WO2012153845A1

WO2012153845A1 - Organic photoelectric conversion element, method for producing same, and solar cell

Info

Publication number: WO2012153845A1
Application number: PCT/JP2012/062168
Authority: WO
Inventors: 大久保　康; 貴宗服部
Original assignee: コニカミノルタホールディングス株式会社
Priority date: 2011-05-12
Filing date: 2012-05-11
Publication date: 2012-11-15
Also published as: JP5920341B2; JPWO2012153845A1

Abstract

[Problem] The objective of the present invention is to provide: an organic photoelectric conversion element that has a high photoelectric conversion efficiency, superior durability, and favorable coating characteristics; a method for producing the organic photoelectric conversion element; and a solar cell that uses the organic photoelectric conversion element. [Solution] The photoelectric conversion element has, in the given order on a transparent substrate, a transparent first electrode, a photoelectric conversion layer having both a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode, and is characterized by the photoelectric conversion layer containing a compound having a substructure represented by general formula (1) as the p-type organic semiconductor material. (In the formula: X each independently represents a fluorine atom or a chlorine atom; R₁-R₃ each independently represents a hydrogen atom, a halogen atom, an alkyl group, a fluoroalkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an alkoxy group, a fluoroalkoxy group, an alkylthio group, a fluoroalkylthio group, an alkylamino group, a fluoroalkylamino group, an aryl group, or a heteroaryl group, or alternatively a linking group wherein said groups are bonded together; the aryl group or the heteroaryl group may be a condensed ring structure; and n each independently represents an integer from 0 to 2.)

Description

ORGANIC PHOTOELECTRIC CONVERSION DEVICE, ITS MANUFACTURING METHOD, AND SOLAR CELL

The present invention relates to an organic photoelectric conversion element, a manufacturing method thereof, and a solar cell, and more particularly to a bulk heterojunction type organic photoelectric conversion element, a manufacturing method thereof, and a solar cell using the organic photoelectric conversion element.

Due to the recent rise in fossil fuels, a system that can generate electricity directly from natural energy is required. Solar cells using single-crystal / polycrystalline / amorphous Si, GaAs and CIGS (copper (Cu), indium (In), Compound-based solar cells such as gallium (Ga) and selenium (Se), or dye-sensitized photoelectric conversion elements (Gretzel cells) have been proposed and put to practical use.

However, the cost of electricity generated by these solar cells is still higher than the cost of electricity generated and transmitted using fossil fuels, which has hindered the spread of electricity. In addition, since heavy glass must be used for the substrate, reinforcement work is required at the time of installation, which is also a factor in increasing the power generation cost.

In such a situation, as a solar cell that can achieve a power generation cost lower than that of fossil fuel, an electron donor layer (p-type organic semiconductor layer) and an electron acceptor layer are provided between the transparent electrode and the counter electrode. A bulk heterojunction photoelectric conversion element sandwiching a photoelectric conversion layer mixed with (n-type organic semiconductor layer) has been proposed, and an efficiency exceeding 5% has been reported (for example, see Non-Patent Document 1).

Since solar cells using these bulk heterojunction photoelectric conversion elements (also referred to as “organic thin film solar cells”) can be formed by coating except for the anode and cathode, they can be manufactured at high speed and at low cost. There is a possibility to solve the problem of power generation cost. Furthermore, unlike the above-described Si-based solar cells, compound-based solar cells, dye-sensitized solar cells, etc., it does not require a manufacturing process that is exposed to high-temperature conditions exceeding 160 ° C., so that it is formed on an inexpensive and lightweight plastic substrate. Is also expected to be possible.

However, in addition to high efficiency, improvement in durability is also required for practical application. For such problems, the use of a metal having a high work function as a counter electrode and a solar cell of the type having a sunlight incident side as a cathode (so-called reverse layer type solar cell) causes deterioration of the electrode and the like. Since it is known that the durability is improved and the durability is improved (see, for example, Patent Document 1), a material capable of achieving high photoelectric conversion efficiency in the reverse layer configuration is demanded.

However, the reverse-layer solar cell has a disadvantageous configuration from the viewpoint of utilization of light because a conductive polymer layer having poor light transmittance exists between the metal electrode and the photoelectric conversion layer. It is required from simulation that the optimum film thickness of the conversion layer is thicker than that of a normal layer solar cell (see, for example, Non-Patent Document 2). Therefore, there is a demand for a material that can generate electricity well even with a thick film (150 nm or more), but many materials have good efficiency in a thin film (100 nm or less) photoelectric conversion layer, but a thick film (100 nm or more) has a curve. The factor (FF) was lowered, and it was difficult to achieve high efficiency.

For such problems, recently, a polymer having a fluorinated benzotriazole group described in Non-Patent Document 3 and a polymer having a fluorinated benzothiadiazole group described in Non-Patent Document 4 are used for the photoelectric conversion layer. Therefore, it has been reported that power can be generated with an efficiency of 7% or more even with a thick film thickness of around 200 nm. Although the solar cells in these reports have a normal layer configuration, it is expected that a solar cell having both high photoelectric conversion efficiency and durability can be obtained when the reverse layer configuration is adopted.

JP 2009-146981 A

However, the durability in organic thin-film solar cells is not only determined by the work function of the electrode material, but is also related to the photo-oxidation stability of the photoelectric conversion material itself, and the oxygen level ( Unless the HOMO level is sufficiently deeper than −5.3 to −5.4 eV), photo-oxidation degradation occurs due to light irradiation in the presence of oxygen, and the photoelectric conversion efficiency decreases with time. There was a problem of going. From such a viewpoint, the polymer having a fluorinated benzotriazole group described in Non-Patent Document 3 has a HOMO level of −5.3 eV, which is not yet sufficiently deep, and has insufficient durability against photooxidation. In the polymer having a fluorinated benzothiadiazole group described in Non-Patent Document 4, the HOMO level has a slightly deep level of -5.4 to -5.5 eV. , Still proved to be inadequate.

Another problem is that fluorine-containing materials generally have a high hydrophobicity, which makes it easier to repel the coating liquid when coating on a layer made of fluorine-containing materials. ing. The materials disclosed in Non-Patent Documents 3 and 4 are also difficult to play when applying a polar solution containing PEDOT: PSS that constitutes the hole transport layer in the case of the reverse layer structure, which is a manufacturing problem. It has been found.

The present invention has been made in view of the above problems, and an object of the present invention is to use an organic photoelectric conversion element having high photoelectric conversion efficiency, excellent durability, and good coating properties, a production method thereof, and the organic photoelectric conversion element. Is to provide a solar cell.

As a result of studying the problems in Non-Patent Documents 3 and 4, the present inventors have found that a p-type organic semiconductor material for a photoelectric conversion layer has a higher electron-withdrawing property than a benzotriazole group and a benzothiadiazole group. It has been found that an organic photoelectric conversion element and an organic thin-film solar cell having high photoelectric conversion efficiency and high durability can be obtained with a polymer having a substituent having a halogenated group even when the film thickness is increased. In addition, when this polymer having a halogenated benzoxadiazole group is used for a photoelectric conversion layer, it is also repelled when a conductive polymer coating solution using a polar solvent is applied on the layer. It was difficult to obtain an organic photoelectric conversion element with a high yield.

That is, the above-described problem of the present invention is achieved by the following configuration.

1. An organic photoelectric conversion element having a transparent first electrode, a photoelectric conversion layer containing a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order on a transparent substrate, The photoelectric conversion layer contains a compound having a partial structure represented by the following general formula (1) as the p-type organic semiconductor material.

(In the formula, each X independently represents a fluorine atom or a chlorine atom. R ₁ to R ₃ each independently represents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, or an alkynyl group. Group, cycloalkyl group, alkoxy group, fluorinated alkoxy group, alkylthio group, fluorinated alkylthio group, alkylamino group, fluorinated alkylamino group, aryl group or heteroaryl group, or a linking group in which these groups are bonded to each other And the aryl group or heteroaryl group may be a condensed ring structure, and each n independently represents an integer of 0 to 2.)
2. 2. The organic photoelectric conversion device according to 1 above, wherein the compound having a partial structure represented by the general formula (1) has a number average molecular weight of 15,000 to 50,000.

3. 3. The organic photoelectric conversion device as described in 1 or 2 above, wherein in the general formula (1), R ₁ represents the same atom as X.

4. 4. The organic photoelectric conversion element as described in any one of 1 to 3 above, wherein in the general formula (1), X represents a fluorine atom.

5. The p-type organic semiconductor material is a copolymer having a structure represented by the general formula (1) and a structure represented by the following general formula (2): The organic photoelectric conversion element in any one of.

(Wherein R ₄ to R ₅ are each independently a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an alkoxy group, a fluorinated alkoxy group, or an alkylthio group. Represents a fluorinated alkylthio group, an alkylamino group, a fluorinated alkylamino group, an aryl group or a heteroaryl group.)
6). 6. The organic photoelectric conversion device as described in any one of 1 to 5 above, wherein in the general formula (1), n is 1.

7. 7. The organic photoelectric conversion device as described in any one of 1 to 6 above, wherein in the general formula (1), R ₂ represents an alkyl group having 8 to 20 carbon atoms.

8). 8. The organic photoelectric conversion device as described in any one of 1 to 7 above, wherein in the general formula (1), R ₂ represents a linear alkyl group.

9. In the general formula (1), R ₂ is a copolymer containing both a partial structure, R ₂ is a partial structure represents an alkyl group or a hydrogen atom of less than 8 carbon atoms represents the alkyl group having 8 or more carbon atoms 9. The organic photoelectric conversion device as described in any one of 1 to 8 above.

10. 10. A method for producing an organic photoelectric conversion element, comprising producing the photoelectric conversion layer of the organic photoelectric conversion element according to any one of 1 to 9 without being exposed to oxygen and moisture during film formation and after film formation.

11. 10. A solar cell comprising the organic photoelectric conversion device according to any one of 1 to 9, wherein the first electrode is a cathode and the second electrode is an anode.

INDUSTRIAL APPLICABILITY According to the present invention, an organic photoelectric conversion element having a high fill factor value, high photoelectric conversion efficiency, excellent durability, and good coatability, a manufacturing method thereof, and a solar cell using the organic photoelectric conversion element are provided. can do.

It is a schematic sectional drawing which shows the example of a structure of the organic photoelectric conversion element of this invention. It is a schematic sectional drawing which shows the other example of a structure of the organic photoelectric conversion element of this invention. It is a schematic sectional drawing which shows the example of the organic photoelectric conversion element of this invention provided with the tandem type photoelectric conversion layer.

The organic photoelectric conversion element of the present invention has a transparent first electrode, a photoelectric conversion layer containing a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order on a transparent substrate. An organic photoelectric conversion device, wherein the photoelectric conversion layer contains a compound having a partial structure represented by the general formula (1) as a p-type organic semiconductor material.

In this invention, the compound which has the partial structure represented by the said General formula (1) as a p-type organic-semiconductor material of the bulk heterojunction type photoelectric converting layer containing a p-type organic-semiconductor material and an n-type organic-semiconductor material especially By using, an organic photoelectric conversion element having a high fill factor value, high photoelectric conversion efficiency, and excellent durability can be provided. Moreover, the organic photoelectric conversion element with favorable applicability | paintability can also be provided.

(Configuration of organic photoelectric conversion element)
FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the organic photoelectric conversion element of the present invention.

The organic photoelectric conversion element 10 has a transparent first electrode 12 on a transparent substrate 11, a hole transport layer 17 on the first electrode 12, and a hole transport layer 17 on the hole transport layer 17. The photoelectric conversion layer 14 is provided, the electron transport layer 18 is provided on the photoelectric conversion layer 14, and the second electrode 13 is provided on the electron transport layer 18.

In the present invention, the substrate 11 and the first electrode 12 are transparent, and light used for photoelectric conversion enters from the direction of the arrow in FIG.

The photoelectric conversion layer 14 is a layer that converts light energy into electric energy, and contains a p-type organic semiconductor material and an n-type organic semiconductor material.

The p-type organic semiconductor material functions relatively as an electron donor (donor), and the n-type organic semiconductor material functions relatively as an electron acceptor.

Here, the electron donor and the electron acceptor are “an electron donor in which, when light is absorbed, electrons move from the electron donor to the electron acceptor to form a hole-electron pair (charge separation state)”. And an electron acceptor ”, which does not simply donate or accept electrons like an electrode, but donates or accepts electrons by a photoreaction.

In FIG. 1, light incident from the first electrode 12 through the substrate 11 is absorbed by the electron acceptor or electron donor in the photoelectric conversion layer 14, and electrons move from the electron donor to the electron acceptor. A pair of holes and electrons (charge separation state) is formed.

The generated electric charge is generated between the electron acceptors due to the internal electric field, for example, when the work functions of the first electrode 12 and the second electrode 13 are different, due to the potential difference between the first electrode 12 and the second electrode 13. And the holes pass between the electron donors and are carried to different electrodes, and a photocurrent is detected.

In the example of FIG. 1, the work function of the first electrode 12 is larger than the work function of the second electrode 13, so that holes are transported to the first electrode 12 and electrons are transported to the second electrode 13. In this case, the second electrode 13 is made of a metal that has a small work function and is easily oxidized. In this case, the first electrode functions as an anode (anode) and the second electrode functions as a cathode (cathode).

Figure 2 shows an example of another configuration.

2, contrary to the case of FIG. 1, the work function of the second electrode 13 is made larger than the work function of the first electrode 12, so that electrons are transferred to the first electrode 12 and holes are transferred to the first electrode 12. This is a configuration when designed to be transported to two electrodes 13. In this case, the electron transport layer 18 is disposed between the first electrode 12 and the photoelectric conversion layer 14, the hole transport layer 17 is disposed between the photoelectric conversion layer 14 and the second electrode 13, The first electrode functions as a cathode (cathode) and the second electrode functions as an anode (anode).

The organic photoelectric conversion element of the present invention has a configuration shown in FIG. 2 in particular from the viewpoint of durability of the second electrode, that is, the first electrode is a cathode (cathode) and the second electrode is an anode (anode). It is preferable that

Although not shown in FIGS. 1 and 2, the organic photoelectric conversion element of the present invention is not limited to the hole blocking layer, the electron blocking layer, the electron injection layer, the hole injection layer, or the smoothing layer. It may have a layer.

Furthermore, for the purpose of improving the solar light utilization rate (photoelectric conversion efficiency), a tandem configuration in which a plurality of photoelectric conversion layers are stacked may be employed. FIG. 3 is a cross-sectional view illustrating an organic photoelectric conversion element including a tandem photoelectric conversion layer.

In the case of the tandem configuration, the first electrode 12 and the first photoelectric conversion layer 14 ′ are stacked on the substrate 11, the charge recombination layer 15 is stacked, the second photoelectric conversion layer 16, and then the second photoelectric conversion layer 15. The electrode 13 is laminated.

The second photoelectric conversion layer 16 may be a layer that absorbs light having the same spectrum as the absorption spectrum of the first photoelectric conversion layer 14 ′ or may be a layer that absorbs light having a different spectrum, but preferably has a different spectrum. It is a layer that absorbs light.

Note that a hole transport layer 17 and an electron transport layer 18 may be provided between the first photoelectric conversion layer 14 ′ and the second photoelectric conversion layer 16 and each electrode. In the tandem configuration, each layer preferably has a reverse layer configuration as shown in FIG.

The materials that make up these layers are described below.

[P-type organic semiconductor materials]
(Compound having a partial structure represented by the general formula (1))
The photoelectric conversion layer contains a compound having a partial structure represented by the general formula (1) as a p-type organic semiconductor material.

The compound is an organic compound having semiconductor characteristics. A compound having only a partial structure of the general formula (1) may be used, but in order to obtain an organic compound having more preferable semiconductor characteristics (specific HOMO / LUMO levels) as an organic thin film solar cell, it is bonded to a donor unit described later. It is preferable that the compound has a structure.

In the said General formula (1), X represents a fluorine atom or a chlorine atom each independently. R ₁ to R ₃ are each independently a hydrogen atom, a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom), alkyl group, fluorinated alkyl group, alkenyl group, alkynyl group, cycloalkyl group, alkoxy group Group, fluorinated alkoxy group, alkylthio group, fluorinated alkylthio group, alkylamino group, fluorinated alkylamino group, aryl group, or heteroaryl group, or a linking group in which these groups are bonded to each other, the aryl group or The heteroaryl group may be a condensed ring structure. n independently represents an integer of 0 to 2.

That is, by having a halogenated benzooxadiazole group in the main chain of the conjugated polymer, HOMO / LUMO deeper than those in Non-Patent Documents 3 and 4 having a halogenated benzotriazole group or a halogenated benzothiadiazole group. Levels can be provided, and higher open-circuit voltage and photooxidation stability can be provided. Further, as in Non-Patent Documents 3 and 4 having a halogenated benzotriazole group or a halogenated benzothiadiazole group, a sufficiently high fill factor and photoelectric conversion efficiency can be provided even with a thick film of 150 nm or more.

The alkyl group is preferably an alkyl group having 1 to 24 carbon atoms, more preferably an alkyl group having 8 to 24 carbon atoms. For example, methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, sec -Butyl, tert-butyl, n-pentyl group, isopentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n- Tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl group, n-icosyl, 2-ethylhexyl, 3-butylnonyl, 3-ethylnonyl, 2-tetraoctyl, 2-hexyldecyl, 1 -Octylnonyl, 2-decyltetradecyl and the like.

The fluorinated alkyl group is a fluorinated alkyl group in which part or all of the hydrogen atoms in the alkyl group are fluorinated. Since the fluorinated alkyl group in which all hydrogen atoms are fluorinated tends to be poor in solubility, the hydrogen atom in the position close to the mother nucleus (benzooxadiazole ring) is not fluorinated, and the terminal hydrogen atom is fluorine. The fluorinated alkyl group is preferable. For example, — (CH ₂ CH ₂ ) —C ₄ F ₉ , — (CH ₂ CH ₂ ) —C ₇ F _{15 and the} like can be mentioned.

The alkenyl group is preferably an alkenyl group having 2 to 20 carbon atoms, and examples thereof include a vinyl group and an allyl group.

The alkynyl group is preferably an alkynyl group having 2 to 20 carbon atoms, and examples thereof include an ethynyl group and a propargyl group.

The cycloalkyl group is preferably a cycloalkyl group having 3 to 20 carbon atoms, more preferably a cycloalkyl group having 4 to 8 carbon atoms, and examples thereof include cyclopropyl, cyclopentyl, cyclohexyl, norbornyl, adamantyl and the like.

The alkoxy group and the fluorinated alkoxy group are preferably an alkoxy group having 1 to 24 carbon atoms and a fluorinated alkoxy group. For example, a methoxy group, an isopropoxy group, a t-butoxy group, a 2-ethylhexyloxy group, and 2-ethyloctyl Examples include an oxy group, an n-dodecyloxy group, a 2-butyloctyloxy group, a trifluoromethoxy group, a group having a structure in which a hydrogen atom of a hydroxyl group is substituted with the aforementioned alkyl group, fluorinated alkyl group, or the like. it can.

The alkylthio group and the fluorinated alkylthio group are preferably an alkylthio group having 1 to 24 carbon atoms and a fluorinated alkylthio group. For example, a methylthio group, an isopropylthio group, a t-butylthio group, a 2-ethylhexylthio group, a trifluoromethylthio group A group having a structure in which a hydrogen atom of a thiol group is substituted with the aforementioned alkyl group, fluorinated alkyl group, or the like.

As the alkylamino group and fluorinated alkylamino group, an alkylamino group having 1 to 24 carbon atoms and a fluorinated alkylamino group are preferable. For example, dimethylamino group, diisopropylamino group, methyl-t-butylamino group, di- Examples thereof include a group having a structure in which one or more hydrogen atoms of an amino group (—NH ₂ ) are substituted with the aforementioned alkyl group, fluorinated alkyl group or the like, such as a 2-ethylhexylamino group.

As the aryl group, an aryl group having 6 to 30 carbon atoms is preferable, an aryl group having 6 to 20 carbon atoms is more preferable, and an aryl group having 6 to 12 carbon atoms is particularly preferable. For example, phenyl, p-methylphenyl, naphthyl , Phenanthryl, pyrenyl and the like.

The heteroaryl group is preferably a heteroaryl group having 1 to 20 carbon atoms, and more preferably a heteroaryl group having 1 to 12 carbon atoms. Examples of the hetero atom include a nitrogen atom, an oxygen atom, and a sulfur atom. Specific examples include imidazolyl, pyridyl, quinolyl, furyl, piperidyl, benzoxazolyl, benzimidazolyl, benzthiazolyl, thienyl, furyl, pyrrole, thiazolyl and the like.

Condensed rings include hetero five-membered rings such as thiophene ring, furan ring, pyrrole ring, cyclopentadiene, and silacyclopentadiene, and structures containing these as condensed rings, specifically, fluorene, silafluorene, carbazole, dithienocyclo. Examples include pentadiene, dithienosilacyclopentadiene, dithienopyrrole, and benzodithiophene.

Further, these substituents may be linking groups bonded to each other.

Among these substituents, R ₁ to R ₃ preferably represent an alkyl group having 8 to 20 carbon atoms. This is because, in order to form a sufficiently thick photoelectric conversion layer using the obtained p-type organic semiconductor material, the p-type organic semiconductor material must have a certain degree of solubility, and the viewpoint of imparting solubility Thus, a material substituted with an alkyl group having 8 or more carbon atoms is preferable. On the other hand, when the alkyl chain length is longer than 20, the portion (conjugated polymer main chain) contributing to charge transport tends to decrease or the short circuit current value tends to decrease. In particular, in the case of a polymer material, in addition to imparting solubility, a linear alkyl group may provide alignment (also referred to as a fastener effect), and may provide high mobility. It is preferable that the p-type organic semiconductor material is substituted with an alkyl group (that is, R ₁ to R ₃ represent a linear alkyl group). Further, in the general formula (1), if there is a partial structure R 1 _~ R ₃ represents an alkyl group having 8 or more carbon atoms, a part as will be described later R _{1 ~} R ₃ is having less than 8 carbon atoms the alkyl group Alternatively, a copolymer having a partial structure representing a hydrogen atom may be used. As will be described later, such a copolymer is preferable because it has a merit that it is easy to achieve both a preferable molecular weight and crystallinity.

In the general formula (1), R ₁ is preferably a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom) as in the case of X. By setting it as such a structure, it can be set as a polymer of a deeper HOMO * LUMO level, and can provide a higher open circuit voltage and photo-oxidation stability. R ₁ is preferably the same atom as X. By adopting such a structure, the symmetry of the molecule is improved, so that the crystallinity of the obtained polymer is improved, and high mobility and a high fill factor are easily obtained.

In particular, in the general formula (1), X is preferably a fluorine atom. The fluorine atom is the smallest of the halogen atoms, and when substituted with a benzooxadiazole group, it does not easily cause steric hindrance with the adjacent thiophene ring and the like, and the planarity of the molecule is easily maintained. As a result, the crystallinity and mobility of the obtained molecule are improved, and an organic photoelectric conversion element having a high fill factor is easily obtained.

In the general formula (1), each n is independently an integer of 0 to 2, and is preferably 1. When n = 0, the resulting polymer may have insufficient solubility. Further, when n = 2, the HOMO / LUMO level of the obtained polymer becomes shallow, and the open circuit voltage may be slightly lowered when an organic photoelectric conversion element is obtained. Moreover, although details are unknown, in the case of a polymer with n = 1, a highly durable one is easily obtained.

The partial structure represented by the general formula (1) is a partial structure generally called an acceptor unit (a unit having a deep HOMO / LUMO level) in a donor-acceptor type p-type organic semiconductor material. . A compound in which a donor unit that functions as a donor (a unit having a shallow HOMO / LUMO level) and an acceptor unit is conjugated to form a material having both long-wavelength absorption and a deep LUMO level, and is a p-type organic semiconductor material Are preferably used.

As the donor unit, for example, any unit that has a LUMO level or a HOMO level shallower than a hydrocarbon aromatic ring (benzene, naphthalene, anthracene, etc.) having the same number of π electrons can be used without limitation. More preferred are heterocyclic 5-membered rings such as thiophene ring, furan ring, pyrrole ring, cyclopentadiene, and silacyclopentadiene, and condensed rings containing these ring structures. Specific examples of the condensed ring include fluorene, silafluorene, carbazole, dithienocyclopentadiene, dithienosilacyclopentadiene, dithienopyrrole, and benzodithiophene.

(Copolymer having the structure represented by the general formula (1) and the structure represented by the general formula (2))
The p-type organic semiconductor material is more preferably a copolymer having a structure represented by the general formula (1) and a structure represented by the general formula (2).

In the general formula (2), R ₄ to R ₅ each independently represent a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an alkoxy group, or a fluorinated alkoxy group. Represents an alkylthio group, a fluorinated alkylthio group, an alkylamino group, a fluorinated alkylamino group, an aryl group or a heteroaryl group. Preferred forms and specific examples of these groups are the same as the groups mentioned in the general formula (1). Such a structure is preferable because it can provide a material with high mobility, high solubility, and absorption up to a long wavelength.

Furthermore, the compound having the partial structure represented by the general formula (1) used as the p-type organic semiconductor material preferably has a number average molecular weight of 15000 to 50000.

By setting the number average molecular weight to 15000 or more, low molecular weight compounds (for example, fullerene derivatives) are widely used as the n-type organic semiconductor material that is the other component constituting the bulk heterojunction photoelectric conversion layer. When the type organic semiconductor material is a polymer, it tends to form a microphase separation structure and to easily generate carrier paths that respectively carry holes and electrons generated in the bulk heterojunction photoelectric conversion layer.

On the other hand, if the molecular weight is too large, the solubility is lowered. Therefore, the number average molecular weight of the p-type organic semiconductor material is preferably 50000 or less. More preferably, it is in the range of 15000 to 30000.

In addition, the solubility substitutes the mother nucleus represented by the general formula (1) or the general formula (1) and the general formula (2) with a substituent having solubility (also referred to as “soluble group”). However, if the amount of the soluble group is excessive, the crystallinity and mobility may be lowered, and the characteristics such as the curve factor of the obtained organic thin film solar cell may be lowered. Therefore, the general formula (1) having a structure substituted with a soluble group and an aryl group substituted with a soluble group, or the structure represented by the general formula (1) and the general formula (2), By copolymerizing the general formula (1) having no solubility group or the structure represented by the general formula (1) and the general formula (2), both the preferable molecular weight range and the crystallinity are achieved. It is also a preferable means.

The number average molecular weight can be measured by gel permeation chromatography (GPC).

Specifically, the number average molecular weight is a value measured by the following method.

Water per 150C ALC / GPC (column: GMHHR-H (S) manufactured by Tosoh Corporation), solvent: 1,2,4-trichlorobenzene), by gel permeation chromatography (GPC) method, The weight average molecular weight (Mw) and the number average molecular weight (Mn) are measured. In addition, the column elution volume is calibrated by the universal calibration method using Tosoh Corporation standard polystyrene.

A compound having a desired molecular weight can be separated by purification using preparative gel permeation chromatography (GPC).

The ratio of the partial structure represented by the general formula (1) contained in the compound having the partial structure represented by the general formula (1) according to the present invention is approximately 20 to 20% with respect to 100% by mass of the total mass of the compound. 80% by mass is preferable, and 25 to 60% by mass is particularly preferable. In the present invention, the compound having the partial structure represented by the general formula (1) is preferably a high molecular weight compound as described above. In this case, the partial structure represented by the general formula (1) is used. The number of repeating units is preferably in the range of 30 to 50 mol% with respect to the total number of repeating units of the whole compound including repeating units other than this partial structure.

Hereinafter, examples of the compound having a partial structure represented by the general formula (1) will be given, but the present invention is not limited thereto.

In the above compound, it is sufficient that the number of partial structures according to the present invention is a value that falls within the aforementioned molecular weight range. For example, in order to fall within the range of the number average molecular weight of 10,000 to 100,000, approximately 10 to 200 is required. It needs to be about.

[Method for Synthesizing Compound According to the Present Invention]
Among the compounds according to the present invention, compounds having a partial structure represented by the general formula (1) Med. Chem. 1995, p. 1786, J. Am. Fluorine Chem. , 2004, p421, and Physical Organic, 1967, p. 909 etc. can be synthesized with reference.

(Synthesis example)
Hereinafter, synthesis examples of compounds having a partial structure represented by the general formula (1) of the present invention will be shown.

(Exemplary Compound 10)

J. Fluorine Chem. , 2004, p421, 1.56 g (10 mmol) of 5,6-difluoro-benzooxadiazole and 10.1 g (40 mmol) of iodine were added to 50 ml of fuming sulfuric acid and stirred at 60 ° C. for 24 hours. After completion of the reaction, water and methylene chloride were added under ice cooling to extract the organic phase. After further washing with a 1N aqueous sodium hydroxide solution three times and then with a sodium hydrogen carbonate aqueous solution, the organic phase was dried over magnesium sulfate, and the magnesium sulfate was filtered off. Got. The obtained crude product was purified by silica gel column chromatography to obtain 3.06 g of 4,7-diiodo-5,6-difluoro-benzooxadiazole (yield 75%).

Next, bis- (5,5'-trimethylstannyl) -3,3'-di-dodecyl-silylene-2,2'-dithiophene was prepared as described in JP-T-2010-507233 and Adv. Mater. , 2010, p-E63 was synthesized with reference.

204 mg (0.5 mmol) of the above 4,7-diiodo-5,6-difluoro-benzooxadiazole and bis- (5,5′-trimethylstannyl) -3,3′-di-dodecyl-silylene-2 , 2′-dithiophene (428 mg, 0.5 mmol) was dissolved in 20 ml of anhydrous toluene. After purging the solution with nitrogen, 12.55 mg (0.014 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 28.80 mg (0.110 mmol) of triphenylphosphine were added. The solution was purged with nitrogen for an additional 15 minutes. Thereafter, the solution was heated to 110 to 120 ° C. and reacted for 40 hours. In order to further endcap, 2-tributyltin thiophene (11 mg, 0.03 mmol) was added and refluxed for 10 hours. Further 2-bromothiophene (10 mg, 0.06 mmol) was added and refluxed for 10 hours. After completion of the reaction, the solvent was distilled off, and the resulting residue was washed with methanol (50 ml × 3 times), and then washed with acetone (50 ml × 3 times).

The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. Each 3 ml of this filtrate was charged into a recycle HPLC (manufactured by Nippon Analytical Chemical Industry) and purified. The high molecular weight fractions were collected to obtain 100 mg of a pure polymer (Mn = 21000) (Exemplary Compound 10).

(Exemplary Compound 20)

First, Non-Patent Document 3, Macromolecules, 2010, 43, p4609, and J. Org. Am. Chem. Soc. , 2007, 129, p4112, 2,6-bis (trimethylstannyl) -4,8-di-3-butylnonyl-benzo [1,2-b: 4,5-b ′] dithiophene was synthesized. .

204 mg (0.5 mmol) of the 4,7-diiodo-5,6-difluoro-benzooxadiazole and 2,6-bis (trimethylstannyl) -4,8-di-3-butylnonyl-benzo [1, 441 mg (0.5 mmol) of 2-b: 4,5-b] dithiophene was dissolved in 20 ml of anhydrous toluene. After purging the solution with nitrogen, 12.55 mg (0.014 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 28.80 mg (0.110 mmol) of triphenylphosphine were added. The solution was purged with nitrogen for an additional 15 minutes. Thereafter, the solution was heated to 110 to 120 ° C. and reacted for 40 hours. In order to further endcap, 2-tributyltin thiophene (11 mg, 0.03 mmol) was added and refluxed for 10 hours. Further 2-bromothiophene (10 mg, 0.06 mmol) was added and refluxed for 10 hours. After completion of the reaction, the solvent was distilled off, and the resulting residue was washed with methanol (50 ml × 3 times), and then washed with acetone (50 ml × 3 times).

The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. Each 3 ml of this filtrate was charged into a recycle HPLC (manufactured by Nippon Analytical Chemical Industry) and purified. The high molecular weight fractions were collected to obtain 140 mg of a pure polymer (Mn = 15000) (Exemplary Compound 20).

(Exemplary Compound 25)

First, 4- (2-ethylhexyl) thiophen-2-yl-trimethyltin was synthesized with reference to Non-Patent Document 3 and the like.

1.58 g (4.4 mmol) of 4- (2-ethylhexyl) thiophen-2-yl-trimethyltin and 814 mg (2.0 mmol) of 4,7-diiodo-5,6-difluoro-benzooxadiazole After dissolving in 20 ml of dehydrated toluene and replacing with argon for 15 minutes, 40 mg of tetrakis (triphenylphosphine) palladium was added and refluxed for 2 hours.

After completion of the reaction, toluene was distilled off, and the crude product was purified by silica gel column chromatography (heptane: ethyl acetate = 100: 0 to 90:10) and recrystallized with isopropanol to obtain 600 mg of orange crystals. (Yield 55%).

Next, 545 mg (1 mmol) of 4,7-bis- (4- (2-ethylhexyl) thiophen-2-yl) -5,6-difluoro-benzooxadiazole obtained above was dissolved in 20 ml of tetrahydrofuran, After adding 392 mg (2.2 mmol) of N-bromosuccinimide (NBS) and stirring overnight at room temperature, saturated brine was added to wash with water, and the organic phase was dried over anhydrous magnesium sulfate, and then the solvent was distilled off. As a result, a crude product was obtained. The obtained crude product was recrystallized from isopropanol to give 4,7-bis- (5-bromo-4- (2-ethylhexyl) thiophen-2-yl) -5,6- 560 mg of difluoro-benzooxadiazole was obtained (yield 79%).

351 mg (0.5 mmol) of 4,7-bis- (5-bromo-4- (2-ethylhexyl) thiophen-2-yl) -5,6-difluoro-benzooxadiazole and 2,6-bis ( 441 mg (0.5 mmol) of trimethylstannyl) -4,8-di-3-butylnonyl-benzo [1,2-b: 4,5-b ′] dithiophene was dissolved in 20 ml of anhydrous toluene. After purging the solution with nitrogen, 12.55 mg (0.014 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 28.80 mg (0.110 mmol) of triphenylphosphine were added. The solution was purged with nitrogen for an additional 15 minutes. Thereafter, the solution was heated to 110 to 120 ° C. and reacted for 40 hours. In order to further endcap, 2-tributyltin thiophene (11 mg, 0.03 mmol) was added and refluxed for 10 hours. Further 2-bromothiophene (10 mg, 0.06 mmol) was added and refluxed for 10 hours. After completion of the reaction, the solvent was distilled off, and the resulting residue was washed with methanol (50 ml × 3 times), and then washed with acetone (50 ml × 3 times).

The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. Each 3 ml of this filtrate was charged into a recycle HPLC (manufactured by Nippon Analytical Chemical Industry) and purified. The high molecular weight fractions were collected to obtain 140 mg of a pure polymer (Mn = 50000) (Exemplary Compound 25).

(Exemplary Compound 31)

4,7-bis- (5-bromothiophene) was synthesized in the same manner as in the synthesis of Exemplified Compound 25 except that 2-thienyltrimethyltin was used instead of 4- (2-ethylhexyl) thiophen-2-yl-trimethyltin. -2-yl) -5,6-difluoro-benzoxadiazole using 4-dodecylthiophen-2-yl-trimethyltin and 4,7-bis- (5-bromo-4-dodecylthiophene-2- Yl) -5,6-difluoro-benzooxadiazole was synthesized. Also, J. Am. Chem. Soc. , 2007, 129, p4112, 2,6-bis (trimethylstannyl) -4,8-didodecyl-benzo [1,2-b: 4,5-b ′] dithiophene was synthesized.

Next, 325 mg (0.4 mmol) of the 4,7-bis- (5-bromo-4-dodecylthiophen-2-yl) -5,6-difluoro-benzooxadiazole and 4,7-bis- (5 -Bromothiophen-2-yl) -5,6-difluoro-benzooxadiazole 48 mg (0.1 mmol) and 2,6-bis (trimethylstannyl) -4,8-didodecyl-benzo [1,2- b: 4,5-b ′] dithiophene (426 mg, 0.5 mmol) was dissolved in 20 ml of anhydrous toluene. After purging the solution with nitrogen, 12.55 mg (0.014 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 28.80 mg (0.110 mmol) of triphenylphosphine were added. The solution was purged with nitrogen for an additional 15 minutes. Thereafter, the solution was heated to 110 to 120 ° C. and reacted for 40 hours. In order to further end-cap, 2-tributyltin thiophene (11 mg, 0.03 mmol) was added and refluxed for 10 hours. Further 2-bromothiophene (10 mg, 0.06 mmol) was added and refluxed for 10 hours. After completion of the reaction, the solvent was distilled off, and the resulting residue was washed with methanol (50 ml × 3 times), and then washed with acetone (50 ml × 3 times).

The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. Each 3 ml of this filtrate was charged into a recycle HPLC (manufactured by Nippon Analytical Chemical Industry) and purified. The high molecular weight fractions were collected to obtain 140 mg of a pure polymer (Mn = 29000) (Exemplary Compound 31).

In addition, other exemplary compounds can be synthesized in the same manner.

[N-type organic semiconductor materials]
The n-type organic semiconductor material used for the photoelectric conversion layer according to the present invention is not particularly limited. Fluoropentacene, perfluorophthalocyanine, etc.), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide and other aromatic carboxylic acid anhydrides and imidized compounds thereof Examples thereof include polymer compounds.

Among these, as the n-type organic semiconductor material, a fullerene derivative capable of efficiently performing charge separation with various p-type organic semiconductor materials at high speed (up to 50 femtoseconds) is preferable.

Fullerene derivatives include fullerene C ₆₀ , fullerene C ₇₀ , fullerene C ₇₆ , fullerene C ₇₈ , fullerene C ₈₄ , fullerene C ₂₄₀ , fullerene C ₅₄₀ , mixed fullerene, fullerene nanotube, multi-wall nanotube, single-wall nanotube, nanohorn (cone Type), etc., and some of these are hydrogen atoms, halogen atoms, substituted or unsubstituted alkyl groups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, cycloalkyl groups, silyl groups, ether groups, thioether groups, The fullerene derivative substituted by the amino group, the silyl group, etc. can be mentioned.

Of these N-Methylfulleropyrrolidine, represented by the following structural formula [6,6] - phenyl _{C 61} - butyric acid methyl ester (abbreviation PCBM or PC61BM), [6,6] - phenyl _{C 61} - butyric acid -n-butyl Esters (PCBnB), [6,6] -Phenyl C ₆₁ -butyric acid-isobutyl ester (PCBiB), [6,6] -Phenyl C ₆₁ -butyric acid-n-hexyl ester (PCBH), Adv. Mater. , Vol. 20 (2008), p2116, etc., aminated fullerenes such as JP-A 2006-199674, metallocene fullerenes such as JP-A 2008-130889, US Pat. No. 7,329,709, etc. Fullerene having a cyclic ether group such as Amer. Chem. Soc. , (2009) vol. 130, p15429, SIMEF, Appl. Phys. Lett. , Vol. 87 (2005), C ₆₀ MC12 described in p203504, etc. It is preferable to use a fullerene derivative having a substituent and having improved solubility as described below. Among these, methanofullerene derivatives such as PCBM, PCBnB, PCBiB, and PCBH are preferable, and PCBM is most preferable.

[Method for forming photoelectric conversion layer]
Examples of a method for forming a photoelectric conversion layer containing a p-type organic semiconductor material and an n-type organic semiconductor material include a vapor deposition method and a coating method (including a casting method and a spin coating method).

Among these, the coating method is preferable in order to increase the area of the interface where charge and electron separation of the above-described holes is performed and to produce a device having high photoelectric conversion efficiency. Also, the coating method is excellent in production speed.

The coating method used at this time is not limited, and examples thereof include spin coating, casting from a solution, dip coating, wire bar coating, gravure coating, spray coating, and blade coating. Furthermore, patterning can also be performed by a printing method such as an ink jet method, a screen printing method, a relief printing method, an intaglio printing method, an offset printing method, or a flexographic printing method.

When coating by such a solution coating method, it is necessary to use a coating liquid composed of three types of a p-type organic semiconductor material, an n-type organic semiconductor material, and a solvent as at least a photoelectric conversion layer coating liquid. The solvent is preferably a solvent that can dissolve both the p-type organic semiconductor material and the n-type organic semiconductor material that are solutes. As such a solvent, for example, aromatic solvents such as toluene, xylene and tetralin, and halogen solvents such as chloroform, dichloroethane, chlorobenzene, dichlorobenzene and trichlorobenzene are preferable. Also, Nature Mat. , Vol. 6 (2007), p497, a poor solvent (octanedithiol, diiodooctane, etc.) that improves the crystallinity of the p-type organic semiconductor material may be further added in an amount of 0.1 to 5% by mass.

The total concentration of the solute in these solvents varies depending on the film thickness to be obtained and the film forming method, but is preferably about 1 to 3% by mass in the spin coating method and the blade coating method. More preferably, it is 1.5 to 2.5% by mass. By setting such a dissolution amount, a photoelectric conversion layer having a thickness of about 150 to 300 nm can be formed by spin coating and blade coating, which are typical film forming methods.

Among these, the mass ratio of the p-type organic semiconductor material and the n-type organic semiconductor material that are solutes can be any value such as 1: 4 to 4: 1. A value of about 1: 2 is preferable.

After application, it is preferable to perform heating in order to cause removal of residual solvent, moisture, and gas, and improvement of mobility and absorption of long wave by crystallization of the semiconductor material.

When annealing is performed at a predetermined temperature during the manufacturing process, a part of the particles is microscopically aggregated or crystallized, and the photoelectric conversion layer can have an appropriate phase separation structure.

As a result, the mobility of holes and electrons (carriers) in the photoelectric conversion layer is improved, and high efficiency can be obtained.

The photoelectric conversion layer may be composed of a single layer in which a p-type organic semiconductor material and an n-type organic semiconductor material are uniformly mixed. However, the photoelectric conversion layer may be a plurality of layers in which the mixing ratio of the electron acceptor and the electron donor is changed. It may be configured. In this case, each layer can be formed by using a material that can be insolubilized after application. As a p-type organic semiconductor material that can be insolubilized after coating, for example, a coating film after coating, such as polythiophene having a polymerizable group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007, P1225. A material that can be insolubilized by polymerization cross-linking, or a soluble substituent reacts by applying energy such as heat as described in US Patent Application Publication No. 2003/136964 and JP-A-2008-16834. Examples thereof include porphyrin compounds that are insolubilized (pigmented). Examples of the n-type organic semiconductor material that can be insolubilized after application include Adv. Mater. , Vol. 20 (2008), p2116, phenyl-C61-glycidyl butyrate (PCBG), and the like.

In addition, since the photoelectric conversion layer is susceptible to photo-oxidation, it is preferable that the photoelectric conversion layer is formed in an environment that is not exposed to oxygen and moisture as a coating environment in the process of forming the photoelectric conversion layer and the process after the photoelectric conversion layer is formed. . The concentrations of oxygen and moisture in the atmosphere are each preferably 5000 ppm or less. More preferably, it is 1000 ppm, More preferably, it is 500 ppm, Most preferably, it is 100 ppm or less.

Normally, in such a dry environment, the solvent contained in the hole transport layer coating solution applied to the upper layer of the photoelectric conversion layer when forming the hole transport layer (HIL) is a hydrophilic solvent. However, the compound of the present invention has good coatability, probably because it has a relatively highly polar benzooxadiazole mother nucleus. In order to suppress such repelling, a hole transport layer coating solution is mixed with alcohols such as methanol, ethanol and isopropanol, or a hydrophilic organic solvent such as acetonitrile, as long as the solute of the hole transport layer does not precipitate. It is also an effective means. Various surfactants may be added to the hole transport layer coating solution.

(Electron transport layer)
The organic photoelectric conversion element of the present invention preferably has an electron transport layer between the photoelectric conversion layer and the cathode. Thereby, it is possible to more efficiently extract charges generated in the photoelectric conversion layer.

In the present invention, the present invention can be particularly preferably applied when the first electrode is a cathode.

The electron transport layer is a layer that is positioned between the cathode and the bulk heterojunction layer as described above, and can more efficiently transfer electrons between the bulk heterojunction layer and the electrode.

The material constituting the electron transport layer is preferably a compound having an LUMO level between the LUMO level of the n-type organic semiconductor material of the bulk heterojunction photoelectric conversion layer and the work function of the cathode.

More preferably, it is a compound having an electron mobility of 10 ⁻⁴ or more.

In addition, by forming an electron transport layer using a material having a HOMO level deeper than that of the p-type organic semiconductor material used for the bulk heterojunction photoelectric conversion layer, holes generated in the bulk heterojunction layer are formed. Can be imparted to the electron transporting layer with a rectifying effect that does not flow to the cathode side.

Such an electron transport layer is also referred to as a hole blocking layer. More preferably, a material having a HOMO level deeper than the HOMO level of the n-type organic semiconductor material is used as the electron transport layer. In addition, in view of the property of blocking holes, it is preferable to use a compound having a hole mobility lower than 10 ⁻⁶ .

As the electron transport layer, octaazaporphyrin, a perfluoro body of a p-type organic semiconductor material (perfluoropentacene, perfluorophthalocyanine, etc.), a carboline compound described in International Publication No. 04/095889, and the like can be used. Similarly, in the electron transport layer having a HOMO level deeper than the HOMO level of the p-type organic semiconductor material used for the photoelectric conversion layer, rectification is performed so that holes generated in the photoelectric conversion layer do not flow to the cathode side. A hole blocking function having an effect is imparted. More preferably, a material deeper than the HOMO level of the n-type organic semiconductor material is used as the electron transport layer. Moreover, it is preferable to use a compound with high electron mobility from the characteristic of transporting electrons.

Examples of such materials include phenanthrene compounds such as bathocuproine, n-type organic semiconductor materials such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide, and titanium oxide. N-type inorganic oxides such as zinc oxide and gallium oxide, and alkali metal compounds such as lithium fluoride, sodium fluoride, and cesium fluoride can be used. Moreover, the layer which consists of a n-type organic-semiconductor material single-piece | unit used for the photoelectric converting layer can also be used.

The means for forming these layers may be either a vacuum vapor deposition method or a solution coating method, but is preferably a solution coating method.

[Hole transport layer (electron blocking layer)]
The organic photoelectric conversion element of the present invention preferably has a hole transport layer between the photoelectric conversion layer and the anode. Thereby, it is possible to more efficiently extract charges generated in the photoelectric conversion layer.

The present invention can be preferably applied when the second electrode is an anode.

As the material constituting the hole transport layer, for example, PEDOT (poly-3,4-ethylenedioxythiophene) -PSS (polystyrene sulfonic acid) such as Startron Vtec, trade name BaytronP, polyaniline and its doped material, The cyanide compounds described in International Publication No. 06/019270 and the like can be used. Note that the hole transport layer having a LUMO level shallower than the LUMO level of the n-type organic semiconductor material used for the photoelectric conversion layer has a rectifying effect so that electrons generated in the photoelectric conversion layer do not flow to the anode side. The electronic block function is provided. Such a hole transport layer is also called an electron block layer, and it is preferable to use a hole transport layer having such a function.

Examples of such materials include triarylamine compounds described in JP-A No. 5-271166, amine compounds such as amine silane coupling agents described in International Publication No. 2008/134492, molybdenum oxide, Metal oxides such as nickel oxide and tungsten oxide can be used. Moreover, the layer which consists of a p-type organic-semiconductor material single-piece | unit used for the photoelectric converting layer can also be used. The means for forming these layers may be either a vacuum deposition method or a solution coating method, but is preferably a solution coating method. Forming a coating film in the lower layer before forming the photoelectric conversion layer is preferable because it has the effect of leveling the coating surface and reduces the influence of leakage and the like.

Similarly, it preferably has a hole mobility higher than 10 ⁻⁴ due to the property of transporting holes, and a compound with electron mobility lower than 10 ⁻⁶ due to the property of blocking electrons. It is preferable to use it.

[Other layers]
The organic photoelectric conversion device of the present invention may have various intermediate layers in the device for the purpose of improving photoelectric conversion efficiency and device life.

Examples of the intermediate layer include a hole injection layer, an electron injection layer, an exciton block layer, a UV absorption layer, a light reflection layer, and a wavelength conversion layer.

〔electrode〕
The organic photoelectric conversion element of the present invention essentially includes the first electrode and the second electrode, and further includes an intermediate electrode (charge recombination layer) when a tandem configuration is employed.

In the present invention, the first electrode is a transparent electrode.

“Transparent” means that the light transmittance is 50% or more.

The light transmittance is the total light in the visible wavelength range measured by a method in accordance with “Testing method of total light transmittance of plastic-transparent material” of JIS K 7361-1: 1997 (corresponding to ISO 13468-1). It refers to transmittance.

As described above, the first electrode of the present invention is preferably a transparent cathode (cathode), and the second electrode is preferably an anode (anode).

[First electrode (transparent cathode)]
Examples of the material used for the first electrode of the present invention include transparent metal oxides such as indium tin oxide (ITO), AZO, FTO, SnO ₂ , ZnO, and titanium oxide, Ag, Al, Au, and Pt. A very thin metal layer or a metal nanowire, a nanowire such as a carbon nanotube or a layer containing nanoparticles, a conductive polymer material such as PEDOT: PSS, polyaniline, or the like can be used.

Also selected from the group consisting of derivatives of polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polyphenylacetylene, polydiacetylene and polynaphthalene. Conductive polymers can also be used. Further, a plurality of these conductive compounds can be combined to form a cathode.

[Second electrode (anode)]
The second electrode may be a single layer made of a conductive material, but in addition to the conductive material, a resin that holds these may be used in combination.

Since the work function of the transparent electrode, which is the cathode, is about −5.0 to −4.0 eV, the built-in potential is necessary for carriers generated in the bulk heterojunction type photoelectric conversion layer to diffuse and reach each electrode. That is, it is preferable that the work function difference between the anode and the cathode is as large as possible.

Therefore, as the conductive material constituting the anode, a metal, an alloy, an electrically conductive compound, and a mixture thereof having a large work function (4 eV or less) are used. Specific examples include gold, silver, copper, platinum, rhodium, indium, nickel, palladium, and the like.

Of these, silver is most preferable from the viewpoint of hole extraction performance, light reflectance, and durability against oxidation.

The cathode can be produced by forming these conductive materials into a thin film by a method such as vapor deposition or sputtering. The film thickness is usually selected from the range of 10 nm to 5 μm, preferably 50 to 200 nm.

Further, when the anode side is made light transmissive, for example, a conductive material suitable for the anode such as aluminum and aluminum alloy, silver and silver compound is formed into a thin film of about 1 to 20 nm, and then the above transparent By providing a film of the conductive light-transmitting material mentioned in the description of the electrode, a light-transmitting anode can be obtained.

Note that the above is a preferable material for the second electrode for the so-called reverse layer type element, which is advantageous for improving the durability, and is a so-called normal layer type (the first electrode is an anode and the second electrode is a cathode). In order to achieve this, the relationship between the work functions of the first electrode and the second electrode may be reversed as described above. However, the types of substantially transparent electrodes are limited, and the work function is relatively low. Since many of them are deep, in practice, a normal layer type organic thin film solar cell can be obtained by using a metal having a shallow work function (less than −4.0 eV) on the second electrode side. Examples of such a metal include aluminum, calcium, magnesium, lithium, sodium, potassium, and the like. In general, aluminum having high reflectivity and high conductivity is used.

[Intermediate electrode (charge recombination layer)]
Further, as the material of the intermediate electrode required in the case of the tandem configuration as shown in FIG. 3, a compound having both transparency and conductivity is preferable, and the materials used in the anode (ITO, AZO, FTO, SnO) are used. ₂ , transparent metal oxides such as ZnO and titanium oxide, very thin metal layers such as Ag, Al, Au, and Pt or metal nanowires, layers containing nanowires such as carbon nanotubes, nanoparticles, PEDOT: PSS, polyaniline, etc. Or the like can be used.

In addition, among the hole transport layer and the electron transport layer described above, there is also a combination that works as an intermediate electrode (charge recombination layer) by stacking them in an appropriate combination. The step of forming a layer can be omitted, which is preferable.

〔substrate〕
In the present invention, the substrate is a transparent substrate, and “transparent” has the same definition as in the above-described electrode.

As the substrate, for example, a glass substrate, a resin substrate, and the like are preferably used, but it is desirable to use a transparent resin film from the viewpoint of light weight and flexibility. There is no restriction | limiting in particular in the transparent resin film which can be preferably used as a transparent substrate by this invention, The material, a shape, a structure, thickness, etc. can be suitably selected from well-known things.

For example, polyolefins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester resin film such as modified polyester, polyethylene (PE) resin film, polypropylene (PP) resin film, polystyrene resin film, cyclic olefin resin, etc. Resin film, vinyl resin film such as polyvinyl chloride, polyvinylidene chloride, polyether ether ketone (PEEK) resin film, polysulfone (PSF) resin film, polyether sulfone (PES) resin film, polycarbonate (PC) resin film, Polyamide resin film, polyimide resin film, acrylic resin film, triacetyl cellulose (TAC) resin film, etc. If the resin film is (380 ~ 800 nm) transmittance of 80% or more in, it can be preferably applied to a transparent resin film according to the present invention.

Among them, from the viewpoint of transparency, heat resistance, ease of handling, strength and cost, it is preferably a biaxially stretched polyethylene terephthalate film, a biaxially stretched polyethylene naphthalate film, a polyethersulfone film, or a polycarbonate film, and biaxially stretched. More preferred are polyethylene terephthalate films and biaxially stretched polyethylene naphthalate films.

The transparent substrate used in the present invention can be subjected to a surface treatment or an easy adhesion layer in order to ensure the wettability and adhesion of the coating solution. A conventionally well-known technique can be used about a surface treatment or an easily bonding layer. For example, the surface treatment includes surface activation treatment such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and laser treatment. Examples of the material constituting the easy-adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer. be able to.

Further, for the purpose of suppressing the permeation of oxygen and water vapor, a barrier coat layer may be formed in advance on the transparent substrate, or a hard coat layer may be formed in advance on the opposite side to which the transparent conductive layer is transferred. Good.

(Optical function layer)
The organic photoelectric conversion element of the present invention may have various optical functional layers for the purpose of more efficient reception of sunlight. As the optical functional layer, for example, a light condensing layer such as an antireflection film or a microlens array, or a light diffusion layer that can scatter the light reflected by the cathode and enter the photoelectric conversion layer again can be provided. Good.

As the antireflection layer, various known antireflection layers can be provided. For example, when the transparent resin film constituting the substrate is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy adhesion layer adjacent to the film. Is preferably 1.57 to 1.63, since the interface reflection between the film substrate and the easy adhesion layer can be reduced and the transmittance can be improved. The method of adjusting the refractive index can be carried out by appropriately adjusting the ratio of the oxide sol having a relatively high refractive index such as tin oxide sol or cerium oxide sol and the binder resin. The easy adhesion layer may be a single layer, but may be composed of two or more layers in order to improve adhesion.

The condensing layer can be provided, for example, by processing so as to provide a microlens array-like structure on the sunlight receiving side of the support substrate, or by combining with a so-called condensing sheet. Thereby, the amount of received light from a specific direction can be increased, and conversely, the dependence on the incident angle of sunlight can be reduced.

As an example of a microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are arranged two-dimensionally on the light extraction side of the substrate. One side is preferably 10 to 100 μm. If it becomes smaller than this, the effect of diffraction will generate | occur | produce and color, and if too large, thickness will become thick and is not preferable.

Examples of the light scattering layer include various antiglare layers, layers in which nanoparticles or nanowires such as metals or various inorganic oxides are dispersed in a colorless and transparent polymer, and the like.

[Patterning]
The method and process for patterning each electrode, photoelectric conversion layer, hole transport layer, electron transport layer and the like according to the present invention are not particularly limited, and known methods can be appropriately applied.

If the material constituting the layer is soluble, such as a photoelectric conversion layer, a charge transport layer, etc., only unnecessary portions may be wiped after the entire surface application such as die coating, dip coating, etc., and methods such as ink jet method and screen printing May be used for direct patterning during coating.

In the case of an insoluble material such as an electrode material, the electrode can be subjected to mask vapor deposition during vacuum deposition or patterned by a known method such as etching or lift-off. Alternatively, the pattern may be formed by transferring a pattern formed on another substrate.

[Solar cell]
The solar cell of this invention has said organic photoelectric conversion element.

The solar cell of the present invention comprises the above-described organic photoelectric conversion element, has a structure in which optimum design and circuit design are performed for sunlight, and optimum photoelectric conversion is performed when sunlight is used as a light source. .

That is, the photoelectric conversion layer has a structure that can be irradiated with sunlight, and when the solar cell of the present invention is configured, the photoelectric conversion layer and each electrode are housed in a case and sealed, Alternatively, it is preferable to seal them entirely with resin.

As a sealing method, since the produced organic photoelectric conversion element is not deteriorated by oxygen, moisture, etc. in the environment, it is preferable to seal not only the organic photoelectric conversion element but also an organic electroluminescence element by a known method. .

For example, a method of sealing a cap made of aluminum or glass by bonding with an adhesive, a plastic film on which a gas barrier layer such as aluminum, silicon oxide, or aluminum oxide is formed and an organic photoelectric conversion element are pasted with an adhesive. Method, spin coating of organic polymer material (polyvinyl alcohol, etc.) with high gas barrier property on organic photoelectric conversion element, inorganic thin film (silicon oxide, aluminum oxide, etc.) or organic film (parylene, etc.) with high gas barrier property And the like, and a method of laminating these sealing materials in a composite manner.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
[Production of organic photoelectric conversion element]
(Preparation of organic photoelectric conversion element 1)
An organic photoelectric conversion element was produced with reference to WO2008 / 134492.

On a PET substrate, an indium tin oxide (ITO) transparent conductive film 150 nm deposited as a first electrode (sheet resistance 12 Ω / sq) is patterned to a width of 10 mm using a normal photolithography technique and wet etching, A first electrode was formed. The patterned first electrode was washed in the order of ultrasonic cleaning with a surfactant and ultrapure water, followed by ultrasonic cleaning with ultrapure water, dried with nitrogen blow, and finally subjected to ultraviolet ozone cleaning. After this, the substrate was brought into the glove box and operated under a nitrogen atmosphere.

On this first electrode, a 0.05 mass% methoxyethanol solution of 3- (2-aminoethyl) -aminopropyltrimethoxysilane manufactured by Aldrich was used with a blade coater so that the dry film thickness was about 5 nm. And dried. Thereafter, heat treatment was performed at 120 ° C. for 1 minute on a hot plate to form an electron transport layer.

Next, 0.8% by mass of Comparative Compound 1 (synthesized based on Non-Patent Document 3), which is a p-type organic semiconductor material, and PC61BM (frontier carbon nanom spectra E100H), which is an n-type organic semiconductor material, in o-dichlorobenzene. ) Was mixed at 1.6% by mass, dissolved by stirring overnight while heating to 110 ° C. in an oven, and then applied using a blade coater so that the dry film thickness was about 200 nm. The film was dried for 2 minutes at a temperature to form a photoelectric conversion layer.

After drying of the photoelectric conversion layer was completed, it was taken out again into the atmosphere, and then, as a hole transport layer, PEDOT-PSS (CLEVIOS (registered trademark) PVP AI 4083, manufactured by Helios Co., Ltd., made of conductive polymer and polyanion, conductivity (1 × 10 ⁻³ S / cm) was diluted with an equal amount of isopropanol, and applied and dried using a blade coater so that the dry film thickness was about 30 nm. Then, it heat-processed with the warm air of 90 degreeC for 20 second, and formed the positive hole transport layer (organic material layer). At the time of application, the atmospheric temperature was 23 ° C. and the humidity was 65%.

Next, the element was set so that the shadow mask having a width of 10 mm was orthogonal to the first electrode (transparent electrode), the inside of the vacuum deposition apparatus was depressurized to 1 × 10 ⁻³ Pa or less, and then the deposition rate was 0.5 nm. A second electrode was formed by laminating 200 nm of Ag metal at a rate of / sec. The obtained laminate was moved to a nitrogen chamber and sandwiched between ^two relief printing transparent barrier films GX (water vapor transmission rate 0.05 g / m ² / d), and UV curable resin (Nagase ChemteX Corporation). Manufactured, manufactured by UV RESIN XNR5570-B1) and then taken out into the atmosphere to obtain an organic photoelectric conversion element 1 having a light receiving portion of about 10 × 10 mm size.

(Preparation of organic photoelectric conversion elements 2 to 11)
Organic photoelectric conversion devices 2 to 11 were obtained in the same manner except that the p-type organic semiconductor material was changed to the materials shown in Table 1 in the production of the organic photoelectric conversion device 1. Comparative compound 2 was synthesized with reference to Non-Patent Document 4. The organic photoelectric conversion elements 5 and 6 are the same polymer (Exemplary Compound 14), but are made of materials having different synthetic lots and different molecular weights as organic photoelectric conversion elements.

[Evaluation of organic photoelectric conversion elements]
(Evaluation of photoelectric conversion efficiency)
The organic photoelectric conversion element after the sealing, was irradiated with light having an intensity of 100 mW / cm ² solar simulator (AM1.5G filter), a superposed mask in which the effective area 1.0 cm ² to the light receiving portion, the short circuit current The density Jsc (mA / cm ² ), the open circuit voltage Voc (V), and the fill factor (fill factor) FF (%) were measured for each of the four light receiving portions formed on the element, and the average value was obtained. Moreover, photoelectric conversion efficiency (eta) (%) was calculated | required according to following formula 1 from measured Jsc, Voc, and FF.

(Durability evaluation of organic photoelectric conversion elements)
The organic photoelectric conversion element for which the photoelectric conversion efficiency was evaluated was heated to 85 ° C. in an open circuit state between the anode and the cathode, and the solar simulator (AM1.5G) light was continuously exposed to the initial conversion efficiency. Assuming that 100 is 100, the time to 80 was measured as LT80. The larger this value is, the better the durability of the organic photoelectric conversion element is.

Table 1 shows the evaluation results.

From Table 1, it can be seen that the reverse layer type organic photoelectric conversion element using the exemplary compound of the present invention exhibits higher durability than the organic photoelectric conversion element using the comparative compound. It can also be seen that the photoelectric conversion efficiency is equal to or higher than that of the comparative organic photoelectric conversion element.

Example 2
[Production of organic photoelectric conversion element]
(Preparation of organic photoelectric conversion element 2 ')
Using the same material and composition as those of the organic photoelectric conversion element 2 prepared in Example 1, the following normal layer type organic photoelectric conversion element was prepared.

The same transparent substrate as in Example 1 was washed in the same process, and then a conductive polymer CLEVIOS P VP AI 4083 was blade-coated to a thickness of 30 nm on the ITO film, and then in the atmosphere at 140 ° C. Heat-dried for 10 minutes.

After this, the substrate was brought into the glove box and worked in a nitrogen atmosphere. First, the substrate was again heat-treated at 140 ° C. for 10 minutes in a nitrogen atmosphere.

As a p-type organic semiconductor material, a solution prepared by dissolving 0.8% by mass of the comparative compound 2 and 1.6% by mass of PCBM as an n-type organic semiconductor material in chlorobenzene was prepared, and similarly, a film thickness of 200 nm was obtained. Blade coating was performed and dried at 80 ° C. for 2 minutes.

Next, the substrate on which the series of organic layers was formed was placed in a vacuum deposition apparatus without being exposed to the atmosphere. The element was set so that the shadow mask with a width of 10 mm was orthogonal to the transparent electrode, and the inside of the vacuum deposition apparatus was depressurized to 10 ⁻³ Pa or less, and then 0.6 nm of lithium fluoride was deposited and 100 nm of aluminum was deposited as a counter electrode. Finally, heating was performed at 120 ° C. for 30 minutes to obtain a comparative organic photoelectric conversion element 2 ′. The deposition rate was 2 nm / second, and the size was 10 mm square.

The obtained organic photoelectric conversion element 2 ′ was prepared by using a UV curable resin (manufactured by Nagase ChemteX Corporation, UV RESIN XNR5570-B1) under a nitrogen atmosphere, and a relief barrier film GX (water vapor transmission rate 0.05 g / m ² / d) and sealed and taken out to the atmosphere.

(Preparation of organic photoelectric conversion element 11 ')
In the production of the organic photoelectric conversion element 2 ′, an exemplary compound 31 was used instead of the comparative compound 2 as a p-type organic semiconductor material, and a normal layer type organic photoelectric conversion element 11 ′ was produced in the same manner.

[Evaluation of organic photoelectric conversion elements]
(Evaluation of photoelectric conversion efficiency)
About the produced organic photoelectric conversion elements 2 ′ and 11 ′ and the organic photoelectric conversion elements 2 and 11 produced in Example 1, the photoelectric conversion efficiency and the durability evaluation of the organic photoelectric conversion elements were evaluated in the same manner as in Example 1.

Table 2 shows the evaluation results.

When comparing the organic photoelectric conversion elements 2 and 11 in Table 2, it can be seen that the organic photoelectric conversion element 11 using the compound 31 of the present invention has higher durability. Further, when LT80 is compared in the organic photoelectric conversion elements 11 and 11 ', it can be seen that the former value is much larger than the latter value, and the reverse layer type organic photoelectric conversion element has particularly high durability.

Example 3
[Production of organic photoelectric conversion element]
(Production of organic photoelectric conversion element 1 ″)
When producing the organic photoelectric conversion element 1 produced in Example 1, the organic photoelectric conversion element 1 ″ was produced by performing the application of the hole transport layer as it was in the glove box (in the GB), not in the atmosphere. .

However, in a very dry environment such as in a glove box, the hydrophilic solvent of the hole transport layer is repelled, and all five of the prepared organic photoelectric conversion elements can be formed. There wasn't.

(Production of organic photoelectric conversion element 2 ″)
When producing the organic photoelectric conversion element 2 produced in Example 1, the organic photoelectric conversion element 2 ″ was produced by applying the hole transport layer as it was in the glove box, not in the atmosphere.

However, in a very dry environment such as in a glove box, the hydrophilic solvent of the hole transport layer is repelled, and four of the prepared five organic photoelectric conversion elements can be formed. There wasn't.

(Production of organic photoelectric conversion elements 4 ″, 7 ″, 9 ″, 11 ″)
When producing the organic photoelectric conversion elements 4, 7, 9, and 11 produced in Example 1, by applying the hole transport layer as it is in the glove box, not in the atmosphere, the organic photoelectric conversion element 4 ″, 7 ", 9", and 11 "were produced. In the organic photoelectric conversion elements 4 ″, 7 ″, 9 ″, and 11 ″, five of the organic photoelectric conversion elements prepared in a very dry environment such as a glove box do not play the hole transport layer. It was possible to form a film.

[Evaluation of organic photoelectric conversion elements]
Regarding the organic photoelectric conversion elements 1 ″, 2 ″, 4 ″, 7 ″, 9 ″, 11 ″ prepared above and the organic photoelectric conversion elements 1, 2, 4, 7, 9, 11 prepared in Example 1, Example 1 and Similarly, durability evaluation of the photoelectric conversion efficiency and the organic photoelectric conversion element was evaluated.

Further, as the HIL (hole transport layer) coating property, it was evaluated how many of the five organic photoelectric conversion elements could be coated without flipping (coating property).

Table 3 shows the obtained results.

In Table 3, when comparing the organic photoelectric conversion elements 4 and 4 ″, 7 and 7 ″, 9 and 9 ″, and 11 and 11 ″, the hole transport layer (HIL) has oxygen and moisture as in the glove box (GB). It can be seen that the durability can be further improved by coating in an environment free from water. However, in such a dry environment, the organic photoelectric conversion elements 1 ″ and 2 ″ using the comparative compounds 1 and 2 cannot be formed because the hole transport layer is repelled, and a process advantageous for durability is performed. It turns out that it cannot be used.

Note that this application is based on Japanese Patent Application No. 2011-106985 filed on May 12, 2011, the disclosure of which is incorporated by reference in its entirety.

10 organic photoelectric conversion elements,
11 substrate,
12 first electrode;
13 second electrode,
14 photoelectric conversion layer,
14 '1st photoelectric converting layer,
15 charge recombination layer,
16 Second photoelectric conversion layer,
17 hole transport layer,
18 Electron transport layer.

Claims

An organic photoelectric conversion element having a transparent first electrode, a photoelectric conversion layer containing a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order on a transparent substrate, The photoelectric conversion layer contains a compound having a partial structure represented by the following general formula (1) as the p-type organic semiconductor material.

(In the formula, each X independently represents a fluorine atom or a chlorine atom. R 1 to R 3 each independently represents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, or an alkynyl group. Group, cycloalkyl group, alkoxy group, fluorinated alkoxy group, alkylthio group, fluorinated alkylthio group, alkylamino group, fluorinated alkylamino group, aryl group or heteroaryl group, or a linking group in which these groups are bonded to each other And the aryl group or heteroaryl group may be a condensed ring structure, and each n independently represents an integer of 0 to 2.)
2. The organic photoelectric conversion device according to claim 1, wherein the compound having a partial structure represented by the general formula (1) has a number average molecular weight of 15,000 to 50,000.
In Formula (1), an organic photoelectric conversion element according to claim 1 or 2, characterized in that R 1 represents the same atom as X.
The organic photoelectric conversion element according to any one of claims 1 to 3, wherein in the general formula (1), X represents a fluorine atom.
The p-type organic semiconductor material is a copolymer having a structure represented by the general formula (1) and a structure represented by the following general formula (2). 5. The organic photoelectric conversion element according to any one of 4 above.

(Wherein R 4 to R 5 are each independently a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an alkoxy group, a fluorinated alkoxy group, or an alkylthio group. Represents a fluorinated alkylthio group, an alkylamino group, a fluorinated alkylamino group, an aryl group or a heteroaryl group.)
The organic photoelectric conversion element according to any one of claims 1 to 5, wherein n is 1 in the general formula (1).
The organic photoelectric conversion device according to any one of claims 1 to 6, wherein in the general formula (1), R 2 represents an alkyl group having 8 to 20 carbon atoms.
The organic photoelectric conversion device according to any one of claims 1 to 7, wherein in the general formula (1), R 2 represents a linear alkyl group.
The partial structure represented by the general formula (1) includes a partial structure in which R 2 represents an alkyl group having 8 or more carbon atoms and a partial structure in which R 3 represents an alkyl group having less than 8 carbon atoms or a hydrogen atom. 9. The organic photoelectric conversion element according to claim 1, wherein the organic photoelectric conversion element is contained.
10. A process for producing an organic photoelectric conversion element according to claim 1, wherein the photoelectric conversion layer of the organic photoelectric conversion element according to claim 1 is produced without being exposed to oxygen and moisture during film formation and after film formation. Method.
10. A solar cell comprising the organic photoelectric conversion device according to claim 1, wherein the first electrode is a cathode and the second electrode is an anode.