JP2011222634A - Manufacturing method for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a solar cell for sufficiently forming a transparent conductive layer and reducing damage of a base of the transparent conductive layer.SOLUTION: A parallel magnetic field is generated on a surface of a target 50 while sputter voltage is applied to the cylindrical target 50 including a formation material of the oxide-based transparent conductive film. An average value of the parallel magnetic field is set to 600 gausses or above and sputtering is performed to form the transparent conductive layer.

Description

  The present invention relates to a method for manufacturing a solar cell.

Conventionally, as a material for solar cell electrodes, a transparent electrode material such as _{ITO (In 2 O 3 -SnO 2} ) it is used. Indium (In), which is a raw material for ITO, is a rare metal and is expected to increase in cost due to difficulty in obtaining it. For this reason, not only ITO but also abundant and inexpensive ZnO-based materials have attracted attention as materials for the transparent conductive layer (for example, see Patent Document 1).

The ZnO-based material is suitable for sputtering that enables uniform film formation on a large substrate, and it is relatively easy to change the target of In ₂ O ₃ -based material such as ITO to the target of ZnO-based material in the film forming apparatus. It is possible to form a film.

JP-A-9-87833

  As a configuration of the solar cell, which will be described later in detail, for example, a solar cell is known in which an upper electrode, a photovoltaic cell, a buffer layer, and a back electrode are sequentially laminated on a glass substrate constituting the surface.

  A transparent conductive layer, such as a buffer layer, constituting such a solar cell can also be formed relatively easily by a magnetron sputtering method or the like. However, negative ions excited by the plasma are accelerated, and the negative ions may damage the bottom cell serving as a base, thereby reducing the conversion efficiency of the solar cell.

  In addition, since the light transmitted through the bottom cell is reflected by the back electrode and re-enters the bottom cell to contribute to power generation, the buffer layer is required to have high light transmittance. Similar problems also exist in transparent conductive layers other than the buffer layer, such as the upper electrode.

  This invention is made | formed in view of such a situation, While being able to form a transparent conductive layer favorably, the manufacturing method of the solar cell which can reduce the damage to the foundation | substrate of a transparent conductive layer is provided. The purpose is to provide.

  A first aspect of the present invention that solves the above problem is a method for producing a solar cell having a transparent conductive layer made of an oxide-based transparent conductive film, and a cylinder provided with a material for forming the oxide-based transparent conductive film A parallel magnetic field is generated on the surface of the target while applying a sputtering voltage to a mold target, and the transparent conductive layer is formed by performing sputtering with an average value of the parallel magnetic field of 600 gauss or more. There is a method for manufacturing a solar cell.

  In the first aspect, by forming a transparent conductive layer using a sputtering apparatus including a cylindrical target, a transparent conductive layer having excellent film quality can be formed, and the conversion efficiency of the solar cell is increased.

  A second aspect of the present invention is the method for manufacturing a solar cell according to the first aspect, wherein the oxide-based transparent conductive film is formed of a material having ZnO as a basic constituent element.

  According to a third aspect of the present invention, there is provided the solar cell manufacturing method according to the first aspect, wherein the oxide-based transparent conductive film is formed of a material made of an oxide containing In.

  In the second or third aspect, the film quality of the transparent conductive layer can be improved more reliably.

  According to a fourth aspect of the present invention, there is provided a solar cell manufacturing method according to the second aspect, wherein GZO is used as a material of the oxide-based transparent conductive film.

  According to a fifth aspect of the present invention, there is provided the solar cell manufacturing method according to the second aspect, wherein AZO is used as a material of the oxide-based transparent conductive film.

A sixth aspect of the present invention is a method for manufacturing a solar cell according to the third aspect, wherein In ₂ O ₃ is used as a material for the oxide-based transparent conductive film.

  A seventh aspect of the present invention is the method for manufacturing a solar cell according to the third aspect, wherein ITO is used as a material for the oxide-based transparent conductive film.

  In the fourth to seventh aspects, the film quality of the transparent conductive layer can be improved more reliably. For example, when GZO is used as the material of the oxide-based transparent conductive film, the contact property with an adjacent film is improved.

  An eighth aspect of the present invention is a buffer layer in which the transparent conductive layer is provided on a side opposite to the light incident side and is disposed between a back electrode functioning as a power extraction electrode and a photovoltaic cell. The method of manufacturing a solar cell according to any one of the first to seventh aspects is characterized by the above.

  In the eighth aspect, the formation of the buffer layer with excellent film quality allows sunlight to be favorably reflected by the back electrode, further increasing the conversion efficiency of the solar cell.

  As described above, according to the present invention, a transparent conductive layer excellent in film quality, for example, a buffer layer can be formed, and damage to the base of the transparent conductive layer can be reduced. Thereby, the conversion efficiency of a solar cell can be improved.

It is sectional drawing which shows the structure of the solar cell which concerns on one Embodiment of this invention. 1 is a schematic configuration diagram of a magnetron sputtering apparatus according to an embodiment of the present invention. It is a figure which shows schematic structure of the film-forming chamber which concerns on one Embodiment of this invention. It is a schematic perspective view which shows the sputtering cathode mechanism which concerns on one Embodiment of this invention. It is a graph which shows the relationship between a horizontal magnetic field strength and the specific resistance of a GZO film. It is a graph which shows the relationship between a horizontal magnetic field strength and the specific resistance of an AZO film. It is a graph which shows the relationship between a horizontal magnetic field strength and the specific resistance of an ITO film. It is a graph which shows the relationship between a horizontal magnetic field strength and a fill factor (FF). It is a graph which shows the relationship between horizontal magnetic field intensity and the conversion efficiency of a solar cell. It is a schematic block diagram which shows the modification of a magnetron sputtering device.

  Hereinafter, the manufacturing method of the solar cell concerning one embodiment of the present invention is explained in detail with reference to drawings. First, the configuration of the solar cell will be described. FIG. 1 is a diagram showing a schematic configuration of a solar cell.

  As shown in FIG. 1, a solar cell 10 includes a glass substrate 11 that constitutes a surface, an upper electrode 12 that is a transparent conductive layer laminated on the glass substrate 11, and a photovoltaic cell 13 that is constituted by amorphous silicon. The buffer layer 14 is a transparent conductive layer made of an oxide-based transparent conductive film, and the back electrode 15 is made of a metal film. That is, the solar cell 10 is a single junction solar cell.

  The photovoltaic cell 13 is composed of three layers of a p layer (13p), an i layer (13i), and an n layer (13n), of which the i layer (13i) is formed of amorphous silicon. .

  In the solar cell 10 having such a configuration, when sunlight hits the i layer 13i, electrons and holes are generated due to the photovoltaic effect, the electrons move toward the n layer, and the holes move to the p layer. Move towards. Electrons generated by the photovoltaic effect are taken out by the upper electrode 12 and the back electrode 15 to convert light energy into electric energy.

  In addition, the sunlight which entered from the glass substrate 11 side passes through each layer laminated | stacked on the glass substrate 11, and is reflected by the back surface electrode 15. FIG. For this reason, in order to improve the conversion efficiency of light energy, the solar cell 10 employs a texture structure aiming at a prism effect for extending the optical path of sunlight incident on the upper electrode 12 and a light confinement effect.

Here, the buffer layer (transparent conductive layer) 14 constituting such a solar cell 10 is made of an oxide-based transparent conductive film formed using a magnetron sputtering apparatus described later. This transparent conductive film is preferably formed of a ZnO-based oxide film such as GZO in which gallium is added to zinc oxide and AZO in which aluminum is added to zinc oxide. Alternatively, the transparent conductive film is preferably formed of a material composed of oxide grains containing indium (In), for example, indium oxide (In ₂ O ₃ ), an ITO film in which tin is added to indium oxide, or the like. In the present embodiment, the upper electrode 12 is also formed of the same oxide-based transparent electrode film as the buffer layer 14.

  When the upper electrode 12 and the photovoltaic cell 13 are laminated on the glass substrate 11 and the buffer layer 14 which is a transparent conductive layer is formed by a magnetron sputtering apparatus, negative ions excited by the plasma are accelerated, There is a possibility that the photovoltaic cell 13 which is the base of the buffer layer 14 is damaged by the negative ions and the conversion efficiency of the solar cell 10 is lowered.

  Therefore, in the present embodiment, when the solar cell 10 is manufactured, the buffer layer 14 that is a transparent conductive layer is formed by the method described below. As a result, it is possible to form the buffer layer 14 with good film quality while suppressing damage to the photovoltaic cell 13 that is the base.

  Hereinafter, a method for manufacturing the solar cell 10, particularly a method for forming the buffer layer 14 will be described. First, the configuration of a magnetron sputtering apparatus used for forming the buffer layer 14 will be described. FIG. 2 is a schematic configuration diagram of a magnetron sputtering apparatus.

  As shown in FIG. 2, the magnetron sputtering apparatus 30 is an inline apparatus, for example, and includes a preparation chamber 31, a film formation chamber 32, and a take-out chamber 33 in order. The preparation chamber 31 and the take-out chamber 33 are connected to rough evacuation means 31p and 33p such as a rotary pump, respectively. The film formation chamber 32 is connected to a high vacuum evacuation means 32p such as a turbo molecular pump. In the sputtering apparatus 30, the substrate S is supported in a vertical shape and carried into the preparation chamber 31, and the preparation chamber 31 is exhausted by the roughing exhaust means 31 p. Next, the substrate S is transferred into the film forming chamber 32 evacuated by the high vacuum evacuation means 32p to perform the film forming process. The substrate S after film formation is carried out from the take-out chamber 33 evacuated by the rough evacuation means 33p.

A gas supply unit 34 for supplying a sputtering gas such as Ar is connected to the film forming chamber 32. For example, a reactive gas such as O ₂ can be supplied from the gas supply means 34. A vertical sputtering cathode mechanism 40 is installed in the film forming chamber 32.

  FIG. 3 is a diagram showing a schematic configuration in the film forming chamber. As shown in FIG. 3, a heater 35 for heating the substrate S is disposed on one side surface of the film forming chamber 32. The sputter cathode mechanism 40 is disposed on the other side surface in the width direction of the film forming chamber 32. The sputter cathode mechanism 40 includes a cylindrical target 50 that is rotatably supported with respect to a rotary shaft 41 and a magnetic circuit 60 that is disposed inside the target 50. The sputtering cathode mechanism 40 includes a DC power source 42 that supplies power to the target 50.

  The target 50 is obtained by uniformly forming a target layer 52 made of a predetermined material on the outer peripheral surface of a metal backing tube 51. The magnetic circuit 60 is for generating a horizontal magnetic field (a magnetic field in a direction substantially parallel to the surface of the target layer 52) on the surface of the target layer 52. Although the configuration of the magnetic circuit 60 is not particularly limited, in the present embodiment, the first magnet 61 and the second magnet 62 having different polarities on the tip side are provided.

  FIG. 4 is a schematic perspective view of the sputtering cathode mechanism. As shown in FIG. 4, the magnetic circuit 60 constituting the sputtering cathode mechanism 40 is arranged inside the target 50. The first magnet 61 is arranged linearly along the rotation axis 41, and the second magnet 62 is arranged in a frame shape at a predetermined distance from the peripheral edge of the first magnet 61. The first magnet 61 and the second magnet 62 are attached to the yoke 63 to constitute a magnetic circuit 60.

  As shown in FIG. 3, a magnetic field is generated by the first magnet 61 and the second magnet 62 having different polarities. Thereby, on the surface of the target layer 52 between the first magnet 61 and the second magnet 62, a position where the vertical magnetic field (magnetic field in a direction substantially orthogonal to the surface of the target layer 52) becomes zero, that is, a parallel magnetic field. A position 55 where the maximum value is generated occurs. At this position 55, the electron is most captured by the magnetic field and high-density plasma is generated, so that the film forming speed can be improved.

  The film forming chamber 32 is provided with a transport means (not shown) for transporting the substrate S in a state of being supported vertically, and the substrate S is transported by the transport means so as to face the sputtering cathode mechanism 40. It has come to be. A thin film is formed on the substrate S by the sputtering cathode mechanism 40 in the process in which the substrate S passes in front of the sputtering cathode mechanism 40.

  As a manufacturing procedure of the solar cell 10, first, the upper electrode 12 is formed on the substrate S. The upper electrode 12 is formed by substantially the same method as that of the buffer layer 14 described later. Next, after the photovoltaic cell 13 is formed on the upper electrode 12, the buffer layer 14 is formed on the photovoltaic cell 13 using the magnetron sputtering apparatus 30 described above.

Specifically, the glass substrate 11 on which the upper electrode 12 and the photovoltaic cell 13 are formed is carried into the film forming chamber 32, and the glass substrate 11 is heated by the heater 35 as necessary. In addition, when heating the glass substrate 11 with the heater 35, it is preferable to heat to 200 degrees C or less. This is because the heat resistance of the photovoltaic cell 13 is taken into consideration. Further, the film formation chamber 32 is evacuated by the high vacuum exhaust means 32p, Ar gas is introduced as a sputtering gas from the gas supply means 34, and the pressure in the film formation chamber 32 is maintained at 2 to 10 mTorr. In this state, while rotating the cylindrical target 50, power having a power density of 1 to 8 w / cm ² is applied to the target 50 by the DC power source 42. Further, a parallel magnetic field is generated on the surface of the target 50 by the magnetic circuit 60. The magnitude of the magnetic field strength is not particularly limited, but the average value of the horizontal magnetic field strength at the position 55 is preferably 600 gauss or more.

  Thereby, as described above, the ions of the sputtering gas excited by the plasma in the film forming chamber 32 collide with the target layer 52 and eject atoms. The jumped-out atoms adhere on the photovoltaic cell 13, whereby the buffer layer 14 that is a transparent conductive layer is formed. Note that the annealing process after the film formation is not performed because the heat film formation is performed, but the annealing process after the film formation may be performed.

  Thereafter, the solar cell 10 is manufactured by forming the back electrode 15 made of a metal film such as Ag or Al on the buffer layer 14.

  In the manufacture of such a solar cell 10, in this embodiment, as described above, the buffer layer 14 that is a transparent conductive layer is formed by the magnetron sputtering apparatus 30 including the cylindrical target 50. That is, the buffer layer 14 is formed on the photovoltaic cell 13 by generating a parallel magnetic field on the surface of the target layer 52 by the magnetic circuit 60 while applying a sputtering voltage to the rotating cylindrical target 50. I tried to do it.

  Thereby, the buffer layer 14 with good film quality can be formed. Specifically, the contact property between the buffer layer 14 and the adjacent film is improved, and the conversion efficiency of the solar cell 10 is improved accordingly. Further, since the buffer layer 14 is made of a GZO film, the contact property of the buffer layer 14 is further improved.

  In addition, since the buffer layer 14 with a uniform crystal lattice can be formed, the specific resistance of the buffer layer 14 can be reduced. By reducing the specific resistance, the thickness of the buffer layer 14 can be reduced to, for example, about 50 nm. Thereby, the light transmittance of the buffer layer 14 is improved, and the conversion efficiency of the solar cell 10 is further improved accordingly. In addition, the manufacturing cost can be reduced by reducing the film thickness.

  Furthermore, in this embodiment, since the upper electrode 12 which is a transparent electrode layer is formed by substantially the same method as the method for forming the buffer layer 14 as described above, the film quality of the upper electrode 12 is also improved.

  Here, a specific resistance is generally considered as a standard for determining the quality of the GZO film constituting the solar cell. In order to prevent loss of carrier current generated in the solar cell, the specific resistance is preferably a relatively low value.

  The inventor of the present application examined the relationship between the average value of the horizontal magnetic field strength (hereinafter simply referred to as “horizontal magnetic field strength”) when forming the GZO film and the specific resistance of the GZO film. Specifically, the change in the specific resistance when the GZO film was formed under other conditions other than changing the horizontal magnetic field strength was examined. FIG. 5 is a graph showing the results. As can be seen from this figure, the specific resistance of the GZO film decreases to about 500 μΩcm as the horizontal magnetic field strength increases until the horizontal magnetic field strength reaches about 600 Gauss, and then stabilizes. From this result, it is considered that the horizontal magnetic field strength at the time of forming the buffer layer 14 made of the GZO film is preferably 600 gauss or more where the specific resistance is low and stable.

  As described above, as the oxide-based transparent conductive film constituting the buffer layer 14 or the like, for example, an AZO film, an ITO film, or the like is preferably used in addition to the GZO film. As a criterion for judging the quality of these AZO films and ITO films, the specific resistance can be considered as in the case of the GZO films. Therefore, the inventors of the present application investigated the relationship between the horizontal magnetic field strength when forming the AZO film and the specific resistance of the AZO film, and the relationship between the horizontal magnetic field strength when forming the ITO film and the specific resistance of the ITO film. It was. FIG. 6 is a graph showing the result of the AZO film, and FIG. 7 is a graph showing the result of the ITO film.

  As can be seen from FIG. 6, the specific resistance of the AZO film decreases to about 450 μΩcm as the horizontal magnetic field strength increases until the horizontal magnetic field strength reaches about 600 Gauss, and then stabilizes. As can be seen from FIG. 7, the specific resistance of the ITO film decreases to about 200 μΩcm as the horizontal magnetic field strength increases until the horizontal magnetic field strength reaches about 600 Gauss, and then stabilizes. From these results, it is considered that the horizontal magnetic field strength when forming the buffer layer 14 made of an AZO film or ITO film is preferably 600 gauss or more which has a low specific resistance and is stable.

  Furthermore, the inventors of the present application also examined the relationship between the horizontal magnetic field strength and the fill factor (FF) when forming the GZO film. That is, the change in FF when the GZO film was formed under the same conditions except that the horizontal magnetic field strength was changed was examined. FIG. 8 is a graph showing the results. As can be seen from this figure, the FF of the GZO film rises to about 0.7 as the horizontal magnetic field strength increases until the horizontal magnetic field strength reaches about 600 Gauss, and then stabilizes. Also from this result, it is considered that the horizontal magnetic field strength at the time of forming the buffer layer 14 made of the GZO film is preferably 600 gauss or more which stabilizes the FF at a high value.

  The inventor of the present application also examined the relationship between the average value of the horizontal magnetic field strength when the buffer layer 14 was formed by the magnetron sputtering apparatus 30 and the conversion efficiency of the solar cell. FIG. 9 is a graph showing the results. As can be seen from this figure, the conversion efficiency of the solar cell 10 increases to about 8.0% as the horizontal magnetic field strength increases until the horizontal magnetic field strength reaches about 600 Gauss, and then stabilizes. As in the case of the above result, it was confirmed from this result that the horizontal magnetic field strength when forming the buffer layer 14 is preferably 600 gauss or more which stabilizes the conversion efficiency at a high value.

  As described above, by setting the average value of the horizontal magnetic field strength when forming the buffer layer 14 made of the GZO film to be 600 gauss or more, the buffer layer 14 having excellent film quality can be formed. The conversion efficiency of the battery can be improved. Similarly, when the buffer layer 14 made of an AZO film or ITO film is formed, the buffer layer 14 having excellent film quality can be formed by setting the average value of the horizontal magnetic field strength to 600 gauss or more. .

  In the present invention, since the buffer layer 14 is formed by the magnetron sputtering apparatus 30 including the cylindrical target 50, the following effects can also be obtained. When a transparent conductive layer made of an oxide-based transparent electrode film is formed by sputtering, such as the buffer layer 14 made of a GZO film, a black oxide called nodules is generated on the target surface, and abnormal discharge occurs on the target. It is known to cause problems such as contamination of foreign matter into the film. In the magnetron sputtering apparatus 30 including the cylindrical target 50, the generation of nodules can be greatly reduced as compared with a conventional apparatus including a flat plate target. Therefore, continuous production for a long time is possible, and the manufacturing cost can be reduced.

  Further, the cylindrical target 50 can significantly reduce the non-erosion region as compared with the flat target. Furthermore, by improving the use efficiency of the target, it is possible to increase the input power and improve the throughput.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment. That is, the present invention can be modified as appropriate without departing from the scope of the present invention.

For example, O ₂ gas may be supplied into the film forming chamber 32 when the buffer layer 14 made of a GZO film is formed. Thereby, an oxygen-rich GZO film is obtained, and the light transmittance of the buffer layer 14 is further improved.

  For example, in the above-described embodiment, the example in which the magnetic circuit 60 is fixed in the target 50 has been described. However, the magnetic circuit 60 may be provided so as to be swingable about the rotation shaft 41.

  Further, for example, in the above-described embodiment, the present invention has been described by exemplifying the in-line type sputtering apparatus 30. However, for example, the sputtering apparatus may be of an inter-back type. Specifically, as shown in FIG. 10, the inter-back type sputtering apparatus 30A includes a preparation / removal chamber 31A and a film formation chamber 32 provided with a sputtering cathode mechanism 40 and the like. In the sputtering apparatus 30A, the substrate is supported in a vertical shape and carried into the preparation / removal chamber 31A, and the preparation / removal chamber 31A is exhausted by the roughing exhaust means 31Ap. Next, the substrate S is transferred to the film forming chamber 32 evacuated by the high vacuum evacuation means 32p, and a film forming process is performed by the sputtering cathode mechanism 40 or the like. The substrate S after film formation is again carried out through the preparation / removal chamber 31A.

  Furthermore, although the sputtering apparatus of the above-described embodiment performs sputtering while supporting the substrate vertically, it is of course possible to perform sputtering while horizontally supporting the substrate. In the sputter cathode mechanism of the embodiment, a DC power source (direct current power source) is adopted, but a DC power source and an RF power source (high frequency power source) can be used in combination.

  Furthermore, in the above-described embodiment, the case of a single-structure solar cell has been described, but the present invention can also be applied to a tandem junction solar cell including two photovoltaic cells with an intermediate electrode interposed therebetween. In this case, like the buffer layer, the intermediate electrode is made of an oxide conductive transparent conductive film. That is, an intermediate electrode having excellent film quality can be formed by adopting the above-described method for manufacturing a buffer layer for manufacturing an intermediate electrode that is a transparent conductive layer. Furthermore, the present invention is not limited to the production of a buffer layer, an intermediate electrode, and the like, but can be applied to the production of any transparent conductive layer made of an oxide-based transparent electrode film constituting a solar cell.

DESCRIPTION OF SYMBOLS 10 Solar cell 11 Glass substrate 12 Upper electrode 13 Photovoltaic cell 14 Buffer layer 15 Back surface electrode 30 Sputtering device 31 Preparation chamber 31p, 33p Coarse grinding exhaust means 32 Deposition chamber 32p High vacuum exhaust means 33 Extraction chamber 34 Gas supply means 35 Heater 40 sputter cathode mechanism 41 rotating shaft 42 DC power supply 50 target 51 backing tube 52 target layer 60 magnetic circuit 61 first magnet 62 second magnet 63 yoke

Claims (8)

A method for producing a solar cell having a transparent conductive layer made of an oxide-based transparent conductive film,
While applying a sputtering voltage to a cylindrical target provided with a material for forming the oxide-based transparent conductive film, a parallel magnetic field is generated on the surface of the target, and the average value of the parallel magnetic field is set to 600 gauss or more to perform sputtering. A method for producing a solar cell, wherein the transparent conductive layer is formed by performing.   The method for manufacturing a solar cell according to claim 1, wherein the oxide-based transparent conductive film is formed of a material containing ZnO as a basic constituent element.   The method for manufacturing a solar cell according to claim 1, wherein the oxide-based transparent conductive film is formed of a material made of an oxide containing In.   The method for manufacturing a solar cell according to claim 2, wherein GZO is used as a material for the oxide-based transparent conductive film.   The method for manufacturing a solar cell according to claim 2, wherein AZO is used as a material for the oxide-based transparent conductive film. The method for manufacturing a solar cell according to claim 3, wherein In ₂ O ₃ is used as a material for the oxide-based transparent conductive film.   The method for manufacturing a solar cell according to claim 3, wherein ITO is used as a material for the oxide-based transparent conductive film.   The transparent conductive layer is a buffer layer provided between a back electrode and a photovoltaic cell, which is provided on the side opposite to the light incident side and functions as a power extraction electrode. The method for producing a solar cell according to any one of claims 7 to 9.