JP7623714B2 - Highly purified tin-containing perovskite semiconductor material - Google Patents

Description

This invention relates to a tin-containing perovskite semiconductor material that has excellent photoelectric conversion efficiency.

To date, solar cells that use lead (Pb ²⁺ )-containing perovskite in the B site have been reported to have high photoelectric conversion efficiencies (PCEs) exceeding 20%. However, solar cells that use lead-based perovskite in the light absorption layer have concerns about the environmental impact of the lead in the material. From the perspective of practical application, solar cells that use tin-containing perovskite in the light absorption layer, in which part or all of the lead is replaced with tin (Sn ²⁺ ), are expected to have a lower environmental impact (Non-Patent Document 1).

However, unlike lead-based ^perovskite , tin-containing perovskite has a problem in that the Sn ²⁺ in the material is easily oxidized to Sn ⁴⁺ , which increases the hole density in the film and reduces the solar cell characteristics.In addition, the photoelectric conversion efficiency of tin-containing perovskite solar cells has a problem in that the lifetime of the carriers generated by photoexcitation is short.

Shi, Z.; Guo, J.; Chen, Y.; Li, Q.; Pan, Y.; Zhang, H.; Xia, Y.; Huang, W. Adv. Mater. 2017, 29, 1605005.

One of the objects of an embodiment of the invention described in this specification is to provide a tin-containing perovskite layer that has good photoelectric conversion efficiency by removing (by capturing) trace amounts of Sn ⁴⁺ present in the system and highly purifying it, thereby making it difficult for Sn ²⁺ to be oxidized to Sn ⁴⁺ .

An object of one embodiment of the invention described in this specification is to provide a luminescent material or a photoelectric conversion device (for example, an organic EL device or a solar cell) having an excellent tin-containing perovskite layer.

The invention described in this specification is not limited to the above object, and may have the object of obtaining the various effects described in this specification.

Certain aspects of the invention described in this specification are based on the finding in the examples that the photoelectric conversion efficiency of a tin-containing perovskite layer can be increased by setting the concentration of Sn ^{+ 4} in the perovskite layer within a specified range.

An invention described in this specification relates to a tin-containing perovskite layer. The tin-containing perovskite layer means a perovskite layer containing tin. The perovskite layer containing tin is also called a tin-containing perovskite layer. This perovskite layer has an Sn+4 40nm value, which is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and the atomic content of divalent tin in a second measurement region, which is a region 40 nm deep from the center of the surface of the tin-containing perovskite layer, of 0% or more and 0.5% or less. It is preferable that _the Sn ^{+ 4} _40nm value is 0.0% or more and 0.3% or less.

It is preferable that the ratio of the Sn ⁺ 4 _surface value, which is the percentage of the tetravalent tin atomic content in the total of the tetravalent tin atomic content and the divalent tin atomic content at the surface center of the tin-containing perovskite layer, to the Sn ⁺⁴ _{40 nm} value is 3 or more.

The Sn+4 20nm value, which is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin in the first measurement region, which is a region 20 nm deep from the center of the surface of the tin-containing perovskite layer, is preferably 0.1% or more and 5% or less. In this example, _the Sn ^{+ 4} _20nm value is preferably 0.1% or more and 2% or less.

It is preferable that the ratio of the Sn ⁺ 4 _surface value, which is the percentage of the tetravalent tin atomic content in the total of the tetravalent tin atomic content and the divalent tin atomic content at the surface center of the tin-containing perovskite layer, to the Sn ⁺⁴ _20nm value is 3 or more and 20 or less.

The atomic content of lead atoms relative to the content of tin atoms is preferably 0% or more and 900% or less.

The Sn ⁺ _420nm value, which is a percentage of the atomic content of tin in the tin-containing alloy, is 0.1% or more and 5% or less.

The tin-containing perovskite layer means a perovskite layer containing tin. The perovskite layer is usually rectangular. Therefore, the central part of the surface of the tin-containing perovskite layer means, for example, the vicinity of the center of gravity of the surface.

The first measurement region, which is a region 20 nm deep in the center of the surface, refers to the center of the surface of the perovskite layer that is exposed by etching the surface of the perovskite layer to remove 20 nm, as described below. Etching may be performed in an oxygen-free atmosphere (e.g., in a vacuum). An example of the etching is argon etching.

The Sn ⁺ _420nm value is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin in the first measurement region. The atomic content of tetravalent tin and the atomic content of divalent tin can be obtained by separating peaks corresponding to divalent tin and tetravalent tin from the spectrum obtained by X-ray photoelectron spectroscopy (XPS) measurement and calculating the area. In addition, the peak separation may be performed by Gaussian fitting, and the area may be calculated automatically using known software or programs.
In other words, the Sn ⁺⁴ _{20 nm} value is calculated by the following formula:
Sn ⁺⁴ _{20 nm} value = 100 x (atomic content of tetravalent tin) / (atomic content of divalent tin) + (atomic content of tetravalent tin)

As demonstrated by the examples described later, when the Sn ⁺⁴ _{20 nm} value is 0.1% or more and 5% or less, the proportion of tetravalent tin decreases, and the photoelectric conversion efficiency is significantly increased while maintaining various physical properties.

The Sn ⁺⁴ _{40 nm} value is the percentage of the tetravalent tin atomic content of the total tetravalent tin atomic content and divalent tin atomic content in the second measurement region, which is a region 40 nm deep from the center of the surface of the tin-containing perovskite layer.
The second measurement region, which is a region at a depth of 40 nm in the center of the surface, means the center of the surface of the perovskite layer that is exposed by removing the surface of the perovskite layer by etching 40 nm.
The Sn ⁺⁴ _{40 nm} value can be determined in the same manner as the Sn ⁺⁴ _{20 nm} value.

The Sn ⁺⁴ _surface value is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin at the center of the surface of the tin-containing perovskite layer. The ratio of the Sn ⁺⁴ _surface value to the Sn ⁺⁴ _{20 nm} value can be calculated by Sn ⁺⁴ _surface value/Sn ⁺⁴ _{20 nm} value.

A preferred example of the tin-containing perovskite layer is one that contains 0.01 ppm to 1000 ppm in total of one or more compounds selected from zero-valent tin, pyrazine-based compounds, silicon-based compounds, and germanium-based compounds.

A preferred example of the use of the above-mentioned tin-containing perovskite layer is a luminescent material having any of the above-mentioned tin-containing perovskite layers.

A preferred example of use of the above-mentioned tin-containing perovskite layer is a display device having any of the above-mentioned tin-containing perovskite layers.

A preferred example of the use of the above-mentioned tin-containing perovskite layer is a photoelectric conversion element having any of the above-mentioned tin-containing perovskite layers.

A preferred example of use of the above-mentioned tin-containing perovskite layer is a solar cell having any of the above-mentioned tin-containing perovskite layers.

According to this specification, it is possible to provide a tin-containing perovskite layer that is highly purified by removing (by capturing) trace amounts of Sn ⁴⁺ present in the system, ^that is less likely to be oxidized to Sn ⁴⁺ , and that has good photoelectric conversion efficiency.

1 is a graph instead of a drawing showing the PL spectrum when reducing agent 1 in Example 1 was used, and a summary of the results. The vertical axis of Fig. 1 is intensity (arbitrary unit), and the horizontal axis is wavelength (nm). 2 is a graph instead of a drawing showing the measurement results of the fluorescence lifetime when the reducing agent 1 in Example 1 was used, and a summary of the results. The vertical axis of Fig. 2 is intensity (arbitrary unit), and the horizontal axis is time (n seconds). 3 is a graph instead of a drawing showing the PL spectrum when reducing agent 2 in Example 1 was used, and a summary of the results. The vertical axis of Fig. 3 is intensity (arbitrary unit), and the horizontal axis is wavelength (nm). 4 is a graph instead of a drawing showing the measurement results of the fluorescence lifetime when the reducing agent 2 in Example 1 was used, and a summary of the results. The vertical axis of Fig. 4 is intensity (arbitrary unit), and the horizontal axis is time (n seconds). 5 is a SEM photograph of the surface of a perovskite film in place of a drawing in Example 2. From the left, the photographs show a case where reducing agent 1 was added at 0.1 mol% relative to _SnI2 (1.0 mol% relative to _SnF2 ), a case where reducing agent 1 was added at 5.0 mol% relative to _SnI2 (50 mol% relative to _SnF2 ), a case where reducing agent 1 was added at 1 mol% relative to _SnI2 (10 mol% relative to _SnF2 ), and a case where reducing agent 1 was added at 5 mol% relative to _SnI2 (50 mol% relative to _SnF2 ). 6 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 2. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. 7 is a SEM photograph of the surface of a perovskite film in place of a drawing in Example 3. From the left, the photographs show a case where reducing agent 2 was added at 0.5 mol% relative to _SnI2 (5 mol% relative to _SnF2 ), a case where reducing agent 2 was added at 1 mol% relative to _SnI2 (10 mol% relative to _SnF2 ), a case where reducing agent 2 was added at 5 mol% relative to _SnI2 (50 mol% relative to _SnF2 ), and a case where reducing agent 2 was added at 10 mol% relative to _SnI2 (100 mol% relative to _SnF2 ). 8 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 3. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. 9 is a graph, instead of a drawing, showing the evaluation results of the solar cell characteristics in Example 4. The vertical axis indicates the count, and the horizontal axis indicates the current density. 10 is a graph, instead of a drawing, showing the evaluation results of the solar cell characteristics in Example 4. The vertical axis indicates the count, and the horizontal axis indicates the voltage. 11 is a graph, instead of a drawing, showing the evaluation results of the solar cell characteristics in Example 4. The vertical axis indicates the count, and the horizontal axis indicates the FF (fill factor). 12 is a graph, instead of a drawing, showing the evaluation results of the solar cell characteristics in Example 4. The vertical axis indicates the count, and the horizontal axis indicates PCE (conversion efficiency). 13 is a SEM photograph of the surface of a perovskite film in place of a drawing in Example 5. From the left, the following are shown: one made from a solution in which a 0.9 M tin-containing perovskite precursor solution was added with 1 mol% of reducing agent 2 relative to _SnI2 , one made from a solution in which a 1.2 M tin-containing perovskite precursor solution was added with 1 mol% of reducing agent 2 relative to _SnI2 , one made from a solution in which a 1.3 M tin-containing perovskite precursor solution was added with 1 mol% of reducing agent 2 relative to _SnI2 , and one made from a solution in which a 1.4 M tin-containing perovskite precursor solution was added with 1 mol% of reducing agent ₂ relative to SnI2. 14 is a SEM photograph of a cross section of a perovskite film in place of a drawing in Example 5. From the left, the following are shown: one made from a solution in which a reducing agent 2 was added at 1 mol% relative to _SnI2 to a 0.9 M tin-containing perovskite precursor solution, one made from a solution in which a reducing agent 2 was added at 1 mol% relative to _SnI2 to a 1.2 M tin-containing perovskite precursor solution, one made from a solution in which a reducing agent 2 was added at 1 mol% relative to _SnI2 to a 1.3 M tin-containing perovskite precursor solution, and one made from a solution in which a reducing agent 2 was added at 1 mol% relative to _SnI2 to a 1.4 M tin-containing perovskite precursor solution. 15 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 5. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. 16-1 is a photograph in lieu of a drawing showing the state before and after the addition of reducing agent 2 in Example 6. The upper left photograph is a photograph of solution (2) before the addition of reducing agent 2, and the lower left photograph is a photograph of solution (2) after the addition of reducing agent 2. The upper center photograph is a photograph of solution (3) before the addition of reducing agent 2, and the lower center photograph is a photograph of solution (3) after the addition of reducing agent 2. The upper right photograph is a photograph of solution (4) before the addition of reducing agent 2, and the lower right photograph is a photograph of solution (4) after the addition of reducing agent 2. 16-2 is a surface SEM photograph of a perovskite film in place of a drawing in Example 6. From the left, entry 1 (reference) not containing reducing agent 2, entry 2 (a DMSO solution of _SnI2 to which reducing agent 2 has been added), entry 3 (a DMSO solution of _SnF2 to which reducing agent 2 has been added), and entry 4 (a DMSO solution of FA _0.75 MA _{0.25 SnI3} to _which reducing agent 2 has been added) are shown. 17 is a graph instead of a drawing showing the PL spectrum when reducing agent 2 in Example 6 was used, and a summary of the results. The vertical axis of Fig. 17 is intensity (arbitrary unit), and the horizontal axis is wavelength (nm). 18 is a graph instead of a drawing showing the measurement results of the fluorescence lifetime when the reducing agent 2 in Example 6 was used, and a summary of the results. The vertical axis of Fig. 18 is intensity (arbitrary unit), and the horizontal axis is time (n seconds). 19 is a SEM photograph of the surface of a perovskite film in Example 6, in place of a drawing. From the left, entry 1 (reference) not containing reducing agent 2, entry 2 (a DMSO solution of _SnI2 to which reducing agent 2 was added), and entry ₄ (a DMSO solution of _{FA0.75MA0.25SnI3} to which reducing agent 2 was added ₎ are shown. 20 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 6. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. 21 is a graph instead of a drawing showing the PL spectrum when reducing agent 2 in Example 7 was used, and a summary of the results. The vertical axis of Fig. 21 is intensity (arbitrary unit), and the horizontal axis is wavelength (nm). 22 is a graph instead of a drawing showing the measurement results of the fluorescence lifetime when the reducing agent 2 in Example 7 was used, and a summary of the results. The vertical axis of Fig. 22 is intensity (arbitrary unit), and the horizontal axis is time (n seconds). 23 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 8. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. 24 is a graph, instead of a drawing, showing the IPCE spectrum in Example 8. The vertical axis shows IPCE, and the horizontal axis shows wavelength (nm). 25 is a graph instead of a drawing showing the chemical shift of _SnI2 in Example 9. The upper figure shows that of Sample 1 (without adding reducing agent 2), and the lower figure shows that of Sample 2 (with adding reducing agent 2). 26 is a graph instead of a drawing showing the chemical shift of _SnF2 in Example 9. The upper figure shows sample 1 (without adding reducing agent 2), and the lower figure shows sample 2 (with adding reducing agent 2). FIG. 27 is a TEM photograph, instead of a drawing, showing that particles were obtained in Example 9. 28 is a graph instead of a drawing showing the chemical shift of _SnI4 in Example 9. The upper figure shows that of Sample 1 (without adding reducing agent 2), and the lower figure shows that of Sample 2 (with adding reducing agent 2). 29 is a graph instead of a drawing showing the chemical shift of a system containing _SnI4 and _SnF2 in Example 9. The upper figure shows sample 1 (without adding reducing agent 2), and the lower figure shows sample 2 (with adding reducing agent 2). Fig. 30 is a graph instead of a drawing showing the measurement results of the fluorescence lifetime when _Et3SiH was used as the reducing agent in Example 10, and a summary of the results. The vertical axis of Fig. 30 is intensity (arbitrary unit), and the horizontal axis is time (n seconds). 31 is a SEM photograph of the surface of a perovskite film in place of a drawing in Example 10. From the left, a reference containing no reducing agent, a sample in which the reducing agent Et ₃ SiH was added at 1 mol% relative to SnI ₂ , a sample in which the reducing agent Et ₃ SiH was added at 5 mol%, and a sample in which the reducing agent Et ₃ SiH was added at 10 mol% relative to SnI ₂ are shown. 32 is a graph, instead of a drawing, showing the solar cell characteristics (JV curve) in Example 10. The vertical axis indicates the current density, and the horizontal axis indicates the voltage. Fig. 33 is a photograph in lieu of a drawing showing the state of the scavenger treatment. Fig. 33 shows photographs of the precursor solution before (left), immediately after (middle), and after 15 minutes of stirring (right) of the reducing agent TM-DHP. FIG. 34 shows SEM images in place of drawings showing (a) the surface and (b) the cross section of a tin-containing perovskite thin film. Fig. 35 shows a diagram for quantitatively evaluating tin ions contained in a perovskite thin film, in which (a) shows a cross-sectional SEM image in place of a drawing, and (b) shows a Sn 3d5/2 XPS spectrum of the tin-containing perovskite thin film. Fig. 36 is a graph instead of a drawing showing the optical property measurement results of a tin-containing perovskite thin film. Fig. 36(a) shows a fluorescence spectrum. The vertical axis of Fig. 36(a) shows fluorescence intensity, and the horizontal axis shows energy (eV). Fig. 36(b) is a graph (time-resolved decay curve) instead of a drawing showing the measurement results of fluorescence lifetime. The vertical axis of Fig. 36(b) shows fluorescence intensity (normalized), and the horizontal axis shows time (n seconds). FIG. 37 is a drawing related to elucidation of the mechanism by scavengers. FIG. 37(a) is a graph instead of a drawing showing the NMR measurement results showing the presence of divalent tin and tetravalent tin in a DMSO-d ₆ solution of SnF ₂ before (upper) and after (lower) the addition of TM-DHP. FIG. 37(b) is a graph instead of a drawing showing the NMR measurement results showing the presence of divalent tin and tetravalent tin in a DMSO-d ₆ solution of SnI ₂ before (upper) and after (lower) the addition of TM-DHP. FIG. 37(c) is a graph instead of a drawing showing the NMR measurement results showing the presence of divalent tin and tetravalent tin in a DMSO-d ₆ solution of SnBr ₂ before (upper) and after (lower) the addition of TM-DHP. Fig. 37(d) is a graph in lieu of a drawing showing the results of NMR measurements indicating the presence of divalent tin and tetravalent tin in a DMSO- _d6 solution of _SnCl2 before (top) and after (bottom) the addition of TM-DHP. Fig. 37(e) is a photograph in lieu of a drawing showing a DMSO- _d6 solution of _SnF2 before (left) and after (right) the addition of TM-DHP. Fig. 37(f) is a TEM photograph in lieu of a drawing showing ^Sn0 nanoparticles formed after the addition of TM-DHP (right). Figure 38 is a graph showing the characteristics of a perovskite solar cell, instead of a drawing, in which (a) shows a current density-voltage curve, and (b) shows the distribution of photoelectric conversion efficiency (PCE) of 40 cells. Figure 39 shows the physical properties of the surface-treated perovskite layer. Figure 39(a) is a graph replacing a drawing showing the current density-voltage curve of a tin-containing perovskite solar cell. Figure 39(b) is a diagram showing an energy level diagram. Figure 39(c) is a graph replacing a drawing showing the external quantum efficiency (EQE) and internal quantum efficiency (IQE). Figure 39(d) is a graph replacing a drawing showing the distribution of photoelectric conversion efficiency (PCE) of 30 cells. Fig. 40 is a graph in lieu of a drawing relating to a _{MASnI1.5Br1.5 perovskite} thin film. Fig. 40(a) shows a fluorescence spectrum. The vertical axis of Fig. 40(a) shows fluorescence intensity, and the horizontal axis shows energy (eV). Fig. 40(b) is a graph in lieu of a drawing showing the measurement results of fluorescence lifetime (time-resolved decay curve). The vertical axis of Fig. 40(b) shows fluorescence intensity (normalized), and the horizontal axis shows time (n seconds). FIG. 41 is a graph in lieu of a drawing relating to a _MASnBr3 perovskite thin film. FIG. 41(a) shows a fluorescence spectrum. The vertical axis of FIG. 41(a) shows fluorescence intensity, and the horizontal axis shows energy (eV). FIG. 41(b) is a graph in lieu of a drawing showing the measurement results of fluorescence lifetime (time-resolved decay curve). The vertical axis of FIG. 41(b) shows fluorescence intensity (normalized), and the horizontal axis shows time (n seconds). FIG. 42 is a graph, instead of a drawing, showing the Sn 3d ^5/2 XPS spectrum of a MASnI _1.5 Br _1.5 perovskite thin film. Figure 43 is a graph, instead of a drawing, relating to an ASnI ₃ -XBrX-based perovskite solar cell element prepared using the scavenger method, in which (a) shows the current density-voltage curve, and (b) shows the external quantum efficiency (EQE). FIG. 44 is a graph in lieu of a drawing relating to _{a Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3 perovskite thin} film. FIG. ₄₄ (a) shows a fluorescence spectrum. The vertical axis of FIG _{. 44} (a) shows fluorescence intensity, and the horizontal axis shows energy (eV). FIG. 44(b) is a graph in lieu of a drawing showing the measurement results of fluorescence lifetime (time-resolved decay curve). The vertical axis of FIG. 44(b) shows fluorescence intensity (normalized), and the horizontal axis shows time (n seconds). Figure 45 is a graph, instead of a drawing, showing the current density-voltage curve of _a solar cell element using a _{Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3} perovskite film. Figure _{45 ( a} ) shows the case where the scavenger method is not used, and Figure 45( _b ) shows the case where the scavenger method is used. FIG. 46 is a graph, instead of a drawing, showing an XPS spectrum for Sn 3d of a Cs _0.1 FA _0.6 MA _0.3 Pb _0.5 Sn _0.5 I ₃ perovskite thin film.

Hereinafter, the embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes appropriate modifications of the embodiments described below within the scope obvious to those skilled in the art.

1. Method for Producing a Perovskite Layer The method for producing a tin-containing perovskite layer described herein includes a step of adding a reducing agent to a solution containing a tin heavy halide to obtain a tin-containing perovskite precursor solution. This method for producing a perovskite layer can appropriately adopt known steps and conditions for producing a perovskite layer. For example, the method may include a step of applying a solution containing a tin-containing perovskite compound to a substrate, a step of applying a poor solvent to the substrate, and a step of annealing the substrate.

Reducing agent The reducing agent is, for example, a reducing agent that reduces tin fluoride in a tin-containing perovskite precursor solution to tin (zero-valent tin) and does not reduce tin heavy halides in a tin-containing perovskite precursor solution to tin. Reducing tin fluoride in a tin-containing perovskite precursor solution to tin does not necessarily mean completely reducing tin fluoride or ions derived from tin fluoride in the solution. It is sufficient to reduce tin fluoride in the solution, for example, 1% or more, 3% or more, 5% or more, or 10% or more. Similarly, the term "not reducing tin heavy halides to tin" means that it is sufficient to not reduce, for example, 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 98% or more of tin heavy halides to tin.

The oxidation-reduction potential of the reducing agent is -1.0 V vs Fc/Fc ⁺ or more and +0.8 V vs Fc/Fc ⁺ or less, more preferably -0.5 V vs Fc/Fc ⁺ or more and +0.3 V vs Fc/Fc ⁺ or more, in cyclic voltammetry. The reducing agent may also be a reducing agent having a silyl group. For example, a reducing agent that has a silyl group as its basic skeleton or as part of its basic skeleton is considered to react selectively with _SnF2 compared to, for example, _SnI2 , since the fluorine atom of _SnF2 and the Si atom of the silyl group react selectively. Among reducing agents having a silyl group, _Et3SiH is effective in extending the fluorescence lifetime, and in this case, it is considered that H- (hydride) generated by coordination of _SnF2 to Si reduces Sn.)

Examples of the reducing agent are any of the compounds represented by the following formulas (I) to (V).

In formula (I), R ¹ to R ⁴ may be the same or different and each represent a hydrogen atom or a C ₁ to C ₄ alkyl group, R ⁵ to R ¹⁰ may be the same or different and each represent a hydrogen atom or a C ₁ to C ₄ alkyl group, and X ₁ and X ₂ may be the same or different and each represent N or a carbon atom.
In formula (I), R ¹ to R ⁴ may be the same or different and each is preferably a hydrogen atom, a methyl group, or an ethyl group, and R ⁵ to R ¹⁰ may be the same or different and each is preferably a methyl group or an ethyl group.

Among the compounds represented by formula (I), those in which _X1 and _X2 are N are the following compounds (Ia).

In formula (Ia), R ¹ to R ⁴ may be the same or different and each is a hydrogen atom, a methyl group, or an ethyl group, and R ⁵ to R ¹⁰ may be the same or different and each is preferably a methyl group or an ethyl group.
For example, R ¹ to R ⁴ may all be hydrogen atoms or methyl groups;
R ¹ and R ⁴ may be hydrogen atoms, and R ² and R ³ may be methyl groups.
R ⁵ to R ¹⁰ may all be methyl groups.

Among the compounds represented by formula (I), those in which X ₁ is N and X ₂ is a carbon atom are the following compounds (Ib).

In formula (Ib), R ¹ to R ⁴ may be the same or different and each is a hydrogen atom, a methyl group, or an ethyl group, and R ⁵ to R ¹⁰ may be the same or different and each is preferably a methyl group or an ethyl group.
For example, R ¹ to R ⁴ may all be hydrogen atoms or methyl groups;
R ¹ and R ⁴ may be hydrogen atoms and R ² and R ³ may be methyl groups, or R ¹ may be a methyl group and R ² to R ⁴ may be hydrogen atoms.
R ⁵ to R ¹⁰ may all be methyl groups.
A specific compound represented by formula (Ib) is a compound in which R ¹ to R ⁴ are all hydrogen atoms, and R ⁵ to R ¹⁰ are all methyl groups.

Among the compounds represented by formula (I), those in which X ₁ and X ₂ are carbon atoms are the following compounds (Ic).

In formula (Ic), R ¹ to R ⁴ may be the same or different and each is a hydrogen atom, a methyl group, or an ethyl group, and R ⁵ to R ¹⁰ may be the same or different and each is preferably a methyl group or an ethyl group.
For example, R ¹ to R ⁴ may all be hydrogen atoms or methyl groups;
^R1 and ^R4 may be hydrogen atoms and ^R2 and ^R3 may be methyl groups, or ^R1 may be a methyl group and ^R2 to ^R4 may be hydrogen atoms. ^R5 to ^R10 may all be methyl groups. A specific compound represented by formula (Ic) is a compound in which ^R1 is a methyl group, ^R2 to ^R4 are hydrogen atoms, and ^R5 to ^R10 are all methyl groups.

In formula (II), R ¹¹ to R ¹⁸ may be the same or different and each represents a hydrogen atom or a C ₁ to C ₄ alkyl group, R ¹⁹ to R ²⁴ may be the same or different and each represents a hydrogen atom or a C ₁ to C ₄ alkyl group, and X ₃ and X ₄ may be the same or different and each represents N or a single bond.
In formula (II), R ¹¹ to R ¹⁸ may be the same or different and each represents a hydrogen atom, a methyl group, or an ethyl group, R ¹⁹ to R ²⁴ may be the same or different and each represents a hydrogen atom, a methyl group, or an ethyl group, and X ₃ and X ₄ may be the same or different and each represents N or a carbon atom.

Among the compounds represented by formula (II), those in which _X3 and _X4 are N are represented by the following formula (IIa).

A specific compound represented by formula (IIa) is a compound in which R ¹¹ to R ¹⁸ are hydrogen atoms and R ¹⁹ to R ²⁴ are methyl groups.

In formula (III), R ³¹ to R ³⁴ may be the same or different and each represent a hydrogen atom, a C ₁ to C ₄ alkyl group, a C ₂ to C ₄ alkenyl group, a C ₂ to C ₄ alkynyl group, a C ₁ to C ₄ alkoxy group, a C ₁ to C ₄ alkylthio group, an aryl group, an aryloxy group, or an arylthio group.

In the above, the aryl group is, for example, an aryl group having 6 to 12 carbon atoms, and examples of the aryl group are benzyl and phenyl groups. The aryloxy group is, for example, an aryloxy group having 6 to ₂ carbon atoms, and an example of the aryloxy group is a phenoxy group. The arylthio group is, for example, an arylthio group having 6 to 12 carbon atoms. The _C2 -C4 alkenyl group is an alkenyl group having a linear or branched side chain having 2 to 4 carbon atoms. Examples of the _C2 - _C4 alkenyl group are vinyl, propenyl, and butenyl groups. The _C2 - _C4 alkynyl group is an alkynyl group having a linear or branched side chain having 2 to 4 carbon atoms. Examples of the _C2 - _C4 alkynyl group are ethynyl and propynyl groups.
The same applies below.

In formula (III),
All of R ³¹ to R ³⁴ may be other than a hydrogen atom (e.g., a methyl group or an ethyl group),
One of R ³¹ to R ³⁴ may be a hydrogen atom, and the rest may be a C ₁ to C ₄ alkyl group, a C ₁ to C ₄ alkoxy group, a C ₁ to C ₄ alkylthio group, an aryl group, an aryloxy group, or an arylthio group.

In the formula (III), the compound in which R ³¹ is a hydrogen atom and R ³² to R ³⁴ are ethyl groups is Et ₃ SiH.

In formula (IV), R ³⁵ to R ³⁷ may be the same or different and each represents a hydrogen atom, a C ₁ to C ₄ alkyl group, a C ₂ to C ₄ alkenyl group, a C ₂ to C ₄ alkynyl group, a C ₁ to C ₄ alkoxy group, a C ₁ to C ₄ alkylthio group, an aryl group, an aryloxy group, or an arylthio group;
_X5 represents a halogen atom.
In formula (IV),
All of R ³⁵ to R ³⁷ may be other than a hydrogen atom (for example, a methyl group or an ethyl group). Examples of halogen atoms are heavy halogen atoms (chlorine atom, bromine atom and iodine atom).

In formula (V), R ⁴¹ to R ⁴⁶ may be the same or different and each represent a hydrogen atom, a C ₁ to C ₄ alkyl group, a C ₂ to C ₄ alkenyl group, a C ₂ to C ₄ alkynyl group, a C ₁ to C ₄ alkoxy group, a C ₁ to C ₄ alkylthio group, an aryl group, an aryloxy group, or an arylthio group.

In formula (V), all of R ⁴¹ to R ⁴⁶ may be other than hydrogen atoms (e.g., methyl groups or ethyl groups), or one of R ⁴¹ to R ⁴⁶ may be a hydrogen atom and the rest may be other than hydrogen atoms (e.g., methyl groups or ethyl groups).

The reducing agent is basically one that reduces tin fluoride in the tin-containing perovskite precursor solution to tin, but does not reduce tin heavy halide in the tin-containing perovskite precursor solution to tin, and is not limited to the reducing agent represented by any of the compounds represented by the above formulas (I) to (V). In addition, it is preferable that the reducing agent does not remain in the layer during the film formation process, or if it remains, it does not adversely affect the perovskite layer, or even if it remains in a small amount, it improves the characteristics of the perovskite layer. As described above, the compounds represented by formulas (1) to (V) are reducing agents of the present invention that have such desirable characteristics. From the same viewpoint, the following compounds are also considered to be effective as reducing agents of the present invention.

Germanium-Based Reducing Agents Examples of germanium-based reducing agents are _GeF2 , _GeCl2 , _GeBr2 , _GeI2 , GeO, GeP, GeS, _GeI4 , and _GeCl4 .

Borane-based reducing agents Examples of borane-based reducing agents are BH ₃ -THF and BH ₃ -SMe _2.

Aluminum-Based Reducing Agents Examples of aluminum-based reducing agents are DIBAL-H (diisobutylaluminum hydride) and LAH (lithium aluminum hydride).

An example of a reducing agent other than those mentioned above is naphthaceno[5,6-cd:11,12-c',d']bis[1,2]dithiole (CAS number 193-44-2) or a derivative thereof (for example, one or more hydrogen atoms in the ring of this compound are substituted with alkyl or alkoxy groups, or some of the carbon atoms in the ring are substituted with nitrogen or sulfur atoms).

Tin heavy halide An example of a solution containing a tin heavy halide (tin-containing perovskite precursor solution) is a solution containing a precursor for forming a tin-containing perovskite layer (tin-containing perovskite precursor solution). This solution contains, for example, tin fluoride as an additive. The content of tin fluoride is usually small. The tin heavy halide contains one or more selected from tin iodide, tin bromide, and tin chloride.

The tin-containing perovskite compound used in the perovskite layer is known, and in this specification, a tin-containing perovskite compound containing Sn (tin) can be used as appropriate. The heavy tin halide is represented, for example, by SnX _m1 (X is one or more of I, Br, and Cl, and m1 is 1.8≦m1≦2.2). The heavy tin halide preferably contains tin iodide. The heavy tin halide may contain tin iodide, tin bromide, and tin chloride. For example, the heavy tin halide is mainly composed of tin iodide and tin bromide. In the tin-containing perovskite precursor solution, the heavy tin halide may be present in an ionized state as ions.

The tin heavy halide may be a tin-containing perovskite compound (also called the perovskite compound of the present invention) represented by formula (VI):
_RSnXj (VI)
[In the formula, the oxidation number of Sn is 1.5 to 4. R represents at least one type of monovalent cation. X represents at least one type of heavy halogen atom. j represents 2.5 to 3.5.]
The oxidation number of Sn is preferably 1.5 to 3.5, but may be 1.5 to 2.5, 1.8 to 2.2, or 1.5 to 2.

In general formula (VI), R is at least one type of monovalent cation. R may be two or more types of cations. Examples of such monovalent cations include alkali metal cations and monovalent transition metal cations.

Examples of alkali metal cations are the sodium cation, the potassium cation, the cesium cation, and the rubidium cation.

Examples of monovalent transition metal cations are copper cation, silver cation, gold cation, iron cation, and ruthenium cation.

A specific example of R is the cation shown below, which is R ⁵¹ NH ³⁺ (R ⁵¹ represents a monovalent substituted or unsubstituted hydrocarbon group). The substituted hydrocarbon group means a hydrocarbon in which the hydrogen atom of the hydrocarbon group is replaced by another atom or a substituent. Another specific example of R is:

NH ₂ ⁺ =C(R ⁵² )-NH ₂

(R ⁴² represents a hydrogen atom or a monovalent substituted or unsubstituted hydrocarbon group.)
It is a cation represented by the formula:

In this specification, examples of a "monovalent hydrocarbon group" are an alkyl group, an aryl group, or an aralkyl group.

The alkyl group is preferably a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, a 2-propyl group, an n-butyl group, a 1-methylpropyl group, a 2-methylpropyl group, a tert-butyl group, an n-pentyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a tert-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 2,2-dimethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 1-ethylbutyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 2-methylpentan-3-yl group, a 3,3-dimethylbutyl group, a 2, These are 2-dimethylbutyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, and cyclohexyl group.

The "aryl group" is preferably an aryl group having a carbon number of 6 to 20. Examples of the aryl group include a phenyl group, an indenyl group, a pentalenyl group, a naphthyl group, an azulenyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, an acenaphthylenyl group, a biphenylenyl group, a naphthacenyl group, and a pyrenyl group.

The "aralkyl group" is preferably an aralkyl group having 7 to 20 carbon atoms. Examples of the aralkyl group include a benzyl group, a phenethyl group, a 1-phenylpropyl group, a 2-phenylpropyl group, a 3-phenylpropyl group, a 1-phenylbutyl group, a 2-phenylbutyl group, a 3-phenylbutyl group, a 4-phenylbutyl group, a 1-phenylpentylbutyl group, a 2-phenylpentylbutyl group, a 3-phenylpentylbutyl group, a 4-phenylpentylbutyl group, a 5-phenylpentylbutyl group, a 1-phenylhexylbutyl group, a 2-phenylhexylbutyl group, a 3-phenylhexylbutyl group, a 4-phenylhexylbutyl group, a 5-phenylhexylbutyl group, a 6-phenylhexylbutyl group, a 1-phenylheptyl group, a 1-phenyloctyl group, a 1-phenylnonyl group, a 1-phenyldecyl group, a 1-phenylundecyl group, a 1-phenyldodecyl group, a 1-phenyltridecyl group, and a 1-phenyltetradecyl group.

Examples of the "substituent" are the above-mentioned monovalent hydrocarbon groups, halogen atoms (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom), -OR ^1a (R ^1a represents a hydrogen atom or the above-mentioned monovalent hydrocarbon group), -SR ^1b (R ^1b represents a hydrogen atom or the above-mentioned monovalent hydrocarbon group), nitro group, amino group, cyano group, sulfo group, carboxy group, carbamoyl group, aminosulfonyl group, and oxo group. The number of substituents, when present, is not particularly limited, and is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less.

As the monovalent hydrocarbon group represented by ^R51 and ^R52 , from the viewpoint that the perovskite compound of the present invention is likely to have a three-dimensional structure, absorb light in a wider wavelength range, and easily improve the power conversion efficiency (PCE) and internal quantum efficiency (IQE), an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms are preferable, an alkyl group having 1 to 6 carbon atoms and an aryl group having 6 to 14 carbon atoms are more preferable, and an alkyl group having 1 to 4 carbon atoms is even more preferable. Also, for the same reason, an alkyl group is preferable as ^R51 and ^R52 , a linear or branched alkyl group is more preferable, and a linear alkyl group is even more preferable. In particular, a methyl group is the most preferable.

As for ^R51 and ^R52 , from the viewpoint that the perovskite compound of the present invention is likely to have a three-dimensional structure, absorb light in a wider wavelength range, and easily improve the power conversion efficiency (PCE) and internal quantum efficiency ( _IQE ), ^R51 is preferably a methyl group and ^R52 is preferably a hydrogen atom. In other words, R is preferably _CH3NH3 ⁺ or the following cations in addition to alkali metal cations and monovalent transition metal cations.

NH ₂ ⁺ =CH-NH ₂

Preferred as R are groups represented by CH ₃ NH ₃ -, (NH ₂ ) ₂ CH-, and (CH ₃ NH _{3 ) x (} (NH ₂ ) ₂ CH) _1-x - (x is a number from 0 to 1, preferably 0.1 to 0.4, and may be 0.2 to 0.3).

In general formula (II), j is preferably 2.8 to 3.2 from the viewpoint of facilitating improvement of the power conversion efficiency (PCE) and the internal quantum efficiency (IQE).

Examples of the perovskite compound of the present invention that meets these conditions include methylammonium tin iodide (CH ₃ NH ₃ SnI ₃ : abbreviated as MASnI ₃ ), (CH ₃ NH ₃ ) ₂ Sn ₃ I ₈ : abbreviated as MA ₂ Sn ₃ I ₈ , methylammonium tin bromide (CH ₃ NH ₃ SnBr ₃ : abbreviated as MASnBr ₃ ), formamidinium tin iodide ((NH ₂ ) ₂ CHSnI ₃ : abbreviated as FASnI ₃ ), and formamidinium tin bromide ((NH ₂ ) ₂ CHSnBr ₃ : abbreviated as FASnBr ₃ ), FA _1-x MA _x SnI ₃ (x is a number from 0 to 1, preferably 0.1 to 0.4, and may be 0.2 to 0.3), CsSnI ₃ , CsSnBr ₃ , and mixtures thereof. Among these, FA _{0.7 5} MA _0.25 SnI ₃ , MASnI ₃ , and FASnI ₃ are preferred.

In the following examples, a method for producing a perovskite layer using a tin heavy halide containing a trace amount of tin fluoride is mainly described. On the other hand, the above reducing agent is expected to have a scavenger effect due to tin nanoparticles derived from tin fluoride even in various tin-containing perovskite layers, such as _ASnX3 type.

The solution containing the tin-containing perovskite compound can basically be obtained by dissolving a tin halide and a compound serving as a halogenated cation source in a solvent. The solvent is preferably a polar solvent, more preferably an aprotic polar solvent. Examples of the compound serving as a halogenated cation source are FAI, MAI, FABr, MABr, FA1 _{- xMAxI} , FA1 _{- xMAxBr} , and mixtures thereof. The molar ratio of the tin halide to the compound serving as a halogenated cation source may be 1:3 or more and 3:1, 1:2 to 2:1, 3:2 to 2:3, or 3:4 to 4:3.

The solvent preferably has a boiling point of about 35 to 250° C. Examples of the solvent include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), sulfolane, N-methylpyrrolidone, propylene carbonate, α-acetyl-γ-butyrolactone, tetramethylene sulfoxide, ethyl cyanoacetate, acetylacetone, 3-methoxy-N,N-dimethylpropanamide, N,N'-dimethylethyleneurea, 1,1,3,3-tetramethylurea, 2-acetylcyclohexanone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3,4-dihydro-1(2H)-naphthalenone, cyclopentanone, cyclohexanone, cycloheptanone, aniline, piperidine, pyridine, Examples of suitable amines include 4-tert-butylpyridine, 4-amylpyridine, 4-aminopyridine, 2-amylpyridine, 4-methylpyridine, pentafluoropyridine, 2,4,6-tetramethylpyridine, 2,6-di-tert-butyl-4-methylpyridine, 4-pyridineethylamine, cyclooctanone, 2,5-dimethoxytetrahydrofuran, 1,4,7,10-tetraoxacyclododecane, ethyl p-toluate, 1,2-dimethoxybenzene, tetrahydrofurfuryl acetate, cyclohexyl acetate, cyclopentyl methyl ether, phenylethylamine, ethylenediamine, triethylamine, diisopropylethylamine, and hydrazine. Among these, N,N-dimethylformamide (DMF) or dimethylsulfoxide (DMSO) are preferred from the viewpoint of forming a coordinate bond to the metal center.

An example of the concentration of the tin halide in the solvent is 0.1 to 5 mol/L (or 0.5 to 3 mol/L). The solution containing the tin-containing perovskite compound can be obtained by appropriately mixing the above-mentioned compound with the above-mentioned solvent. If necessary, the solvent may be appropriately stirred and heated to dissolve the compound.

Substrate As the substrate, a known substrate for a perovskite solar cell or an organic EL element can be appropriately used. Examples of the substrate are a glass substrate, an insulating substrate, a semiconductor substrate, a metal substrate, and a conductive substrate (including a conductive film). In addition, a substrate having at least one film of a metal film, a semiconductor film, a conductive film, and an insulating film formed on a part or all of the surface of the substrate can also be suitably used.

Examples of the metals constituting the metal film include one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, cobalt, zinc, magnesium, calcium, silicon, yttrium, strontium, and barium. Examples of the materials constituting the semiconductor film include simple elements such as silicon and germanium, compounds containing elements of groups 3 to 5 and groups 13 to 15 of the periodic table, metal oxides, metal sulfides, metal selenides, and metal nitrides. Examples of the materials constituting the conductive film include tin-doped indium oxide (ITO), fluorine-doped indium oxide (FTO), zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), and tungsten oxide (WO ₃ ). Examples of materials that can be used to form insulating films include aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), and silicon oxynitride (Si ₄ O ₅ N ₃ ).

Examples of the shape of the substrate include a plate-like shape such as a flat plate or a disk, a fiber-like shape, a rod-like shape, a cylindrical shape, a prismatic shape, a cylindrical shape, a spiral shape, a spherical shape, a ring shape, and a porous structure. Among these, a plate-like substrate is preferred. Examples of the thickness of the substrate are preferably 0.1 μm to 100 mm, and more preferably 1 μm to 10 mm.

When applying a solution containing a tin-containing perovskite compound to a substrate, the substrate may have a semiconductor layer formed thereon as an underlayer. In this case, applying a solution containing a tin-containing perovskite compound to a substrate means applying a solution containing a tin-containing perovskite compound to (onto) the substrate on which the underlayer has been formed.

In order to apply the solution containing the tin-containing perovskite compound to the substrate, spin coating, dip coating, screen printing, roll coating, die coating, transfer printing, spraying, or slit coating may be used. Among these, it is preferable to apply the solution to the substrate by spin coating. Spin coating is a method in which the solution is dropped onto the substrate while rotating it, and the solution is applied to the substrate. The substrate carrying the solution may also be rotated to apply the solution to the substrate. The rotation speed may be a maximum speed of 1,000 to 10,000 rpm for 30 seconds to 5 minutes, 2 to 15 seconds to reach the maximum speed, and 1 to 15 seconds from the maximum speed to stopping.

Next, we will explain the process of applying a poor solvent to the substrate.

A poor solvent means a solvent that has the ability to dissolve a solute but does not have a high solubility in the solute. Examples of poor solvents include substituted aliphatic hydrocarbons such as dichloromethane and chloroform; aromatic hydrocarbons such as toluene and benzene; substituted aromatic hydrocarbons such as chlorobenzene, orthodichlorobenzene, and nitrobenzene; acetic acid; ethers such as diethyl ether and tetrahydrofuran (THF); alcohols such as methanol, ethanol, isopropanol, butanol, and octanol; long-chain hydrocarbons such as hexane (especially C4-10 hydrocarbons); and acetonitrile. These poor solvents can be used alone or in combination of two or more. Among these, chlorobenzene or toluene is preferred.

The poor solvent may be used alone or in combination with a polar solvent. When the poor solvent is mixed with a polar solvent, the ratio of the polar solvent to the poor solvent (poor solvent/polar solvent) is preferably 2.0 to 10.0/1.0 (volume ratio), and more preferably 3.0 to 8.0/1.0 (volume ratio).

When applying the poor solvent, since the tin-containing perovskite compound is applied to the substrate, applying the poor solvent to the substrate means applying the poor solvent to the substrate in a state in which the tin-containing perovskite compound is applied. The method of applying the poor solvent to the substrate is the same as the method of applying the tin-containing perovskite compound. Note that, when applying the tin-containing perovskite compound by spin coating, the poor solvent may be applied to the substrate by dropping the poor solvent onto the substrate. The amount of the poor solvent applied may be appropriately adjusted. The volume ratio of the solution containing the tin-containing perovskite compound to the poor solvent may be 1:10 to 2:1, or 1:5 to 1:1.

The temperature of the poor solvent when applying the poor solvent to the substrate is preferably 45° C. or more and 100° C. or less. Under the conditions shown in the examples described later, when a poor solvent at this temperature is used, crystal growth from the seed crystals can be suppressed and the formation of the seed crystals can be promoted, so that the tin-containing perovskite layer is filled, the unevenness of the tin-containing perovskite layer is reduced, and a flat tin-containing perovskite layer without any gaps can be obtained. In this method, the temperature of the poor solvent may be 45° C. or more and 85° C. or less, or 50° C. or more and 70° C. or less. At this temperature, the tin-containing perovskite compound can be grown without damaging the underlayer. The temperature of the poor solvent may be appropriately adjusted depending on the type of the tin-containing perovskite compound, etc.

The poor solvent is applied by dropping the poor solvent while rotating the substrate, and the rotation is preferably stopped within 0.5 to 7.5 seconds (for example, 1 to 7 seconds, 1 to 6 seconds) after the poor solvent is applied. As demonstrated by the examples described later, by stopping the rotation very quickly after dropping the poor solvent, the state of the tin-containing perovskite compound can be adjusted. Conventionally, the rotation speed of the substrate was usually maintained for about 30 seconds after dropping the poor solvent, and then the rotation of the substrate was decelerated. In this specification, as shown by the examples described later, it is preferable to start decelerating the rotation speed of the substrate immediately to within 10 seconds (within 5 seconds immediately after, within 3 seconds immediately after, within 2 seconds immediately after, within 1 second immediately after, or immediately after) after the poor solvent is dropped. In this way, it is possible to suppress the variation in characteristics within the perovskite layer (film).

In addition, the step of applying the solution containing the tin-containing perovskite compound and the step of applying the poor solvent are preferably performed in a closed system, similar to the annealing treatment step described below. In the closed system, it is preferable that the vapor of the solvent contained in the solution containing the tin-containing perovskite compound is present, and more preferably, the solvent is at a saturated vapor pressure or a partial pressure of 90% or more of the saturated vapor pressure in the closed system.

Next, the process of annealing the substrate will be described. Annealing refers to a process of heating the substrate. The annealing process is preferably performed promptly after the poor solvent is dropped or after the substrate is stopped. As shown in the examples described later, the annealing process preferably includes a process of gradually heating the substrate in a closed system containing solvent vapor. In the closed system, it is preferable that the vapor of the solvent contained in the solution containing the tin-containing perovskite compound is present, and more preferably, the solvent is at a saturated vapor pressure or a partial pressure of 90% or more of the saturated vapor pressure in the closed system.

The step of annealing the substrate preferably involves increasing the temperature in two or more stages, which, as demonstrated in the examples, can promote the growth of the tin-containing perovskite compound and increase the grain size, thereby filling the tin-containing perovskite layer.

When the annealing process includes multiple stages, it means that the substrate temperature is raised to multiple target temperatures, maintained at the set temperatures for a predetermined period of time, and then raised to the next set temperature.
An example of the set temperature for the first stage is 30° C. or more and 60° C. or less, may be 35° C. or more and 55° C. or less, or may be 40° C. or more and 50° C. or less.
The residence time at the set temperature of the first stage may be from 5 seconds to 1 minute, or from 5 minutes to 20 minutes.
The set temperature of the second stage is preferably higher than the set temperature of the first stage. An example of the set temperature of the second stage is 50° C. or higher and 80° C. or lower, may be 55° C. or higher and 75° C. or lower, or may be 60° C. or higher and 70° C. or lower.
The residence time at the set temperature of the second stage may be from 5 seconds to 1 minute, from 5 minutes to 30 minutes, from 5 minutes to 20 minutes, or from 10 minutes to 20 minutes.
The set temperature of the third stage (if the first or second stage is omitted, the set temperature of the second stage) is preferably higher than the set temperature of the first or second stage. An example of the set temperature of the third stage is 70°C or higher and 120°C or lower, or may be 80°C or higher and 110°C or lower, or may be 90°C or higher and 110°C or lower.
The residence time at the set temperature of the third stage may be from 5 seconds to 1 minute, or from 5 minutes to 20 minutes.
The thickness of the perovskite layer that can be obtained in this manner is, for example, 10 nm to 1000 nm. The thickness may be 50 nm to 500 nm, 100 nm to 500 nm, or 250 nm to 500 nm.

After obtaining a perovskite layer by the above-mentioned method for producing a perovskite layer, a perovskite solar cell can be produced according to a normal method. However, since the perovskite layer can also be used for producing an organic EL element, after obtaining a perovskite layer by the above-mentioned method for producing a perovskite layer, an organic EL element can be produced using the perovskite layer.

The next invention described in this specification relates to a perovskite layer and a perovskite type solar cell including the perovskite layer. The perovskite layer includes a tin-containing perovskite compound, and the coverage of the tin-containing perovskite compound is preferably 95% to 100%. The coverage is more preferably 98% to 100%, and more preferably 99% to 100%. However, as long as the characteristics are not impaired, a coverage of 95% to 100% is preferable because the coverage is higher than that produced based on the conventional technology. The perovskite layer preferably has an average particle size of 150 nm to 500 nm of the tin-containing perovskite compound. The coverage can be calculated by taking a SEM image and calculating the area of the image. Specifically, the coverage rate may be determined using image analysis software, or the coverage rate, which is the ratio of the area of the substrate covered by the perovskite compound, may be determined by surrounding the black area not covered by the perovskite compound and determining the area of the surrounded portion. The average particle size of the tin-containing perovskite compound may also be determined by photographing the tin-containing perovskite layer and using the tin-containing perovskite compound boundary surface to determine the average size (e.g., the average value of the maximum length of the boundary surface). The average particle size may be an arithmetic mean value.

2. Perovskite solar cell A perovskite solar cell includes, for example, a transparent electrode, a (hole) blocking layer, an electron transport layer, a perovskite layer (light absorbing layer), a hole transport layer, and a metal electrode in this order. The perovskite solar cell may be a forward type in which an n-type semiconductor layer is provided on a transparent electrode, or an inverted type in which a p-type semiconductor layer is provided on a transparent electrode. Below, the perovskite solar cell is described using as an example a perovskite solar cell including, in this order, a transparent electrode, a (hole) blocking layer, an electron transport layer, a perovskite layer (light absorbing layer), a hole transport layer, and a metal electrode.

2.1 Transparent Electrode The transparent electrode is a support for the electron transport layer and also has the function of extracting a current (electrons) from the perovskite layer (light absorption layer) via the (hole) blocking layer. Therefore, a conductive substrate is preferable, and a transparent conductive layer having translucency that allows the transmission of light that contributes to photoelectric conversion is preferable.

Examples of the transparent conductive layer include a tin-doped indium oxide (ITO) film, an impurity-doped indium oxide (In ₂ O ₃ ) film, an impurity-doped zinc oxide (ZnO) film, a fluorine-doped tin dioxide (FTO) film, and a laminated film formed by laminating these films. There are no particular limitations on the thickness of these transparent conductive layers, and it is usually preferable to adjust the resistance to 5 to 15 Ω/□ (per unit area). The transparent conductive layer can be obtained by a known film formation method depending on the material to be formed.

The transparent conductive layer may be covered with a light-transmitting covering body as necessary to protect it from the outside. Examples of the light-transmitting covering body include resin sheets such as fluororesin, polyvinyl chloride, and polyimide; inorganic sheets such as white plate glass and soda glass; and hybrid sheets made by combining these materials. There are no particular limitations on the thickness of these light-transmitting covering bodies, and it is usually preferable to adjust the resistance to 5 to 15 Ω/□.

2.2. (Hole) Blocking Layer The (hole) blocking layer is a layer provided to prevent leakage of holes, suppress reverse current, and improve solar cell characteristics (particularly photoelectric conversion efficiency), and is preferably provided between the transparent electrode and the perovskite layer (light absorbing layer). The (hole) blocking layer is preferably a layer made of a metal oxide such as titanium oxide, and more preferably a layer in which the surface of the transparent electrode is smoothly and densely covered with an n-type semiconductor such as compact _TiO2 . "Dense" means that the metal compound is packed at a higher density than the packing density of the metal compound in the electron transport layer. Note that pinholes, cracks, etc. may be present as long as the transparent electrode and the electron transport layer are not electrically connected.

The thickness of the (hole) blocking layer is, for example, 5 to 300 nm, and is more preferably 10 to 200 nm from the viewpoint of the efficiency of electron injection into the electrode.

The (hole) blocking layer is formed on the transparent electrode. When a metal oxide is used for the (hole) blocking layer, it can be prepared by performing spray pyrolysis according to a known method (e.g., Non-Patent Document 4, J. Phys. D: Appl. Phys. 2008, 41, 102002, etc.). For example, it can be prepared by spraying an alcohol solution (e.g., isopropyl alcohol solution) of 0.01 to 0.40 M (especially 0.02 to 0.20 M) of a metal alkoxide (titanium alkoxide such as titanium di(isopropoxide)bis(acetylacetonate)) onto a transparent electrode placed on a hot plate heated to 200 to 550°C (especially 300 to 500°C).

The resulting substrate can then be immersed in an aqueous solution of titanium oxide (such as _TiO2 ), titanium alkoxide (such as titanium isopropoxide), or titanium halide (such as _TiCl4 ) and heated to form a denser film.

The concentration of the raw material in the aqueous solution containing the raw material of the (hole) blocking layer is preferably 0.1 to 1.0 mM, more preferably 0.2 to 0.7 mM. The immersion temperature is preferably 30 to 100° C., more preferably 50 to 80° C. Furthermore, the heating conditions are preferably 200 to 1000° C. (particularly 300 to 700° C.) and 5 to 60 minutes (particularly 10 to 30 minutes).

2.3. Electron transport layer The electron transport layer is formed to increase the active surface area of the perovskite layer (light absorbing layer), improve the photoelectric conversion efficiency, and facilitate electron collection. The electron transport layer may be formed on a substrate, but is preferably formed on a (hole) blocking layer. The (hole) blocking layer may function as the electron transport layer, or the electron transport layer may also function as the (hole) blocking layer. The electron transport layer may be a flat layer using an organic semiconductor material such as a fullerene derivative. The electron transport layer may be titanium oxide (TiO ₂ ) (including mesoporous TiO ₂ ), a SnO ₂ layer, or a ZnO layer. The electron transport layer preferably has a porous structure such as mesoporous TiO _2. The porous structure is preferably a collection of granular bodies, needle-shaped bodies, tubular bodies, columnar bodies, etc., and has a porous property as a whole. The pore size is preferably nanoscale. The porous structure, which is nanoscale, significantly increases the active surface area of the light absorption layer, improving solar cell characteristics (particularly photoelectric conversion efficiency) and forming a porous electron transport layer with excellent electron collection.

The electron transport layer may be a layer made of a metal oxide such as titanium oxide or tin oxide. If the metal compound is a semiconductor, it may be doped with a donor. This allows the electron transport layer to function as a window layer for introducing electrons into the perovskite layer (light absorbing layer), and allows the power obtained from the perovskite layer (light absorbing layer) to be extracted more efficiently.

The thickness of the electron transport layer is not particularly limited, and is preferably about 10 to 300 nm, more preferably about 10 to 250 nm, from the viewpoint of collecting more electrons from the perovskite layer (light absorbing layer). The electron transport layer can be obtained by using a known film forming method according to the material to be molded. For example, the electron transport layer can be prepared by applying an alcohol solution (e.g., ethanol solution, etc.) of 5 to 50% by mass (particularly 10 to 30% by mass) of titanium oxide paste on the (hole) blocking layer. Known or commercially available titanium oxide pastes can be used. The preferred application method is spin coating. The application can be performed at, for example, about 15 to 30°C.

2.4. Perovskite layer (light absorbing layer)
The perovskite layer (light absorbing layer) in a perovskite solar cell is a layer that absorbs light and transfers excited electrons to perform photoelectric conversion. The perovskite layer (light absorbing layer) contains a perovskite material or a perovskite complex. The perovskite layer may be manufactured based on the method described above. It is preferable to realize mass production of the perovskite layer by roll-to-roll. It is preferable to apply the mixed liquid to the substrate by spin coating, dip coating, screen printing, roll coating, die coating, transfer printing, spraying, slit coating, or the like, preferably by spin coating.

The tin-containing perovskite layer is described below. This tin-containing perovskite layer has an Sn+4 20nm value, ^which is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin in a first measurement region, which is a region 20 _nm deep from the center of the surface of the tin-containing perovskite layer, of 0.1% to 5%.

The tin-containing perovskite layer means a perovskite layer containing tin. The perovskite layer is usually rectangular. Therefore, the surface center of the tin-containing perovskite layer means the vicinity of the center of gravity of the surface.

The first measurement region, which is a region 20 nm deep in the center of the surface, refers to the center of the surface of the perovskite layer that is exposed by etching the surface of the perovskite layer to remove 20 nm, as described below. Etching may be performed in an oxygen-free atmosphere (e.g., in a vacuum). An example of the etching is argon etching.

The Sn ⁺ _420nm value is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin in the first measurement region. The atomic content of tetravalent tin and the atomic content of divalent tin can be obtained by separating peaks corresponding to divalent tin and tetravalent tin from the spectrum obtained by X-ray photoelectron spectroscopy (XPS) measurement and calculating the area. In addition, the peak separation may be performed by Gaussian fitting, and the area may be calculated automatically using known software or programs.
In other words, the Sn ⁺⁴ _{20 nm} value is calculated by the following formula:
Sn ⁺⁴ _{20 nm} value = 100 x (atomic content of tetravalent tin) / (atomic content of divalent tin) + (atomic content of tetravalent tin)

As demonstrated by the examples described later, if the Sn ⁺⁴ _20nm value is 0.1% or more and 5% or less, the proportion of tetravalent tin is reduced, and the photoelectric conversion efficiency is significantly increased while maintaining various physical properties. The above-mentioned tin-containing perovskite layer preferably has an Sn ⁺⁴ _20nm value of 0.1% or more and 3% or less. The Sn ⁺⁴ _20nm value may be 0.6% or more and 2.4% or less, 0.8% or more and 2% or less, or 1% or more and 1.4% or less. The Sn ⁺⁴ _20nm value can be finely adjusted by finely adjusting the manufacturing conditions with reference to the examples described later.

A preferred example of the tin-containing perovskite layer described above is one in which the Sn ⁺⁴ _40nm value is 0% or more and 0.5% or less. The Sn ⁺⁴ _40nm value may be 0% or more and 0.3% or less, 0.1% or more and 0.3% or less, 0% or more and 0.2% or less, or 0% or more and 0.1% or less.
The Sn ⁺⁴ _40nm value is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin in the second measurement region, which is a region 40 nm deep from the center of the surface of the tin-containing perovskite layer. The second measurement region, which is a region 40 nm deep from the center of the surface, refers to the center of the surface of the perovskite layer that is exposed by etching the surface of the perovskite layer to remove 40 nm. The Sn ⁺⁴ _40nm value can be determined in the same manner as the Sn ⁺⁴ _20nm value.

A preferred example of the tin-containing perovskite layer described above is one in which the ratio of the Sn ⁺⁴ _surface value to the Sn ⁺ _{4 20 nm} value (Sn ⁺⁴ _surface value/Sn ⁺⁴ _{20 nm} value) is 3 or more and 20 or less. This ratio may be 5 or more and 20 or less, 6 or more and 10 or less, or 10 or more and 20 or less.
The Sn ⁺⁴ _surface value is the percentage of the atomic content of tetravalent tin in the total atomic content of tetravalent tin and divalent tin at the center of the surface of the tin-containing perovskite layer. The ratio of the Sn ⁺⁴ _surface value to the Sn ⁺⁴ _20nm value can be calculated by Sn ⁺⁴ _surface value/Sn ⁺ _{4 20nm} value.
A preferred example of the tin-containing perovskite layer described above is one in which the ratio of the Sn ⁺⁴ _surface value to the Sn ⁺ _{4 40 nm} value (Sn ⁺⁴ _surface value/Sn ⁺⁴ _{40 nm} value) is 3 or more. This ratio may be 5 or more, 8 or more, or 10 or more.

Among the above-mentioned tin-containing perovskite layers, a preferred example from the viewpoint of obtaining high photoelectric conversion efficiency is a Pb-Sn mixed perovskite layer containing lead atoms (Pb ⁺ 2). In this case, the atomic content of lead atoms (Pb ⁺² ) relative to the content of tin atoms (the sum of Sn ⁺² and Sn ⁺⁴ ) is preferably 0% or more and 900% or less, more preferably 0% or more and 200% or less, and even more preferably 0% or more and 100% or less.

Among the above-mentioned tin-containing perovskite layers, preferred examples from the viewpoint of reducing the environmental load are those that do not contain any lead atoms, or, if they contain lead atoms, contain lead atoms in an amount of 1/10 or less of the amount of tin atoms. Even if the amount of lead atoms is small, as shown in the following examples, a perovskite layer having preferable properties can be obtained. However, lead may be contained at the level of an impurity.

From the viewpoint of the balance between light absorption efficiency and exciton diffusion length and the absorption efficiency of light reflected by the transparent electrode, the film thickness of the perovskite layer (light absorption layer) is preferably, for example, 50 to 1000 nm, and more preferably 200 to 800 nm. The film thickness of the perovskite layer (light absorption layer) of the present invention is preferably within the range of 100 to 1000 nm, and more preferably within the range of 250 to 500 nm. Specifically, the lower limit of the film thickness of the perovskite layer (light absorption layer) of the present invention is preferably 100 nm or more (particularly 250 nm) or more, and the upper limit is preferably 1000 nm or less (particularly 500 nm or less). The film thickness of the perovskite layer (light absorption layer) of the present invention is measured by a cross-sectional scanning electron microscope (cross-sectional SEM) of a film made of the complex of the present invention.

The flatness of the perovskite layer (light absorbing layer) of the present invention is preferably such that the difference in height is 50 nm or less (-25 nm to +25 nm) in a range of 500 nm x 500 nm in the horizontal direction of the surface measured by a scanning electron microscope, and more preferably the difference in height is 40 nm or less (-20 nm to +20 nm). This makes it easier to balance the light absorption efficiency and the exciton diffusion length, and the absorption efficiency of light reflected by the transparent electrode can be further improved. The flatness of the perovskite layer (light absorbing layer) is measured by a cross-sectional scanning electron microscope (cross-sectional SEM) of the perovskite layer (light absorbing layer) of the present invention, with an arbitrarily determined measurement point as the reference point, the difference between the maximum film thickness and the minimum film thickness within the measurement range as the upper limit, and the difference between the maximum film thickness and the minimum film thickness as the lower limit.

This tin-containing perovskite layer contains one or more selected from zero-valent tin, pyrazine-based compounds, silicon-based compounds, and germanium-based compounds in a total amount of 0.01 ppm to 1000 ppm. This tin-containing perovskite layer can be obtained based on the above-mentioned method for producing a tin-containing perovskite layer, and a predetermined amount of residual substances such as reducing agents are present. The tin-containing perovskite layer has excellent passivation properties due to the presence of a predetermined amount of specific substances remaining. The contents of these substances can be analyzed by performing a component analysis of the tin-containing perovskite layer. In the examples described below, a tin-containing perovskite layer is actually obtained. The above contents have a criticality (there is a significant difference in passivation between outside and within the above numerical range). Examples of pyrazine-based compounds and silicon-based compounds are compounds represented by formulas (I) to (V). The germanium-based compound is a compound produced by reacting the germanium-based reducing agent described above or a compound in the solution with the reducing agent. The total amount may be 0.1 ppm or more and 500 ppm or less, or 1 ppm or more and 500 ppm or less. A luminescent material or a photoelectric conversion element having such a tin-containing perovskite layer will have good characteristics by utilizing the above characteristics.

2.5. Hole transport layer The hole transport layer is a layer that has the function of transporting charges. For example, a conductor, a semiconductor, an organic hole transport material, etc. can be used for the hole transport layer. The material can function as a hole transport material that receives holes from the perovskite layer (light absorption layer) and transports the holes. The hole transport layer is formed on the perovskite layer (light absorption layer). Examples of the conductor and semiconductor include compound semiconductors containing monovalent copper such as CuI, CuInSe ₂ , and CuS; and compounds containing metals other than copper such as GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , and Cr ₂ O _3. Among them, from the viewpoint of more efficiently receiving only holes and obtaining higher hole mobility, a semiconductor containing monovalent copper is preferable, and CuI is more preferable. Examples of organic hole transport materials include polythiophene derivatives such as poly-3-hexylthiophene (P3HT) and polyethylenedioxythiophene (PEDOT); fluorene derivatives such as 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD); carbazole derivatives such as polyvinylcarbazole; triphenylamine derivatives such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA); diphenylamine derivatives; polysilane derivatives; polyaniline derivatives, etc. Among these, from the viewpoint of more efficiently receiving only holes and obtaining higher hole mobility, triphenylamine derivatives, fluorene derivatives, etc. are preferred, and PTAA, spiro-OMeTAD, etc. are more preferred.

In order to further improve the hole transport properties, the hole transport layer may contain an oxidizing agent such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), silver bis(trifluoromethylsulfonyl)imide, trifluoromethylsulfonyloxysilver, NOSbF ₆ , SbCl ₅ , or SbF _5. The hole transport layer may also contain a basic compound such as t-butylpyridine (TBP), 2-picoline, or 2,6-lutidine. The content of the oxidizing agent and basic compound may be the amount that has been conventionally used. The thickness of the hole transport layer is preferably, for example, 30 to 200 nm, and more preferably 50 to 100 nm, from the viewpoint of more efficiently receiving only holes and obtaining higher hole mobility. The method of forming the hole transport layer is preferably performed, for example, under a dry atmosphere. For example, it is preferable to apply (by spin coating or the like) a solution containing an organic hole transport material onto a perovskite layer (light absorbing layer) in a dry atmosphere, and then heat the solution at 30 to 150° C. (particularly 50 to 100° C.).

2.6 Metal Electrode The metal electrode is disposed opposite the transparent electrode and formed on the hole transport layer, enabling charge exchange with the hole transport layer. Any known material used in the industry can be used as the metal electrode, and examples of such materials include metals such as platinum, titanium, stainless steel, aluminum, gold, silver, and nickel, or alloys thereof. Among these, the metal electrode is preferably made of a material that can be formed by a method such as vapor deposition, since the electrode can be formed in a dry atmosphere.
Perovskite solar cells having layer configurations other than those described above can also be manufactured by the same method.

3. Organic electroluminescence element (organic EL element)
The organic EL element is a known element, as described in, for example, JP 2017-123352 A and JP 2015-071619 A, and its manufacturing method is also known. An example of an organic EL element has a substrate, an anode, a cathode, and an organic layer disposed between the anode and the cathode. The organic layer is configured by stacking a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer in this order from the anode side. The compound of the present invention can be used as an electron transport material in the electron transport layer.

4. Manufacturing method of solar cell The present invention also provides a manufacturing method of a solar cell. This method includes the steps of forming an electron transport (blocking) layer on a substrate using the manufacturing method of a perovskite layer described above, forming a perovskite layer on the electron transport layer, forming a hole transport layer on the perovskite layer, and forming an electrode on the hole transport layer.

5. Purification method for tin-containing heavy halide substances One embodiment of the invention described in this specification relates to a purification method for tin-containing heavy halide substances, which removes Sn ⁴⁺ and adjusts the concentration of Sn ²⁺ to be less likely to be oxidized to Sn ⁴⁺ . This method includes a reducing agent addition step of adding a reducing agent to a tin-containing heavy halide solution containing impurities, and an acquisition step of acquiring a tin-containing heavy halide-derived substance after the reducing agent addition step. The tin-containing heavy halide and the reducing agent are as described above. The tin-containing heavy halide solution contains tin fluoride as an additive. The impurities may include tetravalent tin ions resulting from SnO ₂ or SnX ₄ species, or may include both tin fluoride and tetravalent tin ions.

The method for purifying a heavy halide tin-containing material includes a reducing agent addition step, a precipitate removal step for removing a precipitate, and
The method may further include a step of leaving the solution from which the precipitate has been removed still after the step of removing the precipitate.
The obtaining step may include a crystal obtaining step of obtaining the crystals precipitated by the standing step.

Tin heavy halide solution One aspect of the invention described in this specification relates to a solution containing tin heavy halide, tin fluoride, and a reducing agent, which can provide a precursor solution for a tin-containing perovskite layer or a highly pure tin heavy halide-containing material. For example, the perovskite precursor solution described above functions as a tin heavy halide solution. It is difficult to produce a highly pure tin heavy halide: SnX ₂ (X = Cl, Br, I), and impurities such as tetravalent tin ion species (Sn ⁴⁺ ) such as SnO ₂ and SnX ₄ species are mixed in. In a mixed system of tin heavy halide and SnF ₂ , SnF ₂ is reduced to generate Sn-derived nanoparticles, which function as a scavenger, thereby effectively preventing the oxidation of SnX ₂ to SnX _4. As a result, a highly pure tin heavy halide-containing material can be obtained. The tin dihalide-containing substance may be a tin dihalide or a compound that contains a tin dihalide as part of its composition.

This solution contains a tin heavy halide, a tin fluoride, and a reducing agent. The tin heavy halide and the reducing agent are as described above. In addition to the tin fluoride, this solution may contain tetravalent tin ions as an impurity. This solution may be used as a tin-containing perovskite precursor solution. The concentration of the reducing agent used in this tin-containing perovskite precursor solution may be lower than the concentration of the tin fluoride used in the tin-containing perovskite precursor solution.

EXAMPLES The present invention will be specifically described below using examples. The present invention is not limited to the above description or examples, and may include matters that are obvious to a person skilled in the art.

In the examples described below, the following equipment was used:
Photoluminescence (PL) spectrum measurement:
Picosecond laser pulse (wavelength 444nm or 688nm, Advanced Laser Diode Systems, Inc.)
Nitrogen-cooled CCD camera (Princeton Instruments, Inc.)

Time-resolved PL measurement Avalanche photodiode (ID Quantique, Inc.)
Time-correlated single-photon counting board (Becker & Hickl, Inc.)

J-V measurement
OTENTO－SUN－P1G (BUNKOUKEIKI Co., Ltd.)
Keithley 2400

IPCE measurement SM-250 diffuse reflection unit (BUNKOUKEIKI Co., Ltd.)

SEM observation
S8010 (Hitachi High-Technologies Co., Ltd)

^119Sn NMR measurements
Bruker Avance III 600US Plus NMR

TEM observation
JEM-1011 (JEOL Co., Ltd.)

Optical properties of tin-containing perovskite films In a glove box (Ar gas, H ₂ O < 0.1 ppm, H ₂ O < 0.1 ppm), about 200 μL of perovskite precursor solutions (1) and (2) prepared as described below were applied to a quartz substrate and spin-coated. During the spin-coating, 300 μL of chlorobenzene heated to 65 °C was dropped to obtain a brown film (5 s slope at 5000 rpm, 60 s spin-coating, chlorobenzene was dropped between the last 2 s and 1 s, and the slope was stopped at 1 s). The obtained brown film was annealed at 45 °C for 10 min, 65 °C for 10 to 30 min, and then 100 °C for 5 min and 100 °C for 30 min to obtain a black perovskite film.

The obtained perovskite film was placed in an argon-filled sample case, and photoluminescence (PL) spectrum and time-resolved PL measurements were performed. A picosecond laser pulse (wavelength 444 nm or 688 nm, Advanced Laser Diode Systems, Inc) was used as the excitation light for the measurements. The excitation density at the sample position was 127 nJ/ ^cm2 , and measurements were performed under weak excitation conditions. PL spectra were measured using a spectrometer and a nitrogen-cooled CCD camera (Princeton Instruments, Inc). In the time-resolved PL measurements, PL from the sample was detected with an avalanche photodiode (ID Quantique, Inc), and time-resolved decay curves were obtained using a time-correlated single-photon counting board (Becker & Hickl, Inc).

From PL and time-resolved PL measurements, it was found that when reducing agent 1 was added at 0.1 mol% to _SnI2 , the fluorescence lifetime was extended from 6.0 ns to 7.3 ns while maintaining the fluorescence wavelength (Figs. 1 and 2). The fluorescence wavelength shifted to the shorter wavelength side when reducing agent 1 was added up to 10.0 mol% to _SnI2 , which is considered to be due to the effect of all _SnF2 added as an additive being reduced, as described below. In addition, when reducing agent 2 was added, the fluorescence lifetime was significantly extended while maintaining the fluorescence wavelength, and it was extended to 14 ns when reducing agent ₂ was added at 1.0 mol ^% to SnI2 (Figs. 3 and 4). This result suggests that the recombination of carriers generated by photoexcitation was suppressed while maintaining the structure and composition of the perovskite compound by forming a film using a solution containing reducing agents 1 and 2 as a capture agent for Sn4+ species.

The perovskite precursor solutions (1) and (2) were obtained as follows.

Precursor solution (1): Perovskite precursor solution with reducing agent 1 _SnI2 (1341 mg, 3.6 mmol), FAI (464 mg, 2.7 mmol), MAI (143 mg, 0.9 mmol), and _SnF2 (56 mg, _0.36 mmol) were dissolved in ultra-dehydrated DMSO (4.0 mL) at 45 °C in a glove box. After stirring for 1 h at 45 °C, the solution was filtered using a PTFE filter to prepare the _{FA0.75MA0.25SnI3 precursor} solution. 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (1) (7.9 mg, _0.035 mmol) was dissolved in DMF (50 μL) at 65 °C, and 1.3 μL of this solution was added dropwise to 1 mL of the _{FA0.75MA0.25SnI3 precursor} solution. By adding reducing agent 1, the yellow FA _0.75 MA _0.25 SnI ₃ precursor solution changed to a dark green suspension. After stirring for 15 min at 45 °C, the suspension turned yellow again and a precipitate with a metallic luster was formed. The precipitate was removed by filtration using a PTFE filter to obtain the precursor solution (0.1 mol% reducing agent 1 added relative to SnI ₂ ). In a similar manner, solutions in which reducing agent 1 was added at 1.0 and 10.0 mol% relative to SnI ₂ were obtained.

Precursor solution (2): Perovskite precursor solution containing reducing agent 2 _SnI2 (1341 mg, 3.6 mmol), FAI (464 mg, 2.7 mmol), MAI (143 mg, 0.9 mmol), and _SnF2 (56 mg, _0.36 mmol) were dissolved in ultra-dehydrated DMSO (4.0 mL) at 45 °C in a glove box. After stirring at 45 °C for 1 h, the mixture was filtered using a PTFE filter to prepare a _{FA0.75MA0.25SnI3 precursor} solution (0.9 M). 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2) (9.9 mg, 0.035 mmol) was dissolved in DMF (50 μL) at 65 °C, and 1.3 μL of this solution was added dropwise to 1 mL of the FA _0.75 MA _0.25 SnI ₃ precursor solution. The yellow FA _0.75 MA _0.25 SnI ₃ precursor solution changed to a dark green suspension upon addition of the reducing agent 2. After stirring for 15 min at 45 °C, the suspension turned yellow again and a precipitate formed. The precipitate was removed by filtration using a PTFE filter to obtain the precursor solution (0.1 mol% reducing agent 2 added relative to SnI ₂ ). In the same manner, solutions were obtained in which the reducing agent 2 was added at 1.0 and 10.0 mol% relative to SnI ₂ .

Fabrication of an inverted tin-containing perovskite solar cell A patterned transparent conductive glass substrate (ITO, 25 mm × 25 mm, 5 Ω, Geomatec Co., Ltd. Japan) was ultrasonically cleaned with 1 w% neutral detergent solution, acetone, and 2-propanol, in that order, for 10 min each, and finally, UV ozone cleaning was performed for 15 min.

After filtering the aqueous dispersion of PEDOT:PSS (Clevious P VP AI 4083) through a PTFE filter, about 400 μL was applied onto an ITO substrate and spin-coated (500 rpm with a slope of 1 s, spin-coated for 9 s, then 4000 rpm with a slope of 1 s, spin-coated for 60 s, and stopped with a slope of 1 s). The substrate was then heated at 140 °C to deposit a PEDOT:PSS layer (hole transport layer) with a thickness of about 20 nm. The resulting substrate was placed in a glove box for the subsequent deposition of the perovskite layer.

In the same manner as in the preparation of the perovskite precursor solution (1), the perovskite precursor solutions were prepared by adding the reducing agent 1 at 0.1, 0.5, 1.0, and 5.0 mol% relative to _SnI2 . Approximately 200 μL of this solution was applied to the PEDOT:PSS substrate by spin coating, and during this process, chlorobenzene heated to 65 °C was added for 300
(The 5000 rpm ramp was set to 5 seconds, and chlorobenzene was dropped between the last 2 and 1 seconds of the 60-second spin coating, with the ramp stopped at 1 second.) The brown film was annealed at 45 °C for 10 minutes, 65 °C for 10 to 30 minutes, and then 100 °C for 5 minutes and 100 °C for 30 minutes to produce a black perovskite layer.
On the obtained perovskite film, C ₆₀ (20 nm), BCP (8 nm), and Ag (100 nm) were laminated by vacuum deposition to fabricate an inverted-type tin-containing perovskite solar cell element.

SEM observation of the perovskite film surface confirmed that the morphology of the perovskite crystals did not change with the addition of reducing agent 1 or with different amounts of reducing agent 1, and that a dense film with high surface coverage was obtained in both cases (Fig. 5). When the solar cell characteristics were evaluated under an inert gas atmosphere, the short-circuit current density (J _sc (current density J when voltage is 0 V)) and open-circuit voltage (V _oc (voltage V when current density J = 0)) were improved in the device with the addition of reducing agent 1, and the photoelectric conversion efficiency (PCE) reached a maximum of 7.05% by adding 0.5 mol% of reducing agent 1 (Fig. 6, Table 1).

Fabrication of an inverted tin-containing perovskite solar cell In the same manner as in the preparation of the perovskite precursor solution (2), perovskite precursor solutions were obtained in which the reducing agent 2 was added at 0.5, 1.0, 5.0, and 10.0 mol% relative to _SnI2 . Using this, an inverted tin-containing perovskite solar cell element was fabricated in the same manner as in Example 2.
SEM observation of the perovskite film surface confirmed that the morphology of the perovskite crystals did not change with the addition of reducing agent 2 or with different amounts, and that a dense film with high surface coverage was obtained in both cases (Fig. 7). When the solar cell characteristics were evaluated under an inert gas atmosphere, the addition of reducing agent 2 improved J _sc , and the PCE reached a maximum of 8.45% by adding 1.0 mol% of reducing agent 2 to SnI ₂ (Fig. 8, Table 2). The increase in J _sc is believed to be due to the suppression of carrier recombination in the perovskite layer.

Confirmation of reproducibility In the same manner as in the preparation of perovskite precursor solution (2), a perovskite precursor solution was prepared in which reducing agent 2 was added at 1.0 mol% relative to _SnI2 , and in which no reducing agent was added. Using these, 20 pieces of each of inverted tin-containing perovskite solar cell elements were fabricated in the same manner as in Example 2. The solar cell characteristics of these were evaluated under an inert gas atmosphere. As a result, an increase in _Jsc due to the addition of reducing agent 2 was confirmed with good reproducibility, and _Voc and FF showed almost the same values.
(Figs. 9, 10, and 11) As a result, it was found that the PCE improved from 6.9% to 7.5% on average (Fig. 12).

Thickening of Perovskite Layer A tin-containing perovskite solar cell element having an inverted structure was fabricated in the same manner as in Example 2 using the perovskite precursor solution (3) prepared as described below.
SEM observation of the perovskite film surface revealed that the grain size of the perovskite crystals increased from approximately 500 nm to approximately 1 μm by increasing the concentration of the precursor solution from 0.9 M to 1.2, 1.3, and 1.4 M. In addition, it was confirmed that the morphology of the perovskite crystals did not change with or without the addition of reducing agent 2, and that a dense film with a high surface coverage was obtained in all cases (Figure 13).
In addition, cross-sectional SEM observation of the obtained element revealed that the thickness of the perovskite layer increased from 210 nm (0.9 M) to 450 nm (1.4 M) by increasing the concentration of the precursor solution from 0.9 M to 1.2, 1.3, and 1.4 M (Figure 14).
The solar cell characteristics of the obtained device were evaluated under an inert gas atmosphere, and it was found that the addition of reducing agent 2 improved _Jsc regardless of the concentration of the precursor solution (1.2, 1.3, 1.4 M) used (Fig. 15, Table 3). Furthermore, _Jsc increased in correlation with the increase in film thickness, and the device fabricated using a 1.4 M precursor solution containing 1.0 mol% of reducing agent 2 relative to _SnI2 showed the highest PCE of 8.14% in this study. This result demonstrated that the extension of the carrier lifetime enables efficient charge recovery even when a thick perovskite layer of about 450 nm is used.

The perovskite precursor solution (3) was obtained as follows.

Precursor solution (3): Perovskite precursor solution with reducing agent 2 _SnI2 (1341 mg, 3.6 mmol), FAI (464 mg, 2.7 mmol), MAI (143 mg, 0.9 mmol), and _SnF2 (56 mg, _0.36 mmol) were dissolved in ultra-dehydrated DMSO (3.0 mL) at 45 °C in a glove box. After stirring at 45 °C for 1 h, the solution was filtered using a PTFE filter to prepare a _{FA0.75MA0.25SnI3} precursor solution (1.2 M). In the same manner, _{FA0.75MA0.25SnI3 precursor} solutions ( _1.3 M and 1.4 M) were also prepared _.
A FA _0.75 MA 0.25 SnI 3 precursor solution (1.2 M) was prepared. 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2) (9.9 mg, 0.035 mmol) was dissolved in DMF (50 μL) at ₆₅ °C, and 17 μL of the solution was added dropwise to 1 mL of FA 0.75 MA _0.25 SnI ₃ precursor solution (1.2 M). The yellow FA _0.75 MA _0.25 SnI ₃ precursor solution changed to a dark green suspension upon addition of reducing agent 2. After stirring for 15 min at 45 °C, the suspension turned yellow again and a precipitate formed. The precipitate was removed by filtration using a PTFE filter, and a FA _0.75 MA _0.25 SnI ₃ precursor solution (1.2 M) containing 1.0 mol% reducing agent 2 was obtained. Similarly, FA _0.75 MA _0.25 SnI ₃ precursor solutions (1.3 M and 1.4 M) containing 1.0 mol% of reducing agent 2 were prepared.

Optimization of the method of adding reducing agent 2 In a glove box, (1) _SnI2 (335 mg, 0.9 mmol), FAI (116 mg, 0.7 mmol), MAI (36 mg, 0.2 mmol), _SnF2 (14 mg, 0.09 mmol), (2) _SnI2 (335 mg, 0.9 mmol), (3) _SnF2 (14 mg, 0.09 mmol), (4) _SnI2 (335 mg, 0.9 mmol), FAI (116 mg, 0.7 mmol), MAI (36 mg, 0.2 mmol), and _SnF2 (14 mg, 0.09 mmol) were dissolved in ultra-dehydrated DMSO (1.0 mL) at 45 °C, and (1) and (4) DMSO solutions of the FA _0.75 MA _{0.25 SnI3} precursor (0.9 (1) DMSO solution of _SnI2 (0.9 M), and (2) DMSO solution of _SnF2 (0.09 M) were prepared.

2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2) (9.9 mg, 0.035 mmol) was dissolved in DMF (50 μL) at 65 °C, and 13 μL of this solution was added dropwise to 1 mL of solutions (2), (3), and (4). FAI (116 mg, 0.7 mmol), MAI (36 mg, 0.2 mmol), and _SnF2 (14 mg, 0.09 mmol) were added to (2), and _SnI2 (335 mg, 0.9 mmol), FAI (116 mg, 0.7 mmol), and MAI (36 mg, _0.2 mmol) were added to ( ₃ ) to prepare a _{FA0.75MA0.25SnI3} precursor solution (0.9 M). Using these solutions (1) to (4), a perovskite layer was formed on a quartz substrate in the same manner as in Example 1.

SEM observation of the surface of the obtained perovskite film revealed that the grain size of the perovskite crystals had increased to approximately 2 μm only when reducing agent 2 was added to the DMSO solution of SnI ₂ (Entry (2)) (Figure 16-2).

PL and time-resolved PL measurements showed that the PL spectrum of only Entry (2) was shifted to shorter wavelengths by about 0.02 eV and the full width at half maximum was broadened to 104 meV (Fig. 17). The shift to shorter wavelengths is presumed to be due to the increase in the grain size of the perovskite crystals, which reduces the proportion of the crystal surface area that is likely to become a recombination site. In addition, the emission lifetime was extended to 19.0 ns and 16.8 ns when reducing agent 2 was added to the DMSO solution of _SnI2 and FAI + MAI + _SnI2 + _SnF2 (Entry (2) and (4)), respectively, but the increase in the grain size of the perovskite crystals is thought to have contributed greatly to the results of Entry (2) (Fig. 18).

Using these precursor solutions (1), (2), and (4), a perovskite layer was formed on a PEDOT:PSS substrate in the same manner as in Example 2. SEM observation of the surface of the obtained perovskite film revealed that perovskite crystals with a grain size of 1 μm or less were formed regardless of which precursor solution was used (Figure 19). When the solar cell characteristics were evaluated for the inverted structure device fabricated in the same manner as in Example 2 using these films, the best PCE (8.0%) was obtained when reducing agent 2 was added to a DMSO solution of FAI + MAI + _SnI2 + _SnF2 (Entry (4)) (Figure 20, Table 4).

Measurement of optical properties of I-Br mixed perovskite film Using the I-Br mixed perovskite precursor solution (4) containing 0.0 to 25% Br ⁻ , prepared as described below, a perovskite layer was formed on a quartz substrate in the same manner as in Example 1, and PL measurements and time-resolved PL measurements were performed.
From PL and time-resolved PL measurements, it was confirmed that the addition of reducing agent 2 significantly lengthened the fluorescence lifetime of all I-Br mixed perovskite films while maintaining the fluorescence wavelength, from approximately 2 ns to a maximum of ₁₁ ns (Figures ₂₁ and 22). This suggests that, as in the case of _{FA0.75MA0.25SnI3} , the recombination of carriers generated by photoexcitation was suppressed while the structure and composition of the perovskite were maintained.

The perovskite precursor solution (4) was obtained as follows.

Precursor solution (4): I-Br mixed perovskite precursor solution . SnI ₂ (335 mg, 0.9 mmol), FABr (84 mg, 0.7 mmol), MAI (36
SnF 2 (14 mg, 0.09 mmol) and SnF ₂ (14 mg, 0.09 mmol) were dissolved in ultra-dehydrated DMSO (1.0 mL) at 45 °C. After stirring at 45 °C for 1 h, the solution was filtered using a PTFE filter to prepare a FA _0.75 MA _0.25 Sn(I _0.75 Br _0.25 ) ₃ precursor solution containing 25% Br. In the same manner, FA _0.75 MA _0.25 Sn(I _0.95 Br _0.05 ) ₃ and FA _0.75 MA _0.25 Sn(I _0.80 Br _0.10 ) ₃ precursor solutions containing 5% and 10% Br, respectively, were prepared. In addition, 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2) (9.9 mg, 0.035 mmol) was dissolved in DMF (50 μL) at 65 °C, and 6.5 μL of this solution was added dropwise to 500 μL of FA _0.75 MA _0.25 Sn(I _1－x Br _x ) ₃ (x=0.0, 0.05, 0.10, 0.25) precursor solution. The addition of reducing agent 2 gave yellow FA _0.75 MA _0.25 Sn(I _1－x Br _x ) ₃ (x=0.0, 0.05, 0.10, 0.25) precursor solution.
The precursor solution changed to a deep green suspension. After stirring for 15 minutes at 45°C, the suspension turned yellow again and a precipitate formed. The precipitate was removed by filtration using a PTFE filter to obtain a precursor solution containing 1.0 mol% of reducing agent 2 relative to _SnI2 (calculated): _{FA0.75MA0.25Sn} (I1 _{- xBrx} ) ₃ ( _x =0.0, 0.05, 0.10, 0.25).

A transparent conductive glass substrate (FTO, 25 mm × 25 mm, Asahi Glass Co., Ltd., Japan) with a pattern of tin-containing perovskite solar cells with a normal structure was ultrasonically cleaned in a 1w% neutral detergent solution, acetone, 2-propanol, and distilled water, for 10 min each, and then UV ozone cleaning for 15 min.
1 mL of titanium di(isopropoxide)bis(acetylacetonate) (Ti(OiPr) ₂ (acac) ₂ , 75% by mass solution in 2-propanol, Tokyo Chemical Industry Co., Ltd., Japan) was added to 39 mL of ethanol (wako, ultra-dehydrated). The above FTO substrates (transparent electrodes) were arranged on a hot plate at 450 °C, and Ti(OiPr) ₂ (acac) ₂ solution was sprayed (carrier gas: _N2 , 0.5 MPa) to fabricate a _compact TiO2 layer (approximately 30 nm). The resulting substrate was then immersed in 100 mL of an aqueous solution of _TiCl4 (440 μL, special grade, Wako Pure Chemical Industries Ltd., Japan) at 70 °C for 30 min. The substrate was then baked at 500 °C for 20 min to form a (hole) blocking layer.

On the obtained compact _TiO2 layer (hole-blocking layer), approximately 190 μL of an ethanol solution (paste:ethanol = 1:8 (mass ratio)) of _TiO2 paste (PST-18NR, JGC Catalysts and Chemicals Ltd.) was dropped and spin-coated to form a mesoporous _TiO2 layer (electron transport layer) with a thickness of approximately 100 to 150 nm.

The substrate, which had just been treated with UV ozone and had been fabricated with a mesoporous TiO2 _layer (electron transport layer), was placed in a glove box. Approximately 200 μL of the perovskite precursor solution (4) was applied to the PEDOT:PSS substrate and spin-coated. During this process, 300 μL of chlorobenzene heated to 65 °C was dropped to obtain a brown film (5 s ramp at 5000 rpm, 60 s spin-coated, and chlorobenzene was dropped between the last 2 and 1 s, and the ramp was stopped at 1 s). The brown film obtained was annealed at 45 °C for 10 min, 65 °C for 10–30 min, and then 100 °C for 5 min and 100 °C for 30 min to produce a black perovskite layer.

A hole transport material (PTAA; poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], 20.2 mg) and 4-isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (TPFB, 2.7 mg) were dissolved in 1 mL of chlorobenzene. After stirring for 30 min, the solution was filtered through a membrane filter, and the filtrate was spin-coated on the perovskite layer. The resulting substrate was annealed at 70 °C for 5 min to form a hole transport layer, and then an 80 nm gold electrode was deposited on the hole transport layer by vacuum deposition to obtain a tin-containing perovskite solar cell with a normal structure.

When the solar cell characteristics were evaluated under an inert gas atmosphere, the addition of reducing agent 2 improved _Jsc , and the PCE was 2.9%, the highest in this study, in the device fabricated using the _{FA0.75MA0.25Sn} ( _I0.95Br0.05 ) ₃ precursor solution to which reducing agent ₂ was added at 1.0 mol% relative to _SnI2 ( _equivalent ) (Fig. 23, Table 5) _. In addition, when the external quantum yield (EQE) of each device was measured, the device fabricated using the _{FA0.75MA0.25Sn} ( _{I1―xBrx ) 3} (x=0.0, 0.05) precursor solution to which reducing agent 2 was added at 1.0 mol% relative to _SnI2 ( _equivalent ) showed a high IPCE of over 80% (Fig. 24).

In a glove box for ¹¹⁹ Sn NMR measurements , (1) SnI ₂ (88 mg, 0.24 mmol) and (2) SnF ₂ (88 mg, 0.56 mmol) were
(3) _SnI (88 mg, 0.14 mmol), (4) _SnI (88 mg, 0.14 mmol) and _SnF (22 mg, 0.14 mmol) were dissolved in approximately ⁷⁵⁰ μL of DMSO-d ₆ .
NMR measurements (224 MHz, Bruker Avance III 600US Plus NMR) were performed. After that, 1 equivalent of reducing agent 2 was added to each of them in the glove box, and ¹¹⁹ Sn NMR measurements were performed.

First, for (1), a peak derived from _SnI2 was obtained both before and after the addition of reducing agent 2, indicating that reducing agent 2 does not have a high reactivity with _SnI2 (Fig. 25). On the other hand, for (2), the peak derived from _SnF2 disappeared after the addition of reducing agent 2, which suggests that divalent tin in the solution was reduced and precipitated as solid zero-valent tin, suggesting that reducing agent 2 has a high reactivity with _SnF2 (Fig. 26).

Regarding this phenomenon, a suspension obtained by adding reducing agent 2 to a DMSO solution of _SnF2 (0.09 M) was observed with a transmission electron microscope, and it was confirmed that nanoparticles with a particle size of up to about 15 nm were formed (Figure 27).

Next, regarding (3), after the addition of reducing agent 2, in addition to the peaks derived from _SnI4 , a small peak derived from _SnI2 was obtained, confirming that _SnI4 was partially reduced by reducing agent 2 (Fig. 28). Regarding (4), after the addition of reducing agent 2 in the presence of _SnF2 , the peaks derived from tetravalent tin completely disappeared, and only the peaks derived from _SnI2 were obtained (Fig. 29). This result suggests that tetravalent tin was effectively reduced by reacting highly reactive zerovalent Sn nanoparticles generated by the reduction of _SnF2 with _SnI4 in the system.

Effect of adding Et3SiH on optical properties and solar cell characteristics A perovskite precursor solution (5) containing 0.0 to 10.0 mol% _Et3SiH added to _SnI2 , prepared as described below, was used to form _a perovskite layer on a quartz substrate in the same manner as in Example 1, and time-resolved PL measurements were performed.
As a result, it was found that the fluorescence lifetime was extended from 5.9 ns to 8.0 ns by adding 1.0 mol% of Et ₃ SiH to SnI ₂ (Figure 30). This is expected to be because the addition of Et ₃ SiH reduces the number of Sn ^{4+ ions} that act as recombination centers.

Next, a tin-containing perovskite solar cell element with an inverted structure was fabricated in the same manner as in Example 2 using the perovskite precursor solution (5). From the surface SEM images of the obtained perovskite film, it was found that the addition of Et ₃ SiH or its amount did not affect the perovskite crystal morphology (Fig. 31). When the solar cell characteristics were evaluated under an inert gas atmosphere, as expected from the results of the time-resolved PL measurement, the addition of Et ₃ SiH increased J _sc , and the PCE was maximized (5.31%) when Et ₃ SiH was added at 1.0 mol% relative to SnI ₂ (Fig. 32). This result suggests that the recombination of carriers generated in the perovskite layer was suppressed.

Precursor solution (5): Perovskite precursor solution with Et ₃ SiH added. SnI ₂ (1341 mg, 3.6 mmol), FAI (464 mg, 2.7 mmol), MAI (143 mg, 0.9 mmol), and SnF ₂ (56 mg, 0.36 mmol) were dissolved in ultra-dehydrated DMSO (4.0 mL) at 45 °C in a glove box. After stirring at 45 °C for one hour, the solution was filtered using a PTFE filter to prepare the FA _0.75 MA _0.25 SnI ₃ precursor solution. 1.4 μL of degassed and dehydrated Et ₃ SiH was added dropwise to 1 mL of the FA _0.75 MA _0.25 SnI ₃ precursor solution. After stirring at 45 °C for 15 minutes, the solution was filtered using a PTFE filter to obtain the precursor solution (1.0 mol% Et ₃ SiH added relative to SnI ₂ ). Similarly, solutions were obtained in which Et ₃ SiH was added at 5.0 and 10.0 mol% relative to SnI ₂ .

Preparation of perovskite films using the scavenger method In a glove box (Ar gas, O ₂ < 0.1 ppm, H ₂ O < 0.1 ppm), SnI ₂ (335.3 mg,
0.90 mmol) or SnI ₂ (dmf) complex (401.0 mg, 0.90 mmol), FAI (116.1 mg, 0.68 mmol), MAI (35.8 mg, 0.23 mmol), and SnF ₂ (14.1 mg, 0.09 mmol, 10 mol%) were dissolved in ultra-dehydrated DMSO (1.0 mL). The mixture was stirred at 45 °C for 30 min to obtain a 0.9 M FA _0.75 MA _0.25 SnI ₃ precursor solution. This solution was purified by a scavenger method. Specifically, a 0.9 M DMF solution (10 μL, 0.09 mmol, 1 mol%) of the reducing agent 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (TM-DHP) was added dropwise to the precursor solution. The addition of the reducing agent TM-DHP caused the solution to change from a yellow solution to a yellow-gray suspension (Figure 33). After stirring for 15 minutes at 45 °C, the suspension became yellow again, and a precipitate with a metallic luster was formed. After stirring for another 15 minutes, the precipitate was removed by filtration using a PTFE filter. About 200 μL of this solution was applied to a PEDOT:PSS substrate and spin-coated, during which 300 μL of chlorobenzene heated to 65 °C was dropped onto it to obtain a brown film (5 sec ramp at 5000 rpm, 60 sec spin-coating, chlorobenzene dropped between the last 2 and 1 sec, and the ramp was stopped at 1 sec). The brown film obtained was annealed at 45 °C for 10 min, 65 °C for 10-30 min, and 100 °C for 10 min to produce a black perovskite layer.

Fig. 33 is a photograph in lieu of a drawing showing the state of the scavenger treatment. Fig. 33 shows photographs of the precursor solution before (left), immediately after (middle), and after 15 minutes of stirring (right) of the reducing agent TM-DHP.

The surface and cross-sectional SEM observations were performed on perovskite thin films prepared using precursor solutions that were not scavenger-treated and precursor solutions that were scavenger-treated. An SU8010 (Hitachi High-Technologies Co.) was used for the SEM observations.

Figure 34 shows SEM images in lieu of drawings, showing (a) the surface and (b) the cross section of a tin-containing perovskite thin film. Figure 34 shows that the morphology of the thin film hardly changes even when the scavenger treatment is performed, and a thin film with a thickness of about 190 nm and a high surface coverage can be obtained.

Quantification of Sn4 ⁺ by XPSTo quantify the amount of Sn4 ⁺ species contained in the perovskite thin film, X-ray photoelectron spectroscopy (XPS) measurements were performed. An ESCA-3400HSE (Shimadzu Co.) was used for the XPS measurements. To minimize the effect of air exposure when setting the sample, a 20 nm thick BCP protective layer was evaporated onto the perovskite thin film to prepare the measurement sample.

Fig. 35 shows a diagram for quantitatively evaluating tin ions contained in a perovskite thin film, in which (a) shows a cross-sectional SEM image in place of a drawing, and (b) shows a Sn 3d ^5/2 XPS spectrum of the tin-containing perovskite thin film.

As shown in Fig. 35(a), cross-sectional SEM observation of a sample from which only the protective layer was removed by argon etching revealed that the film thickness of the perovskite layer was approximately 190 nm. As shown in Fig. 35(b), the Sn 3d ^5/2 spectrum of this sample revealed that the amount of Sn ⁴⁺ on the surface of the perovskite thin film was reduced from 6.6% to 4.7% by using the scavenger method. One or more 5 mm square measurement samples were then obtained from near the center of gravity (center of the surface) of the 2.5 cm square measurement sample, and XPS measurements were performed using the obtained 5 mm square measurement samples.

Next, to estimate the amount of Sn ⁴⁺ inside the perovskite film, the thin films prepared using the scavenger method were argon etched for 4 or 8 seconds at an applied voltage of 0.5 V and an emission current of 20 mA. As shown in Fig. 35(a), the thicknesses of the perovskite layers in these samples were approximately 170 nm (depth 20 nm) and 150 nm (depth 40 nm), respectively. As shown in Fig. 35(b), the Sn 3d ^5/2 spectrum revealed that the amount of Sn ⁴⁺ inside the perovskite was less than that on the surface, decreasing to 1.2% at a depth of 20 nm and 0.0% at a depth of 40 nm.

Optical properties measurements The perovskite film formed on a quartz substrate by the method described above was placed in an argon-filled sample case, and fluorescence (PL) measurements and time-resolved PL measurements were performed. A picosecond laser pulse (wavelength 688 nm, Advanced Laser Diode Systems Co., Ltd) was used as the excitation light for the measurements. The excitation density at the sample position was 127 nJ/ ^cm2 , and measurements were performed under weak excitation conditions. PL spectra were measured using a spectrometer and a nitrogen-cooled CCD camera (Princeton Instruments). In the time-resolved PL measurements, PL from the sample was detected with an avalanche photodiode (IDQ Co., Ltd), and a time-resolved decay curve was obtained using a time-correlated single-photon counting board (Becker and Hickl Co., Ltd).

36 is a graph instead of a drawing showing the results of measuring the optical properties of a tin-containing perovskite thin film, in which (a) shows the fluorescence spectrum and (b) shows the time-resolved decay curve.

As shown in Figures 36(a) and 36(b), PL measurements and time-resolved PL measurements revealed that when the scavenger method was used, the fluorescence intensity increased by about two times without changing the peak position, and the fluorescence lifetime was significantly extended from 4.0 ns to 14.3 ns. This result suggests that the recombination of carriers generated by photoexcitation was suppressed while maintaining the structure and composition of the perovskite.

^119Sn NMR measurements
One equivalent of the reducing agent TM-DHP was added to a DMSO- _d6 solution of _SnBr4 and _SnCl4 , and ^119Sn NMR measurements (224 MHz, Bruker Avance III 600US Plus NMR) were performed. The results are shown in FIG.

FIG. 37 is a diagram relating to elucidation of the mechanism by scavengers.
FIG. 37(a) is a graph instead of a drawing showing the results of NMR measurement indicating the presence of divalent tin and _tetravalent tin in a DMSO-d solution of _SnF2 before (upper row) and after (lower row) the addition of TM-DHP, and is the same as the graph in FIG. 26.
FIG. 37(b) is a graph instead of a drawing showing the results of NMR measurement indicating the presence of divalent tin and _tetravalent tin in a DMSO-d solution of _SnI2 before (upper row) and after (lower row) the addition of TM-DHP, and is the same as the graph in FIG. 25.
FIG. 37(c) is a graph instead of a drawing showing the results of NMR measurement indicating the presence of divalent tin and _tetravalent tin in a DMSO-d solution of _SnBr2 before (upper row) and after (lower row) the addition of TM-DHP.
FIG. 37(d) is a graph instead of a drawing showing the results of NMR measurement indicating the presence of divalent tin and tetravalent tin in a DMSO- _d solution of _SnCl2 before (upper row) and after (lower row) the addition of TM-DHP.
FIG. 37(e) is a photograph, instead of a drawing, showing a solution of _SnF2 in DMSO- _d6 before (left) and after (right) the addition of TM-DHP.
FIG. 37( f ) is a TEM photograph in place of a drawing showing Sn ⁰ nanoparticles formed after the addition of TM-DHP (right), which is the same as the TEM photograph of FIG. 27 .

As shown in Fig. 37(a), when TM-DHP was added to a solution in which _only SnF2 was dissolved, the peak derived from _SnF2 completely disappeared. Regarding this phenomenon, when the suspension obtained immediately after adding the reducing agent TM-DHP (Fig. 37(e)) was observed with a transmission electron microscope (TEM), it was found that nanoparticles with a particle size of 15 nm or less were formed, as shown in Fig. 37(f).

As shown in Figure 37(b), _SnI2 was not reduced by TM-DHP. Therefore, it is considered that the reduction of _SnI4 occurs in two steps: (i) the generation of ^Sn0 nanoparticles by selective reduction of _SnF2 by TM-DHP, and (ii) the reduction of _SnI4 on the surface of the ^Sn0 nanoparticles. Furthermore, as shown in Figures 37(c) and 37(d), _SnBr2 and _SnCl2 were not reduced by TM-DHP either, confirming the selectivity for _SnF2 .

Therefore, it can be said that the tin-containing perovskite layer preferably contains not only I but also F. It is considered that the atomic ratio I/F of I to F may be 0.1 to 10, 0.2 to 8, 0.3 to 7, 0.5 to 4, or 0.5 to 2.

Fabrication of Perovskite Solar Cells A patterned transparent conductive glass substrate (ITO, 25 mm × 25 mm, 10 Ω, Geomatec Co., Ltd. Japan) was ultrasonically cleaned in water, acetone, cleaning solution (Semicoclean 56, Furuuchi Chemical), water, and 2-propanol for 15 minutes each, and then plasma treatment was performed. PEDOT:PSS
After filtering the aqueous dispersion of (Clevious P VP AI 4083) through a PVDF filter, about 400 μL was applied onto an ITO substrate and spin-coated (500 rpm with a slope of 1 s, spin-coated for 9 s, then 4000 rpm with a slope of 1 s, spin-coated for 60 s, and stopped at a slope of 1 s). The substrate was then heated at 140 °C for 20 min in a glove box and another 20 min at 140 °C to form a PEDOT:PSS layer (hole transport layer) with a thickness of about 20 nm. A perovskite layer was formed on the PEDOT:PSS layer by the method described above. C60 (20 nm) (electron transport layer), BCP
(8 nm) was deposited by vacuum deposition, and finally, Ag (100 nm) was deposited by vacuum deposition as a metal electrode. The solar cell characteristics were evaluated under an inert gas atmosphere. The results are shown in Figure 38 and Table 6.

Figure 38 is a graph showing the characteristics of a perovskite solar cell, instead of a drawing, in which (a) shows a current density-voltage curve, and (b) shows the distribution of photoelectric conversion efficiency (PCE) of 40 cells.

From Fig. 38 and Table 6, it was found that the average photoelectric conversion efficiency (PCE) was improved from 6.6% to 8.9% when the scavenger method was used. As shown in Table 6, the short circuit current density (J _SC ) as well as the open circuit voltage (V _OC ) and fill factor (FF) increased, which indicates that the carrier recombination was effectively suppressed. As shown in Fig. 38(a), the champion cell using the scavenger method achieved a conversion efficiency of 9.9% (J SC = 21.1 mA cm ^-2 , V OC = 0.63 V, FF = 0.74). Also, as shown in Fig. 38(b), the histogram of the conversion efficiencies of 40 cells confirmed that high reproducibility was obtained.

Improving photoelectric conversion efficiency by surface treatment The open circuit voltage (VOC) of the tin-containing perovskite element was a maximum of 0.63 V even when using the scavenger method, which is still insufficient considering the band gap (1.36 eV) of FA _0.75 MA _0.25 SnI _3. We considered that the large voltage loss (0.73 V) was due to the interface between the perovskite layer and the charge transport layer. Therefore, in addition to the scavenger method, we first treated the perovskite surface with ethylenediamine (EDA) and measured various physical properties. The results are shown in Figure 39 and Table 7.

Figure 39 shows the physical properties of the surface-treated perovskite layer. Figure 39(a) is a graph replacing a drawing showing the current density-voltage curve of a tin-containing perovskite solar cell. Figure 39(b) is a diagram showing an energy level diagram. Figure 39(c) is a graph replacing a drawing showing the external quantum efficiency (EQE) and internal quantum efficiency (IQE). Figure 39(d) is a graph replacing a drawing showing the distribution of photoelectric conversion efficiency (PCE) of 30 cells.

As shown in Fig. 39(a) and Table 7, the VOC increased to 0.68 V by the surface treatment. Furthermore, a thin _PC61BM layer (less than 5 nm) was inserted to improve the energy level connection between the perovskite layer and the electron transport layer (C60) and suppress the charge recombination at the interface, as shown in Fig. 39(b). As shown in Fig. 39(c), this improved the conversion efficiency to a maximum of 11.5% (JSC = 22.0 mA cm ^-2 , VOC = 0.76 V, FF = 0.69). The integrated JSC calculated from the external quantum efficiency (EQE) spectrum was 21.6 mA cm ^-2 , which showed good agreement with the value in the J-V curve. Furthermore, as shown in Fig. 39(d), the histogram of the conversion efficiency of 30 cells confirmed that the average PCE was 10.2 ± 0.8%, which was highly reproducible.

This shows that a preferable solar cell or organic EL device can be obtained by cleaning the surface of the perovskite layer, which is the interface between the perovskite layer and the electron transport layer, with an amine solvent such as ethylenediamine. Therefore, this specification also provides a method for manufacturing a solar cell or an organic EL device, which includes a step of treating the surface of the perovskite layer with a solvent (e.g., cleaning treatment), and then forming a layer (e.g., an electron transport layer) on the surface of the treated perovskite layer.

Effect of scavenger method on ASnI3 _- XBrX _system [Preparation of MASnI3 _{-XBrX perovskite} films (X = 1.5, 3) using the scavenger method]
In a glove box (Ar gas, O ₂ < 0.1 ppm, H ₂ O < 0.1 ppm), SnI ₂ (372.5 mg,
1.0 mmol), MAI (159.0 mg, 1.0 mmol), and _SnF2 (14.1 mg, 0.10 mmol, 10 mol%) were dissolved in ultra-dehydrated DMSO (1.0 mL). The mixture was stirred at 45 °C for 30 min to obtain a 1.0 M MASnI3 _precursor solution. _SnBr2 (278.5 mg, 1.0 mmol) or _SnBr2 (dmf) complex (351.6 mg, 1.0 mmol), MABr (112.0 mg, 1.0 mmol), and _SnF2 (14.1 mg, 0.10 mmol, 10 mol%) were dissolved in ultra-dehydrated DMSO (1.0 mL). The mixture was stirred at 45 °C for 30 min to obtain _a 1.0 M MASnBr3 precursor solution.
500 μL _each of the _MASnI3 precursor solution and the 1.0 _{M MASnBr3} precursor solution was mixed to prepare a 1.0 M _{MASnI1.5Br1.5} precursor solution.

A 1.0 M DMF solution (10 μL, 0.10 mmol, 1 mol%) of the reducing agent 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (TM-DHP) was added to 1.0 _mL of the above 1.0 M MASnI _1.5 Br _1.5 solution and 1.0 M MASnBr 3 solution, and the mixture was stirred at 45 °C for 30 min and then filtered using a PTFE filter. Approximately 200 μL of this solution was applied to a quartz substrate and spin-coated, during which 300 μL of chlorobenzene heated to 65 °C was dropped to obtain a brown film (slope was set to 5000 rpm for 5 seconds, and chlorobenzene was dropped between the last 2 and 1 seconds of the 60-second spin coating, and the slope was stopped at 1 second). The obtained brown film was then heated at 45 °C for 10 minutes, 65 °C for 10 to 30 minutes, and 100 μL of chlorobenzene was dropped to obtain a brown film (slope was set to 5000 rpm for 5 seconds, and chlorobenzene was dropped between the last 2 and 1 seconds of the 60-second spin coating, and the slope was stopped at 1 second).
The film was then annealed at ℃ for 10 min to produce a brown perovskite layer.

[Fluorescence properties of MASnI3 _{-XBrX perovskite} films (X = 1.5, 3)]
The perovskite film formed on a quartz substrate by the above method was placed in a sample case filled with argon, and fluorescence (PL) and time-resolved PL measurements were performed. A picosecond laser pulse (wavelength 406 nm, Advanced Laser Diode Systems Co., Ltd) was used as the excitation light for the measurements. The excitation density at the sample position was 782 nJ/ _cm2 for _{MASnI1.5Br1.5} and 10 ^μJ / ^cm2 for _MASnBr3 , and measurements were performed under weak excitation conditions. PL spectra were recorded using a spectrometer and a nitrogen-cooled CCD camera (Princeton
For time-resolved PL measurements, the PL from the sample was detected with an avalanche photodiode (IDQ Co., Ltd), and time-resolved decay curves were obtained using a time-correlated single-photon counting board (Becker & Hickl Co., Ltd).

PL and time-resolved PL measurements of _{MASnI1.5Br1.5 perovskite} films showed that the fluorescence intensity increased by about 10 times and the fluorescence lifetime was significantly extended from 0.78 ns to 2.28 ns when the scavenger method was used, without changing the peak position (Fig. 40). This result suggests that the recombination of carriers generated by photoexcitation was suppressed while maintaining the structure and composition of the perovskite. In addition, for _MASnBr3 perovskite films, the fluorescence lifetime was shorter than the detection limit, but the fluorescence intensity was increased by about 3 times when the scavenger method was used (Fig. 42).

[Quantitative analysis of Sn4 ⁺ by XPS]
X-ray photoelectron spectroscopy (XPS) measurements were performed to quantify the amount of Sn ⁴⁺ species contained in the perovskite thin film. A JPS-9010 (JEOL) was used for the XPS measurements. The samples were set in an argon-filled transfer vessel, so that the measurements were performed without exposing the samples to air.

For the _{MASnI1.5Br1.5 perovskite} thin film, the amount of Sn4 ⁺ was estimated from the Sn 3d5 ^/2 spectrum, and it was found that the amount of Sn4 ⁺ on the surface of the perovskite film was reduced from 2.4% to 0.4% by using the scavenger method (Fig. 42). Furthermore, when the amount of Sn4 ⁺ inside the film prepared using the scavenger method was estimated by argon etching, it was found that the amount of Sn4 ⁺ was 0.0% at a depth of 40 nm (Fig. 42).

[Fabrication of perovskite solar cells]
The patterned transparent conductive glass substrate (ITO, 25 mm × 25 mm, 10 Ω, Geomatec Co., Ltd. Japan) was ultrasonically cleaned in water, acetone, cleaning solution (Semicoclean 56, Furuuchi Chemical), water, and 2-propanol for 15 min each, and then plasma treated. After filtering the aqueous dispersion of PEDOT:PSS (Clevious P VP AI 4083) through a PVDF filter, approximately 300 μL was applied onto the ITO substrate and spin-coated (500 rpm with a slope of 1 s, spin-coated for 9 s, then 4000 rpm with a slope of 1 s, spin-coated for 60 s, and stopped with a slope of 1 s). The substrate was then heated at 140 °C for 20 min in a glove box and then at 140 °C for another 20 min to form a PEDOT:PSS layer (hole transport layer) with a thickness of approximately 20 nm.

In a glove box (Ar gas, O ₂ < 0.1 ppm, H ₂ O < 0.1 ppm), SnI ₂ (232.8 mg,
0.625 mmol), SnBr ₂ (dmf) complex (131.9 mg, 0.375 mmol), FAI (129.0 mg, 0.75 mmol), MAI (40.0 mg, 0.25 mmol), and SnF ₂ (15.8 mg, 0.10 mmol, 10 mol%) were dissolved in ultra-dehydrated DMSO (971
The mixture was stirred at 45 °C for 30 min to obtain a 1.0 M FA _0.75 MA _0.25 SnI _2.25 Br _0.75 precursor solution. Similarly, SnI ₂ (232.8 mg, 0.625 mmol), SnBr ₂ (dmf) complex (131.9 mg, 0.375 mmol), FAI (86.0 mg, 0.50 mmol), MAI (79.5 mg, 0.50 mmol), and SnF ₂ (15.8 mg, 0.10 mmol, 10 mol%) were dissolved in ultra-dehydrated DMSO (971 μL) to obtain a 1.0 M FA _0.50 MA _0.50 SnI _2.25 Br _0.75 precursor solution. These precursor solutions were treated with TM-DHP as a scavenger, and a perovskite layer was formed on the PEDOT:PSS layer by the method described above. _{C 60} (20 nm) (electron transport layer) and BCP (8 nm) were laminated by vacuum deposition, and finally Ag (100
A thin film (nm) was formed by vacuum deposition.

When the solar cell characteristics were evaluated under an inert gas atmosphere, a conversion efficiency of 7.4% (J _SC = 17.1 mA cm ⁻² , V _OC = 0.61 V, FF _0.75 MA _0.25 SnI _2.25 Br _0.75 perovskite) was achieved.
= 0.71), and a conversion efficiency of 7.3% (J _SC = 16.9 mA cm ^-2 , V _OC = 0.58 V, FF = 0.74) was obtained using the FA _0.50 MA _0.50 SnI _2.25 Br _0.75 perovskite (Figure 43, Table 8).

2. Effect of _scavenger method on Pb _{- Sn} mixed perovskite [Preparation of _{Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3 perovskite} film using _scavenger method]
In a glove box (Ar gas, O ₂ < 0.1 ppm, H ₂ O < 0.1 ppm), SnI ₂ (335.3 mg,
SnF ₂ (14.1 mg, _0.09 mmol, 10 mol% compared to SnI ₂ ), Pb(SCN) ₂ (5.8 mg, 0.018 mmol, 2 mol% compared to PbI ₂ ) in super-dehydrated DMSO
(250 μL) and DMF (750 μL). Stirring was continued for 30 min at 45 °C to obtain a 1.8 M _{Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3} precursor solution. A 1.0 M DMF solution (9 μL, _0.09 mmol, _{1 mol} % compared to _{SnI2 )} of the reducing agent 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (TM-DHP) was added dropwise to this _solution . After stirring for 30 min at 45 °C, the solution was filtered using a PTFE filter to remove the precipitate. Approximately 200 μL of this solution was applied to a quartz substrate and spin-coated, during which 400 μL of chlorobenzene was dropped to obtain a brown film (slope 5 s at 1000 rpm, 10 s later at 4000 rpm with a slope of 3 s, and spin-coated for another 40 s. Chlorobenzene was dropped over a 1 s period 20 s after the 4000 rpm step began). The obtained brown film was annealed at 100 °C for 10 min and then stored at 65 °C until spin-coating of all substrates was completed, producing a black perovskite layer.

_{[ Fluorescence properties} of _{Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3 perovskite films} ]
The perovskite film formed on a quartz substrate by the above method was placed in an argon-filled sample case, and fluorescence (PL) and time-resolved PL measurements were performed. A picosecond laser pulse (wavelength 688 nm, Advanced Laser Diode Systems Co., Ltd) was used as the excitation light for the measurements. The excitation density at the sample position ^was 127 nJ/cm2, and measurements were performed under weak excitation conditions. PL spectra were measured using a spectrometer and a nitrogen-cooled CCD camera (Princeton Instruments). In the time-resolved PL measurements, PL from the sample was detected with an avalanche photodiode (IDQ Co., Ltd), and time-resolved decay curves were obtained using a time-correlated single-photon counting board (Becker & Hickl Co., Ltd).
PL and time-resolved PL measurements showed that when the scavenger method was used, the fluorescence intensity increased by about three times without changing the peak position, and the fluorescence lifetime was significantly extended from 1.17 μs to 1.68 μs (Figure 44). This result suggests that the recombination of carriers generated by photoexcitation was suppressed while the structure and composition of the perovskite were maintained.

[Fabrication of perovskite solar cells]
A Pb-Sn mixed perovskite solar cell was fabricated using the same device structure as the above-mentioned tin-containing perovskite solar cell. When the solar cell characteristics were evaluated in an inert gas atmosphere, a conversion efficiency of 20.1% (J _SC = 31.6 mA cm ^-2 , V _OC = 0.80 V, FF = 0.79) was obtained by using the scavenger method (Fig. 45).

[Quantitative analysis of Sn4 ⁺ by XPS]
For the _{Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3 perovskite} thin _film prepared using the scavenger method, the Sn4 ⁺ ratio was estimated from the _Sn3d5 ^/2 _spectrum and found to be 3.0% on the film surface. Furthermore, ^{the Sn4+ ratio} inside the film was estimated by argon etching _and found to be 0.3% at a depth of 40 nm (Figure 46).

The present invention relates to a method for producing a perovskite layer, and therefore can be used in industries for producing solar cells and organic EL elements.

Claims (3)

A tin-containing perovskite layer containing a tin-containing perovskite compound ,
a Sn+4 40nm value, which is the percentage of the tetravalent tin atomic content in the total of the tetravalent tin atomic content and the divalent tin atomic content in a region 40 _nm deep from the center of the surface of the tin-containing ^perovskite layer, is 0% or more and 0.5% or less;
The ratio of the Sn ⁺ 4 _surface value, which is the percentage of the tetravalent tin atomic content in the total of the tetravalent tin atomic content and the divalent tin atomic content at the surface center of the tin-containing perovskite layer to the Sn ⁺⁴ 40 _nm value, is 3 or more ;
The tin-containing perovskite layer has an average particle size of the tin-containing perovskite compound of 150 nm or more and 500 nm or less,
The tin-containing perovskite layer comprises a compound represented by formula (Ia),

(In formula (Ia), R ¹ to R ⁴ may be the same or different and each is a hydrogen atom, a methyl group, or an ethyl group, and R ⁵ to R ¹⁰ may be the same or different and each is a methyl group or an ethyl group.)
containing one or more selected from zero-valent tin, a pyrazine-based compound, a silicon-based compound including a compound represented by formula (Ia), and a germanium-based compound in a total amount of 0.01 ppm or more and 1000 ppm or less,
Solar cell . an Sn+4 20nm value, which is the percentage of the tetravalent tin atomic content in the total of the tetravalent tin atomic content and the divalent tin atomic content in a region 20 _nm deep from the center of the surface of the tin-containing ^perovskite layer, is 0.1% or more and 5% or less;
The ratio of the Sn ⁺⁴ _surface value to the Sn ⁺⁴ _{20 nm} value is 3 to 20 ,
The solar cell according to claim 1 . 2. The solar cell according to claim 1, wherein the atomic content of lead atoms relative to the content of tin atoms is 0% or more and 900% or less.

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