JP2004308001A - Method for forming zinc oxide film and method for forming photovoltaic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously form a thin zinc oxide film by electrolytic deposition without allowing a film to adhere to the rear surface of a substrate. <P>SOLUTION: The zinc oxide film is formed on the substrate 100 by applying an electric current between the substrate 100 and an electrode 121, both the substrate 100 and the electrode 121 being immersed in an aqueous solution containing at least zinc ions and a carbohydrate. After the substrate 100 is taken out of the solution, at least the edge part of the substrate 100 surface not facing the electrode 121 is brought into contact with a water-absorptive member 115 having supplied a chemical liquid or is directly supplied with the chemical liquid and brought into contact with the water-absorptive member 115; thus, a byproduct formed on the substrate 100 surface not facing the electrode 121 is dissolved and removed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a zinc oxide film and a method for forming a photovoltaic element using the same. In particular, the present invention relates to a technique for forming a zinc oxide film in a favorable state only on one surface of a substrate.

  Conventionally, a photovoltaic element made of hydrogenated amorphous silicon, hydrogenated amorphous silicon germanium, hydrogenated amorphous silicon carbide, microcrystalline silicon, polycrystalline silicon, or the like is used to improve the collection efficiency at long wavelengths. In addition, a reflective layer on the back surface has been used. Such a reflective layer desirably exhibits effective reflection characteristics at a wavelength near the band edge of the semiconductor material, where its absorption is reduced, that is, from 800 nm to 1200 nm. Metals such as gold, silver, copper, and aluminum, and alloys thereof, etc., sufficiently satisfy this condition. Also, providing an optically transparent uneven layer in a predetermined wavelength range known as light confinement has been performed. Generally, an uneven transparent conductive layer is provided between the metal layer and the semiconductor active layer. Thus, attempts have been made to improve the short-circuit current density Jsc by effectively using the reflected light. Further, the transparent conductive layer prevents deterioration of characteristics due to a shunt path. Very commonly, these layers are deposited by methods such as vacuum evaporation or sputtering, and have shown improvements in short circuit current density.

  For example, Non-Patent Documents 1 and 2 discuss the reflectance and texture structure of a reflective layer composed of silver atoms. In these examples, the reflection layer is formed of two layers of silver formed by changing the substrate temperature, thereby forming an effective unevenness, thereby forming a short-circuit current due to the light confinement effect in combination with the zinc oxide layer. The company has achieved an increase.

  In Patent Document 1, an electrolytic solution for producing a zinc oxide film, which is an aqueous solution containing 0.001 mol / l to 0.5 mol / l of zinc ions and 0.001 mol / l to 0.5 mol / l of nitrate ions, is used. It is disclosed that the zinc oxide film formed in this manner had a uniform thickness and composition and was formed with excellent optical transparency.

  Further, in Patent Document 2, an electric current is applied between a conductive substrate immersed in one or more aqueous solutions containing at least zinc ions and a counter electrode immersed in at least one of the aqueous solutions to oxidize. In the method of forming a zinc thin film on the conductive substrate, the back film adhesion preventing electrode is immersed in an aqueous solution, and the potential relationship between the back film adhesion preventing electrode, the conductive substrate, and the counter electrode is determined by the following formula: counter electrode> conductive It is disclosed that a zinc oxide thin film can be formed while preventing the film from adhering to the back surface of the substrate by applying a current so that the substrate> the back film adhesion preventing electrode or the counter electrode <the conductive substrate <the back film adhesion preventing electrode. .

  Further, in Patent Document 3, an electric current is passed between a conductive substrate immersed in an aqueous solution containing at least zinc ions and nitrate ions, and further, saccharose or dextrin, and a counter electrode also immersed in the aqueous solution to oxidize. In a device and a method for forming a zinc thin film on the conductive substrate, the counter electrode is disposed in a projection plane from a direction perpendicular to a main surface of the conductive substrate, thereby preventing film adhesion to the back surface of the substrate. It is disclosed that a zinc oxide thin film can be formed.

Japanese Patent No. 3273294 JP-A-11-286799 JP-A-11-222697 "Light Confinement Effect in a-SiGe Solar Cell on 29p-MF-22 Stainless Steel Substrate" (Autumn 1990) Proceedings of 51st Annual Conference of the Japan Society of Applied Physics p747 "P-IA-15a-SiC / a-Si / a-SiGe Multi-Bandgap Stacked Solar Cells With Bandgap Profiling," Sannomiya et al. , Technical Digest of the International PVSEC-5, Kyoto, Japan, p381, 1990.

  As described above, the light confinement layer already disclosed has excellent light conversion characteristics. However, in Non-Patent Document 1, the zinc oxide layer is formed by resistance heating or vacuum evaporation using an electron beam, sputtering, It is formed only by a method such as an ion plating method or a CVD method, and the zinc oxide thin film formed by the above method has an insufficient light confinement effect at a wavelength of 600 nm to 1000 nm. High cost, high depreciation cost of vacuum equipment, and low efficiency of material utilization make the cost of photovoltaic devices using these technologies extremely high, and let solar cells be applied industrially. It is a big barrier in doing so.

  Patent Document 1 discloses a technique relating to the production of a zinc oxide film having a uniform film thickness and composition and excellent optical characteristics, but does not mention the production of a zinc oxide film having a texture structure. Further, there is no description about by-products adhering to the back surface of the substrate.

  Patent Literature 2 is an excellent method for suppressing the formation of by-products on the back surface of a substrate in an electrodeposition method in which the surface shape can be easily controlled by adjusting the manufacturing conditions. When using a metal which is easily ionized and dissolved in an electric field in an electrodeposition bath solution as a material, a problem may occur. For example, when a zinc oxide thin film is formed from an aqueous solution of zinc nitrate, and when silver is used for a reflective layer that is a component of the substrate, by adopting this configuration, the back film adhesion preventing electrode and the substrate may be used depending on manufacturing conditions. The silver in the reflective layer is eluted into the aqueous solution due to the electric field during this time, and the zinc oxide film formed using the same has a problem that desired characteristics cannot be obtained (in particular, the transmittance is reduced). Was.

  Patent Document 3 discloses an excellent method for suppressing the formation of by-products on the back surface of a substrate in an electrodeposition method in which the surface shape can be easily controlled by adjusting the manufacturing conditions. Depending on the manufacturing conditions of the thin film (especially when the current density during electrolytic deposition is increased), there may be a problem that an unintended by-product such as a zinc compound adheres to the vicinity of the edge on the back surface of the substrate. there were.

  Here, if the by-products adhere to the back surface of the substrate, the by-products are generated in the vacuum apparatus in a vacuum atmosphere process (a semiconductor layer forming process or a transparent conductive film forming process) after the substrate is formed. In some cases, degassing occurs, impurities are mixed into the atmosphere gas, and the characteristics are degraded.

  In the formation of a semiconductor layer, when an n-type semiconductor layer or a p-type semiconductor layer is formed, a dopant-containing gas is introduced to control the conductivity type, but a by-product adheres to the back surface of the substrate. Then, a phenomenon occurs in which a large amount of the dopant-containing gas is adsorbed on the by-product. As a result, when a semiconductor layer of another conductivity type is formed, a larger amount of adsorbed dopant gas is released into the atmosphere, which may cause a problem that a film having desired characteristics cannot be obtained.

  In addition, if by-products adhere to the back surface of the substrate, electrical or mechanical contact failure occurs in the device, or the attached by-products are detached. There is a case where a problem that a by-product is mixed occurs.

  When a long substrate is used as the substrate and the substrate is wound up in a roll shape with the by-product adhered to the back surface of the substrate, the state of the by-product and the winding surface Depending on the pressure or the storage time in a rolled state, the by-product adhered to the back surface may be transferred to the front surface.

  The present invention has been made in view of such circumstances, and it is possible to form a zinc oxide film at low cost without contaminating the bath and without attaching by-products to the back surface of the substrate, as compared with the conventional method. An object of the present invention is to provide a highly efficient element at a low cost by incorporating the element into a photovoltaic element.

  The present invention provides (1) energizing between a substrate immersed in an aqueous solution containing at least zinc ions and carbohydrates, and an electrode disposed opposite to the substrate immersed in the aqueous solution, A method of forming a zinc oxide film on a substrate, wherein after removing the substrate from the aqueous solution, at least an end of a surface of the substrate not facing the electrode has a water-absorbing member supplied with a chemical solution. By contacting with, the by-product formed on the surface of the substrate not facing the electrode by the electrolytic deposition method is dissolved and removed.

  Also, the present invention provides (2) energizing between a substrate immersed in an aqueous solution containing at least zinc ions and carbohydrates, and an electrode disposed opposite to the substrate immersed in the aqueous solution, A method of forming a zinc oxide film on the substrate, wherein after removing the substrate from the aqueous solution, a chemical solution is directly supplied to a surface of the substrate that is not opposed to the electrode, and the electrode of the substrate is By contacting at least the end of the non-facing surface with a member having water absorption, a by-product formed on the surface of the base not facing the electrode by the electrolytic deposition method is dissolved and removed. It is characterized by the following.

  Further, the present invention is characterized in that (3) a reflection layer containing silver is formed on the substrate, and a zinc oxide film is formed thereon.

  Further, the present invention is characterized in that (4) the chemical solution is an acid composed of ions contained in the aqueous solution.

  Further, the present invention is characterized in that (5) a step of spraying water on the base is performed after a step of contacting at least an end of a surface of the base not facing the electrode with a member having water absorbency. Further, (6) the step of spraying the water is performed on both surfaces of the base.

  The present invention also provides (7) a photovoltaic method comprising a step of laminating a semiconductor layer by a plasma CVD method on a zinc oxide film formed by using the method for forming a zinc oxide film of the present invention. This is a method for forming a power element.

According to the above-mentioned means (1) and (2), in the formation of a zinc oxide thin film by electrolytic deposition, there is no adhesion of by-products on the back surface of the substrate and no influence of a chemical solution on the film formation surface side. It becomes possible to form a thin film substrate. As a result, in a vacuum atmosphere process (such as a semiconductor layer formation process or a transparent conductive film formation process) after the substrate is formed, degassing due to by-products occurs in the vacuum apparatus, and impurities are mixed into the atmosphere gas. Deterioration of characteristics can be prevented.
According to the above-mentioned means (3), it is possible to form a zinc oxide thin film on only one side of the substrate in good condition without contaminating the bath.
According to the means (4) described above, it is not necessary to newly add a wastewater treatment facility for the chemical solution.
According to the means (5) and (6) described above, it is possible to eliminate the influence of the chemical solution on the film forming surface side and to form a zinc oxide thin film on only one surface of the substrate in a favorable state.
According to the means (7) described above, by applying the method for forming a zinc oxide thin film of the present invention to the method for manufacturing the back reflection layer of a photovoltaic element (solar cell), the short-circuit current density of the solar cell and the photoelectric conversion Increase efficiency and improve non-defective rate. Further, since the material cost and the running cost are very advantageous (about 1/100 of the cost) as compared with the sputtering method and the vapor deposition method, it can contribute to the full-fledged spread of solar power generation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments.

  FIG. 3 is a schematic sectional view showing an example of the photovoltaic device according to the present invention. In the figure, 301 is a substrate, 302-1A is an amorphous n-type semiconductor layer, 302-2A is an i-type semiconductor layer containing a crystalline phase, 302-3A is a p-type semiconductor layer containing a crystalline phase, 303 is a transparent conductive layer, 304 is a collecting electrode.

  FIG. 4 is a schematic cross-sectional view showing one configuration example of the substrate 301 in FIG. In the figure, 301-1 is a substrate, 301-2 is a reflective layer, and 301-3 is a zinc oxide layer. These are constituent members of the substrate 301, and the reflection layer is formed as necessary.

  Hereinafter, each member will be described.

(Substrate)
As the base 301-1, a plate-like member or a sheet-like member made of metal, resin, glass, ceramics, semiconductor bulk, or the like is preferably used. The surface may have fine irregularities. A structure may be employed in which light is incident from the substrate side using a transparent substrate. Further, by forming the base into a long shape, continuous film formation using a roll-to-roll method can be performed. In particular, a flexible material such as stainless steel or polyimide is suitable as a material for the base.

(Reflective layer)
The reflection layer 301-2 has a role as an electrode and a role as a reflection layer that reflects the reached light and reuses it in the semiconductor layer. As the material, Al, Cu, Ag, Au, CuMg, AlSi and alloys thereof can be suitably used. Further, it is also possible to suitably use the reflection layer having a laminated structure with a transition metal such as Ni, Cr, or Ti. By doing so, an effect of further improving the adhesion between the substrate and the reflective layer can be expected. As a method for forming the reflective layer, methods such as vapor deposition, sputtering, electrodeposition, and printing are suitable. It is preferable that the reflective layer has irregularities on its surface. Thereby, the optical path length of the reflected light in the semiconductor layer can be extended, and the short-circuit current can be increased.

(Zinc oxide layer)
The zinc oxide layer 301-3 has a role of increasing irregular reflection of incident light and reflected light and extending an optical path length in the semiconductor layer. In addition, the photovoltaic element has a role of preventing the element of the reflection layer from diffusing or migrating into the semiconductor layer and causing the photovoltaic element to shunt. Further, by having an appropriate resistance, it has a role of preventing a short circuit due to a defect such as a pinhole in the semiconductor layer. It is desirable that the zinc oxide layer has irregularities on its surface so that diffuse reflection is sufficiently large.

  As a condition for forming a zinc oxide film by the electrodeposition method, it is preferable to use an aqueous solution containing nitrate ions and zinc ions in a corrosion-resistant container. The concentrations of nitrate ions and zinc ions are desirably in the range of 0.002 mol / l to 2.0 mol / l, more desirably in the range of 0.01 mol / l to 1.0 mol / l. More preferably, it is in the range of 1 mol / l to 0.5 mol / l. The source of nitrate ion and zinc ion is not particularly limited, and zinc nitrate, which is a source of both ions, or a water-soluble nitrate such as ammonium nitrate, which is a source of nitrate ion, and zinc ion It may be a mixture of zinc salts such as zinc sulfate as a source. Further, it is also preferable to add a carbohydrate such as saccharose or dextrin to the aqueous solution in order to suppress abnormal growth or improve adhesion. However, excessive carbohydrates are not preferable because the action of specifying the C-axis orientation of zinc oxide is enhanced and the surface shape is flattened. From the above, the amount of carbohydrate in the aqueous solution depends on the type of carbohydrate, but is generally in the range of 1 g / l to 500 g / l, more preferably 3 g / l to 100 g / l in the case of saccharose. In the case of dextrin, the preferred range is 0.01 g / l to 10 g / l, more preferably 0.025 g / l to 1 g / l.

  When a zinc oxide film is deposited by an electrodeposition method, it is preferable that a substrate on which the zinc oxide film is deposited in the aqueous solution is used as a cathode and zinc, platinum, carbon, or the like is used as an anode. Here, when the zinc oxide film is formed using the electrodeposition method, the concentration of nitrate ions and zinc ions in the aqueous solution, the temperature of the aqueous solution, the pH of the aqueous solution, the method of stirring the aqueous solution, and the additives such as carbohydrates are controlled. By doing so, it is possible to control the film structure, shape and orientation of the formed zinc oxide, but the film structure of the zinc oxide film is based on the conditions of the above-described electrodeposition method, the material of the substrate, and the surface shape. And the presence or absence of a reflective layer, the material of the reflective layer, the surface shape of the reflective layer, and the like. Further, a zinc oxide film is formed by a first zinc oxide film 301-3A formed by a sputtering method and the first zinc oxide. In the case of a laminated structure of the second zinc oxide film 301-3B formed on the film by an electrodeposition method by an electrochemical reaction from an aqueous solution, depending on the surface shape, the film thickness, and the like of the first zinc oxide film. The zinc oxide film formed by the electrodeposition method It is affected.

The conditions for forming the zinc oxide film (first zinc oxide film 301-3A) by the sputtering method are greatly affected by the method, the type and the flow rate of the gas, the internal pressure, the input power, the film formation rate, the substrate temperature, and the like. For example, when a zinc oxide film is formed by a DC magnetron sputtering method using a zinc oxide target, the types of gas include Ar, Ne, Kr, Xe, Hg, O _{2, and the} like, and the flow rate is controlled by the apparatus. Although it differs depending on the size and the pumping speed, for example, when the volume of the film forming space is 20 liters, it is preferably 1 cm ³ / min (normal) to 100 cm ³ / min (normal). The internal pressure during film formation is preferably from 10 mPa to 10 Pa. The input power depends on the size of the target, but is preferably from 10 W to 10 kW. Although the suitable range of the substrate temperature varies depending on the film formation rate, it is preferably from 70 ° C. to 450 ° C.

(substrate)
In the present invention, a substrate obtained by forming a zinc oxide layer on the substrate is referred to as a substrate. By the above method, a substrate is formed by laminating a zinc oxide layer on a substrate. Further, a reflection layer may be provided on the substrate as needed.

(Semiconductor layer)
When a silicon-based thin film is used for the semiconductor layer, the main material is an amorphous phase or a crystalline phase, or a mixed phase of these. Instead of Si, an alloy of Si and C or Ge may be used. The semiconductor layer contains hydrogen and / or halogen atoms at the same time. The preferred content is 0.1 to 40 atomic%. Further, the semiconductor layer may contain oxygen, nitrogen, and the like. The semiconductor layer contains a Group III element to be a p-type semiconductor layer, and contains a Group V element to be an n-type semiconductor layer.

  Regarding the electrical characteristics of the p-type semiconductor layer and the n-type semiconductor layer, those having an activation energy of 0.2 eV or less are preferable, and those having an activation energy of 0.1 eV or less are optimal. The specific resistance is preferably 100 Ωcm or less, and most preferably 1 Ωcm or less. In the case of a stacked cell (a photovoltaic device having a plurality of pin junctions), it is preferable that the band gap of the i-type semiconductor layer of the pin junction near the light incident side is wide, and the band gap becomes narrower as the pin junction becomes farther. . Further, it is preferable that the band gap has a minimum value closer to the p layer than the center in the thickness direction in the i layer. As the doped layer (p-type layer or n-type layer) on the light incident side, a crystalline semiconductor with low light absorption or a semiconductor with a wide band gap is suitable.

  As an example of a stack cell in which two sets of pin junctions are stacked, a combination of an i-type silicon-based semiconductor layer includes (amorphous semiconductor layer, semiconductor layer containing crystal phase), (semiconductor layer containing crystal phase, crystal Phase-containing semiconductor layer) and (amorphous semiconductor layer, amorphous semiconductor layer). Further, as an example of a photovoltaic element in which three sets of pin junctions are stacked, as a combination of i-type silicon-based semiconductor layers, from the light incident side (amorphous semiconductor layer, amorphous semiconductor layer, semiconductor layer including crystal phase), ( A semiconductor layer containing an amorphous or crystalline phase; a semiconductor layer containing a crystalline phase; and a semiconductor layer containing a crystalline phase, a semiconductor layer containing a crystalline phase, and a semiconductor layer containing a crystalline phase.

The i-type semiconductor layer has an absorption coefficient (α) of light (630 nm) of 5000 cm ⁻¹ or more, and a photoconductivity (σp) of 10 × under simulated sunlight irradiation by a solar simulator (AM 1.5, 100 mW / cm ² ). 10 ^-5 S / cm or more and, dark conductivity (.sigma.d) is 10 × 10 ^-6 S / cm or less, Urbach energy by the constant photocurrent method (CPM) is is preferably not more than 55 meV. As the i-type semiconductor layer, even a slightly p-type or n-type semiconductor layer can be used.

(Method of forming semiconductor layer)
In order to form a silicon-based semiconductor and the above-described semiconductor layer, a high-frequency plasma CVD method is suitable. Hereinafter, a preferred example of a procedure for forming a semiconductor layer by a high-frequency plasma CVD method will be described.

The pressure in the deposition chamber (vacuum chamber) that can be reduced in pressure is reduced to a predetermined deposition pressure. A material gas such as a source gas and a dilution gas is introduced into the deposition chamber, and the deposition chamber is set to a predetermined deposition pressure while the deposition chamber is evacuated by a vacuum pump. The substrate 301 is set at a predetermined temperature by a heater. The high frequency oscillated by the high frequency power supply is introduced into the deposition chamber. The method of introducing high frequency into the deposition chamber is a method in which high frequency is guided by a waveguide and introduced into the deposition chamber through a dielectric window such as alumina ceramics, or high frequency is guided by a coaxial cable and deposited through a metal electrode. There is a method to introduce it indoors. Plasma is generated in the deposition chamber to decompose the source gas, and a deposited film is formed on the substrate 301 placed in the deposition chamber. This procedure is repeated a plurality of times as necessary to form a semiconductor layer. Suitable conditions for forming the semiconductor layer include a substrate temperature in a deposition chamber of 100 to 450 ° C., a pressure of 50 mPa to 1500 Pa, and a high frequency power of 0.001 to 1 W / cm ³ .

Examples of the source gas suitable for forming the silicon-based semiconductor of the present invention and the above-described semiconductor layer include a gasizable compound containing silicon atoms, such as SiH ₄ , Si ₂ H ₆ , and SiF ₄ . In the case of using an alloy, it is desirable to further add a gasizable compound containing Ge or C, such as GeH ₄ or CH ₄ , to the source gas. It is desirable that the source gas be diluted with a dilution gas and introduced into the deposition chamber. Examples of the diluent gas include H ₂ and He. Further, a gasifiable compound containing nitrogen, oxygen or the like may be added as a source gas or a diluent gas. B ₂ H ₆ , BF ₃ or the like is used as a dopant gas for converting the semiconductor layer into a p-type layer. PH ₃ , PF ₃ or the like is used as a dopant gas for converting the semiconductor layer into an n-type layer. When depositing a thin film of a crystalline phase or a layer having a small light absorption or a wide band gap such as SiC, it is preferable to increase the ratio of the diluent gas to the source gas and to introduce a relatively high power high frequency.

(Transparent conductive layer)
The transparent conductive layer 303 is an electrode on the light incident side, and can also serve as an antireflection film by appropriately setting the film thickness. The transparent conductive layer is required to have a high transmittance in a wavelength region in which the semiconductor layer can absorb light and to have a low resistivity. Preferably, the transmittance at 550 nm is at least 80%, more preferably at least 85%. As a material of the transparent conductive layer, ITO, ZnO, In ₂ O ₃ or the like can be preferably used. As the formation method, methods such as vapor deposition, CVD, spray, spin-on, and immersion are suitable. A substance that changes the conductivity may be added to these materials.

(Collecting electrode)
The current collecting electrode 304 is provided on the transparent conductive layer in order to improve current collecting efficiency. As the forming method, a method of forming metal of an electrode pattern by sputtering using a mask, a method of printing a conductive paste or a solder paste, a method of fixing a metal wire with a conductive paste, and the like are preferable.

  According to the method for forming a zinc oxide film of the present invention, when forming a substrate 301 as illustrated in FIG. 4, after forming a zinc oxide film as described above and carrying it out of the electrodeposition bath, By-products formed on the surface not facing the anode electrode such as zinc, platinum, and carbon) are dissolved and removed by using a water-absorbing member, a predetermined chemical solution, and the like. Hereinafter, the water-absorbing member, the chemical solution, and the like will be described.

(Water-absorbing member)
The water-absorbing member used in the present invention preferably has a configuration in which the chemical solution does not touch the film formation surface. Therefore, it is required that the member has water absorption and is excellent in chemical resistance. Specifically, resins such as PVA, PVC, and urethane are preferable. Examples of the shape of the member having water absorbency include a blade shape, a roller shape, and the like. In addition to preventing the chemical solution from touching the film formation surface, damage to the substrate that does not adversely affect the conveyance of the long substrate is given. The roller shape is preferred from the viewpoint that the amount is small. As a method of contacting the roller-shaped member having water absorbency, it is preferable to contact the long substrate with a pressure enough to follow the long substrate.

  In addition, it is preferable that the member having the water absorbing property is installed between the tank for forming the zinc oxide thin film and the washing tank.

(Chemical solution)
The chemical solution for dissolving by-products attached to the back surface of the substrate used in the present invention is preferably an acid containing ions contained in an aqueous solution (electrodeposition bath). The reason is that if the acid contains ions contained in the aqueous solution, it is not necessary to newly add a wastewater treatment facility.

  In addition, when a zinc oxide thin film is electrochemically deposited from an aqueous solution containing zinc ions and nitrate ions, it is preferable to use an aqueous nitric acid solution. In this case, the concentration of the nitric acid aqueous solution is preferably 0.01 wt% to 10 wt%, more preferably 0.05 wt% to 5 wt%. The temperature of the aqueous nitric acid solution is preferably in the range of 10 ° C to 40 ° C, more preferably 20 ° C to 30 ° C.

  As a method of supplying the chemical solution to the back surface of the base, spraying by a shower or application by a member having a water absorbing property is preferable.

(water)
After the chemical is supplied to the back surface of the base and brought into contact with a member having water absorbency as described above, the chemical is washed away with water. At this time, it is preferable to adopt a configuration in which the cleaned liquid is prevented from touching the front surface of the substrate. Specifically, a configuration in which water is sprayed on both surfaces of the substrate is preferable.

  By forming a zinc oxide film as described above, a zinc oxide thin film substrate can be formed without by-products adhering to the back surface of the substrate and without being affected by a chemical solution on the film formation surface side.

  The method for forming a photovoltaic element of the present invention includes a step of laminating and forming the above-described semiconductor layer by a plasma CVD method on a zinc oxide film of a substrate formed as described above. is there. By using the zinc oxide thin film substrate obtained by the present invention, in this semiconductor layer forming step, furthermore, in the transparent conductive film forming step, etc., outgassing due to by-products occurs in a vacuum apparatus, and the atmosphere gas contains It is possible to very effectively prevent impurities from being mixed and deteriorating the characteristics.

  Note that protective layers may be formed on both surfaces of the photovoltaic element as needed. At the same time, a reinforcing material such as a steel plate may be used in combination on the back surface (light incident side and reflection side) of the photovoltaic element.

  In the following examples, the present invention will be specifically described by taking a solar cell as an example of a photovoltaic element, but the present invention is not limited thereto.

(Example 1)
This embodiment is an example in which a substrate (a zinc oxide thin film substrate) is formed using the roll-to-roll experimental apparatus shown in FIG. In FIG. 1, 100 is a long substrate, 101 is a deposited film forming apparatus, 102 is a feeding roller, 103 is a take-up roller, 111 is an electrodeposition tank, 113 is a washing vessel, 114 is a pure water shower, and 115 is water absorbing property. Reference numeral 116 denotes a drying container, 117 denotes an infrared heater, 121 denotes a counter electrode (anode), and 131 denotes a power supply.

  A reflection layer is deposited in advance on a roll-shaped SUS430 2D (400 mm in width, 200 m in length, 0.125 mm in thickness) by a DC magnetron sputtering apparatus for rolls, and 400 nm of silver (4000 °) is deposited thereon. A zinc oxide layer was formed by electrodeposition as follows on a long substrate 100 on which a 200 nm (2000 °) zinc oxide thin film was deposited by a magnetron sputtering apparatus.

The long substrate 100 is transported to the electrodeposition tank 111 via the transport rollers. The electrodeposition bath contains 0.2 mol / l of zinc nitrate and 0.1 g / l of dextrin, and a liquid circulation process is performed to stir the bath. The liquid temperature is maintained at a temperature of 80 ° C., and the pH is maintained at 4.0 to 6.0. As the counter electrode 121, a zinc plate (4-N, width 380 mm, length 150 mm) is used. As for the current, 10 mA / cm ² (1.0 A / dm ² ) is applied between the counter electrode 121 on the anode side and the long substrate 100 while the long substrate 100 on the cathode side is grounded to perform electrolytic deposition. Was.

  In the present embodiment, after the long substrate is carried out of the electrodeposition tank 111, a sponge roller (45 mm in diameter) made of PVA is used as the water-absorbing member 115 on the surface (back surface) not facing the anode of the long substrate. , Width 450 mm) so as to follow the movement of the substrate, and 1% nitric acid was supplied to the sponge roller at a flow rate of 50 ml / min using a metering pump (not shown) to remove by-products adhering to the back surface. Dissolved.

  Immediately after the long substrate passed the sponge roller, both surfaces of the substrate were simultaneously rinsed with pure water using a shower 114. The amount of water in the shower is preferably at least 2 l / min. Further, after being washed in the washing tank 113, it is carried out to the drying furnace 116. The drying furnace 116 has a hot air nozzle (not shown) and an infrared heater 117, and the hot air simultaneously performs water repellency. The hot air from the hot air nozzle was controlled at 80 ° C, and the infrared heater 117 was controlled at 150 ° C.

  The thickness of the zinc oxide thin film obtained as described above is examined from the waveform of the optical characteristics (V-570 manufactured by JASCO Corporation) using the optical interference method, and the back surface of the long substrate (reflection layer, oxidation The state of by-product adhesion on the side where the zinc layer was not laminated) was visually checked. Table 1 shows the results.

(Example 2)
This embodiment is an example in which a substrate (a zinc oxide thin film substrate) is formed using the roll-to-roll experimental apparatus shown in FIG.

  A reflection layer is previously deposited on a roll-shaped SUS430 2D (400 mm in width, 200 m in length, 0.125 mm in thickness) by a DC magnetron sputtering apparatus for rolls in a thickness of 300 nm (3000 mm). A zinc oxide layer was formed by electrodeposition as follows on a long substrate 100 on which a 200 nm (2000 °) zinc oxide thin film was deposited by a magnetron sputtering apparatus.

The long substrate 100 is transported to the electrodeposition tank 111 via the transport rollers. The electrodeposition bath contains 0.2 mol / l of zinc nitrate and 0.15 g / l of dextrin, and liquid circulation treatment is performed to stir the bath. The liquid temperature is maintained at a temperature of 80 ° C., and the pH is maintained at 4.0 to 6.0. As the counter electrode 121, a zinc plate (4-N, width 380 mm, length 150 mm) is used. As for the current, 10 mA / cm ² (1.0 A / dm ² ) is applied between the counter electrode 121 on the anode side and the long substrate 100 while the long substrate 100 on the cathode side is grounded to perform electrolytic deposition. Was.

  In the present embodiment, after the long substrate is carried out of the electrodeposition tank 111, a sponge roller (45 mm in diameter) made of PVA is used as the water-absorbing member 115 on the surface (back surface) not facing the anode of the long substrate. , 450 mm in width) so as to follow the movement of the substrate, and before the long substrate passes through the sponge roller, 1% nitric acid is applied to the back surface of the substrate at a flow rate of 40 ml / min using a metering pump (not shown). It was supplied directly to dissolve by-products attached to the back surface. The nitric acid after dissolving the by-product is absorbed by the sponge roller, thereby preventing nitric acid from flowing around the substrate surface.

  Immediately after the long substrate passed the sponge roller, both surfaces of the substrate were simultaneously rinsed with pure water using a shower 114. The amount of water in the shower is preferably at least 2 l / min. Further, after being washed in the washing tank 113, it is carried out to the drying furnace 116. The drying furnace 116 has a hot air nozzle (not shown) and an infrared heater 117, and the hot air simultaneously performs water repellency. The hot air from the hot air nozzle was controlled at 80 ° C, and the infrared heater 117 was controlled at 150 ° C.

  The thickness of the zinc oxide thin film obtained as described above is examined from the waveform of the optical characteristics (V-570 manufactured by JASCO Corporation) using the optical interference method, and the back surface of the long substrate (reflection layer, oxidation The state of by-product adhesion on the side where the zinc layer was not laminated) was visually checked. Table 1 shows the results.

(Comparative Example 1)
After the long substrate was carried out of the electrodeposition tank, electrolytic deposition was performed in the same manner as in Example 1 except that a PVA-made sponge roller and nitric acid were not used to form a substrate (a zinc oxide thin film substrate).

  The thickness of the obtained zinc oxide thin film is examined from the waveform of the optical characteristics (V-570 manufactured by JASCO Corporation) using an optical interference method, and the back surface of the long substrate (reflection layer, zinc oxide layer is laminated). The side with no by-product) was visually observed. Table 1 shows the results.

(Comparative Example 2)
After the long substrate was carried out of the electrodeposition bath, electrolytic deposition was performed in the same manner as in Example 2 except that a sponge roller made of PVA was not used, to form a substrate (a zinc oxide thin film substrate).

  The thickness of the obtained zinc oxide thin film is examined from the waveform of the optical characteristics (V-570 manufactured by JASCO Corporation) using an optical interference method, and the back surface of the long substrate (reflection layer, zinc oxide layer is laminated). The side with no by-product) was visually observed. Table 1 shows the results.

  Comparing the results of Example 1 and Example 2, Comparative Example 1, and Comparative Example 2 in Table 1, the following can be said.

  That is, after depositing the zinc oxide thin film, the back surface of the long substrate (the surface on which the reflection layer and the zinc oxide layer are not laminated) is brought into contact with a water-absorbing member supplied with a chemical, or the back surface of the long substrate. By supplying a chemical solution directly to the surface (the surface on which the reflective layer and the zinc oxide layer are not laminated) and contacting with a water-absorbing member, by-products on the back surface of the substrate can be dissolved and removed, and the film is formed. The surface (the surface on which the reflective layer and the zinc oxide layer are laminated) is free from the influence of the chemical solution, has a small thickness distribution, and can effectively dissolve and remove by-products.

(Example 3)
In this example, after a substrate (a zinc oxide thin film substrate) was formed using the roll-to-roll experimental apparatus shown in FIG. 1, a photovoltaic element as shown in FIG. 3 was formed using this substrate. It is an example.

  A reflection layer is previously deposited on a roll-shaped SUS430 2D (width 400 mm, length 1000 m, thickness 0.125 mm) with a roll-compatible DC magnetron sputtering apparatus to a thickness of 300 nm (3000 Å), and a similar roll-compatible DC is further deposited thereon. A zinc oxide layer was formed by electrodeposition as follows on a long substrate 100 on which a 200 nm (2000 °) zinc oxide thin film was deposited by a magnetron sputtering apparatus.

The long substrate 100 is transported to the electrodeposition tank 111 via the transport rollers. The electrodeposition bath contains 0.2 mol / l of zinc nitrate and 0.15 g / l of dextrin, and liquid circulation treatment is performed to stir the bath. The liquid temperature is maintained at a temperature of 80 ° C., and the pH is maintained at 4.0 to 6.0. As the counter electrode 121, a zinc plate (4-N, width 380 mm, length 150 mm) is used. As for the current, 10 mA / cm ² (1.0 A / dm ² ) is applied between the counter electrode 121 on the anode side and the long substrate 100 while the long substrate 100 on the cathode side is grounded to perform electrolytic deposition. Was.

  In the present embodiment, after the long substrate is carried out of the electrodeposition tank 111, a sponge roller (45 mm in diameter) made of PVA is used as the water-absorbing member 115 on the surface (back surface) not facing the anode of the long substrate. , Width 450 mm) so as to follow the movement of the substrate, and 1% nitric acid was supplied to the sponge roller at a flow rate of 50 ml / min using a metering pump (not shown) to remove by-products adhering to the back surface. Dissolved.

  Immediately after the long substrate passed the sponge roller, both surfaces of the substrate were simultaneously rinsed with pure water using a shower 114. The amount of water in the shower is preferably at least 2 l / min. Further, after being washed in the washing tank 113, it is carried out to the drying furnace 116. The drying furnace 116 has a hot air nozzle (not shown) and an infrared heater 117, and the hot air simultaneously performs water repellency. The hot air from the hot air nozzle was controlled at 80 ° C, and the infrared heater 117 was controlled at 150 ° C.

  The substrate taken up by the take-up roller 103 is placed in a drying vessel (not shown) connected to a vacuum pump, and dried in a nitrogen atmosphere of 10 kPa at an atmosphere temperature of 250 ° C. for 5 hours. Was completed.

  Next, a photovoltaic element as shown in FIG. 3 was formed using the deposition film forming apparatus shown in FIG.

  The deposition film forming apparatus 201 shown in FIG. 2 is configured by connecting a substrate sending container 202, semiconductor forming vacuum containers 211 to 216, and a substrate winding container 203 via gas gates 221 to 227. A strip-shaped substrate 204 (the previously formed zinc oxide thin film substrate) is set in this deposited film forming apparatus through each container and each gas gate. The band-shaped substrate 204 is unwound from a bobbin provided in the substrate unloading container 202 and wound up by a substrate winding container 203 on another bobbin.

  Each of the semiconductor forming vacuum vessels 211 to 216 has a deposition chamber, and generates a glow discharge by applying high-frequency power from a high-frequency power supply 251 to 256 to discharge electrodes 241 to 246 in the deposition chamber. The source gas is decomposed to deposit a semiconductor layer on the substrate. Further, gas introduction pipes 231 to 236 for introducing a source gas and a dilution gas are connected to each of the semiconductor forming vacuum vessels 211 to 216.

  In each of the vacuum chambers 211 to 216 for semiconductor formation of the deposition film forming apparatus 201 shown in FIG. 2, a film formation region adjustment (not shown) for adjusting the contact area between the substrate 204 and the discharge space in each deposition chamber. A plate is provided, and by adjusting this, the thickness of each semiconductor film formed in each container can be adjusted.

  To form a photovoltaic element, first, a bobbin around which a substrate is wound is mounted on a substrate delivery container 202, and the substrate is wound through a gas gate on the loading side, vacuum containers 211 to 216 for semiconductor formation, and a gas gate on the unloading side. The tension was adjusted to pass through the take-up container 203 so that the belt-shaped substrate 204 was not loosened. Then, the substrate unloading container 202, the semiconductor forming vacuum containers 211 to 216, and the substrate take-up container 203 were sufficiently evacuated by an evacuation system including a vacuum pump (not shown).

  Next, the source gas and the diluent gas were supplied from the gas introduction pipes 231 to 236 to the semiconductor formation vacuum vessels 211 to 216 while operating the vacuum evacuation system.

Further, H ₂ gas of 500 cm ³ / min (normal) was supplied to each gas gate from each gate gas supply pipe (not shown) as a gate gas. In this state, the evacuation capacity of the evacuation system was adjusted to adjust the pressure in the semiconductor forming vacuum vessels 211 to 216 to a desired pressure. The forming conditions are as shown in Table 2.

  When the pressure in the semiconductor formation vacuum containers 211 to 216 was stabilized, the movement of the substrate was started from the substrate delivery container 202 to the substrate take-up container 203.

  Next, a high frequency is introduced from a high frequency power supply 251 to 256 to the discharge electrodes 241 to 246 in the vacuum chambers 211 to 216 for semiconductor formation, and a glow discharge is generated in a deposition chamber in the vacuum chambers 211 to 216 for semiconductor formation. An amorphous n-type semiconductor layer (thickness: 50 nm), an i-type semiconductor layer including a crystal phase (thickness: 3.5 μm), and a p-type semiconductor layer including a crystal phase (thickness: 10 nm) are formed thereon to form a photovoltaic device. The element was formed, and the formed strip-shaped photovoltaic element was processed into a solar cell module of 36 cm × 22 cm using a continuous modularization device (not shown).

(Comparative Example 3)
When producing a zinc oxide thin film, the solar cell module was manufactured in the same procedure as in Example 3 except that the surface (rear surface) of the long substrate not facing the counter electrode was not brought into contact with the water-absorbing member supplied with the chemical solution. Was prepared.

The photoelectric conversion efficiencies of the solar cell modules manufactured in Example 3 and Comparative Example 3 were measured using a solar simulator (AM 1.5, 100 mW / cm ² ). As a result, the photoelectric conversion efficiency of the solar cell module of Example 3 was 1.15 times the photoelectric conversion efficiency of the solar cell module of Comparative Example 3. In particular, the solar cell module of Example 3 was superior in the short-circuit current density to the solar cell module of Comparative Example 3.

  The solar cell modules manufactured in Example 3 and Comparative Example 3 were subjected to SIMS analysis to measure the concentrations of P (phosphorus) and O (oxygen) in the i-type semiconductor layer. The concentration of P (phosphorus) and O (oxygen) in the semiconductor layer was higher than that of the sample of Example 3. This is probably because in Example 3, the by-products on the back surface of the substrate were dissolved and removed, so that the adsorption of the dopant-containing gas and the degassing from the by-products themselves could be prevented.

  In addition, in the solar cell module manufactured in Comparative Example 3, a portion where the by-product adhered to the back surface was transferred to the front surface was seen. In the solar cell module manufactured in Example 3, such a portion was not seen. I couldn't.

  Further, in Example 3, the number of times of discharge interruption occurred during the formation of the semiconductor layer was one third or less of that in Comparative Example 3.

  Furthermore, in Comparative Example 3, residual by-products were confirmed in the semiconductor formation vacuum vessel after the formation of the semiconductor layer.

  From the above, by employing the formation method of the present invention, it is possible to form a zinc oxide thin film substrate without by-products adhering to the back surface of the base and without being affected by the chemical solution on the film formation surface side. In the subsequent vacuum atmosphere process, the generation of degassing due to by-products is suppressed, impurities are prevented from being mixed into the atmosphere gas, and a photovoltaic device having excellent characteristics can be obtained. Has been demonstrated.

  Although the silicon-based photovoltaic element has been described in the above embodiment, the present invention is not limited to this, and can be applied to other photovoltaic elements, for example, dye-sensitized solar cells. In that case, a conventional method can be used for a method of manufacturing a portion not related to the zinc oxide film.

FIG. 2 is a schematic cross-sectional view showing a roll-to-roll experimental apparatus used for forming a zinc oxide film in Examples. FIG. 2 is a schematic cross-sectional view showing a deposited film forming apparatus used for manufacturing a photovoltaic element in an example. It is a typical sectional view showing an example of a photovoltaic element by the present invention. FIG. 1 is a schematic sectional view showing an example of a zinc oxide thin film substrate according to the present invention.

Explanation of reference numerals

REFERENCE SIGNS LIST 100 Long substrate 101 Deposited film forming device 102 Sending roller 103 Winding roller 111 Electrodeposition tank 113 Rinsing container 114 Pure water shower 115 Water-absorbing member 116 Drying container 117 Infrared heater 121 Counter electrode 131 Power supply 201 Deposited film forming device 202 Substrate unloading container 203 Substrate winding container 204 Substrate 211-216 Vacuum container for semiconductor formation 221-227 Gas gate 231-236 Gas introduction tube 241-246 Discharge electrode 251-256 High frequency power supply 301 Substrate 301-1 Substrate 301-2 Reflective layer 301 -3 Zinc oxide layer 301-3A First zinc oxide layer 301-3B Second zinc oxide layer 302-1A Amorphous n-type semiconductor layer 302-2A i-type semiconductor layer including crystal phase 302-3A Crystal phase Including p-type semiconductor layer 3 3 transparent conductive layer 304 collector electrode

Claims (7)

  An electric current is applied between a substrate immersed in an aqueous solution containing at least zinc ions and carbohydrates, and an electrode arranged opposite to the substrate immersed in the aqueous solution to form a zinc oxide film on the substrate. In the method of forming, after carrying out the substrate from the aqueous solution, by contacting at least the end of the surface of the substrate not facing the electrode with a member having a water-absorbing property supplied with a chemical solution, A method for forming a zinc oxide film, comprising dissolving and removing a by-product formed on a surface of the substrate not facing the electrode by an electrolytic deposition method.   An electric current is applied between a substrate immersed in an aqueous solution containing at least zinc ions and carbohydrates, and an electrode arranged opposite to the substrate immersed in the aqueous solution to form a zinc oxide film on the substrate. A method of forming, wherein after carrying out the substrate from the aqueous solution, a chemical solution is directly supplied to a surface of the substrate not facing the electrode, and at least an end of the surface of the substrate not facing the electrode. Contacting the part with a member having water absorption to dissolve and remove by-products formed on the surface of the substrate not facing the electrode by the electrolytic deposition method. Formation method.   The method for forming a zinc oxide film according to claim 1, wherein a reflection layer containing silver is formed on the substrate, and a zinc oxide film is formed thereon.   The method for forming a zinc oxide film according to any one of claims 1 to 3, wherein the chemical liquid is an acid containing ions contained in the aqueous solution.   5. The method according to claim 1, wherein a step of spraying water on the base is performed after the step of bringing at least an end of a surface of the base not facing the electrode into contact with a member having water absorbency. The method for forming a zinc oxide film according to claim 1.   The method for forming a zinc oxide film according to claim 5, wherein the step of spraying the water is performed on both surfaces of the substrate.   7. A method for forming a photovoltaic element, comprising: forming a semiconductor layer on a zinc oxide film formed by the method according to claim 1 by a plasma CVD method. Method.

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