Solar cell and photoelectric conversion element

Abstract

A solar cell (100) includes a first electrode (2), a first electron transport layer (4), a second electron transport layer (3), a photoelectric conversion layer (5), and a second electrode (7). The first electron transport layer (4) includes carbon and a porous electron transport material.

Description

Technical Field

[0001] This disclosure relates to solar cells and photoelectric conversion devices. Background Technology

[0002] In recent years, research and development of organic thin-film solar cells or perovskite solar cells, as new types of solar cells to replace existing silicon-based solar cells, has made progress.

[0003] Perovskite solar cells use perovskite compounds represented by the chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halide anion) as photoelectric conversion materials.

[0004] Non-Patent Document 1 discloses a perovskite solar cell that uses a perovskite compound represented by the chemical formula CH3NH3PbI3 (hereinafter referred to as "MAPbI3") as the photoelectric conversion material for a perovskite solar cell. In the perovskite solar cell disclosed in Non-Patent Document 1, the perovskite compound represented by MAPbI3, TiO2, and Spiro-OMeTAD are used as the photoelectric conversion material, electron transport material, and hole transport material, respectively.

[0005] Non-patent document 2 discloses the use of CH3NH3 + (hereinafter referred to as "MA"), CH(NH2)2 + Perovskite solar cells using a multi-cation perovskite compound (hereinafter referred to as "FA") and Cs as a monovalent cation as photoelectric conversion materials. In the perovskite solar cell disclosed in Non-Patent Document 2, a multi-cation perovskite compound, TiO2, and Spiro-OMeTAD are used as photoelectric conversion materials, electron transport materials, and hole transport materials, respectively.

[0006] Patent Document 1 discloses an organic thin-film solar cell. The organic thin-film solar cell disclosed in Patent Document 1 has a fine, uneven microstructure at the interface between the photoelectric conversion layer and the electrode. Based on this structure, the organic thin-film solar cell disclosed in Patent Document 1 can improve photoelectric energy conversion efficiency.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2014 / 208713

[0010] Non-patent literature

[0011] Non-patent literature 1: Julian Burschka et al., “Sequential deposition as a route to high-performance perovskite-sensitized solar cells”, Nature, vol.499, pp.316-319, 18 July 2013 [DOI:10.1038 / nature12340]

[0012] Non-patent document 2: Taisuke Matsui et al., "Room-Temperature Formation ofHighly Crystalline Multication Perovskites for Efficient, Low-Cost SolarCells", Advanced Materials, Volume29, Issue15, April 18, 2017, 1606258 [DOI:10.1002 / adma. 201606258]

[0013] Non-patent literature 3: Qingfeng Dong et al., Science, 2015, 347, 6225, 967-970 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] The purpose of this disclosure is to provide a solar cell with improved anchoring force of the electron transport layer.

[0016] Methods for solving problems

[0017] This disclosure relates to a solar cell, which comprises:

[0018] First electrode,

[0019] First electron transport layer

[0020] Second electron transport layer

[0021] Photoelectric conversion layer, and

[0022] Second electrode,

[0023] Here, the photoelectric conversion layer is disposed between the first electrode and the second electrode.

[0024] The first electron transport layer is disposed between the photoelectric conversion layer and the first electrode.

[0025] The second electron transport layer is disposed between the first electron transport layer and the first electrode.

[0026] The first electron transport layer comprises carbon and a porous electron transport material.

[0027] Invention Effects

[0028] This disclosure provides a solar cell with improved anchoring force of the electron transport layer. Attached Figure Description

[0029] Figure 1 A cross-sectional view showing the solar cell 100 of the first embodiment.

[0030] Figure 2 A cross-sectional view showing the solar cell 200 of the first embodiment.

[0031] Figure 3A This figure illustrates the protrusion of the concave-convex structure in the solar cell 200 of the first embodiment.

[0032] Figure 3B This figure illustrates the recessed portion of the uneven structure in the solar cell 200 of the first embodiment.

[0033] Figure 3C This diagram illustrates the difference in height and concavity of the uneven structure in the solar cell 200 of the first embodiment.

[0034] Figure 4 A cross-sectional view showing the solar cell 300 of the second embodiment.

[0035] Figure 5 This is a cross-sectional view of the substrate 400 with a photoelectric conversion layer in Example 1.

[0036] Figure 6 The graph represents the carbon distribution obtained by time-of-flight secondary ion mass spectrometry analysis for the first electron transport layer of Example 1.

[0037] Figure 7A A graph showing the results of estimating the relationship between carbon threshold and normalized efficiency in solar cells fabricated on flat substrates or textured substrates with uneven surfaces.

[0038] Figure 7B A graph showing the relationship between firing temperature and carbon threshold.

[0039] Figure 8The graph shows the dependence of the intensity of the C1s bond peak, obtained from the intensity change of the C1s spectrum obtained by X-ray photoelectron spectroscopy, on the UV irradiation time for the first electron transport layer of Example 1.

[0040] Figure 9 This is a graph showing the dependence of film thickness before and after spin-coating solvent on firing temperature after firing the first electron transport layer disposed on a flat substrate.

[0041] Figure 10A A graph showing the dependence of the open-circuit voltage of a solar cell fabricated on a flat substrate on firing temperature after firing the first electron transport layer disposed on the substrate.

[0042] Figure 10B A graph showing the dependence of the short-circuit current density of a solar cell fabricated using a flat substrate on firing temperature after firing the first electron transport layer disposed on the substrate.

[0043] Figure 10C This is a graph showing the dependence of the fill factor of a solar cell fabricated using a flat substrate on firing temperature after firing the first electron transport layer disposed on the substrate.

[0044] Figure 10D A graph showing the dependence of the conversion efficiency of a solar cell made on a flat substrate on firing temperature after firing the first electron transport layer disposed on the substrate.

[0045] Figure 11A To indicate that the estimate is... Figure 10A The graph shows the results of transforming the horizontal axis to the carbon threshold and taking into account the solar cell performance when interlayer short circuits occur in regions with low carbon thresholds.

[0046] Figure 11B To indicate that the estimate is... Figure 10B The graph shows the results of transforming the horizontal axis to the carbon threshold and taking into account the solar cell performance when interlayer short circuits occur in regions with low carbon thresholds.

[0047] Figure 11C To indicate that the estimate is... Figure 10C The graph shows the results of transforming the horizontal axis to the carbon threshold and taking into account the solar cell performance when interlayer short circuits occur in regions with low carbon thresholds. Detailed Implementation

[0048] <Definition of Terminology>

[0049] As used in this specification, the term "perovskite-type compound" refers to a perovskite-type crystalline structure and similar crystalline structures represented by the chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halide anion).

[0050] The term "perovskite solar cell" as used in this specification refers to a solar cell that contains a perovskite compound as a photoelectric conversion material.

[0051] <Insights that form the basis of this public disclosure>

[0052] The following explains the insights that form the basis of this disclosure.

[0053] As disclosed in Non-Patent Document 3, perovskite compounds are characterized by high light absorption coefficients and long diffusion lengths. These properties enable perovskite solar cells to generate electricity efficiently with a thickness of only a few hundred nanometers. Furthermore, perovskite solar cells possess the following characteristics: they use less material compared to existing silicon solar cells; they do not require high temperatures during formation; and they can be formed using coating. Based on these characteristics, perovskite solar cells can also be formed on substrates made of lightweight, flexible materials such as plastics. Therefore, perovskite solar cells can be installed in areas where weight is currently limited. For example, the development of perovskite solar cells can extend to building-integrated solar cells that are combined with existing components, such as building materials. In cases where perovskite solar cells are constructed through combination with building materials, it is necessary, for example, to use a component with a large surface irregularity as a substrate on which the perovskite solar cell is formed.

[0054] Furthermore, to further improve photoelectric conversion efficiency, tandem solar cells, which combine perovskite and silicon solar cells, were explored. Silicon solar cells sometimes have a textured surface to effectively utilize incident light. Therefore, when a silicon solar cell has a textured structure, the perovskite solar cell must be formed on the surface with the textured structure without peeling off.

[0055] If peeling occurs during the coating process of a perovskite solar cell, the substrate will short-circuit through the perovskite solar cell at the peeled site, resulting in reduced power generation efficiency. Consequently, it may not function as a solar cell. The inventors have discovered that during the manufacturing of a perovskite solar cell, when the solvent-loving porous electron transport layer peels off, the capillary force of the photoelectric conversion layer solution may not function in subsequent processes, potentially resulting in portions lacking the photoelectric conversion layer.

[0056] For example, when fabricating tandem solar cells, because the perovskite solar cell film is thinner than the average height of the textured uneven structure, and because the film is formed through coating, the anchoring force on the uneven structure is weak. As a result, the protrusions of the substrate are exposed, and the formation of the perovskite solar cell across the entire surface becomes insufficient. That is, in the protrusions, the perovskite solar cell is damaged, and the substrate penetrates through the perovskite solar cell, short-circuiting with the upper electrode. Consequently, it cannot function as a perovskite solar cell.

[0057] In view of these insights, the inventors have discovered a structure for fabricating perovskite solar cells in which a solvent-friendly porous electron transport layer can be disposed without peeling over the entire area requiring anchoring force through a solution, including surfaces with uneven or three-dimensional structures, until the formation of the perovskite solar cell is complete. The entire surface is covered without defects by the photoelectric conversion layer. Furthermore, it has been found that this structure can improve photoelectric conversion efficiency even when forming solar cells on flat surfaces.

[0058] <Implementation Methods of this Disclosure>

[0059] The following is a reference to the appendix. Figure 1 The embodiments of this disclosure will be described in detail below.

[0060] (First Embodiment)

[0061] Figure 1 A cross-sectional view showing the solar cell 100 of the first embodiment.

[0062] like Figure 1 As shown, the solar cell 100 of the first embodiment includes a substrate 1, a first electrode 2, a second electron transport layer 3, a first electron transport layer 4, a photoelectric conversion layer 5, a hole transport layer 6, and a second electrode 7. Specifically, the substrate 1, the first electrode 2, the second electron transport layer 3, the first electron transport layer 4, the photoelectric conversion layer 5, the hole transport layer 6, and the second electrode 7 are arranged sequentially. The first electron transport layer 4 has a first main surface 4a (i.e., the first main surface facing the photoelectric conversion layer 5) and a second main surface 4b (i.e., the second main surface facing the first electron transport layer 3).

[0063] The first electron transport layer 4 contains carbon and porous electron transport materials.

[0064] In the solar cell 100, the first electron transport layer 4 contains carbon, thus exhibiting high anchoring strength. As a result, during the coating and drying process, the first electron transport layer does not peel off due to uneven solution flow, preventing peeling during the subsequent formation of the photoelectric conversion layer.

[0065] Layers with other functions may also be provided between substrate 1 and first electrode 2, between first electrode 2 and second electron transport layer 3, between photoelectric conversion layer 5 and hole transport layer 6, or between hole transport layer 6 and second electrode.

[0066] Furthermore, examples of the aforementioned "layers with other functions" include layers that have the function of suppressing charge recombination at the interface.

[0067] The first electrode 2 can also have a concave-convex structure.

[0068] Figure 2 A cross-sectional view showing the solar cell 200 of the first embodiment.

[0069] like Figure 2 As shown, the solar cell 200 of the second embodiment includes a substrate 1, a first electrode 2, a second electron transport layer 3, a first electron transport layer 4, a photoelectric conversion layer 5, a hole transport layer 6, and a second electrode 7. Specifically, the substrate 1, the first electrode 2, the second electron transport layer 3, the first electron transport layer 4, the photoelectric conversion layer 5, the hole transport layer 6, and the second electrode 7 are arranged sequentially. The first electron transport layer 4 has a first main surface 4a (i.e., the first main surface facing the photoelectric conversion layer 5) and a second main surface 4b (i.e., the second main surface facing the first electron transport layer 3).

[0070] The first electrode 2 has a first main surface 2a facing the second electron transport layer 3. The first main surface 2a has an uneven structure. The second electron transport layer 3, the first electron transport layer 4, the photoelectric conversion layer 5, the hole transport layer 6, and the second electrode 7, which are disposed on the first main surface 2a of the first electrode 2, have uneven structures reflecting the uneven structure of the first main surface 2a that forms the substrate. Furthermore, in the solar cell 100, the first electrode 2 is disposed on the first main surface 1a of the substrate 1. The first main surface 1a of the substrate 1 has an uneven structure. That is, the uneven structure of the first main surface 2a of the first electrode 2 reflects the uneven structure of the first main surface 1a of the substrate 1 that forms the substrate.

[0071] Here, in this specification, the term "uneven structure" refers to the surface unevenness observed in a cross-sectional image of a scanning transmission electron microscope, where the average height difference between the convex and concave parts exceeds 0.1 μm.

[0072] The “convex” and “concave” parts of the concave-convex structure in this specification are described. Figure 3A This figure illustrates the protrusion of the concave-convex structure in the solar cell 200 of the first embodiment. Figure 3B This figure illustrates the recessed portion of the uneven structure in the solar cell 200 of the first embodiment. Figure 3C This diagram illustrates the height difference of the uneven structure in the solar cell 200 of the first embodiment. The protrusions are as follows: Figure 3A As shown, this refers to the vertex and surrounding portion of the convex shape in a concave-convex structure. The surrounding portion of the vertex, for example, refers to the area above the midpoint between the vertex and the base of the adjacent concave shape. The concave portion is as follows: Figure 3B As shown, this refers to the concave bottom and its surrounding portion of the concave-convex structure. The surrounding portion of the concave bottom, for example, refers to the area below the midpoint between the concave bottom and the vertices of the adjacent convex shape. The height difference of the concave-convex structure is as follows: Figure 3C As shown, the height refers to the distance from the apex of the convex part to the bottom of the concave part of the concave-convex structure. This height can take various values ​​depending on the location (e.g., height difference A, height difference B, etc. in the figure). The difference between the convex and concave structures is represented by the average value of the height difference. Here, the average value of the height difference between the convex and concave parts is obtained as follows: First, using a cross-sectional image from a scanning transmission electron microscope, an arbitrary region with a length of 20 μm is selected within the cross-sectional image. Next, the height differences between all adjacent convex and concave parts are measured for the surface convexity and concaveness of this region. The average value of the height difference is calculated from the obtained measurements. In this way, the average value of the height difference between the convex and concave parts is obtained.

[0073] The average height difference between the convex and concave parts of the first electrode 2 in the solar cell 200 can also be 0.5 μm to 3 μm.

[0074] The following is a reference Figure 2 Each layer is explained in detail.

[0075] (Substrate 1)

[0076] Substrate 1 holds the layers constituting the solar cell 200. For example... Figure 1 As shown, the substrate 1 may also have an uneven structure on the first main surface 1a facing the first electrode 2. The substrate 1 may be formed of a transparent material. Examples of substrate 1 are glass substrates and plastic substrates. The plastic substrate may also be a plastic film. When the first electrode 2 has sufficient strength to maintain each layer, the solar cell 200 may not have a substrate 1.

[0077] (Electrode 1, 2)

[0078] The first electrode 2 is conductive. As described above, the first main surface 2a of the first electrode 2 may also have a concave-convex structure.

[0079] The solar cell 200 has a second electron transport layer 3 and a first electron transport layer 4 between the first electrode 2 and the photoelectric conversion layer 5. Therefore, the first electrode 2 may not have the characteristic of blocking holes moving from the photoelectric conversion layer 5. The first electrode 2 may be made of a material that can form an ohmic contact with the photoelectric conversion layer 5.

[0080] The first electrode 2 may be transparent or opaque. At least one of the first electrode 2 and the second electrode 7 is transparent. For example, light belonging to the region from visible light to near-infrared passes through the first electrode 2.

[0081] The first electrode 2 can, for example, be made of a transparent and conductive material. This material can also be, for example, at least one selected from metal oxides and metal nitrides. Examples of such materials include:

[0082] (i) Titanium oxide doped with at least one of lithium, magnesium, niobium, and fluorine.

[0083] (ii) Doped with gallium oxide selected from at least one of tin and silicon,

[0084] (iii) Doped with gallium nitride selected from at least one of silicon and oxygen,

[0085] (iv) Indium-tin composite oxides,

[0086] (v) Tin oxide doped with at least one of antimony and fluorine,

[0087] (vi) Zinc oxide doped with at least one of boron, aluminum, gallium, and indium, or

[0088] (vii) Their complex.

[0089] The first electrode 2 can also be an electrode made of an opaque material and having a patterned shape that allows light to pass through. Examples of light-transmitting patterns include linear, wavy, lattice-like, or perforated metallic shapes with multiple fine through-holes arranged regularly or irregularly. The first electrode 2 with the above-mentioned patterned shape allows light to pass through the portions of the electrode where no electrode material is present. Examples of opaque materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. The material can also be a conductive carbon material.

[0090] The transmittance of the first electrode 2 can be, for example, 50% or more, or 80% or more. The wavelength of light transmitted through the first electrode 2 depends on the absorption wavelength of the photoelectric conversion layer 5. The first electrode 2 can also have a thickness of, for example, 1 nm to 1000 nm.

[0091] (Second electron transport layer 3)

[0092] The second electron transport layer 3 comprises a semiconductor. The second electron transport layer 3 may also be formed of a semiconductor with a band gap of 3.0 eV or higher. By forming the second electron transport layer 3 with a semiconductor having a band gap of 3.0 eV or higher, visible light and infrared light can pass through to the photoelectric conversion layer 5. Examples of semiconductors include organic or inorganic n-type semiconductors.

[0093] Examples of organic n-type semiconductors include imide compounds, quinone compounds, fullerenes, or fullerene derivatives. Examples of inorganic n-type semiconductors include oxides of metal elements, nitrides of metal elements, or perovskite oxides. Examples of metal oxides include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, and Cr. A more specific example is TiO2. Examples of metal nitrides include GaN. Examples of perovskite oxides include SrTiO3 and CaTiO3.

[0094] Alternatively, the second electron transport layer 3 can also be formed of a material with a band gap greater than 6.0 eV. Examples of materials with a band gap greater than 6.0 eV include:

[0095] (i) Halides of alkali metals or alkaline earth metals such as lithium fluoride or barium fluoride,

[0096] (ii) Oxides of alkaline earth metals such as magnesium oxide, or

[0097] (iii) Silicon dioxide.

[0098] In this case, in order to ensure the electron transport properties of the second electron transport layer 3, the thickness of the second electron transport layer 3 can be, for example, less than 10 nm.

[0099] The second electron transport layer 3 may also comprise multiple layers formed of different materials.

[0100] (Electron transport layer 4)

[0101] The first electron transport layer 4 comprises a porous electron transport material. Hereinafter, the porous electron transport material will be referred to as a porous body. The first electron transport layer 4 may also be composed of a porous body.

[0102] The porous material contains pores. The pores extend from the second principal surface 4b of the first electron transport layer 4, which is in contact with the second electron transport layer 3, to the first principal surface 4a of the first electron transport layer 4, which is in contact with the photoelectric conversion layer 5. In addition, the pores are typically filled with the material constituting the photoelectric conversion layer 5, and electrons can move directly from the photoelectric conversion layer 5 to the second electron transport layer 3.

[0103] Porous bodies are composed, for example, of a series of insulator or semiconductor particles. Examples of insulator particles are alumina particles or silicon oxide particles. Examples of semiconductor particles are inorganic semiconductor particles. Examples of inorganic semiconductors are oxides of metal elements, perovskite oxides of metal elements, sulfides of metal elements, or metal chalcogenides. Examples of oxides of metal elements are oxides of various metal elements such as Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. A specific example of an oxide of a metal element is TiO2. Examples of perovskite oxides of metal elements are SrTiO3 or CaTiO3. Examples of sulfides of metal elements are CdS, ZnS, In2S3, PbS, MO2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides are CdSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0104] The first electron transport layer 4 contains carbon. Carbon only needs to be included as a constituent element of the first electron transport layer 4.

[0105] The carbon contained in the first electron transport layer 4 may, for example, be derived from the carbon of the binder used in forming the porous body. The binder may be, for example, a dispersant such as a surfactant attached to the surface of the particles used in forming the porous body, or an organic compound used to strengthen the bond between the porous body and the substrate layer (e.g., the second electron transport layer 3). The porous body can serve as a base for forming the photoelectric conversion layer 5. By using the binder, the porous body can also be firmly bonded to the protrusions of a surface with an uneven structure. Therefore, when the photoelectric conversion layer 5 is formed on the porous body by coating, the photoelectric conversion layer 5 can be formed on a surface with an uneven structure.

[0106] In the first electron transport layer 4, the ratio of the second carbon intensity obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) to the first carbon intensity obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) on the second principal surface 4b to that on the first principal surface 4a (i.e., second carbon intensity / first carbon intensity) can also be 0.41 to 1.07. Hereinafter, "time-of-flight secondary ion mass spectrometry" will be referred to as "TOF-SIMS". In the first electron transport layer 4, sufficient carbon with a second carbon intensity / first carbon intensity within the above range exists on the second principal surface 2b. Therefore, due to the increased anchoring force of the first electron transport layer 4, the first electron transport layer 4 will not peel off from the substrate. When the photoelectric conversion layer 5 is formed by coating, the photoelectric conversion layer 5 can be formed to cover the entire surface of the substrate with approximately the same film thickness. As a result, problems such as short circuits between the substrate and the upper electrode are less likely to occur, thereby obtaining a highly reliable solar cell.

[0107] To further improve the anchoring force of the first electron transport layer 4, the carbon strength ratio can be 0.49 to 0.90.

[0108] The thickness of the first electron transport layer 4 can be 0.01 μm to 10 μm, 0.01 μm to 1 μm, or 0.01 μm to 0.2 μm. The thickness of the first electron transport layer 4 is, for example, greater than the thickness of the second electron transport layer 3. The first electron transport layer 4 can also have a large surface roughness. Specifically, the surface roughness coefficient of the first electron transport layer 4, obtained by dividing the effective area by the projected area, can be 10 or more, or 100 or more. Furthermore, the projected area refers to the area of ​​the shadow formed behind an object when it is illuminated from directly in front. The effective area refers to the actual surface area of ​​the object. The effective area can be calculated by taking the volume obtained from the object's projected area and thickness, and then taking the specific surface area and bulk density of the material constituting the object.

[0109] (Photoelectric conversion layer 5)

[0110] The photoelectric conversion layer 5 contains a perovskite-type compound. Specifically, the photoelectric conversion layer 5 contains a perovskite-type compound composed of monovalent cations, divalent cations, and halide anions as the photoelectric conversion material. This photoelectric conversion material is a light-absorbing material.

[0111] In this embodiment, the perovskite-type compound can be a compound represented by the chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halide anion).

[0112] In accordance with the usual terminology used for perovskite compounds, A, B, and X are referred to as site A, site B, and site X, respectively, in this specification.

[0113] In this embodiment, the perovskite compound may have a perovskite-type crystalline structure represented by the chemical formula ABX3. As an example, a monovalent cation is located at site A, a divalent cation is located at site B, and a halide anion is located at site X.

[0114] (Site A)

[0115] There is no limitation on the monovalent cation located at site A. Examples of monovalent cation A are organic cations or alkali metal cations. An example of an organic cation is a methylammonium cation (i.e., CH3NH3). + ), formamidinium cation (i.e., NH2CHNH2) + ), phenylethylammonium cation (i.e., C6H5C2H4NH3) + ), or guanidine cation (i.e., CH6N3) +An example of an alkali metal cation is the cesium cation (i.e., Cs). + ).

[0116] For high photoelectric conversion efficiency, the A site may also contain, for example, components selected from CS. + At least one of formaminoonium cation and methylammonium cation.

[0117] The cation constituting site A may also be a mixture of the aforementioned organic cations. The cation constituting site A may also be a mixture of at least one of the aforementioned organic cations and at least one of the aforementioned metal cations.

[0118] (Site B)

[0119] There is no limitation on the divalent cation located at the B site. Examples of divalent cations include those of elements in Group 13 to Genus 15. For instance, the B site can contain the Pb cation, i.e., Pb 2+ It can also contain Sn cations, i.e., Sn 2+ .

[0120] (X site)

[0121] There are no restrictions on the halogen anion located at the X site.

[0122] The elements, i.e. ions, located at the respective sites A, B, and X can be either multiple or a single element.

[0123] The photoelectric conversion layer 5 may also contain materials other than the photoelectric conversion material. For example, the photoelectric conversion layer 5 may further contain a quenching substance to reduce the defect density of the perovskite-type compound. The quenching substance is a fluorine compound such as tin fluoride. The molar ratio of the quenching substance to the photoelectric conversion material may also be 5% to 20%.

[0124] The photoelectric conversion layer 5 may also mainly contain perovskite-type compounds composed of monovalent cations, divalent cations and halide anions.

[0125] The sentence "The photoelectric conversion layer 5 mainly contains a perovskite-type compound composed of monovalent cations, divalent cations and halide anions" means that the photoelectric conversion layer 5 contains more than 70% by mass (preferably more than 80% by mass) of a perovskite-type compound composed of monovalent cations, divalent cations and halide anions.

[0126] The photoelectric conversion layer 5 may contain impurities. The photoelectric conversion layer 5 may also further contain compounds other than the perovskite-type compounds mentioned above.

[0127] The photoelectric conversion layer 5 can also have a thickness of 50 nm to 10 μm. The thickness of the photoelectric conversion layer 5 depends on the amount of light absorption of the photoelectric conversion layer 5. A portion of the material of the photoelectric conversion layer 5 is filled within the pores of the porous body of the first electron transport layer 4. That is, the photoelectric conversion layer 5 and the first electron transport layer 4 are partially mixed together. Therefore, the thickness of the photoelectric conversion layer 5 is also measured including the photoelectric conversion material filled within the pores of the porous body of the first electron transport layer 4, for example, including the thickness of the first electron transport layer 4.

[0128] The perovskite-type layer contained in the photoelectric conversion layer 5 can be formed using solution-based coating or co-evaporation methods.

[0129] The photoelectric conversion layer 5 can also have an uneven structure. When the photoelectric conversion layer 5 is formed on the first main surface 4a of the first electron transport layer 4, the uneven structure of the photoelectric conversion layer 5 can also be formed by following the shape of the uneven structure of the first main surface 4a of the first electron transport layer 4.

[0130] (Hole transport layer 6)

[0131] Hole transport layer 6 contains a hole transport material. A hole transport material is a material that transports holes. Examples of hole transport materials are organic materials or inorganic semiconductors.

[0132] Representative examples of organic compounds used as hole transport materials include 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (hereinafter referred to as "spiro-OMeTAD"), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl) (hereinafter referred to as "P3HT"), and poly(3,4-ethylene dioxythiophene) polystyrene. sulfonate (hereinafter referred to as "PEDOT:PSS") or copper phthalocyanine (hereinafter referred to as "CuPC").

[0133] Inorganic semiconductors are p-type semiconductors. Examples of inorganic semiconductors include Cu₂O, CuGaO₂, CuSCN, CuI, and NiO. x MoO xCarbon materials such as V2O5 or graphene oxide.

[0134] Hole transport layer 6 may also comprise multiple layers formed of different materials.

[0135] The thickness of the hole transport layer 6 is preferably 1 nm to 1000 nm, more preferably 10 nm to 500 nm, and even more preferably 10 nm to 50 nm. When the thickness of the hole transport layer 6 is 1 nm to 1000 nm, it can exhibit sufficient hole transport capability. Furthermore, when the thickness of the hole transport layer 6 is 1 nm to 1000 nm, due to the low resistance of the hole transport layer 6, light is efficiently converted into electricity.

[0136] Hole transport layer 6 may also include a supporting electrolyte and a solvent. The supporting electrolyte and solvent can stabilize the holes in hole transport layer 6.

[0137] Examples of supporting electrolytes are ammonium salts or alkali metal salts. Examples of ammonium salts include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts, or pyridinium salts. An example of an alkali metal salt is LiN(SO₂C₂)₃. n F 2n+1 2. LiPF6, LiBF4, lithium perchlorate, or potassium tetrafluoroborate.

[0138] The solvent contained in hole transport layer 6 can also have high ionic conductivity. Examples of such solvents are aqueous solvents or organic solvents. From the viewpoint of solute stabilization, the solvent can also be an organic solvent. Examples of organic solvents are heterocyclic compound solvents such as tert-butylpyridine, pyridine, or N-methylpyrrolidone.

[0139] The hole transport layer 6 can contain ionic liquids as solvents. Ionic liquids can be used alone or mixed with other solvents. The advantages of ionic liquids are low volatility and high flame retardancy.

[0140] Examples of ionic liquids include imidazolium compounds such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine compounds, alicyclic amine compounds, aliphatic amine compounds, or azo amine compounds.

[0141] The hole transport layer 6 is formed, for example, by coating, printing, or vapor deposition. Examples of coating methods include blade coating, rod coating, spray coating, dip coating, or spin coating. An example of printing methods is screen printing. Alternatively, the hole transport layer 6 can be formed by mixing multiple materials and then subjected to pressure or firing. When the hole transport layer 6 contains low-molecular-weight organic or inorganic semiconductors, it can also be formed by vacuum vapor deposition.

[0142] (Electrode 2, 7)

[0143] The second electrode 7 is conductive.

[0144] When the solar cell 100 does not have a hole transport layer 6, the second electrode 7 has the property of blocking electrons moving from the photoelectric conversion layer 5 (hereinafter referred to as "electron blocking property"). In this case, the second electrode 7 does not make ohmic contact with the photoelectric conversion layer 5. In this specification, electron blocking property refers to the property that allows only holes generated in the photoelectric conversion layer 5 to pass through, but not electrons. The Fermi level of the material with electron blocking property is lower than the energy level at the bottom of the conduction band of the photoelectric conversion layer 5. The Fermi level of the material with electron blocking property may also be lower than the Fermi level of the photoelectric conversion layer 5. Examples of materials with electron blocking property are platinum, gold, or carbon materials such as graphene.

[0145] When the solar cell 100 has a hole transport layer 6 between the second electrode 7 and the photoelectric conversion layer 5, the second electrode 7 may not have electron blocking properties. In this case, the second electrode 7 may be made of a material capable of forming an ohmic contact with the photoelectric conversion layer 5.

[0146] (Instructions for solar cell 200)

[0147] The solar cell 200 of the first embodiment is manufactured as follows, for example.

[0148] First, a conductive substrate, for example having an uneven structure and functioning as a first electrode 2, is prepared as substrate 1. Then, a second electron transport layer 3 is formed on the conductive substrate using, for example, sputtering or spray pyrolysis. A first electron transport layer 4 is formed on the second electron transport layer 3 using, for example, spraying or inkjet printing. The first electron transport layer 4 can also be fabricated using electron transport material particles and a binder. The fabrication of the first electron transport layer 4 is carried out at a relatively low temperature, for example, below 300°C. To remove surfactants or the like adhering to the particles, ultraviolet irradiation can be used instead of heat treatment. A photoelectric conversion layer 5 is formed on the first electron transport layer 4 using a coating technique. The photoelectric conversion layer 5 can also be formed by physical vapor deposition, or a combination of physical vapor deposition and coating techniques. A hole transport layer 6 is formed on the photoelectric conversion layer 5 using a coating technique, physical vapor deposition, or chemical vapor deposition. Finally, a second electrode 7 is formed on the hole transport layer 6 using physical vapor deposition. Examples of coating techniques include spin coating, spray coating, die coating, inkjet coating, gravure coating, flexographic coating, and screen printing. An example of physical vapor deposition is sputtering. Examples of chemical vapor deposition include vapor deposition using heat, light, or plasma.

[0149] (Second Implementation)

[0150] Figure 4 A cross-sectional view showing the solar cell 300 of the second embodiment.

[0151] like Figure 4 As shown, the solar cell 300 of the second embodiment, compared to the solar cell 200 of the first embodiment, has a configuration in which a substrate 1 is not provided, and a composite layer 21 and a second photoelectric conversion layer 22 are further provided between the first electrode 2 and the second electron transport layer 3. That is, the solar cell 300 is a stacked solar cell having two photoelectric conversion layers. Matters described in the first embodiment are omitted as appropriate.

[0152] The second photoelectric conversion layer 22 is disposed between the composite layer 21 and the first electrode 2.

[0153] The solar cell 300 sequentially comprises a first electrode 2, a second photoelectric conversion layer 22, a composite layer 21, a second electron transport layer 3, a first electron transport layer 4, a photoelectric conversion layer (first photoelectric conversion layer) 5, a hole transport layer 6, and a second electrode 7.

[0154] The following describes a configuration that differs from that of solar cell 200.

[0155] A layer with other functions may also be disposed between the first electrode 2 and the second photoelectric conversion layer 22. An example of a layer with other functions is a porous layer.

[0156] (Composite layer 21)

[0157] In tandem solar cells such as solar cell 200, a composite layer 21 is provided, for example. The composite layer 21 has the function of collecting and recombinizing charge carriers generated in the first photoelectric conversion layer 5 and the second photoelectric conversion layer 22. Therefore, it is preferable that the composite layer 21 has a certain degree of conductivity. The composite layer 21 may also be transparent, for example. Light in the visible to near-infrared region can pass through the transparent composite layer 21. The transparent composite layer 21 can be formed of a transparent and conductive material.

[0158] Examples of this type of material include:

[0159] (i) Titanium oxide doped with at least one selected from lithium, magnesium, niobium and fluorine

[0160] (ii) Doped with gallium oxide selected from at least one of tin and silicon,

[0161] (iii) Doped with gallium nitride selected from at least one of silicon and oxygen,

[0162] (iv) Indium-tin composite oxides,

[0163] (v) Tin oxide doped with at least one selected from antimony and fluorine,

[0164] (vi) Zinc oxide doped with at least one of boron, aluminum, gallium, or indium, or

[0165] (vii) Their complex.

[0166] Examples of materials for composite layer 21 include metal oxides such as ZnO, WO3, MoO3, or MoO2, or electron-accepting organic compounds. Examples of electron-accepting organic compounds are those with a CN substituent. Examples of CN substituents include triphenylene derivatives, tetracyanoquinone dimethane derivatives, or indofluorene derivatives. An example of a triphenylene derivative is hexacyanohexaazatriphenylene. Examples of tetracyanoquinone dimethane derivatives are tetrafluoroquinone dimethane or dicyanoquinone dimethane. Electron-accepting substances can be single compounds or mixtures of other organic compounds.

[0167] (Second photoelectric conversion layer 22)

[0168] The photoelectric conversion material constituting the second photoelectric conversion layer 22 has a smaller band gap than the photoelectric conversion material constituting the first photoelectric conversion layer 5. Examples of photoelectric conversion materials constituting the second photoelectric conversion layer 22 include silicon, perovskite compounds, chalcopyrite compounds such as CIGS, or III-V compounds such as GaAs. The second photoelectric conversion layer 22 may also contain silicon. When the second photoelectric conversion layer 22 contains silicon, the solar cell 200 becomes a cascaded solar cell with a silicon solar cell and a perovskite solar cell superimposed. However, there is no restriction on the photoelectric conversion material constituting the second photoelectric conversion layer 22 as long as it has a smaller band gap than the photoelectric conversion material constituting the first photoelectric conversion layer 5.

[0169] (The effect of solar cell 300)

[0170] The basic function of the solar cell 300 is explained below. In the solar cell 300, at least one of the first electrode 2 and the second electrode 7 is light-transmitting. When the second electrode 7 is light-transmitting, light is incident into the solar cell 300, for example, from the surface of the second electrode 7. When light shines into the solar cell 300, the first photoelectric conversion layer 5 absorbs the light, generating excited electrons and holes. The excited electrons move to the first electron transport layer 4 and the second electron transport layer 3. On the other hand, the holes generated in the first photoelectric conversion layer 5 move to the hole transport layer 6. Furthermore, light not absorbed in the first photoelectric conversion layer 5 passes through the first electron transport layer 4, the second electron transport layer 3, and the recombination layer 21, and is absorbed by the second photoelectric conversion layer 22. The second photoelectric conversion layer 22 absorbs the light, generating excited electrons and holes. The excited electrons move to the first electrode 2. On the other hand, the holes generated in the second photoelectric conversion layer 22 move to the recombination layer 21. Electrons moving from the first photoelectric conversion layer 5 to the composite layer 21 and holes moving from the second photoelectric conversion layer 22 to the composite layer 21 are recombinated at the composite layer 21. Current is extracted from the first electrode 2 and the second electrode 7, which function as negative and positive electrodes, respectively.

[0171] (An example of the manufacturing process of solar cell 300)

[0172] Solar cell 300 can be fabricated, for example, by the following method. The following method is an example when the second photoelectric conversion layer 22 is made of silicon.

[0173] First, a second photoelectric conversion layer 22 with an uneven structure, composed of n-type silicon single crystals, is prepared. Then, a first electrode 2 is formed on one main surface of the second photoelectric conversion layer 22 using a coating technique, physical vapor deposition, or chemical vapor deposition. A composite layer 21 is formed on the other main surface of the second photoelectric conversion layer 22 using a physical vapor deposition or vacuum heating vapor deposition. Next, a second electron transport layer 3 and a first electron transport layer 4 are formed on the composite layer 21. A first photoelectric conversion layer 5 is formed on the first electron transport layer 4 using a coating technique. The first photoelectric conversion layer 5 can also be formed using physical vapor deposition, or a combination of physical vapor deposition and coating techniques. A hole transport layer 6 is formed on the first photoelectric conversion layer 5 using a coating technique, physical vapor deposition, or chemical vapor deposition. Finally, a second electrode 7 is disposed on the hole transport layer 6 using physical vapor deposition. Examples of coating techniques include spin coating, spray coating, die coating, inkjet coating, gravure coating, flexographic coating, or screen printing. Examples of physical vapor deposition methods include sputtering. Examples of chemical vapor deposition methods include vapor deposition that uses heat, light, or plasma.

[0174] The solar cell 300 of the second embodiment has two photoelectric conversion layers. That is, the solar cell 300 is a two-layer stacked solar cell formed by bonding two solar cells together. However, the number of solar cells bonded is not limited to two, and it can also be formed by bonding three or more solar cells together.

[0175] (Third implementation)

[0176] This invention describes embodiments of the photoelectric conversion element disclosed herein.

[0177] The photoelectric conversion element of the third embodiment includes:

[0178] First electrode,

[0179] First electron transport layer

[0180] Second electron transport layer

[0181] Photoelectric conversion layer, and

[0182] Second electrode,

[0183] Here, the photoelectric conversion layer is disposed between the first electrode and the second electrode.

[0184] The first electron transport layer is disposed between the photoelectric conversion layer and the first electrode.

[0185] The second electron transport layer is disposed between the first electron transport layer and the first electrode.

[0186] The first electron transport layer comprises carbon and a porous electron transport material.

[0187] The photoelectric conversion element in the third embodiment is, for example, a light sensor. The photoelectric conversion element in the third embodiment functions as a light sensor, for example, by being connected via a wiring connection through a current detection device via a first electrode and a second electrode. A known current detection device can be used.

[0188] In the photoelectric conversion element of the third embodiment, similar to the solar cell 200 of the first embodiment, the first electrode may also have an uneven structure. Even when the substrate has an uneven structure, the photoelectric conversion layer 5 can be formed to cover the entire surface of the substrate with approximately the same film thickness. As a result, it is difficult for short circuits to occur even in the protrusions, thereby obtaining a photoelectric conversion element with high reliability.

[0189] Example

[0190] <Example 1>

[0191] Figure 5This is a cross-sectional view of the substrate 400 with a photoelectric conversion layer in Example 1. Figure 5 As shown, the substrate 400 with a photoelectric conversion layer in Embodiment 1 includes a substrate 11, a first electrode 12, a second electron transport layer 13, a first electron transport layer 14, and a photoelectric conversion layer 15. Furthermore, the substrate 11, first electrode 12, second electron transport layer 13, first electron transport layer 14, and photoelectric conversion layer 15 in the substrate 400 with the photoelectric conversion layer correspond to the substrate 1, first electrode 2, second electron transport layer 3, first electron transport layer 4, and photoelectric conversion layer 5 in the solar cell 100 and solar cell 200 of the first embodiment, respectively.

[0192] The components of the substrate 400 with the photoelectric conversion layer constituting Embodiment 1 are described below.

[0193] • Substrate 11: Textured silicon substrate (average unevenness is 2.0 μm, that is, the average height difference between the convex and concave parts of the textured surface is 2.0 μm)

[0194] • Electrode 12: Tin-doped indium oxide layer (thickness: 100nm)

[0195] • Second electron transport layer 13: TiO2 layer (thickness: 15nm)

[0196] • First electron transport layer 14: Porous TiO2 layer (thickness: 150nm)

[0197] • Photoelectric conversion layer 15: mainly contains CH(NH2)PbI3 as a perovskite-type compound.

[0198] The specific production method is shown below.

[0199] First, a silicon substrate with a tin-doped indium oxide layer is prepared to be formed on the surface of the substrate 11 and the first electrode 12. The silicon substrate has a textured structure with an average height difference of 2.0 μm.

[0200] Next, a TiO2 film with a thickness of 15 nm is formed on the first electrode 12 by sputtering as the second electron transport layer 13.

[0201] Next, the second electron transport layer 13 was heated to 150°C on a table equipped with a heating device. After the first raw material solution was coated using an inkjet printing method, the surface was washed using UV ozone treatment at room temperature to form the first electron transport layer 14. The first raw material solution was a butanol (Wako Pure Chemical Industries) dispersion containing 15 g / L of 30-NR-D (manufactured by Great Cell Solar).

[0202] Next, a second raw material solution is spin-coated onto the first electron transport layer 14 to form a photoelectric conversion layer 15. The second raw material solution is a solution containing 0.92 mol / L PbI2 (manufactured by Tokyo Chemical Industry), 0.17 mol / L PbBr2 (manufactured by Tokyo Chemical Industry), 0.83 mol / L formamidinium iodide (manufactured by Great Cell Solar) (hereinafter referred to as "FAI"), 0.17 mol / L methylammonium bromide (manufactured by Great Cell Solar) (hereinafter referred to as "MABr"), and 0.05 mol / L CsI (manufactured by Iwatani Sangyo) in a solution of dimethyl sulfoxide (manufactured by Acros) and N,N-dimethylformamide (manufactured by Acros). The mixing ratio of dimethyl sulfoxide and N,N-dimethylformamide in the second raw material solution is 1:4 (volume ratio).

[0203] In this way, the substrate 400 with the photoelectric conversion layer of Example 1 is obtained.

[0204] In the above process, except for the process of the first electrode 12, it is carried out in a drying room under a dry environment gas with a dew point of -40°C or below.

[0205] <Comparative Example 1>

[0206] Except as described below, the comparative example substrate 300 with the photoelectric conversion layer was fabricated in the same manner as in Example 1. In the fabrication of the first electron transport layer 14, the second electron transport layer 13 was heated to 150°C on a stage equipped with a heating device. Next, after coating with a first raw material solution using an inkjet printing method, it was fired in an oven at 500°C for 30 minutes. Afterward, the surface was washed using UV ozone treatment at room temperature, thereby forming the first electron transport layer 14. These aspects differ from those of Example 1.

[0207] (TOF-SIMS)

[0208] Using a TOF-SIMS5 (manufactured by ION-TOF), the substrate depth direction quality of Example 1 up to the formation of the first electron transport layer 14 was analyzed. The measurement conditions were primary ion Bi... 3+ (Accelerating voltage is 30kV), sputtered ion C S + (Accelerating voltage is 1kV), the detection polarity of secondary ions is negative, and the analysis area is 80μm×80μm.

[0209] Figure 6 A graph showing the carbon distribution obtained using TOF-SIMS for the first electron transport layer 14 of Example 1 is provided. The carbon distribution confirms a mountain-like structure. In Example 1, sufficient carbon is present on the second principal surface 2b of the first electron transport layer 14.

[0210] (Graph showing the relationship between carbon threshold and power generation efficiency)

[0211] Based on the carbon distribution contained in the first electron transport layer 14 as clearly defined by TOF-SIMS, the ratio of the first carbon intensity (a) of the first principal surface 14a of the first electron transport layer 14 to the second carbon intensity (b) of the second principal surface 14b of the first electron transport layer 14 is defined as the carbon threshold.

[0212] This is expressed as (carbon threshold) = (intensity b) / (intensity a). The inventors have discovered that intensity a is a constant value in the carbon distribution measurement using TOF-SIMS. Furthermore, even in the surface analysis using X-ray photoelectron spectroscopy (XPS) described below, it was similarly confirmed that the carbon concentration of the first principal surface 14a of the first electron transport layer 14 is also a constant value.

[0213] Figure 7A This is a graph showing the relationship between the carbon threshold and the normalized efficiency in a solar cell fabricated on a textured substrate with an uneven surface. The inventors found that if the carbon threshold is between 0.41 and 1.07, the normalized efficiency becomes 0.4 or higher. Furthermore, if the carbon threshold is between 0.49 and 0.90, the normalized efficiency becomes 0.8 or higher.

[0214] In production Figure 7A The graph shown was used to determine the relationship between the thickness variation of the porous material in the first electron transport layer 14 and the carbon threshold. Details will be described later, but... Figure 9 As shown, the difference in film thickness of the first electron transport layer 14 before and after washing at 60°C to 300°C is taken as a first-order approximation and is proportional to the amount of adhesive adhering to the surface of the first electron transport layer 14, i.e., the carbon threshold. Furthermore, from... Figure 6 The carbon distribution shown in Example 1 can also be used to estimate the carbon threshold at 150°C as 0.70. Figure 7B A graph showing the relationship between firing temperature and carbon threshold.

[0215] The performance of solar cells fabricated on flat substrates at various firing temperatures is shown in the figure. Figure 7A and Figures 10A-10D . Figure 7A In the range exceeding the carbon threshold of 0.90, the efficiency decreases due to the increased thickness of the first electron transport layer 14.

[0216] In texture units, peeling can occur due to insufficient binder when the carbon threshold is small, i.e., less than 0.41.

[0217] The carbon threshold of the first electron transport layer 14 is determined after the perovskite material contains organic molecules or other carbon, and the perovskite material is dissolved and removed.

[0218] (XPS)

[0219] For Example 1, the surface of the substrate 400 up to the process of forming the first electron transport layer 14 was analyzed using XPS. The dependence of the C1s bond peak intensity on UV irradiation time was determined based on the intensity change of the C1s spectrum. Figure 8 This is a graph showing the dependence of the C-C bond peak intensity, obtained from the intensity change of the C1s spectrum obtained using XPS, on UV irradiation time for the first electron transport layer 14 of Example 1. In Example 1, the C concentration decreased to the intensity level of Comparative Example 1 after 30 minutes of irradiation following surface washing. In the UV ozone washing process necessary for forming the photoelectric conversion layer 5, the carbon content of the first principal surface 14a of the first electron transport layer 14 was confirmed to converge to a constant value.

[0220] (Estimation of the relationship between carbon threshold and power generation efficiency)

[0221] For the carbon threshold of Example 1 obtained using TOF-SIMS, the relationship between power generation efficiency and carbon threshold is supplemented. After forming the first electron transport layer 14 on a flat substrate, it is fired in an oven at a specified temperature for 30 minutes, and then a solvent for the photoelectric conversion layer 15 without perovskite material is spin-coated to obtain the dependence of the residual thickness of the first electron transport layer 14 on the firing temperature. Figure 9 This is a graph showing the dependence of film thickness before and after spin-coating solvent on firing temperature after firing the first electron transport layer 14 disposed on a flat substrate. With 250°C and 300°C as boundaries, the anchoring force of the first electron transport layer 14 decreases, and the reduction in film thickness (the difference in the graph) increases.

[0222] The results of using a first-order approximation to correlate the temperature dependence of the above film thickness difference with the carbon threshold of 60℃~300℃ obtained by TOF-SIMS carbon distribution measurement are shown in Table 1.

[0223]

[0224] Furthermore, perovskite solar cells were fabricated using the first electron transport layer 14, which was prepared at the aforementioned temperatures, and their power generation performance was compared. The fabrication steps are described below.

[0225] (Production steps)

[0226] The raw material solution used to form the photoelectric conversion layer is a solution containing 0.92 mol / L PbI2 (manufactured by Tokyo Chemical Industry), 0.17 mol / L PbBr2 (manufactured by Tokyo Chemical Industry), 0.83 mol / L FAI (manufactured by Great Cell Solar), 0.17 mol / L MABr (manufactured by Great Cell Solar), and 0.05 mol / L CsI (manufactured by Iwatani Sangyo) in a dimethyl sulfoxide (ACROS) and N,N-dimethylformamide (ACROS) solution. The mixing ratio of dimethyl sulfoxide and N,N-dimethylformamide is 1:4 (volume ratio).

[0227] The raw material solution was coated onto the first electron transport layer 14 using spin coating. At this time, 200 μL of chlorobenzene was added dropwise onto the rotating substrate as a lean solvent.

[0228] Subsequently, the substrate is heat-treated on a hot plate at 115°C for 10 minutes, and then heat-treated on a hot plate at 100°C for 30 minutes, thereby forming a photoelectric conversion layer with a thickness of 500 nm on the first electron transport layer 14.

[0229] Subsequently, polytriallylamine (PTAA, manufactured by Sigma Aldrich) dissolved in toluene was spin-coated onto the photoelectric conversion layer as a hole transport layer to form a hole transport layer with a thickness of 40 nm.

[0230] Next, a 170 nm thick Au film is deposited on the hole transport layer by vapor deposition to form the second electrode. In this way, a perovskite solar cell is obtained.

[0231] (Power generation performance evaluation)

[0232] Figure 10A This is a graph showing the dependence of the open-circuit voltage of a solar cell fabricated using the substrate on the firing temperature after firing the first electron transport layer 14 disposed on a flat substrate. Figure 10B This is a graph showing the dependence of the short-circuit current density of a solar cell fabricated using the substrate on the firing temperature after firing the first electron transport layer 14 disposed on a flat substrate. Figure 10C This is a graph showing the dependence of the fill factor of a solar cell fabricated using the substrate on the firing temperature after firing the first electron transport layer 14 disposed on a flat substrate. Figure 10D A graph showing the dependence of the conversion efficiency of a solar cell made on a flat substrate on firing temperature after firing the first electron transport layer disposed on the substrate. Figure 10A In the diagram, the open-circuit voltage is marked as V. oc . Figure 10B In the diagram, the short-circuit current density is denoted as J. sc . Figure 10C In this context, the fill factor is denoted as FF. Figure 10D In this context, the conversion efficiency is denoted as Eff. A lower firing temperature indicates a higher carbon threshold, meaning that carbon hinders the transport of electrons in the photoelectric conversion layer. Figure 11A To represent the estimate, Figure 10A The graph shows the results of converting the horizontal axis to the carbon threshold and taking into account the interlayer short circuits that occur in regions with low carbon thresholds. Figure 11B To represent the estimate, Figure 10B The graph shows the results of converting the horizontal axis to the carbon threshold and taking into account the interlayer short circuits that occur in regions with low carbon thresholds. Figure 11C To represent the estimate, Figure 10C The graph shows the results of converting the horizontal axis to the carbon threshold and taking into account the interlayer short circuits that occur in regions with low carbon thresholds.

[0233] The results are summarized in Tables 2 and 3. The power generation efficiency of the solar cells on the textured substrate is shown in Table 2. The power generation efficiency of the solar cells on the flat substrate is shown in Table 3. The power generation efficiency of the solar cell cells fabricated on the uniform film under the conditions of Example 1 is normalized to 1.

[0234]

[0235]

[0236] If the carbon threshold is 0.41 or higher, the first electron transport layer 14 has sufficient anchoring force. If the carbon threshold is 1.07 or lower, carbon does not hinder electron transport, preventing a decrease in open-circuit voltage, short-circuit current density, and fill factor. In planar cells, if the carbon threshold is 0.41–0.90, the cell efficiency becomes higher. In textured cells, if the carbon threshold is 0.49–0.90, the cell efficiency becomes higher.

[0237] Industrial availability

[0238] The solar cell disclosed herein can be used in a variety of applications that include those of existing solar cells.

[0239] Symbol explanation:

[0240] 1. 11 substrate

[0241] 2.12 Electrode 1

[0242] 3.13 Second Electron Transport Layer

[0243] 4.14 First Electron Transport Layer

[0244] 4a, 14a First principal plane of the first electron transport layer

[0245] 4b, 14b The second principal plane of the first electron transport layer

[0246] 5, 15 photoelectric conversion layers

[0247] 6. Hole transport layer

[0248] 7. Second electrode

[0249] 21 Composite Layer

[0250] 22 Second photoelectric conversion layer

Claims

1. A solar cell, comprising: First electrode, First electron transport layer Second electron transport layer Photoelectric conversion layer, and Second electrode, Here, the photoelectric conversion layer is disposed between the first electrode and the second electrode. The first electron transport layer is disposed between the photoelectric conversion layer and the first electrode. The second electron transport layer is disposed between the first electron transport layer and the first electrode. The first electron transport layer comprises carbon and a porous electron transport material. The first electron transport layer has a first principal surface facing the photoelectric conversion layer and a second principal surface facing the second electron transport layer. In the first electron transport layer, the ratio of the second carbon intensity obtained by time-of-flight secondary ion mass spectrometry analysis on the second principal surface to the first carbon intensity obtained by time-of-flight secondary ion mass spectrometry analysis on the first principal surface is 0.49 to 0.

90.

2. The solar cell according to claim 1, wherein, The carbon is derived from binders or dispersants.

3. The solar cell according to claim 1 or 2, wherein, The photoelectric conversion layer contains a perovskite-type compound.

4. The solar cell according to claim 1 or 2, wherein, The electron transport material is titanium oxide.

5. The solar cell according to claim 1 or 2, wherein, The first electrode has a concave-convex structure.

6. The solar cell according to claim 1 or 2, wherein, The first electron transport layer is in contact with the second electron transport layer.

7. A photoelectric conversion element, comprising: First electrode, First electron transport layer Second electron transport layer Photoelectric conversion layer, and Second electrode, Here, the photoelectric conversion layer is disposed between the first electrode and the second electrode. The first electron transport layer is disposed between the photoelectric conversion layer and the first electrode. The second electron transport layer is disposed between the first electron transport layer and the first electrode. The first electron transport layer comprises carbon and a porous electron transport material. The first electron transport layer has a first principal surface facing the photoelectric conversion layer and a second principal surface facing the second electron transport layer. In the first electron transport layer, the ratio of the second carbon intensity obtained by time-of-flight secondary ion mass spectrometry analysis on the second principal surface to the first carbon intensity obtained by time-of-flight secondary ion mass spectrometry analysis on the first principal surface is 0.49 to 0.90.

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