Preparation Method and Application of an Improved Tin-Based Perovskite Film

Abstract

The present invention discloses a preparation method of an improved tin-based perovskite thin film and its application. The preparation method of the present invention includes: preparing a hole transport layer on a cleaned conductive glass; preparing a precursor solution containing a cyclic thione compound and a tin-based perovskite material; spin-coating the precursor solution, generating a perovskite thin film in one step using an anti-solvent, and annealing to obtain a tin-based perovskite thin film. A class of cyclic thione compounds is introduced into the coating precursor solution in the present invention. This class of compounds can effectively coordinate with tin ions, thereby significantly slowing down the crystallization rate of the tin-based perovskite material, obtaining a smooth, dense and surface defect-passivated tin-based perovskite thin film. The tin-based perovskite solar cell prepared using this thin film has significantly improved photoelectric conversion performance, stability and process repeatability, and the highest photoelectric conversion efficiency exceeds 12%.

Description

Technical Field

[0001] The present invention relates to a preparation method of an improved tin-based perovskite thin film and its application, specifically to a preparation method of a tin-based perovskite thin film and a solar cell improved by using a cyclic thione compound, belonging to the technical field of optoelectronic materials and devices. Background Art

[0002] Halide perovskites are a large class of novel semiconductor materials with excellent optoelectronic conversion performance. Among them, the preparation process of lead-containing perovskite solar cells has become increasingly mature, and the optoelectronic conversion efficiency in the laboratory has exceeded 25%. However, the serious biological and environmental toxicity of lead limits the large-scale promotion of lead-containing perovskite solar cells. Tin, which is in the same main group as lead and is biocompatible, is the most suitable substitute element for lead in perovskite materials. However, under the existing technical conditions, during the preparation of the active layer of the solar cell, the crystallization of the tin-based perovskite material is too fast, resulting in difficulty in obtaining a flat, dense and high-quality thin film. The thin film with multiple pinholes and defects generated after rapid crystallization is an important reason restricting the performance improvement of tin-based perovskite solar cells.

[0003] To solve the problem of poor quality of tin-based perovskite thin films, the commonly used methods at present are: (1) using a mixed solvent and adjusting the ratio of dimethyl sulfoxide to N,N-dimethylformamide in the solvent; (2) introducing large cations, such as butylammonium and phenethylammonium, to generate a two-dimensional perovskite structure; (3) introducing other types of additives, including fluorides, ethylenediamine, amides, organic acids, etc. However, the above methods have limited effects on improving the morphology and quality of tin-based perovskite thin films. The problem of too fast crystallization of tin-based perovskite has not been solved, and it is still difficult to prepare a dense and pinhole-free thin film, resulting in low performance of the corresponding tin-based perovskite solar cell devices. Summary of the Invention

[0004] The technical problem solved by the present invention is that in the existing preparation method of tin-based perovskite thin films, the crystallization of tin-based perovskite is too fast, resulting in problems such as the obtained thin film being not dense, having poor morphology, and low performance of the corresponding solar cell.

[0005] To solve the above technical problems, the present invention provides a preparation method of an improved tin-based perovskite thin film, including the following steps:

[0006] Step 1: Spin-coat a hole transport material on the cleaned conductive glass and anneal it to obtain a conductive glass with a hole transport layer;

[0007] Step 2: Prepare a precursor solution containing a tin-based perovskite material and a cyclic thione compound;

[0008] Step 3: Spin-coat the precursor solution prepared in Step 2 on the hole transport layer described in Step 1, use an antisolvent to generate a perovskite film in one step, and anneal to obtain a tin-based perovskite film.

[0009] Preferably, the cyclic thione compound in Step 2 is selected from at least one of Formula I and Formula II:

[0010]

[0011] Wherein, n = 1 or 2, and the substituents R1, R2, R3, R4, R5 and R6 are all selected from H or hydrocarbon groups.

[0012] Preferably, the hydrocarbon group is selected from C1-C6 alkyl groups.

[0013] Preferably, the cyclic thione compound in Step 2 is at least one of 1,3-dimethylimidazolidine-2-thione, 1-methylimidazolidine-2-thione and 1,3-dimethylimidazoline-2-thione.

[0014] Preferably, the molar ratio of the cyclic thione compound in Step 2 to the tin ions in the tin-based perovskite material is 0.1-2:1; the tin-based perovskite material is formamidinium tin triiodide.

[0015] Preferably, the solvent used to prepare the precursor solution in Step 2 is N,N-dimethylformamide, dimethyl sulfoxide or a mixture of the two in any proportion.

[0016] Preferably, the antisolvent in Step 3 is toluene.

[0017] Preferably, the process parameters for spin-coating in Steps 1 and 3 are: rotation speed 500-10000 rpm, time 10-60 s; the process parameters for annealing are: annealing temperature 50-150 °C, time 5-60 min.

[0018] The present invention also provides the application of the improved tin-based perovskite film prepared by the preparation method of the above improved tin-based perovskite film in a solar cell.

[0019] The present invention also provides a solar cell, comprising the improved tin-based perovskite film prepared by the preparation method of the above improved tin-based perovskite film, an electron transport layer, a hole blocking layer and a silver electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. By introducing cyclic thione compounds, the present invention effectively slows down the crystallization rate of the tin-based perovskite material during the film-forming process, obtains a smooth and dense tin-based perovskite film, and has excellent crystallinity and vertical orientation;

[0022] 2. By introducing cyclic thione compounds, the present invention inhibits the surface defects of tin-based perovskite thin films, significantly increasing the open-circuit voltage output and remarkably enhancing the energy conversion efficiency of tin-based perovskite solar cells;

[0023] 3. The tin-based perovskite thin films prepared by the present invention have good repeatability and small performance deviations between devices of different batches. Description of the Drawings

[0024] Figure 1 Comparison of tin-based perovskite thin films prepared before annealing in Example 1 (b), Example 2 (c) and Control Example (a);

[0025] Figure 2 Comparison of scanning electron microscope images of tin-based perovskite thin films prepared after annealing in Example 1 (b), Example 2 (c) and Control Example (a). The white scale bar in the figure is 1 μm;

[0026] Figure 3 Comparison of X-ray diffraction results of tin-based perovskite thin films prepared in Example 1 (b) and Control Example (a). The diffraction peaks of the ITO conductive glass substrate are marked by dotted lines in the figure;

[0027] Figure 4 Comparison of photoluminescence lifetimes of tin-based perovskite thin films prepared in Example 1 (b) and Control Example (a);

[0028] Figure 5 Comparison of photocurrent density-voltage characteristic curves of tin-based perovskite solar cells prepared in Example 1 (b) and Control Example (a);

[0029] Figure 6 Comparison of environmental stabilities of tin-based perovskite solar cells prepared in Example 1 (b) and Control Example (a). Environmental conditions: temperature 25 °C, relative air humidity 75%;

[0030] Figure 7 Comparison of statistical distributions of energy conversion efficiencies of tin-based perovskite solar cells prepared in Example 1 (b) and Control Example (a). Detailed Description of the Invention

[0031] To make the present invention more obvious and understandable, preferred embodiments are provided below in conjunction with the accompanying drawings for detailed description.

[0032] Example 1

[0033] Preparation of an improved tin-based perovskite thin film and solar cell:

[0034] Step 1: Cut the ITO conductive glass into square pieces with a side length of 2.5 cm, and ultrasonically clean them in 2% (volume ratio) Triton X-100 ultrapure aqueous solution, absolute ethanol, ultrapure water, and absolute ethanol for 30 minutes each in turn. After purging with nitrogen, clean with ultraviolet light–ozone for 20 minutes. Drop the PEDOT:PSS solution onto the above ITO conductive glass, spin-coat it at a speed of 5000 rpm for 45 s, and anneal it at 135 °C for 20 minutes to obtain an ITO substrate with a hole transport layer.

[0035] Step 2: Dissolve 298 mg (0.80 mmol) of stannous iodide, 117 mg (0.68 mmol) of formamidinium hydroiodide, 30 mg (0.12 mmol) of phenethylamine hydroiodide, and 52 mg (0.40 mmol) of 1,3-dimethylimidazolidine-2-thione in a mixed solvent composed of 800 μL of N,N-dimethylformamide and 200 μL of dimethyl sulfoxide to obtain a perovskite precursor solution containing cyclic thione.

[0036] Step 3: Under a nitrogen atmosphere, drop the precursor solution prepared in Step 2 onto the ITO substrate obtained in Step 1. First, spin-coat it at a speed of 1000 rpm for 10 s, and then spin-coat it at a speed of 5000 rpm for 30 s. During this period, inject 600 μL of toluene to form a brown transparent film layer, as Figure 1 shown in b. After the spin-coating is completed, anneal it at 70 °C for 10 min to obtain a tin-based perovskite film containing 1,3-dimethylimidazolidine-2-thione.

[0037] The scanning electron microscope results of the tin-based perovskite film prepared above are as shown in Figure 2 b. The scanning electron microscope results show that this film is formed by the flat laying of sheet-like grains of tin-based perovskite, with a smooth and dense surface and no obvious visible pinholes. The X-ray diffraction results of the tin-based perovskite film prepared above are as shown in Figure 3 b. The figure shows a strong and sharp diffraction peak of the (100) crystal plane, indicating that the grains in this film have excellent crystallinity and orientation. The photoluminescence lifetime of the tin-based perovskite film prepared above is 43 ns, as shown in Figure 4 b.

[0038] Step 4: Dissolve 18 mg of indene-C 60 bisadduct (ICBA) in 1 mL of chlorobenzene, drop it onto the perovskite film obtained in Step 3, spin-coat it at a speed of 1000 rpm for 30 s, and then anneal it at 70 °C for 10 minutes. Drop a saturated isopropanol solution of bathocuproine (BCP), spin-coat it at a speed of 6000 rpm for 30 s, and then anneal it at 70 °C for 10 minutes.

[0039] Step 5: Evaporate a 70-nm-thick silver electrode on the above multi-layer thin film in a high vacuum to obtain a tin-based perovskite solar cell containing 1,3-dimethylimidazolidine-2-thione.

[0040] The solar cell device prepared in this example was tested for photocurrent-voltage characteristics under simulated sunlight (AM 1.5G), and an open-circuit voltage of 0.78 V, a short-circuit current density of 20.3 mA / cm 2 , a fill factor of 0.75, and an energy conversion efficiency of 11.9% were obtained, as shown in Figure 5 b. After storing this device in a nitrogen environment for 26 days, there was no obvious change in its photovoltaic conversion performance. When exposed to humid air (75% relative humidity) at room temperature for 60 min, the energy conversion efficiency became 85% of the initial value, as shown in Figure 6 b. Multiple devices were prepared in different batches, and the measured distribution range of the energy conversion efficiency was 11 ± 1%, as shown in Figure 7 b.

[0041] Example 2

[0042] Preparation of an improved tin-based perovskite thin film:

[0043] Step 1: The same as in Example 1 above.

[0044] Step 2: Dissolve 298 mg (0.80 mmol) of stannous iodide, 117 mg (0.68 mmol) of formamidinium hydroiodide, 30 mg (0.12 mmol) of phenethylamine hydroiodide, 47 mg (0.36 mmol) of 1,3-dimethylimidazolidine-2-thione, and 5 mg (0.04 mmol) of 1,3-dimethylimidazoline-2-thione in a mixed solvent composed of 900 μL of N,N-dimethylformamide and 100 μL of dimethyl sulfoxide to obtain a perovskite precursor solution containing cyclic thione.

[0045] Step 3: Under a nitrogen atmosphere, drop the precursor solution prepared in Step 2 onto the ITO substrate obtained in Step 1. First, spin-coat at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 5000 rpm for 34 s. During this period, 600 μL of toluene is injected to form a light brown transparent film layer, as shown in Figure 1 c. After the spin-coating is completed, anneal at 80 °C for 10 min to obtain a perovskite thin film containing 1,3-dimethylimidazoline-2-thione.

[0046] The scanning electron microscopy results of the above-prepared tin-based perovskite thin film are as shown in Figure 2 c. The scanning electron microscopy results show that this tin-based perovskite thin film has good crystallinity, and the size of its sheet-like grains is significantly increased, resulting in a reduction in the grain boundaries of the thin film, a smooth and dense surface, and no obvious visible pinholes.

[0047] Control Example 1

[0048] Preparation of a tin-based perovskite thin film and a solar cell:

[0049] Step 1: The same as in Example 1 above.

[0050] Step 2: Dissolve 298 mg (0.80 mmol) of stannous iodide, 117 mg (0.68 mmol) of formamidinium hydroiodide, and 30 mg (0.12 mmol) of phenethylamine hydroiodide in a mixed solvent composed of 800 μL of N,N-dimethylformamide and 200 μL of dimethyl sulfoxide to obtain a perovskite precursor solution without a thione compound.

[0051] Step 3: Under a nitrogen atmosphere, drop the precursor solution prepared in Step 2 onto the ITO substrate obtained in Step 1. First, spin-coat at a speed of 1000 rpm for 10 s, and then spin-coat at a speed of 5000 rpm for 30 s. During this period, inject 600 μL of toluene to form a dark brown, rough and whitish film layer, as Figure 1 shown in a. After the spin-coating is completed, anneal at 70 °C for 10 min to obtain a tin-based perovskite thin film without a thione compound.

[0052] The scanning electron microscope results of the tin-based perovskite thin film prepared above are as Figure 2 shown in a. The electron microscope scanning results show that this thin film is formed by the disordered stacking of cubic grains of tin-based perovskite, and there are pinholes and gaps between the grains, and the porosity is 1.6%. The X-ray diffraction results of the tin-based perovskite thin film prepared above are as shown in 3a. The figure shows the diffraction peaks of each crystal plane, and the peak intensity is similar to the background diffraction of the ITO substrate, that is, the grains in this thin film have no orientation and poor crystallinity. The photoluminescence lifetime of the tin-based perovskite thin film prepared above is 9 ns, as Figure 4 shown in a, indicating that there are still defects in this tin-based perovskite thin film; from Figure 4 it can be seen that compared with the control example, the photoluminescence lifetime of the tin-based perovskite thin film prepared is significantly improved, indicating that 1,3-dimethylimidazolidine-2-thione plays a role in passivating the defects in the tin-based perovskite thin film.

[0053] Steps 4-5: The same as in Example 1 above.

[0054] The solar cell device prepared in this control example was tested for photocurrent-voltage characteristics under simulated sunlight (AM 1.5G), and an open-circuit voltage of 0.69 V, a short-circuit current density of 18.1 mA / cm 2 , a fill factor of 0.69, and an energy conversion efficiency of 8.6% were obtained, as Figure 5 shown in a. This device was exposed to humid air (75% relative humidity) at room temperature for 60 min, and the energy conversion efficiency decay was zero, asFigure 6 As shown in a. Multiple devices were prepared in different batches, and the measured distribution range of the energy conversion efficiency was 6 ± 2%, as Figure 7 shown in a. From Figures 5 to 7 it can be seen that for the tin-based perovskite solar cell prepared by adding the cyclic thione compound in the present invention, its optoelectronic conversion performance, stability and process repeatability have all been significantly improved, and the highest optoelectronic conversion efficiency exceeds 12%.

[0055] The above is only the preferred embodiment of the present invention, and does not impose any formal or substantial limitations on the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the premise of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of an improved tin-based perovskite thin film, characterized in that, It includes the following steps: Step 1: Spin-coat a hole transport material on the cleaned conductive glass and anneal it to obtain a conductive glass with a hole transport layer; Step 2: Prepare a precursor solution containing a tin-based perovskite material and a cyclic thione compound; Step 3: Spin-coat the precursor solution prepared in Step 2 on the hole transport layer described in Step 1, use an antisolvent to generate a perovskite thin film in one step, and anneal it to obtain a tin-based perovskite thin film; The cyclic thione compound in Step 2 is selected from at least one of Formula I and Formula II: wherein, n = 1 or 2, and the substituents R1, R2, R3, R4, R5 and R6 are each selected from H or a hydrocarbon group.

2. The preparation method of the improved tin-based perovskite thin film according to claim 1, characterized in that The hydrocarbon group is selected from C1-C6 alkyl groups.

3. The preparation method of the improved tin-based perovskite thin film according to claim 2, characterized in that, The cyclic thione compound in Step 2 is at least one of 1,3-dimethylimidazolidine-2-thione, 1-methylimidazolidine-2-thione and 1,3-dimethylimidazoline-2-thione.

4. The preparation method of the improved tin-based perovskite thin film according to claim 1, characterized in that The molar ratio of the cyclic thione compound in Step 2 to the tin ions in the tin-based perovskite material is 0.1-2:1; the tin-based perovskite material is formamidinium tin triiodide.

5. The preparation method of the improved tin-based perovskite thin film according to claim 1, characterized in that, The solvent used to prepare the precursor solution in Step 2 is N,N-dimethylformamide, dimethyl sulfoxide or a mixture of the two in any proportion.

6. The preparation method of the improved tin-based perovskite thin film according to claim 1, characterized in that, The antisolvent in Step 3 is toluene.

7. The preparation method of the improved tin-based perovskite thin film according to claim 1, characterized in that, The process parameters for spin-coating in Steps 1 and 3 are: rotation speed 500-10000 rpm, time 10-60 s; the process parameters for annealing are: annealing temperature 50-150 °C, time 5-60 min.

8. Application of the improved tin-based perovskite thin film prepared by the preparation method of the improved tin-based perovskite thin film according to any one of claims 1-7 in a solar cell.

9. A solar cell, characterized in that, It includes the improved tin-based perovskite thin film prepared by the preparation method of the improved tin-based perovskite thin film according to any one of claims 1-7, an electron transport layer, a hole blocking layer and a silver electrode.

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