JP2013114790A - Method for producing transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a transparent conductive film, by which a transparent conductive film having excellent characteristics can be inexpensively produced through simple manufacturing processes.SOLUTION: In forming a transparent conductive film comprising a fluorine-doped tin oxide film on a deposited surface 101 of a transparent substrate 100, the transparent substrate 100 is heated in a heating part 14 so that the temperature at the deposited surface 101 is at 500°C or above, a transparent conductive film is deposited by spraying a raw material solution of the transparent conductive film to the deposited surface 101, in a deposition part 15, and the transparent conductive film is subjected to heat treatment in air atmosphere at temperatures of 400°C or above and 500°C or below during 5 minutes or more and 45 minutes or less, in a heat treatment part 16.

Description

  The present invention relates to a method for producing a transparent conductive film, and more specifically, production of a fluorine-doped tin oxide film (FTO (Fluorine doped Tin Oxide) film) as a transparent conductive film provided on a transparent substrate of a thin film solar cell. Regarding the method.

  Conventionally, a tin oxide film, a zinc oxide film, an indium oxide film, and the like are known as transparent conductive films. Among these, the tin oxide film is not only inexpensively manufactured as compared with other films but also chemically stable, and thus is particularly suitably used as a transparent conductive film provided on a transparent substrate of a thin film solar cell. ing.

  Generally, the characteristics of the transparent conductive film that are important for increasing the photoelectric conversion rate in a thin film solar cell include sheet resistance, light transmittance, and haze rate. Here, the haze ratio is an index indicating the degree of scattering of transmitted light, and is expressed as a ratio (percentage) of diffuse transmittance to total transmittance, and the fineness of the film surface formed by crystallization of the transparent conductive film. Determined by the texture (unevenness) structure.

  The sheet resistance preferably shows a smaller value in order to prevent the current generated by the photoelectric change from being consumed when passing through the transparent conductive film. The light transmittance is preferably higher so that more light incident on the transparent conductive film reaches the photoelectric conversion layer. It is preferable that a haze rate shows a higher value so that the light which injected into the transparent conductive film may be confined in a transparent conductive film by repeating reflection.

  From such a viewpoint, the characteristics of the transparent conductive film used for the thin film solar cell are preferably a sheet resistance of 12Ω / □ or less, a light transmittance of 80% or more, and a haze ratio of about 7% to 15%. It is required to be.

  However, these three required characteristics are in a so-called trade-off relationship in which other characteristics are not satisfied when the film forming conditions of the transparent conductive film are adjusted so as to satisfy any of the characteristics. For example, when the film thickness of the transparent conductive film is increased, the sheet resistance is decreased and the haze ratio is increased, but the light transmittance is significantly decreased. Thus, it has been extremely difficult to realize a transparent conductive film that simultaneously satisfies these three characteristics.

  On the other hand, it is known that the sheet resistance and transmittance of the transparent conductive film can be changed by performing a specific heat treatment after forming the transparent conductive film.

  For example, Japanese Patent Laid-Open No. 63-170813 (Patent Document 1) discloses that after a transparent conductive film is formed, the transparent conductive film is heat-treated in an air atmosphere at a temperature higher than the film forming temperature. Thus, it is disclosed that the light transmittance can be improved.

  Japanese Patent Laid-Open No. 63-184210 (Patent Document 2) discloses a method of performing sheet heat treatment and light resistance by performing heat treatment in a reducing atmosphere such as nitrogen gas or hydrogen gas after forming a transparent conductive film. It is disclosed that the transmittance can be improved.

JP-A 63-170813 JP-A 63-184210

  However, when the methods as disclosed in Patent Documents 1 and 2 are adopted, the following problems arise separately.

  Since the technique disclosed in Patent Document 1 performs heat treatment of the transparent conductive film under a temperature condition higher than the film formation temperature, the productivity is extremely deteriorated and the manufacturing cost is greatly increased. There is. In addition, Patent Document 1 describes that the light transmittance of the transparent conductive film is improved after the heat treatment as compared to immediately after the film formation, but the sheet resistance and the haze ratio are also improved. No mention is made of whether or not is made.

  Since the technique disclosed in Patent Document 2 performs heat treatment of the transparent conductive film in a reducing atmosphere, the carrier density in the transparent conductive film increases and the sheet resistance decreases. As the carrier density increases, there is a concern that the light transmittance will decrease. In addition, in order to perform the heat treatment in a reducing atmosphere, it is necessary to use a large amount of gas such as hydrogen or nitrogen, which causes a problem that the manufacturing cost is greatly increased.

  Therefore, the present invention has been made in view of the above-described problems, and the object of the present invention is to provide a transparent conductive film that can be manufactured at a low cost by a simple manufacturing process with a transparent conductive film having excellent characteristics. It is to provide a method for manufacturing a film.

  As a result of diligent research, the present inventor has conducted heat treatment under specific conditions even when heat treatment after film formation is performed in an air atmosphere in the production of a fluorine-doped tin oxide film as a transparent conductive film. As a result, it was found that the sheet resistance can be reduced without lowering the light transmittance and haze ratio of the formed transparent conductive film, and the present invention has been completed.

  That is, the method for producing a transparent conductive film according to the present invention forms a transparent conductive film made of a fluorine-doped tin oxide film on a film formation surface of a transparent substrate, and the temperature of the film formation surface is The transparent conductive film is formed on the film formation surface by spraying the raw material solution of the transparent conductive film on the film formation surface while heating the transparent substrate so that the temperature becomes 500 ° C. or higher. And a step of heat-treating the transparent conductive film formed on the deposition surface in an air atmosphere of 400 ° C. to 500 ° C. for 5 minutes to 45 minutes. To do.

  Moreover, in the manufacturing method of the transparent conductive film based on the said invention, the raw material solution of the said transparent conductive film is 22at. It may be further characterized by containing water and methanol as a solvent.

  In the method for producing a transparent conductive film according to the present invention, the step of performing the heat treatment is performed subsequent to the step of forming the transparent conductive film, and the transparent conductive film is subjected to −20 ° C./min. It may be further characterized by being carried out by slow cooling at the following temperature gradient.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture the transparent conductive film which has the outstanding characteristic at low cost with a simple manufacturing process. That is, the transparent conductive film manufactured according to the method for manufacturing a transparent conductive film according to the present invention has low sheet resistance, high light transmittance, and high haze ratio.

It is a schematic diagram of the manufacturing apparatus used in the manufacturing method of the transparent conductive film in embodiment of this invention. It is a conceptual diagram of the film-forming apparatus for a test used in the Example and the comparative example. It is a table | surface which shows the measurement results of the manufacturing conditions and various characteristics of the transparent conductive film in Examples 1 to 3 and Comparative Examples 1 to 3. 6 is a graph showing spectral characteristics of light transmittance of a transparent conductive film in Example 3. 12 is a graph showing spectral characteristics of light transmittance of a transparent conductive film in Comparative Example 3. It is a graph which shows the result of the verification test 1 which verified the relationship between the time of heat processing, the temperature of heat processing, and the sheet resistance of a transparent conductive film. It is a graph which shows the result of the verification test 2 which verified the relationship between the time of heat processing, the addition amount of ammonium fluoride, and the sheet resistance of a transparent conductive film. It is a graph which shows the result of the verification test 3 which verified the relationship between the temperature of heat processing, the addition amount of ammonium fluoride, and the sheet resistance of a transparent conductive film. It is a graph which shows the result of the verification test 4 which verified the relationship between the temperature gradient in the slow cooling process in the case of heat processing, and the curvature amount of a transparent substrate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiment described below, first, a case where the present invention is applied to a case where a transparent conductive film is manufactured on a transparent substrate of a thin film solar cell using a continuous film forming apparatus suitable for mass production is used. The description will be given by way of example, and then, various verification tests carried out in completing the examples and comparative examples and the present invention will be specifically described.

  FIG. 1 is a schematic diagram of a manufacturing apparatus used in a method for manufacturing a transparent conductive film in an embodiment of the present invention. The manufacturing method of the transparent conductive film based on this invention is typically implement | achieved by using the continuous film-forming apparatus 10 shown by FIG. In addition, the manufacturing method of the transparent conductive film based on this invention is realizable also when using other types of film-forming apparatuses, such as a batch type, besides using a continuous-type film-forming apparatus.

  As shown in FIG. 1, the film forming apparatus 10 includes a transport mechanism 11, a heating furnace 12, a substrate carry-in unit 13, a heating unit 14, a film forming unit 15, a heat treatment unit 16, and a substrate carry-out unit 17. It has. The heating unit 14, the film forming unit 15, and the heat treatment unit 16 are provided adjacently in this order from the upstream side to the downstream side on the transport path configured by the transport mechanism 11. The heating furnace 12 is disposed so as to straddle the part 15 and the heat treatment part 16. The substrate carry-in unit 13 is provided on the upstream side of the heating furnace 12, and the substrate carry-out unit 17 is provided on the downstream side of the heating furnace 12.

  The transparent substrate 100 is carried in and placed on the conveyance path constituted by the conveyance mechanism 11 in the substrate carry-in unit 13. The transparent substrate 100 placed on the transport path is transported by the transport mechanism 11 along the arrow direction shown in the figure. Thereby, the transparent substrate 100 is sequentially put into the heating unit 14, the film forming unit 15, and the heat treatment unit 16 described above. The transparent substrate 100 after passing through the heat treatment unit 16 is unloaded by being removed from the conveyance path by the substrate unloading unit 17.

  Here, with respect to the transparent substrate 100, predetermined processing is performed in each of the heating unit 14, the film forming unit 15, and the heat treatment unit 16 described above, whereby the film formation surface 101 that is the upper surface of the transparent substrate 100 is processed. A transparent conductive film is formed. As the transparent substrate 100, any substrate can be used as long as it can sufficiently transmit light in the light absorption region of the photoelectric conversion layer of the thin film solar cell. For example, a glass substrate, a resin substrate, or the like can be used. More preferably, an alkali-free glass substrate is used. The transparent conductive film formed on the transparent substrate 100 is an FTO film that is a tin oxide film doped with fluorine. The film thickness of the transparent conductive film is preferably 600 nm or more and 1200 nm or less.

  In the method for producing a transparent conductive film according to the present invention, a transparent conductive film raw material solution is applied to the film formation surface 101 while heating the transparent substrate 100 so that the temperature of the film formation surface 101 is 500 ° C. or higher. The step of forming a transparent conductive film on the film formation surface 101 by spraying, and the transparent conductive film formed on the film formation surface 101 for 5 minutes in an air atmosphere of 400 ° C. to 500 ° C. And a step of performing a heat treatment for 45 minutes or less. Among these, the former process is performed in the heating unit 14 and the film forming unit 15, and the latter process is performed in the heat treatment unit 16. Hereinafter, these steps will be described in order.

  The transparent substrate 100 is heated to 500 ° C. or more, which is the film forming temperature of the transparent conductive film, in the heating unit 14. More specifically, when the transparent substrate 100 passes through the heating furnace 12 in which the transparent substrate 100 is heated, the temperature of the film formation surface 101 is heated to 500 ° C. or higher. By heating the transparent substrate 100 to such a temperature, even if fluorine is taken into the transparent conductive film during the film formation, the crystallinity of the transparent conductive film during the film formation or during the slow cooling process after the film formation. Therefore, the light transmittance can be increased.

  As described above, the heating temperature of the transparent substrate 100 needs to be 500 ° C. or higher, and more preferably 530 ° C. or higher and 700 ° C. or lower. When the heating temperature of the transparent substrate 100 is less than 500 ° C., the film formation temperature is lowered by the sprayed raw material solution, and the crystallinity of the transparent conductive film may be lowered, which is not preferable. When the heating temperature of the transparent substrate 100 exceeds 700 ° C., it is difficult to cause the droplets of the raw material solution to reach the film formation surface 101 of the transparent substrate 100, which may reduce the film formation rate.

  The present embodiment shows a case where the transparent substrate 100 is configured to be heated by convective heat transfer using the heating furnace 12, but the transparent substrate 100 is heated to the predetermined temperature described above. If it is possible, other heating methods may be employed. For example, instead of heating by the heating furnace 12, the transparent substrate 100 may be heated by direct conductive heat transfer using a hot plate or the like, or the transparent substrate 100 may be heated by convective heat transfer using an infrared lamp or the like. May be.

  A transparent conductive film is formed on the transparent substrate 100 in the film forming unit 15. More specifically, a spray mechanism 18 is installed in the film forming unit 15 so as to face the transport path through which the transparent substrate 100 is transported, and the raw material solution of the transparent conductive film is atomized by the spray mechanism 18. By being sprayed toward the film formation surface 101 of the transparent substrate 100, a transparent conductive film is formed on the film formation surface 101 of the transparent substrate 100.

  As a raw material solution for a transparent conductive film, one or two or more materials made of an organometallic or metal halide compound containing tin such as tin tetrachloride, tin dichloride, dibutyltin diacetate, and tetrabutyltin are dissolved in a solvent. Is used. As the solvent, water, an organic solvent, or a mixture thereof is used. Here, for example, methanol, ethanol, acetone, isopropyl alcohol or the like is used as the organic solvent. The raw material solution for the transparent conductive film contains a fluorine compound as a dopant agent. Here, hydrogen fluoride, ammonium fluoride, or the like is used as the fluorine compound.

  As a raw material solution for such a transparent conductive film, the above organic metal or metal halide compound is generally dissolved in a solvent at a concentration of about 0.1 mol / L to 0.3 mol / L. The concentration is not limited. In addition to the above, the raw material solution for the transparent conductive film may further contain other additives such as a surfactant and a pH adjuster.

  The spray mechanism 18 includes a two-fluid spray nozzle that mixes and sprays a raw material solution of a transparent conductive film and a carrier gas. The spray mechanism 18 atomizes the raw material solution into droplets having an average particle diameter of 0.1 μm or more and several tens of μm or less, and sprays this onto the film formation surface 101 of the transparent substrate 100. At this time, the atomized liquid droplets of the raw material solution are sprayed onto the film formation surface 101 of the transparent substrate 100 in a high-pressure carrier gas stream. As the carrier gas, compressed air, nitrogen, hydrogen, water vapor, oxygen, or a mixture thereof can be used.

  In the present embodiment, the raw material solution of the transparent conductive film is atomized using a two-fluid spray nozzle and sprayed onto the film formation surface 101 of the transparent substrate 100, thereby transparent on the film formation surface 101 of the transparent substrate 100. This shows the case where a spray system configured to form a conductive film is used, but in addition to this, the raw material solution of the transparent conductive film is atomized using an ultrasonic vibrator, etc. A mist method of spraying on the deposition surface 101 of the substrate 100 may be employed.

  Here, the mist method is to generate droplets from the liquid surface by applying ultrasonic waves to the raw material solution of the transparent conductive film using, for example, an ultrasonic vibrator. Since there is no kinetic energy, this is sprayed onto the film formation surface 101 of the transparent substrate 100 using a carrier gas. As the carrier gas, the same gas as that used in the above-described spray method can be used. When such a mist method is adopted, it is possible to generate droplets having a fine and relatively uniform particle size, and thus it is advantageous that droplets are difficult to condense during the transport of the droplets. It is done.

  The heat treatment unit 16 performs a predetermined heat treatment on the transparent substrate 100 on which the transparent conductive film is formed on the film formation surface 101. Here, the predetermined heat treatment is a treatment in which the transparent conductive film formed on the film formation surface 101 is exposed in an air atmosphere of 400 ° C. to 500 ° C. for 5 minutes to 45 minutes. More specifically, the transparent substrate 100 having a transparent conductive film formed on the film formation surface 101 is heated in the heating furnace 12 in which the atmosphere in which the inside is heated to a predetermined temperature is introduced in the heat treatment unit 16. By passing through the inside, the transparent conductive film formed on the film formation surface 101 is exposed under the temperature condition and the time condition.

  By performing such a heat treatment, the sheet resistance of the transparent conductive film after the heat treatment maintains its light transmittance as compared with the transparent conductive film before the heat treatment (that is, immediately after film formation), and the haze ratio thereof. As a result, the resistance is lowered. Therefore, by performing the heat treatment, it becomes possible to produce a transparent conductive film having low sheet resistance, high light transmittance, and high haze ratio.

  Here, in the said heat processing part 16, if it is in the range with which the said temperature conditions and time conditions are satisfy | filled, the reheating process which heats again after cooling the transparent substrate 100 in which the transparent conductive film was formed to predetermined temperature once. Alternatively, it may be a slow cooling process that gradually cools the transparent substrate 100 on which the transparent conductive film is formed. In particular, when annealing is employed, heat treatment is performed subsequent to the step of forming the transparent conductive film, and therefore the tact time required for manufacturing the transparent conductive film can be shortened. As a result, productivity is greatly improved, and deformation of the transparent substrate 100 such as warpage can be suppressed.

  When the heat treatment is performed by slow cooling, for example, when the transparent conductive film immediately after film formation is 500 ° C., as an example, if the heat treatment is performed for 5 minutes at a temperature gradient of −20 ° C./min. The temperature of the transparent conductive film after the heat treatment is 400 ° C., which satisfies the above temperature condition and time condition. For example, when the transparent conductive film immediately after film formation is 490 ° C., as another example, if the heat treatment is performed for 45 minutes at a temperature gradient of −2 ° C./min, the temperature of the transparent conductive film after the heat treatment Becomes 400 ° C., which satisfies the above temperature condition and time condition.

  As described above, since it is sufficient to perform the heat treatment in the air atmosphere by adopting the method for manufacturing the transparent conductive film in the present embodiment, in a reducing atmosphere such as nitrogen gas or hydrogen gas. The manufacturing cost can be reduced compared to the case of performing the heat treatment, and the heat treatment at a temperature lower than the film forming temperature is sufficient, so that the productivity is deteriorated as compared with the case of performing the heat treatment higher than the film forming temperature. Increase in manufacturing cost can be suppressed.

  In addition, as a raw material solution of the transparent conductive film mentioned above, a fluorine atom is 22at. It is particularly preferable to use one containing water and methanol as a solvent while containing at a concentration of at least%. By manufacturing a transparent conductive film according to the method for manufacturing a transparent conductive film in the present embodiment described above using such a raw material solution, the sheet resistance of the transparent conductive film after the heat treatment is the sheet of the transparent conductive film before the heat treatment. The resistance is significantly lower than the resistance, and the sheet resistance is 12 Ω / □ or less, the light transmittance is 80% or more, and the haze ratio is a requirement for the characteristics of the transparent conductive film used in the thin film solar cell. All the requirements that the ratio is about 7% to 15% are satisfied.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. FIG. 2 is a conceptual diagram of a test film forming apparatus used in Examples and Comparative Examples described later. In the examples and comparative examples described below, a transparent conductive film is formed on the film formation surface 101 of the transparent substrate 100 using the test film forming apparatus 20 shown in FIG. For the heat treatment carried out in (1), a muffle furnace which is a heating furnace as used in the heat treatment section 16 shown in FIG. 1 was used.

  As shown in FIG. 2, the test film forming apparatus 20 mainly includes a hot plate 21, a spray nozzle 22, and a solution storage unit 26. The hot plate 21 is for heating the transparent substrate 100 placed on the placement surface by direct conduction heat transfer, and heats the transparent substrate 100 to a film forming temperature of 500 ° C. or higher. The solution storage part 26 is a site | part for storing the raw material solution 200 of a transparent conductive film.

  The spray nozzle 22 includes the above-described two-fluid spray nozzle, and is connected to a carrier gas introduction pipe 23 into which a carrier gas is introduced and a raw material solution introduction pipe 24 into which the raw material solution 200 is introduced. The raw material solution introduction pipe 24 is connected to the solution storage section 26 described above, and a liquid feed pump 25 is attached to the raw material solution introduction pipe 24. The liquid feed pump 25 is for supplying the raw material solution 200 stored in the solution storage unit 26 to the spray nozzle 22 via the raw material solution introduction pipe 24.

  Further, the hot plate 21 is configured to be scanned by a driving mechanism (not shown), and is configured to be movable in a direction orthogonal to the spraying direction of droplets sprayed from the spray nozzle 22.

  In the test film formation apparatus 20, the transparent substrate 100 is placed on the hot plate 21, and the temperature of the film formation surface 101 of the transparent substrate 100 reaches the predetermined film formation temperature on the hot plate 21. While the transparent substrate 100 is heated and the hot plate 21 is further scanned, the raw material solution 200 of the transparent conductive film is atomized using the spray nozzle 22 and sprayed onto the film formation surface 101 of the transparent substrate 100, thereby A transparent conductive film is manufactured on the film formation surface 101 of the transparent substrate 100.

  In the following examples and comparative examples, the transparent conductive film formed using the test film forming apparatus 20 is once cooled to room temperature, and in that state, the film thickness, sheet resistance, and light of the transparent conductive film are cooled. Each of the transmittance and haze ratio is measured, and then the transparent conductive film is put into the muffle furnace described above together with the transparent substrate and subjected to the reheating treatment to perform the predetermined heat treatment. Each of the above items was measured again. A four-terminal method was used for measuring the sheet resistance, and a spectroscopic haze meter was used for measuring the light transmittance and the haze ratio.

  In Examples 1 to 3 and Comparative Examples 1 to 3, the concentration of tin chloride pentahydrate and ammonium fluoride is 0.9 mol / L for 100 mL of water as a solvent as the raw material solution 200, respectively. These were prepared by mixing them and further mixed with 10 mL of 35% hydrochloric acid as a pH adjuster. As the transparent substrate 100, an alkali-free glass substrate was used and heated by the hot plate 21 so that the temperature of the film formation surface 101 became 530 ° C.

  In Example 1 and Comparative Example 1, a transparent conductive film was formed while the transparent substrate 100 was kept stationary without film transfer (that is, the transfer speed of the transparent substrate 100 was 0 mm / second). In Example 2 and Comparative Example 2, a transparent conductive film was formed at a conveyance speed of the transparent substrate 100 of 3 mm / second during film formation. In Example 3 and Comparative Example 3, a transparent conductive film was formed at a conveyance speed of the transparent substrate 100 of 10 mm / second during film formation.

  In the heat treatment using the muffle furnace, the temperature inside the muffle furnace is set to 480 ° C. so that the transparent substrate 100 on which the transparent conductive film is formed passes through the muffle furnace over 15 minutes. Set to. In Examples 1 to 3, the atmosphere in the muffle furnace was an air atmosphere, and in Comparative Examples 1 to 3, the atmosphere in the muffle furnace was a nitrogen atmosphere.

  FIG. 3 is a table showing the manufacturing conditions of the transparent conductive film and the measurement results of various characteristics in Examples 1 to 3 and Comparative Examples 1 to 3 described above. FIG. 4 is a graph showing the spectral characteristics of the light transmittance of the transparent conductive film in Example 3. FIG. 5 is a graph showing the spectral characteristics of the light transmittance of the transparent conductive film in Comparative Example 3.

  As shown in FIG. 3, in any of Examples 1 to 3 and Comparative Examples 1 to 3, it was confirmed that the sheet resistance of the transparent conductive film was lower after the heat treatment than before the heat treatment. Moreover, in any of Examples 1 to 3 and Comparative Examples 1 to 3, it was confirmed that a decrease in the haze ratio of the transparent conductive film was suppressed after the heat treatment compared to before the heat treatment.

  On the other hand, in Examples 1 to 3, the light transmittance of the transparent conductive film is maintained after the heat treatment as compared with that before the heat treatment, whereas in Comparative Examples 1 to 3, after the heat treatment, before the heat treatment. It was confirmed that the light transmittance of the transparent conductive film was lower than the above. In Example 3, as shown in FIG. 4, there is no particular change in the spectral characteristics of the light transmittance of the transparent conductive film before and after the heat treatment, whereas in Comparative Example 3, there is no change in FIG. As shown in FIG. 4, the result agrees with the result in which the spectral characteristics of the light transmittance of the transparent conductive film change before and after the heat treatment. That is, in Comparative Example 3, after the heat treatment, a large attenuation is observed in the light transmittance in each of the long wavelength region and the short wavelength region.

  From the above results, the light transmittance of the transparent conductive film can be improved by performing the heat treatment after the film formation in the air atmosphere as in Examples 1 to 3 rather than in the reducing atmosphere as in Comparative Examples 1 to 3. It was confirmed that the decrease can be suppressed. That is, the transparent conductive film having a low sheet resistance, a high light transmittance, and a high haze ratio can be obtained by heat-treating the transparent conductive film after film formation under predetermined conditions in the air atmosphere as in Examples 1 to 3. It has been confirmed that production is possible.

  Next, verification test 1 that verifies the relationship between the heat treatment time and the heat treatment temperature and the sheet resistance of the transparent conductive film will be described. FIG. 6 is a graph showing the results of Verification Test 1 for verifying the relationship between the heat treatment time and the heat treatment temperature and the sheet resistance of the transparent conductive film.

  In the verification test 1, a plurality of transparent substrates on which a transparent conductive film is formed are prepared as samples by performing film formation using the test film forming apparatus 20 described above, and these are prepared using the muffle furnace described above. The heat treatment was performed at different heat treatment times and different heat treatment temperatures, and the sheet resistance of the transparent conductive film after the heat treatment was measured for each sample.

  In each sample, as the raw material solution 200, the concentration of tin chloride pentahydrate is 0.9 mol / L and the concentration of ammonium fluoride is 0.3 mol / L with respect to 70 mL of water as a solvent. These are mixed to prepare (that is, the raw material solution 200 is prepared so as to contain a fluorine atom at a concentration of 33 at.% With respect to the tin atom), and further 35% as a pH adjuster. 30 mL of hydrochloric acid was mixed, and 2.5 mL of methanol as a solvent was added thereto. As the transparent substrate 100, an alkali-free glass substrate was used, and the film formation surface 101 was heated by the hot plate 21 so that the temperature was 540 ° C. For each of these samples, a transparent conductive film was formed by standing without carrying the transparent substrate 100 during film formation.

  In the heat treatment in the muffle furnace for each sample, the heat treatment is performed in an air atmosphere, and the heat treatment time is divided into 5 minutes, 15 minutes, 30 minutes, 45 minutes, 60 minutes, and 90 minutes, and the heat treatment temperature. Was distributed between 480 ° C. and 500 ° C. Various conditions other than the above are basically the same as those in the first to third embodiments.

  As shown in FIG. 6, when heat treatment is performed at any temperature conditions of 480 ° C. and 500 ° C., the heat treatment time is set to 5 minutes or more and 45 minutes or less, so that the heat treatment is performed after the heat treatment compared with the heat treatment. It was confirmed that the sheet resistance of the transparent conductive film was reduced. In addition, although explanation is omitted here for details, the light transmittance after heat treatment of the transparent conductive film in each sample subjected to heat treatment for 5 minutes to 45 minutes is 81-81.5%. Yes, the haze ratio was 10-12% in all cases.

  From the above results, it is determined that setting the heat treatment time after film formation to 5 minutes or more and 45 minutes or less greatly contributes to lowering the sheet resistance of the transparent conductive film.

  Next, verification test 2 for verifying the relationship between the heat treatment time and the amount of ammonium fluoride added and the sheet resistance of the transparent conductive film will be described. FIG. 7 is a graph showing the results of Verification Test 2 in which the relationship between the heat treatment time and the amount of ammonium fluoride added and the sheet resistance of the transparent conductive film was verified.

  The verification test 2 uses as a sample a transparent substrate on which a transparent conductive film is formed by forming a film using the above-described test film forming apparatus 20 using raw material solutions having different amounts of ammonium fluoride. A plurality of samples were prepared, heat-treated at different heat treatment times using the muffle furnace described above, and the sheet resistance of the transparent conductive film after the heat treatment was measured for each sample.

  In each sample, the concentration of ammonium fluoride in the raw material solution 200 of the transparent conductive film used in the verification test 1 described above was varied. Specifically, the raw material solution 200 was prepared so that the concentrations of ammonium fluoride were 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, respectively (that is, the raw material solution 200 was a fluorine atom). Were prepared at concentrations of 11 at.%, 22 at.%, And 33 at.

  In the heat treatment in the muffle furnace for each sample, the heat treatment is performed in an air atmosphere, the temperature of the heat treatment is 480 ° C., and the heat treatment time is 5 minutes, 15 minutes, 30 minutes, 60 minutes, and 90 minutes. Sorted. Various conditions other than those described above are basically the same as in the case of the verification test 1 described above.

  As shown in FIG. 7, in any case where the addition amount of ammonium fluoride is varied, the heat treatment time is set to 5 minutes or more and 45 minutes or less, so that the transparent conductive film after heat treatment is more than before heat treatment. It was confirmed that the sheet resistance of the sheet was lowered. From the above results, regardless of the amount of ammonium fluoride added, the heat treatment time after film formation should be 5 minutes or more and 45 minutes or less, which greatly reduces the sheet resistance of the transparent conductive film. It is judged that it contributes.

  In this verification test 2, for the sample with an ammonium fluoride concentration of 0.1 mol / L, the minimum value of the sheet resistance of the transparent conductive film after the heat treatment exceeded 13 Ω / □. Then, the required characteristic of the transparent conductive film mentioned above cannot be satisfied. On the other hand, for the samples with ammonium fluoride concentrations of 0.2 mol / L and 0.3 mol / L, the minimum values of the sheet resistance of the transparent conductive film after heat treatment are below 11Ω / □ and 9Ω / □, respectively. It was confirmed. Therefore, in order to satisfy the required characteristics of the transparent conductive film described above, the concentration of ammonium fluoride is set to 0.2 mol / L or more (that is, the raw material solution 200 contains 22 atomic% of fluorine atoms with respect to tin atoms). It is judged that it is preferable to prepare the raw material solution of the transparent conductive film so that it is contained in the above concentration.

  Next, verification test 3 that verifies the relationship between the heat treatment temperature and the amount of ammonium fluoride added and the sheet resistance of the transparent conductive film will be described. FIG. 8 is a graph showing the results of Verification Test 3 that verified the relationship between the heat treatment temperature and the amount of ammonium fluoride added and the sheet resistance of the transparent conductive film.

  The verification test 3 uses as a sample a transparent substrate on which a transparent conductive film is formed by forming a film using the above-described test film forming apparatus 20 using raw material solutions having different amounts of ammonium fluoride. A plurality of samples were prepared, heat-treated at different heat treatment temperatures using the muffle furnace described above, and the sheet resistance of the transparent conductive film after the heat treatment was measured for each sample.

  In each sample, the concentration of ammonium fluoride in the raw material solution 200 of the transparent conductive film used in the verification test 1 described above was varied. Specifically, as in the case of the verification test 2 described above, the raw material solution 200 is prepared so that the ammonium fluoride concentrations are 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, respectively. (In other words, the raw material solution 200 was prepared so as to contain fluorine atoms at concentrations of 11 at.%, 22 at.%, And 33 at.%, Respectively, with respect to tin atoms).

  In the heat treatment in the muffle furnace for each sample, the heat treatment was performed in an air atmosphere, the heat treatment time was set to 15 minutes, and the heat treatment temperature was distributed to 400 ° C., 440 ° C., 480 ° C., and 520 ° C. Various conditions other than those described above are basically the same as in the case of the verification test 1 described above.

  As shown in FIG. 8, in any case where the addition amount of ammonium fluoride is varied, the heat treatment is performed at a temperature of 400 ° C. or higher and 480 ° C. or lower. It was confirmed that the sheet resistance of the transparent conductive film was reduced. From the above results and the results of the verification test 1 described above, the temperature of the heat treatment after the film formation is 400 ° C. or more and 500 ° C. or less regardless of the amount of ammonium fluoride added. It is judged that it greatly contributes to lowering the sheet resistance.

  In this verification test 3 as well, for the sample with the ammonium fluoride concentration of 0.1 mol / L, the minimum value of the sheet resistance of the transparent conductive film after the heat treatment exceeded 13Ω / □. Then, the required characteristic of the transparent conductive film mentioned above cannot be satisfied. On the other hand, for the samples with ammonium fluoride concentrations of 0.2 mol / L and 0.3 mol / L, the minimum values of the sheet resistance of the transparent conductive film after heat treatment are below 11Ω / □ and 9Ω / □, respectively. It was confirmed. Therefore, in order to satisfy the required characteristics of the transparent conductive film described above, the concentration of ammonium fluoride is set to 0.2 mol / L or more (that is, the raw material solution 200 contains 22 atomic% of fluorine atoms with respect to tin atoms). It is judged that it is preferable to prepare the raw material solution of the transparent conductive film so that it is contained in the above concentration.

  Next, a verification test 4 that verifies the relationship between the temperature gradient in the annealing process during the heat treatment and the amount of warping of the transparent substrate will be described. FIG. 9 is a graph showing the results of the verification test 4 in which the relationship between the temperature gradient in the slow cooling process during the heat treatment and the amount of warpage of the transparent substrate was verified.

  In the verification test 4, a plurality of white plate glass substrates having a size of 180 mm □ and a thickness of 3.9 mm are prepared as samples, heat-treated using a muffle furnace, and the warp generated in the samples by the heat treatment is respectively obtained. The measurement was performed using a height gauge.

  Here, the heating by the muffle furnace is carried out so that the maximum surface temperature of all the samples becomes 570 ° C. to 580 ° C., and then the surface of the sample during the slow cooling treatment performed in the muffle furnace. The temperature of the muffle furnace (that is, the heat treatment section 16 shown in FIG. 1) of the portion where annealing is performed and the temperature of the sample in the portion so that the temperature gradient at the point where the temperature of 530 ° C. becomes different in each sample. This was done by changing the resting time.

  In addition, when measuring the warpage generated in the sample, place the sample on the surface plate, press the diagonal of the sample against the surface plate, measure the height of the upper surface of the sample at the remaining angle using a height gauge, and The height was measured for each of the four corners by changing the angle pressed against the surface plate, and the four-point average of the difference between the height of the upper surface of the sample and the thickness of the sample at these four corners was calculated.

  As shown in FIG. 9, for the samples with a temperature gradient of −20 ° C./min or less, the warpage amount is 0.1 mm or less, and the amount of warpage is less than when the temperature gradient is −30 ° / min. It was confirmed that can be suppressed to 1/3 or less.

  From the above results, when the slow cooling process is adopted in the heat treatment after the film formation, the transparent substrate 100 is deformed such as warping by setting the temperature gradient in the slow cooling process to −20 ° C./min or less. It is judged that this can be suppressed.

  The above-described embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Film-forming apparatus, 11 Conveyance mechanism, 12 Heating furnace, 13 Substrate carrying-in part, 14 Heating part, 15 Film-forming part, 16 Heat processing part, 17 Substrate carrying-out part, 18 Spraying mechanism, 20 Test film-forming apparatus, 21 Hot plate , 22 spray nozzle, 23 carrier gas introduction pipe, 24 raw material solution introduction pipe, 25 liquid feed pump, 26 solution storage part, 100 transparent substrate, 101 film-forming surface, 200 raw material solution.

Claims (3)

A method for producing a transparent conductive film, comprising forming a transparent conductive film composed of a tin oxide film doped with fluorine on a film formation surface of a transparent substrate,
By spraying the raw material solution of the transparent conductive film onto the film formation surface while heating the transparent substrate so that the temperature of the film formation surface becomes 500 ° C. or higher, Forming the transparent conductive film on
And a step of heat-treating the transparent conductive film formed on the film formation surface in an air atmosphere at 400 ° C. to 500 ° C. for 5 minutes to 45 minutes.   When the raw material solution of the transparent conductive film has a fluorine atom of 22 at. The manufacturing method of the transparent conductive film of Claim 1 which contains water and methanol as a solvent while containing with the density | concentration of% or more.   The step of performing the heat treatment is performed following the step of forming the transparent conductive film, and is performed by gradually cooling the transparent conductive film at a temperature gradient of -20 ° C / min or less. Or the manufacturing method of the transparent conductive film of 2.

Images