A method of confined annealing and a method for preparing a perovskite thin film or a solar cell

Abstract

The present invention discloses a confinement annealing method and a preparation method of a perovskite thin film or a solar cell. The preparation method includes: placing a substrate with a perovskite precursor liquid film coated on the front surface on a heating plate, the heating plate being in direct contact with the back surface of the substrate, setting the temperature of the heating plate to a first temperature, controlling the evaporation amount and the remaining amount of the solvent in the perovskite precursor liquid film by controlling the first temperature and the heating duration, and crystallizing the perovskite precursor material dissolved in the perovskite precursor liquid into perovskite grains to form a perovskite intermediate phase thin film; placing the perovskite intermediate phase thin film on the breathable thin film with the back surface of the substrate facing upward, and continuing to heat, and the residual solvent promotes the dissolution and mutual fusion of the boundaries of adjacent perovskite grains when volatilizing; slowly raising the temperature of the heating plate to a second heating temperature and continuing to heat, and the perovskite grains undergo a phase change to form the perovskite light-absorbing layer. Through this preparation method, the crystallization quality of the perovskite is improved, and the performance parameters of the perovskite light-absorbing layer are improved.

Description

Technical Field

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

[0002] Organic-inorganic hybrid perovskites have been widely studied and developed due to their excellent optoelectronic properties. The efficiency of single-junction perovskite solar devices has increased from 3.8% to 25.7% in the past decade. Due to the limitation of the Shockley-Queisser limit efficiency of single-junction photovoltaic devices, the room for improving the efficiency of traditional single-junction perovskite solar cells is relatively limited. Benefiting from the high absorption coefficient of perovskite materials, planar perovskite photovoltaic devices exhibit good light absorption characteristics, thus eliminating complex processes such as surface texturing. At the same time, combined with the wide spectral tuning range of perovskite, multi-junction tandem solar cells can be realized, expanding the absorption spectrum of photovoltaic materials, reducing energy thermalization loss, and obtaining high-efficiency photovoltaic devices, which will be the next efficiency competition point.

[0003] Although the efficiency of single-junction and double-junction tandem devices based on perovskite materials has made great progress, there is still a large gap between their actual efficiency and theoretical efficiency, mainly due to the poor crystallization quality, small grain size, many defect states, and large non-radiative recombination of perovskite light-absorbing thin films, resulting in poor efficiency of solar cells. To ensure the efficient operation of single-junction solar cells and tandem solar cells, a high-quality perovskite light-absorbing layer is a prerequisite. A high-quality perovskite light-absorbing layer needs to meet the following requirements: 1) good crystallinity, that is, the perovskite grain size needs to be large enough to improve the crystallization quality; 2) a low defect state density, that is, the perovskite light-absorbing thin film should have fewer grain boundaries; 3) a long carrier lifetime to ensure that photo-generated carriers can reach the electrode after a long transport distance and avoid recombination loss.

[0004] Perovskite tandem solar cells need to simultaneously meet the high efficiency of both the wide-bandgap top cell and the narrow-bandgap bottom cell. On the one hand, when preparing a wide-bandgap perovskite thin film, a large amount of halogen bromine needs to be added to increase the bandgap, which will cause phase separation inside the perovskite material, thus affecting the crystallization quality of the perovskite thin film. On the other hand, when preparing a narrow-bandgap perovskite thin film, it is necessary to dope with metal tin ions (Sn 2+ ) to obtain a narrow-bandgap material. Since the crystallization rate of tin-based perovskite is too fast to be precisely controlled, this will lead to poor crystallization quality, small grain size, poor film coverage, and short carrier lifetime of the narrow-bandgap perovskite, thus introducing a large number of grain boundaries and defects and affecting the efficiency of the narrow-bandgap perovskite solar cell.

[0005] For the above perovskite materials, the grain size and crystallization quality seriously affect the energy conversion efficiency of solar cells. A small grain size indicates that a large number of crystal nuclei are generated during the crystallization of perovskite, thus introducing more grain boundaries. These grain boundaries usually exhibit an amorphous state and, as non-radiative recombination centers, cause the recombination loss of photo-generated carriers, thereby affecting the performance of solar cells. Increasing the grain size of the perovskite thin film and reducing the number of grain boundaries are necessary means to improve perovskite solar cells.

[0006] Currently, the main solutions to increase the crystallinity of the perovskite light-absorbing thin film are as follows: 1) Using additives to increase the grain size of perovskite; 2) Adopting a solvent annealing method and introducing solvents to increase the grain size of perovskite, etc. However, the above solutions all have certain drawbacks.

[0007] First of all, the selection and use of additives are not effective for all perovskite components, and additives will introduce impurities, thus affecting the purity and phase stability of perovskite materials. For example, introducing lead thiocyanate (Pb(SCN)2) into narrow-bandgap perovskite has little effect on increasing the grain size, but instead introduces an impurity phase of lead iodide (PbI2).

[0008] Secondly, using ordinary heating methods, as Figure 1 shown, there are the following deficiencies in the perovskite thin film: (1) The grain size of the perovskite thin film is small and the number of grain boundaries is numerous; (2) The crystallization rate of the perovskite thin film is too fast, it is difficult to control the solvent content in the perovskite thin film, the evaporation rate and direction of the solvent cannot be adjusted, and it is difficult to manipulate the crystal growth process.

[0009] Thirdly, for the solvent annealing method, as Figure 2 shown, for tin-containing perovskite components, it will cause holes to appear in the light-absorbing thin film, thus affecting the coverage rate of the perovskite light-absorbing thin film and greatly reducing the photoelectric conversion efficiency. Therefore, the current work on improving the crystallization quality of perovskite has problems such as uncontrollable grain size, complex preparation process, and poor universality. The applicable perovskite components are relatively limited, and the applicability to different perovskite materials is not good. There is no work that can take into account the improvement of the crystallization quality of wide-bandgap perovskite, narrow-bandgap perovskite, and conventional-bandgap perovskite thin films. Summary of the Invention

[0010] To solve the problem of low photoelectric conversion efficiency caused by poor perovskite crystallization quality, the following technical solutions are adopted:

[0011] A confinement annealing method for preparing a perovskite light-absorbing layer, comprising the following steps:

[0012] Step (1) Depositing a perovskite precursor solution on the front side of the substrate by spin coating to form a perovskite precursor solution thin film on the front side of the substrate;

[0013] Step (2): Place the substrate with a perovskite precursor solution film coated on the front side on a heating plate. The heating plate is in direct contact with the back side of the substrate, and heat is sequentially transferred to the substrate and the perovskite precursor solution film. Set the temperature of the heating plate to the first temperature, and control the evaporation amount and remaining amount of the solvent in the perovskite precursor solution film by controlling the first temperature and the heating duration. The perovskite precursor material dissolved in the perovskite precursor solution crystallizes into perovskite grains, thereby forming a perovskite intermediate phase film.

[0014] Step (3): Lay a breathable film on the heating plate. Place the perovskite intermediate phase film containing residual solvent on the breathable film with the back side of the substrate facing up. Keep the temperature at the first temperature and continue heating. When the residual solvent volatilizes, the boundaries of adjacent perovskite grains dissolve and then fuse together. Slowly raise the temperature of the heating plate to the second heating temperature and continue heating. The perovskite grains undergo a phase change to form the perovskite light-absorbing layer.

[0015] The perovskite precursor solution is a solution mixture formed by a perovskite precursor material and a solvent. The optical bandgap range of the perovskite material is between 1.2 and 2.3 electron volts (eV). Preferably, the perovskite material includes: methylammonium lead iodide (MAPbI3), methylammonium lead bromide (MAPbBr3), formamidinium lead iodide (FAPbI3), formamidinium lead bromide (FAPbBr3), formamidinium tin iodide (FASnI3), cesium lead iodide (CsPbI3), cesium lead bromide (CsPbBr3), or any mixture thereof in any proportion.

[0016] The perovskite precursor solution selects a strongly polar solvent and a perovskite precursor material to form a stable solution mixture by the Lewis acid-base method. The strongly polar solvents include: dimethyl sulfoxide, dimethylformamide, gamma-butyrolactone, or any mixture thereof in any proportion.

[0017] Further, the spin coating method in step (1) is divided into two steps: In the first step, first set the spin coating speed to 500 - 1000 revolutions per minute for a duration of 2 - 10 seconds; in the second step, set the spin coating speed to 3000 - 5000 revolutions per minute for a duration of 1 minute. Add an anti-solvent 4 - 30 seconds after the start of rotation in the second step. When preparing the precursor solution film, using an anti-solvent can induce rapid surface crystallization, achieve rapid heterogeneous nucleation on the surface of the perovskite intermediate phase film, and avoid the rough surface formed when the perovskite crystallization rate exceeds the nucleation rate, thereby ensuring the flatness and grain shape of the perovskite intermediate phase film.

[0018] The anti-solvent selects a weakly polar solvent. Preferably, the weakly polar solvents include: diethyl ether, and optionally one or any mixture thereof among chlorobenzene, ethyl acetate, and isopropanol.

[0019] Further, the first temperature in step (2) is 60 - 70 °C, and the heating duration is 10 - 50 seconds; in step (3), the heating duration at the first temperature is 2 - 4 minutes; the second heating temperature is 80 - 120 °C, and the heating duration is 6 - 15 minutes.

[0020] Further, it further includes step (4): Place the substrate face up on the heating plate, with the heating plate in direct contact with the back of the substrate, maintain the second heating temperature, and the heating duration is 1 - 3 minutes. This process can promote the continuous volatilization of the residual solvent, ensure that the crystallized perovskite light-absorbing layer no longer retains organic solvents, and thus ensure good crystallization quality inside the perovskite crystal.

[0021] Further, the breathable film includes: a glass sheet, filter paper, and printing paper. By selecting different breathable films, their release rates of the solvent inside the perovskite are different, thereby affecting the volatilization rate and participation content of the solvent inside the perovskite intermediate phase film, and further affecting the perovskite grain size. The influence of the breathability of the breathable film on the grain size is negatively correlated. The higher the breathability, the smaller the grain size.

[0022] Preferably, the heating plate can be a programmable heating plate, which can set and display the real-time temperature, and can ensure more accurately obtaining the change of the hot stage surface temperature.

[0023] Preferably, the breathable film is filter paper.

[0024] In this application, a perovskite precursor solution is spin-coated on a substrate to form a perovskite precursor solution film. A large amount of solvent is contained in the perovskite precursor solution film and will volatilize during the subsequent heating process. The first temperature is used for preheating. By controlling the heating temperature and heating time, the residual amount of the above-mentioned solvent is precisely adjusted. Through an ion exchange method, perovskite crystalline state is formed, thereby forming a perovskite intermediate phase film; the substrate is placed with its back facing up on the breathable film of a heating plate and reheated at the first temperature. Among them, a certain restricted area is formed between the perovskite intermediate phase film, the breathable film and the heating plate. This restricted area can affect the volatilization path and rate of the residual internal solvent in the perovskite intermediate phase film; during this heating process, the volatilization path of the residual solvent in the perovskite intermediate phase film is blocked, and then it will slowly release in the restricted space and exchange positions with organic cations to form a transformation from the intermediate phase to the crystalline phase. At this time, the perovskite grain boundaries that have been formed originally will fuse with each other by means of the dissolution and recrystallization process of the residual solvent, and adjacent small perovskite grains will be combined together through the Ostwald ripening process and the ordered adsorption process, thereby forming larger-sized perovskite grains; the above-mentioned breathable film will change the volatilization direction and ratio of the residual solvent, generally including two directions of lateral volatilization and longitudinal penetration. The lateral process will expand the horizontal size of the perovskite grains, and the longitudinal diffusion process can reduce the perovskite grain boundaries in the vertical direction to form through-grain crystals; continue to heat the perovskite intermediate phase film to the second temperature. This heating-up process controls the heating rate and the final temperature through a program. After reaching the phase transition temperature of perovskite crystallization, the large grains obtained by combining small grains originally complete crystallization, forming a large-grain, high-quality perovskite light-absorbing layer, reducing the number of grain boundaries, inhibiting defect formation, prolonging the lifetime of photo-generated carriers, and ensuring the high performance of the perovskite light-absorbing layer.

[0025] The present invention can be applied to the preparation of perovskite films with different components, can avoid the influence of external solvents on the perovskite light-absorbing layer, and solves the problem that the crystallization of the perovskite light-absorbing layer is uncontrollable. At the same time, the confinement annealing method avoids the selectivity problem of additives or solvent annealing and other processes for perovskite materials, has better perovskite component compatibility, and has greater advantages compared with the prior art for large-area preparation. Description of the Drawings

[0026] Figure 1 : Schematic diagram of ordinary annealing in the prior art;

[0027] Figure 2 : Schematic diagram of solvent annealing in the prior art;

[0028] Figure 3 : Schematic diagram of heating for the method of preparing the perovskite film in this application;

[0029] Figure 4: Scanning electron microscope images of perovskite thin films obtained by different annealing methods

[0030] In the figure, (A) is the ordinary annealing method; (B) is the solvent annealing method, and (C) is the perovskite thin film preparation method of the present application;

[0031] Figure 5 : Scanning electron microscope images of perovskite thin films prepared by different methods

[0032] In the figure, (D) is the ordinary annealing method; (E) is using glass as the breathable thin film, (F) is using filter paper as the breathable thin film, and (G) is using printing paper as the breathable thin film;

[0033] Figure 6 : Schematic diagram of the influence of different breathable thin films on grain growth

[0034] Figure 7 : Schematic diagram of the mutual fusion of perovskite intermediate phase thin film grains

[0035] Figure 8 : Fourier infrared transmission spectra of narrow-bandgap perovskite thin films obtained at different preheating times at 65°C

[0036] Figure 9 : Scanning electron microscope images of narrow-bandgap perovskite thin films prepared at different preheating times at 65°C

[0037] In the figure, (H) the preheating time is 0 seconds, (I) the preheating time is 10 seconds, (J) the preheating time is 20 seconds, (K) the preheating time is 30 seconds, (L) the preheating time is 40 seconds, and (M) the preheating time is 50 seconds;

[0038] Figure 10 : Schematic diagram of a narrow-bandgap perovskite solar cell

[0039] Figure 11 : J-V curve of a solar cell obtained by preparing a 1.25 eV narrow-bandgap perovskite light-absorbing layer based on different annealing methods

[0040] Figure 12 : Schematic diagram of a wide-bandgap perovskite solar cell

[0041] Figure 13 : J-V curve of a solar cell obtained by preparing a 1.75 eV wide-bandgap perovskite light-absorbing layer based on different annealing methods

[0042] Figure 14 : Schematic diagram of a all-perovskite tandem solar cell

[0043] Figure 15: J-V curve diagram of a perovskite tandem solar cell with both ends made of perovskite, prepared from a 1.75 eV wide-bandgap perovskite light-absorbing layer and a 1.25 eV narrow-bandgap perovskite light-absorbing layer based on different annealing methods. Detailed implementation mode

[0044] In order to make the objectives, technical solutions, and advantages of this application clearer, the following will further describe this application in detail in combination with the accompanying drawings. Hereinafter, terms such as "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features.

[0045] Example 1

[0046] A method for preparing a narrow-band perovskite thin film. The narrow-band perovskite thin film has a planar composite layer structure and includes a substrate and a perovskite light-absorbing layer. The substrate consists of a conductive substrate and a carrier transport layer disposed on its front surface. Its preparation includes the following steps:

[0047] Step (1): Use the spin-coating method to deposit the perovskite precursor solution on the substrate to form a perovskite precursor solution thin film on the surface of the carrier transport layer. The perovskite precursor solution is a solution mixture formed by a perovskite precursor material and a solvent. The perovskite precursor solution thin film contains a large amount of solvent.

[0048] Step (2): Place the substrate face up on a heating plate. The heating plate is in direct contact with the back surface of the substrate, and heat is sequentially transferred to the conductive substrate, the carrier transport layer, and the perovskite precursor solution thin film. Set the temperature of the heating plate to the first temperature, and control the evaporation amount and remaining amount of the solvent in the perovskite precursor solution thin film by controlling the first temperature and the heating duration. The perovskite precursor material dissolved in the perovskite precursor solution crystallizes into perovskite grains on the surface of the carrier transport layer, thereby forming a perovskite intermediate phase thin film.

[0049] Step (3): Lay a breathable film on the heating plate. Place the perovskite intermediate phase thin film containing residual solvent face down on the breathable film, keep the temperature at the first temperature and continue heating. When the residual solvent volatilizes, it dissolves and fuses at the boundaries of adjacent perovskite grains. Slowly raise the temperature of the heating plate to the second heating temperature and continue heating, and the perovskite grains undergo a phase change to form the narrow-band perovskite light-absorbing layer.

[0050] Preferably, the conductive substrate includes: ITO glass substrate, FTO glass substrate, flexible ITO substrate.

[0051] More specifically, in step (2), the first temperature is 65 °C and the heating time is 30 seconds. In step (3), the breathable film is selected as filter paper, such as Figure 3As shown, the heating duration at the first temperature is 2 to 4 minutes; the temperature of the heating plate is slowly raised to the second heating temperature of 100°C and heating continues for 7 minutes.

[0052] For comparison with the technical solution of this embodiment, the preparation steps of using ordinary annealing and solvent annealing in the prior art are given below respectively.

[0053] As Figure 1 , the method for preparing a narrow-band perovskite thin film by using an ordinary annealing method in the prior art includes the following steps:

[0054] (1) Spin-coat a hole transport material on a cleaned conductive substrate, and obtain a hole transport layer after annealing.

[0055] (2) Use an anti-solvent method to spin-coat a narrow-bandgap perovskite precursor solution film on the substrate in (1). The specific spin-coating parameters are a low speed of 1000 revolutions per minute for a duration of 10 seconds, a high speed of 4000 revolutions per minute for a duration of 60 seconds, and the anti-solvent diethyl ether is dropped at the 7th second during the high-speed period to obtain a wet perovskite intermediate film.

[0056] (3) Perform ordinary annealing treatment on the perovskite intermediate film obtained in (2), keep the front side of the substrate upward, first heat on a heating plate at 65°C for 3 minutes; then transfer the perovskite intermediate film to a heating plate at 100°C and continue heating for 7 minutes to obtain a narrow-bandgap perovskite light-absorbing film.

[0057] As Figure 2 , the method for preparing a narrow-band perovskite thin film by using a solvent annealing method in the prior art includes the following steps:

[0058] (1) Spin-coat a hole transport material on a cleaned conductive substrate, and obtain a hole transport layer after annealing.

[0059] (2) Use an anti-solvent method to spin-coat a narrow-bandgap perovskite light-absorbing layer on the substrate in (1). The specific spin-coating parameters are a low speed of 1000 revolutions per minute for a duration of 10 seconds, a high speed of 4000 revolutions per minute for a duration of 60 seconds, and the anti-solvent diethyl ether is dropped at the 7th second during the high-speed period to obtain a wet perovskite intermediate film.

[0060] (3) The perovskite intermediate phase film obtained in (2) is subjected to solvent annealing treatment. The substrate is placed face up on a heating plate at room temperature, and the heating plate is not working yet. A certain amount of dimethylformamide solvent (such as 10 μL) is dropped at a position 1 cm near the perovskite intermediate phase film, and then a glass petri dish is covered, which can cover both the perovskite intermediate phase film and the dimethylformamide solution. Then, the heating program of the heating plate is started, and the heating rate is about 40 °C / min. When it reaches 65 °C, the stabilization time is 3 minutes. Then, the temperature of the heating plate is raised to 100 °C and maintained for 7 minutes. It can be observed that the dimethylformamide solvent gradually volatilizes completely, thereby obtaining a narrow-bandgap perovskite film.

[0061] The narrow-bandgap perovskite light-absorbing films prepared by the above three methods, namely the ordinary annealing, the solvent annealing, and the perovskite film preparation method of the present application, are as Figure 4 shown. Among them, (A) is the perovskite light-absorbing film prepared by the ordinary annealing method. The calculated average grain size is about 400 nm, and the grain size distribution is uneven, indicating that the crystallization quality of the film is poor and the number of grain boundaries is large, which will further affect the recombination of photo-generated carriers and is not conducive to the transport of photo-generated carriers; (B) is the perovskite light-absorbing film obtained by the solvent annealing method. Its grain size is significantly increased, the average grain size is 500 nm, and the number of grain boundaries is reduced. However, some holes are introduced, indicating that the additional dimethylformamide solvent will damage the formed grains, thereby introducing holes and increasing the recombination of photo-generated carriers during the transmission process; (C) is the perovskite film obtained by the perovskite film preparation method of the present application. The grain size is significantly increased, the average grain size is 1000 nm, the number of grain boundaries is significantly reduced, the crystallization quality is improved, and the surface of the perovskite film is flat and uniform, which is conducive to suppressing the generation of defect states and promoting the transport of photo-generated carriers.

[0062] The air permeabilities of filter paper, glass, and printing paper are different, and thus their effects on the volatilization process of solvent molecules in the perovskite intermediate phase film are also different. In order to compare the effects of films with different air permeabilities on the preparation of perovskite films, the air-permeable films described in step (3) of the perovskite film preparation method of the present application are respectively replaced with glass and printing paper.

[0063] Figure 5Scanning electron microscope images of perovskite thin films prepared by different methods are presented. Among them, (D) is the perovskite thin film prepared by ordinary annealing, placed here for comparison. The perovskite grain size is about 400 nm, and there are numerous grain boundaries. Among them, (E) is the narrow-bandgap perovskite light-absorbing thin film prepared by selecting glass as the breathable thin film through a perovskite thin film preparation method of the present application. Its average grain size is about 1500 nm, the grain surface is smooth, and the number of grain boundaries decreases. (F) is the narrow-bandgap perovskite light-absorbing thin film obtained by selecting filter paper as the breathable thin film through the confined annealing method of the present application. The grain size is about 1000 nm, and the grain surface has a certain texture, indicating good crystallization. (G) is the narrow-bandgap perovskite light-absorbing thin film prepared by selecting printing paper as the breathable thin film through the confined annealing method of the present application. The grain size is about 900 nm, but there are a certain amount of small-sized grains near the grain boundaries, which will affect the transport of photo-generated carriers.

[0064] As Figure 6 shown, by using the ordinary annealing method, the volatilization direction of solvent molecules inside the perovskite intermediate phase thin film is vertically upward, so it is not affected by the spatial limitation, and the solvent has little influence on the lateral growth of grains. By using the confined annealing method, when the substrate of the perovskite intermediate phase thin film is placed face-up on different breathable thin films for annealing, due to the different volatilization rates of the three breathable thin films in the horizontal and vertical directions, the volatilization process of internal solvent molecules is different. For glass-confined annealing, the solvent molecules inside the perovskite intermediate phase thin film only volatilize horizontally, which can increase the lateral fusion of grains. The solvent molecules do not volatilize vertically, and there is no texture on the grain surface. For filter paper-confined annealing, the solvent molecules inside the perovskite intermediate phase thin film have both horizontal and vertical components. Experiments show that the volatilization rate of the solvent in the horizontal direction is greater than that in the vertical direction. The horizontally volatilized solvent can promote the lateral fusion between perovskite grains and increase the grain size, while the vertically volatilized solvent molecules will affect the ordered texture on the surface. For printing paper-confined annealing, the solvent molecules inside the perovskite intermediate phase thin film also have both horizontal and vertical components. Experiments show that the volatilization rate of the solvent in the horizontal direction is less than that in the vertical direction. The horizontally volatilized solvent promotes grain fusion, and the grain size grows. The vertically volatilized solvent dominates, which is conducive to the formation of the texture on the grain surface.

[0065] Taking the selection of filter paper as the breathable thin film by the confined annealing method as an example, see Figure 7Schematic diagram of the grain fusion of the perovskite intermediate phase film. From left to right are the perovskite intermediate phase film in the first temperature stage, the confined growth stage, and the final crystallization state. The function of the first temperature is preheating. In this stage, the grain size of the perovskite intermediate phase film is small, and the internal solvent volatilizes longitudinally, controlling the residual content of the internal solvent; in the confined growth stage, the internal solvent volatilizes laterally on the surface of the perovskite intermediate phase film, dissolving the originally existing grain boundaries, making adjacent small grains stick together and grow into large grains; continue annealing, all the remaining solvents are volatilized, and the perovskite film completes the transformation from the intermediate phase to the crystalline phase, that is, a large-grain, high-quality perovskite light-absorbing film is formed.

[0066] The perovskite light-absorbing layer efficiently absorbs the incident light, generates photoexcited electron-hole pairs, and diffuses to the carrier transport layer; the carrier transport layer is disposed between the conductive substrate and the perovskite light-absorbing layer, and is used to transport the carriers collected in the perovskite light-absorbing layer to the conductive substrate. The conductive substrate is used to collect the carriers and transmit them to the external circuit, and also serves as a light-transmitting and supporting function. The carrier transport layer can be replaced with a planar electron transport layer or a hole transport layer as needed to form other perovskite films.

[0067] Example 2

[0068] The heating time of the first temperature in step (2) of Example 1 was adjusted to 0 s, 10 s, 20 s, 30 s, 40 s, and 50 s respectively. Through testing with a Fourier transform infrared transmission spectrometer, the internal molecular vibration spectrum of the perovskite intermediate phase film was obtained, as Figure 8 shown. In this molecular vibration spectrum, when the wave number is 1016 cm -1 , the vibration characteristic peak of the sulfur-oxygen double bond (S=O) is obtained; as the preheating time changes from 0 s to 50 s, the vibration intensity of this sulfur-oxygen double bond changes from strong to weak, indicating that the residual solvent content inside the perovskite intermediate phase film decreases, realizing the precise control of the internal solvent of the perovskite intermediate phase film.

[0069] As Figure 9As shown, a confined annealing method is adopted. Filter paper is selected as the breathable film, and scanning electron microscope images of narrow-bandgap perovskite light-absorbing films are obtained by changing different preheating times. Among them, (H) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 0 seconds, with an average grain size of 1200 nanometers and large pores at the grain boundaries; (I) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 10 seconds, with an average grain size of 1500 nanometers and a smooth grain surface; (J) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 20 seconds, with an average grain size of 1100 nanometers and a smooth grain surface; (K) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 30 seconds, with an average grain size of 1100 nanometers and a textured pattern on the grain surface; (L) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 40 seconds, with an average grain size of 800 nanometers, granularity on the grain surface, and uneven grain sizes; (M) is the narrow-bandgap perovskite light-absorbing film obtained with a preheating time of 50 seconds, with an average grain size of 500 nanometers and a large number of grain boundaries.

[0070] Example 3

[0071] A method for preparing a narrow-bandgap perovskite solar cell, the narrow-bandgap perovskite solar cell is as Figure 10 shown, and it is a planar composite layer structure, including a substrate, a perovskite light-absorbing layer, an electron transport layer, and a metal electrode; the substrate is composed of a conductive substrate and a hole transport layer provided on its front surface, and its preparation includes:

[0072] Step (1) Deposit the perovskite precursor solution on the substrate by spin coating to form a perovskite precursor solution film on the surface of the hole transport layer;

[0073] The spin coating parameters are a low speed of 1000 revolutions per minute for 10 seconds, a high speed of 4000 revolutions per minute for 60 seconds, and the antisolvent diethyl ether is dropped at the 7th second during the high-speed period;

[0074] Step (2) Place the substrate face up on a hot plate at a first temperature of 65 °C and heat for 30 seconds to obtain a perovskite intermediate phase film;

[0075] Step (3) Lay a breathable film on the hot plate, place the perovskite intermediate phase film containing residual solvent face down on the breathable film, heat at the first temperature for 3 minutes, then raise the temperature to a second temperature of 100 °C at a heating rate of 40 °C per minute. After reaching 100 °C, maintain heating for 7 minutes;

[0076] Step (4) Place the substrate face up on a hot plate and continue to heat at the second temperature of 100 °C for 3 minutes to obtain the perovskite light-absorbing layer;

[0077] Step (5) uses the thermal evaporation method to deposit an electron transport layer coupled with a 20-nm C60 layer and an 8-nm BCP layer on the surface of the perovskite light-absorbing layer;

[0078] Step (6) uses the thermal evaporation method to deposit a 100-nm metal electrode on the surface of the electron transport layer, and finally obtains a narrow-bandgap perovskite solar cell.

[0079] The performance of the obtained narrow-bandgap perovskite solar cell is detected, and it is irradiated with simulated sunlight with an energy density of 100 mW / cm 2 , and the specific conditions for J-V measurement are: the scanning voltage range is -0.1 to 0.93 V, the step size is 10 mV, and the scanning speed is 150 mV / s.

[0080] As a comparison, step (3) of this embodiment is replaced with a conventional annealing method. The perovskite intermediate-phase film is placed on a 65°C hot plate and heated for 3 minutes, and then transferred to a 100°C hot plate and heated for another 7 minutes to obtain a narrow-bandgap perovskite light-absorbing film prepared by conventional annealing.

[0081] As a comparison, step (3) of this embodiment is replaced with a solvent annealing method. The perovskite intermediate-phase film is placed on a hot plate at room temperature, and 10 μL of dimethylformamide solvent is dropped at a distance of 1 cm from the perovskite intermediate-phase film. The glass Petri dish is covered, the heating switch of the hot plate is turned on, the heating rate is 40°C / minute, it is heated to 65°C and maintained for 3 minutes, and the hot plate continues to heat to 100°C and is maintained for 7 minutes to obtain a narrow-bandgap perovskite light-absorbing film prepared by solvent annealing.

[0082] It can be seen from Figure 11 that the narrow-bandgap perovskite solar cell prepared by confined annealing has the highest efficiency, reaching 21.51%; while the narrow-bandgap perovskite solar cell prepared by conventional annealing has a slightly lower efficiency, which is 19.63%; the narrow-bandgap perovskite solar cell prepared by solvent annealing has the worst efficiency, only 15.86%.

[0083] Example 4

[0084] A preparation method of a wide-bandgap perovskite solar cell, the wide-bandgap perovskite solar cell is as Figure 12 shown, and is a planar composite layer structure, including a substrate, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode; the substrate is composed of a conductive substrate and an electron transport layer disposed on its front surface, and its preparation includes:

[0085] Step (1) uses the spin-coating method to deposit a perovskite precursor solution on the substrate to form a perovskite precursor solution film on the surface of the electron transport layer;

[0086] The spin-coating parameters are 500 revolutions per minute at low speed for 3 seconds, 4000 revolutions per minute at high speed for 60 seconds, and the anti-solvent diethyl ether is dropped at the 25th second during the high-speed period;

[0087] In step (2), the substrate is placed face up on a hot plate at a first temperature of 65 °C and heated for 3 minutes to obtain a perovskite intermediate-phase film;

[0088] In step (3), a breathable film is laid on the hot plate, and the perovskite intermediate-phase film containing residual solvent is placed on the breathable film with the back of the substrate facing up. It is heated at the first temperature for 3 minutes, then heated to a second temperature of 100 °C at a heating rate of 40 °C per minute. After reaching 100 °C, heating is maintained for 7 minutes;

[0089] In step (4), the substrate is placed face up on a hot plate and further heated at the second temperature of 100 °C for 3 minutes to obtain a perovskite light-absorbing layer;

[0090] In step (5), a hole transport layer is deposited on the surface of the perovskite light-absorbing layer by spin coating;

[0091] In step (6), a metal electrode is deposited on the surface of the hole transport layer by thermal evaporation to finally obtain a wide-bandgap perovskite solar cell.

[0092] The obtained narrow-bandgap perovskite solar cell is subjected to performance testing under simulated sunlight irradiation with an energy density of 100 mW / cm 2 , and the specific conditions for J-V measurement are: the scanning voltage range is -0.1 to 1.3 V, the step size is 10 mV, and the scanning speed is 150 mV / s.

[0093] As a comparison, in step (3) of this example, it is replaced with a conventional annealing method. The perovskite intermediate-phase film is placed on a 65 °C hot plate and heated for 3 minutes, and then transferred to a 100 °C hot plate and further heated for 10 minutes to obtain a wide-bandgap perovskite light-absorbing film by conventional annealing.

[0094] As a comparison, in step (3) of this example, it is replaced with a solvent annealing method. The perovskite intermediate-phase film is placed on a hot plate at room temperature, 10 μL of dimethylformamide solvent is dropped at a distance of 1 cm from the perovskite intermediate-phase film, covered with a glass petri dish, the heating switch of the hot plate is turned on, the heating rate is 40 °C per minute, heated to 65 °C and maintained for 3 minutes, and the hot plate is further heated to 100 °C and maintained for 10 minutes to obtain a wide-bandgap perovskite light-absorbing film by solvent annealing.

[0095] From Figure 13It can be seen that the wide-bandgap perovskite solar cell prepared by confined annealing has the highest efficiency, reaching 18.58%; the wide-bandgap perovskite solar cell prepared by ordinary annealing has the lowest efficiency, which is 17.22%; the wide-bandgap perovskite solar cell prepared by solvent annealing has the worst efficiency, which is 18.14%.

[0096] Example 5

[0097] A preparation method of a tandem solar cell, the tandem solar cell is as Figure 14 shown, which is a planar composite layer structure, including a substrate, a hole transport layer, a wide-bandgap perovskite light-absorbing layer, an electron transport layer, an intermediate connection layer, a hole transport layer, a narrow-bandgap perovskite light-absorbing layer, an electron transport layer, and a metal electrode; the substrate is composed of a conductive substrate and a hole transport layer disposed on its front surface, and its preparation includes:

[0098] Step (1): Deposit a perovskite precursor solution on the substrate by spin coating to form a perovskite precursor solution film on the surface of the hole transport layer;

[0099] The spin coating parameters are a low speed of 500 revolutions per minute, a duration of 3 seconds, a high speed of 4000 revolutions per minute, a duration of 60 seconds, and the antisolvent diethyl ether is dropped at the 25th second during the high speed;

[0100] Step (2): Place the substrate face up on a hot plate at a first temperature of 65°C and heat for 3 minutes to obtain a perovskite intermediate phase film;

[0101] Step (3): Lay a breathable film on the hot plate, place the perovskite intermediate phase film containing residual solvent face down on the breathable film, heat at the first temperature for 30 seconds, raise the temperature to a second temperature of 100°C at a heating rate of 40°C per minute, and after reaching 100°C, maintain heating for 7 minutes;

[0102] Step (4): Place the substrate face up on a hot plate and continue to heat at the second temperature of 100°C for 3 minutes to obtain a wide-bandgap perovskite light-absorbing layer;

[0103] Step (5): Sequentially arrange an electron transport layer, an intermediate connection layer, and a hole transport layer on the surface of the perovskite light-absorbing layer;

[0104] Step (6): Spin coat a perovskite precursor solution on the surface of the hole transport layer in step 5;

[0105] The spin coating parameters are a low speed of 1000 revolutions per minute, a duration of 10 seconds, a high speed of 4000 revolutions per minute, a duration of 60 seconds, and the antisolvent diethyl ether is dropped at the 7th second during the high speed;

[0106] Step (7): Prepare a narrow-bandgap perovskite light-absorbing layer by the confined annealing method;

[0107] Step (8): Deposit an electron transport layer on the surface of the narrow-bandgap perovskite light-absorbing layer;

[0108] Step (9): Deposit a metal electrode on the surface of the hole transport layer by thermal evaporation method to finally obtain a tandem solar cell.

[0109] Perform performance detection on the obtained all-perovskite two-terminal tandem solar cell. The specific conditions for J-V measurement are: the scanning voltage range is -0.1 to 2.2 V, the step size is 10 mV, and the scanning speed is 150 mV / s.

[0110] For comparison, steps (3) and (7) of this embodiment are replaced with a common annealing method. The perovskite intermediate phase film is placed on a 65°C hot plate and heated for 3 minutes, and then transferred to a 100°C hot plate and heated for another 10 minutes to obtain a commonly annealed perovskite light-absorbing film.

[0111] It can be seen from Figure 15 that the tandem solar cell obtained by the combined use of the wide-bandgap perovskite light-absorbing layer and the narrow-bandgap perovskite light-absorbing layer prepared by confined annealing has the highest efficiency, reaching 25.05%; while the tandem solar cell obtained by the combined use of the wide-bandgap perovskite light-absorbing layer and the narrow-bandgap perovskite light-absorbing layer prepared by common annealing has a lower efficiency, which is 22.85%.

[0112] It should be noted that in the performance detection of the above perovskite solar cell of the present invention, if there is no special limitation or specific description of the operation method and operation steps, they are all carried out according to the conventional methods in the art.

[0113] The above content is only an example and illustration of the structure of the present invention. Modifications, supplements, or substitutions in a similar manner made by those skilled in the art to the specific embodiments described without creative efforts still fall within the protection scope of this patent.

Claims

1. A confinement annealing method, characterized in that, It includes the following steps: Step (1): Deposit the perovskite precursor solution on the front side of the substrate by spin coating to form a perovskite precursor solution film on the front side of the substrate; Step (2): Place the substrate with the perovskite precursor solution film on the front side on a hot plate. The hot plate is in direct contact with the back side of the substrate, and the heat is sequentially transferred to the substrate and the perovskite precursor solution film. Set the temperature of the hot plate to the first temperature, and control the evaporation amount and remaining amount of the solvent in the perovskite precursor solution film by controlling the first temperature and the heating duration. The perovskite precursor material dissolved in the perovskite precursor solution crystallizes into perovskite grains, thereby forming a perovskite intermediate phase film. The first temperature is 60-70 °C, and the heating duration is 10-50 seconds; Step (3): Lay a breathable film on the hot plate. Place the perovskite intermediate phase film containing residual solvent on the breathable film with the back side of the substrate facing up, keep the temperature at the first temperature and continue heating. The heating duration at the first temperature is 2-4 minutes. When the residual solvent volatilizes, it promotes the dissolution and mutual fusion of the boundaries of adjacent perovskite grains. Slowly raise the temperature of the hot plate to the second heating temperature and continue heating. The perovskite grains undergo a phase change to form a perovskite light-absorbing layer. The second heating temperature is 80-120 °C, and the heating duration at the second heating temperature is 6-15 minutes.

2. The confined annealing method according to claim 1, wherein the optical bandgap range of the perovskite precursor material is between 1.2 and 2.3 electron volts; the breathable film includes one of a glass sheet, filter paper, printing paper or polymer film.

3. The confined annealing method according to claim 2, wherein the perovskite precursor material includes one of methylammonium lead iodide, methylammonium lead bromide, formamidinium lead iodide, formamidinium lead bromide, formamidinium tin iodide, cesium lead iodide, cesium lead bromide or any proportion mixture thereof; the solvent includes one of dimethyl sulfoxide, dimethylformamide, gamma-butyrolactone or any proportion mixture thereof.

4. The confined annealing method according to claim 1, wherein the perovskite precursor solution is a stable solution mixture formed by dissolving the perovskite precursor material in the solvent by the Lewis acid-base method.

5. The confined annealing method according to claim 1, wherein the spin coating method in step (1) includes: In the first step, first set the spin coating speed to: 500-1000 revolutions per minute, and the duration is 2-10 seconds; In the second step, set the spin coating speed to: 3000-5000 revolutions per minute, and the duration is 1 minute; and add the anti-solvent 4-30 seconds after the start of rotation in the second step.

6. The confined annealing method according to claim 5, wherein the anti-solvent includes: one of diethyl ether, chlorobenzene, ethyl acetate or isopropyl alcohol or any proportion mixture thereof.

7. The confinement annealing method according to any one of claims 1 to 6, characterized in that, It further includes: Step (4): Place the substrate with the front side facing up on a hot plate. The hot plate is in direct contact with the back side of the substrate, keep the second heating temperature, and the heating duration is 1-3 minutes.

8. A method for preparing a perovskite thin film, wherein the perovskite thin film is a narrow-bandgap perovskite thin film or a wide-bandgap perovskite thin film, characterized in that, Use the confined annealing method according to any one of claims 1 to 7.

9. A method for preparing a solar cell, wherein the solar cell is one of a narrow-bandgap perovskite solar cell, a wide-bandgap perovskite solar cell, and a tandem solar cell, and is characterized in that, Use the confined annealing method according to any one of claims 1 to 7.

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