JP4743934B2 - Manufacturing method of integrated hybrid thin film solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an integrated thin film solar cell, and more particularly to a method for manufacturing an integrated thin film solar cell including a crystalline silicon-based photoelectric conversion unit layer having high photoelectric conversion efficiency.
[0002]
[Prior art]
In FIG. 1, a typical example of an integrated thin film solar cell is shown in a schematic sectional view. In each drawing of the present application, dimensional relationships such as length and thickness are appropriately changed for clarity and simplification of the drawings, and do not reflect actual dimensional relationships.
[0003]
In the integrated thin film solar cell 10 as shown in FIG. 1, a glass plate is usually used as the substrate 1. A transparent electrode layer 2 is formed on the glass substrate 1. The transparent electrode layer 2 is separated into a plurality of transparent electrodes corresponding to a plurality of photoelectric conversion cells by separation grooves 2a formed by laser scribing. As the transparent electrode layer 2, a film of transparent conductive oxide (TCO) such as SnO ₂ , ITO (indium tin oxide), ZnO or the like, or a laminate thereof can be generally used.
[0004]
A semiconductor layer 3 including one or more photoelectric conversion unit layers is formed on the transparent electrode layer 2. This semiconductor layer 3 is also divided into a plurality of photoelectric conversion regions corresponding to a plurality of cells by dividing grooves 3a formed by laser scribing.
[0005]
A back electrode layer 4 is formed on the semiconductor layer 3, and the semiconductor layer dividing groove 3 a is filled with the back electrode layer 4. The back electrode layer 4 is also separated into a plurality of back electrodes corresponding to a plurality of cells by separation grooves 4a formed by laser scribing. As the back electrode layer 4, various metal films such as Ag, Al, and Cr can be used. The back electrode layer 4 may be formed as a laminate of a TCO film and a metal film.
[0006]
As can be seen from FIG. 1, in the integrated thin film solar cell 10, the transparent electrode 2 of any cell is electrically connected to the back electrode 4 of the cell adjacent to the left side of the cell via the semiconductor layer dividing groove 3a. Yes. That is, the semiconductor layer dividing groove 3a also functions as a connection groove, whereby a plurality of cells adjacent to the left and right are connected in series. In each cell of such an integrated thin film solar cell 10, a region A where the transparent electrode 2 and the back electrode 4 overlap is an effective power generation region.
[0007]
Meanwhile, the semiconductor layer 3 can include one or more photoelectric conversion unit layers, but one photoelectric conversion unit includes an i-type layer sandwiched between a p-type layer and an n-type layer. The i-type layer that occupies most of the thickness of the photoelectric conversion unit is a substantially intrinsic semiconductor layer, and the photoelectric conversion action mainly occurs in the i-type layer. On the other hand, the p-type and n-type conductive layers play a role of generating a diffusion potential in the photoelectric conversion unit, and the value of the open-end voltage, which is one of the photoelectric conversion characteristics, depends on the magnitude of this diffusion potential. . However, these conductive layers are inactive layers that do not directly contribute to photoelectric conversion, and light absorbed by impurities doped in the conductive layer results in a loss that does not contribute to power generation. Therefore, it is preferable that the p-type and n-type conductive layers have as small a thickness as possible on the premise that a sufficient diffusion potential is generated.
[0008]
For this reason, the photoelectric conversion unit has an amorphous i-type photoelectric conversion layer that occupies the main part regardless of whether the p-type and n-type conductivity type layers included therein are amorphous or crystalline. Are referred to as amorphous units, and those having a crystalline i-type layer are referred to as crystalline units. Here, for example, the wavelength of light that can be photoelectrically converted by i-type amorphous silicon is up to about 800 nm on the long wavelength side, but i-type crystalline silicon photoelectrically converts light having a longer wavelength of about 1100 nm. can do. Therefore, the crystalline photoelectric conversion unit is expected to have higher photoelectric conversion efficiency than the amorphous photoelectric conversion unit.
[0009]
Further, as a method for improving the conversion efficiency of the thin film solar cell, there is a method of stacking two or more photoelectric conversion units into a tandem type. In this method, a front unit including a photoelectric conversion layer having a large energy band gap is arranged on the light incident side of the thin-film solar cell, and a photoelectric conversion layer having a small band gap (for example, SiGe alloy) is sequentially arranged behind the unit. By disposing the rear unit including the photoelectric conversion, it is possible to perform photoelectric conversion over a wide wavelength range of incident light, thereby improving the photoelectric conversion efficiency of the entire solar cell. Among such tandem-type thin film solar cells, a stack of an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit is called a hybrid thin film solar cell. That is, when FIG. 1 represents an integrated hybrid thin film solar cell, the semiconductor layer 3 includes an amorphous unit and a crystalline unit that are sequentially stacked.
[0010]
In the integrated thin film solar cell 10 as shown in FIG. 1, the back surface opposite to the glass substrate 1 is generally protected by a sealing protection means including a sealing resin layer and a protective film. 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.
[0011]
In FIG. 2, a vacuum laminator as an example of a vacuum thermocompression bonding apparatus is shown in a schematic 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 12b made of synthetic rubber. The diaphragm 12b can be heated via a heater and a metal plate not shown.
[0012]
In the lower container 11, a mounting table 14 containing a heater is provided. A thin film solar cell 10 as shown in FIG. 1 is disposed on the mounting table 14, and a sealing resin sheet (including a curing agent) 5 and a protective film 6 are stacked thereon. In this state, the lower container 11 and the upper container 12 are coupled through the hermetic seal 13, and the inside of these containers is exhausted by a rotary pump (not shown) through the intake / exhaust ports 11a and 11b. .
[0013]
Thereafter, the sealing resin sheet 5 is heated by the heater built in the mounting table 14, and the sheet 5 is softened and melted. At this time, the atmosphere is introduced into the upper container 12 through the intake / exhaust port 12a, and the diaphragm 12b is pressed onto the protective film 6. In this state, the melted sealing resin layer 5 can be completely cured in the vacuum laminator 100. However, since the vacuum laminator 100 is expensive and cannot process a large number of thin film solar cells at the same time, the thin film solar cell 10 is taken out from the vacuum laminator 100 when the sealing resin layer 5 is partially cured, and the sealing resin The complete curing of the layer 5 is generally performed by simultaneously processing a plurality of thin film solar cells in a separate curing furnace.
[0014]
The reason why the vacuum laminator is used for forming the sealing protection means is to prevent air bubbles from being mixed between the back surface of the thin film solar cell 10 and the protective film 6 and the sealing resin layer 5. is there.
[0015]
[Problems to be solved by the invention]
In the integrated thin-film solar cell manufactured as described above, considerably good photoelectric conversion characteristics have been obtained in recent years and have already been put into practical use.
[0016]
However, further improvement in photoelectric conversion characteristics is still desired in thin film solar cells, and in particular, improvement in characteristics of thin film solar cells including a crystalline photoelectric conversion unit layer is expected.
[0017]
Then, this invention aims at providing the manufacturing method which can further improve the photoelectric conversion characteristic of the integrated hybrid thin film solar cell containing an amorphous photoelectric conversion unit layer and a crystalline photoelectric conversion unit layer.
[0018]
[Means for Solving the Problems]
According to the present invention, the transparent electrode layer sequentially laminated on the transparent insulating substrate, at least one crystalline semiconductor photoelectric conversion unit layer, and the non-electrode disposed between the transparent electrode layer and the crystalline semiconductor photoelectric conversion unit layer. The crystalline semiconductor photoelectric conversion unit layer and the back electrode layer are separated by a plurality of separation grooves so as to form a plurality of photoelectric conversion cells, and the plurality of cells are electrically connected via a plurality of connection grooves. The integrated hybrid thin film solar cell is connected in series, and the back electrode layer and the back electrode separation groove for separating the back electrode layer into a plurality of regions are covered with a sealing protection means including a resin sealing layer and a protective film. In the manufacturing method, using a vacuum thermocompression bonding device to form a sealing protection means by laminating and bonding a sealing resin sheet to be a sealing resin layer and a protective film on the back electrode layer, In forming the stop protection means, with the pressure in the vacuum heat pressing apparatus is below 667 Pa, the temperature of the substrate is kept at least 30 seconds or more within the range of from the softening point of the sealing resin sheet to the lower 10 ° C. It is characterized by that.
[0019]
When forming the sealing protection means, the pressure in the vacuum thermocompression bonding apparatus is more preferably set to 133 Pa or less.
[0021]
An ethylene vinyl acetate copolymer can be used as the sealing resin sheet. In that case, the temperature of the substrate is maintained within a range of 90 to 100 ° C. for 30 seconds or more when forming the sealing protection means. It is preferable.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
(Comparative Example 1)
The inventor produced a thin-film solar cell 10 as shown in FIG. 1 under the same method and conditions as the conventional integrated thin-film solar cell of Comparative Example 1, and FIG. Seal protection was applied using a vacuum laminator 100 as shown. At this time, the glass substrate 1 having an area of 10 cm × 10 cm was used, and the number of stages of cells connected in series was ten. In addition, an SnO ₂ layer having a thickness of about 700 nm was formed as the transparent electrode layer 2, and the back electrode layer 4 included a ZnO layer having a thickness of about 80 nm and an Ag layer having a thickness of about 300 nm.
[0024]
As the semiconductor layer 3, a single semiconductor layer including only a single crystalline silicon photoelectric conversion unit layer having a thickness of about 2.5 μm is formed, and an amorphous silicon photoelectric conversion unit having a thickness of about 250 nm is formed. A hybrid semiconductor layer was formed in which the layer and a crystalline silicon-based photoelectric conversion unit layer having a thickness of about 2.5 μm were stacked. Hereinafter, a thin film solar cell including such a single type semiconductor layer 3 is referred to as a single thin film solar cell, and a thin film solar cell including the hybrid type semiconductor layer 3 is referred to as a hybrid thin film solar cell.
[0025]
As the sealing resin layer 5, an ethylene vinyl acetate copolymer (EVA) containing a curing (crosslinking) agent was used, and as the protective film 6, a Tedora (registered trademark) film, which is a polyvinyl fluoride film, was used. The sealing resin sheet 5 and the protective film 6 are placed on the back surface of the integrated thin film solar cell 10 on the mounting table 14 heated to 125 ° C., and immediately the lower container 11 is placed in the upper container 12. Both containers were evacuated after closing. Then, by pressing the protective film 6 with the diaphragm 12b heated to 125 ° C., the protective film 6 was bonded to the back surface of the thin-film solar cell 10 by the sealing resin layer 5 that was cured after melting.
[0026]
In this case, the vacuum degree in the lower container 11 was 1333 Pa (10 Torr) at a temperature of 100 ° C. at which the EVA sealing resin sheet 5 began to melt. The temperature of the sealing resin layer 5 was measured with a thermocouple. Thereafter, the sealing resin layer 5 was completely cured at 140 ° C. for 30 minutes in a separate curing furnace.
[0027]
The integrated thin-film solar cell in Comparative Example 1 manufactured in this way is irradiated with pseudo-sunlight having an energy density of 100 mW / cm ² with a spectral distribution of AM1.5 using a solar simulator. When the conversion characteristics were measured, the integrated single thin film solar cell had a fill factor (FF) of 69.8% and a conversion efficiency of 9.0% before being provided with the sealing protection means. Type hybrid thin-film solar cell had an FF of 71.0% and a conversion efficiency of 10.1%. On the other hand, after the sealing protection means is applied, the FF of the integrated single thin film solar cell and the integrated hybrid thin film solar cell is 70% and 71.5%, respectively, and the photoelectric conversion characteristics are improved. all right. The conversion efficiency is improved in proportion to FF.
[0028]
This means that in an integrated thin film solar cell including a crystalline photoelectric conversion unit layer, the sealing protection means provided using a vacuum laminator not only helps prevent deterioration of the photoelectric conversion characteristics, but rather improves the photoelectric conversion characteristics. It means that Such an improvement effect (hereinafter referred to as improvement effect E) is not recognized in an integrated thin film solar cell including only one or more amorphous photoelectric conversion unit layers.
[0029]
The following reasons can be considered as a cause of the above improvement effect E discovered by the present inventor for the first time. That is, the improvement effect E is not recognized by the integrated thin film solar cell including only one or more amorphous photoelectric conversion unit layers, but is detected by the integrated thin film solar cell including at least one crystalline photoelectric conversion unit layer. Therefore, it is considered that the carrier mobility is significantly higher in the crystalline photoelectric conversion layer than in the amorphous photoelectric conversion layer. Further, before the sealing protection means is provided, contaminants such as moisture adsorbed on the side wall of the back electrode separation groove 4a can act as carrier traps or extinction sites. The influence on the characteristics is considered to be remarkable for the crystalline photoelectric conversion layer in which the carrier has a high probability of reaching the side wall of the back electrode separation groove 4a due to its high mobility.
[0030]
In such a situation, if the integrated thin film solar cell is heated in a vacuum laminator under a reduced pressure even for a short time, it is considered that the amount of adsorbed contaminants on the side wall of the back electrode separation groove 4a is reduced. As a result, after applying the sealing protection means to the integrated thin film solar cell including the crystalline photoelectric conversion layer using a vacuum laminator, it is considered that the photoelectric conversion characteristics can be improved as compared to before the application.
[0031]
Based on the knowledge newly found by the present inventors as described above, integrated thin film solar cells as various examples and comparative examples as described below were further produced.
[0032]
Example 1
The integrated thin-film solar cell in Example 1 was basically manufactured under the same method and conditions as in Comparative Example 1. However, the temperature of the mounting plate was set to 90 ° C., and the sealing resin sheet 5 and the protective film 6 were stacked on the back surface of the integrated thin-film solar cell 10 to sufficiently equalize the temperature. And after closing the lower container 11 with the upper container 12, the inside of both containers was exhausted. The exhaust system pipe used at this time has an increased exhaust conductance, for example, by increasing its diameter compared to the conventional pipe. Then, the protective film 6 was pressed with the diaphragm 12b heated to 125 degreeC. At that time, it took about 30 seconds until the temperature of the sealing resin layer 5 reached from 90 ° C. to 100 ° C., and the degree of vacuum in the lower container 11 was increased to 667 Pa (5 Torr) at the time of 100 ° C. .
[0033]
The FF of the integrated single thin film solar cell thus produced in Example 1 was 70.1%, and the FF of the integrated hybrid thin film solar cell was 72.5%.
[0034]
(Example 2)
The integrated thin film solar cell in Example 2 was basically manufactured under the same method and conditions as in Example 1. However, a rotary pump with a larger exhaust capacity was used as a vacuum pump for exhausting the vacuum laminator. The degree of vacuum in the lower container 11 when the temperature of the sealing resin layer 5 was 100 ° C. was further increased to 133 Pa (1 Torr).
[0035]
The FF of the integrated single thin film solar cell produced in this way in Example 2 was 70.1%, and the FF of the integrated hybrid thin film solar cell was 73.0%.
[0036]
(Example 3)
The integrated thin-film solar cell as Example 3 was basically manufactured under the same method and conditions as in Example 2. However, in Example 3, in the state where the integrated thin film solar cell 10, the sealing resin sheet 5, and the protective film 6 are soaked at 90 ° C. on the mounting plate 14, the lower container 11 is the upper container 12. Both containers were evacuated after closing and the pressure in the lower container 11 was reduced to 133 Pa. Thereafter, both the mounting plate 14 and the diaphragm 12b were heated to 125 ° C., and the protective film 6 was pressed by the diaphragm 12b. At this time, it took 180 seconds for the sealing resin layer 5 to rise in temperature from 90 ° C. to 125 ° C.
[0037]
In such Example 3, the FF of the obtained integrated single thin film solar cell was 70.1%, and the FF of the integrated hybrid thin film solar cell was 73.5%.
[0038]
Example 4
The integrated thin film solar cell of Example 4 was basically manufactured under the same method and conditions as in Example 3. However, after the integrated thin film solar cell 10, the sealing resin sheet 5, and the protective film 6 are soaked on the mounting plate 14 maintained at 80 ° C., and the lower container 11 is closed by the upper container 12. Both containers were evacuated, and the mounting plate 14 and the diaphragm 12b were heated to 125 ° C. after the degree of vacuum in the lower container 11 reached 133 Pa. At this time, it took 210 seconds for the sealing resin layer 5 to rise in temperature from 80 ° C. to 125 ° C.
[0039]
The FF of the integrated single thin film solar cell thus obtained in Example 4 was 70.1%, and the FF of the integrated hybrid thin film solar cell was 72.5%.
[0040]
(Comparative Example 2)
The integrated thin film solar cell of Comparative Example 2 was produced basically under the same method and conditions as in Example 4. However, the temperature of the mounting plate 14 was set to 105 ° C., and the thin film solar cell 10, the sealing resin sheet 5, and the protective film 6 were soaked thereon. Then, after closing the lower container 11 with the upper container 12, both containers were evacuated, and the diaphragm 12b at 125 ° C. was pressed against the protective film 6. At this time, it took 120 seconds for the temperature of the sealing resin layer 5 to rise from 105 ° C. to 125 ° C., and the degree of vacuum in the lower container 11 at 125 ° C. was 133 Pa.
[0041]
The FF of the integrated single thin film solar cell thus obtained in Comparative Example 2 was 70.0%, and the FF of the integrated tandem thin film solar cell was 71.5%.
[0042]
In order to further improve the photoelectric conversion characteristics of the integrated thin film solar cell provided with the sealing protection means from the comparison between various comparative examples and examples as described above, the melting start temperature of the sealing resin sheet 5 It can be seen that a low pressure of 667 Pa or less is required as the degree of vacuum at. Further, such a degree of vacuum is required to be maintained for a predetermined time or more and at least 1 second or more within the range from the softening point of the sealing resin sheet to 10 ° C. That is, in Comparative Example 2, since the sealing resin sheet 5 is already melted at 105 ° C. before the lower container 11 is evacuated, it is sufficient to remove the adsorbed contaminants on the side wall of the back electrode separation groove 4a. It is thought that this could not have been done.
[0043]
In addition, although the example which utilized EVA as the sealing resin sheet 5 was demonstrated in the above-mentioned comparative example and Example, ethylene vinyl acetate triallyl isocyanate (EVAT), polyvinyl butyral (PVB), polyisobutylene (PIB), etc. are also included. Can be used. As the curing agent, 2,5-dimethylhexane-2,5-dihydroperoxide or the like can be used. Furthermore, as the protective film 6, in addition to the fluororesin film, an organic film such as polyethylene terephthalate (PET) or a composite film in which a metal box such as an aluminum foil is sandwiched between organic films can be used.
[0044]
Moreover, as a vacuum pump, it cannot be overemphasized that other types of pumps, such as a mechanical booster pump, may be used together with a rotary pump.
[0045]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a manufacturing method that can further improve the photoelectric conversion characteristics of an integrated hybrid thin film solar cell including an amorphous photoelectric conversion unit layer and a crystalline photoelectric conversion unit layer. .
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a typical example of an integrated thin film solar cell.
FIG. 2 is a schematic cross-sectional view showing an example of a vacuum thermocompression bonding apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass substrate, 2 Transparent electrode layer, 2a Transparent electrode separation groove, 3 Semiconductor layer, 3a Semiconductor layer division groove, 4 Back electrode layer, 4a Back electrode separation groove, 5 Sealing resin sheet, 6 Protective film, 10 Integrated thin film Solar cell, 11 lower container, 11a intake / exhaust port, 12 upper container, 12a intake / exhaust port, 12b diaphragm, 13 airtight seal, 14 mounting table, 100 vacuum thermocompression bonding apparatus.

Claims (4)

Transparent electrode layer sequentially laminated on transparent insulating substrate, at least one crystalline semiconductor photoelectric conversion unit layer, and amorphous semiconductor photoelectric conversion disposed between the transparent electrode layer and the crystalline semiconductor photoelectric conversion unit layer The unit layer and the back electrode layer are separated by a plurality of separation grooves so as to form a plurality of photoelectric conversion cells, and the plurality of cells are electrically connected in series via a plurality of connection grooves. Further, the back electrode layer and the back electrode separation groove for separating the back electrode layer into a plurality of regions are a method for manufacturing an integrated hybrid thin film solar cell covered with a sealing protection means including a resin sealing layer and a protective film. And
In order to form the sealing protection means by laminating and bonding the sealing resin sheet to be the sealing resin layer and the protective film on the back electrode layer, the sealing protection is used. When forming the means, the pressure in the vacuum thermocompression bonding apparatus is 667 Pa or less, and the temperature of the substrate is at least 30 seconds or more within the range from the softening point of the sealing resin sheet to 10 ° C. below it. A method of manufacturing an integrated hybrid thin film solar cell, wherein the integrated hybrid thin film solar cell is held. 2. The method of manufacturing an integrated hybrid thin film solar cell according to claim 1, wherein when forming the sealing protection means, the pressure in the vacuum thermocompression bonding apparatus is set to 133 Pa or less. The sealing resin sheet is made of an ethylene vinyl acetate copolymer, and the temperature of the substrate is maintained within a range of 90 to 100 ° C. for 30 seconds or more when forming the sealing protection means. The manufacturing method of the integrated hybrid thin film solar cell of Claim 1 or 2 . The pressure of the vacuum heat-pressing the device prior to or less 667 Pa, according to any one of claims 1 to 3, characterized by heating the substrate at a temperature lower than the softening point of the sealing resin sheet Manufacturing method of integrated hybrid thin film solar cell.

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