JP2009114481A - Method for forming electrodeposition film, thin film solar cell, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely form an electrodeposition film having a desired film thickness over the surface of a substrate having a large surface area by a method for forming the electrodeposition film using light irradiation. <P>SOLUTION: In the method for forming the electrodeposition film on a substrate 101, comprising arranging an electrode 102 on any surface of a light source unit 103, then arranging the substrate 101 on which a semiconductor layer is formed in such a manner that the semiconductor layer opposes to the electrode 102 in an electrolytic solution 106 containing a metal ion, and irradiating the substrate 101 with light emitted from the light source unit 103 and having wavelength to form a photo-excited carrier, the electrode 102 has slits partially transmitting the light emitted from the light source unit 103. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for forming an electrodeposited film, a thin film solar cell, and a method for manufacturing the same, and more particularly to a method for forming an electrodeposited film using a compound semiconductor thin film, a thin film solar cell, and a method for manufacturing the same.

  As a method for forming an electrodeposited film on a semiconductor thin film using an electrodeposition method, a method of supplying current from an external power source while irradiating light on the semiconductor surface is disclosed (for example, see Patent Document 1). As a result, an electrodeposited thin film can be formed without flowing a large current, so that damage to the semiconductor layer can be suppressed.

  On the other hand, development of a compound semiconductor thin film solar cell having a chalcopyrite structure has been actively promoted as a candidate for a thin film solar cell.

These solar cells have a pn heterojunction, and for example, Cu (In, Ga) S ₂ and Cu (In, Ga) Se ₂ are used for the p-type semiconductor layer which is a light absorption layer.

  The n-type semiconductor layer generally uses a cadmium sulfide or ZnO (zinc oxide) thin film, and is formed by a CBD (Chemical Bath Deposition) method or a sputtering method.

  As the transparent conductive film, ZnO or ITO (Indium Tin Oxide) is preferably used, and is usually formed by sputtering or MOCVD in manufacturing (see, for example, Patent Document 2). The MOCVD method is an abbreviation for Molecular Organic Chemical Deposition method.

Further, as another method for forming a ZnO film as a transparent conductive film, a method of forming by a electrochemical method using a solution containing nitrate ions and zinc ions is disclosed (for example, see Patent Document 3).
JP-A-60-189931 JP 2006-332440 A JP-A-11-150282

  By the way, Patent Document 1 does not have a detailed description regarding the light irradiation method. With this technique, it is not always easy to form a desired film thickness over the entire surface of a large-area substrate even though an electrodeposited film having good characteristics can be partially formed.

  On the other hand, the MOCVD method (metal organic vapor phase epitaxy) used as a method for forming a transparent conductive film for solar cell thin films in recent years uses a vacuum facility and requires an exhaust gas treatment facility, resulting in higher costs. Was inevitable.

  Since it was difficult to control the film thickness accurately for each location in the conventional transparent conductive film manufacturing method, the film thickness was designed according to the current value in the vicinity of the collector electrode so as not to cause a decrease in output due to resistance loss. It had been. That is, a transparent conductive film that is thicker than necessary is formed in a place where the distance from the current collecting electrode is far and the current during solar cell operation is small.

  Since the transparent conductive film has a finite absorptance with respect to each wavelength, the light transmittance decreases as the thickness increases, causing a decrease in photocurrent.

  As a countermeasure, it is effective to accurately change the thickness of the transparent electrode film depending on the distance from the collecting electrode. However, the conventional method cannot accurately control the local film thickness.

  Therefore, an object of the present invention is to form an electrodeposited film with a desired film thickness accurately over a large-area substrate using a method for forming an electrodeposited film by light irradiation.

  In particular, in a method for producing a transparent conductive film of a thin film solar cell, by using an electrodeposition method by light irradiation, a method for producing a thin film solar cell at a low cost on a large-area substrate by improving film thickness controllability is provided. The purpose is to do.

  Furthermore, it aims at providing a more efficient thin film solar cell by using the film thickness controllability of a high electrodeposition film.

  As a means for solving the above-mentioned problems, the present invention provides an electrolytic solution in which an electrode is provided on any surface of a light source unit, and the electrode and the substrate on which the semiconductor layer is formed contain metal ions. The semiconductor layer is placed so as to face the electrode, and light having a wavelength that generates photoexcited carriers is applied from the light source unit onto the substrate while applying a voltage to the substrate and the electrode. In the electrodeposition film forming method of forming an electrodeposition film on the substrate, the electrode has a slit that partially transmits light from the light source unit.

  According to the present invention, the counter electrode is formed of a slit, and the light irradiation region and the light irradiation intensity to the substrate side can be accurately controlled by irradiating the light from the back surface of the slit. Therefore, it is possible to improve the controllability of the film thickness of the electrodeposition film in a large-area substrate on which a semiconductor layer is formed.

  In addition, according to the present invention, it is possible to use a low-cost formation method called an electrodeposition method for forming a transparent conductive film on a large-area substrate, so that the cost is lower than that of a conventional sputtering method or MOCVD method. The thin film solar cell can be manufactured.

  Furthermore, according to this invention, it forms so that the film thickness of a transparent conductive film may reduce continuously or in steps as the distance from a transparent conductive film to a current collection electrode becomes large. Therefore, part of the light incident on the solar cell that has been absorbed by the transparent conductive film can be transmitted so that a highly efficient thin film solar cell can be formed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a schematic perspective view showing an apparatus used in a method for forming an electrodeposited film as a first embodiment of the present invention.

  In FIG. 1, 101 is a substrate, 102 is a counter electrode, 103 is a light source unit, 104 is a DC power source, 105 is an electric field tank, 106 is an electrolytic solution, and 107 is a power supply electrode.

  Reference numerals 108 and 109 denote directions on the substrate, where 108 is defined as a direction parallel to the power supply electrode and in the X direction, and 109 is defined as a direction perpendicular to the power supply electrode 107 and the Y direction.

  A substrate 101 in which a pn junction is formed by a p-type semiconductor layer and an n-type semiconductor layer is placed in an electric field tank 105 filled with an electrolytic solution 106 and is opposed to the counter electrode 102. Here, the semiconductor layer formed on the substrate 101 may be any layer that can generate photoexcited carriers by photoelectric conversion. The present invention is not limited to the one in which a pn junction is formed by a p-type semiconductor and an n-type semiconductor, and may be either a p-type semiconductor or an n-type semiconductor.

  The electrolytic solution 106 is an electrolytic solution containing metal ions. For example, when the metal ions are zinc ions, a zinc nitrate aqueous solution or a zinc acetate aqueous solution of 0.1 mol / l to 0.001 mol / l is preferably used.

  The cathode of the DC power source 104 is connected to a metal electrode (not shown) that is an electrode on the back surface side of the substrate 101 via a feeding electrode 107, and the anode is connected to the counter electrode 102.

  The counter electrode 102 has a desired shape such as a striped slit shape or a mesh shape, and has a structure capable of transmitting the light emitted from the light source unit 103 installed behind and irradiating the substrate 101. .

  The light emitted from the light source unit 103 may include any wavelength as long as it includes at least a wavelength greater than or equal to the band gap of the semiconductor layer contributing to photoelectric conversion and generates photoexcited carriers.

  Further, the light intensity emitted from the light source unit 103 is controlled to have a light irradiation intensity distribution in the substrate surface, and each position in the X direction 108 and the Y direction 109 in the substrate is provided. Can be adjusted freely.

  For adjusting the light irradiation intensity within the surface of the substrate 101, a method of adjusting the luminance of the light source unit 103 itself, a method of adjusting the interval and density of the slits, and a light shielding filter having an in-plane distribution are provided on the back surface of the counter electrode 102. There are methods to install.

  The light source unit 103 emits light with a preset light intensity distribution, and a desired DC voltage is applied from the DC power source 104. By doing so, an electrodeposited film having a desired film thickness distribution is formed on the semiconductor layer based on the light irradiation intensity distribution in the substrate surface and the magnitude of the DC voltage applied from the outside. The formed electrodeposition film is formed only in the region irradiated with light.

  In the structure formed in this embodiment mode, the slit width of the counter electrode 102 is 8 mm, and the width of the counter electrode 102 is 7 mm.

  Therefore, the pitch of the electrodes is 15 mm. Since the counter electrode 102 has a thickness of 10 mm, the light from the light source does not reach the substrate 101 if the slit is too narrow. The slit is preferably 5 mm or more.

  The distance between the counter electrode 102 and the feeding electrode 107 was changed from 10 mm to 20 mm. If the distance between the two electrodes becomes too short, the electric field distribution becomes non-uniform.

  Moreover, when it becomes too long, an apparatus will become large and electrolyte solution will be needed in large quantities.

  Therefore, 5 mm to 50 mm is desirable in practice.

  In the electrodeposition method described in Patent Document 1, it is difficult to control the in-plane distribution, but as in this embodiment, the control is performed by irradiating light from the back surface of the counter electrode having a slit. An electrodeposited film having a desired film thickness can be formed well at a desired position. In particular, when a large-area substrate was used, it was difficult to control the in-plane distribution, but this was solved.

  That is, until now, it has been difficult to obtain a desired film thickness over the entire surface of a large-area substrate, but by changing the position and width of the slit or the distance between the substrate 101 and the counter electrode 102, a desired film can be obtained. Thickness can be obtained.

  In addition, since the slit also serves as the counter electrode 102, it is easy to form a uniform electric field distribution with respect to the substrate 101, so that the uniformity of the electrodeposited film due to the electrochemical reaction is improved.

  Furthermore, it is preferable to use the same type of metal material as that formed on the substrate using the electrode 102 as the electrodeposition film.

  As a result, metal ions that decrease with the formation of the electrodeposited film can be directly supplied from the counter electrode. Since the slit-like counter electrode is located opposite to a region substantially equivalent to the region of the substrate on which the electrodeposited film is formed, it is possible to maintain the electrolyte with a small distribution of metal ion concentration and improve uniformity. it can.

  FIG. 2 is a schematic cross-sectional view showing an example in which a light shielding filter is inserted between the counter electrode and the light source unit in FIG.

  By doing so, an electrodeposited film can be formed with a light irradiation intensity distribution in a direction perpendicular to the power supply electrode of the substrate.

  This embodiment is a method for forming an electrodeposited film in the case where an electric field applied to a large-area substrate varies depending on the position in the substrate due to a voltage drop due to the distance from the power supply electrode to the substrate.

  In FIG. 2, 201 is a substrate, 202 is a counter electrode, 203 is a light source unit, 204 is a filter, 205 is a power supply electrode, and 206 is a direction perpendicular to the power supply electrode (Y direction).

  The filter 204 inserted between the counter electrode 202 and the light source unit 203 forms a desired light irradiation intensity distribution in the Y direction 206 of the substrate 201.

  Conventionally, in a large area substrate, even if the irradiation intensity of light is the same, the magnitude of the voltage drop differs depending on the distance from the feeding electrode to the position in each substrate. The film thickness was different.

  That is, if the magnitude of the external electric field applied to the semiconductor layer is different, the ratio of the excited carriers taken out changes, and the distribution of the film thickness formed by changing the amount of flowing current occurs.

  Therefore, a film thickness distribution is formed in the Y direction 206 of the substrate perpendicular to the feeding electrode 205. In the present embodiment, a method for uniformly forming an electrodeposited film formed by intentionally providing a desired light illuminance distribution in the Y direction 206 is provided.

  When the counter electrode 202 is a striped slit, a light shielding filter 204 is mounted between the counter electrode 202 and the light source unit 203 so that the amount of transmitted light increases in proportion to the distance from the power supply electrode 205. Thickness can be formed.

(Second Embodiment)
FIG. 3 is a schematic cross-sectional view showing a light source unit and a counter electrode used in the method for forming an electrodeposited film as the second embodiment of the present invention.

  In the present embodiment, a method of forming an electrodeposition film having a film thickness distribution with higher controllability by inserting a lens into the slit of the counter electrode will be described.

  In FIG. 3, reference numeral 501 denotes a substrate, 502 denotes a counter electrode, 503 denotes a light source unit, 504 denotes a concave lens, and 505 denotes a convex lens.

  By attaching a concave lens or a convex lens to the slit of the counter electrode 502, the controllability of the light irradiation range and irradiation intensity can be improved.

  For example, as shown in FIG. 3A, when it is necessary to make the distance between the counter electrode 502 and the substrate 501 close to some extent, it may not be possible to obtain a uniform light irradiation intensity over the entire surface of the substrate only by the interval between the slits.

  At that time, the concave lens 504 can be attached to supply light to a place where it is difficult for light to reach.

  If a fine film thickness distribution is desired to be formed in the substrate, a convex lens 505 is attached to the slit as shown in FIG. A desired film thickness distribution can be formed by limiting the region to be formed.

  This can be further improved in controllability by combining with the formation method by substrate conveyance described in the third embodiment below.

(Third embodiment)
FIG. 4 is a schematic cross-sectional view showing an example of an apparatus for forming an electrodeposited film on a long belt-like substrate using the method for forming an electrodeposited film as the third embodiment of the present invention.

  In the present embodiment, a method of forming an electrodeposition film having a periodic film thickness distribution on a substrate being transported will be described.

  In FIG. 4, 301 is a long belt-like substrate, 302 is a counter electrode, 303 is a light source unit, 304 is a DC power supply, 304 is a slit, 306 is an electrolyte, 307 is a delivery roller, and 308 is a take-up roller.

  The belt-like substrate 301 is fed out from the feed roller 307 and taken up by the take-up roller 308.

  Striped slits 305 are formed in the counter electrode 302 so as to be substantially orthogonal to the substrate transport direction.

  A semiconductor thin film is formed on the strip substrate 301 in advance. Light having a desired wavelength emitted from the light source unit 303 passes through the slit 305 and is partially irradiated to the belt-like substrate 301.

  Further, a convex lens is attached to the slit 305, and the light emitted from the light source unit 303 is selected so as to converge on a narrow irradiation area width on the substrate 301.

  When the anode of the DC power supply 304 is connected to the counter electrode 302 and the cathode is connected to the substrate 301 and a desired voltage is applied, metal ions dissolved in the electrolyte solution 306 cause an electrochemical reaction at the cathode. As a result, an electrodeposited film of a metal or a compound thereof is formed on the belt-like substrate 301.

  At this time, it is possible to control the film thickness of the deposited electrodeposition film by changing the intensity of light emitted from the light source unit periodically while keeping the substrate conveyance speed constant.

  In particular, electrodeposition having a periodic film thickness distribution in the longitudinal direction of a long substrate is provided by setting the slit pitch to be an integral multiple of the moving distance of the substrate corresponding to one cycle of light intensity change. A film can be formed.

  For example, the slit pitch is 30 mm, the light irradiation area width is 10 mm, the light intensity change period is 1 second (sec), and the substrate transport speed is 10 mm / sec.

  That is, the length of the slit in the substrate transport direction was 10 mm, and the length of the counter electrode was 20 mm.

  With such a manufacturing apparatus and method, it is possible to form an electrodeposited film having a periodic film thickness distribution in a direction parallel to the substrate transport direction at intervals of 10 mm.

  Further, in order to form a periodic film thickness distribution, the moving distance of the substrate corresponding to one period of the light intensity change needs to be at least larger than the light irradiation area width.

  Further, in order to shorten the interval between the periodic film thickness distributions, the focal lens of the convex lens attached to the slit 305 may be narrowed and narrowed, and the electrodeposition film may be formed by increasing the conveyance speed.

  As described above, an electrodeposited film can be formed on a long substrate having a large area with good controllability. Furthermore, it is possible to form an electrodeposited film having a periodic film thickness distribution.

(Fourth embodiment)
FIG. 5: is a schematic sectional drawing which shows the structure of the thin film solar cell in which the electrodeposition film was formed with the formation method of the electrodeposition film as the 4th Embodiment of this invention.

  In FIG. 5, 401 is a substrate, 402 is a metal electrode, 403 is a p-type semiconductor layer, 404 is an n-type semiconductor layer, 405 is a transparent conductive film, and 406 is a collector electrode, which are sequentially stacked on the substrate 401. .

  The substrate 401 may be a conductive substrate such as SUS, or may be an insulating substrate such as soda lime glass.

  The metal electrode 402 is preferably a refractory metal, and molybdenum (Mo), titanium (Ti), tantalum (Ta), or the like is used, and is formed by a sputtering method or the like.

  The p-type semiconductor layer 403 is a p-type compound semiconductor thin film. The following materials are preferably used for the material of the p-type semiconductor layer 403.

Copper indium selenide with a chalcopyrite structure (CuInSe ₂ )
Copper indium gallium selenide (Cu (In, Ga) Se ₂ )
Dicopper zinc tin tin (Cu ₂ ZnSnS ₄ ) having a kesterite structure or a stannite structure
The p-type semiconductor layer 403 is formed by a vapor deposition method, a selenization method (or a sulfurization method), or the like.

  As the n-type semiconductor layer 404, an n-type semiconductor thin film capable of forming a good pn junction with the p-type semiconductor layer 403 is used, and a cadmium sulfide thin film, a ZnO thin film, or the like is preferably used.

  The transparent conductive film 405 is preferably made of zinc oxide (ZnO) or indium tin oxide (ITO) having both high transmittance and conductivity, and is particularly preferably a ZnO film that can form a low resistance film by electrodeposition. .

  The formation of the transparent conductive film 405 uses the electrodeposition film formation method described in the above embodiment.

  The interval between the adjacent collector electrodes 406 was 6 mm. In order to create such a fine periodic structure, it is effective to use the slit with a lens shown in FIG. A light source unit that collects light with a lens was used so that the width of the irradiation area was 0.6 mm.

  The formed ZnO film can adjust conductivity and band mismatch by doping with impurity elements such as boron (B), aluminum (Al), gallium (Ga), sulfur (S), and magnesium (Mg). preferable.

  Here, a structure of a stacked structure of films in which an n-type semiconductor layer and a transparent conductive film are different is shown, but a structure that can serve both as an n-type semiconductor layer and a transparent conductive film, such as a ZnO film, may be used.

  The collector electrode 406 is preferably made of silver (Ag) or Al, which is a low-resistance metal, and any method such as sputtering, vapor deposition, or screen printing may be used.

  Here, in the solar cell of this embodiment, the film thickness of the transparent conductive film 405 is the thickest in the vicinity of the current collecting electrode 406, and decreases continuously or stepwise as the distance from the current collecting electrode 406 increases. It is formed to do.

  If the power loss due to the resistance value of the transparent conductive film is calculated to be the same between the case where it is formed and the case where the film thickness is distributed, the required amount of deposition of the transparent conductive film is Compared to 75% of the maximum.

  For example, it is possible to reduce the average film thickness to 1.2 μm by giving a distribution to a constant transparent conductive film having a film thickness of 1.6 μm.

  Therefore, when ZnO is used as the transparent conductive film, the photoelectric flow rate can be improved due to the improvement in the transmittance loss of sunlight.

  Thus, in the conventional solar cell, since the film thickness of the transparent conductive film is constant, the photoelectric conversion efficiency has been reduced due to the loss of photocurrent more than necessary.

  Therefore, by using the method of the present embodiment, the transparent conductive film 406 can be formed in a minute region by changing the film thickness, and the current density during power generation of the solar cell can be improved. . Therefore, a more efficient solar cell can be provided.

  Although not shown in FIG. 5, a high-resistance buffer layer may be inserted at the interface between the p-type semiconductor layer and the n-type semiconductor layer.

  The high resistance buffer layer serves to compensate for a good pn junction that may not be formed if a low resistance portion exists on the p-type semiconductor surface.

  The present invention can be used for a thin film solar cell using a compound semiconductor thin film and the production thereof.

It is a model perspective view which shows the apparatus used in the formation method of the electrodeposited film as the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the example which inserted the filter for light shielding between the counter electrode and the light source unit in FIG. It is a schematic cross section which shows the light source unit and counter electrode which are used for the formation method of the electrodeposited film as the 2nd Embodiment of this invention. It is a schematic cross section which shows an example of the apparatus which forms an electrodeposition film on a elongate strip | belt-shaped board | substrate using the formation method of the electrodeposition film as the 3rd Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the thin film solar cell in which the electrodeposition film was formed with the formation method of the electrodeposition film as the 4th Embodiment of this invention.

Explanation of symbols

101, 201, 301, 401, 501 Substrate 102, 202, 302, 502 Counter electrode 103, 203, 303, 503 Light source unit 104, 304 DC power source 105 Electrolyzer 106, 306 Electrolyte 107, 205 Feed electrode 108 X direction 109 206 Y direction 204 Filter 305 Slit 307 Delivery roller 308 Winding roller 402 Metal electrode 403 P-type semiconductor layer 404 N-type semiconductor layer 405 Transparent conductive film 406 Current collecting electrode 504 Concave lens 505 Convex lens

Claims (14)

An electrode is provided on any surface of the light source unit so that the electrode and the substrate on which the semiconductor layer is formed are opposed to the electrode in an electrolyte solution containing metal ions. An electrodeposited film that is placed and forms an electrodeposited film on the substrate by irradiating the substrate with light having a wavelength that generates photoexcited carriers while applying a voltage to the substrate and the electrode. In the forming method of
The electrode has a slit that partially transmits light from the light source unit. The method of forming an electrodeposited film according to claim 1, wherein the slit is formed in a striped pattern. The method for forming an electrodeposited film according to claim 1, wherein the electrode contains the same type of metal as the metal ion. The method for forming an electrodeposited film according to claim 2, wherein a light shielding filter is provided between the electrode and the light source unit. The method for forming an electrodeposited film according to claim 1, wherein the slit is provided with a lens. 6. The method for forming an electrodeposited film according to claim 5, wherein the lens is a convex lens. 6. The method of forming an electrodeposited film according to claim 5, wherein the lens is a concave lens. The substrate is strip-shaped,
The substrate is transported at a constant speed during the formation of the electrodeposited film,
The striped slit is formed so as to be substantially orthogonal to the transport direction of the substrate,
The method of forming an electrodeposited film according to claim 6, wherein the intensity of light emitted from the light source unit is periodically changed. 9. The method for forming an electrodeposited film according to claim 8, wherein the pitch of the slit is provided so as to be an integral multiple of the moving distance of the substrate corresponding to one period of light intensity change. In a method for manufacturing a thin film solar cell, in which a pn junction composed of a p-type semiconductor layer and an n-type semiconductor layer is formed on a substrate, and a transparent conductive film is formed on the pn junction.
The method for producing a thin-film solar cell, wherein the transparent conductive film is formed by the method for forming an electrodeposited film according to claim 1. The method of manufacturing a thin-film solar cell according to claim 10, wherein the metal ions are zinc ions. 12. The transparent conductive film is formed by changing the intensity of the light so that the film thickness of the transparent conductive film decreases as the distance from the collecting electrode increases. Manufacturing method of thin film solar cell. In a thin film solar cell in which a pn junction composed of a p-type semiconductor layer and an n-type semiconductor layer is formed on a substrate, and a transparent conductive film is formed on the pn junction.
The thin film solar cell, wherein the film thickness of the transparent conductive film decreases as the distance from the collecting electrode increases. The thin film solar cell according to claim 13, wherein a high resistance buffer layer is provided at an interface between the p-type semiconductor layer and the n-type semiconductor layer.

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