Method for preparing high-performance perovskite thin film by using PbI2 aging process

Abstract

The invention discloses a method for preparing a high-performance perovskite thin film by using a PbI2 aging process. According to the method, PbI2 is aged, holes in the surface of the aged PbI2 are increased and enlarged, the surface area between the PbI2 and the organic ammonium salt solution is increased, diffusion and reaction of the second layer of the organic ammonium salt solution are facilitated, and then the uniform perovskite thin film with good crystallinity can be generated. The porous PbI2 thin film is prepared on the premise of not introducing new substances and not adding complex experimental steps, the perovskite thin film is prepared on the basis and applied to the perovskite solar cell, and the performance of the perovskite solar cell is remarkably improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-performance perovskite film by utilizing a PbI2 aging process, and belongs to the technical field of perovskite solar cells. Background Art

[0002] Perovskite has achieved a rapid growth in efficiency from 3.8% to more than 26% in just ten years. The film quality of perovskite film is crucial to the technological breakthrough of perovskite solar cells. The current methods for preparing perovskite films mainly include one-step method, two-step method and gas-phase solution-assisted method. Compared with the traditional one-step method, the two-step method has more nucleation sites, better controllability and high experimental repeatability. Document 1 uses a two-step deposition method to prepare perovskite devices, further improving the previous one-step spin coating method. The photoelectric conversion efficiency of the perovskite device reaches 15%, and it shows excellent repeatability compared with previous devices (Burschka, J.; Pellet, N.; Moon, S.-J.; et al, Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nat. 2013, 499 (7458), 316-319.). Literature 2 uses the organic material phenylethylamine to implement a surface passivation strategy for perovskite films, and by suppressing the non-radiative recombination of carriers, the efficiency of perovskite devices is increased to 23.3% (Jiang, Q.; Zhao, Y.; Zhang, X.; et al, Surface passivation of perovskite film for efficient solar cells. Nat. Photonics. 2019, 13 (7), 460-466.). The researchers found that the two-step method overcomes the problems of poor crystallization quality and chaotic crystal orientation of the one-step film. At present, the two-step method for preparing high-performance perovskite solar cells has become the choice of most researchers. The two-step preparation process is: first, a layer of lead iodide (PbI2) is prepared by spin coating, and then a certain concentration of MAI solution is spin coated on the PbI2 film, and the mutual diffusion and reaction between the two layers of film are promoted by heating and annealing to form a perovskite film. The morphology of the first-step PbI2 film plays a crucial role in the quality of the perovskite film. The addition of the second layer of organic amine solution is actually a solid-liquid reaction with PbI2. Increasing the surface area of ​​the PbI2 film can promote a more complete reaction and reduce the remaining PbI2 in the device. Therefore, a porous and ordered PbI2 film is the basis for preparing high-quality perovskite films. The traditional two-step method is to add the second layer of solution immediately after the first layer of PbI2 is annealed and cooled to room temperature. However, it was found in the study that the number of holes on the surface of the freshly prepared PbI2 film is small, which is not enough to support the complete reaction of all PbI2.Recently, Chen Yiwang's team added succinamide to PbI2 and then added an ordered array to assist the omnidirectional diffusion of organic amine salts, realizing high-efficiency perovskite devices (Shao, W.; Wang, H.; Ye, F.; et al, Modulation of nucleation and crystallization in PbI2 films promoting preferential perovskite orientation growth for efficient solar cells. Energy Environ. Sci. 2023, 16 (1), 252-264.). Therefore, it is very valuable to develop a method that can prepare porous PbI2 films and realize high-performance perovskite solar cells without introducing new substances or adding complex experimental steps. Summary of the invention

[0003] In view of the existing problems of PbI2 residue and uneven film surface, the present invention provides a method for preparing a high-performance perovskite film using a PbI2 aging process. The method ages PbI2, and the number of pores on the surface of the aged PbI2 increases and becomes larger, thereby increasing the surface area between PbI2 and the organic ammonium salt solution, which is beneficial to the diffusion and reaction of the second layer of the organic ammonium salt solution, and further beneficial to the generation of a uniform perovskite film with good crystallinity.

[0004] The technical solution of the present invention is as follows:

[0005] The method for preparing a high-performance perovskite film using a PbI2 aging process comprises the following steps:

[0006] S1, spin coating an electron transport layer solution on the surface of the conductive glass, and annealing to obtain an electron transport layer;

[0007] S2, spin coating a PbI2 solution on the surface of the electron transport layer obtained in S1, and annealing to obtain a PbI2 thin film;

[0008] S3, under light-proof and oxygen-free conditions, the PbI2 film obtained in S2 is aged for a period of no more than 4.5 h;

[0009] S4. Spin-coating an organic ammonium salt solution on the surface of the aged PbI2 film obtained in S3, and annealing to form a perovskite film.

[0010] Furthermore, in S1, the conductive glass is a conductive glass commonly used in perovskite solar cells, such as ITO, FTO, IWO, ICO, etc.

[0011] Furthermore, in S1, the electron transport layer is an electron transport layer material conventionally used in perovskite solar cells, such as SnO2, TiO2, ZnO, etc.

[0012] Furthermore, in S1, the spin coating parameters are 1500 rpm, 30 s, and the annealing conditions are 70° C., 1 min.

[0013] Furthermore, in S2, the spin coating parameters are 2000 rpm, 30 seconds, the annealing conditions are 150° C., 15 minutes, and the annealing environment requires a humidity of 30-40%.

[0014] Further, in S2, in the PbI2 solution, the solvent is a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a volume ratio of 8:1 to 9.5:0.5, and the concentration of PbI2 is 1.4 to 1.5 M. Preferably, the solvent is a mixed solvent of DMF and DMSO in a volume ratio of 9:1, and the concentration of PbI2 is 1.5 M.

[0015] Further, in S3, the aging time is 1.5 h to 4.5 h. Preferably, the aging time is 3.5 h to 4.5 h.

[0016] Furthermore, in S3, the organic ammonium salt solution is an organic ammonium salt solution conventionally used in perovskite films, the solvent is isopropanol, and the solute is formamidine iodide (FAI), methylamine iodide (MAI), FAI and MAI, FAI, MAI and methylamine chloride (MACl), etc.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The present invention utilizes the PbI2 aging process, and regulates the porous morphology of the PbI2 film surface by regulating the aging time of the PbI2 film. On the one hand, the dense PbI2 film is not conducive to the downward penetration of the organic amine salt solution, which will cause excessive PbI2 to remain, and the excess PbI2 is easy to form non-radiative recombination centers, affecting the photoelectric performance of the device. On the other hand, PbI2 is easy to decompose under light conditions, so tin foil is used to wrap the PbI2 film in a dark state and let it stand for aging. The present invention obtains a porous PbI2 film without introducing new substances and adding complex experimental steps. On this basis, a perovskite film is prepared and applied to a perovskite solar cell, which significantly improves the performance of the perovskite solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 JV curves of the perovskite solar cells prepared in the comparative examples and embodiments;

[0020] Figure 2The scanning electron micrographs of the surfaces of the PbI2 films prepared in the comparative examples and the embodiments;

[0021] Figure 3 The scanning electron micrographs of the surfaces of the perovskite films prepared in Comparative Examples 1 and 4 and Example 1;

[0022] Figure 4 X-ray diffraction spectra of the perovskite films prepared in Comparative Examples 1 and 4 and Example 1;

[0023] Figure 5 This is a storage stability test chart of the perovskite solar cells prepared in Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0025] Comparative Example 1

[0026] Traditional two-step method for preparing perovskite solar cells:

[0027] (1) Cleaning of glass substrate:

[0028] The ITO glass substrate with a size of 1.5 cm × 1.5 cm was placed in a beaker with a polytetrafluoroethylene support frame, and then ultrasonically cleaned with deionized water, acetone, and ethanol solvents for 15 minutes respectively. The cleaned ITO glass substrate was blown dry with a nitrogen gun and placed in a UV ozone cleaning machine for 10 minutes to remove organic matter on the surface and improve the wettability of the glass substrate.

[0029] (2) Preparation of electron transport layer:

[0030] Ultrasonic dispersion of 2.67% SnO2 dispersion was performed for 30 minutes, and then filtered with a 0.22μm water filter. 50μL SnO2 dispersion was taken with a pipette and dropped on the surface of the ITO substrate, the speed was adjusted to 4000rpm, the acceleration was 4000rpm / s, and the spin coating was performed for 30s. After the spin coating was completed, the ITO substrate was placed on a hot plate preheated to 150°C for annealing for 30 minutes. After the annealing was completed, the substrate was cooled to room temperature and then UV-cleaned for 15 minutes, and the substrate was transferred to a nitrogen glove box to obtain an ITO / SnO2 substrate.

[0031] (3) Preparation of perovskite photoactive layer

[0032] Perovskite component (FAPbI3) 0.97 (MAPbBr3) 0.03 The preparation method is a two-step spin coating method.

[0033] Preparation of PbI2PbI2 solution: 691.5 mg of PbI2 was dissolved in a mixed solvent of DMF and DMSO (V DMF :V DMSO =9:1), stirred at 60°C for 6h for use to obtain a 1.5M PbI2 solution, which was filtered with a 0.45μm nylon filter before use.

[0034] Preparation of organic ammonium salt solution: According to FAI:MABr:MACl=90mg:9mg:9mg, FAI, MABr and MACl were mixed and dissolved in 1mL of isopropanol, and shaken in an oscillator for 12h to fully dissolve them. Before use, filter with a 0.45μm nylon filter to obtain an organic ammonium salt solution.

[0035] Preparation by spin coating: 40 μL of PbI2 precursor solution was added to the ITO / SnO2 substrate, the rotation speed was set to 1500 rpm, the acceleration was 1500 rpm / s, and the spin coating time was 30 s. After evenly spin coating, a bright yellow PbI2 layer was obtained. The layer was placed on a hot plate at 70°C for heating and annealing for 1 min, and then cooled to room temperature.

[0036] Then continue to spin-coat the organic ammonium salt solution on the substrate. Take 100 μL of the organic ammonium salt solution, spin at a speed of 2000 rpm and an acceleration of 2000 rpm / s for 30 seconds, and immediately transfer it to an environment with a humidity of 30-40%, anneal at 150°C for 15 minutes, and then transfer it to a nitrogen glove box and cool it to room temperature to obtain a black mirror (FAPbI3) 0.97 (MAPbBr3) 0.03 Perovskite active layer.

[0037] (4) Preparation of hole transport layer:

[0038] Spiro-OMeTAD was used as the hole transport material. 72.3 mg of Spiro-OMeTAD powder was weighed and dissolved in 1 mL of chlorobenzene. After stirring at room temperature for 3 hours, 17.5 μL of lithium salt solution (520 mg of Li-TFSI dissolved in 1 mL of acetonitrile), 17.5 μL of cobalt salt solution (300 mg of FK-209 dissolved in 1 mL of acetonitrile) and 27.5 μL of TBP were added. Stir for several hours until it was completely dissolved, and filter with a 0.45 μm nylon filter head for use. 40 μL of Spiro-OMeTAD solution was dripped on the substrate with a pipette. The hole transport layer was obtained after rotating for 30 seconds at a speed of 4000 rpm and an acceleration of 2000 rpm / s, and then an ITO electrode of about 2 mm was exposed with a utility knife.

[0039] (5) Preparation of Ag electrode:

[0040] Place the conductive glass into the chamber of the vacuum deposition machine, and then evacuate the chamber to 4×10 -4 Pa or less, 0.8~ / s evaporation rate to deposit 100nm thick Ag, the effective area of ​​the battery is 0.0397cm 2 A perovskite solar cell was produced.

[0041] Example 1

[0042] This embodiment is substantially the same as Comparative Example 1, except that (3) the spin coating preparation in the preparation of the perovskite photoactive layer is as follows:

[0043] Spin coating preparation: 40 μL of PbI2 precursor solution was added to the ITO / SnO2 substrate, the rotation speed was set to 1500 rpm, the acceleration was 1500 rpm / s, and the spin coating time was 30 s. After the spin coating was uniform, a bright yellow PbI2 layer was obtained, which was placed on a hot plate at 70°C for heating and annealing for 1 min and then cooled to room temperature. The obtained PbI2 film was then wrapped with tin foil and aged in a N2 glove box for 4.5 h.

[0044] Example 2

[0045] This embodiment is substantially the same as embodiment 1, except that (3) in the preparation of the perovskite photoactive layer, the PbI2 film is wrapped with tin foil and aged in a N2 glove box for 3.5 h.

[0046] Comparative Example 2

[0047] This comparative example is substantially the same as Example 1, except that in the preparation of the perovskite photoactive layer (3), the PbI2 film is wrapped with tin foil and aged in a N2 glove box for 1.5 h.

[0048] Comparative Example 3

[0049] This comparative example is substantially the same as Example 1, except that in the preparation of the perovskite photoactive layer (3), the PbI2 film is wrapped with tin foil and aged in a N2 glove box for 5.5 h.

[0050] Comparative Example 4

[0051] This comparative example is substantially the same as Example 1, except that in the preparation of the perovskite photoactive layer (3), the PbI2 film is wrapped with tin foil and aged in a N2 glove box for 6.5 h.

[0052] Table 1 Photoelectric properties of perovskite solar cells made of PbI2 thin films with different aging times Figure 1Table 1 and Table 2 are the JV curves and photoelectric performance parameter tables of the perovskite solar cells prepared in each embodiment and comparative example, respectively. It can be seen that when the aging time of the PbI2 film is controlled within 4.5 h, the overall photoelectric performance of the device is improved, among which the improvement is more obvious when the aging time is 3.5 h to 4.5 h, and the optimal aging time is 4.5 h. When the aging time is extended to 5.5 h and 6.5 h, the device performance shows a downward trend.

[0053] Figure 2 The following are scanning electron microscope images of the surface of the PbI2 film obtained in each embodiment and comparative example. It can be seen that after PbI2 aging, the pores on the surface of the film change with the extension of aging time, and the pore size increases while the number increases, which is conducive to the penetration of organic ammonium salt solution, reduces the residual PbI2 in the device, and is conducive to the formation of high-quality perovskite film. However, after the aging time is extended to 5.5h, the surface morphology of PbI2 no longer presents small holes, but appears in the form of "gullies" in patches.

[0054] Figure 3 The scanning electron microscope images of the perovskite film surface prepared in Comparative Examples 1, 4 and Example 2 respectively select three representative perovskite films prepared by PbI2 films with different aging times. Compared with Comparative Example 1, after aging PbI2 for 4.5 hours, the surface of the perovskite film is more uniform, the grain size is increased, and the PbI2 residue is less, which is conducive to carrier transport, reduces recombination, and thus reduces voltage loss and improves photoelectric conversion efficiency. When the aging time is extended to 6.5 hours, due to the uneven distribution of PbI2, its reaction with organic amine salts is also unevenly distributed, and phase separation occurs on the surface, which seriously affects the crystallization quality of the perovskite. Therefore, the device prepared under this condition has poor performance, which is consistent with JV.

[0055] Figure 4The X-ray diffraction spectra of the perovskite films obtained in Comparative Examples 1, 4 and Example 1. Among them, the diffraction peak of PbI2 corresponds to 12.8°. The peak value of PbI2 in the perovskite film after aging with PbI2 for 4.5h is significantly lower than the peak value of PbI2 in the perovskite of Comparative Example 1, while the peak value of PbI2 in the perovskite film based on the aging time of 6.5h is significantly increased, even exceeding Comparative Example 1. The remaining PbI2 in the perovskite film is easy to become a non-radiative recombination center, affecting carrier transport and the stability of the device. The characteristic peaks of the (110), (220), and (310) planes of the perovskite are located at 14.6°, 24.97°, and 28.91°, respectively. The characteristic peaks of the perovskite based on the PbI2 aging for 4.5h are significantly improved relative to the standard perovskite film, indicating that the crystallization quality of the perovskite is greatly improved. When the aging time is extended to 6.5h, the diffraction peaks of the (110), (220), and (310) planes are greatly reduced, which indicates that the crystallinity of the perovskite is poor, which is consistent with the SEM results.

[0056] Figure 5 The storage stability test diagram of the perovskite solar cell prepared in Comparative Example 1 and Example 1. The crystallinity of the perovskite is enhanced, which will affect the degradation rate of the perovskite. It can be seen that the stability of the device based on PbI2 after aging for 4.5 hours is greatly improved. At a temperature of 25±5°C and N2 atmosphere, it can still maintain 90.6% of the initial efficiency after 800 hours of storage, while the standard device maintains an efficiency of 70.7% of the initial efficiency.

Claims

1. A method for preparing a high-performance perovskite film using a PbI2 aging process, characterized in that: The following steps are involved: S1, spin coating an electron transport layer solution on the surface of the conductive glass, and annealing to obtain an electron transport layer; S2, spin coating a PbI2 solution on the surface of the electron transport layer obtained in S1, and annealing to obtain a PbI2 thin film; S3, under light-proof and oxygen-free conditions, the PbI2 film obtained in S2 is aged for a period of no more than 4.5 h; S4. Spin-coating an organic ammonium salt solution on the surface of the aged PbI2 film obtained in S3, and annealing to form a perovskite film.

2. The method according to claim 1, characterized in that In S1, the conductive glass is ITO, FTO, IWO or ICO.

3. The method according to claim 1, characterized in that In S1, the electron transport layer material is SnO2, TiO2 or ZnO.

4. The method according to claim 1, characterized in that In S1, the spin coating parameters were 1500 rpm, 30 s, and the annealing conditions were 70 °C, 1 min.

5. The method according to claim 1, characterized in that In S2, the spin coating parameters are 2000 rpm, 30 s, the annealing conditions are 150 °C, 15 min, and the annealing environment requires a humidity of 30-40%.

6. The method according to claim 1, characterized in that In S2, in the PbI2 solution, the solvent is a mixed solvent of DMF and DMSO with a volume ratio of 8:1~9.5:0.5, and the concentration of PbI2 is 1.4~1.5 M.

7. The method according to claim 1, characterized in that In S2, in the PbI2 solution, the solvent is a mixed solvent of DMF and DMSO with a volume ratio of 9:1, and the concentration of PbI2 is 1.5 M.

8. The method according to claim 1, characterized in that In S3, the aging time is 1.5h ~ 4.5h.

9. The method according to claim 1, characterized in that In S3, the aging time is 3.5h ~ 4.5h.

10. The method according to claim 1, characterized in that In S3, in the organic ammonium salt solution, the solvent is isopropanol, and the solutes are formamidine iodide, methylamine iodide, formamidine iodide and methylamine iodide, formamidine iodide, methylamine iodide and methylamine chloride.

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