JPH04299576A - Photovoltaic element and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a doping layer of high conductivity, by increasing doping efficiency. CONSTITUTION:An amorphous semiconductor layer 7 in which impurities determining the conductivity type are mixed is formed by implanting dopant in the surface of an I-type amorphous semiconductor layer 6, by plasma- decomposing mixed gas of hydrogen and gas which contains doping elements.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device that directly converts light energy such as sunlight into electrical energy, and a method for manufacturing the same.

0002

[Prior Art] A conventional photovoltaic device has a transparent electrode made of a light-transmitting conductive oxide such as indium tin oxide (ITO) or tin oxide (SnO2) on an insulating transparent substrate such as glass. A p-type amorphous silicon layer, an i-type amorphous silicon layer that receives light reflection and generates photocarriers mainly electrons and holes, and an n-type amorphous silicon layer are deposited thereon. They are sequentially laminated, and a back electrode made of aluminum (AI), silver (Ag), etc. is further deposited thereon.

0003

Generally, p-type amorphous silicon layers and n-type amorphous silicon layers, that is, doped layers doped with impurities that determine conductivity type, cannot contribute to power generation because they have many defects. Further, in the conventional method of forming a doping layer in which a gas containing a doping element is mixed when forming an amorphous silicon layer, the doping efficiency is low. Because of this, conductivity is low, so in photovoltaic devices such as solar cells, the film thickness has been increased to some extent to reduce loss due to contact resistance of electrodes, etc.

As mentioned above, in the conventional method, the conductivity of the doped layer is low, so in order to obtain sufficient characteristics,
The thickness of the film had to be increased, which made it impossible to use light effectively, which hindered improvement in the efficiency of photovoltaic devices.

The present invention was made to solve the above-mentioned conventional problems, and its purpose is to improve the efficiency of a photovoltaic device by increasing doping efficiency and providing a doped layer with high conductivity. Take it as a challenge.

[0006]

[Means for Solving the Problems] A photovoltaic device of the present invention has an amorphous semiconductor layer of one conductivity type, an i-type amorphous semiconductor layer, and an amorphous semiconductor layer of another conductivity type stacked in this order. In the photovoltaic device, the other conductivity type amorphous semiconductor layer is formed by injecting a dopant into the surface of the i-type amorphous semiconductor layer or into the amorphous semiconductor layer containing a minute amount of a doping element. It is characterized by being formed by

[0007] Furthermore, it is preferable that the concentration of the dopant doped into the other conductivity type amorphous semiconductor layer is 3% or more.

Furthermore, the dopant is preferably implanted by plasma decomposition of a mixed gas of hydrogen and a gas containing the dopant element.

Further, the method for manufacturing a photovoltaic device of the present invention includes forming an amorphous semiconductor layer of one conductivity type and an amorphous semiconductor layer of an i-type on a substrate in this order, and then forming an amorphous semiconductor layer of another conductivity type. The method is characterized in that a mixed gas of hydrogen and a gas containing a dopant element is subjected to plasma decomposition, and the surface of the i-type amorphous semiconductor layer is doped with the dopant element to form an amorphous semiconductor layer of other conductivity type.

0010

[Operation] According to the present invention, in the formation of an amorphous semiconductor layer mixed with an impurity that determines the conductivity type, that is, a doping layer,
A doped layer with high conductivity can be formed by injecting a dopant into the surface of an i-type amorphous semiconductor layer or into an amorphous semiconductor layer containing a minute amount of a doping element.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a solar cell using a photovoltaic element according to an embodiment of the present invention.

In FIG. 1, 1 is an insulating transparent substrate such as glass which becomes the light incident side, and 2 is a transparent electrode made of a translucent conductive oxide such as ITO or SnO2. It is deposited by etc.

3 is a photovoltaic element according to the present invention, which includes a p-type amorphous silicon layer 4, a buffer layer 5, a non-doped i-type non-conductor that generates photocarriers mainly electrons and holes upon reflection of light. It consists of a crystalline silicon layer 6 and an n-type amorphous silicon layer 7 formed by implanting a dopant into the i-type amorphous silicon layer 6.

8 is a back electrode made of aluminum, silver, or the like.

Now, the feature of the present invention lies in the n-type amorphous silicon layer 7 formed by implanting a dopant into the i-type amorphous silicon layer 6. After forming the i-type amorphous silicon layer 6, a mixed gas of hydrogen and a gas containing phosphorus (P) element is subjected to plasma decomposition to form the i-type amorphous silicon layer 6.
The surface is doped with phosphorus (P) to form an n-type amorphous silicon layer 7. This doping method will hereinafter be referred to as a post-doping method.

Next, Table 1 shows specific conditions for forming a solar cell using the photovoltaic element according to the present invention. For comparison, we also prototyped a solar cell using a conventional method. The specific formation conditions are shown in Table 2. All formation temperatures were 200°C. In order to strictly compare the characteristics, i amorphous silicon layer,
The total thickness of the n-amorphous silicon layer was the same.

In the photovoltaic device 3 according to the present invention, the n-type amorphous silicon layer 7 is formed after the i-type amorphous silicon layer 6 is formed.
A mixed gas of phosphine (PH3) and hydrogen (H2) was subjected to plasma decomposition, and the i-type amorphous silicon layer 6 was doped with phosphorus (P).

[0019]

[Table 1]

[0020]

[Table 2]

[0021] The depth distribution of phosphorus (P) in two solar cells produced under each of the above formation conditions was analyzed by SIMS (secondary ion mass spectrometry). The results are shown in Figure 3.
Shown below. In this case, measurements are taken at a location where there is no back electrode (Ag).

It can be seen that the effective thickness of the n-amorphous silicon layer 7 of the solar cell according to the present invention is 100 Å, which is thinner than the n-amorphous silicon layer (400 Å) of the conventional solar cell. This difference in film thickness results in a difference in sensitivity at long wavelengths as shown in FIG.

Table 3 shows the characteristics of the solar cell according to the present invention (invention ①) prepared under the above-mentioned formation conditions and a conventional solar cell.

[0024]

[Table 3]

It can be seen from Table 3 that the current of the solar cell using the photovoltaic element of the present invention increases. The reason for this is that the photosensitivity to long wavelength light has improved as shown in FIG. That is, it shows that light could be effectively utilized according to the present invention.

Furthermore, in a solar cell formed under conventional conditions with an n-amorphous silicon layer having a thickness of 100 Å, a decrease in open-circuit voltage was observed as shown in Table 3, indicating that sufficient potential was not obtained. I understand. This shows that the method for forming an n-amorphous silicon layer according to the present invention can increase doping efficiency and provide a film with sufficient characteristics as a doped layer for solar cells.

[0026] Furthermore, after forming the solar cell of the conventional structure with an n-layer of 100 Å as described above, the same treatment with PH3/H2 as in the example of the present invention was performed. improved as shown. As described above, it can be seen that even in the doped layer formed by the conventional method, the doping efficiency can be improved by further performing post-doping.

In the present invention, the surface layer (near the interface with the metal) has the largest amount of dopant (phosphorus (P) in this case). Therefore, the phosphorus (P) concentration was investigated by AES (Auger electron spectroscopy), and the correlation with the open circuit voltage was investigated. The results are shown in FIG. Conventional example (n film thickness = 100 Å)
It can be seen that the characteristics are more improved when the phosphorus (P) concentration is 3% or more. Therefore, the phosphorus (P) concentration is preferably 3% or more.

Next, an embodiment in which the present invention is applied to a stacked amorphous silicon solar cell having the structure shown in FIG. 5 will be described. FIG. 5 is a schematic diagram showing a stacked amorphous silicon solar cell, a so-called tandem structure solar cell.

In FIG. 5, 1 is an insulating transparent substrate, and 2 is a transparent electrode.

31 is a first layer photovoltaic element according to the present invention, which includes a p-type amorphous silicon layer 41, a buffer layer 51, an i-type amorphous silicon layer 61, and an i-type amorphous silicon layer. It consists of an n-type amorphous silicon layer 71 formed by implanting dopants into 61.

32 is a second layer photovoltaic element according to the present invention, which includes a p-type amorphous silicon layer 42, a buffer layer 52, an i-type amorphous silicon layer 62, and an i-type amorphous silicon layer. It consists of an n-type amorphous silicon layer 72 formed by implanting dopants into 62.

8 is a back electrode made of aluminum, silver, or the like.

The conditions for forming this solar cell were the same as those shown in Table 1, but the thickness of each layer was as shown in Table 4 in order to form a tandem structure.

However, in the present invention, the thickness of the i-type amorphous silicon layer is the sum of the thickness of the n-type amorphous silicon layer (870 Å in the case of i61 and 870 Å in the case of i62), as in the above embodiment. 4100 Å), post-doping was performed under the conditions shown in Table 1.

[0035]

[Table 4]

Table 5 shows the characteristics in this case. In the case of a tandem type, the n/p reverse junction characteristic (n-type amorphous silicon layer 71/p-type amorphous silicon layer 42) has a particularly large influence on the characteristics (particularly the open-circuit voltage). However, it can be seen that in the present invention, the open circuit voltage is high and a good junction is obtained.

[0037]

[Table 5]

In the case of a laminated structure such as the tandem shown here, when the light incidence side is set at the top, there is also a power generation layer (i-type amorphous silicon layer) at the bottom of the reverse junction. Reducing light absorption at the junction leads to improved properties. Therefore, in general, n-type amorphous silicon layer 7 in Table 4
1, the n-type amorphous silicon layer 71 is made thinner than the n-type amorphous silicon layer 72. In such a case, the effects of the present invention will be greater. That is, as shown in the bottom row of Table 5, even if only the reverse joint is formed by the method of the present invention,
It can be seen that the effect is large.

[0039] In the above embodiment, a translucent substrate (glass) is used, and p, i, and n are formed in this order. However, the same applies to the case where the reverse structure is formed, that is, n, i, and p are formed in this order. It is. In this case, the p-type amorphous silicon layer may be formed by the post-doping method of the present invention. Furthermore, a similar effect can be obtained with a solar cell having a three-layer structure using amorphous silicon germanium (a-SiGe).

[0040]

[Effects of the Invention] As explained above, according to the present invention,
Since a more effective doping layer can be obtained, it is effective in improving the characteristics of solar cells made of amorphous semiconductors.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram illustrating a solar cell using a photovoltaic element of the present invention, showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the photosensitivity of a solar cell using the photovoltaic element of the present invention and a conventional solar cell.

FIG. 3 is a characteristic diagram showing the distribution of phosphorus concentration in the depth direction of the present invention and a conventional example.

FIG. 4 is a characteristic diagram showing the dependence of phosphorus concentration in a solar cell using the photovoltaic element of the present invention and a conventional solar cell.

FIG. 5 is a schematic diagram illustrating a second embodiment of the present invention, illustrating a stacked amorphous silicon solar cell using the photovoltaic element of the present invention.

[Explanation of symbols]

1 Insulating transparent substrate 2 Transparent electrode 3 Photovoltaic element 4 P-type amorphous silicon layer 5 Buffer layer 6 I-type amorphous silicon layer 7 N-type amorphous silicon layer 8 Back electrode 31 First layer photovoltaic element 41 p-type amorphous silicon layer 51 Buffer layer 61 I-type amorphous silicon layer 71 N-type amorphous silicon layer 32 Second layer photovoltaic element 42 p-type amorphous silicon layer 52 Buffer layer 62 I-type amorphous silicon layer 72n type amorphous silicon layer

Claims (4)

[Claims] 1. A photovoltaic element comprising an amorphous semiconductor layer of one conductivity type, an i-type amorphous semiconductor layer, and an amorphous semiconductor layer of another conductivity type, which are laminated in this order, A photovoltaic device characterized in that the amorphous semiconductor layer is formed by injecting a dopant into the surface of the i-type amorphous semiconductor layer or into the amorphous semiconductor layer containing a minute amount of a doping element. element. 2. The photovoltaic device according to claim 1, wherein the concentration of the dopant doped into the other conductivity type amorphous semiconductor layer is 3% or more. 3. The photovoltaic device according to claim 1, wherein the dopant is implanted by plasma decomposition of a mixed gas of hydrogen and a gas containing the dopant element. 4. On the substrate, an amorphous semiconductor layer of one conductivity type,
After forming the i-type amorphous semiconductor layer in this order, when a different conductivity type is obtained, a mixed gas of a gas containing a dopant element and hydrogen is plasma decomposed to dope the surface of the i-type amorphous semiconductor layer with a dopant element. 1. A method for manufacturing a photovoltaic device, the method comprising: forming an amorphous semiconductor layer of a different conductivity type.