Nitrate modified titanium dioxide electron transport layer, perovskite solar cell and preparation method of perovskite solar cell

Abstract

The invention relates to a nitrate modified titanium dioxide electron transport layer, a perovskite solar cell and a preparation method of the perovskite solar cell. The preparation method of the nitrate modified titanium dioxide electron transport layer comprises the following steps: (1) adding inorganic nitrate and a titanium tetrachloride solution into deionized water to obtain a titanium dioxide water bath precursor solution; the inorganic nitrate is cerous nitrate (III) hexahydrate, lanthanum nitrate (III) hexahydrate or potassium nitrate, and the molar ratio of the inorganic nitrate to titanium tetrachloride in the titanium dioxide water bath precursor solution is 1-9 mol%; and (2) immersing a substrate in the titanium dioxide water bath precursor solution for hydrolysis reaction to obtain the nitrate modified titanium dioxide electron transport layer.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cells, specifically relating to a nitrate-modified titanium dioxide electron transport layer, a perovskite solar cell, and a method for preparing the same. Background Technology

[0002] With social development and technological advancements, relying solely on traditional fossil fuels can no longer meet humanity's energy needs, inevitably leading to a series of environmental problems. Solar energy, as a green, clean, and sustainable new energy source, perfectly aligns with the concept of sustainable development. Currently, the main way people utilize solar energy is by converting solar energy into electricity through solar cells.

[0003] Perovskite solar cells, as third-generation thin-film solar cells, possess advantages such as high photoelectric conversion efficiency, solution-based fabrication, and low cost, making them a highly promising solar energy utilization technology. Among them, planar perovskite solar cells, compared to mesoporous perovskite solar cells, have attracted considerable attention due to their simpler fabrication process, higher carrier extraction efficiency, and significant application potential in flexible and multilayer devices. In planar perovskite solar cells, the most commonly used inorganic electron transport layer materials are TiO2, SnO2, and ZnO, with SnO2-based perovskite solar cells achieving certified efficiencies exceeding 26%. However, the certified efficiencies of perovskite solar cells based on titanium dioxide electron transport layers still lag significantly behind. This efficiency gap is primarily due to the lower quality of the titanium dioxide electron transport layer and its poor interfacial contact with the perovskite layer.

[0004] Titanium dioxide is a widely used electron transport layer material, and researchers have proposed various methods to prepare titanium dioxide thin films on fluorine-doped tin oxide (FTO) substrates, including atomic layer deposition, magnetron sputtering, electron beam evaporation, and chemical bath deposition. Compared with spin coating, atomic layer deposition, magnetron sputtering, and electron beam evaporation, which require expensive equipment and high processing temperatures, chemical bath deposition has the advantages of low cost, simple operation, and can be achieved at a low temperature of around 70°C. Although chemical bath deposition of titanium dioxide electron transport layers has advantages such as simple process, low cost, and conformal deposition, the rapid and violent hydrolysis reaction during the chemical bath deposition of titanium dioxide leads to significant agglomeration of titanium dioxide nanoparticles and generates a large number of oxygen vacancies. This results in uneven coverage of the titanium dioxide electron transport layer on the FTO substrate, which is not conducive to the growth of perovskite films and also leads to poor contact with the perovskite layer, forming more pores at the TiO2 / perovskite interface, which is not conducive to the effective extraction of charge carriers.

[0005] Therefore, regulating the deposition process of titanium dioxide nanoparticles in the chemical bath deposition process to improve the quality of the titanium dioxide electron transport layer and enhance the TiO2 / perovskite interface contact is an effective method to achieve high-quality perovskite thin films and improve the efficiency and stability of perovskite solar cell devices. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a nitrate-modified titanium dioxide electron transport layer, a perovskite solar cell, and a method for preparing the same. By adding simple inorganic small-molecule compounds to regulate the deposition process of titanium dioxide in a chemical bath, the hydrolysis rate of titanium tetrachloride is slowed down, the aggregation of titanium dioxide nanoparticles is suppressed, and the nucleation and growth of titanium dioxide nanocrystals are controlled. This improves the quality of the titanium dioxide electron transport layer and mitigates problems such as poor interfacial contact between titanium dioxide and the perovskite film, thereby enabling the fabrication of a high-efficiency planar perovskite solar cell with titanium dioxide as the electron transport layer.

[0007] In a first aspect, the present invention provides a method for preparing a nitrate-modified titanium dioxide electron transport layer, the method comprising the following steps: (1) Add inorganic nitrate and titanium tetrachloride solution to deionized water to obtain titanium dioxide water bath precursor solution; The inorganic nitrate is cerium(III) hexahydrate, lanthanum(III) hexahydrate, or potassium nitrate, and the molar ratio of inorganic nitrate to titanium tetrachloride in the titanium dioxide water bath precursor solution is 1-9 mol%. (2) The substrate is immersed in the titanium dioxide water bath precursor solution to carry out a hydrolysis reaction to obtain the nitrate modified titanium dioxide electron transport layer.

[0008] Preferably, in step (1), the concentration of the titanium tetrachloride solution is 0.018 to 3 mol / L, more preferably 2.5 to 3 mol / L, and the volume ratio of the titanium tetrachloride solution to deionized water is 2:(25 to 100).

[0009] Preferably, in step (2), the substrate is FTO; preferably, the substrate is treated in an ultraviolet ozone cleaner for 20 to 60 minutes before immersion.

[0010] Preferably, in step (2), the temperature of the hydrolysis reaction is 40 to 150°C and the reaction time is 0.5 to 6 hours.

[0011] Secondly, the present invention provides a nitrate-modified titanium dioxide electron transport layer obtained according to the above preparation method, wherein the thickness of the nitrate-modified titanium dioxide electron transport layer is 20-120 nm.

[0012] Thirdly, the present invention provides a perovskite solar cell, wherein the structure of the perovskite solar cell, from bottom to top, comprises: a glass substrate, an FTO transparent conductive electrode, the aforementioned nitrate-modified titanium dioxide electron transport layer, a perovskite layer, a passivation layer, a hole transport layer, and a metal electrode layer.

[0013] Preferably, the thickness of the perovskite layer is greater than 500 nm, more preferably 500–1200 nm, and even more preferably 700 nm; The passivation layer material is PEAI, BAI or OACl, and the thickness is 5-30 nm, preferably 10 nm. The hole transport layer is Spiro-OMeTAD, PTAA, PEDOT:PSS, CuSCN, or NiO. X The thickness is 100-300 nm, preferably 150 nm; The metal electrode layer material is Ag, Au, Cu, Al or Pt, and the thickness is 60-120 nm, preferably 100 nm.

[0014] Fourthly, the present invention provides a method for preparing the above-mentioned perovskite solar cell, the method comprising the following steps: sequentially preparing a perovskite thin film, a passivation layer and a hole transport layer on a glass substrate / FTO / the above-mentioned nitrate-modified titanium dioxide electron transport layer, and then preparing a metal electrode layer on the hole transport layer to obtain the perovskite solar cell.

[0015] Beneficial effects This invention modulates the deposition process of titanium dioxide in a chemical bath by adding nitrate to the precursor solution, thereby slowing down the hydrolysis rate of titanium tetrachloride and regulating the nucleation and growth of titanium dioxide nanocrystals. This reduces the aggregation problem of titanium dioxide nanocrystals and improves the interfacial contact between the titanium dioxide electron transport layer and the perovskite film. Furthermore, the nitrate adsorbed on the titanium dioxide surface slows down the crystallization rate of perovskite, improving the quality of the perovskite film. The combined effect of these two factors enables the fabrication of a high-efficiency titanium dioxide-based planar perovskite solar cell. Attached Figure Description

[0016] Figure 1 A schematic diagram of the perovskite solar cell structure based on a nitrate-modified titanium dioxide electron transport layer prepared in Example 1; Figure 2 The images show the surface and cross-sectional morphology of standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1. Figure 3The images show the surface and cross-sectional morphology of perovskite films grown on standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1, with the bar chart representing the perovskite grain size statistics. Figure 4 The JV curves are shown for perovskite solar cells with standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1 as electron transport layers. Figure 5 The JV curves are for perovskite solar cells based on different nitrates. Detailed Implementation

[0017] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0018] First, this invention provides a chemical bath deposition method for preparing a nitrate-modified titanium dioxide electron transport layer. The method for preparing the nitrate-modified titanium dioxide electron transport layer may include the following steps: (1) Add inorganic nitrate and titanium tetrachloride solution to deionized water to obtain titanium dioxide water bath precursor solution; (2) The substrate is immersed in the titanium dioxide water bath precursor solution for heating reaction. After the reaction is completed, the substrate is taken out and its surface is cleaned and dried to obtain the nitrate modified titanium dioxide electron transport layer.

[0019] In some embodiments, in step (1), the inorganic nitrate can be an inorganic salt with nitrate as the anion and which is soluble in water, preferably cerium(III) nitrate hexahydrate, lanthanum(III) nitrate hexahydrate or potassium nitrate.

[0020] In some embodiments, in step (1), the concentration of the titanium tetrachloride solution can be 0.018–3 mol / L, preferably 2.5–3 mol / L, and the volume ratio of the titanium tetrachloride solution to deionized water can be 2:(25–100); preferably, the molar ratio of inorganic nitrate to titanium tetrachloride in the titanium dioxide water bath precursor solution can be 1–9 mol%.

[0021] By controlling the concentration of titanium tetrachloride solution within the aforementioned range, its stable storage can be ensured, reducing concentration fluctuations caused by its volatility. Furthermore, by controlling the volume ratio of titanium tetrachloride solution to deionized water, the concentration of titanium tetrachloride solution participating in the chemical bath reaction can be controlled. Excessive titanium tetrachloride concentration leads to an excessively rapid hydrolysis reaction rate, resulting in large and severely agglomerated deposited titanium dioxide nanoparticles; conversely, insufficient concentration hinders the hydrolysis reaction, resulting in an excessively thin titanium dioxide layer deposited on the substrate surface. Both of these situations negatively impact device performance. Simultaneously, if the molar ratio of inorganic nitrate to titanium tetrachloride is less than 1 mol%, the nitrate cannot effectively inhibit the agglomeration of titanium dioxide nanoparticles, resulting in poor-quality titanium dioxide films with low transmittance. This leads to numerous defects in the titanium dioxide electron transport layer, hindering electron extraction and transport, and negatively affecting the device's performance. SC It has an adverse effect; while a concentration higher than 9 mol% is not conducive to the hydrolysis reaction of titanium tetrachloride, excessively slowing down the hydrolysis reaction rate. Under the same reaction time, the deposited titanium dioxide film is too thin and cannot completely cover the surface of FTO, which is not conducive to electron extraction and transport, increases process cost, and affects device performance.

[0022] In some embodiments, in step (2), the substrate can be FTO; preferably, the substrate is pretreated in an ultraviolet-ozone cleaner for 20-60 minutes before immersion. Ultraviolet-ozone cleaning of the FTO substrate can effectively improve the surface wettability of the FTO substrate, making it easier for titanium dioxide nanoparticles to be adsorbed onto the surface of the FTO substrate.

[0023] In some embodiments, in step (2), the heating reaction temperature can be 40–150°C, and the reaction time can be 0.5–6 hours. By controlling the appropriate heating temperature and heating time, the suitable hydrolysis reaction rate of titanium tetrachloride and the thickness of the titanium dioxide film can be ensured.

[0024] In the preparation method provided by this invention, titanium dioxide is generated by the hydrolysis reaction of titanium tetrachloride and water (TiCl4 + H2O → TiO2 + HCl). This hydrolysis reaction is reversible. Nitrate compounds are mixed with the titanium dioxide hydrolysis precursor solution by dissolving them in water beforehand. The introduced nitrates can participate in the hydrolysis process of titanium tetrachloride (the equilibrium of the hydrolysis reaction moves to the reverse reaction), thereby slowing down the hydrolysis rate, inhibiting the hydrolysis of titanium tetrachloride, and reducing the intensity of the reaction. Moreover, in the subsequent nucleation and growth of titanium dioxide grains, the steric hindrance effect of the inorganic metal cations in the nitrates can inhibit the aggregation and growth of titanium dioxide nanocrystals (without changing its chemical structure), ultimately promoting the formation of a denser and smoother titanium dioxide film. Unlike conventional technical solutions that use organic nitrates for modification, this method utilizes organic cations and Ti... 4+The ligand interactions between them inhibit the aggregation of titanium dioxide nanoparticles by forming chelates through changes in their chemical structure.

[0025] Furthermore, after the titanium dioxide film is formed, the smooth surface morphology can improve the interfacial contact between the titanium dioxide film and the perovskite film; and the nitrate ions adsorbed on the surface of titanium dioxide can slow down the crystallization rate of the perovskite film on the titanium dioxide film, which is conducive to the formation of high-quality perovskite film, reduces interfacial defects, enhances interfacial charge transport, and improves battery efficiency.

[0026] Therefore, in summary, the nitrate compounds introduced in this invention have two effects: (1) for the titanium dioxide thin film layer, they can regulate the nucleation and growth of titanium dioxide, inhibit grain agglomeration, promote the formation of a dense and smooth titanium dioxide thin film, and improve the interfacial contact between the perovskite thin film and the titanium dioxide thin film; (2) for the perovskite thin film layer, the nitrate ions present on the surface of the titanium dioxide thin film can slow down the crystallization rate of the perovskite thin film, reduce interfacial defects, and enhance interfacial charge transport.

[0027] The nitrate-modified titanium dioxide electron transport layer obtained by the preparation method provided by this invention can have a thickness of 20-120 nm.

[0028] Furthermore, the present invention also provides a perovskite solar cell. The structure of the perovskite solar cell, from bottom to top, may consist of: a glass substrate, an FTO transparent conductive electrode, the aforementioned nitrate-modified titanium dioxide electron transport layer, a perovskite layer, a passivation layer, a hole transport layer, and a metal electrode layer.

[0029] In some embodiments, the thickness of the perovskite layer can be greater than 500 nm, preferably 500–1200 nm, and more preferably 700 nm. This ensures that the perovskite film can absorb sufficient light while preventing excessive thickness from causing an increase in photogenerated carrier recombination.

[0030] In some embodiments, the passivation layer material can be PEAI, BAI, or OAC1, and the thickness can be 5–30 nm, preferably 10 nm. The addition of the passivation layer can passivate surface defects in the perovskite thin film; however, excessive thickness can easily affect carrier transport and conductivity.

[0031] In some embodiments, the hole transport layer can be Spiro-OMeTAD, PTAA, PEDOT:PSS, CuSCN, or NiOX; the thickness can be 100–300 nm, preferably 150 nm. This ensures an effective built-in electric field without affecting conductivity.

[0032] In some embodiments, the metal electrode layer material can be Ag, Au, Cu, Al, or Pt; the thickness can be 60–120 nm, preferably 100 nm. This ensures effective electron collection while keeping costs within a controllable range.

[0033] In some embodiments, the performance parameters of the perovskite solar cell provided by the present invention are as follows: short-circuit current density (J / L) SC 25.00-26.20 mA / cm 2 Open circuit voltage (V) OC 1.05-1.17V, fill factor (FF) 75-81%, power conversion efficiency (PCE) 21.50-24.80%.

[0034] The following is an exemplary description of the fabrication method of the perovskite solar cell described above. The fabrication method may include the following steps: sequentially fabricating a perovskite thin film, a passivation layer, and a hole transport layer on a glass substrate / FTO / the aforementioned nitrate-modified titanium dioxide electron transport layer using a spin-coating process; then fabricating a metal electrode layer on the hole transport layer using a vacuum evaporation process to obtain the perovskite solar cell.

[0035] The preparation method provided by this invention regulates the deposition process of titanium dioxide in a chemical bath by adding nitrate to the precursor solution, thereby moderating the hydrolysis rate of titanium tetrachloride and controlling the nucleation and growth of titanium dioxide nanocrystals. This reduces the aggregation problem of titanium dioxide nanocrystals and improves the interfacial contact between the titanium dioxide electron transport layer and the perovskite film. Furthermore, the nitrate adsorbed on the surface of titanium dioxide slows down the crystallization rate of perovskite, improving the quality of the perovskite film. The combined effect of these two methods ultimately enables the preparation of a high-efficiency titanium dioxide-based planar perovskite solar cell.

[0036] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0037] Example 1

[0038] The method for preparing the nitrate-modified titanium dioxide electron transport layer and perovskite solar cell provided in this embodiment includes the following steps: 1. Cleaning the conductive glass substrate: The FTO conductive glass is ultrasonically cleaned once with deionized water, ethanol and deionized water in sequence, each time for 15 minutes. After cleaning, it is dried with dry air to obtain a clean conductive glass substrate. 2. Preparation of titanium dioxide electron transport layer: (1) Add 0.2345 g of cerium(III) nitrate hexahydrate (0.0005 mol) and 6 ml of water to 94 ml of deionized water. (1) A 3M titanium tetrachloride (0.018 mol) solution (the molar ratio of inorganic nitrate to titanium tetrachloride is 3 mol%) was stirred thoroughly to obtain a titanium dioxide water bath precursor solution; (2) The clean FTO substrate was treated under a UV-ozone surface treatment device for 30 min to form a hydrophilic surface. The FTO substrate after ozone treatment was placed in a glass frame and then placed in a glass tank. The FTO substrate was kept vertical in the glass tank. The titanium dioxide water bath precursor solution prepared in step (1) was slowly poured into the glass tank and the precursor solution was used to immerse the FTO substrate. Finally, the glass tank was placed in an oven and heated in the oven at 70°C for 2.5 h. After the reaction was completed, the glass tank was removed from the oven and the hydrolyzed FTO sample was removed from the glass tank and rinsed with deionized water. The rinsed FTO substrate was then ultrasonically cleaned and dried with dry air after rinsing to obtain a nitrate-modified titanium dioxide electron transport layer. 3. Preparation of perovskite thin film layer (FA) 0.92 MA 0.08 PbI3 system: Prepare a 1.5M PbI2 precursor solution in a mixture of DMF and DMSO (9:1 volume ratio). Spin-coat the lead iodide solution onto an FTO / TiO2 substrate at 1500 rpm for 30 seconds. After spin-coating, anneal the lead iodide film on a hot plate at 70°C for 1 minute. Prepare an organic ammonium salt solution by weighing 90 mg FAI, 6.40 mg MAI, and 9 mg MACl and dissolving them in 1 ml isopropanol. Spin-coat the organic ammonium salt solution onto the lead iodide film at 1500 rpm for 30 seconds. After spin-coating, anneal the perovskite film on a hot plate at 150°C for 15 minutes to obtain the perovskite film layer. 4. Preparation of passivation layer: Prepare a 5 mg / ml passivation layer PEAI solution with isopropanol as the solvent; spin-coat the passivation layer solution onto the perovskite film using a spin-coating method at a speed of 3000 rpm for 30 s. After spin-coating, vacuum the sample for 15 min to obtain the passivation layer. 5. Preparation of Spiro-OMeTAD hole transport layer: Weigh 72.3g of Spiro-OMeTAD powder into a bottle, add 1ml of chlorobenzene, dissolve, then add 28.8μl of 4-tert-butylpyridine (t-BP) and 17.5μl of Li-TFSI solution to the solution to increase its conductivity. Stir evenly, then add 29μl of FK209 Co-TFSI solution and stir overnight to ensure that the Spiro-OMeTAD solution is fully oxidized. Spin-coat the Spiro-OMeTAD solution onto the perovskite thin film passivation layer using a spin-coating method at a speed of 4000rpm and a spin-coating time of 30s to obtain the hole transport layer. 6. Preparation of silver electrode: A silver electrode with a thickness of approximately 100 nm was prepared by vacuum evaporation to obtain the perovskite solar cell, with the structure as shown below. Figure 1 As shown.

[0039] The following investigation, referring to the preparation method in Example 1, explores the effect of the modified titanium dioxide electron transport layer with different molar ratios of cerium(III) nitrate hexahydrate to titanium tetrachloride on the performance of the finally prepared perovskite solar cell.

[0040] The main difference between the preparation method and Example 1 is that the concentration of the titanium tetrachloride solution is 0.018 M, and the molar ratio of cerium(III) nitrate hexahydrate to titanium tetrachloride is 0 / 1 / 3 / 5 / 9 mol.

[0041] Table 1 below shows the performance parameters of titanium dioxide-based perovskite solar cells modified with different concentrations of cerium(III) nitrate hexahydrate:

[0042] As shown in Table 1, in this first batch of experiments, when cerium(III) hexahydrate was used as an additive to prepare the nitrate-modified titanium dioxide electron transport layer, the content of cerium(III) hexahydrate had a significant impact on the photoelectric conversion efficiency of the battery. Compared with the control group perovskite solar cell, the photoelectric conversion efficiency of the nitrate-modified titanium dioxide perovskite solar cell was significantly improved. The highest energy conversion efficiency was achieved when 3 mol% of cerium(III) hexahydrate was introduced into a 0.018 M titanium tetrachloride solution.

[0043] The following investigation, referring to the preparation method in Example 1, explores the effect of the modified titanium dioxide electron transport layer with different molar ratios of potassium nitrate and titanium tetrachloride on the performance of the finally prepared perovskite solar cell.

[0044] The main difference between the preparation method and Example 1 is that the added nitrate is potassium nitrate, the concentration of the titanium tetrachloride solution is 0.018M, and the molar ratio of potassium nitrate to titanium tetrachloride is 0 / 1 / 3 / 5 / 9 mol.

[0045] Table 2 below shows the performance parameters of titanium dioxide-based perovskite solar cells modified with different concentrations of potassium nitrate:

[0046] As shown in Table 2, in this second batch of experiments, when potassium nitrate was used as an additive to prepare the nitrate-modified titanium dioxide electron transport layer, the potassium nitrate content had a significant impact on the photoelectric conversion efficiency of the battery. Compared with the control group perovskite solar cell, the photoelectric conversion efficiency of the nitrate-modified titanium dioxide perovskite solar cell was significantly improved. The highest efficiency was achieved when 3 mol% potassium nitrate was introduced into a 0.018 M titanium tetrachloride solution. Furthermore, the data in Tables 1 and 2 show that when the nitrate concentration is too low, the effect on improving the performance of the titanium dioxide electron transport layer is limited, while when the nitrate concentration is too high, it severely inhibits the hydrolysis of titanium tetrachloride, resulting in an excessively thin titanium dioxide film prepared under the same reaction time. This is detrimental to electron transport and extraction, leading to a decrease in device performance.

[0047] The following investigation, referring to the preparation method in Example 1, explores the effect of different nitrate-modified titanium dioxide electron transport layers at the same concentration on the performance of the finally prepared perovskite solar cell.

[0048] In this experiment, the molar ratio of nitrate to titanium tetrachloride was 3 mol%, and the main difference between the preparation method and Example 1 was that the titanium tetrachloride solution concentration was 0.018 M, and Ce(NO3)3·6H2O, La(NO3)3·6H2O, and KNO3 were used as modifiers, respectively. Control indicates that the standard devices modified with nitrate were not added in this third batch of experiments.

[0049] Table 3 below shows the performance parameters of titanium dioxide-based perovskite solar cells modified with different nitrates:

[0050] As can be seen from Table 3 above, in this third batch of experiments, compared with the standard perovskite solar cell (Control) with titanium dioxide as the electron transport layer, the nitrate-modified titanium dioxide-based battery device has higher efficiency, indicating that the nitrate-modified chemical bath deposition method proposed in this invention can be achieved by a variety of simple nitrate compounds and has a certain degree of universality.

[0051] Figure 2The figures show the surface and cross-sectional morphology of standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1. As can be seen from the figures, the surface of the nitrate-modified titanium dioxide is smoother and denser, with a significant reduction in agglomerated protruding structures. The cross-sectional morphology shows that the electron transport layer of the nitrate-modified titanium dioxide is significantly thinner, and the nanocrystals are more uniformly distributed, which is more conducive to electron extraction and transport. This also indicates that the nitrate-modified chemical bath deposition strategy proposed in this invention can significantly regulate the titanium dioxide deposition process and inhibit the agglomeration of titanium dioxide grains.

[0052] Figure 3 Images show the surface and cross-sectional morphology of perovskite films grown on standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1, with the bar chart representing perovskite grain size statistics. Figure 3 As can be seen from the data, the nitrate-modified titanium dioxide substrate can promote the formation of high-quality perovskite films with larger grain size and less lead iodide particle enrichment; from its cross-sectional morphology, it can be seen that the nitrate-modified substrate is more conducive to the growth of perovskite crystals in the vertical direction and the contact is also tighter.

[0053] Figure 4 The JV curves are shown for perovskite solar cells using standard titanium dioxide (Control) and nitrate-modified titanium dioxide (Target) prepared in Example 1 as the electron transport layer. From... Figure 4 As can be seen, the photoelectric conversion efficiency of standard titanium dioxide and nitrate-modified titanium dioxide perovskite solar cells is significantly higher than that of standard titanium dioxide-based solar cells. The optimal device based on the nitrate-modified titanium dioxide electron transport layer achieves a photoelectric conversion efficiency of 24.24%, which is significantly higher than that of standard titanium dioxide-based solar cells. Table 4 below lists a detailed parameter comparison of the two devices, demonstrating that the nitrate-modified titanium dioxide electron transport layer in this invention has outstanding effects in improving the quality of the titanium dioxide electron transport layer, promoting the formation of high-quality perovskite thin films, and enhancing cell performance. Table 4. Comparison of performance parameters of the best-performing devices based on standard titanium dioxide and nitrate-modified titanium dioxide.

[0054] Figure 5 This is a JV curve diagram for perovskite solar cells based on different nitrates. From... Figure 5As can be seen, the titanium dioxide electron transport layer prepared by adding different nitrates has different effects on the efficiency of the battery. The choice of nitrate type is also crucial to the photoelectric conversion efficiency of the battery. When preparing titanium dioxide electron transport layers using the nitrate-modified chemical bath method, the electronegativity, molecular size, configuration, and oxidizing properties of different nitrates will affect the performance of the nitrate-modified titanium dioxide electron transport layer. At the same time, in large-scale production, the choice of different nitrate types will affect the production cost.

[0055] In summary, the nitrate-modified titanium dioxide electron transport layer and its preparation method proposed in this invention solve the problems of rough surface and poor interfacial contact of titanium dioxide films prepared by ordinary chemical bath methods by using simple and low-cost nitrates. It also promotes the formation of high-quality perovskite films, significantly improves the photoelectric conversion efficiency of perovskite solar cells, and is compatible with different perovskite film preparation processes, such as the common two-step spin coating method and one-step spin coating method, and has good commercial potential.

[0056] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a nitrate-modified titanium dioxide electron transport layer, characterized in that, The preparation method includes the following steps: (1) Add inorganic nitrate and titanium tetrachloride solution to deionized water to obtain titanium dioxide water bath precursor solution; The inorganic nitrate is cerium(III) hexahydrate, lanthanum(III) hexahydrate, or potassium nitrate, and the molar ratio of inorganic nitrate to titanium tetrachloride in the titanium dioxide water bath precursor solution is 1-9 mol%. (2) The substrate is immersed in the titanium dioxide water bath precursor solution to carry out a hydrolysis reaction to obtain the nitrate modified titanium dioxide electron transport layer.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the titanium tetrachloride solution is 0.018 to 3 mol / L, preferably 2.5 to 3 mol / L, and the volume ratio of the titanium tetrachloride solution to deionized water is 2:(25 to 100).

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the substrate is FTO; preferably, the substrate is treated in an ultraviolet ozone cleaner for 20 to 60 minutes before immersion.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (2), the temperature of the hydrolysis reaction is 40 to 150°C and the reaction time is 0.5 to 6 hours.

5. A nitrate-modified titanium dioxide electron transport layer obtained by the preparation method according to any one of claims 1-4, characterized in that, The thickness of the nitrate-modified titanium dioxide electron transport layer is 20–120 nm.

6. A perovskite solar cell, characterized in that, The perovskite solar cell has the following structure from bottom to top: a glass substrate, an FTO transparent conductive electrode, a nitrate-modified titanium dioxide electron transport layer as described in claim 5, a perovskite layer, a passivation layer, a hole transport layer, and a metal electrode layer.

7. The perovskite solar cell according to claim 6, characterized in that, The thickness of the perovskite layer is greater than 500 nm, preferably 500–1200 nm, and more preferably 700 nm; The passivation layer material is PEAI, BAI or OACl, and the thickness is 5-30 nm, preferably 10 nm. The hole transport layer is Spiro-OMeTAD, PTAA, PEDOT:PSS, CuSCN, or NiO. X The thickness is 100-300 nm, preferably 150 nm; The metal electrode layer material is Ag, Au, Cu, Al or Pt, and the thickness is 60-120 nm, preferably 100 nm.

8. A method for preparing a perovskite solar cell according to claim 6 or 7, characterized in that, The preparation method includes the following steps: sequentially preparing a perovskite thin film, a passivation layer, and a hole transport layer on a glass substrate / FTO / nitrate-modified titanium dioxide electron transport layer as described in claim 5, and then preparing a metal electrode layer on the hole transport layer to obtain the perovskite solar cell.

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