Copper-based halide light-emitting diode and preparation method thereof

Abstract

The invention provides a copper-based halide light-emitting diode and a preparation method thereof. The method comprises the following steps: step 1, preparing an alkali metal thiocyanate solution; 2, preparing a modified hole injection layer solution; step 3, preparing a crystallization auxiliary agent; 4, preparing a copper-based halide precursor solution; step 5, mixing a crystallization auxiliary agent and the copper-based halide precursor solution; and 6, preparing the copper-based halide light-emitting diode device. The hole injection capability of the light-emitting diode device can be remarkably improved, charge balance is promoted, and the brightness and the external quantum efficiency of the device are greatly improved; thiocyanate radicals and Cu ions interact to improve the crystal quality of the copper-based halide, so that the uniformity of the film is improved; meanwhile, the thiocyanate radical can improve the formation energy of halogen vacancies in the copper-based halide, so that the halogen vacancy defect is passivated, and migration of halogen ions is inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of light-emitting diodes, and particularly relates to a copper-based halide light-emitting diode and a preparation method thereof. Background Art

[0002] Light-emitting diodes (LEDs) have been widely used in daily lighting and displays. At the same time, relevant researchers are developing new display technologies with high color purity and wide color gamut. In recent years, metal halide materials have attracted wide attention due to their excellent properties, such as continuously tunable emission wavelength, narrow full-width at half-maximum, high fluorescence quantum efficiency, and low cost. Among them, lead-based halide materials have become a research hotspot due to their high luminous efficiency. However, as a heavy metal, the toxicity of lead limits the commercial application of lead-based halides. Therefore, non-lead halide materials have become the research focus in the field of light-emitting diodes. In current research, the performance of non-lead halide light-emitting diodes has always been unable to compare with that of lead-based halide light-emitting diodes. Therefore, developing efficient and stable non-lead halide light-emitting diodes is an important and urgent need in this field.

[0003] Among various non-lead halide materials, copper-based halide materials have shown great application prospects in the field of light emission. However, the luminous efficiency of copper-based halide light-emitting diodes is relatively low, which is mainly related to the unbalanced carrier injection in the device and the relatively high defect density of copper-based halides. Copper-based halide materials have a large band gap, and the energy levels at the interfaces of each functional layer do not match, resulting in difficulty in injecting carriers into the light-emitting layer. At the same time, halogen vacancy defects will capture carriers and reduce the luminous efficiency. Therefore, preparing copper-based halide light-emitting diodes with excellent device performance is still a major problem in this field. Summary of the Invention

[0004] Object of the Invention: The technical problem to be solved by the present invention is to provide a copper-based halide light-emitting diode and a preparation method thereof in view of the deficiencies of the prior art. The method uses alkali metal thiocyanate-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT:PSS) to improve the hole injection rate, improve the crystallization quality of copper-based halides, reduce the defect density, and uses polyvinylpyrrolidone (PVP) and polyvinylidene fluoride (PVDF) as crystallization aids to improve the growth morphology of copper-based halides.

[0005] The present invention includes the following steps: Step 1, prepare an alkali metal thiocyanate solution; Step 2, prepare a modified hole injection layer solution; Step 3, prepare a crystallization aid; Step 4, prepare a copper-based halide Cs x Cu2I x+2 precursor solution; Step 5, mix the crystallization assistant and the copper-based halide precursor solution; Step 6, fabricate a copper-based halide light-emitting diode device.

[0006] Step 1 includes: dissolving an alkali metal thiocyanate solid in deionized water and stirring with a stirrer at a rotation speed of 100 - 1000 revolutions per minute for 5 - 120 minutes to obtain an alkali metal thiocyanate solution, where the alkali metal thiocyanate is any one of lithium thiocyanate (LiSCN), potassium thiocyanate (KSCN), sodium thiocyanate (NaSCN), and cesium thiocyanate (CsSCN).

[0007] In Step 1, the concentration of the alkali metal thiocyanate solution is 1 - 220 mg / mL.

[0008] Step 2 includes: mixing the alkali metal thiocyanate solution with a solution of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (the Chinese name of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is the semiconductor material PEDOT:PSS, and its English name is "Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) ") and stirring with a stirrer at a rotation speed of 100 - 1000 revolutions per minute for 15 - 280 minutes to obtain a modified hole injection layer solution.

[0009] In Step 2, the concentration of the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) PEDOT:PSS solution is 1.1 - 1.6 wt.%, diluted with deionized water, and the volume ratio of the alkali metal thiocyanate solution to the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) PEDOT:PSS solution is 1:X1, where the parameter X1 ranges from 2 to 5.

[0010] Step 3 includes: preparing a polyvinylpyrrolidone PVP solution or a polyvinylidene fluoride PVDF solution as the crystallization assistant; The polyvinylpyrrolidone PVP solution is obtained by dissolving polyvinylpyrrolidone PVP solid in dimethyl sulfoxide at a concentration of 1 - 80 mg / mL and stirring with a stirrer at a rotation speed of 100 - 1000 revolutions per minute for 10 - 60 minutes; The polyvinylidene fluoride PVDF solution is obtained by dissolving polyvinylidene fluoride PVDF solid in dimethyl sulfoxide at a concentration of 1 - 80 mg / mL and stirring with a stirrer at a rotation speed of 100 - 1000 revolutions per minute for 10 - 60 minutes.

[0011] Step 4 includes: Dissolving cesium iodide (CsI) and cuprous iodide (CuI) in a molar ratio of x:2 at a concentration of 0.1 - 0.6 M in one of the organic solvents of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, methyl ethyl ketone, and dimethylacetamide, and using a stirrer to stir. The rotation speed of the stirrer is 200 - 600 revolutions per minute, stirring is carried out at 50 - 70 °C for 3 - 10 minutes, and then stirring is carried out at 20 - 30 °C for 5 - 18 hours to obtain a copper-based halide Cs x Cu2I x+2 precursor solution; where the parameter x is 1 or 3.

[0012] Step 5 includes: Mixing a crystallization assistant and the copper-based halide Cs x Cu2I x+2 precursor solution in a volume ratio of 1:X2, and using a stirrer to stir. The rotation speed of the stirrer is 200 - 600 revolutions per minute, stirring is carried out at 20 - 30 °C for 3 - 8 hours to obtain a copper-based halide precursor solution after crystallization assistance treatment; the parameter X2 takes a value of 10 - 20.

[0013] Step 6 includes the following steps: Step 6-1, ultrasonic cleaning of ITO conductive glass: After wiping the ITO conductive glass clean with a dust-free cloth, soak the ITO conductive glass in detergent, deionized water, acetone, and isopropanol in sequence and perform ultrasonic cleaning for 10 - 40 minutes; Step 6-2, ultraviolet ozone treatment of ITO conductive glass: Dry the cleaned ITO conductive glass, and then place it in a closed and light-tight environment and irradiate it with short-wave ultraviolet light; the short-wave ultraviolet light emits two wavelengths of ultraviolet light, 180 - 187 nm and 248 - 257 nm, simultaneously; Step 6-3, spin-coating the hole injection layer: After filtering 100 - 400 uL of the modified hole injection layer solution prepared in Step 2 through a filter head, spin-coat it on the surface of the ITO conductive glass at a rotation speed of 3000 - 9000 revolutions per minute for 10 - 60 seconds, and then anneal it at 110 - 145 °C for 10 - 30 minutes, and then cool it to room temperature to obtain the hole injection layer; Step 6-4, spin-coating the copper-based halide light-emitting layer: After filtering 100 - 300 uL of the copper-based halide precursor solution after crystallization assistance treatment prepared in Step 5 through a filter head, spin-coat it on the surface of the hole injection layer at a first rotation speed of 50 - 200 revolutions per minute for 5 - 12 seconds, and a second rotation speed of 1000 - 6000 revolutions per minute for 10 - 60 seconds, and then anneal it at 50 - 140 °C for 8 - 40 minutes, and then cool it to room temperature to obtain the copper-based halide light-emitting layer; Step 6-5, evaporation of the electron transport layer: At a pressure less than 9×10 -4Under a high vacuum condition of Pa, an electron transport layer is evaporated on the surface of the copper-based halide light-emitting layer at a growth rate of 0.3 - 0.8 Å / s; Step 6-6, evaporating an electrode modification layer: Under a high vacuum condition where the pressure is less than 9×10 -4 Pa, an electrode modification layer is evaporated on the surface of the electron transport layer at a growth rate of 0.04 - 0.11 Å / s; Step 6-7, evaporating a metal electrode: Under a high vacuum condition where the pressure is less than 9×10 -4 Pa, a metal electrode is evaporated on the surface of the electrode modification layer at a growth rate of 1.2 - 1.7 Å / s; Finally, an ITO conductive glass, a hole injection layer, a copper-based halide light-emitting layer, an electron transport layer, an electrode modification layer, and a metal electrode are combined from bottom to top to form a copper-based halide light-emitting diode device; among them, the hole injection layer, the copper-based halide light-emitting layer, the electron transport layer, and the electrode modification layer form a light-emitting unit; The thickness of the ITO conductive glass is 40 - 180 nm, the thickness of the hole injection layer is 10 - 100 nm, the thickness of the copper-based halide light-emitting layer is 30 - 200 nm, the thickness of the electron transport layer is 10 - 100 nm, the thickness of the electrode modification layer is 0.1 - 20 nm, and the thickness of the metal electrode is 40 - 130 nm; The material used for the electron transport layer is one of 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene TPBi and 3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1''-terphenyl]-3,3''-diyl]dipyridine TmPyPB; The material used for the electrode modification layer is one of lithium fluoride LiF and lithium 8-hydroxyquinoline Liq; The material used for the metal electrode is one of aluminum Al, silver Ag, gold Au, and zinc Zn.

[0014] The present invention also provides a copper-based halide light-emitting diode prepared by the above method, which sequentially includes an ITO conductive glass, a hole injection layer, a copper-based halide light-emitting layer, an electron transport layer, an electrode modification layer, and a metal electrode from bottom to top; among them, the hole injection layer, the copper-based halide light-emitting layer, the electron transport layer, and the electrode modification layer form a light-emitting unit.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. For a copper-based halide light-emitting diode of the present invention, by doping PEDOT:PSS with alkali metal thiocyanate, the hole injection layer is modified, the hole injection barrier is reduced, the hole injection ability of the light-emitting diode device is significantly improved, the charge injection is more balanced, and the exciton radiative recombination efficiency is promoted. At the same time, thiocyanate can interact with Cu ions to improve the crystallization quality of copper-based halides and improve the film quality; at the same time, thiocyanate can increase the formation energy of halogen vacancies in copper-based halides, thereby passivating halogen vacancy defects and inhibiting the migration of halogen ions. Therefore, a copper-based halide light-emitting diode of the present invention has good luminous efficiency and stability.

[0016] 2. For a copper-based halide light-emitting diode of the present invention, the growth process of the copper-based halide light-emitting layer can be improved by the method of assisted crystallization with PVP and PVDF, thereby improving the film uniformity, the formed crystal size is uniform, and the external quantum efficiency of the device can be improved.

[0017] 3. A copper-based halide light-emitting diode of the present invention uses a copper-based halide material as the light-emitting layer, does not contain lead elements, is thus environmentally friendly, is conducive to the sustainable development of the environment, and has good application prospects.

[0018] 4. A copper-based halide light-emitting diode of the present invention does not have a hole transport layer, simplifies the device structure and manufacturing process, reduces the production cost of the device, and is convenient for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a copper-based halide light-emitting diode provided by the present invention.

[0020] Figure 2 It is a scanning electron microscope image of the morphology of a copper-based halide film in Example 1 of the present invention.

[0021] Figure 3 It is a scanning electron microscope image of the morphology of a copper-based halide film in Comparative Example 1 of the present invention.

[0022] Figure 4 Comparison of the luminous brightness between the examples and comparative examples of the present invention.

[0023] Figure 5 Comparison of the external quantum efficiency between the examples and comparative examples of the present invention.

[0024] Figure 6 Comparison of the decline of the luminous brightness over time between the examples and comparative examples of the present invention.

[0025] Explanation of the reference numerals: 1: ITO conductive glass, 2: hole injection layer, 3: copper-based halide light-emitting layer, 4: electron transport layer, 5: electrode modification layer, 6: metal electrode. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0027] like Figure 1 As shown, an embodiment of the present invention provides a copper-based halide light-emitting diode, which includes, from bottom to top: ITO conductive glass 1, a hole injection layer 2, a copper-based halide light-emitting layer 3, an electron transport layer 4, an electrode modification layer 5 and a metal electrode 6.

[0028] The following describes a process for preparing a copper-based halide light-emitting diode through Examples 1 to 3.

[0029] In Example 1 of the present invention, a method for preparing a copper-based halide light-emitting diode is provided, comprising the following steps: S1, preparing a KSCN solution: dissolving KSCN solid in deionized water, and stirring with a stirrer at a speed of 300 rpm for 60 minutes to obtain a KSCN solution.

[0030] S2, preparing a modified hole injection layer solution: mixing the KSCN solution and the PEDOT:PSS solution, and stirring them with a stirrer at a speed of 300 rpm for 180 minutes to obtain a modified hole injection layer solution.

[0031] S3, preparing a crystallization auxiliary agent: preparing a PVP solution as a crystallization auxiliary agent; the PVP solution is prepared by dissolving PVP solid in dimethyl sulfoxide at a concentration of 10 mg / mL, and stirring with an agitator at a speed of 200 rpm for 50 minutes.

[0032] S4, preparing a copper-based halide Cs3Cu2I5 precursor solution: dissolving CsI and CuI in a molar ratio of 3:2 at a concentration of 0.2 M in an N,N-dimethylformamide organic solvent, and stirring with a stirrer at a speed of 300 rpm at 55°C for 6 minutes, and then stirring at 25°C for 14 hours to obtain a Cs3Cu2I5 copper-based halide precursor solution.

[0033] S5, Mixing the crystallization assistant and the copper-based halide precursor solution: Mix the crystallization assistant prepared in S3 and the copper-based halide precursor solution prepared in S4 at a volume ratio of 1:10, and stir using a stirrer at a rotational speed of 300 revolutions per minute for 3 hours at 25 °C to obtain the copper-based halide precursor solution after crystallization assistant treatment.

[0034] S6, Preparing a copper-based halide light-emitting diode device: Form an ITO conductive glass 1, a hole injection layer 2, a copper-based halide light-emitting layer 3, an electron transport layer 4, an electrode modification layer 5, and a metal electrode 6 from bottom to top to form a copper-based halide light-emitting diode device; among them, the hole injection layer 2, the copper-based halide light-emitting layer 3, the electron transport layer 4, and the electrode modification layer 5 form a light-emitting unit.

[0035] In the S6, the thickness of the ITO conductive glass is 150 nm, the thickness of the hole injection layer is 15 nm, the thickness of the copper-based halide light-emitting layer is 180 nm, the thickness of the electron transport layer is 45 nm, the thickness of the electrode modification layer is 1.5 nm, and the thickness of the metal electrode is 120 nm.

[0036] In the S1, the KSCN solution is obtained by dissolving KSCN solid in deionized water, and the concentration of the KSCN solution is 120 mg / mL.

[0037] In the S2, the concentration of the PEDOT:PSS solution is 1.5 wt.%, diluted with deionized water, and the volume ratio of the KSCN solution to the PEDOT:PSS solution is 1:3.

[0038] In the S6, the material used for the electron transport layer is TPBi.

[0039] In the S6, the material used for the electrode modification layer is LiF.

[0040] In the S6, the material used for the metal electrode is Al.

[0041] In the S6, preparing a copper-based halide light-emitting diode device includes the following steps: S61, Ultrasonic cleaning of the ITO conductive glass: After wiping the ITO conductive glass clean with a dust-free cloth, soak the ITO conductive glass in dishwashing liquid, deionized water, acetone, and isopropyl alcohol in sequence and perform ultrasonic cleaning for 15 minutes.

[0042] S62, Ultraviolet ozone treatment of the ITO conductive glass: Dry the cleaned ITO conductive glass with a hot air blower, then place it in a closed and light-tight environment and irradiate it with short-wave ultraviolet light; the short-wave ultraviolet light emits two wavelengths of ultraviolet light, 185 nm and 254 nm, simultaneously.

[0043] S63, Spin-coating the hole injection layer: 200 μL of the modified hole injection layer solution prepared in S2 was filtered through a 0.22-μm aqueous filter head, and then spin-coated on the surface of the ITO conductive glass at a rotation speed of 4000 revolutions per minute for 50 seconds. Then, it was annealed at 120 °C for 15 minutes and subsequently cooled to room temperature to obtain the hole injection layer.

[0044] S64, Spin-coating the copper-based halide light-emitting layer: 300 μL of the copper-based halide precursor solution after crystallization-assisted treatment prepared in S5 was filtered through a 0.45-μm polytetrafluoroethylene filter head, and then spin-coated on the surface of the hole injection layer at a first rotation speed of 100 revolutions per minute for 7 seconds and a second rotation speed of 4000 revolutions per minute for 60 seconds. Then, it was annealed at 70 °C for 15 minutes and subsequently cooled to room temperature to obtain the copper-based halide light-emitting layer.

[0045] S65, Evaporating the electron transport layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, the electron transport layer was evaporated on the surface of the copper-based halide light-emitting layer at a growth rate of 0.5 Å / s.

[0046] S66, Evaporating the electrode modification layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, the electrode modification layer was evaporated on the surface of the electron transport layer at a growth rate of 0.1 Å / s.

[0047] S67, Evaporating the metal electrode: Finally, under a high vacuum condition with a pressure < 6.5×10 -4 Pa, the metal electrode was evaporated on the surface of the electrode modification layer at a growth rate of 1.5 Å / s.

[0048] In Example 2 of the present invention, a method for preparing a copper-based halide light-emitting diode is provided, including the following steps: S1, Preparing the NaSCN solution: Dissolve the NaSCN solid in deionized water and stir it with a stirrer at a rotation speed of 400 revolutions per minute for 60 minutes to obtain the NaSCN solution.

[0049] S2, Preparing the modified hole injection layer solution: Mix the NaSCN solution and the PEDOT:PSS solution and stir it with a stirrer at a rotation speed of 400 revolutions per minute for 200 minutes to obtain the modified hole injection layer solution.

[0050] S3, Preparing the crystallization assistant: Prepare a PVP solution as the crystallization assistant; the PVP solution is obtained by dissolving PVP solid in dimethyl sulfoxide at a concentration of 8 mg / mL and stirring it with a stirrer at a rotation speed of 300 revolutions per minute for 40 minutes.

[0051] S4. Preparation of copper-based halide CsCu2I3 precursor solution: Dissolve CsI and CuI at a molar ratio of 1:2 in an organic solvent of dimethylacetamide at a concentration of 0.3 M, and stir using a stirrer at a rotation speed of 400 revolutions per minute. Stir for 6 minutes at 60 °C, and then stir for 18 hours at 20 °C to obtain the Cs1Cu2I3 copper-based halide precursor solution.

[0052] S5. Mixing the crystallization assistant and the copper-based halide precursor solution: Mix the crystallization assistant prepared in S3 and the copper-based halide precursor solution prepared in S4 at a volume ratio of 1:15, and stir using a stirrer at a rotation speed of 400 revolutions per minute. Stir for 5 hours at 20 °C to obtain the copper-based halide precursor solution after crystallization assistant treatment.

[0053] S6. Preparation of copper-based halide light-emitting diode device: Form an ITO conductive glass 1, a hole injection layer 2, a copper-based halide light-emitting layer 3, an electron transport layer 4, an electrode modification layer 5, and a metal electrode 6 from bottom to top to form a copper-based halide light-emitting diode device; among them, the hole injection layer 2, the copper-based halide light-emitting layer 3, the electron transport layer 4, and the electrode modification layer 5 form a light-emitting unit.

[0054] In the above S6, the thickness of the ITO conductive glass is 100 nm, the thickness of the hole injection layer is 20 nm, the thickness of the copper-based halide light-emitting layer is 160 nm, the thickness of the electron transport layer is 50 nm, the thickness of the electrode modification layer is 1 nm, and the thickness of the metal electrode is 100 nm.

[0055] In the above S1, the NaSCN solution is obtained by dissolving NaSCN solid in deionized water, and the concentration of the NaSCN solution is 20 mg / mL.

[0056] In the above S2, the concentration of the PEDOT:PSS solution is 1.3 wt.%, diluted with deionized water, and the volume ratio of the NaSCN solution to the PEDOT:PSS solution is 1:5.

[0057] In the above S6, the material used for the electron transport layer is TPBi.

[0058] In the above S6, the material used for the electrode modification layer is Liq.

[0059] In the above S6, the material used for the metal electrode is Au.

[0060] In the above S6, the preparation of the copper-based halide light-emitting diode device includes the following steps: S61, Ultrasonic cleaning of ITO conductive glass: After wiping the ITO conductive glass clean with a lint-free cloth, soak the ITO conductive glass in dishwashing liquid, deionized water, acetone, and isopropyl alcohol in sequence and perform ultrasonic cleaning for 20 minutes.

[0061] S62, Ultraviolet ozone treatment of ITO conductive glass: Dry the cleaned ITO conductive glass with a hot air blower, then place it in a sealed and light-tight environment and irradiate it with short-wave ultraviolet light; the short-wave ultraviolet light emits two wavelengths of ultraviolet light, 185 nm and 254 nm, simultaneously.

[0062] S63, Spin-coating the hole injection layer: Filter 300 μL of the modified hole injection layer solution prepared in S2 through a 0.22-μm aqueous filter head, then spin-coat it on the surface of the ITO conductive glass at a rotation speed of 4000 revolutions per minute for 50 seconds, and then anneal it at 120 °C for 15 minutes, and then cool it to room temperature to obtain the hole injection layer.

[0063] S64, Spin-coating the copper-based halide light-emitting layer: Filter 200 μL of the copper-based halide precursor solution after crystallization-assisted treatment prepared in S5 through a 0.45-μm polytetrafluoroethylene filter head, then spin-coat it on the surface of the hole injection layer at a first rotation speed of 50 revolutions per minute for 5 seconds and a second rotation speed of 4000 revolutions per minute for 55 seconds, and then anneal it at 70 °C for 10 minutes, and then cool it to room temperature to obtain the copper-based halide light-emitting layer.

[0064] S65, Evaporating the electron transport layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, evaporate the electron transport layer on the surface of the copper-based halide light-emitting layer at a growth rate of 0.4 Å / s.

[0065] S66, Evaporating the electrode modification layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, evaporate the electrode modification layer on the surface of the electron transport layer at a growth rate of 0.11 Å / s.

[0066] S67, Evaporating the metal electrode: Finally, under a high vacuum condition with a pressure < 6.5×10 -4 Pa, evaporate the metal electrode on the surface of the electrode modification layer at a growth rate of 1.3 Å / s.

[0067] In Example 3 of the present invention, a method for preparing a copper-based halide light-emitting diode is provided, including the following steps:

[0068] S1, Preparing the LiSCN solution: Dissolve LiSCN solid in deionized water and stir it with a stirrer at a stirrer rotation speed of 600 revolutions per minute for 50 minutes to obtain the LiSCN solution.

[0069] S2. Prepare the modified hole injection layer solution: Mix the LiSCN solution and the PEDOT:PSS solution, and stir using a stirrer at a rotation speed of 600 revolutions per minute for 150 minutes to obtain the modified hole injection layer solution.

[0070] S3. Prepare the crystallization assistant: Prepare a PVDF solution as the crystallization assistant; the PVDF solution is prepared by dissolving PVDF solids at a concentration of 20 mg / mL in dimethyl sulfoxide and stirring using a stirrer at a rotation speed of 400 revolutions per minute for 40 minutes.

[0071] S4. Prepare the copper-based halide Cs3Cu2I5 precursor solution: Dissolve CsI and CuI at a molar ratio of 3:2 in an organic solvent of dimethylacetamide at a concentration of 0.5 M, and stir using a stirrer at a rotation speed of 600 revolutions per minute. Stir at 70 °C for 3 minutes, and then stir at 30 °C for 8 hours to obtain the Cs3Cu2I5 copper-based halide precursor solution.

[0072] S5. Mix the crystallization assistant and the copper-based halide precursor solution: Mix the crystallization assistant prepared in S3 and the copper-based halide precursor solution prepared in S4 at a volume ratio of 1:20, and stir using a stirrer at a rotation speed of 600 revolutions per minute. Stir at 30 °C for 8 hours to obtain the copper-based halide precursor solution after crystallization assistant treatment.

[0073] S6. Prepare the copper-based halide light-emitting diode device: Form an ITO conductive glass 1, a hole injection layer 2, a copper-based halide light-emitting layer 3, an electron transport layer 4, an electrode modification layer 5, and a metal electrode 6 from bottom to top to form a copper-based halide light-emitting diode device; among them, the hole injection layer 2, the copper-based halide light-emitting layer 3, the electron transport layer 4, and the electrode modification layer 5 form a light-emitting unit.

[0074] In the S6, the thickness of the ITO conductive glass is 40 nm, the thickness of the hole injection layer is 15 nm, the thickness of the copper-based halide light-emitting layer is 100 nm, the thickness of the electron transport layer is 60 nm, the thickness of the electrode modification layer is 0.8 nm, and the thickness of the metal electrode is 40 nm.

[0075] In the S1, the LiSCN solution is obtained by dissolving LiSCN solids in deionized water, and the concentration of the LiSCN solution is 210 mg / mL.

[0076] In the S2, the concentration of the PEDOT:PSS solution is 1.6 wt.%, and it is diluted with deionized water. The volume ratio of the LiSCN solution to the PEDOT:PSS solution is 1:2.

[0077] In S6, the material used for the electron transport layer is TmPyPB.

[0078] In S6, the material used for the electrode modification layer is LiF.

[0079] In S6, the material used for the metal electrode is Au.

[0080] In S6, preparing a copper-based halide light-emitting diode device includes the following steps: S61, ultrasonically cleaning ITO conductive glass: After wiping the ITO conductive glass clean with a dust-free cloth, sequentially soak the ITO conductive glass in dishwashing liquid, deionized water, acetone, and isopropyl alcohol and ultrasonically clean for 30 minutes.

[0081] S62, ultraviolet ozone treating the ITO conductive glass: Dry the cleaned ITO conductive glass with a hot air blower, then place it in a sealed and light-tight environment and irradiate it with short-wave ultraviolet light; the short-wave ultraviolet light emits two wavelengths of ultraviolet light, 185 nm and 254 nm, simultaneously.

[0082] S63, spin-coating the hole injection layer: Filter 400 μL of the modified hole injection layer solution prepared in S2 through a 0.22 μm aqueous filter head, then spin-coat it on the surface of the ITO conductive glass at a rotation speed of 5000 revolutions per minute for 50 seconds, then anneal it at 130 °C for 15 minutes, and then cool it to room temperature to obtain the hole injection layer.

[0083] S64, spin-coating the copper-based halide light-emitting layer: Filter 150 μL of the copper-based halide precursor solution after crystallization-assisted treatment prepared in S4 through a 0.45 μm polytetrafluoroethylene filter head, then spin-coat it on the surface of the hole injection layer at a first rotation speed of 80 revolutions per minute for 12 seconds and a second rotation speed of 5000 revolutions per minute for 30 seconds, then anneal it at 90 °C for 15 minutes, and then cool it to room temperature to obtain the copper-based halide light-emitting layer.

[0084] S65, evaporating the electron transport layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, evaporate the electron transport layer on the surface of the copper-based halide light-emitting layer at a growth rate of 0.45 Å / s.

[0085] S66, evaporating the electrode modification layer: Under a high vacuum condition with a pressure < 6.5×10 -4 Pa, evaporate the electrode modification layer on the surface of the electron transport layer at a growth rate of 0.09 Å / s.

[0086] S67, evaporating the metal electrode: Finally, under a pressure < 6.5×10 -4Under a high vacuum condition of Pa, a metal electrode was evaporated on the surface of the electrode modification layer at a growth rate of 1.25 Å / s.

[0087] Comparative Example 1: In this comparative example, a copper-based halide light-emitting diode was prepared. The preparation method and the amount of raw materials used were the same as those in Example 1, except that the hole injection layer was formed by spin-coating with a PEDOT:PSS solution, and the copper-based halide light-emitting layer was directly spin-coated on the surface of the hole injection layer, that is, neither the hole injection layer was modified nor the copper-based halide precursor was subjected to a crystallization assistance treatment.

[0088] Comparative Example 2: In this comparative example, a copper-based halide light-emitting diode was prepared. The preparation method and the amount of raw materials used were the same as those in Example 2, except that the hole injection layer was formed by spin-coating with a PEDOT:PSS solution, and the copper-based halide light-emitting layer was directly spin-coated on the surface of the hole injection layer, that is, neither the hole injection layer was modified nor the copper-based halide precursor was subjected to a crystallization assistance treatment.

[0089] Figure 2 and Figure 3 respectively show the scanning electron microscope images of the copper-based halide thin film morphologies of Example 1 and Comparative Example 1. By comparing Figure 2 and Figure 3 it can be obtained that the copper-based halide thin film of the example after the modification of the hole injection layer and the crystallization assistance treatment is denser than that of the comparative example, indicating that the crystallization quality of the copper-based halide in the example is higher; Figure 4 shows the luminous brightness of the examples and the comparative examples. By comparing Figure 4 it can be obtained that the examples after the modification of the hole injection layer and the crystallization assistance treatment have higher brightness than the comparative examples. The luminous intensities of Example 1, Example 2 and Example 3 within the full working voltage range are significantly higher than those of Comparative Example 1 and Comparative Example 2, indicating that the energy loss at the interfaces of the functional layers of the device is reduced and the charge injection is more balanced; Figure 5 shows the external quantum efficiency (EQE) of the examples and the comparative examples of the present invention. From Figure 5 it can be seen that the external quantum efficiency (EQE) of the copper-based halide light-emitting diode device after the modification of the hole injection layer and the crystallization assistance treatment is much higher than that of the copper-based halide light-emitting diode device without the modification of the hole injection layer and the crystallization assistance treatment, indicating that the radiative recombination efficiency of the example device is improved; Figure 6 shows the decrease of the brightness of the examples and the comparative examples of the present invention with time under the working voltage. Taking the ratio of the device brightness to the initial brightness as the measurement basis, from Figure 6 it can be seen that the copper-based halide light-emitting diode device after the modification of the hole injection layer and the crystallization assistance treatment has less brightness decrease after the same time, indicating that the stability and service life of the device have been improved.

[0090] Working principle: During the use of the present invention, the copper-based halide light-emitting diode sequentially includes, from bottom to top: ITO conductive glass 1, hole injection layer 2, copper-based halide light-emitting layer 3, electron transport layer 4, electrode modification layer 5, and metal electrode 6; its working process is as follows: A positive voltage is continuously applied to the ITO conductive glass 1 end, and a negative voltage is continuously applied to the metal electrode 6 end. Holes are injected from the ITO conductive glass 1 end, and electrons are injected from the metal electrode 6 end. The holes are injected into the copper-based halide light-emitting layer 3 through the hole injection layer 2, and the electrons are injected into the copper-based halide light-emitting layer 3 through the electrode modification layer 5 and the electron transport layer 4 in sequence. Since the highest occupied orbital energy level (HOMO) of the electron transport layer 4 is relatively low and the lowest unoccupied orbital energy level (LUMO) of the hole injection layer 2 is relatively high, the injected electrons and holes can be effectively confined in the copper-based halide light-emitting layer 3. The holes and electrons recombine in the copper-based halide light-emitting layer 3 to generate excitons, and the excitons undergo radiative transitions to generate photons, and the photons escape from the light-emitting diode device, showing light emission.

[0091] The above copper-based halide light-emitting diode has good light-emitting performance and can meet the requirements of high-quality displays. The present invention uses alkali metal thiocyanate to dope PEDOT:PSS to improve the hole injection rate, and uses PVP and PVDF as crystallization assistants to improve the growth morphology of copper-based halides. For the copper-based halide light-emitting diode and its preparation method described in the present invention, using alkali metal thiocyanate to modify PEDOT:PSS can significantly improve the hole injection ability of the light-emitting diode device, promote the exciton recombination process, and greatly improve the device brightness and external quantum efficiency; the thiocyanate ion interacts with Cu ions to improve the crystallization quality of the copper-based halide precursor, inhibit crystal aggregation, and improve the fluorescence quantum yield and film uniformity; at the same time, the thiocyanate ion can increase the formation energy of halogen vacancies in the copper-based halide and inhibit the migration of halogen ions, thereby passivating the halogen vacancy defects. The copper-based halide light-emitting diode device described in the present invention has good light-emitting performance and stability, and the light-emitting layer uses non-lead materials, which are green and environmentally friendly and can meet the requirements of high-quality displays. The comparison graphs of the data obtained from the examples and the comparative examples are as Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 shown.

[0092] The present invention provides a copper-based halide light-emitting diode and a preparation method. There are many methods and ways to specifically implement this technical solution. The above description is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be implemented by existing technologies.

Claims

1. A preparation method of a copper-based halide light-emitting diode, characterized in that, It includes the following steps: Step 1, preparing an alkali metal thiocyanate solution; Step 2, preparing a modified hole injection layer solution; Step 3, preparing a crystallization assistant; Step 4, prepare a copper-based halide Cs x Cu2I x+2 precursor solution; Step 5, mixing the crystallization assistant and a copper-based halide precursor solution; Step 6, preparing a copper-based halide light-emitting diode device.

2. The method according to claim 1, wherein Step 1 includes: dissolving an alkali metal thiocyanate solid in deionized water and stirring with a stirrer at a rotation speed of 100 to 1000 revolutions per minute for 5 to 120 minutes to obtain an alkali metal thiocyanate solution, and the alkali metal thiocyanate is any one of lithium thiocyanate, potassium thiocyanate, sodium thiocyanate, and cesium thiocyanate.

3. The method according to claim 2, wherein In Step 1, the concentration of the alkali metal thiocyanate solution is 1 to 220 mg / mL.

4. The method according to claim 3, wherein Step 2 includes: mixing the alkali metal thiocyanate solution with a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) PEDOT:PSS solution and stirring with a stirrer at a rotation speed of 100 to 1000 revolutions per minute for 15 to 280 minutes to obtain a modified hole injection layer solution.

5. The method according to claim 4, wherein In Step 2, the concentration of the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) PEDOT:PSS solution is 1.1 to 1.6 wt.%, diluted with deionized water, and the volume ratio of the alkali metal thiocyanate solution to the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) PEDOT:PSS solution is 1:X1, where the parameter X1 takes a value of 2 to 5.

6. The method according to claim 5, characterized in that Step 3 includes: preparing a polyvinylpyrrolidone PVP solution or a polyvinylidene fluoride PVDF solution as a crystallization assistant; The polyvinylpyrrolidone PVP solution is obtained by dissolving polyvinylpyrrolidone PVP solid in dimethyl sulfoxide at a concentration of 1 to 80 mg / mL and stirring with a stirrer at a rotation speed of 100 to 1000 revolutions per minute for 10 to 60 minutes; The polyvinylidene fluoride PVDF solution is obtained by dissolving polyvinylidene fluoride PVDF solid in dimethyl sulfoxide at a concentration of 1 to 80 mg / mL and stirring with a stirrer at a rotation speed of 100 to 1000 revolutions per minute for 10 to 60 minutes.

7. The method according to claim 6, characterized in that, Step 4 includes: dissolving cesium iodide CsI and cuprous iodide CuI at a molar ratio of x:2 in a concentration of 0.1 to 0.6 M in one of the organic solvents of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, methyl ethyl ketone, and dimethylacetamide, and using a stirrer to stir. The rotation speed of the stirrer is 200 to 600 revolutions per minute, and it is stirred for 3 to 10 minutes at 50 to 70 °C, and then stirred for 5 to 18 hours at a temperature of 20 to 30 °C to obtain a copper-based halide Cs x Cu2I x+2 precursor solution; where the parameter x is 1 or 3.

8. The method according to claim 7, wherein Step 5 includes: mixing a crystallization assistant and a copper-based halide Cs x Cu2I x+2 precursor solution in a volume ratio of 1:X2, and stirring with a stirrer at a rotational speed of 200 to 600 revolutions per minute for 3 to 8 hours under the condition of 20 to 30 °C to obtain a copper-based halide precursor solution after crystallization assistant treatment; the parameter X2 takes a value of 10 to 20.

9. The method according to claim 8, wherein Step 6 includes the following steps: Step 6-1, ultrasonically cleaning the ITO conductive glass: After wiping the ITO conductive glass clean with a dust-free cloth, sequentially immersing the ITO conductive glass in dishwashing liquid, deionized water, acetone, and isopropanol and ultrasonically cleaning for 10 to 40 minutes; Step 6-2, ultraviolet ozone treating the ITO conductive glass: Drying the cleaned ITO conductive glass and then placing it in a closed, light-tight environment and irradiating it with short-wave ultraviolet light; The short-wave ultraviolet light emits two wavelengths of ultraviolet light of 180 to 187 nm and 248 to 257 nm at the same time; Step 6-3, spin-coating the hole injection layer: After filtering 100-400 μL of the modified hole injection layer solution prepared in Step 2 through a filter head, spin-coat it on the surface of the ITO conductive glass at a rotation speed of 3000-9000 revolutions per minute for 10-60 seconds, and then anneal it at 110-145 °C for 10-30 minutes, and then cool it to room temperature to obtain the hole injection layer; Step 6-4, spin-coating the copper-based halide light-emitting layer: After filtering 100-300 μL of the copper-based halide precursor solution after crystallization-assisted treatment prepared in Step 5 through a filter head, spin-coat it on the surface of the hole injection layer at a first rotation speed of 50-200 revolutions per minute for 5-12 seconds and a second rotation speed of 1000-6000 revolutions per minute for 10-60 seconds, and then anneal it at 50-140 °C for 8-40 minutes, and then cool it to room temperature to obtain the copper-based halide light-emitting layer; Step 6-5, depositing an electron transport layer: Under a high vacuum condition with a pressure less than 9×10 -4 Pa, deposit an electron transport layer on the surface of the copper-based halide light-emitting layer at a growth rate of 0.3~0.8 Å / s; Step 6-6, evaporating the electrode modification layer: Under a high vacuum condition with a pressure less than 9×10 -4 Pa, evaporate the electrode modification layer on the surface of the electron transport layer at a growth rate of 0.04~0.11 Å / s; Step 6-7, evaporating a metal electrode: Under a high vacuum condition with a pressure less than 9×10 -4 Pa, evaporate a metal electrode on the surface of the electrode modification layer at a growth rate of 1.2~1.7 Å / s; Finally, combine the ITO conductive glass (1), hole injection layer (2), copper-based halide light-emitting layer (3), electron transport layer (4), electrode modification layer (5) and metal electrode (6) from bottom to top to form a copper-based halide light-emitting diode device; among them, the hole injection layer (2), copper-based halide light-emitting layer (3), electron transport layer (4), and electrode modification layer (5) form a light-emitting unit; The thickness of the ITO conductive glass is 40-180 nm, the thickness of the hole injection layer is 10-100 nm, the thickness of the copper-based halide light-emitting layer is 30-200 nm, the thickness of the electron transport layer is 10-100 nm, the thickness of the electrode modification layer is 0.1-20 nm, and the thickness of the metal electrode is 40-130 nm; The material used for the electron transport layer is one of 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene TPBi and 3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1''-terphenyl]-3,3''-diyl]dipyridine TmPyPB; The material used for the electrode modification layer is one of lithium fluoride LiF and lithium 8-hydroxyquinoline Liq; The material used for the metal electrode is one of aluminum Al, silver Ag, gold Au, and zinc Zn.

10. A copper-based halide light-emitting diode prepared by the method according to any one of claims 1 to 9, characterized in that, It includes an ITO conductive glass (1), a hole injection layer (2), a copper-based halide light-emitting layer (3), an electron transport layer (4), an electrode modification layer (5) and a metal electrode (6) from bottom to top in sequence; among them, the hole injection layer (2), copper-based halide light-emitting layer (3), electron transport layer (4), and electrode modification layer (5) form a light-emitting unit.

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