting layer, and an electron transport layer; the hole injection layer is made of H X MoO3 nanoparticle solution was prepared; The H X The preparation method of MoO3 nanoparticle solution comprises the following steps: (1) Dispersing molybdenum powder uniformly in an alcohol solvent to obtain a dispersion of molybdenum powder; adding a hydrogen peroxide solution to the dispersion of molybdenum powder under stirring conditions, stirring and reacting to obtain a solution containing H X A composite system of MoO3 and unreacted raw materials; (2) The composite system obtained in step (1) is filtered and then evaporated to dryness to obtain H X MoO3 powder material; the filtration adopts a filter head with a fineness of 0.2μm; (3) H obtained in step (2) X The MoO3 powder material is stirred and dispersed in an alcohol solvent and then centrifuged. The resulting supernatant is the H2O3 with uniform dispersion and uniform particle size. X MoO3 nanoparticle solution; the centrifugal speed is 10000~15000rpm; The method for preparing the hole injection layer comprises the following steps: X The MoO3 nanoparticle solution is spin-coated on the anode ITO substrate and then subjected to low-temperature annealing treatment; the spin-coating speed is 4000-6000 rpm; the low-temperature annealing treatment temperature is 80-120°C and the time is 10-20 minutes.

2. The quantum dot light-emitting diode according to claim 1, wherein In step (1), the alcohol solvent is ethanol, ethylene glycol or isopropanol; and the particle size of the molybdenum powder is 10-150 μm.

3. The quantum dot light-emitting diode according to claim 1, wherein In step (1), the ratio of molybdenum powder to alcohol solvent is 1 g: (50-200) mL; the ratio of molybdenum powder to hydrogen peroxide is 1 g: (1-4) mL; the concentration of hydrogen peroxide is 30%; and the stirring reaction time is 24-30 h.

4. The quantum dot light-emitting diode according to claim 1, wherein In step (2), the evaporation to dryness is carried out at 100-120°C.

5. The quantum dot light-emitting diode according to claim 1, wherein: In step (3), the alcohol solvent is ethanol, ethylene glycol or isopropanol; H X The concentration of the MoO3 powder material after stirring and dispersing in an alcohol solvent is 10-20 mg / mL; the stirring and dispersing time is 3-5 hours; and the centrifugation time is 10-20 minutes.

6. The quantum dot light-emitting diode according to claim 1, wherein: The quantum dots used in the quantum dot light-emitting layer are ZnCdSe / ZnS quantum dots.

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