QWLED of TADF / PbS / TADF / PbS / TADF laminated multi-well composite light-emitting layer and preparation method thereof

Abstract

The invention discloses a QWLED with a TADF / PbS / TADF / PbS / TADF laminated multi-well composite light emitting layer and a preparation method of the QWLED, PbS quantum dots are prepared by using a thermal injection method, and the PbS quantum dots and a wide bandgap D-A TADF material are laminated and compounded for multiple times to form a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF laminated multi-quantum well composite material with parallel multiple depletion regions and a laminated multi-heterojunction quantum well structure. The multi-depletion region and laminated multi-heterojunction quantum well structure with the parallel characteristic is novel, the device structure is stable and efficient, the prepared TADF / PbS quantum dot / TADF / PbS quantum dot / TADF laminated multi-quantum well composite material has the multi-depletion region and laminated multi-heterojunction quantum well structure with the parallel characteristic, the quantum efficiency is high, the optical characteristic is good, the structural stability is high, and the performance of the device is improved. The prepared multi-depletion region and laminated multi-heterojunction quantum well structure LED device with the parallel characteristic has excellent electroluminescence efficiency and external quantum efficiency, and has huge application potential in the fields of high-brightness, long-life and high-resolution display technology and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of materials science, in particular to a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer and a preparation method thereof. Background Art

[0002] Quantum dots, as quasi-zero-dimensional materials with a particle size in the range of 1-100 nm, can have their size, shape, and excitation wavelength precisely controlled by regulating the growth time, reaction temperature, and ligands. As a narrow-bandgap semiconductor nanomaterial, lead sulfide quantum dots are widely used in mid- to long-wavelength quantum dot optoelectronic devices due to their adjustable bandgap (0.7–2.1 eV), low cost, and good solution processability. However, due to the relatively large size of lead sulfide quantum dots, they have obvious advantages in application fields such as near-infrared light LEDs and solar cells. Nevertheless, due to the presence of a large number of defects on the surface of lead sulfide quantum dots, the optoelectronic efficiency of devices based on lead sulfide quantum dots is usually low, which limits their further development.

[0003] To solve the problem of surface defects in lead sulfide quantum dot materials and further suppress surface defect recombination in quantum dots and Auger recombination in the light-emitting layer, researchers are committed to improving their optoelectronic properties through defect passivation. Relevant research points out that on the one hand, a core-shell structure can be formed, and the temperature and precursor concentration in the synthesis process of the core-shell structure can be strictly controlled, thereby significantly reducing the lattice mismatch. However, this can only slow down the lattice mismatch within a certain range, and ultimately depends on the structures and properties of the two materials in the core-shell structure itself. On the other hand, by introducing other materials to form a composite material with lead sulfide quantum dots, the energy band structure, carrier concentration, and conductivity in the light-emitting layer can be adjusted, thereby improving its optoelectronic properties. For example, Patent (CN114447237A) proposes a quantum dot light-emitting diode based on lead-based quantum dots and their surface-coated block polymers and a preparation method thereof. Among them, the lead-based quantum dots include lead sulfide, lead selenide, and lead telluride, and the block polymer is one or more of polystyrene-poly(4-vinylpyrimidine), poly(4-methylstyrene)-poly(4-vinylpyrimidine), or poly(3-methylstyrene)-poly(4-vinylpyrimidine). These block polymers mainly improve their optoelectronic properties by repairing the surface defects of lead-based quantum dots. Patent (CN114933898A) reports a preparation method of transition metal element-doped lead sulfide quantum dots. This method first synthesizes an organolead precursor doped with transition metal ions, and then synthesizes a colloidal quantum dot stock solution of lead sulfide doped with transition metals by a thermal injection method, and obtains the final product through centrifugation and purification. This kind of lead sulfide quantum dots doped with transition metal elements can also effectively reduce the surface defect rate of quantum dots, thereby improving the optoelectronic properties of quantum dots. Patent (CN103525416A) provides an LED green semiconductor nanocrystal for blue light excitation and a preparation method thereof. This method prepares a ZnS / PbS / ZnS quantum well by an aqueous phase synthesis method. The quantum well can emit green light under the excitation of light with a wavelength of 450-460 nm, and the emission spectrum range is 505-550 nm. However, due to the poor lattice matching between ZnS and PbS, and due to the difficulty in forming the crystal nucleus of ZnS itself, the composition and structure consistency of the obtained quantum well material are poor, which also greatly limits its practical application. Patent (CN118579830A) discloses a PbS quantum dot-SnS2 heterostructure material, a preparation method thereof, and an application thereof. This heterostructure is composed of flower-like SnS2 nanosheets and PbS quantum dots, and is mainly used in the field of gas sensing. By selecting two semiconductor materials with suitable energy bands to form a corresponding heterojunction quantum well composite light-emitting layer, the preparation process is simple, and the synergistic effect of the energy band structure and conductive properties of each component in the composite material can be fully exerted, thereby realizing the improvement of the overall optoelectronic properties of the heterojunction quantum well structure.

[0004] In summary, although a large number of literatures and patents have been involved in the research of lead sulfide quantum dot materials and their devices, most of the research still cannot effectively passivate surface defects theoretically, or it is difficult to form an efficient composite light-emitting layer. This has greatly limited the application of lead sulfide quantum dot materials in the field of electroluminescence. However, in this patent, the TADF / PbS / TADF / PbS / TADF material composite forms a stacked multiple heterojunction quantum well structure, which has relatively simple design and preparation processes, and due to the characteristics of the stacked heterojunction quantum well structure, it has obvious effects in improving photoluminescence and electroluminescence properties. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer and a preparation method thereof. The present invention uses a thermal injection method to prepare PbS quantum dots and composites them with D-A type TADF materials to form a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF composite material with a stacked multiple heterojunction quantum well structure. In addition, the present invention also demonstrates a preparation method of a stacked multiple heterojunction quantum well LED. The stacked multiple heterojunction quantum well structure is novel in design, the overall structure of the device is stable and efficient, and the prepared TADF / PbS quantum dot / TADF / PbS quantum dot / TADF composite material has the following characteristics: a stacked multiple heterojunction quantum well structure; high quantum efficiency; good optical properties; excellent structural stability. The stacked multiple heterojunction quantum well LED device prepared based on this composite material exhibits excellent electroluminescence efficiency and external quantum efficiency, making it have broad application prospects in the fields of high brightness, long life, and high-resolution display technologies.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer includes an electrode, an inorganic electron transport layer, a stacked heterojunction multi-quantum well light-emitting layer, an organic hole transport layer, and an ITO glass substrate from bottom to top. The stacked heterojunction multi-quantum well light-emitting layer is composed of TADF / PbS quantum dot / TADF / quantum dot PbS / TADF materials to form a composite light-emitting layer with a stacked heterojunction multi-quantum well structure.

[0007] 2. The QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 1, characterized in that: the inorganic electron transport layer is a ZnMgO electron transport layer.

[0008] 3. A QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 1, characterized in that: the organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

[0009] The present invention also provides a method for preparing a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer, comprising the following steps: Step (1): Ultrasonically clean the ITO glass substrate with deionized water, acetone, and isopropanol for 15 - 25 min respectively, then dry it with nitrogen and bake it in an oven at 60 °C. Step (2): Spin-coat the PEDOT:PSS solution on the ITO glass substrate obtained in step (1) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (3): Dissolve TFB in a toluene solution, then spin-coat the solution on the conductive glass sample obtained in step (2) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (4): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (3) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (5): Spin-coat the PbS quantum dot solution on the conductive glass sample obtained in step (4) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (6): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (5) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (7): Spin-coat the PbS quantum dot solution on the conductive glass sample obtained in step (6) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. Step (8): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (7) in a glove box with a spin coater, and then place the conductive glass sample on a heating stage for annealing. To prepare more quantum wells, only steps (7) and (8) need to be repeated. Step (9): Spin-coat the Zn 0.85 Mg 0.15 O solution on the conductive glass sample obtained in step (8) in a glove box with a spin coater, and then place the conductive glass on a heating stage for annealing. Step (10): Evaporate the electrodes on the conductive glass sample obtained in step (9) using a thermal evaporation machine, and then a QWLED with a TADF / PbS quantum dot / TADF material stacked heterojunction quantum well composite light-emitting layer is obtained.

[0010] In a preferred embodiment, the PEDOT:PSS solution described in step (2) is first filtered through a 0.22 - 0.45 μm filter head, the annealing temperature is 90 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 40 min.

[0011] In a preferred embodiment, the concentration of the TFB solution described in step (3) is 6 - 15 mg / ml, the annealing temperature is 140 - 200 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 15 - 30 min.

[0012] In a preferred embodiment, the specific method for preparing the D - A TADF material described in steps (4), (6) and (8) is as follows: Step S71: First, take 2,7 - dibromophenanthrene - 9,10 - dione and ethylenediamine and add them to an appropriate amount of acetic acid. Place them together in a three - necked round - bottom flask, stir for a corresponding time under nitrogen protection, cool to room temperature, dilute with an appropriate amount of water, and recrystallize the crude product with hot ethanol to obtain a white solid product 6,11 - dibromodibenzo[f,h]quinoxaline; Step S72: Measure the toluene solution, and add 6,11 - dibromodibenzo[f,h]quinoxaline, N³,N³,N 6 ,N 6 - tetraphenyl - 9H - carbazole - 3,6 - diamine to it. Further add sodium tert - butoxide, tris(dibenzylideneacetone)dipalladium and 2 - dicyclohexylphosphino - 2,6′ - dimethoxybiphenyl, and stir for a corresponding time under nitrogen protection. After the reaction is completed and cooled, extract the mixture with dichloromethane and wash with water. Dry the organic layer with magnesium sulfate and then concentrate it under reduced pressure. The product is purified by column chromatography to obtain a yellow solid, which is 9,9'-(dibenzo[f,h]quinoxaline - 6,11 - diyl)bis(N³,N³,N 6 ,N 6 - tetraphenyl - 9H - carbazole - 3,6 - diamine) (DQBC).

[0013] In a preferred embodiment, the specific method for preparing PbS quantum dots in steps (5) and (7) is as follows: Step S81: Dissolve lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolve sulfur powder in tri - n - octylphosphine and inject it into a three - necked flask. Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n - hexane to obtain a quantum dot solution, and store it under low - temperature conditions; Step S82: Take out the supernatant of the quantum dot solution after standing still for a part, dissolve it with an appropriate amount of ethanol, then add an appropriate amount of n-hexane solution to dissolve and take out the upper layer solution, add an appropriate amount of absolute ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

[0014] In a preferred embodiment, in the synthesis solution of 6,11-dibromodibenzo[f,h]quinoxaline, 2,7-dibromophenanthrene-9,10-dione is 3.20 - 5.46 mmol, ethylenediamine is 3.20 - 5.46 mmol, acetic acid is 50 - 100 ml. All are placed in a three-necked round-bottom flask, stirred at a temperature of 100 - 125 °C under nitrogen protection for 18 - 36 hours. After cooling to room temperature, it is diluted with 80 - 180 ml of water, and the crude product is recrystallized with hot ethanol to obtain a white solid product, which is 6,11-dibromodibenzo[f,h]quinoxaline; in the synthesis solution of 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC), toluene is 30 - 80 ml, 6,11-dibromodibenzo[f,h]quinoxaline is 3.12 - 4.25 mmol, N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine is 5.45 - 8.64 mmol, the added sodium tert-butoxide is 9.35 - 13.25 mmol, tris(dibenzylideneacetone)dipalladium is 0.08 - 0.15 mmol and 2-dicyclohexylphosphino-2,6'-dimethoxybiphenyl is 0.36 - 0.54 mmol. Stir at a temperature of 80 - 120 °C under nitrogen protection for 18 - 36 hours. After the reaction is completed and cooled, the mixture is extracted with dichloromethane and washed with water. The organic layer is dried with magnesium sulfate and concentrated under reduced pressure. The product is purified by column chromatography (eluent: dichloromethane / petroleum ether = 1 / 4), and the obtained yellow solid is 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC).

[0015] In a preferred embodiment, in the lead precursor solution, the amount of lead oxide is 0.4 - 0.6 mmol, oleic acid is 1.0 - 1.2 ml, octadecene is 8 - 10 ml, the stirring temperature is 120 - 150 °C, the stirring time is 5 - 10 min, and after dissolution, the temperature is raised to 270 - 300 °C; the amount of sulfur powder is 0.50 - 0.75 mmol, tri-n-octylphosphine is 1.40 - 1.70 ml, the stirring temperature is 120 - 150 °C, and after dissolution, it is injected into the lead precursor three-necked flask at a rate of 1.0 - 2.0 ml / h, and the holding time is 8 - 10 min; in the quantum dot cleaning, the ratio of the quantum dot supernatant to methanol is 2:1 - 1:1. The precipitate is dissolved in n-hexane, the upper layer solution is extracted, an excessive amount of absolute ethanol is added and centrifuged at 6000 - 8000 rpm for 5 - 10 min, and then the quantum dots are dissolved in n-hexane, and the above cleaning process is repeated twice.

[0016] In a preferred embodiment, the D-A TADF material thereof includes 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC); meta-carbazolyl phthalimide (mCzPI); meta-methylcarbazolyl phthalimide (mMCzPI); ortho-carbazolyl phthalimide (oCzPI) and other series of D-A TADF materials that emit green light, blue light and ultraviolet light.

[0017] In a preferred embodiment, the concentration of the D-A TADF material solution is 15 - 40 mg / ml, the annealing temperature is 60 - 90 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 30 min.

[0018] In a preferred embodiment, the concentration of the PbS quantum dot solution is 10 - 25 mg / ml, the annealing temperature is 60 - 90 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 30 min.

[0019] In a preferred embodiment, in step (9), Zn 0.85 Mg 0.15The concentration of the O solution is 10 - 30 mg / ml, the annealing temperature is 100 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 30 min.

[0020] In a preferred embodiment, the electrode described in step (10) is a silver electrode with a thickness of 100 nm.

[0021] Compared with the prior art, the present invention has the following beneficial effects: By using a TADF material and a PbS quantum dot stacked composite to form a composite light-emitting layer with a stacked multiple quantum well heterojunction structure, and then preparing an LED device including an electrode, an inorganic electron transport layer, a stacked multiple heterojunction quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate. Compared with the prior art, the present invention uses a thermal injection method and a multiple spin-coating process, which not only realizes the stable and controllable of the stacked multiple heterojunction quantum well structure, but also can adjust the balance of electron and hole currents in the composite material. Through the effective coverage, modification, and isolation of the PbS quantum dots at the interface by the TADF material, a stable stacked multiple heterojunction quantum well structure is formed. In view of the band bending at the heterojunction interface and the existence of the depletion region, the effective recombination of electrons and holes is significantly promoted, and a higher overlap of electron and hole wave functions is achieved in terms of material properties. The coverage of the TADF material on the surface of the PbS quantum dots at the interface effectively reduces the generation of surface defects of the PbS quantum dots at the interface and the exciton quenching phenomenon, thereby improving the structural stability, quantum efficiency, and photoluminescence intensity of the stacked multiple quantum well heterojunction. The materials and device preparation process of the present invention are simple and reliable, and the components of the light-emitting layer are easy to adjust. The stacked composite light-emitting layer, as an efficient recombination center of electron and hole currents, provides an effective method for the preparation of high-performance light-emitting stacked multiple heterojunction quantum well materials and devices.

[0022] The present invention can make full use of the excellent band adjustment ability of the stacked heterojunction material in the aspect of stacked multiple quantum well luminescence, prepare a stacked multiple heterojunction quantum well material with PbS quantum dots as the well region, further design and optimize the device structure, and optimize the electro-optical performance of the device; obtain a preparation method of a QWLED with a high external quantum efficiency and high luminous intensity using a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF stacked multiple heterojunction quantum well composite material as the light-emitting layer. Brief Description of the Drawings

[0023] Figure 1 It is a structural diagram of a single PbS quantum dot, a quantum dot / D-A TADF material heterojunction quantum well, and its stacked multiple heterojunction quantum well composite light-emitting layer; Figure 2It is a structural diagram of a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well material LED; Note: Among them, 1 is the heterojunction quantum well structure of a single PbS quantum dot / D-A TADF material on the upper surface of the light-emitting layer, 2 is the structure of a single PbS quantum dot in the middle of the light-emitting layer, 3 is the heterojunction quantum well structure of a single PbS quantum dot / D-A TADF material on the lower surface of the light-emitting layer, 4 is the stacked multiple heterojunction quantum well composite light-emitting layer, 5 is the D-A TADF material, 6 is the PbS quantum dot / D-A TADF contact depletion region, 7 is the undepleted region of the PbS quantum dot, 8 is the silver electrode, 9 is the Zn0.85Mg0.15O electron transport layer, 10 is the TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate. Specific implementation mode

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed description is illustrative and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0026] It should be noted that the terms used herein are only for describing specific implementation modes and are not intended to limit the exemplary implementation modes according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] Example 1 1) Place the ITO glass in a beaker, pour in acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, take it out after ultrasonic cleaning for 25 minutes each, and dry it with nitrogen at 60°C, then put it into a clean and dry petri dish.

[0028] 2) First, filter the PEDOT:PSS solution with a 0.45μm filter head, and then spin-coat it on the ITO glass at a low speed of 300 rpm / s for 5 s and then at a high speed of 3000 rpm / s for 40 s to form a film. Then put the glass sample on a heating table and anneal it at 120°C for 40 minutes.

[0029] 3) Take 15 mg of TFB and 1 ml of toluene solution. After dissolving TFB in toluene to prepare a solution with a concentration of 15 mg / mL, spin-coat it on the above glass slide at a low speed of 300 rpm / s for 5 s and then at a high speed of 2000 rpm / s for 40 s. Spin-coat the TFB toluene solution into a film on the glass slide, and then place the glass slide on a heating stage and anneal it at 200 °C for 30 min.

[0030] 4) Preparation of PbS quantum dots: Add 0.6 mmol of lead oxide, 1.2 ml of oleic acid and 10 ml of octadecene into a three-necked flask, stir at 150 °C for 10 min, and then raise the temperature to 300 °C after dissolution to prepare a lead precursor solution; Take 0.75 mmol of sulfur powder and 1.70 ml of trioctylphosphine, stir at 150 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a rate of 2.0 ml / h. After injection, keep it for 10 min; Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; Then take the quantum dot solution, with the ratio of the quantum dot supernatant to methanol being 2:1. Dissolve the precipitate in n-hexane, extract the upper layer solution, add an excess of absolute ethanol and centrifuge at 8000 rpm for 10 min. Then dissolve the quantum dots in n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 30 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0031] 5) Preparation of D-A TADF materials (taking 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC) as an example): First, add 2,7-dibromophenanthrene-9,10-dione (5.46 mmol) and ethylenediamine (5.46 mmol) to 100 ml of acetic acid, and place them in a three-necked round-bottom flask. Stir at 125 °C for 36 hours under nitrogen protection. After cooling to room temperature, dilute it with 180 ml of water, and recrystallize the crude product with hot ethanol to obtain a white solid product, which is 6,11-dibromodibenzo[f,h]quinoxaline. Subsequently, measure 80 ml of toluene solution, and add 6,11-dibromodibenzo[f,h]quinoxaline (4.25 mmol), N³,N³,N 6 ,N 6- Tetraphenyl - 9H - carbazole - 3,6 - diamine (8.64 mmol), sodium tert - butoxide (13.25 mmol), tris(dibenzylideneacetone)dipalladium (0.15 mmol) and 2 - (dicyclohexylphosphino)-2,6′-dimethoxybiphenyl (0.54 mmol) were further added. The mixture was stirred at 120 °C for 36 h under nitrogen protection. After the reaction was completed and cooled, the mixture was extracted with dichloromethane and washed with water. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure. The product was purified by column chromatography (eluent: dichloromethane / petroleum ether = 1 / 4), and a yellow solid, 9,9'-(dibenzo[f,h]quinoxaline - 6,11 - diyl)bis(N³,N³,N 6 ,N 6 - tetraphenyl - 9H - carbazole - 3,6 - diamine) (DQBC), was obtained.

[0032] 6) The D - A TADF material was diluted with n - octane to 40 mg / ml, and spin - coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then the above - mentioned glass slide was placed on a heating stage and annealed at 90 °C for 30 min.

[0033] 7) The PbS quantum dot colloidal solution was diluted with n - octane to a 25 mg / ml solution, and spin - coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then the above - mentioned glass slide was placed on a heating stage and annealed at 90 °C for 30 min.

[0034] 8) The D - A TADF material was diluted with n - octane to 40 mg / ml, and spin - coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then the above - mentioned glass slide was placed on a heating stage and annealed at 90 °C for 30 min.

[0035] 9) The PbS quantum dot colloidal solution was diluted with n - octane to a 25 mg / ml solution, and spin - coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then the above - mentioned glass slide was placed on a heating stage and annealed at 90 °C for 30 min.

[0036] 10) The D - A TADF material was diluted with n - octane to 40 mg / ml, and spin - coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then the above - mentioned glass slide was placed on a heating stage and annealed at 90 °C for 30 min. Figure 1It is a structural diagram of a composite light-emitting layer of a single PbS quantum dot, a quantum dot / D-A TADF material heterojunction quantum well, and its stacked multiple heterojunction quantum wells; where 1 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the upper surface of the light-emitting layer, 2 is the structure of a single PbS quantum dot in the middle of the light-emitting layer, 3 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the lower surface of the light-emitting layer, 4 is the stacked multiple heterojunction quantum well composite light-emitting layer, 5 is the D-A TADF material, 6 is the PbS quantum dot / D-A TADF contact depletion region, and 7 is the undepleted region of the PbS quantum dot.

[0037] 11) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 30 mg / ml, spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s, and then place the glass sample on a heating table and anneal it at 120 °C for 30 min.

[0038] 12) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well as the composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well material; where 8 is the silver electrode, 9 is the Zn 0.85 Mg 0.15 O electron transport layer, 10 is the TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0039] Example 2 1) Place the ITO glass in a beaker, pour acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, ultrasonically clean each for 20 min and then take it out, dry it with nitrogen at 60 °C, and then place it in a clean and dry petri dish.

[0040] 2) First, filter the PEDOT:PSS solution with a 0.45-μm filter head, and then use a spin coater to spin-coat it at a low speed of 300 rpm / s for 5 s and then at a high speed of 3000 rpm / s for 40 s to form a film of the PEDOT:PSS solution on the ITO glass. Then place the glass sample on a heating table and anneal it at 100 °C for 25 min.

[0041] 3) Take 10 mg of TFB and 1 ml of toluene solution. After dissolving TFB in toluene to prepare a solution with a concentration of 10 mg / mL, spin-coat the TFB toluene solution on the above glass slide at a low speed of 300 rpm / s for 5 s and then at a high speed of 2000 rpm / s for 40 s to form a film. Then place the glass slide on a heating stage and anneal it at 170 °C for 25 min.

[0042] 4) Preparation of PbS quantum dots: Add 0.5 mmol of lead oxide, 1.1 ml of oleic acid and 9 ml of octadecene into a three-necked flask, stir at 135 °C for 7.5 min, and then raise the temperature to 285 °C after dissolution to prepare a lead precursor solution; take 0.60 mmol of sulfur powder and 1.55 ml of trioctylphosphine, stir at 135 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a rate of 1.5 ml / h. After injection, keep it for 9 min; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, and the ratio of the quantum dot supernatant to methanol is 1.5:1. Dissolve the precipitate in n-hexane, extract the upper layer solution, add an excess of absolute ethanol and centrifuge at 7000 rpm for 7.5 min. Then dissolve the quantum dots in n-hexane, repeat the above washing process twice, dissolve the quantum dots in n-hexane to form a 20 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0043] 5) Preparation of D-A TADF material (taking 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC) as an example): First, add 2,7-dibromophenanthrene-9,10-dione (4.20 mmol) and ethylenediamine (4.20 mmol) to 75 ml of acetic acid, and place them in a three-necked round-bottom flask. Stir at 115 °C for 27 hours under nitrogen protection. After cooling to room temperature, dilute it with 130 ml of water, and recrystallize the crude product with hot ethanol to obtain a white solid product, which is 6,11-dibromodibenzo[f,h]quinoxaline. Subsequently, measure 50 ml of toluene solution, and add 6,11-dibromodibenzo[f,h]quinoxaline (3.60 mmol), N³,N³,N 6 ,N 6- Tetraphenyl-9H-carbazole-3,6-diamine (6.20 mmol), sodium tert-butoxide (11.25 mmol), tris(dibenzylideneacetone)dipalladium (0.12 mmol) and 2-(dicyclohexylphosphino)-2,6'-dimethoxybiphenyl (0.45 mmol) were further added. The mixture was stirred at 100 °C for 27 h under nitrogen protection. After the reaction was completed and cooled, the mixture was extracted with dichloromethane and washed with water. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure. The product was purified by column chromatography (eluent: dichloromethane / petroleum ether = 1 / 4) to obtain a yellow solid, which was 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 - tetraphenyl-9H-carbazole-3,6-diamine) (DQBC).

[0044] 6) The D-A TADF material was diluted with n-octane to 25 mg / ml, and spin-coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then, the above glass slide was placed on a heating stage and annealed at 75 °C for 20 min.

[0045] 7) The PbS quantum dot colloidal solution was diluted with n-octane to a 25 mg / ml solution, and spin-coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then, the above glass slide was placed on a heating stage and annealed at 75 °C for 20 min.

[0046] 8) The D-A TADF material was diluted with n-octane to 25 mg / ml, and spin-coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then, the above glass slide was placed on a heating stage and annealed at 75 °C for 20 min.

[0047] 9) The PbS quantum dot colloidal solution was diluted with n-octane to a 25 mg / ml solution, and spin-coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then, the above glass slide was placed on a heating stage and annealed at 75 °C for 20 min.

[0048] 10) The D-A TADF material was diluted with n-octane to 25 mg / ml, and spin-coated at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then, the above glass slide was placed on a heating stage and annealed at 75 °C for 20 min. Figure 1It is a structural diagram of a composite light-emitting layer of a single PbS quantum dot, a quantum dot / D-A TADF material heterojunction quantum well, and its stacked multiple heterojunction quantum wells; among them, 1 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the upper surface of the light-emitting layer, 2 is the structure of a single PbS quantum dot in the middle of the light-emitting layer, 3 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the lower surface of the light-emitting layer, 4 is the stacked multiple heterojunction quantum well composite light-emitting layer, 5 is the D-A TADF material, 6 is the PbS quantum dot / D-A TADF contact depletion region, and 7 is the undepleted region of the PbS quantum dot.

[0049] 11) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 20 mg / ml, spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s, and then place the glass sample on a heating table and anneal it at 110 °C for 20 min.

[0050] 12) Thermally evaporate a 100-nm silver electrode, and a QWLED with a stacked multiple heterojunction quantum well of TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material as the composite light-emitting layer can be obtained. Figure 2 It is a structural diagram of a PbS quantum dot / D-A TADF material three-dimensional heterojunction quantum well material LED, where 6 is the silver electrode, 7 is the Zn 0.85 Mg 0.15 O electron transport layer, 8 is the PbS quantum dot / D-A TADF material three-dimensional heterojunction quantum well composite light-emitting layer, 9 is the TFB hole transport layer, 10 is the PEDOT:PSS hole transport layer, and 11 is the ITO glass substrate. Figure 2 It is a structural diagram of a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well material LED; among them, 8 is the silver electrode, 9 is the Zn 0.85 Mg 0.15 O electron transport layer, 10 is the TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0051] Example 3 1) Place the ITO glass in a beaker, pour acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, ultrasonically clean them for 25 min respectively and then take them out, dry them with 60 °C nitrogen, and then place them in a clean and dry petri dish.

[0052] 2) First, filter the PEDOT:PSS solution with a 0.22 μm filter head, and then spin-coat it on the ITO glass at a low speed of 300 rpm / s for 5 s and then at a high speed of 3000 rpm / s for 40 s to form a film. Then, place the glass sample on a heating table and anneal it at 90 °C for 10 min.

[0053] 3) Take 6 mg of TFB and 1 ml of toluene solution. Dissolve TFB in toluene to prepare a solution with a concentration of 6 mg / mL, and then spin-coat it on the above glass sample at a low speed of 300 rpm / s for 5 s and at a high speed of 2000 rpm / s for 40 s to form a film. Then, place the glass on a heating table and anneal it at 140 °C for 15 min.

[0054] 4) Preparation of PbS quantum dots: Add 0.4 mmol of lead oxide, 1.0 ml of oleic acid, and 8 ml of octadecene to a three-necked flask, stir at 120 °C for 5 min, and then raise the temperature to 270 °C after dissolution to prepare a lead precursor solution; take 0.50 mmol of sulfur powder and 1.40 ml of tri-n-octylphosphine, stir at 120 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a rate of 1.0 ml / h, and keep it for 8 min after injection; finally, quickly cool the quantum dot solution by water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, with the ratio of quantum dot supernatant to methanol being 1:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of absolute ethanol and centrifuge at 6000 rpm for 5 min, and then dissolve the quantum dots with n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 10 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0055] 5) Preparation of D-A TADF material (using 9,9'- (dibenzo [f,h] quinoxaline-6,11-diyl) bis(N³,N³,N 6 ,N 6- (Tetraphenyl-9H-carbazole-3,6-diamine) (taking DQBC as an example): First, add 2,7-dibromophenanthrene-9,10-dione (3.20 mmol) and ethylenediamine (3.20 mmol) to 50 mL of acetic acid, and place them together in a three-necked round-bottom flask. Stir at 100 °C for 18 hours under nitrogen protection. After cooling to room temperature, dilute with 80 mL of water, and recrystallize the crude product with hot ethanol to obtain a white solid product, which is 6,11-dibromodibenzo[f,h]quinoxaline. Subsequently, measure 30 mL of toluene solution, and add 6,11-dibromodibenzo[f,h]quinoxaline (3.12 mmol), N³,N³,N 6 ,N 6 - tetraphenyl-9H-carbazole-3,6-diamine (5.45 mmol), further add sodium tert-butoxide (9.35 mmol), tris(dibenzylideneacetone)dipalladium(0) (0.08 mmol) and 2-dicyclohexylphosphino-2,6′-dimethoxybiphenyl (0.36 mmol). Stir at 80 °C for 18 hours under nitrogen protection. After the reaction is completed and cooled, extract the mixture with dichloromethane and wash with water. Dry the organic layer with magnesium sulfate and concentrate under reduced pressure. Purify the product by column chromatography (eluent: dichloromethane / petroleum ether = 1 / 4) to obtain a yellow solid, which is 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 - tetraphenyl-9H-carbazole-3,6-diamine) (DQBC).

[0056] 6) Dilute the D-A TADF material with n-octane to 15 mg / ml, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s. Then place the above glass slide on a heating table and anneal at 60 °C for 10 min.

[0057] 7) Dilute the PbS quantum dot colloidal solution with n-octane to a 10 mg / ml solution, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s. Then place the above glass slide on a heating table and anneal at 60 °C for 10 min.

[0058] 8) Dilute the D-A TADF material with n-octane to 15 mg / ml, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s. Then place the above glass slide on a heating table and anneal at 60 °C for 10 min.

[0059] 9) Dilute the PbS quantum dot colloidal solution with n-octane to a 10 mg / ml solution, and spin-coat it at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then place the above glass slide on a heating stage and anneal it at 60 °C for 10 min.

[0060] 10) Dilute the D-A TADF material with n-octane to 15 mg / ml, and spin-coat it at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater. Then place the above glass slide on a heating stage and anneal it at 60 °C for 10 min. Figure 1 It is a structural diagram of a composite light-emitting layer of a single PbS quantum dot, a quantum dot / D-A TADF material heterojunction quantum well, and its stacked multiple heterojunction quantum wells; where 1 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the upper surface of the light-emitting layer, 2 is the structure of a single PbS quantum dot in the middle of the light-emitting layer, 3 is the structure of a single PbS quantum dot / D-A TADF material heterojunction quantum well on the lower surface of the light-emitting layer, 4 is the stacked multiple heterojunction quantum well composite light-emitting layer, 5 is the D-A TADF material, 6 is the PbS quantum dot / D-A TADF contact depletion region, and 7 is the undepleted region of the PbS quantum dot.

[0061] 11) Take a Zn 0.85 Mg 0.15 O solution, spin-coat it at a low speed of 300 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s using a spin coater, and then place the glass slide in a heating stage and anneal it at 100 °C for 10 min.

[0062] 12) Thermally evaporate a 100 nm silver electrode to obtain a QWLED with a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well as the composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well material; where 8 is the silver electrode, 9 is the Zn 0.85 Mg 0.15 O electron transport layer, 10 is the TADF / PbS quantum dot / TADF / PbS quantum dot / TADF material stacked multiple heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0063] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer, characterized in that: It includes, from bottom to top in sequence, an electrode, an inorganic electron transport layer, a stacked heterojunction multiple quantum well light-emitting layer, an organic hole transport layer, and an ITO glass substrate. The stacked heterojunction multiple quantum well light-emitting layer is formed by a composite light-emitting layer with a stacked heterojunction multiple quantum well structure from TADF / PbS quantum dots / TADF / quantum dot PbS / TADF materials.

2. The QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 1, characterized in that: The inorganic electron transport layer is a ZnMgO electron transport layer.

3. A QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 1, characterized in that: The organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

4. A method for preparing a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer as claimed in any one of claims 1-3, characterized in that: It includes the following steps: Step (1): Ultrasonically clean the ITO glass substrate with deionized water, acetone, and isopropyl alcohol for 15 - 25 min respectively, then blow dry with nitrogen and dry in an oven at 60 °C. Step (2): Spin-coat the PEDOT:PSS solution on the ITO glass substrate obtained in step (1) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (3): Dissolve TFB in a toluene solution, then spin-coat the solution on the conductive glass sample obtained in step (2) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (4): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (3) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (5): Spin-coat the PbS quantum dot solution on the conductive glass sample obtained in step (4) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (6): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (5) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (7): Spin-coat the PbS quantum dot solution on the conductive glass sample obtained in step (6) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. Step (8): Spin-coat the D-A TADF material solution on the conductive glass sample obtained in step (7) in a glove box using a spin coater, and then place the conductive glass sample on a heating table for annealing. To prepare more quantum wells, only repeat step (7) and step (8). Step (9) In the glove box, Zn 0.85 Mg 0.15 O solution is spin-coated on the conductive glass sample of step (8) using a spin coater, and then the conductive glass sheet is placed on a heating stage for annealing; Step (10): Evaporate the electrode on the conductive glass sample obtained in step (9) using a thermal evaporation machine, and then a QWLED based on a stacked heterojunction quantum well composite light-emitting layer of TADF / PbS quantum dots / TADF materials is obtained.

5. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 4, characterized in that: The PEDOT:PSS solution described in step (2) is first filtered through a 0.22 - 0.45 μm filter head, the annealing temperature is 90 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 40 min.

6. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 4, characterized in that: The concentration of the TFB solution described in step (3) is 6 - 15 mg / ml, the annealing temperature is 140 - 200 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 15 - 30 min.

7. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 4, characterized in that, The specific preparation method of the D-A TADF material described in step (4), step (6) and step (8) is as follows: Step S71: First, take 2,7-dibromophenanthrene-9,10-dione and ethylenediamine and add them to an appropriate amount of acetic acid. Place them in a three-necked round-bottom flask and stir for a corresponding time under nitrogen protection. Cool to room temperature, dilute with an appropriate amount of water, and recrystallize the crude product with hot ethanol to obtain a white solid product 6,11-dibromodibenzo[f,h]quinoxaline; Step S72: Measure the toluene solution, and add 6,11-dibromodibenzo[f,h]quinoxaline and N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine thereto. Further add sodium tert-butoxide, tris(dibenzylideneacetone)dipalladium, and 2-dicyclohexylphosphino-2,6′-dimethoxybiphenyl, and stir for a corresponding time under nitrogen protection. After the reaction is completed and cooled, extract the mixture with dichloromethane and wash with water. Dry the organic layer with magnesium sulfate and concentrate under reduced pressure. Purify the product by column chromatography to obtain a yellow solid, which is 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC).

8. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 4, characterized in that, The specific preparation method of PbS quantum dots in step (5) and step (7) is as follows: Step S81: Dissolve lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolve sulfur powder in trioctylphosphine and inject it into a three-necked flask. Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution, and store it under low-temperature conditions; Step S82: Take out a part of the supernatant of the quantum dot solution after standing, dissolve it with an appropriate amount of ethanol, then add an appropriate amount of n-hexane solution and take out the upper layer solution, add an appropriate amount of absolute ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

9. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 7, characterized in that, In the synthesis solution of 6,11-dibromodibenzo[f,h]quinoxaline, 2,7-dibromophenanthrene-9,10-dione is 3.20 - 5.46 mmol, ethylenediamine is 3.20 - 5.46 mmol, acetic acid is 50 - 100 ml. All are placed in a three-necked round-bottom flask, stirred at a temperature of 100 - 125 °C under nitrogen protection for 18 - 36 hours. After cooling to room temperature, it is diluted with 80 - 180 ml of water, and the crude product is recrystallized with hot ethanol to obtain a white solid product, which is 6,11-dibromodibenzo[f,h]quinoxaline; in the synthesis solution of 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC), toluene is 30 - 80 ml, 6,11-dibromodibenzo[f,h]quinoxaline is 3.12 - 4.25 mmol, N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine is 5.45 - 8.64 mmol, sodium tert-butoxide added is 9.35 - 13.25 mmol, tris(dibenzylideneacetone)dipalladium is 0.08 - 0.15 mmol and 2-dicyclohexylphosphino-2,6'-dimethoxybiphenyl is 0.36 - 0.54 mmol. Stirred at a temperature of 80 - 120 °C under nitrogen protection for 18 - 36 hours. After the reaction is completed and cooled, the mixture is extracted with dichloromethane and washed with water. The organic layer is dried with magnesium sulfate and concentrated under reduced pressure. The product is purified by column chromatography (eluent: dichloromethane / petroleum ether = 1 / 4), and the obtained yellow solid is 9,9'-(dibenzo[f,h]quinoxaline-6,11-diyl)bis(N³,N³,N 6 ,N 6 -tetraphenyl-9H-carbazole-3,6-diamine) (DQBC).

10. The preparation method of a QWLED with a TADF / PbS / TADF / PbS / TADF stacked multi-well composite light-emitting layer according to claim 8, characterized in that, In the lead precursor solution, the amount of substance of lead oxide is 0.4 - 0.6 mmol, oleic acid is 1.0 - 1.2 ml, octadecene is 8 - 10 ml, the stirring temperature is 120 - 150 °C, the stirring time is 5 - 10 min, and after dissolution, it rises to 270 - 300 °C; the amount of substance of sulfur powder is 0.50 - 0.75 mmol, trioctylphosphine is 1.40 - 1.70 ml, the stirring temperature is 120 - 150 °C, and after dissolution, it is injected into the lead precursor three-necked flask at a rate of 1.0 - 2.0 ml / h and kept for 8 - 10 min; in the quantum dot cleaning, the ratio of the quantum dot supernatant to methanol is 2:1 - 1:

1. Dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of absolute ethanol and centrifuge at 6000 - 8000 rpm for 5 - 10 min, and then dissolve the quantum dots with n-hexane. Repeat the above cleaning process twice.

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