Sandwich-structure perovskite thin film, preparation method and application thereof, and perovskite solar cell

Abstract

The invention provides a perovskite thin film with a sandwich structure, a preparation method and application of the perovskite thin film and a perovskite solar cell, and belongs to the technical field of perovskite solar cells. According to the invention, the EDTA-2Na passivation layer is arranged between the ZnO electron transport layer and the perovskite layer, and EDTA-2Na and zinc ions on the surface of ZnO form a stable complex, so that the surface activity of ZnO is reduced, and the reaction between ZnO and methylamine lead iodide is inhibited; the EDTA-2Na can also enhance the interface bonding force between ZnO and perovskite, improve the interface contact state, reduce the interface resistance and facilitate the transmission and collection of charges; by limiting the thickness of the EDTA-2Na passivation layer, the function of the EDTA-2Na passivation layer can be fully played, and the situation that electron transmission is affected by the too thick passivation layer and the passivation effect is not obvious if the passivation layer is too thin is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of perovskite solar cells, and particularly relates to a perovskite thin film with a sandwich structure, a preparation method and application thereof, and a perovskite solar cell. Background Art

[0002] Solar cells convert light energy into electrical energy through the photovoltaic effect, which conforms to the concept of green and environmental protection. Due to its advantages such as a diffusion length of up to 175 m, high carrier mobility, direct optical bandgap, broad absorption range, low-cost processing, and easy manufacturing, solid-state organic-inorganic lead halide perovskite materials have become an excellent choice for fabricating high-efficiency photovoltaic devices.

[0003] At present, the efficiency of perovskite solar cells based on organic-inorganic lead halide perovskite materials has reached 26.7%, and a relatively mature industrialization process has been formed. In the continuous practice of its commercialization path, many research groups have focused on electron transport layer materials. Representative metal oxide materials that have been developed, including titanium dioxide (TiO2), zinc oxide (ZnO), and tin dioxide (SnO2). Among these metal oxides, TiO2 nanoparticles (NPs) are usually used as the electron transport layer because they can provide efficient charge collection. However, the preparation of the TiO2 electron transport layer requires a sintering process at a high temperature (about 500 °C), and this temperature does not meet the requirements for fabricating flexible perovskite solar cells on plastic substrates. Therefore, ZnO nanomaterials with low-temperature film-forming ability and good electron transport have become alternative materials for the electron transport layer in perovskite solar cells. However, when the perovskite thin film is directly spin-coated on the ZnO electron transport layer, its stability is poor during the annealing process. It has been found that due to the presence of hydroxyl groups on the surface of ZnO nanomaterials, hydroxyl groups will enter the perovskite lattice during the annealing process of the perovskite thin film on the ZnO layer, breaking the weak bonds within the perovskite lattice, resulting in the degradation and failure of the perovskite phase and an ineffective perovskite thin film cannot be obtained. Summary of the Invention

[0004] The purpose of the present invention is to provide a perovskite thin film with a sandwich structure, a preparation method and application thereof, and a perovskite solar cell. The perovskite thin film with a sandwich structure provided by the present invention can inhibit the reaction between ZnO and perovskite, improve the stability of the ZnO-perovskite interface, and improve the photoelectric conversion efficiency after assembling the perovskite solar cell.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a perovskite thin film with a sandwich structure, including a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; the thickness of the EDTA-2Na passivation layer is 5-25 nm.

[0007] Preferably, the thickness of the ZnO electron transport layer is 20 - 50 nm.

[0008] Preferably, the thickness of the methylammonium lead iodide calcium titanate layer is 300 - 450 nm.

[0009] The present invention also provides a method for preparing the perovskite thin film with the sandwich structure described in the above technical solution, including the following steps:

[0010] (1) Spin-coat ZnO solution on a substrate for the first time and then perform the first annealing to obtain the ZnO electron transport layer;

[0011] (2) Spin-coat an aqueous solution of EDTA-2Na on the surface of the ZnO electron transport layer obtained in step (1) for the second time and then perform the second annealing to obtain the EDTA-2Na passivation layer; the thickness of the EDTA-2Na passivation layer is 5 - 25 nm;

[0012] (3) Spin-coat a methylammonium lead iodide calcium titanate precursor solution on the surface of the EDTA-2Na passivation layer obtained in step (2) for the third time and then perform the third annealing to obtain the perovskite thin film with the sandwich structure.

[0013] Preferably, the mass concentration of EDTA-2Na in the aqueous solution of EDTA-2Na in step (2) is 1 - 5%.

[0014] Preferably, the parameters of the first spin-coating in step (1) are: rotation speed 3000 - 5000 rpm, acceleration 2000 - 4000 rpm / s, spin-coating duration 30 - 60 s; the temperature of the first annealing is 150 - 200 °C, and the time of the first annealing is 1 - 2.5 h.

[0015] Preferably, the parameters of the second spin-coating in step (2) are: rotation speed 3000 - 5000 rpm, acceleration 2000 - 4000 rpm / s, spin-coating duration 30 - 60 s; the temperature of the second annealing is 150 - 200 °C, and the time of the second annealing is 5 - 15 min.

[0016] Preferably, the parameters of the third spin-coating in step (3) are: rotation speed 1500 - 2500 rpm, acceleration 600 - 1000 rpm / s, spin-coating duration 20 - 40 s; the temperature of the third annealing is 100 - 140 °C, and the time of the third annealing is 5 - 15 min.

[0017] The present invention also provides the application of the perovskite thin film with the sandwich structure described in the above technical solution in perovskite solar cells.

[0018] The present invention also provides a perovskite solar cell, which includes an FTO substrate, a perovskite thin film, a hole transport layer, and a metal electrode arranged in sequence, and the perovskite thin film is the sandwich-structured perovskite thin film described in the above technical solution.

[0019] The present invention provides a sandwich-structured perovskite thin film, which includes a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; the thickness of the EDTA-2Na passivation layer is 5-25 nm. By arranging the EDTA-2Na passivation layer between the ZnO electron transport layer and the perovskite layer, EDTA-2Na forms a stable complex with zinc ions on the surface of ZnO, covering the active sites and reducing the ability of Zn 2+ to adsorb OH - . OH - acts as a mobile group and can be removed as the solvent is removed during the drying process; the amino group in EDTA-2Na weakly coordinates with Pb 2+ in the perovskite component. On the one hand, it reduces the unsaturated dangling bonds Pb 2+ defects on the perovskite surface. On the other hand, it forms a carrier transport channel between ZnO and the perovskite thin film; when used in a perovskite solar cell, EDTA-2Na can also adjust the charge distribution on the surface of ZnO, optimize its energy level matching with the perovskite layer, facilitate electron transport, reduce interfacial charge accumulation, and improve the battery performance; EDTA-2Na can also interact with ZnO and the perovskite to passivate surface defects, reduce non-radiative recombination centers, thereby improving the performance and stability of the thin film; EDTA-2Na can also enhance the interfacial binding force between ZnO and the perovskite, improve the interfacial contact state, reduce the interfacial resistance, and facilitate the transport and collection of charges; by limiting the thickness of the EDTA-2Na passivation layer, its function can be fully exerted, avoiding the influence of too thick a passivation layer on electron transport and too thin a passivation layer having an insignificant passivation effect. The results of the examples show that the sandwich-structured perovskite thin film provided by the present invention has no color change during the annealing (heating at 120°C for 30 min) of the perovskite, and the photoelectric conversion efficiency reaches 20.16% after assembling the perovskite solar cell. Description of the Drawings

[0020] Figure 1 is a schematic diagram of the sandwich-structured perovskite thin film provided by the embodiment of the present invention;

[0021] Figure 2 is a state diagram of the sandwich-structured perovskite thin film provided by Embodiment 1 of the present invention at the annealing time of 1 min;

[0022] Figure 3 is a state diagram of the sandwich-structured perovskite thin film provided by Embodiment 1 of the present invention at the annealing time of 30 min;

[0023] Figure 4 State diagram of the perovskite thin film provided in Comparative Example 1 of the present invention when annealed for 1 minute;

[0024] Figure 5 State diagram of the perovskite thin film provided in Comparative Example 1 of the present invention when annealed for 30 minutes;

[0025] Figure 6 Photovoltaic conversion efficiency curve diagram of the perovskite thin film sandwich structure battery assembled in Example 1 of the present invention;

[0026] Figure 7 XRD pattern of the perovskite thin film obtained by annealing for 5 minutes in Test Example 2 of the present invention;

[0027] Figure 8 XRD pattern of the perovskite thin film obtained by annealing for 10 minutes in Test Example 2 of the present invention;

[0028] Figure 9 XRD pattern of the perovskite thin film obtained by annealing for 20 minutes in Test Example 2 of the present invention;

[0029] Figure 10 XRD pattern of the perovskite thin film obtained by annealing for 30 minutes in Test Example 2 of the present invention;

[0030] Figure 11 XRD pattern of the perovskite thin film obtained by annealing for 40 minutes in Test Example 2 of the present invention;

[0031] Figure 12 XRD pattern of the perovskite thin film obtained by annealing for 50 minutes in Test Example 2 of the present invention;

[0032] Figure 13 XRD pattern of the perovskite thin film obtained by annealing for 60 minutes in Test Example 2 of the present invention;

[0033] Figure 14 XRD pattern of the perovskite thin film obtained by annealing for 70 minutes in Test Example 2 of the present invention;

[0034] Figure 15 XRD pattern of the perovskite thin film of Comparative Example 2 of the present invention. Detailed implementation manners

[0035] For all raw materials of the present invention, there is no special limitation on their sources, and they can be purchased on the market or prepared according to conventional methods well-known to those skilled in the art.

[0036] For all raw materials of the present invention, there is no special limitation on their purity, and the present invention preferably uses high-purity raw materials.

[0037] The present invention provides a perovskite thin film with a sandwich structure, which includes a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; the thickness of the EDTA-2Na passivation layer is 5 to 25 nm.

[0038] The perovskite thin film with a sandwich structure provided by the present invention includes a ZnO electron transport layer. By utilizing the characteristic of the low annealing temperature of the ZnO electron transport layer, a film can be formed on a plastic substrate.

[0039] In the present invention, the thickness of the ZnO electron transport layer is preferably 20 to 50 nm, more preferably 30 to 40 nm; as an embodiment of the present invention, the thickness of the ZnO electron transport layer can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm. The ZnO electron transport layer within the above range is beneficial to the charge transport and the energy level matching with the interface, and further improves the photoelectric conversion efficiency.

[0040] The perovskite thin film with a sandwich structure provided by the present invention further includes an EDTA-2Na passivation layer disposed on the ZnO electron transport layer.

[0041] In the present invention, the thickness of the EDTA-2Na passivation layer is 5 to 25 nm, preferably 8 to 12 nm; as an embodiment of the present invention, the thickness of the EDTA-2Na passivation layer can be 6 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, or 25 nm. By setting the EDTA-2Na passivation layer in the present invention, a stable complex can be formed with the zinc ions on the surface of ZnO, reducing the activity on the surface of ZnO and inhibiting its reaction with methylammonium lead iodide; limiting the thickness of the EDTA-2Na passivation layer within the above range is beneficial to fully exert the role of the passivation layer, ensuring that the perovskite thin film will not decompose the perovskite during annealing and improving the photoelectric conversion efficiency.

[0042] The perovskite thin film with a sandwich structure provided by the present invention further includes a methylammonium lead iodide perovskite layer disposed on the EDTA-2Na passivation layer.

[0043] In the present invention, the thickness of the methylammonium lead iodide perovskite layer is preferably 300 to 450 nm, more preferably 350 to 400 nm; as an embodiment of the present invention, the thickness of the methylammonium lead iodide perovskite layer can be 300 nm, 330 nm, 370 nm, 400 nm, 420 nm, or 450 nm. The thickness of the methylammonium lead iodide perovskite layer within the above range is beneficial to light absorption, charge transport and recombination, and further improves the photoelectric conversion efficiency.

[0044] In the present invention, an EDTA-2Na passivation layer is provided between the ZnO electron transport layer and the perovskite layer. EDTA-2Na forms a stable complex with zinc ions on the surface of ZnO, covering the active sites and reducing the 2+ ability to adsorb OH - . OH - , as a mobile group, can be removed as the solvent is removed during the drying process; the amino group in EDTA-2Na is weakly coordinated with Pb 2+ in the perovskite component. On the one hand, it reduces the unsaturated dangling bonds Pb 2+ defects on the perovskite surface. On the other hand, it forms a carrier transport channel between the ZnO and perovskite films; EDTA-2Na can also adjust the charge distribution on the surface of ZnO, optimize its energy level matching with the perovskite layer, facilitate electron transport, reduce interfacial charge accumulation, and improve the battery performance; EDTA-2Na can also interact with ZnO and perovskite to passivate surface defects and reduce non-radiative recombination centers, thereby improving the performance and stability of the film; EDTA-2Na can also enhance the interfacial bonding force between ZnO and perovskite, improve the interfacial contact state, reduce the interfacial resistance, and facilitate the transport and collection of charges; by limiting the thickness of the EDTA-2Na passivation layer, its function can be fully exerted, avoiding the influence of too thick a passivation layer on electron transport and too thin a passivation layer resulting in an insignificant passivation effect.

[0045] The present invention also provides a method for preparing the perovskite film with the sandwich structure described in the above technical solution, including the following steps:

[0046] (1) Spin-coat a ZnO solution on a substrate for the first time and then perform the first annealing to obtain a ZnO electron transport layer;

[0047] (2) Spin-coat an aqueous solution of EDTA-2Na on the surface of the ZnO electron transport layer obtained in step (1) for the second time and then perform the second annealing to obtain an EDTA-2Na passivation layer; the thickness of the EDTA-2Na passivation layer is 5 - 25 nm;

[0048] (3) Spin-coat a methylammonium lead iodide perovskite precursor solution on the surface of the EDTA-2Na passivation layer obtained in step (2) for the third time and then perform the third annealing to obtain a perovskite film with a sandwich structure.

[0049] In the present invention, a ZnO solution is spin-coated on a substrate for the first time and then the first annealing is performed to obtain a ZnO electron transport layer.

[0050] The present invention has no special requirements for the type of the substrate, and a conventional substrate in the art can be used. As an implementation manner of the present invention, the substrate can be an FTO substrate.

[0051] As an embodiment of the present invention, the substrate can be pre-treated first, and the pre-treatment process can include: ultrasonically treating with deionized water, absolute ethanol, acetone, and isopropyl alcohol for 15 minutes respectively, then drying with nitrogen, and then treating with ultraviolet ozone for 15 minutes.

[0052] The present invention has no special requirements for the type of the ZnO solution, as long as spin coating can be carried out; as an embodiment of the present invention, the ZnO solution can be an ethanol solution of ZnO nanoparticles, and the mass fraction of ZnO nanoparticles in the ethanol solution of ZnO nanoparticles can be 2.5%.

[0053] In the present invention, the rotation speed of the first spin coating is preferably 3000 - 5000 rpm, more preferably 3800 - 4200 rpm; the acceleration of the first spin coating is preferably 2000 - 4000 rpm / s, more preferably 2700 - 3300 rpm / s; the spin coating duration of the first spin coating is preferably 30 - 60 s, more preferably 40 - 50 s. The parameters of the first spin coating within the above ranges are beneficial to controlling the thickness and surface quality of the ZnO electron transport layer, and further improving the charge transport efficiency. As an embodiment of the present invention, the first spin coating can be static spin coating.

[0054] In the present invention, the temperature of the first annealing is preferably 150 - 200 °C, more preferably 160 - 180 °C; the time of the first annealing is preferably 1 - 2.5 h, more preferably 1.5 - 2 h. The parameters of the first annealing within the above ranges are beneficial to the crystallization of the ZnO electron transport layer and further improve the charge transport efficiency.

[0055] After obtaining the ZnO electron transport layer, in the present invention, an aqueous solution of EDTA-2Na is spin-coated on the surface of the ZnO electron transport layer and then second annealed to obtain an EDTA-2Na passivation layer.

[0056] In the present invention, the mass concentration of EDTA-2Na in the aqueous solution of EDTA-2Na is preferably 1 - 5%, more preferably 2 - 4%; as an embodiment of the present invention, the mass concentration of EDTA-2Na in the aqueous solution of EDTA-2Na can be 1%, 2%, 3%, 4% or 5%. The mass concentration of EDTA-2Na in the aqueous solution of EDTA-2Na within the above ranges is beneficial to controlling the thickness of the EDTA-2Na passivation layer and giving full play to the passivation effect.

[0057] The present invention has no particular limitation on the preparation method of the aqueous solution of EDTA-2Na, and a conventional preparation method in the art can be adopted. As an embodiment of the present invention, EDTA-2Na powder can be put into a stirring flask, deionized water is added dropwise, and stirred at 85 °C for 3 h.

[0058] In the present invention, the rotation speed of the second spin coating is preferably 3000 - 5000 rpm, more preferably 3800 - 4200 rpm; the acceleration of the second spin coating is preferably 2000 - 4000 rpm / s, more preferably 2700 - 3300 rpm / s; the spin coating duration of the second spin coating is preferably 30 - 60 s, more preferably 40 - 50 s. When the parameters of the second spin coating are within the above ranges, it is beneficial to control the coating quality and thickness of the EDTA-2Na passivation layer, achieve full coverage of the ZnO electron transport layer, and further improve the passivation effect. As an embodiment of the present invention, the second spin coating can be static spin coating.

[0059] In the present invention, the temperature of the second annealing is preferably 150 - 200 °C, more preferably 160 - 180 °C; the time of the second annealing is preferably 5 - 15 min, more preferably 8 - 12 min. When the parameters of the second annealing are within the above ranges, it is beneficial for the EDTA-2Na passivation layer to form a complete coating and further improve the passivation effect.

[0060] After obtaining the EDTA-2Na passivation layer, in the present invention, a methylammonium lead iodide perovskite precursor solution is spin-coated on the surface of the EDTA-2Na passivation layer for the third time and then the third annealing is carried out to obtain a perovskite thin film with a sandwich structure.

[0061] The present invention has no special limitation on the methylammonium lead iodide perovskite precursor solution, as long as a perovskite layer can be obtained by spin coating. As an embodiment of the present invention, the preparation method of the methylammonium lead iodide perovskite precursor solution can be: dissolving lead iodide (PbI2) and methylammonium iodide (MAI) in a solvent, and the solvent can be a mixed solution of DMF and DMSO, and the volume ratio of DMF to DMSO can be 4:1.

[0062] In the present invention, the rotation speed of the third spin coating is preferably 1500 - 2500 rpm, more preferably 1800 - 2200 rpm; the acceleration of the third spin coating is preferably 600 - 1000 rpm / s, more preferably 700 - 800 rpm / s; the spin coating duration of the third spin coating is preferably 20 - 40 s, more preferably 25 - 35 s. When the parameters of the third spin coating are within the above ranges, it is beneficial to control the coating quality and thickness of the perovskite layer and further improve the photoelectric conversion efficiency. As an embodiment of the present invention, the third spin coating can be static spin coating.

[0063] In the present invention, the temperature of the third annealing is preferably 100 - 140 °C, more preferably 120 - 130 °C; the time of the third annealing is preferably 5 - 15 min, more preferably 8 - 12 min. When the parameters of the third annealing are within the above ranges, it is beneficial to optimize the crystallization quality and stability, and further improve the photoelectric conversion efficiency. As an embodiment of the present invention, air extraction crystallization can be carried out for 1 min before the third annealing.

[0064] The preparation method provided by the present invention has a simple process, and it is easy to control the thickness and uniformity of each layer. Moreover, the spin coating method has obvious cost advantages and wide adaptability, which is beneficial to industrial production.

[0065] The present invention also provides the application of the perovskite thin film with the sandwich structure described in the above technical solution in a perovskite solar cell.

[0066] The present invention has no particular limitation on the application method of the perovskite thin film with the sandwich structure, and the conventional application methods in the art can be adopted.

[0067] The present invention also provides a perovskite solar cell, which includes an FTO substrate, a perovskite thin film, a hole transport layer, and a metal electrode arranged in sequence, and the perovskite thin film is the perovskite thin film with the sandwich structure described in the above technical solution.

[0068] The perovskite solar cell provided by the present invention includes an FTO substrate. The present invention has no particular requirements for the FTO substrate, and the conventional FTO substrate in the art can be adopted.

[0069] The perovskite solar cell provided by the present invention includes a perovskite thin film arranged on the FTO substrate, and the perovskite thin film is the perovskite thin film with the sandwich structure described in the above technical solution.

[0070] The perovskite solar cell provided by the present invention includes a hole transport layer arranged on the perovskite thin film. The present invention has no particular requirements for the parameters of the hole transport layer, and the conventional parameters of the hole transport layer in the art can be adopted. As an embodiment of the present invention, the hole transport layer uses a Spiro-OMeTAD solution and is spin-coated on the surface of the perovskite layer through the fourth spin coating; the rotation speed of the fourth spin coating can be 3000 rpm, the acceleration can be 1500 rpm / s, the spin coating duration can be 30 s, and the fourth spin coating can be static spin coating.

[0071] The perovskite solar cell provided by the present invention includes a metal electrode arranged on the hole transport layer. The present invention has no particular requirements for the metal electrode, and the conventional metal electrode in the art can be adopted. As an embodiment of the present invention, the material of the metal electrode can be silver; a silver metal electrode with a thickness of 1 nm can be prepared by vacuum evaporation.

[0072] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative work belong to the scope of protection of the present invention.

[0073] Example 1

[0074] A perovskite thin film with a sandwich structure, the schematic structural diagram is as Figure 1 shown, which is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer and a methylammonium lead iodide perovskite layer sequentially arranged on an FTO substrate; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 10 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0075] The preparation method is as follows:

[0076] Pretreatment of the FTO substrate: First, ultrasonically treat with deionized water, absolute ethanol, acetone, and isopropanol for 15 minutes respectively, then dry with nitrogen, and then perform ultraviolet ozone treatment for 15 minutes for standby.

[0077] Weigh 0.1 g of EDTA-2Na powder and put it into a special stirring bottle, add 6 mL of deionized water, and stir at 85 °C for 3 h to obtain an EDTA-2Na aqueous solution.

[0078] The ZnO nanoparticle ethanol (2.5 wt%) solution is a commercially available product, the manufacturer is Xi'an Yu Ri Solar Energy Technology Co., Ltd., and the product number is 307009.

[0079] Preparation of the methylammonium lead iodide perovskite precursor solution: Dissolve 1.026 g of PbI2 and 0.356 g of MAI in a mixed solvent of 2.4 mL of DMF and 0.6 mL of DMSO, and magnetically stir and mix evenly at room temperature to obtain it.

[0080] (1) Spin-coat the ZnO nanoparticle ethanol (2.5 wt%) solution statically on the FTO substrate at a speed of 4000 rpm and an acceleration of 2000 rpm / s for 30 s, and then perform the first annealing at 200 °C for 1 h to obtain the ZnO electron transport layer;

[0081] (2) Spin-coat the EDTA-2Na aqueous solution statically on the surface of the ZnO electron transport layer at a speed of 4000 rpm and an acceleration of 2000 rpm / s for 30 s, and then perform the second annealing at 200 °C for 10 min to obtain the EDTA-2Na passivation layer;

[0082] (3) On the surface of the EDTA-2Na passivation layer, the methylammonium lead iodide perovskite precursor solution was spin-coated statically for the third time at a speed of 2000 rpm and an acceleration of 800 rpm / s for 20 s, then air was pumped for crystallization for 1 min, and then the third annealing was carried out at 120 °C for 10 min to obtain a perovskite thin film with a sandwich structure.

[0083] Observe the state of the perovskite thin film during the third annealing. The state at 1 min of annealing is as Figure 2 shown; the state when the annealing time is extended to 30 min is as Figure 3 shown. The 4 samples in the figure are parallel tests. From Figure 2 、 Figure 3 it can be seen that the color of the perovskite layer thin film does not change during the annealing process, indicating that the perovskite does not decompose. Extending the annealing time is to confirm the protection ability of EDTA-2Na on the ZnO / perovskite interface during long-term annealing. If the perovskite thin film fails during the annealing process, it will change from the Figure 2 or Figure 3 shown tan color gradually to the Figures 4 to 5 shown brownish yellow until full yellow. If the perovskite thin film does not fail during the annealing process, the color will not change. Figure 2 、 Figure 3 There are some black shadows in them because the prepared perovskite thin film has a specular reflection effect, and the surface of the thin film can present the image of the person taking the photo or the surroundings, just like a black mirror, so various shadows will appear when taking photos; this is exactly a form that reflects the high perovskite thin film preparation technology in the field.

[0084] Example 2

[0085] A perovskite thin film with a sandwich structure is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 8 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0086] The preparation method is the same as that of Example 1, except that 7 mL of deionized water is added when preparing the EDTA-2Na aqueous solution.

[0087] Example 3

[0088] A perovskite thin film with a sandwich structure is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 6 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0089] The preparation method is the same as that of Example 1, except that 8 mL of deionized water was added when preparing the EDTA-2Na aqueous solution.

[0090] Example 4

[0091] A sandwich-structured perovskite thin film is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 20 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0092] The preparation method is the same as that of Example 1, except that 0.2 g of EDTA-2Na powder was added when preparing the EDTA-2Na aqueous solution.

[0093] Example 5

[0094] A sandwich-structured perovskite thin film is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 18 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0095] The preparation method is the same as that of Example 1, except that 0.15 g of EDTA-2Na powder was added when preparing the EDTA-2Na aqueous solution.

[0096] Comparative Example 1

[0097] A sandwich-structured perovskite thin film is composed of a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, the thickness of the EDTA-2Na passivation layer is 3 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0098] The preparation method is the same as that of Example 1, except that 8 mL of deionized water and 0.05 g of EDTA-2Na powder were added when preparing the EDTA-2Na aqueous solution.

[0099] Comparative Example 2

[0100] A perovskite thin film is composed of a ZnO electron transport layer and a methylammonium lead iodide perovskite layer arranged in sequence; wherein the thickness of the ZnO electron transport layer is 45 nm, and the thickness of the methylammonium lead iodide perovskite layer is 400 nm.

[0101] The preparation method is the same as that of Example 1, except that the EDTA-2Na functional layer was removed.

[0102] Observe the state of the perovskite film during the third annealing process. The state at 1 min of annealing is as shown in Figure 4 ; the state at 30 min of annealing is as shown in Figure 5 . In the figure, the 4 samples are parallel tests. From Figure 4 , Figure 5 , it can be seen that obvious yellowing occurred in the perovskite layer during the annealing process, indicating that the perovskite decomposed and failed ( Figure 5 For the two samples on the right in , the colors look locally white, but they are actually yellow. Due to the lighting problem, they look white in the photo).

[0103] Application Examples 1 - 5 and Comparative Application Example 1

[0104] Assemble the perovskite thin - film sandwich structures provided in Examples 1 - 5 and Comparative Example 1 into perovskite solar cells respectively. The specific steps are as follows:

[0105] Preparation of the hole - transporting layer

[0106] Material: Spiro - OMeTAD solution

[0107] Place the substrate with the perovskite thin - film sandwich structure on the spin coater. Under static conditions, evenly coat the Spiro - OMeTAD solution on the perovskite layer to completely cover it, and then turn on the spin - coating switch to obtain the hole - transporting layer. The spin - coating speed is 3000 rpm, the spin - coating acceleration is 1500 rpm / s, and the spin - coating duration is 30 s.

[0108] Preparation of the metal electrode

[0109] Material: Metallic silver (Ag)

[0110] Select metallic silver (Ag) as the metal electrode, and use a vacuum coating machine to evaporate the metal electrode to prepare a 1 - nm - thick silver metal electrode.

[0111] Test Example 1

[0112] Test the performance of the perovskite solar cells assembled in the application examples respectively. The results are recorded in Table 1. The J - V curve of the cell in Application Example 1 is as shown in Figure 6 .

[0113] Table 1 Record of cell performance parameters

[0114]

[0115]

[0116] From Table 1 and Figure 6It can be seen that the perovskite thin film with a sandwich structure provided by the present invention can effectively inhibit the reaction between ZnO and methylammonium lead iodide and improve the photoelectric conversion efficiency of the battery; when the thickness of the EDTA-2Na passivation layer is 10 nm, the battery efficiency is optimal. When the thickness of the passivation layer is less than 10 nm, the battery efficiency decreases. When the thickness of the passivation layer is less than 5 nm, the battery efficiency drops sharply. When the thickness of the passivation layer is greater than 10 nm, the battery efficiency also decreases.

[0117] Test Example 2

[0118] The third annealing time in step (3) of Example 1 was respectively modified to 5 min, 10 min (i.e., Example 1), 20 min, 30 min, 40 min, 50 min, 60 min, and 70 min. The obtained perovskite thin films were respectively detected for their phase using an X-ray diffractometer to obtain XRD detection patterns, as Figures 7 to 14 shown. The diffraction peaks of methylammonium lead iodide (CH3NH3PbI3) are marked with * symbols, and the remaining unmarked diffraction peaks come from the FTO substrate or other functional layers. The blue lines in the figure represent the rocking curves of the perovskite thin film, and the blue lines in the figure mark the annealing duration after spin-coating the perovskite layer. From Figures 7 to 14 it can be seen that after adding the EDTA-2Na passivation layer, the perovskite thin film always presents a perovskite phase as the annealing time prolongs, and the phase does not change.

[0119] The perovskite thin film provided in Comparative Example 2 was detected for its phase using an X-ray diffractometer to obtain an XRD detection pattern, as Figure 15 shown. Comparing Figure 15 with Figures 7 to 14 it was found that Figure 15 there are no diffraction peaks of methylammonium lead iodide (CH3NH3PbI3), indicating that the methylammonium lead iodide in the perovskite thin film of Comparative Example 2 has decomposed.

[0120] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A perovskite thin film with a sandwich structure, comprising a ZnO electron transport layer, an EDTA-2Na passivation layer, and a methylammonium lead iodide perovskite layer arranged in sequence; the thickness of the EDTA-2Na passivation layer is 5-25 nm.

2. The perovskite thin film with a sandwich structure according to claim 1, wherein The thickness of the ZnO electron transport layer is 20-50 nm.

3. The perovskite thin film with a sandwich structure according to claim 1, wherein The thickness of the methylammonium lead iodide perovskite layer is 300-450 nm.

4. A method for preparing the perovskite thin film with a sandwich structure according to any one of claims 1-3, comprising the following steps: (1) Spin-coat a ZnO solution on a substrate for the first time and then perform the first annealing to obtain a ZnO electron transport layer; (2) Spin-coat an EDTA-2Na aqueous solution on the surface of the ZnO electron transport layer obtained in step (1) for the second time and then perform the second annealing to obtain an EDTA-2Na passivation layer; the thickness of the EDTA-2Na passivation layer is 5-25 nm; (3) Spin-coat a methylammonium lead iodide perovskite precursor solution on the surface of the EDTA-2Na passivation layer obtained in step (2) for the third time and then perform the third annealing to obtain a perovskite thin film with a sandwich structure.

5. The preparation method according to claim 4, wherein, In step (2), the mass concentration of EDTA-2Na in the EDTA-2Na aqueous solution is 1-5%.

6. The preparation method according to claim 4, characterized in that The parameters of the first spin-coating in step (1) are: rotation speed 3000-5000 rpm, acceleration 2000-4000 rpm / s, spin-coating duration 30-60 s; the temperature of the first annealing is 150-200 °C, and the time of the first annealing is 1-2.5 h.

7. The preparation method according to claim 4, wherein The parameters of the second spin-coating in step (2) are: rotation speed 3000-5000 rpm, acceleration 2000-4000 rpm / s, spin-coating duration 30-60 s; the temperature of the second annealing is 150-200 °C, and the time of the second annealing is 5-15 min.

8. The preparation method according to claim 4, characterized in that, The parameters of the third spin-coating in step (3) are: rotation speed 1500-2500 rpm, acceleration 600-1000 rpm / s, spin-coating duration 20-40 s; the temperature of the third annealing is 100-140 °C, and the time of the third annealing is 5-15 min.

9. Application of the perovskite thin film with a sandwich structure according to any one of claims 1-3 or the perovskite thin film with a sandwich structure prepared by the preparation method according to any one of claims 4-8 in a perovskite solar cell.

10. A perovskite solar cell, comprising an FTO substrate, a perovskite thin film, a hole transport layer, and a metal electrode arranged in sequence, wherein the perovskite thin film is the perovskite thin film with a sandwich structure according to any one of claims 1-3 or the perovskite thin film with a sandwich structure prepared by the preparation method according to any one of claims 4-8.

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