Preparation Method and Application of a Wide Bandgap Perovskite Thin Film

Abstract

The present invention relates to the technical field of perovskite thin films, and discloses a preparation method and application of a wide-bandgap perovskite thin film, comprising the following steps: (1) coating a perovskite precursor solution on a substrate, and dropping an antisolvent during the coating process; the chemical formula of the perovskite precursor is Cs x (FA 0.8 MA 0.2 ) 1‑x Pb(I 1‑y Br y )3, where 0

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite thin films, and in particular to a preparation method and application of a wide-bandgap perovskite thin film. Background Art

[0002] Wide-bandgap perovskite materials belong to mixed halogen compounds and usually contain a certain proportion of iodine and bromine. The solubility of bromine-based perovskite components in solution is lower than that of iodine-based perovskite. Therefore, during the annealing of wide-bandgap perovskite thin films, the bromine-based components with low solubility will crystallize and precipitate first on the upper surface, forming a bromine-rich perovskite shell, while there is still a large amount of iodine-rich perovskite solution at the bottom of the thin film, resulting in phase segregation in the longitudinal dimension. At the same time, iodide coordinates with the solvent to form a solvent complex as an intermediate phase, which is only converted into the perovskite phase during thermal annealing. Therefore, different crystallization paths during the annealing process exacerbate the occurrence of phase segregation, leading to the formation of mixed halide perovskites from the initial halide segregated phases.

[0003] At the same time, ion migration induced by external stimuli can also cause phase segregation. The activation energy of ion migration of halogen ions in perovskite is relatively low, belonging to easily migratable components. Due to the difference in the migration activation energy between iodide ions and bromide ions, they will migrate at different rates under external stimuli (such as light and heat) and spontaneously aggregate to form different phase regions rich in bromine and iodine, triggering serious phase segregation problems. This phase segregation not only reduces the uniformity of the thin film composition but also forms regions with different bandgaps within the thin film, blocking the transport of carriers inside the thin film and reducing the carrier concentration. Moreover, the phase-segregated thin film is more prone to phase transformation, turning into a non-perovskite phase and losing its photoactivity. Therefore, phase segregation will not only lead to carrier recombination loss and greater Voc loss but also deteriorate the stability of perovskite.

[0004] Currently, generally, additive engineering is used to regulate the crystallization kinetics and reduce the crystallization rate of bromine-based perovskite, thereby suppressing the occurrence of phase segregation. For example, the invention patent with the publication number CN 110854274 B discloses a method for regulating the perovskite nucleation process, including: the perovskite includes, but is not limited to, lead-based perovskite and multi-component perovskite with lead element as the dominant in the B site. In the preparation of the perovskite precursor solution, by adding an additive AX, in the structural formula of the additive AX, A represents any one of NH 4+ , CH3NH 3+ , NH2CHNH 2+ , CH3NH2CH 3+ , and X represents any one of Cl - , Br - , I - , SCN - , CH3COO -Any one of; regulating the formation rate and density of solvated BX2 compounds and their complexes, and controlling the segregation crystallization of solvated BX2 compounds and their complexes. However, the effect of using additives to inhibit phase segregation is limited, it is not easy to form a perovskite film with good crystallization uniformity, and the cost is relatively high. Summary of the Invention

[0005] In order to solve the phase segregation problem of wide-bandgap perovskite materials during the crystallization process, the present invention provides a preparation method and application of a wide-bandgap perovskite film. By spraying DMF on the surface of the perovskite film to form a liquid film, the solvent penetrates the grain boundaries to induce local dissolution and recrystallization, and then annealing is carried out to complete grain fusion and defect passivation while promoting the volatilization of DMF, thereby obtaining a uniformly crystallized wide-bandgap perovskite film.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a wide-bandgap perovskite film, including the following steps:

[0008] (1) Coating a perovskite precursor solution on a substrate, and adding an antisolvent during the coating process; the chemical formula of the perovskite precursor is Cs x (FA 0.8 MA 0.2 ) 1-x Pb(I 1-y Br y )3, where 0 < x < 1, 0 < y < 1;

[0009] (2) After the coating is completed, pre-anneal at 40 - 70 °C for 30 - 90 s to obtain a film;

[0010] (3) Spraying DMF on the surface layer of the film to form a liquid film, after standing, performing a secondary annealing at 90 - 150 °C for 1 - 30 min to obtain a wide-bandgap perovskite film.

[0011] The present invention prepares a perovskite thin film by an anti-solvent method. A perovskite precursor solution is coated on a substrate, and an anti-solvent is added dropwise before the coating is completed to promote the rapid nucleation and growth of perovskite crystals. During the pre-annealing process, part of the solvent is removed, and an initial crystal structure is formed. The bromine-based component with low solubility will crystallize and precipitate first on the upper surface, and part of the iodine-based component will diffuse and aggregate to the bottom of the thin film, thereby obtaining a perovskite thin film with a bromine-rich layer (bromine-rich perovskite solid-liquid mixture) on the upper layer and an iodine-rich layer (iodine-rich perovskite liquid) on the lower layer. Then, after spraying DMF on the surface of the thin film, the surface-crystallized bromine-rich perovskite will redissolve in DMF to form a liquid film, and there is still a residue of the iodine-rich perovskite solution at the bottom of the thin film. By standing still, the downward diffusion of DMF is enhanced, and the penetration effect is improved. Then, secondary annealing is carried out. During the annealing process, the solvent begins to evaporate, and the solvent at the bottom will also diffuse to the outside. The two solvents will form a convective motion inside, and the temperature gradient during the annealing process will promote the flow and mixing of the bromine-rich perovskite solution and the iodine-rich perovskite solution. The hot solvent at the bottom diffuses and evaporates outward, pushing the cold solution on the surface to carry bromide ions inward to diffuse. After the solvent completely evaporates, uniform crystallization can be formed, thereby solving the phase segregation problem of the wide-bandgap perovskite material during the crystallization process.

[0012] Preferably, the secondary annealing is carried out at 90 - 150 °C for 5 - 30 min.

[0013] Preferably, the spraying speed is 0.05 - 0.2 mL / min, and the pressure is not higher than 1 MPa; the spraying time is 1 - 30 s; the spraying height is 0 - 30 cm from the surface of the thin film.

[0014] Preferably, the standing time is 1 - 60 s, more preferably 10 - 60 s.

[0015] Preferably, the coating method includes spin coating or blade coating.

[0016] Preferably, the thickness of the thin film is 400 - 800 nm.

[0017] Preferably, the concentration of the perovskite precursor solution is 1 - 1.6 M.

[0018] Preferably, the anti-solvent is added dropwise 5 - 10 s before the coating is completed.

[0019] Preferably, the dropping amount of the anti-solvent is 100 - 300 μL.

[0020] The dropping amount of the anti-solvent can be increased or decreased adaptively according to the size of the required perovskite thin film.

[0021] Preferably, the anti-solvent is ethyl acetate or chlorobenzene.

[0022] In a second aspect, the present invention also provides an application of a wide-bandgap perovskite thin film in a solar cell.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The method in the present invention can obtain a uniformly crystallized wide-bandgap perovskite thin film, which has good repeatability and quality consistency, can be automated, reduces production fluctuations, and reduces losses caused by low yield;

[0025] (2) The method in the present invention can be adapted to large-scale production, matches large-scale production technology, and is used to process large-area wide-bandgap perovskite thin films;

[0026] (3) The method in the present invention can be compatible with subsequent interface treatment technologies, simplifying the preparation process of perovskite thin films. Description of the Drawings

[0027] Figure 1 It is a schematic flow chart for preparing a wide-bandgap perovskite thin film according to the present invention.

[0028] Figure 2 It is a photoluminescence spectrum diagram of the wide-bandgap perovskite thin film in Example 1 and Comparative Example 1. Detailed Embodiments

[0029] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0030] The preparation of the wide-bandgap perovskite thin film in the present invention includes the following steps:

[0031] (1) Coating a perovskite precursor solution on a substrate by spin coating or blade coating. The chemical formula of the perovskite precursor is Cs x (FA 0.8 MA 0.2 ) 1-x Pb(I 1-y Br y )3, where 0 < x < 1, 0 < y < 1; 5 - 10 s before the end of coating, drop ethyl acetate, drop ethyl acetate to the center position of the rotating substrate, and continue spin coating until the end;

[0032] (2) After the coating is completed, pre-anneal at 40 - 70 °C for 30 - 90 s to obtain a thin film with a thickness of 400 - 800 nm;

[0033] (3) Spray DMF on the surface of the thin film to form a liquid film. Use a precision spraying device (such as a pneumatic spray gun) to spray evenly at a position 0 - 30 cm away from the surface of the thin film. Control the liquid flow rate at the outlet through nitrogen diversion. The spraying speed is 0.05 - 0.2 mL / min. Control the pressure through a pressure regulator installed on the nitrogen supply pipeline. The spraying pressure is not higher than 1 MPa, and the spraying time is 1 - 30 s. After spraying, let it stand for 1 - 60 s, and then perform secondary annealing at 90 - 150 °C for 1 - 30 min. After the annealing is completed, a wide-bandgap perovskite thin film is obtained.

[0034] In a specific embodiment of the present invention, the preparation of the perovskite precursor solution includes the following steps: Dissolve methylammonium bromide (MABr), cesium iodide (CsI), formamidinium iodide (FAI), lead bromide (PbBr2), and lead iodide (PbI2) in a mixed solvent composed of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (the volume ratio of DMF to DMSO is 4:1). The resulting solution is stirred at 20 - 30 °C for 8 - 18 h, and then filtered through a polytetrafluoroethylene (PTFE) membrane to obtain a perovskite precursor solution with a concentration of 1 - 1.6 M.

[0035] In a specific embodiment of the present invention, the spin-coating process is specifically as follows: Spin-coat the perovskite precursor solution at a speed of 1000 - 2000 rpm for 5 - 15 s, and then spin-coat it at a speed of 4000 - 5000 rpm for 20 - 30 s.

[0036] In a specific embodiment of the present invention, standing after spraying can enhance solvent diffusion and improve the penetration effect. Moreover, the optimization of spraying parameters is also related to the distribution uniformity and penetration depth of the DMF solvent, which in turn affects the secondary crystallization effect of the perovskite thin film. Too low spraying pressure may result in too large droplet size (>50 μm), forming local corrosion. Too high spraying pressure (such as >1 MPa) may damage the surface morphology of the thin film; too close spraying distance is likely to cause solvent accumulation, and too far distance will cause the solvent to volatilize too fast, reducing the penetration effect; too fast spraying rate may cause the solvent to volatilize before fully penetrating and it is not easy to control the spraying uniformity, and too slow rate will prolong the process time.

[0037] In a specific embodiment of the present invention, the parameter conditions of the secondary annealing affect the solvent volatilization and the grain growth process, and thus affect the uniformity of the perovskite film. If the annealing starts too early, that is, without a standing process, the solvent sprayed in the film has not spread sufficiently, which will also lead to a decrease in the film quality, and defects such as pinholes and cracks will appear; if the annealing start point is too late, that is, the standing time is too long, since the surface-crystallized bromine-rich perovskite will redissolve in DMF to form a liquid film, and the excessive solvent volatilization due to too long standing time will result in too high a precursor concentration in the liquid film, leading to too high a nucleation density and finally forming smaller and unevenly distributed grain sizes.

[0038] If the annealing temperature is too low, the perovskite film crystallizes slowly and incompletely, forming smaller and fewer grain sizes, and there are more uncrystallized precursors in the film, resulting in poor film quality and many defects. It will also lead to insufficient phase transformation of the film, and it is still in the intermediate phase; if the annealing temperature is too high, the grain growth will be too fast, and abnormal grain growth and agglomeration will occur, destroying the uniformity of the film, and may also cause thermal decomposition of the perovskite. If the annealing duration is too short, the solvent volatilization is insufficient, the perovskite crystallizes incompletely, and the grain sizes are small and unevenly distributed; if the annealing time is too long, the grains will overgrow and agglomeration will occur, and thermal decomposition of the perovskite may also be triggered.

[0039] Example 1

[0040] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2) and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The obtained solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0041] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. At 5 s before the end of spin-coating, 150 μL of ethyl acetate is dropped onto the center of the rotating substrate, and spin-coating is continued until the end.

[0042] (3) After spin-coating, pre-anneal on a hot plate at 50 °C for 30 s to obtain a film with a thickness of 500 nm.

[0043] (4) Spray DMF on the surface of the thin film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the surface of the thin film. The spraying speed is 0.1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 10 s, then heat it to 100 °C for secondary annealing for 10 min. After the annealing is completed, a wide-bandgap perovskite thin film is obtained.

[0044] Example 2

[0045] The difference from Example 1 is that the standing time is changed to 20 s.

[0046] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2) and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0047] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. At 5 s before the end of spin-coating, drop 150 μL of ethyl acetate onto the center of the rotating substrate, and continue spin-coating until the end.

[0048] (3) After spin-coating, pre-anneal on a hot plate at 50 °C for 30 s to obtain a thin film with a thickness of 500 nm.

[0049] (4) Spray DMF on the surface of the thin film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the surface of the thin film. The spraying speed is 0.1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 20 s, then heat it to 100 °C for secondary annealing for 10 min. After the annealing is completed, a wide-bandgap perovskite thin film is obtained.

[0050] Example 3

[0051] The difference from Example 1 is that the spraying pressure is 0.25 MPa.

[0052] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0053] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. Five seconds before the end of spin-coating, 150 μL of ethyl acetate is dropped onto the center of the rotating substrate, and spin-coating continues until the end.

[0054] (3) After spin-coating, pre-anneal on a hot plate at 50 °C for 30 s to obtain a film with a thickness of 500 nm.

[0055] (4) Spray DMF on the surface of the film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the film surface. The spraying speed is 0.1 mL / min, the spraying pressure is 0.25 MPa, and the spraying time is 5 s. After spraying, let it stand for 10 s, then heat up to 100 °C for secondary annealing for 10 min. After annealing is completed, a wide-bandgap perovskite film is obtained.

[0056] Example 4

[0057] The difference from Example 1 is that the pre-annealing temperature is 40 °C.

[0058] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0059] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. Five seconds before the end of spin-coating, drop 150 μL of ethyl acetate onto the center of the rotating substrate, and continue spin-coating until the end.

[0060] (3) After spin-coating, pre-anneal on a hot plate at 40 °C for 30 s to obtain a film with a thickness of 500 nm.

[0061] (4) Spray DMF on the surface of the film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the film surface. The spraying speed is 0.1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 10 s, then heat up to 100 °C for secondary annealing for 10 min. After the annealing is completed, a wide-bandgap perovskite film is obtained.

[0062] Comparative Example 1 (using the general method)

[0063] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. Stir the resulting solution at 25 °C for 10 h, and then filter it through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain a perovskite precursor solution.

[0064] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. After spin-coating, anneal on a hot plate at 100 °C for 10 min to obtain a wide-bandgap perovskite film.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that the spraying speed is 1 mL / min, resulting in excessive spraying of DMF.

[0067] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0068] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 4000 rpm for 30 s. Five seconds before the end of spin-coating, 150 μL of ethyl acetate is dropped onto the center of the rotating substrate, and spin-coating continues until the end.

[0069] (3) After spin-coating, pre-anneal on a hot plate at 50 °C for 30 s to obtain a film with a thickness of 500 nm.

[0070] (4) Spray DMF on the surface of the film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the film surface. The spraying speed is 1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 10 s, then heat up to 100 °C for secondary annealing for 10 min. After annealing is completed, a wide-bandgap perovskite film is obtained.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that the standing time is too long, standing for 90 s.

[0073] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0074] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a rotation speed of 1000 rpm for 10 s, and then spin-coat at a rotation speed of 4000 rpm for 30 s. At 5 s before the end of spin-coating, add 150 μL of ethyl acetate dropwise to the center of the rotating substrate, and continue spin-coating until the end.

[0075] (3) After spin-coating, pre-anneal on a hot plate at 50 °C for 30 s to obtain a film with a thickness of 500 nm.

[0076] (4) Spray DMF on the surface of the film to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the film surface. The spraying speed is 0.1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 90 s, then heat up to 100 °C for secondary annealing for 10 min. After annealing is completed, a wide-bandgap perovskite film is obtained.

[0077] Comparative Example 4

[0078] The difference from Example 1 is that no pre-annealing is carried out.

[0079] (1) Dissolve 23.8 mg of methylammonium bromide (MABr), 18.2 mg of cesium iodide (CsI), 192.1 mg of formamidinium iodide (FAI), 153.6 mg of lead bromide (PbBr2), and 452.4 mg of lead iodide (PbI2) in 1 mL of a mixed solvent composed of DMF and DMSO with a volume ratio of 4:1. The resulting solution is stirred at 25 °C for 10 h, and then filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm to obtain Cs 0.05 FA 0.8 MA 0.15 Pb(I 0.75 Br 0.25 )3 perovskite precursor solution.

[0080] (2) Spin-coat the perovskite precursor solution on a 2 cm × 2 cm substrate at a rotation speed of 1000 rpm for 10 s, and then spin-coat at a rotation speed of 4000 rpm for 30 s. At 5 s before the end of spin-coating, add 150 μL of ethyl acetate dropwise to the center of the rotating substrate, and continue spin-coating until the end.

[0081] (3)After spin coating, directly spray DMF on the surface to form a liquid film. Use a precision spraying device (pneumatic spray gun) to spray evenly at a position 10 cm away from the film surface. The spraying speed is 0.1 mL / min, the spraying pressure is 0.5 MPa, and the spraying time is 5 s. After spraying, let it stand for 10 s, then heat up to 100 °C for secondary annealing for 10 min. After the annealing is completed, a wide-bandgap perovskite film is obtained.

[0082] Table 1

[0083]

[0084] As Figure 1 shown is the process schematic diagram for preparing the wide-bandgap perovskite film of the present invention. In the first step, a perovskite film is prepared by the anti-solvent method. Since the solubility of bromine-rich perovskite is relatively low, a bromine-rich perovskite shell (bromine-rich region) will form on the surface of the perovskite film after spin coating, while there is still a large amount of iodine-rich perovskite solution (iodine-rich region) at the bottom of the film, resulting in phase segregation. In the second step, spray DMF on the surface of the perovskite film. The surface crystallized bromine-rich perovskite will redissolve in DMF to form a surface liquid film. Let it stand after spraying to enhance solvent diffusion and improve the penetration effect. In the third step, perform secondary annealing. The solvent starts to evaporate, and the solvent at the bottom will also diffuse upward. When the hot solvent at the bottom diffuses and evaporates outward, it will also push the cold solution on the surface to carry bromide ions to diffuse inward. The convective movement of the solvent inside the film and the temperature gradient during the annealing process will promote the flow and mixing of the bromine-rich perovskite solution and the iodine-rich perovskite solution. This process promotes the mixing of bromide ions and iodide ions. In the fourth step, after the solvent completely evaporates, a uniformly crystallized wide-bandgap perovskite film is obtained.

[0085] As Figure 2 shown is the photoluminescence spectrum of the film prepared in Comparative Example 1 and the film prepared in Example 1. In the spectrum of the film in Comparative Example 1, two independent photoluminescence peaks (located at ~645 nm and ~750 nm respectively) can be seen, indicating that there are at least two phases with different bandgaps in the film, that is, phase segregation occurs. In the spectrum of the film in Example 1, the intensity of the peak at short wavelength is significantly weakened (located at ~645 nm), and the intensity of the intrinsic peak is significantly enhanced (located at ~750 nm), indicating that the phase segregation phenomenon is inhibited.

[0086] The wide-bandgap perovskite thin films prepared in Example 1 and Comparative Example 1 were applied to solar cells. The solar cells successively included a silver electrode, an electron transport layer (fullerene), a wide-bandgap perovskite thin film, a hole transport layer (Me-4PACz (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid), and an FTO electrode from top to bottom. The prepared solar cells were measured for cell efficiency under standard test conditions (cell temperature 25°C, spectral distribution AM1.5, light intensity 1000 W / m 2 ).

[0087] As shown in Table 1, the photoelectric conversion efficiency of the cells in Examples 1-4 was significantly higher than that of the cells in Comparative Example 1 (using the general method), indicating that the present invention can solve the phase segregation problem of wide-bandgap perovskite materials and obtain a uniformly crystallized perovskite thin film by spraying DMF and secondary annealing. However, when the parameter settings of the method in the present invention exceed the defined range, the film quality will be greatly affected, resulting in a worse cell efficiency than that of Comparative Example 1. Specifically, in Comparative Example 2, too much DMF was sprayed, which over-dissolved the perovskite, resulting in an uneven thickness of the finally formed thin film and a decrease in film quality. In Comparative Example 3, the standing time after spraying DMF was too long, and DMF volatilized excessively, making the precursor concentration in the liquid film too high, resulting in too high a nucleation density and finally too small and unevenly distributed grain sizes, thus affecting the efficiency of the cell. In Comparative Example 4, the thin film was not pre-annealed, and an initial crystal structure could not be formed, thus still resulting in problems of phase segregation and low film quality. Low-temperature pre-annealing endows the thin film with certain structural stability. On this basis, spraying DMF can make it penetrate more uniformly into the thin film and fully act on the initial crystallization region formed during the pre-annealing process, further promoting the uniform distribution of perovskite components.

[0088] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied to other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for preparing a wide-bandgap perovskite thin film, characterized in that It includes the following steps: (1) Coating a perovskite precursor solution on a substrate, and adding an antisolvent during the coating process; the chemical formula of the perovskite precursor is Cs x (FA 0.8 MA 0.2 ) 1-x Pb(I 1-y Br y )3, where 0 < x < 1, 0 < y < 1; (2) After coating, pre-anneal at 40 - 70 °C for 30 - 90 s to obtain a thin film; (3) Spray DMF on the surface of the thin film to form a liquid film. After standing, perform secondary annealing at 90 - 150 °C for 1 - 30 min to obtain a wide-bandgap perovskite thin film.

2. The preparation method of the wide-bandgap perovskite thin film according to claim 1, wherein, The spraying speed is 0.05 - 0.2 mL / min, and the pressure is not higher than 1 MPa; the spraying time is 1 - 30 s.

3. The preparation method of the wide-bandgap perovskite thin film according to claim 1, wherein The spraying height is 0 - 30 cm from the surface of the thin film.

4. The method for preparing a wide-bandgap perovskite thin film according to claim 1 or 2 or 3, characterized in that The standing time is 1 - 60 s.

5. The preparation method of the wide-bandgap perovskite thin film according to claim 1, wherein The concentration of the perovskite precursor solution is 1 - 1.6 M.

6. The preparation method of the wide-bandgap perovskite thin film according to claim 1, wherein, The coating method includes spin coating or blade coating.

7. The method for preparing a wide-bandgap perovskite thin film according to claim 1 or 5 or 6, characterized in that, In step (2), the thickness of the thin film is 400 - 800 nm.

8. The preparation method of the wide-bandgap perovskite thin film according to claim 1, wherein Add an anti-solvent 5 - 10 s before the end of coating.

9. The method for preparing a wide-bandgap perovskite thin film according to claim 1 or 8, characterized in that, The anti-solvent is ethyl acetate or chlorobenzene.

10. Application of a wide-bandgap perovskite thin film prepared by the preparation method according to any one of claims 1 - 9 in a solar cell.

Images