A compact and ordered cadmium selenide quantum well film and a method for preparing an electroluminescent diode

Abstract

The application relates to a compact and ordered cadmium selenide quantum well film and a method for preparing an electroluminescent diode, and belongs to the field of semiconductor light emission, display and nanotechnology. The application develops a method for obtaining a compact and ordered colloidal quantum well film by using a film preparation technology of two-phase solution repulsion mechanism. The colloidal quantum well is placed into an ethylene glycol solution, then a transparent conductive substrate with a hole injection layer and a transmission layer is immersed into the ethylene glycol solution, and the colloidal quantum well is transferred to the transparent conductive substrate. Subsequently, an electron transmission layer is spin-coated, and an electrode is deposited to obtain a quantum well light emitting diode. The compact and ordered quantum well film of the application significantly improves the charge transmission performance of the quantum well film, improves the light emission coupling efficiency of the quantum well, and the external quantum efficiency is more than 25%, the brightness is more than 50,000 nit, and the application shows great development potential in the field of a new generation of light emission and display.

Description

Technical Field

[0001] This invention belongs to the fields of nanotechnology and light-emitting display, specifically relating to a method for preparing an ordered dense thin film of cadmium selenide quantum well and its electroluminescent diode, which belongs to the fields of semiconductor light emission, display and nanotechnology. Background Technology

[0002] Colloidal quantum wells refer to colloidal semiconductor nanosheets with a one-dimensional strong quantum confinement effect. Their surfaces are linked with organic ligands, exhibiting a monodisperse distribution characteristic and excellent optical properties, such as extremely narrow spectral emission, high fluorescence quantum yield, and excellent light-emitting coupling performance. They have broad application and development prospects in novel light-emitting, display, and detection fields.

[0003] Research on colloidal quantum wells originated in the 1990s. With the development of nanotechnology, researchers discovered the potential applications of these quantum wells in optoelectronic devices. Particularly in photoelectric conversion and optical signal processing, colloidal quantum wells have become a research hotspot due to their superior optical properties and simple synthesis methods. In the 21st century, with in-depth research into their applications in light-emitting diodes, solar cells, and lasers, related technologies have gradually matured, and market demand has grown accordingly.

[0004] Cadmium chalcogenide materials (such as CdSe and CdS) possess excellent optical and electronic properties, including high light absorption coefficients, large exciton binding energies, and superior luminescence characteristics. These materials can produce strong fluorescence in the visible light region, and their size and shape can be precisely controlled through synthesis methods, thereby enabling the tuning of optical properties. Furthermore, cadmium chalcogenide materials exhibit good carrier mobility in semiconductor applications, making them promising for use in devices such as light-emitting diodes (LEDs) and photodetectors. CdSe quantum wells, as important colloidal quantum well materials, demonstrate strong competitiveness in display technology and sensors due to their excellent optoelectronic properties and ease of synthesis. In addition, surface modification techniques for cadmium chalcogenide materials have provided new avenues for improving their stability and biocompatibility, expanding their application range.

[0005] In recent years, light-emitting diode (LED) technology based on colloidal quantum wells has developed rapidly. These devices exhibit excellent luminous efficiency and color purity, and are widely used in display technology and lighting. However, current technology still faces some challenges, such as: 1. Insufficient densification: The arrangement and density of colloidal quantum wells in devices are often insufficient, leading to a decrease in photoluminescence efficiency. Low density may cause light propagation loss and non-radiative recombination, thus affecting the overall performance of the device. 2. Material disorder: During the synthesis and processing of colloidal quantum wells, crystal structure disorder often occurs. This disorder may lead to a decrease in carrier mobility, thus affecting current injection efficiency and light emission efficiency, resulting in unstable device performance. 3. Limitations of spin coating: Although spin coating is a commonly used process for preparing colloidal quantum well LEDs, it has certain limitations in large-area fabrication. The spin coating process makes it difficult to ensure the consistency and uniformity of the thin film, affecting the overall performance of the device. In addition, the spin coating process has high requirements for the substrate, limiting its application scenarios. IV. Interface Defects and Recombination Centers: In quantum well structures, interface defects and inhomogeneities can form recombination centers, leading to increased carrier recombination losses and consequently affecting luminescence efficiency. These defects are often caused by improper material synthesis, surface modification, or device construction. V. Stability and Durability: Colloidal quantum wells typically exhibit poor chemical and photostability. Under prolonged light exposure or thermal stress, they are prone to photodegradation or structural changes, resulting in decreased luminescence performance. This places higher demands on the reliability of devices in practical applications. VI. Economic Efficiency and Scalability: Although there are various methods for synthesizing colloidal quantum wells, large-scale production is costly and difficult to meet commercialization needs. Finding low-cost, high-efficiency synthesis methods and optimizing production processes are crucial for promoting the commercialization of this technology. Therefore, research and improvements addressing these issues are particularly important. Summary of the Invention

[0006] The efficiency of cadmium selenide (CdSe) quantum well (QL) light-emitting diodes (LEDs) lags behind that of traditional quantum dot (QD) LEDs. Due to the uncontrollable high external coupling factor of the quantum well, this invention presents a method for synthesizing CdSe quantum wells and fabricating densely ordered CdSe quantum well LEDs. The method of designing ordered quantum wells facilitates the realization of high-performance LEDs and large-scale production. The unique ordered quantum wells significantly improve light-emitting coupling, thereby obtaining LEDs with high external quantum efficiency and good stability.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing a dense and ordered cadmium selenide quantum well thin film specifically includes the following steps:

[0009] (1) Dissolve sodium tetradecanoate and cadmium nitrate tetrahydrate separately in the first solvent. After they are completely dissolved, mix them to form cadmium tetradecanoate. Filter, wash with the first solvent, and dry for later use.

[0010] (2) Cadmium selenide quantum well core: Mix 0.2-1.6 mmol cadmium tetradecanoate and 0.1-0.8 mmol selenium powder with a solvent, heat to 140-200 degrees Celsius in an inert gas atmosphere, inject cadmium acetate dihydrate, then heat to 200-260 degrees Celsius and keep warm for 5-20 minutes, inject 0.2-1 mL oleic acid, cool down, wash the quantum well with a mixed solution of n-hexane and ethanol, redisperse with a second solvent to form a cadmium selenide quantum well core solution.

[0011] (3) Core-shell structure cadmium selenide / cadmium zinc sulfur: Add 0.1~0.3 mmol of anhydrous cadmium acetate, 0.3~0.9 mmol of anhydrous zinc acetate, 0.5~1.5 mL of oleic acid and 0.2~1 mL of 1-octadecene to the above cadmium selenide quantum well solution. Under an inert gas atmosphere, heat to 70~100 degrees Celsius and keep warm for 0.2~1 hours. Inject 0.2~1 mL of oleylamine and heat to 280~320 degrees Celsius. When the temperature reaches 120~180 degrees Celsius, start injecting octyl mercaptan. Keep warm at 280~320 degrees Celsius for 0.5~1.5 hours and then cool down.

[0012] (4) Wash the cadmium selenide core-shell quantum well with a mixed solution of the second solvent and the first solvent, and redisperse it with the second solvent to form a core-shell structured cadmium selenide / cadmium zinc sulfur quantum well solution; the first solvent is methanol and ethanol, and the second solvent is n-octane, n-hexane or chloroform.

[0013] (5) Prepare a colloidal cadmium selenide quantum well solution with a concentration of 10~50 mg / mL using the above solution;

[0014] (6) Under nitrogen protection and at a temperature of 10-30 degrees Celsius, add the colloidal cadmium selenide quantum trap chloroform solution dropwise to the ethylene glycol solution until the quantum traps cover the surface of the ethylene glycol solution, and then add 1%-10% of tri-n-octylamine by volume of the ethylene glycol solution.

[0015] (7) After standing for 1 to 15 minutes, a dense and ordered cadmium selenide quantum well film is obtained.

[0016] A dense, ordered cadmium selenide quantum well thin film and its electroluminescent diode fabrication method are described below:

[0017] (1) Hole injection material is printed on a transparent conductive substrate to form a hole injection layer with a thickness of 30-70 nanometers, and annealed at 80-140 degrees Celsius for 10-30 minutes. Subsequently, hole transport material is printed on the hole injection layer to form a hole transport layer with a thickness of 30-70 nanometers, and annealed at 100-150 degrees Celsius for 10-30 minutes.

[0018] (2) The dense and ordered quantum well film prepared above is transferred onto the hole transport layer to form an ordered quantum well light-emitting layer with a thickness of 5-20 nanometers, and annealed at 40-90 degrees Celsius for 10-30 minutes.

[0019] (3) Spin-coat a zinc oxide or magnesium-doped zinc oxide ethanol solution with a concentration of 20-50 mg / mL onto the quantum well layer to form an electron transport layer with a thickness of 30-60 nm, and anneal at 60-90 degrees Celsius for 10-30 minutes.

[0020] (4) Metal cathode material is deposited on the electron transport layer by vacuum evaporation to form an electrode with a thickness of 70~100 nanometers, thereby obtaining an electroluminescent diode.

[0021] Furthermore, the hole injection material is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid); the hole transport layer material is poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)]. The transparent conductive substrate is indium-doped tin oxide; the metal cathode material is aluminum.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) Ordered quantum well film formation, compared with the traditional spin coating method, the quantum well orientation is more controllable and dense, which is conducive to controllable production.

[0024] (2) Ordered quantum wells can obtain highly externally coupled quantum wells. Controllable and ordered quantum well films can improve external coupling efficiency and reduce leakage current caused by film inhomogeneity.

[0025] (3) Ordered quantum well light-emitting diodes have low current efficiency and high external quantum efficiency (up to 25%), good operational stability, and long service life, meeting the requirements of practical application conditions. Therefore, the technology of this invention is an important breakthrough in the field of quantum well light emission and has broad application prospects. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of a dense, ordered cadmium selenide quantum well.

[0027] Figure 2 This is a schematic diagram of an ordered quantum well.

[0028] Figure 3 These are the external quantum efficiency curves of the electroluminescent diodes in Examples 1-5.

[0029] Figure 4 These are the external quantum efficiency curves of the electroluminescent diodes in Examples 6-10.

[0030] Figure 5 These are the external quantum efficiency curves of the electroluminescent diodes in Examples 11-13. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0032] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0033] A method for preparing a dense and ordered cadmium selenide quantum well thin film includes the following steps:

[0034] (1) Dissolve sodium tetradecanoate and cadmium nitrate tetrahydrate separately in the first solvent. After they are completely dissolved, mix them to form cadmium tetradecanoate. Filter, wash with the first solvent, and dry for later use.

[0035] (2) Cadmium selenide quantum well core: Mix 0.2-1.6 mmol cadmium tetradecanoate and 0.1-0.8 mmol selenium powder with a solvent, heat to 140-200 degrees Celsius in an inert gas atmosphere, inject cadmium acetate dihydrate, then heat to 200-260 degrees Celsius and keep warm for 5-20 minutes, inject 0.2-1 mL oleic acid, cool down, wash the quantum well with a mixed solution of n-hexane and ethanol, redisperse with a second solvent to form a cadmium selenide quantum well core solution.

[0036] (3) Core-shell structure cadmium selenide / cadmium zinc sulfur: Add 0.1~0.3 mmol of anhydrous cadmium acetate, 0.3~0.9 mmol of anhydrous zinc acetate, 0.5~1.5 mL of oleic acid and 0.2~1 mL of 1-octadecene to the above cadmium selenide quantum well solution. Under an inert gas atmosphere, heat to 70~100 degrees Celsius and hold for 0.2~1 hours. Inject 0.2~1 mL of oleylamine, switch to argon gas, heat to 280~320 degrees Celsius, and start injecting octyl mercaptan when the temperature reaches 120~180 degrees Celsius. Hold at 280~320 degrees Celsius for 0.5~1.5 hours and cool down.

[0037] (4) The cadmium selenide core-shell quantum wells are washed with a mixture of the second solvent and the first solvent, and then redispersed with the second solvent to form a core-shell structured cadmium selenide / cadmium zinc sulfur quantum well solution. The first solvent is methanol and ethanol, and the second solvent is n-octane, n-hexane, or chloroform.

[0038] Prepare a cadmium selenide / cadmium zinc sulfur quantum trap solution with a concentration of 10-50 mg / mL;

[0039] (5) Under nitrogen protection and at a temperature of 10-30 degrees Celsius, add cadmium selenide / cadmium zinc sulfur quantum trap solution dropwise onto ethylene glycol solution until the quantum traps cover the surface of ethylene glycol solution, and then add tri-n-octylamine at a volume ratio of 1% to 10% of the total solution.

[0040] (6) After standing for 1 to 15 minutes, a dense and ordered cadmium selenide quantum well film is obtained.

[0041] Example 1

[0042] A method for preparing dense and ordered cadmium selenide quantum well films includes the following steps:

[0043] (1) Dissolve sodium tetradecanoate and cadmium nitrate tetrahydrate separately in methanol solvent. After they are completely dissolved, mix them to form cadmium tetradecanoate. Filter, wash with methanol solvent, and dry for later use.

[0044] (2) Cadmium selenide quantum well core: 0.8 mmol cadmium tetradecanoate and 0.4 mmol selenium powder were mixed with 30 mL 1-octadecene solvent. The mixture was heated to 140 °C in an inert gas atmosphere, and 20 mg / mL cadmium acetate dihydrate methanol solution was injected. The mixture was then heated to 200 °C and kept at that temperature for 10 minutes. 0.5 mL oleic acid was injected, and the mixture was cooled. The quantum well was washed with a mixture of n-hexane and ethanol, and then redispersed with n-hexane solvent to form the cadmium selenide quantum well core solution.

[0045] (3) Core-shell structured cadmium selenide / zinc cadmium sulfur quantum well: Add 0.1 mmol of anhydrous cadmium acetate, 0.3 mmol of anhydrous zinc acetate, 0.5 mL of oleic acid and 0.2 mL of 1-octadecene to the above cadmium selenide quantum well core solution. Under an inert gas atmosphere, heat to 70 degrees Celsius and hold for 1 hour. Inject 0.5 mL of oleylamine, switch to argon gas, heat to 280 degrees Celsius, and when the temperature reaches 160 degrees Celsius, start injecting 0.4 mmol of octyl mercaptan. Hold at 280 degrees Celsius for 1 hour, cool down, and redisperse using chloroform solvent to form cadmium selenide / zinc cadmium sulfur quantum well solution.

[0046] (4) Prepare a colloidal cadmium selenide quantum well chloroform solution with a concentration of 10 mg / mL. Under nitrogen protection and an ambient temperature of 25°C, drop 10 μL of the quantum well solution onto 20 mL of ethylene glycol solution. Use 20 μL of tri-n-octylamine to promote the orderly arrangement of the quantum wells. Wait for 1 minute to form a dense and ordered cadmium selenide quantum well film, and wait for it to be transferred to the substrate.

[0047] A method for fabricating an electroluminescent diode includes the following steps:

[0048] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 80°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 100°C for 15 min. A cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. An electron transport layer was formed by spin-coating 30 mg / mL magnesium-doped zinc oxide onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70 nm thick silver cathode was then deposited on the electron transport layer by vacuum thermal evaporation.

[0049] Example 2

[0050] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 1.

[0051] A method for fabricating an electroluminescent diode includes the following steps:

[0052] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 100°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 8 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 120°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 40°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0053] Example 3

[0054] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 1.

[0055] A method for fabricating an electroluminescent diode includes the following steps:

[0056] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 120°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 10 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 130°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 50°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0057] Example 4

[0058] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 1.

[0059] A method for fabricating an electroluminescent diode includes the following steps:

[0060] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 140°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 12 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 140°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 60°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0061] Example 5

[0062] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 1.

[0063] A method for fabricating an electroluminescent diode includes the following steps:

[0064] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 150°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 14 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 150°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 70°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0065] Table 1. Performance of quantum wells and their electroluminescent LEDs

[0066]

[0067] As can be seen from the table above, the device efficiency decreases as the hole transport layer concentration and annealing temperature increase. The device with a hole transport layer concentration of 10 mg / mL and annealed at 140°C has the highest efficiency, reaching 19%.

[0068] Example 6

[0069] The method for preparing the dense and ordered cadmium selenide quantum well film in Example 1 is adopted, except that step (4) is performed as follows:

[0070] (4) Prepare a colloidal cadmium selenide quantum well chloroform solution with a concentration of 20 mg / mL. Under nitrogen protection and an ambient temperature of 20°C, drop 20 μL of the quantum well solution onto 20 mL of ethylene glycol solution. Use 100 μL of tri-n-octylamine to promote the orderly arrangement of the quantum wells. Wait 3 minutes to form a dense and ordered cadmium selenide quantum well film, and wait for it to be transferred to the substrate.

[0071] A method for fabricating an electroluminescent diode includes the following steps:

[0072] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 80°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 100°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0073] Example 7

[0074] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 6.

[0075] A method for fabricating an electroluminescent diode includes the following steps:

[0076] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 100°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 8 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 120°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0077] Example 8

[0078] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 6.

[0079] A method for fabricating an electroluminescent diode includes the following steps:

[0080] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 120°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 130°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0081] Example 9

[0082] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 6.

[0083] A method for fabricating an electroluminescent diode includes the following steps:

[0084] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 140°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 140°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0085] Example 10

[0086] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 6.

[0087] A method for fabricating an electroluminescent diode includes the following steps:

[0088] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 150°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 150°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0089] Table 2 Performance of quantum wells and their electroluminescent LEDs

[0090]

[0091] As can be seen from the table above, increasing the concentration of the quantum well solution to 20 mg / mL increased the amount of tri-n-octylamine injected, resulting in a more ordered and compact quantum well film for device fabrication. Furthermore, Examples 6-10 show that increasing the hole transport layer concentration and the hole transport layer annealing temperature initially increases and then decreases the device performance. Under the conditions of Example 7, a high external quantum efficiency of 25% was achieved.

[0092] Example 11

[0093] The method for preparing the dense and ordered cadmium selenide quantum well film in Example 1 is adopted, except that step (4) is performed as follows:

[0094] (4) Prepare a colloidal cadmium selenide quantum well chloroform solution with a concentration of 50 mg / mL. Under nitrogen protection and an ambient temperature of 30°C, drop 30 μL of the quantum well solution onto 20 mL of ethylene glycol solution. Use 200 μL of tri-n-octylamine to promote the orderly arrangement of the quantum wells. Wait 5 minutes to form a dense and ordered cadmium selenide quantum well film, and wait for it to be transferred to the substrate.

[0095] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 80°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 6 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 100°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0096] Example 12

[0097] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 11.

[0098] A method for fabricating an electroluminescent diode includes the following steps:

[0099] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 100°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 8 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 120°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0100] Example 13

[0101] The preparation of the dense and ordered cadmium selenide quantum well film is the same as in Example 11.

[0102] A method for fabricating an electroluminescent diode includes the following steps:

[0103] A hole injection layer was formed by spin-coating 5 mg / mL poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate and annealing at 120°C for 15 min. Subsequently, a hole transport layer was formed by spin-coating 10 mg / mL poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)] onto the hole injection layer and annealing at 140°C for 15 min. A densely ordered cadmium selenide quantum well film was transferred onto the hole transport layer to form an ordered quantum well emitting layer, which was annealed at 30°C for 15 min. Finally, an electron transport layer was obtained by spin-coating 30 mg / mL magnesium-doped zinc oxide electron transport material onto the ordered quantum well emitting layer and annealing at 60°C for 15 min. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0104] Table 3. Performance of quantum wells and their electroluminescent LEDs

[0105]

[0106] As can be seen from the table above, further increasing the concentration of the quantum well solution to 20 mg / mL and increasing the amount of tri-n-octylamine implanted, and then fabricating the quantum well thin film for device fabrication, Examples 11-13 show that increasing the hole transport layer concentration and the hole transport layer annealing temperature initially increases and then decreases the device performance. Under the conditions of Example 12, an external quantum efficiency of 19% was achieved. The efficiency of Examples 11-13 is lower than that of Examples 6-10, indicating that the quantum well solution concentration was too high and the amount of tri-n-octylamine implanted was excessive.

[0107] To demonstrate the universality of the ordered and dense quantum well light-emitting diode of this invention, this embodiment uses red, green, and blue quantum wells to fabricate the light-emitting diode. The fabrication process is the same as in Example 7. The results show that the external quantum efficiency of the ordered and dense red, green, and blue quantum well light-emitting diode is higher than 20%.

[0108] Table 4 Performance of quantum wells and their electroluminescent LEDs

[0109]

[0110] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for preparing a densely ordered cadmium selenide quantum well thin film, characterized in that, Includes the following steps: (1) Dissolve sodium tetradecanoate and cadmium nitrate tetrahydrate separately in the first solvent. After they are completely dissolved, mix them to form cadmium tetradecanoate. Filter, wash with the first solvent, and dry for later use. (2) Cadmium selenide quantum well core: Mix 0.2~1.6 mmol cadmium tetradecanoate, 0.1~0.8 mmol selenium powder with solvent, heat to 140~200 degrees Celsius in an inert gas atmosphere, inject cadmium acetate dihydrate, then heat to 200~260 degrees Celsius and keep warm for 5~20 minutes, inject 0.2~1 mL oleic acid, cool down, wash the quantum well with a mixed solution of n-hexane and ethanol, redisperse with a second solvent to form cadmium selenide quantum well core solution; (3) Core-shell structured cadmium selenide / cadmium zinc sulfur quantum well: Add 0.1~0.3 mmol of anhydrous cadmium acetate, 0.3~0.9 mmol of anhydrous zinc acetate, 0.5~1.5 mL of oleic acid and 0.2~1 mL of 1-octadecene to the core solution of the cadmium selenide quantum well. Under an inert gas atmosphere, heat to 70~100 degrees Celsius and keep warm for 0.2~1 hours. Inject 0.2~1 mL of oleylamine and heat to 280~320 degrees Celsius. When the temperature reaches 120~180 degrees Celsius, start injecting octyl mercaptan. Keep warm at 280~320 degrees Celsius for 0.5~1.5 hours and cool down to obtain the core-shell structured cadmium selenide / cadmium zinc sulfur quantum well. (4) Wash the core-shell structured cadmium selenide / cadmium zinc sulfur quantum well with a mixed solution of the second solvent and the first solvent; redisperse with the second solvent to form a core-shell structured cadmium selenide / cadmium zinc sulfur quantum well solution with a concentration of 10~50 mg / mL; (5) Under nitrogen protection, at 10~30 degrees Celsius, add the core-shell structured cadmium selenide / cadmium zinc sulfur quantum well solution dropwise to the ethylene glycol solution until the quantum wells cover the surface of the ethylene glycol solution, and then add tri-n-octylamine at a volume ratio of 1%~10% of the ethylene glycol solution. (6) After standing for 1 to 15 minutes, a dense and ordered cadmium selenide quantum well film is obtained.

2. The method for preparing a dense and ordered cadmium selenide quantum well thin film according to claim 1, characterized in that, The first solvent is methanol or ethanol, and the second solvent is n-octane, n-hexane, or chloroform.

3. A densely ordered cadmium selenide quantum well thin film, characterized in that: The thin film is prepared by the preparation method described in claim 1 or 2.

4. An electroluminescent diode, characterized in that: The light-emitting layer of the diode comprises the densely ordered cadmium selenide quantum well film as described in claim 3.

5. The method for fabricating an electroluminescent diode according to claim 4, characterized in that, The preparation steps are as follows: (1) Hole injection material is printed on a transparent conductive substrate to form a hole injection layer, and annealed at 80~140 degrees Celsius for 10~30 minutes; then hole transport material is printed on the hole injection layer to form a hole transport layer, and annealed at 100~150 degrees Celsius for 10~30 minutes. (2) A dense and ordered cadmium selenide quantum well film is prepared by the preparation method described in claim 1 or 2 and transferred to the hole transport layer to form an ordered quantum well light-emitting layer, and annealed at 40 to 90 degrees Celsius for 10 to 30 minutes. (3) Spin-coat a zinc oxide or magnesium-doped zinc oxide ethanol solution with a concentration of 20-50 mg / mL onto the quantum well light-emitting layer to form an electron transport layer, and anneal at 60-90 degrees Celsius for 10-30 minutes; (4) Metal cathode material is deposited on the electron transport layer by vacuum evaporation to form an electrode, thereby obtaining an electroluminescent diode.

6. The method for fabricating an electroluminescent diode according to claim 5, characterized in that, The hole injection material is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid); the hole transport layer material is poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)]; the transparent conductive substrate is indium-doped tin oxide; and the metal cathode material is aluminum.

7. The method for fabricating an electroluminescent diode according to claim 5, characterized in that, The hole injection layer has a thickness of 30-70 nanometers, the hole transport layer has a thickness of 30-70 nanometers, the quantum well light-emitting layer has a thickness of 5-20 nanometers, the electron transport layer has a thickness of 30-60 nanometers, and the electrode has a thickness of 70-100 nanometers.

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