Composition, hole transport layer, photoelectric conversion element, and method for manufacturing same

Abstract

The present invention provides: a photoelectric conversion element wherein reproducibility of crystal growth of a perovskite crystal is improved and the manufacturing cost is reduced, and a method for manufacturing the photoelectric conversion element; and a composition and a hole transport layer, with which it is possible to obtain the photoelectric conversion element.　The composition according to the present invention contains a polymer that has a zwitterionic structure and an organic semiconductor compound. The photoelectric conversion element according to the present invention includes: a pair of electrodes comprising an upper electrode and a lower electrode; an active layer positioned between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound; and a hole transport layer positioned between the active layer and the upper electrode or the lower electrode. The hole transport layer contains the composition. The method for manufacturing a photoelectric conversion element according to the present invention includes a step for applying the composition to the active layer.

Description

Composition, hole transport layer, photoelectric conversion element and method for producing the same

[0001] The present invention relates to a composition, a hole transport layer, a photoelectric conversion element, and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2023-213232, filed with the Japan Patent Office on December 18, 2023, the contents of which are incorporated herein by reference.

[0002] Photoelectric conversion elements have an active layer, a buffer layer, and other layers disposed between a pair of electrodes. To improve the photoelectric conversion efficiency of photoelectric conversion elements, the use of organic-inorganic hybrid semiconductor compounds in the active layer has been investigated. Semiconductor compounds with a perovskite structure, in particular, have attracted attention.

[0003] In solar cells equipped with a photoelectric conversion element having an active layer containing a semiconductor compound with a perovskite structure, surface defects of the perovskite crystal may be repaired by passivation to achieve high photoelectric conversion efficiency and long-term durability.

[0004] For example, Non-Patent Document 1 suggests the usefulness of using Lewis acids, Lewis bases, and zwitterions to repair surface defects in perovskite crystals. The following methods are disclosed as techniques for such repair: (1) A method comprising adding a Lewis acid, Lewis base, and zwitterions to a composition used for forming a layer having perovskite crystals. (2) A method comprising forming a surface coating layer containing a Lewis acid, Lewis base, and zwitterions before or after forming a layer having perovskite crystals.

[0005] J. Mater. Chem. A, 2020, 8, 12201-12225.

[0006] However, in method (1), the surface repair effect occurs during the growth of the perovskite crystal, making it difficult to achieve highly reproducible crystal growth, while method (2) requires a step of forming a surface coating layer in addition to a step of forming an active layer containing perovskite crystal, which increases production costs.

[0007] The present invention provides a photoelectric conversion element that improves the reproducibility of crystal growth of perovskite crystals and reduces production costs, a method for producing the same, and a composition and hole transport layer from which the photoelectric conversion element can be obtained.

[0008] As a result of extensive research, the inventors of the present invention have come up with the idea of ​​forming a hole transport layer in contact with an active layer containing an organic-inorganic hybrid semiconductor compound having a perovskite structure using a composition containing a hole transport material and a polymer having a zwitterionic structure. By using this composition to form the hole transport layer, it is possible to simultaneously repair surface defects in the perovskite crystal and form the hole transport layer. The inventors have found that this method improves the reproducibility of crystal growth of the perovskite crystal and reduces the manufacturing cost of photoelectric conversion elements, leading to the completion of the present invention.

[0009] The present invention includes, but is not limited to, the following embodiments [1] to

[23] : [1] A composition containing a polymer having a zwitterionic structure represented by the following formula (2) and an organic semiconductor compound:

[0010]

[0011] In formula (2), R １２represents a hydrogen atom or an alkyl group, and Z represents an alkyl group having a zwitterionic group as a substituent, an aryl group having a zwitterionic group as a substituent, a carboxylic acid ester group having a zwitterionic group as a substituent, a carboxylic acid amide group having a zwitterionic group as a substituent, or an alkoxyl group having a zwitterionic group as a substituent. [2] The composition according to [1], wherein the cation structure of the zwitterionic group in the structure of formula (2) comprises a nitrogen-containing structure. [3] The composition according to [1] or [2], wherein the anion structure of the zwitterionic group in the structure of formula (2) comprises at least one of a phosphorus-containing structure and a sulfur-containing structure. [4] The composition according to any one of [1] to [3], wherein the organic semiconductor compound comprises a conjugated polymer. [5] The composition according to [4], wherein the conjugated polymer comprises an arylamine compound. [6] The composition according to [4] or [5], wherein the conjugated polymer comprises a triarylamine polymer, and wherein the weight-average molecular weight of the triarylamine polymer is 3,000 to 100,000. [7] The composition according to any one of [1] to [6], wherein the weight-average molecular weight of the polymer having the structure of formula (2) is 5,000 to 100,000. [8] The composition according to any one of [1] to [7], wherein the proportion of monomer units having a zwitterionic group among all structural units of the polymer having the structure of formula (2) is 0.1 mol % to 20 mol %. [9] The composition according to any one of [1] to [8], wherein the proportion of the polymer having the structure of formula (2) in the composition is 0.01 to 10 mass % of the total amount of the composition.

[10] A composition containing a polymer having a zwitterionic structure and an organic semiconductor compound.

[11] The composition according to

[10] , wherein the polymer having a zwitterionic structure has a cationic structure, and the cationic structure includes a nitrogen-containing structure.

[12] The composition according to

[10] or

[11] , wherein the polymer having a zwitterionic structure has an anionic structure, and the anionic structure includes at least one of a phosphorus-containing structure and a sulfur-containing structure.

[13] The composition according to any one of

[10] to

[12] , wherein the organic semiconductor compound comprises a conjugated polymer.

[14] The composition according to

[13] , wherein the conjugated polymer comprises an arylamine compound.

[15] The composition according to

[13] or

[14] , wherein the conjugated polymer comprises a triarylamine polymer, and the weight-average molecular weight of the triarylamine polymer is 3,000 to 100,000.

[16] The composition according to any one of

[10] to

[15] , wherein the weight-average molecular weight of the polymer having a zwitterionic structure is 5,000 to 100,000.

[17] The composition according to any one of

[10] to

[16] , wherein the proportion of monomer units having a zwitterionic group among all structural units of the polymer having a zwitterionic structure is 0.1 mol % to 20 mol %.

[18] The composition according to any one of

[10] to

[17] , wherein the proportion of the polymer having a zwitterionic structure in the composition is 0.01 to 10 mass % of the total amount of the composition.

[19] A hole transport layer comprising the composition according to any one of [1] to

[18] .

[20] A photoelectric conversion element comprising a pair of electrodes having an upper electrode and a lower electrode, an active layer positioned between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound, and a hole transport layer positioned between the active layer and the upper electrode or the lower electrode, wherein the hole transport layer comprises the composition described in any one of [1] to

[18] .

[21] The photoelectric conversion element according to

[20] , wherein the hole transport layer comprises: a first layer containing the polymer having a zwitterionic structure; and a second layer laminated on the first layer and containing the organic semiconductor compound.

[22] The photoelectric conversion element according to

[20] , wherein the hole transport layer comprises a mixture of the polymer having a zwitterionic structure and the organic semiconductor compound.

[23] A method for producing a photoelectric conversion element, comprising a step of applying the composition described in any one of [1] to

[18] to an active layer.

[0012] According to the present invention, there are provided a photoelectric conversion element and a method for producing the same that improve the reproducibility of crystal growth of perovskite crystals and reduce production costs; and a composition and hole transport layer from which the photoelectric conversion element can be obtained.

[0013] 1A and 1B are cross-sectional views each showing a schematic example of a photoelectric conversion element, a schematic example of a solar cell, and a schematic example of a solar cell module.

[0014] The meanings of the terms are as follows: The suffix "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The ranges, upper and lower limits of the physical property values ​​disclosed in this specification can be arbitrarily combined to form new ranges of values.

[0015] A semiconductor compound is a compound that can be used as a semiconductor material and exhibits semiconductor properties. Semiconductor properties are defined by the magnitude of hole mobility in a solid state. Hole mobility is an index showing how fast (or how many) charges (electrons or holes) can be moved. The hole mobility of a semiconductor at room temperature (25°C) is preferably 1.0 x 10 －６ cm ２ / V·s or more, more preferably 1.0×10 －５ cm ２ / V·s or more, more preferably 1.0×10 －４ cm ２ / V·s or more, particularly preferably 1.0×10 －３ cm ２ The hole mobility can be calculated from the measurement of the IV characteristics of the field effect transistor.

[0016] Hereinafter, several embodiments will be described in detail. The following description relates to several examples of embodiments, and the present invention is not limited to the following disclosure unless the spirit of the present invention is lost.

[0017] [Photoelectric Conversion Element] According to one embodiment, the photoelectric conversion element includes a pair of electrodes having an upper electrode and a lower electrode, an active layer positioned between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound, and a hole transport layer positioned between the active layer and the upper electrode or the lower electrode, wherein the hole transport layer contains a polymer having a zwitterionic structure and an organic semiconductor compound.

[0018] The photoelectric conversion element 100 shown in FIG. 1 has a pair of electrodes having an upper electrode 105 and a lower electrode 101, an active layer 103 located between the upper electrode 105 and the lower electrode 101 and containing an organic-inorganic hybrid semiconductor compound, a buffer layer 102 located between the active layer 103 and the lower electrode 101, and a buffer layer 104 located between the active layer 103 and the upper electrode 105.

[0019] In the photoelectric conversion element 100, at least one of the buffer layer 102 and the buffer layer 104 is a hole transport layer, and the hole transport layer contains a polymer having a zwitterionic structure and an organic semiconductor compound.

[0020] As shown in FIG. 1 , the photoelectric conversion element may have a substrate 106. In another example, the photoelectric conversion element 100 may further include other components such as an insulator layer (not shown) and a work function tuning layer (not shown). The work function tuning layer can change the work functions of the lower electrode and the upper electrode. The photoelectric conversion element 100 is a photoelectric conversion element used in a general thin-film solar cell, but the photoelectric conversion element according to the present invention is not limited to that shown in FIG. 1 .

[0021] (Pair of Electrodes) In the photoelectric conversion element 100, the pair of electrodes collects holes and electrons generated by light absorption in the active layer 103. As in the photoelectric conversion element 100, one of the pair of electrodes is called the upper electrode, and the other is called the lower electrode. When the photoelectric conversion element 100 has a substrate 106, as in the photoelectric conversion element 100, the electrode closer to the substrate can be called the lower electrode, and the electrode farther from the substrate can be called the upper electrode. The transparent electrode can be called the lower electrode, and the electrode that is less transparent than the lower electrode can be called the upper electrode.

[0022] The pair of electrodes can be an anode suitable for collecting holes and a cathode suitable for collecting electrons. In this case, the photoelectric conversion element 100 may have a forward configuration in which the lower electrode 101 is the anode and the upper electrode 105 is the cathode, or may have an inverted configuration in which the lower electrode 101 is the cathode and the upper electrode 105 is the anode.

[0023] In a pair of electrodes, it is sufficient that either one of them is light-transmitting, or both may be light-transmitting. "Light-transmitting" means that the transmittance of normal sunlight (wavelength 350 to 700 nm) is 40% or more. The sunlight transmittance of the electrode is preferably high, and particularly preferably 70% or more, since more light passes through the transparent electrode and reaches the active layer. The sunlight transmittance can be measured using a spectrophotometer (e.g., U-4100 manufactured by Hitachi High-Technologies Corporation).

[0024] There are no particular limitations on the constituent members and manufacturing methods of the lower electrode 101, upper electrode 105, anode, and cathode, and various techniques can be used. For example, the members and manufacturing methods described in WO 2013 / 171517, WO 2013 / 180230, JP 2012-191194, and the like can be used.

[0025] (Active Layer) In the photoelectric conversion element 100, photoelectric conversion occurs in the active layer 103. When the photoelectric conversion element 100 receives light, the light is absorbed by the active layer 103 and carriers are generated. The generated carriers are extracted from the lower electrode 101 and the upper electrode 105.

[0026] The active layer contains an organic-inorganic hybrid semiconductor compound. The organic-inorganic hybrid semiconductor compound is a compound in which an organic component and an inorganic component are combined at the molecular level or nano-level, and which exhibits semiconductor properties. As the organic-inorganic hybrid semiconductor compound, a semiconductor compound having a perovskite structure (hereinafter, sometimes referred to as a perovskite semiconductor compound) is preferred.

[0027] The perovskite semiconductor compound is not particularly limited, and can be selected from those listed in, for example, Galasso et al. Structure and Properties of Inorganic Solids, Chapter 7 - Perovskite type and related structures. For example, the perovskite semiconductor compound can be a compound represented by the formula AMX ３ AMX expressed as ３ of the type, formula A２ MX ４ A represented by ２ MX ４ Here, M represents a divalent cation, A represents a monovalent cation, and X represents a monovalent anion.

[0028] There are no particular limitations on the monovalent cation A, and those described in the above-mentioned book by Galasso can be used. Examples include cations containing elements of Groups 1 and 13 to 16 of the periodic table. Among these, cesium ions, rubidium ions, potassium ions, optionally substituted ammonium ions, and optionally substituted phosphonium ions are preferred.

[0029] Examples of ammonium ions which may have a substituent include primary ammonium ions and secondary ammonium ions. There are no particular limitations on the substituent. Examples of ammonium ions which may have a substituent include alkylammonium ions and arylammonium ions. In order to avoid steric hindrance, monoalkylammonium ions which form a three-dimensional crystal structure are preferred, and from the viewpoint of improving stability, it is preferable to use alkylammonium ions substituted with one or more fluorine groups. Two or more types of cations may be used in combination as cation A.

[0030] Examples of the monovalent cation A include a methylammonium ion, a methylammonium monofluoride ion, a methylammonium difluoride ion, a methylammonium trifluoride ion, an ethylammonium ion, an isopropylammonium ion, an n-propylammonium ion, an isobutylammonium ion, an n-butylammonium ion, a t-butylammonium ion, a dimethylammonium ion, a diethylammonium ion, a phenylammonium ion, a benzylammonium ion, a phenethylammonium ion, a guanidium ion, a formamidinium ion, an acetamidinium ion, and an imidazolium ion.

[0031] The divalent cation M is not particularly limited, but is preferably a divalent metal cation or semimetal cation. For example, a cation of an element in Group 14 of the periodic table is included. More specifically, for example, a lead cation (Pb ２＋ ), tin cations (Sn ２＋ ), germanium cation (Ge ２＋ In addition, two or more types of cations may be used in combination as the cation M. From the viewpoint of obtaining a stable photoelectric conversion element, it is particularly preferable to use a lead cation or two or more types of cations including a lead cation.

[0032] Examples of monovalent anions X include halide ions, acetate ions, nitrate ions, sulfate ions, borate ions, acetylacetonate ions, carbonate ions, citrate ions, sulfur ions, tellurium ions, thiocyanate ions, titanate ions, zirconate ions, 2,4-pentanedionate ions, and silicofluoride ions. One type of X may be used, or two or more types may be used in any combination and ratio. The band gap of the active layer can be adjusted by the type and combination of X. In order to prevent the band gap of the active layer from becoming excessively wide, it is preferable to primarily use iodide ions or bromide ions. Iodide ions and bromide ions may also be combined in an appropriate ratio.

[0033] As the perovskite semiconductor compound, for example, an organic-inorganic perovskite semiconductor compound is preferable, and a halide-based organic-inorganic perovskite semiconductor compound is particularly preferable. ３ NH ３ PbI ３ , C.H. ３ NH ３ PbBr ３ , C.H. ３ NH ３ PbCl ３ , C.H. ３ NH ３ SnI ３ , C.H. ３ NH ３ SnBr ３ , C.H. ３ NH ３ SnCl ３, C.H. ３ NH ３ PbI （３－ｘ） Cl ｘ , C.H. ３ NH ３ PbI （３－ｘ） Br ｘ , C.H. ３ NH ３ PbBr （３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Br ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Cl ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I ( ３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I （３－ｘ） Br ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Br （３－ｘ） Cl ｘ Here, x is an arbitrary value of 0 or more and 3 or less, and y is an arbitrary value of 0 or more and 1 or less. In addition, in the above compounds, CH ３ NH ３ Instead of CFH ２ NH ３ , C.F. ２ HNH ３ , C.F. ３ NH ３ , N.H. ２ CH=NH ３、 Compounds using Cs and Rb are preferred. ３ NH ３ PbI ３ , C.H. ３ NH３ PbBr ３ , C.H. ３ NH ３ PbCl ３ , C.H. ３ NH ３ PbI （３－ｘ） Cl ｘ , C.H. ３ NH ３ PbI （３－ｘ） Br ｘ , C.H. ３ NH ３ PbBr （３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Br ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Cl ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I （３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I （３－ｘ） Br ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Br （３－ｘ） Cl ｘ And in the above compounds, CH ３ NH ３ Instead of NH ２ CH=NH ３、 Compounds using Cs and Rb are preferred. ３ NH ３ PbI ３ , C.H. ３ NH ３ PbBr ３ , C.H. ３ NH ３ PbI （３－ｘ） Cl ｘ , C.H. ３ NH ３ PbI （３－ｘ） Brｘ , C.H. ３ NH ３ PbBr （３－ｘ） Cl ｘ , and CH in the above compounds ３ NH ３ Instead of NH ２ CH=NH ３、 Examples of the compounds include compounds using Cs and Rb.

[0034] The active layer may contain two or more organic-inorganic hybrid semiconductor compounds. For example, the active layer may contain two or more organic-inorganic hybrid semiconductor compounds in which at least one of A, M, and X is different. The active layer may have a laminated structure formed of multiple layers containing different materials or different components.

[0035] The amount of the organic-inorganic hybrid semiconductor compound contained in the active layer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more of the total mass of the active layer to obtain good semiconductor properties. There is no particular upper limit. The active layer may also contain additives other than the organic-inorganic hybrid semiconductor compound. Examples of additives include inorganic compounds such as inorganic salts such as halides, oxides, sulfides, sulfates, nitrates, and ammonium salts, and organic compounds.

[0036] The ionization potential of the active layer is preferably −6.5 to −4.0 eV, more preferably −6.0 to −4.5 eV, in that this tends to increase power generation efficiency. The ionization potential of the active layer can be adjusted to the above range by, for example, changing the type of organic-inorganic hybrid semiconductor compound. For example, when the perovskite semiconductor compound described above is used, the ionization potential can be adjusted by changing the type of cation.

[0037] The band gap of the active layer is preferably 0.5 to 2.0 eV, more preferably 0.6 to 1.8 eV, even more preferably 0.7 to 1.7 eV, and most preferably 0.8 to 1.6 eV, in terms of readily achieving high power generation efficiency. The band gap of the active layer can be adjusted to the above range by, for example, changing the type of organic-inorganic hybrid semiconductor compound. For example, when the perovskite semiconductor compound described above is used, the band gap can be adjusted by changing the type and ratio of its anions.

[0038] There is no particular limit to the thickness of the active layer. In terms of being able to absorb more light, a thicker active layer is preferable. In one example, the thickness is preferably 10 nm or more, more preferably 50 nm or more, even more preferably 100 nm or more, particularly preferably 150 nm or more, and most preferably 200 nm or more. On the other hand, in terms of reducing the series resistance and improving the charge extraction efficiency, a thinner thickness is preferable. In one example, the thickness is preferably 1500 nm or less, more preferably 1200 nm or less, and even more preferably 800 nm or less.

[0039] The method for forming the active layer is not particularly limited. Examples include coating, vapor deposition, and co-evaporation. Coating is preferred because it allows for easy formation of the active layer. For example, a method can be used in which a coating liquid containing an organic-inorganic hybrid semiconductor compound or a precursor thereof is applied, and then heated and dried as necessary to form the active layer. Furthermore, after applying the coating liquid, a solvent in which the organic-inorganic hybrid semiconductor compound has low solubility can be further applied to precipitate the organic-inorganic hybrid semiconductor compound.

[0040] The precursor of an organic-inorganic hybrid semiconductor compound refers to a compound that becomes an organic-inorganic hybrid semiconductor compound after being applied as a coating liquid. For example, an organic-inorganic hybrid semiconductor compound precursor that becomes an organic-inorganic hybrid semiconductor compound by heating can be used. For example, a coating liquid can be prepared by mixing a compound represented by formula AX, a compound represented by formula MX, and a solvent, and heating and stirring the mixture. After applying the coating liquid, the compound can be dried by heating to obtain a compound represented by formula AMX ３The solvent is not particularly limited as long as it dissolves the organic-inorganic hybrid semiconductor compound and the optional additives, and examples thereof include organic solvents such as N,N-dimethylformamide.

[0041] The method for applying the coating solution for the active layer is not particularly limited, and examples thereof include spin coating, inkjet coating, doctor blade coating, drop casting, reverse roll coating, gravure coating, kiss coating, roll brush coating, spray coating, air knife coating, wire barber coating, pipe doctor coating, impregnation, coating, and curtain coating.

[0042] After the coating liquid is applied, heat drying can be performed. The heating temperature at this time is not particularly limited, but from the viewpoint of sufficiently removing the solvent, it is preferably 60°C or higher, more preferably 80°C or higher. On the other hand, in order to suppress damage to the photoelectric conversion element, the heating temperature is preferably lower than the temperature at the time of preparing the coating liquid. In one example, the heating temperature is preferably less than 150°C, more preferably less than 135°C, even more preferably less than 115°C, more preferably less than 100°C, even more preferably less than 95°C, more preferably less than 90°C, and particularly preferably less than 85°C. There is also no particular limit to the heating time, but from the viewpoint of sufficiently removing the solvent, it is preferably 1 minute or more, more preferably 3 minutes or more, and from the viewpoint of improving production efficiency, it is preferably 10 hours or less, more preferably 1 hour or less. These heatings may be performed under normal pressure or under reduced pressure.

[0043] (Buffer Layer) Each of the buffer layer 102 and the buffer layer 104 may have a single-layer structure or a multi-layer structure of two or more layers. In the photoelectric conversion element 100, at least one of the buffer layer 102 and the buffer layer 104 is a hole transport layer. However, when the hole transport layer is formed by a coating method, the solvent of the coating liquid may affect the active layer 103, so it is preferable that the buffer layer 102 located between the lower electrode 101 and the active layer 103 is a hole transport layer.

[0044] A buffer layer that is not a hole transport layer may be an electron transport layer. A buffer layer provided between a cathode and an active layer is sometimes called an electron transport layer, and a buffer layer provided between an anode and an active layer is sometimes called a hole transport layer. Hereinafter, the hole transport layer and the electron transport layer will be described purely.

[0045] (Hole transport layer) The hole transport layer contains a polymer having a zwitterionic structure and an organic semiconductor compound. The hole transport layer may further contain a dopant in addition to the polymer having a zwitterionic structure and the organic semiconductor compound.

[0046] Some embodiments of the present invention may include a composition containing a polymer having a zwitterionic structure and an organic semiconductor compound, which can be used as a coating liquid for forming a hole transport layer.

[0047] Other embodiments of the present invention may include a composition containing a polymer having a zwitterionic structure represented by the formula (2) described below and an organic semiconductor compound. The composition can also be used as a coating liquid for forming a hole transport layer. These embodiments are described in detail below.

[0048] A polymer having a zwitterionic structure will now be described. In one example, the polymer having a zwitterionic structure has a structural unit represented by the following formula (1) that does not have a zwitterionic structure, and a structural unit represented by the following formula (2) that has a zwitterionic structure. In the case of this copolymer, the polymer having a zwitterionic structure may be a block copolymer or a random copolymer.

[0049]

[0050] In formula (1), R １１ is a hydrogen atom or an alkyl group, and Y is an alkyl group, an aryl group, a carboxylic acid ester group, a carboxylic acid amide group, or an alkoxyl group. １１The alkyl group in the formula (I) is preferably an alkyl group having 1 to 4 carbon atoms. Examples include a methyl group, an ethyl group, a normal propyl group, an isopropyl group, and a normal butyl group. From the viewpoint of polymerization of a copolymer, a hydrogen atom and a methyl group are preferred. From the viewpoint of solubility of a polymer having a zwitterionic structure, a normal propyl group, an isopropyl group, and a normal butyl group are preferred.

[0051]

[0052] In formula (2), R １２ is a hydrogen atom or an alkyl group, and details and preferred embodiments thereof are as follows: R １１ is the same as

[0053] In formula (2), Z represents an alkyl group having a zwitterionic group as a substituent, an aryl group having a zwitterionic group as a substituent, a carboxylic acid ester group having a zwitterionic group as a substituent, a carboxylic acid amide group having a zwitterionic group as a substituent, or an alkoxyl group having a zwitterionic group as a substituent. Therefore, the structure represented by formula (2) has both a cationic structure and an anionic structure.

[0054] The cationic structure in the zwitterionic group may be a nitrogen-containing structure. A quaternary ammonium cation structure is preferred as the nitrogen-containing structure. The anionic structure in the zwitterionic group may be at least one of a phosphorus-containing structure and a sulfur-containing structure. Of these, a sulfur-containing structure is preferred, and a sulfonate anionic structure is more preferred.

[0055] In formula (2), the zwitterionic group Z is preferably a betaine group represented by the following formula (21) or a betaine group represented by the following formula (22).

[0056]

[0057]

[0058] In formula (21) and formula (22), R ２ , R ３ , R ７ , R １０ is an alkylene group. ２ , R３ , R ７ , R １０ R may be a straight chain or may have a branched chain. ２ , R ３ , R ７ , R １０ is preferably an alkylene group having 1 to 4 carbon atoms. Examples of the alkylene group having 1 to 4 carbon atoms include a methylene group, an ethylene group, a propylene group, and various butylene groups.

[0059] In formula (21) and formula (22), R ４ , R ５ , R ６ , R ８ , R ９ is an alkyl group having 1 to 18 carbon atoms. Examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an n-octyl group, a 2-ethylhexyl group, a dodecyl group, and an octadecyl group. These alkyl groups may be further substituted, and may be bonded to each other to form a ring.

[0060] In formula (22), Q is an anion, such as COO-, SO ２ -, PO ３ - are some examples.

[0061] From the viewpoint of achieving both solubility in non-aqueous solvents and passivation function for the active layer made of perovskite, the proportion of monomer units having a zwitterionic group, such as the structure represented by formula (2), among all structural units of the polymer having a zwitterionic structure is preferably 0.1 mol % to 20 mol %, more preferably 0.5 mol % to 5 mol %.

[0062] The weight-average molecular weight of the polymer having a zwitterionic structure is preferably 5,000 to 100,000, more preferably 10,000 to 500,000, and even more preferably 30,000 to 200,000. It is preferable that the weight-average molecular weight of the polymer having a zwitterionic structure is equal to or greater than the lower limit of the aforementioned range, from the viewpoint of increasing the number of coordination sites of the zwitterionic polymer on the perovskite surface. It is preferable that the weight-average molecular weight of the polymer having a zwitterionic structure is equal to or less than the upper limit of the aforementioned range, from the viewpoint of improving solubility in solvents. The weight-average molecular weight of the polymer having a zwitterionic structure is a value determined by the method described in the Examples.

[0063] The organic semiconductor compound will now be described. The organic semiconductor compound transports holes, among the carriers generated by light irradiation, to the electrode. To enhance hole transport performance, it is preferable that the organic semiconductor compound itself does not have a zwitterionic structure. By mixing a polymer with a zwitterionic structure with an organic semiconductor compound without a zwitterionic structure, the polymer with the zwitterionic structure can be unevenly distributed at the interface with the perovskite, contributing to the inactivation of defects. As a result, the organic semiconductor compound can efficiently transport holes to the electrode. Examples of organic semiconductor compounds include small molecule organic semiconductor compounds and polymer organic semiconductor compounds.

[0064] Examples of low molecular weight organic semiconductor compounds include polycyclic aromatic compounds, such as acene compounds (e.g., tetracene, pentacene, etc.), oligothiophene compounds, phthalocyanine compounds, perylene compounds, rubrene compounds, arylamine compounds (e.g., triarylamine compounds), and carbazole compounds.

[0065] Examples of polymer organic semiconductor compounds include polythiophene-based polymers, polyacetylene-based polymers, polyaniline-based polymers, polyphenylene-based polymers, polyphenylene vinylene-based polymers, polyfluorene-based polymers, polypyrrole-based polymers, and arylamine-based polymers.

[0066] From the viewpoint of compound stability, the organic semiconductor compound preferably contains a conjugated polymer. As the organic semiconductor compound, an arylamine compound is preferred, and a triarylamine compound is more preferred. An arylamine compound and a triarylamine compound are preferred in that they can be stably oxidized by a dopant and exhibit good semiconductor properties, and a triarylamine compound is more preferred.

[0067] An arylamine compound is a compound having an arylamine structure, i.e., a bond between an aryl group and a nitrogen atom. The arylamine compound also includes an arylamine polymer. An arylamine polymer is a polymer having a monomer unit having an arylamine structure.

[0068] The triarylamine compound is a compound having a triarylamine structure, i.e., a bond between the same nitrogen atom and three aryl groups. The triarylamine compound also includes a triarylamine polymer. The triarylamine polymer is a polymer having a monomer unit having a triarylamine structure.

[0069] The aryl group may have either a monocyclic structure or a polycyclic structure, or may have a condensed ring structure, or may have a structure in which these are linked by any divalent linking group or single bond (direct bond). The aryl group may be an aromatic hydrocarbon group or an aromatic heterocyclic group.

[0070] From the viewpoint of film-forming properties, the number of carbon atoms in the aryl group is preferably 30 or less, and more preferably 12 or less. Examples of aromatic hydrocarbon groups include polycyclic aromatic hydrocarbon groups in which a benzene ring is bonded via a carbon-carbon single bond, such as a phenyl group, a biphenyl group, a naphthyl group, and a terphenyl group. Examples of aromatic heterocyclic groups include a thienyl group, a furyl group, a pyrrolyl group, a pyridyl group, and an imidazolyl group.

[0071] The aryl group may have an optional substituent. The optional substituent that the aryl group may have is not particularly limited, and examples thereof include a halogen atom, a hydroxyl group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, a thio group, a seleno group, an aromatic hydrocarbon group, and an aromatic heterocyclic group. The substituent is preferably an amino group or an alkyl group having 1 to 6 carbon atoms. The amino group is preferably a dialkylamino group having 2 to 12 carbon atoms, an alkylarylamino group having 7 to 20 carbon atoms, or a diarylamino group having 12 to 30 carbon atoms.

[0072] The weight-average molecular weight of the triarylamine polymer is preferably 3,000 to 100,000, more preferably 5,000 to 50,000, and even more preferably 7,000 to 25,000. It is preferable that the weight-average molecular weight of the triarylamine polymer is equal to or greater than the lower limit of the aforementioned range, from the viewpoint of improving hole mobility. It is preferable that the weight-average molecular weight of the triarylamine polymer is equal to or less than the upper limit of the aforementioned range, from the viewpoint of improving solubility in solvents. The weight-average molecular weight of the triarylamine polymer is a value determined by the weight average value of the molecular weight in terms of polystyrene measured by GPC.

[0073] The dopant will now be described. A dopant refers to a compound that can impart charge to a compound by chemical reaction or electron transfer. The dopant is not particularly limited as long as it is a compound that can impart charge. By using a dopant, the properties of the hole transport layer, such as the hole transport ability, can be controlled, and therefore the hole transport ability of the hole transport layer relative to the active layer can be further optimized.

[0074] Substances that can be used as dopants are not particularly limited, but include boron compounds such as tetrakis(pentafluorophenyl)borate, molybdenum compounds such as tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene]molybdenum, and organic compounds having a tetracyanoquinodimethane skeleton such as 2,3,4,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane.

[0075] The dopant preferably undergoes a charge transfer reaction with at least one organic semiconductor compound before or after the formation of the hole transport layer. As the dopant, a hypervalent iodine compound is preferred because it has excellent solubility and generates an electron-accepting active site that functions as an oxidizing agent upon heating or the like.

[0076] It is known that hypervalent iodine compounds act as dopants for organic semiconductor compounds and exhibit electron-accepting properties (i.e., oxidizing agent properties). Electron-accepting dopants can improve the conductivity or hole transport ability of semiconductor compounds by removing electrons from the semiconductor compounds. In this way, hypervalent iodine compounds can improve the charge transport properties of semiconductor compounds.

[0077] A hypervalent iodine compound is a compound containing hypervalent iodine, and is defined as a compound containing iodine with an oxidation number of +3 or higher. For example, the dopant can be an iodine(III) compound or an iodine(V) compound. An iodine(V) compound containing pentavalent iodine can be, for example, a periodinane compound such as Dess-Martin periodinane. Examples of iodine(III) compounds containing trivalent iodine include compounds having an oxidized iodobenzene structure, such as (diacetoxyiodo)benzene, and diaryliodonium salts. Organic compounds containing trivalent iodine are preferred as dopants, as they exhibit good electron-accepting properties and are less likely to undergo reverse reactions if the molecules are destroyed during the oxidation process. Among these, diaryliodonium salts are more preferred.

[0078] Diaryliodonium salts are compounds represented by the formula [Ar-I ＋ -Ar]X－ Here, each of the two Ars independently represents an aryl group. The aryl group is not particularly limited, and is the same as that described for the arylamine compound. X － represents any anion. － The X ion may be, for example, a halide ion, a trifluoroacetate ion, a tetrafluoroborate ion, or a tetrakis(pentafluorophenyl)borate ion. － is preferably an anion having a fluorine atom, and more preferably tetrakis(pentafluorophenyl)borate anion or tetrakis(2,3,5,6-trifluoro-4-(trifluoromethyl)phenyl)borate anion.

[0079] A preferred embodiment of the dopant is represented by the following formula (3): － represents any anion, examples of which are as described above. ２１ -I ＋ -R ２２ ]X － Formula (3)

[0080] In formula (3), R ２１ and R ２２ are each independently a monovalent organic group. Examples of monovalent organic groups include aliphatic groups or aromatic groups. Examples of aliphatic groups include aliphatic hydrocarbon groups having 1 to 30 carbon atoms or aliphatic heterocyclic groups having 4 to 30 carbon atoms. For example, the aliphatic group may be an alkyl group including a cycloalkyl group, an alkenyl group, or an alkynyl group. More specifically, examples include a methyl group, an ethyl group, a butyl group, a cyclohexyl group, and a tetrahydrofuryl group.

[0081] Examples of the aromatic group include an aromatic hydrocarbon group having 6 to 30 carbon atoms and an aromatic heterocyclic group having 2 to 30 carbon atoms. For example, the aromatic group may be a phenyl group, a naphthyl group, a biphenyl group, a thienyl group, or a pyridyl group.

[0082] The aliphatic group and aromatic group may have a substituent. The substituent may be, but is not particularly limited to, a halogenyl group, a hydroxyl group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, a thio group, a seleno group, an aromatic hydrocarbon group, or an aromatic heterocyclic group.

[0083] R ２１ and R ２２ is preferably an aromatic hydrocarbon group having 6 to 20 carbon atoms, more preferably a phenyl group. Here, it is preferable that the aromatic hydrocarbon group has no substituent or has a linear or branched alkyl group having 1 to 6 carbon atoms. ２１ and R ２２ is particularly preferably a phenyl group having the alkyl group at the para position.

[0084] More preferred dopants include those represented by the following formula (31).

[0085]

[0086] In formula (31), R ２３ , R ２４ , R ２５ , R ２６ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; Ar ２１ represents an aromatic hydrocarbon group or heteroaromatic hydrocarbon group having 6 to 30 carbon atoms which may have a substituent, and n represents an integer of 0 to 5. The term "independently" used here means that R ２３ , R ２４ , R ２５ , R ２６ may be the same as or different from each other.

[0087] In formula (31), Ar ２１ The aromatic hydrocarbon group or heteroaromatic hydrocarbon group having 6 to 30 carbon atoms, which may have a substituent, is represented by R ２１ and R ２２ or an aromatic group of X － The aromatic groups constituting the anions are the same as those of the aromatic groups constituting the anions of the above.

[0088] The content of the dopant is not particularly limited, but is typically 0.001 to 60% by mass, relative to 100% by mass of the total content of the compound contained in the hole transport layer. By making the dopant content 0.001% by mass or more, the conductivity and hole transport ability of the hole transport layer tend to be improved relative to the active layer. More preferably, it is 0.01% by mass or more, even more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more. By making the dopant content 60% by mass or less, the dispersibility of the organic semiconductor material and the dopant in the film can be controlled, and the generation of leakage current in the photoelectric conversion element tends to be suppressed. More preferably, it is 50% by mass or less, and even more preferably 45% by mass or less.

[0089] The content of the dopant represented by formula (3) or formula (31) in the hole transport layer is preferably 1 to 80 wt %, more preferably 10 to 60 wt %, even more preferably 15 to 50 wt %, particularly preferably 20 to 40 wt %, and most preferably 25 to 30 wt %, when the total amount of the organic semiconductor compound in the hole transport layer is taken as 100 wt %. When the content is within the above preferred range, the photoelectric conversion efficiency of the photoelectric conversion element can be increased without impairing the adhesion between the hole transport layer and the layer adjacent thereto.

[0090] The hole transport layer may further contain components other than the polymer having a zwitterionic structure, the organic semiconductor compound, and the dopant, such as, but not limited to, an adhesive functional material, a filler, and a strength additive.

[0091] The proportion of the polymer having a zwitterionic structure can be set arbitrarily depending on the desired performance. From the viewpoint of maintaining both the electrical conductivity of the hole transport layer and the covering effect of the zwitterions, the proportion of the polymer having a zwitterionic structure is preferably 0.01 to 10 mass %, more preferably 0.1 to 5 mass %, and even more preferably 0.5 to 3 mass %, of the total amount of the hole transport layer.

[0092] The thickness of the hole transport layer is preferably as thick as possible, in order to prevent current leakage due to the formation of a conductive path between the upper and lower electrodes and the active layer when the active layer located between the upper and lower electrodes has a high charge transport ability. For example, the thickness is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 5 nm or more. On the other hand, a thin thickness is preferable, in order to prevent resistance in charge transport by the hole transport layer and to reduce costs by saving the amount of compound in the hole transport layer. For example, the thickness is preferably 800 nm or less, more preferably 600 nm or less, and even more preferably 400 nm or less.

[0093] The hole transport layer may have a first layer containing a polymer having a zwitterionic structure and a second layer laminated on the first layer and containing the organic semiconductor compound, or may contain a mixture of a polymer having a zwitterionic structure and an organic semiconductor compound. A hole transport layer containing a mixture of a polymer having a zwitterionic structure and an organic semiconductor compound is preferred in that it reduces the number of manufacturing steps and thereby enables further reduction in manufacturing costs.

[0094] The hole transport layer can be formed by using a composition containing a polymer having a zwitterionic structure and an organic semiconductor compound as a coating solution for the hole transport layer. The formation method is not particularly limited. For example, a coating method, a vapor deposition method, or a co-evaporation method can be used. The coating method is preferred because it allows the hole transport layer to be formed easily.

[0095] The method for applying the coating solution for the hole transport layer is not particularly limited, and examples thereof include spin coating, inkjet coating, doctor blade coating, drop casting, reverse roll coating, gravure coating, kiss coating, roll brush coating, spray coating, air knife coating, wire barber coating, pipe doctor coating, impregnation, coating, and curtain coating.

[0096] After the coating liquid is applied, it can be dried by heating. The details and preferred aspects of the conditions for drying by heating can be the same as those explained for forming the active layer.

[0097] (Electron Transport Layer) The electron transport layer may be made of any material capable of improving the efficiency of electron extraction from the active layer to the cathode, such as inorganic compounds, organic compounds, and organic-inorganic perovskite semiconductor compounds described in WO 2013 / 171517, WO 2013 / 180230, and JP 2012-191194 A.

[0098] Examples of inorganic compounds for the electron transport layer include salts of alkali metals such as lithium, sodium, potassium, and cesium, and metal oxides such as zinc oxide, titanium oxide, aluminum oxide, and indium oxide. Examples of organic compounds for the electron transport layer include bathocuproine (BCP), bathophenanthrene (Bphen), and (8-hydroxyquinolinato)aluminum (Alq). ３ ), boron compounds, oxadiazole compounds, benzimidazole compounds, naphthalenetetracarboxylic anhydride (NTCDA), perylenetetracarboxylic anhydride (PTCDA), fullerene compounds, phosphine oxide compounds, and phosphine sulfide compounds, etc.

[0099] When the active layer located between the upper and lower electrodes has a high charge transport capability, a thicker thickness of the electron transport layer is preferable in order to prevent current leakage due to the formation of a conductive path between the upper and lower electrodes and the active layer. For example, a thickness of 0.5 nm or more is preferable, more preferably 1 nm or more, and even more preferably 5 nm or more. On the other hand, a thinner thickness is preferable in order to prevent resistance in charge transport by the electron transport layer and reduce costs by saving the amount of compound in the electron transport layer. For example, a thickness of 800 nm or less is preferable, more preferably 600 nm or less, and even more preferably 400 nm or less.

[0100] The method for forming the electron transport layer is not particularly limited. For example, a coating method, a vapor deposition method, or a co-evaporation method can be used. The coating method is preferred because it allows the electron transport layer to be easily formed.

[0101] The method for applying the coating liquid for the electron transport layer is not particularly limited, and examples thereof include spin coating, inkjet coating, doctor blade coating, drop casting, reverse roll coating, gravure coating, kiss coating, roll brush coating, spray coating, air knife coating, wire barber coating, pipe doctor coating, impregnation, coating, and curtain coating.

[0102] After the coating liquid is applied, it can be dried by heating. The details and preferred aspects of the conditions for drying by heating can be the same as those explained for forming the active layer.

[0103] (Substrate) As in the photoelectric conversion element 100 shown in Fig. 1, the photoelectric conversion element may have a substrate 106. The material of the substrate is not particularly limited. For example, materials described in documents such as WO 2013 / 171517, WO 2013 / 180230, and JP 2012-191194 A may be used.

[0104] (Photoelectric Conversion Characteristics) The photoelectric conversion characteristics of the photoelectric conversion element can be determined as follows: The photoelectric conversion element 100 is irradiated with light under AM 1.5G conditions using a solar simulator at an irradiation intensity of 100 mW / cm. ２ The photoelectric conversion element is irradiated with light at a wavelength of 1.5 G, and the current-voltage characteristics (IV characteristics) are measured. From the obtained current-voltage curve, photoelectric conversion characteristics such as photoelectric conversion efficiency (PCE), short-circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), series resistance, and shunt resistance can be determined. PCE is the value (%) obtained by dividing the output (maximum output) at the optimum operating point of the IV characteristics of the photoelectric conversion element by the total amount of energy possessed by the irradiated light. For example, when the irradiated light is sunlight with an intensity of AM 1.5 G, the total amount of energy is 100 mW / cm. ２ is.

[0105] (Method for manufacturing photoelectric conversion element) The method for manufacturing a photoelectric conversion element is not particularly limited, and various methods for manufacturing photoelectric conversion elements using perovskite semiconductor compounds can be applied. For example, a photoelectric conversion element can be manufactured by forming each layer of the photoelectric conversion element as already described. A suitable method for manufacturing a photoelectric conversion element includes at least applying a hole transport layer coating liquid containing a polymer having a zwitterionic structure and an organic semiconductor compound to an active layer to form the hole transport layer.

[0106] The photoelectric conversion element can be manufactured by stacking each layer of the photoelectric conversion element. The method for forming each layer is not particularly limited. For example, various methods such as a sheet-to-sheet method or a roll-to-roll method can be applied.

[0107] The roll-to-roll method is a method in which a flexible substrate wound in a roll is unwound and processed while being transported intermittently or continuously until it is wound up by a take-up roll. The roll-to-roll method allows long substrates on the order of kilometers to be processed in one go. Therefore, the roll-to-roll method is more suitable for mass production than the sheet-to-sheet method. However, when attempting to form each layer using the roll-to-roll method, due to its structure, contact between the film-forming surface and the roll may cause scratches on the film or partial peeling.

[0108] The size of the roll that can be used in the roll-to-roll system is not particularly limited as long as it can be handled by a roll-to-roll system manufacturing device, but the upper limit of the outer diameter is preferably 5 m or less, more preferably 3 m or less, and even more preferably 1 m or less, while the lower limit is preferably 10 cm or more, more preferably 20 cm or more, and even more preferably 30 cm or more.

[0109] The upper limit of the outer diameter of the roll core is preferably 4 m or less, more preferably 3 m or less, and more preferably 0.5 m or less. On the other hand, the lower limit is preferably 1 cm or more, more preferably 3 cm or more, more preferably 5 cm or more, even more preferably 10 cm or more, and particularly preferably 20 cm or more. These diameters being equal to or less than the upper limit are preferred in terms of high handleability of the roll, and being equal to or greater than the lower limit are preferred in terms of reducing the possibility of the layers formed in each step being destroyed by bending stress.

[0110] The lower limit of the width of the roll is preferably 5 cm or more, more preferably 10 cm or more, and more preferably 20 cm or more. On the other hand, the upper limit is preferably 5 m or less, more preferably 3 m or less, and more preferably 2 m or less. A width of less than the upper limit is preferred in terms of high handleability of the roll, and a width of more than the lower limit is preferred in terms of increased flexibility in the size of the photoelectric conversion element.

[0111] In the manufacturing method of the photoelectric conversion element 100, after the upper electrode 105 is laminated, the photoelectric conversion element 100 is preferably heated, for example, at a temperature range with a lower limit of 50°C to 80°C and an upper limit of 280°C to 300°C (this heating step may be referred to as an annealing treatment step). The annealing treatment step is preferably performed at a high temperature, since it is more likely to improve the adhesion between the layers of the photoelectric conversion element 100, such as between the buffer layer 102 and the lower electrode 101, or between the buffer layer 102 and the active layer 103. For example, it is preferably performed at 50°C or higher. By improving the adhesion between the layers, the thermal stability and durability of the photoelectric conversion element can be improved. On the other hand, the temperature of the annealing treatment step is preferably low, since the organic compound contained in the photoelectric conversion element 100 is less likely to be thermally decomposed. For example, it is preferably performed at 300°C or lower. In the annealing treatment step, stepwise heating using different temperatures within the above temperature range may be performed.

[0112] The heating time may be 1 minute or more, or 3 minutes or more, to improve adhesion while suppressing thermal decomposition. The heating time may be 180 minutes or less, or 60 minutes or less. The annealing process is preferably terminated when the solar cell performance parameters Voc, Jsc, and FF reach certain values.

[0113] The annealing process is preferably carried out under normal pressure in an inert gas atmosphere to prevent thermal oxidation of the constituent materials. Heating may be performed by placing the photoelectric conversion element on a heat source such as a hot plate, or by placing the photoelectric conversion element in a heated atmosphere such as an oven. Heating may be performed batchwise or continuously.

[0114] To improve durability, the photoelectric conversion element may be sealed. For example, the photoelectric conversion element can be sealed by further laminating a sealing plate on the lower electrode and fixing the base material and the sealing plate with an adhesive.

[0115] (Mechanism of Action) In the photoelectric conversion element described above, the hole transport layer can be formed using a hole transport layer coating solution containing a polymer with a zwitterionic structure and an organic semiconductor compound. Therefore, by forming the hole transport layer after the growth of the perovskite crystal is complete, the hole transport layer can penetrate not only the surface but also the grain boundaries, passivating (inactivating) crystal defects. As a result, the defect density is reduced over a wide region of the perovskite crystal, suppressing charge recombination of photocarriers and achieving higher photoelectric conversion efficiency.

[0116] In addition, the surface repair effect of the active layer containing perovskite crystals can be obtained by forming a hole transport layer containing a polymer with a zwitterionic structure and an organic semiconductor compound, eliminating the need for a film formation step solely for the purpose of surface repair, thereby reducing manufacturing costs.

[0117] Furthermore, even if the hole transport layer is formed first and then the perovskite layer is deposited, the defect repair effect can be exerted at the interface between the hole transport layer and the perovskite layer, which results in suppression of photocarrier recombination and higher photoelectric conversion efficiency.

[0118] [Solar Cell] The photoelectric conversion element according to the present invention is suitable as a solar cell. FIG. 2 shows an example of a solar cell equipped with the photoelectric conversion element of the present invention. The thin-film solar cell 14 shown in FIG. 2 includes a photoelectric conversion element 100 (not shown). The thin-film solar cell 14 includes, in this order, a weather-resistant protective film 1, an ultraviolet-blocking film 2, a gas barrier film 3, a getter material film 4, an encapsulant 5, a solar cell element 6 having a photoelectric conversion element 100 (not shown), an encapsulant 7, a getter material film 8, a gas barrier film 9, and a backsheet 10. The thin-film solar cell 14 is configured such that light is irradiated from the side on which the protective film 1 is formed (the lower side in FIG. 2 ), causing the solar cell element 6 to generate electricity. However, the thin-film solar cell 14 does not need to include all of these components; required components can be selected as desired.

[0119] The thin-film solar cell 14 may be used alone, or a plurality of thin-film solar cells 14 may be connected together, or may be used as a component of a solar cell module in combination with other components. For example, as shown in Fig. 3, a solar cell module 13 having thin-film solar cells 14 on a substrate 12 may be fabricated, and this solar cell module 13 may be installed at the location of use.

[0120] Well-known techniques can be applied to the selection and manufacturing methods of the above-mentioned components, such as those described in WO 2013 / 171517, WO 2013 / 180230, and JP 2012-191194 A.

[0121] The photoelectric conversion element of the present invention and the solar cell and solar cell module including the same are not limited in their applications, and examples thereof include solar cells for building materials, solar cells for automobiles, solar cells for interior decoration, solar cells for railways, solar cells for ships, solar cells for airplanes, solar cells for home appliances, solar cells for mobile phones, and solar cells for toys.

[0122] Although several embodiments have been described above, the present invention is not limited to the embodiments disclosed in this specification and can be appropriately modified and implemented without departing from the spirit of the invention. The embodiments disclosed in this specification can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention.

[0123] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following description.

[0124] [Synthesis of Zwitterionic Polymer] Synthesis was performed with reference to Angew. Chem. Int. Ed. 2020, 59, 10802-10806. １ H-NMR was used to identify the chemical structure and zwitterion concentration.

[0125] [Measurement of number average molecular weight (Mn) and weight average molecular weight (Mw)] The polymer was dissolved in N,N-dimethylformamide (DMF) to a concentration of 0.1% by mass and used as a measurement sample. The number average molecular weight and weight average molecular weight were measured by gel permeation chromatography (GPC) using N,N-dimethylformamide (DMF) in which lithium bromide was dissolved to a concentration of 10 nM as the mobile phase and a differential refractometer as the detector. Monodisperse polystyrene was used as a molecular weight standard. The detailed measurement conditions are as follows. Column: TSKgelGMH ＨＲ Two HPLC columns (7.8 mm x 30 cm, Tosoh) were connected in series. Mobile phase: DMF containing 10 mM lithium bromide. Flow rate: 1.0 ml / sec. Temperature: 40°C. Standard material: standard polystyrene kit (PStQuick Kit-H, Tosoh Corporation).

[0126] [Preparation of Coating Solution for Electron Transport Layer] Ultrapure water was added to a 15% by mass aqueous dispersion of tin (IV) oxide (manufactured by Alfa Aesar) to prepare a 7.5% by mass aqueous dispersion of tin oxide.

[0127] [Preparation of Active Layer Coating Solution] Lead (II) iodide was weighed into a vial and introduced into a glove box. N,N-dimethylformamide was added as a solvent to adjust the concentration of lead (II) iodide to 1.3 mol / L, and the mixture was heated and stirred at 100°C for 1 hour to prepare Active Layer Coating Solution 1. Formamidine hydroiodide (FAI), methylamine hydrobromide (MABr), and methylamine hydrochloride (MACl) were weighed into a separate vial in a mass ratio of 10:1:1.5 and introduced into a glove box. Isopropyl alcohol was added as a solvent to this to prepare Active Layer Coating Solution 2, which had a total concentration of FAI, MABr, and MACl of 0.54 mol / L.

[0128] [Preparation of Coating Solution 1 for Hole Transport Layer] Anisole solution 1 containing 38.7 mg / mL of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] was prepared. Anisole solution 2 containing 101.2 mg / mL of a compound (electron-accepting dopant) represented by the following formula was separately prepared. The two solutions were mixed so that anisole solution 1 and anisole solution 2 were 10% by volume and 90% by volume, respectively. The mixed solution was heated and stirred at 130°C for 1 hour to prepare a carrier-doped hole transport solution.

[0129]

[0130] A compound represented by the following formula (zwitterionic polymer, weight-average molecular weight: 82,500) with a zwitterionic concentration of 1.7 mol% was weighed into a separate bottle, and anisole was added to prepare a zwitterionic polymer solution with a compound concentration of 5.5 mg / mL. The zwitterionic polymer solution and the hole transport liquid were mixed to a concentration of 10 vol% and 90 vol%, respectively. The mixture was then thoroughly stirred to prepare zwitterionic polymer-containing hole transport layer coating solution 1.

[0131]

[0132] [Preparation of Coating Solution 2 for Hole Transport Layer] Anisole solution 1 containing 38.7 mg / mL of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] was prepared. Anisole solution 2 containing 101.2 mg / mL of a compound (electron-accepting dopant) represented by the following formula was separately prepared. Anisole solution 1 and anisole solution 2 were mixed so that the concentration was 10% by volume and 90% by volume, respectively. The resulting mixture was heated and stirred at 130°C for 1 hour to prepare a carrier-doped hole transport liquid. Anisole solution 1 was added at 10% by volume to the carrier-doped hole transport liquid, and the mixture was thoroughly stirred to prepare Coating Solution 2 for Hole Transport Layer containing no zwitterionic polymer.

[0133] Example 1 The above-described electron transport layer coating solution was spin-coated onto a glass substrate having a patterned ITO transparent conductive film (lower electrode) and heated at 150°C for 10 minutes to form a 50-nm-thick electron transport layer. This substrate was then placed in a glove box, and active layer coating solution 1, heated to 100°C, was spin-coated onto the substrate. This was then heated at 100°C for 10 minutes to form a lead iodide layer. Active layer coating solution 2 was then spin-coated onto the substrate and heated at 150°C for 20 minutes to form an active layer (650 nm thick) of an organic-inorganic hybrid perovskite semiconductor compound. A hole transport coating solution containing a zwitterionic polymer was spin-coated onto the active layer and heated at 90°C for 5 minutes to form a 150-nm-thick hole transport layer. A 150-nm-thick gold film was then formed by vacuum deposition to serve as the upper electrode layer. The photoelectric conversion element of Example 1 was thus fabricated.

[0134] Comparative Example 1 A photoelectric conversion element of Comparative Example 1 was prepared in the same manner as in Example 1, except that Coating Liquid 2 for Hole Transport Layer was used.

[0135] [Evaluation of energy conversion efficiency] A mask with a 4 mm square opening was attached to the photoelectric conversion element obtained in each example, and the current-voltage characteristics between the ITO electrode and the upper electrode were measured. For the measurement, a source meter (Keithley, Model 2400) was used, and the irradiation light source was an air mass (AM) of 1.5 G and an irradiance of 100 mW / cm. ２The voltage was swept from positive to negative and then back to positive, and the open circuit voltage Voc (V) and short circuit current density Jsc (mA / cm) were measured. ２ The fill factor FF and photoelectric conversion efficiency PCE (%) were calculated. Table 1 shows the measurement results of Example 1 when the voltage was swept in the negative direction, relative to the comparative example. Table 2 also shows the results of Example 1, obtained by subtracting the calculated value in the positive direction from the calculated value in the negative direction, relative to the comparative example 1.

[0136]

[0137]

[0138] As shown in Table 1, in Example 1, Voc and FF increased, indicating an improvement in conversion efficiency. Furthermore, as shown in Table 2, in Example 1, hysteresis was also improved, and the difference in conversion efficiency depending on the voltage sweep direction was small. These can be considered to be the effect of the zwitterionic polymer repairing the crystal defects in the perovskite layer. In Example 1, a defect repair effect was observed using a simple process similar to the simple hole transport layer formation process, without the additional process of forming an intermediate layer. Zwitterionic polymers are useful because they can repair both positively charged defects and negatively charged defects.

[0139] [Durability Evaluation] The photoelectric conversion elements obtained in each example were sealed in glass cans to which a moisture adsorbent had been attached, and then durability evaluations were performed. Two sealed photoelectric conversion elements were prepared for each example. One element was placed directly in a thermostatic chamber at 100°C, and after a certain period of time, it was removed and an IV measurement was performed. The other element was placed under 1 sun illumination with the anode / cathode shorted, and after a certain period of time, it was removed and an IV measurement was performed. Table 3 also shows the results after 23 hours of 1 sun evaluation, expressed as the maintenance rate from the initial characteristics.

[0140]

[0141] Furthermore, Table 3 shows that the use of a zwitterionic polymer-containing hole transport layer improves light resistance. Comparative Example 1 originally had many defects, which developed into defects accompanied by a deterioration in Voc upon light irradiation, whereas Example 1 appears to have improved the deterioration of characteristics because the original defects were repaired.

[0142] According to the present invention, there are provided a photoelectric conversion element and a method for producing the same that improve the reproducibility of crystal growth of perovskite crystals and reduce production costs; and a composition and hole transport layer from which the photoelectric conversion element can be obtained.

[0143] REFERENCE SIGNS LIST 1 Weather-resistant protective film 2 UV-cut film 3, 9 Gas barrier film 4, 8 Getter material film 5, 7 Sealant 6 Solar cell element 10 Back sheet 12 Substrate 13 Solar cell module 14 Thin-film solar cell 100 Photoelectric conversion element 101 Lower electrode 102 Buffer layer 103 Active layer 104 Buffer layer 105 Upper electrode 106 Substrate

Claims

1. A composition comprising a polymer having a zwitterionic structure represented by the following formula (2) and an organic semiconductor compound: In formula (2), R １２ represents a hydrogen atom or an alkyl group, and Z represents an alkyl group having a zwitterionic group as a substituent, an aryl group having a zwitterionic group as a substituent, a carboxylate group having a zwitterionic group as a substituent, a carboxylic acid amide group having a zwitterionic group as a substituent, or an alkoxyl group having a zwitterionic group as a substituent.

2. The composition of claim 1, wherein the cationic structure of the zwitterionic group in the structure of formula (2) comprises a nitrogen-containing structure.

3. The composition of claim 1, wherein the anionic structure of the zwitterionic group in the structure of formula (2) comprises at least one of a phosphorus-containing structure and a sulfur-containing structure.

4. The composition of claim 1, wherein the organic semiconductor compound comprises a conjugated polymer.

5. The composition of claim 4, wherein the conjugated polymer comprises an arylamine compound.

6. The composition according to claim 4, wherein the conjugated polymer comprises a triarylamine polymer, and the weight average molecular weight of the triarylamine polymer is from 3,000 to 100,000.

7. The composition according to claim 1, wherein the weight average molecular weight of the polymer having the structure of formula (2) is 5,000 to 100,000.

8. The composition according to claim 1, wherein the ratio of monomer units having a zwitterionic group to all structural units of the polymer having the structure of formula (2) is 0.1 mol % to 20 mol %.

9. The composition according to claim 1, wherein the proportion of the polymer having the structure of formula (2) in the composition is 0.01 to 10% by mass of the total amount of the composition.

10. A composition comprising a polymer having a zwitterionic structure and an organic semiconductor compound.

11. The composition of claim 10, wherein the polymer having a zwitterionic structure has a cationic structure, and the cationic structure comprises a nitrogen-containing structure.

12. The composition of claim 10, wherein the polymer having a zwitterionic structure has an anionic structure, and the anionic structure includes at least one of a phosphorus-containing structure and a sulfur-containing structure.

13. The composition of claim 10, wherein the organic semiconductor compound comprises a conjugated polymer.

14. The composition of claim 13, wherein the conjugated polymer comprises an arylamine compound.

15. The composition according to claim 13, wherein the conjugated polymer comprises a triarylamine polymer, and the weight average molecular weight of the triarylamine polymer is from 3,000 to 100,000.

16. The composition according to claim 10, wherein the weight average molecular weight of the polymer having a zwitterionic structure is 5,000 to 100,000.

17. The composition according to claim 10, wherein the ratio of monomer units having a zwitterionic group to all structural units of the polymer having a zwitterionic structure is 0.1 mol % to 20 mol %.

18. The composition according to claim 10, wherein the proportion of the polymer having a zwitterionic structure in the composition is 0.01 to 10% by mass of the total amount of the composition.

19. A hole transport layer comprising the composition of any one of claims 1-18.

20. A photoelectric conversion element comprising: a pair of electrodes having an upper electrode and a lower electrode; an active layer located between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound; and a hole transport layer located between the active layer and the upper electrode or the lower electrode, wherein the hole transport layer comprises the composition according to any one of claims 1 to 18.

21. The photoelectric conversion element according to claim 20, wherein the hole transport layer comprises: a first layer containing the polymer having the zwitterionic structure; and a second layer laminated on the first layer and containing the organic semiconductor compound.

22. The photoelectric conversion element according to claim 20, wherein the hole transport layer contains a mixture of the polymer having a zwitterionic structure and the organic semiconductor compound.

23. A method for producing a photoelectric conversion element, comprising the step of applying the composition according to any one of claims 1 to 18 to an active layer.

Images