A method for synthesizing cesium halide salts for perovskite solar cells

Abstract

This invention discloses a method for synthesizing cesium halide salts for perovskite solar cells, comprising the following steps: First, an aqueous solution of a cesium source is mixed with hydrohalic acid, and after reacting for a period of time, the water is removed by evaporation to obtain crude cesium halide salt; then, the crude product is dissolved in ultrapure water, a certain amount of antisolvent is added to precipitate the cesium halide salt, and the cesium halide salt is then filtered, washed, dried, and collected. By adjusting the rate of addition of antisolvent, the solution temperature, and the stirring rate, the crystal morphology and particle size of the cesium halide salt can be effectively controlled, which can meet the requirements of different types of perovskite solar cells. The cesium halide salt prepared by this invention has a purity >4N, and the process is simple, easy to operate, and easy to implement.

Description

Technical Field

[0001] This invention relates to a method for synthesizing cesium halide salts for perovskite solar cells, belonging to the field of new energy materials. Background Technology

[0002] Halide perovskite materials (structural formula ABX3, where A is a monovalent cation such as methylamine (MA), formamidinium (FA), or Cs, B is a divalent metal cation such as Pb or Sn, and X is a halide anion such as Cl, I, or Br) have been widely used in optoelectronic devices such as solar cells, photodetectors, and light-emitting diodes due to their excellent photoelectric properties. Cesium halide salts are one of the key raw materials for perovskite solar cells. Firstly, the most common organic-inorganic hybrid perovskites (such as MAPbI3) contain methylamine cations, which are prone to thermal decomposition at high temperatures, resulting in poor thermal stability. However, using a small amount of Cs doping can effectively improve the thermal stability of MAPbI3. Secondly, FAPbI3 with formamidinium ions as the A-site cation possesses a suitable band gap, a more suitable tolerance factor, and better thermal stability, and has seen rapid development in recent years. However, due to its low enthalpy of formation, the α-phase FAPbI3 readily transforms from the photoactive black phase to the non-photoactive yellow phase at room temperature. Replacing formamidinium ions with cesium ions or iodide ions with bromide or chloride ions can adjust the tolerance factor of perovskite, allowing (FACs)Pb(IBr)3 perovskite to exist stably in a cubic phase (i.e., the optically active black phase) at room temperature, ultimately enhancing the stability of perovskite solar cells. Furthermore, inorganic perovskite (CsPbX3), lacking organic cations and not decomposing at high temperatures, exhibits excellent thermal stability. The efficiency of single-junction inorganic perovskite solar cells has exceeded 21%, and tandem solar cells based on inorganic perovskite have exceeded 24%, making future commercialization highly likely.

[0003] In summary, both hybrid and inorganic perovskite solar cells rely heavily on cesium halide salts, which play a decisive role in the quality of perovskite thin films and the efficiency and stability of solar cells. In perovskite solar cells, impurities introduced by precursor materials can cause bulk defects in the perovskite film, leading to non-radiative recombination of charge carriers and reduced photoelectric conversion efficiency. Therefore, improving the purity of cesium halide salts is crucial for the fabrication of perovskite solar cells. Secondly, the crystal morphology of cesium halide salts directly affects the final morphology of the perovskite film; grain size, crystal orientation, and crystallinity all influence the stability and quality of the film. Currently, industrially produced cesium halide salts do not meet the requirements of perovskite solar cells due to low purity and uncontrollable grain size, resulting in poor stability and low efficiency in the prepared perovskite films and solar cells. Therefore, there is an urgent need to develop a simple, easy-to-operate, and readily implementable method for synthesizing cesium halide salts suitable for perovskite solar cells. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing cesium halide salts that is simple in process, easy to operate, easy to implement, and applicable to perovskite solar cells.

[0005] The present invention adopts the following technical solution:

[0006] A method for synthesizing cesium halide salts for perovskite solar cells includes the following steps:

[0007] (1) Add a certain amount of cesium source to ultrapure water and stir to form a clear and transparent solution;

[0008] (2) A certain amount of hydrohalic acid is added to the clear and transparent solution obtained in step (1), the pH of the solution is controlled, the solution is heated and stirred, and the reaction is carried out for a certain time to obtain an acidic halide solution.

[0009] (3) Transfer the solution obtained in step (2) into a flask and remove the water from the solution by evaporation to obtain solid powder;

[0010] (4) Dissolve the solid powder obtained in step (3) in ultrapure water, and add antisolvent dropwise until no more precipitate is formed. The concentration of the aqueous solution is 2-5 mol / L, and the antisolvent includes one or more of methanol, ethanol, isopropanol, acetone, and acetonitrile. The stirring rate is 0-500 rpm, the solution temperature is 20-80℃, and the antisolvent drop rate is 0.025-20 mL / s.

[0011] (5) Add washing solvent to the precipitate obtained in step (4), wash the precipitate more than 3 times, then filter to collect the solid product and place it in an oven to dry to obtain cesium halide salt.

[0012] Preferably, the cesium source in step (1) includes one or more of cesium acetate, cesium carbonate, and cesium hydroxide, and the concentration of the solution is 2 to 8 mol / L.

[0013] Preferably, the hydrohalic acid in step (2) includes one or more of hydrochloric acid, hydroiodic acid, and hydrobromic acid.

[0014] Preferably, in step (2), the pH of the solution is controlled between 1 and 4, the reaction temperature is controlled between 40 and 75°C, and the reaction time is 30 minutes to 4 hours.

[0015] Preferably, the evaporation method in step (3) includes rotary evaporation or spray drying.

[0016] Preferably, the washing solvent in step (5) includes one or more of methanol, ethanol, isopropanol, acetone, and acetonitrile.

[0017] Preferably, the drying temperature in step (5) is 80-120℃ and the drying time is 8-24h.

[0018] The technical principles employed in this invention and its advantages compared to existing cesium halide salt synthesis methods are as follows:

[0019] First, this invention uses a simple chemical method to synthesize cesium halide salts. By adjusting parameters such as solution concentration, reaction pH, and reaction time, high-purity cesium halide salts are synthesized. Second, based on the principle that cesium halide salts have different solubilities in different solvents, the cesium halide salts are subjected to anti-solvent post-treatment to improve their purity. By adjusting various parameters of the anti-solvent treatment, cesium halide salts with different grain sizes and crystal morphologies are obtained. The perovskite thin films prepared have fewer defects and can be used to prepare various perovskite thin films. Solar cells prepared using the cesium halide salts of this invention have high efficiency. Attached Figure Description

[0020] Figure 1 X-ray diffraction pattern of cesium bromide synthesized in Example 1;

[0021] Figure 2 Microstructure of cesium bromide powder synthesized in Example 1;

[0022] Figure 3 Microstructure of cesium bromide powder synthesized in Example 2;

[0023] Figure 4 Microstructure of cesium bromide powder synthesized in Example 3;

[0024] Figure 5 Microstructure of cesium bromide powder synthesized in Comparative Example 1;

[0025] Figure 6JV curves of CsPbI2Br inorganic perovskite solar cells prepared using cesium bromide in Examples 1-3 and Comparative Example 1;

[0026] Figure 7 X-ray diffraction pattern of cesium iodide synthesized in Example 4;

[0027] Figure 8 Microscopic morphology of cesium iodide powder synthesized in Example 4. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] Example 1: Preparation of cesium bromide

[0030] A. Weigh 30g of cesium carbonate and add it to a beaker. Pour in 30mL of ultrapure water and stir continuously until the solution is clear and transparent.

[0031] B. Measure 23 mL of hydrobromic acid and slowly add it dropwise to a beaker. The pH is 1.12. Stir continuously at 65°C for 1 hour.

[0032] C. Transfer the solution obtained in step B to a round-bottom flask and remove water using a rotary evaporator. Set the temperature to 70℃, the time to 90min, and the rotation speed to 80rpm.

[0033] D. Place the solid powder obtained in step C into a beaker, add 60 mL of ultrapure water, and stir at 450 rpm at 25 °C until clear and transparent. Then add 500 mL of anhydrous ethanol at a rate of 0.03 mL / s, and a large amount of precipitate is formed.

[0034] E. Collect the precipitate obtained in step D by filtration, then wash the filtered solid product with 45 ml of methanol more than 3 times, and then put the solid product into an oven to dry for 16 hours to obtain the final product.

[0035] X-ray diffraction results are as follows Figure 1 As shown, the final product is CsBr microcrystalline powder, and no impurity phase XRD peaks are present. Figure 2 As shown, the CsBr microcrystalline powder has a regular morphology and uniform size. ICP testing confirmed that the product purity reaches 99.995%.

[0036] Example 2: Preparation of cesium bromide

[0037] The preparation steps in this embodiment are basically the same as those in Example 1 from steps A to E, except that the rate at which the antisolvent is added in step D is 20 mL / s.

[0038] Please refer to the microstructure of the product. Figure 3 The grains are spherical and relatively small in size. ICP testing showed the product purity to be 99.998%.

[0039] Example 3: Preparation of cesium bromide

[0040] The preparation steps in this embodiment are basically the same as those in Example 1 from steps A to E, except that the solution temperature in step D is 65°C.

[0041] Please refer to the microstructure of the product. Figure 4 The grain size is relatively large. ICP testing showed the product purity reached 99.998%.

[0042] Comparative Example 1: Preparation of Cesium Bromide

[0043] In this comparative example of cesium bromide preparation, compared to Example 1, only step C was performed to obtain cesium bromide powder; that is, the anti-solvent operation was not performed. Please refer to [reference needed] for the microstructure of the product. Figure 5 According to ICP testing, the product purity is 99.93%.

[0044] The CsBr powders prepared in Examples 1-3 and Comparative Example 1 were mixed with PbI2 in a 1:1 ratio and dissolved in a DMF:DMSO solvent of 1:9 to prepare CsPbI2Br perovskite precursor solutions. These solutions were then spin-coated onto an ITO / SnO2 substrate to form perovskite films. Inorganic perovskite solar cells were fabricated using the ITO / SnO2 / CsPbI2Br / PTAA / MoO3 / Ag device structure, and the resulting device efficiencies were as follows: Figure 6 As shown in Table 1, the perovskite solar cells prepared using cesium bromide from Examples 1-3 are clearly more efficient. Inorganic perovskites are more sensitive to defects; even a small number of defects can significantly reduce the open-circuit voltage of the solar cell. Furthermore, the purity and grain size of cesium bromide determine the defect density in the perovskite film. Therefore, inorganic perovskite solar cells have higher requirements for cesium bromide raw materials. The cesium bromide prepared by antisolvent in this invention is very suitable for the preparation of inorganic perovskite films, resulting in a high-efficiency CsPbI₂Br inorganic perovskite solar cell.

[0045] Meanwhile, industrially produced 99% pure cesium bromide was purchased to prepare a CsPbI2Br perovskite precursor solution, and solar cells were fabricated using the same device structure. However, the holes in the thin film caused by low-quality cesium bromide resulted in short circuits in the devices, and all devices were inefficient.

[0046] Table 1. Device performance of CsPbI2Br inorganic perovskite solar cells prepared using cesium bromide in Examples 1-3 and Comparative Example 1.

[0047]

[0048] Example 4: Preparation of cesium iodide

[0049] A. Weigh 192g of cesium acetate and add it to a beaker. Pour in 306mL of ultrapure water and stir continuously until the solution is clear and transparent.

[0050] B. Measure 136 mL of hydroiodic acid and slowly add it dropwise to a beaker. The pH is 2.37. Stir continuously at 65°C for 1 hour.

[0051] C. Transfer the solution obtained in step B to a flask and remove water using a rotary evaporator. Set the temperature to 90℃, the time to 150min, and the rotation speed to 50rpm.

[0052] D. Place the solid powder obtained in step C into a beaker, add 310 mL of ultrapure water, stir at 500 rpm at 25 °C until clear and transparent, then add 2.2 L of acetone at a rate of 0.08 mL / s, resulting in a large amount of precipitate.

[0053] E. Collect the precipitate obtained in step D by filtration, then rinse the filtered solid product with 260 ml of methanol more than 3 times, and then put the solid product into an oven to dry for 24 hours to obtain the final product.

Claims

1. A method for synthesizing cesium halide salts for perovskite solar cells, characterized in that, Includes the following steps: (1) Add a certain amount of cesium source to ultrapure water and stir to form a clear and transparent solution; (2) A certain amount of hydrohalic acid is added to the clear and transparent solution obtained in step (1), the pH of the solution is controlled, the solution is heated and stirred, and the reaction is carried out for a certain time to obtain an acidic halide solution; (3) Transfer the solution obtained in step (2) into a flask and remove the water from the solution by evaporation to obtain a solid powder; (4) Dissolve the solid powder obtained in step (3) in ultrapure water, and add antisolvent dropwise until no more precipitate is formed. The concentration of the aqueous solution is 2~5 mol / L, and the antisolvent includes one or more of methanol, ethanol, isopropanol, acetone, and acetonitrile. The stirring rate is 0~500 rpm, the solution temperature is 25℃, and the antisolvent drop rate is 20 mL / s. (5) Add washing solvent to the precipitate obtained in step (4), wash the precipitate more than 3 times, then filter to collect the solid product and place it in an oven to dry, and obtain cesium halide salt with a purity >4N.

2. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, The cesium source mentioned in step (1) includes one or more of cesium acetate, cesium carbonate, and cesium hydroxide, and the concentration of the solution is 2~8 mol / L.

3. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, The hydrohalic acid mentioned in step (2) includes one or more of hydrochloric acid, hydroiodic acid, and hydrobromic acid.

4. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, In step (2), the solution pH is controlled between 1 and 4, the reaction temperature is controlled between 40 and 75°C, and the reaction time is 30 minutes to 4 hours.

5. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, The evaporation method in step (3) includes rotary evaporation or spray drying.

6. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, The washing solvent mentioned in step (5) includes one or more of methanol, ethanol, isopropanol, acetone, and acetonitrile.

7. The method for synthesizing cesium halide salts for perovskite solar cells as described in claim 1, characterized in that, The drying temperature in step (5) is 80-120℃ and the drying time is 8-24h.

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