A method for preparing a covalent triazine framework / bromine lead cesium composite photovoltaic film

Abstract

The application discloses a preparation method of a covalent triazine framework / bromine lead cesium composite photovoltaic film and belongs to the field of composite material preparation. Graphene-like CTFs nanosheets prepared are added into a PbBr2 solution to form a PbBr2 / CTFs precursor solution; secondly, the PbBr2 / CTFs precursor solution is spin-coated and annealed to form a film; then, a CsBr solution is spin-coated and annealed to obtain a CsPbBr3 / CTFs composite photovoltaic film. The graphene-like CTFs are used as a photovoltaic cell modifier to improve the CsPbBr3 film quality, improve crystallinity, increase the grain size, reduce the film grain boundary, and improve the photovoltaic performance of the film by 15 %.

Description

Technical Field

[0001] This invention relates to the field of materials preparation, and in particular to a method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film. Background Technology

[0002] In recent years, the photoelectric conversion efficiency (PCE) of organic-inorganic hybrid perovskite solar cells (PSCs) has increased rapidly, approaching that of silicon-based solar cells, making them the most commercially promising material in the photovoltaic field. However, outdoor instability remains a major obstacle to their commercialization. Many researchers have worked to improve their stability through component engineering, interface passivation, and material encapsulation. However, the migration stress of organic components caused by long-term exposure to humid and hot environments leads to the degradation of the perovskite film, resulting in poor device performance. Therefore, inorganic perovskite devices can be considered the most promising materials with environmental stability. In particular, CsPbBr3 perovskite devices have excellent resistance to humidity and heat, and light, and their fabrication process is simple and the raw materials are inexpensive. However, the film quality of all-inorganic perovskite CsPbBr3 is poor, with many defects, leading to a large number of nonradiative recombinations of charges, which hinders the improvement of device efficiency.

[0003] Passivation is an effective method to suppress nonradiative recombination. Currently, the main approach involves using small molecules with coordination capabilities to form coordination bonds with Pb ions in perovskites, thereby passivating defects and reducing defect density. For example, Zhang Lan et al. used NH4SCN as an additive to significantly reduce defect density, suppress interfacial recombination, and promote charge transfer (ACS Appl. Mater. Interfaces 2020, 12, 10579). Qunwei Tang et al. used lysine as an additive to simultaneously react with Pb... 2+ (Cs + ) and Br -Complexation can reduce the crystallization rate, increase the grain size of CsPbBr3 crystals, effectively reduce grain boundary defects, and thus improve the photovoltaic efficiency of the device (ACS Appl. Mater. Interfaces 2020, 12, 36092.). Recently, Qunwei Tang et al. reported that using multifunctional brominated graphene oxide (Br-GO) significantly reduced defect density, decreased non-radiative recombination, and improved photoelectric conversion efficiency (Chem. Eng. J. 2021, 412, 128727). Covalent triazine frameworks (CTFs) are composed of lightweight elements such as C, N, H, O, and S. Compared to two-dimensional crystalline materials like graphene, they have greater designability, allowing for the design of various structures at the atomic level, making them excellent optoelectronic materials. However, there are few reports on exfoliating these bulk CTFs into graphene-like materials and using them as additives for surface modification of CsPbBr3 solar cells. Summary of the Invention

[0004] The main technical problem solved by this invention is to provide a method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film. The method uses a covalent triazine framework material as an additive to regulate the crystal formation of bromine-lead-cesium, which can improve the crystal quality of the film, enhance crystallinity, increase grain size, reduce grain boundaries, and improve its photovoltaic performance.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film is provided, comprising the following steps:

[0007] (1) Preparation of graphene-like CTF nanosheets: CTFs were mixed with ethanol, refluxed, cooled, filtered, and freeze-dried; a certain amount of the treated CTFs were dispersed in the exfoliation solvent, and the CTFs dispersion was ultrasonically exfoliated using an ultrasonic cell disruptor, and then freeze-dried to obtain graphene-like CTF nanosheets.

[0008] (2) Preparation of CsPbBr3 composite film: A certain amount of graphene-like CTFs nanosheets were dispersed in PbBr2 solution to obtain PbBr2 / CTFs precursor solution; the PbBr2 / CTFs precursor solution was spin-coated, annealed to form a film, and then CsBr solution was spin-coated and annealed to form a covalent triazine framework / bromolead-cesium composite photovoltaic film.

[0009] Preferably, the graphene-like CTFs nanosheets have a sheet thickness of 3.80-4.20 nm and a size of 1-10 μm.

[0010] Preferably, the structure of CTFs includes:

[0011] .

[0012] Preferably, the CTFs are refluxed in ethanol for 2-5 hours.

[0013] Preferably, the ultrasonic cell disruptor has a frequency of 19.5-20.5 kHz, a power of 1200-1500 W, and an ultrasonic time of 80-120 min.

[0014] Preferably, the concentration of CTF nanosheets in the PbBr2 precursor solution is 2.5-10 mg / L.

[0015] Preferably, the solvent for preparing the CTFs dispersion is N,N-dimethylformamide; the solvent for the PbBr2 solution is N,N-dimethylformamide.

[0016] Preferably, the molar ratio of PbBr2 in the PbBr2 / CTFs precursor solution to CsBr in the CsBr solution is 1:0.8-1.2.

[0017] Preferably, the concentration of the PbBr2 solution is 0.5-1.2 mol / L.

[0018] Preferably, the concentration of the CsBr solution is 0.05-0.1 mol / L.

[0019] Following the above procedure, the spin-coating of CsBr solution and subsequent annealing steps were repeated multiple times.

[0020] The present invention improves the crystallinity of CTFs / CsPbBr3 composite photovoltaic films by adding graphene-like CTFs nanosheets, thereby enhancing crystallinity, increasing grain size, reducing grain boundaries, and improving photovoltaic performance by up to 15%. Attached Figure Description

[0021] Figure 1 and Figure 2 TEM images of CTFs (structure 1) and CTFs (structure 2) nanosheets, respectively;

[0022] Figure 3 XRD patterns of CTFs / CsPbBr3 films with different concentrations of CTFs added;

[0023] Figure 4 Statistical charts of photovoltaic performance parameters for an FTO / SnO2 / (CTFs / CsPbBr3) / carbon device structure using CTFs / CsPbBr3 thin film as the absorber layer: (a) Voc, (b) Jsc, (c) FF, (d) PCE.

[0024] Figure 5 SEM images of CTFs / CsPbBr3 composite films with different CTFs contents are shown, where: (a) 0 mg / L; (b) 2.5 mg / L; (c) 5 mg / L; (d) 10 mg / L. Detailed Implementation

[0025] The invention will be further described below with reference to examples.

[0026] Example 1

[0027] A method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film includes the following steps:

[0028] (1) Preparation of graphene-like CTF nanosheets: 0.6 g of CTFs (structure 1) was mixed with 25 mL of ethanol, refluxed at 80 °C for 3 h, cooled, filtered, and freeze-dried. 50 mg of CTFs was dispersed in 10 mL of N,N-dimethylformamide, and the suspension was sonicated for 120 min in an EP tube equipped with a circulating water system using an ultrasonic cell disruptor at 20 kHz and 1200 W power.

[0029] (2) Preparation of CTFs / CsPbBr3 composite photovoltaic thin film: Graphene-like CTFs (structure 1) nanosheets were added to a 1M N,N-dimethylformamide solution of PbBr2 to achieve a CTFs nanosheet concentration of 2.5 mg / L. Next, 80 μL of the PbBr2 / CTFs solution was spin-coated onto FTO using a pipette and annealed at 100℃ for 30 min. Then, 80 μL of a 0.1 mol / L CsBr methanol solution was spin-coated and annealed at 250℃ for 5 min. This process was repeated 8 times, finally yielding a film with an area of ​​0.40 cm². 2 The orange-yellow CTFs / CsPbBr3 film.

[0030] Example 2

[0031] A method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film includes the following steps:

[0032] (1) Preparation of graphene-like CTF nanosheets: 0.6 g of CTFs (structure 2) was mixed with 25 mL of ethanol, refluxed at 80 °C for 3 h, cooled, filtered, and freeze-dried. 50 mg of CTFs was dispersed in 10 mL of N,N-dimethylformamide, and the suspension was sonicated for 80 min at 20 kHz and 1500 W using an ultrasonic cell disruptor in an EP tube equipped with a circulating water system.

[0033] (2) Preparation of CTFs / CsPbBr3 composite photovoltaic thin film: Graphene-like CTFs (structure 2) nanosheets were added to a 1M N,N-dimethylformamide solution of PbBr2 to achieve a CTFs nanosheet concentration of 5 mg / L. Next, 80 μL of the PbBr2 / CTFs solution was spin-coated onto FTO using a pipette and annealed at 100℃ for 30 min. Then, a 0.1 mol / L CsBr methanol solution was spin-coated and annealed at 250℃ for 5 min. This process was repeated 8 times to obtain a thin film with an area of ​​0.40 cm². 2 The orange-yellow CTFs / CsPbBr3 film.

[0034] Example 3

[0035] A method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film includes the following steps:

[0036] (1) Preparation of graphene-like CTF nanosheets: 0.6 g of CTF (structure 1) was mixed with 25 mL of ethanol, refluxed at 80 °C for 3 h, cooled, filtered, and freeze-dried. 50 mg of CTFs were dispersed in 10 mL of N,N-dimethylformamide, and the suspension was sonicated for 100 min in an EP tube equipped with a circulating water system using an ultrasonic cell disruptor at 20 kHz and 1300 W power.

[0037] (2) Preparation of CTFs / CsPbBr3 composite photovoltaic thin film: Graphene-like CTFs (structure 1) nanosheets were added to a 1M N,N-dimethylformamide solution of PbBr2 to achieve a CTFs nanosheet concentration of 10 mg / L. Then, 80 μL of this solution was spin-coated onto FTO using a pipette and annealed at 100℃ for 30 min. Next, a 0.05 mol / L CsBr methanol solution was spin-coated and annealed at 250℃ for 5 min. This process was repeated 16 times to obtain a thin film with an area of ​​0.40 cm². 2 The orange-yellow CTFs / CsPbBr3 film.

[0038] Fabrication and characterization of photovoltaic devices:

[0039] SnCl2·2H2O and thiourea were dissolved in deionized water, stirred, and centrifuged. The supernatant was filtered through a polytetrafluoroethylene filter to obtain a SnO2 solution. FTO glass was irradiated with UV ozone and then preheated on a heating stage with the SnO2 solution. While still hot, the SnO2 solution was spin-coated onto the FTO substrate, followed by annealing to prepare a dense SnO2 layer. A precursor solution containing PbBr2 and a CsBr solution were then spin-coated sequentially onto the SnO2 to prepare a CsPbBr3 film. Finally, carbon paste was coated onto the CsPbBr3 film, and the film was heated again to prepare a complete FTO / SnO2 / (CTFs / CsPbBr3) / carbon device structure. The performance of the thin films in this case was then tested and characterized using a solar simulator. The device with the graphene-like CTFs concentration of 5 mg / L showed the best performance, with a photoelectric conversion efficiency of 9.49% and a current density (Jsc) of 7.49 mA / cm². 2 The open-circuit voltage (Voc) is 1.568 V, and the fill factor (FF) is 80.81%, which is 15% higher than the PCE of the original device, which is only 8.28%.

[0040] Figure 1 and Figure 2 TEM images of CTFs (structure 1) and CTFs (structure 2) nanosheets, respectively; Figure 3 XRD patterns of CTFs / CsPbBr3 films with different concentrations of CTFs added; Figure 4 Statistical charts of photovoltaic performance parameters for an FTO / SnO2 / (CTFs / CsPbBr3) / carbon device structure using CTFs / CsPbBr3 thin film as the absorber layer: (a) Voc, (b) Jsc, (c) FF, (d) PCE. Figure 5 SEM images of CTFs / CsPbBr3 composite films with different CTFs contents are shown, where: (a) 0 mg / L; (b) 2.5 mg / L; (c) 5 mg / L; (d) 10 mg / L. Figure 5 (a) shows a CsPbBr3 film without CTFs, revealing a high number of small grains; compared to... Figure 5 (a) In comparison, Figure 5 (b)-(d) show increased grain size and better film quality. Figure 5 (b) is a SEM image of CsPbBr3 with a concentration of 2.5 mg / LCTFs. The film formed is more dense and the grain size is larger than that of the unmodified sample. Figure 5(c) is a SEM image of CsPbBr3 at a concentration of 5 mg / L CTFs. It can be clearly seen that the grain size has increased, the film quality is good, and the surface morphology is relatively smooth and uniform. There are no pores on the film surface and few grain boundaries.

[0041] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a covalent triazine framework / bromine-lead-cesium composite photovoltaic thin film, characterized in that, Includes the following steps: (1) Preparation of graphene-like CTF nanosheets: CTFs were mixed with ethanol, refluxed, cooled, filtered, and freeze-dried; a certain amount of the treated CTFs were dispersed in the exfoliation solvent, and the CTFs dispersion was ultrasonically exfoliated using an ultrasonic cell disruptor, filtered, and then freeze-dried to obtain graphene-like CTF nanosheets. (2) Preparation of CsPbBr3 composite film: A certain amount of graphene-like CTFs nanosheets were dispersed in PbBr2 solution to obtain PbBr2 / CTFs precursor solution; the PbBr2 / CTFs precursor solution was spin-coated, annealed to form a film, and then CsBr solution was spin-coated and annealed to form a covalent triazine framework / bromolead-cesium composite photovoltaic film.

2. The preparation method according to claim 1, characterized in that: The graphene-like CTFs nanosheets have a sheet thickness of 3.80-4.20 nm and a size of 1-10 μm.

3. The preparation method according to claim 1, characterized in that: The structure of CTFs includes: 。 4. The preparation method according to claim 1, characterized in that: The reflux time in step (1) is 2-5 hours.

5. The preparation method according to claim 1, characterized in that... In step (1), the frequency of the ultrasonic cell disruptor is 19.5-20.5 kHz, the power is 1200-1500 W, and the ultrasonic time is 80-120 min.

6. The preparation method according to claim 1, characterized in that... Step (2) The concentration of CTF nanosheets in the precursor solution containing PbBr2 is 2.5-10 mg / L.

7. The preparation method according to claim 1, characterized in that... The solvent used to prepare the CTFs stripping solution is N,N-dimethylformamide; the solvent used to prepare the PbBr2 solution is N,N-dimethylformamide.

8. The preparation method according to claim 1, characterized in that... The molar ratio of PbBr2 in the PbBr2 / CTFs precursor solution to CsBr in the CsBr solution is 1:0.8-1.

2.

9. The preparation method according to claim 1, characterized in that... Repeat the spin-coating of CsBr solution and subsequent annealing steps multiple times.

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