JP2948236B2 - Photovoltaic device - Google Patents

Description

The present invention relates to a photovoltaic device having a pin structure including an i-layer of amorphous silicon (hereinafter a-Si).

[Conventional technology]

Generally, taking an a-Si solar cell as a photovoltaic device having a pin structure as an example, the diffusion constant of boron [B], which is an impurity in the p-layer, is determined by the following equation.
(1983), p771 at a temperature of 100 ° C., about 10 ^-22 c
m ² / sec (where activation energy 1.5 eV, pre Expo nen shear Ruch actor ^{5 × (10 -2 ~10 -3)} cm 2 / sec) is, the B concentration of the initial p-layer 10 ²⁰ cm ^{- 3} and B concentration is 10 ¹⁸
Considering that the case of cm ^-3 or more is a p-layer, at a temperature of 100 ° C., the B of the p-layer is diffused into the i-layer and the i-layer becomes a p-layer at a temperature of 100 ° C. , P layer is about one and a half months
It increases by about 10 °, and it takes time to increase the p-layer further, and it will increase by about 100 ° in about 20 years.

[Problems to be solved by the invention]

As described above, the p-layer having the optimum thickness of about 100 ° increases with time due to the p-layer phenomenon of the i-layer due to the diffusion of B at a high temperature, so that the solar cell can be used for a long period of time. During use, there is a problem that the characteristics of the solar cell gradually deteriorate due to an increase in the thickness of the p-layer.

This is considered to be because diffusion of impurities such as B into the i-layer cannot be suppressed when the amount of bonded hydrogen in the a-Si i-layer is relatively large, 15 to 25%.

The present invention has been made in consideration of the above points,
In particular, it is an object of the present invention to suppress the diffusion of impurities into the i-layer of a-Si having an amount of bonded hydrogen of 15 to 25% over time and prevent deterioration of the characteristics of the photovoltaic device.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a photovoltaic device comprising p, i, and n layers, wherein the i layer is made of amorphous silicon having a bonding hydrogen content of 15 to 25%. Alternatively, an impurity diffusion preventing layer made of amorphous silicon having a bonding hydrogen amount of 10% or less and a thickness of 50 to 400 ° is provided on at least one of the n-layer and the n-layer.

(Operation)

According to the present invention configured as described above, in a photovoltaic device having a pin structure provided with an i-layer made of amorphous silicon having a bonding hydrogen amount of 15 to 25%, the p-layer or the n-layer to the i-layer The diffusion of impurities over time can be significantly reduced by the impurity diffusion prevention layer of the same material as that of the i-layer and having an appropriate thickness without lowering the conversion efficiency.
The deterioration of the characteristics of the photovoltaic device over time can be prevented.

〔Example〕

 Embodiments will be described with reference to the drawings.

Embodiment 1 First, Embodiment 1 will be described with reference to FIGS. 1 and 2. FIG.

In FIG. 1, (1) is a light-transmitting substrate made of glass or the like, and (2) is a tin oxide [Sn formed on the substrate (1).
O ₂ ], a transparent conductive film made of ITO (Indium Tin Oxide) or the like;
(3) a-Si: H is made of amorphous silicon carbide (a-SiC: H) or microcrystalline silicon (μc-Si: H) or microcrystalline silicon carbide (μc-SiC: H).
Layer (4) is an impurity diffusion preventing layer, the amount of bonded hydrogen of which is about
It is made of i-type a-Si: H having a thickness of 50 to 400 mm with a thickness of 10% or less,
It is formed on the p-layer (3).

(5) is an i-layer composed of a-Si: H formed on the prevention layer (4), and (6) is composed of a-Si: H or μc-Si: H formed on the i-layer (5). (7) is a metal electrode,
It is formed on the n-layer (6). Here, light enters from the substrate (1) side.

By the way, as a method of forming i-type a-Si: H having an amount of bonded hydrogen of 10% or less, (i) disilane [Si ₂ H ₆ ] is irradiated with light energy of a low-pressure mercury lamp having a wavelength of 186 nm or a deuterium lamp having a wavelength of 161 nm. Direct excitation light CVD method to decompose (ii) HOMOCVD method to decompose Si ₂ H ₆ by heating the chamber wall or facing heater without heating the substrate (iii) RF or DC that decomposes silane [SiH ₄ ] by plasma
Glow discharge method (iv) Collision of hydrogen atoms excited by microwaves with SiH ₄
Excited species CVD method to decompose SiH ₄ (V) Reactive sputtering method in which a mixed plasma of hydrogen gas and rare gas is applied to a target of polysilicon or crystalline silicon is effective.

In the cases of (i) to (iv), the substrate temperature is set to 350 ° C. or higher, and in the case of (V), the mixing ratio of hydrogen is reduced to reduce the a- S
The prevention layer (4) made of i: H can be formed, and among them, in order to suppress the diffusion of impurities during film formation, the method (i) or (ii) not using plasma is preferable.

Meanwhile, as shown in FIG. 1, a photovoltaic device I having an impurity diffusion preventing layer (4) formed thereon and the preventing layer (4)
For the conventional photovoltaic device II without the, when the accelerated deterioration test of the photoelectric conversion efficiency under high temperature of 140 ℃,
The result was as shown in FIG.

In FIG. 2, the horizontal axis represents time, the vertical axis represents normalized conversion efficiency, and ○ and × represent measurement points.

As apparent from FIG. 2, the conversion efficiency of the photovoltaic device I provided with the prevention layer (4) hardly deteriorates even after 90 days, whereas the conventional photovoltaic device I without the prevention layer (4) has In the photovoltaic device II, the conversion efficiency is reduced by 9% after 90 days from the start of the test, and the normalized conversion efficiency is reduced to 0.91.

At this time, it is considered that the time required for the conversion efficiency to be degraded by one digit longer each time the temperature drops by 20 ° C. Therefore, in the conventional photovoltaic device II, the conversion efficiency is degraded by 9%. 900 days (about 2.5 years) at 120 ° C, 100 ° C
At a temperature of 9000 days (about 25 years).

If the amount of bonded hydrogen in the prevention layer (4) is more than 10%, the diffusion of impurities over time cannot be sufficiently suppressed. Therefore, the amount of bonded hydrogen in the prevention layer (4) is reduced to about 10% or less. Is good.

If the thickness of the prevention layer (4) is smaller than 50 °, the effect of suppressing the diffusion of impurities from the p layer (3) to the i layer (5) cannot be obtained, while the amount of bonded hydrogen is 10% or less. From the above, because the film quality is not good in the first place, when the film thickness is set to 400 mm or more, the conversion efficiency is significantly reduced, and from these,
The optimal thickness of the prevention layer (4) is 50 to 400 °.

Therefore, the diffusion of the impurity from the p layer (3) to the impurity diffusion preventing layer (4) with time is reduced from the p layer in the conventional configuration to the i level.
Significantly less than the diffusion of impurities into the layer,
The prevention layer (4) between the p-layer (3) and the i-layer (5) can prevent diffusion of boron as an impurity from the p-layer (3) to the i-layer (5). It is possible to prevent deterioration of characteristics over time of a photovoltaic device having a pin structure made of a-Si and having a bonding hydrogen content of 15 to 25%.

Embodiment 2 Embodiment 2 will be described with reference to FIG.

In the same figure, the same symbols as those in FIG. 1 indicate the same or corresponding ones. The difference from FIG. 1 is that an electrode (7), an n-layer (6), and an i-layer (5) are provided on a substrate (1). , Prevention layer (4), p
The point is that the layer (3) and the transparent conductive film (2) are sequentially laminated so that light is incident from the side opposite to the substrate (1).

Third Embodiment A third embodiment will be described with reference to FIG.

2, the same reference numerals as those in FIG. 1 denote the same parts, and the point different from FIG. 1 is that the impurity diffusion preventing layer (4) is also provided between the i-layer (5) and the n-layer (6). Similarly, the amount of bonded hydrogen 10
% Of i-type a-Si: H impurity diffusion preventing layer (8) is formed, whereby the diffusion of impurities from n layer (6) to i layer (5) can be suppressed. In addition, it is possible to stabilize the characteristics of the photovoltaic device.

Note that an impurity diffusion preventing layer may be formed only between the i-layer and the n-layer in order to prevent diffusion of the n-layer impurities into the i-layer.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are obtained.

In a photovoltaic device comprising p, i, and n layers, and the i-layer is made of amorphous silicon having a bonding hydrogen content of 15 to 25%, at least one of the i-layer and the p-layer or the n-layer On the other hand, when the amount of bonded hydrogen is 10% or less and the thickness is
Since the impurity diffusion preventing layer made of amorphous silicon of 0 ° is provided, the p-layer or the n-layer of this type of photovoltaic device having a pin structure provided with an i-layer made of amorphous silicon having a bonding hydrogen content of 15 to 25%. The diffusion of impurities over time from the i-layer to the i-layer can be significantly reduced by the impurity diffusion preventing layer of the same material as the i-layer and having an appropriate thickness without lowering the conversion efficiency. Characteristic deterioration can be prevented.

[Brief description of the drawings]

The drawings show an embodiment of the photovoltaic device of the present invention. FIGS. 1 and 2 show Embodiment 1, FIG. 1 is a schematic diagram, and FIG. 2 shows the relationship between time and normalized conversion efficiency. FIG. 3, FIG. 3 and FIG. 4 are schematic diagrams of Embodiment 2 and Embodiment 3, respectively. (1) ... translucent substrate, (2) ... transparent conductive film, (3)
... p-layer, (4), (8) ... impurity diffusion preventing layer,
(5) ... i-layer, (6) ... n-layer.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masato Nishikuni 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Shoichi Nakano 2--18 Keihanhondori, Moriguchi-shi, Osaka (56) References JP-A-62-165374 (JP, A) JP-A-63-304673 (JP, A) JP-A-62-60271 (JP, A)

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein each of the p-, i-, and n-layers comprises 15 to 2 layers.
A photovoltaic device comprising amorphous silicon having a hydrogen bonding amount of 5%, wherein at least one of the i-layer and the p-layer or the n-layer has a bonding hydrogen amount of 10% or less and a thickness of 10% or less. 50-400
A photovoltaic device provided with an impurity diffusion preventing layer made of amorphous silicon as described in (1).