JP2005294303A - Organic photoelectric converter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic photoelectric converter which stabilizes characteristics and which has a long lifetime. <P>SOLUTION: The organic photoelectric converter includes at least a pair of electrodes 12, 16, a photoelectric conversion region (layer) 15 containing at least an electron donative organic substance and an electron receptive organic substance, and a buffer layer 14 interposed between the photoelectric conversion region and at least one of the pair of the electrodes and made of at least one type of inorganic substance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic photoelectric conversion element and a method for producing the same, and more particularly to an organic photoelectric conversion element having stable characteristics expected to be applied as a solar cell or an optical sensor.

  Inorganic solar cells using silicon such as amorphous silicon are clean devices that are being put into practical use. However, inorganic solar cells, which are clean power generators, have become a serious problem in recent years in terms of environmental burdens for disposal. Under such circumstances, since the environmental load for disposal is small and the manufacturing cost is low, photoelectric conversion elements using organic semiconductor materials are being developed for practical use (see Patent Document 1). .

  Such an organic photoelectric conversion element is configured to generate an electromotive force between electrodes by light incident on an organic semiconductor material, and the schematic configuration is as shown in FIG. The anode 2, the charge transport layer 3, the photoelectric conversion layer 4, and the cathode 5 (5a, 5b) are laminated.

  The photoelectric conversion layer 4 includes an electron donating material and an electron accepting material.

  When light enters the photoelectric conversion layer 4, light absorption occurs here, excitons of electron-hole pairs are formed, carriers are then separated, and electrons pass through the electron-accepting semiconductor material to the cathode 5. The holes move to the anode 2 through the electron donating semiconductor material. As a result, an electromotive force is generated between both electrodes, and the power can be taken out by connecting these electrodes and an external circuit.

  Such a photoelectric phenomenon is likely to occur at an interface where materials having different electron affinities and ionization potentials are in contact with each other, and in order to produce a highly efficient photoelectric conversion element, a plurality of materials having different electron affinities and the like are connected to a wider interface. It is necessary to contact with. Further, from the viewpoint of effective use of generated carriers, it is desirable that excitons are efficiently transported to the anode 2 and the cathode 5 without recombination. Furthermore, it is important to reduce defects in the photoelectric conversion layer 4 so that carriers are not trapped by defects or the like, or leakage current is generated.

  In order to meet such various demands, research and development of organic photoelectric conversion elements have been intensively studied from both the material side and the process side. Currently, the dye sensitizing type is about 10%, and even in the case of a solid thin film type, the carrier By improving the separation efficiency, an energy conversion efficiency of 3% has been obtained.

JP-T 8-500701

  However, the organic photoelectric conversion element has a problem in that characteristic deterioration is likely to occur and the lifetime is short. That is, when organic photoelectric conversion elements are used in products such as solar cells and optical sensors, the lifetime required for these products is different, but the current organic photoelectric conversion elements are still used for any purpose. There was a problem that the required life could not be sufficiently satisfied.

  The present invention has been made to solve the conventional problems, and an object thereof is to provide a long-life organic photoelectric conversion element while stabilizing characteristics.

The organic photoelectric conversion element of the present invention includes at least one pair of electrodes, a photoelectric conversion region disposed between the electrodes, and including at least an electron donating organic material and an electron accepting material, the photoelectric conversion region, and the 1 And a buffer layer made of at least one inorganic material interposed between at least one of the pair of electrodes.
With this configuration, it is possible to obtain a long-life organic photoelectric conversion element by suppressing the diffusion of the element constituent material and stabilizing the characteristics.

  Moreover, as for the organic photoelectric conversion element of this invention, the said photoelectric conversion area | region contains an organic thin film.

In the organic photoelectric conversion device of the present invention, the organic thin film includes a polymer film formed by coating on one of the electrodes.
With this configuration, since the photoelectric conversion region can be formed by a coating method, it can be formed without going through a vacuum process. The buffer layer may also be formed by a coating method.

  The organic photoelectric conversion element of the present invention includes those in which the electron donating material is composed of a conductive polymer material.

  In the organic photoelectric conversion device of the present invention, the electron-accepting material includes at least one of modified or unmodified fullerenes and carbon nanotubes.

  With this configuration, the electron mobility is increased by the modified or unmodified fullerenes and carbon nanotubes, so that the electrons donated from the electron donating organic material can be rapidly transferred to the cathode due to the high electron mobility of the electron accepting material. It becomes possible to transport and the photoelectric conversion efficiency is improved, and these electron-donating organic material and electron-accepting material can be mixed and used, and the cost can be reduced.

Although the reason is not clear, according to the above configuration, the element characteristics can be stabilized and the reliability can be improved by interposing the buffer layer. This is only a guess, but it is thought to be due to the following reasons.
In the organic photoelectric conversion element, excitons are formed by light energy supplied to the photoelectric conversion layer by light absorption, and a photoelectromotive force is generated by passing these excited electrons between materials. Usually, the generated electromotive force is as very small as 1.0 V or less, and since the amount of generated current is very small, when the series resistance inside the element is high, the generated electrons do not reach the electrode, and the electromotive force It becomes impossible to take out. In order to reduce the series resistance, means such as ohmic bonding between the constituent materials is taken. Another important factor is physical bonding between the constituent materials. It is considered that the buffer layer contributes to the improvement of the adhesion of the bonding surface, and a long-life organic photoelectric conversion element can be realized by maintaining the bonding state stably for a long time.
It is also considered possible to suppress deterioration of the constituent materials. In general solid thin film type organic photoelectric conversion elements, a PEDOT: PSS layer (mixture of polythiophene and polystyrene sulfonic acid) is used to improve conversion efficiency. This PEDOT: PSS layer is effective for improving the initial characteristics, but long-term stability is a problem, and when it is reduced, an ionic component is produced, which is another constituent material such as organic semiconductor materials. Cause deterioration. The buffer layer is considered to be able to realize a long-life organic photoelectric conversion element by suppressing the reduction of the PEDOT: PSS layer and also reducing the diffusion of ionic components.

Moreover, as for the organic photoelectric conversion element of this invention, a buffer layer contains an oxide.
As mentioned above, organic thin films, especially PEDOT: PSS layers, have the property of being vulnerable to reduction, but because they are connected to the photoelectric conversion region via oxides, PEDOT: PSS layers are less likely to be reduced and have a longer lifetime. Can be realized.

  In the organic photoelectric conversion element of the present invention, the buffer layer contains an oxide of a transition metal.

  Moreover, the organic photoelectric conversion element of this invention contains that a buffer layer consists of an oxide of molybdenum or vanadium.

  As oxides used here, in addition to oxides of vanadium and molybdenum, chromium (Cr), tungsten (W), niobium (Nb), tantalum (Ta), titanium (Ti), zirconium ( Zr), hafnium (Hf), scandium (Sc), yttrium (Y), thorium (Tr), manganese (Mn), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), nickel ( Ni), copper (Cu), zinc (Zn), cadmium (Cd), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead ( Pb), antimony (Sb), bismuth (Bi) or oxides such as so-called rare earth elements from lanthanum (La) to lutetium (Lu) can be mentioned. Among these, aluminum oxide (AlO), copper oxide (CuO), and silicon oxide (SiO) are particularly effective for extending the life.

In this way, in particular, the buffer layer can be selected from oxides or nitrides of transition metals such as molybdenum and vanadium.
For example, since transition metal compounds have a plurality of oxidation numbers, it is possible to take a plurality of potential levels, thereby facilitating the extraction of charges from the organic semiconductor layer as the photoelectric conversion layer, and achieving stabilization. It is thought that power generation efficiency can be increased.

Moreover, in the organic photoelectric conversion element of this invention, a buffer layer contains nitride.
Nitride is stable, and in addition to the effect of improving adhesion, the reduction of the PEDOT: PSS layer can be suppressed, and the lifetime can be further increased.

  In the organic photoelectric conversion element of the present invention, the buffer layer contains a transition metal nitride.

  There are numerous types of nitrides, many of which are used as functional materials. Films can be formed mainly by sputtering or CVD. Various compounds are known, ranging from those used as semiconductors to those with very high insulation properties. However, as a result of various experiments, the film thickness of highly insulating compounds is about 5 nm during film formation. It was found that the charge can be taken out by the following. Specific examples of the compound include the following, and titanium nitride (TiN) is preferable. TiN is known as a very robust material and is stable to heat.

  In addition, gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), boron nitride (BN), silicon nitride (SiN), magnesium nitride (MgN), molybdenum nitride (MoN), calcium nitride (CaN) Niobium nitride (NbN), tantalum nitride (TaN), vanadium nitride (BaN), zinc nitride (ZnN), zirconium nitride (ZrN), iron nitride (FeN), copper nitride (CuN), barium nitride (BaN), nitride Lanthanum (LaN), chromium nitride (CrN), yttrium nitride (YN), lithium nitride (LiN), titanium nitride (TiN), and composite nitrides thereof are also applicable.

Moreover, in the organic photoelectric conversion element of this invention, a buffer layer contains an oxynitride.
Since the oxynitride has a strong oxygen resistance and becomes a dense and highly reliable film, the interface can be stably maintained.

In the organic photoelectric conversion device of the present invention, the buffer layer contains a transition metal oxynitride.
For example, ruthenium (Ru) oxynitride crystals such as Ru ₄ Si ₂ O ₇ N ₂ are also extremely heat-resistant (1500 ° C) and stable, so they can be applied as a buffer layer by forming a thin film. is there. In this case, the film can be formed by performing a heat treatment after forming the film by a sol-gel method.

In addition, barium sialon (BaSiAlON), calcium sialon (CaSiAlON), cerium sialon (CeSiAlON), lithium sialon (LiSiAlON), magnesium sialon (MgSiAlON), scandium sialon (ScSiAlON), yttrium sialon (YSiAlON), erbium sialon (E) IA, IIA, IIIA sialons such as Neodymium Sialon (NdSiAlON), or oxynitrides such as multiple sialons are applicable. These can be formed by CVD, sputtering, or the like. In addition, lanthanum silicon oxynitrate (LaSiON), lanthanum silicon lanthanum europium (LaEuSi ₂ O ₂ N ₃ ), silicon oxynitride (SiON ₃ ), and the like are also applicable. Since these are mostly insulators, it is necessary to reduce the film thickness to about 1 nm to 5 nm.

In the organic photoelectric conversion element of the present invention, the buffer layer includes a transition metal composite oxide.
Although the reason is not clear, when a transition metal composite oxide is used for the buffer layer, stable characteristics can be obtained.

  In addition, there are a great many types of complex oxides, and many of them have electronically interesting properties. Specific examples include the following compounds.

For example, barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ), potassium niobate (KNbO ₃ ), bismuth iron oxide (BiFeO ₃ ), lithium niobate (LiNbO ₃₎ ), sodium vanadate (Na ₃ VO _4), vanadium iron (FeVO _3), titanate vanadium (TiVO _3), chromic acid vanadium (CRVO _3), vanadium, nickel (NiVO _3), magnesium vanadate (MgVO ₃ ), calcium vanadate (Cavo _3), vanadium lanthanum (LaVO _3), molybdate vanadium (VMoO _5), molybdate vanadium (V ₂ MoO _8), lithium vanadate (LiV ₂ O _5), magnesium silicate (Mg ₂ SiO ₄ ), magnesium silicate (MgSiO ₃ ), zirconium titanate (ZrTiO ₄ ), strontium titanate (SrTiO ₃ ), lead magnesium acid (P bMgO ₃ ), lead niobate (PbNbO ₃ ), barium borate (BaB ₂ O ₄ ), lanthanum chromate (LaCrO ₃ ), lithium titanate (LiTi ₂ O ₄ ), lanthanum cuprate (LaCuO ₄ ), titanate Zinc (ZnTiO ₃ ), calcium tungstate (CaWO ₄ ), or the like can be used.

Although any of these can be used to carry out the present invention, barium titanate (BaTiO ₃ ) is preferably used. BaTiO ₃ is a typical dielectric and is a complex oxide with high insulating properties, but it is possible to extract charges when used in thin films based on the results of various experiments. I understood. BaTiO ₃ and strontium titanate (SrTiO ₃ ) are stable as compounds and have a very large dielectric constant, so that it is possible to efficiently extract charges. For film formation, a sputtering method, a sol-gel method, a CVD method, or the like can be selected as appropriate.

  In addition, in the said compound, the compound from which a valence differs easily exists, and what takes the form of the compound from which a valence differs other than what was illustrated is also included.

The organic photoelectric conversion element of the present invention includes an electrode formed on the substrate surface, a PEDOT: PSS layer formed on the electrode, a buffer layer including an inorganic film formed on the upper layer, an organic semiconductor layer, An electrode is formed on the organic semiconductor layer.
According to this configuration, by interposing a buffer layer including an inorganic film at the interface between the PEDOT: PSS layer and the photoelectric conversion layer, the phase separation of the PEDOT: PSS layer is suppressed, and the charge transport property is stably maintained. It is possible to provide a photoelectric conversion element having high efficiency and stable characteristics over a long period of time.

  This is thought to be due to the following mechanism. This PEDOT: PSS layer can be easily formed by spin coating or the like, and by interposing between the electrode and the photoelectric conversion layer, the electromotive force can be increased, and as a charge transport layer It is a de facto standard material.

  However, this PEDOT: PSS layer is a mixture of two polymeric substances, polystyrene sulfonic acid and polythiophene, as described above, the former being ionic and the latter having local polarity in the polymer chain. Both are loosely coupled by the Coulomb interaction resulting from the anisotropy of the charge, thereby exhibiting excellent carrier (charge) transportability.

  In order for the PEDOT: PSS layer to exhibit excellent properties, close interaction between the two is indispensable, but in general, a mixture of polymer substances is prone to phase separation due to subtle differences in solubility in solvents. . This is no exception for the PEDOT: PSS layer. The occurrence of phase separation means that the loose bond between the two macromolecules can be removed relatively easily. During driving, PEDOT: PSS may be unstable, As a result, it has been shown that components that have not contributed to bonding, particularly ionic components, can be diffused by an internal electric field generated by light irradiation and have an undesirable effect on other functional layers. Thus, although the PEDOT: PSS layer has excellent charge transport properties, it cannot be said to be a stable substance.

  However, by interposing a buffer layer at the interface between the PEDOT: PSS layer and the photoelectric conversion layer, the phase separation of PEDOT can be suppressed and the charge transport property can be stably maintained.

  In the organic photoelectric conversion element of the present invention, the photoelectric conversion region includes an electron donating layer containing an electron donating organic material and an electron accepting layer containing an electron accepting material.

  In the organic photoelectric conversion element of the present invention, the buffer layer includes an element interposed between the electron donating layer and the electrode.

  The organic photoelectric conversion element of the present invention includes one in which the buffer layer is interposed between the electron-accepting layer and the electrode.

  In the organic photoelectric conversion element of the present invention, the photoelectric conversion region includes an organic semiconductor layer in which an electron donating organic material and an electron accepting organic material are dispersed.

  The method for producing an organic photoelectric conversion element of the present invention includes a step of forming an electrode, a step of forming a buffer region containing an inorganic substance, a step of forming an organic photoelectric conversion region on the buffer region, and the organic photoelectric conversion region. Forming an electrode thereon.

  With this configuration, a long-life organic photoelectric conversion element can be easily formed simply by adding a buffer layer forming step.

In the organic photoelectric conversion device of the present invention, the step of forming the buffer region includes a step of forming a buffer layer on the electrode by a wet method.
With this configuration, for example, an inorganic film is formed by a sol-gel method or the like, and according to this method, it can be easily formed without requiring a vacuum process.

  In the present invention, since at least one of the electrodes is in contact with the organic semiconductor film through a buffer layer made of an inorganic material, it is possible to suppress deterioration in characteristics after the device is manufactured and to provide a long-life organic photoelectric conversion device. It can be provided.

(Embodiment 1)
Embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, as shown in FIG. 1, a buffer layer 14 made of an inorganic film made of molybdenum oxide (MoO ₃ ) is interposed between the organic photoelectric conversion layer 15 and the anode 12. .

  That is, as shown in FIG. 1, the buffer layer 14 made of an inorganic substance is connected to the charge transport layer 13 in order to prevent a substance constituting the charge transport layer 13, particularly an ionic substance from diffusing into the organic photoelectric conversion layer 15. It is provided between the organic photoelectric conversion layer 15 and is formed by sequentially laminating the anode 12, the charge transport layer 13, the buffer layer 14, the organic photoelectric conversion layer 15, and the cathode 16 on the substrate 11.

With this configuration, an organic photoelectric conversion element with high efficiency and stable characteristics can be obtained.
The reason why high efficiency and stable characteristics can be obtained in this way is considered to be as follows.
In this organic photoelectric conversion element, a charge transport layer 13 made of a mixed material of an ionic substance and a polarizable substance is provided to reduce the recombination probability of excitons generated by increasing the charge transport efficiency.

  In order for the charge transport layer 13 to exhibit excellent charge transport characteristics, it is indispensable to loosely bond between the ionic substance and the polarizable substance. In general, however, a mixture of polymer substances has a subtle solubility in a solvent. Phase separation is likely to occur due to the difference, and when the phase separation occurs, the loose bond between the two polymers is relatively easily broken. Therefore, if such a bond is unstable or there are a large number of components that have not contributed to the bond as a result of phase separation, the desired transport properties cannot be exhibited.

In particular, if an ionic substance diffuses into the organic photoelectric conversion layer due to heat or an internal electric field, the component ratio in the charge transport layer changes to deteriorate the transport efficiency, or the component diffused into the organic photoelectric conversion layer is excited. It is expected that the generation efficiency of the child itself will be adversely affected, or it may act as a carrier trap. Such diffusion varies depending on the usage environment such as time and temperature, and is considered to have unstable characteristics.
Therefore, it is considered that by interposing a buffer layer containing a stable inorganic substance, the diffusion of the ionic substance can be prevented and the characteristics can be stabilized.

  As the buffer layer 14, oxides or nitrides of many transition metals such as molybdenum oxide, vanadium, copper, nickel, ruthenium, titanium, zirconium, yttrium, and lanthanum can be used.

  Glass is generally used as the substrate 11, but a flexible material such as a plastic film can also be used in order to make use of the flexibility of the organic material. In addition, polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polyether sulfone, polyvinyl fluoride, polypropylene, polyethylene, polyacrylate, amorphous polyolefin, various polymer materials such as fluorine resin, silicon wafer, gallium arsenide, gallium nitride, etc. The compound semiconductor substrate or the like can be applied.

The anode 12, ITO (indium tin oxide), ATO _(Sn0 2 doped with Sb), is applicable and the like AZO (ZnO-doped Al), also Al as cathode 17, Ag, metal such as Au Material is applicable. At this time, since the material of the anode 12 has translucency, light from the substrate 11 can be incident on the organic photoelectric conversion layer 15. However, when light is incident from the cathode 16, a film is formed so as to have translucency. A device such as setting the thickness is necessary.

  The cathode 16 is formed in a two-layer structure of a metal electrode 16b such as aluminum and a layer 16a for improving electron extraction efficiency on the cathode side. The 16a includes an inorganic dielectric thin film such as LiF or a metal fluoride. Compounds, oxides, etc. can be used. The layer 16a is not essential in the present invention, and may be used as necessary.

  As the charge transport layer 13 on the anode side, a PEDOT: PSS layer (a mixture of polythiophene and polystyrene sulfonic acid) is applicable. The life of the charge transport layer can be further improved by using an inorganic material such as a multi-value oxide such as MoOx instead of PEDOT.

The organic photoelectric conversion layer 15 includes an electron donating organic material and an electron accepting material.
As an electron-donating organic material, phenylene vinylene such as methoxy-ethylhexoxy polyphenylene vinylene (MEH-PPV), fluorene, rubazole, indole, pyrene, pyrrole, picoline, thiophene, acetylene, diacetylene and the like are repeated. A polymer having a unit and a copolymer with another monomer, a derivative thereof, and a group of polymer materials collectively referred to as a dendrimer are used.

  In addition, it is not limited to a polymer, for example, porphyrin compounds such as porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine, titanium phthalocyanine oxide, 1,1-bis {4- (di-P-tolylamino) phenyl} cyclohexane 4,4 ′, 4 ″ -trimethyltriphenylamine, N, N, N ′, N′-tetrakis (P-tolyl) -P-phenylenediamine, 1- (N, N-di-P-tolylamino) naphthalene, 4,4′-bis (dimethylamino) -2-2′-dimethyltriphenylmethane, N, N, N ′, N′-tetraphenyl-4,4′monodiaminopiphenyl, N, N′-diphenyl- Aromatic tertiary compounds such as N, N′-di-m-tolyl-4,4′-diaminobiphenyl and N-phenylcarbazole , Stilbene compounds such as 4-di-P-tolylaminostilbene, 4- (di-P-tolylamino) -4 ′-[4- (di-P-tolylamino) styryl] stilbene, triazole derivatives, oxazizazole derivatives, Imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine dielectrics, annealed amine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazones Derivatives, silazane derivatives, polysilane aniline copolymers, polymer oligomers, styrylamine compounds, aromatic dimethylidin compounds, poly-3-methylthiophene, and the like are also applicable.

  Examples of the electron-accepting material include fullerenes such as C60 and C70, carbon nanotubes, and derivatives thereof, 1,3-bis (4-tert-butylphenyl-1,3,4-oxadiazolyl) phenylene ( Oxadiazole derivatives such as 0XD-7), anthraquinodimethane derivatives, diphenylquinone derivatives, and the like can be used.

  Note that the organic photoelectric conversion layer 15 is not limited to the above materials, and for example, a material having a functional group such as acrylic acid, acetamide, dimethylamino group, cyano group, carboxyl group, nitro group in the film, , Benzoquinone derivatives, tetracyanoethylene and tetracyanoquinodimethane and their derivatives, materials that can accept electrons, such as amino groups, triphenyl groups, alkyl groups, hydroxyl groups, alkoxy groups, phenyl groups, etc. Materials having functional groups, substituted amines such as phenylenediamine, anthracene, benzoanthracene, substituted benzoanthracenes, pyrene, substituted pyrene, carbazole and derivatives thereof, tetrathiafulvalene and derivatives thereof, etc. Including material that can be a donor It is, may be subjected to so-called doping treatment.

Doping means introducing an electron accepting molecule (acceptor) or an electron donating molecule (donor) into the organic semiconductor film as a dopant. Therefore, the doped organic semiconductor film is a film containing the condensed polycyclic aromatic compound and the dopant. As the dopant used in the present invention, either an acceptor or a donor can be used. As this acceptor, a halogen such as Cl ₂ , Br ₂ , I ₂ , ICl, ICl ₃ , IBr, IF, Lewis acid such as PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BC 1 ₃ , BBr ₃ , SO ₃ , HF HC1, HNO ₃ , H ₂ SO ₄ , HClO ₄ , FSO ₃ H, ClSO ₃ H, CF ₃ SO ₃ H and other protic acids, acetic acid, formic acid, amino acids and other organic acids, FeCl ₃ , FeOCl, TiCl ₄ , Transition metals such as ZrCl ₄ , HfCl ₄ , NbF ₅ , NbCl ₅ , TaCl ₅ , MoCl ₅ , WF ₅ , WCl ₆ , UF ₆ , LnCl ₃ (Ln = La, Ce, Nd, Pr, and other lanthanoids and Y) Examples thereof include compounds, electrolyte anions such as Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , AsF ₅ ⁻ , SbF ₆ ⁻ , BF ₄ ⁻ , and sulfonate anions. As donors, alkali metals such as Li, Na, K, Rb, and Cs, alkaline earth metals such as Ca, Sr, and Ba, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy , Ho, Er, Yb, and other rare earth metals, ammonium ions, R ₄ P ⁺ , R ₄ As ⁺ , R ₃ S ⁺ , acetylcholine, and the like.

As a method for introducing these dopants, it is possible to use either a method in which an organic semiconductor film is formed in advance and a dopant is introduced later, or a method in which a dopant is introduced at the time of forming an organic semiconductor film. As the doping method in the former method, gas phase doping using a dopant in a gas state, liquid phase doping in which a solution or a liquid dopant is brought into contact with the thin film, and a dopant in a solid state in contact with the thin film are added. Examples of the method include solid phase doping for diffusion doping. In liquid phase doping, the doping efficiency can be adjusted and the dopant concentration can be adjusted by performing electrolytic treatment . In the latter method, a mixed solution or dispersion of an organic semiconductor compound and a dopant may be simultaneously applied and dried. For example, when using a vacuum evaporation method, a dopant can be introduce | transduced by co-evaporating a dopant with an organic-semiconductor compound. In addition, when a thin film is formed by a sputtering method, the dopant can be introduced into the thin film by sputtering using a binary target of an organic semiconductor compound and a dopant.

  As a method for forming these organic semiconductor films, a vacuum deposition method, a molecular beam epitaxial growth method, an ion cluster beam method, a low energy ion beam method, an ion plating method, a CVD method, a sputtering method, a plasma polymerization method, an electrolytic polymerization method, Examples include chemical polymerization, spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, die coating, and LB, and can be used depending on the material. However, in terms of productivity, spin coating method, blade coating method, dip coating method, roll coating method, bar coating method, die coating method, etc. that can form a thin film easily and precisely using an organic semiconductor solution. preferable. Although there is no restriction | limiting in particular as the film thickness of the thin film which consists of these organic semiconductors, The characteristic of the obtained photoelectric conversion element is largely influenced by the film thickness of an organic semiconductor film, and the film thickness is organic semiconductor. Generally, it is 1 μm or less, particularly 10 to 300 nm.

  As the buffer layer, in addition to the above materials, molybdenum oxide, chromium, tungsten, vanadium, niobium, tantalum, titanium, zirconium, hafnium, scandium, yttrium, so-called rare earth elements from lanthanum to lutetium, thorium, manganese, iron, ruthenium , Oxides and nitrides of osmium, cobalt, nickel, copper, zinc, cadmium, aluminum, gallium, indium, silicon, germanium, tin, lead, antimony, bismuth, etc. Examples thereof include complex oxides and nitrides with alkaline earth metals.

  These materials can be formed by using a general thin film forming method such as a vacuum evaporation method by resistance heating method, electron beam evaporation, sputtering, CVD, PVD or the like.

  The film thickness at that time should be appropriately selected depending on the material used. In general, the range of 1 nm to 1 μm is preferable. For example, in the case of molybdenum oxide, the range of 3 nm to 100 nm is preferable.

  When the buffer layer is thin, it is difficult to obtain a uniform thin film. On the other hand, when the buffer layer is thick, the electrical resistance increases and the carrier extraction efficiency decreases and the film uniformity decreases. .

  Further, the material and film thickness of the buffer layer are appropriately determined depending on the operation expected for the organic photoelectric conversion element.

  As the cathode, a conductive thin film such as a metal is generally used. For example, a metal such as gold, copper, aluminum, platinum, chromium, palladium, indium, nickel, magnesium, silver, gallium or an alloy thereof, tin, Oxide semiconductors such as indium oxide, polysilicon, amorphous silicon, tin oxide, indium oxide, and titanium oxide, and compound semiconductors such as gallium arsenide and gallium nitride are applicable.

(Example 1)
Next, examples will be described. First, an ITO film 12 having a thickness of 150 nm is formed on the glass substrate 11 by a sputtering method, and a resist material (OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied on the ITO film by a spin coating method to a thickness of 5 μm. The resist film was formed. Then, masking, exposure, and development were performed to pattern the resist into the shape of the anode 12.

  Thereafter, the glass substrate 11 is immersed in an aqueous hydrochloric acid solution of 18N at 60 ° C., and the ITO film 12 where the resist film is not formed is etched and washed with water. Finally, the resist film is removed to obtain a predetermined pattern shape. An anode 12 made of the ITO film was formed.

  Next, the glass substrate 11 is subjected to ultrasonic cleaning for 5 minutes with a detergent (Semico Clean, manufactured by Furuuchi Chemical Co., Ltd.), ultrasonic cleaning for 10 minutes with pure water, and aqueous hydrogen peroxide with respect to ammonia water 1 (volume ratio). After cleaning in the order of ultrasonic cleaning for 5 minutes with a solution of 1 and water 5 and ultrasonic cleaning for 5 minutes with pure water at 70 ° C., moisture attached to the glass substrate 11 is removed with a nitrogen blower, Heat to 250 ° C. to dry.

  Subsequently, poly (3,4) ethylenedioxythiophene / polystyrene sulphonate (PEDT / PSS) is dropped on the glass substrate 11 on which the ITO film 12 is formed through a 0.45 μm filter, and spin coating is performed. Was applied uniformly. This was heated in a 200 ° C. clean oven for 10 minutes to form a charge transport layer 13 having a thickness of 60 nm.

Next, the glass substrate 11 on which the charge transport layer 13 is thus formed is placed in a resistance heating vapor deposition apparatus, and the pressure is reduced to a vacuum degree of 0.27 mPa (= 2 × 10 ⁻⁶ Torr) or less. Molybdenum oxide was deposited to form a 5 nm buffer layer 14.

  Then, poly (2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylenevinylene) (MEH-PPV) functioning as an electron-donating organic material having a molecular structure as shown in FIG. After spin-coating a chlorobenzene solution consisting of [5,6] -phenyl C61 butyric acid methyl ester ([5,6] -PCBM) having a weight ratio of 1: 4, which functions as a functional material, in a clean oven at 100 ° C. For 30 minutes to form an organic photoelectric conversion layer 15 having a thickness of about 100 nm.

  Note that MEH-PPV is a P-type organic semiconductor, [5, 6] -PCBM is an n-type organic semiconductor, and exciton electrons generated by light absorption diffuse a conduction band as shown in FIG. The holes are diffused to the [5, 6] -PCBM and to the MEH-PPV by diffusing the valence band and conducted to the cathode 16 and the anode 12.

  This [5,6] -PCBM is a modified fullerene, has a very high electron mobility, and in addition, a mixture with MEH-PPV, which is an electron donating material, can be used. There is an advantage that the transfer can be efficiently performed, the photoelectric efficiency is increased, and the low-cost production is possible.

Finally, LiF is about 1 nm and then Al is about 10 nm in a resistance heating vapor deposition apparatus reduced in pressure to 0.27 mPa (= 2 × 10 ⁻⁶ Torr) or less on the organic photoelectric conversion layer 15. The cathode 16 was formed by forming a film with a thickness of 5 nm.

  Then, the organic photoelectric conversion element was obtained by forming the passivation film which is not illustrated on this.

  Compared with the conventional organic photoelectric conversion element which does not use the buffer layer 14, the organic photoelectric conversion element having such a configuration has stable characteristics and a long life even under various environments such as high temperatures.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the first embodiment, the photoelectric conversion layer 15 is configured as a single layer, and the photoelectric conversion layer 15 includes an electron donating material and an electron accepting material. In this embodiment, FIG. As described above, the electron-accepting layer 15a and the electron-donating layer 15b are configured in a two-layer structure, and a pn junction is formed at this interface. Other parts are structurally similar to the organic photoelectric conversion element described in the first embodiment.

In the photoelectric conversion element having such a configuration, since transfer of carriers is limited to only the pn junction interface, excitons generated inside the electron donating layer far from the interface cannot pass electrons to the electron accepting material. Therefore, it can be considered to adversely affect the PEDOT: PSS layer etc., but this can be suppressed by introducing a buffer layer,
The characteristics of the organic photoelectric conversion element can be stabilized and the lifetime can be increased.
Note that the buffer layer may be interposed not only between the electron-donating layer and the electrode, but also between the electron-accepting layer and the electrode. In this case, the life can be extended.

(Example 2)
Next, Example 2 will be described. As in Example 1, first, an anode 12 made of an ITO film having a predetermined pattern shape was formed on a glass substrate 11 by a sputtering method.

  Next, the glass substrate 11 is washed and heated to dry, and a charge transport layer 13 made of a poly (3,4) ethylenedioxythiophene / polystyrene sulfonate PEDOT: PSS layer is formed on the substrate 11. did.

Next, this substrate 11 is put in a resistance heating vapor deposition apparatus, and molybdenum oxide is vapor-deposited in a state where the pressure is reduced to a vacuum degree of 0.27 mPa (= 2 × 10 ⁻⁶ Torr) or less, and a 5 nm buffer layer 14 is formed. Formed.

  Then, an electron donating organic material layer 15a composed of a polymer layer containing poly (2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylenevinylene) (MEH-PPV) is spin-coated, Electron-accepting material layers 15b made of fullerene (C60) were formed by a vacuum deposition method, and an organic photoelectric conversion layer 15 of about 100 nm was formed.

  Note that MEH-PPV is a P-type organic semiconductor, C60 is an n-type semiconductor, and exciton electrons generated by light absorption diffuse into a conduction band as shown in FIG. 3, and holes are valence. The band is diffused and supplied to the MEH-PPV, which is conducted to the cathode 16 and the anode 12.

  This C60 has a very high electron mobility, and can efficiently carry out separation and transport of electron-hole pairs.

  Finally, in the same manner as in Example 1, a cathode 16 was formed by depositing LiF on the organic photoelectric conversion layer 15 to a thickness of about 1 nm and subsequently forming Al to a thickness of about 10 nm.

  Then, the organic photoelectric conversion element was obtained by forming the passivation film which is not illustrated on this.

  The organic photoelectric conversion element having such a configuration has stable characteristics and a long lifetime.

  In the above-described embodiment, an example in which a PEDOT: PSS layer is used as a charge transport layer has been described, but instead of the PEDOT: PSS layer, an inorganic material or only a buffer layer made of an inorganic material is used as a photoelectric conversion layer and an electrode. By interposing between them, an unstable factor is eliminated, so that further stabilization can be achieved.

  The present invention operates stably without causing a decrease in photoelectric conversion efficiency even when driven for a long time, and can be used in various environments such as high temperatures, so that it can be used in solar cells, image sensors, optical sensors, etc. Applicable.

It is a figure which shows the organic photoelectric conversion element in Embodiment 1 of this invention. It is a figure for demonstrating Example 1 of this invention. It is a figure for demonstrating Example 1 of this invention. It is a figure which shows the organic photoelectric conversion element in Embodiment 2 of this invention. It is a figure which shows the conventional organic photoelectric conversion element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Charge transport layer 4 Photoelectric conversion layer 5 Cathode 11 Substrate 12 Anode 13 Charge transport layer 14 Buffer layer 15 Photoelectric conversion layer 16 Cathode

Claims (19)

At least one pair of electrodes;
A photoelectric conversion region disposed between the electrodes and including at least an electron-donating organic material and an electron-accepting material;
An organic photoelectric conversion element comprising: a buffer layer made of at least one inorganic material interposed between the photoelectric conversion region and at least one of the pair of electrodes. The organic photoelectric conversion device according to claim 1,
The photoelectric conversion region is an organic photoelectric conversion element including an organic thin film. The organic photoelectric conversion device according to claim 2,
The organic thin film is an organic photoelectric conversion element including a polymer film formed by coating on one surface of the electrode. The organic photoelectric conversion device according to claim 2,
An organic photoelectric conversion element comprising the electron donating material composed of a conductive polymer material. It is an organic photoelectric conversion element in any one of Claims 1 thru | or 4, Comprising:
The organic photoelectric conversion element in which the electron-accepting material includes at least one of modified or unmodified fullerenes and carbon nanotubes. An organic photoelectric conversion element according to any one of claims 1 to 5,
An organic photoelectric conversion element in which the buffer layer contains an oxide. The organic photoelectric conversion device according to claim 6,
The organic photoelectric conversion element in which the buffer layer contains an oxide of a transition metal. The organic photoelectric conversion element according to claim 7,
An organic photoelectric conversion element in which the buffer layer contains an oxide of molybdenum or vanadium. An organic photoelectric conversion element according to any one of claims 1 to 5,
An organic photoelectric conversion element in which the buffer layer contains a nitride. The organic photoelectric conversion device according to claim 9,
The organic photoelectric conversion element in which the buffer layer contains a nitride of a transition metal. An organic photoelectric conversion element according to any one of claims 1 to 5,
The organic photoelectric conversion element in which the said buffer layer contains an oxynitride. The organic photoelectric conversion device according to claim 11,
The organic photoelectric conversion element in which the said buffer layer contains the oxynitride of a transition metal. An organic photoelectric conversion element according to any one of claims 1 to 5,
The organic photoelectric conversion element in which the said buffer layer contains the complex oxide containing a transition metal. An organic photoelectric conversion device according to any one of claims 1 to 13,
The photoelectric conversion region is an organic photoelectric conversion element including an electron donating layer containing an electron donating organic material and an electron accepting layer containing an electron accepting material. The organic photoelectric conversion element according to any one of claims 1 to 14,
The buffer layer is an organic photoelectric conversion element interposed between the electron donating layer and the electrode. The organic photoelectric conversion device according to any one of claims 1 to 15,
The buffer layer is an organic photoelectric conversion element interposed between the electron-accepting layer and the electrode. An organic photoelectric conversion device according to any one of claims 1 to 13,
The photoelectric conversion region is an organic photoelectric conversion element including an organic semiconductor layer in which an electron donating organic material and an electron accepting material are dispersed. Forming an electrode;
Forming a buffer region containing an inorganic substance;
Forming an organic photoelectric conversion region;
Forming an electrode on the organic photoelectric conversion region. It is a manufacturing method of the organic photoelectric conversion element according to claim 18,
The step of forming the buffer region includes:
The manufacturing method of the organic photoelectric conversion element including the process of forming a buffer layer with a wet method.

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