WO2019181673A1 - Solar cell - Google Patents

Abstract

The purpose of the present invention is to provide a solar cell that exhibits excellent incident photoelectric conversion efficiency. The present invention pertains to a solar cell having a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode in this order, wherein: the photoelectric conversion layer comprises an organic/inorganic perovskite compound represented by general formula R―M―X₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom); and the photoelectric conversion layer has a porous structure in both surfaces.

Description

Solar cell

The present invention relates to a solar cell excellent in photoelectric conversion efficiency.

Conventionally, a solar cell including a laminate (photoelectric conversion layer) in which an N-type semiconductor layer and a P-type semiconductor layer are arranged between opposing electrodes has been developed. In such a solar cell, photocarriers (electron-hole pairs) are generated by photoexcitation, and an electric field is generated when electrons move through an N-type semiconductor and holes move through a P-type semiconductor.

Currently, most of solar cells in practical use are inorganic solar cells manufactured using an inorganic semiconductor such as silicon. However, inorganic solar cells are expensive to manufacture and are difficult to increase in size.
In recent years, perovskite solar cells having a photoelectric conversion layer containing an organic / inorganic perovskite compound have attracted attention. A perovskite solar cell can be expected to have high photoelectric conversion efficiency and can be manufactured by a printing method. Therefore, even a large-sized solar cell can be manufactured with greatly reduced manufacturing costs (for example, Patent Document 1). Non-Patent Document 1).

JP 2014-72327 A

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

In perovskite solar cells, an electron transport layer is often provided between the photoelectric conversion layer and the cathode, and a hole transport layer is provided between the photoelectric conversion layer and the anode. The electron transport layer and the hole transport layer play a role of improving the photoelectric conversion efficiency of the solar cell by efficiently moving electrons and holes generated by photoexcitation without recombination. However, even such a perovskite solar cell still has insufficient photoelectric conversion efficiency, and further improvement in photoelectric conversion efficiency is desired.

An object of this invention is to provide the solar cell excellent in photoelectric conversion efficiency.

The present invention is a solar cell having a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode in this order, wherein the photoelectric conversion layer has the general formula RMX ₃ (where R is an organic molecule) , M is a metal atom, and X is a halogen atom or a chalcogen atom.), And the photoelectric conversion layer is a solar cell having a porous structure on both surfaces.
The present invention is described in detail below.

The present inventors examined a solar cell having a cathode, an electron transport layer, a photoelectric conversion layer containing an organic / inorganic perovskite compound, a hole transport layer, and an anode in this order. In such a solar cell, how efficiently electrons and holes generated by photoexcitation in the photoelectric conversion layer can move to the electron transport layer and the hole transport layer greatly affects the photoelectric conversion efficiency. The present inventors have increased the surface area of the photoelectric conversion layer by making the photoelectric conversion layer have a porous structure on both surfaces, and efficiently move electrons and holes generated by photoexcitation without recombination. Thus, it has been found that the photoelectric conversion efficiency can be improved. As a result, the present invention has been completed.

The solar cell of the present invention has a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode in this order.
In this specification, the layer means not only a layer having a clear boundary but also a layer having a concentration gradient in which 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 element distribution of the specific element. In addition, in this specification, a layer means not only a flat thin film-like layer but also a layer that can form a complicated and complicated structure together with other layers.

The material of the cathode is not particularly limited, and a conventionally known material can be used. Examples of cathode materials include 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 etc. are mentioned. In addition, gold, silver, titanium, molybdenum, tantalum, tungsten, carbon, nickel, chromium, and the like can be given. These materials may be used alone or in combination of two or more.

The material for the electron transport layer is not particularly limited, and examples thereof include an N-type metal oxide, an N-type conductive polymer, an N-type low molecular organic semiconductor, an alkali metal halide, an alkali metal, and a surfactant. Specific examples include cyano group-containing polyphenylene vinylene, boron-containing polymer, bathocuproine, bathophenanthrene, hydroxyquinolinato aluminum, oxadiazole compound, and benzimidazole compound. Also, naphthalene tetracarboxylic acid compound, perylene derivative, phosphine oxide compound, phosphine sulfide compound, fluoro group-containing phthalocyanine, titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, etc. It is done.

The electron transport layer may consist 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 part and an organic / inorganic perovskite compound part are combined, a more complex composite film (a more complicated and complicated structure) is obtained. In order to increase efficiency, it is preferable that the composite film is formed on the porous electron transport layer.

The preferable lower limit of the thickness of the electron transport layer is 1 nm, and the preferable upper limit is 2000 nm. If the thickness is 1 nm or more, holes can be sufficiently blocked. If the said thickness is 2000 nm or less, it will become difficult to become resistance at the time of electron transport, and photoelectric conversion efficiency will become 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 still more preferable lower limit is 5 nm, and the still more preferable upper limit is 500 nm.

The photoelectric conversion layer includes 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). The solar cell in which the photoelectric conversion layer includes the organic / inorganic perovskite compound is also referred to as an organic / inorganic hybrid solar cell.
By using the organic-inorganic perovskite compound for the photoelectric conversion layer, the photoelectric conversion efficiency of the solar cell can be improved.

The R is an organic molecule, and is preferably represented by C ₁ N _m H _n (l, m, and n are all positive integers).
Specifically, 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, Azole, pyrrole, aziridine, azirine, azetidine, azeto, imidazoline, carbazole and their ions and phenethylammoni Beam, and the like. Examples of the ion, for example, such as ammonium _{(CH 3} NH 3) is. Of these, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, formamidine, acetamidine and their ions and phenethylammonium are preferred, and methylamine, ethylamine, propylamine, formamidine and these ions are more preferred. preferable.

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 etc. are mentioned. These metal atoms may be used independently and 2 or more types may be used together. Among these, lead and tin are preferable because the band gap is appropriate and the crystallinity is good.

X is a halogen atom or a chalcogen atom, and examples thereof include chlorine, bromine, iodine, oxygen, sulfur, and selenium. When 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 these, the halogen atom is preferable because the organic / inorganic perovskite compound becomes soluble in an organic solvent and can be applied to an inexpensive printing method by containing halogen in the structure. Furthermore, iodine is more preferable because the energy band gap of the organic-inorganic perovskite compound becomes narrow.

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

In addition, the degree of crystallization can be evaluated as an index of crystallization. The degree of crystallinity is determined by separating the crystalline-derived scattering peak detected by the X-ray scattering intensity distribution measurement and the halo derived from the amorphous part by fitting, obtaining the respective intensity integrals, Can be obtained by calculating the ratio.
A preferable lower limit of the crystallinity of the organic-inorganic perovskite compound is 30%. When the crystallinity is 30% or more, the mobility of electrons in the organic / inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved. A more preferred lower limit of the crystallinity is 50%, and a more preferred lower limit is 70%.
Examples of the method for increasing the crystallinity of the organic / inorganic perovskite compound include thermal annealing, irradiation with intense light such as laser, and plasma irradiation.

The crystallite diameter can also be evaluated as another crystallization index. The crystallite diameter can be calculated by the holder-Wagner method from the half width of the scattering peak derived from the crystal detected by the X-ray scattering intensity distribution measurement.
The minimum with the preferable crystallite diameter of the said organic inorganic perovskite compound is 5 nm. When the crystallite diameter is 5 nm or more, the mobility of electrons in the organic / inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved. A more preferred lower limit of the crystallite diameter is 10 nm, and a more preferred lower limit is 20 nm.

The photoelectric conversion layer has a porous structure on both surfaces.
By making the photoelectric conversion layer have a porous structure on both surfaces, the surface area of the photoelectric conversion layer is increased so that electrons and holes generated by photoexcitation can move efficiently without recombination. The photoelectric conversion efficiency can be improved. The porous structure refers to a sponge-like structure having a large number of pores. The surfaces on both sides of the photoelectric conversion layer refer to both the surface on the electron transport layer side and the surface on the hole transport layer side of the photoelectric conversion layer.
In a conventional perovskite solar cell, it is difficult to form a photoelectric conversion layer having a porous structure on both surfaces as well as on one surface. In particular, it has been difficult to form a photoelectric conversion layer having a porous structure on both surfaces and having a sufficiently high crystallinity and crystallite size of the organic / inorganic perovskite compound as described above.

In the photoelectric conversion layer, the thickness of the part having a porous structure is preferably 50 nm or more on both surfaces. When the thickness of the portion having the porous structure is 50 nm or more, the surface area of the photoelectric conversion layer is increased, and the photoelectric conversion efficiency of the solar cell is improved. The thickness of the portion having the porous structure is more preferably 75 nm or more, and further preferably 100 nm or more.
Although the upper limit of the thickness of the site | part which has the said porous structure is not specifically limited, A preferable upper limit is 200 nm. When the thickness of the portion having the porous structure is 200 nm or less, the photoelectric conversion layer can sufficiently absorb light, and the photoelectric conversion efficiency is increased. The upper limit with more preferable thickness of the site | part which has the said porous structure is 150 nm.

The photoelectric conversion layer preferably has a porosity of a portion having a porous structure of 10% or more on both surfaces. If the porosity of the part which has the said porous structure is 10% or more, the surface area of the said photoelectric converting layer will increase, and the photoelectric conversion efficiency of a solar cell will improve. The porosity of the part having the porous structure is more preferably 25% or more, and still more preferably 40% or more.
The upper limit of the porosity of the part having the porous structure is not particularly limited, but a preferable upper limit is 80%. If the porosity of the part which has the said porous structure is 80% or less, the said photoelectric converting layer will be able to fully absorb light, and a photoelectric conversion efficiency will become high. The upper limit with more preferable porosity of the site | part which has the said porous structure is 70%.

The photoelectric conversion layer has a porous structure on both surfaces, the thickness of the portion having the porous structure, and the porosity of the portion having the porous structure should be confirmed and calculated as follows. Can do.
That is, the cross-section of the solar cell is, for example, a transmission electron microscope (TEM) (for example, JEM-ARM200F manufactured by JEOL Ltd.), a scanning electron microscope (SEM) (for example, S-4800 manufactured by Hitachi High-Technologies Corporation), etc. A cross section is observed using an electron microscope. By calculating the ratio of the void area (area filled with the electron transport layer or hole transport layer) to the area having the porous structure, the porosity of the portion having the porous structure is obtained. In the calculation of the area, the start and end of the porous structure portion are determined by the following method. First, a cross-sectional image of the solar cell is taken using an electron microscope or the like, and a straight line perpendicular to the thickness direction of the solar cell is drawn on the cross-sectional image. The straight line is translated from the anode side to the cathode side of the image, and the position on the straight line when the photoelectric conversion layer is in contact with the straight line for the first time is the beginning of the porous structure part, and finally the hole transport layer is in contact with the line. The position on the straight line at this time is the end of the porous structure. In addition, for the porous structure portion on the electron transport layer side, the position on the straight line when the electron transport layer is in contact with the straight line for the first time is the beginning of the porous structure portion, and is finally in contact with the photoelectric conversion layer. The position on the straight line at this time is the end of the porous structure.

The following method (A) is mentioned as a method of forming the said photoelectric converting layer, ie, the photoelectric converting layer which has a porous structure in the surface of both sides, for example.
First, a thin film electron transport layer and a porous electron transport layer are formed in this order on the cathode. Next, a photoelectric conversion layer is formed on the porous electron transport layer by a printing method using a solution in which the raw material of the organic / inorganic perovskite compound is dissolved. Since the photoelectric conversion layer is formed on the porous electron transport layer, the surface of the obtained photoelectric conversion layer on the electron transport layer side has a porous structure. At this time, an additive for forming a porous structure such as a polymer, a low molecular compound, or a surfactant is blended in a solution in which the raw material for the organic / inorganic perovskite compound is dissolved. Thereby, as the crystal structure of the organic / inorganic perovskite compound is formed from the raw material of the organic / inorganic perovskite compound, the porous structure forming additive is unevenly distributed on the upper surface portion of the layer, and the resulting photoelectric conversion layer A porous structure is also formed on the surface on the hole transport layer side.

The additive for forming a porous structure is not particularly limited, and examples thereof include a polymer, a low molecular compound, and a surfactant. Among these, a polymer is preferable because a porous structure is easily formed. Although the said polymer is not specifically limited, The polymer which has a functional group containing a nitrogen atom is preferable.

The functional group containing a nitrogen atom may be contained in the main chain of the polymer having a functional group containing the nitrogen atom, or may be contained in a side chain. The main chain means the main skeleton of the polymer, that is, the longest chain, and the side chain means a portion branched from the main skeleton of the polymer. Especially, since the photoelectric conversion efficiency of a solar cell improves, it is preferable that the functional group containing the said nitrogen atom is contained in the side chain of the polymer which has the said functional group containing a nitrogen atom.
The functional group containing a nitrogen atom is not particularly limited, and examples thereof include an amino group, an amide group, an imino group, an imide group, a pyridyl group, an azo group, an azide group, an isocyanate group, and a urethane bond. These functional groups containing a nitrogen atom may be used alone or in combination of two or more. Among these, an amino group, an amide group, an imino group, an imide group, or a pyridyl group is preferable because it has a high affinity for both the photoelectric conversion layer and the hole transport layer and the interface defect density is small.

The functional group containing a nitrogen atom may contain an electron-withdrawing group bonded to the nitrogen atom. One of the electron-withdrawing groups may be bonded to a nitrogen atom, or two or more may be bonded.
The electron withdrawing group is not particularly limited, and examples thereof include a sulfonyl group, a sulfide group, a thioester group, a thioketone group, an ester group, an ether group, a carbonyl group, an amide group, a urethane group, a sulfinyl group, and a phosphonyl group. These electron withdrawing groups may be used independently and 2 or more types may be used together. Of these, a sulfonyl group is more preferable.

When the functional group containing a nitrogen atom contains the electron-withdrawing group, it may further contain a conjugated cyclic skeleton bonded to the electron-withdrawing group. Since the conjugated cyclic skeleton is bonded to the electron-withdrawing group, the acidity of the nitrogen atom is increased and the recombination of electrons and holes can be further suppressed, so that the photoelectric conversion efficiency of the solar cell is improved. To do. Specifically, the pKa of the functional group containing a nitrogen atom is preferably 3 or less.

The polymer having a functional group containing a nitrogen atom preferably further contains a fluorine atom. The polymer having a functional group containing a nitrogen atom can be easily dissolved in an organic solvent by containing a fluorine atom, and can be easily incorporated into the photoelectric conversion layer.

The polymer having a functional group containing a nitrogen atom is preferably a polymer or copolymer having a structural unit derived from a monomer having a functional group containing a nitrogen atom.
The monomer having a functional group containing a nitrogen atom is not particularly limited as long as it has a functional group containing the nitrogen atom and has a polymerizable property. Specifically, for example, allylamine, ethyleneimine, (meth) acrylamide, N-succinimidyl (meth) acrylate, trimethyl [3-((meth) acryloylamino) propyl] aminium chloride, N, N-dimethyl (meth) acrylamide N-isopropyl (meth) acrylamide and the like. These monomers having a functional group containing a nitrogen atom may be used alone or in combination of two or more. Among them, since it is electrically neutral and does not affect the carrier density of the photoelectric conversion layer and the hole transport layer, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-isopropyl ( Meth) acrylamide is preferred.

The minimum with preferable content of the structural unit derived from the monomer which has a functional group containing the said nitrogen atom is 10 weight%. If content of the said structural unit is 10 weight% or more, the defect of a porous interface will be suppressed and the photoelectric conversion efficiency of a solar cell will improve. The minimum with more preferable content of the said structural unit is 25 weight%. The upper limit of the content of the structural unit is not particularly limited, and may be 100% by weight.

When the polymer having a functional group containing a nitrogen atom further contains a fluorine atom, the monomer having a functional group containing a nitrogen atom may further have a functional group containing a fluorine atom. In addition, the polymer having a functional group containing a nitrogen atom has a constituent unit derived from a monomer having a functional group containing a fluorine atom in addition to the constituent unit derived from a monomer having a functional group containing a nitrogen atom. It may be a polymer.
The functional group containing a fluorine atom is not particularly limited, but a fluorine atom, or an alkyl group or aryl group in which some or all of hydrogen atoms are substituted with fluorine is preferable.

When the monomer having a functional group containing a nitrogen atom further has a functional group containing a fluorine atom, examples of such a monomer include (4-styrenesulfonyl) -trifluoromethanesulfonylimide, N- (5-amino -2-fluorophenyl) -n-methylacrylamide 2-methyl-N- [3- (trifluoromethyl) phenyl] oxirane-2-carboxamide and the like. These monomers may be used independently and 2 or more types may be used together. Of these, (4-styrenesulfonyl) -trifluoromethanesulfonylimide is preferable because the interface formation of the photoelectric conversion layer is good. Such a monomer preferably contains an electron-withdrawing group bonded to a nitrogen atom as described above, and at least one of the fluorine atoms is bonded to the electron-withdrawing group or the α-position of the electron-withdrawing group. More preferably.

Examples of the monomer having a functional group containing a fluorine atom include methyl pentafluoroethyl (meth) acrylate, 3-perfluorobutyl-1,2-epoxypropane, and methyl trifluoroethyl (meth) acrylate. . These monomers having a functional group containing a fluorine atom may be used alone or in combination of two or more. Of these, methyl trifluoroethyl (meth) acrylate is preferred because of its high solubility in coating solvents.

The minimum with preferable content of the structural unit derived from the monomer which has the functional group containing the said fluorine atom is 1 weight%, and a preferable upper limit is 100 weight%. If content of the said structural unit is this range, the photoelectric conversion efficiency of a solar cell will improve. A more preferable lower limit of the content of the structural unit is 10% by weight, and a more preferable upper limit is 90% by weight.

In addition to the structural unit derived from the monomer having a functional group containing a nitrogen atom and the structural unit derived from a monomer having a functional group containing a fluorine atom, the polymer having a functional group containing a nitrogen atom, You may have the structural unit. The other structural units are not particularly limited, and examples thereof include structural units derived from styrene derivatives, (meth) acrylic acid esters, vinyl ethers, and the like.

As a method for synthesizing a polymer having a functional group containing a nitrogen atom, for example, a monomer having a functional group containing a nitrogen atom may be polymerized or co-polymerized with a monomer having a functional group containing a fluorine atom, if necessary. The method of superposing | polymerizing is mentioned. In addition, the functional group containing the nitrogen atom, the electron-withdrawing group bonded to the nitrogen atom, or the monomer having no functional group containing the fluorine atom is polymerized or copolymerized, and then the functional group containing the nitrogen atom. In addition, a method of adding an electron-withdrawing group bonded to the nitrogen atom, a functional group containing the fluorine atom, or the like as required by a chemical reaction is also included.

As for the average degree of polymerization of the polymer, the preferred lower limit is 5, the preferred upper limit is 10,000, the more preferred lower limit is 10, the more preferred upper limit is 5000, the still more preferred lower limit is 20, and the more preferred upper limit is 3000.
The average degree of polymerization is determined by dividing the weight average molecular weight calculated by gel permeation chromatography by the molecular weight of the monomer.

The low molecular compound is not particularly limited, and examples thereof include 2,2,2-trifluoroethylamine, 3,3,3-trifluoropropylamine, 1,1,1-trifluoro-2-propanamine, 2,2 , 2-trifluoro-N-methylethanamine, trifluoromethanesulfonimide, bis (1,1,2,2,3,3,4,4,4-nonafluoro-1-butanesulfonyl) imide and the like.

The surfactant is not particularly limited. For example, heptadecafluorooctane sulfonic acid, lithium nonafluoro-1-butanesulfonate, potassium hepadecafluoro-1-octanesulfonate, ammonium pentadecafluorooctanoate, nonafluoro-1- Examples include butanesulfonic acid.

The compounding amount of the additive for forming a porous structure is not particularly limited, but a preferable lower limit with respect to 100% by weight of the raw material of the organic / inorganic perovskite compound is 0.1% by weight, and a preferable upper limit is 50% by weight. If the compounding quantity of the said additive for porous structure formation is this range, it will become easy to form a porous structure and the photoelectric conversion efficiency of a solar cell will improve. A more preferable lower limit of the amount of the porous structure forming additive is 1% by weight, and a more preferable upper limit is 25% by weight.

Moreover, the following method (B) is also mentioned as a method of forming the said photoelectric converting layer, ie, the photoelectric converting layer which has a porous structure on the surface of both sides, for example.
First, a thin film electron transport layer and a porous electron transport layer are formed in this order on the cathode. Next, a photoelectric conversion layer is formed on the porous electron transport layer by a printing method using a solution in which the raw material of the organic / inorganic perovskite compound is dissolved. Since the photoelectric conversion layer is formed on the porous electron transport layer, the surface of the obtained photoelectric conversion layer on the electron transport layer side has a porous structure. A dispersion solution of inorganic p-type semiconductor nanoparticles is applied thereon, and then placed in a solvent atmosphere and baked. Thereby, the surface of the crystal of the organic / inorganic perovskite compound is once dissolved, and after the nanoparticle is taken in and recrystallized, a porous structure is also formed on the surface on the hole transport layer side.

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 effects of the present invention are not impaired. Note that the organic semiconductor or inorganic semiconductor here may serve 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). In addition, for example, conductive polymers having a polyparaphenylene vinylene skeleton, a polyvinyl carbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton, and the like can be given. Further, for example, compounds having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, or a benzoporphyrin skeleton, a spirobifluorene skeleton, etc., and carbon-containing materials such as carbon nanotubes, graphene, and fullerene that may be surface-modified Also 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 , _{MoS 2, MoSe 2, Cu 2} S , and the like.

In the case where the photoelectric conversion layer includes the organic-inorganic perovskite compound and the organic semiconductor or the inorganic semiconductor, the photoelectric conversion layer is a laminated body in which a thin-film organic semiconductor or an inorganic semiconductor portion and a thin-film organic-inorganic perovskite compound portion are stacked. May be. Moreover, the composite film which compounded the organic-semiconductor or inorganic-semiconductor site | part and the organic-inorganic perovskite compound site | part may be sufficient. A laminated body is preferable in that the production method is simple, and a composite film is preferable in that the charge separation efficiency in the organic semiconductor or the inorganic semiconductor can be improved.

The preferable lower limit of the thickness of the thin-film organic / inorganic perovskite compound site is 5 nm, and the preferable upper limit is 5000 nm. If the thickness is 5 nm or more, light can be sufficiently absorbed, and the photoelectric conversion efficiency is increased. If the said thickness is 5000 nm or less, since it can suppress that the area | region which cannot carry out charge separation generate | occur | produces, it will lead to the improvement of photoelectric conversion efficiency. The more preferable lower limit of the thickness is 10 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 20 nm, and the still more preferable upper limit is 500 nm.

When the photoelectric conversion layer is a composite film in which an organic semiconductor or an inorganic semiconductor part and an organic / inorganic perovskite compound part are combined, a preferable lower limit of the thickness of the composite film is 30 nm, and a preferable upper limit is 3000 nm. If the thickness is 30 nm or more, light can be sufficiently absorbed, and the photoelectric conversion efficiency is increased. If the said thickness is 3000 nm or less, since it becomes easy to reach | attain an electrode, a photoelectric conversion efficiency becomes high. The more preferable lower limit of the thickness is 40 nm, the more preferable upper limit is 2000 nm, the still more preferable lower limit is 50 nm, and the still more preferable upper limit is 1000 nm.

The photoelectric conversion layer is preferably subjected to thermal annealing (heat treatment) after the photoelectric conversion layer is formed. By performing thermal annealing (heat treatment), the degree of crystallinity of the organic-inorganic perovskite compound in the photoelectric conversion layer can be sufficiently increased, and the decrease in photoelectric conversion efficiency (photodegradation) due to continued irradiation with light is further increased. Can be suppressed.

When performing the thermal annealing (heat treatment), the temperature for heating the photoelectric conversion layer is not particularly limited, but is preferably 100 ° C. or higher and lower than 250 ° C. When the heating temperature is 100 ° C. or higher, the crystallinity of the organic / inorganic perovskite compound can be sufficiently increased. If the said heating temperature is less than 250 degreeC, it can heat-process, without thermally degrading the said organic-inorganic perovskite compound. A more preferable heating temperature is 120 ° C. or higher and 200 ° C. or lower. The heating time is not particularly limited, but is preferably 3 minutes or longer and 2 hours or shorter. When the heating time is 3 minutes or longer, the crystallinity of the organic-inorganic perovskite compound can be sufficiently increased. If the heating time is within 2 hours, the organic inorganic perovskite compound can be heat-treated without causing thermal degradation.
These heating operations are preferably performed in a vacuum or under an inert gas, and the dew point temperature is preferably 10 ° C or lower, more preferably 7.5 ° C or lower, and further preferably 5 ° C or lower.

The material for the hole transport layer is not particularly limited, and examples thereof include a P-type conductive polymer, a P-type low molecular organic semiconductor, a P-type metal oxide, a P-type metal sulfide, and a surfactant. Specific examples include compounds having a thiophene skeleton such as poly (3-alkylthiophene). In addition, for example, conductive polymers having a triphenylamine skeleton, a polyparaphenylene vinylene skeleton, a polyvinyl carbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton, and the like can be given. Furthermore, for example, compounds having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, and a benzoporphyrin skeleton, a spirobifluorene skeleton, and the like can be given. Furthermore, molybdenum oxide, vanadium oxide, tungsten oxide, nickel oxide, copper oxide, tin oxide, molybdenum sulfide, tungsten sulfide, copper sulfide, tin sulfide, etc., fluoro group-containing phosphonic acid, carbonyl group-containing phosphonic acid, CuSCN, CuI, etc. Examples thereof include carbon-containing materials such as copper compounds, carbon nanotubes, and graphene.

A part of the hole transport layer may be immersed in the photoelectric conversion layer (a structure complicated with the photoelectric conversion layer may be formed) or arranged in a thin film on the photoelectric conversion layer. May be. The thickness when the hole transport layer is in the form of a thin film has a preferred lower limit of 1 nm and a preferred upper limit of 2000 nm. If the thickness is 1 nm or more, electrons can be sufficiently blocked. If the said thickness is 2000 nm or less, it will become difficult to become resistance at the time of hole transport, and a photoelectric conversion efficiency will become high. The more preferable lower limit of the thickness is 3 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 5 nm, and the still more preferable upper limit is 500 nm.

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

The solar cell of the present invention may further have a substrate or the like. The said board | substrate is not specifically limited, For example, transparent glass substrates, such as soda-lime glass and an alkali free glass, a ceramic substrate, a plastic substrate, a metal substrate, etc. are mentioned.

In the solar cell of the present invention, a laminate having the cathode, the electron transport layer, the photoelectric conversion layer, the hole transport layer, and the anode in this order 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. The barrier layer material may be a combination of the thermosetting resin or thermoplastic resin and the inorganic material.

Examples of the thermosetting resin or thermoplastic resin include epoxy resin, acrylic resin, silicone resin, phenol resin, melamine resin, urea resin, and the like. Moreover, butyl rubber, polyester, polyurethane, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, ABS resin, polybutadiene, polyamide, polycarbonate, polyimide, polyisobutylene, and the like can be given.

When the material of the barrier layer is a thermosetting resin or a thermoplastic resin, 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 50000 nm, a still more preferable lower limit is 1000 nm, and a still more preferable upper limit is 20000 nm.

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

When the material of the barrier layer is an inorganic material, 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. If the thickness is 3000 nm or less, even if the thickness of the inorganic layer is increased, the generated stress is small, and therefore, the peeling between the inorganic layer and the laminate can be suppressed. The more preferable lower limit of the thickness is 50 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 100 nm, and the still more preferable upper limit is 500 nm.
The thickness of the inorganic layer can be measured using an optical interference film thickness measuring device (for example, FE-3000 manufactured by Otsuka Electronics Co., Ltd.).

Of the materials for the barrier layer, the method for sealing the laminate with the thermosetting resin or thermoplastic resin is not particularly limited. For example, the laminate is sealed using a sheet-like barrier layer material. Methods and the like. In addition, a method in which a solution in which the material of the barrier layer is dissolved in an organic solvent is applied to the laminate, and after the liquid monomer to be the barrier layer is applied to the laminate, the liquid monomer is crosslinked or polymerized by heat or UV. Examples thereof include a method and a method of cooling the material of the barrier layer after applying heat to melt it.

Of the materials for the barrier layer, vacuum deposition, sputtering, gas phase reaction (CVD), and ion plating are preferred as methods for sealing the laminate with the inorganic material. Of these, 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 material on the laminate to form a film.

The barrier layer may be covered with another material such as a resin film or a resin film coated with an inorganic material. Thereby, 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 (a thin film electron transport layer 31 and a porous electron transport layer 32), a photoelectric conversion layer 4, a hole transport layer 5 and an anode 6 on a cathode 2. They are stacked in order. The photoelectric conversion layer 4 has a porous structure on both the surface 41a and the surface 41b. By having such a photoelectric conversion layer 4, the solar cell 1 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. For example, there is a method of forming the cathode, the electron transport layer, the photoelectric conversion layer, the hole transport layer, and the anode in this order on the substrate. Can be mentioned.
The method for forming the photoelectric conversion layer is not particularly limited, and examples thereof include a vacuum deposition method, a sputtering method, a gas phase reaction method (CVD), an electrochemical deposition method, and a printing method. Especially, the solar cell which can exhibit high photoelectric conversion efficiency can be simply formed in a large area by employ | adopting the printing method. Examples of the printing method include a spin coating method and a casting method, and examples of a method using the printing method include a roll-to-roll method. As a method for forming a photoelectric conversion layer having a porous structure on both surfaces, for example, the method (A) and the method (B) described above can be used.

ADVANTAGE OF THE INVENTION According to this invention, the solar cell excellent in the photoelectric conversion efficiency can be provided.

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. It is the photograph which observed the cross section of the cross section of the solar cell obtained in Example 1 using the scanning electron microscope (SEM).

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, 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 successively formed on a glass substrate by an electron beam evaporation method, and this was used as a cathode.
Next, titanium oxide was sputtered on the surface of the cathode using a sputtering apparatus (manufactured by ULVAC) to form a thin-film electron transport layer having a thickness of 30 nm. Further, an ethanol dispersion of titanium oxide nanoparticles (a mixture of average particle diameters of 10 nm and 30 nm) was applied onto the thin-film electron transport layer by a spin coating method, and then baked at 200 ° C. for 10 minutes to form a porous film having a thickness of 150 nm. A quality electron transport layer was formed.

Next, CH ₃ NH ₃ I and PbI ₂ were dissolved at a molar ratio of 1: 1 using N, N-dimethylformamide (DMF) as a solvent as a solution for forming an organic inorganic perovskite compound, and the total of CH ₃ NH ₃ I and PbI ₂ The weight concentration was adjusted to 20%. To this solution, polyacrylamide (average polymerization degree 50) as a polymer having a functional group containing a nitrogen atom was added so as to be 2% by weight with respect to 100% by weight of the total weight of CH ₃ NH ₃ I and PbI ₂ . . After laminating this solution on the electron transport layer by spin coating, it was baked at 100 ° C. for 10 minutes to form a photoelectric conversion layer.
As the crystal structure of the organic / inorganic perovskite compound is formed from CH ₃ NH ₃ I and PbI ₂ , polyacrylamide is unevenly distributed on the upper surface portion of the layer, and has a porous structure on the surface on the electron transport layer side. And the photoelectric converting layer which has a porous structure also in the upper surface part was obtained.

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

On the obtained hole transport layer, an ITO film having a thickness of 200 nm is formed as an anode by sputtering using a sputtering apparatus (manufactured by ULVAC), and the cathode / electron transport layer / photoelectric conversion layer / hole transport layer / anode A stacked solar cell was obtained.

The cross section of the obtained solar cell was observed with a scanning electron microscope (SEM) (S-4800, manufactured by Hitachi High-Technologies Corporation), and it was confirmed that the photoelectric conversion layer had a porous structure on both surfaces. did. In addition, FIG. 3 is the photograph which observed the cross section of the cross section of the solar cell obtained in Example 1 using the scanning electron microscope (SEM). Further, on the surface on the electron transport layer side and the surface on the hole transport layer side, the area of the electron transport layer or the hole transport layer with respect to the area having a porous structure (area filled with the electron transport layer or the hole transport layer) By calculating the ratio, the porosity and thickness of the portion having a porous structure were obtained.
In the calculation of the area, the start and end of the porous structure portion were determined by the following method. First, a straight line perpendicular to the thickness direction of the solar cell was drawn on the cross-sectional image taken by the scanning electron microscope. The straight line is translated from the anode side to the cathode side of the image, and the position on the straight line when the photoelectric conversion layer is in contact with the straight line for the first time is the beginning of the porous structure part, and finally the hole transport layer is in contact with the line. The position on the straight line at the time was the end of the porous structure. In addition, for the porous structure portion on the electron transport layer side, the position on the straight line when the electron transport layer is in contact with the straight line for the first time is the beginning of the porous structure portion, and is finally in contact with the photoelectric conversion layer. The position on the straight line at the time was the end of the porous structure.

(Examples 2 to 16)
Except that the porosity and thickness of the part having the porous structure were changed as shown in Table 1 by changing the kind and concentration of the porous structure forming additive used, the same as in Example 1. The solar cell was obtained.

(Comparative Example 1)
Examples except that the porous electron transport layer was not formed on the thin film electron transport layer and that polyallylamine (average degree of polymerization 5) was not added to the organic inorganic perovskite compound forming solution. In the same manner as in Example 1, a solar cell was obtained. The obtained photoelectric conversion layer did not have a porous structure on any surface.

(Comparative Example 2)
A solar cell was obtained in the same manner as in Example 1 except that polyallylamine (average polymerization degree 5) was not added to the organic / inorganic perovskite compound forming solution. The obtained photoelectric conversion layer had a porous structure only on the surface on the electron transport layer side.

(Comparative Example 3)
A solar cell was obtained in the same manner as in Example 1 except that the porous electron transport layer was not formed on the thin film electron transport layer. The obtained photoelectric conversion layer had a porous structure only on the surface on the hole transport layer side.

<Evaluation>
About the solar cell obtained by the Example and the comparative example, it evaluated by the following method. The results are shown in Table 1.

(1) Evaluation of photoelectric conversion efficiency A power source (made by KEITHLEY, model 236) is connected between the electrodes of the solar cell, and a current-voltage curve is drawn using a solar simulation (made by Yamashita Denso Co., Ltd.) with an intensity of 100 mW / cm _2. The photoelectric conversion efficiency was calculated.
The case where the obtained photoelectric conversion efficiency was 120% or more compared with the photoelectric conversion efficiency obtained in Comparative Example 1, ◎, less than 120% 100% or more, ◯, less than 100% 90% or more The case was Δ, and the case of less than 90% was ×.

ADVANTAGE OF THE INVENTION According to this invention, the solar cell excellent in the photoelectric conversion efficiency can be provided.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Cathode 3 Electron transport layer 31 Thin-film electron transport layer 32 Porous electron transport layer 4 Photoelectric conversion layer 41a, 41b Surface of photoelectric conversion layer 5 Hole transport layer 6 Anode (patterned electrode)

Claims (3)

A solar cell having a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer and an anode in this order,
The photoelectric conversion layer includes an organic / inorganic perovskite compound represented by a general formula RMX ₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom),
The photoelectric conversion layer has a porous structure on both surfaces. 2. The solar cell according to claim 1, wherein the photoelectric conversion layer has a thickness of a portion having a porous structure on both surfaces of 50 nm or more. 3. The solar cell according to claim 1, wherein the photoelectric conversion layer has a porosity of 10% or more in a portion having a porous structure on both surfaces.

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