QWLEDs based on ZnS / cuprous selenide / ZnS quantum well light-emitting layers and their fabrication methods

Abstract

This invention discloses a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer and its fabrication method. Based on cubic ZnS seeds, a ZnS / Cu2Se / ZnS cubic quantum well structure is synthesized. Using this structure as the light-emitting layer, an LED device comprising an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer is fabricated. This invention utilizes a hot-injection method to fabricate ZnS / Cu2Se / ZnS quantum well materials with a cubic heterostructure and demonstrates a quantum well LED fabrication method. The core-shell quantum well structure is novel, and the device structure is stable and efficient. The fabricated quantum well material possesses a continuous PN heterostructure, high quantum efficiency, good optical properties, and structural stability. The fabricated quantum well LED device exhibits excellent electroluminescence efficiency and external quantum efficiency, showing great application potential in high-brightness, long-lifetime, and high-resolution display technologies.

Description

Technical Field

[0001] This invention belongs to the field of materials science, specifically relating to a QWLED based on a ZnS / Cu2Se (copper selenide) / ZnS quantum well light-emitting layer and its preparation method. Background Technology

[0002] Quantum dots are quasi-zero-dimensional materials with three-dimensional scales ranging from 1 to 20 nm. Their size, shape, and excitation wavelength can be controlled by adjusting the growth time, reaction temperature, and ligands. Cuprous selenide quantum dots belong to the p-type semiconductor nanomaterials. Because of their hexagonal crystal phase, cuprous selenide is stable at room temperature and has a direct band gap of 2.1–2.39 eV, it exhibits excellent performance and wide applications in solar cells, photodetectors, and QLEDs. Due to its good stability, low toxicity, and low cost, it is considered one of the most promising quantum dot display materials and has been extensively studied.

[0003] However, current research on cuprous selenide materials remains largely focused on macroscopic bulk materials, with only a few studies addressing the nanoscale. Furthermore, reported quantum yields of copper selenide quantum dots are low, and particle size distributions are uneven. To improve the optoelectronic properties of copper selenide quantum dots, researchers have been seeking ways to passivate defects, reduce lattice mismatch between quantum dot shells, and further enhance their optical properties.

[0004] Studies have shown that strictly controlling the temperature and shell thickness during the synthesis of quantum dots can significantly reduce lattice mismatch and passivate surface defects. Some studies have also incorporated other materials into cuprous selenide quantum dots to form composite materials, thereby adjusting the band structure and improving their optical properties. CN103803511A discloses a method for preparing copper selenide fluorescent quantum dots and its applications: a synthesis method combining an aqueous solution containing copper salts as the aqueous phase and an organic solvent containing long-chain ligands as the oil phase. CN114533868A discloses a method for preparing gold-composite copper selenide nanoparticles and their applications: gold is grown in situ on the periphery of cuprous selenide, forming a dense core-shell structure, improving biocompatibility and photothermal properties. CN107265411A discloses a method for preparing copper selenide (Cu2-xSe) nanoparticles of different particle sizes: using ascorbic acid reducing agent as a ligand, and effectively preparing copper selenide quantum dots of different particle sizes by adjusting the concentrations of ascorbic acid and copper source. (CN105531804A) discloses a method for preparing copper selenide nanoparticles: using selenool as a selenium source improves the stability of quantum dots. While their method improves the performance of copper selenide quantum dots to some extent, it lacks flexibility in core-shell structure and material composition. Therefore, further research is needed to effectively leverage the synergistic effects of various components in the core-shell structure during the energy excitation process of quantum dots through artificial design of core-shell structures, thereby improving the overall performance of lead selenide materials.

[0005] In summary, most of the copper selenide quantum dot materials mentioned in literature or patents cannot theoretically effectively eliminate the lattice mismatch and surface defects caused by the core-shell structure, and they also contain heavy metals, which can easily cause environmental harm, thus affecting the application of copper selenide quantum dot materials in display technology. At the same time, the core-shell structures of copper selenide quantum dots in current patents are relatively simple, resulting in copper selenide quantum dots that, due to their simple structure and energy level mismatch between the core and shell materials, have limited effect on improving their optical performance. Summary of the Invention

[0006] The purpose of this invention is to provide a QWLED based on a ZnS / Cu2Se (copper selenide) / ZnS quantum well light-emitting layer and its fabrication method. This invention uses a hot-injection method to prepare a cubic heterostructure ZnS / Cu2Se / ZnS quantum well material and demonstrates a method for preparing a quantum well LED. The core-shell quantum well structure is novel, and the device structure is stable and efficient. The prepared quantum well material has a continuous PN heterostructure, high quantum efficiency, good optical properties, and structural stability. The prepared quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in fields such as high brightness, long lifespan, and high resolution display technology.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer is disclosed. Based on cubic ZnS seeds, a ZnS / Cu2Se / ZnS cubic quantum well structure is synthesized. Using this structure as the light-emitting layer, an LED device comprising an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer is fabricated.

[0009] The above-mentioned method for fabricating QWLEDs based on ZnS / Cu2Se / ZnS quantum well light-emitting layers specifically includes the following steps:

[0010] (1) Clean the ITO conductive glass with deionized water, acetone and isopropanol for 15-25 min respectively, and dry it with nitrogen at a certain temperature;

[0011] (2) In the glove box, spin coat the PEDOT:PSS solution onto the ITO conductive glass from step (4) using a spin coater, and then place the conductive glass sheet on the heating table for annealing;

[0012] (3) Dissolve TFB in toluene solution, then spin coat the solution onto the conductive glass sheet from step (5) in a glove box using a spin coater, and then place the conductive glass sheet on a heating table for annealing;

[0013] (4) In the glove box, spin coat the ZnS / Cu2Se / ZnS quantum well solution onto the conductive glass sheet from step (6) using a spin coater, and then place the conductive glass sheet on the heating stage for annealing;

[0014] (5) In the glove box, spin coat the Zn0.85Mg0.15O solution onto the conductive glass sheet from step (7) using a spin coater, and then place the conductive glass sheet on the heating table for annealing;

[0015] (6) The conductive glass sheet obtained in step (8) is used to deposit electrodes using a thermal evaporation machine, thereby obtaining the one-dimensional core-shell heterostructure ZnS / Cu2Se / ZnS quantum well material LED preparation method.

[0016] Further, the PEDOT:PSS solution described in step (2) is first filtered through a 0.45μm filter head, the annealing temperature is 100-120℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1ppm, and the annealing time is 20-30min.

[0017] Further, the concentration of the TFB solution in step (3) is 8-10 mg / ml, the annealing temperature is 160-200℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1 ppm, and the annealing time is 15-30 min.

[0018] Furthermore, the concentration of the ZnS / Cu2Se / ZnS quantum well solution in step (4) is 20-40 mg / ml, the annealing temperature is 60-80℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1 ppm, and the annealing time is 10-20 min.

[0019] Further, the concentration of the Zn0.85Mg0.15O solution in step (5) is 15-25 mg / ml, the annealing temperature is 100-120℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1 ppm, and the annealing time is 10-20 min.

[0020] Furthermore, the electrode mentioned in step (6) is a silver electrode with a thickness of 100 nm.

[0021] The beneficial effects of this invention are as follows: Based on cubic ZnS seeds, a ZnS / Cu2Se / ZnS cubic quantum well structure was synthesized. Using this structure as the light-emitting layer, an LED device comprising an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer was fabricated. Compared with existing technologies, this invention, due to the use of hot injection and spin-coating thin film methods, possesses the characteristic of regulating the balance of electron and hole currents. Simultaneously, the effective encapsulation and isolation of cuprous selenide with a zinc selenide core and shell effectively forms a PN heterostructure. The interface contact of the heterojunction introduces band bending, and the presence of the depletion region promotes electron and hole recombination. This results in higher overlap of electron and hole wave functions in terms of material properties, reduces the generation of interface defects and exciton quenching, and improves the structural stability, quantum efficiency, and photoluminescence intensity of the quantum well material. Furthermore, the device fabrication process of this invention is coherent and simple, the thickness of each layer is easily adjustable, and the light-emitting layer serves as the recombination center for electron and hole currents, making it an effective method for fabricating high-performance light-emitting quantum well materials and devices.

[0022] This invention can fully utilize the excellent bandgap tuning capability of PN heterojunction materials in quantum well luminescence to prepare PN junction quantum well materials with copper selenide as the well region, and further design device structures and optimize the electroluminescence performance of the devices; thus obtaining a QWLED with high external quantum efficiency and high luminescence intensity using ZnS / Cu2Se / ZnS quantum well as the light-emitting layer. Attached Figure Description

[0023] Figure 1 This is a structural diagram of the ZnS / Cu2Se / ZnS quantum well material;

[0024] Figure 2 This is a diagram of the LED structure made of ZnS / Cu2Se / ZnS quantum well material;

[0025] Note: 1 represents the ZnS core, 2 represents the Cu₂Se trap, 3 represents the ZnS shell, 4 represents the silver electrode, and 5 represents the ZnS core. 0.85 Mg 0.15 0 is the electron transport layer, 6 is the ZnS / Cu2Se / ZnS quantum well material light-emitting layer, 7 is the TFB hole transport layer, 8 is the PEDOT:PSS hole transport layer, and 9 is the ITO glass substrate. Detailed Implementation

[0026] This invention aims to provide a method for fabricating QWLEDs based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer, which will now be described in conjunction with the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] 1) Place the ITO glass in a beaker, and pour in acetone solution, isopropanol solution, and deionized water solution in sequence. Sonicate each solution for 25 minutes. Remove the glass, dry it under nitrogen at 60°C, and place it in a clean, dry petri dish.

[0029] 2) After filtering the PEDOT:PSS solution with a 0.45μm filter head, spin coat it onto the ITO glass using a spin coater at a low speed of 500rpm / s for 5s and a high speed of 3000rpm / s for 40s. Then place the glass slide on a heating stage and anneal it at 120℃ for 30min.

[0030] 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 the solution at a low speed of 500 rpm / s for 5 seconds and a high speed of 2000 rpm / s for 40 seconds. Then place the glass slide on a heating stage and anneal at 200℃ for 20 minutes.

[0031] 4) Preparation of ZnS / Cu2Se / ZnS quantum well: 24 mmol zinc acetate, 24 mmol oleic acid, and 400 mL TOA were heated to 120 °C and evacuated for 15 min to remove excess moisture. The mixture was then heated to 270 °C in an inert atmosphere for 10 min. The mixture was then cooled to 220 °C, 30 mL of zinc sulfide core solution was added, and the temperature was increased to 320 °C. The zinc sulfide core solution was obtained by the following steps: 18 mmol oleic acid, 12 mmol oleylamine, and 400 mL TOP were heated to 120 °C and evacuated for 15 min. The mixture was then heated to 250 °C in an inert atmosphere for 70 min. The temperature was lowered to 240 °C, and the zinc and sulfur precursor mixture was rapidly injected. The temperature was increased to 300 °C and reacted for 1 h. The mixture was then cooled to room temperature to obtain the zinc sulfide core solution. The mixed solution of zinc and sulfur precursors was obtained by dissolving 12 mmol of zinc acetate, 6 ml of TOP-S (2M), and 12 mmol of DPP (diphenylphosphine) in an inert atmosphere. Then, 7 mmol of copper stearate powder and 50 ml of octadecene were dissolved at 110 °C, followed by the addition of 16 ml of TOP-Se (2M) solution. This mixture was injected into a reactor vessel and reacted at 320 °C for 30 min, yielding zinc sulfide / cuprous selenide material. Next, 24 ml of zinc oleate and 28 ml of TOP-S (2M) were injected, and the reaction was maintained at 320 °C for 30 min to obtain a cubic zinc sulfide / cuprous selenide / zinc sulfide quantum well solution. The zinc oleate was obtained by dissolving zinc acetate (20 mmol) and oleic acid (40 mmol) in 100 ml of TOA (trioctylamine) at a molar ratio of 1:2 and reacting at 280 °C for 1 h under an inert atmosphere. Quantum dots were separated and cleaned by centrifugation with ethanol and n-hexane. The ZnS / Cu2Se / ZnS quantum well colloidal solution was diluted to 25 mg / ml with n-octane. The solution was then spin-coated 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. The glass slide was then placed on a heating stage and annealed at 80 °C for 15 min. Figure 1 This is a structural diagram of a ZnS / Cu₂Se / ZnS quantum well material. 1 represents the ZnS core, 2 represents the Cu₂Se well, and 3 represents the ZnS shell.

[0032] 5) Take a Zn0.85Mg0.15O 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 on a heating stage to anneal at 80℃ for 10 min.

[0033] 6) A 100nm silver electrode can be thermally deposited to obtain a QWLED with a ZnS / Cu2Se / ZnS quantum well as the light-emitting layer. Figure 2This is a structural diagram of a ZnS / Cu2Se / ZnS quantum well material LED, where 4 is the silver electrode and 5 is the Zn electrode. 0.85 Mg 0.15 0 is the electron transport layer, 6 is the ZnS / Cu2Se / ZnS quantum well material light-emitting layer, 7 is the TFB hole transport layer, 8 is the PEDOT:PSS hole transport layer, and 9 is the ITO glass substrate.

[0034] Example 2

[0035] 1) Place the ITO glass in a beaker, and pour in acetone solution, isopropanol solution, and deionized water solution in sequence. Sonicate each solution for 25 minutes. Remove the glass, dry it under nitrogen at 60°C, and place it in a clean, dry petri dish.

[0036] 2) After filtering the PEDOT:PSS solution with a 0.45μm filter head, spin coat it onto the ITO glass at a low speed of 500rpm / s for 5s and a high speed of 3500rpm / s for 40s using a spin coater. Then place the glass slide on a heating stage and anneal it at 150℃ for 25min.

[0037] 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 the solution at a low speed of 500 rpm / s for 5 seconds and a high speed of 3000 rpm / s for 40 seconds. Then place the glass slide on a heating stage and anneal at 150°C for 15 minutes.

[0038] 4) Preparation of ZnS / Cu2Se / ZnS quantum well: 24 mmol zinc acetate, 24 mmol oleic acid, and 400 mL TOA were heated to 120 °C and evacuated for 15 min to remove excess moisture. The mixture was then heated to 270 °C in an inert atmosphere for 10 min. The mixture was then cooled to 220 °C, 30 mL of zinc sulfide core solution was added, and the temperature was increased to 320 °C. The zinc sulfide core solution was obtained by the following steps: 18 mmol oleic acid, 12 mmol oleylamine, and 400 mL TOP were heated to 120 °C and evacuated for 15 min. The mixture was then heated to 250 °C in an inert atmosphere for 70 min. The temperature was lowered to 240 °C, and the zinc and sulfur precursor mixture was rapidly injected. The temperature was increased to 300 °C and reacted for 1 h. The mixture was then cooled to room temperature to obtain the zinc sulfide core solution. The mixed solution of zinc and sulfur precursors was obtained by dissolving 12 mmol of zinc acetate, 6 ml of TOP-S (2M), and 12 mmol of DPP (diphenylphosphine) in an inert atmosphere. Then, 7 mmol of copper stearate powder and 50 ml of octadecene were dissolved at 110 °C, followed by the addition of 16 ml of TOP-Se (2M) solution. This mixture was injected into a reactor vessel and reacted at 320 °C for 30 min, yielding zinc sulfide / cuprous selenide material. Next, 24 ml of zinc oleate and 28 ml of TOP-S (2M) were injected, and the reaction was maintained at 320 °C for 30 min to obtain a cubic zinc sulfide / cuprous selenide / zinc sulfide quantum well solution. The zinc oleate was obtained by dissolving zinc acetate (20 mmol) and oleic acid (40 mmol) in 100 ml of TOA (trioctylamine) at a molar ratio of 1:2 and reacting at 280 °C for 1 h under an inert atmosphere. Quantum dots were separated and cleaned by centrifugation with ethanol and n-hexane. The ZnS / Cu2Se / ZnS quantum well colloidal solution was diluted to 25 mg / ml with n-octane. The solution was then spin-coated 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. The glass slide was then placed on a heating stage and annealed at 80 °C for 15 min. Figure 1 This is a structural diagram of a ZnS / Cu₂Se / ZnS quantum well material. 1 represents the ZnS core, 2 represents the Cu₂Se shell, and 3 represents the ZnS shell.

[0039] 5) Take a Zn0.85Mg0.15O 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 on a heating stage to anneal at 60℃ for 20 min.

[0040] 6) A 100nm silver electrode can be thermally deposited to obtain a QWLED with a ZnS / Cu2Se / ZnS quantum well as the light-emitting layer. Figure 2This is a structural diagram of a ZnS / Cu2Se / ZnS quantum well material LED, where 4 is the silver electrode and 5 is the Zn electrode. 0.85 Mg 0.15 0 is the electron transport layer, 6 is the ZnS / Cu2Se / ZnS quantum well material light-emitting layer, 7 is the TFB hole transport layer, 8 is the PEDOT:PSS hole transport layer, and 9 is the ITO glass substrate.

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer, characterized in that: Based on cubic ZnS seeds, a ZnS / Cu2Se / ZnS cubic quantum well structure was synthesized. Using this structure as the light-emitting layer, a QWLED containing an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer was prepared. The method for fabricating the QWLED based on the ZnS / Cu2Se / ZnS quantum well light-emitting layer includes the following steps: (1) Clean the ITO conductive glass with deionized water, acetone and isopropanol for 15-25 min respectively, and dry it with nitrogen at 60℃; (2) In the glove box, spin coat the PEDOT:PSS solution onto the ITO conductive glass from step (1) using a spin coater, and then place the conductive glass sheet on a heating table for annealing; (3) Dissolve TFB in toluene solution, then spin coat the solution onto the conductive glass sheet from step (2) in a glove box using a spin coater, and then place the conductive glass sheet on a heating table for annealing; (4) In the glove box, spin coat the ZnS / Cu2Se / ZnS quantum well solution onto the conductive glass sheet from step (3) using a spin coater, and then place the conductive glass sheet on the heating stage for annealing; (5) Place Zn in the glove box 0.85 Mg 0.15 The O solution was spin-coated onto the conductive glass sheet from step (4) using a spin coater, and then the conductive glass sheet was placed on a heating table for annealing. (6) The conductive glass sheet obtained in step (5) is used to deposit electrodes using a thermal evaporation machine to obtain a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer.

2. The method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer according to claim 1, characterized in that: The PEDOT:PSS solution described in step (2) is first filtered through a 0.45μm filter head, the annealing temperature is 100-120℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1ppm, and the annealing time is 20-30min.

3. The method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer according to claim 1, characterized in that: The concentration of the TFB solution mentioned in step (3) is 8-10 mg / ml, the annealing temperature is 160-200℃, the environmental conditions are in a glove box with a nitrogen atmosphere where oxygen and water are both less than 1 ppm, and the annealing time is 15-30 min.

4. The method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer according to claim 1, characterized in that: The concentration of the ZnS / Cu2Se / ZnS quantum well solution in step (4) is 20-40 mg / ml, the annealing temperature is 60-80℃, the environmental conditions are a glove box with a nitrogen atmosphere where oxygen and water are both less than 1 ppm, and the annealing time is 10-20 min.

5. The method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer according to claim 1, characterized in that: The Zn mentioned in step (5) 0.85 Mg 0.15 The concentration of O solution is 15-25 mg / ml, the annealing temperature is 100-120℃, the environmental conditions are 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.

6. The method for fabricating a QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer according to claim 1, characterized in that: The electrode mentioned in step (6) is a silver electrode with a thickness of 100 nm.

7. A QWLED based on a ZnS / Cu2Se / ZnS quantum well light-emitting layer, prepared by the method according to any one of claims 1-6.

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