JP7246045B2 - organic gas sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas sensitive body for an organic gas sensor, an organic gas sensor, and a solar cell.

2. Description of the Related Art Conventionally, as a gas sensor, there is known a gas sensor that uses a material whose electrical characteristics (electrical resistance) change depending on the concentration of a gas to be detected as a gas sensitive body.

For example, Patent Document 1 describes a gas sensitive body formed by an aggregate of composite particles and having electrical characteristics that change with adsorption of a gas to be detected, and a gas sensor equipped with the gas sensitive body. ing. Composite particles are formed by supporting a material to be supported on a metal oxide support. The carrier is made of at least one selected from the group consisting of metals, alloys, oxides, and composite oxides containing a predetermined metal element. The metal oxide support is an oxide of at least one element selected from the group consisting of Y, Ce, Ti, Zr, Nb, Fe, Zn, Al, and Si. This gas sensitive body has an electrical resistance that changes with the adsorption of an organic gas such as acetone.

Humidity sensors using graphene oxide (GO) are also known. For example, Non-Patent Document 1 describes a humidity sensor using a nanocomposite film in which graphene oxide and a polymer electrolyte are laminated. In this humidity sensor, two coil-shaped electrodes are formed on a polyimide (PI) substrate, and a humidity sensing film is formed on the substrate and the electrodes. The humidity sensing film comprises two poly(diallyldimethylammonium chloride) (PDDA)/poly(sodium 4-styrenesulfonate) (PSS) bilayers and five GO/PDDA bilayers.

On the other hand, attempts have been made to use graphene oxide for a hole-transporting layer in a solar cell. For example, Non-Patent Document 2 describes a perovskite solar cell in which (GO)-doped poly(3,4-ethylenedioxythiophene) (PEDOT):(polystyrene sulfonic acid) PSS is used as the hole transport layer. there is

WO2017/064865

Sensors and Actuators B: Chemical, 2014, Vol.203, p.263-270 Scientific Reports，2018, Vol.8, Article number: 1070

In the technique described in Patent Document 1, the carrier of the gas-sensitive body is a metal, alloy, oxide, or composite oxide containing a predetermined metal element. Patent Document 1 does not describe that the gas sensing material contains graphene oxide. On the other hand, the technique described in Non-Patent Document 1 relates to a humidity sensor. Accordingly, the present invention provides a gas sensitive member for an organic gas sensor that contains graphene oxide and can impart desired properties to the organic gas sensor. The present invention also provides an organic gas sensor including such a gas sensitive body.

According to the technique described in Non-Patent Document 2, it is necessary to use PEDOT:PSS. Accordingly, the present invention provides a solar cell that includes a layer containing graphene oxide and is advantageous in exhibiting desired characteristics without using PEDOT:PSS.

The present invention
at least one polymer layer comprising a cationic polymer;
at least one graphene oxide layer;
The polymer layer and the graphene oxide layer are adjacent to form a laminate,
A gas sensitive body for an organic gas sensor is provided.

In addition, the present invention
a pair of electrodes;
and the above-described gas sensitive body for an organic gas sensor, which connects the pair of electrodes,
An organic gas sensor is provided.

In addition, the present invention
at least one polymer layer comprising a cationic polymer;
at least one graphene oxide layer;
The polymer layer and the graphene oxide layer are adjacent to form a laminate,
Provide solar cells.

The above-described gas sensitive body for organic gas sensors can impart desired properties to organic gas sensors.
The above solar cell is advantageous in exhibiting desired characteristics without using PEDOT:PSS.

FIG. 1 is a diagram showing an example of an organic gas sensor according to the present invention. FIG. 2 is a diagram showing an example of a solar cell according to the present invention. FIG. 3 is a diagram conceptually showing a measuring device for evaluating the performance of a gas sensor. 4 is a graph showing the performance of the gas sensor according to Example 1. FIG. 5 is a graph showing the performance of the gas sensor according to Comparative Example 1. FIG. 6 is a graph showing the performance of the gas sensor according to Example 2. FIG. 7 is a graph showing the performance of the gas sensor according to Example 3. FIG. FIG. 8 is a graph showing the performance comparison results of the gas sensors according to Examples 1-3. FIG. 9 is a graph showing the performance comparison results of the gas sensors according to Examples 1-3.

In the process of developing a sensor for detecting organic gases such as acetone gas, the present inventors investigated whether graphene oxide could be used as a gas sensitive body of an organic gas sensor. As a result, it was found that an organic gas sensor provided with a gas sensitive body obtained by applying a graphene oxide dispersion may not exhibit sufficient characteristics in some cases. Therefore, as a result of extensive trial and error, the present inventors produced an organic gas sensor by producing a gas sensitive body using a laminated body in which a graphene oxide layer and a predetermined polymer layer are adjacent to each other. It was newly found that the characteristics can be enhanced. Based on this new knowledge, the present inventors devised a gas sensitive body and an organic gas sensor according to the present invention. Furthermore, the present inventors thought that the performance of a solar cell could be improved by applying a laminate in which a graphene oxide layer and a predetermined polymer layer are adjacent to each other to a solar cell. I devised such a solar cell.

Embodiments of the present invention will be described below. In addition, the following description relates to an example of the present invention, and the present invention is not limited to this embodiment.

As shown in FIG. 1, the organic gas sensor 100 includes a gas sensitive body 10 and a pair of electrodes 20. As shown in FIG. The gas sensitive body 10 connects a pair of electrodes 20 . The gas sensitive body 10 comprises at least one polymer layer 11 and at least one graphene oxide layer 12 . Polymer layer 11 contains a cationic polymer. In the gas sensitive body 10, the polymer layer 11 and the graphene oxide layer 12 are adjacent to each other to form a laminate.

Graphene oxide is not particularly limited. Graphene oxide preferably satisfies at least one of being anionic and having an anionic group, and has a negative charge on its surface. In the gas sensitive body 10, the polymer layer 11 and the graphene oxide layer 12 are adjacent to each other to form a laminate. Due to the electrostatic interaction between the cationic polymer contained in the polymer layer 11 and the graphene oxide forming the graphene oxide layer 12, the laminate of the polymer layer 11 and the graphene oxide layer 12 tends to have a desired structure. For example, the graphene oxide layer 12 tends to have a dense structure. As a result, the organic gas sensor 100 tends to exhibit desired characteristics. For example, the organic gas sensor 100 can stably detect an organic gas even when the concentration of the organic gas is low. Also, the organic gas sensor 100 can exhibit high sensitivity to organic gases. Further, the gas sensitive body 10 has sensitivity to the gas to be detected even at a relatively low temperature (for example, 100° C. or less). A dense structure means a structure in which gaps in the in-plane direction between the graphene oxide layers forming the graphene oxide layer 12 are small. The graphene oxide layer 12 is preferably a single layer and has a dense structure.

As shown in FIG. 1, in the organic gas sensor 100, the gas sensitive body 10 is formed on a pair of electrodes 20 and a substrate 25, for example. The polymer layer 11 includes, for example, an underlying film 11a. The base film 11a is formed on the surface 22 made of an inorganic material. The inorganic material forming surface 22 is, for example, glass or a metal oxide. Note that silicon oxide is included in the term “metal oxide” in this specification. When a coating film of a dispersion of graphene oxide is directly formed on the surface 22, it is difficult for graphene oxide to form a film with a dense structure. However, since the polymer layer 11 is formed on the surface 22 and the polymer layer 11 and the graphene oxide layer 12 are adjacent to form a laminate, the graphene oxide layer 12 tends to have a dense structure.

In the gas sensitive body 10, for example, at least one polymer layer 11 and at least one graphene oxide layer 12 are alternately arranged. Thereby, the graphene oxide of each graphene oxide layer 12 tends to electrostatically interact with the cationic polymer contained in the polymer layer 11 .

The number of polymer layers 11 and the number of graphene oxide layers 12 included in the gas sensitive body 10 are not limited to specific numbers. From the viewpoint of increasing the sensitivity of the gas sensitive body 10 to organic gases, the gas sensitive body 10 desirably includes two or more polymer layers 11 and two or more graphene oxide layers 12 . In this case, two or more graphene oxide layers 12 allow graphene oxide to exist throughout the in-plane direction of the gas sensitive body 10 . As a result, a path for electron transfer is easily formed in the gas sensitive body 10 . Of the two or more graphene oxide layers 12, the graphene oxide layer 12 distal to the surface 22 is likely to come into contact with the organic gas. Therefore, the ratio of the number of graphene oxide layers 12 affected by the presence of the organic gas is high with respect to the total number of graphene oxide layers 12, and the gas sensitive body 10 tends to have high sensitivity to the organic gas. As a result, the organic gas sensor 100 tends to exhibit desired characteristics more reliably. In some cases, the number of polymer layers 11 and the number of graphene oxide layers 12 included in the gas sensitive body 10 may each be one.

The cationic polymer contained in polymer layer 11 is not limited to a specific polymer. Cationic polymers, for example, have ammonium ions. This facilitates electrostatic interaction between the cationic polymer and graphene oxide. Note that the ammonium ion also includes an amino group ion-exchanged with graphene oxide. When a polymer having an amino group is allowed to act on graphene oxide having an acidic functional group on its surface, the polymer having an amino group substantially becomes a polymer having ammonium ions due to an acid-base neutralization reaction. A polymer having such an amino group is also suitable as the cationic polymer of the present invention. Cationic polymers, for example, have constitutional units containing side chains with ammonium ions.
Examples of such cationic polymers include PDDA, polyethyleneimine, aminated acrylic polymer, aminated methacrylic polymer, polyallylamine, polydiallylamine, polyalkylallylamine, polyalkyldiallylamine, and acid salts thereof. The ammonium ions possessed by the cationic polymer are desirably quaternary ammonium ions.

The ratio (Nc/No) of the number of carbon atoms (Nc) to the number of oxygen atoms (No) in the graphene oxide forming the graphene oxide layer 12 is, for example, 3 or more. This makes it easier for the organic gas sensor 100 to exhibit desired characteristics more reliably. The ratio Nc/No may be 4 or more, or 5 or more. The ratio Nc/No is, for example, 19 or less.

Substrate 25 can be, for example, a glass substrate or a metal oxide substrate. The electrode 20 is made of a material such as Indium Tin Oxide (ITO), which has an electric resistance of a predetermined value (eg, 100Ω/□) or less. The distance between the pair of electrodes 20 is, for example, 5 μm to 100 μm.

The surface 22 made of inorganic material may be part of a substrate 25 made of inorganic material. On the other hand, surface 22 is desirably a surface formed of an inorganic material different from that of substrate 25 . For example, face 22 is desirably formed with a large surface area to facilitate interaction with gas. Specifically, it is desirable that a layer containing a nanometer-sized structure of metal oxide such as a nanorod of metal oxide having an aspect ratio of 2 or more be present between the substrate 25 and the gas sensitive body 10 . As a result, the sensitivity of the organic gas sensor 100 is likely to increase. Furthermore, it is desirable that the layer containing the nanometer-sized structure of the metal oxide has a structure permeable to the gas sensitive material described later. Sensitivity is likely to increase when the gas sensitive body is partially in contact with the electrode.

Inorganic particles of a different kind from the metal oxide may be supported on the nanometer-sized structure of the metal oxide. The inorganic particles are desirably at least one particle selected from metals, alloys and oxides containing elements belonging to groups 7 to 11 of the periodic table. As a result, the sensitivity of the organic gas sensor 100 is likely to increase. Furthermore, it is desirable that the inorganic particles are not in continuous contact with each other, but are discontinuously present, for example, in the form of islands. Thereby, the catalytic effect is more likely to be exhibited.

As shown in FIG. 1 , when the organic gas sensor 100 operates, the pair of electrodes 20 are connected to, for example, a power source 40 and a predetermined voltage is applied to the pair of electrodes 20 . Due to the action of the graphene oxide layer 12, the electrical resistance of the gas sensitive body 10 of the organic gas sensor 100 increases due to adsorption of the gas to be detected. Thereby, for example, the organic gas sensor 100 can detect the presence or absence of the gas to be detected in the gas to be inspected, and can also detect the concentration of the gas to be detected in some cases. The organic gas sensor 100 can stably detect the organic gas even when the concentration of the organic gas is low. Therefore, according to the organic gas sensor 100, the gas to be detected can be detected appropriately even when the gas to be detected has high humidity and the concentration of the gas to be detected is low. In addition, according to the organic gas sensor 100, it is possible to detect the gas to be detected at a relatively low temperature.

The gas sensitive body 10 is sensitive to acetone gas, for example. Therefore, the organic gas sensor 100 can detect acetone gas.

The organic gas sensor 100 can be produced, for example, as follows. First, a pair of electrodes 20 are formed on the substrate 25 . A method for forming the pair of electrodes 20 on the substrate 25 is not limited to a specific method. For example, when the substrate 25 is a glass substrate and the electrodes 20 are made of ITO, the ITO film-coated glass substrate is subjected to photolithography and etching to form a pair of electrodes 20 on the substrate 25 at predetermined intervals. can be formed. In this case, as photolithography and etching, a known method used for patterning ITO can be used. Alternatively, the pair of electrodes 20 may be formed on the substrate 25 at predetermined intervals by an ink jet method using an ink containing a component having electrical conductivity equal to or higher than a predetermined value.

If desired, a layer containing nanometer-sized structures of metal oxide may be formed on the substrate 25 . In this case, a coating film is formed on the substrate 25 with a previously prepared dispersion of metal oxide nanometer-sized structures. The coating film may be formed by applying the dispersion onto the substrate 25 or by immersing the substrate 25 in the dispersion. After that, if necessary, the coating film of the dispersion may be washed with a solvent such as ultrapure water. By this operation, the substrate 25 and the layer containing the nanometer-sized structures of the metal oxide are integrated, and the layer containing the nanometer-sized structures is formed substantially as part of the substrate 25 by the inorganic material. form a flat surface 22 .

The thickness of the layer containing the metal oxide nanometer-sized structures is not limited to a specific thickness. The thickness of the layer containing nanometer-sized structures of metal oxide is desirably such that, for example, when the gas-sensitive material permeates, a portion of the layer can come into contact with the electrode. Specifically, the thickness of the layer containing nanometer-sized metal oxide structures is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 200 nm or less.

Next, a coating film of a cationic polymer solution such as PDDA is formed on the substrate 25 . The coating film may be formed by coating the substrate with the cationic polymer solution, or by immersing the substrate 25 in the cationic polymer solution. After that, if necessary, the coating film is washed with ultrapure water. This allows removal of excess cationic polymer.

Next, a coating film of the graphene oxide dispersion is formed on the coating film of the cationic polymer solution. The coating film of the graphene oxide dispersion may be formed by applying the graphene oxide dispersion to the coating film of the cationic polymer solution, or by immersing the substrate in the graphene oxide dispersion. good too. After that, the coating film of the graphene oxide dispersion is washed with ultrapure water as needed. This removes the graphene oxide that is not electrostatically interacting with the cationic polymer, making it easier to obtain a monolayer graphene oxide layer. If necessary, the formation of a coating film of the cationic polymer solution and the formation of a coating film of the graphene oxide dispersion are alternately repeated.

Next, the temperature around the substrate 25 is maintained at a predetermined temperature for a predetermined time to cure these coating films. As a result, the graphene oxide is reduced, and the ratio Nc/No of the graphene oxide forming the graphene oxide layer 12 is easily adjusted to a desired range. The temperature around the substrate 25 for curing the coating film is, for example, 100 to 300° C., and the time for keeping the temperature around the substrate 25 within this temperature range is, for example, 0.1 to 5 hours. Thus, the organic gas sensor 100 can be produced.

As shown in FIG. 2, solar cell 200 comprises at least one polymer layer 61 and at least one graphene oxide layer 62 . Polymer layer 61 contains a cationic polymer. The polymer layer 61 and the graphene oxide layer 62 are adjacent to each other to form a laminate.

The solar cell 200 is configured as an organic solar cell or an organic-inorganic hybrid solar cell. A stack of at least one polymer layer 61 and at least one graphene oxide layer 62 constitutes the buffer layer 60 in the solar cell 200 . The solar cell 200 is, for example, a planar inverted perovskite solar cell. The solar cell 200 has a perovskite layer 50, for example. As a material forming the perovskite layer 50, a material known as a material forming a perovskite layer in a perovskite solar cell can be used. As one preferred form, a stack of at least one polymer layer 61 and at least one graphene oxide layer 62 constitutes the buffer layer 60 . The buffer layer 60 has a hole transport function in the solar cell 200, for example. Solar cell 200 may be a type of perovskite solar cell other than the planar inverted type. The solar cell 200 may be configured as an organic solar cell or an organic-inorganic hybrid solar cell other than perovskite solar cells.

Due to the electrostatic interaction between the cationic polymer contained in the polymer layer 61 and the graphene oxide forming the graphene oxide layer 62, a desired laminate of at least one polymer layer 61 and at least one graphene oxide layer 62 is formed. Easy to have structure. For example, in the buffer layer 60, the graphene oxide layer 62 tends to have a dense structure. Thereby, the solar cell 200 tends to exhibit high performance. Thus, a stack of at least one polymer layer 61 and at least one graphene oxide layer 62 can be used as a buffer layer for solar cells. The buffer layer may desirably double as the electron transfer layer.

In the buffer layer 60, for example, at least one polymer layer 61 and at least one graphene oxide layer 62 are alternately laminated. This makes it easier for the graphene oxide in each graphene oxide layer 62 to electrostatically interact with the cationic polymer contained in the polymer layer 61 .

The number of polymer layers 61 and the number of graphene oxide layers 62 included in the buffer layer 60 are not limited to specific numbers. The buffer layer 60 preferably comprises three polymer layers 61 and three graphene oxide layers 62 . In this case, the three graphene oxide layers 62 allow graphene oxide to exist throughout the in-plane direction of the buffer layer 60 . This facilitates the formation of appropriate paths for hole transport in the buffer layer 60 . In addition, the buffer layer 60 has a small thickness and low resistance to hole transport. Depending on the case, the number of polymer layers 11 and the number of graphene oxide layers 12 included in the buffer layer 60 may each be 1 to 2, or 4 or more.

The cationic polymer contained in polymer layer 61 is not limited to a specific polymer. Cationic polymers, for example, have ammonium ions. This facilitates electrostatic interaction between the cationic polymer and graphene oxide. Note that the ammonium ion also includes an amino group ion-exchanged with graphene oxide. When a polymer having an amino group is allowed to act on graphene oxide having an acidic functional group on its surface, the polymer having an amino group substantially becomes a polymer having ammonium ions due to an acid-base neutralization reaction. A polymer having such an amino group is also suitable as the cationic polymer of the present invention. Cationic polymers, for example, have constitutional units containing side chains with ammonium ions. Examples of such cationic polymers include PDDA, polyethyleneimine, aminated acrylic polymer, aminated methacrylic polymer, polyallylamine, polydiallylamine, polyalkylallylamine, polyalkyldiallylamine, and acid salts thereof. The ammonium ions possessed by the cationic polymer are desirably quaternary ammonium ions.

The ratio (Nc/No) of the number of carbon atoms (Nc) to the number of oxygen atoms (No) in the graphene oxide forming the graphene oxide layer 62 is, for example, 3 or more and 19 or less. This makes it easier for the solar cell 200 to more reliably exhibit high performance. The ratio Nc/No may be 4 or more and 19 or less, or may be 5 or more and 9 or less.

As shown in FIG. 2, the solar cell 200 has a transparent conductive film 71, for example. The transparent conductive film 71 is made of an inorganic material. The transparent conductive film 71 is made of, for example, metal oxide. At least one polymer layer 61 includes an underlying film 61a. The base film 61a is formed on the transparent conductive film 71, for example. When a coating film of a dispersion of graphene oxide is directly formed on the transparent conductive film 71, it is difficult to form a film having a dense structure of graphene oxide. On the other hand, by forming the polymer layer 61 on the transparent conductive film 71 and stacking the graphene oxide layer 62 on the polymer layer 61, the graphene oxide layer 12 tends to have a dense structure.

As a material forming the transparent conductive film 71, a known material as a material forming a transparent conductive film in a solar cell can be used. The material forming the transparent conductive film 71 is, for example, ITO.

As shown in FIG. 2, the solar cell 200 further comprises, for example, a glass substrate 72, an electron transport layer 81, a ZnO layer 82, and an electrode 83 in the case of a perovskite solar cell. A transparent conductive film 71 is formed on a glass substrate 72 . In solar cell 200 , one main surface of perovskite layer 50 is in contact with buffer layer 60 , and the other main surface of perovskite layer 51 is in contact with electron transport layer 81 . As a material forming the electron transport layer 81, a known material as a material forming an electron transport layer in a perovskite solar cell can be used. Electron transport layer 81 includes, for example, phenyl _C61 butyric acid methyl ester (PCBM). A ZnO layer 82 is formed on the electron transport layer 81 and an electrode 83 is formed on the ZnO layer. Electrode 83 is, for example, a silver electrode or an aluminum electrode.

Solar cell 200 can be fabricated, for example, as follows. First, an ITO film-coated glass substrate is prepared, and the surface of the ITO film is irradiated with ultraviolet rays (UV). Thereafter, a coating film of a cationic polymer solution such as PDDA is formed on the ITO film of the ITO film-coated glass substrate. The coating film may be formed by coating the substrate with the cationic polymer solution, or by immersing the ITO film-coated glass substrate in the cationic polymer solution. After that, if necessary, the coating film may be washed with ultrapure water. Thereby, the excessively attached cationic polymer can be removed.

Next, a coating film of the graphene oxide dispersion is formed on the coating film of the cationic polymer solution. The coating film of the graphene oxide dispersion may be formed by applying the graphene oxide dispersion to the coating film of the cationic polymer dispersion, or by applying the graphene oxide dispersion to the glass substrate with an ITO film. You may perform by immersion. After that, the coating film of the graphene oxide dispersion may be washed with ultrapure water as needed. As a result, the graphene oxide that does not electrostatically interact with the cationic polymer is removed, and a monolayer graphene oxide layer is easily obtained. After that, if necessary, the formation of the coating film of the cationic polymer solution and the formation of the coating film of the graphene oxide dispersion are alternately repeated.

Next, the temperature around the ITO film-coated glass substrate is maintained at a predetermined temperature for a predetermined time to cure these coating films. As a result, the graphene oxide is reduced, and the ratio Nc/No of the graphene oxide forming the graphene oxide layer is easily adjusted to a desired range. The ambient temperature of the ITO film-coated glass substrate for curing the coating film is, for example, 100 to 300° C., and the time for maintaining the ambient temperature of the ITO film-coated glass substrate in this temperature range is, for example, 0.1. ~5 hours. Thus, the buffer layer 60 can be formed.

Next, a coating film of a coating liquid for forming a perovskite layer is formed on the buffer layer 60 . The coating film is formed by a coating method such as spin coating. After that, the temperature around the ITO film-coated glass substrate is maintained at a predetermined temperature for a predetermined time to cure the coating film. The ambient temperature of the ITO film-coated glass substrate for curing the coating film is, for example, 50 to 150° C., and the time for keeping the ambient temperature of the ITO film-coated glass substrate within this temperature range is, for example, 0.1. ~300 minutes. Thereby, the perovskite layer 50 is formed.

A coating of PCBM solution is then formed on the perovskite layer 50 . The coating film is formed by a coating method such as spin coating. After that, the coating film is cured to form the electron transport layer 81 .

Next, a coating film of a ZnO dispersion is formed on the electron transport layer 81 . The coating film is formed by applying a coating liquid containing ZnO particles, for example, by a coating method such as spin coating. After that, the coating film is cured to form the ZnO layer 82 .

An electrode 83 is then formed on the ZnO layer 82 . The method for forming the electrode 83 is not particularly limited, but for example, the electrode 83 can be formed by vapor deposition.

The present invention will be described in detail below using examples. In addition, the following examples are examples of the present invention, and the present invention is not limited to the following examples.

<Example 1>
(Preparation of graphene oxide dispersion)
50 parts by mass of concentrated sulfuric acid (reagent special grade, manufactured by Wako Pure Chemical Industries) and 1.00 parts by mass of natural graphite (flaky graphite, average particle size: 25 μm, product name: Z-25, manufactured by Ito Graphite Industry Co., Ltd.) A mixture was obtained by adding to the reactor. While stirring the mixture, 3 parts by mass of potassium permanganate (reagent special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added to the mixture. After adding potassium permanganate, the mixture was heated to 35° C. and aged for 2 hours while maintaining the temperature of the mixture at 35° C. to obtain a product slurry (graphite oxide-containing slurry). Next, 20 parts by mass of the slurry was added to another container containing 80 parts by mass of ion-exchanged water while stirring the ion-exchanged water, and 30% hydrogen peroxide water (reagent special grade, manufactured by Wako Pure Chemical Industries) was added to 1.0%. Additional parts by mass were added. The contents of the vessel were agitated for 30 minutes and agitation was stopped. After stopping the agitation, the contents of the vessel were allowed to stand overnight to separate into a sediment layer and a supernatant. The contents of the vessel were then decanted. After that, ion-exchanged water of the same volume as the supernatant taken out to wash the sediment layer is added to the container, the contents of the container are stirred for 30 minutes, and the contents of the container are left to stand for 5 hours or more after stopping the stirring. Then, the supernatant was taken out again. The operation of adding ion-exchanged water, stirring the contents, and removing the supernatant was repeated until the pH of the supernatant reached 2 or higher. After that, an appropriate amount of ion-exchanged water was added to the obtained sediment layer, and graphene oxide contained in the sediment layer was dispersed using a homogenizer. Next, ion-exchanged water was further added to dilute the contents to obtain a graphene oxide dispersion. The concentration of graphene oxide in the obtained graphene oxide dispersion was 1% by mass.

(Fabrication of gas sensor)
Photolithography and etching were performed on an ITO film-coated glass substrate (ITO film thickness: 0.15 μm, glass substrate thickness: 0.7 mm) to form a pair of ITO electrodes with a distance of 1000 μm. Electrodes were formed on a glass substrate. The width of the electrodes was 2 mm. Next, UV irradiation (wavelength: 172 nm) was performed on the main surface of the glass substrate on which the pair of electrodes was formed and the pair of electrodes. The glass substrate was reciprocated twice at a speed of 2 mm/sec in the UV irradiation area.

After the glass substrate was immersed in an aqueous PDDA solution (PDDA concentration: 2% by weight) for 600 seconds, the glass substrate was lifted from the PDDA aqueous solution at a speed of 1 mm/sec to form a PDDA coating film. Next, the PDDA coating was brought into contact with ultrapure water for 10 seconds to wash the PDDA coating. Next, after the glass substrate was immersed in the graphene oxide dispersion for 600 seconds, the glass substrate was lifted from the graphene oxide dispersion at a speed of 0.5 mm/second to form a GO coating film. The formation of the PDDA coating and the formation of the GO coating were carried out once more in this order to obtain a coating in which two PDDA coatings and two GO coatings were alternately laminated. Next, the temperature around the glass substrate was maintained at 200° C. for 1 hour to cure the coating film and form a gas sensitive body. Thus, a gas sensor according to Example 1 was obtained.

<Examples 2 and 3>
(Formation of metal oxide nanorod layer)
With reference to Example 1 of Japanese Patent Application 2018-037275, 22.6 g of basic aluminum acetate (manufactured by Sigma-Aldrich) and 1.2 g of acetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) were added to 560 g of water to prepare a solution. bottom. This solution was placed in an autoclave and hydrothermally treated at 200° C. for 24 hours. After that, the autoclave was cooled to room temperature and the reaction solution was taken out from the autoclave. A part of this reaction solution was dried to obtain a dried product. From SEM observation and XRD analysis of this dried product, it was confirmed that this dried product was an aggregate of boehmite nanorods. A white powder was obtained by baking the dried product at 550° C. for 1 hour. When this white powder was subjected to XRD (X-ray diffraction) measurement, a diffraction peak of γ-alumina was observed. Further, observation of this white powder with a transmission electron microscope revealed that this white powder has a minor axis length of 5 to 30 nm, a major axis length of 20 to 1000 nm, and an aspect ratio of 2 to 200. They were rod-shaped alumina nanorods. The alumina nanorods were dispersed in water at a concentration of 10% by mass to obtain an alumina nanorod dispersion liquid A according to Example 2.

4.68 g of a PtPVP colloid aqueous solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., Pt content: 4.0 wt %) was added to half the above reaction solution and mixed. After that, the mixed liquid was placed in an environment of 100° C. under reduced pressure by a rotary evaporator to remove the solvent from the mixed liquid to obtain a solid. Next, the obtained solid matter was calcined in an air atmosphere at a temperature of 550° C. for 1 hour and then pulverized to obtain composite particles B. The loading ratio of Pt in this composite particle B was 5% by mass. From the XRD analysis of Composite Particle B, a Pt diffraction peak and a γ-alumina diffraction peak were observed. When the crystallite size of Pt was calculated from the diffraction peak of the Pt (311) plane near 2θ=81.5°, the crystallite size of Pt was 4.7 nm. The BET specific surface area of Composite Particle B was 119 m ² /g. The composite particles B were dispersed in water at a concentration of 10% by mass to obtain an alumina nanorod dispersion liquid B according to Example 3.

Before the formation of the coating film of the PDDA aqueous solution, a diluted dispersion obtained by diluting the alumina nanorod dispersion A and the alumina nanorod dispersion B with the same volume of ultrapure water was used, and a 10 mmφ glass rod was placed on the substrate. After dropping this diluted dispersion into the gap between the substrate and the glass rod, it was applied to the glass substrate at 60° C. and 10 mm/sec using the meniscus method to form alumina nanorod layers A and B, respectively. obtained gas sensors according to Examples 2 and 3 in the same manner as in Example 1.

<Comparative Example 1>
A gas sensor according to Comparative Example 1 was produced in the same manner as in Example 1 except for the following points. Instead of forming an alternating coating of two PDDA and two GO coatings, the above graphene oxide dispersion was spin-coated at 4000 rotations per minute (rpm) to connect a pair of electrodes. A glass substrate and a pair of electrodes were coated as follows. The temperature around the glass substrate was maintained at 200° C. for 1 hour to cure the coating film of the graphene oxide dispersion to form a gas sensitive body. Thus, a gas sensor according to Comparative Example 1 was obtained.

<Gas sensor performance measurement>
(measuring device)
A measuring device 300 shown in FIG. 3 was prepared. The measuring device 300 was equipped with seven mass flow controllers 32a, 32b, 32c, 32d, 32e, 32f and 32g. In addition, the measuring device 300 was equipped with a first high-pressure gas container 31a and a second high-pressure gas container 31b. Acetone was stored in the first high-pressure gas container 31a, and dry air was stored in the second high-pressure gas container 31b. The measurement device 300 further included a first container 33a, a second container 33b, a third container 33c, a fourth container 33d, a fifth container 33e, and a measurement container 35. These containers were closed containers. The first container 33 a is a container for diluting the acetone gas with dry air and for preparing and storing the gas to be supplied to the measurement container 70 . The second container 33b is a container for compressing and storing the dry air to be supplied to the measuring container 35 . Water is stored inside the third container 33c, and the third container 33c is a container for bubbling air against water. Water is stored inside the fourth container 33d, and the fourth container 33d is a container for bubbling air against the water. The fifth container 33e is a container for preparing and storing the gas to be supplied to the measuring container 35. FIG. As shown in FIG. 3, in the measuring device 300, the mass flow controller, the high-pressure gas container, and the container are connected by pipes, and valves such as solenoid valves, check valves, and on-off valves are attached to specific pipes. .

(Measuring method)
The environment of the measuring device 300 was kept at about 30°C. A gas sensor according to Example 1 or Comparative Example 1 was arranged in the measurement container 35 . The temperature inside the measurement container 35 was kept at about 30°C. A voltage of 1.5 V was applied to the pair of electrodes of the gas sensor. A picoammeter was used to measure the current value flowing between the pair of electrodes. By operating the mass flow controller and each valve of the measuring device 300, a mixed gas having a volume-based concentration of acetone gas of 0.2 to 4 ppm or 1 to 5 ppm and dry air were alternately supplied to the measuring vessel 35. FIG. 4 shows the time change of the current value between the pair of electrodes in the measurement using the gas sensor according to Example 1. As shown in FIG. Also, FIG. 5 shows the time change of the current value between the pair of electrodes in the measurement using the gas sensor according to Comparative Example 1. As shown in FIG.

As shown in FIG. 4, the gas sensor according to Example 1 stably detected low-concentration acetone gas of 0.2 to 4 ppm. The gas sensor according to Example 1 had high sensitivity to acetone gas. As shown in FIG. 5, in the gas sensor according to Comparative Example 1, the current value increased over time in the initial stage of measurement, and it was difficult to stably detect low-concentration acetone gas.

The evaluation results of the gas sensors obtained in Examples 2 and 3 are shown in FIGS. 6 and 7, respectively. FIG. 8 shows a comparison of the sensitivities (rates of change in response and current value [%]) for each acetone concentration in Examples 1, 2, and 3. FIG. In addition, FIG. 9 shows a comparison of changes in current values when the acetone concentration is 4 ppm. From these results, the sensitivity of the gas sensor improved in the order of Examples 1, 2, and 3, and the response (reaction) time to acetone also increased in the order of Examples 1, 2, and 3, and the introduction of acetone was stopped. It was also found that the recovery time of the current at the time of recovery was shorter in the order of Examples 1, 2, and 3. Table 1 shows specific comparison results. From these results, it was found that the use of an alternately laminated film of graphene oxide and PDDA films as the gas-sensitive layer improves the sensitivity of the gas sensor compared to the case of using a non-alternated laminated film. Furthermore, it was found that the sensitivity, response, and recovery time of the gas sensor are improved by forming the alumina nanorod layer, and the sensitivity, response, and recovery time of the gas sensor are further improved by supporting the platinum catalyst.

<Example 4-6>
(Fabrication of solar cell)
UV irradiation (wavelength: 172 nm) was performed on the ITO film of the ITO film-coated glass substrate (ITO film thickness: 0.15 μm, glass substrate thickness: 0.7 mm). The glass substrate was reciprocated four times at a speed of 10 mm/sec in the UV irradiation area.

After the glass substrate was immersed in an aqueous PDDA solution (PDDA concentration: 0.1% by weight) for 600 seconds, the glass substrate was lifted from the PDDA aqueous solution at a speed of 1 mm/sec to form a PDDA coating film. Next, the glass substrate was immersed in ultrapure water for 1 second, and pulled up from the ultrapure water at a speed of 20 mm/sec. An operation including immersion of the glass substrate in ultrapure water and pulling the glass substrate out of the ultrapure water was repeated 10 times in total. Thus, a PDDA coating was formed. After that, the glass substrate was immersed in the graphene oxide dispersion for 600 seconds, and then pulled out of the ultrapure water at a speed of 0.5 mm/second. Next, the glass substrate was immersed in ultrapure water for 1 second, and pulled up from the ultrapure water at a speed of 20 mm/sec. An operation including immersion of the glass substrate in ultrapure water and pulling the glass substrate out of the ultrapure water was repeated 10 times in total. Thus, a GO coating film was formed. Samples with one, two, and three graphene oxide layers were manufactured by adjusting the number of times of the above operation to 1, 2, and 3, respectively.

Next, the temperature around the glass substrate was maintained at 120° C. for 30 minutes to cure the PDDA coating and GO coating to form a buffer layer.

Perovskite precursor solution (PbI2 concentration: 1.2M, methylammonium iodide (MAI) concentration: 1.14M, methylammonium bromide (MABr) concentration: 0.06M, solvent: dimethyl sulfoxide (DMSO) and γ-butyrolactone (GBL) )) was spin-coated onto the buffer layer at 500 rpm and 5 seconds and then spin-coated onto the buffer layer at 3000 rpm and 50 seconds. Next, while rotating the glass substrate at a rotation speed of 5000 rpm, 70 μl of chlorobenzene was dropped toward the buffer layer for 20 seconds. After that, the glass substrate was annealed at 100° C. for 20 minutes in a nitrogen atmosphere. This formed a perovskite layer.

A PCBM solution (PCBM concentration: 30 g/l) was spin-coated onto the perovskite layer at 2000 rpm for 50 seconds. This formed an electron transport layer. Next, a ZnO particle dispersion (ZnO particle concentration: 2.7% by weight, average particle size of ZnO particles: 10-15 nm, dispersion medium: 2-propanol) was applied to the electron transport layer at 4000 rpm for 50 seconds. spin coated. This formed a ZnO layer. Next, aluminum was deposited on the ZnO layer to a thickness of 80 nm to form an electrode. Thus, a solar cell according to Examples 4-6 was obtained. The number of graphene oxide layers in the buffer layers of the solar cells according to Examples 4, 5, and 6 was one, two, and three, respectively.

<Comparative Example 2>
A solar cell according to Comparative Example 2 was produced in the same manner as in Example 4 except for the following points. In forming the buffer layer, the glass substrate was immersed in the graphene oxide dispersion for 600 seconds without being immersed in the PDDA aqueous solution, and then pulled up from the ultrapure water at a speed of 0.5 mm/sec. Next, the glass substrate was immersed in ultrapure water for 1 second, and pulled up from the ultrapure water at a speed of 20 mm/sec. An operation including immersion of the glass substrate in ultrapure water and pulling the glass substrate out of the ultrapure water was repeated 10 times in total. Thus, a GO coating film was formed. Next, the temperature around the glass substrate was maintained at 120° C. for 30 minutes to cure the GO coating and form a buffer layer.

<IV characteristics>
The IV characteristics of the solar cells according to Examples 4-6 and the solar cell according to Comparative Example 2 were measured according to IEC 60904-1:2006. From the measurement results, the open-circuit voltage V _OC , the short-circuit current density J _SC [mA/cm ² ], the fill factor FF, and the energy conversion efficiency PCE [ %]It was determined. Table 2 shows the results. As shown in Table 2, the PCE of the solar cells according to Examples 4-6 was higher than the PCE of the solar cell according to Comparative Example 2. It has been suggested that a buffer layer in which a graphene oxide layer is stacked on a polymer layer containing a cationic polymer improves the properties of a solar cell.

REFERENCE SIGNS LIST 10 gas sensitive body 11 polymer layer 11a base layer 12 graphene oxide layer 20 electrode 61 polymer layer 61a base layer 62 graphene oxide layer 71 transparent conductive film 100 organic gas sensor 200 solar cell

Claims (6)

at least one polymer layer comprising a cationic polymer;
at least one graphene oxide layer;
The polymer layer and the graphene oxide layer are adjacent to form a laminate,
The laminate is formed on a layer containing rod-shaped alumina nanorods having a minor axis length of 5 to 30 nm, a major axis length of 20 to 1000 nm, and an aspect ratio of 2 to 200.
Sensitive material for organic gas sensors. 2. The gas sensitive element for an organic gas sensor according to claim 1, wherein said cationic polymer has ammonium ions. 3. The gas sensitive element for an organic gas sensor according to claim 1, wherein the ratio of the number of carbon atoms to the number of oxygen atoms in the graphene oxide forming said graphene oxide layer is 3 or more and 19 or less. 4. The gas sensing element for an organic gas sensor according to claim 1, which is sensitive to acetone gas. a pair of electrodes;
and the gas sensing element for an organic gas sensor according to any one of claims 1 to 4, which connects the pair of electrodes,
Organic gas sensor. having a surface formed of an inorganic material,
wherein the at least one polymer layer comprises an underlayer formed on the surface;
The organic gas sensor according to claim 5.

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