High-purity fluorine salt slurry, preparation method and application

Abstract

This invention relates to the field of fluoride salt technology. It discloses a high-purity fluoride salt slurry, its preparation method, and its application in the preparation of mesoporous framework layers for perovskite solar cells. Addressing the bottlenecks of the easy catalytic degradation of perovskite by traditional titanium dioxide mesoporous frameworks under ultraviolet light and the difficulty in dispersing high-purity nano-fluoride salts, this invention provides a slurry prepared by mixing high-purity lithium fluoride nanoparticles with a purity of 5N and high-purity cesium fluoride. The fluoride salt is subjected to in-situ photolysis via a micro-fluidized bed combined with deep ultraviolet irradiation to remove residual polymeric surfactants and repair the particle surface. This slurry is then coated and sintered to form a mesoporous framework layer, and 4-fluoroanisole is introduced as an interface wetting aid layer. The incorporation of trace amounts of cesium fluoride forms an interfacial dipole moment at the physical interface, effectively reducing the Schottky barrier. Furthermore, the synergistic passivation of anions and cations enhances interfacial defects, improving charge extraction efficiency, long-term ultraviolet light stability, and photoelectric conversion efficiency of the cell.

Description

Technical Field

[0001] This invention relates to the field of fluoride salt technology, and in particular to a high-purity fluoride salt slurry, its preparation method, and its application. Background Technology

[0002] Perovskite solar cells, representing third-generation photovoltaic technology, have become a research hotspot in the photovoltaic field due to their advantages such as high efficiency, low cost, and solution-processability. Currently, the photoelectric conversion efficiency of perovskite cells has exceeded 27%, demonstrating enormous commercial potential. However, their long-term stability remains a key bottleneck restricting industrial applications. Among these issues, the degradation mechanism of the perovskite active layer under light, humidity, and thermal stress is particularly prominent.

[0003] In conventional nip-type solar cell structures, mesoporous titanium dioxide (meso-TiO2) is widely used as an electron transport layer and also serves as the framework structure for the perovskite layer to support the perovskite film. Its large specific surface area facilitates maximum adsorption of perovskite materials and provides space for the directional growth of the perovskite film. However, the TiO2 surface contains many oxygen vacancies, which, under the influence of light and oxygen, eventually generate positively charged, strongly oxidizing photogenerated holes (h holes). + This process attacks and oxidizes perovskite materials in contact with the TiO2, leading to the decomposition of organic cations and the loss of iodine ions. Simultaneously, the deep charge traps on the TiO2 surface possess a strong ability to extract electrons from I... - The efficient extraction of electrons from the perovskite to generate iodine leads to a disordered crystal structure and triggers an irreversible photocatalytic decomposition reaction. In other words, traditional mesoporous titanium dioxide materials exhibit strong microscopic photocatalytic activity under ultraviolet (UV) irradiation, easily inducing irreversible degradation of perovskite films and severely limiting the long-term UV stability of devices.

[0004] In contrast, lithium fluoride (LiF) possesses a wide bandgap, high chemical stability, and excellent UV resistance, making it a highly promising alternative framework layer material. However, traditional low-purity (e.g., 3N level) lithium fluoride materials contain numerous metallic impurities, which can form severe charge recombination centers during battery operation, limiting battery efficiency. Furthermore, due to LiF's unique surface energy and chemical inertness, it is difficult to prepare high-purity, highly dispersed, and long-term stable nanoslurries using conventional aqueous or simple organic phase fragmentation methods, leading to a high tendency for particle agglomeration. In addition, perovskite precursor solutions exhibit extremely poor wettability on lithium fluoride substrates, making direct film formation difficult and resulting in severe grain boundary defects. Therefore, developing an ultra-high purity, high-stability lithium fluoride nanoslurry preparation process and solving the wettability problem at the perovskite layer interface are currently pressing technical bottlenecks in the field of optoelectronic devices. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in related technologies. To this end, this invention provides a high-purity fluoride salt slurry, its preparation method, and its application, to solve the problems of the catalytic degradation of perovskite materials under ultraviolet light by traditional mesoporous framework layers and the difficulty in stably dispersing high-purity nano-fluoride salts.

[0006] The first technical solution provided by this invention is: A high-purity fluorinated salt slurry is composed of high-purity lithium fluoride nanoparticles, high-purity cesium fluoride, and a mixed solvent; the mixed solvent is a mixture of ethanolamine and N,N-dimethylformamide; the mass ratio of the high-purity lithium fluoride nanoparticles to the high-purity cesium fluoride is 15~25:1; the purity of both the high-purity lithium fluoride nanoparticles and the high-purity cesium fluoride reaches the 5N level.

[0007] The second technical solution provided by this invention is as follows: A method for preparing a high-purity fluoride salt slurry includes the following steps: Preparation of high-purity lithium fluoride nanoparticles: After obtaining a suspension of lithium fluoride nanoparticles, solid products are obtained by solid-liquid separation. The solid products are then subjected to thermal pretreatment, followed by fluidized bed ultraviolet deep impurity removal to obtain the high-purity lithium fluoride nanoparticles. Preparation of high-purity cesium fluoride: After obtaining cesium fluoride powder, it is subjected to thermal pretreatment, followed by secondary crystallization and drying to obtain an intermediate product. The intermediate product is then subjected to fluidized bed ultraviolet deep purification to obtain the high-purity cesium fluoride. Slurry preparation: The high-purity lithium fluoride nanoparticles and the high-purity cesium fluoride are mixed with a mixed solvent to obtain a fluoride salt slurry precursor; the fluoride salt slurry precursor is ball-milled and filtered to obtain the high-purity fluoride salt slurry.

[0008] Furthermore, the specific process for preparing the lithium fluoride nanoparticle suspension is as follows: ammonium fluoride, ethanol, and polyethylene glycol are dissolved in water, and then lithium nitrate solution is slowly added dropwise to react and generate the lithium fluoride nanoparticle suspension. The heat pretreatment conditions are: baking in a mixture of oxygen and nitrogen with an oxygen volume fraction of 30-40% at 250-300°C.

[0009] Furthermore, the specific process of the fluidized bed ultraviolet deep purification is as follows: the particles to be purified are loaded into a micro fluidized bed; fluidizing gas is introduced from the bottom of the micro fluidized bed to suspend the particles in a fluidized state, and an ultraviolet light source is turned on to irradiate the particles during the fluidization process. The fluidizing gas is a mixture of oxygen and argon, with the oxygen volume fraction being 18-22% and the flow rate being 50-150 sccm; the wavelength of the ultraviolet light source is 285 nm, and the duration of the irradiation treatment is 3-9 hours.

[0010] Further, the specific process for preparing cesium fluoride powder is as follows: cesium carbonate solid is added to an aqueous solution containing ammonium fluoride, ethanol and polyethylene glycol to react, and after the reaction is completed, the mixture is concentrated by distillation and cooled to crystallize and precipitate the cesium fluoride powder; the specific process for secondary crystallization is as follows: the product after the heat pretreatment is dissolved in deionized water, and a mixed solvent of ethanol and isopropanol is added to precipitate cesium fluoride crystals.

[0011] Furthermore, the specific process of mixing the high-purity lithium fluoride nanoparticles, the high-purity cesium fluoride, and the mixed solvent is ultrasonic mixing; The specific parameters for the ball milling process are as follows: using zirconia grinding balls, with a ball-to-material mass ratio of 3:1, a ball milling speed of 300~400 rpm, and a ball milling time of 24~48 hours.

[0012] The third technical solution provided by this invention is: Application of the above-mentioned high-purity fluoride salt slurry or the high-purity fluoride salt slurry prepared by the above method in the preparation of the mesoporous framework layer of perovskite solar cells. The high-purity fluoride salt slurry is used to construct the mesoporous framework layer on the electron transport layer of the perovskite solar cell, so as to serve as a support framework for the directional growth of the perovskite thin film. The mesoporous framework layer is composed of lithium fluoride and cesium fluoride components in high-purity fluoride slurry.

[0013] Furthermore, the process of preparing the mesoporous framework layer includes: The high-purity fluoride slurry is coated onto the surface of the electron transport layer and then dried to obtain a dried product. The dried product is subjected to sintering treatment to form an interconnected structure of the solid components in the high-purity fluoride slurry, thereby obtaining the mesoporous framework layer.

[0014] Furthermore, after obtaining the mesoporous framework layer, the method further includes: A solution containing 4-fluoroanisole is spin-coated onto the surface of the mesoporous framework layer and then annealed to obtain an anti-wetting layer; A perovskite precursor solution is coated onto the surface of the aid-wetting layer and then subjected to crystallization annealing to form a perovskite layer.

[0015] Furthermore, fluoride ions in the mesoporous framework layer form coordination bonds with uncoordinated divalent lead ions at the bottom of the perovskite layer to fill halogen vacancies at the bottom of the perovskite layer; cesium ions in the mesoporous framework layer are enriched at the physical interface between the mesoporous framework layer and the perovskite layer, and some of the cesium ions enter the lattice of the perovskite layer to stabilize the perovskite phase.

[0016] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: 1. Through the micro fluidized bed -285nm ultraviolet deep purification technology, photon energy can effectively break the bond energy of residual polymer surfactants on the particle surface. Combined with the highly active oxygen clusters generated in situ, the gas-solid high-efficiency reaction is completely realized, removing trace carbon impurities that cannot be removed by conventional high temperature, obtaining fluoride with a purity of 5N level, and eliminating defective recombination centers introduced by impurities. 2. By using a high-purity LiF mesoporous layer to completely replace the traditional TiO2 framework, the micro-catalytic degradation of TiO2 under ultraviolet light is avoided, and the operational stability of the battery under long-term ultraviolet light irradiation is greatly improved. 3. A 4-fluoroanisole interface wetting aid layer was successfully introduced, which effectively overcame the inherent drawback of surface energy mismatch in inorganic fluoride porous layers, promoted the standardized growth of perovskite large grains, and significantly improved the device's fill factor and short-circuit current density.

[0017] 4. Incorporating trace amounts of cesium fluoride (CsF) as a modulator during the mesoporous layer preparation stage not only creates a favorable interfacial dipole moment at the physical interface, reducing the Schottky barrier and improving charge extraction efficiency (compensating for the insulation shortcomings of LiF), but also releases fluorine ions to fill halogen vacancies in the underlying layer. Cesium ions effectively compensate for cation vacancies at the perovskite A-sites and alleviate lattice stress, significantly improving the device's fill factor (FF) and overall photoelectric conversion efficiency.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1The Fourier transform infrared (FTIR) spectra of the high-purity LiF nanoparticles prepared in this invention before and after deep purification in a fluidized bed under ultraviolet light are compared. Figure 2 This is a comparison of the contact angles of the mesoporous lithium fluoride porous surface of the present invention before and after the introduction of 4-fluoroanisole and the addition of perovskite precursor solution. Figure 3 This is a SEM image of meso-LiF containing CsF in this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention but cannot be used to limit the scope of this invention.

[0022] Example 1: Preparation of 5N (≥99.999%) high-purity fluoride and its slurry 1. Preparation of lithium fluoride nanoparticles: Ammonium fluoride, ethanol, and polyethylene glycol (PEG200) were dissolved in water in a ratio of 1:10:1 to prepare an ammonium fluoride solution. The concentration of ammonium fluoride was controlled at 0.5~1.5 mol / L. The solution was placed in a beaker made of polytetrafluoroethylene and stirred.

[0023] A lithium nitrate solution with the same molar concentration as ammonium fluoride was slowly added dropwise to an ammonium fluoride solution to generate a suspension of lithium fluoride nanoparticles. The reaction of lithium nitrate was controlled to be complete.

[0024] The solids were initially filtered using a 500-mesh filter membrane to remove any small amount of large particle agglomerates that might be present. Then, a 0.22μm microporous filter membrane was used for pressure filtration. After that, the solids were separated by centrifugation at 5000 rpm for 60-90 minutes and then eluted with deionized water.

[0025] Elution is mainly used to remove unreacted ammonium fluoride, but it can also remove organic matter such as ethanol and polyethylene glycol at the same time.

[0026] Post-processing purification: The solid product is calcined at 250~300℃ in an oxygen / nitrogen mixture with an oxygen volume fraction of 30~40% to initially remove organic components and moisture.

[0027] To thoroughly remove residual organic components and repair particle surfaces, this invention introduces a self-developed micro fluidized bed-high-energy ray treatment system. The specific process is as follows: Equipment Composition: The system comprises a vertically placed miniature fluidized bed reactor tube (10 mm inner diameter, made of quartz) with a gas distribution plate at the bottom. This entire unit is placed within an ultraviolet treatment device to ensure uniform irradiation of the entire fluidized bed area.

[0028] Operating Procedure: Pre-treated LiF nanoparticles are loaded into a microfluidic bed. At room temperature, an O2 / Ar mixture (O2 volume fraction of 18-22%, 20% in this example) is introduced from the bottom as the fluidization and reaction medium, with a gas flow rate controlled at 50-150 sccm (standard mL / min) to ensure stable suspension of the particle bed in a microfluidic state, forming good gas-solid contact. A 285 nm ultraviolet light source is turned on, and irradiation is performed simultaneously with particle fluidization for 3-9 hours.

[0029] Purification Mechanism: The 285 nm photon energy (approximately 4.35 eV) far exceeds the bond energies of chemical bonds in organic molecules such as CC, CO, and CH, directly exciting residual PEG fragments and carbonized intermediates adsorbed on the particle surface to a dissociated state, causing bond breakage and generating active free radicals. Furthermore, O2 molecules in the fluidized bed undergo photolysis to produce ground-state atomic oxygen O (3P) and excited-state O (1D), while O2 combines with atomic oxygen to generate ozone (O3), a highly oxidizing compound. These short-lived, highly reactive active oxygen clusters are generated in situ on the particle surface, further reacting with the organic components on the nanoparticle surface. The intense gas-solid mixing provided by the micro-fluidized bed continuously exposes the particle surface to ultraviolet light and the active oxygen atmosphere, ensuring uniform treatment of each nanoparticle. Simultaneously, gaseous products such as CO2 and H2O generated during the reaction are immediately carried away by the airflow, inhibiting reverse reactions and re-adsorption.

[0030] 2. Preparation of cesium fluoride (auxiliary agent): Ammonium fluoride, ethanol, and polyethylene glycol (PEG200) were dissolved in water in a ratio of 1:10:1 to prepare an ammonium fluoride solution. The concentration of ammonium fluoride was controlled at 0.5~1.5 mol / L.

[0031] Cesium carbonate solid was slowly added to an ammonium fluoride solution while stirring continuously, and cesium fluoride (CsF) was generated. The reaction of cesium carbonate was controlled to be complete.

[0032] After the reaction is complete, the solution is concentrated by vacuum distillation, and cooled to crystallize out cesium fluoride powder. The product is then calcined in an oxygen / nitrogen mixture at 250-300℃ with an oxygen volume fraction of 30-40%. The calcined product is dissolved in deionized water, and a mixed solvent of ethanol / isopropanol (V / V=4:1) is slowly added to allow the cesium fluoride crystals to recrystallize again. After filtration, the product is dried under vacuum (maintaining a pressure <10Pa and a temperature of 150℃ until constant weight) to obtain the intermediate product.

[0033] Unreacted reactants were removed by recrystallization, and CsF was purified. Residual ethanol / isopropanol was removed by vacuum drying, and trace amounts were removed by ultraviolet light treatment.

[0034] The intermediate product was processed under the same control conditions as the high-purity LiF product through a microfluidic bed and a 285 nm ultraviolet light source to obtain a cesium fluoride product with a purity of 5N.

[0035] 3. Slurry preparation: 200 mg of a mixture of high-purity lithium fluoride nanoparticles and high-purity cesium fluoride (LiF to CsF mass ratio 15~25:1, preferably 20:1) was ultrasonically mixed with 15 mL of ethanolamine / DMF (N,N-dimethylformamide) mixed solvent (volume ratio 1:50) for 60 min to obtain lithium fluoride slurry precursor A.

[0036] The above-mentioned A was placed in a planetary ball mill jar, and 0.03 mm diameter zirconia grinding balls (ball-to-particle mass ratio 3:1) were added. The mixture was then ball-milled at 300-400 rpm for 24-48 hours. This process aims to fully break up the agglomeration of LiF nanoparticles and achieve their uniform and stable dispersion in the organic phase. The mixture was then filtered through a 500-mesh filter to remove the grinding balls and any trace large particles, ultimately obtaining lithium fluoride nanoparticle slurry B.

[0037] High-purity LiF paste alone can lead to a large series resistance (Rs) in the device, which limits the fill factor (FF) performance. Therefore, a certain mass ratio of CsF is added as a regulator.

[0038] Comparative Example 1: Preparation of 3N Low-Purity Fluoride Slurry Lithium fluoride particles with a purity of 3N were fed into a planetary ball mill jar, water was added as a dispersant, and zirconia grinding balls with diameters of 0.1 mm, 0.05 mm, and 0.03 mm (ball-to-particle mass ratio 10:1) were added in a mass ratio of 1:2:5. The mixture was ball-milled at a speed of 500-600 rpm for 36-72 hours. After the process was completed, the particles were sent to a vacuum drying oven, maintaining a pressure <10 Pa and a temperature of 150℃ to remove volatile impurities, thus obtaining lithium fluoride nanoparticles with a purity of 3N.

[0039] 3N lithium fluoride nanoparticles, 3N cesium fluoride, ethanolamine, and DMF were ultrasonically mixed in the above proportions for 60 minutes to obtain lithium fluoride slurry precursor C.

[0040] Place the above-mentioned C in a planetary ball mill jar, add zirconia grinding balls with a diameter of 0.03 mm (ball-to-material mass ratio 3:1), and ball mill at a speed of 300-400 rpm for 24-48 hours. Filter the above mixture through a 500-mesh filter membrane to obtain the final lithium fluoride nano-slurry D.

[0041] Experimental data characterization To verify that the purity of the lithium fluoride (LiF) nanoparticles and cesium fluoride (CsF) crystals prepared in this invention reaches the 5N level, inductively coupled plasma (ICP) was used for full elemental scanning and quantitative analysis of metallic impurities in both. 100–200 mg of fluoride particles obtained through deep purification under ultraviolet light in a microfluidic bed were accurately weighed and placed in an acid-washed and purified polytetrafluoroethylene digestion vessel. 2 mL of pure concentrated nitric acid (approximately 68%) and 0.5 mL of ultrapure water were added, and the mixture was gently digested on a 120°C heating plate until completely dissolved. Then, 100 μL of boric acid solution (5% wt) was added. The solution was transferred to a clean volumetric flask and diluted to 50 mL with ultrapure water. A blank control solution was prepared simultaneously.

[0042] The LiF content is the remainder after subtracting the sum of the measured values ​​of metal impurity elements from 100%. Based on the data in the table below, the purity of high-purity LiF nanoparticles is 99.9991% (>5N). The test results are detailed in Table 1.

[0043] Table 1. Content of various metal impurity ions in high-purity lithium fluoride (LiF) nanoparticles

[0044] The purity test data for CsF is 99.9996% (>5N). The test results are detailed in Table 2.

[0045] Table 2. Content of various metal impurity ions in high-purity cesium fluoride (CsF) additives

[0046] like Figure 1 As shown, after the fluidized bed ultraviolet purification process, the organic impurities contained in lithium fluoride have been effectively removed, and the structural peaks of the organic components in its infrared spectrum have all disappeared.

[0047] Example 2: Battery fabrication and photovoltaic performance testing To fully demonstrate the advanced nature of the present invention, three battery device structures with different framework layer structures were constructed: The battery device structure of control group 1 (blank group) is: FTO / ZnO / meso-TiO2 / perovskite / Spiro-OMeTAD / Au.

[0048] The battery device structure of control group 2 is: FTO / ZnO / meso-LiF(3N) / perovskite / Spiro-OMeTAD / Au.

[0049] The experimental group of battery devices has the following structure: FTO / ZnO / meso-LiF(5N) / perovskite / Spiro-OMeTAD / Au.

[0050] 1. Battery preparation process of control group 1 (blank group) 1.1 Etching and Cleaning of FTO Conductive Glass Substrate A 2cm x 2cm FTO (fluorine-doped tin oxide) glass substrate was locally etched using laser marking equipment to form the desired electrode pattern. After etching, residues were rinsed off with deionized water. The etched FTO substrate was then sequentially immersed in a deionized water solution containing 2% glass cleaner, followed by deionized water, acetone, and anhydrous ethanol, and ultrasonically cleaned for 15 minutes in each medium. After cleaning, the substrate was dried with dry nitrogen gas and immediately placed in a UV-ozone cleaner for 15 minutes to thoroughly remove surface organic matter and improve surface wettability.

[0051] 1.2 Preparation of ZnO dense electron transport layer Preparation of ZnO precursor solution: A solution of 0.2 M zinc acetate, 0.05 M magnesium acetate, and 0.05 M ethanolamine as stabilizers was prepared using isopropanol as a solvent. The solution was stirred at room temperature for 2 hours until completely dissolved, yielding a clear and transparent solution. This solution was allowed to stand for 24 hours before use. The ZnO precursor solution was spin-coated onto a clean FTO substrate at 3000 rpm for 30 seconds, and then annealed in air on a hot plate at 150°C for 10 minutes. Finally, the ZnO-coated substrate was placed in a muffle furnace and calcined in air at 500°C for 1 hour to form a smooth, dense ZnO layer.

[0052] 1.3 Preparation of mesoporous meso-TiO2 framework layer Commercial TiO2 nanoparticle slurry (Dyesol 18NR-T) was diluted with isopropanol at a mass ratio of 1:8 and sonicated at room temperature for 1 hour to ensure thorough dispersion. The diluted TiO2 slurry was spin-coated onto a dense ZnO layer at 4000 rpm for 30 seconds. After spin-coating, the substrate was dried on a hot plate at 100°C for 5 minutes. The dried substrate was then transferred to a muffle furnace and heated to 500°C at a rate of 5°C / min, sintered in air for 30 minutes, and allowed to cool naturally to room temperature. This step facilitated the formation of good interconnections between the TiO2 nanoparticles and removed all organic binders, yielding a mesoporous TiO2 layer with a thickness of approximately 200 nm.

[0053] 1.4 Preparation of perovskite precursor solution In a nitrogen glove box, cesium iodide (CsI), formamidinium iodide (FAI), and lead iodide (PbI2) were mixed in a molar ratio of 1:9:10 and dissolved in a mixed solvent of anhydrous N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 4:1) to prepare a perovskite precursor solution with a total concentration of 1.3 M.

[0054] Add methylamine chloride (MACl) with a molar ratio of 5% PbI2 to improve crystallinity, stir at 60°C for 2 hours until completely dissolved, and filter using a 0.22 μm polytetrafluoroethylene filter for later use.

[0055] 1.5 Preparation of Perovskite Thin Films A two-step spin-coating procedure was used on a meso-TiO2 substrate: spin-coating at 1000 rpm for 10 seconds, followed by spin-coating at 6000 rpm for 30 seconds. 10–12 seconds before the end of the high-speed spin-coating phase, 200 μL of antisolvent (chlorobenzene) was rapidly added dropwise to the center of the substrate to promote rapid nucleation. Immediately after spin-coating, the substrate was annealed on a 100°C hot plate for 40 minutes, during which the perovskite film changed from pale yellow to a deep black mirror finish.

[0056] 1.6 Fabrication of Spiro-OMeTAD Hole Transport Layer Dissolve 72.3 mg of Spiro-OMeTAD powder in 1 mL of anhydrous chlorobenzene, then add 17.5 μL of lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) acetonitrile solution (520 mg / mL) and 28.8 μL of 4-tert-butylpyridine (tBP) sequentially, and shake thoroughly until completely dissolved. Spin-coat the above Spiro-OMeTAD solution onto a perovskite film at 3000 rpm for 30 seconds to form a uniform hole transport layer. The substrate is then placed in a sealed dark chamber with dry air (humidity <1%) for oxidation for 12–16 hours.

[0057] 1.7 Gold electrode evaporation The oxidized substrate is transferred to the mask in a thermal evaporation coating apparatus, under a vacuum level below 5 × 10⁻⁶. - Under 4 Pa ​​conditions, a gold film approximately 80 nm thick was thermally deposited at an evaporation rate of 0.5–1.0 Å / s, forming an effective area of ​​0.1 cm². 2 The top electrode.

[0058] 2. Battery preparation process for experimental and control groups. The difference between the experimental group and control group 2 in the battery device fabrication process lies in the material of the meso layer and the fabrication process of the framework layer; the remaining steps are exactly the same as those of the blank group. Other processes are consistent with the battery fabrication process of control group 1 (blank group).

[0059] 2.1 Preparation of mesoporous meso-LiF framework layer Before use, slurry B (5N) was ultrasonically dispersed at room temperature for 1 hour to ensure uniform dispersion. Then, LiF slurry was spin-coated onto a dense ZnO layer at 4500 rpm for 30 seconds. After spin-coating, the substrate was dried on a hot plate at 100°C for 5 minutes. The dried substrate was then transferred to a muffle furnace and heated to 500°C at a rate of 5°C / min. Sintering was carried out in air for 30 minutes, followed by natural cooling to room temperature to obtain a mesoporous LiF layer with a thickness of approximately 200 nm.

[0060] 2.2 Preparation of 4-fluoroanisole as an aid in wetting layer To ensure the wettability of the perovskite precursor solution on the fluoride substrate, a 1 mg / mL isopropanol solution of 4-fluoroanisole is also spin-coated. This prepared solution is spin-coated onto a meso-LiF substrate at 3000 rpm for 25 seconds. After the spin-coating process, the substrate is annealed on a 100°C hot plate for 10 minutes to form a 4-fluoroanisole wetting layer. The perovskite spin-coating step is then performed on this 4-fluoroanisole wetting layer. Without this step, the perovskite cannot be effectively spread and formed directly on the meso-LiF substrate.

[0061] like Figure 2 As shown, the contact angle between the meso-LiF substrate and the perovskite precursor solution is significantly reduced after spin-coating with a 4-fluoroanisole co-wetting layer, making it easier to coat the perovskite into a film.

[0062] 3. Photovoltaic performance testing and result evaluation 3.1 Battery core efficiency parameter testing (JV characteristics): The battery efficiency of the blank group and the experimental group was obtained by testing the JV curve of the device under AM 1.5G illumination intensity.

[0063] Before the test begins, the simulated solar light source is calibrated using a calibrated standard silicon reference cell to ensure that its output spectrum and irradiance meet the AM 1.5G standard.

[0064] After calibration, a linear scanning voltage is applied to the device under the illumination condition, and the current density-voltage (JV) characteristic curve is recorded. By using specialized software to fit and analyze the parameters of the obtained curve, the four core photovoltaic performance indicators of the device can be extracted: open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and photoelectric conversion efficiency (PCE).

[0065] Table 3 Comparison of core photovoltaic performance parameters of battery devices in each group

[0066] A comparison between control group 1 and the experimental group shows that the novel fluoride mesoporous layer, with its superior structure, significantly improves battery efficiency. Furthermore, a comparison between control group 2 and the experimental group reveals that low-purity fluoride raw materials severely restrict battery performance, indicating that impurities in fluorides are a significant factor affecting battery efficiency.

[0067] 3.2 Monochromatic light incident photoelectric conversion efficiency test (IPCE) The integrated current area of ​​the above devices was measured using a fluorescence quantum efficiency testing system to evaluate the improvement of charge transport capability by fluoride mesopores. The monochromatic incident photon-to-electron conversion efficiency (IPCE) of different groups of battery samples was analyzed using the Enlitech QE-R quantum efficiency system. The tests focused on comparing the performance differences of each group of perovskite solar cells in the 300–900 nm operating wavelength range, and the results are shown in Table 4.

[0068] Table 4. Integral current density of each battery group in the 300-900nm optical region.

[0069] 3.3 Ultraviolet (UV) Operational Stability Test: Each group of devices was placed under 350nm ultraviolet light irradiation to evaluate the system's improvement in ultraviolet light stability. The normalized long-term efficiency as a function of aging time is shown in Table 5. Table 5. Stability degradation tracking of the device under continuous irradiation with 350nm ultraviolet light (%)

[0070] The results above show that meso-LiF, as a mesoporous layer, exhibits better UV stability. Furthermore, the use of lower-purity raw materials in control group 2 significantly negatively impacted battery life, indicating that raw material purity is a crucial factor affecting battery performance.

[0071] In battery design, the traditional titanium dioxide mesoporous layer is abandoned in favor of fluorides, which possess excellent chemical stability and a suitable band structure, as an independent mesoporous framework layer. High-purity fluorides (≥5N) serve as wide-bandgap insulating materials and have fewer vacancy defects, fundamentally eliminating the risk of perovskite decomposition caused by TiO2 photocatalysis. Furthermore, the metal ions in fluorides are chemically stable and do not easily migrate, providing a robust mesoporous support structure, while fluoride ions (F...)... -This approach is expected to provide effective passivation at the interface, filling halogen vacancies at the perovskite interface. The strategy aims to provide a method for preparing high-purity fluorides and their mesoporous slurries, and a strategy for improving battery performance, by constructing a chemically inert and stable fluoride mesoporous layer.

[0072] like Figure 3 As shown in the figure, SEM testing reveals that the meso-LiF prepared in this invention possesses a mesoporous structure constructed from LiF nanoparticles, and its surface exhibits CsF needle-like crystals.

[0073] Uncoordinated Pb is easily generated at the bottom of perovskite films during the crystallization process. 2+ Defects and halogen vacancies (such as iodine vacancies). During spin coating and annealing, CsF can spontaneously undergo interfacial ion exchange and compensation, in which F... - Able to interact with uncoordinated Pb 2 + Strong coordination bonds are formed to fill halogen vacancies, while Cs + Due to their large ionic radii, they tend to accumulate at the framework interface and effectively compensate for cation vacancies at the A-sites of perovskites. This synergistic targeted passivation effect of anions and cations significantly reduces the density of deep-level defects at the interface.

[0074] Although high-purity lithium fluoride (LiF) possesses excellent chemical stability and a wide bandgap, its intrinsic insulation can increase the barrier to electron extraction to some extent. The uniform incorporation of trace amounts of CsF forms a favorable interfacial dipole layer at the physical interface between the mesoporous layer and the perovskite. This dipole layer effectively reduces the Schottky barrier height, not only compensating for the weak conductivity of LiF but also significantly enhancing the efficiency of photogenerated charge extraction and transport at the interface.

[0075] Trace amounts of Cs dissolved at the interface + It can partially enter the perovskite lattice, alleviate the lattice stress caused by the tolerance factor deviation, stabilize the underlying perovskite phase (α phase), induce high-quality, large-size crystallization of the perovskite film from the bottom, further block the ion migration channel, and thus synergistically improve the thermal stability and output lifetime of the device under long-term operation.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-purity fluoride slurry, characterized in that, It is composed of high-purity lithium fluoride nanoparticles, high-purity cesium fluoride, and a mixed solvent; the mixed solvent is a mixture of ethanolamine and N,N-dimethylformamide; the mass ratio of the high-purity lithium fluoride nanoparticles to the high-purity cesium fluoride is 15~25:1; the purity of both the high-purity lithium fluoride nanoparticles and the high-purity cesium fluoride reaches the 5N level.

2. A method for preparing a high-purity fluoride slurry, used to prepare the high-purity fluoride slurry as described in claim 1, characterized in that, Includes the following steps: Preparation of high-purity lithium fluoride nanoparticles: After obtaining a suspension of lithium fluoride nanoparticles, solid products are obtained by solid-liquid separation. The solid products are then subjected to thermal pretreatment, followed by fluidized bed ultraviolet deep impurity removal to obtain the high-purity lithium fluoride nanoparticles. Preparation of high-purity cesium fluoride: After obtaining cesium fluoride powder, it is subjected to thermal pretreatment, followed by secondary crystallization and drying to obtain an intermediate product. The intermediate product is then subjected to fluidized bed ultraviolet deep purification to obtain the high-purity cesium fluoride. Slurry preparation: The high-purity lithium fluoride nanoparticles and the high-purity cesium fluoride are mixed with a mixed solvent to obtain a fluoride salt slurry precursor; the fluoride salt slurry precursor is ball-milled and filtered to obtain the high-purity fluoride salt slurry.

3. The method for preparing high-purity fluoride slurry according to claim 2, characterized in that, The specific process for preparing the lithium fluoride nanoparticle suspension is as follows: ammonium fluoride, ethanol, and polyethylene glycol are dissolved in water, and then lithium nitrate solution is slowly added dropwise to react and generate the lithium fluoride nanoparticle suspension. The heat pretreatment conditions are: baking in a mixture of oxygen and nitrogen with an oxygen volume fraction of 30-40% at 250-300°C.

4. The method for preparing high-purity fluoride slurry according to claim 2, characterized in that, The specific process of fluidized bed ultraviolet deep purification is as follows: the particles to be purified are loaded into a micro fluidized bed; fluidizing gas is introduced from the bottom of the micro fluidized bed to suspend the particles in a fluidized state, and an ultraviolet light source is turned on to irradiate the particles during the fluidization process. The fluidizing gas is a mixture of oxygen and argon, with the oxygen volume fraction being 18-22% and the flow rate being 50-150 sccm; the wavelength of the ultraviolet light source is 285 nm, and the duration of the irradiation treatment is 3-9 hours.

5. The method for preparing high-purity fluoride slurry according to claim 2, characterized in that, The specific process for obtaining cesium fluoride powder is as follows: cesium carbonate solid is added to an aqueous solution containing ammonium fluoride, ethanol and polyethylene glycol to react. After the reaction is completed, the mixture is concentrated by distillation and cooled to crystallize and precipitate the cesium fluoride powder. The specific process for secondary crystallization is as follows: the product after the heat pretreatment is dissolved in deionized water, and a mixed solvent of ethanol and isopropanol is added to precipitate cesium fluoride crystals.

6. The method for preparing high-purity fluoride slurry according to claim 2, characterized in that, The specific process of mixing the high-purity lithium fluoride nanoparticles, the high-purity cesium fluoride, and the mixed solvent is ultrasonic mixing. The specific parameters for the ball milling process are as follows: using zirconia grinding balls, with a ball-to-material mass ratio of 3:1, a ball milling speed of 300~400 rpm, and a ball milling time of 24~48 hours.

7. The application of a high-purity fluoride salt slurry as described in claim 1 or a high-purity fluoride salt slurry prepared by the method described in any one of claims 2-6 in the preparation of a mesoporous framework layer for perovskite solar cells, characterized in that, The high-purity fluoride salt slurry is used to construct the mesoporous framework layer on the electron transport layer of the perovskite solar cell, so as to serve as a support framework for the directional growth of the perovskite thin film. The mesoporous framework layer is composed of lithium fluoride and cesium fluoride components in high-purity fluoride slurry.

8. The application of the high-purity fluoride salt slurry according to claim 7 in the preparation of the mesoporous framework layer of perovskite solar cells, characterized in that, The process for preparing the mesoporous framework layer includes: The high-purity fluoride slurry is coated onto the surface of the electron transport layer and then dried to obtain a dried product. The dried product is subjected to sintering treatment to form an interconnected structure of the solid components in the high-purity fluoride slurry, thereby obtaining the mesoporous framework layer.

9. The application of the high-purity fluoride salt slurry according to claim 7 in the preparation of the mesoporous framework layer of perovskite solar cells, characterized in that, After obtaining the mesoporous framework layer, the process further includes: A solution containing 4-fluoroanisole is spin-coated onto the surface of the mesoporous framework layer and then annealed to obtain an anti-wetting layer; A perovskite precursor solution is coated onto the surface of the aid-wetting layer and then subjected to crystallization annealing to form a perovskite layer.

10. The application of the high-purity fluoride salt slurry according to claim 7 in the preparation of the mesoporous framework layer of perovskite solar cells, characterized in that, Fluoride ions in the mesoporous framework layer form coordination bonds with uncoordinated divalent lead ions at the bottom of the perovskite layer to fill halogen vacancies at the bottom of the perovskite layer; cesium ions in the mesoporous framework layer are enriched at the physical interface between the mesoporous framework layer and the perovskite layer, and some of the cesium ions enter the crystal lattice of the perovskite layer to stabilize the perovskite phase.

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