JP2006165082A - Solar cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell and its manufacturing method capable of securely preventing characteristics from being deteriorated owing to peeling of an electrode layer by further improving adhesion force of the electrode layer to a substrate. <P>SOLUTION: The electrode layer formed on the insulating flexible substrate comprises a plurality of layers each containing silver (Ag). A layer situated close to the substrate among the plurality of the layers contains at least one kind of oxide (MO<SB>n</SB>) selected from a group consisting of copper oxide, aluminum oxide, zinc oxide, and tin oxide. The content (Ag/(Ag+MO<SB>n</SB>)) of Ag in the electrode layer changes stepwise or continuously from the layer situated close to the substrate toward its film thickness direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar cell in which at least an electrode layer and a photoelectric conversion layer are laminated on an insulating flexible substrate, and a method for manufacturing the solar cell.

  In a solar cell, an electrode layer and a photoelectric conversion layer are generally laminated on an insulating flexible substrate. As the electrode layer, a single metal such as Ag or Al or an alloy thereof is used. As a photoelectric conversion layer, a pn junction whose main component is amorphous silicon is typical. In the case of forming an electrode layer, a thin film having a uniform composition is generally formed by direct current sputtering using a target of a single metal or an alloy having a uniform composition.

  However, although the electrode layer formed in this way is directly attached to the substrate, the adhesive force with the substrate is not sufficient. For this reason, when the solar cell is attached to a curved surface, the electrode layer may be peeled off from the substrate, resulting in poor conduction or poor power generation. In particular, when forming electrode layers on both sides of the substrate, after forming the electrode layer on one side, the electrode layer is formed on the opposite side, so when forming the electrode layer on the opposite side, Since the temperature control of the substrate becomes unstable due to the presence of the electrode layer formed first, the adhesion of the electrode layer to be formed later was inferior.

Therefore, in Japanese Patent Laid-Open No. 9-326696, an electrode layer is made of an alloy of Ag, at least one of Cu, Al, and Zn, and the electrode layer is made into a plurality of layers, and among these layers, a substrate is formed. The adjacent layer contains a large amount of Cu, Al, and Zn, which have high adhesion to the substrate, and the layer adjacent to the photoelectric conversion layer contains a large amount of Ag that has a good ohmic property with the photoelectric conversion layer. While maintaining low resistance as a whole, the adhesion between the electrode layer and the substrate is improved.
Japanese Patent Laid-Open No. 9-326496

  As disclosed in the above-mentioned document, by forming the layer adjacent to the substrate from an Ag-based alloy containing a large amount of Cu, Al, and Zn, the adhesion to the substrate is surely improved. However, even if it is formed of such an alloy, there is a considerable deterioration in characteristics due to peeling, and it is necessary to further improve the adhesion of the electrode layer to the substrate.

  Therefore, in view of the above problems, the present invention provides a solar cell and a method for manufacturing the same that can further improve the adhesion of the electrode layer to the substrate and reliably prevent the deterioration of characteristics due to the peeling of the electrode layer. The purpose is to provide.

  In order to achieve the above object, a solar cell according to the present invention is a solar cell in which an electrode layer and a photoelectric conversion layer are stacked on an insulating flexible substrate, and the electrode layer contains Ag. The layer adjacent to the substrate among the plurality of layers includes at least one oxide selected from the group consisting of copper oxide, aluminum oxide, zinc oxide, and tin oxide. The content of Ag in the electrode layer varies stepwise or continuously from the layer adjacent to the substrate toward the film thickness direction.

  In addition, in this specification, the plurality of layers constituting the electrode layer include a plurality of layers in which the composition of the electrode layer is changed stepwise and each layer can be clearly distinguished, and the composition of the electrode layer is continuous. It also includes those that have changed and can not clearly distinguish each layer.

  As described above, the electrode layer is formed into a plurality of layers, and among these layers, the layer adjacent to the substrate is added with copper oxide, aluminum oxide, zinc oxide, or tin oxide in Ag having excellent conductivity, thereby being attached to the substrate. Wearing power can be improved dramatically. In addition, by changing the content of Ag in the electrode layer stepwise or continuously from the layer adjacent to the substrate in the film thickness direction, the oxide does not deteriorate the conductivity of the entire electrode layer. Can be introduced. Therefore, since the adhesion to the substrate is remarkably improved, it is possible to reliably prevent peeling even against bending, and the low resistance is maintained as a whole, so that a solar cell with less power loss can be obtained.

  The substrate is preferably at least one selected from the group consisting of polyamide, polyimide, liquid crystal polymer, polyethylene naphthalate, polyethylene terephthalate, polyetherimide, polyethersulfone, polystyrene, and polycarbonate.

  Among the plurality of layers of the electrode layer, the Ag content of the layer adjacent to the substrate may be 2 to 99.95 at%, and the Ag content of at least one other layer may be 95 at% or more. preferable.

  Further, the change in the content of Ag in the electrode layer may be increased stepwise or continuously from the layer adjacent to the substrate in the film thickness direction, or may decrease. It may be increased after decreasing.

  Another aspect of the present invention is a method for manufacturing a solar cell, which is at least selected from the group consisting of silver and copper oxide, aluminum oxide, zinc oxide, and tin oxide on an insulating flexible substrate. A step of forming a layer comprising one kind of oxide, and silver or silver and at least one kind on the layer so that the silver content changes stepwise or continuously from the silver content of the layer. And a step of forming an electrode layer together with the layer. The respective layers are preferably formed by sputtering to form the electrode layer, and the gas pressure at that time is preferably 0.1 to 5 Pa.

  As described above, according to the present invention, since the adhesive force of the electrode layer to the substrate is further improved, a solar cell and a method for manufacturing the solar cell in which characteristic deterioration due to peeling of the electrode layer is reliably prevented are provided. Can do.

  Hereinafter, an embodiment of a solar cell and a manufacturing method thereof according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic view showing one embodiment of a solar cell according to the present invention, in which (a) is a plan view thereof, (b) is a cross-sectional view taken along the line XX ′ shown in FIG. (C) is the bottom view.

  As shown in FIG. 1, the solar cell 50 having metal electrodes on both surfaces of the substrate 51 is different from the photoelectric conversion layer 53 (the front side of the substrate) of the substrate 51 in order to improve the photoelectric conversion efficiency per substrate area. Electrode layers 52b and 55 for taking out generated electric power are formed on the opposite surface (rear side), and connection with the front electrode layers 52a and 54 is made through holes 56 and 57 formed in the substrate 51.

  That is, the first electrode layer 52 a formed on the front side of the substrate 51 is connected to the second electrode layer 52 b formed on the opposite surface of the substrate 51 through the first hole 56. Further, the third electrode layer 54 which is a transparent electrode is connected to a fourth electrode layer 55 formed on the opposite surface of the substrate 51 through the second hole 57.

  The substrate 51 is not particularly limited as long as it is insulating and flexible, but is selected from the group consisting of polyamide, polyimide, liquid crystal polymer, polyethylene naphthalate, polyethylene terephthalate, polyetherimide, polyethersulfone, polystyrene, and polycarbonate. It is preferable that it is formed from at least one of the above. By forming the substrate 51 from these materials, a film solar cell can be formed. In particular, it is more preferable to use polyimide.

Each of the first and second electrode layers 52 is composed of a plurality of layers, and each of these layers is silver (Ag), silver (Ag) and copper oxide (CuO), aluminum oxide (Al ₂ O ₃ ), It is formed from at least one oxide selected from the group consisting of zinc oxide (ZnO) and tin oxide (SnO ₂ ) (hereinafter referred to as MO _n , where M is Cu, Al, Zn or Sn). Yes. Of these layers, the layer adjacent to the substrate 51 is made of Ag and MO _n . As described above, by introducing copper oxide, aluminum oxide, zinc oxide, or tin oxide into Ag in a layer adjacent to the substrate 51, the adhesion to the substrate can be remarkably improved. Further, by introducing these oxides, the texture structure (surface morphology) of the electrode layer can be controlled. Of the above oxides, it is particularly preferable to use aluminum oxide or tin oxide, which can greatly improve the adhesion. The Ag content in the layer adjacent to the substrate 51 is preferably 2 to 99.95 at%, and more preferably 96 to 99.9 at%.

Further, the Ag content in the first and second electrode layers 52a and 52b is changed in the film thickness direction (from the layer adjacent to the substrate 51 to the photoelectric conversion layer 53 or the fourth electrode layer 56). In other words, the resistivity of the first and second electrode layers 52a and 52b as a whole can be prevented from increasing by changing the content of MO _{n in} the film thickness direction. . In particular, the Ag content in at least one layer other than the layer directly attached to the substrate 51 is preferably 95 at% or more. Thereby, the resistance loss by the serial resistance component of a solar cell can be reduced.

  FIG. 2 is a graph showing a change in composition in the film thickness direction of the first electrode layer 52a, where (a) shows a stepwise change in composition and (b) to (d) show a composition change. This is a case of continuous change. The vertical axis indicates the content (at%) of Ag in the first electrode layer 52a. The horizontal axis indicates the film thickness of the first electrode layer 52 a, and the intersection with the vertical axis is the contact point with the substrate 51.

As shown in FIG. 2 (a) and (b), the first electrode layer 52a composed of a plurality of layers, a composition containing a large amount of MO _n is a layer directly adhered to the substrate 51, toward the thickness direction MO By laminating layers whose compositions are changed so that _n decreases, the resistivity of the first electrode layer 52a as a whole can be prevented from increasing. Note that the same effect can be obtained by changing the composition of the second electrode layer 52b in the same manner.

On the other hand, as shown in FIG. 2C, the layer directly attached to the substrate 51 has a composition containing a small amount of MO _n , and a layer whose composition is changed so that the MO _n increases in the film thickness direction is laminated. Thus, while securing the adhesion between the first electrode layer 52a and the substrate 51, the photoelectric conversion layer 53 mainly composed of a-Si or the like formed on the first electrode layer 52a, or the first if necessary. Adhesive force with the conductive oxide layer stacked between the one electrode layer 52a and the photoelectric conversion layer 53 can be strengthened.

Further, as shown in FIG. 2D, the layer directly adhering to the substrate 51 has a composition containing a large amount of MO _n, and after decreasing MO _n in the film thickness direction, the composition layer so as to increase again. Are stacked, the photoelectric conversion layer 53 mainly composed of a-Si or the like formed on the first electrode layer 52a, while ensuring the adhesion between the first electrode layer 52a and the substrate 51, If necessary, the adhesive force between the first electrode layer 52a and the conductive oxide layer stacked between the photoelectric conversion layer 53 can be strengthened.

  The photoelectric conversion layer 53 is not particularly limited as long as it is an organic semiconductor having photoelectric conductivity, but is preferably composed mainly of amorphous silicon (a-Si) or amorphous silicon germanium (a-SiGe). The structure is preferably a pn junction or a pin junction. In particular, when the photoelectric conversion layer 53 is amorphous silicon (a-Si) or amorphous silicon germanium (a-SiGe), the change in the composition of the first electrode layer 52a is shown in FIG. Can be strengthened.

  If necessary, a conductive oxide layer (not shown) is provided between the first electrode layer 52a and the photoelectric conversion layer 53, or between the second electrode layer 52b and the fourth electrode layer 55. You can also. Thereby, a diffusion barrier, adhesion improvement, and an optical reflection increasing function can be added. As such a conductive oxide, it is preferable to use zinc oxide, indium tin oxide (ITO), or the like. In particular, when this conductive oxide is provided, the adhesive force can be strengthened by changing the composition of the first and second electrode layers 52a and 52b to that shown in FIG.

  Although it will not specifically limit if it is a transparent conductive material as the 3rd electrode layer 54, For example, an indium tin oxide (ITO), a zinc oxide, etc. are preferable. The fourth electrode layer 55 is preferably made of a single metal such as silver or nickel.

  Next, the manufacturing method of the solar cell 50 provided with said structure is demonstrated. First, after forming the first hole 56 in the substrate 51, the first electrode layer 52 a is formed on the front side of the substrate 51, and further, the second electrode layer 52 b is formed on the back side of the substrate 51. The electrode layer 52 is not particularly limited as long as the Ag content can be changed in the film thickness direction, but a sputtering method or a reactive evaporation method can be used. It is preferable to use a sputtering method.

As a target used in the sputtering method, an Ag target containing MO _n may be prepared from the beginning, but it is preferable to use an Ag-M alloy target. In this case, by forming a film while introducing a sputtering gas mixed with O ₂ , Ag in the alloy target is not oxidized, but only M is oxidized to MO _n , and an Ag film containing MO _n is formed. Can do.

  Furthermore, the composition of the electrode layer 52 can be changed toward the film thickness direction by using a roll-to-roll film forming apparatus described below. Roll-to-roll film formation includes a stepping method and a continuous method. In the stepping method, the substrate is deposited while stopping for a certain period of time for each of the plurality of deposition units. In the continuous method, the substrate continuously passes through the deposition unit at a constant rate.

  FIG. 3 is a cross-sectional view schematically showing a stepping film forming apparatus. The substrate 51 is fed from the feed roll 12 and taken up by the take-up roll 13. Each film forming unit 20 includes a target 21 on or serving as an anode, a cathode 27 with a built-in heater, and a power source 28 in a set of three points. In contact with. Since the targets 21a, 21b, and 21c have different compositions, electrode layers having compositions corresponding to the respective compositions of the targets 21a, 21b, and 21c are sequentially formed and stacked on the substrate 51. Therefore, the composition in the film thickness direction of the electrode layer can be changed stepwise as shown in FIG.

  In the stepping film forming apparatus, a partition 30 can be provided between the film forming units 20 as shown in FIG. The partition 30 is closed during film formation to control the sputtering conditions of each film forming unit 20, and the substrate 51 is moved in the opened state. Thereby, it becomes possible to control the sputtering conditions of each film forming unit 20 independently. In particular, the adhesion of the electrode layer to the substrate can be further improved by controlling the gas pressure in the range of 0.1 to 5 Pa when forming the layer directly attached to the substrate 51.

  FIG. 5A is a cross-sectional view schematically showing a continuous film forming apparatus. In addition, the same code | symbol is attached | subjected about the structure similar to FIG. As shown in FIG. 5A, in the continuous method, the number of film forming units 40 may be one, and the film forming unit 40 includes a target 41, a cathode 47, and a power supply 48. In order to continuously change the composition of the electrode layer formed on the substrate 51, the target 41 can be simply used by combining a plurality of partial targets having different compositions. FIG. 5B shows a plan view of the target 41.

  As shown in FIG. 5 (b), the two types of partial targets 43 and 44 having different compositions have the same shape of a right triangle that is elongated in the substrate moving direction, and by laying them alternately, The composition can be continuously changed. Further, in order to eliminate the composition change between the initial part and the end part of the electrode layer 52 and to ensure familiarity with adjacent layers, it is preferable to provide rectangular partial targets 42 and 45 at both ends of the target 41, respectively. . The partial targets 42 and 43 have the same composition, and 44 and 45 have the same composition. With such a continuous film forming apparatus using the target 41, the composition in the film thickness direction of the electrode layer can be continuously changed as shown in FIG.

In the target 41 shown in FIG. 5 (b), the location where the two types of partial targets 43 and 44 having different compositions are alternately arranged is provided only once in the substrate moving direction, but the direction is reversed. In this case, the composition in the film thickness direction of the electrode layer can be changed to an inverted V shape as shown in FIG.

  After the first and second electrode layers 52a and 52b are formed on both surfaces of the substrate 51 as described above, a conductive oxide layer is formed on the first or second electrode layers 52a and 52b as necessary. A film may be formed. This conductive oxide is preferably formed by sputtering as with the electrode layer 52.

  Next, as shown in FIG. 1, after the second hole 57 is formed in the substrate 51, the photoelectric conversion layer 53 is formed on the first electrode layer 52a. The photoelectric conversion layer 53 is preferably formed using a plasma CVD apparatus. Then, a third electrode layer 54 made of a transparent conductive material is further formed on the photoelectric conversion layer 53 except for the periphery of the first hole 56. On the other hand, a metal fourth electrode layer 55 is formed on the second electrode layer 52b on the back side. The third electrode layer 54 and the fourth electrode layer 55 are preferably formed by sputtering similarly to the electrode layer 52.

  After the film is formed in this way, the laminate of the front surface and the back surface of the substrate 51 is cut and divided by the cutting portions 58a and 58b so as to have the same shape. As a result,-(fourth electrode layer 55-second electrode layer 52b-first hole 56-first electrode layer 52a-photoelectric conversion layer 53-third electrode layer 54-second hole 57). -Series connection is completed with () in the adjacent fourth electrode layer 55... As one unit cell of the solar battery.

Example 1
An electrode layer whose composition continuously changed in the film thickness direction was formed using the continuous film forming apparatus shown in FIG. The substrate used was a polyimide resin sheet having a thickness of 50 μm. Moreover, the target used the thing of two types, a right-angled triangle and a rectangle, using two types of partial targets with composition Al2at% containing Ag and Ag100at%, respectively.

The sputtering conditions were a mixed gas of Ar and O ₂ (O ₂ : 6%) as a sputtering gas, a gas pressure of 2 Pa, a DC voltage of 300 V, and a substrate moving speed of 0.5 m / min. After the first electrode layer was formed on the front side of the substrate having the first holes, it was inverted and the second electrode layer was formed on the back side. In both electrode layers, Ag was not oxidized, but only Al was oxidized, and an Ag film mixed with aluminum oxide was formed. In terms of film thickness, from the substrate side, the Ag 98 at% layer was about 80 nm, the composition change layer was 40 nm, and the Ag 100 at% layer was 80 nm, for a total of about 200 nm.

The adhesion of the obtained electrode layer was evaluated by a tensile test method. In the tensile test method, the substrate having the electrode layers formed on both sides as described above is cut into 50 mm × 50 mm test pieces, and cylindrical test pieces having an area of 1.0 cm ² are respectively formed on the first and second electrode layers. After bonding, the piece was pulled in the direction of the central axis, and the force when the electrode layer peeled from the substrate was measured. As a result, even on the back side where adhesion force was low (30 to 500 N), the adhesion force was 1050 N or more, which sufficiently satisfied the practical adhesion force range of 850 N or more.

  Further, a photoelectric conversion layer, a third electrode layer, and a fourth electrode layer were formed, and the stack on the substrate was cut and divided to produce a solar cell. When the photoelectric conversion efficiency of this solar cell was measured, it was equivalent to the photoelectric conversion efficiency of the solar cell having the same configuration except that the first and second electrode layers were formed of only Ag.

(Example 2)
Using the stepping roll type film forming apparatus shown in FIG. 3, an electrode layer whose composition changes stepwise in the film thickness direction was formed. The substrate used was a polyimide resin sheet having a thickness of 50 μm, as in Example 1. Using four types of targets of Ag-Al alloy with Ag content of 90, 95 and 99 at% and 100 at% of Ag, while introducing a mixed gas of Ar and O ₂ (O ₂ : 6%), the above-mentioned An electrode layer having a four-stage composition was formed in this order from the substrate side. The film thickness was 200 nm in total of 40 nm, 40 nm, 40 nm, and 80 nm from the substrate side.

  When the adhesion force of the electrode layer was examined in the same manner as in Example 1, it was possible to obtain an excellent adhesion force equivalent to that in Example 1. Moreover, when the solar cell was produced and the photoelectric conversion efficiency was investigated, it was the photoelectric conversion efficiency equivalent to Ag100% similarly to Example 1. FIG.

(Example 3)
The electrode layer was formed in the same procedure as in Example 2 except that the stepping roll type film forming apparatus provided with the partition shown in FIG. 4 was used and the gas pressure during sputtering in each film forming chamber was changed. . When the change in the adhesion force of the obtained electrode layer was examined, it was found that only the gas pressure at the time of forming the layer in direct contact with the substrate had an effect on the adhesion force. Further, in the pressure range of 0.1 to 5 Pa, the adhesive force exceeded 850 N, which is a practical adhesive force.

Example 4
The electrode layers were formed in the same procedure as in Example 1 except that Zn and Sn were used instead of Al. When the adhesion force of these electrode layers was examined, an excellent adhesion force equivalent to that of Example 1 could be obtained. Moreover, when the solar cell was produced and the photoelectric conversion efficiency was investigated, it was the photoelectric conversion efficiency equivalent to Ag100% similarly to Example 1. FIG.

1 shows an embodiment of a solar cell according to the present invention, in which (a) is a plan view, (b) is a cross-sectional view taken along the line X-X ′, and (c) is a bottom view. It is a graph which shows the change of the composition with respect to the film thickness direction of the 1st electrode layer shown in FIG. 1, Comprising: When (a) is changing a composition in steps, (b)-(d) is a continuous composition. It is a case where it is changing. It is sectional drawing which shows typically the film-forming apparatus of a stepping system. It is sectional drawing which shows the case where a partition is provided between each film-forming chamber of the film-forming apparatus of FIG. (A) is sectional drawing which shows the continuous-type film-forming apparatus typically, (b) is a top view of the target.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 Sending roll 13 Winding roll 20 Film-forming part 21 Target 27 Cathode 28 Power supply 30 Partition 40 Film-forming part 41 Target 42-45 Partial target 47 Cathode 48 Electrode 50 Solar cell 51 Flexible substrate 52a 1st electrode layer 52b 1st Second electrode layer 53 Photoelectric conversion layer 54 Third electrode layer 55 Fourth electrode layer 56 First hole 57 Second hole 58 Cutting portion

Claims (8)

  A solar cell in which an electrode layer is formed on an insulative flexible substrate, wherein the electrode layer is composed of a plurality of layers containing Ag, and among the plurality of layers, on the substrate The adjacent layer includes at least one oxide selected from the group consisting of copper oxide, aluminum oxide, zinc oxide and tin oxide, and the content of Ag in the electrode layer is adjacent to the substrate. A solar cell that changes stepwise or continuously from the layer toward the film thickness direction.   2. The solar cell according to claim 1, wherein the substrate is at least one selected from the group consisting of polyamide, polyimide, liquid crystal polymer, polyethylene naphthalate, polyethylene terephthalate, polyetherimide, polyethersulfone, polystyrene, and polycarbonate. .   The layer adjacent to the substrate among the plurality of layers of the electrode layer has an Ag content of 2 to 99.95 at%, and at least one other layer has an Ag content of 95 at% or more. Or the solar cell of 2.   The change in the content of Ag in the electrode layer is a stepwise or continuous increase from the layer adjacent to the substrate in the film thickness direction. Solar cell.   The change in the content of Ag in the electrode layer is a stepwise or continuous decrease from the layer adjacent to the substrate toward the film thickness direction. Solar cell.   4. The change in the content of Ag in the electrode layer increases after decreasing stepwise or continuously in the film thickness direction from a layer adjacent to the substrate. 5. The solar cell according to item. Forming a layer of silver and at least one oxide selected from the group consisting of copper oxide, aluminum oxide, zinc oxide and tin oxide on an insulating flexible substrate;
Further forming on the layer at least one layer composed of silver or silver and the at least one oxide so that the silver content changes stepwise or continuously from the silver content of the layer, And a step of forming an electrode layer together with the layer.   The method for manufacturing a solar cell according to claim 7, wherein each layer is formed by sputtering to form the electrode layer, and the gas pressure at that time is 0.1 to 5 Pa.

Images