Black-phase formamidine lead iodide microcrystal as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of chemical synthesis, and relates to a black-phase formamidine lead iodide microcrystal as well as a preparation method and application thereof. The invention provides a preparation method of black-phase formamidine lead iodide microcrystals. The preparation method comprises the following steps: mixing a salt compound containing divalent lead, hydriodic acid, formamidine acetate, a reducing acid compound for inhibiting oxidation of iodine anions and deionized water as precursor liquid; and performing high-pressure hydrothermal treatment on the precursor liquid to obtain the black-phase formamidine lead iodide microcrystal. According to the preparation method provided by the invention, water is adopted as a solvent, so that the use of an organic solvent is avoided, and the prepared black-phase formamidine lead iodide microcrystal has high crystallinity and stability and can be stored in a room-temperature air condition for a long time without phase change.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis and relates to black-phase formamidine lead iodide microcrystals and a preparation method and application thereof. Background Art

[0002] Formamidinium lead iodide (FAPbI3) is a perovskite material commonly used in photovoltaic devices. + ) is a commonly used A-site cation. Compared with MA, FA exhibits lower band gap (Eg), improved optoelectronic properties and higher thermal stability. The larger size of the FA cation causes FAPbI3 to form a Pm3m cubic perovskite lattice instead of the lower symmetry MAPbI3 tetragonal 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 presents a polymorphic network structure, and the high symmetry structure originates from the randomly distributed local lower symmetry (distorted) structural units. The average lattice parameter values ​​of the α phase (i.e., black phase) of FAPbI3 at room temperature range from 6.352 to 6.365Å, 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 the phase stability at room temperature, but resulting in a wider band gap.

[0003] α-FAPbI3 is a photoactive phase with high photoelectric conversion efficiency, but it tends to transform into a non-photoactive yellow phase formamidine lead iodide (δ-FAPbI3) at room temperature. This phase change can lead to material degradation and battery performance degradation. The traditional method for preparing α-FAPbI3 microcrystals (patent number: CN202110252152.0) usually uses high-purity lead iodide and formamidine hydroiodide to prepare the precursor solution, which requires the use of organic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and γ-butyrolactone (GBL). Precipitation is induced by anti-solvents such as ethyl acetate, chlorobenzene or ether, and finally the product is generated by high-temperature annealing. These preparation methods all rely on organic solvents and organic anti-solvents, and the purity of the obtained α-FAPbI3 is low and the stability is poor. Summary of the invention

[0004] The purpose of the present invention is to improve the preparation process of black-phase formamidine lead iodide microcrystals in a simple and low-cost manner, so that the purity and stability of the prepared black-phase formamidine lead iodide microcrystals are high, and the use of organic solvents and organic anti-solvents is avoided. To this end, the present invention provides a black-phase formamidine lead iodide microcrystal and a preparation method and application thereof to solve this need in the art.

[0005] On the one hand, the present invention relates to a method for preparing black-phase formamidine lead iodide microcrystals, which comprises: mixing a salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits oxidation of iodine 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-phase formamidine 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; The reducing acid compound that inhibits the oxidation of iodine anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphorous acid and formic acid.

[0007] Furthermore, in the method for preparing black phase formamidine lead iodide microcrystals provided by the present invention, the molar ratio of the hydroiodic acid to the lead element in the divalent lead-containing salt compound is 3 to 10:1; The molar ratio of the formamidine acetate to the lead element in the divalent lead salt compound is 1-5:1; The molar ratio of the reducing acid compound that inhibits the oxidation of iodine anions to the lead element in the salt compound containing divalent lead is 0.01-1:1.

[0008] Furthermore, in the method for preparing black phase formamidine lead iodide microcrystals provided by the present invention, the mass ratio of deionized water to formamidine acetate is 1 to 10:1.

[0009] Furthermore, in the method for preparing black phase formamidine lead iodide microcrystals provided by the present invention, the reaction temperature of the high-pressure hydrothermal treatment is 150-250° C., the pressure is 1-10 MPa, and the reaction time is 2-12 h.

[0010] Furthermore, in the method for preparing black phase formamidine lead iodide microcrystals provided by the present invention, the high-pressure hydrothermal treatment uses at least one of nitrogen and inert gas to adjust the pressure.

[0011] On the other hand, the present invention relates to a black phase formamidine lead iodide microcrystal, which is prepared by adopting the preparation method of the black phase formamidine lead iodide microcrystal.

[0012] Furthermore, in the black phase formamidine lead iodide microcrystals provided by the present invention, the time for the black phase formamidine lead iodide microcrystals to transform from the black phase to the yellow phase is not less than 72 hours at room temperature of 30° C., humidity of 45%, and without inert gas protection.

[0013] On the other hand, the present invention relates to the use of the black phase formamidine lead iodide microcrystals provided by the present invention in the preparation of solar cells.

[0014] 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 the black phase formamidine lead iodide microcrystals provided by the present invention.

[0015] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: The invention provides a method for preparing black-phase formamidine lead iodide microcrystals, which adopts a one-step hydrothermal method to avoid the tediousness and complexity of multi-step reactions in a traditional preparation process. High-quality black-phase formamidine lead iodide microcrystals can be obtained by simple raw material mixing and high-pressure hydrothermal treatment. This method is not only simple to operate, but also has low equipment requirements and is easy to promote and apply in industrial production.

[0016] The invention provides a method for preparing black-phase formamidine lead iodide microcrystals, in which water can be selected as a solvent, thereby avoiding the use of organic solvents and organic anti-solvents in traditional methods. This not only reduces production costs, but also reduces environmental pollution, which is in line with the sustainable development concept currently advocated globally.

[0017] The α-FAPbI3 microcrystals prepared by the present invention have high stability. Under the conditions of room temperature of 30°C, humidity of 45%, and no inert gas protection, the time for transformation from the black phase to the yellow phase is not less than 72 hours. Therefore, applying it to solar cells can significantly improve the service life of the solar cells. This characteristic enables the solar cells made of the α-FAPbI3 microcrystals to maintain long-term stable operation in harsh environments.

[0018] The α-FAPbI3 microcrystals prepared by the present invention have high crystallinity and good photoelectric properties, so that the solar cell has a higher fill factor and photoelectric conversion efficiency. This is of great significance for improving the power generation capacity of solar cells and reducing the power generation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a diagram of the preparation process of black phase formamidine lead iodide microcrystals.

[0021] Figure 2 The following is a comparison chart of the appearance of black-phase formamidine lead iodide microcrystals of Examples 2, 3, 4 and Comparative Example placed in air. DETAILED DESCRIPTION

[0022] The technical scheme of the present invention is described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials can be purchased on the market unless otherwise specified. The % in the following embodiments, unless otherwise specified, are all mass percentages. The ratios in the following embodiments, unless otherwise specified, are all mass ratios.

[0023] Example 1 This embodiment provides a method for preparing black-phase formamidine lead iodide microcrystals.

[0024] Reference Figure 1 The preparation process of the black phase formamidine lead iodide microcrystals shown is as follows: Step 1: Weigh a salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits oxidation of iodine anions, and water, and mix them to form a precursor liquid.

[0025] Optionally, in step 1, the mixing and adding method of the above raw materials is not particularly limited. After hydroiodic acid is prepared into a hydroiodic acid aqueous solution, and the reducing acid compound that inhibits the oxidation of iodine anions is prepared into an aqueous solution of the reducing acid compound that inhibits the oxidation of iodine anions, the salt compound containing divalent lead, formamidine acetate, the hydroiodic acid aqueous solution, and the aqueous solution of the reducing acid compound that inhibits the oxidation of iodine anions are mixed.

[0026] Optionally, in step 1, the salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound that inhibits oxidation of iodine anions, and water are directly mixed.

[0027] Exemplarily, 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 iodine anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphorous acid, and formic acid.

[0028] Specifically, in step 1, the molar ratio of hydroiodic acid to the lead element in the salt compound containing divalent lead is 3-10:1; the molar ratio of formamidine acetate to the lead element in the salt compound containing divalent lead is 1-5:1; the molar ratio of the reducing acid compound that inhibits the oxidation of iodine anions to the lead element in the salt compound containing divalent lead is 0.01-1:1; and the mass ratio of deionized water to formamidine acetate is 1-10:1.

[0029] Step 2: Place the precursor liquid in a high-pressure reactor, seal it, and perform high-pressure hydrothermal treatment.

[0030] Generally, in step 2, the high-pressure reactor used has a polytetrafluoroethylene or enamel lining, has good acid resistance and corrosion resistance, and is equipped with temperature and pressure sensors.

[0031] Step 3: Control the reaction temperature to 150~250°C, the pressure to 1~10MPa, and the reaction time to 2~12h.

[0032] Optionally, in step 3, the pressure is adjusted by pumping nitrogen or argon into the high-pressure reactor.

[0033] Step 4: After the reaction is completed, cool naturally to room temperature, filter, and rinse with deionized water and ethanol.

[0034] Step 5: Dry the material to obtain black α-FAPbI3 microcrystals.

[0035] Example 2 This embodiment provides a specific preparation process of black phase formamidine lead iodide microcrystals.

[0036] Weigh 100 g (0.3 mol) of lead acetate, 32 g (0.3 mol) of formamidine acetate, 243 g (47 wt% aqueous hydroiodic acid solution, 0.9 mol of hydrogen iodide content), 0.4 g (50 wt% aqueous hypophosphorous acid solution, 0.003 mol of hypophosphorous acid content), and 32 ml of deionized water, and mix and stir evenly.

[0037] The mixed precursors were placed in a 500 mL acid-resistant high-pressure reactor equipped with a temperature sensor and a pressure sensor and sealed.

[0038] The reaction temperature was set at 150°C, nitrogen was introduced to adjust the pressure to 1 MPa, and the reaction was carried out for 12 hours.

[0039] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, rinsed with deionized water and ethanol, and dried at 80°C to obtain 163 g of black α-FAPbI3 microcrystals with a yield of 83.5%.

[0040] Example 3 This embodiment provides a specific preparation process of black phase formamidine lead iodide microcrystals.

[0041] Weigh 22 g (0.1 mol) of lead oxide, 52 g (0.5 mol) of formamidine acetate, 270 g of 47 wt% aqueous hydroiodic acid solution (hydrogen iodide content: 1 mol), 17 g (0.1 mol) of ascorbic acid, and 520 ml of deionized water, and mix and stir evenly.

[0042] The mixed precursors were placed in a 1000 mL acid-resistant high-pressure reactor equipped with temperature and pressure sensors and sealed.

[0043] The reaction temperature was set at 250°C, nitrogen was introduced to adjust the pressure to 10 MPa, and the reaction was carried out for 2 hours.

[0044] 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%.

[0045] Example 4 This embodiment provides a specific preparation process of black phase formamidine lead iodide microcrystals.

[0046] Weigh 25 g (0.1 mol) of lead metaborate monohydrate, 40 g (0.4 mol) of formamidine acetate, 200 g of 47 wt% hydroiodic acid aqueous solution (hydrogen iodide content 0.7 mol), 2 g (0.02 mol) of oxalic acid, and 80 ml of deionized water, and mix and stir evenly.

[0047] The mixed precursors were placed in a 500 mL acid-resistant autoclave equipped with a temperature and pressure sensor, and sealed. The reaction temperature was set to 180°C, nitrogen was introduced to adjust the pressure to 5 MPa, and the reaction was continued for 6 hours.

[0048] 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%.

[0049] Comparative Example This comparative example provides a specific preparation process of black phase formamidine lead iodide microcrystals.

[0050] Weigh 20 g of iodoformamidine, 50 g of lead iodide, and 250 mL of γ-butyrolactone into a 1 L three-necked flask with a mechanical stirrer, and stir at 60 °C for 2 h under nitrogen protection until completely dissolved; Use a dropping funnel to slowly add 200 mL of ethyl acetate, and a yellow precipitate gradually precipitates. After the addition of ethyl acetate is completed, continue stirring for 1 h, filter to obtain a bright yellow δ-FAPbI3 powder, and rinse with ethyl acetate several times; The bright yellow powder was transferred into a vacuum oven and dried at 150 °C for 5 h to obtain 56 g of black α-FAPbI3 microcrystals with a yield of 81.3%.

[0051] Test Example 1 The black phase formamidine lead iodide microcrystals prepared in Examples 2 to 4 and the comparative example were evaluated for sample purity and stability.

[0052] The purity test was conducted by potentiometric titration, using 0.1M silver nitrate standard solution as titrant, observing the potential jump to determine the titration endpoint, and calculating the sample purity by the sample mass and the volume of the consumed silver nitrate standard solution. The stability evaluation was conducted by visual observation, at room temperature of 30°C and humidity of 45%, without inert gas protection, to measure the time it takes for the black phase to transform into the yellow phase. The test results are shown in Table 1.

[0053] Table 1: Purity and stability evaluation results

[0054] As can be seen from Table 1, the black phase formamidine lead iodide microcrystals prepared in Example 2 to Example 4 show high purity, all exceeding 99.9%, and good stability. Under the conditions of room temperature of 30°C and humidity of 45%, without inert gas protection, the phase transition time is more than 72 hours, which is significantly better than the comparative example (purity of 99.87%, phase transition time of less than 8 hours).

[0055] Test Example 2 The black phase formamidine lead iodide microcrystals prepared in Examples 2 to 4 and the comparative example were subjected to device evaluation.

[0056] The structure of the inverse perovskite solar cell used to evaluate the performance of α-FAPbI3 microcrystals is: ITO / NiOx / α-FAPbI3 / PCBM / SnO2 / Ag, where NiOx and SnO2 are prepared by atomic layer deposition (ALD) technology, α-FAPbI3 and PCBM are prepared by solution spin coating, and the Ag electrode is prepared by vacuum thermal evaporation. The test results are shown in Table 2.

[0057] Table 2: Device evaluation results

[0058] As shown in Table 2, the inverse perovskite solar cells (structured as ITO / NiOx / α-FAPbI3 / PCBM / SnO2 / Ag) prepared from the black-phase formamidine lead iodide microcrystals prepared in Examples 2 to 4 exhibited high short-circuit current density (Jsc), open-circuit voltage (Voc), photoelectric conversion efficiency (PCE) and fill factor (FF), among which the device performance of Example 2 was the best, with a PCE of 20.04%, which was significantly improved compared to the comparative example (PCE of 18.76%). This shows that the black-phase formamidine lead iodide microcrystals prepared by the method described in the example have significant advantages in improving the performance of perovskite solar cells.

[0059] As described above, the basic principle, main features and advantages of the present invention are well described. The above embodiments and descriptions are only descriptions of the preferred implementation modes of the present invention, and the present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, various changes and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the protection scope determined by the present invention.

Claims

1. A method for preparing black phase formamidine lead iodide microcrystals, characterized in that: include: A salt compound containing divalent lead, hydroiodic acid, formamidine acetate, a reducing acid compound for inhibiting oxidation of iodine anions and water are mixed as a precursor liquid, and the precursor liquid is subjected to high-pressure hydrothermal treatment to obtain black-phase formamidine lead iodide microcrystals.

2. The method for preparing black phase formamidine lead iodide microcrystals according to claim 1, characterized in that: The divalent lead 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 iodine anions is selected from at least one of ascorbic acid, oxalic acid, hypophosphorous acid and formic acid.

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

1.

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

1.

5. The method for preparing black phase formamidine lead iodide microcrystals according to claim 1, characterized in that: The reaction temperature of the high-pressure hydrothermal treatment is 150-250° C., the pressure is 1-10 MPa, and the reaction time is 2-12 h.

6. The method for preparing black phase formamidine lead iodide microcrystals according to claim 1, characterized in that: The high-pressure hydrothermal treatment uses at least one of nitrogen and inert gas to adjust the pressure.

7. A black phase formamidine lead iodide microcrystal, characterized in that: The black phase formamidine lead iodide microcrystals are prepared by the preparation method of any one of claims 1 to 6.

8. The black phase formamidine lead iodide microcrystals according to claim 7, characterized in that: The black phase formamidine lead iodide microcrystals transform from a black phase to a yellow phase in a time of not less than 72 hours at room temperature of 30° C., humidity of 45%, and without inert gas protection.

9. Use of the black phase formamidine lead iodide microcrystals according to claim 7 in the preparation of solar cells.

10. A perovskite solar cell, comprising a transparent conductive substrate, a hole transport layer, a perovskite light absorption layer, an electron transport layer, a buffer layer and a metal electrode, characterized in that: The perovskite light-absorbing layer comprises the black phase formamidine lead iodide microcrystals as described in claim 7.

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