CsPbBr3 / graphene composite material and preparation method thereof

Abstract

The application provides a CsPbBr3 / graphene composite material and a preparation method thereof.The composite material is prepared by using a precursor CsBr, a precursor PbBr2, oleic acid, oleylamine and graphene nanosheets as raw materials through an improved anti-solvent method to realize in-situ growth preparation.The all-inorganic perovskite nanocrystal / graphene structure obtained by the application combines the all-inorganic perovskite layer with high photon absorption and the graphene carrier transport layer, so that the all-inorganic perovskite nanocrystal / graphene structure has high light absorption, high conductivity and strong carrier separation capacity, and provides a reference and reference value for future new high-performance optoelectronic devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of perovskite composite materials, and particularly relates to a CsPbBr3 / graphene composite material and a preparation method thereof. The CsPbBr3 / graphene composite material is a kind of all-inorganic cesium lead bromide perovskite and graphene nanosheet composite material. The CsPbBr3 / graphene composite material has high thermal stability and carrier separation efficiency. BACKGROUND

[0002] All-inorganic metal halide perovskite CsPbX3(X=Cl, Br, I) nanocrystals have high light absorption coefficient, long carrier diffusion distance, strong photoluminescence and slow non-radiative charge recombination, which are ideal materials for preparing high-performance optoelectronic devices, such as solar cells, light-emitting diodes, lasers and photodetectors. Although these unique characteristics make CsPbX3 nanomaterials have broad application prospects in optoelectronic devices, their poor stability and inability to achieve effective separation of carriers have always been a difficult problem in improving the performance of perovskite optoelectronic devices.

[0003] In order to improve the stability of CsPbX3 nanomaterials, various inorganic and organic materials have been applied to improve their stability. In this process, organic polymer matrices can prevent CsPbX3 nanomaterials from contacting water vapor in the air, thereby effectively improving their humidity stability (patents CN 115747942 A, CN 116536042 A and CN 113355083 A; literature: DOI: 10.1021 / acsami.8b02857 and 10.1021 / acs.jpclett.6b02045). However, the heat-sensitive properties of these polymers make it almost impossible to optimize the thermal stability of CsPbX3 nanomaterials. Relatively speaking, inorganic matrices have the ability to enhance the thermal stability of CsPbX3 nanomaterials due to their superior heat resistance.

[0004] Currently, the preparation of all-inorganic perovskite nanocrystal composite materials usually requires high temperature and inert gas protection, which seriously hinders its large-scale application (patents: CN 112892573 A and CN 113318761 A). Therefore, it is of great significance to develop a low-cost, scalable, high-thermal-stability and carrier-separation-promoting preparation method of CsPbBr3 perovskite composite material. SUMMARY

[0005] The application aims to provide a full-inorganic perovskite nanocrystal / graphene composite material with high thermal stability and carrier separation promotion and a preparation method thereof. The composite material is prepared by in-situ growth through a modified anti-solvent method with CsBr precursor, PbBr2 precursor, oleic acid, oleylamine and graphene nanosheet as raw materials. The two materials are compounded through the anti-solvent method. Compared with the traditional anti-solvent method, the precursor solution is added in two steps in the application, so that the graphene nanosheet first adsorbs lead ions in the PbBr2 precursor solution, and then the CsPbBr3 nanocrystal is formed in-situ at the position of the adsorbed lead ions after the CsBr-OA-OAm precursor solution is added, thereby obtaining the CsPbBr3 / graphene composite material. The synthesis method is simple, does not require high temperature, is easy to operate, and the obtained composite has excellent stability.

[0006] To this end, the first aspect of the application provides a CsPbBr3 / graphene composite material with high thermal stability and carrier separation efficiency.

[0007] The second aspect of the application provides a preparation method of the CsPbBr3 / graphene composite material, which comprises the following steps:

[0008] (i) According to the molar ratio of the structural formula, the same molar ratio of CsBr and PbBr2 precursors is measured and added into N,N-dimethylformamide solution at room temperature, stirred and ultrasonicated until the precursors are completely dissolved, and the solution is clear, thereby preparing a CsBr precursor solution and a PbBr2 precursor solution.

[0009] (ii) The CsBr precursor solution obtained in step (i) is taken, and oleic acid (OA) and oleylamine (OAm) are sequentially added and stirred until completely dispersed, thereby forming a uniform solution, and the obtained solution is named as a CsBr-OA-OAm precursor solution, which is the same below.

[0010] (iii) The graphene nanosheet is dispersed in toluene solution and ultrasonically treated to make the graphene uniformly dispersed in the toluene solution, thereby obtaining a graphene-toluene solution.

[0011] (vi) The PbBr2 precursor solution obtained in (i) and the CsBr-OA-OAm precursor solution obtained in (ii) are added into the graphene-toluene solution obtained in (iii) and stirred intensively, thereby obtaining a precipitate.

[0012] (v) The precipitate is transferred into a centrifugal tube and centrifuged, then the upper solution is poured out, leaving the precipitate, and toluene is added, thereby obtaining the CsPbBr3 / graphene composite material dispersed in toluene.

[0013] Further, the concentration of the CsBr and PbBr2 precursor solution in the (i) is 0.01-0.06 mmol / mL. For example, the concentration of the CsBr and PbBr2 precursor solution in the (i) is 0.01 mmol / mL, 0.015 mmol / mL, 0.02 mmol / mL, 0.025 mmol / mL, 0.03 mmol / mL, 0.035 mmol / mL, 0.04 mmol / mL, 0.045 mmol / mL, 0.05 mmol / mL, 0.055 mmol / mL or 0.06 mmol / mL. Preferably, the concentration of the CsBr and PbBr2 precursor solution in the (i) is 0.04 mmol / mL.

[0014] Further, the volume ratio of oleic acid:oleylamine:CsBr precursor solution in the (ii) is 1-4:0.1-3:20. For example, the volume ratio of oleic acid:oleylamine:CsBr precursor solution in the (ii) is 1:0.1-3:20, 1.5:0.1-3:20, 2:0.1-3:20, 2.5:0.1-3:20 or 3:0.1-3:20. Preferably, the volume ratio of oleic acid:oleylamine:CsBr precursor solution in the (ii) is 2:1:20.

[0015] Further, the concentration of graphene in the (iii) is 1 mg / mL-5 mg / mL, preferably 2 mg / mL-3 mg / mL. For example, the concentration of graphene in the (iii) is 1 mg / mL, 1.5 mg / mL, 2 mg / mL, 2.5 mg / mL, 3 mg / mL, 3.5 mg / mL, 4 mg / mL, 4.5 mg / mL or 5 mg / mL.

[0016] Further, in the (vi), the PbBr2 precursor solution should be added to the graphene-toluene solution first, and then the CsBr-OA-OAm precursor solution should be added quickly, and the volume ratio of PbBr2 precursor solution:CsBr-OA-OAm precursor solution is 1:1.

[0017] Further, in the (vi), the volume ratio of (PbBr2 precursor solution and / or CsBr-OA-OAm precursor solution):graphene-toluene solution is 1-5:50. For example, the volume ratio of (PbBr2 precursor solution and / or CsBr-OA-OAm precursor solution):graphene-toluene solution is 1:50, 1.5:50, 2:50, 2.5:50, 3:50, 3.5:50, 4:50, 4.5:50 or 5:50.

[0018] Further, in the (vi), the temperature of the graphene-toluene solution is 0°C-50°C.

[0019] Further, the stirring time in the (vi) is 40-80s.

[0020] Further, the centrifuge speed in the (v) is 12000rpm, and the centrifugation time is 5min.

[0021] Advantages of the present application:

[0022] 1. The synthesis method of the perovskite nanocrystal / graphene composite material in the present application has simple process, low equipment requirement and low energy consumption, avoids the shortcomings of the traditional CsPbBr3 composite material synthesis by using hot injection method, and has good industrialization prospect and application prospect.

[0023] 2. The composite material prepared in the present application has higher stability than single perovskite, and overcomes the disadvantage of poor stability of traditional single perovskite.

[0024] 3. The CsPbBr3 / graphene structure obtained in the present application combines the all-inorganic perovskite layer with high photon absorption and the graphene carrier transport layer, so that it has high light absorption and high conductivity, and provides reference and reference value for future new type of high performance optoelectronic devices. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 X-ray diffraction spectrum of the CsPbBr3 / graphene composite material prepared in Example 1.

[0026] Figure 2 Transmission electron microscope image and high-resolution transmission electron microscope image of the CsPbBr3 / graphene composite material prepared in Example 1 of the present application.

[0027] Figure 3 Fluorescence emission spectrum (excitation light wavelength is 365nm) of the CsPbBr3 / graphene composite material synthesized in Example 1 and the CsPbBr3 nanocrystal synthesized in Comparative Example 1.

[0028] Figure 4 Time-resolved fluorescence emission spectrum (excitation light wavelength is 365nm) of the CsPbBr3 / graphene composite material synthesized in Example 1 and the CsPbBr3 nanocrystal synthesized in Comparative Example 1.

[0029] Figure 5 Comparison of fluorescence emission intensity of the CsPbBr3 / graphene composite material synthesized in Example 1 and the CsPbBr3 nanocrystal synthesized in Comparative Example 1 after heat treatment at different temperatures (the same sample is sequentially subjected to 40℃, 80℃, 120℃ and 160℃ for 20min, and the fluorescence intensity is tested after cooling to room temperature at each temperature, and then the temperature is increased for testing). DETAILED DESCRIPTION

[0030] The present application will be further described with reference to the drawings and preferred embodiments, the embodiments are given only to illustrate the present application, and are not intended to limit the scope of the present application.

[0031] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified;

[0032] The experimental methods in the following examples are conventional methods unless otherwise specified;

[0033] In the following examples and comparative examples:

[0034] The equipment used for X-ray diffraction test is D8 Advance powder X-ray diffractometer;

[0035] The equipment used for transmission electron microscopy is JEM2100Plus transmission electron microscope;

[0036] The equipment used for fluorescence emission spectrum is Hitachi F-4600 fluorescence spectrophotometer;

[0037] The equipment used for fluorescence lifetime is FluoroMax PLUS multifunctional fluorescence spectrometer.

[0038] Example 1

[0039] (i) Take 0.147g PbBr2, add 10mL N,N-dimethylformamide (DMF), place in a 20mL sample bottle, magnetically stir at room temperature, ensure complete dissolution, form a uniform solution, obtain PbBr2 precursor solution. Take 0.085g CsBr, add 10mL DMF, place in a 20mL sample bottle, 45℃ magnetically stir and ultrasonic for a short time, ensure complete dispersion, form a uniform solution, obtain CsBr precursor solution.

[0040] (ii) Take the CsBr precursor solution obtained in step (i), add 1mL oleic acid and 0.5mL oleylamine in sequence, and stir until completely dispersed to form a uniform solution, obtain CsBr-OA-OAm precursor solution.

[0041] (iii) Disperse 25mg graphene nanosheet (thickness: 4-20nm size: 5-10μm) in 10mL toluene solution, ultrasonic treatment, make the graphene uniformly dispersed in the toluene solution, obtain graphene-toluene solution.

[0042] (vi) Take 0.5mL PbBr2 precursor solution obtained in (i) and 0.5mL CsBr-OA-OAm precursor solution obtained in (ii) and add to the graphene-toluene solution obtained in (iii) in a 25℃ water bath, stir vigorously to obtain a precipitate.

[0043] (v) The precipitate was transferred to a centrifuge tube and centrifuged (12000 rpm for 5 min), then the supernatant was poured out, leaving the precipitate, and toluene was added to obtain 0.5-CsPbBr3 / 25-graphene-25 °C composite dispersed in toluene.

[0044] Example 2

[0045] (i) 0.147 g of PbBr2was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and stirred with a magnetic stirrer at room temperature to ensure complete dissolution and form a uniform solution to obtain a PbBr2precursor solution. 0.085 g of CsBr was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and stirred with a magnetic stirrer at 45 °C and ultrasonically for a short time to ensure complete dispersion and form a uniform solution to obtain a CsBr precursor solution.

[0046] (ii) The CsBr precursor solution obtained in step (i) was taken and 1 mL of oleic acid and 0.5 mL of oleylamine were added in sequence and stirred until completely dispersed to form a uniform solution to obtain a CsBr-OA-OAm precursor solution.

[0047] (iii) 25 mg of graphene nanosheets (thickness: 4-20 nm, size: 5-10 μm) were dispersed in 10 mL of toluene solution and ultrasonically treated to disperse the graphene uniformly in the toluene solution to obtain a graphene-toluene solution.

[0048] (vi) The 0.25 mL of PbBr2precursor solution obtained in (i) and the 0.25 mL of CsBr-OA-OAm precursor solution obtained in (ii) were added to the graphene-toluene solution in a 25 °C water bath in (iii) and stirred vigorously to obtain a precipitate.

[0049] (v) The precipitate was transferred to a centrifuge tube and centrifuged (12000 rpm for 5 min), then the supernatant was poured out, leaving the precipitate, and toluene was added to obtain 0.5-CsPbBr3 / 25-graphene-25 °C composite dispersed in toluene.

[0050] Example 3

[0051] (i) 0.147 g of PbBr2was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and stirred with a magnetic stirrer at room temperature to ensure complete dissolution and form a uniform solution to obtain a PbBr2precursor solution. 0.085 g of CsBr was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and stirred with a magnetic stirrer at 45 °C and ultrasonically for a short time to ensure complete dispersion and form a uniform solution to obtain a CsBr precursor solution.

[0052] (ii) Take the CsBr precursor solution obtained in step (i), add 1 mL of oleic acid and 0.5 mL of oleylamine in sequence, and stir until completely dispersed to form a uniform solution to obtain a CsBr-OA-OAm precursor solution.

[0053] (iii) Disperse 25 mg of graphene nanosheets (thickness: 4-20 nm, size: 5-10 μm) in 10 mL of toluene solution, and ultrasonically treat to uniformly disperse the graphene in the toluene solution to obtain a graphene-toluene solution.

[0054] (vi) Take the 0.01 mL of PbBr2 precursor solution obtained in (i) and the 0.01 mL of CsBr-OA-OAm precursor solution obtained in (ii) and add to the graphene-toluene solution obtained in (iii) in a 25 °C water bath, and stir vigorously to obtain a precipitate.

[0055] (v) Transfer the precipitate to a centrifuge tube and centrifuge (centrifuge at 12000 rpm for 5 min), then pour out the upper solution to leave the precipitate, and add toluene to obtain a 0.01-CsPbBr3 / 25-graphene-25 °C composite dispersed in toluene.

[0056] Example 4

[0057] (i) Take 0.147 g of PbBr2, add to 10 mL of DMF, and place in a 20 mL sample bottle, and magnetically stir at room temperature to ensure complete dissolution to form a uniform solution to obtain a PbBr2 precursor solution. Take 0.085 g of CsBr, add to 10 mL of DMF, and place in a 20 mL sample bottle, and magnetically stir at 45 °C and ultrasonically treat briefly to ensure complete dispersion to form a uniform solution to obtain a CsBr precursor solution.

[0058] (ii) Take the CsBr precursor solution obtained in step (i), add 1 mL of oleic acid and 0.5 mL of oleylamine in sequence, and stir until completely dispersed to form a uniform solution to obtain a CsBr-OA-OAm precursor solution.

[0059] (iii) Disperse 20 mg of graphene nanosheets (thickness: 4-20 nm, size: 5-10 μm) in 10 mL of toluene solution, and ultrasonically treat to uniformly disperse the graphene in the toluene solution to obtain a graphene-toluene solution.

[0060] (vi) Take the 0.5 mL of PbBr2 precursor solution obtained in (i) and the 0.5 mL of CsBr-OA-OAm precursor solution obtained in (ii) and add to the graphene-toluene solution obtained in (iii) heated in a 50 °C water bath, and stir vigorously to obtain a precipitate.

[0061] (v) The precipitate was transferred to a centrifuge tube and centrifuged (12000 rpm for 5 min), then the supernatant was poured out, leaving the precipitate, and toluene was added to obtain 0.5-CsPbBr3 / 20-graphene-50 composite dispersed in toluene.

[0062] Comparative Example 1

[0063] (i) 0.147 g of PbBr2was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and magnetically stirred at room temperature to ensure complete dissolution, forming a uniform solution, to obtain a PbBr2precursor solution. 0.085 g of CsBr was taken and added to 10 mL of DMF, placed in a 20 mL sample bottle, and magnetically stirred at 45°C and ultrasonically for a short time to ensure complete dispersion, forming a uniform solution, to obtain a CsBr precursor solution.

[0064] (ii) The CsBr precursor solution obtained in step (i) was taken and 1 mL of oleic acid and 0.5 mL of oleylamine were added in sequence, and stirred until completely dispersed, forming a uniform solution, to obtain a CsBr-OA-OAm precursor solution.

[0065] (iii) 0.5 mL of the PbBr2precursor solution obtained in (i) and 0.5 mL of the CsBr-OA-OAm precursor solution obtained in (ii) were added to 10 mL of toluene solution and stirred vigorously to obtain a precipitate.

[0066] (v) The precipitate was transferred to a centrifuge tube and centrifuged, then the supernatant was poured out, leaving the precipitate, and toluene was added to obtain CsPbBr3nanocrystals dispersed in toluene.

[0067] Experimental results:

[0068] Figure 1 The X-ray diffraction pattern of the CsPbBr3 / graphene composite prepared in the present application is shown. As can be seen from the figure, there are 7 characteristic peaks at 15.2°, 21.5°, 30.4°, 30.7°, 34.4°, 37.7° and 43.7°, of which the main characteristic peaks at 15.2°, 21.5°, 30.7°, 37.6° and 43.7° correspond to the (001), (110), (002), (200), (210), (211) and (202) crystal planes of the monoclinic CsPbBr3crystal structure (PDF #18-0364). The characteristic peak at 26.4° corresponds to the (002) plane of graphene (PDF #41-1487). In addition, there are no extra peaks, indicating that the introduction of graphene does not change the crystal phase structure of CsPbBr3. And it is proved that the composite is successfully prepared.

[0069] Figure 2The transmission electron microscope image of the CsPbBr3 / graphene composite prepared by the present application is shown. It can be clearly observed that the CsPbBr3nanocrystals are loaded on the graphene nanosheet. The lattice spacing of the nanocrystals is about 0.29 nm, which can correspond to the (200) crystal plane of the monoclinic CsPbBr3, as measured from the high-resolution transmission electron microscope in the lower right corner. The transmission electron microscope image proves that the perovskite material and the graphene have good interface contact, and this close combination is conducive to the rapid transport and efficient separation of photo-generated carriers.

[0070] Figure 3 The fluorescence emission spectra of the CsPbBr3 / graphene composite prepared in Example 1 and the CsPbBr3nanocrystals prepared in Comparative Example 1 are compared. It can be known from the results that the emission peak positions of both are almost the same, about 522.4 nm, indicating that the presence of graphene has no effect on the formation of the CsPbBr3nanocrystals. More importantly, the fluorescence of the CsPbBr3 / graphene composite is quenched compared to the pure CsPbBr3nanocrystals, because the graphene as a conductor of photo-generated carriers forms an electron transfer pathway of non-radiative quenching.

[0071] Figure 4 The fluorescence lifetime of the CsPbBr3 / graphene composite prepared in Example 1 and the CsPbBr3nanocrystals prepared in Comparative Example 1 is compared. The fluorescence lifetime of the CsPbBr3nanocrystals is 13.3 ns and the lifetime of the CsPbBr3 / graphene composite is 9.31 ns, as calculated by fitting. It is shown that the efficient transfer and separation of carriers occur in the composite, which shortens the fluorescence lifetime. Figure 5 The thermal stability of the CsPbBr3 / graphene composite prepared in Example 1 and the CsPbBr3nanocrystals prepared in Comparative Example 1 is compared. For the CsPbBr3nanocrystals, the fluorescence emission intensity continuously decreases with the increase of the treatment temperature, and the fluorescence emission completely disappears at 160℃, indicating that the increase of the temperature seriously destroys the crystal structure of the CsPbBr3nanocrystals. For the CsPbBr3 / graphene composite, the fluorescence emission remains stable after heat treatment at 40℃ to 160℃, indicating that the crystal structure of the CsPbBr3nanocrystals loaded on the graphene in the CsPbBr3 / graphene composite is stable. The experimental results confirm that due to the excellent thermal conductivity of the graphene, the composite can still maintain good stability when the temperature rises.

[0072] The above only describes the embodiments of the present application, and does not limit the scope of the present application, and any equivalent structure or equivalent process transformation made by using the content of the present application specification, or directly or indirectly applied in other related technical fields, are also included in the protection scope of the present application.

Claims

1. A method for preparing a CsPbBr3 / graphene composite material, the method comprising the following steps: (i) taking the same molar ratio of CsBr and PbBr2 precursors according to the molar ratio of the structural formula, adding them into N, N-dimethylformamide solution at room temperature, stirring and ultrasonicating until the precursors are completely dissolved, and the solution is clear, to prepare a CsBr precursor solution and a PbBr2 precursor solution; (ii) taking the CsBr precursor solution obtained in step (i), adding oleic acid (OA) and oleylamine (OAm) in sequence, and stirring until they are completely dispersed to form a uniform solution, to obtain a CsBr-OA-OAm precursor solution; (iii) dispersing graphene nanosheets in toluene solution, and ultrasonicating to make the graphene uniformly dispersed in the toluene solution, to obtain a graphene-toluene solution; (iv) taking the PbBr2 precursor solution obtained in step (i) and the CsBr-OA-OAm precursor solution obtained in step (ii), and adding them into the graphene-toluene solution obtained in step (iii), to obtain a precipitate; (v) transferring the precipitate to a centrifuge tube, centrifuging, then pouring out the upper solution to leave the precipitate, and adding toluene to obtain a CsPbBr3 / graphene composite material dispersed in toluene; wherein in step (i), the concentration of the CsBr and PbBr2 precursors in the precursor solution is 0.015-0.055 mmol / mL; wherein in step (ii), the volume ratio of oleic acid: oleylamine: CsBr precursor solution is 1-4: 0.1-3: 20; wherein in step (iii), the concentration of the graphene is 1 mg / mL-5 mg / mL; wherein in step (vi), the PbBr2 precursor solution should be added into the graphene-toluene solution first, and then the CsBr-OA-OAm precursor solution is added, and the volume ratio of the PbBr2 precursor solution: CsBr-OA-OAm precursor solution is 1: 1; wherein in step (vi), the volume ratio of the PbBr2 precursor solution or CsBr-OA-OAm precursor solution: graphene-toluene solution is 1-5:

50. 2.The method according to claim 1, wherein in step (vi), the temperature of the graphene-toluene solution is 0-50℃. 3.The method according to claim 1, wherein in step (vi), the stirring time is 40-80 s. 4.The method according to claim 1, wherein in step (v), the centrifuge speed is 12000 rpm, and the centrifuging time is 5 min. ​ ​ ​ ​ ​ ​ ​ ​ ​

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