A black-phase formamidinium lead iodide microcrystal, its preparation method and application

Abstract

This invention belongs to the field of chemical synthesis technology and relates to a black-phase formamidine lead iodide microcrystal, its preparation method, and its application. The invention provides a method for preparing black-phase formamidine lead iodide microcrystal, comprising: mixing a divalent lead salt compound, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits the oxidation of iodide anions, and deionized water as a precursor liquid; and subjecting the precursor liquid to high-pressure hydrothermal treatment to obtain black-phase formamidine lead iodide microcrystal. The preparation method provided by this invention uses water as a solvent, avoiding the use of organic solvents, and the resulting black-phase formamidine lead iodide microcrystal has high crystallinity and stability, and can be stored at room temperature without phase change for a long time.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, and relates to a black phase formamidinium lead iodide microcrystal, its preparation method and application. Background Technology

[0002] Formamidinium lead iodide (FAPbI3) is a perovskite material commonly used in photovoltaic devices, comprising formamidinium (FA), methylamine (MA), and cesium ions (Cs). + FAPbI3 is a commonly used A-site cation. Compared to MA, FAPbI3 exhibits a lower band gap (Eg), improved photoelectric properties, and higher thermal stability. The larger size of the FA cation leads to the formation of a Pm3m cubic perovskite lattice in FAPbI3, rather than the lower symmetry tetragonal MAPbI3 lattice. The lower Eg value of FAPbI3 originates from the high overlap of Pb 6s-I 5p orbitals and the reduction of octahedral tilt. The lattice of FAPbI3 exhibits a polymorphic network structure, with the high symmetry structure originating from randomly distributed local lower symmetry (twisted) structural units. The average lattice parameter value of the α phase (i.e., the black phase) of FAPbI3 ranges from 6.352 to 6.365 Å at room temperature, and its high symmetry sacrifices phase stability. By alloying FA with Cs, MA, or both at the A-site, the effective A-site radius of FAPbI3 can be reduced, improving phase stability at room temperature, but this leads to a widening of the band gap.

[0003] α-FAPbI3 is a photoactive phase with high photoelectric conversion efficiency, but it tends to transform into the non-photoactive yellow formamidine lead iodide (δ-FAPbI3) at room temperature. This phase transition leads to material degradation and decreased battery performance. Traditional methods for preparing α-FAPbI3 microcrystals (patent number: CN202110252152.0) typically use high-purity lead iodide and formamidine hydroiodate to prepare a precursor solution, requiring organic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and γ-butyrolactone (GBL). Precipitation is induced by antisolvents such as ethyl acetate, chlorobenzene, or diethyl ether, and finally, the product is obtained through high-temperature annealing. These preparation methods all rely on organic solvents and organic antisolvents, resulting in α-FAPbI3 with low purity and poor stability. Summary of the Invention

[0004] The purpose of this invention is to improve the preparation process of black phase formamidine lead iodide microcrystals in a simple and low-cost manner, so as to obtain black phase formamidine lead iodide microcrystals with high purity and stability, and to avoid the use of organic solvents and organic anti-solvents. To this end, this invention provides black phase formamidine lead iodide microcrystals, their preparation method, and applications to address this need in the art.

[0005] On one hand, the present invention relates to a method for preparing black phase formamidine lead iodide microcrystals, comprising: mixing a salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits the oxidation of iodide anions, and deionized water as a precursor liquid, and subjecting the precursor liquid to high-pressure hydrothermal treatment to obtain black phase formamidine lead iodide microcrystals.

[0006] Furthermore, in the method for preparing black formamidinium lead iodide microcrystals provided by the present invention, the salt compound containing divalent lead is selected from at least one of lead iodide, lead acetate, lead nitrate, lead oxide, and lead metaborate.

[0007] The reducing acid compound that inhibits the oxidation of iodide anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphite, and formic acid.

[0008] Furthermore, in the method for preparing black formamidinium lead iodide microcrystals provided by the present invention, the molar ratio of hydroiodic acid to lead in the divalent lead salt compound is 3~10:1.

[0009] The molar ratio of formamidine acetate to lead in the divalent lead salt compound is 1~5:1;

[0010] The molar ratio of the reducing acid compound that inhibits the oxidation of iodide anions to the lead element in the salt compound containing divalent lead is 0.01 to 1:1.

[0011] Furthermore, in the method for preparing black formamidine lead iodide microcrystals provided by the present invention, the mass ratio of deionized water to formamidine acetate is 1~10:1.

[0012] Furthermore, in the method for preparing black phase formamidinium lead iodide microcrystals provided by the present invention, the reaction temperature of the high-pressure hydrothermal treatment is 150~250℃, the pressure is 1~10MPa, and the reaction time is 2~12h.

[0013] Furthermore, in the method for preparing black phase formamidinium lead iodide microcrystals provided by the present invention, the high-pressure hydrothermal treatment uses at least one of nitrogen and inert gas for pressure regulation.

[0014] On the other hand, the present invention relates to a black phase formamidine lead iodide microcrystal, which is prepared by the aforementioned method for preparing black phase formamidine lead iodide microcrystal.

[0015] Furthermore, in the black phase formamidinium lead iodide microcrystals provided by the present invention, the black phase formamidinium lead iodide microcrystals transform from the black phase to the yellow phase in a time of not less than 72 hours under the conditions of room temperature 30°C, humidity 45%, and no inert gas protection.

[0016] On the other hand, the present invention relates to the application of the black phase formamidinium lead iodide microcrystals provided by the present invention in the preparation of solar cells.

[0017] On the other hand, the present invention relates to a perovskite solar cell, comprising a transparent conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, a buffer layer, and a metal electrode, wherein the perovskite light-absorbing layer comprises black phase formamidinium lead iodide microcrystals provided by the present invention.

[0018] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0019] This invention provides a method for preparing melaninized lead iodide microcrystals using a one-step hydrothermal method, avoiding the cumbersome and complex multi-step reactions of traditional preparation processes. High-quality melaninized lead iodide microcrystals can be obtained through simple raw material mixing and high-pressure hydrothermal treatment. This method is not only simple to operate but also requires low-level equipment, making it easy to promote and apply in industrial production.

[0020] This invention provides a method for preparing black-phase formamidinium lead iodide microcrystals, which allows the use of water as a solvent, avoiding the use of organic solvents and organic anti-solvents in traditional methods. This not only reduces production costs but also reduces environmental pollution, aligning with the current global advocacy for sustainable development.

[0021] The α-FAPbI3 microcrystals prepared by this invention have high stability. Under conditions of room temperature 30°C, humidity 45%, and no inert gas protection, the time for them to transform from the black phase to the yellow phase is no less than 72 hours. Therefore, when applied to solar cells, they can significantly improve the service life of solar cells. This characteristic enables solar cells made from these α-FAPbI3 microcrystals to maintain stable operation for a long time under harsh environments.

[0022] The α-FAPbI3 microcrystals prepared by this invention possess high crystallinity and excellent photoelectric properties, resulting in solar cells with higher fill factors and photoelectric conversion efficiencies. This is of great significance for improving the power generation capacity of solar cells and reducing power generation costs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a diagram illustrating the preparation process of black formamidinium lead iodide microcrystals.

[0025] Figure 2The images show the appearance of Examples 2, 3, and 4 compared to the comparative example of black-phase formamidinium lead iodide microcrystals placed in air. Detailed Implementation

[0026] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0027] Example 1

[0028] This embodiment provides a method for preparing black formamidinium lead iodide microcrystals.

[0029] Reference Figure 1 The preparation process of the black phase formamidinium lead iodide microcrystals shown is as follows:

[0030] Step 1: Weigh out the salt compound containing divalent lead, hydroiodic acid, formamidine acetate, reducing acid compound that inhibits the oxidation of iodide anions, and water, and mix them together as the precursor liquid.

[0031] Optionally, in step 1, the mixing and addition method of the above raw materials is not particularly limited. After preparing hydroiodic acid into an aqueous solution and preparing the reducing acid compound that inhibits the oxidation of iodide anions into an aqueous solution, the salt compound containing divalent lead, formamidine acetate, the aqueous solution of hydroiodic acid, and the aqueous solution of the reducing acid compound that inhibits the oxidation of iodide anions are mixed.

[0032] Optionally, in step 1, the salt compound containing divalent lead, hydroiodic acid, formamidine acetate, reducing acid compound that inhibits the oxidation of iodide anions, and water are directly mixed.

[0033] For example, in step 1, the salt compound containing divalent lead is selected from at least one of lead iodide, lead acetate, lead nitrate, lead oxide, and lead metaborate; the reducing acid compound that inhibits the oxidation of iodide anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphite, and formic acid.

[0034] Specifically, in step 1, the molar ratio of hydroiodic acid to lead in the divalent lead-containing salt compound is 3~10:1; the molar ratio of formamidine acetate to lead in the divalent lead-containing salt compound is 1~5:1; the molar ratio of the reducing acid compound that inhibits the oxidation of iodide anions to lead in the divalent lead-containing salt compound is 0.01~1:1; and the mass ratio of deionized water to formamidine acetate is 1~10:1.

[0035] Step 2: Place the precursor liquid in a high-pressure reactor, seal it, and then perform high-pressure hydrothermal treatment.

[0036] Generally, in step 2, the high-pressure reactor used has a polytetrafluoroethylene or enamel lining, which has good acid resistance and corrosion resistance, and is equipped with temperature and pressure sensors.

[0037] Step 3: Control the reaction temperature to 150~250℃, the pressure to 1~10MPa, and the reaction time to 2~12h.

[0038] Optionally, in step 3, the pressure is adjusted by pumping nitrogen or argon into the high-pressure reactor.

[0039] Step 4: After the reaction is complete, allow it to cool naturally to room temperature, filter it, and rinse it with deionized water and ethanol.

[0040] Step 5: Dry the material to obtain black α-FAPbI3 microcrystals.

[0041] Example 2

[0042] This embodiment provides a specific preparation process for black phase formamidinium lead iodide microcrystals.

[0043] Weigh out 100g (0.3mol) of lead acetate, 32g (0.3mol) of formamidin acetate, 243g of 47wt% hydroiodic acid aqueous solution (hydrogen iodide content 0.9mol), 0.4g of 50wt% hypophosphoric acid aqueous solution (hypophosphoric acid content 0.003mol), and 32ml of deionized water, and mix them thoroughly.

[0044] The mixed precursors were placed in a 500mL acid-resistant high-pressure reactor equipped with temperature and pressure sensors and then sealed.

[0045] The reaction temperature was set at 150℃, nitrogen gas was introduced to adjust the pressure to 1 MPa, and the reaction was carried out for 12 hours.

[0046] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed with deionized water and ethanol, and dried at 80°C to obtain 163g of black α-FAPbI3 microcrystals, with a yield of 83.5%.

[0047] Example 3

[0048] This embodiment provides a specific preparation process for black phase formamidinium lead iodide microcrystals.

[0049] Weigh out 22g (0.1mol) of lead oxide, 52g (0.5mol) of formamidin acetate, 270g of 47wt% hydroiodic acid aqueous solution (hydrogen iodide content 1mol), 17g (0.1mol) of ascorbic acid, and 520ml of deionized water, and mix them thoroughly.

[0050] The mixed precursors were placed in a 1000mL acid-resistant high-pressure reactor equipped with temperature and pressure sensors and then sealed.

[0051] The reaction temperature was set at 250℃, nitrogen gas was introduced to adjust the pressure to 10 MPa, and the reaction was carried out for 2 hours.

[0052] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed with deionized water and ethanol, and dried at 80°C to obtain 127 g of black α-FAPbI3 microcrystals, with a yield of 89.4%.

[0053] Example 4

[0054] This embodiment provides a specific preparation process for black phase formamidinium lead iodide microcrystals.

[0055] Weigh out 25g (0.1mol) of lead metaborate monohydrate, 40g (0.4mol) of formamidin acetate, 200g of 47wt% hydroiodic acid aqueous solution (hydrogen iodide content 0.7mol), 2g (0.02mol) of oxalic acid, and 80ml of deionized water, and mix them thoroughly.

[0056] The mixed precursors were placed in a 500 mL acid-resistant high-pressure reactor equipped with temperature and pressure sensors, and then sealed. The reaction temperature was set to 180 °C, and nitrogen gas was introduced to adjust the pressure to 5 MPa. The reaction was carried out for 6 hours.

[0057] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed with deionized water and ethanol, and dried at 80°C to obtain 103 g of black α-FAPbI3 microcrystals, with a yield of 88.0%.

[0058] Comparative Example

[0059] This comparative example provides a specific preparation process for black phase formamidinium lead iodide microcrystals.

[0060] Weigh 20g of formamidine and 50g of lead iodide, and place 250 mL of γ-butyrolactone into a 1L three-necked flask equipped with a mechanical stirrer. Stir at 60°C for 2 hours under nitrogen protection until completely dissolved.

[0061] 200 mL of ethyl acetate was slowly added using a dropping funnel, and a yellow precipitate gradually formed. After the ethyl acetate was added, the mixture was stirred for 1 hour. The powder was then filtered to obtain a bright yellow δ-FAPbI3 powder, which was washed several times with ethyl acetate.

[0062] The above bright yellow powder was transferred to a vacuum oven and dried at 150°C for 5 hours to obtain 56 g of black α-FAPbI3 microcrystals, with a yield of 81.3%.

[0063] Test Example 1

[0064] The purity and stability of the black formamidinium lead iodide microcrystals prepared in Examples 2-4 and the comparative examples were evaluated.

[0065] Purity testing was performed using potentiometric titration with 0.1M silver nitrate standard solution as the titrant. The titration endpoint was determined by observing the potential jump, and the sample purity was calculated based on the sample mass and the volume of silver nitrate standard solution consumed. Stability evaluation was conducted by visually observing the time it took for the sample prepared at room temperature (30℃) and humidity (45%) without inert gas protection to transform from the black phase to the yellow phase. The experimental results are shown in Table 1.

[0066] Table 1: Results of Purity and Stability Evaluation

[0067]

[0068] As shown in Table 1, the black formamidinium lead iodide microcrystals prepared in Examples 2 to 4 exhibited high purity, all exceeding 99.9%, and good stability. Under the conditions of room temperature 30°C and humidity 45%, without inert gas protection, the phase transition time was all over 72 hours, which was significantly better than the comparative example (purity of 99.87%, phase transition time less than 8 hours).

[0069] Test Example 2

[0070] The black phase formamidinium lead iodide microcrystals prepared in Examples 2-4 and the comparative examples were used for device evaluation.

[0071] The inverted perovskite solar cell structure used to evaluate the performance of α-FAPbI3 microcrystals is: ITO / NiOx / α-FAPbI3 / PCBM / SnO2 / Ag. NiOx and SnO2 are prepared by atomic layer deposition (ALD) technology, α-FAPbI3 and PCBM are prepared by solution spin coating, and Ag electrode is prepared by vacuum thermal evaporation. The experimental results are shown in Table 2.

[0072] Table 2: Device Evaluation Results

[0073]

[0074] As shown in Table 2, the inverted perovskite solar cells (structure: ITO / NiOx / α-FAPbI3 / PCBM / SnO2 / Ag) prepared by the black-phase formamidinium lead iodide microcrystals obtained in Examples 2 to 4 exhibited high short-circuit current density (Jsc), open-circuit voltage (Voc), power conversion efficiency (PCE), and fill factor (FF). Among them, the device in Example 2 showed the best performance, with a PCE of 20.04%, which is a significant improvement compared to the comparative example (PCE of 18.76%). This indicates that the black-phase formamidinium lead iodide microcrystals prepared by the method described in the examples have significant advantages in improving the performance of perovskite solar cells.

[0075] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing black-phase formamidinium lead iodide microcrystals, characterized in that, include: A precursor liquid is prepared by mixing a salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits the oxidation of iodide anions, and water. The precursor liquid is then subjected to high-pressure hydrothermal treatment to obtain black phase formamidine lead iodide microcrystals. The divalent lead-containing salt compound is selected from at least one of lead iodide, lead acetate, lead nitrate, lead oxide, and lead metaborate. The reducing acid compound that inhibits the oxidation of iodide anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphite, and formic acid.

2. The method for preparing black-phase formamidinium lead iodide microcrystals according to claim 1, characterized in that, The molar ratio of hydroiodic acid to lead in the divalent lead salt compound is 3~10:1; The molar ratio of formamidine acetate to lead in the divalent lead salt compound is 1~5:1; The molar ratio of the reducing acid compound that inhibits the oxidation of iodide anions to the lead element in the salt compound containing divalent lead is 0.01 to 1:

1.

3. The method for preparing black-phase formamidinium lead iodide microcrystals according to claim 1, characterized in that, The mass ratio of water to formamidine acetate is 1~10:

1.

4. The method for preparing black-phase formamidinium lead iodide microcrystals according to claim 1, characterized in that, The high-pressure hydrothermal treatment has a reaction temperature of 150~250℃, a pressure of 1~10MPa, and a reaction time of 2~12h.

5. The method for preparing black-phase formamidinium lead iodide microcrystals according to claim 1, characterized in that, The high-pressure hydrothermal treatment uses at least one of nitrogen or inert gas for pressure regulation.

6. A type of black-phase formamidinium lead iodide microcrystal, characterized in that, It was prepared by the method described in any one of claims 1 to 5 for the preparation of black phase formamidinium lead iodide microcrystals.

7. The black-phase formamidinium lead iodide microcrystals according to claim 6, characterized in that, The black-phase formamidinium lead iodide microcrystals transform from the black phase to the yellow phase in no less than 72 hours under conditions of room temperature (30°C), humidity (45%), and without inert gas protection.

8. The application of the black phase formamidinium lead iodide microcrystals as described in claim 6 in the preparation of solar cells.

9. A perovskite solar cell, comprising a transparent conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, a buffer layer, and a metal electrode, characterized in that, The perovskite light-absorbing layer comprises the black phase formamidinium lead iodide microcrystals as described in claim 6.

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