JP2567643B2 - Photovoltaic device manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing a photovoltaic device used for photovoltaic power generation, an optical sensor, or the like.

(B) Conventional technology As this type of photovoltaic device, a photoactive layer of an amorphous semiconductor that generates photocarriers mainly contributing to photoelectric conversion when exposed to light, and a photoactive layer in front of the light incident side of the photoactive layer The window layer of the p-type amorphous semiconductor provided, the light-receiving surface electrode of the transparent conductive oxide provided in front of the light incident side of the window layer, and the back surface side of the photoactive layer were arranged. Those having a back electrode are already known, and the photoactive layer and the window layer are formed by decomposing the raw material gas with plasma energy such as glow discharge or light energy such as a low pressure mercury lamp or an ultraviolet laser. To be done. That is, the photoactive layer and the window layer are formed by plasma chemical vapor deposition.
n: CVD) method or optical CVD method.

Since the window layer is provided mainly in front of the light incident side with respect to the photoactive layer that performs photoelectric conversion operation, the window layer must be guided to the photoactive layer without absorbing the incident light transmitted through the light-receiving surface electrode. . Therefore, a so-called wide bandgap material having a wider optical bandgap Egopt than that of the photoactive layer is used for the window layer, and boron (B) which is a p-type determining impurity with an Egopt of about 1.8 to 2.1 (eV) is currently used. ) Hydrogenated amorphous silicon carbide (hereinafter B-doped a-SiC:
(Abbreviated as H) is preferably used. Such B-dope a
-SiC: As a raw material gas during the deposition of the H, silane as a silicon source gas (SiH _4), disilane (Si ₂ H _6), p
Diborane (B ₂ H ₆ ) as boron source gas for typing impurities
But then methane (CH ₄₎ as a carbon source gas for the wide-band, acetylene (C ₂ H ₂₎ or the like has been used.

However, if B ₂ H ₆ gas is used as the boron source gas,
It has been found by the applicant of the present application that it is difficult to obtain B-doped a-SiC: H that simultaneously satisfies the electrical and optical properties required for the window layer. That is, when attempting to widen the optical bandgap Egopt, the carbon content increases, so the electrical conductivity decreases, and the electrical conductivity decreases. Therefore, if the B content is increased, then Egopt becomes smaller. That leads to conflicting development.

Therefore, the applicant of the present application, as a measure to solve such conflicting developments at the same time, uses trimethylboron (B (CH ₃ ) ₃ ) in place of B ₂ H ₆ gas as a boron source gas, but it is a wide band. It was discovered that B-doped a-SiC: H with low resistance can be obtained, and Japanese Patent Application No. 60-168709 (Japanese Unexamined Patent Publication No. 62-29132).
Patent application) and Japanese Patent Application No. 60-183349 (Japanese Patent Application Laid-Open No. 62-43120).

However, the B-doped a-SiC: H film obtained by using B (CH ₃ ) ₃ as a boron source gas has a resistance and a wide band optical band gap as a single film,
When it was used as the window layer of a photovoltaic device, no improvement in the photoelectric conversion properties could be seen as the electrical and optical properties of the film were improved.

(C) Problems to be Solved by the Invention In the manufacturing method of the present invention, the p-type amorphous semiconductor obtained by using B (CH ₃ ) ₃ as a boron source gas has excellent film electrical and optical characteristics. Nevertheless, it is intended to solve the problem that when it is used as a window layer of a photovoltaic device, it does not contribute much to an increase in photoelectric conversion characteristics.

(D) Means for Solving the Problems The present invention provides a photoactive layer of an amorphous semiconductor that generates photocarriers that contribute to photoelectric conversion when irradiated with light, and a photoactive layer provided in front of the light incident side of the photoactive layer. A p-type amorphous semiconductor window layer, a light-transmissive conductive oxide light-receiving surface electrode provided in front of the light incident side of the window layer, and a back surface disposed on the back surface side of the photoactive layer. In order to solve the above-mentioned problems, the p-type amorphous semiconductor forming the window layer contains at least a silicon source gas and a boron source gas as source gases. Is formed by a chemical vapor deposition (CVD) method, in which the first component thin layer of the window layer in contact with the light-receiving surface electrode uses diborane (B ₂ H ₆ ) gas as a boron source gas, and The second component thin layer of the window layer which is in contact with the photoactive layer is used as a boron source gas for trimethylne. Boron (B
(CH ₃ ) ₃ ) is used.

(E) Action As described above, the window layer is composed of the first component thin layer in contact with the light-receiving surface electrode and the second component thin layer in contact with the photoactive layer. When the first component thin layer is formed by the CVD method, By using B ₂ H ₆ gas as the boron source gas and using B (CH ₃ ) ₃ as the boron source gas as the second component thin layer, a second component thin layer having excellent electrical and optical characteristics can be obtained. Even when it is used as a window layer of a photovoltaic device, at least the first component thin layer exists between the light-transmitting conductive oxide and the light-receiving surface electrode, so that it does not come into direct contact.

(F) Example FIG. 1 shows a cross section of a typical photovoltaic device manufactured by the manufacturing method of the present invention. (1) is a translucent and insulating material having one main surface (1a) as a light receiving surface. Substrate, (2) is In ₂ O ₃ , SnO ₂ , IT deposited on the other main surface (1b) of the substrate (1).
A light receiving surface electrode of a transparent conductive oxide (hereinafter abbreviated as TCO) represented by O or the like, (3) is the light receiving surface electrode (2) and the first
A window layer of a p-type amorphous semiconductor in direct contact with the thin component layer (3 ₁ ), an i-type or a substantial layer in which (4) is in direct contact with the second component thin layer (3 ₂ ) of the window layer (3). A photoactive layer of an i-type amorphous semiconductor, (5) is a highly doped layer of an n-type amorphous semiconductor in direct contact with the photoactive layer (4), and (6) is a highly doped layer (5). When a light is incident on the back electrode in ohmic contact with the substrate (1), photocarriers of electrons and holes in a free state are generated mainly in the photoactive layer (4), and the window layer (3) is generated. , Pi due to photoactive layer (4) and highly doped layer (5)
The light is attracted by the n-junction electric field and is collected by the light-receiving surface electrode (2) and the back electrode (6) to be extracted as a photoelectromotive force.

The manufacturing method of the present invention is characterized in that the boron source gas used for forming the window layer (3) is in contact with the light-receiving surface electrode (2), the first component thin layer (3 ₁ ) and the photoactive layer. (4) and the second component layer (3 ₂ ) in contact therewith are different. That is, B ₂ H ₆ gas is used as the boron source gas for the first component thin layer (3 ₁ ), and the electrical and optical characteristics of the second component thin layer (3 ₂ ) depend on B ₂ H ₆ . B (CH ₃ ) _{3, which} is superior to the one used. The specific formation of such a window layer (3) is as follows.

[Formation condition of window layer (3) by plasma CVD method] (i) Common items Capacitively coupled plasma CV using 13.56MHz high frequency power supply
Method D High frequency power supply: 10 to 50 W (typical value 30 W) Substrate temperature: 100 to 300 ° C (typical value 200 ° C) Reaction pressure: 0.01 to 1.0 Torr (typical value 0.2 Torr) (ii) First component thin layer (3 ₁ ) Silicon source gas: SiH ₄ gas 1 to 20SCCM (typical value 5SCC
M) Carbon source gas: CH ₄ gas 1 to 20SCCM (typical value 10SCC
M) Boron source gas: B ₂ H ₆ gas 0.01 to 0.05 SCCM (typical value 0.02
SCCM) Film thickness: 5 to 50Å (typical value 20Å) (iii) Second component thin layer (3 ₂ ) Silicon source gas: SiH ₄ gas 1 to 20SCCM (typical value 10SCC
M) Carbon source gas: CH ₄ gas 1 to 20 SCCM (typical value 5 SCCM) Boron source gas: B (CH ₃ ) ₃ 0.01 to 0.05 SCCM (typical value 0.02
SCCM) Film thickness: 100 to 200Å (typical value 150Å) The following table shows that B ₂ H ₆ was obtained as a boron source and the first component thin layer (3 ₁ ) and B (CH ₃ ) ₃ were obtained as a boron source. was one in which the photoelectric conversion characteristic of the second component thin layer (3 ₂₎ window layer (3) photovoltaic device manufactured by the manufacturing method of the present invention having a consisting measured. In the table, Voc is open circuit voltage, Isc is short circuit current, FF
Indicates the film factor, and η indicates the photoelectric conversion efficiency. The numerical values in the table are different from those of the examples of the present invention except that only the window layer (3) was obtained by using B ₂ H ₆ gas as the boron source for the total thickness of the first and second component thin layers. Each characteristic of the common comparative example 1 is standardized as 100. Further, as a comparative example 2, B (CH ₃ ) _{3 was used} for all the films of the first and second component thin layers.
Using the window layer (3) obtained by using, a photovoltaic device having the same structure as in Example and Comparative Example 1 was measured.

As described above, in the example of the present invention, the photoelectric conversion characteristics exceeding that can be obtained not only in the comparative example 1 but also in the comparative example 2 in which the window layer (3) is all formed by using B (CH ₃ ) _3. I understand.

Next, an example of forming the window layer (3) by the photo CVD method will be briefly described. The light source used is a low-pressure mercury lamp that radiates ultraviolet light, and its output has an intensity of about 1 mW / cm ² at the substrate surface. The silicon source is disilane (Si ₂ H ₆ ) for both the first component thin layer (3 ₁ ) and the second component thin layer (3 ₂ ), and the flow rate thereof is 5 to 40 SCCM, typically 20 SCCM. Acetylene (C ₂ H ₂ ) is commonly used as a carbon source. Then, in the first component thin layer (3 ₁ ) as a boron source, the flow rate is 0.02 to
0.2 SCCM, typically 0.1 SCCM B _{2 H 6} gas is used, and 0.02 to 0.4 SCCM, typically in the second component thin layer (3 ₂ ).
0.2 SCCM of B (CH ₃ ) ₃ is used. The common conditions of the photo-CVD method are a substrate temperature of 100 to 300 ° C., typically 200 ° C., a reaction pressure of 0.1 to 10 Torr, and typically 2 Torr.

Further, in the photo CVD method, it is obvious that mercury may be used as a sensitizer and other light sources may be used.

First and second component thin layers (3 ₁ ) (3 ₂ ) produced by such optical CVD method
In a photovoltaic device with a window layer (3) consisting of
It exhibited high photoelectric conversion characteristics as in the case of the plasma CVD method.

(F) Effect of the Invention As is apparent from the above description, the manufacturing method of the present invention includes the first component thin layer in which the window layer is in contact with the light-receiving surface electrode and B ₂ H ₆ gas is used as the boron source gas, and the photoactive layer. A second component thin layer in contact with the layer and using B (CH ₃ ) ₃ as a boron source gas, and the second component thin layer having excellent electrical and optical characteristics is provided in the window of the photovoltaic device. Even when it is used as a layer, it does not come into direct contact with the light-receiving surface electrode of TCO, and such excellent film characteristics can be reflected in the improvement of photoelectric conversion characteristics.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a typical example of a photovoltaic device manufactured based on the manufacturing method of the present invention. (1) ... Substrate, (2) ... Light-receiving surface electrode, (3) ... Window layer, (3 ₁ ) ... First component thin layer, (3 ₂ ) ... Second component thin layer, (4 ) ... Photoactive layer, (6) ... Back electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-29132 (JP, A) JP 62-43120 (JP, A) JP 63-284809 (JP, A) JP 62- 33478 (JP, A) JP-A-63-185070 (JP, A)

Claims (1)

(57) [Claims] 1. A photoactive layer of an amorphous semiconductor which generates photocarriers mainly contributing to photoelectric conversion when exposed to light,
A window layer of a p-type amorphous semiconductor provided in front of the light incident side of the photoactive layer, a light receiving surface electrode of a transparent conductive oxide provided in front of the light incident side of the window layer, A method for manufacturing a photovoltaic device comprising a back electrode disposed on the back side of a photoactive layer, wherein the p-type amorphous semiconductor forming the window layer contains at least a silicon source gas and a boron source gas. Diborane (B ₂ H ₆ ) gas is used as the boron source gas for the first component thin layer of the window layer that is formed by the chemical vapor deposition (CVD) method using the source gas and is in contact with the light-receiving surface electrode at that time. At the same time, the second component thin layer of the window layer which is in contact with the photoactive layer uses trimethylboron (B (CH ₃ ) ₃ ) as a boron source gas.