JP3978121B2 - Method for manufacturing thin film solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film solar cell, and the present invention relates to an improvement of an i-type silicon layer of a microcrystalline silicon thin film solar cell having a pin structure.
[0002]
[Prior art]
As a thin film solar cell, a microcrystalline silicon thin film solar cell having a pin structure is known. Such a thin film solar cell includes a p-type microcrystalline silicon layer (polycrystalline silicon layer), an i-type microcrystalline silicon layer, and an n-type microcrystalline silicon layer. These layers are formed in the order of p-type layer, i-type layer, and n-type layer, or vice versa. The i-type layer has a function of generating carriers (that is, electrons and holes) by the photoelectric effect, and the p-type layer and the n-type layer separate the electrons and holes by applying an internal electric field to the i-type layer. It has a function to do.
[0003]
Such a thin film solar cell is typically formed by the following procedure. After an electrode is formed on the substrate, a p-type or n-type first microcrystalline silicon layer is formed on the electrode. Subsequently, an i-type microcrystalline silicon layer is formed on the first microcrystalline silicon layer, and further, a third microcrystalline silicon layer having a conductivity type opposite to that of the first microcrystalline silicon layer is formed. The first, second and third microcrystalline silicon layers are formed by plasma CVD (Chemical Vapor Deposition) using silane gas and hydrogen gas as source gases.
[0004]
In order to improve the efficiency of the thin film solar cell, it is effective to increase the grain size of the i-type microcrystalline silicon layer. Large crystal grains increase the efficiency of carrier generation in the i-type microcrystalline silicon layer and effectively improve the efficiency of the thin-film solar cell.
[0005]
The increase in the grain size of the crystal grains can be achieved by forming a silicon thin film under conditions where the proportion of hydrogen gas in the source gas is relatively low. However, if the i-type microcrystalline silicon layer is formed under such conditions, amorphous silicon is likely to be formed in the initial stage of forming the i-type microcrystalline silicon layer. That is, amorphous silicon is easily formed at the interface between the i-type microcrystalline silicon layer and the first microcrystalline silicon layer therebelow. Since carriers easily recombine in amorphous silicon, the efficiency with which carriers reach the p-type layer or the n-type layer decreases. Therefore, the presence of amorphous silicon at the interface reduces the conversion efficiency of the thin film solar cell.
[0006]
It is desired to provide a technique for effectively suppressing the formation of amorphous silicon in the initial stage of forming the i-type microcrystalline silicon layer.
[0007]
As a technology that can be related to the present application, Non-Patent Document 1 uses carbon dioxide plasma or hydrogen plasma on the surface of i-type amorphous silicon before forming a p-type microcrystalline silicon layer on i-type amorphous silicon. Discloses a technique for plasma processing. Plasma treatment using carbon dioxide plasma or hydrogen plasma optimizes the nucleation of the p-type microcrystalline silicon layer and enables the formation of a p-type microcrystalline silicon layer having good characteristics. However, Non-Patent Document 1 has no description about the formation of the i-type microcrystalline silicon layer.
[0008]
[Non-Patent Document 1]
P. Pernet, M. Goetz, H. Keppner, and A. Shar, Growth of Thin <p> μc-Si: H on Intrinsic a-Si: H for <nip> Solar Cells Application, "Proceedings of the MRS Symposium, Fall Meeting ", December 1996, Boston, 1997, vol. 452, p.889-894.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a technique for effectively suppressing the formation of amorphous silicon in the initial stage of forming an i-type microcrystalline silicon layer of a microcrystalline silicon solar cell having a pin structure.
[0010]
[Means for Solving the Problems]
Hereinafter, means for solving the problem will be described using the numbers and symbols used in the [Embodiments of the Invention]. These numbers and symbols are added to clarify the correspondence between the description of [Claims] and the description of [Embodiments of the Invention]. However, the added numbers and symbols shall not be used for the interpretation of the technical scope of the invention described in [Claims].
[0015]
A method for producing a thin-film solar cell according to the present invention includes:
Forming a first conductivity type first silicon layer (3, 24) on the upper surface side of the substrate (1, 21);
And forming the first silicon layer (3, 24), oxidized layer on the surface portion of the first silicon layer is exposed to an oxygen-containing atmosphere (3, 24) and (4, 25),
By plasma CVD using a material gas containing hydrogen gas, on the oxidized layer (4, 25), the intrinsic and, forming a second silicon layer of the microcrystalline (5,26),
Forming a third silicon layer (6, 27) of a second conductivity type opposite to the first conductivity type on the second silicon layer (5, 26). When the second microcrystalline silicon layer is formed directly on the first silicon layer, the ratio of hydrogen gas to the source gas is low enough to form amorphous silicon in the initial stage of formation. It is formed. Forming on the surface of the oxidized layer (4, 25) a first silicon layer (3, 24) is amorphous silicon in the initial stage of the formation of the second silicon layer is a microcrystalline silicon film (5,26) Is effectively prevented from forming. Exclusion of amorphous silicon from the second silicon layer (5, 26) effectively improves the conversion efficiency of the thin film solar cell.
[0016]
From the viewpoint of simplifying the manufacturing process, the oxygen atmosphere used for forming the silicon oxide layer (4, 25) is preferably air.
[0017]
The thin film solar cell manufacturing method includes controlling the amount of water vapor contained in the oxygen atmosphere used to form the silicon oxide layer (4, 25). Can be stabilized. More specifically, dry air is preferably used as the oxygen atmosphere.
[0018]
When dry air is used as the oxygen atmosphere, the thin-film solar cell manufacturing method further includes the step of exposing the first silicon layer (3, 24) while exposing the first silicon layer (3, 24) to the oxygen atmosphere. It is preferable to comprise heating. The formation of the silicon oxide layer (4, 25) by dry air is preferable in terms of stabilizing the thickness of the silicon oxide layer (4, 25), while the oxidation rate of silicon by the dry air is determined by oxygen containing water vapor. Slower than the rate of silicon oxidation by the atmosphere. By heating the first silicon layer (3, 24), the oxidation rate of silicon can be compensated.
[0019]
In order not to hinder the operation of the thin film solar cell, the silicon oxide layer (4, 25) is preferably thin enough to allow a tunnel current to flow.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a thin film solar cell and a manufacturing method thereof according to the present invention will be described with reference to the accompanying drawings.
[0021]
(First embodiment)
FIG. 1 shows a first embodiment of a thin film solar cell according to the present invention. A transparent and conductive TCO (Transparent Conductive Oxide) layer 2 is formed on a transparent and insulating glass substrate 1. A p-type microcrystalline silicon layer 3 is formed on the TCO layer 2. An oxidation treatment layer 4 is provided on the upper surface of the p-type microcrystalline silicon layer 3 (the surface opposite to the glass substrate 1). The oxidized layer 4 is a thin silicon oxide film formed by oxidizing the surface portion of the p-type microcrystalline silicon layer 3 in an oxygen atmosphere containing oxygen. An i-type microcrystalline silicon layer 5 is formed on the oxidation treatment layer 4. As will be described later, the oxidation treatment layer 4 serves to effectively prevent the formation of amorphous silicon (amorphous phase silicon) in the initial stage of the formation of the i-type microcrystalline silicon layer 5 formed thereon. The oxidized layer 4 is extremely thin, and the thickness of the oxidized layer 4 is so thin that a tunnel current easily flows. On the i-type microcrystalline silicon layer 5, an n-type microcrystalline silicon layer 6, a ZnO layer 7 and an Ag layer 8 are sequentially formed.
[0022]
Sunlight used for power generation is incident on the p-type microcrystalline silicon 3, the i-type microcrystalline silicon layer 5, and the n-type microcrystalline silicon layer 6 through the glass substrate 1 and the TCO layer 2. When sunlight enters these microcrystalline silicon layers, power is generated by the photovoltaic effect. Since the thickness of the oxidation treatment layer 4 is extremely thin, the oxidation treatment layer 4 does not adversely affect the operation of the thin film solar cell.
[0023]
The thin film solar cell of FIG. 1 is formed by the following process. After the TCO layer 2 is formed on the glass substrate 1, the p-type microcrystalline silicon layer 3 is formed by plasma CVD using silane gas and hydrogen gas as source gases.
[0024]
After the formation of the p-type microcrystalline silicon layer 3, the surface of the p-type microcrystalline silicon layer 3 is exposed to an oxygen-containing atmosphere containing oxygen, typically air. By exposure to the oxygen-containing atmosphere, the surface of the p-type microcrystalline silicon 3 is oxidized, and an extremely thin oxidized layer 4 is formed on the surface of the p-type microcrystalline silicon 3.
[0025]
After the formation of the oxidized layer 4, the i-type microcrystalline silicon layer 5 is formed by plasma CVD using silane gas and hydrogen gas as source gases. The i-type microcrystalline silicon layer 5 is formed under the condition that the proportion of hydrogen gas in the raw material gas is relatively low. Thereby, i-type microcrystalline silicon layer 5 having large crystal grains is formed.
[0026]
As described in the prior art, when a silicon layer is grown under a condition where the proportion of hydrogen gas in the source gas is relatively low, the silicon layer tends to be amorphous. However, in this embodiment, the formation of the amorphous silicon is suppressed by providing the oxidation treatment layer 4, and the amorphous silicon is excluded from the i-type microcrystalline silicon layer 5. Therefore, the manufacturing method of the thin-film battery according to the present embodiment can form the i-type microcrystalline silicon layer 5 having large crystal grains while excluding amorphous silicon.
[0027]
After the formation of the i-type microcrystalline silicon layer 5, the n-type microcrystalline silicon layer 6, the ZnO layer 7, and the Ag layer 8 are sequentially formed, and the formation of the thin film solar cell of the present embodiment is completed.
[0028]
FIG. 2 is a graph showing the dependence of the conversion efficiency of the thin film solar cell on the time during which the p-type microcrystalline silicon layer 3 is exposed to the atmosphere. The atmospheric humidity is 50% and the temperature is 25 ° C. The graph of FIG. 2 shows that when the humidity is 50% and the temperature is 25 ° C., the conversion efficiency of the thin-film solar cell is effectively improved by exposure to the atmosphere for 12 to 36 hours. That is, the conversion efficiency of the thin-film solar cell is effectively improved by inserting the oxidation treatment layer 4.
[0029]
Furthermore, the inventor has demonstrated through experiments that the short-circuit photocurrent, open-circuit voltage, and form factor can all be improved by inserting the oxidation treatment layer 4.
[0030]
The structure of FIG. 1 is particularly effective for improving the conversion efficiency of the short wavelength component of sunlight. In the present embodiment, since sunlight used for power generation is incident from the glass substrate 1 side, the short wavelength component is mainly a portion of the i-type microcrystalline silicon layer 5 close to the p-type microcrystalline silicon layer 3. Absorbed in. By inserting the oxidation treatment layer 4, amorphous silicon is excluded from the portion of the i-type microcrystalline silicon layer 5 close to the p-type microcrystalline silicon layer 3, thereby improving the conversion efficiency of short-wavelength light.
[0031]
In order to stabilize the formation of the oxidation treatment layer 4, it is preferable that the amount of water vapor contained in the oxygen-containing atmosphere to which the p-type microcrystalline silicon layer 3 is exposed is controlled. As is widely known, the amount of water vapor has a great influence on the rate of the oxidation reaction of silicon.
[0032]
For example, the oxidation treatment of the p-type microcrystalline silicon layer 3 is preferably performed in dry air. In dry air from which water vapor is excluded, the thickness of the oxidation treatment layer 4 can be stably formed. However, since the water vapor is excluded, the speed of the oxidation reaction of silicon decreases. When the oxidation treatment of the p-type microcrystalline silicon layer 3 is performed in dry air, heating at a low temperature is preferably performed. Typically, when dry air is used, the oxidation treatment of the p-type microcrystalline silicon layer 3 is preferably performed at 100 ° C. to 200 ° C.
[0033]
As described above, in the thin film solar cell and the manufacturing method thereof according to the present embodiment, the oxidation treatment layer is formed on the p-type microcrystalline silicon layer 3 by the oxidation treatment of the surface of the p-type microcrystalline silicon layer 3. 4 is formed. This oxidation treatment layer 4 suppresses the generation of amorphous silicon in the initial stage of forming the i-type microcrystalline silicon layer 5. Thereby, all of the conversion efficiency of a thin film solar cell, a short circuit photocurrent, an open circuit voltage, and a form factor can be improved.
[0034]
In order to further improve the conversion efficiency, as shown in FIG. 3, the p-type amorphous silicon layer 9, the i-type amorphous silicon layer 10, and the n-type amorphous silicon layer 11 are connected to the TCO layer 2 and the p-type fine silicon layer. It is preferable to be provided between the crystalline silicon layers 3. The p-type amorphous silicon layer 9 is formed on the TCO layer 2, the i-type amorphous silicon layer 10 is formed on the p-type amorphous silicon layer 9, and the n-type amorphous silicon layer 11 is an i-type amorphous silicon layer. 10 is formed. Even in this case, it is confirmed that the conversion efficiency in the wavelength range of 600 to 650 nm is improved by the insertion of the oxidation treatment layer 4.
[0035]
(Second embodiment)
FIG. 4 shows a second embodiment of the thin film solar cell according to the present invention. A metal electrode layer 22 and a ZnO layer 23 are sequentially formed on a transparent and insulating glass substrate 21. On the ZnO layer 23, an n-type microcrystalline silicon layer 24 is formed. An oxidation treatment layer 25 is provided on the upper surface of the n-type microcrystalline silicon layer 24 (the surface opposite to the glass substrate 21). The oxidized layer 25 is a thin silicon oxide film formed by oxidizing the surface portion of the n-type microcrystalline silicon layer 24 in an atmosphere containing oxygen. An i-type microcrystalline silicon layer 26 is formed on the oxidation treatment layer 25. Similar to the oxidation treatment layer 4 of the first embodiment, the oxidation treatment layer 25 effectively prevents the formation of amorphous silicon silicon on the lower surface of the i-type microcrystalline silicon layer 26 (the surface on the same side as the glass substrate 21). To play a role. The oxidation treatment layer 25 is extremely thin, and the thickness of the oxidation treatment layer 25 is so thin that a tunnel current easily flows. A p-type microcrystalline silicon layer 27 and a ZnO layer 28 are sequentially formed on the i-type microcrystalline silicon layer 26. An Ag layer 29 is formed on the ZnO layer 28. The Ag layer 29 does not cover the entire top surface of the ZnO layer 28.
[0036]
Sunlight used for power generation is converted into a p-type microcrystalline silicon layer 27, an i-type microcrystalline silicon layer 26, and an n-type microcrystalline silicon layer through a portion of the ZnO layer 28 that is not covered with the Ag layer 29. 24 is incident. When sunlight enters these microcrystalline silicon layers, power is generated by the photovoltaic effect.
[0037]
The thin film solar cell of FIG. 4 is formed by the following process. After the metal electrode layer 22 and the ZnO layer 23 are sequentially formed on the glass substrate 21, the n-type microcrystalline silicon layer 24 is formed by plasma CVD using silane gas and hydrogen gas as source gases.
[0038]
After the formation of the n-type microcrystalline silicon layer 24, the surface of the n-type microcrystalline silicon layer 24 is exposed to an oxygen-containing atmosphere containing oxygen, typically air. By exposure to the oxygen-containing atmosphere, the surface of the n-type microcrystalline silicon layer 24 is oxidized, and an extremely thin oxidized layer 25 is formed on the surface of the n-type microcrystalline silicon layer 24.
[0039]
After the formation of the oxidation treatment layer 25, the i-type microcrystalline silicon layer 26 is formed by plasma CVD using silane gas and hydrogen gas as source gases. The i-type microcrystalline silicon layer 26 is formed under the condition that the ratio of hydrogen gas in the raw material gas is relatively low. Thereby, the i-type microcrystalline silicon layer 26 having large crystal grains is formed. Furthermore, by providing the oxidation treatment layer 25, the formation of amorphous silicon in the initial stage of formation of the i-type microcrystalline silicon layer 26 is suppressed, and the amorphous phase is excluded from the i-type microcrystalline silicon layer 26. Thereby, the i-type microcrystalline silicon layer 26 having large crystal grains can be formed while removing amorphous silicon.
[0040]
After the formation of the i-type microcrystalline silicon layer 26, an n-type microcrystalline silicon layer 27, a ZnO layer 28, and an Ag layer 29 are sequentially formed, and the formation of the thin film solar cell of the present embodiment is completed.
[0041]
FIG. 5 is a graph showing the dependence of the conversion efficiency of the thin-film solar cell on the time during which the n-type microcrystalline silicon layer 24 is exposed to the atmosphere. The atmospheric humidity is 50% and the temperature is 25 ° C. The graph of FIG. 5 shows that when the humidity is 50% and the temperature is 25 ° C., the conversion efficiency of the thin-film solar cell is effectively improved by atmospheric exposure for 12 to 36 hours. That is, the conversion efficiency of the thin film solar cell is effectively improved by inserting the oxidation treatment layer 25.
The structure of FIG. 5 is particularly effective in improving the conversion efficiency of the long wavelength component of sunlight. In the present embodiment, since sunlight used for power generation is incident from the ZnO layer 28 side, the short wavelength component is mainly a portion of the i-type microcrystalline silicon layer 26 close to the p-type microcrystalline silicon layer 27. Absorbed in. In the vicinity of the portion where the oxidation treatment layer 25 is provided, a long wavelength component is mainly used for power generation. By providing the oxidation treatment layer 25 on the n-type microcrystalline silicon layer 24, amorphous silicon is excluded from the portion that generates power from the long wavelength component, and the conversion efficiency of the long wavelength component is effectively improved.
[0043]
As in the first embodiment, in order to stabilize the formation of the oxidation treatment layer 25, the amount of water vapor contained in the oxygen-containing atmosphere to which the n-type microcrystalline silicon layer 24 is exposed must be controlled. Is preferred. In particular, it is preferable that the oxidation treatment of the n-type microcrystalline silicon layer 24 is performed in dry air because the thickness of the oxidation treatment layer 4 can be stably formed. When the oxidation treatment of the n-type microcrystalline silicon layer 24 is performed in dry air, heating at a low temperature is preferably performed. Typically, when dry air is used, the oxidation treatment of the n-type microcrystalline silicon layer 24 is preferably performed at 100 ° C. to 200 ° C.
[0044]
As described above, in the thin film solar cell and the manufacturing method thereof according to the present embodiment, the oxidation treatment layer is formed on the n-type microcrystalline silicon layer 24 by the oxidation treatment of the surface of the n-type microcrystalline silicon layer 24. 25 is formed. The oxidation treatment layer 25 suppresses the generation of amorphous silicon in the initial stage of forming the i-type microcrystalline silicon layer 26. Thereby, all of the conversion efficiency of a thin film solar cell, a short circuit photocurrent, an open circuit voltage, and a form factor can be improved.
[0045]
In order to further improve the conversion efficiency, as shown in FIG. 6, the n-type amorphous silicon layer 30, the i-type amorphous silicon layer 31, and the p-type amorphous silicon layer 32 are replaced with a p-type microcrystalline silicon layer 27. And ZnO layer 28 are preferably provided. The n-type amorphous silicon layer 30 is formed on the p-type microcrystalline silicon layer 27, the i-type amorphous silicon layer 31 is formed on the n-type amorphous silicon layer 30, and the p-type amorphous silicon layer 32 is i. It is formed on the type amorphous silicon layer 31. The structure of FIG. 6 can effectively use short wavelength components by power generation, and effectively improves the efficiency of the thin film solar cell.
[0046]
【The invention's effect】
The present invention provides a technique for effectively suppressing the formation of amorphous silicon in the initial stage of forming an i-type microcrystalline silicon layer of a microcrystalline silicon solar cell having a pin structure.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of a thin-film solar cell according to the present invention.
FIG. 2 is a graph showing the dependence of the conversion efficiency of the thin film solar cell of the first embodiment on the exposure time to the atmosphere.
FIG. 3 is a cross-sectional view showing a modification of the thin film solar cell of the first embodiment.
FIG. 4 is a cross-sectional view showing a second embodiment of the thin-film solar cell according to the present invention.
FIG. 5 is a graph showing the dependence of the conversion efficiency of the thin film solar cell of the second embodiment on the exposure time to the atmosphere.
FIG. 6 is a cross-sectional view showing a modification of the thin film solar cell of the second embodiment.
[Explanation of symbols]
1: Glass substrate 2: TCO layer 3: p-type microcrystalline silicon layer 4: oxidation treatment layer 5: i-type microcrystalline silicon layer 6: n-type microcrystalline silicon layer 7: ZnO layer 8: Ag layer 9: p-type amorphous Silicon layer 10: i-type amorphous silicon layer 11: n-type microcrystalline silicon layer 21: glass substrate 22: metal electrode layer 23: ZnO layer 24: n-type microcrystalline silicon layer 25: oxidized layer 26: i-type microcrystalline silicon Layer 27: p-type microcrystalline silicon layer 28: ZnO layer 29: Ag layer 30: n-type microcrystalline silicon layer 31: i-type amorphous silicon layer 32: p-type amorphous silicon layer

Claims (9)

Forming a first conductivity type first silicon layer on the upper surface side of the substrate;
Exposing the first silicon layer to an oxygen-containing atmosphere to form an oxidation treatment layer on a surface portion of the first silicon layer;
Forming an intrinsic and microcrystalline second silicon layer on the oxidized layer by plasma CVD using a source gas containing hydrogen gas;
Forming a third silicon layer of a second conductivity type opposite to the first conductivity type on the second silicon layer,
When the second silicon layer is formed directly on the first silicon layer, the ratio of hydrogen gas in the source gas is low enough to form amorphous silicon in the initial stage of formation , and , A method of manufacturing a thin film solar cell , wherein amorphous silicon is not formed on the second silicon layer . In the thin-film solar cell manufacturing method according to claim 1,
The method for producing a thin film solar cell, wherein the oxygen-containing atmosphere is air. In the thin-film solar cell manufacturing method according to claim 1,
In addition,
A method for producing a thin-film solar cell, comprising controlling the amount of water vapor contained in the oxygen-containing atmosphere. In the thin-film solar cell manufacturing method according to claim 1,
The oxygen-containing atmosphere is dry air. In the thin-film solar cell manufacturing method according to claim 4,
In addition,
A method of manufacturing a thin-film solar cell, comprising: heating the substrate on which the first silicon layer is formed while exposing the first silicon layer to an oxygen-containing atmosphere. In the thin-film solar cell manufacturing method according to claim 5,
The temperature at which the substrate is heated is 100 ° C. or higher and 200 ° C. or lower. In the thin-film solar cell manufacturing method according to claim 1,
The method for manufacturing a thin-film solar cell, wherein the oxidation treatment layer is thin enough to allow a tunnel current to flow. In the thin-film solar cell manufacturing method according to claim 1,
The oxygen-containing atmosphere is an atmosphere having a humidity of 50% and a temperature of 25 ° C .;
The method of manufacturing a thin film solar cell, wherein the first silicon layer is exposed to the atmosphere for 12 to 36 hours. In the thin-film solar cell manufacturing method according to claim 1,
In addition,
Forming a third conductivity type fourth silicon layer on the upper surface side of the substrate;
Forming an intrinsic and amorphous fifth silicon layer bonded to the fourth silicon layer;
Forming a sixth silicon layer of a fourth conductivity type that is opposite to the third conductivity type and is bonded to the fifth silicon layer.

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