TWI568008B - Production method of transparent conductive film and method for manufacturing thin film solar cell - Google Patents

Description

Method for producing transparent conductive film and method for manufacturing thin film solar cell

The present invention relates to a method for producing a transparent conductive film in which a transparent conductive film is formed on a light-transmitting substrate, and a method for producing a thin film solar cell. The present application claims priority on the basis of Japanese Patent Application No. 2010-188027, filed on Jan.

A transparent conductive film having high conductivity and high transmittance in the visible light region is used for solar cells, liquid crystal display elements, electrodes of various other light-receiving elements, and the like, and is also used as a hot-line reflection for automobile windows or buildings. Various anti-fog transparent heating elements such as membranes, anti-static films, and refrigerated display cabinets.

The transparent conductive film is made of a film of tin oxide (SnO ₂ ), zinc oxide (ZnO), or indium oxide (In ₂ O ₃ ). Tin oxide is made by using bismuth as a dopant (ATO) or fluorine as a dopant (FTO). The zinc oxide system utilizes aluminum as a dopant (AZO) or gallium as a dopant (GZO). Industrially, the most widely used transparent conductive film is indium oxide, and indium oxide containing tin as a dopant is called an ITO (Indium-Tin-Oxide) film, and it is particularly easy to obtain a film having a low resistance. It has been widely used so far.

In recent years, problems such as the increase in carbon dioxide have caused problems in the global environmental problems and the rise in the price of fossil fuels, and thin-film solar cells that can be manufactured in a relatively low-cost manner have attracted attention. The thin film solar cell generally includes a transparent conductive film sequentially laminated on a light-transmitting substrate, one or more semiconductor thin film photoelectric conversion units, and a back surface electrode. Due to the abundant resources of the tantalum material, the tantalum thin film solar cell using the lanthanoid thin film as the photoelectric conversion unit (light absorbing layer) in the thin film solar cell has been put into practical use for a long time, and the development of research and development is becoming more and more active. .

In addition, the type of the lanthanide-based thin-film solar cell is more diverse, and it is used in the amorphous ruthenium in addition to the amorphous thin-film solar cell of the amorphous thin film or the like in the former light absorbing layer. A microcrystalline thin film solar cell of a microcrystalline film or a crystalline thin film solar cell using a crystalline thin film composed of crystalline germanium has also been developed, and these laminated thin film solar cells have also been put into practical use.

Here, the photoelectric conversion unit or the thin film solar cell is amorphous, crystalline or microcrystalline regardless of the p-type and n-type conductive semiconductor layers contained therein, and the photoelectric conversion layer which is the main part is amorphous. It is called an amorphous unit or an amorphous thin film solar cell. If the photoelectric conversion layer is crystalline, it is called a crystalline unit or a crystalline thin film solar cell. If the photoelectric conversion layer is microcrystalline, it is called a microcrystalline unit or Microcrystalline thin film solar cells.

However, the transparent conductive film is used as a surface transparent electrode of a thin film solar cell, and in order to effectively enclose light incident on the light-transmitting substrate side in the photoelectric conversion unit, a large number of fine irregularities are usually formed on the surface.

An index of the degree of the unevenness of the transparent conductive film is a haze. In the light transmitted when the light of the specific light source is incident on the light-transmitting substrate with the transparent conductive film, the scattering component of the optical path curvature is measured by the C light source containing visible light.

In general, the height difference of the concavities and convexities is larger, or the interval between the convex portions and the convex portions of the concavities and convexities is larger, and the blurring rate is higher, and the light incident into the photoelectric conversion unit is effectively closed, that is, the light encapsulation effect is excellent.

A thin film solar cell is a thin film solar cell which is a single layer of a light absorbing layer of amorphous germanium, crystalline germanium or microcrystalline germanium, or a mixed thin film solar cell as described above, as long as the blurring rate of the transparent conductive film can be sufficiently increased. By encapsulating the light, a high short-circuit current density (Jsc) can be achieved, and a thin-state solar cell with high conversion efficiency can be manufactured.

In view of the above-mentioned object, the convexity of the concavities and convexities is improved as a transparent conductive film having a high blur rate, and a metal oxide material containing tin oxide as a main component produced by a thermal CVD method is known, and is widely used as a transparent electrode of a thin film solar cell. .

The conductive semiconductor layer formed on the surface of the transparent conductive film is generally produced by a plasma CVD method in a gas atmosphere containing hydrogen. In order to increase the formation temperature of the microcrystals in the conductive semiconductor layer, the reduction of the metal oxide is promoted by the presence of hydrogen. In the case of a transparent conductive film containing tin oxide as a main component, transparency due to hydrogen reduction can be seen. Loss of sex. When such a transparent conductive film having deterioration in transparency is used, a thin film solar cell having high conversion efficiency cannot be realized.

As a method of preventing reduction by hydrogen of a transparent conductive film containing tin oxide as a main component, Non-Patent Document 1 proposes a transparent conductive film made of tin oxide having a high degree of unevenness formed by a thermal CVD method. A method of forming a thin zinc oxide film excellent in reduction resistance by sputtering. Since zinc oxide is strongly bonded to oxygen, it is excellent in hydrogen reduction resistance. Therefore, by forming the above structure, it is possible to maintain high transparency of the transparent conductive film.

However, in order to obtain the transparent conductive film of the above structure, it is necessary to form a film by combining two kinds of methods, and it is not practical to increase the cost. In addition, the method of producing a laminated film of a tin oxide-based transparent conductive film and a zinc oxide-based transparent conductive film by a sputtering method is not possible because a sputtering method cannot produce a transparent tin oxide-based transparent conductive film. It is considered impossible to achieve.

On the other hand, Non-Patent Document 2 proposes a method of obtaining a transparent conductive film having surface irregularities and high blur ratio by sputtering using zinc oxide as a main component. In this method, a sintered body target to which 2 wt% of zinc oxide of Al ₂ O _{3 is} added is used, and a substrate temperature of 200 to 400 ° C is applied to form a film at a high gas pressure of 3 to 12 Pa. However, a 6-inch-thick target was put into a power of DC80W to form a film, and the power density applied to the target was only 0.442 W/cm ^{2 which was} considerably low. Therefore, the film formation rate is 14 to 35 nm/min, which is extremely slow and is not practical in the industry.

Further, in Non-Patent Document 3, it is disclosed that zinc oxide is used as a main component, and a transparent conductive film having a small surface unevenness which is produced by a previous sputtering method is obtained, and then the surface of the film is etched by acid etching to make the surface roughened. A method of manufacturing a transparent conductive film having a high blur rate. However, in this method, it is necessary to dry the film in a vacuum process by a dry process, and then perform an acid etching in the atmosphere to dry, and then form a semiconductor layer by a dry process CVD method, and the steps become complicated. Problems such as higher costs.

Among the zinc oxide-based transparent conductive film materials, AZO containing aluminum as a dopant has been proposed to use a target in which zinc oxide is mixed as a main component, and a DC magnetron sputtering method is used to manufacture C. A method of axially aligning an AZO transparent conductive film (see Patent Document 1). In this case, in order to form a film at a high speed and increase the power density applied to the target to form a film by DC sputtering, an arc (abnormal discharge) frequently occurs. When an arc is generated in the production step of the film forming line, a film defect or a film having a specific film thickness cannot be obtained, and it is impossible to stably manufacture a high-quality transparent conductive film.

Therefore, the inventors of the present invention have proposed a sputtering target in which aluminum oxide is mixed with zinc oxide as a main component and an abnormal discharge is reduced by the addition of a third element (Ti, Ge, Al, Mg, In, Sn) (refer to Patent Document 2). Here, a GZO sintered body containing gallium as a dopant is used, and at least one type of ZnO phase selected from a group consisting of Ga, Ti, Ge, Al, Mg, In, and Sn is solid-solved as a structure. The main constituent phase is an intermediate compound phase represented by at least one of the above-mentioned ZnGa ₂ O ₄ (spinel phase) in the other constituent phase. In such a GZO target to which a third element such as aluminum is added, the abnormal discharge described in Patent Document 1 can be reduced, but it cannot be completely eliminated. In the continuous production line of film formation, even if only one abnormal discharge occurs, the product at the time of film formation becomes a defective product and image-to-manufacturing productivity.

In order to solve this problem, the inventors of the present invention have proposed an oxide sintered body of aluminum and gallium containing zinc oxide as a main component and further containing an additive element, thereby optimizing the content of aluminum and gallium, and simultaneously producing a crystal phase during sintering. The type and composition, especially by controlling the composition of the spinel crystal phase to be optimal, makes it difficult to generate particles even when the sputtering apparatus is continuously formed for a long time, even if a high DC power is dropped. An oxide sintered body for a target which does not cause abnormal discharge at all (see Patent Document 3). When this target material is used, it is possible to form a high-quality transparent conductive film having lower resistance than that of the prior art, and thus it is applicable to the production of a solar cell having high conversion efficiency.

However, in recent years, a solar cell that pursues higher conversion efficiency requires a high-quality transparent conductive film. In addition, productivity improvement of a solar cell having a high conversion ratio is also expected.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 62-122011

[Patent Document 2] Japanese Patent Laid-Open No. Hei 10-306367

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2008-110911

[Non-patent literature]

[Non-Patent Document 1] K. Sato et al., "Hydrogen Plasma Treatment of ZnO-Coated TCO Films", Proc. of 23th IEEE Photovoltaic Specialists Conference, Louisville, 1993, pp. 855-859.

[Non-Patent Document 2] T. Minami, et. al., "Large-Area Milkey Transparent Conducting Al-Doped ZnO Films Prepared by Magnetron Sputtering", Japanese Journal of Applied Physics, [31] (1992), pp. L1106- 1109.

[Non-Patent Document 3] J. Muller, et. al., Thin Solid Films, 392 (2001), p. 327.

The present invention has been made in view of the above circumstances, and provides a method for producing a transparent conductive film which can produce an excellent transparent conductive film in a short period of time, can improve the productivity of a high-efficiency thin film solar cell, and a thin film solar cell. Production method.

In order to solve the related problems of the prior art, the inventors of the present invention found that the transparent conductive film for the thin-film solar cell to be a surface transparent electrode was changed to a sputtering gas of argon gas and hydrogen gas as a result of repeated research. Under the specific sputtering conditions of the gas species, an oxide sintered body target containing zinc oxide as a main component is used for film formation, whereby excellent film characteristics can be obtained, and the present invention has been completed.

In other words, in the method for producing a transparent conductive film according to the present invention, an oxide sintered body target containing zinc oxide as a main component is used, and a surface electrode film made of a transparent conductive film is formed on the light-transmitting substrate. A method for producing a transparent conductive substrate having a surface electrode, characterized in that a mixed gas of argon and hydrogen is used as a sputtering gas species, and a molar ratio of H ₂ /(Ar+H ₂ )=0.01 to 0.43 in the mixed gas is used. A transparent conductive film is formed under the conditions of a sputtering gas pressure of 2.0 to 15.0 Pa and a substrate temperature of 300 to 600 °C.

Further, a method for producing a thin film solar cell according to the present invention is characterized in that a mixed gas of argon and hydrogen is used as a sputtering gas species, and a molar ratio of H ₂ /(Ar+H ₂ )=0.01 in the mixed gas. ～0.43, a sputtering gas pressure of 2.0 to 15.0 Pa, and a substrate temperature of 300 to 600 ° C, using an oxide sintered body target containing zinc oxide as a main component, and forming a transparent conductive film on the light-transmitting substrate. On the transparent conductive film, a photoelectric conversion layer unit and a back electrode layer are sequentially formed.

According to the present invention, it is possible to reduce the surface resistance and to manufacture a transparent conductive film having excellent surface unevenness in a short period of time, and it is possible to improve the productivity of a highly efficient thin film solar cell.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings in the following order.

1. Method for producing transparent conductive film

2. Transparent conductive film

3. Method for manufacturing thin film solar cell

<1. Method for Producing Transparent Conductive Film>

As a method for producing a transparent conductive film according to a specific example of the present invention, an oxide sintered body target containing zinc oxide as a main component is used, and a surface electrode film made of a transparent conductive film is formed on a light-transmitting substrate. A method for producing a transparent conductive substrate with a surface electrode, wherein a mixed gas of argon (Ar) and hydrogen (H ₂ ) is used as a sputtering gas species, and a molar ratio of H ₂ /(Ar+H ₂ ) in the mixed gas is 0.01 to 0.43, a sputtering gas pressure of 2.0 to 15.0 Pa, and a substrate temperature of 300 to 600 ° C, a transparent conductive film is formed.

By forming a film under these conditions, even if it is attempted to increase the power density of the target into a high-speed film formation of 2.760 W/cm ² or more, it is possible to produce a surface roughness (Ra) of 35.0 nm or more and a surface resistance of A transparent conductive film having a surface roughness of 25 Ω/□ or less. In particular, even when a film thickness of 400 to 1000 nm is used, these characteristics can be realized, and a thin film can make the transmittance higher.

The mixing ratio (molar ratio) of a mixed gas of argon (Ar) and hydrogen (H ₂ ) used as a sputtering gas species is preferably such that H ₂ /(Ar+H ₂ )=0.01 to 0.43 is preferable. As described below. When H ₂ /(Ar+H ₂ ) is less than 0.01, in order to obtain a film having a surface roughness of 35 nm or more, it is necessary to increase the film thickness (for example, up to 2200 nm or more) or to lower the target. When the power density is lowered (for example, 2.21 W/cm ² or less), productivity is deteriorated. In addition, when H ₂ /(Ar+H ₂ ) exceeds 0.43, the adhesion of the transparent conductive film to the substrate may be lowered, or the transparent conductive film may become too thick to deteriorate the conductivity, so that it is practically impossible to use the sun. The electrodes of the battery are used.

Further, when the sputtering gas pressure is less than 2.0 Pa, it is not easy to obtain a film having a large surface unevenness, and a film having an Ra value of 35.0 nm or more cannot be obtained. On the other hand, when it exceeds 15.0 Pa, the film formation speed becomes slow, and the adhesion of the transparent conductive film to the substrate is also lowered, which is not preferable. For example, it is necessary to reduce the sputtering gas pressure to a film forming speed of 40 nm/min or more in order to obtain a film forming speed of 40 nm/min or more in order to obtain a film forming speed of a direct current input power density of 1.66 W/cm ² or higher. Below 15.0Pa.

The conductivity of the zinc oxide-based transparent conductive film largely depends on the substrate heating temperature at the time of film formation. This is because when the substrate heating temperature becomes high, the crystallinity of the film is improved, and the mobility of the carrier electrons is increased. In the present embodiment, it is preferred to heat the substrate to 300 to 600 °C. When the substrate is heated to a high temperature to form a film, the crystallinity of the obtained transparent conductive film is improved, and excellent conductivity can be achieved for the above reasons. When the temperature is less than 300 ° C, the particles of the transparent conductive film grow poorly, and thus a film having a large Ra value cannot be obtained. In addition, when the temperature exceeds 600 ° C, the amount of electric power required for heating increases, which causes problems such as an increase in manufacturing cost, and when the glass substrate is used, the softening point is exceeded, and problems such as deterioration of the glass occur.

When the input power to the target is increased, the film formation speed is increased, and the productivity of the film is improved. However, it is difficult to obtain the above characteristics by the prior art. By using a mixed gas of argon (Ar) and hydrogen (H ₂ ) as in the present embodiment, the electric power input to the target can be increased to 2.76 W/cm ² or more, and sputtering can be performed to form a film. Thereby, for example, it is possible to achieve a film formation rate of 90 nm/min or more in the stationary counter film formation, and to increase the surface unevenness, thereby obtaining a zinc oxide-based transparent conductive film having a high blur ratio. In addition, the upper limit of the electric power input to the target is not particularly limited, but is approximately 5.5 W/cm ^{2 in} consideration of power consumption, device configuration, and the like.

In addition, a through-type film formation (transfer film formation) in which a film is formed on a substrate by a substrate, for example, at a same input power density, is removed by a film formation of 5.1 nm m/min (transport speed (m/min)). In the case of the high-speed transfer film formation of the obtained film thickness (nm), a zinc oxide-based transparent conductive film having excellent surface unevenness and a high blur ratio can be obtained. Further, the film formation speed in this case is not particularly limited as long as the object of the present invention can be attained.

The sintered body target containing zinc oxide as a main component is composed of an oxide sintered body having the same composition as that of the transparent conductive film. When an oxide film is obtained by a sputtering method using an oxide sintered body target, the composition of the target and the film is equivalent when the volatile substance is not contained.

The transparent conductive film containing zinc oxide as a main component may be composed mainly of zinc oxide (the weight ratio is 90% or more), and may contain an additive metal element. As an additive metal element which contributes to the conductivity of the transparent conductive film, it is preferable to add one or more selected from aluminum (Al) or gallium (Ga) in order to prevent abnormal discharge under high DC power input. . No abnormal discharge occurs at all even under high DC power input.

A zinc oxide sintered body target containing one or more kinds of added metal elements selected from aluminum or gallium, by adding/mixing gallium oxide powder and alumina powder to zinc oxide powder as a raw material powder, and then, powder The slurry obtained by mixing the raw material powder with the aqueous medium is subjected to a forming of a powder/mixture, and then the molded body is sintered. The detailed production method is described in the above-mentioned Patent Document 3 (JP-A-2008-110911).

Further, in addition to zinc, aluminum, gallium, and oxygen, such a transparent conductive film, for example, indium, titanium, tantalum, niobium, tungsten, molybdenum, niobium, tantalum, niobium, tantalum, magnesium, niobium, fluorine, and the like are not impaired. It may also be contained within the scope of the object of the present invention.

<2. Transparent conductive film>

The transparent conductive film of the present embodiment is preferably one having a surface roughness (Ra) of 35.0 nm or more obtained by the above production method. When the surface roughness (Ra) is less than 35.0 nm, a zinc oxide-based transparent conductive film having a high blur rate cannot be obtained, and when a lanthanide-based solar cell is produced, the light-sealing effect is poor, and high conversion efficiency cannot be achieved. In order to have a sufficient light encapsulation effect, Ra is preferably 35.0 nm or more. However, when the surface roughness (Ra) of the transparent conductive film exceeds 70 nm, the growth of the lanthanoid film formed on the transparent conductive film is affected, and a gap is formed at the interface between the transparent conductive film and the lanthanoid film to make contact. Deterioration makes the solar cell characteristics worse, so it is not good.

Further, the surface resistivity of the transparent conductive film of the present embodiment is preferably 25 Ω / □ or less. When the surface resistance exceeds 25 Ω/□, when the surface electrode of the solar cell is used, the power loss at the surface electrode is increased, and a highly efficient solar cell cannot be realized. The transparent conductive film of the present embodiment can be obtained by the above-described production method and can be 25 Ω/□ or less. The surface resistance of the zinc oxide-based transparent conductive film of the present embodiment is preferably 15 Ω/□ or less, and more preferably 9 Ω/□ or less.

The transparent conductive film used for the surface electrode has a lower surface resistance and a smaller power loss at the surface electrode portion, so that a highly efficient solar cell can be realized even with a large battery area. This can be achieved by making the zinc oxide-based transparent conductive film a crystalline film. On the other hand, if the surface resistance of the surface electrode is high, when the cell of the solar cell is large, the power loss at the surface electrode is too large to be ignored, so it is necessary to reduce the cell area and the metal wiring with low resistance. A large number of small cells are connected to increase the area. For example, when the surface electrode is 65 Ω/□, a solar cell of about 5 cm □ can be realized, but if it is 25 Ω/□, a solar cell of about 10 cm □ can be realized, and if it is 20 Ω/□, about 12 cm □ The solar cell can be realized without taking into account the influence of power loss at the surface electrode.

For a small cell area of a solar cell, it is necessary to connect by metal wiring, because the cell spacing is increased, and the like, the power generation per unit area of a module fabricated not only by the cell is reduced, and the cell area per unit area is small. The increase in manufacturing costs will also be a problem, so it is not good.

In the transparent conductive film of the present embodiment, a transparent conductive film which does not have high unevenness but has high conductivity can be used as a lower substrate and formed thereon. In this case, the electrical conductivity exhibited by the laminate of the first transparent conductive film and the second transparent conductive film of the lower layer is excellent due to the high conductivity of the original transparent conductive film, and can be made large. Solar cell.

The transparent conductive film used as the lower layer can be obtained by a sputtering method. For example, it may be a film containing indium oxide represented by indium oxide (In-Sn-O, ITO) containing tin oxide as a main component, or may be substituted by zinc oxide added with gallium oxide and/or aluminum oxide. Zinc is the main component of the film. When a film having indium oxide as a main component is used as a film and a gas mixture of argon and oxygen is used at a gas pressure of 0.1 to 1.0 Pa to form a film at a temperature of from room temperature to 500 ° C, a surface can be obtained. A transparent conductive film having small unevenness but high conductivity can be used as a lower base film. In particular, when a film is formed on a substrate heated to 150 ° C or higher, a film having a low electrical resistance can be obtained.

Further, a step of forming a film by a gas mixture of argon and oxygen at a temperature of from 0.1 to 1.0 Pa on a substrate having a temperature of from room temperature to 150 ° C, and heating to 200 ° C or higher in a vacuum or an inert gas is carried out. A low-resistance film can also be obtained, which can be used as a lower base film. When a film having zinc oxide as a main component is used as an oxide target and an argon gas is used at a gas pressure of 0.1 to 1.0 Pa to form a film at a temperature of from room temperature to 400 ° C, surface unevenness can be obtained. A highly conductive transparent conductive film can be used as a lower base film. Further, the film containing zinc oxide as a main component may be formed by pressing a film of a temperature of 0.1 to 1.0 Pa with argon gas on a substrate having a temperature of from room temperature to 150 ° C, and then forming a film in a vacuum or an inert gas. The step of heating to 200 ° C or higher gives a film having a low electrical resistance and can be used as a lower base film.

Further, the transparent conductive film used as the lower substrate may be a laminated conductive oxide film (TCO) and an extremely thin metal film (M) (for example, a laminate of TCO/M/TCO). In this case, the metal film is preferably a silver film, and may be pure silver or contain at least one type of silver selected from the group consisting of palladium, platinum, copper, and gold in order to improve corrosion resistance. The silver-based film is preferably 5 to 14 nm in thickness in order to maintain transparency. The conductive oxide film (TCO) may be a film mainly composed of zinc oxide or a film mainly composed of indium oxide, or may be mainly composed of titanium oxide, cerium oxide, cerium oxide or gallium oxide. membrane. The conductive oxide film (TCO) is also preferably a thickness of 5 nm or more necessary for coating the metal film.

The transparent conductive film of the present embodiment can achieve the above characteristics even in a film thickness of 400 to 2000 nm and further 400 to 1000 nm. The thinner the film thickness, the more advantageous it is not only on the material cost side, but also because the film itself has a small amount of light absorption, so that a film having a high transmittance can be realized, which contributes to an improvement in characteristics of the solar cell.

Since the transparent conductive film of the present embodiment is composed of a zinc oxide-based crystal, it is excellent in hydrogen-reducing property, has surface irregularities, and has a high-blurring ratio and high conductivity, and can be directly sputter-coated. Since it is manufactured by the method, it is an excellent transparent conductive film as a surface transparent electrode of a thin film solar cell.

<3. Thin film solar cell>

The solar cell of the present embodiment is a photoelectric conversion element in which the transparent conductive film is used as an electrode. The structure of the solar cell element is not particularly limited, and examples thereof include a PN junction type in which a p-type semiconductor and an n-type semiconductor are laminated, and a PIN junction type in which an insulating layer (I layer) is interposed between the p-type semiconductor and the n-type semiconductor. .

The p-type or n-type conductivity type semiconductor layer functions to generate an internal electric field in the photoelectric conversion unit, and the value of the open voltage (Voc) which is one of important characteristics of the thin film solar cell by the magnitude of the internal electric field. The i-type layer is substantially a true semiconductor layer occupying most of the thickness of the photoelectric conversion unit, and the photoelectric conversion action is mainly generated in the i-type layer. Therefore, this i-type layer is generally referred to as an i-type photoelectric conversion layer or simply as a photoelectric conversion layer. The photoelectric conversion layer is not limited to the true semiconductor layer, and may be doped with a p-type or n-type layer in a small amount within a range in which loss of light absorbed by the doped impurity (dopant) is not a problem.

In addition, the solar cell can be roughly classified into a solar cell using a lanthanoid semiconductor such as a monocrystalline cerium, a polycrystalline cerium, or an amorphous cerium, depending on the type of the semiconductor, and a CuInSe-based or Cu(In,Ga)Se-based system is used. Ag(In,Ga)Se-based, CuInS-based, Cu(In,Ga)S-based, Ag(In,Ga)S-based or a solid solution of these, a thin film of a compound semiconductor such as a GaAs-based or CdTe-based compound In the compound film-based solar cell, a dye-sensitized solar cell (also referred to as a Graetzel Cell type solar cell) using an organic dye, the solar cell of the present embodiment can be used as the transparent conductive film in any of the cases. The electrode is used to achieve high efficiency.

In particular, in the case of a solar cell or a compound film-based solar cell using an amorphous germanium, the electrode on the side on which the sunlight is incident (on the light-receiving side, the front side) is inevitably lacking the transparent conductive film, and the transparent conductive of this embodiment is used. The film can exhibit high conversion efficiency characteristics.

Fig. 1 is a view showing an example of the structure of a lanthanide-based amorphous thin film solar cell. A bismuth-based thin film solar cell using a lanthanoid thin film for a photoelectric conversion unit (light absorbing layer), in addition to an amorphous thin film solar cell, a microcrystalline thin film solar cell, a crystalline thin film solar cell, a laminated thin film solar The battery has also been put to practical use. Further, as described above, in the photoelectric conversion unit or the thin film solar cell, the photoelectric conversion layer which is the main part is amorphous, and it is called an amorphous unit or an amorphous thin film solar cell, and further, a photoelectric conversion layer Those who are crystalline are called crystalline units or crystalline thin film solar cells. Further, when the photoelectric conversion layer is microcrystalline, it is called a microcrystalline unit or a crystalline thin film solar cell.

As a method for improving the conversion efficiency of a thin film solar cell, there is a method in which two or more photoelectric conversion units are stacked to form a tandem type solar cell. In this method, since the light-input side of the thin film solar cell is configured to include a front side unit of the photoelectric conversion layer having a large energy band gap, a photoelectric conversion layer having a small band gap is sequentially disposed behind the square unit. It is possible to perform photoelectric conversion across a wide wavelength range of incident light, thereby improving the conversion efficiency of the entire solar cell. Even among the tandem solar cells, in particular, an amorphous photoelectric conversion unit and a crystalline or microcrystalline photoelectric conversion unit are referred to as a hybrid thin film solar cell.

Fig. 2 is a view showing an example of the structure of a hybrid thin film solar cell. In a hybrid thin film solar cell, for example, the wavelength region of light that can be photoelectrically converted by i-type amorphous germanium is only about 800 nm on the long wavelength side, but the i-type crystalline or microcrystalline germanium can be subjected to photoelectric conversion. Light of a wavelength of about 1150 nm longer than it.

Next, the configuration of the thin film solar cell will be described more specifically with reference to Figs. In the first and second embodiments, the uneven zinc oxide-based transparent conductive film 2 of the present embodiment is formed on the light-transmitting substrate 1. As the light-transmitting substrate 1, a plate-shaped member or a thin plate-shaped member made of glass, a transparent resin or the like is used. An amorphous photoelectric conversion unit 3 is formed on the transparent conductive film 2. The amorphous photoelectric conversion unit 3 is composed of an amorphous p-type tantalum carbide layer 31, an undoped amorphous i-type germanium photoelectric conversion layer 32, and an n-type germanium-based interface layer 33. The amorphous p-type tantalum carbide layer 31 is formed at a substrate temperature of 180 ° C or lower in order to prevent a decrease in transmittance due to reduction of the transparent conductive film 2 .

In the hybrid thin film solar cell shown in FIG. 2, a crystalline photoelectric conversion unit 4 is formed on the amorphous photoelectric conversion unit 3. The crystalline photoelectric conversion unit 4 is composed of a crystalline p-type germanium layer 41, a crystalline i-type germanium photoelectric conversion layer 42, and a crystalline n-type germanium layer 43. The formation of the amorphous photoelectric conversion unit 3 and the crystalline photoelectric conversion unit 4 (hereinafter, the unit of both units is simply referred to as a photoelectric conversion unit) is preferably a high-frequency plasma CVD method. The formation conditions of the photoelectric conversion unit are preferably a substrate temperature of 100 to 250 ° C (but the amorphous p-type tantalum carbide layer 31 is 180 ° C or less), a pressure of 30 to 1500 Pa, and a high frequency power density of 0.01 to 0.5 W/cm ^{2 .} . As the material gas used for the photoelectric conversion unit, a helium-containing gas such as SiH ₄ or Si ₂ H ₆ or a mixture of these gases and H ₂ is used. The doping gas for forming the p-type or n-type layer of the photoelectric conversion unit is preferably B ₂ H ₆ or PH ₃ or the like.

A back electrode 5 is formed on the n-type lanthanide interface layer 43. The back surface electrode 5 is composed of a transparent reflection layer 51 and a back reflection layer 52. As the transparent reflective layer 51, a metal oxide such as ZnO or ITO is used, and in the back surface reflective layer 52, Ag, Al, or an alloy of these is preferably used. For the formation of the back electrode 5, a method such as sputtering or vapor deposition is preferably used. The back electrode 5 usually has a thickness of 0.5 to 5 μm, preferably 1 to 3 μm. After the formation of the back surface electrode 5, the ambient temperature of the amorphous p-type tantalum carbide layer 31 is heated at an ambient temperature or higher to complete the solar cell. As the gas used in the heating atmosphere, it is preferable to use a mixture of air, nitrogen, nitrogen and oxygen. Further, the vicinity of the atmospheric pressure is approximately in the range of 0.5 to 1.5 atm.

Further, the structure of the hybrid thin film solar cell is shown in Fig. 2. However, it is not necessary to have two photoelectric conversion units, a single amorphous or crystalline structure, or a three-layer or more layer-based solar cell structure.

Further, as shown in FIGS. 3 and 4, the light-transmitting substrate 1 can be used for a plate-like or sheet-like member 11 made of glass, a transparent resin or the like, and has high conductivity without high unevenness. The transparent conductive film 12 is formed to be the lower bottom of the transparent conductive film 2 of the present embodiment. In this case, the transparent conductive film 12 to be the lower layer is provided on the side of the uneven zinc oxide-based transparent conductive film 2 in the light-transmitting substrate 1, and the transparent conductive film 12 is laminated with the transparent conductive film 2 of the present embodiment. The body functions as a surface electrode of a solar cell. The same components as those of the thin film solar cells shown in Figs. 1 and 2 are denoted by the same reference numerals and will not be described.

The transparent conductive film 12 used as the lower layer can be obtained by a sputtering method. For example, it may be a film containing indium oxide represented by indium oxide (In-Sn-O, ITO) containing tin oxide as a main component, or may be substituted by zinc oxide added with gallium oxide and/or aluminum oxide. Zinc is the main component of the film. When a film having indium oxide as a main component is used as a film and a gas mixture of argon and oxygen is used at a gas pressure of 0.1 to 1.0 Pa to form a film at a temperature of from room temperature to 500 ° C, a surface can be obtained. A transparent conductive film having small unevenness but high conductivity can be used as a lower base film. In particular, when a film is formed on a substrate heated to 150 ° C or higher, a film having a low electrical resistance can be obtained. Further, a step of forming a film by a gas mixture of argon and oxygen at a temperature of from 0.1 to 1.0 Pa on a substrate having a temperature of from room temperature to 150 ° C, and heating to 200 ° C or higher in a vacuum or an inert gas is carried out. A low-resistance film can also be obtained, which can be used as a lower base film. When a film having zinc oxide as a main component is used as an oxide target and an argon gas is used at a gas pressure of 0.1 to 1.0 Pa to form a film at a temperature of from room temperature to 400 ° C, surface unevenness can be obtained. A highly conductive transparent conductive film can be used as a lower base film. Further, the film containing zinc oxide as a main component may be formed by pressing a film of a temperature of 0.1 to 1.0 Pa with argon gas on a substrate having a temperature of from room temperature to 150 ° C, and then forming a film in a vacuum or an inert gas. The step of heating to 200 ° C or higher gives a film having a low electrical resistance and can be used as a lower base film.

Further, the transparent conductive film 12 used as the lower substrate may be a laminated conductive oxide film (TCO) and an extremely thin metal film (M) (for example, a laminate of TCO/M/TCO). In this case, the metal film is preferably a silver film, and may be pure silver or contain at least one type of silver selected from the group consisting of palladium, platinum, copper, and gold in order to improve corrosion resistance. The silver-based film is preferably 5 to 14 nm in thickness in order to maintain transparency. The conductive oxide film (TCO) may be a film mainly composed of zinc oxide or a film mainly composed of indium oxide, or may be mainly composed of titanium oxide, cerium oxide, cerium oxide or gallium oxide. membrane. The conductive oxide film (TCO) is also preferably a thickness of 5 nm or more necessary for coating the metal film.

In the thin film solar cell of the present embodiment, the zinc oxide based transparent conductive film 2 on the light-transmitting substrate 1 is formed by a sputtering method. Specifically, a mixed gas of argon and hydrogen is used as the sputtering gas species, and the molar ratio of the mixed gas is H ₂ /(Ar+H ₂ )=0.01 to 0.43, and the sputtering gas pressure is 2.0 to 15.0 Pa, and the substrate temperature. It is formed by forming an oxide sintered body target containing zinc oxide as a main component under conditions of 300 to 600 °C.

The zinc oxide-based transparent conductive film 2 obtained in this manner is excellent in hydrogen-reducing property, is excellent in light-sealing effect, and has low surface resistance. Then, the photoelectric conversion layer unit and the back electrode layer are sequentially formed on the zinc oxide-based transparent conductive film 2, whereby a highly efficient thin film solar cell can be provided at low cost.

As described above, by using a mixed gas of argon and hydrogen as a sputtering gas species, a high electric power density of 2.76 kW/cm ² or more can be put into the sputtering target to form a transparent conductive film at a high speed. Further, even when high-speed film formation is performed, a transparent conductive film having excellent surface unevenness, high light-sealing effect, and low electrical resistance can be produced. In particular, the above characteristics can also be achieved with a thin film thickness of 400 to 1000 nm. Therefore, it is advantageous not only for material cost reduction or transmittance improvement but also for reduction in manufacturing cost, and it can be provided at a lower cost than the transparent conductive film of the prior thermal CVD method.

In addition, the transparent conductive film produced by the present method has an advantage of high transmittance, and has excellent surface concavity and high light-sealing effect, and is effective as an electrode of various solar cells. In particular, it contributes to the improvement of the characteristics of the lanthanide thin film solar cell, and has industrial applicability such as a lanthanide thin film solar cell which can provide high efficiency at a low cost in a simple process.

[Examples]

Hereinafter, the zinc oxide-based transparent conductive film will be described using examples, but the present invention is not limited to these examples.

(1) The film thickness was measured by the following procedure. Before the film formation, a part of the substrate is pre-coated with an oil-based marker ink, and after forming a film, the ink is wiped off with alcohol to form a portion without a film, and a contact surface shape measuring device (Alpha-Step IQ manufactured by KLA Tencor Co., Ltd.) is used. The difference in height between the portion having the film and the portion having no film was determined.

(2) The composition of the obtained transparent conductive film was quantitatively analyzed by an ICP (Inductively Coupled Plasma) luminescence spectrometer (SPS4000 manufactured by Seiko Instruments Inc.).

(3) The adhesion of the film to the substrate was evaluated in accordance with JIS C0021. The evaluation was evaluated as good (○) in the case where the film was not peeled off, and insufficient (×) in the case where the film was peeled off.

(4) Further, the specific resistance of each transparent conductive film was measured by a four-probe method using a resistivity meter Loresta EP (manufactured by Daya Instruments Co., Ltd. (already incorporated into Mitsubishi Chemical Analytech Co., Ltd. model MCP-T360).

(5) Further, the total light transmittance, the parallel light transmittance, the total light reflectance, and the parallel light reflectance of the substrate were measured by a spectrophotometer (manufactured by Hitachi, Ltd., U-4000).

(6) Surface roughness (Ra) of the film An area of 5 μm × 5 μm was measured using an atomic force microscope (manufactured by Digitto Instruments Co., Ltd., NS-III, D5000 system).

(7) The crystallinity and the alignment property of the film were examined by X-ray diffraction measurement using an X-ray diffraction apparatus (M18XHF22, manufactured by Mark Scientific Co., Ltd.) using a CuKα line.

[Examples 1 to 3 (when a 0.27 wt% Al ₂ O ₃ ZnO film was added)]

A zinc oxide-based transparent conductive film having a large surface unevenness was produced as follows, using a zinc oxide sintered body target (manufactured by Sumitomo Metal Mine) containing aluminum as an additive element.

The composition of the target used was quantitatively analyzed by an ICP emission spectrometer (SPS4000 manufactured by Seiko Instruments Inc.), and Al/(Zn+Al) was 0.43 atom%. Further, the target used had a purity of 99.999%, and the target had a size of 6 inches (Φ) × 5 mm (thickness).

The sputtering target was mounted on a cathode of a ferromagnetic target for a DC magnetron sputtering apparatus (manufactured by TOKKI Co., Ltd., SPF 503K) (the horizontal magnetic field strength at a position of 1 cm from the surface of the target, the maximum is about 80kA/m (1kG)), the opposite surface of the sputtering target was mounted with a Corning 7059 glass substrate with a thickness of 1.1 mm. Further, the distance between the sputtering target and the substrate was 50 mm. Moreover, the average light transmittance of the visible light wavelength region of Corning 7059 glass substrate itself was 92%.

Next, the vacuum chamber is evacuated, and when the degree of vacuum reaches 2 × 10 ^-4 Pa or less, a mixture of argon gas having a purity of 99.9999% by mass and hydrogen gas H ₂ is introduced into the vacuum chamber to make the gas pressure 3.0. Pa. The mixing ratio of hydrogen, that is, the molar ratio of H ₂ /(Ar + H ₂ ), was 0.01 (Example 1), 0.25 (Example 2), and 0.43 (Example 3). A substrate temperature of 400 ℃, the DC input power 500W (power density on the target input DC input power = ÷ target surface area ^{= 500W ÷ 181cm 2 = 2.760W /} cm 2), to put in between the target and the substrate, so that Produces DC plasma. In order to clean the surface of the target, after pre-sputtering for 10 minutes, the substrate was allowed to stand directly above the center of the target, and sputtering was performed to form a film. Because it is high input power, the film formation speed is as fast as 90 to 92 nm/min. Further, the properties of the obtained transparent conductive film were evaluated by the methods (1) to (7) above.

The properties of the films obtained in Examples 1 to 3 are shown in Table 1. The composition of the obtained film was analyzed by ICP emission spectrometry, and the result was almost identical to the composition of the target. Further, the film thickness is 800 to 810 nm. Further, the film formation rate is 91 to 92 nm/min, and film formation can be performed in a short time. The surface roughness Ra measured by an atomic force microscope showed a high value of 35 nm or more. When the surface of the films of Examples 1 to 3 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the surface resistance is 25 Ω/□ or less, indicating high conductivity. Therefore, it was confirmed by Examples 1 to 3 that a zinc oxide-based transparent conductive film having a high blur ratio and excellent conductivity can be obtained. This film is very useful as a surface electrode of a lanthanide thin film solar cell.

[Comparative Examples 1 to 3 (changing the amount of H ₂ mixed)]

In the production methods of Examples 1 to 3, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of aluminum, except that the mixing ratio of the H ₂ gas was changed, under the same conditions. The mixing ratio of hydrogen gas H ₂ , that is, the molar ratio of H ₂ /(Ar + H ₂ ), was 0 atom% (Comparative Example 1), 0.005 atom% (Comparative Example 2), and 0.50 atom% (Comparative Example 3). Except for changing the mixing ratio of the H ₂ gas, the same conditions as in Examples 1 to 3 were carried out.

The properties of the obtained transparent conductive film were evaluated in the same manner as in Examples 1 to 3. The evaluation results are shown in Table 1. The composition of the resulting film is almost identical to the composition of the target. The power density of the target applied to the target at the time of film formation was 2.760 W/cm ² as in the case of Examples 1 to 3, so that a film formation rate of 91 to 92 nm/min was obtained. However, in the films of Comparative Examples 1 and 2, although the conductivity was good, unlike the Examples 1 to 3, the Ra value was a film having a low value of less than 35 nm.

Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell. Further, in the film of Comparative Example 3, although the Ra value was high, the surface resistance was too high, so that it could not be used as an electrode of a solar cell. Further, the film of Comparative Example 3 had a problem that the adhesion to the substrate was extremely weak.

[Examples 4 to 5, Comparative Example 4]

In the production method of the second embodiment, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of aluminum, except that the substrate temperature was changed, under the same conditions. The substrate temperature was 300 ° C (Example 4), 600 ° C (Example 5), and 250 ° C (Comparative Example 4). The same conditions as in Example 2 were carried out except that the substrate temperature was changed.

The properties of the obtained transparent conductive film were evaluated in the same manner as in Examples 1 to 3. The evaluation results are shown in Table 1. The composition of the resulting film was almost identical to the composition of the target. The power density of the target applied to the target at the time of film formation was 2.760 W/cm ² as in the case of Example ² , so that a film formation rate of 91 to 92 nm/min was obtained. The surface roughness Ra measured by an atomic force microscope showed a high value of 35 nm or more. When the surface of the films of Examples 4 to 5 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the surface resistance is 25 Ω/□ or less, indicating high conductivity. Therefore, it was confirmed by Examples 4 to 5 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode of a lanthanide thin film solar cell.

However, the film of Comparative Example 4 had a good conductivity, but unlike Examples 4 to 5, the Ra value was a film having a low value of less than 35 nm. Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell.

[Examples 6 to 8 and Comparative Examples 5 to 6]

In the production method of the third embodiment, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of aluminum, except that the substrate temperature and the gas pressure were changed, under the same conditions. The substrate temperature was 350 ° C within the specified range of the present embodiment, and the gas pressure was 2.0 Pa (Example 6), 8.0 Pa (Example 7), 15.0 Pa (Example 8), and 1.0 Pa (Comparative Example 5). 20.0 Pa (Comparative Example 6). The same conditions as in Example 3 were carried out except that the substrate temperature and the gas pressure were changed.

The properties of the obtained transparent conductive film were evaluated in the same manner as in Examples 1 to 3. The evaluation results are shown in Table 1. The composition of the resulting film was almost identical to the composition of the target. The power density applied to the target at the time of film formation was 2.760 W/cm ² as in Example 3. Therefore, in Examples 6 to 8 and Comparative Example 5, a film formation rate of 82 to 94 nm/min was obtained. However, Comparative Example 6 was 73 nm/min, and the surface roughness Ra measured by an atomic force microscope showed a high value of 35 nm or more. When the surface of the films of Examples 6 to 8 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the films of Examples 6 to 8 had a surface resistance of 25 Ω/□ or less and exhibited high conductivity. Therefore, it was confirmed by Examples 6 to 8 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode of a lanthanide thin film solar cell.

On the other hand, in the film of Comparative Example 5, although the conductivity was good, unlike the Examples 6 to 8, the Ra value was a film having a low value of less than 35 nm. Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell.

Further, in the film of Comparative Example 6, although the Ra value was high, the surface resistance was too high, so that it could not be used as an electrode of a solar cell. Further, the film of Comparative Example 6 had a problem that the adhesion to the substrate was extremely weak.

[Examples 9 to 11 and Comparative Example 7]

The manufacturing method of the second embodiment is carried out under the same conditions except that the substrate temperature and the gas pressure are changed and the input electric power to the target is changed within a predetermined range, and the zinc oxide sintered body target having the same composition containing aluminum is used. A zinc oxide-based transparent conductive film was produced. The substrate temperature was 450 ° C in the specified range, and the gas pressure was 4.0 Pa. Further, in Comparative Example 7 and Example 9, the input DC power was 2.760 W/cm ² , and in Examples 10 and 11, it was 3.312 W/cm ² . Next, by changing the film formation time, various transparent film thicknesses of 450 nm (Example 9), 1450 nm (Example 10), 2150 nm (Example 11), and 380 nm (Comparative Example 7) were produced. The same conditions as in Example 2 were carried out except that the substrate temperature, the gas pressure, and the film thickness were changed.

The characteristics of the obtained transparent conductive film were evaluated in the same manner as in Example 2. The evaluation results are shown in Table 1. The composition of the resulting film was almost identical to the composition of the target. The film formation rate was as fast as the input power density was higher, and a film formation rate of 90.5 nm/min was obtained in Example 9 in which 2.760 W/cm ² was charged, and Examples 10 and 11 were placed at 3.312 W/cm ² . A film formation rate of 108 to 109 nm/min was obtained. The surface roughness Ra of the films of Examples 9 to 11 was measured by an atomic force microscope to show a high value of 35 nm or more. Further, when the surface of the films of Examples 9 to 11 was observed by SEM, the film was composed of large grains, and the surface unevenness was large.

Further, the surface resistance is 25 Ω/□ or less, indicating high conductivity. Therefore, it was confirmed by Examples 9 to 11 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode of a lanthanide thin film solar cell.

On the other hand, in the film of Comparative Example 7, the surface resistance was high, and the Ra value was also a film which was as low as 35 nm. Therefore, it cannot be utilized as a surface transparent electrode of a highly efficient solar cell.

[Comparative Examples 8 to 10]

In the production method of Comparative Example 1, except that only the input power density to the target was changed, the zinc oxide sintered target having the same composition containing aluminum was used under the same conditions, and zinc oxide-based transparent conductive was produced without using hydrogen gas. membrane. The input power density was 0.442 W/cm ² (Comparative Example 8), 1.105 W/cm ² (Comparative Example 9), and 2.210 W/cm ² (Comparative Example 10), and the film formation time was adjusted to obtain a film thickness of about 800 nm.

The characteristics of the obtained transparent conductive film were evaluated in the same manner. The evaluation results are shown in Table 1. The composition of the resulting film was almost identical to the composition of the target. When the power density of the target is small at the time of film formation, a film having a large Ra value can be obtained even at a film thickness of approximately 800 nm, but the film formation rate is remarkably slowed, so that it is not practical.

[Comparative Example 11]

In the production method of Comparative Example 1, except that the film thickness was changed, a zinc oxide-based transparent conductive film was produced without using hydrogen gas from the zinc oxide sintered body target having the same composition containing aluminum under the same conditions. The film thickness was 1530 nm (Comparative Example 11), and the film formation time was adjusted to obtain a specific film thickness.

The characteristics of the obtained transparent conductive film were evaluated in the same manner. The evaluation results are shown in Table 1. The composition of the resulting film was almost identical to the composition of the target. When hydrogen was introduced in the same manner as in the case of Comparative Example 1, even if the film thickness was 1530 nm, the Ra value was insufficient. Further, the film thickness of Comparative Example 11 was close to about 2.7 times the film thickness of Example 1, so that the production cost was not high, and the transmittance was lowered due to light absorption of the film, which was not practical. When the average value of the total light transmittance of the wavelength of 400 to 800 nm was compared, the film of Comparative Example 11 was about 4% lower than that of the film of Example 1.

[Examples 12 to 14 (When a 1.5 wt% Ga ₂ O ₃ ZnO film was added)]

A zinc oxide-based transparent conductive film having a large surface unevenness was produced as follows, using a zinc oxide sintered body target containing gallium as an additive element (manufactured by Sumitomo Metal Mine).

The composition of the target used was quantitatively analyzed by an ICP emission spectrometer (SPS4000 manufactured by Seiko Instruments Inc.), and Ga/(Zn + Ga) was 1.31 at%. Further, the target used had a purity of 99.999%, and the target had a size of 6 inches (Φ) and 5 mm (thickness).

The sputtering target was mounted on a cathode of a ferromagnetic target for a DC magnetron sputtering apparatus (manufactured by TOKKI Co., Ltd., SPF 503K) (the horizontal magnetic field strength at a position of 1 cm from the surface of the target, the maximum is about 80kA/m (1kG)), the opposite surface of the sputtering target was mounted with a Corning 7059 glass substrate with a thickness of 1.1 mm.

Further, the distance between the sputtering target and the substrate was 60 mm. Moreover, the average light transmittance of the visible light wavelength region of Corning 7059 glass substrate itself was 92%.

Next, the vacuum chamber is evacuated, and when the degree of vacuum reaches 2 × 10 ^-4 Pa or less, a mixture of argon gas having a purity of 99.9999% by mass and hydrogen gas H ₂ is introduced into the vacuum chamber to make the gas pressure 3.0. Pa. The mixing ratio of hydrogen, that is, the molar ratio of H ₂ /(Ar + H ₂ ), was 0.01 (Example 12), 0.25 (Example 13), and 0.42 (Example 14). A substrate temperature of 400 ℃, the DC input power 500W (of the target electric power density of the target surface area = DC input power ^{= 500W ÷ 181cm 2 = 2.760W /} cm 2), to put in between the target and the substrate to produce DC plasma. In order to clean the surface of the target, after pre-sputtering for 10 minutes, the substrate was allowed to stand directly above the center of the target, and sputtering was performed to form a film. Because of the high input power, the film formation rate is as fast as 91 to 93 nm/min. Further, the properties of the obtained transparent conductive film were evaluated by the methods (1) to (7) above.

The properties of the films obtained in Examples 12 to 14 are shown in Table 2. The composition of the obtained film was analyzed by ICP emission spectrometry, and the result was almost identical to the composition of the target. Further, the film thickness is 700 to 710 nm, and the film formation rate is as fast as 91 to 92 nm/min. The surface roughness Ra measured by an atomic force microscope showed a high value of 35 nm or more. When the surface of the films of Examples 12 to 14 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the surface resistance is 25 Ω/□ or less, indicating high conductivity. Therefore, it was confirmed by Examples 12 to 14 that a zinc oxide-based transparent conductive film having a high blur ratio and excellent conductivity can be obtained. This film is very useful as a surface electrode for solar cells.

[Comparative Examples 12 to 14 (changing the amount of H ₂ mixed)]

In the production methods of Examples 12 to 14, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of gallium, except that the mixing ratio of the H ₂ gas was changed, under the same conditions. The mixing ratio of hydrogen gas H ₂ , that is, the molar ratio of H ₂ /(Ar + H ₂ ), was 0 atom% (Comparative Example 12), 0.005 atom% (Comparative Example 13), and 0.50 atom% (Comparative Example 14). Except for changing the mixing ratio of the H ₂ gas, the same conditions as in Examples 12 to 14 were made.

The properties of the obtained transparent conductive film were evaluated in the same manner as in Examples 12 to 14. The evaluation results are shown in Table 2. The composition of the resulting film is almost identical to the composition of the target. The power density of the target applied to the target at the time of film formation was 2.760 W/cm ² as in the case of Examples 12 to 14, so that a film formation rate of 91 to 92 nm/min was obtained. However, in the films of Comparative Examples 12 and 13, although the conductivity was good, unlike the examples 12 to 14, the Ra value was a film having a low level of less than 35 nm. Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell. Further, in the film of Comparative Example 14, although the Ra value was high, the surface resistance was too high, so that it could not be used as an electrode of a solar cell. Further, the film of Comparative Example 14 had a problem that the adhesion to the substrate was extremely weak.

[Examples 15 to 16 and Comparative Example 15]

In the production method of Example 13, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of gallium, except that the substrate temperature was changed, under the same conditions. The substrate temperature was 310 ° C (Example 15), 550 ° C (Example 16), and 270 ° C (Comparative Example 15). The same conditions as in Example 13 were carried out except that the substrate temperature was changed.

The properties of the obtained transparent conductive film were evaluated in the same manner as in Examples 12 to 14. The evaluation results are shown in Table 2. The composition of the resulting film was almost identical to the composition of the target. The power density of the target applied to the target at the time of film formation was 2.760 W/cm ² as in Example 13, so that a film formation rate of 92 to 93 nm/min was obtained. The surface roughness Ra measured by an atomic force microscope showed a high value of 35 nm or more. When the surface of the films of Examples 15 to 16 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the surface resistance is 25 Ω/□ or less, indicating high conductivity. Therefore, it was confirmed by Examples 15 to 16 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode for solar cells.

On the other hand, the film of Comparative Example 15 had a good conductivity, but unlike Examples 15 to 16, the Ra value was a film having a low value of less than 35 nm. Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell.

[Examples 17 to 19 and Comparative Examples 16 to 17]

In the production method of the fourteenth embodiment, a zinc oxide-based transparent conductive film was produced from a zinc oxide sintered body target having the same composition of gallium, except that the substrate temperature and the gas pressure were changed under the same conditions. The substrate temperature was 340 ° C in the specified range, and the gas pressure was 2.0 Pa (Example 17), 8.0 Pa (Example 18), 15.0 Pa (Example 19), 1.0 Pa (Comparative Example 16), 20.0 Pa ( Comparative Example 17). The same conditions as in Example 14 were carried out except that the substrate temperature and the gas pressure were changed.

The characteristics of the obtained transparent conductive film were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2. The composition of the resulting film was almost identical to the composition of the target. The power density applied to the target at the time of film formation was 2.760 W/cm ² as in Example 14, so that the film formation speeds of 83 to 96 nm/min were obtained in Examples 17 to 19 and Comparative Example 16. On the other hand, the film formation speed of Comparative Example 17 was as slow as 76 nm/min.

The surface roughness Ra value measured by an atomic force microscope showed a value higher than 35 nm in addition to Comparative Example 16. When the surface of the films of Examples 17 to 19 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the surface resistance was 25 Ω/□ or less in addition to Comparative Example 17, and showed high conductivity. Therefore, it was confirmed by Examples 17 to 19 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode for solar cells.

On the other hand, the film of Comparative Example 16 had a good conductivity, but unlike Examples 17 to 19, the Ra value was a film having a low value of less than 35 nm. Therefore, the light sealing effect is not sufficient, and therefore it cannot be utilized as a surface transparent electrode of a highly efficient solar cell. Further, in the film of Comparative Example 17, although the Ra value was high, the surface resistance was too high, so that it could not be used as an electrode of a solar cell.

Further, the film of Comparative Example 17 had a problem that the adhesion to the substrate was extremely weak.

[Examples 20 to 22, Comparative Example 18]

The manufacturing method of the embodiment 13 is carried out under the same conditions except that the substrate temperature and the gas pressure are changed and the input power to the target is changed within a predetermined range, and the zinc oxide sintered body target having the same composition containing gallium is used. A zinc oxide-based transparent conductive film was produced. The substrate temperature was 480 ° C in the specified range, and the gas pressure was 4.0 Pa. Further, in Comparative Example 18 and Example 20, the input DC power was 2.760 W/cm ² , and in Examples 21 to 22, it was 3.312 W/cm ² . Next, various transparent film thicknesses of 420 nm (Example 20), 1350 nm (Example 21), 1850 nm (Example 22), and 365 nm (Comparative Example 18) were produced by changing the film formation time.

The same conditions as in Example 13 were carried out except that the substrate temperature, the gas pressure, and the film thickness were changed.

The characteristics of the obtained transparent conductive film were evaluated in the same manner as in Example 13. The evaluation results are shown in Table 2. The composition of the resulting film was almost identical to the composition of the target. The deposition rate is faster the higher electric power density, the input 2.760W / cm ² of Example 20 to give 90.5 nm / min deposition rate of the faster, 3.312W / cm ² of Example Embodiment inputs 21 and 22 A film formation rate of 110 to 115 nm/min was obtained. The surface roughness Ra of the films of Examples 20 to 22 was measured by an atomic force microscope to show a high value of 35 nm or more. When the surface of the films of Examples 20 to 22 was observed by SEM, the film was composed of large grains, and the surface unevenness was large. Further, the films of Examples 20 to 22 had a surface resistance of 25 Ω/□ or less and exhibited high conductivity.

Therefore, it was confirmed by Examples 20 to 22 that a zinc oxide-based transparent conductive film having a high Ra value and excellent conductivity can be obtained. This film is very useful as a surface electrode for solar cells.

On the other hand, in the film of Comparative Example 18, the surface resistance was high, and the Ra value was also a film which was as low as 35 nm. Therefore, it cannot be utilized as a surface transparent electrode of a highly efficient solar cell.

[Comparative Examples 19 to 21]

In the production method of Comparative Example 12, except that only the input power density to the target was changed, the zinc oxide sintered target having the same composition containing gallium was produced under the same conditions, and zinc oxide-based transparent conductive was produced without using hydrogen gas. membrane. The input power density was 0.442 W/cm ² (Comparative Example 19), 1.105 W/cm ² (Comparative Example 200), and 2.210 W/cm ² (Comparative Example 21), and the film formation time was adjusted to obtain a film thickness of about 700 nm.

The characteristics of the obtained transparent conductive film were evaluated in the same manner. The evaluation results are shown in Table 2. The composition of the resulting film was almost identical to the composition of the target. When the power density of the target is small at the time of film formation, a film having a large Ra value can be obtained even at a film thickness of approximately 700 nm. However, the film formation rate is remarkably slow, which is not practical.

[Comparative Example 22]

In the production method of Comparative Example 12, a zinc oxide-based transparent conductive film was produced without using hydrogen gas, except that only the film thickness was changed, under the same conditions, and the zinc oxide sintered compact target having the same composition containing gallium was used. The film thickness was 1730 nm (Comparative Example 22), and the film formation time was adjusted to obtain a specific film thickness.

The characteristics of the obtained transparent conductive film were evaluated in the same manner. The evaluation results are shown in Table 2. The composition of the resulting film was almost identical to the composition of the target. When hydrogen was introduced in the same manner as in the case of Comparative Example 1, even if the film thickness was 1730 nm, the Ra value was insufficient. On the other hand, the film thickness of Comparative Example 22 was close to 3.2 times the film thickness of Example 13, so that the production cost was not high, and the transmittance was lowered due to light absorption of the film, which was not practical. When the average value of the total light transmittance of the wavelength of 400 to 800 nm was compared, the film of Comparative Example 22 was about 5% lower than that of the film of Example 13.

[Example 23]

The same experiment as in Examples 1 to 11 and Comparative Examples 1 to 11 was carried out using a zinc oxide sintered body target (manufactured by Sumitomo Metal Mine) containing aluminum in a ratio of 1.59 atom% of Al/(Zn+Al), and all the experiments were carried out in the same manner as in Examples 1 to 11 and Comparative Examples 1 to 11, The same tendency.

[Example 24]

A zinc oxide sintered body target (manufactured by Sumitomo Metal Mine) containing aluminum in a ratio of Al/(Zn+Al) of 0.49 atomic % and a ratio of Ga/(Zn+Ga) of 0.49 atomic % is used. The same experiments as in Examples 1 to 11 and Comparative Examples 1 to 11 all had the same tendency.

[Example 25]

The formation of the transparent conductive film of the present embodiment was attempted on a glass substrate on which a transparent conductive film of a lower underlayer film was formed. The transparent conductive film of the lower base film was synthesized in the following steps/conditions using the film forming apparatus used in Example 1. In other words, an indium oxide sintered body target (ITO target) containing tin oxide in a ratio of 7.5 at% of Sn/(In+Sn) was used, and the glass substrate heated to 300° C. was placed at a position directly above the center of the target. DC magnetron sputtering is performed to form a film. The distance between the target and the substrate was 50 mm, and argon gas containing 3 vol% of oxygen was used as a sputtering gas, and a film formation pressure was 0.6 Pa to form a film. On the glass substrate, the ITO film having the same composition as the target was formed only to have a film thickness of 180 nm, and its surface resistance was 10.5 Ω/□. Further, the average value of the transmittance at a wavelength of 400 to 800 nm was 85% or more, and the transmittance was also good.

The second transparent conductive film was produced in the same manner and under the same conditions as in Example 9 using the glass substrate on which the first transparent conductive film of the lower film was formed. The Ra value of the second transparent conductive film formed on the surface of the first transparent conductive film of the lower base film was 37.5 nm, and the surface unevenness equivalent to that of the transparent conductive film of Example 9 formed on the glass substrate was exhibited. In addition, when the surface resistance value was measured in the same manner as in Example 9, the surface of the second transparent conductive film formed on the first transparent conductive film of the lower base film was 8.5 Ω/□. The evaluation results are shown in Table 3. In other words, the conductivity of the first transparent conductive film and the second transparent conductive film in which the underlayer film is laminated is significantly improved as compared with the transparent conductive film of the ninth embodiment.

Therefore, it can be said that the surface unevenness is large, the light sealing effect is excellent, and the surface resistance value is low, so that it can be said to be useful for the surface electrode of a solar cell.

[Example 26]

Using the film forming apparatus used in Example 1, the transparent conductive film of the lower base film was synthesized in the following steps/conditions. In other words, an indium oxide sintered body target (ITiO target) containing titanium oxide in a ratio of 1.5 atom% of Ti/(In+Ti) is used, and the glass substrate heated to 350 ° C is placed directly above the center of the target. DC magnetron sputtering is performed to form a film.

The distance between the target and the substrate was 60 mm, and argon gas containing 4% by volume of oxygen was used as a sputtering gas, and a film formation pressure was set to 0.2 Pa to form a film. On the glass substrate, the ITiO film having the same composition as the target was formed only to have a film thickness of 220 nm, and its surface resistance was 11.5 Ω/□. Further, the average value of the transmittance at a wavelength of 400 to 800 nm was 85% or more, and the transmittance was also good.

The second transparent conductive film was produced in the same manner and under the same conditions as in Example 14 using the glass substrate on which the first transparent conductive film (ITiO film) of the lower film was formed. The Ra value of the second transparent conductive film formed on the first transparent conductive film of the lower base film was 55.5 nm, and the surface unevenness equivalent to that of the transparent conductive film of Example 14 formed on the glass substrate was exhibited. In addition, when the surface resistance value was measured in the same manner as in Example 14 on the surface of the second transparent conductive film formed on the first transparent conductive film of the lower base film, it was 9.2 Ω/□. The evaluation results are shown in Table 3. In other words, the conductivity of the first transparent conductive film (ITiO film) and the second transparent conductive film in which the underlayer film is laminated is significantly improved as compared with the transparent conductive film of the fourteenth embodiment.

Therefore, it can be said that the surface unevenness is large, the light sealing effect is excellent, and the surface resistance value is low, so that it can be said to be useful for the surface electrode of a solar cell.

[Example 27]

Using the film forming apparatus used in Example 1, the transparent conductive film of the lower base film was synthesized in the following steps/conditions. That is, a zinc oxide sintered body target (GZO target) containing gallium oxide in a ratio of a molar ratio of Ga/(Zn + Ga) of 4.96 atomic % is used, and a glass substrate heated to 190 ° C is allowed to stand at the center of the target. Directly above, DC magnetron sputtering is performed to form a film. The distance between the target and the substrate was 70 mm, and argon gas was used as a sputtering gas, and a film formation pressure was set to 0.2 Pa to form a film. On the glass substrate, the GZO film having the same composition as the target was formed only to have a film thickness of 380 nm, and its surface resistance was 11.3 Ω/□. Further, the average value of the transmittance at a wavelength of 400 to 800 nm was 85% or more, and the transmittance was also good.

A second transparent conductive film was produced in the same manner and under the same conditions as in Example 20, using the glass substrate on which the first transparent conductive film (GZO film) of the lower film was formed. The Ra value of the second transparent conductive film formed on the first transparent conductive film of the lower base film was 36.9 nm, and the surface unevenness equivalent to that of the transparent conductive film of Example 20 formed on the glass substrate was exhibited. In addition, when the surface resistance value was measured in the same manner as in Example 20, the surface of the second transparent conductive film formed on the first transparent conductive film of the lower base film was 8.1 Ω/□. The evaluation results are shown in Table 3. That is, the conductivity is remarkably improved by laminating the first transparent conductive film (GZO film) of the underlayer film and the second transparent conductive film as compared with the transparent conductive film of Example 20 formed on the glass substrate. .

Therefore, it can be said that the surface unevenness is large, the light sealing effect is excellent, and the surface resistance value is low, so that it can be said to be useful for the surface electrode of a solar cell.

[Example 28]

Using the film forming apparatus used in Example 1, the transparent conductive film of the lower base film was synthesized in the following steps/conditions. That is, a zinc oxide sintered body target (AZO target) containing alumina in a ratio of Al/(Zn+Al) atomic ratio of 1.59 atomic % is used, and the glass substrate heated to 250 ° C is allowed to stand at the center of the target. Directly above, DC magnetron sputtering is performed to form a film. The distance between the target and the substrate was 50 mm, and argon gas was used as a sputtering gas, and a film formation pressure was 0.4 Pa to form a film. On the glass substrate, the AZO film having the same composition as the target was formed only to have a film thickness of 505 nm, and its surface resistance was 13.1 Ω/□.

Further, the average value of the transmittance at a wavelength of 400 to 800 nm was 85% or more, and the transmittance was also good.

The second transparent conductive film was produced under the same procedure and conditions as in Example 9 using the glass substrate on which the first transparent conductive film (AZO film) of the lower film was formed. The Ra value of the second transparent conductive film formed on the surface of the first transparent conductive film of the lower base film was 35.7 nm, and the surface unevenness equivalent to that of the transparent conductive film of Example 9 formed on the glass substrate was exhibited. In addition, the surface of the second transparent conductive film formed on the first transparent conductive film of the lower base film was measured to have a surface resistance value of 9.6 Ω/□ in the same manner as in Example 9. The evaluation results are shown in Table 3. That is, the conductivity is remarkably improved by laminating the first transparent conductive film (AZO film) of the underlayer film and the second transparent conductive film as compared with the transparent conductive film of Example 9 formed on the glass substrate. .

Therefore, it can be said that the surface unevenness is large, the light sealing effect is excellent, and the surface resistance value is low, so that it can be said to be useful for the surface electrode of a solar cell.

1. . . Light transmissive substrate

2. . . Transparent conductive film

3. . . Amorphous photoelectric conversion unit

4. . . Crystalline photoelectric conversion unit

5. . . Back electrode

11. . . Flaky member

12. . . Lower base film

Fig. 1 is a cross-sectional view showing a configuration example of a thin film solar cell according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view showing another configuration example (one) of a thin film solar cell according to an embodiment of the present invention.

Fig. 3 is a cross-sectional view showing another configuration example (part 2) of the thin film solar cell according to the embodiment of the present invention.

Fig. 4 is a cross-sectional view showing another configuration example (part 3) of the thin film solar cell according to the embodiment of the present invention.

1. . . Light transmissive substrate

2. . . Transparent conductive film

3. . . Amorphous photoelectric conversion unit

5. . . Back electrode

31. . . Amorphous p-type tantalum carbide layer

32. . . Undoped amorphous i-type germanium photoelectric conversion layer

33. . . N-type lanthanide interface layer

51. . . Transparent reflective layer

52. . . Back reflection layer

Claims (5)

A method for producing a transparent conductive film, which is a method for producing a transparent conductive film in which a transparent conductive film is formed on a light-transmitting substrate by using an oxide sintered body target containing zinc oxide as a main component, and is characterized in that it is used as a sputtering gas A mixed gas of argon and hydrogen is used, and the molar ratio of the mixed gas is H ₂ /(Ar+H ₂ )=0.01 to 0.35, the sputtering gas pressure is 3.0 to 4.0 Pa, and the substrate temperature is 300 to 600 ° C. When the material power density is 2.76 to 5.5 W/cm ² , the film formation rate is 90 nm/min or more, the film thickness is 400 nm to 2000 nm, and the surface roughness (Ra) is 35.0 nm or more by DC sputtering. The surface resistance is A transparent conductive film having surface unevenness of 25 Ω/□ or less. The method for producing a transparent conductive film according to the first aspect of the invention, wherein the oxide sintered body target contains one or more components selected from aluminum and gallium. The method for producing a transparent conductive film according to claim 1 or 2, wherein the light-transmitting substrate is a glass substrate. The method for producing a transparent conductive film according to any one of claims 1 to 3, wherein the light-transmitting substrate is a glass substrate on which a lower base film is formed, and the transparent conductive film is formed on the lower base film. A method for manufacturing a thin film solar cell, characterized in that a mixed gas of argon and hydrogen is used as a sputtering gas species, and a molar ratio of H ₂ /(Ar+H ₂ )=0.01 to 0.35 in the mixed gas, sputtering pressure It is 3.0 to 4.0 Pa, the substrate temperature is 300 to 600 ° C, and the target electric power density is 2.76 to 5.5 W/cm ² , and an oxide sintered body target containing zinc oxide as a main component is used. A transparent conductive film having surface unevenness at a deposition rate of 90 nm/min or more, a film thickness of 400 nm to 2000 nm, a surface roughness (Ra) of 35.0 nm or more, and a surface resistance of 25 Ω/□ or less by DC sputtering. On the transparent conductive film, a photoelectric conversion layer unit and a back electrode layer are sequentially formed.