JP4459424B2 - Method for manufacturing thin film solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor thin film solar cell, and more particularly to a method for manufacturing a back surface sealed thin film solar cell.
[0002]
[Prior art]
FIG. 3 is a schematic cross-sectional view illustrating a conventional method of sealing the back surface of a thin film solar cell using a vacuum laminator, and FIG. 4 shows an example of the thin film solar cell sealed by the method. It is typical sectional fragmentary drawing. In each drawing of the present application, the thickness, length, width, and the like are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Further, the same reference numerals in the drawings represent the same or corresponding parts.
[0003]
As shown in FIG. 4, in the thin film solar cell, the photoelectric conversion unit layer 2 is generally formed on a transparent glass substrate 1 having a thickness of about 4 mm. The photoelectric conversion unit layer 2 generally has a very thin thickness of about several μm, and includes a front electrode layer of a transparent conductive oxide, a semiconductor photoelectric conversion layer, and a back metal electrode layer sequentially stacked on the substrate 1. It is out. The peripheral portion of the photoelectric conversion unit layer 2 is retracted about 5 mm from the periphery of the glass substrate 1 in order to protect the end face. A thin-film solar cell including a plurality of submodules on one substrate 1 (see JP 2000-49369 A) includes an internal electrical wiring portion 3 disposed on the photoelectric conversion unit layer 2. The internal wiring portion 3 includes a local insulating sheet 3a and a metal foil 3b thereon. Here, the insulating sheet 3a and the metal foil 3b each have a thickness of 0.2 mm, for example, and the entire internal wiring portion 3 has a thickness of about 0.4 mm. In addition, the internal wiring portion 3 is usually disposed at a position about 40 mm away from one side of the substrate 1 because of the relationship with the position of a current extraction terminal box (not shown).
[0004]
The photoelectric conversion unit layer 2 and the internal wiring part 3 are protected by sealing protection means including a bonding resin 4 and a protective film 5a bonded thereby. This sealing protection means is for preventing the photoelectric conversion characteristics from deteriorating due to physical or chemical influence from the outside on the back side of the thin film solar cell, and is applied using a vacuum thermocompression bonding apparatus. Can be done.
[0005]
In FIG. 3, a vacuum laminator as an example of a vacuum thermocompression bonding apparatus is shown in a schematic cross-sectional view. The vacuum laminator 100 includes a lower container 11 and an upper container 12, which are detachable from each other via an airtight seal 13. The lower container 11 and the upper container 12 include intake / exhaust ports 11a and 12a, respectively, and the upper container 12 also includes a diaphragm portion 12b made of synthetic rubber.
[0006]
In the lower container 11, a mounting table 14 incorporating a heater is provided, which acts as a heating plate. The substrate 1 is placed on the mounting table 14 that has been heated to a predetermined temperature in advance. A photoelectric conversion unit layer 2 and an internal wiring portion 3 are already formed on the substrate 1, and a bonding resin sheet (including a curing agent) 4 and a protective material layer 5 (a protective film in the case of FIG. 4) 5a) is superimposed. In this state, the lower container 11 and the upper container 12 are coupled via the hermetic seal 13, and the inside of these containers is exhausted by a rotary pump (not shown) via the intake / exhaust ports 11a and 12b. The
[0007]
The bonding resin sheet 4 is heated by the mounting table 14 that has been heated to a predetermined temperature by a built-in heater, and the sheet 4 is softened and melted. At this time, atmospheric pressure is introduced into the upper container 12 through the intake / exhaust port 12a, and the diaphragm 12b is pressed onto the protective material layer 5 at the atmospheric pressure. In this state, the molten bonding resin 4 can be cured in the vacuum laminator 100.
[0008]
The reason why the vacuum laminator is used for forming the sealing protection means is to prevent air bubbles from being mixed into the boundary or inside of the sealing resin layer 4 which is cured after being melted.
[0009]
[Problems to be solved by the invention]
In the conventional thin film solar cell by the sealing method as shown in FIG. 4, a composite film in which an aluminum foil is sandwiched between PVF (polyvinyl fluoride) films is generally used as the protective film 5a. Here, the reason why the aluminum foil is sandwiched is to effectively prevent the permeation of moisture. However, since the PVF film sandwiching the aluminum foil is thin, pinholes and scratches may occur in some cases, and a leakage current through the aluminum foil may occur on the back surface of the solar cell. Further, if such a leakage current flows in the presence of moisture, the corrosion of the aluminum foil may proceed.
[0010]
In view of such problems in the conventional technology, the present invention has an object to provide a method for manufacturing a back surface-sealed thin film solar cell with higher reliability.
[0011]
[Means for Solving the Problems]
According to the present invention, the back surface of the thin film photoelectric conversion unit layer is sealed by the bonding resin sheet and the sealing glass plate , including the internal electrical wiring portion disposed on the thin film photoelectric conversion unit layer formed on the glass substrate. In the method for manufacturing a thin film solar cell, a laminate in which a bonding resin sheet covering the entire back surface of the photoelectric conversion unit layer and a sealing glass plate are sequentially laminated is prepared, and the laminate is placed on a hot plate of a vacuum laminator. In addition, a spacer having a predetermined thickness is disposed at the end of the laminated body, the vacuum laminator is exhausted, and after the bonding resin sheet is melted, the sealing glass plate is pressed by the diaphragm in the laminator, and the bonding resin is put in this state. It is characterized in that it is cured to perform back surface sealing .
[0012]
It is preferable that the spacer has a thickness increased by 0 to 1 mm from the thickness from the lower surface of the substrate to the upper surface of the sealing glass plate in the internal wiring portion after the bonding resin is cured.
[0013]
The diaphragm of the vacuum laminator preferably presses the sealing glass plate with a pressure in the range of 0.02 MPa to atmospheric pressure.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In view of the above-mentioned problem in the conventional method of sealing the back surface of a thin film solar cell using a composite film 5a in which an aluminum foil is sandwiched with a PVF film, the present inventor has a thickness of 3 instead of the composite protective film 5a. A sealing method using a protective glass plate of about 4 mm was examined. This is because the glass plate is much stronger than the composite protective film 5a and has an excellent ability to block moisture permeation.
[0015]
FIG. 2 is a schematic partial sectional view showing an example of a thin film solar cell whose back surface is sealed using a protective glass plate. Also in the thin film solar cell of FIG. 2, the photoelectric conversion unit layer 2 is formed on the glass substrate 1 similarly to FIG. On the photoelectric conversion unit layer 2, an internal wiring portion 3 is disposed. And these photoelectric conversion unit layers 2 and the internal wiring part 3 are protected by the sealing protection means containing the joining resin 4 and the protective glass board 5b joined by it.
[0016]
By the way, when the protective glass board 5b was utilized instead of the protective film 5a for back surface sealing of a thin film solar cell, it turned out that another incidental problem arises. Unlike the protective film 5a, this is a problem caused by the protective glass plate 5b having a small elasticity and being a brittle material.
[0017]
That is, as in the case of FIG. 3, a bonding resin sheet 4 and a layer of protective material on the glass substrate 1 on which the photoelectric conversion unit layer 2 and the internal wiring part 3 are formed (however, in the case of the thin film solar cell of FIG. When the thin film solar cell is taken out after the joining resin layer 4 is cured from being melted in a state where the plate 5b) is stacked and pressed with the diaphragm 12b in the vacuum laminator 100, the protective glass plate 5b is elastically deformed during pressing. Therefore, as shown in FIG. 2, the protective glass plate 5b is fixed in a slightly curved state from the convex portion B such as the internal wiring portion 3 to the end portion A of the substrate 1 close thereto. . And when this bending degree was large, it turned out that the phenomenon of the delayed fracture that the protective glass plate 5b cracks after several days after sealing passes.
[0018]
Specifically, with reference to FIG. 2, a thin film photoelectric conversion unit layer 2 having a thickness of several μm was formed on a glass substrate 1 having a thickness of 4 mm. On the photoelectric conversion unit layer 2, a local insulating sheet 3a having a thickness of 0.2 mm made of a glass fiber nonwoven fabric and a copper foil 3b having a thickness of 0.2 mm thereon were disposed. And the EVA (ethylene vinyl acetate copolymer) joining resin sheet 4 containing a hardening | curing agent and the protective glass plate 5b of thickness 3mm were piled up so that the photoelectric conversion unit layer 2 and the internal wiring part 3 might be covered. This laminate was placed on a mounting table 14 heated to 165 ° C. in the vacuum laminator of FIG. Then, after the vacuum laminator 100 was evacuated and the EVA bonded resin sheet 4 was melted, atmospheric pressure was introduced through the intake / exhaust holes 12a of the upper container 12, and the protective glass plate 5a was pressed by the diaphragm 12b. After the pressure of the diaphragm was maintained for 20 minutes to cure the bonding resin layer 4, the back surface sealed thin film solar cell was taken out from the laminate 100.
[0019]
In this case, the distance between the substrate end A and the internal wiring portion B is 40 mm, and the thickness between the lower surface of the glass substrate 1 and the upper surface of the protective glass plate 5b is between the internal wiring portion B and the substrate end A. There was a difference of 0.37 mm between them. In the thin film solar cell whose back surface was sealed in such a state using the protective glass plate 5b, cracks occurred in the protective glass plate 5b when 5 days had passed after the sealing.
[0020]
In view of the above-mentioned incidental problems found by the present inventor, the present inventor further conducted various studies.
[0021]
As a result, as shown in FIG. 1, if the back surface sealing of the thin film solar cell is performed with the spacer 6 having a predetermined thickness disposed at the end of the substrate 1 in the vacuum laminator 100, the protective glass plate 5b It was found that the delayed destruction of can be prevented. In that case, the thickness of the spacer 6 is desirably 0 to 1.0 mm larger than the thickness of the internal wiring portion B after the bonding resin layer 4 is cured, and more preferably 0.2 to 1.0 mm. Preferably it is larger by 0.5 to 1.0 mm.
[0022]
More specifically, under the same conditions as those of the thin film solar cell described with reference to FIG. 2 described above, the back surface sealing as shown in FIG. 1 is performed using a spacer 6 having a thickness of 8 mm. When stopping, the difference in thickness between the B part and the A part was reduced to 0.18 mm, and the protective glass plate 5b was not delayed and destroyed even after 6 months had elapsed after sealing.
[0023]
Further examination shows that it is preferable to reduce the pressing pressure of the diaphragm 12b as well as the spacer 6 at the time of sealing the back surface. The press pressure of the diaphragm 12b can be adjusted by a pressure control valve (not shown) connected to the intake / exhaust port 12a of the upper container 12. Specifically, when the press pressure of the diaphragm 12b is reduced to 0.05 MPa, which is smaller than the atmospheric pressure, the difference in thickness between the B part and the A part is further reduced to 0.12 mm, and the distortion of the protective glass plate 5b. Was further relaxed. However, if the pressing pressure of the diaphragm 12b is less than 0.02 MPa, bubbles start to remain in the bonding resin layer 4 in the vicinity of the convex portion of the internal wiring portion 3, which is not preferable.
[0024]
On the other hand, in the thin film solar cell under the same conditions as described above, when only the press pressure of the diaphragm 12b is reduced to 0.05 MPa without using the spacer 6, the difference in thickness between the B part and the A part is 0. Although it became 23 mm, a crack occurred in the protective glass plate 5b two days after sealing. Here, in the case where the difference in thickness between the B part and the A part is 0.37 mm, the protective glass plate 5b is cracked after 5 days after the sealing, and after the sealing, a shorter 2 It is considered that the cracks occurred on the basis of the non-uniformity in the protective glass plate 5b, which is a brittle material.
[0025]
In the above specific example, the temperature of the mounting table 14 is set to 165 ° C., but the temperature can be preferably set within a range of 160 to 180 ° C. If the set temperature is high, the bonding resin 4 is melted quickly and curing proceeds rapidly. Conversely, if the set temperature is low, the melting and curing of the bonding resin 4 can be delayed.
[0026]
Moreover, although the example which used the EVA sheet | seat as a joining resin sheet was demonstrated in the above specific example, another suitable joining resin sheet can also be used like a PVB (polyvinyl butyral) sheet | seat containing a hardening | curing agent, for example. .
[0027]
【The invention's effect】
As described above, according to the manufacturing method of the present invention, it is possible to backside reliable than the conventional to provide a thin film solar cell sealed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating a back surface sealing method of a thin film solar cell using a vacuum laminator according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional partial view showing a state where a back surface of a thin film solar cell is sealed using a protective glass plate.
FIG. 3 is a schematic cross-sectional view illustrating a conventional back surface sealing method for a thin film solar cell using a vacuum laminator.
FIG. 4 is a schematic partial sectional view showing a thin-film solar cell whose back surface is sealed by a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass substrate, 2 Photoelectric conversion unit layer, 3 Internal wiring part, 3a Local insulation sheet, 3b Metal foil, 4 Bonding resin layer, 5 Layer of protective material, 5a Composite protective film, 5b Sealing glass plate, 11 Lower side Vessel, 11a intake / exhaust port, 12 upper vessel, 12a intake / exhaust port, 12b diaphragm, 13 hermetic seal, 14 mounting table, 100 vacuum laminator.

Claims (3)

The internal electric wiring portion disposed on formed on a glass substrate thin film photoelectric conversion unit layer seen including, by bonding a resin sheet and the sealing glass plate of thin-film solar cell rear surface is sealed thin film photoelectric conversion unit layer In the manufacturing method,
Prepare a laminate in which a bonding resin sheet and a sealing glass plate covering the entire back surface of the photoelectric conversion unit layer are stacked in order,
Place the laminate on the hot plate of the vacuum laminator and place a spacer with a predetermined thickness at the end of the laminate,
The vacuum laminator is evacuated, and after the bonding resin sheet is melted, the sealing glass plate is pressed by a diaphragm in the laminator, and the bonding resin is cured in that state to perform back surface sealing. A method for producing a thin-film solar cell. The spacer has a thickness that is increased by a range of 0 to 1 mm from a thickness from a lower surface of the substrate to an upper surface of the sealing glass plate in the internal wiring portion after the bonding resin is cured. The manufacturing method of the thin film solar cell of Claim 1 characterized by these. The method of manufacturing a thin-film solar cell according to claim 1 or 2, wherein the diaphragm presses the sealing glass plate with a pressure within a range of 0.02 MPa to atmospheric pressure.

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