A pyridyl perovskite nanocrystal material, preparation and application thereof

Abstract

The present application relates to a kind of pyridyl perovskite nanocrystal materials and its preparation and application, using PyMA as surface ligand, through the amino group on PyMA and the defect site on perovskite inorganic lattice Effective coordination bond is prepared to obtain new perovskite nanocrystal material.Compared with prior art, the nanocrystal material of the present application shows significantly enhanced nonlinear optical absorption performance in ultrafast femtosecond laser, different waveband region, which is due to the introduction of PyMA surface ligand, passivates the defect site in perovskite nanocrystal, improves the stability of perovskite nanocrystal structure.In addition, the aromatic structure of PyMA, promotes the regular arrangement of ligand on the surface of perovskite nanocrystal, improves the conductivity, enhances the electronic coupling between nanocrystal.Two kinds of factors synergistically endow the target material with excellent nonlinear absorption performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nonlinear optical materials, and relates to a pyridyl perovskite nanocrystal material and preparation and application thereof. BACKGROUND

[0002] Since all-inorganic cesium halide perovskite (CsPbX3, X = Cl, Br, and I) was reported in 2015 (Protesescu L., Yakunin S., Bodnarchuk M.I., et al. Nanocrystals of cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I): Novel optoelectronic materials showing bright emission with wide color gamut. Nano Letters, 2015, 15, 3692-3696.), all-inorganic halide perovskite nanocrystals have become a hot topic in the field of new generation optoelectronics due to their nanoscale characteristics, which exhibit intrinsic surface-rich properties and quantum confinement effects. It is particularly possible to develop nonlinear optical materials based on perovskite nanocrystals. For example, Sun et al. prepared a 9 nm-sized CsPbBr3 perovskite nanocrystal by a hot-injection method, and tested it using an 800 nm laser. The material exhibited strong two-photon absorption, and its two-photon absorption cross-section could reach 1.2 x 10 5 GM, thereby opening up the application of all-inorganic perovskite nanocrystals in the field of nonlinear optics for the first time (Wang Y., Li X., Zhao X., et al. Nonlinear absorption and low-threshold multiphoton pumped stimulated emission from all-inorganic perovskite nanocrystals. Nano Letters, 2016, 16, 448-453.).

[0003] Compared with three-dimensional bulk perovskite, perovskite nanocrystals have greatly improved stability, but there are still many defect sites on the surface, such as vacancies or dangling bonds, which will weaken the quantum yield of perovskite nanocrystals and affect their photon performance. In most methods for preparing perovskite nanocrystals, oleic acid and oleylamine are used, which have long molecular chains, hydrophobicity and steric hindrance, and can effectively improve the stability of nanocrystals. However, these long-chain ligands are usually electrically insulating, have energy barriers, and hinder the carrier transport within the perovskite nanocrystals; on the other hand, due to their molecular chain length, the spacing between each nanocrystal particle is too large, which also affects the charge transport between perovskite nanocrystals and the interface of the conductive contact layer, and reduces the carrier mobility, which is not conducive to the development of photonic devices. Therefore, preparing perovskite nanocrystals with sufficient light absorption capacity and excellent charge transport performance is an important challenge for the development of high-performance perovskite-based nonlinear photonic devices.

[0004] The present application is proposed based on the above background. SUMMARY

[0005] The purpose of the present application is to provide a pyridyl perovskite nanocrystal material and its preparation and application, by effectively coordinating the protonated amino group of 4-(aminomethyl)pyridine (PyMA) with the halide anion on the perovskite inorganic lattice, thereby anchoring on the surface of the perovskite nanocrystal as a surface ligand, effectively passivating the perovskite defects, and obtaining a new type of pyridyl perovskite nanocrystal material with high nonlinear optical absorption performance.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] In a first aspect, the present application provides a pyridyl perovskite nanocrystal material, which uses PyMA as a surface ligand and forms a bond with the uncoordinated halide anion in the perovskite through its protonated amino group.

[0008] Further, the chemical formula of the perovskite is CsPbX3, wherein Cs is a monovalent inorganic cesium cation, Pb is a divalent metal lead cation, and X3 is a halogen monovalent halide anion.

[0009] In a second aspect, the present application provides a preparation method of a pyridyl perovskite nanocrystal material, comprising the following steps:

[0010] (1) configuring a lead halide precursor solution mixed and dissolved by lead halide, oleic acid, 1-octadecene, oleylamine and 4-(aminomethyl)pyridine;

[0011] (2) injecting the cesium oleate precursor solution into the lead halide precursor solution, reacting, and cooling;

[0012] (3) Adding a dispersion medium to the reaction product solution cooled in step (2) and centrifuging the solution to obtain perovskite nanocrystals, which are the target product.

[0013] Furthermore, in step (1), the mass ratio of 4-(aminomethyl)pyridine to oleylamine is 0.015 to 0.25:1;

[0014] Furthermore, in step (1), the feed ratio of lead halide, oleic acid, 1-octadecene, and oleylamine is (0.45-0.56) mmol: (1.5-1.8) mL: (12-20) mL: (2.2-3) mL.

[0015] Furthermore, in step (2), the cesium oleate precursor solution is prepared by the following method:

[0016] Cesium carbonate, oleic acid, and 1-octadecene were weighed and mixed in a ratio of 162.8 mg: (0.5-0.7) mL: (7-9) mL. The mixture was then stirred and heated to 110-130° C., vacuum dried for 0.5-1.5 h, and then continued to heat to 145-155° C. under a nitrogen atmosphere until the solution became transparent.

[0017] Furthermore, in step (2), before hot injection, the temperature of the cesium oleate precursor solution is maintained at 140-150°C, and the temperature of the lead halide precursor solution is maintained at 165-170°C.

[0018] Furthermore, in step (2), before hot injection, the lead halide precursor solution is first heated at 110-120° C. and degassed for 0.5-1 h, and then continued to be heated at 165-170° C. and degassed for 10-30 min.

[0019] Furthermore, in step (2), the reaction time is 5-8 s. After the reaction is completed, the reaction product solution is quickly placed in an ice bath for cooling.

[0020] Furthermore, in step (3), the dispersion medium is methyl acetate, n-hexane, or toluene.

[0021] In a third aspect, the present invention provides an application of a pyridine-based perovskite nanocrystalline material as a nonlinear optical absorption material.

[0022] The perovskite nanocrystal prepared by the application has excellent nonlinear optical absorption performance. Experimental test results show that under 800nm femtosecond laser excitation, the nonlinear absorption coefficient of the material is 2 times that of the original perovskite nanocrystal material; and under 515nm laser, the material is 1.3 times that of the original nanocrystal material (i.e. the perovskite nanocrystal material without PyMA modification). Mechanically, this is due to the partial substitution of the long alkyl chain oleic acid ligand by the PyMA surface ligand, passivation of the surface defects, reduction of the trap state density, improvement of the stability of the nanocrystal crystal structure, and promotion of the coupling of the nanocrystal internal plasmonic excitons. In addition, the aromatic characteristics of the short chain PyMA also promote the charge transfer between the perovskite nanocrystal lattice particles, thereby improving the nonlinear optical absorption performance of the material. Therefore, the perovskite nanocrystal material modified by PyMA has a stable structure and can exhibit very competitive nonlinear optical absorption performance.

[0023] Compared with the prior art, the application has the following advantages:

[0024] (1) The preparation method of the pyridyl perovskite nanocrystal material of the application can obtain a perovskite nanocrystal material with a stable structure, and can be applied to the development of various halogen perovskite nanocrystals, and has a wide application range.

[0025] (2) The preparation method of the pyridyl perovskite nanocrystal material of the application has the advantages of easy acquisition of raw materials, saving of materials, low price, and simple preparation process.

[0026] (3) The pyridyl perovskite nanocrystal material of the application has good solubility, can be dispersed in a high molecular polymer, and is convenient for large-scale preparation of thin film materials.

[0027] (4) The pyridyl perovskite nanocrystal material produced by the application has stable chemical properties compared with the original perovskite nanocrystal. Under 800nm femtosecond laser, the nonlinear absorption coefficient of the pyridyl perovskite nanocrystal is 2 times that of the original perovskite nanocrystal; under 515nm femtosecond laser, the nonlinear absorption coefficient of the modified perovskite nanocrystal is 1.3 times that of the original perovskite nanocrystal, showing excellent development potential under wide-band ultrafast laser time domain. The application shows that the pyridyl perovskite nanocrystal material overcomes the disadvantage of low nonlinear optical performance of perovskite materials, and provides a new reference for constructing high-performance perovskite-based photonic devices. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The bonding schematic diagram of the pyridyl perovskite nanocrystal material prepared by the application.

[0029] Figure 2X-ray diffraction patterns of the pyridyl perovskite nanocrystal materials (different contents of PyMA) prepared in the application and the original perovskite nanocrystal materials.

[0030] Figure 3 Transmission electron microscope images of the pyridyl perovskite nanocrystal materials (different contents of PyMA) prepared in the application and the original perovskite nanocrystal materials.

[0031] Figure 4 Time-resolved fluorescence spectra of the pyridyl perovskite nanocrystal materials (different contents of PyMA) prepared in the application and the original perovskite nanocrystal materials.

[0032] Figure 5 Open aperture Z-scan curves of the pyridyl perovskite nanocrystal materials and the original perovskite nanocrystal materials under femtosecond laser excitation at 800 nm and 515 nm, respectively. DETAILED DESCRIPTION

[0033] The application will be described in detail below with reference to the drawings and specific embodiments. The embodiments are implemented on the premise of the technical solutions of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following embodiments.

[0034] In the following embodiments, the nonlinear optical absorption performance of the pyridyl perovskite nanocrystal materials and the original perovskite nanocrystal materials under femtosecond laser in the visible and near-infrared regions is tested by an open aperture Z-scan device. The laser used in the open aperture Z-scan device is from a titanium sapphire regenerative amplifier (Spitfre ACE-35F-2KXP, Spectra-Physics type) developed and produced by the United States Newport Company, with an output wavelength of 800 nm and 515 nm, a pulse width of 35 fs, and a repetition frequency of 1000 Hz.

[0035] Embodiment:

[0036] Here, the application uses PyMA as the perovskite surface ligand, and by adjusting the ratio, perovskite nanocrystal materials with different contents of PyMA ligand are prepared, which are respectively marked as "0.075PyMA-CsPbBr3", "0.15PyMA-CsPbBr3", and "0.25PyMA-CsPbBr3", and the nonlinear absorption performance of the materials is tested under the open aperture Z-scan device.

[0037] The preparation process of each type of perovskite nanocrystal material is as follows:

[0038] (1) Synthesis of cesium oleate: 162.8 mg of cesium carbonate, 0.6 mL of oleic acid, and 8 mL of 1-octadecene were weighed and added to a two-necked flask. The mixture was then stirred and heated to 120°C and vacuum dried for 1 h. The solution was then heated to 150°C under a nitrogen atmosphere until it became transparent and set aside.

[0039] (2) Synthesis of CsPbBr3 perovskite nanocrystals: Weigh 0.2g of lead bromide, 1.5mL of oleic acid, 15mL of 1-octadecene, and 3mL of oleylamine into a two-necked flask, and then repeatedly fill and discharge nitrogen three times. Heat to 120℃ and stir, and degas with a vacuum pump for 30 minutes. After completion, heat the mixed solution to 170℃ under a nitrogen atmosphere and stir for 10 minutes. When the solution becomes transparent, use a glass syringe to quickly draw cesium oleate solution at 150℃ and quickly inject it into the mixed solution in the two-necked flask. After 5 seconds, quickly place the two-necked flask in an ice bath to cool, and shake the two-necked flask continuously. The solution turns bright yellow-green. After the reaction is complete, 50 mL of methyl acetate is added to the crude mixed solution, and the mixture is centrifuged at 8000 rpm for 5 minutes. The supernatant is then removed, and the precipitate is redispersed in 2.5 mL of n-hexane. Another 2.5 mL of methyl acetate is added, and the mixture is centrifuged at 8000 rpm for 2 minutes. The supernatant is then removed, and the precipitate is redispersed in 5 mL of n-hexane, and centrifuged at 4000 rpm for 5 minutes. The supernatant is then removed, and the precipitate is dispersed in toluene to obtain CsPbBr3 perovskite nanocrystals.

[0040] (3) Synthesis of Pyridyl CsPbBr3 Perovskite Nanocrystals (PyMA-CsPbBr3): The synthesis method follows the same steps as for the synthesis of CsPbBr3 perovskite nanocrystals, with the difference that when preparing CsPbBr3 perovskite nanocrystals with different PyMA contents, the PyMA ligand content was varied to 0.075, 0.15, and 0.25 of the mass of oleylamine added. Except for the amounts of lead bromide, oleic acid, and 1-octadecene, the amounts of other reagents were varied as follows:

[0041] 0.075PyMA-CsPbBr3: 75.3mg PyMA, 2.775mL oleylamine;

[0042] 0.15PyMA-CsPbBr3: 150.6 mg PyMA, 2.55 mL oleylamine;

[0043] 0.25PyMA-CsPbBr3: 251.1 mg PyMA, 2.25 mL oleylamine.

[0044] (4) The nonlinear absorption properties of two perovskite nanocrystal materials under 800nm ​​and 515nm femtosecond laser irradiation were tested by the open-aperture Z-scan method.

[0045] Figure 1 Schematic diagram of the bonding of the pyridyl perovskite nanocrystal material prepared in the present application. The present application is prepared by bonding PyMA as a surface ligand with the uncoordinated halide anion in the peroviskite. As shown, the PyMA part containing the amino group replaces the long-chain oleylamine ligand and forms a bond with the uncoordinated bromide anion (negative charge defect due to the absence of cesium cation) in the peroviskite, forming a new type of pyridyl peroviskite nanocrystal. Figure 1

[0046] Figure 2 X-ray diffraction patterns of the pyridyl peroviskite nanocrystal material prepared above (different PyMA contents) and the original peroviskite nanocrystal material. The XRD spectra of all samples have three obvious XRD diffraction peaks at 15.1°, 21.7°, and 30.7°, respectively, corresponding to the (100), (110), and (200) crystal planes of the cubic structure of the peroviskite nanocrystal. Other several weaker XRD peaks are also related to the lattice structure of the peroviskite nanocrystal. This shows that the introduction of the PyMA ligand still maintains the integrity of the cubic structure of the peroviskite nanocrystal. This means that the PyMA molecule with less steric hindrance has a relatively slight effect on the crystal structure and morphology during the synthesis of the peroviskite nanocrystal.

[0047] Figure 3 Transmission electron microscopy images of the pyridyl peroviskite nanocrystal material prepared above (different PyMA contents) and the original peroviskite nanocrystal material. Whether PyMA is added or not or the amount of PyMA changes, all peroviskite nanocrystals maintain the integrity of the orthorhombic crystal structure and the cubic morphology. The lattice fringes with a spacing of 0.58 nm correspond to the (110) crystal plane of the orthorhombic phase of the peroviskite nanocrystal CsPbBr3. This is the same as the XRD spectrum result, indicating that the introduction of the PyMA ligand does not destroy the inherent crystal structure of the peroviskite nanocrystal. From the TEM images, it can also be seen that the size of the CsPbBr3 nanocrystal gradually increases after the PyMA modification. Figure 3 It can also be seen that the cubic size of the CsPbBr3 nanocrystal gradually increases after the PyMA modification. This shows that the introduction of the PyMA ligand has a relatively significant effect on the nucleation and growth kinetics of the peroviskite nanocrystal during the synthesis of the peroviskite nanocrystal.

[0048] Figure 4 ​Time-resolved fluorescence spectra of the prepared pyridyl perovskite nanocrystal materials (different content of PyMA) and the original perovskite nanocrystal materials. Compared with the original CsPbBr3 perovskite nanocrystal, the fluorescence decay rate of the CsPbBr3 nanocrystal modified by PyMA is slower, and the lifetime is longer. In addition, with the increase of the content of PyMA, the nanocrystal crystal size also increases, which weakens the quantum confinement effect, resulting in a longer lifetime. This shows that, compared with the long-chain oleylamine ligand, the introduction of the PyMA ligand has smaller steric hindrance, thereby having greater freedom and flexibility, which can passivate defects that long-chain oleylamine cannot reach, effectively reduce the trap state density, and thus inhibit the non-radiative recombination of the perovskite nanocrystal material.

[0049] Figure 5 Open aperture Z-scan curves of the prepared pyridyl perovskite nanocrystal materials and the original perovskite nanocrystal materials under 800 nm and 515 nm femtosecond laser excitation, respectively. Compared with the original CsPbBr3 perovskite nanocrystal, the reverse saturation absorption performance of the CsPbBr3 modified by the PyMA ligand is significantly enhanced. Under 800 nm laser excitation, the nonlinear absorption coefficient β value (β = 231.99 x 10 -3 cm GW -1 ) of the CsPbBr3 modified by the PyMA ligand is nearly 2 times that of the original CsPbBr3 nanocrystal (β = 117.52 x 10 -3 cm GW -1 ); under 515 nm laser excitation, the nonlinear absorption coefficient β value (β = -129.58 x 10 -3 cm GW -1 ) of the CsPbBr3 modified by the PyMA ligand is 1.3 times that of the original CsPbBr3 nanocrystal (β = -96.42 x 10 -3 cm GW -1 ). The reason is that the PyMA surface ligand partially replaces the long alkyl chain ligand, passivates the surface defects, thereby reducing the trap state density, improving the structural stability of the nanocrystal crystal, promoting the coupling of the nanocrystal internal plasmonic excitons, and improving the nonlinear optical absorption performance.

[0050] The above description of the embodiments is to facilitate the ordinary skilled person in the art to understand and use the application. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A pyridine-based perovskite nanocrystalline material, characterized in that: It consists of 4-(aminomethyl)pyridine as a surface ligand, which bonds with uncoordinated halide anions in the perovskite through its protonated amino groups; The chemical formula of the perovskite is CsPbX3, wherein Cs is a monovalent inorganic cesium cation, Pb is a divalent metal lead cation, and X is a monovalent halogen anion.

2. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 1, wherein: The following steps are involved: (1) preparing a lead halide precursor solution prepared by mixing and dissolving lead halide, oleic acid, 1-octadecene, oleylamine, and 4-(aminomethyl)pyridine; (2) hot-injecting the cesium oleate precursor solution into the lead halide precursor solution, reacting, and cooling; (3) Adding a dispersion medium to the reaction product solution cooled in step (2) and centrifuging the solution to obtain perovskite nanocrystals, which are the target product.

3. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, wherein: In step (1), the mass ratio of 4-(aminomethyl)pyridine to oleylamine is 0.015-0.25:1; the feed ratio of lead halide, oleic acid, 1-octadecene, and oleylamine is (0.45-0.56) mmol: (1.5-1.8) mL: (12-20) mL: (2.2-3) mL.

4. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, wherein: In step (2), the cesium oleate precursor solution is prepared by the following method: Weigh cesium carbonate, oleic acid, and 1-octadecene in a ratio of 162.8 mg: (0.5-0.7) mL: (7-9) mL. Stir and heat to 110-130°C. Vacuum dry for 0.5-1.5 h. Continue heating to 145-155°C under a nitrogen atmosphere until the solution becomes transparent.

5. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, wherein: In step (2), before hot injection, the temperature of the cesium oleate precursor solution is maintained at 140-150°C, and the temperature of the lead halide precursor solution is maintained at 165-170°C.

6. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, characterized in that: In step (2), before hot injection, the lead halide precursor solution is first heated at 110-120°C and degassed for 0.5-1 h, and then continued to be heated at 165-170°C and degassed for 10-30 min.

7. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, wherein: In step (2), the reaction time is 5-8 s. After the reaction is completed, the reaction product solution is quickly placed in an ice bath for cooling.

8. The method for preparing a pyridine-based perovskite nanocrystalline material according to claim 2, characterized in that: In step (3), the dispersion medium is methyl acetate, n-hexane, and toluene.

9. Use of the pyridine-based perovskite nanocrystalline material as claimed in claim 1 as a nonlinear optical absorption material.

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