JP3419108B2 - Manufacturing method of thin film solar cell - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film solar cell.

[0002]

2. Description of the Related Art Conventionally, a thin film solar cell including amorphous silicon is formed by sequentially laminating a transparent electrode layer, a thin film semiconductor layer, and a back electrode layer on an insulating transparent substrate. The generated electric power is obtained by extracting the electron-hole pairs generated in the thin film semiconductor layer by the light incident from the side to the transparent electrode layer side and the back electrode layer side using the internal electric field of the pn junction. In such a thin-film solar cell, various improvements have been made so far in order to increase the amount of light entering the thin-film semiconductor layer. For example, a transparent electrode layer, an amorphous silicon layer having a p-i-n junction as a thin film semiconductor layer, and a back electrode layer are sequentially laminated on an insulating transparent substrate, and the back electrode layer has high reflectance in an effective wavelength range. It has been attempted to increase the amount of light reaching a thin film semiconductor layer by reflecting incident light between a back electrode layer and a transparent electrode layer using a silver electrode. The purpose of this is to increase the reflectance of the back electrode to effectively use the long-wavelength light that has passed through the inside of the thin film semiconductor layer, thereby improving the photocurrent. As described above, silver (Ag) is most commonly used as the back electrode material having a high reflectance.

[0003]

However, silver has poor adhesion strength to thin film semiconductors and ceramics, and silver is sintered by heat treatment or the like to obtain a practical level of adhesion strength as a back electrode of a thin film solar cell. A method of intentionally adding impurities has been adopted. However, high temperature exposure by heat treatment is not suitable for thin film semiconductors in terms of diffusion rate of metal components, and the addition of impurities significantly reduces the reflectance of silver, making it impossible to effectively use the long-wavelength light described above. Therefore, it has been a problem that silver alone cannot be used as a back electrode of a thin film solar cell at a practical level. On the other hand, a high reflectance back electrode structure has been proposed in which a high reflectance metal such as silver or aluminum is laminated on a transparent conductive metal compound such as indium tin oxide, tin oxide, zinc oxide or cadmium sulfide. However, although the adhesive strength of aluminum is lower than when it is directly laminated on a thin film semiconductor, and the adhesive strength of silver is slightly higher than when it is simple substance, it is not at a practical level. It was And regarding these back electrode structures,
At present, it was used only for producing top data for presentations at academic conferences.

[0004]

The present invention solves these problems and provides a method for producing a thin film solar cell having a back electrode structure which has both high adhesive strength with a thin film semiconductor layer and high reflectance. is there. Such invention, a transparent electrode layer on an insulating transparent substrate, a thin film semiconductor layer, a method of manufacturing a thin film solar cell of sequentially stacking a back electrode layer, a first transparent conductive on the thin film semiconductor layer After laminating the metal compound layer, the transparent conductive metal compound plasma region and silver or
Part of each plasma region with aluminum alone
Inside the reaction chamber, where
In a region in which active species composing the region are mixed, the substrate on which the first transparent conductive metal compound layer is laminated is moved from the transparent conductive metal compound side toward the silver or aluminum simple substance side, On the transparent conductive metal compound layer of
Second transparent conductive metal compound layer and silver or aluminum single
By laminating the body layer before on the thin film semiconductor layer
Serial is a method for manufacturing a thin-film solar cells laminated first transparent conductive metal compound layer and the back electrode layer made of the second transparent conductive metal compound layer and the silver or pure aluminum layer. And said plurality of possible to form a plasma region by applying a voltage to the sputtering target; plasma territory a discharge power density to form a plasma region by the transparent conductive metal compound according to the silver or pure aluminum
10% or less of the discharge power density forming the zone ;
The transparent conductive metal compound used to form the plasma region, it is used the first transparent conductive metal compound layer and the same material; in the first transparent conductive metal compound, indium tin oxide, tin oxide , zinc oxide, may be employed in combination, the use of one of cadmium sulfide.

[0005]

In the method of manufacturing a thin film solar cell of the present invention, the adhesive strength of the back electrode is improved by the following actions. First, a transparent electrode layer such as indium tin oxide (hereinafter simply referred to as ITO), tin oxide (hereinafter simply referred to as SnO2), zinc oxide (hereinafter simply referred to as ZnO), and amorphous silicon on an insulating transparent substrate such as glass. Thin film semiconductor layers such as
At this time, the thin film semiconductor layer is a p-type, i-type, and n-type stacked body. Next, a first transparent conductive metal compound layer is laminated on this thin film semiconductor layer. Adhesive strength between the thin film semiconductor layer and the first transparent conductive metal compound layer is of a sufficiently practical level. Then, following this, the transparent conductive metal compound formed in the reaction chamber and silver or
In a plurality of plasma regions adjacent to each other by a simple substance of minium ,
The substrate on which the first transparent conductive metal compound layer is laminated is moved from the transparent conductive metal compound side toward the simple silver or aluminum side, and the second transparent conductive metal compound layer is formed on the first transparent conductive metal compound layer. Metal compound layer and silver or aluminum
The body layers are sequentially laminated. The back electrode is formed by stacking the first transparent conductive metal compound layer, the second transparent conductive metal compound layer, and the simple silver or aluminum layer on the thin film semiconductor layer in this manner. Conventionally, silver (hereinafter simply referred to as “A”) is directly formed on the first transparent conductive metal compound layer referred to here.
g)) and aluminum (hereinafter simply referred to as Al) are laminated, but in this case, different materials come into contact with each other, resulting in a decrease in adhesive strength as described above. However, in the above method of the present invention, the second transparent conductive metal compound layer and the silver or silver compound are formed on the first transparent conductive metal compound layer .
Is a transparent conductive metal when laminated with a single aluminum layer
By forming a plurality of adjacent plasma regions of the compound and simple substance of silver or aluminum , the composition of the second transparent conductive metal compound layer is adjusted from the interface side with the first transparent conductive metal compound layer to silver or aluminum. It is possible to continuously increase the content ratio of the constituent components of the silver or aluminum simple substance layer contained in the second transparent conductive metal compound layer toward the interface side with the simple substance layer. Therefore, since the different kinds of materials do not come into contact with each other on the both interfaces as in the conventional case, the adhesive strength can be improved. Such silver or aluminum in the second transparent conductive metal compound layer
The gradient of the content ratio of the constituent elemental layer of the elemental aluminum is such that the active species forming the respective plasmas are diffused under a low pressure in the reaction chamber by arranging the plurality of plasma regions adjacent to each other, so that the two regions are mixed with each other. Because there exists. That is, the second transparent conductive metal compound and silver
Or, since the existence probability of the active species of each component is higher in each plasma region targeted for the aluminum single layer, the above-mentioned substrate on which the first transparent conductive metal compound layer is formed is moved in the plurality of plasma regions. By doing so, a gradient of the above components can be formed.

Due to the above-mentioned effects, forming the plurality of plasma regions by applying a voltage to the sputtering target leads to obtaining a more stable plasma region by a simple method and is also reproduced. It is possible to overlap some of the plurality of plasma regions with each other with good performance, and an effective action for obtaining the gradient with good reproducibility can be obtained. Further, the discharge power density in forming a plurality of plasma regions, the discharge power density of the second transparent conductive metal compound and less than 10% of the discharge power density of the metal, the second transparent conductive metal It is possible to make the compound layer as thin as possible.
That is, the second transparent conductive metal compound layer is the same as the first transparent conductive metal compound layer and silver or aluminum.
This is because it is provided in order to secure sufficient adhesive strength with the simple substance layer, so that it is desirable that it is as thin as possible. Discharge power density of the second transparent conductive metal compound, silver or exceeds 10% of the discharge power density of pure aluminum, silver or pure aluminum content of the second transparent conductive metal compound layer is low However, different materials come into contact with each other between the second transparent conductive metal compound layer and the silver or aluminum simple substance layer, and the adhesive strength aimed at by the present invention cannot be improved, which is not desirable. When the same material as the first transparent conductive metal compound layer is used for the transparent conductive metal compound used to form one of the plurality of plasma regions, contact between the first and second transparent conductive metal compound layers Are in contact with each other, and work to further improve the adhesive strength. Since any of ITO, SnO 2, ZnO, and cadmium sulfide (hereinafter simply referred to as CdS) is used for the first transparent conductive metal compound,
The effect of obtaining higher stability for the thin film semiconductor can be obtained.

[0007]

EXAMPLES Examples of the present invention will be described below. First, as an insulating transparent substrate, a glass substrate coated with silicon oxide (hereinafter simply referred to as SiO2) with a film thickness of 500 Å was used, and SnO2 containing fluorine was formed with a film thickness of about 8000 Å to be transparent. The electrode layer was formed. At this time, minute irregularities are formed on the surface of SnO 2 for the purpose of reducing loss due to reflection. Then, a p-type hydrogenated amorphous silicon carbide (hereinafter simply referred to as a-SiC: H) having a film thickness of 150 Å was formed on the substrate having the transparent electrode layer formed thereon by a plasma CVD apparatus to obtain i-type non-hydrogenated Amorphous silicon (hereinafter simply referred to as a-Si: H) with a film thickness of 4000 Å and n-type hydrogenated microcrystalline silicon (hereinafter simply referred to as μc-Si: H) with a film thickness of 500 Å are laminated in that order. A thin film semiconductor layer was obtained. Subsequently, as shown in FIG. 1, the substrate 5 having the thin film semiconductor layers laminated is set in the reaction chamber 3 of the magnetron type in-line sputtering apparatus 1 (substrate position A), and the reaction chamber 3 is vacuum pumped. 6x1
After exhausting to 0-6 torr, argon gas (hereinafter simply referred to as A
(indicated as r) is introduced from the gas system 4 to adjust the internal pressure to 3 × 10 −3.
The ZnO target 7 was sputtered while maintaining the torr and moving the substrate 5 at an RF power density of 0.8 W / cm 2, and a 800 Å first transparent conductive metal compound layer was laminated on the thin film semiconductor layer (substrate Position B). ZnO
The target 7 is made of aluminum oxide (hereinafter simply referred to as Al2
5% Al is added in the form of O3). The distance between the ZnO target 7 and the substrate 5 is about 5 cm. Here, as shown in FIG. 1, the present sputtering apparatus 1
Adjacent to the ZnO target 7 and the Ag target 9
However, when the first transparent conductive metal compound layer is laminated, the Ag target 9 is not discharged.

Next, the substrate 5 on which the first transparent conductive metal compound layer is laminated is returned to the substrate position A, the Ag target 9 has an RF power density of 0.8 W / cm 2, and the ZnO target 7 has 0.05 W. Each is discharged at an RF power density of / cm 2. Then, as shown in FIG.
A plurality of plasma regions Pz and Pa are formed on the target 7 and the Ag target 9, and a part where the plurality of plasma regions Pz and Pa overlap each other, that is, two plasma regions Pz and Pa. An extremely weak plasma region Pza in which active species due to plasma are mixed is formed. In such a discharge state, the substrate 5a on which the first transparent conductive metal compound layer described above is laminated is placed at the substrate position A.
From the substrate position to the substrate position C, the second transparent conductive metal compound layer and the metal layer made of Ag were continuously laminated. At this time, the discharge power density of the ZnO target 9 is Ag.
Since the discharge power density of the target 7 is as small as about 10% or less, a very small amount of ZnO starts to be stacked in the vicinity of the ZnO target 9 (substrate position D), and at the same time, the plasma region moves as the substrate 5a moves. The Ag active species present in Pza will start to stack. This is because the film formation rate in sputtering is 1 discharge power density.
This is because if it becomes 0% or less, it will decrease in the order of one to several digits. Then, the substrate 5a continues to have a plasma region P.
Since it moves from za to the plasma region Pa, the proportion of Ag in the active species that contributes to the deposition gradually increases. When the substrate 5a reaches the vicinity of the Ag target 7 (substrate position E), a sufficient discharge power density is given to the Ag target 7, so that almost 100% A
g metal layers are stacked.

Therefore, in this embodiment, the second transparent conductive metal compound layer is laminated until the substrate 5 reaches the substrate position E from the substrate position D, and then the second transparent conductive metal compound layer approaches the substrate position E. After that, Ag is laminated, and a back electrode having a three-layer structure is formed together with the first transparent conductive metal compound layer which is laminated first.

The Ag used here is a material capable of obtaining a high reflectance as the back electrode layer, and Al is used as the second highest reflectance. Both have a thickness of 100
0 Å is the thickness necessary to obtain the characteristics of the solar cell, but it is appropriately set within a range of up to about 1 μm depending on various purposes such as mechanical strength maintenance and coverage of the connection step portion in the integrated structure. Further, Ag may be laminated on the second transparent conductive metal compound layer to secure the reflectance, and Al may be further laminated thereon to secure the mechanical strength.

Further, the drawings referred to are merely for specifically explaining the content of the present invention, and strictly define the regions where the second transparent conductive metal compound layer and Ag are laminated respectively. The plasma regions Pz, Pa, and Pza are not shown, and the plasma regions Pz, Pa, and Pza are not limited to the positions shown in the drawing.

With respect to the thin film solar cell of the present invention thus produced, a back electrode composed only of Ag was used in Comparative Example 1 by a conventional manufacturing method, and a back electrode having a two-layer structure of ZnO and Ag was used in Comparative Example 2. Each one was manufactured, and the adhesive strength and power generation characteristics of the back electrodes of both were investigated. here,
Regarding the adhesive strength of the back surface electrode, a peeling test using "paste and peelable tape" and "Scotch tape" manufactured by Sumitomo 3M Ltd.
The evaluation was made by the short circuit current density at a light intensity of −100 mW / cm 2. The relationship between the adhesive strength of the above tapes is "tape that can be pasted and removed"<"Scotch tape
Is. As a result, in Comparative Example 1, the tape was easily peeled off with the "stickable tape", and in Comparative Example 2, the "Scotch tape".
Most of the backside electrode peeled off due to Ag and slightly Ag around the substrate.
Was only left. Then, when the peeled portion was observed, it was found that ZnO remained and peeled at the Ag / ZnO interface. On the other hand, the back electrode of the present invention did not peel at all with either "pasted and peelable tape" or "Scotch tape", and when a peeling test was conducted with gum tape, peeling of the back electrode did not occur and glass was used instead. The result was that the substrate was cracked. As described above, according to the present invention, the adhesion strength of the back electrode can be dramatically improved in the thin film solar cell without using special heat treatment such as sintering while using Ag as the back electrode material.

Regarding the power generation characteristics, the short-circuit current density was 17 mA / cm 2 in both Comparative Example 1 and Comparative Example 2, whereas it was 18 mA / cm 2 in the present invention, and the reflectance at the back electrode layer was also improved. It turned out. The cause of this is that the interface with low adhesive strength in each comparative example is a discontinuous surface in microscopic view, and one of the reasons is that efficient reflection is not performed by this. I can guess.

In addition to the above examples, in the present invention, glass is used as an insulating transparent substrate and SiO 2 is used as an ion barrier film.
Coated with P or P that has been attracting attention in recent years
A heat resistant transparent resin film such as ET or polyimide can also be used. When such a transparent resin film is used, the solar cell can be made flexible. Further, as the transparent electrode layer, ITO, SnO2 or the like can be used in addition to ZnO, and as described above, it is preferable that the surface is provided with an uneven shape so that long wavelength light can be confined inside the thin film semiconductor layer. As the first transparent conductive metal compound layer, ITO, SnO2 or the like can be used in addition to ZnO. In order to obtain higher adhesive strength, the same materials should be brought into contact with each other in the back electrode layer, that is, It is desirable that the first transparent conductive metal compound layer and the second transparent conductive metal compound layer are made of the same material. As the thin film semiconductor layer, one p-i-type of an amorphous silicon semiconductor as described in the above embodiment is used.
In addition to those having an n-junction, tandem type in which a plurality of such layers are stacked, thin film polycrystalline silicon, copper indium selenide (hereinafter simply referred to as CuInSe2)
A system semiconductor and a composite film thereof can also be used.
When CuInSe2 is used, Cd is used for the transparent electrode layer and the first and second transparent conductive metal compound layers.
It is desirable to use S.

Further, as a method of forming the back electrode layer, the following method is also possible other than the above-mentioned embodiment. That is, in FIG. 2, the normal discharge power density is supplied to the ZnO target 7 until the substrate 5 reaches the substrate position D, and when the substrate 5 reaches the substrate position D, the discharge power is supplied to the Ag target 9 and the plasma region is reached. simultaneously makes a Pa, discharge power density of Ag target 9 of the discharge power density of 10% or less in the overlooked and the plasma region Pz of ZnO target 7, P
za is formed, and while the substrate 5 is continuously moved, a second transparent conductive metal compound layer is laminated between the substrate position D and the substrate position E, and an Ag electrode layer is laminated from the substrate position E ahead. Good. In this method, as described in the above embodiment, after the first transparent conductive metal compound layer is laminated, the first and second substrates 5 are continuously moved without moving the substrate 5 in the opposite direction once. The transparent conductive metal compound layer and the Ag layer are laminated. However, after stacking the first transparent conductive metal compound layer on the stacked thin film semiconductor layers, the transparent conductive metal compound formed in the reaction chamber 3 and a plurality of adjacent plasma regions P made of Ag are formed.
Ag in z, Pza, Pa from the ZnO target 7 side
By moving the substrate 5 on which the first transparent conductive metal compound layer is laminated toward the target 9 side, the first transparent conductive metal compound layer and the second transparent conductive metal compound are formed on the thin film semiconductor layer . There is no change in stacking the back electrode layer made of the Ag layer and the Ag layer. Moreover, you may use what installed three targets for a 1st transparent conductive metal compound layer, a 2nd transparent conductive metal compound layer, and an Ag layer in the sputtering apparatus. Further, after stacking the first transparent conductive metal compound layer on the thin film semiconductor layer by another film forming apparatus, the second transparent conductive metal compound layer and Ag are formed by using the sputtering apparatus shown in FIGS. The layers may be laminated. However, in this case, if the adsorbed impurities between the first transparent conductive metal compound layer and the second transparent conductive metal compound layer are concerned, before the formation of the second transparent conductive metal compound layer, The adsorbed impurities on the surface may be removed by performing Ar bombardment treatment or the like in the sputtering apparatus.

FIG. 3 shows a cross-sectional structure of the thin film solar cell manufactured by the manufacturing method of the present invention.
As shown in the figure, the back surface electrode 11 includes the first transparent conductive metal compound layer 13 and the second transparent conductive metal compound layer 15, and
Since the Ag layer 17 has a three-layer structure and the composition of the second transparent conductive metal compound layer 15 is continuously changed, the composition of the upper and lower layers of the second transparent conductive metal compound layer 15 can be improved. Different interfaces do not come into contact with each other at both interfaces as in the conventional case, and as a result, high adhesive strength is obtained. It was confirmed that the second transparent conductive metal compound layer 15 had a sufficient film thickness even if it had an extremely thin film thickness of about 20 Å. In the figure, 19 is an insulating transparent substrate, 20 is a SiO 2 coat layer, 21 is a transparent electrode layer, and 23 is p-type a.
-SiC: H23p, i-type a-Si: H23i, n-type μ
Each of the thin-film semiconductor layers made of c-Si: H23n is shown.

[0017]

According to the present invention as described in the above section, the following excellent effects can be obtained. A transparent electrode layer on an insulating transparent substrate, a thin film semiconductor layer, the method of manufacturing the thin film solar cell of sequentially stacking a back electrode layer, the thin <br/> semiconductor layer on the first transparent conductive metal compound layer After lamination, the plasma region and silver with transparent conductive metal compound
Or the plasma region of aluminum alone
The reaction chamber formed by overlapping parts of each other
In the region where the active species that constitute the Zuma area are mixed, by moving the substrate laminated to the first transparent conductive metal compound layer from the transparent conductive metal compound side to the silver or pure aluminum side, the first Second transparent conductive metal compound layer and silver or aluminum on the first transparent conductive metal compound layer
The composition of the second transparent conductive metal compound layer is changed from the interface side with the first transparent conductive metal compound layer toward the interface side with the silver or aluminum simple substance layer by sequentially laminating the simple substance layers. Since the content ratio of the constituent components of the simple layer of silver or aluminum contained in the transparent conductive metal compound layer of No. 2 is continuously increased, there is no contact action between different materials as in the conventional case at both interfaces. Therefore, the adhesive strength of the back electrode is significantly improved. The degree of improvement in the adhesive strength is sufficiently high to withstand a practical level.

The inclination of the content ratio of the silver or aluminum simple substance layer constituent in the second transparent conductive metal compound layer constitutes each plasma by adjoining the plurality of plasma regions. This is because, as a result of the active species diffusing under a low pressure in the reaction chamber, there are regions where both are mixed with each other, and in the respective plasma regions targeted for the second transparent conductive metal compound and the silver or aluminum simple substance layer. The existence probability of the active species of the component is higher. Therefore, in the plurality of plasma regions, the first
By moving the substrate on which the transparent conductive metal compound layer is formed, it is possible to form a gradient of the above components, and thus it is possible to obtain the above advantageous effects without using a device having a particularly complicated mechanism. it can.

Since the short-circuit current density can be further improved, it can be said that the manufacturing method of the present invention is an effective means not only for improving the adhesive strength of electrodes but also for improving power generation characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a sputtering apparatus used in the manufacturing method of the present invention.

FIG. 2 is an explanatory diagram showing a plasma region in a sputtering apparatus used in the manufacturing method of the present invention.

FIG. 3 is a structural explanatory view of a thin film solar cell obtained by the manufacturing method of the present invention.

[Explanation of symbols]

1 Sputtering equipment Pz, Pa, Pza
Multiple plasma regions 3 Reaction chamber 4 Gas system 5, 5a Substrate 6 Vacuum pump 7 ZnO target 9 Ag target 11 Backside electrode 13 First transparent conductive metal compound layer 15 Second transparent conductive metal compound layer 17 Ag layer 19 Insulating transparent substrate 20 SiO2 coat layer 21 Transparent electrode layer 23 Thin film semiconductor layer 23p p-type a-SiC: H 23i i-type a-Si: H 23n n-type μc-Si: H

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-5-102503 (JP, A) JP-A-3-241617 (JP, A) JP-A-2-73967 (JP, A) JP-A-62-1 10809 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (5)

(57) [Claims] 1. A transparent electrode layer on an insulating transparent substrate, a thin film semiconductor layer, a method of manufacturing a thin film solar cell of sequentially stacking a back electrode layer, a first transparent conductive metal compound on the thin film semiconductor layer After stacking layers, plasma region with transparent conductive metal compound
And the plasma region of silver or aluminum alone
The reaction chamber formed by overlapping some of these
In the region where the active species that compose the plasma region are mixed, from the transparent conductive metal compound side to the silver or aluminum single substance.
Toward the body side by moving the substrate laminated to the first transparent conductive metal compound layer, the first transparent conductive metal compound
Second transparent conductive metal compound layer and silver or aluminum on the object layer
By laminating the iodonium simple layer, a thin film for laminating the first transparent conductive metal compound layer and the back electrode layer made of the second transparent conductive metal compound layer and the silver or pure aluminum layer on the thin film semiconductor layer Method for manufacturing solar cell. 2. The method for manufacturing a thin film solar cell according to claim 1, wherein the plurality of plasma regions are formed by applying a voltage to a sputtering target. Wherein the plasma by the transparent conductive metal compound
The discharge power density forming the area is set to the silver or aluminum
The method for producing a thin film solar cell according to claim 1 or 2, wherein the discharge power density for forming a plasma region by a simple substance is 10% or less. 4. Used to form the plasma region
The transparent conductive metal compound is added to the first transparent conductive metal compound.
4. The same material as the compound layer is used, according to claim 1.
The method for manufacturing a thin film solar cell according to. 5. The first transparent conductive metal compound is oxidized to
Indium tin, tin oxide, zinc oxide, cadmium sulfide
The method for manufacturing a thin-film solar cell according to claim 1, wherein the difference is used .