A method for preparing TiO2 nanoparticle colloids without organic and acid / base stabilizers and its application.

Abstract

This invention discloses a method for preparing TiO2 nanoparticle colloids without organic and acid / base stabilizers and their applications. The method for preparing TiO2 nanoparticle colloids includes the following steps: S1, mixing a low-element amine, a hydrohalic acid, and a low-element alcohol to obtain reactant A; S2, adding a titanium salt to reactant A to obtain reactant B; S3, adding deionized water dropwise to reactant B and stirring thoroughly to obtain TiO2 nanoparticle colloids. x Precursor sol C; S4. Sol C is placed in a reactor and subjected to hydrothermal reaction to obtain TiO2 nanoparticle colloid. The TiO2 nanoparticles of this invention have uniform particle size and high crystallinity. The colloid does not contain acids, alkalis, or non-volatile organic compounds, and does not damage the substrate during subsequent film formation and device fabrication, eliminating the need for high-temperature annealing. When TiO2 nanoparticles are used as a mesoporous electron transport layer in perovskite solar cells, rigid cells can achieve a photoelectric conversion efficiency of over 22%, and flexible cells can achieve a photoelectric conversion efficiency of over 20%.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials and devices, specifically relating to a method for preparing TiO2 nanoparticle colloids without organic and acid / base stabilizers and their applications. Background Technology

[0002] TiO2 is a classic n-type semiconductor material with excellent performance, low cost, and good stability, making it widely used in coatings, photocatalysis, solar cells, and energy storage batteries. For example, TiO2 nanoparticles are the most commonly used electron transport layer material for low-cost, high-efficiency perovskite solar cells. The TiO2 nanoparticle colloidal coating method is an important approach for preparing TiO2 thin films. Therefore, the composition and particle properties of the TiO2 nanoparticle colloid have a crucial impact on the preparation process and performance of TiO2 thin films. To obtain fine, uniform, and stable TiO2 nanoparticle colloids, it is often necessary to add non-volatile organic compounds such as high alcohols, macromolecules, or polymers as stabilizers to the reaction precursor. After film formation, these organic compounds need to be removed by high-temperature sintering (~500℃) (J. Phys. Chem. C 2012, 116, 8888-8893). High-temperature sintering is an energy-intensive and time-consuming post-processing method and cannot be applied to flexible plastic substrates and flexible devices that are not heat-resistant. Without using non-volatile organic compounds and polymeric stabilizers, it is often necessary to control the size and stability of TiO2 nanoparticles by adding high concentrations of acids / bases (hydrochloric acid, nitric acid, acetic acid, sodium hydroxide, etc.). Existing techniques utilize high-concentration aqueous acetic acid solutions as solvents to effectively slow down the hydrolysis of isopropyl titanate, forming a uniform and stable sol. This sol, through which highly crystalline anatase TiO2 nanoparticles with a particle size of ~30 nm can be prepared via hydrothermal reaction, enabling the low-temperature preparation of TiO2 thin films (ACS Appl. Mater. Interfaces 2015, 7, 19431-19438). However, the high concentration of acetic acid in the colloid is highly irritating and corrosive, harmful to human health. Furthermore, in photovoltaic and optoelectronic device applications, the acid in this TiO2 colloid can corrode the conductive layers or other functional layers of commonly used substrates such as ITO (Sn-doped In2O3) and metal nanowires, hindering the fabrication of high-performance electrodes and devices, and even causing device failure.

[0003] Therefore, developing a simple process that does not require non-volatile organic stabilizers or acid / base stabilizers to prepare TiO2 nanoparticle colloids with controllable particle size, high crystallinity, and excellent stability is essential for achieving low-temperature fabrication of high-quality TiO2 thin films. This is also key to narrowing the performance gap between rigid devices fabricated at high temperatures and flexible devices fabricated at low temperatures. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing TiO2 nanoparticle colloids without organic and acid / base stabilizers and its application.

[0005] The problem to be solved by this invention is to provide a simple process for preparing highly crystalline anatase TiO2 nanoparticle colloids with adjustable and uniform particle size, good stability and repeatability, and a high-efficiency perovskite solar cell based on the mesoporous electron transport layer of the TiO2 nanoparticles, without using non-volatile organic solvents, macromolecules / polymers or acid / base stabilizers.

[0006] This invention utilizes R generated by the reaction of a low-element amine in solution with a hydrogen halide acid HX (X = Cl, Br, I) x NH 4-x + (R = CH3, CH3CH2, etc., x = 1, 2, 3) Cations are used as adsorbed ions to synthesize stable TiO2 nanoparticle colloids. The added trace amounts of hydrogen halide acid HX (X = Cl, Br, I) are consumed in the reaction. The particle size of the TiO2 nanoparticles is tunable in the range of 10-35 nm. Using this TiO2 nanoparticle colloid, a high-quality mesoporous electron transport layer is prepared by a low-temperature annealing process, thereby obtaining rigid perovskite solar cells with high repeatability and high photoelectric conversion efficiency (photoelectric conversion efficiency exceeding 22%) and flexible perovskite solar cells based on plastic conductive substrates (photoelectric conversion efficiency up to 20.5%).

[0007] The TiO2 nanoparticles of this invention are obtained by the controlled hydrolysis and sol-gelation of titanium salts such as isopropyl titanate in a mixed solution of low-element amines, trace amounts of hydrogen halides HX (X = Cl, Br, I), and low-element alcohols, followed by a hydrothermal reaction. The colloid is stabilized by adsorbing small-radius cations generated by the reaction of low-element alcohols and hydrogen halides.

[0008] The mesoporous TiO2 nanoparticle electron transport layer described in this invention is obtained by annealing after TiO2 nanoparticle colloidal coating.

[0009] The perovskite solar cell of the present invention comprises a transparent conductive substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode.

[0010] Preferably, the transparent conductive substrate is FTO, ITO conductive glass, or ITO / PEN, ITO / PET flexible substrate.

[0011] Preferably, the perovskite light-absorbing layer is FA. x MA 1-x PbI3.

[0012] Preferably, the hole transport layer is a mixed solution of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD), lithium bis(trifluoromethanesulfonate imide) (LiTFSI), 4-tert-butylpyridine and tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III)tris[bis(trifluoromethane)sulfonylimide (FK209).

[0013] Preferably, the metal electrode is a gold electrode.

[0014] To achieve the objectives of this invention, the following technical solution is adopted.

[0015] This invention provides a method for preparing TiO2 nanoparticle colloids, comprising the following steps:

[0016] (1) Add the low-element amine, trace amount of hydrohalic acid HX (X = Cl, Br, I), and ionic salt to the low-element alcohol and dissolve them completely to obtain a mixed solution;

[0017] (2) Mix the titanium salt and the mixed solution obtained in step (1) evenly (preferably stir for 60 min) to obtain a titanium salt solution;

[0018] (3) Under ice-water bath conditions, deionized water is added dropwise to the titanium salt solution obtained in step (2), and the reaction is carried out for a certain time with stirring at an appropriate temperature to obtain TiO2. x Sol;

[0019] (4) Add the TiO2 obtained in step (3) x An appropriate amount of deionized water was added to the sol, and then it was transferred to a hydrothermal reactor. After the hydrothermal reaction was completed, TiO2 nanoparticle colloids were obtained by ultrasonic dispersion.

[0020] Further, the low-element amine mentioned in step (1) is one or more of ethylenediamine, propylenediamine, and diethylamine, and the concentration of the low-element amine in the mixed solution is 1-30 mmol / L.

[0021] Further, the concentration of the hydrohalic acid in step (1) in the mixed solution is 1-20 mmol / L.

[0022] Further, the ionic salt in step (1) is one or more of LiCl, SnCl2, and NbCl5, which can be used to prepare element-doped TiO2 nanoparticles. The concentration of the ionic salt in the mixed solution is 0.3-6 mmol / L.

[0023] Further, the low alcohol in step (1) is one or more of methanol, ethanol, and isopropanol.

[0024] More preferably, the low alcohol in step (1) is ethanol.

[0025] More preferably, the low-element amine in step (1) is ethylenediamine, and its concentration in the mixed solution is 10 mmol / L.

[0026] More preferably, the hydrohalic acid in step (1) is HI, and its concentration in the mixed solution is 8 mmol / L.

[0027] Further, the titanium salt in step (2) is one or more of tetrabutyl titanate and isopropyl titanate, and the volume ratio of the titanium salt to the mixed solution is 1-20 mL: 100 mL.

[0028] More preferably, the titanium salt in step (2) is selected as isopropyl titanate, and the volume ratio of the titanium salt to the mixed solution is 10 mL: 100 mL.

[0029] Furthermore, in step (3), when water is added dropwise to the titanium salt solution, the titanium salt solution is placed in an ice-water bath; the volume ratio of deionized water to titanium salt solution in step (3) is 50-3000 μL: 100 mL.

[0030] Furthermore, the temperature of the stirring reaction in step (3) is 20-70℃; the stirring reaction time is 2-12h.

[0031] More preferably, the volume ratio of deionized water to titanium salt solution in step (3) is 1500 μL: 100 mL.

[0032] More preferably, the temperature of the stirring reaction in step (3) is 50°C; and the stirring reaction time is 12h.

[0033] Further, the deionized water and TiO2 in step (4) x The volume ratio of the sol is 0-6 mL: 100 mL.

[0034] Furthermore, the temperature of the hydrothermal reaction in step (4) is 150-240℃, and the time of the hydrothermal reaction is 4-20h.

[0035] More preferably, the temperature of the hydrothermal reaction in step (4) is 220°C; and the time of the hydrothermal reaction is 12 hours.

[0036] This invention provides a TiO2 nanoparticle colloid prepared by the above-described preparation method. Specifically, the TiO2 nanoparticle colloid of this invention is obtained by controlled hydrolysis and sol-gelation of titanium salts such as isopropyl titanate in a mixed solution of low-electro-amine, hydrogen halide HX (X = Cl, Br, I), and low-electro-ol with deionized water, followed by hydrothermal reaction and ultrasonic dispersion.

[0037] This invention provides a mesoporous TiO2 nanoparticle electron transport layer, which is obtained by coating the TiO2 nanoparticle colloid onto a conductive substrate or other functional thin film and annealing it at 80-450℃ for 15-60 min.

[0038] The present invention provides a perovskite solar cell comprising a conductive substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer and a metal electrode stacked sequentially, wherein the electron transport layer is prepared from the TiO2 nanoparticle colloid.

[0039] The present invention provides a method for preparing perovskite solar cells, comprising the following steps:

[0040] (1) Clean the conductive substrate, dry it, spin-coat TiO2 nanoparticle colloid onto the conductive substrate, heat it for annealing treatment, and obtain the mesoporous TiO2 electron transport layer.

[0041] (2) A perovskite light-absorbing layer is prepared on the mesoporous TiO2 electron transport layer;

[0042] (3) Spin-coating the hole transport layer solution onto the perovskite light-absorbing layer to obtain the hole transport layer;

[0043] (4) A metal electrode is deposited on the hole transport layer to obtain the perovskite solar cell.

[0044] Furthermore, the annealing temperature in step (1) is 80-450℃, and the annealing time is 15-60min.

[0045] More preferably, the annealing temperature in step (1) is 100°C; and the annealing time is 30 min.

[0046] Furthermore, the perovskite light-absorbing layer in step (2) is FA. x MA 1-x PbI3.

[0047] Further, the hole transport layer solution in step (3) is a mixed solution of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD), lithium bis(trifluoromethanesulfonate)imide (LiTFSI), 4-tert-butylpyridine and tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III)tris[bis(trifluoromethane)sulfonylimide (FK209)], wherein the concentration of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene is 73 mM, the concentration of lithium bis(trifluoromethanesulfonate)imide is 42 mM, the concentration of 4-tert-butylpyridine is 55 mM, and the concentration of FK209 is 2.5 mM.

[0048] Furthermore, the metal electrode is a gold electrode (Au).

[0049] Furthermore, the TiO2 thin film formation method in step (1) can also be spraying or dipping.

[0050] Further, the transparent conductive substrate in step (1) is FTO conductive glass, ITO conductive glass, Ag conductive glass or ITO / PEN, ITO / PET, Ag / PET flexible substrate.

[0051] The TiO2 nanoparticle colloid of this invention is prepared by adding deionized water dropwise to an alcoholic solution of titanium salts such as isopropyl titanate containing a low-level amine and a hydrogen halide acid HX (X = Cl, Br, I), followed by a controlled hydrolysis reaction to obtain a sol, which is then subjected to hydrothermal crystallization. The TiO2 nanoparticles of this invention have uniform size, an adjustable particle size within the range of 10-35 nm, and are stable colloids. The TiO2 nanoparticle colloid prepared by this invention is coated onto a conductive substrate and annealed to obtain a mesoporous TiO2 electron transport layer. When the mesoporous TiO2 electron transport layer is applied to perovskite solar cells, rigid structure cells can achieve a photoelectric conversion efficiency exceeding 22%, while flexible structure cells can achieve a photoelectric conversion efficiency of approximately 20%. In one embodiment of this invention, using the TiO2 nanoparticle colloid alone to prepare a mesoporous TiO2 electron transport layer for fabricating a flexible structure perovskite solar cell achieves a photoelectric conversion efficiency of 19.6%. As a further optimization, in another embodiment of the present invention, a dense SnO2 barrier layer is first spin-coated on a conductive substrate, and then TiO2 nanoparticle colloid is spin-coated on the dense SnO2 layer to construct a SnO2+TiO2 bilayer electron transport layer, which can further improve the efficiency of flexible battery to 20.4%.

[0052] This invention utilizes the in-situ reaction of a low-level amine (primary / secondary amine) in a solvent with a hydrohalic acid HX (X = Cl, Br, I) to generate R. x NH 4-x + (R = CH3, CH3CH2, x = 1, 2, 3) cations, and further controlled by the hydrolysis of titanium salts such as isopropyl titanate in the mixed solution and R x NH 4-x +A stable sol precursor is formed by ion surface adsorption, followed by a hydrothermal crystallization process to prepare highly crystalline anatase TiO2 nanoparticle colloids. This method is characterized by its simple process, mild reaction conditions, easy reproducibility, and low cost, which is conducive to the application and promotion of the technology. When the TiO2 nanoparticle colloids prepared by this invention are used as the electron transport layer of perovskite solar cells, the preparation process is simple and the processing temperature is low, while improving the photoelectric conversion efficiency and stability of perovskite solar cells, which is beneficial to the industrial production of perovskite solar cells.

[0053] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0054] (1) In the preparation method of TiO2 nanoparticles provided by the present invention, the synthesized TiO2 nanoparticle colloid does not contain any non-volatile organic solvents, macromolecules and polymer stabilizers. After film formation, there is no need for high-temperature annealing to remove organic residues and other steps, which is conducive to the rapid and low-cost preparation of TiO2 thin films.

[0055] (2) In the preparation method of TiO2 nanoparticles provided by the present invention, the added trace amount of HX (X = Cl, Br, I) acid is consumed by the reaction. Therefore, the synthesized TiO2 nanoparticle colloid contains almost no acid or alkali, is non-corrosive, non-irritating, environmentally friendly, and does not corrode or etch conductive coatings such as ITO and Ag. This is beneficial for preparing high-performance TiO2 thin films and devices on different substrates.

[0056] (3) In the TiO2 nanoparticle colloid provided by the present invention, the surface of the TiO2 particles adsorbs R x NH 4-x + (R=CH3,CH3CH2;x=1,2,3) It is a positively charged cation, which does not easily aggregate. The colloid is very stable and can be stored for more than 1 year.

[0057] (4) The present invention can achieve doping of TiO2 by introducing ionic salts. Using elements to dop TiO2 in the n-type can effectively improve the electron mobility, thereby further improving its photoelectric conversion efficiency when used as an electron transport layer in perovskite solar cells.

[0058] (5) The TiO2 nanoparticle colloid provided by the present invention has excellent crystallinity of anatase TiO2 particles and does not contain non-volatile organic compounds. It can prepare a highly conductive electron transport layer at low temperature and is suitable for low-temperature, flexible perovskite solar cells.

[0059] (6) The process provided by this invention is simple, reproducible, and low-cost, offering a new feasibility for preparing high-efficiency perovskite solar cells. The TiO2 nanoparticle colloid of this invention also has broad application prospects in other photovoltaic devices, optoelectronic devices, and photocatalysis. Attached Figure Description

[0060] Figure 1 This is a transmission electron microscope image of the TiO2 nanoparticles prepared in Example 1.

[0061] Figure 2 This is the X-ray diffraction pattern of the TiO2 nanoparticles prepared in Example 1.

[0062] Figure 3 This is a transmission electron microscope image of the TiO2 nanoparticles prepared in Example 2.

[0063] Figure 4 This is a transmission electron microscope image of the TiO2 nanoparticles prepared in Example 3.

[0064] Figure 5 This is a transmission electron microscope image of the TiO2 nanoparticles prepared in Example 4.

[0065] Figure 6 This is the JV curve of the perovskite solar cell prepared in Example 5.

[0066] Figure 7 This is the JV curve of the perovskite solar cell prepared in Example 6.

[0067] Figure 8 This is the JV curve of the perovskite solar cell prepared in Example 7.

[0068] Figure 9 This is the JV curve of the perovskite solar cell prepared in Example 8.

[0069] Figure 10 This is the JV curve of the perovskite solar cell prepared in Example 9. Detailed Implementation

[0070] The specific implementation of the present invention will be further described below with reference to embodiments and accompanying drawings, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0071] Example 1

[0072] Preparation of TiO2 nanoparticle colloids:

[0073] 1 mmol of ethylenediamine and 0.8 mmol of HBr were dissolved in 100 mL of anhydrous ethanol and mixed thoroughly to obtain a transparent ethylenediamine / HBr / ethanol mixed solution. 9.8 mL of isopropyl titanate was placed in a sealed sample bottle, and 100 mL of the mixed solution was added. The mixture was stirred for 60 min to obtain an isopropyl titanate-ethylenediamine / HBr / ethanol solution. After cooling to 0-5℃ in an ice-water bath, 1.1 mL of deionized water was added dropwise to the isopropyl titanate-ethylenediamine / HBr / ethanol solution under stirring. The mixture was stirred at 60℃ for 6 h to obtain a stable, light milky white Ti precursor sol. 3 mL of deionized water was added dropwise to the Ti precursor sol, and after mixing thoroughly, the mixture was transferred to a 150 mL hydrothermal reactor with a polytetrafluoroethylene liner. The mixture was hydrothermally reacted at 180℃ for 12 h. After natural cooling, the resulting product was ultrasonically dispersed for 30 min to obtain a white TiO2 nanoparticle colloid with a TiO2 solid content of 2.57%. Transmission electron microscopy shows (e.g.) Figure 1 As shown in the figure, the prepared TiO2 nanoparticles have a particle size of ~13 nm and are well dispersed. X-ray diffraction results (as shown in the figure) Figure 2 As shown in the figure, the prepared TiO2 nanoparticles are anatase crystals and have excellent crystallinity.

[0074] Example 2

[0075] Preparation of TiO2 nanoparticle colloids:

[0076] Dissolve 2.5 mmol of diethylamine and 1.2 mmol of HI in 100 mL of anhydrous ethanol / isopropanol (v:v = 2:1), mix thoroughly to obtain a colorless and transparent diethylamine / HI / ethanol / isopropanol mixed solution; place 20 mL of tetrabutyl titanate in a sealed sample bottle, and pour in 100 mL of the diethylamine / HI / ethanol / isopropanol mixed solution, stir for 60 min to mix thoroughly to obtain a tetrabutyl titanate-diethylamine / HI / ethanol / isopropanol solution; use After cooling to 0-5℃ in an ice-water bath, 3.0 mL of deionized water was added dropwise to a tetrabutyl titanate-diethylamine / HI / ethanol / isopropanol solution under stirring. The mixture was stirred at 70℃ for 2 h to obtain a milky white Ti precursor sol. The Ti precursor sol was transferred to a 200 mL hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 240℃ for 4 h. After natural cooling, the resulting material was ultrasonically dispersed for 30 min to obtain white TiO2 nanoparticle colloids with a TiO2 solid content of 4.5%. The prepared TiO2 nanoparticles were anatase crystals, as shown by transmission electron microscopy (e.g., ...). Figure 3 As shown in the figure, the prepared TiO2 nanoparticles have a particle size of ~30nm and are well dispersed.

[0077] Example 3

[0078] Preparation of TiO2 nanoparticle colloids.

[0079] 0.2 mmol of propylenediamine and 0.1 mmol of HCl were dissolved in 100 mL of anhydrous ethanol and mixed thoroughly to obtain a colorless and transparent propylenediamine / HCl / ethanol mixed solution. 2.5 mL of isopropyl titanate was placed in a sealed sample bottle, and 100 mL of the propylenediamine / HCl / ethanol mixed solution was added to it. The mixture was stirred for 60 min to ensure homogeneity, resulting in an isopropyl titanate-propylenediamine / HCl / ethanol solution. After cooling to 0-5 °C in an ice-water bath, 0.05 mL of deionized water was added dropwise to the isopropyl titanate-propylenediamine / HCl / ethanol solution under stirring. The mixture was stirred at 20 °C for 12 h to obtain a stable, light milky white Ti precursor sol. The Ti precursor sol was transferred to a 150 mL hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 150 °C for 20 h. After natural cooling, the resulting product was ultrasonically dispersed for 30 min to obtain a white TiO2 nanoparticle colloid with a TiO2 solid content of 0.62%. The prepared TiO2 nanoparticles are anatase crystals, as shown by transmission electron microscopy (e.g., Figure 4 As shown in the figure, the prepared TiO2 nanoparticles have a particle size of ~11 nm and are well dispersed.

[0080] Example 4

[0081] Preparation of Nb-doped TiO2 nanoparticle colloids:

[0082] Dissolve 1 mmol of ethylenediamine and 0.8 mmol of HI in 100 mL of anhydrous ethanol, then add 91 mg of NbCl5 and mix thoroughly to obtain a clear NbCl5-ethylenediamine / HI / ethanol mixed solution. Place 10 mL of isopropyl titanate in a sealed sample vial and pour in 100 mL of the NbCl5-ethylenediamine / HI / ethanol mixed solution. Stir for 60 min to obtain an isopropyl titanate-NbCl5-ethylenediamine / HI / ethanol mixed solution. Cool to 0-5 °C using an ice-water bath. Under stirring conditions, 1.2 mL of deionized water was added dropwise to a mixed solution of isopropyl titanate-NbCl5-ethylenediamine / HI / ethanol, and the reaction was carried out at 50 °C for 6 h to obtain a stable, light milky white Ti precursor sol. 4 mL of deionized water was added to the Ti sol, and the mixture was stirred until homogeneous. The mixture was then transferred to a 150 mL hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 240 °C for 12 h. After natural cooling, the resulting material was ultrasonically dispersed for 30 min to obtain white TiO2 nanoparticle colloids with a TiO2 solid content of 2.60%. The prepared TiO2 nanoparticles exhibited anatase crystal form and excellent crystallinity, as shown by transmission electron microscopy (e.g., ...). Figure 5 As shown in the figure, the TiO2 nanoparticles have a particle size of ~15nm and are well dispersed.

[0083] Example 5

[0084] (1) Preparation of TiO2 nanoparticle colloid: Same as in Example 1.

[0085] (2) Cleaning of FTO conductive glass substrate:

[0086] The FTO conductive glass was ultrasonically cleaned with glass cleaner, deionized water, acetone, and ethanol, and finally dried with nitrogen to obtain a clean FTO conductive glass substrate.

[0087] (3) Preparation of TiO2 electron transport layer:

[0088] TiO2 was coated using a spin coater. x The sol (obtained by dissolving 0.5 mL of n-butyl titanate in a mixed solution of 4 mL of n-butanol / isopropanol (v:v = 2:1)) was spin-coated onto a clean FTO substrate, and then annealed at 450 °C for 15 min to obtain a dense TiO2 layer. The TiO2 nanoparticle colloid obtained in step (1) was uniformly spin-coated onto the dense TiO2 layer; then annealed at 450 °C for 30 min to obtain a mesoporous TiO2 electron transport layer with a thickness of approximately 140 nm.

[0089] (4)FA x MA 1-x Preparation of PbI3 perovskite light-absorbing layer:

[0090] 1) Weigh 216.7 mg of formamidine iodophor (FAI), 634.8 mg of PbI2, and 30.4 mg of methylchloromethylamine (MACl) powder into a sample vial, then add 800 μL of dimethylformamide (DMF) and 100 μL of dimethyl sulfoxide (DMSO) solvent. Stir at room temperature for 6 h, then filter using a microfilter (0.22 μm, organic system). Collect the filtrate to obtain a perovskite precursor solution.

[0091] 2) The perovskite precursor solution was spin-coated onto the TiO2 electron transport layer electrode using a spin coater, and then annealed at 150°C for 20 min in an air environment with a humidity of 30%-40% to obtain FA. x MA 1-x PbI3 perovskite light-absorbing layer, FA x MA 1-x The thickness of the PbI3 perovskite light-absorbing layer is 750 nm.

[0092] (5) Preparation of the hole transport layer:

[0093] A hole transport layer solution was prepared by dissolving 90 mg of Spiro-OMeTAD (2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene) in 1 mL of chlorobenzene. After stirring for 3 h, 39.5 μL of 4-tert-butylpyridine, 23 μL of lithium salt solution (520 mg of lithium bis(trifluoromethanesulfonylimide) dissolved in 1 mL of acetonitrile solvent), and 10 μL of cobalt salt solution (375 mg of FK209-Co(III)-TFSI cobalt dissolved in 1 mL of acetonitrile solvent) were added sequentially to obtain the hole transport layer solution. The hole transport layer solution was then spin-coated onto a perovskite light-absorbing layer using a spin coater to obtain a hole transport layer with a thickness of 150 nm.

[0094] (6) Preparation of metal electrodes:

[0095] The sample with the hole transport layer spin-coated is placed in a vacuum thermal evaporation equipment to deposit an 80nm thick gold electrode, thus obtaining a perovskite solar cell.

[0096] (7) Test: At AM1.5 standard, 100mW·cm -2 Under light intensity, the effective active layer area is 0.09 cm². 2 The photoelectric performance of perovskite solar cells was tested. For example... Figure 6 As shown, the photoelectric performance parameters of this battery are: open-circuit voltage 1.09V, short-circuit current density 24.2mA·cm⁻¹. -2 The fill factor is 0.81, and the photoelectric conversion efficiency is 21.2%. This indicates that the TiO2 nanoparticle colloid prepared in this invention can be used to prepare high-performance mesoporous electron transport layers and perovskite solar cells by high-temperature annealing.

[0097] Example 6

[0098] (1) Preparation of TiO2 nanoparticle colloid: Same as in Example 1.

[0099] (2) Cleaning of the FTO conductive glass substrate: Same as in Example 5

[0100] (3) Preparation of TiO2 electron transport layer:

[0101] The spin coater uses TiO2 to coat TiO2. x The sol (obtained by dissolving 0.5 mL of n-butyl titanate in a mixed solution of 4 mL of n-butanol / isopropanol (v:v = 2:1)) was spin-coated onto a clean FTO substrate, and then annealed at 450 °C for 15 min to obtain a dense TiO2 layer. The TiO2 nanoparticle colloid obtained in step (1) was uniformly spin-coated onto the dense TiO2 layer; then annealed at 180 °C for 30 min to obtain a mesoporous TiO2 electron transport layer with a thickness of approximately 150 nm.

[0102] (4)FA x MA 1-x Preparation of PbI3 perovskite light-absorbing layer: Same as in Example 5.

[0103] (5) Preparation of hole transport layer: Same as in Example 5.

[0104] (6) Preparation of metal electrodes: Same as in Example 5.

[0105] (7) Test: At AM1.5 standard, 100mW·cm -2 Under light intensity, the effective active layer area is 0.09 cm². 2 The photoelectric performance of perovskite solar cells was tested. For example... Figure 7 As shown, the photoelectric performance parameters of the battery are: open-circuit voltage 1.09V, short-circuit current density 24.6mA·cm⁻¹. -2 The fill factor is 0.77, and the photoelectric conversion efficiency is 20.7%. Compared with the perovskite solar cell prepared in Example 5, which has a TiO2 electron transport layer annealed at 450℃, the device based on the TiO2 electron transport layer with a lower annealing temperature (180℃) still maintains a high photoelectric conversion efficiency. This indicates that the TiO2 nanoparticle colloid and its electron transport layer prepared in this invention exhibit excellent low-temperature processability and have very good application prospects.

[0106] Example 7

[0107] (1) Preparation of TiO2 nanoparticle colloid: Same as in Example 1.

[0108] (2) Cleaning of ITO / PEN flexible conductive substrate:

[0109] The ITO / PEN flexible substrate was cleaned with a cleaning agent and then rinsed with deionized water. It was then placed in an ultrasonic cleaner and ultrasonically cleaned sequentially with ethanol and deionized water for 5 minutes each. Finally, it was dried with nitrogen gas to obtain a clean ITO / PEN flexible conductive substrate.

[0110] (3) Fabrication of the low-temperature electron transport layer:

[0111] The TiO2 nanoparticle colloid obtained in step (1) was uniformly spin-coated onto a clean ITO / PEN substrate; then annealed at 100°C for 30 min to obtain a mesoporous TiO2 electron transport layer with a thickness of about 200 nm.

[0112] (4)FA x MA 1-x Preparation of PbI3 perovskite light-absorbing layer: Same as in Example 5.

[0113] (5) Preparation of hole transport layer: Same as in Example 5.

[0114] (6) Preparation of metal electrodes: Same as in Example 5.

[0115] (7) Test: At AM1.5 standard, 100mW·cm -2 Under light intensity, the effective active layer area is 0.09 cm². 2 The photoelectric performance of flexible perovskite solar cells was tested. For example... Figure 8 As shown, the photoelectric performance parameters of the battery are: open-circuit voltage 1.06V, short-circuit current density 23.5mA·cm⁻¹. -2 The fill factor is 0.782, and the photoelectric conversion efficiency is 19.6%. This indicates that the TiO2 nanoparticle colloid prepared by this invention is also suitable for low-temperature fabrication of flexible photovoltaic devices.

[0116] Example 8

[0117] (1) Preparation of TiO2 nanoparticle colloid: Same as in Example 1.

[0118] (2) Cleaning of ITO / PEN flexible conductive substrate: Same as in Example 7.

[0119] (3) Fabrication of the low-temperature electron transport layer:

[0120] SnO2 nanoparticle dispersion (purchased from Alfa, SnO2 particle size approximately 5 nm, mass concentration 3%) was spin-coated onto a clean ITO / PEN substrate using a spin coater, and then annealed at 120°C for 15 min to obtain a dense SnO2 layer. The TiO2 nanoparticle colloid obtained in step (1) was uniformly spin-coated onto the dense SnO2 layer; then annealed at 100°C for 30 min to obtain a SnO2 dense layer + mesoporous TiO2 bilayer electron transport layer, the thickness of which was approximately 150 nm.

[0121] (4)FA x MA 1-x Preparation of PbI3 perovskite light-absorbing layer: Same as in Example 5.

[0122] (5) Preparation of hole transport layer: Same as in Example 5.

[0123] (6) Preparation of metal electrodes: Same as in Example 5.

[0124] (7) Test: At AM1.5 standard, 100mW·cm -2 Under light intensity, the effective active layer area is 0.09 cm². 2 The photoelectric performance of flexible perovskite solar cells was tested. For example... Figure 9As shown, the photoelectric performance parameters of the battery are: open-circuit voltage 1.11V, short-circuit current density 23.4mA·cm⁻¹. -2 The fill factor is 0.788, and the photoelectric conversion efficiency is 20.4%. This indicates that the SnO2 dense layer + mesoporous TiO2 bilayer electron transport layer obtained through cell structure optimization can further improve the performance of flexible photovoltaic devices.

[0125] Example 9

[0126] (1) Preparation of Nb-doped TiO2 nanoparticle colloids: Same as in Example 4.

[0127] (2) Cleaning of FTO conductive glass substrate: Same as in Example 5.

[0128] (3) Preparation of TiO2 electron transport layer: Same as in Example 7.

[0129] (4)FA x MA 1-x Preparation of PbI3 perovskite light-absorbing layer: Same as in Example 5.

[0130] (5) Preparation of hole transport layer: Same as in Example 5.

[0131] (6) Preparation of metal electrodes: Same as in Example 5.

[0132] (7) Test: At AM1.5 standard, 100mW·cm -2 Under light intensity, the effective active layer area is 0.09 cm². 2 The photoelectric performance of perovskite solar cells was tested. For example... Figure 10 As shown, the photoelectric performance parameters of the battery are: reverse sweep open-circuit voltage 1.10V, short-circuit current density 25.4mA·cm⁻¹. -2 The fill factor is 0.80, the photoelectric conversion efficiency is 22.3%, the forward scan open-circuit voltage is 1.09V, and the short-circuit current density is 25.3mA·cm. -2 The fill factor was 0.798, and the photoelectric conversion efficiency was 22.0%. This indicates that elemental doping can further improve the performance of the prepared TiO2 nanoparticle colloid and the efficiency of the solar cell prepared using this colloid.

Claims

1. A method for preparing TiO2 nanoparticle colloids, characterized in that, Includes the following steps: (1) Add the low-element amine, hydrohalic acid HX, where X = Cl, Br, I, and ionic salt to the low-element alcohol and dissolve them completely to obtain a mixed solution; the low-element amine is one or more of ethylenediamine, propylenediamine, and diethylamine, and its concentration in the mixed solution is 1-30 mmol / L; the concentration of the hydrohalic acid in the mixed solution is 1-20 mmol / L; the ionic salt is one or more of LiCl, SnCl2, and NbCl5, and its concentration in the mixed solution is 0.3-6 mmol / L; (2) Mix the titanium salt with the mixed solution obtained in step (1) until homogeneous to obtain a titanium salt solution; (3) Under ice-water bath conditions, deionized water was added dropwise to the titanium salt solution obtained in step (2), and the reaction was stirred to obtain TiO2. x Sol; (4) TiO2 obtained in step (3) x Deionized water was added to the sol, which was then transferred to a hydrothermal reactor for hydrothermal reaction. After cooling, TiO2 nanoparticle colloids were obtained by ultrasonic dispersion.

2. The method for preparing TiO2 nanoparticle colloids according to claim 1, characterized in that, The low alcohol mentioned in step (1) is one or more of methanol, ethanol, and isopropanol.

3. The method for preparing TiO2 nanoparticle colloids according to claim 1, characterized in that, The titanium salt in step (2) is one or more of tetrabutyl titanate and isopropyl titanate; the volume ratio of the titanium salt in step (2) to the mixed solution is 1-20 mL: 100 mL.

4. The method for preparing TiO2 nanoparticle colloids according to claim 1, characterized in that, The volume ratio of deionized water to titanium salt solution in step (3) is 50-3000 μL: 100 mL; the temperature of the stirring reaction in step (3) is 20-70℃, and the stirring reaction time is 2-12 h.

5. The method for preparing TiO2 nanoparticle colloids according to claim 1, characterized in that, Step (4) involves the deionized water and TiO2. x The volume ratio of the sol is 0-6 mL: 100 mL; the temperature of the hydrothermal reaction in step (4) is 150-240℃, and the time of the hydrothermal reaction is 4-20 h.

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