Composition, and method for producing photoelectric conversion layer

Abstract

This composition contains a perovskite compound precursor, a first solvent, and a second solution. The first solvent has a boiling point of 50°C or higher and a dipole moment of 3.0 D or less, and does not dissolve a perovskite compound formed from the perovskite compound precursor. The second solvent has a dipole moment of greater than 3.0 D and dissolves the perovskite compound.

Description

Composition and method for producing photoelectric conversion layer using the same

[0001] The present disclosure relates to a composition and a method for producing a photoelectric conversion film using the same.

[0002] Non-Patent Document 1 discloses a method of forming a film by adding diethyl ether, which is a poor solvent, to a perovskite precursor solution.

[0003] Chongyang Xu, 2 others, J. Mater. Chem. C, 2020, 8, 15860-15867

[0004] An object of the present disclosure is to provide a composition suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0005] The composition of the present disclosure includes a perovskite compound precursor, a first solvent, and a second solution, wherein the first solvent has a boiling point of 50°C or higher, a dipole moment of 3.0 D or less, and does not dissolve a perovskite compound formed from the perovskite compound precursor, and the second solvent has a dipole moment of more than 3.0 D and dissolves the perovskite compound.

[0006] The present disclosure provides a composition suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0007] Fig. 1 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 100. Fig. 2 is a graph showing IV curves of the photoelectric conversion elements of Examples 1 to 6. Fig. 3 is a graph showing IV curves of the photoelectric conversion elements of Reference Examples 1 to 6. Fig. 4 is a graph showing IV curves of the photoelectric conversion elements of Reference Examples 7 and 8.

[0008] (Summary of one aspect of the present disclosure) A composition according to a first aspect of the present disclosure includes a perovskite compound precursor, a first solvent, and a second solvent, wherein the first solvent has a boiling point of 50°C or higher, a dipole moment of 3.0 D or less, and does not dissolve a perovskite compound formed from the perovskite compound precursor, and the second solvent has a dipole moment of more than 3.0 D, and dissolves the perovskite compound.

[0009] The composition according to the first aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0010] In the second aspect of the present disclosure, for example, in the composition according to the first aspect, the first solvent may have a dipole moment of 1.78 D or less.

[0011] The composition according to the second aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0012] In a third aspect of the present disclosure, for example, in the composition according to the first or second aspect, the first solvent may have a boiling point of 100° C. or higher.

[0013] The composition according to the third aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0014] In a fourth aspect of the present disclosure, for example, in the composition according to any one of the first to third aspects, the first solvent may contain a compound having a benzene ring.

[0015] The composition according to the fourth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0016] In a fifth aspect of the present disclosure, for example, in the composition according to the first or second aspect, the first solvent may include at least one selected from the group consisting of tetrahydrofuran, dipropyl ether, diisopropyl ether, toluene, chlorobenzene, methoxybenzene, and methoxytoluene.

[0017] The composition according to the fifth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0018] In a sixth aspect of the present disclosure, for example, in the composition according to any one of the first to fifth aspects, the perovskite compound precursor may contain monovalent cations, divalent cations, and monovalent anions.

[0019] The composition according to the sixth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0020] In a seventh aspect of the present disclosure, for example, in the composition according to the sixth aspect, the monovalent cation may include an inorganic cation.

[0021] The composition according to the seventh aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0022] In an eighth aspect of the present disclosure, for example, in the composition according to the sixth or seventh aspect, the divalent cation may include at least one selected from the group consisting of Pb and Sn.

[0023] The composition according to the eighth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0024] In a ninth aspect of the present disclosure, for example, in the composition according to any one of the first to eighth aspects, the second solvent may include at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, gamma butyrolactone, and N-methyl-2-pyrrolidone.

[0025] The composition according to the ninth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0026] In a tenth aspect of the present disclosure, for example, in the composition according to any one of the first to ninth aspects, the volume ratio of the second solvent to the total of the first solvent and the second solvent may be 80% or more and 97% or less.

[0027] The composition according to the tenth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional perovskite compounds more easily than conventional films.

[0028] In an eleventh aspect of the present disclosure, for example, in the composition according to the tenth aspect, the volume ratio may be 85% or more and 93% or less.

[0029] The composition according to the eleventh aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional perovskite compounds more easily than conventional perovskite compounds.

[0030] In a twelfth aspect of the present disclosure, for example, the composition according to any one of the first to eleventh aspects may further contain an ammonium salt.

[0031] The composition according to the twelfth aspect is suitable for producing a film containing a perovskite compound that can achieve improved properties, for example, improved photoelectric conversion efficiency, more easily than before.

[0032] In a thirteenth aspect of the present disclosure, for example, in the composition according to the twelfth aspect, the ammonium salt may include a quaternary ammonium salt.

[0033] The composition according to the thirteenth aspect is suitable for producing a film containing a perovskite compound that can realize improved properties, for example, improved photoelectric conversion efficiency, compared to conventional methods, more easily than conventional methods.

[0034] In a fourteenth aspect of the present disclosure, for example, in the composition according to the twelfth or thirteenth aspect, the ammonium salt may include at least one selected from the group consisting of tetrabutylammonium iodide and tetrabutylammonium fluoride.

[0035] The composition according to the fourteenth aspect is suitable for producing a film containing a perovskite compound that can realize improved properties, for example, improved photoelectric conversion efficiency, compared to conventional films, more easily than conventional films.

[0036] In a fifteenth aspect of the present disclosure, for example, the composition according to any one of the first to fourteenth aspects may further contain a compound containing F and the same element as the divalent cation contained in the perovskite compound precursor.

[0037] The composition according to the fifteenth aspect is suitable for producing a film containing a perovskite compound having properties comparable to those of conventional films more easily than conventional films.

[0038] A method for producing a photoelectric conversion layer according to a sixteenth aspect of the present disclosure includes producing a photoelectric conversion layer using a composition according to any one of the first to fifteenth aspects.

[0039] According to the production method of the sixteenth aspect, a film containing a perovskite compound having properties comparable to those of conventional films can be produced more easily than conventional films.

[0040] In a seventeenth aspect of the present disclosure, for example, in the manufacturing method according to the sixteenth aspect, the photoelectric conversion layer may be formed by spin coating the composition.

[0041] According to the manufacturing method of the seventeenth aspect, a film containing a perovskite compound having properties comparable to those of conventional films can be produced more easily than conventional films.

[0042] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0043] (First Embodiment) The composition of the first embodiment includes a perovskite compound precursor, a first solvent, and a second solvent. The first solvent has a boiling point of 50°C or higher, a dipole moment of 3.0D or less, and does not dissolve the perovskite compound formed from the perovskite compound precursor. The second solvent has a dipole moment of more than 3.0D and dissolves the perovskite compound.

[0044] According to the composition of the first embodiment having the above configuration, a film containing a perovskite compound having properties comparable to those of conventional films can be produced more easily than conventional films. As an example, the composition of the first embodiment can achieve a photoelectric conversion efficiency comparable to that of films containing conventional perovskite compounds. Furthermore, according to the composition of the first embodiment, for example, a film containing a homogeneous perovskite compound can also be produced easily and with high reproducibility. In other words, by producing a perovskite film using the composition of the first embodiment, variations within the film can be reduced.

[0045] Conventionally, when preparing a film containing a perovskite compound, a method is known in which a precursor solution of the perovskite compound is spin-coated onto a substrate on which the film containing the perovskite compound is to be prepared, while a poor solvent is dropped onto the substrate. In this method, the distance from the substrate to which the poor solvent is dropped and the flow rate of the dropped poor solvent are difficult to achieve with good reproducibility, especially when these are not fully automated. As a result, there are problems with the formation of a non-uniform film, or with the inability to achieve a homogeneous film with high reproducibility.

[0046] Furthermore, the conventional method of spin-coating a substrate on which a film containing a perovskite compound is to be formed while dropping a poor solvent onto the substrate has the problem of using a large amount of poor solvent. This problem is one of the causes of increased manufacturing costs, for example, when a large-area film containing a perovskite compound is to be formed. In contrast, when the composition of the first embodiment is used to form a film containing a perovskite compound, there is no need to drop a poor solvent as in the conventional method, and therefore the effect of being able to significantly reduce the amount of poor solvent can be obtained.

[0047] Non-Patent Document 1 discloses a method for forming a film by adding diethyl ether, a poor solvent, to a precursor solution of MAPbI, a perovskite compound. Note that "MA" stands for "CHNH." This method uses diethyl ether, which has a low boiling point, as the poor solvent, which poses a problem of evaporation of the poor solvent during spin coating or preparation of the precursor solution, even at room temperature.

[0048] By using the composition of the first embodiment as a precursor of a perovskite film, a homogeneous perovskite film can be produced with high reproducibility without using a complicated method of dropping a poor solvent with high precision.

[0049] Each component will be described below.

[0050] (First Solvent) The first solvent has a boiling point of 50°C or higher and a dipole moment of 3.0 D or less. The first solvent is a solvent that does not dissolve the perovskite compound. Here, in this specification, a solvent that does not dissolve the perovskite compound refers to a solvent in which the dissolved concentration of the perovskite compound does not exceed 0.01 mol / L.

[0051] To improve reproducibility, the first solvent may have a dipole moment of 1.78 D or less.

[0052] The first solvent may have a boiling point of 100° C. or higher.

[0053] The first solvent may contain a compound having a benzene ring.

[0054] The first solvent may include at least one selected from the group consisting of tetrahydrofuran, dipropyl ether, diisopropyl ether, toluene, chlorobenzene, methoxybenzene, and methoxytoluene.

[0055] The boiling points and dipole moments of tetrahydrofuran, dipropyl ether, diisopropyl ether, toluene, chlorobenzene, methoxybenzene, and 4-methoxytoluene are as follows:

[0056] Tetrahydrofuran: boiling point 66°C, dipole moment 1.75D Dipropyl ether: boiling point 90°C, dipole moment 1.15D Diisopropyl ether: boiling point 68°C, dipole moment 1.22D Toluene: boiling point 110.6°C, dipole moment 0.36D Chlorobenzene: boiling point 132°C, dipole moment 1.54D Methoxybenzene: boiling point 153.8°C, dipole moment 1.38D 4-Methoxytoluene: boiling point 175°C, dipole moment 1.20D

[0057] (Perovskite Compound Precursor) The perovskite compound precursor may contain monovalent cations, divalent cations, and monovalent anions.

[0058] Examples of monovalent cations include organic cations and inorganic cations. The monovalent cations may include inorganic cations. The monovalent cations may be inorganic cations.

[0059] An example of an organic cation is the methylammonium cation (CH3NH3 + ) or formamidinium cation (NH2CHNH2 + )

[0060] Examples of inorganic cations are the Cs or Rb cations.

[0061] Examples of divalent cations are Pb cations or Sn cations, i.e., the divalent cations may include at least one selected from the group consisting of Pb cations and Sn cations.

[0062] Second Solvent The second solvent has a dipole moment greater than 3.0D.

[0063] The second solvent may include at least one selected from the group consisting of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), gamma butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP).

[0064] The boiling points and dipole moments of DMSO, DMF, GBL, and NMP are as follows:

[0065] DMSO: boiling point 189°C, dipole moment 3.96D DMF: boiling point 153°C, dipole moment 3.82D GBL: boiling point 204°C, dipole moment 4.12D NMP: boiling point 202°C, dipole moment 4.09D

[0066] The volume ratio of the second solvent to the total of the first solvent and the second solvent may be 80% or more and 97% or less, or 85% or more and 93% or less.

[0067] (Other Components) The composition of the first embodiment may further contain an ammonium salt.

[0068] The composition of the first embodiment having the above configuration makes it possible to produce a film containing a perovskite compound with improved properties compared to conventional films, for example, a film containing a perovskite compound with improved photoelectric conversion efficiency. In other words, the composition of the first embodiment having the above configuration makes it possible to easily produce a photoelectric conversion layer with improved photoelectric conversion efficiency.

[0069] In order to obtain a film with improved photoelectric conversion efficiency, the ammonium salt may contain at least one selected from the group consisting of an alkyl group and an aryl group. The number of carbon atoms in the alkyl group may be 1 to 10. The number of carbon atoms in the alkyl group may be 1 to 7.

[0070] In order to obtain a film with improved photoelectric conversion efficiency, the ammonium salt may contain a quaternary ammonium salt. The ammonium salt may be a quaternary ammonium salt.

[0071] To obtain a film with improved photoelectric conversion efficiency, the ammonium salt may contain a halogen element, such as fluorine, chlorine, bromine, or iodine.

[0072] The ammonium salt may contain iodine. Examples of such ammonium salts are tetrapropylammonium iodide, tetrabutylammonium iodide, tetraamylammonium iodide, tetrahexylammonium iodide, or tetraheptylammonium iodide.

[0073] The ammonium salt may contain fluorine. An example of such an ammonium salt is tetrabutylammonium fluoride.

[0074] The ammonium salt may include at least one selected from the group consisting of tetrabutylammonium iodide (TBAI) and tetrabutylammonium fluoride (TBAF). That is, the composition of the first embodiment may further include at least one selected from the group consisting of tetrabutylammonium iodide (TBAI) and tetrabutylammonium fluoride (TBAF), in addition to the perovskite compound precursor and the first solvent.

[0075] The composition according to the first embodiment may further contain a compound containing F and the same element as the divalent cation contained in the perovskite compound precursor. For example, when the perovskite compound precursor contained in the composition according to the first embodiment contains Sn cations as divalent cations, the composition according to the first embodiment may contain SnF2 as the compound. When the perovskite compound to be produced contains Sn cations as divalent cations, the composition according to the first embodiment may further contain SnF2, thereby making it possible to obtain a perovskite compound film with reduced Sn defects.

[0076] The composition of the first embodiment can be produced, for example, by the following method.

[0077] The composition of the first embodiment can be obtained by, for example, mixing a perovskite compound precursor with a first solvent. A second solvent may also be mixed therewith.

[0078] Here, a case will be described in which the perovskite compound precursor contains a monovalent cation, a divalent cation, and a monovalent anion, and the monovalent anion is a halogen anion.

[0079] The perovskite compound precursor includes a first compound including a monovalent cation, such as CsI, and a halogen, and a second compound including a divalent cation, such as SnI2, and a halogen.

[0080] The composition of the first embodiment may further include a compound containing a divalent cation and F, such as SnF2.

[0081] An example of a method for producing a composition according to the first embodiment will be described below, taking as an example a case where the composition according to the first embodiment further contains, in addition to the perovskite compound precursor and the first solvent, a second solvent and a compound containing a divalent cation such as SnF2 and F. A first solution is prepared by adding the first compound containing a monovalent cation and a halogen and the second compound containing a divalent cation and a halogen to a mixed solvent of the first solvent and the second solvent. A second solution is prepared by adding the compound containing a divalent cation such as SnF2 and F to the second solvent. The composition according to the first embodiment is obtained by mixing the first solution and the second solution.

[0082] (Second embodiment) In the second embodiment, a method for producing a photoelectric conversion layer using the composition according to the first embodiment will be described. Hereinafter, in the second embodiment, a photoelectric conversion layer obtained using the composition of the first embodiment and a photoelectric conversion element including the photoelectric conversion layer will be described. The matters described in the first embodiment may be omitted as appropriate.

[0083] Hereinafter, the photoelectric conversion layer manufactured by the manufacturing method of the second embodiment will be referred to as the photoelectric conversion layer of the second embodiment. Also, a photoelectric conversion element including the photoelectric conversion layer manufactured by the manufacturing method of the second embodiment will be referred to as the photoelectric conversion element of the second embodiment.

[0084] The manufacturing method of the second embodiment includes producing a photoelectric conversion layer using the composition of the first embodiment.

[0085] The photoelectric conversion layer of the second embodiment is produced using the composition of the first embodiment. Therefore, the photoelectric conversion element of the second embodiment including the photoelectric conversion layer of the second embodiment has high photoelectric conversion efficiency.

[0086] In the manufacturing method of the second embodiment, the photoelectric conversion layer may be formed by spin coating the composition of the first embodiment.

[0087] The photoelectric conversion element of the second embodiment is not particularly limited. For example, the photoelectric conversion element of the second embodiment includes a first electrode, a photoelectric conversion layer, and a second electrode in this order. The photoelectric conversion element of the second embodiment is, for example, a solar cell, a light-emitting element, or a photosensor.

[0088] The photoelectric conversion element of the second embodiment is, for example, a solar cell. The solar cell is, for example, a perovskite solar cell.

[0089] FIG. 1 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 100 according to the second embodiment.

[0090] The photoelectric conversion element 100 according to the second embodiment includes a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6 in this order.

[0091] The photoelectric conversion layer 4 is produced using the composition of the first embodiment.

[0092] The photoelectric conversion element 100 may not include the substrate 1 , the electron transport layer 3 , and the hole transport layer 5 .

[0093] When light is irradiated onto the photoelectric conversion element 100, the photoelectric conversion layer 4 absorbs the light and separates into electrons and holes. Electrons generated by this charge separation pass through the electron transport layer 3 and move to the first electrode 2. Meanwhile, holes generated in the photoelectric conversion layer 4 move to the second electrode 6 via the hole transport layer 5. This allows the photoelectric conversion element 100 to extract current from the first electrode 2, which functions as a negative electrode, and the second electrode 6, which functions as a positive electrode.

[0094] Each component of the photoelectric conversion element 100 will be specifically described below.

[0095] (Substrate 1) This plays a role of supporting each layer of the photoelectric conversion element 100.

[0096] The substrate 1 can be made of a transparent material, such as a glass substrate or a plastic substrate. The plastic substrate can be, for example, a plastic film.

[0097] When the second electrode 6 is light-transmitting, the substrate 1 may be made of a material that does not transmit light, such as a metal, a ceramic, or a resin material with low light transmittance.

[0098] If the first electrode 2 has sufficient strength, the layers can be held by the first electrode 2, and therefore the substrate 1 does not need to be provided.

[0099] (First Electrode 2) The first electrode 2 has electrical conductivity.

[0100] The first electrode 2 has a light-transmitting property, for example, transmitting light in the visible to near-infrared region.

[0101] The first electrode 2 is made of, for example, a transparent and conductive material. Examples of such materials include metal oxides and metal nitrides. Examples of such materials include: (i) titanium oxide doped with at least one element selected from the group consisting of lithium, magnesium, niobium, and fluorine; (ii) gallium oxide doped with at least one element selected from the group consisting of tin and silicon; (iii) gallium nitride doped with at least one element selected from the group consisting of silicon and oxygen; (iv) tin oxide doped with at least one element selected from the group consisting of antimony and fluorine; (v) zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium; (vi) indium-tin composite oxide; or (vii) a composite thereof.

[0102] The first electrode 2 may be formed with a light-transmitting pattern. Examples of the light-transmitting pattern include a linear, wavy, lattice, or punched metal pattern in which a large number of fine through-holes are regularly or irregularly arranged. When the first electrode 2 has such a pattern, light can pass through portions where no electrode material is present. Therefore, by providing a light-transmitting pattern, a non-transparent material can be used. Examples of non-transparent electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of these. A conductive carbon material may also be used as the non-transparent electrode material.

[0103] The light-transmitting property of the first electrode 2 does not have to be achieved by the light-transmitting pattern described above. For example, the first electrode 2 may be formed of a thin metal film formed to a thickness of about 10 nm. Such a thin metal film may be, for example, platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of these. Instead of these metal materials, a conductive carbon material may be used.

[0104] When the photoelectric conversion element 100 does not include the electron transport layer 3, the first electrode 2 has a blocking property for holes from the photoelectric conversion layer 4. In this case, the first electrode 2 does not make ohmic contact with the photoelectric conversion layer 4. Furthermore, the blocking property for holes from the photoelectric conversion layer 4 refers to a property that allows only electrons generated in the photoelectric conversion layer 4 to pass through, but does not allow holes to pass through. The Fermi energy of a material having such a property is higher than the energy of the top of the valence band of the photoelectric conversion layer 4. The Fermi energy of a material having such a property may be higher than the Fermi energy of the photoelectric conversion layer 4. A specific example of such a material is aluminum.

[0105] When the photoelectric conversion element 100 includes the electron transport layer 3, the first electrode 2 does not need to have the ability to block holes from the photoelectric conversion layer 4. In this case, the first electrode 2 may be made of a material that can form an ohmic contact with the photoelectric conversion layer 4. In this case, the first electrode 2 may or may not be in ohmic contact with the photoelectric conversion layer 4.

[0106] The light transmittance of the first electrode 2 may be, for example, 50% or more, or 80% or more. The wavelength of light that the first electrode 2 should transmit depends on the absorption wavelength of the photoelectric conversion layer 4.

[0107] The thickness of the first electrode 2 may be, for example, not less than 1 nm and not more than 1000 nm.

[0108] (Electron Transport Layer 3) The electron transport layer 3 contains an electron transport material. The electron transport material is a material that transports electrons. The electron transport material may be a semiconductor. The electron transport layer 3 may be formed from a semiconductor having a band gap of 3.0 eV or more. This allows visible light and infrared light to transmit to the photoelectric conversion layer 4.

[0109] Examples of electron transporting materials are inorganic n-type semiconductors.

[0110] Examples of inorganic n-type semiconductors include metal oxides, metal nitrides, and perovskite oxides. Examples of metal oxides include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Examples of metal oxides include TiO2 or SnO2. Examples of metal nitrides include GaN. Examples of perovskite oxides include SrTiO3 or CaTiO3.

[0111] To allow ultraviolet light to effectively pass through to the photoelectric conversion layer 4, the electron transport layer 3 may be made of a semiconductor having a band gap of 6.0 eV or more. Examples of such semiconductors include alkali metal or alkaline earth metal halides such as lithium fluoride and calcium fluoride, alkali metal oxides such as magnesium oxide, and silicon dioxide. In this case, in order to ensure the electron transport properties of the electron transport layer 3, the electron transport layer 3 may have a thickness of, for example, 10 nm or less.

[0112] The electron transport layer 3 may include a plurality of layers made of different materials.

[0113] (Photoelectric conversion layer 4) The photoelectric conversion layer 4 includes a photoelectric conversion material. The photoelectric conversion layer 4 is produced using the composition of the first embodiment. The perovskite compound is represented, for example, by the composition formula ABX3. Here, A is a monovalent cation, B is a divalent metal cation, and X is a monovalent anion.

[0114] Examples of monovalent cations A are organic cations or alkali metal cations.

[0115] An example of an organic cation is the methylammonium cation (CH3NH3 + ) or formamidinium cation (NH2CHNH2 + )

[0116] Examples of alkali metal cations are the Cs cation or the Rb cation.

[0117] Examples of divalent cations B are Pb or Sn cations.

[0118] Examples of monovalent anions X are halogen anions, such as chlorine, bromine, or iodine.

[0119] A, B, and X may each contain multiple types of ions.

[0120] The thickness of the photoelectric conversion layer 4 is, for example, not less than 50 nm and not more than 10 μm.

[0121] (Hole Transport Layer 5) The hole transport layer 5 contains a hole transport material. The hole transport material is a material that transports holes. The hole transport material is, for example, an organic semiconductor or an inorganic semiconductor.

[0122] Examples of organic semiconductors are triphenylamine, triallylamine, phenylbenzidine, phenylenevinylene, tetrathiafulvalene, vinylnaphthalene, vinylcarbazole, thiophene, aniline, pyrrole, carbazole, triptycene, fluorene, azulene, pyrene, pentacene, perylene, acridine, or phthalocyanine.

[0123] Typical examples of organic semiconductors used as hole transport materials include 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter also referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl), poly(3,4-ethylenedioxythiophene), and copper phthalocyanine.

[0124] The inorganic semiconductor used as the hole transport material is a p-type semiconductor. Examples of inorganic semiconductors include CuO, CuGaO, CuSCN, CuI, and NiO. x , MoO x , VO, or a carbon material such as graphene oxide, where x satisfies x>0.

[0125] The hole transport layer 5 may include multiple layers made of different materials. For example, multiple layers may be stacked so that the ionization potentials of the hole transport layers 5 are successively smaller than the ionization potential of the photoelectric conversion layer 4, thereby improving the hole transport properties.

[0126] The thickness of the hole transport layer 5 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 50 nm or less. This allows sufficient hole transport properties to be exhibited. Therefore, the photoelectric conversion element can maintain low resistance and achieve high photoelectric conversion efficiency.

[0127] The hole transport layer 5 is formed by, for example, a coating method, a printing method, or a vapor deposition method, similar to the photoelectric conversion layer 4. Examples of coating methods include a doctor blade method, a bar coating method, a spray method, a dip coating method, an inkjet method, a slit coating method (i.e., a die coating method), or a spin coating method. An example of a printing method is a screen printing method. If necessary, the hole transport layer 5 may be prepared by mixing multiple materials, and then pressurized or baked. When the material of the hole transport layer 5 is an organic low-molecular-weight substance or an inorganic semiconductor, the hole transport layer 5 can also be prepared by a vacuum vapor deposition method.

[0128] The hole transport layer 5 may contain not only a hole transport material but also an additive to enhance conductivity. Examples of the additive are a supporting electrolyte, a solvent, or a dopant. The supporting electrolyte and the solvent have the effect of stabilizing holes in the hole transport layer 5. The dopant has the effect of increasing the number of holes in the hole transport layer 5.

[0129] Examples of supporting electrolytes include ammonium salts, alkaline earth metal salts, and transition metal salts. Examples of ammonium salts include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts, and pyridinium salts. Examples of alkali metal salts include lithium perchlorate and potassium tetrafluoride. Examples of alkaline earth metal salts include lithium bis(trifluoromethanesulfonyl)imide and calcium(II) bis(trifluoromethanesulfonyl)imide. Examples of transition metal salts include zinc(II) bis(trifluoromethanesulfonyl)imide and tris[4-tert-butyl-2-(1H-pyrazol-1-yl)pyridine]cobalt(III) tris(trifluoromethanesulfonyl)imide.

[0130] An example of the dopant is a fluorine-containing aromatic boron compound, such as tris(pentafluorophenyl)borane.

[0131] The solvent contained in the hole transport layer 5 may have excellent ion conductivity. The solvent may be an aqueous solvent or an organic solvent. In order to further stabilize the solute, the solvent contained in the hole transport layer 5 may be an organic solvent. Examples of the organic solvent are heterocyclic compound solvents such as tert-butylpyridine, pyridine, and n-methylpyrrolidone.

[0132] Ionic liquids may be used as the solvent. The ionic liquids may be used alone or in combination with other solvents. Ionic liquids are desirable because of their low volatility and high flame retardancy.

[0133] Examples of ionic liquids are imidazolium-based ionic liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine-based ionic liquids, alicyclic amine-based ionic liquids, aliphatic amine-based ionic liquids, or azonium amine-based ionic liquids.

[0134] (Second Electrode 6) The second electrode 6 has electrical conductivity.

[0135] When the photoelectric conversion element 100 does not include the hole transport layer 5, the second electrode 6 has a blocking property for electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 does not make ohmic contact with the photoelectric conversion layer 4. The blocking property for electrons from the photoelectric conversion layer 4 means a property of passing only holes generated in the photoelectric conversion layer 4 and not passing electrons. The Fermi energy of a material having such a property is lower than the energy of the bottom of the conduction band of the photoelectric conversion layer 4. The Fermi energy of a material having such a property may be lower than the Fermi energy of the photoelectric conversion layer 4. Specific examples of such materials include platinum, gold, and carbon materials such as graphene.

[0136] When the photoelectric conversion element 100 includes the hole transport layer 5, the second electrode 6 does not need to have a blocking property for electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 may be made of a material that can form an ohmic contact with the photoelectric conversion layer 4. This allows the second electrode 6 to be formed to have light-transmitting properties.

[0137] Of the first electrode 2 and the second electrode 6, it is sufficient that the electrode on the light incident side has light-transmitting properties. Therefore, one of the first electrode 2 and the second electrode 6 does not have to have light-transmitting properties. In other words, one of the first electrode 2 and the second electrode 6 does not have to use a light-transmitting material or have a pattern including openings that transmit light.

[0138] (Porous Layer) The porous layer is formed on the electron transport layer 3 by, for example, a coating method. When the photoelectric conversion element 100 does not include the electron transport layer 3, the porous layer is formed on the first electrode 2.

[0139] The pore structure introduced by the porous layer serves as a base for forming the photoelectric conversion layer 4. The porous layer does not inhibit light absorption by the photoelectric conversion layer 4 or electron transfer from the photoelectric conversion layer 4 to the electron transport layer 3.

[0140] The porous layer includes a porous body.

[0141] The porous body is formed, for example, by a series of insulating or semiconducting particles. Examples of insulating particles include aluminum oxide particles or silicon oxide particles. Examples of semiconducting particles include inorganic semiconductor particles. Examples of inorganic semiconductors include metal oxides, perovskite oxides of metal elements, sulfides of metal elements, and metal chalcogenides. Examples of metal oxides include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Examples of metal oxides include TiO2. Examples of perovskite oxides of metal elements include SrTiO3 or CaTiO3. Examples of sulfides of metal elements are CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides are CsSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0142] The thickness of the porous layer may be 0.01 μm or more and 10 μm or less, or 0.05 μm or more and 1 μm or less.

[0143] The surface roughness of the porous layer may have a surface roughness coefficient of 10 or more, or even 100 or more, given by effective area / projected area. Projected area is the area of ​​the shadow cast behind an object when it is illuminated with light from directly in front of it. Effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume determined from the projected area and thickness of the object, and the specific surface area and bulk density of the material that makes up the object. The specific surface area is measured, for example, by nitrogen adsorption.

[0144] The voids in the porous layer are connected from one main surface of the porous layer to the other main surface. That is, the voids in the porous layer are connected from the main surface of the porous layer in contact with the photoelectric conversion layer 4 to the main surface of the porous layer in contact with the electron transport layer 3. This allows the material of the photoelectric conversion layer 4 to fill the voids in the porous layer and reach the surface of the electron transport layer 3. Therefore, the photoelectric conversion layer 4 and the electron transport layer 3 are in direct contact with each other, allowing electrons to be exchanged.

[0145] The provision of a porous layer has the effect of facilitating the formation of the photoelectric conversion layer 4. By providing the porous layer, the material of the photoelectric conversion layer 4 penetrates into the voids in the porous layer, and the porous layer serves as a scaffold for the photoelectric conversion layer 4. Therefore, the material of the photoelectric conversion layer 4 is less likely to be repelled or aggregate on the surface of the porous layer. Therefore, the photoelectric conversion layer 4 can be easily formed as a uniform film. The photoelectric conversion layer 4 can be formed by the above-mentioned coating method, printing method, vapor deposition method, or the like.

[0146] Light scattering caused by the porous layer is also expected to have the effect of increasing the optical path length of light passing through the photoelectric conversion layer 4. When the optical path length increases, the amount of electrons and holes generated in the photoelectric conversion layer 4 is expected to increase.

[0147] Hereinafter, the present disclosure will be described in more detail with reference to examples.

[0148] Hereinafter, preparation of raw material solutions for the photoelectric conversion layer and the hole transport layer and film formation were carried out in a glove box with oxygen and moisture concentrations of 1 ppm or less.

[0149] <Fabrication of Photoelectric Conversion Element: Examples 1 to 6> First, a glass substrate was prepared. The substrate serves as a support material for the photoelectric conversion element of the present disclosure.

[0150] An ITO (Indium Tin Oxide) layer and an ATO (Antimony Tin Oxide) layer were formed in this order on the substrate by sputtering, thus forming a first electrode.

[0151] Next, a dense layer of titanium oxide (TiO2) was formed on the ATO layer by sputtering. This dense layer of titanium oxide corresponds to, for example, the electron transport layer described in the second embodiment above.

[0152] Next, 0.45 g of titanium oxide paste (30NR-D, manufactured by Gratcell Solar Materials Pty Ltd.) was dissolved in 2 mL of butanol solution. The resulting solution was applied to the electron transport layer by spin coating and then baked at 500°C for 20 minutes. In this way, a porous titanium oxide layer was formed. Spin coating was performed at 4000 rpm for 20 seconds. Both the dense titanium oxide layer and the porous titanium oxide layer possess electron transport properties. Therefore, it is also possible to consider that the electron transport layer is composed of the dense titanium oxide layer and the porous titanium oxide layer.

[0153] The precursor solution for the photoelectric conversion layer was applied to the porous layer by spin coating, and then allowed to stand at room temperature for 10 minutes. The resulting mixture was then baked at 160°C for 1 minute and then at 220°C for 10 minutes. Thus, a photoelectric conversion layer was formed. Spin coating was performed at 5000 rpm for 30 seconds. No poor solvent was added dropwise during spin coating.

[0154] The precursor solutions for the photoelectric conversion layer in the examples were obtained as follows. The precursor solutions for the photoelectric conversion layer in the examples correspond to the composition of the first embodiment. First, a 1.2 mol / L first solution was prepared by adding SnI and CsI to a mixed solvent of DMF, DMSO, and a first solvent (volume ratio of DMF:DMSO:first solvent = 2:7:1). Tetrahydrofuran, diisopropyl ether, dipropyl ether, chlorobenzene, methoxybenzene, and 4-methoxytoluene were used as the first solvents in Examples 1 to 6.

[0155] Next, a second solution (1.2 mol / L) was prepared by adding SnF to a mixed solvent of DMF and DMSO (DMF:DMSO = 1:4 by volume), and a third solution (1.2 mol / L) was prepared by adding TBAI to a mixed solvent of DMF and DMSO (DMF:DMSO = 1:4 by volume).

[0156] The second solution and the third solution were added to the first solution. Thus, a precursor solution of the photoelectric conversion layer in the example was obtained. The precursor solution in the example contained DMF and DMSO as the second solvent. In the example, the volume ratio of the second solvent to the total volume of the first solvent and the second solvent was 92%.

[0157] In the precursor solution of the photoelectric conversion layer, the additive concentration of the second solution was 16 mol %, and the additive concentration of the third solution was 5 mol %. As described above, the photoelectric conversion layer was obtained by baking the coated film of the precursor solution at 160°C for 1 minute and then baking it at 220°C for 10 minutes.

[0158] Next, the raw material solution for the hole transport layer was applied onto the photoelectric conversion layer by spin coating. In this way, the hole transport layer was formed. The raw material solution for the hole transport layer was prepared by dissolving 18 mg of PTAA (poly[bis(4-phenyl)(2,4,6-triphenyl)amine]) in 1 mL of chlorobenzene. Spin coating was performed at 4000 rpm for 20 seconds.

[0159] Next, a gold film was formed on the hole transport layer by vapor deposition, thus forming a second electrode having a thickness of 200 nm.

[0160] Finally, a UV-curable epoxy resin was applied to the periphery of the substrate, and the substrate was attached to another glass substrate and irradiated with UV light. In this way, the epoxy resin was cured and the power generating element was sealed.

[0161] <Fabrication of Photoelectric Conversion Elements: Reference Examples 1 to 6> The processes from the formation of the glass substrate to the formation of the electron transport layer were carried out in the same manner as in the Examples.

[0162] The precursor solution for the photoelectric conversion layer was applied to the porous layer by spin coating, and then allowed to stand at room temperature for 10 minutes. The layer was then baked at 160°C for 1 minute, followed by 220°C for 10 minutes. In this way, the photoelectric conversion layer was formed. Spin coating was performed at 5000 rpm for 30 seconds. A solvent with a small dipole moment was added dropwise during spin coating. The solvents used with a small dipole moment were tetrahydrofuran, which has properties between a poor solvent and a good solvent, and diisopropyl ether, dipropyl ether, methoxybenzene, 4-methoxytoluene, and toluene, which are poor solvents.

[0163] The precursor solutions of the photoelectric conversion layer in Reference Examples 1 to 6 were obtained as follows. First, a 1.2 mol / L first solution was prepared by adding SnI2 and CsI to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4). Next, a 1.2 mol / L second solution was prepared by adding SnF2 to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4). Next, a 1.2 mol / L third solution was prepared by adding TBAI to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4).

[0164] The second solution and the third solution were added to the first solution, thereby obtaining precursor solutions for the photoelectric conversion layers in Reference Examples 1 to 6.

[0165] In the precursor solution of the photoelectric conversion layer, the additive concentration of the second solution was 16 mol %, and the additive concentration of the third solution was 5 mol %. As described above, the photoelectric conversion layer was obtained by baking the coated film of the precursor solution at 160°C for 1 minute and then baking it at 220°C for 10 minutes.

[0166] The subsequent steps from the formation of the hole transport layer to sealing were carried out in the same manner as in the example.

[0167] <Fabrication of Photoelectric Conversion Element: Reference Examples 7 and 8> The steps from the formation of the glass substrate to the formation of the electron transport layer were carried out in the same manner as in the Examples.

[0168] The precursor solution of the photoelectric conversion layer was applied to the porous layer by spin coating, and then allowed to stand at room temperature for 10 minutes. The layer was then baked at 160°C for 1 minute and then at 220°C for 10 minutes. Thus, a photoelectric conversion layer was formed. Note that, unlike Reference Examples 1 to 6, in Reference Examples 7 and 8, no poor solvent was added dropwise during spin coating.

[0169] The precursor solution of the photoelectric conversion layer in Reference Example 7 was obtained as follows. First, SnI2 and CsI were added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 0.9 mol / L first solution. Next, SnF2 was added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 0.9 mol / L second solution. Next, TBAI was added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 0.9 mol / L third solution.

[0170] The precursor solution of the photoelectric conversion layer in Reference Example 8 was obtained as follows. First, SnI2 and CsI were added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 1.5 mol / L first solution. Next, SnF2 was added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 1.5 mol / L second solution. Next, TBAI was added to a mixed solvent of DMF and DMSO (volume ratio of DMF:DMSO = 1:4) to prepare a 1.5 mol / L third solution.

[0171] In Reference Examples 7 and 8, the precursor solutions for the photoelectric conversion layer had an additive concentration of the second solution of 16 mol % and an additive concentration of the third solution of 5 mol %. As described above, the photoelectric conversion layer was obtained by baking the coated film of the precursor solution at 160°C for 1 minute and then baking it at 220°C for 10 minutes.

[0172] <Evaluation of Characteristics of Photoelectric Conversion Element> The photoelectric conversion elements of the examples and reference examples were evaluated for current-voltage characteristics (i.e., IV characteristics).

[0173] The characteristics were evaluated using a solar simulator (manufactured by Bunkoukeiki Co., Ltd.) and an electrochemical analyzer ALS (manufactured by BAS Co., Ltd.). The photoelectric conversion element was irradiated with simulated sunlight of 1 sun. The output of the solar simulator was 100 mW / cm. 2 The IV characteristics of the photoelectric conversion element were measured by measuring the output current value while changing the applied voltage using an electrochemical analyzer.

[0174] Fig. 2 is a graph showing IV curves of the photoelectric conversion elements of Examples 1 to 6. Fig. 3 is a graph showing IV curves of the photoelectric conversion elements of Reference Examples 1 to 6. Fig. 4 is a graph showing IV curves of the photoelectric conversion elements of Reference Examples 7 and 8.

[0175] The measurement results of Examples 1 to 6 are shown in Table 1. The measurement results of Reference Examples 1 to 6 are shown in Table 2. The measurement results of Reference Examples 7 and 8 are shown in Table 3. η in the table represents conversion efficiency. J SC represents the short-circuit current density. oc represents the open circuit voltage. FF represents the fill factor.

[0176]

[0177]

[0178]

[0179] (Discussion) The photoelectric conversion elements of Examples 1 to 6 have IV characteristics equal to or better than those of the photoelectric conversion elements of Reference Examples 1 to 6, which were prepared by a conventional method (i.e., a method in which a poor solvent is dropped). As can be seen from FIG. 4 and Table 3, the photoelectric conversion elements of Reference Examples 7 and 8, which were prepared without using any poor solvent, had significantly poorer characteristics than the photoelectric conversion elements of Examples 1 to 6 and Reference Examples 1 to 6.

[0180] The photoelectric conversion elements of the Examples could be easily prepared because no poor solvent was added when spin-coating the precursor solution for the photoelectric conversion layer. Furthermore, in the Examples, the amount of poor solvent used could be reduced to about 1 / 18 of that used in conventional methods. Furthermore, in Reference Examples 7 and 8, in which no poor solvent was used at all, the device characteristics were significantly reduced. This shows that poor solvents significantly affect the performance of the resulting photoelectric conversion element, specifically the performance of the resulting photoelectric conversion layer. Furthermore, it is clear that adding a poor solvent that affects performance in this way is likely to cause characteristic variations. In the Examples, it is believed that a homogeneous film was prepared because the operation of adding a poor solvent, which is likely to cause variations in the resulting film (in this Example, the photoelectric conversion layer), was not performed.

[0181] As is clear from a comparison of Example 1 with Reference Example 1, when tetrahydrofuran was used as a poor solvent, the photoelectric conversion element prepared by the conventional method did not exhibit photoelectric conversion characteristics, whereas the photoelectric conversion element prepared by the method of the present invention exhibited good IV characteristics.

[0182] The photoelectric conversion element of the present disclosure can be used, for example, in a solar cell.

Claims

1. A perovskite compound precursor, a first solvent, and a second solvent, the first solvent has a boiling point of 50° C. or higher, a dipole moment of 3.0 D or less, and does not dissolve the perovskite compound formed from the perovskite compound precursor; The second solvent has a dipole moment greater than 3.0 D and dissolves the perovskite compound. composition.

2. The first solvent has a dipole moment of 1.78 D or less. The composition of claim 1.

3. The first solvent has a boiling point of 100° C. or higher. The composition of claim 1.

4. The first solvent contains a compound having a benzene ring. The composition of claim 1.

5. The first solvent includes at least one selected from the group consisting of tetrahydrofuran, dipropyl ether, diisopropyl ether, toluene, chlorobenzene, methoxybenzene, and methoxytoluene; The composition of claim 1.

6. The perovskite compound precursor comprises a monovalent cation, a divalent cation, and a monovalent anion. The composition of claim 1.

7. The monovalent cation includes an inorganic cation. The composition of claim 6.

8. The divalent cation includes at least one selected from the group consisting of Pb cations and Sn cations; The composition of claim 6.

9. The second solvent includes at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, gamma butyrolactone, and N-methyl-2-pyrrolidone; The composition of claim 1.

10. A volume ratio of the second solvent to the total volume of the first solvent and the second solvent is 80% or more and 97% or less. The composition of claim 1.

11. The volume ratio is 85% or more and 93% or less. The composition of claim 10.

12. Further comprising an ammonium salt, The composition of claim 1.

13. The ammonium salt includes a quaternary ammonium salt. The composition of claim 12.

14. The ammonium salt includes at least one selected from the group consisting of tetrabutylammonium iodide and tetrabutylammonium fluoride. The composition of claim 12.

15. The perovskite compound precursor further contains a compound containing F and the same element as the divalent cation contained in the perovskite compound precursor. The composition of claim 1.

16. Producing a photoelectric conversion layer using the composition according to any one of claims 1 to 15; The method for producing a photoelectric conversion layer includes the steps of:

17. The photoelectric conversion layer is prepared by spin-coating the composition. The method for producing a photoelectric conversion layer according to claim 16 .