Colloidal quantum dot film preparation method and infrared detector

Abstract

The invention provides a colloidal quantum dot film preparation method and an infrared detector, and the method comprises the steps: providing a colloidal quantum dot ink solution with a target concentration; providing a substrate, and dropwise adding a preset amount of colloidal quantum dot ink solution onto the substrate after the substrate is heated to a target temperature; keeping the target temperature, and spin-coating the colloidal quantum dot ink solution on the substrate to form a film; and carrying out thermal annealing treatment on the formed colloidal quantum dot film.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for preparing a colloidal quantum dot film and an infrared detector. Background Art

[0002] Shortwave infrared detection technology has a wide range of applications in military, industrial and medical fields, such as face recognition, night vision imaging, machine vision and cancer detection.

[0003] At present, the mainstream market uses indium gallium arsenide (InGaAs) semiconductors as short-wave infrared detection materials, but this type of material needs to be epitaxially grown on high-quality indium phosphide single crystal substrates under high-temperature vacuum process conditions; further, it is necessary to connect the prepared epitaxial indium gallium arsenide detectors to silicon-based CMOS readout circuits through complex, high-precision alignment flip-chip interconnection technology to read out the detector signal. The limited accuracy of flip-chip interconnection technology limits the development of small pixel integration of short-wave infrared detector chips; in addition, harsh process conditions and expensive indium phosphide substrates also greatly increase its production costs, thereby limiting its application and expansion of production in the field of short-wave infrared detection. Another commonly used material for short-wave infrared detection is germanium semiconductor, which can be epitaxially grown on silicon substrates. However, due to the limitations of epitaxial technology, there is a large amount of lattice mismatch at the germanium-silicon interface, resulting in a very large dark current of the germanium-silicon detector, which seriously affects the detector signal-to-noise ratio. Therefore, it is very challenging to achieve high-quality germanium-silicon short-wave infrared detector chips.

[0004] Colloidal quantum dots are a type of semiconductor nanomaterial that can be processed and synthesized by the solution method. Due to the existence of quantum confinement effects, they have adjustable and size-dependent band gap characteristics, and their light absorption range can cover the range from visible light to medium-wave areas. In addition, colloidal quantum dots have a variety of film-forming methods, and can be directly integrated with various substrates through spin coating, scraping, inkjet printing and other methods, so that they can be easily applied to indium gallium arsenide semiconductors or germanium silicon semiconductors to achieve special functions. For example, they can be directly integrated on a silicon-based CMOS readout circuit chip to achieve low-cost, high-performance short-wave infrared photodetectors, and there is hope that they can be expanded to new application areas such as flexible devices.

[0005] At present, among the various film-forming methods of colloidal quantum dot thin films, spin coating is the most mature, and the device performance prepared is the best. However, in the current film preparation process, after the spin coating process is completed, a large number of physical defects such as cracks will appear on the film surface. The presence of these cracks will lead to an increase in the carrier defect concentration and a significant increase in the defect-assisted dark current in the infrared detector. Summary of the invention

[0006] In order to solve the existing technical problems, the present application provides a colloidal quantum dot film preparation method and an infrared detector that can effectively reduce cracks on the film surface, thereby reducing defects in the film.

[0007] In a first aspect, a method for preparing a colloidal quantum dot film is provided, comprising:

[0008] providing a colloidal quantum dot ink solution of a target concentration;

[0009] Providing a substrate, and after the substrate is heated to a target temperature, taking a preset amount of colloidal quantum dot ink solution and dropping it onto the substrate;

[0010] Maintaining the target temperature, spin coating the colloidal quantum dot ink solution on the substrate to form a film;

[0011] The formed colloidal quantum dot film is subjected to thermal annealing treatment.

[0012] In a second aspect, an infrared detector is provided, comprising a colloidal quantum dot film prepared by the colloidal quantum dot film preparation method described in any embodiment of the present application.

[0013] In the method for preparing the colloidal quantum dot film provided in the above embodiment, the substrate is first heated to the target temperature, and then the colloidal quantum dot ink solution of the target concentration is dripped onto the substrate, and the colloidal quantum dot ink solution is spin-coated to form a film while being maintained at the target temperature. Synchronous heating is introduced into the spin-coating process of the colloidal quantum dot film, and the substrate is heated during the spin-coating process and maintained at the target temperature until the film is formed. In this way, the residual stress of the film during the spin-coating process can be released, and after the spin-coating is completed, uniform thermal annealing is performed, thereby effectively reducing the cracking of the film surface and reducing the defects in the film. Accordingly, the dark current of the photodetector prepared therefrom is significantly reduced, and the strong coupling phenomenon of quantum dots is exhibited, which greatly improves the detector performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Flow chart of a method for preparing a colloidal quantum dot film in one embodiment.

[0015] Figure 2 The schematic diagram of the surface of the colloidal quantum dot film obtained by the known method for preparing the colloidal quantum dot film at room temperature is shown.

[0016] Figure 3 This is a schematic diagram of the surface of a colloidal quantum dot film obtained by the colloidal quantum dot film preparation method provided in an embodiment of the present application.

[0017] Figure 4 The present invention is a flow chart of a method for preparing a colloidal quantum dot film in an optional specific example.

[0018] Figure 5 The present invention is a flow chart of a method for preparing a colloidal quantum dot film in another optional specific example.

[0019] Figure 6 Photoluminescence spectra of colloidal quantum dot films prepared at different heating temperatures.

[0020] Figure 7 The transient fluorescence lifetime of colloidal quantum dot films prepared at different heating temperatures.

[0021] Figure 8 The defect conditions of colloidal quantum dot films prepared at different heating temperatures. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. The described embodiments should not be regarded as limiting the present application. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of this application.

[0024] In the following description, the expression "some embodiments" is involved, which describes a subset of all possible embodiments. It should be noted that "some embodiments" may be the same subset or different subsets of all possible embodiments, and may be combined with each other without conflict.

[0025] In the currently known preparation process of colloidal quantum dot films, after the spin coating process is completed, a large number of physical defects such as cracks will appear on the surface of the film. The presence of these cracks will lead to an increase in the concentration of carrier defects, which will lead to a substantial increase in the dark current of the defect-assisted type in the detector. In order to realize an excellent short-wave infrared photodetector of colloidal quantum dots, it is necessary to obtain a colloidal quantum dot film with high stability and excellent photoelectric performance. The inventors of this application found in their research that during the preparation process of colloidal quantum dot films, the presence of cracks on the surface of the film is due to the stress release caused by the vacancies left after the solvent evaporates during the spin coating process. For this reason, this problem can be alleviated by a thermal annealing process. Thermal annealing can not only remove the solvent remaining in the film, but also realize the reassembly arrangement of the colloidal quantum dots, making the colloidal quantum dots more densely arranged, which greatly reduces the cracks. However, as the research progresses, it is found that microscopic cracks are still inevitable.

[0026] To this end, the inventors of the present application further proposed a technical concept of maintaining synchronous heating during the process of spin coating to prepare colloidal quantum dot thin films. By maintaining synchronous heating during the spin coating process to prepare colloidal quantum dot thin films, the evaporation of the solvent can be accelerated extremely quickly, thereby releasing the residual stress in the film to a great extent and promoting the reassembly of the colloidal quantum dots. Finally, a dense, crack-free film can be achieved through uniform annealing. The colloidal thin film quantum dots prepared by synchronous heating have a denser lattice arrangement and more effectively suppressed physical defects, which can reduce the leakage current of the detector while improving the carrier transport and photoelectric detection performance. An embodiment of the method for preparing a colloidal quantum dot thin film using this technical concept is shown below.

[0027] See also Figure 1 , is a flow chart of a method for preparing a colloidal quantum dot film provided in an embodiment of the present application, comprising the following steps:

[0028] S101, providing a colloidal quantum dot ink solution of target concentration.

[0029] Quantum dots are 2-10 nanometer semiconductor particles. The frequency of the light they emit changes with the size. Therefore, by adjusting the size of these nano-semiconductors, the color of the light they emit can be controlled to obtain high-quality pure monochromatic light. Colloidal quantum dots usually refer to nano-sized crystals synthesized and processed in solution, which can be evenly dispersed in the solution, and their surface is covered with a layer of organic ligands, which are connected to the surface of the quantum dots through coordination bonds.

[0030] The target concentration of colloidal quantum dot ink solution can be prepared by solution-phase ligand exchange, which refers to replacing the original non-functional ligand with a ligand with a specific function, thereby giving the material additional properties, such as improving the solubility, stability and biocompatibility of quantum dots.

[0031] The concentration of the colloidal quantum dot ink solution refers to the number density of quantum dot particles in the solution. The target concentration can be achieved by adjusting the size and number of quantum dots in the colloidal quantum dot ink solution.

[0032] S103, providing a substrate, and after the substrate is heated to a target temperature, taking a preset amount of colloidal quantum dot ink solution and dropping it onto the substrate.

[0033] The substrate is a basic material used to support and construct other functional layers in the manufacturing process of semiconductor devices. In this embodiment, the substrate can be materials such as glass and wafers of various sizes. The selection of the target temperature is related to the solvent and concentration of the ink. After the substrate is heated to the target temperature, a preset amount of colloidal quantum dot ink is dropped on the substrate to ensure that the substrate has reached the target temperature when the colloidal quantum dot ink solution is spin-coated on the substrate.

[0034] S105, maintaining the target temperature, and spin coating the colloidal quantum dot ink solution on the substrate to form a film.

[0035] Spin coating refers to a technique that uses centrifugal force to evenly apply a colloidal quantum dot ink solution to a substrate, such as dropping a colloidal quantum dot ink solution on a rotating substrate, and using the centrifugal force generated by the high-speed rotation of the substrate to evenly spread the colloidal quantum dot ink solution on the substrate, thereby forming a uniform thin film. In this embodiment, the colloidal quantum dot ink solution is spin-coated on the substrate to prepare a thin film at a target temperature, which can release the residual stress of the thin film during the spin coating process and promote the reassembly of the colloidal quantum dots, which is conducive to achieving a dense, crack-free thin film.

[0036] S107, performing thermal annealing treatment on the formed colloidal quantum dot film.

[0037] The thermal annealing process can remove the solvent remaining in the film and also help to achieve the reassembly arrangement of the colloidal quantum dots. In this embodiment, the synchronous heating method is introduced into the spin coating process of the colloidal quantum dot film. By heating the substrate during the spin coating process and keeping it at the target temperature, the residual stress of the film during the spin coating process is released, and the uniform thermal annealing is performed after the spin coating is completed, which can make the colloidal quantum dots more densely arranged, effectively reduce the cracking of the film surface, and thus reduce the defects in the film.

[0038] In the method for preparing the colloidal quantum dot film provided in the above embodiment, the substrate is first heated to the target temperature, and then the colloidal quantum dot ink solution of the target concentration is dripped onto the substrate, and the colloidal quantum dot ink solution is spin-coated to form a film while being maintained at the target temperature. Synchronous heating is introduced into the spin-coating process of the colloidal quantum dot film, and the substrate is heated during the spin-coating process and maintained at the target temperature until the film is formed. In this way, the residual stress of the film during the spin-coating process can be released, and after the spin-coating is completed, uniform thermal annealing is performed, thereby effectively reducing the cracking of the film surface and reducing the defects in the film. Accordingly, the dark current of the photodetector prepared therefrom is significantly reduced, and the strong coupling phenomenon of quantum dots is exhibited, which greatly improves the detector performance.

[0039] See also Figure 2 and Figure 3 , respectively, are surface schematic diagrams of a colloidal quantum dot film obtained by a known method for preparing a colloidal quantum dot film at room temperature, and are surface schematic diagrams of a colloidal quantum dot film obtained by the method for preparing a colloidal quantum dot film provided in an embodiment of the present application. By comparing the two figures, it can be seen that the quantum dot lattice arrangement in the colloidal quantum dot film prepared by synchronous heating is denser, and physical defects are significantly and effectively suppressed.

[0040] In some embodiments, step S103 includes:

[0041] Provide a glue machine and set the target temperature;

[0042] After reaching the target temperature, the substrate is placed in a coating machine and allowed to stand for a preset time to heat the substrate to the target temperature, and then a preset amount of colloidal quantum dot ink solution is dripped onto the substrate.

[0043] Spin coater, also known as spin coating instrument, is a laboratory equipment used in the material film preparation process. Its principle is to use the centrifugal force generated by the high-speed rotation of the motor to evenly coat the glue on the surface of the substrate material to form a uniform film with a thickness of micrometers or nanometers. In this embodiment, by setting the target temperature of the spin coater, the substrate is heated by using the heating function of the spin coater, and the substrate is heated to the target temperature before the colloidal quantum dot ink solution is dripped onto the substrate. The substrate is heated during the spin coating process to keep it at the target temperature, so that the residual stress of the film during the spin coating process can be released, and the cracks in the film can be effectively reduced, so as to obtain a highly stable colloidal quantum dot film with excellent photoelectric properties.

[0044] Optionally, the preset time length is 30s, and the preset volume is 10ul-1mL.

[0045] The target temperature of the coating machine is set, and after the temperature of the coating machine rises to the specified temperature, the substrate is placed in the coating machine and left to stand for 30 seconds until the substrate reaches the target temperature. After the substrate is heated to the target temperature, 10ul (microliter)-1mL (milliliter) of colloidal quantum dot ink solution is dripped onto the substrate to ensure that the colloidal quantum dot ink solution can be initially spread more quickly and evenly on the substrate after being dripped onto the substrate.

[0046] In some embodiments, in steps S103 and S105, heating the substrate to a target temperature and maintaining the target temperature include:

[0047] A glove box filled with inert gas is provided, the temperature inside the glove box is set to the target temperature, and the coating machine is placed in the glove box.

[0048] The glove box is a laboratory equipment that fills the box with high-purity inert gas and circulates to filter out the active substances in it. In the preparation process of colloidal quantum dot thin film, during the spin coating process, the thickness of the film is controlled by controlling the time, rotation speed, dripping amount of the coating, and the concentration and viscosity of the solution used. The use of the glove box can provide a dry, dust-free, and oxygen-free operating environment for the coating machine. For the processing of materials with high purity requirements or those sensitive to humidity and oxygen, it can protect the materials from contamination and ensure the smooth progress of the spin coating process. In addition, the glove box can effectively prevent operators from direct contact with materials, reduce human errors, and improve the safety of operations.

[0049] In the above embodiment, in the method for preparing the colloidal quantum dot film, a glove box is used in combination with a coater to maintain the target temperature of the substrate during the entire spin coating process, which helps to maintain the stability of the environment, ensure the precise control of parameters during the spin coating process, and more accurately obtain the required film thickness, thereby improving the film quality.

[0050] In some embodiments, step S105 includes:

[0051] Maintaining the target temperature, accelerating the substrate from a static state at a preset acceleration until the spin coating speed of the coating machine reaches a preset speed threshold and the spin coating time reaches a first time length;

[0052] The spin coating speed of the coating machine is adjusted to a preset film forming speed range, and the spin coating is maintained at a speed within the preset film forming speed range for a second time period to obtain a colloidal quantum dot film formed after the solvent in the ink evaporates.

[0053] In this embodiment, after the substrate is heated to the target temperature and a preset amount of colloidal quantum dot ink solution is dripped onto the substrate, static spin coating can be used for spin coating of the colloidal quantum dot ink solution on the substrate to form a film. First, the substrate is accelerated from a static state at a preset acceleration until a preset speed threshold is reached, and the entire process lasts for a first time period. This process can evenly spread the ink on the substrate; then, while the substrate is heated to maintain the target temperature, the colloidal quantum dot ink solution that has been initially spread is spin coated at a rotation speed within a preset film-forming speed range to form a film.

[0054] Optionally, the preset acceleration is 600 rpm / min, the preset speed threshold is 1200 rpm, and the first time length is 1 to 10 s;

[0055] The preset film forming speed range is 2000 rpm to 3500 rpm, and the second time length is 40s to 120s.

[0056] During the static spin coating process, when the substrate is heated to the target temperature and the colloidal quantum dot ink solution is dripped onto the substrate surface, the substrate is rotated from a static state at 600rpm / min until the spin coating rate reaches 1200rpm. The whole process lasts for 1 to 10 seconds to ensure that the colloidal quantum dot ink solution is evenly spread on the substrate. Subsequently, the speed of the coating machine is adjusted to the preset film forming speed range of 2000rpm to 3500rpm, and the spin coating is continued at a speed of 2000rpm to 3500rpm for 40s to 120s. During this process, the solvent of the ink in the colloidal quantum dot ink solution will evaporate in large quantities, leaving a dense colloidal quantum dot film.

[0057] In some embodiments, step S105 includes:

[0058] Maintaining the target temperature, adjusting the spin coating speed of the coating machine to a preset uniform speed interval, and maintaining the spin coating at the preset uniform speed interval for a first time period;

[0059] The spin coating speed of the coating machine is adjusted to a preset film forming speed range, and the spin coating is maintained at a speed within the preset film forming speed range for a second time period to obtain a colloidal quantum dot film formed after the solvent in the ink evaporates.

[0060] In this embodiment, after the substrate is heated to the target temperature and a preset amount of colloidal quantum dot ink solution is dripped onto the substrate, the spin coating of the colloidal quantum dot ink solution on the substrate to form a film can be performed by dynamic spin coating. During the dynamic spin coating process, the speed of the coating machine is first adjusted to a preset uniform speed range for spin coating, and the entire process lasts for a first time. Through this process, the ink is first uniformly spread on the substrate; then, the substrate is heated to maintain the target temperature, and the colloidal quantum dot ink solution after preliminary uniform coating is spin coated at a speed within the preset film forming speed range to form a film.

[0061] Optionally, the preset uniform opening speed range is 700 rpm to 1200 rpm, and the first time length is 1 to 10 s;

[0062] The preset film forming speed range is 2000 rpm to 3500 rpm, and the second time length is 40s to 120s.

[0063] During the dynamic spin coating process, when the substrate is heated to the target temperature and the colloidal quantum dot ink solution is dripped onto the substrate surface, the speed of the coating machine is first adjusted to 700rpm~1200rpm for spin coating. The whole process lasts for 1~10s to ensure that the colloidal quantum dot ink solution is first spread on the substrate. Subsequently, the speed of the coating machine is adjusted to the preset film forming speed range of 2000rpm~3500rpm, and the spin coating is continued at a speed of 2000rpm~3500rpm for 40s~120s. During this process, the solvent of the ink in the colloidal quantum dot ink solution will evaporate in large quantities, leaving a dense colloidal quantum dot film.

[0064] In some embodiments, in step S107 , the annealing temperature is 50-120° C., and the annealing time is 5-30 min.

[0065] After the spin coating process is completed, whether static spin coating or dynamic spin coating is used, annealing treatment is used. Depending on the ink concentration in the colloidal quantum dot ink solution, the annealing temperature can be 50-120°C, and the annealing time is controlled at 5-30min. By combining annealing with the spin coating process with synchronous heating during spin coating, the residual stress of the film during the spin coating process can be released during the film formation of the colloidal quantum dot film, and the reassembly of the colloidal quantum dots can be promoted, so that the lattice arrangement of the film quantum dots is more dense, and the stress release after the solvent evaporates and leaves vacancies after film formation causes cracks, thereby effectively reducing the surface cracks of the film after film formation. After spin coating, further annealing treatment can be used to further remove the solvent that may remain in the film, assist the reassembly and arrangement of the colloidal quantum dots, and make the colloidal quantum dots more densely arranged. Overall, by combining annealing with the spin coating process with synchronous heating during spin coating, the colloidal quantum dot film obtained shows a strong coupling phenomenon of quantum dots, which can effectively reduce the dark current of the photodetector prepared therefrom.

[0066] In order to have a more comprehensive understanding of the colloidal quantum dot film preparation method provided in the embodiments of the present application, please refer to Figure 4 and Figure 5 , the following is a specific example to illustrate:

[0067] S11, preparing a colloidal quantum dot ink solution by solution phase ligand exchange, with a concentration of 50 mg / ml-400 mg / ml.

[0068] S12, before the spin coating process, the target temperature of spin coating is set to X°C by using a heated coating machine. After the temperature rises to the target temperature, the substrate is placed in the coating machine, and it is left to stand for 30 seconds until the substrate is also heated to the target temperature, and 10ul-1mL of colloidal quantum dot ink solution is dripped on the substrate.

[0069] Optionally, the target temperature is usually higher than room temperature and not greater than 55°C. Optionally, a glove box filled with inert gas is provided, the glove box temperature is set to a target temperature of X°C, and a coating machine is placed in the glove box. The target temperature X can be selected from the range of: 25°C, 27°C, 29°C-35°C, 37°C-55°C, and the thin film is prepared by spin coating by heating the substrate to the target temperature and maintaining it at the target temperature. In an optional specific example, the target temperature is 45°C, see Figures 6 to 8 , are the test results of the inventor of this application preparing colloidal quantum dot films at different target temperatures, Figure 6 The figure shows the emission measurement of colloidal quantum dot films prepared at different target temperatures. The higher the emission peak (PLIntensity) at the corresponding wavelength (Wavelength), the fewer film defects there are; Figure 7 Shown is the measurement of transient fluorescence lifetime (TRPL) of colloidal quantum dot films prepared at different target temperatures. The longer the TRPL lifetime, the fewer film defects. Figure 8 Shown are the measurements of spatially confined charge (SCLC) of colloidal quantum dot films prepared at different target temperatures, V TFL The smaller the value, the less cracking of the film and the better the quality of the film. trap Represents the number of defects in the film.

[0070] S13, maintaining the target temperature, and using a static spin coating process to spin-coat the colloidal quantum dot ink solution dripped on the substrate into a film.

[0071] During the static spin process, after the colloidal quantum dot ink solution is dropped on the substrate, the substrate is accelerated from a static state at an acceleration of 600rpm / min until the spin coating rate reaches 1200rpm. The whole process lasts 1-10s. Usually, the ink concentration can be from 50mg / ml to 400mg / ml. The duration of this process mainly depends on the ink concentration. In this process, the colloidal quantum dot ink solution is first evenly spread on the substrate; then the speed of the coating machine is adjusted to 2000rpm-3500rpm and the spin coating is continued for 40s-120s. In this process, the solvent in the colloidal quantum dot ink solution will evaporate in large quantities, leaving a dense colloidal quantum dot film.

[0072] Or, S14, maintaining the target temperature, and using a dynamic spin coating process to spin-coat the colloidal quantum dot ink solution dropped on the substrate into a film.

[0073] During the dynamic spin coating process, first adjust the speed of the coater to 700-1200rpm, take 10ul-1mL of colloidal quantum dot ink solution and drop it on the rotating substrate, and then continue the whole process for 1-10s; then adjust the speed of the coater to 2000rpm-3500rpm and continue to spin coat for 40s-120s, leaving a dense colloidal quantum dot film.

[0074] Regarding how to set the target temperature in the spin coating process, and maintain the rotation speed at the target temperature when spin coating the colloidal quantum dot ink solution on the substrate to form a film, so that the solvent can fully evaporate to release stress and reduce cracks during the film formation process of the colloidal quantum dot film, the inventors of the present application have conducted in-depth research and testing, and provided an embodiment of the following optimized combination of target concentration, target temperature and rotation speed during spin coating.

[0075] Optionally, in the step of spin coating the colloidal quantum dot ink solution on the substrate to form a film, the corresponding relationship between the spin coating process parameters and the concentration of the colloidal quantum dot ink solution includes at least one of the following:

[0076] The target concentration is 50 mg / ml, and the spin coating process parameters include: the target temperature is 55° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 800 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm;

[0077] The target concentration is 100 mg / ml, and the spin coating process parameters include: the target temperature is 50° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm;

[0078] The target concentration is 150 mg / ml, and the spin coating process parameters include: the target temperature is 47° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm;

[0079] The target concentration is 200 mg / ml, and the spin coating process parameters include: the target temperature is 45° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm;

[0080] The target concentration is 300 mg / ml, and the spin coating process parameters include: the target temperature is 40° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1200 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm;

[0081] The target concentration is 400 mg / ml, and the spin coating process parameters include: the target temperature is 35° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1200 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm.

[0082] Among them, the above-mentioned embodiments of the target concentration of the colloidal quantum dot ink solution, the target temperature, and the optimized combination of the uniform rotation speed and the film-forming rotation speed during spin coating can cover the preparation of colloidal quantum dot films with a concentration range of 50 mg / ml to 400 mg / ml of the colloidal quantum dot ink solution. The preparation can meet different detector performance and application requirements by selecting inks of different concentrations.

[0083] S15, thermal annealing treatment is performed. Depending on the ink concentration, the annealing temperature can be 50-120°C and the annealing time is controlled within 5-30 minutes. Finally, annealing treatment is required after the spin coating process in S13 or S14 is completed.

[0084] In the above embodiment, by introducing a synchronous heating method into the spin coating process of the colloidal quantum dot ink film, by heating the substrate during the spin coating process and maintaining the substrate at the target temperature, the residual stress of the film during the spin coating process can be released, and uniform thermal annealing is performed after the spin coating is completed, which effectively reduces the cracking of the film surface and the defects of the film. The colloidal quantum dot film after film formation will show a strong coupling phenomenon of quantum dots, effectively reducing the dark current of the photodetector prepared therefrom.

[0085] On the other hand, an embodiment of the present application further provides an infrared detector, comprising a colloidal quantum dot thin film prepared by the colloidal quantum dot thin film preparation method described in any embodiment of the present application.

[0086] In an optional specific example, the infrared detector includes from bottom to top: a transparent substrate (SUB), a first electrode layer (E1), an electron transport layer (ETL), a quantum dot absorption layer (CQDs), a hole transport layer (HTL) and a second electrode (E2). Among them, the quantum dot absorption layer can be a colloidal quantum dot film layer prepared by the colloidal quantum dot film preparation method described in the embodiment of the present application. By obtaining a colloidal quantum dot film with higher density and no cracks, the dark current phenomenon of the infrared detector can be effectively improved, and the strong coupling phenomenon of quantum dots is exhibited, so that the detector performance is greatly improved.

[0087] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a colloidal quantum dot film, characterized in that: include: providing a colloidal quantum dot ink solution of a target concentration; Providing a substrate, and after the substrate is heated to a target temperature, taking a preset amount of colloidal quantum dot ink solution and dropping it onto the substrate; Maintaining the target temperature, spin coating the colloidal quantum dot ink solution on the substrate to form a film; The formed colloidal quantum dot film is subjected to thermal annealing treatment.

2. The method for preparing a colloidal quantum dot thin film according to claim 1, characterized in that: The step of providing a substrate, heating the substrate to a target temperature, and then dropping a preset amount of colloidal quantum dot ink solution onto the substrate comprises: Provide a glue machine and set the target temperature; After reaching the target temperature, the substrate is placed in a coating machine and allowed to stand for a preset time to heat the substrate to the target temperature, and then a preset amount of colloidal quantum dot ink solution is dripped onto the substrate.

3. The method for preparing a colloidal quantum dot thin film according to claim 2, characterized in that: The preset time length is 30s, and the preset volume is 10ul-1mL.

4. The method for preparing a colloidal quantum dot thin film according to claim 1, characterized in that: Heating the substrate to a target temperature, and maintaining the target temperature, comprises: A glove box filled with inert gas is provided, the temperature inside the glove box is set to the target temperature, and the glue spinner is placed in the glove box.

5. The method for preparing a colloidal quantum dot thin film according to claim 1, characterized in that: The step of maintaining the target temperature and spin coating the colloidal quantum dot ink solution on the substrate to form a film comprises: Maintaining the target temperature, accelerating the substrate from a static state at a preset acceleration until the spin coating speed of the coating machine reaches a preset speed threshold and the spin coating time reaches a first time length; The spin coating speed of the coating machine is adjusted to a preset film forming speed range, and the spin coating is maintained at a speed within the preset film forming speed range for a second time period to obtain a colloidal quantum dot film formed after the solvent in the ink evaporates.

6. The method for preparing a colloidal quantum dot thin film according to claim 5, characterized in that: The preset acceleration is 600 rpm / min, the preset speed threshold is 1200 rpm, and the first time length is 1 to 10 seconds; The preset film forming speed range is 2000 rpm to 3500 rpm, and the second time length is 40s to 120s.

7. The method for preparing a colloidal quantum dot thin film according to claim 1, characterized in that: The step of maintaining the target temperature and spin coating the colloidal quantum dot ink solution on the substrate to form a film comprises: Maintaining the target temperature, adjusting the spin coating speed of the coating machine to a preset uniform speed interval, and maintaining the spin coating at the preset uniform speed interval for a first time period; The spin coating speed of the coating machine is adjusted to a preset film forming speed range, and the spin coating is maintained at a speed within the preset film forming speed range for a second time period to obtain a colloidal quantum dot film formed after the solvent in the ink evaporates.

8. The method for preparing a colloidal quantum dot thin film according to claim 7, characterized in that: The preset uniform opening speed range is 700 rpm to 1200 rpm, and the first time length is 1 to 10 seconds; The preset film forming speed range is 2000 rpm to 3500 rpm, and the second time length is 40s to 120s.

9. The method for preparing a colloidal quantum dot thin film according to any one of claims 1 to 8, characterized in that: The annealing temperature is 50-120°C and the annealing time is 5-30min.

10. The method for preparing a colloidal quantum dot thin film according to any one of claims 1 to 8, characterized in that: In the step of spin coating the colloidal quantum dot ink solution on the substrate to form a film, the corresponding relationship between the spin coating process parameters and the concentration of the colloidal quantum dot ink solution includes at least one of the following: The target concentration is 50 mg / ml, and the spin coating process parameters include: the target temperature is 55° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 800 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm; The target concentration is 100 mg / ml, and the spin coating process parameters include: the target temperature is 50° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm; The target concentration is 150 mg / ml, and the spin coating process parameters include: the target temperature is 47° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm; The target concentration is 200 mg / ml, and the spin coating process parameters include: the target temperature is 45° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1000 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm; The target concentration is 300 mg / ml, and the spin coating process parameters include: the target temperature is 40° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1200 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm; The target concentration is 400 mg / ml, and the spin coating process parameters include: the target temperature is 35° C., the rotation speed of first spreading the colloidal quantum dot ink solution on the substrate is 1200 rpm, and then the rotation speed of spin coating the colloidal quantum dot ink solution on the substrate to form a film is 2400 rpm.

11. An infrared detector, characterized in that: The invention comprises a colloidal quantum dot film prepared by the colloidal quantum dot film preparation method according to any one of claims 1 to 10.

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