A high-performance perovskite solar cell passivated by polyacrylic acid-grafted carbon nanotubes and a preparation method thereof

Abstract

The present invention relates to a high-performance perovskite solar cell passivated by polyacrylic acid grafted carbon nanotubes and a preparation method thereof, belonging to the application field of perovskite solar cells. The present invention is a simple and effective method that can not only improve the device performance of perovskite solar cells but also inhibit the release of lead (II). Adding the synthesized polyacrylic acid grafted carbon nanotubes as an additive to the perovskite precursor solution can accelerate the nucleation of perovskite and regulate the growth of perovskite in a way of preferentially vertical orientation and reducing defect states. In addition, the addition of highly conductive carbon nanotubes improves the hole mobility and electron mobility of perovskite. The perovskite solar cell device added with polyacrylic acid grafted carbon nanotubes obtains a higher power conversion efficiency (PCE) than that without addition, and the stability is significantly improved. In addition, due to the excellent lead adsorption ability of polyacrylic acid grafted carbon nanotubes, about 70% of lead leakage is prevented, which provides a new perspective for environmentally friendly perovskite solar cells.

Description

Technical Field

[0001] The present invention relates to a high-performance perovskite solar cell passivated by polyacrylic acid-grafted carbon nanotubes and a preparation method thereof, and a study on inhibiting lead pollution, belonging to the application field of perovskite solar cells. Background Art

[0002] Solar energy is one of the new energy sources attracting much attention in the 21st century. In the past few decades, the field of solar cells has been considered one of the most promising alternatives to traditional fossil fuels. Among numerous photovoltaic devices, the power conversion efficiency of perovskite solar cells has achieved the fastest development in recent years. Perovskite has become an ideal material for photovoltaic power generation due to its high optical absorption coefficient, high carrier mobility, long carrier diffusion length, etc.

[0003] However, the defects of perovskite severely restrict the efficiency and stability of the device. Effectively passivating the defect states between perovskite grain boundaries in the perovskite active layer is of great significance for perovskite light-responsive devices. On the other hand, the toxic lead component in perovskite poses a great threat to the ecosystem and human health, which is a major obstacle to the practical application of perovskite. Recently, in order to avoid the toxicity of lead, new lead-free perovskites have been tried. However, the efficiency of lead-free perovskite solar cells is much lower, which indicates the important role of lead in the perovskite structure. Therefore, implementing a lead pollution prevention and control strategy is a necessary choice by strongly controlling lead ions within the perovskite layer without leakage from the device. Summary of the Invention

[0004] The present invention develops a high-performance perovskite solar cell passivated by polyacrylic acid-grafted carbon nanotubes and a preparation method thereof, which is a simple and effective method that can not only inhibit the release of lead (II) but also improve the performance of perovskite solar cell devices. Adding the synthesized polyacrylic acid-grafted carbon nanotubes as an additive to the perovskite precursor solution can accelerate the nucleation of perovskite, regulate the growth of perovskite in a way of preferentially vertical orientation and reducing defect states, and improve the hole mobility and electron mobility of perovskite. Moreover, the perovskite battery device based on the organic-inorganic hybrid composite material obtains a higher power conversion efficiency (PCE), and the stability is significantly improved. In addition, due to the excellent lead adsorption ability of functionalized carbon nanotubes, about 70% of lead leakage is prevented, and an environmentally friendly perovskite solar cell is obtained.

[0005] In order to achieve the above technical objectives, the technical solution of the present invention includes:

[0006] The present invention provides a high-performance perovskite solar cell passivated by polyacrylic acid grafted carbon nanotubes. The cell includes an ITO conductive base layer, an electron transport layer, a perovskite light absorption layer, a hole transport layer, and a metal electrode from bottom to top. The perovskite light absorption layer is a perovskite light absorption layer passivated by functionalized carbon nanotubes.

[0007] Preferably, the electron transport layer is a SnO2 electron transport layer.

[0008] Preferably, the perovskite light absorption layer is an APbX3 lead-based perovskite light absorption layer, where A is selected from CH3NH 3+ (MA + ), CH(NH2) 2+ (FA + ) and Cs + or one or more of them; X is selected from Cl - , Br - and I - or one or more of them.

[0009] Preferably, the hole transport layer is a Spiro-OMeTAD [2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene] hole transport layer.

[0010] Preferably, the metal electrode is an Au electrode.

[0011] The present invention also provides a preparation method of the above high-performance perovskite solar cell passivated by polyacrylic acid grafted carbon nanotubes, including the following steps:

[0012] (1) Deposit an electron transport layer on the ITO conductive base layer;

[0013] (2) Deposit a perovskite light absorption layer passivated by functionalized carbon nanotubes on the electron transport layer in step (1);

[0014] (3) Deposit a hole transport layer on the perovskite light absorption layer in step (2);

[0015] (4) Deposit a metal electrode on the hole transport layer in step (3), and a high-performance perovskite solar cell passivated by polyacrylic acid grafted carbon nanotubes and inhibiting lead pollution is obtained.

[0016] Preferably, the ITO conductive base layer needs to be ultrasonically treated with a cleaning agent, deionized water, acetone, and isopropyl alcohol in sequence before use, dried with nitrogen, and then treated with ultraviolet ozone plasma.

[0017] Preferably, the electron transport layer is a SnO2 electron transport layer, and its deposition method is as follows: spin-coat the SnO2 precursor solution on a clean ITO substrate at a speed of 4000 rpm for 30 s, the annealing temperature is 150 °C, and the annealing time is 30 min. The SnO2 precursor solution is prepared from 15% aqueous SnO2 solution: deionized water (V\V) = 1:3.

[0018] Preferably, the preparation method of the perovskite precursor solution is as follows: dissolve PbI2 and MAI in a mixed solvent composed of DMF and DMSO (volume ratio 4:1), and stir and react at 60 °C for 1 h to form a perovskite precursor. Add CNT-PAA to the perovskite precursor and stir overnight at 60 °C. Drop the solution onto the SnO2-coated ITO substrate at a speed of 4000 rpm / min for 40 s. After spin-coating for 10 s, chlorobenzene is quickly dropped onto the sample surface, and then the film is annealed at 70 °C for 10 min.

[0019] Preferably, the preparation method of the polyacrylic acid grafted carbon nanotubes is as follows:

[0020] (1) Ultrasonically disperse carbon nanotubes in concentrated nitric acid, and after acidification reaction, carbon nanotubes with many carboxyl sites on the surface (CNT-COOH) are obtained for subsequent functionalization. React the acidified carbon nanotubes with thionyl chloride to obtain acylated carbon nanotubes (CNT-COCl). Ultrasonically disperse the acylated carbon nanotubes in a diol compound, and the acyl groups on the surface of the carbon nanotubes are replaced by hydroxyl groups to obtain hydroxylated carbon nanotubes (CNT-OH). Disperse the hydroxylated carbon nanotubes in N-methylpyrrolidone (NMP), add 2-bromoisobutyryl bromide, and further modify the carbon nanotubes (CNT) with active initiating groups to obtain brominated carbon nanotubes (CNT-Br), which are used as initiators for atom transfer radical polymerization (ATRP).

[0021] (2) Ultrasonically mix the brominated carbon nanotubes (CNT-Br), polymer monomers, catalysts for active polymerization reactions, cocatalysts, and solvents, and react to obtain functionalized carbon nanotubes grafted with complexing polymers (CNT-g-polymer).

[0022] Furthermore, in the step (1): the carbon nanotubes include both single-walled carbon nanotubes and can also be double-walled carbon nanotubes or multi-walled carbon nanotubes.

[0023] Furthermore, in the step (1): the diols can include, but are not limited to, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1,6-hexanediol, octanediol, nonanediol, diglycol, etc.

[0024] Furthermore, in the step (1): the active initiating groups are:

[0025]

[0026] X is Br or Cl.

[0027] Further, in the step (2): the ATRP polymerization catalyst is a monovalent copper compound, and the monovalent copper compound includes but is not limited to copper salts such as CuBr, CuCl, etc. and monovalent copper complexes such as CuBr(PPh3)3, [Cu(CH3CN)4]PF6, etc., and the co-catalyst is PMDETA.

[0028] Further, in the step (2): when preparing polyacrylic acid-based carbon nanotubes (CNT-PAA), first use tert-butyl acrylate (tBA) as the polymer monomer to react according to the above steps to obtain carbon nanotubes based on poly(tert-butyl acrylate) (CNT-PtBA), and then hydrolyze to obtain polyacrylic acid-based carbon nanotubes. The specific hydrolysis steps are as follows: Disperse the carbon nanotube-based poly(tert-butyl acrylate) in dichloromethane, add an excessive amount of trifluoroacetic acid, and react under magnetic stirring for 24 h. After the reaction is completed, centrifuge the product, wash it several times with absolute ethanol, and dry it in a vacuum oven at 50 °C for 24 h to obtain polyacrylic acid-based carbon nanotubes.

[0029] Further, in the step (2): the temperature and time of the living polymerization reaction are related to the type of polymer monomer, and the reaction time can be adjusted according to the situation. Different reaction times can obtain polymer layers with different thicknesses. The temperature of the polymerization reaction can be 25 °C to 120 °C, and the reaction time is preferably 8 h to 48 h.

[0030] Preferably, the hole transport layer is a Spiro-OMeTAD hole transport layer. The deposition method is as follows: Spin-coat Spiro-MeOTAD on the perovskite film, and the spin-coated mixed solution contains Spiro-MeOTAD, 4-TBP, Li-TFSI, and stock solution acetonitrile.

[0031] Preferably, deposit an 80-nm gold film on the HTM film as the metal electrode by thermal evaporation under low vacuum.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. The present invention synthesizes a novel functional carbon nanotube, with a dense covalently grafted polyacrylic acid layer on its surface, and introduces it as an additive into perovskite. The carbon nanotube has certain P-type semiconductor properties. Introducing it into the perovskite active layer can reduce the defect states on the crystal surface and effectively improve the charge transport ability, thereby enhancing the performance of the light-responsive device. At the same time, introducing some polymers containing passivating groups (such as carboxyl, amino, pyridyl, cyano, etc.) into the perovskite layer can effectively passivate the trap states at the perovskite grain boundaries and inhibit the migration of lead ions. The polymers can carry more functional groups, which interact with the coordinatively unsaturated halide ions and lead ions in the perovskite grain boundaries respectively, thus achieving the effects of passivating defect states and inhibiting lead release. This organic-inorganic hybrid composite combines the high electron transport property of carbon nanotubes, the passivation effect of functionalized polymers, and the high carrier mobility of perovskite. It can be used to prepare high-performance perovskite solar cells that are harmless to the environment. In addition, the polymer connected to the surface of the carbon nanotube can greatly enhance the dispersibility of the carbon nanotube in the solution, which is beneficial to the uniform dispersion of CNT-PAA in the film when preparing the perovskite active layer film.

[0034] 2. The present invention innovatively designs a polymer-assisted deposition method to uniformly coat perovskite on the surface of carbon nanotubes, obtaining a functionalized carbon nanotube-polymer / perovskite ternary system. This organic-inorganic hybrid composite combines the high electron transport property of carbon nanotubes, the passivation effect of functionalized polymers, and the high carrier mobility of perovskite.

[0035] 3. The present invention creatively grafts or coats a functionalized polymer on the surface of the carbon nanotube, which acts as a complexing agent in the composite material, assisting in the growth of perovskite nanocrystals, tightly connecting the carbon nanotube and perovskite, and at the same time acting as a Lewis acid (or Lewis base) dopant, interacting with perovskite, improving the interface contact, having the effect of passivating the surface defect states of perovskite. Without using perovskite defect state passivation materials, it reduces the defect state density at the interface, thereby enhancing the efficiency and stability of the light-responsive device.

[0036] 4. The present invention innovatively constructs a tightly bound composite system, which is equivalent to installing many high-speed electron transport tunnels inside the perovskite nanocrystals. The carbon nanotubes can also be regarded as internal electrodes, and their spacing is several orders of magnitude smaller than that of macroscopic production electrodes. Therefore, the transit time of carriers is greatly reduced, which will also lead to a significant increase in the response speed of the device. The polyacrylic acid chain grafted on the surface of the carbon nanotube in the present invention can strongly chelate with Pb 2+ to show a high Pb 2+The capture ability makes it easy to precipitate from water and reduces the lead (II) leakage exposed to water to below the hazardous waste limit. Therefore, adding CNT-PAA can effectively inhibit lead pollution, which provides a new perspective for environmentally friendly perovskite solar cells.

[0037] 5. For the first time, the present invention adds the polymer PAA grafted on the surface of carbon nanotubes to the perovskite light absorption layer, which has not been reported before. The prepared perovskite solar cells have outstanding results in terms of lead adsorption performance, humidity stability, optoelectronic performance, etc.

[0038] The perovskite light absorption layer is the perovskite light absorption layer lead passivated by polyacrylic acid grafted carbon nanotubes. Compared with adding carbon nanotubes, polymer PAA, or a mixture of carbon nanotubes and polymer PAA to the perovskite light absorption layer alone, it is greatly improved in terms of lead adsorption performance, humidity stability, optoelectronic performance, etc. Description of the Drawings

[0039] Figure 1 Top view (a, b, c) and SEM cross-sectional view (d, e, f) of the perovskite thin films after being passivated by CNT-PAA-S and CNT-PAA-L in Examples 1 and 2, and the perovskite thin film without passivation treatment in Comparative Example 1.

[0040] Figure 2 Physical pictures of (I) pure CNT-PAA aqueous solution and (II) the mixture of CNT-PAA and PbI2 in aqueous solution prepared in Example 1.

[0041] Figure 3 (a) Storage stability and (b) PCE in ambient air of the perovskite thin films after being passivated by CNT-PAA-S and CNT-PAA-L in Examples 1 and 2, and the perovskite thin film without passivation treatment in Comparative Example 1.

[0042] Figure 4 Current-voltage curve of the perovskite solar cell. Detailed Embodiments

[0043] The following will further elaborate on the present invention in combination with specific embodiments:

[0044] Example 1

[0045] A high-performance perovskite solar cell based on polyacrylic acid grafted carbon nanotube passivation includes the following steps:

[0046] (1) Synthesis of ATRP initiator CNT-Br

[0047] First, the original carbon nanotubes (0.4 g) were treated with 10 mL of 60% HNO3 aqueous solution at 120 °C for 13 h, then the pH was adjusted to neutral with water, washed with ethanol, and filtered. The resulting CNT-COOH was dried overnight in vacuo at 60 °C. Subsequently, CNT-COOH was reacted with 8 mL of SOCl2 at 65 °C for 24 h, and the product was obtained by centrifugation. Then the generated CNT-COCl was reacted with an excess of ethylene glycol at 120 °C for 48 h to form CNT-OH, which was dried overnight in vacuo at 50 °C. CNT-OH was stirred in 15 mL of anhydrous NMP. Then 10 mL of 2-bromo-2-methylpropionyl bromide was slowly added, and the mixture was stirred at 0 °C for 2 h and then continued to be stirred at room temperature for 48 h. Finally, the black solid product CNT-Br was filtered and separated, washed three times with an appropriate amount of chloroform, and dried overnight in vacuo at 50 °C.

[0048] (2) Synthesis of CNT-g-PtBA via ATRP using CNT-Br initiator

[0049] 0.0503 g of CNT-Br (0.021 mmol of Br), 6.0 mg (0.042 mmol) of CuBr, 0.0073 g (0.042 mmol) of PMDETA, and 0.25 mL of DMF were placed in a 10 mL flask. After evacuation and filling with nitrogen three times, 0.1006 g (0.78 mmol) of tBA was injected into the flask using a syringe. The flask was immersed in an oil bath at 60 °C. The mixture was stirred for 4 h, then diluted with CHCl3 and vacuum filtered using a 0.22 μm polycarbonate membrane. The filtered material was dispersed in CHCl3, then filtered and washed with CHCl3, and the solid was dried in a vacuum drying oven for 24 h to obtain CNT-PtBA.

[0050] (3) Synthesis of CNT-g-PAA by hydrolyzing the tert-butyl ester groups of the PtBA block

[0051] 0.0020 g of CNT-PtBA and 5 mL of CHCl3 were placed in a 10 mL round-bottom flask. After ultrasonic dispersion, 0.5 mL of trifluoroacetic acid was added to the mixture, and the mixture was stirred at room temperature for 24 h. The precipitate was collected by centrifugation and washed several times with ethanol, and the solid was dried in a vacuum drying oven for 24 h to obtain CNT-g-PAA.

[0052] (4) Synthesis of CNT-g-PAA / CsPbBr3 hybrid nanocomposites

[0053] Dissolve CNT-g-PAA (10 mg) in DMF (20 mL) at room temperature by ultrasonic wave. Then add PbBr2 (75.3 mg) to the reaction system. Stir the mixture under argon for 1 hour to ensure that the PAA block is filled with the precursor. Then slowly heat the reaction system to 180 °C. Inject Cs2CO3 powder (35.5 mg) dissolved in deionized water into the reaction system with a syringe, and reflux the reaction system for 2 h. Obtain the product by centrifugation, wash it with ethanol and dry it.

[0054] (5) Fabrication of solar cells

[0055] S1. Ultrasonically clean the ITO glass in cleaning agent, deionized water, acetone and isopropanol in sequence for 10 minutes. Then dry it at 80 °C and treat it with ultraviolet ozone plasma for 30 minutes.

[0056] S2. The SnO2 precursor solution is prepared in 15% aqueous SnO2 solution: deionized water (V\V) = 1:3. Spin-coat it on the clean ITO substrate at a speed of 4000 rpm for 30 s and anneal it in ambient air at 150 °C for 30 min. After that, the substrate is transferred to the glove box for further treatment.

[0057] S3. For the perovskite precursor, first, dissolve 1.25 mmol PbI2 and MAI in 1 mL of a mixed solvent composed of DMF and DMSO (volume ratio 4:1), and stir and react at 60 °C for one hour to form the perovskite precursor. Add 2.5 mg of CNT-g-PAA (the obtained sample is denoted as CNT-PAA-S, where the proportion of PAA is 22.4%) to 1 ml of the perovskite precursor, and stir it overnight at 60 °C for use. Drop the solution onto the SnO2-coated ITO substrate at a speed of 4000 rpm / min for 40 s. After spin-coating for 10 s, quickly drop chlorobenzene onto the surface of the sample, and then anneal the film at 70 °C for 10 minutes.

[0058] S4. Spin-coat Spiro-MeOTAD on the perovskite film. The spin-coated mixed solution contains 72.3 mg of Spiro-MeOTAD, 28.8 μL of 4-TBP, and 17.5 μL of Li-TFSI (520 mg of Li-TFSI, 1 mL of acetonitrile).

[0059] S5. Finally, deposit an 80-nm gold film as the back electrode on the HTM film by thermal evaporation under low vacuum.

[0060] Example 2

[0061] A high-performance perovskite solar cell based on the passivation of polyacrylic acid grafted carbon nanotubes, comprising the following steps:

[0062] Except for step (5) S3, the preparation methods of the remaining steps are the same as those in Example 1.

[0063] Step (5) S3 of this example is specifically as follows: For the perovskite precursor, first, 1.25 mmol of PbI2 and MAI are dissolved in 1 mL of a mixed solvent composed of DMF and DMSO (volume ratio 4:1), and stirred at 60 °C for one hour to form a perovskite precursor. 4.0 mg of CNT-g-PAA (the obtained sample is denoted as CNT-PAA-L, where the proportion of PAA is 35.1%) is added to 1 ml of the perovskite precursor, and stirred overnight at 60 °C. The solution is dropped onto an ITO substrate coated with SnO2 at a speed of 4000 rpm / min for 40 seconds. After spin-coating for 10 seconds, chlorobenzene is quickly dropped onto the sample surface, and then the film is annealed at 70 °C for 10 minutes.

[0064] Comparative Example 1 Perovskite solar cell without passivation treatment of polyacrylic acid-grafted carbon nanotubes

[0065] This cell consists of an ITO conductive base layer, an SnO2 electron transport layer, a perovskite light absorption layer, a Spiro-OMeTAD hole transport layer, and an Au electrode from bottom to top. The perovskite light absorption layer is a perovskite light absorption layer without CNT-PAA treatment. Its preparation method is the same as that of Example 1 except for step (5) S3.

[0066] Step (5) S3 of this example is specifically as follows: For the perovskite precursor, first, 1.25 mmol of PbI2 and MAI are dissolved in 1 mL of a mixed solvent composed of DMF and DMSO (volume ratio 4:1), and stirred at 60 °C for one hour to form a perovskite precursor. The solution is dropped onto an ITO substrate coated with SnO2 at a speed of 4000 rpm / min for 40 seconds. After spin-coating for 10 seconds, chlorobenzene is quickly dropped onto the sample surface, and then the film is annealed at 70 °C for 10 minutes.

[0067] As Figure 1 shown, by comparing Example 1, 2 and Comparative Example 1, it can be found that with the addition of CNT-PAA, the grain size increases ( Figure 1 a-1c). In addition, due to the presence of conductive CNTs, some obvious white spots appear in the perovskite with the addition of CNT-PAA ( Figure 1 b and 1c). It can be seen from the SEM cross-sectional images of Figure 1 e-1f that CNTs are inserted into perovskite particles, indicating that the growth of perovskite starts from the surface of carbon nanotubes.

[0068] Performance test of the example

[0069] (1) Lead(II) Adsorption Test

[0070] A small amount of PbI2 was added to the CNT-g-PAA and CNT-g-PAA / CsPbBr3 aqueous solutions prepared in Example 1 respectively. After ultrasonic treatment, it was left standing for 12 h.

[0071] As Figure 2 shown, pure CNT-PAA can be well dispersed in water to form a uniform black solution. After adding some PbI2 to the solution, CNT-PAA precipitates at the bottom of the bottle. This is because Pb 2+ ions attach to the surface of CNT-PAA, resulting in a decrease in its solubility in water. After standing for 24 hours, the black solution based on bare CNT-PAA is still well dispersed; while the mixed solution is completely transparent, and all CNTs precipitate at the bottom without residual PbI2. These results indicate that CNT-PAA can strongly associate with lead ions in water even under high-power ultrasonic treatment, and the adsorbed Pb 2+ can be easily separated from the polluted water to form insoluble CNT-PAA-PbI2. This shows that the present invention has great potential in preventing lead(II) emissions.

[0072] (2) Humidity Stability Test

[0073] The perovskite solar cells passivated with CNT-PAA with different mass fractions prepared in Examples 1 and 2 and the perovskite solar cell without passivation prepared in Comparative Example 1 were stored in an N2 atmosphere for 1400 hours and stored in ambient air with a relative humidity of 30% for 800 hours, and their performance changes were recorded.

[0074] As Figure 3 (a) shown, after adding CNT-PAA to the perovskite, the stability of the perovskite solar cell is significantly enhanced. Especially after storing CNT-PAA-S and CNT-PAA-L in an N2 atmosphere for 1400 hours, the initial efficiency of the device remains above 80%, showing good storage stability. As Figure 3 (b) shown, after storing in ambient air with a relative humidity of 30% for 800 hours, the initial PCEs of the pristine perovskite, CNT-PAA-S and CNT-PAA-L perovskites are retained at 25.2, 80.1 and 80.9% respectively, indicating that the water resistance of the device is also enhanced. The improvement in stability is mainly due to the increase in perovskite crystallinity and the strong binding between the PAA chains and the Pb 2+ ions on the perovskite particles, which can significantly slow down the penetration of moisture and improve the stability of the perovskite structure.

[0075] (3) Photoelectric Performance Test

[0076] Under simulated sunlight irradiation conditions, the current-voltage curves (J-V) of the perovskite solar cells prepared in Example 1, Example 2, and Comparative Example 1 were tested respectively. The results are shown in Table 1 and Figure 4 .

[0077] From Figure 4 and Table 1, it can be seen that the open-circuit voltage (Voc), fill factor (FF), and current density (Jsc) have all been improved after the CNT-PAA passivation treatment, and the performance under the CNT-PAA-L condition is the best. Moreover, the photoelectric conversion efficiency of the cells treated with CNT-PAA in Example 1 and Example 2 is higher than that of the untreated cells in Comparative Example 1. It shows that the photoelectric performance parameters of Example 2 and Example 3 are superior to those of Comparative Example 1, proving that the treatment of CNT-PAA plays a role in improving the photoelectric performance of perovskite solar cells.

[0078] Table 1 Photoelectric performance parameters of each perovskite solar cell:

[0079]

[0080] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitution are within the protection scope required by the present invention.

Claims

1. A high-performance perovskite solar cell passivated by polyacrylic acid grafted carbon nanotubes, comprising the following steps: (1) Synthesis of ATRP initiator CNT-Br First, 0.4 g of pristine carbon nanotubes was treated with 10 mL of 60% aqueous HNO3 solution at 120 °C for 13 h, then the pH was adjusted to neutral with water, washed with ethanol, and filtered; the resulting CNT-COOH was dried overnight in vacuo at 60 °C; Subsequently, CNT-COOH was reacted with 8 mL of SOCl2 at 65 °C for 24 h, and the product was obtained by centrifugation; then the resulting CNT-COCl was reacted with an excess of ethylene glycol at 120 °C for 48 h to form CNT-OH, which was dried overnight in vacuo at 50 °C; CNT-OH was stirred in 15 mL of anhydrous NMP; then 10 mL of 2-bromoisobutyryl bromide was added, stirred at 0 °C for 2 h, and continued to stir at room temperature for 48 h; finally, the black solid product CNT-Br was filtered and separated, washed three times with an appropriate amount of chloroform, and dried overnight in vacuo at 50 °C; (2) Synthesis of CNT- g -PtBA using the CNT-Br initiator via ATRP 0.0503 g of CNT-Br Br, 6.0 mg of CuBr, 0.0073 g of PMDETA, and 0.25 mL of DMF were placed in a 10 mL flask; after evacuation and purging with nitrogen three times, 0.1006 g of 0.78 mmol of tBA was injected into the flask with a syringe; the flask was immersed in an oil bath at 60 °C; the mixture was stirred for 4 h, then diluted with CHCl3 and vacuum filtered using a 0.22 μm polycarbonate membrane; the filtered material was dispersed in CHCl3, then filtered and washed with CHCl3, and the solid was dried in a vacuum drying oven for 24 h to obtain CNT-PtBA; (3) Synthesize CNT- g -PAA by hydrolyzing the tert-butyl ester groups of the PtBA block Place 0.0020 g of CNT-PtBA and 5 mL of CHCl3 in a 10 mL round-bottom flask. After ultrasonic dispersion, add 0.5 mL of trifluoroacetic acid to the mixture and stir at room temperature for 24 h; centrifuge to collect the precipitate and wash it several times with ethanol. Dry the solid in a vacuum drying oven for 24 h to obtain CNT- g -PAA; (4) Fabrication of the solar cell S1. The ITO glass was ultrasonically cleaned in a cleaning agent, deionized water, acetone, and isopropanol in sequence for 10 minutes; then dried at 80 °C and treated with ultraviolet ozone plasma for 30 minutes; S2. The SnO2 precursor solution was prepared from a 15% aqueous SnO2 solution: deionized water volume ratio of 1:3; it was spin-coated on the clean ITO substrate at 4000 rpm for 30 s and annealed in ambient air at 150 °C for 30 min; thereafter, the substrate was transferred to a glove box for further processing; S3. For the perovskite precursor, first, dissolve 1.25 mmol of PbI2 and MAI in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1, and stir and react at 60 °C for one hour to form the perovskite precursor; add 2.5 mg of CNT- g -PAA, and the obtained sample is denoted as CNT-PAA-S, where PAA accounts for 22.4% by weight, add it to 1 ml of the perovskite precursor, and stir overnight at 60 °C for use; drop the solution onto the SnO2-coated ITO substrate at a speed of 4000 rpm for 40 seconds. After spin-coating for 10 seconds, chlorobenzene is quickly dropped onto the surface of the sample, and then the film is annealed at 70 °C for 10 minutes; S4. Spiro-MeOTAD was spin-coated on the perovskite film, and the spin-coated mixed solution contained 72.3 mg of Spiro-MeOTAD, 28.8 μL of 4-TBP, 17.5 μL of Li-TFSI 520 mg of Li-TFSI, and 1 mL of acetonitrile; S5. Finally, an 80 nm gold film was deposited as the back electrode on the HTM film under low vacuum by thermal evaporation.

Images