Method for preparing solar cell by spraying method based on perovskite precursor solvent modification

Abstract

The invention belongs to the technical field of perovskite solar cells, and discloses a method for preparing a solar cell by a spraying method based on perovskite precursor solvent modification, which is a local solvent volatilization strategy. According to the strategy, gamma-butyrolactone is introduced into a perovskite precursor solvent and subjected to system modification, and the volatilization behavior of the solvent in the spraying process is effectively regulated and controlled. According to the method, the compact and smooth perovskite thin film can be rapidly and uniformly prepared, complete substrate covering is achieved, crystallization kinetics of perovskite can be finely regulated and controlled, and highly ordered growth of crystals and remarkable (100) crystal face orientation are promoted. In addition, the introduction of gamma-butyrolactone also enhances the surface and interface properties of the precursor solution, supports the uniform growth of the film and effectively releases internal stress, thereby synchronously improving the photoelectric conversion efficiency and long-term stability of the cell.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, and relates to a method for preparing solar cells based on solvent modification of perovskite precursors through spraying. Background Technology

[0002] Perovskite solar cells have attracted widespread attention in academia and industry due to their excellent photoelectric properties and simple fabrication process. Spray coating technology, as a promising fabrication method, can rapidly and scalably prepare large-area perovskite thin films on complex substrates (including three-dimensional substrates), bringing application potential to building-integrated photovoltaics, transportation optoelectronics (such as automobiles and aircraft), and multilayer optoelectronic devices on complex curved surfaces. Despite its promising prospects, the performance of spray-coated perovskite devices still lags significantly behind other efficient solution processing technologies such as spin coating and printing.

[0003] In classic perovskite solution systems, the high viscosity, strong coordination ability, low volatility of solvents (strong coordination solvents), and the reversible perovskite-ligand-solvent-gel system make the crystallization process of perovskite difficult to predict in spray coating applications. To induce crystallization, techniques such as anti-solvent or gas-assisted solvent extraction are typically used to rapidly remove solvent molecules, thereby bringing the system into a supersaturated state and promoting uniform and rapid nucleation. However, when these solvent extraction strategies are applied to spray coating processes, they face practical limitations. Rapid, supersaturated, and uniform film growth cannot be achieved, leading to multiple competing crystallization pathways, which often result in phase impurities and non-uniform grain growth. Furthermore, the layer-by-layer deposition inherent in spray coating processes introduces a cyclical dissolution-precipitation-redissolution process, further promoting side reactions and increasing the defect density within the final film.

[0004] To upgrade spraying technology from a scalable but performance-limited process to a method capable of producing high-quality perovskite films suitable for commercial applications, a fundamental understanding of the nucleation mechanism and crystallization pathway of perovskites is essential. Summary of the Invention

[0005] This invention provides a method for fabricating solar cells using a spray coating process based on solvent modification of perovskite precursors. To achieve uniform and orientation-controlled perovskite crystal growth during the spray coating process, a local solvent evaporation strategy is proposed. This strategy effectively controls the solvent evaporation behavior during the spray coating process by introducing γ-butyrolactone (GBL) into the perovskite precursor solvent and systematically modifying it. This method can rapidly and uniformly prepare dense and smooth perovskite films, achieving complete substrate coverage, and can finely control the crystallization kinetics of perovskite, promoting highly ordered crystal growth and significant (100) crystal plane orientation. In addition, the introduction of GBL enhances the surface and interfacial properties of the precursor solution, supports uniform film growth, and effectively releases internal stress, thereby simultaneously improving the photoelectric conversion efficiency and long-term stability of the cell.

[0006] The technical solution of this invention:

[0007] A method for fabricating solar cells using a spray coating method based on solvent modification of perovskite precursors, comprising the following steps:

[0008] 1) Preparation of perovskite precursor solution: Cesium iodide (CsI), methylamine iodide (MAI), formamidinium iodide (FAI), and lead iodide (PbI2) were dissolved in N,N-dimethylformamide (DMF) with a solute molar ratio of CsI:MAI:FAI:PbI2 = 1:2:17:20. A 1.2-1.5 M solution was prepared and stirred at 30-60 °C for 1-2 h to ensure complete dissolution. Subsequently, N-methylformamide (NMP) and GBL were added to the solution in a solvent volume ratio of DMF:NMP:GBL = 8:1:1. After being mixed with GBL, a perovskite precursor solution is obtained. Due to the high boiling point and low volatility of GBL, this ternary solvent system can induce Magranny flow during the spraying process due to the difference in the evaporation rate of each component, thereby slowing down the crystallization rate of perovskite and promoting the uniform growth of large-area films.

[0009] 2) Perovskite light-absorbing layer deposition: The perovskite precursor solution prepared above is injected into the spraying equipment. The gap between the nozzle and the substrate is adjusted to 1~2 cm, the injection rate of the perovskite precursor solution is 0.1~0.5 mm / min, the atomization pressure is 0.1~0.5 MPa, and the scanning speed of the nozzle along the X-axis is 30~60 mm / min. This process is completed in air with a humidity of 30%-57% RH. After the substrate is completely covered by the perovskite precursor, the wetted substrate is immediately transferred to the vacuum chamber. The vacuum degree is evacuated to less than 1 bar within 10 s and maintained for 2~3 min. Then it is transferred to ambient air and annealed at 120~170 ℃ for 5~15 min to completely transform it into a black phase.

[0010] The beneficial effects of this invention are as follows: By introducing high-boiling-point, low-volatility GBL into the perovskite precursor solution used for high-throughput spraying, the volatilization behavior of the DMF / NMP / GBL ternary solvent system is controlled, effectively promoting the uniform deposition of large-area perovskite films. The addition of GBL significantly slows down the perovskite crystallization kinetics and broadens the process window, thereby supporting the controllable fabrication of high-quality, high-throughput perovskite solar cells. Attached Figure Description

[0011] Figure 1 This is a SEM image of the surface of a perovskite solar cell prepared by GBL solvent-modified spraying.

[0012] Figure 2 This is a graph showing the photoelectric conversion efficiency of perovskite solar cells prepared by GBL solvent-modified spraying;

[0013] Figure 3 This is a SEM image of the cross-section of a perovskite solar cell after GBL solvent modification;

[0014] Figure 4 This is a surface SEM of a perovskite solar cell prepared without the addition of GBL;

[0015] Figure 5 This is a graph showing the photoelectric conversion efficiency of perovskite solar cells prepared without the addition of GBL. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0017] Example 1: Preparation of GBL-doped perovskite thin films

[0018] Step (1): Cleaning and treatment of FTO substrate. The substrate is ultrasonically cleaned for 15 min each with detergent solution, deionized water, anhydrous ethanol and isopropanol, and then treated with UV-ozone for 10 min.

[0019] Step (2): Deposit hole transport layer. Spin-coating the FTO substrate surface cleaned in step (1) with 0.5 mg / ml of 4-methyl-4-phenyl-1,3-diazole in ethanol at a rotation speed of 3000 rpm / min. Then anneal at 100℃ for 10 min to obtain a hole transport layer with a thickness of about 60 nm.

[0020] Step (3) Preparation of perovskite light-absorbing layer

[0021] 1) Preparation of perovskite precursor solution: 0.075 mmol CsI, 0.15 mmol MAI, 1.275 mmol FAI, and 1.5 mmol PbI2 were added to a mixed solution of DMF, NMP, and GBL (900 μL DMF + 200 μL GBL + 200 μL NMP). The precursor solution was stirred at 60 °C for 1 h and filtered through a 0.22 μm polytetrafluoroethylene membrane before use.

[0022] 2) Preparation of perovskite thin films: The composition of Cs... 0.15 FA 0.85 A perovskite precursor solution injection and spraying system was used for PbI3. The gap between the nozzle and the PI substrate was approximately 1 cm, the perovskite solution injection rate was 0.25 mm / min, the atomization pressure was 0.15 MPa, and the nozzle scanning speed along the X-axis was 50 mm / min. The process was carried out in air with a humidity of 30%–57% RH. After the substrate was completely covered with the perovskite precursor, the wetted substrate was immediately transferred to a vacuum chamber, and the vacuum level was reduced to less than 1 bar within 10 seconds and maintained for 2 minutes. Then, the substrate was transferred to ambient air and annealed at 150°C for 10 minutes to completely transform it into a black phase.

[0023] Step (4) Deposition of C60 electron transport layer: The perovskite film prepared in the above steps is placed in a vacuum evaporation chamber. After the vacuum level is lower than 9×10-4 Pa, C60 is evaporated at a rate of 0.1 Å / s to a thickness of 30 Å to complete the preparation.

[0024] Step (5) Deposition of BCP electron blocking layer: The film is placed in a vacuum evaporation chamber, and after the vacuum degree is lower than 9×10-4Pa, the BCP is evaporated at a rate of 0.1Å / s to a thickness of 10 Å to complete the preparation.

[0025] Step (6), Depositing metal electrodes: Place the multilayer thin film prepared in the above steps into a mask, and then place it into a vacuum evaporation chamber. The deposition process is carried out under a vacuum level lower than 9*10. -4 After Pa, the silver electrode was evaporated at a rate of 0.1 Å / s to a thickness of 600 Å to complete the device fabrication.

[0026] The cross-sectional microstructure of the GBL-modified perovskite solar cell was observed using a field emission scanning electron microscope (JSM-7610F Plus, Hitachi, Japan). The results are shown in [Figure number missing]. Figure 1 .

[0027] Perovskite solar cells prepared based on GBL modification were used at AM1.5 and 100 mW / cm². 2 The photoelectric performance of the battery was tested using a Keithley 2400 under illumination, and the statistical results are shown in Table 1 and 2. Figure 2 .

[0028] Cross-sectional SEM images of GBL solvent-modified perovskite solar cells are shown below. Figure 3 As shown.

[0029] Comparative Example 1: Perovskite solar cells without GBL modification

[0030] The preparation and testing methods are basically the same as in Example 1, except that the solvent ratio of the perovskite precursor in step (3)a is different. Specifically, 0.075 mmol CsI, 0.15 mmol MAI, 1.275 mmol FAI, and 1.5 mmol PbI2 are weighed and added to a mixed solution of DMF and NMP (900 μL DMF + 400 μL NMP). The precursor solution is stirred at 60 °C for 1 h and filtered through a 0.22 μm polytetrafluoroethylene membrane before use.

[0031] SEM images of the surface of perovskite solar cells prepared without the addition of GBL, as shown in Figure 1. Figure 4 As shown, the preparation and testing methods are the same as those in the examples.

[0032] Perovskite solar cells prepared without GBL showed performance at AM1.5 and 100 mW / cm². 2 The photoelectric performance of the battery was tested using a Keithley 2400 under illumination, and the statistical results are shown in Table 1 and 2. Figure 5 .

[0033] This invention, by adding GBL to the perovskite precursor solution, effectively slows down the crystallization rate of the perovskite film while improving the evaporation rate of the sprayed droplets, resulting in large-sized perovskite crystals. This not only reduces the formation of defects in the perovskite layer but also improves the contact between the perovskite layer and the top hole transport layer, thereby enhancing the charge transport dynamics of perovskite solar cells prepared by the spraying method, ultimately improving the cell performance. SEM results of the device surfaces in Examples and Comparative Example 1 show that the perovskite layer modified with GBL forms larger grains. Efficiency test results show that the photoelectric conversion efficiency of the perovskite solar cell based on GBL modification is increased to 24.64%, which is 4.25% higher than the efficiency of the unmodified device. These results demonstrate that the method of this invention can effectively control the crystallization behavior of the perovskite film, improve film quality and device stability, and significantly improve the photoelectric conversion efficiency of the device. Furthermore, this method is simple to operate and has significant implications for the future commercial application of perovskite solar cells.

[0034] Table 1. Specific test results of perovskite solar cells

[0035]

[0036] V OC J is the open-circuit voltage. SC is the short-circuit current, FF is the fill factor, and PCE is the photoelectric conversion efficiency.

Claims

1. A method for preparing a solar cell based on a spray method of perovskite precursor solvent modification, characterized by, The steps are as follows: 1) Preparation of perovskite precursor solution: CsI, MAI, FAI and PbI2 are dissolved in DMF to prepare a solution with a concentration of 1.2-1.5 M, and stirred at 30-60℃ for 1-2 h to ensure complete dissolution; Subsequently, NMP and GBL are added to the above solution, and the perovskite precursor solution is obtained after mixing uniformly; 2) Deposition of perovskite light-absorbing layer: the perovskite precursor solution prepared above is injected into a spraying device for spraying; after the substrate is completely covered with the perovskite precursor, the wet substrate is immediately transferred to a vacuum chamber, the vacuum degree is reduced to less than 1 bar within 10 s and maintained for 2-3 min; then transferred to the ambient air, and annealed to completely convert to black phase.

2. The method for preparing a solar cell by a spray method based on modification of a perovskite precursor solvent according to claim 1, characterized in that, In step 1), the molar ratio of CsI, MAI, FAI and PbI2 is 1:2:17:

20.

3. The method for preparing a solar cell by a spray method based on modification of a perovskite precursor solvent according to claim 1, characterized in that, In step 1), the volume ratio of DMF:NMP:GBL is 8:1:

1.

4. The method for preparing a solar cell by a spray method based on modification of a perovskite precursor solvent according to claim 1, characterized in that, In step 2), the process conditions for spraying are as follows: the gap between the nozzle and the substrate is adjusted to 1-2 cm, the injection speed of the perovskite precursor solution is 0.1-0.5 mm / min, the atomization pressure is 0.1-0.5 Mpa, and the scanning speed of the nozzle along the X-axis direction is 30-60 mm / min, and the process is completed in air with a humidity of 30%-57% RH.

5. The method for preparing a solar cell by a spray method based on modification of a perovskite precursor solvent according to claim 1, characterized in that, In step 2), the annealing conditions are as follows: annealing at 120-170℃ for 5-15 min.

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