JP5653667B2 - Fullerene purified product and method for producing the same - Google Patents

Description

  The present invention relates to a purified fullerene having a high sublimation rate in vapor deposition operation and containing a small amount of gaseous impurities, a method for producing the same, and a method for evaluating an organic semiconductor material such as a purified fullerene.

Fullerene is a carbon-based material that has attracted attention in recent years.
Fullerene is a collective term for carbon allotropes having a spherical closed shell structure, and allotrope molecules include C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C _84, etc., but in 1990 a fullerene mass synthesis method was established. Since then, research on fullerene has been vigorously developed.
Fullerenes have unique properties derived from molecular structures such as ultraviolet absorption properties, photoconductivity, and photosensitization properties, so they can be used in electronic materials such as organic semiconductors, functional optical materials, and conventional amorphous carbon. A wide range of applications for coating materials that replace thin films is expected. In particular, the application of fullerene as an organic semiconductor material attracts the most attention.

When fullerene is industrially synthesized, a mixture of fullerene allotropes such as C ₆₀ and C ₇₀ can be obtained. Since the characteristics of fullerene, such as the band gap, depend on the type of allotrope molecule, when applying fullerene to organic semiconductors, the fullerene allotrope molecule is usually separated from the mixture of fullerene allotrope molecules. .

  Moreover, when applying fullerene to an organic semiconductor use, the method of forming a fullerene thin film by sublimating the fullerene used as a vapor deposition source and vapor-depositing fullerene on the target base material is generally employ | adopted. Since the nature of the organic semiconductor largely depends on the purity of the fullerene thin film, the purity of the fullerene as a deposition source should be as high as possible.

Conventional separation / purification methods for fullerenes are disclosed in Patent Documents 1 to 4 and the like. However, these methods are techniques to separate any more fullerene species (e.g. C ₆₀ and other fullerenes allotrope molecules), are not techniques for purifying a type of fullerene allotrope molecules with high purity.

In addition, as a study on high purity in fullerene, in Non-Patent Document 1, fullerene C _{60, which} has been subjected to sublimation purification while circulating nitrogen gas at normal pressure, used secondary ion mass spectrometry (SIMS). It is reported by the measurement that the purity is 7 Nine (99.99999%) or higher. In this method, fullerene is sublimated at 720 ° C., and the purity is increased by slowing the precipitation rate and increasing the crystallinity.
Further, in the organic thin-film solar cells using fullerene C ₆₀ was purified, it has achieved conversion efficiency 5.3% of the world's highest level. This result is because the photoelectric conversion layer can be thickened by reducing impurities in fullerene that can be a trap in the charge transfer of the organic thin film solar cell, so that the sunlight in the visible region can be absorbed almost 100%. It is considered.

On the other hand, when fullerene with high crystallinity and high purity is used as the evaporation source, the impurities in the material certainly tend to decrease, but not only the cost is increased, but the actual size of the crystal is increased. There have been problems that the sublimation speed during use is remarkably slow and the sublimation speed varies due to non-uniform crystal size. Variation or reduction in the sublimation speed leads to a decrease in productivity in the production of organic semiconductor devices, which can be a big problem in industrial production.
As described above, the fullerene serving as a vapor deposition source for the organic semiconductor fullerene thin film needs to have a high purity of the target fullerene allotrope molecule and a sufficient sublimation rate to increase productivity. On the other hand, fullerene C ₆₀ obtained by sublimation purification by the method of Non-Patent Document 1 described above is a single crystal reaching a size of several millimeters to 1 cm square, and its surface area is relatively small, so that the purity is high. There was a problem that the sublimation rate was insufficient.

Moreover, the separation / purification fullerene (fullerene purified product) used as a vapor deposition source needs to evaluate the impurity content at the ppm level. Among impurities, oxygen often becomes a major cause of lowering semiconductor characteristics in organic semiconductors, which are application applications of fullerenes, and high-precision evaluation of the oxygen content of fullerenes as vapor deposition sources is desired.
However, HPLC (High Performance Liquid Chromatography), GC (Gas Chromatography), titration method and the like, which are conventional methods for evaluating the purity of organic materials, cannot evaluate oxygen in fullerene at the ppm level.
On the other hand, Non-Patent Document 1 described above reports that the purity of fullerene (purified fullerene) was evaluated at the ppm level by measurement using SIMS. However, this method is a special analysis method that requires an expensive apparatus, and has a problem that the quantitative accuracy of oxygen, which is a main impurity in fullerene, is particularly low.

Japanese Patent No. 3134414 Japanese Patent Laid-Open No. 5-116922 JP-A-9-227111 Japanese Patent No. 3073986

Applied Physics Vol. 77, No. 5, 2008, p539-544

As described above, there are still many problems with respect to a method for producing a fullerene purified product substantially composed of fullerene allotrope molecules used as a vapor deposition source or the like and an evaluation method thereof.
Under such circumstances, an object of the present invention is to provide a purified fullerene having a sublimation rate and purity (oxygen content) suitable for manufacturing an organic semiconductor device, and a method for manufacturing the same.
Another object of the present invention is to provide an organic semiconductor material evaluation method capable of quantitative analysis of ppm level impurities contained in an organic semiconductor material such as a purified fullerene.

  As a result of intensive studies to solve the above problems, the present inventor has found that the following inventions meet the above object, and have reached the present invention.

That is, the present invention relates to the following inventions.
<1> Fullerene purified product comprising at least 99.99% fullerene C ₆₀ having a sublimation rate at 720 ° C. determined by the following method 1 of 50 μg / min or more and an oxygen content of 80 ppm by weight or less. .
Method 1:
A 5 mg sample (purified fullerene) was weighed in a platinum pan (5 mmφ × 5 mmH), and the temperature was raised to 720 ° C. with N ₂ (200 ml / min) in a thermogravimetric analyzer. Then, the sample is kept at 720 ° C., and the sample weight loss (sublimation amount) is measured, and the average sample weight loss rate (μg / min) between 10% and 70% of the sample weight loss is defined as the sublimation rate of the fullerene purified product.
<2> A laminate having a thin film formed by sublimation precipitation of the purified fullerene according to <1>.
<3> A photoelectric conversion element comprising the laminate according to <2>.
<4> An organic thin film solar cell comprising the laminate according to <2>.
<5> the a method for producing a fullerene purified product of <1>, the fullerene C ₆₀ was sublimed by heating the raw material fullerene containing 99% or more to 730 ° C. or higher, lower deposition temperature than the heating temperature The method for producing a purified fullerene, wherein the purified fullerene is precipitated.
<6> The method for producing a purified fullerene according to <5>, wherein the precipitation temperature is 450 ° C. or higher and 700 ° C. or lower.
<7> The method for producing a purified fullerene according to <5> or <6>, wherein the sublimation purification of the raw material fullerene is carried out by circulating an inert gas.

The purified fullerene of the present invention has a high sublimation rate and a small amount of oxygen contained as an impurity. Therefore, it can be suitably used as a fullerene vapor deposition source used for an organic semiconductor device or the like.
Moreover, according to the method for producing a purified fullerene of the present invention, the purified fullerene of the present invention can be suitably obtained by sublimation purification at a heating temperature of 730 ° C. or higher.
In addition, the organic semiconductor material evaluation method of the present invention is a simple method and enables quantitative analysis of ppm level impurities in organic semiconductor materials including purified fullerenes.

It is a schematic sectional drawing of the laminated body which has a fullerene thin film which consists of a fullerene refinement | purification thing of this invention. It is a schematic diagram of the sublimation purification apparatus which concerns on the manufacturing method of the fullerene purified product of this invention. It is a schematic diagram which shows an example of the element structure of the organic thin film solar cell formed using the fullerene refinement | purification material of this invention.

The present invention relates to a purified fullerene having a sublimation rate at 720 ° C. of 50 μg / min or more and an oxygen content of 80 ppm by weight or less.
In the present invention, “purified fullerene” means only a specific allotrope molecule among allotrope molecules of fullerene represented by molecular formulas such as C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₄ ( Means at least 99.99% or more). That is, for the specific target fullerene allotrope molecule, allotrope molecules of other fullerenes are regarded as impurities like oxygen.
The purified fullerene may be a single crystal, a polycrystal, an amorphous material, or a mixture thereof as long as the molecular formula is the same allotrope molecule.
Incidentally, the fullerene purified product of the present invention, from the viewpoint of industrial productivity, is preferably made of fullerene C _60.

The sublimation rate at 720 ° C. of the fullerene purified product of the present invention is 50 μg / min or more, preferably 53 μg / min or more.
The method for measuring the sublimation rate of the purified fullerene is not particularly limited, but in order to accurately measure the set temperature and the change in weight, it is preferable to measure using a thermogravimetric analyzer.
Specifically, a sample (purified fullerene) of about 1 to 30 mg is weighed in a platinum pan, and the sample temperature is raised to 720 ° C. with a thermogravimetric analyzer, and then the temperature is increased to 720 ° C. The average sample weight reduction rate (μg / min) between 10% and 70% of the sample weight loss held and measured is defined as the sublimation speed of the fullerene purified product.
The atmosphere for measuring the sublimation rate may be an atmosphere that does not react with the purified fullerene, and is usually measured in an inert gas atmosphere by circulating an inert gas such as N ₂ , He, Ar in a thermogravimetric analyzer. Is done.

The oxygen content of the fullerene purified product of the present invention is 80 ppm by weight or less, preferably 40 ppm by weight or less, and particularly preferably 10 ppm by weight or less.
The oxygen content of the fullerene purified product is the oxygen concentration generated when the predetermined amount of the fullerene purified product is heated from room temperature to 850 ° C. in a vacuum or under an inert gas flow such as N ₂ , He, Ar, etc. It can be calculated from the amount of generated oxygen obtained by continuously measuring with an analyzer and integrating the oxygen concentration.
The measuring device is not particularly limited, but is preferably a device combining a temperature programmed desorption analyzer and a mass spectrometer. As such an apparatus, a commercially available temperature-programmed desorption mass spectrometer can be used. As a specific example, a temperature-programmed desorption mass spectrometer combining an infrared furnace manufactured by ULVAC and AGS-7000 manufactured by Canon Anelva Co., Ltd. Can be mentioned.
The measurement conditions are appropriately determined in consideration of the sample to be measured and the configuration of the apparatus. To illustrate suitable measurement conditions, an inert gas such as He is used for a sample of about several hundred mg (fullerene purified product). For example, a constant temperature increase rate (about 5 to 30 ° C./min) can be given in a state where it is circulated at about 200 ml / min, and the oxygen concentration generated when the temperature is increased is determined from the accumulated oxygen amount in the sample. The oxygen content (hereinafter, sometimes referred to as “impurity oxygen amount”) can be calculated.

In addition, since the evaluation method of the oxygen content of the fullerene purified product described above uses a mass spectrometer capable of analyzing various gases simultaneously, the evaluation of gaseous impurities other than oxygen contained in the fullerene purified product is used. It can also be applied to.
In other words, the gas concentration generated when the fullerene purified product is heated in a vacuum or under an inert gas flow is continuously measured with a mass spectrometer, and from the amount of generated gas obtained by integrating the gas concentration, The amount of gaseous impurities contained in the purified fullerene can be calculated.
Various conditions such as the rate of temperature rise, the degree of vacuum, and the amount of inert gas flow are the same as in the evaluation of the amount of impurity oxygen. In the case where N ₂ and Ar may be contained as gaseous impurities, it is desirable to use high-purity He as an inert gas.
According to the evaluation method of the fullerene purified product, there is an advantage that other gaseous impurities can be measured with high sensitivity and easily in parallel with the evaluation of the amount of impurity oxygen. The purity of the purified fullerene and the kind of impurities contained can be easily evaluated.
A typical example of the target impurity gas is oxygen (O ₂ ), but other examples include CO, CO ₂ , H ₂ O, N ₂ , unreacted raw materials, low molecular organic compounds such as organic solvents, and the like. .
The evaluation method of the present invention can also be used as a purity analysis method for organic semiconductor materials in which trace impurities greatly affect physical properties.
Such organic semiconductor materials include polycyclic aromatic hydrocarbons pentacene, anthracene, rubrene, and other low-molecular compounds such as oligothiophene derivatives, phthalocyanines, porphyrins, perylene derivatives, tetracyanoquinodimethane, high Examples of the molecular compound include polythiophenes such as poly-3-hexylthiophene (P3HT), polyacetylenes, polyfluorenes, polyphenylene vinylenes, polyanilines, and polypyrroles.

In addition, when applying fullerene to organic semiconductor applications, it is used as a laminate having a fullerene thin film using fullerene as an n-type semiconductor layer. However, since the properties of organic semiconductors greatly depend on the purity of fullerene, The purity of the constituent fullerene should be as high as possible. Since the purified fullerene of the present invention has a high sublimation rate and a low content of oxygen as an impurity, it is suitable as the fullerene thin film.
Therefore, the laminated body having a thin film formed by sublimating precipitation of the fullerene purified product of the present invention can be suitably used as an organic semiconductor device reflecting the physical properties of fullerene. Examples of the organic semiconductor device include a photoelectric conversion element including the laminate and an organic thin film solar cell. Thus, since the high-purity fullerene thin film has few impurities that can trap carriers, it exhibits better semiconductor characteristics and is preferably used for these applications.

Hereinafter, a laminate using a fullerene thin film made of the purified fullerene of the present invention as an n-type organic semiconductor layer (hereinafter referred to as “laminate of the present invention”) will be described.
A general schematic cross-sectional view of the laminate of the present invention is shown in FIG.
The laminate 1 according to the present invention has a structure in which a first electrode 3, a photoelectric conversion layer 4 in which a p-type semiconductor thin film and a fullerene thin film are laminated, and a second electrode 5 are further formed on one surface of a substrate 2. .

  The substrate 2 is not particularly limited as long as it is transparent or opaque. For example, when the substrate side is a light receiving surface, it is preferably a transparent substrate. Examples of the transparent substrate include quartz glass, Pyrex (registered trademark), a synthetic quartz substrate, and flexible flexible substrates such as a transparent resin film and an optical resin substrate. The thickness of the board | substrate 2 will not be specifically limited if the self-supporting property of the laminated body 1 is securable, For example, it is about 10 micrometers-about 5 mm.

Although it will not specifically limit if the 1st electrode 3 has electroconductivity, What is necessary is just to select suitably in consideration of the irradiation function of the light, the work function of the material which forms the 2nd electrode 5 mentioned later, etc. Specifically, indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), gold (Au), osmium ( Os), palladium (Pd), and the like.
The material of the second electrode 5 is not particularly limited as long as it is a conductive material, and preferably has a low electrical resistance at the contact surface with the lower layer. Specifically, calcium (Ca), magnesium (Mg), Aluminum (Al), silver (Ag), etc. are mentioned.
As a method for forming these electrodes, conventionally known methods can be used, and examples thereof include a method for forming electrodes using a vacuum deposition method, a sputtering method, a photolithographic method, and a lift-off method.
When the laminate 1 is applied to an organic thin film solar cell, it is desirable that at least one surface of the laminate 1 be sufficiently transparent to the sunlight spectrum in order to obtain highly efficient photoelectric conversion characteristics. For this purpose, the first electrode 3 or the second electrode 5 may be formed by using a known conductive material so as to ensure a predetermined translucency by a method such as vapor deposition or sputtering.
In addition, the thickness of the 1st electrode 3 and the 2nd electrode 5 does not have a restriction | limiting in particular, Usually, it is about 0.1-500 nm.

The photoelectric conversion layer 4 is formed of a p-type semiconductor thin film and a fullerene thin film.
Materials for p-type semiconductor thin films include pentacene, anthracene, rubrene, which are polycyclic aromatic hydrocarbons, and other low molecular compounds such as oligothiophene derivatives, phthalocyanines, porphyrins, perylene derivatives, tetracyanoquinodimethane, high Examples of the molecular compound include polythiophenes such as poly-3-hexylthiophene (P3HT), polyacetylenes, polyfluorenes, polyphenylene vinylenes, polyanilines, and polypyrroles. The thickness is not particularly limited, and is usually about 0.1 to 1500 nm.
The method for forming the p-type semiconductor thin film on the first electrode 3 is not particularly limited, and a known film forming method can be used. For example, a method in which a solution prepared by dissolving the above-described p-type semiconductor material in an appropriate solvent is formed by a known coating technique such as cast coating, spin coating, inkjet method, ablation method, vacuum deposition, sputtering, plasma, etc. And dry film forming methods such as ion plating.

The fullerene thin film is formed by vacuum deposition on the p-type semiconductor thin film using the purified fullerene of the present invention as a deposition source. As suitable vacuum deposition conditions, it is preferable to sublimate the purified fullerene using a resistance heating method, and to control the substrate temperature constant during film formation. The film thickness of the fullerene thin film is generally 5 μm or less, and particularly preferably 10 to 1000 nm.
Moreover, the photoelectric conversion layer 4 can also vapor-deposit (co-evaporate) p-type organic-semiconductor material and a fullerene refined material simultaneously, and can form the blend structure which disperse | distributed both over the whole layer.

Note that the structure shown here is one embodiment of the laminate of the present invention, and the present invention is not limited to this. For example, a buffer layer may be provided to prevent a short circuit between the first electrode 3 and the second electrode 5 and to improve the organic / metal interface characteristics. As the buffer layer, a hole transport layer can be provided between the first electrode 3 and the photoelectric conversion layer 4, and an electron transport layer can be provided between the photoelectric conversion layer 4 and the second electrode 5.
The material for forming the hole transport layer is not particularly limited as long as it has a function as an electron donor, but a material having a high hole mobility is preferable. Specifically, substances having functional groups such as thiophene, ferrocene, paraphenylene vinylene, carbazole, pyrrole, aniline, diamine, phthalocyanine, hydrazone, V ₂ O ₅ , MoO ₃ , NiO, etc. The metal compound can be mentioned.
The material for forming the electron transport layer is not particularly limited as long as it has a function as an electron acceptor, but a material having high electron mobility is preferable. Specific examples include metal oxides such as TiOx, ZnO, and CsO, and derivatives such as bathocuproin (BCP), fullerene, oxadiazole, oxadore, perylene, naphthalene, and metal complexes.
Although the film thickness of a positive hole transport layer and an electron carrying layer is not specifically limited, It is preferable that it is the range of 0.1-1500 nm.

Subsequently, the manufacturing method of the fullerene refined material of this invention is demonstrated.
In the fullerene purified product of the present invention, a fullerene before purification as a raw material (hereinafter sometimes referred to as “raw fullerene”) is a known separation method from fullerenes produced by a conventionally known method. And fullerenes separated in (1).
As the raw material fullerene, those containing 99% or more, preferably 99.9% or more, more preferably 99.99% or more of the target fullerene allotrope molecule are used. The “target fullerene allotrope molecule” is a fullerene allotrope molecule that is purified and recovered from the fullerene allotrope molecules (C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₄ etc.) contained in the raw material fullerene. Means. From the viewpoint of industrial productivity, the fullerene allotrope molecule of interest is preferably a fullerene C _60.
In addition to the target fullerene allotrope molecule, the raw material fullerene contains impurities such as allotrope molecules of other fullerenes and compounds thereof, atmospheric gases used for fullerene production, solvents, and decomposition products thereof. In particular, since raw material fullerene is produced in an oxidizing atmosphere, in most cases, oxygen is included as an impurity gas.

The method for producing a fullerene purified product of the present invention is a method for sublimation purification of raw material fullerene, wherein the raw material fullerene is sublimated by heating to a temperature of 730 ° C. or higher, and fullerene purification is performed at a precipitation temperature lower than the heating temperature. Precipitates.
The production method of the present invention is characterized in that the raw material fullerene is heated to 730 ° C. or higher (preferably 750 ° C. or higher). By heating the raw material fullerene to a high temperature of 730 ° C. or higher (preferably 750 ° C. or higher), the target fullerene allotrope molecules contained in the raw material fullerene tend to sublime at the single molecule level, not in clusters. Therefore, the purified fullerene product that precipitates not only has a very small amount of impurities, but also tends to have a smaller particle size and a higher sublimation rate.
When the sublimation temperature is lower than 730 ° C., the obtained fullerene purified product does not satisfy the sublimation rate of 50 μg / min or more and the oxygen content of 80 ppm by weight or less.

In the purification method of the present invention, in order to selectively precipitate the target fullerene allotrope molecule, the deposition temperature is preferably set to 450 to 700 ° C.
When the temperature is lower than 450 ° C., impurities other than the target fullerene allotrope molecule may be precipitated, the impurity concentration in the purified fullerene product may be high, and the crystallinity of the fullerene purified product may be reduced. Impurities inside the crystal may increase. On the other hand, when it exceeds 700 degreeC, precipitation of a fullerene refined product will become slow and productivity will fall.

In the purification method of the present invention, it is preferable to perform sublimation purification of the raw material fullerene under an inert gas flow.
The purification of raw material fullerene is usually carried out in an inert gas atmosphere or under reduced pressure. However, in the case where inert gas is not circulated or only under reduced pressure, the sublimation of fullerene molecules or gaseous impurities in the vicinity of the surface of the raw material fullerene is performed. Is likely to occur, and sublimation of fullerene is suppressed, so that the purity of the fullerene purified product may be insufficient.
On the other hand, when sublimation purification of raw material fullerene is carried out under an inert gas flow, retention of sublimated fullerene molecules and gaseous impurities near the surface of raw material fullerene is suppressed, so that sublimation of raw material fullerene is promoted, The purity of the fullerene purified product can be improved. Sublimation purification can also be performed under reduced pressure (about 0.01 MPa) under an inert gas flow. By reducing the pressure, the sublimation purification rate of the raw material fullerene increases, and the productivity is further improved.

  Hereinafter, a preferred method for producing a fullerene purified product of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic diagram of a sublimation purification apparatus according to the method for producing a fullerene purified product of the present invention.
The sublimation purification apparatus 10 includes a sublimation purification container 12, electric furnaces 13, 14, 15 for heating the sublimation purification container 12, an inert gas introduction device 16, a decompression pump 17, and a discharged gas. And a cooling trap 18 for collecting the agglomerated components.

The sublimation purification container 12 is a cylindrical tube made of quartz glass, and the corresponding heating units A1, A2, A3 can be heated to different temperatures by independent electric furnaces 13, 14, 15.
The inert gas introducer 16 supplies an inert gas such as He, N ₂ , Ar, etc. from the gas inlet 12a of the sublimation purification container 12 into the container 12 and discharges it from the gas outlet 12b. Flow can be formed. Although the gas flow rate depends on the volume of the sublimation purification container 12 and the purity of the raw material R, the purified product P, etc., the gas flow rate (linear velocity) is usually 1 to 20 cm / min, preferably 2 to 10 cm / min. .
The decompression pump 17 can reduce the pressure in the sublimation purification container 12 and can reduce the pressure even when an inert gas flows under the above conditions. When sublimation purification is performed at normal pressure, the vacuum pump 17 is not used.

In the purification method of the present invention, the raw material R (raw material fullerene before purification) is charged into the heating part A1 heated in the electric furnace 13 in the sublimation purification container 12, and the fullerene molecules are sublimated by heating to 730 ° C. or higher. The fullerene molecules are deposited on the wall surface of the sublimation purification container 12 by setting the temperatures of the heating parts A2 and A3 heated in the electric furnaces 14 and 15 to be lower than the temperature of A1. In addition, the component (impurity component) which did not precipitate in A2 and A3 is deposited as a precipitate W in the non-heated part A4 or collected by the cooling trap 18, and the gaseous impurity component can be directly or under reduced pressure pump. 17 is exhausted.
After the purified fullerene is precipitated by the above procedure, the sublimation purification container 12 is cooled to room temperature, and the fullerene purified product is recovered.

Here, by setting the temperature of the heating part A2 to be higher than the temperature of the heating part A3, it is possible to cause the heating part A2 to precipitate the purified fullerene P1 having a high purity, and the heating part A3 has a lower purity than the purified product P1. The fullerene purified product P2 can be precipitated.
The temperature of the heating part A2 is set so that the purified product P1 deposited in the heating part A2 has a sublimation rate and an oxygen content as the above-mentioned fullerene purified product of the present invention.
Specifically, in order to precipitate the fullerene purified product of the present invention in the heating unit A2, the temperature of the heating unit A2 is preferably 450 to 700 ° C., and the target fullerene purified product is C ₆₀ . In the case, the temperature of the heating part A2 is preferably 450 to 700 ° C, more preferably 500 to 650 ° C.
Moreover, in order to obtain a purified product having higher purity, the purified product P1 may be used as the raw material fullerene R and purified again.

The temperature of the heating part A3 is set lower than the temperature of the heating part A2. The purified product P2 that precipitates in the heating part A3 often has a higher purity than the raw material fullerene R, and therefore can be used as the raw material fullerene R after recovery.
When the purified product P2 is reused as the raw material fullerene R, the temperature of the heating part A3 is lower than the temperature of A2, and is preferably 300 to 700 ° C, more preferably 350 to 650 ° C. When the temperature is lower than 300 ° C., impurities other than the target fullerene allotrope molecule accumulate in the purified product P2, the content thereof increases, and it becomes inappropriate as the raw material fullerene R.

In addition, in FIG. 2, although the so-called gas flow type purification method for purifying the raw material fullerene in an inert gas flow was described, the method for producing the fullerene purified product of the present invention is not limited thereto.
Further, in the embodiment shown in FIG. 2, a sublimation purification apparatus having three heating parts, that is, a heating part A1 for raw material fullerene sublimation and heating parts A2 and A3 for fullerene precipitation is used. If the temperature of the heating part A2 can be set within a predetermined range, the heating part A3 may be omitted. Further, the number of heating units may be increased if there is no problem in designing the apparatus.
In FIG. 2, the fullerene sublimation purification apparatus 10 is installed sideways, that is, a cylindrical tube made of quartz glass, which is a sublimation purification container 12, with the gas inlet 12a and the gas outlet 12b positioned on the left and right. An inert gas is circulated in the direction and the operation is performed by dividing the heated portion, but the sublimation purification container 12 is placed vertically and the gas inlet 12a and the gas outlet 12b are installed vertically. It is also possible to perform sublimation purification by flowing an inert gas as an upward flow or a downward flow.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example.

First, the sublimation rate and oxygen content of the fullerene purified product were measured by the following methods.
A thermogravimetric analyzer (model number: TG / DTA6200) manufactured by Rigaku Corporation was used to measure the sublimation rate of the purified fullerene. Moreover, the TPD-MS apparatus (model number: AGS-7000) made from Canon Anerva Co., Ltd. was used for the measurement of the amount of oxygen contained in the purified fullerene.

1. Sublimation rate measurement method A 5 mg sample (purified fullerene) was weighed in a platinum pan (5 mmφ × 5 mmH), and this was passed through a thermogravimetric analyzer under N ₂ (200 ml / min) flow to a sample temperature of 720 ° C. After raising the temperature, the temperature was kept at 720 ° C. and the sample weight loss (sublimation amount) was measured. The average sample weight reduction rate (μg / min) between 10% and 70% of the sample weight loss was defined as the sublimation speed of the fullerene purified product.

2. Method for measuring oxygen content Place 300 mg of sample (purified fullerene) on a quartz boat and heat from high temperature to 850 ° C at a heating rate of 10 ° C / min while flowing high purity He at a flow rate of 80 mL / min. The generated gas was scanned between m / z = 6 and 200 with a mass spectrometer attached to the TPD-MS apparatus, and the mass spectrum was continuously measured (measurement condition: EI method 70 eV).
Of the obtained mass spectrum, the amount of generated oxygen was calculated by integrating the mass spectrum of m / z = 32 corresponding to the oxygen concentration (oxygen generation rate), and this was used as the amount of oxygen contained in the purified fullerene. .
Calibration of the sensitivity of the mass spectrometer is performed using calcium oxalate monohydrate. The calibration curve factor is obtained from CO ₂ generated by thermal decomposition of calcium oxalate monohydrate, and oxygen, CO ₂ and From the device sensitivity coefficient ratio, an oxygen calibration curve was created.

Example 1
As the sublimation purification apparatus, the sublimation purification apparatus 10 having the configuration shown in FIG. 2 was used. A sublimation purification container 12 was a 50 mmφ quartz tube.
As a sublimation fullerene, C ₆₀ (product number: nanom purple SUH, C ₆₀ content: 99.99%) manufactured by Frontier Carbon Co., Ltd. was used.
5 g of fullerene for sublimation was charged into the container 12 of the heating unit A1 in the sublimation purification container, and N ₂ was flowed from the inert gas inlet 12a at a flow rate of 100 mL / min (linear velocity 5.1 cm / min).
After the inside of the sublimation purification container 12 was replaced with N ₂ , the heating part A2 was heated to 550 ° C. and the heating part A3 was heated to 400 ° C. Subsequently, heating part A1 which is a sublimation part was heated up to 750 degreeC over 2 hours, and the sublimation refinement | purification for 24 hours was performed.
After 24 hours, the heating furnace was cooled to obtain a fullerene purified product C ₆₀ -A (3.8 g) deposited on the heating part A2.
When the obtained fullerene purified product (C ₆₀ -A) was evaluated by the above sublimation rate measuring method and oxygen content measuring method, the sublimation rate at 720 ° C. was 57 μg / min, and the oxygen content was 7 ppm by weight. Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Example 2
Using the fullerene purified product (C ₆₀ -A) obtained in Example 1 as a sublimation fullerene, sublimation purification is performed again by the same procedure as in Example 1, and the fullerene purified product is precipitated in the heating part A2. It was. The process of sublimation purification of the obtained fullerene purified product again by the same procedure as in Example 1 was repeated three times to obtain a fullerene purified product C ₆₀ -B (2.4 g).
When the obtained fullerene purified product (C ₆₀ -B) was evaluated by the above sublimation rate measurement method and oxygen content measurement method, the sublimation rate at 720 ° C. was 55 μg / min, and the oxygen content was It was 5 ppm by weight. Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Example 3
A purified fullerene (C ₆₀ ) was produced in the same manner as in Example 1, except that C ₆₀ (product number: nanom purple ST, C ₆₀ content: 99.0%) manufactured by Frontier Carbon Co. was used as the sublimation fullerene. -C) 2.5 g was obtained.
When the obtained fullerene purified product (C ₆₀ -C) was evaluated by the above sublimation rate measuring method and oxygen content measuring method, the sublimation rate at 720 ° C. was 55 μg / min, and the oxygen content was 2 0.5 ppm by weight. The results are shown in Table 1, and the evaluation results are shown in Table 2.

Comparative Example 1
A fullerene purified product (C ₆₀ -D) was obtained in the same manner as in Example 1 except that the temperature of the heating part A1 was changed to 720 ° C.
The obtained fullerene purified product (C ₆₀ -D) was evaluated by the above-described sublimation rate measurement method and oxygen content measurement method. The sublimation rate at 720 ° C. was 45 μg / min, and the oxygen content was detected. It was below the limit (1 ppm by weight). Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Comparative Example 2
In Example 1, the inert gas introduction part 12a is closed, the pressure is reduced to 0.002 Pa by the vacuum pump 17, the heating part A2 and the heating part A3 are heated to 300 ° C., and then the heating part A1 (sublimation part) is set to 2 The temperature was raised to 570 ° C. over time, and sublimation purification was performed for 24 hours.
After 24 hours, the heating furnace was cooled to obtain sublimation-purified fullerene C ₆₀ -E (4 g) for heating section A2.
When the obtained fullerene purified product (C ₆₀ -E) was evaluated by the above sublimation rate measuring method and oxygen content measuring method, the sublimation rate at 720 ° C. was 56 μg / min, and the oxygen content was It was 86 ppm by weight. Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Comparative Example 3
C ₆₀ (Product No .: nano purple ST) manufactured by Frontier Carbon Co. was evaluated by the above-described sublimation rate measurement method and oxygen content measurement method without purification, and the sublimation rate at 720 ° C. was 31 μg / min. The oxygen content was 474 ppm by weight. Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Comparative Example 4
Fullerene-C ₆₀ (99.5%) manufactured by Aldrich was evaluated by the above-described sublimation rate measurement method and oxygen content measurement method without purification, and the sublimation rate at 720 ° C. was 32 μg / min. The oxygen content was 125 ppm by weight. Table 1 shows the sublimation purification conditions, and Table 2 shows the evaluation results.

Evaluation of Organic Thin Film Solar Cell Using Purified Fullerene Products Fullerene purified products (C ₆₀ -C and C ₆₀ -E) obtained in Example 3 or Comparative Example 2 as n-type semiconductors, and zinc phthalocyanine as p-type semiconductors. The used organic thin film solar cell 21 was produced. The element structure is shown in FIG. A substrate 22 provided with an ITO electrode 23 as a lower electrode (first electrode), and an aluminum electrode with a thickness of 100 nm provided with a lithium fluoride layer 26 having a thickness of 0.1 nm as an upper electrode (second electrode) 27 was used. As the p-type semiconductor layer 24, zinc phthalocyanine purified by the method described in JP 2007-24642 A was used with a thickness of 50 nm. using fullerene purified product C ₆₀ -C or C ₆₀ -E thickness 50nm as an n-type semiconductor layer 25, respectively, in Example 4, was an organic thin film solar cell of Comparative Example 5.
The solar cell characteristics are evaluated under current-voltage characteristics under irradiation of pseudo-sunlight (Air Mass 1.5 Global 100 mW / cm ² ), short-circuit photocurrent (Isc), open-circuit voltage (Voc), form factor (FF), Solar cell parameters of energy conversion efficiency (PCE) were derived. The results are shown in Table 3.

From Table 3, it can be seen that the organic thin film solar cell of Example 4 using C ₆₀ -C exceeds all the characteristics of the organic thin film solar cell of Comparative Example 5 using C ₆₀ -E.
From the above results, it was confirmed that the characteristics of the organic thin-film solar cell were greatly improved by using a purified fullerene having a high sublimation rate in the vapor deposition operation and containing a small amount of gaseous impurities as a raw material.

  Since the purified fullerene of the present invention has a high sublimation rate and a low impurity oxygen content, it can be suitably used as a fullerene vapor deposition source used for organic semiconductor devices and the like.

DESCRIPTION OF SYMBOLS 1 Laminated body 2 Board | substrate 3 1st electrode 4 Photoelectric conversion layer 5 2nd electrode 10 Sublimation purification apparatus 12 Sublimation purification container 12a Gas introduction port 12b Gas exhaust port 13, 14, 15 Electric furnace 16 Inert gas introduction device 17 Pressure reduction pump 18 Cooling trap 21 Organic thin film solar cell 22 Substrate 23 ITO electrode 24 P-type semiconductor (zinc phthalocyanine) layer 25 N-type semiconductor (fullerene C ₆₀ ) layer 26 Lithium fluoride layer 27 Aluminum electrode A1, A2, A3 Heating part A4 Non-heating Part R Raw Material Fullerene P1 (High Purity) Precipitate P2 (Low Purity) Precipitate W Impurity

Claims (7)

A purified fullerene comprising at least 99.99% fullerene C ₆₀ having a sublimation rate at 720 ° C. determined by the following method 1 of 50 μg / min or more and an oxygen content of 80 ppm by weight or less.
Method 1:
A 5 mg sample (purified fullerene) was weighed in a platinum pan (5 mmφ × 5 mmH), and the temperature was raised to 720 ° C. with N ₂ (200 ml / min) in a thermogravimetric analyzer. Then, the sample is kept at 720 ° C., and the sample weight loss (sublimation amount) is measured, and the average sample weight loss rate (μg / min) between 10% and 70% of the sample weight loss is defined as the sublimation rate of the fullerene purified product.   A laminate having a thin film formed by sublimation deposition of the purified fullerene according to claim 1.   A photoelectric conversion element comprising the laminate according to claim 2.   An organic thin film solar cell comprising the laminate according to claim 2. A method for producing fullerenes purified product of claim 1, the fullerene C ₆₀ was sublimed by heating the raw material fullerene containing 99% or more to 730 ° C. or higher, at a lower deposition temperature than the heating temperature, fullerene A method for producing a purified fullerene, comprising precipitating a purified product.   The said precipitation temperature is 450 degreeC or more and 700 degrees C or less, The manufacturing method of the fullerene refined product of Claim 5 characterized by the above-mentioned.   The method for producing a purified fullerene according to claim 5 or 6, wherein the sublimation purification of the raw material fullerene is performed under an inert gas flow.

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