JP2006265035A - Carbon nanotube-containing thin film, method for manufacturing the thin film, and photoelectric conversion material, photoelectric transducer, electroluminescent material and electroluminescence device equipped with the thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film in which carbon nanotubes exist in a mutually separated state and exists in a state in which photoelectric conversion function and electroluminescence function which separated single-wall carbon nanotubes (SWNT) have originally can be exhibited to the fullest. <P>SOLUTION: The thin film is a carbon nanotube-containing thin film in which a plurality of single-wall carbon nanotubes are dispersed in a mutually separated state in a soluble polyphenylene vinylene substitution product or a copolymer of such products, or a carbon nanotube-containing thin film in which a plurality of single-wall carbon nanotubes are dispersed in a mutually separated state in a soluble polythiophene substitution product. A method for manufacturing the carbon nanotube-containing thin film is also provided which comprises centrifuging a mixed liquid containing the soluble polyphenylene vinylene substitution product or a copolymer of such products or the soluble polythiophene substitution product and carbon nanotubes, and casting the resulting supernatant liquid on a substrate to form a film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon nanotube-containing thin film having a structure in which single-walled carbon nanotubes (for convenience, expressed simply as “SWNT”) are dispersed one by one in a matrix polymer, and the same thin film And a photoelectric conversion material and a photoelectric conversion element provided with the thin film, an electroluminescent material and an electroluminescent element, and a photoelectric conversion element / electroluminescent element comprising the thin film.

  Single-walled carbon nanotubes (SWNT) have attracted a great deal of attention as a new material that can exhibit various new functions, and are actively researched and developed all over the world. In the future, in order to effectively use in various industrial applications, it is an essential task to form SWNTs into a homogeneous thin film. In addition, research results have recently been reported that show that it is important to separate tubes one by one when utilizing the optical and electronic functions of SWNTs (see, for example, Non-Patent Document 1).

In other words, when the tubes are bundled, the electronic physical properties are greatly changed by the interaction between the tubes, and the properties and functions inherent to SWNT cannot be fully exhibited. On the other hand, when the tubes are separated one by one using the surfactant, the original characteristics of SWNT are observed.
That is, in the SWNT / surfactant-dispersed aqueous solution, the peak of the light absorption spectrum is remarkably sharper than that of the bundled tube, and at the same time, light emission due to the interband optical transition is observed.
The absorption peak becomes sharp because the electronic state is no longer spread due to the interaction between tubes, and the emission is observed because the thermal excitation deactivation due to the interaction between tubes is lost.

Thus, in order to promote the utilization of SWNTs to industrial technology in the future, it is extremely important to develop a technique for forming tubes separated into individual pieces (hereinafter referred to as separated SWNTs) into a homogeneous thin film. It is important.
Conventionally, as such a SWNT-containing thin film, a thin film in which SWNT dispersed by a surfactant is combined with polyvinylpyrrolidone / polyvinyl alcohol has been reported (for example, see Non-Patent Document 2).

However, in this method, aggregation of the tube occurs in the thin film formation process, and the obtained SWNT becomes a bundle having a diameter of about 30 nm (the separation SWNT itself has a diameter of about 1 nm). Also, the peak of the absorption spectrum is broad, there is no description as to whether luminescence is observed, and the optical micrograph shows that this thin film is quite inhomogeneous.
That is, it is clear that such a thin film cannot fully utilize the optical, electronic characteristics and functions inherent in SWNT.

The present inventors have proposed a thin film containing SWNTs dispersed one by one using gelatin or a cellulose derivative as a matrix polymer (see Patent Documents 1 and 2).
This can be obtained by mixing SWNTs directly with these polymers, or by dispersing them with a surfactant and then mixing them with the polymer, so that a uniform SWNT-containing thin film can be obtained one by one. The emission peak in the near-infrared region, which is a characteristic of SWNT separated into two, can be observed.
However, according to subsequent studies by the present inventors, in these methods, since the matrix polymer is an electrically insulating material, it is difficult to pass a sufficient amount of current through the thin film. Up to now, it has been difficult to produce a photoelectric conversion element that converts light into current / voltage or an electroluminescence element that converts current into light using these thin films.

  Photoelectric conversion and electroluminescence are important optical / electronic functions expected for SWNTs having semiconductor properties (hereinafter also referred to as semiconductor SWNTs). In particular, since the light absorption / emission wavelength region of the semiconductor SWNT is in the near infrared region (800-2000 nm) that is important for optical communication technology, the photoelectric conversion element and the electroluminescence element using the semiconductor SWNT are extremely useful industrially. It is expected.

It has been experimentally proved that the semiconductor SWNT has these photoelectric conversion function and electroluminescence function (Non-Patent Documents 3 and 4).
However, in these reports, SWNTs dispersed in a solvent are dropped and dried on a silicon oxide film, and then an experiment is conducted using a scanning electron microscope from a very large number of randomly distributed SWNTs. Only one isolated SWNT suitable for the purpose is selected, and then a metal electrode is attached to the location using electron beam lithography, thereby measuring the photoelectric conversion characteristics and electroluminescence characteristics of the isolated SWNT.

In such a method, it is necessary to spend a great deal of time and labor to make one element, and it is difficult to control the reproducibility and reliability of element characteristics and to develop mass production technology. It could not be used industrially advantageously.
If SWNTs that are separated one by one are formed into a uniform thin film and a sufficient amount of current can flow through the thin film, photoelectric conversion functions such as photoconductivity and photovoltaic functions However, the electroluminescence function can be exhibited and its industrial utility value is extremely large, but a thin film that meets such a demand has not been developed yet.
Band gap fluorescence from individual single-walled carbonnanotubes, Science, vol. 297, pp 593-596 (2002) July 26, 2002 Poly (vinylalcohol) / SWNT Composite Film, Nano Letters, vol. 3, pp 1285-1288 (2003) September 2003 Photoconductivity of Single Carbon Nanotubes, Nano Letters, vol. 3, pp 1067-1071 (2003) Aug 2003 Electrically induced optical emission from a carbonnanotube FET, Science, vol.300, pp 783-786 (2003) May 2, 2003 Japanese Patent Application No. 2004-058033 Japanese Patent Application No. 2004-377140

  The present invention is a carbon nanotube-containing thin film in which single-walled carbon nanotubes are present in a state where they are separated from each other, and can fully exhibit the photoelectric conversion function and electroluminescence function inherent in semiconductor single-walled carbon nanotubes An object of the present invention is to provide a method for producing the thin film, a photoelectric conversion material and a photoelectric conversion element provided with the thin film, an electroluminescent material, and an electroluminescent element.

According to this application, the following invention is provided.
(1) A carbon nanotube-containing thin film characterized in that a plurality of single-walled carbon nanotubes are dispersed in a soluble polyphenylene vinylene substituted product or a copolymer thereof in a state of being separated from each other.
(2) A carbon nanotube-containing thin film characterized in that a plurality of single-walled carbon nanotubes are dispersed in a soluble polythiophene substitution product in a state of being separated from each other.

Moreover, the following invention can be provided.
(3) Soluble polyphenylene vinylene substituted product or a copolymer thereof, or a mixed solution containing a soluble polythiophene substituted product and a carbon nanotube is centrifuged, and the carbon nanotube-containing product is produced from the obtained supernatant Thin film manufacturing method.
(4) The method for producing a carbon nanotube-containing thin film according to (3), wherein the carbon nanotube-containing thin film is produced from a mixed solution in which a plurality of single-walled carbon nanotubes are dispersed in a mutually separated state.

Furthermore, this application can provide the following invention.
(5) A photoelectric conversion material and a photoelectric conversion element comprising the carbon nanotube-containing thin film according to (1) or (2).
(6) An electroluminescent material and an electroluminescent element comprising the carbon nanotube-containing thin film according to (1) or (2).

  The carbon nanotube-containing thin film of the present invention can exist in a state where single-walled carbon nanotubes are separated from each other, and has sufficient photoelectric conversion function and electroluminescence function originally possessed by semiconductor single-walled carbon nanotubes. It has an excellent effect that it can be exhibited.

The SWNT used in the present invention is not particularly limited, and a conventionally known SWNT can be used. There is no particular restriction on the diameter and length of SWNT, but it is preferable to use a SWNT having a diameter of about 0.4 to 2.0 nm and a length of about 0.1 to 1 μm.
The soluble polyphenylene vinylene substituted product or a copolymer thereof or the soluble polythiophene substituted product used in the present invention is not particularly limited, and a conventionally known one can be used, and a molecular weight of about 40000 to 250,000 is used. Is good.

  Examples of solubilized polyparaphenylene vinylene substituted products or copolymers thereof include poly (2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylene vinylene) (MEHPPV), poly [2- Methoxy-5- (3 ', 7'-dimethyloctyloxy) -1,4-phenylenevinylene], poly [2,5-bis (3', 7'-dimethyloctyloxy) -1,4-phenylenevinylene] Poly [2,5-bisoctyloxy) -1,4-phenylenevinylene], poly [2- [2 ', 5'-bis (2 "-ethylhexyloxy) phenyl] -1,4-phenylenevinylene], Poly [(m-phenylene vinylene) -co- (2,5-dioctoxy-p-phenylene vinylene)] and the like are preferably used.

As the substituted polythiophene, poly- (3-hexylthiophene), poly- (3-octylthiophene) (P3OT), poly- (3-decylthiophene), poly- (3-dodecylthiophene), etc. are preferably used Is done.
The SWNT-containing thin film of the present invention is dispersed in a thin film composed of a soluble polyphenylene vinylene substitution product, a copolymer thereof, or a soluble polythiophene substitution product in a state where a plurality of SWNTs are separated from each other without aggregation. Has a structure.
The SWNT-containing thin film has a thickness of 0.01 to 10 μm, preferably 0.05 to 1 μm. Further, the dispersion concentration (ratio) of the SWNT is 0.01 to 3% by weight. However, these numerical values show a preferable range, and it is natural that the numerical values can be adopted as needed even outside this numerical range.

In order to preferably produce the SWNT-containing thin film of the present invention, first, a commercially available mixed solution of SWNT and polymer is prepared. As the solvent, toluene, chloroform or the like is preferably used. In this case, the concentration of SWNT is 0.005 to 1% by weight, preferably 0.01 to 0.2% by weight, and the concentration of polymer is 0.005 to 1% by weight, preferably 0.01 to 0.2%. % By weight. In this case, dispersion promoting means such as ultrasonic treatment can be used in combination for dispersion of SWNTs.
The dispersion thus obtained is centrifuged to recover the supernatant containing fine SWNTs, and this supernatant is preferably used as the SWNT dispersion. In the centrifugation in this case, the rotation speed is 2000 to 20000 rpm, preferably 6000 to 12000 rpm, and the centrifugation time is 1 to 5 minutes.
It should be noted that these production conditions also indicate a preferable range and can be changed as necessary.

The SWNT-containing thin film of the present invention can be obtained by casting the SWNT / polymer mixture prepared as described above on a substrate. The film forming method is not limited to the cast film forming method, and various film forming methods such as a dip coating method and a spin coating method can be used.
The SWNT thin film thus obtained has a state in which SWNTs are separated from each other in a liquid by an excellent dispersion action of having a soluble polyphenylene vinylene substitution product, a copolymer thereof or a soluble polythiophene substitution product. It is contained while being held.
That is, SWNTs dispersed in the film exist in a state of being separated from each other without causing aggregation.

The fact that the thin films are separated from each other can be confirmed by observing a sharp emission peak peculiar to the separated SWNTs in the near infrared region when the thin film is irradiated with a laser beam of 662 nm. Further, by measuring the light absorption spectrum of the obtained thin film, the dispersion concentration of SWNT in the thin film was estimated to be 0.01 to 3% by weight.
When producing a photoelectric conversion element / electroluminescence device, a SWNT-polymer mixed solution is cast on the ITO film to produce a SWNT-containing thin film.
In this case, hole transport and hole injection can be promoted by previously coating ITO with poly (3,4-oxyethyleneoxythiophene) / poly (styrene sulfonate) (abbreviated as PEDOT). .
Next, an aluminum electrode or a silver electrode is vacuum-deposited on the SWNT-containing thin film to complete a photoelectric conversion element / electroluminescence element.

When the device thus obtained was irradiated with light in the near infrared region, a photocurrent was observed. When the wavelength dependence of the photocurrent was measured, a photocurrent spectrum that closely matched the near-infrared absorption spectrum of the semiconductor SWNT was observed.
From this, it is found that in this element, the light absorbed by the semiconductor SWNT is converted into a current, and it is proved that the photoelectric conversion function originally possessed by the separation SWNT is effectively expressed. .
When a voltage was applied to the device, it was observed that light emission occurred in the near infrared region. When the emission spectrum was measured, it was found that an emission peak appeared at substantially the same wavelength position as the near-infrared absorption spectrum of the separated SWNT and the emission spectrum obtained by irradiating the separated SWNT with laser light. This proves that the electroluminescence function inherent in the separation SWNT is effectively expressed in this element.

  As described above, the single-walled carbon nanotube-containing thin film according to the present invention forms a thin film in a state where SWNTs are separated from each other, and is a polyphenylene vinylene substituted substance or a copolymer thereof soluble or soluble as a matrix material. By using a conductive polymer such as a polythiophene-substituted product, the photoelectric conversion function and the electroluminescence function inherent in the semiconductor SWNT can be sufficiently expressed. It can be advantageously used as a near-infrared electroluminescent device.

  Next, the present invention will be described in more detail based on examples. In addition, the following description is for making an understanding of this invention easy, and is not restrict | limited to this. That is, all modifications, embodiments, and other examples based on the technical idea of the present invention are included in the present invention.

Example 1
10 mg of SWNT and 13 mg of poly (2-methoxy-5- (2-ethyl-hexyl) -1,4-para-phenylenevinylene) (MEHPPV) were mixed in 20 ml of toluene, and the mixture was dispersed by sonication. Centrifugation was performed at a rotational speed of 6000-12000 rpm.
By measuring the absorption spectrum and emission spectrum of the supernatant after centrifugation and referring to the data of Non-Patent Document 1 (Science, 297, 593-596 (2002)), the separated SWNTs are contained in the supernatant. Confirmed that it was included.
This dispersed aqueous solution was cast on a glass substrate and allowed to dry at room temperature to obtain a SWNT-containing thin film. The obtained thin film was visually confirmed to be optically homogeneous.

FIG. 1a shows the light absorption spectrum of this cast thin film. A series of sharp absorption peaks are observed in the near infrared region of 900-1500 nm, and SWNTs are separated from each other in this thin film by comparing with literature (Science, 297, 593-596 (2002)). Was found to exist.
Furthermore, when this thin film was irradiated with 662 nm laser light, an emission spectrum as shown in FIG. 1b was observed. Such light emission is not observed from the agglomerated SWNTs. In this thin film, the SWNTs are separated from each other, and the light emission function of the semiconductor SWNTs is kept good. It is proved that.

(Example 2)
10 mg of SWNT and 13 mg of poly- (3-octylthiophene) (P3OT) were mixed in 20 ml of toluene, and the mixture was dispersed by sonication, and then centrifuged at a rotational speed of 6000 to 12000 rpm. By measuring the absorption spectrum and emission spectrum of the supernatant after centrifugation and referring to the data in the literature (Science, 297, 593-596 (2002)), the separated SWNT is contained in this supernatant. It was confirmed.
This dispersed aqueous solution was cast on a glass substrate and allowed to dry at room temperature to obtain a SWNT-containing thin film. The obtained thin film was visually confirmed to be optically homogeneous.
FIG. 2 shows the light absorption spectrum of this cast thin film. A series of sharp absorption peaks are observed in the near infrared region of 900-1500 nm, and SWNTs are separated from each other in this thin film by comparing with literature (Science, 297, 593-596 (2002)). Was found to exist.

(Example 3)
PEDOT was spin-coated on an ITO-coated quartz substrate and annealed at 110 ° C. for 30 minutes in a nitrogen atmosphere. On top of this, the SWNT-MEHPPV mixed dispersion produced in Example 1 was cast into a film. The film thickness was about 500-1000 nm. An element having a structure of ITO / PEDOT / SWNT-MEHPPV / Al was produced thereon by vacuum-depositing an aluminum electrode.
When a voltage of −2 V was applied to the ITO side and the semiconductor SWNT was irradiated with near infrared light having light absorption, it was observed that photocurrent was generated. When the photocurrent spectrum was measured, it was found that a photocurrent peak appeared at substantially the same wavelength position as the absorption spectrum of the semiconductor SWNT (FIG. 3b), as shown in FIG. 3a. This indicates that the light absorbed by the semiconductor SWNT has been converted into an electric current, and proves that the photoelectric conversion function of the semiconductor SWNT can be effectively expressed.

Example 4
PEDOT was spin-coated on an ITO-coated quartz substrate and annealed at 110 ° C. for 30 minutes in a nitrogen atmosphere. On top of this, the SWNT-P3OT mixed dispersion prepared in Example 2 was cast into a film.
The film thickness was about 500-1000 nm. An element having a structure of ITO / PEDOT / SWNT-P3OT / Al was produced by vacuum-depositing an aluminum electrode thereon.
When a voltage of −2 V was applied to the ITO side and the semiconductor SWNT was irradiated with near infrared light having light absorption, it was observed that photocurrent was generated.
When the photocurrent spectrum was measured, it was found that a photocurrent peak appeared at substantially the same wavelength position as the absorption spectrum of the semiconductor SWNT (FIG. 4b), as shown in FIG. 4a. This indicates that the light absorbed by the semiconductor SWNT is converted into a current, and proves that the photoelectric conversion function of the semiconductor SWNT can be effectively expressed.

(Example 5)
When a voltage of 16 V was applied to the ITO side of the element having the structure of ITO / PEDOT / SWNT-MEHPPV / Al produced in the same manner as in Example 3, it was observed that light emission occurred.
When the emission spectrum was measured, as shown in FIG. 5a, the near-infrared absorption spectrum (FIG. 5b) of the separated SWNT and the emission (PL) spectrum (FIG. 5c) obtained by irradiating the separated SWNT with laser light were almost the same. It was found that an emission peak appears at the same wavelength position.
From this, it is proved that the electroluminescence function originally possessed by the semiconductor SWNT is effectively developed in this element.

  The carbon nanotube-containing thin film of the present invention can sufficiently exhibit the photoelectric conversion function and the electroluminescence function originally possessed by the semiconductor single-walled carbon nanotube, so that it has a response sensitivity in the near-infrared wavelength region. In addition, it is extremely useful as an electroluminescent device having an emission wavelength in the near infrared region.

It is a figure which shows the absorption spectrum (a) and light emission (PL) spectrum (b) (excitation wavelength: 662 nm) of the SWNT containing thin film obtained in Example 1. FIG. 6 is a graph showing an absorption spectrum of a SWNT-containing thin film obtained in Example 2. FIG. It is a figure which shows the photocurrent spectrum (a) and light absorption spectrum (b) of the SWNT-MEHPPV thin film element obtained in Example 3. It is a figure which shows the photocurrent spectrum (a) and light absorption spectrum (b) of the SWNT-P3OT thin film element obtained in Example 4. It is a figure which shows the electroluminescence spectrum (a) of the SWNT-MEHPPV thin film element obtained in Example 5, the absorption spectrum (b), and the emission (PL) spectrum (c) (excitation wavelength: 735 nm).

Claims (6)

  A carbon nanotube-containing thin film, wherein a plurality of single-walled carbon nanotubes are dispersed in a soluble polyphenylene vinylene substituted product or a copolymer thereof in a state of being separated from each other.   A thin film containing carbon nanotubes, characterized in that a plurality of single-walled carbon nanotubes are dispersed in a soluble polythiophene substitution product in a state of being separated from each other.   Production of carbon nanotube-containing thin film characterized by producing a soluble polyphenylene vinylene substituted product or a copolymer thereof, or a mixed solution containing a soluble polythiophene substituted product and carbon nanotube, by centrifugation, and producing the resulting supernatant. Method.   4. The method for producing a carbon nanotube-containing thin film according to claim 3, wherein the carbon nanotube-containing thin film is produced from a mixed solution in which a plurality of single-walled carbon nanotubes are dispersed in a mutually separated state.   A photoelectric conversion material and a photoelectric conversion element comprising the carbon nanotube-containing thin film according to claim 1. An electroluminescent material and an electroluminescent element comprising the carbon nanotube-containing thin film according to claim 1.

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