QWLED of CdSe / PbS / CdSe laminated heterojunction quantum well composite light-emitting layer and preparation method of QWLED of CdSe / PbS / CdSe laminated heterojunction quantum well composite light-emitting layer

Abstract

The invention discloses a QWLED with a CdSe / PbS / CdSe laminated heterojunction quantum well composite light-emitting layer and a preparation method of the QWLED. PbS quantum dots and CdSe quantum dots are respectively prepared by using a thermal injection method, and the two kinds of quantum dot solutions are respectively and sequentially spin-coated to form films, so that the CdSe / PbS / CdSe laminated heterojunction quantum well composite light-emitting layer is prepared. And finally, a CdSe / PbS / CdSe laminated heterojunction material compound with a parallel interface laminated depletion region and a laminated heterojunction quantum well structure is formed, a preparation method of the LED with the laminated depletion region and the laminated heterojunction quantum well structure is shown, the laminated depletion region and the laminated heterojunction quantum well structure are novel, the device structure is stable and efficient, and the device is suitable for large-scale production. The prepared CdSe / PbS / CdSe laminated heterojunction composite material has a laminated depletion region and a laminated heterojunction structure with parallel interfaces, high quantum efficiency, good optical characteristics and structural stability, and the prepared LED device with the laminated depletion region and the laminated heterojunction quantum well structure has excellent electroluminescent efficiency and external quantum efficiency, and is suitable for the field of organic light emitting devices. And the method has huge application potential in the fields of high-brightness, long-service-life and high-resolution display technology and the like.

Description

Technical Field

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

[0002] Quantum dots, as quasi-zero-dimensional materials with all three-dimensional scales in the range of 1-100 nm, can control the size, shape, and emission wavelength of quantum dots 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 bandgap tunability. Lead sulfide quantum dots are considered an excellent choice for applications such as near-infrared light-emitting LEDs and solar cells due to their relatively large size, but there is still room for expansion 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, by forming a stacked composite material of lead sulfide quantum dots and other quantum dots, the energy band structure at the contact interface between the quantum dots can be adjusted, 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: 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 a 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 a water-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 properties 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, mainly used in the gas-sensing field, and its optoelectronic properties are limited.In addition, the luminescence performance of quantum dot light-emitting diodes ultimately depends on the charge distribution and properties of the quantum dot light-emitting layer, and is directly related to 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 more unfavorable it is to the semiconductor luminescence performance. Therefore, the effective photoelectric effect of diodes usually occurs in the depletion region. This kind of stacked heterojunction 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 of each component in the stacked interface material, thereby realizing the improvement of the overall optoelectronic performance of the stacked heterojunction.

[0004] In summary, 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. However, in this patent, a stacked heterojunction structure is designed and prepared by combining CdSe quantum dots and PbS quantum dots. The preparation process is relatively simple, and the prepared CdSe / PbS / CdSe quantum dot stacked heterojunction has a stacked heterojunction depletion region and a quantum well structure parallel to the light-emitting layer at the stacked interface, which has a significant effect on improving its photoluminescence and electroluminescence performance. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a QWLED of a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer and its preparation method. The present invention uses the thermal injection method to prepare PbS quantum dots and CdSe quantum dots respectively, and further spin-coats the two quantum dot solutions in sequence to form a CdSe / PbS / Cdse quantum dot stacked material composite with a stacked depletion region and a stacked heterojunction quantum well structure at the interface, and demonstrates a preparation method for a stacked heterojunction quantum well LED. The stacked heterojunction quantum well structure is novel, the device structure is stable and efficient. The prepared CdSe / PbS / CdSe stacked heterojunction quantum well material has a stacked heterojunction quantum well structure, high quantum efficiency, good optical properties, and structural stability. The prepared stacked heterojunction quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in the fields of high brightness, long life, and high-resolution display technology.

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

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

[0008] In a preferred embodiment, 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 preparation method for a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer, including the following steps: Step (1): Clean the ITO conductive glass with deionized water, acetone, and isopropanol for 15 - 25 minutes respectively, and dry it with nitrogen. Step (2): Spin-coat the PEDOT:PSS solution on the ITO conductive glass in step (1) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing. Step (3): Dissolve TFB in toluene solution, and then spin-coat the solution on the conductive glass sheet in step (2) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing. Step (4): Spin-coat the CdSe quantum dot solution on the conductive glass sample in step (3) with a spin coater in a glove box, and then put the conductive glass sample on a heating table for annealing. Step (5): Spin-coat the PbS quantum dot solution on the conductive glass sample in step (4) with a spin coater in a glove box, and then put the conductive glass sample on a heating table for annealing. Step (6): Spin-coat the CdSe quantum dot solution on the conductive glass sample in step (5) with a spin coater in a glove box, and then put the conductive glass sample on a heating table for annealing. Step (7): Spin-coat the Zn 0.85 Mg 0.15 O solution on the conductive glass sample in step (6) with a spin coater, and then put the conductive glass sheet on a heating table for annealing. Step (8) uses a thermal evaporation machine to evaporate electrodes on the conductive glass wafer obtained in step (7), thereby obtaining a QWLED based on a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer.

[0010] In a preferred embodiment, the PEDOT:PSS solution in step (2) is first filtered through a 0.22 - 0.45 μm filter head, the annealing temperature is 100 - 120 °C, the environmental conditions are 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.

[0011] In a preferred embodiment, the concentration of the TFB solution in step (3) is 8 - 10 mg / ml, the annealing temperature is 160 - 200 °C, the environmental conditions are 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 methods for preparing CdSe quantum dots in steps (4) and (6) are as follows: Step S71: Dissolve a certain amount of selenium powder and TOP solution by stirring at a set temperature to prepare a selenium precursor solution; stir a certain amount of cadmium oxide and oleic acid at a set temperature for a set time, then inject a small amount of ODE solution and raise the solution temperature; take the selenium precursor solution and quickly inject it into the cadmium precursor solution when the solution temperature reaches the set value and maintain for a set time, while using an ultraviolet lamp for excitation; 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 S72: Take out the supernatant of a part of the quantum dot solution after standing, dissolve oleic acid with an appropriate amount of methanol, 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.

[0013] In a preferred 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 trioctylphosphine and inject it into a three-necked flask at a certain speed, and 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 a part 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.

[0014] In a preferred embodiment, in the precursor solution of selenium, the mass of selenium powder is 0.084 g - 0.128 g, and the stirring temperature is 120 - 150 °C; the mass of cadmium oxide is 0.0182 g - 0.0257 g, the stirring temperature is 120 - 150 °C, the ODE solution is injected when the stirring time reaches 30 min, and at the same time the temperature is raised to 270 - 300 °C, the precursor solution of selenium is rapidly injected, the holding time is 8 - 10 min, and it is excited by an ultraviolet lamp at 2 min; in the cleaning of the quantum dots, 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 revolutions for 5 - 10 min, and then the quantum dots are dissolved in n - hexane, and the above cleaning process is repeated twice.

[0015] In a preferred embodiment, in the precursor solution of lead, the amount of substance of lead oxide is 0.4 - 0.6 mmol, 1.0 - 1.2 ml of oleic acid, 8 - 10 ml of octadecene, 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 substance of sulfur powder is 0.50 - 0.75 mmol, 1.40 - 1.70 ml of tri - n - octylphosphine, the stirring temperature is 120 - 150 °C, and after dissolution, it is injected into the three - neck flask of the lead precursor at a rate of 1.0 - 2.0 ml / h, and the holding time is 8 - 10 min; in the cleaning of the quantum dots, 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 revolutions 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 concentration of the finally prepared CdSe quantum dot solution is 10 - 30 mg / ml.

[0017] In a preferred embodiment, the concentration of the finally prepared PbS quantum dot solution is 10 - 30 mg / ml.

[0018] In a preferred embodiment, in steps (4) and (6), the concentration of the CdSe 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.

[0019] In a preferred 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.

[0020] In a preferred embodiment, in step (7), the concentration of the Zn0.85Mg0.15O 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.

[0021] In a preferred embodiment, in step (8), the electrode is a silver electrode with a thickness of 100 nm.

[0022] Compared with the prior art, the present invention has the following beneficial effects: By using CdSe quantum dots and PbS quantum dots in a stacked composite to form a composite light-emitting layer with a stacked quantum well heterojunction structure, and then preparing an LED device including an electrode, an inorganic electron transport layer, a stacked 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 adopts a thermal injection method and a multiple spin-coating process, which not only realizes the stable control of the stacked heterojunction quantum well structure but also can adjust the balance of electron and hole currents in the composite material. Through the effective coverage and isolation of PbS quantum dots at the interface by CdSe quantum dots, a stable stacked heterojunction quantum well structure is formed. Due to 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 CdSe quantum dots on the surface of PbS quantum dots at the interface effectively reduces the generation of surface defects of PbS quantum dots at the interface and the exciton quenching phenomenon, thereby improving the structural stability, quantum efficiency, and photoluminescence intensity of the stacked quantum well heterojunction. The materials and device preparation processes 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 for electron and hole currents, provides an effective method for the preparation of high-performance light-emitting stacked heterojunction quantum well materials and devices.

[0023] The present invention can make full use of the excellent energy band regulation ability of the stacked heterojunction material in stacked quantum well light emission, prepare a stacked 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 CdSe / PbS / CdSe quantum dot stacked heterojunction quantum well composite material as the light-emitting layer, which has a high external quantum efficiency and high light emission intensity. Description of the Drawings

[0024] Figure 1 It is a structural diagram of a single CdSe quantum dot, a PbS quantum dot, their CdSe / PbS / CdSe heterojunction quantum well, and a stacked heterojunction quantum well composite light-emitting layer; Figure 2 It is a structural diagram of an LED of a CdSe / PbS / CdSe stacked heterojunction quantum well material; Note: Among them, 1 is a single CdSe quantum dot in the packet depletion region, 2 is a single CdSe quantum dot, 3 is a single PbS quantum dot, 4 is a single PbS quantum dot in the packet depletion region, 5 is a stacked heterojunction quantum well composite light-emitting layer, 6 is the neutral region of the CdSe quantum dot material, 7 is the CdSe quantum dot contact depletion region, 8 is the CdSe quantum dot 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 CdSe / PbS / CdSe quantum dot 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. Specific embodiments

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] It should be noted that the following detailed description is exemplary and is intended to provide further illustration 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 this application belongs.

[0027] 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 forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0028] Example 1 1) Place the ITO glass in a beaker, and pour 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.

[0029] 2) After filtering the PEDOT:PSS solution with a 0.45 μm filter head, spin-coat it on the ITO glass with 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. Then put the glass slide on a heating table and anneal it at 120 °C for 30 min.

[0030] 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 with a spin coater at a low speed of 500 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s. Then place the glass slide on a heating stage and anneal it at 200 °C for 30 min.

[0031] 4) Preparation of CdSe quantum dots: Add 0.128 g of selenium powder and 2 ml of TOP solution to a three-necked flask, stir and dissolve at 150 °C to prepare a selenium precursor solution; stir 0.0257 g of cadmium oxide and 5 ml of oleic acid at 150 °C for 30 min, then inject 15 ml of ODE solution and raise the solution temperature to 300 °C; take the selenium precursor solution and quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 300 °C and keep it for 10 min. At the same time, use an ultraviolet lamp to excite at 2 min; 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, the ratio of the quantum dot supernatant to methanol is 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 with n-hexane, repeat the above washing 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.

[0032] 5) Preparation of PbS quantum dots: Add 0.6 mmol of lead oxide, 1.2 ml of oleic acid and 10 ml of octadecene to a three-necked flask, stir at 150 °C for 10 min, and 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, then inject it into the three-necked flask of the lead precursor at a rate of 2.0 ml / h, and keep it for 10 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, the ratio of the quantum dot supernatant to methanol is 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 with n-hexane, repeat the above washing 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.

[0033] 6) Dilute the CdSe quantum dot colloidal solution to 30 mg / ml with n-octane, 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 sample on a heating stage and anneal it at 90 °C for 30 min.

[0034] 7) Dilute the PbS quantum dot colloidal solution with n-octane to a 30 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 slides on a heating stage and anneal them at 90 °C for 30 min.

[0035] 8) Dilute the CdSe quantum dot colloidal solution with n-octane to 30 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 slides on a heating stage and anneal them at 90 °C for 30 min. Figure 1 It is a structural diagram of a composite light-emitting layer of single CdSe quantum dots, PbS quantum dots, their CdSe / PbS / CdSe heterojunction quantum wells, and stacked heterojunction quantum wells; where 1 is a single CdSe quantum dot in the depletion region, 2 is a single CdSe quantum dot, 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 CdSe quantum dot material, 7 is the contact depletion region of the CdSe quantum dot, 8 is the CdSe quantum dot at 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 non-interface.

[0036] 9) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 25 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 slides in a heating stage and anneal them at 120 °C for 20 min.

[0037] 10) Thermally evaporate a 100 nm silver electrode to obtain a QWLED with a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a CdSe / PbS / CdSe 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 CdSe / PbS / CdSe quantum dot 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.

[0038] Example 2 1) Place the ITO glass in a beaker, pour acetone solution, isopropanol solution, and deionized water solution 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.

[0039] 2) After filtering the PEDOT:PSS solution with a 0.45 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 110 °C for 25 min.

[0040] 3) Take 9 mg of TFB and 1 ml of toluene solution. Dissolve TFB in toluene to prepare a solution with a concentration of 9 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 180 °C for 20 min.

[0041] 4) Preparation of CdSe quantum dots: Add 0.106 g of selenium powder and 2 ml of TOP solution to a three-necked flask, stir and dissolve at 135 °C to prepare a selenium precursor solution; stir 0.0214 g of cadmium oxide and 5 ml of oleic acid at 135 °C for 30 min, then inject 15 ml of ODE solution and raise the solution temperature to 290 °C; take the selenium precursor solution and quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 290 °C and keep it for 9 min. At the same time, use an ultraviolet lamp to excite at 2 min; 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, 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 excessive anhydrous ethanol and centrifuge at 7000 rpm for 7 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.

[0042] 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, and raise the temperature to 285 °C after dissolution 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 lead precursor three-necked flask at a speed of 1.5 ml / h, and keep it for 9 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, 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 excessive anhydrous ethanol and centrifuge at 7000 rpm for 7 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 20 mg / ml quantum dot solution, and store it under low temperature conditions.

[0043] 6) Dilute the CdSe quantum dot 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.

[0044] 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.

[0045] 8) Dilute the CdSe quantum dot 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 a structural diagram of a composite light-emitting layer of single CdSe quantum dots, PbS quantum dots, CdSe / PbS / CdSe heterojunction quantum wells, and stacked heterojunction quantum wells; where 1 is a single CdSe quantum dot in the depletion region, 2 is a single CdSe quantum dot, 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 CdSe quantum dot material, 7 is the contact depletion region of the CdSe quantum dot, 8 is the CdSe quantum dot 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.

[0046] 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.

[0047] 10) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer. Figure 2 It is a structural diagram of an LED of CdSe / PbS / CdSe 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 CdSe / PbS / CdSe quantum dot 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.

[0048] Example 3 1) Place the ITO glass in a beaker, and successively pour in acetone solution, isopropanol solution, and deionized water solution, and ultrasonically clean each for 15 min. Take it out, dry it with nitrogen at 60 °C, and place it in a clean and dry petri dish.

[0049] 2) After filtering the PEDOT:PSS solution with a 0.22 μm filter head, spin-coat it on the ITO glass with 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. Then place the glass slide on a heating table and anneal it at 100 °C for 20 min.

[0050] 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 with a spin coater at a low speed of 500 rpm / s for 5 s and 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.

[0051] 4) Preparation of CdSe quantum dots: Add 0.084 g of selenium powder and 2 ml of TOP solution to a three-necked flask, stir and dissolve at 120 °C to prepare a selenium precursor solution; stir 0.0182 g of cadmium oxide and 5 ml of oleic acid at 120 °C for 30 min, then inject 15 ml of ODE solution, and raise the solution temperature to 270 °C; take the selenium precursor solution, and quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 270 °C and keep it for 8 min. At the same time, use an ultraviolet lamp to excite at 2 min; 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, the ratio of the quantum dot supernatant to methanol is 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 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.

[0052] 5) Preparation of PbS quantum dots: Add 0.4 mmol of lead oxide, 1.0 ml of oleic acid and 8 ml of octadecene into a three-necked flask, stir at 120 °C for 5 min, and 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 trioctylphosphine, 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, keep it for 8 min; 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 the 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, and then dissolve the quantum dots in 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.

[0053] 6) Dilute the CdSe quantum dot 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 with a spin coater, and then place the above glass slide on a heating table and anneal it at 60 °C for 10 min.

[0054] 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 with a spin coater, and then place the above glass slide on a heating table and anneal it at 60 °C for 10 min.

[0055] 8) Dilute the CdSe quantum dot 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 with a spin coater, and then place the above glass slide on a heating table and anneal it at 60 °C for 10 min. Figure 1 It is the structural diagram of a single CdSe quantum dot, a PbS quantum dot, and their CdSe / PbS / CdSe heterojunction quantum well and stacked heterojunction quantum well composite light-emitting layers; where 1 is a single CdSe quantum dot in the depletion region, 2 is a single CdSe quantum dot, 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 CdSe quantum dot material, 7 is the contact depletion region of the CdSe quantum dot, 8 is a CdSe quantum dot at a non-interface position, 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 a PbS quantum dot at a non-interface position.

[0056] 9) Take Zn with a concentration of 15 mg / ml 0.85 Mg0.15 The O solution was spin-coated at a low speed of 500 rpm / s for 5 s and then at a high speed of 1000 rpm / s for 40 s using a spin coater. Then, the glass slide was placed on a heating stage and annealed at 100 °C for 10 min.

[0057] 10) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a CdSe / PbS / CdSe stacked heterojunction quantum well material; where 12 is the silver electrode, 13 is Zn 0.85 Mg 0.15 O electron transport layer, 14 is the CdSe / PbS / CdSe quantum dot 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.

[0058] 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 covered by the present invention.

Claims

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

2. The QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer according to claim 1, wherein: The inorganic electron transport layer is a Zn 0.85 Mg 0.15 O electron transport layer.

3. The QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum 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 preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer as described in any one of claims 1-3, characterized in that: It includes the following steps: Step (1): Clean the ITO conductive glass with deionized water, acetone, and isopropanol for 15 - 25 min respectively, and dry it with nitrogen. Step (2): Spin-coat the PEDOT:PSS solution on the ITO conductive glass obtained in step (1) in a glove box using a spin coater, and then put the conductive glass sheet on a heating table for annealing. Step (3): Dissolve TFB in toluene solution, and then spin-coat the solution on the conductive glass sheet obtained in step (2) in a glove box using a spin coater, and then put the conductive glass sheet on a heating table for annealing. Step (4): Spin-coat the CdSe quantum dot solution on the conductive glass sample obtained in step (3) in a glove box using a spin coater, and then put 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 put the conductive glass sample on a heating table for annealing. Step (6): Spin-coat the CdSe quantum dot solution on the conductive glass sample obtained in step (5) in a glove box using a spin coater, and then put the conductive glass sample on a heating table for annealing. Step (7) In the glove box, Zn 0.85 Mg 0.15 The solution is spin-coated on the conductive glass sample of step (6) using a spin coater, and then the conductive glass sheet is placed on a heating stage for annealing; Step (8): Evaporate the electrode on the conductive glass sample obtained in step (7) using a thermal evaporator, and then a QWLED based on the CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer is obtained.

5. The preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum 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 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.

6. The preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer according to claim 4, characterized in that: The concentration of the TFB solution described in step (3) 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.

7. The preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer according to claim 4, characterized in that, The specific method for preparing CdSe quantum dots in steps (4) and (6) is as follows: Step S71: Stir and dissolve selenium powder and TOP solution at a set temperature to prepare a selenium precursor solution; stir cadmium oxide and oleic acid at a set temperature for a set time, then inject a small amount of ODE solution, and raise the solution temperature. Take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the solution temperature reaches the set value and keep it for the set time, and at the same time use an ultraviolet lamp for excitation; 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 S72: Take out the supernatant of the quantum dot solution after standing still for a part. Dissolve oleic acid with an appropriate amount of methanol, 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. Finally, dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

8. The preparation method of the QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer according to claim 4, characterized in that, The specific method for preparing PbS quantum dots in the said step (5) 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 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 and take out the upper layer solution. Add an appropriate amount of absolute ethanol for centrifugation. Finally, dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

9. The preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum well composite light-emitting layer according to claim 7, characterized in that, In the selenium precursor solution, the mass of selenium powder is 0.084 g - 0.128 g, and the stirring temperature is 120 - 150 °C; the mass of cadmium oxide is 0.0182 g - 0.0257 g, the stirring temperature is 120 - 150 °C, when the stirring time reaches 30 min, inject the ODE solution, and at the same time raise the temperature to 270 - 300 °C, quickly inject the selenium precursor solution, and keep it for 8 - 10 min. Excite it with an ultraviolet lamp at 2 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 revolutions for 5 - 10 min, and then dissolve the quantum dots with n-hexane and repeat the above cleaning process twice.

10. The preparation method of a QWLED with a CdSe / PbS / CdSe stacked heterojunction quantum 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, raise the temperature 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, inject it into the lead precursor three-necked flask at a speed of 1.0 - 2.0 ml / h, and keep it for 8 - 10 min; in the said 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 revolutions for 5 - 10 min, and then dissolve the quantum dots with n-hexane and repeat the above cleaning process twice.

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