JP2013254912A - Organic photoelectric conversion element and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic photoelectric conversion element excellent in photoelectric conversion efficiency, and a solar cell using the same.SOLUTION: The organic photoelectric conversion element comprises a first electrode, a bulk-heterojunction photoelectric conversion layer containing a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order. The photoelectric conversion layer contains carbon nanotubes which is surface-modified so that the work function of the surface thereof is larger than that of the carbon nanotubes themselves.

Description

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

  In recent years, in order to cope with global warming, reduction of carbon dioxide emissions has been strongly desired. In addition, fossil fuels such as oil, coal, and natural gas are expected to be depleted in the near future, and there is an urgent need to secure an earth-friendly energy resource to replace them. Therefore, development of power generation technology using sunlight, wind power, geothermal heat, nuclear power, and the like has been actively performed, and solar power generation is particularly attracting attention because of its high safety.

  In solar power generation, light energy is directly converted into electric power using a photoelectric conversion element utilizing the photovoltaic effect. Generally, a photoelectric conversion element has a structure in which a photoelectric conversion layer (light absorption layer) is sandwiched between a pair of electrodes, and light energy is converted into electric energy in the photoelectric conversion layer. The photoelectric conversion element is a silicon-based photoelectric conversion element using single-crystal / polycrystalline / amorphous Si, GaAs, CIGS (copper (Cu), indium (In), depending on the material used for the photoelectric conversion layer and the form of the element. Compound-based photoelectric conversion elements using a compound semiconductor such as gallium (Ga) and selenium (Se)), dye-sensitized photoelectric conversion elements (Gretzel cells), and the like have been proposed and put to practical use.

  However, the power generation cost when these solar cells are used is still higher than the cost when generating and transmitting power using fossil fuels, which hinders the spread of solar power generation. In addition, since heavy glass must be used for the substrate, reinforcement work is required when it is installed on a roof or the like, which has also contributed to a rise in power generation costs.

  As a technique for reducing power generation costs in solar power generation, a mixture of an electron-donating organic compound (p-type organic semiconductor) and an electron-accepting organic compound (n-type organic semiconductor) between a transparent electrode and a counter electrode A bulk heterojunction (BHJ) type photoelectric conversion element is proposed (see, for example, Non-Patent Document 1).

  Bulk heterojunction organic photoelectric conversion elements are lightweight and flexible, and are expected to be applied to various products. In addition, since the structure is relatively simple and a photoelectric conversion layer can be formed by applying a p-type organic semiconductor and an n-type organic semiconductor, it is suitable for mass production and contributes to the early diffusion of solar cells due to cost reduction. It is thought to do. More specifically, in a bulk heterojunction organic photoelectric conversion element, a metal layer or a metal oxide layer constituting electrodes (anode and cathode) can be formed by a vapor deposition method, but other layers are coated. It can be formed using a process. Therefore, it is expected that the production of the bulk heterojunction photoelectric conversion element can be performed at high speed and at low cost, and it is considered that there is a possibility that the above-mentioned problem of power generation cost can be solved. Furthermore, the bulk heterojunction organic photoelectric conversion element is different from the conventional production of silicon photoelectric conversion elements, compound photoelectric conversion elements, dye-sensitized photoelectric conversion elements, etc. Since it is not essential, it is expected that it can be formed on a cheap and lightweight plastic substrate.

  However, it cannot be said that the organic photoelectric conversion element has sufficient photoelectric conversion efficiency and durability against heat and light compared to other types of photoelectric conversion elements.

In order to improve the photoelectric conversion efficiency of the bulk heterojunction type organic photoelectric conversion element, a method of increasing the film thickness of the power generation layer can be considered in order to obtain a sufficient amount of light absorption. However, when the thickness of the power generation layer is increased, carriers such as holes or electrons generated in the power generation layer are recombined in the power generation layer before reaching the electrodes and the charge transport layer, and thus it is difficult to recover the carriers. . Therefore, the film thickness of the power generation layer cannot be increased, and there is a trade-off between the power generation layer thickness in the short circuit current density (J _SC ) and the fill factor (FF) as element performance.

  As a solution to the above problem, high mobility nanostructures are incorporated into a bulk heterojunction type photoelectric conversion layer (BHJ layer) to improve the mobility of electrons and holes for efficient charge extraction. Efforts are being made to improve device performance. Since the mobility of carriers can be improved by incorporating a nanostructure with high mobility in the BHJ layer, sufficient charge can be taken out even when the BHJ layer is thickened. It has been reported that the trade-off is eliminated (for example, Non-Patent Document 2). Among these, carbon nanotubes (CNT) are materials that have high carrier mobility and are useful as carrier paths (for example, Non-Patent Document 3). Non-Patent Document 3 reports that the addition of CNTs in the BHJ layer of an organic photoelectric conversion element improves hole transportability and increases Jsc. Further, Patent Document 1 reports a technique of providing a carrier blocking layer on the surface of a CNT added to the BHJ layer. In this technique, a fullerene derivative, bathocuproin (BCP), or the like is coated as a hole block layer around the CNT, thereby providing selectivity to the carrier transported to the CNT.

US Patent Application Publication No. 2010/030759

A. Heeger et al. , Nature Mat. , Vol. 6 (2007), p497 Chin-Yu Chang et al. , Angew. Chem. Int. Ed. vol. 50 (2011), p9386-9390 Gwang H.G. Jun et al. , CARBON. vol. 50 (2012) p40-46

  However, as a result of investigations by the present inventors, it has been found that it is difficult to achieve sufficient photoelectric conversion efficiency even with the technique described in the above document. That is, as in Non-Patent Document 2 or Non-Patent Document 3, when a nanostructure such as CNT is added in the BHJ layer, the CNTs are compared with the energy level of the highest occupied orbital (HOMO) of the p-type organic semiconductor material. Because of the built-in potential, the open circuit voltage (Voc) of the device is the lowest empty orbital (LUMO) energy level of n-type organic semiconductor materials such as fullerene and the work function of nanostructures such as CNT. It was determined that Voc decreased. In particular, many new polymer designs aiming at high efficiency are designed so that the HOMO level of the p-type organic semiconductor material becomes deeper in order to obtain a high Voc, and the decrease in Voc due to CNT is more remarkable.

  Furthermore, it is difficult to make different materials for CNT, and it is common that CNT having properties close to metal and CNT having semiconducting properties are mixed in a sample. If only semiconducting CNTs are used, the carrier transportability is improved. However, the inclusion of metallic CNTs makes it easier for carriers to recombine on the surface of the metallic CNTs, thereby improving the carrier transportability. It has been found that there is a problem that the parallel resistance (Rsh) decreases and the FF decreases as the amount of CNT added increases.

  In other words, if CNT is simply added to the BHJ layer, Jsc can be improved, but Voc and FF will decrease. Therefore, the overall improvement in photoelectric conversion efficiency is small, and the effect of adding CNT is sufficient. Was not obtained.

  On the other hand, the method described in Patent Document 1 is to coat fullerene derivatives, BCP, etc. as a hole blocking layer around CNTs. However, as a result of investigations by the present inventors, since CNT is excellent in hole transportability, the recombination of carriers is further induced when the surface of the CNT is coated with a hole blocking layer, and the Rsh is greatly reduced. It turns out that it is caused. Further, Patent Document 1 does not disclose a specific means for coating the hole blocking layer on the surface of the CNT, and it is possible to selectively around the CNT simply by mixing the materials of the CNT and the hole blocking layer. It was not possible to coat with a block layer, and it was found that the block performance of the carrier was not sufficient.

Therefore, the present invention solves the above-described problem, and even when a photoelectric conversion layer is thickened, a high _JSC and FF make both photoelectric conversion elements excellent in photoelectric conversion efficiency, and a solar cell using the same The purpose is to provide.

  The present inventors have conducted intensive research to solve the above-mentioned problems, and found that the above-mentioned problems can be solved by the following constitution, thereby completing the present invention.

  That is, the above object of the present invention is achieved by the following configuration.

  1. A photoelectric conversion element having a first electrode, a bulk heterojunction photoelectric conversion layer having a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order, wherein the photoelectric conversion layer is An organic photoelectric conversion element comprising carbon nanotubes whose surface has been modified such that the work function of the surface is greater than the work function of the carbon nanotubes themselves.

  2. 2. The organic photoelectric conversion device according to 1 above, wherein a work function of the surface of the surface-modified carbon nanotube is 0.2 eV or more larger than a work function of the carbon nanotube itself.

  3. 3. The organic photoelectric conversion device according to 1 or 2 above, wherein the surface-modified carbon nanotube is a carbon nanotube surface-modified with a dipole material having an electron-withdrawing group.

  4). 4. The organic photoelectric conversion device according to 3 above, wherein a dipole moment of the dipole material is −0.1 to −13D.

  5. The organic photoelectric conversion element according to any one of 1 to 4, wherein a HOMO level of the p-type organic semiconductor material is 5.2 eV or less.

  6). 6. The organic photoelectric conversion element according to any one of 1 to 5, wherein a difference between a HOMO level of the p-type organic semiconductor material and a work function of the surface of the modified carbon nanotube is 0.1 eV or less.

  7). The solar cell which has an organic photoelectric conversion element of any one of said 1-6.

  According to the present invention, by introducing surface-modified carbon nanotubes into the photoelectric conversion layer, the carrier transport property can be improved without causing a reduction in open circuit voltage. For this reason, in the photoelectric conversion element, a high short-circuit current density and a fill factor are compatible while maintaining a high open-circuit voltage, and the photoelectric conversion efficiency can be improved.

It is the cross-sectional schematic which represented typically the organic photoelectric element which concerns on one Embodiment of this invention. It is the elements on larger scale of the photoelectric converting layer of the organic photoelectric element which concerns on one Embodiment of this invention. It is the cross-sectional schematic which represented typically the organic photoelectric element which concerns on other one Embodiment of this invention. It is the cross-sectional schematic which represented typically the organic photoelectric element provided with the tandem type photoelectric conversion layer which concerns on other one Embodiment of this invention.

  Embodiments of the present invention will be described below. In this specification, “work function” is defined as the minimum energy required to extract one electron from the surface of a substance to the vacuum level, and generally has a large work function (deep). The material has a property that it is difficult to be oxidized, and a material having a small work function (shallow) is easily oxidized. In this specification, the work function is measured by an ultraviolet photoelectron spectrum spectrometer (UPS method). Moreover, the measuring method of the HOMO level of p-type organic-semiconductor material shall be measured with an ultraviolet photoelectron spectrum spectrometer (UPS method).

  The “dipole moment” indicates the product of the vector from the negative charge to the positive charge and the magnitude of the charge. Specifically, the vector and size can be obtained from calculation by the density functional (DFT) method.

  The present invention is a photoelectric conversion element having a first electrode, a bulk heterojunction photoelectric conversion layer having a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order, The photoelectric conversion layer is an organic photoelectric conversion element including carbon nanotubes whose surface is modified so that the work function of the surface is larger than the work function of the carbon nanotubes themselves.

  Preferably, the photoelectric conversion layer has a surface state such that the work function of the surface measured by ultraviolet photoelectron spectroscopy is 4.8 eV or deeper, more preferably 5.2 eV or deeper. Includes CNTs with adjusted position.

  In order to obtain a sufficient open-circuit voltage (Voc) in principle in an organic photoelectric conversion element, it is necessary to have a sufficient potential difference between the work function of the hole transport layer and the work function of the first electrode, that is, the cathode. preferable. In the present invention, preferably, the potential difference is 0.8 eV or more. When the potential difference is 0.8 eV or more, a practical open circuit voltage (Voc) can be obtained.

In general, a Voc greater than the potential difference between both electrodes (or both charge transport layers) cannot be obtained. Further, “a potential difference formed at the pn interface of the photoelectric conversion layer (p-type organic semiconductor material and n”). In an organic photoelectric conversion element having a p-type organic semiconductor material, a relationship of “difference between a HOMO level of a p-type organic semiconductor material and a LUMO level of an n-type organic semiconductor material) −0.3 eV ≧ open circuit voltage (V _oc )” Is obtained as a rule of thumb. Therefore, in order to develop higher Voc, it is important to deepen the HOMO level of the p-type organic semiconductor material. However, as in Non-Patent Document 2, as a carrier path in the BHJ layer, another carbon nanotube or the like is used. When the HOMO level or work function of the other semiconductor material is shallower than the HOMO level of the p-type organic semiconductor material in the BHJ layer, the Voc of the element is the other semiconductor material. It is determined by the difference between the HOMO level or work function of the material and the LUMO level of the n-type organic semiconductor material, and is smaller than the original Voc.

  Therefore, in order to obtain the original Voc obtained from the p-type organic semiconductor material and the n-type organic semiconductor material constituting the BHJ layer, the work function of the material added as a carrier path in the BHJ layer is changed to that of the p-type organic semiconductor material. It is necessary to design the same or deeper than the HOMO level. Further, since the built-in electric field strength (E) in the element is proportional to the potential difference (V) and inversely proportional to the film thickness (d), the carrier density inside the photoelectric conversion layer is substantially reduced by widening the potential difference between the electrodes. When uniform, it is preferable to widen the potential difference between the two electrodes in order to reduce the film thickness dependency and improve the conversion efficiency.

  In particular, it is considered that the carrier selectivity on the surface can be simultaneously imparted by adjusting the work function of the surface of the CNT using a dipole material. This mechanism is estimated as follows. By covering the surface of the CNT with a dipole material having an electron-withdrawing dipole moment, the vacuum level of the CNT surface can be controlled deeper than the work function of the CNT itself. By controlling this vacuum level to a level equivalent to or close to the HOMO level of the p-type organic semiconductor material, a level mismatch between the p-type organic semiconductor material and the CNT interface in the BHJ layer does not occur. Can be controlled. Thus, it is estimated that not only can the hole transport property of CNTs, which originally has a strong hole transport property, be improved, but also a block layer with respect to electrons, resulting in improved carrier selectivity. This effect is more prominent when CNT has a metal-like nature. When the block layer is not coated, both carriers are transported, and when the block layer for holes is coated as in Patent Document 1, the selectivity of the carrier is lowered, and in either case, recombination is induced. However, carrier recombination can be effectively suppressed by coating the surface with a dipole material.

  Hereinafter, the organic photoelectric device of the present invention will be described with reference to the accompanying drawings. However, the technical scope of the present invention should be determined by the description of the scope of claims, and is not limited to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

(Element structure)
FIG. 1 is a schematic cross-sectional view schematically showing an organic photoelectric conversion device according to an embodiment of the present invention. Specifically, the organic photoelectric conversion element 10 of FIG. 1 includes an anode (first electrode) 11, a hole transport layer 26, a photoelectric conversion layer 13, an electron transport layer 27, and a cathode (second electrode) on a substrate 25. Electrode) 12 is laminated in this order. Here, as shown in FIG. 2, in addition to the p-type organic semiconductor material 15 and the n-type organic semiconductor material 16, the photoelectric conversion layer 13 is made of nanometers made of carbon nanotubes controlled so as to increase the work function of the surface. A structure 14 is included. When the organic photoelectric conversion element 10 shown in FIG. 1 is operated, light is irradiated from the substrate 25 side. In the present embodiment, the anode 11 is made of a transparent electrode material (for example, ITO) so that the irradiated light reaches the photoelectric conversion layer 13. The light irradiated from the substrate 25 side reaches the photoelectric conversion layer 13 through the transparent anode 11 and the hole transport layer 26.

  In FIG. 1, light incident from the anode 11 through the substrate 25 is absorbed by the electron acceptor or the electron donor in the photoelectric conversion layer 13, electrons move from the electron donor to the electron acceptor, and holes and electrons are absorbed. Pair (charge separation state) is formed.

  When the generated electric charges have different internal electric fields, for example, when the work functions of the anode 11 and the cathode 12 are different, the potential difference between the anode 11 and the cathode 12 causes the electrons and holes to be carried to different electrodes, and a photocurrent is detected. . At this time, the nanostructure 14 made of carbon nanotubes whose surface has been modified so as to increase the work function in the photoelectric conversion layer 13 plays a role of improving hole transportability.

  The hole transport layer 26 is formed of a material having a high hole mobility, and is generated at the pn junction interface of the photoelectric conversion layer 13 and more efficiently transports holes transported by the nanostructure 14. It is responsible for transporting to 11. On the other hand, the electron transport layer 27 is made of a material having high electron mobility, and has a function of efficiently transporting electrons to the cathode 12.

  FIG. 3 is a schematic cross-sectional view schematically showing an organic photoelectric conversion element according to another embodiment of the present invention. The organic photoelectric conversion element 20 of FIG. 3 has an anode (first electrode) 11 and a cathode (second electrode) 12 disposed at opposite positions as compared to the organic photoelectric conversion element 10 of FIG. The difference is that the hole transport layer 26 and the electron transport layer 27 are disposed at opposite positions. That is, the organic photoelectric conversion element 20 in FIG. 3 includes a cathode (second electrode) 12, an electron transport layer 27, a photoelectric conversion layer 13, a hole transport layer 26, and an anode (first electrode) on a substrate 25. 11 has a configuration in which the layers are stacked in this order.

  FIG. 4 is a schematic cross-sectional view schematically illustrating an organic photoelectric conversion element including a tandem (multi-junction type) photoelectric conversion layer according to another embodiment of the present invention. The organic photoelectric conversion element 30 in FIG. 4 has a configuration in which a first cell and a second cell are connected in parallel or in series in the intermediate layer 38, and instead of the photoelectric conversion layer 13 of the organic photoelectric conversion element 10 in FIG. The first cell includes the photoelectric conversion layer 13a, and the second cell includes the photoelectric conversion layer 13b. At this time, the intermediate layer 38 becomes a charge extraction electrode when the first cell and the second cell are connected in parallel, and becomes a charge recombination electrode when they are connected in series. In the present embodiment, at least one layer of the photoelectric conversion layer 13a and the photoelectric conversion layer 13b contains a nanostructure made of CNTs controlled to increase WF in the photoelectric conversion layer. In the tandem organic photoelectric conversion element 30 shown in FIG. 4, photoelectric conversion materials (p-type organic semiconductors and n-types) having different absorption wavelengths are respectively formed in the photoelectric conversion layer 13 a of the first cell and the photoelectric conversion layer 13 b of the second cell. By using a type organic semiconductor), it becomes possible to efficiently convert light in a wider wavelength range into electricity.

[Carbon nanotubes (CNT)]
The carbon nanotube as the nanostructure is not particularly limited, and any carbon nanotube such as a single-walled carbon nanotube, a double-walled carbon nanotube, or a multi-walled carbon nanotube may be used, or two or more of these may be combined. The single-walled carbon nanotube may be a metallic carbon nanotube, a semiconducting carbon nanotube, or a mixture thereof.

  In the present invention, a carbon nanotube (CNT) as a nanostructure has a shape whose length is sufficiently longer than a diameter (thickness). Examples of the shape of the CNT include a hollow tube shape, a wire shape, and a fiber shape.

  The CNTs that can be used in the present invention are considered to function as an auxiliary to the electrodes by forming a three-dimensional carrier path network when the CNTs contact each other in the organic film. Therefore, a longer CNT is preferable because it is advantageous for forming a conductive network. As the CNT that can be used in the present invention, in order to form a long conductive path with one CNT, the average length is preferably 3 μm or more, more preferably 4 to 500 μm, and particularly preferably 5 to 300 μm. It is preferable. In addition, the relative standard deviation of the length is preferably 40% or less. On the other hand, if the length of the CNT is 500 μm or less, it can be prevented that the nanowires of the CNT are entangled to generate an aggregate, and therefore, deterioration of optical properties due to the generation of such an aggregate is suppressed. be able to. Since formation of a conductive network and aggregate formation are affected by the rigidity and diameter of the CNT, it is preferable to use one having an optimal average aspect ratio (aspect ratio = length / diameter). As a rough guide, the average aspect ratio is preferably 5 to 50,000, more preferably 10 to 10,000, and still more preferably 100 to 1,000.

  The average diameter of CNTs is preferably small from the viewpoint of transparency, while larger ones are preferable from the viewpoint of conductivity. In the present invention, the average diameter of CNT is preferably 10 to 300 nm, more preferably 20 to 200 nm, and particularly preferably 30 to 100 nm. In addition, the relative standard deviation of the diameter is preferably 20% or less. Note that the length and diameter of the CNTs are measured by high-magnification TEM observation, and more specifically, average values obtained by measuring 500 CNTs by TEM observation are adopted.

  In the present invention, the means for producing CNTs is not particularly limited, and can be synthesized using, for example, arc discharge, laser evaporation, CVD, or hydrocarbon pyrolysis. The end of the closed nanotube may be opened using a purification method such as combustion oxidation. Commercially available CNTs may also be used.

  In the present invention, the CNT is characterized by being surface-modified so that the work function of the surface is larger than the work function of the carbon nanotube itself.

  Preferably, the surface-organized carbon nanotube has a work function of 0.2 eV or more larger than the work function of the carbon nanotube itself. When the surface is modified so as to be 0.2 eV or more, the effect of the present invention can be obtained more remarkably.

  The work function of the surface of the CNT is preferably adjusted so as to be larger than the HOMO level of the p-type organic semiconductor material, and becomes larger in the range of 0.1 eV than the HOMO level of the p-type organic semiconductor material. It is further preferable that the adjustment is made as described above. When the work function of the surface of CNT is larger (deeper) than the HOMO level of the p-type organic semiconductor material, there is an effect in improving Voc. If the difference between the HOMO level of the p-type organic semiconductor material and the work function of the surface of the CNT is within 0.1 eV, the hole transport is unlikely to be hindered. Can be improved.

  The method for modifying the work function of the surface of the carbon nanotube so as to be larger than the work function of the carbon nanotube itself is not particularly limited. For example, a method of applying a dipole material having an electron-withdrawing group that can increase the work function of the surface of the carbon nanotube to the surface of the CNT can be used. Further, the work function of the surface can be increased by oxidizing the surface of the CNT using air, oxygen plasma, or acid.

As a method for oxidizing the surface of CNTs using air, for example, CNTs are oxidized by heating them to 800 to 1000 ° C. in an air stream. The oxygen plasma treatment of the CNT surface is performed, for example, by leaving the CNT in an oxygen atmosphere and irradiating the plasma. Although it does not restrict | limit especially as a plasma irradiation apparatus, For example, a glow discharge format etc. are used. The acid treatment can be performed, for example, by heating CNT in HNO ₃ , H ₂ SO ₄ , or a mixed solution thereof. Preferably, the CNT surface is oxidized by acid treatment.

  In addition, the oxidation using air, oxygen plasma, or acid on the surface of the CNT as described above may be performed on untreated CNT or on surface-modified CNT.

  There is no particular limitation on the method of applying a dipole material having a dipole moment to the surface of the CNT that can increase the work function of the surface of the carbon nanotube.

  Since CNT alone has low solubility in a solvent for forming a BHJ layer, it is known that the surface is appropriately modified with an amine or the like in order to improve the solubility in an organic solvent. As a typical example, CARBON. vol. 50 (2012) p40-46, it is possible to impart solubility to an organic solvent by modifying the surface of CNT with octadecylamine or the like. In the present invention, a dipole material having a dipole moment can be applied to the CNT surface by a synthesis scheme similar to the above.

  For example, in the case of a dipole material having NH at the terminal, by first treating the CNT with an acid such as a nitric acid / sulfuric acid mixed solution, a -COOH group is introduced on the CNT surface, and the dipole material of the dipole material is introduced into the -COOH group. An alkylamide bond is generated by reacting the terminal —NH, and a dipole material is introduced to the CNT surface. The reaction conditions of the CNT having a —COOH group introduced on the surface and the dipole material are not particularly limited, but are preferably 50 to 180 ° C., more preferably 50 to 120 ° C., and preferably 1 to 200 hours, more preferably The reaction is carried out with stirring for 1 to 120 hours.

  In addition, by using a dipole material having an adsorbing group, the dipole material can be selectively adsorbed on the CNT surface by the adsorbing group. However, since CNT has a weak interaction with the adsorbing group, the work function can be adjusted. Since the dipole material may not be sufficiently coated, it is preferable to coat the dipole material by the above synthesis.

  The surface-modified CNT as described above is preferably 0.01 to 2% by mass, more preferably 0.05 to 1% by mass, and still more preferably 0% with respect to the p-type organic semiconductor material in the photoelectric conversion layer. 0.05 to 0.5% by weight can be added. When the amount of the surface-modified CNT added is 0.01% by mass or more, the effect of improving hole transportability is high. Moreover, if it is 2 mass% or less, when the film thickness of a photoelectric converting layer is about 200-300 nm, the possibility of the leak of an element may be reduced.

[Dipole material]
In general, the amount of change in work function of a nanostructure (carbon nanotube) to which a surface modifying molecule is adsorbed is proportional to the density at which the surface modifying molecule is adsorbed and the magnitude of the dipole moment of the surface modifying molecule. Therefore, in order to construct a nanostructure having an appropriate work function, a surface modifying molecule having a dipole moment can be used as a dipole material. Although the dipole moment of the dipole material can be appropriately selected, in the present invention, since the CNT vacuum level is controlled to be deep by the electroattractive (having an electron withdrawing group) dipole material, −0. 1 to −13D is preferable, and −4 to −12D is particularly preferable.

Here, as described above, the dipole moment in the present invention is the dipole moment calculated by the density functional (DFT) method for the molecular structure adsorbed to one silver (Ag) atom via an adsorbing group on the surface modification molecule. Point to. Examples of the electron withdrawing group, a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine _{atom), - CF 3, -COOCF 3} , -SO 2 CF 3, -COCF 3, -CHO, -COOCH 3, -SO _{2 CH 3, -SO 2 NH 2} , -COCH 3, include -CN, or -NO _2. These dipole materials can be easily coated with a dipole material on the surface by reacting a dipole material having an amine end with a CNT modified with a carboxylic acid at the end. Moreover, it can also be made to adsorb | suck to the surface of CNT by having adsorption groups, such as a thiol group, a dithiocarbamate group, a xanthate group, a sulfide group, a disulfide group, on the surface.

  In order to simultaneously impart dispersibility of CNTs in an organic solvent, the dipole material is preferably a dipole material in which the alkyl chain has a C5 or higher alkyl chain. More preferably, it is a dipole material in which the alkyl chain has a C10 or higher alkyl chain.

  Specifically, examples of the dipole material include the following compounds.

In the above formula, n is an integer of 0 to 17, R is H, CH ₃ , or CH ₂ CH ₃ EA represents an electron accepting group, and two or more same symbols exist in the same compound In this case, each symbol may represent the same thing or a different thing. EA 'is bond, -Y = Z- (Y is -N =, - CH =, or -C _(CH 3) = represents, Z is = N -, = CH-, or = C _(CH 3) - Represents —OC (O) —, —CO (O) —, —C (O) —, or —SO ₂ —.

Examples of the electron accepting group represented by EA, for example, a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine _{atom), - CF 3, -BF 3} , -COOCF 3, -SO 2 CF 3, -COCF 3 , -CHO, -COOCH ₃ , -SO ₂ CH ₃ , -SO ₂ NH ₂ , -COCH ₃ , -CN or -NO ₂ , -BF ₃ , -SO ₂ F, and -COOCF ₃ . The substitution position of EA is not particularly limited, but is preferably the o position.

  Or in the above formula,

May be a structure represented by:

  Further, as the dipole material, the following compounds may be used.

In the above formulas (A) to (H), n is an integer of 0 to 3, X represents N or CH, preferably N, and X ′ independently represents —N═ or —CH═. represents preferably an -N =, Y is -N =, - CH =, or -C _(CH 3) = represents, Z is = N -, = CH-, or = C (CH ₃₎ - and EA ′ represents —OC (O) —, —CO (O) —, —C (O) —, and —SO ₂ —. In the above formulas (A) to (H), EA represents an electron-accepting group, and when two or more same symbols exist in the same compound, each symbol represents a different one even if it represents the same one. Also good.

As an electron-accepting group represented by EA, a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom), —CF ₃ , —BF ₃ , —COOCF ₃ , —SO ₂ CF ₃ , —COCF ₃ , — _{CHO, -COOCH 3, -SO 2 CH} 3, -SO 2 NH 2, -COCH 3, -CN or _{-NO 2, -BF 3, -SO 2} F, is -COOCF ₃ like. The substitution position of EA is not particularly limited, but is preferably the o position.

  In the above formula (G), each R ″ independently represents a hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms. It does not represent a hydrogen atom.

  Among the above formulas, specific examples of preferable dipole materials include compounds having the following structures.

(Photoelectric conversion layer)
The organic photoelectric conversion element 10 of this embodiment includes a photoelectric conversion layer 13 between the above-described cathode 12 and anode 11.

  The photoelectric conversion layer has a function of converting light energy into electric energy using the photovoltaic effect. The photoelectric conversion layer essentially includes a p-type organic semiconductor material and an n-type organic semiconductor material as a photoelectric conversion material, and CNTs whose surface has been modified. When light is absorbed by these photoelectric conversion materials, excitons are generated, which are separated into holes and electrons at the pn junction interface, and the holes and electrons pass through the p-type organic semiconductor material or CNT. The electrons are transported to the anode, and the electrons are transported to the cathode through the n-type organic semiconductor material.

<P-type organic semiconductor material>
Examples of the p-type organic semiconductor material used for the photoelectric conversion layer according to the present invention include various condensed polycyclic aromatic low molecular compounds and conjugated polymers.

  Examples of the condensed polycyclic aromatic low molecular weight compound include anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, thacumanthracene, bisanthene, zeslene. , Heptazethrene, pyranthrene, violanthene, isoviolanthene, cacobiphenyl, anthradithiophene, etc., porphyrin, copper phthalocyanine, tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene ( BEDTTTTF) -perchloric acid complexes, and derivatives and precursors thereof.

  Examples of the derivative having the above-mentioned condensed polycycle include WO 03/16599 pamphlet, WO 03/28125 pamphlet, US Pat. No. 6,690,029, JP 2004-107216 A. A pentacene derivative having a substituent described in JP-A-2003-136964, a pentacene precursor described in US Patent Application Publication No. 2003/136964, and the like; Amer. Chem. Soc. , Vol. 127, no. 14, p 4986, J. MoI. Amer. Chem. Soc. , Vol. 123, p9482; Amer. Chem. Soc. , Vol. 130 (2008), no. 9, acene compounds substituted with a trialkylsilylethynyl group described in p2706 and the like. Alternatively, as described in US Patent Application Publication No. 2003/136964, Japanese Patent Application Laid-Open No. 2008-16834, etc., a soluble substituent reacts and becomes insoluble by applying energy such as heat (pigment) Material) and the like.

  As the conjugated polymer, for example, a polythiophene such as poly-3-hexylthiophene (P3HT) and an oligomer thereof, or a technical group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007, P1225. Polythiophene, Nature Material, (2006) vol. 5, p328, polythiophene-thienothiophene copolymer, polythiophene-diketopyrrolopyrrole copolymer described in International Publication No. 2008/000664 pamphlet, Adv. Mater. , 2007, p4160, a polythiophene-thiazolothiazole copolymer, Nature Mat. , Vol. 6 (2007), p497 described in PCPDTBT, etc., polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, Examples thereof include polymer materials such as σ-conjugated polymers such as polysilane and polygermane.

  In addition, oligomeric materials instead of polymer materials include thiophene hexamer α-sexual thiophene α, ω-dihexyl-α-sexual thiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3 Oligomers such as -butoxypropyl) -α-sexithiophene can be preferably used.

  More preferably, it is a copolymer having an electron donating group (donor unit) and an electron withdrawing group (acceptor unit) in the main chain as a p-type conjugated polymer. More specifically, the p-type conjugated polymer has a structure in which donor units and acceptor units are alternately arranged. Thus, by arranging the donor unit and the acceptor unit alternately, the absorption region of the p-type organic semiconductor can be expanded to a long wavelength region. That is, since the p-type conjugated polymer can absorb light in a long wavelength region (for example, 700 to 1000 nm) in addition to the absorption region (for example, 400 to 700 nm) of the conventional p-type organic semiconductor, It becomes possible to efficiently absorb radiant energy over a wide range of the optical spectrum.

  The donor unit that can be included in the p-type conjugated polymer is a unit in which the LUMO level or the HOMO level is shallower than a hydrocarbon aromatic ring (benzene, naphthalene, anthracene, etc.) having the same number of π electrons. If there is, it can be used without restriction. For example, a unit including a thiophene ring, a furan ring, a pyrrole ring, a hetero 5-membered ring such as cyclopentadiene, silacyclopentadiene, and a condensed ring thereof.

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

  On the other hand, acceptor units that can be included in the p-type conjugated polymer include, for example, quinoxaline skeleton, pyrazinoquinoxaline skeleton, benzothiadiazole skeleton, benzooxadiazole skeleton, benzoselenadiazole skeleton, benzotriazole skeleton, pyrido Thiadiazole skeleton, thienopyrazine skeleton, phthalimide skeleton, 3,4-thiophenedicarboxylic acid imide skeleton, isoindigo skeleton, thienothiophene skeleton, diketopyrrolopyrrole skeleton, 4-acyl-thieno [3,4-b] thiophene skeleton, thienopyrrole Examples thereof include a dione skeleton, a thiazolothiazole skeleton, a pyrazolo [5,1-c] [1,2,4] triazole skeleton, and a dioxopyrrolothiophene skeleton. In addition, the donor unit or acceptor property contained in the p-type conjugated polymer of this embodiment may be used alone or in combination of two or more.

  Among these, Appl. Phys. Lett. Vol. 98, p043301 is preferably a material that can form a thick power generation layer with high mobility. By using a material that can form a thick power generation layer, it is possible to obtain high external quantum efficiency in all spectral regions, and because the mobility is high even when the power generation layer is thick (the built-in electric field is reduced), the fill factor is Since it does not decrease, both high external quantum efficiency and fill factor can be achieved, and a highly efficient device can be obtained.

  Specifically, the p-type organic semiconductor material is represented by the following general formula 3 or general formula 3 ':

It is preferable to have a structure represented by as a donor unit. In the above general formula 3, X ₃ represents a carbon atom, a silicon atom, or a germanium atom, and R ₁₃ and R ₁₄ each independently represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, carbon A cycloalkyl group having 3 to 20 atoms, an aryl group having 6 to 30 carbon atoms, or a heteroaryl group having 1 to 30 carbon atoms is represented. Here, R ₁₃ and R ₁₄ may be the same or different. Further, R ₁₃ and R ₁₄ in each structural unit may be the same or different. R ₁₃ and R ₁₄ are each independently more preferably a linear or branched alkyl group having 1 to 12 carbon atoms, and a linear or branched alkyl group having 1 to 8 carbon atoms. Even more preferred.

  Here, the alkyl group having 1 to 20 carbon atoms is not particularly limited. For example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, tert-butyl group, n-pentyl group, isopentyl, neopentyl, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n -Dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, 2-hexyldecyl group, And linear or branched alkyl groups such as

  The cycloalkyl group having 3 to 20 carbon atoms is not particularly limited, and examples thereof include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group, and an adamantyl group.

  The aryl group having 6 to 30 carbon atoms is not particularly limited, and examples thereof include non-condensed hydrocarbon groups such as a phenyl group, a biphenyl group, and a terphenyl group; a pentarenyl group, an indenyl group, a naphthyl group, an azulenyl group, and a heptaenyl group. Group, biphenylenyl group, fluorenyl group, acenaphthylenyl group, preadenenyl group, acenaphthenyl group, phenalenyl group, phenanthryl group, anthryl group, fluoranthenyl group, acephenanthrenyl group, aceanthrylenyl group, triphenylenyl group, pyrenyl group, Examples thereof include condensed polycyclic hydrocarbon groups such as a chrycenyl group and a naphthacenyl group.

  The heteroaryl group having 1 to 30 carbon atoms is not particularly limited, and examples thereof include pyridyl group, pyrimidyl group, pyrazinyl group, triazinyl group, furanyl group, pyrrolyl group, thiophenyl group (thienyl group), quinolyl group, and furyl. Group, piperidyl group, coumarinyl group, silafluorenyl group, benzofuranyl group, benzimidazolyl group, benzoxazolyl group, benzthiazolyl group, dibenzofuranyl group, benzothiophenyl group, dibenzothiophenyl group, indolyl group, carbazolyl group, pyrazolyl group , Imidazolyl group, oxazolyl group, isoxazolyl group, thiazolyl group, indazolyl group, benzothiazolyl group, pyridazinyl group, cinnolyl group, quinazolyl group, quinoxalyl group, phthalazinyl group, phthalazine dionyl group, phthalamidyl group, Nyl group, naphtholactamyl group, quinolonyl group, naphthalidinyl group, benzimidazolonyl group, benzoxazolonyl group, benzothiazolonyl group, benzothiazothionyl group, quinazolonyl group, quinoxalonyl group, phthalazonyl group, dioxopyrimidinyl Group, pyridonyl group, isoquinolonyl group, isoquinolinyl group, isothiazolyl group, benzisoxazolyl group, benzisothiazolyl group, indazironyl group, acridinyl group, acridonyl group, quinazoline dionyl group, quinoxaline dionyl group, benzoxazine dionyl Group, benzoxazinonyl group, naphthalimidyl group, dithienocyclopentadienyl group, dithienosylcyclopentadienyl group, dithienopyrrolyl group, benzodithiophenyl group and the like.

Further, the substituent is not particularly limited when the alkyl group, cycloalkyl group, aryl group, or heteroaryl group has a substituent. For example, alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, acyl group, alkoxycarbonyl group, (alkyl) amino group, alkoxy group, cycloalkyloxy group, aryloxy group, aryloxycarbonyl group, an alkyl ester group, an ester group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a silyl group (-SiH _3), a sulfonyl group, Sulfinyl group, ureido group, phosphoric acid amide group, halogen atom, hydroxyl group (—OH), mercapto group (—SH), cyano group (—CN), sulfo group (—SO ₃ H), carboxyl group (—COOH) , Nitro group ( -NO _2), a hydroxamic acid group (-C (= O) -NH- OH), a sulfino group (-S (= O) OH) , a hydrazino group (-NHNH _2), such as an imino group can be exemplified. The above substituent is not the same as R ₁₃ or R ₁₄ to be substituted. For example, when R ₁₃ or R ₁₄ is an alkyl group, it is not further substituted with an alkyl group.

  In the general formula 3, a compound in which X3 is silicon is preferable because synthesis is easy and a crystal having high mobility and high mobility can be easily obtained.

In the general formula 3 ′, R ₁₂ ′ and R ₁₅ ′ each independently represent a hydrogen atom, a halogen atom, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. Here, since the definition of each substituent representing R ₁₂ ′ and R ₁₅ ′ is the same as that in the above general formula 3, description thereof is omitted here. Preferably, R ₁₂ and R ₁₅ are hydrogen atoms.

R ₁₃ ′ and R ₁₄ ′ are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms. A substituted or unsubstituted alkoxy group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, or a substituted or unsubstituted carbon group having 1 to 30 carbon atoms Represents a heteroaryl group. Here, among the substituents representing R ₁₃ ′ and R ₁₄ ′, the alkoxy group having 1 to 24 carbon atoms is not particularly limited, and examples thereof include a methoxy group, an ethoxy group, an isopropoxy group, and a tert group. -Butoxy group, n-octyloxy group, n-decyloxy group, n-hexadecyloxy group, 2-ethylhexyloxy group, 2-hexyldecyloxy group and the like. The definition of other substituents is the same as in the above general formula 3. Preferably, R ₁₃ ′ and R ₁₄ ′ each independently represent a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 30 carbon atoms. Represents a group.

  The molecular weight of the p-type conjugated polymer is not particularly limited, but the number average molecular weight is preferably 5,000 to 500,000, more preferably 10,000 to 100,000, and further preferably 15,000 to 50,000. When the number average molecular weight is 5000 or more, the effect of improving the fill factor becomes more remarkable. On the other hand, when the number average molecular weight is 500,000 or less, the solubility of the p-type conjugated polymer is improved, so that productivity can be increased. In addition, in this specification, the value measured by gel permeation chromatography (GPC) is employ | adopted for a number average molecular weight.

  In addition, although the photoelectric converting layer in this invention essentially contains the p-type conjugated polymer mentioned above, it may contain other p-type organic semiconductor materials. Examples of such other p-type organic semiconductor materials include triarylamine compounds, benzidine compounds, pyrazoline compounds, styrylamine compounds, hydrazone compounds, triphenylmethane compounds, carbazole compounds, polysilane compounds, thiophene compounds, phthalocyanine compounds, Cyanine compounds, merocyanine compounds, oxonol compounds, polyamine compounds, indole compounds, pyrrole compounds, pyrazole compounds, polyarylene compounds, condensed aromatic carbocyclic compounds (naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, Fluoranthene derivatives) and metal complexes having a nitrogen-containing heterocyclic compound as a ligand. However, from the viewpoint of remarkably expressing the effects of the present invention, the mass ratio of the p-type conjugated polymer in the p-type organic semiconductor material contained in the photoelectric conversion layer is preferably 5% by mass or more, More preferably, it is 10 mass% or more, More preferably, it is 50 mass% or more, Especially preferably, it is 90 mass% or more, Most preferably, it is 100 mass%.

  In the present invention, the band gap of the p-type organic semiconductor material contained in the photoelectric conversion layer is preferably 1.8 eV or less, and more preferably 1.6 to 1.1 eV. When the band gap is 1.8 eV or less, sunlight can be widely absorbed. On the other hand, when the band gap is 1.1 eV or more, the open circuit voltage Voc (V) is easily generated, and the conversion efficiency can be improved. In addition, the HOMO level of the p-type organic semiconductor material according to the present invention is more preferably larger than 5.2 eV. When the HOMO level of the p-type organic semiconductor material is larger than 5.2 eV, the effect of the present invention can be obtained more remarkably. In this embodiment, the p-type organic semiconductor material may be used alone or in combination of two or more.

<N-type organic semiconductor materials>
The n-type organic semiconductor material used for the photoelectric conversion layer of this embodiment is not particularly limited as long as it is an acceptor (electron-accepting) organic compound, and materials that can be used in this technical field can be appropriately employed. . Examples of such compounds include fullerenes, carbon nanotubes, octaazaporphyrins, or perfluoro compounds in which hydrogen atoms of the p-type organic semiconductor material are substituted with fluorine atoms (for example, perfluoropentacene and perfluorophthalocyanine). ), Aromatic compounds such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide, and polymer compounds containing imidized compounds thereof as skeletons. .

  Of these, fullerenes, carbon nanotubes, or derivatives thereof are preferably used from the viewpoint that charge separation can be efficiently performed with a p-type organic semiconductor material at high speed (up to 50 fs). More specifically, fullerene C60, fullerene C70, fullerene C76, fullerene C78, fullerene C84, fullerene C240, fullerene C540, mixed fullerene, fullerene nanotube, multi-walled carbon nanotube, single-walled carbon nanotube, carbon nanohorn (conical type), etc. , And some of these are hydrogen atoms, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, iodine atoms), substituted or unsubstituted alkyl groups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, And a fullerene derivative substituted with a cycloalkyl group, a silyl group, an ether group, a thioether group, an amino group, or the like.

  In particular, [6,6] -phenyl C61-butyric acid methyl ester (abbreviation PCBM or PC61BM), [6,6] -phenyl C61-butyric acid-nbutyl ester (PCBnB), [6,6] -phenyl C61-butyric acid-isobutyl ester (PCBiB), [6,6] -phenyl C61-butyric acid-n-hexyl ester (PCBH), [6,6] -phenyl C71-butyric acid methyl ester (abbreviation PC71BM) Adv. Mater. , Vol. 20 (2008), p2116, aminated fullerene described in JP-A 2006-199674, metallocene fullerene described in JP-A 2008-130889, US Pat. No. 7,329,709 It is preferable to use a fullerene derivative whose solubility is improved by a substituent, such as fullerene having a cyclic ether group described in the specification. In this embodiment, the n-type organic semiconductor material may be used alone or in combination of two or more.

  The junction form of the p-type organic semiconductor and the n-type organic semiconductor in the photoelectric conversion layer of this embodiment is a bulk heterojunction. In a planar heterojunction, a p-type organic semiconductor layer including a p-type organic semiconductor and an n-type organic semiconductor layer including an n-type organic semiconductor are stacked, and a surface where these two layers contact is a pn junction interface. A bulk heterojunction is formed by applying a mixture of a p-type organic semiconductor and an n-type organic semiconductor. In this single layer, a domain of the p-type organic semiconductor and a domain of the n-type organic semiconductor are formed. Takes a microphase separation structure. Therefore, in a bulk heterojunction, as compared with a planar heterojunction, many pn junction interfaces exist over the entire layer. Therefore, most of the excitons generated by light absorption can reach the pn junction interface, and the efficiency leading to charge separation can be increased.

  In the present invention, the mixing ratio of the p-type organic semiconductor material and the n-type organic semiconductor material contained in the photoelectric conversion layer is preferably in the range of 2: 8 to 8: 2, more preferably 3: 7 to 7 in terms of mass ratio. : 3 range. Moreover, the film thickness of a photoelectric converting layer becomes like this. Preferably it is 50-400 nm, More preferably, it is 80-300 nm.

  Further, an inorganic p-type semiconductor material and an n-type semiconductor material may be included as necessary.

  Furthermore, the photoelectric conversion element of the present invention may include two or more photoelectric conversion layers as necessary.

<Hole transport layer>
The organic photoelectric conversion element of this embodiment preferably includes a hole transport layer as an essential component. The hole transport layer has a function of transporting holes and a property of extremely small ability to transport electrons (for example, 1/10 or less of the mobility of holes). The hole transport layer is provided between the photoelectric conversion layer and the anode and prevents recombination of electrons and holes by blocking the movement of electrons while transporting holes to the anode. Can do. Therefore, in this specification, a positive hole injection layer, an electronic block layer, etc. are also included in the concept of a positive hole transport layer.

  The hole transport material used for the hole transport layer is not particularly limited, and any material that can be used in this technical field can be appropriately employed. For example, a conductive polymer, a low molecular organic semiconductor, a metal oxide, and the like. Can be preferably used.

  The conductive polymer preferably used in the present invention is not particularly limited, but preferably comprises a π-conjugated polymer and a polyanion. Such a polymer can be easily produced by subjecting a precursor monomer forming a π-conjugated polymer to chemical oxidative polymerization in the presence of an appropriate oxidizing agent, an oxidation catalyst, and a polyanion described later.

  Examples of the π-conjugated polymer that can be used in the present invention include polythiophenes (including basic polythiophenes, the same applies hereinafter), polypyrroles, polyindoles, polycarbazoles, polyanilines, polyacetylenes, polyfurans, and polyparaffins. A chain conductive polymer of phenylene vinylenes, polyazulenes, polyparaphenylenes, polyparaphenylene sulfides, polyisothianaphthenes, polythiazyl compounds can be used. Of these, polythiophenes and polyanilines are preferable from the viewpoints of conductivity, transparency, stability, and the like. Furthermore, polyethylenedioxythiophenes are preferable.

  The polyanion preferably used in the present invention is not particularly limited, but it is more preferable to have a sulfo group as the anionic group. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid ethyl sulfonic acid, polyacrylic acid butyl sulfonic acid, poly-2-acrylamido-2-methylpropane sulfonic acid, polyisoprene sulfone. An acid etc. are mentioned. These homopolymers may be sufficient and 2 or more types of copolymers may be sufficient.

  Moreover, the polyanion which has a fluorine (F) in a compound may be sufficient. Specifically, Nafion (made by Dupont) containing a perfluorosulfonic acid group, Flemion (made by Asahi Glass Co., Ltd.) made of perfluoro vinyl ether containing a carboxylic acid group, and the like can be mentioned.

  As the conductive polymer, known materials and commercially available materials can be preferably used. For example, PEDOT: PSS such as trade name Clevios (registered trademark) -P manufactured by Heraeus Co., Ltd., and fluorine-based polyanions (Nafion ( Registered trademark)), or a fluorine-based polyanion-added structure as disclosed in JP-A-2006-225658, polythienothiophenes described in European Patent No. 1647566, and sulfonated polythiophene described in JP-A-2010-206146 , Polyaniline and its doping materials, cyan compounds described in WO 2006/019270 pamphlet, etc., Aldrich as PEDOT-PASS 483095, 560598, Nagase Chemtex from Denatron (registered trademark) It is commercially available as Leeds. Polyaniline is commercially available from Nissan Chemical as the ORMECON (registered trademark) series. In the present invention, such an agent can also be preferably used.

  Also, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives Further, stilbene derivatives, silazane derivatives, aniline copolymers, conductive polymer oligomers, particularly thiophene oligomers, and the like can also be used.

  In addition to these, porphyrin compounds, aromatic tertiary amine compounds, styrylamine compounds, and the like can be used, and among these, aromatic tertiary amine compounds are preferably used. In some cases, the hole transport layer may be formed using an inorganic compound such as p-type-Si, p-type-SiC, nickel oxide, molybdenum oxide, vanadium oxide, or tungsten oxide.

  Further, a polymer material in which a structural unit contained in the above compound is introduced into a polymer chain, or a polymer material having the above compound as a polymer main chain can also be used as a hole transport material. JP-A-11-251067, J. Org. Huang et. al. , Applied Physics Letters, 80 (2002), p. A hole transport material made of a p-type organic semiconductor compound as described in 139 can also be used. Furthermore, a hole transport material with high p property doped with impurities can be used. For example, JP-A-4-297076, JP-A-2000-196140, JP-A-2001-102175, J. Pat. Appl. Phys. , 95, 5773 (2004), Appl. Phys. Lett. , 98, 073311 (2011), and the like.

Furthermore, examples of the organic semiconductor material include a metal complex of an 8-quinolinol derivative, a phthalocyanine derivative, and a polyfluorene derivative. Among these, the metal complex of the 8-quinolinol derivative is not particularly limited, and examples thereof include tris (8-quinolinol) aluminum (Alq ₃ ), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,5). 7-dibromo-8-quinolinol) aluminum, tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and their metals Examples include metal complexes in which the central metal of the complex is replaced with In, Mg, Cu, Ca, Sn, Ga, or Pb. In addition, the phthalocyanine derivative is not particularly limited, but, for example, one in which the central metal of phthalocyanine contains Cu, Sn, Si, Zn, Al, or the like. In addition, those having a side chain structure covalently or coordinately bonded to these central metals. Examples thereof include phthalocyanine chloroaluminum, phthalocyanine alkylsilane, metal-free and metal phthalocyanine, or those having a terminal substituted with an alkyl group, a sulfonic acid group, a halogen group, or the like. The polyfluorene derivative is not particularly limited, and examples thereof include polydioctylfluorene-butylphenyldiphenylamine (commonly referred to as TFB) described in APPLIED PHYSICS LETTERS 96, 063303 2010, FIG. 4a and FIG. Examples include the fluorene derivative described in 4b.

  In addition, these hole transport materials may be used individually by 1 type, and may use together or dope 2 or more types. It is also possible to form a hole transport layer by laminating two or more layers made of each material.

  The thickness of the hole transport layer made of such a conductive polymer or organic semiconductor compound is not particularly limited, but is usually 1 to 2000 nm. From the viewpoint of further improving the leak prevention effect, the thickness is preferably 5 nm or more. Further, from the viewpoint of maintaining high transmittance and low resistance, the thickness is preferably 1000 nm or less, and more preferably 200 nm or less.

In general, the conductivity of the hole transport layer is preferably as high as possible. However, if the conductivity is too high, the ability to prevent electrons from moving may be reduced, and rectification may be reduced. Therefore, the conductivity of the hole transport layer is preferably 10 ⁻⁵ to 1 S / cm, and more preferably 10 ⁻⁴ to 10 ⁻² S / cm.

  As a hole transport layer which can be preferably used in the present invention, a form mainly composed mainly of metal oxide can also be used. Here, the “main component” means that the proportion of the metal oxide in the total amount of 100 mass% of the constituent materials of the hole transport layer is 50 mass% or more. However, the ratio of the metal material to the total amount of 100% by mass of the constituent materials of the metal oxide layer is preferably 60% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Yes, most preferably 100% by weight.

Metal oxides used for the metal oxide layer (including some nonmetallic materials) include molybdenum (Mo), vanadium (V), tungsten (W), chromium (Cr), 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 lanthanum (La) to lutetium (Lu) Oxides of rare earth elements and the like that. Among these, metal oxides such as molybdenum trioxide (MoO ₃ ), nickel oxide (NiO), tungsten trioxide (WO ₃ ), and vanadium pentoxide (V ₂ O ₅ ) are used from the viewpoint of excellent hole transport ability. In particular, molybdenum trioxide, tungsten trioxide, and divanadium pentoxide are particularly preferable. These inorganic oxides may be used alone or in combination of two or more or may be used by doping the above-described conductive polymer or organic semiconductor material.

  The thickness of the hole transport layer made of a metal oxide is not particularly limited, but is preferably about 3 to 20 nm, and more preferably about 5 to 15 nm, from the viewpoint of photoelectric conversion efficiency and durability.

  The hole transport layer can be formed by using a general film forming method, for example, vacuum deposition method, heating vacuum deposition method, electron beam deposition method, laser beam deposition method, sputtering method, CVD method, atmospheric pressure plasma method, etc. A wet process such as a dry process, a coating method, a plating method, or an electric field forming method can be used. Among the coating methods, a direct patterning method using a printing technique, for example, an ink jet printing method can be preferably used.

  In addition, the hole transport layer material that can be used in the present invention has an energy level for transporting holes (mainly coincident with the work function and the HOMO level) in the range of 4.8 eV to 6.5 eV. Is preferred. More preferably, it is 5.0 eV-6.0 eV, Most preferably, it is 5.0 eV-5.7 eV. If it is larger than 4.8 eV, a sufficient open circuit voltage (Voc) of the element can be obtained, and if it is 6.5 eV or less, it can be said that the stability of the element is sufficient.

<Electron transport layer>
The organic photoelectric conversion element of the present invention preferably includes an electron transport layer. The electron transport layer is a layer that is located between the cathode and the photoelectric conversion layer and plays a role of more efficiently transferring electrons between the photoelectric conversion layer and the electrode. The electron transport layer has a property of transporting electrons and having a remarkably small ability to transport holes. The electron transport layer is provided between the photoelectric conversion layer and the cathode, and prevents the recombination of electrons and holes by blocking the movement of holes while transporting electrons to the cathode. it can. Therefore, in this specification, an electron injection layer, a hole block layer, an exciton block layer, and the like are also included in the concept of the electron transport layer.

  There is no restriction | limiting in particular in the electron transport material used for an electron carrying layer, The material which can be used in this technical field can be employ | adopted suitably. Examples include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives, and the like. In addition, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron-withdrawing group can also be used as an electron transport material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

In addition, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq ₃ ), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) Aluminum, tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and the central metals of these metal complexes are In, Mg A metal complex substituted with Cu, Ca, Sn, Ga or Pb can also be used as an electron transporting material. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transporting material. As with the hole transport layer described above, an inorganic semiconductor such as n-type-Si or n-type-SiC, or an inorganic oxide having n-type conductivity (such as titanium oxide or zinc oxide) should be used as an electron transport material. Can do.

  A material species that forms an interface dipole by bonding a dipole material to an electrode and improves charge extraction, for example, 3- (2-aminoethyl) aminopropyltrimethoxy described in WO2008 / 134492 Silane (AEAP-TMOS) etc. can be mentioned as a material of an electron carrying layer.

  Further, as the electron transport layer, an electron transport layer having a high n property doped with impurities can be used. Examples thereof include JP-A-4-297076, JP-A-10-270172, JP-A-2000-196140, JP-A-2001-102175, J. Pat. Appl. Phys. 95, 5773 (2004), and the like.

  Specific examples include N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) and 4,4′-bis [N- (naphthyl)- Aromatic diamine compounds such as N-phenyl-amino] biphenyl (α-NPD) and derivatives thereof, oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, polyarylalkane, butadiene, 4 , 4 ', 4 "-tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA), porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine, titanium phthalocyanine oxide, etc. , Triazole derivatives, oxa Use of zazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, annealed amine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, silazane derivatives, etc. In the polymer material, polymers such as phenylene vinylene, fluorene, carbazole, indole, pyrene, pyrrole, picoline, thiophene, acetylene, diacetylene, and derivatives thereof can be preferably used.

  The thickness of the electron transport layer is not particularly limited, but is usually 1 to 2000 nm. From the viewpoint of further improving the leak prevention effect, the thickness is preferably 5 nm or more. Further, from the viewpoint of maintaining high transmittance and low resistance, the thickness is preferably 1000 nm or less, more preferably 200 nm or less, and further preferably 50 nm or less.

<Charge recombination layer; intermediate electrode>
In a tandem (multi-junction) organic photoelectric conversion element having two or more photoelectric conversion layers as shown in FIG. 4, a charge recombination layer (intermediate electrode) is formed between the photoelectric conversion layers.

  The material used for the charge recombination layer (intermediate electrode) is not particularly limited as long as it is a material having both conductivity and translucency. Examples of the electrode material described above include ITO, AZO, FTO, and titanium oxide. Transparent metal oxides, metals such as Ag, Al, and Au, carbon materials such as carbon nanoparticles and carbon nanowires, conductive polymers such as PEDOT: PSS, polyaniline, and the like can be used. These materials may be used alone or in combination of two or more. It is also possible to form a charge recombination layer by laminating two or more layers made of each material. In addition, the hole transport layer and the electron transport layer described above also have a combination that works as an intermediate electrode (charge recombination layer) by stacking them in an appropriate combination. With such a configuration, the charge recombination layer (intermediate layer) Electrode) It is preferable because the step of forming one layer can be omitted.

The electric conductivity of the charge recombination layer is preferably high from the viewpoint of obtaining high conversion efficiency. Specifically, it is preferably 5 to 50,000 S / cm, and preferably 100 to 10,000 S / cm. Is more preferable. The thickness of the charge recombination layer is not particularly limited, but is preferably 1 to 1000 nm, and preferably 5 to 50 nm. By setting the thickness to 1 nm or more, the film surface can be smoothed. On the other hand, by setting the thickness to 1000 nm or less, it is possible to reduce the decrease in the short-circuit current density J _sc (mA / cm ² ).

<Board>
The organic photoelectric conversion element of the present invention may include a substrate as necessary. The substrate has a role as a member to be coated with a coating solution when the electrode is formed by a coating method.

  When light that is photoelectrically converted enters from the substrate side, the substrate is preferably a member that can transmit the light that is photoelectrically converted, that is, a member that is transparent to the wavelength of the light to be photoelectrically converted. As the substrate, for example, a glass substrate, a resin substrate and the like are preferably mentioned, but it is desirable to use a transparent resin film from the viewpoint of light weight and flexibility.

  There is no restriction | limiting in particular in the transparent resin film which can be preferably used as a transparent substrate by this invention, The material, a shape, a structure, thickness, etc. can be suitably selected from well-known things. For example, polyolefins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester resin film such as modified polyester, polyethylene (PE) resin film, polypropylene (PP) resin film, polystyrene resin film, cyclic olefin resin, etc. Resin films, vinyl resin films such as polyvinyl chloride and polyvinylidene chloride, polyether ether ketone (PEEK) resin films, polysulfone (PSF) resin films, polyether sulfone (PES) resin films, polycarbonate (PC) resin films , Polyamide resin film, polyimide resin film, acrylic resin film, triacetyl cellulose (TAC) resin film, and the like. If the resin film transmittance of 80% or more in from zero to eight hundred nanomolar), can be preferably applied to a transparent resin film according to the present invention. Among these, from the viewpoint of transparency, heat resistance, ease of handling, strength and cost, it is preferably a biaxially stretched polyethylene terephthalate film, a biaxially stretched polyethylene naphthalate film, a polyethersulfone film, or a polycarbonate film. More preferred are a stretched polyethylene terephthalate film and a biaxially stretched polyethylene naphthalate film.

  The transparent substrate used in the present invention can be subjected to a surface treatment or an easy adhesion layer in order to ensure the wettability and adhesiveness of the coating solution. A conventionally well-known technique can be used about a surface treatment or an easily bonding layer. For example, the surface treatment includes surface activation treatment such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and laser treatment. Examples of the easy adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer.

  For the purpose of suppressing the permeation of oxygen and water vapor, a barrier coat layer may be formed in advance on the transparent substrate, or a hard coat layer may be formed in advance on the opposite side to which the transparent conductive layer is transferred. Good.

<Other layers>
As the configuration of the organic photoelectric conversion element of the present invention, in addition to the above-described members (each layer), various intermediate layers may be included in the element for the purpose of improving photoelectric conversion efficiency and improving the lifetime of the element. Good.

  Examples of the intermediate layer include an exciton block layer, a UV absorption layer, a light reflection layer, a wavelength conversion layer, and a smoothing layer. Further, a layer such as a silane coupling agent may be provided in order to make the metal oxide fine particles unevenly distributed in the upper layer more stable. Further, a metal oxide layer may be laminated adjacent to the photoelectric conversion layer of the present invention.

  Moreover, the organic photoelectric conversion element of this invention may have various optical function layers for the purpose of more efficient light reception of sunlight. Examples of the optical functional layer include a light condensing layer such as an antireflection film and a microlens array, and a light diffusion layer that can scatter light reflected by the cathode and enter the power generation layer again.

  Various known antireflection layers can be provided as the antireflection layer. For example, when the transparent resin film is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy adhesion layer adjacent to the film is 1.57. It is more preferable to set it to ˜1.63 because the interface reflection between the film substrate and the easy adhesion layer can be reduced and the transmittance can be improved. The method for adjusting the refractive index can be carried out by appropriately adjusting the ratio of the oxide sol having a relatively high refractive index such as tin oxide sol or cerium oxide sol and the binder resin. The easy adhesion layer may be a single layer, but may be composed of two or more layers in order to improve adhesion.

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

  As an example of the microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are two-dimensionally arranged on the light extraction side of the substrate. One side is preferably 10 to 100 μm. If it becomes smaller than this, the effect of diffraction will generate | occur | produce and color, and if too large, thickness will become thick and is not preferable.

  Examples of the light scattering layer include various antiglare layers, layers in which nanoparticles or nanowires such as metals or various inorganic oxides are dispersed in a colorless and transparent polymer, and the like.

<Method for producing organic photoelectric conversion element>
There is no restriction | limiting in particular in the manufacturing method of the organic photoelectric conversion element of the above-mentioned this form, It can manufacture by referring a conventionally well-known method suitably. Hereinafter, the manufacturing method of the organic photoelectric conversion element shown in FIG. 1 will be described as an example, and a preferable manufacturing method of the organic photoelectric conversion element of this embodiment will be described. However, each process in the manufacturing method can be applied not only to the organic photoelectric conversion element of FIG. 1 but also to the organic photoelectric conversion element shown in FIG. 3 and the tandem type manufacturing as shown in FIG.

  The method for producing an organic photoelectric conversion element of the present embodiment includes a step of forming a cathode as a first electrode, and a surface-modified carbon containing a p-type organic semiconductor material and an n-type organic semiconductor material on the cathode. Forming a photoelectric conversion layer having nanotubes, and forming an anode as a second electrode on the photoelectric conversion layer. Hereinafter, each process of the manufacturing method of the organic photoelectric conversion element of this form is demonstrated in detail.

  In the manufacturing method of this embodiment (one embodiment of FIG. 1), first, a substrate is prepared, and a cathode is formed on the substrate. In addition, you may perform the process of forming an auxiliary electrode by a transparent conductive film etc. as needed before the process of forming a cathode. The method of forming the cathode is not particularly limited, but it is easy to operate and can be produced on a roll-to-roll basis using a device such as a die coater. Preferably, the method is a method of applying and drying. In addition, a commercially available thin film electrode material may be used as it is.

  After forming the cathode by the above method, an electron transport layer may be formed on the cathode as necessary. The means for forming the electron transport layer may be either a dry process such as a vapor deposition method or a wet process such as a solution coating method, but from the viewpoint of ease of film formation, a solution coating method is preferred. In the case of forming an electron transport layer using a solution coating method, a solution obtained by dissolving and dispersing the above-described electron transport material in a suitable solvent is coated on the cathode using a suitable coating method and dried. That's fine. The coating methods used for the solution coating method include cast method, spin coating method, blade coating method, wire bar coating method, gravure coating method, spray coating method, dipping (dipping) coating method, bead coating method, air knife coating method. Ordinary methods such as curtain coating method, inkjet method, screen printing method, letterpress printing method, intaglio printing method, offset printing method, flexographic printing method, Langmuir-Blodgett method (LB method), etc. Can do. Among these, it is particularly preferable to use a spin coating method or a blade coating method because the film can be easily formed.

  In addition, although the solid content concentration of the solution used for the coating method may vary depending on the coating method and the film thickness, it is preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass.

  The temperature of the coating solution and / or the coating surface during coating is not particularly limited, but is preferably 30 to 180 ° C. from the viewpoint of preventing precipitation and unevenness due to temperature fluctuations during coating and drying. Preferably it is 50-160 degreeC. Furthermore, there is no restriction | limiting in particular also about the specific form of drying, A conventionally well-known knowledge can be referred suitably. An example of drying (heat treatment) conditions is exemplified by conditions of about 90 to 180 ° C. and about 5 to 90 minutes. Examples of the apparatus used for drying include a hot plate, hot air drying, an infrared heater, a microwave, and a vacuum dryer. Of course, other drying apparatuses can be used.

  Next, a photoelectric conversion layer including a p-type organic semiconductor material, an n-type organic semiconductor material, and a surface-modified carbon nanotube is formed on the cathode or the electron transport layer formed as described above. There are no particular restrictions on the specific method for forming the photoelectric conversion layer, but preferably, p-type organic semiconductor material and n-type organic semiconductor material, and surface-modified carbon nanotubes, respectively, or in a lump are appropriately used. A solution dissolved and dispersed in a suitable solvent may be applied on the cathode using an appropriate application method (the specific form is as described above) and dried. After that, it is preferable to perform heating in order to cause removal of residual solvent, moisture, gas, and improvement of mobility and absorption absorption by crystallization of the semiconductor material. When annealing is performed at a predetermined temperature during the manufacturing process, a part of the particles is microscopically aggregated or crystallized and the photoelectric conversion layer can have an appropriate phase separation structure. As a result, the mobility of holes and electrons (carriers) in the photoelectric conversion layer is improved, and high efficiency can be obtained. In this way, the p-type organic semiconductor and the n-type organic semiconductor are uniformly mixed, and a bulk heterojunction organic photoelectric conversion element can be obtained.

  On the other hand, in the case of forming a photoelectric conversion layer (for example, a pin structure) composed of a plurality of layers having different mixing ratios of the p-type organic semiconductor material and the n-type organic semiconductor material, after applying one layer, It is possible to form the layer by insolubilizing (pigmenting) the layer and then applying another layer.

  The step of forming the photoelectric conversion layer is preferably performed in a glove box under a nitrogen atmosphere so as not to be exposed to oxygen or moisture. Thus, by performing in a nitrogen atmosphere, it is possible to prevent the p-type organic semiconductor material from being deteriorated by oxygen or moisture in the air, and to increase the durability of the element.

  Next, a hole transport layer is formed on the photoelectric conversion layer. The hole transport layer is formed using a vapor deposition method or a solution coating method, preferably a vapor deposition method (for example, a vacuum vapor deposition method). In addition, it is preferable to perform the process of forming the said positive hole transport layer within the glove box of nitrogen atmosphere similarly to the process of forming the said photoelectric converting layer. As described above, by performing in a nitrogen atmosphere, the hole transport layer can be prevented from being deteriorated by oxygen or moisture in the air, and the durability of the element can be improved.

  Thereafter, an anode as a second electrode is formed on the hole transport layer formed as described above. The means for forming the anode is not particularly limited and may be either a vapor deposition method or a solution coating method, but a vapor deposition method (for example, a vacuum vapor deposition method) is preferably used. In addition, it is preferable to perform the process of forming the said anode in the glove box in nitrogen atmosphere similarly to the process of forming the said photoelectric converting layer.

  Furthermore, when layers other than the various layers described above are included, a step for forming these layers can be appropriately added by using a solution coating method, a vapor deposition method, or the like.

<Patterning>
The electrodes (cathode / anode), photoelectric conversion layer, hole transport layer, electron transport layer, and the like can be patterned as necessary. The patterning method is not particularly limited, and a known method can be appropriately applied. For example, when patterning soluble materials used in bulk heterojunction type photoelectric conversion layers, hole transport layers, electron transport layers, etc., only unnecessary portions may be wiped after the entire surface of die coating, dip coating, etc. Alternatively, patterning may be performed by ablation using a carbonic acid laser or the like after film formation, by direct scraping with a scriber, or by direct patterning at the time of coating using a method such as an inkjet method or screen printing. . On the other hand, in the case of insoluble materials used in electrodes, etc., vacuum deposition method, vacuum sputtering method, plasma CVD method, screen printing method using ink in which fine particles of electrode material are dispersed, gravure printing method, ink jet method, etc. Various printing methods, and known methods such as etching or lift-off of the deposited film can be used. Alternatively, the pattern may be formed by transferring a pattern formed on another substrate.

<Sealing>
Moreover, the organic photoelectric conversion element of this embodiment can be sealed as necessary in order to prevent deterioration due to oxygen, moisture, and the like in the environment. There is no restriction | limiting in particular in the method of sealing, It can carry out by the well-known method used with an organic photoelectric conversion element, an organic electroluminescent element, etc. For example, (1) a method of sealing by bonding a cap made of aluminum or glass with an adhesive; (2) a plastic film on which a gas barrier layer such as aluminum, silicon oxide, aluminum oxide or the like is formed and organic photoelectric conversion (3) A method of spin-coating an organic polymer material (polyvinyl alcohol, etc.) having a high gas barrier property; (4) An inorganic thin film (silicon oxide, aluminum oxide, etc.) having a high gas barrier property Alternatively, a method of depositing an organic film (parylene or the like) under vacuum; and (5) a method of laminating these in a composite manner may be mentioned.

  Furthermore, the organic photoelectric conversion element of this embodiment may have a configuration in which the entire element is sealed with two substrates with a barrier from the viewpoint of improving energy conversion efficiency and element lifetime, and preferably includes a moisture getter, an oxygen getter, and the like. It is more preferable that the configuration is as described above.

<Uses of organic photoelectric conversion elements>
According to the other form of this invention, the solar cell which has the organic photoelectric conversion element which concerns on the above-mentioned embodiment, and the organic photoelectric conversion element obtained by the said manufacturing method is provided. Since the organic photoelectric conversion element of this form has the outstanding photoelectric conversion efficiency and durability, it can be used suitably for the solar cell which uses this as an electric power generation element.

  Moreover, according to the further another form of this invention, the optical sensor array by which the organic photoelectric conversion element mentioned above is arranged in the array form is provided. That is, the organic photoelectric conversion element of this embodiment can also be used as an optical sensor array that converts an image projected on the optical sensor array into an electrical signal using the photoelectric conversion function.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

[P-type organic semiconductor materials]
The poly-3-hexylthiophene (P3HT) and benzodithiophene-dioxopyrrolothiophene copolymer (PBDTDPT2) used in the following examples and comparative examples were synthesized according to a known synthesis method or commercially available. Using.

  As a p-type organic semiconductor material, a benzodithiophene-dioxopyrrolothiophene copolymer (PBDTDPT2) represented by the following chemical formula is used in Chem. Commun. , 2010, 46, 4997-4999, and synthesized. The number average molecular weight of the obtained PBDTDP2 was 50,000.

  The HOMO level of the p-type organic semiconductor material was measured by the UPS method (ESCALab200R and UPS-1 manufactured by Vacuum Generators).

<Preparation of surface-modified CNT>
Dipole materials and precursors thereof used in the following Examples and Comparative Examples were synthesized according to a known synthesis method or commercially available. The structures of the dipole materials A to C used in this example are shown below.

  Octadecylamine (ODA) -modified CNT (1) is obtained from CARBON.RTM. Using carbon nanotubes (average diameter: 1.0 ± 0.3 nm, length: 400-2300 nm, aspect ratio:> 1000) manufactured by Aldrich. vol. 50 (2012) p40-46.

Specifically, 500 mg of purified CNTs was placed in a solution in which sulfuric acid and nitric acid were mixed at a volume ratio of 1: 3, and subjected to ultrasonic treatment for 1 hour to introduce —COOH groups on the CNT surface. Thereafter, 100 mg of CNT was taken out, introduced into a mixed solution of 20 ml of SOCl and 1 ml of dimethylformamide, and stirred at 70 ° C. for 24 hours. Subsequently, the solid content was removed by centrifugation, washed, and vacuum-dried to obtain CNTs having —COCl groups on the surface. Next, 2 g of octadecylamine (ODA) was added to CNTs having —COCl groups on the surface, and heated at 100 ° C. for 96 hours. Thereafter, the mixture was cooled to room temperature, excess ODA was removed, washed with ethanol and dichloromethane, and vacuum-dried to obtain CNT having a —CONH (CH ₂ ) ₁₇ CH ₃ group on the surface (ODA-modified CNT).

  The ODA-modified CNT (1) powder synthesized above is heated in a mixed solution of nitric acid and sulfuric acid at 130 ° C. for 1 hour for surface oxidation, then filtered and washed with distilled water to oxidize the surface. ODA-modified CNT (2) was synthesized.

  In addition, after synthesizing CNT whose surface is modified with -COOH, the above three kinds of dipole materials A to C are reacted, respectively, so that the surface is modified with dipole materials A to C (3) to (3) (5) was synthesized respectively.

  Specifically, 500 mg of purified CNTs was placed in a solution in which nitric acid and sulfuric acid were mixed at a volume ratio of 1: 3, and sonicated for 1 hour to introduce —COOH groups on the CNT surface. Thereafter, CNTs were taken out, washed and vacuum dried. 2 g of the above-mentioned dipole material A was added to 100 mg of CNTs having —COOH groups introduced on the surface, and heated at 100 ° C. for 50 hours. Thereafter, the mixture was cooled to room temperature, excess dipoles were removed, washed with ethanol and dichloromethane, and vacuum-dried to obtain surface-modified CNTs. Dipole materials B and C were prepared in the same procedure.

  Each of the CNTs (1) to (5) obtained above was dissolved in o-dichlorobenzene at a concentration of 0.1% by mass, and coated and dried on an ITO substrate to form a CNT single film. The function was measured by the UPS method (ESCALab200R and UPS-1 manufactured by Vacuum Generators). The obtained work function values are shown in Table 1 below. In addition, the work function of CNT which is not surface-modified is 4.8 eV.

[Preparation of photoelectric conversion layer solution]
1% by mass of poly-hexylthiophene (P3HT) (Rieke Metal) (Mn = 54000), which is a p-type organic semiconductor material, and PC60BM (made by Sigma Aldrich), which is an n-type organic semiconductor material, in o-dichlorobenzene. ) Was mixed at 0.8% by mass to obtain a photoelectric conversion layer solution A.

  A photoelectric conversion layer solution B in which 0.1% by mass of the previously synthesized CNT (1) was added to this photoelectric conversion layer solution A with respect to P3HT, and a photoelectric conversion layer solution B ′ in which 0.5% by mass was added. Each was prepared.

  CNTs (2), (3), and (5) were also added to the photoelectric conversion layer solution A in the same procedure to prepare photoelectric conversion layer solutions C to E and C ′ to E ′, respectively.

  In the above photoelectric conversion layer solution A, a photoelectric conversion solution F was prepared in which the p-type semiconductor material was changed from P3HT to PBDDTPT2. To this photoelectric conversion solution F, the photoelectric conversion layer solutions G to K added with 0.1% by mass of the CNTs (1) to (5) prepared above with respect to PBDDTPT2, and the photoelectric conversion added with 0.5% by mass, respectively. Layer solutions G ′ to K ′ were respectively prepared.

Comparative Example 1 Preparation of Organic Photoelectric Conversion Device SC-101 A 150 nm thick indium tin oxide (ITO) transparent conductive film deposited on a glass substrate (sheet resistance: 10Ω / □) was used for photolithography and hydrochloric acid. The first electrode (transparent electrode; cathode) was formed by patterning to a width of 20 mm using wet etching. The patterned first electrode is ultrasonically cleaned using a mixture of surfactant and ultrapure water, then ultrasonically cleaned using ultrapure water, dried by nitrogen blowing, and finally UV ozone. Washing was performed.

  Next, in order to form an electron transport layer, the ZnO precursor solution was spin-coated on the transparent electrode in the atmosphere (rotation speed 2000 rpm, rotation time 180 seconds) and wiped off in a predetermined pattern. And this was heat-processed in air at 400 degreeC for 10 minute (s), and the electron carrying layer which consists of ZnO with a film thickness of about 40 nm was formed.

  The 150 mM ZnO precursor solution was prepared by the following method (sol-gel method). Zinc acetate (manufactured by Sigma-Aldrich) was dissolved in 2-methoxyethanol containing 0.5M and ethanolamine (Tokyo Kasei) 0.5M to obtain a precursor solution.

  Subsequently, the substrate on which the electron transport layer was formed was placed in a glove box (oxygen concentration <1 ppm, dew point temperature <−80 ° C.), and the previously prepared photoelectric conversion layer solution A was spin-coated in a nitrogen atmosphere. It apply | coated so that a dry film thickness might be set to 150 nm, and formed the photoelectric converting layer into a film.

  Thereafter, in order to form a hole transport layer, polystyrenesulfonic acid was used for a PEDOT: PSS (Clevios (registered trademark) P4083, manufactured by Heraeus) dispersion (solid content: about 3% by mass) composed of a conductive polymer and a polyanion. Solution B containing 0.1 wt% sodium (Polynas (registered trademark) PS-1, manufactured by Tosoh Organic Chemical Co., Ltd.) and 20 wt% isopropanol was prepared. While filtering the obtained solution B with a 0.45 μm PVDF filter, the solution B was applied and dried on the photoelectric conversion layer using a blade coater so that the dry film thickness was about 100 nm. Furthermore, it heat-processed for 10 minutes at 120 degreeC, and formed the positive hole transport layer into a film.

Next, the substrate on which the series of functional layers is formed is moved into a vacuum deposition apparatus chamber, and the inside of the vacuum deposition apparatus is depressurized to 1 × 10 ⁻⁴ Pa or less. A second electrode was formed by laminating 100 nm at 1.0 nm / second. The obtained organic photoelectric conversion element is moved to a nitrogen chamber, and sealing is performed using a sealing cavity glass and an epoxy-based UV curable resin (manufactured by Nagase Chemtech Co., Ltd.), and the light receiving part is an organic having a size of about 5 mm × 20 mm. Photoelectric conversion element SC-101 was completed.

Comparative Example 2 Production of Organic Photoelectric Conversion Device SC-102 In production of organic photoelectric conversion device SC-101, the same as SC-101 except that photoelectric conversion layer solution A was changed to photoelectric conversion layer solutions B and B ′. According to the procedure, organic photoelectric conversion elements SC-102 having CNT addition amounts of 0.1 wt% and 0.5 wt% were respectively produced.

Examples 1 to 3 Production of Organic Photoelectric Conversion Elements SC-103 to 105 In production of the organic photoelectric conversion element SC-102, the photoelectric conversion layer solutions B and B ′ were changed to C to E and C ′ to E ′. Except for this, organic photoelectric conversion elements SC-103 to 105 having an addition amount of CNT of 0.1 wt% and 0.5 wt% were prepared in the same procedure as SC-102, respectively.

Comparative Example 3 Production of Organic Photoelectric Conversion Element SC-201 In the production of organic photoelectric conversion element SC-101, the same procedure as SC-101 was performed except that photoelectric conversion layer solution A was changed to photoelectric conversion layer solution F. Thus, an organic photoelectric conversion element SC-201 was produced.

Comparative Example 4 Production of Organic Photoelectric Conversion Element SC-202 In the production of organic photoelectric conversion element SC-201, the procedure was the same as SC-201 except that the photoelectric conversion layer solution F was changed to G and G ′. The organic photoelectric conversion element SC-202 having an addition amount of CNT of 0.1% by mass and 0.5% by mass was prepared.

Examples 4 to 7 Production of Organic Photoelectric Conversion Device SC-203 to 206 In production of the organic photoelectric conversion device SC-102, the photoelectric conversion layer solutions G and G ′ were changed to H to K and H ′ to K ′. Except for this, organic photoelectric conversion elements SC-203 to 206 having an addition amount of CNT of 0.1% by mass and 0.5% by mass were prepared in the same procedure as SC-102, respectively.

<Evaluation of conversion efficiency>
Photoelectric conversion element fabricated (Examples and Comparative Example) In the above, a solar simulator (EKO Instruments Ltd.: AM1.5G filter) was irradiated with light having an intensity of 100 [mW / cm ^2] of the effective area to 1 cm ² The shorted current density Jsc [mA / cm ² ], the open circuit voltage Voc [V], and the parallel resistance Rsh [Ω] were measured by overlaying the mask on the light receiving portion and evaluating the IV characteristics. As represented by the following formula 1, the photoelectric conversion efficiency η of the device increases as the values of the short circuit current density Jsc [mA / cm ² ] and the open circuit voltage Voc [V] increase. In the following formula 1, FF represents a fill factor. The parallel resistance Rsh [Ω] was obtained from the reciprocal of the slope of the tangent of the IV curve when the open end voltage of the IV curve was 0 V (Isc). The results are shown in Table 1.

  As shown in the above table, by adjusting the work function (WF) of the CNT surface to be deeper than the HOMO of the p-type organic semiconductor, Voc is reduced compared to the case where CNT is not added. It is possible to improve Jsc without making it. Furthermore, since the electron blocking function can be provided by controlling the work function of the surface of the CNT with a dipole material, the Jsc can be further improved without increasing the Rsh by increasing the amount of CNT added. Can do.

10, 20, 30 organic photoelectric conversion element,
11 Anode,
12 cathode,
13 photoelectric conversion layer,
13a a first photoelectric conversion layer,
13b Second photoelectric conversion layer 14 Nanostructure (carbon nanotube),
15 p-type organic semiconductor material,
16 n-type organic semiconductor material 25 substrate,
26 hole transport layer,
27 electron transport layer,
38 Middle layer.

Claims (7)

A photoelectric conversion element having a first electrode, a bulk heterojunction photoelectric conversion layer having a p-type organic semiconductor material and an n-type organic semiconductor material, and a second electrode in this order,
The photoelectric conversion layer is an organic photoelectric conversion element including carbon nanotubes whose surface has been modified such that the work function of the surface is larger than the work function of the carbon nanotubes themselves.   The organic photoelectric conversion device according to claim 1, wherein a work function of the surface of the surface-modified carbon nanotube is 0.2 eV or more larger than a work function of the carbon nanotube itself.   The organic photoelectric conversion device according to claim 1, wherein the surface-modified carbon nanotube is a carbon nanotube surface-modified with a dipole material having an electron-withdrawing group.   The organic photoelectric conversion element of Claim 3 whose dipole moment of the said dipole material is -0.1-13D.   The organic photoelectric conversion element of any one of Claims 1-4 whose HOMO level of the said p-type organic-semiconductor material is 5.2 eV or less.   The organic photoelectric conversion device according to claim 1, wherein a difference between a HOMO level of the p-type organic semiconductor material and a work function of the surface of the modified carbon nanotube is 0.1 eV or less. .   The solar cell which has an organic photoelectric conversion element of any one of Claims 1-6.

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