Method for manufacturing photoelectric conversion element, photoelectric conversion element, and photoelectric conversion material

Abstract

A method for manufacturing a photoelectric conversion element according to the present disclosure comprises a step for forming a first electrode, a step for forming a photoelectric conversion layer, and a step for forming a second electrode. The step of forming a photoelectric conversion layer includes: preparing a solution mixture by mixing, to a precursor solution of a perovskite compound, a solution having dissolved therein at least one selected from the group consisting of phosphonium salts and sulfonium salts; and forming a coating film using the solution mixture.

Description

Photoelectric conversion element manufacturing method, photoelectric conversion element, and photoelectric conversion material

[0001] The present disclosure relates to a method for manufacturing a photoelectric conversion element, a photoelectric conversion element, and a photoelectric conversion material.

[0002] Non-Patent Document 1 discloses a technology in which quantum dot particles made of CsPbI3 are prepared, then dissolved in a solvent, a sulfonium salt is added and reacted, and a film of this solution is formed to prepare a solar cell, whereby the sulfonium salt fills in surface defects, improving efficiency.

[0003] Donglin Jia, and 4 others, Energy Environ. Sci. , 2022, Volume 15, p. 4201-4212

[0004] An object of the present disclosure is to provide a novel photoelectric conversion element capable of improving photoelectric conversion efficiency.

[0005] The method for manufacturing a photoelectric conversion element according to the present disclosure includes the steps of forming a first electrode, forming a photoelectric conversion layer, and forming a second electrode, and the step of forming the photoelectric conversion layer includes preparing a mixed solution by mixing a solution in which at least one selected from the group consisting of phosphonium salts and sulfonium salts is dissolved with a precursor solution of a perovskite compound, and forming a coating film using the mixed solution.

[0006] According to the manufacturing method of the present disclosure, a novel photoelectric conversion element capable of improving photoelectric conversion efficiency can be provided.

[0007] FIG. 1A shows the molecular structure of tributylmethylphosphonium iodide, an example of a quaternary phosphonium salt that can be used as a phosphonium salt in the photoelectric conversion element of the first embodiment. FIG. 1B shows the molecular structure of tributylsulfonium iodide, an example of a tertiary sulfonium salt that can be used as a sulfonium salt in the photoelectric conversion element of the first embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 100, an example of a photoelectric conversion element of the first embodiment. FIG. 3 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 1, Example 2, and Comparative Example 1. FIG. 4 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 1, Example 2, and Comparative Example 1. FIG. 5 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 1, Example 3, and Comparative Example 1. FIG. 6 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 1, Example 3, Comparative Example 1, and Comparative Example 2. FIG. 7 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 2, Example 4, Example 5, and Comparative Example 1. FIG. 8 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Examples 2, 4, 5, Comparative Example 1, and Comparative Example 2. FIG. 9 is a graph showing the IV characteristics of the photoelectric conversion elements of Examples 6, 7, and Comparative Example 1. FIG. 10 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Examples 6, 7, Comparative Example 1, and Comparative Example 2. FIG. 11 is a graph showing the photoluminescence (PL) spectrum of a photoelectric conversion layer single film formed from CsSnI3 + 16 mol% SnF2. FIG. 12 is a graph showing the PL spectrum of a photoelectric conversion layer single film formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylmethylphosphonium iodide. FIG. 13 is a graph showing the PL spectrum of a photoelectric conversion layer single film formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylsulfonium iodide. Figure 14 is a graph showing the PL lifetime of a photoelectric conversion layer single film formed from CsSnI3 + 16 mol% SnF2. Figure 15 is a graph showing the PL lifetime of a photoelectric conversion layer single film formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylmethylphosphonium iodide.Figure 16 is a graph showing the PL lifetime of a single photoelectric conversion layer formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylsulfonium iodide. Figure 17 shows a SEM (scanning electron microscope) photograph of a photoelectric conversion layer formed from CsSnI3 + 16 mol% SnF2 taken from the top. Figure 18 shows a SEM photograph of a photoelectric conversion layer formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylmethylphosphonium iodide taken from the top. Figure 19 shows a SEM photograph of a photoelectric conversion layer formed from CsSnI3 + 16 mol% SnF2 + 5 mol% tributylsulfonium iodide taken from the top.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0009] First Embodiment In the first embodiment, an embodiment of a method for manufacturing a photoelectric conversion element and a photoelectric conversion element according to the present disclosure will be described.

[0010] The photoelectric conversion element manufactured by the manufacturing method of the first embodiment is a photoelectric conversion element including a first electrode, a photoelectric conversion layer, and a second electrode.

[0011] The manufacturing method of the first embodiment includes a step of forming a first electrode, a step of forming a photoelectric conversion layer, and a step of forming a second electrode, and the step of forming the photoelectric conversion layer includes a step of preparing a mixed solution by mixing a solution in which at least one selected from the group consisting of phosphonium salts and sulfonium salts is dissolved with a precursor solution of a perovskite compound, and a step of forming a coating film using the mixed solution.

[0012] According to the above manufacturing method, a photoelectric conversion element with improved photoelectric conversion efficiency can be provided.

[0013] The mixed solution prepared in the step of forming the photoelectric conversion layer is a precursor solution of a material constituting the photoelectric conversion layer (hereinafter referred to as "photoelectric conversion material"). That is, in the step of forming the photoelectric conversion layer, a precursor solution of the photoelectric conversion material is prepared, and the photoelectric conversion layer is formed by a coating film formed from the precursor solution of the photoelectric conversion material.

[0014] In the step of forming the photoelectric conversion layer, the preparation of the mixed solution may include, for example, preparing a first solution containing a compound containing a monovalent cation and a halogen anion, a compound containing a divalent cation and a halogen anion, and a solvent, a second solution containing a compound containing a divalent cation and an F anion, and a solvent, and a third solution containing at least one selected from the group consisting of a phosphonium salt and a sulfonium salt, and a solvent, and mixing the second solution and the third solution with the first solution.

[0015] According to the above manufacturing method, a photoelectric conversion element with improved photoelectric conversion efficiency can be provided.

[0016] The step of forming the photoelectric conversion layer may further include baking the coating film.

[0017] According to the above manufacturing method, it is possible to provide a photoelectric conversion element with improved photoelectric conversion efficiency.

[0018] The solvent used in the step of forming the photoelectric conversion layer may be a single solvent or a mixed solvent containing multiple solvents, such as a mixed solvent containing DMF (dimethylformamide) and DMSO (dimethyl sulfoxide).

[0019] In the process of forming the photoelectric conversion layer, for example, the prepared mixed solution is applied to a substrate by a coating method such as spin coating, and the resulting coating film is left to stand for a predetermined time to allow crystal nuclei to grow in the coating film. The film obtained by spin coating is then baked. For example, when a mixed solvent of DMF and DMSO (e.g., a volume ratio of DMF:DMSO = 1:4) is used, for example, crystal nuclei may be grown in the coating film at room temperature, and then the coating film may be baked at a temperature of about 120 ° C or higher and 220 ° C or lower. For example, the photoelectric conversion layer can be obtained by growing crystal nuclei in the coating film at room temperature, followed by baking at 120 ° C for 1 minute, then at 160 ° C for 1 minute, and finally at 200 ° C for 10 minutes. In another example, the photoelectric conversion layer can be obtained by growing crystal nuclei in the coating film at room temperature, followed by baking at 50 ° C for 3 minutes, then at 70 ° C for 10 minutes, then at 120 ° C for 1 minute, and finally at 160 ° C for 10 minutes. The substrate is a base material when a photoelectric conversion layer is formed, and is, for example, a material adjacent to the photoelectric conversion layer in a photoelectric conversion element. When the photoelectric conversion layer is disposed on a first electrode and in contact with the first electrode, the substrate is the first electrode.

[0020] The photoelectric conversion element of the first embodiment can be obtained, for example, by the manufacturing method of the first embodiment. The photoelectric conversion element of the first embodiment includes a first electrode, a photoelectric conversion layer, and a second electrode, and the photoelectric conversion layer contains a perovskite compound and at least one selected from the group consisting of a phosphonium ion and a sulfonium ion.

[0021] By having the above configuration, the photoelectric conversion element of the first embodiment can improve the photoelectric conversion efficiency.

[0022] As described above, the photoelectric conversion layer in the photoelectric conversion element of the first embodiment includes a perovskite compound and at least one selected from the group consisting of phosphonium ions and sulfonium ions. For example, in the photoelectric conversion layer, the perovskite compound may be mixed with at least one selected from the group consisting of phosphonium ions and sulfonium ions, or the perovskite compound and at least one selected from the group consisting of phosphonium ions and sulfonium ions may be uniformly mixed throughout. Such a photoelectric conversion layer can be formed, for example, by the step of forming the photoelectric conversion layer in the manufacturing method of the first embodiment, i.e., using a mixed solution containing a precursor solution of the perovskite compound and at least one selected from the group consisting of phosphonium salts and sulfonium salts. One reason for the improved photoelectric conversion efficiency of such a photoelectric conversion layer is thought to be that forming the photoelectric conversion layer using a mixed solution containing at least one selected from the group consisting of phosphonium salts and sulfonium salts increases the particle size of the crystals of the perovskite compound in the photoelectric conversion layer, thereby reducing carrier recombination. Since a photoelectric conversion layer formed from a mixed solution containing at least one selected from the group consisting of phosphonium salts and sulfonium salts has an extended PL emission lifetime, it is believed that the carrier diffusion length is extended by including at least one selected from the group consisting of phosphonium ions and sulfonium ions.

[0023] In the photoelectric conversion element of the first embodiment, the average primary particle diameter of the perovskite compound contained in the photoelectric conversion layer may be, for example, 1 μm or more. Note that the primary particles of the perovskite compound contained in the photoelectric conversion layer are, for example, polycrystalline.

[0024] When the average primary particle diameter of the perovskite compound is 1 μm or more, carrier recombination is further reduced. This further improves the photoelectric conversion efficiency of the photoelectric conversion element of the first embodiment. The average primary particle diameter of the perovskite compound in the photoelectric conversion layer of the photoelectric conversion element of the first embodiment is determined by measuring the primary particle diameter of the perovskite compound using an SEM image and calculating an average value from the measured values. Here, the measured primary particle diameter is the average value of the maximum and minimum diameters of the primary particles. For example, 50 particles in the SEM image are selected in descending order of primary particle diameter. The average value is calculated using the primary particle diameters of these 50 particles, and the obtained value is defined as the average primary particle diameter. The average primary particle diameter of the perovskite compound is, for example, 100 μm or less.

[0025] Hereinafter, the "at least one ion selected from the group consisting of phosphonium ions and sulfonium ions" contained in the photoelectric conversion layer of the photoelectric conversion element of the first embodiment will be referred to as "phosphonium ions and / or sulfonium ions."

[0026] In the photoelectric conversion layer of the photoelectric conversion element of the first embodiment, phosphonium ions and / or sulfonium ions may be present between the crystals of the perovskite compound. The presence of phosphonium ions and / or sulfonium ions in this state in the photoelectric conversion layer is thought to form carrier paths between the crystals of the perovskite compound, thereby further suppressing carrier recombination. Therefore, with this configuration, the photoelectric conversion element of the first embodiment can further improve its photoelectric conversion efficiency.

[0027] The PL peak energy of the photoelectric conversion layer in the photoelectric conversion element of the first embodiment may be substantially the same as the PL peak energy of the perovskite compound contained in the photoelectric conversion layer. That is, the band gap of the photoelectric conversion layer in the photoelectric conversion element of the first embodiment may be substantially the same as the band gap of the perovskite compound contained in the photoelectric conversion layer. In other words, in the photoelectric conversion layer of the photoelectric conversion element of the first embodiment, the crystal structure of the perovskite compound does not change depending on the presence or absence of phosphonium ions and / or sulfonium ions, and the crystal structure of the perovskite compound to which neither phosphonium ions nor sulfonium ions are added can be maintained. Therefore, with this configuration, the photoelectric conversion layer in the photoelectric conversion element of the first embodiment can further improve photoelectric conversion efficiency without changing the light absorption characteristics (e.g., the wavelength of light absorbed). Here, "substantially the same PL peak energy" means that the difference in PL peak energy is within a range of 0 eV to 0.03 eV. Furthermore, the band gap being substantially the same means that the difference in band gap is within the range of 0 eV to 0.03 eV.

[0028] The PL peak energy of the photoelectric conversion layer in the photoelectric conversion element of the first embodiment may be, for example, smaller than 1.55 eV. That is, the PL peak wavelength of the photoelectric conversion layer in the photoelectric conversion element of the first embodiment may be greater than 800 nm. By having such a PL peak, the photoelectric conversion element of the first embodiment can further improve the photoelectric conversion efficiency. The PL peak energy of the photoelectric conversion layer in the photoelectric conversion element of the first embodiment may be, for example, 1.1 eV or more. That is, the PL peak wavelength of the photoelectric conversion material of the first embodiment may be 1127 nm or less.

[0029] In the photoelectric conversion element of the first embodiment, for example, the phosphonium ion is a cation that constitutes a part of the phosphonium salt, and the sulfonium ion is a cation that constitutes a part of the sulfonium salt. In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium ion salt and / or the sulfonium salt may contain at least one selected from the group consisting of an alkyl group and an aryl group. The number of carbon atoms in the alkyl group may be 1 or more and 10 or less. The number of carbon atoms in the alkyl group may be 1 or more and 7 or less.

[0030] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium salt and / or sulfonium salt may contain an alkyl group, and the number of carbon atoms in the alkyl group may be 1 or more and 10 or less. The number of carbon atoms in the alkyl group may be 1 or more and 7 or less.

[0031] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt may contain a quaternary phosphonium salt. The phosphonium salt may contain a quaternary phosphonium salt and a phosphonium salt other than the quaternary phosphonium salt. In order to further improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium salt may be a quaternary phosphonium salt.

[0032] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the sulfonium salt may contain a tertiary sulfonium salt. The sulfonium salt may contain a tertiary sulfonium salt and a sulfonium salt other than the tertiary sulfonium salt. In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the sulfonium salt may be a tertiary sulfonium salt.

[0033] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium salt and / or sulfonium salt may contain a halogen element, such as fluorine, chlorine, bromine, or iodine.

[0034] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium salt and / or sulfonium salt may contain iodine as the halogen element.

[0035] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the phosphonium salt may contain an iodine-containing phosphonium salt, which may contain at least one selected from the group consisting of tributylmethylphosphonium iodide, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide.

[0036] When a quaternary phosphonium salt containing iodine is used as the iodine-containing phosphonium salt, in order to further improve the photoelectric conversion efficiency of the photoelectric conversion element, the iodine-containing phosphonium salt may be at least one selected from the group consisting of tributylmethylphosphonium iodide, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide. Figure 1A shows the molecular structure of tributylmethylphosphonium iodide, an example of a quaternary phosphonium salt that can be used as the phosphonium salt in the photoelectric conversion element of the first embodiment. Hereinafter, tributylmethylphosphonium iodide will be referred to as "TBMPI."

[0037] In order to improve the photoelectric conversion efficiency of the photoelectric conversion element, the sulfonium salt may contain an iodine-containing sulfonium salt, which may contain at least one selected from the group consisting of tributylsulfonium iodide and trimethylsulfonium iodide.

[0038] When a tertiary sulfonium salt containing iodine is used as the iodine-containing sulfonium salt, the iodine-containing sulfonium salt may be at least one selected from the group consisting of tributylsulfonium iodide and trimethylsulfonium iodide, in order to further improve the photoelectric conversion efficiency of the photoelectric conversion element. Figure 1B shows the molecular structure of tributylsulfonium iodide, an example of a tertiary sulfonium salt that can be used as the sulfonium salt in the photoelectric conversion element of the first embodiment. Hereinafter, tributylsulfonium iodide will be referred to as "TBSI."

[0039] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion element, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound in the photoelectric conversion layer of the photoelectric conversion element of the first embodiment may be 0.01 or more and 0.50 or less.

[0040] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion element, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be 0.01 or more and 0.20 or less.

[0041] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion element, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be 0.05 or more and 0.10 or less.

[0042] The molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be defined by any combination selected from the following numerical values: 0.01, 0.05, 0.07, 0.1, 0.15, 0.2, and 0.5.

[0043] Perovskite compounds have a high light absorption coefficient in the wavelength region of the solar spectrum and high carrier mobility, so photoelectric conversion elements including a photoelectric conversion layer containing a perovskite compound have high photoelectric conversion efficiency.

[0044] The perovskite compound may contain a halogen anion, i.e., the perovskite compound may be a halide.

[0045] The perovskite compound may be composed of monovalent cations, divalent cations, and halogen anions, where the divalent cations may include at least one selected from the group consisting of Sn cations, Ge cations, and Pb cations.

[0046] The monovalent cations in the perovskite compound may comprise 50 mol % or more of inorganic cations.

[0047] Perovskite compounds are, for example, represented by the composition formula ABX3, where A is a monovalent cation, B is a divalent metal cation, and X is a monovalent anion.

[0048] Examples of the monovalent cation A are organic cations or alkali metal cations. As mentioned above, the monovalent cation A may contain 50 mol % or more of inorganic cations, i.e., alkali metal cations.

[0049] An example of an organic cation is the methylammonium cation (CH3NH3 + ), formamidinium cation (NH2CHNH2 + ) or guanidinium ion (C(NH2)3 + )

[0050] Examples of alkali metal cations are the Cs cation or the Rb cation.

[0051] B is a divalent metal cation. Examples of the divalent cation B are Pb, Sn, or Ge cations.

[0052] X is a monovalent anion. An example of the anion X is a halogen anion. The halogen anion is, for example, chlorine, bromine, or iodine.

[0053] Each of the sites of cation A, cation B, and anion X may contain multiple types of ions.

[0054] The perovskite compound may be at least one selected from the group consisting of CsSnI3, CsGeI3, and CsPbI3.

[0055] The photoelectric conversion layer in the photoelectric conversion element of the first embodiment may further contain SnF. When the perovskite compound contains Sn cations as divalent cations, the inclusion of SnF can reduce Sn defects. Therefore, the inclusion of SnF in the photoelectric conversion layer in the photoelectric conversion element of the first embodiment can improve the photoelectric conversion efficiency.

[0056] The configuration of the photoelectric conversion element of the first embodiment will be described in more detail below.

[0057] As described above, the photoelectric conversion element according to the first embodiment includes a first electrode, a photoelectric conversion layer, and a second electrode. The photoelectric conversion element according to the first embodiment may include the first electrode, the photoelectric conversion layer, and the second electrode in this order.

[0058] The photoelectric conversion element according to the first embodiment is, for example, a solar cell. In this specification, the light source of the solar cell is not limited to sunlight, and may be indoor lighting.

[0059] FIG. 2 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 100 as an example of the first embodiment.

[0060] The photoelectric conversion element 100 includes, in this order, a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. The substrate 1, the electron transport layer 3, and the hole transport layer 5 may not be provided.

[0061] The photoelectric conversion layer 4 may be a single layer or may be composed of multiple layers. When the photoelectric conversion layer 4 is a single layer, the photoelectric conversion layer 4 is the above-mentioned photoelectric conversion layer. When the photoelectric conversion layer 4 is composed of multiple layers, at least one layer of the multiple layers is the above-mentioned photoelectric conversion layer.

[0062] When light is irradiated onto the photoelectric conversion element 100, the photoelectric conversion layer 4 absorbs the light and separates into electrons and holes. Electrons generated by this charge separation pass through the electron transport layer 3 and move to the first electrode 2. Meanwhile, holes generated in the photoelectric conversion layer 4 move to the second electrode 6 via the hole transport layer 5. This allows the photoelectric conversion element 100 to extract current from the first electrode 2, which functions as a negative electrode, and the second electrode 6, which functions as a positive electrode.

[0063] Each component of the photoelectric conversion element 100 will be specifically described below.

[0064] (Substrate 1) The substrate 1 serves to support each layer of the photoelectric conversion element 100. The substrate 1 can be made of a transparent material. For example, a glass substrate or a plastic substrate can be used as the substrate 1. The plastic substrate may be, for example, a plastic film.

[0065] When the second electrode 6 is light-transmitting, the substrate 1 may be made of a material that does not transmit light, such as a metal, a ceramic, or a resin material with low light transmittance.

[0066] If the first electrode 2 has sufficient strength, the layers can be held by the first electrode 2, and therefore the substrate 1 does not need to be provided.

[0067] (First Electrode 2) The first electrode 2 has electrical conductivity.

[0068] The first electrode 2 has a light-transmitting property, for example, transmitting light in the visible to near-infrared region.

[0069] The first electrode 2 is made of, for example, a transparent and conductive material. Examples of such materials include metal oxides and metal nitrides. Examples of such materials include: (i) titanium oxide doped with at least one element selected from the group consisting of lithium, magnesium, niobium, and fluorine; (ii) gallium oxide doped with at least one element selected from the group consisting of tin and silicon; (iii) gallium nitride doped with at least one element selected from the group consisting of silicon and oxygen; (iv) tin oxide doped with at least one element selected from the group consisting of antimony and fluorine; (v) zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium; (vi) indium-tin composite oxide; or (vii) a composite thereof.

[0070] The first electrode 2 may be formed with a light-transmitting pattern. Examples of the light-transmitting pattern include a linear, wavy, lattice, or punched metal pattern in which a large number of fine through-holes are regularly or irregularly arranged. When the first electrode 2 has such a pattern, light can pass through portions where no electrode material is present. Therefore, by providing a light-transmitting pattern, a non-transparent material can be used. Examples of non-transparent electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of these. A conductive carbon material may also be used as the non-transparent electrode material.

[0071] The light-transmitting property of the first electrode 2 does not have to be achieved by the light-transmitting pattern described above. For example, the first electrode 2 may be formed of a thin metal film formed to a thickness of about 10 nm. Such a thin metal film may be, for example, platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of these. Instead of these metal materials, a conductive carbon material may be used.

[0072] When the photoelectric conversion element 100 does not include the electron transport layer 3, the first electrode 2 has a blocking property for holes from the photoelectric conversion layer 4. In this case, the first electrode 2 does not make ohmic contact with the photoelectric conversion layer 4. Furthermore, the blocking property for holes from the photoelectric conversion layer 4 refers to a property that allows only electrons generated in the photoelectric conversion layer 4 to pass through, but does not allow holes to pass through. The Fermi energy of a material having such a property is higher than the energy of the top of the valence band of the photoelectric conversion layer 4. The Fermi energy of a material having such a property may be higher than the Fermi energy of the photoelectric conversion layer 4. A specific example of such a material is aluminum.

[0073] When the photoelectric conversion element 100 includes the electron transport layer 3, the first electrode 2 does not need to have the ability to block holes from the photoelectric conversion layer 4. In this case, the first electrode 2 may be made of a material that can form an ohmic contact with the photoelectric conversion layer 4. In this case, the first electrode 2 may or may not be in ohmic contact with the photoelectric conversion layer 4.

[0074] The light transmittance of the first electrode 2 may be, for example, 50% or more, or 80% or more. The wavelength of light that the first electrode 2 should transmit depends on the absorption wavelength of the photoelectric conversion layer 4.

[0075] The thickness of the first electrode 2 may be, for example, not less than 1 nm and not more than 1000 nm.

[0076] (Electron Transport Layer 3) The electron transport layer 3 contains an electron transport material. The electron transport material may be a semiconductor. The electron transport layer 3 may be formed from a semiconductor having a band gap of 3.0 eV or more. This allows visible light and infrared light to transmit to the photoelectric conversion layer 4.

[0077] Examples of electron transporting materials are inorganic n-type semiconductors.

[0078] Examples of inorganic n-type semiconductors include metal oxides, metal nitrides, and perovskite oxides. Examples of metal oxides include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Examples of metal oxides include TiO2 or SnO2. Examples of metal nitrides include GaN. Examples of perovskite oxides include SrTiO3 or CaTiO3.

[0079] To allow ultraviolet light to effectively pass through to the photoelectric conversion layer 4, the electron transport layer 3 may be made of a semiconductor having a band gap of 6.0 eV or more. Examples of such semiconductors include alkali metal or alkaline earth metal halides such as lithium fluoride and calcium fluoride, alkali metal oxides such as magnesium oxide, and silicon dioxide. In this case, in order to ensure the electron transport properties of the electron transport layer 3, the electron transport layer 3 may have a thickness of, for example, 10 nm or less.

[0080] The electron transport layer 3 may include a plurality of layers made of different materials.

[0081] (Photoelectric conversion layer 4) As described above, the photoelectric conversion layer 4 corresponds to the photoelectric conversion layer in the photoelectric conversion element of the first embodiment described above. That is, the photoelectric conversion layer 4 contains a perovskite compound and phosphonium ions and / or sulfonium ions. In the photoelectric conversion layer 4, the phosphonium ions and / or sulfonium ions may be mixed with the perovskite compound, or the perovskite compound and the phosphonium ions and / or sulfonium ions may be mixed uniformly throughout. The photoelectric conversion layer 4 may have a uniform composition in the thickness direction, or may have a uniform composition throughout.

[0082] The photoelectric conversion layer 4 only needs to contain a perovskite compound and phosphonium ions and / or sulfonium ions, and may contain defects or impurities.

[0083] The photoelectric conversion layer 4 may further contain a component other than the perovskite compound, and the phosphonium ion and / or the sulfonium ion.

[0084] The thickness of the photoelectric conversion layer 4 is, for example, not less than 50 nm and not more than 10 μm.

[0085] The photoelectric conversion layer 4 can be formed by a solution coating method, a printing method, or a vapor deposition method. Examples of the coating method include a doctor blade method, a bar coating method, a spray method, a dip coating method, an inkjet method, a slit coating method (i.e., a die coating method), and a spin coating method.

[0086] (Hole Transport Layer 5) The hole transport layer 5 contains a hole transport material. The hole transport material is a material that transports holes. The hole transport material is, for example, an organic semiconductor or an inorganic semiconductor.

[0087] Examples of organic semiconductors are triphenylamine, triallylamine, phenylbenzidine, phenylenevinylene, tetrathiafulvalene, vinylnaphthalene, vinylcarbazole, thiophene, aniline, pyrrole, carbazole, triptycene, fluorene, azulene, pyrene, pentacene, perylene, acridine, or phthalocyanine.

[0088] Typical examples of organic semiconductors used as hole transport materials include 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter also referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl), poly(3,4-ethylenedioxythiophene), and copper phthalocyanine.

[0089] The inorganic semiconductor used as the hole transport material is a p-type semiconductor. Examples of inorganic semiconductors include CuO, CuGaO, CuSCN, CuI, and NiO. x , MoO x , VO, or a carbon material such as graphene oxide, where x satisfies x>0.

[0090] The hole transport layer 5 may include multiple layers made of different materials. For example, multiple layers may be stacked so that the ionization potentials of the hole transport layers 5 are successively smaller than the ionization potential of the photoelectric conversion layer 4, thereby improving the hole transport properties.

[0091] The thickness of the hole transport layer 5 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 50 nm or less. This allows sufficient hole transport properties to be exhibited. Therefore, the photoelectric conversion element 100 can maintain low resistance and achieve high photoelectric conversion efficiency.

[0092] The hole transport layer 5 is formed by, for example, a coating method, a printing method, or a vapor deposition method, similar to the photoelectric conversion layer 4. Examples of coating methods include a doctor blade method, a bar coating method, a spray method, a dip coating method, an inkjet method, a slit coating method (i.e., a die coating method), or a spin coating method. An example of a printing method is a screen printing method. If necessary, the hole transport layer 5 may be prepared by mixing multiple materials, and then pressurized or baked. When the material of the hole transport layer 5 is an organic low-molecular-weight substance or an inorganic semiconductor, the hole transport layer 5 can also be prepared by a vacuum vapor deposition method.

[0093] The hole transport layer 5 may contain not only a hole transport material but also an additive to enhance conductivity. Examples of the additive are a supporting electrolyte, a solvent, or a dopant. The supporting electrolyte and the solvent have the effect of stabilizing holes in the hole transport layer 5. The dopant has the effect of increasing the number of holes in the hole transport layer 5.

[0094] Examples of supporting electrolytes include ammonium salts, alkali metal salts, alkaline earth metal salts, and transition metal salts. Examples of ammonium salts include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts, and pyridinium salts. Examples of alkali metal salts include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate, and potassium tetrafluoride. Examples of alkaline earth metal salts include lithium bis(trifluoromethanesulfonyl)imide and calcium(II) bis(trifluoromethanesulfonyl)imide. Examples of transition metal salts include zinc(II) bis(trifluoromethanesulfonyl)imide and tris[4-tert-butyl-2-(1H-pyrazol-1-yl)pyridine]cobalt(III) tris(trifluoromethanesulfonyl)imide.

[0095] An example of the dopant is a fluorine-containing aromatic boron compound, such as tris(pentafluorophenyl)borane.

[0096] The solvent contained in the hole transport layer 5 may have excellent ion conductivity. The solvent may be an aqueous solvent or an organic solvent. To further stabilize the solute, the solvent contained in the hole transport layer 5 may be an organic solvent. Examples of the organic solvent include heterocyclic compound solvents such as tert-butylpyridine (tBP), pyridine, and n-methylpyrrolidone.

[0097] For example, PTAA may be used as the hole transport material, and LiTFSI and tBP may be used as the additives.

[0098] Ionic liquids may be used as the solvent. The ionic liquids may be used alone or in combination with other solvents. Ionic liquids are desirable because of their low volatility and high flame retardancy.

[0099] Examples of ionic liquids are imidazolium-based ionic liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine-based ionic liquids, alicyclic amine-based ionic liquids, aliphatic amine-based ionic liquids, or azonium amine-based ionic liquids.

[0100] (Second Electrode 6) The second electrode 6 has electrical conductivity.

[0101] When the photoelectric conversion element 100 does not include the hole transport layer 5, the second electrode 6 has a blocking property for electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 does not make ohmic contact with the photoelectric conversion layer 4. The blocking property for electrons from the photoelectric conversion layer 4 means a property of passing only holes generated in the photoelectric conversion layer 4 and not passing electrons. The Fermi energy of a material having such a property is lower than the energy of the bottom of the conduction band of the photoelectric conversion layer 4. The Fermi energy of a material having such a property may be lower than the Fermi energy of the photoelectric conversion layer 4. Specific examples of such materials include platinum, gold, and carbon materials such as graphene.

[0102] When the photoelectric conversion element 100 includes the hole transport layer 5, the second electrode 6 does not need to have a blocking property for electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 may be made of a material that can form an ohmic contact with the photoelectric conversion layer 4. This allows the second electrode 6 to be formed to have light-transmitting properties.

[0103] Of the first electrode 2 and the second electrode 6, it is sufficient that the electrode on the light incident side has light-transmitting properties. Therefore, one of the first electrode 2 and the second electrode 6 does not have to have light-transmitting properties. In other words, one of the first electrode 2 and the second electrode 6 does not have to use a light-transmitting material or have a pattern including openings that transmit light.

[0104] (Porous Layer) The porous layer is formed on the electron transport layer 3 by, for example, a coating method. When the photoelectric conversion element 100 does not include the electron transport layer 3, the porous layer is formed on the first electrode 2.

[0105] The pore structure introduced by the porous layer serves as a base for forming the photoelectric conversion layer 4. The porous layer does not inhibit light absorption by the photoelectric conversion layer 4 or electron transfer from the photoelectric conversion layer 4 to the electron transport layer 3.

[0106] The porous layer includes a porous body.

[0107] The porous body is formed, for example, by a series of insulating or semiconducting particles. Examples of insulating particles include aluminum oxide particles or silicon oxide particles. Examples of semiconducting particles include inorganic semiconductor particles. Examples of inorganic semiconductors include metal oxides, perovskite oxides of metal elements, sulfides of metal elements, and metal chalcogenides. Examples of metal oxides include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Examples of metal oxides include TiO2. Examples of perovskite oxides of metal elements include SrTiO3 or CaTiO3. Examples of sulfides of metal elements are CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides are CsSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0108] The thickness of the porous layer may be 0.01 μm or more and 10 μm or less, or 0.05 μm or more and 1 μm or less.

[0109] The surface roughness of the porous layer may have a surface roughness coefficient of 10 or more, or even 100 or more, given by effective area / projected area. Projected area is the area of ​​the shadow cast behind an object when it is illuminated with light from directly in front of it. Effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume determined from the projected area and thickness of the object, and the specific surface area and bulk density of the material that makes up the object. The specific surface area is measured, for example, by nitrogen adsorption.

[0110] The voids in the porous layer are connected from one main surface of the porous layer to the other main surface. That is, the voids in the porous layer are connected from the main surface of the porous layer in contact with the photoelectric conversion layer 4 to the main surface of the porous layer in contact with the electron transport layer 3. This allows the material of the photoelectric conversion layer 4 to fill the voids in the porous layer and reach the surface of the electron transport layer 3. Therefore, the photoelectric conversion layer 4 and the electron transport layer 3 are in direct contact with each other, allowing electrons to be exchanged.

[0111] The provision of a porous layer has the effect of facilitating the formation of the photoelectric conversion layer 4. By providing the porous layer, the material of the photoelectric conversion layer 4 penetrates into the voids in the porous layer, and the porous layer serves as a base for the photoelectric conversion layer 4. Therefore, the material of the photoelectric conversion layer 4 is less likely to be repelled or aggregate on the surface of the porous layer. Therefore, the photoelectric conversion layer 4 can be easily formed as a uniform film. The photoelectric conversion layer 4 can be formed by the above-mentioned coating method or the like.

[0112] Light scattering caused by the porous layer is also expected to have the effect of increasing the optical path length of light passing through the photoelectric conversion layer 4. When the optical path length increases, the amount of electrons and holes generated in the photoelectric conversion layer 4 is expected to increase.

[0113] Second Embodiment A first example of a photoelectric conversion material according to a second embodiment includes a perovskite compound and phosphonium ions.

[0114] A second example of the photoelectric conversion material of the second embodiment includes a perovskite compound and a sulfonium ion.

[0115] A third example of the photoelectric conversion material of the second embodiment includes a perovskite compound, a phosphonium ion, and a sulfonium ion.

[0116] Hereinafter, the first to third examples of the photoelectric conversion material of the second embodiment will be collectively referred to as the photoelectric conversion material of the second embodiment. That is, the photoelectric conversion material of the second embodiment is a photoelectric conversion material containing a perovskite compound and at least one ion selected from the group consisting of a phosphonium ion and a sulfonium ion.

[0117] With the above configuration, the photoelectric conversion material of the second embodiment can improve the photoelectric conversion efficiency.

[0118] The photoelectric conversion material of the second embodiment may be, for example, a mixed material in which a perovskite compound is mixed with at least one selected from the group consisting of phosphonium ions and sulfonium ions. The photoelectric conversion material of the second embodiment may also be a uniform mixture of a perovskite compound and at least one selected from the group consisting of phosphonium ions and sulfonium ions. Therefore, with such a configuration, the photoelectric conversion material of the second embodiment can further improve the photoelectric conversion efficiency. One reason for this improvement in photoelectric conversion efficiency is believed to be that the inclusion of at least one selected from the group consisting of phosphonium ions and sulfonium ions increases the particle size of the crystals of the perovskite compound in the photoelectric conversion material, thereby reducing carrier recombination. Since the inclusion of at least one selected from the group consisting of phosphonium ions and sulfonium ions extends the PL emission lifetime, the inclusion of at least one selected from the group consisting of phosphonium ions and sulfonium ions is also believed to extend the carrier diffusion length.

[0119] In the photoelectric conversion material of the second embodiment, the average primary particle diameter of the perovskite compound may be, for example, 1 μm or more. The primary particles of the perovskite compound contained in the photoelectric conversion material are, for example, polycrystalline. When the average primary particle diameter of the perovskite compound is 1 μm or more, carrier recombination is further reduced. This further improves the photoelectric conversion efficiency of the photoelectric conversion material of the second embodiment. The average primary particle diameter of the perovskite compound in the photoelectric conversion material of the second embodiment is determined by measuring the primary particle diameter of the perovskite compound using an SEM image and calculating an average value from the measured values. Here, the measured primary particle diameter is the average value of the maximum and minimum diameters of the primary particles. For example, 50 particles in the SEM image are selected in descending order of primary particle diameter. The average value is calculated using the primary particle diameters of these 50 particles, and the obtained value is the average primary particle diameter. The average primary particle diameter of the perovskite compound is, for example, 100 μm or less.

[0120] Hereinafter, the "at least one salt selected from the group consisting of phosphonium ions and sulfonium salts" contained in the photoelectric conversion material of the second embodiment will be referred to as "phosphonium ions and / or sulfonium ions."

[0121] In the photoelectric conversion material of the second embodiment, phosphonium ions and / or sulfonium ions may be present between the crystals of the perovskite compound. The presence of phosphonium ions and / or sulfonium ions in this state in the photoelectric conversion material is thought to form carrier paths between the crystals of the perovskite compound, thereby further suppressing carrier recombination. Therefore, with this configuration, the photoelectric conversion material of the second embodiment can further improve photoelectric conversion efficiency.

[0122] The PL peak energy of the photoelectric conversion material of the second embodiment may be substantially the same as the PL peak energy of the perovskite compound contained in the photoelectric conversion material. That is, the band gap of the photoelectric conversion material of the second embodiment may be substantially the same as the band gap of the perovskite compound contained in the photoelectric conversion material. In other words, the crystal structure of the photoelectric conversion material of the second embodiment does not change depending on the presence or absence of phosphonium ions and / or sulfonium ions, and the crystal structure of the perovskite compound to which neither phosphonium ions nor sulfonium ions are added can be maintained. Therefore, with this configuration, the photoelectric conversion material of the second embodiment can further improve photoelectric conversion efficiency without changing the light absorption characteristics (e.g., the wavelength of light absorbed). Here, "substantially the same PL peak energy" means that the difference in PL peak energy is within a range of 0 eV to 0.03 eV. Furthermore, "substantially the same band gap" means that the difference in band gap is within a range of 0 eV to 0.03 eV.

[0123] The PL peak energy of the photoelectric conversion material of the second embodiment may be, for example, smaller than 1.55 eV. That is, the PL peak wavelength of the photoelectric conversion material of the second embodiment may be greater than 800 nm. By having such a PL peak, the photoelectric conversion material of the second embodiment can further improve the photoelectric conversion efficiency. The PL peak energy of the photoelectric conversion material of the second embodiment may be, for example, 1.1 eV or greater. That is, the PL peak wavelength of the photoelectric conversion material of the second embodiment may be 1127 nm or less.

[0124] In the photoelectric conversion material of the second embodiment, for example, the phosphonium ion is a cation that constitutes a part of the phosphonium salt, and the sulfonium ion is a cation that constitutes a part of the sulfonium salt. In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt and / or the sulfonium salt may contain at least one selected from the group consisting of an alkyl group and an aryl group. The number of carbon atoms in the alkyl group may be 1 or more and 10 or less. The number of carbon atoms in the alkyl group may be 1 or more and 7 or less.

[0125] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt and / or sulfonium salt may contain an alkyl group, and the number of carbon atoms in the alkyl group may be 1 or more and 10 or less. The number of carbon atoms in the alkyl group may be 1 or more and 7 or less.

[0126] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt may contain a quaternary phosphonium salt. The phosphonium salt may contain a quaternary phosphonium salt and a phosphonium salt other than the quaternary phosphonium salt. In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt may be a quaternary phosphonium salt.

[0127] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the sulfonium salt may contain a tertiary sulfonium salt. The sulfonium salt may contain a tertiary sulfonium salt and a sulfonium salt other than the tertiary sulfonium salt. In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the sulfonium salt may be a tertiary sulfonium salt.

[0128] To improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt and / or sulfonium salt may contain a halogen element, such as fluorine, chlorine, bromine, or iodine.

[0129] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt and / or sulfonium salt may contain iodine as the halogen element.

[0130] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the phosphonium salt may include an iodine-containing phosphonium salt, and the iodine-containing phosphonium salt may include at least one selected from the group consisting of TBMPI, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide.

[0131] When a quaternary phosphonium salt containing iodine is used as the iodine-containing phosphonium salt, in order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the iodine-containing phosphonium salt may be at least one selected from the group consisting of TBMPI, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide. The molecular structure of TBMPI is as shown in Figure 1A.

[0132] In order to improve the photoelectric conversion efficiency of the photoelectric conversion material, the sulfonium salt may contain an iodine-containing sulfonium salt, which may contain at least one selected from the group consisting of tributylsulfonium iodide and trimethylsulfonium iodide.

[0133] When a tertiary sulfonium salt containing iodine is used as the iodine-containing sulfonium salt, the iodine-containing sulfonium salt may be at least one selected from the group consisting of TBSI and trimethylsulfonium iodide, in order to further improve the photoelectric conversion efficiency of the photoelectric conversion material. The molecular structure of TBSI is as shown in Figure 1B.

[0134] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, in the photoelectric conversion material of the second embodiment, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be 0.01 or more and 0.50 or less.

[0135] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be 0.01 or more and 0.20 or less.

[0136] In order to further improve the photoelectric conversion efficiency of the photoelectric conversion material, the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be 0.05 or more and 0.10 or less.

[0137] The molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound may be defined by any combination selected from the following numerical values: 0.01, 0.05, 0.07, 0.1, 0.15, 0.2, and 0.5.

[0138] Perovskite compounds have a high light absorption coefficient in the wavelength region of the solar spectrum and high carrier mobility, so photoelectric conversion materials containing perovskite compounds have high photoelectric conversion efficiency.

[0139] The perovskite compound may contain a halogen anion, i.e., the perovskite compound may be a halide.

[0140] The perovskite compound may be composed of monovalent cations, divalent cations, and halogen anions, where the divalent cations may include at least one selected from the group consisting of Sn cations, Ge cations, and Pb cations.

[0141] The monovalent cations in the perovskite compound may comprise 50 mol % or more of inorganic cations.

[0142] Perovskite compounds are, for example, represented by the composition formula ABX3, where A is a monovalent cation, B is a divalent metal cation, and X is a monovalent anion.

[0143] Examples of the monovalent cation A are organic cations or alkali metal cations. As mentioned above, the monovalent cation A may contain 50 mol % or more of inorganic cations, i.e., alkali metal cations.

[0144] An example of an organic cation is the methylammonium cation (CH3NH3 + ), formamidinium cation (NH2CHNH2 + ) or guanidinium ion (C(NH2)3 + )

[0145] Examples of alkali metal cations are the Cs cation or the Rb cation.

[0146] B is a divalent metal cation. Examples of the divalent cation B are Pb, Sn, or Ge cations.

[0147] X is a monovalent anion. An example of the anion X is a halogen anion. The halogen anion is, for example, chlorine, bromine, or iodine.

[0148] Each of the sites of cation A, cation B, and anion X may contain multiple types of ions.

[0149] The perovskite compound may be at least one selected from the group consisting of CsSnI3, CsGeI3, and CsPbI3.

[0150] The photoelectric conversion material of the second embodiment may further contain SnF. When the perovskite compound contains Sn cations as divalent cations, the inclusion of SnF can reduce Sn defects. Therefore, the photoelectric conversion material of the second embodiment can improve photoelectric conversion efficiency by further containing SnF.

[0151] The photoelectric conversion material of the second embodiment can be produced, for example, by the following method.

[0152] First, a precursor solution of the photoelectric conversion material of the second embodiment is prepared. The precursor solution of the photoelectric conversion material of the second embodiment can be prepared, for example, by mixing a solution of a phosphonium salt and / or sulfonium salt with a precursor solution of a perovskite compound. Raw materials used in preparing the precursor solution of the photoelectric conversion material of the second embodiment include, for example, a compound containing a monovalent cation and a halogen anion, such as CsI, a compound containing a divalent cation and a halogen anion, such as SnI, and a compound containing a divalent cation and an F anion, such as SnF. A single solvent may be used as the solvent, or a mixed solvent containing multiple solvents may be used. The solvent may be, for example, a mixed solvent containing DMF and DMSO.

[0153] The precursor solution of the photoelectric conversion material of the second embodiment may be prepared, for example, by first preparing a first solution containing a compound containing a monovalent cation and a halogen anion, a compound containing a divalent cation and a halogen anion, and a solvent, a second solution containing a compound containing a divalent cation and an F anion, and a solvent, and a third solution containing a phosphonium salt and / or a sulfonium salt, and a solvent, and then mixing the second solution and the third solution with the first solution.

[0154] Next, the prepared precursor solution of the photoelectric conversion material of the second embodiment is applied to a substrate by a coating method such as spin coating, and the resulting coating film is left to stand for a predetermined time to allow crystal nuclei to grow in the coating film. The film obtained by spin coating is then baked. For example, when a mixed solvent of DMF and DMSO (e.g., a volume ratio of DMF:DMSO = 1:4) is used, crystal nuclei may be grown in the coating film at room temperature, and then the coating film may be baked at a temperature of about 120 ° C or higher and 220 ° C or lower.

[0155] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0156] (Technology 1) A method for manufacturing a photoelectric conversion element, comprising: a step of forming a first electrode; a step of forming a photoelectric conversion layer; and a step of forming a second electrode, wherein the step of forming the photoelectric conversion layer comprises: preparing a mixed solution by mixing a solution in which at least one selected from the group consisting of a phosphonium salt and a sulfonium salt is dissolved with a precursor solution of a perovskite compound; and forming a coating film using the mixed solution.

[0157] According to this manufacturing method, a novel photoelectric conversion element capable of improving photoelectric conversion efficiency can be provided.

[0158] (Technology 2) In the step of forming the photoelectric conversion layer, the preparation of the mixed solution includes preparing a first solution containing a compound containing a monovalent cation and a halogen anion, a compound containing a divalent cation and a halogen anion, and a solvent, a second solution containing a compound containing a divalent cation and an F anion, and a solvent, and a third solution containing at least one selected from the group consisting of the phosphonium salt and the sulfonium salt, and a solvent, and mixing the second solution and the third solution with the first solution.

[0159] According to this manufacturing method, the photoelectric conversion efficiency of the manufactured photoelectric conversion element can be further improved.

[0160] (Technology 3) The method for producing a photoelectric conversion element according to Technology 1 or 2, wherein the step of forming the photoelectric conversion layer further includes baking the coating film.

[0161] According to this manufacturing method, the photoelectric conversion efficiency of the manufactured photoelectric conversion element can be further improved.

[0162] (Technology 4) A photoelectric conversion element comprising: a first electrode, a photoelectric conversion layer, and a second electrode, wherein the photoelectric conversion layer contains a perovskite compound and at least one selected from the group consisting of a phosphonium ion and a sulfonium ion.

[0163] This configuration makes it possible to provide a novel photoelectric conversion element capable of improving photoelectric conversion efficiency.

[0164] (Technology 5) The photoelectric conversion element according to Technology 4, wherein the perovskite compound has an average primary particle size of 1 μm or more.

[0165] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0166] (Technology 6) The photoelectric conversion element according to Technology 4 or 5, wherein at least one selected from the group consisting of phosphonium ions and sulfonium ions is present between crystals of the perovskite compound.

[0167] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0168] (Technology 7) The photoelectric conversion element according to any one of Technologies 4 to 6, wherein the photoelectric conversion layer has a photoluminescence emission peak energy that is substantially the same as the photoluminescence emission peak energy of the perovskite compound.

[0169] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element without changing the light absorption characteristics (for example, the wavelength of light to be absorbed).

[0170] (Technology 8) The photoelectric conversion element according to any one of Technologies 4 to 7, wherein the phosphonium ion is a cation that constitutes a part of a phosphonium salt, the sulfonium ion is a cation that constitutes a part of a sulfonium salt, and at least one selected from the group consisting of the phosphonium salt and the sulfonium salt includes at least one selected from the group consisting of an alkyl group and an aryl group.

[0171] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0172] (Technology 9) The photoelectric conversion element according to Technology 8, wherein at least one selected from the group consisting of the phosphonium salt and the sulfonium salt contains an alkyl group, and the alkyl group has 1 or more and 10 or less carbon atoms.

[0173] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0174] (Technology 10) The photoelectric conversion element according to Technology 8 or 9, wherein the phosphonium salt includes a quaternary phosphonium salt.

[0175] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0176] (Technology 11) The photoelectric conversion element according to Technology 8 or 9, wherein the sulfonium salt includes a tertiary sulfonium salt.

[0177] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0178] (Technology 12) The photoelectric conversion element according to any one of Techniques 8 to 11, wherein at least one selected from the group consisting of the phosphonium salt and the sulfonium salt contains a halogen element.

[0179] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0180] (Technology 13) The photoelectric conversion material according to Technology 12, wherein the halogen element includes iodine.

[0181] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0182] (Technology 14) The photoelectric conversion material according to any one of Techniques 8 to 13, wherein the phosphonium salt includes an iodine-containing phosphonium salt.

[0183] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0184] (Technology 15) The photoelectric conversion element according to Technology 14, wherein the iodine-containing phosphonium salt includes at least one selected from the group consisting of tributylmethylphosphonium iodide, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide.

[0185] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0186] (Technology 16) The photoelectric conversion element according to any one of Techniques 8 to 15, wherein the sulfonium salt includes an iodine-containing sulfonium salt.

[0187] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0188] (Technology 17) The photoelectric conversion element according to Technology 16, wherein the iodine-containing sulfonium salt includes at least one selected from the group consisting of tributylsulfonium iodide and trimethylsulfonium iodide.

[0189] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0190] (Technology 18) The photoelectric conversion element according to any one of Techniques 8 to 17, wherein a molar ratio of the phosphonium salt or the sulfonium salt to the perovskite compound is 0.01 or more and 0.50 or less.

[0191] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0192] (Technology 19) The photoelectric conversion element according to Technology 18, wherein the molar ratio is 0.05 or more and 0.10 or less.

[0193] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0194] (Technology 20) The photoelectric conversion element according to any one of Techniques 4 to 19, wherein the perovskite compound contains a halogen anion.

[0195] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0196] (Technology 21) The photoelectric conversion element according to any one of Technologies 4 to 20, wherein the perovskite compound is composed of monovalent cations, divalent cations, and halogen anions, and the divalent cations include at least one selected from the group consisting of Sn cations, Ge cations, and Pb cations.

[0197] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0198] (Technology 22) The photoelectric conversion element according to Technology 21, wherein the monovalent cations contain 50 mol % or more of inorganic cations.

[0199] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0200] (Technology 23) The photoelectric conversion element according to Technology 21 or 22, wherein the perovskite compound is at least one selected from the group consisting of CsSnI3, CsGeI3, and CsPbI3.

[0201] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0202] (Technology 24) The photoelectric conversion element according to any one of Techniques 4 to 23, wherein the photoelectric conversion layer further contains SnF2.

[0203] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion element.

[0204] (Technology 25) A photoelectric conversion material comprising a perovskite compound and a phosphonium ion.

[0205] This configuration makes it possible to provide a novel photoelectric conversion material that can improve photoelectric conversion efficiency.

[0206] (Technology 26) The photoelectric conversion material according to Technology 25, wherein the perovskite compound has an average primary particle size of 1 μm or more.

[0207] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion material.

[0208] (Technology 27) A photoelectric conversion material comprising a perovskite compound and a sulfonium ion.

[0209] This configuration makes it possible to provide a novel photoelectric conversion material that can improve photoelectric conversion efficiency.

[0210] (Technology 28) The photoelectric conversion material according to Technology 27, wherein the perovskite compound has an average primary particle size of 1 μm or more.

[0211] This configuration can further improve the photoelectric conversion efficiency of the photoelectric conversion material.

[0212] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0213] Hereinafter, preparation of raw material solutions for the photoelectric conversion layer and the hole transport layer and film formation were carried out in a glove box with oxygen and moisture concentrations of 1 ppm or less.

[0214] <Fabrication of Photoelectric Conversion Element> Example 1 First, a glass substrate was prepared. The substrate served as a support material for the photoelectric conversion element of the present disclosure.

[0215] An ITO (Indium Tin Oxide) layer was formed on the substrate by sputtering. An ATO (Antimony Tin Oxide) layer was further formed on the ITO layer by sputtering. In this manner, a first electrode was formed.

[0216] Next, a dense layer of titanium oxide (TiO2) was formed on the ATO layer of the first electrode by sputtering. This dense layer of titanium oxide (TiO2) corresponds to, for example, the electron transport layer described in the first embodiment.

[0217] Next, 0.45 g of titanium oxide paste (30NR-D, manufactured by Gratcell Solar Materials Pty Ltd.) was dissolved in 2 mL of butanol solution. The resulting solution was applied to the electron transport layer by spin coating and then baked at 500°C for 20 minutes. In this way, a porous titanium oxide layer was formed. Spin coating was performed at 4000 rpm for 20 seconds. Both the dense titanium oxide layer and the porous titanium oxide layer possess electron transport properties. Therefore, it is also possible to consider that the electron transport layer is composed of the dense titanium oxide layer and the porous titanium oxide layer.

[0218] The precursor solution of the photoelectric conversion material was applied to the porous layer by spin coating and then allowed to stand at room temperature for 10 minutes. The coating film was then baked at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 200°C for 10 minutes. In this way, a photoelectric conversion layer was formed. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds.

[0219] The precursor solutions of the photoelectric conversion material were obtained as follows. First, a 1.5 mol / L first solution was prepared by adding SnI2 and CsI to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4). Next, a 1.5 mol / L second solution was prepared by adding SnF2 to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4). Furthermore, a 1.5 mol / L third solution was prepared by adding TBMPI to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4). The second and third solutions were then added to the first solution. As a result, a precursor solution of the photoelectric conversion material was obtained.

[0220] In Example 1, a precursor solution was used in which the additive concentration of the second solution was 16 mol % and the additive concentration of the third solution was 5 mol % relative to the first solution. As described above, the photoelectric conversion layer was obtained by baking a coating film formed using the precursor solution at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 200°C for 10 minutes.

[0221] Next, the raw material solution for the hole transport layer was applied onto the photoelectric conversion layer by spin coating. In this way, the hole transport layer was formed. The raw material solution for the hole transport layer was prepared by dissolving 18 mg of PTAA (poly[bis(4-phenyl)(2,4,6-triphenyl)amine]) in 1 mL of chlorobenzene. Spin coating was performed at 4000 rpm for 20 seconds.

[0222] Next, a gold film was formed on the hole transport layer by vapor deposition, thus forming a second electrode having a thickness of 200 nm.

[0223] Finally, a UV-curable epoxy resin was applied to the periphery of the substrate, and the substrate was attached to another glass substrate and irradiated with UV light. In this way, the epoxy resin was cured and the power generating element was sealed.

[0224] (Example 2) A photoelectric conversion element was produced in the same manner as in Example 1, except that in preparing the precursor solution of the photoelectric conversion material in the production of the photoelectric conversion layer, the addition concentration of the third solution was set to 7.5 mol%.

[0225] (Example 3) A photoelectric conversion element was produced in the same manner as in Example 1, except that in producing the photoelectric conversion layer, the baking temperature of the coating film formed from the precursor solution of the photoelectric conversion material was set to 120°C for 1 minute, then 160°C for 1 minute, and finally 180°C for 10 minutes.

[0226] (Example 4) A photoelectric conversion element was produced in the same manner as in Example 1, except that in producing the photoelectric conversion layer, when preparing the precursor solution of the photoelectric conversion material, the addition concentration of the third solution was set to 7.5 mol%, and the baking temperature of the coating film formed from the precursor solution of the photoelectric conversion material was set to 120°C for 1 minute, then 160°C for 1 minute, and finally 180°C for 10 minutes.

[0227] (Example 5) In the production of the photoelectric conversion layer, a precursor solution of the photoelectric conversion material with an additive concentration of the third solution of 7.5 mol% was used when preparing the precursor solution of the photoelectric conversion material, and the baking temperature of the coating film formed from the precursor solution of the photoelectric conversion material was set to 120°C for 1 minute, then 160°C for 1 minute, and finally 220°C for 10 minutes. A photoelectric conversion element was produced in the same manner as in Example 1, except for this.

[0228] Example 6 A photoelectric conversion element was produced in the same manner as in Example 1, except that in producing the photoelectric conversion layer, TBSI was used instead of TBMPI as the solute of the third solution when preparing the precursor solution of the photoelectric conversion material, and the baking temperatures of the coating film formed from the precursor solution of the photoelectric conversion material were 120°C for 1 minute, then 160°C for 1 minute, and finally 180°C for 10 minutes.

[0229] (Example 7) A photoelectric conversion element was produced in the same manner as in Example 1, except that in preparing the precursor solution of the photoelectric conversion material in the production of the photoelectric conversion layer, TBSI was used instead of TBMPI as the solute of the third solution.

[0230] Comparative Example 1 A photoelectric conversion element was produced in the same manner as in Example 1, except that the photoelectric conversion layer was produced by the following method.

[0231] In Comparative Example 1, the precursor solution of the photoelectric conversion material was prepared as follows. First, SnI2 and CsI were added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:1) to prepare a 0.9 mol / L first solution. Next, SnF2 was added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:1) to prepare a 0.9 mol / L second solution. The second solution was added to the first solution. The concentration of the second solution relative to the first solution was 16 mol%. In this way, a precursor solution was obtained. That is, in Comparative Example 1, the third solution (i.e., a solution containing a phosphonium salt or sulfonium salt) was not added when preparing the precursor solution of the photoelectric conversion material.

[0232] The precursor solution of the photoelectric conversion material was applied to the porous layer by spin coating, and then allowed to stand at room temperature for 10 minutes. The applied film was then baked at 240°C for 10 minutes. In this way, a photoelectric conversion layer was formed. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds.

[0233] Comparative Example 2 A photoelectric conversion element was produced in the same manner as in Comparative Example 1, except that in producing the photoelectric conversion layer, the baking temperature of the coating film was set to 200°C.

[0234] <Evaluation of Characteristics of Photoelectric Conversion Elements> The photoelectric conversion elements of Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated for current-voltage characteristics (i.e., IV characteristics).

[0235] The characteristics were evaluated using a solar simulator (manufactured by Bunkoukeiki Co., Ltd.) and an electrochemical analyzer ALS (manufactured by BAS Co., Ltd.). The photoelectric conversion element was irradiated with simulated sunlight of 1 sun. The output of the solar simulator was 100 mW / cm. 2 The IV characteristics of the photoelectric conversion element were measured by measuring the output current value while changing the applied voltage using an electrochemical analyzer.

[0236] The measurement results are shown in Table 1. η represents the conversion efficiency. SC represents the short-circuit current density. ocrepresents the open-circuit voltage. The open-circuit voltage shown in Table 1 is the higher of the open-circuit voltage in the forward sweep and the open-circuit voltage in the reverse sweep. FF represents the fill factor. Tables 1 and 2 also show the additives (i.e., phosphonium salts or sulfonium salts) and their concentrations in the perovskite compound CsSnI3 that constitutes the photoelectric conversion layer, as well as the firing temperature for forming the photoelectric conversion layer. In the tables, the molar concentrations of the added phosphonium salts or sulfonium salts are shown in terms of the amounts charged. The molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound can be determined from the raw material charge ratio. It has been confirmed through preliminary experiments by the applicant that the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound determined from the raw material charge ratio is not significantly different from the molar ratio of the phosphonium salt or sulfonium salt to the perovskite compound determined using the composition ratio determined from elemental analysis of the fabricated photoelectric conversion layer. In the table, phosphonium salts and sulfonium salts are referred to as "organic salts."

[0237] FIG. 3 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 1, Example 2, and Comparative Example 1. FIG. 4 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 1, Example 2, and Comparative Example 1. Specifically, FIG. 4 is a graph showing the increase in open-circuit voltage Voc depending on the concentration of TBMPI added to CsSnI3. FIG. 5 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 1, Example 3, and Comparative Example 1. FIG. 6 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 1, Example 3, Comparative Example 1, and Comparative Example 2. Specifically, FIG. 6 is a graph showing the increase in open-circuit voltage Voc depending on the final baking temperature of the photoelectric conversion layer when 5 mol% TBMPI is added. FIG. 7 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 2, Example 4, Example 5, and Comparative Example 1. FIG. 8 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 2, Example 4, Example 5, Comparative Example 1, and Comparative Example 2. Specifically, Fig. 8 is a graph showing the increase in open-circuit voltage Voc depending on the final baking temperature of the photoelectric conversion layer when 7.5 mol% TBMPI is added. Fig. 9 is a graph showing the IV characteristics of Example 6, Example 7, and Comparative Example 1. Fig. 10 is a graph showing the open-circuit voltages of the photoelectric conversion elements of Example 6, Example 7, Comparative Example 1, and Comparative Example 2. Specifically, Fig. 10 is a graph showing the increase in open-circuit voltage Voc depending on the final baking temperature of the photoelectric conversion layer when 5 mol% TBSI is added.

[0238]

[0239] As shown in Table 1, the photoelectric conversion elements of Examples 1 to 7, which had photoelectric conversion layers formed using precursor solutions of photoelectric conversion materials containing a phosphonium salt and / or a sulfonium salt, had higher conversion efficiencies than the photoelectric conversion elements of Comparative Examples 1 and 2, which had photoelectric conversion layers formed using precursor solutions of photoelectric conversion materials containing neither a phosphonium salt nor a sulfonium salt.

[0240] Comparing Examples 1 and 2 with Comparative Examples 1 and 2, higher conversion efficiencies were obtained when the TBMPI addition concentrations were 5 mol % and 7.5 mol %. As shown in Table 1 and Figures 3 to 4, the open-circuit voltages of the photoelectric conversion elements of Examples 1 and 2 were higher than those of the photoelectric conversion elements of Comparative Examples 1 and 2. As a result, the photoelectric conversion elements of Examples 1 and 2 were able to achieve conversion efficiencies that were approximately 1% higher than those of the photoelectric conversion elements of Comparative Examples 1 and 2.

[0241] Comparing Examples 1 and 3 with Comparative Examples 1 and 2, particularly high conversion efficiencies were obtained when the final baking temperature of the photoelectric conversion layer to which 5 mol % of TBMPI was added was 200°C. As shown in Figures 5 and 6, the open-circuit voltages of the photoelectric conversion elements of Examples 1 and 3 were higher than those of the photoelectric conversion elements of Comparative Examples 1 and 2. As a result, the photoelectric conversion elements of Examples 1 and 3 were able to obtain higher conversion efficiencies than the photoelectric conversion elements of Comparative Examples 1 and 2. In particular, the photoelectric conversion element of Example 1 was able to obtain a conversion efficiency that was about 1% higher than that of the photoelectric conversion elements of Comparative Examples 1 and 2.

[0242] Comparing Examples 2, 4, and 5 with Comparative Examples 1 and 2, even when 7.5 mol % of TBMPI was added, Example 2, in which the final baking temperature of the photoelectric conversion layer was 200° C., achieved a particularly high conversion efficiency. As shown in FIGS. 7 to 8, the photoelectric conversion elements of Examples 2, 4, and 5 had higher open-circuit voltages than the photoelectric conversion elements of Comparative Examples 1 and 2. As a result, the photoelectric conversion elements of Examples 2, 4, and 5 were able to achieve higher conversion efficiencies than the photoelectric conversion elements of Comparative Examples 1 and 2. In particular, the photoelectric conversion element of Example 2 was able to achieve a conversion efficiency that was about 1% higher than the photoelectric conversion elements of Comparative Examples 1 and 2.

[0243] Comparing Examples 6 and 7 with Comparative Examples 1 and 2, when 5 mol% of TBSI was added, a particularly high conversion efficiency was obtained when the final baking temperature of the photoelectric conversion layer was 180°C. As shown in Table 1 and Figures 9 and 10, the photoelectric conversion elements of Examples 6 and 7 had higher open-circuit voltages and short-circuit current densities than the photoelectric conversion elements of Comparative Examples 1 and 2. As a result, the photoelectric conversion elements of Examples 7 and 8 were able to obtain higher conversion efficiencies than the photoelectric conversion elements of Comparative Examples 1 and 2. In particular, the photoelectric conversion element of Example 6 was able to obtain a conversion efficiency that was about 1% higher than the photoelectric conversion elements of Comparative Examples 1 and 2.

[0244] <Evaluation of PL Emission and Lifetime of Photoelectric Conversion Layer> In order to measure the PL emission lifetime of the photoelectric conversion layer, the following three measurement samples were prepared in the same procedure as for the photoelectric conversion layer of the photoelectric conversion element.

[0245] The precursor solution of the photoelectric conversion material used in Comparative Examples 1 and 2 (i.e., CsSnI3 + 16 mol% SnF2) was applied to a glass substrate by spin coating, and the applied film was then baked at 200°C, 220°C, or 240°C for 10 minutes. Chlorobenzene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 30 seconds. Next, a UV-curable epoxy resin was applied to the periphery of the substrate, which was then attached to another glass substrate and irradiated with UV light. In this way, the epoxy resin was cured, sealing the measurement sample.

[0246] The precursor solution of the photoelectric conversion material used in Example 1 (i.e., CsSnI3 + 16 mol% SnF2 + 5 mol% TBMPI) was applied to a glass substrate by spin coating, and the applied film was baked at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 200°C for 10 minutes. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds. Next, a UV-curable epoxy resin was applied to the periphery of the substrate, which was then bonded to another glass substrate and irradiated with UV light. In this way, the epoxy resin was cured, and the measurement sample was sealed.

[0247] The precursor solution of the photoelectric conversion material used in Examples 6 and 7 (i.e., CsSnI + 16 mol% SnF + 5 mol% TBSI) was applied to a glass substrate by spin coating, and the applied film was baked at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 180°C for 10 minutes. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds. Next, a UV-curable epoxy resin was applied to the periphery of the substrate, which was then bonded to another glass substrate and irradiated with UV light. In this way, the epoxy resin was cured and the measurement sample was sealed.

[0248] The PL lifetime was measured using a near-infrared fluorescence lifetime measurement system (Hamamatsu Photonics, C7990VIS / NIR). The photosensor module used was H7422. The measurement results were analyzed using the fluorescence lifetime software U8167-03.

[0249] FIG. 11 is a graph showing the PL emission spectrum of a single photoelectric conversion layer formed from CsSnI3 + 16 mol % SnF2.

[0250] FIG. 12 is a graph showing the PL emission spectrum of a single photoelectric conversion layer formed from CsSnI 3 + 16 mol % SnF 2 + 5 mol % TBMPI.

[0251] FIG. 13 is a graph showing the PL emission spectrum of a single photoelectric conversion layer formed from CsSnI3 + 16 mol % SnF2 + 5 mol % TBSI.

[0252] FIG. 14 is a graph showing the PL emission lifetime of a single photoelectric conversion layer formed from CsSnI3 + 16 mol % SnF2.

[0253] FIG. 15 is a graph showing the PL emission lifetime of a single photoelectric conversion layer formed of CsSnI 3 + 16 mol % SnF 2 + 5 mol % TBMPI.

[0254] FIG. 16 is a graph showing the PL emission lifetime of a single photoelectric conversion layer formed of CsSnI 3 +16 mol % SnF 2 +5 mol % TBSI.

[0255] As is clear from Figure 11, the PL emission peak of the photoelectric conversion layer single film formed by CsSnI3 + 16 mol% SnF2 was 1.28 eV to 1.30 eV. Furthermore, as is clear from Figure 12, when 5 mol% TBMPI was added to CsSnI3 + 16 mol% SnF2, the PL emission peak of the resulting photoelectric conversion layer single film was 1.28 eV. Furthermore, as is clear from Figure 13, when 5 mol% TBSI was added to CsSnI3 + 16 mol% SnF2, the PL emission peak of the resulting photoelectric conversion layer single film was 1.28 eV. Thus, it was considered that the band gap was almost unchanged before and after the addition of TBMPI or TBSI.

[0256] As is clear from a comparison of the PL lifetime shown in Fig. 15 with that shown in Fig. 14, the addition of 5 mol% TBMPI to CsSnI3 + 16 mol% SnF2 significantly extended the PL lifetime of the photoelectric conversion layer from a range of 6.5 ns to 9.6 ns to 12.6 ns. As is clear from a comparison of the PL lifetime shown in Fig. 16 with that shown in Fig. 14, the addition of 5 mol% TBSI to CsSnI3 + 16 mol% SnF2 significantly extended the PL lifetime of the photoelectric conversion layer from a range of 6.5 ns to 9.6 ns to 12.4 ns.

[0257] <Evaluation of SEM Photographs of Photoelectric Conversion Layer> A photoelectric conversion layer was formed on a porous layer prepared in the same manner as in Example 1.

[0258] Specifically, a precursor solution of the photoelectric conversion material used in Comparative Examples 1 and 2 (i.e., CsSnI+16 mol% SnF) was applied by spin coating onto a glass substrate on which the porous layer had been formed, and then baked at 160° C. for 1 minute and then at 240° C. for 10 minutes to form a single film. Chlorobenzene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 30 seconds.

[0259] The precursor solution of the photoelectric conversion material used in Example 1 (i.e., CsSnI + 16 mol% SnF + 5 mol% TBMPI) was applied to a glass substrate by spin coating, and the applied film was then baked at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 200°C for 10 minutes to form a single film. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds.

[0260] The precursor solution of the photoelectric conversion material used in Examples 6 and 7 (i.e., CsSnI + 16 mol% SnF + 5 mol% TBSI) was applied to a glass substrate by spin coating, and the applied film was then baked at 120°C for 1 minute, then at 160°C for 1 minute, and finally at 180°C for 10 minutes to form a single film. Toluene, a poor solvent, was added dropwise during spin coating at 5000 rpm for 40 seconds.

[0261] The SEM photographs were taken using a field emission scanning electron microscope (SU8200, manufactured by Hitachi High-Technologies Corporation).

[0262] FIG. 17 shows an SEM photograph taken from the top of a photoelectric conversion layer formed from a precursor solution of CsSnI3 + 16 mol % SnF2.

[0263] FIG. 18 shows an SEM photograph taken from the top of a photoelectric conversion layer formed from a precursor solution of CsSnI3 + 16 mol % SnF2 + 5 mol % TBMPI.

[0264] FIG. 19 shows an SEM photograph taken from the top of a photoelectric conversion layer formed from a precursor solution of CsSnI3 + 16 mol % SnF2 + 5 mol % TBSI.

[0265] As is clear from a comparison of the SEM photographs in Figures 18 and 19 with the SEM photograph in Figure 17, the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBMPI was added (Figure 18) or the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBSI was added (Figure 19) was confirmed to have larger crystal particle sizes than the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBMPI or TBSI was not added (Figure 17). From the particles in the SEM images, 50 particles were selected in descending order of primary particle size, and the average value was calculated using the primary particle sizes of these 50 particles. The resulting value was used as the average primary particle size. The primary particle size of each particle was calculated as the average of the maximum and minimum diameters of each particle. The average primary particle size of the perovskite compound contained in the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBMPI was added, as shown in Figure 18, and the average primary particle size of the perovskite compound contained in the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBSI was added, as shown in Figure 19, were both 1 μm or more. Thus, the addition of TBMPI or TBSI can increase the crystal grain size, which is thought to reduce grain boundaries in the photoelectric conversion layer and reduce carrier recombination. Therefore, it is thought that a photoelectric conversion element including a photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBMPI or TBSI was added was able to improve photoelectric conversion efficiency.

[0266] The perovskite compound contained in the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBMPI was added shown in FIG. 18 had larger crystal grain sizes and denser crystals than the perovskite compound contained in the photoelectric conversion layer formed using the precursor solution of the photoelectric conversion material to which TBSI was added shown in FIG. 19 . Furthermore, the final baking temperature for the photoelectric conversion layer shown in FIG. 18 was 200°C, i.e., the same as that for the photoelectric conversion layer in Example 1. On the other hand, the final baking temperature for the photoelectric conversion layer shown in FIG. 19 was 180°C, i.e., the same as that for the photoelectric conversion layer in Example 6. The conversion efficiency of the photoelectric conversion element in Example 1 was 3.24%, which was higher than the conversion efficiency of the photoelectric conversion element in Example 6 (3.01%). These results suggest that TBMPI is more effective than TBSI in increasing the crystal grain size and improving photoelectric conversion efficiency.

[0267] The photoelectric conversion element provided by the present disclosure can be used, for example, in a solar cell.

Claims

1. forming a first electrode; forming a photoelectric conversion layer; forming a second electrode; The step of forming the photoelectric conversion layer includes: preparing a mixed solution by mixing a solution in which at least one selected from the group consisting of a phosphonium salt and a sulfonium salt is dissolved with a precursor solution of a perovskite compound; forming a coating film using the mixed solution; Including, A method for manufacturing a photoelectric conversion element.

2. In the step of forming the photoelectric conversion layer, the mixed solution is prepared by: preparing a first solution containing a compound containing a monovalent cation and a halogen anion, a compound containing a divalent cation and a halogen anion, and a solvent; a second solution containing a compound containing a divalent cation and an F anion, and a solvent; and a third solution containing at least one selected from the group consisting of the phosphonium salt and the sulfonium salt, and a solvent; mixing the first solution with the second solution and the third solution; Including, The method for manufacturing the photoelectric conversion element according to claim 1 .

3. a first electrode, a photoelectric conversion layer, and a second electrode; The photoelectric conversion layer contains a perovskite compound and at least one selected from the group consisting of a phosphonium ion and a sulfonium ion. Photoelectric conversion element.

4. The average primary particle size of the perovskite compound is 1 μm or more. The photoelectric conversion element according to claim 3 .

5. at least one selected from the group consisting of phosphonium ions and sulfonium ions is present between crystals of the perovskite compound; The photoelectric conversion element according to claim 3 .

6. The phosphonium ion is a cation that constitutes a part of a phosphonium salt, The sulfonium ion is a cation that constitutes a part of a sulfonium salt, At least one selected from the group consisting of the phosphonium salt and the sulfonium salt contains at least one selected from the group consisting of an alkyl group and an aryl group. The photoelectric conversion element according to claim 3 .

7. at least one selected from the group consisting of the phosphonium salt and the sulfonium salt contains an alkyl group; the alkyl group has 1 or more and 10 or less carbon atoms; The photoelectric conversion element according to claim 6 .

8. The phosphonium salt includes a quaternary phosphonium salt. The photoelectric conversion element according to claim 6 .

9. The sulfonium salt includes a tertiary sulfonium salt. The photoelectric conversion element according to claim 6 .

10. At least one selected from the group consisting of the phosphonium salt and the sulfonium salt contains a halogen element. The photoelectric conversion element according to claim 6 .

11. The halogen element includes iodine. The photoelectric conversion element according to claim 10.

12. The phosphonium salt includes an iodine-containing phosphonium salt. The photoelectric conversion element according to claim 6 .

13. The iodine-containing phosphonium salt includes at least one selected from the group consisting of tributylmethylphosphonium iodide, methyltriphenylphosphonium iodide, ethyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide. The photoelectric conversion element according to claim 12 .

14. The sulfonium salt includes an iodine-containing sulfonium salt. The photoelectric conversion element according to claim 6 .

15. The iodine-containing sulfonium salt includes at least one selected from the group consisting of tributylsulfonium iodide and trimethylsulfonium iodide. The photoelectric conversion element according to claim 14.

16. the molar ratio of the phosphonium salt or the sulfonium salt to the perovskite compound is 0.01 or more and 0.50 or less; The photoelectric conversion element according to claim 6 .

17. the perovskite compound is composed of monovalent cations, divalent cations, and halogen anions; The divalent cations include at least one selected from the group consisting of Sn cations, Ge cations, and Pb cations. The photoelectric conversion element according to claim 3 .

18. The perovskite compound is CsSnI 3 , CsGeI 3 , and CsPbI 3 At least one selected from the group consisting of: The photoelectric conversion element according to claim 17.

19. The photoelectric conversion layer is made of SnF 2 further comprising: The photoelectric conversion element according to claim 3 .