JPH0548127A - Amorphous silicon solar battery and its manufacture - Google Patents

Abstract

PURPOSE:To enable an amorphous silicon solar battery having an intrinsic a-Si layer to have a performance equivalent to that of amorphous silicon solar batteries having no intrinsic a-Si layer without increasing the contact resistance between the intrinsic a-Si layer and a rear surface electrode layer by forming the intrinsic a-Si layer on an n-layer and diffusing the rear surface electrode in the intrinsic a-Si layer. CONSTITUTION:An amorphous silicon (a-Si) solar battery element is constituted of a transparent electrode layer 2, p-layer 31, i-layer 32, and n-layer 33 which are successivel.y formed on the layer 2 and respectively composed of a-Si films, and rear surface electrode layer 4 which is formed so that the layer 4 can be diffused in an intrinsic a-Si layer 34 formed on the layer 33. Especially, the a-Si layer 34 is provided and, at the same time, the electrode layer 4 is diffused in the layer 34. Therefore, the contact resistance between the layers 3 and 4 does not increase and a performance which is equivalent to that of amorphous silicon solar batteries having no intrinsic a-Si layer 34 can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device used for a solar cell, an optical sensor, etc. and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 2 shows a transparent electrode layer 2 on an insulating substrate 1, an amorphous silicon layer 3 (hereinafter referred to as "a-Si layer") as an amorphous semiconductor layer, and a back electrode layer. FIG. 3 is a structural diagram of a unit solar cell element formed by stacking metal electrode layers 4. This type of solar cell element is prepared by first placing I on the glass substrate 1.
TO (indium tin oxide), SnO ₂ (tin oxide)
A transparent electrode layer 2 made of a transparent electric film such as is formed over the entire surface by electron beam evaporation, sputtering or thermal CVD to a thickness of about 4500Å. Next, the a-Si layer 3 is an intrinsic a-Si layer 32 (hereinafter referred to as "i layer") from the transparent electrode layer 2 side, for example, a p-type a-Si layer 31 having a thickness of about 200Å.
To a film of 0.2-1.0 μm and an n-type a-Si layer 33 of about 500
Å Grow with plasma discharge decomposition of silane gas to a thickness. Boron and carbon are added to the p-type, and phosphorus is added to the n-type. After that, the back surface electrode 4 is formed by the sputtering method or the vapor deposition method. This back electrode 4 has a film thickness of 2000Å
The above metals such as aluminum and silver are used.

The performance of the solar cell element depends on the thickness of the a-Si layer 3. In the conventional film forming method, p-type, i-type and n-type a-Si layers are formed in the same reaction chamber. Therefore, residual impurities (phosphorus) adhering to the inner wall of the reaction chamber, the high frequency electrode, etc. are easily taken in during the film formation, which causes deterioration of the film quality. That is, in the same reaction chamber system, the performance of the solar cell is influenced by the influence of phosphorus, which is an impurity added to the n layer formed before forming the solar cell. In order to improve the efficiency of the a-Si solar cell, it is desirable to minimize the residual phosphorus concentration. In order to solve the problem, a separation type plasma CVD method for forming a p layer, an i layer and an n layer in separate reaction chambers has been developed, and is disclosed in, for example, Japanese Patent Laid-Open No. 56-114387.

[0004]

Discrete type plasma CVD
According to the method, since there are three or more reaction chambers and the transportation mechanism for feeding the substrate into each reaction chamber is complicated, the apparatus becomes expensive. An object of the present invention is to suppress the influence of phosphorus in the n layer previously formed by the plasma CVD method using a single reaction chamber, to achieve a reproducible, high-performance and low-cost a-Si solar cell and its manufacture. To provide a method.

[0005]

In order to achieve the above object, an amorphous silicon solar cell of the present invention comprises a transparent electrode layer formed on a glass substrate and a pin junction formed on the transparent electrode layer. Comprising an amorphous silicon layer having: an intrinsic type amorphous silicon layer formed on the amorphous silicon layer, and a back electrode formed by diffusing into the intrinsic type amorphous silicon layer. Is. Further, in the method for manufacturing an amorphous silicon solar cell of the present invention, an amorphous silicon layer having a pin junction is provided on an insulating transparent substrate coated with a transparent electrode layer, and then an intrinsic type amorphous silicon layer is formed. However, after the metal back surface electrode is attached, heat treatment is performed.

[0006]

Since the intrinsic type amorphous silicon layer has a function of suppressing the phosphorus concentration, it is possible to prevent the deterioration of the electrical characteristics of the solar cell element due to the phosphorus taken in the i layer, and at the same time, the back electrode layer has the intrinsic type. Due to the diffusion in the amorphous silicon layer, the contact resistance between the amorphous silicon layer and the back electrode does not increase. Further, in the manufacturing process, after the formation of the solar cell, the thin film intrinsic type amorphous silicon layer is subsequently formed and then heat-treated, so that the influence of phosphorus on the solar cell to be formed later can be suppressed. It enables high-performance and low-cost amorphous silicon solar cells with high reproducibility even in a reaction chamber plasma CVD apparatus.

[0007]

EXAMPLE FIG. 1 shows the structure of an a-Si solar cell element of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals. The a-Si solar cell element includes a transparent electrode layer 2 formed on a glass substrate 1, a p-layer 31, an i-layer 32 and an n-layer 33 formed by an a-Si film formed on the transparent electrode layer 2.
It is composed of an intrinsic type a-Si layer (phosphorus concentration suppressing layer) 34 formed on the n layer 33, and a back surface electrode 4 formed so as to diffuse into the intrinsic type a-Si layer 34. There is. The a-Si solar cell element having the above structure is an intrinsic type a-S
By providing the i layer 34, it is possible to prevent deterioration of electrical characteristics of the solar cell element due to phosphorus taken in the i layer, and the back electrode layer is diffused in the intrinsic a-Si layer. The contact resistance between the a-Si layer 3 and the back surface electrode 4 does not increase, and the same performance as that without the intrinsic a-Si layer 34 can be provided.

To manufacture an a-Si solar cell element, SnO ₂ having a thickness of about 4500Å is first thermally CVD-coated on the glass substrate 1.
The transparent electrode layer 2 is formed by the method. Then, an a-Si film 3 having a pin junction (p layer 31, i layer 32, n layer 3
3) is formed to a thickness of about 0.4 μm by using the plasma CVD method, and then is formed in the same reaction chamber in order to suppress the phosphorus concentration.
A 300 Å intrinsic a-Si layer 34 (i layer) is subsequently formed. Further, aluminum is formed as the back surface electrode 4 to a thickness of about 2000 Å by a sputtering method.

Since the high resistance intrinsic layer 34 (i layer) is present between the n layer 33 and the back electrode layer 4 in the a-Si solar cell element manufactured by the above method, the contact resistance is large as it is. Satisfactory properties cannot be obtained. Therefore, heat treatment is performed after the above manufacturing process to diffuse the metal into the i layer 34 and improve the contact characteristics between the n layer 33 and the back electrode layer 4. In the heat treatment, the heat treatment time and the temperature change depending on the film thickness of the i layer 34 and the type of the back electrode, so that the heat treatment time and the temperature that maximize the average efficiency are selected. FIG. 3 is an example showing the dependence of the average efficiency on the heat treatment time. This example is about 300Å to i layer, a data when the heat treatment temperature 175 ⁰ C, the average efficiency heat treatment time at this time is highest at 20 minutes, lower more or less than that Shows a tendency to become.

By the way, i of 500Å is formed on the n layer or the p layer.
It is known that when a layer is formed, the impurity concentration in the film is reduced by about 3 orders of magnitude. However, if the i-layer thickness is 500
Impurity concentration does not change even if the thickness is more than Å. for that reason,
If the i-layer is thick, the heat treatment time is long and the temperature must be high, which is disadvantageous in manufacturing.
If the film thickness is made much thinner than 300Å, the effect of suppressing the phosphorus concentration becomes small. Therefore, the selection of the film thickness of the i layer is
It is performed in relation to the material of the back electrode, heat treatment time, heat treatment temperature, and the like.

FIG. 4 shows the effect of heat treatment on the a-Si solar cell element of the present invention. FIG. 4A shows the characteristics before the heat treatment, which is clearly deteriorated by the high resistance intrinsic layer. As shown in Fig. 4 (b), at 175 ° C, about 2
When the heat treatment was performed for 0 minutes, the performance could be sufficiently improved (see Table 1). As an output, a high efficiency of 8.6% was obtained when the incident light was 100 mW / cm ² (see Table 2). Table 1 shows main characteristic values of the a-Si solar cell element shown in FIG. Table 2 is a comparison of the characteristics of the conventional solar cell element and the solar cell element of the present invention.

Table 1 Before heat treatment After heat treatment Area cm ² 3.2 3.2 Light intensity mW / cm ² 100 100 Maximum power obtained mW 9.992 22.144 Optimum operating current mA 27.58 34.60 Optimum operating voltage V 0.36 0.64 Short circuit current mA 39.58 41.79 Open voltage V 0.69 0.90 short-circuit current density mA / cm ² 12.48 13.06 optimum operating current density mA / cm ² 8.62 10.81 fill factor 0.361 0.586 conversion efficiency% 3.11 6.89

Table 2 Types of solar cells Efficiency Open circuit voltage Short circuit current density Fill factor% V mW / cm ² Conventional type 7.90 0.91 14.61 0.594 Present invention 8.58 0.88 14.84 0.657

[0014]

As described above, according to the present invention, since the back electrode layer is diffused in the intrinsic a-Si layer, a
The contact resistance between the -Si layer and the back electrode 4 does not increase, and the same performance as that without the intrinsic a-Si layer 34 can be provided. Further, according to the method of the present invention, after the formation of the a-Si solar cell, the intrinsic type a-S having a predetermined film thickness is further formed.
By forming the i layer, forming the back electrode, and then performing heat treatment, it is possible to suppress the influence of phosphorus on the solar cells to be formed later.
Even with a single reaction chamber plasma CVD apparatus, an a-Si solar cell with high reproducibility, high performance and low cost can be manufactured.

[Brief description of drawings]

FIG. 1 is a structural diagram of an amorphous silicon solar cell element.

FIG. 2 is a structural diagram of a conventional amorphous silicon solar cell element.

FIG. 3 is a diagram showing heat treatment dependency of average efficiency.

FIG. 4 is a diagram for explaining the effect of heat treatment in the solar cell element of the present invention, FIG. 4A is a current-voltage characteristic before heat treatment, and FIG. 4B is a current-voltage characteristic after heat treatment.

[Explanation of symbols]

 1 Glass Substrate 2 Transparent Electrode Layer 3 Amorphous Silicon (a-Si) Layer 31 p-type Amorphous Silicon Layer 32 i-type Amorphous Silicon Layer 33 n-type Amorphous Silicon Layer 34 Phosphorus Concentration Suppression i-layer 4 Backside Metal electrode

Claims (2)

[Claims] 1. A transparent electrode layer formed on a glass substrate,
An amorphous silicon layer having a pin junction formed on the transparent electrode layer, an intrinsic type amorphous silicon layer formed on the amorphous silicon layer, and diffused in the intrinsic type amorphous silicon layer An amorphous silicon solar cell comprising a back electrode formed by the above process. 2. An amorphous silicon layer having a pin junction is provided on an insulating transparent substrate coated with a transparent electrode layer, then an intrinsic type amorphous silicon layer is formed, a metal back electrode is attached, and then heat treatment is performed. A method for manufacturing an amorphous silicon solar cell, which comprises: