solar cells

Abstract

This solar cell 100 comprises a first electrode 2, an intermediate layer 8, a photoelectric conversion layer 3, and a second electrode 4, in that order, wherein the intermediate layer 8 includes at least one compound A selected from a predetermined compound group I and at least one compound B selected from a predetermined compound group II.

Description

[Technical Field]

[0001] The present disclosure relates to solar cells. [Background technology]

[0002] In recent years, research and development has been progressing on perovskite solar cells, which use perovskite-type crystals represented by the composition formula ABX3 (A is a monovalent cation, B is a divalent cation, and X is a halogen anion) and similar structures (hereinafter referred to as "perovskite compounds") as photoelectric conversion materials. Various efforts are being made to improve the photoelectric conversion efficiency, light durability, and heat durability of perovskite solar cells.

[0003] Non-Patent Document 1 describes a method for adding fullerene (C) to the interface between the electron transport layer (hereinafter also referred to as "ETL") and the photoelectric conversion layer of a perovskite solar cell. 60 ), a self-assembled monolayer (hereinafter also referred to as "C60SAM") with 4-(1',5'-Dihydro-1'-methyl-2'H-[5,6]fullereno-C 60 They disclose that by disposing C60SAM (C60-Ih-[1,9-c]pyrrol-2'-yl)benzoic acid (hereinafter also referred to as "SAM[1]"), electron extraction is improved and photoelectric conversion efficiency is increased. Here, the oxygen of the carboxyl group of C60SAM faces the ETL side and acts as an anchor, while the C60SAM faces the photoelectric conversion layer side. 60 It has been suggested that they self-assemble in an array oriented toward the center.

[0004] Non-Patent Document 2 discloses that the light durability is improved by disposing the C60SAM described in Non-Patent Document 1 at the interface between the ETL and the photoelectric conversion layer of a perovskite solar cell.

[0005] Non-Patent Document 3 discloses that the oxygen of the carboxyl group of isonicotinic acid faces the titanium oxide (ie, TiO2) side and acts as an anchor, adsorbing to the titanium oxide and modifying the surface.

[0006] Non-patent document 4 states that C6H 12 From C 18 H 36 C60SAM with a long alkyl chain (hereinafter referred to as "long-chain C60SAM") and C 60 C6H without 12 From C 18 H 36 It is disclosed that by mixing a self-assembled monolayer having a long alkyl chain (hereinafter also referred to as "long-chain SAM") with a C60 SAM, the curvature of the long-chain C60 SAM can be suppressed and its orientation can be improved.

[0007] Non-Patent Document 5 discloses a group of C60SAMs that have a size similar to that of the C60SAMs described in Non-Patent Document 1 and have a carboxyl group, a catechol group, or a phosphoryl group as an anchor.

[0008] Non-Patent Document 6 describes a method for suppressing the photodegradation reaction of perovskite solar cells by suppressing the cathode reaction (Pb 2+ +2e - →Pb 0 This suggests that suppressing [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Konrad Wojciechowski and 10 others, ACS Nano, November 2014, Vol. 8, pp. 12701-12709. [Non-patent document 2] Meiyue Liu, 4 others, Materials Chemistry Frontiers, January 2019, Volume 3, p.496-504. [Non-patent document 3] J. Schnadt, et al., Physical Review B, June 2003, Volume 67, p.235420. [Non-patent document 4] Artoem Khassanov, et al., Accounts of chemical research, June 2015, Volume 48, p.1901-1908. [Non-Patent Document 5] Steven K. Hau, et al., ACS Applied Materials & Interfaces, June 2010, Volume 2, p.1892-1902. [Non-patent document 6] Takeyuki Sekimoto and 5 others, ACS Applied Energy Materials, June 2019, Vol. 2, pp. 5039-5049. [Non-Patent Document 7] Mojtaba Abdi-Jalebi, et al., Science Advances, February 2019, Volume 5, p.eaav2012. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present disclosure is to provide a solar cell having high photoelectric conversion efficiency. [Means for solving the problem]

[0011] The solar cell of the present disclosure comprises: a first electrode, an intermediate layer, a photoelectric conversion layer, and a second electrode, in this order; The intermediate layer contains at least one compound A selected from compound group I consisting of the following formulas (1) to (4) and at least one compound B selected from compound group II consisting of the following formulas (5) and (6). (Compound group I) [ka] Here, in the above formulas (1) to (4), X 1 is a fullerene or a fullerene derivative, X 2is a pyrroline ring, a pyrrole ring, a pyrrolidine ring, a cyclohexane ring, or a cyclohexene ring, X 3 is a cyclohexadiene ring. (Compound group II) [ka] Here, in the above formulas (5) and (6), X 4 is a heterocycle containing a heteroatom having one or more lone pairs of electrons and having a size of 900 pm or less, in which at least a portion of the hydrogen atoms may be substituted with halogen atoms. [Effects of the Invention]

[0012] The present disclosure provides a solar cell with high photoelectric conversion efficiency. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a state in which the surface of an electron transport layer is modified with SAM[1], which is an example of a C60SAM. [Figure 2] FIG. 2 is a schematic diagram showing an example of a state in which the surface of an electron transport layer is modified with SAM[1], which is an example of a C60SAM, and isonicotinic acid, which is an example of a gap-modifying SAM. [Figure 3] Figure 3 shows an example of a mass spectrum obtained by time-of-flight secondary ion mass spectrometry (i.e., TOF-SIMS) analysis of the surface of an intermediate layer covering the surface of an electron transport layer when the intermediate layer consists of SAM[1] or SAM[1] and isonicotinic acid. [Figure 4] Figure 4 shows an example of a mass spectrum obtained by TOF-SIMS analysis of the surface of an intermediate layer covering the surface of an electron transport layer when the intermediate layer consists of SAM[1] or SAM[1] and isonicotinic acid. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a first example of a solar cell according to an embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a second example of a solar cell according to an embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a third example of a solar cell according to an embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing a fourth example of a solar cell according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Knowledge that forms the basis of this disclosure> C60SAM is a C 60 The carbon nanotube is composed of a carbon nanotube (C60) SAM (size: 0.7 nm) and a chain portion (size: about 1 nm) containing a carboxyl group or the like. Figure 1 is a schematic diagram showing an example of a state in which SAM[1], an example of a C60 SAM, modifies the surface of an electron transport layer. As shown in Figure 1, SAM[1] 1A has the oxygen of the carboxyl group, which serves as an anchor, facing the electron transport layer 1B side, and the C60 SAM faces the photoelectric conversion layer side. 60 The improvement in photoelectric conversion efficiency by introducing C60SAM in Non-Patent Document 1 is due to the defect termination at the interface between the electron transport layer and the photoelectric conversion layer caused by the modification of the surface of the electron transport layer by C60SAM, and the formation of highly conductive C 60 The improvement in light durability due to the introduction of C60SAM in Non-Patent Document 2 can be interpreted as the suppression of degradation due to the cathodic reaction at the interface between the electron transport layer and the photoelectric conversion layer, as pointed out in Non-Patent Document 6, due to the improved extraction efficiency of high-energy photoexcited electrons by the introduction of C60SAM.

[0015] Thus, the introduction of C60 SAM at the interface between the electron transport layer and the photoelectric conversion layer can improve light durability. 60Because of the large size of the C60SAM, steric hindrance causes unmodified gaps on the surface of the electron transport layer when the surface of the electron transport layer is terminated. As a result, the electron transport layer and the photoelectric conversion layer come into direct contact with each other, leaving areas with many interface defects and poor electron extraction, which hinders the full effectiveness of the C60SAM. This problem remains even when the C60SAM group described in Non-Patent Document 5 is used.

[0016] The long-chain C60 SAM described in Non-Patent Document 4 has poor conductivity in the long alkyl chain portion, which results in the problem of resistive loss. Even if the orientation is improved by introducing a long-chain SAM, the resistive loss is not improved because the long-chain SAM itself has a long alkyl chain.

[0017] As described in Non-Patent Document 3, when only isonicotinic acid, a small-sized (<1 nm) SAM, is introduced at the interface between the electron transport layer and the photoelectric conversion layer, surface defects in the electron transport layer can be terminated without steric hindrance. However, the negatively charged nitrogen atoms in the pyridine ring of isonicotinic acid repel electrons, reducing the electron collection ability and resulting in a decrease in photoelectric conversion efficiency. Furthermore, as the electron extraction efficiency deteriorates, high-energy photoexcited electrons accumulate at the interface between the electron transport layer and the photoelectric conversion layer under light irradiation, promoting the cathode reaction at the interface. Therefore, light durability is also expected to decrease.

[0018] In view of these considerations, the present inventors have conducted extensive research and have found the following. Figure 2 is a schematic diagram showing an example of a state in which the surface of an electron transport layer is modified with SAM[1], an example of a C60SAM, and isonicotinic acid, an example of a gap-modifying SAM. As shown in Figure 2, it has been found that by arranging SAM[1] 2A and isonicotinic acid 2C as a SAM that modifies the gap (i.e., gap-modifying SAM), it is possible to reduce interfacial defects caused by contact between the electron transport layer 2B and the photoelectric conversion layer (not shown). Furthermore, isonicotinic acid 2C repels electrons, thereby reducing the C in SAM[1] 2A. 60It has been found that increasing electron collection into the C60 SAM can further improve photoelectric conversion efficiency while suppressing photodegradation. In this disclosure, the term "interstitial-modified SAM" refers to a self-assembled monolayer that includes a heterocyclic compound that can enter the interstices of adjacent C60 SAMs, and the heterocyclic compound has a heterocycle that includes an element with one or more lone electron pairs.

[0019] <Summary of one aspect of the present disclosure> The solar cell according to the first aspect of the present disclosure comprises: a first electrode, an intermediate layer, a photoelectric conversion layer, and a second electrode, in this order; The intermediate layer contains at least one compound A selected from compound group I consisting of the following formulas (1) to (4) and at least one compound B selected from compound group II consisting of the following formulas (5) and (6). (Compound group I) [ka] Here, in the above formulas (1) to (4), X 1 is a fullerene or a fullerene derivative, X 2 is a pyrroline ring, a pyrrole ring, a pyrrolidine ring, a cyclohexane ring, or a cyclohexene ring, X 3 is a cyclohexadiene ring. (Compound group II) [ka] Here, in the above formulas (5) and (6), X 4 is a heterocycle containing a heteroatom having one or more lone pairs of electrons and having a size of 900 pm or less, in which at least a portion of the hydrogen atoms may be substituted with halogen atoms.

[0020] In the solar cell according to the first embodiment, the interfacial recombination caused by the direct contact between the first electrode and the photoelectric conversion layer can be suppressed. In addition, the element having a lone pair in the heterocycle of compound B is negatively charged and effectively repels electrons moving from the photoelectric conversion layer, so that X of compound A 1 Therefore, in the solar cell according to the first aspect, it is possible to improve the photoelectric conversion efficiency while suppressing the photodegradation phenomenon.

[0021] In a second aspect of the present disclosure, for example, the solar cell according to the first aspect may further include an electron transport layer, and the electron transport layer may be disposed between the first electrode and the intermediate layer.

[0022] The solar cell according to the second embodiment further comprises an electron transport layer, thereby allowing electrons to be efficiently transferred to the first electrode. Therefore, the solar cell according to the second embodiment allows current to be efficiently extracted. Furthermore, since an intermediate layer is disposed between the electron transport layer and the photoelectric conversion layer, interface recombination due to direct contact between the electron transport layer and the photoelectric conversion layer is also suppressed. The element having a lone electron pair in the heterocycle of compound B is negatively charged and effectively repels electrons moving from the photoelectric conversion layer, so that X of compound A 1 Therefore, according to the second aspect, it is possible to further improve the photoelectric conversion efficiency while suppressing the photodegradation phenomenon.

[0023] In a third aspect of the present disclosure, for example, in the solar cell according to the first or second aspect, the compound A may be at least one selected from the compounds represented by the following formulas (7) to (11), and the compound B may be at least one selected from the group consisting of isonicotinic acid, nicotinic acid, and picolinic acid. [ka] [ka] [ka] [ka] [ka]

[0024] According to the third aspect, it is possible to further improve the photoelectric conversion efficiency while suppressing the photodegradation phenomenon.

[0025] In the fourth aspect of the present disclosure, for example, in the solar cell according to the third aspect, the compound A may be a compound represented by the above formula (7).

[0026] According to the fourth aspect, it is possible to further improve the photoelectric conversion efficiency while suppressing the photodegradation phenomenon.

[0027] In a fifth aspect of the present disclosure, for example, in the solar cell according to any one of the first to fourth aspects, the photoelectric conversion layer may contain a perovskite compound.

[0028] Perovskite compounds have a high light absorption coefficient in the wavelength region of the solar light spectrum and high carrier mobility, so the solar cell according to the fifth aspect can be expected to have high photoelectric conversion efficiency.

[0029] In a sixth aspect of the present disclosure, for example, in the solar cell according to the second aspect, the electron transport layer may contain titanium oxide or tin oxide.

[0030] The energy levels of the conduction band minimums of titanium oxide and tin oxide and the LUMO level of compound A are close to the energy level of the conduction band minimum of perovskite compounds. Therefore, compound A does not interfere with electron transport from the photoelectric conversion layer to the electron transport layer. Here, the energy levels of the conduction band minimums of titanium oxide and tin oxide are, for example, 4.0 eV to 4.2 eV. The LUMO level of C60SAM, an example of compound A, is, for example, 3.9 eV. The energy levels of the conduction band minimums of perovskite compounds are, for example, 3.9 eV to 4.1 eV. Furthermore, the band gaps of TiO2 are 3.0 eV to 3.2 eV, and the band gaps of SnO2 are 3.8 eV to 4.2 eV, which are wider than the band gaps of common perovskite compounds, 1.3 eV to 1.7 eV. Therefore, by including titanium oxide or tin oxide in the electron transport layer, light absorption loss by the electron transport layer is reduced. On the other hand, since the intermediate layer has a thickness of about a monomolecular, the light absorption loss due to the intermediate layer is extremely small, and therefore the solar cell according to the sixth embodiment can be expected to have high photoelectric conversion efficiency.

[0031] <Embodiment> The solar cell of the present disclosure comprises: a first electrode, an intermediate layer, a photoelectric conversion layer, and a second electrode, in this order; The intermediate layer contains at least one compound A selected from compound group I consisting of the above formulas (1) to (4) and at least one compound B selected from compound group II consisting of the above formulas (5) and (6).

[0032] In the above formulas (1) to (4), X 1 is a fullerene or a fullerene derivative, and X 2 is a pyrroline ring, a pyrrole ring, a pyrrolidine ring, a cyclohexane ring, or a cyclohexene ring, and X 3 is a cyclohexadiene ring.

[0033] In the above formulas (5) and (6), X 4is a heterocycle containing a heteroatom having one or more lone pairs of electrons and having a size of 900 pm or less, in which at least a portion of the hydrogen atoms may be substituted with halogen atoms.

[0034] Heteroatoms with one or more lone pairs of electrons represent nitrogen, oxygen, and sulfur.

[0035] The size of a heterocycle means the sum of the distance between the two most distant atoms among the atoms constituting the heterocycle and the atomic radii of the two atoms.

[0036] The size of the heterocycle can be measured, for example, by X-ray diffraction, neutron diffraction, electron diffraction, or crystalline sponge method.

[0037] In the above formulas (5) and (6), X 4 may be a heterocycle having a size of 795 pm or less.

[0038] In the above formulas (5) and (6), X 4 The heterocycle represented by the formula (I) may be a pyridine ring, a pyran ring, a furan ring, an oxetane ring, an oxazole ring, an isoxazole ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a tetrazine ring, a triazole ring, a thiophene ring, a thiazole ring, a dioxane ring, a pyrazole ring, an imidazole ring, a phosphinine ring, an oxirane ring, a thiirane ring, a thietane ring, an imidasoline ring, a dioxolane ring, a tetrahydrofuran ring, a tetrahydrothiophene ring, a morpholine ring, a diazine ring, a quinuclidine ring, or an azaadamantane ring. According to the above-described configuration, photodegradation can be suppressed while further improving photoelectric conversion efficiency.

[0039] The solar cell of the present disclosure may further include an electron transport layer, which may be disposed between the first electrode and the intermediate layer.

[0040] The TOF-SIMS intensity ratio R1 is defined as the ratio of the sum of the secondary ion intensities of the peaks (m / z = 78, 79, 94, 122, and 123) derived from isonicotinic acid, nicotinic acid, or picolinic acid to the sum of the secondary ion intensities of the peaks (m / z = 720 and 897.1) derived from SAM[1] in a mass spectrum obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS measurements are obtained, for example, using the following apparatus and measurement conditions. TOF-SIMS equipment: TOF.SIMS5 (manufactured by ION-TOF) Primary ion: Bi3 + Primary ion acceleration voltage: 30 kV Detected secondary ion polarity: Negative ·Analysis area: 200μm×200μm

[0041] TOF-SIMS measurements are performed on a portion where the intermediate layer is exposed, where no layers subsequent to the photoelectric conversion layer are formed, or on a portion where the intermediate layer is exposed by dissolving and removing the photoelectric conversion layer in a DMSO / DMF mixed solution with a volume ratio of DMSO:DMF = 4:1.

[0042] Figure 3 shows an example of a mass spectrum obtained by time-of-flight secondary ion mass spectrometry (i.e., TOF-SIMS) analysis of the surface of an intermediate layer coating the surface of an electron transport layer when the intermediate layer is composed of SAM[1] or SAM[1] and isonicotinic acid. Figure 4 shows an example of a mass spectrum obtained by TOF-SIMS analysis of the surface of an intermediate layer coating the surface of an electron transport layer when the intermediate layer is composed of SAM[1] or SAM[1] and isonicotinic acid.

[0043] There is a positive correlation between the TOF-SIMS intensity ratio R1 and the charge concentration ratio of isonicotinic acid, nicotinic acid, and picolinic acid. Therefore, the TOF-SIMS intensity ratio R1 essentially represents the relative amount of compound B, which is at least one selected from the group consisting of isonicotinic acid, nicotinic acid, and picolinic acid, relative to compound A, which is SAM[1]. The charge concentration ratio of isonicotinic acid, nicotinic acid, and picolinic acid is calculated using the formula: a × c2 / c1, where a is the concentration of the saturated solution of C60SAM, c1 is the molar concentration of SAM[1], and c2 is the molar concentration of isonicotinic acid, nicotinic acid, and picolinic acid.

[0044] Fullerenes, for example, are common C 60 In addition to fullerenes, polymeric fullerenes consisting of 70 or more carbon atoms and endohedral fullerenes, which contain atoms or molecules within the hollow skeleton of fullerenes, may also be used. Fullerene derivatives are compounds in which new chemical species are introduced into fullerenes by chemical modification such as addition reactions. Fullerene derivatives include, for example, Phenyl-C 61 -Butyric-Acid-Methyl-Ester(PCBM), Indene-C 60 -Monoadduct, Indene-C 60 -Bisadduct, N-Methylfulleropyrrolidine, N-2-Diphenyl

[60] fulleropyrrolidine, or N-Phenyl-2-hexyl

[60] fulleropyrrolidine.

[0045] Compound A may be at least one selected from the compounds represented by the above formulas (7) to (11), and compound B may be at least one selected from the group consisting of isonicotinic acid, nicotinic acid, and picolinic acid. Isonicotinic acid, nicotinic acid, and picolinic acid are represented by the following formulas (12) to (14). [ka] [ka] [ka]

[0046] Compound A may be a compound represented by the above formula (7).

[0047] Hereinafter, regarding the solar cell according to the embodiment of the present disclosure, as an example, the compound A is X in the above formulas (1) to (4). 1 Fullerene C 60 Here, four structural examples (examples 1 to 4) of solar cells and their manufacturing methods will be described in detail with reference to the drawings. Hereinafter, compound A will be referred to as C60SAM, and compound B will be referred to as gap-modified SAM.

[0048] FIG. 5 is a schematic cross-sectional view showing a first example of a solar cell according to an embodiment.

[0049] The solar cell 100 shown in Figure 5 includes, in this order, a substrate 1, a first electrode 2, an electron transport layer 5, an intermediate layer 8, a photoelectric conversion layer 3, and a second electrode 4. The intermediate layer 8 contains a C60 SAM and a gap-modified SAM. The solar cell 100 does not necessarily have to include the substrate 1. The solar cell 100 does not necessarily have to include the electron transport layer 5.

[0050] When the solar cell 100 is irradiated with light, the photoelectric conversion layer 3 absorbs the light and generates excited electrons and holes. These excited electrons pass through the intermediate layer 8 and the electron transport layer 5 to the first electrode 2. Meanwhile, the holes generated in the photoelectric conversion layer 3 pass through the second electrode 4. This allows the solar cell 100 to extract current from the first electrode 2, which acts as a negative electrode, and the second electrode 4, which acts as a positive electrode. If there is a portion on the surface of the electron transport layer 5 that is not modified with the C60 SAM and gap-modifying SAM contained in the intermediate layer 8, the excited electrons may pass directly through the electron transport layer 5 to the first electrode 2.

[0051] The solar cell 100 can be produced, for example, by the following method.

[0052] First, a first electrode 2 is formed on the surface of the substrate 1 by chemical vapor deposition, sputtering, or the like. Next, an electron transport layer 5 is formed by chemical vapor deposition, sputtering, solution coating, or the like. Next, an intermediate layer 8 is formed by a method described in the embodiment, or the like. Next, a photoelectric conversion layer 3 is formed on the intermediate layer 8. For example, a perovskite compound may be cut to a predetermined thickness to form the photoelectric conversion layer 3, which is then placed on the first electrode 2. Next, a second electrode 4 is formed on the photoelectric conversion layer 3. In this manner, a solar cell 100 can be obtained.

[0053] The solar cell of the present disclosure may include a porous layer 6. Fig. 6 is a schematic cross-sectional view showing a second example of a solar cell according to an embodiment.

[0054] The solar cell 200 shown in FIG. 6 includes a substrate 1, a first electrode 2, an electron transport layer 5, a porous layer 6, an intermediate layer 8, a photoelectric conversion layer 3, and a second electrode 4, in this order. The porous layer 6 includes a porous body. The porous body includes pores. The solar cell 200 does not necessarily have to include the substrate 1. The solar cell 200 does not necessarily have to include the electron transport layer 5.

[0055] The solar cell of the present disclosure may include a hole transport layer 7. Fig. 7 is a schematic cross-sectional view showing a third example of a solar cell according to an embodiment.

[0056] 7 includes, in this order, a substrate 1, a first electrode 2, an electron transport layer 5, an intermediate layer 8, a photoelectric conversion layer 3, a hole transport layer 7, and a second electrode 4. The solar cell 300 does not necessarily have to include the substrate 1. The solar cell 300 does not necessarily have to include the electron transport layer 5.

[0057] When light is irradiated onto the solar cell 300, the photoelectric conversion layer 3 absorbs the light and generates excited electrons and holes. These excited electrons move to the electron transport layer 5 via the intermediate layer 8. Meanwhile, the holes generated in the photoelectric conversion layer 3 move to the hole transport layer 7. The electron transport layer 5 is connected to the first electrode 2, and the hole transport layer 7 is connected to the second electrode 4. This allows the solar cell 300 to extract current from the first electrode 2, which functions as a negative electrode, and the second electrode 4, which functions as a positive electrode.

[0058] FIG. 8 is a schematic cross-sectional view showing a fourth example of a solar cell according to an embodiment.

[0059] 8 includes, in this order, a substrate 1, a first electrode 2, an electron transport layer 5, a porous layer 6, an intermediate layer 8, a photoelectric conversion layer 3, a hole transport layer 7, and a second electrode 4. The solar cell 400 does not necessarily have to include the substrate 1. The solar cell 400 does not necessarily have to include the electron transport layer 5.

[0060] Each component of the solar cell will be specifically described below.

[0061] (Substrate 1) The substrate 1 is an ancillary component. The substrate 1 serves to support each layer of the solar cell. The substrate 1 can be made of a transparent material. For example, a glass substrate or a plastic substrate can be used as the substrate 1. The plastic substrate can be, for example, a plastic film. Furthermore, if the second electrode 4 is translucent, the material of the substrate 1 may be a non-translucent material. For example, the material of the substrate 1 can be metal, ceramic, or a resin material with low translucency. If the first electrode 2 has sufficient strength, the first electrode 2 can support each layer, so the substrate 1 is not necessary.

[0062] (1st electrode 2) The first electrode 2 is conductive. When the solar cell does not include an electron transport layer 5, the first electrode 2 is made of a material that does not form ohmic contact with the photoelectric conversion layer 3. Furthermore, the first electrode 2 has the ability to block holes from the photoelectric conversion layer 3. The ability to block holes from the photoelectric conversion layer 3 means that only electrons generated in the photoelectric conversion layer 3 pass through, while holes are blocked. A material with such a property is a material whose Fermi energy is higher than the energy of the top of the valence band of the photoelectric conversion layer 3. The above material may also have a Fermi energy higher than the Fermi energy of the photoelectric conversion layer 3. A specific example of such a material is aluminum. When the solar cell includes an electron transport layer 5 between the first electrode 2 and the photoelectric conversion layer 3, the first electrode 2 does not necessarily have the ability to block holes migrating from the photoelectric conversion layer 3. The first electrode 2 may be made of a material that can form ohmic contact with the photoelectric conversion layer 3.

[0063] The first electrode 2 is translucent. For example, it transmits light from the visible region to the near-infrared region. The first electrode 2 can be formed using, for example, a transparent and conductive metal oxide and / or metal nitride. Examples of such materials include titanium oxide doped with at least one element selected from the group consisting of lithium, magnesium, niobium, and fluorine; gallium oxide doped with at least one element selected from the group consisting of tin and silicon; gallium nitride doped with at least one element selected from the group consisting of silicon and oxygen; tin oxide doped with at least one element selected from the group consisting of antimony and fluorine; zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium; indium-tin composite oxide; and composites thereof.

[0064] The first electrode 2 can also be formed using a non-transparent material and provided with a light-transmitting pattern. Examples of light-transmitting patterns include linear, wavy, lattice, and punched metal patterns with numerous fine through-holes arranged regularly or irregularly. When the first electrode 2 has such a pattern, light can transmit through areas where no electrode material is present. Examples of non-transparent electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, and alloys containing any of these. Alternatively, a conductive carbon material can also be used.

[0065] The light transmittance of the first electrode 2 may be, for example, 50% or more, or may be 80% or more. The wavelength of light to be transmitted depends on the absorption wavelength of the photoelectric conversion layer 3. The thickness of the first electrode 2 is, for example, in the range of 1 nm to 1000 nm.

[0066] (electron transport layer 5) The electron transport layer 5 includes a semiconductor. The electron transport layer 5 may be a semiconductor having a band gap of 3.0 eV or more. By forming the electron transport layer 5 from a semiconductor having a band gap of 3.0 eV or more, visible light and infrared light can be transmitted to the photoelectric conversion layer 3. Examples of the semiconductor include inorganic n-type semiconductors.

[0067] Examples of inorganic n-type semiconductors that can be used include oxides of metal elements, nitrides of metal elements, and perovskite oxides. Examples of oxides of metal elements that can be used 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. More specific examples include TiO2 and SnO2. Examples of nitrides of metal elements include GaN. Examples of perovskite oxides include SrTiO3 and CaTiO3.

[0068] The electron transport layer 5 may be formed of a substance having a band gap greater than 6.0 eV. Examples of substances having a band gap greater than 6.0 eV include alkali metal or alkaline earth metal halides such as lithium fluoride and calcium fluoride, alkali metal oxides such as magnesium oxide, and silicon dioxide. In this case, to ensure the electron transport properties of the electron transport layer 5, the electron transport layer 5 is configured to have a thickness of, for example, 10 nm or less.

[0069] The electron transport layer 5 may include multiple layers made of different materials.

[0070] (Middle class 8) Intermediate layer 8 comprises a C60 SAM and an interstitial-modified SAM.

[0071] C60SAM is a polymer modifying group, C 60 C 60 The compound is composed of a benzene ring, X, which is more conductive than a long alkyl chain, which has high electrical resistance. 2 , or X 3 It bonds to the anchor COOH, (OH)2, or PO(OH)2 via the 60 The resistive loss when transporting the electrons collected in the C60 SAM to the electron transport layer is reduced. The C60 SAM terminates the electron transport layer 5. If the solar cell does not include the electron transport layer 5, the C60 SAM terminates the first electrode 2.

[0072] As the C60SAM, compound C represented by the following formula (15) 60 Pyrrolidine tris-acid and the compound represented by the following formula (16) (1,2-Methanofullerene C 60 )-61-carboxylic acid is inappropriate. 60 This is because the size of the skeleton excluding the above is small, making it impossible to secure gaps into which the gap-modifying SAM described below can enter, or because an appropriate gap-modifying SAM does not exist, leaving unterminated regions at the interface between the electron transport layer 5 or the first electrode 2 and the photoelectric conversion layer 3. [ka] [ka]

[0073] The COOH and PO(OH)2 of the gap-modifying SAM act as anchors, terminating the electron transport layer 5 via oxygen atoms. Here, the COOH may terminate the electron transport layer 5 as COOH or may become COO and terminate the electron transport layer 5. If the solar cell does not include an electron transport layer 5, the first electrode 2 is terminated.

[0074] The size of the gap-modified SAM is X of C60SAM. 1 This allows it to fit into the gap between adjacent C60SAMs. 1 If the size of the skeleton is larger than the size excluding the carboxyl group, the number of unterminated sites due to steric hindrance may increase.

[0075] The intermediate layer 8 uses the gap-modifying SAM to terminate defects at the interface between the electron transport layer 5 or the first electrode 2 and the photoelectric conversion layer 3, which could not be terminated with only the C60 SAM due to steric hindrance. This suppresses interfacial recombination caused by direct contact between the electron transport layer 5 or the first electrode 2 and the photoelectric conversion layer 3. In addition, the X of the gap-modifying SAM 4 The element having a lone pair of electrons is negatively charged. This effectively repels electrons moving from the photoelectric conversion layer 3, so X of C60SAM 1 Therefore, the intermediate layer 8 further improves the photoelectric conversion efficiency while suppressing the photodegradation phenomenon of the solar cell 100.

[0076] The intermediate layer 8 may contain impurities as long as it contains the C60 SAM and the gap-modifying SAM. The intermediate layer 8 may further contain other compounds different from the C60 SAM and the gap-modifying SAM.

[0077] X 4At least a portion of the hydrogen atoms in X may be substituted with halogen atoms, for example, bromine atoms. 4 The hydrogen atoms in may be unsubstituted.

[0078] When the C60SAM is SAM[1] and the gap-modifying SAM is at least one selected from the group consisting of isonicotinic acid, nicotinic acid, and picolinic acid, the TOF-SIMS intensity ratio R1 of the intermediate layer 8 may be 2.11 or more and 24.5 or less.

[0079] When the TOF-SIMS intensity ratio R1 is 2.11 or more, the defect termination at the interface between the electron transport layer 5 and the photoelectric conversion layer 3 is sufficient. This further improves the photoelectric conversion efficiency. When the TOF-SIMS intensity ratio R1 is 24.5 or less, the C in the SAM [1] 60 This increases the electron collection to the SiO 2 layer, further improving the photoelectric conversion efficiency.

[0080] (Method of manufacturing intermediate layer) An example of a method for manufacturing the intermediate layer 8 will be described below. Here, a dipping method will be described as an example, but the method for manufacturing the intermediate layer 8 is not limited to this.

[0081] First, a C60SAM solution is prepared. The C60SAM solution is obtained by adding C60SAM to an organic solvent. The organic solvent used is a mixture of tetrahydrofuran and ethanol in a volume ratio of 1:1. A saturated C60SAM solution is obtained by passing a supersaturated C60SAM solution through a polytetrafluoroethylene filter (pore size 0.2 μm). A low-concentration C60SAM solution is obtained by diluting a saturated C60SAM solution with a mixture of tetrahydrofuran and ethanol in a volume ratio of 1:1.

[0082] Next, a gap-modifying SAM solution is prepared. The gap-modifying SAM solution is obtained by adding the gap-modifying SAM to an organic solvent. The organic solvent used is a mixed solution of tetrahydrofuran and ethanol in a volume ratio of 1:1. The concentration of the gap-modifying SAM may be 0.01 g / L or more and 1 g / L or less.

[0083] Next, the substrate 1 on which the electron transport layer 5 and the first electrode 2 are formed is immersed in the C60SAM solution for 30 minutes and then removed. The removed substrate 1 is thoroughly rinsed with an ethanol solution and then annealed on a hot plate at 100°C for 30 minutes. After annealing, the substrate is naturally cooled to room temperature to obtain a substrate 1 modified with C60SAM.

[0084] Next, the substrate 1 modified with the C60 SAM is immersed in the gap-modifying SAM solution for 30 minutes and then removed. The removed substrate is thoroughly rinsed with an ethanol solution and then annealed on a hot plate at 100°C for 30 minutes. After annealing, the substrate is naturally cooled to room temperature, yielding a substrate 1 further modified with the gap-modifying SAM. In this way, an intermediate layer 8 is formed.

[0085] The above-described method for producing the intermediate layer 8 is a two-step process in which the substrate 1 on which the electron transport layer 5 and the first electrode 2 are formed is treated with a C60 SAM and then further treated with a gap-modifying SAM, resulting in two SAM treatments. However, it is also possible to form the intermediate layer in a single step in which the SAM treatment is performed once using a mixed solution of a C60 SAM and a gap-modifying SAM whose concentration has been adjusted in advance. That is, the intermediate layer 8 can also be formed by immersing the substrate 1 on which the electron transport layer 5 and the first electrode 2 are formed in a mixed solution of a C60 SAM and a gap-modifying SAM for 30 minutes, removing the substrate, thoroughly rinsing it with an ethanol solution, annealing it on a hot plate at 100°C for 30 minutes, and then naturally cooling it to room temperature.

[0086] When the solar cell does not include the electron transport layer 5, the intermediate layer 8 may be formed on the first electrode 2. In this case, the intermediate layer 8 functions as the electron transport layer 5.

[0087] (Photoelectric conversion layer 3) The photoelectric conversion layer 3 contains a perovskite compound represented by the composition formula ABX3. A is a monovalent cation. Examples of the monovalent cation include monovalent cations such as alkali metal cations and organic cations. More specifically, methylammonium cation (MA + or CH3NH3 + ), formamidinium cation (FA + or HC(NH2)2 + ), ethylammonium cation (CH3CH2NH3 + ), guanidinium cation (CH6N3 + ), potassium cation (K + ), cesium cation (Cs + ), and rubidium cation (Rb + ) and B is a divalent lead cation (Pb 2+ ) and tin cations (Sn 2+ ) X is a monovalent anion such as a halogen anion. Each of the A, B, and X sites may be occupied by multiple types of ions.

[0088] The thickness of the photoelectric conversion layer 3 is, for example, 50 nm or more and 10 μm or less. The photoelectric conversion layer 3 can be formed by using a solution coating method, a printing method, a vapor deposition method, or the like. The photoelectric conversion layer 3 may also be formed by cutting out a perovskite compound.

[0089] The photoelectric conversion layer 3 may primarily contain a perovskite compound represented by the composition formula ABX3. Here, "the photoelectric conversion layer 3 primarily contains a perovskite compound represented by the composition formula ABX3" means that the photoelectric conversion layer 3 contains 90 mass% or more of a perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 3 may also contain 95 mass% or more of a perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 3 may be made of a perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 3 may contain a perovskite compound represented by the composition formula ABX3, and may contain defects or impurities.

[0090] The photoelectric conversion layer 3 may further contain another compound different from the perovskite compound represented by the composition formula ABX3. Examples of the other compound include a compound having a Ruddlesden-Popper type layered perovskite structure.

[0091] (Porous layer 6) The porous layer 6 is formed on the electron transport layer 5 by, for example, a coating method. If the solar cell does not include the electron transport layer 5, the porous layer 6 is formed on the first electrode 2. The pore structure introduced by the porous layer 6 serves as a base when the photoelectric conversion layer 3 is formed. The porous layer 6 does not inhibit light absorption by the photoelectric conversion layer 3 or electron transfer from the photoelectric conversion layer 3 to the electron transport layer 5.

[0092] In the solar cells 200 and 400, the electron transport layer 5 has a portion in contact with the photoelectric conversion layer 3 via the intermediate layer 8. The porous body contained in the porous layer 6 has a portion in contact with the photoelectric conversion layer 3 via the intermediate layer 8. If the surface modification of the porous body contained in the electron transport layer 5 or the porous layer 6 by the intermediate layer 8 is insufficient, a portion in contact between the electron transport layer 5 or the porous layer 6 and the photoelectric conversion layer 3 may occur.

[0093] The porous layer 6 includes a porous body. Examples of the porous body include a porous body in which insulating or semiconducting particles are connected. Examples of insulating particles include aluminum oxide and silicon oxide particles. Examples of semiconducting particles include inorganic semiconductor particles. Examples of inorganic semiconductors include oxides of metal elements, perovskite oxides of metal elements, sulfides of metal elements, and metal chalcogenides. Examples of oxides of metal elements 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 perovskite oxides of metal elements include SrTiO3 and CaTiO3. Examples of sulfides of metal elements include CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, and Cu2S. Examples of metal chalcogenides include CsSe, In2Se3, WSe2, HgS, PbSe, and CdTe.

[0094] The thickness of the porous layer 6 may be 0.01 μm or more and 10 μm or less, or may be 0.05 μm or more and 1 μm or less.

[0095] The surface roughness of the porous layer 6 may have a surface roughness coefficient of 10 or more, or even 100 or more, given by the effective area / projected area. The projected area is the area of ​​the shadow cast behind an object when irradiated with light from directly in front of it. The effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume determined from the projected area and thickness of the object, and the specific surface area and bulk density of the material that makes up the object. The specific surface area is measured, for example, by nitrogen adsorption.

[0096] The pores in the porous layer 6 are connected from the portion in contact with the photoelectric conversion layer 3 or the portion in contact with the photoelectric conversion layer 3 via the intermediate layer 8 to the portion in contact with the electron transport layer 5 or the portion in contact with the electron transport layer 5 via the intermediate layer 8. That is, the pores in the porous layer 6 are connected from one main surface of the porous layer 6 to the other main surface. This allows the material of the intermediate layer 8 or the photoelectric conversion layer 3 to fill the pores in the porous layer 6 and reach the surface of the electron transport layer 5. Therefore, the photoelectric conversion layer 3 and the electron transport layer 5 are in contact with each other directly or via the intermediate layer 8, allowing electrons to be exchanged.

[0097] The provision of the porous layer 6 has the effect of facilitating the formation of the photoelectric conversion layer 3. By providing the porous layer 6, the material of the photoelectric conversion layer 3 penetrates into the pores of the porous layer 6, and the porous layer 6 serves as a foothold for the photoelectric conversion layer 3. As a result, the material of the photoelectric conversion layer 3 is less likely to be repelled or aggregate on the surface of the porous layer 6. Therefore, the photoelectric conversion layer 3 can be easily formed as a uniform film. This is also true when the intermediate layer 8 is formed on the porous layer 6. The photoelectric conversion layer 3 can be formed by the above-mentioned coating method, printing method, vapor deposition method, etc.

[0098] Light scattering caused by the porous layer 6 is also expected to have the effect of increasing the optical path length of light passing through the photoelectric conversion layer 3. As the optical path length increases, the amount of electrons and holes generated in the photoelectric conversion layer 3 is expected to increase.

[0099] (Hole transport layer 7) The hole transport layer 7 contains a hole transport material. The hole transport material is a material that transports holes. The hole transport layer 7 is made of a hole transport material such as an organic material or an inorganic semiconductor.

[0100] Representative examples of organic compounds used as hole transport materials include 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter sometimes abbreviated as "PTAA"), poly(3-hexylthiophene-2,5-diyl), poly(3,4-ethylenedioxythiophene), and copper phthalocyanine.

[0101] Inorganic semiconductors used as hole transport materials are p-type semiconductors. Examples of inorganic semiconductors include Cu2O, CuGaO2, CuSCN, CuI, and NiO. x , MoO x , V2O5, or carbon materials such as graphene oxide.

[0102] The hole transport layer 7 may include multiple layers made of different materials. For example, multiple layers may be stacked so that the ionization potentials of the hole transport layers 7 are successively smaller than the ionization potential of the photoelectric conversion layer 3, thereby improving the hole transport properties.

[0103] By selecting an appropriate hole transport layer 7 depending on the constituent material of the photoelectric conversion layer 3, defects in the photoelectric conversion layer 3 are terminated by atoms or molecules of the hole transport layer 7, thereby improving the hole transport properties. Examples of such materials that terminate defects in the photoelectric conversion layer 3 and allow holes to pass through include tetracene.

[0104] The thickness of the hole transport layer 7 may be from 1 nm to 1000 nm, or from 10 nm to 50 nm. Within this range, sufficient hole transport properties can be exhibited and low resistance can be maintained, allowing for highly efficient photovoltaic power generation.

[0105] The hole transport layer 7 can be formed by a coating method, a printing method, a vapor deposition method, or the like, similar to the method for the photoelectric conversion layer 3. Examples of coating methods include doctor blade, bar coating, spraying, dip coating, and spin coating. Examples of printing methods include screen printing. If necessary, the hole transport layer 7 may be formed by mixing multiple materials, followed by pressing or baking. When the material for the hole transport layer 7 is an organic low-molecular-weight compound or an inorganic semiconductor, the hole transport layer 7 can also be formed by a vacuum vapor deposition method.

[0106] The hole transport layer 7 may contain a supporting electrolyte and a solvent, which have the effect of stabilizing holes in the hole transport layer 7.

[0107] Examples of the supporting electrolyte include ammonium salts and alkali metal salts. Examples of the ammonium salt include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts, and pyridinium salts. Examples of the alkali metal salt include lithium perchlorate and potassium boron tetrafluoride.

[0108] The solvent contained in the hole transport layer 7 may be one having excellent ion conductivity. Either an aqueous solvent or an organic solvent may be used. To further stabilize the solute, the solvent contained in the hole transport layer 7 may be an organic solvent. Specific examples include heterocyclic compound solvents such as tert-butylpyridine, pyridine, and n-methylpyrrolidone.

[0109] Ionic liquids may be used alone or in combination with other solvents as the solvent, and are desirable because of their low volatility and high flame retardancy.

[0110] Examples of the ionic liquid include imidazolium-based ionic liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine-based ionic liquids, alicyclic amine-based ionic liquids, aliphatic amine-based ionic liquids, and azonium amine-based ionic liquids.

[0111] (2nd electrode 4) The second electrode 4 is conductive. When the solar cell does not include a hole transport layer 7, the second electrode 4 is made of a material that does not make ohmic contact with the photoelectric conversion layer 3. Furthermore, the second electrode 4 has blocking properties against electrons from the photoelectric conversion layer 3. Here, blocking properties against electrons from the photoelectric conversion layer 3 refer to the property of allowing only holes generated in the photoelectric conversion layer 3 to pass through and not allowing electrons to pass through. A material having such properties is a material whose Fermi energy is lower than the energy of the bottom of the conduction band of the photoelectric conversion layer 3. The above material may also have a Fermi energy lower than the Fermi energy of the photoelectric conversion layer 3. Specific examples of such materials include platinum, gold, and carbon materials such as graphene. When the solar cell includes a hole transport layer 7, the second electrode 4 does not need to have blocking properties against electrons from the photoelectric conversion layer 3. That is, the material of the second electrode 4 may be a material that makes ohmic contact with the photoelectric conversion layer 3. Therefore, the second electrode 4 can be formed to be light-transmitting.

[0112] Of the first electrode 2 and the second electrode 4, it is sufficient that the electrode on the light incident side has light-transmitting properties. Therefore, one of the first electrode 2 and the second electrode 4 does not have to have light-transmitting properties. In other words, one of the first electrode 2 and the second electrode 4 does not have to use a light-transmitting material or have a pattern including openings that allow light to pass through. [Example]

[0113] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0114] In the examples and comparative examples, solar cells were fabricated using perovskite compounds, and the initial characteristics of the solar cells and the characteristics after a light irradiation test were evaluated.

[0115] The solar cells of Examples 1 to 11 and Comparative Examples 1 to 10 have the following configurations. The solar cells of Examples 1 to 10, Comparative Examples 1 to 5, Comparative Example 7, and Comparative Example 8 had the same structure as solar cell 400 shown in FIG. 6. The solar cell of Comparative Example 9 had a structure in which intermediate layer 8 was removed from solar cell 400. The solar cells of Example 11 and Comparative Example 6 had the same structure as solar cell 300 shown in FIG. 5. The solar cell of Comparative Example 10 had a structure in which intermediate layer 8 was removed from solar cell 300. Substrate 1: Glass substrate First electrode 2: Transparent electrode Indium-tin composite oxide layer Electron transport layer 5: titanium oxide or tin oxide Porous layer 6: Mesoporous titanium dioxide ·Intermediate layer 8 (C60SAM): 4-(1′,5′-Dihydro-1′-methyl-2′H-[5,6]fullereno-C 60 -Ih-[1,9-c]pyrrol-2′-yl)benzoic acid (Sigma-Aldrich) (hereinafter referred to as “SAM[1]”), or (1,2-Methanofullerene C 60 )-61-carboxylic acid (Sigma-Aldrich) (hereinafter referred to as "SAM[7]") Intermediate layer 8 (gap-modified SAM): isonicotinic acid (Tokyo Chemical Industry Co., Ltd.), nicotinic acid (Tokyo Chemical Industry Co., Ltd.), picolinic acid (Tokyo Chemical Industry Co., Ltd.), 2-bromoisonicotinic acid (Tokyo Chemical Industry Co., Ltd.), or isonipecotic acid (Sigma-Aldrich) Photoelectric conversion layer 3: A layer mainly containing HC(NH2)2PbI3 Hole transport layer 7: Layer containing n-butylammonium bromide (GreatcellSolar) / Layer containing mainly PTAA (however, containing tris(pentafluorophenyl)borane (Tokyo Chemical Industry Co., Ltd.) as an additive) ·Second electrode 4:Au

[0116] <Fabrication of solar cells> Example 1 First, a substrate 1 was prepared, the substrate 1 having a transparent conductive layer on its surface which functions as a first electrode 2. In this example, a glass substrate having a thickness of 0.7 mm was used as the substrate 1.

[0117] As the first electrode 2, a layer of indium-tin composite oxide was formed on the substrate 31 by sputtering.

[0118] Next, a titanium oxide layer was formed as the electron transport layer 5 on the first electrode 2 by sputtering.

[0119] Titanium oxide with a mesoporous structure was used for the porous layer 6. 30NR-D (manufactured by Greatcell Solar) was applied by spin coating onto the electron transport layer 5, and then baked at 500°C for 30 minutes, thereby forming the porous layer 6 made of titanium oxide with a mesoporous structure.

[0120] Next, the intermediate layer 8 was formed using the immersion method described in the embodiment. The conditions for forming the intermediate layer 8 in Example 1 are shown in Table 1. Here, the tetrahydrofuran and ethanol used were those manufactured by Fujifilm Wako Pure Chemical Industries.

[0121] Next, a raw material solution of a photoelectric conversion material was applied by spin coating to form a photoelectric conversion layer 3 containing a perovskite compound. The raw material solution was a solution containing 0.92 mol / L lead(II) iodide (Tokyo Chemical Industry Co., Ltd.), 0.17 mol / L lead(II) bromide (Tokyo Chemical Industry Co., Ltd.), 0.83 mol / L formamidinium iodide (GreatCell Solar Co., Ltd.), 0.17 mol / L methylammonium bromide (GreatCell Solar Co., Ltd.), 0.05 mol / L cesium iodide (Iwatani Corporation), and 0.05 mol / L rubidium iodide (Iwatani Corporation). The solvent for the solution was a mixture of dimethyl sulfoxide (Acros Co., Ltd.) and N,N-dimethylformamide (Acros Co., Ltd.). The mixture ratio of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in the first raw material solution (DMSO:DMF) was 1:4 by volume.

[0122] Next, a raw material solution of a hole transport material was applied by spin coating onto the photoelectric conversion layer 3 to form a hole transport layer 7 containing PTAA. The solvent for the raw material solution was toluene (manufactured by Acros), and the solution contained 10 g / L of PTAA.

[0123] Next, an Au film was deposited by vacuum deposition on the hole transport layer 7 to form the second electrode 4. In this way, the solar cell of Example 1 was obtained.

[0124] Examples 2 to 10 Solar cells of Examples 2 to 10 were obtained in the same manner as in Example 1 except for the conditions for forming the intermediate layer 8. The conditions for forming the intermediate layer 8 of Examples 2 to 10 are shown in Table 1.

[0125] Example 11 In Example 11, the electron transport layer 5 was formed of tin oxide. In addition, in Example 11, the porous layer 6 was not formed. Otherwise, the solar cell of Example 11 was obtained in the same manner as in Example 1.

[0126] (Comparative Examples 1 to 5) Solar cells of Comparative Examples 1 to 5 were obtained under the same conditions as in Example 1 except for the conditions for forming intermediate layer 8. The conditions for forming intermediate layer 8 in Comparative Examples 1 to 5 are shown in Table 1.

[0127] (Comparative Example 6) A solar cell of Comparative Example 6 was obtained under the same conditions as in Example 11 except for the conditions for forming intermediate layer 8. The conditions for forming intermediate layer 8 of Comparative Example 6 are shown in Table 2.

[0128] (Comparative Examples 7 and 8) Solar cells of Comparative Examples 7 and 8 were obtained in the same manner as in Example 1 except for the conditions for forming intermediate layer 8. The conditions for forming intermediate layer 8 of Comparative Examples 7 and 8 are shown in Table 3.

[0129] (Comparative Example 9) In Comparative Example 9, the intermediate layer 8 was not formed. Otherwise, the solar cell of Comparative Example 9 was obtained in the same manner as in Example 1.

[0130] (Comparative Example 10) In Comparative Example 10, the intermediate layer 8 was not formed. Otherwise, the solar cell of Comparative Example 10 was obtained in the same manner as in Example 11.

[0131] <Photoelectric conversion efficiency measurement> The photoelectric conversion efficiency of the obtained solar cells of Examples 1 to 11 and Comparative Examples 1 to 10 was measured.

[0132] The photoelectric conversion efficiency of the solar cell was measured using an electrochemical analyzer (ALS440B, manufactured by BAS) and a xenon light source (BPS X300BA, manufactured by Bunkoukeiki). Before the measurement, the light intensity was adjusted to 1 Sun (100 mW / cm) using a silicon photodiode. 2 The voltage sweep rate was 100 mV / s. No preconditioning such as light irradiation or prolonged forward bias application was performed before the start of the measurement. To fix the effective area and reduce the influence of scattered light, an aperture of 0.1 cm was used. 2 The solar cells were masked with a black mask and irradiated with light from the mask / substrate side. The photoelectric conversion efficiency was measured at room temperature in dry air (<2% RH). The initial efficiencies of the solar cells of Examples 1 to 11 and Comparative Examples 1 to 10 measured as described above are shown in Tables 1, 2, and 3.

[0133] <Light irradiation test> A light irradiation test was carried out on the solar cells of Examples 1 to 11 and Comparative Examples 1 to 10. In the light irradiation test, the solar cells were sealed in the atmosphere with UV-curable resin using sealing glass with a moisture / oxygen getter attached inside, and then irradiated with light equivalent to 1 sun from the substrate side for 1 hour while maintaining the substrate temperature at 50°C and maintaining the temperature near the optimum operating point.

[0134] Table 1 shows the type of C60 SAM, the type of gap-modifying SAM, and the molar concentration of the material used in the first and second intermediate layer 8 formation processes, as well as the initial efficiency (%), which is the photoelectric conversion efficiency before the light irradiation test, and the normalized efficiency after the light irradiation test, for Examples 1 to 10 and Comparative Examples 1 to 5 (where the material of the electron transport layer 5 was titanium oxide and the porous layer 6 was mesoporous titanium oxide). In Table 1, the concentration of the saturated solution of C60 SAM is designated as a. The unit of concentration in Table 1 is mol / L. The values ​​in parentheses in the initial efficiency column are the initial efficiencies of each Example normalized by the conversion efficiency of Comparative Example 1. The normalized efficiency after light irradiation is the photoelectric conversion efficiency of the cell after the light irradiation test normalized by the average photoelectric conversion efficiency of Comparative Example 1, 16.7%, from 0 to 1 hour after light irradiation.

[0135] [Table 1]

[0136] Table 2 shows the type of C60SAM, the type of gap-modifying SAM, and the molar concentration of the materials used in the first and second intermediate layer 8 formation processes, as well as the initial efficiency (%), which is the photoelectric conversion efficiency before the light irradiation test, and the normalized efficiency after the light irradiation test, for Example 11 and Comparative Example 6 (where the material of the electron transport layer 5 is tin oxide and there is no porous layer 6). In Table 2, the concentration of the saturated solution of C60SAM is designated as a. The unit of concentration in Table 2 is mol / L. The values ​​in parentheses in the initial efficiency column are values ​​obtained by normalizing the initial efficiency of each Example with the conversion efficiency of Comparative Example 6. The normalized efficiency after light irradiation is a value obtained by normalizing the photoelectric conversion efficiency of the cell after the light irradiation test with the average photoelectric conversion efficiency of Comparative Example 6, 13.3%, from 0 to 1 hour after light irradiation.

[0137] [Table 2]

[0138] Table 3 shows the type of C60 SAM, the type of gap-modifying SAM, and the molar concentration of the mixture in the first and second intermediate layer 8 formation processes, as well as the initial efficiency (%), which is the photoelectric conversion efficiency before the light irradiation test, and the normalized efficiency after the light irradiation test, for Comparative Examples 7 to 9 (where the electron transport layer 5 is made of titanium oxide and the porous layer 6 is made of mesoporous titanium oxide) and Comparative Example 10 (where the electron transport layer 5 is made of tin oxide and there is no porous layer 6). In Table 3, the concentration of the saturated solution of C60 SAM is designated as a. The unit of concentration in Table 3 is mol / L. The parenthesized values ​​in the initial efficiency column for Comparative Examples 7 to 9 are the initial efficiencies of each Example normalized by the conversion efficiency of Comparative Example 1 shown in Table 1. The parenthesized value in the initial efficiency column for Comparative Example 10 is the value normalized by the conversion efficiency of Comparative Example 6 shown in Table 2. The normalized efficiency after light irradiation of Comparative Examples 7 to 9 is a value obtained by normalizing the photoelectric conversion efficiency of the cells after the light irradiation test by the average value of 16.7% of the photoelectric conversion efficiency from 0 to 1 hour after light irradiation of Comparative Example 1. The normalized efficiency after light irradiation of Comparative Example 10 is a value obtained by normalizing the average value of 13.3% of the photoelectric conversion efficiency from 0 to 1 hour after light irradiation of Comparative Example 6.

[0139] [Table 3]

[0140] <Confirmation of the effect of gap-modifying SAM> As shown in Table 1, Examples 1 to 10 have normalized efficiencies after light irradiation greater than 1,000, and thus have higher photoelectric conversion efficiencies after light irradiation than Comparative Example 1, which is treated only with the conventional C60SAM. Therefore, by applying the gap-modified SAM treatment in addition to the C60SAM treatment, solar cells with high photoelectric conversion efficiency can be obtained while suppressing photodegradation.

[0141] <Confirming the requirements for gap-modifying SAM> In Example 4, the effect of steric hindrance was investigated by using 2-bromoisonicotinic acid, which has a structure in which isonicotinic acid is modified with bromine, as the gap-modified SAM. 2-Bromoisonicotinic acid has the structure shown in the following formula (17). [ka]

[0142] As shown in Table 1, Example 4 had a normalized efficiency of 1.02 after light irradiation, which was higher than that of Comparative Example 1. This indicates that the bromine-modified gap-modified SAM also suppresses photodegradation and provides a solar cell with high photoelectric conversion efficiency after light irradiation. On the other hand, Example 4 had a lower initial efficiency than Examples 1 to 3, Examples 5 to 10, and Comparative Example 1. This is thought to be because 2-bromoisonicotinic acid has some difficulty entering the gaps in the SAM [1], and the SAM [1] and 2-bromoisonicotinic acid are unable to sufficiently modify the surface of the electron transport layer 5, resulting in a lower initial efficiency.

[0143] The gap-modifying SAM in this example contains the largest heterocycle, 2-bromoisonicotinic acid, used in Example 4. The size of the heterocycle refers to the distance between the two most distant atoms, i.e., the distance from the bromine atom to the hydrogen atom at the para-position of the bromine atom. Therefore, the size of the heterocycle is 795 pm, which is the sum of the carbon-bromine bond length (194 pm), the diameter of the benzene ring (278 pm), the carbon-hydrogen bond length (150 pm), the radius of the hydrogen atom (53 pm), and the radius of the bromine atom (120 pm).

[0144] In Comparative Example 2, isonipecotic acid (also known as 4-piperidine carboxylic acid) was used as the gap-modifying SAM to investigate the effect of electron repulsion due to the lone electron pair present in the ring of the heterocyclic compound of the gap-modifying SAM. Isonipecotic acid has the structure shown in the following formula (18). The piperidine ring of isonipecotic acid does not contain any element with a lone electron pair. Isonipecotic acid has an appropriate size to fit into the gap of the SAM [1]. [ka]

[0145] As shown in Table 1, both the initial efficiency and the normalized efficiency after light irradiation were lower in Comparative Example 2 compared to Comparative Example 1. This indicates that even if the size of the gap-modified SAM is appropriate, the desired effect cannot be obtained if there is no lone electron pair in the ring of the heterocyclic compound of the gap-modified SAM. Isonipecotic acid does not cause electron repulsion, and the C of C60 SAM 60 The initial efficiency was reduced because electrons that should have been collected in the first place were collected via the gap-modified SAM, which has a large resistance loss. The efficiency after light irradiation was reduced because electrons were collected via isonicotinic acid, a gap-modified SAM with a large resistance loss, i.e., via a layer that is inefficient at extracting high-energy photoexcited electrons. This accelerated the cathode reaction at the interface between the electron transport layer 5 and the photoelectric conversion layer 3, which is thought to have reduced light durability.

[0146] These results demonstrate that photodegradation can be suppressed and solar cells with high photoelectric conversion efficiency after light irradiation can be obtained when the gap-modified SAM is composed of materials having a lone electron pair in the ring of a heterocyclic compound, as shown in Examples 1 to 10. Furthermore, as shown in Examples 1 to 3 and 5 to 10, when the gap-modified SAM is composed of materials having a lone electron pair in the ring of a heterocyclic compound and the gap-modified SAM has a size with little steric hindrance, it can be seen that photodegradation can be suppressed and high photoelectric conversion efficiency can be obtained.

[0147] <Confirmation when the intermediate layer contains only gap-modifying SAM> As shown in Table 1, in Comparative Examples 3 to 5, in which the intermediate layer 8 was formed by treatment with only the gap-modifying SAM alone, both the initial efficiency and the normalized efficiency after light irradiation were significantly reduced compared to Comparative Example 1. This is because the lone electron pair of the nitrogen in the pyridine ring repels electrons, preventing electron collection in the electron transport layer 5. In other words, the decrease in initial efficiency is caused by an increase in resistance loss, and the decrease in normalized efficiency after light irradiation, i.e., the decrease in light durability, is thought to be due to the accumulation of high-energy photoexcited electrons at the interface between the electron transport layer 5 and the photoelectric conversion layer 3 under light irradiation, which promotes a cathodic reaction at the interface.

[0148] <Confirmation of the Influence of the Material of the Electron Transport Layer 5> As shown in Table 2, by comparing Example 11 and Comparative Example 6, it was examined whether the effect of the gap-modified SAM depends on the material of the electron transport layer 5. In Example 11 and Comparative Example 6, the electron transport layer 5 is tin oxide. Compared with Comparative Example 6 in which the intermediate layer 8 is only SAM[1], Example 11 in which the intermediate layer 8 contains SAM[1] and isonicotinic acid showed high values both in the initial efficiency and the normalized efficiency after light irradiation. Therefore, it was confirmed that the effect of the gap-modified SAM can be obtained similarly even when the material of the electron transport layer 5 is tin oxide.

[0149] <Confirmation of the Influence of the Size of C60SAM> When SAM[7] with a smaller skeleton size excluding C 60 was used as the C60SAM compared with SAM[1], it was examined whether the effect of the gap-modified SAM can be obtained. Comparative Example 7 is the case where the intermediate layer 8 contains only SAM[7]. On the other hand, Comparative Example 8 is the case where, in forming the intermediate layer 8, first SAM[7] was formed and then an attempt was made to perform gap modification with isonicotinic acid. As shown in Table 3, Comparative Example 7 showed an initial efficiency equivalent to that of Comparative Example 1 in Table 1, but the efficiency after light irradiation deteriorated compared with Comparative Example 1. This suggests that, compared with SAM[1], SAM[7] has a large steric hindrance due to repulsion between C 60 and the modification of the surface of the electron transport layer 5 is insufficient. Compared with Comparative Example 7, Comparative Example 8 had a lower initial efficiency and the efficiency after light irradiation decreased. This is because the skeleton size of SAM[7] excluding C 60 is too small, so isonicotinic acid cannot enter the gap of SAM[7] and the surface of the electron transport layer 5 cannot be sufficiently modified. Also, the decrease in the efficiency after light irradiation is due to an increase in electron collection through a layer with a large resistance loss. That is, by passing through a layer with a poor extraction efficiency of high-energy photoexcited electrons, the cathodic reaction at the interface between the electron transport layer 5 and the photoelectric conversion layer 3 was promoted and light degradation occurred. Therefore, the C of C60SAM 60If the size of the skeleton excluding [the specified part] is smaller than that of the gap-modified SAM, there will not be enough space for the gap-modified SAM to enter, and the desired effect cannot be obtained.

[0150] <Confirmation of the Effect of C60SAM> In Comparative Examples 9 and 10, the intermediate layer 8 does not exist. The electron transport layer 5 in Comparative Example 9 is mesoporous titanium oxide, corresponding to the case where there is no SAM[1] in the intermediate layer 8 in Comparative Example 1. The electron transport layer 5 in Comparative Example 10 is tin oxide, corresponding to the case where there is no SAM[1] in the intermediate layer 8 in Comparative Example 6. As shown in Tables 1 to 3, compared with Comparative Examples 1 and 6 where SAM[1] in the intermediate layer 8 exists, although the initial efficiencies of Comparative Examples 9 and 10 are almost the same, the normalized efficiency after light irradiation decreased significantly. This indicates that when the intermediate layer 8 does not exist, there are many defects at the interface between the electron transport layer 5 and the photoelectric conversion layer 3, and the electron extraction is poor, promoting light degradation.

[0151] From the above results, it was confirmed that including appropriate C60SAM and gap-modified SAM as the intermediate layer 8 is very effective in improving the photoelectric conversion efficiency.

Industrial Applicability

[0152] The present disclosure is a solar cell having a novel self-assembled monolayer, and when the self-assembled monolayer is used in the intermediate layer of the solar cell, it can improve the photoelectric conversion efficiency, and it can be said that the industrial applicability is extremely high.

Explanation of Symbols

[0153] 1A,2A SAM[1] 1B,2B,5 Electron transport layer 2C Isonicotinic acid 1 Substrate 2 First electrode 3 Photoelectric conversion layer 4 Second electrode 6 Porous layer 7 Hole transport layer 8 Intermediate layer 100,200,300,400 solar cells

Claims

1. A solar cell, a first electrode, an intermediate layer, a photoelectric conversion layer, and a second electrode, in this order; the photoelectric conversion layer contains a perovskite compound, The intermediate layer contains at least one compound A selected from compound group I consisting of the following formulas (1) to (4) and at least one compound B selected from compound group II consisting of the following formulas (5) and (6), (Compound group I) 【Chemical 1】 Here, in the above formulas (1) to (4), X 1 is a fullerene or a fullerene derivative, X 2 is a pyrroline ring, a pyrrole ring, a pyrrolidine ring, a cyclohexane ring, or a cyclohexene ring, X 3 is a cyclohexadiene ring, (Compound group II) 【Chemistry 2】 Here, in the above formulas (5) and (6), X 4 is a heterocycle containing one or more lone pair heteroatoms and having a size of 900 pm or less; When the solar cell does not include an electron transport layer, the compound A and the compound B terminate the first electrode, and when the solar cell further includes an electron transport layer, the compound A and the compound B terminate the electron transport layer; wherein the COOH of the compound A and the COOH of the compound B terminate the first electrode or the electron transport layer in a COOH state or a COO − state, respectively, and the OH of the compound A and the OH of the compound B terminate the first electrode or the electron transport layer in an OH state or an O − state, respectively. Solar cell.

2. the heterocycle is a pyridine ring, a pyran ring, a furan ring, an oxetane ring, an oxazole ring, an isoxazole ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a tetrazine ring, a triazole ring, a thiophene ring, a thiazole ring, a dioxane ring, a pyrazole ring, an imidazole ring, a phosphinine ring, an oxirane ring, a thiirane ring, a thietane ring, an imidasoline ring, a dioxolane ring, a tetrahydrofuran ring, a tetrahydrothiophene ring, a morpholine ring, a diazine ring, a quinuclidine ring, or an azaadamantane ring; The solar cell according to claim 1 .

3. In the heterocycle, at least a part of the hydrogen atoms is substituted with a halogen atom. The solar cell according to claim 1 or 2.

4. further comprising an electron transport layer; The solar cell according to claim 1 , wherein the electron transport layer is disposed between the first electrode and the intermediate layer.

5. The compound A is at least one selected from the compounds represented by the following formulas (7) to (11), and the compound B is at least one selected from the group consisting of isonicotinic acid, nicotinic acid, and picolinic acid: The solar cell according to claim 1 . 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】 【Chemistry 7】

6. The compound A is a compound represented by the formula (7). The solar cell according to claim 5 .

7. the electron transport layer contains titanium oxide or tin oxide; The solar cell according to claim 4 .

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