JP2012234877A - Organic photoelectric conversion element and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic photoelectric conversion element which has high photoelectric conversion efficiency and excellent durability, and a solar cell using the same.SOLUTION: A photoelectric conversion layer contains a compound having a partial structure represented by general formula (1) as a p-type organic semiconductor material. (In the formula, Yrepresents -CR= or -N=, and Rrepresents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a cyano group and may have a condensed ring structure.)

Description

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

  Due to the recent rise in fossil energy, a system that can generate electric power directly from natural energy has been demanded. Solar cells using single crystal, polycrystal, and amorphous Si, GaAs, CIGS (copper (Cu), indium (In) ), Semiconductor materials such as gallium (Ga) and selenium (Se)), and dye-sensitized photoelectric conversion elements (Gretzel cells) have been proposed and put to practical use.

  However, the cost of generating electricity with these solar cells is still higher than the price of electricity generated and transmitted using fossil fuels, which has hindered widespread use. In addition, since heavy glass must be used for the substrate, reinforcement work is required at the time of installation, which is one of the causes that increase the power generation cost.

  For 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 semiconductor layer) and an electron acceptor layer (p-type semiconductor layer) are provided between the transparent electrode and the counter electrode. A bulk heterojunction photoelectric conversion element sandwiching a photoelectric conversion layer mixed with an n-type semiconductor layer) has been proposed, and an efficiency exceeding 5% has been reported (for example, see Non-Patent Document 1).

  Solar cells using these bulk heterojunction photoelectric conversion elements can be formed by coating other than the anode and cathode, so they can be manufactured at high speed and at low cost. There is a possibility. Furthermore, unlike the Si-based solar cells, semiconductor-based solar cells, dye-sensitized solar cells, etc., since there is no manufacturing process at a temperature higher than 160 ° C., it is expected that it can be formed on a cheap and lightweight plastic substrate. Is done.

  However, further improvement in photoelectric conversion efficiency is required to reduce power generation costs. In order to obtain a photoelectric conversion efficiency of 10% or more in an organic thin film solar cell, Non-Patent Document 2 requires a compound having a specific band gap (bg) and LUMO level as a p-type semiconductor. According to this document, the band gap is required to be 1.3 to 1.7 eV, and the LUMO level is required to be -3.9 to -4.0 eV.

  In addition, this condition is a necessary condition, and in order to actually obtain a photoelectric conversion efficiency of 10%, it is necessary to satisfy other conditions. In the said nonpatent literature 2, two conditions that an external quantum efficiency (EQE) is 65% and a fill factor (FF) are 65% are set as a precondition.

  Here, the external quantum efficiency (EQE) is a value indicating how many electrons can be generated from one photon of sunlight decomposed into a spectrum, and the fill factor (FF) is the resistance inside the solar cell. This value is the ratio of the actual maximum power on the IV characteristic and the product of the open circuit voltage and the short circuit current.

  This fill factor and external quantum efficiency are said to be related to the mobility of the semiconductor material in the power generation layer. If the mobility is high, the series resistance inside the solar cell is low, and the fill factor can be improved. In addition, since the length of the carrier that can be taken out is the product of the mobility, the carrier lifetime and the built-in electric field, ideally a material with higher mobility can produce a thicker power generation layer, and the absorbance can be increased. High external quantum efficiency can be aimed at.

  Accordingly, one important condition is to have a high mobility. However, since the mobility is generally higher for a crystalline material than for an amorphous material, it is important to select a crystalline p-type semiconductor material. In particular, in the case of an organic compound as in the present invention, in order to improve crystallinity, it is important that the material be as flat as possible.

  That is, as a material for the power generation layer of the organic thin film solar cell, a compound having a deeper LUMO level and a larger π conjugate length (small band gap and high crystallinity) is required.

  In order to obtain such a deep LUMO level, as in Non-Patent Document 1, a donor unit (thiophene, etc.) having a high electron donating property and an acceptor unit (nitrogen-containing aromatic ring, etc.) having a high electron withdrawing property are used. Many copolymers have been studied.

  In addition, an attempt has been made to obtain a p-type polymer material having a deep LUMO level and a low band gap by adding an electron-withdrawing group to thiophene known as a high-mobility mother nucleus.

  Patent Document 1 discloses a material in which the terminal α-position of oligothiophene is substituted with a tricyanovinylene group, but it is formed by a vapor deposition process because of poor solubility, leading to a highly productive coating process. Application of was difficult.

  Non-Patent Document 3 discloses a structure in which a dicyanomethylene group is added to a thiophene ring, but the dicyanomethylene group causes steric hindrance with the adjacent thiophene ring and twists the π-conjugated surface, or the mobility is insufficient. The conversion efficiency was also low, less than 1%.

  Non-Patent Document 4 discloses a structure in which a carboxycyanovinylene group is added to a thienothiophene ring, but the efficiency is as low as 2%.

  Patent Document 2 discloses a monomer in which the α-position and β-position of the thieno [3,4-b] thiophene ring are substituted with a cyano group. However, when the cyano group is substituted at the β-position of such a thieno [3,4-b] thiophene ring, the rigid cyano group may cause steric hindrance with the adjacent monomer, and the polymer has low planarity and moves. There is a risk of a low degree polymer. Moreover, the evaluation result using the polymerized polymer is not disclosed.

  Patent Document 3 partially describes that a polymer obtained by electropolymerizing cyanothiophene may be used as an example of a polymer for a transparent electrode. However, these are insoluble and materials for power generation layers of organic thin-film solar cells. It could not be used as.

  In addition, there is a problem that the durability needs to be improved for practical use of the organic thin film solar cell. However, the electrode is not easily deteriorated and a metal having a high work function is used as a counter electrode. Since it is known that durability is improved in a solar cell of a cathode type (so-called reverse layer type solar cell) (see, for example, Patent Document 4), a material capable of providing high photoelectric conversion efficiency in a reverse layer configuration is desired. It was done.

  However, the reverse layer type is disadvantageous from the viewpoint of light utilization because of the relationship between the metal electrode and the power generation layer that has a conductive polymer layer inferior in light transmittance. It is calculated | required from simulation that it becomes thick compared with a layer type solar cell (for example, refer nonpatent literature 5). Therefore, there is a demand for a material that can generate power even with a thick film (from 150 nm), but many materials have good efficiency in the thin film + forward layer configuration, but there are very many materials that have efficiency in the thick film + reverse layer configuration. It had the problem of being few. This is mainly due to the low mobility, that is, the structure in which the intermolecular π stack is weak and it is difficult to obtain molecular crystals.

International Publication No. 2006-092134 Pamphlet International Publication No. 2010-008672 Pamphlet JP 2011-65799 A JP 2009-146981 A

A. Heeger et. al. , Nature Mat. , Vol. 6 (2007), p497 C. J. et al. Brabec et. al. , Adv. Mater. 2006, Vol. 18, p789 Tsuyoshi Endo et. al. , Journal of Polymer Science Part A: Polymer Chemistry, volume 49 (2010), Issue 1, p234. Tsuyoshi Endo et. al. , Journal of Polymer Science Part A: Polymer Chemistry, volume 49 (2010), Issue 1, p1427. J. et al. Peet et. al. , Appl. Phys. Lett. , 98, 043301 (2011)

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

  The above object of the present invention is achieved by the following configurations.

  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, Y ₁ represents —CR ₁ ═ or —N═. R ₁ represents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a hetero group. Represents an aryl group or a cyano group, and may be a condensed ring structure.)
2. 2. The organic photoelectric conversion device according to 1 above, wherein the compound having the structure represented by the general formula (1) has a number average molecular weight of 15,000 to 50,000.

3. In the general formula (1), an organic photoelectric conversion element as described in 1 or 2 groups represented by Y ₁ is characterized in that it is a -CR 1 _=.

  4). The compound having a partial structure represented by the general formula (1) is a compound having any partial structure represented by the following general formula (2A), (2B), (2C) or (2D) The organic photoelectric conversion element according to any one of 1 to 3, wherein:

(In the formula, A ₁ and A ₂ represent an aromatic ring or a heteroaromatic ring, and m and n represent an integer of 0 to _2. R _{2 to} R ₃ represent a hydrogen atom, a halogen atom, an alkyl group, a fluorine atom. Represents an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a heteroaryl group or a cyano group.)
5. 5. The organic photoelectric conversion element as described in 4 above, wherein the p-type organic semiconductor material is a compound having a partial structure represented by the general formula (2C).

  6). 6. The organic photoelectric conversion element as described in 4 or 5 above, wherein in the general formula (2C), m is 0.

  7). The p-type organic semiconductor material is a copolymer of a structure represented by the general formulas (1) and (2A) to (2D) and a structure represented by the following general formula (3). The organic photoelectric conversion device according to any one of 1 to 6, which is characterized in that

(In the formula, Z represents a carbon atom, a nitrogen atom or a silicon atom substituted with an alkyl group.)
8). 8. The organic photoelectric conversion element as described in 7 above, wherein in the general formula (3), Z is silicon substituted with an alkyl group.

  9. 9. The solar cell comprising the organic photoelectric conversion element according to any one of 1 to 8, wherein the first electrode is a cathode and the second electrode is an anode.

  The above means of the present invention can provide an organic photoelectric conversion element having a high fill factor value, high photoelectric conversion efficiency and excellent durability, and a solar cell using the organic photoelectric conversion element.

The schematic sectional drawing which shows the example of a structure of the organic photoelectric conversion element of this invention. The schematic sectional drawing which shows the other example of a structure of the organic photoelectric conversion element of this invention. The 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 present inventors only provide deep HOMO / LUMO, that is, high Voc, due to the strong electron-withdrawing property of the cyano group when the β-position of the thiophene ring bonded to the conjugated polymer main chain at the α-position is substituted with a cyano group. In addition, the present inventors have found that a structure having no steric hindrance with an adjacent monomer can maintain high planarity, and high mobility and a high fill factor can be obtained. With such a material, it is possible to increase the thickness even in a reverse layer structure having excellent durability, and good photoelectric conversion efficiency can be obtained.

  The present invention is 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 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.

(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 photoelectric conversion layer 14 on the first electrode 12, and a first electrode on the photoelectric conversion layer 14. It has two electrodes 13.

  In the example of FIG. 1, a hole transport layer 17 described later is provided between the first electrode 12 and the photoelectric conversion layer 14, and an electron transport layer described later is provided between the photoelectric conversion layer 14 and the second electrode 13. 18

  In this invention, the board | substrate 11 and the 1st electrode 12 are transparent, and the light used for photoelectric conversion injects from the direction of the arrow of FIG.

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

  The p-type semiconductor material functions relatively as an electron donor (donor), and the n-type semiconductor material functions relatively as an electron acceptor (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 the electron donor in the photoelectric conversion layer 14 of the photoelectric conversion layer 14, and from the electron donor to the electron acceptor. Electrons move and a hole-electron pair (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, a metal having a small work function and easily oxidized is used for the second electrode 13. In this case, the first electrode functions as an anode (anode) and the second electrode functions as a cathode (cathode).

  FIG. 2 shows an example of another configuration.

  In FIG. 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, whereby electrons are transferred to the first electrode 12. The case where it designed so that it might convey to the 2nd electrode 13 was shown. In this case, an electron transport layer 18 is provided between the first electrode 12 and the photoelectric conversion layer 14, and a hole transport layer 17 described later is provided 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).

  In the present invention, from the viewpoint of durability, in particular, the configuration shown in FIG. 2, that is, the first electrode is a cathode (cathode) and the second electrode is an anode (anode) is a preferred embodiment.

  Although not shown in FIGS. 1 and 2, the organic photoelectric conversion element of the present invention has a layer such as a hole blocking layer, an electron blocking layer, an electron injection layer, a hole injection layer, or a smoothing layer. You may have.

  Furthermore, it is good also as a tandem-type structure which laminated | stacked such a photoelectric conversion element for the purpose of the improvement of sunlight utilization factor (photoelectric conversion efficiency). 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. By stacking the electrodes 13, a tandem configuration can be obtained.

  The second photoelectric conversion layer 16 may be a layer that absorbs the same spectrum as the absorption spectrum of the first photoelectric conversion layer 14 'or may be a layer that absorbs a different spectrum, but is preferably a layer that absorbs a different spectrum. is there.

  Further, 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. Also in the configuration, each photoelectric conversion layer preferably has a configuration as shown in FIG.

  Below, the material which comprises these layers is described.

[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. Although only the compound having the partial structure of the general formula (1) may be used, 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 combined with a donor unit described later. It is preferable that the compound has a structure.

In the general formula (1), Y ₁ represents -CR ₁ = or -N =. R ₁ represents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a heteroaryl group or a cyano group, and may be a condensed ring structure.

  That is, when the main chain of the conjugated polymer is a thiophene ring, it is expected that a high mobility factor, that is, a high fill factor can be obtained even when the power generation layer is thickened. In addition, by arranging a cyano group that is an electron-withdrawing group at the β-position of thiophene, high planarity can be obtained because there is no steric hindrance with the adjacent polymer main chain linked at the α-position of thiophene. And higher mobility can be expected.

Y ₁ represents —CR ₁ = (thiophene ring) or —N = (thiazole ring), and Y ₁ is preferably —CR ₁ = from the viewpoint of easily obtaining higher mobility.

The alkyl group represented by R ₁ preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, and particularly preferably 1 to 8 carbon atoms. For example, methyl, ethyl, iso-propyl, tert -Butyl, n-octyl, n-decyl, n-hexadecyl, 2-ethylhexyl and the like.

The fluorinated alkyl group is a fluorinated alkyl group in which some or all of these are fluorinated. A completely fluorinated fluorinated alkyl group is liable to lower the solubility, and therefore, a position close to the mother nucleus is preferably an alkyl group, and a terminal portion is a fluorinated alkyl group having a fluorinated alkyl group. For example _{- (CH 2 CH 2) -C} 4 F 9, - (CH 2 CH 2) -C 7 F 15, and the like.

  The cycloalkyl group preferably has 4 to 8 carbon atoms, and examples thereof include cyclopropyl, cyclopentyl, cyclohexyl, norbornyl, adamantyl and the like.

  Examples of the alkenyl group include a vinyl group and an allyl group.

  Examples of the alkynyl group include an ethynyl group and a propargyl group.

  Examples of the cycloalkyl group include a cyclopentyl group and a cyclohexyl group.

  The aryl group preferably has 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, and particularly preferably 6 to 12 carbon atoms, and examples thereof include phenyl, p-methylphenyl, naphthyl, phenanthryl, and pyrenyl. It is done.

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

  Condensed rings include 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.

  Alternatively, a linking group in which a plurality of these are bonded to each other may be used.

Among these substituents, an alkyl group having _{6 to 16} carbon atoms is preferable. This is because the p-type semiconductor material to be obtained needs to have a certain level of solubility in order to be formed with a sufficiently thick film, and in terms of imparting solubility, a material substituted with these substituents It is preferable that In particular, in the case of a polymer material, in addition to imparting solubility, a linear alkyl group may provide alignment and may provide high mobility (also referred to as a fastener effect). A p-type material substituted with an alkyl group is preferred.

In the general formula (1), the group represented by Y ₁ represents —CR ₁ ═ and N═, and as the steric hindrance, a compound having smaller planarity and a smaller planarity can be obtained. .

(Compound having a partial structure represented by the general formulas (2A) to (2D))
The compound having the partial structure represented by the general formula (1) is preferably a compound having any partial structure represented by the general formulas (2A) to (2D) having a β-cyanothiophene structure. .

In formula (2A) ~ (2D), A 1 and _{A 2} represents an aromatic ring or a heteroaromatic ring, m, n represents an integer of 0 to 2. R _{2 to} R ₃ represent a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a cyano group.

Examples of the aromatic ring and heteroaromatic ring represented by A ₁ and A ₂ include benzene, naphthalene, thiophene, pyrrole, and silole.

The alkyl group, the fluorinated alkyl group, the alkenyl group, the alkynyl group, the cycloalkyl group, the aryl group, and the heteroaryl group represented by R _{2 to} R ₃ are each represented by R ₁ in the general formula (1) It is synonymous.

  Thus, a structure in which at least one cyano group is substituted at the β-position of a structure in which a plurality of thiophene rings are linked or condensed is preferable because higher mobility can be expected.

  More preferably, in the compound having the structure represented by the general formulas (2A) to (2D), any one of the two β-positions of the thiophene ring or two are cyano groups. Such a structure is preferable because a compound having a more appropriate HOMO / LUMO level is obtained and the symmetry is improved and the mobility is also improved.

  More preferably, it is a compound having a structure in which m and n are 0 in the structure represented by the general formula (2C) or (2D). This is because such a structure (thienothiophene ring) is known as a high mobility mother nucleus in the use of an organic thin film transistor, and high mobility can be expected even in a compound substituted with a cyano group. More preferred are compounds of general formula (2C).

  The partial structures represented by the general formulas (1) and (2A) to (2D) are partial structures generally called an acceptor unit when placed on a donor-acceptor type p-type organic semiconductor polymer material. A compound combined with a donor unit (a unit having a shallow HOMO / LUMO level) functioning as a donor is conjugated with an acceptor unit (a unit having a deep HOMO / LUMO level) to combine long wavelength absorption and a deep LUMO level. It is a compound that can be used as a p-type organic semiconductor material.

  As the donor unit, for example, a unit having 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 preferably, it is a structure containing a hetero five-membered ring such as a thiophene ring, a furan ring, a pyrrole ring, cyclopentadiene, silacyclopentadiene or the like as a condensed ring.

  Specific examples include fluorene, silafluorene, carbazole, dithienocyclopentadiene, dithienosylcyclopentadiene, dithienopyrrole, and benzodithiophene.

(Copolymer of the structure represented by the general formulas (1) and (2A) to (2D) and the structure represented by the general formula (3))
More preferably, the p-type organic semiconductor material is represented by the structure represented by the general formulas (1) and (2A) to (2D) and the general formula (3). It is a copolymer with the structure.

  In the general formula (3), Z represents a carbon atom, a nitrogen atom or a silicon atom substituted with an alkyl group. Such a structure is preferable because it can provide a material with high mobility, high solubility, and absorption up to a long wavelength. More preferably, Z is silicon substituted with an alkyl group.

  Further, the p-type semiconductor material having the partial structure represented by the general formula (1) preferably has a number average molecular weight of 15,000 to 50,000.

  This is because a low-molecular compound (fullerene derivative) is widely used as an n-type organic semiconductor, which is the other component constituting the bulk heterojunction type photoelectric conversion layer. This is because a microphase-separated structure is formed, and it is easy to 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, so the number average molecular weight is preferably 50,000 or less. More preferably, it is the range of 15000-30000.

  The solubility can be improved by replacing the mother nucleus represented by the general formulas (1), (2A) to (2D) and (3) with a soluble substituent. If it is excessive, the crystallinity and mobility may be lowered, and the characteristics such as the fill factor of the resulting organic thin film solar cell may be degraded. Therefore, substitution with a soluble group or an aryl group substituted with a soluble group, etc. The structures represented by the general formulas (1), (2A) to (2D), (3) having the structure described above, and the general formulas (1), (2A) to (2D) having no soluble group It is also a preferable means to achieve both the preferable molecular weight range and crystallinity by copolymerizing with the structure represented by (3).

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

  The number average molecular weight here refers to that measured by the following method.

  By using 150C ALC / GPC manufactured by Waters (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.

  Purification according to molecular weight can also be performed by preparative gel permeation chromatography (GPC).

  The ratio of the partial structure according to the present invention (the partial structure represented by the general formulas (1) and (2A) to (2D)) in the compound having the partial structure according to the present invention is generally 20 to 80 mass% is preferable and 25-60 mass% is especially preferable. In the present invention, the compound is preferably a high molecular weight compound as described above. In this case, the compound has a partial structure as a repeating unit, and the entire compound including a repeating unit other than the partial structure is used. , Preferably in the range of 30 to 50 mol%.

  Although the example of the compound which has the partial structure represented by General formula (1) and (2A)-(2D) below is given, this invention is not limited to these.

  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 range of the molecular weight described above. For example, in order to fall within the range of the number average molecular weight of 10,000 to 100,000, about 10 It needs to be about ~ 200.

[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) include Chemistry-A European Journal, 2006, p1244, and Synthesis 2004, p23, J. Org. Org. Chem. , 1986, p230 and the like.

  Of the compounds according to the present invention, compounds having a partial structure represented by the general formula (2A) are disclosed in J. Pat. Org. Chem. , 1972, p1712, Tetrahedron (2010), p9560 and the like.

  Of the compounds according to the present invention, compounds having a partial structure represented by the general formula (2B) are disclosed in J. Org. Chem. Res. 1996, p1285, J.A. Org. Chem. , 2002, p9275, J. et al. Chem. Res. , 1996, p1285, etc.

  Of the compounds according to the present invention, compounds having partial structures represented by the general formulas (2C) and (2D) are disclosed in Chem. Commun. , 2005, p1161, etc., and a dibromo compound was synthesized. Org. Chem. , 1972, p1712, and can be synthesized by cyanating Br with copper cyanide.

(Synthesis example)
Hereafter, the synthesis example of the compound for organic photoelectric conversion elements of this invention is described.

  (Exemplary Compound 15)

  2,5-Dibromo-3,4-dicyanothiophene was synthesized according to Tetrahedron (2010), p9560. Further, bis- (5,5′-trimethylstannyl) -3,3′-di-ethylhexyl-silylene-2,2′-dithiophene was synthesized with reference to JP-T-2010-507233.

  146 mg (0.5 mmol) of the above 2,5-dibromo-3,4-dicyanothiophene and bis- (5,5′-trimethylstannyl) -3,3′-di-ethylhexyl-silylene-2,2′- 372 mg (0.5 mmol) of 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. Furthermore, in order to perform an 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), and then washed with acetone (3 × 50 ml).

  The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. A 3 ml portion of the solution was loaded on a recycle HPLC (Nihon Analytical Chemical Industries) for purification. The high molecular weight fractions were collected to obtain 100 mg of a pure polymer (Mn = 20000) (Exemplary Compound 15).

  (Exemplary Compound 16)

  J. et al. Chem. Res. , 1996, p1285, 2.16 g (10 mmol) of 3,3′-dicyano-2,2′-bithiophene was dissolved in 100 ml of dehydrated THF under a nitrogen atmosphere and immersed in a dry ice-methanol bath at −78 ° C. Then, 30 ml (60 mmol) of a 2.0M lithium diisopropylamide 25% tetrahydrofuran / ethylbenzene / heptane solution manufactured by Tokyo Chemical Industry Co., Ltd. was added dropwise, stirred for 15 minutes, then warmed to room temperature and stirred for 1 hour. The mixture was cooled again to −78 ° C., 7.2 g (45 mmol) of bromine was added dropwise, stirring was continued at −78 ° C. for 2 hours, and then stirred at room temperature overnight.

  After adding 50 ml of saturated aqueous ammonium chloride solution and washing with water, the organic layer was extracted with methylene chloride and dried over magnesium sulfate, and then the solvent was distilled off to obtain a crude product. The obtained crude product was purified by silica gel column chromatography (heptane: ethyl acetate = 9: 1 to 3: 1) to obtain 2.06 g (yield 55%) of Exemplary Compound 16-1.

  187 mg (0.5 mmol) of the above exemplified compound 16-1 and 372 mg (0.5 mmol) of bis- (5,5′-trimethylstannyl) -3,3′-di-ethylhexyl-silylene-2,2′-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. Furthermore, in order to perform an 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), and then washed with acetone (3 × 50 ml).

  The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. A 3 ml portion of the solution was loaded on a recycle HPLC (Nihon Analytical Chemical Industries) for purification. The high molecular weight fractions were collected to obtain 70 mg of a pure polymer (Mn = 15000) (Exemplary Compound 16).

  (Exemplary Compound 18)

  Tokyo Chemical Co., Ltd. 3,6-dibromo-thieno [3,2-b] thiophene 600 mg (2 mmol) and copper cyanide 540 mg (6 mmol) were dissolved in DMF 10 ml and stirred at 140 ° C. overnight. After completion of the reaction, the reaction solution was poured into 100 ml of water, and the precipitated crystals were collected by filtration. The obtained crystals were purified by silica gel column chromatography to obtain 250 mg (yield 66%) of Exemplary Compound 18-1.

  250 mg (1.3 mmol) of Exemplified Compound 18-1 was dissolved in 25 ml of dehydrated THF under a nitrogen atmosphere, immersed in a dry ice-methanol bath to −78 ° C., and then 2.0M lithium diisopropylamide 25% manufactured by Tokyo Chemical Industry. A tetrahydrofuran / ethylbenzene / heptane solution (3.8 ml, 7.6 mmol) was added dropwise, and the mixture was stirred for 15 minutes, then warmed to room temperature and stirred for 1 hour, then cooled to -78 ° C again, and bromine 1.0 g (6.3 mmol) was added dropwise, and stirring was continued at -78 ° C for 2 hours, and then at room temperature overnight.

  After adding 50 ml of saturated aqueous ammonium chloride solution and washing with water, the organic layer was extracted with methylene chloride and dried over magnesium sulfate, and then the solvent was distilled off to obtain a crude product. The obtained crude product was purified by silica gel column chromatography (heptane: ethyl acetate = 9: 1 to 3: 1) to obtain 180 mg (yield 40%) of Exemplary Compound 18-2.

  174 mg (0.5 mmol) of the above exemplary compound 18-2, 372 mg (0.5 mmol) of bis- (5,5′-trimethylstannyl) -3,3′-di-ethylhexyl-silylene-2,2′-dithiophene Were 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 another 10 hours. Further 2-bromothiophene (10 mg, 0.06 mmol) was added and refluxed for an additional 10 hours. After completion of the reaction, the solvent was distilled off, and the resulting residue was washed with methanol (50 ml × 3), and then washed with acetone (3 × 50 ml).

  The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. A 3 ml portion of the solution was loaded on a recycle HPLC (Nihon Analytical Chemical Industries) for purification. The high molecular weight fractions were collected to obtain 70 mg of a pure polymer (Mn = 22000) (Exemplary Compound 18).

  (Exemplary Compound 23)

  After dissolving 3.6 g (10 mmol) of 2-bromo-3-tetradecylthiophene in 100 ml of dehydrated THF under a nitrogen atmosphere and dipping in a dry ice-methanol bath to −78 ° C., 1.6 M n manufactured by Tokyo Chemical Industry Co., Ltd. -10 ml (16 mmol) of butyllithium solution was added dropwise and stirred for 15 minutes. After warming to room temperature and stirring for 1 hour, the mixture was cooled to -78 ° C again, and 4.0 g (20 mmol) of trimethyltin chloride was added. A solution dissolved in 20 ml of heptane was dropped, and stirring was continued at −78 ° C. for 2 hours, and then stirred overnight at room temperature.

  After adding 50 ml of saturated aqueous ammonium chloride solution and washing with water, the organic layer was extracted with methylene chloride and dried over magnesium sulfate, and then the solvent was distilled off to obtain a crude product. The obtained crude product was purified by silica gel column chromatography (heptane 100%) using silica gel previously treated with triethylamine to obtain 3.6 g (yield 80%) of Exemplary Compound 23-1.

  2.2 g (5 mmol) of Exemplified Compound 23-1 and 1.74 g (5 mmol) of Exemplified Compound 18-2 were dissolved in 100 ml of anhydrous toluene. After purging the solution with nitrogen, 125.5 mg (0.14 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 288 mg (1.10 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. After completion of the reaction, the residue obtained by distilling off the solvent was purified by silica gel column chromatography (heptane: ethyl acetate = 10: 0 to 8: 2) to obtain 2.7 g of Exemplified Compound 23-2 (yield 72). %)Obtained.

  2.7 g (3.6 mmol) of the exemplified compound 23-2 was dissolved in 50 ml of chloroform, and 1.28 g (7.2 mmol) of N-bromosuccinimide was added at room temperature, followed by stirring all day and night. After completion of the reaction, the organic layer was extracted by washing with water. The organic layer was dried over magnesium sulfate, and then the solvent was distilled off to obtain a crude product. The obtained crude product was purified by silica gel column chromatography (heptane: ethyl acetate = 10: 0 to 8: 2) to obtain 3.0 g of Exemplified Compound 23-3 (yield 92%).

  453 mg (0.5 mmol) of the above exemplified compound 23-3 and 372 mg (0.5 mmol) of bis- (5,5′-trimethylstannyl) -3,3′-di-ethylhexyl-silylene-2,2′-dithiophene Were 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. Furthermore, in order to perform an 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), and then washed with acetone (3 × 50 ml).

  The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. A 3 ml portion of the solution was loaded on a recycle HPLC (Nihon Analytical Chemical Industries) for purification. The high molecular weight fractions were collected to obtain 140 mg of a pure polymer (Mn = 28000) (Exemplary Compound 23).

  (Exemplary Compound 36)

  453 mg (0.5 mmol) of the above exemplified compound 23-3, 303 mg of 2,6-bis (trimethyltin) -4,8-didodecyloxybenzo [1,2-b: 4,5-b ′] dithiophene (0 0.5 mmol) was dissolved in 20 ml of anhydrous toluene. After purging this 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. Furthermore, in order to perform an 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), and then washed with acetone (3 × 50 ml).

  The recovered polymer product was heated and dissolved in chloroform (30 ml), and filtered through a 0.45 μm membrane. A 3 ml portion of the solution was loaded on a recycle HPLC (Nihon Analytical Chemical Industries) for purification. The high molecular weight fractions were collected to obtain 110 mg of a pure polymer (Mn = 43000) (Exemplary Compound 36).

[N-type semiconductor materials]
The n-type organic semiconductor material used for the photoelectric conversion layer according to the present invention is not particularly limited. For example, perfluoro compounds (perfluorocarbons such as fullerene, octaazaporphyrin, etc.) in which hydrogen atoms of a p-type organic semiconductor are substituted with fluorine atoms. Fluoropentacene, perfluorophthalocyanine, etc.), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide and other aromatic carboxylic acid anhydrides and imidized products thereof Examples thereof include polymer compounds.

  Among these, as the n-type organic semiconductor material, a fullerene derivative that can efficiently perform charge separation with various p-type 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.

Among them, N-methylfullropyrrolidine, [6,6] -phenyl C ₆₁ -butyric acid methyl ester (abbreviation PCBM) represented by the following structural formula, [6,6] -phenyl C ₆₁ -butyric acid-n-butyl ester ( 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.

[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 charges and electrons are separated from each other as described above and to produce a device having high photoelectric conversion efficiency. Also, the coating method is excellent in production speed.

  Although there is no restriction | limiting in the application | coating method used in this case, For example, a spin coat method, the cast method from a solution, a dip coat method, a wire bar coat method, a gravure coat method, a spray coat method etc. are mentioned. 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 p-type semiconductor material, n-type semiconductor material, and solvent at least for the photoelectric conversion layer coating liquid. As the solvent, a solvent capable of dissolving both the p-type semiconductor material and the n-type semiconductor material which are solutes is preferable. 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.

  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 1.5-2.5 mass%. By setting it as such melt | dissolution amount, the photoelectric converting layer of a film thickness of about 150-300 nm can be formed with the spin coat method and the blade coat method which are typical film forming methods.

  Among these, the mass ratio of the p-type semiconductor and the n-type semiconductor, which are solutes, can be any value, for example, 1: 4 to 4: 1, but is actually about 1: 1 to 1: 2. A value is preferred.

  After coating, it is preferable to perform heating in order to cause removal of residual solvent, moisture and gas, and improvement of mobility and absorption longwave due to 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. It may be configured. In this case, it can be formed by using a material that can be insolubilized after application. As a p-type semiconductor material that can be insolubilized after coating, for example, the coating film is polymerized 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 crosslinking, or a soluble substituent reacts and insolubilizes by applying energy such as heat as described in US Patent Application Publication No. 2003/136964 and JP-A-2008-16834 And porphyrin compounds to be pigmented. Examples of the n-type semiconductor material that can be insolubilized after application include Adv. Mater. , Vol. 20 (2008), p2116, phenyl-C61-glycidyl butyrate (PCBG), and the like.

(Electron transport layer)
In the organic photoelectric conversion element of the present invention, since an electron transport layer is formed between the photoelectric conversion layer and the cathode, it is possible to more efficiently extract charges generated in the photoelectric conversion layer. It is preferable to have.

  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 and can transfer electrons between the bulk heterojunction layer and the electrode more efficiently. is there.

  More specifically, a compound having an LUMO level intermediate between the LUMO level of the n-type semiconductor material of the bulk heterojunction photoelectric conversion layer and the work function of the cathode is suitable as the electron transporting layer.

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

  In the electron transport layer, the electron transport layer having a HOMO level deeper than the HOMO level of the p-type semiconductor material used for the bulk hetero junction type photoelectric conversion layer was formed in the bulk hetero junction layer. A hole blocking function having a rectifying effect that prevents holes from flowing to the cathode side is provided.

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 semiconductor is used for the electron transport layer. Moreover, it is preferable to use the compound whose hole mobility is lower than 10 ^<-6> from the characteristic which blocks a hole.

  As the electron transport layer, octaazaporphyrin, p-type semiconductor perfluoro compounds (perfluoropentacene, perfluorophthalocyanine, etc.), carboline compounds described in International Publication No. 04/095889, and the like can be used. The electron transport layer having a HOMO level deeper than the HOMO level of the p-type semiconductor material used for the photoelectric conversion layer has a rectifying effect so that holes generated in the photoelectric conversion layer do not flow to the cathode side. The hole blocking function is imparted. More preferably, a material deeper than the HOMO level of the n-type semiconductor 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 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 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.

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

  The present invention is preferably applicable when the second electrode is a hole transport layer.

  As a material constituting these layers, for example, as a hole transport layer, PEDOT (poly-3,4-ethylenedioxythiophene) -PSS (polystyrene sulfonic acid) such as Stark Vitec, trade name BaytronP, Polyaniline and a doping material thereof, cyan 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 semiconductor material used for the photoelectric conversion layer has a rectifying effect that prevents electrons generated in the photoelectric conversion layer from flowing to the anode side. It has an electronic block function. 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.

  As such a material, a triarylamine compound described in JP-A-5-271166 or a metal oxide such as molybdenum oxide, nickel oxide, or tungsten oxide can be used. Moreover, the layer which consists of a p-type 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]
As a structure of the organic photoelectric conversion element of this invention, it is good also as a structure which has various intermediate | middle layers in an element for the purpose of the improvement of a photoelectric conversion efficiency, and the improvement of element lifetime.

  Examples of the intermediate layer include a hole block layer, an electron block layer, 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 has the first electrode and the second electrode. When the tandem configuration is adopted, the tandem configuration can be achieved by using the intermediate electrode.

  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 transmittance in the visible light wavelength region measured by a method according to “Testing method of total light transmittance of plastic-transparent material” of JIS K 7361-1 (corresponding to ISO 13468-1). Say.

  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, 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 conductive material layer, but in addition to a 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 approximately −5.0 to −4.0 eV, the built-in potential is necessary for the carriers generated in the bulk heterojunction 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 for the anode, a material having a work function (4 eV or less) metal, alloy, electrically conductive compound and a mixture thereof as an electrode material is used. Specific examples of such an electrode material include gold, silver, copper, platinum, rhodium, indium, nickel, palladium, and the like.

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

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

  In addition, 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 made thin with a film thickness of about 1 to 20 nm, and then the transparent electrode A light-transmitting anode can be obtained by providing the conductive light-transmitting material film mentioned in the description.

  In the above description, preferred materials for the second electrode material for making a so-called reverse layer type element, which is advantageous for improving durability, have been described. ), The relationship between the work functions of the first electrode and the second electrode may be reversed as described above, but the types of substantially transparent electrodes are limited, and the work functions are compared. In many cases, a deep layer 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 metal include aluminum, calcium, magnesium, lithium, sodium, potassium, and the like. In general, aluminum having high reflectivity and high conductivity is used.

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

  In addition, in 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 appropriately combining and laminating. Is preferable.

〔substrate〕
In the present invention, the substrate is a transparent substrate, and the term “transparent” has the same meaning as described above for the electrodes.

  As the substrate, for example, a glass substrate, a resin substrate, and the like are preferably exemplified, but it is desirable to use a transparent resin film from the viewpoint of lightness 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 films, vinyl resin films such as polyvinyl chloride and polyvinylidene chloride, polyether ether ketone (PEEK) resin films, polysulfone (PSF) resin films, polyether sulfone (PES) resin films, polycarbonate (PC) resin films , Polyamide resin film, polyimide resin film, acrylic resin film, triacetyl cellulose (TAC) resin film, and the like. If the resin film transmittance of 80% or more in from zero to eight hundred nanomolar), 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. More preferred are a stretched polyethylene terephthalate film and a biaxially stretched polyethylene naphthalate film.

  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 adhesiveness 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 easy adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer.

  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, a light diffusing layer that can scatter the light reflected by the cathode and enter the power generation layer again may be provided. .

  Various known antireflection layers can be provided as the antireflection layer. For example, when the transparent resin film is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy adhesion layer adjacent to the film is 1.57. It is more preferable to set it to ˜1.63 because 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.

  As the condensing layer, for example, it is processed so as to provide a structure on the microlens array on the sunlight receiving side of the support substrate, or the amount of light received from a specific direction is increased by combining with a so-called condensing sheet. Conversely, the incident angle dependency of sunlight can be reduced.

  As an example of the microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are two-dimensionally arranged 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 it is a soluble material such as a photoelectric conversion layer and a transport layer, only unnecessary portions may be wiped after the entire surface of die coating, dip coating, etc., or patterning is directly performed at the time of coating using a method such as an ink jet method or screen printing. May be.

  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 with high gas barrier property (polyvinyl alcohol, etc.), inorganic thin film with high gas barrier property (silicon oxide, aluminum oxide, etc.) or organic film (parylene etc.) are deposited under vacuum. Examples thereof include a method and a method of laminating these in a composite manner.

  EXAMPLES 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)
With reference to Japanese Patent Application Laid-Open No. 2009-146981, a reverse layer type organic photoelectric conversion element was produced.

  On a glass substrate, an indium tin oxide (ITO) transparent conductive film deposited with a thickness of 110 nm (surface resistivity 13Ω / □) is patterned to a width of 2 mm using a normal photolithography technique and hydrochloric acid etching, A transparent electrode was formed.

  The patterned transparent 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.

Next, the substrate was brought into a glove box, and a 150 mmol / L (liter) TiO _x precursor solution prepared by the following procedure was spin-coated (rotation speed 2000 rpm, rotation time 60 s) on the transparent substrate in a nitrogen atmosphere. A predetermined pattern was wiped off.

Next, the TiO _x precursor was hydrolyzed by being left in the air. Next, the TiO _x precursor was heat-treated at 150 ° C. for 1 hour to obtain a 30 nm TiO _x layer.

(Preparation of TiO _x precursor: sol-gel method)
First, 12.5 ml of 2-methoxyethanol and 6.25 mmol of titanium tetraisopropoxide were placed in a 100 ml three-necked flask and cooled in an ice bath for 10 minutes. Next, 12.5 mmol of acetylacetone was slowly added and stirred in an ice bath for 10 minutes. Next, the mixed solution was heated at 80 ° C. for 2 hours and then refluxed for 1 hour. Finally, it was cooled to room temperature and adjusted to a predetermined concentration (150 mmol / L) using methoxyethanol to obtain a TiO _x precursor. The above steps were all performed in a nitrogen atmosphere.

Next, a bulk heterojunction layer was formed on the TiO _x layer. A solution in which 0.9% by mass of Comparative Compound 1 as a p-type semiconductor material and 0.9% by mass (total solid concentration 1.8% by mass) of PCBM (manufactured by Frontier Carbon, Nano Spectra E100H) as an n-type semiconductor material The solution filtered through a 0.45 μm filter was applied with a blade coater and dried at 100 ° C. for 30 minutes to obtain a photoelectric conversion layer having a dry film thickness of 220 nm. Comparative compound 1 was synthesized based on Non-Patent Document 3.

  Next, an organic solvent-based PEDOT: PSS dispersion (Enocoat HC200, manufactured by Kaken Sangyo) was blade coated on the organic semiconductor layer and air-dried to form a hole transport layer having a dry film thickness of 30 nm.

Next, after vacuum-depositing a silver electrode layer on the conductive polymer layer so as to have a film thickness of about 200 nm, a heat treatment is performed at 120 ° C. for 10 minutes, whereby the reverse layer type organic photoelectric conversion element is obtained. Prepared and bonded with a relief printing transparent barrier film GX (water vapor transmission rate 0.05 g / m ² / d) using a UV curable resin (manufactured by Nagase ChemteX Corporation, UV RESIN XNR5570-B1) in a nitrogen atmosphere. After sealing, the organic photoelectric conversion element 1 was produced by taking it out into the atmosphere.

(Preparation of organic photoelectric conversion elements 2 to 13)
In the production of the organic photoelectric conversion element 1, the p-type semiconductor material is changed to the material shown in Table 1, and the p: n ratio is the composition shown in Table 1 (the total solid content concentration is fixed at 1.8% by mass). The organic photoelectric conversion elements 2 to 13 were obtained in the same manner except for the above.

[Evaluation of organic photoelectric conversion elements]
(Evaluation of photoelectric conversion efficiency)
The organic photoelectric conversion device prepared above, 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 9.0 mm ² on the light receiving portion, the short circuit current density Jsc Four light receiving portions formed on the same element were measured for (mA / cm ² ), open circuit voltage Voc (V), and fill factor (fill factor) FF, and average values were obtained. In addition, the photoelectric conversion efficiency η (%) was obtained from Jsc, Voc, and FF according to Equation 1.

Formula 1 η (%) = Jsc (mA / cm ² ) × Voc (V) × FF
The evaluation results are shown in Table 1.

  In the table, p: n represents the mass ratio of the p-type semiconductor (polymer) and the n-type semiconductor (PCBM).

  Table 1 shows that the reverse layer type organic photoelectric conversion element using the compound of the present invention exhibits higher photoelectric conversion efficiency than the organic photoelectric conversion element using the comparative compound.

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.

  After the same transparent substrate as in Example 1 was washed in the same process, on the ITO film, Baytron P4083 (manufactured by Starck Vitec), which is a conductive polymer, was spin-coated so as to have a film thickness of 30 nm. Heat drying at 140 ° C. for 10 minutes in the air.

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

  As a p-type semiconductor material, 0.6% by mass of the comparative compound 2 and 0.9% by mass of PCBM as an n-type semiconductor material are dissolved in chlorobenzene to prepare a 1.2% by mass chlorobenzene solution. While being filtered through a 45 μm filter, spin coating was performed at 700 rpm for 60 seconds, then at 2200 rpm for 1 second, and left at room temperature for 30 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 device was set so that the shadow mask with a width of 2 mm was orthogonal to the transparent electrode, and the inside of the vacuum deposition apparatus was depressurized to 10 ⁻³ Pa or less. 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 2 mm square.

The obtained organic photoelectric conversion element 2 ′ was prepared by using a UV curable resin (manufactured by Nagase Chemtex Co., Ltd., 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 6 ')
In the production of the organic photoelectric conversion element 2 ', a normal layer type organic photoelectric conversion element 6' was produced in the same manner except that the exemplified compound 23 was used instead of the comparative compound 2 as the p-type semiconductor material.

[Production of organic photoelectric conversion element]
(Evaluation of photoelectric conversion efficiency)
About the produced organic photoelectric conversion element and the organic photoelectric conversion elements 2 and 3 produced in Example 1, as in Example 1, the short-circuit current density Jsc (mA / cm ² ), the open circuit voltage Voc (V), and the curve A factor (fill factor) FF was determined, and the photoelectric conversion efficiency η (%) was calculated.

(Durability evaluation)
Store in a container kept at a temperature of 80 ° C. and a humidity of 80%, periodically take out and measure the voltage-current characteristics, and reduce the initial photoelectric conversion efficiency to 80% of the initial photoelectric conversion efficiency, assuming 100 as the initial photoelectric conversion efficiency. Time was evaluated as LT80.

  The evaluation results are shown in Table 2.

  When comparing the organic photoelectric conversion elements 2 and 6 in Table 2, it can be seen that the organic photoelectric conversion element 6 using the compound 23 of the present invention has higher durability. Further, when LT80 is compared in the organic photoelectric conversion elements 6 and 6 ', it can be seen that the former value is larger than the latter value, and the reverse layer type organic photoelectric conversion element has particularly high durability.

DESCRIPTION OF SYMBOLS 10 Organic photoelectric conversion element 11 Board | substrate 12 1st electrode 13 2nd electrode 14 Photoelectric conversion layer 14 '1st photoelectric conversion layer 15 Charge recombination layer 16 2nd photoelectric conversion layer 17 Hole transport layer 18 Electron transport layer

Claims (9)

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, Y ₁ represents —CR ₁ ═ or —N═. R ₁ represents a hydrogen atom, a halogen atom, an alkyl group, a fluorinated alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a hetero group. Represents an aryl group or a cyano group, and may be a condensed ring structure.)   2. The organic photoelectric conversion device according to claim 1, wherein the compound having a 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 groups represented by Y ₁ is characterized in that it is a -CR 1 _=. The compound having a partial structure represented by the general formula (1) is a compound having any partial structure represented by the following general formula (2A), (2B), (2C) or (2D) The organic photoelectric conversion element according to any one of claims 1 to 3, wherein

(In the formula, A ₁ and A ₂ represent an aromatic ring or a heteroaromatic ring, and m and n represent an integer of 0 to _2. R _{2 to} R ₃ represent a hydrogen atom, a halogen atom, an alkyl group, a fluorine atom. Represents an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, a heteroaryl group or a cyano group.)   The organic photoelectric conversion element according to claim 4, wherein the p-type organic semiconductor material is a compound having a partial structure represented by the general formula (2C).   In the said General formula (2C), m is 0, The organic photoelectric conversion element of Claim 4 or 5 characterized by the above-mentioned. The p-type organic semiconductor material is a copolymer of a structure represented by the general formulas (1) and (2A) to (2D) and a structure represented by the following general formula (3). The organic photoelectric conversion element according to any one of claims 1 to 6, wherein

(In the formula, Z represents a carbon atom, a nitrogen atom or a silicon atom substituted with an alkyl group.)   In the said General formula (3), Z is the silicon substituted by the alkyl group, The organic photoelectric conversion element of Claim 7 characterized by the above-mentioned.   The 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.

Images