JP2822358B2 - 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 has a pin junction mainly made of amorphous silicon (hereinafter abbreviated as a-Si), and is provided with a light from a p-layer through a transparent insulating substrate and a transparent electrode. The present invention relates to a method for manufacturing a thin-film solar cell which generates an electromotive force by incidence of light.

[0002]

2. Description of the Related Art An a-Si thin film formed by glow discharge decomposition or photolysis of monosilane gas or the like can be easily formed into a large area because it is obtained by a vapor phase growth method, and is used for a photoelectric conversion layer of a low-cost solar cell. Can be

Normally, an a-Si solar cell has a SnO ₂ film 2 formed as a transparent conductive film for a transparent electrode on a light-transmitting insulating substrate 1 such as glass as shown in FIG. On top of that, SiH ₄ and CH ₄ are used as main gases, and B ₂ H ₆
Plasma as a doping gas and H ₂ as a dilution gas
Amorphous silicon carbide (hereinafter a-SiC)
) Is formed to a thickness of 80 to 150 mm. The SiH ₄ Then main gas to form the i layer 5 and H ₂ as diluent gas, further SiH ₄ main gas, diluent gas and H _2, PH ₃
Is formed as a doping gas to form an n-layer 6 with a thickness of 100 to 2000 ° and a back electrode 7.
In the case shown in the figure, an a-SiC interface layer 4 doped with a non-doped or a small amount of boron is formed between the p layer 3 and the i layer 5, whereby the open voltage V
_OC can be improved.

[0004]

In FIG. 3, a broken line 31 shows the relationship between the p-layer thickness and the cell characteristics of a single cell having a thickness of 4000 ° of the i-layer. As can be seen from the figure, the thinner the p layer, the smaller the optical absorption loss in the p layer, and thus the higher the short-circuit current density J _SC . On the other hand, when the thickness of the p-layer is set to 100 ° or less, there is a problem that V _OC is greatly reduced.
Therefore, in the conventional solar cell, the p-layer thickness needs to be 100 ° or more, and J _SC is low.

[0005] An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a method of manufacturing a thin-film solar cell in which a high conversion efficiency can be obtained without reducing V _OC even when the layer is thinned.

[0006]

In order to achieve the above object, a method for manufacturing a thin-film solar cell according to the present invention comprises forming a transparent electrode by sequentially laminating a SnO ₂ film and a ZnO film on a transparent insulating substrate. After formation, Zn in a hydrogen atmosphere containing silane gas
Discharge treatment is performed on the surface of the O film under conditions for forming microcrystalline silicon by plasma CVD, and then a p-layer, an i-layer, and an n-layer mainly composed of a-Si are stacked from the p-layer side And
It is assumed that a back electrode that contacts the surface of the n-layer is formed.
It is effective to set the thickness of the ZnO film to 150 to 400 mm. Further, the p-layer is made of a-SiC, and its thickness is 30
It is effective to set it to ~ 80Å. Further, the silane gas in the discharge atmosphere is SiH ₄ , and the growth rate of the microcrystalline silicon layer in the plasma CVD method under the same conditions as the B ₂ H ₆ added to the discharge atmosphere or the discharge treatment. It is also effective that the product of the discharge processing time and the discharge processing time is 10 to 100 mm.

[0007]

[Function] SnO on the surface_TwoForm p-layer on substrate with film deposited
Then, SnO_TwoFrom the diffusion of Sn and O into the p layer,
It turns out that a p-film with a thickness of several tens of mm is not a good p-layer.
Was. This diffusion, SnO_TwoCoating the film with ZnO film
A good film from the initial stage of p-layer formation.
It is formed. However, a ZnO film is formed on the surface of the transparent electrode.
Then, there is a large gap between ZnO and the p-layer of a-SiC or a-Si.
Potential barrier, and V_OCBecomes lower. this
In contrast, before forming the p-layer,
Recon (hereinafter abbreviated as μc-Si)
H including _TwoWhen discharge treatment is performed in an atmosphere,
As the tension barrier becomes smaller, V _OCIs improved.

[0008]

FIG. 1 shows a single cell of an a-Si solar cell according to one embodiment of the present invention, and portions common to those in FIG. 2 are denoted by the same reference numerals. The difference from the cross-sectional structure of FIG. 2 is that the ZnO layer 2 between the SnO ₂ film 2 and the p-layer 3 of a-SiC constitutes a transparent electrode.
That is, the O film 8 is inserted.

This solar cell was manufactured as follows. First, a fluorine-doped SnO ₂ film 2 was placed on a glass substrate 1.
Is formed to a thickness of 3000-10000 mm. On top of it, 150-40
A ZnO film 8 having a thickness of 0 ° is laminated to form a SnO ₂ / ZnO transparent conductive film. The ZnO film 8 was formed by a sputtering method using a target doped with 1% of Al. This substrate was mounted on a plasma CVD apparatus, and was first diluted 100 times with H ₂ .
SiH ₄ and a doping gas B ₂ H ₆ were introduced, and discharging was performed for about 2 to 5 minutes at a power about 10 times that of forming a normal a-Si film. This film formation condition is a condition under which μc-Si grows constantly, but the transmittance of the substrate does not change in a processing time of 2 to 5 minutes. Analysis results by X-ray photoelectron spectroscopy (XPS) showed that after discharge treatment for 2 to 5 minutes, the transmittance did not change because transparent SiO ₂ grew due to diffusion of oxygen from ZnO.

Next, SiH ₄ and CH ₄ are used as main gases, and H ₂
A as a diluent gas and B ₂ H ₆ as a doping gas.
Was formed to a thickness of 30 to 80 °. Subsequently, the interface layer 4 of a-SiC was added to the layer 60 to 12 without adding boron.
0Å thick, and an i-layer 5 of a-Si
00 °, n layer 6 was sequentially formed to a thickness of 150 °, and finally Al was deposited as back electrode 7.

The solid line 32 in FIG. 3 has the structure of FIG.
The relationship between the thickness of the p-layer 3 of the single cell in which the thickness of the film 8 is 150 ° and the thickness of the i-layer 5 is 4000 ° and the cell characteristics are shown. In the conventional structure of FIG. 2, when the thickness of the p-layer 3 is reduced to 100 ° or less, V _OC is greatly reduced. On the other hand, by implementing the present invention, the same value of V _OC is obtained even when the thickness of the p-layer 3 is set to 40 °. Maintained. As described above, according to the present invention, the thickness of the p layer 3 can be reduced, and J _SC can be improved without lowering V _OC . As a result, the maximum value of the conversion efficiency η was 11.8% at the film thickness of the p layer 3 of 100 ° in the conventional structure, whereas the maximum value of the conversion efficiency η was 40% at the film thickness of the p layer 3 in the embodiment of the present invention.
It improved to 12.4%. As can be seen from the figure, the range of the p-layer thickness at which the present invention is effective and high efficiency is obtained is as follows.
30-80Å. Note that the fill factor FF does not depend on the p-layer thickness in both the conventional structure and the embodiment of the present invention.

FIG. 4 shows the relationship between the thickness of the ZnO film 8 coated on the SnO ₂ film 2 and the cell characteristics. From the figure, it is understood that when the thickness of the ZnO film 8 is set to 100 ° or less, V _OC and J _SC decrease. This is because when the ZnO film thickness is 100 °
_This is because the diffusion of Sn and O from ₂ into the p layer cannot be completely prevented. On the other hand, when the thickness of the ZnO film 8 is set to 200 ° or more, J _SC gradually decreases. This is due to the optical absorption loss of ZnO. From the above, the thickness at which the ZnO film 8 exhibits the effect of increasing the efficiency is 150 to 400 mm.

Next, a discharge performed before the formation of the p-layer of a-SiC.
The treatment was discussed. No discharge treatment, B-doped μc-Si
And non-doped μc-Si under discharge conditions
SiH _FourH without mixing gas_TwoStudy on plasma treatment
did. Table 1 shows the results.

[0014]

[Table 1]

Here, the thickness of the deposited p-layer 3 is 40 °,
The discharge powers of the μc-Si processing and the H ₂ plasma processing are all constant, and are about 10 times that of ordinary a-SiC film formation. All treatment times were 5 minutes. From the table, it can be seen that when no processing is performed, V _OC is low. It is considered that this is because, as described above, a large potential barrier occurs between the ZnO film 8 and the a-SiC p layer 3 when no treatment is performed, so that a sufficient diffusion potential cannot be obtained with the p layer 40 #. . On the other hand, by performing the μc-Si treatment,
It was found that V _OC was improved irrespective of the presence or absence, and high conversion efficiency η was obtained. This is probably because the potential barrier described above was reduced or an extremely thin contact layer was formed. On the other hand, in the plasma processing performed only with H ₂ without introducing SiH ₄ , the FF is greatly reduced,
The conversion efficiency was smaller than the untreated case. From the above, it is effective to perform discharge treatment under μc-Si film formation conditions after the formation of the ZnO film.

Next, the thickness of the film formed by the discharge treatment under the μc-Si condition was examined. However, since it is difficult to measure the thickness of the actually formed film, the growth rate (D) in the case where a somewhat thick μc-Si film is formed by performing a plasma CVD method under the conditions is obtained. The product (D × T) of the speed and the discharge processing time (T) was considered as the film thickness. FIG. 5 shows D ×
The relationship between T and cell characteristics is shown. For example, D × T = 50 ° is μc−
In the case of Si, this is a case where the discharge treatment was performed for 4 minutes under the condition that a growth rate of 12.5 ° / min was obtained. From the figure, D × T ≧ 30Å
It can be seen that sufficient V _OC can be obtained by setting
Also, film grown in the range of D × T ≦ 60 Å is not a optical absorption loss for the SiO _2. Therefore J _SC has remained constant value does not decrease. From the above, the value of D × T is
20 to 60 mm is desirable, but if it is 10 to 100 mm, practical characteristics can be obtained.

[0017]

According to the present invention, when the p-layer is laminated on the SnO ₂ film, the quality of the p-layer is degraded due to the diffusion of Sn and O from SnO _2. By interposing it, the potential barrier generated between the ZnO film and the p layer is reduced by discharging the surface of the ZnO film in H ₂ containing silane gas under the same conditions as the μc-Si film. Even when the thickness of the p-layer was reduced, V _OC did not decrease, and the J _{SC of the} thin-film solar cell could be improved. In this case, it is effective that the silane gas in the atmosphere during the discharge treatment is SiH ₄ gas, and B ₂ H ₆ may be added to the atmosphere. When the ZnO film thickness is set to 150 ° or more, diffusion of Sn and O can be prevented. However, when the ZnO film thickness is set to 400 ° or less, the optical absorption loss does not increase remarkably. When a-SiC having an optical absorption coefficient smaller than that of a-Si is used for the p-layer, high conversion efficiency can be obtained by setting the thickness to 30 to 80 °. Further, the product of the film growth rate and the discharge time when μc-Si is formed by the discharge process is 10 to 100 Å.
Is effective to obtain a high J _SC .

[Brief description of the drawings]

FIG. 1 is a sectional structural view of an a-Si solar cell according to one embodiment of the present invention.

FIG. 2 is a cross-sectional structural view of an a-Si solar cell according to a conventional method.

FIG. 3 is a diagram showing the relationship between cell characteristics and p-layer thickness of a-Si solar cells according to the conventional method and the present invention.

FIG. 4 shows cell characteristics and ZnO of an a-Si solar cell according to the present invention.
Relationship diagram of film thickness

FIG. 5 is a diagram showing the relationship between the cell characteristics of the a-Si solar cell according to the present invention and the product of the μc-Si film thickness to be generated by the discharge treatment and the discharge treatment time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 SnO film 3 p-a-SiC layer 4 Interface layer 5 ia-Si layer 6 na-Si layer 7 Back electrode 8 ZnO film

Claims (6)

(57) [Claims] A transparent electrode is formed by sequentially laminating a tin oxide film and a zinc oxide film on a light-transmitting insulating substrate, and then forming a transparent electrode on the surface of the zinc oxide film in a hydrogen atmosphere containing silane gas.
A discharge treatment is performed under the conditions for forming microcrystalline silicon by a plasma CVD method. Subsequently, a p-layer, an i-layer, and an n-layer mainly composed of amorphous silicon are stacked from the p-layer side, and an n-layer is formed. A method for manufacturing a thin-film solar cell, comprising forming a back electrode in contact with a front surface. 2. The method according to claim 1, wherein the zinc oxide film has a thickness of 150 to 400 °. 3. The method according to claim 1, wherein
The p layer is made of amorphous silicon carbide, and its thickness is
A method for manufacturing a thin-film solar cell having a thickness of 30 to 80 mm. 4. The method according to claim 1, wherein the silane gas is a monosilane gas. 5. The method according to claim 1, wherein B ₂ H ₆ is added to the discharge treatment atmosphere. 6. The method according to claim 1, wherein the product of the growth rate of the microcrystalline silicon layer and the discharge processing time during plasma CVD under the same conditions as the discharge processing is 10%.
A method for manufacturing a thin-film solar cell of about 100 mm2.