Porous mesoscopic tiO2 electron transport material, preparation method thereof and perovskite solar cell

Abstract

The application belongs to the technical field of perovskite solar cells, and discloses a porous mesoscopic TiO2 electron transport material, a preparation method thereof and a perovskite solar cell. The material is in an anatase phase and has a mesopore-macropore multi-level pore structure, wherein the mesopore diameter is 10-40 nm, and the macropore diameter is 50-800 nm. The preparation method comprises the following steps: mixing TiO2 colloid as a titanium source, an alcohol dispersion medium and a hydroxyl-containing organic coordination / film-forming assistant, adding a mesopore structure regulator to prepare a TiO2 precursor; adding polystyrene microspheres, polymethyl methacrylate microspheres or ammonium bicarbonate pore-forming agents to prepare a composite slurry, coating, drying and performing sectional annealing to obtain the porous mesoscopic TiO2 electron transport material. The application can improve the porosity and pore connectivity of the electron transport layer, promote the full filling of perovskite, reduce the interface recombination, and improve the photoelectric conversion efficiency of the device.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, specifically relating to a method for preparing a porous mesoscopic electron transport layer. Background Technology

[0002] Perovskite solar cells, as a novel high-efficiency photovoltaic device, have become a research hotspot in the new energy field due to their advantages such as high photoelectric conversion efficiency, low manufacturing cost, and strong solution processability, and are expected to achieve large-scale industrial application. The electron transport layer, as a core component of perovskite solar cells, plays a crucial role in collecting and transporting electrons generated by the perovskite absorber layer and blocking holes. Its pore structure, electron transport performance, and compatibility with perovskite filling directly determine the cell's efficiency, stability, and mass production potential. Mesoporous TiO2, due to its large specific surface area, controllable electron transport path, and good compatibility with perovskite materials, is currently one of the most widely used electron transport materials in perovskite solar cells. However, traditional mesoporous TiO2 electron transport materials have significant performance limitations: On the one hand, traditional mesoporous TiO2 has low porosity and uniform pore size (mainly mesopores of 10-20 nm), resulting in poor pore connectivity. This makes it difficult for perovskite precursors to fully penetrate and fill the pores, forming numerous interfacial voids, increasing the probability of electron-hole recombination, and reducing charge collection efficiency. On the other hand, when the thickness of the mesoporous TiO2 film is adapted to the screen printing mass production process (>1.0 μm), problems such as film cracking and pore collapse are prone to occur, further restricting battery performance and mass production yield. To improve the porosity of mesoporous TiO2, existing technologies mostly employ hard or soft template methods for modification. While soft template methods (such as surfactant templates) can regulate mesoporous structures, the improvement in porosity is limited, and the template agent is not completely removed, leaving impurities. Traditional hard template methods (such as SiO2 microspheres and carbon spheres) can prepare high-porosity materials, but they have problems such as complex template agent synthesis, high cost, and easy damage to the mesoporous structure during the removal process, making them difficult to adapt to large-scale production.

[0003] Therefore, there is an urgent need to develop a modification method that is simple in process, low in cost, and highly adaptable to mass production, to solve the pore bottleneck of traditional mesoporous TiO2 and promote the large-scale development of perovskite solar cells. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies, such as low porosity, single pore size, and incomplete perovskite filling in traditional mesoporous TiO2, as well as the complex preparation, high cost, and poor mass production adaptability of existing modification methods. This invention provides a porous mesoscopic TiO2 electron transport material, its preparation method, and its applications. The method uses one of the following as pore-forming agents: polystyrene (PS), polymethyl methacrylate (PMMA) microspheres, ammonium bicarbonate, or polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO, P123, hereinafter referred to as P123). Stepwise annealing achieves template removal and TiO2 crystallization, constructing a multi-level porous structure, improving porosity and pore connectivity. Simultaneously, the preparation process is simple, cost-controllable, and reproducible, adaptable to screen printing mass production processes, providing support for the industrialization of high-efficiency perovskite solar cells.

[0005] A porous mesoscopic electron transport layer material, wherein the material is based on anatase TiO2 and has a mesoporous-macroporous hierarchical pore structure; the pore size of the mesopores is 10~40 nm and the pore size of the macropores is 50~800 nm.

[0006] The mesopores are formed by a mesopore template agent through a sol-gel and annealing process, and the macropores are formed by a macropore template agent through a physical site-pyrolysis removal or a chemical gas generation-pore expansion mechanism.

[0007] When the macroporous template agent is polystyrene microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(2-15); when the macroporous template agent is polymethyl methacrylate microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(3-12); when the macroporous template agent is ammonium bicarbonate, its dispersion concentration is 15-35 mg / mL, and the mass of the ammonium bicarbonate accounts for 4-12% of the mass of the TiO2 precursor; when the macroporous template agent is block copolymer P123, its solution concentration is 4-10 mg / mL, and the mass of P123 accounts for 2-8% of the mass of the TiO2 precursor.

[0008] The polystyrene microspheres have a particle size of 80-1000 nm, the polymethyl methacrylate microspheres have a particle size of 150-600 nm, the ammonium bicarbonate powder has a particle size of 80-1000 nm, and the block copolymer P123 has a number average molecular weight of 4000-8000.

[0009] A method for preparing a porous mesoscopic electron transport layer includes the following steps: (1) providing a conductive substrate and preparing a hole blocking layer on the surface of the conductive substrate; (2) mixing TiO2 colloid, ethanol and terpineol and ball milling to form TiO2 sol, adding a mesoporous template agent, and stirring to obtain a mesoporous TiO2 precursor; (3) adding a macroporous template agent to the mesoporous TiO2 precursor, mixing and stirring, adding a thickener to obtain a composite slurry; (4) coating the composite slurry onto the surface of the hole blocking layer by screen printing, preheating to remove the solvent, and obtaining a composite film; (5) annealing the composite film at 280~320℃ for 12 hours, then annealing at 480~520℃ for 24 hours, and cooling to obtain the porous mesoscopic electron transport layer; wherein, the mesoporous template agent is used to form mesopores with a pore size of 10~40 nm; the macroporous template agent is used to form macropores with a pore size of 50~800 nm.

[0010] The mesoporous template agent is selected from one or more of polyethylene glycol and ethyl cellulose.

[0011] The macroporous template agent is selected from one of polystyrene microspheres, polymethyl methacrylate microspheres, ammonium bicarbonate, or block copolymer P123.

[0012] The amount of the mesoporous template agent added is 5-20% of the mass of TiO2 colloid.

[0013] When the macroporous template agent is polystyrene microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(2-15); when the macroporous template agent is polymethyl methacrylate microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(3-12); when the macroporous template agent is ammonium bicarbonate, its dispersion concentration is 1535 mg / mL, and the mass of the ammonium bicarbonate accounts for 4-12% of the mass of the TiO2 precursor; when the macroporous template agent is block copolymer P123, its solution concentration is 4-10 mg / mL, and the mass of P123 accounts for 2-8% of the mass of the TiO2 precursor.

[0014] In step (2), the volume ratio of TiO2 colloid, ethanol, and terpineol is 1:(3~8):(0.05~0.3).

[0015] In step (3), the thickener is ethyl cellulose or polyethylene glycol, and the amount added is 2 to 6% of the total mass of the composite slurry.

[0016] In step (4), the screen printing process parameters are: screen mesh number of 150~600 mesh, printing spacing of 0.8~2.5 mm, printing speed of 10~30 cm / s, and printing pressure of 0.05~0.3 MPa.

[0017] In step (4), the preheating temperature is 100~150℃ and the preheating time is 10~30 min; the wet film thickness of the composite film is 1.0~2.5 μm and the dry film thickness is 0.8~1.5 μm.

[0018] In step (5), the annealing heating rate is 3~15℃ / min.

[0019] In step (3), baking soda is added as an auxiliary pore-forming agent, and the mass ratio of baking soda to the macroporous template agent is (0.05~0.5):1.

[0020] In step (5), when the macroporous template agent is polymethyl methacrylate microspheres, the annealing at 280~320℃ is carried out under nitrogen protection; when the macroporous template agent is polystyrene microspheres, ammonium bicarbonate or block copolymer P123, the annealing at 280~320℃ is carried out in an air atmosphere.

[0021] A perovskite solar cell includes a conductive substrate, a hole blocking layer, an electron transport layer, a perovskite absorber layer, a hole transport layer, and an electrode layer stacked sequentially; wherein the electron transport layer is a porous mesoscopic electron transport layer material.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention uses a pore-forming agent as a soft / hard template and combines it with a stepwise annealing process to construct a multi-level pore structure of "mesoporous-macroporous", which improves the porosity of mesoporous TiO2 and optimizes the pore connectivity, thus solving the technical bottleneck of low porosity of traditional mesoporous TiO2.

[0024] (2) The present invention selects a pore-forming agent as a soft / hard template agent, which has the advantages of low cost, uniform particle size, good dispersibility and easy thermal decomposition. It can be completely decomposed and volatilized by annealing at 280~320 ℃, leaving no impurities. This avoids the problems of complicated removal and easy introduction of impurities in traditional template agents.

[0025] (3) The preparation process of this invention is simple and highly controllable. The mixed slurry is suitable for screen printing process, which can realize the preparation of thick film (1.0~2.0 μm). The step-by-step annealing process can effectively avoid film cracking and improve the uniformity and stability of the film. The preparation process does not require complex equipment, has good repeatability, greatly reduces production costs, and is suitable for roll-to-roll continuous mass production.

[0026] (4) The modification method of the present invention can flexibly adjust the particle size ratio of the pore-forming agent to achieve precise control of the multi-level pore structure and can realize the preparation of electron transport layers of different thicknesses. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for preparing the pore-forming agent modified mesoporous TiO2 electron transport material of the present invention;

[0028] Figure 2 The images show scanning electron microscope (SEM) images of the upper surface of the mesoporous TiO2 film before and after polystyrene modification in Example 1 of this invention (a is unmodified, b is modified).

[0029] Figure 3 The images shown are cross-sectional scanning electron microscope (SEM) images of the mesoporous TiO2 films before and after polystyrene modification in Example 1 of this invention (a is unmodified, b is modified).

[0030] Figure 4 The figures show the current-voltage curves of the perovskite solar cells in Embodiment 1 and Comparative Example 1 of this invention.

[0031] Marking explanation: 1-Conductive substrate, 2-Hole blocking layer, 3-Mesoporous TiO2 electron transport layer; Detailed Implementation

[0032] This invention discloses a method for preparing a porous mesoscopic electron transport layer. Using TiO2 colloid as the titanium source, this invention selects one of the following as a pore-forming agent: polystyrene (PS), polymethyl methacrylate (PMMA) microspheres, ammonium bicarbonate (NH4HCO3), or polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO, P123, hereinafter referred to as P123). By controlling the particle size, addition amount, and process parameters of the pore-forming agent, a regular and interconnected pore structure is constructed within the mesoporous TiO2 through sol-gel, screen printing, and stepwise annealing processes. The pore-forming agent achieves directional control of the porosity of the mesoporous TiO2 through mechanisms such as "physical site occupation-pyrolysis removal," "self-assembly-pyrolysis pore formation," or "chemical gas generation-pore expansion," ultimately obtaining a mesoscopic electron transport material with high porosity. When the PS-modified porous mesoscopic electron transport layer of this invention is applied to perovskite solar cells, its photoelectric conversion efficiency is increased from 15.85% to over 20%. The present invention has a simple preparation process, low cost, and strong adaptability to mass production. It solves the technical bottlenecks of low porosity and incomplete perovskite filling in traditional mesoporous TiO2, and provides key materials and technical support for the large-scale industrialization of perovskite solar cells.

[0033] Some embodiments of this patent include the following technical solutions:

[0034] A method for preparing a porous mesoscopic TiO2 electron transport material includes the following steps:

[0035] (1) Substrate preparation: Conductive glass FTO was used as the substrate for fabricating screen-printed perovskite devices. The conductive glass FTO was ultrasonically cleaned in acetone, deionized water and ethanol in sequence for 15 min each time. It was then dried with nitrogen gas and set aside for later use.

[0036] (2) Preparation of hole blocking layer: Tetrabutyl titanate is used as titanium source, hydrochloric acid is added as nucleation inhibitor, and water is used as solvent. The mixture is kept at 75 °C for 45 min, then rinsed with water, and then annealed at 200~250 °C for 1~2 hours. After cooling to room temperature, a dense TiO2 film, i.e. hole blocking layer, is obtained. After being treated with ultraviolet ozone for 15 min, it is ready for use.

[0037] (3) Preparation of pore-forming agent dispersion / solution:

[0038] a. PS microspheres as pore-forming agent: PS microspheres are dispersed in ethanol and ultrasonically dispersed for 15-30 min to prepare a dispersion with a concentration of 10-15 mg / mL. The particle size of the PS microspheres is 100-800 nm.

[0039] b. PMMA microspheres as pore-forming agent: Disperse PMMA microspheres in ethanol, sonicate for 15-30 min, and prepare a dispersion with a concentration of 10-15 mg / mL. The PMMA microspheres have a particle size of 200-500 nm.

[0040] c. NH4HCO3 as a pore-forming agent: Disperse NH4HCO3 in ethanol, sonicate for 5-10 min, and prepare a dispersion with a concentration of 20-30 mg / mL;

[0041] d. Block copolymer P123 as a pore-forming agent: Dissolve P123 in ethanol and stir magnetically until completely dissolved to prepare a solution with a concentration of 5~8 mg / mL;

[0042] (4) Preparation of mesoporous TiO2 precursor: Using TiO2 colloid as titanium source, ethanol as solvent, terpineol as chelating agent, ball milling until a uniform TiO2 sol is formed, then adding mesoporous template agent (polyethylene glycol or ethyl cellulose), and continuing to stir for 1 to 3 hours to obtain mesoporous TiO2 precursor;

[0043] (5) Preparation of mixed slurry: PS microsphere dispersion is added to the mesoporous TiO2 precursor obtained in step (4) at a volume ratio of 1:(3~10) or PMMA microsphere dispersion to TiO2 precursor at a volume ratio of 1:(4~8), or NH4HCO3 dispersion accounts for 5%~10% of the mass of TiO2 precursor, or P123 solution accounts for 3%~6% of the mass of TiO2 precursor, and magnetically stirred for 2~4 hours; 2%~5% ethyl cellulose is added for thickening to obtain composite precursor;

[0044] (6) Preparation of composite film: The mixed slurry obtained in step (5) is coated on the surface of FTO / hole blocking layer by screen printing. The wet film thickness is 1.2~2.2 μm. After preheating at 100~150 ℃ for 10~30 min to remove solvent, a composite film with a dry film thickness of 0.8~1.5 μm is obtained.

[0045] (7) Stepwise annealing modification: The composite film obtained in step (6) is first annealed at 280~320 °C for 1~2 hours to allow the pore-forming agent to thermally decompose and volatilize, and then annealed at 480~520 °C for 2~4 hours to allow TiO2 to crystallize. After cooling to room temperature, a high porosity mesoporous TiO2 electron transport material modified with pore-forming agent is obtained.

[0046] (8) Construction of perovskite solar cells: A FAPbI3 perovskite solution and a Spiro-OMeTAD hole transport layer were spin-coated onto the surface of the modified electron transport layer, followed by the deposition of 120 nm silver as electrodes. The fabricated device structure consisted of a conductive substrate / hole blocking layer / modified TiO2 electron transport layer / perovskite absorber layer / hole transport layer / electrode layer, with an effective cell area greater than 0.07 cm². 2 .

[0047] In the above preparation method, preferably, in step (4), the volume ratio of TiO2 colloid, ethanol and terpineol is 1:(4~6):(0.1~0.2), the mesoporous template agent is polyethylene glycol or ethyl cellulose, and the amount added is 5%~15% of the mass of TiO2 colloid. The mesoporous template agent is used to regulate the mesoporous structure of TiO2 and improve porosity and connectivity.

[0048] In the above preparation method, preferably, in step (5), ethyl cellulose can be replaced with polyethylene glycol as a thickener, and the amount added is 2% to 5% of the total mass of the mixed paste, so that the mixed paste is suitable for screen printing process;

[0049] In the above preparation method, preferably, in step (5), the particle size of the PS microspheres is 100~800 nm, the particle size is uniform, and a regular macroporous structure can be formed; when the pore-forming agent is NH4HCO3, the powder particle size is 100~800 nm; when the pore-forming agent is block copolymer P123, its number average molecular weight is 5000~6000; the ammonium bicarbonate is preferably a food-grade high-purity reagent (purity ≥99.5%).

[0050] In the above preparation method, preferably, the screen printing process parameters in step (5) are: screen mesh number of 200~500 mesh, printing spacing of 1.0~2.0 mm, printing speed of 15~25 cm / s, and printing pressure of 0.1~0.2 MPa.

[0051] Furthermore, the present invention also protects the modified porous mesoscopic TiO2 electron transport material obtained by the above preparation method. This material is anatase phase and has a multi-level pore structure of "mesoporous-macropore". The mesopore diameter is 10~40 nm and the macropore diameter is 50~800 nm. Compared with unmodified mesoporous TiO2, the porosity is improved.

[0052] Example 1

[0053] A method for preparing a porous mesoscopic TiO2 electron transport material includes the following steps:

[0054] (1) Substrate preparation: Conductive glass FTO was used as the substrate for fabricating screen-printed perovskite devices. The conductive glass FTO was ultrasonically cleaned by sequentially immersing it in acetone, deionized water, and ethanol for 15 min each time, and then dried with nitrogen gas for later use.

[0055] (2) Preparation of hole blocking layer: Tetrabutyl titanate is used as titanium source, hydrochloric acid is added as nucleation inhibitor, and water is used as solvent. The mixture is kept at 75 °C for 45 min, then rinsed with water, and then annealed at 200~250 °C for 1~2 hours. After cooling to room temperature, a dense TiO2 film, i.e. hole blocking layer, is obtained. After being treated with ultraviolet ozone for 15 min, it is ready for use.

[0056] (3) Preparation of mesoporous TiO2 precursor: Take 10 mL of TiO2 colloid, add 40 mL of ethanol, stir evenly, add 0.2 mL of terpineol as a chelating agent, ball mill for 5 hours to form a uniform TiO2 sol, then add 0.8 g of polyethylene glycol (molecular weight 2000) as a mesoporous template agent, continue stirring for 1 hour to obtain mesoporous TiO2 precursor.

[0057] (4) Preparation of PS / TiO2 mixed slurry: PS microspheres with a particle size of 100 ~ 750 nm were dispersed in ethanol and ultrasonically dispersed for 20 min to obtain a PS microsphere dispersion with a concentration of 10 mg / mL; 200 μL of PS microsphere dispersion was added to 1 mL of the mesoporous TiO2 precursor obtained in step (3) and ball-milled for 2 hours; 0.03 g of ethyl cellulose was added as a thickener and stirred for 30 min to obtain PS / TiO2 mixed slurry.

[0058] (5) Preparation of PS / TiO2 composite film: The above mixed slurry was coated on the surface of FTO / hole blocking layer by screen printing, and the wet film thickness was 2.0 μm; after preheating at 120℃ for 20 min, the solvent was removed to obtain a PS / TiO2 composite film with a dry film thickness of 1.2 μm.

[0059] (6) Stepwise annealing modification: The composite film is placed in a muffle furnace and heated to 300°C at a heating rate of 5°C / min. It is annealed for 1 hour to allow the PS microspheres to thermally decompose and volatilize. Then, it is heated to 500°C at the same heating rate and annealed for 3 hours to allow TiO2 to crystallize. It is cooled to room temperature to obtain PS-modified high-porosity mesoporous TiO2 electron transport material.

[0060] (7) Construction of perovskite solar cells: A FAPbI3 perovskite solution and a Spiro-OMeTAD hole transport layer were spin-coated onto the surface of the modified electron transport layer, followed by the deposition of 120 nm silver as electrodes. The fabricated device structure consisted of a conductive substrate / hole blocking layer / modified TiO2 electron transport layer / perovskite absorber layer / hole transport layer / electrode layer, with an effective cell area greater than 0.07 cm². 2 .

[0061] Example 2

[0062] A method for preparing a porous mesoscopic TiO2 electron transport material includes the following steps:

[0063] (1) Substrate preparation: Conductive glass FTO was used as the substrate for fabricating screen-printed perovskite devices. The conductive glass FTO was ultrasonically cleaned by sequentially immersing it in acetone, deionized water, and ethanol for 15 min each time, and then dried with nitrogen gas for later use.

[0064] (2) Preparation of hole blocking layer: Tetrabutyl titanate is used as titanium source, hydrochloric acid is added as nucleation inhibitor, and water is used as solvent. The mixture is kept at 75 °C for 45 min, then rinsed with water, and then annealed at 200~250 °C for 1~2 hours. After cooling to room temperature, a dense TiO2 film, i.e. hole blocking layer, is obtained. After being treated with ultraviolet ozone for 15 min, it is ready for use.

[0065] (3) Preparation of mesoporous TiO2 precursor: Take 10 mL of TiO2 colloid, add 40 mL of ethanol, stir evenly, add 0.2 mL of terpineol as a chelating agent, ball mill for 5 hours to form a uniform TiO2 sol, then add 0.8 g of polyethylene glycol (molecular weight 2000) as a mesoporous template agent, continue stirring for 1 hour to obtain mesoporous TiO2 precursor.

[0066] (4) Preparation of PMMA / TiO2 mixed slurry: PMMA microspheres with a particle size of 350 nm were dispersed in ethanol and ultrasonically dispersed for 20 min to obtain a PMMA microsphere dispersion with a concentration of 10 mg / mL; 200 μL of PMMA microsphere dispersion was added to 1 mL of the mesoporous TiO2 precursor obtained in step (3) and ball-milled for 2 hours; 0.03 g of ethyl cellulose was added as a thickener and stirred for 30 min to obtain PMMA / TiO2 mixed slurry.

[0067] (5) Preparation of PMMA / TiO2 composite film: The above mixed slurry was coated on the surface of FTO / hole blocking layer by screen printing, and the wet film thickness was 2.0 μm; after preheating at 120℃ for 20 min, the solvent was removed to obtain a PMMA / TiO2 composite film with a dry film thickness of 1.2 μm.

[0068] (6) Stepwise annealing modification: The composite film is placed in a muffle furnace and heated to 300°C at a heating rate of 5°C / min. It is annealed for 1 hour to allow the PMMA microspheres to thermally decompose and volatilize. Then, it is heated to 500°C at the same heating rate and annealed for 3 hours to allow TiO2 to crystallize. It is cooled to room temperature to obtain PMMA-modified high-porosity mesoporous TiO2 electron transport material.

[0069] (7) Construction of perovskite solar cells: A FAPbI3 perovskite solution and a Spiro-OMeTAD hole transport layer were spin-coated onto the surface of the modified electron transport layer, followed by the deposition of 120 nm silver as electrodes. The fabricated device structure consisted of a conductive substrate / hole blocking layer / modified TiO2 electron transport layer / perovskite absorber layer / hole transport layer / electrode layer, with an effective cell area greater than 0.07 cm². 2 .

[0070] Example 3

[0071] A method for preparing a porous mesoscopic TiO2 electron transport material includes the following steps:

[0072] (1) Substrate preparation: Conductive glass FTO was used as the substrate for fabricating screen-printed perovskite devices. The conductive glass FTO was ultrasonically cleaned by sequentially immersing it in acetone, deionized water, and ethanol for 15 min each time, and then dried with nitrogen gas for later use.

[0073] (2) Preparation of hole blocking layer: Tetrabutyl titanate is used as titanium source, hydrochloric acid is added as nucleation inhibitor, and water is used as solvent. The mixture is kept at 75 °C for 45 min, then rinsed with water, and then annealed at 200~250 °C for 1~2 hours. After cooling to room temperature, a dense TiO2 film, i.e. hole blocking layer, is obtained. After being treated with ultraviolet ozone for 15 min, it is ready for use.

[0074] (3) Preparation of mesoporous TiO2 precursor: Take 10 mL of TiO2 colloid, add 40 mL of ethanol, stir evenly, add 0.2 mL of terpineol as a chelating agent, ball mill for 5 hours to form a uniform TiO2 sol, then add 0.8 g of polyethylene glycol (molecular weight 2000) as a mesoporous template agent, continue stirring for 1 hour to obtain mesoporous TiO2 precursor.

[0075] (4) Preparation of NH4HCO3 / TiO2 mixed slurry: Take NH4HCO3 powder with a particle size of 500 nm, disperse it in ethanol, and ultrasonically disperse it for 20 min to obtain an NH4HCO3 dispersion with a concentration of 20 mg / mL; take 200 μL of NH4HCO3 dispersion, add it to 1 mL of the mesoporous TiO2 precursor obtained in step (3), and ball mill for 2 hours; then add 0.03 g of ethyl cellulose as a thickener, and continue stirring for 30 min to obtain NH4HCO3 / TiO2 mixed slurry.

[0076] (5) Preparation of NH4HCO3 / TiO2 composite film: The above mixed slurry was coated on the surface of FTO / hole blocking layer by screen printing, and the wet film thickness was 2.0 μm; after preheating at 120℃ for 20 min, the solvent was removed to obtain an NH4HCO3 / TiO2 composite film with a dry film thickness of 1.2 μm.

[0077] (6) Stepwise annealing modification: The composite film is placed in a muffle furnace and heated to 300°C at a heating rate of 5°C / min. It is annealed for 1 hour to allow NH4HCO3 to thermally decompose and volatilize. Then, it is heated to 500°C at the same heating rate and annealed for 3 hours to allow TiO2 to crystallize. It is cooled to room temperature to obtain NH4HCO3 modified high porosity mesoporous TiO2 electron transport material.

[0078] (7) Construction of perovskite solar cells: A FAPbI3 perovskite solution and a Spiro-OMeTAD hole transport layer were spin-coated onto the surface of the modified electron transport layer, followed by the deposition of 120 nm silver as electrodes. The fabricated device structure consisted of a conductive substrate / hole blocking layer / modified TiO2 electron transport layer / perovskite absorber layer / hole transport layer / electrode layer, with an effective cell area greater than 0.07 cm². 2 .

[0079] Example 4

[0080] A method for preparing a porous mesoscopic TiO2 electron transport material includes the following steps:

[0081] (1) Substrate preparation: Conductive glass FTO was used as the substrate for fabricating screen-printed perovskite devices. The conductive glass FTO was ultrasonically cleaned by sequentially immersing it in acetone, deionized water, and ethanol for 15 min each time, and then dried with nitrogen gas for later use.

[0082] (2) Preparation of hole blocking layer: Tetrabutyl titanate is used as titanium source, hydrochloric acid is added as nucleation inhibitor, and water is used as solvent. The mixture is kept at 75 °C for 45 min, then rinsed with water, and then annealed at 200~250 °C for 1~2 hours. After cooling to room temperature, a dense TiO2 film, i.e. hole blocking layer, is obtained. After being treated with ultraviolet ozone for 15 min, it is ready for use.

[0083] (3) Preparation of mesoporous TiO2 precursor: Take 10 mL of TiO2 colloid, add 40 mL of ethanol, stir evenly, add 0.2 mL of terpineol as a chelating agent, ball mill for 5 hours to form a uniform TiO2 sol, then add 0.8 g of polyethylene glycol (molecular weight 2000) as a mesoporous template agent, continue stirring for 1 hour to obtain mesoporous TiO2 precursor.

[0084] (4) Preparation of P123 / TiO2 mixed slurry: P123 was diluted with ethanol to obtain a P123 solution with a concentration of 5 mg / mL; 200 μL of P123 solution was added to 1 mL of the mesoporous TiO2 precursor obtained in step (3), and ball milled for 2 hours; then 0.03 g of ethyl cellulose was added as a thickener, and stirring was continued for 30 min to obtain P123 / TiO2 mixed slurry.

[0085] (5) Preparation of P123 / TiO2 composite film: The above mixed slurry was coated on the surface of FTO / hole blocking layer by screen printing, and the wet film thickness was 2.0 μm; after preheating at 120℃ for 20 min, the solvent was removed to obtain a P123 / TiO2 film with a dry film thickness of 1.2 μm.

[0086] (6) Stepwise annealing modification: The composite film is placed in a muffle furnace and heated to 300°C at a heating rate of 5°C / min. It is annealed for 1 hour to allow P123 to thermally decompose and volatilize. Then, it is heated to 500°C at the same heating rate and annealed for 3 hours to allow TiO2 to crystallize. It is cooled to room temperature to obtain P123 modified high porosity mesoporous TiO2 electron transport material.

[0087] (7) Construction of perovskite solar cells: A FAPbI3 perovskite solution and a Spiro-OMeTAD hole transport layer were spin-coated onto the surface of the modified electron transport layer, followed by the deposition of 120 nm silver as electrodes. The fabricated device structure consisted of a conductive substrate / hole blocking layer / modified TiO2 electron transport layer / perovskite absorber layer / hole transport layer / electrode layer, with an effective cell area greater than 0.07 cm². 2 .

[0088] Comparative Example 1

[0089] A mesoporous TiO2 electron transport material, its preparation method, and its application in perovskite solar cells, comprising the following steps:

[0090] Hole-blocking layers and mesoporous TiO2 electron transport materials were prepared using the same method as in Example 1, but without pore-forming agent modification; the remaining steps were identical. Comparing Example 1 and Comparative Example 1, it can be seen that the present invention, through pore-forming agent modification, can reduce the defect state density of mesoporous TiO2 and improve electron mobility, porosity, and pore connectivity.

[0091] Based on the comparison of the test results of Example 1 and Comparative Example 1, the photoelectric conversion efficiency increased from 15.85% in Example 1 to 20.14% in Example 1.

[0092] Meanwhile, the multi-level porous transport material obtained in Example 1 mainly comprises two types of pores: mesopores and macropores. The mesopore size is concentrated in the range of 10–40 nm, while the macropore size ranges from 50–800 nm. In Comparative Example 1, no macropore template agent was added, and the resulting transport layer contained only mesopores (10–40 nm), while the macropores disappeared.

[0093] In addition, the test results are as follows Figure 1 As shown, Example 1 exhibits a better current density compared to the material in Comparative Example 1.

[0094] Comparative Example 2

[0095] The same preparation method as in Example 1 was used, except that a one-step annealing process was employed. Specifically, the annealing was carried out directly at 500°C for 3 hours without a low-temperature pre-decomposition stage.

[0096] Because the temperature is directly raised to 500°C, the PS microspheres will decompose rapidly during the heating process, and the gas release will be more concentrated, resulting in uneven pore structure and local pore collapse. The porosity will decrease from 61% in Example 1 to 47%.

[0097] The electron transport material obtained under these conditions has a PCE of 17.4% as tested.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical solutions of the present invention, using the methods and techniques disclosed above.

[0099] Therefore, any simple modifications, equivalent substitutions, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A porous mesoscopic electron transport layer material, characterized in that, The material uses anatase TiO2 as a matrix and has a mesoporous-macroporous hierarchical pore structure; the pore size of the mesopores is 10~40 nm and the pore size of the macropores is 50~800 nm.

2. A method for preparing a porous mesoscopic electron transport layer, characterized in that, Includes the following steps: (1) Provide a conductive substrate and prepare a hole blocking layer on the surface of the conductive substrate; (2) Mix TiO2 colloid, ethanol and terpineol and ball mill to form TiO2 sol, add mesoporous template agent and stir to obtain mesoporous TiO2 precursor; (3) Add the macroporous template agent to the mesoporous TiO2 precursor, mix and stir, add a thickener to obtain a composite slurry; (4) The composite paste is screen-printed onto the surface of the cavity blocking layer, and the solvent is removed by preheating to obtain a composite film; (5) The composite film is first annealed at 280~320℃ for 12 hours, then annealed at 480~520℃ for 24 hours, and then cooled to obtain the porous mesoscopic electron transport layer; The mesoporous template agent is used to form mesopores with a pore size of 10~40 nm; the macroporous template agent is used to form macropores with a pore size of 50~800 nm.

3. The preparation method according to claim 2, characterized in that, The mesoporous template agent is selected from one or more of polyethylene glycol and ethyl cellulose; the macroporous template agent is selected from one of polystyrene microspheres, polymethyl methacrylate microspheres, ammonium bicarbonate or block copolymer P123.

4. The preparation method according to claim 2, characterized in that, The amount of the mesoporous template agent added is 5-20% of the mass of TiO2 colloid.

5. The preparation method according to claim 2, characterized in that, When the macroporous template agent is polystyrene microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(2-15); when the macroporous template agent is polymethyl methacrylate microspheres, its dispersion concentration is 8-18 mg / mL, and the volume ratio of the dispersion to the TiO2 precursor is 1:(3-12); when the macroporous template agent is ammonium bicarbonate, its dispersion concentration is 1535 mg / mL, and the mass of the ammonium bicarbonate accounts for 4-12% of the mass of the TiO2 precursor; when the macroporous template agent is block copolymer P123, its solution concentration is 4-10 mg / mL, and the mass of P123 accounts for 2-8% of the mass of the TiO2 precursor.

6. The preparation method according to claim 2, characterized in that, In step (2), the volume ratio of TiO2 colloid, ethanol and terpineol is 1:(3~8):(0.05~0.3); in step (3), the thickener is ethyl cellulose or polyethylene glycol, and the amount added is 2~6% of the total mass of the composite slurry.

7. The preparation method according to claim 2, characterized in that, In step (4), the preheating temperature is 100~150℃ and the preheating time is 10~30 min; the wet film thickness of the composite film is 1.0~2.5 μm and the dry film thickness is 0.8~1.5 μm.

8. The preparation method according to claim 8, characterized in that, In step (5), the annealing heating rate is 3~15℃ / min. When the macroporous template agent is polymethyl methacrylate microspheres, the annealing at 280~320℃ is carried out under nitrogen protection. When the macroporous template agent is polystyrene microspheres, ammonium bicarbonate or block copolymer P123, the annealing at 280~320℃ is carried out in an air atmosphere.

9. The preparation method according to claim 8, characterized in that, In step (3), baking soda is added as an auxiliary pore-forming agent, and the mass ratio of baking soda to the macroporous template agent is (0.05~0.5):

1.

10. A perovskite solar cell, characterized in that, It comprises a conductive substrate, a hole blocking layer, an electron transport layer, a perovskite absorption layer, a hole transport layer, and an electrode layer stacked sequentially; wherein the electron transport layer is the porous mesoscopic electron transport layer material as described in any one of claims 1-2.

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