JP6921582B2 - Solar cell - Google Patents

Description

The present invention relates to a solar cell having a large open circuit voltage and excellent photoelectric conversion efficiency.

Conventionally, a solar cell having a laminate (photoelectric conversion layer) in which an N-type semiconductor layer and a P-type semiconductor layer are arranged between facing electrodes has been developed. In such a solar cell, an optical carrier (electron-hole pair) is generated by photoexcitation, and an electric field is generated by moving electrons through an N-type semiconductor and holes moving through a P-type semiconductor.

Most of the solar cells currently in practical use are inorganic solar cells manufactured by using an inorganic semiconductor such as silicon. However, inorganic solar cells are expensive to manufacture, difficult to increase in size, and have a limited range of use. Therefore, organic solar cells manufactured using organic semiconductors instead of inorganic semiconductors and organic semiconductors are used. Organic-inorganic solar cells combined with inorganic semiconductors are attracting attention.

Among them, a perovskite solar cell having a photoelectric conversion layer containing an organic-inorganic perovskite compound can be expected to have high photoelectric conversion efficiency and can be manufactured by a printing method, so that the manufacturing cost can be significantly reduced (for example, Patent Documents). 1. Non-patent document 1). However, even with such a perovskite solar cell, the photoelectric conversion efficiency is still insufficient, and further improvement in the photoelectric conversion efficiency is desired.

Japanese Unexamined Patent Publication No. 2014-72227

M. M. Lee, et al, Science, 2012, 338, 643

An object of the present invention is to provide a solar cell having a large open circuit voltage and excellent photoelectric conversion efficiency.

The present invention is a solar cell having a cathode, an electron transport layer, a photoelectric conversion layer and an anode in this order, and the photoelectric conversion layer is of the general formula RMX ₃ (where R is an organic molecule and M is a metal. The atom and X contain an organic-inorganic perovskite compound represented by a halogen atom or a chalcogen atom), and further have a layer containing an alkali metal arranged between the electron transport layer and the photoelectric conversion layer. It is a solar cell.
Hereinafter, the present invention will be described in detail.

The present inventors examined a solar cell having a cathode, an electron transport layer, a photoelectric conversion layer, and an anode in this order.
The present inventors use a specific organic-inorganic perovskite compound for the photoelectric conversion layer of such a solar cell, and further provide a layer containing an alkali metal between the electron transport layer and the photoelectric conversion layer to provide the solar cell. We have found that it is possible to obtain excellent photoelectric conversion efficiency by increasing the open circuit voltage of the above, and have completed the present invention.
The photoelectric conversion efficiency is obtained by, for example, the product of the open circuit voltage, the short circuit current, and the fill factor (FF). The larger the open circuit voltage, the higher the photoelectric conversion efficiency.

The solar cell of the present invention has a cathode, an electron transport layer, a photoelectric conversion layer, and an anode in this order.
In the present specification, the layer means not only a layer having a clear boundary but also a layer having a concentration gradient in which the contained elements gradually change. The elemental analysis of the layer can be performed, for example, by performing FE-TEM / EDS line analysis measurement of the cross section of the solar cell and confirming the elemental distribution of the specific element. Further, in the present specification, the layer means not only a flat thin film layer but also a layer capable of forming a complicated and intricate structure together with other layers.

The material of the cathode is not particularly limited, and conventionally known materials can be used.
As the cathode material, for example, FTO (fluorine-doped tin oxide), sodium, sodium-potassium alloy, lithium, magnesium, aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / Al ₂ O ₃ mixture, Al / LiF mixture, gold, silver, titanium, molybdenum, tantalum, tungsten, carbon, nickel, chromium and the like can be mentioned. These materials may be used alone or in combination of two or more.

The material of the electron transport layer is not particularly limited, and examples thereof include n-type metal oxides, N-type conductive polymers, N-type low-molecular-weight organic semiconductors, and surfactants. Specific examples thereof include titanium oxide. , Tin oxide, cyano group-containing polyphenylene vinylene, boron-containing polymer, vasocuproin, vasofenantrene, hydroxyquinolinatoaluminum, oxadiazole compound, benzoimidazole compound, naphthalenetetracarboxylic acid compound, perylene derivative, phosphine oxide compound, phosphine sulfide compound, Fluorogroup-containing phthalocyanines and the like can be mentioned. Of these, titanium oxide and tin oxide are preferable because the wettability of the layer containing an alkali metal, which will be described later, is improved.

The electron transport layer may be composed of only a thin-film electron transport layer, but preferably includes a porous electron transport layer. In particular, when the photoelectric conversion layer is a composite film in which an organic semiconductor or an inorganic semiconductor moiety and an organic-inorganic perovskite compound moiety are composited, a more complicated composite film (more complicated structure) can be obtained, and photoelectric conversion can be obtained. Since the efficiency is high, it is preferable that the composite film is formed on the porous electron transport layer.

The preferred lower limit of the thickness of the electron transport layer is 1 nm, and the preferred upper limit is 2000 nm. If the thickness is 1 nm or more, holes can be sufficiently blocked. When the thickness is 2000 nm or less, it is unlikely to become a resistance during electron transport, and the photoelectric conversion efficiency becomes high. The more preferable lower limit of the thickness of the electron transport layer is 3 nm, the more preferable upper limit is 1000 nm, the further preferable lower limit is 5 nm, and the further preferable upper limit is 500 nm.

The photoelectric conversion layer contains an organic-inorganic perovskite compound represented by the general formula R-MX ₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom). A solar cell in which the photoelectric conversion layer contains the organic-inorganic perovskite compound is also called an organic-inorganic hybrid solar cell.
By using the organic-inorganic perovskite compound in the photoelectric conversion layer, the photoelectric conversion efficiency of the solar cell can be improved.

The above R is an organic molecule, and is preferably represented by C _l N _m H _n (all l, m, and n are positive integers).
Specifically, the R is, for example, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropyl. Amine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, ethylbutylamine, formamidine, acetamidine, guanidine, imidazole, Examples thereof include azole, pyrrole, aziridine, azirin, azetidine, azeto, azole, imidazoline, carbazole, ions thereof (for example, methylammonium (CH ₃ NH ₃ ), etc.), phenethylammonium and the like. Among them, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, formamidine, acetamidine and their ions and phenethylamidine are preferable, and methylamine, ethylamine, propylamine, formamidine and these ions are more preferable. preferable.

The above M is a metal atom, for example, lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, Europium and the like can be mentioned. These metal atoms may be used alone or in combination of two or more. Of these, lead and tin are preferable because the bandgap is appropriate and the crystallinity is good.

The X is a halogen atom or a chalcogen atom, and examples thereof include chlorine, bromine, iodine, oxygen, sulfur, and selenium. When the X is a halogen atom or a chalcogen atom, the absorption wavelength of the organic-inorganic perovskite compound is widened, and high photoelectric conversion efficiency can be achieved. These halogen atoms or chalcogen atoms may be used alone or in combination of two or more. Among them, a halogen atom is preferable because the inclusion of halogen in the structure makes the organic-inorganic perovskite compound soluble in an organic solvent and can be applied to an inexpensive printing method or the like. Further, iodine is more preferable because the energy band gap of the organic-inorganic perovskite compound is narrowed.

The organic-inorganic perovskite compound preferably has a cubic structure in which a metal atom M is arranged at the body center, an organic molecule R is arranged at each apex, and a halogen atom or a chalcogen atom X is arranged at the face center.
FIG. 1 shows an example of the crystal structure of an organic-inorganic perovskite compound, which is a cubic structure in which a metal atom M is arranged at the body center, an organic molecule R is arranged at each apex, and a halogen atom or a chalcogen atom X is arranged at the face center. It is a schematic diagram. Although the details are not clear, the orientation of the octahedron in the crystal lattice can be easily changed by having the above structure, so that the mobility of electrons in the organic-inorganic perovskite compound is high, and the photoelectric of the solar cell is high. It is estimated that the conversion efficiency will improve.

The organic-inorganic perovskite compound is preferably a crystalline semiconductor. The crystalline semiconductor means a semiconductor capable of measuring the X-ray scattering intensity distribution and detecting the scattering peak. Since the organic-inorganic perovskite compound is a crystalline semiconductor, the mobility of electrons in the organic-inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved.

It is also possible to evaluate the degree of crystallization as an index of crystallization. The crystallinity is determined by separating the scattering peak derived from the crystalline substance and the halo derived from the amorphous part detected by the X-ray scattering intensity distribution measurement by fitting, and obtaining the intensity integration of each to obtain the crystal part of the whole. It can be obtained by calculating the ratio of.
The preferable lower limit of the crystallinity of the organic-inorganic perovskite compound is 30%. When the degree of crystallization is 30% or more, the mobility of electrons in the organic-inorganic perovskite compound becomes high, and the photoelectric conversion efficiency of the solar cell is improved. A more preferable lower limit of crystallinity is 50%, and a more preferable lower limit is 70%.
Further, as a method for increasing the crystallinity of the organic-inorganic perovskite compound, for example, thermal annealing, irradiation with strong light such as a laser, plasma irradiation and the like can be mentioned.

When the photoelectric conversion layer contains the organic-inorganic perovskite compound, the photoelectric conversion layer may further contain an organic semiconductor or an inorganic semiconductor in addition to the organic-inorganic perovskite compound as long as the effect of the present invention is not impaired. It may be included. The organic semiconductor or the inorganic semiconductor referred to here may play a role as a hole transport layer or an electron transport layer.
Examples of the organic semiconductor include compounds having a thiophene skeleton such as poly (3-alkylthiophene). Further, for example, a conductive polymer having a polyparaphenylene vinylene skeleton, a polyvinylcarbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton and the like can be mentioned. Further, for example, a compound having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, a benzoporphyrin skeleton, a spirobifluorene skeleton, and carbon-containing materials such as carbon nanotubes, graphene, and fullerene which may be surface-modified. Can also be mentioned.

Examples of the inorganic semiconductor include titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, CuSCN, Cu ₂ O, CuI, MoO ₃ , V ₂ O ₅ , WO ₃ , and so on. Examples thereof include MoS _{2 , MoSe 2} , Cu ₂ S and the like.

When the organic-inorganic perovskite compound and the organic semiconductor or the inorganic semiconductor are contained, the photoelectric conversion layer is a laminate in which a thin-film organic semiconductor or inorganic semiconductor moiety and a thin-film organic-inorganic perovskite compound moiety are laminated. It may be a composite film in which an organic semiconductor or an inorganic semiconductor moiety and an organic-inorganic perovskite compound moiety are composited. A laminated body is preferable in terms of simple manufacturing method, and a composite film is preferable in that the charge separation efficiency in the organic semiconductor or the inorganic semiconductor can be improved.

The thickness of the thin-film organic-inorganic perovskite compound moiety has a preferable lower limit of 5 nm and a preferable upper limit of 5000 nm. When the thickness is 5 nm or more, light can be sufficiently absorbed and the photoelectric conversion efficiency becomes high. When the thickness is 5000 nm or less, it is possible to suppress the occurrence of a region where charge separation is not possible, which leads to an improvement in photoelectric conversion efficiency. The more preferable lower limit of the thickness is 10 nm, the more preferable upper limit is 1000 nm, the further preferable lower limit is 20 nm, and the further preferable upper limit is 500 nm.

When the photoelectric conversion layer is a composite film in which an organic semiconductor or an inorganic semiconductor moiety and an organic-inorganic perovskite compound moiety are composited, the preferable lower limit of the thickness of the composite film is 30 nm, and the preferable upper limit is 3000 nm. When the thickness is 30 nm or more, light can be sufficiently absorbed and the photoelectric conversion efficiency becomes high. When the thickness is 3000 nm or less, the electric charge easily reaches the electrode, so that the photoelectric conversion efficiency is high. The more preferable lower limit of the thickness is 40 nm, the more preferable upper limit is 2000 nm, the further preferable lower limit is 50 nm, and the further preferable upper limit is 1000 nm.

The method for forming the photoelectric conversion layer is not particularly limited, and examples thereof include a vacuum deposition method, a sputtering method, a vapor phase reaction method (CVD), an electrochemical deposition method, and a printing method. In particular, by adopting the printing method, it is possible to easily form a solar cell capable of exhibiting high photoelectric conversion efficiency in a large area. Examples of the printing method include a spin coating method and a casting method, and examples of the method using the printing method include a roll-to-roll method.

The material of the anode is not particularly limited, and conventionally known materials can be used. The anode is often a patterned electrode.
Examples of the anode material include metals such as gold, and conductivity such as CuI, ITO (indium tin oxide), SnO ₂ , AZO (aluminum zinc oxide), IZO (indium zinc oxide), and GZO (gallium zinc oxide). Examples thereof include sex-transparent materials and conductive transparent polymers. These materials may be used alone or in combination of two or more.

The solar cell of the present invention further has a layer containing an alkali metal, which is arranged between the electron transport layer and the photoelectric conversion layer.
By providing the layer containing the alkali metal between the electron transport layer and the photoelectric conversion layer, the open circuit voltage of the solar cell can be increased and excellent photoelectric conversion efficiency can be obtained. It is considered that the reason for this is that the wettability of the photoelectric conversion layer containing the organic-inorganic perovskite compound as described above with respect to the layer containing the alkali metal is good, so that the defect density at the interface of the photoelectric conversion layer becomes small. Be done.
In addition, having a layer containing an alkali metal means having a layer containing an alkali metal as a layer, and does not mean that the electron transport layer or the photoelectric conversion layer is doped with an alkali metal. The existence of the layer containing the alkali metal as a layer can be confirmed by observing the cross section of the solar cell with TEM-EDS.

Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium and ions thereof. These alkali metals may be used alone or in combination of two or more. Of these, potassium, rubidium, and cesium are preferable because the wettability of the photoelectric conversion layer is better.

The thickness of the layer containing the alkali metal is not particularly limited, but the preferable lower limit is 0.5 nm and the preferable upper limit is 100 nm. When the thickness is 0.5 nm or more, the wettability between the electron transport layer and the photoelectric conversion layer is improved, the open circuit voltage of the solar cell is increased, and the photoelectric conversion efficiency is improved. When the thickness is 100 nm or less, it does not become a resistance during electron transfer from the photoelectric conversion layer to the electron transport layer.
The more preferable lower limit of the thickness is 1 nm, and the more preferable upper limit is 50 nm.

As a method for forming the layer containing the alkali metal, for example, a method of applying a solution of an alkali metal salt in a solvent at a concentration of about 10 to 100 mM on the electron transport layer and drying the solvent. Examples thereof include a method of forming a metal containing an alkali metal on the electron transport layer by vapor deposition. Examples of the method of applying the solution include spin coating and die coating.
The alkali metal salt is not particularly limited as long as it is a salt containing an alkali metal as described above, but when the alkali metal is potassium, for example, potassium acetate, potassium iodide, potassium chloride, potassium carbonate and the like can be mentioned. When the alkali metal is lithium, for example, lithium acetate, lithium hydroxide and the like can be mentioned. When the alkali metal is sodium, for example, sodium acetate and the like can be mentioned. When the alkali metal is rubidium, for example, rubidium acetate, rubidium iodide, rubidium carbonate, rubidium chloride and the like can be mentioned. When the alkali metal is cesium, for example, cesium acetate and the like can be mentioned.

In the solar cell of the present invention, a hole transport layer may be arranged between the photoelectric conversion layer and the anode.
The material of the hole transport layer is not particularly limited, and examples thereof include a P-type conductive polymer, a P-type low molecular weight organic semiconductor, a P-type metal oxide, a P-type metal sulfide, and a surfactant. Examples thereof include compounds having a thiophene skeleton such as poly (3-alkylthiophene). Further, for example, a conductive polymer having a triphenylamine skeleton, a polyparaphenylene vinylene skeleton, a polyvinylcarbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton and the like can be mentioned. Further, for example, a compound having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, a benzoporphyrin skeleton, a spirobifluorene skeleton, molybdenum oxide, vanadium oxide, tungsten oxide, nickel oxide, copper oxide, tin oxide, sulfide. Examples thereof include molybdenum, tungsten sulfide, copper sulfide, tin sulfide and the like, fluorogroup-containing phosphonic acid, carbonyl group-containing phosphonic acid, copper compounds such as CuSCN and CuI, and carbon-containing materials such as carbon nanotubes and graphene.

A part of the hole transport layer may be immersed in the photoelectric conversion layer, or may be arranged in a thin film on the photoelectric conversion layer. When the hole transport layer is present as a thin film, the preferable lower limit is 1 nm and the preferable upper limit is 2000 nm. When the thickness is 1 nm or more, electrons can be sufficiently blocked. When the thickness is 2000 nm or less, it is unlikely to become a resistance during hole transportation, and the photoelectric conversion efficiency becomes high. The more preferable lower limit of the thickness is 3 nm, the more preferable upper limit is 1000 nm, the further preferable lower limit is 5 nm, and the further preferable upper limit is 500 nm.

The solar cell of the present invention may further have a substrate or the like. The substrate is not particularly limited, and examples thereof include transparent glass substrates such as soda lime glass and non-alkali glass, ceramic substrates, plastic substrates, and metal substrates.

The solar cell of the present invention has the cathode, the electron transport layer, the photoelectric conversion layer, and the anode as described above in this order, and is further arranged between the electron transport layer and the photoelectric conversion layer. Further, the laminate having the layer containing the alkali metal may be sealed with a barrier layer.
The material of the barrier layer is not particularly limited as long as it has a barrier property, and examples thereof include a thermosetting resin, a thermoplastic resin, and an inorganic material.
Examples of the thermosetting resin or thermoplastic resin include epoxy resin, acrylic resin, silicone resin, phenol resin, melamine resin, urea resin, butyl rubber, polyester, polyurethane, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, and poly. Examples thereof include vinyl acetate, ABS resin, polybutadiene, polyamide, polycarbonate, polyimide, polyisobutylene and the like.

When the material of the barrier layer is a thermosetting resin or a thermoplastic resin, the thickness of the barrier layer (resin layer) has a preferable lower limit of 100 nm and a preferable upper limit of 100,000 nm. A more preferable lower limit of the thickness is 500 nm, a more preferable upper limit is 50,000 nm, a further preferable lower limit is 1000 nm, and a further preferable upper limit is 20000 nm.

Examples of the inorganic material include oxides, nitrides or oxynitrides of Si, Al, Zn, Sn, In, Ti, Mg, Zr, Ni, Ta, W, Cu or alloys containing two or more of them. .. Of these, oxides, nitrides or oxynitrides of metal elements containing both Zn and Sn metal elements are preferable in order to impart water vapor barrier properties and flexibility to the barrier layer.

When the material of the barrier layer is an inorganic material, the thickness of the barrier layer (inorganic layer) has a preferable lower limit of 30 nm and a preferable upper limit of 3000 nm. When the thickness is 30 nm or more, the inorganic layer can have a sufficient water vapor barrier property, and the durability of the solar cell is improved. When the thickness is 3000 nm or less, even when the thickness of the inorganic layer is increased, the stress generated is small, so that peeling between the inorganic layer and the laminated body can be suppressed. The more preferable lower limit of the thickness is 50 nm, the more preferable upper limit is 1000 nm, the further preferable lower limit is 100 nm, and the further preferable upper limit is 500 nm.
The thickness of the inorganic layer can be measured using an optical interference type film thickness measuring device (for example, FE-3000 manufactured by Otsuka Electronics Co., Ltd.).

Among the materials of the barrier layer, the method of sealing the laminate with the thermosetting resin or the thermoplastic resin is not particularly limited, and for example, the material of the sheet-shaped barrier layer is used to seal the laminate. Method, a method of applying a solution of a barrier layer material dissolved in an organic solvent to the laminate, a method of applying a liquid monomer to be a barrier layer to the laminate, and then cross-linking or polymerizing the liquid monomer with heat or UV or the like. Examples thereof include a method, a method in which the material of the barrier layer is heated to melt it, and then cooled.

Among the materials for the barrier layer, a vacuum deposition method, a sputtering method, a vapor phase reaction method (CVD), and an ion plating method are preferable as a method for sealing the laminate with the inorganic material. Among them, the sputtering method is preferable for forming a dense layer, and the DC magnetron sputtering method is more preferable among the sputtering methods.
In the sputtering method, an inorganic layer made of an inorganic material can be formed by using a metal target and oxygen gas or nitrogen gas as raw materials and depositing the raw materials on the laminate to form a film.
The material of the barrier layer may be a combination of the thermosetting resin or the thermoplastic resin and the inorganic material.

In the solar cell of the present invention, the barrier layer may be further covered with another material such as a resin film or a resin film coated with an inorganic material. That is, the solar cell of the present invention may have a configuration in which the laminate and the other material are sealed, filled or adhered by the barrier layer. As a result, even if there is a pinhole in the barrier layer, water vapor can be sufficiently blocked, and the durability of the solar cell can be further improved.

FIG. 2 is a cross-sectional view schematically showing an example of the solar cell of the present invention.
The solar cell 1 shown in FIG. 2 has an electron transport layer 3 (thin-film electron transport layer 31 and a porous electron transport layer 32) on the cathode 2, and a photoelectric conversion layer 4 containing an organic-inorganic perovskite compound as described above. , The hole transport layer 5 and the anode 6 are provided in this order, and further, a layer 7 containing an alkali metal is provided between the electron transport layer 3 and the photoelectric conversion layer 4. By having the layer 7 containing such an alkali metal, the solar cell 1 has a large open circuit voltage and is excellent in photoelectric conversion efficiency. In the solar cell 1 shown in FIG. 2, the anode 6 is a patterned electrode.

The method for producing the solar cell of the present invention is not particularly limited, and for example, the cathode, the electron transport layer, the layer containing the alkali metal, the photoelectric conversion layer, the hole transport layer, and the anode are placed on the substrate. Examples thereof include a method of forming in order.

According to the present invention, it is possible to provide a solar cell having a large open circuit voltage and excellent photoelectric conversion efficiency.

It is a schematic diagram which shows an example of the crystal structure of an organic-inorganic perovskite compound. It is sectional drawing which shows typically an example of the solar cell of this invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
An aluminum film having a thickness of 200 nm and a molybdenum film having a thickness of 50 nm were continuously formed on a glass substrate by an electron beam vapor deposition method, and this was used as a cathode.
Next, titanium oxide was sputtered on the surface of the cathode using a sputtering device (manufactured by ULVAC, Inc.) to form a thin-film electron transport layer having a thickness of 30 nm. Further, an ethanol dispersion of titanium oxide (a mixture of an average particle size of 10 nm and 30 nm) is applied onto the thin-film electron transport layer by a spin coating method, and then fired at 200 ° C. for 10 minutes to form a porous body having a thickness of 150 nm. An electron transport layer was formed.

Then, a solution was prepared in which 25 mM of potassium acetate was dissolved as an alkali metal salt in ethanol. This solution was applied onto the electron transport layer by a spin coating method and then dried at 200 ° C. for 10 minutes to form a layer containing an alkali metal having a thickness of 5 nm.

Next, as a solution for forming an organic-inorganic perovskite compound, CH ₃ NH ₃ I and Pb I ₂ were dissolved in a molar ratio of 1: 1 _{using N, N-dimethylformamide (DMF) as a solvent, and the sum of CH 3} NH ₃ I and PbI ₂ was added. The weight concentration was adjusted to 20%. This solution was laminated on a layer containing an alkali metal by a spin coating method, and then calcined at 100 ° C. for 10 minutes to form a photoelectric conversion layer.

Next, a solution prepared by dissolving 68 mM of Spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM of t-butylpyridine, and 9 mM of bis (trifluoromethylsulfonyl) imide / silver salt in 1 mL of chlorobenzene was applied by a spin coating method. A hole transport layer having a thickness of 150 nm was formed.

An ITO film having a thickness of 200 nm is formed as an anode on the obtained hole transport layer by sputtering using a sputtering device (manufactured by ULVAC), and a cathode / electron transport layer / layer containing an alkali metal / photoelectric conversion layer / A solar cell having a laminated hole transport layer / anode was obtained.

(Examples 2 to 3)
By changing the concentration of potassium acetate, which is an alkali metal salt, as shown in Table 1, the thickness of the layer containing the alkali metal was changed as shown in Table 1. Got

(Examples 4 to 11)
A solar cell was obtained in the same manner as in Example 1 except that the type of alkali metal salt was changed as shown in Table 1.

(Comparative Example 1)
A solar cell was obtained in the same manner as in Example 1 except that a layer containing an alkali metal was not formed.

(Comparative Examples 2 to 4)
A solar cell was obtained in the same manner as in Example 1 except that the compounds shown in Table 1 were used instead of the alkali metal salt.

<Evaluation>
The solar cells obtained in Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.

(1) Measurement of open circuit voltage and photoelectric conversion efficiency A power supply (236 model manufactured by KEITHLEY) is connected between the electrodes of the solar cell, and a current-voltage is used using a solar simulation (manufactured by Yamashita Denso Co., Ltd.) ^{with a strength of 100 mW / cm 2.} A curve was drawn and the open circuit voltage and photoelectric conversion efficiency were calculated.
Regarding the photoelectric conversion efficiency, the value of 100% or more with respect to the photoelectric conversion efficiency obtained in Comparative Example 1 is 〇, the value of less than 100% and the value of 80% or more is Δ, and the value is less than 80%. The case where it was a value was regarded as x.

According to the present invention, it is possible to provide a solar cell having a large open circuit voltage and excellent photoelectric conversion efficiency.

1 Solar cell 2 Cathode 3 Electron transport layer 31 Thin-film electron transport layer 32 Porous electron transport layer 4 Photoelectric conversion layer 5 Hole transport layer 6 Anode (patterned electrode)
7 Layer containing alkali metal

Claims (2)

A solar cell having a cathode, an electron transport layer, a photoelectric conversion layer, and an anode in this order.
The photoelectric conversion layer contains an organic-inorganic perovskite compound represented by the general formula R-MX ₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom).
Further, it is characterized by having a layer arranged between the electron transport layer and the photoelectric conversion layer and containing at least one selected from the group consisting of lithium, sodium, potassium, rubidium and ions thereof. Solar cell. The solar cell according to claim 1, wherein the electron transport layer contains titanium oxide or tin oxide.

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