Apparatus and method for roll-to-roll preparation of colloidal quantum dot monolayer films

Abstract

The application discloses a device and a method for preparing a colloidal quantum dot monolayer film in a roll-to-roll mode, which comprises a spreading groove, a solution spreading assembly and a roll-to-roll transfer mechanism, the roll-to-roll transfer mechanism is composed of a flexible substrate, a driving roller, a driven roller and two guide rollers, supports are arranged at four corners of the spreading groove, the two ends of the driving roller are respectively installed on the two supports on the left side of the spreading groove, the two ends of the driven roller are respectively installed on the two supports on the right side of the spreading groove, the two guide rollers are installed in the spreading groove, a fixing frame is arranged in the spreading groove, the solution spreading assembly is fixed on the inclined surface of the fixing frame in the spreading groove, the solution spreading assembly is composed of a silicon wafer, a glass sheet and a capillary tube, one end of the flexible substrate is fixed on the driven roller and sequentially passes through the two guide rollers, the other end is fixed on the driving roller, and the spreading groove contains a liquid carrier. The application can quickly and efficiently prepare a large-area quantum dot monolayer film.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductors, and in particular relates to a device and method for roll-to-roll preparation of a colloidal quantum dot monolayer film. Background Art

[0002] Semiconductor technology has brought great convenience to human life, and people's requirements for the performance of electronic devices and the functions of electronic products are constantly increasing. For example, the demand for high-performance lighting and display devices, flexible electronic devices, etc. is growing. The reliable large-scale growth and preparation of semiconductor materials is the foundation for the development of high-performance new electronic devices. Semiconductor quantum dots are nanocrystals with a diameter of 2-20nm. They not only have excellent semiconductor properties and excellent optical properties, but can also be synthesized in large quantities through low-cost wet chemical methods. They have broad application prospects in the fields of high-efficiency lighting and displays. By controlling the electrical properties of solid quantum dot films, they can also serve as the active layer of electronic devices such as field-effect transistors. However, the large-scale controllable preparation of quantum dot monolayer films remains a problem, which seriously limits the application of colloidal quantum dots in lighting, displays and electronic devices.

[0003] Self-assembly at the gas-liquid interface is an important method for preparing large-area monolayer structures. Currently, the Langmuir-Blodgett (LB) technique has been used to achieve large-scale preparation of quantum dot monolayer structures at the gas-liquid interface. However, the LB technique requires the assembly to be dispersed onto the gas-liquid interface before forming the monolayer structure through a sliding barrier extrusion process, resulting in low preparation efficiency. Furthermore, small nanoparticles have a large surface energy and are prone to aggregation at the gas-liquid interface, spontaneously forming multiple growth centers. This introduces numerous film defects, reduces device stability and reproducibility, and hinders the large-scale application of large-area quantum dot films. Further reducing film defects or minimizing their impact, improving the efficiency of quantum dot monolayer preparation, effectively regulating the composition and structure of quantum dot films, and achieving precise and controllable preparation of quantum dot film structures will greatly advance the large-scale, efficient preparation and practical application of high-performance lighting, display devices, and flexible electronics. Summary of the Invention

[0004] The present invention aims to limit the random crystallization behavior of colloidal quantum dots during the self-assembly process at the gas-liquid interface and improve the preparation efficiency and quality of quantum dot single-layer film structures. It provides a roll-to-roll device and method for preparing colloidal quantum dot single-layer films, which can enable colloidal quantum dots to continuously crystallize into films at the gas-liquid interface, effectively reduce film defects, and achieve precise regulation of the film structure. The film structure is continuously transferred through the roll-to-roll device to achieve continuous and controllable preparation of quantum dot single-layer film structures.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A roll-to-roll device for preparing a colloidal quantum dot monolayer film includes a spreading trough, a solution spreading assembly, and a roll-to-roll transfer mechanism. The roll-to-roll transfer mechanism consists of a flexible substrate, a driving roller, a driven roller, and two guide rollers. Brackets are respectively provided at the four corners of the spreading trough, and the brackets are provided with mounting holes. The two ends of the driving roller are respectively mounted on the two brackets on the left side of the spreading trough, and the two ends of the driven roller are respectively mounted on the two brackets on the right side of the spreading trough. The two guide rollers are installed in the spreading trough, and a fixed frame is provided in the spreading trough. The two guide rollers are located below the fixed frame. The solution spreading assembly is fixed on the inclined surface of the fixed frame in the spreading trough. The solution spreading assembly consists of a silicon wafer, a glass sheet perpendicular to the silicon wafer, and a capillary. One end of the flexible substrate is fixed on the driven roller and passes through the two guide rollers in sequence. The other end is fixed on the driving roller. The spreading trough contains a liquid carrier, and the lower end of the silicon wafer is immersed in the liquid carrier.

[0007] Furthermore, the silicon wafer is fixed on the inclined surface of the fixing frame, the glass sheet is fixed on the silicon wafer, the capillary is fixed on the glass sheet, the distance between the bottom end of the capillary and the silicon wafer is 1.0-1.5 mm, and the capillary is connected to an external ink supply device.

[0008] Furthermore, the active roller is driven by a stepping motor.

[0009] Furthermore, the included angle between the inclined surface of the fixing frame and the horizontal plane is 30°, and the flexible substrate passes under the fixing frame.

[0010] Furthermore, the height of the driving roller is higher than that of the driven roller.

[0011] Furthermore, both ends of the guide roller are respectively fixed on the front and rear walls of the spreading groove, and the two guide rollers in the spreading groove are located on the same horizontal plane.

[0012] The method for preparing a colloidal quantum dot monolayer film using the above-mentioned device is as follows: the quantum dot solution is injected into the capillary through the ink supply device, the quantum dot solution is first transferred to the angle between the silicon wafer and the glass wafer, and expands along the contact line at the angle, the quantum dots are spread into a ribbon solution along the contact line on the silicon wafer, the ribbon solution is spread on the silicon wafer to form a uniform liquid film, and after the liquid film extends to a certain distance, it contacts the carrier solution, and the surface flow is stimulated at the contact line of the carrier solution. The quantum dot solution is continuously transported to the surface of the carrier solution by the surface flow, thereby forming a quantum dot monolayer film on the surface of the carrier solution. As the quantum dot monolayer film continues to grow, the quantum dot monolayer film is transferred to the flexible substrate and continuously transferred as the flexible substrate moves.

[0013] Furthermore, the liquid carrier is one or a mixture of two or more of ethylene glycol, diethylene glycol, water and vegetable oil.

[0014] To prepare a quantum dot monolayer, a quantum dot solution of a certain concentration is injected into a capillary via an ink supply. The solution is then transferred to the contact line between the silicon wafer and the glass sheet, where it first expands at the contact line before spreading across the wafer to form a uniform liquid film. After the film extends a certain distance, it contacts the liquid carrier, stimulating Marangoni flow, which transports the colloidal quantum dots in a targeted manner to the gas-liquid interface. As the quantum dot solvent rapidly evaporates, the quantum dot film at the front of the surface flow is exposed to the solvent. The steric hindrance between the quantum dots weakens, generating capillary forces. The colloid loses stability, causing quantum dots to aggregate and form condensation nuclei, initiating the growth of the quantum dot monolayer. During this growth process, the quantum dot film, pulled by surface tension, continuously moves along the surface flow, achieving continuous and controllable growth.

[0015] During the self-assembly process of the quantum dot monolayer film at the gas-liquid interface, a roll-to-roll transfer mechanism is used to slowly drive a flexible substrate such as PET to continuously transfer the quantum dot monolayer film to the flexible substrate. During the transfer process, the growth rate of the quantum dot film and the horizontal movement rate of the flexible substrate reach a balance.

[0016] A certain amount of polymers such as PMMA or PDMS is added to the quantum dot solution, and the ordered crystallization of the polymer under the action of solvent evaporation is used to form a film, thereby inducing the directional self-assembly of quantum dots and reducing the impact of film defects and film defects on device performance.

[0017] By regulating the ratio of quantum dots to nanoparticles, polymers, etc. in the solution, the co-assembly of multi-structures is achieved in the surface flow, and the quantum dots are embedded in the solid matrix to achieve precise control of the composition and structure of the quantum dot monolayer film.

[0018] The beneficial effects of the present invention are: 1. Compared with the existing gas-liquid interface self-assembly technology, the present invention uses short-range surface flow to change the technical method of first dispersing and then forming a film at the gas-liquid interface, thereby improving the preparation efficiency and quality of quantum dot films.

[0019] 2. Realize the co-assembly of multiple assemblies in surface flow, precisely regulate the composition and structure of quantum dot films, and effectively control the optoelectronic properties of quantum dot films.

[0020] 3. Using a roll-to-roll transfer device, the continuous and controllable preparation of quantum dot single-layer film structures can be achieved, which is suitable for the large-scale preparation of quantum dot single-layer film structures.

[0021] 4. The relevant device has a simple structure, low production cost, is compatible with a variety of device processing technologies, and is suitable for large-scale preparation of devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the device for roll-to-roll preparation of colloidal quantum dot monolayer film in Example 1 of the present invention;

[0023] Figure 2 This is a schematic structural diagram of the spreading trough in Example 1 of the present invention;

[0024] Figure 3 This is a side view of the device in Example 1 of the present invention;

[0025] Figure 4 Schematic diagram of the structure of the solution spreading component in Example 1 of the present invention;

[0026] Figure 5 Schematic diagram of the solution transport and transfer process during the quantum dot self-assembly process in Example 1 of the present invention, with the inset being a left view of the solution spreading assembly;

[0027] Figure 6 The fluorescence image and film microstructure characterization of the colloidal quantum dot monolayer film structure in Example 1 of the present invention;

[0028] Figure 7 Schematic diagram of the structure and electroluminescent performance of a single-layer quantum dot film and a traditional spin-coated QLED device in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further illustrated below with reference to the accompanying drawings and specific examples. The quantum dots used below were synthesized independently in the laboratory.

[0030] like Figure 1-5As shown, this embodiment provides a roll-to-roll device for preparing a colloidal quantum dot monolayer film, the device includes a spreading tank 1, a solution spreading component 5 and a roll-to-roll transfer mechanism, the roll-to-roll transfer mechanism consists of a flexible substrate 3, an active roller 7, a driven roller 2 and two guide rollers 4 and 6. The two left corners of the spreading tank 1 are respectively provided with brackets 104, and the brackets 104 are provided with mounting holes 105. The two ends of the active roller 7 are fixed in the mounting holes 105 on the brackets 104. The two right corners of the spreading tank 1 are provided with brackets 103, and the brackets 103 are provided with mounting holes 101. The two ends of the driven roller 2 are fixed in the mounting holes 101 on the brackets 103. The guide rollers 4 and 6 for transferring the flexible substrate are fixed in two pairs of holes 106 and 107 on the front and rear walls of the spreading tank. A fixing frame 10 is provided in the spreading tank 1. 2, the flexible substrate 3 passes under the fixed frame 102. The fixed frame 102 is provided in the spreading tank 1, and two guide rollers 4 and 6 are located below the fixed frame 102. The solution spreading assembly 5 is fixed to the inclined surface of the fixed frame 102 in the spreading tank 1. The solution spreading assembly 5 consists of a silicon wafer 504, a glass sheet 502 perpendicular to the silicon wafer 504, and a capillary 501. A contact line 503 is formed at the angle between the silicon wafer 504 and the glass sheet 502. One end of the flexible substrate 3 is fixed to the driven roller 2 and passes through the two guide rollers 4 and 6 in sequence. The other end is fixed to the active roller 7. The spreading tank 1 contains a liquid carrier 12. The lower end of the silicon wafer 504 is immersed in the liquid carrier 12. The silicon wafer 504 is divided into two parts by the liquid carrier 12, one part is immersed in the liquid carrier 12, and the other part is used to form a uniform liquid film.

[0031] The silicon wafer 504 is fixed on the inclined surface of the fixing frame 102, the glass wafer 502 is fixed on the silicon wafer 504, the capillary 501 is fixed on the glass wafer 502, the distance between the bottom end of the capillary 501 and the silicon wafer 504 is 1.0-1.5 mm, and it is connected to the external ink supply device. The capillary 501 is a glass capillary or a polytetrafluoroethylene capillary with a diameter of about 1 mm.

[0032] Among them, the active roller 7 is driven by a stepping motor.

[0033] The included angle between the inclined surface of the fixing frame 102 and the horizontal plane is 30°, and the flexible substrate 3 passes under the fixing frame 102 .

[0034] In this embodiment, the driving roller 7 is higher than the driven roller 2 .

[0035] The two ends of the guide rollers 4 and 6 are respectively fixed on the front and rear walls of the spreading trough 1 , and the two guide rollers 4 and 6 in the spreading trough 1 are located on the same horizontal plane.

[0036] The method for preparing a colloidal quantum dot monolayer film using the above-mentioned device is as follows: the quantum dot solution is injected into the capillary 501 through the ink supply device, and the quantum dot solution is first transferred to the contact line 503 formed by the silicon wafer 504 and the glass wafer 502 to expand, and the quantum dots are spread into a strip solution 8 along the contact line 503 on the silicon wafer 504, and the strip solution 8 is spread on the silicon wafer 504 to form a uniform liquid film 9. After the liquid film 9 extends to a certain distance, it contacts the carrier solution 12, and the surface flow 11 is stimulated at the contact line 10 of the carrier solution 12. The quantum dot solution is continuously transported to the surface of the carrier solution 12 by the surface flow 11, thereby forming a quantum dot monolayer film 13 on the surface of the carrier solution 12. As the quantum dot monolayer film 13 continues to grow, the quantum dot monolayer film 13 is transferred to the flexible substrate 3 and continuously transferred as the flexible substrate 3 moves.

[0037] In this embodiment, the liquid carrier 12 is one or a mixture of two or more of ethylene glycol, diethylene glycol, water and vegetable oil.

[0038] By adjusting the quantum dot solvent, quantum dot concentration, etc., the self-assembly process of colloidal quantum dots at the gas-liquid interface can be effectively regulated. The colloidal quantum dots are transported to the surface of the liquid carrier 12 by the directional surface flow 11. As the quantum dot solvent evaporates rapidly, the solvent at the front end of the surface flow 11 decreases rapidly, the quantum dots leak out of the solvent, the spatial steric effect weakens, capillary forces appear between the quantum dots, the colloidal quantum dots lose stability, and begin to aggregate to form condensation nuclei. The colloidal quantum dots are continuously transported to the vicinity of the condensation nuclei by the surface flow 11, realizing the controllable self-assembly growth of the quantum dot monolayer film 13. By adjusting the horizontal movement speed of the flexible substrate 3 to match the growth speed of the quantum dot monolayer film 13, the two reach a dynamic balance, and the quantum dot monolayer film 13 is continuously transferred by the continuously moving flexible substrate 3 in the transmission device.

[0039] The roll-to-roll quantum dot monolayer fabrication apparatus and method described in this application are suitable for colloidal quantum dots of various diameters. Specifically, a green CdSe / ZnS quantum dot solution with a concentration of 6 mg / mL, using n-octane and n-hexane in a 2:1 volume ratio, was used. The quantum dot diameter was 11 nm. Ethylene glycol was added to the spreading tank 1 as the liquid carrier 12.

[0040] The quantum dot solution is injected into the capillary 501 through the ink supply device. The solution is first transferred to the contact line 503 between the silicon wafer 504 and the glass wafer 502 and spreads on the silicon wafer 504 to form a uniform liquid film 9. After contacting with ethylene glycol, it grows into a continuous and controllable monolayer film on the liquid surface. Figure 6(a) shows an optical photograph of a large-area green quantum dot monolayer film (25 cm × 13 cm). The self-assembly efficiency of the quantum dot monolayer film at the gas-liquid interface is high, and large-area thin film self-assembly can be completed within 2 minutes. Combined with a roll-to-roll transfer mechanism, the continuous and controllable preparation of quantum dot monolayer film structures can be achieved. Figure 6 (b) is an optical image of a quantum dot multilayer film after eight transfers. The resulting quantum dot single-layer film can be controllably transferred multiple times and superimposed into a multilayer film. Figure 6 (c) is the atomic force characterization of the corresponding single-layer film structure. From the characterization data, it can be seen that the film thickness is about 11nm. The prepared quantum dot film is a single-layer film structure. The film is relatively flat, with an average roughness R q =1.74nm, the quantum dots in the film are densely arranged and can be used to construct high-performance QLED devices and flexible electronic devices.

[0041] Multilayer quantum dot film QLED devices were made by spin coating. The patterned ITO glass was placed in a UV-Ozone surface plasma treatment device for 15 minutes and then taken out. 3-4 drops of PEDOT:PSS were spin coated on the ITO glass on a coater at a speed of 5000 r / min for 16 s. The electrode was wiped with water and annealed at 130 °C on a heating table for 15 min. After cooling, it was transferred to a glove box and spin coated with 40 μL of 8 mg / mL TFB chlorobenzene solution at a speed of 3000 r / min for 20 s and annealed at 150 °C for 30 min. After cooling, 40 μL of 18 mg / mL green CdSe / ZnS quantum dot n-octane solution was spin coated (after drying, the quantum dot layer thickness was 30 nm ~40 nm). Then, 40 μL of 30 mg / mL ZnO ethanol solution was spin coated at a speed of 3000 r / min for 20 s. The electrode was wiped with chlorobenzene and annealed at 60 °C for 30 min. min; after cooling, 100 nm of aluminum is evaporated in a thermal evaporation coating instrument as an electrode; finally, UV curing glue is dripped on the aluminum for packaging to complete the preparation of the QLEDs device. The PEDOT:PSS layer, TFB layer and ZnO layer in the quantum dot single-layer film QLED device are still prepared by spin coating, and the process is the same as above. The quantum dot layer in the device is prepared by the gas-liquid interface quantum dot single-layer film self-assembly method, and is transferred from the ethylene glycol liquid carrier to the TFB layer by the horizontal transfer method, followed by spin coating of zinc oxide, aluminum electrode plating, and packaging (the process is the same as the preparation of multi-layer quantum dot film QLED devices). Figure 7 The figure shows a simplified diagram of the QLED device structure and its electroluminescent performance. The single-layer quantum dot thin film device has higher brightness at the same voltage. In the high voltage and high brightness area, the single-layer film device has higher efficiency. Specifically, the maximum brightness of the quantum dot single-layer film QLED device is 92710 Cd / m 2At the same voltage, the maximum brightness of the spin-coated multi-layer quantum dot film device is only 62280 Cd / m 2 After the high voltage of 5.4V and 55780 Cd / m 2 At high brightness, compared with the multi-layer quantum dot film QLED device with a maximum external quantum efficiency of 2.86%, the single-layer quantum thin film QLED device has a higher external quantum efficiency of 3.91%, and has certain development potential in high-power light-emitting devices in the future.

[0042] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A roll-to-roll device for preparing a colloidal quantum dot monolayer film, characterized in that: The roll-to-roll transfer mechanism comprises a spreading trough, a solution spreading assembly and a roll-to-roll transfer mechanism. The roll-to-roll transfer mechanism consists of a flexible substrate, an active roller, a driven roller and two guide rollers. The two ends of the guide roller are respectively fixed on the front and rear walls of the spreading trough. The two guide rollers in the spreading trough are located on the same horizontal plane. Brackets are respectively provided at the four corners of the spreading trough, and mounting holes are provided on the brackets. The two ends of the active roller are respectively installed on the two brackets on the left side of the spreading trough, and the two ends of the driven roller are respectively installed on the two brackets on the right side of the spreading trough. The two guide rollers are installed in the spreading trough. A fixed frame is provided in the spreading trough. The two guide rollers are located below the fixed frame. The solution spreading assembly is fixed on the inclined surface of the fixed frame in the spreading trough. The solution spreading assembly consists of a silicon wafer, a glass sheet perpendicular to the silicon wafer and a capillary. The silicon wafer is fixed on the inclined surface of the fixed frame, the glass sheet is fixed on the silicon wafer, the capillary is fixed on the glass sheet, and the distance between the bottom end of the capillary and the silicon wafer is 1.0-1.5 mm, the capillary is connected to the external ink supply device; one end of the flexible substrate is fixed on the driven roller and passes through two guide rollers in sequence, and the other end is fixed on the active roller. The spreading tank is filled with liquid carrier, and the lower end of the silicon wafer is immersed in the liquid carrier.

2. The roll-to-roll device for preparing a colloidal quantum dot monolayer film according to claim 1, characterized in that: The active roller is driven by a stepper motor.

3. The roll-to-roll device for preparing a colloidal quantum dot monolayer film according to claim 1, characterized in that: The included angle between the inclined surface of the fixing frame and the horizontal plane is 30 degrees, and the flexible substrate passes under the fixing frame.

4. The roll-to-roll device for preparing a colloidal quantum dot monolayer film according to claim 1, characterized in that: The height of the active roller is higher than that of the driven roller.

5. A method for preparing a colloidal quantum dot monolayer film using the apparatus according to any one of claims 1 to 4, characterized in that: The process is as follows: the quantum dot solution is injected into the capillary through the ink supply device. The quantum dot solution is first transferred to the angle between the silicon wafer and the glass wafer, and expands along the contact line at the angle. The quantum dots are spread into a ribbon solution along the contact line on the silicon wafer. The ribbon solution is spread on the silicon wafer to form a uniform liquid film. After the liquid film extends to a certain distance, it contacts the carrier solution. The surface flow is stimulated at the contact line of the carrier solution. The quantum dot solution is continuously transported to the surface of the carrier solution by the surface flow, thereby forming a quantum dot monolayer film on the surface of the carrier solution. As the quantum dot monolayer film continues to grow, the quantum dot monolayer film is transferred to the flexible substrate and continuously transferred as the flexible substrate moves.

6. The method for preparing a colloidal quantum dot monolayer film according to claim 5, characterized in that: The liquid carrier is one or a mixture of two or more of ethylene glycol, diethylene glycol, water and vegetable oil.

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