JP2013037768A - Formation method of transparent conductive film - Google Patents

Abstract

A method for producing a transparent conductive film with improved scattering performance for light in a wide wavelength range is provided.
A method of manufacturing a transparent conductive film includes a film forming step of forming a transparent conductive film containing zinc oxide as a main component on a substrate by a sputtering method, an annealing step of annealing the transparent conductive film, and a transparent conductive film. And an etching step of performing wet etching. The annealing process may be performed before the etching process. The temperature of the annealing treatment of the transparent conductive film may be 300 to 600 ° C.
[Selection] Figure 2

Description

  The present invention relates to a transparent conductive film technique suitable for a solar cell.

In recent years, energy demand on a global scale has been increasing with the rapid economic development of emerging countries. As a result, the cost of fossil energy such as oil is rising. In addition, the increase in fossil energy consumption in these emerging countries has led to an increase in CO ₂ emissions on a global scale, causing serious environmental destruction. As a promising candidate for solving these problems, active use of natural energy is screamed, and in particular, expectations for solar power generation using solar cells are extremely high.

  In the solar cell, a transparent conductive film having a low resistivity and a high transmittance for visible light is used as an electrode. As the transparent conductive film, ITO (Indium Tin Oxide), zinc oxide or the like is known. In particular, zinc oxide-based transparent conductive films are attracting attention from the viewpoints of material costs and material supply stability.

  In recent years, attempts have been made to improve the conversion efficiency of thin film solar cells by scattering light by forming a texture structure on the surface of a transparent conductive film. For example, Patent Document 1 discloses a technique for forming a texture structure on the surface of a ZnO-based transparent conductive film using a sputtering film forming technique.

Tadatsugu MINAMI et al., “Large-Area Milky Transparent Conducting Al-Doped ZnO Films Prepared by Magnetron Sputtering”, Jpn. J. Appl. Phys., 1992, Vol. 31, No. 8A, pp. L1106-L1109

  By the way, the thin film solar cell which assumed that the transparent conductive film was formed at the time the above-mentioned technique was devised was a solar cell which used polycrystalline Si alone as a photoelectric converting layer. Therefore, the performance required for the transparent conductive film was sufficient to enhance the scattering effect in the near infrared region.

  However, in recent years, in order to achieve higher conversion efficiency, so-called tandem thin-film Si solar cells in which three layers of amorphous Si thin film / microcrystalline Si thin film / Si—Ge thin film are laminated have been developed. This type of solar cell can achieve high conversion efficiency because it can convert sunlight with a wider wavelength from short wavelength to long wavelength region by laminating thin films with different band gaps. Therefore, a transparent conductive film suitable for such a tandem-type thin film solar cell is required to scatter light in a wider wavelength region.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a transparent conductive film with improved scattering performance for light in a wide wavelength range.

  In order to solve the above problems, a method for producing a transparent conductive film according to an aspect of the present invention includes a film forming step of forming a transparent conductive film containing zinc oxide as a main component on a substrate by a sputtering method, An annealing process for annealing treatment and an etching process for wet etching the transparent conductive film are provided.

  According to this aspect, it is possible to form a transparent conductive film with improved scattering performance for light in a wide wavelength range.

  The annealing process may be performed before the etching process. Thereby, the transparent conductive film which has a surface shape with higher scattering performance can be manufactured.

  In the annealing step, the temperature of the annealing treatment of the transparent conductive film may be 300 to 600 ° C. Thereby, the carrier density of a transparent conductive film can be reduced.

  In the annealing step, the time for annealing the transparent conductive film may be 1 to 5 minutes. Thereby, it is suppressed that the electrical property of a transparent conductive film falls by annealing treatment.

  In the etching step, the transparent conductive film may be etched using hydrochloric acid. Thereby, etching can be performed more easily.

  In the film forming step, the transparent conductive film may be formed by magnetron sputtering. Thereby, the transparent conductive film which has a more suitable surface form can be manufactured.

  In the film formation step, the transparent conductive film may be formed using a sputtering voltage in which high-frequency power is superimposed on DC power. Thereby, it is possible to form a transparent conductive film having a texture structure with a larger change in surface shape.

  In the film forming step, a zinc oxide sintered body doped with aluminum may be used as a raw material for the transparent conductive film. Thereby, the transparent conductive film which has a desired electrical property with an inexpensive material can be manufactured.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, the transparent conductive film which improved the scattering performance with respect to the light of a wide wavelength range can be manufactured.

It is a schematic diagram for demonstrating the surface structure calculated | required by a transparent conductive film. It is a figure which shows the flowchart of the manufacturing method of the transparent conductive film which concerns on this Embodiment. It is principal part sectional drawing which showed typically an example of the magnetron sputtering apparatus which concerns on this Embodiment. It is a figure which shows the SEM image of the surface of the transparent conductive film formed by performing magnetron sputtering which applied only DC power. It is a figure which shows the SEM image of the surface of the transparent conductive film formed by performing magnetron sputtering which applied only the high frequency electric power. It is a figure which shows the SEM image of the surface of the transparent conductive film formed by performing magnetron sputtering which applied the DC power which superimposed the high frequency electric power. It is a figure which shows each SEM image of the surface at the time of carrying out the same depth etching of the transparent conductive film from which film thickness differs. It is a figure which shows the relationship between the perpendicular | vertical transmittance | permeability of an AZO transparent conductive film (etching depth of 300 nm) with a film thickness of 1000 nm and 2000 nm formed by magnetron sputtering to which DC power superimposed with high frequency power is applied. It is a figure which shows the relationship between the diffuse transmittance | permeability of an AZO transparent conductive film (etching depth of 300 nm) with a film thickness of 1000 nm and 2000 nm formed by magnetron sputtering to which DC power superimposed with high frequency power is applied. FIG. 10A shows a SEM image of the surface when a transparent conductive film having a thickness of 2000 nm formed by magnetron sputtering to which only DC power is applied is subjected to RTA treatment and etched (etching depth: 300 nm). (B) is the figure which shows the SEM image of the surface at the time of carrying out RTA process and etching (etching depth 300nm) of the 2000-nm-thick transparent conductive film formed by the magnetron sputtering which applied the DC power which superimposed the high frequency power. is there. It is a figure which shows the relationship between the vertical transmittance | permeability of a transparent conductive film (without RTA process) shown in FIG.7 (d), and the transparent conductive film (with RTA process) shown in FIG.10 (b), and a wavelength. It is a figure which shows the relationship between the diffuse transmittance | permeability of a transparent conductive film (without RTA process) shown in FIG.7 (d), and the transparent conductive film (with RTA process) shown in FIG.10 (b), and a wavelength. It is a figure which shows the relationship between the haze rate and wavelength of the transparent conductive film (no RTA process) shown in FIG.7 (d) and the transparent conductive film (with RTA process) shown in FIG.10 (b). FIG. 14A shows a SEM image of the sample surface of the transparent conductive film (iii), and FIG. 14B shows a SEM image of the sample surface of the transparent conductive film (ii). It is the figure which showed the relationship between each haze rate and wavelength of three types of transparent conductive films (i)-(iii). It is a figure which shows the SEM image of the surface of the GZO transparent conductive film formed by the magnetron sputtering which applied the DC power which superimposed the high frequency electric power.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate.

(Transparent conductive film)
First, the current state of transparent conductive films for thin film solar cells will be described. In recent years, ZnO (zinc oxide) based transparent conductive films have been developed as transparent electrodes for CIGS (copper, indium, gallium, selenium compound) and thin film Si solar cells. Further, as a thin-film Si-based solar cell, in addition to a solar cell composed of a single layer of an amorphous Si thin film, a so-called tandem in which three layers of an amorphous Si thin film / a microcrystalline Si thin film / Si-Ge thin film are laminated as described above. The development of type thin film Si solar cells is also underway.

  A tandem-type thin film Si solar cell has a different spectral sensitivity spectrum of each layer. For example, an amorphous Si thin film has sensitivity to light with a wavelength in the range of about 300 to 700 nm, and a microcrystalline Si thin film has sensitivity to light with a wavelength in the range of about 500 to 1100 nm. In the case of a microcrystalline Si—Ge thin film, it has sensitivity to light having a wavelength in the range of about 700 to 1300 nm. That is, the tandem-type thin film Si solar cell can convert light in a wide range of wavelengths into electricity compared to a single-layer thin film Si solar cell.

  Therefore, a transparent conductive film for a thin-film Si-based solar cell is required to have a surface structure for scattering and confining a wider range of light from the visible light region to the near infrared light region.

(Scattering mechanism)
When light passes through a small uneven surface or passes through a medium containing small particles, the traveling direction of the light is scattered irregularly.

A Rayleigh scattering coefficient k _s shown in the following formula (1) is known as a representation of such a degree of scattering.
k _s = A · (d ⁶ / λ ⁴ ) (1)
(A: constant, d: particle size (unevenness), λ: wavelength of light)

  As shown in Expression (1), the intensity of scattering is related to the wavelength of light and the size of the particles (irregularities), and is stronger for shorter wavelengths and weaker for longer wavelengths. That is, as the wavelength λ becomes larger (closer to the longer wavelength side), the scattering coefficient becomes smaller (not scattered). Therefore, by increasing the interval between the irregularities on the surface of the transparent conductive film, light having a longer wavelength can be scattered.

  FIG. 1 is a schematic diagram for explaining a surface structure required for a transparent conductive film. 1 has a structure in which a transparent conductive film 104, an amorphous Si layer 106, a microcrystalline Si layer 108, and a back electrode 110 are stacked on a glass substrate 102.

  The transparent conductive film 104 has an uneven surface with a large period and an uneven surface with a small period formed in a concave part of the uneven surface with a large period. In the transparent conductive film 104 having such a texture structure, the long wavelength light L1 is scattered by the irregular surface having a large period, and the short wavelength light L2 is scattered by the irregular surface having a small period. It is possible to scatter light in a wide wavelength range.

  Therefore, the present inventors have developed a ZnO-based transparent conductive film having a surface texture structure that effectively scatters light from the visible light region to the near-infrared light region as a transparent conductive film for thin-film Si-based solar cells. I went diligently. As a result, the inventors have arrived at the following method suitable for producing a ZnO-based transparent conductive film having a desired surface texture structure.

  FIG. 2 is a diagram showing a flowchart of the method for manufacturing the transparent conductive film according to the present embodiment. The manufacturing method of the transparent conductive film according to the present embodiment includes a film forming step (S10) for forming a transparent conductive film containing zinc oxide as a main component on a substrate by a sputtering method, and an annealing step for annealing the transparent conductive film. (S12) and an etching step (S14) for wet-etching the transparent conductive film.

(Film formation process)
FIG. 3 is a main part sectional view schematically showing an example of the magnetron sputtering apparatus 10 according to the present embodiment. FIG. 3 shows the configuration accommodated in the vacuum chamber 70 among the configurations of the magnetron sputtering apparatus 10.

  In the magnetron sputtering apparatus 10, a target 20 and a base body 30 that is a base on which a thin film is formed are arranged to face each other. An anode 60 is provided in contact with the surface of the substrate 30 opposite to the target 20. The anode 60 functions as a substrate holder that holds the substrate 30 on which the components of the sputtered target 20 are formed as a thin film. On the other hand, the target 20 is held by a magnetron cathode portion 22 having a target holder.

  The magnetron cathode portion 22 is made of a metal such as stainless steel. Further, the magnetron cathode portion 22 is supplied with DC power superimposed with AC power (high frequency power) by a power supply source 40 having a high frequency power source and a DC power source, and also functions as a cathode. A magnet 50 and a yoke 52 are provided on the back surface of the magnetron cathode portion 22 as magnetic field generating means. In the gap between the magnet 50 and the yoke 52, a pipe 54 for circulating a coolant such as cooling water is provided as means for cooling the magnetron cathode portion 22. As the magnet 50, a permanent magnet or an electromagnet may be used.

  The means for cooling the magnetron cathode portion 22 is not limited to heat radiation by circulating cooling water, and may be heat radiation by a metal such as an aluminum block. The magnet 50 and the yoke 52 are surrounded by a shield plate 43 formed of a metal such as stainless steel. The shield plate 43 prevents discharge and sputtering other than above the erosion portion of the target 20.

  The vacuum chamber 70 can maintain the space including the target 20 and the substrate 30 at a desired degree of vacuum. The gas supply source 72 that supplies the sputtering gas and the inside of the vacuum chamber are evacuated to obtain the desired degree of vacuum. A vacuum pump 74 for obtaining is attached. Further, a heating means (not shown) for changing the temperature of the substrate 30 during film formation is provided.

  Next, a method for manufacturing a transparent conductive film using the magnetron sputtering apparatus 10 according to the above-described embodiment will be described.

  First, the target 20 and the substrate 30 used in the magnetron sputtering apparatus 10 will be described.

  The target 20 is made of ZnO, which is a high-density sintered body of 127 mm × 275 mm, doped with Al (AZO). Note that the shape of the target is not limited to a square but may be any shape such as a circle, and may be appropriately selected according to the apparatus, material, and film forming conditions. By using a zinc oxide sintered body doped with aluminum as a raw material of the transparent conductive film, a transparent conductive film having desired electrical characteristics can be manufactured with an inexpensive material.

  A 200 mm × 200 mm glass substrate (non-alkali glass OA-10 (manufactured by Nippon Electric Glass Co., Ltd.)) is used for the substrate 30. Then, the target 20 and the substrate 30 are disposed at predetermined positions of the magnetron sputtering apparatus 10, and the vacuum chamber 70 is evacuated by the vacuum pump 74 so as to achieve a desired degree of vacuum. In that case, the glass substrate which is the base | substrate 30 is heated to 200 degreeC with a heating means (not shown).

  In a state where the vacuum chamber 70 has a desired degree of vacuum, a sputtering gas containing Ar as a main component is supplied from the gas supply source 72 into the vacuum chamber 70. Here, the sputtering gas pressure is 0.2 Pa. And it applies to the magnetron cathode part 22 from the electric power supply source 40, and forms a transparent conductive film on a base | substrate. The power supply source 40 is configured to be able to apply DC power, high-frequency power, and DC power superimposed with high-frequency power to the magnetron cathode unit 22. The magnitude of the high-frequency power or DC power may be set as appropriate in consideration of various film forming conditions. For example, the high frequency power is 100 W and the direct current power is 80 W.

  Here, the high frequency power may be set in the range of 30% to 300%, more preferably 60% to 200% of the DC power. This is because if the ratio of the high frequency power is too small or too large, one of the characteristics of the direct current component and the high frequency component is too strong.

  Further, the frequency of the high frequency power superimposed on the DC power is preferably in the range of 2 MHz to 700 MHz. This is because, when the frequency is less than 2 MHz, it is difficult to generate plasma, whereas when the frequency is greater than 700 MHz, the power loss increases and the sputtering efficiency deteriorates. More preferably, it may be in the range of 10 MHz to 100 MHz, and for example, a frequency of 13.56 MHz is suitably used.

(Etching process)
Next, the formed transparent conductive film is subjected to wet etching. Etching is performed by immersing the transparent conductive film in an aqueous hydrochloric acid solution having a concentration of 0.1 [mol / l] and a solution temperature of 25 ° C. The concentration of hydrochloric acid is 0.05 to 0.3 [mol / l], preferably 0.1 to 0.2 [mol / l]. Hydrochloric acid is easy to handle and can be etched more easily.

  And several samples from which the depth of etching and the kind of applied electric power in magnetron sputtering differ were produced, and the surface was observed with the scanning electron microscope (SEM).

  FIG. 4 is a view showing an SEM image of the surface of the transparent conductive film formed by performing magnetron sputtering to which only DC power is applied. 4A shows a state immediately after film formation (film thickness 1000 [nm]), FIG. 4B shows an etching depth of 100 [nm], FIG. 4C shows an etching depth of 200 [nm], and FIG. (D) is an SEM image with an etching depth of 400 nm.

  FIG. 5 is a view showing an SEM image of the surface of a transparent conductive film formed by magnetron sputtering to which only high-frequency power is applied. FIG. 5A shows a state immediately after film formation (film thickness 1000 [nm]), FIG. 5B shows an etching depth of 100 [nm], FIG. 5C shows an etching depth of 200 [nm], and FIG. (D) is an SEM image with an etching depth of 400 nm.

  FIG. 6 is a view showing an SEM image of the surface of a transparent conductive film formed by performing magnetron sputtering in a state where DC power superimposed with high frequency power is applied. 6A shows a state immediately after film formation (film thickness 1000 [nm]), FIG. 6B shows an etching depth of 100 [nm], FIG. 6C shows an etching depth of 200 [nm], and FIG. (D) is an SEM image of the surface of the transparent conductive film having an etching depth of 400 [nm].

  Compared with the surface state of the transparent conductive film formed by magnetron sputtering to which only DC power is applied as shown in FIG. 4, the surface state of the transparent conductive film formed by magnetron sputtering to which high frequency power is applied as shown in FIGS. It can be seen that not only small irregularities but also large irregularities are formed by etching. In particular, larger irregularities are formed in the transparent conductive film when DC power superimposed with high-frequency power shown in FIG. 6 is applied. That is, it is possible to form a transparent conductive film having a texture structure with a greater change in surface shape. By forming such irregularities, it becomes possible to scatter light having a longer wavelength.

  Next, the relationship between the film thickness of the transparent conductive film and the size of the unevenness will be described. FIG. 7 is a diagram showing SEM images of the surface when transparent conductive films having different thicknesses are etched to the same depth (300 nm). FIG. 7A shows an SEM image of the surface of a transparent conductive film having a thickness of 1000 nm formed by magnetron sputtering to which only DC power is applied, and FIG. 7B shows a film formed under the same conditions as FIG. 7A. FIG. 7C is a SEM image of the surface of the transparent conductive film having a thickness of 2000 nm. FIG. 7C is an SEM image of the surface of the transparent conductive film having a thickness of 1000 nm formed by magnetron sputtering to which direct current power superimposed with high frequency power is applied. d) is an SEM image of the surface of a transparent conductive film having a thickness of 2000 nm formed under the same conditions as in FIG. As shown in FIG. 7, it can be seen that the transparent conductive film having a larger film thickness has larger irregularities.

Next, the tendency of the qualitative shape as described above will be described based on optical characteristics. Conventionally, vertical transmittance and diffuse transmittance are known as methods for evaluating the optical characteristics of a transparent conductive film.
Vertical transmittance [%] = (transmitted light / incident light) × 100 (2)
Diffuse transmittance [%] = ((transmitted light + scattered light) / (incident light)) × 100 (3)

  FIG. 8 is a graph showing the relationship between the vertical transmittance and wavelength of an AZO transparent conductive film (etching depth 300 nm) having a film thickness of 1000 nm and 2000 nm formed by magnetron sputtering to which direct current power superimposed with high frequency power is applied. FIG. 9 is a diagram showing the relationship between the diffusion transmittance and wavelength of an AZO transparent conductive film (etching depth: 300 nm) having a film thickness of 1000 nm and 2000 nm formed by magnetron sputtering to which direct current power superimposed with high frequency power is applied.

As shown in FIGS. 8 and 9, it can be seen that both the vertical transmittance and the diffuse transmittance are drastically lowered with respect to light on the long wavelength side (for example, light having a wavelength of 1000 nm or more). This is considered to be caused by absorption and reflection of light due to plasma resonance oscillation in a long wavelength region having a wavelength of 1000 nm or more because the carrier density of the produced AZO transparent conductive film is as high as 10 ²⁰ [cm ⁻³ ]. It is done.

  Accordingly, the present inventors have conceived that the transmittance for light in the long wavelength region can be improved by heat-treating (annealing) the transparent conductive film after film formation to reduce the carrier density.

(Annealing process)
Specifically, rapid thermal annealing (RTA) treatment is performed on the transparent conductive film after the film formation step. As conditions for the RTA treatment, the treatment temperature may be 300 ° C to 600 ° C. Thereby, the carrier density of a transparent conductive film can be reduced efficiently. More preferably, it is the range of 400 to 500 degreeC. Processing time is good in it being 1 minute-5 minutes. Thereby, it is suppressed that the electrical property of a transparent conductive film falls by annealing treatment. The treatment time is more preferably in the range of 2 minutes to 3 minutes. In this embodiment, the RTA treatment is performed in an air atmosphere at a temperature of 500 ° C. for 3 minutes.

  FIG. 10A shows a SEM image of the surface when a transparent conductive film having a thickness of 2000 nm formed by magnetron sputtering to which only DC power is applied is subjected to RTA treatment and etched (etching depth: 300 nm). (B) is the figure which shows the SEM image of the surface at the time of carrying out RTA process and etching (etching depth 300nm) of the 2000-nm-thick transparent conductive film formed by the magnetron sputtering which applied the DC power which superimposed the high frequency power. is there.

  As shown in FIG. 10, the unevenness on the surface of the transparent conductive film is smooth and large by applying the RTA process to the transparent conductive film.

  FIG. 11 is a diagram showing the relationship between the vertical transmittance and wavelength of the transparent conductive film (without RTA treatment) shown in FIG. 7 (d) and the transparent conductive film (with RTA treatment) shown in FIG. 10 (b). is there. FIG. 12 is a diagram showing the relationship between the diffuse transmittance and wavelength of the transparent conductive film (without RTA treatment) shown in FIG. 7 (d) and the transparent conductive film (with RTA treatment) shown in FIG. 10 (b). is there.

  As shown in FIG. 11, the transparent conductive film subjected to the RTA treatment has a relatively improved vertical transmittance with respect to light on the long wavelength side. Further, as shown in FIG. 12, the transparent conductive film subjected to the RTA treatment has improved overall diffuse transmittance for light having a wavelength of 1000 nm or more.

Here, attention is focused on the haze rate calculated from the vertical transmittance and the diffuse transmittance. The haze ratio is calculated by the following formula (4).
Haze rate [%] = ((diffuse transmittance−vertical transmittance) / diffuse transmittance) × 100 (4)

From Formula (2)-Formula (4),
Haze ratio [%] = scattered light / (transmitted light + scattered light) × 100 (5)
Is calculated.

  Therefore, the haze ratio was calculated using the values measured when obtaining the vertical transmittance and the diffuse transmittance. FIG. 13 is a diagram showing the relationship between the haze ratio and wavelength of the transparent conductive film (without RTA treatment) shown in FIG. 7 (d) and the transparent conductive film (with RTA treatment) shown in FIG. 10 (b). . As shown in FIG. 13, in the transparent conductive film subjected to the RTA treatment, the haze ratio is improved as a whole, and the haze ratio for light having a wavelength of 1000 nm or more is particularly improved. That is, according to the surface form of the transparent conductive film shown in FIG. 10 and the relationship between the haze ratio and the wavelength shown in FIG. 13, the transparent conductive film manufacturing method according to the present embodiment has improved scattering performance for long-wavelength light. It can be seen that the prepared transparent conductive film can be easily produced.

  Conventionally, when a texture structure is formed on the surface of a ZnO-based transparent conductive film, it is difficult to form particularly large irregularities (irregularities that can scatter light having a longer wavelength), and there are limits to using ordinary etching techniques. is there.

  However, it is possible to form a very large texture structure by applying a newly developed RTA treatment as a pre-process of an etching process using an acid or alkali solution. In addition, since the RTA process has a processing time as short as several minutes, the electrical characteristics of the transparent conductive film are hardly deteriorated. In addition, productivity (throughput) is also high.

  Thus, the method for producing a transparent conductive film according to the present embodiment can form a texture structure with improved scattering performance for light in a wide wavelength region on the surface of the transparent conductive film. Extremely expensive.

  Next, a suitable timing for the RTA process will be described. Three AZO transparent conductive film samples having a film thickness of 2000 nm were formed by magnetron sputtering to which direct current power superimposed with high frequency power was applied in the same manner as described above. The transparent conductive film (i) is a sample obtained by etching the above-described sample to a depth of 400 nm, and the transparent conductive film (ii) is etched at a depth of 400 nm at 400 ° C. The sample subjected to the RTA treatment, the transparent conductive film (iii), is a sample obtained by subjecting the above-described sample to RTA treatment at 400 ° C. and then etching to a depth of 400 nm. The concentration of the hydrochloric acid solution used for etching is 0.1 mol / l.

  FIG. 14A shows a SEM image of the sample surface of the transparent conductive film (iii), and FIG. 14B shows a SEM image of the sample surface of the transparent conductive film (ii). As shown in FIGS. 14 (a) and 14 (b), when the transparent conductive film (iii) subjected to RTA treatment before etching and the transparent conductive film (ii) subjected to RTA treatment after etching are compared, It can be seen that the surface structure formed is greatly changed. As can be seen from the SEM images of the surface of each sample shown in FIG. 14, the transparent conductive film (iii) subjected to RTA treatment before etching has a surface structure with larger irregularities. That is, in the method for manufacturing a transparent conductive film according to the present embodiment, the annealing process may be performed before the etching process. Thereby, the transparent conductive film which has a surface shape with higher scattering performance can be manufactured. Such a tendency was recognized regardless of the film formation method, but the surface texture structure obtained is greatly influenced by the film formation method.

  The influence of these surface structure differences on the optical characteristics is shown in FIG. FIG. 15 is a diagram showing the relationship between the haze ratio and the wavelength of each of the three types of transparent conductive films (i) to (iii). As shown in FIG. 15, in the transparent conductive film (iii) etched after the RTA treatment, a high haze ratio of 60% or more is realized at a wavelength of about 1.1 μm from the visible light region to the near infrared light. ing.

(GZO transparent conductive film)
In addition to the above-described AZO transparent conductive film, ZnO doped with Ga (GZO) is known as the ZnO-based transparent conductive film. Then, the transparent conductive film was manufactured like the above using the GZO sintered compact as a raw material. The manufacturing conditions are almost the same as in the case of the AZO transparent conductive film.

  FIG. 16 is a diagram showing an SEM image of the surface of a GZO transparent conductive film formed by performing magnetron sputtering to which direct current power superimposed with high frequency power is applied. 16A shows a state immediately after film formation (film thickness 1000 [nm]), FIG. 16B shows an etching depth of 100 [nm], FIG. 16C shows an etching depth of 200 [nm], and FIG. (D) is an SEM image of the surface of the transparent conductive film having an etching depth of 400 [nm]. As shown in FIG. 16, the surface form of the GZO transparent conductive film shows a surface texture structure having the same tendency as that of the AZO transparent conductive film.

  By using the transparent conductive film manufactured by the manufacturing method according to the present embodiment, the conversion efficiency of the thin-film Si-based solar cell is expected to be improved by about 10 to 20% compared to the efficiency achieved at present. it can. Thin film solar cells have a drawback in that their conversion efficiency is low compared to polycrystalline and single crystal Si solar cells that are currently in practical use. However, if the conversion efficiency can be improved by about 20% according to the present invention, the advantage of the thin-film Si-based solar cell that can be manufactured in a large area and at a low cost is utilized to realize the performance that can sufficiently compete with other crystalline solar cells. it can. Thin-film Si-based solar cells require less raw materials than crystalline Si-based solar cells, so the environmental impact is small and it can be expected to have a very significant effect on the progress of green energy technology development.

  As described above, the present invention has been described with reference to the above-described embodiment. However, the present invention is not limited to the above-described embodiment, and the present invention can be appropriately combined or replaced with the configuration of the embodiment. It is included in the present invention. In addition, it is possible to appropriately change the combinations and the order of steps in the embodiments based on the knowledge of those skilled in the art and to add various modifications such as various design changes to the embodiments. The described embodiments can also be included in the scope of the present invention.

  10 magnetron sputtering, 20 target, 22 magnetron cathode part, 25 solution temperature, 30 substrate, 40 power supply source, 43 shield plate, 50 magnet, 52 yoke, 54 pipe, 60 anode, 70 vacuum chamber, 72 gas supply source, 74 Vacuum pump, 100 solar cell, 102 glass substrate, 104 transparent conductive film, 106 amorphous Si layer, 108 microcrystalline Si layer, 110 back electrode.

Claims (8)

A film forming step of forming a transparent conductive film mainly composed of zinc oxide on a substrate by a sputtering method;
An annealing step of annealing the transparent conductive film;
An etching step of wet etching the transparent conductive film;
A method for producing a transparent conductive film comprising:   The method for manufacturing a transparent conductive film according to claim 1, wherein the annealing step is performed before the etching step.   The method of manufacturing a transparent conductive film according to claim 1 or 2, wherein, in the annealing step, the temperature of the annealing treatment of the transparent conductive film is 300 to 600 ° C.   The method for producing a transparent conductive film according to claim 3, wherein in the annealing step, the time for annealing the transparent conductive film is 1 to 5 minutes.   5. The method of manufacturing a transparent conductive film according to claim 1, wherein, in the etching step, the transparent conductive film is etched using hydrochloric acid.   6. The method for producing a transparent conductive film according to claim 1, wherein the transparent conductive film is formed by a magnetron sputtering method in the film forming step.   The method for producing a transparent conductive film according to claim 1, wherein, in the film forming step, the transparent conductive film is formed using a sputtering voltage in which high-frequency power is superimposed on DC power. .   The method for producing a transparent conductive film according to any one of claims 1 to 7, wherein a zinc oxide sintered body doped with aluminum is used as a raw material of the transparent conductive film in the film forming step.