JP5362017B2 - Organic thin film solar cell - Google Patents

Description

  The present invention relates to an organic thin film solar cell using an organic semiconductor.

  An organic thin film solar cell is a solar cell using an organic thin film semiconductor in which a conductive polymer, fullerene, or the like is combined. Organic thin-film solar cells can be produced by a simpler method than solar cells based on inorganic materials, and have the advantage of low cost. On the other hand, the photoelectric conversion efficiency and life of the organic thin film solar cell have a problem that it is lower than that of a conventional inorganic solar cell.

  Therefore, various ideas for improving the photoelectric conversion efficiency of the organic thin film solar cell have been made (for example, Patent Document 1 and Patent Document 2). Patent Document 1 discloses an organic thin film solar cell element in which fullerene nanowhiskers are contained in a photoelectric conversion layer. Patent Document 2 discloses an organic thin film solar cell in which a polythiophene derivative and / or a polyphenylene vinylene (PPV) derivative is contained in a hole transport layer and a polyfluorene derivative and / or fullerene derivative is contained in an electron transport layer. Yes.

JP 2008-91575 A JP 2006-245073 A

  An object of the present invention is to provide an organic thin-film solar cell with high photoelectric conversion efficiency.

The organic thin-film solar cell of the present invention includes a pair of electrodes that are spaced apart from each other and at least one of which is light transmissive, and a p-type organic semiconductor and an n-type organic semiconductor provided between the electrodes. The n-type organic semiconductor includes 0.1 wt% to 10 wt% of fullerene C70 and the balance of C70PCBM .

  ADVANTAGE OF THE INVENTION According to this invention, an organic thin film solar cell with high photoelectric conversion efficiency can be provided.

FIG. 1 is a cross-sectional view of an organic thin-film solar cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of an organic thin-film solar cell according to another embodiment of the present invention. FIG. 3 is a diagram showing the results of calculating the internal quantum efficiency of fullerenes. FIG. 4 is a conceptual diagram showing the structure of the photoelectric conversion layer of the organic thin film solar cell of the present invention. FIG. 5 is a diagram for explaining an operation mechanism of a bulk heterojunction solar cell. FIG. 6 is a diagram showing the conversion efficiency of the organic thin-film solar cells of Examples 1-10.

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

  FIG. 1 is a cross-sectional view of an organic thin-film solar cell according to an embodiment of the present invention.

  The organic thin film solar cell shown in FIG. 1 includes a pair of electrodes (anode 11 and cathode 12) that are spaced apart from each other, and a photoelectric conversion layer 13 that is disposed between the electrodes 11 and 12. It has a configuration arranged on the substrate 10. Optionally, a hole transport layer 14 is provided between the anode 11 and the photoelectric conversion layer 13.

  FIG. 2 is a cross-sectional view of an organic thin-film solar cell according to another embodiment of the present invention. The organic thin film solar cell shown in FIG. 2 further includes an electron transport layer 15 between the cathode 12 and the photoelectric conversion layer 13.

  Hereinafter, each structural member of the organic thin-film solar cell of this invention is demonstrated concretely.

(substrate)
The substrate 10 is for supporting other constituent members. The substrate 10 is preferably one that is not altered by heat or an organic solvent. Examples of the material of the substrate 10 include inorganic materials such as alkali-free glass and quartz glass, plastics such as polyethylene, PET, PEN, polyimide, polyamide, polyamideimide, liquid crystal polymer, and cycloolefin polymer, polymer film, SUS, and silicon. And the like, and the like. The substrate 10 is not particularly limited, whether it is transparent or opaque. However, when an opaque substrate is used, it is preferable that the electrode opposite to the substrate is transparent or translucent. The thickness of the substrate is not particularly limited as long as it has sufficient strength to support other components.

(anode)
The anode 11 is stacked on the substrate 10. The material of the anode 11 is not particularly limited as long as it has conductivity. Usually, a transparent or translucent conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. For example, a conductive metal oxide film, a translucent metal thin film, or the like can be used as the anode 11. Specifically, a film formed using conductive glass made of indium oxide, zinc oxide, tin oxide, or a composite thereof such as indium tin oxide (ITO), FTO, indium zinc oxide, etc. (NESA etc.), gold, platinum, silver, copper, etc. are used. In particular, ITO or FTO is preferable. Further, as an electrode material, polyaniline and a derivative thereof, which is an organic conductive polymer, polythiophene and a derivative thereof, or the like may be used. In the case of ITO, the film thickness of the anode 11 is preferably 30 to 300 nm. If it is thinner than 30 nm, the conductivity is lowered, the resistance is increased, and the photoelectric conversion efficiency is lowered. If it is thicker than 300 nm, ITO becomes inflexible and cracks when stress is applied. The sheet resistance of the anode 11 is preferably as low as possible, and is preferably 10Ω / □ or less. The anode 11 may be a single layer or may be a laminate of layers made of materials having different work functions.

(Hole transport layer)
The hole transport layer 14 is arbitrarily disposed between the anode 11 and the photoelectric conversion layer 13. The function of the hole transport layer 14 is to level the unevenness of the lower electrode to prevent a short circuit of the solar cell element, to efficiently transport only holes, and to excitons generated near the interface of the photoelectric conversion layer 13. It is to prevent the disappearance of As a material for the hole transport layer 14, a polythiophene polymer such as PEDOT / PSS (poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate)), or an organic conductive polymer such as polyaniline or polypyrrole is used. be able to. As a typical product of the polythiophene-based polymer, for example, BaytronP AI4083 manufactured by Starck Co., Ltd. may be mentioned.

  When BaytronP AI4083 is used as the material for the hole transport layer 14, the film thickness is preferably 20 to 200 nm. If it is too thin, the effect of preventing the lower electrode from being short-circuited is lost, and a short circuit occurs. If it is too thick, the current generated by increasing the film resistance is limited, and the light conversion efficiency is lowered.

  The method for forming the hole transport layer 14 is not particularly limited as long as it is a method capable of forming a thin film. For example, a spin coating method can be used. After applying the material of the hole transport layer 14 to a desired film thickness, it is heated and dried with a hot plate or the like. As the solution to be applied, one previously filtered with a filter may be used.

(Photoelectric conversion layer)
The photoelectric conversion layer 13 is disposed between the anode 11 and the cathode 12. The solar cell according to the present invention is a bulk hetero type organic thin film solar cell. The photoelectric conversion layer 13 is formed by stacking a mixture of a p-type organic semiconductor and an n-type organic semiconductor, and has a micro layer separation structure. In the bulk hetero type, a mixed n-type organic semiconductor and p-type organic semiconductor form a pn junction having a nano-order size in the photoelectric conversion layer, and a current is obtained using photocharge separation generated at the junction surface. The n-type organic semiconductor is composed of a material having an electron-accepting property. On the other hand, the p-type organic semiconductor is composed of a material having an electron donating property.

  The present invention uses an n-type organic semiconductor in which fullerene derivatives are doped with fullerene C70. Fullerene C70 acts as a photocarrier generator, and fullerene derivatives act as charge transport agents. Thus, by using the configuration utilizing each function, the photoelectric conversion efficiency of the organic thin film solar cell can be enhanced comprehensively.

  As will be described in detail later, the photoelectric conversion process of the organic thin-film solar cell includes: a) a process in which organic molecules absorb light to generate excitons, b) a process of exciton migration and diffusion, c) exciton processes The process of charge separation can be roughly divided into d) the process of charge transport to both electrodes. In the n-type organic semiconductor in the solar cell of the present invention, a fullerene derivative is used to efficiently perform the processes c) and d) of the photoelectric conversion process, and an optical carrier is used to efficiently perform the process a). Fullerene C70 having high generation efficiency is used.

  The fullerene derivative acting as a charge transfer agent is not particularly limited as long as it is a derivative having a fullerene skeleton. Specific examples include derivatives composed of C60, C70, C76, C78, C84, etc. as the basic skeleton. In the fullerene derivative, carbon atoms in the fullerene skeleton may be modified with an arbitrary functional group, and these functional groups may be bonded to each other to form a ring. Fullerene derivatives also include fullerene bonded polymers. A fullerene derivative having a functional group with high affinity for the solvent and high solubility in the solvent is preferred.

  Examples of the functional group in the fullerene derivative include hydrogen atom; hydroxyl group; halogen atom such as fluorine atom and chlorine atom; alkyl group such as methyl group and ethyl group; alkenyl group such as vinyl group; cyano group; methoxy group and ethoxy group. Alkoxy groups such as phenyl groups, aromatic hydrocarbon groups such as naphthyl groups, and aromatic heterocyclic groups such as thienyl groups and pyridyl groups. Specific examples include hydrogenated fullerenes such as C60H36 and C70H36, oxide fullerenes such as C60 and C70, and fullerene metal complexes.

  Among the above-described compounds, it is particularly preferable to use 60PCBM ([6,6] -phenyl C61 butyric acid methyl ester) or 70PCBM ([6,6] -phenyl C71 butyric acid methyl ester) as the fullerene derivative.

Examples of specific structures of fullerene derivatives used in the present invention are shown below.

Fullerene C70 which acts as a photocarrier generator has the following structure.

  Commonly referred to as higher-order fullerenes include C70, C76, C78, C84, etc. Among them, C70 has a particularly high photocarrier generation efficiency. Therefore, in the present invention, fullerene C70 is used as a photocarrier generator in the n-type organic semiconductor.

  It can be confirmed by comparing the internal quantum efficiency that the photocarrier generation efficiency of fullerene C70 is higher than that of other fullerenes. The internal quantum efficiency is determined by the Xerographic Discharge method (see J. Mort, M. Machonkin, I. Chen, and R. Ziolo, Phylos. Mag. Lett. 67, 77 (1993)). Can be measured. Here, the measurement of internal quantum efficiency is performed in the literature (Technical Report of IEICE. OME, Organic Electronics Technical report of IEICE. OME 95 (50) pp. 29-34 19950519 “Light of C70 dispersed in polymer. Conduction ") was performed as a reference.

As the matrix polymer, a polystyrene polymer that hardly causes a charge transfer interaction with the fullerene molecule was used. In addition, triphenyldiamine (TPD) having a small dipole moment was used as a charge transfer agent in order to avoid hole trapping and internal electric field due to Coulomb interaction between photocarriers and dipoles. The structural formula of TPD is shown below.

  The composition of the organic film was 49% by weight of polystyrene, 50% by weight of TPD, and 1% by weight of fullerenes. These were dissolved in chlorobenzene using an ultrasonic disperser. This solution was applied on a 200 nm thick aluminum film deposited on a 1 mm thick glass substrate with a spin coater to obtain an organic film having a thickness of about 2 μm. Finally, it was dried at 100 ° C. with a vacuum dryer to prepare a sample.

  Measurement of the internal quantum efficiency by the charged light attenuation method was performed using a paper analyzer EPA-8100 (manufactured by Kawaguchi Electric Co., Ltd.). The sample surface is charged by corona discharge, and light is emitted from the surface of the sample to generate photocarriers. The generated photocarrier is moved by the electric field formed by charging, and the surface potential is attenuated by canceling the surface charge.

  Based on the measurement results, the internal quantum efficiency of fullerenes was determined using the following equation. The light absorptance of the sample was calculated by spectroscopically irradiating the sample substrate with a xenon light source and irradiating the sample substrate, measuring the power of light passing through the sample substrate at each wavelength, and subtracting the light absorptance of the substrate. An optical power meter TQ8210 manufactured by ADC Co., Ltd. was used as the optical power meter.

J = C (dV / dt) (1)
Φ = J / eI (2)
Here, J is the photocurrent, Φ is the internal quantum efficiency, C is the capacitance of the sample, I is the number of photons absorbed by the sample, and e is the elementary charge.

  The results of calculating the internal quantum efficiency of fullerenes are shown in FIG. As fullerenes, fullerene C60, fullerene C70, 60PCBM ([6,6] -phenyl C61 butyric acid methyl ester) and 70PCBM ([6,6] -phenyl C71 butyric acid methyl ester) were used. FIG. 3 shows that the internal quantum efficiency of fullerene C70 is superior to other fullerenes. That is, when fullerene C70 is used as an acceptor of an organic thin film solar cell, it shows that a highly efficient organic thin film solar cell can be produced.

  However, fullerene C70 has poor solubility in a solvent, and it is difficult to form a uniform film. Therefore, even when fullerene C70 is used as an n-type organic semiconductor of a solar cell produced by a coating method, a solar cell with good conversion efficiency could not be obtained conventionally.

  On the other hand, when a fullerene derivative is used as the n-type organic semiconductor, the solubility in a solvent is good and the film forming property is also excellent, so that a self-organized structure can be formed. However, as described above, the photocarrier generation efficiency of the fullerene derivative is inferior to that of fullerene C70.

  Therefore, in the present invention, an n-type organic semiconductor having a composition in which fullerene C70 is doped into a fullerene derivative having good film forming properties is used.

  FIG. 4 is a conceptual diagram showing the structure of the photoelectric conversion layer of the organic thin film solar cell of the present invention. The p-type organic semiconductor 1 and the fullerene derivative 4 which is an n-type organic semiconductor are oriented by self-organization, and the fullerene derivative 4 is doped with fullerene C70 represented by 3.

  Since the fullerene derivative has good solubility in a solvent and excellent film forming property, such a self-organized structure can be formed. In addition, a film formed from a solution in which fullerene derivatives and fullerene C70 are mixed has a tendency to reduce aggregation of fullerene C70. The photocarrier generated in the fullerene C70 having high photoexcitation efficiency is transported to the electrode through the self-assembled fullerene derivative.

  With such a configuration, it is possible to use fullerene C70, which has been difficult to produce by a coating method until now, and reflect the high photoexcitation efficiency of fullerene C70 in the photoelectric conversion efficiency of the device. I was able to do it.

  As for the mixing ratio of the fullerene derivative and fullerene C70 in the n-type organic semiconductor, it is preferable that the fullerene C70 is 0.1 to 80% by weight and the remainder is the fullerene derivative. When the content of fullerene C70 is less than 0.1% by weight, the generation efficiency of photocarriers cannot be increased, and a solar cell with high photoelectric conversion efficiency cannot be provided. On the other hand, if the content of fullerene C70 exceeds 80% by weight, fullerene C70 is not uniformly dispersed in the solvent, and a uniform film cannot be formed. As a result, the transport path of the optical carrier becomes non-uniform, leading to a decrease in photoelectric conversion efficiency.

  Preferably, the mixing ratio of the fullerene derivative and fullerene C70 in the n-type organic semiconductor is 0.1 to 10% by weight of the fullerene C70, and the remainder is the fullerene derivative.

  More preferably, the mixing ratio of the fullerene derivative and fullerene C70 in the n-type organic semiconductor is 0.1 to 4.0% by weight of the fullerene C70, and the remainder is the fullerene derivative.

  A p-type organic semiconductor is an electron donating material. For example, polythiophene and its derivatives, polypyrrole and its derivatives, pyrazoline derivatives, arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, oligothiophene and its derivatives, polyvinylcarbazole and its derivatives, polysilane and its derivatives, side chain or main chain Polysiloxane derivatives having an aromatic amine, polyaniline and derivatives thereof, phthalocyanine derivatives, porphyrin and derivatives thereof, polyphenylene vinylene and derivatives thereof, polythienylene vinylene and derivatives thereof, and the like may be used in combination. . These copolymers may be used, and examples thereof include a thiophene-fluorene copolymer, a phenylene ethynylene-phenylene vinylene copolymer, and the like.

  A preferred p-type organic semiconductor is polythiophene which is a conductive polymer having π conjugation and derivatives thereof. Polythiophene and its derivatives can ensure excellent stereoregularity and have relatively high solubility in a solvent. Polythiophene and derivatives thereof are not particularly limited as long as they are compounds having a thiophene skeleton. Specific examples of polythiophene and derivatives thereof include polyalkylthiophenes such as poly-3-methylthiophene, poly-3-butylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, poly-3-decylthiophene, poly-3-dodecylthiophene, etc. Polyarylthiophene such as poly-3-phenylthiophene and poly-3- (p-alkylphenylthiophene); poly-3-butylisothionaphthene, poly-3-hexylisothionaphthene, poly-3-octylisothionaphthene, poly-3- And polyalkylisothionaphthene such as decylisothionaphthene; polyethylenedioxythiophene and the like.

  These conductive polymers can be formed by applying a solution dissolved in a solvent. Therefore, there is an advantage that a large-area organic thin film solar cell can be manufactured at low cost with inexpensive equipment by a printing method or the like.

  The mixing ratio of the n-type organic semiconductor and the p-type organic semiconductor in the photoelectric conversion layer is preferably such that the content of the n-type organic semiconductor is 30 to 70% by weight.

  In order to apply an organic semiconductor, it is necessary to dissolve in a solvent. Examples of the solvent used therefor include toluene, xylene, tetralin, decalin, mesitylene, n-butylbenzene, sec-butylbesen, tert-butylbenzene and the like. Unsaturated hydrocarbon solvents, halogenated aromatic hydrocarbon solvents such as chlorobenzene, dichlorobenzene, trichlorobenzene, carbon tetrachloride, chloroform, dichloromethane, dichloroethane, chlorobutane, bromobutane, chloropentane, chlorohexane, bromohexane, chloro Halogenated saturated hydrocarbon solvents such as cyclohexane, and ethers such as tetrahydrofuran and tetrahydropyran. In particular, a halogen-based aromatic solvent is preferable.

  As a method of applying a solution to form a film, spin coating, dip coating, casting, bar coating, roll coating, wire bar coating, spraying, screen printing, gravure printing, flexographic printing, offset Examples thereof include a printing method, gravure offset printing, dispenser coating, nozzle coating method, capillary coating method, and ink jet method, and these coating methods can be used alone or in combination.

(Electron transport layer)
The electron transport layer 15 is arbitrarily disposed between the cathode 12 and the photoelectric conversion layer 13. Usually, a transparent or translucent material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. Examples of the electron transport layer material include quinolines such as Alq ₃ , phenanthroline derivatives such as BCP, oxadiazole derivatives such as BND and PBD, and OXD, oxadiazole dimers, starburstaxadiazole, triazole derivatives, Examples of the phenylquinoxaline derivative, silole derivative, and inorganic substance include alkali metals such as titanium oxide, fullerenes, and lithium fluoride, halides and oxides of alkaline earth metals. The appropriate film thickness of the electron transport layer 15 varies greatly depending on the material and needs to be adjusted, but is generally in the range of 0.1 nm to 100 nm. When the film thickness is thinner than the above range, the hole blocking effect is reduced, so that the generated excitons are deactivated before dissociating into electrons and holes, and current cannot be efficiently extracted. When the film thickness is thick, the electron transport layer acts as a resistor and causes a voltage drop. Further, it takes a long time to form the electron transport layer 15, which damages the organic layer and degrades the performance. Further, since a large amount of material is used, the occupation time of the film forming apparatus becomes long, leading to an increase in cost.

(cathode)
The cathode 12 is laminated on the photoelectric conversion layer 13 (or the electron transport layer 15). Usually, a transparent or translucent conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. Examples of the electrode material include a conductive metal oxide film and a metal thin film. When the anode 11 is formed using a material having a high work function, it is preferable to use a material having a low work function for the cathode 12. Examples of the material having a low work function include alkali metals and alkaline earth metals. Specific examples include Li, In, Al, Ca, Mg, Sm, Tb, Yb, Zr, Li, Na, K, Rb, Cs, Sr, Ba, and the like.

  The cathode 12 may be a single layer or may be a laminate of layers made of materials having different work functions. Alternatively, an alloy of one or more of the materials having a low work function with gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, tin, or the like may be used. Examples of the alloy include a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-indium alloy, a magnesium-silver alloy, a magnesium-indium alloy, a magnesium-aluminum alloy, an indium-silver alloy, and a calcium-aluminum alloy.

  The film thickness of the cathode 12 is 1 nm to 500 nm, preferably 10 nm to 300 nm. When the film thickness is smaller than the above range, the resistance becomes too large and the generated charge cannot be sufficiently transmitted to the external circuit. When the film thickness is thick, it takes a long time to form the cathode 12, which damages the organic layer and degrades the performance. Furthermore, since a large amount of material is used, the occupation time of the film forming apparatus becomes long, leading to an increase in cost.

  As described above, the organic thin film solar cell having the structure in which the anode is stacked on the substrate and the cathode is disposed on the opposite side of the substrate has been described. However, the positions of the anode and the cathode may be reversed.

  As a post-treatment, the solar cell element obtained as described above is annealed on a hot plate at 150 ° C. for 30 minutes. The element after annealing is sealed by adhering a sealing glass whose center is cut with an epoxy resin. Finally, an extraction electrode is taken out from the positive and negative electrodes to obtain an organic thin film solar cell.

  Next, the power generation reaction of the organic thin film solar cell of the present invention will be described.

  FIG. 5 is a diagram for explaining an operation mechanism of a bulk heterojunction solar cell. As described above, the photoelectric conversion process of the organic thin film solar cell includes a) a process in which organic molecules absorb light to generate excitons, b) a process of exciton transfer and diffusion, and c) charge separation of excitons. D) The process can be roughly divided into the process of charge transport to both electrodes.

  In step a), excitons are generated by absorption of light by the donor or acceptor. Let this generation efficiency be η1. Next, in step b), the generated excitons move to the p / n junction surface by diffusion. This diffusion efficiency is assumed to be η2. Since excitons have a lifetime, they can move only about the diffusion length. In step c), excitons that have reached the p / n junction are separated into electrons and holes. The efficiency of exciton separation is η3. Finally, in step d), each optical carrier is transported through the p / n material to the electrode and taken out to an external circuit. This transport efficiency is assumed to be η4.

  In the present invention, the steps c) and d) are improved by using a fullerene derivative, and the step a) is improved by using fullerene C70.

The external extraction efficiency of the generated carriers for the irradiated photons can be expressed by the following equation. This value corresponds to the quantum efficiency of the solar cell.
η _EQE = η1, η2, η3, η4.

  In the following Examples 1 to 10, photoelectric conversion when the ratio of the fullerene C70 in the n-type organic semiconductor is changed with the ratio of the p-type organic semiconductor being 50% by weight and the ratio of the n-type organic semiconductor being 50% by weight. Efficiency was measured.

[Example 1]
First, the solid content of the organic semiconductor used as a photoelectric converting layer was prepared.
50 parts by weight of P3HT (poly-3-hexylthiophene) as a p-type organic semiconductor, 49.95 parts by weight of 70PCBM and 0.05 part by weight of fullerene C70 as n-type organic semiconductors were prepared and mixed (n-type) The content of fullerene C70 in the organic semiconductor is 0.1% by weight).

  Next, with respect to 1 ml of monochlorobenzene as a solvent, 25 mg of the solid content is added into a sample bottle, and ultrasonic waves are applied at 50 ° C. for 2 hours in an ultrasonic cleaning machine (US-2 manufactured by Inoue Seieido Co., Ltd.). It melt | dissolved by irradiating and obtained the coating solution of the photoelectric converting layer. Finally, the photoelectric conversion layer coating solution was filtered through a 0.2 μm filter.

  The substrate is a glass substrate having a size of 20 mm × 20 mm and a thickness of 0.7 mm. An ITO transparent conductive layer having a thickness of 140 nm was deposited on this glass substrate by a sputtering method, and an ITO glass substrate obtained by patterning the ITO portion into a rectangular shape of 3.2 mm × 20 mm by a photolithography method was obtained.

This substrate was ultrasonically cleaned with pure water containing 1% of a surfactant (NCW1001 manufactured by Wako Pure Chemical Industries) for 5 minutes, and then washed with flowing pure water for 15 minutes. Furthermore, it was ultrasonically cleaned with acetone for 5 minutes, ultrasonically cleaned with isopropyl alcohol (IPA) for 5 minutes, and then dried in a constant temperature bath at 120 ° C. for 60 minutes.
Thereafter, the substrate was UV-treated for 10 minutes to make the surface hydrophilic.

Film formation by coating was performed as follows.
First, a PEDOT / PSS aqueous solution (Poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate), trade name Baytron P AI4083, manufactured by Starck Co., Ltd.) as a hole transport layer is spin coated on a glass substrate with ITO. The film was formed to a thickness of 50 nm by heating at 200 ° C. for 5 minutes on a hot plate. In addition, the PEDOT / PSS aqueous solution used what was previously filtered with the 0.1 micrometer filter.

  Next, the coating solution for the photoelectric conversion layer was dropped onto the hole transport layer, and an organic semiconductor layer to be a 140 nm-thick photoelectric conversion layer was formed by spin coating.

Next, the cathode was formed into a film by a vapor deposition method using a vacuum vapor deposition apparatus. The ITO-attached glass substrate on which the photoelectric conversion layer had been applied to the substrate holder was set, and the cathode pattern mask was overlaid and placed in the vapor deposition machine. The cathode pattern mask had a rectangular slit with a width of 3.2 mm, and was arranged so that the ITO layer and the slit intersected. Therefore, the area of the organic thin film solar cell element is the area of this intersecting portion, and is 0.1024 cm ² (3.2 mm × 3.2 mm). The vapor deposition apparatus was evacuated until the degree of vacuum became 3 × 10 ⁻⁶ torr, the Al wire rod was resistance-heated, and the aluminum layer was deposited to a thickness of 80 nm.

Next, the substrate after vapor deposition was annealed on a hot plate at 150 ° C./30 minutes.
Next, the substrate after annealing was sealed by adhering a sealing glass whose center was cut with an epoxy resin.
Finally, the extraction electrode was taken out from the positive and negative electrodes to obtain an organic thin film solar cell.

For the organic thin-film solar cell thus produced, the photoelectric conversion efficiency η _n was measured with an electrical output measuring device (Maki Seisakusho Co., Ltd.). As a measurement light source, a solar simulator attached to the apparatus was used, and the input energy by irradiation light was set to 100 mW / cm ² . The IV characteristic due to the electronic load was measured by this apparatus, and the photoelectric conversion efficiency was obtained. In the measurement in which the input energy by the irradiation light is normalized at 100 mW / cm ² , the photoelectric conversion efficiency η _n is
η _n = V _OC・ J _SC・ FF
Given in. Here, V _OC is an open circuit voltage, J _SC is a short circuit current density, and FF is a fill factor. The calculated photoelectric conversion efficiency was 2.93%.

[Examples 2 to 10]
About Examples 2-10, the ratio of the fullerene derivative and fullerene C70 in an n-type organic semiconductor was changed as shown in Table 1, and it tested similarly to Example 1. FIG. The p-type organic semiconductor and fullerene derivative used are the same as in Example 1.

[Examples 11 to 14]
About Examples 11-14, the ratio of a p-type organic semiconductor and an n-type organic semiconductor was changed as shown in Table 1, and it tested similarly to Example 1. FIG. In Examples 11 to 14, the ratio of fullerene C70 in the n-type organic semiconductor was 0.6% by weight. The p-type organic semiconductor and fullerene derivative used are the same as in Example 1.

[Comparative Example 1]
The composition of the coating solution for the photoelectric conversion layer was 50 parts by weight of P3HT (poly-3-hexylthiophene), which is a p-type organic semiconductor, and 50 parts by weight of 70 PCBM, which is an n-type organic semiconductor.

  Others produced the organic thin film solar cell like Example 1, and measured the photoelectric conversion efficiency. The calculated photoelectric conversion efficiency was 0.95%.

[Comparative Example 2]
The composition of the coating solution for the photoelectric conversion layer was 50 parts by weight of P3HT (poly-3-hexylthiophene) as a p-type organic semiconductor and 50 parts by weight of fullerene C70 as an n-type organic semiconductor.

  Others produced the organic thin film solar cell like Example 1, and measured the photoelectric conversion efficiency. The calculated photoelectric conversion efficiency was 0.1%.

  When the photoelectric conversion layer was observed with an optical microscope, many aggregates of fullerene C70 were observed, and a uniform film could not be obtained.

The results obtained in Examples 1-14 and Comparative Examples 1-2 are summarized in the following table.

  From the results of Examples 1 to 10, a graph showing the relationship between the ratio of fullerene C70 in the n-type organic semiconductor and the photoelectric conversion efficiency is prepared and shown in FIG.

When the ratio of fullerene C70 in the n-type organic semiconductor is 0.1 to 10% by weight, a photoelectric conversion efficiency of 2.3% or more is obtained, and the ratio of fullerene C70 in the n-type organic semiconductor is 0.1 to 4 A photoelectric conversion efficiency of 2.7% or more is obtained in the range of wt%.
The invention described in the claims at the beginning of the application will be appended.
[1]
A pair of electrodes disposed at a distance from each other, at least one of which is light transmissive;
A bulk heterojunction photoelectric conversion layer including a p-type organic semiconductor and an n-type organic semiconductor provided between the electrodes;
An organic thin film solar cell comprising:
The n-type organic semiconductor includes 0.1% by weight to 80% by weight of fullerene C70 and the remaining fullerene derivative.
[2]
The organic thin film solar cell according to claim 1, wherein the n-type organic semiconductor contains 0.1 wt% to 10 wt% of fullerene C70.
[3]
The organic thin-film solar cell according to item 1, wherein the n-type organic semiconductor contains 0.1 wt% to 4.0 wt% of fullerene C70.
[4]
Item 2. The organic thin-film solar cell according to Item 1, wherein the fullerene derivative is a C70 derivative.
[5]
The organic thin-film solar cell according to claim 1, wherein the p-type organic semiconductor is a thiophene-based conductive polymer.
[6]
The organic thin-film solar cell according to claim 1, wherein the fullerene C70 is a photocarrier generator, and the fullerene derivative is a charge transport agent.

  DESCRIPTION OF SYMBOLS 1 ... P-type organic semiconductor, 3 ... Fullerene C70, 4 ... Fullerene derivative, 10 ... Substrate, 11 ... Anode, 12 ... Cathode, 13 ... Photoelectric conversion layer, 14 ... Hole transport layer, 15 ... Electron transport layer.

Claims (4)

A pair of electrodes disposed at a distance from each other, at least one of which is light transmissive;
An organic thin-film solar cell comprising a bulk heterojunction photoelectric conversion layer including a p-type organic semiconductor and an n-type organic semiconductor provided between the electrodes,
The n-type organic semiconductor includes 0.1 wt% to 10 wt% of fullerene C70 and the balance C70PCBM .   2. The organic thin film solar cell according to claim 1, wherein the n-type organic semiconductor includes 0.1 wt% to 4.0 wt% of fullerene C70.   The organic thin film solar cell according to claim 1, wherein the p-type organic semiconductor is a thiophene-based conductive polymer. 2. The organic thin film solar cell according to claim 1, wherein the fullerene C70 is a photocarrier generator, and the C70PCBM is a charge transport agent.

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