A QLED device and its manufacturing method

Abstract

The present invention discloses a QLED device and a preparation method thereof. The preparation method includes the steps of: providing a substrate, where the substrate includes a first electrode; performing cold treatment on the substrate or placing the substrate under a first temperature condition, and depositing a quantum dot solution on the substrate to form a quantum dot film layer; wherein, the absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5°C, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5°C; and preparing a second electrode on the quantum dot film layer. The preparation method provided by the present invention can maximize the avoidance of the problem of uneven light emission of the QLED device caused by ligand detachment of the quantum dot material, and can significantly reduce the phenomenon of fluorescence quenching.

Description

Technical Field

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

[0002] Quantum dot light-emitting diodes (QLEDs) are emerging display devices. Their structure is similar to that of organic light-emitting diodes (OLEDs), and they form a sandwich structure similar to a p-i-n junction through a hole injection layer, a hole transport layer, a quantum dot film layer, an electron transport layer, etc. The core technology of QLEDs is quantum dots, whose particle diameters are usually less than 10 nm. Common quantum dots are composed of IV, II-VI, IV-VI, or III-V elements. When quantum dots are stimulated by electricity or light, they emit various monochromatic lights according to the materials and diameters of the quantum dots. Quantum dots have the characteristics of a narrow emission wavelength range, high color saturation, and adjustable emission wavelength. Therefore, the images of quantum dot displays are clearer and brighter than those of liquid crystal displays. In addition, QLEDs have a long lifespan, a simple packaging process or no packaging required, and are expected to become the next-generation displays with broad development prospects.

[0003] However, the actual working lifespan of the QLED devices prepared at the present stage far from reaches the theoretical length, and the phenomenon of fluorescence quenching occurs, which is highly related to the ligand detachment of the quantum dot material. The occurrence of this situation greatly restricts the R & D progress of quantum dot light-emitting devices. At the same time, ligand detachment also causes the film to be uneven, thereby resulting in uneven light emission of the device.

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

[0005] The present invention aims to disclose a QLED device and a preparation method thereof, aiming to solve the problem of uneven light emission of the device caused by ligand detachment of the quantum dot material in the existing technology.

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

[0007] A preparation method of a QLED device, which includes the steps of:

[0008] Providing a substrate, wherein the substrate includes a first electrode;

[0009] Performing cold treatment on the substrate or placing the substrate under a first temperature condition, and depositing a quantum dot solution on the substrate to form a quantum dot film layer; wherein, the absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5 °C, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5 °C;

[0010] A second electrode is fabricated on the quantum dot film layer to obtain the QLED device.

[0011] A QLED device, which is obtained by using the preparation method of the QLED device of the present invention.

[0012] Advantageous effects: Since the molecular mobility of the quantum dot film layer material is weak under the storage temperature conditions and its ligands are not easily detached, in the process of preparing the quantum dot film layer in the present invention, by performing cold treatment on the substrate or placing the substrate under the first temperature condition, both the first temperature and the temperature of the cold treatment are the same as the storage temperature of the quantum dot solution, and then preparing the quantum dot film layer on the substrate can maximally avoid the problem of uneven light emission of the QLED device caused by ligand detachment of the quantum dot material, and can significantly reduce the phenomenon of fluorescence quenching. Description of the Drawings

[0013] Figure 1 It is a flowchart of the first embodiment of the preparation method of a QLED device provided by the present invention.

[0014] Figure 2 It is a flowchart of the second embodiment of the preparation method of a QLED device provided by the present invention.

[0015] Figure 3 It is a flowchart of the third embodiment of the preparation method of a QLED device provided by the present invention.

[0016] Figure 4 It is a flowchart of the fourth embodiment of the preparation method of a QLED device provided by the present invention.

[0017] Figure 5 It is a result diagram of thin film morphology detection of the QLED device obtained in Example 1.

[0018] Figure 6 It is a result diagram of thin film morphology detection of the QLED device obtained in Example 2.

[0019] Figure 7 It is a result diagram of thin film morphology detection of the QLED device obtained in Example 3.

[0020] Figure 8 It is a result diagram of thin film morphology detection of the QLED device obtained in the comparative example. Detailed Embodiments

[0021] The present invention provides a QLED device and its preparation method. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] QLED has been widely studied in recent years due to its excellent development prospects. However, there are still many problems in the R & D process. Among them, the uneven light emission of quantum dot devices prepared by the spin coating process is an important factor affecting the R & D process. The reasons for the problems are as follows:

[0023] In the process of preparing quantum dot materials, quantum dot ligands can control the growth rate of quantum dots by affecting the reaction activity. Therefore, the surface ligands of quantum dots have a great influence on the light emission performance of quantum dots. At room temperature or a higher temperature environment, the molecular mobility increases, and some ligands on the surface of the quantum dot material fall off, which not only affects the dispersibility of the quantum dot material, causes uneven light emission of QLED devices, but also may cause fluorescence quenching.

[0024] Based on this, this embodiment provides a method for preparing a QLED device, as Figure 1 shown, which includes the steps:

[0025] S10. Provide a substrate, and the substrate includes a first electrode;

[0026] S20. Place the substrate under a first temperature condition, deposit a quantum dot solution on the substrate to form a quantum dot film layer, and the absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5°C;

[0027] S30. Prepare a second electrode on the quantum dot film layer to obtain the QLED device.

[0028] In this embodiment, since the molecular mobility of the quantum dot solution is weak under the storage temperature condition, its surface ligands are not easily detached. Therefore, in the process of preparing the quantum dot film layer in this embodiment, by placing the substrate under the first temperature condition, the absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5°C, and then preparing the quantum dot film layer on the substrate can maximize the problem of uneven light emission of the QLED device caused by ligand detachment of quantum dots, and can significantly reduce the phenomenon of fluorescence quenching.

[0029] In some specific embodiments, the first temperature is -15 - 5°C. Under this temperature condition, the molecular mobility of quantum dots is weak, and its surface ligands are not easily detached.

[0030] In some embodiments, in the step of placing the substrate under the first temperature condition and depositing a quantum dot solution on the substrate to form a quantum dot film layer, it further includes: placing the substrate in a room temperature environment and annealing the quantum dot solution to obtain the quantum dot film layer.

[0031] In this embodiment, at room temperature, the quantum dot solution deposited on the substrate is annealed to remove the solvent in the quantum dot film layer, obtaining a uniform quantum dot film layer. As an example, a hot plate can be used to thermally anneal the quantum dot solution to evaporate the solvent. In this embodiment, the room temperature, also called normal temperature or ambient temperature, can be 25 - 35 °C. As an example, the normal temperature can be 25 °C.

[0032] In some embodiments, since the substrate needs to be replaced from the first temperature condition to the room temperature environment during the thermal annealing of the quantum dot solution, this increases the complexity of the experimental operation. Based on this, this embodiment provides another method to remove the solvent in the quantum dot film layer without environmental replacement, that is, evacuating the placement environment of the substrate under the first temperature condition to lower the boiling point of the solvent in the quantum dot solution, thereby quickly removing the solvent to form a quantum dot film layer. In this embodiment, due to the high thermal sensitivity of the quantum dot film layer, removing the solvent by evacuation at a relatively low first temperature condition can improve the flatness of the quantum dot film layer, and at the same time avoid damage to the quantum dot film layer by heat baking the device, thereby improving the luminescence performance of the QLED device.

[0033] In some specific embodiments, the degree of vacuum after evacuating the placement environment of the substrate is less than or equal to 3×10 -4 Pa. Under this degree of vacuum condition, the solvent in the quantum dot film layer can be effectively removed.

[0034] In some embodiments, another method for preparing a QLED device is also provided. As Figure 2 shown, it includes the steps:

[0035] S100. Provide a substrate, and the substrate includes a first electrode;

[0036] S200. Cold-treat the substrate, deposit a quantum dot solution on the substrate to form a quantum dot film layer, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5 °C;

[0037] S300. Prepare a second electrode on the quantum dot film layer to obtain the QLED device.

[0038] In this embodiment, since the molecular mobility of the quantum dot solution is weak under the storage temperature condition and its surface ligands are not easily detached, during the process of preparing the quantum dot film layer in this embodiment, by performing cold treatment on the substrate, the substrate is maintained at a lower temperature when preparing the quantum dot film layer. The temperature of the cold treatment is the same as the storage temperature of the quantum dot solution. Then, preparing the quantum dot film layer on the substrate can maximally avoid the problem of uneven light emission of the QLED device caused by the detachment of quantum dot ligands and can significantly reduce the phenomenon of fluorescence quenching.

[0039] In some embodiments, during the steps of performing cold treatment on the substrate and depositing the quantum dot solution on the substrate to form a quantum dot film layer, it further includes: annealing the quantum dot solution or evacuating the placement environment of the substrate at room temperature to form a quantum dot film layer on the substrate.

[0040] In this embodiment, since the substrate is at room temperature when preparing the quantum dot film layer after cold treatment, whether annealing the quantum dot solution to remove the solvent or evacuating the placement environment of the substrate to remove the solvent in this embodiment, there is no need for environment replacement, which can reduce the complexity of experimental operations.

[0041] In some specific embodiments, the temperature of the cold treatment is -15 - 5°C. Under this temperature condition, the molecular mobility of the quantum dot film layer material is weak and its surface ligands are not easily detached.

[0042] In some embodiments, the preparation of the quantum dot film layer can be a chemical method or a physical method. The chemical method includes, but is not limited to, one or more of chemical vapor deposition, sequential ionic layer adsorption and reaction, anodic oxidation, electrodeposition, coprecipitation; the physical method includes, but is not limited to, solution methods (such as spin coating, printing, doctor blading, dip coating, immersion, spraying, roll coating, casting, slot die coating or bar coating, etc.), evaporation methods (such as thermal evaporation, electron beam evaporation, magnetron sputtering or multi-arc ion plating, etc.), deposition methods (such as physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc.). By way of example, spin coating can be used to prepare the quantum dot film layer on the substrate.

[0043] In some embodiments, the quantum dot film layer material is a direct bandgap compound semiconductor with light-emitting ability, including but not limited to one or more of II-VI group compound semiconductor materials, III-V group compound semiconductor materials, II-V group compound semiconductor materials, III-VI compound semiconductor materials, IV-VI group compound semiconductor materials, I-III-VI group compound semiconductor materials, II-IV-VI group compound semiconductor materials, or group IV elemental substances. Specifically, the II-VI group compound semiconductor materials include but not limited to nanocrystals of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS, PbSe, PbTe, and other binary, ternary, and quaternary II-VI semiconductors; the III-V group compound semiconductor materials include but not limited to nanocrystals of GaP, GaAs, InP, InAs, and other binary, ternary, and quaternary III-V semiconductors.

[0044] In some specific embodiments, the quantum dot film layer material includes but not limited to one or more of doped or undoped inorganic perovskite semiconductors. Specifically, the general structural formula of the inorganic perovskite semiconductor is AMX3, where A is a Cs + ion; M is a divalent metal cation, including but not limited to Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ ; X is a halogen anion, including but not limited to Cl - , Br - , I - .

[0045] In some specific embodiments, the quantum dot film layer material includes but not limited to one or more of organic-inorganic hybrid perovskite semiconductors. Specifically, the general structural formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including but not limited to CH3(CH2) n-2 NH3 + (n≥2) or NH3(CH2) n NH3 2+(n ≥ 2). When n = 2, the inorganic metal halide octahedra MX64- are connected by sharing vertices. The metal cation M is located at the center of the halogen octahedron, and the organic amine cation B fills the voids between the octahedra, forming an infinitely extended three-dimensional structure; when n > 2, the inorganic metal halide octahedra MX64- connected by sharing vertices extend in two dimensions to form a layered structure, and a bilayer of organic amine cations (protonated monoamine) or a monolayer of organic amine cations (protonated diamine) is inserted between the layers. The organic layer and the inorganic layer overlap with each other to form a stable two-dimensional layered structure; M is a divalent metal cation, including but not limited to Pb 2+ 、Sn 2+ 、Cu 2+ 、Ni 2+ 、Cd 2+ 、Cr 2+ 、Mn 2+ 、Co 2+ 、Fe 2+ 、Ge 2+ 、Yb 2+ 、Eu 2+ ; X is a halogen anion, including but not limited to Cl - 、Br - 、I - .

[0046] In some embodiments, the substrate further includes a hole functional layer disposed on the first electrode. The hole functional layer is one or more of an electron blocking layer, a hole injection layer, and a hole transport layer. The first electrode is an anode, and the second electrode is a cathode. The QLED device prepared in this embodiment is a normal-type device. Taking the hole functional layer including a hole injection layer and a hole transport layer as an example, as Figure 3 shown, the preparation method of the QLED device includes the following steps:

[0047] S01. Prepare an anode on a substrate;

[0048] S02. Prepare a hole injection layer on the anode;

[0049] S03. Prepare a hole transport layer on the hole injection layer to form a substrate;

[0050] S04. Perform cold treatment on the substrate or place the substrate under a first temperature condition, and deposit a quantum dot solution on the substrate to form a quantum dot film layer. The absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5°C, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5°C;

[0051] S05. Prepare an electron transport layer on the quantum dot film layer;

[0052] S06. Prepare a cathode on the electron transport layer to obtain the quantum dot light-emitting diode.

[0053] Since the molecular mobility of the quantum dot solution is weak under the storage temperature conditions and its ligands are not easily detached, in the process of preparing the quantum dot film layer in this embodiment, by cold-treating the substrate or placing the substrate under a first temperature condition, both the first temperature and the temperature of the cold treatment are the same as the storage temperature of the quantum dot film layer material, and then preparing the quantum dot film layer on the substrate can maximally avoid the problem of uneven light emission of the QLED device caused by the detachment of quantum dot ligands and can significantly reduce the phenomenon of fluorescence quenching.

[0054] In some embodiments, to ensure that the obtained QLED device has better light extraction efficiency, the optical band gaps of the hole injection layer and the hole transport layer are greater than or equal to the optical band gap of the quantum dot film layer material.

[0055] In some embodiments, the hole injection layer material includes, but is not limited to, one or more of PEDOT:PSS, CuPc, F4-TCNQ, HATCN, transition metal oxides, and transition metal chalcogenides. Among them, the transition metal oxides include one or more of NiOx, MoOx, WOx, CrOx, and CuO. The metal chalcogenides include one or more of MoSx, MoSex, WSx, WSex, and CuS.

[0056] In some embodiments, the hole transport layer material includes, but is not limited to, at least one of poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine), polyvinylcarbazole, poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine), 4,4',4”-tris(carbazol-9-yl)triphenylamine, 4,4'-bis(9-carbazolyl)biphenyl, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, graphene, and C60; and / or the hole transport layer material includes, but is not limited to, at least one of NiOx, MoOx, WOx, CrOx, CuO, MoSx, MoSex, WSx, WSex, and CuS.

[0057] In some embodiments, the electron transport layer material includes, but is not limited to, one or more of ZnO, TiO2, SnO2, Ta2O3, ZrO2, NiO, TiLiO, ZnAlO, ZnMgO, ZnSnO, ZnLiO, and InSnO.

[0058] In some specific embodiments, the first electrode material and the second electrode material include, but are not limited to, one or more of a metal material, a carbon material, and a metal oxide.

[0059] Specifically, the metal material includes, but is not limited to, one or more of Al, Ag, Cu, Mo, Au, Ba, Ca, Mg; the carbon material includes, but is not limited to, one or more of graphite, carbon nanotubes, graphene, carbon fibers; the metal oxide includes, but is not limited to, a doped or undoped metal oxide and a composite electrode with a metal sandwiched between a doped or undoped transparent metal oxide; the doped or undoped metal oxide includes, but is not limited to, one or more of ITO, FTO, ATO, AZO, GZO, IZO, MZO, AMO; the composite electrode includes, but is not limited to, one or more of AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, TiO2 / Ag / TiO2, TiO2 / Al / TiO2, ZnS / Ag / ZnS, ZnS / Al / ZnS, TiO2 / Ag / TiO2, TiO2 / Al / TiO2.

[0060] In some specific embodiments, the QLED device is a top-emitting device, and the thickness of the top electrode metal part does not exceed 20 nm and the visible light transmittance is not less than 90%.

[0061] In some other embodiments, the substrate further includes an electron functional layer disposed on the first electrode. The electron functional layer is one or more of a hole blocking layer, an electron injection layer, and an electron transport layer. The first electrode is a cathode and the second electrode is an anode. The QLED device prepared in this embodiment is an inverted device. Taking the electron functional layer including an electron transport layer as an example, as Figure 4 shown, the preparation method of the QLED device includes the following steps:

[0062] S001. Prepare a cathode on a substrate;

[0063] S002. Prepare an electron transport layer on the cathode to form a substrate;

[0064] S003. Perform cold treatment on the substrate or place the substrate under a first temperature condition, and deposit a quantum dot solution on the substrate to form a quantum dot film layer. The absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5 °C, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5 °C;

[0065] S004. Prepare a hole transport layer on the quantum dot film layer;

[0066] S005. Prepare a hole injection layer on the hole transport layer;

[0067] S006. Prepare an anode on the hole injection layer to obtain the quantum dot light-emitting diode.

[0068] Since the molecular mobility of the quantum dot solution is weak under the storage temperature conditions, its ligands are not likely to fall off. Therefore, in the process of preparing the quantum dot film layer in this embodiment, by cold-treating the substrate or placing the substrate under the first temperature condition, both the first temperature and the temperature of the cold treatment are the same as the storage temperature of the quantum dot solution, and then preparing the quantum dot film layer on the substrate can maximize the avoidance of the problem of uneven light emission of the QLED device caused by the ligand shedding of the quantum dots, and can significantly reduce the phenomenon of fluorescence quenching.

[0069] The following further explains and illustrates a method for preparing a QLED device of the present invention through specific embodiments:

[0070] Example 1

[0071] This example is a positive top-emitting QLED device, and the preparation method of the core solution is adopted. The specific steps are as follows:

[0072] A. Spin-coat PEDOT:PSS as the hole injection layer on the ITO substrate at a rotation speed of 5000 revolutions per minute for 30 seconds, and then heat at 150 °C for 15 minutes;

[0073] B. Spin-coat TFB as the hole transport layer on the hole injection layer, with a TFB concentration of 8 mg / mL, at a rotation speed of 3000 revolutions per minute for 30 seconds, and then heat at 80 °C for 10 minutes;

[0074] C. Replace the spin-coating environment with -10 °C;

[0075] D. Spin-coat the quantum dot film layer on the hole transport layer, with a quantum dot concentration of 20 mg / ml, at a rotation speed of 2000 revolutions per minute for 30 s;

[0076] E. Replace the spin-coating environment with room temperature and heat the quantum dot film layer at 80 °C for 10 minutes;

[0077] F. Spin-coat ZnO as the electron transport layer on the quantum dot layer, with a ZnO concentration of 30 mg / ml, at a rotation speed of 3000 revolutions per minute for 30 s, and then heat at 80 °C for 30 minutes;

[0078] G. At a vacuum degree not higher than 3×10 -4Under a Pa environment, Ag is evaporated by thermal evaporation at a rate of 1 Å / second for 200 seconds with a thickness of 20 nm, thus obtaining a top-emitting upright quantum dot light-emitting diode.

[0079] The device is encapsulated and subjected to a constant-current operating life test with a current of 2 mA. The test is stopped when the device brightness decreases to 95% of the maximum value, as shown in Table 1. And the thin-film morphology of the device is detected, such as Figure 5 shown.

[0080] Example 2

[0081] This example is a positive top-emitting QLED device, and the preparation method of the preferred scheme is adopted. The specific steps are as follows:

[0082] A. On the ITO substrate, PEDOT:PSS is spin-coated as a hole injection layer at a rotation speed of 5000 revolutions per minute for 30 seconds, and then heated at 150 °C for 15 minutes;

[0083] B. TFB is spin-coated as a hole transport layer on the hole injection layer. The concentration of TFB is 8 mg / mL, the rotation speed is 3000 revolutions per minute, the spin-coating time is 30 seconds, and then it is heated at 80 °C for 10 minutes;

[0084] C. Replace the spin-coating environment with -10 °C;

[0085] D. A quantum dot film layer is spin-coated on the hole transport layer. The concentration of the quantum dots is 20 mg / ml, the rotation speed is 2000 revolutions per minute, and the spin-coating time is 30 s;

[0086] E. Place the device in a vacuum chamber with a vacuum degree not higher than 3×10-4 Pa for 10 minutes;

[0087] F. Replace the spin-coating environment with room temperature. After the device temperature returns to room temperature, ZnO is spin-coated as an electron transport layer on the quantum dot layer. The concentration of ZnO is 30 mg / ml, the rotation speed is 3000 revolutions per minute, the spin-coating time is 30 s, and then it is heated at 80 °C for 30 minutes;

[0088] G. Under a vacuum degree not higher than 3×10 -4 Pa environment, Ag is evaporated by thermal evaporation at a rate of 1 Å / second for 200 seconds with a thickness of 20 nm, thus obtaining a top-emitting upright quantum dot light-emitting diode.

[0089] The device is encapsulated and subjected to a constant-current operating life test with a current of 2 mA. The test is stopped when the device brightness decreases to 95% of the maximum value, as shown in Table 1. And the thin-film morphology of the device is detected, such as Figure 6 shown.

[0090] Example 3

[0091] This embodiment is a positive top-emitting QLED device, and the preparation method adopts a cold treatment scheme. The specific steps are as follows:

[0092] A. Spin-coat PEDOT:PSS on the ITO substrate as the hole injection layer at a speed of 5000 revolutions per minute for 30 seconds, and then heat it at 150 °C for 15 minutes;

[0093] B. Spin-coat TFB on the hole injection layer as the hole transport layer. The concentration of TFB is 8 mg / mL, the speed is 3000 revolutions per minute, the spin-coating time is 30 seconds, and then heat it at 80 °C for 10 minutes;

[0094] C. Cold-treat the device for 5 minutes to reduce the device temperature to -10 °C. After taking out the device, spin-coat the quantum dot film layer. The concentration of the quantum dots is 20 mg / ml, the speed is 2000 revolutions per minute, the spin-coating time is 30 seconds, and then heat it at 80 °C for 10 minutes;

[0095] D. Spin-coat ZnO on the quantum dot layer as the electron transport layer. The concentration of ZnO is 30 mg / ml, the speed is 3000 revolutions per minute, the spin-coating time is 30 s, and then heat it at 80 °C for 30 minutes;

[0096] E. Under an environment with a vacuum degree not higher than 3×10 -4 Pa, evaporate Ag by thermal evaporation at a speed of 1 Å / second for 200 seconds and a thickness of 20 nm, then the top-emitting positive quantum dot light-emitting diode is obtained.

[0097] Package the device and conduct a constant-current working life test on it. The current is 2 mA, and the test stops when the device brightness decreases to 95% of the maximum value, as shown in Table 1. And conduct thin-film morphology detection on the device, as Figure 7 shown.

[0098] Comparative Example

[0099] The preparation method of this embodiment is for a positive top-emitting QLED device. The specific steps are as follows:

[0100] A. Spin-coat PEDOT:PSS on the ITO substrate as the hole injection layer at a speed of 5000 revolutions per minute for 30 seconds, and then heat it at 150 °C for 15 minutes;

[0101] B. Spin-coat TFB on the hole injection layer as the hole transport layer. The concentration of TFB is 8 mg / mL, the speed is 3000 revolutions per minute, the spin-coating time is 30 seconds, and then heat it at 80 °C for 10 minutes;

[0102] C. Spin-coat the quantum dot film layer on the hole transport layer. The concentration of the quantum dots is 20 mg / ml, the speed is 2000 revolutions per minute, the spin-coating time is 30 seconds, and then heat it at 80 °C for 10 minutes;

[0103] D. Spin-coat ZnO on the quantum dot layer as the electron transport layer. The concentration of ZnO is 30 mg / ml, the rotation speed is 3000 revolutions per minute, and the spin-coating time is 30 s. Then heat it at 80 °C for 30 minutes;

[0104] E. Under an environment with a vacuum degree not higher than 3×10 -4 Pa, evaporate Ag by thermal evaporation at a speed of 1 Å / s for 200 s with a thickness of 20 nm, and then the top-emitting upright quantum dot light-emitting diode is obtained.

[0105] Package the device and conduct a constant-current operating life test on it. The current is 2 mA, and the test stops when the device brightness decreases to 95% of the maximum value, as shown in Table 1. And conduct thin-film morphology detection on the device, as Figure 8 shown.

[0106] Conduct a constant-current operating life test on the QLED devices prepared in Example 1, Example , Example 3 and the comparative example respectively. The current is 2 mA, and the test stops when the device brightness decreases to 95% of the maximum value. The test results are shown in Table 1:

[0107] Table 1 Comparison of the operating life of QLED devices in the examples and the comparative example

[0108]

[0109]

[0110] Among them, L (cd / m 2 ) represents the maximum brightness of the device; T95 (h) represents the time taken for the device brightness to decay to 95% under a constant current drive of 2 mA; T95-1K (h) represents the time required for the device brightness to decay to 95% when the brightness is 1000 nit. It can be seen that compared with the comparative example, the QLED devices prepared in the examples have higher brightness and longer time taken for the brightness to decay to 95%, indicating that the service life of the devices is longer. Among them, Example 2, the preferred scheme, is more obvious. The QLED device prepared by this scheme not only has a maximum brightness close to 2 times that of the QLED device in the comparative example, but also the time taken for the brightness to decay to 95% under a constant current drive of 2 mA is more than that in the comparative example, and the time required for the device brightness to decay to 95% when the brightness is 1000 nit is close to 4 times that in the comparative example, proving that the QLED device prepared by the preferred scheme greatly improves the service life of the device.

[0111] Conduct thin-film morphology detection on the QLED devices prepared in Example 1, Example 2, Example 3 and the comparative example respectively. The results are as Figures 5 - 8As shown, the detection results show that the QLED device prepared in Example 2 has the most uniform light emission, followed by the QLED devices prepared in Example 1 and Example 3, and the QLED device prepared in the comparative example has the worst light emission uniformity.

[0112] In summary, the low-temperature spin-coating process of the quantum dot solution disclosed in the present invention can avoid light emission non-uniformity caused by ligand shedding of the quantum dot material to the greatest extent and can significantly reduce the possibility of fluorescence quenching. Moreover, the QLED device prepared by the low-temperature spin-coating process has better stability and a significant improvement in service life.

[0113] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a QLED device, characterized in that, Including steps: Providing a substrate, the substrate including a first electrode; Performing cold treatment on the substrate or placing the substrate under a first temperature condition, and depositing a quantum dot solution on the substrate to form a quantum dot film layer; wherein, the absolute difference between the first temperature and the storage temperature of the quantum dot solution is 0 - 5 °C, and the absolute difference between the temperature of the cold treatment and the storage temperature of the quantum dot solution is 0 - 5 °C; Preparing a second electrode on the quantum dot film layer; Wherein, the quantum dot material of the quantum dot film layer has ligands; The first temperature is -15 - 5 °C; the temperature of the cold treatment is -15 - 5 °C.

2. The preparation method of the QLED device according to claim 1, wherein, The step of placing the substrate under a first temperature condition and depositing a quantum dot solution on the substrate to form a quantum dot film layer includes: Placing the substrate with the quantum dot solution deposited on its surface in a normal temperature environment, and performing annealing treatment on the quantum dot solution to obtain the quantum dot film layer.

3. The preparation method of the QLED device according to claim 1, characterized in that, The step of placing the substrate under a first temperature condition and depositing a quantum dot solution on the substrate to form a quantum dot film layer includes: Performing vacuum pumping treatment on the placement environment of the substrate under a first temperature condition, and forming a quantum dot film layer on the substrate.

4. The manufacturing method of the QLED device according to claim 1, characterized in that, The step of performing cold treatment on the substrate and depositing a quantum dot solution on the substrate to form a quantum dot film layer includes: Under a normal temperature environment, performing annealing treatment on the quantum dot solution or performing vacuum pumping treatment on the placement environment of the substrate, and forming a quantum dot film layer on the substrate.

5. The method for preparing a QLED device according to claim 3 or 4, characterized in that, The vacuum degree after evacuating the placement environment of the substrate is less than or equal to 3x10 -4 Pa.

6. The method for preparing a QLED device according to claim 1, wherein, The substrate further includes a hole functional layer provided on the first electrode, the hole functional layer being one or more of an electron blocking layer, a hole injection layer, and a hole transport layer, the first electrode being an anode, and the second electrode being a cathode.

7. The method for preparing a QLED device according to claim 6, wherein, The first electrode is one or more of a metal material, a carbon material, and a metal oxide; and / or, the quantum dot is one or more of a II-VI group compound semiconductor material, a III-V group compound semiconductor material, a II-V group compound semiconductor material, a III-VI compound semiconductor material, a IV-VI group compound semiconductor material, a I-III-VI group compound semiconductor material, a II-IV-VI group compound semiconductor material, or a Group IV element; and / or, the hole injection layer material is one or more of PEDOT:PSS, CuPc, F4-TCNQ, HATCN, a transition metal oxide, and a transition metal chalcogenide; and / or, the hole transport layer material is one or more of poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine), polyvinylcarbazole, poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine), 4,4’,4”-tris(carbazol-9-yl)triphenylamine, 4,4'-bis(9-carbazol)biphenyl, N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine, graphene, C60, and CuS.

8. The manufacturing method of the QLED device according to claim 1, wherein, The substrate further includes an electronic functional layer disposed on the first electrode, and the electronic functional layer is one or more of a hole blocking layer, an electron injection layer, and an electron transport layer. The first electrode is a cathode, and the second electrode is an anode.

9. A QLED device, characterized in that, It is prepared by using the preparation method of the QLED device according to any one of claims 1-8.

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