JPH1126787A - Thin film solar cell - Google Patents

Abstract

(57) [Problem] To reduce the photoelectric conversion characteristics of a solar cell capable of maintaining high reliability even for long-term outdoor use by suppressing sulfuration of an Ag layer constituting a back electrode layer. Without providing it. SOLUTION: In a thin film solar cell in which a transparent electrode layer (2), a semiconductor layer mainly composed of silicon (3), and a back electrode layer (4) are sequentially formed on a transparent substrate (1), a back electrode is provided. The layer (4) has a layer containing Ag as a main component and containing Pd, and a Pd content of a portion of the layer containing Ag as a main component and containing Pd close to the transparent substrate has a Pd content of Ag as a main component. A thin-film solar cell, wherein the Pd content is lower than the Pd content in a portion far from the transparent substrate in the layer containing the thin-film solar cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an integrated thin-film solar cell having a semiconductor layer containing silicon as a main component such as an amorphous silicon semiconductor layer, a polycrystalline silicon semiconductor layer, and a microcrystalline silicon semiconductor layer. The present invention relates to a thin-film solar cell that is devised so that reliability does not decrease even when used.

[0002]

2. Description of the Related Art An amorphous silicon semiconductor layer, a polycrystalline silicon semiconductor layer,
In a thin-film solar cell in which a thin-film semiconductor layer containing silicon as a main component such as a microcrystalline silicon semiconductor layer is formed, a stacked structure of a metal oxide layer and an Ag layer is generally used as a back electrode. This is because a higher reflectance can be obtained in relation to the refractive index as compared with a normal Ag electrode, so that the power generation efficiency of the solar cell can be increased by the "light confinement effect", and alloying of Ag and the semiconductor layer is performed. This is because it is possible to suppress the adhesion and increase the adhesion strength with the semiconductor layer, and improve the reliability of the solar cell.

[0003]

By the way, even if such a solar cell having improved reliability by providing a metal oxide between the semiconductor layer and the Ag layer, it can be used as a solar cell when used outdoors for a long period of time. There is a problem that characteristics are deteriorated and reliability is reduced. This is mainly due to the fact that the surface side of the back electrode layer which is directly exposed to the external environment takes in moisture in the air and corrodes. For this reason, the exposed side of the back electrode layer, that is, the surface on the side opposite to the side on which the transparent substrate is laminated is sealed with a resin. However, a solar cell sealed with such a resin layer is used. However, the present inventors have found that the characteristics as a solar cell gradually deteriorate when the device is used outdoors for a long period of time. This is because no matter how the back electrode layer is resin-sealed, there is air that permeates the resin layer, so that SO _X in the permeated air sulfides Ag and embrittles the Ag layer. As a result, they have found that the cause is that moisture invades between the sealing resin layer whose adhesion strength has decreased and the back electrode layer. The cause of the embrittlement of the Ag layer is not limited to sulfurization alone, but it is assumed that the main cause is the sulfurization phenomenon. If the moisture that has penetrated between the Ag layer and the sealing resin layer is allowed to stand, corrosion of the back electrode layer proceeds due to the electrolytic corrosion reaction, and eventually the electrode itself disappears, and there is even a danger that the function of the solar cell itself may be lost. Here, the case where the exposed side of the back electrode layer is sealed with a sealing resin layer as an example is Ag.
Although the problem of the sulfuration of the layer was described, the sulfuration of the Ag layer is caused by the contact with air, and the sulfuration of the Ag layer is more serious when the back electrode layer is not sealed with resin.

[0004] From the understanding of such a phenomenon, in order to ensure the reliability of the solar cell when used outdoors for a long period of time, a metal oxide layer is interposed on the back electrode layer on the side in contact with the semiconductor layer. In addition, it was concluded that merely providing a sealing resin layer on the opposite surface was not sufficient, and that measures to suppress sulfurization of the Ag layer were indispensable. The present invention has been made based on this recognition,
By suppressing the sulfuration of the layer, it is intended to prevent the deterioration of the characteristics of the solar cell due to the embrittlement of the Ag layer.
A solar cell capable of maintaining high reliability for a long period of time even when used outdoors, by using other measures for preventing deterioration such as the above-described interposition of the metal oxide layer and resin sealing. It is.

[0005]

Means and Action for Solving the Problems The present inventors have made the above-mentioned object an object of the present invention is to provide a method in which Pd (palladium) is contained in an Ag layer, and a portion of the layer containing Ag as a main component and containing Pd which is close to the transparent substrate. Of Pd with Ag as the main component
It has been found that the problem can be solved by setting the Pd content lower than that of the portion far from the transparent substrate in the layer containing d.

The thickness of a portion of the layer containing Ag as a main component and containing Pd close to the transparent substrate is 300 nm or less.
It is preferable that the thickness of a portion far from the transparent substrate in the layer containing g as a main component and Pd is 100 nm or less.

[0007] The Pd content of the portion close to the transparent substrate in the layer containing Ag as the main component and containing Pd is 0.5 wt% or less based on the total of Ag and Pd.
It is desired that the Pd content in a portion far from the transparent substrate in the layer containing d is set to 1 to 10 wt% with respect to the total of Ag and Pd. Here, the meaning of suppressing the Pd content in the portion in contact with the metal oxide to 0.5 wt% or less means
The case where the Pd content is 0 wt%, that is, the case where Pd is not included, is naturally covered. The reason why the Pd content is suppressed to 0.5 wt% or less is to prevent the reflection effect of the back electrode layer from being lowered and to prevent the diffusion of Pd into the metal oxide as described above. There is also a meaning to reduce the amount of used.

The layer containing Ag as a main component and containing Pd may be composed of a plurality of metal layers. The Pd content of the metal layer closest to the transparent substrate is 0.5 to the sum of Ag and Pd.
wt% or less, while the Pd content of the metal layer farthest from the transparent substrate is 1 to 10 w with respect to the sum of Ag and Pd.
It is preferable to make t%.

The back electrode layer has a layer containing Ag as a main component and containing Pd and a metal oxide layer, and the metal oxide layer mainly contains a layer containing Ag as a main component and containing Pd and silicon. A structure formed between the semiconductor layer and a component can be employed.

Although the surface of the back electrode layer opposite to the transparent substrate may be exposed, it is preferable to form a sealing resin layer to block direct contact between the back electrode layer and air.

In the thin-film solar cell having such a structure, Pd contained in the Ag layer suppresses the sulfuration of the Ag layer and prevents the Ag layer from being embrittled. Further, the Pd content of the portion close to the transparent substrate is
Since the Pd content is set to be lower than the Pd content of the portion containing Ag as a main component and far from the transparent substrate in the layer containing Pd, the presence of Pd does not lower the light reflection effect of the back electrode layer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will now be described with reference to the illustrated embodiments. FIG. 1 shows an embodiment of a thin-film solar cell (hereinafter, simply referred to as a solar cell) of the present invention, and schematically shows a laminated structure. In the solar cell of the present invention, a transparent electrode layer 2, a thin film semiconductor layer 3, and a back electrode layer 4 are sequentially formed on a glass substrate 1, the exposed side of which is covered with a sealing resin layer 5, and the outside thereof is a fluorine-based material. This is a structure covered with a cover film 6 made of resin (Tedlar film), and is a structure in which light L is incident from the glass substrate 1 side. In the present embodiment, a blue plate glass having a thickness of 4 mm is used as the glass substrate 1 and SnO ₂ is used as the transparent electrode layer 2. However, white plate glass may be used instead of the blue plate glass, or ITO may be used instead of SnO 2. Good. The thin film semiconductor layer 3 is a semiconductor layer containing silicon as a main component, and specifically uses an amorphous silicon semiconductor layer, a polycrystalline silicon semiconductor layer, a microcrystalline silicon semiconductor layer, or the like. Here, a p-type a.SiC: H semiconductor layer, an i-type a.Si:H semiconductor layer, and an n-type microcrystalline Si semiconductor layer are stacked. Hydrogen or the like can be added to the silicon semiconductor layer as needed. The thickness of the semiconductor layer containing silicon as a main component is 300 to 500.
nm is preferred.

The material of the sealing resin layer 5 is EVA, P
One or more resins selected from the group consisting of VB, PIB, and silicone are exemplified. The thickness of the sealing resin layer is 10
0 to 1000 μm is preferred.

The solar cell of the present invention is characterized in that the structure of the back electrode layer 4 is special in such a structure. In the back electrode layer 4 in the figure, a metal oxide layer 4a made of ZnO is disposed on the side in contact with the thin-film semiconductor layer 3, and A
The g layer 4b is adjacent. The reason why the metal oxide layer 4a is provided here is to increase the reflection efficiency of light transmitted through the thin film semiconductor layer 3 and incident on the back electrode layer 4, and to prevent Ag from diffusing into the thin film semiconductor layer 3. . Metal oxide layer 4a
Are Zn, In, Sn, Ti, Cr, A
One or more metal oxides selected from the group consisting of I, Zr, and Si are exemplified. The material of the metal oxide layer 4a is preferably ZnO. ZnO to which B, Al, Ga, In or the like is added is also preferably used. In this case, the addition ladder is preferably 1 to 10 atomic% with respect to Zn. The thickness of the metal oxide layer is preferably 5 to 100 nm, and 10 to 5 nm.
0 nm is more preferred.

In the present invention, the Ag layer 4b contains Pd. By containing Pd, sulfuration of Ag is suppressed,
Ag is less likely to become brittle even in contact with air, and the adhesion strength between the sealing resin layer 5 and the Ag layer 4b does not decrease. In order to make such an effect effective, the amount of Pd contained in the Ag layer 4b needs to be set to 1 to 10 wt% with respect to the total of Ag and Pd in a portion in contact with the sealing resin layer 5. . If it is less than 1 wt%, the effect of suppressing the sulfuration of the Ag layer 4b is not sufficient. Further, even if Pd is contained in an amount exceeding 10 wt%, the cost is relatively high and the effect of suppressing sulfuration is not so improved. On the other hand, the need to include Pd decreases as the distance from the portion in contact with the sealing resin layer decreases. The Pd content of the metal layer closest to the transparent substrate is
0.5 wt% or less with respect to the sum of Ag and Pd,
More preferably, the metal layer does not contain Pd. If the Pd content in these portions is large, not only is the cost increased, but also the reflectance at the back electrode is reduced, and the short-circuit current of the solar cell is undesirably reduced.

In the Ag layer 4b, the Pd content is 0.5
The method of providing the portion of not more than 1 wt% and the portion of 1 wt% to 10 wt% is such that the entire Ag layer is formed as a single layer and inside this single layer, gradually from the sealing resin layer 5 side toward the metal oxide layer 3 side. Pd
Although the content may be reduced, in this embodiment, the first Ag layer (4b-1) in which the Pd content is set to 0.5 wt% or less is provided on the metal oxide layer 3 side. P on the side
The second Ag layer (4b) having a d content of 1 to 10 wt%
-2) and a structure in which both layers are laminated is adopted. When the first Ag layer (4b-1) is formed by the same apparatus as the film forming apparatus for forming the second Ag layer (4b-2), a small amount of material for forming the second Ag layer (4b-2) is inevitably mixed. Therefore, it is difficult for the production equipment to make the first Ag layer (4b-1) a layer containing no Pd. However, theoretically, the first Ag layer (4b-1) is a layer containing no Pd. Preferably, there is. The thickness t1 of the first Ag layer (4b-1) is 3
It is preferable to set the thickness to not more than 00 nm, especially 100 to 200 nm, while the thickness t2 of the second Ag layer (4b-2)
Is preferably set to 100 nm or less, particularly 2 to 50 nm, more preferably 2 to 10 nm or less. When manufacturing a large area solar cell, the thickness of the back electrode is 2 nm.
Considering that it is difficult to control in the following steps, the lower limit of the film thickness is 2 nm.

When the entire metal layer in the back electrode layer is formed by the same film forming apparatus, from the viewpoint of avoiding impurity contamination,
It is advantageous in terms of production to form the entire metal layer using the same metal as the main material, but if the amount of impurities can be controlled to a substantially negligible level, the second Ag layer (4b-2) may be used instead. Stable layers of metals other than Ag, such as Ti and C
It is also conceivable to use a layer made of r or the like.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS To confirm the effects of the present invention,
Example of the present invention in which Pd is contained in the Ag layer according to
Solar cell and the Ag layer under conditions outside the scope of the present invention.
solar cell containing d, and A without Pd
For each of the solar cells using the g layer, the degree of sulfuration
Was evaluated. Specifically, pulling the sealing resin layer from the solar cell
Perform a peeling test to determine the adhesion between the back electrode and the sealing resin layer.
The degree of sulfidation was measured by evaluating the properties. Used for testing
The procedure for fabricating a solar cell and its testing procedure are as follows.
You. (Example 1) Solar having an area of 12.7 cm x 12.7 cm
-800nm tin oxide film on lime glass by thermal CVD
The formed product is laser-scribed for integration.
After turning, an a-Si layer was formed thereon by plasma CV.
Formed by Method D. Patterning method is XY table
Set on top and use a Q-switched YAG laser to
Released. The operating condition of the laser is the second harmonic 532
nm, pulse width 3 kHz, average output 500 mw,
The pulse width is 10 nsec. The separation width is 50 μm,
The ring width is 10 mm. Separately processed base slope above
At 200 ° C. using the plasma CVD chamber of the separation forming apparatus
, P-type a-SiC: H semiconductor layer, i-type a-Si: H semiconductor
Body layer and n-type microcrystalline Si semiconductor layer are sequentially deposited and
A joint was formed. p-type semiconductor layer, i-type semiconductor layer, n-type semiconductor
The gas for forming each of the body layers is 10 s, respectively.
SiH at flow rates of ccm, 50 sccm and 10 sccm_Four
Form p-type semiconductor layer and n-type semiconductor layer based on gas
When forming this SiH_Four1000 ppm hydrogen diluted in gas
Shaku no B _TwoH₆And PH_ThreeMixed at a flow rate of 200 sccm
In addition, when forming the p-type semiconductor layer, 3
0 sccm CH_ThreeInto carbon alloy by mixing
Was done. Input power is 500W for each layer, 50
W, 30 W, and the reaction pressure is 1 torr, 0.5
torr and 1 torr. The thickness of the formed layer is
It is estimated to be 15 nm, 320 nm, and 30 nm, respectively.

After these films are formed, they are set on an XX table, and the semiconductor layer and the ZnO layer are simultaneously patterned by using a Q-switched YAG laser by simultaneously shifting the patterning position of the SnO ₂ layer by 100 μm. Was.
The operating condition of the laser uses the second harmonic 532 nm,
Pulse width 3kHz, average output 500mw, pulse width 10
nsec. By shifting the focus position, the separation width becomes 1
It was set to 00 μm. Thereafter, a metal electrode layer having a thickness of 80 nm was formed by magnetron sputtering using a ZnO target by DC discharge. Argon gas pressure is 2 mtor
r, discharge power 200 W, and film formation temperature 200 ° C.
Next, by direct current discharge using a magnetron sputtering device on the upper layer, using an Ag target under a room temperature environment,
A metal electrode layer having a thickness of 200 nm was formed. The argon gas pressure was 2 mtorr and the discharge power was 200 W.
Further, the upper layer was subjected to direct current discharge using another Pd-Ag target provided in the same vacuum chamber of the above-mentioned magnetron sputtering apparatus, under the same conditions as those used for the above-mentioned Ag film formation, to form a 20 nm film. Pd content with thickness
A 5 wt% Ag layer was formed. Finally, the substrate was taken out of the magnetron sputtering apparatus, set on an XY table, and the Ag layer was removed using a Q-switched YAG laser to separate and process a position 100 μm away from the semiconductor layer processing portion. The operating conditions of the laser were exactly the same as the processing conditions of the semiconductor layer. Separation width is 70μ
m, the string width is also 100 mm.

Next, after wiring for taking out the electrodes is performed, the EVA sheet and the fluorine-based film are stacked, and the solar cell is sealed and framed using a vacuum laminator to complete the solar cell. Was.

The completed solar cell was subjected to 100 mW / cm ²
The characteristics were measured under an AM1.5 solar simulator. Table 1 shows the results. 1. Cut the solar cell immediately after completion from the sealing surface side with a cutter knife.
After dividing the encapsulating resin layer into a grid in such a manner that one of the 5 cm × 2.5 cm areas becomes a square of 5 mm square, a 50 mm wide gum tape is attached so as to collectively cover these adjacent divided surfaces, A slow peel test was performed.
As a result, none of the divided pieces came off, and the gum tape came off the sealing resin layer. As a result, it was confirmed that the back electrode of the solar cell immediately after completion and the sealing resin layer had sufficient adhesiveness and no sulfidation phenomenon. Next, after exposing the completed solar cell outdoors for one year, the sealing resin layer was divided and subjected to a peeling test as in the test. As a result, similar to the result for the solar cell immediately after completion, there was no peeling, and the solar cell of the present invention did not progress sulfurization even after the one-year exposure test, and the back electrode and the sealing resin layer had sufficient adhesion. It was confirmed that it was maintained.

(Comparative Example 1) A solar cell was manufactured and measured and tested in exactly the same manner as in Example 1, except that all Ag layers of 220 nm were formed of Ag having a Pd content of 1.5 wt%. Table 1 shows the measurement results. As a result of the peeling test after exposure for one year, there was no peeling as in Example 1. (Comparative Example 2) A solar cell was fabricated in exactly the same manner as in Example 1 except that all Ag layers of 220 nm were formed of Ag having a Pd content of 0.1 wt%, and measurements and tests were performed. Table 1 shows the measurement results. The results of the peel test after one year of exposure showed that 21 of 25 squares peeled off.

[0023]

[Table 1]

The results of these tests show that the solar cell of Example 1, which is the thin-film solar cell of the present invention, did not undergo sulfurization even after one year of outdoor exposure, and the adhesion between the back electrode layer and the sealing resin layer did not proceed. The reliability has not been reduced and it has been found that it has high reliability.
Moreover, it can be seen that the device for obtaining such an effect of suppressing sulfuration does not adversely affect the photoelectric conversion characteristics. On the other hand, Pd is applied to all the 220 nm Ag layers by 1.5 watts.
It can be seen that the solar cell of Comparative Example 1 containing t% has the same excellent sulfurization suppressing effect as that of Example 1 and can maintain the adhesiveness, but the photoelectric conversion characteristics are slightly inferior. Also 220
In the solar cell of Comparative Example 2 in which Pd was contained in all of the Ag layers having a thickness of 0.1 wt% or less, the photoelectric conversion characteristics were not deteriorated, but the Pd content was small, so that the effect of suppressing sulfuration was not exhibited and the adhesion was maintained. It was confirmed that the effect of the above could not be exhibited.

[0025]

According to the thin-film solar cell of the present invention, Pd contained in the Ag layer suppresses sulfidation of the Ag layer, thereby preventing the Ag layer from being embrittled. In the Ag layer, the Pd content is increased in a portion far from the transparent substrate, where the sulfidation phenomenon is likely to occur, and the Pd content is reduced in a portion near the transparent substrate where the sulfidation phenomenon hardly occurs, The sulfuration of the Ag layer can be effectively suppressed without lowering the light reflection effect of the back electrode layer, and the reliability of the solar cell during long-term outdoor use can be improved without lowering the photoelectric conversion characteristics. .

The back electrode layer is composed of Ag as a main component and Pd
And a metal oxide layer, wherein the metal oxide layer is formed between a layer containing Ag as a main component and containing Pd and a semiconductor layer containing silicon as a main component. In this case, the interposition of the metal oxide layer improves the adhesion strength to the semiconductor layer and also has the effect of preventing migration. In addition, since the thin-film solar cell uses only a required minimum amount of Pd, the increase in manufacturing cost can be minimized.

When a sealing resin layer is formed on the surface of the back electrode layer opposite to the transparent substrate, the Ag layer can be prevented from coming into direct contact with air, so that the sulfuration of the Ag layer is further suppressed. . Since the sulfuration at the sealing resin interface is suppressed, the adhesion strength between the Ag layer and the sealing resin layer is high, and the reliability of the solar cell is further improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a laminated structure of a thin film solar cell of the present invention.

[Explanation of symbols]

 L light 1 glass substrate 2 transparent electrode layer 3 thin film semiconductor layer 4 back electrode layer 3a p-type a.SiC: H semiconductor layer 3b i-type a.Si:H semiconductor layer 3c n-type microcrystalline Si semiconductor layer 4a metal oxide layer 4b Ag layer 4b-1 First Ag layer 4b-2 Second Ag layer 5 Sealing resin layer 6 Cover film

Claims (6)

[Claims] 1. A thin-film solar cell in which a transparent electrode layer, a semiconductor layer containing silicon as a main component, and a back electrode layer are sequentially formed on a transparent substrate, wherein the back electrode layer contains Ag as a main component and Pd. Pd content of a portion close to the transparent substrate in a layer containing Ag as a main component and containing Pd
A thin-film solar cell, wherein the Pd content is lower than the Pd content at a portion far from the transparent substrate in a layer containing g as a main component and containing Pd. 2. A layer containing Ag as a main component and containing Pd having a thickness of 300 nm or less at a portion close to the transparent substrate.
2. The thin-film solar cell according to claim 1, wherein a part of the layer containing g as a main component and containing Pd, which is far from the transparent substrate, has a thickness of 100 nm or less. 3. The Pd content of a portion close to the transparent substrate in a layer containing Ag as a main component and containing Pd is 0.5 wt% or less with respect to the total of Ag and Pd. 2. The thin-film solar cell according to claim 1, wherein the Pd content in a portion of the Pd-containing layer far from the transparent substrate is 1 to 10 wt% with respect to the total of Ag and Pd. 4. A layer containing Ag as a main component and containing Pd is composed of a plurality of metal layers, and the Pd content of the metal layer closest to the transparent substrate is 0.5 wt% with respect to the sum of Ag and Pd.
2. The thin-film solar cell according to claim 1, wherein the Pd content of the metal layer furthest from the transparent substrate is 1 to 10 wt% with respect to the total of Ag and Pd. 5. The back electrode layer has a layer containing Ag as a main component and containing Pd and a metal oxide layer, and the metal oxide layer contains a layer containing Ag as a main component and containing Pd and silicon. The thin-film solar cell according to claim 1, wherein the thin-film solar cell is formed between the thin-film solar cell and a semiconductor layer containing as a main component. 6. The thin-film solar cell according to claim 1, wherein a sealing resin layer is formed on a surface of the back electrode layer opposite to the transparent substrate.