Photoelectric conversion element, photoelectric conversion device, light detection method, and method for producing photoelectric conversion element

Abstract

This photoelectric conversion element (100) comprises, in the following order as a photoelectric conversion layer (103): a first layer (104) configured from a plurality of particles containing a perovskite structure (201) as a main component, or from an aggregate or thin film of the particles; a second layer (105) configured from a plurality of particles containing an inorganic transition metal (205) as a main component, or an aggregate or thin film of the particles; and a third layer (106) configured from a plurality of particles containing an organic ligand (206) as the main component, or an aggregate or thin film of the particles. The inorganic transition metal (205) in the second layer (105) is different from a central metal contained in the perovskite structure (201). At an interface (S1) between the first layer (104) and the second layer (105), the perovskite structure (201) and the inorganic transition metal (205) in the second layer (105) form a one-to-one layer arrangement. At an interface (S2) between the second layer (105) and the third layer (106), the inorganic transition metal (205) in the second layer (105) and the organic ligand (206) in the third layer (106) together form an organometallic complex layer (108) composed of an organometallic complex (208).

Description

Photoelectric conversion element, photoelectric conversion device, light detection method, and method for manufacturing photoelectric conversion element

[0001] The present invention relates to a photoelectric conversion element, a photoelectric conversion device, a light detection method, and a method for manufacturing a photoelectric conversion element. This application claims priority based on Japanese Patent Application No. 2022-130971 filed on August 19, 2022, the contents of which are incorporated herein by reference.

[0002] Techniques for amplifying photocurrent using photoelectric conversion elements such as avalanche photodiodes and photomultiplier tubes are known. Avalanche photodiodes are photodiodes that amplify photocurrent by irradiating a pn junction made of an inorganic semiconductor with light while applying a reverse voltage, causing collisions of generated electrons and holes with a crystal lattice and the generation of electrons and holes from the collided crystal lattice in a chain reaction. Photomultiplier tubes are composed of multiple dynodes and a vacuum tube containing them, and amplify photocurrent by irradiating one dynode with light, causing collisions of generated electrons with the dynode and the generation of electrons from the collided dynode in a chain reaction.

[0003] Patent Document 1 discloses a photoelectric conversion element which is formed by sequentially laminating a first layer composed of a plurality of particles or their aggregates or a thin film containing an inorganic semiconductor as a main component, a second layer composed of a plurality of particles or their aggregates or a thin film containing a perovskite structure as a main component on the surface of the particles or their aggregates, and a third layer composed of a plurality of particles or their aggregates or a thin film containing an organometallic complex as a main component, wherein the energy level of the second layer is higher than that of the first layer in the conduction band, and the energy level of the third layer is higher than that of the second layer, and the energy level of the second layer is higher than that of the third layer in the valence band.

[0004] International Publication No. 2020 / 162317

[0005] There is a demand for a photoelectric conversion element that is highly efficient and sensitive to weak optical signals while minimizing environmental impact, and that has a better response than the photoelectric conversion element of Patent Document 1.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a photoelectric conversion element that is highly efficient and sensitive to weak optical signals while minimizing the environmental load, and that has superior responsiveness, a photoelectric conversion device, a light detection method, and a method for manufacturing a photoelectric conversion element.

[0007] In order to solve the above problems, the present invention proposes the following means: (1) A photoelectric conversion element according to a first aspect of the present invention comprises, as a photoelectric conversion layer, a first layer constituted by a plurality of particles containing a perovskite structure as a main component, or an aggregate thereof, or a thin film thereof, a second layer constituted by a plurality of particles containing an inorganic transition metal as a main component, or an aggregate thereof, or a thin film thereof, and a third layer constituted by a plurality of particles containing an organic ligand as a main component, or an aggregate thereof, or a thin film thereof, in this order, wherein the inorganic transition metal of the second layer is different from the central metal contained in the perovskite structure, and the perovskite structure and the inorganic transition metal of the second layer form a one-to-one layer arrangement at the interface between the first layer and the second layer, and the inorganic transition metal of the second layer and the organic ligand of the third layer together form an organometallic complex layer at the interface between the second layer and the third layer. (2) Aspect 2 of the present invention relates to the photoelectric conversion element of Aspect 1, wherein, in the conduction band, the energy level of the LUMO of the conduction band of the organometallic complex layer may be higher than the energy level of the conduction band of the first layer, and, in the valence band, the energy level of the valence band of the first layer may be higher than the energy level of the HOMO of the valence band of the organometallic complex layer. (3) Aspect 3 of the present invention relates to the photoelectric conversion element of Aspect 1 or Aspect 2, wherein the second layer may be a layer formed by segregating the inorganic transition metal on the surface of the first layer. (4) Aspect 4 of the present invention relates to the photoelectric conversion element of any one of Aspects 1 to 3, wherein the second layer may be a monoatomic layer of the inorganic transition metal. (5) Aspect 5 of the present invention relates to the photoelectric conversion element of any one of Aspects 1 to 4, wherein the organic ligand may be α-methylbenzylamine or terpyridine. (6) Aspect 6 of the present invention is directed to the photoelectric conversion element of any one of Aspects 1 to 5, wherein the central metal contained in the perovskite structure is lead, the inorganic transition metal of the second layer is europium, the inorganic transition metal of the second layer constituting the organometallic complex is europium, and the organic ligand constituting the organometallic complex may be α-methylbenzylamine or terpyridine.(7) A seventh aspect of the present invention is the photoelectric conversion element according to any one of the first to sixth aspects, wherein the perovskite structure has a formula CH. ３ NH ３ PbI ３(8) A photoelectric conversion device of Aspect 8 of the present invention includes the photoelectric conversion element of Aspect 1, wherein a negative electrode layer is stacked on the opposite side of the second layer with the first layer sandwiched therebetween, and a positive electrode layer is stacked on the opposite side of the second layer with the third layer sandwiched therebetween. (9) A light detection method of Aspect 9 of the present invention includes the steps of: causing the photoelectric conversion layer to receive visible light and / or near-infrared light, thereby flowing a current between the negative electrode layer and the positive electrode layer; and measuring the current to detect the visible light and / or near-infrared light in the photoelectric conversion device of Aspect 8. (10) A method for producing a photoelectric conversion element according to a tenth aspect of the present invention includes: a first step of coating a surface of a substrate with a mixture containing a raw material for a perovskite structure and an inorganic transition metal contained in the raw material for the perovskite structure and different from a central metal contained in the perovskite structure; a second step of forming, after the first step, a first layer composed of a plurality of particles containing the perovskite structure as a main component, or aggregates thereof, or a thin film thereof, and a second layer composed of a plurality of particles containing the inorganic transition metal as a main component, or aggregates thereof, or a thin film thereof; and a third step of forming, after the second step, an organometallic complex layer composed of an organometallic complex by coordinating an organic ligand to the inorganic transition metal on a second surface of the second layer, the second surface being the surface opposite to the surface in contact with the first surface. (11) Aspect 11 of the present invention relates to the method for manufacturing a photoelectric conversion element of Aspect 10, wherein in the conduction band, the energy level of a LUMO of the organometallic complex layer may be higher than the energy level of a conduction band of the first layer, and in the valence band, the energy level of the valence band of the first layer may be higher than the energy level of a HOMO of the organometallic complex layer. (12) Aspect 12 of the present invention relates to the method for manufacturing a photoelectric conversion element of Aspect 10 or Aspect 11, wherein in the second step, the second layer may be formed by segregating the inorganic transition metal on a surface of the first layer.(13) Aspect 13 of the present invention relates to the method for manufacturing a photoelectric conversion element according to any one of Aspects 10 to 12, wherein the second layer is a monoatomic layer of the inorganic transition metal. (14) Aspect 14 of the present invention relates to the method for manufacturing a photoelectric conversion element, comprising: a mixing step of mixing raw materials for a perovskite structure with an inorganic transition metal contained in the raw materials for the perovskite structure and different from a central metal contained in the perovskite structure to obtain a mixture; a coating step of coating a surface of a base material with the mixture to form a coating layer; a heating step of heating the coating layer after the coating step to form a first layer composed of a plurality of particles, or aggregates thereof, or a thin film containing the perovskite structure as a main component, and a second layer composed of a plurality of particles, or aggregates thereof, or a thin film containing the inorganic transition metal as a main component; and a step of applying a solution containing an organic ligand to a surface of the second layer opposite to a surface that contacts the first layer, after the heating step.

[0008] According to the above aspects of the present invention, it is possible to provide a photoelectric conversion element that is highly efficient and sensitive to weak optical signals while minimizing the environmental load, and that has superior responsiveness, a photoelectric conversion device, a light detection method, and a method for manufacturing a photoelectric conversion element.

[0009] 1 is a cross-sectional view of a photoelectric conversion element according to one embodiment of the present invention; FIG. 2 is a cross-sectional view of an example of a method for manufacturing the photoelectric conversion element of FIG. 1; FIG. 3 shows the energy band structure of each layer during operation of the photoelectric conversion element of FIG. 1; FIG. 4 is a graph showing the photocurrent response speed obtained in a photoelectric conversion element according to Example 1 of the present invention; FIG. 5 is a diagram showing the relationship between Eu concentration and surface potential upon light irradiation; the upper row in the figure shows the experimental results for the test group with "light irradiation," while the lower row in the figure shows the experimental results for the control test group with "no light irradiation." In addition, the right side of the potential image at each Eu concentration shows a potential level bar (lower limit 0.2 V to upper limit 0.5 V) expressed in shades of gray.

[0010] Hereinafter, a photoelectric conversion element, a photoelectric conversion device, a light detection method, and a manufacturing method of a photoelectric conversion element according to embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional ratios of each component may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the present invention.

[0011] (Photoelectric Conversion Element) Fig. 1 is a cross-sectional view schematically illustrating the configuration of a photoelectric conversion element 100 according to one embodiment of the present invention. The photoelectric conversion element 100 includes a positive electrode layer (positive electrode member) 101, a negative electrode layer (negative electrode member) 102, and a photoelectric conversion layer 103 located between the positive electrode layer 101 and the negative electrode layer 102. In the photoelectric conversion element 100, the negative electrode layer 102 is stacked on the opposite side of the second layer 105 with the first layer 104 sandwiched therebetween. In addition, in the photoelectric conversion element 100, the positive electrode layer 101 is stacked on the opposite side of the second layer 105 with the third layer 106 sandwiched therebetween.

[0012] When the positive electrode layer (positive electrode member) 101 or the negative electrode layer (negative electrode member) 102 is used on the light transmitting side, it is preferable to use a light-transmitting material (i.e., a transparent or translucent electrode material). Examples of electrode materials for these electrode layers include conductive metal oxide films and translucent metal thin films. Specifically, for example, films made using conductive materials such as indium oxide, zinc oxide, tin oxide, and their composites, such as tin-doped indium oxide (indium tin oxide) (ITO), indium zinc oxide (IZO), and NESA, as well as films made using gold, platinum, silver, copper, etc. are used. Among these electrode materials, ITO, indium zinc oxide, and tin oxide are preferred. Examples of electrode fabrication methods include vacuum deposition, sputtering, ion plating, and plating. Organic transparent conductive films such as polyaniline and its derivatives, polythiophene and its derivatives, etc. may also be used as electrode materials.

[0013] The other electrode, which does not need to transmit light, does not need to be transparent. Metals, conductive polymers, and the like can be used as the electrode material for the other electrode. Specific examples of electrode materials include metals (first metals) such as aluminum (Al) and zinc (Zn), alloys of two or more of these metals, alloys of one or more of the first metals with one or more metals selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), copper (Cu), manganese (Mn), titanium (Ti), cobalt (Co), nickel (Ni), tungsten (W), and tin (Sn), graphite, graphite intercalation compounds, polyaniline, polythiophene, and other conductive polymers. Examples of alloys include magnesium-silver alloys, magnesium-indium alloys, magnesium-aluminum alloys, indium-silver alloys, lithium-aluminum alloys, lithium-magnesium alloys, lithium-indium alloys, and calcium-aluminum alloys.

[0014] In order to capture light into the photoelectric conversion layer 103, the anode layer 102 is preferably made of a light-transmitting material, such as antimony-doped tin oxide (ATO), tin-doped indium oxide (ITO), zinc oxide, tin oxide, fluorine-doped tin oxide (FTO), etc. Since heat treatment is required in the manufacturing process of the photoelectric conversion element 100 of this embodiment, among these materials, ATO, which has heat resistance, is preferred as the material for the anode layer 102.

[0015] As shown in FIG. 1 , the photoelectric conversion layer 103 according to this embodiment includes, in this order: a first layer 104 composed of a plurality of particles, or aggregates thereof, or a thin film containing a perovskite structure 201 as a primary component; a second layer 105 composed of a plurality of particles, or aggregates thereof, or a thin film containing an inorganic transition metal 205, which is different from the central metal contained in the perovskite structure 201, as a primary component; and a third layer 106 composed of a plurality of particles, or aggregates thereof, or a thin film containing an organic ligand 206 as a primary component. The photoelectric conversion element 100 includes a positive electrode layer 101, a third layer 106, a second layer 105, a first layer 104, and a negative electrode layer 102 stacked in this order. Here, the second layer 105 and the third layer 106 form an organometallic complex layer 108. The photoelectric conversion layer 103 is preferably configured so that a conductive path is formed from the positive electrode layer 101 to the negative electrode layer 102. The more conductive paths formed, the better. In this embodiment, the term "layer" refers to a film formed by one or more film-forming processes, and is not limited to being flat, and does not necessarily have to be integral.

[0016] In the photoelectric conversion layer 103, the materials and compositions of the first layer 104 and the organometallic complex layer 108 are preferably determined so that the energy level of the conduction band (Lowest Unoccupied Molecular Orbital (LUMO), excited state) of the organometallic complex layer 108 is higher than that of the first layer 104, and the energy level of the valence band (Highest Occupied Molecular Orbital (HOMO), ground state) of the first layer 104 is higher than that of the organometallic complex layer 108. In the conduction band, the energy level of the LUMO of the conduction band of the organometallic complex layer 108 is higher than that of the conduction band of the first layer 104. For example, the first layer 104 can have a valence band energy level of −5.5 eV or higher and a conduction band energy level of −3 eV or lower. Furthermore, for the organometallic complex layer 108 (preferably, for example, ions of the inorganic transition metal 205), it is preferable to have a valence band HOMO energy level of −6 eV or higher and a conduction band LUMO energy level of −2 eV or lower. Incidentally, the energy levels can be measured, for example, by ultraviolet photoelectron spectroscopy (UPS) in a vacuum or in an air atmosphere. In some cases, values ​​of the energy levels already published in literature may be used instead.

[0017] The photoelectric conversion layer 103 according to this embodiment may comprise, in this order: an inorganic semiconductor layer 107 containing an inorganic semiconductor as a main component; a first layer 104 constituted of a plurality of particles or their aggregates or a thin film containing a perovskite structure 201 as a main component; a second layer 105 constituted of a plurality of particles or their aggregates or a thin film containing, as a main component, an inorganic transition metal 205 different from the central metal contained in the perovskite structure 201; and a third layer 106 constituted of a plurality of particles or their aggregates or a thin film containing an organic ligand 206 as a main component.

[0018] (When Inorganic Semiconductor Layer 107 Is Present) When the inorganic semiconductor layer 107 is present, the inorganic semiconductor layer 107 is provided on the negative electrode layer 102. The form of the inorganic semiconductor layer 107 is not particularly limited. The inorganic semiconductor layer 107 may be, for example, a porous film made of an aggregate of a plurality of particles and having a plurality of voids between the particles. When the inorganic semiconductor layer 107 is made of particles, it is preferable that the particles in contact with the first layer 104 be in direct contact with the negative electrode layer 102 or indirectly via other particles so as to be electrically connected to the negative electrode layer 102.

[0019] The inorganic semiconductor contained in the inorganic semiconductor layer 107 preferably has an absorption wavelength in the ultraviolet light range, such as titanium oxide or zinc oxide. The thickness of the first layer 104 is preferably about 10 nm or more and 1000 nm or less, and more preferably about 50 nm or more and 500 nm or less. The inorganic semiconductor layer 107 may be composed of only an inorganic semiconductor.

[0020] (First layer 104) The first layer 104 is composed of a plurality of particles or aggregates thereof containing the perovskite structure 201 as a main component, or a thin film. The first layer 104 is preferably in the form of a thin film. The content of the perovskite structure 201 in the first layer 104 is 60 mass % or more with respect to the total mass of the first layer 104. The content of the perovskite structure 201 is more preferably 80 mass % or more. Since the first layer 104 may be composed only of the perovskite structure 201, the upper limit of the content of the perovskite structure 201 is 100 mass %.

[0021] The perovskite structure 201 constituting the first layer 104 is, for example, a compound ABX3 composed of three types of ions A, B, and X. The perovskite structure 201 is preferably an inorganic perovskite compound in order to segregate an inorganic transition metal 205 different from the central metal contained in the perovskite structure 201. Specifically, the ions B and X are arranged in a plurality of units (BX) having an octahedral structure. ６ ) ４－The octahedral structures of adjacent units share one face. Ion B is located at the center of the octahedron, and ion X is located at the vertices of the octahedron. Here, the central metal is ion B located at the center of the octahedron. Ion A is located at a position circumscribing the octahedral structure of each unit. Ion A is, for example, Cs ＋ , K. ＋ , Rb ＋ metal cations such as CH ３ NH ３ ＋ (MA), NH=CHNH ２ ＋ (FA). Ion B is a lead ion (Pb ２＋ ), tin ions (Sn ２＋ ) X is I － , Cl － ,Br － The size and shape of the band gap can be changed by selecting an ion from ion A, ion B, and ion X. Adding tin to the perovskite structure 201 narrows the band gap, improving the responsiveness to long-wavelength light such as near-infrared light.

[0022] Furthermore, it is preferable that the energy level of the valence band of the first layer 104 is higher than the energy level of the HOMO of the valence band of the organometallic complex layer 108 and is intermittently connected to the same energy level. Examples of the composition of the first layer 104 (perovskite structure) that satisfies these conditions include CsPbX ３ (X=Br or I), CH ３ NH ３ PbI ３ etc.

[0023] There is no particular limitation on the thickness of the first layer 104. For example, the thickness of the first layer 104 is 1 to 10 nm.

[0024] The second layer 105 is preferably a layer formed by segregating an inorganic transition metal 205 on the surface of the first layer 104 so as to be directly bonded to the perovskite structure of the first layer 104. The second layer 105 is preferably a monoatomic layer of the inorganic transition metal 205. The content of the inorganic transition metal 205 in the second layer 105 is 60 mass % or more with respect to the total mass of the second layer 105. The content of the inorganic transition metal 205 is more preferably 80 mass % or more. Since the second layer 105 may be composed only of the inorganic transition metal 205, the upper limit of the content of the inorganic transition metal 205 is 100 mass %. The inorganic transition metal 205 is preferably a metal cation. As the metal cation, for example, Eu, which has a reduction level of LUMO, may be used. ３＋ , Cr ３＋ Ru whose oxidation level is HOMO ２＋ , Fe ２＋ , Mn ２＋ , Co ２＋ Particularly preferred is Eu ３＋ The inorganic transition metal 205 in the second layer 105 is different from the central metal (ion B) contained in the first layer 104. The inorganic transition metal 205 in the second layer 105, which is different from the central metal contained in the perovskite structure 201, is different from the metal contained in the first layer 104, so that the hole collection efficiency can be further increased and the response speed of the photoelectric conversion element 100 can be improved.

[0025] The third layer 106 is provided on and in contact with the second layer 105. To achieve photocurrent amplification, the organometallic complex 208 is preferably bonded to the molecules of the perovskite structure so that the organic ligand 206 and the inorganic transition metal ion 205, which is different from the central metal contained in the perovskite structure 201, are arranged in this order in a current path from the positive electrode layer 101 side to the second layer 105 side. In other words, the organometallic complex layer 108 is divided into the second layer 105 composed of inorganic transition metal ions and the third layer 106 composed of organic ligand ions. The third layer 106 is preferably a monolayer of the organic ligand 206. The content of the organic ligand 206 in the third layer 106 is 60% by mass or more relative to the total mass of the third layer 106. More preferably, the content of the organic ligand 206 is 80% by mass or more. The third layer 106 may be composed only of the organic ligand 206, and therefore the upper limit of the content of the organic ligand 206 is 100 mass %. Note that the boundary between these two layers can sometimes be confirmed using, for example, a transmission electron microscope (TEM).

[0026] Examples of the organic ligand 206 include general metal complex ligands, such as (i) organic compounds having a carboxyl group, a nitro group, a sulfo group, a phosphate group, a hydroxy group, an oxo group, or an amino group; (ii) ethylenediamine derivatives; (iii) organic ligands containing a ring heteroatom, such as terpyridine derivatives, phenanthroline derivatives, and bipyridine derivatives; and (iv) acetylacetonate-based organic ligands, such as catechol derivatives, quinone derivatives, naphthoic acid derivatives, and acetylacetonate derivatives (specifically, for example, acetylacetone). (Here, "acetylacetonate-based organic ligand" refers to an organic ligand that can form a coordinate bond with many transition metal ions (e.g., by forming a six-membered ring) via two oxygen atoms.) The terpyridine derivative has a structure represented by the following formula (1). The organic ligand 206 is preferably α-methylbenzylamine or terpyridine. α-Methylbenzylamine has a structure represented by the following formula (2).

[0027]

[0028]

[0029] In the photoelectric conversion element 100, at the interface S1 between the first layer 104 and the second layer 105, the perovskite structure 201 and the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, form a one-to-one layer arrangement. Here, "at the interface S1 between the first layer 104 and the second layer 105, the perovskite structure 201 and the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, form a one-to-one layer arrangement" means that at the interface S1 between the first layer 104 and the second layer 105, atoms of the inorganic transition metal 205, which is different from the central metal contained in one perovskite structure 201, are arranged relative to one octahedral structure at positions circumscribing the octahedral structure of the unit constituting the perovskite structure 201. At the interface S1 between the first layer 104 and the second layer 105, the perovskite structure 201 and the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, form a one-to-one layer arrangement, thereby achieving more efficient uniform collection of holes, and thereby improving the response speed of the photoelectric conversion element 100.

[0030] At the interface S1 between the first layer 104 and the second layer 105, the perovskite structure 201 and the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, are arranged in a one-to-one layer arrangement, which can be confirmed, for example, by observing the cross section of the photoelectric conversion element 100 with an SEM or by measuring the surface potential with a scanning probe microscope.

[0031] Incidentally, a scanning probe microscope is normally a technique for observing the surface shape and surface structure of a sample, but for example, in addition to observing the surface shape of the sample (i.e., obtaining height information), other physical property information of the sample surface, such as current, potential, hardness, and viscoelasticity, can be measured, and then analysis such as a texture display for displaying the other physical property information superimposed on the height information, or a 3D cross-sectional shape analysis function can be performed to evaluate the presence or absence, state, properties, and influence of coordinate bonds from the obtained image. In this way, by understanding the charge state of the obtained sample surface and examining the presence or absence and state of coordinate bonds between the perovskite structure 201 and the inorganic transition metal 205, it can be indirectly confirmed that the perovskite structure 201 and the inorganic transition metal 205 form a one-to-one layer arrangement at a position circumscribing the octahedral structure of the unit constituting the perovskite structure 201. Furthermore, atomic force microscopy is also a technique for observing the surface shape of a sample. Because it is capable of measuring interatomic distances, it is possible to observe changes in the distance between the perovskite structure 201 and the inorganic transition metal 205. This makes it possible to indirectly confirm that the perovskite structure 201 and the inorganic transition metal 205 form a one-to-one layer arrangement at a position circumscribing the octahedral structure of the units constituting the perovskite structure 201. Furthermore, as with the scanning probe microscope described above, by using a conductive or magnetic cantilever, electric forces (electric gradient forces) and magnetic images can be observed simultaneously with surface shape images, and the presence, state, properties, and effects of coordinate bonds can be evaluated from the obtained images. Other techniques include optical methods (e.g., a method in which optical changes caused by intramolecular electronic transitions in coordinate bonds for forming a one-to-one layer arrangement are detected by spectroscopy using light absorption or scattering), magnetic methods (e.g., a method in which magnetic changes caused by changes in the spin state of transition metal ions are detected by electron magnetic resonance).

[0032] In the photoelectric conversion element 100, at the interface S2 between the second layer 105 and the third layer 106, the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, and the organic ligands 206 of the third layer 106 combine to form an organometallic complex layer 108 made of the organometallic complex 208. By combining the inorganic transition metal 205 and the organic ligands 206 of the third layer 106 to form the organometallic complex layer 108 made of the organometallic complex 208, it is possible to efficiently amplify the photocurrent of the photoelectric conversion element 100 even in response to a weak optical signal.

[0033] In the photoelectric conversion element 100, it can be confirmed by, for example, X-ray photoelectron spectroscopy (XPS) or infrared spectroscopy (FT-IR) that the inorganic transition metal 205 of the second layer 105, which is different from the central metal contained in the perovskite structure 201, and the organic ligands 206 of the third layer 106 together form the organometallic complex layer 108 at the interface S2 between the second layer 105 and the third layer 106.

[0034] When the photoelectric conversion element 100 of this embodiment is applied to an optical sensor, the photoelectric conversion element 100 is mounted on a semiconductor substrate such as silicon or a glass substrate. In this case, the following device configuration can be given, for example. (1) A configuration in which the transparent anode layer 102 is formed on the top layer farthest from the semiconductor substrate (i.e., a configuration in which, from the top layer on the light incident side, the (transparent) anode layer 102 / first layer 104 / organometallic complex layer 108 / cathode layer 101 / (Si) substrate are laminated in this order); (2) A configuration in which the transparent anode layer 101 is formed on the top layer farthest from the semiconductor substrate (i.e., a configuration in which, from the top layer on the light incident side, the (transparent) cathode layer 101 / organometallic complex layer 108 / first layer 104 / anode layer 102 / (Si) substrate are laminated in this order); (3) A configuration in which the transparent anode layer 102 is formed adjacent to the glass substrate (i.e., a configuration in which, from the top layer on the light incident side, the (glass) substrate / anode layer 102 / first layer 104 / organometallic complex layer 108 / cathode layer 101 are laminated in this order). Another example of a device configuration is one in which the inorganic semiconductor 107 is present between the (transparent) negative electrode layer 102 and the first layer 104 in the device configurations (1) to (3) above.

[0035] In the photoelectric conversion element 100, it is preferable that the central metal contained in the perovskite structure 201 is lead, the inorganic transition metal 205 in the second layer 105 is europium, the inorganic transition metal in the second layer 105 constituting the organometallic complex 208 is europium, and the organic ligand 206 constituting the organometallic complex 208 is α-methylbenzylamine or terpyridine.

[0036] 2( a ) to 2 ( f ) are cross-sectional views showing an example of a manufacturing process for the photoelectric conversion element 100. The photoelectric conversion element 100 can be manufactured mainly through the following steps. For reference, FIG. 2( d ) shows an example of a manufacturing process as an additional step in the case where the inorganic semiconductor 107 is present between the (transparent) negative electrode layer 102 and the first layer 104.

[0037] First, as shown in FIG. 2( a), a substrate 110 including an anode layer 102 for forming a photoelectric conversion layer 103 is prepared. The substrate 110 includes a support substrate 102A and an anode layer 102 disposed on the support substrate 102A. When light is introduced from the substrate 110 side, the support substrate 102A and the anode layer 102 are optically transparent. The support substrate 10A is made of, for example, glass. The anode layer 102 functions as the anode layer and uses a transparent, conductive electrode material. A buffer layer (not shown) may be formed on one side of the anode layer 102. The buffer layer can be formed by applying a material solution to the anode layer 102 using a spin coating method or the like and then heating (drying) the solution. This heating may be performed, for example, at approximately 120 to 450°C for approximately 10 to 60 minutes. The material application conditions (e.g., application time) may be adjusted so that the buffer layer has a thickness of, for example, approximately 1 to 100 nm.

[0038] Incidentally, when an inorganic semiconductor 107 is present between the (transparent) negative electrode layer 102 and the first layer 104, as in the above-mentioned "other device configuration," an intermediate member having a desired configuration can be manufactured instead of the intermediate member shown in FIG. 2(a) by adding the following procedure, as shown in FIG. 2(b). First, an inorganic semiconductor layer 107 containing an inorganic semiconductor as a main component is formed on one side of the negative electrode layer 102 (with a buffer layer sandwiched between them, if any). The method for forming the inorganic semiconductor layer 107 is not particularly limited. For example, the inorganic semiconductor layer 107 may be formed by vacuum deposition, or may be formed by applying a dispersion of particles containing an inorganic semiconductor to the negative electrode layer 102 and heating the applied layer. The conditions for applying the dispersion (e.g., application time) may be adjusted so that the thickness of the first layer 104 is, for example, about 10 to 1,000 nm, preferably about 50 to 500 nm. In the subsequent manufacturing process, the photoelectric conversion element 100 can be manufactured by using the intermediate member shown in FIG. 2(b) instead of the intermediate member shown in FIG. 2(a) through a similar procedure (i.e., FIGS. 2(c) to 2(f)).

[0039] 2(c), the surface of the substrate 110 is coated with a mixture containing raw materials for the perovskite structure 201 and an inorganic transition metal different from the central metal contained in the perovskite structure 201 (first step). Specifically, the anode layer 102 (and, if an inorganic semiconductor layer 107 is present, the inorganic semiconductor layer 107) is coated with a mixture containing raw materials for the perovskite structure and an inorganic transition metal 205 different from the central metal contained in the perovskite structure 201. In this way, a coating layer 120 is formed. A method for forming the coating layer 120 will be described below.

[0040] First, a mixture is obtained by mixing raw materials for the perovskite structure with an inorganic transition metal (hereinafter sometimes referred to as a second-layer inorganic transition metal) 205 that is contained in the raw materials for the perovskite structure and is different from the central metal contained in the perovskite structure 201 (mixing step). Examples of raw materials for the perovskite structure include a compound containing ion A and ion X (hereinafter sometimes referred to as a first compound) and a compound containing ion B and ion X (hereinafter sometimes referred to as a second compound). Examples of compounds containing ion A and ion X include CsCl, CsBr, CsI, MACl, MABr, MAI, FACl, FABr, and FAI. The MA in MACl is CH ３ NH ３ ＋ FA represents NH=CHNH ２ ＋ The compound containing ion B and ion X is PbCl ２ , PbBr ２ , PbI ２ , SnCl ２ , SnBr ２ , SnI ２ Examples include:

[0041] The second-layer inorganic transition metal in the mixture may be contained as a metal element or as a compound containing the second-layer inorganic transition metal. The mixture preferably contains a compound containing a second-layer inorganic transition metal. The compound containing the second-layer inorganic transition metal is, for example, a compound containing a second-layer inorganic transition compound and an ion X (hereinafter, sometimes referred to as a third compound). Examples of the compound containing a second-layer inorganic transition compound and an ion X include EuCl ２ , EuBr ２ , EuI ２ , YbCl ２ , YbBr ２ , YbI ２ Examples include:

[0042] The proportions of the first compound, the second compound, and the third compound in the mixture as a whole are preferably determined so that the molar ratio of ions A, ions B, ions X, and the second-layer inorganic transition metal (ions A: ions B: ions X: second-layer inorganic transition metal) satisfies 1:1:3:0.3 to 1. For example, in order to make the second layer 105 a monoatomic layer, the molar ratio of ions A, ions B, ions X, and the second-layer inorganic transition metal in the mixture as a whole is preferably 1:1:3:0.3 so that the composition ratio of the final film is 1:1:3:0.01. In this case, a specific procedure for making the second layer 105 a monoatomic layer is, for example, as described in Example 1 below, to form a film using a solution containing ions B, ions X, and a second-layer inorganic transition metal (the molar ratio of ions B:ions X:second-layer inorganic transition metal in the entire mixture is 1:3:0.3), and then apply a solution containing ions A (the molar ratio of ions A in the entire mixture is 1) to form a two-layer coating layer. Furthermore, the total content of the first compound, second compound, and third compound in the entire mixture is 90% by mass or more relative to the total mass of the mixture. The entire mixture may be composed only of the first compound, second compound, and third compound, so the upper limit of the total content of the first compound, second compound, and third compound in the entire mixture is 100% by mass.

[0043] The mixture may be a solution containing raw materials for the perovskite structure and a second-layer inorganic transition metal, or a combination of a solution containing some of the raw materials for the perovskite structure and the second-layer inorganic transition metal and a solution containing other parts of the raw materials for the perovskite structure. A solution containing the raw materials for the perovskite structure and the second-layer inorganic transition metal, or a combination of a solution containing some of the raw materials for the perovskite structure and the second-layer inorganic transition metal and a solution containing other parts of the raw materials for the perovskite structure, can be used to form a coating layer 120 of uniform thickness using spin coating or the like. When the mixture is a solution, the solvent is not particularly limited as long as it can dissolve the first compound, the second compound, and the third compound. Examples of the solvent include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and γ-butyrolactone. When the mixture is a solution, the total content of the first compound, the second compound, and the third compound is 90% by mass or more based on the total mass of the mixture after drying. The entire mixture after drying may be composed of only the first compound, the second compound, and the third compound, and therefore the upper limit of the total content of the first compound, the second compound, and the third compound in the entire mixture after drying is 100 mass%.

[0044] Next, the surface of the substrate 110 is coated with the mixture to form the coating layer 120 (coating step). The method for forming the coating layer 120 is not particularly limited. Examples of methods for forming the coating layer 120 include spin coating and dipping. The coating layer 120 is preferably formed by applying a solution containing the raw materials for the perovskite structure and the second-layer inorganic transition metal, or a combination of a solution containing a portion of the raw materials for the perovskite structure, the second-layer inorganic transition metal, and a solution containing another portion of the raw materials for the perovskite structure, followed by heating and drying. Heating is preferably performed, for example, at approximately 40 to 100°C for approximately 5 to 10 minutes. The material application conditions (e.g., application time) are adjusted so that the thickness of the coating layer 120 is, for example, approximately 1 to 10 nm. The coating layer 120 may be a single layer containing all of the first compound, second compound, and third compound in the entire mixture. Alternatively, the coating layer 120 may be composed of two or more layers. An example of the coating layer 120 being composed of two or more layers is a layer containing a second compound and a third compound, and a layer containing a first compound provided on the layer containing the second compound and the third compound.

[0045] Next, as shown in FIG. 2(d), after the first step, a one-to-one layer arrangement is formed between the perovskite structure 201 and the second-layer inorganic transition metal 205, thereby forming a first layer composed of a plurality of particles, aggregates thereof, or a thin film containing the perovskite structure 201 as a primary component, and a second layer composed of a plurality of particles, aggregates thereof, or a thin film containing the second-layer inorganic transition metal 205 as a primary component (second step). The method for forming a one-to-one layer arrangement between the perovskite structure 201 and the second-layer inorganic transition metal 205 is not particularly limited. For example, the coating layer 120 may be heated to form a first layer 104 composed of a plurality of particles, aggregates thereof, or a thin film containing the perovskite structure 201 as a primary component, and a second layer 105 composed of a plurality of particles, aggregates thereof, or a thin film containing the second-layer inorganic transition metal 205 as a primary component (heating step). The first layer 104 is preferably in the form of a thin film. The second layer 105 is preferably in the form of a thin film. By heating, a perovskite structure 201 is formed from the first compound and the second compound. The formation of this perovskite structure 201 forms the first layer 104. At this time, as the first layer 104 is formed, the second-layer inorganic transition metal 205 is segregated on the surface of the first layer 104 to form the second layer 105, and a one-to-one layer arrangement is formed between the perovskite structure 201 and the second-layer inorganic transition metal 205. The second layer 105 is preferably a monoatomic layer.

[0046] The heating temperature is not particularly limited as long as the perovskite structure 201 is formed and the second-layer inorganic transition metal 205 can be segregated on the surface of the first layer 104. The heating temperature is, for example, 200°C to 300°C. The heating time is not particularly limited as long as the perovskite structure 201 is formed and the second-layer inorganic transition metal 205 can be segregated on the surface of the first layer 104. The heating time is preferably, for example, 5 minutes or more. More preferably, it is, for example, 5 minutes or more and 60 minutes or less. Even more preferably, it is, for example, 20 minutes or more and 30 minutes or less.

[0047] Next, as shown in FIG. 2( e), a third layer 106 composed of a plurality of particles, aggregates thereof, or a thin film containing organic ligands 206 as a main component is formed on the second layer 105. The third layer 106 is preferably in the form of a monomolecular thin film. At this time, the organic ligands 206 are coordinated to the second-layer inorganic transition metal 205 on the second surface 105 b, which is the surface opposite the surface 105 a that contacts the first layer 104 of the second layer 105, to form an organometallic complex layer 108 (third step). The method for coordinating the organic ligands 206 to the second-layer inorganic transition metal 205 is not particularly limited. For example, a solution containing the organic ligands 206 is applied to the second layer 105 (application step) and held for a certain period of time (e.g., 30 seconds). The organometallic complex layer 108 may be formed by drying after holding. It is preferable to remove the organic ligands 206 that do not form the organometallic complex 208. There is no particular limitation on the method for removing the organic ligands 206. For example, the organic ligands 206 that do not form the organometallic complexes 208 can be removed by washing the substrate 110 with an organic solvent or the like.

[0048] 2( f), the positive electrode layer 101 is formed on the third layer 106, more specifically, on the layer made of organic ligands, thereby obtaining the photoelectric conversion element 100 of this embodiment. The method for forming the positive electrode layer 101 is not particularly limited. The positive electrode layer 101 may be formed by vacuum deposition or by applying a conductive paste, for example.

[0049] 3A to 3D are diagrams illustrating the operating principle (action) of the photoelectric conversion element 100 according to this embodiment. They respectively show the energy band structures of each layer before light irradiation, immediately after light irradiation, and after a predetermined time has elapsed since light irradiation.

[0050] In the absence of light irradiation, the energy level of the conduction band of the organometallic complex layer 108 is higher on the positive electrode layer 101 side than the Fermi level of the positive electrode layer 101, and as shown in FIG. 3( a), current flowing from the positive electrode layer 101 to the negative electrode layer 102 is blocked.

[0051] When light is irradiated onto the photoelectric conversion element 100, the perovskite structure constituting the first layer 104 absorbs the light and generates electrons and holes, and the electrons move to the conduction band and the holes move to the valence band as shown in FIG. 3(b).

[0052] At this time, the energy level E of the conduction band of the first layer 104 ｃ２ , the LUMO energy level E of the conduction band of the organometallic complex layer 108 ｃ３ But, E ｃ３ >E ｃ２ 3C, electrons generated in the first layer 104 and transferred to the conduction band of the same layer are transferred to the conduction band of the organometallic complex layer 108, which is in a lower energy state. ｃ３Ａ represents the LUMO energy level of the conduction band of the second layer 105, and E ｃ３Ｂ represents the energy level of the LUMO of the conduction band of the third layer 106. Here, the energy level E ｃ３ Is E ｃ３Ａ and E ｃ３Ｂ In addition, when the inorganic semiconductor 107 is present between the (transparent) negative electrode layer 102 and the first layer 104, the energy level E ｃ１ , the energy level E of the conduction band of the first layer 104 ｃ２ , the LUMO energy level E of the conduction band of the organometallic complex layer 108 ｃ３ But, E ｃ３ >E ｃ２ >E ｃ１ Therefore, electrons generated in the first layer 104 and transferred to the conduction band of the same layer are transferred to the conduction band of the organometallic complex layer 108, which is in a lower energy state, and then transferred to the conduction band of the inorganic semiconductor layer 107, which is in an even lower energy state. ｃ３Ａ represents the LUMO energy level of the conduction band of the second layer 105, and E ｃ３Ｂ represents the LUMO energy level of the conduction band of the third layer 106. Here, the LUMO energy level E ｃ３ Is E ｃ３Ａ and E ｃ３Ｂ Let's say.

[0053] On the other hand, the energy level E of the valence band of the first layer 104 ｖ２ , the energy level E of the HOMO of the valence band of the organometallic complex layer 108 ｖ３ But, E ｖ２ >E ｖ３ 3(c), holes generated in the first layer 104 and transferred to the valence band are trapped in the valence band of the first layer 104, which is in a relatively high energy state (low for holes) compared to the organometallic complex layer 108. When the inorganic semiconductor 107 is present between the (transparent) anode layer 102 and the first layer 104, the energy level E ｖ１ , the energy level E of the valence band of the first layer 104 ｖ２ , the energy level E of the HOMO of the valence band of the organometallic complex layer 108 ｖ３ But, E ｖ２ >E ｖ１ , E ｖ２ >E ｖ３ Therefore, holes generated in the first layer 104 and transferred to the valence band are trapped in the valence band of the first layer 104, which is in a relatively high energy state (low for holes) compared to the inorganic semiconductor layer 107 and the organometallic complex layer 108.

[0054] Due to the influence (positive potential) of the trapped holes distributed in a concentrated manner, the potential energy of electrons decreases near the valence band of the first layer 104, lowering the energy level of the conduction band. The energy level of the conduction band decreases significantly closer to the first layer 104 where the holes are trapped. Therefore, the LUMO energy level of the conduction band of the organometallic complex layer 108 is lower on the first layer 104 side, and the positive electrode layer side has a pointed shape. Therefore, for electrons present in the positive electrode layer 101, the energy barrier of the organometallic complex layer 108 becomes thinner, allowing them to tunnel to the negative electrode layer side. In other words, when light is irradiated onto the photoelectric conversion element 100, a large number of electrons on the positive electrode side (electrons in a state where light is not irradiated) that were blocked by the energy barrier of the organometallic complex layer 108 tunnel (transmit) through the thinner energy barrier and flow into the negative electrode side, which is thought to achieve a significant amplification of the current directly generated by the irradiated light.

[0055] The total thickness of the second layer 105 and the third layer 106 is preferably equal to or greater than the thickness of a monolayer of the organometallic complex 208. The second layer 105 and the third layer 106 preferably form a monolayer of the organometallic complex 208. The total thickness of the second layer 105 and the third layer 106 is preferably equal to or less than 10 nm. If the total thickness of the second layer 105 and the third layer 106 is greater than 10 nm, the energy barrier becomes too thick, making it impossible to obtain a sufficient tunneling probability, thereby hindering the amplification of photocurrent in the photoelectric conversion element 100. Furthermore, if the second layer 105 and the third layer 106 are thinner than a monolayer of the organometallic complex 208, a tunneling current will flow even when no light is irradiated and the band is not bent, thereby making the photodetection function of the photoelectric conversion element 100 meaningless.

[0056] (Light detection method) The light detection method using the photoelectric conversion element 100 includes a step of detecting visible light and / or near-infrared light by causing the photoelectric conversion layer 103 to receive visible light and / or near-infrared light, causing a current to flow between the negative electrode layer 102 and the positive electrode layer 101, and measuring this current to detect visible light and / or near-infrared light. The current generated by receiving light can be measured by a known method. The photoelectric conversion element 100 detects the absorbed light by 10 ５ Since it can amplify light by an order of magnitude, even weak light can be easily detected.

[0057] As described above, the photoelectric conversion element 100 according to this embodiment generates a photocurrent when irradiated with light by applying a voltage between the positive electrode layer 101 and the negative electrode layer 102. Furthermore, since the photoelectric conversion element 100 can be driven at a low voltage, output can be achieved with reduced noise, improving the accuracy of photocurrent measurement. Therefore, photoelectric conversion devices such as optical sensors and cameras equipped with the photoelectric conversion element 100 can achieve high amplification even at a driving voltage of, for example, 1 V or less, eliminating the need for a high bias (i.e., a high-voltage driving circuit) and enabling compact products. Furthermore, the photoelectric conversion element 100 has a one-to-one layer arrangement of the perovskite structure 201 and the second-layer inorganic transition metal 205, thereby improving response speed. Furthermore, the photoelectric conversion element 100 according to this embodiment can easily change the shape of its energy levels by adjusting the combination and composition of the materials in each layer, thereby enhancing response sensitivity and selectively absorbing light of a desired wavelength.

[0058] The photoelectric conversion element 100 may include a buffer layer (not shown) between the negative electrode layer 102 and the photoelectric conversion layer 103. The energy level Ecb of the conduction band of the buffer layer is between the energy level of the negative electrode layer 102 and the energy level of the conduction band of the first layer 104 (or the inorganic semiconductor layer 107, if present). The buffer layer may be made of, for example, europium oxide (Eu ２ O ３ ), titanium oxide, tin oxide, etc.

[0059] The effects of the present invention will be made clearer by the following examples. Note that the present invention is not limited to the following examples and can be practiced with appropriate modifications within the scope of the present invention.

[0060] Example 1 A photoelectric conversion element of Example 1 was fabricated under the following conditions.

[0061] First, a member containing antimony-doped tin oxide (ATO) was prepared as a member to be used as a negative electrode layer including a substrate. One surface of this member was spin-coated with 200 μl of a 0.18 M ethanol solution of titanium diisopropylate diacetylacetonate at a rotation speed of 3000 rpm. Next, the mixture spin-coated on the member was heated at 500° C. for 30 minutes, thereby forming a film substantially composed of titanium oxide (TiO ２ ) A buffer layer made of a dense film was formed.

[0062] Next, a 1.25M concentration of lead iodide (PbI ２ ) and a concentration of 0.375 M europium chloride (EuCl ２ 150 μl of a dimethyl sulfoxide (DMSO) solution of 0.07 M cesium chloride (CsCl) was dropped onto the surface of the buffer layer (the surface opposite the anode layer) and spin-coated at 2000 rpm. The spin-coated member was then heated at 150° C. for 30 minutes (Step A). ２ 100 μl of an anhydrous methanol solution of 100 μl of the hydroxybenzoate was dropped onto the spin-coated surface of the member, and spin-coated at 3000 rpm. By performing these steps in order, a two-layer coating layer was formed on the member (Step B). Next, the member with the coating layer was heated at 250° C. for 5 minutes. By repeating this operation (Steps A and B) five times, a first layer of a perovskite structure and a second layer of an inorganic transition metal segregated on the first layer and different from the central metal contained in the perovskite structure were formed.

[0063] Next, 200 μl of isopropyl alcohol (IPA) solution containing 1-phenylethylamine at a concentration of 20 mM was dropped onto the surface of the second layer and held for 30 seconds. After that, spin coating was performed at 3000 rpm. The substrate was then heated at 100°C for 15 minutes to form a third layer primarily composed of 1-phenylethylamine.

[0064] Finally, a positive electrode layer (Ag) was formed on the opposite side of the negative electrode layer, with the stack consisting of the first layer, second layer, and third layer sandwiched therebetween, so as to be in contact with the third layer, thereby obtaining the photoelectric conversion element of Example 1. When the energy levels of the photoelectric conversion element thus obtained were calculated based on the combination of raw materials used, the energy level of the LUMO of the conduction band of the organometallic complex layer of Example 1 was higher than the energy level of the conduction band of the first layer, and the energy level of the valence band of the first layer of Example 1 was higher than the energy level of the HOMO of the valence band of the organometallic complex layer.

[0065] Comparative Example 1 A photoelectric conversion element of Comparative Example 1 was fabricated under the following conditions.

[0066] First, a member containing antimony-doped tin oxide (ATO) was prepared as a member to be used as a negative electrode layer including a substrate. Europium chloride hydrate (EuCl ) was applied to the surface of this member at a concentration of 10 mM. ３ ・6H ２ Ethanol (C ２ H ５ The substrate after spin coating was heated at 120° C. for 10 minutes and then at 450° C. for 1 hour, whereby europium oxide (Eu ２ O ３ ) buffer layer was formed.

[0067] Next, titanium oxide (TiO ２ 120 μL of a mixture containing titanium dioxide paste (PST18NR, manufactured by JGC Catalysts and Chemicals Co., Ltd.) and ethanol in a weight ratio of 1:3.5 was dropped onto the surface of the buffer layer and spin-coated at 6000 rpm. The spin-coated substrate was then heated at 120°C for 10 minutes and then at 450°C for 1 hour to form an inorganic semiconductor layer composed of multiple titanium dioxide particles.

[0068] Next, lead iodide (PbI) was added at a concentration of 0.5M or less. ２100 μl of a mixed solution of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) containing methylammonium was dropped onto the substrate and spin-coated at 5000 rpm. The spin-coated substrate was then heated at 40° C. for 5 minutes, 70° C. for 5 minutes, and 100° C. for 10 minutes, in this order, to form a perovskite structure (CH ３ NH ３ PbI ３ ) as the main component to form a first layer.

[0069] After the first layer was formed, europium chloride (EuCl ３ 100 μL of an isopropyl alcohol (IPA) solution containing europium was dropped onto the substrate, and the substrate was spin-coated at 5000 rpm. The spin-coated substrate was then heated at 100° C. for 15 minutes to form a second layer containing europium as a main component on the first layer.

[0070] After the second layer was formed, 200 μl of an isopropyl alcohol (IPA) solution containing 20 mM terpyridine (2,2′:6′,2″-terpyridine) was dropped onto the surface of the europium-based layer and held for 30 seconds. The resulting solution was then spin-coated at 3000 rpm. The substrate was then heated at 100° C. for 15 minutes to form a third layer primarily composed of terpyridine.

[0071] Finally, a positive electrode layer (Ag) was formed on the opposite side of the negative electrode layer, sandwiching the laminate consisting of the inorganic semiconductor layer, the first layer, the second layer, and the third layer, and in contact with the third layer, thereby obtaining a photoelectric conversion element of Comparative Example 1.

[0072] Example 2 The photoelectric conversion element of Example 2 was fabricated by the following method. A member containing antimony-doped tin oxide (ATO) was prepared as a member for forming a negative electrode layer including a substrate. 120 μl of a mixture containing titanium oxide (TiO2) paste (PST18NR, manufactured by JGC Catalysts and Chemicals Co., Ltd.) and ethanol in a weight ratio of 1:3.5 was spin-coated onto one surface of this member at a rotation speed of 6000 rpm. The mixture spin-coated onto the substrate was then heated at 120°C for 10 minutes and then at 450°C for 1 hour, thereby forming a porous film consisting essentially of a plurality of particles made of titanium oxide.

[0073] Next, lead iodide (PbI) with a concentration of 0.5M was added. ２ 100 μl of a mixed solution of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) containing methylammonium hydroxide and 0.5 M methylammonium was dropped onto the surface of the porous film (the surface opposite to the negative electrode layer) and spin-coated at 5000 rpm. The spin-coated member was then heated at 40° C. for 5 minutes, 70° C. for 5 minutes, and 100° C. for 10 minutes, in that order, to form a perovskite structure (CH ３ NH ３ PbI ３ ) as the main component to form a first layer.

[0074] Next, europium chloride (EuCl) was added at a concentration of 1 mM. ３ 100 μL of an isopropyl alcohol (IPA) solution containing europium was dropped onto the surface of the first layer (the spin-coated surface opposite the negative electrode layer), and spin-coated at 5000 rpm. The spin-coated member was then heated at 100° C. for 15 minutes to form a second layer containing europium as a main component on the first layer, thereby producing the photoelectric conversion element of Example 2.

[0075] Example 3: Europium chloride (EuCl) at a concentration of 5 mM ３ A photoelectric conversion element of Example 3 was produced under the same conditions as in Example 2, except that an isopropyl alcohol (IPA) solution containing methyl methyl acrylate was used.

[0076] Example 4: Europium chloride (EuCl) at a concentration of 7.5 mM ３ A photoelectric conversion element of Example 4 was produced under the same conditions as in Example 2, except that an isopropyl alcohol (IPA) solution containing methyl methyl acrylate was used.

[0077] Example 5: Europium chloride (EuCl) at a concentration of 10 mM ３ A photoelectric conversion element of Example 5 was produced under the same conditions as in Example 2, except that an isopropyl alcohol (IPA) solution containing methyl methyl acrylate was used.

[0078] (Confirmation of Layer Arrangement of Perovskite Structure and Inorganic Transition Metal) The following procedure can be used to confirm that the perovskite structure and the inorganic transition metal different from the central metal contained in the perovskite structure have a one-to-one layer arrangement. By observing the cross section of the photoelectric conversion element 100 with an SEM or measuring the surface potential with a scanning probe microscope, it can be confirmed that the perovskite structure and the inorganic transition metal different from the central metal contained in the perovskite structure exist as a layer having a thickness of several nanometers and having a one-to-one layer arrangement. This can also be confirmed by measuring the presence and bonding state of inorganic transition metal ions present within a few nanometers of the surface using X-ray photoelectron spectroscopy (XPS).

[0079] (Confirmation of Formation of an Organometallic Complex Layer) The formation of an organometallic complex can be confirmed by the following procedure. By observing the cross section of the photoelectric conversion element 100 with a TEM, it can be confirmed that an organometallic complex formed by a coordinate bond between an inorganic transition metal and an organic ligand has formed a layer. In addition, X-ray photoelectron spectroscopy (XPS) or FT-IR can be used to confirm that an organometallic complex has formed a layer.

[0080] (Response Speed) The photoelectric conversion element of Example 1 was irradiated with light at a predetermined timing under the specified light irradiation conditions, and the photocurrent generated in the photoelectric conversion element was measured. The voltage applied between the positive electrode layer and the negative electrode layer was set to −0.5 V. The wavelength, irradiance, and irradiation interval (frequency) of the light irradiated onto the photoelectric conversion element were set to 550 nm, 1 mW / cm, and 1 mW / cm, respectively. ２4 is a graph showing the measurement results corresponding to the photoelectric conversion element of Example 1. In this graph, the horizontal axis represents the elapsed time (s) and the vertical axis represents the photocurrent (A / cm ２ ) is shown.

[0081] From the graph of FIG. 4, it can be seen that the photocurrent in the photoelectric conversion element of Example 1 instantaneously reaches approximately the maximum value (maximum value: approximately 1 A / cm ２ The response speed of the photoelectric conversion element of Example 1 was 14 μs. On the other hand, it was 30 to 70 μs in the case of Comparative Example 1. The gain of the photoelectric conversion element of Example 1 was as high as 1600.

[0082] (Potential Evaluation Measurement) Next, the relationship between the amount of second-layer inorganic transition metal 205 on the surface of the first layer 104 and the hole collection efficiency was investigated. Specifically, a scanning probe microscope (Shimadzu Corporation SPM-9700HT) was used to measure the surface potential of the photoelectric conversion elements of Examples 2 to 4, which were fabricated with different Eu concentrations. The cantilevers used were coated with Pt. The surface potential was measured by light irradiation (irradiation condition 1 mW / cm ２ ) (i.e., a test plot demonstrating the properties and effects of the present invention) and no light irradiation (i.e., a control test plot demonstrating the properties and effects of the present invention).

[0083] Figure 5 shows the results of the surface potential measurement. A potential level bar (lower limit 0.2 V to upper limit 0.5 V) is shown on the right side of the potential image. Note that, for values ​​higher than the center value (0.35 V) of the potential level bar, darker shaded areas indicate higher potential. On the other hand, for values ​​lower than the center value (0.35 V) of the potential level bar, lighter shaded areas indicate lower potential. By comparing the shading in the potential level bar with the shading in the potential image, the detailed distribution and state of the potential level in the potential image can be understood. Without light irradiation, no significant changes were observed in any of the potential images, and the potential generally indicated values ​​lower than the center value of the potential level bar. However, with light irradiation, the darker areas increased throughout the potential image up to 7.5 mM, and the potential consistently indicated values ​​higher than the center value of the potential level bar throughout the potential image. This indicates that Eu covering the surface allows for efficient hole collection. However, when the concentration exceeded 10 mM, the dark areas in the potential image decreased overall, and the average potential level was lower than the average potential level at 7.5 mM. This indicates that as the thickness of the second layer increases, the hole collection efficiency decreases. It is estimated that up to 7.5 mM, the surface of the first layer 104 is covered at the monoatomic layer level. From the above results, it is estimated that the photoelectric conversion element of Example 1 can efficiently collect holes, thereby improving the response speed.

[0084] Incidentally, the surface potential measurement results of each sample observed using a scanning probe microscope (Shimadzu SPM-9700HT) in the above potential evaluation measurement are shown in Figure 5. The surface potential measurement results are obtained by measuring the surface potential of the sample in the above-mentioned "member comprising a first layer of a perovskite structure and a second layer of an inorganic transition metal segregated on the first layer and different from the central metal contained in the perovskite structure" (paragraph no.

[0085] The texture display is a surface potential image superimposed on a surface shape image (i.e., height image) observed using a scanning probe microscope (SPM-9700HT manufactured by Shimadzu Corporation) under the conditions of "with light irradiation" and "without light irradiation" using a sample of perovskite structure 201 (see reference 1) as a measurement target. At an Eu concentration of 7.5 mM, values ​​higher than the center value (0.35 V) of the potential level bar are uniformly displayed throughout the potential image, which indirectly confirms that, at this Eu concentration, the perovskite structure 201 and the inorganic transition metal 205 form a 1:1 layer arrangement at a position circumscribing the octahedral structure of the units constituting the perovskite structure 201. At an Eu concentration of 5 mM, values ​​higher than the center value (0.35 V) of the potential level bar are scattered throughout the potential image, and although there is a lack of uniformity, it can also be confirmed that in partial regions, the perovskite structure 201 and the inorganic transition metal 205 form a one-to-one layer arrangement at positions circumscribing the octahedral structure of the unitary units that make up the perovskite structure 201. On the other hand, at an Eu concentration of 10 mM, the number of values ​​higher than the center value (0.35 V) of the potential level bar decreases, and the average potential level is lower than the average potential level at 7.5 mM, confirming that the perovskite structure 201 and the inorganic transition metal 205 do not properly form a one-to-one layer arrangement at positions circumscribing the octahedral structure of the unitary units that make up the perovskite structure 201. In this way, for a sample in which the amount of inorganic transition metal different from the central metal contained in the perovskite structure has been adjusted, by checking the texture display obtained by superimposing a surface potential image on a surface shape image observed using a scanning probe microscope, it is possible to confirm whether the perovskite structure 201 and the inorganic transition metal 205 properly form a one-to-one layer arrangement.

[0086] The above test results confirmed that the photoelectric conversion element (photoelectric conversion device) of the present invention has an excellent response speed due to the one-to-one layer arrangement of the perovskite structure and the inorganic transition metal different from the central metal contained in the perovskite structure 201. Furthermore, an excellent hole collection effect (i.e., more efficient collection) by the second layer was confirmed.

[0087] The photoelectric conversion element of the present disclosure has high efficiency and high sensitivity to weak optical signals while minimizing the environmental impact, and therefore has high industrial applicability.

[0088] 100 Photoelectric conversion element, 101 Positive electrode layer, 102 Negative electrode layer, 103 Photoelectric conversion layer, 104 First layer, 105 Second layer, 106 Third layer, 107 Inorganic semiconductor layer, 108 Layer of organometallic complex, 201 Perovskite structure, 205 Second layer inorganic transition metal, 206 Organic ligand, 208 Organometallic complex

Claims

1. A photoelectric conversion element comprising, in this order as a photoelectric conversion layer, a first layer composed of a plurality of particles, or aggregates thereof, or a thin film containing a perovskite structure as a main component; a second layer composed of a plurality of particles, or aggregates thereof, or a thin film containing an inorganic transition metal as a main component; and a third layer composed of a plurality of particles, or aggregates thereof, or a thin film containing an organic ligand as a main component, wherein the inorganic transition metal of the second layer is different from the central metal contained in the perovskite structure, and at the interface between the first layer and the second layer, the perovskite structure and the inorganic transition metal of the second layer form a one-to-one layer arrangement, and at the interface between the second layer and the third layer, the inorganic transition metal of the second layer and the organic ligand of the third layer together form an organometallic complex layer.

2. The photoelectric conversion element according to claim 1, characterized in that, in the conduction band, the energy level of the LUMO of the conduction band of the organometallic complex layer is higher than the energy level of the conduction band of the first layer, and, in the valence band, the energy level of the valence band of the first layer is higher than the energy level of the HOMO of the valence band of the organometallic complex layer.

3. The photoelectric conversion element according to claim 1, wherein the second layer is a layer formed by segregating the inorganic transition metal on the surface of the first layer.

4. The photoelectric conversion element according to claim 1, wherein the second layer is a monoatomic layer of the inorganic transition metal.

5. The photoelectric conversion element according to claim 1, wherein the organic ligand is α-methylbenzylamine or terpyridine.

6. The photoelectric conversion element according to claim 5, wherein the central metal contained in the perovskite structure is lead, the inorganic transition metal of the second layer is europium, the inorganic transition metal of the second layer constituting the organometallic complex is europium, and the organic ligand constituting the organometallic complex is α-methylbenzylamine or terpyridine.

7. The perovskite structure has the formula CH ３ NH ３ PbI ３ 7. The photoelectric conversion element according to claim 1, wherein the compound is a compound represented by the formula:

8. A photoelectric conversion device comprising a photoelectric conversion element according to claim 1, wherein a negative electrode layer is laminated on the opposite side of the second layer with the first layer sandwiched therebetween, and a positive electrode layer is laminated on the opposite side of the second layer with the third layer sandwiched therebetween.

9. A method for detecting light, comprising the steps of: causing the photoelectric conversion layer to receive visible light and / or near-infrared light, thereby causing a current to flow between the negative electrode layer and the positive electrode layer; and measuring the current, thereby detecting the visible light and / or near-infrared light, in the photoelectric conversion device described in claim 8.

10. A method for manufacturing a photoelectric conversion element, comprising: a first step of coating a surface of a substrate with a mixture containing raw materials for a perovskite structure and an inorganic transition metal contained in the raw materials for the perovskite structure and different from the central metal contained in the perovskite structure; a second step of forming, after the first step, a first layer composed of a plurality of particles containing the perovskite structure as a main component, or aggregates thereof, or a thin film thereof, and a second layer composed of a plurality of particles containing the inorganic transition metal as a main component, or aggregates thereof, or a thin film thereof, by forming a one-to-one layer arrangement between the perovskite structure and the inorganic transition metal; and a third step of forming, after the second step, an organometallic complex layer composed of an organometallic complex by coordinating an organic ligand to the inorganic transition metal on a second surface of the second layer, which is the surface opposite to the surface in contact with the first surface.

11. A method for manufacturing a photoelectric conversion element according to claim 10, wherein, in the conduction band, the energy level of the LUMO of the conduction band of the organometallic complex layer is higher than the energy level of the conduction band of the first layer, and, in the valence band, the energy level of the valence band of the first layer is higher than the energy level of the HOMO of the valence band of the organometallic complex layer.

12. The method for producing a photoelectric conversion element according to claim 10, wherein in the second step, the second layer is formed by segregating the inorganic transition metal on the surface of the first layer.

13. The method for producing a photoelectric conversion element according to claim 10, wherein the second layer is a monoatomic layer of the inorganic transition metal.

14. A method for manufacturing a photoelectric conversion element, comprising: a mixing step of mixing raw materials for a perovskite structure with an inorganic transition metal contained in the raw materials for the perovskite structure and different from the central metal contained in the perovskite structure to obtain a mixture; a coating step of coating a surface of a base material with the mixture to form a coating layer; a heating step of heating the coating layer after the coating step to form a first layer composed of a plurality of particles, or aggregates thereof, or a thin film containing the perovskite structure as a main component, and a second layer composed of a plurality of particles, or aggregates thereof, or a thin film containing the inorganic transition metal as a main component; and a step of applying a solution containing an organic ligand to a surface of the second layer opposite to the surface in contact with the first layer after the heating step.