JPH0634404B2 - Method for manufacturing amorphous silicon solar cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an amorphous silicon solar cell, and more particularly to an amorphous silicon solar cell having good photoconductivity and suppressed photodegradation characteristics. The present invention relates to a manufacturing method.

[Conventional technology]

In an amorphous silicon solar cell, it is important to reduce the internal stress of the amorphous silicon layer, which is the power generation region, in order to suppress its photodegradation characteristics and improve its reliability (Itagaki et al. 46th Applied Physics) Academic Conference Proceedings October 60, Nakamura et al. 11th International
Conference Amorphous and Liquid Semi-Conference Proceedings September 60 Rome (G. Nakamura et al.
Proc. 11th ICALS)). In particular, an amorphous silicon layer having a pin structure is usually used in an amorphous silicon solar cell. Among them, reducing the internal stress in an i-type layer (hereinafter referred to as an i layer) in which carriers are generated is described above. It is especially necessary to suppress the photodegradation characteristics.

On the other hand, conventionally, in an amorphous silicon solar cell, an amorphous silicon layer including an i layer (hereinafter referred to as aS
i: Referred to as the H layer. ) Is a plasma CV using SiH ₄ gas as a main component gas so that excellent photoconductive characteristics can be obtained.
According to the D method, with a relatively low RF power density of about 30 W, the SiH ₄ gas supply rate was 50 cc / min (actually with He gas).
The total flow rate of the SiH ₄ gas diluted to 10% is 500 per minute.
Supply as cc. It is known that under the growth condition of (1), which has a relatively low growth rate, the hydrogen bonding state inside thereof is formed only by Si—H bonds.

[Problems to be solved by the invention]

As described above, the a-Si: H layer in the conventional amorphous silicon solar cell is usually formed by a plasma CVD method using SiH ₄ gas so that excellent photoconductive characteristics can be obtained. Are formed under the growth conditions with a low growth rate, such that Si has only Si-H bonds.
However, the compressive stress of the a-Si: H layer is mainly proportional to the concentration of Si-H bond in the layer, and if the hydrogen bond state in the a-Si: H layer is Si-H bond only, photoconductivity is increased. Although the characteristics are good, on the other hand, the internal stress in the layer becomes very large due to this Si-H bond, and as a result, the photodegradation characteristics such as the photoconductive characteristics gradually decreasing with the use of the solar cell become remarkable. There was a problem of becoming. In particular, when the internal stress of the i layer that generates carriers due to the incidence of light is large, this photodegradation characteristic becomes more prominent.

This invention has been made to solve the above conventional problems, without impairing good photoconductive characteristics,
It is intended to obtain an amorphous silicon solar cell capable of suppressing photodegradation characteristics.

[Means for solving problems]

The method for manufacturing an amorphous silicon solar cell according to the present invention decomposes Si ₂ H ₆ gas in a plasma atmosphere to produce a-
When the Si: H layer is formed, the decomposition efficiency of the Si ₂ H ₆ gas is lowered, so that a tensile stress is generated in the formed a-Si: H layer. Si-H ₂ or (Si-H ₂ ) n bond , Which is a factor that determines the above decomposition efficiency.
When the power and the flow rate of the raw material gas are made the same as those in the case of decomposing the SiH ₄ gas in the plasma atmosphere and forming the a-Si: H layer so that the hydrogen bonding state inside thereof is only the Si—H bond, A-Si: H obtained by decomposition of Si ₂ H ₆ gas
Taking advantage of the fact that there are many Si-H ₂ or (Si-H ₂ ) n bonds in the layer and the stress of the entire layer becomes tensile stress,
The SiH ₄ gas is decomposed in a plasma atmosphere to obtain a-Si:
The hydrogen bond state in the a-Si: H layer when the H layer is formed
Under growth conditions (RF power and the raw material gas supply amount) to only the SiH bond, and a SiH ₄ gas and Si ₂ H ₆ gas molar ratio of Si ₂ H ₆ gas is 2.5~20mol /% The i-type amorphous silicon layer is formed by using the mixed gas thus mixed as a raw material gas.

Furthermore, the method for producing an amorphous silicon solar cell according to the present invention provides a hydrogen bond in the a-Si: H layer when the SiH ₄ gas is decomposed in a plasma atmosphere to form the a-Si: H layer. The first i-type amorphous silicon layer is formed by using Si ₂ H ₆ gas as a raw material gas under the growth condition (RF power and raw material gas supply amount) in which the state is only Si—H bond, and the above is alternately performed. The second i-type amorphous silicon layer is formed by using SiH ₄ gas as a source gas.

[Action]

In the present invention, the hydrogen bonding state in the i-type amorphous silicon layer, Si-H bonds and Si-H _2, or (Si-H ₂₎ from n bond can be moderately mixed state,
The i-type amorphous silicon layer, said Si-H with show good photoconductivity by coupling, the pressure of the entire layer is Si-H bonds compressive stress and Si-H _2, or by (Si-H ₂₎ n It is possible to prevent the deterioration of the good photoconductive property of the amorphous silicon layer over time, which is relaxed by the tensile stress due to the bonding.

Further, in the present invention, the i-type amorphous silicon layer is caused to have a hydrogen bond consisting of Si—H ₂ or (Si—H ₂ ) n bond inside, and thus the photoconductivity is slightly poor,
The first i-layer in which the stress of the entire film becomes tensile stress and the hydrogen bonding state inside the i-layer shows only the Si-H bond, and exhibits extremely excellent photoconductive characteristics. The stress in the entire film becomes compressive stress. Since the i-type amorphous silicon layer has a good photoconducting property by the second i-layer, the stress of the entire i-type amorphous silicon layer is The tensile stress due to the Si-H ₂ or (Si-H ₂ ) n bond of the i layer is relaxed by the compressive stress due to the Si-H bond of the second i layer, and the good photoconductive property of the amorphous silicon layer is improved over time. It is possible to prevent the deterioration.

〔Example〕

Hereinafter, the basic principle of the present invention will be described, and the embodiments of the present invention will be described together.

A− obtained by decomposing Si ₂ H ₆ gas in a plasma atmosphere
For Si: H film, decomposition efficiency of Si ₂ H ₆ gas in plasma atmosphere In the film with high resolution, the internal stress is the compression pressure due to the Si-H bond, but due to the decrease in the decomposition efficiency, Si-H ₂ or (Si
The −H ₂ ) n concentration increases, and the internal stress changes continuously from compressive stress to tensile stress.

Figure 1 shows that the RF power density was kept constant (30 W) under an atmospheric pressure of 0.4 Toor, and the Si ₂ H ₆ gas supply amount (here, Si
The total flow rate of the gas obtained by diluting ₂ H ₆ gas with He gas to 10% is shown for 1 minute, and the actual flow rate of Si ₂ H ₆ gas is 1/10 of the value on the horizontal axis of the figure. A) formed by changing
The change in pressure in the Si-H film is shown. SiH in the figure
₄ (-○-) is an RF power density of 30 W under an atmospheric pressure of 0.4 Toor, the SiH ₄ gas is diluted with He gas to 10%, and the supply amount of the gas is 500 cc per minute (the supply amount of the SiH ₄ gas is When it is set to 50 cc / min, the hydrogen bonding state inside the
Only Si-H bond shows the most excellent photoconductivity
It shows that a -Si: H layer is formed.

On the other hand, FIG. 3 (a) shows a-Si: H films formed in accordance with the respective supply amounts when the a-Si: H film is formed by changing the supply amount of Si ₂ H ₆ gas in FIG. Si-H bond between Si: H films
Si-H ₂ and (Si-H ₂₎ is a view showing a change in abundance of n bonds, characteristic line of 2000 cm ^-1 in FIG. (- ○ -) is S
Infrared absorption peak corresponding to -H bond, 2090 cm ^-1
Is the infrared absorption peak corresponding to Si-H ₂ and (Si-H ₂ ) n bond.
As the supply amount of Si ₂ H ₆ gas increases, the decomposition efficiency of Si ₂ H ₆ gas decreases and the a-Si: H film grows.
Si-H bonds decreases, Si-H ₂ and (Si-H ₂₎ it can be seen that the n coupling increases.

Further, FIG. 2 shows the same growth condition as that described above in which the hydrogen bonding state inside the grown film when only SiH ₄ gas is used is only Si—H bond, that is, the RF power density is 30 W and the supply of the source gas is performed. The amount is 50 cc / min, and the mixed gas of SiH ₄ gas and Si ₂ H ₆ gas is used as a raw material gas. The mol ratio of Si ₂ H ₆ gas in the mixed gas (Si ₂ H ₆ / SiH ₄ + Si ₂ H ₆ ) To change a-
Si: a change in the internal stress in the film when the H film was formed, the same growth conditions as described above, i.e., the RF power density 30 W, the supply amount of the raw material gas in the growth conditions per minute 50 cc, Si ₂ H ₆
Si-H ₂ was grown inside the grown film grown using the gas as the source gas.
Or a lot of (Si-H ₂ ) n bonds were generated ~ 4 × 10 ⁹ dynes
a first a-Si: H film having a tensile stress of about / cm ² and SiH ₄
A second a-Si: H film having a compressive force of about 10 × 10 ⁹ dynes / cm ^{2 in} which the hydrogen bond state inside the grown film was grown only by Si—H bond, using a gas as a source gas. It shows changes in internal stress in the entire laminated film when the film thickness of these films of an a-Si: H film having a thin film laminated structure alternately laminated is changed. From this figure, RF power density 30W
In the case of forming an a-Si: H film using a mixed gas of SiH ₄ gas and Si ₂ H ₆ gas as a raw material gas under a growth condition in which the supply amount of the raw material gas is 50 cc / min, Si ₂ H ₆ gas It can be seen that when the mol ratio is 2.5 to 20%, the value of the compressive or tensile stress applied to the obtained film becomes smaller than 3 × 10 ⁹ dynes / cm ² , and the photodegradation property can be reduced. Also, RF
Power density of 30 W, supply rate of raw material gas 50 cc / min
When a first a-Si: H film formed by using SiH ₄ gas as a raw material gas and a second a-Si: H film formed by using Si ₂ H ₆ gas as a raw material gas are stacked under the growth conditions described above. It can be seen that, when these film thicknesses are set in the range of 50 to 200Å, the value of the compressive stress applied to the entire laminated film becomes smaller than 4 × 10 ⁹ dynes / cm ² , and the photodegradation characteristics can be reduced. On the other hand, FIG. 3 (b) shows the formed a when the mol ratio of Si ₂ H ₆ gas in FIG. ₂ was changed to 2.5 to 20%.
-Si: Si-H bonds and Si-H ₂ and between H film (Si-
FIG. 2 is a diagram showing changes in the abundance of H ₂ ) n bonds,
The characteristic line at −000 cm ⁻¹ (− ◯ −) is the infrared absorption peak corresponding to the S—H bond, and the characteristic line at 2090 cm ⁻¹ (− □).
−) Is an infrared absorption peak corresponding to Si—H ₂ and (Si—H ₂ ) n bond, and this figure shows that the molar ratio of Si ₂ H ₆ gas is 2.5 to 2
Changing to 0%, as mol ratio of Si ₂ H ₆ gas is increased by decomposition efficiency of Si ₂ H ₆ gas is lowered, growing a-Si: Si-H ₂ and the H film ( Si−
H ₂ ) n bonds increase, but Si-H bonds do not decrease so much,
It has been demonstrated that the stress of the a-Si: H film is relaxed and good photoconductive properties can be maintained.

The data shown in the above figure is the data when the a-Si: H film was formed under the atmospheric pressure of 0.4 Toor, but the atmospheric pressure was changed within the general range of 0.1 to 5 Toor. Even in the case, the characteristics (trend) similar to the above can be obtained under the atmospheric pressure.

Based on the principle of the present invention as described above, the following amorphous silicon solar cell can be produced.

(I) Hydrogen bonding state in an amorphous silicon film (a-Si: H layer) formed by decomposition of SiH ₄ gas using a mixed gas of SiH ₄ gas and Si ₂ H ₆ gas as a source gas Is decomposed under growth conditions (RF power density and raw material gas flow rate) where only Si-H bonds are generated, so that Si-H bonds due to the decomposition of SiH ₄ gas and the decomposition of Si ₂ H ₆ gas inside are decomposed. An amorphous silicon layer in which Si—H ₂ or (Si—H ₂ ) n bonds are mixed is formed, and an amorphous silicon solar cell having this as an i-type amorphous silicon layer is prepared. This makes it possible to obtain an amorphous silicon solar cell in which good photoconductive properties do not deteriorate for a long period of time.

The mixing ratio of the mixed gas of SiH ₄ gas and Si ₂ H ₆ gas is preferably 2.5 to 20 mol /%, and particularly preferably 10
˜20 mol /%. As is clear from FIG. 2, when the mixing ratio of the mixed gas is 2.5 to 20 mol /%, the compressive or tensile stress of the i-type amorphous silicon layer is smaller than 4 × 10 ⁹ dynes / cm ^2. Yes, again
When the amount is 10 to 20 mol /%, the compressive or tensile stress of the i-type amorphous silicon layer is 1.5 × 10 ⁹ d.
The amount of Si-H bond and Si-H ₂ or Si-H ₂ or (Si-H ₂ ) n bond in the layer can be reduced to less than ynes / cm ² and the reliability of the amorphous silicon solar cell can be further improved. .

(Ii) The Si ₂ H ₆ gas is used as a source gas, and the source gas is
Growth conditions where the hydrogen bond state in the amorphous silicon film (a-Si: H film) formed by decomposition of H ₄ gas is only Si-H bond (RF power density and source gas flow rate)
Then, by decomposing, a first i-type amorphous silicon layer in which Si—H ₂ or (Si—H ₂ ) n bond is formed by the decomposition of Si ₂ H ₆ gas is formed. Alternately, by using SiH ₄ gas as a raw material gas and decomposing the raw material gas under the same growth conditions as the growth conditions (RF power density and raw material gas flow rate) of the first amorphous silicon layer, the inside thereof is decomposed. The second i-type amorphous silicon layer is formed so that the hydrogen bonding state is only Si-H bond, and an amorphous silicon solar cell including this laminated film as the i-type amorphous silicon layer is prepared. This makes it possible to obtain an amorphous silicon solar cell in which good photoconductive characteristics are not deteriorated.

The layer thickness of the first and second i-type amorphous silicon layers is preferably 50 to 200Å, and particularly preferably 5
0 to 150Å. As is clear from FIG. 2, when the layer thickness is 50 to 200Å, the compressive stress of the i-type amorphous silicon layer can be made smaller than 4 × 10 ⁹ dynes / cm ² , and when it is 50 to 150Å, 3 x 10 ⁹ dynes / cm ²
The size can be made smaller, and in these cases, the reliability of the amorphous silicon solar cell can be further improved.

〔The invention's effect〕

As described above, according to the present invention, the hydrogen bonding state inside the i layer of the amorphous silicon layer is Si--H.
Bond and Si-H _2, or (Si-H ₂₎ n bond is appropriately mixed, the i layer overall stress is reduced, moreover, since the show a good photoconductivity, excellent photoconductivity It is possible to obtain an amorphous silicon layer capable of maintaining the temperature for a long period of time, and it is possible to obtain a highly reliable amorphous silicon solar cell.

Further, according to the present invention, i of the amorphous silicon layer is
The first i-layer, in which a large amount of Si-H ₂ or (Si-H ₂ ) n bonds are generated inside the layer, the photoconductive characteristics are slightly poor and the stress of the entire film becomes tensile stress, and the inside thereof It has excellent photoconductivity because its hydrogen bond state is composed of only Si-H bonds, and it has a superior photoconductivity because it is composed by interlacing a second i layer in which the stress of the entire film becomes a compressive stress. It is possible to obtain an amorphous silicon layer capable of maintaining the characteristics for a long period of time, and it is possible to obtain a highly reliable amorphous silicon solar cell.

[Brief description of drawings]

1 to 3 are diagrams for explaining the principle of the present invention. FIG. 1 shows changes in internal stress in the growing a-Si: H film when the Si ₂ H ₆ gas flow rate is changed. Figures and 2 show the mixture gas of SiH ₄ gas and Si ₂ H ₆ gas as the raw material gas and the molar ratio of Si ₂ H ₆ gas in the mixture gas (Si ₂ H ₆ / SiH ₄ + Si ₂ H
₆ ) is changed to form an a-Si: H film, the internal stress in the film changes, and Si ₂ H ₆ gas is used to produce Si inside.
-H ₂ or (Si-H ₂ ) n-type first a-Si: H film formed with a large number of (n-Si ₂ ) n-bonds and slightly poor in photoconductivity and in which the stress of the entire film becomes tensile stress, and SiH ₄ gas A second a-Si: H film having extremely excellent photoconductive characteristics, in which the stress of the entire film is a compressive stress. Stacked alternately,
A diagram showing changes in in-film stress when the thickness of each layer is changed,
FIGS. 3 (a) and 3 (b) are diagrams showing the results of measurement of infrared absorption of the amorphous films shown in FIGS. 1 and 2, respectively.

Claims (3)

[Claims] 1. An amorphous silicon layer (a-Si: H layer)
In a method of manufacturing an amorphous silicon solar cell according to the power generation region, the i layer of the amorphous silicon layer, the molar ratio of the SiH ₄ gas and Si ₂ H ₆ gas Si ₂ H ₆ gas (Si ₂ H ₆ /
SiH ₄ + Si ₂ H ₆ ) is mixed as 2.5 to 20 mol /% as a raw material gas, and the RF power and the raw material gas flow rate at that time are measured by the plasma CVD method using the SiH ₄ gas as the raw material gas. Amorphous silicon solar cells characterized by being deposited by the plasma CVD method in the same manner as in the case of forming an a-Si: H layer so that the hydrogen bonds inside the grown film are only Si-H bonds. Production method. 2. An amorphous silicon layer (a-Si: H layer)
In the method for producing an amorphous silicon solar cell in which the power generation region is as follows, the i layer in the amorphous silicon layer is formed by a plasma CVD method using SiH ₄ gas as a raw material.
Hydrogen bonding that occurs within the growing film is first i-type a-Si with the RF power and the flow rate of the raw gas such that only the Si-H bond: a first step of depositing form H layer, Si ₂ Using H ₆ gas as a source gas, the RF power and the flow rate of the source gas at that time were changed to Si--H by the plasma CVD method using the above SiH ₄ gas as the source gas.
A second i-type a-Si: H layer is deposited and formed by a plasma CVD method in the same manner as in the case of depositing and forming the first i-type a-Si: H layer so that only the bonds are formed. The method of manufacturing an amorphous silicon solar cell is characterized in that the steps of and are alternately performed. 3. The first i-type a-Si: H layer and the second i-type a-Si: H layer.
The method for producing an amorphous silicon solar cell according to claim 2, wherein the type a-Si: H layers are each formed to have a layer thickness of 50 to 200Å.