QWLED device based on CdS-PbS-CdS single-lamination deep trap composite light-emitting structure

Abstract

The invention provides a QWLED device based on a CdS-PbS-CdS single-lamination deep well composite light-emitting structure. The QWLED device sequentially comprises an electrode, an inorganic electron transport layer, a lamination heterojunction deep quantum well light-emitting layer, an organic hole transport layer and an ITO glass substrate from top to bottom. The laminated heterojunction deep quantum well light-emitting layer is of a deep quantum well structure formed by sequentially and alternately stacking a CdS nanosheet layer, a PbS quantum dot layer and a CdS nanosheet layer, and the CdS nanosheet layer and the PbS quantum dot layer are synthesized through a hot injection method and deposited layer by layer through a spin-coating process; the surface of the PbS quantum dot is covered with the CdS nanosheet layer, a depletion region parallel to an interface is formed, PbS surface defects are passivated, electron-hole recombination is promoted through heterojunction energy band bending, and the photoluminescence efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical fields such as nano-semiconductor materials and optoelectronic devices technology, and particularly relates to a QWLED device based on a CdS-PbS-CdS single-stack deep-well composite light-emitting structure. Background Art

[0002] Quantum dots, as quasi-zero-dimensional materials with all three-dimensional scales in the nanometer range, can control the quantum dot size, shape, and emission wavelength by adjusting parameters such as quantum dot growth time, reaction temperature, and ligands. Lead sulfide quantum dots, as a type of P-type semiconductor nanomaterial, have an adjustable bandgap (0.7–2.1 eV) and are an excellent choice for wavelength-tunable quantum dot devices due to their low cost, solution processability, and adjustable bandgap. Lead sulfide quantum dots are regarded as an excellent choice for applications such as near-infrared light-emitting LEDs and solar cells due to their relatively large size. However, there is still room for improvement in the research on lead sulfide quantum dots within the visible light excitation wavelength range.

[0003] To address the surface defects of lead sulfide quantum dot materials and increase the probability of forming effective composite excitons in the light-emitting layer, researchers have been seeking ways to passivate defects and further improve their optoelectronic properties. Some studies have shown that on the one hand, by forming a core-shell structure and strictly controlling the temperature and precursor concentration during the synthesis of the quantum dot core-shell structure, the lattice mismatch can be greatly reduced. On the other hand, a stacked composite material can be formed by combining lead sulfide quantum dots with other quantum dots to adjust the energy band structure at the contact interface between the quantum dots, thereby improving their optoelectronic properties. (CN114447237A) provides a quantum dot light-emitting diode based on lead-based quantum dots and a block polymer coated on the surface of the lead-based quantum dots, and its preparation method: among them, the lead-based quantum dots are lead sulfide, lead selenide, and lead telluride; the block polymer is one or more of polystyrene-poly(4-vinylpyrimidine), poly(4-methylstyrene)-poly(4-vinylpyrimidine), and poly(3-methylstyrene)-poly(4-vinylpyrimidine). These block polymers are mainly used to repair the surface defects of lead-based quantum dots in order to improve the optoelectronic properties of the quantum dots. (CN114933898A) reports a preparation method of transition metal element-doped lead sulfide quantum dots: first, synthesize an organolead precursor doped with transition metal ions, and use the thermal injection method to obtain a stock solution of lead sulfide colloidal quantum dots doped with transition metals. After centrifugation and purification, lead sulfide colloidal quantum dots doped with transition metal elements are obtained. These lead sulfide quantum dots doped with transition metal elements can effectively reduce the surface defect rate of the quantum dots and improve the optoelectronic properties of the quantum dots. (CN103525416A) provides a green semiconductor nanocrystal for a blue light-excited LED and its preparation method: ZnS / PbS / ZnS quantum wells are synthesized by the aqueous phase synthesis method, which 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, effectively improving the photoluminescence performance of lead sulfide quantum dots. However, due to the poor lattice matching between ZnS and PbS in this quantum well material and the difficulty in forming ZnS crystal nuclei, the obtained quantum well material has poor consistency. (CN118579830A) discloses a PbS quantum dot-SnS2 heterostructure material, its preparation method and application: this heterojunction is composed of flower-like SnS2 nanosheets and PbS quantum dots, which is mainly used in the gas sensing field, and its optoelectronic applications are limited.In addition, the luminescence performance of quantum dot light-emitting diodes ultimately depends on the charge distribution and performance of the quantum dot light-emitting layer, and is directly related to characteristics such as the carrier concentration in the light-emitting layer. Generally speaking, the higher the carrier concentration, the shorter the lifetime of photo-generated carriers or electro-generated carriers in the semiconductor, the higher the probability of Auger recombination, and the lower the probability of forming excitonic pairs for effective optoelectronic recombination, which is more unfavorable to the luminescence performance of the semiconductor. Generally, the effective optoelectronic effect of a diode usually occurs in the depletion region. This type of stacked heterojunction deep quantum well composite light-emitting layer formed by means of a stacked heterojunction with a stacked depletion region has a simple preparation process and can effectively utilize the synergistic effect of the energy bands and material conductivity properties of each component in the stacked interface material, thereby achieving an improvement in the overall optoelectronic performance of the stacked heterojunction.

[0004] In summary, at present, the lead sulfide quantum dot materials and devices mentioned in most literatures or patents cannot effectively passivate surface defects or form an effective composite light-emitting layer in theory, thus affecting the application of lead sulfide quantum dot materials in electroluminescence. Summary of the Invention

[0005] Aiming at the defects and deficiencies existing in the prior art, the present invention provides a preparation method of a QWLED based on a CdS nanosheet-PbS quantum dot-CdS nanosheet stacked deep well composite light-emitting layer. PbS quantum dots and CdS nanosheets are respectively synthesized by a thermal injection method, and a CdS / PbS / CdS single stacked heterojunction deep quantum well structure is sequentially deposited by a spin coating process, where: Interface depletion region and deep quantum well characteristics: A stacked heterojunction depletion region parallel to the light-emitting layer is formed at the stacked interface. The surface of the narrow-bandgap PbS quantum dots is covered by the wide-bandgap CdS nanosheets, significantly passivating the surface defects of PbS. At the same time, the band bending of the heterojunction promotes electron-hole recombination. Device performance: The prepared stacked deep quantum well composite light-emitting layer has high quantum efficiency and electroluminescence efficiency, and excellent structural stability. Application potential: It provides an innovative solution for high-brightness, long-life, and high-resolution display technologies, and is especially suitable for high-efficiency light-emitting devices in the visible light band.

[0006] The technical solution specifically adopted by the present invention to solve its technical problems is: A QWLED device based on a CdS-PbS-CdS single stacked deep well composite light-emitting structure: sequentially includes an electrode, an inorganic electron transport layer, a stacked heterojunction deep quantum well light-emitting layer, an organic hole transport layer, and an ITO glass substrate from top to bottom; The stacked heterojunction deep quantum well light-emitting layer is formed by sequentially stacking a CdS nanosheet layer, a PbS quantum dot layer, and a CdS nanosheet layer to form a deep quantum well structure. The CdS nanosheets and the PbS quantum dot layer are synthesized by a thermal injection method and are sequentially deposited layer by layer by a spin coating process. The CdS nanosheets cover the surface of the PbS quantum dots, forming a depletion region parallel to the interface; passivating the surface defects of PbS and promoting electron-hole recombination through the band bending of the heterojunction to improve the photoluminescence efficiency.

[0007] Further, the inorganic electron transport layer is a Zn 0.85 Mg 0.15 O electron transport layer.

[0008] Further, the organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

[0009] Further, the precursor of the CdS nanosheets synthesized by the thermal injection method includes cadmium nitrate tetrahydrate, sulfur powder and an organic ligand; the precursor of the PbS quantum dots synthesized by the thermal injection method includes lead oxide, sulfur powder and tri-n-octylphosphine.

[0010] Further, the annealing temperature of the CdS nanosheets and the PbS quantum dot layer by the thermal injection method is 60-90 °C, and the annealing time is 10-30 min.

[0011] Further, the CdS nanosheet layer is formed by a CdS nanosheet solution with a concentration of 10-30 mg / ml, and the preparation of the CdS nanosheet solution includes the following steps: (1a) Dissolve 120-220 mg of cadmium nitrate tetrahydrate and 7-15 mg of sodium myristate in methanol respectively, and mix and stir to react to generate cadmium myristate; (1b) Mix the cadmium myristate generated in step (1a), 7-15 mg of sulfur powder and 10-18 ml of octadecene, heat to 170-260 °C under an inert atmosphere, add 60-100 mg of cadmium acetate dihydrate, and after reacting for 5-15 minutes, inject 0.3-0.8 ml of oleic acid; (1c) Mix the mixed solution in step (1b) with methanol in a volume ratio of 2:1 to 1:1, centrifuge, add n-hexane to dissolve the precipitate, and repeat the washing twice to obtain a purified CdS nanosheet solution.

[0012] The size control and surface passivation ability of the CdS nanosheets are achieved through the above steps to ensure the formation of the interface depletion region.

[0013] Further, the PbS quantum dot layer is formed by a PbS quantum dot solution with a concentration of 10-30 mg / ml, and the preparation of the PbS quantum dot solution includes the following steps: (2a) Mix 0.4-0.6 mmol of lead oxide, 1.0-1.2 ml of oleic acid and 8-10 ml of octadecene, stir and dissolve at 120-150 °C, and raise the temperature to 270-300 °C; (2b) Dissolve 0.50 - 0.75 mmol of sulfur powder in 1.40 - 1.70 ml of tri-n-octylphosphine, and inject it into the lead precursor solution in step (2a) at a rate of 1.0 - 2.0 ml / h. After reacting for 8 - 10 minutes, quickly cool it through a water bath; (2c) Mix the mixed solution in step (2b) with ethanol at a volume ratio of 2:1 to 1:1, centrifuge, add n-hexane to dissolve the precipitate, and repeat the washing twice to obtain a purified PbS quantum dot solution.

[0014] The size and monodispersity of PbS quantum dots directly affect the interface matching with CdS nanosheets, avoiding defects caused by lattice mismatch.

[0015] Furthermore, the inorganic electron transport layer is formed by spin-coating a Zn 0.85 Mg 0.15 O solution with a concentration of 15 - 25 mg / ml, and anneal it at 100 - 120 °C for 10 - 20 minutes.

[0016] Furthermore, the TFB layer is formed by spin-coating a TFB toluene solution with a concentration of 8 - 10 mg / ml, and anneal it at 160 - 200 °C for 15 - 30 minutes.

[0017] Furthermore, the PEDOT:PSS layer is formed by spin-coating a PEDOT:PSS solution filtered through a 0.22 - 0.45 μm pore size, and anneal it at 100 - 120 °C for 20 - 30 minutes.

[0018] Furthermore, the ITO glass substrate is pretreated by the following steps: (3a) Ultrasonically clean it with deionized water, acetone, and isopropanol in sequence for 15 - 25 minutes; (3b) Dry it in a nitrogen atmosphere at 60 - 80 °C.

[0019] Furthermore, the electrode is a silver electrode with a thickness of 80 - 120 nm, formed by a thermal evaporation process.

[0020] Compared with the prior art, the present invention and its preferred solutions at least include the following beneficial effects: Stacked deep quantum well structure design: Form a single three-layer heterojunction deep quantum well by alternately stacking CdS nanosheets and PbS quantum dots, establish a parallel depletion region at the interface, passivate the surface defects of PbS and promote carrier recombination; Device performance optimization: The prepared QWLED device has excellent external quantum efficiency and electroluminescence efficiency; Process controllability: CdS nanosheets and PbS quantum dots were synthesized by the hot injection method and deposited layer by layer by the spin coating process; The annealing temperature (60 - 90 °C) and time (10 - 30 min) match the interface stability requirements; Defect passivation and exciton confinement: The coverage of CdS nanosheets effectively suppresses the surface defects of PbS and reduces the non-radiative recombination of excitons; Application compatibility: Suitable for high-efficiency light-emitting devices in the visible light band, providing solutions for high-brightness display technology. Brief Description of the Drawings

[0021] The present invention will be further described in detail below with reference to the drawings and specific embodiments: Figure 1 It is a structural diagram of a composite light-emitting layer of a single CdS nanosheet, PbS quantum dots, and a CdS nanosheet / PbS / CdS nanosheet heterojunction quantum well and a stacked heterojunction quantum well in an embodiment of the present invention; Figure 2 It is a structural diagram of an LED of a CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well material in an embodiment of the present invention; Among them, 1 is a single CdS nanosheet in the depletion region, 2 is a single CdS nanosheet, 3 is a single PbS quantum dot, 4 is a single PbS quantum dot in the depletion region, 5 is a stacked heterojunction quantum well composite light-emitting layer, 6 is the neutral region of the CdS nanosheet material, 7 is the CdS nanosheet contact depletion region, 8 is the CdS nanosheet at non-interface, 9 is the neutral region of the PbS quantum dot material, 10 is the PbS quantum dot contact depletion region, 11 is the PbS quantum dot at non-interface, 12 is the silver electrode, 13 is Zn 0.85 Mg 0.15 O electron transport layer, 14 is the CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well composite light-emitting layer, 15 is the TFB hole transport layer, 16 is the PEDOT:PSS hole transport layer, 17 is the ITO glass substrate. Detailed Description of the Embodiments

[0022] To make the features and advantages of the present invention more obvious and understandable, specific embodiments are given below for detailed description as follows: It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0023] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments 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 "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0024] The embodiment of the present invention first provides a structure of a QWLED of a CdS nanosheet / PbS / CdS nanosheet stacked deep well composite light-emitting layer: from top to bottom, it includes an electrode, an inorganic electron transport layer, a stacked heterojunction deep quantum well light-emitting layer, an organic hole transport layer and an ITO glass substrate, wherein the stacked heterojunction deep quantum well light-emitting layer is formed by CdS nanosheets / PbS ​​quantum dots / CdS nanosheets materials to form a composite light-emitting layer with a stacked heterojunction deep quantum well structure.

[0025] Among them, the inorganic electron transport layer is Zn 0.85 Mg 0.15 O electron transport layer.

[0026] The organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

[0027] The typical preparation process of the QWLED device provided above includes the following steps: (1) Clean the ITO conductive glass with deionized water, acetone, and isopropanol for 15-25 minutes respectively, and dry it with nitrogen at a certain temperature; (2) In a glove box, a PEDOT:PSS solution is spin-coated on the ITO conductive glass in step (1) using a spin coater, and then the conductive glass sheet is placed on a heating table for annealing; (3) dissolving TFB in a toluene solution, and then spin coating the solution on the conductive glass sheet in step (2) using a spin coater in a glove box, and then placing the conductive glass sheet on a heating table for annealing; (4) In a glove box, spin-coat the CdS nanosheet solution on the conductive glass sample in step (3) using a spin coater, and then place the conductive glass sample on a heating table for annealing; (5) In a glove box, spin-coat the PbS quantum dot solution on the conductive glass sample in step (4) using a spin coater, and then place the conductive glass sample on a heating table for annealing; (6) In a glove box, spin-coat the CdS nanosheet solution on the conductive glass sample in step (5) using a spin coater, and then place the conductive glass sample on a heating table for annealing; (7) In the glove box, Zn 0.85 Mg 0.15The O solution is spin-coated on the conductive glass sample in step (6) using a spin coater, and then the conductive glass sheet is placed on a heating stage for annealing; (8) The conductive glass sample obtained in step (7) is used to evaporate electrodes by a thermal evaporation machine, and a QWLED based on a CdS nanosheet / PbS / CdS nanosheet stacked deep well composite light-emitting layer is thus obtained.

[0028] As a preferred solution of this embodiment, in step (2), the PEDOT:PSS solution is first filtered through a 0.22 - 0.45 μm filter head, 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 20 - 30 min.

[0029] As a preferred solution of this embodiment, in step (3), the concentration of the TFB solution is 8 - 10 mg / ml, the annealing temperature is 160 - 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.

[0030] As a preferred solution of this embodiment, the specific method for preparing CdS nanosheets in steps (4) and (6) is as follows: Step S71: Cadmium nitrate tetrahydrate and sodium myristate are respectively dissolved in methanol. After complete dissolution, the solutions are mixed and vigorously stirred for reaction. After the reaction, cadmium myristate is obtained through centrifugation, washing, and vacuum drying; Step S72: Take the cadmium myristate obtained in step S71, mix it with sulfur and octadecene, degas for 0.5 h at room temperature to remove excess oxygen and volatile solvents; then heat the solution under an inert atmosphere, quickly add cadmium acetate dihydrate to the reaction, inject a small amount of oleic acid after the reaction for a period of time, and cool the solution temperature to room temperature to obtain a cadmium sulfide nanosheet solution, which is stored at low temperature; Step S73: Take out the supernatant of the partially static nanosheet solution, dissolve oleic acid with an appropriate amount of methanol, 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 CdS nanosheet solution.

[0031] As a preferred solution of this embodiment, the specific method for preparing PbS quantum dots in step (5) is as follows: Step S81: Dissolve a certain amount of lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolve a certain amount of sulfur powder in tri - n - octylphosphine and inject it into a three - necked flask at a certain speed. Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n - hexane to obtain a quantum dot solution, which is stored 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 it 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.

[0032] As a preferred solution of this embodiment, in the cadmium sulfide nanosheet precursor solution, cadmium myristate is 120 - 220 mg, sulfur powder is 7 - 15 mg, and ODE is 10 - 18 ml; in the degassing process, stir at room temperature and under vacuum, and the stirring time is 10 - 40 minutes to remove excess oxygen and volatile solvents; subsequently, during the reaction growth process, introduce argon and heat under an argon atmosphere, the heating temperature is 170 - 195 °C, quickly add cadmium acetate dihydrate to the three-necked flask, and the amount of cadmium acetate dihydrate added is 60 - 100 mg, and further heat up to the specified temperature and keep it growing for the corresponding time, the heating and temperature rising temperature is 200 - 260 °C, the growth time is 5 - 15 minutes, then, inject 0.3 - 0.8 ml of OA, and cool the solution to room temperature; in the nanosheet cleaning, the ratio of the nanosheet 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, and repeat the above cleaning process twice.

[0033] As a preferred solution of this 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, it is raised to 270 - 300 °C; in the sulfur precursor solution, 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 speed 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, 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, and repeat the above cleaning process twice.

[0034] Finally, the concentration of the CdS nanosheet solution is 10 - 30 mg / ml.

[0035] Finally, the concentration of the PbS quantum dot solution is 10 - 30 mg / ml.

[0036] As a preferred solution of this embodiment, in steps (4) and (6), the concentration of the CdS nanosheet solution is 10 - 30 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.

[0037] As a preferred solution of this embodiment, in step (5), the concentration of the PbS quantum dot solution is 10 - 30 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.

[0038] As a preferred solution of this embodiment, in step (7), Zn 0.85 Mg 0.15 The concentration of the O solution is 15 - 25 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 - 20 min.

[0039] As a preferred solution of this embodiment, in step (8), the electrode is a silver electrode with a thickness of 100 nm.

[0040] The following further provides 3 specific preferred preparation examples to further demonstrate this solution: Example 1 1) Put the ITO glass into a beaker, pour in acetone solution, isopropyl alcohol solution and deionized water solution in sequence, and ultrasonically clean each for 25 min. Take it out, dry it with nitrogen at 60 °C, and put it into a clean and dry petri dish.

[0041] 2) After filtering the PEDOT:PSS solution with a 0.45 μm filter head, spin - coat it on the ITO glass with a low - speed of 500 rpm / s for 5 s and a high - speed of 3000 rpm / s for 40 s using a spin coater. Then put the glass slide on a heating table and anneal it at 120 °C for 30 min.

[0042] 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 it on the glass slide with a low - speed of 500 rpm / s for 5 s and a high - speed of 2000 rpm / s for 40 s using a spin coater. Then put the glass slide on a heating table and anneal it at 200 °C for 30 min.

[0043] 4) Preparation of cadmium sulfide nanosheet material: 220 mg of cadmium myristate, 15 mg of sulfur, and 18 mL of ODE were loaded into a three-necked flask. Stirring was carried out at room temperature and under vacuum for 40 minutes to remove excess oxygen and volatile solvents. Then, the solution was heated to 260 °C under an argon atmosphere. When the temperature reached 195 °C, 100 mg of cadmium acetate dihydrate was quickly added to the reaction. After the solution grew at 260 °C for about 15 minutes, 0.8 mL of OA was injected, and the solution temperature was lowered to room temperature. After precipitation purification, the obtained cadmium sulfide nanoplates were dissolved in hexane. Subsequently, the nanosheet solution was taken, and the ratio of the supernatant of the nanosheet solution to methanol was 2:1. The precipitate was dissolved in n-hexane, the upper layer solution was extracted, an excessive amount of absolute ethanol was added, and centrifugation was carried out at 8000 rpm for 10 min. Then, the nanosheets were dissolved in n-hexane, and the above cleaning process was repeated twice. The nanosheets were dissolved in n-hexane to form a 30 mg / ml nanosheet solution, which was stored under low-temperature conditions.

[0044] 5) Preparation of PbS quantum dots: 0.6 mmol of lead oxide, 1.2 ml of oleic acid, and 10 ml of octadecene were added to a three-necked flask. Stirring was carried out at 150 °C for 10 min. After dissolution, the temperature was raised to 300 °C to prepare a lead precursor solution; 0.75 mmol of sulfur powder and 1.70 ml of trioctylphosphine were taken, and stirring was carried out at 150 °C until completely dissolved. Subsequently, it was injected into the three-necked flask of the lead precursor at a rate of 2.0 ml / h, and it was maintained for 10 min after injection; finally, the quantum dot solution was quickly cooled by means of a water bath, diluted with n-hexane to obtain a quantum dot solution; subsequently, the quantum dot solution was taken, and the ratio of the supernatant of the quantum dot to methanol was 2:1. The precipitate was dissolved in n-hexane, the upper layer solution was extracted, an excessive amount of absolute ethanol was added, and centrifugation was carried out at 8000 rpm for 10 min. Then, the quantum dots were dissolved in n-hexane, and the above cleaning process was repeated twice. The quantum dots were dissolved in n-hexane to form a 30 mg / ml quantum dot solution, which was stored under low-temperature conditions.

[0045] 6) Dilute the CdS nanosheet colloidal solution to 30 mg / ml with n-octane, and spin-coat it at a low speed of 300 rpm / s for 5 s and at a high speed of 2000 rpm / s for 40 s with a spin coater. Then, place the above glass slide on a heating table and anneal it at 90 °C for 30 min.

[0046] 7) Dilute the PbS quantum dot colloidal solution to 30 mg / ml solution with n-octane, and spin-coat it at a low speed of 300 rpm / s for 5 s and at a high speed of 2000 rpm / s for 40 s with a spin coater. Then, place the above glass slide on a heating table and anneal it at 90 °C for 30 min.

[0047] 8) Dilute the CdS nanosheet colloidal solution with n-octane to 30 mg / ml, and spin-coat it on 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 stage and anneal it at 90 °C for 30 min. Figure 1 It is the structural diagram of a composite light-emitting layer of a single CdS nanosheet, PbS quantum dots, a CdS nanosheet / PbS / CdS nanosheet heterojunction quantum well, and a stacked heterojunction quantum well; where 1 is a single CdS nanosheet in the depletion region, 2 is a single CdS nanosheet, 3 is a single PbS quantum dot, 4 is a single PbS quantum dot in the depletion region, 5 is a stacked heterojunction quantum well composite light-emitting layer, 6 is the neutral region of the CdS nanosheet material, 7 is the contact depletion region of the CdS nanosheet, 8 is the CdS nanosheet at a non-interface, 9 is the neutral region of the PbS quantum dot material, 10 is the contact depletion region of the PbS quantum dot, and 11 is the PbS quantum dot at a non-interface.

[0048] 9) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 25 mg / ml, spin-coat it on a spin coater at a low speed of 500 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s, and then place the glass slide on a heating stage and anneal it at 120 °C for 20 min.

[0049] 10) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a CdS nanosheet / PbS / CdS nanosheet stacked deep well composite light-emitting layer. Figure 2 It is the structural diagram of an LED with a CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well material; where 12 is the silver electrode, 13 is the Zn 0.85 Mg 0.15 O electron transport layer, 14 is the CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well composite light-emitting layer, 15 is the TFB hole transport layer, 16 is the PEDOT:PSS hole transport layer, and 17 is the ITO glass substrate.

[0050] Example 2 1) Place the ITO glass in a beaker, pour acetone solution, isopropyl alcohol solution, and deionized water solution into it in sequence, and ultrasonically clean each for 20 min. Take it out, dry it with nitrogen at 60 °C, and place it in a clean and dry petri dish.

[0051] 2) After filtering the PEDOT:PSS solution with a 0.45-μm filter head, spin-coat it on a spin coater at a low speed of 500 rpm / s for 5 s and a high speed of 3000 rpm / s for 40 s. Spin-coat the PEDOT:PSS solution on the ITO glass, and then place the glass slide on a heating stage and anneal it at 110 °C for 25 min.

[0052] 3) Take 9 mg of TFB and 1 ml of toluene solution. After dissolving TFB in toluene to prepare a solution with a concentration of 9 mg / mL, spin-coat it at a low speed of 500 rpm / s for 5 s and then at a high speed of 2000 rpm / s for 40 s using a spin coater. Then, place the glass slide on a heating stage and anneal it at 180 °C for 20 min.

[0053] 4) Preparation of cadmium sulfide nanosheet material: 170 mg of cadmium myristate, 11 mg of sulfur, and 14 ml of ODE are loaded into a three-necked flask. Stir at room temperature and under vacuum for 25 minutes to remove excess oxygen and volatile solvents. Then, heat the solution to 230 °C under an argon atmosphere. When the temperature reaches 185 °C, 100 mg of cadmium acetate dihydrate is quickly added to the reaction. After the solution grows at 230 °C for about 10 minutes, 0.5 mL of OA is injected, and the solution temperature is lowered to room temperature. After precipitation purification, the obtained cadmium sulfide nanoplates are dissolved in hexane. Subsequently, take the nanosheet solution, with the ratio of nanosheet supernatant to methanol being 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 min. Then, dissolve the nanosheets in n-hexane, repeat the above washing process twice, dissolve the nanosheets in n-hexane to form a 20 mg / ml nanosheet solution, and store it under low-temperature conditions.

[0054] 5) Preparation of PbS quantum dots: Add 0.5 mmol of lead oxide, 1.1 ml of oleic acid, and 9 ml of octadecene to a three-necked flask. Stir at 135 °C for 7 min. After dissolution, raise the temperature to 285 °C to prepare a lead precursor solution; take 0.625 mmol of sulfur powder and 1.55 ml of tri-n-octylphosphine, 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, maintain 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; subsequently, take the quantum dot solution, with the ratio of quantum dot supernatant to methanol being 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 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.

[0055] 6) Dilute the CdS nanosheet colloidal solution to 20 mg / ml with n-octane, and spin-coat it at a low speed of 300 rpm / s for 5 s and then at a high speed of 2000 rpm / s for 40 s using a spin coater. Then, place the above glass sample on a heating stage and anneal it at 75 °C for 20 min.

[0056] 7) Dilute the PbS quantum dot colloidal solution with n-octane to a 20 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 table and anneal it at 75 °C for 20 min.

[0057] 8) Dilute the CdS nanosheet colloidal solution with n-octane to 20 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 table and anneal it at 75 °C for 20 min. Figure 1 It is the structural diagram of the composite light-emitting layer of a single CdS nanosheet, PbS quantum dots, and its CdS nanosheet / PbS / CdS nanosheet heterojunction quantum well and stacked heterojunction quantum well; where 1 is a single CdS nanosheet in the depletion region, 2 is a single CdS nanosheet, 3 is a single PbS quantum dot, 4 is a single PbS quantum dot in the depletion region, 5 is the stacked heterojunction quantum well composite light-emitting layer, 6 is the neutral region of the CdS nanosheet material, 7 is the contact depletion region of the CdS nanosheet, 8 is the CdS nanosheet at the non-interface, 9 is the neutral region of the PbS quantum dot material, 10 is the contact depletion region of the PbS quantum dot, and 11 is the PbS quantum dot at the non-interface.

[0058] 9) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 20 mg / ml, spin-coat it at a low speed of 500 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 table and anneal it at 110 °C for 15 min.

[0059] 10) Thermally evaporate a 100 nm silver electrode to obtain a QWLED with a CdS nanosheet / PbS / CdS nanosheet stacked deep well composite light-emitting layer. Figure 2 It is the structural diagram of the LED of the CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well material; where 12 is the silver electrode, 13 is the Zn 0.85 Mg 0.15 O electron transport layer, 14 is the CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well composite light-emitting layer, 15 is the TFB hole transport layer, 16 is the PEDOT:PSS hole transport layer, and 17 is the ITO glass substrate.

[0060] Example 3 1) Put the ITO glass into a beaker, pour in acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, and ultrasonically clean each for 15 min. Take it out, dry it with nitrogen at 60 °C, and put it into a clean and dry petri dish.

[0061] 2) After filtering the PEDOT:PSS solution with a 0.22 μm filter head, spin-coat it on the ITO glass at a low speed of 500 rpm / s for 5 s and then at a high speed of 3000 rpm / s for 40 s. Then place the glass slide on a heating table and anneal it at 100 °C for 20 min.

[0062] 3) Take 8 mg of TFB and 1 ml of toluene solution. Dissolve TFB in toluene to prepare a solution with a concentration of 8 mg / mL. Then spin-coat it on the glass slide at a low speed of 500 rpm / s for 5 s and at a high speed of 2000 rpm / s for 40 s. Then place the glass slide on a heating table and anneal it at 160 °C for 15 min.

[0063] 4) Preparation of cadmium sulfide nanosheet material: 120 mg of cadmium myristate, 7 mg of sulfur, and 10 ml of ODE are loaded into a three-necked flask. Stir at room temperature and under vacuum for 10 minutes to remove excess oxygen and volatile solvents. Then heat the solution to 200 °C under an argon atmosphere. When the temperature reaches 170 °C, 60 mg of cadmium acetate dihydrate is quickly added to the reaction. After the solution grows at 200 °C for about 5 minutes, 0.3 mL of OA is injected, and the solution temperature is lowered to room temperature. After precipitation purification, the obtained cadmium sulfide nanoplates are dissolved in hexane. Subsequently, take the nanosheet solution, with the ratio of nanosheet supernatant to methanol being 1:1. Dissolve the precipitate in n-hexane, extract the upper layer solution, add an excess of absolute ethanol, and centrifuge at 6000 rpm for 5 min. Then dissolve the nanosheets in n-hexane, repeat the above washing process twice, dissolve the nanosheets in n-hexane to form a 10 mg / ml nanosheet solution, and store it under low-temperature conditions.

[0064] 5) 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. After dissolution, raise the temperature to 270 °C 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. After injection, maintain for 8 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 quantum dot supernatant to methanol being 1:1. Dissolve the precipitate in n-hexane, extract the upper layer solution, add an excess of absolute ethanol, and centrifuge at 6000 rpm for 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 10 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0065] 6) Dilute the CdS nanosheet colloidal solution with n-octane to 10 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.

[0066] 7) 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.

[0067] 8) Dilute the CdS nanosheet colloidal solution with n-octane to 10 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 the structural diagram of a single CdS nanosheet, PbS quantum dots, and their CdS nanosheet / PbS / CdS nanosheet heterojunction quantum well and stacked heterojunction quantum well composite light-emitting layer; where 1 is a single CdS nanosheet in the depletion region, 2 is a single CdS nanosheet, 3 is a single PbS quantum dot, 4 is a single PbS quantum dot in the depletion region, 5 is the stacked heterojunction quantum well composite light-emitting layer, 6 is the neutral region of the CdS nanosheet material, 7 is the CdS nanosheet contact depletion region, 8 is the CdS nanosheet at non-interface, 9 is the neutral region of the PbS quantum dot material, 10 is the PbS quantum dot contact depletion region, and 11 is the PbS quantum dot at non-interface.

[0068] 9) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 15 mg / ml, spin-coat it at a low speed of 500 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.

[0069] 10) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a CdS nanosheet / PbS / CdS nanosheet stacked deep well composite light-emitting layer. Figure 2 It is the structural diagram of an LED with a CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well material; where 12 is the silver electrode, 13 is the Zn 0.85 Mg 0.15 O electron transport layer, 14 is the CdS nanosheet / PbS / CdS nanosheet stacked heterojunction quantum well composite light-emitting layer, 15 is the TFB hole transport layer, 16 is the PEDOT:PSS hole transport layer, and 17 is the ITO glass substrate.

[0070] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Words such as "comprising" or "including" mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Upper", "lower", "left", "right", etc. are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0071] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in any other form. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

[0072] The present invention is not limited to the above best mode. Anyone inspired by the present invention can obtain various other forms of QWLED devices based on the CdS-PbS-CdS single-stack deep-well composite light-emitting structure. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A QWLED device based on a CdS-PbS-CdS single-stack deep well composite light-emitting structure, characterized in that: It includes an electrode, an inorganic electron transport layer, a stacked heterojunction deep quantum well light-emitting layer, an organic hole transport layer, and an ITO glass substrate from top to bottom in sequence; The stacked heterojunction deep quantum well light-emitting layer is formed by alternately stacking CdS nanosheet layers, PbS quantum dot layers, and CdS nanosheet layers in sequence to form a deep quantum well structure. Among them, the CdS nanosheets and the PbS quantum dot layers are synthesized by a thermal injection method and deposited layer by layer through a spin coating process; The CdS nanosheet layer covers the surface of the PbS quantum dots, forming a depletion region parallel to the interface.

2. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, characterized in that: The inorganic electron transport layer is a Zn 0.85 Mg 0.15 O electron transport layer.

3. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure 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. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, wherein: The precursor of the CdS nanosheets synthesized by the thermal injection method contains cadmium nitrate tetrahydrate, sulfur powder, and an organic ligand; the precursor of the PbS quantum dots synthesized by the thermal injection method contains lead oxide, sulfur powder, and tri-n-octylphosphine.

5. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, characterized in that: The annealing temperature of the thermal injection method for the CdS nanosheets and the PbS quantum dot layers is 60 - 90 °C, and the annealing time is 10 - 30 min.

6. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, characterized in that: The CdS nanosheet layer is formed by a CdS nanosheet solution with a concentration of 10 - 30 mg / ml. The preparation of the CdS nanosheet solution includes the following steps: (1a) Dissolve 120 - 220 mg of cadmium nitrate tetrahydrate and 7 - 15 mg of sodium myristate in methanol respectively, and mix and stir to react to generate cadmium myristate; (1b) Mix the cadmium myristate generated in step (1a), 7 - 15 mg of sulfur powder, and 10 - 18 ml of octadecene, heat to 170 - 260 °C under an inert atmosphere, add 60 - 100 mg of cadmium acetate dihydrate, and inject 0.3 - 0.8 ml of oleic acid after reacting for 5 - 15 minutes; (1c) Mix the mixed solution in step (1b) with methanol at a volume ratio of 2:1 to 1:1, centrifuge, add n-hexane to dissolve the precipitate, and repeat the washing twice to obtain a purified CdS nanosheet solution.

7. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, characterized in that: The PbS quantum dot layer is formed by a PbS quantum dot solution with a concentration of 10 - 30 mg / ml. The preparation of the PbS quantum dot solution includes the following steps: (2a) Mix 0.4 - 0.6 mmol of lead oxide, 1.0 - 1.2 ml of oleic acid, and 8 - 10 ml of octadecene, stir and dissolve at 120 - 150 °C, and raise the temperature to 270 - 300 °C; (2b) Dissolve 0.50 - 0.75 mmol of sulfur powder in 1.40 - 1.70 ml of tri-n-octylphosphine, and inject it into the lead precursor solution in step (2a) at a rate of 1.0 - 2.0 ml / h. After reacting for 8 - 10 minutes, quickly cool it by water bath; (2c) Mix the mixed solution in step (2b) with ethanol at a volume ratio of 2:1 to 1:1, centrifuge, add n-hexane to dissolve the precipitate, and repeat the washing twice to obtain a purified PbS quantum dot solution.

8. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 2, characterized in that: The inorganic electron transport layer is formed by spin coating with a Zn 0.85 Mg 0.15 O solution with a concentration of 15 - 25 mg / ml, and annealed at 100 - 120 °C for 10 - 20 minutes. 0.85 Mg 0.15 O solution spin coating, and annealed at 100 - 120 °C for 10 - 20 minutes.

9. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 3, characterized in that: The TFB layer is formed by spin-coating a toluene solution of TFB with a concentration of 8-10 mg / ml and annealed at 160-200 °C for 15-30 minutes; The PEDOT:PSS layer is formed by spin-coating a PEDOT:PSS solution filtered through a 0.22-0.45 μm pore size and annealed at 100-120 °C for 20-30 minutes.

10. The QWLED device based on the CdS-PbS-CdS single-stack deep well composite light-emitting structure according to claim 1, characterized in that: The ITO glass substrate is pretreated by the following steps: (3a) Ultrasonically clean with deionized water, acetone, and isopropanol in sequence for 15-25 minutes; (3b) Dry in a nitrogen atmosphere at 60-80 °C.

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