JPH08298332A - Manufacture of photovoltaic device - Google Patents

Abstract

PURPOSE: To prevent constituent elements diffusing from an insulating layer to semiconductor, abate the influence of partial defect of a semiconductor layer, and improve photovoltaic characteristics, by forming the insulating layer after the semiconductor layer is formed, when a photovoltaic device having unevenness on the light incidence side is manufactured. CONSTITUTION: After unevenness is formed on the surface of an N-type polycrystalline silicon film 1 (a), an I-type amorphous silicon layer 2 and a P-type amorphous silicon layer 3 are continuously formed on the polycrystalline silicon film 1 by using a plasma CVD method (b), and an insulating layer 7 composed of an SiO2 film is formed on the amorphous silicon layer 3 (c). A surface electrode 4 composed of an ITO film is formed on the insulating layer 7 (d). Finally a collecting electrode 5 composed of a Ti/Ag film is formed on the front electrode 4, and a rear electrode 6 is formed on the other flat surface of the polycrystalline silicon film 1 (e). An insulating layer composed of SiO2 or SiN may be formed by oxidizing or nitriding a part of the P-type amorphous silicon layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photovoltaic device in which semiconductor layers are laminated.

[0002]

2. Description of the Related Art In a photovoltaic device, the light confinement effect is utilized by making the surface on the light incident side uneven so as to lengthen the optical path and increase the absorption amount so that the irradiation light can be used efficiently. Is being done. FIG. 6 is a structural diagram of such a conventional photovoltaic device. In FIG.
Reference numeral 51 is an n-type polycrystalline silicon film having irregularities on the surface. An i-type amorphous silicon layer is formed on the polycrystalline silicon film 51.
52 and a p-type amorphous silicon layer 53 are laminated in this order. On the amorphous silicon layer 53, a light-incident side surface electrode
A collector electrode 55 and a collector electrode 55 are formed, and a back surface electrode 56 is formed on the flat surface of the polycrystalline silicon film 51.

Certainly, although the current taken out is increased by adopting the concave-convex shape on the light incident side as described above, it is difficult to form a thin semiconductor layer on the concave or convex portion of the polycrystalline silicon film 51. It is difficult to uniformly deposit a thin semiconductor layer on the surface of an uneven semiconductor such as the polycrystalline silicon film 51. Therefore, it is unavoidable that the semiconductor thin film to be formed is partially defective (portion A in FIG. 6) or thin, and as a result, there is a problem that the photovoltaic characteristics are rather deteriorated.

As a means for solving such a problem, an insulating layer is formed in advance on a concavo-convex transparent electrode on glass, and a plurality of amorphous thin film semiconductor layers having different conductivity types (for example, p.
An amorphous photovoltaic device having an in-amorphous silicon laminated body has been devised (Japanese Patent Publication No. 5-74951). In this photovoltaic device, by forming an insulating layer on the transparent electrode, the uneven state of the uneven surface of the transparent electrode is relaxed, and the amorphous semiconductor layer is easily laminated evenly on the transparent electrode. The convex portion is prevented from penetrating the amorphous thin film semiconductor layer laminated on the insulating layer, and the improvement of the photovoltaic characteristic due to the concave and convex shape can be ensured.

[0005]

However, in the photovoltaic device disclosed in Japanese Patent Publication No. 5-74951, the insulating layer and the amorphous thin film semiconductor layer are formed in this order. However, when the amorphous thin film semiconductor layer is formed, it is exposed to heat and plasma, so that the constituent elements of the insulating layer diffuse into the amorphous thin film semiconductor layer, and the film characteristics deteriorate and the photovoltaic characteristics decrease. There was a problem of doing.

The present invention has been made in view of such circumstances, and by forming an insulating layer after forming a thin film semiconductor layer, deterioration of photovoltaic characteristics due to a partial defect of the thin film semiconductor layer is prevented. It is an object of the present invention to provide a method for manufacturing a photovoltaic device, which is capable of preventing the deterioration of photovoltaic characteristics due to diffusion of constituent elements of the insulating layer.

[0007]

According to a first aspect of the present invention, there is provided a method for manufacturing a photovoltaic device, which comprises laminating one or a plurality of semiconductor thin films on a semiconductor having unevenness on the surface. A method of manufacturing a photovoltaic device that generates an electromotive force by irradiating a semiconductor thin film with light, comprising the step of forming an insulating layer on the semiconductor thin film.

In the method for manufacturing a photovoltaic device according to the second aspect of the present invention, one or a plurality of semiconductor thin films are laminated on a semiconductor having unevenness on the surface, and the semiconductor and the semiconductor thin film are irradiated with light. A method of manufacturing a photovoltaic device that generates an electromotive force according to claim 1, comprising the step of insulating the upper portion of the semiconductor thin film to form an insulating layer.

[0009]

In the first aspect of the invention, the semiconductor thin film and the insulating layer are laminated in this order on the semiconductor having unevenness on the surface. Also,
In the second invention, a semiconductor thin film is laminated on a semiconductor having unevenness on the surface, and the upper portion of the semiconductor thin film is converted into an insulating layer by oxidation treatment or nitriding treatment. This solves the conventional problem that the constituent elements of the insulating layer diffuse inside the semiconductor thin film when it is formed, and prevents the deterioration of the photovoltaic characteristics. Further, even if the semiconductor thin film is damaged, the insulating layer is formed on the uneven surface of the light incident side. Therefore, in the defective part, the semiconductor layer / insulating layer /
An MIS type solar cell having an electrode structure is formed to compensate for a decrease in photovoltaic characteristics due to a defect in a semiconductor thin film.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

In a heterojunction photovoltaic device in which amorphous silicon is formed on polycrystalline silicon, poly-Si (n-type)
/ A-Si (i type) / a-Si (p type) HIT (Heteroju
An embodiment of the present invention will be described with respect to a photovoltaic device of the nction with Intrinsic Thin-layer type.

FIG. 1 is a structural diagram of such a HIT type photovoltaic device manufactured by the manufacturing method of the present invention. FIG.
In FIG. 1, 1 is an n-type polycrystalline silicon film (thickness: 300 μm) having irregularities on the surface, and an i-type amorphous silicon layer 2 (thickness: 10 to 200 Å) on the polycrystalline silicon film 1. ) And a p-type amorphous silicon layer 3 (film thickness: 50 to 200 Å) are laminated in this order. On the amorphous silicon layer 3, S
An insulating layer 7 (film thickness: 5 to 50Å) made of an iO ₂ film is formed. On the insulating layer 7, a surface electrode 4 made of an ITO film (film thickness: 500 to 1500Å) and a collector electrode 5 made of a Ti / Ag film (width 5 μm or less × thickness 5 μm) are formed. A back electrode 6 (thickness of 2 μm or less) made of an Al film is formed on the flat surface of the film 1. It should be noted that there is a portion (B portion) where the amorphous silicon layers 2 and 3 to be laminated are not formed and are missing.

Next, a method of manufacturing the photovoltaic device having such a structure will be described.

FIG. 2 is a sectional view showing the steps of the first example of the manufacturing method. First, after cleaning the n-type polycrystalline silicon film 1, unevenness having a pitch and a height of about 10 μm is formed on one surface of the polycrystalline silicon film 1 by plane orientation etching using an aqueous solution of sodium hydroxide. (Fig. 2
(A)). Next, the i-type amorphous silicon layer 2 and the p-type amorphous silicon layer 3 are continuously formed on the uneven surface of the polycrystalline silicon film 1 by plasma CVD (FIG. 2).
(B)). At this time, the amorphous silicon layers 2 and 3 are not partially formed, and a defective portion (C portion) is generated. The formation conditions by plasma CVD at this time are as follows. i-type amorphous silicon layer 2 source gas: SiH ₄ , film forming temperature: 120 ° C., pressure: 0.2T
orr, power: 30 mW / cm ² p-type amorphous silicon layer 3 source gas: B ₂ H ₆ : SiH ₄ : H ₂ = 0.1: 5: 100
, Film formation temperature: 120 ℃, Pressure: 0.2 Torr, Power: 3
0 mW / cm ²

Next, an insulating layer 7 made of a SiO ₂ film is formed on the amorphous silicon layer 3 by plasma CVD (FIG. 2 (c)). Then, the surface electrode 4 made of an ITO film is formed on the insulating layer 7 by the sputtering method (FIG. 2).
(D)). Finally, a collector electrode 5 made of a Ti / Ag film is formed on the surface electrode 4 and a back electrode 6 made of an Al film is formed on the other flat surface of the polycrystalline silicon film 1 by vapor deposition (see FIG. 2 ( e)).

FIG. 3 is a sectional view showing the steps of the second example of the manufacturing method. First, after cleaning the n-type polycrystalline silicon film 1, unevenness having a pitch and a height of about 10 μm is formed on one surface of the n-type polycrystalline silicon film 1 by the same method as in the first example (FIG. 3).
(A)). Next, the i-type amorphous silicon layer 2 and the p-type amorphous silicon layer 3 are continuously formed on the uneven surface of the polycrystalline silicon film 1 by plasma CVD (FIG. 3).
(B)). The formation conditions by plasma CVD at this time are the same as those in the first example. At this time, the amorphous silicon layers 2 and 3 are insufficiently formed and a portion (D portion) where the film thickness is smaller than other regions partially occurs.

Next, this intermediate is immersed in nitric acid, and a part of the formed amorphous silicon layer 3 on the surface layer side is oxidized to be insulated to form an insulating layer 7 made of a SiO ₂ film. (FIG.3 (c)). In addition, the amorphous silicon layer 2,
In the portion where the film formation of 3 is insufficient, both amorphous silicon layers 2 and 3 are oxidized to become the insulating layer 7 (SiO ₂ film). The thickness of the insulating layer 7 formed here depends on the concentration of nitric acid and the temperature.
Therefore, it is determined by _the immersion time. As an example, in this embodiment, HNO ₃ : 50 g / H ₂ O: 1 liter was immersed for 1 minute at 50 ° C., thereby forming a SiO ₂ film having a thickness of 20 Å. The oxidation reaction of silicon with nitric acid is as follows. Si + 4HNO ₃ → SiO ₂ + 4NO ₂ + 2H ₂ O

Then, similarly to the above-mentioned first example, after the surface electrode 4 made of an ITO film is formed on the insulating layer 7 by the sputtering method (FIG. 3 (d)), Ti / on the surface electrode 4 is formed. A collector electrode 5 made of an Ag film and a back electrode 6 made of an Al film are both formed on the other flat surface of the polycrystalline silicon film 1 by vapor deposition (FIG. 3 (e)).

In the above-described embodiments, single crystal silicon may be used instead of polycrystalline silicon. Further, germanium may be used instead of silicon. Further, germanium, silicon germanium, or silicon carbon may be used instead of amorphous silicon. Further, fine crystals may be used instead of amorphous. The texturing may be performed by mechanical processing using a cutting jig, in addition to the above-described etching.

As the insulating layer 7, in addition to the above-mentioned oxide such as SiO ₂ , a nitride such as SiN or SiC.
Carbides such as are also effective. Further, as a method of forming the insulating layer 7, in addition to the above-described example, a treatment method of oxidizing and nitriding amorphous silicon by plasma can be considered.

For the surface electrode 4, in addition to the above-mentioned ITO, Z
nO, SnO ₂ or the like can be used, and the forming method includes a CVD method other than the sputtering method. Further, as a method of forming the collecting electrode 5, a sputtering method other than the above vapor deposition is also possible.

Next, the photovoltaic device of the present invention having the structure shown in FIG. 1 (hereinafter referred to as the present invention example) and the conventional photovoltaic device having the structure shown in FIG. 6 described above (hereinafter referred to as the conventional example). The photovoltaic characteristics of and are shown in Table 1 below. The conventional example is different only in that the insulating layer 7 (SiO ₂ film) does not exist,
The configuration of the other parts is exactly the same as the example of the present invention.

[0023]

[Table 1]

The effect of the present invention and the insulating layer 7 (Si
In order to verify the optimum film thickness of the O ₂ film), FIG. 4 shows the relationship between the film thickness of the insulating layer 7 (SiO ₂ film) and the photovoltaic characteristic in the example of the present invention.

As can be seen from the results in Table 1 and FIG. 4, by inserting the insulating layer 7, the open circuit voltage V of the photovoltaic characteristic is
_OC and short circuit current I _SC are improved. If the amorphous silicon formed on the polycrystalline silicon is not partially formed due to the unevenness of the underlying layer, in the conventional example, the effect of the defective portion causes the deterioration of the photovoltaic characteristics. It was In the structure of the example of the present invention, the MIS type photovoltaic device in which the insulating layer 7 is sandwiched is formed in the defective portion (B portion in FIG. 1), and the deterioration of the photovoltaic characteristic can be compensated. In the MIS type photovoltaic device, the film thickness of the insulating layer has a great influence on its photovoltaic characteristics. From Fig. 4, the thickness of the insulating layer is 20
In case of Å, the conversion efficiency η is the highest, and in the case of 5 to 50Å, the photovoltaic characteristic is improved as compared with the conventional example in which the insulating layer does not exist. This is because the open circuit voltage V _OC of the MIS type photovoltaic device increases with the film thickness of the insulating layer, but the short circuit current I _SC tends to decrease as the film thickness increases.

Next, an application example of the present invention to an amorphous silicon photovoltaic device will be described. FIG. 5 is a structural diagram of such a photovoltaic device. In FIG. 5, reference numeral 11 is a substrate having irregularities formed on its surface. On the substrate 11, an n-type amorphous silicon layer 12 (film thickness: 500Å), an i-type amorphous silicon layer 13 (film thickness: 6000Å), a p-type amorphous silicon layer 14
(Film thickness: 100Å) is laminated in this order. On the amorphous silicon layer 14, an insulating layer 15 made of a SiO ₂ film, a surface electrode 16 made of an ITO film as a light incident side electrode, and a collector electrode 17 made of a Ti / Ag film are formed. Formed in order.

Next, a method of manufacturing the photovoltaic device having the structure shown in FIG. 5 will be briefly described. An n-type amorphous silicon layer 12, an i-type amorphous silicon layer 13, and a p-type amorphous silicon layer 14 are successively formed on the substrate 11 by the plasma CVD method. The formation conditions by plasma CVD at this time are as follows. n-type amorphous silicon layer 12 source gas: PH ₃ : SiH ₄ = 1: 10, film formation temperature: 120
° C, pressure: 0.2 Torr, power: 30 mW / cm ² i-type amorphous silicon layer 13 source gas: SiH ₄ , deposition temperature: 200 ° C, pressure: 0.2 T
orr, power: 30 mW / cm ² p-type amorphous silicon layer 14 same as the above-mentioned amorphous silicon layer 3

After that, as in the above-mentioned embodiment, the insulating layer 15 is formed by immersing it in nitric acid and oxidizing the amorphous silicon layer 14. Then, the surface electrode 16 is formed by a sputtering method, and the collecting electrode 17 is formed by vapor deposition.

After forming a SiO ₂ film as an insulating layer,
Exposing the SiO ₂ film to the process temperature of the semiconductor layer activates diffusion of an element of the SiO ₂ film, and mixing of this element causes deterioration of the characteristics of the semiconductor layer. However, even in the present embodiment, since the SiO ₂ film serving as the insulating layer is formed after the semiconductor layer is formed, such a problem does not occur.

For comparison, an amorphous silicon photovoltaic device as shown in FIG. 5 was annealed at 200 ° C. for 1 hour after forming an insulating layer of SiO ₂ film, and Si was used.
Two types of photovoltaic devices were manufactured by forming a surface electrode of an ITO film in both cases where the insulating layer of the O ₂ film was formed and then allowed to stand at room temperature, and the respective photovoltaic properties were measured. . The measurement results are shown in Table 2 below. When the annealing treatment is performed, the photovoltaic characteristics are deteriorated.

[0031]

[Table 2]

In this embodiment, germanium, silicon germanium, or silicon carbon may be used instead of amorphous silicon. Further, fine crystals may be used instead of amorphous.

When the amorphous semiconductor is formed by plasma CVD after forming the insulating layer, the surface energy of the plasma is applied in addition to the heat, so that the diffusion of the constituent elements of the insulating layer is further activated. It is expected that. Therefore, according to the method of forming the insulating layer after the formation of the semiconductor layer as in the present invention, the characteristics of the manufactured photovoltaic device can be improved.

[0034]

As described above, according to the present invention, an insulating layer is formed after forming a semiconductor thin film, or a part of the semiconductor thin film is formed into an insulating layer by oxidation, nitriding or the like to form the insulating layer. As a result, a film-type junction photovoltaic device such as a HIT structure in which a thin film semiconductor layer is formed on the surface of a crystalline substrate, and a non-recessed amorphous semiconductor layer is formed on the surface of the amorphous semiconductor layer. In a photovoltaic device such as a photovoltaic device in which a crystalline semiconductor is formed and joined, a conventional problem that a constituent element of an insulating layer diffuses in a semiconductor thin film and deteriorates photovoltaic characteristics is solved. As a result, a photovoltaic device having improved photovoltaic characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a structural diagram of a photovoltaic device manufactured according to the present invention.

FIG. 2 is a cross-sectional view showing steps of the manufacturing method of the present invention.

FIG. 3 is a cross-sectional view showing the steps of the manufacturing method of the present invention.

FIG. 4 is a graph showing the relationship between the film thickness of an insulating layer and photovoltaic characteristics.

FIG. 5 is a structural diagram of a photovoltaic device manufactured according to the present invention.

FIG. 6 is a structural diagram of a photovoltaic device manufactured by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polycrystalline silicon film (n type) 2 Amorphous silicon layer (i type) 3 Amorphous silicon layer (p type) 4 Front surface electrode 5 Collection electrode 6 Back surface electrode 7 Insulating layer 11 Substrate 12 Amorphous silicon layer ( n type) 13 amorphous silicon layer (i type) 14 amorphous silicon layer (p type) 15 insulating layer 16 surface electrode 17 collector electrode

Claims (2)

[Claims] 1. A method of manufacturing a photovoltaic device, comprising one or a plurality of semiconductor thin films laminated on a semiconductor having an uneven surface, wherein the semiconductor and the semiconductor thin film generate an electromotive force by light irradiation. A method for manufacturing a photovoltaic device, comprising a step of forming an insulating layer on the semiconductor thin film. 2. A method for manufacturing a photovoltaic device, comprising one or a plurality of semiconductor thin films laminated on a semiconductor having an uneven surface, wherein the semiconductor and the semiconductor thin film generate an electromotive force by light irradiation. A method for manufacturing a photovoltaic device, comprising the step of insulating the upper part of the semiconductor thin film to form an insulating layer.