JP6490035B2 - Electrolyte, solar cell and solar cell module - Google Patents

Description

  The present invention relates to an electrolyte, a solar cell, and a solar cell module.

  Conventionally, a dye-sensitized solar cell using a copper complex as a redox pair has been proposed as a solar cell (see, for example, Patent Document 1). This solar cell is said to have good photoelectric conversion characteristics without corroding the platinum counter electrode by the monovalent or divalent copper complex. In addition, 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 used as the above has been proposed (for example, see Non-Patent Document 1). In this solar cell, the power generation efficiency can be increased.

JP 2006-302849 A

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

  In the above-mentioned Non-Patent Document 1, since the position of the valence band (VBM) of the copper complex is deeper than that of a general electrolyte, the difference from the conductor level (CBM) of the photoelectrode becomes large. Open circuit voltage (Voc) increases. However, when a solar cell is actually constructed, even if the energy level is theoretically deep using a copper complex, reverse electron transfer from the photoelectrode to the electrolyte occurs, resulting in a loss of voltage and a reduction in open circuit voltage. was there.

  This invention is made | formed in view of such a subject, and it aims at providing the electrolyte, solar cell, and solar cell module which can improve a solar cell characteristic more.

  As a result of diligent research to achieve the above-mentioned object, the present inventors have improved the rectifying property and the open circuit voltage and output density more when a specific heterocyclic compound and a copper complex are combined. The present invention has been completed.

That is, the electrolyte disclosed in this specification is
An electrolyte used 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,
Among the heterocyclic compounds having 1 or more nitrogen and having 2 or more rings and monocyclic heterocyclic compounds having 2 or more nitrogen, one or more cyclic compounds and a copper complex are included.

The solar cell disclosed in this specification is:
A photoelectrode having a light absorbing layer;
A counter electrode arranged to face the photoelectrode;
The electrolyte described above interposed between the photoelectrode and the counter electrode;
It is equipped with.

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

  This electrolyte, solar cell, and solar cell module can further improve the solar cell characteristics. The reason why such an effect is obtained is presumed as follows. For example, with the copper complex alone, the photoelectron and the copper complex are in direct contact with each other, causing reverse electron transfer to the electrolyte and the like, resulting in a loss of voltage. However, this heterocyclic compound is complexed to form this reverse electron transfer. It is presumed that the solar cell characteristics can be further improved, for example, the open circuit voltage Voc is increased and the output density is improved. Furthermore, it is considered that the output characteristics of the solar cell are improved due to the effect of improving the electrical characteristics of the electrolyte and lowering the resistance by complexing the heterocyclic compound with the copper complex.

Explanatory drawing of the energy level of an n-type semiconductor layer, an organic pigment | dye, and electrolyte. FIG. 3 is a cross-sectional view illustrating an example of a schematic configuration of a solar cell module 10. FIG. 3 is a cross-sectional view illustrating an example of a schematic configuration of a solar cell 40. Sectional drawing which shows an example of the outline of a structure of the solar cell module 10B. Sectional drawing which shows an example of the outline of a structure of the solar cell 40B. The measurement result of the current-voltage characteristic of Experimental Examples 1 and 3 during 1 sun irradiation and in the dark. AC impedance measurement results of Experimental Examples 1 and 3. The measurement result of the output density at the time of LED light source 1000 lux light irradiation of Experimental example 1,2,4, an open circuit voltage, and a current density. The measurement result of the power density at the time of LED light source 1000 lux light irradiation of Experimental example 5 and 6 and an open circuit voltage and an electric current density. The durability test result of Experimental example 1 and 2 at the time of 1000 lux light irradiation of LED light source which sealed the cell after exposure in air | atmosphere. The durability test result of Experimental example 1 at the time of LED light source 1000 lux light irradiation which sealed the cell in nitrogen atmosphere.

(Electrolytes)
The electrolyte described in this embodiment is used between a photoelectrode and a counter electrode of a solar cell including a photoelectrode having a light absorption layer and a counter electrode arranged so as to face the photoelectrode. is there. This electrolyte contains one or more cyclic compounds among a heterocyclic compound having one or more nitrogen and having two or more rings and a monocyclic heterocyclic compound having two or more nitrogen and a copper complex. FIG. 1 is an explanatory diagram of energy levels of an n-type semiconductor layer, an organic dye, and an electrolyte. As shown in FIG. 1, since the position of the valence band is much deeper than that of a conventional inorganic p-type semiconductor (for example, CuI), the copper complex has a conductor lower end CBM of titanium oxide which is an n-type semiconductor layer and an electrolyte. There is an advantage that the theoretical open-circuit voltage (Voc) determined by the difference from the upper end VBM of the valence electron is higher. However, when the solar cell is composed of only the copper complex, the rectification property is poor and the open circuit voltage Voc and the conversion efficiency Eff are lowered. Here, these solar cell characteristics are improved by compounding a cyclic compound and a copper complex.

  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 is preferably basic. Therefore, in these structures, since basicity is high, an imidazole structure is preferable. The cyclic compound may be a liquid or a solid in a use temperature range (for example, near room temperature to 10 ° C. to 40 ° C.). When the cyclic compound is a liquid, the electrolyte may be an electrolytic solution, and when the cyclic compound is a solid, the electrolyte may be a solid electrolyte. The cyclic compound includes one or more ring structures, but may have a structure in which two or more ring structures are joined by a carbon chain, or a condensed ring structure, but preferably has a condensed ring structure. This cyclic compound contains 1 or more of nitrogen, but preferably contains 2 or more. In addition, the cyclic compound includes one or more ring structures, but preferably includes two or more. The heterocyclic ring may contain oxygen, sulfur, etc. in addition to nitrogen. Further, the cyclic compound may have a substituent or a hetero atom in its structure. For example, you may have a hydrogen group, the alkyl group which substituted the hydrogen group, etc. The alkyl group is preferably in the range of 1 to 6 carbon atoms.

  Specifically, the cyclic compound may be any one or more of chemical formulas (1) to (8). In this formula, R may be hydrogen (H) and an alkyl group having 1 to 6 carbon atoms. The alkyl group may be linear or may have a branched chain. Chemical formulas (1) to (5) are heterocyclic compounds containing one or more nitrogen atoms and having two or more rings. Chemical formula (1) is benzimidazole and its derivatives, and examples thereof include N-methylbenzimidazole and N-butylbenzimidazole. Chemical formula (2) is a pyrimidine base, for example, 1,3,4,6,7,8-hexahydro-2H-pyrimido [1,2-a] pyrimidine, 1,3,4,6,7, And 8-hexahydro-1-methyl-2H-pyrimido [1,2a] pyrimidine. Chemical formula (3) is quinoline and may be a derivative thereof. Chemical formula (4) is benzoxazole and may be a derivative thereof. Chemical formula (5) is benzothiazole and may be a derivative thereof. Chemical formulas (6) to (8) are monocyclic heterocyclic compounds having two or more nitrogen atoms. Chemical formula (6) is imidazole and its derivatives. Chemical formula (7) is pyrazole and its derivatives. Chemical formula (8) is imidazoline and its derivatives.

The copper complex preferably has, for example, an organic ligand and copper changes in valence. This copper complex is good also as what has any one or more structures among Chemical formula (9)-(15). As an organic ligand, it is good also as what has a heterocyclic structure which has 1 or 2 or more rings, for example. Examples of the organic ligand include 2,9-dimethyl-1,10-phenanthroline (dmp, chemical formula (9)), 1,10-phenanthroline (phen, chemical formula (10)), [(-)- Sparteine-N, N ′] (SP, chemical formula (11)), 2,6-bis (benzimidazol-2′-ylthiomethyl) pyridine (bbtmp, chemical formula (12)), N, N-bis (benzimidazole— 2′-ylthiomethyl) methylamine (bbtma, chemical formula (13)), 2,6-bis (benzimidazol-2′-yl) pyridine (bzmpy, chemical formula (14)), 2,6-bis (ethylthiomethyl) Examples thereof include pyridine (betmp, chemical formula (15)). The copper complex may have one or more other ligands, for example, a monodentate ligand (monovalent anion ligand). When there are a plurality of these ligands, each may be the same ligand or different ligands. Among these, it is more preferable that these ligands are all the same. This ligand may be one or more selected from, for example, -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 be composed of a cation having an organic ligand and containing copper and an anion. Examples of the anion include trifluoromethylsulfonic acid (CF ₃ SO ₃ ), bis (trifluoromethylsulfonyl) imide (TFSI), hexafluorophosphoric acid (PF ₆ ), and the like.

Specific examples of such a copper complex include, for example, 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), [} (-) - sparteine -N, N '] (Mareo nitrile dithio Lato -S, S') of copper ([Cu (SP (Mmt)]), 2,6-bis (benzimidazol-2'-ylthiomethyl) pyridine nitrate ([Cu (bbtmp) (NO 3)] NO 3) , and the like.

This electrolyte may contain a solvent and an additive. As the solvent, nitrile solvents such as acetonitrile (AcCN) and valeronitrile (VaCN), ether solvents such as diethyl ether, tetrahydrofuran, ethylene glycol dialkyl ether, polyethylene glycol dialkyl ether, methanol, ethanol, ethylene glycol, propylene glycol, Examples include alcohol solvents such as polyethylene glycol. These can be used alone or in combination. As the additive, for example, as to increase the electron injection efficiency to improve the short-circuit current density Jsc of lowering the conduction band of the photoelectrode material (CBM) from the dye to the TiO _2, such as TiO _2, LiTFSI, LiI, etc. Is mentioned. These can be used alone or in combination.

(Solar cell)
The solar cell described in this embodiment includes a photoelectrode having a light absorption layer, a counter electrode disposed so as to face the photoelectrode, and any one of the above-described electrolytes interposed between the photoelectrode and the counter electrode. It is provided. The photoelectrode may have an n-type semiconductor layer (electron transport layer) covered with a light absorption layer on a light-transmitting conductive substrate. FIG. 2 is a cross-sectional view illustrating an example of a schematic configuration of the solar cell module 10. As shown in FIG. 2, the solar cell module 10 according to this embodiment has a configuration in which a plurality of solar cells 40 (hereinafter also referred to as cells) are sequentially arranged 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 between the cells, and a flat protective member 34 is formed on the surface of the sealing material 32 on the side opposite to the light-transmitting conductive substrate 14. Has been. The solar cell 40 according to this embodiment includes a photoelectrode 20 including an electron transport layer 24 including a light absorption layer and an n-type semiconductor layer on a light-transmitting conductive substrate 14 via a base layer 22, and a photoelectrode 20 Counter electrode 30 disposed so as to face each other, an electrolyte layer 26 interposed between the photoelectrode 20 and the counter electrode 30, and a separator 29. The photoelectrode 20 includes a light-transmitting conductive substrate 14 on which a light-transmitting conductive film 12 that transmits light is formed on the surface of a light-transmitting substrate 11 that transmits light, and an electron transport layer formed on the light-transmitting conductive film 12. 24. The electron transport layer 24 is a layer that is disposed on the light-transmitting conductive film 12 formed separately on the surface opposite to the light-receiving surface 13 of the light-transmitting substrate 11 and emits electrons upon receiving light. In the solar cell 40 of the present invention, the electron transport layer 24 is provided with a light absorbing material that absorbs light.

The light transmissive conductive substrate 14 is composed of the light transmissive substrate 11 and the light transmissive conductive film 12, and has light transmissive and conductive properties. 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 transmissive electrode in which tin oxide or indium oxide is doped with cations or anions having different valences, or a metal electrode having a structure capable of transmitting light, such as a mesh shape or a stripe shape, is provided on a substrate such as a glass substrate. Can also be used. Current 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, and electric power generated by the solar cell 40 via the current collecting electrodes 16 and 17 is used. can do.

  Examples of the light transmitting substrate 11 include transparent glass, a transparent plastic plate, a transparent plastic film, and an inorganic transparent crystal, and among these, transparent glass is preferable. The light transmitting substrate 11 may be a transparent glass substrate, a glass substrate whose surface is appropriately roughened to prevent light reflection, or a light-transmitting substrate such as a frosted glass-like translucent glass substrate. The light transmissive conductive film 12 can be formed, for example, by depositing tin oxide on the light transmissive substrate 11. In particular, if a metal oxide such as tin oxide (FTO) doped with fluorine is used, a suitable light-transmitting conductive film 12 can be formed. The light transmissive conductive film 12 has grooves 18 formed at predetermined intervals, and a plurality of regions of the light transmissive conductive film 12 are separately formed 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. For example, a light-transmitting and conductive material is preferable. Examples include n-type semiconductors such as titanium, zinc oxide, and tin oxide. Among these, titanium oxide is more preferable. This is because titanium oxide suppresses and prevents leakage current and easily allows electrons to flow from the electron transport layer 24 to the light-transmitting conductive substrate 14. The underlayer 22 is preferably made of a denser material than the electron transport layer 24. Note that even if the base layer 22 is not formed, the base layer 22 may be omitted because it functions sufficiently as the solar cell 40.

The electron transport layer 24 is formed of a light absorbing material and a porous n-type semiconductor layer containing the light absorbing material. As the n-type semiconductor, a metal oxide semiconductor or a metal sulfide semiconductor is suitable. For example, titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), cadmium sulfide (CdS), sulfide It is preferable that it is at least 1 or more among zinc (ZnS), and among these, porous titanium oxide is more preferable. By thinning these semiconductor materials into a microcrystalline or polycrystalline state, a good porous n-type semiconductor layer can be formed. In particular, the porous titanium oxide layer is suitable as the n-type semiconductor layer of the photoelectrode 20. Further, as titanium oxide, anatase TiO ₂ is preferable to rutile 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 include one or more light absorbing materials among organic dyes, metal complexes, and organic metal halide compounds. This light absorbing material may be an organic dye. Examples of organic dyes include BODIPY dyes (such as BODIPY-FL), indoline dyes (such as D131, D149, D205, and D358), carbazole dyes (such as MK2), and coumarin dyes (C343, NKX-2587, NKX-). 2677 or the like) or squarylium dye (SQ2 or the like). The organic dye may have an aromatic amine as a donor and a cyanocarboxylic acid anchor group via a π-conjugated molecule. Examples of such a dye include 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 (16)) and the like, and it is preferable to use this dye. Further, the light absorbing material may be a metal complex. Examples of the metal contained in the metal complex include Zn, Cu, Fe, Pd, Pt, Ni, Co, Ru, and the like. Among these, Ru complexes (Ruthenizer 470 (Ru470), N719, Z907, etc.), metal porphyrin dyes (PtTPTBP, PdTPTBP, DTBC, etc.), metal phthalocyanine dyes (CuPc, ZnPc, etc.) and metal naphthalocyanine dyes (CuNc, ZnNc) Etc.) may be one or more. These light absorbing materials may be used alone or in combination. Of these, Ru complex compounds (Z907, N719), Zn porphyrin compounds (DTBC), carbazole dyes (MK2), indoline double rhodanine compounds (D149 and D358) and the like are preferable. Examples of the organic metal halide compound as the light absorbing material include perovskite crystals such as CH ₃ NH ₃ PbI ₃ . The structural formulas of the exemplified compounds are shown in the following chemical formula. Although not shown in the following chemical formula, PdTPTBP is obtained by changing Pt of PtTPTBP to Pd, ZnPc is obtained by changing Cu of CuPc to Zn, and ZnNc is obtained by changing Cu of CuNc to Zn.

  The electrolyte layer 26 is formed adjacent to the photoelectrode 20. The electrolyte layer 26 includes any of the electrolytes described above. When the electrolyte layer 26 is solid, the structure of the solar cell module 10 can be adopted.

  The separator 29 is formed in 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 the separator 29 is in contact with the groove 18 on the light transmitting conductive substrate 14. Thereby, the direct contact with the photoelectrode 20 and the counter electrode 30 is avoided. The separator 29 is made of an insulating material, and may be formed of, for example, glass beads, silicon dioxide (silica), rutile titanium oxide, or the like. The separator 29 is preferably an insulator in which silica particles are sintered. Silica particles are preferable for the separator because they have a low refractive index, low light scattering, and good transparency. The separator 29 preferably has an average particle size of 5 to 200 nm from the viewpoint of ensuring good transparency. The separator may be air or an air layer.

  The counter electrode 30 is formed in an L-shaped cross section so as to contact the outer surface of the separator 29 and the back surface 27 of the electrolyte layer 26. One end of the counter electrode 30 is connected to the back surface 27 of the electrolyte layer 26, and the other end is connected to the adjacent light transmitting conductive film 12 via the connection portion 21. The surface of the counter electrode 30 that is in contact with the back surface 27 faces the photoelectrode 20 at a predetermined interval. 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 these, carbon is preferable.

  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 protection member 34 is a member that protects the solar cell 40, and can be, for example, a moisture-proof film or protective glass.

  When the solar cell 40 is irradiated with light from the light receiving surface 13 side of the transparent substrate 11, the light reaches the electron transport layer 24 through the light receiving surface 15 of the transparent conductive film 12 and the light receiving surface 23 of the base layer 22. The light absorbing material absorbs light and generates electrons. The generated electrons move from the photoelectrode 20 to the adjacent counter electrode 30 via the transparent conductive film 12 and the connection portion 21. In the solar cell 40, an electromotive force is generated by the movement of the electrons, and the power generation action of the battery is obtained. In this solar cell module 10, in the electrolyte layer 26, one or more cyclic compounds of a heterocyclic compound having one or more nitrogen and having two or more rings and a monocyclic heterocyclic compound having two or more nitrogen and copper, Since the complex is contained, the solar cell characteristics can be further improved, for example, the open circuit voltage Voc and the conversion efficiency Eff are improved.

  This 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 as a manufacturing method. In the substrate manufacturing process, the transparent conductive film 12 is formed on the transparent substrate 11 while forming the grooves 18 between the plurality of transparent conductive films 12. In the electron transport layer forming step, an n-type semiconductor layer is formed on the transparent conductive film 12 via the base layer 22, a light absorbing material is formed on the n-type semiconductor layer, and the electron transport layer 24 is formed. Here, porous titanium oxide is used as the n-type semiconductor layer. Next, in the electrolyte layer forming step, the above-described electrolyte layer may be supplied to the back surface 25 of the electron transport layer 24 and then dried to form the electrolyte layer 26. Here, a material containing the above-described cyclic compound and a copper complex is used as the electrolyte layer. Subsequently, in the separator forming step, a separator 29 is formed on the side surface of the photoelectrode 20 in alignment with the groove 18. In the counter electrode forming step, the counter electrode 30 is formed 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, the sealing material 32 is formed so as to cover each cell, and the protective member 34 is formed on the sealing material 32. In this way, the solar cell 40 and the solar cell module 10 with improved power generation characteristics can be produced.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the solar cell module 10 is used. However, the solar cell module 10 is not particularly limited thereto, and may be a solar cell 40 illustrated in FIG. FIG. 3 is a cross-sectional view illustrating an example of a schematic configuration of the solar cell 40. 3, the same components as those described in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted. As shown in FIG. 3, when the solar cell 40 is used as a single unit, the counter electrode 30 may be formed in a flat plate shape instead of an L shape. Further, the separator 29 may be omitted. The counter electrode 30 may be, for example, one having the same configuration as that of the light-transmitting conductive substrate 14, or may be one in which platinum is attached to the transparent conductive film 12 or a metal thin film such as platinum.

  In the embodiment described above, the case where the electrolyte layer 26 is solid has been described. However, the present invention is not particularly limited thereto, and may be an electrolyte layer 26B containing an electrolytic solution as shown in FIG. FIG. 4 is a cross-sectional view illustrating an example of a schematic configuration of the solar cell module 10B. The solar cell module 10B includes a plurality of solar cells 40B having an electrolyte layer 26B. In FIG. 4, the base layer 22 and the separator 29 are omitted. The electrolyte layer 26B contains a liquid or gel electrolyte, and is preferably a layer containing an electrolyte solution in a porous body, for example. The porous body is not particularly limited as long as it is capable of holding an electrolytic solution and does not have electron conductivity. For example, a porous body formed of rutile titanium oxide particles is used as the porous body. May be used. The porous body has a portion that covers the back surface 25 of the electron transport layer 24 and a jaw-shaped edge portion that is in close contact with the side surface adjacent to the back surface 25 of the electron transport layer 24, and is formed in an L-shaped cross section. Yes. This bowl-shaped edge portion is inserted into the groove 18 having a depth at which the surface of the transparent substrate 11 is exposed, and is in direct contact with the transparent substrate 11. In the electrolyte layer 26B, the porous body may be omitted, and the electrolytic solution may be accommodated in the space between the photoelectrode 20 and the counter electrode 30B.

The electrolytic solution contained in the electrolyte layer 26B includes one or more cyclic compounds among the above-described heterocyclic compounds having one or more nitrogen and having two or more rings and monocyclic heterocyclic compounds having two or more nitrogens, and What is necessary is just to include a copper complex. The concentration of the cyclic compound contained in the electrolytic solution is preferably in the range of 0.01 mol / L or more and 5.0 mol / L or less, for example. The concentration of the copper complex contained in the electrolytic solution is preferably in the range of 0.01 mol / L to 5.0 mol / L, for example. The solvent mentioned above can be used for the solvent contained in electrolyte solution. Examples of the additive contained in the electrolytic solution include LiTFSI, guanidine thiocyanate, and LiI. By adding such an additive, the durability of the solar cell is further improved. Furthermore, the conduction band lower end (CBM) of the photoelectrode material such as TiO ₂ can be lowered to improve the efficiency of electron injection from the dye to TiO ₂ , and the short-circuit current density Jsc can be increased. The concentration of the additive in the electrolytic solution is preferably in the range of 0.01 mol / L to 2.0 mol / L. The counter electrode 30B is formed in an L-shaped cross section having a bowl-shaped edge portion so as to contact the back surface 27 of the electrolyte layer 26B and the bowl-shaped edge portion. The counter electrode 30 </ b> B is connected to the back surface of the electrolyte layer 26, and the flange-shaped edge portion is connected to the adjacent transparent conductive film 12 via the connection portion 21. The surface of the counter electrode 30B that is in contact with the back surface 27 of the electrolyte layer 26B is opposed to the photoelectrode 20 at a predetermined interval. The counter electrode 30B is not particularly limited as long as it has conductivity and bondability with the electrolyte layer 26B, and examples thereof include Pt, Au, and carbon. Among these, carbon is preferable. The counter electrode 30B may be, for example, a porous carbon electrode formed using carbon black particles, graphite particles, and conductive oxide particles such as anatase-type titanium oxide particles as constituent materials. The counter electrode 30B may carry, for example, catalyst fine particles such as Pt fine particles in a dispersed manner from the viewpoint of more promptly increasing the speed of the electrode reaction. Also in the solar cell module 10B formed in this way, as in the above-described embodiment, the electrolyte layer 26B includes the cyclic compound and the copper complex, and thus the open-circuit voltage Voc and the conversion efficiency Eff are improved. The characteristics can be further improved.

  In the above-described embodiment, the solar cell module 10B is used. FIG. 5 is a cross-sectional view illustrating an example of a schematic configuration of the solar battery 40B. In FIG. 5, the same components as those described in FIGS. As shown in FIG. 5, in the single solar cell 40B, the electrolyte layer 26B and the counter electrode 30B may be formed in a flat plate shape with the cross-section not being L-shaped but omitting the bowl-shaped edge portion. Further, the counter electrode 30B may be, for example, one having the same configuration as that of the light-transmitting conductive substrate 14, or may be one in which platinum is attached to the transparent conductive film 12, or a metal thin film such as platinum. Furthermore, the electrolyte layer 26 </ b> B may omit the porous body and contain the electrolyte in the space between the photoelectrode 20 and the counter electrode 30. Even in this case, since the electrolyte layer 26 includes the cyclic compound and the copper complex, the solar cell characteristics can be further improved, such as the open circuit voltage Voc and the conversion efficiency Eff are improved.

  Below, the example which produced the electrolyte and solar cell of this invention concretely is demonstrated as an experiment example. In the following examples, Experimental Examples 1, 5, and 6 correspond to Examples of the present invention, Experimental Examples 3 and 4 correspond to Comparative Examples, and Experimental Example 2 corresponds to a Reference Example.

[Electrolyte of Experimental Example 1]
A mixed solution of 80% by volume of acetonitrile (AcCN) and 20% by volume of valeronitrile (VaCN) was used as a solvent. To this mixed solution, 0.2 M copper (I) bis (2,9-dimethyl-1,10-phenanthroline) bis (trifluoromethylsulfonyl) imide ((Cu (dmp) ₂ TFSI) as a copper complex, copper (II) Bis (2,9-dimethyl-1,10-phenanthroline) bis [bis (trifluoromethylsulfonyl) imide] ((Cu (dmp) ₂ (TFSI) ₂ ) 0.05M, LiTFSI 0.1M Each of N-methylbenzimidazole (NMBI) as a cyclic compound was added to a concentration of 0.5 M. The obtained electrolyte (electrolytic solution) was used as the electrolyte of Experimental Example 1.

[Electrolyte of Experimental Example 2]
The electrolyte obtained in Experimental Example 2 was obtained in the same manner as in Experimental Example 1 except that 4-tert-butylpyridine (TBP) was added to 0.5 M instead of NMBI.

[Electrolyte of Experimental Example 3]
The electrolyte obtained in Experimental Example 3 was obtained in the same manner as in Experimental Example 1 without adding the cyclic compound NMBI.

[Production of dye-sensitized solar cells of Experimental Examples 1 to 3]
A dense TiO ₂ film (10 nm) is formed on an electrode of a transparent conductive film (SnO ₂ ) by an atomic layer deposition method, titanium oxide particles (particle diameter: several tens of nm to 400 nm) are printed, and sintered at 500 ° C. Then, it was immersed in a titanium compound and further heated at 500 ° C. to prepare a TiO ₂ electrode (photoelectrode). An indoline double rhodanine red organic dye (Dye 1; D358) is adsorbed on the photoelectrode, filled with the prepared electrolyte, and after removing the solvent, the platinum counter electrode is placed facing the photoelectrode, A dye-sensitized solar cell fixed with a seal was prepared.

[Solar Cell of Experimental Example 4]
An indoor commercial solar cell in which the light absorption layer was amorphous Si (a-Si) was used as Experimental Example 4.

[Preparation of dye-sensitized solar cells of Experimental Examples 5 and 6]
Experimental Example 1 except that the organic dye is a red organic dye represented by the chemical formula (16) (Dye 2: having an aromatic amine as a donor and having a cyanocarboxylic acid anchor group via a π-conjugated molecule) A solar cell of Experimental Example 5 was made in the same manner. A solar cell of Experimental Example 6 was prepared in the same manner as Experimental Example 5 except that the cyclic compound was N-butylbenzimidazole (NBBI).

(Evaluation of solar cells)
The current-voltage characteristics of the solar cell at 1 sun were evaluated with 1000 lux LED light source irradiation and pseudo sunlight (Xe + Ha) lamp. Moreover, the current-voltage characteristic in the dark without irradiating light was also evaluated. The internal resistance was evaluated based on the AC impedance when the Xe lamp was irradiated with 1 sun light. In addition, for Experimental Examples 1 and 2, a cell durability test was performed in which an output change was observed in an operating state in which an external load resistor was connected to a solar cell under irradiation of a light source of 1000 lux. In the endurance test, evaluation was performed using the solar cells of Experimental Examples 1 and 2 that were sealed after the cells were exposed to the atmosphere and the solar cell of Experimental Example 1 that sealed the cells in a nitrogen atmosphere.

(Results and discussion)
Table 1 summarizes the types of light absorbing layers, types of cyclic compounds, open circuit voltage Voc (V), short circuit current density Jsc (mA / m ² ), and output density (mW / m ² ) of Experimental Examples 1 to 6. It was. FIG. 6 shows the current-voltage characteristic measurement results of Experimental Examples 1 and 3 during 1 sun irradiation and in the dark. As shown in FIG. 6, in the dye-sensitized solar cell of Experimental Example 3 in which no cyclic compound was added, the rectifying property was poor in the dark when irradiated with 1 sun, and the open-circuit voltage and the conversion efficiency were low. On the other hand, in Experimental Example 1 in which the cyclic compound was added to the copper complex, the rectification was good, and the open circuit voltage and the conversion efficiency were high. FIG. 7 shows AC impedance measurement results of Experimental Examples 1 and 3. As shown in FIG. 7, in Experimental Example 3 in which no cyclic compound was added, the internal resistance was 500Ω, whereas in Experimental Example 1 in which a cyclic compound was added, the internal resistance was 60Ω, and the internal resistance was significantly reduced. did. From this result, the output improvement of the solar cell was expected. FIG. 8 shows the measurement results of the output density, open circuit voltage, and current density when the LED light source 1000 lux light was irradiated in Experimental Examples 1, 2, and 4 in consideration of room light. As shown in FIG. 8 and Table 1, it was found that Experimental Example 1 using NMBI improves the output density and open circuit voltage compared to Experimental Example 2 using TBP. Further, it was found that under low light irradiation, the output density was twice or more that of a conventional amorphous silicon solar cell. FIG. 9 shows the measurement results of the output density, the open circuit voltage, and the current density when the LED light source of Example 5 and 6 is irradiated with 1000 lux light. As shown in FIG. 9 and Table 1, in Experimental Example 6 using NBBI, the short-circuit current density Jsc was comparable to that in Experimental Example 5 using NMBI, but the open-circuit voltage Voc was further improved. , Power density improved. FIG. 10 shows the endurance test results when the LED light source of Experimental Examples 1 and 2 was irradiated with 1000 lux light after the cell was sealed after being exposed to the atmosphere. FIG. 11 shows a durability test result when the LED light source of Experimental Example 1 was irradiated with 1000 lux light in which the cell was sealed in a nitrogen atmosphere. As shown in FIGS. 10 and 11, the solar cell of Experimental Example 1 was found to have a feature that the output density maintenance rate was higher than that of Experimental Example 2.

  From the above experimental results, it was found that when NMBI or NBBI, which is a basic organic compound containing nitrogen, is combined with a copper complex, particularly a copper complex in which copper has a valence change, the solar cell characteristics are further improved. As the basic organic compound, for example, it is presumed that the same effects as those of the chemical formulas (2) to (8) can be obtained.

  The present invention can be suitably used for solar cells and solar cell modules.

  10, 10B Solar cell module, 11 Transparent substrate, 12 Transparent conductive film, 13 Light receiving surface, 14 Light transmitting conductive substrate, 15 Light receiving surface, 16, 17 Current collecting electrode, 18 Groove, 20 Photo electrode, 21 Connection portion, 22 Underlayer, 23 Light-receiving surface, 24 Electron transport layer, 25 Back surface, 26, 26B Electrolyte layer, 27 Back surface, 29 Separator, 30, 30B Counter electrode, 32 Seal material, 34 Protection member, 40, 40B Solar cell.

Claims (9)

An electrolyte used 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 comprising a cyclic compound, which is a heterocyclic compound having one or more nitrogen atoms and having two or more rings, and a copper complex.   The electrolyte according to claim 1, wherein the cyclic compound has one or more of an imidazole structure, a pyridine structure, a pyrimidine structure, an oxazole structure, and a thiazole structure. The electrolyte according to claim 1 or 2, wherein the cyclic compound is any one or more of chemical formulas (1) to ( 5 ).
  The electrolyte according to any one of claims 1 to 3, wherein the copper complex has an organic ligand and copper changes in valence. The electrolyte according to any one of claims 1 to 4, wherein the copper complex has any one or more structures of chemical formulas ( 6 ) to ( 12 ).
A photoelectrode having a light absorbing layer;
A counter electrode arranged to face the photoelectrode;
The electrolyte according to any one of claims 1 to 5, which is interposed between the photoelectrode and the counter electrode,
Solar cell with   The solar cell according to claim 6, wherein the photoelectrode includes one or more of the light absorption layers of an organic dye, a metal complex, and an organic metal halide compound.   The solar cell according to claim 6 or 7, wherein the photoelectrode includes an n-type semiconductor layer covered with the light absorption layer on a light-transmitting conductive substrate.   The solar cell module provided with two or more solar cells of any one of Claims 6-8.