A method for preparing perovskite solar cells using liquid crystal dynamic transition spontaneous interface healing

Abstract

A method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing, comprising: selecting fluorine-doped tin oxide glass as a glass substrate, generating an electron transport layer on the glass substrate by chemical bath deposition; dissolving a functionalized liquid crystal material in a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide, stirring and dissolving to obtain a liquid crystal additive solution; mixing PbI2, NH2CH=NH2I, CH3NH3Br, and CsI and dissolving them in the liquid crystal additive solution to obtain a perovskite precursor solution containing the liquid crystal additive; applying the perovskite precursor solution to the electron transport layer of the glass substrate by spin coating to form a perovskite absorption layer; applying a Spiro-OMeTAD solution to the perovskite absorption layer of the glass substrate by spin coating to form a hole transport layer; and generating an electrode by evaporation on the hole transport layer of the glass substrate to obtain a perovskite solar cell. The present invention effectively improves the crystallization quality of the perovskite film and the electron extraction capacity at the interface between the perovskite and the electron transport layer.

Description

Technical Field

[0001] The present invention relates to the field of thin-film solar cells, and in particular to a method for preparing a perovskite solar cell by utilizing liquid crystal dynamic transition and spontaneous interface healing. Background Art

[0002] Low-temperature solution processing of thin-film semiconductors is a promising approach for rapidly fabricating cost-effective electronic and optoelectronic devices. In recent years, organic-inorganic hybrid metal halide perovskites based on low-temperature (<300°C) solution processing have attracted significant attention in applications such as solar cells, X-ray detectors, light-emitting diodes, memristors, and transistors due to their exceptional properties, including low exciton binding energy, long carrier diffusion lengths and lifetimes, high mobility, high performance, tunable band gaps, and compositional versatility. In particular, the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs) has increased from 3.8% in 2009 to 25.7% in 2022, approaching that of single-crystalline silicon solar cells.

[0003] Due to the rapid crystallization of perovskite films during low-temperature solution processing, many defects appear in the absorber layer, such as vacancies, antisites, interstitials in the bulk phase, grain boundaries, and dangling bonds at the interface. In addition, due to the thermal expansion mismatch between the perovskite and the substrate during the annealing step, the residual tensile stress at the interface is also detrimental to PCE and stability. To address these two issues (rapid crystallization of the film leading to excessive defects and residual tensile stress at the interface), a combined approach of interface passivation and bulk additive engineering was adopted. The approach involves: first, the interface is passivated by a layer of soft molecules to release the residual stress, and then some additives are added to the precursor solution to delay crystallization. However, although this approach solves the above technical problems to a certain extent, it has the following drawbacks: (1) their combination makes the experimental processing complicated; (2) the balance of this combination is easily broken, resulting in increased interface resistance and reduced PCE. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing perovskite solar cells using liquid crystal dynamic transition spontaneous interface healing, which uses the method of liquid crystal dynamic transition spontaneous interface healing to solve the technical problem that the rapid crystallization of perovskite films produces excessive defects and residual tensile stress at the interface, resulting in the attenuation of the photovoltaic performance of perovskite solar cells.

[0005] To achieve the above object, the present invention provides a method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing, which comprises the following steps:

[0006] S1. Select fluorine-doped tin oxide glass as a glass substrate, clean it, and treat it with ultraviolet ozone, and then form an electron transport layer on the glass substrate by any of the following methods: chemical bath deposition, water bath deposition, spin coating, doctor blade coating, or screen printing;

[0007] S2. Dissolving the functionalized liquid crystal material in a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide, stirring and dissolving to obtain a liquid crystal additive solution with a concentration of 2 to 8 mg / mL; mixing and dissolving PbI2, NH2CH=NH2I, CH3NH3Br, and CsI in molar amounts of 1.20 to 1.80 mmol, 1.20 to 1.80 mmol, 0.15 to 0.2 mmol, and 0.08 to 0.10 mmol, respectively, in 1 mL of the liquid crystal additive solution to obtain a perovskite precursor solution containing the liquid crystal additive;

[0008] S3, coating the perovskite precursor solution on the electron transport layer of the glass substrate by spin coating to form a perovskite absorption layer;

[0009] S4, forming a hole transport layer made of Spiro-OMeTAD, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine or nickel oxide on the perovskite absorption layer on the glass substrate;

[0010] S5, forming an electrode on the hole transport layer of the glass substrate by evaporation, and finally obtaining a perovskite solar cell;

[0011] Wherein, the structural formula of the functionalized liquid crystal material is shown in formula (1):

[0012]

[0013] In formula (1), n ​​represents the number of carbon atoms and is an integer of 2-12.

[0014] As a further preferred technical solution of the present invention, the material of the electron transport layer in step S1 is any one of TiO2, ZnO, and SnO2.

[0015] As a further preferred technical solution of the present invention, in step S1, the method for forming the electron transport layer when the material is TiO2 is as follows:

[0016] First, a fluorine-doped tin oxide glass substrate was selected and ultrasonically cleaned in glass cleaning solution, deionized water, and ethanol for 15 to 30 minutes each, dried with nitrogen, and then treated with ultraviolet ozone for 10 to 15 minutes.

[0017] Then, the glass substrate was placed in a 0.15-0.2 mol / L TiCl4 aqueous solution at 60-70°C for 45-60 minutes, and then washed alternately with deionized water and ethanol for multiple times;

[0018] Finally, the glass substrate is annealed at 180-200° C. for 20-30 minutes, and a TiO2 electron transport layer is prepared on the glass substrate by a chemical bath deposition method.

[0019] As a further preferred technical solution of the present invention, in step S2, when n=6 in formula (1), the preparation method of the functionalized liquid crystal material is as follows:

[0020] First, 4′-hydroxy-4-biphenylnitrile and 1,6-dibromohexane were subjected to Williamson etherification to obtain bromine-terminated alkoxycyanobiphenyl;

[0021] Then, under N2 atmosphere, a mixture of bromine-terminated alkoxycyanobiphenyl, thiourea and anhydrous ethanol is heated under reflux for 15 to 20 hours, an aqueous NaOH solution is added and further heated under reflux for 3 to 4 hours, cooled to room temperature, and then water is added and acidified with dilute hydrochloric acid;

[0022] Finally, the acidified mixture is extracted with dichloromethane, the organic phases are combined, dried over anhydrous magnesium sulfate, filtered, and the solvent is removed under reduced pressure to obtain a concentrate; the concentrate is purified by silica gel column chromatography using a mixture of petroleum ether and ethyl acetate as an eluent to obtain a compound of a functionalized liquid crystal material.

[0023] As a further preferred technical solution of the present invention, before the spin coating in step S3, the glass substrate needs to be treated with ultraviolet ozone for 10-20 minutes to enhance its surface wettability.

[0024] As a further preferred technical solution of the present invention, step S3 specifically includes the following steps:

[0025] The perovskite precursor solution is dropped onto the electron transport layer of the glass substrate and the first stage of spin coating is performed at a speed of 500-1500 rpm / s for 5-20 seconds;

[0026] Then, the second stage of spin coating is carried out at a speed of 2000-5000 rpm / s for 30-50 seconds. When the second stage is carried out for 20-40 seconds, 100-300 μL of ethyl acetate is added dropwise.

[0027] After the second stage of spin coating is completed, annealing treatment is performed at a temperature of 120 to 200° C. and an annealing time of 10 to 30 minutes to form a perovskite absorption layer.

[0028] As a further preferred technical solution of the present invention, the hole transport layer made of Spiro-OMeTAD is generated in step S4, which specifically includes the following steps:

[0029] Spiro-OMeTAD, Li-TFSI acetonitrile solution and 4-tert-butylpyridine were mixed and dissolved in chlorobenzene, stirred at room temperature for 10 to 12 hours, and filtered to prepare a Spiro-OMeTAD solution;

[0030] The Spiro-OMeTAD solution was dropped onto the perovskite absorption layer of the glass substrate and spin-coated at a rotation speed of 4000-5000 rpm for 20-30 seconds to prepare a hole transport layer.

[0031] As a further preferred technical solution of the present invention, the electrode is a gold electrode, and the thickness of the gold electrode is 70-100 nm.

[0032] The method of preparing a perovskite solar cell by utilizing liquid crystal dynamic transition spontaneous interface healing of the present invention can achieve the following beneficial effects by adopting the above technical solution:

[0033] 1) The preparation method of the present invention utilizes a method for achieving spontaneous interface healing through dynamic liquid crystal transitions using functionalized liquid crystal materials, which can simultaneously address two issues: excessive defects generated by rapid crystallization of perovskite films, and residual tensile stress at the interface between the perovskite and electron transport layers. Compared to traditional methods that combine interface passivation and bulk additive engineering, this method can achieve simultaneous improvements in these issues in a simpler and more convenient manner, greatly simplifying the experimental operation process and avoiding the complexity of traditional combined methods. It effectively improves the crystallization quality of the perovskite film and the electron extraction capacity at the interface between the perovskite and electron transport layers.

[0034] 2) The preparation method of the present invention comprises adding a functional liquid crystal material to a conventional perovskite solution, wherein the perovskite material is a bipolar semiconductor material with the characteristics of low cost, easy film formation, narrow bandgap, high absorption coefficient, and high carrier mobility. The functional liquid crystal material is added to the perovskite solution as a bifunctional additive. On the one hand, the functionalized liquid crystal material contains functional groups (cyano and disulfide bonds) that can interact with PbI2 in the perovskite bulk, which helps it to combine with the perovskite colloid to form an intermediate adduct to delay crystallization and obtain a high-quality perovskite film. On the other hand, under the stimulation of the annealing temperature, the liquid crystal material undergoes a multi-step dynamic transformation. Due to the strong interaction between the liquid crystal molecules and the carrier transport layer, and the diffusion of the mobile liquid crystal molecules during the cooling process, the liquid crystal molecules dynamically transfer to the lower interface and enrich at the lower interface, thereby achieving the adjustment of thermal mismatch and releasing the residual stress between the perovskite and the electron transport layer.

[0035] 3) Compared with traditional perovskite cells, the perovskite solar cell device prepared based on the method of the present invention has a champion efficiency of up to 24.38%. After exposure to an environment of 25°C and a relative humidity of about 30% for 2000 hours, the bare device without any packaging maintains 93.0% of its initial efficiency. After aging for 500 hours under continuous single-sun irradiation at 45°C, its initial PCE still remains at 96.3%, which has important practical value and guiding significance for the industrialization of perovskite cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Figure 1 Characterization of the perovskite films prepared in Comparative Example 1 and Example 1, (a) and (b) are top views of SEM images, and (c) is an XRD pattern;

[0038] Figure 2 Figure 3 shows the composition distribution of the liquid crystal compound CBO6SS6OCB in the perovskite absorber layer, ToF SIMS 3D images of the perovskite film prepared in Example 1 on a TiO2 / fluoride-doped tin oxide (FTO)-coated glass substrate before (a) and after (b) annealing, and ToF-SIMS depth profiles before (c) and after (d) annealing.

[0039] Figure 3 Figure 3 shows the effect of the liquid crystal compound CBO6SS6OCB on the lower interface, (a) GIXRD spectra of the perovskite film prepared in Comparative Example 1 and (b) the perovskite film prepared in Example 1 at different grazing incidence angles, (c) d-spacing values ​​of the (211) plane of the perovskite films prepared in Comparative Example 1 and Example 1 as a function of the grazing incidence angle.

[0040] Figure 4 is the carrier dynamics curve of transient absorption spectrum of perovskite film + hole (a) / electron (b) transport layer;

[0041] Figure 5 This is a comparison chart of the photoelectric performance of the perovskite solar cells prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0042] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Terms such as "upper," "lower," "left," "right," "center," and "one" used in the preferred embodiments are for ease of description and are not intended to limit the scope of the present invention. Changes or adjustments to these relative terms, without substantially altering the technical content, are also considered within the scope of the present invention.

[0044] Liquid crystals (LCs) are soft matter materials with a variety of unique properties, including rich phase transition behaviors, excellent optoelectronic properties, long-range orientation order, strong self-assembly characteristics, and strong crystallinity. During heating and cooling, thermotropic LCs can undergo multi-step dynamic transitions, for example, monotropic LC phase transitions: (1) solid-(2) liquid-(3) liquid crystal-(4) solid; and reversible LC phase transitions: (1) solid-(2), liquid crystal-(3), liquid-(4), liquid crystal-(5) solid. In addition, their strong self-assembly and morphological control capabilities can be used to regulate crystal growth and film morphology. Combining functional LC materials with lead halide to prepare functionalized perovskite materials has the potential to further improve the film quality of perovskite materials, achieve spontaneous interface healing through dynamic LC transitions, and thus improve the stability of perovskite solar cells.

[0045] Based on the above innovative ideas, this application proposes a method for preparing perovskite solar cells using liquid crystal dynamic transition spontaneous interface healing, which specifically includes the following steps:

[0046] S1. Select fluorine-doped tin oxide glass as a glass substrate. After cleaning and ultraviolet ozone treatment, generate an electron transport layer on the glass substrate by any one of chemical bath deposition, water bath deposition, spin coating, doctor blade coating, and screen printing. The electron transport layer is any one of TiO2, ZnO, and SnO2.

[0047] Taking the formation of a TiO2 electron transport layer by chemical bath deposition as an example, the specific operation of step S1 is as follows:

[0048] First, fluorine-doped tin oxide glass is selected as a glass substrate, and ultrasonically cleaned in glass cleaning solution, deionized water and ethanol for 15 to 30 minutes respectively, blown dry and cleaned with nitrogen, and then treated with ultraviolet ozone for 10 to 15 minutes; then, the glass substrate is placed in a TiCl4 aqueous solution with a concentration of 0.15 to 0.2 mol / L at 60 to 70°C for 45-60 minutes, and then washed alternately with deionized water and ethanol multiple times; finally, the glass substrate is annealed at 180 to 200°C for 20 to 30 minutes, and a TiO2 electron transport layer is prepared on the glass substrate by chemical bath deposition.

[0049] S2. Dissolve the functionalized liquid crystal material in a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 4:1, and stir to dissolve to obtain a liquid crystal additive solution with a concentration of 2 to 8 mg / mL; according to the molar amounts of PbI2, NH2CH=NH2I(FAI), CH3NH3Br(MABr) and CsI, which are 1.20 to 1.80 mmol, 1.20 to 1.80 mmol, 0.15 to 0.2 mmol and 0.08 to 0.10 mmol, respectively, they are mixed and dissolved in 1 mL of the liquid crystal additive solution to obtain a perovskite precursor solution containing liquid crystal additives.

[0050] Specifically, the structural formula of the functionalized liquid crystal material (also known as liquid crystal compound) is shown in formula (1):

[0051]

[0052] In formula (1), n ​​represents the number of carbon atoms and is an integer between 2 and 12, preferably n = 6. The molecular formula of the functionalized liquid crystal material when the number of carbon atoms is 6 is CBO6SS6OCB, and its structural formula is shown in formula (2):

[0053]

[0054] The functionalized liquid crystal material CBO6SS6OCB is prepared by the following method:

[0055] First, 4′-hydroxy-4-biphenylnitrile and 1,6-dibromohexane were subjected to a Williamson etherification reaction to obtain a bromine-terminated alkoxycyanobiphenyl; then, under a N2 atmosphere, a mixture of the bromine-terminated alkoxycyanobiphenyl (1.14 g, 3.18 mmol), thiourea (0.27 g, 3.50 mmol) and anhydrous ethanol (40 mL) was heated under reflux for 15-20 hours, and then a NaOH aqueous solution (0.64 mL, 3.18 mmol) was added and further heated under reflux for 3-4 hours. After cooling to room temperature, water was added and the mixture was acidified with dilute hydrochloric acid; finally, the acidified mixture was extracted with dichloromethane, the organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and the solvent was removed under reduced pressure to obtain a concentrate; the concentrate was purified by silica gel column chromatography using a mixture of petroleum ether and ethyl acetate (volume ratio 5:1) as an eluent to obtain a functionalized liquid crystal material compound CBO6SS6OCB.

[0056] In the above steps of preparing CBO6SS6OCB, replacing 1,6-dibromohexane with other alkyl chains can realize the synthesis of compounds with other n values, such as 1,3-dibromopropane.

[0057] S3. Spin-coating the perovskite precursor solution on the electron transport layer of the glass substrate to form a perovskite absorption layer.

[0058] The specific operation of step S3 is as follows: the perovskite precursor solution is dropped or coated on the electron transport layer of the glass substrate, and the first stage of spin coating is performed at a rotation speed of 500-1500 rpm / s and a spin coating time of 5-20s; then the second stage of spin coating is performed at a rotation speed of 2000-5000 rpm / s and a spin coating time of 30-50s, and 100-300uL of ethyl acetate is added dropwise when the second stage is 20-40s; after the second stage of spin coating is completed, annealing treatment is performed at an annealing temperature of 120-200°C and an annealing time of 10-30min to form a perovskite absorption layer.

[0059] S4. Generating a hole transport layer made of Spiro-OMeTAD, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) or nickel oxide on the perovskite absorption layer on the glass substrate.

[0060] Among the aforementioned hole transport layers, the Spiro-OMeTAD hole transport layer has the best energy level match with the perovskite layer, the best charge transport performance, and the simplest method to generate. The specific steps for generating the Spiro-OMeTAD hole transport layer in step S4 are as follows:

[0061] Spiro-OMeTAD (Chinese name: 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene), Li-TFSI acetonitrile solution and 4-tert-butylpyridine were mixed and dissolved in chlorobenzene, stirred at room temperature for 10 to 12 hours, and filtered using an injector equipped with a mechanical filter to obtain a Spiro-OMeTAD solution; the Spiro-OMeTAD solution was dropwise added to the perovskite absorption layer of the glass substrate and spin-coated at a speed of 4000 to 5000 rpm for 20 to 30 seconds to obtain a hole transport layer.

[0062] S5. An electrode is formed on the hole transport layer of the glass substrate by evaporation, preferably a gold electrode with a thickness of 70-100 nm, to finally obtain a perovskite solar cell.

[0063] The present invention uses functionalized liquid crystal materials to achieve dynamic liquid crystal transition and spontaneous interface healing, which can spontaneously slow down the crystallization rate of the perovskite film (perovskite absorber layer) during the annealing process and in situ release the residual stress formed at the interface between perovskite and titanium dioxide. The specific principles are as follows:

[0064] First, the functionalized liquid crystal material contains functional groups (cyano and disulfide bonds) that can interact with PbI2 in the perovskite bulk, which helps it combine with the perovskite colloid to form an intermediate adduct to delay crystallization and increase the grain size. Secondly, under the stimulation of annealing temperature, the liquid crystal material will undergo a multi-step dynamic transition, providing the possibility for the liquid crystal material to transfer from the perovskite grain boundary to the lower interface formed between the perovskite and the carrier transport layer. Ultimately, due to the strong interaction between the liquid crystal molecules and the carrier transport layer, and the thermal diffusion of the mobile liquid crystal molecules during the cooling process, the liquid crystal molecules dynamically transfer to the lower interface and enrich at the lower interface, thereby achieving the adjustment of thermal mismatch and releasing the residual stress between the perovskite and the carrier transport layer.

[0065] In order to enable those skilled in the art to further understand the technical solution of the present invention, the technical solution of the present invention is further described in detail below through specific embodiments and comparative examples.

[0066] Example 1: A perovskite solar cell is prepared using the method of the present invention for dynamic liquid crystal transformation and self-healing interface. The specific steps are as follows:

[0067] Step 1: Select fluorine-doped tin oxide (FTO) glass as the glass substrate, and ultrasonically clean it in glass cleaning solution, deionized water, and ethanol for 30 minutes each, then blow dry the cleaned glass substrate with nitrogen, and treat it with ultraviolet ozone for 15 minutes before use;

[0068] Step 2: The glass substrate was placed in a 0.2 mol / L TiCl4 aqueous solution at 70°C for 60 minutes, then washed three times with deionized water and ethanol alternately, and finally annealed at 200°C for 30 minutes. A TiO2 electron transport layer was then prepared on the glass substrate by chemical bath deposition.

[0069] Step 3, prepare a perovskite precursor solution containing liquid crystal additives: first, dissolve the functionalized liquid crystal material CBO6SS6OCB in a mixed solution of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (the volume ratio of the two is 4:1), and stir to dissolve to obtain a liquid crystal additive solution with a concentration of 4 mg / mL; then, according to the molar amounts of PbI2, NH2CH=NH2I (FAI), CH3NH3Br (MABr) and CsI of 1.60 mmol, 1.31 mmol, 0.15 mmol, and 0.08 mmol, respectively, mix and dissolve in 1 mL of liquid crystal additive solution to obtain a perovskite precursor solution containing liquid crystal additives.

[0070] Step 4: Spin-coat the perovskite precursor solution prepared in step 3 on the electron transport layer to form a perovskite absorption layer. The specific operations are as follows: (1) The glass substrate on which the TiO2 electron transport layer is formed in step 2 is treated with ultraviolet ozone for 20 minutes to enhance its surface wettability; (2) About 50 μL of the perovskite precursor solution prepared in step 3 is dropped on the TiO2 electron transport layer of the glass substrate, and the solution is spin-coated at 2000 rpm for 10 seconds, then rotated at 5000 rpm for 30 seconds, and 10 seconds before the end of the 5000 rpm step, 200 μL of ethyl acetate is quickly added to the surface to form a perovskite film; (3) Annealing is performed at 150°C for 20 minutes to form a Cs 0.05 FA 0.85 MA 0.10 Pb(I 0.97 Br 0.03 )3Perovskite absorption layer.

[0071] Step 5: Spin-coating a hole transport layer, Spiro-OMeTAD, on the perovskite absorption layer by a spin coating method. The specific operation is as follows: 72.3 mg of Spiro-OMeTAD, 35 μL of Li-TFSI acetonitrile solution (concentration: 520 mg / mL) and 30 μL of 4-tert-butylpyridine are mixed and dissolved in 1 mL of chlorobenzene, and then stirred at room temperature for 12 hours. The mixture is filtered through a 0.45 μm syringe filter to obtain the desired Spiro-OMeTAD solution; the Spiro-OMeTAD solution is spin-coated on the perovskite absorption layer at a spin coating speed of 5000 rpm and a spin coating time of 30 s to obtain a hole transport layer;

[0072] Step 6: Evaporate a gold film about 80 nm thick on the hole transport layer Spiro-OMeTAD as an electrode. The cell area is 0.09 cm 2 , ultimately forming a perovskite solar cell.

[0073] Comparative Example 1: Perovskite solar cell prepared without using the method of dynamic liquid crystal transition and spontaneous healing interface

[0074] Except for step 3, all other steps were the same as in Example 1, except that in step 3 of Comparative Example 1, a perovskite precursor solution without a liquid crystal additive was prepared without using a functionalized liquid crystal material. Step 3 was as follows: PbI2, NH2CH=NH2I, CH3NH3Br, and CsI were dissolved in 1 mL of a mixed solvent (DMF and DMSO in a 4:1 volume ratio) at molar amounts of 1.60 mmol, 1.31 mmol, 0.15 mmol, and 0.08 mmol, respectively. The perovskite precursor solution was prepared.

[0075] Comparative Example 2: Preparation of perovskite solar cells using the method of interface purification under liquid crystal materials

[0076] Except for step 4, the other steps are the same as those in comparative example 1, the only difference being that in step 4 of comparative example 1, the lower interface purifier is spin-coated before the perovskite precursor solution containing the liquid crystal additive is spin-coated. Step 4 is as follows: (1) 4 mg of the functionalized liquid crystal material CBO6SS6OCB is dissolved in 1 mL of isopropanol to prepare a lower interface purifier; (2) the glass substrate prepared in step 2 is treated with ultraviolet ozone for 20 minutes to enhance its surface wettability; (3) 50 μL of the lower interface purifier prepared above is dropped onto the TiO2 electron transport layer, and then rotated at 2000 rpm for 30 seconds; (4) about 50 μL of the perovskite precursor solution prepared in step 3 is continued to be dropped onto the lower interface purifier, spin-coated at 2000 rpm for 10 seconds, and then rotated at 5000 rpm for 30 seconds, and 10 seconds before the end of the 5000 rpm step, 200 μL of ethyl acetate is quickly dropped onto the surface to prepare a perovskite film; (5) the perovskite film is annealed at 150°C for 20 minutes to obtain Cs 0.05 FA 0.85 MA 0.10 Pb(I 0.97 Br 0.03 )3Perovskite absorption layer.

[0077] The products of the perovskite absorption layer formed in step 3 of the above-mentioned embodiments and comparative examples are named as perovskite films. The inventors characterized the performance of the perovskite films prepared in Example 1 and Comparative Example 1. The beneficial effects of the method for preparing perovskite solar cells using liquid crystal dynamic transition and spontaneous interface healing proposed in the present invention on preparing perovskite films are described below from three aspects: delayed crystallization, dynamic liquid crystal transition and spontaneous interface healing.

[0078] (1) Delaying crystallization

[0079] The dynamic film crystallization process of the perovskite films prepared in Example 1 and Comparative Example 1 was detected by in situ UV-visible absorption spectroscopy. As the annealing process began, the intensity from 450nm to 800nm ​​gradually increased, indicating the formation of black perovskite. In the test, the nucleation time of the perovskite film in Comparative Example 1 started at 9.8s, and the nucleation time of the perovskite film in Example 1 started after 15.5s. The X-ray diffraction peak positions of the perovskite films prepared in Example 1 and Comparative Example 1 remained unchanged ( Figure 1 c), but the intensity of the main diffraction peak of the perovskite film prepared in Example 1 increased slightly, indicating that its texture or crystallinity was enhanced, which is very consistent with the slightly enlarged grains (from 0.22 μm to 0.31 μm) in the scanning electron microscope image ( Figure 1The above results show that the functionalized liquid crystal material CBO6SS6OCB used in Example 1 can slow down the crystallization rate of the perovskite film and improve the film quality.

[0080] (2) Dynamic liquid crystal transition

[0081] The spatial distribution of the functionalized liquid crystal material CBO6SS6OCB in the perovskite film at different times was studied by time-of-flight secondary ion mass spectrometry. In the perovskite film prepared in Example 1, element S was detected before and after annealing to mark the functionalized liquid crystal material in the body. Figure 2 In the 3D images in a and 2b, S is marked in green, perovskite including PbI2 is marked in red, and Ti is marked in blue. Functionalized liquid crystal material (green) mixed with perovskite (red) is Figure 2 The brown color in a indicates that before annealing, the functionalized liquid crystal material CBO6SS6OCB is evenly distributed in the entire perovskite phase. However, after annealing, there is almost no green in the perovskite phase, and the pure green area exists at the lower interface formed between the perovskite phase and the electron transport layer. This means that there is almost no functionalized liquid crystal material CBO6SS6OCB in the bulk phase after annealing. Figure 2 (b) Figure 2 Figures c and d show the variation of element concentration with sputtering depth before and after annealing, respectively. The sputtering depth increases with sputtering time, first etching the perovskite bulk layer and gradually etching into the TiO2 electron transport layer. Figure 2 Figure c shows that the concentrations of the functionalized liquid crystal material and PbI2 are much higher than that of TiO2 at the beginning, which means that the functionalized liquid crystal material is in the perovskite phase before annealing. Figure 2 In image d, the PbI2 concentration decreases sharply at the beginning of the TiO2 layer, while the TiO2 concentration increases from zero to a peak value with sputtering time. The concentration of the functionalized liquid crystal follows a similar trend to that of TiO2, increasing from zero to a peak at the interface between the perovskite and TiO2. The results indicate that the functionalized liquid crystal accumulates primarily at the lower interface after annealing, suggesting that the functionalized liquid crystal, which was uniformly distributed in the perovskite bulk before annealing, migrates to the interface between the perovskite and TiO2 after annealing.

[0082] (3) Spontaneous interface healing

[0083] Since the most reliable structural symmetry information can be provided by a high diffraction angle with a multiplication factor, the crystal plane (211) was selected from the three planes with a strong diffraction peak for further depth-dependent grazing incidence X-ray diffraction (GIXRD) analysis. When the incident angle increases from 0.3° to 1.5°, the diffraction peak of the perovskite film prepared in Comparative Example 1 at 2θ of 31.65° gradually shifts to a lower angle, while the diffraction peak of the perovskite film prepared in Example 1 has almost no change and is independent of the incident angle ( Figure 3 (a, b). The shift of the diffraction peak of the perovskite film prepared in Comparative Example 1 to a lower angle is due to the increase in the inter-plane crystal spacing, which leads to lattice expansion and generates stress and strain. When the incident angle changes from 0.3° to 1.5°, it is observed that the spacing of the perovskite film prepared in Comparative Example 1 increases significantly, while the spacing of the perovskite film prepared in Example 1 remains almost unchanged, as shown in FIG. Figure 3 c. The results show that the perovskite film prepared in Example 1 has almost no residual stress, which indicates that the functionalized liquid crystal material undergoes a dynamic transformation, transferring from the perovskite bulk phase to the lower interface, effectively releasing the residual stress at the interface between the perovskite and the electron transport layer.

[0084] The inventors further investigated the role of dynamic liquid crystal transitions in spontaneously healing interfaces in determining the carrier extraction process at the perovskite / hole transport layer and electron transport layer / perovskite interfaces. Figure 4 In Figure a, when the hole transport layer in Example 1 is coated on top of the perovskite film, the kinetic decay curve does not change significantly. This result shows that the hole extraction remains unchanged after the method of dynamic liquid crystal transition and spontaneous healing interface is adopted. In contrast, for the lower interface formed by the perovskite and the electron transport layer, the kinetic decay curve of the perovskite film prepared in Example 1 seems to decrease much faster than that in Comparative Example 1 ( Figure 4 (b) This result demonstrates that the method of using dynamic liquid crystal transition to spontaneously heal the interface significantly accelerates the extraction and collection of electrons from the perovskite to the electron transport layer.

[0085] In order to further demonstrate the beneficial effects of the present invention, the inventors tested the photoelectric performance of the perovskite cells prepared in Example 1, Comparative Example 1 and Comparative Example 2. The test results are listed in Tables 1 and Figure 5. As can be seen from Table 1, the efficiency of the perovskite cell prepared by the dynamic liquid crystal transition spontaneous healing interface method is 24.38%, the efficiency of the perovskite solar cell prepared without the dynamic liquid crystal transition spontaneous healing interface method is 23.01%, and the efficiency of the perovskite solar cell prepared by the method of interface purification under the liquid crystal material is 23.94%. Comparison of the above research results fully illustrates that the dynamic liquid crystal transition spontaneous healing interface method proposed in the present invention can delay the crystallization of perovskite in the bulk phase to improve the quality of the perovskite film during the preparation of the perovskite cell. The annealing process causes the functionalized liquid crystal material to undergo a dynamic transformation, transferring from the perovskite bulk phase to the interface between the perovskite and the electron transport layer, effectively releasing the residual stress at the interface between the perovskite and the electron transport layer, and significantly accelerating the extraction and collection of electrons from the perovskite to the electron transport layer. Finally, after being placed for 2160 hours at an air humidity of 30±5%, a temperature of 25±5°C, and without packaging, the perovskite solar cell efficiency prepared in Example 1 still maintained 93.0% of its initial PCE. In comparison, the perovskite cell prepared in Comparative Example 1 only maintained 79.7% of its initial value under the same aging conditions. A photostability test of the unencapsulated perovskite cell was carried out in a nitrogen-filled glove box at 45°C under sunlight for one day. The results showed that the perovskite cell prepared in Example 1 maintained an initial efficiency of more than 96.3%, while the perovskite cell prepared in Comparative Example 1 maintained only 71.1%.

[0086] Table 1. Performance test results of solar cells prepared in Example 1, Comparative Example 1 and Comparative Example 2

[0087]

[0088] In summary, the method of preparing perovskite solar cells by utilizing liquid crystal dynamic transition and spontaneous interface healing proposed in the present invention not only improves the efficiency of perovskite cell devices, but also improves the air stability and light stability of the devices, thereby realizing the preparation of efficient and stable perovskite solar cells by utilizing the method of dynamic liquid crystal transition and spontaneous interface healing.

[0089] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for preparing perovskite solar cells using liquid crystal dynamic transition spontaneous interface healing, characterized in that: The following steps are involved: S1. Select fluorine-doped tin oxide glass as a glass substrate, clean it, and treat it with ultraviolet ozone, and then form an electron transport layer on the glass substrate by any of the following methods: chemical bath deposition, water bath deposition, spin coating, doctor blade coating, or screen printing; S2. Dissolving the functionalized liquid crystal material in a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide, stirring and dissolving to obtain a liquid crystal additive solution with a concentration of 2 to 8 mg / mL; mixing and dissolving PbI2, NH2CH=NH2I, CH3NH3Br, and CsI in molar amounts of 1.20 to 1.80 mmol, 1.20 to 1.80 mmol, 0.15 to 0.2 mmol, and 0.08 to 0.10 mmol, respectively, in 1 mL of the liquid crystal additive solution to obtain a perovskite precursor solution containing the liquid crystal additive; S3, coating the perovskite precursor solution on the electron transport layer of the glass substrate by spin coating to form a perovskite absorption layer; S4, forming a hole transport layer made of Spiro-OMeTAD, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine or nickel oxide on the perovskite absorption layer on the glass substrate; S5, forming an electrode on the hole transport layer of the glass substrate by evaporation, and finally obtaining a perovskite solar cell; Wherein, the structural formula of the functionalized liquid crystal material is shown in formula (1): In formula (1), n ​​represents the number of carbon atoms and is an integer of 2-12.

2. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: The material of the electron transport layer in step S1 is any one of TiO2, ZnO, and SnO2.

3. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: In step S1, when the material of the electron transport layer is TiO2, the method for forming the electron transport layer is as follows: First, a fluorine-doped tin oxide glass substrate was selected and ultrasonically cleaned in glass cleaning solution, deionized water, and ethanol for 15 to 30 minutes each, dried with nitrogen, and then treated with ultraviolet ozone for 10 to 15 minutes. Then, the glass substrate was placed in a 0.15-0.2 mol / L TiCl4 aqueous solution at 60-70°C for 45-60 minutes, and then washed alternately with deionized water and ethanol for multiple times; Finally, the glass substrate is annealed at 180-200° C. for 20-30 minutes, and a TiO2 electron transport layer is prepared on the glass substrate by a chemical bath deposition method.

4. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: When n=6 in formula (1), the preparation method of the functionalized liquid crystal material is as follows: First, 4′-hydroxy-4-biphenylnitrile and 1,6-dibromohexane were subjected to Williamson etherification to obtain bromine-terminated alkoxycyanobiphenyl; Then, under N2 atmosphere, a mixture of bromine-terminated alkoxycyanobiphenyl, thiourea and anhydrous ethanol is heated under reflux for 15-20 hours, an aqueous NaOH solution is added and further heated under reflux for 3-4 hours, cooled to room temperature, and then water is added and acidified with dilute hydrochloric acid; Finally, the acidified mixture is extracted with dichloromethane, the organic phases are combined, dried over anhydrous magnesium sulfate, filtered, and the solvent is removed under reduced pressure to obtain a concentrate; the concentrate is purified by silica gel column chromatography using a mixture of petroleum ether and ethyl acetate as an eluent to obtain a compound of a functionalized liquid crystal material.

5. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: Before the spin coating in step S3, the glass substrate needs to be treated with ultraviolet ozone for 10 to 20 minutes to enhance its surface wettability.

6. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: Step S3 specifically includes the following steps: The perovskite precursor solution is dropped onto the electron transport layer of the glass substrate and the first stage of spin coating is performed at a speed of 500-1500 rpm / s for 5-20 seconds; Then, the second stage of spin coating is carried out at a speed of 2000-5000 rpm / s for 30-50 seconds. When the second stage is carried out for 20-40 seconds, 100-300 μL of ethyl acetate is added dropwise. After the second stage of spin coating is completed, annealing treatment is performed at a temperature of 120 to 200° C. and an annealing time of 10 to 30 minutes to form a perovskite absorption layer.

7. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to claim 1, characterized in that: In step S4, a hole transport layer made of Spiro-OMeTAD is generated, which specifically includes the following steps: Spiro-OMeTAD, Li-TFSI acetonitrile solution and 4-tert-butylpyridine were mixed and dissolved in chlorobenzene, stirred at room temperature for 10 to 12 hours, and filtered to prepare a Spiro-OMeTAD solution; The Spiro-OMeTAD solution was dropped onto the perovskite absorption layer of the glass substrate and spin-coated at a rotation speed of 4000-5000 rpm for 20-30 seconds to prepare a hole transport layer.

8. The method for preparing a perovskite solar cell using liquid crystal dynamic transition spontaneous interface healing according to any one of claims 1 to 7, characterized in that: The electrode is a gold electrode, and the thickness of the gold electrode is 70-100 nm.

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