QWLED Based on CdSe / PbS / CdS Core-Shell Quantum Well Light-Emitting Layer and Its Preparation Method

Abstract

The present invention discloses a QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer and a preparation method thereof. The light-emitting layer is a quantum well material composed of cadmium selenide as a core, lead sulfide as an intermediate layer, and cadmium sulfide as a shell, and the prepared LED device includes an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer. The present invention uses a hot injection method to prepare a CdSe / PbS / CdS quantum well material with a one-dimensional core-shell heterostructure, and demonstrates a method for preparing a quantum well LED. The core-shell quantum well structure is novel, 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, and the prepared quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in the fields of high brightness, long life, and high-resolution display technology.

Description

Technical Field

[0001] The present invention belongs to the field of material science, and in particular relates to a QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer and a preparation method thereof. Background Art

[0002] Quantum dots are quasi-zero-dimensional materials with three-dimensional dimensions ranging from 1 to 100 nm. Their size, shape, and excitation wavelength can be controlled by regulating the growth time, reaction temperature, and ligands. Lead sulfide quantum dots (PbS) are p-type semiconductor nanomaterials with a tunable band gap (0.7–2.1 eV). Their low cost, solution processability, and band gap tunability make them an excellent choice for wavelength-tunable quantum dot devices. Due to their large size, PbS QDs are considered an excellent choice for applications such as near-infrared light-emitting LEDs and solar cells. However, research on PbS QDs within the visible light excitation wavelength range remains promising.

[0003] To address the lattice mismatch and surface defects in lead sulfide core-shell quantum dot materials, researchers have been seeking ways to passivate defects, reduce the lattice mismatch between quantum dot shells, and further improve their optical properties. Studies have shown that strictly controlling the temperature and precursor concentration during the synthesis of quantum dot core-shell structures can significantly reduce lattice mismatch. Other studies have also incorporated other materials into lead sulfide quantum dots to form composite materials to modulate the band structure and thus improve their optical properties. (CN114316947A) provides large-sized PbS quantum dots, quantum dot inks, printed solar cells, and their preparation methods: hexamethyldisilathane is used as a sulfur source, and a lead acetate solution with a concentration of 5-10 mg / ml is added. (CN114933898A) provides a method for preparing transition metal-doped lead sulfide quantum dots: a micron / submicron-sized lead source doped with transition metal ions is synthesized by aqueous precipitation, then reacted with an organic reagent to form a lead precursor, which reacts with elemental sulfur to synthesize transition metal-doped lead sulfide quantum dots. CN103525416A provides green semiconductor nanocrystals for blue-light-excited LEDs and their preparation methods. ZnS / PbS / ZnS quantum wells were synthesized using an aqueous synthesis method. These quantum wells emit green light under excitation at wavelengths of 450–460 nm, with an emission spectrum ranging from 505–550 nm, effectively improving the photoluminescence performance of lead sulfide quantum dots. CN106566526A also provides multi-well core-shell quantum dots and their preparation methods. This multi-well quantum well structure was achieved through a cation exchange method. While this method improves the photoelectric performance of lead sulfide quantum dot materials and LED devices to a certain extent, it is relatively simple in terms of structural design and shell composition. Therefore, further research is needed to optimize the material structure and shell composition to effectively leverage the synergistic effects of the energy bands and conductive properties of the nanoparticles, thereby improving their overall performance.

[0004] In summary, most of the lead sulfide quantum dot materials and devices mentioned in literature or patents are theoretically incapable of effectively passivating surface defects and regulating the electron-hole transport speed in LEDs, thus hindering their application in electroluminescence. Furthermore, the core-shell structure of the lead sulfide quantum dot materials in current patents is relatively simple. As a result, the prepared lead sulfide quantum dot materials have limited effectiveness in improving their photoluminescence and electroluminescence performance due to their simple structure and the lack of a continuous PN heterostructure. Summary of the Invention

[0005] The purpose of the present invention is to provide a QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer and a preparation method thereof. The present invention uses a hot injection method to prepare a CdSe / PbS / CdS quantum well material with a core-shell heterostructure and demonstrates a method for preparing a quantum well LED. The core-shell quantum well structure is novel, 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, and the prepared quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in the fields of high brightness, long life and high-resolution display technology.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer includes, from bottom to top, an electrode, an inorganic electron transport layer, a quantum well material light-emitting layer, an organic hole transport layer, and an ITO glass substrate. The quantum well material light-emitting layer is composed of cadmium selenide as the core, lead sulfide as the intermediate layer, and cadmium sulfide as the shell.

[0008] A method for preparing a QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer as described above comprises the following steps:

[0009] (1) Clean the ITO conductive glass with deionized water, acetone, and isopropyl alcohol for 15-25 minutes respectively, and dry it with nitrogen at a certain temperature;

[0010] (2) In a glove box, the PEDOT:PSS solution was spin-coated on the ITO conductive glass in step (4) using a spin coater, and then the conductive glass was placed on a heating table for annealing;

[0011] (3) Dissolving TFB in a toluene solution, and then spin-coating the solution on the conductive glass sheet in step (5) using a spin coater in a glove box, and then placing the conductive glass sheet on a heating table for annealing;

[0012] (4) In a glove box, spin-coat the CdSe / PbS / CdS quantum well solution onto the conductive glass sheet prepared in step (6) using a spin coater, and then place the conductive glass sheet on a heating table for annealing;

[0013] (5) In a glove box, a Zn0.85Mg0.15O solution was spin-coated on the conductive glass sheet in step (7) using a spin coater, and then the conductive glass sheet was placed on a heating table for annealing;

[0014] (6) Using a thermal evaporation machine to deposit electrodes on the conductive glass sheet obtained in step (8), the QWLED based on the CdSe / PbS / CdS core-shell quantum well light-emitting layer is obtained.

[0015] Furthermore, the PEDOT:PSS solution described in step (2) is first filtered through a 0.45 μm filter head, the annealing temperature is 100-120° C., the environmental condition is a nitrogen atmosphere glove box with oxygen and water less than 1 ppm, and the annealing time is 20-30 min.

[0016] Furthermore, 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 where both oxygen and water are less than 1 ppm, and the annealing time is 15-30 min.

[0017] Furthermore, the concentration of the CdSe / PbS / CdS quantum well solution in step (4) is 20-40 mg / ml, the annealing temperature is 60-80°C, the environmental conditions are in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10-20 min.

[0018] Furthermore, the concentration of the Zn0.85Mg0.15O solution in step (5) is 15-25 mg / ml, the annealing temperature is 100-120°C, the environmental condition is 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.

[0019] Furthermore, the electrode described in step (6) is a silver electrode with a thickness of 100 nm.

[0020] The beneficial effects of the present invention are: a cadmium selenide core, a lead sulfide intermediate layer, and a quantum well material with a cadmium sulfide shell as a light-emitting layer, comprising an organic hole transport layer, an inorganic electron transport layer, and a quantum well light-emitting layer, are prepared. Compared with the prior art, the invention adopts a hot injection method and a spin-coating thin film method, which not only has the advantages of a controllable core-shell structure, but also has the characteristics of adjusting the balance of electron and hole currents. At the same time, the lead sulfide is effectively wrapped and isolated by the cadmium selenide core and the cadmium sulfide shell, effectively forming a PN heterostructure. The interface contact of the heterojunction brings about the bending of the energy band, and the presence of the depletion region promotes the recombination of electrons and holes, which not only brings higher electron and hole wave function overlap in material properties, but also reduces the generation of interface defects and exciton quenching, and improves the structural stability, quantum efficiency and photoluminescence intensity of the quantum well material. In addition, the device process of the present invention is coherent and simple, the thickness of each layer component is easy to adjust, and the light-emitting layer serves as the recombination center of the electron and hole currents, which is an effective method for preparing high-performance light-emitting quantum well materials and devices.

[0021] The present invention can fully utilize the excellent band adjustment ability of PN heterojunction materials in quantum well luminescence to prepare PN junction quantum well materials with lead sulfide as the well region, and further design the device structure based on this to optimize the electroluminescent performance of the device; thus obtaining a QWLED preparation method with high external quantum efficiency and high luminescence intensity using CdSe / PbS / CdS core-shell quantum well as the light-emitting layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of the CdSe / PbS / CdS quantum well material structure;

[0023] Figure 2 This is a diagram of the CdSe / PbS / CdS quantum well material LED structure;

[0024] Note: 1 is CdS core, 2 is PbS shell, 3 is CdS shell, 4 is silver electrode, 5 is Zn 0.85 Mg 0.15 O is an electron transport layer, 6 is a CdSe / PbS / CdS quantum well material light-emitting layer, 7 is a TFB hole transport layer, 8 is a PEDOT:PSS hole transport layer, and 9 is an ITO glass substrate. DETAILED DESCRIPTION

[0025] The present invention aims to provide a novel QWLED preparation method based on CdSe / PbS / CdS core-shell quantum well light-emitting layer, which is now described in conjunction with the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] 1) Place the ITO glass in a beaker and pour in acetone solution, isopropyl alcohol solution, and deionized water solution, sequentially. Ultrasonic clean the glass for 25 minutes each. Remove the glass and blow dry it with nitrogen at 60°C. Place it in a clean, dry Petri dish.

[0028] 2) Filter the PEDOT:PSS solution through a 0.45 μm filter and spin coat it onto the ITO glass using a spin coater at a low speed of 500 rpm / s for 5 seconds and a high speed of 3000 rpm / s for 40 seconds. Then, anneal the glass slide on a heating plate at 120°C for 30 minutes.

[0029] 3) Dissolve 8 mg of TFB in 1 ml of toluene solution to a concentration of 8 mg / mL. 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 using a spin coater. Then, anneal the glass slide on a heating plate at 200°C for 20 minutes.

[0030] 4) Preparation of CdSe / PbS / CdS quantum wells: 0.3 mmol of cadmium oxide, 0.3 ml of oleic acid, and 10 ml of octadecene were added to a three-necked flask. The temperature was raised to 300°C. 0.125 mmol of sulfur powder was dissolved in 0.5 ml of ODE and injected into the three-necked flask. After 12 minutes of reaction, 0.1 mmol of cadmium oxide was dissolved in 0.2 ml of oleic acid and injected into the three-necked flask. After 10 minutes of reaction, 0.1 mmol of tellurium powder was dissolved in 0.1 ml of tri-n-octylphosphine and injected into the three-necked flask at a rate of 5 ml / h. 0.6 mmol of cadmium oxide was dissolved in 1. 2ml of oleic acid was injected into a three-necked flask. After reacting for 5 minutes, 0.75mmol of sulfur powder was dissolved in 1.55ml of tri-n-octylphosphine and injected into the three-necked flask at a rate of 2ml / h to obtain CdSe / PbS / CdS quantum wells. The quantum dots were cleaned by centrifugation with ethanol and n-hexane. The CdSe / PbS / CdS quantum well colloidal solution was diluted to 25mg / ml with n-octane. The solution was spin-coated at a low speed of 500rpm / s for 5s and a high speed of 2000rpm / s for 40s. The glass slide was then placed on a heating table and annealed at 80°C for 15min. Figure 1 This is a diagram of the CdSe / PbS / CdS quantum well material structure, where 1 is the CdS core, 2 is the PbS shell, and 3 is the CdS shell.

[0031] 5) Take a 20 mg / ml Zn0.85Mg0.15O solution and spin coat it at a low speed of 500 rpm / s for 5 seconds and a high speed of 1000 rpm / s for 40 seconds. Then place the glass slide on a heating plate and anneal it at 80°C for 10 minutes.

[0032] 6) Thermally evaporate a 100nm silver electrode to obtain a QWLED with a CdSe / PbS / CdS core-shell quantum well as the light-emitting layer. Figure 2 This is the structure diagram of the CdSe / PbS / CdS quantum well material LED, where 4 is the silver electrode and 5 is the Zn 0.85 Mg 0.15 O is an electron transport layer, 6 is a CdSe / PbS / CdS quantum well material light-emitting layer, 7 is a TFB hole transport layer, 8 is a PEDOT:PSS hole transport layer, and 9 is an ITO glass substrate.

[0033] Example 2

[0034] 1) Place the ITO glass in a beaker and pour in acetone solution, isopropyl alcohol solution, and deionized water solution, sequentially. Ultrasonic clean the glass for 25 minutes each. Remove the glass and blow dry it with nitrogen at 60°C. Place it in a clean, dry Petri dish.

[0035] 2) Filter the PEDOT:PSS solution through a 0.45 μm filter and spin coat it onto the ITO glass using a spin coater at a low speed of 500 rpm / s for 5 seconds and a high speed of 3500 rpm / s for 40 seconds. Then, anneal the glass slide on a heating plate at 150°C for 25 minutes.

[0036] 3) Dissolve 8 mg of TFB in 1 ml of toluene solution to a concentration of 8 mg / mL. 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 using a spin coater. Then, anneal the glass slide on a heating plate at 150°C for 15 minutes.

[0037] 4) Preparation of CdSe / PbS / CdS quantum wells: 0.5 mmol of cadmium oxide, 0.5 ml of oleic acid, and 10 ml of octadecene were added to a three-necked flask. The temperature was raised to 300°C. 0.2 mmol of sulfur powder was dissolved in 0.75 ml of ODE and injected into the three-necked flask. After 12 minutes of reaction, 0.2 mmol of cadmium oxide was dissolved in 0.4 ml of oleic acid and injected into the three-necked flask. After 10 minutes of reaction, 0.125 mmol of tellurium powder was dissolved in 0.5 ml of tri-n-octylphosphine and injected into the three-necked flask at a rate of 5 ml / h. 0.6 mmol of cadmium oxide was dissolved in 1 .2ml of oleic acid was injected into a three-necked flask. After reacting for 5 minutes, 0.95mmol of sulfur powder was dissolved in 1.85ml of tri-n-octylphosphine and injected into the three-necked flask at a rate of 2ml / h to obtain CdSe / PbS / CdS quantum wells. The quantum dots were cleaned by centrifugation with ethanol and n-hexane. The CdSe / PbS / CdS quantum well colloidal solution was diluted to 20mg / ml with n-octane. The solution was spin-coated at a low speed of 500rpm / s for 5s and a high speed of 2000rpm / s for 40s using a spin coater. The glass slide was then placed on a heating table and annealed at 60℃ for 20min. Figure 1 This is a diagram of the CdSe / PbS / CdS quantum well material structure, where 1 is the CdS core, 2 is the PbS shell, and 3 is the CdS shell.

[0038] 5) Spin coat a 20 mg / ml Zn0.85Mg0.15O solution at a low speed of 500 rpm / s for 5 seconds and a high speed of 1000 rpm / s for 40 seconds on a spin coater. Then anneal the glass slide on a heating plate at 60°C for 20 minutes.

[0039] 6) Thermally evaporate a 100nm silver electrode to obtain a QWLED with a CdSe / PbS / CdS core-shell quantum well as the light-emitting layer. Figure 2This is the structure diagram of the CdSe / PbS / CdS quantum well material LED, where 4 is the silver electrode and 5 is the Zn 0.85 Mg 0.15 O is the electron transport layer, 6 is the CdSe / PbS / CdS 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.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer, characterized by: From bottom to top, it includes electrodes, inorganic electron transport layer, quantum well material light-emitting layer, organic hole transport layer and ITO glass substrate. The quantum well material light-emitting layer is composed of cadmium selenide as the core, lead sulfide as the middle layer and cadmium sulfide as the shell. The method for preparing the QWLED of the CdSe / PbS / CdS core-shell quantum well light-emitting layer comprises the following steps: (1) Clean the ITO conductive glass with deionized water, acetone, and isopropyl alcohol for 15-25 minutes respectively, and dry it with nitrogen at a certain temperature; (2) In a glove box, the PEDOT:PSS solution was spin-coated on the ITO conductive glass in step (1) using a spin coater, and then the conductive glass was placed on a heating table for annealing; (3) Dissolving TFB in a toluene solution, and then spin-coating the solution on the conductive glass sheet in step (2) using a spin coater in a glove box, and then placing the conductive glass sheet on a heating table for annealing; (4) In a glove box, spin-coat the CdSe / PbS / CdS quantum well solution onto the conductive glass sheet prepared in step (3) using a spin coater, and then place the conductive glass sheet on a heating table for annealing; (5) In the glove box, Zn 0.85 Mg 0.15 The O solution is spin-coated on the conductive glass sheet in step (4) using a spin coater, and then the conductive glass sheet is placed on a heating table for annealing; (6) Using a thermal evaporation machine to deposit electrodes on the conductive glass sheet obtained in step (5), a QWLED based on a CdSe / PbS / CdS core-shell quantum well light-emitting layer is obtained; The concentration of the CdSe / PbS / CdS quantum well solution in step (4) is 20-40 mg / ml, the annealing temperature is 60-80°C, the environmental conditions are in a glove box with a nitrogen atmosphere with less than 1 ppm of oxygen and water, and the annealing time is 10-20 min.

2. The QWLED based on the CdSe / PbS / CdS core-shell quantum well 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 based on the CdSe / PbS / CdS core-shell quantum well 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. The QWLED based on the CdSe / PbS / CdS core-shell 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 0.45 μm filter head, and the annealing temperature is 100-120°C 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 minutes.

5. The QWLED based on the CdSe / PbS / CdS core-shell quantum well light-emitting layer according to claim 1, 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 conditions are in a nitrogen atmosphere glove box with oxygen and water less than 1 ppm, and the annealing time is 15-30 min.

6. The QWLED based on the CdSe / PbS / CdS core-shell quantum well light-emitting layer according to claim 1, characterized in that: The Zn in step (5) 0.85 Mg 0.15 The concentration of the O solution is 15-25 mg / ml, the annealing temperature is 100-120° C., the environmental condition is a glove box with a nitrogen atmosphere in which both oxygen and water are less than 1 ppm, and the annealing time is 10-20 min.

7. The QWLED based on the CdSe / PbS / CdS core-shell quantum well light-emitting layer according to claim 1, characterized in that: The electrode described in step (6) is a silver electrode with a thickness of 100 nm.

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