JP7290953B2 - Electrolytes, solar cells and solar modules - Google Patents

Description

Disclosed herein are electrolytes, solar cells and solar cell modules.

Conventionally, as a solar cell, a dye-sensitized solar cell using a copper complex as a redox pair has been proposed (see, for example, Patent Document 1). It is said that this solar cell does not corrode the platinum counter electrode and has good photoelectric conversion characteristics by containing the monovalent and divalent copper complexes. Moreover, as a solar cell, a copper complex of copper (I) bis(2,9-dimethyl-1,10-phenanthroline) or copper (II) bis(2,9-dimethyl-1,10-phenanthroline) is used as a solid electrolyte. A dye-sensitized solar cell has been proposed (see, for example, Non-Patent Document 1). It is said that this solar cell can improve power generation efficiency.

JP 2006-302849 A

Energy Environ. Sci. , 2015, 8, 2634-2637

By the way, in a solar cell using a copper complex as a solid electrolyte, such as the above-mentioned Patent Document 1, an electrolytic solution containing a copper complex and a solvent is injected into a porous TiO electrode on which a dye is adsorbed, and then _the solvent is removed. Electrolyte filling may be performed at However, the solar cell produced in this way has a durability problem that the solar cell characteristics deteriorate with the lapse of time. It has been desired to further improve the durability of a solar cell provided with an electrolyte containing a copper complex.

The present disclosure has been made in view of such problems, and the main purpose of the present disclosure is to provide an electrolyte, a solar cell, and a solar cell module that contain a copper complex and can further increase the durability of the solar cell. do.

As a result of intensive research to achieve the above-described object, the present inventors have found that when two or more copper complexes having different organic ligands are included, the output density is further improved and the durability at high temperatures is further improved. The inventors have found that the solar cell characteristics can be further improved, such as by increasing

Thus, the electrolytes disclosed herein are
An electrolyte interposed between the photoelectrode and the counter electrode of a solar cell comprising a photoelectrode having a light absorption layer and a counter electrode arranged to face the photoelectrode,
A copper complex having an organic ligand and copper having a plurality of valences contains two or more kinds of copper complexes in which the structure of the organic ligand is different.

The solar cells disclosed herein are
a photoelectrode having a light absorption layer;
a counter electrode arranged to face the photoelectrode;
the electrolyte interposed between the photoelectrode and the counter electrode;
is provided.

The solar cell module disclosed in this specification includes a plurality of the solar cells described above.

The electrolyte, solar cell, and solar cell module that contain a copper complex can further enhance the solar cell characteristics. The reason why such an effect is obtained is presumed as follows. For example, in a solar cell using a copper complex as a solid electrolyte, the electrolyte may be filled by adding a solvent as described above. ) was found to be desirable. That is, it is presumed that it is important to employ a composition that allows the copper complex to remain in an amorphous state without crystallization. In the present disclosure, since it contains two or more kinds of copper complexes having different organic ligands, i.e., it contains a plurality of organic ligands with different structures, alignment of the copper complexes, i.e., crystallization is likely to be structurally inhibited, It is presumed that the copper complex becomes easier to maintain an amorphous state. For this reason, it is speculated that the copper complex is less likely to crystallize, a high output density can be secured in the initial characteristics, and high-temperature durability, etc., when left in a dark place at a high temperature of 60° C., can be further improved. be.

FIG. 2 is a cross-sectional view showing an example of a schematic configuration of a solar cell module 10; FIG. 2 is a cross-sectional view showing an example of a schematic configuration of a solar cell 40; The measurement result of Jsc of an open cell and the measurement time after electrolyte injection. 4 shows measurement results of electrolyte compositions of evaluation cells of Experimental Examples 1 and 2. FIG. Solar cell characteristics of the evaluation cells of Experimental Examples 2-5 and 2-6. Measurement results of the electrolyte composition of the evaluation cells of Experimental Examples 2-4 to 2-6. NMR measurement results of electrolyte compositions of evaluation cells of Experimental Examples 2-4 to 2-6. Measurement results of output density in Experimental Examples 3 and 4 when left in a high-temperature dark place. Measurement results of output retention rate (%) when left in a dark place at high temperature in Experimental Examples 3 and 4. Photograph after adding a solvent to the copper complex. Initial power density for Examples 5-8. Initial relative power densities for Examples 5-8. Output retention rate after being left in the dark at 60° C. in Experimental Examples 5-8.

(Electrolytes)
The electrolyte of the present disclosure is used by interposing between a photoelectrode and a counter electrode of a solar cell comprising a photoelectrode having a light absorbing layer and a counter electrode arranged to face the photoelectrode. This electrolyte contains two or more copper complexes having different organic ligand structures. It includes a copper complex having an organic ligand and copper having multiple valences. Since the position of the valence band of the copper complex is considerably deeper than that of a conventional inorganic p-type semiconductor (for example, CuI), the conduction band bottom CBM of titanium oxide, which is the n-type semiconductor layer, and the valence band top VBM of the electrolyte There is an advantage that the theoretical open-circuit voltage (Voc) determined by the difference between is increased. The electrolyte may contain a solvent. When the solvent is present in the electrolyte, crystallization of the copper complex is further suppressed, and the characteristics of the solar cell using the copper complex can be further improved.

A copper complex has, for example, an organic ligand, and the valence of copper changes. Examples of organic ligands include phenanthroline ligands, bipyridylalkyl ligands, bipyridine ligands, sparteine ligands, bisbenzimidazolylthiomethylpyridine ligands, bisbenzimidazolyl It is preferably one or more of a luthiomethylmethylamine-based ligand, a bisbenzimidazolylpyridine-based ligand, and a bisethylthiomethylpyridine-based ligand. Phenanthroline-based ligands include phenanthroline structures and derivatives thereof. The bipyridylalkyl-based ligand has a structure in which a pyridyl group is bonded to the ends of an alkyl chain, and includes a bipyridylethane structure and derivatives thereof. Bipyridine-based ligands include bipyridine structures and derivatives thereof. A sparteine-based ligand includes a sparteine structure or derivative. Bisbenzimidazolylthiomethylpyridine-based ligands include benzimidazolylthiomethylpyridine structures and derivatives thereof. Bisbenzimidazolylthiomethylmethylamine-based ligands include benzimidazolylthiomethylmethylamine structures and derivatives thereof, and bisbenzimidazolylpyridine-based ligands include benzimidazolylpyridine structures and derivatives thereof. Bisethylthiomethylpyridine-based ligands include ethylthiomethylpyridine structures and derivatives thereof.

This copper complex may have a structure represented by one or more of chemical formulas (1) to (4). The organic ligand may have, for example, a heterocyclic structure containing one or more nitrogen atoms. Examples of this organic ligand include 2,9-dimethyl-1,10-phenanthroline (dmp, chemical formula (1)) and 1,1-bis(2-pyridyl)ethane (bpye, chemical formula (2)). , 4,4′,6,6′-tetramethyl-2,2′-bipyridine (tmby, chemical formula (3)), 6,6′-dimethyl-2,2′-bipyridine (dmby, chemical formula (4)) etc. Examples of the organic ligand include 1,10-phenanthroline (phen, chemical formula (5)), [(−)-sparteine-N,N′] (SP, chemical formula (6)), 2, 6-bis(benzimidazol-2′-ylthiomethyl)pyridine (bbtmp, chemical formula (7)), N,N-bis(benzimidazol-2′-ylthiomethyl)methylamine (bbtma, chemical formula (8)), 2,6 -bis(benzimidazol-2′-yl)pyridine (bzmpy, chemical formula (9)), 2,6-bis(ethylthiomethyl)pyridine (betmp, chemical formula (10)), and the like. Moreover, the copper complex may have one or more other ligands, for example, a monodentate ligand (monovalent anion ligand). When there are a plurality of ligands, they may be the same ligand or different ligands. Among these, it is more preferable that all of these ligands are the same. This ligand may be, for example, one or more selected from -F, -Cl, -Br, -I, -OH, -CN, -SCN, and -NCS. Of these, -SCN and -NCS are preferred, and -NCS is more preferred. This copper complex may consist of a cation having an organic ligand and containing copper, and an anion. Examples of anions include trifluoromethylsulfonic acid (CF ₃ SO ₃ ), bis(trifluoromethylsulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI), hexafluorophosphoric acid (PF ₆ ), and the like. mentioned.

Specific examples of such copper complexes include copper (I) bis(2,9-dimethyl-1,10-phenanthroline)bis(trifluoromethylsulfonyl)imide (Cu(dmp) ₂ TFSI), copper ( II) Bis(2,9-dimethyl-1,10-phenanthroline)bis[bis(trifluoromethylsulfonyl)imide](Cu(dmp) ₂ (TFSI) ₂ ), copper(I) bis(1,10-phenanthroline) ) bis(trifluoromethylsulfonyl)imide (Cu(phen) ₂ TFSI), copper (II) bis(1,10-phenanthroline) bis[bis(trifluoromethylsulfonyl)imide] (Cu(phen) ₂ (TFSI) ₂ ), [(-)-spartein-N,N'] (maleonitriledithiolato-S,S') copper ([Cu(SP)(mmt)]), 2,6-bis(benzimidazole-2 '-ylthiomethyl)pyridine nitrate ([Cu(bbtmp)(NO ₃ )]NO ₃ ) and the like.

This electrolyte contains two or more copper complexes having different organic ligand structures. If two or more kinds of copper complexes are included, the copper complexes are less likely to crystallize, and the amorphous state is likely to be maintained. Therefore, it is possible to further suppress deterioration of solar cell characteristics that may occur due to crystallization of the copper complex. The organic ligands may have the same basic structure but different substituents, such as derivatives, or may have different basic structures, but different basic structures are more preferable. If the basic structure is different, alignment of the copper complex, that is, crystallization is likely to be structurally inhibited, so that the amorphous state is more likely to be maintained, which is more preferable. For example, organic ligands having the same basic structure include a combination of a phenanthroline ligand and its derivative, a combination of a bipyridylalkyl ligand and its derivative, a combination of a bipyridine ligand and its derivative, and the like. is mentioned. Organic ligands with different basic structures include a combination of a phenanthroline ligand and a bipyridylalkyl ligand, a combination of a phenanthroline ligand and a bipyridine ligand, a bipyridylalkyl ligand and bipyridine. A combination with a system ligand and the like can be mentioned. Specific examples of such electrolytes include bis(2,9-dimethyl-1,10-phenanthroline) copper complex and bis(4,4′,6,6′-tetramethyl-2,2′-bipyridine ) combinations of two copper complexes and the like are preferred. The compounding ratio of the copper complex is, for example, when at least a cuprous complex and a cupric complex having different organic ligands are included, the number of moles M1 of the cuprous complex and the number of moles Ma of the entire copper complex The ratio M1 / Ma × 100 (mol%) is preferably in the range of 30 mol% to 70 mol%, more preferably in the range of 33 mol% to 67 mol%, and in the range of 40 mol% to 60 mol% It may be a certain one. Also, when only two kinds of copper complexes are included, the same range as above is preferable. In addition, in the copper complex, even if the molar ratio X (Cu ^II /(Cu ^I + Cu ^II ) of bivalent copper to the total of copper (monovalent + divalent) is within the range of 0 ≤ X < 0.2 It is preferable that the presence of a divalent copper complex is less in the molar ratio X. As shown in chemical formulas (1) to (4), copper that differs only in the number of valences and anions of copper Complexes and copper complexes in which only the types of anions differ as shown in chemical formulas (1) and (1') are not included in the above-mentioned "copper complexes with different organic ligand structures".

The electrolyte may contain solvents including organic solvents and/or ionic liquids. The organic solvent has, for example, a boiling point of 200° C. or higher, a dielectric constant εr of 30 or more and 100 or less, and a viscosity η of 0.5 mPa·s or more and 10 mPa·s or less at 25° C. Preferred (hereinafter simply referred to as an organic solvent). This is because the organic solvent is difficult to volatilize and remains in the electrolyte, thereby further suppressing the crystallization of the copper complex. From the viewpoint of volatility, the organic solvent preferably has a higher boiling point. For example, the boiling point is preferably 220° C. or higher, more preferably 240° C. or higher, and may be 260° C. or higher. The boiling point of the organic solvent may be, for example, 400° C. or lower. The organic solvent preferably has a dielectric constant ∈r of 35 or more, more preferably 40 or more, and may be 50 or more. Further, the organic solvent may have a dielectric constant εr of 90 or less, or 80 or less. The viscosity of this organic solvent is preferably lower, and the viscosity at 25° C. is preferably 8 mPa·s or less, more preferably 6 mPa·s or less, and may be 5 mPa·s or less. Further, the organic solvent may have a viscosity at 25° C. of 0.5 mPa·s or more, or 1 mPa·s or more.

Organic solvents include carbonates including ethylene carbonate, propylene carbonate and butylene carbonate, cyclic esters including γ-butyllactone and γ-valerolactone, nitriles including adiponitrile, pyrrolidones including N-methylpyrrolidone, 3-methyl It may be one or more of oxazolidones including -2-oxazolidone and dinitriles including glutaronitrile. Among these, oxazolidones and dinitriles are more preferable, and 3-methyl-2-oxazolidone and glutaronitrile are more preferable from the viewpoint of boiling point, viscosity, relative dielectric and the like.

The solvent may contain an ionic liquid having a viscosity η of 300 mPa·s or less at 25° C. (hereinafter simply referred to as an ionic liquid). The ionic liquid preferably has a lower viscosity, preferably a viscosity at 25° C. of 250 mPa·s or less, more preferably 160 mPa·s or less, even more preferably 100 mPa·s or less. Also, the ionic liquid may have a viscosity at 25° C. of 10 mPa·s or more, or 20 mPa·s or more. The ionic liquid preferably has a dielectric constant ∈r of 5 or more and 30 or less, and may be 8 or more and 20 or less. The ionic liquid preferably has a lower melting point, more preferably 20° C. or lower, more preferably 15° C. or lower, and even more preferably 10° C. or lower.

The ionic liquid may contain one or more cations selected from imidazolium cations, pyridium cations, alicyclic amine cations, aliphatic amine cations, sulfonium ions, phosphonium ions, and the like. Imidazolium-based cations include imidazolium structures and derivatives thereof. Pyridium-based cations include pyridium structures and derivatives thereof. Alicyclic amine-based cations include alicyclic amine structures and derivatives thereof. Aliphatic amine-based cations include aliphatic amine structures and derivatives thereof. This ionic liquid preferably contains one or more cations of chemical formulas (11) to (17). However, in the chemical formulas, R, R ¹ to R ⁴ may be the same group or different groups, and are either a chain hydrocarbon group having 1 to 6 carbon atoms or H. The chain hydrocarbon group may contain an ether bond or may have one or more substituents. The substituent may include, for example, an alkyl group having 3 or less carbon atoms, halogen, and the like. Examples of imidazolium-based cations include cations of chemical formula (11). Examples of pyridium-based cations include cations of chemical formula (12). Alicyclic amine-based cations include cations of chemical formulas (13) and (14). Examples of aliphatic amine-based cations include cations of chemical formula (15). Sulfonium ions include cations of chemical formula (16). , Phosphonium ions include cations of the chemical formula (17). Moreover, this ionic liquid includes Br ⁻ , Cl ⁻ , SCN ⁻ , HSO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ CO ₂ ⁻ , (C ₂ F ₅ ) ₃ PF ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ and (FSO ₂ ) ₂ N ⁻ . Such ionic liquids specifically include ionic liquids represented by one or more of chemical formulas (18) to (38). Among them, 1-ethyl-3-methylimidazolium tetracyanoborate (EMITCB) is preferred.

By containing an organic solvent and/or an ionic liquid, the electrolyte can further suppress the crystallization of the copper complex. More preferably, the solvent contains a high-boiling organic solvent and an ionic liquid. If these two types are included, the volatility (boiling point), viscosity, relative permittivity, etc. can be set in more suitable ranges. As for this solvent, the ratio Mi/Ms×100 (mol %) of the number of moles Mi of the ionic liquid to the number of moles Ms of the organic solvent is preferably in the range of 10 mol % or more and 50 mol % or less. Within this range, the volatility, viscosity, dielectric constant and the like can be made more suitable. This molar ratio is preferably 15 mol % or more, more preferably 20 mol % or more, and may be 30 mol % or more. Also, the molar ratio is preferably 45 mol % or less, more preferably 40 mol % or less, and may be 35 mol % or less.

Also, the electrolyte preferably further contains an additive. The additive includes, for example, one or more cyclic compounds selected from heterocyclic compounds containing one or more nitrogen atoms and having two or more rings and monocyclic heterocyclic compounds having two or more nitrogen atoms. The cyclic compound may have one or more of an imidazole structure, a pyridine structure, a pyrimidine structure, an oxazole structure and a thiazole structure. This cyclic compound preferably has basicity and preferably has an imidazole structure. In addition, the cyclic compound may have a substituent or a heteroatom in its structure, or may have a hydrogen group, an alkyl group substituted for a hydrogen group, or the like. The alkyl group preferably has 1 to 6 carbon atoms. Specifically, the cyclic compound may be one or more of chemical formulas (39) to (46). In this formula, R may be hydrogen (H) or an alkyl group having 1 to 6 carbon atoms. The alkyl group may be linear or branched. Chemical formulas (39) to (43) are heterocyclic compounds containing one or more nitrogen atoms and having two or more rings. Chemical formula (39) is benzimidazole and derivatives thereof, such as N-methylbenzimidazole and N-butylbenzimidazole. Chemical formula (40) is a pyrimidine base, such as 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, 1,3,4,6,7, 8-hexahydro-1-methyl-2H-pyrimido[1,2a]pyrimidine and the like. Chemical formula (41) is quinoline and may be a derivative thereof. Chemical formula (42) is benzoxazole, and may be a derivative thereof. Chemical formula (43) is benzothiazole and may be a derivative thereof. Chemical formulas (44) to (46) are monocyclic heterocyclic compounds having two or more nitrogen atoms. Chemical formula (44) is imidazole and its derivatives. Chemical formula (45) is pyrazole and its derivatives. Chemical formula (46) is imidazoline and its derivatives. The cyclic compound is preferably contained in the electrolytic solution so that the molar ratio X, which is the ratio of the number of moles of the cyclic compound to the number of moles of the copper complex, is within the range of 0.4≦X≦4. This range is preferable because the effect of adding the cyclic compound can be sufficiently exhibited. This molar ratio X may be 0.8 or more, or may be 1.0 or more. Alternatively, this molar ratio Y may be 3.0 or less, or 2.0 or less. Further, as additives, for example, LiTFSI, which lowers the bottom of the conduction band (CBM) of a photoelectrode material such as TiO ₂ to improve the electron injection efficiency from the dye to TiO ₂ and increase the short-circuit current density Jsc, LiI and the like. These can be used singly or in combination.

(solar cell)
The solar cell of the present disclosure includes a photoelectrode having a light absorption layer, a counter electrode arranged to face the photoelectrode, and any of the electrolytes described above interposed between the photoelectrode and the counter electrode. is. The photoelectrode may comprise an n-type semiconductor layer (electron transport layer) coated with a light absorbing layer on a light transmissive conductive substrate. FIG. 1 is a cross-sectional view showing an example of a schematic configuration of a solar cell module 10. As shown in FIG. As shown in FIG. 1 , the solar cell module 10 has a configuration in which a plurality of solar cells 40 (hereinafter also referred to as cells) are arranged sequentially on a light-transmitting conductive substrate 14 . These cells are connected in series. In this solar cell module 10, a sealing material 32 is formed so as to fill the spaces between the cells, and a flat protective member 34 is formed on the surface of the sealing material 32 opposite to the light-transmitting conductive substrate 14. It is The solar cell 40 includes a photoelectrode 20 having an electron transport layer 24 including a light absorption layer and an n-type semiconductor layer on a light-transmitting conductive substrate 14 with an underlying layer 22 interposed therebetween, and the photoelectrode 20 is arranged to face the photoelectrode 20 . , an electrolyte layer 26 interposed between the photoelectrode 20 and the counter electrode 30 , and a separator 29 . The photoelectrode 20 consists of a light-transmitting conductive substrate 14 having a light-transmitting light-transmitting conductive film 12 formed on the surface of a light-transmitting substrate 11, and an electron transport layer formed on the light-transmitting conductive film 12. 24 and. The electron transport layer 24 is a layer provided on the light-transmitting conductive film 12 separately formed on the surface opposite to the light-receiving surface 13 of the light-transmitting substrate 11 and emitting electrons upon receiving light. In the solar cell 40, the electron transport layer 24 is provided with a light absorbing material that absorbs light.

The light-transmitting conductive substrate 14 is composed of the light-transmitting substrate 11 and the light-transmitting conductive film 12, and has light transmittance and conductivity. Specific examples include fluorine-doped SnO ₂ -coated glass, ITO-coated glass, ZnO:Al-coated glass, and antimony-doped tin oxide (SnO ₂ --Sb)-coated glass. In addition, a light-transmitting electrode obtained by doping tin oxide or indium oxide with cations or anions having different valences, or a metal electrode having a structure that allows light to pass through, such as a mesh or stripe, provided on a substrate such as a glass substrate. can also be used. Collecting electrodes 16 and 17 are provided at both ends of the light-transmitting conductive substrate 14 on the light-transmitting conductive film 12 side. can do.

Examples of the light-transmissive substrate 11 include transparent glass, transparent plastic plate, transparent plastic film, and inorganic transparent crystals, among which transparent glass is preferred. The light-transmitting substrate 11 may be a transparent glass substrate, a glass substrate whose surface is appropriately roughened to prevent reflection of light, or a translucent frosted glass substrate that transmits light. The light-transmitting conductive film 12 can be formed, for example, by depositing tin oxide on the light-transmitting substrate 11 . In particular, if a metal oxide such as fluorine-doped tin oxide (FTO) is used, a suitable light-transmitting conductive film 12 can be formed. The light-transmitting conductive film 12 has grooves 18 formed at predetermined intervals, and a plurality of regions of the light-transmitting conductive film 12 are separated at intervals corresponding to the width of the grooves 18 .

The underlayer 22 is a layer that suppresses or prevents leakage current (reverse electron transfer) from the light-transmitting conductive substrate 14 to the electrolyte layer 26, and is preferably made of, for example, a light-transmitting and conductive material. Examples include n-type semiconductors such as titanium, zinc oxide, and tin oxide, and among these, titanium oxide is more preferable. This is because titanium oxide suppresses/prevents leakage current and allows electrons to easily flow from the electron transport layer 24 to the light-transmitting conductive substrate 14 . The underlying layer 22 is preferably made of a denser material than the electron transporting layer 24 . Note that the solar cell 40 functions sufficiently even if the underlayer 22 is not formed, so the underlayer 22 may be omitted.

The electron transport layer 24 is formed of a light absorbing material and a porous n-type semiconductor layer containing the light absorbing material. Suitable n-type semiconductors include metal _oxide semiconductors and metal _sulfide semiconductors. At least one of zinc (ZnS) is preferable, and among these, porous titanium oxide is more preferable. A good porous n-type semiconductor layer can be formed by making these semiconductor materials into a microcrystalline or polycrystalline state and thinning the film. In particular, a porous titanium oxide layer is suitable as the n-type semiconductor layer of the photoelectrode 20 . As titanium oxide, anatase-type TiO ₂ is preferable to rutile-type TiO ₂ because the energy level at the lower end of the conduction band is higher and the open-circuit voltage is higher.

The light-absorbing layer may contain one or more light-absorbing materials selected from organic dyes, metal complexes, and organic metal halide compounds. This light absorbing material may be an organic dye. Organic dyes include, for example, BODIPY dyes (BODIPY-FL, etc.), indoline dyes (D131, D149, D205, D358, etc.), carbazole dyes (MK2, etc.), coumarin dyes (C343, NKX-2587, NKX- 2677, etc.) and squarylium-based dyes (SQ2, etc.). Alternatively, the organic dye may have an aromatic amine as a donor and a cyanocarboxylic acid anchor group via a π-conjugated molecule. Such dyes include, for example, 3-[6-[4-[bis(2',4'-dibutyloxybiphenyl-4yl)amino-]phenyl]-4,4-dihexyl-cyclopenta-[2,1 -b;3,4-b']dithiophene-2-yl]-2-cyanoacylic acid dye (chemical formula (A)), etc., and this dye is preferably used. Also, the light absorbing material may be a metal complex. Examples of metals contained in metal complexes include Zn, Cu, Fe, Pd, Pt, Ni, Co, and Ru. Among them, Ru complexes (Ruthenizer470 (Ru470), N719, Z907, etc.), metal porphyrin dyes (PtTPTBP, PdTPTBP, DTBC, etc.), metal phthalocyanine dyes (CuPc, ZnPc, etc.) and metal naphthalocyanine dyes (CuNc, ZnNc etc.). These light absorbing materials may be used alone or in combination. Among them, Ru complex compounds (Z907, N719), Zn porphyrin compounds (DTBC), carbazole dyes (MK2), and indoline double rhodanine compounds (D149 and D358) are preferable as dyes. Moreover, perovskite crystals such as CH ₃ NH ₃ PbI ₃ and the like can be used as the organic metal halide compound as the light absorbing material. The structural formulas of the exemplified compounds are shown below. Although not shown in the chemical formulas below, PdTPTBP is Pt in PtTPTBP replaced by Pd, ZnPc is Cu in CuPc in which Cu is replaced by Zn, and ZnNc is CuNc in which Cu is replaced by Zn.

The electrolyte layer 26 is formed adjacent to the photoelectrode 20 . This electrolyte layer 26 contains any of the electrolytes described above. This structure of solar cell module 10 can be employed when electrolyte layer 26 comprises a solid.

The separator 29 is formed to have an I-shaped cross section so as to be adjacent to one side surface of the photoelectrode 20 and the electrolyte layer 26 on which the base layer 22 and the electron transport layer 24 are laminated. One end of separator 29 is in contact with groove 18 on light-transmissive conductive substrate 14 . This avoids direct contact between the photoelectrode 20 and the counter electrode 30 . The separator 29 is made of an insulating material, and may be made of, for example, glass beads, silicon dioxide (silica), rutile-type titanium oxide, or the like. As the separator 29, an insulator obtained by sintering silica particles is preferable. Silica particles are preferable for separators because they have a low refractive index, low light scattering, and good transparency. From the viewpoint of ensuring good transparency, the separator 29 preferably has an average particle size of 5 to 200 nm. Also, the separator may be air or an air layer.

The counter electrode 30 has an L-shaped cross section so as to be in contact with the outer surface of the separator 29 and the back surface 27 of the electrolyte layer 26 . The counter electrode 30 has one end connected to the back surface 27 of the electrolyte layer 26 and the other end connected to the adjacent light-transmitting conductive film 12 via the connecting portion 21 . The surface of the counter electrode 30 in contact with the back surface 27 faces the photoelectrode 20 with a predetermined gap therebetween. The counter electrode 30 is not particularly limited as long as it has conductivity and bondability with the electrolyte layer 26, and examples thereof include Pt, Au, and carbon, among which carbon is preferred.

The sealing material 32 can be used without particular limitation as long as it is an insulating member. As the sealing material 32, for example, a thermoplastic resin film such as polyethylene or an epoxy adhesive can be used.

The protective member 34 is a member intended to protect the solar cells 40, and may be, for example, a moisture-proof film or protective glass.

When the solar cell 40 is irradiated with light from the side of the light-receiving surface 13 of the light-transmitting substrate 11 , the light passes through the light-receiving surface 15 of the light-transmitting conductive film 12 and the light-receiving surface 23 of the underlying layer 22 to the electron transport layer 24 . When it reaches the light absorber, the light is absorbed and electrons are generated. The generated electrons move from the photoelectrode 20 to the adjacent counter electrode 30 via the light-transmitting conductive film 12 and the connecting portion 21 . In the solar cell 40, electromotive force is generated by this movement of electrons, and the power generation action of the cell is obtained. In the solar cell module 10, the electrolyte layer 26 contains two or more copper complexes having organic ligands and having a plurality of valences of copper and having different structures of the organic ligands.

The solar cell module 10 can be manufactured through a substrate manufacturing process, an electron transport layer forming process, an electrolyte layer forming process, a separator forming process, a counter electrode forming process, and a protective member forming process. In the substrate manufacturing process, the light-transmitting conductive film 12 is formed on the light-transmitting substrate 11 while forming the grooves 18 between the plurality of light-transmitting conductive films 12 . In the electron transport layer forming step, an n-type semiconductor layer is formed on the light-transmitting conductive film 12 with the base layer 22 interposed therebetween, a light absorbing material is formed on the n-type semiconductor layer, and the electron transport layer 24 is formed. Porous titanium oxide may be used as the n-type semiconductor layer.

Next, in the electrolyte layer forming step, the electrolyte described above is supplied to the back surface 25 of the electron transport layer 24 to form the electrolyte layer 26 . In this step, a plurality of copper complexes having organic ligands and copper having multiple valences are blended and mixed in a solvent, and this electrolyte solution is applied or discharged to form an electrolyte on the photoelectrode. good too. As for the type, content, compounding ratio, and the like of the copper complex, the high-boiling organic solvent, and the ionic liquid, any one of those described above for the electrolyte can be appropriately used. In this electrolyte layer forming step, an electrolyte containing a solvent containing an organic solvent excluding carbonates including ethylene carbonate, propylene carbonate and butylene carbonate may be formed on the photoelectrode in the air. When this organic solvent is used, for example, deterioration due to water present in the atmosphere can be suppressed, and an electrolyte layer can be produced in the atmosphere. On the other hand, in this electrolyte layer forming step, an electrolyte containing a solvent containing an organic solvent such as carbonates may be formed on the photoelectrode in an inert atmosphere. Even when carbonates are used, they may be produced in an inert atmosphere so as not to be affected by water. Further, in this step, in addition to the above organic solvent and ionic liquid, a low boiling point organic solvent having a boiling point of less than 200° C. may be included, and the low boiling point organic solvent may be removed by drying after forming the electrolyte layer. . By doing so, it is easy to adjust the viscosity of the electrolyte solution, etc., and to easily form the electrolyte layer on the photoelectrode. Examples of low-boiling organic solvents include acetonitrile, acetone, and alcohol.

Subsequently, in the separator forming step, a separator 29 is formed on the side surface of the photoelectrode 20 so as to match the groove 18 . In the counter electrode forming step, the counter electrode 30 is formed so as to be in contact with the separator 29 and the electrolyte layer 26 . The counter electrode 30 may be carbon, for example. In the protective member forming step, a sealing member 32 is formed so as to cover each cell, and a protective member 34 is formed on the sealing member 32 . Thus, the solar cell 40 and the solar cell module 10 with improved power generation characteristics can be manufactured.

In the electrolyte, solar cell, and solar cell module of the present disclosure described above, the solar cell characteristics can be further enhanced in those containing a copper complex. The reason why such an effect is obtained is presumed as follows. For example, in a solar cell using a copper complex as a solid electrolyte, the electrolyte may be filled by adding a solvent as described above. ) was found to be desirable. That is, it is presumed that it is important to employ a composition that allows the copper complex to remain in an amorphous state without crystallization. In the present disclosure, since it contains two or more kinds of copper complexes having different organic ligands, i.e., it contains a plurality of organic ligands with different structures, alignment of the copper complexes, i.e., crystallization is likely to be structurally inhibited, It is presumed that the copper complex becomes easier to maintain an amorphous state. For this reason, it is speculated that the copper complex is less likely to crystallize, a high output density can be secured in the initial characteristics, and high-temperature durability, etc., when left in a dark place at a high temperature of 60° C., can be further improved. be.

It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

For example, in the above-described embodiment, the solar cell module 10 is used, but the present invention is not limited to this, and the solar cell 40 shown in FIG. 2 may be used. FIG. 2 is a cross-sectional view showing an example of a schematic configuration of the solar cell 40. As shown in FIG. In FIG. 2, the same reference numerals are given to the same components as those described in FIG. 1, and the description thereof will be omitted. As shown in FIG. 2, when the solar cell 40 is used as a single unit, the cross section of the counter electrode 30 may be formed in a plate shape instead of an L shape. Also, the separator 29 may be omitted. The counter electrode 30 may have the same structure as the light-transmitting conductive substrate 14, may have platinum attached to the light-transmitting conductive film 12, or may be a metal thin film such as platinum. .

Experimental examples will be described below in which the electrolyte and the solar cell of the present disclosure are specifically produced. In the following examples, Experimental Examples 1 and 2 correspond to Reference Examples, Experimental Examples 3 to 7 correspond to Examples, and Experimental Example 8 corresponds to Comparative Example.

[Examination of electrolyte]
An evaluation cell was produced by a conventional production method. After forming dense TiO ₂ (10 nm) on a transparent conductive film (SnO ₂ ) electrode by atomic layer deposition, titanium oxide particles (particle diameter: several tens of nm to 400 nm) are printed and then sintered at 500°C. A TiO ₂ photoelectrode was prepared by immersion in a titanium compound and heating at 500°C. A rutile-type TiO ₂ layer separator was printed on the photoelectrode, and a carbon electrode was laminated thereon to prepare a three-layer structure electrode. After the red organic dye was adsorbed, the electrolyte was filled, and the solvent was removed to produce a three-layer structure type dye-sensitized solar cell. Here, a photoelectrode/transparent conductive film (FTO) glass and a counter electrode/glass substrate were sandwiched by a sealant, and an electrolyte solution was introduced under reduced pressure from a small hole for electrolyte injection provided in the glass substrate. Then, drying was performed under reduced pressure to remove the solvent, thereby forming an electrolyte layer on the photoelectrode (filling method). As for the materials used, the dye was the compound of the chemical formula (A). Cu(dmp) ₂ TFSI (monovalent: chemical formula (1)) and Cu(dmp) ₂ TFSI ₂ (bivalent) were used as copper complexes. This is referred to as Experimental Example 1 as a closed cell. The component ratio of the copper complexes with different valences was such that the concentration of bivalent was 0.05M and the total concentration of monovalent and divalent was 0.25M. Cu(tmby) ₂ TFSI (chemical formula (3)) was also used as a copper complex. Also, 0.1 M LiTFSI and 0.5 M N-butylbenzimidazole (NBBI) were added as additives to acetonitrile (ACN) as a solvent. The above copper complex was added to this to form an electrolyte solution, which was formed on the photoelectrode.

Here, the electrolyte was examined using an open cell that is not sealed. An open cell is an evaluation cell that is prepared by a dropping method, which will be described later, and is opened without using a sealing material. This open cell was produced using raw materials (pigments, additives, etc.) having the same composition as in Experimental Example 1, which is a closed cell. An open-cell reference example 1 using Cu(dmp) ₂ TFSI as the copper complex, and an open-cell reference example 2 using Cu(tmby) ₂ TFSI as the copper complex. FIG. 3 shows the measurement results of Jsc (mA/m ² ) with respect to the measurement time (S) after electrolyte injection in the open cells of Reference Examples 1 and 2. FIG. As shown in FIG. 3, in the open cell, both Reference Examples 1 and 2 showed high Jsc at the initial stage, but decreased with the lapse of time. This is presumably because the solvent remained in the electrolyte layer at the beginning, but the solvent volatilized with the passage of time and disappeared from the open cells, and the copper complex crystallized with the passage of time, resulting in a decrease in Jsc. rice field. From this result, it was inferred that it is desirable for the electrolyte to contain a solvent.

Next, the composition of the electrolyte of the evaluation cell of Experimental Example 1, which is the closed cell produced above, was evaluated. Table 1 summarizes the composition (preparation composition) at the time of preparation of the evaluation cell as Experimental Example 1-1, and the results of analyzing the components inside the cell after the test as Experimental Example 1-2. Also, FIG. 4A shows the compositions of Experimental Examples 1-1 and 1-2. Table 1 and FIG. 4A show the molar ratios of other components normalized to the molar ratio of the monovalent copper complex of 0.25. Also, the molar ratio in Experimental Example 1-2 was obtained from NMR measurements. As shown in Table 1 and FIG. 4A, acetonitrile as a solvent had a molar ratio of 19 in the charged composition, but the molar ratio decreased to 3.4 after power generation.

Next, a study was conducted by changing the method of preparing the evaluation cell and the solvent. Here, the electrolyte was formed on the photoelectrode by a dropping method in which a small amount of the electrolyte solution was dropped onto the photoelectrode in the atmosphere, instead of the filling method described above. The photoelectrode had a size of 1 cm×0.75 cm, and 3 μL of electrolyte solution was dropped. After that, the counter electrode was superimposed with a Himilan frame seal, and then an evaluation cell was produced by sealing the outer periphery of the cell with an epoxy curing resin. When the electrolyte solution of Experimental Example 1 was used in the evaluation cell produced by this dropping method, almost no power was generated. It is speculated that this is because the amount of solvent in the charged composition is small and the solvent evaporates quickly during preparation and disappears during power generation. Therefore, the solvent was a mixed solvent in which propylene carbonate (PC), valeronitrile (VALN), and acetonitrile (ACN) were mixed at a volume ratio of 32:14:54. An electrolyte solution was then prepared by adding 0.5 M Cu(dmp) ₂ TFSI, 1 M NBBI, and 0.4 M LiTFSI to the solvent. Table 2 shows Experimental Example 2-1, which is the composition (preparation composition) at the time of preparation of the evaluation cell prepared by the dropping method, and Experimental Examples 2-1 and 2-2, which are the results of analyzing the components inside the evaluation cell after preparation. Summarized as Experimental Example 2-1 is an evaluation cell prepared by dropping an electrolyte solution using a micropipette, and Experimental Example 2-2 is an evaluation cell prepared by spraying an electrolyte solution in the form of a mist. Table 2 shows the molar ratios of other components with the molar ratio of the monovalent copper complex normalized to 0.50. The molar ratio in Experimental Example 2 was obtained from NMR measurements. FIG. 4 shows the measurement results of the electrolyte composition of the evaluation cells of Experimental Examples 1 and 2, FIG. 4A is the composition of Experimental Examples 1-1 and 1-2, and FIG. -3 composition. As shown in FIG. 4 and Table 2, assuming that the concentration in Experimental Example 2 is about half, including the volume of the electrolyte, the number of moles of the Cu complex in Experimental Example 1 is about 6 in Experimental Example 2. 8 times, and Experimental Example 1 is estimated to be approximately 16 times that of Experimental Example 2. That is, in Experimental Example 2 prepared by the dropping method, it was estimated that the amounts of electrolyte and solvent were considerably smaller than in Experimental Example 1.

Next, an electrolyte was examined in which valeronitrile in Experimental Example 2-1 was changed to dimethylformamide (DMF). Experimental Example 2-4 was an evaluation cell using an electrolyte prepared in the same manner as in Experimental Example 2-1, except that a mixed solvent of PC, DMF, and ACN was used. Experimental Example 2-5 was obtained by leaving Experimental Example 2-4 in a dark place at room temperature for 3 weeks. Experimental Example 2-6 was obtained by leaving Experimental Example 2-4 in a dark place at 60° C. for 300 hours. Solar cell characteristics were measured when the evaluation cells of Experimental Examples 2-5 and 2-6 were irradiated with an LED light source of 1000 (lux). Also, the compositions of the electrolytes of Experimental Examples 2-4 to 2-6 were measured. FIG. 5 shows the solar cell characteristics of the evaluation cells of Experimental Examples 2-5 and 2-6. FIG. 6 shows the measurement results of the electrolyte composition of the evaluation cells of Experimental Examples 2-4 to 2-6. FIG. 6 shows the molar ratios of other components with the molar ratio of the monovalent copper complex normalized to 0.50. As shown in FIGS. 6 and 7, the evaluation cells of Experimental Example 2-6 left at 60° C. had lower solar cell characteristics and produced more PC alterations than the cells of Experimental Example 2-5 left at room temperature. I found out that FIG. 7 shows the NMR measurement results of the electrolyte composition of the evaluation cells of Experimental Examples 2-4 to 2-6. As shown in FIG. 7, in Experimental Examples 2-5 and 2-6, a new product peak was observed, which was presumed to be propylene glycol, which is a hydrolyzate of PC. In Experimental Example 2, since the electrolytic solution was dropped in the atmosphere to prepare the solvent, it was presumed that water was mixed in the solvent, and the hydrolysis of PC was promoted particularly at high temperatures.

Next, using the following electrolyte, an evaluation cell was produced by a dropping method, and the power density and the power retention rate over time were examined. As a copper complex, 0.2M Cu(dmp) ₂ TFSI (monovalent), 0.1M Cu(tmby) ₂ TFSI (monovalent), 0.24M LiTFSI, and 0.24M N-butylbenzimidazole (NBBI). It was mixed with the following solvent so as to be 6M. The solvent used was a mixture of ACN, PC and ionic liquid at a volume ratio of 70:20:10. Using this electrolyte solution, the dropping method was performed in a glove box in a nitrogen atmosphere to form an electrolyte layer on the photoelectrode. An evaluation cell obtained through such steps was referred to as Experimental Example 3. As copper complexes, 0.3M Cu(dmp) ₂ TFSI (monovalent), 0.24M LiTFSI, and 0.6M NBBI were mixed in the following solvents. The solvent used was a mixture of ACN and PC at a volume ratio of 70:30. Experimental Example 4 is an evaluation cell obtained through the same steps as in Experimental Example 3 using this electrolyte solution. The evaluation cells of Experimental Examples 3 and 4 were irradiated with 1000 (lux) from an LED light source every predetermined time, and the solar cell characteristics were measured. FIG. 8 shows the measurement results of the output densities of Experimental Examples 3 and 4 when left in a high-temperature dark place. FIG. 9 shows the measurement results of the output retention rate (%) of Experimental Examples 3 and 4 when left in a high-temperature dark place. Table 3 shows the initial power density (mW/m ² ) of Experimental Examples 3 and 4, the power density (mW/m ² ) after being left in the dark at 60°C, and the power retention rate (%) after being left in the dark at 60°C. ) are collectively shown. Although not shown in the figure, the evaluation cell prepared by the dropping method using the electrolyte of Experimental Example 1 did not yield an initial power generation amount. On the other hand, as shown in FIGS. 8 and 9, it was found that Experimental Examples 3 and 4 produced by the dropping method exhibit high initial power densities. Moreover, although the hydrolysis of the organic solvent PC due to water contamination was suppressed by fabricating the cell in nitrogen, in Experimental Example 4, a decrease in output was observed over time in the high-temperature endurance test. This is presumed to be due to the gradual volatilization of PC from the pores of the titanium oxide due to heating and the progress of crystallization of the copper complex, thereby deteriorating the power generation characteristics. On the other hand, in Experimental Example 3 containing two or more copper complexes having different organic ligands, it was found that the high-temperature durability could be greatly improved without deteriorating the initial power generation characteristics. This is because, for example, in Experimental Example 3, since organic ligands with different structures are included, alignment of the copper complex, that is, crystallization is easily hindered structurally, and the copper complex maintains a more amorphous state. It was presumed that this is because the copper complex becomes difficult to crystallize.

[Examination of electrolyte crystallinity]
Crystallinity of an electrolyte containing either Cu(dmp) ₂ TFSI (monovalent, chemical formula (1)) or Cu(tmby) ₂ TFSI (monovalent, chemical formula (3)) as a copper complex was investigated. FIG. 10 is a photograph after adding a solvent to the copper complex, FIG. 10A is only chemical formula (1), FIG. 10B is a mixture of chemical formulas (1) and (3), and FIG. 10C is chemical formula (3) only. is a photograph of Cu(dmp) ₂ TFSI of 0.25 M, LiTFSI of 0.2 M, and NBBI of 1.0 M were mixed with ACN as an organic solvent and dropped onto a glass plate (FIG. 10A). In addition, 0.25 M Cu(tmby) ₂ TFSI, 0.2 M LiTFSI, and 1.0 M NBBI were mixed with ACN as an organic solvent and dropped onto a glass plate (FIG. 10C). Also, a mixture of the above two solutions at a volume ratio of 1:1 was dropped onto a glass plate (FIG. 10B). As a result, in the solution containing only one type of copper complex, a solid (crystal) precipitated rapidly as the organic solvent volatilized. On the other hand, the solution containing two types of copper complexes was able to maintain a gel-like wet state for several hours. That is, it was found that when two kinds of copper complexes having different organic ligands are mixed and used, crystallization can be suppressed and an amorphous state can be maintained.

[Study of electrolytes in Experimental Examples 5 to 8]
Experimental Examples 5 to 8 were evaluation cells prepared in the same manner as in Experimental Example 2 using electrolytes prepared with the composition ratios shown in Table 4. 3-methyl-2-oxazoline (NMO) was used as a high-boiling organic solvent. Using this evaluation cell, the initial power generation characteristics and the solar cell characteristics after durability after being left in a dark place at 60° C. for 1000 hours were measured. Here, the solar cell characteristics were measured under irradiation of 1000 lux from an LED light source. Table 5 summarizes the measurement results. FIG. 11 shows the initial power densities of Experimental Examples 5-8. FIG. 12 shows the initial relative power densities for Examples 5-8. FIG. 13 shows the output retention rate after being left in the dark at 60° C. in Experimental Examples 5-8. For the relative output density, the other measurement results were normalized with Experimental Example 8 set to 100. As shown in Table 5 and FIGS. 11 to 13, in Experimental Examples 5 to 7 containing multiple types of copper complexes, compared to Experimental Example 8, the initial output density and the output retention when left at high temperature at 60 ° C in the dark It was found that the rate could be improved. The reason for this is that, as described above, the crystallization of the copper complex is further suppressed, so the initial output density is improved, and the amorphous state of the copper complex can be further maintained, so that the output retention rate is further improved. presumed to be possible. In particular, the use of a copper complex having two or more organic ligands with different basic structures of the organic ligands was presumed to be more preferable from the viewpoint of structure inhibition.

INDUSTRIAL APPLICABILITY The present disclosure can be suitably used for solar cells and solar cell modules.

Reference Signs List 10 solar cell module 11 light-transmitting substrate 12 light-transmitting conductive film 13 light-receiving surface 14 light-transmitting conductive substrate 15 light-receiving surface 16, 17 collecting electrode 18 groove 20 photoelectrode 21 connecting portion 22 Base layer 23 Light receiving surface 24 Electron transport layer 25 Back surface 26 Electrolyte layer 27 Back surface 29 Separator 30 Counter electrode 32 Sealing material 34 Protective member 40 Solar cell.

Claims (10)

An electrolyte interposed between the photoelectrode and the counter electrode of a solar cell comprising a photoelectrode having a light absorption layer and a counter electrode arranged to face the photoelectrode,
An electrolyte containing two or more kinds of copper complexes having organic ligands with different organic ligand structures, a monovalent copper complex, and no divalent copper complex. The organic ligand is a phenanthroline-based ligand, a pyridylethane-based ligand, a bipyridine-based ligand, a sparteine-based ligand, a bisbenzimidazolylthiomethylpyridine-based ligand, a bisbenzimidazolylthio 2. The electrolyte according to claim 1, comprising said copper complex that is one or more of a methylmethylamine-based ligand, a bisbenzimidazolylpyridine-based ligand, and a bisethylthiomethylpyridine-based ligand. 3. The electrolyte according to claim 1, wherein the copper complex includes any two or more of chemical formulas (1) to (4).

bis(2,9-dimethyl-1,10-phenanthroline) copper complex and bis(4,4′,6,6′-tetramethyl-2,2′-bipyridine) copper complex are included at least. 4. The electrolyte according to any one of 1 to 3. The ratio M1/Ma×100 ( mol%) is in the range of 30 mol% or more and 70 mol% or less. Any one of claims 1 to 5, further comprising one or more cyclic compounds among a heterocyclic compound containing one or more nitrogen atoms and having two or more rings, and a monocyclic heterocyclic compound having two or more nitrogen atoms. The electrolyte described in . a photoelectrode having a light absorption layer;
a counter electrode arranged to face the photoelectrode;
The electrolyte according to any one of claims 1 to 6 interposed between the photoelectrode and the counter electrode,
solar cell with 8. The solar cell of claim 7, wherein the photoelectrode has the light absorbing layer containing one or more of organic dyes, metal complexes and organic metal halide compounds. 9. The solar cell according to claim 7, wherein said photoelectrode comprises an n-type semiconductor layer coated with said light absorbing layer on a light transmissive conductive substrate. A solar cell module comprising a plurality of solar cells according to any one of claims 7 to 9.

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