Photoelectric conversion element and method for manufacturing photoelectric conversion element

Abstract

A photoelectric conversion element 100 according to the present disclosure comprises a first electrode 2, a photoelectric conversion layer 4 containing a perovskite compound, and a second electrode 6. The perovskite compound includes Sn. The photoelectric conversion layer 4 further contains a metal element and a halogen element present in a near-surface region that includes a surface facing the second electrode 6. The metal element has a standard oxidation-reduction potential that is more negative than that of Sn4+.

Description

Photoelectric conversion element and method for manufacturing a photoelectric conversion element

[0001] This disclosure relates to a photoelectric conversion element and a method for manufacturing a photoelectric conversion element.

[0002] In recent years, perovskite solar cells have been researched and developed. In perovskite solar cells, perovskite compounds represented by the chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halogen anion) are used as photoelectric conversion materials.

[0003] Various techniques have been proposed to improve the photoelectric conversion efficiency of perovskite solar cells. For example, Non-Patent Document 1 discloses a technique for forming a TBAPbI3 protective layer on the surface of a CsPbI3 layer by first depositing a layer made of CsPbI3 and then depositing a layer made of tetrabutylammonium iodide (TBAI) on top of that layer.

[0004] Xiamomin Liu, et al., Angewandte Chemie, 2021, Vol. 133, pp. 12459–12463.

[0005] This disclosure aims to provide a technology for improving the photoelectric conversion efficiency in a photoelectric conversion device that includes a perovskite compound as a photoelectric conversion material.

[0006] The photoelectric conversion element of the present disclosure comprises a first electrode, a photoelectric conversion layer containing a perovskite compound, and a second electrode, wherein the perovskite compound contains Sn, and the photoelectric conversion layer further contains a metal element and a halogen element present in a near-surface region including the surface on the second electrode side, wherein the metal element is Sn 4+ Its standard oxidation-reduction potential is more negative than that of [another substance].

[0007] This disclosure describes how to improve the photoelectric conversion efficiency in a photoelectric conversion device that includes a perovskite compound as a photoelectric conversion material.

[0008] Figure 1 is a cross-sectional view showing the schematic configuration of the photoelectric conversion element 100 of the first embodiment. Figure 2 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 2 and Reference Example 2. Figure 3 shows the X-ray diffraction measurement results for the near-surface region of the photoelectric conversion layer of the photoelectric conversion elements of Example 2 and Reference Example 2.

[0009] Embodiments of the present disclosure will be described below with reference to the drawings.

[0010] (First Embodiment) The photoelectric conversion element according to the first embodiment comprises a first electrode, a photoelectric conversion layer, and a second electrode. The photoelectric conversion element according to the first embodiment may also comprise the first electrode, the photoelectric conversion layer, and the second electrode in this order. The photoelectric conversion layer further comprises a metallic element and a halogen element present in a near-surface region including the surface on the second electrode side. The metallic element is Sn 4+ Its standard oxidation-reduction potential is more negative than that of [another substance].

[0011] For example, when a hole transport layer is placed between the photoelectric conversion layer and the second electrode, the surface of the photoelectric conversion layer on the second electrode side is the surface of the photoelectric conversion layer on the hole transport layer side. When the photoelectric conversion layer and the hole transport layer are in contact, the surface of the photoelectric conversion layer on the second electrode side corresponds to the surface in contact with the hole transport layer. In this case, in other words, the metal element and the halogen element can be said to be present in the region near the interface with the hole transport layer in the photoelectric conversion layer.

[0012] The photoelectric conversion element according to the first embodiment, having the above configuration, can increase the open-circuit voltage. As a result, the photoelectric conversion element according to the first embodiment can improve the photoelectric conversion efficiency.

[0013] A photoelectric conversion element is, for example, a solar cell.

[0014] Figure 1 is a cross-sectional view showing the schematic configuration of the photoelectric conversion element 100 of the first embodiment.

[0015] The photoelectric conversion element 100 comprises 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, in this order. Note that the substrate 1, electron transport layer 3, and hole transport layer 5 are not required.

[0016] When light is shone on the photoelectric conversion element 100, the photoelectric conversion layer 4 absorbs the light and separates its charge into electrons and holes. The electrons generated by this charge separation move to the first electrode 2 through the electron transport layer 3. Meanwhile, the holes generated in the photoelectric conversion layer 4 move to the second electrode 6 via the hole transport layer 5. As a result, the photoelectric conversion element 100 can extract current from the first electrode 2, which acts as the negative electrode, and the second electrode 6, which acts as the positive electrode.

[0017] The following describes in detail each component of the photoelectric conversion element 100.

[0018] (Photoelectric Conversion Layer 4) As described above, the photoelectric conversion layer 4 contains a perovskite compound. Perovskite compounds have a high light absorption coefficient in the wavelength range of the solar spectrum and high carrier mobility. Therefore, the photoelectric conversion element 100 equipped with a photoelectric conversion layer 4 containing a perovskite compound as a photoelectric conversion material has high photoelectric conversion efficiency.

[0019] As described above, the photoelectric conversion layer 4 further includes the metal element and halogen element present in the near-surface region 41, including the surface 4a on the second electrode 6 side. When a hole transport layer 5 is provided between the photoelectric conversion layer 4 and the second electrode 6, as in the photoelectric conversion element 100 shown in Figure 1, the surface 4a of the photoelectric conversion layer 4 is in contact with the hole transport layer 5. Therefore, in this case, the metal element and halogen element are present on the surface 4a of the photoelectric conversion layer 4 that is in contact with the hole transport layer 5. With this configuration, the photoelectric conversion element 100 can further improve its photoelectric conversion efficiency. By having the metal element and halogen element present on the surface 4a, the metal element and halogen element can improve the electrical and chemical junctions between the photoelectric conversion layer 4 and the hole transport layer 5, and reduce the surface of the photoelectric conversion layer 4 that has been oxidized during the film formation process, thereby improving the open-circuit voltage.

[0020] Here, the near-surface region 41 of the photoelectric conversion layer 4 is, for example, the region from the center in the thickness direction of the photoelectric conversion layer 4 to the surface 4a on the second electrode side, and may also be the region from the surface 4a of the photoelectric conversion layer 4 to a depth of about 50 nm. For example, when a porous layer is provided between the photoelectric conversion layer 4 and the electron transport layer 3, and it is difficult to determine the center in the thickness direction of the photoelectric conversion layer 4, the center in the thickness direction of the total thickness of the porous layer and the photoelectric conversion layer 4 may be determined, and the region from that center to the surface 4a on the second electrode side may be defined as the near-surface region 41. Similarly in this case, the region from the surface 4a of the photoelectric conversion layer 4 to a depth of about 50 nm may be defined as the near-surface region 41. The metal element and the halogen element may be present in high concentrations in the region from the surface 4a of the photoelectric conversion layer 4 to a depth of about 50 nm.

[0021] The presence of the above-mentioned metal element and halogen element in the region 41 near the surface of the photoelectric conversion layer 4 can be confirmed, for example, by X-ray diffraction measurement.

[0022] The above metal element is, as stated above, Sn 4+ Its standard oxidation-reduction potential is more negative than that of Sn. 4+ Examples of metals whose standard redox potential is more negative than that include Sr, Ca, Eu, Yb, Ti, Mn, V, Zn, Fe, Cd, Co, and Ni. The above metal elements may also be metal elements that can have a valence of +2. The above metal elements may be, for example, Zn.

[0023] The above halogen element may include fluorine. The presence of fluorine in the near-surface region 41 of the photoelectric conversion layer 4 allows the photoelectric conversion element 100 to further improve its photoelectric conversion efficiency.

[0024] The above-mentioned metal element may include zinc. The presence of zinc in the near-surface region 41 of the photoelectric conversion layer 4 allows the photoelectric conversion element 100 to further improve its photoelectric conversion efficiency.

[0025] The above metal element may include zinc, and the above halogen element may include fluorine. The presence of zinc and fluorine in the near-surface region 41 of the photoelectric conversion layer 4 allows the photoelectric conversion element 100 to further improve its photoelectric conversion efficiency.

[0026] The total proportion of the metal element and halogen element in the region 41 near the surface of the photoelectric conversion layer 4 may be, for example, 50% by mass or more and 100% by mass or less.

[0027] Perovskite compounds may contain halogen anions; that is, perovskite compounds may be halides.

[0028] The perovskite compound may be composed of a monovalent cation, a divalent cation, and a halogen anion. Here, the divalent cation may include an Sn cation.

[0029] The monovalent cation in the perovskite compound may also contain inorganic cations. For example, the monovalent cation in the perovskite compound may contain 50 mol% or more of inorganic cations.

[0030] Perovskite compounds are represented, for example, by the compositional formula ABX3, where A is a monovalent cation, B is a divalent metal cation, and X is a monovalent anion.

[0031] Examples of monovalent cation A are organic cations or alkali metal cations. As mentioned above, monovalent cation A may also contain inorganic cations, i.e., alkali metal cations. Monovalent cation A may contain 50 mol% or more of inorganic cations, i.e., alkali metal cations.

[0032] An example of an organic cation is the methylammonium cation (CH3NH3) + ), formamidinium cation (NH2CHNH2 + ) or guanidinium ion (C(NH2)3 + )

[0033] Examples of alkali metal cations are Cs cations or Rb cations.

[0034] B is a divalent metal cation. Examples of the divalent cation B are Sn cations.

[0035] X is a monovalent anion. Examples of the anion X are halogen anions. The halogen anions are, for example, chlorine, bromine, or iodine.

[0036] Each site of cation A, cation B, and anion X may contain a plurality of types of ions, respectively.

[0037] The perovskite compound may contain CsSnI3.

[0038] The perovskite compound may contain a monovalent cation as formamidinium cation (NH2CHNH2 + ).

[0039] The photoelectric conversion layer 4 may further contain SnF2. When the perovskite compound contains Sn cation as a divalent cation, SnF2 can be further contained to reduce Sn defects. Therefore, by further containing SnF2 in the photoelectric conversion material of the first embodiment, the photoelectric conversion efficiency can be improved.

[0040] In order to increase the photoelectric conversion efficiency, the photoelectric conversion layer 4 may further contain, as an additive, a compound that can increase the open voltage of the photoelectric conversion element, for example. As an example, the photoelectric conversion layer 4 may contain, as an additive, at least one compound selected from the group consisting of triphenylene and triphenylene derivatives. By the photoelectric conversion layer 4 containing a perovskite compound and at least one compound selected from the group consisting of triphenylene and triphenylene derivatives, the open voltage of the photoelectric conversion element can be increased. Thereby, the photoelectric conversion efficiency of the photoelectric conversion element is improved.

[0041] The average primary particle size of the perovskite compound is, for example, 2 μm or more. When the average primary particle size of the perovskite compound is 2 μm or more, carrier recombination is further reduced. As a result, the photoelectric conversion efficiency of the photoelectric conversion element 100 of the first embodiment is further improved. In the photoelectric conversion element 100 of the first embodiment, the average primary particle size of the perovskite compound contained in the photoelectric conversion layer 4 is obtained by measuring the primary particle size of the perovskite compound using a scanning electron microscope (SEM) image and calculating the average value from the measured values. Here, the measured primary particle size is the maximum diameter of the primary particle. For example, 50 particles are selected in order from the largest primary particle diameter among the particles in the SEM image. The average value is calculated using these 50 primary particle diameters, and the obtained value is taken as the average primary particle size. The average primary particle size of the perovskite compound may be 5 μm or more, or may be 10 μm or more. The average primary particle size of the perovskite compound is, for example, 100 μm or less.

[0042] The thickness of the photoelectric conversion layer 4 is, for example, 50 nm or more and 10 μm or less.

[0043] The photoelectric conversion layer 4 in which the metal element and the halogen element are present in the surface vicinity region 41 can be obtained, for example, by forming a precursor layer of a photoelectric conversion layer containing a perovskite compound containing Sn, applying a solution containing a solvent, a metal element, and a halogen element to the surface of the precursor layer, and removing the solvent on the surface of the precursor layer to which the solution has been applied. The metal element is Sn as described above. 4+ A metal element having a standard redox potential more negative and larger than that.

[0044] The precursor layer of the photoelectric conversion layer 4 can be formed by a coating method using a solution, a printing method, or a vapor deposition method. Examples of the coating method are 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.

[0045] (Substrate 1) The substrate 1 plays the role of holding each layer of the photoelectric conversion element 100. The substrate 1 can be formed from 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.

[0046] If the second electrode 6 is translucent, the substrate 1 may be made of a material that is not translucent. Such materials can include metals, ceramics, or resin materials with low translucency.

[0047] If the first electrode 2 has sufficient strength, the first electrode 2 can hold each layer, so the substrate 1 does not need to be provided.

[0048] (First electrode 2) The first electrode 2 is conductive.

[0049] The first electrode 2 is light-transmitting. For example, it transmits light from the visible region to the near-infrared region.

[0050] The first electrode 2 is made of, for example, a transparent and conductive material. Examples of such materials are metal oxides or metal nitrides. Examples of such materials are: (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine; (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon; (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen; (iv) tin oxide doped with at least one selected from the group consisting of antimony and fluorine; (v) zinc oxide doped with at least one selected from the group consisting of boron, aluminum, gallium, and indium; (vi) indium-tin composite oxide; or (vii) composites thereof.

[0051] The first electrode 2 may be formed with a light-transmitting pattern. Examples of light-transmitting patterns include linear, wavy, grid-like, or perforated metal-like patterns with a large number of fine through-holes arranged regularly or irregularly. When the first electrode 2 has such patterns, light can pass through areas where there is no electrode material. Therefore, by providing a light-transmitting pattern, an opaque material can be used. Examples of opaque electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. Conductive carbon materials may also be used as opaque electrode materials.

[0052] The light transmittance of the first electrode 2 does not necessarily have to be achieved by the light transmission pattern described above. For example, the first electrode 2 may be formed of a thin film of metal with a thickness of about 10 nm. Such thin film metals include, for example, platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. A conductive carbon material may be used instead of these metallic materials.

[0053] If the photoelectric conversion element 100 does not have an electron transport layer 3, the first electrode 2 has blocking properties 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, blocking properties for holes from the photoelectric conversion layer 4 refer to the property of allowing only electrons generated in the photoelectric conversion layer 4 to pass through, while preventing holes from passing through. The Fermi energy of a material having such properties is higher than the energy at the top of the valence band of the photoelectric conversion layer 4. The Fermi energy of a material having such properties may also be higher than the Fermi energy of the photoelectric conversion layer 4. Aluminum is a specific example of such a material.

[0054] If the photoelectric conversion element 100 includes an electron transport layer 3, the first electrode 2 does not need to have blocking properties for holes from the photoelectric conversion layer 4. In this case, the first electrode 2 may be made of a material capable of forming 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.

[0055] 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.

[0056] The thickness of the first electrode 2 may be, for example, 1 nm or more and 1000 nm or less.

[0057] (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 with a band gap of 3.0 eV or more. This allows visible light and infrared light to be transmitted to the photoelectric conversion layer 4.

[0058] An example of an electron transport material is an inorganic n-type semiconductor.

[0059] Examples of inorganic n-type semiconductors are metal oxides, metal nitrides, or perovskite oxides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Metal oxides are, for example, TiO2 or SnO2. Metal nitrides are, for example, GaN. Perovskite oxides are, for example, SrTiO3 or CaTiO3.

[0060] To effectively transmit ultraviolet light to the photoelectric conversion layer 4, the electron transport layer 3 may use a semiconductor with a band gap of 6.0 eV or greater. 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, or silicon dioxide. In this case, 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.

[0061] The electron transport layer 3 may include multiple layers made of different materials.

[0062] (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.

[0063] Examples of organic semiconductors include triphenylamine, triallylamine, phenylbenzidine, phenylenevinylene, tetrathiafulvalene, vinylnaphthalene, vinylcarbazole, thiophene, aniline, pyrrole, carbazole, triptycene, fluorene, azulene, pyrene, pentacene, perylene, acridine, or phthalocyanine.

[0064] 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), or copper phthalocyanine.

[0065] Inorganic semiconductors used as hole transport materials are p-type semiconductors. Examples of inorganic semiconductors include Cu₂O, CuGaO₂, CuSCN, CuI, and NiO. x MoO x This is a carbon material such as V2O5 or graphene oxide, where x satisfies x > 0.

[0066] The hole transport layer 5 may include multiple layers made of different materials. For example, the hole transport characteristics can be improved by stacking multiple layers such that the ionization potential of the hole transport layer 5 decreases sequentially with respect to the ionization potential of the photoelectric conversion layer 4.

[0067] 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 for sufficient hole transport characteristics to be achieved. Therefore, the low resistance of the photoelectric conversion element 100 can be maintained, and high photoelectric conversion efficiency can be realized.

[0068] The hole transport layer 5 is formed, for example, by coating, printing, or vapor deposition. This is the same as for the photoelectric conversion layer 4. Examples of coating methods include doctor blade method, bar coating method, spray method, dip coating method, inkjet method, slit coating method (i.e., die coating method), or spin coating method. An example of a printing method is screen printing. If necessary, the hole transport layer 5 may be fabricated by mixing multiple materials and then pressurized or fired. If the material of the hole transport layer 5 is an organic low molecular weight or an inorganic semiconductor, it is also possible to fabricate the hole transport layer 5 by vacuum deposition.

[0069] The hole transport layer 5 may contain additives in addition to the hole transport material to enhance conductivity. Examples of additives include supporting electrolytes, solvents, or dopants. Supporting electrolytes and solvents have the effect of stabilizing holes in the hole transport layer 5. Dopants have the effect of increasing the number of holes in the hole transport layer 5.

[0070] Examples of supporting electrolytes are ammonium salts, alkaline earth metal salts, or transition metal salts. Examples of ammonium salts are tetrabutylammonium perchlorate, tetraethylammonium hexafluoride phosphate, imidazolium salts, or pyridinium salts. Examples of alkali metal salts are lithium perchlorate or potassium borotetrafluoride. Examples of alkaline earth metal salts are lithium bis(trifluoromethanesulfonyl)imide or bis(trifluoromethanesulfonyl)imide calcium(II). Examples of transition metal salts are bis(trifluoromethanesulfonyl)imide zinc(II) or tris[4-tert-butyl-2-(1H-pyrazole-1-yl)pyridine]cobalt(III)tris(trifluoromethanesulfonyl)imide.

[0071] An example of a dopant is a fluorine-containing aromatic boron compound. An example of a fluorine-containing aromatic boron compound is tris(pentafluorophenyl)borane.

[0072] The solvent contained in the hole transport layer 5 may have excellent ionic conductivity. This 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 organic solvents are heterocyclic compound solvents such as tert-butylpyridine, pyridine, and n-methylpyrrolidone.

[0073] Ionic liquids may be used as solvents. Ionic liquids may be used alone or in mixtures with other solvents. Ionic liquids are desirable because they have low volatility and high flame retardancy.

[0074] Examples of ionic liquids include imidazolium-based liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine-based liquids, alicyclic amine-based liquids, aliphatic amine-based liquids, or azonium amine-based liquids.

[0075] (Second electrode 6) The second electrode 6 is conductive.

[0076] If the photoelectric conversion element 100 does not have a hole transport layer 5, the second electrode 6 has blocking properties 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. Blocking properties for electrons from the photoelectric conversion layer 4 refer to the property of allowing only holes generated in the photoelectric conversion layer 4 to pass through, while preventing electrons from passing through. The Fermi energy of a material having such properties is lower than the energy of the lower end of the conduction band of the photoelectric conversion layer 4. The Fermi energy of a material having such properties may also be lower than the Fermi energy of the photoelectric conversion layer 4. Specific materials include platinum, gold, or carbon materials such as graphene.

[0077] If the photoelectric conversion element 100 includes a hole transport layer 5, the second electrode 6 does not need to block electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 may be made of a material capable of forming ohmic contact with the photoelectric conversion layer 4. This allows the second electrode 6 to be formed to be translucent.

[0078] Of the first electrode 2 and the second electrode 6, the electrode on the side into which light is incident only needs to be translucent. Therefore, one of the first electrode 2 and the second electrode 6 does not need to be translucent. In other words, one of the first electrode 2 and the second electrode 6 does not need to be made of a translucent material, nor does it need to have a pattern that includes an opening that transmits light.

[0079] (Porous layer) The porous layer is formed on the electron transport layer 3, for example, by a coating method. If the photoelectric conversion element 100 does not have an electron transport layer 3, the porous layer is formed on the first electrode 2.

[0080] The porous structure introduced by the porous layer serves as the foundation for forming the photoelectric conversion layer 4. The porous layer does not hinder the light absorption of the photoelectric conversion layer 4 or the electron transfer from the photoelectric conversion layer 4 to the electron transport layer 3.

[0081] The porous layer contains a porous material.

[0082] Porous materials are formed, for example, by a series of insulating or semiconductor particles. Examples of insulating particles are aluminum oxide particles or silicon oxide particles. Examples of semiconductor particles are inorganic semiconductor particles. Examples of inorganic semiconductors are metal oxides, perovskite oxides of metallic elements, sulfides of metallic elements, or metal chalcogenides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. An example of a metal oxide is TiO2. An example of a perovskite oxide of a metallic element is SrTiO3 or CaTiO3. Examples of metal element sulfides include CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides include CsSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0083] 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.

[0084] The surface roughness of the porous layer may be 10 or greater, or 100 or greater, given by the effective area / projected area. The projected area is the area of ​​the shadow cast behind an object when it is illuminated directly from the front. The effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume obtained from the projected area and thickness of the object, and from the specific surface area and bulk density of the materials constituting the object. The specific surface area is measured, for example, by the nitrogen adsorption method.

[0085] The voids within the porous layer are connected from one main surface of the porous layer to the other main surface. That is, the voids within 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. As a result, the material of the photoelectric conversion layer 4 can fill the voids in the porous layer and reach the surface of the electron transport layer 3. Therefore, since the photoelectric conversion layer 4 and the electron transport layer 3 are in direct contact, electron transfer is possible.

[0086] By providing a porous layer, the photoelectric conversion layer 4 can be easily formed. The porous layer allows the material of the photoelectric conversion layer 4 to penetrate the voids within it, and the porous layer acts as a scaffold for the photoelectric conversion layer 4. Therefore, the material of the photoelectric conversion layer 4 is less likely to be repelled or aggregated on the surface of the porous layer. Consequently, the photoelectric conversion layer 4 can be easily formed as a uniform film. The photoelectric conversion layer 4 can be formed by the coating method described above.

[0087] The porous layer is expected to cause light scattering, which increases the optical path length of light passing through the photoelectric conversion layer 4. An increase in optical path length is predicted to increase the amount of electrons and holes generated in the photoelectric conversion layer 4.

[0088] (Method for manufacturing a photoelectric conversion element) The photoelectric conversion element of the first embodiment can be manufactured, for example, by the following manufacturing method of the first embodiment.

[0089] The manufacturing method of the first embodiment includes the steps of forming a first electrode, forming a photoelectric conversion layer, and forming a second electrode, wherein the step of forming the photoelectric conversion layer includes forming a precursor layer of the photoelectric conversion layer containing a perovskite compound containing Sn, applying a solution containing a solvent, a metal element, and a halogen element to the surface of the precursor layer, and removing the solvent from the surface of the precursor layer to which the solution has been applied. The metal element is Sn 4+ It is a metal element whose standard oxidation-reduction potential is more negative than that of other elements.

[0090] According to the above manufacturing method, it is possible to provide a photoelectric conversion element with improved photoelectric conversion efficiency.

[0091] For the solution containing a Sn-containing perovskite compound for fabricating the precursor layer of the photoelectric conversion layer, and for the solvent used in the solution containing the above metal element and the above halogen element, one solvent may be used, or a mixed solvent containing multiple solvents may be used. The solvent may be, for example, a mixed solvent containing DMF (dimethylformamide) and DMSO (dimethyl sulfoxide).

[0092] As described above, the precursor layer of the photoelectric conversion layer containing the perovskite compound can be prepared, for example, by a coating method using a solution containing the perovskite compound. For example, a solution containing the perovskite compound can be applied to a substrate by a coating method such as spin coating, and the resulting coating film can be fired. Before firing, the coating film may be left to stand for a predetermined time to allow crystal nuclei to grow in the coating film. The firing temperature may be, for example, 50°C or higher and 250°C or lower. As an example, if a mixed solvent of DMF and DMSO (for example, 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 fired at a temperature of about 50°C or higher and 180°C or lower. The above-mentioned substrate is the structure that serves as the base when forming the photoelectric conversion layer, and for example, the structure adjacent to the photoelectric conversion layer in a photoelectric conversion element. When the photoelectric conversion layer is placed on the first electrode in contact with the first electrode, the above-mentioned substrate is the first electrode. When the photoelectric conversion layer is placed in contact with an electron transport layer formed on the first electrode, the substrate is a laminate of the first electrode and the electron transport layer.

[0093] As a method for removing the solvent after applying the solution containing the metal element and the halogen element to the surface of the precursor layer, heat treatment may be performed. In this case, the temperature of the heat treatment may be, for example, 70°C or higher and 120°C or lower.

[0094] The manufacturing method of the first embodiment may further include steps such as forming an electron transport layer and forming a hole transport layer, depending on the configuration of the photoelectric conversion element to be manufactured.

[0095] [Other Embodiments] (Note) The above description of embodiments discloses the following technologies.

[0096] (Technology 1) A first electrode, a photoelectric conversion layer containing a perovskite compound, and a second electrode, wherein the perovskite compound contains Sn, and the photoelectric conversion layer further contains a metal element and a halogen element present in a near-surface region including the surface on the second electrode side, wherein the metal element is Sn 4+ A photoelectric conversion element with a standard oxidation-reduction potential that is more negative than that of other elements.

[0097] This configuration allows the photoelectric conversion element of Technology 1 to improve its photoelectric conversion efficiency.

[0098] (Technology 2) The photoelectric conversion element described in Technology 1, wherein the metal element is a metal element that can have a valence of +2.

[0099] This configuration allows the photoelectric conversion element in Technology 2 to further improve its photoelectric conversion efficiency.

[0100] (Technology 3) The photoelectric conversion element according to Technology 1 or 2, wherein the halogen element contains fluorine.

[0101] This configuration allows the photoelectric conversion element in Technology 3 to further improve its photoelectric conversion efficiency.

[0102] (Technical 4) The photoelectric conversion element according to any one of Technical 1 to 3, wherein the metal element includes zinc.

[0103] This configuration allows the photoelectric conversion element in Technology 4 to further improve its photoelectric conversion efficiency.

[0104] (Technical 5) The photoelectric conversion element according to any one of Technical 1 to 4, wherein the perovskite compound is composed of a monovalent cation, a divalent cation, and a halogen anion, and the divalent cation includes a Sn cation.

[0105] This configuration allows the photoelectric conversion element in Technology 5 to further improve its photoelectric conversion efficiency.

[0106] (Technical 6) The photoelectric conversion element according to Technical 5, wherein the monovalent cation includes an inorganic cation.

[0107] This configuration allows the photoelectric conversion element in technology 6 to further improve its photoelectric conversion efficiency.

[0108] (Technical 7) The photoelectric conversion element according to Technical 5 or 6, wherein the perovskite compound comprises CsSnI3.

[0109] This configuration allows the photoelectric conversion element in Technology 7 to further improve its photoelectric conversion efficiency.

[0110] (Technical 8) A photoelectric conversion element according to any one of Technical 5 to 7, wherein the monovalent cation comprises a formamidinium cation.

[0111] This configuration allows the photoelectric conversion element in Technology 8 to further improve its photoelectric conversion efficiency.

[0112] (Technical 9) The photoelectric conversion element according to any one of Technical 1 to 8, wherein the photoelectric conversion layer further comprises SnF2.

[0113] This configuration allows the photoelectric conversion element in technology 9 to further improve its photoelectric conversion efficiency.

[0114] (Technical 10) The photoelectric conversion element further comprises a hole transport layer disposed between the photoelectric conversion layer and the second electrode, wherein the surface of the photoelectric conversion layer on the second electrode side is in contact with the hole transport layer, as described in any one of Technical 1 to 9.

[0115] With this configuration, the photoelectric conversion material of technology 10 can improve the photoelectric conversion efficiency of the photoelectric conversion material.

[0116] (Technical 11) The process includes: forming a first electrode; forming a photoelectric conversion layer; and forming a second electrode, wherein the process of forming the photoelectric conversion layer includes: forming a precursor layer of the photoelectric conversion layer containing a perovskite compound containing Sn; applying a solution containing a solvent, a metal element, and a halogen element to the surface of the precursor layer; and removing the solvent from the surface of the precursor layer to which the solution has been applied, wherein the metal element is Sn 4+ A method for manufacturing a photoelectric conversion element, wherein the standard oxidation-reduction potential is more negative than that of the specified method.

[0117] This method allows the manufacturing method of technology 11 to produce a photoelectric conversion element with improved photoelectric conversion efficiency.

[0118] (Technical 12) The method for manufacturing a photoelectric conversion element according to Technical 11, wherein the metal element includes zinc.

[0119] This method allows the manufacturing method of technology 12 to produce a photoelectric conversion element with improved photoelectric conversion efficiency.

[0120] (Technical 13) A method for manufacturing a photoelectric conversion element according to Technical 11 or 12, wherein the halogen element includes fluorine.

[0121] This method allows the manufacturing method of technology 13 to produce a photoelectric conversion element with improved photoelectric conversion efficiency.

[0122] The present disclosure will be described in more detail below with reference to examples, comparative examples, and reference examples.

[0123] The preparation of the raw material solutions for the photoelectric conversion layer and hole transport layer, and the deposition of the films, were carried out in a glove box with oxygen and moisture concentrations of 1 ppm or less.

[0124] <Fabrication of Photoelectric Conversion Element> (Example 1) First, a glass substrate was prepared. This substrate serves as a support material in the photoelectric conversion element of this disclosure.

[0125] A layer of ITO (Indium Tin Oxide) was formed on the substrate by sputtering. Furthermore, a layer of ATO (Antimony Tin Oxide) was formed on top of the ITO layer by sputtering. In this way, the first electrode was formed.

[0126] Next, a dense layer of titanium oxide (TiO2) was formed on the ATO layer of the first electrode by the sol-gel method. In the sol-gel method, a solution mixed in the volume ratio of titanium(IV) isopropoxide:ethanol:hydrochloric acid = 0.1:1:0.001 was applied by spin coating, and then fired at 500°C for 30 minutes. The spin coating was performed at 4000 rpm for 10 seconds. This dense layer of titanium oxide (TiO2) corresponds, for example, to the electron transport layer described in the first embodiment above.

[0127] Next, 0.45 g of titanium dioxide 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 fired at 500°C for 30 minutes. In this way, a porous layer of titanium dioxide was formed. Spin coating was performed at 4000 rpm for 10 seconds. Both the dense layer of titanium dioxide and the porous layer of titanium dioxide possess electron transport properties. Therefore, it is possible to consider that the electron transport layer is composed of the dense layer of titanium dioxide and the porous layer of titanium dioxide.

[0128] The precursor solution for the photoelectric conversion layer was applied to the porous layer by spin coating, and then left to stand at room temperature for 10 minutes. Afterward, the coated film was baked at 50°C for 3 minutes, followed by 70°C for 10 minutes, and finally 160°C for 10 minutes. In this way, the photoelectric conversion layer was formed. Chlorobenzene, a poor solvent, was added dropwise during the spin coating process at 5000 rpm for 40 seconds.

[0129] The solution for forming the precursor layer of the photoelectric conversion layer was obtained as follows. First, a first solution with a concentration of 1.5 mol / L of SnI2 and CsI was prepared by adding SnI2 and CsI to a mixed solvent of DMF and DMSO in a volume ratio of 2:8. Next, a second solution with a concentration of 1.5 mol / L of SnF2 was prepared by adding SnF2 to DMSO. The amount of Zn powder added was weighed to be 10 mol% relative to the first solution, and the first and second solutions were added thereto to obtain a solution for forming the precursor layer of the photoelectric conversion layer. In the solution for forming the precursor layer of the photoelectric conversion layer in Example 1, the second solution was added to the first solution at a concentration of 15 mol%.

[0130] The surface of the precursor layer of the formed photoelectric conversion layer was surface-treated using a ZnF2 solution, which was used as a solution containing a solvent, a metal element (zinc in this example), and a halogen element (fluorine in this example). Specifically, ZnF2 was added to IPA (isopropyl alcohol) to prepare a 0.04 M (i.e., 0.04 mol / L) ZnF2 solution, and this ZnF2 solution was applied to the surface of the precursor layer of the photoelectric conversion layer and fired at 100°C for 10 minutes.

[0131] The photoelectric conversion layer was fabricated using the method described above.

[0132] 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.

[0133] Next, a gold film was formed on the hole transport layer by vapor deposition. In this way, a second electrode with a thickness of 100 nm was formed.

[0134] Finally, UV-curing epoxy resin was applied around the substrate, bonded to another glass substrate, and then UV-cured. In this way, the epoxy resin was cured and the power generation element was sealed.

[0135] (Example 2) In the fabrication of the photoelectric conversion layer, in order to prepare a solution for forming the precursor layer of the photoelectric conversion layer, a third solution was prepared in addition to the first and second solutions used in Example 1. A third solution with a triptycene concentration of 1.5 mol / L was prepared by adding triptycene to a mixed solvent of DMF and DMSO (volume ratio of 2:8). The second and third solutions were added to the first solution to obtain a solution for forming the precursor layer of the photoelectric conversion layer. In the solution for forming the precursor layer of the photoelectric conversion layer in Example 2, the amount of Zn powder added was weighed to be 10 mol% relative to the first solution, and the first solution, the second solution at an addition concentration of 15 mol%, and the third solution at an addition concentration of 2 mol% relative to the first solution were added thereto. The firing conditions for the coated film formed with the solution for forming the precursor layer of the photoelectric conversion layer were 50°C for 3 minutes, followed by 70°C for 10 minutes, and finally 160°C for 10 minutes. The surface of the precursor layer of the formed photoelectric conversion layer was surface-treated using a ZnF2 solution, which was used as a solution containing a solvent, a metal element (zinc in this example), and a halogen element (fluorine in this example). Specifically, ZnF2 was added to IPA (isopropyl alcohol) to prepare a 0.02 M (i.e., 0.02 mol / L) ZnF2 solution, and this ZnF2 solution was applied to the surface of the precursor layer of the photoelectric conversion layer and fired at 100°C for 10 minutes. Except for these changes, the photoelectric conversion element of Example 2 was fabricated in the same manner as in Example 1.

[0136] (Example 3) In the fabrication of the photoelectric conversion layer, in order to prepare a solution for forming the precursor layer of the photoelectric conversion layer, a third solution was prepared in addition to the first and second solutions used in Example 1. A third solution with a TBAI concentration of 1.5 mol / L was prepared by adding tetrabutylammonium iodide (TBAI) to a mixed solvent of DMF and DMSO (1:1 volume ratio). The second and third solutions were added to the first solution to obtain a solution for forming the precursor layer of the photoelectric conversion layer. In the solution for forming the precursor layer of the photoelectric conversion layer in Example 2, the amount of Zn powder added was weighed to be 10 mol% relative to the first solution, and then the second solution was added at a concentration of 15 mol% and the third solution at a concentration of 2 mol% relative to the first solution. The firing conditions for the coated film formed with the solution for forming the precursor layer of the photoelectric conversion layer were 50°C for 3 minutes, followed by 70°C for 10 minutes, and finally 160°C for 10 minutes. Aside from these modifications, the photoelectric conversion element of Example 3 was fabricated using the same method as in Example 2.

[0137] (Reference Example 1) In the fabrication of the photoelectric conversion layer, surface treatment of the precursor layer of the photoelectric conversion layer using a ZnF2 solution was not performed. Except for this point, the photoelectric conversion element was fabricated in the same manner as in Example 1. That is, ZnF2 was not present in the near-surface region of the photoelectric conversion layer of the comparative example.

[0138] (Reference Example 2) In the fabrication of the photoelectric conversion layer, a photoelectric conversion element was fabricated in the same manner as in Example 2, except that the surface treatment of the precursor layer of the photoelectric conversion layer using a ZnF2 solution was not performed. That is, in the reference example, the photoelectric conversion layer contained triptycene compounds as in Example 2, but ZnF2 was not present in the region near the surface of the photoelectric conversion layer.

[0139] <Evaluation of Photoelectric Conversion Elements> The current-voltage characteristics (i.e., IV characteristics) of the photoelectric conversion elements in Examples 1 to 3, Reference Example 1, and Reference Example 2 were evaluated.

[0140] A solar simulator (manufactured by Spectrometer Co., Ltd.) and an electrochemical analyzer ALS (manufactured by BAS Corporation) were used to evaluate the characteristics. The photoelectric conversion element was irradiated with simulated sunlight of 1 sun. The output of the solar simulator was 100 mW / cm². 2 The settings were adjusted. The IV characteristics of the photoelectric conversion element were measured by measuring the output current value while varying the applied voltage using an electrochemical analyzer.

[0141] The measurement results are shown in Table 1. PCE represents the conversion efficiency. J SC V represents the short-circuit current density. oc represents the open-circuit voltage. FF represents the fill factor. Table 1 also shows whether or not the precursor layer of the photoelectric conversion layer has been surface-treated (i.e., treated with a ZnF2 solution), and whether or not additives (triptycene compounds, TBAI) have been added to CsSnI3, the perovskite compound that constitutes the photoelectric conversion layer.

[0142] Figure 2 is a graph showing the IV characteristics of the photoelectric conversion elements of Example 2 and Reference Example 2. In other words, Figure 2 allows for a comparison of the IV characteristics of the photoelectric conversion element of Example 2 and the photoelectric conversion element of Reference Example 2, which differ only in the presence or absence of treatment with ZnF2 solution, i.e., the presence or absence of metallic and halogen elements in the region near the surface of the photoelectric conversion layer.

[0143] <Confirmation of the presence of ZnF2 in the near-surface region of the photoelectric conversion layer> X-ray diffraction measurements were performed on the near-surface region of the photoelectric conversion layer of the photoelectric conversion elements in Example 2 and Reference Example 2. Specifically, the X-ray diffraction measurements were performed using the following method. For the X-ray diffraction measurements, samples were prepared by depositing film up to the ZnF2 treatment of the photoelectric conversion element in Example 2, and up to the photoelectric conversion layer of the photoelectric conversion element in Reference Example 2. Figure 3 shows the X-ray diffraction measurement results for the near-surface region of the photoelectric conversion layer of the photoelectric conversion elements in Example 2 and Reference Example 2. As shown in Figure 3, in Reference Example 2, where the surface treatment of the precursor layer of the photoelectric conversion layer with ZnF2 solution was not performed, the presence of ZnF2 in the near-surface region of the photoelectric conversion layer was not confirmed. In contrast, in Example 2, where the surface treatment of the precursor layer of the photoelectric conversion layer with ZnF2 solution was performed, the presence of ZnF2 (i.e., the presence of zinc as a metallic element and fluorine as a halogen element) was confirmed in the near-surface region of the photoelectric conversion layer.

[0144]

[0145] As shown in Table 1, the photoelectric conversion elements of Examples 1 to 3, which underwent surface treatment with a ZnF2 solution containing metallic and halogen elements, that is, photoelectric conversion elements having a photoelectric conversion layer in the near-surface region including the surface on the second electrode side, exhibited higher conversion efficiency than the photoelectric conversion elements of Reference Examples 1 and 2, which did not have such a configuration.

[0146] The photoelectric conversion material disclosed herein can be used, for example, in a solar cell.

Claims

1. The device comprises a first electrode, a photoelectric conversion layer containing a perovskite compound, and a second electrode, wherein the perovskite compound contains Sn, and the photoelectric conversion layer further contains a metal element and a halogen element present in a near-surface region including the surface on the second electrode side, wherein the metal element is Sn 4+ A photoelectric conversion element with a standard oxidation-reduction potential that is more negative than that of other elements.

2. The photoelectric element according to claim 1, wherein the metal element is a metal element that can have a valence of +2.

3. The photoelectric conversion element according to claim 1, wherein the halogen element includes fluorine.

4. The photoelectric conversion element according to claim 1, wherein the metal element includes zinc.

5. The photoelectric conversion element according to claim 1, wherein the perovskite compound is composed of a monovalent cation, a divalent cation, and a halogen anion, and the divalent cation includes a Sn cation.

6. The photoelectric conversion element according to claim 5, wherein the monovalent cation includes an inorganic cation.

7. The photoelectric conversion element according to claim 5, wherein the perovskite compound comprises CsSnI3.

8. The photoelectric element according to claim 5, wherein the monovalent cation comprises a formamidinium cation.

9. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion layer further comprises SnF2.

10. The photoelectric conversion element according to claim 1, further comprising a hole transport layer disposed between the photoelectric conversion layer and the second electrode, wherein the surface of the photoelectric conversion layer on the second electrode side is in contact with the hole transport layer.

11. The process includes the steps of forming a first electrode, forming a photoelectric conversion layer, and forming a second electrode, wherein the step of forming the photoelectric conversion layer includes forming a precursor layer of the photoelectric conversion layer containing a perovskite compound containing Sn, applying a solution containing a solvent, a metal element, and a halogen element to the surface of the precursor layer, and removing the solvent from the surface of the precursor layer to which the solution has been applied, wherein the metal element is Sn 4+ A method for manufacturing a photoelectric conversion element, wherein the standard oxidation-reduction potential is more negative than that of the specified method.

12. The method for manufacturing a photoelectric conversion element according to claim 11, wherein the metal element includes zinc.

13. The method for manufacturing a photoelectric conversion element according to claim 11, wherein the halogen element includes fluorine.

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