JP4964258B2 - Organic photoelectric conversion device using benzophosphole compound - Google Patents

Description

  The present invention relates to an organic photoelectric conversion element using a benzophosphole compound.

  Conventionally, solar cells using polycrystalline silicon have been developed and put into practical use. However, high-purity silicon is required for its manufacture, and the manufacturing process consists of a high-temperature process. Considering the energy required for manufacturing, it cannot be said that the solar cell necessarily contributes sufficiently to energy-saving technology.

  In addition to outdoor power generation applications, for example, problems remain in the fabrication of elements on plastic substrates, which are required for portable solar cells.

  On the other hand, in optical sensors, image reading devices using scanners with one-dimensional sensors using silicon crystals have been put to practical use as image sensors in facsimile machines and copiers, but large-area two-dimensional sensors that do not require scanning have been put into practical use. It has not been.

  However, in recent years, in order to improve the above-mentioned problems, solar cells using organic materials that can be applied to a coating process that can be expected to save energy in manufacturing and that can be easily increased in area have been developed.

  As a wet solar cell using organic materials, a dye-sensitized type has been studied, but since it is a system using an electrolyte solution, there are problems of liquid leakage and iodine loss in the liquid. Not reached.

On the other hand, all solid-state organic thin-film solar cells are classified into a heterojunction type and a bulk heterojunction type according to the design of the active layer. In the heterojunction type, a layer made of an electron donor and a layer made of an electron acceptor are stacked, and photoinduced charge transfer at the bonding interface is utilized. Non-Patent Document 1 reports a conversion efficiency of 1% using copper phthalocyanine as an electron donor and a perylene derivative as an electron acceptor. In addition to this, condensed polycyclic aromatic compounds such as pentacene and tetracene are considered as an electron donor, a fullerene compound such as C ₆₀ is used as the electron acceptor.

Another bulk heterojunction type is an active layer formed by mixing an electron donor and an electron acceptor at an appropriate ratio, and is different from a heterojunction type in which an active layer is formed in a two-layer structure. . The junction between the electron donor and the electron acceptor is uniformly present in the bulk of the mixed active layer, and is characterized by the effective use of sunlight. The bulk heterojunction type device can be produced by vacuum depositing an electron donor and an electron acceptor to form an active layer, or by applying a mixture of the two by spin coating or printing. There is something to form. In the vacuum deposition method, an active layer composed of copper phthalocyanine and C ₆₀ has been reported (Non-Patent Document 2), and in the wet coating method, it is a soluble derivative of polythiophene and fullerene, which are conjugated polymers [6,6]- A typical example is a system in which phenyl C ₆₁ -butyric acid methyl ester (abbreviation PCBM) is mixed (Non-patent Document 3).

  In the bulk heterojunction type, in order to further increase the efficiency, the active layer is composed of an electron donor layer (p-layer), a mixed layer of electron donor and electron acceptor (i-layer), an electron acceptor layer (n-layer). ) And a pin-type three-layer structure (Non-patent Document 4).

  In any of the above element structures, in order to efficiently transport photocarriers (holes and electrons) generated by light absorption to the electrode, a buffer layer is provided between the electrode and the active layer. . A conductive polymer is often used between the anode and the anode, and examples thereof include poly (3,4-ethylenedioxythiophene) poly (styrenesulfonic acid) (abbreviation PEDOT: PSS) and the like (Non-patent Document 3). ). Further, an inorganic material such as lithium fluoride (Non-patent Document 3) or bathocuproine (abbreviated as BCP) (Non-patent Document 2) is used between the cathode and the active layer.

C.W. Tang: Appl. Phys. Lett., 48, 183-185, 1986 S. Uchida et al .: Appl. Phys. Lett., 84, 4218-4220, 2004 S.E. Shaheen et al .: Appl. Phys. Lett., 78, 841-843, 2001 M. Hiramoto et al .: Appl. Phys. Lett., 58, 1062-1064, 1991

  In the above organic thin-film solar cell, particularly when the cathode buffer layer provided between the cathode and the active layer is lithium fluoride, an ultra-thin film of 1 nm or less is required. Uniform coating on the active layer surface is difficult. As for bathocuproine, although the film thickness can be controlled to about 6 nm, the stability of the device is a problem because of its poor heat resistance.

  This invention is made | formed in view of the above situation, and makes it a subject to provide the organic photoelectric conversion element which the film-forming property and heat resistance of a cathode buffer layer are favorable, and also has high energy conversion efficiency. .

  The present invention is characterized by the following in order to solve the above problems.

  1st: In the organic photoelectric conversion element which has the active layer which consists of an electron donor and an electron acceptor arrange | positioned on the board | substrate between the anode and cathode which at least one is transparent, an active layer and a cathode An organic photoelectric conversion element having a layer made of a benzophosphole compound represented by the following general formula (I) between them.

Wherein R ¹ , R ² and R ³ each independently represent a saturated or unsaturated aliphatic hydrocarbon group, alkoxy group, aromatic hydrocarbon group or aromatic heterocyclic group having 1 to 6 carbon atoms. , N represents 2 or 3. a, b, c, and d each independently represent a hydrogen atom or a carbon atom or a nitrogen atom bonded to a substituent, and E represents an oxygen atom, a sulfur atom, a selenium atom, or tellurium. Indicates an atom.)
Second: The first organic photoelectric conversion element as described above, wherein the active layer contains a porphyrin compound or a phthalocyanine compound as an electron donor and a fullerene compound as an electron acceptor.

  Third: The active layer contains a benzoporphyrin compound represented by the following general formula (II) or (III) as an electron donor, and the benzoporphyrin compound is formed by thermal conversion from a soluble precursor. Said 2nd organic photoelectric conversion element.

( ^Wherein Z ^ia and Z ^ib (i = 1 to 4) represent a hydrogen atom, a halogen atom, or a monovalent organic group, and Z ^ia and Z ^ib may combine to form a ring. R ^{4 to} R ⁷ each independently represents a hydrogen atom, a halogen atom, or a monovalent organic group, M is a divalent metal atom, or an atomic group in which a trivalent or higher metal is bonded to another atom. Is shown.)
Fourth: The first organic photoelectric conversion element as described above, wherein the active layer contains a conjugated polymer as an electron donor and a fullerene compound as an electron acceptor.

  Fifth: After the formation of the benzophosphole-containing layer represented by the general formula (I), annealing is performed in a temperature range of 50 to 250 ° C. Any organic photoelectric conversion element.

  According to the organic photoelectric conversion element of the present invention, since a layer containing a specific benzophosphole having good film forming properties and heat resistance is provided as a buffer layer between the active layer and the cathode, photoelectric conversion characteristics are provided. It is possible to obtain an element excellent in the above.

  Therefore, the organic photoelectric conversion element according to the present invention can be applied to a photovoltaic power generation element and an image sensor, and its technical value is great.

It is the schematic cross section which showed an example of the organic photoelectric conversion element. It is the schematic cross section which showed another example of the organic photoelectric conversion element. It is the schematic cross section which showed another example of the organic photoelectric conversion element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of the organic photoelectric conversion device of the present invention, wherein 1 is a transparent substrate, 2 is a transparent anode, 3 is an anode buffer layer, 4 is an active layer, and 5 is a cathode buffer layer. , 6 each represents a cathode.

  The transparent substrate 1 serves as a support for the organic photoelectric conversion element, and a quartz or glass plate, a plastic film, a sheet, or the like is used. In particular, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, or polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too low, the organic photoelectric conversion element may be deteriorated by outside air passing through the substrate. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on one side or both sides of the synthetic resin substrate is also a preferable method.

  A transparent electrode 2 is provided on the transparent substrate 1, and the transparent electrode 2 has a function of transmitting light and absorbing it into the active layer 4, and also serves as an anode buffer for holes that are photocarriers generated in the active layer 4. It plays the role of receiving through layer 3. The transparent electrode 2 is usually made of a metal oxide such as indium / tin oxide or indium / zinc oxide. The formation of the transparent electrode 2 is often performed by a sputtering method, a vacuum deposition method, or the like. The film thickness of the transparent electrode 2 is set so that the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the film thickness is usually about 10 to 1000 nm, preferably about 50 to 300 nm.

  An anode buffer layer 3 is provided on the transparent electrode 2. A requirement for the material used for the anode buffer layer 3 is that holes generated in the active layer 4 can be efficiently transported to the transparent electrode 2. For this purpose, it is first necessary that the hole mobility is high or the conductivity is high. Moreover, it is required that the hole injection barrier between the transparent electrode 2 and the transparent electrode 2 is small. Furthermore, it is also necessary for the material to be highly transparent to visible light.

  As a compound often used as a material of the anode buffer layer 3, poly (3,4-ethylenedioxythiophene) poly (styrenesulfonic acid) (abbreviation PEDOT: PSS), which is a polythiophene mixed with an electron accepting compound, Similarly, conductive polymers such as polyaniline and polypyrrole mixed with an electron-accepting compound are representative examples.

  As a thin film forming method of the anode buffer layer 3, a wet coating method such as spin coating or inkjet can be used.

  The film thickness of the anode buffer layer 3 thus formed is usually 3 to 200 nm, preferably 10 to 100 nm.

  An active layer 4 is provided on the anode buffer layer 3. The active layer 4 includes an electron donor and an electron acceptor. The material used for this active layer must have high mobility to efficiently absorb visible to near-infrared light and efficiently transport light-induced holes or electrons. It is. In addition, it is important that the contact area between the electron donor and the electron acceptor is large, and for that purpose, it is necessary to form a phase separation structure with a size about the diffusion length of exciton for efficient charge separation. Desired.

  In order to efficiently perform charge separation of hole-electron pairs generated by light absorption, a heterojunction type and a bulk heterojunction type have been proposed so far. As shown in FIG. 2, the heterojunction device has a two-layer structure of a p-layer 4a made of an electron donor and an n-layer 4b made of an electron acceptor, and charge separation is performed at the pn junction interface. Is called. In another bulk heterojunction device, which is another concept, an active layer 4 is formed by mixing an electron donor and an electron acceptor (FIG. 1). The contact area between the electron donor and the electron acceptor can be increased by forming a phase separation structure. As a structure for more efficiently performing charge separation in this bulk heterojunction element, a p-i-n junction element having a three-layer structure shown in FIG. 3 has been studied. In this structure, a p-layer 4a made of an electron donor, an i-layer 4c made of a mixture of an electron donor and an electron acceptor, and an n-layer 4b made of an electron acceptor are stacked.

  Examples of the electron donor used in the active layer 4 include porphyrin compounds and phthalocyanine compounds having an absorption band from visible to near infrared, and these compounds may have a central metal or a metal-free compound. It may be a thing. As a porphyrin compound, the benzoporphyrin compound represented by the said general formula (II) or (III) is mentioned.

In the general formulas (II) and (III), Z ^ia and Z ^ib (i = 1 to 4) represent a hydrogen atom, a halogen atom, or a monovalent organic group, and are bonded to Z ^ia and Z ^ib to form a ring. May be formed. Specific examples of the monovalent organic group include an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an aralkyl group such as a benzyl group; an alkenyl group such as a vinyl group; a cyano group; an amino group; An alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; an aryloxy group such as a phenoxy group and a benzyloxy group; a diethylamino group; Dialkylamino groups such as diisopropylamino groups; diaralkylamino groups such as dibenzylamino groups and diphenethylamino groups; α-haloalkyl groups such as trifluoromethyl groups; hydroxyl groups; phenyl groups optionally having substituents; Aromatic hydrocarbon ring group such as naphthyl group; optionally substituted thienyl group, pyridyl group And aromatic heterocyclic groups such as groups. Examples of the substituent include a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; and 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group. Alkoxycarbonyl groups of 1 to 6 carbon atoms such as methoxy groups and ethoxy groups; aryloxy groups such as phenoxy groups and benzyloxy groups; acyls such as dimethylamino groups, dialkylamino groups such as diethylamino groups, and acetyl groups Group, haloalkyl group such as trifluoromethyl group, cyano group and the like.

Specific examples of the organic group in which Z ^ia and Z ^ib combine to form a ring include a ring formed as a structure of Z ^ia —CH═CH—Z ^ib ; an ^optionally substituted benzene ring , Naphthalene ring, anthracene ring, etc .; aromatic hydrocarbon ring such as optionally substituted pyridine ring, quinoline ring, furan ring, thiophene ring, etc .; non-aromatic cyclic hydrocarbon such as cyclohexane ring Etc. Examples of the substituent include a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; and 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group. Alkoxycarbonyl groups of 1 to 6 carbon atoms such as methoxy groups and ethoxy groups; aryloxy groups such as phenoxy groups and benzyloxy groups; acyls such as dimethylamino groups, dialkylamino groups such as diethylamino groups, and acetyl groups Group, haloalkyl group such as trifluoromethyl group, cyano group and the like.

R ^{4 to} R ⁷ represent a hydrogen atom, a halogen atom, or a monovalent organic group. Specific examples of the monovalent organic group include an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an aralkyl group such as a benzyl group; an alkenyl group such as a vinyl group; a cyano group; an amino group; Alkoxy groups having 1 to 6 carbon atoms such as methoxy group and ethoxy group; alkoxycarbonyl groups having 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; aryloxy groups such as phenoxy group and benzyloxy group; Dialkylamino groups such as diisopropylamino groups; diaralkylamino groups such as dibenzylamino groups and diphenethylamino groups; α-haloalkyl groups such as trifluoromethyl groups; hydroxyl groups; phenyl groups optionally having substituents; Aromatic hydrocarbon ring group such as naphthyl group; optionally substituted thienyl group, pyridyl group And aromatic heterocyclic groups such as groups. Examples of the substituent include a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; and 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group. Alkoxycarbonyl groups of 1 to 6 carbon atoms such as methoxy groups and ethoxy groups; aryloxy groups such as phenoxy groups and benzyloxy groups; acyls such as dimethylamino groups, dialkylamino groups such as diethylamino groups, and acetyl groups Group, haloalkyl group such as trifluoromethyl group, cyano group and the like.

R ^{4 to} R ⁷ are preferably a single atom such as a hydrogen atom or a halogen atom from the viewpoint of enhancing the planarity of the molecule.

M is a divalent metal atom, for example, Zn, Cu, Fe, Ni, Co, or an atomic group in which a trivalent or higher metal is bonded to another atom, for example, Fe-B ¹ , Al-B. ² , Ti = O, Si-B ³ B ^{4 and the} like. Here, B ¹ , B ² , B ³ , and B ⁴ represent monovalent groups such as halogen atoms, alkyl groups, and alkoxy groups.

  Furthermore, in the present invention, two porphyrin rings are commonly coordinated to one atom, two porphyrin rings are bonded to each other by sharing one or more atoms or atomic groups, or Those in which three or more of them are connected to form a long chain may be used.

  Specific examples of preferred benzoporphyrin compounds are shown below, but the benzoporphyrin compounds used in the present invention are not limited to these. In addition, molecular structures with good symmetry are mainly exemplified, but an asymmetric structure by a combination of partial structures may be used.

  Said benzoporphyrin compound may be used independently, or 2 or more types may be mixed and used for it.

  In addition to the benzoporphyrin compounds shown above, 2,3,7,8,12,13,17,18-21H, 23H-porphine platinum and the like can also be mentioned.

  Specific examples of the phthalocyanine compound include 29H, 31H-phthalocyanine, copper phthalocyanine, zinc phthalocyanine, tin phthalocyanine, titanium phthalocyanine oxide, copper 4,4 ', 4' ', 4' ''-tetraaza-29H, 31H-phthalocyanine, etc. Is mentioned.

The active layer containing the benzoporphyrin compound can be formed by a vacuum deposition method or a wet coating method, but the wet coating method is preferred for the purpose of controlling the crystallinity and shape of the thin film. In the case of the wet coating method, the benzoporphyrin compound is difficult to apply because of its low solubility in organic solvents, but as a means for solving this problem, a soluble precursor represented by the following general formulas (IV) and (V) It has been found that it is effective to form a layer composed of a target compound by heat conversion after coating film formation.

In the general formulas (IV) and (V), Z ^ia and Z ^ib , R ^{4 to} R ⁷ and M are the same as those in the general formulas (II) and (III), respectively. Y ^{1 to} Y ⁴ each independently represents a monovalent atom or atomic group. Y ^{1 to} Y ⁴ are each four, but Y ¹ , Y ² , Y ³ , and Y ⁴ may be the same or different.

Examples of Y ¹ to Y ^4, as the atom, such as hydrogen atom. On the other hand, examples of the atomic group include a hydroxyl group and an alkyl group. Here, the carbon number of the alkyl group is preferably 1 to 3. Examples of the alkyl group include a methyl group and an ethyl group.

  A method for forming an electron donor layer by wet coating will be described below by taking the exemplified compound (BP-1) as an example.

  The benzoporphyrin compound can be derived using the corresponding bicyclo compound as its precursor. Since this precursor does not have a planar structure, it has high solubility in a solvent and is difficult to crystallize. Therefore, application from a solution gives an amorphous or a good film close to amorphous. A benzoporphyrin compound film having high planarity can be obtained by heat-treating this film and removing ethylene. The structure of the unsubstituted and metal-free body is represented by the following chemical reaction.

The above reaction proceeds quantitatively by heating to 100 ° C or higher, preferably 150 ° C or higher. In addition, since it is an ethylene molecule that desorbs, it hardly remains in the system, and there is no problem in terms of toxicity and safety.

In addition to the low molecular weight compound, a conjugated polymer is also used as an electron donor capable of wet coating. Specific examples of the conjugated polymer include those having polythioephene, polyparaphenylene vinylene, or polyfluorene as a basic skeleton. Specific examples are shown below.

The role of the electron acceptor used in the active layer 4 is to efficiently receive electrons from the electron donor during light absorption and efficiently transport them to the cathode 6 through the cathode buffer layer 5. For this purpose, the relative relationship between the lowest empty orbit (LUMO) of the electron acceptor and the electron donor is important, and in other words, the LUMO of the electron donor material is 0.3 eV or more above the LUMO of the electron acceptor material. In other words, the electron affinity of the electron acceptor layer material is 0.3 eV or more greater than the electron affinity of the electron donor layer material. In addition, the electron mobility is required to be high, and it is required to have a mobility of 10 ⁻⁴ [cm ² / Vs] or more.

  Examples of the electron acceptor material that satisfies such conditions include fullerene compounds. Specific examples of fullerene compounds that are preferably used in the present invention are shown below.

  As a method for forming the active layer 4, a vacuum deposition method or a wet coating method is selected according to the properties of the electron donor and the electron acceptor used. When each material has sublimability, the active layer 4 is formed by vacuum deposition. When each material is soluble in an appropriate solvent, spin coating, casting, blade coating, ink jet, gravure printing, etc. A coating method is applied.

  In the heterojunction element structure shown in FIG. 2, a layer composed of an electron donor and an electron acceptor may be stacked by any film forming method. In the bulk heterojunction device shown in FIGS. 1 and 3, it is necessary to form a mixed layer of an electron donor and an electron acceptor. In the vacuum deposition method, the electron donor and the electron acceptor are co-evaporated. In the coating method, a mixed solution containing an electron donor and an electron acceptor can be used.

  The average film thickness of the active layer 4 formed as described above is usually 10 to 2000 nm, preferably 20 to 100 nm.

  In the present invention, the cathode buffer layer 5 made of benzophosphole represented by the general formula (I) is laminated on the active layer 4 in order to develop high photoelectric conversion characteristics and heat resistance.

The function of the cathode buffer layer 5 is to transport electrons, which are photocarriers generated in the active layer, to the cathode 6 without being deactivated by recombination. A function of confining excitons generated in the active layer is also assumed. Furthermore, it is considered that it also has a function of preventing damage to the active layer when forming the cathode.

In the general formula (I), R ¹ , R ² and R ³ are each independently a saturated or unsaturated aliphatic hydrocarbon group, alkoxy group, aromatic hydrocarbon group or aromatic heterocycle having 1 to 6 carbon atoms. Indicates a group.

  Specific examples of the aliphatic hydrocarbon group include a linear or branched alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group, and a linear or branched chain having 1 to 6 carbon atoms such as a vinyl group. And alkenyl groups.

  Specific examples of the alkoxy group include linear or branched alkoxy groups having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group.

  Specific examples of the aromatic hydrocarbon group include aryl groups having 6 to 14 carbon atoms such as a phenyl group and a naphthyl group. These may have a substituent such as a linear or branched alkyl group having 1 to 6 carbon atoms.

  Specific examples of the aromatic heterocyclic group include a pyridyl group and a quinolyl group.

  In the general formula (I), a, b, c and d each independently represent a hydrogen atom or a carbon atom or a nitrogen atom bonded to a substituent. Specific examples of the substituent on the carbon atom include 6 to 14 carbon atoms such as a straight or branched alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group, a halogen atom, a cyano group, and a phenyl group. And aryl groups.

The benzopolyphosphole compound of the general formula (I) is synthesized, for example, by the method described in T. Sanji et al .: Organic Letters, Vol. 10, page 2689, 2008 and JP 2008-56630 A. Hereinafter, preferred specific examples of the benzophosphole compound of the general formula (I) according to the present invention will be given, but the present invention is not limited to these compounds. In the following, molecular structures having good symmetry are mainly exemplified, but an asymmetric structure having a combination of these partial structures may be used.

  The cathode buffer layer 5 made of the benzophosphole compound is laminated on the active layer by a vacuum deposition method or a wet coating method. The film thickness of the cathode buffer layer is usually 1 to 100 nm, preferably 2 to 50 nm. If the film thickness is less than 1 nm, the active layer cannot be completely covered, and the open circuit voltage (Voc) may be lowered. When the film thickness exceeds 100 nm, the series resistance of this layer itself cannot be ignored, and the fill factor (FF) may be lowered.

  The cathode 6 plays a role of efficiently receiving the electrons separated in the active layer through the cathode buffer layer 5. The material used as the cathode 6 is preferably a metal having good contact with the cathode buffer layer 5 in order to efficiently collect electrons, and an appropriate metal such as magnesium, indium, calcium, aluminum, silver, or an alloy thereof is used. .

  The film thickness of the cathode 6 is usually 50 to 300 nm.

After the cathode 6 is formed, the element is annealed in a temperature range of 50 to 250 ° C., thereby improving the thermal stability of the element and improving the contact between the cathode 6 and the cathode buffer layer 5. be able to. This annealing treatment is also effective for relaxing the structure of the active layer and promoting crystallization. For this reason, the cathode buffer material is required to have a glass transition temperature (Tg) that is an index of heat resistance of 120 ° C. or higher.

1, 2 and 3 show one embodiment of the organic photoelectric conversion device according to the present invention, and the present invention is not limited to the illustrated configuration. For example, a stacked structure opposite to that shown in FIG. 1 can be used, that is, the cathode 6, the cathode buffer layer 5, the active layer 4, the anode buffer layer 3, and the anode 2 can be stacked on the substrate 1 in this order. The same applies to the structures of FIGS.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.
<Synthesis Example 1>
Exemplary compound (2) was synthesized by the method shown below.
Synthesis of 3,7-dibromo-1,2,5,6-tetraphenylbenzo [1,2-b-4,5-b '] diphosphole sulfide

  To a mixture of 1,4-dibromo-2,5-di (phenylethynyl) benzene (2.16 g, 4.95 mmol) and diethyl ether (25 mL) at -78 ° C, butyllithium (13.0 mL, 1.58 M, pentane solution) And stirred for 2 hours. To this mixture was added chlorodiethylaminophenylphosphine (2.34 g, 10.9 mmol), and the mixture was further stirred for 15 minutes, and then the solvent was distilled off under reduced pressure. . Tetrahydrofuran (25.0 mL) was added to this mixture at −78 ° C. and the temperature was raised to 0 ° C., phosphorus tribromide (2.80 mL, 29.7 mmol) was added, and the mixture was stirred with heating under reflux for 14 hr. The resulting orange precipitate was filtered, and the solid on the filter paper was washed with water and methanol to give 3,7-dibromo-1,2,5,6-tetraphenylbenzo [1,2-b-4 , 5-b '] diphosphole was obtained. This compound, lithium chloride (112 mg, 2.90 mmol) and sulfur (153 mg, 4.78 mmol) were stirred in toluene (14.5 mL) for 15 hours, and then the solvent was distilled off under reduced pressure to give a yellow crude product. Got. Purification by silica gel column chromatography gave the target compound (1.02 g, 1.42 mmol, 29%). The product was a mixture of cis and trans diastereomers.

Synthesis of 1,2,3,5,6,7-hexaphenylbenzo [1,2-b-4,5-b '] diphosphole sulfide (2) Compound obtained above (591 mg, 0.825 mmol) , Phenylboronic acid (329 mg, 2.70 mmol), Pd ₂ (dba) ₃・ CHCl ₃ complex (43.5 mg, 0.0420 mmol), 2-dicyclohexylphosphino-2 ', 6'-dimethoxybiphenyl (69.1 mg, 0.168 mmol) ), Potassium carbonate (450 mg, 3.26 mmol) in a mixed solvent of toluene (4.20 mL) and water (1.60 mL) at 80 ° C. for 5 hours with stirring, sulfur (6.40 mg, 0.198 mmol) was added, The mixture was further heated and stirred at 80 ° C. for 2.5 hours. After the organic layer and the aqueous layer were separated, the aqueous layer was extracted twice with chloroform, and the chloroform layer was combined with the previous organic layer. After passing this solution through silica gel, the solvent was distilled off under reduced pressure to obtain a yellow crude product. Recrystallization from toluene and subsequent purification by gel permeation chromatography (developing solvent: chloroform) yielded Exemplified Compound (2) (422 mg, 72%) as a diastereomeric mixture of cis and trans isomers.

The glass transition temperature of the above exemplary compound (2) by differential calorimetry (DSC) measurement was 158 ° C.
<Example 1>
An organic thin film solar cell having the structure shown in FIG. 3 was produced by the following method.

  A transparent electrode is formed by patterning a 145nm thick indium tin oxide (ITO) transparent conductive film (sheet resistance 8.4Ω) on a glass substrate into a 2mm wide stripe using normal photolithography and hydrochloric acid etching. did. The patterned ITO substrate was cleaned in the order of ultrasonic cleaning with a surfactant, water with ultrapure water, and ultrasonic cleaning with ultrapure water, then dried with nitrogen blow, and finally subjected to ultraviolet ozone cleaning.

  On this transparent substrate, PEDOT: PSS (product name: Baytron PH), a conductive polymer, was spin-coated as an anode buffer layer 3 with a film thickness of 40 nm, and then at 120 ° C. for 10 minutes in the atmosphere. After heat drying, heat treatment was performed at 180 ° C. for 3 minutes in nitrogen.

  Next, an anode buffer layer is prepared by using a solution obtained by dissolving the precursor of the tetrabenzoporphyrin compound (BP-1) shown above in a mixed solvent of chlorobenzene and chloroform (2: 1 by weight) at 0.5% by weight. Spin coated on top. After the application, heat treatment was performed on a hot plate at 180 ° C. for 20 minutes. By this heat treatment, the brown precursor film was thermally converted into a green tetrabenzoporphyrin film, and a crystalline p-layer 4a having an average film thickness of 25 nm was obtained.

  Subsequently, an active layer composed of the above benzoporphyrin using a solution obtained by dissolving tetrabenzoporphyrin and fullerene compound (SIMEF) in a mixed solvent of chlorobenzene and chloroform (weight ratio 1: 1) at 0.6% by weight and 1.4% by weight, respectively. The (p-layer) 4a was spin coated. After coating, heat treatment was performed at 180 ° C. for 20 minutes to laminate an active layer (i-layer) 4b.

  After the heat treatment, an active layer 4c (n-layer) was laminated on the active layer 4b by spin coating using a toluene solution (1.2% by weight) of a fullerene compound (SIMEF). After the application, a drying treatment was performed at 65 ° C. for 10 minutes.

Next, the substrate on which the series of organic layers was formed was placed in a vacuum deposition apparatus. After roughly exhausting the apparatus with an oil rotary pump, the apparatus was exhausted with a cryopump until the degree of vacuum in the apparatus was 1.4 × 10 ⁻⁴ Pa. Vapor deposition was performed by heating the benzodiphosphole compound (2) in a metal boat placed in the apparatus. The degree of vacuum during vapor deposition was 1.4 × 10 ⁻⁴ Pa, the vapor deposition rate was 0.05 nm / second, and a 5 nm thick film was laminated on the active layer 4 c to complete the cathode buffer layer 5.

Subsequently, as a mask for the upper electrode, a 2 mm wide striped shadow mask is brought into close contact with the element so as to be orthogonal to the ITO stripe of the transparent electrode 2 and installed in a separate vacuum deposition chamber in the same manner as the organic layer. The degree of vacuum in the apparatus was evacuated to 2.5 × 10 ⁻⁴ Pa.

As the cathode 6, aluminum was formed in the cathode buffer layer 5 with a film thickness of 72 nm at a deposition rate of 0.5 nm / second. The degree of vacuum during deposition was 2.5 × 10 ⁻⁴ Pa.

  After the device was taken out of the glove box, an annealing treatment was performed at 120 ° C. for 10 minutes. After the annealing, the element was bonded and sealed with a photocuring resin using a back glass plate.

  As described above, an organic thin-film solar cell having a light-receiving area portion having a size of 2 mm × 2 mm was obtained.

When this element was irradiated with solar simulator (AM1.5G) light at an irradiation intensity of 100 mW / cm ² and the voltage-current characteristics were measured, the open-circuit voltage (Voc) was 0.72 V and the short-circuit current (Jsc) was 10.4 mA. The photoelectric conversion characteristics of / cm ² , fill factor (FF) 0.61, energy conversion efficiency (hp) 4.58% were obtained.
<Example 2>
An organic thin film solar cell was produced in the same manner as in Example 1 except that the benzodiphosphole compound (1) was used for the cathode buffer layer.

When this element was irradiated with solar simulator (AM1.5G) light at an irradiation intensity of 100 mW / cm ² and the voltage-current characteristics were measured, the open circuit voltage (Voc) was 0.71 V and the short circuit current (Jsc) was 10.6 mA. The photoelectric conversion characteristics of / cm ² , fill factor (FF) 0.60, energy conversion efficiency (hp) 4.52% were obtained.
<Comparative Example 1>
A device was fabricated in the same manner as in Example 1 except that the following compound (BCP) was used as the cathode buffer layer.

When this element was irradiated with solar simulator (AM1.5G) light at an irradiation intensity of 100 mW / cm ² and the voltage-current characteristics were measured, the open circuit voltage (Voc) was 0.22 V and the short-circuit current (Jsc) was 7.8 mA. The photoelectric conversion characteristics of / cm ₂ , fill factor (FF) 0.33, energy conversion efficiency (hp) 0.57% were obtained.
<Comparative example 2>
A device was fabricated in the same manner as in Example 1 except that the cathode buffer layer was not provided.

The device was irradiated with solar simulator (AM1.5G) light at an irradiation intensity of 100 mW / cm ² and measured for voltage-current characteristics. The open circuit voltage (Voc) was 0.48 V and the short-circuit current (Jsc) was 8.5 mA. The photoelectric conversion characteristics of / cm ² , fill factor (FF) 0.40, energy conversion efficiency (hp) 1.61% were obtained.

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Transparent anode 3 Anode buffer layer 4 Active layer 4a p-type active layer 4b n-type active layer 4c i-type active layer 5 Cathode buffer layer 6 Cathode

Claims (5)

In an organic photoelectric conversion element having an active layer composed of an electron donor and an electron acceptor disposed between an anode and a cathode, at least one of which is transparent, on a substrate, between the active layer and the cathode, An organic photoelectric conversion element comprising a layer made of a benzophosphole compound represented by the following general formula (I):

Wherein R ¹ , R ² and R ³ each independently represent a saturated or unsaturated aliphatic hydrocarbon group, alkoxy group, aromatic hydrocarbon group or aromatic heterocyclic group having 1 to 6 carbon atoms. , N represents 2 or 3. a, b, c, and d each independently represent a hydrogen atom or a carbon atom or a nitrogen atom bonded to a substituent, and E represents an oxygen atom, a sulfur atom, a selenium atom, or tellurium. Indicates an atom.)   The organic photoelectric conversion element according to claim 1, wherein the active layer contains a porphyrin compound or a phthalocyanine compound as an electron donor and a fullerene compound as an electron acceptor. The active layer contains a benzoporphyrin compound represented by the following general formula (II) or (III) as an electron donor, and the benzoporphyrin compound is formed by thermal conversion from a soluble precursor. Item 3. The organic photoelectric conversion device according to Item 2.

( ^Wherein Z ^ia and Z ^ib (i = 1 to 4) represent a hydrogen atom, a halogen atom, or a monovalent organic group, and Z ^ia and Z ^ib may combine to form a ring. R ^{4 to} R ⁷ each independently represents a hydrogen atom, a halogen atom, or a monovalent organic group, M is a divalent metal atom, or an atomic group in which a trivalent or higher metal is bonded to another atom. Is shown.)   The organic photoelectric conversion element according to claim 1, wherein the active layer contains a conjugated polymer as an electron donor and a fullerene compound as an electron acceptor.   The layer according to any one of claims 1 to 4, wherein the layer containing benzophosphole represented by the general formula (I) is annealed in a temperature range of 50 to 250 ° C after the formation of the layer. The organic photoelectric conversion element as described.

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