阅读说明：本技术 一种调整混合卤素钙钛矿带隙的方法及应用 (Method for adjusting band gap of mixed halogen perovskite and application ) 是由 丁建旭 王开宇 孙海清 刘瑞 姚青 张�杰 于 2021-06-25 设计创作，主要内容包括：本发明涉及金属卤化物钙钛矿材料领域,具体涉及一种调整混合卤素钙钛矿带隙的方法及其应用。该方法为：将金属卤化物钙钛矿晶体溶解于溶剂中制备成待测液,采用电位滴定法测定待测液中卤素含量,计算出带隙宽度,再与计算的最优带隙值进行比较,依据比较结果对卤素的比例进行调整,直至获得最佳带隙宽度。该方法是本领域内首次直接通过检测钙钛矿晶体中的卤素比例来调控带隙宽度,也是首次基于电化学中的电位滴定法测定混合卤素钙钛矿中的卤素含量,利用该方法可准确测定出晶体中卤素离子的相对含量,从而使金属卤化物钙钛矿中光学带隙的调整更为精确。(The invention relates to the field of metal halide perovskite materials, in particular to a method for adjusting band gap of mixed halogen perovskite and application thereof. The method comprises the following steps: dissolving the metal halide perovskite crystal in a solvent to prepare a solution to be detected, measuring the content of halogen in the solution to be detected by adopting a potentiometric titration method, calculating the band gap width, comparing with the calculated optimal band gap value, and adjusting the proportion of the halogen according to the comparison result until the optimal band gap width is obtained. The method is characterized in that the band gap width is firstly and directly regulated by detecting the proportion of halogen in the perovskite crystal, the halogen content in the mixed halogen perovskite is firstly determined based on a potentiometric titration method in electrochemistry, and the relative content of halogen ions in the crystal can be accurately determined by utilizing the method, so that the adjustment of the optical band gap in the metal halide perovskite is more accurate.)

1. A method for adjusting the band gap of mixed halogen perovskite is characterized in that: dissolving the metal halide perovskite crystal in a solvent to prepare a solution to be detected, measuring the content of halogen in the solution to be detected by adopting a potentiometric titration method, calculating the band gap width, comparing the band gap width with an optimal band gap value, and adjusting the proportion of the halogen according to the comparison result until the optimal band gap width is obtained.

2. The method of claim 1, wherein: the solvent is selected from one or more of water, gamma-butyrolactone GBL and dimethylformamide DMF; preferably DMF.

3. The method of claim 1, wherein: the halogen element in the metal halide perovskite is I and/or Br.

4. The method of claim 1, wherein: the potentiometric titration method comprises the step of neutralizing a solution by using a peristaltic pumpDropwise adding AgNO₃Solution by recording Ag in solution⁺To measure the halogen content in the mixed-halogen perovskite.

5. The method of claim 4, wherein: AgNO₃The concentration of the standard solution is not more than 0.02mol/L, and is preferably 0.017 mol/L.

6. The method of claim 4, wherein: AgNO in peristaltic pump₃The flow rate of the solution was 0.7 mL/min.

7. The method of claim 1, wherein: in the potentiometric titration method, the potentiometric titration method is firstly utilized to measure the content of halogen in a standard sample, verify the accuracy of the potentiometric titration experiment and then test the liquid to be tested;

the halogen source of the standard sample solution is selected from CsBr and/or CsI and/or CsCl.

8. The method of claim 1, wherein: in the potentiometric titration method, a calomel electrode is used as a reference electrode, and a silver electrode is used as a working electrode.

9. The method of claim 1, wherein: in the potentiometric titration method, the change in potential in the solution is recorded with an electrochemical workstation.

10. Use of the method of any one of claims 1-9 in the field of light emitting devices, photoelectrocatalysis, photodetectors and solar cells.

Technical Field

The invention relates to the field of metal halide perovskite materials, in particular to a method for adjusting band gap of mixed halogen perovskite and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

Since the first report of metal halide perovskite solar cells in 2009, novel semiconductor materials such as metal halide perovskites have attracted great attention in the scientific research and industrial fields. The novel perovskite material has the advantages of adjustable band gap, high defect tolerance, long carrier diffusion length and mobility, strong light absorption, solution-based processability and the like, so that the metal halide perovskite and semiconductor devices such as photovoltaics, photoelectricity and the like based on the perovskite are deeply and widely researched.

For metal halide perovskite materials, a suitable energy gap is critical to their performance. However, according to the schockelylqueeisser limit curve, the optimal band gap of the single-junction solar cell light absorbing material is 1.4 eV. Therefore, in order to obtain a light absorbing material with an optimal band gap width, the most common method is to adjust the optical band gap size by adjusting the ratio of the halogen ions I, Br, and Cl. However, the inventors have found that since metal halide perovskite materials (thin films, single crystals, quantum dots, etc.) are generally prepared by a solution method, a serious problem is caused when mixed halogens are used for optical band gap control, namely: the proportion of the halogen ions in the precursor solution is often greatly different from the actual proportion in the solid perovskite material, so that the halogen content in the perovskite material is deviated. Therefore, how to accurately measure the proportion of halogen ions in the crystal becomes an urgent problem to be solved.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides a method for adjusting the band gap of a mixed halogen perovskite and application thereof, and the method for adjusting the optical band gap of a metal halide perovskite and application thereof are characterized in that the band gap width is firstly and directly regulated by detecting the proportion of halogen in perovskite crystals, and the halogen content in the mixed halogen perovskite is firstly measured based on a potentiometric titration method in electrochemistry.

The invention provides a method for adjusting the band gap of mixed halogen perovskite, which comprises the following steps: dissolving the metal halide perovskite crystal in a solvent to prepare a solution to be detected, measuring the halogen content in the solution to be detected by adopting a potentiometric titration method, accurately measuring the halogen content of the metal halide perovskite, further calculating the band gap width, comparing the band gap width with an optimal band gap value, and adjusting the proportion of the halogen in the crystal according to the comparison result until the optimal band gap width is obtained.

The second aspect of the invention provides the application of the method in the fields of luminescent devices, photoelectrocatalysis, photodetectors, solar cells and the like.

One or more embodiments of the present invention have at least the following advantageous effects:

(1) compared with the original method, the method for adjusting the band gap of the mixed halogen perovskite provided by the invention can accurately obtain the halogen content of the metal halide perovskite, avoids band gap regulation and control errors caused by the deviation of the proportion of halogen ions in the precursor solution and the actual proportion in the solid perovskite material, and ensures that the whole band gap adjusting process is more accurate and the adjusting efficiency is higher.

(2) The method adopts a potentiometric titration method for regulation and control, has accurate test result, simple and easily-controlled method, low requirement on equipment, short test period and lower cost.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 shows Ag in various solvents in example 1 of the present invention⁺Potential dependent AgNO₃Curve of change in solution volume.

FIG. 2 shows Ag in various solvents in example 1 of the present invention⁺Potential dependent AgNO₃First order differential curve of solution volume.

FIG. 3 shows Ag in examples 2 to 5 of the present invention⁺Potential dependent AgNO₃Curve of change in solution volume.

Wherein, Curve A is Ag in the standard sample of example 2⁺Potential dependent AgNO³Curve of change in solution volume. Curve B is Ag in the standard sample of example 3⁺Potential dependent AgNO³Curve of change in solution volume. Curve C is Ag in the test solution of example 4⁺Potential dependent AgNO³Curve of change in solution volume. Curve D is Ag in the test solution of example 5⁺Potential dependent AgNO³Curve of change in solution volume.

FIG. 4 shows Ag in accordance with embodiments 2 to 5 of the present invention⁺Potential dependent AgNO₃First order differential curve of solution volume.

Wherein, Curve A is Ag in the standard sample of example 2⁺Potential dependent AgNO₃First order differential curve of solution volume. Curve B is Ag in the standard sample of example 3⁺Potential dependent AgNO₃First order differential curve of solution volume. Curve C is Ag in the test solution of example 4⁺Potential dependent AgNO₃First order differential curve of solution volume. Curve D is the Ag content of the test solution of example 5⁺Potential dependent AgNO₃First order differential curve of solution volume.

FIG. 5 shows (FA) of examples 4 to 5 of the present invention_1-x-yMA_xCs_y)Pb(I_1-zBr_z)₃A UV-visible absorption profile of the single crystal; the ultraviolet-visible absorption spectrum adopts an Shimadzu UV-2550 ultraviolet-visible spectrophotometer, a small integrating sphere accessory is adopted, barium sulfate powder is used as a reference, a test sample is powder particles, and the scanning wavelength range is 600-900 nm.

Wherein curve A is (FA) of example 4_0.9MA_0.05Cs_0.05)Pb(I_0.9Br_0.1)₃A UV-visible absorption profile of the single crystal; curve B is (FA) of example 5_0.85MA_0.1Cs_0.05)Pb(I_0.85Br_0.15)₃A UV-visible absorption profile of the single crystal;

FIG. 6 shows (FA) in examples 4 to 5 of the present invention_1-x-yMA_xCs_y)Pb(I_1-zBr_z)₃A band gap diagram of a single crystal;

wherein curve A is (FA) of example 4_0.9MA_0.05Cs_0.05)Pb(I_0.9Br_0.1)₃A band gap diagram of a single crystal; curve B is (FA) of example 5_0.85MA_0.1Cs_0.05)Pb(I_0.85Br_0.15)₃Band gap diagram of single crystal.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As described in the background art, in the prior art, the optical band gap of metal halide perovskite is generally adjusted by adjusting the proportion of halogen ions in the precursor solution, but the proportion of halogen ions in the precursor solution is often greatly different from the actual proportion in the solid perovskite material, so that the content of halogen in the perovskite material is deviated, and the adjustment of the optical band gap is not accurate enough.

In order to solve the technical problems, the first aspect of the present invention provides a method for adjusting a band gap of a mixed halogen perovskite, specifically: dissolving the metal halide perovskite crystal in a solvent to prepare a solution to be detected, measuring the content of halogen in the solution to be detected by adopting a potentiometric titration method, calculating the band gap width, comparing the band gap width with an optimal band gap value, and adjusting the proportion of the halogen according to the comparison result until the optimal band gap width is obtained.

The invention firstly proposes to regulate the band gap width by directly testing the halogen content in the metal halide perovskite crystal, avoids the error generated by regulating the band gap width by regulating the proportion of halogen ions in a precursor solution in the prior method (namely the band gap regulation error caused by the deviation of the proportion of the halogen ions in the precursor solution and the actual proportion in the solid perovskite material), and ensures that the whole band gap regulation process is more accurate and the regulation efficiency is higher.

Although some other methods such as EDS, XPS, ICP, IC and the like can be selected in the prior art for the specific detection method of the halogen content ratio in the perovskite crystal, in the testing methods, on one hand, the sample preparation is complicated, the testing process is complicated, on the other hand, the accuracy cannot be guaranteed, and volatile halogen easily causes pollution to testing equipment, for example, when the XPS is used for testing the I content, the volatile I ions cause secondary pollution to a sample cabin due to the fact that a vacuum environment is needed; furthermore, the use of ion chromatography is limited due to the possible presence of organic ions in the perovskite. The method adopts the potentiometric titration method to measure the halogen content in the perovskite crystal, thereby realizing the effective adjustment of the optical width, mainly considering that the potentiometric titration method has very accurate test, and simultaneously, the method has high efficiency and simple equipment, and elements in the perovskite can not cause adverse effects on the instrument and the equipment.

The present invention also emphasizes that the means for element analysis in the art have inaccuracy in the differentiation of halogen content, and although the existing method for determining the element ratio in the material by electrochemical titration is generally applicable to the case where the difference between the two element contents is large, the present invention can make the halogen contents close to each other be accurately measured and differentiated by the selection of the specific solvent. As a preferred embodiment, the solvent is selected from one or more of water, gamma-butyrolactone (GBL), Dimethylformamide (DMF); preferably DMF.

In one or more embodiments of the invention, the halogen element in the metal halide perovskite is I and/or Br and/or Cl.

In one or more embodiments of the invention, the potentiometric titration method is to quantitatively drop AgNO into the solution by using a peristaltic pump₃Solution by recording Ag in solution⁺To measure the halogen content in the mixed-halogen perovskite.

In one or more embodiments of the invention, AgNO₃The concentration of the standard solution is not more than 0.02mol/L, and is preferably 0.017 mol/L.

In one or more embodiments of the invention, AgNO in peristaltic pumps₃The flow rate of the solution was 0.7 mL/min.

In one or more embodiments of the present invention, in the potentiometric titration method, the potentiometric titration method is used to measure I, Br and Cl content in the standard sample, verify the accuracy of the potentiometric titration experiment, and then perform the test on the solution to be tested;

the halogen source of the standard solution is selected from CsBr and/or CsI and/or CsCl.

In one or more embodiments of the present invention, in the potentiometric titration method, a calomel electrode is used as a reference electrode, and a silver electrode is used as a working electrode.

In one or more embodiments of the invention, the change in potential in the solution is recorded with an electrochemical workstation.

The second aspect of the invention provides the application of the method in the fields of luminescent devices, photoelectrocatalysis, photodetectors, solar cells and the like.

In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

Example 1

To FAPBI₃：MAPbBr₃In a molar ratio of 9:1, respectively mixing and dissolving in GBL, DMF and DMSO to obtain a mixed solution with the halogen concentration of 0.01mol/L, and fully and uniformly stirring the solution to obtain a mixture I, Br of 9:1 labelSample solution, 50ml of standard sample solution was transferred to a beaker. At this time, AgNO was added dropwise to the standard solution at a rate of 0.7mL/min using a peristaltic pump₃Standard solution, recorded by electrochemical workstation, Ag in solution⁺The potential change, titration I and Br time ratio was about 9:1, consistent with the content ratio in the standard. Wherein, Ag⁺Potential dependent AgNO₃The change curve of the volume of the solution is shown in FIG. 1, AgNO₃The first order differential curve of the solution volume is shown in FIG. 2, from which FIG. 2 AgNO can be determined₃End point of titration of the solution.

Example 2

To FAPBI₃：MAPbBr₃The molar ratio is 9:1, mixing and dissolving in DMF to obtain a mixed solution with the halogen concentration of 0.01mol/L, and fully and uniformly stirring the solution to obtain a mixture with I: Br of 9:1, 50ml of the standard solution is transferred to a beaker. The halogen content of the crystals, Ag in solution, was determined according to the method of example 1⁺The change in potential is shown in the curve a of fig. 3.

Example 3

To FAPBI₃：PbCl₂The molar ratio of 18: 3, respectively mixing and dissolving in DMF to obtain a mixed solution with the halogen concentration of 0.01mol/L, and fully and uniformly stirring the solution to obtain a mixture I, Br of 9:1, 50ml of the standard solution is transferred to a beaker. The halogen content of the crystals, Ag in solution, was determined according to the method of example 1⁺The change in potential is shown in the curve B of fig. 3.

Example 4

Taking a precursor solution I: crystals with Br of 9:1 (FA)_0.9MA_0.05Cs_0.05)Pb(I_0.9Br_0.1)₃The ultraviolet absorption edge is 842nm, and the optical band gap is 1.51 eV. The content of Br in the crystals was unknown (not more than 15%), and the crystals were dissolved in DMF to obtain a mixed solution having a halogen concentration of less than 0.01mol/L, and the halogen content in the crystals and Ag in the solution were measured by the method of example 1⁺The change of the potential is shown by the curve C of FIG. 3Shown in the figure.

Example 5

Taking a precursor solution I: crystals with Br of 17:3 (FA)_0.85MA_0.1Cs_0.05)Pb(I_0.85Br_0.15)₃When the Br content in the crystals was unknown (not more than 20%), the crystals were dissolved in DMF to give a mixed solution having a halogen concentration of less than 0.01mol/L, and the halogen content in the crystals and Ag in the solution were measured by the method of example 1⁺The change in potential is shown in the D curve of fig. 3.

As shown in FIGS. 1 and 2, when the electric potential is dropped, the halogen ions in the solution to be measured will react with AgNO₃Ag in standard solution⁺Bonding to make Ag in solution⁺The potential changes, the potential of the silver electrode obviously jumps before and after the stoichiometric point, and the corresponding volume when the potential jumps is the consumed AgNO at the end point₃Volume of standard solution.

Table 1 halogen content of different solvent samples in example 1

	GBL	DMF	DMSO
				I(mL)	26.95	27.04	27.40
Br(mL)	3.05	2.96	2.6
				Br(％)	10.17％	9.86％	8.67％

From the results in Table 1, it can be seen that the titration results of different solutions as solutions are quite different for the same sample, and that the ratio of halogens in GBL or DMF as solvents is found to be much closer to the true ratio of halogens in the sample, while the Br content of the data measured in DMSO as a solvent is significantly lower, and in addition, it should be noted that AgNO is used₃The solubility in GBL is low and cannot reach 0.017mol/L, so that DMF is a preferred solvent.

FIG. 4 shows Ag of examples 2 to 5⁺Potential dependent AgNO₃First order differential curves of solution volumes from which the I and Br contents were calculated, respectively, Table 2 shows AgNO for titrations I, Br and Cl in examples 2-5₃Volume of solution and Br content in examples 2-5.

Table 2 halogen content of samples of examples 2-4

	A	B	C	D
					I(mL)	27.2	27.0	26.5	25.5
Br(mL)	2.8	3	3.5	4.5
					Cl(％)	0	10％	0	0
Br(％)	9.33％	0％	11.6％	15％

From the results in table 2, it can be found that there is a certain difference between the proportion of halogen ions in the precursor solution and the actual proportion in the solid perovskite crystal material, and it is not ensured that the proportion of positive halogen in the crystal is consistent with the proportion of halogen in the precursor, and if the band gap width is adjusted by controlling the proportion of halogen in the precursor solution, a large error is inevitably caused. The method provided by the invention can reflect the proportion of the halogen in the perovskite crystal more accurately, so that the actual band gap width of the perovskite can be accurately obtained, the actual band gap width is compared with any band gap value to be regulated, the proportion of the halogen is further regulated and detected again according to the comparison result, and the perovskite crystal material with the ideal band gap width can be finally obtained after repeated regulation.

FIG. 5 is a graph showing the UV-VIS absorption of the crystals of examples 4-5. The absorption spectrum range of the perovskite single crystal of the embodiment 4-5 is 810-840 nm.

FIG. 6 shows the bandgap results in examples 4, 5; wherein curve A is (FA) of example 4_0.9MA_0.05Cs_0.05)Pb(I_0.9Br_0.1)₃A band gap diagram of a single crystal; curve B is (FA) of example 5_0.85MA_0.1Cs_0.05)Pb(I_0.85Br_0.15)₃Band gap diagram of single crystal.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.