Photoelectric conversion element and method for producing same

Abstract

The present invention provides: a photoelectric conversion element that uses a reverse-structure-type porous structure which has high reliability and high light utilization efficiency during electricity generation; and a method for producing the same. A method for producing a photoelectric conversion element according to the present disclosure comprises: a laminate formation step for forming a laminate A that has a first conductive layer 1, a porous hole transport layer 4, a porous electron transport layer 6, and a second conductive layer 8 in this order; a solution dripping step for dripping, from the second conductive layer 8 side of the laminate A, precursor solution B that can constitute a perovskite compound and causing the precursor solution B to permeate the laminate A, thereby obtaining a laminate A filled with the precursor solution B; and a heating step for heating the laminate A that has been subjected to the solution dripping step. The precursor solution B does not contain an additive which increases affinity to the porous electron transport layer 6 but does contain a solvent that has higher ability than γ-butyrolactone to permeate the porous electron transport layer 6.

Description

Photoelectric conversion element and its manufacturing method

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

[0002] Photoelectric conversion elements are used in various optical sensors, copiers, solar cells, etc. In particular, solar cells are becoming increasingly popular as a representative example of renewable energy utilization. Silicon-based solar cells, CIGS-based solar cells, CdTe-based solar cells, etc. are becoming increasingly popular.

[0003] Meanwhile, research is being conducted into using organic materials as photoelectric conversion materials instead of the inorganic materials typically used in solar cells, and the development of organic thin-film solar cells and dye-sensitized solar cells is also progressing. These solar cells can be manufactured using a coating process without using a vacuum process, which has the potential to significantly reduce manufacturing costs, and they are therefore expected to be next-generation solar cells. However, organic thin-film solar cells and dye-sensitized solar cells currently have insufficient photoelectric conversion efficiency and poor durability compared to solar cells using inorganic materials.

[0004] In recent years, perovskite solar cells, which use perovskite compounds as photoelectric conversion materials, have attracted attention because they have been able to achieve photoelectric conversion efficiencies comparable to those of silicon-based solar cells. Among photoelectric conversion elements using perovskite compounds, photoelectric conversion elements with porous structures are known, and one such structure is known as a forward structure (forward type).

[0005] A normal-structure photoelectric conversion element generally has a structure in which a hole-blocking layer, a porous electron transport layer, a porous spacer layer (porous insulator layer), and a hole-collecting layer serving as a second electrode (a counter electrode to the first electrode) are stacked in this order on a substrate having a first electrode. In manufacturing a normal-structure photoelectric conversion element, a method of filling a photoelectric conversion element stack (a stack before being filled with a perovskite compound) with a perovskite compound is known, as disclosed in Patent Document 1, in which a precursor solution capable of forming a perovskite compound is dripped from the second electrode side (hole-collecting layer side) of the stack and allowed to penetrate.

[0006] Special Publication No. 2016-523453

[0007] 2 is a cross-sectional view showing, as a comparative example, a solution dropping step for dropping a precursor solution capable of forming a perovskite compound (hereinafter also referred to as "perovskite precursor solution") into a stack of a normal-structured photoelectric conversion element. The normal-structured photoelectric conversion element stack A1 shown in FIG. 2 includes a substrate 101 having a first electrode 102, a hole-blocking layer 103, a porous electron transport layer 104, a porous spacer layer (porous insulator layer) 105, and a hole-collection layer 108 as a second electrode, stacked in this order. When a perovskite precursor solution B' is dropped into this stack A1 from the hole-collection layer 108 side, the perovskite precursor solution B' penetrates and fills the pores of the porous electron transport layer 104 and the porous spacer layer 105 with the perovskite precursor solution B', forming a solution-filled portion 107. After being filled with the perovskite precursor solution B', the layered body A1 is heated and sintered, whereby a perovskite compound is formed in the solution-filled portion 107, and a light-absorbing portion is formed.

[0008] In order to allow the perovskite precursor solution B' to penetrate all the way to the end of the porous electron transport layer 104 on the first electrode 102 side, it is preferable to add an additive to the perovskite precursor solution B', such as 5-aminovaleric acid hydroiodide (5-AVAI), which increases the affinity with the porous electron transport layer 104. By using this additive, the perovskite precursor solution B' can be filled all the way to the end of the porous electron transport layer 104 on the first electrode 102 side due to the interaction between the metal oxide constituting the porous electron transport layer 104 and the additive.

[0009] Photoelectric conversion elements using general perovskite compounds (i.e., those without a porous structure) can be classified into forward structure types (forward type) and inverted structure types (inverted type). Inverted structure photoelectric conversion elements, which do not use a porous structure and have a structure in which the electron and hole extraction directions are reversed, have the advantage of having less hysteresis and higher reliability than forward structure types. However, inverted structure photoelectric conversion elements using perovskite compounds with a porous structure cannot achieve the desired performance, such as reliability, which poses a major challenge.

[0010] Fig. 3 is a cross-sectional view schematically illustrating the state in which the dropping method of Fig. 2 was attempted on a photoelectric conversion element stack using an inverted porous structure. The photoelectric conversion element stack A2 using the inverted porous structure shown in Fig. 3 has a structure in which a dense hole transport layer 203, a porous hole transport layer 204, a porous spacer layer (porous insulator layer) 205, a porous electron transport layer 206, and a second electrode 208 (a counter electrode to the first electrode) are stacked in this order on a substrate 201 having a first electrode 202. By configuring a perovskite compound in the pores of the porous hole transport layer 204, the porous spacer layer 205, and the porous electron transport layer 206, a light absorbing portion can be formed. However, when perovskite precursor solution B' is dropped onto this laminate A2 to form a light absorbing section, the perovskite precursor solution B' remains in the porous electron transport layer 206, and the solution-filled section 207 is unevenly distributed on the porous electron transport layer 206 side. As a result, the perovskite precursor solution B' cannot be filled evenly up to the end of the porous hole transport layer 204 on the first electrode 202 side, which poses a problem of deterioration in light utilization efficiency and reliability during power generation.

[0011] The contents of the present disclosure have been discovered in consideration of the above-mentioned circumstances regarding inverted structure photoelectric conversion elements containing perovskite compounds, and a primary object of the present disclosure is to provide a photoelectric conversion element using an inverted porous structure that has high light utilization efficiency and reliability during power generation, and a method for manufacturing the same.

[0012] In order to solve the above problems, the present disclosure provides a method for manufacturing a photoelectric conversion element comprising a perovskite compound, the method comprising: a laminate-forming step of forming a laminate having a first conductive layer, a porous hole transport layer, a porous electron transport layer, and a second conductive layer in this order; a solution-dropping step of dripping a precursor solution capable of forming a perovskite compound from the second conductive layer side of the laminate and allowing it to penetrate, thereby obtaining a filled laminate filled with the precursor solution; and a heating step of heating the filled laminate, wherein the precursor solution does not contain an additive that increases affinity with the porous electron transport layer, and the precursor solution contains a solvent that has higher permeability to the porous electron transport layer than γ-butyrolactone.

[0013] In the method for producing a photoelectric conversion element described above, it is preferable that the porous electron transport layer contains a metal oxide, and the additives not contained in the precursor solution are an organic onium salt containing a carboxylic acid and a silane coupling agent.

[0014] In the above-described method for producing a photoelectric conversion element, the solvent is preferably at least one selected from the group consisting of N,N-dimethylformamide, dimethyl sulfoxide, N-methylformamide, and γ-valerolactone.

[0015] In order to solve the above problems, the photoelectric conversion element of the present disclosure has a first conductive layer, a porous layer, and a second conductive layer in this order, a light absorbing layer having a light absorbing portion provided in the pores of the porous layer, the porous layer having a porous hole transport layer on the first conductive layer side of the light absorbing portion, or a porous electron transport layer on the second conductive layer side of the light absorbing portion, and the light absorbing portion does not contain an organic onium salt containing a carboxylic acid or a silane coupling agent.

[0016] In the above photoelectric conversion element, the light absorbing portion preferably contains a perovskite compound.

[0017] In addition, in the above-mentioned photoelectric conversion element, it is preferable that a porous spacer layer is provided between the porous hole transport layer and the second conductive layer, or between the porous electron transport layer and the first conductive layer.

[0018] In the photoelectric conversion element, it is preferable that a dense hole transport layer is provided between the first conductive layer and the porous hole transport layer.

[0019] The photoelectric conversion element and the manufacturing method thereof according to the present disclosure have excellent effects such as improving the light utilization efficiency and reliability during power generation.

[0020] 1 is a cross-sectional view schematically illustrating a solution dropping step of dropping a perovskite precursor solution into a stack of a photoelectric conversion element according to an embodiment of the present disclosure. 2 is a cross-sectional view schematically illustrating a solution dropping step of dropping a perovskite precursor solution into a stack of a normal structure photoelectric conversion element as a comparative example. 3 is a cross-sectional view schematically illustrating an example of an attempt to drop the perovskite precursor solution of FIG. 2 into a stack of a reverse structure photoelectric conversion element.

[0021] The method for manufacturing a photoelectric conversion element according to the present disclosure includes a laminate-forming step, a solution-dropping step, and a heating step. The laminate formed in the laminate-forming step includes a first electrode, a porous layer, and a second electrode, in this order. The porous layer includes, from the first electrode side, a porous hole transport layer and a porous electron transport layer, in this order. The porous layer does not necessarily have to include both a porous hole transport layer and a porous electron transport layer; it may include at least one of a porous hole transport layer or a porous electron transport layer. The porous layer may also include a porous spacer layer located between the porous hole transport layer and the porous electron transport layer. The phrase "a position between the porous hole transport layer and the porous electron transport layer" refers to a position where the first electrode, porous spacer layer, and porous electron transport layer are located in this order when the porous hole transport layer is not present. On the other hand, when the porous electron transport layer is not present, the phrase "a position where the porous hole transport layer, porous spacer layer, and second electrode are located in this order (hereinafter, the term "corresponding position" has the same meaning). In the solution dropping step, a precursor solution capable of forming a perovskite compound (perovskite precursor solution) is dropped onto the laminate to penetrate the laminate, thereby obtaining a laminate filled with the perovskite precursor solution (hereinafter referred to as a filled laminate). In the heating step, the filled laminate is heated to obtain a photoelectric conversion element as a sintered product.

[0022] Hereinafter, embodiments of a photoelectric conversion element and a manufacturing method thereof according to the present disclosure will be described with reference to the drawings.

[0023] 1 is a cross-sectional view schematically illustrating a solution dropping step in which a perovskite precursor solution is dropped into a laminate of a photoelectric conversion element according to an embodiment of the present disclosure. As shown in FIG. 1, a laminate A includes a first conductive layer 2, a porous layer (porous hole transport layer 4 or porous electron transport layer 6), and a second conductive layer 8, which are arranged in this order on a substrate 1. A dense hole transport layer 3 may be provided between the first conductive layer 2 and the porous layer, and a porous spacer layer 5 may be provided at a position corresponding to the position between the porous hole transport layer 4 and the porous electron transport layer 6.

[0024] Porous may also be referred to as porous or mesoporous, and may be the same as or contain these. In the present disclosure, porous means something that can contain a light-absorbing portion (for example, a perovskite compound) in its voids (which can be variously expressed as gaps, holes, or holes). In the present disclosure, unless otherwise contradictory, "voids of a certain component" means "a region where a certain component is not present in a region where a certain component is generally distributed in a dispersed or continuous manner." In addition, porous is not limited to something that can contain a perovskite compound in the voids, but may also be something that can contain a material other than a perovskite compound that has photoelectric conversion function in the voids.

[0025] The dense material is also called a compact or compact substance, and may be the same as or include these terms. A dense material means a material in which, upon cross-sectional observation, no light-absorbing portion (perovskite compound in this embodiment, hereinafter referred to as perovskite compound) is present on one side (the lower side, as an example) of the dense material in the thickness direction. In other words, even if a perovskite compound is present on the upper side of the dense material, it is possible to ensure that it does not penetrate to the lower side of the dense material. Furthermore, a dense material preferably means a material with extremely small voids. Preferably, a dense material means a material in which the maximum void width is less than 5 nm. More preferably, a dense material means a material in which the perovskite compound cannot be contained in the voids or a material in which the perovskite compound does not exist continuously throughout the thickness of the dense material. In other words, a dense material is sufficient if, upon observation using SEM or EDX, it is clear that there are no portions in which the perovskite compound exists throughout the layer thickness. In the present disclosure, unless otherwise stated, SEM observation may be performed on a 400 nm wide cross-sectional SEM (or EDX) image and confirmed. For example, if a 400 nm wide cross-sectional SEM or EDX image shows no portion where the perovskite compound is present throughout the layer thickness, the layer can be said to be dense.

[0026] A porous layer has many pores that are interconnected, allowing a liquid to penetrate the layer when dropped. In contrast, a dense layer has few pores, and the pores that do exist are largely independent and disconnected, meaning that a liquid hardly penetrates the layer when dropped. In other words, in the solution dropping step, the perovskite precursor solution B fills the pores of the porous hole transport layer 4, the porous spacer layer 5, and the porous electron transport layer 6, which are the solution filling sections 7 shown in FIG. 1 .

[0027] Examples of methods for forming the dense hole transport layer 3, the porous hole transport layer 4, the porous spacer layer 5, the porous electron transport layer 6, and the second conductive layer 8 in the laminate A include coating and film formation methods using known methods such as screen printing, spin coating, and bar coating.

[0028] In the following, first, the laminate A formed in the laminate formation step will be described for each component, and then the perovskite precursor solution B used in the solution dropping step will be described.

[0029] 1. Laminate Formed in the Laminate Forming Step <Base> The base 1 is the base of the photoelectric conversion element 10 and may be the same as or include the substrate or base material. It may be hard and highly rigid, or it may be flexible and have low rigidity. The base 1 may have, for example, a flat, sheet, or cylindrical shape. When a photoelectric conversion element is used in which light is irradiated onto the surface on the base 1 side, it is preferable that the base 1 be light-transmitting. In this case, examples of the material for the base 1 include transparent materials such as glass and heat-resistant resins. Examples of glass include soda-lime glass and alkali-free glass. Examples of heat-resistant resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyetherimide (PEI), polytetrafluoroethylene (PTFE), polyamideimide (PAI), and polyethylene naphthalate (PEN). In the case of a photoelectric conversion element in which light is irradiated from a surface other than the surface on the side of the substrate 1, the substrate 1 may be opaque.

[0030] <First Conductive Layer (First Electrode)> The first conductive layer 2 serving as the first electrode is a member having electrical conductivity. The first conductive layer 2 is disposed on or above the substrate 1, and corresponds to the positive electrode of the photoelectric conversion element according to the embodiment of the present disclosure. Examples of a method for forming the first conductive layer 2 include known film formation methods such as sputtering film formation and chemical vapor deposition (CVD) method.

[0031] Examples of materials that can be used to form the first conductive layer 2 include conductive transparent materials such as fluorine-doped tin oxide (FTO), CuI, indium tin oxide (ITO), SnO2, aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), gallium-doped zinc oxide (GZO), and antimony-doped tin oxide (ATO); and conductive transparent polymers.

[0032] The thickness of the first conductive layer 2 is not particularly limited as long as it can exhibit the desired properties (for example, hole transportability and transparency).

[0033] <Hole Transport Layer> The hole transport layer is a layer that transports holes generated in the light absorbing section to the first conductive layer 2, which is the positive electrode. The hole transport layer preferably also functions as an electron blocking layer that suppresses the movement of electrons generated in the light absorbing section to the first conductive layer 2. Note that, as long as the photoelectric conversion element has a photoelectric conversion function, it is self-evident that the hole transport layer located on the hole transport side (or the positive electrode side, similarly in the present disclosure) of the light absorbing section or on the hole transport side of the light absorbing layer has the function of transporting holes, and there is no need to confirm the ability to transport holes, which is difficult to confirm in practice. In other words, as long as the photoelectric conversion element has a photoelectric conversion function, a layer located on the hole transport side of the light absorbing section or on the hole transport side of the light absorbing layer and made of an appropriate material is called a hole transport layer.

[0034] The hole transport layer is preferably composed of an inorganic material having, for example, a band gap of 2 eV or more and an absolute value of the ionization potential smaller than 5.3 eV (i.e., a shallow VBM). The conduction band minimum is referred to as CBM, and the valence band maximum is referred to as VBM. Regarding CBM and VBM, "deep" means "the corresponding electron affinity or ionization energy is large or far from the vacuum level," while "shallow" means "the corresponding electron affinity or ionization energy is small or close to the vacuum level." Furthermore, the absolute value of the difference between the vacuum level and the conduction band minimum can be rephrased as (the absolute value of) the electron affinity, and the absolute value of the difference between the vacuum level and the valence band maximum can be rephrased as (the absolute value of) the ionization potential.

[0035] The hole transport layer is mainly composed of a hole transport material. Examples of the hole transport material include metal oxides (P-type metal oxides) such as molybdenum oxide, vanadium oxide, tungsten oxide, nickel oxide, copper oxide, and tin oxide; metal sulfides (P-type metal sulfides) such as molybdenum sulfide, tungsten sulfide, copper sulfide, and tin sulfide; copper compounds such as fluoro-group-containing phosphonic acid, carbonyl-group-containing phosphonic acid, CuSCN, and CuI; and carbon-containing materials such as optionally surface-modified carbon nanotubes and graphene. Examples of components contained in the hole transport layer other than the hole transport material include an organic binder resin and a plasticizer.

[0036] The hole transport layer preferably contains 70% by mass or more, and more preferably 85% by mass to 100% by mass of the hole transport material. The hole transport layer may be composed of only the hole transport material without containing an organic binder resin, a plasticizer, or the like.

[0037] The hole transport layer may have a structure in which a plurality of hole transport material particles are bound by an organic binder resin, or a structure in which a plurality of hole transport material particles are molded or sintered, for example.

[0038] The hole transport layer may include a dense hole transport layer 3 and a porous hole transport layer 4. The dense hole transport layer 3 is disposed on the first conductive layer 2, and the porous hole transport layer 4 is disposed on the dense hole transport layer 3. Alternatively, the dense hole transport layer 3 may be omitted.

[0039] 1 , the dense hole transport layer 3 is a hole transport layer with a relatively small porosity, and the porous hole transport layer 4 is a hole transport layer with a larger porosity than the dense hole transport layer 3. For example, the dense hole transport layer 3 has a porosity of 35% or less relative to the layer area in cross-sectional observation, and the porous hole transport layer 4 has a porosity of more than 35% relative to the layer area in cross-sectional observation.

[0040] When the perovskite precursor solution B is dropped onto the laminate A in the solution dropping step, the perovskite precursor solution B penetrates into the porous hole transport layer 4, but hardly penetrates into the dense hole transport layer 3. Therefore, by providing the dense hole transport layer 3, contact between the light absorbing part (solution filled part 7 in FIG. 1 ) and the first conductive layer 2 can be suppressed.

[0041] In the solution dropping step, the perovskite precursor solution B is filled into the pores of the porous hole transport layer 4. Next, in the heating step, the laminate A after being filled with the perovskite precursor solution B is heated to dry the perovskite precursor solution B, whereby a perovskite compound is formed in the pores and light absorbing portions are formed. The porous hole transport layer 4 is preferably made of a mesoporous material, in other words, is preferably a mesoporous hole transport layer.

[0042] The thickness of the dense hole transport layer 3 is preferably 5 nm or more and 200 nm or less, and the thickness of the porous hole transport layer 4 is preferably 100 nm or more and 500 nm or less.

[0043] <Porous Spacer Layer> As shown in FIG. 1 , a porous spacer layer 5 may be provided between the porous hole transport layer 4 and the porous electron transport layer 6. The provision of the porous spacer layer 5 prevents contact between the porous hole transport layer 4 and the porous electron transport layer 6, thereby suppressing leakage current. Adding the porous spacer layer increases the distance between the first conductive layer (including the hole transport layer, if present) and the second conductive layer (including the electron transport layer, if present), thereby suppressing physical contact between the materials on both sides and suppressing recombination of electrons and holes generated in the light-absorbing portion. In other words, adding the porous spacer layer can improve the performance of the photoelectric conversion element and contribute to achieving commercialized performance. In other words, the porous spacer layer is present between the first conductive layer (including the hole transport layer, if present) and the second conductive layer (including the electron transport layer, if present), contributing to increasing the distance between the two sides, resulting in a commercialized photoelectric conversion element. It is sufficient for the porous spacer layer to be present between the first conductive layer (including the hole transport layer, if present) and the second conductive layer (including the electron transport layer, if present) and contributes to increasing the distance between the two sides, resulting in a commercialized photoelectric conversion element. For example, it is not necessary to confirm physical properties such as insulation performance, which are difficult to measure.

[0044] The porous spacer layer 5 is mainly composed of an insulating material or a high-resistance semiconductor material. Examples of insulating materials or high-resistance semiconductor materials include metal oxides such as titanium oxide, zirconium dioxide, and aluminum oxide, and oxides such as silicon dioxide. Components contained in the porous spacer layer other than the insulating material and high-resistance semiconductor material include an organic binder resin and a plasticizer.

[0045] The porous spacer layer 5 preferably contains 70% by mass or more, and more preferably 85% by mass to 100% by mass, of an insulating material or a high-resistance semiconductor material. The hole transport layer may be composed of only an insulating material or a high-resistance semiconductor material without containing an organic binder resin, a plasticizer, or the like.

[0046] Examples of the structure of the porous spacer layer 5 include a structure in which multiple insulating material particles or high-resistance semiconductor material particles are bonded together with an organic binder resin, and a structure in which multiple insulating material particles or high-resistance semiconductor material particles are molded or sintered.

[0047] In the solution dropping step, the perovskite precursor solution B is filled into the pores of the porous spacer layer 5. Next, in the heating step, the laminate A after being filled with the perovskite precursor solution B is heated to dry the perovskite precursor solution B, whereby a perovskite compound is formed in the pores and light absorbing portions are formed. The porous spacer layer 5 is preferably made of a mesoporous material, in other words, is preferably a mesoporous spacer layer.

[0048] The thickness of the porous spacer layer 5 is preferably 500 nm or more and 3000 nm or less, and more preferably 1000 nm or more and 2000 nm or less.

[0049] <Electron transport layer> The electron transport layer is a layer having a function of transporting electrons generated in the light absorbing portion. Note that, as long as the photoelectric conversion element has a photoelectric conversion function, it is self-evident that the electron transport layer located on the electron transport side (or on the negative electrode side, similarly in the present disclosure) from the light absorbing portion or on the electron transport side of the light absorbing layer has a function of transporting electrons, and there is no need to confirm the electron transport function, which is difficult to actually confirm. In other words, as long as the photoelectric conversion element has a photoelectric conversion function, a layer located on the electron transport side from the light absorbing portion or on the electron transport side of the light absorbing layer and made of an appropriate material is called an electron transport layer.

[0050] <Porous Electron Transport Layer> The porous electron transport layer 6 is a layer that transports electrons generated in the light absorbing portion to the second conductive layer 8, which is the negative electrode. The porous electron transport layer 6 preferably also functions as a hole blocking layer that suppresses the movement of holes generated in the light absorbing portion to the second conductive layer 8.

[0051] The porous electron transport layer 6 is mainly composed of an electron transport material, such as metal oxides (N-type metal oxides) such as titanium oxide, zinc oxide, indium oxide, tin oxide, aluminum oxide, and gallium oxide; and metal sulfides (N-type metal sulfides) such as tin sulfide, indium sulfide, and zinc sulfide.

[0052] Among these, it is preferable that the porous electron transport layer 6 contains a metal oxide. When the porous electron transport layer contains a metal oxide, the affinity between an organic onium salt containing a carboxylic acid (e.g., 5-AVAI) and the metal oxide is particularly high, and therefore, even if a perovskite precursor solution containing the organic onium salt is dropped, there is a significant problem that the perovskite precursor solution is captured in the porous electron transport layer, which is the upper layer, and does not reach the porous hole transport layer, which is the lower layer. However, according to the manufacturing method of a photoelectric conversion element disclosed herein, it is possible to cause the perovskite precursor solution to penetrate all the way to the end of the porous hole transport layer on the first electrode side.

[0053] Components contained in the porous electron transport layer 6 other than the electron transport material include an organic binder resin and a plasticizer.

[0054] The porous electron transport layer 6 preferably contains 70% by mass or more, and more preferably 85% by mass to 100% by mass, of the electron transport material. The porous electron transport layer 6 may be composed of only the electron transport material without containing an organic binder resin, a plasticizer, or the like.

[0055] The porous electron transport layer 6 may have a structure in which a plurality of electron transport material particles are bound by an organic binder resin, or a structure in which a plurality of electron transport material particles are molded or sintered.

[0056] In the solution dropping step, the perovskite precursor solution B is filled into the pores of the porous electron transport layer 6. Next, in the heating step, the laminate A after being filled with the perovskite precursor solution B is heated to dry the perovskite precursor solution B, whereby a perovskite compound is formed in the pores and light absorbing portions are formed. The porous electron transport layer 6 is preferably made of a mesoporous material, in other words, is preferably a mesoporous electron transport layer.

[0057] The thickness of the porous electron transport layer 6 is preferably 100 nm or more and 20,000 nm or less, and more preferably 200 nm or more and 1,500 nm or less.

[0058] <Light-Absorbing Portion, Light-Absorbing Layer> The photoelectric conversion element according to the embodiment of the present disclosure has a light-absorbing layer in which a light-absorbing portion is provided in the pores of a porous layer. The light-absorbing portion is a portion capable of absorbing light. For example, the light-absorbing portion includes a perovskite compound. The light-absorbing portion is a portion capable of absorbing light incident on the photoelectric conversion element and generating electrons and holes. The electrons move to the second conductive layer side, and the holes move to the first conductive layer side. The fact that the light-absorbing portion absorbs light and generates electrons and holes is self-evident as long as the photoelectric conversion element has a photoelectric conversion function, and does not require confirmation. As long as a material having a light-absorbing function is included, it can be assumed that the light-absorbing portion absorbs light and generates electrons and holes. It is not necessary to confirm that the light is absorbed and electrons and holes are generated, which is difficult to actually confirm.

[0059] The light-absorbing portion can refer to a portion that is an arbitrary region that absorbs light. If there are other light-absorbing portions in addition to the light-absorbing portion shown, they can be collectively described as a light-absorbing layer. In other words, the light-absorbing portion can refer to a portion that is an arbitrary region in the light-absorbing layer. Furthermore, the light-absorbing layer can refer to a collection of light-absorbing portions that have a thickness (similar to the definition of "layer," which does not need to be constant, for example) and exist discretely or continuously in a region mainly in a certain direction.

[0060] The light absorbing layer may be a member occupying a certain area, but is not limited thereto. It may also be a member occupying a certain thickness, but is not limited thereto. The light absorbing layer may be a layer of porous material in which a light absorbing layer or a light absorbing portion is provided. In other words, the light absorbing layer may be a layer of porous material in which a light absorbing layer or a light absorbing portion is provided in the pores of the porous material. Although the term "light absorbing layer" is used, a more appropriate term would be a light absorbing portion that can be made of the same material as the light absorbing layer. In other words, a more appropriate term would be a layer of porous material in which a light absorbing portion is provided in the pores of the porous material. In this case, the electron transport layer or the hole transport layer, or both the electron transport layer and the hole transport layer, may also be porous materials. In other words, the light absorbing layer may have a portion in which a light absorbing portion is provided in the pores of the porous layer. The light absorbing layer may have a portion in which a light absorbing portion is provided in the pores of an insulator or a porous spacer layer made of a porous material. The light absorbing layer may be provided between the electron transport layer and the hole transport layer, or between the electron transport layer and the porous electrode. In this case, the light absorbing portion may also be provided in the pores of the porous electrode.

[0061] A light-absorbing portion may be provided in the voids of the porous layer. The light-absorbing portion refers to the same component as the light-absorbing layer, but the more specific term "portion" is used to avoid misunderstanding of the component's shape. A "layer" preferably refers to a component having a constant film thickness, but is not limited thereto; it may have portions of different thicknesses, or may be patterned or island-like. However, generally, a "layer" refers to a component having portions primarily arranged in a constant direction, while a "portion" refers to a component having portions arranged in a certain region. That is, a "layer" is preferably (1) a component having a constant film thickness that is continuous in a certain direction, (2) a component having portions that are continuous in a certain direction but with different film thicknesses, or (3) a component having discrete pattern-like or island-like portions, each of which is primarily arranged in a certain direction. A "portion" can refer to a portion that is a certain region of a "layer." Each pattern or island portion of a discretely arranged pattern-like or island-like "layer" can be referred to as a "portion." That is, a light-absorbing layer is provided in the voids of the porous spacer layer, in which discrete light-absorbing portions are arranged one by one in the same direction as the direction in which the porous spacer layer is arranged, which is mainly a fixed direction. Note that, when three-dimensional observation is possible, the pattern or island-like portion does not necessarily have to have multiple discrete portions, but may have a single pattern in which all patterns are connected. Observation is usually possible only in a plane in which an arbitrary cross section is observed, and in such cases, the pattern or island-like portion is often divided into multiple discrete portions. That is, when the porous spacer layer is observed in cross section, the light-absorbing portions, i.e., the perovskite compound in this embodiment, are provided in the voids of the porous spacer layer, and the light-absorbing portions are arranged discretely in roughly the same direction as the porous spacer layer extends, and a certain portion of these light-absorbing portions can be collectively referred to as the light-absorbing layer.

[0062] The light absorbing layer preferably contains a perovskite compound or an organic-inorganic hybrid compound. This compound can generate electrons and holes in the light absorbing layer. The thickness of the light absorbing layer 6 is preferably in the range of about 500 nm to 1000 nm.

[0063] <Second Conductive Layer 8> The second conductive layer 8 as a second electrode is disposed on the porous electron transport layer 6 or on the porous layer, and corresponds to the negative electrode of the photoelectric conversion element according to the embodiment of the present disclosure.

[0064] Examples of materials that can be used to form the second conductive layer 8 include metal electrode materials such as fluorine-doped tin oxide (FTO), gold, silver, titanium, sodium, sodium-potassium alloy, lithium, magnesium, aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / Al2O3 mixture, and Al / LiF mixture; and conductive carbon materials such as graphite, graphene, carbon nanowires, carbon nanofibers, carbon nanotubes, and carbon black. Organic electrode materials may also be used.

[0065] It is even more preferable that the second conductive layer 8 is made of a material having a work function of, for example, 4.3 eV or less. When the second conductive layer 8 is made of a material having a shallow work function (4.3 eV or less), a bending of the band structure that allows a smooth flow of electrons is easily generated at the interface between the electron transport layer and the second conductive layer 8.

[0066] In an embodiment of the present disclosure, since the perovskite precursor solution B is dripped from the second conductive layer 8 side in the solution dripping step, the second conductive layer 8 is preferably porous, and more preferably composed of a mesoporous material. Mesoporous carbon is a suitable mesoporous material. When the second conductive layer is porous, it can be included in the porous layer. This is because, similar to the porous electron transport layer, porous hole transport layer, and porous spacer layer, the perovskite precursor is filled and a perovskite compound is formed in the voids of the porous second conductive layer by the heating step. The voids of the porous second conductive layer may have portions where the perovskite compound is formed and portions where it is not. The second conductive layer 8 may include a porous, electrically conductive carbon material.

[0067] The thickness of the second conductive layer 8 is not particularly limited as long as it can exhibit the desired properties (for example, electron transport properties).

[0068] 2. Perovskite precursor solution used in the solution dropping step In the solution dropping step, the perovskite precursor solution B is dropped from the second conductive layer 8 side of the laminate A and allowed to penetrate, thereby obtaining a laminate A (filled laminate) filled with the perovskite precursor solution B. By this step, the porous hole transport layer 4, the porous spacer layer 5, and the porous electron transport layer 6 are filled with the perovskite precursor solution B.

[0069] <Perovskite Precursor Solution B> The perovskite precursor solution B used in the solution dropping step is a solution containing at least a precursor capable of forming a perovskite compound and a solvent.

[0070] As described above, the perovskite precursor solution used in the prior art contains an "additive that enhances affinity with the porous electron transport layer." In contrast, the perovskite precursor solution B used in the solution dropping step according to the embodiment of the present disclosure does not contain an "additive that enhances affinity with the porous electron transport layer." By not adding this additive, it is possible to alleviate the problem of the perovskite precursor solution remaining in the porous electron transport layer and not being able to evenly fill the edge of the porous hole transport layer on the first electrode side (the dense hole transport layer side).

[0071] However, simply not adding an additive that increases the affinity with the porous electron transport layer makes it impossible to fill the perovskite precursor solution evenly to the edge of the porous hole transport layer on the first electrode side. The present inventors have discovered that by changing the solvent used in the perovskite precursor solution without adding an additive that increases the affinity with the porous electron transport layer to the perovskite precursor solution, it is possible to fill the perovskite precursor solution to the edge of the porous hole transport layer on the first electrode side, thereby realizing an inverted-structure photoelectric conversion element that can improve light utilization efficiency and reliability during power generation.

[0072] That is, in an embodiment of the present disclosure, an "additive that increases the affinity with the porous electron transport layer" is not added to the perovskite precursor solution B, and a solvent having a higher permeability to the porous electron transport layer than γ-butyl lactone is used as the solvent for the perovskite precursor solution B.

[0073] Therefore, the light absorbing portion of the photoelectric conversion element according to the embodiment of the present disclosure does not contain an "additive that enhances affinity with the porous electron transport layer." Note that "additive-free" in the present disclosure means that no peaks derived from additives are observed in a diffraction chart in an X-ray diffraction method that observes the diffraction that occurs when an X-ray is irradiated onto a sample to be measured. In other words, even if a trace amount of additive is contained, as long as no peak derived from the additive is detectable, this is included in the concept of "additive-free" in the present disclosure.

[0074] Specific examples of conventionally used "additives that increase affinity with the porous electron transport layer" include organic onium salts containing carboxylic acid and silane coupling agents. Examples of organic onium salts containing carboxylic acid include 5-aminovaleric acid hydroiodide, 5-aminovaleric acid hydrobromide, 5-aminovaleric acid hydrochloride, and β-alanine hydroiodide.

[0075] When the perovskite precursor solution contains an "organic onium salt containing a carboxylic acid," an interaction occurs between the metal oxide of the porous electron transport layer and the organic onium salt, which is advantageous for the permeability of the perovskite precursor solution in a normal-structure photoelectric conversion element. However, in an inverted-structure photoelectric conversion element, the dropped perovskite precursor solution tends to remain in the porous electron transport layer, which prevents the perovskite precursor solution from filling evenly. Furthermore, when the perovskite precursor solution contains a silane coupling agent, it is thought to bond the perovskite compound and the porous electron transport layer, which is advantageous for the permeability of the perovskite precursor solution in a normal-structure photoelectric conversion element. However, in an inverted-structure photoelectric conversion element, the dropped perovskite precursor solution tends to remain in the porous electron transport layer, which prevents the perovskite precursor solution from filling evenly.

[0076] As for the solvent of the perovskite precursor solution B, examples of solvents having higher permeability to the porous electron transport layer 6 than γ-butyllactone include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylformamide (NMF), and γ-valerolactone (GVL). These solvents may be used alone or in combination of two or more.

[0077] In the heating step, the laminate A after being filled with the perovskite precursor solution B is heated, and a photoelectric conversion element is obtained as a sintered product. The heating step dries the perovskite precursor solution B, and a perovskite compound is formed in the region previously filled with the perovskite precursor solution B, forming a light-absorbing portion. In the light-absorbing portion, the perovskite compound generates electrons and holes upon photoexcitation. The light-absorbing portion may contain a substance other than the perovskite compound. Furthermore, the light-absorbing portion may contain a solvent for the perovskite precursor solution B, but preferably does not contain the solvent (no solvent remains).

[0078] The perovskite compound is composed of a compound represented by the general formula: ABX3 (1). While the composition ratio of each element is preferably 1:1:3, it does not necessarily have to be 1:1:3. The content of each element may vary as appropriate, and each constituent element does not necessarily have to be a single type. As long as the light-absorbing portion has a photoelectric conversion function, the perovskite compound contained in the light-absorbing portion exhibits the photoelectric conversion function. Therefore, even if there is a degree of freedom in the configuration as described in the composition ratio and the type of constituent elements, it is reasonable to consider that the function is exhibited. In general formula (1), A is an organic molecule (including an organic group or an organic cation, as defined in the present disclosure) or an inorganic atom or molecule (including an inorganic group or an inorganic cation, as defined in the present disclosure), or a combination thereof; B is a metal atom or molecule (including a metal cation, as defined in the present disclosure); and X is a halogen atom or molecule or a chalcogen atom or molecule (including a halogen anion or a chalcogen anion, as defined in the present disclosure). In general formula (1), the three Xs may be the same or different from one another. As long as the photoelectric conversion element has a photoelectric conversion function, the perovskite compound contained in the light absorbing portion exhibits the photoelectric conversion function, and this fact should be taken into consideration. That is, if it is confirmed that a compound has A, B, and X, it is reasonable to consider it a perovskite compound exhibiting a photoelectric conversion function. For example, it is sufficient to know that it has organic molecules, metal atoms, and halogen atoms. Furthermore, as long as the photoelectric conversion element has a photoelectric conversion function, it can be confirmed that it is a perovskite compound if elements corresponding to A, B, and X are detected. For example, molecules containing carbon, nitrogen, and hydrogen are suitable as organic molecules, and therefore it is sufficient to detect carbon, nitrogen, hydrogen, metal elements, and halogens or chalcogens. Alternatively, it is sufficient that a compound is a perovskite compound if it has A, B, and X, for example, it is sufficient to know that it has inorganic atoms, metal atoms, and halogen atoms. Furthermore, as long as the photoelectric conversion element has a photoelectric conversion function, it can be confirmed that it is a perovskite compound if elements corresponding to A, B, and X are detected.For example, cesium or rubidium is suitable as the inorganic atom, and therefore, it is sufficient to detect cesium or rubidium, a metal element, and a halogen or chalcogen. Furthermore, since it is a natural consequence that a photoelectric conversion element has a crystalline structure as long as it has a photoelectric conversion function, it is not necessary to confirm that the compound is a perovskite compound. This does not exclude the inclusion of compounds other than perovskite compounds in the light-absorbing portion.

[0079] The light absorbing portion may contain an organic-inorganic hybrid compound. An organic-inorganic hybrid compound refers to a compound containing an inorganic material and an organic material. Organic-inorganic hybrid compounds also include perovskite compounds, and solar cells using perovskite compounds are also called organic-inorganic hybrid solar cells. "Organic" typically refers to a material composed of multiple carbon atoms as constituent elements. Note that graphite, graphene, carbon nanowires, carbon nanofibers, carbon nanotubes, and carbon materials such as carbon and carbon black that function as electrodes are not considered to be organic materials. In other words, organic refers to a material that contains multiple carbon atoms as one of its constituent elements, excluding the above-mentioned carbon materials such as graphite. "Inorganic" refers to a material that is not organic.

[0080] The light-absorbing portion may contain quantum dots. Quantum dots refer to dots with a maximum width of 100 nm or less. The shape of the quantum dots is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, they may have a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof. The quantum dots are typically made of a semiconductor. The semiconductor may be any material capable of absorbing light and may include at least the materials described below. The semiconductor may include, for example, at least one selected from the group consisting of II-VI compounds, III-V compounds, chalcogenides, and perovskite compounds. Note that a II-VI compound refers to a compound containing a II group element and a VI group element, and a III-V compound refers to a compound containing a III group element and a V group element. Furthermore, Group II elements may include Group 2 elements and Group 12 elements, Group III elements may include Group 3 elements and Group 13 elements, Group V elements may include Group 5 elements and Group 15 elements, and Group VI elements may include Group 6 elements and Group 16. Here, the numbering of element groups using Roman numerals is based on the old IUPAC system or the old CAS system, and the numbering of element groups using Arabic numerals is based on the current IUPAC system. The semiconductor includes, for example, at least one selected from the group consisting of MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, GaAs, GaP, InN, InAs, InP, and InSb.

[0081] In general formula (1), examples of the organic molecule represented by A include alkylamine, alkylammonium, and nitrogen-containing heterocyclic compounds. In the perovskite compound, the organic molecule represented by A may be only one type of organic molecule, or may be two or more types of organic molecules.

[0082] Examples of alkylamines include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, and ethylbutylamine.

[0083] The alkylammonium is an ionized product of the alkylamine. Examples of the alkylammonium include methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, dimethylammonium, diethylammonium, dipropylammonium, dibutylammonium, dipentylammonium, dihexylammonium, trimethylammonium, triethylammonium, tripropylammonium, tributylammonium, tripentylammonium, trihexylammonium, ethylmethylammonium, methylpropylammonium, butylmethylammonium, methylpentylammonium, hexylmethylammonium, ethylpropylammonium, and ethylbutylammonium.

[0084] Examples of the nitrogen-containing heterocyclic compound include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, and carbazole. The nitrogen-containing heterocyclic compound may be an ionized compound. As the ionized nitrogen-containing heterocyclic compound, phenethylammonium is preferred.

[0085] In general formula (1), the organic molecule represented by A is preferably methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, or phenethylammonium, more preferably methylamine, ethylamine, propylamine, methylammonium, ethylammonium, or propylammonium, and even more preferably methylammonium.

[0086] In general formula (1), examples of the metal atom represented by B include lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, and europium. In the perovskite compound, the metal atom represented by B may be only one type of metal atom, or may be two or more types of metal atoms. From the viewpoint of improving the light absorption properties and charge generation properties of the perovskite compound, the metal atom represented by B is preferably a lead atom or a tin atom. From the viewpoint of reducing lead, a tin atom is preferred.

[0087] In general formula (1), examples of halogen atoms represented by X include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, and examples of chalcogen atoms include oxygen atoms, sulfur atoms, selenium atoms, and tellurium atoms. In the perovskite compound, the halogen atoms or chalcogen atoms represented by X may be one type or two or more types. As the halogen atom represented by X, an iodine atom is preferred from the viewpoint of enabling the perovskite compound to utilize light in a wide wavelength range. Specifically, of the three Xs, it is preferred that at least one X represents an iodine atom, and it is more preferred that all three Xs represent iodine atoms.

[0088] As the perovskite compound, a compound represented by the general formula "CH3NH3PbX3 (wherein X represents a halogen atom)" is preferred, with CH3NH3PbI3 being more preferred. By using a compound represented by the general formula "CH3NH3PbX3" (particularly CH3NH3PbI3) as the perovskite compound, electrons and holes can be generated more efficiently in the perovskite compound, and as a result, the photoelectric conversion efficiency of the photoelectric conversion element can be further improved.

[0089] A photoelectric conversion layer is a layer that converts light into electricity. It can include a porous layer and a light-absorbing portion, and refers to a layer located between the first conductive layer and the second conductive layer. As long as a photoelectric conversion element has a photoelectric conversion function, it is a natural consequence that the photoelectric conversion layer exists between the first conductive layer and the second conductive layer. Therefore, as long as a photoelectric conversion element has a photoelectric conversion function, the layer located between the first conductive layer and the second conductive layer is the photoelectric conversion layer, and there is no need to confirm the photoelectric conversion function of the layer itself to confirm the presence of the photoelectric conversion layer. The light-absorbing portion is often located between the first conductive layer and the second conductive layer, and in such cases, the photoelectric conversion layer is also located only between the first conductive layer and the second conductive layer. However, if the first conductive layer and the second conductive layer have a special shape, such as porous, the light-absorbing portion may exist in the region including the first conductive layer and the second conductive layer themselves. In such cases, the first conductive layer and the second conductive layer themselves, where the light-absorbing portion exists, can be included in the photoelectric conversion layer. Even in this case, the photoelectric conversion layer is disposed at least between the first conductive layer and the second conductive layer. That is, in any case, the photoelectric conversion element is provided with the first conductive layer, the photoelectric conversion layer, and the second conductive layer in this order, and does not exclude the first conductive layer and the second conductive layer themselves from being included therein, nor does it exclude the photoelectric conversion layer from being present in a portion other than the region between the first conductive layer and the second conductive layer.

[0090] The method for preparing the perovskite precursor solution B that can constitute the perovskite compound (ABX3) is not particularly limited, but it can be prepared, for example, by mixing an AX solution and a BX2 solution.

[0091] In the photoelectric conversion element according to the embodiment of the present disclosure, the abundance ratio of the perovskite compound is preferably 1% or more, and more preferably 5% or more, at the end of the porous hole transport layer 4 on the side of the first conductive layer 2. According to the method for producing a photoelectric conversion element according to the present disclosure, the perovskite precursor solution B does not remain in the porous electron transport layer 6 but penetrates into the porous hole transport layer 4, and therefore a photoelectric conversion element having such an abundance ratio can be realized.

[0092] In the present disclosure, the "abundance rate of perovskite compounds" refers to the proportion of the area of ​​the perovskite-existing region (the region where a substance having the characteristics of a perovskite compound is detected) to the area of ​​the object to be observed, as measured by observing the cross section of the object to be measured with an energy dispersive X-ray spectroscopy (SEM-EDX) at a width of 200 nm.

[0093] In the photoelectric conversion element according to the embodiment of the present disclosure, the abundance rate of the perovskite compound at the end of the porous hole transport layer 4 on the first conductive layer 2 side may be higher than the abundance rate of the perovskite compound at the end of the porous electron transport layer 6 on the second conductive layer 8 side.

[0094] 3. Example A dense NiO layer as the dense hole transport layer 3, a mesoporous NiO layer as the porous hole transport layer 4, a mesoporous ZrO layer as the porous spacer layer 5, a mesoporous TiO layer as the porous electron transport layer 6, and a mesoporous carbon layer as the second conductive layer 8 were laminated in this order by a screen printing method on a transparent conductive substrate (corresponding to the base material 1 and the first conductive layer 2) having fluorine-doped tin oxide (FTO) on a glass substrate, and then fired to obtain a laminate.

[0095] 12 μL of a perovskite precursor solution (1.2 M CHNHPbI solution) using N-methylformamide (NMF) as a solvent was dropped onto the obtained laminate from the mesoporous carbon layer side and allowed to penetrate, thereby obtaining a filled laminate filled with the perovskite precursor solution.

[0096] The filled laminate was heated at 100°C to dry the perovskite precursor solution, yielding a photoelectric conversion element containing the perovskite compound. The obtained photoelectric conversion element contained the perovskite compound evenly throughout the mesoporous NiO layer, even at the edge on the FTO side, and exhibited high light utilization efficiency during power generation.

[0097] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included.

[0098] DESCRIPTION OF SYMBOLS 1 Substrate 2 First conductive layer (first electrode) 3 Dense hole transport layer 4 Porous hole transport layer 5 Porous spacer layer 6 Porous electron transport layer 7 Solution-filled portion (region that will become a light-absorbing portion after sintering) 8 Second conductive layer (second electrode) A Laminate of photoelectric conversion element B Precursor solution capable of forming a perovskite compound

Claims

1. A method for manufacturing a photoelectric conversion element containing a perovskite compound, comprising: a laminate formation step of forming a laminate having a first conductive layer, a porous hole transport layer, a porous electron transport layer, and a second conductive layer in this order; a solution dropping step of dripping a precursor solution capable of forming a perovskite compound from the second conductive layer side of the laminate and allowing it to penetrate, thereby obtaining a filled laminate filled with the precursor solution; and a heating step of heating the filled laminate, wherein the precursor solution does not contain an additive that increases affinity with the porous electron transport layer, and the precursor solution contains a solvent that has a higher permeability to the porous electron transport layer than γ-butyrolactone.

2. A method for producing a photoelectric conversion element according to claim 1, wherein the porous electron transport layer contains a metal oxide, and the additives not contained in the precursor solution are an organic onium salt containing a carboxylic acid and a silane coupling agent.

3. A method for producing a photoelectric conversion element according to claim 1 or 2, wherein the solvent is at least one selected from the group consisting of N,N-dimethylformamide, dimethyl sulfoxide, N-methylformamide and γ-valerolactone.

4. A photoelectric conversion element comprising a first conductive layer, a porous layer and a second conductive layer in this order, a light absorbing layer having a light absorbing portion provided in the pores of the porous layer, the porous layer having a porous hole transport layer on the first conductive layer side of the light absorbing portion, or a porous electron transport layer on the second conductive layer side of the light absorbing portion, the light absorbing portion not containing an organic onium salt containing a carboxylic acid or a silane coupling agent.

5. A photoelectric conversion element according to claim 4, wherein the light absorbing portion contains a perovskite compound.

6. A photoelectric conversion element according to claim 4 or claim 5, characterized in that a porous spacer layer is provided between the porous hole transport layer and the second conductive layer, or between the porous electron transport layer and the first conductive layer.

7. A photoelectric conversion element according to any one of claims 4 to 6, characterized in that a dense hole transport layer is provided between the first conductive layer and the porous hole transport layer.

8. A photoelectric conversion element according to any one of claims 4 to 7, characterized in that the second conductive layer contains a porous carbon material having electrical conductivity.

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