Method for manufacturing dispersions, thin films, and methods for manufacturing photoelectric conversion elements

Abstract

The objective is 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. [Solution] The dispersion of the present disclosure is a dispersion containing tin oxide nanoparticles, wherein the tin oxide has a stoichiometric composition, the tin is tetravalent, and the cumulative 95% particle diameter in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 55 nm or less. Preferably, the cumulative 50% particle diameter in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 5 nm or more and 30 nm or less.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses an invention related to tin oxide particles containing a plurality of types of tin having different valences in the range of divalent to tetravalent, substantially not containing a dopant element, and having conductivity. In Patent Document 1, it is disclosed to apply the tin oxide particles to a transparent conductive film or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a photoelectric conversion device such as an organic solar cell or a perovskite solar cell, an electron transport layer for efficiently transporting electrons is provided.

[0005] By forming a thin film using a dispersion containing tin oxide particles, an electron transport layer containing the tin oxide particles can be formed. At this time, a dispersion having high dispersibility was required. It was found that when the dispersibility is low, the electrical resistivity of the electron transport layer becomes high and the power generation characteristics become insufficient.

[0006] The present disclosure has been made in view of the above problems, and an object thereof is to provide a dispersion containing tin oxide nanoparticles having excellent dispersibility, a thin film containing the tin oxide nanoparticles, and a photoelectric conversion device containing the tin oxide nanoparticles in an electron transport layer.

Means for Solving the Problems

[0007] The dispersion in this disclosure is SnO 2 of A dispersion containing tin oxide nanoparticles, wherein the cumulative 95% particle size in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 35 nm or more and 40 nm or less, and the cumulative 50% particle size in the cumulative particle size distribution measured by dynamic light scattering of the tin oxide nanoparticles is 12 nm or more and 30 nm or less. Furthermore, the tin oxide nanoparticles contain halogens and have a pH of 1 or more and 8 or less. It is characterized by the following:

[0008] Thin film of the disclosure Manufacturing method The dispersion described above Using Film formation do It is characterized by the following.

[0009] Photoelectric conversion element disclosed herein Manufacturing method teeth, electric The nanotransport layer, the active layer, and the hole transport layer The process of forming The device comprises, and the active layer includes a perovskite-type semiconductor. Furthermore, the electron transport layer is formed by the thin film manufacturing method described above. It is characterized by the following. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide a dispersion containing tin oxide nanoparticles that exhibits excellent dispersibility. By forming a thin film containing tin oxide nanoparticles using a 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. [Brief explanation of the drawing]

[0011] [Figure 1] This is a partial cross-sectional view of the solar cell of this embodiment. [Figure 2] It exhibits a perovskite structure. [Modes for carrying out the invention]

[0012] Hereinafter, an embodiment of the present disclosure (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof.

[0013] <Overview of the solar cell 101> FIG. 1 is a partial cross-sectional view showing an example of the solar cell 101 of the present embodiment. The solar cell 101 shown in FIG. 1 includes a first electrode 41 as a cathode and a second electrode 42 as an 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. Note that the stacking structure may be reversed.

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

[0015] The second electrode 42 has conductivity. Among the first electrode 41 and the second electrode 42, if the electrode on the light incident side has light transmittance, the other electrode does not necessarily have to have light transmittance. For example, the second electrode 42 is formed of a material having transparency and conductivity. The first electrode 41 and the second electrode 42 have a function of collecting holes and electrons generated by light absorption in the active layer 44. Thereby, electricity can be generated.

[0016] In the solar cell 101 of the present embodiment, the hole transport layer 45 is made of an inorganic substance or an organic substance having a function of transporting holes. The hole transport layer 45 is preferably made of an inorganic substance, and for example, is preferably formed of an inorganic oxide such as NiO or WO3. The hole transport layer 45 is particularly preferably formed of NiO nanoparticles. Further, for example, Al2O3 or the like can be mixed with NiO in the hole transport layer 45. Further, Li, Mg, Al, etc. may be doped into the metal oxide. Further, the hole transport layer 45 may be an inorganic substance other than an inorganic oxide. The electron transport layer 43 will be described later.

[0017] In this embodiment, the oxygen deficiency of the metal oxide constituting the electron transport layer 43 and the hole transport layer 45 is preferably smaller than that of the bulk material. That is, it is preferably a stoichiometric composition or close to the stoichiometric composition. The "bulk material" refers to a massive material containing the metal oxide, and its size and shape are not limited.

[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 (holes) upon receiving sunlight may be of any of the i-type, n-type, and 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 so that sunlight can be incident is called an n-i-p type solar cell, and the case where it is formed on the hole transport layer 45 side 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 FIG. 2. For example, M shown in FIG. 2 is Pb, O is Br or I, and R is NH3CH3.

[0021] Perovskite solar cells have sensitivity throughout the visible light region and are excellent in power generation efficiency. Also, compared with conventional silicon-based solar cells, they have the characteristic that the power generation efficiency dependence on the intensity (illuminance) of incident light is small. That is, they can be used not only outdoors but also indoors.

[0022] By using a perovskite semiconductor for the active layer 44, low-temperature processes such as coating, which were difficult to achieve with conventional silicon semiconductors, can be applied. In silicon solar cells, there are limitations on the installation area due to load problems. Therefore, in recent years, perovskite solar cells that can eliminate the limitations on the installation area and have high power generation efficiency are expected.

[0023] <Background leading 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 methods of fabricating solar cells using titanium dioxide (TiO2) require high-temperature firing (e.g., around 500°C), which raises concerns about high manufacturing costs and the potential for deformation of the film substrate. Furthermore, using mesoporous TiO2 thin films raises concerns about decomposition of other layers due to the photocatalytic effect, leading to a decrease in luminous 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 an electron transport layer is formed using tin oxide particles having multiple valencies, the carrier transport properties differ between the divalent and tetravalent states. This can lead to a mismatch in carrier balance with the active layer, impairing electron transport and resulting in insufficient power generation efficiency.

[0028] Furthermore, even when using tin oxide with essentially a single valency, if non-nanoparticle tin oxide particles were used, the lack of film density could impair transportability. Additionally, when using dispersions with low dispersibility, particles would aggregate, easily compromising film uniformity during coating. This could lead to poor formation of each layer, including subsequent processes, potentially resulting in defects such as short circuits.

[0029] Therefore, after diligent research by the inventors, we have developed a dispersion containing tin oxide nanoparticles with excellent dispersibility.

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

[0031] "Tin oxide nanoparticles" refer to nanoparticles whose main component is tin oxide, but do not exclude the presence of other minor or unavoidable components. Compositional analysis can be observed by X-ray diffraction (XRD). Furthermore, tin oxide nanoparticles consist of numerous single particles (one particle) in the dispersion. In this embodiment to improve dispersibility, it is preferable, though not limited, that a large number of nearly single particles are dispersed, but 90% or more, preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more of the particles exist as single particles. The tin oxide component contained in the tin oxide nanoparticles accounts for 90% or more, preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more of the total nanoparticles.

[0032] Tin oxide is SnO x This can be shown as follows. The tin oxide is preferably in a stoichiometric composition, and x is preferably 2. That is, the tin is tetravalent and preferably SnO2. Divalent tin (SnO) may be mixed in, but it is preferable that 90% or more, preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more of the particles are SnO2.

[0033] "Nanoparticles" refer to particles with an average particle size on the nanoscale. This makes it possible to improve the density of thin films formed using a dispersion containing tin oxide nanoparticles.

[0034] For dispersions containing tin oxide nanoparticles, the particle size distribution can be determined by dynamic light scattering. Dynamic light scattering is a method that derives the particle size (particle diameter) based on fluctuations in scattered light intensity, which depend on the Brownian motion of the particles, detected when laser light is irradiated onto a solution in which particles are dispersed and the change in scattered light is measured.

[0035] In this embodiment, the cumulative 95% particle size (D95) in the cumulative particle size distribution measured by dynamic light scattering of tin oxide nanoparticles is 55 nm or less. Furthermore, D95 is preferably 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less. By keeping D95 within the above range, the particle size of the tin oxide nanoparticles can be reduced. That is, aggregation of tin oxide nanoparticles is suppressed, and as described above, the majority of the tin oxide nanoparticles exist as single particles. This suppresses particle sedimentation and turbidity in the dispersion, reduces changes in dispersibility over time, and allows for excellent dispersibility over a long period.

[0036] Furthermore, in this embodiment, it is preferable that the cumulative 50% particle size (D50) in the cumulative particle size distribution measured by dynamic light scattering of tin oxide nanoparticles is 30 nm or less. More preferably, D50 is 20 nm or less, and even more preferably 18 nm or less. This makes it possible to reduce the particle size of the tin oxide nanoparticles and suppress variations, thereby obtaining better dispersibility. While there is no limit to the lower limit of D50, it may be, for example, 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 2nm and 10nm, and D90 can be larger than D50 and smaller than D95 and between 20nm and 40nm.

[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 the mixture is 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 order to include halogens in the tin oxide nanoparticles, for example, prolonged stirring of tin chloride and water as described above will produce SnO2 and HCl, and further stirring will allow Cl to be placed on the surface of the tin oxide nanoparticles as a ligand. Alternatively, a halogen compound may be added and the mixture may be 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 form containing tin oxide nanoparticles of this embodiment> 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] While not limiting the crystallite size of the tin oxide thin film, the crystallite size at the crystal plane (211) can be adjusted to be between 2 nm and 6 nm. A crystallite size of 2 nm and 5 nm is more preferable. The crystallite size can be measured, for example, by X-ray diffraction (e.g., Rigaku Mini Flex600C). Furthermore, while not limiting the surface roughness Sa of the thin film, it can be adjusted to be between 20 nm. Surface roughness Sa is a three-dimensional surface roughness and is expressed as the average value of the surface roughness in the measurement area. A surface roughness Sa of 10 nm or less is more preferable, and even more preferable is 5 nm or less. Also, since a smaller surface roughness Sa is 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 atomic force microscopy (AFM) (e.g., Park NX10).

[0047] As a result, the conductivity of the thin film can be improved. The dispersion of this embodiment has a small particle size of tin oxide nanoparticles, and since aggregation does not occur or occurs at a low rate, it has good dispersibility, and thereby the above-mentioned degree of crystallinity and surface roughness Sa can be obtained.

[0048] As described above, the thin film containing tin oxide nanoparticles of this embodiment has excellent conductivity and can therefore be preferably 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, the energy levels can be matched with those of the perovskite semiconductor, and excellent power generation characteristics can be obtained. [Examples]

[0049] The effects of this disclosure will be explained below with reference to the examples and comparative examples provided. However, this disclosure is not limited in any way to the following examples. In the experiment, a dispersion of tin oxide nanoparticles was prepared.

[0050] <Example 1> Weighed tin(II) chloride dihydrate and added it to deionized water at 25°C, and carried out mixing and stirring for 24 hours using a stirrer. Water was added to the obtained tin oxide nanoparticles, ultrasonic dispersion was performed, and a dispersion containing tin oxide nanoparticles dispersed in water was prepared. By long-time stirring, Cl is arranged on the surface of the tin oxide nanoparticles and functions as a ligand.

[0051] <Example 2> Manufactured under the same conditions as in 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.

[0052] <Comparative Example 1> To synthesize SnO2 nanoparticles, weighed tin chloride pentahydrate, put an aqueous sodium hydroxide solution into a stainless steel autoclave, and heated it at 150°C for 6 hours. The precipitate was centrifuged, thoroughly washed with deionized water and absolute ethanol, and then mixed and stirred in ion-exchanged water for dispersion.

[0053] <Comparative Example 2> After adding and dispersing an aqueous hydrochloric acid solution to the tin oxide nanoparticles of Comparative Example 1, tetramethylammonium hydroxide (TMAH) was added as a pH adjuster.

[0054] <Method for Measuring Particle Size Distribution> The particle size distribution of the tin oxide nanoparticles in the dispersion was measured with a particle size distribution measuring device. The measurement principle is the dynamic light scattering method. <Method for Measuring pH> The measurement was carried out using a pH meter. <Visual Observation> The dispersibility was evaluated by visual observation. Samples without precipitation and turbidity even over several days were marked as ○. Also, samples with precipitation and turbidity after 24 hours were marked as △. Further, samples with precipitation and turbidity immediately after the visual test were marked as ×.

[0055] <Method for Measuring Electrical Resistivity> The prepared tin oxide dispersion was applied to a glass substrate by spin coating to a thickness of approximately 100 nm, and then fired at 100°C for 30 minutes to form a thin film of tin oxide nanoparticles.

[0056] 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 cells was evaluated. The evaluation was performed using the following equipment.

[0057] 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).

[0058] A perovskite solar cell was fabricated as follows: A nickel oxide dispersion was deposited on an ITO substrate to obtain a hole transport layer. Lead iodide was then deposited on its surface by spin coating, followed by coating with methylammonium iodide. The lead iodide film and methylammonium iodide reacted to form an active layer (perovskite layer) consisting of lead iodide methylammonium.

[0059] Next, a thin film containing tin oxide nanoparticles of this example or comparative example was deposited on the surface of the active layer to obtain an electron transport layer. Silver was deposited on the surface of the electron transport layer as the upper electrode to fabricate a perovskite solar cell. Table 1 shows the experimental results for each sample.

[0060] [Table 1]

[0061] 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.

[0062] 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.

[0063] Furthermore, as shown in Table 1, in Examples 1 and 2, the pH of the dispersion was found to be between 1 and 8. On the other hand, in Comparative Examples 1 and 2, the pH of the dispersion was greater than 8.

[0064] 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.

[0065] In Examples 1 and 2, the reason for the excellent dispersibility obtained was primarily that the D95 of the cumulative particle size distribution measured by dynamic light scattering was reduced, specifically to 55 nm or less, which suppressed 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.

[0066] As shown in Table 1, in the examples, 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.

[0067] Furthermore, the energy conversion efficiency (PCE) was achieved to over 20%. 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. [Explanation of Symbols]

[0068] 41: 1st electrode 42:Second electrode 43: Electron transport layer 44:Active layer 45: Hole transport layer 46: Glass substrate 101: Solar cell

Claims

1. SnO ２ A dispersion containing tin oxide nanoparticles, The cumulative particle size distribution of the tin oxide nanoparticles measured by dynamic light scattering is such that the cumulative 95% particle size is between 35 nm and 40 nm. The cumulative particle size distribution of the tin oxide nanoparticles measured by dynamic light scattering is such that the cumulative 50% particle size is between 12 nm and 30 nm. The tin oxide nanoparticles further contain a halogen, The pH is between 1 and 8. A dispersion characterized by the following features.

2. The cumulative 50% particle size is 12 nm or more and 15 nm or less. The dispersion according to feature 1.

3. The halogen comprises at least chlorine. The dispersion according to feature 1.

4. The dispersion according to claim 2, characterized in that it contains at least one of the following as an organic solvent: alcohols, aromatic compounds, amide skeletons, or sulfoxide skeletons.

5. A method for producing a thin film, characterized by forming a film using the dispersion described in claim 1 or claim 2.

6. The electrical resistivity of the thin film is 1.0 × 10 ６ It is less than or equal to Ω·cm. The method for manufacturing a thin film according to claim 5.

7. The method for manufacturing a thin film according to claim 5, characterized in that it is used for forming an electron transport layer of a photoelectric conversion element.

8. A method comprising the steps of forming an electron transport layer, an active layer, and a hole transport layer, wherein the active layer comprises a perovskite semiconductor, and the electron transport layer is formed by the thin film manufacturing method described in Claim 7. A method for manufacturing a photoelectric conversion element, characterized by the above.

9. The tin oxide nanoparticles have a single valency (SnO). ２ Includes, A method for manufacturing a photoelectric conversion element according to claim 8, characterized in that the photoelectric conversion efficiency is 20% or more under sunlight.

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