JP7009898B2 - Photoelectric conversion element and its manufacturing method - Google Patents

Description

The present invention relates to a photoelectric conversion element (for example, a solar cell or the like) having a perovskite layer containing a compound having a perovskite type structure and polysilane, and a method for producing the same.

In the field of solar cells, perovskite-type solar cells using a compound having a perovskite-type structure as a light absorption layer are attracting attention. Perovskite solar cells can be molded by an easy method such as coating without the need for a vacuum process, and the raw materials are relatively inexpensive, so the manufacturing cost can be significantly reduced compared to conventional solar cells. .. In recent years, research and development of perovskite-type solar cells have been rapidly advanced, and their conversion efficiencies are comparable to those of conventional solar cells. Therefore, further research and development for practical use are expected in the future.

Under these circumstances, development is underway to improve the durability of perovskite solar cells. For example, Japanese Patent Application Laid-Open No. 2017-69533 (Patent Document 1) describes that a perovskite-type compound (for example, CH ₃ NH ₃ PbI ₃ or the like) is decomposed into low molecular weight components by the influence of light, moisture, or the like. For example, as shown in the following formula, it is decomposed into low molecular weight components, and then metallic lead Pb is generated from the produced lead iodide PbI ₂ , and the generated carriers are trapped by photoexcitation by this metallic lead Pb. , It is described that the characteristics of the photoelectric conversion element are deteriorated.

Therefore, Patent Document 1 discloses that by using a mixture containing a quinone-based compound and a perovskite-type compound, metal formation can be suppressed by the oxidizing action of the quinone-based compound, and a photoelectric conversion element capable of stable driving can be realized. Has been done.

However, Patent Document 1 cannot suppress the formation of metal halides and cannot sufficiently suppress the deterioration of the photoelectric conversion element.

In Japanese Patent Application Laid-Open No. 2016-51891 (Patent Document 2), the substrate / first electrode / electron transport layer / predetermined photoelectric conversion layer / compound layer having a perovskite structure / hole transport layer / second electrode is described. A method for manufacturing a solar cell to be laminated in order is disclosed, and it is described that polysilane or the like may be used as a hole transport layer.

However, Patent Document 2 does not describe adding polysilane to the perovskite layer or suppressing deterioration of the photoelectric conversion element, and the durability of the element cannot be sufficiently improved.

JP-A-2017-69533 (Claims, [0005] [0006] [0014]) JP-A-2016-51891 (Claim 7, [0031])

Therefore, another object of the present invention is to provide a perovskite type photoelectric conversion element capable of effectively suppressing deterioration of the element and a method for manufacturing the same.

Another object of the present invention is to provide a perovskite type photoelectric conversion element having high photoelectric conversion efficiency (hereinafter, also simply referred to as conversion efficiency) and a method for manufacturing the same.

As a result of diligent studies to achieve the above problems, the present inventors have formed a perovskite layer containing a compound having a perovskite-type structure and polysilane in a perovskite-type photoelectric conversion element, which causes deterioration of the element. We have found that the formation of metal halides such as ₂ can be suppressed, and completed the present invention.

That is, the photoelectric conversion element of the present invention is a photoelectric conversion element including a perovskite layer containing a compound having a perovskite-type structure, and the perovskite layer contains polysilane.

The polysilane may contain at least one structural unit selected from the structural units represented by the following formulas (2a) and (2b).

(In the formula, R ¹ to R ³ independently represent a hydrogen atom, a hydroxyl group, an organic group or a silyl group, respectively.)

In the formula (2a), at least one of R ¹ and R ² may be an aryl group-containing group, and in the formula (2b), R ³ may be an aryl group-containing group. Further, in the above formula (2a), both R ¹ and R ² may be aryl group-containing groups. The aryl group-containing group is a C _6-12 aryl group, a C _6-12 aryl-C _1-6 alkyl group, a C _6-12 aryl oxy group or a C _6-12 aryl-C _1-6 alkoxy group. May be good. The ratio of the structural unit represented by the formula (2a) may be 50 mol% or more with respect to the entire polysilane. The polysilane may be cyclic polysilane. The weight average molecular weight of the polysilane may be about 300 to 25,000. The ratio of the polysilane may be about 0.01 to 10 parts by weight with respect to 100 parts by weight of the compound having a perovskite type structure.

The compound having a perovskite-type structure is a compound represented by the formula AMX ₃ (in the formula, A is an organic ammonium, M is a divalent atom, and X is a halogen atom), and A is C _1- . ₄ At least one organic ammonium selected from alkylammonium and C _1-4 amidinium, M is at least one atom selected from Group 14 and Group 2 elements of the periodic table, X is iodine I, It may be at least one halogen atom selected from bromine Br and chlorine Cl.

The present invention also includes a method for producing the photoelectric conversion element by forming a perovskite layer containing the compound having the perovskite type structure and the polysilane.

In the present invention, in a perovskite-type photoelectric conversion element, a perovskite layer containing a compound having a perovskite-type structure and polysilane is formed, so that deterioration of the element can be effectively suppressed. It is also possible to manufacture a perovskite-type photoelectric conversion element having a high photoelectric conversion efficiency (hereinafter, also simply referred to as conversion efficiency).

FIG. 1 is a schematic view of a photoelectric conversion element manufactured in an example. FIG. 2 shows the results of X-ray diffraction measurement of the photoelectric conversion elements manufactured in Examples 1 to 3 and Comparative Example 1. FIG. 3 is a surface observation image of the photoelectric conversion element produced in Examples 1 to 3 and Comparative Example 1 by an optical microscope. FIG. 4 is a current density-voltage curve of the photoelectric conversion element produced in Examples 1 to 3 and Comparative Example 1. FIG. 5 is a measurement result of the external quantum efficiency (IPCE) of the photoelectric conversion element manufactured in Examples 1 to 3 and Comparative Example 1.

[Structure of photoelectric conversion element]
The photoelectric conversion element of the present invention is a photoelectric conversion element including a perovskite layer containing a compound having a perovskite-type structure (also simply referred to as a perovskite compound), and the perovskite layer contains polysilane. In addition to the perovskite layer, the perovskite-type photoelectric conversion element includes, for example, a first electrode (transparent electrode), an electron transport layer (ETL), a hole (or hole) transport layer (HTL), and a second electrode (metal). Alternatively, it may contain a carbon electrode) or the like.

As a typical structure of the photoelectric conversion element, for example, a plane heterojunction type in which a first electrode / an electron transport layer (ETL) / a perovskite layer / a hole transport layer / a second electrode are laminated in this order; Inverse structure type in which the order of the first electrode and the second electrode is changed with respect to the plane heterojunction type; adjacent to the electron transport layer in the vicinity of the interface of the perovskite layer with the electron transport layer in the plane heterojunction type. A porous portion containing a porous oxide is formed, and a nanostructured type including a layer (a first perovskite layer described later) in which a compound having a perovskite type structure is infiltrated (or impregnated) into the porous portion is formed. Can be mentioned. The structure of the photoelectric conversion element may be any structure, and from the viewpoint of having a large surface area and easily improving characteristics such as conversion efficiency, it is usually a nanostructure type, that is, as shown in FIG. 1, the first structure is used. The electrode 1 / electron transport layer 2 / the first perovskite layer 3a containing the porous portion and the perovskite compound / the second perovskite layer 3b containing the perovskite compound / the hole transport layer 4 / the second electrode 5 are laminated in this order. In many cases, it has a structure.

(Perovskite layer)
The perovskite layer (or the first perovskite layer 3a and / or the second perovskite layer 3b) contains a compound having a perovskite-type structure and polysilane.

(1) Perovskite compound The perovskite compound is not particularly limited, and is usually a compound represented by the formula AMX ₃ (1) (in the formula, A represents an organic ammonium, M represents a divalent atom, and X represents a halogen atom). Organic and inorganic perovskite compounds such as are often used.

In the formula (1), examples of the organic ammonium represented by A include methylammonium, ethylammonium, n-propylammonium, i-propylammonium, n-butylammonium, i-butylammonium, s-butylammonium, and t. -C _1-6 alkylammonium such as butylammonium; C _{6-10arylammonium} such as anilinium; C _6-10aryl C _1-6 alkylammonium such as benzylammonium and phenethylammonium; formamidinium, acetoamidinium, etc. C _1-6 Amidinium and the like can be mentioned.

These organic ammoniums can be used alone or in combination of two or more. Among these organic ammoniums, C _1-4 alkylammonium, C _1-4 amidinium and the like are preferable, and among them, C _1-2 alkylammonium such as methylammonium and _C1-2 amidinium such as formamidinium (particularly). Methylammonium) is preferred.

In the formula (1), examples of the divalent atom represented by M include elements of Group 14 of the Periodic Table such as Pb, Sn, and Ge; Group 2 of the Periodic Table such as Ra, Ba, Sr, Ca, and Mg. Elements (or alkaline earth metals) and the like can be mentioned. These divalent atoms can be used alone or in combination of two or more. Among these divalent atoms, Group 14 elements of the Periodic Table such as Pb, Sn, and Ge, Group 2 elements of the Periodic Table such as Ba, Sr, Ca, and Mg are preferable, and Pb is particularly preferable. , Sn and the like, the 14th group element of the periodic table (particularly Pb) is preferable.

Examples of the halogen atom represented by X in the formula (1) include iodine I, bromine Br, chlorine Cl and the like. These halogen atoms can be used alone or in combination of two or more. Of these halogen atoms, iodine I and chlorine Cl (particularly iodine I) are preferable.

Typical compounds represented by the formula (1) include, for example, a compound in which A is methylammonium and M is Pb, CH ₃ NH ₃ PbI ₃ , CH ₃ NH ₃ PbBr ₃ , CH ₃ NH ₃ PbCl ₃ , and the like. CH ₃ NH ₃ PbI _3-n Br _n , CH ₃ NH ₃ PbI _3-n Cl _n , CH ₃ NH ₃ PbBr _3-n Cl _n , etc .; compounds in which A is methylammonium and M is Sn, CH ₃ NH ₃ SnI ₃ , CH ₃ NH ₃ SnBr ₃ , CH ₃ NH ₃ SnCl ₃ , CH ₃ NH ₃ SnI _3-n Br _n , CH ₃ NH ₃ SnI 3 _{- n} Cl _n , CH ₃ NH _{3 SnCl} Can be mentioned. Note that n represents the doping amount (or ratio) of the halogen atom X, for example, 0.01 to 2, preferably 0.03 to 1.5, and more preferably 0.05 to 1 (for example, 0.1 to 1). It may be about 0.5). If n is too large, the photoelectric conversion efficiency may decrease.

These perovskite compounds can also be used alone or in combination of two or more. Among these perovskite compounds, the compound in which A is methylammonium and M is Pb is preferable in the formula (1), and among them, CH ₃ NH ₃ PbI ₃ , CH ₃ NH ₃ PbI _3-n Br _n , CH ₃ Compounds such as NH ₃ PbI _3-n Cl _n containing at least iodine I in X (particularly CH ₃ NH ₃ PbI ₃ ) are preferred.

(2) Polysilane The polysilane is not particularly limited as long as it is a linear, cyclic, branched chain, and / or network-like (or network-like) compound having a Si—Si bond, but is usually expressed in the following formula (2a). In many cases, the structural unit represented by (2b) and (2b) has at least one structural unit.

(In the formula, R ¹ to R ³ independently represent a hydrogen atom, a hydroxyl group, an organic group or a silyl group).

In the formulas (2a) and (2b), the organic group represented by the groups (or side chains) R ¹ to R ³ includes a hydrocarbon group (alkyl group, alkenyl group, cycloalkyl group, cycloalkenyl group, aryl). Groups, aralkyl groups), ether groups corresponding to these hydrocarbon groups (alkoxy groups, cycloalkyloxy groups, aryloxy groups, aralkyloxy groups, etc.) and the like can be mentioned. Usually, the organic group is often a hydrocarbon group such as an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group or an aralkyl group. In addition, hydrogen atoms, hydroxyl groups, alkoxy groups, silyl groups, etc. are often substituted at the ends.

In R ¹ to R ³ of the formulas (2a) and (2b), the alkyl group includes a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an i-butyl group, an s-butyl group, and t. -C _1-14 alkyl groups such as butyl group, pentyl group and hexyl group (preferably C _1-10 alkyl group, more preferably C _1-6 alkyl group and the like) and the like can be mentioned.

Examples of the alkoxy group include a C _1-14 alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, an i-butoxy group, an s-butoxy group, a t-butoxy group and a pentyloxy group. Can be mentioned.

Examples of the alkenyl group include a C _2-14 alkenyl group such as a vinyl group, an allyl group, a butenyl group and a pentenyl group.

Examples of the cycloalkyl group include a C _5-14 cycloalkyl group such as a cyclopentyl group, a cyclohexyl group and a methylcyclohexyl group.

Examples of the cycloalkyloxy group include C _5-14 cycloalkyloxy groups such as cyclopentyloxy group and cyclohexyloxy group.

Examples of the cycloalkenyl group include a C _5-14 cycloalkenyl group such as a cyclopentenyl group and a cyclohexenyl group.

Examples of the aryl group include C _6-20 aryl groups (preferably C _6-15 aryl groups, more preferably C _6- ) such as phenyl group, methyl phenyl group (tolyl group), dimethyl phenyl group (chysilyl group) and naphthyl group. Examples thereof include a ₁₂ aryl group (for example, a _C6-10 aryl group such as a phenyl group).

Examples of the aryloxy group include a _C6-20 aryloxy group such as a phenoxy group and a naphthyloxy group.

Examples of the aralkyl group include a C _6-20 aryl-C _1-6 alkyl group such as a benzyl group, a phenethyl group and a phenylpropyl group.

Examples of the aralkyloxy group include a C _6-20 aryl-C _1-6 alkyloxy group such as a benzyloxy group, a phenethyloxy group and a phenylpropyloxy group.

Examples of the silyl group include a Si _1-10 silanyl group (preferably Si _1-6 silanyl group) such as a silyl group, a disilanyl group and a trisilanyl group.

Further, when R ¹ to R ³ are the organic group (alkyl group, aryl group, etc.) or silyl group, at least one of the hydrogen atoms is substituted with a substituent (or functional group). good. Such a substituent (or functional group) may be the same as the above-exemplified group such as, for example, a hydroxyl group, an alkyl group, an aryl group, an alkoxy group and the like.

Further, in the formula (2a), the types of R ¹ and R ² may be different from each other, and are usually the same in many cases.

Of these R ¹ to R ³ , usually an alkyl group (for example, a C _1-4 alkyl group such as a methyl group), an aryl group-containing group [an aryl group (for example, a C _6-20 aryl group such as a phenyl group), etc.) and the like. ], Etc., and it is preferable to contain at least an aryl group-containing group from the viewpoint of easily improving the hole transport efficiency after charge separation. That is, in the above formula (2a), at least one of R ¹ and R ² is an aryl group-containing group (particularly, both R ¹ and R ² are aryl group-containing groups), and in the above formula (2b). It is preferable that R ³ is an aryl group-containing group.

Examples of the aryl group-containing group include an aryl group, an aralkyl group, an aryloxy group, and a group similar to the aralkyloxy group exemplified as the organic group. Preferred aryl group-containing groups include C _6-12 aryl groups (eg, phenyl groups, naphthyl groups, biphenylyl groups, etc.) and C _6-12 aryl-C _1-6 alkyl groups (eg, C _6-10 aryl-C). _1-4 alkyl groups), C _6-12 aryloxy groups (eg, C _6-10 aryloxy groups), C _6-12 aryl-C _1-6 alkoxy groups (eg, C _6-10 aryl-C _1- ). ₄ alkoxy groups) and the like, and in particular, an aryl group (for example, a _C6-10 aryl group, particularly a phenyl group) is preferable.

As a preferred structural unit, typically, in formula (2a), one of R ¹ and R ² is an aryl group-containing group and the other is an alkyl group [for example, an alkyl-aryl-silane unit (for example, an alkyl-aryl-silane unit). , C _1-6 alkyl-C _6-10 aryl-silane units such as methyl-phenyl-silane units)]; Structural units in which both R ¹ and R ² are aryl group-containing groups [eg, diaryl-silanes]. Units (eg, diC _6-10 aryl-silane units such as diphenyl-silane units)]; In the formula (2b) above, structural units in which R3 is an aryl group ^- containing group [eg, aryl-silane units (eg, aryl-silane units). For example, _C6-10 aryl-silane unit such as phenyl-silane unit)], etc.], among others, in the formula (2a), both R ¹ and R ² are aryl group-containing groups. (Especially, a diphenyl-silane unit) is particularly preferable. These structural units may be used alone or in combination of two or more.

The ratio of the aryl group-containing group in the side chain of the polysilane is, for example, about 10 mol% or more (for example, 30 to 100 mol%) with respect to the entire side chain of the polysilane (for example, the total amount of R ¹ to R ³ ). It can be selected from the range, for example, 50 mol% or more (for example, 60 to 99.9 mol%), preferably 70 mol% or more (for example, 80 to 99 mol%), and more preferably 90 mol% or more (for example, 90 mol%). It may be about 95 mol%) or about 95 mol% or more (for example, substantially 100 mol%). If the proportion of aryl group-containing groups is too small, the photoelectric conversion efficiency may decrease.

When the polysilane has a non-cyclic structure (straight chain, branched chain, mesh), the terminal may or may not be sealed. In polysilanes whose ends are not sealed, the silicon atom at the end is usually a hydrogen atom, a hydroxyl group, a halogen atom (chlorine atom, etc.), etc. (particularly hydroxyl) in addition to the organic group (methyl group, phenyl group, etc.). In many cases, it has a group). Further, polysilane may contain a reactive group (for example, a radically polymerizable group), and may or may not contain substantially.

Typical polysilanes include, for example, linear or cyclic polysilane having a structural unit represented by the formula (2a), polysilane having a structural unit represented by the formula (2b) (mesh polysilane), and the above. Examples thereof include polysilane (branched chain-shaped or network-shaped polysilane) having a combination of structural units represented by the formulas (2a) and (2b). In these polysilanes, the structural units represented by the formulas (2a) and (2b) may be used alone or in combination of two or more. The branched chain or network polysilane may further contain a structural unit represented by the following formula (2c).

The shape of polysilane is not particularly limited and may be linear, cyclic, branched chain, or mesh-like, but usually, it is often linear, cyclic, or mesh-like, and is linear or linear. When it is annular (particularly annular), it seems that it is easy to improve the conversion efficiency. Therefore, polysilane preferably contains at least the structural unit represented by the formula (2a) among the structural units represented by the formulas (2a) and (2b).

When the polysilane contains the structural unit represented by the formula (2a), the ratio of the structural unit represented by the formula (2a) is, for example, 10 mol% or more (for example, 30 to 30 to the total structural unit of the polysilane). It can be selected from a range of about 100 mol%), for example, 50 mol% or more (for example, 60 to 99 mol%), preferably 70 mol% or more (for example, 80 to 97 mol%), and more preferably 90 mol% or more. (For example, substantially 100 mol%) may be used. If the ratio of the structural unit represented by the formula (2a) is too small, the photoelectric conversion efficiency may not be improved.

Specific examples of the chain or cyclic polysilane having the structural unit represented by the formula (2a) include polydialkylsilanes [for example, polydimethylsilane, polymethylpropylsilane, polymethylbutylsilane, and polymethylpentylsilane. , Polydibutylsilane, polydihexylsilane, dimethylsilane-methylhexylsilane copolymer, etc.]; Polyalkylarylsilane [eg, polymethylphenylsilane, methylphenylsilane-phenylhexylsilane copolymer, etc.]; For example, polydiphenylsilane); dialkylsilane-alkylarylsilane copolymer (eg, dimethylsilane-methylphenylsilane copolymer, dimethylsilane-phenylhexylsilane copolymer, dimethylsilane-methylnaphthylsilane copolymer, etc.) ); Alkylarylsilane-diarylsilane copolymer (for example, methylphenylsilane-diphenylsilane copolymer, etc.) and the like.

Examples of the network-like polysilane having the structural unit represented by the formula (2b) include polyalkylsilane (for example, polymethylsilane, polypropylsilane, polybutylsilane, polyhexylsilane, etc.); polyarylsilane (for example). , Polyphenylsilane, etc.).

These polysilanes can be used alone or in combination of two or more. Of these polysilanes, linear or cyclic polyalkylarylsilanes (eg, linear or cyclic polyC _1-6 alkyl-C _6-12 arylsilanes such as polymethylphenylsilane), linear or cyclic Polydiarylsilane (eg, linear or cyclic polydiC _{6-12arylsilane} such as polydiphenylsilane), linear or cyclic alkylarylsilane-diarylsilane copolymer (eg, linear or cyclic methylphenyl) Linear or cyclic C _1-6 alkyl-C _6-12 arylsilane-di C _6-12 arylsilane copolymers such as silane-diphenylsilane copolymers), reticulated polyarylsilanes (eg, reticulated poly). _{Reticulated polyC 6-12} arylsilanes such as phenylsilanes) are preferred, among others linear or cyclic polydiarylsilanes (eg, linear or cyclic polydiC _{6-10arylsilanes} such as polydiphenylsilanes). In particular, cyclic polydi C _6-10 arylsilane such as decaphenylcyclopentasilane) is particularly preferable.

The weight average molecular weight Mw of polysilane can be selected from, for example, in the range of 300 or more (for example, about 300 to 50,000) in the measurement method by GPC (polystyrene conversion), and is, for example, 300 to 25,000 (for example, 350 to 20,000), preferably. May be 400 to 14000 (for example, 450 to 10000), more preferably 500 to 3000 (for example, 500 to 1000, particularly 700 to 1000). If the weight average molecular weight is too small, deterioration of the photoelectric conversion element may not be effectively suppressed, and if it is too large, the solubility (or dispersibility) in the solvent may decrease, making it difficult to manufacture the photoelectric conversion element. There is.

The average degree of polymerization of polysilane can be selected from a wide range of, for example, about 3 to 500 (preferably 3 to 100) in terms of silicon atoms (that is, the average number of silicon atoms per molecule), for example, 3 to 50. It may be preferably about 4 to 10, more preferably about 5 to 7 (for example, 5 to 6, especially 5).

Polysilane may be in a liquid state or a solid state at room temperature (for example, about 20 ° C.).

Polysilane is a conventional method, for example, a method of dehalogenating and polycondensing halosilanes using magnesium as a reducing agent (“Magazine reduction method”, WO98 / 29476, etc.), and dehalogenation of halosilanes in the presence of an alkali metal. Polymerization method ("Kipping method", J.Am.Chem.Soc., 110,124 (1988), Macromolecules, 23,3423 (1990), etc.), Dehalogenation polycondensation method of halosilanes by electrode reduction (J.Chem) .Soc., Chem.Commun., 1161 (1990), J.Chem.Soc., Chem.Commun., 897 (1992), etc.), Method of dehydrocondensation polymerizing hydrosilanes in the presence of metal catalyst (special It can be obtained by a method by anionic polymerization of disylene crosslinked with biphenyl or the like (Macromolecules, 23,4494 (1990), etc.), a method by ring-opening polymerization of cyclic silanes, etc.

The ratio of polysilane is, for example, 0.01 to 10 parts by weight (for example, 0.05 to 5 parts by weight), preferably 0.1 to 2 parts by weight (for example) with respect to 100 parts by weight of the compound having a perovskite-type structure. , 0.3 to 1.5 parts by weight), more preferably about 0.5 to 1 part by weight (for example, 0.6 to 0.9 parts by weight). If the proportion of polysilane is too small, the formation of metal halides such as lead iodide PbI ₂ may not be effectively suppressed, or the growth of perovskite crystals may not be promoted. If the proportion of polysilane is too large, polysilane may be difficult to dissolve, making it difficult to form a perovskite layer, or the conversion efficiency may decrease.

When the photoelectric conversion element is of the nanostructure type, the perovskite layer is formed of a porous portion containing a porous oxide adjacent to an electron transport layer and a perovskite compound infiltrated (or impregnated) into the porous portion. It may also include a first perovskite layer and a second perovskite layer intervening between the first perovskite layer and the hole transport layer and having a perovskite compound.

In the first perovskite layer, typical porous oxides constituting the porous portion include, for example, titanium oxide (IV), zinc oxide (II), tin oxide (IV), aluminum oxide, and zirconium oxide (IV). ) And other metal oxides. These metal oxides can also be used alone or in combination of two or more. Among these metal oxides, metal oxides (particularly, titanium oxide (IV)) having photoactive ability (participating in charge transport) such as titanium oxide (IV), zinc oxide (II), and tin oxide (IV). ) Is preferable. The porous oxide may be different from the electron transport material forming the electron transport layer described later, but is usually the same.

The average thickness of the first perovskite layer can be selected from the range of, for example, about 100 to 1000 nm, and may be, for example, about 150 to 980 nm, preferably about 200 to 950 nm, and more preferably about 300 to 900 nm. If the average thickness of the first perovskite layer is too large, the production efficiency may decrease, and if it is too small, the conversion efficiency may decrease. The thickness of the first perovskite layer (or porous portion) may be measured by a transmission electron microscope (TEM), an atomic force microscope (AFM), or the like.

The second perovskite layer contains a perovskite compound without containing a porous portion. Further, the type of the perovskite compound used for the second perovskite layer may be the same as or different from the type of the perovskite compound used for the first perovskite layer, and is usually the same.

The average thickness of the second perovskite layer (the average thickness of the perovskite layer when the photoelectric conversion element is a planar heterozygotes type or an inverse structure type) can be selected from the range of, for example, about 5 to 1000 nm, for example, 10 to 500 nm. It may be preferably about 30 to 300 nm, more preferably about 50 to 200 nm. If the average thickness of the second perovskite layer is too large, the production efficiency and conversion efficiency may decrease.

(First electrode)
The first electrode is attached to at least a part of one surface of a transparent substrate (for example, an inorganic material such as glass, a transparent resin such as a methacrylic resin or a polycarbonate resin), for example, FTO (Fluorine-doped Tin Oxide), ITO. A transparent electrode formed by applying or coating a transparent conductive metal oxide such as (Indium Tin Oxide) or ZnO (Zinc Oxide) (for example, vacuum vapor deposition). Of the metal oxides, FTO is preferable from the viewpoint of heat resistance.

Further, the metal oxide may form a desired pattern by etching or the like. Further, a functional layer such as an antireflection layer or a hard coat layer may be formed on the other surface of the transparent substrate. The first electrode may be an anode, but is usually a cathode in many cases.

The average thickness of the transparent conductive metal oxide coating film on the first electrode can be selected from the range of, for example, about 5 to 2000 nm, for example, about 100 to 1500 nm, preferably about 500 to 1200 nm, and more preferably about 800 to 1000 nm. May be. If the average thickness is too large, the weight of the photoelectric conversion element may increase, and if it is too small, the durability may decrease. The average thickness of the transparent substrate in the first electrode can be selected depending on the material, and may be, for example, about 0.1 to 3 mm, preferably about 1 to 2 mm.

(Electron Transport Layer (ETL))
The electron transport layer can efficiently move electrons to improve properties such as conversion efficiency, and can prevent the perovskite layer and the hole transport layer from coming into contact with the cathode and short-circuiting. In the electron transport layer, the electron transport material is usually densely (not porous) on the surface of the first electrode coated with the metal oxide (one surface of the second electrode in the case of the reverse structure type). It is deposited and formed.

Examples of the electron transporting material include metal oxides such as titanium oxide (IV), zinc oxide (II), and tin (IV) oxide, and [6,6] _-phenyl -C61-butyric acid methyl ester ([]. 60] Fullerenes such as PCBM) and the like can be mentioned. These electron transport materials can also be used alone or in combination of two or more. Among these electron transport materials, metal oxides are preferable, and titanium oxide (IV) and zinc oxide (II) [particularly titanium (IV) oxide] are preferable.

The electron transport layer may be doped with other atoms. When the electron transport material is a metal oxide, an atom having a higher valence than the metal atom in the metal oxide may be doped. For example, in titanium oxide (IV), a pentavalent atom (for example, Nb, V) may be doped. , Ta, etc.), and in zinc oxide (II), trivalent atoms (eg, Ga, In, Al, etc.) may be doped.

The average thickness of the electron transport layer can be selected from the range of, for example, about 5 to 100 nm, and may be, for example, about 10 to 80 nm, preferably about 20 to 60 nm, and more preferably about 30 to 50 nm. If the average thickness is too large, the electrical resistance may increase, and if it is too small, electrons may not move efficiently.

(Hole transport layer)
The hole transport layer contains a hole transport material. Examples of the hole transporting material include conventional hole transporting materials such as metal salts [eg, copper (I) thiocyanate], metal oxides [eg, nickel (II) oxide, vanadium (V) oxide, copper oxide). Aluminum (CuAlO ₂ ), etc.], metal iodides [eg, copper (I) iodide, cesium tin iodide (CsSnI ₃ ), etc.], carbon materials (eg, graphene oxide, etc.), polysilanes (eg, the perovskite layer). Inorganic compounds such as polysilanes; phthalocyanines (eg, phthalocyanine, naphthalocyanine, subphthalocyanine, etc.), carbazoles [eg, 1,3,5-tris [2,7- (N, N- (p-methoxyphenyl)) ) Amino) -9H-carbazole-9-yl] benzene (SGT405), etc.], thiophenes [for example, 2,5-bis [4- (N, N-bis (p-methoxyphenyl) amino) phenyl] -3 , 4-ethylenedioxythiophene (H101), 2,3,4,5-tetrakis [4- (N, N-bis (p-methoxyphenyl) amino) phenyl] thiophene (H111), etc.], triptycene [eg , 2,6,14-Tris [5'-(4- (N, N-bis (p-methoxyphenyl) amino) phenyl) -thiophene-2'-yl] trypticene (T103), etc.], Spirovifluorenes Low molecular weight compounds such as (for example, a compound represented by the following formula (3) described later); polythiophenes [for example, poly (3-hexylthiophene-2,5-diyl) (P3HT), poly [N-9 '-Heptadecanyl-2,7-carbazole-alt-5,5-(4', 7'-di-2-thienyl-2', 1', 3'-benzothiazol)] (PCDTBT), poly [N- 9'-Heptadecanyl-2,7-carbazole-alt-3,6-bis (thiophene-5-yl) -2,5-dioctyl-2,5-dihydropyrroro [3,4] pyrrole-1,4-dione ] (PCBTDPP), Poly [2,6- (4,4-bis- (2-ethylhexyl) -4H-cyclopenta [2,1-b; 3,4-b'] dithiophene) -alt-4,7- (2,1,3-Benzothiazol)] (PCPDTBT)], polytriarylamines [eg, poly [bis (phenyl-4-yl)-(2,4,6-trimethylphenyl) -amine] ( PTAA), poly [bis (phenyl-4-yl)-(4-butylfene) Enyl) -amine] (PolyTPD)], polyfluorene [eg, poly [9,9-dioctylfluorene-co-bis-N, N'-(4-butylphenyl) -bis-N, N'-phenyl -1,4-phenylenediamine] (PFB) and the like] and the like.

These hole transporting materials can also be used alone or in combination of two or more. Among these hole transport materials, spirobifluorenes, for example, compounds represented by the following formula (3) are widely used.

(In the formula, Z independently represents an arene ring, R ⁴ independently represents an alkoxy group, and k independently represents an integer of 0 or more).

In the above formula (3), examples of the aromatic hydrocarbon ring (arene ring) represented by Z include a monocyclic aromatic hydrocarbon ring (monocyclic arene ring) such as a benzene ring and a polycyclic aromatic. Examples thereof include group hydrocarbon rings (polycyclic arene rings), and examples of the polycyclic aromatic hydrocarbon rings include fused polycyclic aromatic hydrocarbon rings (condensed polycyclic arene rings) and ring aggregate fragrances. Group hydrocarbon rings (ring-aggregated arene rings) and the like are included.

Examples of the fused polycyclic arene ring include a fused bicyclic arene ring (for example, a fused bicyclic _C10-16 arene ring such as a naphthalene ring) and a fused tricyclic arene ring (for example, an anthracene ring and a phenanthrene ring). Etc.), such as fused two- to four-cyclic arene rings. Preferred fused polycyclic arene rings include fused polycyclic C _10-16 arene rings (preferably fused polycyclic C _10-14 arene rings) such as naphthalene rings and anthracene rings, and naphthalene rings are particularly preferable. preferable.

The ring-assembled arene ring includes a bi-C 6-12 arene ring such as a biphenyl ring, a binaphthyl ring, a phenylnaphthalene ring (1-phenylnaphthalene ring, 2-phenylnaphthalene ring, etc.), a tellarene ring (for example, a biphenyl ring, a biphenyl ring, a 2-phenylnaphthalene ring, etc.), and a tellarene ring (for example, a bi-C _6-12 arene ring). For example, a tel C _6-12 arene ring such as a terphenylene ring) can be exemplified. Preferred ring-set arene rings include biC _6-10 arene rings and the like, with biphenyl rings being particularly preferred.

Among these rings Z, a _C6-12 arene ring such as a benzene ring, a naphthalene ring, and a biphenyl ring is preferable, and a _C6-10 arene ring such as a benzene ring (particularly a benzene ring) is particularly preferable. Also, the types of the eight rings Z may be different from each other and are usually the same. The position of the nitrogen atom to which the ring Z is bonded is not particularly limited and may be any position.

In the above formula (3), the alkoxy group represented by ^R4 is a straight chain such as a methoxy group, an ethoxy group, a propoxy group, an n-butoxy group, an i-butoxy group, an s-butoxy group, and a t-butoxy group. Examples thereof include a linear or branched C _1-6 alkoxy group (preferably a linear or branched C _1-4 alkoxy group, and more preferably a C _1-2 alkoxy group such as a methoxy group).

The substitution number k of the group ^R4 can be selected according to the type of the ring Z, for example, an integer of 0 to 8 (for example, an integer of 0 to 6), preferably an integer of 0 to 4 (for example, 0 to 2). It may be an integer), more preferably 0 or 1 (particularly 1). The eight ks may be different from each other and may usually be the same. Further, when k is 2 or more, the types of the groups ^R4 substituting for the same ring Z may be the same or different from each other.

The substitution position of the group R ⁴ is not particularly limited as long as it is a position other than the position where the ring Z and the nitrogen atom are bonded. For example, when the ring Z is a benzene ring and k is 1, the substitution position of the group ^R4 is any of the o-position, the m-position, and the p-position with respect to the bond position of the ring Z with the nitrogen atom. It may be a position, preferably an m-position or a p-position, and more preferably a p-position.

In the above formula (3), the position where the four nitrogen atoms are bonded to each of the four benzene rings forming the spirobifluorene skeleton is not particularly limited, and for example, each of the four nitrogen atoms is a spirobifluorene ring. Any one position from 2-position to 4-position, any one position from 5-position to 7-position, any one position from 2'-position to 4'-position, and 5' It may be bonded to any one position from the − position to the 7'-position. The four nitrogen atoms may preferably be attached to the 2,2', 7,7'-position of the spirobifluorene ring.

As the compound represented by the formula (3), for example, in the formula (3), eight rings Z are benzene rings and eight k are one tetrakis [bis (alkoxyphenyl) amino]. -9,9'-spirobifluorenes, eg 2,2', 7,7'-tetrakis- [N, N-bis (4-methoxyphenyl) amino] -9,9'-spirobifluorene (Spiro) -OMeTAD), 2,2', 7,7'-tetrakis- [N- (4-methoxyphenyl) -N- (3-methoxyphenyl) -amino] -9,9'-spirobifluorene, 2,2 ', 7,7'-Tetrakiss- [N- (4-methoxyphenyl) -N- (2-methoxyphenyl) -amino] -9,9'-spirobifluorene, 2,2', 7,7'- Tetrakiss- [N, N-bis (4-ethoxyphenyl) amino] -9,9'-spirobifluorene, etc. Tetrakiss [bis (C _1-4 alkoxyphenyl) amino] -9,9'-spirobifluorene, etc. Can be mentioned.

These compounds represented by the formula (3) can be used alone or in combination of two or more. Among these compounds represented by the formula (3), tetrakis [bis (C _1-2 alkoxyphenyl) amino] -9,9'-spirobifluorene such as Spiro-OMeTAD is preferable. As the compound represented by the above formula (3), a commercially available product or the like may be used.

The ratio of the compound represented by the formula (3) to the entire hole transport material is, for example, 10% by weight or more (for example, 30 to 100% by weight), preferably 50% by weight or more (for example, 60 to 99% by weight). ), More preferably 70% by weight or more (for example, 80 to 95% by weight), 90% by weight or more (95% by weight or more, for example, substantially 100% by weight (represented by the above formula (3)). It may be about)).

Further, when the hole transport material contains the compound represented by the above formula (3), polysilane may be further contained. The ratio of the compound represented by the formula (3) to polysilane is, for example, the former / the latter (weight ratio) = 10/90 to 99.9 / 0.1 (for example, 30/70 to 99.5 / 0). It can be selected from a range of about .5), for example, 50/50 to 99/1 (for example, 60/40 to 97/3), preferably 70/30 to 95/5 (for example, 75/25 to 93/7). ), More preferably about 80/20 to 91/9 (for example, 85/15 to 90/10).

The hole transport layer does not necessarily have to contain an additive in addition to the hole transport material, but may further contain a conventional additive (for example, a dopant), if necessary. .. Examples of the dopant (or p-type dopant) include a metal salt [for example, lithium bis (trifluoromethylsulfonyl) imide (Li-TFSI)], a metal complex [for example, tris (p-bromophenyl) ammonium hexachloroantimonate). , Tris (2- (1H-pyrazole-1-yl) pyridine) Cobalt (III) Tris [bis (trifluoromethylsulfonyl) imide], Molybdenum Tris [1,2-bis (trifluoromethyl) ethane-1,2 -Dithiolen], etc.], metal chlorides [eg, tin chloride (IV), antimony chloride (V), iron (III) chloride, etc.], metal oxides [eg, tungsten oxide (VI), etc.] and other metal compounds; Examples thereof include non-metal compounds such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane.

When the hole transport material is combined with an additive, the proportion of the additive (eg, dopant, etc.) is, for example, 0.1 to 30 parts by weight, preferably 1 to 1 to 100 parts by weight of the total amount of the hole transport material. It may be about 20 parts by weight, more preferably about 5 to 15 parts by weight.

The thickness (average thickness) of the hole transport layer can be selected from the range of about 5 to 50 nm, and may be, for example, 10 to 50 nm, preferably 20 to 47 nm, and more preferably about 30 to 45 nm. If the average thickness of the hole transport layer is too small, holes may not move efficiently, and if it is too large, the electrical resistance may increase. The thickness may be measured using a transmission electron microscope (TEM) or the like.

(Second electrode)
The second electrode is usually adjacent to the hole transport layer (electron transport layer in the case of an inverted structure) and has a work function such as metal (eg, Au, Ag, Cu, Al, etc.); C. It is a metal or carbon electrode formed of a conductor of 2 eV or less. Of these conductors (or electrode forming materials), Au is preferable. Further, the second electrode may be a cathode corresponding to the first electrode, but is usually an anode in many cases.

The average thickness of the second electrode can be selected from the range of, for example, about 100 to 500 nm, and may be, for example, about 120 to 300 nm, preferably about 150 to 250 nm, and more preferably about 180 to 220 nm. If the average thickness is too large, the manufacturing efficiency may decrease, and if it is too small, the current may not be collected efficiently.

[Manufacturing method and characteristics of photoelectric conversion element]
Each layer forming the photoelectric conversion element can be formed (or laminated) by a conventional method (spin coating method, doctor blade method, coating or printing method such as screen printing method, vapor deposition method such as vacuum vapor deposition method, etc.), and is particularly limited. Not done. As a typical manufacturing method of each layer, the following methods can be mentioned.

(Electron transport layer forming process)
In the electron transport layer forming step, the electron transport layer precursor solution (or the electron transport layer precursor solution) containing the electron transport material or its precursor and a solvent (or dispersion medium) on the surface coated with the conductive metal oxide of the first electrode. Dispersion solution) is applied (or coated) to form an electron transport layer.

The first electrode may be subjected to a cleaning treatment before the application of the precursor solution. The method of cleaning treatment is not particularly limited. For example, it is immersed in ketones (acetone, etc.) or alcohols (methanol, etc.) for ultrasonic cleaning, and dried under an inert gas (nitrogen gas, noble gas, etc.). Method; UV-ozone treatment method; a method combining these methods and the like.

As the precursor of the electron transport material, a compound corresponding to the electron transport material exemplified in the section of the electron transport layer, for example, a titanium oxide (IV) precursor [for example, titanium diisopropoxidebis (acetylacetonate) or the like, etc. Titanium complex, alkyl titanate such as tetraisopropoxytitanium (IV), etc.]; zinc oxide (II) precursor [eg, zinc carbonate, etc.] and the like.

Solvents include, for example, water; alcohols (eg, C _1-6 alkane monools such as methanol, ethanol, 2-propanol, n-butanol, t-butanol; alkanediols, etc.); ethers (tetratetra, etc.); Glycol ethers [eg, cellosolves, carbitols; (poly) alkylene glycol dialkyl ethers, etc.]; Glycol ether acetates [eg, cellosolves acetates, carbitol acetates, etc.), (poly) alkylene glycol monoalkyl ether acetates. Etc.]; Ketones (such as acetone); Esters (such as ethyl acetate); Carbonates (such as propylene carbonate); Carous acids (such as acetic acid); nitriles (such as acetonitrile); Amides (N, N-dimethylformamide, etc.) Etc.); Sulfoxides (dimethylsulfoxide, etc.); Hydrocarbons (hexane, cyclohexane, toluene, etc.); Halogenated hydrocarbons (eg, chloroform, chlorobenzene, etc.); and mixed solvents thereof and the like. Among these solvents, C _1-5 alkane monool such as n-butanol is preferable.

The concentration of the electron transport material or the precursor thereof in the electron transport layer precursor solution may be, for example, about 0.01 to 1 M, preferably about 0.1 to 0.4 M. In addition, in order to form the electron transport layer in close contact with the first electrode and densely, two or more kinds of solutions having different concentrations may be prepared and applied in order of increasing concentration of the solutions.

After the coating, a heat treatment may be performed to remove the solvent, and the heating temperature thereof may be, for example, about 80 to 200 ° C., preferably about 100 to 150 ° C. Further, in order to form a metal oxide from the precursor, heat treatment may be further performed at a high temperature, and the heating temperature thereof can be selected according to the precursor, for example, 300 to 800 ° C., preferably 400 to 400 ° C. It may be about 600 ° C.

(Perovskite layer formation process)
In the perovskite layer forming step, a perovskite layer precursor solution (or a dispersion medium) containing a perovskite compound precursor, polysilane, and a solvent (or dispersion medium) is contained on the surface of the electron transport layer of the laminate formed in the electron transport layer forming step. The dispersion liquid) is applied (or coated), and further heat-treated to form a perovskite layer.

When the photoelectric conversion element is of the nanostructure type, the porous portion (the porous portion of the first perovskite layer) for contacting the perovskite compound over a wide surface area is electron-generated before the application of the perovskite layer precursor solution. It may be formed in the transport layer. The porous portion is formed by applying a porous portion-forming solution containing a metal oxide, a polymer compound, water, an organic compound, and a surfactant, and further heat-treating the porous portion.

Examples of the metal oxide include the same as the metal oxide exemplified as the porous oxide in the section of the first perovskite layer, including preferable embodiments. The metal oxide may be in the form of powder or the like.

Examples of the polymer compound include polyethylene glycol, polyvinyl alcohol, poly (meth) acrylic acid derivative (for example, poly (meth) acrylic acid or a salt thereof, poly (meth) acrylamide, etc.), cellulose derivative (for example, carboxymethyl cellulose or). Examples thereof include water-soluble polymer compounds such as salts thereof and cellulose ethers such as hydroxypropyl cellulose). The number average molecular weight or the weight average molecular weight of the polymer compound may be, for example, about 10,000 to 30,000, preferably about 15,000 to 25,000. The ratio of the polymer compound may be, for example, about 1 to 30 parts by weight, preferably about 5 to 15 parts by weight, based on 100 parts by weight of the metal oxide.

The water is preferably ultrapure water. The ratio of water may be, for example, about 100 to 1000 parts by weight, preferably about 300 to 700 parts by weight, based on 100 parts by weight of the metal oxide.

Examples of the organic compound include complex-forming organic compounds such as acetylacetone. The ratio of the organic compound may be, for example, about 0.1 to 10 parts by volume, preferably about 1 to 5 parts by volume with respect to 100 parts by volume of water.

Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants and the like, and nonionic surfactants [for example, polyethylene glycol- (t-octyl). Polyoxyethylene (C _6-20 alkyl-phenyl) ethers such as phenyl) ethers] are preferred. The ratio of the surfactant may be, for example, about 0.05 to 5 parts by volume, preferably about 0.1 to 3 parts by volume with respect to 100 parts by volume of water.

The porous portion forming solution may be prepared by mixing a metal oxide and a polymer compound with water and stirring, and then adding an organic compound and a surfactant to this solution and stirring. .. Further, in order to remove air bubbles from the solution, the solution may be allowed to stand for about 1 hour to 2 days (for example, 12 hours to 1 day) after preparation.

The heat treatment temperature after the application of the porous portion forming solution may be, for example, about 300 to 800 ° C., preferably about 400 to 600 ° C.

The perovskite compound precursor contained in the perovskite layer precursor solution is a precursor corresponding to the above formula (1), that is, the formula AX (1a) (in the formula, A and X are the same as the above formula (1), respectively). It may be a compound represented by the above formula and a compound represented by the formula MX ₂ (1b) (wherein M and X are the same in the formula (1), respectively). In the formulas (1a) and (1b), A, M and X are the same as those of A, M and X exemplified in the section of the formula (1), including preferred embodiments.

As a typical compound represented by the above formula (1a), for example, in the formula (1a) such as CH ₃ NH ₃ I, CH ₃ NH ₃ Br, CH ₃ NH ₃ Cl, A is C such as methyl ammonium. Examples thereof include compounds which are _1-6 alkylammonium. These compounds may be used alone or in combination of two or more. Of these compounds, CH ₃ NH ₃ I is preferred.

As a typical compound represented by the above formula (1b), for example, in the formula (1b) such as PbI ₂ , PbBr ₂ , PbCl ₂ , M is a Group 14 element such as Pb, Sn (particularly Pb). Examples include compounds that are. These compounds may be used alone or in combination of two or more. Of these compounds, PbI ₂ is preferred.

The ratio of the compound represented by the formula (1a) to the compound represented by the formula (1b) is, for example, the former / the latter (molar ratio) = 1 / 0.9 to 1 / 1.1, preferably 1 / 0.9 to 1 / 1.1. It may be about 1 / 0.95 to 1 / 1.05, and it is preferably about 1 / 0.95 to 1 / 1.05.

As the polysilane, the polysilane exemplified in the section of the perovskite layer can be used. The ratio of polysilane is, for example, 0.01 to 10 parts by weight (for example, 0.05) with respect to 100 parts by weight of the total amount of the compound represented by the formula (1a) and the compound represented by the formula (1b). Up to 5 parts by weight), preferably 0.1 to 2 parts by weight (for example, 0.3 to 1.5 parts by weight), more preferably 0.5 to 1 part by weight (for example, 0.6 to 0.9 parts by weight). Part) may be about.

Solvents include lactones (eg, C _3-7 lactones such as γ-butyrolactone, δ-valerolactone, ε-caprolactone); amides (eg, N, N-dimethylformamide (DMF), N, N- Dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), etc.) and the like. These solvents can also be used alone or in combination of two or more. Of these solvents, γ-butyrolactone and N, N-dimethylformamide are preferable. As the solvent, a mixed solvent of lactones (for example, γ-butyrolactone) and amides (for example, DMF) is often used. When the mixed solvent is used, the ratio of the lactones and the amides is, for example, the former / the latter (volume ratio) = 1/99 to 99/1 (10/90 to 90/10), preferably 30/70 to 80. It may be about / 20 (50/50 to 70/30). The ratio of the solvent is, for example, 50 to 200 parts by weight, preferably 100 to 180 parts by weight (for example) with respect to 100 parts by weight of the total amount of the compounds represented by the formulas (1a) and (1b) and polysilane. , 120 to 150 parts by weight).

The compound represented by the formula (1a), the compound represented by the formula (1b), polysilane and the solvent may be mixed while being heated to a temperature equal to or lower than the boiling point of the solvent, and the heating temperature is, for example, 40. It may be about 80 ° C., preferably about 50 to 70 ° C. The perovskite layer precursor solution thus prepared may be applied to the porous portion (or electron transport layer) while being heated to a temperature equal to or lower than the boiling point of the solvent, and the heating temperature is, for example, 50 to 90 ° C. It may be preferably about 60 to 80 ° C. The perovskite layer precursor solution may be applied at one time, but it is preferably applied in a plurality of times from the viewpoint of efficiently impregnating or immersing the porous portion.

The heat treatment temperature after applying the perovskite layer precursor solution may be, for example, about 80 to 120 ° C., preferably about 90 to 110 ° C. The heat treatment may usually be performed in an atmospheric atmosphere. In the case of coating over a plurality of times, the heat treatment may be performed each time the coating is applied, or the heat treatment may be performed at one time after the plurality of coatings are completed.

(Hole transport layer forming step)
In the hole transport layer forming step, the hole transport material (for example, the compound represented by the formula (3), polysilane, etc.) and the solvent (for example, polysilane) are placed on the surface of the perovskite layer of the laminate formed in the perovskite layer forming step. Alternatively, the hole transport layer is formed by applying (or coating) a hole transport layer forming solution (or dispersion) containing (or a dispersion medium).

The solvent is, for example, hydrocarbons (eg, aliphatic hydrocarbons such as hexane, alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as toluene, xylene, etc.); halogenated hydrocarbons (eg,). , Dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, etc.); Alcohols (eg, methanol, ethanol, 2-propanol, n-butanol, t-butanol, etc. C _1-6 alkanemonool; C, ethylene glycol, etc. _2-4 Alcandiol, etc.); Ethers (chain ethers such as diisopropyl ether, cyclic ethers such as tetrahydrofuran, etc.); Glycol ethers [for example, cellosolves (methylcellosolve, etc.), carbitols (methylcarbitol, etc.) Etc.), (poly) C _2-4 alkylene glycol mono C _1-4 alkyl ethers such as triethylene glycol monomethyl ether and propylene glycol monomethyl ether; (poly) C _2-4 alkylene such as ethylene glycol dimethyl ether and dipropylene glycol dimethyl ether. Glycoldi C _1-4 alkyl ethers, etc.]; Glycol ether acetates [eg, cellosolve acetates (eg, C _1-4 alkyl cellosolve acetates such as methyl cellosolve acetate), carbitol acetates (eg, methyl carbitol acetate, etc.) C _1-4 alkyl carbitol acetate, etc.), propylene glycol monomethyl ether acetate, dipropylene glycol monobutyl ether acetate, etc. (poly) C _2-4 alkylene glycol mono C _1-4 alkyl ether acetate, etc.]; Ketones ( Chain ketones such as acetone and methyl ethyl ketone, cyclic ketones such as cyclohexanone, etc.); Esters (acetate esters such as ethyl acetate, lactic acid esters such as methyl lactate, etc.); Carbonates (chain carbonates such as dimethyl carbonate, ethylene carbonate, etc.) Cyclic carbonates such as propylene carbonate); Carbodies (acetic acid, propionic acid, etc.); nitriles (acetoether, propionitrile, etc.); Amidos (N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl) -2-Pyrolidone, etc.); Sulfoxides (dimethylsulfoxide, etc.); Water; and mixed solvents thereof And so on.

Of these solvents, halogenated hydrocarbons such as chlorobenzene are preferred. The ratio of the solvent may be, for example, about 500 to 2000 parts by weight, preferably about 1000 to 1500 parts by weight, based on 100 parts by weight of the total amount of the hole transport material.

Further, the hole transport layer forming solution may contain the additives exemplified in the section of the hole transport layer (for example, dopants such as Li-TFSI) and the like, if necessary, and these additives may be contained. The ratio may be the same as the ratio described in the section of the hole transport layer, including the preferred embodiment. Additives such as dopants may be added after being dissolved or dispersed in a solvent similar to the hole transport material (for example, nitriles such as acetonitrile).

Further, the hole transport layer forming solution may contain amines, if necessary, from the viewpoint of improving the open circuit voltage by changing the quasi Fermi level. Examples of amines include heterocyclic amines (eg, C _1-6 alkyl pyridines such as 4-t-butyl pyridine), tertiary amines (eg, tri C _1-6 alkyl amines such as triethylamine, triethanol). Tri-C _1-6 alkanolamines such as amines) and the like. These amines can also be used alone or in combination of two or more. Among these amines, heterocyclic amines such as 4-t-butylpyridine are preferable. The ratio of amines may be, for example, about 0.1 to 10 parts by volume, preferably about 1 to 5 parts by volume with respect to 100 parts by volume of the solvent.

The hole transport layer forming solution may be prepared while heating, and the heating temperature may be, for example, about 50 to 100 ° C, preferably about 60 to 80 ° C. The hole transport layer forming solution does not have to be heat-treated after coating from the viewpoint of suppressing decomposition of the hole transport material (for example, the compound represented by the formula (3)).

(Second electrode forming step)
In the second electrode forming step, the conductor (metal or carbon) exemplified in the section of the second electrode is vapor-deposited (for example) on the surface of the hole transporting layer of the laminate formed in the hole transporting layer forming step. , Vacuum vapor deposition, etc.) to form a second electrode.

After forming the second electrode, a photoelectric conversion element may be manufactured by connecting wiring or attaching a cover, if necessary.

(Characteristics of photoelectric conversion element)
The photoelectric conversion element obtained by the present invention has a high short-circuit current density and conversion efficiency. The short-circuit current density measured under the conditions of illuminance 100mWcm ^-2 , AM1.5, irradiation area ^0.090cm2 , and room temperature (about 25 ° C.) is, for example, 5 to 30mAcm ^-2 , preferably 7 to 25mAcm ^-2 , and further. It may be preferably about 10 to 20 mAcm − ² . The conversion efficiency may be, for example, 2 to 20%, preferably 3 to 15%, and more preferably 5 to 12%.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The method for preparing the raw materials used is shown below.

[Preparation of raw materials]
(FTO substrate (first electrode))
A glass substrate coated with fluorine-doped tin oxide (thickness of glass substrate: 1.8 mm, thickness of FTO coating film: about 900 nm) is ultrasonically washed in acetone and then ultrasonically in methanol. Washed. Further, this substrate was dried under nitrogen gas and then subjected to UV-ozone treatment for 20 minutes.

(Electron transport layer precursor solution (0.15M))
Titanium diisopropoxide bis (acetyl acetonate) [Titanium diisopropoxide bis (acetyl acetonate), manufactured by Sigma-Aldrich] 0.055 mL and 1-butanol (manufactured by Nacalai Tesque Co., Ltd., purity 99%) 1 mL are mixed. , Stirred and prepared.

(Electron transport layer precursor solution (0.30M))
Titanium diisopropoxide bis (acetylacetonate) was prepared by mixing 0.11 mL and 1 mL of 1-butanol and stirring.

(Porous part forming solution)
To 100 mg of TiO ₂ powder (“AEROXIDE TiO ₂ P25” manufactured by Nippon Aerodil Co., Ltd.) and 10 mg of polyethylene glycol (“PEG (# 20000)” manufactured by Nacalai Tesque Co., Ltd.), 0.5 mL of ultrapure water was added and stirred. .. Furthermore, acetylacetone (manufactured by Wako Pure Chemical Industries, Ltd., purity 99%) 10.0 μL, 4- (1,1,3,3-tetramethylbutyl) phenyl-polyethylene glycol (manufactured by Sigma-Aldrich) "Triton-X" -100 ”) was added in an amount of 5.0 μL, stirred for 30 minutes, and then allowed to stand for 12 hours to prepare.

(Perovskite layer precursor solution)
CH ₃ NH ₃ I (monomethylamine hydroiodide, Showa Chemical Industry Co., Ltd., purity 95%) 98.8 mg, PbI ₂ (lead iodide (II), manufactured by Sigma-Aldrich, purity 99.999 %) 289.3 mg, polysilane 3 mg, γ-butyrolactone (manufactured by Nakaraitesk Co., Ltd., purity 98%) 0.3 mL, and N, N-dimethylformamide (DMF, manufactured by Sigma-Aldrich) 0.2 mL are mixed. , 60 ° C. and stirred overnight.

(Hole transport layer forming solution)
2,2', 7,7'-tetrakis- [N, N-di (4-methoxyphenyl) amino] -9,9'-spirobifluorene (2,2', 7,7'-tetrakis- [N , N-di (4-methoxyphenyl) amino]-
Solution A was prepared by adding 36.1 mg of 9,9'-spirobifluorene, manufactured by Luminescence Technology, simply referred to as Spiro-OMeTAD) to 0.5 mL of chlorobenzene (manufactured by Wako Pure Chemical Industries, Ltd.) and stirring for 12 hours. In addition, 260 mg of lithium bis (trifluoromethylsulfonyl) imide (Li-TFSI, manufactured by Tokyo Chemical Industry Co., Ltd.) is added to 0.5 mL of acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.), and the solution is stirred for 12 hours. B was prepared. The total amount of the solution A, 8.8 μL of the solution B and 14.4 μL of 4-t-butyl pyridine (manufactured by Sigma-Aldrich) were mixed and stirred at 70 ° C. for 30 minutes to prepare a hole transport layer forming solution. ..

[Manufacturing of photoelectric conversion element]
(Example 1)
The photoelectric conversion element shown in FIG. 1 was manufactured using the above raw materials. That is, after the electron transport layer precursor solution (0.15M) was dropped onto the FTO substrate and spin-coated (3000 rpm, 30 seconds) using a spin coater (“MS-A100” manufactured by Mikasa Co., Ltd.). , Heat-treated on a hot plate (125 ° C., 5 minutes). Then, the electron transport layer precursor solution (0.30 M) was added dropwise, and spin coating (3000 rpm, 30 seconds) was performed. The electron transport layer precursor solution (0.30 M) was spin-coated twice and then heat-treated (125 ° C., 5 minutes) on a hot plate. Further, heat treatment (500 ° C., 30 minutes) was performed in an electric furnace (“MSF-1” manufactured by AS ONE Co., Ltd.) to form an electron transport layer (dense TiO ₂ layer) having a thickness of about 40 nm.

A porous portion-forming solution is dropped onto the electron transport layer, spin-coated (5000 rpm, 30 seconds), and then heat-treated in an electric furnace (500 ° C., 30 minutes) to form a porous material having a thickness of about 300 to 900 nm. A quality part ( ₂ parts of porous TiO) was formed.

A perovskite layer precursor solution heated to 70 ° C. was added dropwise to the inside (or void) of the porous portion so as to infiltrate, and spin coating (2000 rpm, 60 seconds) was performed. After performing this operation four times, heat treatment is performed on a hot plate (100 ° C., 30 minutes, in an atmospheric atmosphere), and a first perovskite layer having a thickness of about 300 to 900 nm (CH ₃ NH ₃ PbI in the voids of the porous portion) is used. ₃ and a layer impregnated or infiltrated with polysilane) and a second perovskite layer (layer containing CH ₃ NH ₃ PbI ₃ and polysilane) having a thickness of about 100 nm were formed. In the preparation of the perovskite layer precursor solution, poly (methylphenylsilane) (“OGSOL SI-10-10” manufactured by Osaka Gas Chemical Co., Ltd., hereinafter simply referred to as PMPS) was used as polysilane.

A hole transport layer forming solution was dropped onto the second perovskite layer and spin coated (4000 rpm, 30 seconds) to form a hole transport layer having a thickness of about 40 nm.

Gold Au is vapor-filmed (or film-formed) on the hole transport layer by a vacuum vapor deposition apparatus (“VPC-260F” manufactured by ULVAC Kiko Co., Ltd.), and a second electrode (metal electrode) having a thickness of about 200 nm is formed. And said. In this way, the photoelectric conversion element shown in FIG. 1 was manufactured.

(Example 2)
Except for using polyphenylsilane (“OGSOL SI-20-10” manufactured by Osaka Gas Chemical Co., Ltd., hereinafter simply referred to as PPS) instead of PMPS, the polysilane used in the preparation of the perovskite layer precursor solution is used. A photoelectric conversion element was produced by the same method as in Example 1.

(Example 3)
The polysilane used in the preparation of the perovskite layer precursor formation solution is decaphenylcyclopentasilane (“OGSOL SI-30-10” manufactured by Osaka Gas Chemical Co., Ltd., hereinafter simply referred to as DPPS) instead of PMPS. Except for this, a photoelectric conversion element was produced by the same method as in Example 1.

(Comparative Example 1)
A photoelectric conversion element was produced by the same method as in Example 1 except that the perovskite layer precursor solution prepared without adding polysilane was used.

[XRD (X-ray diffraction) measurement]
The photoelectric conversion elements produced in Examples 1 to 3 and Comparative Example 1 were measured using an X-ray diffractometer (“D2 PHASER” manufactured by Bruker AXS). The results are shown in FIG. 2 and Table 1. The crystallite size D was calculated by the following Scherrer's equation.

D = 0.9xλ / (βxcosθ)
[In the formula, D is the crystallite size, λ is the wavelength of the X-ray used (0.15405 nm), β is the full width at half maximum (FWHM), and θ is the Bragg angle].

As is clear from FIG. 2, in Comparative Example 1, a peak derived from PbI ₂ is observed, whereas in Examples 1 to 3 to which polysilane is added, the peak disappears (or the intensity decreases). From this, it was found that the production of PbI ₂ was effectively suppressed. Further, in Examples 1 to 3, the peak intensity of the (100) plane was increased, and the crystallite size D was also increased from the results in Table 1. Therefore, the addition of polysilane effectively produced PbI ₂ . It was found that the growth of perovskite crystals was promoted while being suppressed. The reason for this is not clear, but in the perovskite layer precursor solution, a mixed solvent of γ-butyrolactone and DMF, CH ₃ NH ₃ I (monomethylamine hydroiodide), PbI ₂ (lead iodide (II)). , And the affinity with polysilane is presumed to have an effect. Further, in the example, since the inter-plane distance d is slightly smaller than that of Comparative Example 1, it is expected that the band gap will be slightly larger.

[Observation with an optical microscope]
The photoelectric conversion elements produced in Examples 1 to 3 and Comparative Example 1 were observed using an optical microscope (“ECLIPSE E600” manufactured by Nikon Corporation) on the surface of a portion where an Au electrode was not formed. The results are shown in FIG.

As is clear from FIG. 3, it was confirmed that the fine particles of the perovskite crystals were formed in a uniform size in all the examples. Further, in Examples 1 and 2 and Comparative Example 1, the particle size of the fine particles is about 10 μm, whereas in Example 3, the particles grow as large as about 20 to 40 μm, and the distance between the particles is narrow. It was found that a dense structure was formed.

[Characteristic evaluation of photoelectric conversion element]
Using an automatic polarization system ("HSV-110" manufactured by Hokuto Denko Co., Ltd.), a solar simulator ("XES-301S" manufactured by Sannaga Denki Seisakusho Co., Ltd., light source: xenon lamp, illuminance: 100 mWcm ^-2 ). The current density-voltage curves of the photoelectric conversion elements obtained in Examples 1 to 3 and Comparative Example 1 were measured under the conditions of AM1.5, an illuminance area of 0.090 cm ² , and room temperature (about 25 ° C.). Light was irradiated through the FTO substrate side of the photoelectric conversion element. The measurement results are shown in Table 1 and FIG. In Table 1, J _sc indicates the short-circuit current density, V _oc indicates the release voltage, FF indicates the curve factor, and η and η _ave indicate the maximum value and the average value of the photoelectric conversion efficiency (simply also referred to as conversion efficiency). Specifically, η and η _ave are the maximum and average values of conversion efficiencies measured at four different locations of the photoelectric conversion element. At each measurement point, measurement is performed once (twice in total) under the conditions of Forward (forward scan, scanning in the direction of voltage increase) and Reverse (reverse scan, scanning in the direction of voltage decrease), and these two times. The average value of the measured values was taken as the conversion efficiency at each measurement point. In addition, FIG. 4 shows a graph averaging the measurements of Forward and Reverse.

Further, the external quantum efficiency (or photoelectric conversion quantum yield, IPCE) of the photoelectric conversion element obtained in Examples 1 to 3 and Comparative Example 1 was measured at room temperature using "QE-R3011" manufactured by Enli Technology. It was measured under the conditions of (about 25 ° C.) and a wavelength of 300 to 800 nm. The results are shown in FIG.

As is clear from Table 2 and FIG. 4, the open circuit voltage _Voc was improved in each of the examples. In particular, in Example 3, since it is significantly improved as compared with Examples 1 and 2, it is presumed that DPPS having many phenyl groups greatly contributed to the improvement of carrier mobility. Since the open circuit voltage value of a general single crystal silicon solar cell is about 0.706V at the maximum, it is expected to be used in fields that require a higher voltage. Further, in Examples 1 and 2, the conversion efficiency η is slightly lower than that in Comparative Example 1, but in Example 3, the short-circuit current density J _sc is greatly increased, and the maximum conversion efficiency η is 10.15. % (Maximum 10.46% under Reverse conditions), which is almost twice as high as that of Comparative Example 1.

As is clear from FIG. 5, in Examples 1 and 2, it is suggested that the energy value of the valence band of the perovskite layer may decrease and the band gap may increase by about 0.02 eV as compared with Comparative Example 1. It seems that there is a correlation between the change in bandgap and the results in Table 2 above. On the other hand, in Example 3 to which DPPS was added, the energy values of the valence band and the conduction band of the perovskite layer were reduced to the same extent because the change in the bandgap was small even though the open circuit voltage was improved. Conceivable. Further, since the IPCE is improved in the wide wavelength region around 400 to 750 nm as compared with Comparative Example 1, it is considered that the short-circuit current density J _sc of the photoelectric conversion element of Example 3 is improved.

The mechanism by which the short-circuit current density J _sc and the conversion efficiency η were greatly improved by the addition of _DPPS is not clear, but the formation of a dense interface structure by promoting the grain growth of perovskite crystals and improving the surface coverage; It is presumed that the promotion of perovskite crystal growth due to the above; improvement of hole transport efficiency after charge separation by many phenyl groups of DPPS is affected. In particular, regarding the growth of perovskite crystals, it is presumed from the observation results obtained by the above-mentioned optical microscope that the perovskite crystal particles grew large in Example 3 and formed a dense structure, which contributed to the improvement of the conversion efficiency. .. That is, it is considered that as the crystal grain size increases, the area of the crystal grain boundaries that cause scattering of carriers (electrons, holes, etc.) decreases, and the electrical resistance decreases, so that the conversion efficiency improves.

INDUSTRIAL APPLICABILITY The present invention can be effectively used as a perovskite-type photoelectric conversion element (or solar cell) having high conversion efficiency.

1 ... 1st electrode 2 ... Electron transport layer (ETL)
3a ... 1st perovskite layer 3b ... 2nd perovskite layer 4 ... hole (or hole) transport layer (HTL)
5 ... Second electrode

Claims (6)

A photoelectric conversion element including a perovskite layer containing a compound having a perovskite-type structure.
The perovskite layer contains polysilane and contains
The compound having a perovskite-type structure is a compound represented by the formula AMX ₃ (in the formula, A represents an organic ammonium, M represents a divalent atom, and X represents a halogen atom).
In the above formula, A is at least one organic ammonium selected from C _1-4 alkylammonium and C _1-4 amidinium, and M is at least one selected from the Group 14 element of the Periodic Table and the Group 2 element of the Periodic Table. The species atom, X, is at least one halogen atom selected from iodine I, bromine Br and chlorine Cl.
The polysilane is the following formulas (2a) and (2b).

(In the formula, R ¹ to R ³ independently represent a hydrogen atom, a hydroxyl group, an organic group or a silyl group, respectively.)
Contains at least one structural unit selected from the structural units represented by
In the formula (2a), at least one of R ¹ and R ² is an aryl group-containing group, and in the formula (2b), R ³ is an aryl group-containing group.
The weight average molecular weight of the polysilane is 300 to 25,000, and the weight average molecular weight is 300 to 25,000.
A photoelectric conversion element in which the proportion of polysilane is 0.01 to 10 parts by weight with respect to 100 parts by weight of the compound having the perovskite type structure . The photoelectric conversion element according to claim 1 , wherein both R ¹ and R ² are aryl group-containing groups in the formula (2a). Claimed that the aryl group-containing group is a C _6-12 aryl group, a C _6-12 aryl-C _1-6 alkyl group, a C _6-12 aryl oxy group or a C _6-12 aryl-C _1-6 alkoxy group. The photoelectric conversion element according to 1 or 2 . The photoelectric conversion element according to any one of claims 1 to 3 , wherein the ratio of the structural unit represented by the formula (2a) is 50 mol% or more with respect to the entire polysilane. The photoelectric conversion element according to any one of claims 1 to 4 , wherein the polysilane is cyclic polysilane. The method for producing a photoelectric conversion element according to any one of claims 1 to 5 , wherein a perovskite layer containing a compound having a perovskite-type structure and polysilane is formed.

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