JP6520349B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion device, and more particularly to a photoelectric conversion device using a halide-based organic-inorganic hybrid perovskite as a light absorption layer.

Recently, a halide organic-inorganic hybrid type perovskite (for example, a compound represented by a general formula: CH ₃ NH ₃ MX ₃ where M is a divalent metal ion, and X is F, Cl, Br, or Perovskite solar cells using the light absorbing layer I.) as a light absorbing layer show high conversion efficiency, and therefore are attracting attention as next-generation solar cells (Patent Document 1). Improvements have been made since perovskite solar cells were reported to show a conversion efficiency of 3.8% in 2009, and a conversion efficiency of 19.3% has also been reported. The absorption over a wide wavelength range and the high open circuit voltage of the halide organic-inorganic hybrid perovskite show that there is a possibility of realizing a conversion efficiency exceeding 20%.

  As a factor for further improving the conversion efficiency of the perovskite solar cell, it is conceivable to improve the extraction rate of charge carriers excited by sunlight. However, in the perovskite solar cell, the extraction rates of electrons and holes are 400 ps and 600 ps, respectively, and the hot carrier cooling time (0.4 s) is also very slow.

JP, 2014-072327, A

  The problem to be solved by the present invention is to improve the electron extraction rate in a photoelectric conversion element using a halide-based organic-inorganic hybrid perovskite as a light absorption layer.

In order to solve the said subject, the photoelectric conversion element which concerns on this invention is equipped with the following structures.
(1) The photoelectric conversion element is
Lower electrode,
An electron transport layer of a metal oxide semiconductor formed on the surface of the lower electrode;
A light absorbing layer formed of a halide organic-inorganic hybrid perovskite formed on the surface of the electron transporting layer;
Nitrogen-functionalized nanographene inserted at the interface between the electron transport layer and the light absorption layer;
A hole transport layer formed on the surface of the light absorption layer;
And a counter electrode formed on the surface of the hole transport layer.
(2) The nitrogen-functionalized nanographene consists of nanographene in which a π-conjugated nitrogen functional group is introduced.
(3) The average mass of the nitrogen-functionalized nanographene is not less than 1000 m / z and not more than 50000 m / z.

  In a photoelectric conversion device using a halide-based organic-inorganic hybrid perovskite as a light absorption layer, when nitrogen-functionalized nanographene is inserted at the interface between the electron transport layer and the light absorption layer, the electron extraction rate is improved. This is considered to be because electrons excited in the light absorption layer are transferred to the electron transport layer through the nitrogen-functionalized nanographene.

It is a cross-sectional schematic diagram of the photoelectric conversion element which concerns on this invention. FIG. 2 is a schematic view of nitrogen-functionalized nanographene and a diagram showing the relationship between a reagent used for introducing a nitrogen functional group and the introduced nitrogen functional group. FIG. 6 shows a comparison of the decay spectrum of transient absorption at 760 nm and the electron extraction rate.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Photoelectric conversion element]
FIG. 1 is a schematic cross-sectional view of the photoelectric conversion element according to the present invention. In FIG. 1, the photoelectric conversion element 10 has the following configuration.
(1) The photoelectric device 10 is
A lower electrode 14;
An electron transport layer 16 formed of a metal oxide semiconductor formed on the surface of the lower electrode 14;
A light absorbing layer 18 formed of a halide organic-inorganic hybrid perovskite formed on the surface of the electron transport layer 16;
Nitrogen-functionalized nanographene 20 inserted at the interface between the electron transport layer 16 and the light absorption layer 18;
A hole transport layer 22 formed on the surface of the light absorption layer 18;
And a counter electrode 24 formed on the surface of the hole transport layer 22.
(2) Nitrogen Functionalized Nanographene 20 consists of nanographene with a π-conjugated nitrogen functional group attached.
(3) The average mass of the nitrogen functionalized nanographene 20 is 1000 m / z or more and 50000 m / z or less.

[1.1. Lower electrode]
The lower electrode 14 is one of the electrodes of the photoelectric conversion element 10. The lower electrode 14 may be a film or a plate having a thickness capable of supporting itself, or may be a thin film formed on the substrate 12. Further, the lower electrode 14 and the substrate 12 for supporting the same may be made of a translucent material, or may be made of a non-transmissive material. When the lower electrode 14, the substrate 12, and the counter electrode 24 are all made of a translucent material, incident light can be made incident from any direction on the lower electrode 14 side or the counter electrode 24 side. On the other hand, when the lower electrode 14 or the substrate 12 is made of a non-light transmitting material, incident light is made to enter from the side of the counter electrode 24.

As the lower electrode 14, for example,
(A) Tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), indium zinc oxide (IZO), zinc oxide (ZnO), etc. Self-supporting film of conductive metal oxide,
(B) Free-standing films of conductive polymers such as polyacetylene type, polypyrrole type, polythiophene type and polyphenylene vinylene type
(C) a thin film of conductive metal oxide or conductive polymer formed on the substrate 12
and so on.

Also, as the substrate 12, for example,
(A) Glass plate,
(B) Synthetic resin plate or synthetic resin film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester, polycarbonate, polyimide, etc.
and so on.

The lower the surface resistance of the lower electrode 14, the better. In order to obtain high conversion efficiency, the surface resistance of the lower electrode 14 is preferably 20 Ω / □ or less. The surface resistance is more preferably 5 Ω / □ or less.
The thickness of the lower electrode 14 is not particularly limited, and an optimum thickness is selected according to the material of the lower electrode 14, the characteristics required for the lower electrode 14, and the like.

[1.2. Electron transport layer]
The electron transport layer 16 is for transporting the electrons excited by the light absorption layer 18 to the lower electrode 14 side, and is formed on the surface of the lower electrode 14. In the present invention, a metal oxide semiconductor is used for the electron transport layer 16. The metal oxide semiconductor may have any function of transporting electrons.
In addition, as the metal oxide semiconductor, one having a predetermined LUMO energy level is preferable. The LUMO energy level will be described later.

As the metal oxide semiconductor, for example, titanium oxide (TiO ₂ ), strontium titanate (SrTiO ₃ ), zinc oxide (ZnO), tin oxide (SnO), niobium oxide (Nb ₂ O ₅ ), tungsten oxide (WO ₃₎ )and so on. The electron transport layer 16 may be made of any one of these metal oxide semiconductors, or may be made of a composite containing two or more metal oxide semiconductors.

The electron transport layer 16 may be dense or porous. When a porous metal oxide semiconductor is used as the electron transport layer 16, the area of the interface between the electron transport layer 16 and the light absorption layer 18 is increased. An increase in interface area contributes to an increase in electron extraction rate.
In order to obtain a high electron extraction rate, the specific surface area of the electron transport layer 16 is preferably 20 m ² / g or more. The specific surface area is more preferably 40 m ² / g or more.

The thickness of the electron transport layer 16 is not particularly limited, and an optimum thickness can be selected according to the purpose. In general, if the thickness of the electron transport layer 16 is too thin, leakage current will occur. Therefore, the thickness of the electron transport layer 16 is preferably 10 nm or more. The thickness of the electron transport layer 16 is more preferably 20 nm or more.
On the other hand, if the thickness of the electron transport layer 16 is too thick, the collection of electrons from the light absorption layer 18 is suppressed. Therefore, the thickness of the electron transport layer 16 is preferably 2 μm or less. The thickness of the electron transport layer 16 is more preferably 1 μm or less.

[1.3. Light absorbing layer]
In the present invention, the light absorption layer 18 is made of a halide organic-inorganic hybrid perovskite. The light absorption layer 18 is formed on the surface of the electron transport layer 16.
“Halide organic-inorganic hybrid perovskite (hereinafter, also simply referred to as“ hybrid perovskite ”)” means an octahedral network in which a metal halide octahedron MX ₆ consisting of a metal element M and a halogen X shares a vertex, and A compound having an organic framework A located in 12 coordination holes between _six octahedral networks.
As a hybrid perovskite,
(A) Simple perovskite represented by general formula: ABX ₃ (A: organic skeleton, B: metal element, X: halogen)
(B) There are layered perovskites represented by the general formula: A ₂ BX ₄ and the like.

The inorganic framework of hybrid-type perovskites consists of metal halide octahedra that share an apex. The metal halide octahedra become anionic in order to balance the positive charge from the cationic organic backbone. Therefore, the metal ion M is divalent.
Specific examples of the metal ion M constituting the hybrid type perovskite include Pb ²⁺ , Mn ²⁺ , Cu ²⁺ , Ni ²⁺ , Fe ²⁺ , Co ²⁺ , Pd ²⁺ , Ge ^{2+ and the} like. is there.
The halide constituting the hybrid perovskite is fluoride, chloride, bromide, iodide or a combination thereof.

Specifically as a hybrid perovskite,
(A) CH ₃ NH ₃ PbI ₃ , CH ₃ NH ₃ PbBr _3, etc. A simple perovskite represented by the general formula: CH ₃ NH ₃ MX ₃ (where M is a divalent metal ion, X is F, Cl, Br or I. The same shall apply hereinafter),
(B) General formula such as (CH ₃ (CH ₂ ) _n CHCH ₃ NH ₃ ) ₂ PbI ₄ (n = 5 to 8): (CH ₃ (CH ₂ ) _n CHCH ₃ NH ₃ ) ₂ MX ₄ (n = Layered perovskites represented by 5 to 8),
(C) Layered perovskites represented by the general formula: (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ MX ₄ such as (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbBr ₄ ,
and so on.
The light absorption layer 18 may be made of any one of these hybrid perovskites, or may be made of two or more hybrid perovskites.

  The thickness of the light absorption layer 18 is not particularly limited, and an optimum thickness can be selected according to the purpose.

[1.4. Nitrogen Functionalized Nano Graphene]
In the present invention, nitrogen-functionalized nanographene 20 is inserted at the interface between the electron transport layer 16 and the light absorption layer 18. This point is different from the conventional one.

[1.4.1. Definition]
“Nitrogen-functionalized nanographene” refers to nanographene in which a π-conjugated nitrogen functional group is introduced.
The “nano-graphene” includes one having a two-dimensional sheet-like structure composed of a ring structure of carbon and an aromatic ring capable of sp ² bonding. The nanographene may be composed of a single layer sheet or may be composed of a multilayer sheet.

The “π-conjugated nitrogen functional group” refers to a functional group containing a nitrogen atom having a noncovalent electron pair as a constituent element.
Examples of the π-conjugated nitrogen functional group include an amine group, a dimethylamine group, an azo group, a naphthalenediamine group, a phenylenediamine group, a nitrophenyl group, a methyl red group and a diaminonaphthalene group. The nitrogen-functionalized nanographene may contain any one of these π-conjugated nitrogen functional groups, or may contain two or more kinds.

“The π conjugated nitrogen functional group is introduced” means
(A) A part of carbon constituting nanographene is substituted by a π-conjugated nitrogen functional group,
(B) that a π-conjugated nitrogen functional group is bonded to the edge and / or basal plane of nanographene, or
(B) It means that a compound having a π-conjugated nitrogen functional group is adsorbed between the surface or sheet of nanographene.
The π-conjugated nitrogen functional group introduced into nanographene may be present in any one form of substitution, bonding or adsorption, or may be present in two or more forms.
Details of the compound having a π-conjugated nitrogen functional group will be described later.

[1.4.2. Average mass]
The mass number (size) of the nitrogen-functionalized nanographene 20 affects the transmittance of sunlight. If the nitrogen functionalized nanographene 20 becomes too large, the transmission in the visible region will be reduced. Accordingly, the average mass of the nitrogen functionalized nanographene 20 is preferably 50000 m / z or less. The average mass is more preferably 10000 m / z or less, still more preferably 5000 m / z or less.
On the other hand, when the average mass of the nitrogen-functionalized nanographene 20 becomes too small, the LUMO energy level becomes large and it does not function as an electron extraction layer. Therefore, the average mass of the nitrogen functionalized nanographene 20 is preferably 1000 m / z or more. The average mass is more preferably 1100 m / z or more, still more preferably 1200 m / z or more.

[1.4.3. LUMO energy level]
The LUMO energy level of nitrogen functionalized nanographene 20 influences the electron extraction rate. In the case of a photoelectric conversion element that does not include the nitrogen-functionalized nanographene 20, excited electrons move from the light absorption layer 18 directly to the electron transport layer 16.
On the other hand, when nitrogen-functionalized nanographene 20 is intervened at the interface between light absorbing layer 18 and electron transport layer 16, when the LUMO energy level of nitrogen-functionalized nanographene 20 is optimized, excited electrons are Transfer from the absorber layer 18 to the electron transport layer 16 via the nitrogen functionalized nanographene 20. As a result, the electrons move easily, and the electron extraction speed increases.

In order to accelerate the electron extraction rate, the LUMO energy level of the nitrogen-functionalized nanographene 20 is preferably between the LUMO energy level of the light absorption layer 18 and the LUMO energy level of the electron transport layer 16 .
The LUMO energy level of the nitrogen functionalized nanographene 20 mainly depends on the type of π-conjugated nitrogen functional group introduced into the nanographene. Therefore, the LUMO energy level of the nitrogen-functionalized nanographene 20 can be optimized by selecting the optimum π-conjugated nitrogen functional group according to the materials of the light absorption layer 18 and the electron transport layer 16.

[1.4.4. Insertion amount]
The amount of insertion of the nitrogen-functionalized nanographene 20 is not particularly limited, and an optimum amount can be selected according to the purpose.
In addition, the nitrogen functionalization nano graphene 20 should just be inserted in the interface of the electron transport layer 16 and the light absorption layer 18 at least. In the case where the electron transport layer 16 is a porous layer, when a dispersion liquid of nitrogen-functionalized nanographene 20 is applied to the surface of the electron transport layer 16, the nitrogen-functionalized nanographene 20 becomes the electron transport layer 16 and the light absorption layer 18. In addition to being inserted at the interface, the nitrogen functionalized nanographene 20 may penetrate to the vicinity of the lower electrode 14. FIG. 1 schematically shows such a state.

[1.5. Hole transport layer]
The hole transport layer 22 is for transporting the holes excited by the light absorption layer 18 to the counter electrode 24 side, and is formed on the surface of the light absorption layer 18. In the present invention, the material of the hole transport layer 22 is not particularly limited, and various materials can be used according to the purpose.

  As a material of the hole transport layer 22, for example, poly (3-hexylthiophene) (P3HT), poly [2-methoxy-5- (2-ethylhexoxy) -1,4-phenylenevinylene] (MEH-PPV) ), Poly (9,9-dioctylfluorene-co-N- (4- (3-methylpyropyl) -diphenylamine)) (TFB), 2,2'-7,7'-tetrakis (N, N'-di (2) 4-methoxyphenyl) amine) -9,9'-spirobifluorene (Spiro-OMeTAD), fullerene, carbon nanotube and the like.

  The thickness of the hole transport layer 22 is not particularly limited, and an optimum thickness can be selected according to the purpose.

[1.6. Counter electrode]
The counter electrode 24 is the other electrode of the photoelectric conversion element 10, and is formed on the surface of the hole transport layer 22. In the present invention, the material of the counter electrode 24 is not particularly limited, and various materials can be used according to the purpose.

As a material of the counter electrode 24, for example,
(A) Metals such as aluminum, gold, silver, platinum, palladium, etc.
(B) Tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), indium zinc oxide (IZO), zinc oxide (ZnO), etc. Conductive metal oxide,
(C) Conducting polymers such as acetylene type, polypyrrole type, polythiophene type, polyphenylene vinylene type,
and so on.

  The thickness and shape of the counter electrode 24 are not particularly limited, and an optimum one can be selected according to the purpose.

[1.7. Electron extraction rate]
As discussed above, interposing the nitrogen functionalised nanographene 20 between the light absorbing layer 18 and the electron transport layer 16 changes the electron extraction rate. In addition, when the material of the nitrogen-functionalized nanographene 20 is optimized according to the materials of the light absorption layer 18 and the electron transport layer 16, the electron extraction rate is accelerated.

Specifically, the relative electron extraction rate (R) represented by the following equation (a) is 10% or more and 60% or less by optimizing the combination of materials.
R = r ₁ × 100 / r ₂ (a)
However,
r ₁ is the electron extraction rate (ps) of the photoelectric conversion device containing the nitrogen-functionalized nanographene, which is calculated by measuring the decay time of the transient absorption at 760 nm,
r ₂ is the addition of nitrogen-free functionalized nanographene by using a photoelectric conversion element having the same structure as the photoelectric conversion device used for measurement of the r _1, before Symbol r ₁ and under the same conditions Measured and calculated electron extraction rate (ps).

[2. Method for producing nitrogen functionalized nanographene (1)]
The first method for producing nitrogen functionalized nanographene is
dispersing the graphite oxide or graphene oxide in an aqueous solution in which a compound having a π-conjugated nitrogen functional group is dissolved;
And heating the aqueous solution at 60 ° C. or higher.

[2.1. Dispersion process]
First, graphite oxide or graphene oxide is dispersed in an aqueous solution in which a compound having a π-conjugated nitrogen functional group is dissolved (dispersion step).

[2.1.1. Compound Having a π-Conjugating Nitrogen Functional Group]
The “compound having a π-conjugated nitrogen functional group (hereinafter also referred to as“ nitrogen-containing compound ”)” is a compound having a functional group containing a nitrogen atom having an unshared electron pair as a constituent element, and is soluble in water Or it means something that can be dispersed. As the starting material, any one of nitrogen-containing compounds may be used, or two or more may be used.
The nitrogen-containing compound is used in the form of an aqueous solution dissolved or dispersed in water. The concentration of the nitrogen-containing compound contained in the aqueous solution is not particularly limited, and an optimum concentration may be selected according to the type of the starting material, the required characteristics, and the like. The concentration of the nitrogen-containing compound is usually 0.1 to 10 mol / L.

  Examples of the nitrogen-containing compound include 2,3-diaminonaphthalene (DAN), o-phenylenediamine (o-PD), aniline, ammonia, dimethylformamide, diphenylphosphate azide, and paramethyl red.

[2.1.2. Graphite oxide and graphene oxide]
In “graphite oxide”, an oxygen-containing functional group (eg, —COOH group, —OH group, —C—O—C— group, etc.) is bonded to the edge and / or basal plane of the graphene layer constituting the graphite Say what you are doing. Graphite oxide is obtained, for example, by oxidizing graphite in a strong acid (concentrated sulfuric acid) using an oxidizing agent (such as potassium permanganate or potassium nitrate).

The “graphene oxide” refers to a sheet-like substance obtained by peeling the layers of graphite oxide. Graphene oxide can be obtained, for example, by dispersing graphite oxide in an aqueous solution and irradiating it with ultrasonic waves.
In the present invention, as the starting material, either one of graphite oxide before delamination or graphene oxide separated by delamination may be used, or both of them may be used.

  Graphite oxide and / or graphene oxide are added to the aqueous solution containing the nitrogen-containing compound. The amount of graphite oxide and / or graphene oxide contained in the aqueous solution is not particularly limited, and an optimum amount may be selected according to the type of the starting material, the required characteristics, and the like. The amount of graphite oxide and / or graphene oxide is usually 0.1 to 50 g / L.

[2.2. Heating process]
Next, after graphite oxide and / or graphene oxide are dispersed in an aqueous solution in which a nitrogen-containing compound is dispersed, the aqueous solution is heated (heating step).
Heating is performed to accelerate the reaction. When the heating temperature exceeds the boiling point of the aqueous solution, the heating is performed in a closed vessel.

If the heating temperature is too low, the reaction does not proceed sufficiently in a realistic time. Therefore, the heating temperature needs to be 60 ° C. or more. The heating temperature is more preferably 70 ° C. or more, still more preferably 80 ° C. or more.
On the other hand, if the heating temperature becomes too high, there is a risk that the substituted or bonded nitrogen may be eliminated. In addition, an expensive pressure-resistant container is required, which increases the manufacturing cost. Therefore, the heating temperature is preferably 200 ° C. or less. The heating temperature is more preferably 180 ° C. or less, still more preferably 160 ° C. or less.

  The heating time is selected in accordance with the heating temperature. Generally, the higher the heating temperature, the shorter the reaction can be progressed. The heating time is usually 1 to 20 hours.

Optimizing the heating conditions can control the nitrogen content, average thickness, and average size of the nitrogen functionalized nanographene. Generally, the higher the heating temperature and / or the longer the heating time, the lower the nitrogen content, the thinner the average thickness or the smaller the average size.
The obtained nitrogen-functionalized nanographene may be used as it is for the production of a photoelectric conversion device, or, if necessary, washing, filtration and / or dialysis may be performed.

[3. Method for producing nitrogen functionalized nanographene (2)]
A second method for producing nitrogen functionalized nanographene is
A nanographene manufacturing process for manufacturing nanographene,
dispersing nanographene in an aqueous solution in which a compound having a π-conjugated nitrogen functional group is dissolved;
And heating the aqueous solution at 60 ° C. or higher.

[3.1. Nano-graphene manufacturing process]
Nanographene can be synthesized by dispersing graphite oxide or graphene oxide in an aqueous alkaline solution and heating the dispersion in a closed vessel at 60 ° C. or higher. Alternatively, nanographite particles can be synthesized, for example, by oxidation using an oxidizing agent (such as potassium permanganate or potassium nitrate) in a strong acid (concentrated sulfuric acid).

[3.2. Dispersion process, heating process]
Next, nanographene is dispersed in an aqueous solution in which a compound having a π-conjugated nitrogen functional group is dissolved (dispersion step), and the aqueous solution is heated at 60 ° C. or higher (heating step). Thereby, the π-conjugated nitrogen functional group is introduced into the nanographene.
The other steps of the dispersing step and the heating step are the same as in the first method, and thus the description thereof is omitted.

[4. Method of manufacturing photoelectric conversion element]
The photoelectric conversion element according to the present invention is
(1) forming an electron transport layer 16 on the surface of the lower electrode 14 (electron transport layer forming step);
(2) nitrogen-functionalized nanographene 20 is adsorbed on the surface of the electron transport layer 16 (nitrogen-functionalized nanographene formation step),
(3) A light absorbing layer 18 made of a halide organic-inorganic hybrid perovskite is formed on the surface of the electron transporting layer 16 on which the nitrogen-functionalized nanographene 20 is adsorbed (light absorbing layer forming step)
(4) forming a hole transport layer 22 on the surface of the light absorption layer 18 (hole transport layer forming step);
(5) The counter electrode 24 is formed on the surface of the hole transport layer 22 (counter electrode forming step)
Can be manufactured by

[4.1. Electron transport layer formation process]
First, the electron transport layer 16 is formed on the surface of the lower electrode 14 (electron transport layer formation step). The method of forming the electron transport layer 16 is not particularly limited, and various methods can be used depending on the purpose.
For example, the porous electron transport layer 16 can be manufactured by applying a metal oxide semiconductor nanoparticle or colloid to the surface of the lower electrode 14 and heating it. The thickness of the electron transport layer 16 can be controlled by the amount of nanoparticles or colloid applied. The specific surface area of the electron transport layer 16 can be controlled by the particle size of the nanoparticles or colloid and the heating temperature.
The dense electron transport layer 16 can be manufactured by, for example, a sputtering method, a vacuum evaporation method, a CVD method, a PVD method, or the like.

[4.2. Nitrogen-functionalized nanographene formation process]
Next, nitrogen-functionalized nanographene 20 is adsorbed on the surface of the electron transport layer 16 (nitrogen-functionalized nanographene formation step).
Specifically, a dispersion liquid in which nitrogen-functionalized nanographene 20 is dispersed in a dispersion medium is applied to the surface of the electron transport layer 16 to evaporate the solvent. When the electron transport layer 16 is a porous layer, part of the dispersion may penetrate not only to the surface of the electron transport layer 16 but also into open pores (see FIG. 1). The type of dispersion medium, the concentration of the dispersion, the drying conditions and the like are not particularly limited, and an optimum one can be selected according to the purpose.

[4.3. Light Absorbing Layer Forming Step]
Next, the light absorption layer 18 made of a halide organic-inorganic hybrid perovskite is formed on the surface of the electron transport layer 16 to which the nitrogen-functionalized nanographene 20 is adsorbed (light absorption layer formation step).
Specifically, a solution in which the hybrid perovskite is dissolved in a solvent is applied to the surface of the electron transport layer 16 to evaporate the solvent. When the electron transport layer 16 is a porous layer, part of the solution may penetrate into the open pores of the electron transport layer 16. The type of solvent, the concentration of the solution, the drying conditions and the like are not particularly limited, and an optimal one can be selected according to the purpose.

[4.4. Hole transport layer formation process]
Next, the hole transport layer 22 is formed on the surface of the light absorption layer 18 (hole transport layer formation step).
The hole transport layer can be produced by a solution coating method or the like. Specifically, a solution in which a material constituting the hole transport layer 22 is dissolved in a solvent or a dispersion in which a dispersion medium is dispersed is applied to the surface of the light absorption layer 18, and the solvent or dispersion medium is volatilized. The type of solvent or dispersion medium, the concentration of the solution or dispersion, the drying conditions, and the like are not particularly limited, and an optimum one can be selected according to the purpose.

[4.5. Counter electrode formation process]
Next, the counter electrode 24 is formed on the surface of the hole transport layer 22 (counter electrode forming step). The method of forming the counter electrode 24 is not particularly limited, and an optimal method can be selected according to the purpose. Examples of a method of forming the counter electrode 24 include a vacuum evaporation method, a sputtering method, a solution coating method, and the like.

[5. Action]
In a photoelectric conversion element using a halide organic-inorganic hybrid perovskite as a light absorption layer, electrons excited in the light absorption layer generally move from the light absorption layer to the electron transport layer.
In such a photoelectric conversion device, when nitrogen-functionalized nanographene is inserted at the interface between the electron transport layer and the light absorption layer, the electron extraction rate changes. In particular, when the LUMO energy level of the nitrogen-functionalized nanographene is between the LUMO energy level of the light absorption layer and the LUMO energy level of the electron transport layer, the electron extraction speed is increased.
This is considered to be because the excited electrons move from the light absorption layer to the electron transport layer through the nitrogen-functionalized nanographene and thereby the electrons are easily moved.

(Reference Example 1, Example 2, Reference Examples 3 to 4, Example 5 and Comparative Example 1)
[1. Preparation of sample]
[1.1. Comparative Example 1]
[1.1.1. Formation of TiO ₂ layer]
As a transparent conductive substrate, a substrate in which a tin-doped indium oxide (ITO) film was formed on a glass substrate was used. For formation of the TiO ₂ layer (electron transport layer), a solution of 0.3 g of titanium paste (manufactured by DYESOL, 18 NR-T) dissolved in 0.75 g of absolute ethanol was used.
After cleaning the surface of the transparent conductive substrate with UV / ozone, a TiO ₂ solution was applied on the substrate under conditions of 2,000 rpm for 30 seconds using a spin coater. The substrate was heat-treated in air at 550 ° C. for 30 minutes to form a porous TiO ₂ layer.

[1.1.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
A methylamine solution in which 33 wt% methylamine (CH ₃ NH ₂ ) was dissolved in ethanol, and a hydrogen iodide solution in which 57 wt% hydrogen iodide (HI) was dissolved in water were prepared. To 38 mL (0.3 mol) of methylamine solution, 40 mL (0.3 mol) of a hydrogen iodide solution was dropped while nitrogen bubbling was performed, and the mixture was stirred for 2 hours in an ice bath. This solution was dried using a rotary evaporator and repurified to synthesize methyl iodide (CH ₃ NH ₃ I).
Next, the synthesized methyl iodide and lead iodide (PbI ₂ ) are dissolved in dimethylsulfoxide ((CH ₃ ) ₂ SO) in a molar ratio of 1: 1 so that the concentration becomes 30 wt%, and CH _A solution of ₃ NH ₃ PbI ₃ in dimethyl sulfoxide was prepared.

[1.1.3. Fabrication of photoelectric conversion element]
A solution of a halide organic-inorganic hybrid perovskite (CH ₃ NH ₃ PbI ₃ ) in dimethyl sulfoxide was spread on the surface of a porous TiO ₂ layer on a transparent conductive substrate for 300 seconds at 3,000 rpm. Next, by drying at 100 ° C. for 45 minutes, brown-brown crystals of the hybrid perovskite compound (CH ₃ NH ₃ PbI ₃ ) were formed on the surface of the porous TiO ₂ layer.
Next, a Spiro thin film was formed on this surface as a hole transport layer. Finally, a thin film of silver was formed as a counter electrode on the uppermost layer of these stacked films to fabricate a photoelectric conversion element.

[1.2. Reference Example 1 ]
[1.2.1. Formation of TiO ₂ layer]
In the same manner as Comparative Example 1, a porous TiO ₂ layer was formed on a transparent conductive substrate.
[1.2.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
In the same manner as Comparative Example 1, CH ₃ NH ₃ PbI ₃ was synthesized.

[1.2.3. Synthesis of diaminonaphthalene modified nanographene]
The synthesis of nanographene having a diaminonaphthalene group was performed by dispersing nanographene in an aqueous solution to which 2,3-diaminonaphthalene (DAN) is added, and heat treatment in an autoclave.
10 mg of nanographene was dispersed in 5 mL of ion exchanged water. To the obtained dispersion, 20 mg of 2,3-diaminonaphthalene was further added and dispersed. The obtained dispersion was heated at 180 ° C. for 12 hours in a closed vessel. After heating, thorough washing was performed to separate the diaminonaphthalene group-modified nanographene (see FIG. 2).

[1.2.4. Fabrication of photoelectric conversion element]
The diaminonaphthalene group-modified nanographene solution was developed at 2,000 rotations for 30 seconds on the surface of the porous TiO ₂ layer on the transparent conductive substrate using a spin coater. Next, it was dried at 70 ° C. for 30 minutes to form a nanographene layer on the surface of TiO ₂ .
Furthermore, a dimethylsulfoxide solution of a halide-based organic-inorganic hybrid perovskite (CH ₃ NH ₃ PbI ₃ ) was spread on the nanographene layer for 300 seconds at 3,000 rpm and coated. Next, by drying at 100 ° C. for 45 minutes, brown-brown crystals of the hybrid perovskite compound (CH ₃ NH ₃ PbI ₃ ) were formed on the surface of the nanographene layer.
Next, a Spiro thin film was formed on this surface as a hole transport layer. Finally, a thin film of silver was formed as a counter electrode on the uppermost layer of these stacked films to fabricate a photoelectric conversion element.

[1.3. Example 2]
[1.3.1. Formation of TiO ₂ layer]
In the same manner as Comparative Example 1, a porous TiO ₂ layer was formed on a transparent conductive substrate.
[1.3.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
In the same manner as Comparative Example 1, CH ₃ NH ₃ PbI ₃ was synthesized.

[1.3.3. Synthesis of phenylenediamine modified nanographene]
The synthesis of the nanographene having a phenylenediamine group was performed by dispersing the nanographene in an aqueous solution to which o-phenylenediamine (oPD) is added and performing heat treatment in an autoclave.
10 mg of nanographene was dispersed in 5 mL of ion exchanged water. To the obtained dispersion, 20 mg of o-phenylenediamine was further added and dispersed. The obtained dispersion was heated at 180 ° C. for 12 hours in a closed vessel. After heating, thorough washing was performed to separate phenylenediamine group-modified nanographene (see FIG. 2).

[1.3.4. Fabrication of photoelectric conversion element]
The phenylenediamine group-modified nanographene solution was spread on the surface of the porous TiO ₂ layer on the transparent conductive substrate using a spin coater at 2,000 rotations for 30 seconds. Next, it was dried at 70 ° C. for 30 minutes to form a nanographene layer on the surface of TiO ₂ .
Thereafter, in the same manner as in Reference Example 1 , a photoelectric conversion element was produced.

[1.4. Reference Example 3 ]
[1.4.1. Formation of TiO ₂ layer]
In the same manner as Comparative Example 1, a porous TiO ₂ layer was formed on a transparent conductive substrate.
[1.4.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
In the same manner as Comparative Example 1, CH ₃ NH ₃ PbI ₃ was synthesized.

[1.4.3. Synthesis of azo group modified nanographene]
Aniline (37.2 mg) is added to a mixture of concentrated hydrochloric acid (3.4 mL) and ion-exchanged water (4 mL) in an ice bath (5 ° C. or less), and then slowly sodium nitrite (28 mg) and ion-exchanged water A mixture of (0.24 mL) was added. After confirming that the potassium iodide starch paper turned blue, the reaction solution was slowly added to a mixture of nanographene (2.4 mg), ion exchanged water (0.4 mg) and sodium hydroxide (12 mg), A black-red precipitate formed.

  Furthermore, the reaction solution was slightly alkalized with a mixture of sodium hydroxide (120 mg) and ion-exchanged water (1.2 mL) and stirred for 1 hour. The reaction solution was centrifuged (13400 rpm, 30 min), and the precipitate was collected and redispersed with ion exchanged water. Three days of dialysis (1000 Da) were performed and purified. The purified aqueous dispersion was lyophilized to obtain the desired azo group-modified nanographene (FIG. 2).

[1.4.4. Fabrication of photoelectric conversion element]
On the surface of the porous TiO ₂ layer on the transparent conductive substrate, an azo group-modified nanographene solution was developed at 2,000 rotations for 30 seconds using a spin coater. Next, it was dried at 70 ° C. for 30 minutes to form a nanographene layer on the surface of TiO ₂ .
Thereafter, in the same manner as in Reference Example 1 , a photoelectric conversion element was produced.

[1.5. Reference Example 4 ]
[1.5.1. Formation of TiO ₂ layer]
In the same manner as Comparative Example 1, a porous TiO ₂ layer was formed on a transparent conductive substrate.
[1.5.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
In the same manner as Comparative Example 1, CH ₃ NH ₃ PbI ₃ was synthesized.

[1.5.3. Synthesis of amine group modified nanographene]
Nanographene (5 mg) was dispersed in ion-exchanged water (3.1 mL), 28% aqueous ammonia (1.9 mL) was added, and ultrasonication was applied for 30 minutes. The dispersion was placed in an autoclave made of polytetrafluoroethylene (PTFE) and heat-treated (100 ° C., 5 h).
The reaction dispersion was filtered through a 0.2 μm PTFE filter, and the filtrate was placed in a dialysis tube (1000 Da) and dialyzed for 3 days. The purified aqueous dispersion was freeze-dried to obtain the desired substance, amine group-modified nanographene (FIG. 2).

[1.5.4. Fabrication of photoelectric conversion element]
On the surface of the porous TiO ₂ layer on the transparent conductive substrate, an amine group-modified nanographene solution was developed at 2,000 rotations for 30 seconds using a spin coater. Next, it was dried at 70 ° C. for 30 minutes to form a nanographene layer on the surface of TiO ₂ .
Thereafter, in the same manner as in Reference Example 1 , a photoelectric conversion element was produced.

[1.6. Example 5]
[1.6.1. Formation of TiO ₂ layer]
In the same manner as Comparative Example 1, a porous TiO ₂ layer was formed on a transparent conductive substrate.
[1.6.2. Synthesis of CH ₃ NH ₃ PbI ₃ ]
In the same manner as Comparative Example 1, CH ₃ NH ₃ PbI ₃ was synthesized.

[1.5.3. Synthesis of dimethylamine group modified nanographene]
Nanographene (5 mg) was dispersed in dimethylformamide (5 mL), sonicated (30 min), and the dispersion was refluxed (24 h). After the reaction, the dimethylformamide dispersion was evaporated and re-dispersed with ion exchanged water.
The aqueous dispersion was filtered through a 0.2 μm PTFE filter, and the filtrate was placed in a dialysis tube (1000 Da) and dialyzed for 3 days. The purified aqueous dispersion was lyophilized to obtain the target product dimethylamine group-modified nanographene (FIG. 2).

[1.6.4. Fabrication of photoelectric conversion element]
The dimethylamine group-modified nanographene solution was developed at 2,000 rotations for 30 seconds on the surface of the porous TiO ₂ layer on the transparent conductive substrate using a spin coater. Next, it was dried at 70 ° C. for 30 minutes to form a nanographene layer on the surface of TiO ₂ .
Thereafter, in the same manner as in Reference Example 1 , a photoelectric conversion element was produced.

[2. Test method]
[2.1. LUMO energy level]
The LUMO energy level was measured by cyclic voltammetry (CV) method. CV measurements were performed with a standard 3-electrode system. Here, a platinum wire was used as a counter electrode, and a silver wire was used as a reference electrode. The working electrode was made by dropping and drying a dispersion solution of nitrogen functionalized nanographene on a glassy carbon disk. As an electrolyte, an acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate was used. The measurement was performed by measuring the current by drawing the potential of the working electrode between -2V and 2V.

[2.3. Electron extraction rate]
The time change of transient absorption at 760 nm was measured by a femtosecond transient absorption time-resolved spectrometer. The electron extraction rate was calculated by approximating the decay of transient absorption with an exponential function.

[3. result]
[3.1. LUMO energy level]
FIG. 2 shows a schematic diagram of nitrogen-functionalized nanographene and the relationship between a reagent used for introducing a nitrogen functional group and the introduced nitrogen functional group.
The 2,3-diaminonaphthalene group and the o-phenylenediamine group are each in the form (R) bound to one R of nanographene and the form (R-R) bound to two adjacent R It is believed that there are two forms of bonding.

Treatment of nanographene with ammonia introduces two functional groups, -CONH ₂ and -NH ₂ groups. Of these, the -NH ₂ group is a π-conjugated nitrogen functional group, but the -CONH ₂ group is not a π-conjugated nitrogen functional group.
Similarly, N, Treatment of nanographene with N- dimethylformamide, -CON (CH _{3) 2} group and -N (CH _{3) 2} of the two functional groups are introduced. Of these, it is -N (CH _{3) 2} group is a π conjugated nitrogen functionality, -CON (CH _{3) 2} group is not a π-conjugated nitrogen functionality.

The LUMO energy levels of these nitrogen-functionalized nanographenes are -3.75 eV ( Reference Example 1 ), -4.04 eV (Example 2), -3.72 eV ( Reference Example 3 ), -3.98 eV, respectively. ( Reference Example 4 ) and -4.02 eV (Example 5). That is, it was found that the LUMO energy level of nitrogen-functionalized nanographene changes depending on the type of π-conjugated nitrogen functional group introduced into nanographene.

[3.2. Electron extraction rate]
FIG. 3 shows a comparison of the decay spectrum of transient absorption at 760 nm and the electron extraction rate. The electron extraction rate of the photoelectric conversion element obtained in Comparative Example 1 was 283 (ps). On the other hand, the electron extraction rates of the photoelectric conversion elements obtained in Reference Example 1, Example 2, Reference Examples 3 to 4, and Example 5 are 146 (ps) ( Reference Example 1 ) and 44 (ps) (Implementation Examples 2), 163 (ps) ( Reference Example 3 ), 94 (ps) ( Reference Example 4 ), or 88 (ps) (Example 5), all of which were faster than Comparative Example 1. In addition, as the LUMO energy level of nitrogen-functionalized nanographene decreases, the electron extraction rate tends to increase.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited at all to the said embodiment, A various change is possible within the range which does not deviate from the summary of this invention.

  The photoelectric conversion element according to the present invention can be used for a solar power generation device.

10 photoelectric conversion element 14 lower electrode 16 electron transport layer 18 light absorption layer 20 nitrogen functionalization nanographene 22 hole transport layer 24 counter electrode

Claims (4)

The photoelectric conversion element provided with the following structures.
(1) The photoelectric conversion element is
Lower electrode,
An electron transport layer of a metal oxide semiconductor formed on the surface of the lower electrode;
A light absorbing layer formed of a halide organic-inorganic hybrid perovskite formed on the surface of the electron transporting layer;
Nitrogen-functionalized nanographene inserted at the interface between the electron transport layer and the light absorption layer;
A hole transport layer formed on the surface of the light absorption layer;
And a counter electrode formed on the surface of the hole transport layer.
(2) The nitrogen-functionalized nanographene consists of nanographene in which a π-conjugated nitrogen functional group is introduced.
(3) The average mass of the nitrogen-functionalized nanographene is not less than 1000 m / z and not more than 50000 m / z.
(4) The π-conjugated nitrogen functional group includes a dimethylamine group and / or a phenylenediamine group. The halide organic-inorganic hybrid perovskite is
(A) CH ₃ NH ₃ MX ₃ (where M is a divalent metal ion, X is F, Cl, Br or I. hereinafter the same.)
(B) (CH ₃ (CH ₂ ) _n CHCH ₃ NH ₃ ) ₂ MX ₄ (n = 5 to 8), and
_{(C) (C 6 H 5} C 2 H 4 NH 3) 2 MX 4
The photoelectric conversion element according to claim 1, comprising any one or more selected from the group consisting of: The photoelectric conversion device according to claim 1 , wherein the LUMO energy level of the nitrogen-functionalized nanographene is intermediate between the LUMO energy level of the light absorption layer and the LUMO energy level of the electron transport layer. The photoelectric conversion device according to any one of claims 1 to 3, wherein a relative electron extraction rate (R) represented by the following formula (a) is 10% or more and 60% or less.
R = r ₁ × 100 / r ₂ (a)
However,
r ₁ is the electron extraction rate (ps) of the photoelectric conversion device containing the nitrogen-functionalized nanographene, which is calculated by measuring the decay time of the transient absorption at 760 nm,
r ₂ is the addition of nitrogen-free functionalized nanographene by using a photoelectric conversion element having the same structure as the photoelectric conversion device used for measurement of the r _1, before Symbol r ₁ and under the same conditions Measured and calculated electron extraction rate (ps).

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