Method for analyzing perovskite film

Abstract

The present invention addresses the problem that, when a perovskite film is etched using Ar-GCIB, artifacts are formed, and it is thus difficult to obtain a depth profile reflecting the original distribution of a perovskite component with high depth resolution. The present invention has been made to address the problem of providing a component distribution analysis method in which an analysis usually performed at room temperature is performed under sample cooling, so as to obtain a depth profile closer to the original component distribution of a perovskite component and obtain a depth profile with high depth resolution.　The present invention is a perovskite film analysis method, wherein an etching treatment with ions is continuously or intermittently performed on a perovskite film under cooling of the perovskite film, and a component of a surface or an exposed surface of the perovskite film resulting from the etching treatment is analyzed at least once before, during, or at the end of the etching treatment.

Description

Analysis methods for perovskite films

[0001] The present invention relates to a method for analyzing perovskite films.

[0002] Perovskite solar cells are solar cells that use a material with a crystalline structure called perovskite. They are attracting attention as a next-generation novel solar cell material due to their high light energy conversion efficiency, light weight, and flexibility.

[0003] Perovskite films used in perovskite solar cells can be easily fabricated using techniques such as coating (spin coating), but the distribution of components within the film significantly affects the battery performance. In recent years, processing techniques for organic modification layers on perovskite films have been actively developed to improve the performance of perovskite solar cells (for example, Patent Document 1). Investigating the correlation between the effect of such processing techniques on the component distribution within the film and battery performance is important for designing higher-performance solar cells. Therefore, accurate analysis of the component distribution within perovskite films is required.

[0004] On the other hand, the perovskite crystals of the perovskite film may contain organic substances such as methylammonium (hereinafter sometimes referred to as MA) and formamidium (hereinafter sometimes referred to as FA). Furthermore, the upper and lower layers of the perovskite film, the organic modification layer, and the additives in the perovskite film may also contain organic substances. Therefore, analytical methods that minimize the destruction of organic substances during analysis are required.

[0005] For analyzing the depth distribution of components in perovskite films, GCIB-TOF-SIMS, a combination of etching with an argon gas cluster ion beam (Ar-GCIB) and acquisition of mass spectra by time-of-flight secondary ion mass spectrometry (TOF-SIMS), has been used. Ar-GCIB is an ion beam capable of etching without damaging organic materials.

[0006] When depth profiling of perovskite films by GCIB-TOF-SIMS is performed under generally widely used conditions, the perovskite crystals are damaged and depth profiles of each component cannot be correctly obtained. In particular, the influence on organic molecules such as MA and FA is large, and the intensity tends to decrease toward the deeper part. Also, the sharpness of the depth profiles of each component at the interface is poor and gentle, that is, the resolution in the depth direction of the analysis is poor.

[0007] In Non-Patent Document 1, the perovskite film is etched with Ar-GCIB from both the front and back sides using a TOF-SIMS apparatus for depth profiling. However, it has been experimentally shown that the intensity of MA decreases in the deeper part, that is, artifacts are formed during the measurement. Since the primary ions used have a higher dose density than the conditions used in normal TOF-SIMS, the artifacts are considered to include those caused by damage by the primary ions. As a method for reducing this artifact, a method of changing the ions used for etching (hereinafter sometimes referred to as etching ions) to cesium ions of 1 keV has been devised. However, in this method, the intensities of Pb and I in the perovskite slightly decrease toward the deeper part, and the original distribution of the perovskite film cannot be sufficiently captured.

[0008] In Non-Patent Document 2, it is stated that when the etching ions are changed to cesium ions of 500 eV or Ar-GCIB (Ar of 20 keV) with optimized conditions for etching, selective etching of organic substances is suppressed, so the artifacts are reduced and the depth profile is improved compared to the case of using Ar-GCIB under normal conditions. However, only the depth profile of the negative secondary ions is shown as a result, and the behavior of the positive secondary ions reflecting the intensities of MA and FA is unknown. The depth profile of CN of the negative secondary ions is obtained at a constant intensity on the surface side of the perovskite film, but since the intensity increases near the interface with the lower layer, it is推测 that artifacts remain in this method. Also, although the depth resolution is not described, for the TiO in the lower layer of the perovskite film ５００ ＋ ), － Although the depth profile of CN of the negative secondary ions is obtained at a constant intensity on the surface side of the perovskite film, since the intensity increases near the interface with the lower layer, it is推测 that artifacts remain in this method. Also, although the depth resolution is not described, for the TiO in the lower layer of the perovskite film２ - Judging from the slope of the depth profile, it was also an insufficient method in terms of depth resolution.

[0009] International Publication No. WO 2018 / 043385

[0010] Steven P. Harvey, Fei Zhang, Axel Palmstrom, Joseph M. Luther, Kai Zhu, and Joseph J. Berry, ACS Appl. Mater. Interfaces 2019, 11, 30911.Celine Noel, Sara Pescetelli, Antonio Agresti, Alexis Franquet, Valentina Spampinato, Alexandre Felten, Aldo di Carlo, Laurent Houssiau, Yan Busby, Materials 2019, 12, 726.

[0011] As described above, conventionally, it has been difficult to etch a perovskite film without creating artifacts and obtain a depth profile that reflects the original component distribution of the perovskite film with high depth resolution. Attempts have been made to solve this problem by changing the type of etching ions and finely adjusting the conditions, but the range of those conditions is very narrow and a complete solution has not been achieved.

[0012] The present invention has been made in view of the above situation, and provides a method for analyzing a component distribution capable of obtaining component information inside a film closer to the original component distribution of a perovskite film, and further a depth profile, and obtaining a depth profile with high depth resolution. [[ID=十六]]

[0013] [[ID=十七]] In all of the studies in the aforementioned prior art, they were carried out at room temperature (around 25°C), and there is no prior art that focuses on the temperature during analysis. The inventors of the present invention conceived the present invention by focusing on the temperature during analysis.

[0014] It should be noted that in the original text, the text in Chinese characters has been translated into Japanese in the English translation above. If you have any other special requirements or corrections, please feel free to let me know.The present invention and its preferred embodiments have the following configurations: [1] A method for analyzing a perovskite film, comprising: continuously or intermittently applying an ionic etching treatment to the perovskite film while the perovskite film is cooled; and analyzing the components of the surface or the exposed surface of the perovskite film by the etching treatment at least once before, during, and at the end of the etching treatment.

[0015] [2] The method for analyzing a perovskite film according to [1], wherein the temperature at which the perovskite film is cooled is 0°C or lower.

[0016] [3] The method for analyzing a perovskite film according to [1], wherein the temperature at which the perovskite film is cooled is -140°C or lower.

[0017] [4] The method for analyzing a perovskite film according to [2] or [3], wherein the temperature at which the perovskite film is cooled is -196°C or higher.

[0018] [5] A method for analyzing a perovskite film according to any one of [1] to [4], wherein the above analysis is performed multiple times to obtain information on the component distribution in the depth direction of the perovskite film.

[0019] [6] A method for analyzing a perovskite film according to any one of [1] to [5], using secondary ion mass spectrometry.

[0020] [7] The method for analyzing a perovskite film according to [6], wherein the secondary ion mass spectrometer is of the time-of-flight type.

[0021] [8] The method for analyzing a perovskite film according to any one of [1] to [7], wherein the ion beam used for the etching process is selected from the group consisting of an argon gas cluster ion beam, an argon ion beam, a cesium ion beam, an oxygen ion beam, a fullerene ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam.

[0022] [9] The method for analyzing a perovskite film according to any one of [1] to [8], wherein the ion beam used for the etching process is selected from the group consisting of an argon gas cluster ion beam, a fullerene ion beam, a bismuth ion beam, a gallium ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam.

[0023]

[10] The method for analyzing a perovskite film according to any one of [1] to [9], wherein the ion beam used for the etching process is an argon gas cluster ion beam.

[0024] By using the analytical method of the present invention, it is possible to perform component analysis of the interior of a perovskite film, as well as component analysis in the depth direction, with high depth resolution while retaining the original component information, which was difficult with conventional techniques, and to obtain high-quality data. The present invention is not limited to GCIB-TOF-SIMS, but can also provide high-quality data for depth profiling analysis techniques using ion etching, such as secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES).

[0025] Positive secondary ion depth profile obtained in Example 1 of the present invention Negative secondary ion depth profile obtained in Example 1 of the present invention Positive secondary ion depth profile obtained in Comparative Example 1 using a conventional method Negative secondary ion depth profile obtained in Comparative Example 1 using a conventional method Positive secondary ion depth profile obtained in Example 2 of the present invention Positive secondary ion depth profile obtained in Comparative Example 2 using a conventional method

[0026] In the present invention, the perovskite film of the target perovskite solar cell has a crystalline structure called a perovskite structure, and preferably consists of metallic elements such as lead, tin, cesium, rubidium, silver, copper, bismuth, antimony, and germanium, halogens such as bromine, iodine, and chlorine, and organic ions such as MA and FA. However, the applicable materials in the present invention are not limited to the above and also include organic-inorganic hybrid materials.

[0027] In the perovskite film analysis method of the present invention, the perovskite film is cooled. By cooling the perovskite film, the formation of artifacts (selective etching and volatilization of organic matter) is suppressed, and a depth profile that reflects the original component distribution can be obtained. Cooling of the perovskite film in the present invention can be performed either inside or outside the analytical instrument. Preferred cooling methods include direct cooling by contact between a refrigerant such as ice, dry ice, or liquid nitrogen and the sample, or indirect cooling via heat transfer. From the viewpoint of achieving the desired temperature, ease of handling, and prevention of contamination, cooling by heat transfer from liquid nitrogen inside the analytical instrument is preferred.

[0028] In the present invention, when cooling within the analytical instrument, it is preferable to introduce the sample stage into the instrument's pre-exhaust chamber, evacuate it thoroughly in the pre-exhaust chamber, then move the sample stage to the instrument's main chamber, and cool the sample stage by heat conduction from liquid nitrogen or the like. The cooling temperature of the sample is preferably 0°C or lower. By cooling the sample to 0°C or lower, more preferably to -140°C or lower, the formation of artifacts can be suppressed more effectively. Furthermore, by using liquid nitrogen, a general-purpose refrigerant, cooling down to -196°C is possible. The sample may be moved to the main chamber after being cooled in the pre-exhaust chamber, but if the moisture pressure is high, ice may adhere to the sample due to condensation. Therefore, it is preferable to cool the sample after evacuating or replacing it with an inert gas such as nitrogen gas or argon gas.

[0029] In the present invention, preferred means for cooling the sample include, in addition to heat conduction by liquid nitrogen, heat conduction by liquid helium, depressurized exhaust of liquid helium, a Peltier cooler, a dilution refrigerator, nuclear adiabatic demagnetization refrigeration, and the like.

[0030] In the present invention, the perovskite film is subjected to continuous or intermittent ion etching while the perovskite film is cooled. This etching process is a means of drilling the perovskite film in the depth direction by irradiating it with an ion beam in an analytical instrument. Preferably, the etching ion is one selected from the group consisting of an argon gas cluster ion beam, an argon ion beam, a cesium ion beam, an oxygen ion beam, a fullerene ion beam, a bismuth ion beam, a gallium ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam. The ion beam used for etching is more preferably one selected from the group consisting of an argon gas cluster ion beam, a fullerene ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam. Even more preferably, the ion beam used for etching is an argon gas cluster ion beam. The energy of the etching ion is not particularly limited.

[0031] In the present invention, under the cooling of the perovskite film, at least once before, during, or after the etching treatment, the components of the surface or the exposed surface of the perovskite film by the etching treatment are analyzed. Preferably, under the cooling of the perovskite film, at least once during or after the etching treatment, the components of the exposed surface of the perovskite film by the etching treatment are analyzed. Note that in this preferred embodiment, it is not excluded that the components of the surface of the perovskite film are further analyzed before the etching treatment. By performing the analysis in this way, analysis results closer to the original components can be obtained for the surface and inside of the perovskite film. Further, by performing the analysis multiple times, information on the component distribution in the depth direction of the perovskite film can be obtained, and a depth profile closer to the original component distribution of the perovskite film can be obtained. As an analysis method, one selected from the group consisting of secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) is preferably exemplified. Among them, it is preferable to use secondary ion mass spectrometry. Examples of the type of mass spectrometer for SIMS include a time-of-flight type, a quadrupole type, a double-focusing type, an ion trap type, etc. In particular, it is preferable to use a time-of-flight type for secondary ion mass spectrometry.

[0032] Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

[0033] [Example 1, Comparative Example 1] (Sample) The samples used in Example 1 and Comparative Example 1 were the same for comparison, and the perovskite film was formed on an ITO (Indium-Tin Oxide) electrode. A perovskite film with a thickness of 500 nm was used. This perovskite film contains cesium (Cs), lead (Pb), formamidinium (FA), methylammonium (MA), iodine (I), and bromine (Br) as constituent components, and the composition formula is Cs ０．０５ FA ０．８０ MA ０．１５ PbI ２．７５ Br ０．２５This is a polycrystalline film represented by [the formula shown]. This sample is used to confirm the accuracy of the analytical method of the present invention, and it is possible to predict that the component distribution is uniform. It does not contain any modification layers or additives other than the perovskite film.

[0034] (Example 1) The sample stage was cooled to -150°C, and depth profiling was performed from the sample surface to the ITO electrode by GCIB-TOF-SIMS measurement.

[0035] The etching ion is 10 keV Ar-GCIB, the etching ion raster size is 500 μm square, and the primary ion is 60 keV Bi ３ ＋＋ The raster size for the primary ions was set to 200 μm square. By repeatedly irradiating with etching ions and primary ions alternately, the etching process and analysis were performed intermittently.

[0036] The depth resolution of the positive secondary ion depth profile is due to positive secondary ions originating from ITO. １１３ In ＋ The strength was determined by the difference between the depth at which the strength corresponds to 84% of the maximum strength and the depth at which it corresponds to 16%.

[0037] The obtained positive secondary ion depth profile is shown in Figure 1, and the negative secondary ion depth profile is shown in Figure 2. The vertical axis of the depth profile represents the relative intensity (Pb in the plateau region near the center of the perovskite layer). ＋ , PbI ３ － The horizontal axis represents depth (normalized so that the perovskite layer / ITO interface is 500 nm deep), based on the average strength standard.

[0038] Figure 1 shows Pb, a positive secondary ion derived from Pb in a perovskite film. ＋ , Cs, a positive secondary ion derived from Cs in the perovskite film ＋ , a positive secondary ion originating from FA in the perovskite film. １３ CH ５ N ２ ＋ CH, a positive secondary ion derived from MA in the perovskite film. ６ N ＋, a positive secondary ion originating from the ITO electrode. １１３ In ＋ The depth profile was shown.

[0039] Figure 2 shows PbI, a negative secondary ion derived from Pb and I in the perovskite film. ３ － CsI ​​is a negative secondary ion derived from Cs and I in the perovskite film. ２ － I, a negative secondary ion derived from I in the perovskite film. － , Br, a negative secondary ion derived from Br in the perovskite film － InO, a negative secondary ion originating from the ITO electrode. ２ － The depth profile was shown.

[0040] In Figures 1 and 2, the secondary ion intensity originating from the perovskite film remains approximately constant within the perovskite layer, reflecting the original component distribution. １１３ In ＋ The depth resolution, determined from the depth profile, was 40 nm.

[0041] (Comparative Example 1) Depth profiling was performed in the same manner as in Example 1, except that the temperature of the sample stage was kept at 25°C. The obtained positive secondary ion depth profile is shown in Figure 3, and the negative secondary ion depth profile is shown in Figure 4.

[0042] Figures 3 and 4 show Pb, a secondary ion derived from the perovskite membrane. ＋ , １３ CH ５ N ２ ＋ ,CH ６ N ＋ PbI ３ － , CsI ２ － The intensity decreases from 0 to 100 nm, and due to artifact formation, a depth profile that reflects the inherently uniform compositional distribution of the polycrystalline film is not obtained. (Figure 3) １１３ In ＋The depth resolution obtained from the depth profile was 186 nm. In Comparative Example 1, １１３ In ＋ Since the ionic intensity had not reached a plateau region (a region where the intensity is constant), the endpoint of the measurement was defined as the maximum intensity.

[0043] (Discussion) In Example 1, cooling the sample to -150°C resulted in a significant improvement compared to Comparative Example 1, which was measured at room temperature. The depth resolution improved by approximately 4.7 times, from 186 nm to 40 nm, and the organic component-derived ions ( １３ CH ５ N ２ ＋ ,CH ６ N ＋ The strength stability in the depth direction of the perovskite membrane was significantly improved. Furthermore, it was confirmed that all secondary ions originating from the perovskite membrane maintained a constant strength within the membrane.

[0044] Of particular note is that the selective etching and intensity reduction of organic components such as MA and FA, which were problematic in conventional techniques (Non-Patent Documents 1 and 2), were effectively suppressed by cooling. This result indicates that the sample temperature during ion beam irradiation has a significant impact on artifact formation.

[0045] The ability to obtain a high-quality depth profile that reflects the original component distribution without complex optimization of ion species or irradiation conditions, through the simple method of cooling, is extremely advantageous in practical applications. In this example, particularly excellent results were obtained at a low temperature of -150°C, but from the relationship between sample temperature and artifact suppression effect, it is understood that similar effects can be obtained at higher temperatures (e.g., 0°C, -50°C, -100°C, etc.), albeit to a lesser degree, compared to room temperature.

[0046] [Example 2, Comparative Example 2] (Sample) The samples used in Example 2 and Comparative Example 2 were identical for comparison purposes, and consisted of a perovskite film deposited on an ITO electrode. A perovskite film with a thickness of 500 nm was used. This perovskite film had the composition formula Cs ０．０５ FA ０．８０ MA ０．１５ PbI ２．７５ Br０．２５ This is a polycrystalline film represented by [the formula shown], prepared by adding organic additives.

[0047] (Example 2) The sample stage was cooled to -150°C, and depth profiling was performed from the sample surface to the ITO electrode by GCIB-TOF-SIMS measurement.

[0048] The etching ion is 10 keV Ar-GCIB, the etching ion raster size is 600 μm square, and the primary ion is 60 keV Bi ３ ＋＋ The raster size for the primary ions was set to 200 μm square. By repeatedly irradiating with etching ions and primary ions alternately, the etching process and analysis were performed intermittently.

[0049] The depth resolution of the positive secondary ion depth profile is due to positive secondary ions originating from ITO. １１３ The In+ intensity was determined by the difference between the depth at which the In+ intensity corresponds to 84% of the maximum intensity and the depth at which it corresponds to 16%.

[0050] The obtained positive-secondary ion depth profile is shown in Figure 5. The vertical axis of the depth profile represents the relative intensity (Pb in the plateau region near the center of the perovskite layer). ＋ The horizontal axis represents depth (normalized so that the perovskite layer / ITO interface is 500 nm deep), based on the average strength standard.

[0051] Figure 5 shows the depth profiles of secondary ions derived from organic additives, in addition to the ion species shown in Figure 1. A biased distribution of organic additives was observed at the perovskite surface and the perovskite layer / ITO interface, with both its rise and fall being steep. １１３ In ＋ The depth resolution, determined from the depth profile, was 31 nm.

[0052] (Comparative Example 2) Depth profiling was performed in the same manner as in Example 2, except that the temperature of the sample stage was kept at 25°C. The obtained positive quadratic ion depth profile is shown in Figure 6.

[0053] Figure 6 shows Pb, a secondary ion derived from the perovskite membrane. ＋,CH ６ N ＋ The intensity decreases from 0 to 100 nm, and the depth profile does not reflect the original compositional distribution due to artifact formation. Furthermore, compared to Example 2, the decline of secondary ions derived from organic additives near the perovskite surface is steeper with less influence from artifact formation, but a peak due to artifact formation is observed around 50 nm, and the original distribution is not obtained. Also, artifact formation progresses at the perovskite layer / ITO interface, and compared to Example 2, the slopes of the depth profiles of secondary ions derived from organic additives and ITO are smaller. (Figure 6) １１３ In ＋ The depth resolution, determined from the depth profile, was 173 nm.

Claims

1. A method for analyzing a perovskite film, comprising: continuously or intermittently applying an ionic etching treatment to the perovskite film while the perovskite film is cooled; and analyzing the components of the surface or the exposed surface of the perovskite film due to the etching treatment at least once before, during, and after the etching treatment.

2. The method for analyzing a perovskite film according to claim 1, wherein the temperature at which the perovskite film is cooled is 0°C or lower.

3. The method for analyzing a perovskite film according to claim 1, wherein the temperature at which the perovskite film is cooled is -140°C or lower.

4. The method for analyzing a perovskite film according to claim 2 or 3, wherein the temperature at which the perovskite film is cooled is -196°C or higher.

5. A method for analyzing a perovskite film according to any one of claims 1 to 3, wherein the above analysis is performed multiple times to obtain information on the component distribution in the depth direction of the perovskite film.

6. A method for analyzing a perovskite film according to any one of claims 1 to 3, wherein the analysis is performed using secondary ion mass spectrometry.

7. The method for analyzing a perovskite film according to claim 6, wherein the secondary ion mass spectrometer is a time-of-flight type.

8. The method for analyzing a perovskite film according to any one of claims 1 to 3, wherein the ion beam used in the etching process is selected from the group consisting of an argon gas cluster ion beam, an argon ion beam, a cesium ion beam, an oxygen ion beam, a fullerene ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam.

9. The method for analyzing a perovskite film according to any one of claims 1 to 3, wherein the ion beam used in the etching process is selected from the group consisting of an argon gas cluster ion beam, a fullerene ion beam, a bismuth ion beam, a gallium ion beam, a water cluster ion beam, and a carbon dioxide gas cluster ion beam.

10. The method for analyzing a perovskite film according to any one of claims 1 to 3, wherein the ion beam used in the etching process is an argon gas cluster ion beam.

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