JPH0554272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel amorphous silicon-based photovoltaic device. WESpear and others discovered that the conductivity of amorphous silicon obtained by plasma decomposition of silane (SiH ₄ ) could be greatly changed by doping it with PH ₃ or B ₂ H ₆ (1976). Since solar cells using amorphous silicon were prototyped by Carlson et al. (1976), they have attracted attention, and research has been actively conducted to improve the efficiency of amorphous silicon thin-film solar cells. Research has shown that amorphous silicon thin-film photovoltaic devices can be structured as Schottky barrier type, pin type, MIS type, or heterojunction type, of which the first three are considered to be promising as high-efficiency solar cells. i.e. 5.5 for shot key barrier type.
% (DE Carlson et al., 1977), 4.8% for MIS type
(JIB Wilson et al., 1978), and a pin type conversion efficiency of 4.5% (Keihiro Hamakawa, 1978) has been achieved. pin In the case of junction type solar cells, p-type or n-type amorphous silicon has a short carrier life and is not an effective carrier, and the light absorption coefficient is larger than that of the i-layer, so light in the p-layer is The problem was that the absorption loss was large. Inverted to improve these shortcomings
A pin-type photoelectric element has been proposed. That is, n
This is an element that irradiates light from the amorphous silicon side. This element is considered to be somewhat advantageous because it has a relatively small light absorption coefficient compared to the p-type element. However, this n-type amorphous silicon is no different from the p-type in that there is light absorption loss. As a result of intensive research in order to improve the efficiency of _{pin - type} photoelectric conversion, the present inventor discovered that p-type or It was discovered that by using an n-type doped thin film in at least one of the p or n layer of a pin junction photoelectric device, the short circuit current and open circuit voltage can be greatly improved. It can be used as The details will be explained below. The amorphous silicon used in the present invention is prepared using a mixed gas of silane (SiH ₄ ) or its derivatives, fluorinated silane or its derivatives, or a mixture thereof, and hydrogen or an inert gas such as argon or helium diluted with hydrogen. , by high frequency glow decomposition or direct current glow discharge decomposition using a capacitive coupling method or an inductive coupling method. The concentration of silane in the mixed gas is usually 0.5 to 50%, preferably 1 to 20%. The temperature of the substrate is preferably 200 to 300℃, and includes all substrates necessary for the construction of photovoltaic elements such as solar cells, such as glass, polymer film, and metal with transparent electrodes (ITO, Sno _2, etc.) vapor-deposited. . Representative examples of the basic configuration of a photovoltaic device are shown in FIG. 1, a and b. A is a type that irradiates light from the p side, for example, glass-transparent electrode-p-i-n-
The configuration of Al, b is the type that irradiates light from the n side,
For example, the structure is a stainless steel pin transparent electrode. In addition, a structure in which a thin insulating layer or a thin metal layer is provided between the p-layer or n-layer and the transparent electrode may be used. In short, any structure may be used as long as it is based on a pin junction. A localized level density of about 10 ¹⁷ cm ^-3 eV ^-1 or less with a carrier lifetime of about 10 ^-7 seconds or more obtained by glow discharge decomposition of silane or its derivatives, or fluorinated silanes or its derivatives, or mixtures thereof. and
Intrinsic amorphous silicon (hereinafter referred to as i-type a-Si) with a mobility of 10 ^-3 cm ² /V or more is used as the i layer, and a pin junction structure is created in which p-type and n-type doped semiconductors are joined. However, in the present invention, p layer or n
At least one of the layers, that is, at least the side to which light is irradiated, is represented by the general formula a-Si _(1-xy) C _x N _y ,
It is also characterized by using a p-type or n-type doped thin film of an amorphous semiconductor containing hydrogen or fluorine. It may be used for both the p layer and the n layer. The other doped layer that does not use this amorphous semiconductor is
When the i-type a-Si is used as a p-type, it may be doped with an element of the periodic table group, and when it is used as an n-type, it may be doped with an element of the periodic table group. The amorphous semiconductor has the general formula a-
Amorphous silicon denoted by Si _(1-xy) C _x N _y
It is carbon nitride. This is obtained by glow discharge decomposition of hydrogen or fluorine compounds of silicon and hydrogen or fluorine compounds of carbon and nitrogen, and contains 0.5 to 30 atom% of hydrogen and/or fluorine. Also, this is p-type or n-type
It is desirable that the mold be doped with impurities. More preferably, the optical bandgap is about 1.85 eV or more, the electrical conductivity at 20°C is about 10 ^-8 (Ωcm) ^-1 or more, and the pin
A p-type or n-type amorphous semiconductor having a diffusion potential Vd of approximately 1.1 Volts or more when bonded is recommended. This amorphous semiconductor has a large optical bandgap, so if it is used as a window material for a pin junction photovoltaic device, it is natural that the short circuit current Jsc will increase, but in any case, the Indicates voltage Voc. In the photovoltaic device of the present invention, as in Japanese Patent Application No. 56-66689, there is a correlation between the diffusion potential Vd of the band profile shown in FIG. 2 and the open circuit voltage Voc of the device. In the case of the present invention, Vd is preferably about 1.1 volts or more, but this relationship shows almost the same tendency regardless of the type of amorphous semiconductor on the side to which light is irradiated. This diffusion potential Vd is obtained by subtracting the difference between the fermi levels Ef of the p- and n-doped layers from the optical bandgap Eg.opt of the amorphous semiconductor on the side to which light is irradiated. In other words, as shown in Figure 2, the energy level of the n-side conduction band Ecn,p
Assuming the energy level of the side valence band as Evp,
Activation energies ΔEp and ΔEn can be determined from the temperature dependence of electrical conductivity. For p-type, ΔEp=Ef
−Evp, for n-type ΔEn=Ecn−Ef and eVd=Eg.
opt−(ΔEp+ΔEn). In the case of light irradiation from the n side, it is similarly determined by subtracting the difference between the p and n fermi levels Ef from the optical band gap Eg.opt of the n-type amorphous semiconductor. The amorphous semiconductor represented by the general formula a-Si _(1-xy) C _x N _y used in the present invention has an Eg.opt of approximately 1.85 eV.
It is desirable that the voltage is above and that Vd is about 1.1 volts or above. A heterojunction photovoltaic device using an amorphous semiconductor that satisfies these conditions has Jsc and Voc.
is significantly improved. The above-mentioned semiconductor used in the present invention can further be used at room temperature (20
It is desirable that the electrical conductivity at ℃) is 10 ^-8 (Ω cm) ^-1 or higher. This is because if it is less than this, the film factor FF becomes small and the conversion efficiency becomes impractical. The heterojunction photovoltaic device of the present invention will be specifically described below using examples thereof. The typical structure is transparent electrode/p type a-
With the structure of Si _(1-xy) C _x N _y /i-type a-Si/n-type a-Si/electrode, light is irradiated from the transparent electrode side. The transparent electrode is preferably made of ITO or SnO ₂ , particularly SnO ₂ , and may be used by being vapor-deposited on a glass substrate in advance, or may be directly vapor-deposited on a p-type amorphous semiconductor. The thickness of the p-type a-Si _(1-xy) C _x N _y layer on the side that is irradiated with light is approximately 30 Å.
300 Å, preferably 50 Å to 200 Å, and the thickness of the i-type a-Si layer is not limited in the case of the present invention, but is about 2500 Å to 200 Å.
10000 Å is used. The thickness of the n-type a-Si layer is not limited, but approximately 150 Å to 600 Å is used. Moreover, n-type a-Si _(1-xy) C _x N _y may be used instead of this n-type a-Si. Another typical structure is transparent electrode/p type a-Si _(1-xy) C _x N _y /i type a-
With a Si/p-type a-Si/electrode structure, light is irradiated from the transparent electrode side. n-type a- on the side that irradiates light
The thickness of Si _(1-xy) C _x N _y is about 30 Å to 300 Å, preferably 50 Å to 200 Å, and the thickness of the i-type a-Si layer is not limited, but is usually about 2,500 Å to 10,000 Å. p
The thickness of the type a-Si layer is not limited, but is approximately 150 Å to 600 Å.
Å is used. Moreover, p-type a-Si _(1-xy) C _x N _y of the present invention may be used instead of this p-type a-Si. The material and vapor deposition method for the transparent electrode are the same as before. Next, the effects of the present invention will be explained. Inner diameter 11cm
Glow discharge decomposition is performed using a high frequency of 13.56MHz using a quartz reaction tube. I-type a-Si is obtained by glow discharge decomposition of silane diluted with hydrogen at 2 to 10 Torr. N-type a-Si can be similarly obtained by glow discharge decomposition of silane diluted with hydrogen and phosphine (PH ₃ ) (PH ₃ /SiH ₄ =0.5 mol %). p type a-
Si _(1-xy) C _x N _y is silane diluted with hydrogen, methane (CH ₄ ), ammonia (NH ₃ ), diporane (B ₂ H ₆ )
(B/(Si+C+N)=0.5 atom%) is similarly obtained by glow discharge decomposition. Here a−Si _(1-xy) C _x
Ny varies the gas composition during glow discharge, and its atomic flux (x+y) is 0.80 to 0.05.
I made it so that The solar cell has a p-type a-Si _(1-xy) C _x on the SnO ₂ surface of a glass substrate with a 25Ω/□ SnO ₂ thin film.
_AM - ¹ (100
The solar cell characteristics were investigated using a solar simulator (mW/cm ² ). Substrate temperature during glow discharge is 250℃
I went there. Also, the i layer is 5000 Å, the n layer is 500 Å, and the p
The thickness of the type a-Si _(1-xy) C _x N _y layer is 135 Å. p
Table 1 shows the solar cell characteristics when the film compositions x and y of type a-Si _(1-xy) C _x N _y were varied.

【table】

[Table] As can be seen from this table, in the case of 100% silane, the conversion efficiency (hereinafter referred to as η) is 4.6%, whereas when using a-Si _(1-xy) C _x N _y , x = 0.05 y =0.05
However, it increases to η = 6.5% and improves to η = 7.3% when x = 0.10 and y = 0.20. When x=0.3 and y=0.3, η=7.6%, which is an extremely high value compared to when silane is 100%. The important point here is a-
Si _(1-xy) C _x N _y has a larger optical bandgap than a-Si, so it is natural that the short circuit current Jsc will increase, but the increase in the open circuit voltage Voc is unexpected, and both This improvement in efficiency has been achieved through improvements in . These results were exactly the same even when SiF ₄ , CH ₄ , and NH ₃ were used. This a-Si _(1-xy) C _x N _y optical bandgap
Since Eg.opt shows a larger value than a-Si as shown in Table 1, it is naturally expected that Jsc will increase if these amorphous semiconductors are used as window materials. However, not only Jsc but also Voc is significantly improved. As for the reason for this, when we examine the relationship between the diffusion potential Vd and Voc, we find that Voc and
It can be seen that there is a clear linear relationship between Vd. That is, Voc increases linearly as Vd increases. This means that if an amorphous semiconductor with a large optical bandgap is used as the window material for a pin junction photovoltaic element, the VV
It also shows that it can be improved. In summary, the amorphous semiconductor ₍ 0.05≦ _{x ≦} 0.75,
0.05≦y≦0.75, 0.05≦x+y≦0.80), i.e.
The window material is an amorphous semiconductor whose Eg.opt is approximately 1.85 eV or higher, the electrical conductivity at 20°C is 10 ^-8 (Ωcm) ^-1 or higher, and the pin junction diffusion potential Vd is 1.1 volt or higher. The heterojunction photovoltaic device is
Not only Jsc but also Voc is significantly improved, and as a result, photoelectric conversion efficiency η is also significantly improved.
These effects are similarly exhibited even when n-type a-Si _(1-xy) C _x N _y is used on the n-side in the solar cell configuration shown in FIG. 1b.

[Brief explanation of the drawing]

Figure 1a is a structural diagram showing a photovoltaic element of the type that irradiates light from the p-layer side, in which 1 is glass, 2 is a transparent electrode, 3 is a p-type amorphous semiconductor, and 4 is an i-type a -Si, 5 is an n-type semiconductor (e.g. n
Type a-Si), 6 is an electrode. Figure b is a structural diagram showing a type in which light is irradiated from the n-layer side, where 7 is an electrode substrate, 8 is a p-type a-Si, 9 is an i-type a-Si, and 10 is an n-layer.
type amorphous semiconductor, 11 is a transparent electrode.
FIG. 2 is an energy band profile of a heterop-i-n junction photovoltaic device according to the present invention. FIG. 3 is a graph showing the relationship between the diffusion potential Vd and the open circuit voltage when a p-type amorphous semiconductor is placed on the window side.

Claims (1)

[Claims] 1. A p-type film using intrinsic amorphous silicon in the i-layer.
In an amorphous solar cell in which electrodes are provided on both the front and back sides of a -i-n junction element, an optical bandgap exists at least in the doped layer on the side to which light is irradiated.
At 1.85eV or higher, the electrical conductivity at 20℃ is 10 ^-8 (Ω
cm) ^-1 or more, and the diffusion potential Vd in the case of pin junction is 1.1 Volt or more.
An amorphous silicon-based heterojunction photovoltaic device characterized by using a p-type or n-type doped thin film of an amorphous semiconductor represented by Si _(1-xy) C _x N _y . 2. The amorphous semiconductor used for the doped layer on the light irradiation side has the following properties: 0.05≦x≦0.75, 0.05≦y≦0.75,
The amorphous silicon-based photovoltaic device according to claim 1, characterized in that 0.05≦x+y≦0.80.