Perovskite nanocrystal preparation method and device based on second-order microfluidic system

Abstract

The invention discloses a perovskite nanocrystal preparation method and device based on a second-order microfluidic system, and the method comprises the steps: injecting a cation precursor solution and a lead halide precursor solution into the microfluidic system through an injection pump, and respectively preheating the precursor solutions; and mixing the preheated precursor solution in a microfluidic system, and carrying out primary heating and secondary heating. And finally, cooling to obtain the nanocrystal at the outlet of the microfluidic system. The invention also provides a microfluidic device for realizing the preparation method, and the microfluidic device comprises an injection pump, a precursor preheating module, a multi-interface communicator, and a heating module I, a refrigeration module, a heating module II and a quenching module which are cascaded in sequence. The temperature of different reaction stages is independently adjusted through the precursor preheating module, the heating module I and the heating module II, the crystallization and growth process is optimized, the problem of micro-pipeline blockage caused by precursor precipitation at high temperature is avoided, the system stability is improved, and batch preparation of high-performance perovskite photoelectric materials is supported.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology and relates to the preparation of nanocrystals, and in particular to a method and device for preparing perovskite nanocrystals based on a second-order microfluidic system. Background Art

[0002] Perovskite nanocrystals are composed of a limited number of atoms, and the sizes of the three dimensions are all in the nanometer order. They are semiconductor nanostructures that bind excitons in one or more spatial directions. Compared with traditional nanocrystals, perovskite nanocrystals not only have the advantages of wide excitation spectrum, narrow luminescence spectrum, adjustable luminescence color, large absorption cross section and long fluorescence lifetime, but also have broad development prospects in the field of optoelectronic devices such as solar cells, light-emitting diodes and lasers.

[0003] Microfluidic synthesis strategies have been widely used in the mass production of perovskite nanocrystals due to their advantages such as high heat transfer efficiency, precise controllable reaction time, and high degree of precursor conversion. However, there are still some problems with the existing microfluidic preparation process. For example, the microscale flow system usually only contains one heating reaction area, which means that the two processes of crystallization and growth can only be completed at a single temperature after the precursors converge. It is difficult to dynamically adjust the temperature during the reaction, which limits the fine control of the crystallization and growth processes, and thus affects the quality and structural richness of the product. At the same time, at higher reaction temperatures, some precursors (such as PbBr2) are easily precipitated in the polytetrafluoroethylene tube, causing blockage of the microchannel, thereby affecting the stability of perovskite nanocrystal production. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a method and device for preparing perovskite nanocrystals based on a second-order microfluidic system. By designing multiple independent temperature control areas in the microfluidic system, the temperature of the perovskite nanocrystals in the crystallization and growth stages is dynamically adjusted, solving the problem of single synthesis temperature in the traditional microfluidic method. At the same time, the goal of growing perovskite nanocrystals at a higher temperature is achieved, avoiding the problem of micro-channel blockage caused by precursor precipitation during high-temperature synthesis. Efficient preparation of perovskite nanocrystals is ensured, which is suitable for large-scale production.

[0005] A method for preparing perovskite nanocrystals based on a second-order microfluidic system, using a syringe pump to inject a cationic precursor solution and a lead halide precursor solution into the microfluidic system at the same speed, and preheat the precursor solutions respectively. Then, the preheated precursor solutions are mixed, heated once, and heated twice in the microfluidic system. Finally, the temperature is lowered, and APbX3 nanocrystals are obtained at the outlet of the microfluidic system. The size, morphology, and exciton confinement type of the APbX3 nanocrystals cover quantum dots, nanorods, and nanosheets, where A is Cs + 、MA + , FA+ One or more of, X is Cl - Br - ,I - One or more of .

[0006] Preferably, the flow rate of the precursor solution entering the microfluidic system is controlled by a syringe pump to be 0.23-0.53 mL / min.

[0007] Preferably, the precursor solution is preheated at a temperature of 20 to 170° C. and a preheating time of 3 to 35 s.

[0008] Preferably, the temperature difference between the first heating and the second heating in the microfluidic system is -105°C to 170°C.

[0009] Preferably, the primary heating temperature is set to 80-170°C, and the heating time is set to 1-50 s; the secondary heating temperature is set to 65-250°C, and the heating time is set to 1-50 s.

[0010] Preferably, the cationic precursor solution is a mixed solution of one or more of cesium acetate, cesium carbonate, formamidine acetate, methylamine, octadecene, and oleic acid, wherein the volume ratio of octadecene to oleic acid is (0.33-15): 1. The lead halide precursor solution is a mixed solution of lead halide, octadecene, oleic acid, and oleylamine, wherein the volume ratio of octadecene, oleic acid, and oleylamine is 10: (1-3): (1-3), and the lead halide is lead chloride, lead bromide, lead iodide, or a mixture of any two.

[0011] Preferably, the concentration ratio of cations in the cationic precursor solution to lead ions in the lead halide precursor solution is 1:(0.16-10).

[0012] Preferably, the cation concentration in the cation precursor solution is 0.008-0.25 mol / L, and the lead ion concentration in the lead halide precursor solution is 0.012-0.120 mol / L.

[0013] The perovskite nanocrystal preparation device based on the second-order microfluidic system includes a syringe pump, two precursor preheating modules, a multi-interface connector, a heating module I, a cooling module, a heating module II and a quenching module. The precursor preheating module, the heating module I and the heating module II all include a microfluidic pipeline and a heater, and the cooling module and the quenching module all include a microfluidic pipeline and a refrigerator, wherein the heater or refrigerator is used to heat or cool the microfluidic pipeline.

[0014] The two precursor preheating modules independently control the heating temperature through the heater, the microfluidic pipeline inlet is connected to the injection pump outlet respectively, and the outlet is connected to the microfluidic pipeline inlet of the heating module I through a multi-interface connector. The microfluidic pipelines are connected in sequence according to the order of heating module I, refrigeration module, heating module II and quenching module. When the heating temperature of heating module II is set lower than that of heating module I, the refrigeration module is used to cool down.

[0015] Preferably, the heating rates of the precursor preheating module, heating module I and heating module II are set to 80°C / s to 100°C / s, and the cooling rates of the refrigeration module and quenching module are set to 150 to 170°C / s.

[0016] The present invention has the following beneficial effects: (1) Dynamic temperature control: By independently adjusting the temperature of different reaction stages, the crystallization and growth processes are optimized, overcoming the limitations of single temperature reaction in existing technologies.

[0017] (2) Prevent pipeline blockage: By heating in stages, the problem of micro-pipeline blockage caused by the precipitation of precursors (such as PbBr2) at high temperatures can be avoided, thereby improving system stability.

[0018] (3) High-temperature preparation: Achieve high-temperature growth of nanocrystals, trigger the mixed growth mode, and induce the formation of large-sized or special-morphology nanocrystals.

[0019] (4) Adaptability to large-scale production: The system can flexibly adjust the heating temperature and logically set the preparation process, which is suitable for continuous production and large-scale application, and supports the batch preparation of high-performance perovskite optoelectronic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the perovskite nanocrystal preparation device based on the second-order microfluidic system.

[0021] Figure 2 The fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in Example 1.

[0022] Figure 3 The transmission electron microscope image of the perovskite nanocrystals prepared in Example 1 and the corresponding size distribution diagram.

[0023] Figure 4 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 2 and the corresponding size distribution diagram.

[0024] Figure 5 The transmission electron microscope image of the perovskite nanocrystals prepared in Example 4 and the corresponding size distribution diagram.

[0025] Figure 6The transmission electron microscope image of the perovskite nanocrystals prepared in Example 6 and the corresponding size distribution diagram.

[0026] Figure 7 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 10 and the corresponding size distribution diagram.

[0027] Figure 8 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 12.

[0028] Fig. 9 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 13 and the corresponding size distribution diagram.

[0029] Fig.10 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 14 and the corresponding size distribution diagram.

[0030] Fig.11 These are the fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in Example 15.

[0031] Fig.12 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 15 and the corresponding size distribution diagram.

[0032] Fig.13 These are the fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in Example 16.

[0033] Fig.14 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 16 and the corresponding size distribution diagram.

[0034] Fig.15 These are the fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in Example 17.

[0035] Fig.16 This is the transmission electron microscope image of the perovskite nanocrystals prepared in Example 17 and the corresponding size distribution diagram.

[0036] Fig.17 These are the fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in Example 18.

[0037] Fig.18 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 18 and the corresponding size distribution diagram.

[0038] Fig.19 This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 19.

[0039] Fig. 20This is a transmission electron microscope image of the perovskite nanocrystals prepared in Example 20 and the corresponding size distribution diagram. DETAILED DESCRIPTION

[0040] The present invention is further explained below in conjunction with the accompanying drawings; based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work all belong to the protection scope of the present invention. The experimental methods in the following embodiments are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified.

[0041] Example 1 like Figure 1 As shown, a perovskite nanocrystal preparation device based on a second-order microfluidic system includes a syringe pump, two precursor preheating modules, a three-way joint, a heating module I, a cooling module, a heating module II and a quenching module. The precursor preheating module, the heating module I and the heating module II all include a microfluidic pipeline and a heater, and the cooling module and the quenching module all include a microfluidic pipeline and a refrigerator, wherein the heater or refrigerator is used to heat or cool the microfluidic pipeline. The microfluidic pipeline is a polytetrafluoroethylene tube with an inner diameter of 0.5 mm, the heater is an aluminum heating plate, and the refrigerator is an aluminum cooling plate. Grooves are provided on the surface of the heater and the refrigerator for fixing the polytetrafluoroethylene tube.

[0042] The microfluidic pipeline inlets of the multiple precursor preheating modules are respectively connected to the outlets of the injection pumps, and the outlets are connected to the microfluidic pipeline inlet of the heating module I through a three-way joint. The microfluidic pipelines are connected in sequence according to the order of heating module I, cooling module, heating module II and quenching module.

[0043] The flow rate of the precursor solution entering the precursor preheating module is controlled by a syringe pump, and the reaction time can be controlled by changing the length of the microfluidic channel.

[0044] A method for preparing perovskite nanocrystals based on a second-order microfluidic system, specifically comprising the following steps: Step 1: Prepare cationic precursor solution 0.13 mmol cesium acetate, 12 mL octadecene, and 1 mL oleic acid were added to a three-necked flask with a volume of 50 mL. The flask was connected to a vacuum pump and evacuated continuously for 10 minutes to completely evaporate the water. While maintaining the vacuum, the mixture in the flask was heated to 110-130 °C and maintained for 1 hour. After the cesium acetate was completely reacted, it was cooled to room temperature to obtain the cationic precursor solution, in which the concentration of cesium ions was 0.01 mol / L. The solution was transferred to a sample bottle and sealed for subsequent use.

[0045] Step 2: Preparation of lead halide precursor solution 0.42 mmol lead iodide, 10 mL octadecene, 1 mL oleic acid, and 1 mL oleylamine were added to a 50 mL three-necked flask, and the flask was connected to a vacuum pump to continuously evacuate the water to completely evaporate. Under the condition of maintaining vacuum, the mixture in the flask was heated to 110-130 ° C and maintained for 1 hour. After the lead iodide was completely reacted, the lead halide precursor solution was obtained, wherein the concentration of lead iodide was 0.035 mol / L. The solution was transferred to a sample bottle and sealed for subsequent use.

[0046] Step 3: Prepare APbX3 nanocrystals using the perovskite nanocrystal preparation device based on the second-order microfluidic system The cationic precursor solution and the lead halide precursor solution are preheated in different precursor preheating modules through a syringe pump, and the injection speed of the syringe pump is set to 0.25 mL / min. The cationic precursor solution is preheated at 20°C, and the lead halide precursor solution is preheated at 160°C. The preheated precursor solutions are mixed through a three-way joint and enter the heating module I, heated at 160°C for 1s, and then enter the heating module II through the refrigeration module, and heated at 210°C for 5s to complete the secondary heating. Finally, the quenching module is passed through the quenching module, and the temperature is lowered at a rate of 170°C / s. The perovskite nanocrystals are collected at the outlet of the microfluidic pipeline of the quenching module, and the perovskite nanocrystals are dispersed in n-hexane after washing and centrifugation.

[0047] The fluorescence spectrum and absorption spectrum of the perovskite nanocrystals prepared in this example are as follows: Figure 2 The transmission electron microscopy images and size distribution histograms are shown in Figure 3 As shown, it can be seen from the size distribution histogram that the average size of the perovskite nanocrystals prepared in this embodiment is 15.9 nm.

[0048] Example 2 In this example, based on Example 1, the time for secondary heating using heating module II in step 3 was modified to 20 seconds. The transmission electron microscope image and size distribution histogram of the prepared perovskite nanocrystals are shown in FIG. Figure 4 As shown in Figure 2, the average size of the obtained perovskite nanocrystals is 22.0 nm. From the transmission electron microscopy image, it can be seen that the synthesized perovskite nanocrystals have both monomer growth and fusion growth characteristics.

[0049] Example 3 In this embodiment, based on the embodiment 1, the time for the secondary heating using the heating module II in step 3 is modified to 50 seconds.

[0050] Example 4 In this example, based on Example 1, the concentration of lead iodide in the lead halide precursor solution prepared in step 2 was adjusted to 0.07 mol / L, and the transmission electron microscopy image and size distribution histogram of the prepared perovskite nanocrystals were as follows: Figure 5 As shown, the average size of the obtained perovskite nanocrystals is 12.4 nm.

[0051] Example 5 In this embodiment, based on the embodiment 4, the time for the secondary heating using the heating module II in step 3 is modified to 50 seconds.

[0052] Example 6 In this example, based on Example 1, the concentration of lead iodide in the lead halide precursor solution prepared in step 2 was adjusted to 0.017 mol / L, and the transmission electron microscopy image and size distribution histogram of the prepared perovskite nanocrystals were as follows: Figure 6 As shown, the average size of the obtained perovskite nanocrystals is 15.2 nm.

[0053] Example 7 In this embodiment, based on the embodiment 6, the time for the secondary heating using the heating module II in step 3 is modified to 50 seconds.

[0054] Example 8 In this embodiment, based on Embodiment 1, the heating time of heating module 1 in step 3 is modified to 5 s.

[0055] Example 9 In this embodiment, based on the embodiment 8, the time for the secondary heating using the heating module II in step 3 is modified to 50 seconds.

[0056] Example 10 In this embodiment, based on the embodiment 1, the heating time of the heating module I in step 3 is modified to 50 seconds. The transmission electron microscope image and size distribution histogram of the prepared perovskite nanocrystals are shown in FIG. Figure 7 As shown, the average size of the obtained perovskite nanocrystals is 14.7 nm.

[0057] Embodiment 11 In this embodiment, based on Embodiment 10, the time for secondary heating using heating module II in step 3 is modified to 50 seconds.

[0058] Example 12 In this embodiment, based on the embodiment 1, the temperature for preheating the lead halide precursor solution in step 3 is changed to 80°C, the temperature for the first heating using the heating module I is changed to 80°C, and the time for the second heating using the heating module II is changed to 1 s. The transmission electron microscope image of the prepared perovskite nanocrystal is as follows: Figure 8 As shown, it can be seen that the obtained perovskite nanocrystals have triangular morphological characteristics.

[0059] Example 13 In this example, based on Example 1, the temperature of the two precursor preheating modules in step 3 was set to 20° C. The transmission electron microscope image and size distribution histogram of the prepared perovskite nanocrystals are as follows: Fig. 9 As shown, the average size of the obtained perovskite nanocrystals is 13.0 nm and the fluorescence quantum yield is 67%.

[0060] Embodiment 14 In this embodiment, based on the embodiment 1, the heating temperature of the two precursor preheating modules in step 3 is set to 160°C, and the cationic precursor solution and the lead halide precursor solution are preheated respectively. The transmission electron microscopy image and size distribution histogram of the prepared perovskite nanocrystals are shown in FIG. Fig.10 As shown, the average size of the obtained perovskite nanocrystals is 15.8 nm.

[0061] Embodiment 15 In this example, on the basis of Example 1, the lead iodide used to prepare the lead halide precursor solution in step 2 was replaced with 0.42 mmol of lead bromide, the temperature for preheating the cationic precursor solution in step 3 was changed to 170°C, the temperature for the first heating using heating module I was changed to 170°C, and the heating time for the second heating using heating module II was changed to 12 s. The fluorescence spectrum and absorption spectrum of the prepared perovskite nanocrystals are shown in FIG. Fig.11 The transmission electron microscopy images and size distribution histograms are shown in Fig.12 As shown, the average size of the obtained perovskite nanocrystals is 14.0 nm.

[0062] Example 16 In this example, on the basis of Example 1, the lead iodide used in preparing the lead halide precursor solution in step 2 is replaced by a mixture of 0.42 mmol of lead bromide and lead iodide, wherein the molar ratio of lead bromide to lead iodide is 1:1. The heating time of the secondary heating using heating module II in step 3 is modified to 1 s, and the heating temperature is 250 °C. The fluorescence spectrum and absorption spectrum of the prepared perovskite nanocrystals are shown in FIG. Fig.13 The transmission electron microscopy images and size distribution histograms are shown in Fig.14As shown, the average size of the obtained perovskite nanocrystals is 12.3 nm.

[0063] Embodiment 17 In this example, on the basis of Example 1, the lead iodide used to prepare the lead halide precursor solution in step 2 was replaced with 0.42 mmol of lead bromide, the temperature for preheating the cationic precursor solution in step 3 was changed to 170°C, the temperature for the first heating using heating module I was changed to 170°C, the heating time for the second heating using heating module II was changed to 12s, and the heating temperature was 250°C. The fluorescence spectrum and absorption spectrum of the prepared perovskite nanocrystals are shown in Figure 1. Fig.15 The transmission electron microscopy images and size distribution histograms are shown in Fig.16 As shown, the average size of the obtained perovskite nanocrystals is 28.2 nm, and the fluorescence quantum yield is 40%. From the transmission electron microscope image, it can be seen that large-sized nanocrystals with rare polyhedral morphology are synthesized in this embodiment.

[0064] Embodiment 18 In this embodiment, based on the embodiment 1, the heating temperature of the secondary heating using the heating module II in step 3 is modified to 250°C. The fluorescence spectrum and absorption spectrum of the prepared perovskite nanocrystals are as follows: Fig.17 The transmission electron microscopy images and size distribution histograms are shown in Fig.18 As shown, from the transmission electron microscope image, it can be seen that large-sized nanocrystals with rare polyhedral morphology are synthesized in this embodiment, and the average size is 33.0 nm.

[0065] Embodiment 19 In this example, based on Example 18, 5 mmol of formamidinium acetate, 5 mL of octadecene, and 15 mL of oleic acid were used to prepare a cationic precursor solution, wherein the concentration of formamidinium ions was 0.25 mol / L. 1.4625 mmol of lead bromide, 15 mL of octadecene, 3 mL of oleic acid, and 3 mL of oleylamine were used to prepare a lead halide precursor solution, wherein the concentration of lead ions was 0.069 mol / L. The transmission electron microscopy image of the prepared perovskite nanocrystals is shown in FIG. Fig.19 As shown, it can be seen that large-sized nanosheets were synthesized in this embodiment.

[0066] Embodiment 20 In this embodiment, based on the embodiment 1, the heating temperature of the secondary heating using the heating module II in step 3 is modified to 65°C. Since the temperature of the secondary heating is lower than the temperature of 160°C used in the primary heating, it is necessary to use a cooling module between the heating module I and the heating module II for cooling, and the cooling rate of the cooling module is set to 150°C / s. The transmission electron microscopy image and size distribution histogram of the prepared perovskite nanocrystals are shown in FIG. Fig. 20 As shown, the average size of the obtained perovskite nanocrystals is 14.0 nm.

[0067] The statistical results of the fluorescence emission peak position and fluorescence half-width of the perovskite nanocrystals prepared in Examples 1 to 20 are shown in Table 1: Fluorescence emission peak (nm) Fluorescence half-width (nm) Example 1 688.8 34.9 Example 2 692.6 32.9 Example 3 692.1 33.1 Example 4 684.3 34.0 Example 5 691.6 33.2 Example 6 687.9 33.8 Example 7 692.6 33.2 Example 8 688.3 32.5 Example 9 692.2 32.7 Example 10 684.5 35.1 Embodiment 11 690.6 33.3 Example 12 679.0 57.9 Example 13 685.5 34.2 Embodiment 14 688.8 33.3 Embodiment 15 515.2 18.5 Example 16 599.4 28.0 Embodiment 17 517.4 17.7 Embodiment 18 694.1 32.6 Embodiment 19 535.0 21.9 Embodiment 20 688.2 34.0 From the data in the table, it can be seen that, except for the fluorescent emission peak of the synthetic sample of Example 12, which is bimodal, the fluorescent half-width is wide. The fluorescent emission peaks of the samples obtained in other examples are all single-peaked, the fluorescent half-width of the luminescent wavelength in the red light range is less than 35.1 nm, and the fluorescent half-width of the luminescent wavelength in the green light range is less than 21.9 nm. Therefore, except for Example 12, the samples obtained in the other examples can all present a higher color purity, and when used as fluorescent display materials, the color gamut of the display device can be significantly improved, which is beneficial to the application of perovskite nanocrystals in display.

[0068] In summary, this method can successfully prepare perovskite nanocrystal products with excellent optical properties and long-term stability. By dynamically controlling the temperature at different stages of the nanocrystal synthesis process, it can achieve efficient perovskite nanocrystal preparation and significantly reduce the risk of pipeline blockage in the microfluidic system, ensuring the stability and repeatability of production, and providing a technical route suitable for large-scale preparation.

[0069] 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 and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing perovskite nanocrystals based on a second-order microfluidic system, characterized in that: A cationic precursor solution and a lead halide precursor solution are injected into the microfluidic system at the same speed using a syringe pump to preheat the precursor solutions respectively; the preheated precursor solutions are then mixed, heated once and heated twice in the microfluidic system; finally, the temperature is lowered to obtain APbX3 nanocrystals at the outlet of the microfluidic system, wherein the size, morphology and exciton confinement type of the APbX3 nanocrystals cover quantum dots, nanorods and nanosheets, wherein A is Cs + 、MA + , FA + One or more of, X is Cl - Br - ,I - One or more of .

2. A method for preparing perovskite nanocrystals based on a second-order microfluidic system as claimed in claim 1, characterized in that: The flow rate of the precursor solution entering the microfluidic system was controlled by a syringe pump to be 0.23~0.53 mL / min.

3. A method for preparing perovskite nanocrystals based on a second-order microfluidic system as claimed in claim 1, characterized in that: The preheating temperature of the precursor solution is 20~170°C, and the preheating time is 3~35 s.

4. The method for preparing perovskite nanocrystals based on a second-order microfluidic system according to claim 1, characterized in that: The temperature difference between the first heating and the second heating in the microfluidic system is -105℃~170℃.

5. A method for preparing perovskite nanocrystals based on a second-order microfluidic system as claimed in claim 1 or 4, characterized in that: Set the primary heating temperature to 80~170 ℃ and the heating time to 1~50 s; set the secondary heating temperature to 65~250 ℃ and the heating time to 1~50 s.

6. The method for preparing perovskite nanocrystals based on a second-order microfluidic system according to claim 1, characterized in that: The cationic precursor solution is a mixed solution of one or more of cesium acetate, cesium carbonate, formamidine acetate, methylamine, octadecene, and oleic acid, wherein the volume ratio of octadecene to oleic acid is (0.33-15):1; the lead halide precursor solution is a mixed solution of lead halide, octadecene, oleic acid, and oleylamine, wherein the volume ratio of octadecene, oleic acid, and oleylamine is 10:(1-3):(1-3), and the lead halide is lead chloride, lead bromide, lead iodide, or a mixture of any two.

7. A method for preparing perovskite nanocrystals based on a second-order microfluidic system according to claim 1 or 6, characterized in that: The concentration ratio of the cations in the cation precursor solution to the lead ions in the lead halide precursor solution is 1:(0.16-10).

8. A method for preparing perovskite nanocrystals based on a second-order microfluidic system as claimed in claim 7, characterized in that: The cation concentration in the cation precursor solution is 0.008-0.25 mol / L, and the lead ion concentration in the lead halide precursor solution is 0.012-0.120 mol / L.

9. A perovskite nanocrystal preparation device based on a second-order microfluidic system, characterized in that: Used to implement the method for preparing perovskite nanocrystals as described in any one of claims 1 to 4 or 6, the device includes a syringe pump, two precursor preheating modules, a multi-port connector, a heating module I, a refrigeration module, a heating module II and a quenching module; the precursor preheating module, the heating module I and the heating module II all include a microfluidic pipeline and a heater, the refrigeration module and the quenching module all include a microfluidic pipeline and a refrigerator, wherein the heater is used to heat the microfluidic pipeline to achieve preheating, primary heating and secondary heating; the refrigerator of the refrigeration module is used to cool the microfluidic pipeline when the secondary heating temperature is lower than the primary heating temperature; the refrigerator of the quenching module is used to cool the microfluidic pipeline; The two precursor preheating modules independently control the heating temperature through a heater, the microfluidic pipeline inlets are respectively connected to the injection pump outlets, and the outlets are connected to the microfluidic pipeline inlets of the heating module I through a multi-interface connector; the microfluidic pipelines are connected in sequence according to the order of heating module I, refrigeration module, heating module II and quenching module.

10. The perovskite nanocrystal preparation device based on the second-order microfluidic system as claimed in claim 9, characterized in that: The heating rates of the precursor preheating module, heating module I and heating module II are set to 80°C / s-100°C / s, and the cooling rates of the refrigeration module and quenching module are set to 150-170°C / s.

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