Dispersion liquid, thin film, and photoelectric conversion element

Abstract

The purpose of the present invention is to provide a dispersion liquid containing tin oxide nanoparticles having excellent dispersibility, a thin film containing the tin oxide nanoparticles, and a photoelectric conversion element containing the tin oxide nanoparticles in an electron transport layer. A dispersion liquid according to the present disclosure contains tin oxide nanoparticles, and is characterized in that a cumulative 95% particle diameter of the tin oxide nanoparticles in a cumulative particle size distribution as measured by dynamic light scattering is 55 nm or less. It is preferable that a cumulative 50% particle diameter of the tin oxide nanoparticles in a cumulative particle size distribution as measured by dynamic light scattering is 5-30 nm inclusive.

Description

Dispersion, thin film, and photoelectric conversion element

[0001] This disclosure relates to a dispersion containing tin oxide nanoparticles, a thin film containing the tin oxide nanoparticles, and a photoelectric conversion element containing the tin oxide nanoparticles in an electron transport layer.

[0002] Patent Document 1 discloses an invention relating to tin oxide particles that contain multiple types of tin with different valencies ranging from divalent to tetravalent, substantially free of dopant elements, and possess conductivity. Patent Document 1 also discloses the application of tin oxide particles to transparent conductive films and the like.

[0003] Japanese Patent Publication No. 2011-026172

[0004] Incidentally, photoelectric conversion elements such as organic solar cells and perovskite solar cells are provided with an electron transport layer to efficiently transport electrons.

[0005] By forming a thin film using a dispersion containing tin oxide particles, an electron transport layer containing tin oxide particles can be created. In this process, a highly dispersible dispersion was required. It was found that low dispersibility resulted in a high electrical resistivity of the electron transport layer, leading to insufficient power generation characteristics.

[0006] This disclosure has been made in view of the above-mentioned problems, and aims to provide a dispersion containing tin oxide nanoparticles with excellent dispersibility, a thin film containing the tin oxide nanoparticles, and a photoelectric conversion element containing the tin oxide nanoparticles in an electron transport layer.

[0007] The dispersion of the present disclosure is a dispersion containing tin oxide nanoparticles, characterized in that the cumulative 95% particle size in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 55 nm or less.

[0008] The thin film of this disclosure is formed from the dispersion described above and is characterized by containing the tin oxide nanoparticles.

[0009] The photoelectric conversion element of the present disclosure comprises an electron transport layer, an active layer, and a hole transport layer formed from the thin film described above, wherein the active layer contains a perovskite-type semiconductor.

[0010] According to this disclosure, a dispersion containing tin oxide nanoparticles with excellent dispersibility can be provided. By forming a thin film containing tin oxide nanoparticles using this dispersion with excellent dispersibility, conductivity can be improved, and by using this thin film as an electron transport layer, a photoelectric conversion element with excellent electron transport properties can be provided.

[0011] This is a partial cross-sectional view of the solar cell of this embodiment. It shows a perovskite structure. This is a graph showing the relationship between the pH and zeta potential of the tin oxide thin film in each sample. This is a graph showing the relationship between the pH and zeta potential of the tin oxide thin film using an approximate formula, based on the results in Figure 3.

[0012] Hereinafter, one embodiment of this disclosure (hereinafter abbreviated as "Embodiment") will be described in detail. However, this disclosure is not limited to the following embodiment, and can be implemented in various modifications within the scope of its gist.

[0013] <Overview of Solar Cell 101> Figure 1 is a partial cross-sectional view showing an example of the solar cell 101 of this embodiment. The solar cell 101 shown in Figure 1 comprises a first electrode 41 which is the cathode and a second electrode 42 which is the anode, and an electron transport layer 43, an active layer 44, and a hole transport layer 45 are provided between the first electrode 41 and the second electrode 42. The stacked structure may be reversed.

[0014] For example, the first electrode 41 is formed on a glass substrate 46. A plastic substrate or film may be used instead of the glass substrate 46. The substrate and film are preferably transparent.

[0015] The second electrode 42 is conductive. Of the first electrode 41 and the second electrode 42, if the electrode on the side into which light is incident is translucent, the other electrode does not need to be translucent. For example, the second electrode 42 is made of a transparent and conductive material. The first electrode 41 and the second electrode 42 have the function of collecting holes and electrons generated by light absorption in the active layer 44. This allows electricity to be generated.

[0016] In the solar cell 101 of this embodiment, the hole transport layer 45 is made of an inorganic or organic substance that has the function of transporting holes. The hole transport layer 45 is preferably made of an inorganic substance, for example, NiO or WO ３ It is preferable that the hole transport layer 45 be formed from inorganic oxides such as the above. In particular, it is preferable that the hole transport layer 45 be formed from NiO nanoparticles. Alternatively, the hole transport layer 45 may be formed from, for example, NiO with Al ２ O ３ These can also be mixed. Furthermore, the metal oxide may be doped with Li, Mg, Al, etc. The hole transport layer 45 may also be an inorganic substance other than an inorganic oxide. The electron transport layer 43 will be described later.

[0017] In this embodiment, it is preferable that the oxygen vacancies in the metal oxides constituting the electron transport layer 43 and the hole transport layer 45 are smaller than those in the bulk material. That is, it is preferable that the composition is stoichiometric or close to stoichiometric. "Bulk material" refers to a lump containing the metal oxide, and its size and shape are not considered.

[0018] In this embodiment, the active layer 44 is a photoelectric conversion layer that absorbs light incident on the solar cell 101 and generates electrons and holes.

[0019] In the solar cell 101, the semiconductor material of the active layer 44 that generates electrons and holes when exposed to sunlight may be i-type, n-type, or p-type. The electron transport layer 43 is an n-type semiconductor, and the hole transport layer is a p-type semiconductor. A solar cell 101 in which a transparent electrode is formed on the electron transport layer 43 side to allow sunlight to enter is called an n-i-p type solar cell, and when it is formed on the hole transport layer 45 side, it is called a p-i-n type solar cell.

[0020] In this embodiment, a perovskite semiconductor is used for the active layer 44. The structure of the perovskite semiconductor is shown in Figure 2. For example, in Figure 2, M is Pb, O is Br or I, and R is NH ３ CH ３ That is the case.

[0021] Perovskite solar cells are sensitive to the entire visible light spectrum and offer excellent power generation efficiency. Furthermore, compared to conventional silicon solar cells, they have a lower dependence on the intensity of incident light (illuminance) for power generation efficiency. This means they can be used in both outdoor and indoor applications.

[0022] By using a perovskite semiconductor in the active layer 44, low-temperature processes such as coating, which were difficult to achieve with conventional silicon semiconductors, become applicable. Silicon solar cells have limitations on installation area due to load issues. For this reason, perovskite solar cells, which can overcome installation area limitations and have high power generation efficiency, have been highly anticipated in recent years.

[0023] <Background to this embodiment> Photoelectric conversion elements (photoelectric conversion devices) such as organic solar cells and perovskite solar cells are provided with an electron transport layer (ETL) for efficiently transporting electrons.

[0024] As mentioned above, existing silicon solar cells have limitations in terms of installation area and weight, and against this backdrop, there is a growing trend towards developing flexible solar cells using film substrates.

[0025] Conventional titanium oxide (TiO ２ When solar cells are fabricated using ), high-temperature firing (for example, around 500°C) is required, which raises concerns about increased manufacturing costs and the possibility of deformation of the film substrate. ２ When thin films were used, there was a concern that the photocatalytic effect would decompose other layers, leading to a decrease in luminescence efficiency.

[0026] For example, a method is known in which an electron transport layer is formed by a thin film that is coated and dried using a dispersion containing tin oxide particles with a spin coater or the like.

[0027] As shown in Patent Document 1, when forming an electron transport layer using tin oxide particles having a plurality of valences, since the carrier transport properties in divalent and tetravalent states are different, a mismatch in carrier balance with the active layer is caused, and the electron transport property is impaired, so that sufficient power generation efficiency may not be obtained.

[0028] Further, even when using tin oxide having substantially only a single valence, when using tin oxide particles that are not nanoparticles, the film may have poor density and thus may have impaired transport properties. Also, when using a dispersion liquid with low dispersibility, the particles may aggregate, and the uniformity of the film is likely to be impaired during coating formation. Therefore, it may cause poor formation of each layer including the next process, leading to defects such as short circuits.

[0029] Therefore, as a result of intensive research by the present inventors, a dispersion liquid containing tin oxide nanoparticles with excellent dispersibility has been developed.

[0030] <Regarding the characteristic configuration of the present embodiment> In the present embodiment, a dispersion liquid containing tin oxide nanoparticles is characterized in that the cumulative 95% particle diameter in the cumulative particle size distribution measured by the dynamic light scattering method of the tin oxide nanoparticles is 55 nm or less.

[0031] "Tin oxide nanoparticles" means that the main component is tin oxide, but it does not exclude containing sub-components or inevitable components other than tin oxide. Composition analysis can be observed by X-ray diffraction method (XRD). Also, in the case of a large number of single particles (one particle) of tin oxide nanoparticles existing in the dispersion liquid. In the present embodiment for improving dispersibility, it is preferably in a state where a large number of substantially single particles are dispersed. Although not limited, 90% or more, preferably 95% or more, more preferably 97% or more, and still more preferably 99% or more of the particles exist as single particles. The tin oxide component contained in the tin oxide nanoparticles occupies 90% or more, preferably 95% or more, more preferably 97% or more, and still more preferably 99% or more of the entire nanoparticles.

[0032] Tin oxide can be represented by SnO ｘ It is preferably in a stoichiometric composition, and x is preferably 2. That is, tin is tetravalent, and SnO２ is preferable. Although divalent tin (SnO) may be mixed, 90% or more, preferably 95% or more, more preferably 97% or more, and still more preferably 99% or more of the total particles are SnO ２ is suitable.

[0033] "Nanoparticles" means particles having an average particle diameter on the nano order. Thereby, the denseness of the thin film formed using the dispersion liquid containing tin oxide nanoparticles can be improved.

[0034] In the dispersion liquid containing tin oxide nanoparticles, the particle size distribution measured by the dynamic light scattering method can be defined. The "dynamic light scattering method" is a method of deriving the size (particle diameter) of particles based on the fluctuation of the scattered light intensity depending on the Brownian motion of the particles detected when a laser beam is irradiated to a solution in which the particles are dispersed and the change in the scattered light is measured.

[0035] In the present embodiment, the cumulative 95% particle diameter (D95) in the cumulative particle size distribution measured by the dynamic light scattering method of the tin oxide nanoparticles is 55 nm or less. Further, D95 is preferably 50 nm or less, more preferably 45 nm or less, and still more preferably 40 nm or less. By keeping D95 within the above range, the particle diameter of the tin oxide nanoparticles can be reduced. That is, the aggregation of the tin oxide nanoparticles is suppressed, and as described above, most of the tin oxide nanoparticles exist as single particles. Thereby, sedimentation and turbidity of the particles in the dispersion liquid can be suppressed, the change in dispersibility over time can be suppressed, and excellent dispersibility can be obtained over a long period of time.

[0036] Further, in the present embodiment, the cumulative 50% particle diameter (D50) in the cumulative particle size distribution measured by the dynamic light scattering method of the tin oxide nanoparticles is preferably 30 nm or less. Further, D50 is more preferably 20 nm or less, and still more preferably 18 nm or less. Thereby, the particle diameter of the tin oxide nanoparticles can be reduced and the variation can be suppressed, and more excellent dispersibility can be obtained. Also, the lower limit value of D50 is not limited, but for example, it may be 5 nm or more, 10 nm or more, or 12 nm or more.

[0037] While not a limitation, D10 can be smaller than D50 and between 2 nm and 10 nm, and D90 can be larger than D50, smaller than D95, and between 20 nm and 40 nm.

[0038] Furthermore, in this embodiment, it is preferable that the tin oxide nanoparticles further contain a halogen. By including a halogen, better dispersibility can be obtained. The halogen functions as a ligand and is preferably positioned on the surface of the tin oxide nanoparticles. The halogen includes at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), but it is preferable that it includes at least chlorine.

[0039] Halogens are arranged on the surface of tin oxide nanoparticles as halogen-containing compounds, halogen-containing groups, or elemental halogens. They may be uniformly arranged on the surface of the tin oxide nanoparticles, or, for example, areas where elemental halogens are arranged and areas where halogen-containing compounds are arranged may be mixed.

[0040] Furthermore, in this embodiment, the dispersion containing tin oxide nanoparticles preferably has a pH of 1 to 8, more preferably 1 to 7, and even more preferably 2 to 7. Thus, the dispersion is preferably acidic or neutral. The solvent contains at least water. The dispersion's pH is adjusted to 1 to 8 through chemical bonding between hydrogen in water and halogens. This suppresses aggregation of tin oxide nanoparticles and provides excellent dispersibility. In addition to water, an organic solvent may also be included. Although not limited to water, for example, the organic solvent may contain at least one of alcohols, aromatic compounds, amide skeletons, or sulfoxide skeletons. By including tin oxide nanoparticles in the above organic solvent, the dispersibility of the tin oxide nanoparticles can be enhanced.

[0041] <Method for producing a dispersion containing tin oxide nanoparticles> The following describes a method for producing a dispersion containing tin oxide nanoparticles, but this is just one example and is not limited to the method described below.

[0042] For example, tin(II) chloride dihydrate is weighed and added to deionized water at a predetermined temperature, and mixed and stirred using a stirring bar for several hours to more than ten hours. At this time, the temperature should be between 20°C and 35°C when adding to the deionized water, and the stirring time should be 24 hours or more. This will produce tin oxide nanoparticles. In addition, to include halogens in the tin oxide nanoparticles, for example, by stirring tin chloride and water for a long period of time as described above, SnO ２ This results in HCl, and further stirring allows the Cl to be positioned on the surface of the tin oxide nanoparticles as a ligand. Alternatively, a halogen compound may be added and the mixture stirred.

[0043] The obtained tin oxide nanoparticles are dispersed in the presence of water as a solvent and an organic solvent. The concentration of tin oxide nanoparticles in the dispersion is approximately 0.5% to 10%, although this is not limited to this concentration.

[0044] <Regarding the embodiment containing tin oxide nanoparticles> In this embodiment, a thin film, an electron transport layer, and a photoelectric conversion element can be provided using a dispersion containing tin oxide nanoparticles.

[0045] The thin film can be formed by depositing a dispersion containing tin oxide nanoparticles onto a substrate and performing a predetermined drying process. The thin film containing tin oxide nanoparticles can be used as the electron transport layer 43 shown in Figure 1.

[0046] The crystallite size of the tin oxide thin film is not limited, but can be 1.5 nm to 6.0 nm or 2.0 nm to 5.0 nm, preferably 1.8 nm to 3.0 nm, and more preferably 1.8 nm to 2.5 nm. Specifically, the crystallite size on crystal plane (211) can be 2.0 nm to 6.0 nm, preferably 2.0 nm to 3.0 nm, and more preferably 2.0 nm to 2.5 nm. The crystallite size on crystal plane (101) can be 1.5 nm to 3.0 nm, preferably 1.8 nm to 2.6 nm. The crystallite size on crystal plane (110) can be 2.0 nm to 3.0 nm, preferably 2.0 nm to 2.5 nm. The crystallite size on crystal plane (200) can be 2.0 nm to 3 nm, preferably 2.0 nm to 2.5 nm. Furthermore, the full width at half maximum of the diffraction peaks on each crystal plane in XRD can be set to 3.0° (deg) or more and 5.0° or less, preferably 3.3° or more and 4.5° or less. In this embodiment, the crystallite size can be reduced, and as a result, dense film formation becomes possible, improving the electrical properties.

[0047] Furthermore, the density of the tin oxide thin film is 1.0 g / cm³. ３ 6.0g / cm or more ３ Preferably, 2 g / cm³ ３ 5.0g / cm or more ３ More preferably, 3 g / cm³ ３ 4.5g / cm or more ３ The following can be done. Note that the density of the bulk tin oxide thin film is 6.95 g / cm³. ３ Therefore, the density of the tin oxide thin film in this embodiment can be made lower than the density of the bulk tin oxide thin film. The lower density of the tin oxide thin film relieves internal stress, improving mechanical properties such as delamination and cracking.

[0048] Furthermore, the zeta potential of the tin oxide thin film is 20 mV or less in absolute value, preferably 15 mV or less in absolute value, and more preferably 10 mV or less in absolute value, within the pH range of pH 6 to pH 8. For example, at pH 7, the zeta potential can be reduced to 5 mV or less in absolute value.

[0049] While tin oxide thin films can be used as electron transport layers in perovskite solar cells, controlling the zeta potential can improve film thinning of the tin oxide thin film when the active layer (perovskite layer) is applied, allowing for the formation of a uniform perovskite layer.

[0050] Furthermore, although not limited, the surface roughness Sa of the thin film can be adjusted to 20 nm or less. Surface roughness Sa is a three-dimensional surface roughness and is expressed as the average value of the surface roughness in the measurement area. Surface roughness Sa is more preferably 10 nm or less, and even more preferably 5 nm or less. Also, since the smaller the surface roughness Sa, the better, there is no lower limit, but for example, it may be 1 nm or more. Surface roughness Sa can be measured, for example, by an atomic force microscope (AFM) (e.g., Park NX10).

[0051] As a result, the conductivity of the thin film can be improved. The dispersion of this embodiment has small particle size tin oxide nanoparticles and does not aggregate, or the degree of aggregation is small, so it has good dispersibility, and thereby the above-mentioned surface roughness Sa can be obtained.

[0052] As described above, the thin film containing tin oxide nanoparticles of this embodiment has excellent conductivity and can therefore be suitably applied to the electron transport layer of a photoelectric conversion element. In particular, by using it as the electron transport layer 43 of a perovskite solar cell, energy loss between the perovskite semiconductor can be reduced, and excellent power generation characteristics can be obtained.

[0053] Furthermore, the electron transport layer may contain alkali metals. Li can be given as an example of an alkali metal. The inclusion of alkali metals in the electron transport layer increases the carrier density and decreases the film resistance. As a result, the electron mobility of the electron transport layer is improved, and the surface of the tin oxide nanoparticles is passivated, which improves the interface quality with the active layer and improves the power generation efficiency.

[0054] The effects of this disclosure will be explained below with reference to the examples and comparative examples provided herein. However, this disclosure is not limited in any way by the following examples. In the experiment, a dispersion of tin oxide nanoparticles was prepared.

[0055] <Example 1> 5.6 g of tin(II) chloride dihydrate (Kanto Chemical, purity 97.0%) was weighed and added to 50 g of deionized water at 25°C. The mixture was stirred using a stirring bar for 24 hours. Water was added to the resulting tin oxide nanoparticles, and ultrasonic dispersion was performed to prepare a dispersion containing the tin oxide nanoparticles dispersed in water. Through prolonged stirring, Cl was arranged on the surface of the tin oxide nanoparticles and functioned as a ligand.

[0056] <Example 2> This product was manufactured under the same conditions as Example 1, except for the Cl content. As shown in Table 1 below, there was a difference in the pH of the dispersion between Example 1 and Example 2.

[0057] <Comparative Example 1> SnO ２ To synthesize nanoparticles, 5.6 g of tin(IV) chloride pentahydrate (Kanto Chemical purity >98%) was weighed and dissolved in 50 g of deionized water at 25°C. A 1 mol / L potassium hydroxide aqueous solution was added until a white precipitate formed. The resulting precipitate was collected using a centrifuge and further washed with deionized water. The resulting precipitate was vacuum-dried and heated in an oven at 300°C for 3 hours. Water was added to the resulting tin oxide particles, and ultrasonic treatment was performed to obtain a tin oxide dispersion.

[0058] <Comparative Example 2> Hydrochloric acid aqueous solution was added to the tin oxide nanoparticles of Comparative Example 1 and dispersed, and then TMAH (tetramethylammonium hydroxide) was added as a pH adjuster.

[0059] <Method for measuring particle size distribution> The particle size distribution of tin oxide nanoparticles in the dispersion was measured using a particle size distribution analyzer. The measurement principle is dynamic light scattering. <Method for measuring pH> pH was measured using a pH meter. <Visual observation> Dispersibility was evaluated by visual observation. Samples that did not show precipitation or turbidity even after several days were marked with ○. Samples that showed precipitation and turbidity after 24 hours were marked with △. Samples that showed precipitation and turbidity immediately after the visual test were marked with ×.

[0060] <Method for measuring electrical resistivity> The prepared tin oxide dispersion was applied to a glass substrate by spin coating to a thickness of approximately 50 nm, and then fired at 150°C for 30 minutes to form a thin film of tin oxide nanoparticles.

[0061] Then, the electrical resistivity (volume resistivity) was measured using a high-resistivity resistivity meter, the Hi-Lester UX (manufactured by Nitto Seiko Co., Ltd.). <Evaluation of power generation characteristics> The photoelectric conversion efficiency of the fabricated perovskite solar cell was evaluated. The evaluation was carried out using the following equipment.

[0062] A power supply (KEITHLEY, Model 236) was connected between the electrodes, and the photoelectric conversion efficiency was measured using a single-source solar simulator with an intensity of 100 mW / cm². These measured values ​​were calculated as the average photoelectric conversion efficiency (average efficiency).

[0063] A perovskite solar cell was fabricated as follows: A dispersion containing tin oxide nanoparticles of this example or comparative example was spin-coated onto an ITO substrate, and then dried on a hot plate at 150°C for 30 minutes to obtain an electron transport layer. Subsequently, a perovskite solution was prepared by dissolving lead iodide (Tokyo Chemical Industries: product code L0279) and methylammonium iodide (Tokyo Chemical Industries: product code M2556) in a 1:1 ratio in a 1:1 mixed solvent of DMF and DMSO. The prepared perovskite solution was applied by spin-coating, a chlorobenzene solution was added dropwise as a poor solvent, and then annealed on a hot plate at 130°C for 15 minutes to crystallize and obtain an active layer.

[0064] Next, Spiro-OMeTAD (manufactured by Nippon Seika) was mixed with a chlorobenzene solution at a concentration of 50 mg / ml, coated onto the surface of the active layer, dried, and formed to obtain a hole transport layer. Gold was deposited on the surface of the hole transport layer as the upper electrode to fabricate a perovskite solar cell. Table 1 shows the experimental results for each sample.

[0065]

[0066] As shown in Table 1, in Examples 1 and 2, the cumulative 95% particle size (D95) in the cumulative particle size distribution measured by dynamic light scattering of tin oxide nanoparticles was found to be 55 nm or less. On the other hand, in Comparative Examples 1 and 2, the D95 was larger than 55 nm.

[0067] Furthermore, as shown in Table 1, in Examples 1 and 2, it was found that the cumulative 50% particle size (D50) in the cumulative particle size distribution measured by dynamic light scattering of tin oxide nanoparticles fell within the range of 5 nm to 30 nm.

[0068] Furthermore, as shown in Table 1, it was found that in Examples 1 and 2, the pH of the dispersion was between 1 and 8. On the other hand, in Comparative Examples 1 and 2, the pH of the dispersion was greater than 8.

[0069] Furthermore, as shown in Table 1, in Examples 1 and 2, visual observation revealed no precipitation or turbidity in the dispersion over a long period, indicating good dispersibility. However, in Comparative Examples 1 and 2, precipitation and turbidity in the dispersion were observed over a long period within 24 hours, indicating poor dispersibility.

[0070] In Examples 1 and 2, the reason for the excellent dispersibility was primarily that the D95 of the cumulative particle size distribution measured by dynamic light scattering was reduced, specifically to 55 nm or less, thereby suppressing the aggregation of tin oxide nanoparticles. In addition, keeping D50 within a predetermined range, including halogens, and adjusting the pH to neutral or acidic are also considered to be reasons for the suppression of aggregation.

[0071] As shown in Table 1, in the example, the electrical resistivity of the thin film containing tin oxide nanoparticles was 1.0 × 10⁻⁶. ６ It was reduced to less than Ω·cm.

[0072] Furthermore, the energy conversion efficiency (PCE) was achieved to 15% or higher. Thus, it was found that by using tin oxide nanoparticles as the electron transport layer in this embodiment, a perovskite-type solar cell with excellent power generation characteristics can be provided.

[0073] <Experiment on the crystal size of tin oxide thin films> In the experiment, thin films were formed from dispersions containing three types of tin oxide particles corresponding to this embodiment. The dispersion used for the first thin film sample (corresponding to Table 2) was an aqueous dispersion, the dispersion used for the second thin film sample (corresponding to Table 3) was an IPA dispersion, and the dispersion used for the third thin film sample (corresponding to Table 4) was an aqueous dispersion.

[0074] In the experiment, each thin film sample was prepared with a layer structure of glass / ITO / tin oxide thin film, and XRD analysis was performed on each tin oxide thin film. A Rigaku Smart Lab was used for the XRD analysis. The X-ray source was CuKα (using a multilayer mirror), the measurement step (2θχ) was 0.05°, the scan speed was 0.1° / min, the incident angle was 0.3°, and the scanning method was 2θχ continuous scan. The thickness of the ITO film was approximately 100 nm, and the thickness of the tin oxide thin film was approximately 30 nm.

[0075] Tables 2, 3, and 4 below summarize the full width at half maximum, crystallite size, crystal planes, etc.

[0076]

[0077]

[0078]

[0079] Based on these experiments, the crystallite size was set to 1.5 nm to 6.0 nm or 2.0 nm to 5.0 nm, preferably 1.8 nm to 3.0 nm, and more preferably 1.8 nm to 2.5 nm. For each crystal plane, the crystallite size on crystal plane (211) was set to 2.0 nm to 6.0 nm, preferably 2.0 nm to 3.0 nm, and more preferably 2.0 nm to 2.5 nm. The crystallite size on crystal plane (101) was set to 1.5 nm to 3 nm, preferably 1.8 nm to 2.6 nm. The crystallite size on crystal plane (110) was set to 2.0 nm to 3.0 nm, preferably 2.0 nm to 2.5 nm. The crystallite size on crystal plane (200) was set to 2.0 nm to 3.0 nm, preferably 2.0 nm to 2.5 nm.

[0080] <Experiment on the Density of Tin Oxide Thin Films> In this experiment, the first, second, and third thin film samples used in the <Experiment on the Crystal Size of Tin Oxide Thin Films> above were analyzed using an X-ray diffractometer by X-ray reflectivity (XRR). The experimental results are shown in Table 5. The experimental conditions were as follows: • X-ray reflectivity measuring device: Rigaku SmartLab • Incident X-ray wavelength: 0.15406 nm (CuKa 1 line) • Output: 45 kV, 200 mA • Measurement range (angle with the sample surface): 0.0 to 4.0° • Measurement step: 0.002°

[0081]

[0082] As shown in Table 5, the density of the tin oxide thin film was 1.0 g / cm³. ３ 6.0g / cm or more ３ Preferably, 2 g / cm³ ３ 5.0g / cm or more ３ More preferably, 3 g / cm³ ３ 4.5g / cm or more ３ The following was created.

[0083] <Experiment on the Zeta Potential of Tin Oxide Thin Films> In this experiment, the zeta potential of the tin oxide thin films was determined by asymmetric electrophoresis for the first, second, and third thin film samples used in the <Experiment on the Crystal Size of Tin Oxide Thin Films> described above.

[0084] The measurement device used was the ELSZneo zeta potential, particle size, and molecular weight measurement system manufactured by Otsuka Electronics. A semiconductor laser was used as the light source, a micro-plate cell was used, the voltage was 30V, and the measurement temperature was 25°C.

[0085] Furthermore, a pH-adjusted 10 mM NaCl aqueous solution was used as the measurement solution, and monitor particles manufactured by Otsuka Electronics (polystyrene latex coated with hydroxypropyl cellulose) were added. HCl and NaOH were used to adjust the pH. Zeta potentials were measured multiple times at each pH, ​​and the average value was calculated. The experimental results are shown in Figure 3 and Table 6. The average value was rounded to the first decimal place.

[0086]

[0087] The isoelectric points shown in Table 6 were obtained by plotting the average values ​​at each pH shown in Table 6 and approximating them using the least squares method as shown in Figure 4.

[0088] The experimental results shown in Figure 3 indicate that the zeta potential of the tin oxide thin film can be reduced to 20 mV or less in absolute value within the pH range of pH 6 to pH 8, preferably to 15 mV or less in absolute value, and more preferably to 10 mV or less in absolute value.

[0089] <Experiment on elemental analysis of the electron transport layer> In the experiment, glass / ITO / SnO ２ A device was fabricated with the following configuration: / PVK / Spiro-OmeTAD / A or Ag. ２ The first layer is an electron transport layer (film thickness 30 nm), the second layer is a perovskite layer (film thickness 500 nm), and the third layer is a hole transport layer (film thickness 100 nm).

[0090] In the experiment, the first and third thin film samples used in the above-mentioned <Experiment on the Crystal Size of Tin Oxide Thin Films> were used as electron transport layers, and devices A and B with the above-mentioned layer configurations were fabricated, respectively. Elemental analysis of the electron transport layers was performed using time-of-flight secondary ion mass spectrometry (GCIB-TOF-SIMS). An M6 (IONTOF Corporation) was used as the measurement device, with primary ion: Bi ３ ＋＋ Secondary ion polarity: positive and negative, etching ion: Ar-GCIB.

[0091]

[0092] As shown in Table 7, both devices A and B contain Li (lithium), which is a component doped into the hole transport layer. From this, it was found that the Li in the hole transport layer diffuses to the electron transport layer.

[0093] This application is based on Japanese Patent Application No. 2025-010195, filed on January 24, 2025. All of its contents are included here.

Claims

1. A dispersion containing tin oxide nanoparticles, characterized in that the cumulative 95% particle size in the cumulative particle size distribution of the tin oxide nanoparticles measured by dynamic light scattering is 55 nm or less.

2. The dispersion according to claim 1, characterized in that the cumulative 95% particle size is 35 nm or more and 40 nm or less.

3. The dispersion according to claim 1, characterized in that the cumulative 50% particle size in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 30 nm or less.

4. The dispersion according to claim 3, characterized in that the cumulative 50% particle size is 12 nm or more and 15 nm or less.

5. The dispersion according to claim 1 or 4, characterized in that the tin oxide nanoparticles further contain a halogen.

6. The dispersion according to claim 5, characterized in that the halogen contains at least chlorine.

7. The dispersion according to claim 1 or 4, characterized in that the pH is 1 or more and 8 or less.

8. A thin film formed from the dispersion according to claim 1 or claim 4, characterized in that it contains the tin oxide nanoparticles.

9. The electrical resistivity is 1.0 × 10⁻⁶ ６ The thin film according to claim 8, characterized in that it is Ω·cm or less.

10. The thin film according to claim 8, characterized in that the crystallite size of the tin oxide thin film is 1.5 nm or more and 6.0 nm or less.

11. The density of the tin oxide thin film is 1.0 g / cm³. ３ 6.0g / cm or more ３ The thin film according to feature 8, which is as follows:

12. The thin film according to claim 8, characterized in that the zeta potential of the tin oxide thin film is 20 mV or less in absolute value in the range of pH 6 to pH 8.

13. The thin film according to claim 8, characterized in that it is used as an electron transport layer for a photoelectric conversion element.

14. A photoelectric conversion element comprising the electron transport layer, active layer, and hole transport layer described in claim 10, wherein the active layer includes a perovskite semiconductor.

15. The photoelectric conversion element according to claim 14, characterized in that the electron transport layer contains an alkali metal.

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