JP2016171317A - Organic photoelectric conversion device and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic photoelectric conversion device and a solar battery that can improve and stabilize the photoelectric conversion characteristic and has excellent performance and durability.SOLUTION: An organic photoelectric conversion device comprises a pair of electrodes, an organic photoelectric conversion layer disposed between the pair of electrodes, and a buffer layer provided between at least one of the pair of electrodes and the organic photoelectric conversion layer. The organic photoelectric conversion layer is formed by using an electron-donating material and an electron-accepting material of conjugated polymers which have both of an electron-donating molecular structure and an electron-accepting molecular structure in molecules. The buffer layer is formed of metal oxide, and has a deteriorated portion formed by a heat treatment.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an organic photoelectric conversion device and a solar cell using the same.

  The photoelectric conversion device is used for a solar cell, for example. In recent years, in order to promote effective use of solar energy as alternative energy such as petroleum energy, development of solar cells that convert light energy into electric energy has been widely performed.

Among them, organic solar cells are attracting attention because they have advantages such as low manufacturing cost, flexibility and weight reduction, and wide selection of materials compared to silicon-based inorganic solar cells. . As a specific example of such an organic solar cell, Non-Patent Document 1 describes poly (3-hexylthiophene) (P3HT) as a conjugated polymer that is an electron-donating material and [6 as a fullerene derivative that is an electron-accepting material. , 6] -Phenyl C ₆₁ butyric acid methyl ester (PCBM) mixed, and a buffer layer of polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) between the photoelectric conversion layer and the transparent electrode An organic thin film solar cell is described.

Wanli Ma, Cuiying Yang, Xiong Gong, Kwaghee Lee, Alan J. Heeger, Adv. Funct. Mater. 15, 1617-1622 (2005)

  However, current organic thin-film solar cells have not been widely spread because of insufficient photoelectric conversion characteristics and durability.

  The present invention provides an organic photoelectric conversion device and a solar cell, which are improved and stabilized in photoelectric conversion characteristics and excellent in performance and durability.

  The organic photoelectric conversion device according to the present invention is provided between a pair of electrodes, an organic photoelectric conversion layer disposed between the pair of electrodes, and at least one of the pair of electrodes and the organic photoelectric conversion layer. A buffer layer, and the organic photoelectric conversion layer includes an electron-donating material and an electron-accepting material of a conjugated polymer including both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule, The buffer layer is formed of a metal oxide and has an altered portion formed by heat treatment. Moreover, this invention is widely applicable also to the solar cell provided with such an organic photoelectric conversion device.

  According to the present invention, the photoelectric conversion characteristics can be improved and stabilized, and an organic photoelectric conversion device and a solar cell excellent in performance and durability can be realized.

1 is a schematic cross-sectional view of an organic photoelectric conversion device according to Embodiment 1 of the present invention. The schematic sectional drawing of the organic photoelectric conversion device which concerns on Embodiment 2 of this invention. The figure showing the relationship between Mo5 + / Mo6 + of the molybdenum oxide layer as a buffer layer of this invention and a comparative example, and the incident angle of a measurement X-ray. The figure showing the relationship between the x value of MoOx of the molybdenum oxide layer as a buffer layer of this invention and a comparative example, and the incident angle of a measurement X-ray.

  Hereinafter, the present invention will be described in detail based on embodiments. The embodiment of the present invention described below is an example for explaining various concepts such as a superordinate concept, a middle concept, and a subordinate concept of the present invention. Therefore, the technical scope of the present invention is not limited to the following embodiments.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a photoelectric conversion element which is an example of an organic photoelectric conversion device according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the organic photoelectric conversion device (element) 10 of the present embodiment includes a pair of electrodes 1 and 2, an organic photoelectric conversion layer 3 provided between the pair of electrodes 1 and 2, and the above-described configuration. Between at least one of the electrodes 1 and 2 and the organic photoelectric conversion layer 3, a buffer layer (intermediate layer) 4 provided with a modified portion 4a by heat treatment is provided.

<Photoelectric conversion layer>
The organic photoelectric conversion layer 3 is a layer that generates charges by incident light, and is an electron donating material composed of a conjugated polymer containing both an electron donating molecular structure and an electron accepting molecular structure in the molecule, preferably benzo It is formed from a conjugated polymer electron-donating material having a thiadiazole skeleton and an electron-accepting material, and may have a single layer structure or a multilayer structure. For example, the organic photoelectric conversion layer 3 of the present embodiment has a single-layer structure including a mixture of a conjugated polymer electron-donating material having a benzothiadiazole skeleton and an electron-accepting material.

  In the present invention, the electron-donating material of a conjugated polymer containing both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule is a donor organic compound, and is mainly represented by a hole-transporting organic compound. An organic compound that has the property of easily donating electrons. More specifically, it refers to an organic compound (electron-donating organic material) having a smaller ionization potential when two organic materials are used in contact with each other. Therefore, any organic compound can be used as the donor organic compound as long as it is an organic compound having an electron donating property composed of a conjugated polymer containing both an electron donating molecular structure and an electron accepting molecular structure in the molecule. is there. The donor organic compound preferably has a benzothiadiazole skeleton.

  As a suitable example of an electron-donating material of a conjugated polymer containing both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule, PCPDTBT (poly [2,6- (4,4-bis- (2 -Ethylhexyl) -4H-cyclopenta [2,1-b; 3,4-b ']-dithiophene) -alt-4,7- (2,1,3-benzothiadiazole)]), PCDTBT (poly [N- 9'-heptadecanyl-2,7-carbazole-alt- 5,5- (4 ', 7'-di- 2-thienyl-2', 1 ', 3'-benzothiadiazole)], poly [[9- ( 1-octylnonyl) -9H-carbazole-2,7-diyl] -2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]), PBDTTT- EF (PTB7 / poly [[4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5-b '] dithiophene-2,6-diyl] [3-fluoro-2- [(2-Ethylhexyl) carboni Ru] thieno [3,4-b] thiophenediyl]]), PBDTTT-EFT (PCE10 / PTB7-Th / poly [4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1 , 2-b; 4,5-b '] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenediyl]), PFFBT4T- 2OD (PCE11 / poly [(5,6-difluoro-2,1,3-benzothiadiazole-4,7-diyl) -ortho- (3,3 '' '-di (2-octyldodecyl) -2,2 '; 5', 2 ''; 5 '', 2 '' '-Quaterthiophene-5,5' ''-diyl)], in particular, electron donating properties of conjugated polymers with a benzothiadiazole skeleton As a suitable example of the material, PCPDTBT (poly [2,6- (4,4-bis- (2-ethylhexyl) -4H-cyclopenta [2,1-b; 3,4-b ′]-dithiophene) -alt -4,7- (2,1,3-benzothiadiazole)]), PCDTBT [N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4 ', 7'-di- 2-thienyl-2', 1 ', 3'-benzothiadiazole)], poly [[ 9- (1-Octylnonyl) -9H-carbazole-2,7-diyl] -2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]) Is mentioned.

  These materials have an electron-donating molecular structure such as benzodithiophene, cyclopentadithiophene, and carbazole, and an electron-accepting group such as thienothiophene and benzothiadiazole in the same molecule. Therefore, long wavelength light absorption based on charge transfer absorption in the molecule is possible. That is, by using these materials for the photoelectric conversion layer, the organic photoelectric conversion device of the present invention has high photoelectric conversion efficiency.

The electron-donating organic material of the present invention may be composed only of a conjugated polymer containing both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule, or may contain other compounds. The content of the conjugated polymer containing both the electron-donating molecular structure and the electron-accepting molecular structure in the electron-donating organic material is preferably in the range of 1 to 100% by weight. More preferably, it is in the range of ˜100 wt%. Examples of other compounds include polythiophene polymers, poly-p-phenylene vinylene polymers, poly-p-phenylene polymers, polyfluorene polymers, polypyrrole polymers, polyaniline polymers, polyacetylene polymers. Conjugated polymers such as polymers, polythienylene vinylene polymers, phthalocyanine derivatives such as H ₂ phthalocyanine (H ₂ Pc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), porphyrin derivatives, N, N′— Diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine (TPD), N, N′-dinaphthyl-N, N′-diphenyl-4,4 ′ -Triarylamine derivatives such as diphenyl-1,1'-diamine (NPD), 4,4'-di (carbazol-9-yl) bif Carbazole derivatives such as sulfonyl (CBP), oligothiophene derivatives (terthiophene, quarter thiophene, sexithiophene, octyl thiophene, etc.) the low molecular organic compound, and the like, not limited.

  On the other hand, the electron acceptor organic material used for the organic photoelectric conversion device 10 according to the above-described embodiment is an acceptor organic material, mainly represented by an electron transport organic compound, and has a property of easily accepting electrons. An organic compound. More specifically, it refers to an organic compound (electron-accepting organic material) having a higher electron affinity when two organic compounds are used in contact with each other. Therefore, as the acceptor organic compound, any organic compound can be used as long as it is an electron-accepting organic compound.

  Examples of the electron-accepting organic material include fullerene and derivatives thereof (PCBM and the like), carbon nanotube and derivatives thereof, perylene and derivatives thereof (PTCDA and PTCDI and the like), naphthalene derivatives (NTCDA and NTCDI and the like), pyridine and derivatives thereof, and the like. Oligomers and polymers having a skeleton, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and their derivatives, tris (8-hydroxyquinolinato) aluminum complexes, bis (4-methyl-8-quinolinato) aluminum complexes, distyryl Examples include arylene derivatives and silole compounds, and fullerene derivatives (PCBM and the like) are preferably used, but not limited thereto.

  The above-described materials are examples, and conjugated polymer electron-donating organic materials and electron-accepting organic materials composed of conjugated polymers containing both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule. As the material, a precursor of the corresponding material may be used, and the precursor may be converted into the corresponding material by post-processing after film formation.

  Moreover, as thickness of the photoelectric converting layer 3, although it does not specifically limit, For example, 10-1000 nm is preferable and 50-500 nm is especially preferable.

<Buffer layer>
The buffer layer 4 is made of a metal oxide and plays a role of improving various characteristics of the photoelectric conversion device 10 directly or indirectly. For example, charge injection from the photoelectric conversion layer 3 to the electrode 1 or 2 Lowering of barrier, prevention of exciton diffusion from photoelectric conversion layer 3 to electrode 1 or 2, charge rectifying action, reaction of electrode 1 or 2 with electron donating organic material or electron accepting organic material of photoelectric conversion layer 3 One of the effects is prevention and prevention of short circuit between electrodes.

  Suitable examples of the metal oxide forming the buffer layer 4 include molybdenum oxide, vanadium oxide, titanium oxide, and zinc oxide. In the case where the electrode in contact with the buffer layer functions as a positive electrode, it is particularly preferable to use a substance having a hole transporting property such as molybdenum oxide or vanadium oxide. On the other hand, when the electrode in contact with the buffer layer functions as a negative electrode, it is particularly preferable to use a substance having an electron transporting property such as titanium oxide or zinc oxide, or lithium fluoride or calcium.

  The thickness of the buffer layer 4 is not particularly limited, but is preferably 5 to 100 nm.

  Moreover, the buffer layer 4 in the present invention includes an altered portion 4a formed by heat treatment. The altered portion 4 a is a portion provided for the purpose of preventing a decrease in photoelectric conversion efficiency of the photoelectric conversion device 10, and even if distributed throughout the buffer layer 4, it is distributed locally in the buffer layer 4. However, depending on the function, it may be preferable to distribute on the surface of the buffer layer, particularly on the surface of the photoelectric conversion layer. Specific examples thereof include a surface (surface layer) obtained by heat-treating molybdenum oxide in the case of a buffer layer using molybdenum oxide. When heat treatment is performed on molybdenum oxide, the surface thereof becomes substantially rough, and the interface area between the surface and the photoelectric conversion layer is increased. In addition, oxidation of the surface proceeds (the ratio of Mo5 + decreases and the ratio of Mo6 + increases, or the value of x of MoOx increases), and there are few lattice defects (oxygen defects) that can be trapped charge carriers in the device. Become. Due to these effects and the like, the charge transfer between the photoelectric conversion layer and the buffer layer can be performed more smoothly, and a decrease in the photoelectric conversion efficiency of the photoelectric conversion device 10 can be prevented.

  Here, when polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) is used as the positive electrode side buffer layer, PEDOT / PSS is durable due to the influence of oxygen and moisture in the atmosphere due to its hygroscopicity and acidity. It was found that it caused a decrease in sex. Under such circumstances, the photoelectric conversion element 10 of the present embodiment uses a metal oxide such as molybdenum oxide having low reactivity for the buffer layer 4 and has an altered portion 4a due to heat treatment. Various characteristics such as photoelectric conversion efficiency can be improved without reducing the durability of the conversion device.

<Electrode>
The material forming the pair of electrodes 1 and 2 is not particularly limited, but the type of constituent material of the adjacent or adjacent layer (the organic photoelectric conversion layer 3 or the buffer layer 4 in this embodiment) and light are irradiated. It is preferable to select appropriately depending on the combination of direction and work function.

For example, when the material forming the electrode 1 is a material having a low work function, the material forming the electrode 2 is preferably a material having a high work function. Examples of the material having a low work function include Li, In, Al, Ca, Mg, Sm, Tb, Yb, Zr, and LiF. Examples of the material having a high work function include Au, Ag, Co, Ni, Pt, C, ITO, SnO ₂ , fluorine-doped SnO ₂ , and ZnO.

  Here, the electrode 1 or 2 on the light irradiation side, that is, the incident light side is preferably formed of an optimal material in order to improve photoelectric conversion efficiency. In particular, the organic photoelectric conversion layer 3 is preferably made of a material that transmits incident light that reacts in charge generation, and the electrode on the incident light side is preferably formed.

  In addition, the electrode on the incident light side has a wavelength other than the wavelength of incident light in which the organic layer portion of the photoelectric conversion layer 3 directly reacts in charge generation (the organic layer portion is inherently capable of photoelectric conversion). You may form with the material which is easy to permeate | transmit light. When light is irradiated perpendicularly to the electrode plane, the electrode on the light irradiation side is formed of a transparent material.

Examples of such transparent materials include In—Sn—O (ITO), In—Zn—O (IZO), zinc oxide (ZnO), tin oxide (SnO ₂ ), tin oxide doped with fluorine, and PEDOT: Examples thereof include a transparent conductive polymer such as PSS.

  In addition to the materials described above, for example, a carbon-based transparent electrode material is preferable, and more preferably, a material that forms a lattice-shaped thin film in which a plurality of carbon atoms are formed in a planar shape is used. Is good. Specifically, graphene, which is a material in which carbon atoms are hexagonal and spread in a plane, is preferably used as the electrode material on the incident light side. For example, graphene is easy to flow electrons and has properties as a high-strength material. Therefore, if it is used as an electrode material on the incident light side as a photoelectric conversion device, it is extremely advantageous in improving photoelectric conversion efficiency while withstanding a large current. It is.

  When the electrodes 1 and 2 are graphene thin films, the photoelectric conversion layer 3 on the lower side is preferably formed of a material sensitive to infrared rays, but the layer structure of the photoelectric conversion layer 3 is particularly limited. Is not to be done. When the n-type of the graphene electrode is relatively strong (when the charge transport property is strong), it is preferable to increase the abundance ratio of the n-type organic semiconductor on the graphene electrode side, but when the p-type of the graphene electrode is relatively strong It is preferable to increase the abundance ratio of the p-type organic semiconductor on the graphene electrode side. In any case, the structure (gradient / direction of pn bond ratio) of the organic photoelectric conversion layer 3 is preferably selected as appropriate according to the work function relationship of the graphene electrode, the electron / hole mobility relationship, or the like.

<Example of manufacturing method>
Hereinafter, an example of the manufacturing method of the photoelectric conversion element 10 of this embodiment is demonstrated. First, the buffer layer 4 is formed on the electrode 2. Here, before the buffer layer 4 is formed, the surface of the buffer layer 4 (the surface of the electrode 2 in the present embodiment) is subjected to a surface treatment such as plasma treatment for the purpose of improving surface properties and energy state. May be.

  The electrode 2 may be formed on a substrate, and the substrate may be transparent or opaque. For example, when the substrate side is a light receiving surface, a transparent substrate is preferable. As a material of the transparent substrate, for example, a transparent rigid material having no flexibility such as quartz glass, Pyrex (registered trademark), a synthetic quartz plate, or a transparent material having flexibility such as a transparent resin film or an optical resin plate is used. Can be mentioned.

  For example, if the substrate is a flexible material such as a transparent resin film, it is useful for realizing a reduction in manufacturing cost, weight reduction, and an organic thin film solar cell that is difficult to break, and applicability to various applications such as application to curved surfaces. Is preferable in terms of spreading.

  The method for forming the buffer layer 4 is preferably selected as appropriate depending on the constituent material. For example, dry deposition methods such as various deposition methods, sputtering methods, plasma CVD methods, spin coating methods, casting methods, gravure coating methods, dip coating methods, spray coating methods, shower coating methods, curtain coating methods, electrodeposition coatings Wet film forming methods such as a method, an electrostatic coating method (ESD method), a die coating method, a screen printing method, and an ink jet printing method can be appropriately selected.

  Subsequently, the buffer layer 4 thus formed is subjected to a heat treatment to form an altered portion 4a by the heat treatment. What is necessary is just to select suitably from the well-known technique as a heat processing method, For example, the heating by a hotplate etc. are mentioned. The heat treatment temperature is preferably 50 to 250 ° C, more preferably 100 to 200 ° C, and particularly preferably 140 to 200 ° C. The heat treatment time is preferably 1 to 60 minutes, more preferably 5 to 30 minutes.

  Thereby, for example, when molybdenum oxide is used for the buffer layer 4, an altered portion 4 a having a change in its surface roughness and transmittance is formed. In addition, by subjecting the buffer layer 4 to heat treatment before forming the photoelectric conversion layer 3, a conjugated polymer electron-donating organic material and electron-accepting organic material having a benzothiadiazole skeleton used in the photoelectric conversion layer 3. The deteriorated portion 4a can be formed without causing deterioration (performance degradation) due to heat.

  Next, the photoelectric conversion layer 3 is formed on the buffer layer 4. As a method for forming the photoelectric conversion layer 3, known techniques can be used as appropriate, but a spin coating method, a casting method, a gravure coating method, a dip coating method, a spray coating method, a shower coating method, a curtain coating method, and an electrodeposition coating. A wet film forming method such as a method, an electrostatic coating method (ESD method), a die coating method, a screen printing method, or an ink jet printing method is more preferable.

  Furthermore, the electrode 1 is formed on the organic photoelectric conversion layer 3. As a method for forming the electrode 1, a known method such as a vacuum deposition method, a sputtering method, or various coating methods can be appropriately used. Thereby, the photoelectric conversion element 10 of this embodiment can be formed.

  Here, the case where the buffer layer 4 including the altered portion 4a by the heat treatment is between the electrode 2 and the photoelectric conversion layer 3 and is sequentially stacked from the electrode 2 has been described. However, the buffer including the altered portion 4a by the heat treatment has been described. The layer 4 may be disposed between the electrode 1 and the photoelectric conversion layer 3 and sequentially stacked from the electrode 1 side.

(Embodiment 2)
FIG. 2 is a schematic cross-sectional view of a photoelectric conversion element that is an example of an organic photoelectric conversion device according to Embodiment 2 of the present invention.

  As shown in FIG. 2, the organic photoelectric conversion device 20 of the present embodiment is the same as that of Embodiment 1 described above except that the buffer layer 5 is provided between the organic photoelectric conversion layer 3 and the electrode 1. In the present embodiment, the same components as those in the first embodiment (FIG. 1) described above are denoted by the same reference numerals, and the description thereof is omitted.

  Here, the buffer layer 5 plays a role of improving various characteristics of the photoelectric conversion device 10 directly or indirectly. For example, the buffer layer 5 lowers the charge injection barrier from the photoelectric conversion layer 3 to the electrode 1, Prevention of exciton diffusion from the conversion layer 3 to the electrode 1, charge rectification action, prevention of reaction between the electrode 1 and the electron-donating organic material or the electron acceptor organic material of the photoelectric conversion layer 3, prevention of short-circuit between electrodes One of the effects.

  A material for forming the buffer layer 5 is not particularly limited, but is appropriately selected so as to obtain a desired effect. Specifically, when the electrode 1 functions as a negative electrode, it is preferable to use, for example, a substance having an electron transporting property such as titanium oxide or zinc oxide, lithium fluoride, calcium, or the like. On the other hand, when the electrode 1 functions as a negative electrode, it has hole transport properties such as molybdenum oxide, vanadium oxide, polyethylenedioxythiophene (PEDOT), polystyrene sulfonic acid (PSS), or a mixture of these polymer materials. It is preferable to use a substance.

  As described above, the photoelectric conversion element 20 of the present embodiment can improve the photoelectric conversion efficiency by providing the buffer layer 5 between the photoelectric conversion layer 3 and the electrode 1. Reduction of charge injection barrier from conversion layer 3 to electrode 1, prevention of exciton diffusion from photoelectric conversion layer 3 to electrode 1, charge rectification action, electron donating organic material or electron acceptor of electrode 1 and photoelectric conversion layer 3 Effects such as prevention of reaction with the conductive organic material and prevention of short circuit between electrodes can be obtained.

  In addition, the manufacturing method of the photoelectric conversion element 20 of this embodiment can be made to be the same as that of Embodiment 1 mentioned above except the buffer layer 5. FIG. The method for forming the buffer layer 5 is not particularly limited, but a method that does not apply a thermal load to the photoelectric conversion layer 3 at the time of formation is suitable. A formation method in which the temperature of the photoelectric conversion layer 3 is 100 ° C. or lower is preferable, and a formation method in which the temperature of the photoelectric conversion layer 3 is 100 ° C. or lower is more preferable.

(Other embodiments)
As mentioned above, although this invention was demonstrated in detail based on Embodiment 1, 2, this invention is not limited to each Embodiment 1, 2 mentioned above. For example, in each of the first and second embodiments described above, the element configuration is illustrated as an example of the photoelectric conversion device. However, the present invention is of course not limited thereto, and, for example, a photoelectric conversion function, an optical rectification function, or the like is used. To various photoelectric conversion devices such as photovoltaic cells (solar cells (photovoltaic power generation devices)), photovoltaic elements, electronic devices (optical sensors, optical switches, phototransistors, etc.), optical recording materials (optical memory, etc.), etc. Application is possible. In particular, it is useful for solar cells (organic thin film solar cells, organic inorganic thin film solar cells, silicon-based solar cells, etc.) and photovoltaic elements. Moreover, there is no problem even if the unit layer structure is laminated (tandem) according to the application.

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

[Example 1]
(Preparation of solution for photoelectric conversion layer)
23 mg of PCPDTBT (produced by Luminescence Technology Corp., LT-S949) and 41.4 mg of [70] PCBM (manufactured by Frontier Carbon Co., nanospectra E110) were weighed and mixed, and chlorobenzene (Wako Pure Chemical Industries, Ltd.) was mixed therewith. 2 ml of 1,8-diiodooctane (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.05 ml were added and stirred at room temperature for 60 hours.

  Then, it filtered with the syringe filter (The GE Healthcare Japan company make, 13 mm GD / X syringe filter (PVDF 0.45 micrometer)), and obtained the PCPDTBT: [70] PCBM mixed solution as a solution for photoelectric conversion layers.

(Create photoelectric conversion device)
A glass substrate with an ITO film in which an ITO film was patterned as a transparent conductive film on a glass substrate (2 cm square, thickness 0.7 mm) was prepared. Hereinafter, this substrate is referred to as an “ITO substrate”.

  The ITO substrate was ultrasonically cleaned with a liquid detergent, acetone, and 2-propanol, and then subjected to UV-ozone treatment.

Next, a molybdenum oxide film was formed on the ITO substrate by resistance heating vacuum deposition to form a buffer layer. The film thickness of the molybdenum oxide film was 39 nm, the film formation rate was 2-5 Å / s, and the pressure during film formation was 5 × 10 ⁻⁴ Pa or less.

  Subsequently, the ITO substrate on which the molybdenum oxide film as the buffer layer was formed was heat-treated on a hot plate at 160 ° C. for 5 minutes in a nitrogen atmosphere to form an altered portion due to the heat treatment.

  The photoelectric conversion layer solution prepared by the above method is spin-coated (1500 rpm, 1 minute) in a nitrogen atmosphere on an ITO substrate on which a molybdenum oxide film as a buffer layer subjected to heat treatment is formed, and photoelectric conversion is performed. As a layer, a PCPDTBT: [70] PCBM mixed layer having a thickness of 100 nm was obtained.

An Al film as an electrode was formed on the photoelectric conversion layer by resistance heating vacuum deposition. The film thickness of the Al film was 80 nm, the film formation rate was 1-5 Å / s, and the pressure during film formation was 1 × 10 ⁻³ Pa or less. Moreover, vapor deposition was performed through the shadow mask and the photoelectric conversion device which has an effective photoelectric conversion area of 3 square mm, ie, 0.09 cm < ² >, was produced.

[Example 2]
(Preparation of solution for photoelectric conversion layer)
11.6 mg of PTB7 (manufactured by 1-material) and 17.4 mg of [70] PCBM (manufactured by Solenen BV) were weighed and mixed, and chlorobenzene (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 0. 97 ml and 1,8-diiodooctane (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.03 ml were added, and the mixture was stirred at 60 ° C. for 3 hours to obtain a PTB7: [70] PCBM mixed solution as a solution for a photoelectric conversion layer.

(Create photoelectric conversion device)
Using the PTB7: [70] PCBM mixed solution as a solution for the photoelectric conversion layer, the solution was spin-coated (2000 rpm, 2 minutes) under a nitrogen atmosphere, and a PTB7: [70] PCBM mixture having a thickness of 100 nm was formed as the photoelectric conversion layer. A photoelectric conversion device was produced in the same manner as in Example 1 except that the layer was obtained.

[Example 3]
(Preparation of solution for photoelectric conversion layer)
8 mg of PCE10 (manufactured by 1-material) and 12 mg of [70] PCBM (manufactured by Solene BV) were weighed and mixed, and 0.97 ml of chlorobenzene (special grade by Wako Pure Chemical Industries, Ltd.) and 1, 8-Diiodooctane (manufactured by Tokyo Chemical Industry Co., Ltd.) (0.03 ml) was added, and the mixture was stirred at 60 ° C. for 3 hours to obtain a PCE10: [70] PCBM mixed solution as a solution for a photoelectric conversion layer.

(Create photoelectric conversion device)
Using the PCE10: [70] PCBM mixed solution as a solution for the photoelectric conversion layer, the solution was spin-coated (2000 rpm, 2 minutes) under a nitrogen atmosphere, and a PCE10: [70] PCBM mixture having a thickness of 100 nm was formed as the photoelectric conversion layer. A photoelectric conversion device was produced in the same manner as in Example 1 except that the layer was obtained.

[Comparative Example 1]
A comparative photoelectric conversion device was produced in the same manner as in Example 1 except that the ITO substrate on which the molybdenum oxide film as the buffer layer was not subjected to heat treatment and an altered portion due to the heat treatment was not formed.

[Comparative Example 2]
A comparative photoelectric conversion device was produced in the same manner as in Example 2 except that the ITO substrate on which the molybdenum oxide film as the buffer layer was not subjected to heat treatment and an altered portion due to the heat treatment was not formed.

[Comparative Example 3]
A comparative photoelectric conversion device was produced in the same manner as in Example 3 except that the ITO substrate on which the molybdenum oxide film as the buffer layer was not subjected to heat treatment and an altered portion due to the heat treatment was not formed.

[Comparative Example 4]
A comparative photoelectric conversion device was produced in the same manner as in Example 1 except that a PEDOT: PSS film obtained by the following method was used as the buffer layer instead of the molybdenum oxide film.

  Spin coating (5000 rpm, 1 minute) with PEDOT: PSS (manufactured by Heraeus, CleviosPH500) on the ITO substrate, followed by drying treatment on a hot plate at 140 ° C. for 10 minutes in the atmosphere as a buffer layer A 39 nm thick PEDOT: PSS film was obtained.

[Evaluation]
About the produced photoelectric conversion device, a solar simulator and a current density-voltage characteristic measurement under a simulated sunlight irradiation having an AM1.5G spectral distribution and a light intensity of 100 mW / cm ² It measured using the apparatus (The spectrometer company make, CEP-25BX).

  The short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and photoelectric conversion efficiency (η) of the devices of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by measurement are shown in Table 1 below. did.

Further, after the devices of Example 1 and Comparative Example 2 were allowed to stand in the atmosphere at room temperature for a predetermined time, the pseudo-sun having a spectral distribution of AM1.5G and a light intensity of 100 mW / cm ² as described above. The current density-voltage characteristics under light irradiation were measured, and the result of obtaining the conversion efficiency maintenance ratio with respect to the initial photoelectric conversion efficiency (conversion efficiency when measured immediately after device fabrication) before standing from the following formula is shown below. It described in Table 2.
Conversion efficiency maintenance rate [%] = (photoelectric conversion efficiency after standing for a predetermined time) / (conversion efficiency immediately after device fabrication) × 100

  As described above, the photoelectric conversion device of the present invention exhibits high performance for photoelectric conversion and exhibits excellent durability.

[Example 4]
(Preparation of samples for evaluation of altered parts by heat treatment)
A sample for evaluation was obtained by forming only a molybdenum oxide buffer layer including an altered portion by heat treatment on the substrate in the same manner as in Example 1 except that a glass substrate on which an ITO film was formed on the entire surface was used as the substrate.

[Comparative Example 5]
A comparative evaluation sample was obtained in the same manner as in Example 4 except that the ITO substrate on which the molybdenum oxide film as the buffer layer was formed was not subjected to heat treatment and an altered portion due to the heat treatment was not formed.

[Evaluation]
[Photoelectron spectroscopy (XPS)]
FIG. 3 and FIG. 4 show the measurement results of the oxidized state of molybdenum oxide, which was performed on the prepared evaluation sample using an X-ray photoelectron spectrometer (AXISNOVA manufactured by Kratos (Shimadzu Corporation)).

  The vertical axis in FIG. 3 is Mo5 + / Mo6 +, the vertical axis in FIG. 4 is x of MoOx, and in both FIGS. 3 and 4, the horizontal axis is the X-ray incident angle. The incident angle of the X-ray is an angle at which 0 degree is incident on the sample perpendicularly to the sample, and the penetration depth of the X-ray into the sample is the deepest (the measurement range is widened). As the angle increases, the surface layer portion of molybdenum oxide is measured (measurement range becomes narrower).

  As shown in FIG. 3, the heat treatment example 4 has a smaller value of Mo5 + / Mo6 + on the lower angle side than the comparative example 5 which has not been heat treatment, and the molybdenum oxide film serving as a buffer layer. The rate of change in the film thickness direction (measurement X-ray incident angle) is relatively small.

  Further, as shown in FIG. 4, the heat treatment example 4 is higher in the value of x of MoOx than the comparative example 5 which is not heat treatment, and the oxidation of the buffer layer. There is relatively little increase or decrease in the film thickness direction (measurement X-ray incident angle) of the molybdenum film.

  From these results, it was confirmed that in Example 4 and Examples 1 to 3 that had undergone the same manufacturing process, the altered portion accompanied with the above-described change in physical properties was formed in the molybdenum oxide film that is the buffer layer by the heat treatment.

[Surface roughness measurement]
About the produced sample for evaluation, the root mean square roughness (RMS) of the surface of the molybdenum oxide film was measured using an atomic force microscope (Multimode 8 manufactured by Bruker Corporation). As a result, Example 4 with heat treatment was 2.1 nm, and Comparative Example 5 without heat treatment was 0.4 nm.

  Also from this result, it was confirmed that in Example 4 and Examples 1 to 3 that passed through the same manufacturing process, the altered portion accompanied with the above physical property change was formed in the molybdenum oxide film as the buffer layer by the heat treatment.

[Transmittance measurement]
About the produced sample for evaluation, the light transmission spectrum of the molybdenum oxide film was measured using the ultraviolet visible spectrophotometer (JASCO (JASCO Corporation V-650)). As a result, the average transmittance of light having a wavelength of 550 to 900 nm was 89.7% in Example 4 where heat treatment was performed, and 94.8% in Comparative Example 5 where heat treatment was not performed.

  Also from this result, it was confirmed that in Example 4 and Examples 1 to 3 that passed through the same manufacturing process, the altered portion accompanied with the above physical property change was formed in the molybdenum oxide film as the buffer layer by the heat treatment.

DESCRIPTION OF SYMBOLS 1, 2 Electrode 3 Organic photoelectric conversion layer 4 Buffer layer 4a Alteration part by heat processing 10 Organic photoelectric conversion device

Claims (17)

A pair of electrodes;
An organic photoelectric conversion layer disposed between the pair of electrodes;
A buffer layer provided between at least one of the pair of electrodes and the organic photoelectric conversion layer,
The organic photoelectric conversion layer is formed using a conjugated polymer electron-donating material containing both an electron-donating molecular structure and an electron-accepting molecular structure in the molecule, and an electron-accepting material.
The said buffer layer is formed from a metal oxide, and has an altered part formed by heat processing, The organic photoelectric conversion device characterized by the above-mentioned.   2. The organic photoelectric conversion device according to claim 1, wherein the buffer layer is made of at least one metal oxide of molybdenum oxide, vanadium oxide, tungsten oxide, zinc oxide, and titanium oxide.   The organic photoelectric conversion device according to claim 2, wherein the metal oxide is molybdenum oxide (MoOx).   4. The organic photoelectric conversion device according to claim 1, wherein the altered portion of the buffer layer due to heat treatment is located on the organic photoelectric conversion layer side of the buffer layer. 5.   The organic photoelectric conversion device according to any one of claims 1 to 4, wherein the altered portion of the buffer layer by heat treatment has a thickness of 10 nm or less.   6. The altered portion of the buffer layer by heat treatment has a rate of change of Mo5 + / Mo6 + in the thickness direction of the buffer layer that is three times or less. Organic photoelectric conversion device.   The organic photoelectric conversion device according to any one of claims 3 to 6, wherein the altered portion of the buffer layer by heat treatment has a Mo5 + / Mo6 + value of 0.13 or less.   8. The change in the altered portion of the buffer layer due to heat treatment has an increase or decrease in the film thickness direction of the buffer layer of an x value of MoOx of 0.05 or less. Organic photoelectric conversion device.   The organic photoelectric conversion device according to any one of claims 3 to 8, wherein the altered portion of the buffer layer by heat treatment has an x value of MoOx of 2.93 or more.   10. The organic photoelectric conversion device according to claim 1, wherein the altered portion of the buffer layer has a surface root mean square roughness (RMS) of 2 nm to 5 nm.   11. The organic photoelectric conversion device according to claim 1, wherein the altered portion of the buffer layer has an average transmittance of light having a wavelength of 550 nm to 900 nm of 92% or less. .   The electron-donating material is a conjugated polymer containing at least one of the molecular structures of benzodithiophene, thienothiophene, benzothiadiazole, cyclopentadithiophene, and carbazole in the molecule. The organic photoelectric conversion device according to any one of claims 1 to 11.   The organic photoelectric conversion layer is formed using any one of electron donating materials of PCPDTBT, PCDTBT, PBDTTTT-EF, PBDTTTT-EFT, and PFFBT4T-20D. The organic photoelectric conversion device according to item 1.   The one of the pair of electrodes, the buffer layer, the organic photoelectric conversion layer, and the other of the pair of electrodes are arranged on the substrate in this order. Organic photoelectric conversion device.   The organic photoelectric conversion device according to any one of claims 1 to 14, wherein the altered portion is formed by a heat treatment in a range of 140 to 200 ° C.   The organic photoelectric conversion device according to claim 1, wherein the altered portion is formed by a heat treatment before the formation of the organic photoelectric conversion layer.   A solar cell comprising the organic photoelectric conversion device according to any one of claims 1 to 16.