Preparation of array-type TiO2 / CdS composite electron transport layer and its application in bulk heterojunction solar cells

Abstract

The present invention discloses the preparation of an array-type TiO2 / CdS composite electron transport layer and its application in bulk heterojunction solar cells. First, a spin-coating process is used to prepare a dense TiO2 layer. Second, a hydrothermal method is used to prepare CdS nanorods on the TiO2 dense layer substrate to obtain an array-type TiO2 / CdS composite nanostructured electron transport layer, thereby designing a bulk heterojunction solar cell. In the composite nanostructured electron transport layer prepared by the present invention, the deposition of the dense TiO2 layer facilitates the vertical growth of the CdS nanorods on the substrate, resulting in a high-quality one-dimensional structured electron transport layer. The TiO2 / CdS composite electron transport layer forms an ideal gradient energy level arrangement with the solar cell absorption layer material, improving the efficiency of photogenerated electron extraction at the interface. The vertical growth characteristics of the CdS nanorods provide a more efficient carrier transmission path, helping to suppress charge recombination within the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and in particular relates to the preparation of an array-type TiO2 / CdS composite electron transport layer and its application in bulk heterojunction solar cells. Background Art

[0002] Solar energy is a new type of green energy with great application prospects, attracting extensive attention and research from governments and scientists worldwide. Solar cells can directly convert sunlight into electricity, making them a highly efficient way to utilize solar energy. The development of new, high-efficiency, low-cost, and long-life solar cells is a current research hotspot in photovoltaic technology.

[0003] The electron transport layer is one of the important components of solar cells, and plays an important role in transporting electrons and blocking holes. TiO2 is a traditional electron transport material and is widely used in various new photovoltaic solar cells, including dye-sensitized solar cells (DSCs), quantum dot-sensitized solar cells (QDSCs) and perovskite solar cells (PSCs). The wide use of TiO2 is due to its suitable conduction band bottom position, wide optical band gap (~3.2eV) and low preparation cost. However, TiO2 usually has a low electron mobility (only 10 -4 cm 2 ·V -1 ·s -1 ), far lower than other common n-type inorganic semiconductors such as SnO2, ZnO, and CdS. The metal sulfide semiconductor CdS has been demonstrated as a highly efficient electron transport material in traditional thin-film solar cells, boasting an electron mobility two orders of magnitude higher than that of TiO2. From a stability perspective, CdS exhibits excellent chemical stability, resisting UV light and generating no defect states. Furthermore, it can be prepared using a low-cost, low-temperature chemical bath method, facilitating large-scale industrial production.

[0004] At present, CdS materials with morphologies such as one-dimensional nanowires / rods, three-dimensional flowers, hollow spheres and nanoparticles have been successfully prepared. The preparation techniques involved mainly include hydrothermal method, chemical vapor deposition method, chemical vapor deposition method, template method, high-temperature pyrolysis method, solvent thermal method, etc. Among them, the nanomaterials prepared by the hydrothermal method have high purity, good crystal form, good dispersibility, controllable shape and size, and the reaction is carried out in a closed autoclave, which is conducive to the synthesis reaction of toxic systems. In view of the unique optoelectronic properties of one-dimensional CdS nanorods, they have received extensive attention and research in various optoelectronic devices. Based on the one-dimensional nanorod structure, the electron transport layer can be designed and constructed into a bulk heterojunction solar cell, which is beneficial to efficient charge transport inside the device (Xiangchun Zhao et al., J.Phys.D:Appl.Phys.2021,54,134001). Ideal one-dimensional CdS nanorod structures require vertical growth and a suitable aspect ratio. Growing high-quality CdS nanorods on rough FTO conductive substrates is challenging. Therefore, there is an urgent need to explore suitable technical solutions for producing vertically grown one-dimensional CdS nanorods and further constructing ideal bulk heterojunction solar cells. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a method for preparing an array-type TiO2 / CdS composite electron transport layer and its application in bulk heterojunction solar cells. The radially transporting composite nanoelectron transport layer of the present invention enables efficient carrier transport, improves interfacial charge extraction, and reduces charge recombination within the device, thereby achieving high-performance solar cells.

[0006] The composite nano-electron transport layer designed in the present invention is prepared by spin coating a dense TiO2 layer on a conductive glass, and further growing one-dimensional CdS nanorods on the TiO2 substrate using a hydrothermal method to obtain an array-type TiO2 / CdS composite electron transport layer.

[0007] In the composite electron transport layer, the thickness of the TiO2 dense layer (c-TiO2) is 20-30 nm, and the length of the CdS nanorod is 100-500 nm.

[0008] The method for preparing an array-type TiO2 / CdS composite electron transport layer of the present invention comprises the following steps:

[0009] Step 1: Place the cleaned conductive substrate into the UV ozone cleaning machine and treat with ozone for 15-25 minutes;

[0010] Step 2: Prepare a 0.1-0.2 mol / L n-butanol solution of bis(acetylacetonato)diisopropyl titanate and stir at room temperature for 1-2 hours to form a dense layer precursor solution;

[0011] Step 3: Take 40-120 μL of dense layer precursor solution and drop it onto the conductive substrate, and spin-coat it at a speed of 500-1000 rpm for 3-6 seconds, and then spin-coat it at a speed of 2000-3000 rpm for 30-50 seconds;

[0012] Step 4: After spin coating, place the sample on a heating table and anneal at 100-500°C for 10-20 minutes. Finally, place it in a muffle furnace and gradually heat it to 450-550°C at a heating rate of 5-10°C / min. Sinter it for 30-60 minutes to form a dense TiO2 layer.

[0013] Step 5: 0.005-0.015 M Cd(NO3)2·4H2O, 0.02-0.04 M thiourea, and 0.003-0.012 M glutathione (GSH) were added to 60-100 mL of deionized water in sequence and stirred at room temperature for 10-20 min.

[0014] Step 6: Immerse the conductive glass / TiO2 dense layer with the conductive surface facing down into the solution of step 5 and transfer it to a reactor. After hydrothermal reaction at 180-220°C for 50-150 minutes, take it out, rinse it with plenty of clean water, and place it in a drying oven to dry to obtain a light yellow CdS film, which is the TiO2 / CdS nanorod array composite nanostructure.

[0015] The present invention utilizes an array-type TiO2 / CdS composite electron transport layer in a bulk heterojunction solar cell using the TiO2 / CdS nanorod array composite nanostructure as the electron transport layer. The bulk heterojunction solar cell has a device structure consisting of: conductive substrate / TiO2 dense layer / CdS nanorods / perovskite layer / hole transport layer / metal electrode.

[0016] The bulk heterojunction solar cell includes a perovskite solar cell or an antimony-based chalcogenide thin film solar cell.

[0017] The specific steps include:

[0018] Step 7: Preparation of the Absorbent Layer

[0019] 7a. Perovskite thin film

[0020] At ambient temperature, 400-500 mg of PbI2, 150-200 mg of MAI (or MAI / FAI, MAI / FAI / CsI, etc.), and 60-80 mg of DMSO (molar ratio of 1:1:1) were dissolved in 500-700 mg of DMF. The mixture was stirred in a nitrogen atmosphere in a glove box for 1 hour to obtain a perovskite precursor solution. 40-60 μL of the perovskite precursor solution was dropwise added to the surface of a FTO / c-TiO2 / CdS nanorod array film, followed by spin coating at 3000-5000 rpm for 20-30 seconds. After 6-8 seconds, a drop (60-120 μL) of the antisolvent ethyl acetate was added to the rotating substrate. The coated film was heat-treated on a hot plate at 100-120°C for 6-12 minutes. During the drying process at 100-120°C, the film color changed from light yellow to dark brown, indicating the formation of a perovskite film.

[0021] 7b. Antimony-based chalcogenide thin films

[0022] 40 mL of deionized water and 15-25 mM potassium antimony tartrate were mixed and stirred until clear, and then 60-100 mM sodium thiosulfate pentahydrate and 0-20 mM selenourea were added and stirred for 2-3 minutes. Then, the CdS film was immersed face down in the mixed solution and transferred to a reactor for hydrothermal reaction at 120-140° C. for 100-120 minutes. After the hydrothermal reaction, the sample was washed and dried with nitrogen, and then annealed at 340-360° C. for 10-20 minutes in a nitrogen-filled tube furnace to obtain an antimony-based chalcogenide compound absorption layer film.

[0023] Step 8: Preparation of hole transport layer

[0024] 1-1.2 mL of a chlorobenzene solution containing 70-75 mg of spiro-OMeTAD, 28-30 μL of tert-butylpyridine, and 17-18 μL of lithium bis(trifluoromethylstyryl)imide dissolved in acetonitrile (0.5-0.6 g / mL) was cast onto the perovskite surface and rotated at 2000-4000 rpm for 25-30 s to form a hole transport layer. The sample was then placed in the dark in air for 12-24 h.

[0025] Step 9: Electrode deposition

[0026] The sample prepared in step 8 is placed in a thermal evaporation device to evaporate a metal electrode, thereby finally completing the preparation of a perovskite solar cell with high charge extraction capability. The device structure is conductive substrate / c-TiO2 / CdS nanorods / perovskite layer / hole transport layer / metal electrode.

[0027] In step 1, the conductive substrate is FTO, ITO or AZO conductive glass.

[0028] In step 7, the perovskite film is a perovskite absorption layer film such as MAPbI3, FAPbI3, (Cs, MA, FA)PbI3, etc.

[0029] In step 7, the antimony-based chalcogenide film is a compound absorption layer film such as Sb2(S,Se)3 and Sb2S3.

[0030] In step 8, the hole transport layer is spiro-OMeTAD or P3HT.

[0031] In step 9, the metal electrode is a gold or silver electrode.

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

[0033] 1. The deposition of a dense TiO2 layer is conducive to the vertical growth of CdS nanorods on the substrate, obtaining a high-quality one-dimensional structure electron transport layer.

[0034] 2. The TiO2 / CdS composite electron transport layer and the solar cell absorption layer material form an ideal gradient energy level arrangement, which can improve the efficiency of photogenerated electron extraction at the interface;

[0035] 3. The vertical growth characteristics of CdS nanorods provide a more efficient transmission path for carriers, which helps to suppress charge recombination inside the device.

[0036] 4. The introduction of the TiO2 dense layer can effectively prevent the light absorption layer such as perovskite and antimony-based chalcogenide film from directly contacting the FTO conductive substrate, causing current loss.

[0037] 5. The preparation method of the composite electron transport layer in the present invention has the advantages of simple process, low cost, easy operation and safety, and has good application prospects in photovoltaic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of an array-type TiO2 / CdS composite nanostructured electron transport layer. 1 is the conductive glass; 2 is the dense TiO2 layer; and 3 is the CdS nanorod.

[0039] Figure 2 This is a surface SEM image of an array-type TiO2 / CdS composite nanostructured electron transport layer. As can be seen, the CdS film exhibits a typical nanorod array structure with relatively uniform nanorod diameters. The film's surface contains voids, which facilitate the formation of a three-dimensional bulk heterojunction structure between the nanorod array and the absorber film.

[0040] Figure 3This is a cross-sectional SEM image of an arrayed TiO2 / CdS composite nanostructured electron transport layer. It can be seen that the hydrothermally grown CdS nanorods on the dense TiO2 layer exhibit oriented growth and high uniformity. These characteristics facilitate the formation of orderly electron transport pathways, enabling efficient charge transport.

[0041] Figure 4 Schematic diagram of the MAPbI3 perovskite solar cell device structure based on an array-type TiO2 / CdS composite nanostructured electron transport layer. Figure 1 is conductive glass; 2 is a dense TiO2 layer; 3 is CdS nanorods; 4 is the perovskite absorption layer; 5 is the hole transport layer; and 6 is the metal electrode.

[0042] Figure 5 Schematic diagram of the energy band structure of a MAPbI3 perovskite solar cell based on an array-type TiO2 / CdS composite nanostructured electron transport layer. Figure 1 represents FTO, 2 represents a dense TiO2 layer, 3 represents CdS nanorods, 4 represents MAPbI3, 5 represents spiro-OMeTAD, and 6 represents Ag.

[0043] Figure 6 The photocurrent density-voltage (JV) curve of a perovskite solar cell based on an array-type TiO2 / CdS composite nanostructure electron transport layer prepared using the method of the present invention. DETAILED DESCRIPTION

[0044] Example 1:

[0045] The specific steps for preparing a perovskite solar cell based on an array-type TiO2 / CdS composite nanostructured electron transport layer are as follows:

[0046] 1. Ultrasonic cleaning of the etched FTO glass was performed with standard deionized water, IPA, and PA in sequence for 15 minutes, followed by immediate drying with a nitrogen gun and UVO treatment for 20 minutes.

[0047] 2. Take 80 μL of TiO2 precursor solution and drop it onto FTO, and spin-coat it at a speed of 500 rpm for 3 seconds, then at a speed of 2000 rpm for 30 seconds. After the spin coating is completed, anneal it at 135 ° C on a heating table for 10 minutes, and finally place it in a muffle furnace at 500 ° C for 30 minutes to form a dense layer;

[0048] 3. Add 0.01 M Cd(NO3)2·4H2O, 0.03 M thiourea and 0.006 M glutathione (GSH) to 80 mL of deionized water in sequence and stir at room temperature for 15 min.

[0049] 4. Immerse the FTO containing the TiO2 dense layer downward into the solution and transfer it to the reactor. After hydroheating at 200°C for 80 minutes, take it out, rinse it with plenty of clean water, and place it in a drying oven to dry to obtain a light yellow CdS nanorod array film.

[0050] 5. Spread 100 mL of perovskite precursor solution on the CdS nanorods at a spin coating speed of 4000 rpm. After 6 to 8 seconds of spin coating, add ethyl acetate antisolvent dropwise onto the substrate. After spin coating, heat the substrate on a heating table at 105°C for 10 minutes to obtain a perovskite film.

[0051] 6. Spin coat 40 μL of a mixture of 72.3 mg of spiro-OMeTAD, 1 mL of chlorobenzene, 28.8 μL of 4-tert-butylpyridine, and 17.5 μL of LI-TFSI at 4000 rpm for 30 s. After spin coating, heat the sample on a heating plate at 100°C for 10 min to obtain a hole transport layer.

[0052] 7. Deposit 80nm of Ag electrode by thermal evaporation under vacuum.

[0053] The prepared MAPbI3 perovskite solar cell has an efficiency of 18.36%.

[0054] Example 2:

[0055] The difference from Example 1 is that the hydrothermal time in step 4 is 90 minutes, and the efficiency of the prepared MAPbI3 perovskite solar cell is 18.72%.

[0056] Example 3:

[0057] The difference from Example 1 is that the hydrothermal time in step 4 is 100 minutes, and the efficiency of the prepared MAPbI3 perovskite solar cell is 19.01%.

[0058] Example 4:

[0059] The difference from Example 1 is that the hydrothermal time in step 4 is 110 min, and the efficiency of the prepared MAPbI3 perovskite solar cell is 18.34%.

[0060] Example 5:

[0061] The difference from Example 1 is that the hydrothermal time in step 4 is 120 min, and the efficiency of the prepared MAPbI3 perovskite solar cell is 17.06%.

[0062] The hydrothermal time used to prepare CdS nanorods significantly affects the photoelectric conversion efficiency of perovskite cells, with device efficiency initially increasing and then decreasing. The MAPbI3 perovskite cell achieves the highest efficiency when the hydrothermal time is 100 minutes. This is due to the fact that the length of the CdS nanorods increases with increasing hydrothermal time. Shorter CdS nanorods lack distinct array characteristics, preventing the formation of a bulk heterojunction. Excessively long CdS nanorods increase charge recombination within the device. Therefore, optimizing the preparation process to achieve CdS nanorods of optimal length is crucial for improving solar cell performance.

[0063] Example 6:

[0064] The antimony selenide sulfide solar cell based on the TiO2 / CdS nanorod composite nanostructure electron transport layer is prepared by the following steps:

[0065] 1. Ultrasonic cleaning of the etched FTO glass was performed with standard deionized water, IPA, and PA in sequence for 15 minutes, followed by immediate drying with a nitrogen gun and UVO treatment for 20 minutes.

[0066] 2. Stir 30 mL of cadmium nitrate and 39 mL of the mixed solution until clear. After stirring, add 210 mL of deionized water and 19.2 mL of thiourea and stir for another 1 to 2 minutes.

[0067] 3. Place the FTO glass vertically into the mixed solution of the previous step and transfer it to a magnetic heating stirrer water bath for 16 minutes to prepare a CdS film;

[0068] 4. After the water bath is completed, take it out for cleaning and blow dry with nitrogen. Then spin-coat CdCl2 solution at 3000 rpm for 30 seconds, then anneal on a 400℃ heating table for 10 minutes and cool naturally to room temperature.

[0069] 5. Mix 40 mL of deionized water and 0.267 g of potassium antimony tartrate and stir until clear. Then add 0.794 g of sodium thiosulfate pentahydrate and 0.02 g of selenourea and stir for 2-3 minutes. Then, place the CdS film face down in the mixed solution and transfer it to a reactor for hydrothermal reaction at 135°C for 110 minutes.

[0070] 6. After the hydrothermal reaction, the sample was cleaned and dried with nitrogen, then dried in a vacuum drying oven at 110°C for 1 minute, and finally annealed in a nitrogen-filled tube furnace at 350°C for 10 minutes to obtain an antimony selenide sulfide absorption layer;

[0071] 7. Evenly apply 40 μL of a mixture of 72.3 mg of spiro-OMeTAD, 1 mL of chlorobenzene, 28.8 μL of 4-tert-butylpyridine, and 17.5 μL of LI-TFSI on the antimony selenide sulfide film and spin coat at 4000 rpm for 30 s. After spin coating, place the sample on a heating table at 100°C for 10 min to obtain a hole transport layer.

[0072] 8. Deposit 80nm of Au electrode by thermal evaporation under vacuum.

[0073] The efficiency of the antimony selenide sulfide solar cell prepared based on TiO2 / CdS nanorod composite nanostructure electron transport layer is 7.14%.

[0074] Example 7:

[0075] The difference from Example 6 is that no CdCl2 and annealing post-treatment are performed in step 4, and the efficiency of the prepared antimony selenide sulfide solar cell based on the TiO2 / CdS nanorod composite nanostructure electron transport layer is 5.68%.

[0076] Whether the composite nanostructured electron transport layer is treated with CdCl2 and annealed significantly affects the photoelectric conversion efficiency of antimony selenide sulfide cells. CdCl2 and annealing effectively passivate the charge recombination on the surface of the array-type TiO2 / CdS composite electron transport layer film prepared by the solution method, improving the crystallinity of the CdS material, increasing charge collection efficiency, and thus improving solar cell performance.

Claims

1. A method for preparing an array-type TiO2 / CdS composite electron transport layer, characterized by: A dense TiO2 layer was prepared by spin coating on conductive glass, and one-dimensional CdS nanorods were further grown on the TiO2 substrate using a hydrothermal method to obtain a TiO2 / CdS nanorod composite electron transport layer. In the composite electron transport layer, the thickness of the TiO2 dense layer is 20-30 nm, and the length of the CdS nanorods is 100-500 nm; The preparation method comprises the following steps: Step 1: Place the cleaned conductive substrate into the UV ozone cleaning machine and treat with ozone for 15-25 minutes; Step 2: Prepare a 0.1-0.2 mol / L n-butanol solution of bis(acetylacetonato)diisopropyl titanate and stir at room temperature for 1-2 hours to form a dense layer precursor solution; Step 3: Take 40-120 μL of dense layer precursor solution and drop it onto the conductive substrate, and spin-coat it at a speed of 500-1000 rpm for 3-6 seconds, and then spin-coat it at a speed of 2000-3000 rpm for 30-50 seconds; Step 4: After spin coating, place the sample on a heating table for annealing, and finally place it in a muffle furnace, gradually increase the temperature to 450-550°C, and sinter for 30-60 minutes to form a dense TiO2 layer; Step 5: Cd(NO3)2·4H2O, thiourea and glutathione are sequentially added to deionized water and stirred at room temperature for 10-20 minutes to obtain a mixed solution; the concentration of Cd(NO3)2·4H2O in the mixed solution is 0.005-0.015M, the concentration of thiourea is 0.02-0.04M, and the concentration of glutathione is 0.003-0.012M; Step 6: Immerse the conductive glass / TiO2 dense layer with the conductive surface facing down into the mixed solution of step 5, and transfer it to a reactor for hydrothermal reaction. The temperature of the hydrothermal reaction is 180-220°C, and the reaction time is 50-150 minutes. After the reaction is completed, take it out, rinse it with plenty of clean water, and place it in a drying oven to dry to obtain a light yellow CdS film, which is the TiO2 / CdS nanorod array composite nanostructure.

2. The preparation method according to claim 1, wherein: In step 4, the annealing temperature is 100-500° C., and the annealing time is 10-20 minutes.

3. The preparation method according to claim 1, wherein: In step 4, the heating rate of the gradient heating is 5-10°C / min.

4. Use of the TiO2 / CdS nanorod composite electron transport layer prepared by the preparation method according to any one of claims 1 to 3, characterized in that: A bulk heterojunction solar cell is constructed using the array-type TiO2 / CdS composite nanostructure as an electron transport layer; the device structure of the bulk heterojunction solar cell is: conductive substrate / TiO2 dense layer / CdS nanorods / perovskite layer / hole transport layer / metal electrode.

5. The use according to claim 4, characterized in that: The bulk heterojunction solar cell includes a perovskite solar cell or an antimony-based chalcogenide thin film solar cell.

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