Formamidinium reference two-dimensional perovskite film, preparation method and application thereof

Abstract

The application relates to a formamidine-based two-dimensional perovskite film and a preparation method and application thereof, a molecular formula of the formamidine-based two-dimensional perovskite film is (C x H 2x (NH3)2)(CH(NH2)2) n‑ 1Pb n I 3n+1 Wherein x is an integer of 2-8, and n is an integer of 3-10. The straight-chain organic diamine spacer cation is selected to form a two-dimensional perovskite layered crystal structure, which can weaken the dependence of the crystal structure on the van der Waals force between the spacer cations, is beneficial to improving the long-term stability of the perovskite film, and is beneficial to avoiding the decomposition of the perovskite under light by using formamidine instead of methylamine as a component of the perovskite film. The crystallization quality of the formamidine-based two-dimensional perovskite film can be further optimized by changing the solvent ratio and the dropping time of the anti-solvent, so that the device efficiency of a solar cell based on the formamidine-based two-dimensional perovskite film is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of perovskite photovoltaic, in particular to a formamidinium-based two-dimensional perovskite thin film and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of society, maintaining normal individual life and social operation is gradually increasing the dependence of human beings on energy. Due to the limited reserves of non-renewable energy such as oil and natural gas, and the destructiveness of fossil energy byproducts to the ecological environment, it is increasingly important to improve the status of clean energy in the energy structure. At present, in addition to wind power generation and hydroelectric power generation, photovoltaic technology has gradually become an important development strategy for various countries and regions. The solar cell that has been maturely applied to industry and daily life is still based on the first generation of silicon-based solar cells. However, due to the complexity and high cost of the process, the research direction in the field has begun to focus on the development of the third generation of solar cells. Among them, perovskite solar cells have received widespread attention due to their excellent photoelectric properties.

[0003] Perovskite has high light absorption, bipolar carrier transport, high carrier mobility, easy-to-adjust band gap, low raw material price and other advantages. At the same time, due to its excellent photoelectric properties, the conversion efficiency of three-dimensional perovskite solar cells can already be comparable to that of silicon-based solar cells, and the single-junction open-circuit voltage is higher than that of traditional silicon-based solar cells. However, due to the sensitivity of three-dimensional perovskite solar cells to environmental factors such as water, oxygen and light, the long-term running stability is the most urgent problem to be solved at present.

[0004] Based on the above, it is also necessary to develop a new perovskite thin film and a preparation method thereof from the perspective of material and process design, to provide a new idea for improving the stability of perovskite solar cells. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide a formamidinium-based two-dimensional perovskite thin film and a preparation method and application thereof. The molecular formula of the formamidinium-based two-dimensional perovskite thin film is (C x H 2x (NH3)2)(CH(NH2)2) n-1 Pb n I 3n+1, wherein x is an integer from 2 to 8, and n is an integer from 3 to 10. The present application selects a linear organic diamine spacer cation to form a layered crystal structure of a two-dimensional perovskite, which can weaken the dependence of the crystal structure on the van der Waals force between the spacer cations, improve the long-term stability of the perovskite film, and effectively avoid the decomposition of the perovskite under light by using formamidine instead of methylamine as a component of the perovskite film. In addition, the crystalline quality of the formamidine-based two-dimensional perovskite film can be further optimized by changing the solvent ratio and the dropping time of the anti-solvent, so that the device efficiency of the solar cell based on the formamidine-based two-dimensional perovskite film is effectively improved.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a formamidine-based two-dimensional perovskite film, which has a molecular formula of (C x H 2x (NH3)2)(CH(NH2)2) n-1 Pb n I 3n+1 , wherein x is an integer from 2 to 8, for example, 2, 3, 4, 5, 6, 7 or 8, and n is an integer from 3 to 10, for example, 3, 4, 5, 6, 7, 8, 9 or 10.

[0008] The present application selects a linear organic diamine spacer cation to form a layered crystal structure of a two-dimensional perovskite, which can weaken the dependence of the crystal structure on the van der Waals force between the spacer cations, improve the long-term stability of the perovskite film, and effectively avoid the decomposition of the perovskite under light by using formamidine instead of methylamine as a component of the perovskite film.

[0009] In a second aspect, the present application provides a preparation method of the formamidine-based two-dimensional perovskite film according to the first aspect, which comprises the following steps:

[0010] (1) preparing a perovskite precursor solution, which comprises an organic diamine iodine salt, formamidine iodine, lead iodide and a solvent; the organic diamine iodine salt has a molecular formula of (C x H 2x (NH3)2)I2, wherein x is an integer from 2 to 8; the molar ratio of the organic diamine iodine salt, formamidine iodine and lead iodide in the perovskite precursor solution is 1:(n-1):n, wherein n is an integer from 3 to 10;

[0011] (2) spin-coating the perovskite precursor solution of step (1) on a substrate, and dropping an anti-solvent during the spin-coating process to obtain a perovskite precursor film;

[0012] (3) annealing the perovskite precursor film of step (2) to obtain the formamidinium reference two-dimensional perovskite film.

[0013] It should be noted that the molecular formula of the organic diamine iodine salt in step (1) of the present application is (C x H 2x NH3)2)I2, wherein x is an integer from 2 to 8, such as 2, 3, 4, 5, 6, 7 or 8, preferably x = 5, i.e. the pentanediamine iodine (C5H 10 NH3)2)I2, the properties of the perovskite film obtained are better; the molar ratio of the organic diamine iodine salt, formamidinium iodine and lead iodide in the perovskite precursor solution of step (1) is 1: (n-1): n, wherein n is an integer from 3 to 10, such as 3, 4, 5, 6, 7, 8, 9 or 10, preferably n = 6, the properties of the perovskite film obtained are better.

[0014] The molecular formula of the formamidinium reference two-dimensional perovskite film obtained is (C x H 2x NH3)2) (CH (NH2) 2) I2. n-1 Pb n I 3n+1 The value of n in the formula (C x H 2x NH3)2) (CH (NH2) 2) I2. n-1 Pb n I 3n+1 .

[0015] The following is a preferred technical solution of the present application, but not as a limitation of the technical solutions provided by the present application, through the following technical solutions, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0016] As a preferred technical solution of the present application, the solvent of step (1) includes a mixed solvent of N, N-dimethylformamide and dimethyl sulfoxide, and the volume fraction of N, N-dimethylformamide in the mixed solvent is 50-100%, such as 50%, 60%, 70%, 80%, 90% or 100%, etc., but not limited to the listed values, other values not listed in the above range are also applicable.

[0017] It is worth emphasizing that the sum of the volume fractions of N,N-dimethylformamide and dimethyl sulfoxide in the solvent should be kept at 100%, wherein, when the solvent comprises N,N-dimethylformamide with a volume fraction of 100%, the volume fraction of dimethyl sulfoxide is 0%, that is, the solvent is composed of pure N,N-dimethylformamide without dimethyl sulfoxide; the present application optimizes the crystallization quality of the formamidinium standard two-dimensional perovskite thin film by adjusting the ratio of N,N-dimethylformamide and dimethyl sulfoxide in the solvent, but it should be noted that using N,N-dimethylformamide or dimethyl sulfoxide alone as a solvent, or using N,N-dimethylformamide and dimethyl sulfoxide with any volume fraction ratio outside the preferred range of the present application as a solvent, can also produce perovskite thin films with the molecular formula (CH x H 2x (NH3)2)(CH(NH2)2) n-1 Pb n I 3n+1 The present application can make the formamidinium standard two-dimensional perovskite thin film have excellent crystallization quality by limiting the volume fraction of the solvent within the preferred range, so that the device based on this thin film can have higher conversion efficiency.

[0018] As a preferred technical solution of the present application, the concentration of the organic diamine iodine salt in the perovskite precursor solution in step (1) is 0.2-0.3 mmol / mL, such as 0.2 mmol / mL, 0.21 mmol / mL, 0.22 mmol / mL, 0.23 mmol / mL, 0.24 mmol / mL, 0.25 mmol / mL, 0.26 mmol / mL, 0.27 mmol / mL, 0.28 mmol / mL, 0.29 mmol / mL or 0.3 mmol / mL, etc., but not limited to the listed values, other values not listed within the above numerical range are also applicable.

[0019] As a preferred technical solution of the present application, the perovskite precursor solution in step (1) is filtered using a polytetrafluoroethylene filter before the spin coating in step (2).

[0020] Preferably, the spin coating speed in step (2) is 3000-4500 rpm, such as 3000 rpm, 3100 rpm, 3200 rpm, 3300 rpm, 3400 rpm, 3500 rpm, 3600 rpm, 3700 rpm, 3800 rpm, 3900 rpm, 4000 rpm, 4100 rpm, 4200 rpm, 4300 rpm, 4400 rpm or 4500 rpm, etc., but not limited to the listed values, other values not listed within the above numerical range are also applicable.

[0021] Preferably, the spin-coating time of the spin-coating in step (2) is 20-40 s, for example 20 s, 22 s, 24 s, 26 s, 28 s, 30 s, 32 s, 34 s, 36 s, 38 s, or 40 s, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0022] Preferably, the start time of the anti-solvent dropping in step (2) is 10-13 s after the start of the spin-coating, for example 10 s, 10.5 s, 11 s, 11.5 s, 12 s, 12.5 s, or 13 s, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0023] The start time of the anti-solvent dropping in step (2) also affects the crystalline quality of the perovskite film, but as long as the anti-solvent dropping operation is completed at any time during the spin-coating process, a perovskite film with the molecular formula (CH(NH2)2)PbI3 can be manufactured, and when the anti-solvent dropping starts at the preferred range of 10-13 s, the reference two-dimensional perovskite film with the molecular formula (CH(NH2)2)PbI3 can be brought to an optimal state. It should be further noted that the anti-solvent dropping is completed in one time. x H 2x (NH3)2)(CH(NH2)2) n-1 Pb n I 3n+1 The start time of the anti-solvent dropping in step (2) also affects the crystalline quality of the perovskite film, but as long as the anti-solvent dropping operation is completed at any time during the spin-coating process, a perovskite film with the molecular formula (CH(NH2)2)PbI3 can be manufactured, and when the anti-solvent dropping starts at the preferred range of 10-13 s, the reference two-dimensional perovskite film with the molecular formula (CH(NH2)2)PbI3 can be brought to an optimal state. It should be further noted that the anti-solvent dropping is completed in one time.

[0024] Preferably, the anti-solvent in step (2) comprises chlorobenzene.

[0025] Preferably, the amount of the anti-solvent in step (2) is 15-25% of the volume of the solvent in step (1), for example 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0026] Preferably, the annealing temperature of the annealing in step (3) is 110-130℃, for example 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃, 124℃, 126℃, 128℃, or 130℃, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0027] Preferably, the annealing time of the annealing in step (3) is 20-30 min, for example 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0028] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0029] (1) using a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide, and the volume fraction of N,N-dimethylformamide in the mixed solvent is 50-100%, to prepare a perovskite precursor solution comprising an organic diamine iodine salt, formamidinium iodide and lead iodide; wherein the molecular formula of the organic diamine iodine salt is (C x H 2x (NH3)2)I2, x is an integer of 2-8; the concentration of the organic diamine iodine salt in the perovskite precursor solution is 0.2-0.3 mmol / mL, and the molar ratio of the organic diamine iodine salt, formamidinium iodide and lead iodide is 1:(n-1):n, wherein n is an integer of 3-10;

[0030] (2) using a polytetrafluoroethylene filter to filter the perovskite precursor solution in step (1) and drop it onto a substrate, and spin coating at 3000-4500 rpm for 20-40 s, wherein at the 10th-13th second after the start of spin coating, 15-25% of the volume of the mixed solvent in step (1) of an anti-solvent chlorobenzene is added, to obtain a perovskite precursor film;

[0031] (3) annealing the perovskite precursor film in step (2) at 110-130℃ for 20-30 min to obtain the formamidinium-based two-dimensional perovskite thin film.

[0032] In a third aspect, the present application provides a perovskite thin film solar cell, which comprises a conductive substrate, and further comprises, from bottom to top, an electron transport layer, an active layer comprising the formamidinium-based two-dimensional perovskite thin film as described in the first aspect of the present application, a hole transport layer and a metal anode layer on one side of the conductive substrate.

[0033] Compared with the prior art, the present application has at least the following beneficial effects:

[0034] (1) The present application selects linear organic diamine spacer cations to form a two-dimensional perovskite layered crystal structure, which can weaken the dependence of the crystal structure on the van der Waals force between the spacer cations, thereby facilitating the improvement of the long-term stability of the perovskite film; the present application also facilitates the avoidance of the decomposition of perovskite under light by using formamidine instead of methylamine as a component of the perovskite film, and weakens the influence of the decomposition of the components of the perovskite active layer on the stability of the device during long-term use.

[0035] (2) The preparation method can improve the surface morphology and crystalline quality of the perovskite film by adjusting the volume ratio of N,N-dimethylformamide and dimethyl sulfoxide in the solvent, and can further optimize the perovskite film by adjusting the time of adding the antisolvent during the spin coating process, thereby effectively adjusting and improving the conversion efficiency of the solar cell based on the formamidine reference two-dimensional perovskite film, and the preparation method is stable and has good repeatability, which can provide a new feasible idea for the commercialization of perovskite film solar cells. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a structural schematic diagram of a perovskite film solar cell prepared using the formamidine reference two-dimensional perovskite film of the present application; wherein 1 is a conductive substrate, 2 is an electron transport layer, 3 is an active layer composed of a formamidine reference two-dimensional perovskite film, 4 is a hole transport layer, and 5 is a metal anode layer.

[0037] Figure 2 is a photovoltaic performance test curve diagram of a perovskite film solar cell prepared using the formamidine reference two-dimensional perovskite film of Example 1 and Examples 4-6. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0039] Example 1

[0040] The present embodiment provides a formamidine reference two-dimensional perovskite film, the molecular formula of which is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidine reference two-dimensional perovskite film comprises the following steps:

[0041] (1) 800 μL of N,N-dimethylformamide and 200 μL of dimethyl sulfoxide are used to dissolve 90 mg of pentanediamine iodine (C5H 10(NH3)2)I2, 215 mg of formamidinium iodide and 692 mg of lead iodide to prepare a perovskite precursor solution; wherein the concentration of pentanediamine iodine in the perovskite precursor solution is 0.25 mmol / mL, and the molar ratio of pentanediamine iodine, formamidinium iodide and lead iodide is 1:5:6;

[0042] (2) The perovskite precursor solution of step (1) is filtered using a polytetrafluoroethylene filter and dropped onto a substrate, and spin-coated at 4000 rpm for 30 s, and at the 12th second after the start of spin-coating, 200 μL of anti-solvent chlorobenzene is added, which is 20% of the volume of the solvent in step (1), to obtain a perovskite precursor film;

[0043] (3) The perovskite precursor film of step (2) is annealed at 150°C for 30 min to obtain the formamidinium reference two-dimensional perovskite film.

[0044] Example 2

[0045] The present example provides a formamidinium reference two-dimensional perovskite film, and the molecular formula of the formamidinium reference two-dimensional perovskite film is (C2H4(NH3)2)(CH(NH2)2)2Pb3I 10 The preparation method of the formamidinium reference two-dimensional perovskite film comprises the following steps:

[0046] (1) 500 μL of N,N-dimethylformamide and 500 μL of dimethyl sulfoxide are used to prepare a solvent, and 70 mg of (C2H4(NH3)2)I2, 76 mg of formamidinium iodide and 304 mg of lead iodide are dissolved to prepare a perovskite precursor solution; wherein the concentration of (C2H4(NH3)2)I2 in the perovskite precursor solution is 0.22 mmol / mL, and the molar ratio of (C2H4(NH3)2)I2, formamidinium iodide and lead iodide is 1:2:3;

[0047] (2) The perovskite precursor solution of step (1) is filtered using a polytetrafluoroethylene filter and dropped onto a substrate, and spin-coated at 3000 rpm for 20 s, and at the 10th second after the start of spin-coating, 150 μL of anti-solvent chlorobenzene is added, which is 15% of the volume of the solvent in step (1), to obtain a perovskite precursor film;

[0048] (3) The perovskite precursor film of step (2) is annealed at 110°C for 25 min to obtain the formamidinium reference two-dimensional perovskite film.

[0049] Example 3

[0050] The present example provides a formamidinium reference two-dimensional perovskite film, and the molecular formula of the formamidinium reference two-dimensional perovskite film is (C8H 16(NH3)2)(CH(NH2)2)9Pb 10 I 31 , the preparation method of the formamidinium reference two-dimensional perovskite film comprises the following steps:

[0051] (1) using 600 μL of N,N-dimethylformamide and 400 μL of dimethyl sulfoxide to constitute a solvent, dissolving 112 mg of (C8H 16 (NH3)2)I2, 433 mg of formamidinium iodide and 1291 mg of lead iodide to prepare a perovskite precursor solution; wherein the concentration of (C8H 16 (NH3)2)I2 in the perovskite precursor solution is 0.28 mmol / mL, and the molar ratio of (C8H 16 (NH3)2)I2, formamidinium iodide and lead iodide is 1:9:10;

[0052] (2) using a polytetrafluoroethylene filter to filter the perovskite precursor solution in step (1) and drop it onto a substrate, spin coating at 4500 rpm for 40 s, and adding 250 μL of anti-solvent chlorobenzene at the 13th second after the start of spin coating, the amount of which is 25% of the volume of the solvent in step (1), to obtain a perovskite precursor film;

[0053] (3) annealing the perovskite precursor film in step (2) at 130°C for 20 min to obtain the formamidinium reference two-dimensional perovskite film.

[0054] Example 4

[0055] The present embodiment provides a formamidinium reference two-dimensional perovskite film, the molecular formula of the formamidinium reference two-dimensional perovskite film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 , in step (1) of the preparation method of the formamidinium reference two-dimensional perovskite film, only N,N-dimethylformamide is used as a solvent, that is, step (1) is:

[0056] using 1000 μL of N,N-dimethylformamide as a solvent, dissolving 90 mg of pentanediamine iodine (C5H 10 (NH3)2)I2, 433 mg of formamidinium iodide and 1291 mg of lead iodide to prepare a perovskite precursor solution; wherein the concentration of (C8H

[0057] The present embodiment is identical to Example 1 except for step (1).

[0058] Example 5

[0059] The present embodiment provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of the formamidinium reference two-dimensional perovskite thin film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film is identical to that of Example 1, except that 900 μL of a solvent composed of N,N-dimethylformamide and 100 μL of dimethyl sulfoxide is used in step (1).

[0060] Example 6

[0061] The present embodiment provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of the formamidinium reference two-dimensional perovskite thin film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film is identical to that of Example 1, except that 700 μL of a solvent composed of N,N-dimethylformamide and 300 μL of dimethyl sulfoxide is used in step (1).

[0062] Example 7

[0063] The present embodiment provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of the formamidinium reference two-dimensional perovskite thin film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film is identical to that of Example 1, except that 500 μL of a solvent composed of N,N-dimethylformamide and 500 μL of dimethyl sulfoxide is used in step (1).

[0064] Example 8

[0065] The present embodiment provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of the formamidinium reference two-dimensional perovskite thin film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film is identical to that of Example 1, except that 200 μL of a solvent composed of N,N-dimethylformamide and 800 μL of dimethyl sulfoxide is used in step (1).

[0066] Example 9

[0067] The present embodiment provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of the formamidinium reference two-dimensional perovskite thin film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19, the preparation method of the formamidinium reference two-dimensional perovskite film, only dimethyl sulfoxide is used as a solvent in step (1), that is, step (1) is:

[0068] 1000 μL of dimethyl sulfoxide is used as a solvent to dissolve 90 mg of pentamethylenediamine iodine (C5H 10 (NH3)2)I2, 215 mg of formamidinium iodine and 692 mg of lead iodide to prepare a perovskite precursor solution; wherein the concentration of pentamethylenediamine iodine in the perovskite precursor solution is 0.25 mmol / mL, and the molar ratio of pentamethylenediamine iodine, formamidinium iodine and lead iodide is 1:5:6;

[0069] The other steps and conditions of this embodiment are completely same as those of example 1 except step (1).

[0070] Example 10

[0071] This embodiment provides a formamidinium reference two-dimensional perovskite film, the molecular formula of the formamidinium reference two-dimensional perovskite film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite film is completely same as that of example 1 except that in step (2), the starting time of dropping the anti-solvent is adjusted from the 12th second after the start of spin coating to the 5th second after the start of spin coating.

[0072] Example 11

[0073] This embodiment provides a formamidinium reference two-dimensional perovskite film, the molecular formula of the formamidinium reference two-dimensional perovskite film is (C5H 10 (NH3)2)(CH(NH2)2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite film is completely same as that of example 1 except that in step (2), the starting time of dropping the anti-solvent is adjusted from the 12th second after the start of spin coating to the 25th second after the start of spin coating.

[0074] Example 12

[0075] This embodiment provides a formamidinium reference two-dimensional perovskite film, the molecular formula of the formamidinium reference two-dimensional perovskite film is (C5H 10 (NH3)2)(CH(NH2)2)4Pb5I 16 The preparation method of the formamidinium reference two-dimensional perovskite film is completely same as that of example 1 except that in step (1), 90 mg of pentamethylenediamine iodine (C5H 10(NH3)2)I2, 172 mg of formamidinium iodide and 576 mg of lead iodide, so that the concentration of pentanediamine iodine in the perovskite precursor solution is 0.25 mmol / mL, and the molar ratio of pentanediamine iodine, formamidinium iodide and lead iodide is 1:4:5, and other conditions are exactly the same as those in Example 1.

[0076] Comparative Example 1

[0077] The present comparative example provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of which is (C5H 10 (NH3)2)(CH3NH2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film comprises the following steps:

[0078] (1) 90 mg of pentanediamine iodine (C5H 10 (NH3)2)I2, 199 mg of methylamine iodide and 692 mg of lead iodide are prepared into a perovskite precursor solution; wherein the concentration of pentanediamine iodine in the perovskite precursor solution is 0.25 mmol / mL, and the molar ratio of pentanediamine iodine, methylamine iodide and lead iodide is 1:5:6;

[0079] (2) The perovskite precursor solution in step (1) is filtered using a polytetrafluoroethylene filter and dropped onto a substrate, and spin-coated at 4000 rpm for 30 s; at the 12th second after the start of spin-coating, 200 μL of anti-solvent chlorobenzene is added, which is 20% of the volume of the solvent in step (1), to obtain a perovskite precursor film;

[0080] (3) The perovskite precursor film in step (2) is annealed at 150°C for 30 min to obtain the formamidinium reference two-dimensional perovskite thin film.

[0081] Comparative Example 2

[0082] The present comparative example provides a formamidinium reference two-dimensional perovskite thin film, the molecular formula of which is (C5H 10 (NH3)2)(CH3NH2)5Pb6I 19 The preparation method of the formamidinium reference two-dimensional perovskite thin film is exactly the same as that in Comparative Example 1, except that 900 μL of N,N-dimethylformamide and 100 μL of dimethyl sulfoxide are used as the solvent in step (1).

[0083] The formamidinium reference two-dimensional perovskite thin films obtained in each example and the formamidinium reference two-dimensional perovskite thin films obtained in each comparative example are made into perovskite thin film solar cells, which comprises the following steps:

[0084] S1. Put the indium tin oxide transparent conductive glass into a cleaning rack, and sequentially ultrasonic clean in clean water, deionized water, acetone and isopropyl alcohol for 20 min, respectively, and then clean in an ultraviolet ozone machine for 15 min to obtain a conductive substrate;

[0085] S2. Disperse tin dioxide nanoparticles in ammonia water, and control the molar ratio of tin dioxide to ammonia water to be 1:5, shake the solution vigorously, then drop it on the conductive substrate described in step S1, spin coat at 4000-4500 rpm for 30 s, and then anneal at 150-160°C for 20-30 min to form an electron transport layer, thereby obtaining a composite A;

[0086] S3. Use the preparation method of the perovskite film provided in the examples or comparative examples, take the composite A obtained in step S2 as a substrate, and prepare a perovskite film on the side of the electron transport layer in the composite A to form an active layer, thereby obtaining a composite B;

[0087] S4. Prepare a 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene solution with a concentration of 73 mg / mL, and drop 30-40 μL of the solution on the side of the active layer in the composite B described in step S3, then spin coat at 3000-4000 rpm for 30 s to form a hole transport layer, thereby obtaining a composite C;

[0088] S5. Transfer the composite C described in step S4 to a high vacuum evaporation instrument, set the vacuum degree to 1×10 -4 Pa, and evaporate a metal material on the side of the hole transport layer in the composite C, wherein the metal material comprises gold, to form a 60-80 nm thick metal anode layer, thereby preparing the perovskite film solar cell.

[0089] Figure 1 A schematic structural diagram of a perovskite film solar cell prepared using the formamidinium reference two-dimensional perovskite film described in the present application, wherein the perovskite film solar cell comprises a conductive substrate 1, and further comprises, from bottom to top, an electron transport layer 2, an active layer 3 composed of the formamidinium reference two-dimensional perovskite film, a hole transport layer 4, and a metal anode layer 5 on the side of the conductive substrate 1.

[0090] Figure 2 A photovoltaic performance test curve of a perovskite film solar cell prepared using the formamidinium reference two-dimensional perovskite film described in Example 1 and Examples 4-6, from which the short circuit current and open circuit voltage data of the tested solar cell can be obtained, and the fill factor and conversion efficiency of the tested solar cell can be calculated, and the results are shown in Table 1, and the test results of the perovskite film solar cells obtained in other examples and comparative examples are also included in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] From Table 1, it can be seen that:

[0095] (1) By comparing Example 1 and Examples 4-7, it can be found that the proportion of dimethyl sulfoxide in the solvent used in Example 1 and Examples 4-7 gradually increases, but the volume fraction is still within the preferred range of 0-50%. This change causes the open-circuit voltage of the obtained solar cell to gradually increase, which is related to the strong coordination ability of dimethyl sulfoxide, which slows down the crystallization process of the perovskite film and makes the film growth process more continuous, so the efficiency of the obtained solar cell gradually increases. For example, in Example 1, when the volume fraction of N,N-dimethylformamide is 80% and the volume fraction of dimethyl sulfoxide is 20%, the conversion efficiency of the obtained solar cell can reach 11.43%; in Example 6, when the volume fraction of N,N-dimethylformamide is 70% and the volume fraction of dimethyl sulfoxide is 30%, the conversion efficiency of the obtained solar cell can reach 11.04%;

[0096] However, due to the high boiling point of dimethyl sulfoxide, a higher proportion of dimethyl sulfoxide will result in slower solvent evaporation. For example, in Example 8, the volume fraction of dimethyl sulfoxide in the solvent is 80%, and in Example 9, only pure dimethyl sulfoxide is used as the solvent. Therefore, a large number of pinholes will be left at the bottom of the perovskite film obtained, which will cause the interface contact to deteriorate, the carrier transport ability to weaken, and the fill factor of the obtained solar cell to decrease. The conversion efficiency of the obtained solar cell does not increase with the increase of the proportion of dimethyl sulfoxide in the solvent. Based on the above results, it can be concluded that there is an optimal range of the ratio of N,N-dimethylformamide to dimethyl sulfoxide in the solvent, which can simultaneously improve the various parameters of the performance of the obtained solar cell device;

[0097] (2) By comparing Example 1 with Example 10 and Example 11, it can be found that the starting time of dropping the anti-solvent is crucial to the conversion efficiency of the final solar cell, the starting time of dropping the anti-solvent in Example 10 is 5s after the start of spin coating, and the anti-solvent is removed too early to remove the solvent at the moment when the perovskite film is not fully nucleated, which leads to rapid crystallization, which will make the growth of the film discontinuous, and will affect the performance of the solar cell; the starting time of dropping the anti-solvent in Example 11 is 25s after the start of spin coating, and at this time the perovskite has entered the crystallization process before the solvent evaporates, at this time the dropping of the anti-solvent cannot promote the rapid crystallization of the film, and the perovskite film cannot reach the optimal state, so the conversion efficiency of the solar cell obtained is lower than that of Example 1;

[0098] (3) In the preparation method described in the present application, the molar ratio of the organic diamine iodine salt, the formamidinium iodine and the lead iodide in the perovskite precursor solution is 1:(n-1):n, wherein n is an integer of 3-10, and preferably n=6, for example, in Example 1, when n=6, the conversion efficiency of the solar cell obtained is 11.43%, and when n=5, as shown in Example 12, the conversion efficiency of the solar cell obtained is reduced to 8.19%, it should be noted that when n is small, for example, 3 or 4, the solar cell obtained has a lower conversion efficiency due to the influence of the molecular structure of the perovskite itself;

[0099] (4) By comparing Example 1 with Comparative Example 1 and comparing Example 5 with Comparative Example 2, it can be found that under the condition of consistent solvent ratio, Comparative Example 1 and Comparative Example 2 use methylamine as raw material to prepare the methanaminium-based two-dimensional perovskite film, the conversion efficiency of the solar cell obtained in Comparative Example 1 is 9.89%, and the conversion efficiency of the solar cell obtained in Comparative Example 2 is 8.13%, both of which are lower than the conversion efficiencies of 11.43% obtained in Example 1 and 8.55% obtained in Example 5, which shows that the use of formamidine instead of methylamine as a component of the perovskite film in the present application can achieve good results, and under the appropriate solvent ratio, the performance of the solar cell obtained can be maintained at a high level.

[0100] The above examples are used to illustrate the detailed structural features of the present application, but the present application is not limited to the above detailed structural features, i.e. it does not mean that the present application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the components selected by the present application, addition of auxiliary components, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.

[0101] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0102] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0103] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A formamidinium-based two-dimensional perovskite thin film, characterized in that, The molecular formula of the formamidinium-based two-dimensional perovskite thin film is (C x H 2x (NH3)2)(CH(NH2)2) n-1 Pb n I 3n+1 , where x is an integer from 5 to 8, and n is an integer from 6 to 10; The method for preparing the formamidin-based two-dimensional perovskite thin film includes the following steps: (1) Prepare a perovskite precursor solution, wherein the perovskite precursor solution comprises an organic diamine iodide, formamidine iodide, lead iodide, and a solvent; the molecular formula of the organic diamine iodide is (C x H 2x (NH3)2)I2, where x is an integer from 5 to 8; the molar ratio of organic diamine iodide, formamidine iodide and lead iodide in the perovskite precursor solution is 1:(n-1):n, where n is an integer from 6 to 10; (2) Spin-coat the perovskite precursor solution described in step (1) onto the substrate, and add an anti-solvent during the spin-coating process to obtain a perovskite precursor film. (3) Anneal the perovskite precursor film described in step (2) to obtain a formamidinium-based two-dimensional perovskite film; The solvent in step (1) includes a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide, wherein the volume fraction of N,N-dimethylformamide in the mixed solvent is 70-80%.

2. A method for preparing a formamidinium-based two-dimensional perovskite thin film according to claim 1, characterized in that, The preparation method includes the following steps: (1) Prepare a perovskite precursor solution, wherein the perovskite precursor solution comprises an organic diamine iodide, formamidine iodide, lead iodide, and a solvent; the molecular formula of the organic diamine iodide is (C x H 2x (NH3)2)I2, where x is an integer from 5 to 8; the molar ratio of organic diamine iodide, formamidine iodide and lead iodide in the perovskite precursor solution is 1:(n-1):n, where n is an integer from 6 to 10; (2) Spin-coat the perovskite precursor solution described in step (1) onto the substrate, and add an anti-solvent during the spin-coating process to obtain a perovskite precursor film. (3) Anneal the perovskite precursor film described in step (2) to obtain a formamidinium-based two-dimensional perovskite film; The solvent in step (1) includes a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide, wherein the volume fraction of N,N-dimethylformamide in the mixed solvent is 70-80%.

3. The preparation method according to claim 2, characterized in that, The concentration of organic diamine iodide in the perovskite precursor solution in step (1) is 0.2-0.3 mmol / mL.

4. The preparation method according to claim 2, characterized in that, The perovskite precursor solution described in step (1) is filtered using a polytetrafluoroethylene filter before spin coating in step (2).

5. The preparation method according to claim 2, characterized in that, The spin coating speed in step (2) is 3000-4500 rpm.

6. The preparation method according to claim 2, characterized in that, The spin coating time in step (2) is 20 to 40 seconds.

7. The preparation method according to claim 2, characterized in that, The start time for adding the antisolvent in step (2) is 10 to 13 seconds after the spin coating begins.

8. The preparation method according to claim 2, characterized in that, The antisolvent in step (2) includes chlorobenzene.

9. The preparation method according to claim 2, characterized in that, The amount of antisolvent used in step (2) is 15-25% of the volume of the solvent used in step (1).

10. The preparation method according to claim 2, characterized in that, The annealing temperature in step (3) is 110-130℃.

11. The preparation method according to claim 2, characterized in that, The annealing time in step (3) is 20 to 30 minutes.

12. The preparation method according to claim 2, characterized in that, The preparation method includes the following steps: (1) A perovskite precursor solution comprising an organic diamine iodide, formamidinium iodide, and lead iodide is prepared using a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide, wherein the volume fraction of N,N-dimethylformamide in the mixed solvent is 70-80%; wherein the molecular formula of the organic diamine iodide is (C x H 2x (NH3)2)I2, where x is an integer from 5 to 8; the concentration of organic diamine iodide in the perovskite precursor solution is 0.2 to 0.3 mmol / mL, and the molar ratio of organic diamine iodide, formamidinium iodide and lead iodide is 1:(n-1):n, where n is an integer from 6 to 10; (2) The perovskite precursor solution described in step (1) is filtered using a polytetrafluoroethylene filter and dropped onto the substrate. The solution is then spin-coated at 3000-4500 rpm for 20-40 s. In the 10th-13th s after the spin-coating begins, 15-25% of the volume of the mixed solvent described in step (1) of the anti-solvent chlorobenzene is added to obtain the perovskite precursor film. (3) Anneal the perovskite precursor film obtained in step (2) at 110-130°C for 20-30 min to obtain the formamidinium-based two-dimensional perovskite film.

13. A perovskite thin-film solar cell, characterized in that, The perovskite thin-film solar cell includes a conductive substrate, and further includes an electron transport layer, an active layer composed of a formamidinium-based two-dimensional perovskite thin film as described in claim 1, a hole transport layer, and a metal anode layer, which are sequentially disposed from bottom to top on one side of the conductive substrate.

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