Preparation method of perovskite solar cell of self-assembled monomolecular layer based on micromolecule modification

Abstract

The invention provides a preparation method of a perovskite solar cell of a self-assembly monomolecular layer based on micromolecule modification, and relates to the technical field of preparation of solar cells, the method comprises the following steps: spin-coating a blended solution on the surface of a substrate, then performing annealing treatment, and forming a modification layer on the substrate; wherein the 1, 4-benzene diphosphonic acid is anchored on the surface of the substrate through a phosphate radical group at one end of the 1, 4-benzene diphosphonic acid, gaps among SAM molecules are filled, a uniformly covered film is formed, and meanwhile, a phosphate radical group at the other end of the 1, 4-benzene diphosphonic acid is exposed on the surface of the modification layer; depositing a perovskite precursor solution on the surface of the formed modification layer, and performing crystallization treatment to form a perovskite light absorption layer; wherein the wettability of the perovskite precursor solution on the surface of the modification layer is improved by the phosphate radical group exposed on the surface of the modification layer. According to the invention, SAM molecular gaps are filled with 1, 4-benzene diphosphonic acid (the coverage rate is greater than 99.5%), and the pinhole defect is thoroughly eliminated.

Description

Technical Field

[0001] This invention relates to the field of titanium ore preparation technology, and in particular to a method for preparing perovskite solar cells based on a self-assembled monolayer modified with small molecules. Background Technology

[0002] In recent years, perovskite solar cells (PSCs) have become a strong competitor to traditional silicon-based photovoltaic technologies due to their excellent photoelectric conversion efficiency (with the highest certified efficiency reaching 27%), low manufacturing cost, and solution processing potential. In pin-inverted device structures, self-assembled monolayers (SAMs) have attracted widespread attention as hole transport layers (HTLs) due to their unique advantages.

[0003] It can be prepared by low-temperature full solution method (such as spin coating), which reduces energy consumption; the ultra-thin thickness (nanoscale) significantly reduces the amount of material used; low layer resistance improves charge extraction efficiency; and the ordered arrangement of molecules generates interfacial dipole moments, optimizing energy level matching.

[0004] However, SAMs have the following key drawbacks in practical applications:

[0005] Substrate surface roughness prevents SAM molecules from being completely covered, and large steric hindrance groups such as carbazole cores hinder the close arrangement of molecules. Fluctuations in deposition conditions (concentration, temperature) cause molecular aggregation. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a perovskite solar cell based on a self-assembled monolayer modified by small molecules, wherein 1,4-phenylenediphosphonic acid fills the gaps between SAM molecules (coverage > 99.5%), completely eliminating pinhole defects.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] A method for preparing a perovskite solar cell based on a self-assembled monolayer modified with small molecules, the method comprising:

[0009] Step 1: Dissolve the self-assembled monolayer material and 1,4-phenyl diphosphonic acid together in ethanol solvent to form a blend solution containing SAM and 1,4-phenyl diphosphonic acid;

[0010] Step 2: Spin-coat the blended solution obtained in Step 1 onto the substrate surface, and then perform annealing treatment to form a modification layer on the substrate; wherein, 1,4-phenyl diphosphonic acid is anchored to the substrate surface through the phosphate group at one end, filling the gaps between SAM molecules to form a uniformly covered film, while the phosphate group at the other end of 1,4-phenyl diphosphonic acid is exposed on the surface of the modification layer.

[0011] Step 3: Deposit a perovskite precursor solution on the surface of the modified layer formed in step 2, and perform crystallization treatment to form a perovskite light-absorbing layer; wherein, the phosphate groups exposed on the surface of the modified layer improve the wettability of the perovskite precursor solution on the surface of the modified layer.

[0012] Further, in step 1, the self-assembled monolayer material and 1,4-phenylenediamine are dissolved together in an ethanol solvent to form a blend solution containing SAM and 1,4-phenylenediamine, comprising:

[0013] 1,4-Benzodiphosphonic acid is dissolved in ethanol solvent to form an ethanol solution containing 1,4-Benzodiphosphonic acid;

[0014] The self-assembled monolayer material (SAM) was dissolved in the obtained ethanol solution containing 1,4-phenyl diphosphonic acid to form a mixed solution containing SAM and 1,4-phenyl diphosphonic acid.

[0015] The resulting mixed solutions are thoroughly mixed to obtain a blended solution containing SAM and 1,4-phenyl diphosphonic acid; wherein, 1,4-phenyl diphosphonic acid is dispersed in the ethanol solution of step 1 to inhibit aggregation during subsequent SAM dissolution; the ethanol solution containing 1,4-phenyl diphosphonic acid serves as a solvent carrier to achieve the dissolution of SAM molecules in the 1,4-phenyl diphosphonic acid coexistence system.

[0016] Further, in step 2, the blended solution obtained in step 1 is spin-coated onto the substrate surface, followed by annealing to form a modification layer on the substrate, including:

[0017] The obtained blend solution containing SAM and 1,4-phenylbisphosphonic acid was spin-coated onto the surface of the pretreated substrate to form a liquid composite film.

[0018] After spin coating, the ethanol solvent in the liquid composite film is partially evaporated, inducing SAM molecules and 1,4-phenylenediamine molecules to initially align on the substrate surface.

[0019] The treated membrane is annealed to trigger molecular-level reconstruction; among which,

[0020] 1,4-Benzodium diphosphonate is chemically bonded and anchored to the substrate surface through phosphate groups; SAM molecules complete self-assembly into a monolayer under thermal drive.

[0021] After thermally driven bonding and assembly, a continuous covering modification layer is formed on the substrate; wherein,

[0022] Anchored 1,4-phenyldiphosphonic acid molecules occupy the gaps between SAM molecules, forming a physical isolation layer;

[0023] The exposed phosphate groups form a hydrophilic terminal interface.

[0024] Furthermore, phosphate group anchoring includes:

[0025] 1,4-Benzodium diphosphonate molecules achieve molecular fixation by forming covalent bonds with metal oxides on the substrate surface through the phosphate group at one end;

[0026] SAM self-assembly enhancement includes:

[0027] Under thermal drive, SAM molecules undergo ordered self-assembly and arrangement with the 1,4-phenylenediamine anchored in step (a) as the positioning site.

[0028] Gap filling and isolation, including:

[0029] The gaps formed after the SAM molecules are arranged in step (b) of 1,4-phenylphosphonic acid molecule filling process block the direct contact channel between the perovskite layer and the substrate.

[0030] The construction of hydrophilic interfaces includes:

[0031] The phosphate group at the other end of the 1,4-benzenediphosphonic acid molecule is oriented to be exposed on the surface of the modified layer, forming a hydrophilic interface layer.

[0032] Further, the obtained blend solution containing SAM and 1,4-phenylenediamine is spin-coated onto the surface of the pretreated substrate to form a liquid composite film, comprising:

[0033] The blend solution is quantitatively applied to the central region of the pretreated substrate surface;

[0034] Initiate substrate rotation to allow the applied blend solution to spread radially along the substrate surface under centrifugal force;

[0035] Maintaining the rotational state allows the radially spread solution to form a liquid film layer of uniform thickness;

[0036] By controlling the rotation process, the solvent components in the liquid film layer are partially evaporated to form a liquid composite film containing oriented molecular groups; wherein, the SAM molecules and 1,4-phenylenediamine molecules are pre-oriented in a centrifugal force field.

[0037] Furthermore, after spin coating, the ethanol solvent in the liquid composite film is partially evaporated, inducing SAM molecules and 1,4-phenylenediamine molecules to initially align on the substrate surface, including:

[0038] The substrate rotation is terminated, so that the formed liquid composite film is in a static environment;

[0039] During static evaporation, SAM molecules and 1,4-phenylenediamine molecules migrate to and accumulate on the substrate surface;

[0040] As the ethanol solvent continues to evaporate, the molecules enriched on the substrate surface undergo directional alignment driven by the solid-liquid interface energy.

[0041] When the ethanol evaporation reaches 30%-50%, a transition film layer with preliminary molecular orientation is formed; wherein, the 1,4-phenyl diphosphonic acid molecules are oriented with their phosphate groups toward the substrate; and the SAM molecules are aligned with their functional end groups toward the gas phase.

[0042] Furthermore, the treated membrane is annealed to trigger molecular-level reconstruction, including:

[0043] The transition film layer with preliminary orientation is placed in a thermal field of 100-120℃;

[0044] Thermal energy gives molecules in the transition film layer migration energy, causing them to move directionally on the substrate surface.

[0045] Dual-mechanism reconstruction:

[0046] 1,4-Benzodium diphosphonate molecules form POM covalent bonds with substrate metal atoms through phosphate groups; SAM molecules complete π-π stacking self-assembly with the bonded 1,4-Benzodium diphosphonate as anchor points;

[0047] Maintain the hot zone for 5-15 minutes to solidify the molecular arrangement.

[0048] Further, in step 3, a perovskite precursor solution is deposited on the surface of the modified layer formed in step 2, and then crystallized to form a perovskite light-absorbing layer, including:

[0049] A perovskite precursor solution is applied to the surface of the modified layer;

[0050] The exposed phosphate groups on the surface of the modified layer ensure that the contact angle of the precursor solution is ≤15°;

[0051] Gradient spin coating:

[0052] First stage: Rotate at 500-1000 rpm to spread the solution radially;

[0053] Second stage: Rotate at 3000-4000 rpm to form a uniform liquid film;

[0054] At the end of the second stage, an antisolvent is added dropwise to induce the instantaneous formation of perovskite crystal nuclei;

[0055] The crystal nucleus liquid film is annealed at 100-110℃ to complete crystal growth.

[0056] The above-described solution of the present invention has at least the following beneficial effects:

[0057] 1,4-Benzodium phosphonic acid fills the intermolecular gaps of SAM (coverage > 99.5%), completely eliminating pinhole defects (comparative example coverage ≤ 90%); it blocks direct contact between the perovskite layer and the substrate, reducing the interfacial nonradiative recombination current by 37.2%; the phosphate groups on the surface of the modified layer reduce the contact angle of the perovskite precursor solution from > 60° (pure SAM) to ≤ 15°; the perovskite grain size increases to 1.2-1.5 μm (comparative example 0.8-1.0 μm), and the pinhole density decreases by 89%. Detailed Implementation

[0058] Exemplary embodiments of this disclosure are described in more detail below; however, it should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0059] Example 1

[0060] Preparation of the blend solution: Weigh 5 mg of 1,4-phenyldiphosphonic acid and add it to 10 mL of anhydrous ethanol. Stir magnetically for 30 minutes until completely dissolved to form a 2.3 mM 1,4-phenyldiphosphonic acid ethanol solution. Then add 10 mg of self-assembled monolayer material (SAM, octadecyltrichlorosilane) to the solution and continue stirring for 60 minutes, during which ultrasonic dispersion is used for 10 minutes to obtain a homogeneous blend solution with a SAM concentration of 0.01 g / mL and a 1:2 mass ratio of 1,4-phenyldiphosphonic acid to SAM.

[0061] Modification layer preparation: A pretreated ITO glass substrate was selected (it was ultrasonically cleaned sequentially with deionized water, acetone, and isopropanol for 15 minutes, dried with nitrogen, and then subjected to plasma treatment for 5 minutes). 50 μL of the blend solution was taken using a micropipette and added to the center of the substrate. The spin coater was started, initially rotating at 500 rpm for 5 seconds to allow the solution to spread initially, then rotating at 3000 rpm for 30 seconds to form a liquid composite film. After spin coating, the substrate was placed at room temperature for 2 minutes to allow approximately 40% of the ethanol solvent to evaporate, inducing initial molecular orientation. The substrate was then transferred to a hot plate and annealed at 100°C for 10 minutes. During this annealing process, 1,4-phenylenediphosphonic acid (SAM) was anchored to the In₂O₃ on the ITO surface via a phosphate group at one end, forming a PO-In covalent bond. SAM molecules completed ordered self-assembly using the anchored 1,4-phenylenediphosphonic acid as a positioning point, ultimately forming a continuously covering modification layer. The exposed phosphate groups on the surface constitute a hydrophilic interface.

[0062] Preparation of the perovskite light-absorbing layer: A perovskite precursor solution was prepared (PbI2 and MAI were dissolved in a mixed solvent of DMF and DMSO at a molar ratio of 1:1.05, with a total concentration of 1.25M, where the volume ratio of DMF to DMSO was 4:1). 80 μL of the precursor solution was dropped onto the surface of the modified layer, with a contact angle of 12°. A gradient spin coater was then used: the first stage involved spinning at 800 rpm for 10 seconds to ensure uniform spreading of the solution; the second stage involved spinning at 3500 rpm for 30 seconds, and at the 20th second, 150 μL of chlorobenzene was rapidly added as an anti-solvent to induce crystal nucleation. After spin coating, the substrate was annealed at 100℃ for 30 minutes to complete crystal growth and form a uniform and dense perovskite light-absorbing layer.

[0063] Example 2

[0064] Preparation of the blend solution: Weigh 8 mg of 1,4-phenyldiphosphonic acid and add it to 10 mL of anhydrous ethanol. Stir magnetically for 40 minutes until completely dissolved to form a 3.7 mM 1,4-phenyldiphosphonic acid ethanol solution. Add 12 mg of SAM material (dodecyl phosphate) to this solution and stir for 90 minutes, ultrasonically dispersing for 5 minutes every 20 minutes during the process to obtain a blend solution with a SAM concentration of 0.012 g / mL and a 1,4-phenyldiphosphonic acid to SAM mass ratio of 2:3.

[0065] Modification layer preparation: An FTO glass substrate was ultrasonically cleaned sequentially with deionized water, ethanol, and diethyl ether for 20 minutes, dried with nitrogen, and then treated with ultraviolet ozone for 10 minutes. 60 μL of the blend solution was dropped onto the center of the substrate. Spin-coating parameters were set as follows: 600 rpm for 8 seconds, followed by 4000 rpm for 25 seconds, forming a liquid composite film. After spin-coating, the substrate was allowed to stand at room temperature for 3 minutes to allow approximately 35% of the ethanol to evaporate, completing the initial molecular orientation. The substrate was then transferred to a hot plate and annealed at 110°C for 15 minutes. 1,4-Benzodium diphosphonate formed PO-Sn covalent bonds with SnO2 on the FTO surface through phosphate groups. SAM molecules self-assembled under thermal drive, using anchored molecules as a reference. 1,4-Benzodium diphosphonate filled the molecular gaps, forming a continuous modification layer. The surface hydrophilic terminal contact angle was measured to be 10°.

[0066] Preparation of the perovskite absorbing layer: A perovskite precursor solution (CsPbI3 and FAI dissolved in DMF at a molar ratio of 0.15:0.85, concentration 1.5M) was prepared. 90 μL of the precursor solution was dropped onto the surface of the modified layer, and a gradient spin-coating process was performed: the first stage was 1000 rpm for 12 seconds, the second stage was 3000 rpm for 35 seconds, and 200 μL of toluene was added as an antisolvent at the 25th second. After spin-coating, the substrate was annealed at 105℃ for 25 minutes to form the perovskite absorbing layer. X-ray diffraction analysis showed that it had good crystallinity.

[0067] Example 3

[0068] Preparation of the blend solution: Weigh 6 mg of 1,4-phenyldiphosphonic acid and add it to 10 mL of anhydrous ethanol. Stir magnetically for 35 minutes until completely dissolved to form a 2.8 mM 1,4-phenyldiphosphonic acid ethanol solution. Add 8 mg of SAM material (phenylphosphonic acid) to this solution and stir for 75 minutes, during which time ultrasonic dispersion is performed for 15 minutes to obtain the blend solution, wherein the SAM concentration is 0.008 g / mL and the mass ratio of 1,4-phenyldiphosphonic acid to SAM is 3:4.

[0069] Preparation of the modified layer: An ITO substrate modified with a TiO2 electron transport layer was selected (after standard cleaning, a TiO2 thin film was prepared by the sol-gel method and annealed at 500℃ for 30 minutes). 55 μL of the blend solution was dropped onto the center of the substrate, and spin-coating parameters were: 550 rpm for 6 seconds, then 3800 rpm for 28 seconds, forming a liquid composite film. After spin-coating, the substrate was allowed to stand for 2.5 minutes to allow approximately 45% of the ethanol to evaporate, inducing molecular orientation. The substrate was annealed at 120℃ for 5 minutes. 1,4-phenylenediamine (PPA) was anchored to TiO2 via phosphate groups through a PO-Ti covalent bond, and SAM molecules completed self-assembly. The surface of the modified layer showed a contact angle of 8°, indicating excellent hydrophilicity.

[0070] Preparation of the perovskite light-absorbing layer: A ternary perovskite precursor solution (MAPbI3:FAPbBr3:CsPbI3 dissolved in a 1.3M mixed solvent of DMF and DMSO at a molar ratio of 0.6:0.3:0.1, with a solvent volume ratio of 5:1) was prepared. 85 μL of the precursor solution was dropped onto the surface of the modified layer. The gradient spin-coating parameters were: 700 rpm for 11 seconds, 3700 rpm for 32 seconds, and 180 μL of ethyl acetate was added as an anti-solvent at the 22nd second. After spin-coating, the substrate was annealed at 110℃ for 20 minutes. Scanning electron microscopy revealed that the formed perovskite layer had uniform grain size and no obvious pores.

[0071] Example 4

[0072] Preparation of the blend solution: Accurately weigh 4 mg of 1,4-phenyldiphosphonic acid and add it to 15 mL of anhydrous ethanol. Stir magnetically for 60 minutes in a 50 °C water bath to form a 1.5 mM 1,4-phenyldiphosphonic acid ethanol solution. After the solution cools to room temperature, add 15 mg of self-assembled monolayer material (SAM, 4-tert-butylbenzoic acid), and continue stirring for 90 minutes, with ultrasonic vibration for 5 minutes every 15 minutes to ensure complete dissolution, to obtain a blend solution with a SAM concentration of 0.001 g / mL and a molar ratio of 1,4-phenyldiphosphonic acid to SAM of 1:4.

[0073] Modification layer preparation: An ITO substrate modified with ZnO nanoparticles was used (the ZnO electron transport layer, approximately 30 nm thick, was prepared via spin coating). The substrate was treated in a UV ozone cleaner for 8 minutes, then 70 μL of the blend solution was dropped onto the center of the substrate. The spin coating parameters were set as follows: 400 rpm for 10 seconds, then 3200 rpm for 40 seconds, forming a liquid composite film. After spin coating, the substrate was transferred to a nitrogen-filled glove box and allowed to stand for 4 minutes to allow approximately 30% of the ethanol solvent to evaporate. Subsequently, it was annealed at 105 °C for 12 minutes, allowing 1,4-phenylenediamine to bind with the ZnO surface via phosphate groups. 2+ By forming PO-Zn covalent bonds, SAM molecules complete self-assembly and arrangement based on the anchored 1,4-phenylenediamine, forming a continuous and uniform modified layer. The surface roughness is 0.8 nm as detected by atomic force microscopy.

[0074] Preparation of perovskite light-absorbing layer: Preparation of mixed cationic perovskite precursor solution (Cs 0.05 (FA 0.83 MA 0.17 ) 0.95 Pb(I 0.83 Br 0.17 3) Dissolved in a DMF / DMSO mixed solvent (total concentration 1.4M, volume ratio 4:1). 100 μL of the precursor solution was dropped onto the surface of the modified layer; the contact angle was measured to be 13°. A gradient spin-coating process was used: the first stage was 600 rpm for 15 seconds, the second stage was 3800 rpm for 35 seconds, and at the 25th second of spin-coating, 220 μL of methylbenzoic acid was added as an anti-solvent. After spin-coating, the substrate was annealed on a 100℃ hot plate for 40 minutes. The resulting perovskite light-absorbing layer had a uniform surface morphology and a grain size of approximately 500-800 nm.

[0075] Example 5

[0076] Preparation of the blend solution: Weigh 10 mg of 1,4-phenyldiphosphonic acid and add it to 8 mL of anhydrous ethanol. Stir magnetically for 75 minutes under ice bath conditions to form a 5.7 mM 1,4-phenyldiphosphonic acid ethanol solution. Add 18 mg of SAM material (4-methoxyphenylphosphonic acid) to this solution, slowly heat to 40 °C and continue stirring for 80 minutes. During this period, perform three pulsed ultrasonic treatments (3 minutes each) to obtain the blend solution, in which the SAM concentration is 0.00225 g / mL and the mass ratio of 1,4-phenyldiphosphonic acid to SAM is 5:9.

[0077] Modification layer preparation: FTO substrates treated with oxygen plasma for 5 minutes were selected. 45 μL of the blend solution was dropped onto the center of the substrate, and spin-coating parameters were: 700 rpm for 7 seconds, then 3600 rpm for 30 seconds, forming a liquid composite film. After spin-coating, the substrate was placed in an environment with 20% humidity and allowed to stand for 2.5 minutes to allow approximately 45% of the ethanol to evaporate. Subsequently, it was annealed on a hot plate at 115℃ for 8 minutes. 1,4-Benzodium diphosphonate formed chemical bonds with SnO2 on the FTO surface through phosphate groups, and the SAM molecules achieved ordered arrangement. The resulting modified layer surface exhibited good hydrophilicity, with a water contact angle of 9°.

[0078] Preparation of perovskite light-absorbing layer: Preparation of two-dimensional / three-dimensional hybrid perovskite precursor solution ((PEA)2(MA)4Pb5I) 16 Dissolved in DMF (concentration 1.3M), 75 μL of the precursor solution was dropped onto the surface of the modified layer, with a contact angle of 11°. Gradient spin coating was performed: first stage at 900 rpm for 12 seconds, second stage at 3400 rpm for 38 seconds. At the 30-second mark, 160 μL of a chlorobenzene / diethyl ether mixture (volume ratio 1:1) was added as an antisolvent. After spin coating, the substrate was annealed at 108°C for 28 minutes. The resulting perovskite absorbing layer exhibited a distinct layered structure, and the absorption spectrum showed a band gap of approximately 1.58 eV.

[0079] Example 6

[0080] Preparation of the blend solution: Weigh 7 mg of 1,4-phenyldiphosphonic acid and add it to 12 mL of anhydrous ethanol. Stir magnetically for 50 minutes at room temperature to form a 2.5 mM 1,4-phenyldiphosphonic acid ethanol solution. Add 10 mg of SAM material (2,4,6-trimethylphenylphosphonic acid) to this solution and continue stirring for 120 minutes, sonicating for 10 minutes every 30 minutes to obtain the blend solution, in which the SAM concentration is 0.00083 g / mL and the molar ratio of 1,4-phenyldiphosphonic acid to SAM is 1:1.5.

[0081] Preparation of the modified layer: An FTO substrate modified with a TiO2 nanotube array (TiO2 nanotubes, approximately 200 nm in length, were prepared via anodic oxidation) was used. The substrate was subjected to UV ozone treatment for 12 minutes, and then 65 μL of a blended solution was dropped onto the center of the substrate. Spin-coating parameters were set as follows: 500 rpm for 9 seconds, then 3300 rpm for 32 seconds, forming a liquid composite film. After spin-coating, the substrate was allowed to stand in a nitrogen atmosphere for 3 minutes to allow approximately 38% of the ethanol to evaporate. Subsequently, it was annealed at 120°C for 6 minutes. 1,4-Benzodium diphosphonate formed chemical bonds with the TiO2 nanotube surface through phosphate groups, and SAM molecules completed self-assembly using anchor molecules as positioning points, forming a uniformly covered modified layer. X-ray photoelectron spectroscopy analysis showed that the phosphorus content in the modified layer was 1.2 at.

[0082] Preparation of the perovskite absorbing layer: A fully inorganic perovskite precursor solution (CsPbI₂Br dissolved in a DMF / DMSO mixed solvent, concentration 1.6M, volume ratio 3:1) was prepared. 95 μL of the precursor solution was dropped onto the surface of the modified layer, with a contact angle of 8°. A gradient spin-coating process was used: the first stage was 800 rpm for 14 seconds, and the second stage was 3900 rpm for 33 seconds. At the 23rd second of spin-coating, 190 μL of ethyl acetate was added as an antisolvent. After spin-coating, the substrate was annealed on a hot plate at 110℃ for 18 minutes. The resulting perovskite absorbing layer exhibited good crystallinity, and X-ray diffraction patterns showed that it had a pure cubic phase structure.

[0083] Example 7

[0084] Preparation of the blend solution: Accurately weigh 9 mg of 1,4-phenyldiphosphonic acid and add it to 13 mL of anhydrous ethanol. Stir magnetically at 60 °C for 45 minutes to form a 3.3 mM 1,4-phenyldiphosphonic acid ethanol solution. After the solution cools to room temperature, add 14 mg of self-assembled monolayer material (SAM, 4-cyanobenzylphosphonic acid), and continue stirring for 100 minutes, sonicating for 8 minutes every 20 minutes during this period to obtain the blend solution, in which the SAM concentration is 0.00108 g / mL and the mass ratio of 1,4-phenyldiphosphonic acid to SAM is 9:14.

[0085] Modification layer preparation: A plasma-treated ITO / PCBM substrate (PCBM layer thickness approximately 20 nm) was selected. 62 μL of the blend solution was dropped onto the center of the substrate, and spin-coating parameters were set as follows: 650 rpm for 11 seconds, then 3100 rpm for 37 seconds, forming a liquid composite film. After spin-coating, the substrate was placed in a vacuum environment of 0.1 Pa for 3.5 minutes to allow approximately 42% of the ethanol solvent to evaporate. Subsequently, it was annealed at 118 °C for 7 minutes. 1,4-Benzodium diphosphonate formed chemical bonds with the residual metal oxides on the PCBM surface through phosphate groups, resulting in an ordered arrangement of SAM molecules. The resulting modification layer was approximately 2.5 nm thick with a surface water contact angle of 11°.

[0086] Preparation of the perovskite absorbing layer: A mixed halide perovskite precursor solution was prepared (FAPb(I0.9Br0.1)3 dissolved in a DMF / DMSO mixed solvent, concentration 1.35M, volume ratio 7:3). 88 μL of the precursor solution was dropped onto the surface of the modified layer, with a solution contact angle of 14°. A gradient spin-coating process was used: the first stage was 550 rpm for 17 seconds, the second stage was 3600 rpm for 34 seconds, and at the 28th second of spin-coating, 210 μL of ethyl methyl benzoate was added as an anti-solvent. After spin-coating, the substrate was annealed on a hot plate at 102℃ for 35 minutes. The resulting perovskite absorbing layer had a uniform surface morphology and an absorption edge of approximately 820 nm.

[0087] Example 8

[0088] Preparation of the blend solution: Weigh 5 mg of 1,4-phenyldiphosphonic acid and add it to 11 mL of anhydrous ethanol. Stir magnetically for 80 minutes at room temperature to form a 2.1 mM 1,4-phenyldiphosphonic acid ethanol solution. Add 16 mg of SAM material (3,5-bis(trifluoromethyl)phenylphosphonic acid) to this solution and continue stirring for 110 minutes, during which time pulsed sonication is performed four times (5 minutes each time) to obtain the blend solution, in which the SAM concentration is 0.00145 g / mL and the molar ratio of 1,4-phenyldiphosphonic acid to SAM is 1:3.

[0089] Modification layer preparation: An FTO / TiO2 substrate (with a dense TiO2 layer thickness of approximately 50 nm) treated with UV-Ozone for 15 minutes was selected. 58 μL of the blend solution was dropped onto the center of the substrate, and spin-coating parameters were: 800 rpm for 8 seconds, followed by 3500 rpm for 29 seconds, to form a liquid composite film. After spin-coating, the substrate was placed in a nitrogen atmosphere with 15% humidity and allowed to stand for 2.8 minutes to allow approximately 37% ethanol to evaporate. Subsequently, it was annealed at 100°C for 14 minutes. 1,4-Benzodium diphosphonate formed PO-Ti covalent bonds with the TiO2 surface through phosphate groups, and SAM molecules completed self-assembly based on anchored molecules. The resulting modification layer exhibited good uniformity, and atomic force microscopy showed a surface roughness of 0.6 nm.

[0090] Preparation of perovskite light-absorbing layer: Preparation of two-dimensional Ruddlesden-Popper type perovskite precursor solution ((BA)2(MA)4Pb5I) 16Dissolved in DMF (concentration 1.2M). 72 μL of the precursor solution was dropped onto the surface of the modified layer, with a contact angle of 10°. Gradient spin coating was performed: first stage at 950 rpm for 13 seconds, second stage at 3300 rpm for 40 seconds. At the 32nd second, 170 μL of a chlorobenzene / ethyl ether mixed solvent (volume ratio 2:1) was added as an antisolvent. After spin coating, the substrate was annealed at 107℃ for 32 minutes. The resulting perovskite light-absorbing layer exhibited a distinct layered structure, and X-ray diffraction showed high intensity of the (002) crystal plane peak.

[0091] Example 9

[0092] Preparation of the blend solution: Accurately weigh 12 mg of 1,4-phenyldiphosphonic acid and add it to 14 mL of anhydrous ethanol. Stir magnetically at 45 °C for 65 minutes to form a 3.8 mM 1,4-phenyldiphosphonic acid ethanol solution. After the solution cools to room temperature, add 9 mg of SAM material (4-trifluoromethoxyphenylphosphonic acid), and continue stirring for 70 minutes, sonicating for 6 minutes every 15 minutes during this period to obtain the blend solution, in which the SAM concentration is 0.00064 g / mL and the mass ratio of 1,4-phenyldiphosphonic acid to SAM is 4:3.

[0093] Modification layer preparation: An ITO substrate modified with Zn₂SnO₄ nanoparticles was used (prepared by solution spin coating, with a thickness of approximately 40 nm). The substrate was treated in oxygen plasma for 7 minutes, and then 68 μL of the blend solution was dropped onto the center of the substrate. The spin coating parameters were set as follows: 450 rpm for 13 seconds and 3400 rpm for 31 seconds to form a liquid composite film. After spin coating, the substrate was allowed to stand in a nitrogen atmosphere for 3.2 minutes to allow approximately 40% of the ethanol to evaporate. Subsequently, it was annealed on a hot plate at 112 °C for 10 minutes. 1,4-Benzodium diphosphonate formed chemical bonds with the metal atoms on the Zn₂SnO₄ surface through phosphate groups, and the SAM molecules were arranged in an ordered manner. The resulting modification layer was approximately 3 nm thick with a water contact angle of 12°.

[0094] Preparation of the perovskite light-absorbing layer: A cesium-based all-inorganic perovskite precursor solution (CsPbI3 dissolved in a DMF / DMSO mixed solvent, concentration 1.5M, volume ratio 5:2) was prepared. 92 μL of the precursor solution was dropped onto the surface of the modified layer, with a contact angle of 7°. A gradient spin-coating process was used: the first stage was 750 rpm for 16 seconds, and the second stage was 3700 rpm for 36 seconds. At the 26th second of spin-coating, 180 μL of butyl acetate was added as an anti-solvent. After spin-coating, the substrate was annealed on a hot plate at 109 °C for 25 minutes. The resulting perovskite light-absorbing layer exhibited good crystallinity, and the photoluminescence spectrum showed its emission peak at 710 nm.

[0095] Comparative Example 1

[0096] Solution preparation: Weigh 10 mg of self-assembled monolayer material (SAM, octadecyltrichlorosilane), dissolve it directly in 10 mL of anhydrous ethanol, stir magnetically for 60 minutes and sonicate for 10 minutes to form an ethanol solution containing only SAM with a concentration of 0.01 g / mL.

[0097] Modification layer preparation: Using the same pretreated ITO glass substrate as in Example 1, 50 μL of the above SAM solution was dropped onto the center of the substrate. The spin-coating parameters were the same as in Example 1 (500 rpm for 5 seconds, 3000 rpm for 30 seconds) to form a liquid film. After spin-coating, the substrate was allowed to stand for 2 minutes and then annealed at 100°C for 10 minutes to form the modification layer.

[0098] Preparation of perovskite light-absorbing layer: The same perovskite precursor solution and preparation process as in Example 1 were used to deposit and crystallize on the surface of the modified layer.

[0099] Comparative Example 2

[0100] Preparation of blend solution: Weigh 5 mg of 1,4-benzenediphosphonic acid and dissolve it in 10 mL of anhydrous ethanol to form a 2.3 mM solution; add 10 mg of SAM material (dodecyltrichlorosilane is selected, as long-chain alkyl groups have no π-π stacking ability), stir for 60 minutes and sonicate for 10 minutes to form a blend solution.

[0101] Modification layer preparation: The same FTO substrate as in Example 2 was used, and the spin coating parameters, standing and annealing conditions were the same as in Example 2 (600 rpm for 8 seconds, 4000 rpm for 25 seconds, annealing at 110°C for 15 minutes).

[0102] Preparation of perovskite light-absorbing layer: The light-absorbing layer was prepared using the same perovskite precursor solution and process as in Example 2.

[0103] Comparative Example 3

[0104] Preparation of blend solution: As in Example 3, 6 mg of 1,4-phenyldiphosphonic acid and 8 mg of phenylphosphonic acid (SAM) were weighed to prepare a blend solution.

[0105] Modification layer preparation: The same TiO2 modified ITO substrate as in Example 3 was selected, and the spin coating parameters were the same as in Example 3 (550 rpm for 6 seconds, 3800 rpm for 28 seconds), but the annealing temperature was changed to 80℃ (below the range of 100-120℃) and the annealing time was 10 minutes.

[0106] Preparation of perovskite light-absorbing layer: The light-absorbing layer was prepared using the same precursor solution and process as in Example 3.

[0107] Comparison of comparative examples and embodiments, and the beneficial effects of each embodiment.

[0108] In Comparative Example 1, due to the absence of 1,4-phenylenediphosphonic acid, SAM molecules easily aggregated during self-assembly, resulting in large intermolecular gaps, exposed areas in the modified layer, and a perovskite precursor solution contact angle exceeding 35°, leading to poor wettability and porous light-absorbing layers after crystallization. In contrast, Examples 1-9 all incorporated 1,4-phenylenediphosphonic acid, which anchors the substrate and fills the SAM gaps through its phosphate groups. The modified layer provides continuous coverage, and the hydrophilic terminals on the surface reduce the precursor contact angle to ≤15°, significantly improving wettability and laying the foundation for a uniform perovskite layer.

[0109] Comparative Example 2 used a SAM material without π-π stacking capability, which was difficult to self-assemble in an orderly manner under thermal drive. The molecules in the modified layer were arranged randomly, and 1,4-phenylenediamine could not effectively fill the gaps using it as a positioning point. The perovskite had a high proportion of direct contact with the substrate, resulting in severe interfacial recombination. The SAM materials used in Examples 1-9 (such as octadecyltrichlorosilane, phenylphosphonic acid, etc.) have π-π stacking capability. Under thermal drive, they are arranged in an orderly manner with 1,4-phenylenediamine as an anchor point. Combined with gap filling, they form a physical isolation layer, reducing interfacial recombination and improving carrier transport efficiency.

[0110] In Comparative Example 3, due to the excessively low annealing temperature (80℃), the covalent bonding between 1,4-phenylenediphosphonic acid and the substrate metal oxide was insufficient, resulting in incomplete self-assembly of SAM molecules, a loose modified layer structure, low exposure of surface phosphate groups, and decreased precursor wettability and crystal quality. Examples 1-9 strictly controlled the annealing temperature at 100-120℃ to ensure sufficient molecular-level reconstruction, strong covalent bonding, and orderly arrangement of SAM molecules, resulting in a stable modified layer structure and providing a high-quality interface for perovskite crystallization.

[0111] Specifically, Example 1 uses octadecyltrichlorosilane as SAM, paired with an ITO substrate, with a 1,4-phenylenediphosphonic acid to SAM mass ratio of 1:2. The modified layer exhibits excellent continuity, uniform perovskite grain size (500-800 nm), and a photoelectric conversion efficiency 18% higher than Comparative Example 1. Example 2 uses dodecyl phosphate SAM on an FTO substrate, with annealing at 110°C to promote bonding. The perovskite exhibits high crystallinity, and the X-ray diffraction peak intensity is 25% higher than Comparative Example 2. Example 3 uses phenylphosphonic acid as SAM, and a stable modified layer is achieved by annealing at 120°C for 5 minutes on a TiO2 substrate. The perovskite layer is free of pores, and its stability (after 1000 hours of light exposure testing) is 30% higher than Comparative Example 3.

[0112] Example 4 uses 4-tert-butylbenzoic acid (SAM), with a modification layer roughness of only 0.8 nm on a ZnO substrate. The bandgap matching of the mixed cation perovskite light-absorbing layer is optimized, achieving a short-circuit current density of 24.5 mA / cm². 2Example 5 uses 4-methoxyphenylphosphonic acid SAM, which has a distinct two-dimensional / three-dimensional mixed perovskite layered structure and increases the open-circuit voltage to 1.12V. Example 6 uses 2,4,6-trimethylphenylphosphonic acid as SAM, and the P element in the modification layer on the TiO2 nanotube array substrate is uniformly distributed. The all-inorganic cubic perovskite phase has high purity and excellent thermal stability.

[0113] Example 7 uses 4-cyanophenylphosphonic acid SAM, with a precise modification layer thickness (2.5 nm) on an ITO / PCBM substrate, extending the absorption edge of the mixed halide perovskite to 820 nm and expanding the light absorption range; Example 8 uses 3,5-bis(trifluoromethyl)phenylphosphonic acid SAM, with significant perovskite (002) crystal plane orientation on an FTO / TiO2 substrate, resulting in a 40% increase in carrier mobility; Example 9 uses 4-trifluoromethoxyphenylphosphonic acid as SAM, with a narrow half-maximum width at half maximum (25 nm) of the cesium-based perovskite photoluminescence peak on a Zn2SnO4 substrate, exhibiting high luminous efficiency and a cell fill factor of 80%.

[0114] In summary, Examples 1-9, through the synergistic effect of 1,4-phenylenediphosphonic acid and specific SAMs and optimized process parameters, outperformed the comparative examples in terms of modified layer continuity, perovskite wettability and crystal quality, and interface stability, ultimately achieving a comprehensive improvement in the photoelectric performance and stability of perovskite solar cells.

[0115] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a perovskite solar cell based on a self-assembled monolayer modified with small molecules, characterized in that, The method includes: Step 1: Dissolve the self-assembled monolayer material and 1,4-phenyl diphosphonic acid together in ethanol solvent to form a blend solution containing SAM and 1,4-phenyl diphosphonic acid; Step 2: Spin-coat the blended solution obtained in Step 1 onto the substrate surface, and then perform annealing treatment to form a modification layer on the substrate; wherein, 1,4-phenyl diphosphonic acid is anchored to the substrate surface through the phosphate group at one end, filling the gaps between SAM molecules to form a uniformly covered film, while the phosphate group at the other end of 1,4-phenyl diphosphonic acid is exposed on the surface of the modification layer. Step 3: Deposit a perovskite precursor solution on the surface of the modified layer formed in step 2, and perform crystallization treatment to form a perovskite light-absorbing layer; wherein, the phosphate groups exposed on the surface of the modified layer improve the wettability of the perovskite precursor solution on the surface of the modified layer.

2. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 1, characterized in that, Step 1: Dissolve the self-assembled monolayer material and 1,4-phenylenediamine in an ethanol solvent to form a blend solution containing SAM and 1,4-phenylenediamine, including: 1,4-Benzodiphosphonic acid is dissolved in ethanol solvent to form an ethanol solution containing 1,4-Benzodiphosphonic acid; The self-assembled monolayer material (SAM) was dissolved in the obtained ethanol solution containing 1,4-phenyl diphosphonic acid to form a mixed solution containing SAM and 1,4-phenyl diphosphonic acid. The resulting mixed solutions are thoroughly mixed to obtain a blended solution containing SAM and 1,4-phenyl diphosphonic acid; wherein, 1,4-phenyl diphosphonic acid is dispersed in the ethanol solution of step 1 to inhibit aggregation during subsequent SAM dissolution; the ethanol solution containing 1,4-phenyl diphosphonic acid serves as a solvent carrier to achieve the dissolution of SAM molecules in the 1,4-phenyl diphosphonic acid coexistence system.

3. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 2, characterized in that, Step 2: Spin-coating the blended solution obtained in Step 1 onto the substrate surface, followed by annealing to form a modification layer on the substrate, including: The obtained blend solution containing SAM and 1,4-phenylbisphosphonic acid was spin-coated onto the surface of the pretreated substrate to form a liquid composite film. After spin coating, the ethanol solvent in the liquid composite film is partially evaporated, inducing SAM molecules and 1,4-phenylenediamine molecules to initially align on the substrate surface. The treated membrane is annealed to trigger molecular-level reconstruction; among which, 1,4-Benzodium diphosphonate is chemically bonded and anchored to the substrate surface through phosphate groups; SAM molecules complete self-assembly into a monolayer under thermal drive. After thermally driven bonding and assembly, a continuous covering modification layer is formed on the substrate; wherein, Anchored 1,4-phenyldiphosphonic acid molecules occupy the gaps between SAM molecules, forming a physical isolation layer; The exposed phosphate groups form a hydrophilic terminal interface.

4. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 3, characterized in that, Phosphate group anchoring includes: 1,4-Benzodium diphosphonate molecules achieve molecular fixation by forming covalent bonds with metal oxides on the substrate surface through the phosphate group at one end; SAM self-assembly enhancement includes: Under thermal drive, SAM molecules undergo ordered self-assembly and arrangement with the 1,4-phenylenediamine anchored in step (a) as the positioning site. Gap filling and isolation, including: The gaps formed after the SAM molecules are arranged in step (b) of 1,4-phenylphosphonic acid molecule filling process block the direct contact channel between the perovskite layer and the substrate. The construction of hydrophilic interfaces includes: The phosphate group at the other end of the 1,4-benzenediphosphonic acid molecule is oriented to be exposed on the surface of the modified layer, forming a hydrophilic interface layer.

5. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 4, characterized in that, The obtained blend solution containing SAM and 1,4-phenyl diphosphonic acid was spin-coated onto the surface of a pretreated substrate to form a liquid composite film, comprising: The blend solution is quantitatively applied to the central region of the pretreated substrate surface; Initiate substrate rotation to allow the applied blend solution to spread radially along the substrate surface under centrifugal force; Maintaining the rotational state allows the radially spread solution to form a liquid film layer of uniform thickness; By controlling the rotation process, the solvent components in the liquid film layer are partially evaporated to form a liquid composite film containing oriented molecular groups; wherein, the SAM molecules and 1,4-phenylenediamine molecules are pre-oriented in a centrifugal force field.

6. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 5, characterized in that, After spin coating, the ethanol solvent in the liquid composite film is partially evaporated, inducing the initial orientation of SAM molecules and 1,4-phenylenediamine molecules on the substrate surface, including: The substrate rotation is terminated, so that the formed liquid composite film is in a static environment; During static evaporation, SAM molecules and 1,4-phenylenediamine molecules migrate to and accumulate on the substrate surface; As the ethanol solvent continues to evaporate, the molecules enriched on the substrate surface undergo directional alignment driven by the solid-liquid interface energy. When the ethanol evaporation reaches 30%-50%, a transition film layer with preliminary molecular orientation is formed; wherein, the 1,4-phenyl diphosphonic acid molecules are oriented with their phosphate groups toward the substrate; and the SAM molecules are aligned with their functional end groups toward the gas phase.

7. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 6, characterized in that, The treated membrane is annealed to trigger molecular-level reconstruction, including: The transition film layer with preliminary orientation is placed in a thermal field of 100-120℃; Thermal energy gives molecules in the transition film layer migration energy, causing them to move directionally on the substrate surface. Dual-mechanism reconstruction: 1,4-Benzodium diphosphonate molecules form POM covalent bonds with substrate metal atoms through phosphate groups; SAM molecules complete π-π stacking self-assembly with the bonded 1,4-Benzodium diphosphonate as anchor points; Maintain the hot zone for 5-15 minutes to solidify the molecular arrangement.

8. The method for preparing a perovskite solar cell based on a small molecule-modified self-assembled monolayer according to claim 7, characterized in that, Step 3: Deposit a perovskite precursor solution on the surface of the modified layer formed in Step 2, and perform crystallization treatment to form a perovskite light-absorbing layer, including: A perovskite precursor solution is applied to the surface of the modified layer; The exposed phosphate groups on the surface of the modified layer ensure that the contact angle of the precursor solution is ≤15°; Gradient spin coating: First stage: Rotate at 500-1000 rpm to spread the solution radially; Second stage: Rotate at 3000-4000 rpm to form a uniform liquid film; At the end of the second stage, an antisolvent is added dropwise to induce the instantaneous formation of perovskite crystal nuclei; The crystal nucleus liquid film is annealed at 100-110℃ to complete crystal growth.