JP2022088091A - Photoelectric conversion element and manufacturing method of the same - Google Patents

Abstract

To provide a photoelectric conversion element having an excellent photoelectric conversion efficiency and a low manufacturing cost, and provide a manufacturing method of the same.SOLUTION: A photoelectric conversion element 20 comprises: an electronic transportation layer 4; a hole transport layer 7; and a light absorption layer 6 arranged between the electronic transportation layer 4 and the hole transport layer 7. The light absorption layer 6 includes a porous region including a needle crystal particle of a perovskite compound. The hole transport layer 7 contains a hole transport material and a polycarbonate resin.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photoelectric conversion element and a method for manufacturing the same.

Photoelectric conversion elements are used in, for example, optical sensors, copiers, and solar cells. Among these, solar cells are becoming widespread in earnest as a typical method of using renewable energy. As the solar cell, a solar cell using an inorganic photoelectric conversion element (for example, a silicon-based solar cell, a CIGS-based solar cell, and a CdTe-based solar cell) has become widespread.

As the solar cell, a solar cell using an organic photoelectric conversion element (for example, an organic thin film solar cell, a dye-sensitized solar cell, a perovskite type solar cell, etc.) is also being studied. Since a solar cell using such an organic photoelectric conversion element can be manufactured by a coating process, there is a possibility that the manufacturing cost can be reduced. Therefore, a solar cell using an organic photoelectric conversion element is expected as a next-generation solar cell. In particular, perovskite solar cells have been actively studied (see, for example, Patent Documents 1 and 2).

WO2016 / 152704A1 WO2017 / 104792A1

However, the shape of the crystal particles of the perovskite compound is easily affected by the moisture (humidity) present in the production environment. Specifically, when a photoelectric conversion element using a perovskite compound is formed in an atmospheric atmosphere (particularly, in an atmospheric atmosphere with a humidity of 50% RH or more), needle-like crystal particles of the perovskite compound are formed due to the influence of moisture and are porous. A quality light absorption layer is formed. When the charge transport layer is formed by coating on such a porous light absorption layer, the charge transport material permeates into the pores (voids) of the porous light absorption layer, and the photoelectric conversion efficiency is lowered due to a short circuit. do. Therefore, the photoelectric conversion element using the perovskite compound is generally manufactured in an environment where the humidity is as low as possible (for example, in a glove box). In such an environment, since plate-like crystal particles of the perovskite compound are formed, it is possible to suppress a decrease in photoelectric conversion efficiency due to the above-mentioned short circuit. However, if a photoelectric conversion element using a perovskite compound is manufactured in such an environment, the manufacturing cost increases. Further, when the perovskite solar cell absorbs moisture, the perovskite crystals are decomposed and the photoelectric conversion characteristics are deteriorated.
The present invention has been made in view of the above-mentioned problems, and provides a photoelectric conversion element having excellent photoelectric conversion efficiency and low manufacturing cost, and a method for manufacturing the same.

The present invention includes an electron transport layer, a hole transport layer, and a light absorption layer arranged between the electron transport layer and the hole transport layer, and the light absorption layer is a needle-like crystal particle of a perovskite compound. Provided is a photoelectric conversion element having a porous region containing, wherein the hole transport layer contains a hole transport material and a polycarbonate resin represented by the following structural formula.

式中、Ｒ₃、Ｒ₄、Ｒ₅又はＲ₆は、同一又は異なって、水素原子、ハロゲン原子、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基である、Ｚは 置換基を有してもよい環状アルキルを形成するのに必要な原子群である。

In the formula, R ₃ , R ₄ , R ₅ or R ₆ is an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group which may have a hydrogen atom, a halogen atom and a substituent, which may be the same or different. , Z is a group of atoms required to form a cyclic alkyl which may have a substituent.

The light absorbing layer has a porous region containing acicular crystal particles of a perovskite compound. Therefore, the light absorption layer can be formed in the atmosphere of the atmosphere, and the manufacturing cost of the photoelectric conversion element can be reduced.
Even when the hole transport layer is formed on the light absorption layer (including the inside of the pores) having the porous region containing the acicular crystal particles of the perovskite compound, since the hole transport layer contains the polycarbonate resin, It is possible to prevent the hole transport material contained in the hole transport layer from coming into contact with the electron transport layer, and it is possible to suppress a decrease in photoelectric conversion efficiency due to a short circuit. In addition, this polycarbonate resin has excellent gas barrier properties and coats the light absorption layer in a state where electric charges can be exchanged between the needle-shaped crystal particles of the perovskite compound and the hole transport material, so that moisture and oxidizing gas are emitted. Deterioration of the perovskite compound due to infiltration into the absorption layer can be suppressed. Therefore, the durability and moisture resistance of the photoelectric conversion element can be improved. Further, since the polycarbonate resin has flexibility and is excellent in mechanical strength, the mechanical strength of the photoelectric conversion element can be improved.
Since the hole transport layer contains the polycarbonate resin represented by the structural formula of Chemical formula 1, it is possible to use a solvent that does not erode perovskite compounds such as toluene and chlorobenzene when the hole transport layer is formed by the coating method. It is possible to prevent the perovskite compound from being deteriorated by the solvent.

It is a schematic sectional drawing of the photoelectric conversion element of one Embodiment of this invention. It is a schematic sectional drawing of the photoelectric conversion element of one Embodiment of this invention. It is a figure which shows the basic unit cell of the crystal structure of a perovskite compound. It is a photograph of the light absorption layer of a photoelectric conversion element (A-1). It is a photograph of the hole transport layer of a photoelectric conversion element (A-1). It is a photograph of the light absorption layer of a photoelectric conversion element (A-3). It is a photograph of the hole transport layer of the photoelectric conversion element (A-3).

The photoelectric conversion element of the present invention includes an electron transport layer, a hole transport layer, and a light absorption layer arranged between the electron transport layer and the hole transport layer, and the light absorption layer is made of a perovskite compound. It has a porous region containing needle-shaped crystal particles, and the hole transport layer is characterized by containing a hole transport material and a polycarbonate resin represented by the following structural formula.

式中、Ｒ₃、Ｒ₄、Ｒ₅又はＲ₆は、同一又は異なって、水素原子、ハロゲン原子、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基である、Ｚは 置換基を有してもよい環状アルキルを形成するのに必要な原子群である。

In the formula, R ₃ , R ₄ , R ₅ or R ₆ is an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group which may have a hydrogen atom, a halogen atom and a substituent, which may be the same or different. , Z is a group of atoms required to form a cyclic alkyl which may have a substituent.

The present invention comprises a first charge transport layer forming step of forming a first charge transport layer containing a first charge transport material, and a light absorption layer forming step of forming a light absorption layer on the first charge transport layer. Also provided is a method for manufacturing a photoelectric conversion element including a second charge transport layer forming step of forming a second charge transport layer containing a second charge transport material on the light absorption layer. Here, of the first charge transport layer containing the first charge transport material and the second charge transport layer containing the second charge transport material, one is an electron transport layer containing an electron transport material and the other is an electron transport layer. It is a hole transport layer containing a hole transport material, the light absorption layer has a porous region containing acicular crystal particles of a perovskite compound, and the hole transport layer contains a polycarbonate resin and the hole transport material. contains.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiment, and can be appropriately modified within the scope of the object of the present invention. In the drawings, the same or corresponding parts may be referred to with the same reference numerals and description thereof may be omitted. Unless otherwise specified, each material described in the embodiment of the present invention may be used alone or in combination of two or more.

<First Embodiment: Photoelectric conversion element>
The first embodiment relates to a photoelectric conversion element. The photoelectric conversion element according to the present embodiment includes an electron transport layer, a hole transport layer, and a light absorption layer. The light absorption layer is arranged between the electron transport layer and the hole transport layer. The light absorption layer contains acicular crystal particles of the perovskite compound. The hole transport layer contains a polycarbonate resin and carbon nanotubes (hole transport material) or a specific organic charge transport material (hole transport material).

1 and 2 are schematic cross-sectional views of the photoelectric conversion element of the present embodiment.
Hereinafter, the photoelectric conversion element 20 according to the present embodiment will be described with reference to FIGS. 1 and 2. The photoelectric conversion element 20 shown in FIG. 1 has a substrate 2, a first conductive layer 3, an electron transport layer 4, a light absorption layer 6, a hole transport layer 7, and a second conductive layer in order from one surface. Equipped with 8. As shown in FIG. 1, the electron transport layer 4 has a two-layer structure including a dense titanium oxide layer 11 on the first conductive layer 3 side and a porous titanium oxide layer 12 on the light absorption layer 6 side. However, as shown in FIG. 2, the electron transport layer 4 may have a one-layer structure including only the dense titanium oxide layer 11. When the photoelectric conversion element 20 is used, for example, the surface on the substrate 2 side is irradiated with light (for example, sunlight) (in this case, the substrate 2 can be a transparent substrate). However, when the photoelectric conversion element 20 is used, the surface on the second conductive layer 8 side may be irradiated with light.

As described above, the light absorption layer 6 contains acicular crystal particles of the perovskite compound. The hole transport layer 7 contains carbon nanotubes (hole transport material) or a specific organic charge transport material (hole transport material), and a polycarbonate resin. The photoelectric conversion element 20 according to the present embodiment having such a configuration has the following first to fifth advantages.

The first advantage will be described. The light absorption layer 6 has a porous region formed by a plurality of acicular crystal particles of the perovskite compound. When the hole transport material permeates the pores (voids) in the porous region of the light absorption layer 6 when the hole transport layer is formed, the electron transport material and the hole transport material contained in the electron transport layer 4 are separated from each other. In close proximity or contact, electrical resistance may decrease, causing a short circuit between the conductive layers (ie, between the first conductive layer 3 and the second conductive layer 8). Further, when the hole transport layer has an opening such as a pinhole, metal may enter the opening and cause a short circuit when the second conductive layer 8 is formed.
However, in the present embodiment, the hole transport layer 7 contains not only carbon nanotubes, which are hole transport materials, but also a polycarbonate resin. Further, since it is a polycarbonate resin having a specific structure, it has high solubility in a solvent and easily forms a good coating film. The present inventors have found that if the carbon nanotubes are provided with appropriate insulating properties by the polycarbonate resin, even when the coating liquid for the hole transport layer permeates the voids in the porous region of the light absorbing layer 6. It has been found that short circuits between conductive layers can be suppressed. By suppressing the short circuit between the conductive layers, the photoelectric conversion efficiency of the photoelectric conversion element 20 is improved.

The second advantage will be described. As described in the first advantage, the photoelectric conversion element 20 according to the present embodiment can suppress a short circuit between conductive layers even when acicular crystal particles of a perovskite compound are used. Therefore, it is not necessary to produce plate-like crystal particles of the perovskite compound in an environment where the humidity is as low as possible (for example, in a glove box). Therefore, the photoelectric conversion element 20 according to the present embodiment can be manufactured in an atmospheric atmosphere, so that the manufacturing cost is low.

The third advantage will be described.
Unlike the polyvinyl butyral resin, the polycarbonate resin contained in the hole transport layer 7 does not have a hydroxyl group, so that it does not easily absorb water and has excellent gas barrier properties. Therefore, the hole transport layer 7 can function as a barrier layer for preventing moisture and oxidizing gas in the atmosphere from permeating into the light absorption layer 6, and the perovskite compound is deteriorated by moisture and oxidizing gas. It can be suppressed. Therefore, it is possible to prevent the photoelectric conversion efficiency from decreasing with time, and it is possible to improve the durability, moisture resistance, environmental resistance, and the like of the photoelectric conversion element 20.

The fourth advantage will be described.
Since the polycarbonate resin contained in the hole transport layer 7 has flexibility and abrasion resistance and is excellent in mechanical strength, it is possible to improve the mechanical strength and mechanical durability of the photoelectric conversion element. Since the polycarbonate resin has abrasion resistance, it is used for the surface layer of an organic photoconductor used in a copying machine or the like.

The fifth advantage will be described.
Unlike carbon nanotubes, the specific organic charge transport material (hole transport material) contained in the hole transport layer 7 is transparent to visible light and irradiates the light absorption layer 6 with light from the opposite surface (second conductive layer 8 side). can do. Therefore, it is possible to irradiate the light absorption layer 6 with light from both sides of the first conductive layer 3 side and the second conductive layer 8 side, and the light from both sides can be used.

Next, the constituent elements constituting the photoelectric conversion element 20 will be described.
[Hypokeimenon]
Examples of the shape of the substrate 2 include a flat plate shape, a film shape, and a cylindrical shape. When the surface of the photoelectric conversion element 20 on the substrate 2 side is irradiated with light, the substrate 2 is transparent. In this case, examples of the material of the substrate 2 include transparent glass (more specifically, soda lime glass, non-alkali glass, etc.) and a heat-resistant transparent resin. When the surface of the photoelectric conversion element 20 on the second conductive layer 8 side is irradiated with light, the substrate 2 may be opaque. In this case, examples of the material of the substrate 2 include aluminum, nickel, chromium, magnesium, iron, tin, titanium, gold, silver, copper, tungsten, alloys thereof (for example, stainless steel), and ceramics.

[First conductive layer]
The first conductive layer 3 corresponds to the cathode of the photoelectric conversion element 20. Examples of the material constituting the first conductive layer 3 include a transparent conductive material and a non-transparent conductive material. Examples of the transparent conductive material include copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO ₂ ), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and indium zinc oxide. (IZO) and gallium-doped zinc oxide (GZO). Examples of the non-transparent conductive material include sodium, sodium-potassium alloy, lithium, magnesium, aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, and aluminum-aluminum oxide mixture (Al / Al ₂ O ₃ ). ) And aluminum-lithium fluoride mixture (Al / LiF). The film thickness of the first conductive layer 3 is not particularly limited, and may be any film thickness that can exhibit desired characteristics (for example, electron transportability and transparency).

[Electron transport layer]
The electron transport layer 4 is a layer that transports electrons generated by photoexcitation in the light absorption layer 6 to the first conductive layer 3. Therefore, it is preferable that the electron transport layer 4 contains a material that easily moves the electrons generated in the light absorption layer 6 to the first conductive layer 3. The electron transport layer 4 contains, for example, titanium oxide as an electron transport material. The content ratio of titanium oxide in the electron transport layer 4 is preferably 95% by mass or more, and more preferably 100% by mass.
As shown in FIG. 1, the electron transport layer 4 may include, for example, a dense titanium oxide layer 11 and a porous titanium oxide layer 12 which is a porous layer. Further, as shown in FIG. 2, the electron transport layer 4 may be a single dense titanium oxide layer 11. Hereinafter, the dense titanium oxide layer 11 and the porous titanium oxide layer 12 will be described.

(Dense titanium oxide layer)
The porosity of the dense titanium oxide layer 11 is lower than that of the porous titanium oxide layer 12. Therefore, even when the light absorbing material (perovskite compound) used for forming the light absorbing layer 6 at the time of manufacturing the photoelectric conversion element 20 passes through the porous titanium oxide layer 12, the layer of the dense titanium oxide layer 11 is formed. It is difficult to penetrate inside. Therefore, since the photoelectric conversion element 20 includes the dense titanium oxide layer 11, the contact between the light absorbing material and the first conductive layer 3 is suppressed. Further, since the photoelectric conversion element 20 includes the dense titanium oxide layer 11, contact between the first conductive layer 3 and the second conductive layer 8 which causes a decrease in electromotive force is suppressed. As shown in FIG. 1, when the electron transport layer 4 includes two layers of the dense titanium oxide layer 11 and the porous titanium oxide layer 12, the film thickness of the dense titanium oxide layer 11 is preferably 5 nm or more and 200 nm or less, preferably 10 nm. More preferably 100 nm or less. As shown in FIG. 2, when the electron transport layer 4 is one dense titanium oxide layer 11, the film thickness of the dense titanium oxide layer 11 is thicker than that when two layers are included, and is preferably 200 nm or more and 1000 nm or less.

(Porous titanium oxide layer)
When the photoelectric conversion element 20 includes the porous titanium oxide layer 12, the following advantages can be obtained. The porosity of the porous titanium oxide layer 12 is higher than that of the dense titanium oxide layer 11. Therefore, when the photoelectric conversion element 20 is manufactured, the light absorption material used for forming the light absorption layer 6 permeates the pores of the porous titanium oxide layer 12, and the contact area between the light absorption layer 6 and the electron transport layer 4 becomes large. Increase. As a result, the electrons generated by photoexcitation in the light absorption layer 6 efficiently move to the electron transport layer 4. Further, the unevenness of the surface of the porous titanium oxide layer 12 is larger than that of the dense titanium oxide layer 11. When the light absorption layer 6 is formed on the porous titanium oxide layer 12 having large surface irregularities, the acicular crystal particles of the perovskite compound do not grow too much and have an appropriate size. The voids in the porous region formed by the plurality of perovskite compound needle-like crystal particles having an appropriate size have an appropriate size so that the hole transport material does not permeate too much, and the short circuit between the conductive layers is further suppressed. The film thickness of the porous titanium oxide layer 12 is preferably 100 nm or more and 2,000 nm or less, and more preferably 200 nm or more and 1,500 nm or less.

[Light absorption layer]
The light absorption layer 6 is a layer that absorbs light incident on the photoelectric conversion element 20 to generate electrons and holes. Specifically, when light is incident on the light absorption layer 6, low-energy electrons contained in the light-absorbing material are photoexcited, and high-energy electrons and holes are generated. The generated electrons move to the electron transport layer 4. The generated hole moves to the hole transport layer 7. Such movement of electrons and holes results in charge separation.
The light absorption layer 6 contains needle-shaped crystal particles of a perovskite compound as a light absorption material. The light absorption layer 6 has a porous region formed by a plurality of perovskite compound needle-like crystal particles. At least a part of the voids in the porous region of the light absorption layer 6 is filled with the polycarbonate resin and the hole transport material (carbon nanotubes or the like) that have penetrated when the hole transport layer 7 is formed.

(Perovskite compound)
The perovskite compound is a compound having a perovskite-type crystal structure. The crystal particles of the perovskite compound used in this embodiment are acicular crystal particles. In the present specification, the needle-shaped crystal particles refer to crystal particles in which the ratio (aspect ratio) of the major axis length of the particles to the minor axis length of the particles is 5 or more.
The major axis length of the crystal particles of the perovskite compound is preferably 5 μm or more and 50 μm or less, and more preferably 7 μm or more and 20 μm or less. The aspect ratio of the crystal particles of the perovskite compound is preferably 5 or more and 20 or less, and more preferably 7 or more and 15 or less. Since the major axis length and aspect ratio of the crystal particles of the perovskite compound are within the above ranges, the polycarbonate is formed in the voids of the porous region formed by the plurality of perovskite compound crystal particles when the hole transport layer 7 is formed. The resin and the hole transport material (carbon nanotube or organic charge transport material) can be easily filled.

In the present specification, the major axis length and the aspect ratio of the crystal particles of the perovskite compound mean the arithmetic mean value of the major axis length of the perovskite compound crystal particles and the arithmetic mean value of the aspect ratio, respectively. These arithmetic mean values are measured by the method described in the examples.
The size and shape of the acicular crystal particles of the perovskite compound can be changed by the following method. For example, the higher the humidity of the manufacturing environment when forming the light absorption layer 6, the larger the aspect ratio of the crystal particles of the perovskite compound. Further, the higher the water content of the material used for production, the larger the aspect ratio of the crystal particles of the perovskite compound. Further, the more the acicular crystal particles of the perovskite compound are formed on the surface having less unevenness, the shorter the major axis length and the minor axis length of the acicular crystal particles are.

From the viewpoint of improving the photoelectric conversion efficiency, the perovskite compound contained in the light absorption layer 6 includes a compound represented by the general formula: ABX ₃ (1) (hereinafter, may be referred to as a perovskite compound (1)). preferable.
In the general formula (1), A is an organic molecule, B is a metal atom, and X is a halogen atom. In the general formula (1), the three Xs may represent the same halogen atom or different halogen atoms.
The perovskite compound (1) is an organic-inorganic hybrid compound. The organic-inorganic hybrid compound is a compound composed of an inorganic component and an organic component. The photoelectric conversion element 20 using the perovskite compound (1), which is an organic-inorganic hybrid compound, is also called an organic-inorganic hybrid photoelectric conversion element.

FIG. 3 shows the basic unit cell of the cubic system of the crystal structure of the perovskite compound (1). This basic unit cell includes an organic molecule A arranged at each vertex, a metal atom B arranged at the body center, and a halogen atom X arranged at each face center.
It can be confirmed by using the X-ray diffraction method that the light absorbing material has a cubic basic unit cell. Specifically, a light absorption layer 6 containing a light absorption material is produced on a glass plate, the light absorption layer 6 is recovered in powder form, and the light absorption layer 6 is recovered in powder form using a powder X-ray diffractometer. Measure the diffraction pattern of (light absorbing material). Alternatively, the light absorbing layer 6 is recovered in powder form from the photoelectric conversion element 20, and the diffraction pattern of the recovered light absorbing layer 6 (light absorbing material) is measured using a powder X-ray diffractometer.

Examples of the organic molecule represented by A in the general formula (1) include alkylamines, alkylammoniums, nitrogen-containing heterocyclic compounds and the like. In the perovskite compound (1), the organic molecule represented by A may be only one kind of organic molecule or two or more kinds of organic molecules.

Examples of the alkylamine include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine and tri. Examples thereof include butylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, ethylbutylamine and the like.

Alkylammonium is an ionized product of the above-mentioned alkylamine. Examples of the alkylammonium include methylammonium (CH ₃ NH ₃ ), ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, dimethylammonium, diethylammonium, dipropylammonium, dibutylammonium, dipentylammonium, dihexylammonium, and the like. Trimethylammonium, triethylammonium, tripropylammonium, tributylammonium, tripentylammonium, trihexylammonium, ethylmethylammonium, methylpropylammonium, butylmethylammonium, methylpentylammonium, hexylmethylammonium, ethylpropylammonium, ethylbutylammonium, etc. Can be mentioned.

Examples of the nitrogen-containing heterocyclic compound include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azete, azole, imidazoline, and carbazole. The nitrogen-containing heterocyclic compound may be an ionized product. As the nitrogen-containing heterocyclic compound which is an ionized product, phenethylammonium is preferable.
As the organic molecule represented by A, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium or phenethylammonium are preferable. Amines, ethylamines, propylamines, methylammoniums, ethylammoniums, or propylammoniums are more preferred, and methylammoniums are even more preferred.

In the general formula (1), examples of the metal atom represented by B include lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium and indium. , Aluminum, manganese, chromium, molybdenum, and europium. In the perovskite compound (1), the metal atom represented by B may be only one kind of metal atom or two or more kinds of metal atoms. From the viewpoint of improving the light absorption characteristics and the charge generation characteristics of the light absorption layer 6, the metal atom represented by B is preferably a lead atom.

Examples of the halogen atom represented by X in the general formula (1) include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like. In the perovskite compound (1), the halogen atom represented by X may be one kind of halogen atom or two or more kinds of halogen atoms. As the halogen atom represented by X, an iodine atom is preferable from the viewpoint of narrowing the energy band gap of the perovskite compound (1). Specifically, it is preferable that at least one of the three Xs represents an iodine atom, and it is more preferable that the three Xs represent an iodine atom.

As the perovskite compound (1), a compound represented by the general formula “CH ₃ NH ₃ PbX ₃ (where X represents a halogen atom)” is preferable, and CH ₃ NH ₃ PbI ₃ is more preferable. By using a compound represented by the general formula "CH ₃ NH ₃ PbX ₃ " (particularly CH ₃ NH ₃ PbI ₃ ) as the perovskite compound (1), electrons and holes are generated more efficiently in the light absorption layer 6. As a result, the photoelectric conversion efficiency of the photoelectric conversion element 20 can be further improved.

[Hall transport layer]
The hole transport layer 7 is a layer that captures the holes generated in the light absorption layer 6 and transports them to the second conductive layer 8 which is an anode. The film thickness of the hole transport layer 7 is preferably 20 nm or more and 2,000 nm or less, and more preferably 200 nm or more and 600 nm or less. By setting the film thickness of the hole transport layer 7 to 20 nm or more and 2,000 nm or less, the holes generated in the light absorption layer 6 can be smoothly and efficiently moved to the second conductive layer 8.
The hole transport layer 7 contains a carbon nanotube or a specific organic charge transport material which is a hole transport material and a polycarbonate resin which is a binder resin.

(carbon nanotube)
Examples of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes. As the carbon nanotube, multi-walled carbon nanotube is preferable. The hole transport layer 7 may contain only carbon nanotubes as the hole transport material. The shape of the carbon nanotubes is an outer diameter of 5 nm to 40 nm, preferably 10 nm to 20 nm, and a length of 0.1 μm to 10 μm, preferably 1 μm to 2 μm.
The content ratio of the carbon nanotubes in the hole transport layer 7 is preferably 10% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 60% by mass or less, and further preferably 40% by mass or more and 60% by mass or less. When light is incident from the second conductive layer 8 side, it is preferable to reduce the content of the carbon nanotubes and to contain the carbon nanotubes in a content ratio such that the hole transport layer 7 becomes translucent.
The ratio MC / MR of the mass MC of the carbon nanotube to the mass MR of the polycarbonate resin is preferably 0.3 or more and 1.5 or less, and more preferably 0.5 or more and 1.0 or less. When the ratio MC / MR is within the above range, the polycarbonate resin imparts appropriate insulating properties to the carbon nanotubes, and short circuits between the conductive layers can be further suppressed.

(Organic charge transport material)
The hole transport layer 7 can contain an organic charge transport material which is a hole transport material instead of the carbon nanotube which is a hole transport material. In this case, the hole transport layer 7 contains an organic charge transport material which is a hole transport material and a polycarbonate resin which is a binder resin.
Even when light is incident from the second conductive layer 8 side, the hole transport layer 7 is substantially transparent to visible light, so that the content is not limited as in the case of carbon nanotubes.
The ratio MC / MR of the mass MC of the organic charge transport material to the mass MR of the polycarbonate resin is preferably 4 or more and 15 or less, and more preferably 5 or more and 10 or less. When the ratio MC / MR is within the above range, the organic charge transport material has lower conductivity than carbon nanotubes, and therefore needs to be contained in a larger amount. Further, when the ratio MC / MR is within the above range, the polycarbonate resin imparts appropriate insulating properties to the organic charge transport material, and short circuit between the conductive layers can be further suppressed.
The organic charge transport material is, for example, a compound represented by the following structural formula.

式中、Ｒ₇は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₈は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₉は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₁₀は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有してもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。
例えば、有機電荷輸送材料は、表１に示したＲ₇～Ｒ₁₀を有する化合物例１～１１である。

In the formula, R ₇ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group. R ₈ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group. R ₉ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group, or an aryl group. R ₁₀ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group, or an aryl group.
For example, the organic charge transport material is Compound Examples 1 to 11 having R ₇ to R ₁₀ shown in Table 1.

For example, Compound Example 4 is a compound represented by the following structural formula.

(Polycarbonate resin)
The light absorbing layer 6 contains a specific polycarbonate resin because it has excellent affinity with carbon nanotubes and can impart appropriate insulating properties to carbon nanotubes. The polycarbonate resin is soluble in a solvent (for example, toluene or chlorobenzene) that does not easily affect the crystal structure of the perovskite compound contained in the light absorption layer 6. Therefore, when a coating liquid for a hole transport layer containing such a solvent and a polycarbonate resin dissolved in the solvent is applied to the light absorption layer 6 to form the hole transport layer 7, the light absorption layer 6 is formed. It is possible to suppress the change in the crystal structure of the contained perovskite compound.
The specific polycarbonate resin is a polycarbonate resin having a structural unit represented by the following structural formula as a main repeating unit.

式中、Ｒ₃は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有していてもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₄は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有していてもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₅は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有していてもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｒ₆は、水素原子であってもよく、ハロゲン原子であってもよく、置換基を有していてもよい、アルキル基、アルコキシ基、シクロアルキル基又はアリール基であってもよい。Ｚは、置換基を有していてもよい環状アルキルを形成するのに必要な原子群である。
また、ポリカーボネート樹脂は、下記構造式で表される樹脂であってもよい。

In the formula, R ₃ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group. .. R ₄ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group, or an aryl group. R ₅ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group, or an aryl group. R ₆ may be a hydrogen atom, a halogen atom, a substituent, an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group. Z is a group of atoms required to form a cyclic alkyl which may have a substituent.
Further, the polycarbonate resin may be a resin represented by the following structural formula.

Since such a polycarbonate resin does not have a hydroxyl group, it is difficult to contain water. Therefore, the polycarbonate resin in the hole transport layer 7 serves as a barrier to prevent the moisture in the atmosphere from permeating into the light absorption layer 6, and can suppress the deterioration of the perovskite compound due to the moisture. The measured value of the water content of the polycarbonate resin specified in ISO is 0.1 to 1%.
Further, since the polycarbonate resin having a bisphenol Z structure such as Chemical formula 6 is particularly excellent in gas barrier property, the polycarbonate resin in the hole transport layer 7 allows an oxidizing gas in the atmosphere (for example, oxygen gas) to penetrate into the light absorption layer 6. It serves as a barrier to prevent the deterioration of the perovskite compound due to the oxidizing gas. In the organic photoconductor used in a copying machine or the like, a polycarbonate resin having a bisphenol Z structure is used for improving ozone resistance and oxidation resistance gas.

[Second conductive layer]
The second conductive layer 8 corresponds to the anode of the photoelectric conversion element 20. Examples of the material constituting the second conductive layer 8 include a metal, a transparent conductive inorganic material, conductive fine particles, and a conductive polymer (particularly, a transparent conductive polymer). Metals include, for example, gold, silver, and platinum. Examples of the transparent conductive inorganic material include copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO ₂ ), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and indium zinc. Oxides (IZO) and gallium-doped zinc oxide (GZO) can be mentioned. Examples of the conductive fine particles include silver nanowires and carbon nanofibers. Examples of the transparent conductive polymer include a polymer (PEDOT / PSS) containing poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid.

When light is incident on the photoelectric conversion element 20 from the second conductive layer 8 side, the incident light reaches the light absorption layer 6, so that the second conductive layer 8 is more preferably transparent or translucent. As the material constituting the transparent or translucent second conductive layer 8, a transparent conductive inorganic material or a transparent conductive polymer is preferable. The film thickness of the second conductive layer 8 is preferably 50 nm or more and 1,000 nm or less, and more preferably 100 nm or more and 300 nm or less.

[others]
As described above, the photoelectric conversion element 20 which is an example of the photoelectric conversion element according to the present embodiment has been described with reference to FIGS. 1 and 2. However, the photoelectric conversion element according to the present embodiment is not limited to the photoelectric conversion element 20, and for example, the following points can be changed.
The photoelectric conversion element according to the present embodiment may further include a surface layer on the second conductive layer. The surface layer is a layer that suppresses deterioration of the inside of the photoelectric conversion element due to moisture and oxygen in the air. The surface layer is a layer that protects the outer surface from impacts and scratches when the photoelectric conversion element is used. As the material constituting the surface layer, a material having a high gas barrier property is preferable. This is because the gas barrier property of the polycarbonate resin is further reinforced. The surface layer can be formed using, for example, a resin composition, a shrink film, a wrap film, or a clear paint. On the other hand, it is preferable that the photoelectric conversion element housed in a closed container and used does not have a surface layer. When light is incident from the surface layer side of the photoelectric conversion element, the surface layer is preferably transparent or translucent, and more preferably transparent.

The electron transport layer of the photoelectric conversion element according to the present embodiment does not have to contain titanium oxide. For example, the electron transport layer may include a dense layer made of a material other than titanium oxide and a porous layer made of a material other than titanium oxide. Further, the electron transport layer may be a single layer or may have a multi-layer structure of three or more layers.

The photoelectric conversion element according to the present embodiment does not have to include a substrate, a first conductive layer, and a second conductive layer. That is, in the photoelectric conversion element, the substrate, the first conductive layer, and the second conductive layer may be omitted. Further, when the photoelectric conversion element according to the present embodiment includes a substrate, the substrate may have conductivity. In this case, the substrate also functions as a first conductive layer.

<Second Embodiment: Manufacturing Method of Photoelectric Conversion Element>
The second embodiment relates to a method for manufacturing a photoelectric conversion element. The method for manufacturing a photoelectric conversion element according to the present embodiment includes a first charge transport layer forming step, a light absorption layer forming step, and a second charge transport layer forming step. In the first charge transport layer forming step, the first charge transport layer containing the first charge transport material is formed. In the light absorption layer forming step, the light absorption layer is formed on the first charge transport layer. In the second charge transport layer forming step, the second charge transport layer containing the second charge transport material is formed on the light absorption layer. One of the first charge transport layer containing the first charge transport material and the second charge transport layer containing the second charge transport material is the electron transport layer containing the electron transport material. The other of the first charge transport layer containing the first charge transport material and the second charge transport layer containing the second charge transport material is the hole transport layer containing the hole transport material. The light absorption layer contains acicular crystal particles of the perovskite compound. The hole transport layer contains a polycarbonate resin and a carbon nanotube or an organic charge transport material which is a hole transport material.
The photoelectric conversion element obtained by the manufacturing method according to the present embodiment is, for example, the photoelectric conversion element according to the first embodiment. The photoelectric conversion element obtained by the manufacturing method according to the present embodiment has excellent photoelectric conversion efficiency and low manufacturing cost for the same reason as described in the first embodiment.

In the method for manufacturing a photoelectric conversion element according to the present embodiment, the first charge transport layer containing the first charge transport material is an electron transport layer containing an electron transport material, and the second charge transport material is contained. The charge transport layer is preferably a hole transport layer containing a hole transport material. That is, in the method for manufacturing a photoelectric conversion element according to the present embodiment, it is preferable to form an electron transport layer in the first charge transport layer forming step and to form a hole transport layer in the second charge transport layer forming step.

The manufacturing method of the photoelectric conversion element 20 will be described as an example of the manufacturing method of the photoelectric conversion element according to the present embodiment with reference to FIGS. 1 and 2 again. The method for manufacturing the photoelectric conversion element 20 shown in FIG. 1 includes, for example, a laminate preparation step of preparing a laminate including a substrate 2 and a first conductive layer 3, and an electron transport material on the first conductive layer 3 in the laminate. An electron transport layer forming step of forming an electron transport layer 4 containing the above, a light absorption layer forming step of forming a light absorption layer 6 on the electron transport layer 4, and a hole transport material contained on the light absorption layer 6. It includes a hole transport layer forming step of forming the hole transport layer 7 and a second conductive layer forming step of forming the second conductive layer 8 on the hole transport layer 7. In this manufacturing method, the electron transport material is the first charge transport material, the electron transport layer 4 is the first charge transport layer, the electron transport layer forming step is the first charge transport layer forming step, and the hole transport material is. The second charge transport material, the hole transport layer 7 is the second charge transport layer, and the hole transport layer forming step is the second charge transport layer forming step.

[Laminate preparation process]
In this step, a laminated body including the substrate 2 and the first conductive layer 3 is prepared. The laminate can be obtained, for example, by forming the first conductive layer 3 on the substrate 2. Examples of the method for forming the first conductive layer 3 on the substrate 2 include a vacuum vapor deposition method, a sputtering method, and a plating method.

[Electron transport layer forming process]
In this step, an electron transport layer 4 containing an electron transport material is formed on the first conductive layer 3 of the laminated body. Specifically, when manufacturing the photoelectric conversion element 20 shown in FIG. 1, this step includes a step of forming a dense titanium oxide layer and a step of forming a porous titanium oxide layer. Alternatively, when the photoelectric conversion element 20 shown in FIG. 2 is manufactured, this step includes only a step of forming a dense titanium oxide layer.

(Dense titanium oxide layer forming process)
In this step, the dense titanium oxide layer 11 is formed on the first conductive layer 3 of the laminated body. As a method of forming the dense titanium oxide layer 11 on the first conductive layer 3, for example, a method of applying a coating liquid for a dense titanium oxide layer containing a titanium chelate compound on the first conductive layer 3 and then firing it. Can be mentioned. Examples of the method for applying the coating liquid for the dense titanium oxide layer onto the first conductive layer 3 include a spin coating method, a screen printing method, a casting method, a dip coating method, a roll coating method, a slot die method, and a spray pyrolysis method. , And the aerosol deposition method. After firing, the formed dense titanium oxide layer 11 may be immersed in an aqueous solution of titanium tetrachloride. By this treatment, the denseness of the dense titanium oxide layer 11 can be increased.

Examples of the solvent of the coating liquid for the dense titanium oxide layer include alcohol (particularly 1-butanol). Examples of the titanium chelate compound contained in the coating liquid for the dense titanium oxide layer include a compound having an acetoacetic ester chelate group and a compound having a β-diketone chelate group.

The compound having an acetoacetic acid ester chelating group is not particularly limited, and for example, diisopropoxytitanium bis (methylacetate), diisopropoxytitanium bis (ethylacetate), diisopropoxytitanium bis (propylacetacetate). , Diisopropoxytitanium bis (butylacetate), dibutoxytitanium bis (methylacetate), dibutoxytitanium bis (ethylacetate), triisopropoxytitanium (methylacetate), triisopropoxytitanium (ethylacetate acetate) ), Tributoxytitanium (methylacetacetate), Tributoxytitanium (ethylacetate acetate), Isopropoxytitanium tri (methylacetate acetate), Isopropoxytitanium tri (ethylacetacetate), Isobutoxytitanium tri (methylacetacetate), And isobutoxytitanium tri (ethylacetacetate).

The compound having a β-diketone chelating group is not particularly limited, and for example, diisopropoxytitanium bis (acetylacetonate), diisopropoxytitanium bis (2,4-heptandionate), and dibutoxytitanium bis (acetyl). Acetonate), Dibutoxytitanium Bis (2,4-Heptangionate), Triisopropoxytitanium (Acetylacetonate), Triisopropoxytitanium (2,4-Heptangionate), Tributoxytitanium (Acetylacetonate) , Tributoxytitanium (2,4-heptanionate), Isopropoxytitaniumtri (acetylacetonate), Isopropoxytitaniumtri (2,4-heptangionate), Isobutoxytitaniumtri (acetylacetonate), and Iso Butoxytitanium tri (2,4-heptangionate) can be mentioned.

As the titanium chelate compound, a compound having an acetoacetic ester chelate group is preferable, and diisopropoxytitanium bis (acetylacetonate) is more preferable. As the titanium chelate compound, a commercially available product such as the "TYZOR® AA" series manufactured by DuPont may be used.

(Porous titanium oxide layer forming process)
In this step, the porous titanium oxide layer 12 is formed on the dense titanium oxide layer 11. Examples of the method for forming the porous titanium oxide layer 12 include a method in which a coating liquid for a porous titanium oxide layer containing titanium oxide is applied onto the dense titanium oxide layer 11 and then fired. The coating liquid for the porous titanium oxide layer may further contain, for example, a solvent and an organic binder. When the coating liquid for the porous titanium oxide layer contains an organic binder, the organic binder is removed by firing. Examples of the method for applying the coating liquid for the porous titanium oxide layer to the dense titanium oxide layer 11 include a spin coating method, a screen printing method, a casting method, a dip coating method, a roll coating method, a slot die method, and a spray pyrolysis method. , And the aerosol deposition method.

The pore diameter and porosity of the porous titanium oxide layer 12 can be adjusted, for example, by adjusting the particle size of the titanium oxide particles contained in the coating liquid for the porous titanium oxide layer, and the type and content of the organic binder.
The titanium oxide contained in the coating liquid for the porous titanium oxide layer is not particularly limited, and examples thereof include anatase-type titanium oxide. The coating liquid for the porous titanium oxide layer may be, for example, titanium oxide particles (more specifically, "AEROXIDE (registered trademark) TiO ₂ P25" manufactured by Nippon Aerodil Co., Ltd.) and alcohol (more specifically, ethanol or the like). ) Can be prepared. For the coating liquid for the porous titanium oxide layer, for example, the titanium oxide paste (more specifically, "PST-18NR" manufactured by JGC Catalysts and Chemicals Co., Ltd., etc.) is diluted with alcohol (more specifically, ethanol, etc.). It can also be prepared.

When the coating liquid for the porous titanium oxide layer contains an organic binder, ethyl cellulose or acrylic resin is preferable as the organic binder. The acrylic resin has excellent low-temperature decomposability, and organic substances are unlikely to remain in the porous titanium oxide layer 12 even when firing at a low temperature. The acrylic resin preferably decomposes at a temperature of about 300 ° C. Examples of the acrylic resin include a polymer of at least one (meth) acrylic monomer. Examples of the (meth) acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, and isobutyl (meth) acrylate. Examples thereof include cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isoboronyl (meth) acrylate, n-stearyl (meth) acrylate, benzyl (meth) acrylate, and (meth) acrylic monomer having a polyoxyalkylene structure.

[Light absorption layer forming step]
In this step, the light absorption layer 6 is formed on the electron transport layer 4 (specifically, on the porous titanium oxide layer 12 shown in FIG. 1 or on the dense titanium oxide layer 11 shown in FIG. 2). The light absorption layer 6 is a porous layer containing acicular crystal particles of a perovskite compound. The needle-shaped crystal particles of the perovskite compound can be produced more stably than the plate-shaped crystal particles of the perovskite compound, and the yield is excellent.

When the perovskite compound contained in the light absorption layer 6 is a perovskite compound (1) (general formula: a compound represented by ABX ₃ (1)), the light absorption layer 6 is, for example, the following one-step method or two-step method. It can be formed by the method.
In the one-step method, a solution containing a compound represented by the general formula "AX" (hereinafter referred to as compound (AX)) and a compound represented by the general formula "BX ₂ " (hereinafter referred to as compound (BX ₂ )). ) And the solution containing) are mixed to obtain a mixed solution. A, B, and X in the general formula "AX" and the general formula "BX ₂ " are synonymous with A, B, and X in the general formula (1), respectively. By applying this mixed solution on the electron transport layer 4 and drying it, a porous layer containing the perovskite compound (1) represented by the general formula "ABX ₃ " is formed. Examples of the method of applying the mixed solution onto the electron transport layer 4 include a dip coating method, a roll coating method, a spin coating method, and a slot die method.

In the two-step method, a solution containing the compound (BX ₂ ) is applied onto the electron transport layer 4 to form a coating film. A solution containing the compound (AX) is applied onto the coating film, and the compound (BX ₂ ) and the compound (AX) are reacted in the coating film. Next, the coating film is dried to form a porous layer containing the perovskite compound (1) represented by the general formula "ABX ₃ ". Examples of the method of applying the solution containing the compound (BX ₂ ) to the electron transport layer 4 and the method of applying the solution containing the compound (AX) onto the coating film include a dip coating method, a roll coating method, and a spin. The coat method and the slot die method can be mentioned.

When the light absorption layer 6 is formed under an atmospheric atmosphere (normal environment), acicular crystal particles of the perovskite compound (1) are formed due to the influence of humidity in either the one-step method or the two-step method. To. Since the light absorption layer 6 can be formed by coating in an atmospheric atmosphere, the photoelectric conversion element 20 can be manufactured at low cost according to the manufacturing method according to the present embodiment.
In the light absorption layer forming step, in addition to the above method, for example, a coating liquid for a light absorption layer containing a perovskite compound and a binder resin may be applied onto the electron transport layer 4.

[Hole transport layer forming process]
In this step, a hole transport layer 7 containing a hole transport material is formed on the light absorption layer 6. Specifically, the hole transport layer 7 is formed by applying the coating liquid for the hole transport layer on the light absorption layer 6. The coating liquid for the hole transport layer contains a polycarbonate resin, carbon nanotubes as a hole transport material, and a solvent. Alternatively, the coating liquid for the hole transport layer contains a polycarbonate resin, an organic charge transport material, and a solvent.

As the solvent contained in the coating liquid for the hole transport layer, an organic solvent is preferable, an organic solvent in which the light absorption layer 6 is not dissolved and the polycarbonate resin is dissolved is more preferable, and toluene or chlorobenzene is further preferable. By using a solvent in which the light absorption layer 6 is not dissolved, the acicular crystal particles of the perovskite compound in the light absorption layer 6 can be suitably maintained. Further, by using a solvent in which the polycarbonate resin is dissolved, the carbon nanotubes are thinly and uniformly coated with the dissolved polycarbonate resin, and appropriate insulating properties can be imparted to the carbon nanotubes. The content ratio of the carbon nanotubes in the coating liquid for the hole transport layer is, for example, 0.5% by mass or more and 5.0% by mass or less. The content ratio of the polycarbonate resin in the coating liquid for the hole transport layer is, for example, 0.5% by mass or more and 5.0% by mass or less.

In the case of an organic charge transport material, the charge transport rate is slow, so it is necessary to increase the content ratio with respect to the polycarbonate resin. The content ratio of the organic charge transport material in the coating liquid for the hole transport layer is, for example, 2.0% by mass or more and 5.0% by mass or less. The content ratio of the polycarbonate resin in the coating liquid for the hole transport layer is, for example, 0.5% by mass or more and 5.0% by mass or less.

The coating liquid for the hole transport layer is prepared by putting carbon nanotubes and a polycarbonate resin in a solvent and dispersing them. For dispersion, for example, a homogenizer or an ultrasonic disperser is used. Since carbon nanotubes are broken when a strong share is applied, it is preferable to set loose dispersion conditions.

Alternatively, the coating liquid for the hole transport layer is prepared by dissolving the organic charge transport material and the polycarbonate resin in a solvent. Since the organic charge transport material is soluble in the solvent, the coating liquid can be prepared only with a stirrer.

Examples of the coating method for the hole transport layer include a dip coating method, a spray coating method, a slide hopper coating method, a roll coating method, a spin coating method, a screen coating method, a bar coating method, and an applicator coating method. .. The coating liquid for the hole transport layer is preferably applied by a dip coating method, a roll coating method, or a spin coating method.

[Second conductive layer forming step]
In this step, the second conductive layer 8 is formed on the hole transport layer 7. The method for forming the second conductive layer 8 on the hole transport layer 7 is not particularly limited, and is the same as the method for forming the first conductive layer 3 (more specifically, a vacuum vapor deposition method, a sputtering method, and plating). Law, etc.) can be used.

[others]
As described above, as an example of the manufacturing method of the photoelectric conversion element according to the present embodiment, the manufacturing method of the photoelectric conversion element 20 shown in FIGS. 1 and 2 has been described. However, the method for manufacturing a photoelectric conversion element according to the present embodiment is not limited to the above-mentioned manufacturing method, and for example, the following points can be changed.
The method for manufacturing a photoelectric conversion element according to the present embodiment may further include a surface layer forming step of forming a surface layer on the second conductive layer. Further, the method for manufacturing a photoelectric conversion element according to the present embodiment does not have to include a laminate preparation step and a second conductive layer forming step. Further, in the electron transport layer forming step, the electron transport layer may be formed by a method other than the above-mentioned dense titanium oxide layer forming step and porous titanium oxide layer forming step.
Further, the description of the photoelectric conversion element of the first embodiment also applies to the second embodiment as long as there is no contradiction.

Hereinafter, the present invention will be further described with reference to examples. However, the present invention is not limited to the examples.
<Manufacturing of photoelectric conversion element>
The photoelectric conversion elements (A-1) to (A-11) and (B-1) to (B-3) shown in Table 2 were manufactured by the following methods. The manufacturing environment of each photoelectric conversion element was an environment of a temperature of 25 ° C. and a humidity of 60% RH.

[Photoelectric conversion element (A-1)]
(Laminate preparation process)
A transparent glass plate on which fluorine-doped tin oxide was vapor-deposited (manufactured by Sigma-Aldrich, film thickness: 2.2 mm) was cut into a size of 25 mm in width and 25 mm in length. As a result, a laminate having a substrate (transparent glass plate) and a first conductive layer (fluorine-doped tin oxide film) was prepared. The laminate was subjected to ultrasonic cleaning treatment (10 minutes) and UV cleaning treatment (15 minutes) in ethanol.

(Dense titanium oxide layer forming process)
A 1-butanol solution (manufactured by Sigma-Aldrich) containing diisopropoxytitanium bis (acetylacetonate), which is a titanium chelate compound, at a concentration of 75% by mass was diluted with 1-butanol. As a result, a coating liquid for a dense titanium oxide layer having a concentration of the titanium chelate compound of 0.02 mol / L was prepared. By the spin coating method, a coating liquid for a dense titanium oxide layer was applied onto the first conductive layer in the above-mentioned laminated body, and the mixture was heated at 450 ° C. for 15 minutes. As a result, a dense titanium oxide layer having a film thickness of 50 nm was formed on the first conductive layer.

(Porous titanium oxide layer forming process)
A coating liquid for a porous titanium oxide layer was prepared by diluting 1 g of titanium oxide paste (“PST-18NR” manufactured by JGC Catalysts and Chemicals Co., Ltd.) containing titanium oxide and ethanol with 2.5 g of ethanol. A coating liquid for a porous titanium oxide layer was applied onto the above-mentioned dense titanium oxide layer by a spin coating method, and then calcined at 450 ° C. for 1 hour. As a result, a porous titanium oxide layer having a film thickness of 300 nm was formed on the dense titanium oxide layer.

(Light absorption layer forming step)
The light absorption layer was formed in an atmospheric atmosphere. 922 mg of PbI ₂ (manufactured by Tokyo Chemical Industry Co., Ltd.) and 318 mg of CH ₃ NH ₃ I (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 1.076 mL of N, N-dimethylformamide (DMF) by heating. The molar ratio of PbI ₂ and CH ₃ NH ₃ I was 1: 1. As a result, a mixed solution having a solid content concentration of 55% by mass was prepared. This mixed solution was applied onto the above-mentioned porous titanium oxide layer by a spin coating method. When a few drops of toluene were dropped on the liquid film immediately after application, the liquid film changed from yellow to black. As a result, it was confirmed that the perovskite compound (CH ₃ NH ₃ PbI ₃ ) was formed. Then, the liquid film was dried at 100 ° C. for 60 minutes. As a result, a light absorption layer having a film thickness of 500 nm containing a perovskite compound was formed on the porous titanium oxide layer.

(Hole transport layer forming process)
Using an ultrasonic disperser, 0.2 g of carbon nanotubes (multi-walled carbon nanotubes) and a polycarbonate resin represented by the following structural formula (“PCZ200” manufactured by Mitsubishi Gas Chemicals Corporation, described as PCZ in Table 2) 0. 2 g was dispersed in 12.21 mL of toluene (polycarbonate resin: carbon nanotubes = 1: 1 (mass ratio)). As a result, a coating liquid for the hole transport layer was prepared. A coating liquid for a hole transport layer was applied onto the above-mentioned light absorption layer by a spin coating method. Then, the coated liquid for the hole transport layer was dried at 100 ° C. for 30 minutes to remove the organic solvent (toluene). As a result, a hole transport layer having a film thickness of 500 nm was formed on the above-mentioned light absorption layer.

(Second conductive layer forming step)
A second conductive layer was formed on the above-mentioned hole transport layer by a vacuum vapor deposition method. The second conductive layer was a gold-deposited film having a film thickness of 150 nm, a width of 5 mm and a length of 5 mm, and was provided as an anode. Thereby, the substrate, the first conductive layer, the electron transport layer (specifically, the dense titanium oxide layer and the porous titanium oxide layer), the light absorption layer, the hole transport layer, and the second conductive layer are provided. A photoelectric conversion element (A-1) was obtained.

The photoelectric conversion elements (A-2) to (A-11) and (B-1) to (B-3) are manufactured by the same method as the photoelectric conversion element (A-1) except that the following points are changed. Manufactured.

[Photoelectric conversion element (A-2)]
In the production of the photoelectric conversion element (A-2), chlorobenzene was used instead of toluene as the solvent of the coating liquid for the hole transport layer in the hole transport layer forming step. Since the boiling point of the solvent is high, it was dried at 140 ° C. for 30 minutes.

[Photoelectric conversion element (A-3)]
In the production of the photoelectric conversion element (A-3), in the hole transport layer forming step, instead of 0.2 g of carbon nanotubes, which is a hole transport material, 1.0 g of a hole transport material represented by the following structure, which is Compound Example 4, is used. Was used to form a hole transport layer having a film thickness of 100 nm (polycarbonate resin: hole transport material = 1: 5 (mass ratio)).

[Photoelectric conversion element (A-4)]
In the production of the photoelectric conversion element (A-4), chlorobenzene was used instead of toluene as the solvent of the coating liquid for the hole transport layer in the hole transport layer forming step. Since the boiling point of the solvent is high, it was dried at 140 ° C. for 30 minutes. Further, instead of 0.2 g of carbon nanotubes, which is a hole transport material, 1.0 g of a hole transport material represented by the above structural formula, which is Compound Example 4, was used to form a hole transport layer having a film thickness of 100 nm (polycarbonate). Resin: Hall transport material = 1: 5 (mass ratio)).

[Photoelectric conversion element (A-5)]
In the production of the photoelectric conversion element (A-5), a hole transport layer was formed by using 0.2 g of carbon nanotubes and 0.4 g of a polycarbonate resin in the hole transport layer forming step (polycarbonate resin: carbon nanotubes = 2: 1 (mass ratio)).

[Photoelectric conversion element (A-6)]
In the production of the photoelectric conversion element (A-6), a hole transport layer was formed by using 0.2 g of carbon nanotubes and 0.3 g of a polycarbonate resin in the hole transport layer forming step (polycarbonate resin: carbon nanotubes = 3: 2 (mass ratio)).

[Photoelectric conversion element (A-7)]
In the production of the photoelectric conversion element (A-7), a hole transport layer was formed by using 0.1 g of carbon nanotubes and 0.3 g of a polycarbonate resin in the hole transport layer forming step (polycarbonate resin: carbon nanotubes = 3: 1 (mass ratio)).

[Photoelectric conversion element (A-8)]
In the production of the photoelectric conversion element (A-8), in the hole transport layer forming step, instead of 0.2 g of carbon nanotubes, 0.6 g of the charge transport material of Compound Example 4 is used to form a hole transport layer having a film thickness of 100 nm. Formed (polycarbonate resin: hole transport material = 1: 3 (mass ratio)).

[Photoelectric conversion element (A-9)]
In the production of the photoelectric conversion element (A-9), a hole transport layer was formed by using 0.3 g of carbon nanotubes and 0.2 g of a polycarbonate resin in the hole transport layer forming step (polycarbonate resin: carbon nanotubes = 2: 3 (mass ratio)).

[Photoelectric conversion element (A-10)]
In the production of the photoelectric conversion element (A-10), in the hole transport layer forming step, instead of 0.2 g of carbon nanotubes, 2.2 g of the charge transport material which is Compound Example 4 is used to form a hole transport layer having a thickness of 100 nm. Formed (polycarbonate resin: hole transport material = 1:11 (mass ratio)).

[Photoelectric conversion element (A-11)]
In the production of the photoelectric conversion element (A-11), in the hole transport layer forming step, instead of 0.2 g of carbon nanotubes, 2.0 g of the charge transport material which is Compound Example 4 is used to form a hole transport layer having a film thickness of 100 nm. Formed (polycarbonate resin: hole transport material = 1:10 (mass ratio)).

[Photoelectric conversion element (B-1)]
In the production of the photoelectric conversion element (B-1), 0.2 g of polyvinyl butyral resin (“ESREC BL-S” manufactured by Sekisui Chemical Co., Ltd.) is used instead of 0.2 g of polycarbonate resin in the hole transport layer forming step. A hole transport layer was formed (polyvinyl butyral resin: carbon nanotubes = 1: 1 (mass ratio)).

[Photoelectric conversion element (B-2)]
In the production of the photoelectric conversion element (B-2), a hole transport layer is used as a coating liquid for a hole transport layer (a carbon nanotube dispersion liquid that does not contain a binder resin) in which 0.2 g of carbon nanotubes is dispersed in 12.21 mL of toluene. Formed.

[Photoelectric conversion element (B-3)]
In the production of the photoelectric conversion element (B-3), a coating liquid for a hole transport layer (organic charge transport material not containing a binder resin) in which 0.2 g of the charge transport material of Compound Example 4 is dissolved in 12.21 mL of chlorobenzene is dissolved. Liquid) was used to form a hole transport layer.

<Observation of light absorption layer>
After the light absorption layer forming step and before the hole transport layer forming step, the light absorption layers of the photoelectric conversion elements (A-1) and (A-3) were observed.

(Observation of the light absorption layer of the photoelectric conversion element (A-1))
The surface of the light absorption layer of the photoelectric conversion element (A-1) was observed at a magnification of 2000 times using an optical microscope. FIG. 4 shows a photograph of the surface of the observed light absorption layer of the photoelectric conversion element (A-1). The scale bars shown in the photographs of FIGS. 4 and 5 to 7, which will be described later, have a length of 10.00 μm. From the photograph shown in FIG. 4, the light absorption layer of the photoelectric conversion element (A-1) is composed of a plurality of needle-shaped crystal particles Y of the perovskite compound, and is porous by the plurality of needle-shaped crystal particles Y of the perovskite compound. It was confirmed that the quality region was formed.
FIG. 5 is a photograph of the surface of the hole transport layer formed by applying the coating liquid for the hole transport layer on the light absorption layer and drying it.

(Observation of the light absorption layer of the photoelectric conversion element (A-3))
The surface of the light absorption layer of the photoelectric conversion element (A-3) was observed at a magnification of 2000 times using an optical microscope. FIG. 6 shows a photograph of the surface of the observed light absorption layer of the photoelectric conversion element (A-3). From the photograph shown in FIG. 6, the light absorption layer of the photoelectric conversion element (A-3) is composed of a plurality of needle-like crystal particles Y of the perovskite compound, and is porous due to the plurality of needle-like crystals Y of the perovskite compound. It was confirmed that the region was formed.
FIG. 7 is a photograph of the surface of the hole transport layer formed by applying the coating liquid for the hole transport layer on the light absorption layer and drying it.
From the photographs shown in FIGS. 6 and 7, it can be seen that the hole transport layer of the photoelectric conversion element (A-3) is transparent.

<Measurement of major axis length and aspect ratio of needle-shaped crystal particles of perovskite compound>
After the light absorption layer forming step and before the hole transport layer forming step, the light absorbing layer of the photoelectric conversion element (A-1) was observed, and the major axis length and the aspect ratio of the acicular crystal particles of the perovskite compound were measured. ..

(Measurement of photoelectric conversion element (A-1))
The surface of the light absorption layer of the photoelectric conversion element (A-1) was observed at a magnification of 2000 times using an optical microscope. For any 20 needle-like crystal particles of the perovskite compound confirmed on the surface of the light absorption layer, the major axis length and aspect ratio were measured, and the total of the 20 measured values was divided by the number of measurements (20). By doing so, the arithmetic mean value was calculated. For the needle-shaped crystal particles of the perovskite compound contained in the light absorption layer of the photoelectric conversion element (A-1), the arithmetic mean value of the major axis length was 20 μm, and the arithmetic mean value of the aspect ratio was 15.

<Observation of hall transport layer>
After the hole transport layer forming step and before the second conductive layer forming step, the surfaces of the hole transport layers of the photoelectric conversion elements (A-1) and (A-3) were observed at a magnification of 2000 times using an optical microscope. .. FIG. 5 shows a photograph of the surface of the hole transport layer of the observed photoelectric conversion element (A-1). FIG. 7 shows a photograph of the surface of the hole transport layer of the observed photoelectric conversion element (A-3). From the photograph shown in FIG. 5, it was confirmed that the voids in the porous region of the light absorption layer formed by the acicular crystal particles Y of the perovskite compound were filled with the carbon nanotubes and the polycarbonate resin. Further, from the photograph shown in FIG. 7, it was confirmed that the voids in the porous region of the light absorption layer were filled with the organic charge transport material and the polycarbonate resin. Since there are no pinholes on the surface of the hole transport layer, it is judged that a short circuit between the conductive layers is prevented.

<Evaluation of photoelectric conversion characteristics>
For each of the photoelectric conversion elements (A-1) to (A-11) and (B-1) to (B-3), the short-circuit current, open circuit voltage, curve factor, and photoelectric conversion efficiency are measured by Solar Simulator (Co., Ltd.). It was measured using Wacom Denso). The photoelectric conversion element was connected to the solar simulator so that the second conductive layer on the surface layer side of the photoelectric conversion element became the anode and the first conductive layer on the substrate side became the cathode. The photoelectric conversion element was irradiated with pseudo-sunlight of 100 mW / cm ² obtained by passing the light of a xenon lamp through an air mass filter (“AM-1.5” manufactured by Nikon Corporation). The current-voltage characteristics of the photoelectric conversion element at the time of irradiation were measured, and a current-voltage curve was obtained. From the current-voltage curve, the short-circuit current (Jsc), open circuit voltage (Voc), and curve factor (FF) were obtained, and the photoelectric conversion efficiency (η) was calculated.

An element having a photoelectric conversion efficiency of 10% or more is evaluated as "◎", an element having a photoelectric conversion efficiency of 8% or more and less than 10% is evaluated as "○", and a photoelectric conversion efficiency is 4% or more and 8%. The evaluation of the element having less than 4% was given as "Δ", and the evaluation of the element having the photoelectric conversion efficiency of less than 4% was given as "x".
After another month, the same measurement was performed to measure the change in photoelectric conversion efficiency.
An element having a photoelectric conversion efficiency retention rate of 90% or more is evaluated as "◎", and an element having a photoelectric conversion efficiency retention rate of 80% or more and less than 90% is evaluated as "○". The evaluation of the element having a retention rate of 60% or more and less than 80% was given as "Δ", and the evaluation of the element having a retention rate of photoelectric conversion efficiency of less than 60% was given as "x". The results are shown in Table 2.

As shown in Table 2, the photoelectric conversion elements (A-1) to (A-11) have better conversion efficiency after one month than the photoelectric conversion elements (B-1) to (B-3). Met.
When the resin component was large as in the element (A-7), the photoelectric conversion efficiency was slightly low, but the deterioration was small. Further, even in the organic charge transport material such as the device (A-8), when the resin component is large, the photoelectric conversion efficiency is slightly low, but the deterioration is small.
Further, when the resin component was small as in the element (A-9), the photoelectric conversion efficiency was high, but the deterioration was slightly large. Further, even in the organic charge transport material such as the element (A-10), when the resin component is small, the photoelectric conversion efficiency is high, but the deterioration is slightly large.

On the other hand, the photoelectric conversion element (B-1) was better in the initial stage than the photoelectric conversion elements (A-1) to (A-11), but the photoelectric conversion efficiency after one month was good. There wasn't. It is considered that this is because the polyvinyl butyral resin in the hole transport layer has high moisture permeability in the photoelectric conversion element (B-1), and the perovskite crystals in the light absorption layer are deteriorated by the moisture.
Further, when the hole transport layer does not contain a resin component as in the elements (B-2) and (B-3), the deterioration of the perovskite crystal due to moisture absorption is large, and the element cannot be used after one month.

The photoelectric conversion element according to the present invention can be used for a photovoltaic power generation system such as a mega solar system, a solar cell, a power source for a small portable device, and the like.

2: Base 3: First conductive layer 4: Electron transport layer 6: Light absorption layer 7: Hole transport layer 8: Second conductive layer 11: Dense titanium oxide layer 12: Porous titanium oxide layer 20: Photoelectric conversion element

Claims (10)

The electron transport layer, the hole transport layer, and the light absorption layer arranged between the electron transport layer and the hole transport layer are provided.
The light absorption layer has a porous region containing acicular crystal particles of a perovskite compound.
The hole transport layer is a photoelectric conversion element containing a hole transport material and a polycarbonate resin represented by the following structural formula.

In the formula, R ₃ , R ₄ , R ₅ or R ₆ is an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group which may have a hydrogen atom, a halogen atom and a substituent, which may be the same or different. , Z is a group of atoms required to form a cyclic alkyl which may have a substituent. The photoelectric conversion element according to claim 1, wherein the polycarbonate resin is a resin represented by the following structural formula.

The photoelectric conversion element according to claim 1 or 2, wherein the hole transport material is a carbon nanotube. The photoelectric conversion according to claim 3, wherein the hole transport layer contains the polycarbonate resin and the carbon nanotubes so that the ratio of the mass of the carbon nanotubes to the mass of the polycarbonate resin is 0.5 or more and 1.0 or less. element. The photoelectric conversion element according to claim 1 or 2, wherein the hole transport material is a compound represented by the following structural formula.

In the formula, R ₇ , R ₈ , R ₉ or R ₁₀ is an alkyl group, an alkoxy group, a cycloalkyl group or an aryl group which may have a hydrogen atom, a halogen atom and a substituent, which may be the same or different. .. The photoelectric conversion element according to claim 1 or 2, wherein the hole transport material is a compound represented by the following structural formula.

The photoelectric conversion according to claim 5 or 6, wherein the hole transport layer includes the polycarbonate resin and the hole transport material so that the ratio of the mass of the hole transport material to the mass of the polycarbonate resin is 5 or more and 10 or less. element. The perovskite compound is any one of claims 1 to 7, which is a compound represented by the general formula: ABX ₃ (in the formula, A is an organic molecule, B is a metal atom, and X is a halogen atom). The photoelectric conversion element according to one. The photoelectric conversion element according to any one of claims 1 to 8, wherein the electron transport layer contains titanium oxide. The first charge transport layer forming step of forming the first charge transport layer containing the first charge transport material, and
A light absorption layer forming step of forming a light absorption layer on the first charge transport layer, and a second charge transport layer forming a second charge transport layer containing a second charge transport material on the light absorption layer. Including the process
In the second charge transport layer forming step, a coating liquid in which a polycarbonate resin and a hole transport material which is a second charge transport material are dissolved in toluene or chlorobenzene is immersed and coated, a roll coating method, a spin coating method, and a screen coating method. , A method for manufacturing a photoelectric conversion element, which comprises forming a second charge transport layer by coating by a bar coating method, a spray coating method or an applicator coating method.

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