QWLED with CdZnS / PbS / CdZnS laminated deep trap composite light-emitting layer and preparation method of QWLED

Abstract

The invention discloses a QWLED (Quantum White Light Emitting Diode) with a CdZnS / PbS / CdZnS laminated deep well composite light emitting layer and a preparation method thereof, PbS quantum dots and CdZnS quantum dots are respectively prepared by using a thermal injection method, the two quantum dot solutions are respectively and sequentially spin-coated to form a film, and finally a CdZnS / PbS / CdZnS laminated heterojunction material compound with a parallel interface laminated depletion region and a laminated heterojunction deep quantum well structure is formed. The invention also discloses a preparation method of the LED with the laminated depletion region and the laminated heterojunction deep quantum well structure, the laminated depletion region and the laminated heterojunction deep quantum well structure are novel, and the device structure is stable and efficient. The prepared CdZnS / PbS / CdZnS laminated heterojunction deep-well composite material has a laminated depletion region with a parallel interface, a laminated heterojunction structure, a deep quantum well characteristic, high quantum efficiency, good optical characteristic and structural stability, and the prepared LED device with the laminated depletion region and the laminated heterojunction deep-quantum well structure has excellent electroluminescent efficiency and external quantum efficiency. 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 field of materials science and technology, in particular to a QWLED with a CdZnS / PbS / CdZnS stacked deep 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 to 100 nm, 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 considered 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 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, a stacked composite material can be formed by combining lead sulfide quantum dots with other quantum dots to regulate 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, as well as a preparation method thereof: 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, an organolead precursor doped with transition metal ions is synthesized, and a colloidal quantum dot stock solution of lead sulfide doped with transition metals is obtained by a thermal injection method. 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 a preparation method thereof: a ZnS / PbS / ZnS quantum well is synthesized by a water-phase synthesis method, which can emit green light under light excitation 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, a preparation method thereof, and an application thereof: 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 properties 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 exciton 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 effects 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, most of the lead sulfide quantum dot materials and devices mentioned in the literature 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, the composite of CdZnS quantum dots and PbS quantum dots is used to form a stacked heterojunction deep well structure. The design and preparation have a relatively simple process, and the prepared CdZnS / PbS / CdZnS quantum dot stacked heterojunction has a stacked heterojunction depletion region parallel to the light-emitting layer and a deep quantum well structure 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 with a CdZnS / PbS / CdZnS stacked deep well composite light-emitting layer and its preparation method. The present invention uses the thermal injection method to separately prepare PbS quantum dots and CdZnS quantum dots, and further spin-coats the two quantum dot solutions in sequence to form a CdZnS / PbS / CdZnS quantum dot stacked material composite with a stacked depletion region and a stacked heterojunction deep quantum well structure at the interface, and demonstrates a preparation method for a stacked heterojunction deep quantum well LED. The stacked heterojunction deep quantum well structure is novel, the device structure is stable and efficient, the prepared CdZnS / PbS / CdZnS stacked heterojunction deep quantum well material has a stacked heterojunction deep quantum well structure, high quantum efficiency, good optical characteristics, and structural stability. The prepared stacked heterojunction deep quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in fields such as 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 CdZnS / PbS / CdZnS stacked deep well composite light-emitting layer, which 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 bottom to top. The stacked heterojunction deep quantum well light-emitting layer is formed by CdZnS / PbS / CdZnS quantum dot materials to form a composite light-emitting layer with a stacked heterojunction deep 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 CdZnS / PbS / CdZnS stacked deep 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 CdZnS 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 CdZnS 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) vapor-deposits electrodes on the conductive glass wafer obtained in step (7), and thus a QWLED based on a CdZnS / PbS / CdZnS stacked deep well composite light-emitting layer is obtained.

[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 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.

[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 condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 15 - 30 min.

[0012] In a preferred embodiment, the specific methods for preparing CdZnS quantum dots in steps (4) and (6) are as follows: Step S71: Dissolve sulfur powder and TOP solution by stirring at a set temperature to prepare a sulfur precursor solution; stir cadmium oxide, zinc acetate, 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 sulfur precursor solution, quickly inject it into the cadmium-zinc solution when the solution temperature reaches the set value and maintain for a set time, and simultaneously excite it with an ultraviolet lamp; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane, obtain a quantum dot solution, and store it under low-temperature conditions; Step S72: Take out a part of the supernatant 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 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, and finally quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane, obtain a quantum dot solution, and store it under low-temperature conditions; Step S82: Take out a part of the supernatant of the quantum dot solution after standing, dissolve it with an appropriate amount of ethanol, then add an appropriate amount of n-hexane solution and take out the upper layer solution, add an appropriate amount of absolute ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

[0014] In a preferred embodiment, in the sulfur precursor solution, the amount of sulfur powder is 0.5 - 1 mmol, TOP is 1 - 3 ml, the stirring temperature is 40 - 80 °C, and the stirring time is 10 - 30 minutes to obtain the sulfur precursor solution; in the cadmium zinc precursor solution, the amount of cadmium oxide is 0.3 - 0.5 mmol, the amount of zinc acetate is 2 - 5 mmol, the amount of oleic acid is 4 - 8 ml, the amount of ODE is 10 - 20 ml. After degassing for 30 minutes under nitrogen at 120 - 160 °C, and then stirring under vacuum for 2 hours to obtain a transparent cadmium zinc precursor solution, and then introducing nitrogen and raising the temperature to 290 - 310 °C; subsequently, quickly injecting the sulfur precursor solution into the cadmium zinc precursor solution, maintaining for 8 - 10 min, and exciting 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 excess of absolute ethanol and centrifuge at 6000 - 8000 rpm for 5 - 10 min, and then dissolve the quantum dots with n - hexane, repeating the above cleaning process twice.

[0015] In a preferred embodiment, in the lead precursor solution, the amount of lead oxide is 0.4 - 0.6 mmol, the amount of oleic acid is 1.0 - 1.2 ml, the amount of 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; in the sulfur precursor solution, the amount of sulfur powder is 0.50 - 0.75 mmol, the amount of tri - n - octylphosphine 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 rate of 1.0 - 2.0 ml / h, maintaining for 8 - 10 min; in the quantum dot cleaning, the ratio of the quantum dot supernatant to methanol is 2:1 - 1:1. Dissolve the precipitate in n - hexane, extract the upper layer solution, add an excess of absolute ethanol and centrifuge at 6000 - 8000 rpm for 5 - 10 min, and then dissolve the quantum dots with n - hexane, repeating the above cleaning process twice.

[0016] In a preferred embodiment, the concentration of the finally prepared CdZnS 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 CdZnS 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 the oxygen and water are both 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 CdZnS quantum dots and PbS quantum dots in a stacked composite to form a composite light-emitting layer with a stacked deep quantum well heterojunction structure, an LED device including an electrode, an inorganic electron transport layer, a stacked heterojunction deep quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate is prepared. 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 deep 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 CdZnS quantum dots, a stable stacked heterojunction deep quantum well structure is formed. In view of the band bending at the heterojunction interface and the existence of the depletion region, the effective recombination of electrons and holes is significantly promoted, and a higher overlap of electron and hole wave functions is achieved in terms of material properties. The coverage of CdZnS 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 deep quantum well heterojunction. The material and device preparation process of the present invention is simple and reliable, and the components of the light-emitting layer are easy to adjust. The stacked deep quantum well heterojunction 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 deep quantum well materials and devices.

[0023] The present invention can make full use of the excellent energy band regulation ability of the stacked heterojunction deep quantum well material in stacked deep quantum well light emission, prepare a stacked heterojunction deep quantum well material with PbS quantum dots as the well region, further design and optimize the device structure, and optimize the electro-optical performance of the device; obtain a preparation method of a QWLED with a high external quantum efficiency and high light emission intensity using a CdZnS / PbS / CdZnS quantum dot stacked heterojunction deep quantum well composite material as the light-emitting layer. Description of the Drawings

[0024] Figure 1 It is a structural diagram of a composite light-emitting layer of a single CdZnS quantum dot, a PbS quantum dot, and a CdZnS / PbS / CdZnS heterojunction quantum well and a stacked heterojunction quantum well; Figure 2 It is a structural diagram of an LED of a CdZnS / PbS / CdZnS stacked heterojunction quantum well material; Note: Among them, 1 is a single CdZnS quantum dot in the depletion region, 2 is a single CdZnS 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 CdZnS quantum dot material, 7 is the contact depletion region of the CdZnS quantum dot, 8 is the CdZnS 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, 11 is the PbS quantum dot at a non-interface position, 12 is the silver electrode, 13 is the Zn0.85Mg0.15O electron transport layer, 14 is the CdZnS / PbS / CdZnS 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. 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 form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] Example 1 1) Put the ITO glass into 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 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 stage and anneal it at 120 °C for 30 min.

[0030] 3) Take 10 mg of TFB and 1 ml of toluene solution. Dissolve TFB in toluene to prepare a solution with a concentration of 10 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 stage and anneal it at 200 °C for 30 min.

[0031] 4) Preparation of CdZnS quantum dots: Add 1 mmol of sulfur powder and 3 ml of TOP solution to a three-necked flask, stir at 80 °C for 30 minutes to dissolve it, and prepare a sulfur precursor solution; stir 0.5 mmol of cadmium oxide, 5 mmol of zinc acetate and 8 ml of oleic acid at 150 °C for 30 min, then inject 20 ml of ODE solution, degas under nitrogen at 160 °C for 30 minutes, and stir under vacuum for 2 hours to obtain a transparent cadmium zinc precursor solution. Then introduce nitrogen and raise the temperature to 310 °C; take the selenium precursor solution, quickly inject it into the cadmium zinc precursor solution when the temperature of the cadmium zinc precursor solution reaches 310 °C and keep it for 10 min. At the same time, use an ultraviolet lamp to excite it 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 in 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 into a three-necked flask, stir at 150 °C for 10 min, and then raise the temperature to 300 °C after dissolution to prepare a lead precursor solution; Take 0.75 mmol of sulfur powder and 1.70 ml of trioctylphosphine, stir at 150 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a rate of 2.0 ml / h. After injection, keep it for 10 min; Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; Then take the quantum dot solution, 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, and then dissolve the quantum dots with n-hexane. Repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 30 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0033] 6) Dilute the CdZnS quantum dot colloidal solution with n-octane to 30 mg / ml, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s, and then place the above glass slide on a heating table 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 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, and then place the above glass slide on a heating table and anneal it at 90 °C for 30 min.

[0035] 8) Dilute the CdZnS quantum dot colloidal solution with n-octane to 30 mg / ml, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s, and then place the above glass slide on a heating table and anneal it at 90 °C for 30 min. Figure 1 It is the structural diagram of a single CdZnS quantum dot, a PbS quantum dot, and their CdZnS / PbS / CdZnS heterojunction quantum well and stacked heterojunction quantum well composite light-emitting layer; where 1 is a single CdZnS quantum dot in the depletion region, 2 is a single CdZnS 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 CdZnS quantum dot material, 7 is the contact depletion region of the CdZnS quantum dot, 8 is the CdZnS 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.

[0036] 9) Take Zn with a concentration of 25 mg / ml 0.85Mg 0.15 The MgO solution was spin-coated 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 the glass slide was placed on a heating stage and annealed at 120 °C for 20 min.

[0037] 10) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a CdZnS / PbS / CdZnS stacked deep well composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a CdZnS / PbS / CdZnS 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 CdZnS / PbS / CdZnS 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 and sequentially pour in acetone solution, isopropyl alcohol solution, and deionized water solution, 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 a high speed of 3000 rpm / s for 40 s using a spin coater, and then place the glass slide on a heating stage and anneal it at 110 °C for 25 min.

[0040] 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 a high speed of 2000 rpm / s for 40 s using a spin coater, and then place the glass slide on a heating stage and anneal it at 180 °C for 20 min.

[0041] 4) Preparation of CdZnS quantum dots: Add 0.7 mmol of sulfur powder and 2 ml of TOP solution into a three-necked flask, stir at 60 °C for 20 minutes to dissolve it, and prepare a sulfur precursor solution; Add 0.4 mmol of cadmium oxide, 4 mmol of zinc acetate and 6 ml of oleic acid, stir at 140 °C for 30 min, then inject 15 ml of ODE solution, degas under nitrogen at 160 °C for 30 minutes, and stir under vacuum for 2 hours to obtain a transparent cadmium zinc precursor solution. Subsequently, introduce nitrogen and raise the temperature to 310 °C; Take the selenium precursor solution, quickly inject it into the cadmium zinc precursor solution when the temperature of the cadmium zinc precursor solution reaches 300 °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 means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; Subsequently, 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 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.

[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 into 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 trioctylphosphine, stir at 135 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a speed of 1.5 ml / h, and keep it for 9 min after injection; 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, the ratio of the quantum dot supernatant to methanol is 1.5:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excess of absolute ethanol and centrifuge at 7000 rpm for 7 min. Then dissolve the quantum dots in n-hexane, repeat the above washing process twice, dissolve the quantum dots in n-hexane to form a 20 mg / ml quantum dot solution, and store it under low temperature conditions.

[0043] 6) Dilute the CdZnS quantum dot colloidal solution with n-octane to 20 mg / ml, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s. Then place the above glass slide on a heating table and anneal 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 slides on a heating table and anneal them at 75 °C for 20 min.

[0045] 8) Dilute the CdZnS 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 slides on a heating table and anneal them at 75 °C for 20 min. Figure 1 It is the structural diagram of the composite light-emitting layer of single CdZnS quantum dots, PbS quantum dots, their CdZnS / PbS / CdZnS heterojunction quantum wells, and stacked heterojunction quantum wells; where 1 is a single CdZnS quantum dot in the depletion region, 2 is a single CdZnS quantum dot, 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 CdZnS quantum dot material, 7 is the contact depletion region of the CdZnS quantum dot, 8 is the CdZnS 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.

[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 slides in a heating table and anneal them at 110 °C for 15 min.

[0047] 10) Thermally evaporate a 100 nm silver electrode to obtain a QWLED with a CdZnS / PbS / CdZnS stacked deep well composite light-emitting layer. Figure 2 It is the structural diagram of the LED of the CdZnS / PbS / CdZnS 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 CdZnS / PbS / CdZnS 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, pour 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 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 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 stage 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 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 stage and anneal it at 160 °C for 15 min.

[0051] 4) Preparation of CdZnS quantum dots: Add 0.5 mmol of sulfur powder and 1 ml of TOP solution to a three-necked flask, stir at 40 °C for 10 minutes to dissolve it, and prepare a sulfur precursor solution; stir 0.3 mmol of cadmium oxide, 2 mmol of zinc acetate, and 4 ml of oleic acid at 120 °C for 30 min, then inject 10 ml of ODE solution, degas under nitrogen at 120 °C for 30 minutes, and stir under vacuum for 2 hours to obtain a transparent cadmium-zinc precursor solution. Then introduce nitrogen and raise the temperature to 290 °C; take the sulfur precursor solution and quickly inject it into the cadmium-zinc precursor solution when the temperature of the cadmium-zinc precursor solution reaches 290 °C and maintain it for 8 min. At the same time, use an ultraviolet lamp for excitation at 2 min; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, with the ratio of the quantum dot supernatant to methanol being 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.

[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 then raise the temperature to 270 °C after dissolution to prepare a lead precursor solution; Take 0.50 mmol of sulfur powder and 1.40 ml of 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 means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; Then take the quantum dot solution, with the ratio of the quantum dot supernatant to methanol being 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.

[0053] 6) Dilute the CdZnS quantum dot colloidal solution to 10 mg / ml with n-octane, 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. 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 to 10 mg / ml solution with n-octane, 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. Then place the above glass slide on a heating table and anneal it at 60 °C for 10 min.

[0055] 8) Dilute the CdZnS quantum dot colloidal solution to 10 mg / ml with n-octane, 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. 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 CdZnS quantum dot, PbS quantum dot, CdZnS / PbS / CdZnS heterojunction quantum well and its stacked heterojunction quantum well composite light-emitting layer; where 1 is a single CdZnS quantum dot in the depletion region, 2 is a single CdZnS quantum dot, 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 CdZnS quantum dot material, 7 is the contact depletion region of the CdZnS quantum dot, 8 is the CdZnS 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 the 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 CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer. Figure 2 It is a structural diagram of an LED with a CdZnS / PbS / CdZnS 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 CdZnS / PbS / CdZnS 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 of the present invention.

Claims

1. A QWLED with a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer, characterized in that: From bottom to top, it includes electrodes, inorganic electron transport layers, laminated heterojunction deep quantum well light-emitting layers, organic hole transport layers and ITO glass substrates, wherein the laminated heterojunction deep quantum well light-emitting layers are formed by CdZnS / PbS / CdZnS quantum dot materials to form a composite light-emitting layer with a laminated heterojunction deep quantum well structure.

2. The QWLED of CdZnS / PbS / CdZnS stacked deep well composite light emitting layer according to claim 1, characterized in that: The inorganic electron transport layer is Zn 0.85 Mg 0.15 O electron transport layer.

3. The QWLED of CdZnS / PbS / CdZnS stacked deep well composite light emitting layer according to claim 1, characterized in that: The organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

4. A method for preparing a QWLED having a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Step (1) cleaning the ITO conductive glass with deionized water, acetone, and isopropanol for 15-25 minutes respectively, and drying with nitrogen; Step (2) Spin-coating the PEDOT:PSS solution on the ITO conductive glass in step (1) using a spin coater in a glove box, and then placing the conductive glass sheet on a heating table for annealing; Step (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; Step (4) Spin-coating the CdZnS quantum dot solution on the conductive glass sample in step (3) using a spin coater in a glove box, and then placing the conductive glass sample on a heating table for annealing; Step (5) Spin-coating the PbS quantum dot solution on the conductive glass sample in step (4) using a spin coater in a glove box, and then placing the conductive glass sample on a heating table for annealing; Step (6) Spin-coating the CdZnS quantum dot solution on the conductive glass sample in step (5) using a spin coater in a glove box, and then placing the conductive glass sample on a heating table for annealing; Step (7) In a glove box, Zn 0.85 Mg 0.15 The O solution is spin-coated on the conductive glass sample in step (6) by a spin coater, and then the conductive glass sample is placed on a heating table for annealing; Step (8) The conductive glass sample obtained in step (7) is subjected to electrode deposition using a thermal evaporator, thereby obtaining a QWLED based on a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer.

5. The method for preparing a QWLED with a CdZnS / PbS / CdZnS stacked deep-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 method for preparing a QWLED with a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer according to claim 4, characterized in that: The concentration of the TFB solution in step (3) is 8-10 mg / ml, the annealing temperature is 160-200° C., the environmental condition is a glove box with a nitrogen atmosphere in which both oxygen and water are less than 1 ppm, and the annealing time is 15-30 min.

7. The method for preparing a QWLED with a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer according to claim 4, characterized in that: The specific method for preparing CdZnS quantum dots in step (4) and step (6) is: Step S71: stirring and dissolving sulfur powder and TOP solution at a set temperature to prepare a sulfur precursor solution; stirring cadmium oxide, zinc acetate and oleic acid at a set temperature for a set time, then injecting a small amount of ODE solution, and raising the solution temperature; taking the sulfur precursor solution, when the solution temperature reaches a set value, quickly injecting it into the cadmium zinc solution and maintaining it for a set time, while using an ultraviolet lamp for excitation; finally, quickly cooling the quantum dot solution by means of a water bath, diluting it with n-hexane, obtaining a quantum dot solution, and storing it under low temperature conditions; Step S72: Take out part of the supernatant of the quantum dot solution after standing, use an appropriate amount of methanol to dissolve oleic acid, then add an appropriate amount of n-hexane solution to dissolve and take out the upper solution, add an appropriate amount of anhydrous ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

8. The method for preparing a QWLED with a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer according to claim 4, characterized in that: The specific method for preparing PbS quantum dots in step (5) is: Step S81: dissolving lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolving sulfur powder in tri-n-octylphosphine and injecting it into a three-necked flask, and finally rapidly cooling the quantum dot solution in a water bath, diluting it with n-hexane to obtain a quantum dot solution, and storing it under low temperature conditions; Step S82: Take out part of the supernatant of the quantum dot solution after standing, dissolve it with an appropriate amount of ethanol, then add an appropriate amount of n-hexane solution to dissolve and take out the upper solution, add an appropriate amount of anhydrous ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified quantum dot solution.

9. The method for preparing a QWLED of a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer according to claim 7, characterized in that: In the sulfur precursor solution, sulfur powder is 0.5-1mmol, TOP is 1-3ml, the stirring temperature is 40-80℃, and the stirring time is 10-30 minutes to obtain a sulfur precursor solution; in the cadmium zinc precursor solution, cadmium oxide is 0.3-0.5mmol, zinc acetate is 2-5mmol, oleic acid is 4-8ml, ODE is 10-20ml, degassing under nitrogen at 120-160℃ for 30 minutes, and stirring under vacuum for 2 hours to obtain a transparent cadmium zinc precursor solution, then nitrogen is introduced, and the temperature is raised to 290-310℃; then, the sulfur precursor solution is quickly injected into the cadmium zinc precursor solution, and the holding time is 8-10 min, and ultraviolet light is used for excitation at 2min; in the quantum dot cleaning, the ratio of quantum dot supernatant to methanol is 2:1-1:1, the precipitate is dissolved in n-hexane, the upper solution is extracted, excess anhydrous ethanol is added and centrifuged at 6000-8000 rpm for 5-10min, and then n-hexane is used to dissolve the quantum dots, and the above cleaning process is repeated twice.

10. The method for preparing a QWLED of a CdZnS / PbS / CdZnS stacked deep-well composite light-emitting layer according to claim 8, characterized in that: In the lead precursor solution, the mass of lead oxide is 0.4-0.6mmol, oleic acid is 1.0-1.2ml, octadecene is 8-10ml, the stirring temperature is 120-150°C, the stirring time is 5-10min, and the temperature rises to 270-300°C after dissolution; in the sulfur precursor solution, the mass of sulfur powder is 0.50-0.75mmol, tri-n-octylphosphine is 1.40-1.70ml, 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 retention time is 8-10min; in the quantum dot cleaning, the ratio of quantum dot supernatant to methanol is 2:1-1:1, the precipitate is dissolved in n-hexane, the upper solution is extracted, excess anhydrous ethanol is added and centrifuged at 6000-8000 rpm for 5-10min, and then n-hexane is used to dissolve the quantum dots, and the above cleaning process is repeated twice.

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