JP2016127160A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element in which reduction of an open-circuit voltage is less than an open-circuit voltage under pseudo sunlight even in a case of faint light.SOLUTION: In a photoelectric conversion element having an electron transport layer, a photoelectric conversion layer, a hole transport layer and an electrode which are successively laminated on a conductor film, the electron transport layer has a first layer containing metal oxide and a second layer provided between the first layer and the photoelectric conversion layer, and the second layer contains a basic compound having at least one carboxylic acid group.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photoelectric conversion element.
In this specification, the photoelectric conversion element represents an element that converts light energy into electric energy or an element that converts electric energy into light energy, and specifically includes a solar cell or a photodiode.

  In recent years, the driving power in electronic circuits has become very small, and various electronic components such as sensors can be driven even with weak power (μW order). Furthermore, when using sensors, it is expected to be applied to energy harvesting elements as a self-sustaining power source that can generate and consume on the spot. Among them, solar cells (a type of photoelectric conversion element) are elements that can generate electricity anywhere if there is light. It attracts attention.

As solar cells, silicon-based solar cells are most prevalent, and many have been reported to have high conversion efficiency under sunlight (for example, Non-Patent Document 1).
However, it is generally known that silicon-based solar cells have excellent conversion efficiency under sunlight, but are low in conversion efficiency under weak light such as indoors (for example, Non-Patent Document 2).

On the other hand, a dye-sensitized solar cell announced by Graetzel et al. Of Lausanne University of Technology in Switzerland has been reported to have a higher photoelectric conversion characteristic than a silicon solar cell under weak light (for example, Non-Patent Document 3). reference).
Usually, the illuminance of indoor light such as LED lights and fluorescent lamps is about 20 Lux to 1000 Lux, which is called weak light, which is very weak light compared to direct sunlight (about 100,000 Lux). Graetzel et al. Significantly improved the photoelectric conversion efficiency by making a metal oxide semiconductor electrode such as titanium oxide porous to increase the surface area and adsorbing a ruthenium complex as a dye on a single molecule basis (for example, Patent Documents). 1, see Non-Patent Documents 4 and 5).

It is also known that a bulk heterojunction organic thin film solar cell, which is a mixture of a P-type organic semiconductor developed by Heeger et al. And an N-type organic semiconductor typified by fullerene, has a relatively high power generation capability under weak light ( Non-patent document 8). In recent years, P-type organic semiconductors have been vigorously developed, and conversion efficiency under sunlight has been improved.
In the construction of an organic thin film solar cell, when a photoelectric conversion layer was provided directly on a transparent conductive substrate, it was generated by the charge injected from the electrode due to the contact between the transparent conductive substrate and the photoelectric conversion layer. It is known that the electric charge is neutralized and the power is reduced. In order to compensate for this drawback, a method of providing an intermediate layer called a buffer layer having a function of transporting only holes or electrons between the electrode and the photoelectric conversion layer has been reported. As typical examples, a PEDOT: PSS thin film (poly (3,4-ethylenedioxythiophene): polystyrene sulfonic acid thin film) and a zinc oxide thin film are known. By providing these layers, charge recombination can be prevented without impeding the transport of holes or electrons, and the photoelectric conversion efficiency can be improved.

Furthermore, in recent years, some ideas have been applied to the buffer layer, and attempts have been made to improve conversion efficiency under simulated sunlight.
For example, a method of adsorbing a dye such as that used in a dye-sensitized solar cell on a zinc oxide film (Non-Patent Document 6) and a method of adsorbing a fullerene derivative (Non-Patent Document 7) have been reported.
Further, according to Non-Patent Document 8, a method for improving the photoelectric conversion efficiency by further applying a basic resin on the zinc oxide film has been reported.
Non-patent document 6 reports that the fill factor has improved, and non-patent document 7 reports that the short circuit current density and fill factor have improved. In Non-Patent Document 8, it is reported that the open circuit voltage, the short circuit current density, the fill factor and all the factors have improved. All of these reports are under simulated sunlight.

In general, in the solar cell characteristics, the short-circuit current density is proportional to the amount of light under weak light, but it is known that the open-circuit voltage greatly decreases as the amount of light decreases. This is a major factor that deteriorates battery characteristics. This trend is no exception in conventional organic thin-film solar cells, and there is a demand for improvement in low open-circuit voltage under weak light. This is because the open-circuit voltage obtained with an organic thin-film solar cell under sunlight is about 0.7 to 0.8 V per unit cell. The voltage drops under weak light, and the open circuit voltage becomes 1/2 or less.
Since this open circuit voltage value is insufficient for driving an actual device, it is necessary to connect a plurality of cells in series to increase the voltage to drive the device. When the number of series connections is increased, there are disadvantages such as an increase in loss current in the circuit and a decrease in the aperture ratio of the module. As a result, the characteristics of the module are deteriorated. Therefore, it is necessary to reduce the number of series connections. Therefore, a high open circuit voltage is required in a single cell.
Even in the technologies disclosed in the above-mentioned cost patent documents 6 to 8, the characteristics under simulated sunlight are improved, but the open-circuit voltage drop under weak light is not improved.

  In view of the above problems, an object of the present invention is to provide a photoelectric conversion element in which a decrease in open circuit voltage is small compared to an open circuit voltage under simulated sunlight even in the case of weak light.

The above problem is solved by the “photoelectric conversion element” described in the following (1).
(1) “A photoelectric conversion element in which an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an electrode are sequentially stacked on a conductive film, wherein the electron transport layer is a first layer containing a metal oxide. And a second layer provided between the first layer and the photoelectric conversion layer, wherein the second layer contains a basic compound having at least one carboxylic acid group. Characteristic photoelectric conversion element ".

  According to the present invention, it is possible to provide a photoelectric conversion element with little voltage drop even under weak light.

It is a figure which shows one structural example of the photoelectric conversion element of this invention.

The present invention relates to the “photoelectric conversion element” described in the above (1). The “photoelectric conversion element”, as will be understood from the detailed description below, includes the following (2) to ( 7) includes a “photoelectric conversion element” and a “solar cell module”.
(2) “The photoelectric conversion element according to (1), wherein the basic compound having a carboxylic acid group is a tertiary amine derivative having the carboxylic acid group.”
(3) The photoelectric conversion element according to (1) or (2), wherein the basic compound having a carboxylic acid group is represented by the following general formula (1).

（上式（１）中、ｎは１〜４の整数、ｍは１〜６整数でｎ≧ｍであり、Ｒ１、Ｒ２は炭素数１〜６のアルキル基を表わし、Ｘは炭素数４〜１０の２価の芳香族基または炭素数１〜６のアルキル基を表わす。Ｒ１とＲ２は結合して環を形成してもよい。）」
（４）「前記金属酸化物が、少なくとも１つの酸化チタン、酸化亜鉛、酸化スズから選ばれたものであることを特徴とする前記（１）乃至（３）のいずれかに記載の光電変換素子。」
（５）「前記金属酸化物からなる電子輸送層の膜厚が１０ｎｍ〜６０ｎｍであることを特徴とする前記（１）乃至（４）のいずれかに記載の光電変換素子。」
（６）「太陽電池として用いることを特徴とする前記（１）乃至（５）のいずれかに記載の光電変換素子。」
（７）「前記（１）乃至（６）のいずれかに記載の光電変換素子が２次電池と接続されてなることを特徴とする太陽電池モジュール。」

(In the above formula (1), n is an integer of 1 to 4, m is an integer of 1 to 6 and n ≧ m, R 1 and R 2 represent an alkyl group having 1 to 6 carbon atoms, and X is 4 to 4 carbon atoms. 10 represents a divalent aromatic group or an alkyl group having 1 to 6 carbon atoms. R1 and R2 may combine to form a ring.
(4) "The photoelectric conversion element according to any one of (1) to (3) above, wherein the metal oxide is selected from at least one of titanium oxide, zinc oxide, and tin oxide. . "
(5) "The photoelectric conversion element according to any one of (1) to (4) above, wherein a film thickness of the electron transport layer made of the metal oxide is 10 nm to 60 nm."
(6) “The photoelectric conversion element according to any one of (1) to (5), which is used as a solar cell.”
(7) “A solar cell module, wherein the photoelectric conversion element according to any one of (1) to (6) is connected to a secondary battery.”

Hereinafter, the photoelectric conversion element according to the present invention will be described with reference to the drawings.
The present invention is not limited to the embodiments described below, and other embodiments, additions, modifications and deletions can be changed within a range that can be conceived by those skilled in the art. As long as the effects and effects of the present invention are exhibited. It is included in the scope of the present invention.

Regarding the mode shown in FIG. 1. on the substrate. A conductive film is formed; 2. An electron transport layer is formed on the conductive film, a basic carboxylic acid derivative is adsorbed on the electron transport layer, a photoelectric conversion layer is formed thereon, a hole transport layer is formed on the photoelectric conversion layer, and a hole transport layer is formed on the hole transport layer. The example of the structure by which the electrode was formed is shown in figure.
Details will be described below.

<Basic carboxylic acid derivative>
In the present invention, the basic carboxylic acid derivative is adsorbed on the electron transport layer. Among the basic carboxylic acid derivatives, tertiary amine derivatives having a carboxylic acid machine are preferred, and derivatives represented by the following general formula (1) are more preferred, represented by the general formula (2). More preferably, it is a derivative.

（上式（１）中、ｎは１〜４の整数、ｍは１〜６整数でｎ≧ｍであり、Ｒ１、Ｒ２は炭素数１〜６のアルキル基を表わし、Ｘは炭素数４〜１０の２価の芳香族基または炭素数１〜６のアルキル基を表わす。Ｒ１とＲ２は結合して環を形成してもよい。）

(In the above formula (1), n is an integer of 1 to 4, m is an integer of 1 to 6 and n ≧ m, R 1 and R 2 represent an alkyl group having 1 to 6 carbon atoms, and X is 4 to 4 carbon atoms. 10 represents a divalent aromatic group or an alkyl group having 1 to 6 carbon atoms, and R1 and R2 may combine to form a ring.

（上式（２）中、Ｒ１、Ｒ２は炭素数１〜６のアルキル基を表わし、Ｘは炭素数４〜１０の２価の芳香族基または炭素数１〜６のアルキル基を表わす。Ｒ１とＲ２は結合して環を形成してもよい。）

(In the above formula (2), R 1 and R 2 represent an alkyl group having 1 to 6 carbon atoms, and X represents a divalent aromatic group having 4 to 10 carbon atoms or an alkyl group having 1 to 6 carbon atoms. R 1 And R2 may combine to form a ring.)

The reason is not clear, but as a result of intensive studies, by adsorbing the basic carboxylic acid derivative shown above to the electron transport layer, the amount of decrease in open-circuit voltage is small even under weak light compared to under simulated sunlight. A conversion element could be obtained.
It is known in dye-sensitized solar cells and the like that acidic groups typified by carboxylic acid derivatives are suitably adsorbed on metal oxides. In the present invention, the basic carboxylic acid derivative is adsorbed on the electron transport layer by skillfully using the adsorptivity. A basic low-molecular material having no carboxylic acid dissolves when the photoelectric conversion layer is applied, does not remain on the electron transport layer, and cannot exhibit the effect. In addition, a basic layer can be provided between the photoelectric conversion layer and the electron transport layer by applying a basic polymer material on the electron transport layer. However, since the basic polymer material is insulative, if the salt film thickness is thick, the electron transport property is hindered. Further, the effect of suppressing the voltage drop under weak light is not observed because the adhesion between the electron transport layer and the basic layer is poor by simple application.
On the other hand, since the basic carboxylic acid derivative can be adsorbed as a monomolecular layer on the electron transport layer, there is no inhibition of the electron transport property and it is in close contact with the carboxylic acid, or the voltage suppression effect under weak light is effective. high.

  Specific examples of the compound represented by the general formula (1) are shown below, but are not limited thereto.

As a method of adsorbing the basic carboxylic acid derivative, an electron current collecting electrode containing an electron transport layer in a solution or dispersion of the basic carboxylic acid derivative (an electrode on which a substrate, a conductive film, or an electron transport layer is formed) ). In addition, a method in which a solution or dispersion is applied to the electron transport layer and adsorbed can be used.
In the former case, an immersion method, a dip method, a roller method, an air knife method, or the like can be used. In the latter case, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin coating method, a spray method, or the like can be used.
Further, it may be adsorbed in a supercritical fluid using carbon dioxide or the like.
When adsorbing the basic carboxylic acid derivative, a condensing agent may be used in combination. The condensing agent has a catalytic action that is considered to physically or chemically bond the photosensitizing compound and the electron transporting material to the inorganic surface, or acts stoichiometrically to advantageously improve the chemical equilibrium. Any of those to be moved may be used.
Furthermore, a thiol or a hydroxy compound may be added as a condensation aid.

  Solvents that dissolve or disperse the basic carboxylic acid derivative include, for example, alcohol solvents such as water, methanol, ethanol, and isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethyl formate, and acetic acid. Ester solvents such as ethyl or n-butyl acetate, ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl- Amide solvents such as 2-pyrrolidone, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, full Halogenated hydrocarbon solvents such as lobenzene, bromobenzene, iodobenzene, or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, Examples thereof include hydrocarbon solvents such as toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene, and these can be used alone or as a mixture of two or more.

<Board>
The substrate used in the present invention is not particularly limited, and a known substrate can be used. The substrate 1 is preferably made of a transparent material, and examples thereof include glass, a transparent plastic plate, a transparent plastic film, and an inorganic transparent crystal.

<Conductive film, electrode>
At least one of the conductive film and the electrode may be transparent to visible light, and the other may be transparent or opaque.
The electrode transparent to visible light is not particularly limited, and a known electrode used for a normal photoelectric conversion element or a liquid crystal panel can be used. For example, tin-doped indium oxide (hereinafter referred to as “ITO”) , Fluorine-doped tin oxide (hereinafter referred to as “FTO”), antimony-doped tin oxide (hereinafter referred to as “ATO”), zinc oxide doped with aluminum or gallium (hereinafter referred to as “AZO” and “GZO”, respectively) And conductive metal oxides.
The average thickness of the transparent electrode with respect to the visible light is preferably 5 nm to 10 μm, and more preferably 50 nm to 1 μm.
The electrode transparent to visible light is preferably provided on a substrate made of a material transparent to visible light in order to maintain a certain degree of hardness, and an electrode and substrate integrated may be used. Examples thereof include FTO-coated glass, ITO-coated glass, zinc oxide: aluminum-coated glass, FTO-coated transparent plastic film, and ITO-coated transparent plastic film.
The transparent electrode with respect to visible light includes a metal electrode having a structure capable of transmitting light, such as a mesh shape or a stripe shape, on a substrate such as a glass substrate, carbon nanotube, graphene, or the like having transparency. It may be laminated on. These may be used singly or as a mixture of two or more or laminated ones.
Furthermore, a metal lead wire or the like may be used for the purpose of reducing the substrate resistance. Examples of the material of the metal lead wire include metals such as aluminum, copper, silver, gold, platinum, and nickel. For example, the metal lead wire may be installed on the substrate by vapor deposition, sputtering, pressure bonding, or the like, and ITO or FTO may be provided thereon.
Examples of the case where an opaque electrode is used for either the electron collector electrode or the hole collector electrode include metals such as platinum, gold, silver, copper, and Al, and graphite. In the case of the opaque electrode, the thickness is not particularly limited, and it may be used alone or in a laminated structure of two or more.

<Electron transport layer>
The material for forming the electron transport layer can be appropriately selected according to the purpose. For example, an electron-accepting organic material (for example, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide, oxazole derivative, triazole derivative, An inorganic material such as a phenanthroline derivative, a phosphine oxide derivative, a fullerene compound, CNT, CN-PPV, etc.), zinc oxide, titanium oxide, lithium fluoride, calcium metal, or the like can be formed by a sol-gel method or sputtering. Among these, in the present invention, metal oxides such as zinc oxide, titanium oxide, and tin oxide are preferable for adsorbing the basic carboxylic acid derivative.
There is no restriction | limiting in particular in the average thickness of the said electron carrying layer, Although it can select suitably according to the objective, It is preferable to cover the whole surface thinly as much as possible, and 10 nm-60 nm are more preferable.

<Hole transport layer>
A hole transport layer can be provided to improve hole collection efficiency. Specifically, conductive polymers such as PEDOT: PSS (polyethylenedioxythiophene: polystyrene sulfonic acid), hole transporting organic compounds such as aromatic amine derivatives, positive oxides such as molybdenum oxide, vanadium oxide, and nickel oxide. An inorganic compound having a hole transporting property is formed by spin coating, a sol-gel method, or sputtering. In the present invention, it is preferable to provide molybdenum oxide.
There is no restriction | limiting in particular in the average thickness of the said positive hole transport layer, Although it can select suitably according to the objective, It is preferable to cover the whole surface thinly as much as possible, and 1 nm-50 nm are more preferable.

<Photoelectric conversion layer>
The photoelectric conversion layer is formed between the electron transport layer and the hole transport layer as a bulk hetero photoelectric conversion layer by mixing a P-type organic semiconductor and an N-type organic semiconductor.
In the bulk heterojunction type, a nano-sized pn junction is formed in the photoelectric conversion layer by mixing a P-type organic semiconductor and an N-type organic semiconductor, and an electric current is obtained using photocharge separation generated at the junction surface. The p-type organic semiconductor is composed of an electron donating material. On the other hand, the n-type semiconductor is composed of an electron-accepting material.

Examples of the p-type organic semiconductor include polythiophene and derivatives thereof, arylamine derivatives, stilbene derivatives, oligothiophene and derivatives thereof, phthalocyanine derivatives, porphyrin and derivatives thereof, polyphenylene vinylene and derivatives thereof, polythienylene vinylene and derivatives thereof, benzo Conjugated polymers and low molecular compounds such as dithiophene derivatives and diketopyrrolopyrrole derivatives can be used, and these may be used in combination.
A preferred p-type organic semiconductor is polythiophene which is a conductive polymer having π conjugation and derivatives thereof. Polythiophene and its derivatives can ensure excellent stereoregularity and have relatively high solubility in a solvent. Polythiophene and derivatives thereof are not particularly limited as long as they are compounds having a thiophene skeleton. Specific examples of polythiophene and derivatives thereof include polyalkylthiophene represented by poly-3-hexylthiophene, polyalkylthiophene such as poly-3-hexylisothionaphthene, poly-3-octylisothionaphthene, and poly-3-decylisothionaphthene. Isothionaphthene; polyethylenedioxythiophene and the like.

In recent years, PTB7 (Poly ({4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,4), which is a copolymer of benzodithiophene, carbazole, benzothiadiazole, and thiophene. 5-b ′] dithiophene-2,6-diyl} {3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenedyl})) and PCDTBT (poly [N-9 ”- Derivatives such as hepta-decanyl-2,7-carbazole-alt-5,5- (4 ′, 7′-di-2-thienyl-2 ′, 1 ′, 3′-benzothiadiazole)]) It is known as a compound that can obtain photoelectric conversion efficiency.
Furthermore, not only conjugated polymers but also low molecular weight compounds in which an electron donating unit and an electron withdrawing unit are combined are known as compounds capable of obtaining excellent photoelectric conversion efficiency. (Non-patent document 9)

<N-type organic material>
Examples of the n-type organic semiconductor material include fullerene and fullerene derivatives. Among these, fullerene derivatives are preferable from the viewpoint of charge separation and charge transport.
As said fullerene derivative, what was synthesize | combined suitably may be used and a commercial item may be used. Examples of the commercially available products include PC71BM (phenyl C71 butyric acid methyl ester, manufactured by Frontier Carbon), PC61BM, fullerene indene 2-adduct, and the like.

As a method for forming the photoelectric conversion layer, for example, spin coating, blade coating, slit die coating, screen printing coating, bar coater coating, mold coating, printing transfer method, dip pulling method, ink jet method, spray method, vacuum deposition Law. From these, thickness control and orientation control can be appropriately selected according to the characteristics of the organic material thin film to be produced.
For example, when spin coating is performed, the P-type organic semiconductor material and the n-type organic semiconductor material preferably have a concentration of 5 mg / mL to 30 mg / mL. Can be easily manufactured.

In order to remove the organic solvent, the produced organic material thin film may be subjected to an annealing treatment under reduced pressure or under an inert atmosphere (nitrogen or argon atmosphere). The temperature of the annealing treatment is preferably 40 ° C to 300 ° C, and more preferably 50 ° C to 200 ° C. Further, by performing the annealing treatment, the effective area where the stacked layers permeate and contact each other at the interface increases, and the short circuit current can be increased. In addition, you may perform the said annealing process after formation of an electrode.
The average thickness of the organic material thin film is preferably 50 nm to 400 nm, and more preferably 60 nm to 250 nm. When the average thickness is less than 50 nm, light absorption by the organic material thin film is small and carrier generation may be insufficient. When it exceeds 400 nm, the transport efficiency of carriers generated by light absorption may be further reduced. is there.

  The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. For example, methanol, ethanol, butanol, toluene, xylene, o-chlorophenol, acetone, ethyl acetate, ethylene glycol, tetrahydrofuran, dichloromethane, Examples include chloroform, dichloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, chloronaphthalene, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and γ-butyrolactone. These may be used individually by 1 type and may use 2 or more types together. Among these, chlorobenzene, chloroform, and orthodichlorobenzene are preferable.

  In order to control the phase separation structure of the p-type organic semiconductor material and the n-type organic semiconductor material, an additive of 0.1% by mass to 10% by mass may be added to the solvent. Examples of the additive include diiodoalkane (for example, 1,8-diiodooctane, 1,6-diiodohexane, 1,10-diiododecane, etc.), alkanedithiol (for example, 1,8-octanedithiol, 1,6-hexanedithiol, 1,10-decanedithiol, etc.), 1-chloronaphthalene, polydimethylsiloxane derivatives and the like.

<Application>
The photoelectric conversion element of the present invention can be applied to a power supply device by combining with a circuit board for controlling the generated current. Examples of devices using such a power supply device include an electronic desk calculator and a wristwatch. In addition, the power supply device having the photoelectric conversion element of the present invention can be applied to a mobile phone, an electronic notebook, electronic paper, and the like. Moreover, the power supply device which has the photoelectric conversion element of this invention can also be used as an auxiliary power supply for extending the continuous use time of a rechargeable or dry battery type electric appliance. Furthermore, it can be applied as an image sensor.

[Example 1]
(Preparation of electron transport layer)
1 g of zinc acetate (manufactured by aldrich), 0.28 g of ethanolamine (manufactured by aldrich), and 10 ml of methoxyethanol (manufactured by Wako) were stirred overnight at room temperature to prepare a zinc oxide precursor solution. A zinc oxide precursor solution was applied onto an ITO substrate by spin coating so as to have a film thickness of 20 nm, dried at 200 ° C. for 10 minutes, and then an electron transport layer was formed.

(Coating of basic carboxylic acid derivative)
4-Dimethylaminobenzoic acid (manufactured by TCI) was dissolved in THF to 5 mM to prepare an adsorbing solution. In a spin coater, 0.02 mL of an adsorbing solution was dropped on the electron transport layer, allowed to stand for 30 seconds, and then rotated at 2000 rpm for 30 seconds to adsorb 4-dimethylaminobenzoic acid.

(Preparation of photoelectric conversion layer)
10 mg of PTB7 (manufactured by aldrich) and 15 mg of ICBA (manufactured by frontier carbon) were dissolved in 1 ml of chlorobenzene containing 3 vol% diiodooctane (manufactured by TCI) to prepare a photoelectric conversion solution. A photoelectric conversion solution was applied onto the electron transport layer on which the adsorbent described above was adsorbed using a spin coat so as to have a film thickness of 100 nm to form a photoelectric conversion layer.

(Creation of hole transport layer and metal electrode)
On the photoelectric conversion layer, molybdenum oxide (manufactured by Kokusei Kagaku Co., Ltd.) was formed in a thickness of 10 nm and silver in a thickness of 100 nm in this order to form a solar cell element.
The open voltage of the obtained solar cell under pseudo-sunlight irradiation (AM1.5, 100 mW / cm ² ) and white LED irradiation (0.01 mW / cm ² ) were measured. Vr / Vs was measured with Vs as the open-circuit voltage under simulated sunlight irradiation and Vr as the open-circuit voltage under white LED irradiation.
Simulated sunlight is Eihiro Seiki's Solar Simulator SS-80XIL White LED is Cosmo Techno's Desk Lamp CDS-90α (Study Mode), and the evaluation equipment is NF Circuit Design Block's Solar Cell Evaluation System As-510-PV03 It was measured. The results are shown in Table 2.

[Example 2]
In Example 1, it produced and evaluated like Example 1 except having used 4- (4-methyl piperazinyl) benzoic acid (made by TCI) instead of 4-dimethylamino benzoic acid.
The results are shown in Table 2.

[Example 3]
In Example 1, it produced and evaluated like Example 1 except having used 4-piperidinyl-benzoic acid (made by Wako Co., Ltd.) instead of 4-dimethylaminobenzoic acid.

[Example 4]
In Example 1, it produced and evaluated like Example 1 except having used N, N- dimethylglycine (made by TCI) instead of 4-dimethylaminobenzoic acid.
The results are shown in Table 2.

[Example 5]
In Example 1, it produced and evaluated like Example 1 except having used 3- (diethylamino) propionic acid (made by TCI) instead of 4-dimethylaminobenzoic acid.
The results are shown in Table 2.

[Example 6]
The production of the photoelectric conversion layer of Example 1 was changed as follows.
10 mg of polythiol-based p-type organic semiconductor material (P3HT manufactured by Aldrich) and 10 mg of ICBA (manufactured by frontier carbon) were dissolved in 1 ml of chlorobenzene to prepare a photoelectric conversion solution. The photoelectric conversion solution was applied on the electron transport layer on which the adsorbent described in Example 1 was adsorbed using a spin coat so as to have a film thickness of 100 nm, and dried at 150 ° C. for 10 minutes to form a photoelectric conversion layer.
Others were produced and evaluated in the same manner as in Example 1.
The results are shown in Table 2.

[Example 7]
The photoelectric conversion element of Example 1 was changed as follows.
10 mg of the compound represented by Structural Formula A and 15 mg of fullerene n-type organic semiconductor material (ICBA manufactured by frontier carbon) were dissolved in 1 ml of chlorobenzene containing 1 vol% diiodooctane (manufactured by TCI) to prepare a photoelectric conversion solution. The photoelectric conversion solution was applied on the electron transport layer on which the adsorbent described in Example 2 was adsorbed using a spin coat so as to have a film thickness of 100 nm, thereby forming a photoelectric conversion layer.
Others were produced and evaluated in the same manner as in Example 1.

The compound represented by the structural formula A was synthesized by the synthesis method shown below.
Structural formula A was synthesized according to the following scheme. In addition, the compound 7 in the said scheme was synthesize | combined according to Angelwandte Chemie, International Edition (2011), 50, (41), 9697-9702.

<Synthesis of Compound 2>
Compound 1 (10.0 g, 33.3 mmol), 2-ethylhexyl bromide (19.3 g, 99.9 mmol), and K ₂ CO ₃ (18.4 g, 133 mmol) were mixed in dry DMF (300 mL), The mixture was stirred at 120 ° C. for 24 hours. After cooling to room temperature, the reaction mixture was poured into a large amount of ice water to form a precipitate. The resulting precipitate was collected by filtration and washed with water and methanol.
The obtained product was purified by silica gel column chromatography (eluent: CHCl ₃ / hexane = 1: 1, v / v), recrystallized from CHCl ₃ / methanol, dried under vacuum, reddish brown solid Compound 2 was obtained (Yield = 8.89 g, 51%).

About the obtained compound 2, the result of ¹ H NMR and ¹³ C NMR was shown below.
¹ H NMR and ¹³ C NMR were performed by AVANCE III 500 manufactured by Bruker. Thereafter, the same analysis was performed.

¹ H NMR (500 MHz, CDCl ₃ ): δ 8.89 (dd, J = 4.0 Hz, 1.5 Hz, 2H), 7.63 (dd, J = 5.0 Hz, 1.5 Hz, 2H), 7 .27 (dd, J = 5.0 Hz, 4.0 Hz, 2H), 4.07-3.98 (m, 4H), 1.89-1.84 (m, 2H), 1.40-1. 20 (m, 16H), 0.89-0.84 (m, 12H).

¹³ C NMR (125 MHz, CDCl 3): δ 161.78, 140.45, 135.25, 130.49, 129.87, 128.42, 107.98, 45.89, 39.11, 30.24 28.39, 23.58, 23.06, 14.01, 10.50.

<Synthesis of Compound 3>
N-bromosuccinimide (NBS, 1.69 g, 9.52 mmol) was slowly added to a stirred solution of the compound 2 (5.00 g, 9.52 mmol) in dry CHCl ₃ (300 mL) at 0 ° C. .
The resulting mixture was warmed to room temperature and stirred overnight. Water was poured into the resulting reaction mixture and then extracted with CHCl ₃ . The resulting organic phase was washed with water and dried over anhydrous MgSO ₄ . After filtration and evaporation, the product is purified by silica gel column chromatography (eluent: toluene / hexane = 4: 1, v / v), recrystallized from CHCl ₃ / methanol and dried under vacuum to give red Compound 3 was obtained as a brown solid (Yield = 2.59 g, 45%).
About the obtained compound 3, the result of ¹ H NMR and ¹³ C NMR was shown below.

¹ H NMR (500 MHz, CDCl ₃ ): δ 8.90 (dd, J = 4.0 Hz, 1.5 Hz, 1H), 8.63 (d, J = 4.0 Hz, 1H), 7.64 (dd , J = 5.0 Hz, 1.0 Hz, 1H), 7.28-7.26 (m, 2H), 7.22 (d, J = 4.5 Hz, 1H), 4.03-3.99 ( m, 2H), 3.98-3.92 (m, 2H), 1.88-1.80 (m, 2H), 1.38-1.23 (m, 16H), 0.90-0. 84 (m, 12H).

¹³ C NMR (125 MHz, CDCl ₃ ): δ 161.69, 161.52, 140.92, 138.98, 135.53, 135.09, 131.40, 131.29, 130.82, 129.78 , 128.51, 118.62, 108.20, 107.84, 45.98, 45.95, 39.15, 39.09, 30.22, 28.36, 23.60, 23.57, 23 .05, 23.04, 14.01, 10.49.

<Synthesis of Compound 4>
To a stirred solution of 1-bromo-4-hexylbenzene (5.00 g, 20.7 mmol) in dry THF (200 mL) at −78 ° C., n-butyllithium (1.62 M in hexane, 15.4 mL). 24.9 mmol) was added dropwise. The resulting mixture was reacted at that temperature for 1 hour. Then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (4.63 g, 24.9 mmol) was added and the mixture was stirred at room temperature overnight.
The resulting reaction mixture was poured into water and extracted with diethyl ether. The resulting organic phase was washed with water and dried over anhydrous MgSO ₄ . After filtration and evaporation, the product was purified by silica gel column chromatography (eluent: hexane) and dried under vacuum to give Compound 4 as a colorless oil (yield = 4.09 g, 68%).
About the obtained compound 4, the result of ¹ H NMR and ¹³ C NMR was shown below.

¹ H NMR (500 MHz, CDCl ₃ ): δ 7.73 (d, J = 8.0 Hz, 2H), 7.18 (d, J = 8.0 Hz, 2H), 2.60 (t, J = 8 .0Hz, 2H), 1.63-1.57 (m, 2H), 1.33 (s, 12H), 1.30-1.27 (m, 6H), 0.87 (t, J = 7) .0Hz, 3H).

¹³ C NMR (125 MHz, CDCl ₃ ): δ 146.39, 134.91, 127.93, 83.58, 36.26, 31.79, 31.37, 29.03, 24.91, 22.66 , 14.14.

<Synthesis of Compound 5>
A mixture of the compound 3 (2.50 g, 4.14 mmol) and the compound 4 (1.70 g, 4.55 mmol) in dry THF (40 mL) was mixed with Pd (PPh ₃ ) ₄ (0. 24 g, 0.21 mmol), and aqueous K ₂ CO ₃ (2.0 M, 20 mL; bubbled with nitrogen before use).
The resulting mixture was stirred at 60 ° C. for 24 hours. After cooling to room temperature, the reaction mixture was poured into water and then extracted with CHCl ₃ . The resulting organic phase was washed with water and dried over anhydrous MgSO ₄ . After filtration and evaporation, the product was purified by silica gel column chromatography (eluent: CHCl ₃ ), recrystallized from CHCl ₃ / methanol and dried under vacuum to give solid dark purple compound 5 (yield) = 2.75 g, 96%)
About the obtained compound 5, the result of ¹ H NMR and ¹³ C NMR was shown below.

¹ H NMR (500 MHz, CDCl ₃ ): δ 8.98 (d, J = 4.0 Hz, 1H), 8.87 (dd, J = 4.0 Hz, 1.0 Hz, 1H), 7.61 (dd, J = 5.0 Hz, 1.0 Hz, 1H), 7.59 (d, J = 8.5 Hz, 2H), 7.43 (d, J = 4.0 Hz, 1H), 7.28-7.26. (M, 1H), 7.24 (d, J = 8.0 Hz, 2H), 4.10-4.00 (m, 4H), 2.64 (t, J = 7.5 Hz, 2H), 1 97-1.92 (m, 1H), 1.90-1.85 (m, 1H), 1.67-1.60 (m, 2H), 1.42-1.23 (m, 22H) , 0.92-0.84 (m, 15H).

¹³ C NMR (125 MHz, CDCl ₃ ): δ 161.91, 161.68, 150.31, 144.22, 140.63, 139.74, 137.10, 135.00, 130.62, 130.28, 129.97, 129.23, 128.40, 128.23, 126.10, 124.04, 108.21, 107.83, 45.98, 45.93, 39.24, 39.12, 35. 76, 31.71, 31.29, 30.28, 30.26, 28.95, 28.59, 28.40, 23.71, 23.60, 23.12, 23.07, 22.61, 14.09, 14.06, 14.02, 10.58, 10.53.

<Synthesis of Compound 6>
N-bromosuccinimide (NBS, 0.71 g, 4.01 mmol) was slowly added at 0 ° C. to a stirred solution of the compound 5 (2.50 g, 3.65 mmol) in dry CHCl ₃ (50 mL). . The resulting mixture was warmed to room temperature and stirred overnight. The resulting reaction mixture was poured into water and then extracted with CHCl ₃ .
The resulting organic phase was washed with water and dried over anhydrous MgSO ₄ . After filtration and evaporation, the product was purified by silica gel column chromatography (eluent: CHCl ₃ ), recrystallized from CHCl ₃ / methanol and dried under vacuum to give compound 6 as a dark brown solid. (Yield = 2.70 g, 97%).
About the obtained compound 6, the result of ¹ H NMR and ¹³ C NMR was shown below.

¹ H NMR (500 MHz, CDCl ₃ ): δ 8.99 (d, J = 4.0 Hz, 1H), 8.61 (d, J = 4.0 Hz, 1H), 7.58 (d, J = 8 .5 Hz, 2 H), 7.43 (d, J = 4.5 Hz, 1 H), 7.24 (d, J = 8.5 Hz, 2 H), 7.21 (d, J = 4.0 Hz, 1 H) , 4.10-4.01 (m, 2H), 4.00-3.90 (m, 2H), 2.64 (t, J = 8.0 Hz, 2H), 1.96-1.90 ( m, 1H), 1.87-1.82 (m, 1H), 1.66-1.60 (m, 2H), 1.41-1.23 (m, 22H), 0.92-0. 89 (m, 15H).

¹³ C NMR (125 MHz, CDCl ₃ ): δ 161.80, 161.39, 150.65, 144.31, 141.04, 138.19, 137.41, 134.81, 131.42, 131.36 , 130.55, 129.24, 128.13, 126.10, 124.09, 118.28, 108.43, 107.67, 46.02, 39.23, 39.15, 35.77, 31 71, 31.28, 30.36, 30.24, 28.95, 28.57, 28.37, 23.70, 23.62, 23.11, 23.05, 22.97, 22.61 , 14.08, 14.06, 14.02, 10.57, 10.52.

<Synthesis of 2DPP-TBDT>
In a mixture of the compound 6 (0.80 g, 0.88 mmol) and the compound 7 (1.42 g, 1.86 mmol) in dry DMF (20 mL), Pd (PPh ₃ ) ₄ (0.05 g , 0.004 mmol) was added.
The resulting mixture was stirred at 85 ° C. for 24 hours.
After cooling to room temperature, the resulting reaction mixture was poured into water and then extracted with CHCl ₃ . The resulting organic phase was washed with water and dried over anhydrous MgSO ₄ . After filtration and evaporation, the product was purified by silica gel column chromatography (eluent: CHCl ₃ ), recrystallized with CHCl ₃ / methanol and dried under vacuum to give 2DPP-TBDT, a dark purple solid. . The resulting compound was further purified by gel permeation chromatography (GPC) before use (yield = 1.39 g, 81%).
About obtained 2DPP-TBDT, the result of ¹ H NMR and ¹³ C NMR was shown below.

¹ H NMR (500 MHz, CDCl ₃ ): δ 9.02 (d, J = 4.0 Hz, 2H), 9.00 (d, J = 4.0 Hz, 2H), 7.62 (s, 2H), 7.48 (d, J = 7.5 Hz, 4H), 7.39 (d, J = 3.5 Hz, 2H), 7.34 (d, J = 4.0 Hz, 2H), 7.25 (d , J = 4.0 Hz, 2H), 7.12 (d, J = 7.5 Hz, 4H), 6.99 (d, J = 3.5 Hz, 2H), 4.00-3.94 (m, 8H), 2.96 (d, J = 6.5 Hz, 4H), 2.54-2.50 (m, 4H), 1.91-1.85 (m, 4H), 1.82-1. 77 (m, 2H), 1.57-1.28 (m, 64H), 1.03 (t, J = 7.5 Hz, 6H), 0.97 (t, J = 6.8 Hz, 6H), 0.95-0.87 ( m, 30H).

¹³ C NMR (125 MHz, CDCl ₃ ): δ 161.41, 161.36, 149.97, 146.26, 144.03, 141.79, 139.77, 138.96, 138.52, 137.36 , 136.75, 136.65, 136.52, 130.42, 129.07, 128.99, 128.18, 128.08, 125.74, 125.54, 123.74, 120.56, 120 .29, 108.41, 107.89, 45.88, 41.43, 39.45, 39.34, 35.72, 34.50, 32.67, 31.69, 31.15, 30.40 29.03, 29.01, 28.61, 25.78, 23.66, 23.20, 23.16, 23.13, 22.62, 14.24, 14.14, 14.09, 10 . 93, 10.68, 10.58.

It analyzed Calculated _{C 118 H 150 N 4 O 4} S 8: C, 72.87; H, 7.77; N, 2.88; O, 3.29; S, 13.19.
Found: C, 72.75; H, 7.70; N, 2.80.
The results are shown in Table 2.

[Example 8]
In Example 1, it produced and evaluated similarly to Example 1 except having made the film thickness of the electron carrying layer into 10 nm.
The results are shown in Table 2.

[Example 9]
In Example 1, it produced and evaluated similarly to Example 1 except having made the film thickness of the electron carrying layer into 60 nm.
The results are shown in Table 2.

[Example 10]
In Example 1, the electron transport layer was changed to titanium oxide. The manufacturing method is shown below.
An electron transport layer made of titanium metal oxide was formed on the ITO glass substrate by reactive sputtering with oxygen gas using a target made of metal titanium. A sputtering apparatus (DVD-Spinter) manufactured by UNAXIS was used for the sputtering film formation. The thickness of the electron transport layer was 10 nm.
Others were produced and evaluated in the same manner as in Example 1.
The results are shown in Table 2.

[Example 11]
In Example 9, production evaluation was performed in the same manner as in Example 9 except that the film thickness of titanium oxide was changed to 60 nm.
The results are shown in Table 2.

[Example 12]
In Example 9, production was evaluated in the same manner as in Example 9 except that the electron transport layer was changed from titanium oxide to tin oxide.
The results are shown in Table 2.

[Example 13]
Production evaluation was performed in the same manner as in Example 10 except that titanium oxide was changed to tin oxide in Example 10.
The results are shown in Table 2.

[Example 14]
In Example 1, it produced and evaluated similarly to Example 1 except having made the film thickness of the electron carrying layer which consists of zinc oxide into 3 nm.
The results are shown in Table 2.

[Example 15]
In Example 1, it produced and evaluated similarly to Example 1 except having made the film thickness of the electron carrying layer which consists of zinc oxide into 65 nm.
The results are shown in Table 2.

[Comparative Example 1]
It was produced and evaluated in the same manner as in Example 1 except that 4-dimethylaminobenzoic acid was not adsorbed in Example 1.
The results are shown in Table 2.

[Comparative Example 2]
In Example 1, it produced and evaluated like Example 1 except having used the carboxylic acid derivative of the following structure instead of 4-dimethylaminobenzoic acid.

（ＡＣＳ Ａｐｐｌ，Ｍａｔｅｒ．Ｉｎｔｅｒｆａｃｅｓ ２０１０，２，１８９２を参照して合成した。）
結果を表２に示す。

(Synthesized with reference to ACS Appl, Mater. Interfaces 2010, 2, 1892)
The results are shown in Table 2.

[Comparative Example 3]
In Example 1, it produced and evaluated like Example 1 except having used the carboxylic acid derivative of the following structure instead of 4-dimethylaminobenzoic acid.

結果を表２に示す。

The results are shown in Table 2.

[Comparative Example 4]
In Example 1, instead of 4-dimethylaminobenzoic acid, a polyethyleneimine 80% ethoxylation solution (37 w% H2O, manufactured by Aldrich) was diluted to 0.4 w% with methoxyethanol, and the solution was diluted at 5000 rpm for 1 minute. It was prepared and evaluated in the same manner as in Example 1 except that spin coating was performed.

[Comparative Example 5]
In Example 6, it produced and evaluated like Example 6 except not having adsorbed 4-dimethylaminobenzoic acid.
The results are shown in Table 2.

[Comparative Example 6]
In Example 7, it produced and evaluated like Example 7 except not having adsorbed 4-dimethylaminobenzoic acid.
The results are shown in Table 2.

  Thus, it can be said that the solar cell produced based on this invention is excellent in the weak light, with the fall of an open circuit voltage being small compared with a comparative solar cell.

[Example 16]
The production conditions of the secondary battery (semiconductor battery) that charges the electric power generated by the photoelectric conversion element created in Example 1 are described below.
On the glass substrate, ITO was formed to a thickness of 200 nm by sputtering. A solution obtained by dissolving tin 2-ethylhexanoate (0.24 g) and silicon oil (TSF433, 1.2 g) in toluene (1.28 mL) was applied by spin coating. Baked for 1 hour. The obtained film was irradiated with ultraviolet rays having a wavelength of 254 nm at an intensity of 40 mW / cm ² for 5 hours.
Next, nickel oxide was formed at 150 nm and ITO was formed at 200 nm by sputtering to produce a semiconductor battery. Finally, after three cells of the photoelectric conversion elements produced in Example 1 were connected in series, the second electrode of the photoelectric conversion element and the first electrode of the semiconductor battery obtained above were connected with an alligator clip, and the photoelectric conversion element The first electrode and the second electrode of the semiconductor battery were connected with an alligator clip.
The performance of the photoelectric conversion element / semiconductor cell composite element thus prepared was evaluated as follows.
Pseudo sunlight was irradiated from the 1st electrode side of the photoelectric conversion element on the conditions made into the open circuit. As a result of measuring the photoelectromotive force of the electrode during this irradiation, it was confirmed that the photoelectrode (first electrode) produced a negative electromotive force with respect to the counter electrode by the light irradiation. That is, by this light irradiation, the electrode active material constituting the photoelectrode was reduced and the battery was charged. Light irradiation was continued and it was confirmed that the voltage of the photoelectrode was saturated, and then the light irradiation was stopped and the charging was terminated.
When the charged battery was placed in the dark, the external circuit was closed and the output voltage was measured with a potentiostat, it was 1.7V. When discharge was performed at a constant current density of 10 μA / cm ² with the photoelectrode as the negative electrode and the counter electrode as the positive electrode, the discharge capacity was 0.533 μAh / cm ² .

[Comparative Example 7]
Production evaluation was performed in the same manner as in Example 14 except that the photoelectric conversion element used in Example 14 was changed to the photoelectric conversion element (3-cell series) created in Comparative Example 1. As a result, the secondary battery (semiconductor battery) was charged in the same manner as in Example 14, but could not be charged. This indicates that since the output voltage of the semiconductor battery is 1.7 V, the voltage when the three photoelectric conversion elements of Comparative Example 1 are connected in series is insufficient and cannot be charged.

  From the above results, the photoelectric conversion element of the present invention maintains a high voltage even under weak light, and can charge a secondary battery with a small number of cells. Since it can be reduced, manufacturing is easy.

Japanese Patent No. 2664194

Panasonic Electric Works Technical Report, 56 (2008) 87 Nature, 353 (1991) 737 J. et al. Am. Chem. Soc. , 115 (1993) 6382 Semicond. Sci. Technol. , 10 (1995) 1689 Toshiba Review Vol. 69 No. 6 2014 ACS Appl. Mater. Interfaces 2014, 6, 803-810 ACS Appl. Mater. Interfaces 2010, 2, 1892-1902 Adv. Mater. 2013, 25, 2397-2402 Yongsheng Chen, Xiangjian Wan and Guankui Long, Accounts of chemical research, 3b2, ver. 9, Mac; ar-2013-00088c, www pubs. aca. org / accounts (Nov, 2013)

Claims (7)

  A photoelectric conversion element in which an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an electrode are sequentially stacked on a conductive film, wherein the electron transport layer includes a first layer containing a metal oxide, and the first layer And a second layer provided between the one layer and the photoelectric conversion layer, and the second layer includes a basic compound having at least one carboxylic acid group. Conversion element.   The photoelectric conversion device according to claim 1, wherein the basic compound having a carboxylic acid group is a tertiary amine derivative having the carboxylic acid group. 3. The photoelectric conversion device according to claim 1, wherein the basic compound having a carboxylic acid group is represented by the following general formula (1).

(In the above formula (1), n is an integer of 1 to 4, m is an integer of 1 to 6 and n ≧ m, R 1 and R 2 represent an alkyl group having 1 to 6 carbon atoms, and X is 4 to 4 carbon atoms 10 represents a divalent aromatic group or an alkyl group having 1 to 6 carbon atoms, and R1 and R2 may combine to form a ring.   The photoelectric conversion element according to any one of claims 1 to 3, wherein the metal oxide is selected from at least one of titanium oxide, zinc oxide, and tin oxide.   5. The photoelectric conversion element according to claim 1, wherein a film thickness of the electron transport layer made of the metal oxide is 10 nm to 60 nm.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is used as a solar cell.   A solar cell module comprising the photoelectric conversion element according to claim 1 connected to a secondary battery.

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