JP4779321B2 - Microwave heating method for thin film - Google Patents

Description

  The present invention relates to microwave heating of a thin film used for heating a semiconductor thin film by microwave irradiation, such as during firing of a semiconductor particle thin film for adsorbing a required dye on a semiconductor electrode of a dye-sensitized solar cell. It is about the method.

  Conventionally, silicon solar cells using crystalline silicon, amorphous silicon, or the like as the photoelectric conversion material have been the mainstream, but in recent years, the photoelectric conversion material has been sensitized with a dye instead of the silicon material. Dye-sensitized solar cells that have been made to use the prepared semiconductor thin film have been developed, and such dye-sensitized solar cells can be manufactured at a lower cost than the silicon-based solar cells. Has attracted attention.

The basic structure of the dye-sensitized solar cell is configured as shown in FIG. That is, a transparent conductive film (semiconductor) 3 made of, for example, fluorine-doped tin oxide (FTO) or a compound made of indium oxide and tin oxide (ITO) is provided on one side of a glass substrate 2 by vapor deposition or the like. The transparent electrode 1 which is a conductive glass substrate is formed. On the surface of the transparent conductive film 3 in the transparent electrode 1, a porous semiconductor particle thin film 4 formed by sintering fine particles of titanium oxide (TiO ₂ ) is provided. A sensitive dye is adsorbed to form a semiconductor electrode 5 including the semiconductor particle thin film 4 adsorbed with the dye on the transparent electrode 1. Further, the transparent conductive film 3 in the transparent electrode 1 composed of the substrate 2 and the transparent conductive film 3 made of ITO or the like is formed on the semiconductor particle thin film 4 side on which the dye is adsorbed in the semiconductor electrode 5. A counter electrode 6 deposited with Pt (not shown) on the surface is overlapped, and an electrolyte solution 7 containing an oxidation-reduction pair such as iodine-iodine compound or bromine-bromine compound is impregnated in the gap between the electrodes 5 and 6. The periphery of the semiconductor electrode 5 and the counter electrode 6 is sealed with a sealing member (not shown) so that the electrolyte solution 7 does not leak outside.

As a result, as shown in FIG. 2 (b), when the light 8 is applied to the dye-sensitized solar cell, the dye 9 adsorbed on the semiconductor particle thin film 4 of the semiconductor electrode 5 is converted into the light 8. The electrons are absorbed and emitted, and the emitted electrons are quickly received by the titanium oxide forming the semiconductor particle thin film 4 and transmitted from the semiconductor thin film 4 to the transparent conductive film 3 of the transparent electrode 1. . The electrons reaching the transparent conductive film 3 are transmitted to the counter electrode 6 after passing through an external load 10 connected between the semiconductor electrode 5 and the counter electrode 6, and at the portion of the counter electrode 6, For example, triiodide ions (I ₃ ⁻ ) in the electrolyte solution 7 containing iodine-iodide as an oxidation-reduction product are reduced to iodide ions (I ⁻ ). The generated iodide ions (I ⁻ ) are oxidized by the dye 9 that has released the electrons adsorbed on the semiconductor particle thin film 4 of the semiconductor electrode 5, and the iodide ions (I ⁻ ) and triiodide ions are oxidized. When (I ₃ ⁻ ) cycles between the semiconductor electrode 5 and the counter electrode 6, the function as a battery is exhibited.

  By the way, when manufacturing the semiconductor electrode 5 used for the dye-sensitized solar cell, conventionally, nano-order ultrafine titanium oxide powder, preferably anatase-type titanium oxide powder, is used as the metal oxide. A paste (slurry) or a colloidal solution dispersed in a required dispersion medium such as squeegee method, screen printing, etc. on the surface of the transparent transparent conductive film 3 in the transparent electrode 1 Then, a thin film which is an aggregate of titanium oxide powder as semiconductor particles is formed by applying to a thickness of about 10 μm by a doctor blade method, spin coating, and the like, and thereafter, the transparent electrode 1 Each of these titanium oxide powders is put into an electric furnace and heated to a high temperature of about 400 ° C. and sintered. Porous whose effective surface area is about 1000 times on the surface of the transparent conductive film 3 of the transparent electrode 1 by mechanically and electrically bonding particles of ultrafine titanium oxide powder in a thin film as an aggregate. Thus, a large amount of dye can be adsorbed to the semiconductor particle thin film 4 and the current value generated per unit area of the dye-sensitized solar cell can be increased. It was like that.

  However, as described above, when the sintering operation of the semiconductor particle thin film 4 is performed using an electric furnace, the semiconductor particle thin film 4 alone cannot be heated, and the entire furnace body is heated. There is a problem that it takes time to cool down, and there is also a problem that electric power required for processing increases.

  Therefore, as one of the techniques for shortening the temperature raising time and temperature lowering time required for sintering the semiconductor particle thin film 4, the semiconductor particle thin film 4 may be heated by microwave irradiation. It has been.

  That is, a microwave having a frequency of 2.45 GHz is also used in a general microwave oven, and an application of a high-frequency 28 GHz is attempted for uniform heating in sintering of a ceramic bulk body. When the dielectric is irradiated, since the microwave is an electromagnetic wave having an electric field and a magnetic field, the electronic dipoles of the dielectric material try to align the direction according to the electric field of the microwave. However, it becomes impossible to follow as the frequency increases, and friction between molecules due to vibration and rotation occurs, so that the dielectric substance itself can generate heat. This energy loss is so-called dielectric loss, which is the principle of microwave heating. Therefore, according to such microwave heating, a portion having a large dielectric loss can be selectively heated, and a dielectric to be heated can be directly heated without waiting for a temperature rise of a furnace body or the like as in an electric furnace. The temperature can be raised in a short time, and since the temperature rise is limited to the dielectric and the peripheral portion that receives heat conduction from the dielectric, the temperature can be lowered in a short time.

  Therefore, as shown in FIG. 3A, a titanium oxide powder paste is applied to the surface of the transparent conductive film 3 in the transparent electrode 1 composed of the glass substrate 2 and the transparent conductive film 3 in the same manner as described above. After drying, a thin film (hereinafter referred to as a titanium oxide particle aggregate thin film) 4a that is an aggregate of titanium oxide powder is formed, and then the titanium oxide oxide 11 is placed on the substrate 2 side of the transparent electrode 1 on the alumina mount 11. The particle assembly thin film 4a side is placed in a position where it is placed on top and irradiated with, for example, a microwave 12 having a frequency of 28 GHz from the titanium oxide particle assembly thin film 4a side, or as shown in FIG. As shown, after the titanium oxide particle assembly thin film 4a is formed on the surface of the transparent conductive film 3 of the transparent electrode 1, the titanium oxide particle assembly thin film 4a side is placed on the alumina mount 11 as shown above. In addition, the transparent electrode 1 The plate 2 is placed in an upside position, and the same microwave 12 as above is irradiated from the substrate 2 side of the transparent electrode 1, whereby the titanium oxide particle aggregate thin film 4a is heated by microwaves. It has been proposed to sinter.

  In this case, in the posture shown in FIG. 3A, heat generated from the transparent conductive film 3 and the titanium oxide particle aggregate thin film 4a of the transparent electrode 1 is radiated to the substrate 2 made of glass and the atmosphere. On the other hand, in the posture shown in FIG. 3B, the heat generated from the transparent conductive film 3 and the titanium oxide particle aggregate thin film 4a is transferred to the glass substrate 2 and the alumina gantry 11 and then radiated to the atmosphere. Therefore, heat dissipation can be performed more quickly. For this reason, when the titanium oxide particle aggregate thin film 4a is heated and sintered in the posture shown in FIG. 3 (a), the glass substrate 2 is often broken during the temperature rise. This is presumed that since the microwave 12 is directly irradiated to the titanium oxide particle aggregate thin film 4a, the glass substrate 2 is damaged due to a sudden thermal stress. FIG. When the heating is performed in the posture shown in FIG. 2, since it is considered that the titanium oxide particle aggregate thin film 4a and the glass substrate 2 are heated relatively uniformly, it is advantageous for preventing the glass substrate 2 from being damaged. It has been reported that Reference numeral 11a in the figure indicates a thermocouple.

  Furthermore, instead of the glass substrate 2, a transparent electrode 1 in which a transparent conductive film 3 made of ITO is attached to a film substrate 2 made of resin, for example, PET may be used as the transparent electrode 1. It has been proposed (see Non-Patent Document 1, for example).

  As a method for reducing the processing temperature when sintering the particles of the fine particle titanium oxide powder in order to produce a semiconductor particle thin film in the semiconductor electrode of the dye-sensitized solar cell similar to the above, high frequency plasma, microwave When performing a sintering operation by plasma or a hybrid type plasma treatment thereof (for example, see Patent Document 1), or when performing a heating operation of a thin film that is an aggregate of titanium oxide particles as semiconductor particles, It has been conventionally proposed to use irradiation of electromagnetic waves such as ultraviolet rays, visible rays, infrared rays, and microwaves (see, for example, Patent Document 2).

JP 2003-308893 A JP 2002-134435 A Tomi, Uchida, Takizawa, “Sintering of titanium oxide film by 28 GHz microwave and application to dye-sensitized solar cell”, Functional Materials, June 2003, Vol 23, No. 6, p. 58-63

  However, microwave heating is a function of temperature because the dielectric loss coefficient as an efficiency converted to heat of input energy is a function of temperature. .

  That is, as shown in FIGS. 3A and 3B, in the method of heating the titanium oxide particle aggregate thin film 4a by the irradiation of the microwave 12, the semiconductor particle thin film 4 formed by sintering (FIG. ) (See (b)), or when the substrate 2 of the transparent electrode 1 is made of resin, the resin substrate 2 often ignites plasma, making practical application difficult. Is the current situation. All of these damages are thought to be caused by the thermal runaway associated with microwave heating as described above, and as a countermeasure, it has been considered that thermal runaway can only be prevented by devising heat dissipation.

  In Patent Document 1 and Patent Document 2, a titanium oxide semiconductor particle thin film constituting a semiconductor electrode of a dye-sensitized solar cell is sintered by high-frequency plasma, microwave plasma, or a hybrid plasma treatment thereof. However, it is described that the irradiation of electromagnetic waves such as ultraviolet rays, visible rays, infrared rays, and microwaves is used in combination when the semiconductor particle thin film is heated. No specific measures for preventing the occurrence of damage, such as plasma ignition, are shown and are not even suggested.

  Therefore, the present inventors have been able to perform semiconductor irradiation by microwave irradiation without causing damage such as cracking of the semiconductor particle thin film 4 and plasma ignition of the substrate 2 made of resin as has conventionally occurred when performing microwave heating. As a result of repeated efforts and research for heating the particle thin film 4 to enable sintering, the cause of damage such as cracking of the semiconductor particle thin film 4 and plasma ignition of the resin substrate 2 is as follows. It was found that the main cause was not dielectric breakdown but electrical breakdown and discharge ignition.

  That is, the present inventors have observed in detail the state of damage to the semiconductor particle thin film 4 that occurs in the process of heating and firing the semiconductor particle thin film 4 by microwave irradiation. From this, it was inferred that the damage caused to the semiconductor particle thin film 4 by the microwave irradiation was caused by the creeping discharge phenomenon. That is, when microwave irradiation is performed to sinter the semiconductor particle thin film 4, a partial potential difference is generated inside the semiconductor particle thin film 4. At this time, the semiconductor particle thin film 4 is as thin as about 10 μm. In spite of being a thin film, it is a semiconductor and therefore has the required electrical conductivity inside, and the above film regardless of the state of being attached on the transparent conductive film 3 of the transparent electrode 1. It was considered that a creeping discharge phenomenon that flows in the external space occurs rather than energizing the inside of the film due to the potential difference generated inside, and thus the semiconductor particle thin film 4 is cracked due to dielectric breakdown. Further, when the substrate 2 is made of resin, the resin on the substrate 2 is gasified by plasma along with the creeping discharge phenomenon, and this gas burns to cause plasma ignition of the resin substrate 2. It was thought that.

  In view of these ideas, the present inventors have prevented the occurrence of creeping discharge phenomenon when heating a semiconductor thin film by microwaves, thereby preventing the cracking of the semiconductor thin film or the resin. The present invention has been made by finding that it is possible to prevent the possibility of damage such as plasma ignition of a manufactured substrate.

  Accordingly, an object of the present invention is to provide a microwave heating method for a thin film so that heating can be performed by microwave irradiation without causing damage to the semiconductor thin film. .

In order to solve the above-mentioned problems, the present invention corresponds to the invention according to claim 1, wherein the transparent conductivity in a transparent electrode comprising a glass or resin substrate and a transparent conductive film provided on the surface of the substrate is provided. the surface of the membrane to form a thin film as an aggregate of semiconductor particles, by contacting the surface of the conductor over the entire anti-transparent conductive film side surface of the thin film, and thereafter, the thin film is irradiated with microwaves A method of heating is used.

Further, in correspondence with the invention according to claim 2, as an aggregate of semiconductor particles on the surface of the transparent conductive film in a transparent electrode comprising a glass or resin substrate and a transparent conductive film provided on the surface of the substrate. films were formed of contacting a surface of the conductor over the entire anti-transparent conductive film side surface of the thin film, and thereafter, a method of heating the thin film by irradiating microwave from Hanshirubeden side.

Further, the surface on the side of the conductor into contact with the surface of the thin film in the invention according to the claim 1 or 2, and smooth surface.

Furthermore, the surface on the side of the conductor into contact with the surface of the thin film in the invention according to the claim 1 or 2, as the porous surface, Ru surface of the conductive member is contacted points throughout the surface of the thin film Like that.

The semiconductors particles child in the structure described above and fine particles of titanium dioxide.

According to the microwave heating method of a thin film of the present invention, the following excellent effects are exhibited.
(1) to form a thin film as a collection surface to the semiconductor particles of the transparent conductive film of the transparent electrode comprising a transparent conductive film provided on the surface of the glass or plastic substrate and the substrate, the anti of the film contacting the surface of the conductor over the entire transparent conductive film surface, and thereafter, since the microwave irradiation are as for heating the thin film, the portion in the interior of the thin film the microwave is irradiated Even if a potential difference occurs, the high potential portion and the low potential portion can be energized through the conductor in contact with the surface of the thin film, so that the partial potential difference generated in the thin film can be eliminated. Therefore, it is possible to prevent the occurrence of a creeping discharge phenomenon that flows in the outer space of the thin film, so in the case where the thin film is cracked due to the occurrence of the creeping discharge phenomenon or the thin film is supported on a resin substrate. The thin film can be heated while preventing the occurrence of damage such as plasma ignition of the substrate.
(2) In the above, by irradiating microwaves from the side of the anticonductor, loss of microwaves due to transmission through the conductor can be avoided.
(3) By making the surface of the conductor on the side in contact with the surface of the thin film a smooth surface , the contact area between the thin film and the conductor can be widened to efficiently release heat from the thin film to the conductor. Therefore, it is advantageous when suppressing the possibility of thermal runaway when the thin film is heated by microwave irradiation.
(4) The surface of the conductor on the side contacting the surface of the thin film, as a porous surface, the surface of the conductive body by so as to contact points throughout the surface of the thin film, the conductive thin film Therefore, even when the microwave is weak, the thin film can be efficiently heated.
(5) In the above configuration, thin films, so are a thin film is an aggregate of semiconductors grains element attached to the surface of the transparent conductive film of the transparent electrode, the semiconductive material particles children in the thin film By sintering, a porous semiconductor particle thin film for adsorbing and holding the sensitizing dye at the semiconductor electrode of the dye-sensitized solar cell can be formed.
(6) the semiconductors grain child by the fine particles of titanium dioxide, a transparent conductive film surface of the transparent electrode of the semiconductor electrode of the dye-sensitized solar cell, by sintering the porous semiconductor particle thin film by a titanium oxide Can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 shows a semiconductor particle which is a component of a semiconductor electrode 5 in a dye-sensitized solar cell similar to that shown in FIGS. An example of application to the case where the thin film 4 is sintered on the surface of the transparent conductive film (semiconductor) 3 provided on the transparent electrode 1 is shown. That is, as shown in FIGS. 3 (a) and 3 (b), fine titanium oxide powder is formed on the surface of the transparent conductive film 3 in the transparent electrode 1 composed of the substrate 2 and the transparent conductive film 3 provided on the surface thereof. After the paste is applied and dried to form the titanium oxide particle assembly thin film 4a, the titanium oxide particle assembly thin film 4a is placed on the tray 13 or the conductor 13 in the form of a sheet. Then, the surface of the titanium oxide particle assembly thin film 4 a is brought into contact with the conductor 13. Further, if necessary, as shown by a two-dot chain line in FIG. 1, the holding plate 14 is placed on the substrate 2 and restrained from above, so that the conductor 13 and the titanium oxide particle aggregate thin film 4a are bonded. Make sure to keep it in contact. After that, the semiconductor particle thin film 4 is formed by irradiating the microwave 12 from above the holding plate 14 on the side of the anticonductor 13 to heat and sinter the titanium oxide particle aggregate thin film 4a. Like that. FIG. 1 shows a state after sintering of the semiconductor particle thin film 4, and the thin film of the titanium oxide particle aggregate before sintering is indicated by reference numeral 4a in parentheses.

  The conductor 13 may be a metal body such as nickel, aluminum, iron, or stainless steel having an electrical conductivity greater than that of the semiconductor particle thin film 4 made of titanium oxide.

  Furthermore, in order to efficiently suppress thermal runaway during microwave heating, the surface of the conductor 13 is in contact with the entire surface of the titanium oxide particle aggregate thin film 4a. What is necessary is just to be able to escape heat efficiently to the conductor 13 from the semiconductor particle thin film 4 of the titanium oxide sintered as what is provided with the smooth surface. In this case, the conductor 13 is provided with a heat radiation function by, for example, making the shape on the anti-thin film contact surface side into a shape that can actively dissipate heat to the external space, etc. You may make it acquire the runaway prevention effect positively. On the other hand, when it is desired to suppress the escape of heat from the titanium oxide particle aggregate thin film 4a to be heated because the output of the microwave 12 to be irradiated is weak, the conductor 13 has a porous surface. As a matter of course, the conductor 13 may be brought into point contact evenly over the entire surface within a range in which energization between the two can be ensured, not the entire surface contact with the film surface of the titanium oxide particle aggregate thin film 4a.

  The holding plate 14 is made of a material that has a dielectric loss coefficient sufficiently smaller than the titanium oxide particle aggregate thin film 4a that is desired to be heated, transmits the microwave 12 to be irradiated, and has a required heat resistance. Any material may be used.

  The substrate 2 may be made of glass, PET, or other resin as long as the dielectric loss coefficient is sufficiently small and the microwave absorption is smaller than that of the titanium oxide particle aggregate thin film 4a to be heated.

  When the titanium oxide particle aggregate thin film 4a provided on the surface of the transparent conductive film 3 of the transparent electrode 1 is irradiated with the microwave 12 according to the above-described microwave heating method of the thin film of the present invention, the titanium oxide which is a dielectric substance The particle aggregate thin film 4a is heated to be sintered to form a semiconductor particle thin film 4 of titanium oxide.

  At this time, even if a potential difference occurs inside the semiconductor particle thin film 4 during microwave irradiation due to the very thin thickness of the semiconductor particle thin film 4 to be formed, a portion having a high potential and a potential having a low potential are generated. Since the portions are connected and conducted through the conductor 13, the potential difference generated in the semiconductor particle thin film 4 can be eliminated, and therefore a creeping discharge phenomenon may occur in the semiconductor particle thin film 4. Can be prevented.

  Accordingly, the simple method of bringing the conductor 13 into contact with the surface of the thin film may cause breakage of the formed semiconductor particle thin film 4 or damage such as plasma ignition even when the substrate 2 is a resin. It is possible to perform microwave heating of the thin film in a state where the above is prevented.

  Further, the microwave 12 is not a special frequency of 28 GHz, and a stable thin film can be heated even with the microwave 12 of a general frequency of 2.45 GHz employed in a general microwave oven. it can.

  Furthermore, since the titanium oxide particle aggregate thin film 4a can be directly heated by the microwave 12, the time required for temperature increase and decrease can be reduced as compared with the case where an electric furnace is used for the sintering operation. It is possible to reduce the power required for this.

  Furthermore, since the irradiation of the microwave 12 is performed from the side of the anticonductor 13 with respect to the titanium oxide particle assembly thin film 4a, loss of the irradiated microwave 12 can be avoided.

  After the sintering process of the semiconductor particle thin film 4 by microwave heating is finished, the pressing plate 14 is removed, and then the transparent electrode on which the semiconductor particle thin film 4 is formed on the surface of the transparent conductive film 3 from the conductor 13. 1 may be collected and sent to the subsequent dye adsorption step.

  The present invention is not limited only to the above-described embodiment, and the conductor 13 has a thin film surface so that a potential difference generated inside the semiconductor particle thin film 4 to be heated and sintered can be eliminated during microwave irradiation. Any shape other than a tray or a sheet may be used as long as it has a surface that can be contacted evenly over almost the entire surface, and further, the thin film without blocking the microwave during microwave irradiation. As long as the contact state between the surface and the conductor 13 can be maintained, any means may be adopted as the means for holding the conductor 13 and the thin film in contact with each other, and the irradiation of the microwave 12 on the titanium oxide particle assembly thin film 4a However, if the conductor 13 is as thin as, for example, an aluminum foil and has a required microwave transmission property, the microwave is used. 2 may be irradiated from the conductor 13 side, and the irradiated microwave may be 2.45 GHz used for a general microwave oven if the thin film to be heated has a dielectric loss, or The microwave heating method for the thin film according to the present invention may have a dielectric loss coefficient that can be heated by microwave irradiation, and there is a potential difference inside the film during microwave irradiation. As long as it is a thin film such as a semiconductor that may cause creeping discharge, it is not limited to the laminated structure of the thin film as shown in FIG. 1, and further, a semiconductor used for a semiconductor electrode of a dye-sensitized solar cell Needless to say, the present invention can be applied to heating of a thin film other than the particle thin film, and various modifications can be made without departing from the scope of the present invention.

It is a schematic side view which shows one Embodiment of the microwave heating method of the thin film of this invention. An example of a dye-sensitized solar cell is shown, (A) is a schematic cut side view, (B) is a figure which shows the outline | summary of an electric power generation mechanism. In order to sinter the semiconductor particle thin film of titanium oxide on the surface of the transparent conductive film of the transparent electrode, this shows a thin film heating method that has been proposed by microwave irradiation. (B) is a schematic side view showing the case where irradiation is performed from the titanium particle aggregate thin film side, and (b) is the case where irradiation is performed from the substrate side.

Explanation of symbols

1 Transparent electrode 2 Substrate 3 Transparent conductive film (semiconductor)
4 Semiconductor particle thin film (thin film)
4a Titanium oxide particle aggregate thin film (thin film)
12 Microwave 13 Conductor

Claims (5)

The transparent electrode comprising a transparent conductive film provided on a glass or plastic substrate and the substrate surface to form a thin film as an aggregate of semiconductor particles to the surface of the transparent conductive film, anti transparent conductive the film A method for heating a thin film by microwaves , wherein the surface of the conductor is brought into contact over the entire surface on the film side , and then the thin film is heated by irradiation with microwaves. The transparent electrode comprising a transparent conductive film provided on a glass or plastic substrate and the substrate surface to form a thin film as an aggregate of semiconductor particles to the surface of the transparent conductive film, anti transparent conductive the film A method for heating a thin film by microwaves , wherein the surface of the conductor is brought into contact over the entire surface of the film side , and then the microwave is irradiated from the side of the non-conductor to heat the thin film. The microwave heating method for a thin film according to claim 1 or 2, wherein the surface of the conductor on the side in contact with the surface of the thin film is a smooth surface . The surface on the side of the conductor into contact with the surface of the thin film, and a porous surface, the thin film according to claim 1 or 2, wherein was set to the surface of the conductive member contacting points throughout the surface of the thin film micro Wave heating method. Microwave heating method of a thin film according to claim 1, 2, 3 or 4, wherein the semiconductor body particles child was fine particles of titanium dioxide.

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