Bismuth-based perovskite material and preparation method thereof

Abstract

The invention discloses a bismuth-based perovskite crystal material and a preparation method thereof, the chemical formula of the material is ABI2X8, A represents three different types of positive divalent organic amine cations, and X represents I, Br or Cl; the perovskite is prepared by taking a bismuth source and haloid acid as raw materials and different types of organic amines as structure-directing agents through solvothermal reaction in methanol. The preparation method is easy and convenient to operate and good in repeatability, the photoelectric property of the material can be effectively regulated and controlled by changing different types of organic amines, meanwhile, the toxic element lead is replaced with the metal element bismuth, and harm to the human body and pollution to the environment are reduced. The material disclosed by the invention is good in thermal stability, water stability and acid stability, excellent in photoelectric property and good in semiconductor performance, and has a wide application prospect in the fields of solar cells, photoelectric materials, photoelectric detection, X-ray detection, photoelectrocatalysis and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic materials, and in particular relates to a bismuth-based perovskite material and a preparation method thereof. Background Art

[0002] Photoelectric detection technology has achieved key applications in many fields such as military and defense, industry and automation, autonomous driving and intelligent systems, remote sensing and imaging technology, scientific research and special scenarios due to its high sensitivity and wide-band response characteristics. X-ray detection has important research significance in security inspection, non-destructive testing, medical diagnosis and basic science. Organic-inorganic hybrid halide perovskite materials have shown broad application prospects in the fields of photoelectric detection and X-ray detection due to their unique photoelectric properties. Since Kojima et al. first studied the use of perovskite materials as light-absorbing layers for solar cells in 2009, this type of material has shown excellent application potential in solar cells, lasers, photoelectric detection, X-ray detection, photocatalysis, photoelectrocatalysis and other fields. At present, most perovskite materials are mainly lead (Pb)-based perovskite materials. However, lead is toxic, which not only causes harm to the human body, but also seriously pollutes the environment. In addition, the material has poor stability, which hinders its commercial development.

[0003] The excellent optical properties of perovskite are mainly due to its unique crystal structure and composition characteristics. 2 +) is located at the B position of the perovskite structure, and its 6s 2 The lone pair of electrons forms a strong coupling with the p orbital of the halogen ion, producing a wide absorption spectrum (covering 300 to 1100 nm), giving the material a high light absorption coefficient (>10 4 cm -1 ). Bi is an adjacent element of Pb, trivalent Bi 3+ Also has 6s 2 lone pair of electrons, and thus can be used to replace Pb at the B site 2+ Cations. Moreover, bismuth (Bi 3 +) has a high atomic number (Z = 83), which has a strong attenuation effect on X-ray photons, significantly improving the X-ray energy conversion efficiency. Bismuth-based perovskites have high X-ray absorption efficiency, high resistivity, and excellent carrier mobility lifetime product (μτ), supporting efficient charge collection. In addition, Bi 3+The larger effective charge generated by the polarity leads to a higher dielectric constant, increasing the screening of charged defects. Bismuth-based perovskites exhibit excellent environmental stability compared to lead-based perovskites. Therefore, a series of bismuth-based perovskites (such as Cs3Bi2I9 [Nature Communications 2020, 11, 2304], Cs2AgBiBr6 [Nature Photonics 2017, 11, 726 - 732], and MA3Bi2I9 [Advanced Materials 2020, 32, 2001981]) show great application potential in photodetection, X-ray detection, etc. It is worth noting that two-dimensional or low-dimensional perovskites are relatively stable even under high electric fields, and large cations tend to construct low-dimensional perovskites. However, low-dimensional perovskites often suffer from the problem of low efficiency of photo-generated carrier separation and collection, resulting in poor optoelectronic performance. This problem mainly boils down to two aspects: (1) low carrier mobility in the organic part; (2) high energy barrier between the inorganic framework and organic cations. To solve this problem, the main method currently adopted is to develop interlayer engineering by regulating the A-site organic cations to achieve the regulation of the crystal structure and optoelectronic properties of perovskites [Advanced Functional Materials 2020, 30, 1910648]. For example, in 2023, the team of Shengzhong Liu prepared large single crystals (SCs) of AG3Bi2I9 with more N-H··I hydrogen bonds by designing the A-site cations, successfully shortening the interlayer distance and increasing the mobility-lifetime product from 2.87×10 -3 cm 2 V -1 (MA3Bi2I9 SC) to 7.94×10 -3 cm 2 V -1 [Advanced Materials 2023, 35, 2211977]. However, these studies mainly focus on increasing the carrier transport between inorganic structures by adjusting the inorganic interlayer distance, and the role of organic cations in the carrier separation and transport of bismuth-based perovskites has rarely been studied.

[0004] Recent research progress has revealed the crucial role of A-site cations in regulating the physicochemical and optoelectronic properties of perovskites. Stranks et al. demonstrated the tunable electronic coupling between inorganic lead halides and the organic layer, revealing the organic-inorganic charge transfer state [Journal of the American Chemical Society 2023, 145(39), 21330-21343]. Our previous study found that methyl viologen cations can form bismuth halide perovskites as the A-site, and their optoelectronic stability is improved [Advanced Optical Materials 2023, 11(9), 2203148]. Kuang et al. demonstrated that π-conjugated diamine cations with delocalized electrons directly contribute to the electronic structure, thereby reducing the bandgap [Science Bulletin 2024, 69(24), 3849-3859]. Therefore, improving the charge separation / transport effect of A-site cations through π-conjugation extension is expected to solve the carrier transport problem of low-dimensional perovskites, enabling them to have good optoelectronic properties while ensuring stability. Summary of the Invention

[0005] Aiming at the common problem of poor stability of perovskites, the present invention provides a bismuth-based perovskite crystal material with good stability in water and acid solutions, excellent optoelectronic properties, and good semiconductor properties, and provides a preparation method for this material that is simple to operate, inexpensive, and has good repeatability.

[0006] The chemical formula of the bismuth-based perovskite crystal material provided by the present invention is ABi2X8, where A represents a divalent cation with the nitrogen atom on the pyridine ring in the organic amine methylated, and X represents any one of I, Br, and Cl; the organic amine is any one of 1,4-bis(4-pyridyl)benzene, 2,5-dipyridyl-[3,2-B]thiophenothiophene, and 2,5-bis(pyridin-4-yl)thiazolo[5,4-D]thiazole; the crystal structure of this material contains a [BiX6] inorganic chain part and the divalent cation part, where the inorganic chain part is a one-dimensional chain formed by the edge-sharing of [BiX6] octahedrons, and the chains are filled by the divalent cations through weak π-π stacking.

[0007] Furthermore, when the above organic amine is 1,4-bis(4-pyridyl)benzene and X is I, the chemical formula of the bismuth-based perovskite crystal material is (C 18 H 18 N2)Bi2I8. The crystallization of this material belongs to the monoclinic system, space group P21 / n, and the unit cell parameters are: α = 90°, β = 97.042°, γ = 90°, and the unit cell volume

[0008] Furthermore, when the above-mentioned organic amine is 2,5-dipyridyl-[3,2-B]thiophenothiophene and X is I, the chemical formula of the bismuth-based perovskite crystal material is (C 18 H 16 N2S2)Bi2I8. The crystallization of this material belongs to the triclinic system, space group P-1 / (2), and the unit cell parameters are: α = 107.745°, β = 92.197°, γ = 92.280°, and the unit cell volume

[0009] Furthermore, when the above-mentioned organic amine is 2,5-bis(pyridin-4-yl)thiazolo[5,4-D]thiazole and X is I, the chemical formula of the bismuth-based perovskite crystal material is (C 16 H 16 N4S2)Bi2I8. The crystallization of this material belongs to the triclinic system, space group P-1 / (2), and the unit cell parameters are: α = 107.581°, β = 91.732°, γ = 92.509°, and the unit cell volume

[0010] The preparation method of the bismuth-based perovskite crystal material of the present invention is as follows: Add bismuth source, hydrohalic acid, and organic amine into methanol, stir at room temperature for 5 - 60 minutes, then react at 100 - 230°C for 1 - 96 hours under closed conditions. After the reaction, naturally cool to room temperature to precipitate single crystals from methanol, and wash ultrasonically to obtain the bismuth-based perovskite crystal material.

[0011] Furthermore, the above-mentioned bismuth source is any one of bismuth oxide, bismuth iodide, bismuth bromide, and bismuth chloride.

[0012] Furthermore, the above-mentioned hydrohalic acid is any one of hydrogen iodide, hydrogen bromide, and hydrogen chloride.

[0013] For the above preparation method, it is preferred that the molar ratio of the bismuth source to the hydrohalic acid and the organic amine is 1:1 - 100:0.5 - 3.

[0014] For the above preparation method, it is further preferred that the molar ratio of the bismuth source to the hydrohalic acid and the organic amine is 1:1 - 30:0.5 - 1.

[0015] For the above preparation method, it is preferred to react at 140 - 170°C for 48 - 60 hours under closed conditions.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. The present invention first introduces a conjugated extended organic amine cation as the A-site for the synthesis of bismuth-based organic-inorganic hybrid halide perovskites. This large conjugated cation significantly increases the temperature resistance, moisture resistance, and acid resistance of the perovskite material, enabling the material to remain stable after being calcined at 200 °C for 1 day, soaked in water for 5 months, or soaked in an acidic solution with pH = 1 for 30 days. This ultra-stable property increases the possibility of using this material in harsh environments. More importantly, after introducing the large conjugated cation into the bismuth-based organic-inorganic hybrid halide perovskite, a crystal internal heterojunction is formed between the inorganic part and the organic part of the material, promoting the light absorption and photoelectric separation efficiency of the material, and increasing its photoelectric response performance and X-ray response performance. Therefore, this type of material is a photoelectric detection material with great development potential.

[0018] 2. Compared with traditional lead-based perovskite materials, the bismuth-based perovskite crystal material of the present invention has good water stability, good thermal stability, excellent optoelectronic properties, good semiconductor properties, a relatively narrow bandgap, and significant light response characteristics. It has similar optoelectronic properties to lead-based perovskite materials and high stability that lead-based perovskite materials do not have, and is expected to replace lead-based perovskite materials and be used in fields such as solar cells, optoelectronic materials, photoelectric detection, X-ray detection, and photoelectrocatalysis.

[0019] 3. The bismuth-based perovskite crystal material of the present invention uses a bismuth source and hydrohalic acid as raw materials, and different types of organic amines as structure-directing agents, and is prepared by a solvothermal reaction in methanol. The preparation method is simple to operate, has good repeatability, and the raw materials used have low toxicity, rich reserves, and low prices. By changing different types of organic amines, the optoelectronic properties of the material can be effectively regulated. At the same time, the use of the metal element bismuth instead of the toxic element lead reduces the harm to the human body and environmental pollution, and is expected to achieve commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the organic amine cation and inorganic chain structure of the (C 18 H 18 N2)Bi2I8 material prepared in Example 1.

[0021] Figure 2 is a crystal structure diagram of the (C 18 H 18 N2)Bi2I8 material prepared in Example 1.

[0022] Figure 3 is a schematic diagram of the organic amine cation and inorganic chain structure of the (C 18 H 16 N2S2)Bi2I8 material prepared in Example 2.

[0023] Figure 4 is the (C18 H 16 Crystal structure diagram of (C

[0024] Figure 5 H 16 H 16 Schematic diagram of the organic amine cation and inorganic chain structure of (C

[0025] Figure 6 H 16 H 16 Crystal structure diagram of (C

[0026] Figure 7 SEM images of the bismuth-based perovskite crystal materials prepared in Examples 1-3.

[0027] Figure 8 Comparison of XRD of the bismuth-based perovskite crystal materials prepared in Examples 1-3 with single crystal simulated XRD and XRD patterns after 5 months in water.

[0028] Figure 9 XRD patterns of the bismuth-based perovskite crystal materials prepared in Examples 1-3 after being placed in harsh environments such as acidic environments, high temperatures, and low temperatures.

[0029] Figure 10 Thermal stability test diagrams of the bismuth-based perovskite crystal materials prepared in Examples 1-3.

[0030] Figure 11 UV absorption diagrams and optical band gap diagrams of the bismuth-based perovskite crystal materials prepared in Examples 1-3.

[0031] Figure 12 Photovoltaic response performance test of the bismuth-based perovskite crystal materials prepared in Examples 1-3 under 300W xenon lamp irradiation.

[0032] Figure 13 Relationship between the X-ray absorption coefficient and photon energy of the bismuth-based perovskite crystal materials prepared in Examples 1-3.

[0033] Figure 14 Relationship curve between thickness and attenuation efficiency calculated according to the attenuation coefficient of the bismuth-based perovskite crystal materials prepared in Examples 1-3.

[0034] Figure 15 Response photocurrent of the bismuth-based perovskite crystal materials prepared in Examples 1-3 under 40KeV X-ray light irradiation at 200V bias voltage. Detailed implementation mode

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments only.

[0036] Example 1

[0037] 0.590 g (1 mmol) of bismuth iodide, 0.116 g (0.5 mmol) of 1,4-bis(4-pyridyl)benzene (denoted as ExBIPY, chemical formula C 16 H 12 N2), 4 mL (1.8 mmol) of hydrogen iodide, and 8 mL of methanol were added to a polytetrafluoroethylene reaction kettle, stirred at room temperature for 30 minutes, then the polytetrafluoroethylene reaction kettle was sealed and placed in a constant temperature oven, and kept at 150 °C for 60 hours. After the reaction, it was naturally cooled to room temperature, and single crystals precipitated from methanol. They were washed ultrasonically with methanol multiple times to obtain a red bismuth-based perovskite crystal material, whose chemical formula is (C 18 H 18 N2)Bi2I8, denoted as Me2ExBIPYBi2I8. The crystallization of the material belongs to the monoclinic system, space group P21 / n, and the unit cell parameters are: α = 90°, β = 97.042°, γ = 90°, and the unit cell volume The crystal structure of the material contains an inorganic chain part of [BiI6] and a divalent cation C with the nitrogen atom on the pyridine ring methylated 18 H 18 N2 2+ part, see Figure 1 . Among them, the inorganic chain part is a one-dimensional chain formed by the edge sharing of [BiI6] octahedrons. This one-dimensional chain extends infinitely along the a-axis direction, and there is no contact between the chains. The divalent cation C 18 H 18 N2 2+ (Me2ExBIPY 2+ ) is filled between the chains through weak π-π stacking to balance the charge and form a stable structure, see Figure 2 .

[0038] Example 2

[0039] 0.465 g (1 mmol) of bismuth oxide, 0.294 g (1 mmol) of 2,5-dipyridyl-[3,2-B]thiophenothiophene (denoted as Py2TTp, chemical formula C 16 H 104 mL (1.8 mmol) of hydrogen iodide and 8 mL of methanol were added to a polytetrafluoroethylene reaction kettle, stirred at room temperature for 30 minutes, then the polytetrafluoroethylene reaction kettle was sealed and placed in a constant temperature oven, and reacted at 170 °C for 48 hours. After the reaction, it was naturally cooled to room temperature, and single crystals precipitated from methanol and were ultrasonically washed with methanol multiple times to obtain a red bismuth-based perovskite material with the chemical formula (C 18 H 16 N2S2)Bi2I8, denoted as Me2Py2TTpBi2I8. The crystallization of the material belongs to the triclinic system, space group P-1 / (2), and the unit cell parameters are: α = 107.745°, β = 92.197°, γ = 92.280°, and the unit cell volume The crystal structure of the material contains an inorganic chain part of [BiI6] and a divalent cation C in which the nitrogen atom on the pyridine ring is methylated 18 H 16 N2S2 2+ part, see Figure 3 . Similar to the crystal structure obtained in Example 1, the inorganic chain part is a one-dimensional chain formed by the edge-sharing of [BiI6] octahedrons, and the chains are filled by the weak π-π stacking of the divalent cation C 18 H 16 N2S2 2+ (Me2Py2TTp 2+ ) to balance the charge and form a stable structure, see Figure 4 .

[0040] Example 3

[0041] 1.18 g (2 mmol) of bismuth iodide, 0.297 g (1 mmol) of 2,5-bis(pyridin-4-yl)thiazolo[5,4-D]thiazole (denoted as Py2TTz, chemical formula C 14 H 10 N4S2), 6 mL (2.7 mmol) of hydrogen iodide, and 10 mL of methanol were added to a polytetrafluoroethylene reaction kettle, stirred at room temperature for 30 minutes, then the polytetrafluoroethylene reaction kettle was sealed and placed in a constant temperature oven, and reacted at 160 °C for 60 hours. After the reaction, it was naturally cooled to room temperature, and single crystals precipitated from methanol and were ultrasonically washed with methanol multiple times to obtain a red bismuth-based perovskite material with the chemical formula (C 16 H 16 N4S2)Bi2I8, denoted as Me2Py2TTzBi2I8. The crystallization of the material belongs to the triclinic system, space group P-1 / (2), and the unit cell parameters are: α = 107.581°, β = 91.732°, γ = 92.509°, and the unit cell volume The crystal structure of the said material contains an inorganic chain part of [BiI6] and a divalent cation C in which the nitrogen atoms on the pyridine ring are methylated 16 H 16 N4S2 2+ portion, see Figure 5 . Similar to the crystal structure obtained in Example 1, where the inorganic chain part is a one-dimensional chain formed by the edge-sharing of [BiI6] octahedra, and the chains are filled by the divalent organic cation C 16 H 16 N4S2 2+ (Me2Py2TTz 2+ ) through weak π-π stacking to balance the charge and form a stable structure, see Figure 6 .

[0042] Example 4

[0043] Add 0.465 g (1 mmol) of bismuth oxide, 0.116 g (0.5 mmol) of ExBIPY, 4 mL (35 mmol) of hydrogen bromide, and 5 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 150 °C for 60 hours. After the reaction, let it cool naturally at room temperature. Single crystals precipitate from methanol and are ultrasonically washed with methanol multiple times to obtain a yellow bismuth-based perovskite material with the chemical formula (C 18 H 18 N2)Bi2Br8.

[0044] Example 5

[0045] Add 0.449 g (1 mmol) of bismuth bromide, 0.147 g (0.5 mmol) of Py2TTp, 5 mL (44 mmol) of hydrogen bromide, and 8 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 160 °C for 48 hours. After the reaction, let it cool naturally at room temperature. Single crystals precipitate from methanol and are ultrasonically washed with methanol multiple times to obtain a brownish-red bismuth-based perovskite material with the chemical formula (C 18 H 16 N2S2)Bi2Br8.

[0046] Example 6

[0047] Add 0.449 g (1 mmol) of bismuth bromide, 0.147 g (0.5 mmol) of Py2TTz, 4 mL (35 mmol) of hydrogen bromide, and 6 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 150 °C for 48 hours for reaction. After the reaction, cool down naturally at room temperature. Single crystals precipitate from methanol and are washed ultrasonically with methanol for several times to obtain a brownish-yellow bismuth-based perovskite material with the chemical formula (C 16 H 16 N4S2)Bi2Br8.

[0048] Example 7

[0049] Add 0.316 g (1 mmol) of bismuth chloride, 0.116 g (0.5 mmol) of ExBIPY, 3 mL (36 mmol) of hydrochloric acid, and 6 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 150 °C for 60 hours for reaction. After the reaction, cool down naturally at room temperature. Single crystals precipitate from methanol and are washed ultrasonically with methanol for several times to obtain a yellowish-white bismuth-based perovskite material with the chemical formula (C 18 H 18 N2)Bi2Cl8.

[0050] Example 8

[0051] Add 0.465 g (1 mmol) of bismuth oxide, 0.294 g (1 mmol) of Py2TTp, 4 mL (48 mmol) of hydrochloric acid, and 8 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 160 °C for 48 hours for reaction. After the reaction, cool down naturally at room temperature. Single crystals precipitate from methanol and are washed ultrasonically with methanol for several times to obtain a yellow bismuth-based perovskite material with the chemical formula (C 18 H 16 N2S2)Bi2Cl8.

[0052] Example 9

[0053] Add 0.316 g (1 mmol) of bismuth chloride, 0.147 g (0.5 mmol) of Py2TTz, 4 mL (48 mmol) of hydrochloric acid, and 6 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant-temperature oven, keep the temperature at 170 °C for 48 hours for reaction. After the reaction, cool down naturally at room temperature. Single crystals precipitate from methanol and are washed ultrasonically with methanol for several times to obtain a yellowish-white bismuth-based perovskite material with the chemical formula (C 16 H 16N4S2)Bi2Cl8。

[0054] Example 10

[0055] Add 0.590 g (1 mmol) of bismuth iodide, 0.232 g (1 mmol) of ExBIPY, 4 mL (1.8 mmol) of hydrogen iodide, and 8 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant temperature oven, keep the temperature at 150 °C for 60 hours for reaction. After the reaction is completed, cool it naturally at room temperature. Single crystals precipitate from methanol, and wash them ultrasonically with methanol for several times to obtain a red bismuth-based perovskite crystal material, whose chemical formula is (C 18 H 18 N2)Bi2I8。

[0056] Example 11

[0057] Add 0.233 g (0.5 mmol) of bismuth oxide, 0.294 g (1 mmol) of Py2TTp, 4 mL (1.8 mmol) of hydrogen iodide, and 8 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant temperature oven, keep the temperature at 170 °C for 48 hours for reaction. After the reaction is completed, cool it naturally at room temperature. Single crystals precipitate from methanol, and wash them ultrasonically with methanol for several times to obtain a red bismuth-based perovskite material, whose chemical formula is (C 18 H 16 N2S2)Bi2I8。

[0058] Example 12

[0059] Add 1.18 g (2 mmol) of bismuth iodide, 0.594 g (2 mmol) of Py2TTz, 6 mL (2.7 mmol) of hydrogen iodide, and 10 mL of methanol into a polytetrafluoroethylene reaction kettle, stir at room temperature for 30 minutes, then seal the polytetrafluoroethylene reaction kettle and place it in a constant temperature oven, keep the temperature at 160 °C for 60 hours for reaction. After the reaction is completed, cool it naturally at room temperature. Single crystals precipitate from methanol, and wash them ultrasonically with methanol for several times to obtain a red bismuth-based perovskite material, whose chemical formula is (C 16 H 16 N4S2)Bi2I8。

[0060] Perform performance tests such as scanning electron microscopy, powder X-ray diffraction (XRD), thermal stability, ultraviolet absorption, photoelectric response, X-ray absorption attenuation, and X-ray response on the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 above. The results are shown in Figures 7 - 15 。

[0061] From Figure 7It can be seen from the scanning electron microscope images that the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 are long strip-shaped bulk crystals.

[0062] From Figure 8 the powder XRD analysis test results, it can be seen that the XRD patterns of the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 correspond well to their respective simulated XRD patterns. And after being placed in water for 5 months, there is no obvious change in their XRD, proving their good stability in water.

[0063] From Figure 9 the powder XRD analysis test results, it can be seen that when the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 are placed in extreme environments such as low temperature (-196 °C for 3 hours), high temperature (calcined at 200 °C for 1 day), and acidic solution (soaked in an acidic solution with pH = 1 for 30 days), there is no obvious change in their XRD, proving that they can stably exist in harsh environments, indicating their potential in actual application environments.

[0064] From Figure 10 the thermal stability test results, it can be seen that the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 exhibit high stability, and the thermal decomposition temperatures are all 350 °C.

[0065] From Figure 11 the ultraviolet absorption test results, it can be seen that the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 exhibit a wide light absorption range (200 - 1000 nm), and have good light absorption edges at 600 nm, 680 nm, and 640 nm respectively. This phenomenon may be due to the different light absorption abilities of different organic amine cations. At the same time, the inorganic chain part completely separated by divalent cations can promote effective energy transfer. By calculating their optical band gaps, the optical band gaps of the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 are 1.59 eV, 1.63 eV, and 2.00 eV respectively.

[0066] Figure 12The optoelectronic response test was carried out by hot pressing the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3, applying a pressure of 10 MPa, maintaining it at 100 °C for 1 hour, pressing them into wafers, and fabricating a photoconductive optoelectronic detection device. Under the irradiation of a 300 W xenon lamp and applying a 10 V bias voltage, the I-V curves and photocurrent in the illuminated or dark state were measured. The results showed that the bismuth-based perovskite crystal materials prepared in Examples 1 to 3 all had obvious optoelectronic response characteristics, and the difference in photocurrent between the illuminated and dark conditions was huge, with the on-off ratios reaching 10, 15, and 120 respectively. This may be due to the increase in the π-conjugated structure of the organic amine, which enhanced its own electron transport ability, promoted the intermolecular / intramolecular charge transfer and the electron coupling between the organic and inorganic parts, making the perovskite material have excellent optoelectronic properties and a large on-off ratio, and having great application potential in optoelectronic detection, photocatalysis, etc.

[0067] Figure 13 It is the relationship between the X-ray absorption coefficient and photon energy of Si, α-Se, and the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 calculated according to the data provided by the NIST X-COM database. It can be seen from the figure that the attenuation coefficients of the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 are much higher than those of the commercial semiconductors Si and α-Se in the whole photon energy range, which proves that they have good commercial potential.

[0068] Figure 14 It is the relationship curve between the thickness and attenuation efficiency calculated according to the attenuation coefficient. It can be seen from the curve graph that when the thickness increases to 950 μm, the attenuation of the three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 for 40 keV X-ray photons is as high as 99.99%, which means that almost all X-ray photons can be absorbed by the perovskite, which is better than the commercial semiconductors Si and α-Se, proving that they have good commercial potential.

[0069] Figure 15 The three bismuth-based perovskite crystal materials prepared in Examples 1 to 3 were hot pressed, applying a pressure of 10 MPa, maintaining it at 100 °C for 1 hour, pressing them into wafers, and fabricating a vertical structure X-ray detection device. The response current of X-rays at different dose rates under the irradiation of 40 keV X-ray light was measured, and the results proved their potential in the field of X-ray detection.

Claims

1. A bismuth-based perovskite crystal material, characterized in that: The chemical formula of the material is ABi2X8, wherein A represents a divalent positive cation in which the nitrogen atom on the pyridine ring in the organic amine is methylated, and X represents any one of I, Br, and Cl; the organic amine is any one of 1,4-di(4-pyridyl)benzene, 2,5-dipyridyl-[3,2-B]thienothiophene, and 2,5-bis(pyridin-4-yl)thiazolyl[5,4-D]thiazole; the crystal structure of the material contains an [BiX6] inorganic chain portion and the divalent positive cation portion, wherein the inorganic chain portion is a one-dimensional chain formed by edge sharing of [BiX6] octahedrons, and the chains are filled with the divalent positive cations through weak π-π stacking.

2. The bismuth-based perovskite crystal material according to claim 1, characterized in that: The organic amine is 1,4-di(4-pyridyl)benzene, and when X is 1, the chemical formula of the bismuth-based perovskite crystal material is (C 18 H 18 N2)Bi2I8, the crystallization of this material belongs to the monoclinic system, P21 / n space group, and the unit cell parameters are: α=90°,β=97.042°,γ=90°,unit cell volume 3. The bismuth-based perovskite crystal material according to claim 1, characterized in that: The organic amine is 2,5-bipyridyl-[3,2-B]thienothiophene, and when X is 1, the chemical formula of the bismuth-based perovskite crystal material is (C 18 H 16 N2S2)Bi2I8, the crystallization of this material belongs to the triclinic system, P-1 / (2) space group, and the unit cell parameters are: α=107.745°,β=92.197°,γ=92.280°,unit cell volume 4. The bismuth-based perovskite crystal material according to claim 1, characterized in that: The organic amine is 2,5-bis(pyridin-4-yl)thiazo[5,4-D]thiazole, and when X is 1, the chemical formula of the bismuth-based perovskite crystal material is (C 16 H 16 N4S2)Bi2I8, the crystallization of this material belongs to the triclinic system, P-1 / (2) space group, and the unit cell parameters are: α=107.581°,β=91.732°,γ=92.509°,unit cell volume 5. A method for preparing the bismuth-based perovskite crystal material according to claim 1, characterized in that: A bismuth source, a hydrohalic acid, and an organic amine are added to methanol, stirred at room temperature for 5 to 60 minutes, and then reacted at 100 to 230° C. for 1 to 96 hours under closed conditions. After the reaction is completed, the temperature naturally drops to room temperature to precipitate a single crystal from the methanol, and ultrasonically washed to obtain a bismuth-based perovskite crystal material; The bismuth source is any one of bismuth oxide, bismuth iodide, bismuth bromide and bismuth chloride; The hydrohalic acid is any one of hydrogen iodide, hydrogen bromide and hydrogen chloride; The organic amine is any one of 1,4-di(4-pyridyl)benzene, 2,5-dipyridyl-[3,2-B]thienothiophene, and 2,5-bis(pyridin-4-yl)thiazo[5,4-D]thiazole.

6. The method for preparing the bismuth-based perovskite crystal material according to claim 5, characterized in that: The molar ratio of the bismuth source to the hydrohalic acid and the organic amine is 1:1-100:0.5-3.

7. The method for preparing the bismuth-based perovskite crystal material according to claim 5, characterized in that: The molar ratio of the bismuth source to the hydrohalic acid and the organic amine is 1:1-30:0.5-1.

8. The method for preparing the bismuth-based perovskite crystal material according to claim 5, characterized in that: The reaction is carried out at 140-170°C under closed conditions for 48-60 hours.

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