JP5639783B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element used for a photoelectric device such as a solar cell or an optical sensor.

  A photoelectric conversion element is an element provided with a pair of electrodes consisting of an anode and a cathode, and an organic active layer provided between the pair of electrodes. In the photoelectric conversion element, one of the electrodes is made of a transparent or translucent material, and light is incident on the organic active layer from the transparent or translucent electrode side. Charges (holes and electrons) are generated in the organic active layer by the energy (hν) of light incident on the organic active layer, and the generated holes are directed to the anode and the electrons are directed to the cathode. By connecting an external circuit to the electrode, current (I) is supplied to the external circuit.

  The organic active layer is composed of an electron-accepting compound (n-type semiconductor) and an electron-donating compound (p-type semiconductor). An organic active layer in which an electron-accepting compound (n-type semiconductor) and an electron-donating compound (p-type semiconductor) are mixed and used is called a bulk hetero-type organic active layer.

  In the bulk hetero-type organic active layer, the electron-accepting compound and the electron-donating compound constitute a continuous phase of fine and complicated shape from one electrode side to the other electrode side, and are separated from each other However, it forms a complex interface.

An organic material used for the organic active layer of the photoelectric conversion element is an organic compound that absorbs light based on a π-π ^* transition. For example, a photoelectric conversion element including an organic active layer manufactured by applying a solution using an electron donating compound, an electron accepting compound, xylene, or the like as a solvent on a substrate has been proposed. (Non-Patent Document 1).

APPLIED PHYSICS LETTERS 2007, Vol. 90, p. 193506

  However, the photoelectric conversion element has a problem that the photoelectric conversion efficiency is low.

  Then, an object of this invention is to provide a photoelectric conversion element with high photoelectric conversion efficiency.

That is, the present invention first has an anode, a cathode, and an organic active layer provided between the anode and the cathode, and an electron donating compound and an electron accepting compound are contained in the organic active layer. An image of the organic active layer observed with a transmission electron microscope, and the image of the organic active layer binarized from light to dark, wherein the bond length between the electron donating compound and the electron accepting compound is The photoelectric conversion element is 100 μm or more per 1 μm ² of the image.

  Secondly, the present invention provides the photoelectric conversion element, wherein the lifetime of at least one of the electron donating compound in the organic active layer and the electron accepting compound in the organic active layer is 1 ns or less.

  Thirdly, the present invention has an anode, a cathode, and an organic active layer provided between the anode and the cathode, and has an electron donating compound and an electron accepting compound in the organic active layer. An image of an organic active layer in the range of 900 nm × 900 nm observed with a transmission electron microscope, in which brightness and darkness are binarized to form a white part and a black part, is divided into nine sections having an equal area And the photoelectric conversion element whose standard deviation computed from the area fraction of the black part of each division is 0.09 or less is provided.

  Fourthly, the present invention has an anode, a cathode, and an organic active layer provided between the anode and the cathode, and has an electron donating compound and an electron accepting compound in the organic active layer. Provided is a photoelectric conversion element in which the lifetime of at least one of an electron donating compound in the organic active layer and an electron accepting compound in the organic active layer is 1 ns or less.

  The fifth aspect of the present invention is the photoelectric conversion comprising the step of producing an organic active layer by applying a solution containing an electron donating compound, an electron accepting compound, and a solvent having a boiling point of 100 ° C. or less on the anode or the cathode. A manufacturing method for manufacturing an element is provided.

（式（Ｉ）中、Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄、Ｒ₅及びＲ₆は、同一又は相異なり、水素原子又は置換基を表す。また、Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄、Ｒ₅、Ｒ₆は、それぞれ互いに連結して環状構造を形成してもよい。Ｘ₁、Ｘ₂及びＸ₃は、同一又は相異なり、硫黄原子、酸素原子、セレン原子、−Ｎ（Ｒ₇）−又は−Ｃ（Ｒ₈）＝Ｃ（Ｒ₉）−を表す。Ｒ_7、Ｒ₈及びＲ₉は、同一又は相異なり、水素原子又は置換基を表す。ｎ及びｍは、同一又は相異なり、０〜５の整数を表す。Ｒ₁、Ｒ₂、Ｒ₅、Ｒ₆、Ｘ₁、Ｘ₃が複数個ある場合、それらは同一であっても相異なっていてもよい。） Sixth, the present invention includes a step of producing an organic active layer by applying a solution containing an electron-donating compound, an electron-accepting compound, and a solvent having a boiling point of 100 ° C. or less on an anode or a cathode. And at least one of the organic compound and the electron-accepting compound is a polymer compound containing a repeating unit represented by the formula (I), wherein all the repeating units contained in the polymer compound have the formula (I) The manufacturing method of the photoelectric conversion element which is a polymer compound with the largest ratio of the repeating unit represented by these is provided.

(In the formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are the same or different and represent a hydrogen atom or a substituent. Also, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be connected to each other to form a cyclic structure, and X ₁ , X ₂ and X ₃ are the same or different and are a sulfur atom, an oxygen atom, a selenium atom, —N (R ₇ ) — or —C (R ₈ ) ═C (R ₉ ) — R _7, R ₈ and R ₉ are the same or different and represent a hydrogen atom or a substituent, and n and m are The same or different and represents an integer of 0 to _{5. When} there are a plurality of R ₁ , R ₂ , R ₅ , R ₆ , X ₁ and X ₃ , they may be the same or different. )

  7thly this invention provides the photoelectric conversion element manufactured with the said manufacturing method.

  Eighthly, the present invention provides a solar cell module including the photoelectric conversion element.

  Since the photoelectric conversion element of the present invention has high photoelectric conversion efficiency, the present invention is extremely useful.

The photoelectric conversion element of the present invention has an anode, a cathode, and an organic active layer provided between the anode and the cathode, and has an electron donating compound and an electron accepting compound in the organic active layer. In the image of the organic active layer observed with a transmission electron microscope and binarized, the bond length between the electron donating compound and the electron accepting compound is It is 100 μm or more per 1 μm ^{2 of the} image.

  The anode, the organic active layer, the electron donating compound and the electron accepting compound constituting the organic active layer, the cathode, and other components formed as necessary, which constitute the photoelectric conversion element according to the present invention, are described below. This will be explained in detail.

(Basic form of photoelectric conversion element)
As a basic form of the photoelectric conversion element of the present invention, a pair of electrodes, at least one of which is transparent or translucent, an electron donating compound (p-type organic semiconductor) and an electron-accepting compound (n-type organic semiconductor, etc.) And a bulk hetero-type organic active layer formed from an organic composition.

(Basic operation of photoelectric conversion element)
Light energy incident from a transparent or translucent electrode is absorbed by the electron-accepting compound and / or the electron-donating compound, thereby generating excitons formed by electron-hole coulomb bonding. When the generated excitons move and reach the heterojunction interface where the electron-accepting compound and the electron-donating compound are adjacent, the highest occupied molecular orbital (HOMO) energy and the lowest unoccupied molecular orbital (LUMO) at the interface. ) Electrons and holes are separated by energy difference, and charges (electrons and holes) that can move independently are generated.
Each generated electric charge can be taken out as electric energy (current) to the outside by moving to the electrode.
Since the photoelectric conversion element of the present invention has an organic active layer that efficiently generates photocharge separation and charge transport, the photoelectric conversion efficiency is increased.

(substrate)
The photoelectric conversion element of the present invention is usually formed on a substrate. The substrate may be any substrate that does not chemically change when the electrodes are formed and the organic layer is formed. Examples of the material for the substrate include glass, plastic, polymer film, and silicon. In the case of an opaque substrate, the opposite electrode (that is, the electrode far from the substrate) is preferably transparent or translucent.

(electrode)
Examples of the transparent or translucent electrode material include a conductive metal oxide film and a translucent metal thin film. Specifically, it is manufactured using indium oxide, zinc oxide, tin oxide, and conductive materials such as indium tin oxide (ITO), indium zinc oxide (IZO), and NESA that are composites thereof. Films, gold, platinum, silver, copper, etc. are used, and ITO, indium / zinc / oxide, and tin oxide are preferable. Examples of the method for producing the electrode include a vacuum deposition method, a sputtering method, an ion plating method, a plating method, and the like. Moreover, you may use organic transparent conductive films, such as polyaniline and its derivative (s), polythiophene, and its derivative (s) as an electrode material. The transparent or translucent electrode may be an anode or a cathode.

  The other electrode may not be transparent, and a metal, a conductive polymer, or the like can be used as an electrode material of the electrode. Specific examples of the electrode material include metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, aluminum, scandium, vanadium, zinc, yttrium, indium, cerium, samarium, europium, terbium, ytterbium, etc. And one or more alloys selected from the group consisting of gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, and tin. Examples include alloys with metals, graphite, graphite intercalation compounds, polyaniline and derivatives thereof, and polythiophene and derivatives thereof. Examples of the alloy include magnesium-silver alloy, magnesium-indium alloy, magnesium-aluminum alloy, indium-silver alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, and calcium-aluminum alloy.

(Buffer layer)
As a means for improving the photoelectric conversion efficiency, an additional intermediate layer (such as a charge transport layer) other than the organic active layer may be used. Examples of the material used for the intermediate layer include alkali metal or alkaline earth metal halides or oxides such as lithium fluoride, and specifically lithium fluoride.
In addition, fine particles of inorganic semiconductor such as titanium oxide, a mixture of PEDOT (poly (3,4-ethylenedioxythiophene)) and PSS (poly (4-styrenesulfonate)) (PEDOT: PSS), etc. are used for the intermediate layer. It may be used as a material.

(Organic active layer)
The organic active layer contained in the photoelectric conversion element of the present invention contains an electron donating compound and an electron accepting compound.
The electron-donating compound and the electron-accepting compound are relatively determined from the HOMO or LUMO energy levels of these compounds.

  At least one of the electron donating compound and the electron accepting compound is preferably a polymer compound, and both the electron donating compound and the electron accepting compound are more preferably polymer compounds.

(Electron donating compound)
The electron-donating compound is not limited as long as it has absorption in the radiation wavelength region of sunlight, but the energy level of its highest occupied molecular orbital is −4.7 eV or less, and its lowest A polymer compound having an empty molecular orbital energy level of −4.0 eV or more is preferred. The electron donating compound may be a low molecular compound or a high molecular compound, but a high molecular compound is preferable. Examples of the electron donating compound include pyrazoline derivatives, arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, oligothiophene and derivatives thereof, polyvinylcarbazole and derivatives thereof, polysilane and derivatives thereof, and aromatic amines in side chains or main chains. And polysiloxane derivatives, polyaniline and derivatives thereof, polythiophene and derivatives thereof, polypyrrole and derivatives thereof, polyphenylene vinylene and derivatives thereof, polythienylene vinylene and derivatives thereof, among which polymer compounds are preferred.
The polymer compound which is a p-type semiconductor is preferably a polythiophene and its derivative, a polymer compound having a structure containing a 2 to 5 mer of thiophene or a structure containing a 2 to 5 mer of a thiophene derivative, and polythiophene and its Derivatives are more preferred. Here, the polythiophene derivative is a polymer compound having a thiophenediyl group having a substituent.
Polythiophene and its derivatives are preferably homopolymers. A homopolymer is a polymer formed by bonding only a plurality of groups selected from the group consisting of a thiophenediyl group and a substituted thiophenediyl group. The thiophene diyl group is preferably a thiophene-2,5-diyl group, and the thiophene diyl group having a substituent is preferably an alkylthiophene-2, 5-diyl group. Specific examples of polythiophene that is a homopolymer and derivatives thereof include poly (3-hexylthiophene-2,5-diyl) (P3HT), poly (3-octylthiophene-2,5-diyl), and poly (3-dodecyl). Thiophene-2,5-diyl) and poly (3-octadecylthiophene-2,5-diyl). Among polythiophenes and derivatives thereof which are homopolymers, polythiophene homopolymers composed of thiophene diyl groups substituted with alkyl groups having 6 to 30 carbon atoms are preferred.

  Examples of the polymer compound that is an electron donating compound include polymer compound A represented by the following structural formula (4).

(Electron-accepting compound)
The electron accepting compound is a polymer compound having an energy level of the highest occupied molecular orbital of −5.0 eV or lower and an energy level of the lowest unoccupied molecular orbital of −4.3 eV or higher. Is preferred.
Examples of the electron-accepting compound include oxadiazole derivatives, anthraquinodimethane and derivatives thereof, benzoquinone and derivatives thereof, naphthoquinone and derivatives thereof, anthraquinones and derivatives thereof, tetracyanoanthraquinodimethane and derivatives thereof, and fluorenone derivatives. , diphenyldicyanoethylene and derivatives thereof, diphenoquinone derivatives, metal complexes of 8-hydroxyquinoline and its derivatives, polyquinoline and its derivatives, polyquinoxaline and its derivatives, polyfluorene and its derivatives, fullerene and derivatives thereof such as C _60, bathocuproine etc. Phenanthrene derivatives, metal oxides such as titanium oxide, and carbon nanotubes. The electron accepting compound is preferably a compound containing a benzothiadiazole structure, a polymer compound containing a benzothiadiazole structure in a repeating unit, a compound containing a quinoxaline structure, a polymer compound containing a quinoxaline structure in a repeating unit, titanium oxide, carbon Nanotubes, fullerenes, fullerene derivatives, more preferably fullerenes, fullerene derivatives, compounds containing a benzothiadiazole structure, polymer compounds containing a benzothiadiazole structure in a repeating unit, compounds containing a quinoxaline structure, and a quinoxaline structure in a repeating unit More preferably, it is a compound containing a benzothiadiazole structure, a polymer compound containing a benzothiadiazole structure in a repeating unit, a compound containing a quinoxaline structure, a repeating unit To a polymer compound containing a quinoxaline structure, particularly preferably a polymer compound containing a benzothiadiazole structure in the repeating unit, a polymer compound containing a quinoxaline structure repeating units.
The n-type semiconductor is preferably a conjugated polymer compound.

  Examples of the polymer compound containing a benzothiadiazole structure in the repeating unit include a polymer compound represented by the formula (4).

Examples of _{fullerene, C 60 fullerene, C 70 fullerene, C 76 fullerene, C 78} fullerene _{include C 84} fullerene.
Examples of fullerene derivatives include derivatives of C ₆₀ fullerene, C ₇₀ fullerene, C ₇₆ fullerene, C ₇₈ fullerene, and C ₈₄ fullerene.

Specific examples of the C ₆₀ fullerene derivative include the following.

Specific examples of the C ₇₀ fullerene derivative include the following.

  Examples of fullerene derivatives include [6,6] phenyl-C61 butyric acid methyl ester (C60PCBM, [6,6] -Phenyl C61 butyric acid methyl ester), [6,6] phenyl-C71 butyric acid methyl ester (C70PCBM). [6,6] -Phenyl C71 butyric acid methyl ester), [6,6] phenyl-C85 butyric acid methyl ester (C84PCBM, [6,6] -Phenyl C85 butyric acid methyl ester), [6,6] thienyl- Examples thereof include C61 butyric acid methyl ester ([6,6] -Thienyl C61 butyric acid methyl ester).

  In the organic active layer, the use ratio of the electron accepting compound to the electron donating compound is preferably 10 to 1000 parts by weight, and preferably 20 to 500 parts by weight with respect to 100 parts by weight of the electron donating compound. More preferred.

  The thickness of the organic active layer is usually preferably 1 nm to 100 μm, more preferably 2 nm to 1000 nm, still more preferably 5 nm to 500 nm, and particularly preferably 20 nm to 200 nm.

  The photoelectric conversion element of the present invention is a polymer compound in which at least one of an electron-donating compound and an electron-accepting compound includes a repeating unit represented by the formula (I), and is included in the polymer compound Among all the repeating units, a polymer compound having the largest ratio of repeating units represented by formula (I) is preferable.

In formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are the same or different and represent a hydrogen atom or a substituent. R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be connected to each other to form a cyclic structure. X ₁ , X ₂ and X ₃ are the same or different and each represents a sulfur atom, an oxygen atom, a selenium atom, —N (R ₇ ) — or —C (R ₈ ) ═C (R ₉ ) —. R _7, R ₈ and R ₉ are the same or different and each represents a hydrogen atom or a substituent. n and m are the same or different and each represents an integer of 0 to 5. When there are a plurality of R ₁ , R ₂ , R ₅ , R ₆ , X ₁ , and X ₃ , they may be the same or different.

In formula (I), n and m are the same or different and each represents an integer of 0 to 5. n and m are preferably an integer of 1 to 3, and more preferably 1.
R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are the same or different and each represents a hydrogen atom or a substituent. When R < ₁ > -R < ₆ > is a substituent, a C1-C30 group is preferable. Substituents include alkyl groups such as methyl, ethyl, butyl, hexyl, octyl and dodecyl, alkoxy such as methoxy, ethoxy, butoxy, hexyloxy, octyloxy and dodecyloxy. Groups, aryl groups such as phenyl and naphthyl, and the like.
R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be connected to each other to form a cyclic structure. Specific examples of the cyclic structure formed by linking R ₁ and R ₂ and the cyclic structure formed by linking R ₅ and R ₆ include the following cyclic structures.

Specific examples of the cyclic structure formed by linking R ₃ and R ₄ include the following cyclic structures.

In the formula, R ₁₂ and R ₁₃ are the same or different and each represents a hydrogen atom or a substituent.

Examples of the substituent represented by R ₁₂ and R ₁₃ include the same groups as the substituents represented by R _{1 to} R ₆ described above.

R _{1 to} R ₆ are preferably a hydrogen atom or an alkyl group, and more preferably a hydrogen atom.

X ₁ , X ₂ and X ₃ are the same or different and each represents a sulfur atom, an oxygen atom, a selenium atom, —N (R ₇ ) — or —C (R ₈ ) ═C (R ₉ ) —. R _7, R ₈ and R ₉ are the same or different and each represents a hydrogen atom or a substituent. When R _7, R ₈ , and R ₉ are substituents, examples of the substituent include alkyl groups such as methyl group, ethyl group, butyl group, hexyl group, octyl group, and dodecyl group, and aryl groups such as phenyl group and naphthyl group. Groups and the like.
X ₁ , X ₂ and X ₃ are preferably sulfur atoms.

  As the repeating unit represented by the formula (I), a repeating unit represented by the formula (I-1) is preferable.

The polymer compound used in the present invention is a polymer compound containing a repeating unit represented by the formula (I), and among all the repeating units contained in the polymer compound, the compound represented by the formula (I) The content (number of moles) of the repeating unit represented is the largest.
In the polymer compound used in the present invention, it is preferable that the repeating unit represented by the formula (I) exceeds 50% with respect to the total of all repeating units in the polymer compound. By using a polymer compound exceeding 50% for the photoelectric conversion element, the photoelectric conversion efficiency is higher than that of the photoelectric conversion element using the polymer compound not exceeding 50%. More preferably, the repeating unit represented by the formula (I) is 52% or more based on the total of all repeating units in the polymer compound. More preferably, the repeating unit represented by the formula (I) is 55% or more with respect to the total of all repeating units in the polymer compound.
Moreover, it is preferable that the repeating unit represented by a formula (I) is less than 100% with respect to the sum total of all the repeating units in a high molecular compound. More preferably, the repeating unit represented by the formula (I) is preferably 98% or less with respect to the total of all repeating units in the polymer compound. More preferably, the repeating unit represented by the formula (I) is 70% or less with respect to the total of all repeating units in the polymer compound. The polymer compound used in the present invention preferably contains a repeating unit other than the repeating unit represented by the formula (I).

  The polymer compound may further contain a repeating unit represented by the formula (II).

In formula (II), ring A and ring B are the same or different and each represents an aromatic ring. R ₁₀ and R ₁₁ are the same or different and each represents a hydrogen atom or a substituent. R ₁₀ and R ₁₁ may be linked to form a cyclic structure.

When R ₁₀ and R ₁₁ are substituents, examples of the substituent include methyl, ethyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, Examples thereof include alkyl groups such as tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group and eicosyl group, and aryl groups such as phenyl group and naphthyl group. R ₁₀ and R ₁₁ are preferably hydrocarbon groups such as alkyl groups and aryl groups, and more preferably alkyl groups. Moreover, when R < ₁₀ >, R < ₁₁ > is a substituent, it is preferable that carbon number is 12 or more.

  Examples of ring A and ring B include aromatic hydrocarbon rings such as benzene ring and naphthalene ring, aromatic heterocycles such as thiophene, and the like. Ring A and ring B are preferably 5- to 10-membered rings, and more preferably benzene rings or naphthalene rings.

  As the repeating unit represented by the formula (II), a repeating unit represented by the formula (II-1) is preferable.

In formula (II-1), R ₁₀ and R ₁₁ represent the same meaning as described above.

  When the polymer compound used in the present invention contains a repeating unit represented by the formula (II) in addition to the repeating unit represented by the formula (I), the compound represented by the formula (II) among all the repeating units contained in the polymer compound: It is preferable that the ratio of the repeating unit represented by the formula (I) is next to the ratio of the repeating unit represented by the formula (I). The case where the repeating unit of the polymer compound is only the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II) is more preferable.

  The method for producing the polymer compound used in the present invention is not particularly limited, but a method using a Suzuki coupling reaction is preferred from the viewpoint of ease of synthesis of the polymer compound.

(Other ingredients)
In order to express various functions, the organic active layer may contain other components as necessary. Examples thereof include an ultraviolet absorber, an antioxidant, a sensitizer for sensitizing the function of generating charges by absorbed light, and a light stabilizer for increasing stability from ultraviolet rays.

Components other than the electron-donating compound and the electron-accepting compound constituting the organic active layer are each 5 parts by weight or less, particularly 0.01 to 100 parts by weight based on the total amount of the electron-donating compound and the electron-accepting compound. It is effective to blend in the proportion of 3 parts by weight.
Further, the organic active layer may contain a polymer compound other than the electron donating compound and the electron accepting compound as a polymer binder in order to improve mechanical properties. As the polymer binder, those that do not inhibit the electron transport property or hole transport property are preferable, and those that do not strongly absorb visible light are preferably used. Examples of the polymer binder include poly (N-vinylcarbazole), polyaniline and derivatives thereof, polythiophene and derivatives thereof, poly (p-phenylene vinylene) and derivatives thereof, poly (2,5-thienylene vinylene) and derivatives thereof, Polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like can be mentioned.

The organic active layer of the photoelectric conversion element of the present invention is an image of the organic active layer observed with a transmission electron microscope, and the image of the organic active layer in which light and dark are binarized. The bonding length is 100 μm or more per 1 μm ² of the organic active layer image.

  Examples of the method for measuring the bonding length between the electron donating compound and the electron accepting compound include a method of observing the active layer using a transmission electron microscope (TEM) and determining the length. The electron-donating compound and the electron-accepting compound can be separated and observed by an image characteristic of the element contained in the electron-donating compound and the electron-accepting compound. An image characteristic of the element includes an element mapping image by an energy filter TEM, an energy loss image using an energy value that gives the same contrast as the element mapping image, and an energy dispersive X-ray analysis (STEM) using a scanning transmission electron microscope. -EDX) and the like element mapping image. By comparing the electron-donating compound phase with the electron-accepting compound phase, and performing binarization processing of the image in which the bright phase is white and the dark phase is black, the electron-donating compound and the electron-accepting compound are The joining length of can be calculated.

The bonding length between the electron donating compound and the electron accepting compound is preferably 100 μm or more and 300 μm or less, more preferably 115 μm or more and 250 μm or less, per 1 μm ² of the image of the organic active layer.

  Since the phase separation structure of the electron donating compound material and the electron accepting compound material in the organic active layer is appropriately controlled, the photoelectric conversion device of the present invention can efficiently generate photocharge separation and charge transport. And high photoelectric conversion efficiency.

  Another aspect of the photoelectric conversion device of the present invention includes an anode, a cathode, and an organic active layer provided between the anode and the cathode, and an electron donating compound and an electron accepting property in the organic active layer. 9 sections of an image of an organic active layer having a compound and having an area of 900 nm × 900 nm, in which white and black portions are formed by binarizing light and dark, and having an equal area It is a photoelectric conversion element whose standard deviation calculated from the area fraction of the black part of each section is 0.09 or less.

  When at least one of the electron-donating compound material and the electron-accepting compound material contains a sulfur atom, examples of the method for binarizing the brightness of the organic active layer include the following methods. An image showing phase separation of the electron donating compound material and the electron accepting compound material in the layer is obtained as a mapping image of sulfur atoms by a three window method of electron energy loss spectroscopy (TEM-EELS) using a transmission electron microscope. Then, a histogram of the mapping image of the obtained sulfur atom is calculated, and the phase containing the compound having a high sulfur atom (S) composition is white with the peak top of the obtained histogram as a threshold, and the polymer compound having a low S composition Binarization is performed by setting the phase including the black as black.

  The image of the obtained organic active layer in a range of 900 nm × 900 nm, in which the white portion and the black portion, in which the brightness is binarized, is divided into nine sections having an equal area. The standard deviation calculated from the area fraction of the black part is preferably 0.03 to 0.09, and more preferably 0.04 to 0.08.

  Since the phase separation structure of the electron donating compound material and the electron accepting compound material in the organic active layer is appropriately controlled, the photoelectric conversion device of the present invention can efficiently generate photocharge separation and charge transport. And high photoelectric conversion efficiency.

The material of the electrode included in the photoelectric conversion element of this embodiment, the electron donating compound, the electron accepting compound, and the other constituent material formed as necessary include the material of the electrode included in the photoelectric conversion element of the above embodiment. , Electron-donating compound, electron-accepting compound, and the same materials as those of other components formed as necessary.
In the photoelectric conversion element of this embodiment, at least one of the electron-donating compound and the electron-accepting compound is a polymer compound containing a repeating unit represented by the formula (I), and is included in the polymer compound Among all the repeating units, a polymer compound having the largest ratio of repeating units represented by formula (I) is preferable.

  Another aspect of the photoelectric conversion device of the present invention includes an anode, a cathode, and an organic active layer provided between the anode and the cathode, and an electron donating compound and an electron accepting property in the organic active layer. And a lifetime of an excited state of at least one of an electron donating compound in the organic active layer and an electron accepting compound in the organic active layer is 1 ns or less.

Here, the excited state means an excited singlet or an excited triplet generated as a result of absorbing light, and the excited state lifetime means the number of excited states or the initial number of excited states generated. Or it means the time to decrease to 1 / e of the concentration.
Here, the lifetime of the excited singlet or triplet of the compound is evaluated from the time when the initial absorption intensity of the excited state decreases to 1 / e by pump probe transient absorption spectroscopy using a femtosecond laser as the excitation light source. be able to. E means the base of natural logarithm.
A method for measuring transient absorption will be described using an organic thin film solar cell as an example. A bulk hetero type organic active layer composed of an electron donating compound and an electron accepting compound is produced on a glass substrate by the same operation as the production of the organic thin film solar cell. Here, the absorbance of the active layer measured when not photoexcited is A0. A0 is defined as A0 = log (Ip / I0), where Ip is the intensity of the probe light incident on the active layer, and I0 is the intensity of the probe light transmitted through the active layer. Further, the absorbance of the active layer measured after the active layer is photoexcited with pump light and the time t has elapsed is defined as A (t). A (t) is A (t) = log (Ip, where I is the intensity of the probe light that has passed through the active layer out of the probe light that has entered the active layer after time t has elapsed after photoexcitation with pump light. / I). Here, the absorption intensity (ΔA) of a chemical species newly generated (increased) or extinguished (decreased) in the active layer by photoexcitation is defined as ΔA = A (t) −A0. That is, it is defined by ΔA = log (Ip / I) −log (Ip / I0) = log (I0 / I). Here, by measuring the value of ΔA at different delay times t, it is possible to evaluate the temporal change in absorption intensity at the wavelength of the probe light used. Furthermore, by changing the wavelength of the probe light to be used, an absorption spectrum of a chemical species newly generated (increased) or extinguished (decreased) in the active layer can be obtained at a certain delay time t as compared to before photoexcitation. Furthermore, a time resolution of 100 fs can be achieved by using pulsed light with a femtosecond laser as a light source for both the probe light and the pump light.

  The lifetime of the excited state is preferably 1 ns or less, more preferably 100 ps or less, and even more preferably 10 ps or less.

  When the lifetime of the excited state of at least one of the electron donating compound in the organic active layer and the electron accepting compound in the organic active layer is 1 ns or less, the charge separation efficiency is high in the organic active layer, and photoelectric conversion The photoelectric conversion efficiency of the device is increased.

The material of the electrode included in the photoelectric conversion element of this embodiment, the electron donating compound, the electron accepting compound, and the other constituent material formed as necessary include the material of the electrode included in the photoelectric conversion element of the above embodiment. , Electron-donating compound, electron-accepting compound, and the same materials as those of other components formed as necessary.
In the photoelectric conversion element of this embodiment, at least one of the electron-donating compound and the electron-accepting compound is a polymer compound containing a repeating unit represented by the formula (I), and is included in the polymer compound Among all the repeating units, a polymer compound having the largest ratio of repeating units represented by formula (I) is preferable.

  Another aspect of the photoelectric conversion device of the present invention includes an anode, a cathode, and an organic active layer provided between the anode and the cathode, and an electron donating compound and an electron accepting property in the organic active layer. The photoelectric conversion element has a compound and a fluorescence quenching rate of at least one of an electron donating compound in the organic active layer and an electron accepting compound in the organic active layer is 60% or more.

A method for measuring the fluorescence quenching rate will be described by taking an organic thin-film solar cell having a bulk hetero type organic active layer composed of an electron donating compound and an electron accepting compound as an example. A bulk hetero type organic active layer is produced on a glass substrate by the same operation as the production of the organic thin film solar cell. Using a spectrofluorometer, at least one of the electron donating compound and the electron accepting compound forming the active layer is photoexcited, and the observed fluorescence intensity from the electron donating compound or the electron accepting compound is defined as Φ1. The absorbance of the electron donating compound or electron accepting compound at this photoexcitation wavelength is A1. An electron-donating property when an active layer made of only an electron-donating compound or an electron-accepting compound is produced on a glass substrate by the same operation and photoexcited under the same conditions as in the case of a bulk hetero-type organic active layer except that the active layer is different. The fluorescence intensity from the compound or electron accepting compound is Φ2, and the absorbance of the electron donating compound or electron accepting compound at the photoexcitation wavelength is A2. Here, the fluorescence quenching rate of the electron-donating compound or electron-accepting compound in the bulk-type organic active layer (.PHI.q) is, Φq = (1-Φ1 / (1-10 -A1) / Φ2 / (1-10 - ^A2 )) x 100.
The fluorescence quenching rate (Φq) of the active layer of the photoelectric conversion element of the present invention is preferably 60% or more, and more preferably 70% or more. Since Φq is 60% or more, the charge separation efficiency is high in the organic active layer, and the photoelectric conversion efficiency of the photoelectric conversion element is high.

The material of the electrode included in the photoelectric conversion element of this embodiment, the electron donating compound, the electron accepting compound, and the other constituent material formed as necessary include the material of the electrode included in the photoelectric conversion element of the above embodiment. , Electron-donating compound, electron-accepting compound, and the same materials as those of other components formed as necessary.
In the photoelectric conversion element of this embodiment, at least one of the electron-donating compound and the electron-accepting compound is a polymer compound containing a repeating unit represented by the formula (I), and is included in the polymer compound Among all the repeating units, a polymer compound having the largest ratio of repeating units represented by formula (I) is preferable.

(Method for producing organic active layer)
The organic active layer included in the photoelectric conversion element of the present invention is a bulk hetero type, and is formed by film formation from a solution containing the electron-donating compound, the electron-accepting compound, and other components blended as necessary. Can be formed. For example, the solution can be applied on the anode or cathode to form an organic active layer. Then, another electrode can be formed on an organic active layer, and a photoelectric conversion element can be manufactured.

The solvent used for film formation from a solution is not particularly limited as long as it dissolves the above-described electron-donating compound and electron-accepting compound of the present invention, and a plurality of solvents may be mixed. The boiling point of one kind of solvent is 200 ° C. or less, preferably 150 ° C., more preferably 100 ° C. or less. Examples of such solvents include unsaturated hydrocarbon solvents such as toluene, xylene, mesitylene, tetralin, decalin, bicyclohexyl, n-butylbenzene, sec-butylbenzene, tert-butylbenzene, carbon tetrachloride, chloroform, dichloromethane. Halogenated saturated hydrocarbon solvents such as chloroethane, dichlorobenzene, and trichlorobenzene Examples thereof include hydrocarbon solvents, ether solvents such as tetrahydrofuran and tetrahydropyran. The organic material constituting the organic active layer can usually be dissolved in the solvent in an amount of 0.1% by weight or more.
From the viewpoint of increasing the photoelectric conversion efficiency of the photoelectric conversion element by controlling the junction length between the electron donating compound and the electron accepting compound, preferred solvents include carbon tetrachloride, chloroform, dichloromethane, dichloroethane, dichloropropane, chlorobutane, and the like. And a halogenated saturated hydrocarbon solvent having a boiling point of 100 ° C. or lower, and an ether solvent having a boiling point of 100 ° C. or lower, such as tetrahydrofuran or tetrahydropyran.
A more preferred solvent is chloroform.

  For film formation, spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dip coating method, spray coating method, screen printing method, gravure printing, flexographic printing Application methods such as printing method, offset printing method, inkjet printing method, dispenser printing method, nozzle coating method, capillary coating method can be used, spin coating method, flexographic printing method, gravure printing method, inkjet printing method, dispenser printing The method is preferred.

  A preferred embodiment of the method for producing a photoelectric conversion element is a step of producing an organic active layer by applying a solution containing an electron donating compound, an electron accepting compound, and a solvent having a boiling point of 100 ° C. or less on an anode or a cathode. Wherein at least one of the electron-donating compound and the electron-accepting compound is a polymer compound containing a repeating unit represented by the formula (I), and is contained in all repeating units contained in the polymer compound This is a method for producing a photoelectric conversion element which is a polymer compound having the largest ratio of repeating units represented by formula (I).

In formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are the same or different and represent a hydrogen atom or a substituent. R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be connected to each other to form a cyclic structure. X ₁ , X ₂ and X ₃ are the same or different and each represents a sulfur atom, an oxygen atom, a selenium atom, —N (R ₇ ) — or —C (R ₈ ) ═C (R ₉ ) —. R _7, R ₈ and R ₉ are the same or different and each represents a hydrogen atom or a substituent. n and m are the same or different and each represents an integer of 0 to 5. When there are a plurality of R ₁ , R ₂ , R ₅ , R ₆ , X ₁ , and X ₃ , they may be the same or different.

(Application of the device)
The photoelectric conversion element of the present invention can be operated as an organic thin film solar cell by irradiating light such as sunlight from a transparent or translucent electrode to generate a photovoltaic force between the electrodes. It can also be used as an organic thin film solar cell module by integrating a plurality of organic thin film solar cells.

  In addition, when light is incident from a transparent or translucent electrode in a state where a voltage is applied between electrodes or in a state where no voltage is applied, a photocurrent flows and the organic light sensor can be operated. It can also be used as an organic image sensor by integrating a plurality of organic photosensors.

(Solar cell module)
The organic thin film solar cell can basically have the same module structure as a conventional solar cell module. The solar cell module generally has a structure in which cells are formed on a support substrate such as metal or ceramic, and the cell is covered with a filling resin or protective glass, and light is taken in from the opposite side of the support substrate. It is also possible to use a transparent material such as tempered glass for the support substrate, configure a cell thereon, and take in light from the transparent support substrate side. Specifically, a module structure called a super straight type, a substrate type, and a potting type, a substrate integrated module structure used in an amorphous silicon solar cell, and the like are known. Even in an organic thin film solar cell to which the organic photoelectric conversion element of the present invention is applied, these module structures can be appropriately selected depending on the purpose of use, the place of use and the environment.

  In a typical super straight type or substrate type module, cells are arranged at regular intervals between support substrates that are transparent on one or both sides and subjected to antireflection treatment, and adjacent cells are connected by metal leads or flexible wiring. It is connected, and the collector electrode is arrange | positioned in the outer edge part, It has the structure which takes out generated electric power outside. Various types of plastic materials such as ethylene vinyl acetate (EVA) may be used between the substrate and the cell in the form of a film or a filling resin depending on the purpose in order to protect the cell and improve the current collection efficiency. In addition, when used in a place where it is not necessary to cover the surface with a hard material such as a place where there is little impact from the outside, the surface protection layer is made of a transparent plastic film, or the protective function is achieved by curing the filling resin. It is possible to eliminate the supporting substrate on one side. The periphery of the support substrate is fixed in a sandwich shape with a metal frame in order to ensure internal sealing and module rigidity, and the support substrate and the frame are hermetically sealed with a sealing material. In addition, if a flexible material is used for the cell itself, the support substrate, the filling material, and the sealing material, a solar cell can be formed on the curved surface.

  In the case of a solar cell using a flexible support such as a polymer film, cells are sequentially formed while feeding out a roll-shaped support, cut to a desired size, and then the periphery is sealed with a flexible and moisture-proof material. Thus, the battery body can be produced. Also, a module structure called “SCAF” described in Solar Energy Materials and Solar Cells, 48, p383-391 may be used. Furthermore, a solar cell using a flexible support can be used by being bonded and fixed to a curved glass or the like.

  Examples of the present invention will be described below. The following examples are preferred examples for explaining the present invention, and do not limit the present invention.

Synthesis example 1
(Production of polymer compound A)

  A reaction vessel was charged with 0.945 g (1.60 mmol) of monomer (1), 0.918 g of monomer (2) (2.00 mmol) and 25 mg of tetrakis (triphenylphosphine) palladium (0), and the reaction was performed. The inside of the container was sufficiently replaced with argon gas. To this reaction vessel, 50 g of toluene deaerated previously by bubbling with argon gas was added. The resulting solution was stirred at 100 ° C. for about 10 minutes. Next, 5 ml of a tetraethylammonium hydroxide solution (20% aqueous solution) previously deaerated by bubbling with argon gas was added dropwise to the obtained solution, and then refluxed for 3.5 hours. Next, after adding 0.55 g of phenylboric acid to the obtained reaction solution, it was refluxed for 8.5 hours. The reaction was performed in an argon gas atmosphere.

After completion of the reaction, the reaction solution was cooled at room temperature (25 ° C.), and then the obtained reaction solution was allowed to stand and a separated toluene layer was recovered. Next, the obtained toluene layer was poured into methanol and re-precipitated, and the generated precipitate was collected. This precipitate was dried under reduced pressure and then dissolved in chloroform. Next, the obtained chloroform solution was filtered to remove insoluble matters, and then passed through an alumina column for purification. Next, the obtained chloroform solution was concentrated under reduced pressure, poured into methanol, re-precipitated, and the generated precipitate was collected. This precipitate was washed with methanol and then dried under reduced pressure to obtain 0.93 g of a polymer. Hereinafter, this polymer is referred to as polymer compound A. The polymer compound A had a polystyrene equivalent weight average molecular weight of 2.0 × 10 ⁴ and a polystyrene equivalent number average molecular weight of 4.7 × 10 ³ .
The ratio of the repeating unit represented by the formula (2 ′) calculated from the charging ratio among all the repeating units of the polymer compound A was 55.6%.

Example 1
(Production and evaluation of organic thin-film solar cells)
A glass substrate with an ITO film having a thickness of 300 nm formed by vacuum deposition was subjected to ultrasonic cleaning in this order for 15 minutes in toluene, acetone and ethanol, respectively, and then surface treatment was performed by ozone UV treatment. A mixture of PEDOT (poly (3,4-ethylenedioxythiophene)) and PSS (poly (4-styrenesulfonate)) (PEDOT: PSS) (manufactured by HCStarck, PH500) on a surface-treated ITO substrate Was spin-coated to a thickness of about 40 nm, and heated in the air on a hot plate at 140 ° C. for 10 minutes. Next, a chloroform solution containing a high molecular compound A which is an electron-accepting compound and poly (3-hexylthiophene-2,5-diyl) (P3HT) (Resiregular, manufactured by Aldrich Co.) which is an electron-donating compound (high A weight ratio of molecular compound A / P3HT = 1/1, and the total concentration of polymer compound A and P3HT was 1% by weight) was applied onto this PEDOT: PSS film by spin coating to produce an organic active layer. The thickness of the organic active layer was about 70 nm. Thereafter, lithium fluoride was vapor-deposited with a thickness of 1 nm by a vacuum vapor deposition machine, and then Al was vapor-deposited with a thickness of 80 nm. Thereafter, the organic thin film solar cell was heated at 140 ° C. for 10 minutes in the glove box. The shape of the obtained organic thin film solar cell was a circle having a radius of 1.5 mm. The organic thin-film solar cell obtained was irradiated with a certain amount of light using a solar simulator (Eagle Engineering, 500W xenon light source device LHX-500E3: AM1.5G filter, irradiance 100 mW / cm ² ) The voltage was measured to determine photoelectric conversion efficiency, short circuit current density, open circuit voltage, and fill factor. Jsc (short circuit current density) was 3.94 mA / cm ² , Voc (open circuit voltage) was 1.19 V, ff (fill factor) was 0.42, and photoelectric conversion efficiency (η) was 1.95%.

(Measurement of HOMO energy level and LUMO energy level)
The energy level of HOMO was measured with a photoelectron spectrometer AC-2 (manufactured by Riken Keiki Co., Ltd.). The LUMO energy level was calculated from the end of the absorption wavelength (λth (nm)) using the following equation.
(LUMO energy level) = (HOMO energy level) + 1240 / λth
The HOMO energy level of the polymer compound A was −5.5 ev, and the LUMO energy level was −3.6 eV. The energy level of HOMO of P3HT was -4.9 eV, and the energy level of LUMO was -3.0 eV.

(Measurement of fluorescence quenching rate)
The blend film produced on the glass substrate by the same operation as the production of the organic thin film solar cell was excited at 392 nm, and the fluorescence quenching rate (Φq) of the polymer compound A was estimated. As a result, Φq was 71%.

(Observation of phase separation structure)
After forming the organic active layer on the substrate by the method of Example 1, observation of phase separation between the phase containing the electron-donating compound and the phase containing the electron-accepting compound was conducted using a transmission electron microscope (TEM). This was performed by obtaining a mapping image of sulfur atoms by a three-window method of spectroscopy (TEM-EELS). A sample for TEM observation was obtained by floating a film prepared by spin casting on water and scoring with a TEM grid. For TEM, JEM2200FS (manufactured by JEOL Ltd.) was used at an acceleration voltage of 200 kV, and a layer in the range of 900 nm × 900 nm at 20000 times was observed with 512 × 512 pixels. A histogram of the mapping image of the obtained sulfur atom is calculated, and the phase containing the polymer compound having a high sulfur atom (S) composition is white with the peak top of the obtained histogram as a threshold, and the polymer compound having a low S composition Binarization was performed by setting the phase containing the black as black. The binarized image obtained as described above was divided into nine sections having an equal area, and the area fraction of the black portion of each section was determined. The above image analysis was performed using image analysis software image-J. The average value and standard deviation of the area fractions of the nine black sections obtained were calculated. As a result, the average value of the area fraction of the black portion was 0.454, and the standard deviation of the area fraction of the black portion was 0.074.

Comparative Example 1
(Production and evaluation of organic thin-film solar cells)
An organic thin film solar cell was prepared and evaluated in the same manner as in Example 1 except that chlorobenzene was used instead of chloroform. As a result, Jsc was 0.91 mA / cm ² , Voc was 1.06 V, ff was 0.48, and the photoelectric conversion efficiency (η) was 0.46%.
Under this condition, the fluorescence quenching rate (Φq) of the polymer compound A was estimated. As a result, Φq was 50%.
Moreover, the average value of the area fraction of the black part observed by TEM was 0.581, and the standard deviation of the area fraction of the black part was 0.171.

Comparative Example 2
(Production and evaluation of organic thin-film solar cells)
An organic thin film solar cell was prepared and evaluated in the same manner as in Example 1 except that o-dichlorobenzene was used instead of chloroform. As a result, Jsc was 0.84 mA / cm ² , Voc was 0.80 V, ff was 0.36, and the photoelectric conversion efficiency (η) was 0.24%.
Moreover, the average value of the area fraction of the black part observed by TEM was 0.535, and the standard deviation of the area fraction of the black part was 0.221.

Comparative Example 3
(Production and evaluation of organic thin-film solar cells)
An organic thin film solar cell was prepared and evaluated in the same manner as in Example 1 except that xylene was used instead of chloroform. As a result, Jsc was 1.37 mA / cm ² , Voc was 0.91 V, ff was 0.54, and the photoelectric conversion efficiency (η) was 0.67%.
Moreover, the average value of the area fraction of the black part observed by TEM was 0.476, and the standard deviation of the area fraction of the black part was 0.099.

Claims (7)

Comprising an anode, a cathode, and an organic active layer provided between the anode and the cathode, the organic active layer is an electron-donating compound and an electron-accepting compound and a boiling point between 100 ° C. or less of the solvent In the image of the organic active layer produced by coating from a solution and observed with a transmission electron microscope and binarized, the electron donating compound and the electron accepting compound A photoelectric conversion element having a junction length of 100 μm or more per 1 μm ² of the image of the organic active layer ,
The electron donating compound is a polymer compound having an energy level of the highest occupied molecular orbital of −4.7 eV or lower and an energy level of the lowest unoccupied molecular orbital of −4.0 eV or higher. Polythiophene or a derivative thereof, wherein the electron-accepting compound is a polymer compound having a benzothiadiazole structure or a quinoxaline structure, and the energy level of the highest occupied molecular orbital is −5.0 eV or less, and The photoelectric conversion element which is a polymer compound whose energy level of the lowest unoccupied molecular orbital is −4.3 eV or more . ^{2. The} photoelectric conversion element according to claim 1, wherein the junction length between the electron donating compound and the electron accepting compound is 300 μm or less per 1 μm ² of the image of the organic active layer.   3. The photoelectric conversion device according to claim 1, wherein the lifetime of at least one of the electron donating compound in the organic active layer and the electron accepting compound in the organic active layer is 1 ns or less. . Repeat previous SL electron-accepting compound, a polymer compound containing a repeating unit represented by formula (I), based on all repeating units contained in the polymer compound, represented by formula (I) the proportion of units having the greatest polymer compound, photoelectric conversion device according to any one of claims 1-3.

(In the formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are the same or different and represent a hydrogen atom or a substituent. Also, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be connected to each other to form a cyclic structure, and X ₁ , X ₂ and X ₃ are the same or different and are a sulfur atom, an oxygen atom, a selenium atom, —N (R ₇ ) — or —C (R ₈ ) ═C (R ₉ ) — R _7, R ₈ and R ₉ are the same or different and represent a hydrogen atom or a substituent, and n and m are The same or different and represents an integer of 0 to _{5. When} there are a plurality of R ₁ , R ₂ , R ₅ , R ₆ , X ₁ and X ₃ , they may be the same or different. ) On the anode or cathode, comprising the step of electron-donating compound and an electron-accepting compound and a boiling point to produce the organic active layer solution was applied including a 100 ° C. or less of the solvent, any one of claims 1-4 1 The manufacturing method which manufactures the photoelectric conversion element as described in a term . The solar cell module containing the photoelectric conversion element of any one of Claims 1-4 . The image sensor containing the photoelectric conversion element of any one of Claims 1-4 .