Perovskite gradient band gap thin film and preparation method and application thereof

Abstract

The application belongs to the technical field of solar cells, and relates to a perovskite gradient band gap film and a preparation method and application thereof. The perovskite gradient band gap film with different band gap ranges is prepared by stacking a wide band gap perovskite layer and a narrow band gap perovskite layer, the band gap range of the perovskite gradient band gap film is 1.35eV-2.3eV, and the perovskite gradient band gap film is matched with multiple scene applications. According to the spectral variation range of a light source, the perovskite polycrystal film superposition structure with a matched band gap is flexibly regulated and controlled, and then the optimal ambient light utilization efficiency is realized, and the efficient utilization of the spectrum in different application scenes is realized. The perovskite gradient band gap film prepared by using the layer-by-layer sequential deposition method has high crystallinity and good uniformity. By precisely regulating and controlling the thickness ratio of the evaporated lead halide and the organic salt, the annealing temperature and time, a multilayer high-quality perovskite film superposition structure with a gradient band gap is prepared.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and relates to a perovskite gradient bandgap thin film, its preparation method, and its application. Background Technology

[0002] Metal halide hybrid perovskite solar cells have attracted significant attention from both academia and industry due to their high power conversion efficiency and low cost. Currently, the wet-process fabrication of perovskite thin films is only suitable for small-scale laboratory fabrication (<100 cm²). 2 Large-area component fabrication is limited. To achieve commercialization, large-area fabrication processes suitable for industrial applications must be developed. Furthermore, the solvents used in wet processes are harmful to the underlying functional layers and the environment.

[0003] In contrast, dry fabrication processes avoid these drawbacks, allowing for the uniform deposition of different precursor materials onto the substrate. Furthermore, the film thickness can be precisely controlled during vacuum evaporation, making it suitable for large-scale industrial production. Currently, dry fabrication processes mainly include three categories: co-evaporation, layer-by-layer sequential deposition, and vapor / liquid phase assisted deposition. However, vapor / liquid phase assisted deposition still has limitations in large-area component fabrication, while co-evaporation and layer-by-layer sequential deposition both have the potential to achieve large-area component fabrication. However, a mature and efficient dry fabrication process is currently lacking to address the limitations in film thickness control and the lack of uniformity in component selection for controlling the bandgap of perovskite layers, issues inherent in wet fabrication processes.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, the present invention provides a perovskite gradient bandgap thin film, its preparation method and application, so as to solve the problem that the existing wet preparation process cannot realize the "layer-by-layer" preparation of gradient bandgap perovskite thin films.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] On one hand, the present invention provides a perovskite gradient bandgap thin film, which is formed by stacking at least one wide bandgap perovskite layer and at least one narrow bandgap perovskite layer;

[0008] The material of the wide-bandgap perovskite layer is MA ( 1-x1 )FA x1 Pb(I (1-y1-y2) Br y1 Cl y2)3, wherein: the range of x1 is 0≤x1≤1; the range of y1 is 0≤y1≤1; the range of y2 is 0≤y2≤1; y1 and y2 are not both 0; the band gap width Eg1 of the wide bandgap perovskite layer is 1.6eV<Eg1≤2.3eV;

[0009] The material of the narrow bandgap perovskite layer is MA ( 1-x2 )FA x2 Pb z Sn (1-z) PbI3, wherein: x2 ranges from 0 to 1; z ranges from 0 to 1; and the band gap width Eg2 of the narrow band gap perovskite layer ranges from 1.35 eV to 1.6 eV.

[0010] Specifically, the number of layers in both the wide-bandgap perovskite layer and the narrow-bandgap perovskite layer is an integer between 1 and 5.

[0011] Specifically, the band gap width of the perovskite gradient band gap film ranges from 1.35 eV to 2.3 eV.

[0012] Furthermore, the wide-bandgap perovskite layer can be prepared by separately vapor-depositing lead halide Al and organic salt A2, followed by annealing at 60–150°C for 10–30 min. The thickness of lead halide Al is 10–100 nm; the thickness ratio of lead halide Al to organic salt A2 is 1:(1–2.5).

[0013] Specifically, the lead halide Al is at least one of PbI2, PbBr2, and PbCl2; the organic salt A2 is at least one of FAI, FABr, FACl, MAI, MABr, and MACl.

[0014] Furthermore, the narrow bandgap perovskite layer can be prepared by separately vapor-depositing lead halide B1 and organic salt B2, followed by annealing at a temperature of 60–150°C for 10–30 min. The thickness of lead halide B1 is 10–100 nm; the thickness ratio of lead halide B1 to organic salt B2 is 1:(1–2.5).

[0015] Specifically, the lead halide B1 is at least one of PbI2 and SnI2; the organic salt B2 is at least one of FAI and MAI.

[0016] Furthermore, the evaporation currents of lead halide A1 and lead halide B1 are each independently 1.8–2.0 A; the evaporation rates are each independently [missing information].

[0017] Furthermore, the evaporation currents of organic salt A2 and organic salt B2 are each independently 0.8–1.0 A; the evaporation rates are each independently [missing information].

[0018] On the other hand, the present invention provides a method for preparing a perovskite gradient bandgap thin film, which is prepared by stacking at least one wide bandgap perovskite layer and at least one narrow bandgap perovskite layer, and then annealing at a temperature of 60 to 150°C for 10 to 30 minutes; wherein all narrow bandgap perovskite layers are located above all wide bandgap perovskite layers.

[0019] In another aspect, the present invention also provides the application of the above-mentioned perovskite gradient bandgap thin film in perovskite solar cells.

[0020] Furthermore, the present invention also provides a perovskite solar cell based on the above-mentioned perovskite gradient bandgap thin film, specifically:

[0021] The perovskite solar cell has an upright structure (nip type) and includes, from bottom to top, a transparent conductive substrate, an electron transport layer (ETL), a perovskite gradient bandgap film, a hole transport layer (HTL), and a metal electrode stacked sequentially; the perovskite gradient bandgap film is formed by stacking several wide bandgap perovskite layers and several narrow bandgap perovskite layers.

[0022] Alternatively, the perovskite solar cell is an inverted structure (pin type) and includes, from bottom to top, a transparent conductive substrate, a hole transport layer (HTL), a perovskite gradient bandgap film, an electron transport layer (ETL), and a metal electrode stacked sequentially; the perovskite gradient bandgap film is formed by stacking several wide bandgap perovskite layers and several narrow bandgap perovskite layers.

[0023] This invention does not impose any particular limitation on the transparent conductive substrate for perovskite solar cells; any conductive substrate known in the art can be used, as long as it achieves the objectives of this invention. For example, the transparent conductive substrate may include a flexible conductive substrate or a rigid conductive substrate; wherein, the flexible conductive substrate may be a fluorine-doped tin oxide (FTO) flexible conductive substrate or an indium-doped tin oxide (ITO) flexible conductive substrate; the rigid conductive substrate may be an FTO conductive glass substrate or an ITO conductive glass substrate.

[0024] This invention does not impose any particular limitation on the material of the electron transport layer in perovskite solar cells. It can be any material or combination thereof known to those skilled in the art, such as titanium dioxide (TiO2) electron transport layer, tin dioxide (SnO2) electron transport layer, fullerene electron transport layer, C60 electron transport layer, or zinc oxide (ZnO) electron transport layer. Furthermore, this invention does not impose any particular limitation on the thickness of the electron transport layer, as long as it achieves the purpose of this invention; for example, the thickness of the electron transport layer can be 20–100 nm. This application does not impose any particular limitation on the fabrication process of the electron transport layer. For example, solution spin coating, solution blade coating, solution spraying, slot coating, or hydrothermal growth methods can be used. In some embodiments of this application, the electron transport layer is fabricated using the slot coating method.

[0025] This invention does not impose any particular limitation on the hole transport layer of perovskite solar cells. It can be any material or combination thereof known to those skilled in the art, such as nickel oxide, doped nickel oxide, cuprous iodide, cuprous thiocyanate, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), PEDOT:PSS, or Spiro-OMeTAD layered structures. Furthermore, this invention does not impose any particular limitation on the thickness of the hole transport layer, as long as it achieves the purpose of this invention; for example, it can be 10 nm to 100 nm. Moreover, this invention does not impose any particular limitation on the preparation process of the hole transport layer; for example, it can be prepared using solution spin coating, solution blade coating, slot coating, or vapor phase coating. In some embodiments of this invention, the hole transport layer is prepared using slot coating.

[0026] This invention does not impose any particular limitation on the material of the metal electrode for perovskite solar cells. It can be any material or combination thereof known to those skilled in the art, such as any one of gold (Au), silver (Ag), aluminum (Al), or copper (Cu) electrodes. Furthermore, this invention does not impose any particular limitation on the thickness of the metal electrode, as long as it achieves the purpose of this invention. For example, it can be 50–100 nm, and better results can be obtained within this range. Of course, those skilled in the art can choose an appropriate electrode thickness as needed. This invention does not impose any particular limitation on the fabrication process of the metal electrode; for example, thermal evaporation can be used.

[0027] Furthermore, it should be noted that, depending on the needs, the perovskite solar cell provided by the present invention can also include other layers. For example, in order to reduce the electronic state density, a passivation layer can be provided in the perovskite layer and the hole transport layer, and the material of the passivation layer can be phenylpropylammonium iodide (PPAI).

[0028] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0029] (1) The perovskite gradient bandgap thin film prepared by the layer-by-layer sequential deposition method of this invention has high crystallinity and good uniformity. By precisely controlling the thickness ratio of lead halide and organic salt, the deposition rate of lead halide and organic salt and the deposition current, a multilayer high-quality perovskite thin film stacked structure with gradient bandgap is prepared; and the structure of the charge transport layer is optimized based on energy level control, thereby realizing the high-efficiency preparation of multilayer perovskite photovoltaic devices with gradient bandgap.

[0030] (2) This invention prepares perovskite gradient bandgap thin films with different bandgap ranges by stacking wide-bandgap perovskite layers and narrow-bandgap perovskite layers, so that the bandgap range is 1.35eV to 2.3eV, thereby matching multiple application scenarios; and flexibly adjusts the stacked structure of perovskite polycrystalline thin films with matching bandgap according to the spectral variation range of the light source, thereby achieving the optimal ambient light utilization efficiency and realizing the efficient utilization of the spectrum in different application scenarios. Attached Figure Description

[0031] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 A schematic diagram of a perovskite solar cell with an upright structure (nip type);

[0034] Figure 2 A schematic diagram of a pin-type perovskite solar cell with an inverted structure;

[0035] Figure 3 Electron micrographs (SEM) of the first narrow bandgap perovskite layers prepared in Examples 1 to 5 (scale bar: 10 μm);

[0036] Figure 4 Electron micrographs (SEM) of the first narrow bandgap perovskite layers prepared in Example 1 and Comparative Examples 1 to 3 (scale bar: 10 μm);

[0037] Figure 5 The current density-voltage curves of the perovskite solar cells prepared in Examples 1 to 5 under standard sunlight are shown.

[0038] Figure 6 The current density-voltage curves of the perovskite solar cells prepared in Example 1 and Comparative Examples 1 to 3 are shown under standard sunlight. Detailed Implementation

[0039] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0040] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] This embodiment provides a method for fabricating a pin-type perovskite solar cell, as detailed below:

[0043] <Preparation of transparent conductive substrates>

[0044] The ITO conductive glass substrate was cleaned sequentially with ITO cleaning agent, water, and ethanol for 15 minutes, treated with an ultraviolet-ozone cleaning instrument for 15 minutes, and then transferred to an ultra-clean bench and dried with an infrared drying lamp for later use.

[0045] <Preparation of Hole Transport Layer>

[0046] First, prepare a 1.5 mg / mL solution. -1 A chlorobenzene solution of F4-TCNQ was prepared by stirring at 70°C for 15 min, and a 1.5 mg / mL solution was prepared simultaneously. -1 A PTAA chlorobenzene solution was prepared. After the PTAA dissolved, a 1% (w / w) F4-TCNQ chlorobenzene solution was added to the PTAA chlorobenzene solution, and the mixture was stirred at room temperature for 4 hours. Then, 70 μL of the prepared PTAA solution was dropped onto an ITO conductive glass substrate treated with UV-ozone, spin-coated at 6000 rpm for 30 seconds, and then annealed at 100°C for 10 minutes to complete the preparation of the hole transport layer.

[0047] <Preparation of Perovskite Gradient Bandgap Thin Films>

[0048] ①Preparation of the first wide-bandgap perovskite layer:

[0049] First, a thin layer of PbBr2 is deposited above the hole transport layer (the deposition current of PbBr2 is 1.8 A, and the deposition rate is...). The thickness is 50 nm; then, FACl is deposited by single-source evaporation (FACl evaporation current is 0.8 A, evaporation rate is...). The first wide-bandgap perovskite layer is obtained by annealing at 100℃ for 20 min, with a thickness of 100 nm.

[0050] ②Preparation of the first narrow bandgap perovskite layer:

[0051] A thin layer of a mixture of PbI2 and SnI2 (mass ratio of PbI2 to SnI2 9:1, deposition current of 2.0 A, deposition rate of [missing information]) is first deposited above the first wide-bandgap perovskite layer. The thickness is 100 nm; then, single-source evaporation deposition of FAI is used (the evaporation current of FAI is 1.0 A, and the evaporation rate is...). The thickness is 160 nm; then it is annealed at 100 °C for 20 min to obtain the first narrow bandgap perovskite layer, thus completing the preparation of the perovskite gradient bandgap thin film.

[0052] The thickness ratio of PbBr2 to FACl in the first wide-bandgap perovskite layer is 1:2; the thickness ratio of the mixture of PbI2 and SnI2 in the first narrow-bandgap perovskite layer to FACl is 1:1.6.

[0053] <Fabrication of Electron Transport Layer and Metal Electrode>

[0054] At air pressure < 4.5 × 10 -4 Under the condition of Pa, C is deposited sequentially. 60 The pin-type perovskite solar cell was fabricated using BCP (40nm thick), Ag (6nm thick), and BCP (120nm thick).

[0055] Example 2

[0056] This embodiment provides a method for fabricating a nip-type perovskite solar cell, as detailed below:

[0057] <Preparation of transparent conductive substrates>

[0058] Clean the ITO conductive glass substrate sequentially with ITO cleaning agent, water, and ethanol for 15 minutes, then treat it with an ultraviolet-ozone cleaning instrument for 15 minutes, and finally transfer it to an ultra-clean bench and dry it with an infrared drying lamp for later use.

[0059] <Preparation of Electron Transport Layer>

[0060] A 20 nm SnO2 buffer layer was prepared on an ITO conductive glass substrate using an atomic layer deposition (ALD) system with a radio frequency sputtering SnO2 target.

[0061] <Preparation of Perovskite Gradient Bandgap Thin Films>

[0062] ①Preparation of the first wide-bandgap perovskite layer:

[0063] First, a thin layer of a mixture of PbBr2 and PbI2 is deposited above the electron transport layer (the mass ratio of PbBr2 to PbI2 is 20:1, the deposition current range for the PbBr2 and PbI2 mixture is 1.8 A, and the deposition rate is...). The thickness is 100 nm; then, FABr is deposited by single-source evaporation (the evaporation current of FABr is 0.8 A, and the evaporation rate is...). The first wide-bandgap perovskite layer is obtained by annealing at 150°C for 15 minutes after the first layer is 100 nm thick.

[0064] ②Preparation of the first narrow bandgap perovskite layer:

[0065] First, a thin layer of PbI2 is deposited on top of the first wide-bandgap perovskite layer (the PbI2 deposition current is 2.0 A, and the deposition rate is...). The thickness is 100 nm; then, single-source evaporation deposition of FAI is used (the evaporation current of FAI is 1.0 A, and the evaporation rate is...). The thickness is 100 nm; then it is annealed at 150 °C for 15 min to obtain the first narrow bandgap perovskite layer.

[0066] The thickness ratio of the PbBr2 and PbI2 mixture in the first wide-bandgap perovskite layer to FABr is 1:1; the thickness ratio of PbI2 and FAI in the first narrow-bandgap perovskite layer is 1:1.

[0067] <Preparation of Hole Transport Layer>

[0068] NiO was deposited on the surface of a perovskite gradient bandgap film using ALD deposition and radio frequency sputtering. x The target material was sputtered at 90 W at 0.3 Pa argon gas and room temperature for 10 min, resulting in the deposition of 30 nm NiO. x Hole transport layer. To remove the target material, the target was sputtered for 4 minutes before formal deposition.

[0069] <Preparation of Metal Electrodes>

[0070] At air pressure < 4.5 × 10 -4 Under the condition of Pa, Au electrodes (120 nm thick) were deposited by vapor deposition to complete the fabrication of nip-type perovskite solar cells.

[0071] Example 3

[0072] Based on Example 1, the difference from Example 1 lies in the following: <Preparation of perovskite gradient bandgap thin films>, specifically as follows:

[0073] ①Preparation of the first wide-bandgap perovskite layer:

[0074] First, a thin layer of PbBr2 is deposited above the hole transport layer (the deposition current of PbBr2 is 1.8 A, and the deposition rate is...). The thickness is 50 nm; then a mixture of FABr and FACl is deposited by evaporation (the mass ratio of FABr to FACl is 30:1, the evaporation current of the FABr and FACl mixture is 0.8 A, and the evaporation rate is...). The thickness is 100 nm; then it is annealed at 60 °C for 30 min.

[0075] ② A first narrow bandgap perovskite layer is prepared above the first wide bandgap perovskite layer:

[0076] A thin layer of PbI2 was deposited on top of the first wide-bandgap perovskite layer (the deposition current of PbI2 was 2.0 A, and the deposition rate was...). The thickness is 100 nm; then, single-source evaporation deposition of FAI is used (the evaporation current of FAI is 1.0 A, and the evaporation rate is...). The thickness is 250 nm; then it is annealed at 60 °C for 30 min, thus completing the preparation of the perovskite gradient bandgap thin film.

[0077] In the first narrow-bandgap perovskite layer, the thickness ratio of PbI2 to FAI is 1:2.5, and in the first wide-bandgap perovskite layer, the thickness ratio of PbBr2 to the mixture of FABr and FACl is 1:2.

[0078] Example 4

[0079] Based on Example 1, the difference lies in the preparation of the first narrow bandgap perovskite layer during the preparation of the perovskite gradient bandgap film, as detailed below:

[0080] First, a mixture layer of PbI2 and PbCl2 is deposited by vapor deposition (the mass ratio of PbI2 to PbCl2 is 50:1, the deposition current of the PbI2 and PbCl2 mixture is 2.0 A, and the deposition rate is...). The thickness is 100 nm; then FAI is deposited by evaporation (the evaporation current of FAI is 1.0 A, and the evaporation rate is...). The thickness is 160 nm; then it is annealed at 150 °C for 10 min to obtain the first narrow bandgap perovskite layer.

[0081] The thickness ratio of the mixture of PbI2 and PbCl2 in the first narrow bandgap perovskite layer to that of FAI is 1:1.6.

[0082] Example 5

[0083] Based on Example 1, the difference from Example 1 is that in the <Preparation of Perovskite Gradient Bandgap Thin Film>, the narrow bandgap perovskite layer includes a first narrow bandgap perovskite layer and a second narrow bandgap perovskite layer; the wide bandgap perovskite layer includes a first wide bandgap perovskite layer and a second wide bandgap perovskite layer. The specific preparation process is as follows:

[0084] ① Preparation of the first wide-bandgap perovskite layer: First, a thin layer of PbBr2 is deposited by evaporation (evaporation current is 1.8A, evaporation rate is...). The thickness was 50 nm, and then FAC1 was deposited by single-source evaporation (evaporation current was 0.8 A, evaporation rate was...). A first wide-bandgap perovskite layer with a thickness of 100 nm was prepared.

[0085] ② Preparation of the second wide-bandgap perovskite layer: First, a thin layer of a mixture of PbBr2 and PbI2 is deposited by vapor deposition (the mass ratio of PbBr2 to PbI2 is 50:1, the deposition current of the PbBr2 and PbI2 mixture is 1.8A, and the deposition rate is...). The thickness is 50 nm, and then FABr is deposited by single-source evaporation (evaporation current is 0.8 A, evaporation rate is...). A second wide-bandgap perovskite layer with a thickness of 100 nm was prepared.

[0086] ③ Preparation of the first narrow bandgap perovskite layer: First, a mixture of PbI2 and SnI2 is deposited by evaporation (mass ratio of PbI2 to SnI2 9:1, evaporation current of PbI2 and SnI2 mixture is 2.0 A, evaporation rate is... The thickness is 100 nm; then a FAI layer is deposited by evaporation (evaporation current is 1.0 A, evaporation rate is...). The thickness is 160nm.

[0087] ④ Preparation of the second narrow bandgap perovskite layer: First, a mixture of PbI2 and SnI2 is deposited by vapor deposition (mass ratio of PbI2 to SnI2 8:2, vapor deposition current of PbI2 and SnI2 mixture is 2.0 A, vapor deposition rate is...). The thickness is 100 nm; then a FAI layer is deposited by evaporation (evaporation current is 1.0 A, evaporation rate is...). The thickness is 160nm.

[0088] Comparative Example 1

[0089] In the preparation of the first narrow bandgap perovskite layer, the thickness of the PbI2 vapor deposition is 100 nm, and the thickness of the FAI vapor deposition is 80 nm, wherein the thickness ratio of PbI2 to FAI is 5:4; the rest is the same as in Example 1.

[0090] Comparative Example 2

[0091] In the preparation of the first narrow bandgap perovskite layer, the thickness of the PbI2 vapor deposition is 100 nm, and the thickness of the FAI vapor deposition is 300 nm, wherein the thickness ratio of PbI2 to FAI is 1:3; the rest is the same as in Example 1.

[0092] Comparative Example 3

[0093] In the section on "Preparation of Perovskite Gradient Bandgap Thin Films," regarding the preparation of the first narrow bandgap perovskite layer, the evaporation current of PbI2 is 2.0 A, and the evaporation rate is... The rest is the same as in Example 1.

[0094] The verification process for narrow bandgap perovskite thin films is as follows:

[0095] ① The narrow bandgap perovskite films prepared in Examples 1-5 were observed under a scanning electron microscope (SEM), and the corresponding SEM morphology images were obtained. See [link to SEM image]. Figure 3 As shown; the narrow bandgap perovskite films prepared in Example 1 and those prepared in Comparative Examples 1-3 were observed under a scanning electron microscope (SEM), and the corresponding SEM morphology images were obtained. See [link to SEM image]. Figure 4 As shown.

[0096] ② Plot the JV characteristic curves of the corresponding perovskite solar cells in Examples 1-5 (see...) Figure 5 The JV characteristic curves of the corresponding perovskite solar cells in Example 1 and Comparative Examples 1-3 are shown in (see Example 1). Figure 6 ).

[0097] Depend on Figure 3 It can be seen that Examples 1-5 can all produce uniform and dense high-quality perovskite films. Figure 5 It can be seen that Examples 1-5 can all achieve the fabrication of high-quality devices with an efficiency of over 19%, and with the increase of perovskite grains, the most efficient dry evaporation process can exceed 23%. Thus, this invention provides a high-efficiency device fabrication process.

[0098] Depend on Figure 4 It can be seen that the surface morphology of the perovskite films prepared in Comparative Examples 1-3 is significantly worse, with more pores, incomplete coverage, and a rougher morphology. By comparing Comparative Examples 1-3 with Example 1, and combining... Figure 6The curves and related data show that the photoelectric conversion efficiency of the perovskite gradient bandgap film in Example 1 is 23.26%, while the photoelectric conversion efficiencies of the perovskite gradient bandgap films in Comparative Examples 1, 2, and 3 are 10.68%, 13.71%, and 17.08%, respectively. This indicates that the photoelectric conversion efficiency of the perovskite gradient bandgap film in Example 1 is significantly better than that of Comparative Examples 1-3. Furthermore, the photoelectric performance (open-circuit voltage VOC, short-circuit current density JSC, fill factor FF) of the device based on the perovskite gradient bandgap film prepared in Example 1 is far superior to that of the devices based on the perovskite gradient bandgap film prepared in Comparative Examples 1-3. Therefore, the thickness ratio of lead halides (B1, Al) and organic salts (B2, A2) needs to be controlled within the range of 1:(1-2.5), and the evaporation rate of lead halide needs to be controlled within a certain range. Only within a certain range can devices based on perovskite gradient bandgap thin films be guaranteed to have good optoelectronic performance.

[0099] It should be noted that the influence trends of parameters such as the lead halide to organic salt thickness ratio and evaporation rate on the wide bandgap perovskite layer and the narrow bandgap perovskite layer in this invention are similar, differing only in the bandgap range. Specifically, the bandgap range of Eg2 for the narrow bandgap perovskite layer is 1.35 eV < Eg2 ≤ 1.6 eV; the bandgap range of Eg1 for the wide bandgap perovskite layer is 1.6 eV < Eg1 ≤ 2.3 eV. Therefore, the above verification process only focuses on the narrow bandgap perovskite film, and the verification of the wide bandgap perovskite film will not be elaborated here.

[0100] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0101] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A perovskite gradient bandgap thin film, characterized in that, It is formed by stacking at least one wide-bandgap perovskite layer and at least one narrow-bandgap perovskite layer; The material of the wide-bandgap perovskite layer is MA. (1-x1) FA x1 Pb (I (1-y1-y2) Br y1 Cl y2 )3, wherein: the range of x1 is 0≤x1≤1; the range of y1 is 0≤y1≤1; the range of y2 is 0≤y2≤1; y1 and y2 are not both 0; the band gap width Eg1 of the wide bandgap perovskite layer is 1.6eV<Eg1≤2.3eV; The material of the narrow bandgap perovskite layer is MA. (1-x2) FA x2 Pb z Sn (1-z) I3, where: x2 ranges from 0 to 1; Z ranges from 0 to 1; and the bandgap width Eg2 of the narrow bandgap perovskite layer ranges from 1.35 eV to 1.6 eV. The wide-bandgap perovskite layer is prepared by separately depositing lead halide A1 and organic salt A2 and then annealing; the narrow-bandgap perovskite layer is prepared by separately depositing lead halide B1 and organic salt B2 and then annealing. The evaporation currents for lead halide B1 and lead halide A1 are both 1.8~2.0A, and the evaporation rates are both 2~6 Å / S; the evaporation currents for organic salt B2 and organic salt A2 are both 0.8~1.0A, and the evaporation rates are both 2~3 Å / S.

2. The perovskite gradient bandgap thin film according to claim 1, characterized in that, The number of layers in both the wide-bandgap perovskite layer and the narrow-bandgap perovskite layer is an integer between 1 and 5.

3. The perovskite gradient bandgap thin film according to claim 1, characterized in that, The annealing process parameters for the wide-bandgap perovskite layer and the narrow-bandgap perovskite layer are the same, specifically: annealing temperature is 60~150℃, and annealing time is 10~30min.

4. The perovskite gradient bandgap thin film according to claim 1, characterized in that, The thickness ratio of lead halide A1 to organic salt A2 in the wide bandgap perovskite layer is 1:(1~2.5); the thickness ratio of lead halide B1 to organic salt B2 in the narrow bandgap perovskite layer is 1:(1~2.5).

5. The perovskite gradient bandgap thin film according to claim 1, characterized in that, The lead halide Al is at least one of PbI2, PbBr2, and PbCl2; the organic salt A2 is at least one of FAI, FABr, FACl, MAI, MABr, and MACl.

6. The perovskite gradient bandgap thin film according to claim 1, characterized in that, The lead halide B1 is at least one of PbI2 and SnI2; the organic salt B2 is at least one of FAI and MAI.

7. A method for preparing a perovskite gradient bandgap thin film according to any one of claims 1 to 6, characterized in that, It is prepared by stacking at least one wide-bandgap perovskite layer and at least one narrow-bandgap perovskite layer, and then annealing at a temperature of 60~150℃ for 10~30 min.

8. An application of the perovskite gradient bandgap thin film according to any one of claims 1 to 6 in perovskite solar cells, characterized in that, The perovskite solar cell can be a positive or negative structure.

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