Solar cells and methods for manufacturing solar cells

Abstract

A solar cell 100 according to the present disclosure is provided with, in the order given, a first electrode 2, a photoelectric conversion layer 3, an intermediate layer 4, a hole transport layer 5, and a second electrode 6. The second electrode 6 contains an oxide. The intermediate layer 4 contains at least one compound selected from the group consisting of iodide and bromide. The compound contains a monovalent organic cation. The photoelectric conversion layer 3 may contain, for example, a perovskite compound.

Description

[Technical Field]

[0001] This disclosure relates to solar cells and methods for manufacturing solar cells. [Background technology]

[0002] In recent years, research and development of organic thin-film solar cells and perovskite solar cells have been progressing as new solar cells to replace existing silicon-type solar cells. Perovskite solar cells use perovskite crystals represented by ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a monovalent anion) and similar structures (hereinafter referred to as "perovskite compounds") as photoelectric conversion materials. Non-Patent Document 1 discloses a solar cell that uses a perovskite compound represented by CH3NH3PbI3 (hereinafter also referred to as "MAPbI3") as the photoelectric conversion material, TiO2 as the electron transport material, and Spiro-OMeTAD as the hole transport material. Non-Patent Document 2 discloses a tandem structure in which silicon solar cells and perovskite solar cells are stacked on top of each other, with the aim of further improving photoelectric conversion efficiency. Furthermore, Non-Patent Document 3 discloses a see-through type perovskite solar cell aimed at building material integration as a new application. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] “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] [Non-Patent Document 2] “Monolithic perovskite / silicon-homojunction tandem solar cell with over 22% efficiency”, Energy Environ. Sci., 2017,10, 2472. [DOI: 10.1039 / c7ee02288c] [Non-Patent Document 3] “Comparing energy performance of different semi-transparent, building-integrated photovoltaic cells applied to “reference” buildings”, Energy Procedia 126 (201709) 219. [DOI: 10.1016 / j.egypro.2017.08.143.] [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The purpose of this disclosure is to provide a solar cell having an electrode containing an oxide, which has a configuration suitable for suppressing a decrease in photoelectric conversion characteristics. [Means for solving the problem]

[0005] The solar cells disclosed herein are The device comprises a first electrode, a photoelectric conversion layer, an intermediate layer, a hole transport layer, and a second electrode, in this order. The second electrode contains an oxide, The intermediate layer comprises at least one compound selected from the group consisting of iodide and bromide. The aforementioned compound contains a monovalent organic cation. [Effects of the Invention]

[0006] This disclosure provides a solar cell having an oxide-containing electrode and a configuration suitable for suppressing a decrease in photoelectric conversion characteristics. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows a cross-sectional view of a solar cell 100 according to an embodiment of the present disclosure. [Figure 2] Figure 2 shows a cross-sectional view of a solar cell 200 according to an embodiment of the present disclosure. [Figure 3] Figure 3 shows a cross-sectional view of a solar cell 300 according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0008] <Knowledge that forms the basis of this disclosure> As shown in the paper "Qingfeng Dong et al., Science, 2015, 347, 6225, 967-970," perovskite solar cells can generate electricity with high efficiency at a thickness of several hundred nanometers due to the characteristic properties of perovskite compounds: a high light absorption coefficient and a long diffusion length. Furthermore, perovskite solar cells have features such as using fewer materials compared to existing silicon solar cells, not requiring high temperatures during the formation process, and being able to be formed by coating. As a result, perovskite solar cells can be developed into building material-integrated solar cells combined with building materials, and into see-through solar cells by direct formation on glass (for example, Non-Patent Document 3).

[0009] To further improve photoelectric conversion efficiency, the construction of tandem solar cells, which involve stacking perovskite solar cells with silicon solar cells, is being considered (for example, Non-Patent Document 2).

[0010] To achieve the above configuration, it is necessary to introduce light into the perovskite solar cell from the metal electrode side, such as gold, which is conventionally used as an electrode. For this reason, the perovskite solar cell must be a light-transmitting perovskite solar cell.

[0011] When using a light-transmissive oxide instead of a metal as the electrode material, in order to reduce the damage to the solar cell during electrode formation, Non-Patent Document 2 proposes providing molybdenum oxide or the like between the hole transport layer and the electrode by vacuum deposition. Since this makes the manufacturing process of the solar cell complicated, direct formation of an oxide electrode on the hole transport layer is desired. However, when an oxide electrode is directly formed on the hole transport layer, the power generation characteristics (i.e., photoelectric conversion characteristics) of the solar cell deteriorate.

[0012] In view of these findings, as a result of intensive research, the present inventors have found a novel structure of a solar cell in which even when an electrode containing an oxide is directly formed on a hole transport layer, a decrease in photoelectric conversion characteristics can be suppressed.

[0013] The term "perovskite solar cell" used in this specification means a solar cell containing a perovskite compound as a photoelectric conversion material or a light absorption material.

[0014] <Embodiment of the present disclosure> The solar cell according to an embodiment of the present disclosure includes a first electrode, a photoelectric conversion layer, an intermediate layer, a hole transport layer, and a second electrode in this order. The second electrode contains an oxide. The intermediate layer contains at least one compound selected from the group consisting of iodides and bromides. The compound contains a monovalent organic cation.

[0015] The solar cell according to this embodiment includes a second electrode containing an oxide. In the solar cell according to this embodiment, an intermediate layer containing at least one compound selected from the group consisting of iodides and bromides is provided between the photoelectric conversion layer and the hole transport layer. With this configuration, the solar cell according to this embodiment can mitigate the damage to the solar cell (e.g., damage to the hole transport layer) when forming the second electrode and suppress the degradation of the photoelectric conversion characteristics. That is, the solar cell according to this embodiment has a configuration suitable for suppressing the degradation of the photoelectric conversion characteristics in a solar cell including an electrode containing an oxide. Note that the damage to the solar cell when forming the second electrode may be, for example, when the second electrode is formed by sputtering, the hole transport layer may be damaged by plasma and its characteristics may deteriorate.

[0016] In the solar cell according to this embodiment, the second electrode may be in contact with the hole transport layer. Since the solar cell according to this embodiment includes the above intermediate layer, even if the second electrode containing an oxide is directly formed on the hole transport layer, the degradation of the photoelectric conversion characteristics can be suppressed.

[0017] The solar cell according to this embodiment may further include a substrate.

[0018] FIG. 1 shows a cross-sectional view of a solar cell 100 according to an embodiment of the present disclosure. The solar cell 100 has a first configuration example of the solar cell of the present disclosure.

[0019] As shown in FIG. 1, the solar cell 100 includes a substrate 1, a first electrode 2, a photoelectric conversion layer 3, an intermediate layer 4, a hole transport layer 5, and a second electrode 6 in this order.

[0020] The solar cell according to this embodiment may further include an electron transport layer. The electron transport layer is, for example, disposed between the first electrode and the photoelectric conversion layer. FIG. 2 shows a cross-sectional view of a solar cell 200 according to an embodiment of the present disclosure. The solar cell 200 has a second configuration example of the solar cell of the present disclosure.

[0021] As shown in Figure 2, the solar cell 200 comprises a substrate 1, a first electrode 2, an electron transport layer 7, a photoelectric conversion layer 3, an intermediate layer 4, a hole transport layer 5, and a second electrode 6, in this order.

[0022] The solar cell according to this embodiment may further include a porous layer. The porous layer is, for example, located between the electron transport layer and the photoelectric conversion layer. Figure 3 shows a cross-sectional view of a solar cell 300 according to an embodiment of the present disclosure. The solar cell 300 has a third configuration example of the solar cell of the present disclosure.

[0023] As shown in Figure 3, the solar cell 300 comprises a substrate 1, a first electrode 2, an electron transport layer 7, a porous layer 8, a photoelectric conversion layer 3, an intermediate layer 4, a hole transport layer 5, and a second electrode 6, in this order.

[0024] The solar cell according to this embodiment may be manufactured, for example, by the following manufacturing method.

[0025] The manufacturing method according to this embodiment is, for example, (A) To form an intermediate layer comprising at least one selected from the group consisting of iodide and bromide, (B) Forming a hole transport layer containing a hole transport material, and (C) Forming an electrode containing an oxide by sputtering.

[0026] The electrode formed in (C) above is, for example, a second electrode. In the above manufacturing method, the electrode containing oxide is formed in (C) above by sputtering, but in (A) above, an intermediate layer containing at least one selected from the group consisting of iodide and bromide is formed, thereby mitigating damage to the solar cell, particularly the hole transport layer, by the sputtering method. Therefore, according to the above manufacturing method, a solar cell with suppressed degradation of photoelectric conversion characteristics can be manufactured.

[0027] In (A) above, the intermediate layer may be formed by a coating method. By such a method, a solar cell in which the deterioration of photoelectric conversion characteristics is suppressed can be easily manufactured.

[0028] In (B) above, the hole transport layer may be formed by a coating method. By such a method, a solar cell in which the deterioration of photoelectric conversion characteristics is suppressed can be easily manufactured.

[0029] Here, we will explain an example of how to manufacture the solar cell 300, which is the third configuration example.

[0030] Solar cell 300 is manufactured, for example, by the following method.

[0031] First, a first electrode 2 is formed on the surface of the substrate 1 by chemical vapor deposition (CVD) or sputtering. Next, an electron transport layer 7 is formed on the first electrode 2 by, for example, sputtering. A porous layer 8 is formed on the electron transport layer 7 by, for example, coating. Then, a photoelectric conversion layer 3 is formed on the porous layer 8 by, for example, coating. After that, an intermediate layer 4 is formed on the photoelectric conversion layer 3 by, for example, coating. A hole transport layer 5 is formed on the intermediate layer 4 by, for example, coating. A second electrode 6 is formed on the hole transport layer 5 by, for example, sputtering. In this way, a solar cell 300 is obtained.

[0032] Furthermore, the solar cell 100 of the first configuration example according to this embodiment can be manufactured in the same manner as the solar cell 300, except that the electron transport layer 7 and the porous layer 8 are not formed. The solar cell 200 of the second configuration example according to this embodiment can be manufactured in the same manner as the solar cell 300, except that the porous layer 8 is not formed.

[0033] The following describes in detail each component of the solar cell described herein.

[0034] (Circuit board 1) Substrate 1 serves to hold each layer of the solar cell. Substrate 1 can be formed from a transparent material. Such materials can include a glass substrate or a plastic substrate. The plastic substrate may also be a plastic film.

[0035] If the first electrode 2 has sufficient strength, the first electrode 2 can hold each layer, so the substrate 1 does not need to be provided.

[0036] (1st electrode 2) The first electrode 2 is conductive.

[0037] The first electrode 2 may be light-transmitting. For example, the first electrode 2 transmits light from the visible region to the near-infrared region.

[0038] The first electrode 2 may be composed of, for example, a transparent and conductive metal oxide. Examples of such metal oxides are: (i) Indium-tin composite oxide, (ii) Indium-zinc composite oxide, (iii) Antimony-doped tin oxide, (iv) Fluorine-doped tin oxide, (v) Zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium, or (vi) These composites, That is the case.

[0039] The first electrode 2 may be formed using an opaque material with a light-transmitting pattern. Examples of light-transmitting patterns include linear (e.g., stripes), wavy, grid-like (e.g., mesh), or perforated metal-like patterns with a large number of fine through-holes arranged regularly or irregularly. When the first electrode 2 has these patterns, light can pass through areas where the electrode material is not present. Examples of opaque materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. Conductive carbon materials may be used as the opaque material.

[0040] If the solar cell does not have an electron transport layer 7, the first electrode 2 has blocking properties for holes from the photoelectric conversion layer 3. In this case, the first electrode 2 does not make ohmic contact with the photoelectric conversion layer 3. Furthermore, blocking properties for holes from the photoelectric conversion layer 3 refer to the property of allowing only electrons generated in the photoelectric conversion layer 3 to pass through, while preventing holes from passing through. The Fermi energy of a material having such properties is higher than the energy level at the top of the valence band of the photoelectric conversion layer 3. The Fermi energy of a material having such properties may also be higher than the Fermi energy of the photoelectric conversion layer 3. Aluminum is a specific example of such a material. Note that aluminum is not translucent. Therefore, when forming a translucent electrode using aluminum, for example, an electrode with the pattern shape described above is used.

[0041] If the solar cell includes an electron transport layer 7 between the first electrode 2 and the photoelectric conversion layer 3, the first electrode 2 does not need to have blocking properties for holes from the photoelectric conversion layer 3. In this case, the first electrode 2 may be made of a material capable of forming ohmic contact with the photoelectric conversion layer 3. In this case, the first electrode 2 may or may not be in ohmic contact with the photoelectric conversion layer 3.

[0042] The light transmittance of the first electrode 2 may be, for example, 50% or more, or 80% or more. The wavelength of light that the first electrode 2 should transmit depends on the absorption wavelength of the photoelectric conversion layer 3. Furthermore, when the first electrode 2 is used as the light incident cell of a tandem solar cell, the transmittance of light with wavelengths of 700 or more and 1100 nm may be 50% or more, or 80% or more, so that light outside the wavelength range absorbed by the photoelectric conversion layer 3 can reach the lower cell of the tandem solar cell located below through the first electrode 2.

[0043] The first electrode 2 may have a thickness of, for example, 1 nm or more and 1000 nm or less.

[0044] (electron transport layer 7) The electron transport layer 7 contains a semiconductor. Preferably, the electron transport layer 7 is formed from a semiconductor with a band gap of 3.0 eV or greater. This allows visible light and infrared light to be transmitted to the photoelectric conversion layer 3. Examples of semiconductors include organic n-type semiconductors or inorganic n-type semiconductors.

[0045] Examples of organic n-type semiconductors are imide compounds, quinone compounds, fullerenes, or fullerene derivatives. Examples of inorganic n-type semiconductors are metal oxides or perovskite oxides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, or Cr. Examples of metal oxides are TiO2 or SnO2. Examples of perovskite oxides are SrTiO3 or CaTiO3.

[0046] The electron transport layer 7 may contain material with a band gap larger than 6 eV. Examples of material with a band gap larger than 6 eV include: (i) Halides of alkali metals or alkaline earth metals such as lithium fluoride and calcium fluoride, (ii) an oxide of an alkaline earth metal such as magnesium oxide, or (iii) Silicon dioxide, In this case, the electron transport layer 7 may have a thickness of, for example, 10 nm or less in order to ensure electron transport.

[0047] The electron transport layer 7 may include multiple layers made of different materials.

[0048] (Porous layer 8) The porous layer 8 is, for example, positioned between the photoelectric conversion layer 3 and the electron transport layer 7. The porous layer 8 can serve as a base for forming the photoelectric conversion layer 3 on top of the electron transport layer 7. The porous layer 8 does not hinder the light absorption of the photoelectric conversion layer 3 or the electron transfer from the photoelectric conversion layer 3 to the electron transport layer 7.

[0049] The porous layer 8 contains a porous material. The porous material contains voids. The voids contained in the porous layer 8 are connected from the portion in contact with the electron transport layer 7 to the portion in contact with the photoelectric conversion layer 3.

[0050] These vacancies are typically filled with the material constituting the photoelectric conversion layer 3, allowing electrons to move directly from the photoelectric conversion layer 3 to the electron transport layer 7.

[0051] Porous materials are formed, for example, by a series of insulating or semiconductor particles. Examples of insulating particles are aluminum oxide particles or silicon oxide particles. Examples of semiconductor particles are inorganic semiconductor particles. Examples of inorganic semiconductors are metal oxides, perovskite oxides of metallic elements, sulfides of metallic elements, or metal chalcogenides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. An example of a metal oxide is TiO2. An example of a perovskite oxide of a metallic element is SrTiO3 or CaTiO3. Examples of sulfides of metallic elements are CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or CuS2. Examples of metal chalcogenides include CdSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0052] The thickness of the porous layer 8 may be 0.01 μm or more and 10 μm or less, or 0.1 μm or more and 1 μm or less.

[0053] The porous layer 8 may have a high surface roughness. Specifically, the surface roughness coefficient, given by the effective area / projected area ratio, may be 10 or greater, or 100 or greater. The projected area is the area of ​​the shadow cast behind an object when it is illuminated directly from the front. The effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume obtained from the projected area and thickness of the object, and from the specific surface area and bulk density of the materials constituting the object.

[0054] (Photoelectric conversion layer 3) The photoelectric conversion layer 3 contains a photoelectric conversion material.

[0055] The photoelectric conversion material may be, for example, a perovskite compound. That is, the photoelectric conversion layer 3 may contain a perovskite compound. Perovskite compounds have a high light absorption coefficient in the wavelength range of the solar spectrum and high carrier mobility. Therefore, a solar cell containing a perovskite compound (i.e., a perovskite solar cell) has high photoelectric conversion efficiency.

[0056] Perovskite compounds are represented, for example, by the chemical formula ABX3, where A is a monovalent cation. Examples of cation A are alkali metal cations or organic cations. An example of an alkali metal cation is the methylammonium cation (CH3NH3). + ) or formamidinium cation (NH2CHNH2 + ) is an example of an organic cation, cesium cation (Cs +) is a divalent metal cation. Examples of cation B are Pb cations, Sn cations, or Ge cations. X is a monovalent anion. Examples of anion X are halogen anions. Halogen anions are, for example, iodine or bromine. Each site of cation A, cation B, and anion X may be occupied by multiple types of ions.

[0057] The thickness of the photoelectric conversion layer 3 depends on the magnitude of its light absorption, but for example, it is between 100 nm and 2000 nm.

[0058] The photoelectric conversion layer 3 can be formed using methods such as a solution coating method.

[0059] (Middle class 4) The intermediate layer 4 contains at least one compound selected from the group consisting of bromides and iodides. This compound contains a monovalent organic cation.

[0060] The intermediate layer 4 functions, for example, as a layer that mitigates damage to the hole transport layer 5 when forming the second electrode 6.

[0061] The compound contained in the intermediate layer 4 may contain an ammonium cation. That is, the monovalent organic cation may be an ammonium cation.

[0062] The compound contained in the intermediate layer 4 may contain carbon and have 8 or fewer carbon atoms. If the number of carbon atoms is 8 or fewer, the increase in hydrophobicity can be suppressed, making it easier to uniformly coat the hole transport layer 5 formed on top of it.

[0063] The compound contained in the intermediate layer 4 may contain carbon and have a number of carbon atoms between 4 and 8. By having a number of carbon atoms between 4 and 8 in the compound, the intermediate layer 4 can further mitigate damage to, for example, the hole transport layer 5 when forming the second electrode 6, and can suppress the hydrophobicity of the intermediate layer 4 from becoming too strong.

[0064] The compound contained in the intermediate layer 4 may be represented, for example, by the following formula (1). R-NH3X …(1) Here, in equation (1) above, R is a hydrocarbon group, X is at least one selected from the group consisting of iodine and bromine.

[0065] In formula (1) above, R may be a hydrocarbon group having 8 or fewer carbon atoms. Alternatively, R may be a hydrocarbon group having 4 or more carbon atoms and 8 or fewer carbon atoms.

[0066] In formula (1) above, R may be an alkyl group, a phenyl group, or a phenylalkyl group.

[0067] The above compound may be at least one selected from the group consisting of butylammonium bromide, hexylammonium bromide, octylammonium bromide, phenylethylammonium bromide, and phenylethylammonium iodide.

[0068] From the viewpoint of high affinity for both the photoelectric conversion material (e.g., a perovskite compound) and the hole transport material, the compound may be butylammonium bromide.

[0069] From the viewpoint of high heat resistance, the compound may be phenylethylammonium iodide.

[0070] To avoid inhibiting charge injection, the thickness of the intermediate layer 4 may be 10 nm or less.

[0071] (Hole transport layer 5) The hole transport layer 5 contains a hole transport material. The hole transport material is a material that transports holes.

[0072] The hole transport material may be a triphenylamine derivative.

[0073] Examples of triphenylamine derivatives are poly[bis(4-phenyl)(2,4,6-triphenylmethyl)amine] (hereinafter referred to as "PTAA") or PTAA derivatives. In PTAA derivatives, at least some of the hydrogen atoms or methyl groups of PTAA may be replaced with other functional groups. For example, at least some of the methyl groups of PTAA may be replaced with hydrogen atoms or methoxy groups. Alternatively, at least some of the hydrogen atoms of PTAA may be replaced with methyl groups or methoxy groups.

[0074] The hole transport layer 5 may contain not only a triphenylamine derivative but also other hole transport materials. Examples of hole transport materials include organic or inorganic semiconductors.

[0075] Examples of organic materials used as hole transport materials include Poly(3-hexylthiophene-2,5-diyl) (hereinafter referred to as "P3HT") or poly(3,4-ethylenedioxythiophene) (hereinafter referred to as "PEDOT"). The molecular weight is not particularly limited, but polymers are also acceptable.

[0076] Examples of inorganic semiconductors used as hole transport materials include Cu2O, CuGaO2, CuSCN, CuI, CuPC, and NiO. x1 MoO x2 , V2O5, or a carbon-based material such as graphene oxide. Here, 0 <x1であり、1≦x1≦1.5であってもよい。また、0<x2であり、2≦x2≦3であってもよい。

[0077] The hole transport layer 5 may contain not only the hole transport layer material but also a fluoroboron compound. The fluoroboron compound is added as an additive to increase the hole concentration. The fluoroboron compound has high stability and a suitable redox potential for oxidizing the hole transport material.

[0078] Fluoroboron compounds are, for example, boron compounds having a pentafluorophenyl group. Examples of such compounds include tris(pentafluorophenyl)borane (TPFPB), 4-Isopropyl-4'-methyldiphenyliodoniumtetrakis(pentafluorophenyl)borate, or N,N-Dimethylanilinium Tetrakis(pentafluorophenyl)borate.

[0079] The fluoroborone compound may be TFPPB or a TFPPB derivative.

[0080] The hole transport layer 5 may include multiple layers formed from different materials.

[0081] The thickness of the hole transport layer 5 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 500 nm or less, from the viewpoint of low resistance.

[0082] Examples of methods for forming the hole transport layer 5 include coating or printing. Examples of coating methods include doctor blade method, bar coating method, spray method, dip coating method, or spin coating method. An example of a printing method is screen printing. The hole transport layer 5 may also be formed by pressurizing or firing a film obtained by mixing multiple materials. If the hole transport material is a low-molecular-weight organic or inorganic semiconductor, the hole transport layer 5 may be formed by vacuum deposition.

[0083] The hole transport layer 5 may contain a supporting electrolyte and a solvent. The supporting electrolyte and solvent have the effect of stabilizing the holes in the hole transport layer 5.

[0084] Examples of supporting electrolytes are ammonium salts or alkali metal salts. Examples of ammonium salts are tetrabutylammonium perchlorate, tetraethylammonium hexafluoride phosphate, imidazolium salts, or pyridinium salts. Examples of alkali metal salts are lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and LiN(SO2C). n F 2n+1 )2, LiPF6, LiBF4, lithium perchlorate, or potassium borotetrafluoride.

[0085] The solvent contained in the hole transport layer 5 may have high ionic conductivity. This solvent may be either an aqueous solvent or an organic solvent. From the viewpoint of solute stabilization, this solvent may be an organic solvent. Examples of organic solvents are heterocyclic compounds such as tert-butylpyridine (hereinafter referred to as "tBP"), pyridine, or n-methylpyrrolidone.

[0086] Ionic liquids may be used as solvents, either alone or in mixture with other solvents. Ionic liquids have low volatility and high flame retardancy.

[0087] Examples of ionic liquids include imidazolium compounds such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine compounds, alicyclic amine compounds, aliphatic amine compounds, or azonium amine compounds.

[0088] (2nd electrode 6) Since the solar cell of this disclosure has a hole transport layer 5, the second electrode 6 does not need to block electrons from the photoelectric conversion layer 3. That is, the material constituting the second electrode 6 may be a material that makes ohmic contact with the photoelectric conversion layer 3.

[0089] The second electrode 6 is conductive and translucent. The second electrode 6 contains an oxide. For example, the second electrode 6 may be composed of an oxide that is transparent and conductive. Examples of such oxides are indium-tin composite oxide, indium-zinc composite oxide, or indium-tungsten composite oxide. Thus, the second electrode 6 may contain a conductive oxide with indium oxide as the matrix. From the viewpoint of film quality stability, the second electrode 6 may contain an indium-zinc composite oxide.

[0090] An example of a method for forming the second electrode 6 is vapor phase growth. Examples of vapor phase growth methods include Chemical Vapor Deposition (CVD) or sputtering. [Examples]

[0091] The present disclosure will be described in more detail below with reference to examples.

[0092] <Example 1> The components of the solar cell according to Example 1 are as follows:

[0093] Substrate: Glass substrate (thickness: 0.7mm) Electrode 1: Indium-tin composite oxide (indium-doped SnO2 layer, surface resistance 10Ω / sq., manufactured by Geomatec) Electron transport layer: TiO2 (thickness: 20nm, manufactured by Geomatec) Porous layer: TiO2 Photoelectric conversion layer: A layer mainly containing the perovskite compound CH(NH2)2PbI3 (thickness: approximately 500 nm) Intermediate layer: Butylammonium bromide (C4H9NH3Br) (manufactured by Tokyo Chemical Industry Co., Ltd.) Hole transport layer: PTAA (Aldrich) (contains TFPPB (Tokyo Chemical Industries) as an additive) (thickness: approximately 50 nm) Second electrode: Indium-zinc composite oxide (IZO: 10wt% ZnO-doped In2O3) or indium-tin composite oxide (ITO: 10wt% SnO2-doped In2O3) (thickness 100nm)

[0094] The solar cell according to Example 1 was fabricated as follows.

[0095] A 0.7 mm thick conductive glass substrate (manufactured by Geomatec), with an indium-tin composite oxide layer (indium-doped SnO2 layer) and a TiO2 layer formed on it, was used as the substrate, first electrode, and electron transport layer. A solution of 150 mg of titanium oxide nanoparticle paste (NR-D30, manufactured by Greatcell Solar) diluted with 1 mL of ethanol was applied to the TiO2 layer by spin coating, and then fired at 500°C for 30 minutes. In this way, a porous layer was formed.

[0096] Next, a solution containing PbI2 (0.92 M, manufactured by Tokyo Chemical Industry Co., Ltd.), PbBr2 (0.17 M, manufactured by Tokyo Chemical Industry Co., Ltd.), FAI (0.83 M, manufactured by Greatcell Solar Co., Ltd.), MABr (0.17 M, manufactured by Greatcell Solar Co., Ltd.), CsI (0.05 M, manufactured by Iwatani Corporation Co., Ltd.), and RbI (0.05 M, manufactured by Iwatani Corporation Co., Ltd.) was prepared. The solvent of this solution was a mixture of dimethyl sulfoxide (DMSO, manufactured by Acros Organics) and N,N-dimethylformamide (DMF, manufactured by Acros Organics). The mixing ratio of DMSO and DMF in this solution was 1:4 by volume. This solution was spin-coated onto a porous layer and annealed on a hot plate at 100°C for 45 minutes. In this way, a photoelectric conversion layer was formed.

[0097] Next, a solution containing 1 mg of butylammonium bromide (BABr) (manufactured by Tokyo Chemical Industry Co., Ltd.) and 1 mL of isopropanol (IPA) (manufactured by Acros Organics) was prepared. This solution was spin-coated onto the photoelectric conversion layer. In this way, an intermediate layer was formed.

[0098] Next, 1 mL of a toluene (Acros Organics) solution containing 10 mg of PTAA and 1.8 mg of TPFPB was prepared. This solution was spin-coated onto the intermediate layer. In this way, a hole transport layer was formed.

[0099] Finally, on top of the hole transport layer, using a 10%wt ZnO-doped In2O3 target, back pressure: 2.8×10 -4 Pa, substrate-target distance: 100 mm, substrate temperature: room temperature, power: 20 W, pressure: 1.0 Pa, oxygen concentration: 0.4%, an IZO layer with a thickness of 100 nm was deposited by sputtering. In this way, the second electrode was formed.

[0100] As described above, the solar cell according to Example 1 was obtained. Among the above-described steps, except for the step of forming the second electrode, it was carried out in a dry room under a dry atmosphere having a dew point of -40°C or lower.

[0101] <Example 2> Instead of BABr contained in the solution for forming the intermediate layer, hexylammonium bromide (HABr) (C6H 13 NH3Br) (manufactured by Greatcell Solar) was used, and in the same manner as in Example 1, the solar cell according to Example 2 was obtained.

[0102] <Example 3> Instead of BABr contained in the solution for forming the intermediate layer, octylammonium bromide (OABr) (C8H 17 NH3Br) (manufactured by Greatcell Solar) was used, and in the same manner as in Example 1, the solar cell according to Example 3 was obtained.

[0103] <Example 4> Instead of BABr contained in the solution for forming the intermediate layer, phenylethylammonium bromide (PEABr) (C8H9NH3Br) (manufactured by Tokyo Chemical Industry) was used, and in the same manner as in Example 1, the solar cell according to Example 4 was obtained.

[0104] <Example 5> Instead of BABr contained in the solution for forming the intermediate layer, phenylethylammonium iodide (PEAI) (C8H9NH3I) (manufactured by Tokyo Chemical Industry) was used, and in the same manner as in Example 1, the solar cell according to Example 5 was obtained.

[0105] <Comparative Example 1> A solar cell according to Comparative Example 1 was obtained in the same manner as in Example 1, except that an intermediate layer was not formed.

[0106] <Comparative Example 2> A solar cell according to Comparative Example 2 was obtained in the same manner as in Example 1, except that phenylethylammonium iodide (PEAI) (C8H9NH3I) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of BABr in the solution for forming the intermediate layer, and gold was formed as the second electrode by vacuum deposition.

[0107] <Comparative Example 3> A solar cell according to Comparative Example 3 was obtained in the same manner as in Example 1, except that an intermediate layer was not formed and gold was formed as the second electrode by vacuum deposition.

[0108] <Example 6> As a mixed solution for forming the hole transport layer, 1 mL of toluene (Acros Organics) solution containing 10 mg of PTAA, 6 μL of tBP, and 4.8 μL of acetonitrile solution in which LiTFSI was dissolved at a concentration of 1.8 M were mixed. The solar cell according to Example 6 was obtained in the same manner as in Example 1, except that the hole transport layer was formed by spin-coating this mixed solution onto the intermediate layer.

[0109] <Comparative Example 4> A solar cell according to Comparative Example 4 was obtained in the same manner as in Example 6, except that an intermediate layer was not formed.

[0110] <Example 7> A solar cell according to Example 7 was obtained in the same manner as in Example 6, except that ITO (10wt%SnO2-doped In2O3) was used as the second electrode instead of IZO (10wt%ZnO-doped In2O3).

[0111] <Example 8> A solar cell according to Example 8 was obtained in the same manner as in Example 7, except that phenylethylammonium iodide (PEAI) (C8H9NH3I) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of BABr in the solution for forming the intermediate layer.

[0112] <Comparative Example 5> A solar cell according to Comparative Example 5 was obtained in the same manner as in Example 7, except that an intermediate layer was not formed.

[0113] [Evaluation of Solar Cell Characteristics] The characteristics of the solar cells in Examples 1 to 8 and Comparative Examples 1 to 5 were measured using a solar simulator (ALS440B, manufactured by BAS) at 100 mW / cm². 2 The output was set to a specific value and evaluated under simulated sunlight. The output current value relative to the applied voltage was varied from 1.2V to 0V and recorded, and the conversion efficiency was calculated. Table 1 shows the initial efficiency of the solar cells for Examples 1 to 5 and Comparative Examples 1 to 3. Table 2 shows the initial efficiency of the solar cells for Example 6 and Comparative Example 4. Table 3 shows the initial efficiency of the solar cells for Examples 7 to 8 and Comparative Example 5.

[0114] [Maintenance rate of photoelectric conversion efficiency] Thermal endurance tests were conducted on the solar cells according to Examples 1 to 5 and Comparative Example 1.

[0115] The target solar cell was stored in a constant temperature chamber at 85°C for 100 hours. After being removed from the chamber after 100 hours, it was subjected to a solar simulator test at 100 mW / cm². 2 The output was set to a specific value, and the characteristics of the solar cell were evaluated under simulated sunlight. The output current value relative to the applied voltage was varied from 1.2V to 0V and recorded, and the conversion efficiency was calculated. The rate of change of photoelectric conversion efficiency was calculated as (initial photoelectric conversion efficiency at 0 hours - photoelectric conversion efficiency after 100 hours of storage at 85°C) / initial photoelectric conversion efficiency at 0 hours. The retention rates of the photoelectric conversion efficiency of the solar cells in Examples 1 to 5 and Comparative Example 1 are shown in Table 1.

[0116] [Table 1]

[0117] [Table 2] [Table 3]

[0118] (Consideration) As shown in Table 1, the solar cells according to Examples 1 to 5, which had an intermediate layer containing at least one compound selected from the group consisting of iodide and bromide, showed higher conversion efficiency than the solar cell according to Comparative Example 1, which did not have the intermediate layer 4.

[0119] As is clear from comparing Example 5 and Comparative Example 2 with Comparative Examples 1 and 3, respectively, it was confirmed that providing an intermediate layer has a significant effect on improving efficiency when using IZO, an oxide, as the second electrode.

[0120] In the examples, when the intermediate layer contained BABr, high conversion efficiency was demonstrated. When the intermediate layer contained PEAI, a high efficiency retention rate was demonstrated during high-temperature storage.

[0121] As is evident when comparing Example 6 with Comparative Example 4, as shown in Table 2, a similar effect was observed even in systems where the hole transport layer included a supporting electrolyte and a solvent. As shown in Table 3, and as is clear from comparing Examples 7 to 8 with Comparative Example 5, the effect of efficiency improvement due to the intermediate layer was confirmed even when ITO, an oxide, was used as the second electrode. [Industrial applicability]

[0122] The solar cell disclosed herein can be used in a variety of applications, including those of conventional solar cells. [Explanation of Symbols]

[0123] 1 circuit board 2 1st electrode 3. Photoelectric conversion layer 4. Middle Class 5. Hole transport layer 6 Second electrode 7 Electron transport layer 8. Porous layer 100, 200, 300 solar cells

Claims

1. The device comprises a first electrode, a photoelectric conversion layer, an intermediate layer, a hole transport layer, and a second electrode, in this order. The second electrode contains an oxide, The aforementioned oxide includes an indium-zinc composite oxide. The intermediate layer comprises at least one compound selected from the group consisting of phenylethylammonium iodide and butylammonium bromide. The photoelectric conversion layer comprises a perovskite compound, Solar cell.

2. The compound contained in the intermediate layer includes butylammonium bromide. The solar cell according to claim 1.

3. The compound contained in the intermediate layer includes phenylethylammonium iodide. The solar cell according to claim 1.

4. The hole transport layer comprises a hole transport material, The hole transport material comprises poly[bis(4-phenyl)(2,4,6-triphenylmethyl)amine], A solar cell according to any one of claims 1 to 3.

5. The second electrode is in contact with the hole transport layer. A solar cell according to any one of claims 1 to 4.

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