Preparation method and application of high-purity cesium iodide

Abstract

The application discloses a preparation method and application of high-purity cesium iodide, which comprises the following steps: firstly, mixing an industrial-grade cesium source powder and an iodine source solution, and preparing a solid powder after vacuum rotary evaporation and drying; then repeatedly washing the powder by using a special detergent, removing impurities, and drying; sintering at a temperature of 200-350 DEG C; dissolving the sintered powder in deionized warm water, and cooling and crystallizing at 0 DEG C; and finally collecting and drying the crystallization product to obtain the high-purity cesium iodide (CsI) finished product. The CsI powder prepared by the application has a purity of more than 99.99%, can obtain more excellent comprehensive performance, and has a simple and controllable process, and has a wide application prospect in the field of perovskite solar cells.

Description

A method for preparing high-purity cesium iodide and its application Technical Field

[0001] This invention belongs to the field of new energy materials, specifically relating to a method for preparing high-purity cesium iodide for perovskite solar cells and its application. Background Technology

[0002] Perovskite solar cells boast high photoelectric conversion efficiency and are core components in the photovoltaic power generation field, with enormous market application prospects. Perovskite materials are compounds with a perovskite (ABX3) structure, where the A-site is typically an organic cation such as methylamine (MA) and formamidinium (FA), the B-site is typically a transition metal cation such as Pb or Sn, and the X-site is a halide anion such as I or Br. Previous studies have found that lead iodide has an excellent band gap, and formamidinium-lead iodide films, composed of lead iodide and formamidinium ions, can approach the theoretical limit of photoelectric conversion efficiency. However, formamidinium ions, as A-site cations, readily react with water, leading to structural damage. This negative impact is a major reason for the low lifespan of perovskite cells. In recent years, research has shown that partially replacing formamidinium ions with large-diameter alkali metal cations such as cesium can effectively improve structural stability. Therefore, cesium-doped formamidinium-lead iodide has become a focus of research in the optoelectronic materials industry. In perovskite solar cell materials, interfacial defects caused by impurities are the main culprit for nonradiative recombination of charge carriers, leading to reduced photoelectric conversion efficiency. Therefore, cesium iodide incorporated into lead formamidinium iodide requires extremely high purity. Currently, the price of cesium iodide on the market remains high, especially for high-purity cesium iodide (99.99%), which has reached as high as 10 yuan / g. Therefore, how to prepare high-purity cesium iodide at low cost has become a key issue of great concern and urgent need for resolution in the perovskite solar cell industry. Summary of the Invention

[0003] To address the urgent need for core materials in the photovoltaic industry, this invention provides a simple, low-cost, and easily mass-producible method for preparing high-purity (99.99%) CsI. The specific details of the invention are as follows:

[0004] High-purity cesium iodide is prepared according to the following main steps:

[0005] S1: Take industrial-grade cesium source powder and add it to deionized water to prepare a colorless solution with a concentration of not less than 80%; then take industrial-grade iodine source solution and add it to the above colorless solution by peristaltic pump or dropper; wherein, by controlling the amount of iodine source solution added, the pH value of the mixed solution is ≤2.

[0006] S2: The mixed solution prepared in S1 is placed in a rotary evaporation flask and vacuum rotary evaporated. After the mixed solution is fully dehydrated, a solid intermediate product is obtained.

[0007] S3: Place the solid intermediate obtained in S2 into a rotary evaporation flask, add a special detergent and shake, then let it stand and pour out the solution, leaving the solid precipitate at the bottom of the rotary evaporation flask; add the detergent again to dissolve and wash the precipitate; repeat this washing process 3 times to obtain a pure solid precipitate; wherein, the special washing solvent is characterized by the fact that cesium iodide is slightly soluble in the solvent, while elemental iodine is readily soluble in the solvent;

[0008] S4: Place the solid precipitate obtained in S3 in a drying oven and dry it for 6-8 hours. Then, put the dried product into a box-type resistance furnace and sinter it at a temperature of 200-350℃ for 2-5 hours.

[0009] Alternatively, the solid precipitate obtained in S3 can be placed in a rotary evaporation flask, dissolved completely in a special detergent, and then subjected to a second vacuum rotary evaporation at a temperature of 90–160°C for 20–50 min and a rotation speed of 50–80 r / min. After all the liquid in the flask has evaporated, the temperature is raised to 180°C and rotary evaporation is continued for 2 h. The solid intermediate product is obtained after the second rotary evaporation.

[0010] S5: Dissolve the sintered product or the secondary rotary evaporation solid product obtained in S4 in a container filled with deionized water. During the dissolution process, heat and stir simultaneously at a temperature of 50-80°C. After the solid product is completely dissolved, place it in a crystallizer and cool it at 0°C for crystallization. Filter it while it is cold and collect the filtered solid. Repeat this step 1-2 times.

[0011] S6: Load the solid crystalline product obtained in S5 into a ceramic container and place it in a vacuum drying oven. Dry it at 30-80℃ for 5-10 hours. The resulting product is the final product.

[0012] Preferably, in step S1, the purity of the cesium source powder is 99% to 99.9%, and the purity of the iodine source solution is 45% to 57%.

[0013] Preferably, the cesium source in step S1 is one or more of cesium sulfate, cesium carbonate, and cesium hydroxide; and the iodine source is hydrogen iodide.

[0014] Preferably, in step S1, the cesium source is selected from 50% cesium hydroxide and 50% cesium carbonate by mass fraction; the iodine source is selected from 55% hydrogen iodide by mass fraction.

[0015] Preferably, the vacuum rotary evaporation in step S2 is carried out at a temperature of 90–180°C, a time of 40–60 min, and a rotation speed of 50–80 r / min.

[0016] Preferably, the special detergent mentioned in steps S3 and S4 includes one or more of ethanol, isopropanol, acetone, benzene, and carbon tetrachloride.

[0017] Preferably, the detergent used in steps S3 and S4 is selected as 80% ethanol + 20% isopropanol by volume percentage.

[0018] Preferably, the filter material used in step S5 includes one or more of PVP, PVE, and cation exchange resin.

[0019] The present invention also proposes an application of high-purity cesium iodide in perovskite solar cells, wherein the high-purity cesium iodide is prepared by any of the preparation methods described above.

[0020] The principles and advantages of this invention are as follows:

[0021] This invention uses industrial-grade (99%–99.9%) raw materials to prepare experimental-grade high-purity CsI products (99.99%). The raw material cost is low, the process is simple, and there are no toxic or hazardous byproducts, which facilitates environmentally friendly design and large-scale production.

[0022] Existing processes for preparing cesium iodide are not only complex and costly in terms of raw materials, but also contain high levels of impurities that are difficult to remove. Industrial-grade iodine source solutions (such as 45%–57% hydrogen iodide) are prone to oxidation and decomposition due to light and high temperatures, leading to the deposition of elemental iodine and a dark brown color. When the iodine source solution is mixed with a cesium source solution to form a cesium iodide solution, elemental iodine is also introduced. Therefore, removing elemental iodine is the first step in impurity removal. Since hydroiodic acid is volatile and elemental iodine is easily sublimated, the first step is to perform vacuum rotary evaporation on the iodine-containing cesium iodide solution to remove a large amount of residual hydroiodic acid and elemental iodine. However, the rotary evaporation product tends to clump, preventing the elemental iodine inside the clumps from distilling out. Furthermore, a large amount of sublimated iodine adheres to the condenser of the rotary evaporator, making it difficult to remove. If the condenser is not cleaned thoroughly, iodine may flow back into the volumetric flask. Therefore, deep cleaning of the condenser is necessary, resulting in a cumbersome and complex process.

[0023] Through repeated experiments, this invention has identified a special washing solvent. The solvent is characterized by the slight soluble nature of cesium iodide, while elemental iodine is readily soluble in it. Using this solvent to repeatedly and thoroughly wash cesium iodide in a volumetric flask, followed by rotary evaporation, effectively removes iodine impurities from the cesium iodide. Simultaneous stirring during the washing process thoroughly breaks up any agglomerated products. Repeating this process 2-3 times removes most of the iodine impurities and also cleans away iodine that has sublimated onto the condenser.

[0024] At this point, trace amounts of elemental iodine remain in the rotary evaporation product (CsI). This invention further employs high-temperature sintering to remove iodine impurities. The principle is that iodine has extremely low solubility in water, but its solubility increases significantly in water containing iodide ions, due to the formation of I3. - Ions. Once cesium iodide in the rotary evaporation product dissolves in water, I3 - The ions will undergo a reversible reaction in water, releasing iodide ions and elemental iodine. This invention first employs a calcination method, heating the rotary evaporation product to 200–350°C in air and sintering for 2–5 hours, thus enabling the I3+ ions to react. - Ion decomposition releases elemental iodine, thus completely removing iodine impurities. Finally, to remove insoluble impurities from the CsI powder and further reduce the content of metal cation impurities, the present invention repeatedly re-dissolves, crystallizes, and filters it to finally obtain a high-purity (99.99%) cesium iodide product. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit the invention.

[0026] Example 1

[0027] This embodiment discloses a method for preparing high-purity cesium iodide for perovskite solar cells and its application. The preparation process includes the following steps:

[0028] S1: Take 326g of cesium carbonate powder with a purity of 99.9% and add it to 400mL of deionized water to prepare a colorless solution; then take 495g of 55% hydroiodic acid and add it to the cesium carbonate solution while stirring using a peristaltic pump at a rate of 40ml / min, and stop when the pH of the mixed solution is no greater than 2.

[0029] S2: The mixed solution obtained in S1 was placed in a rotary evaporation flask and subjected to vacuum rotary evaporation at a temperature of 135℃ for 40 min and a rotation speed of 60 r / min. After the mixed solution was fully dehydrated, a solid intermediate product was obtained.

[0030] S3: Place the solid intermediate obtained by rotary evaporation in S2 into a rotary evaporation flask, add 550 mL of a detergent solution prepared from ethanol and isopropanol (volume ratio 4:1), shake for 3–5 min, let stand for 5 min, then pour out the solution, leaving the solid precipitate at the bottom of the flask; add another 550 mL of the above-mentioned clean detergent solution to dissolve and wash the precipitate. Repeat this washing process 3 times. Place the washed product in a forced-air drying oven and dry for 6 h.

[0031] S4: Place the dried product obtained in S3 into a box-type resistance furnace and sinter at 300℃ for 4 hours.

[0032] S5: Dissolve the sintered product obtained in S4 in a container containing 350 mL of deionized water, heating and stirring simultaneously at 60°C. After the solid product is completely dissolved, place it in a crystallizer and cool it at 0°C for crystallization. Filter the solution while cold using a cation exchange resin as the filter material. Collect and dry the filtered solid. Dissolve the filtered product in a container containing 200 mL of deionized water, and repeat the above dissolution, heating, stirring, cooling crystallization, filtration, and collection process once more.

[0033] S6: Load the solid crystalline product obtained in S5 into a ceramic container and place it in a vacuum drying oven. Dry it under vacuum at 60°C for 8 hours. The resulting product is the final product.

[0034] Example 2

[0035] This embodiment discloses a method for preparing high-purity cesium iodide for perovskite solar cells and its application. The preparation process includes the following steps:

[0036] S1: Take 150g of cesium hydroxide powder with a purity of 99.9%, add it to 220mL of deionized water to prepare a colorless solution, then take 130g of 45% hydroiodic acid and add it dropwise to the cesium carbonate solution while stirring. The titration endpoint is when the pH value of the mixed solution is not greater than 2.

[0037] S2: The mixed solution obtained in S1 was placed in a rotary evaporation flask and subjected to vacuum rotary evaporation at a temperature of 120℃ for 60 min and a rotation speed of 75 r / min. After the mixed solution was fully dehydrated, a solid intermediate product was obtained.

[0038] S3: Place the solid intermediate obtained from rotary evaporation in S2 into a rotary evaporation flask, add 150 mL of a detergent solution prepared from benzene and carbon tetrachloride (molar ratio 1:1), shake for 3–5 min, let stand for 5 min, then pour out the solution, leaving the solid precipitate at the bottom of the flask; add another 150 mL of the above-mentioned clean detergent solution to dissolve and wash the precipitate. Repeat this washing process 3 times. Place the washed product in a forced-air drying oven and dry for 6 h.

[0039] S4: The solid product obtained in S3 was placed in a rotary evaporation flask and dissolved completely in a solvent prepared with ethanol and acetone (molar ratio 1:3). A second vacuum rotary evaporation was then performed at 140℃ for 30 min at a rotation speed of 75 r / min. After all the liquid in the flask had evaporated, the temperature was raised to 180℃, and rotary evaporation continued for 2 h. The solid intermediate product was obtained after the second rotary evaporation.

[0040] S5: Dissolve the solid obtained from the secondary rotary evaporation in S4 in a container containing 160 mL of deionized water. During the dissolution process, heat and stir simultaneously at a temperature of 60–75 °C. After the solid product is completely dissolved, place it in a crystallizer and cool it at 0 °C for crystallization. Filter the product while it is still cold using a cation exchange resin as the filter material and collect the filtered solid. Then dissolve the filtered product in a container containing 100 mL of deionized water and repeat the above dissolution, heating, stirring, cooling crystallization, filtration, and collection process once more.

[0041] S6: Load the solid crystalline product obtained in S5 into a ceramic container and place it in a vacuum drying oven. Dry it under vacuum at 70°C for 8 hours. The resulting product is the final product.

[0042] Example 3

[0043] This embodiment is basically the same as the steps from S2 to S6 in Embodiment 1. The difference is that the mixed solution used in S2 is the filtrate left after several filtrations in step S5 of Embodiment 1.

[0044] Comparative Example 1

[0045] The preparation steps of this comparative example are the same as S1, S2, S4, S5, and S6 of Example 1, except that the solvent washing process in step S3 is not performed.

[0046] Comparative Example 2

[0047] The preparation steps of this comparative example are the same as S1, S2, S3, S5, and S6 of Example 1 or 2, except that the high-temperature sintering or secondary rotary evaporation process in step S4 is not performed.

[0048] Comparative Example 3

[0049] The preparation steps of this comparative example are the same as S1, S2, S3, S4 and S6 of Example 1, except that the recrystallization process in step S5 is not performed.

[0050] The purity of the prepared products was evaluated using ICP combined with XRD analysis. The preparation processes and final product test results of the three examples and three comparative examples are listed in Table 1.

[0051] Table 1. Preparation processes and final product test results of the examples and comparative examples.

[0052]

[0053] As shown in Table 1, the preparation process of this invention can successfully produce high-purity cesium iodide powder with a purity of 99.99%, and the product is pure white. Compared with Example 1, Example 2 did not perform sintering in step S4, but instead underwent secondary high-temperature rotary evaporation, achieving the same purification effect even with a small amount of material. Example 3 did not specifically prepare a mixed solution of cesium and iodine sources, but instead used the filtrate from the crystal filtration in step S5 of Example 1 to treat it using the purification process of this invention, which also successfully produced a high-purity cesium iodide product with a purity of 99.99%, which is of great significance for improving the overall yield of raw materials.

[0054] Compared with Example 1, Comparative Example 1 did not perform repeated solvent washing in step S3, resulting in a significant increase in metal cation impurities in the product; Comparative Example 2 did not perform high-temperature sintering or secondary rotary evaporation in step S4, resulting in incomplete removal of iodine from the product and a yellowish color; Comparative Example 3 did not perform recrystallization and filtration in step S5, resulting in higher levels of insoluble impurities and metal cation impurities in the product.

Claims

1. A method for preparing high-purity cesium iodide, characterized in that, Includes the following steps: S1: Add industrial-grade cesium source powder to deionized water to prepare a colorless solution with a concentration of not less than 80%; then add industrial-grade iodine source solution to the above colorless solution by peristaltic pump or dropper; wherein, the pH value of the mixed solution is ≤2 by controlling the amount of iodine source solution added; S2: Place the mixed solution prepared in S1 in a rotary evaporation flask for vacuum rotary evaporation, and after the mixed solution is fully dehydrated, a solid intermediate product is obtained; S3: The solid intermediate product obtained in S2... The sample was placed in a rotary evaporation flask, a special detergent was added and shaken, and after standing, the solution was poured out, leaving the solid precipitate at the bottom of the flask. The precipitate was then dissolved and washed with the special detergent again. This washing process was repeated three times to obtain a pure solid precipitate. The special detergent is characterized by the fact that cesium iodide is slightly soluble in it, while elemental iodine is readily soluble. S4: The solid precipitate obtained in S3 was dried in a drying oven for 6-8 hours, and then the dried product was placed in a box-type electric resistance furnace. In step S3, sinter at 200-350℃ for 2-5 hours; or, place the solid precipitate obtained in S3 into a rotary evaporation flask, dissolve it completely in a special detergent, and then perform a second vacuum rotary evaporation at 90-160℃ for 20-50 minutes at a rotation speed of 50-80 r / min; after all the liquid in the flask has evaporated, raise the temperature to 180℃ and continue rotary evaporation for 2 hours; after the second rotary evaporation, a solid intermediate product is obtained; S5: sinter the product obtained in S4. Alternatively, the solid product obtained from secondary rotary evaporation can be dissolved in a container filled with deionized water. During the dissolution process, heating and stirring are carried out simultaneously at a temperature of 50-80°C. After the solid product is completely dissolved, it is placed in a crystallizer and cooled to crystallize at 0°C. The product is then filtered while cold, and the filtered solid is collected. This step is repeated 1-2 times. S6: The solid crystal product obtained in S5 is loaded into a ceramic container and placed in a vacuum drying oven. It is dried at a temperature of 30-80°C for 5-10 hours. The resulting product is the final product.

2. The preparation method according to claim 1, characterized in that, In step S1, the purity of the cesium source powder is 99%~99.9%, and the purity of the iodine source solution is 45%~57%.

3. The preparation method according to claim 2, characterized in that, The cesium source in step S1 is one or more of cesium sulfate, cesium carbonate, and cesium hydroxide; the iodine source is hydrogen iodide.

4. The preparation method according to claim 3, characterized in that, In step S1, the cesium source is selected as 50% cesium hydroxide and 50% cesium carbonate by mass fraction; the iodine source is selected as 55% hydrogen iodide by mass fraction.

5. The preparation method according to claim 1, characterized in that, The vacuum rotary evaporation in step S2 is carried out at a temperature of 90~180℃, a time of 40~60min, and a rotation speed of 50~80r / min.

6. The preparation method according to claim 1, characterized in that, The special detergents mentioned in steps S3 and S4 include one or more of ethanol, isopropanol, acetone, benzene, and carbon tetrachloride.

7. The preparation method according to claim 6, characterized in that, The special detergent mentioned in steps S3 and S4 is selected as 80% ethanol + 20% isopropanol by volume percentage.

8. The preparation method according to claim 1, characterized in that, The filter material used in step S5 includes one or more of PVP, PVE, and cation exchange resin.

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