Preparation method of cesium iodide, cesium iodide and application

Abstract

The invention discloses a preparation method of cesium iodide, cesium iodide and application, and relates to the technical field of inorganic materials. According to the preparation method disclosed by the invention, the original crystal form morphology of cesium iodide is changed by adding a specific type of surfactant and using a high-temperature and high-pressure hydrothermal reaction, so that polyhedral crystal forms such as a truncated octahedron, a cube and a rhombic dodecahedron are formed, the specific surface area of cesium iodide is further increased, a larger contact area can be provided, and the stability of a product is improved; and the solubility of cesium iodide in an organic solvent can be improved, and the application effect of cesium iodide in a perovskite material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic materials, in particular to a preparation method of cesium iodide, cesium iodide and application. BACKGROUND

[0002] Cesium iodide (CsI) is an important inorganic compound, widely used in scintillator materials, X-ray imaging, photoelectric materials and other fields. As an additive or component, cesium iodide forms a "mixed cation" perovskite, significantly improving the stability, photoelectric performance of perovskite materials and the efficiency and service life of the final device. However, the solubility of cesium iodide in DMF / DMSO is low, which limits its application in organic solvent systems. In addition, the application of cesium iodide in perovskite materials is also limited by crystal form and morphology. In the prior art, the preparation method of cesium iodide cannot accurately control the crystal form and morphology, so that the performance of cesium iodide cannot be fully utilized.

[0003] Therefore, the preparation process of cesium iodide (CsI) is continuously optimized at present to better control the crystal form and morphology of cesium iodide and improve the solubility in organic solvent systems.

[0004] Therefore, the present application is proposed. In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of cesium iodide, cesium iodide and application, aiming to prepare high-performance cesium iodide products with high crystal form stability and high solubility in organic solvents, and to improve the application effect in perovskite materials.

[0006] The present application is realized as follows: In a first aspect, the present application provides a preparation method of cesium iodide, comprising: mixing a cesium source, an iodine source and a surfactant in a hydroalcoholic solution, and then performing a hydrothermal reaction. Preferably, the non-ionic surfactant is selected from at least one of polyvinyl alcohol and polyvinylpyrrolidone; and the cationic surfactant is selected from at least one of hexadecyl trimethyl ammonium chloride and hexadecyl trimethyl ammonium bromide.

[0007] In an optional embodiment, the addition amount of the surfactant accounts for 0.05%-7.0% of the total mass of the cesium source and the iodine source, preferably 1%-2%.

[0008] In an optional embodiment, the molar ratio of cesium of the cesium source to iodine of the iodine source is 1: (1.01-1.10).

[0009] In an optional embodiment, the cesium source is selected from at least one of cesium chloride, cesium bromide, cesium carbonate, cesium phosphate and cesium nitrate. and / or, the iodine source is selected from at least one of iodine element, hydroiodic acid, potassium iodide and sodium iodide; when the iodine source is iodine element, a reducing agent is added to the raw material, and the reducing agent is selected from at least one of hydrazine hydrate and ascorbic acid.

[0010] In an optional embodiment, the water-alcohol solution is obtained by mixing water and an alcohol solvent, and the volume ratio of water to the alcohol solvent is 1: (4-9).

[0011] In an optional embodiment, the water-alcohol solution is added in an amount of 4-10 times the total mass of the cesium source and the iodine source.

[0012] In an optional embodiment, the hydrothermal reaction temperature is 80-300℃, and the hydrothermal reaction time is 4-8h. and / or, the hydrothermal reaction pressure is 10-20MPa. and / or, after the hydrothermal reaction is completed, solid-liquid separation is performed, and the obtained solid material is washed and dried.

[0013] In an optional embodiment, during the mixing of the cesium source, the iodine source and the surfactant in the water-alcohol solution, the stirring temperature is controlled to be 5-40℃, and the stirring time is 0.5-2.0h. and / or, the stirring speed is 200-1500rpm. and / or, the cesium source and the iodine source are first dissolved in the water-alcohol solution and stirred for 0.5-2.0h, and then mixed with the surfactant.

[0014] In a second aspect, the present application provides a cesium iodide prepared by the preparation method of any one of the foregoing embodiments. Preferably, the crystal morphology of the cesium iodide is a truncated polyhedral structure. Preferably, the solubility of the cesium iodide in N, N-dimethylformamide solvent is greater than 0.197g / 10mL.

[0015] In a third aspect, the present application provides the use of the cesium iodide of the foregoing embodiments as a perovskite material.

[0016] The present application has the following beneficial effects: the present application adds a specific type of surfactant, changes the original crystal morphology of cesium iodide by high-temperature and high-pressure hydrothermal reaction, forms truncated octahedron, cube, rhombic dodecahedron and other polyhedral crystal forms, further increases the specific surface area of cesium iodide, can provide more contact area, and improves the stability of the product; can also improve the solubility of cesium iodide in organic solvents, and has higher photoelectric conversion efficiency when used as a perovskite material. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0018] Figure 1 The standard PDF card of the X-ray diffraction (XRD) pattern of the high-performance cesium iodide provided in Examples 1-4 and the amorphous cesium iodide provided in Comparative Examples 1-2; Figure 2 is a scanning electron microscope (SEM) image of the high-performance cesium iodide provided in Example 1; Figure 3 is a scanning electron microscope (SEM) image of the high-performance cesium iodide provided in Example 2; Figure 4 is a scanning electron microscope (SEM) image of the amorphous cesium iodide provided in Comparative Example 1; Figure 5 is a scanning electron microscope (SEM) image of the amorphous cesium iodide provided in Comparative Example 2; Figure 6 is a comparative analysis chart of the performance of perovskite solar cells in J-V test. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0020] In view of the problems that the morphology of cesium iodide crystals is difficult to accurately control and the solubility in organic solvents is low, the present application optimizes the preparation method of cesium iodide. By introducing a specific type of surfactant, the original crystal morphology of cesium iodide is changed by high-temperature and high-pressure hydrothermal reaction, further increasing the specific surface area of cesium iodide, which can provide more contact area and improve the stability of the product. It can also improve the solubility of cesium iodide in organic solvents, and has higher photoelectric conversion efficiency when used as perovskite material.

[0021] The present application provides a preparation method of cesium iodide, comprising: mixing a cesium source, an iodine source and a surfactant in a water-alcohol solution, and then performing a high-temperature and high-pressure hydrothermal reaction to obtain a specific crystal type high-performance cesium iodide.

[0022] The surface active agent is selected from at least one of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), cetyltrimethylammonium chloride (CTAC) and cetyltrimethylammonium bromide (CTAB), and the surface active agent can be any one or more of the above. By controlling the type of surface active agent, the crystal morphology of cesium iodide can be better controlled, and the solubility thereof is improved.

[0023] In some embodiments, the amount of the surface active agent added accounts for 0.05%-7.0% of the total mass of the cesium source and the iodine source, such as 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, etc., preferably 1%-2%. The amount of the surface active agent is preferably within the above range, which can further improve the stability and solubility of the product and improve the performance in the application of perovskite materials.

[0024] In some embodiments, the cesium source is selected from at least one of cesium chloride, cesium bromide, cesium carbonate, cesium phosphate and cesium nitrate, and the cesium source can be any one or more of the above. The iodine source is selected from at least one of elemental iodine, hydroiodic acid, potassium iodide and sodium iodide, and the iodine source can be any one or more of the above. By controlling the amount of the cesium source and the iodine source, the molar ratio of cesium in the cesium source to iodine in the iodine source is 1:(1.01-1.10), such as 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.10, etc. When the iodine source is elemental iodine, a reducing agent is further added to the raw materials, and the reducing agent is selected from at least one of hydrazine hydrate and ascorbic acid, and the reducing agent can be any one or more of the above. The amount of the reducing agent is sufficient to reduce the elemental iodine.

[0025] Further, the water-alcohol solution is obtained by mixing water and an alcohol solvent, and the volume ratio of the water to the alcohol solvent is 1:(4-9), such as 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, etc. The amount of the water-alcohol solution added is 4 times to 10 times of the total mass of the cesium source and the iodine source, such as 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, etc. The water-alcohol solution with a specific ratio is used as the reaction solvent, and the solubility difference of cesium iodide in water and alcohol is utilized to precisely control the crystal morphology thereof.

[0026] It should be noted that, by the synergistic effect of the water-alcohol ratio and the surface active agent, the crystallization process of cesium iodide is controlled in the embodiments of the present application, so that the cesium iodide forms a specific crystal form, thereby significantly improving the solubility of the cesium iodide in DMF. The method is simple in operation, low in cost and easy to be industrialized, and provides a new idea and approach for the application of cesium iodide in the DMF system.

[0027] In some embodiments, the order of mixing the cesium source, the iodine source and the surfactant in the hydroalcoholic solution is not limited, for example, the cesium source and the iodine source can be dissolved in the hydroalcoholic solution and stirred for 0.5-2.0 hours, and then mixed with the surfactant. During the mixing process, the stirring temperature is controlled to be 5-40℃, for example, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, etc.; the stirring time is 0.5-2.0 hours, for example, 0.5 hours, 1.0 hour, 1.5 hours, 2.0 hours, etc.; and the stirring speed is 200-1500 rpm, for example, 200 rpm, 500 rpm, 800 rpm, 1000 rpm, 1300 rpm, 1500 rpm, etc.

[0028] In some embodiments, the hydrothermal reaction is carried out in a sealed hydrothermal reactor, and the hydrothermal reaction temperature is 80-300℃, for example, 80℃, 100℃, 130℃, 150℃, 180℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the hydrothermal reaction time is 4-8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.; and the hydrothermal reaction pressure is 10-20 MPa, for example, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, etc. By adjusting the temperature, pressure and time of the hydrothermal reaction, the crystal morphology of cesium iodide can be better controlled, and the solubility can be improved.

[0029] Further, after the hydrothermal reaction is completed, solid-liquid separation can be performed by centrifugal separation or the like, and the obtained solid material can be washed and dried. The reagent used for washing can be cold ethanol, but is not limited thereto.

[0030] The embodiment of the present application also provides a cesium iodide prepared by the preparation method provided by the embodiment of the present application. The prepared cesium iodide product has a specific crystal form, high stability and high solubility, and better performance in the application of perovskite materials.

[0031] Specifically, the cesium iodide crystal form has a specific morphology, including but not limited to a cube, a cuboid, a truncated polyhedron (such as a truncated octahedron).

[0032] The solubility of the cesium iodide prepared by the embodiment of the present application in dimethylformamide (DMF) is greater than 0.197 g / 10 mL. The solubility of the cesium iodide crystal form in dimethylformamide (DMF) is more than 20% higher than that of amorphous cesium iodide. In addition, the cesium iodide crystal form has higher photoelectric conversion efficiency and stability in perovskite materials.

[0033] The application also provides application of the above-mentioned cesium iodide crystal form in a perovskite material, and the photoelectric conversion efficiency of the cesium iodide crystal form in the perovskite material is increased by more than 1% compared with that of a conventional material.

[0034] The cesium iodide prepared in the application has high stability and high solubility, and has higher photoelectric conversion efficiency as a perovskite material, and is a high-performance cesium iodide, and has the following characteristics: (1) The high-performance cesium iodide prepared in the application can form stronger intermolecular forces with a DMF (dimethylformamide) / DMSO (dimethyl sulfoxide) mixed solvent due to its highly ordered lattice structure. The lattice parameters of the high-performance cesium iodide are more matched with the polarity and solubility parameters of the solvent, thereby significantly improving the solubility rate and uniformity. This characteristic helps to achieve uniform dispersion of the CsI in a perovskite precursor solution and avoid film forming defects caused by local agglomeration of amorphous CsI.

[0035] (2) When the high-performance cesium iodide prepared in the application is blended with a perovskite material (such as MAPbI3 or FAPbI3) to form a film, the regular crystal structure of the high-performance cesium iodide can act as a lattice template to guide the perovskite crystal grains to grow along a specific orientation. This synergistic crystallization behavior can reduce stress concentration and ion migration channels at the grain boundaries and inhibit the formation of halogen vacancies and other defects, thereby significantly improving the mechanical stability and environmental degradation resistance (such as humidity and oxygen erosion) of the thin film.

[0036] (3) The energy band structure of the high-performance cesium iodide prepared in the application can be regulated by the lattice symmetry and is more matched with the energy level of the perovskite light-absorbing layer. For example, the conduction band minimum position of the cubic CsI is closer to the conduction band of the perovskite, which can reduce the interface electron transport barrier and reduce the loss of carrier recombination.

[0037] (4) The high crystallinity of the high-performance cesium iodide prepared in the application endows it with excellent thermodynamic stability. During perovskite annealing or device operation (temperature > 85℃), the lattice of the high-performance cesium iodide can act as a "thermal buffer layer" to anchor the organic cations (such as MA + or FA + ) in the perovskite lattice, thereby inhibiting ion disorder migration and phase separation at high temperatures. Studies have shown that the perovskite thin film with the specific crystal form of CsI prepared in the application can still maintain 90% of the initial efficiency after 1000 hours of aging at 85℃, while the amorphous system is attenuated to less than 60%.

[0038] The features and performance of the application are further described in detail in the following examples.

[0039] Example 1 The present example provides a preparation method of cesium iodide, and the steps are as follows: The 5.98 g of iodine was added into the water-alcohol solution (8 mL of pure water, 72 mL of anhydrous ethanol) and stirred, 0.8 g of 80% hydrazine hydrate was added dropwise to make it fully react, then 7.60 g of cesium carbonate was added, and stirred at 800 rpm for 1 hour at room temperature (about 25°C) to make it fully react. After the reaction was completed, 0.24 g of cetyltrimethylammonium bromide was added and stirred, and then transferred to a polytetrafluoroethylene-lined hydrothermal reactor, heated at 15 MPa and 180°C for 6 hours, and then the cesium iodide crystals were obtained by centrifugal separation, washed with anhydrous ethanol, and dried at 150°C under vacuum to obtain high-performance cesium iodide.

[0040] Note: The amount of surfactant added in this example accounts for 1.77% of the total mass of the cesium source and iodine source, and the volume ratio of water and alcohol solvent is 1:9.

[0041] Example 2 This example provides a method for preparing cesium iodide, and the steps are as follows: The 5.98 g of iodine was added into the water-alcohol solution (8 mL of pure water, 72 mL of anhydrous ethanol) and stirred, 0.8 g of 80% hydrazine hydrate was added dropwise to make it fully react, then 7.60 g of cesium carbonate was added, and stirred at 800 rpm for 1 hour at room temperature (about 25°C) to make it fully react. After the reaction was completed, 0.24 g of cetyltrimethylammonium bromide was added and stirred, and then transferred to a polytetrafluoroethylene-lined hydrothermal reactor, heated at 15 MPa and 180°C for 6 hours, and then the cesium iodide crystals were obtained by centrifugal separation, washed with anhydrous ethanol, and dried at 150°C under vacuum to obtain high-performance cesium iodide.

[0042] The difference between Example 2 and Example 1 is only that the type of surfactant is changed, and cetyltrimethylammonium bromide is replaced by polyvinylpyrrolidone.

[0043] Example 3 This example provides a method for preparing cesium iodide, and the steps are as follows: The 5.98 g of iodine was added into the water-alcohol solution (8 mL of pure water, 72 mL of anhydrous ethanol) and stirred, 0.8 g of 80% hydrazine hydrate was added dropwise to make it fully react, then 7.60 g of cesium carbonate was added, and stirred at 800 rpm for 1 hour at room temperature (about 25°C) to make it fully react. After the reaction was completed, 0.24 g of cetyltrimethylammonium bromide was added and stirred, and then transferred to a polytetrafluoroethylene-lined hydrothermal reactor, heated at 15 MPa and 180°C for 6 hours, and then the cesium iodide crystals were obtained by centrifugal separation, washed with anhydrous ethanol, and dried at 150°C under vacuum to obtain high-performance cesium iodide.

[0044] The main difference between Example 3 and Example 1 is that the type of iodine source is changed.

[0045] Example 4 The difference from Example 1 is that the amount of the surfactant cetyltrimethylammonium bromide added is 0.048 g, and the other steps are completely consistent with Example 1.

[0046] Note: The amount of surfactant added in this example accounts for 0.35% of the total mass of the cesium source and the iodine source.

[0047] Example 5 The difference from Example 1 is that the amount of the surfactant cetyltrimethylammonium bromide added is 0.48 g, and the other steps are completely consistent with Example 1.

[0048] Note: The amount of surfactant added in this example accounts for 3.53% of the total mass of the cesium source and the iodine source.

[0049] Example 6 The difference from Example 1 is that the volume of the water-alcohol body is 16 mL of water and 64 mL of ethanol, and the other steps are completely consistent with Example 1.

[0050] Note: The volume ratio of water and alcohol solvents in this example is 1:4.

[0051] Example 7 The difference from Example 1 is that the temperature in the hydrothermal reaction is 220°C, and the reaction time is 4 h, and the other steps are completely consistent with Example 1.

[0052] Example 8 The difference from Example 1 is that the temperature in the hydrothermal reaction is 140°C, and the reaction time is 8 h, and the other steps are completely consistent with Example 1.

[0053] Example 9 The difference from Example 1 is that the type of surfactant is changed, and cetyltrimethylammonium bromide is replaced by polyvinyl alcohol.

[0054] Example 10 The difference from Example 1 is that the type of surfactant is changed, and cetyltrimethylammonium bromide is replaced by cetyltrimethylammonium chloride.

[0055] Example 11 The difference from Example 1 is that the temperature in the hydrothermal reaction is 80°C.

[0056] Example 12 The difference from Example 1 is that the temperature in the hydrothermal reaction is 300°C.

[0057] Example 13 The difference from Example 1 is that the amount of the surfactant cetyltrimethylammonium bromide added is 0.00679 g, and the other steps are completely consistent with Example 1.

[0058] Note: The amount of surfactant added in this example accounts for 0.05% of the total mass of the cesium source and the iodine source.

[0059] Example 14 The difference from Example 1 is that the amount of the surfactant cetyltrimethylammonium bromide added is 0.95 g, and the other steps are completely consistent with Example 1.

[0060] Note: The amount of surfactant added in this example accounts for 7% of the total mass of the cesium source and the iodine source.

[0061] Comparative Example 1 This comparative example provides an amorphous cesium iodide prepared by the following steps: 5.98 g of iodine is added to a water-alcohol solution (8 mL of pure water, 72 mL of anhydrous ethanol) and stirred to mix, 0.8 g of 80% hydrazine hydrate (diluted ten times with pure water and added dropwise) is slowly added to make it fully react, and then 7.60 g of cesium carbonate is added. Stir at room temperature at a speed of 800 rpm for 1 hour to make it fully react. After the reaction is complete, add a polyol to precipitate cesium iodide from the solution by solvent crystallization method, filter the crystals, put them into a vacuum oven at 150°C for drying, and grind after cooling to room temperature to obtain.

[0062] Comparative Example 2 This comparative example provides an amorphous cesium iodide prepared by the following steps: 7.60 g of cesium carbonate and 12.58 g of 47% hydroiodic acid aqueous solution are added to a water-alcohol solution (1.3 mL of pure water, 72 mL of anhydrous ethanol), and stirred to mix at a speed of 800 rpm at room temperature for 1 hour to make it fully react. After the reaction is complete, add a polyol to precipitate cesium iodide from the solution by solvent crystallization method, filter the crystals, put them into a vacuum oven at 150°C for drying, and grind after cooling to room temperature to obtain.

[0063] Comparative Example 3 The difference from Example 1 is only that the type of surfactant is changed, and cetyltrimethylammonium bromide is replaced by sodium dodecyl sulfate.

[0064] Comparative Example 4 The difference from Example 1 is only that the type of surfactant is changed, and cetyltrimethylammonium bromide is replaced by sodium dodecylbenzenesulfonate.

[0065] Test Example 1 Test sample: cesium iodide products prepared in examples and comparative examples.

[0066] Test items: solubility test, X-ray diffraction, scanning electron microscope, J-V curve test.

[0067] To verify that the above high-performance cesium iodide phase has certain advantages in photoelectric conversion efficiency compared with amorphous cesium iodide, the following examples and comparative examples are designed and prepared, and the specific preparation process is as follows.

[0068] Example: high-performance perovskite solar cell Substrate pretreatment: the ITO conductive glass was sequentially placed in detergent, ultrapure water, ethanol, isopropanol, and ultrasonically cleaned for 15 minutes to completely remove surface organic and inorganic contaminants. After cleaning, dry with high-purity nitrogen, and perform ultraviolet ozone treatment for 30 minutes to further improve the surface energy and work function.

[0069] Hole transport layer preparation: the treated ITO substrate was transferred to a nitrogen glove box. The SAM (4PADCB, 0.5 mg / ml dissolved in isopropanol) was spin-coated at a speed of 3000 rpm for 30 seconds, and then annealed at 100°C for 10 minutes to form a dense and efficient hole selective interface.

[0070] Perovskite active layer preparation: then, 1.67 M Cs 0.05 MA 0.1 FA 0.85 PbI3(0.075 mmol CsI, 0.15 mmol MAI, 1.275 mmol FAI, and 1.5 mmol PbI2) perovskite precursor solution was dissolved in 1 milliliter of DMF / DMSO mixed solvent (V DMF :V DMSO = 4:1), and 35 mg of PbI2 and 15 mg of MACl were additionally added. Then, spin-coat at a speed of 1000 rpm for 10 seconds, spin-coat at a speed of 5000 rpm for 30 seconds, and drop 150 microliters of CB as an anti-solvent in the last 10 seconds. Then, the perovskite film was annealed at 100°C for 30 minutes to form a high-quality, high-coverage polycrystalline perovskite light-absorbing layer.

[0071] Electron transport layer and electrode preparation: the sample was transferred to a vacuum evaporation instrument, and 30 nm C -5 , 5 nm BCP and 100 nm Ag were sequentially thermally evaporated and deposited under high vacuum conditions at about 10 60 Torr.

[0072] Note: the CsI used in this example is the CsI of the above example.

[0073] Comparative example: ordinary perovskite solar cell The comparative example is identical to the example except that the CsI used is the same as that in the comparative example described above.

[0074] To quantitatively evaluate the performance advantages of perovskite solar cells based on high-performance cesium iodide (CsI), standard current density-voltage (JV) tests were performed on the devices fabricated in the examples and comparative examples. The tests were conducted using a Keithley 2401 power meter at a light intensity of 100 mW / cm². -2 Device efficiency was tested under AM 1.5G conditions (device area 0.04 cm²). 2 The scanning voltage ranged from 1.2V to -0.2V, with a voltage compensation of 10mV. The test results are shown in Table 1 below. Figures 1-6 As shown: Table 1. Sample test results of the examples and comparative examples.

[0075] As shown in Table 1, the high-performance cesium iodide prepared by the method described in this invention has a purity of approximately 99.99%. The solubility of the cesium iodide with altered crystal morphology is 0.0187~0.0245 g / mL (the 10 mL solvent mentioned in the table is DMF solvent), while the solubility of cesium iodide without added surfactant is 0.0161~0.0180 g / mL. This demonstrates that the high-performance cesium iodide preparation method provided by the above embodiments of this invention, by adding a certain mass of surfactant and using a high-temperature, high-pressure hydrothermal reaction to alter the original crystal morphology of cesium iodide, forms polyhedral crystals such as truncated octahedrons, cubes, and rhombic dodecahedrons, further increasing the specific surface area of ​​cesium iodide, providing more contact area, and exhibiting good stability.

[0076] Based on the sample test results shown in Table 1, the photoelectric conversion efficiency (PCE) data obtained through JV curve testing clearly demonstrates that the devices prepared in the embodiments of this invention are significantly superior to the comparative examples in terms of photoelectric performance. In Examples 1 to 14, the PCE values ​​range from 21.8% to 23.0%, showing stable performance at a relatively high level; while the PCE values ​​of Comparative Examples 1 to 4 are concentrated in the range of 20.5% to 21.3%, which are generally lower than those of the Example group.

[0077] Further comparison of the average values ​​shows that the average PCE of the example group reached approximately 22.36%, while the average PCE of the comparative group was approximately 20.85%, a difference of approximately 1.51 percentage points, representing a relative improvement of approximately 7.2%. This difference fully demonstrates that the preparation method described in this invention—introducing a surfactant and controlling the crystal form and morphology of cesium iodide via a high-temperature, high-pressure hydrothermal reaction—can effectively enhance the photoelectric response capability of the material in the device, thereby significantly improving the photoelectric conversion efficiency of the final device.

[0078] Therefore, the JV test results not only verified the effectiveness of the present invention in material structure control, but also demonstrated its practical application potential in improving the performance of solar cells and related optoelectronic devices.

[0079] Figure 1 Standard PDF cards containing X-ray diffraction (XRD) patterns of the high-performance cesium iodide provided in Examples 1-3 and the amorphous cesium iodide provided in Comparative Examples 1-3, from... Figure 1 In the comparison, it can be found that the prepared samples are all pure phases and consistent with the cesium iodide standard card. In a preferred embodiment of the present invention (Example 1), precise control of the preferred orientation of the crystal is achieved by adding the surfactant hexadecyltrimethylammonium bromide and reacting under high temperature and high pressure. Figure 1 As shown, in the X-ray diffraction pattern of Example 1, the diffraction peak intensity of the (200) crystal plane is significantly lower than that of Comparative Examples 1, 2, and 3, indicating that the growth of this crystal plane is effectively suppressed; at the same time, the diffraction peak intensity of the (211) crystal plane is significantly enhanced compared to Comparative Examples 1, 2, and 3, indicating that the growth of this crystal plane is selectively promoted. The above-mentioned preferred orientation growth mode leads to the preferential growth of the crystal along the (211) crystal plane direction, forming a crystal structure with a specific exposed crystal plane.

[0080] Due to the higher surface energy and more active sites of the (211) crystal facet, this specific crystal form exhibits higher solubility when in contact with DMF, thereby significantly improving the solubility of the active ingredient. Solubility test data from Example 1 show that its solubility in DMF is increased by 36.1%, 45.8%, and 48.5% compared to Comparative Examples 1, 2, and 3, respectively, verifying the breakthrough improvement in solubility performance of this crystal structure.

[0081] Figure 2 This is a scanning electron microscope (SEM) image of the high-performance cesium iodide provided in Example 1; Figure 3 This is a scanning electron microscope (SEM) image of the high-performance cesium iodide provided in Example 2; Figure 4 This is a scanning electron microscope (SEM) image of amorphous cesium iodide provided in Comparative Example 1; Figure 5 This is a scanning electron microscope (SEM) image of amorphous cesium iodide provided in Comparative Example 2. From...Figure 2 The SEM image shows that the cesium iodide crystals exhibit a truncated octahedral shape; from Figure 3 The SEM image shows that the cesium iodide crystals exhibit a cubic shape; from Figure 4 The SEM image shows that the cesium iodide crystals are in an amorphous state; from Figure 5 The SEM image shows that the cesium iodide crystals are in an amorphous state.

[0082] Figure 6 This is a comparative analysis chart of the performance of perovskite solar cells tested by JV. The data shows that the power conversion efficiency (PCE) of the example is highly concentrated, distributed within a narrow range of 22.5% to 23%, exhibiting good consistency and stability. In contrast, the PCE values ​​of the comparative example are more dispersed, ranging from 20.5% to 21.5%, indicating greater performance fluctuations and weaker reproducibility. This comparison not only demonstrates that the example is significantly more efficient than the comparative example but also reflects its potential for better uniformity and reliability in material system or process control. Based on the above experimental verification, the high-performance cesium iodide prepared by controlling the crystal form through hydrothermal reaction provided by this invention exhibits excellent solubility and maintains high performance stability during long-term use, effectively ensuring stable device operation. Furthermore, the preparation process of this invention is simple and easy to implement, highly stable, easy to operate, and has good cost control, possessing broad application prospects and potential industrialization value.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of preparing high-performance cesium iodide by controlling the crystal form through hydrothermal reaction, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing cesium iodide, characterized in that, include: A hydrothermal reaction was carried out after mixing a cesium source, an iodine source, and a surfactant in an aqueous alcohol solution. The surfactant is selected from at least one of nonionic surfactants and cationic surfactants; preferably, the nonionic surfactant is selected from at least one of polyvinyl alcohol and polyvinylpyrrolidone; and the cationic surfactant is selected from at least one of hexadecyltrimethylammonium chloride and hexadecyltrimethylammonium bromide.

2. The method for preparing cesium iodide according to claim 1, characterized in that, The amount of surfactant added is 0.05%-7.0% of the total mass of the cesium source and the iodine source, preferably 1%-2%.

3. The method for preparing cesium iodide according to claim 1, characterized in that, The molar ratio of cesium in the cesium source to iodine in the iodine source is 1:(1.01-1.10).

4. The method for preparing cesium iodide according to claim 3, characterized in that, The cesium source is selected from at least one of cesium chloride, cesium bromide, cesium carbonate, cesium phosphate, and cesium nitrate; And / or, the iodine source is selected from at least one of elemental iodine, hydroiodic acid, potassium iodide, and sodium iodide; when the iodine source is elemental iodine, a reducing agent is also required to prepare the raw materials, and the reducing agent is selected from at least one of hydrazine hydrate and ascorbic acid.

5. The method for preparing cesium iodide according to claim 1, characterized in that, The aqueous alcohol solution is obtained by mixing water and alcohol solvent, with a volume ratio of water to alcohol solvent of 1:(4-9).

6. The method for preparing cesium iodide according to claim 1 or 5, characterized in that, The amount of the aqueous alcohol solution added is 4 to 10 times the total mass of the cesium source and the iodine source.

7. The method for preparing cesium iodide according to claim 1, characterized in that, The hydrothermal reaction temperature is 80℃-300℃, and the hydrothermal reaction time is 4h-8h; And / or, the hydrothermal reaction pressure is 10MPa-20MPa; And / or, after the hydrothermal reaction is completed, solid-liquid separation is performed, and the resulting solid material is washed and dried.

8. The method for preparing cesium iodide according to claim 1, characterized in that, During the mixing of the cesium source, the iodine source, and the surfactant in the aqueous alcohol solution, the stirring temperature is controlled at 5℃-40℃, and the stirring time is 0.5h-2.0h. And / or, the stirring speed is 200rpm-1500rpm; And / or, first dissolve the cesium source and the iodine source in the aqueous alcohol solution and stir for 0.5h-2.0h, then mix with the surfactant.

9. A cesium iodide, characterized in that, Prepared by the preparation method according to any one of claims 1-8; Preferably, the cesium iodide crystal morphology is a truncated polyhedral structure; Preferably, the solubility of cesium iodide in N,N-dimethylformamide solvent is greater than 0.197 g / 10 mL.

10. The use of cesium iodide as described in claim 9 as a perovskite material.

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