Lead iodide crystal and method for adjusting preferred orientation of lead iodide crystal face

Abstract

The invention belongs to the technical field of lead iodide crystal preparation, and discloses a lead iodide crystal and a method for adjusting the preferred orientation of a lead iodide crystal face, the method for adjusting the preferred orientation of the lead iodide crystal face comprises the following steps: step 1, adding an acid solution into a lead iodide solution, and diluting the lead iodide solution until the concentration of lead iodide is 10mM-50mM; 2, the diluted lead iodide solution is subjected to aging treatment, a solid-liquid mixture is obtained, the aging temperature ranges from 25 DEG C to 120 DEG C, the aging pressure is smaller than or equal to 6 Mpa, and the aging time ranges from 2 h to 4 h; and step 3, controlling the cooling rate of the solid-liquid mixture to be 6-10 DEG C / min for cooling, and then separating to obtain solid lead iodide. According to the method disclosed by the invention, the preferred growth condition of the lead iodide crystal face is controlled through concentration control, an aging process and a sectional cooling process under the condition that a complexing agent, a surfactant or a template agent does not need to be additionally added.

Description

Technical Field

[0001] The invention relates to the technical field of lead iodide crystal preparation, and in particular to a lead iodide crystal and a method for adjusting the preferred orientation of a lead iodide crystal surface. Background Art

[0002] Lead iodide is the core precursor material of the light absorption layer of perovskite solar cells. The currently disclosed methods for synthesizing lead iodide mainly include solid-phase chemical reaction method, chemical precipitation method and gas spray method. They have problems in ensuring purity, micromorphology and particle size, and the preparation process is complicated.

[0003] Based on this, prior art 1: Chinese patent 201711022633.2 discloses a method for preparing monodisperse high-purity lead iodide. The lead iodide prepared by this method has high purity and has certain control over the particle size and morphology of the product; the patent specification states: "A method for preparing monodisperse high-purity lead iodide, comprising the following steps: step 1, preparing a lead salt solution, and adjusting the pH of the lead salt solution to between 0.5 and 7; step 2, preparing a soluble iodine salt solution, and adjusting the pH of the iodine salt solution to between 0.5 and 7; step 3, contacting the lead salt solution in step 1 with the iodine salt solution in step 2 to perform a precipitation reaction to obtain a precipitated suspension of lead iodide; step 4, aging the precipitated suspension of lead iodide in step 3 at room temperature for 1 to 48 hours, filtering, washing, and drying to obtain a high-purity lead iodide powder product;

[0004] Further, 10 liters of 0.1M lead nitrate solution and 10 liters of 0.11M potassium iodide solution are prepared, and their respective pH values ​​are pre-adjusted to 3, and then added dropwise to 10 liters of an aqueous solution at a rate of 0.5 liters / minute, while maintaining stirring. The pH value of the aqueous solution is pre-adjusted to 3, and 0.1% polyvinyl pyrrolidone K-30 and 0.5% sodium citrate are pre-added. After the addition is completed, stirring and aging are continued for 10 hours, filtered, washed three times with deionized water, and dried at 80 degrees Celsius; monodisperse lead iodide powder is obtained, and the monodisperse lead iodide powder has a flat, disc-shaped morphology and an average diameter of 3 microns.

[0005] It can be seen that the prior art 1 uses a surfactant such as polyvinyl pyrrolidone K-30 to prepare lead iodide with good dispersibility.

[0006] According to the research findings of Chiu et al. (Solar RRL 2022, 6, 2200609), the preferential growth of lead iodide on crystal planes is conducive to inducing the formation of specific perovskite phases, which is then related to the pros and cons of core performance such as the photoelectric conversion efficiency of perovskite solar cells; however, the prior art 1 did not study the preferential growth of lead iodide on crystal planes, and it was difficult to prepare lead iodide with better photoelectric conversion efficiency.

[0007] Prior art 2: Chinese Patent 202310535735.3 discloses a lead iodide with preferential growth on the (001) crystal plane, its preparation method and application. The technical solution of this patent can prepare lead iodide with preferential growth on the (001) crystal plane, which can effectively improve the photoelectric conversion efficiency.

[0008] According to the description in the specification of the prior art 2: "3) Add at least one of the templating agents P123 and F127 to the mixed solution obtained in step 2) and continue heating and stirring for 10 - 30 minutes", it can be seen that the prior art 2 induces the preferential growth of the (001) crystal plane of lead iodide by adding the templating agents P123 and F127; many prior arts, like the prior art 1 and the prior art 2, use some complexing agents such as ethylenediaminetetraacetic acid and sodium ethylenediaminetetraacetate; or surfactants including sodium alkyl sulfonate, sodium alkyl aryl sulfonate, and templating agents P123 and F127 and other substances to affect the preferential orientation of the crystal plane of lead iodide, but these additional additives increase the washing difficulty and affect the purity of the lead iodide finished product.

[0009] Therefore, it is necessary to find a preparation method of lead iodide that does not require additional additives, so as to be able to adjust the preferential orientation of the crystal plane of lead iodide. Summary of the Invention

[0010] One of the purposes of the present invention is to provide a method for adjusting the preferential orientation of the crystal plane of lead iodide, which controls the preferential growth of the crystal plane of lead iodide through concentration control, aging process, and segmented cooling process without the need to additionally add complexing agents, surfactants, or templating agents.

[0011] Another purpose of the present invention is to provide a lead iodide crystal, the strongest peak of which is the 011 crystal plane, which can have higher conductivity and carrier mobility, and can further improve the photoelectric conversion efficiency.

[0012] At the same time, the present invention also provides a lead iodide crystal, the strongest peak of which is the 001 crystal plane, which has excellent photoelectric conversion efficiency and does not need to be prepared through additional additives, effectively reducing the washing difficulty, thereby improving the purity of the lead iodide finished product.

[0013] To achieve the above purposes, the present invention provides a method for adjusting the preferential orientation of the crystal plane of lead iodide, including the following steps:

[0014] Step 1: Add an acid solution to the lead iodide solution and dilute the lead iodide solution until the lead iodide concentration is 10 - 50 mM.

[0015] Step 2: Age the diluted lead iodide solution to obtain a solid-liquid mixture, where the aging temperature is 25 - 120 °C, the aging pressure ≤ 6 Mpa, and the aging duration is 2 - 4 h.

[0016] Step 3: Control the cooling rate of the solid-liquid mixture at 6 - 10 °C / min for cooling, and then separate to obtain solid lead iodide.

[0017] It should be noted that the unit mM of the lead iodide concentration described in this application is millimole per liter, which is a commonly used unit in the art to represent the concentration of solute in a solution, that is, 1 mM = 1 mmol / L.

[0018] The technical solution of the present invention requires diluting the lead iodide solution to a certain concentration and then aging it. The preferred crystal plane orientation of lead iodide is adjusted by specific aging temperature and aging pressure. At the same time, controlling the cooling rate of cooling crystallization after aging can further adjust the preferred crystal plane orientation of lead iodide; the three work together to enable precise adjustment of the preferred growth of the crystal plane of lead iodide.

[0019] Further, the method for adjusting the preferred crystal plane orientation of lead iodide further includes Step 4: Wash and dry the solid lead iodide in sequence.

[0020] Since the present invention does not add a complexing agent, a surfactant or a templating agent additionally, the washing difficulty is greatly reduced, and those skilled in the art can use existing simple washing means to wash the solid lead iodide to obtain high-purity lead iodide.

[0021] Preferably, the specific operation of the washing is: Wash the solid lead iodide with at least one of pure water, ethanol, methanol, isopropanol, ethylene glycol, and acetone 1 - 3 times, and the washing solid-liquid ratio is 1:1.

[0022] More preferably, the specific operation of the washing is: Wash the solid lead iodide with pure water at 5 - 10 °C 1 - 3 times, and the washing solid-liquid ratio is 1:1.

[0023] Preferably, the drying can use commonly used drying means in the art; more preferably, vacuum drying is used, the vacuum degree < -0.08 MPa, and the drying temperature is 140 - 160 °C.

[0024] Preferably, the pH value of the acid solution in Step 1 is 1.5 - 3.0.

[0025] Further preferably, the acid solution is at least one of acetic acid, sulfuric acid, nitric acid, hydrochloric acid, carbonic acid, and boric acid.

[0026] The lead iodide solution used in the present invention can be prepared by conventional means in the art or obtained by purchasing from the market.

[0027] Preferably, the lead iodide solution used in Step 1 is prepared through the following steps:

[0028] Using the lead compound solution as the synthesis bottom liquid, adding the iodine compound solution dropwise to the synthesis bottom liquid for reaction to obtain the lead iodide solution; during the process, controlling the temperature at 60 - 80°C, the stirring speed at 200 - 250 rpm, and the pH value during the dropping process ≤ 3.

[0029] Further, the lead compound solution is any one of lead nitrate, lead acetate, lead chloride, lead carbonate, and lead sulfate.

[0030] Further, the iodine compound is any one of potassium iodide, sodium iodide, lithium iodide, ammonium iodide, and magnesium iodide.

[0031] The present invention also provides a lead iodide crystal, which is prepared by using the method for adjusting the preferential orientation of the lead iodide crystal plane as described above;

[0032] The specific operation of Step 2 is: subjecting the diluted lead iodide solution to aging treatment to obtain a solid-liquid mixture, where the aging temperature is 25 - 80°C, the aging pressure ≤ 6 Mpa, and the aging duration is 2 - 4 h;

[0033] This lead iodide crystal preferentially grows in the <011> crystal plane.

[0034] Current research in the prior art is basically focused on the preferential orientation of the <001>, <003>, <004> and other crystal planes of lead iodide. However, the present invention discovers that by controlling the concentration of the lead iodide solution before aging, the aging process, and the cooling process after aging, the preferential growth of the lead iodide crystal plane can be effectively controlled, so that the strongest peak of lead iodide is <011> and other peaks will not grow preferentially synchronously.

[0035] Regarding the preferential orientation of the lead iodide crystal plane, the <011> crystal plane has higher conductivity and carrier mobility compared to other crystal planes (such as <001>); this characteristic is particularly important in optoelectronic devices, which can significantly enhance the charge transport efficiency and thus improve the optoelectronic conversion performance of the device; the exposure of the <011> crystal plane can improve the energy level matching between the material and other functional layers, reduce the interfacial energy loss, and further enhance the overall efficiency of the device; the <011> crystal plane can improve the stability by inhibiting ion migration and material decomposition.

[0036] The present invention also provides a lead iodide crystal, which is prepared by the method for adjusting the preferred orientation of the lead iodide crystal plane described above;

[0037] The specific operation of step 2 is as follows: aging the diluted lead iodide solution to obtain a solid-liquid mixture, where the aging temperature is 80-120°C, the aging pressure ≤ 6 Mpa, and the aging duration is 2-4 h;

[0038] This lead iodide crystal preferentially grows in the <001> crystal plane.

[0039] Meanwhile, the present invention also finds that by the method for adjusting the preferred orientation of the lead iodide crystal plane of the present invention, a lead iodide crystal with preferential growth in the <001> crystal plane can be prepared without adding a complexing agent, a surfactant or a templating agent, reducing the washing difficulty, making the entire production process simpler, and can be applied to large-scale production.

[0040] Beneficial effects

[0041] Compared with the prior art, the present invention has at least the following advantages:

[0042] (1) The present invention provides a method for adjusting the preferred orientation of the lead iodide crystal plane, and controls the preferential growth of the lead iodide crystal plane through concentration control, aging process and stepwise cooling process without the need to additionally add a complexing agent, a surfactant or a templating agent;

[0043] (2) The present invention studies the preferential growth of the <011> crystal plane. By controlling the concentration of the lead iodide solution before aging, the aging process and the cooling process after aging, the preferential growth of the lead iodide crystal plane can be effectively controlled, so that the strongest peak of the lead iodide is <011>; the lead iodide crystal with preferential growth in the <011> crystal plane of the present invention has higher conductivity and carrier mobility, can significantly enhance the charge transport efficiency, and thus improve the optoelectronic conversion performance of the device;

[0044] (3) By controlling the concentration of the lead iodide solution before aging, the aging process and the cooling process after aging, the present invention can prepare a lead iodide crystal with preferential growth in the <001> crystal plane without adding a complexing agent, a surfactant or a templating agent, reducing the washing difficulty, making the entire production process simpler, and can be applied to large-scale production. Description of the drawings

[0045] The present invention will be further described below in conjunction with the drawings and embodiments;

[0046] Figure 1 It is the XRD pattern of Example 1;

[0047] Figure 2 It is the XRD pattern of Example 2;

[0048] Figure 3 XRD pattern of Comparative Example 1;

[0049] Figure 4 XRD pattern of Comparative Example 2;

[0050] Figure 5 XRD pattern of Comparative Example 3. Detailed implementation mode

[0051] The present invention will be further described below in conjunction with embodiments, but it does not constitute any limitation to the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0052] In order to elaborate on the technical content of the present invention, further explanations will be given below in conjunction with the implementation modes.

[0053] In the following examples and comparative examples, the lead iodide solution was prepared by the following steps:

[0054] Step a: Weigh lead acetate trihydrate crystals, add pure water to prepare a lead acetate solution with a concentration of 100 g / L, and then add 99.5% acetic acid to the solution to adjust the pH to 2.5;

[0055] Step b: Add analytical pure potassium iodide powder to pure water according to a solid-liquid ratio of 163:652 to prepare a potassium iodide solution;

[0056] Step c: Use the lead acetate solution as the synthesis bottom liquid, and drop the potassium iodide solution into the synthesis bottom liquid for reaction to obtain a lead iodide solution; during the process, control the temperature at 70 ± 5 °C, the stirring speed at 250 rpm, and the pH value during the dropping process ≤ 3.

[0057] Example 1

[0058] A lead iodide crystal with preferential growth on the 011 crystal plane was prepared by the following steps:

[0059] Step 1: Drop acetic acid with a pH value of 2.7 into the lead iodide solution, and dilute the lead iodide solution to a lead iodide concentration of 50 mM;

[0060] Step 2: Carry out aging treatment on the diluted lead iodide solution to obtain a solid-liquid mixture, where the aging temperature is 80 °C and the aging pressure ≤ 6 Mpa;

[0061] Step 3: Cool the solid-liquid mixture at a cooling rate of 8 °C / min, and then separate to obtain solid lead iodide.

[0062] Example 2

[0063] A lead iodide crystal with preferential growth on the 001 crystal plane is prepared by the following steps:

[0064] Step 1: Add acetic acid with a pH value of 2.5 to the lead iodide solution, and dilute the lead iodide solution to a lead iodide concentration of 25 mM.

[0065] Step 2: Aging the diluted lead iodide solution to obtain a solid-liquid mixture, where the aging temperature is 120 °C and the aging pressure ≤ 6 Mpa.

[0066] Step 3: Cool down the solid-liquid mixture, and then separate to obtain solid lead iodide.

[0067] Step 3: Cool down the solid-liquid mixture at a cooling rate of 6 °C / min, and then separate to obtain solid lead iodide.

[0068] Comparative Example 1

[0069] Generally the same as Example 1, except that in Step 1, acetic acid with a pH value of 2.7 is added to the lead iodide solution, and the lead iodide solution is diluted to a lead iodide concentration of 65 mM.

[0070] Comparative Example 2

[0071] Generally the same as Example 1, except that in Step 1, acetic acid with a pH value of 2.7 is added to the lead iodide solution, and the lead iodide solution is diluted to a lead iodide concentration of 5 mM.

[0072] Comparative Example 3

[0073] Generally the same as Example 1, except that the aging temperature in Step 2 is 160 °C.

[0074] The lead iodide obtained in Examples 1-2 and Comparative Examples 1-3 was respectively subjected to XRD detection, and the results are as Figures 1-5 shown;

[0075] Among them:

[0076] Figure 1 is the XRD pattern of Example 1;

[0077] Figure 2 is the XRD pattern of Example 2;

[0078] Figure 3 is the XRD pattern of Comparative Example 1;

[0079] Figure 4 is the XRD pattern of Comparative Example 2;

[0080] Figure 5 is the XRD pattern of Comparative Example 3;

[0081] According to Figure 1 It can be seen that by controlling the concentration of lead iodide solution before aging, the aging process, and the cooling process after aging, the present application can effectively control the preferential growth of the crystal planes of lead iodide, so that the strongest peak of lead iodide is 011; and this strongest peak is significantly different from other peaks, indicating that the technical solution adopted in Example 1 of the present invention can promote the preferential growth of the 011 peak and avoid the preferential growth of other peaks.

[0082] According to Figure 1 and Figure 3 、 Figure 4 By comparison, it can be seen that the control of the concentration of lead iodide solution before aging in the present application has a great influence on the preferential orientation of the crystal planes of lead iodide. Too high or too low concentration will cause the preferential growth of other peaks, resulting in the peak intensity of 011 being not much different from that of other peaks, indicating that it is difficult to control the preferential orientation of the crystal planes of lead iodide without controlling the concentration of lead iodide solution before aging.

[0083] According to Figure 1 、 Figure 2 and Figure 5 From the data comparison, it can be seen that the aging temperature also has an obvious influence on the preferential orientation of lead iodide. It is necessary to combine the concentration of lead iodide solution before aging, the cooling process after aging at a suitable aging temperature to effectively control the preferential orientation of the crystal planes of lead iodide.

[0084] The embodiments presented herein are only the implementation manners selected according to the combinations of all possible embodiments. The appended claims should not be limited by the embodiments illustrating the present invention. Some numerical ranges used in the claims include sub-ranges within them, and the variations within these ranges should also be covered by the appended claims.

Claims

1. A method for adjusting the preferred orientation of a lead iodide crystal plane, characterized in that: The steps include: Step 1: adding an acid solution to the lead iodide solution to dilute the lead iodide solution to a lead iodide concentration of 10 to 50 mM; Step 2: aging the diluted lead iodide solution to obtain a solid-liquid mixture, wherein the aging temperature is 25 to 120° C., the aging pressure is ≤6 MPa, and the aging time is 2 to 4 hours; Step 3: Cool the solid-liquid mixture at a cooling rate of 6 to 10° C. / min, and then separate to obtain solid lead iodide.

2. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 1, characterized in that: The method also includes step 4: washing and drying the solid lead iodide in sequence.

3. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 1, characterized in that: The pH value of the acid solution in step 1 is 1.5 to 3.

0.

4. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 3, characterized in that: The acid solution is at least one of acetic acid, sulfuric acid, nitric acid, hydrochloric acid, carbonic acid, and boric acid.

5. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 1, characterized in that: The lead iodide solution used in step 1 is prepared by the following steps: A lead compound solution is used as a synthetic base liquid, and an iodine compound solution is added dropwise to the synthetic base liquid to react to obtain a lead iodide solution; during the process, the temperature is controlled at 60-80° C., the stirring speed is 200-250 rpm, and the pH value during the dropping process is controlled to be ≤3.

6. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 5, characterized in that: The lead compound solution is any one of lead nitrate, lead acetate, lead chloride, lead carbonate and lead sulfate.

7. The method for adjusting the preferred orientation of the lead iodide crystal plane according to claim 5, characterized in that: The iodine-containing compound is any one of potassium iodide, sodium iodide, lithium iodide, ammonium iodide and magnesium iodide.

8. A lead iodide crystal, characterized in that Prepared by the method for adjusting the preferred orientation of the lead iodide crystal plane as described in any one of claims 1 to 7; The specific operation of step 2 is: aging the diluted lead iodide solution to obtain a solid-liquid mixture, wherein the aging temperature is 25 to 80° C., the aging pressure is ≤6 MPa, and the aging time is 2 to 4 hours; The lead iodide crystal preferentially grows toward the 011 crystal plane.

9. A lead iodide crystal, characterized in that: Prepared by the method for adjusting the preferred orientation of the lead iodide crystal plane as described in any one of claims 1 to 7; The specific operation of step 2 is: aging the diluted lead iodide solution to obtain a solid-liquid mixture, wherein the aging temperature is 80-120° C., the aging pressure is ≤6 MPa, and the aging time is 2-4 hours; The lead iodide crystal preferentially grows toward the 001 crystal plane.

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