JPS6143872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photovoltaic device having P-type and I-type (intrinsic type) amorphous semiconductor layers stacked by a gas reaction in a silicon compound atmosphere.

FIG. 1 shows a conventional device of this type, in which 1 is a transparent glass substrate, 2 is a transparent first electrode film made of indium/tin oxide film, etc., deposited on the substrate;
3, 4 and 5 are P layers stacked sequentially on the film, respectively.
type, I type (intrinsic type), and N ⁺ type amorphous silicon (hereinafter referred to as a-Si) layers, each of which is composed of P
In the case of type I or N ⁺ type, in an atmosphere of silane (SiH ₄ ), which is a silicon compound gas containing an appropriate conductivity type determining impurity gas such as deborane (B ₂ H ₆ ) or phosphine (PH ₃ ), or in the case of I type. They are formed by glow discharge in a silane atmosphere that does not contain the impurity gas. 6 is I type a via N ⁺ type a-Si layer 5
- A second electrode film made of an aluminum film or the like that is in ohmic contact with the Si layer 4.

In the above device, when light is incident from the substrate 1 side, carriers in a free state are generated mainly in the I-type a-Si layer 4, and these carriers are collected on the first and second electrode films 2 and 6, and the light is emitted. extracted as electric current. The output characteristics are better as the series resistance of the device is smaller.

However, the present inventor has proposed that the P-type a-
It was discovered that a high resistance layer that causes the increase in series resistance is generated between the Si layer 3 and the I-type a-Si layer 4, and the reason for this is that it has already been formed when the I-type a-Si layer 4 is formed. Some P-type impurity diffuses from the P-type a-Si layer 3 into the I-type a-Si layer 4, so that the P-type a-Si layer
It was concluded that this is due to the formation of a weak P-type layer near the boundary with the -Si layer 3. The high resistance of such a weak P-type layer is a characteristic of a-Si obtained using a silicon compound as a raw material gas, as described above, and this is shown in FIG. That is, in the same figure, the horizontal axis shows the gas volume ratio of silane (SiH ₄ ) and impurity B ₂ H ₆ or PH ₃ ), and the vertical axis shows the conductivity of a-Si. Electrical conductivity in Si (gas volume ratio above)
10 ^-6 or less), in the case of N type, the conductivity increases as the gas volume ratio increases, but in the case of P type, the conductivity increases once the gas volume ratio is around 5 × 10 ^-5 . rate becomes minimal. Since the above gas volume ratio is approximately proportional to the impurity concentration of the formed a-Si, impurity diffusion occurs from the P-type a-Si layer 3 to the I-type 4 and the P-type a- When a weak P-type layer is formed near the boundary with the Si layer 3, the above-mentioned layer region of minimal conductivity is formed in that portion.

The present invention has been made in view of the above points.
As shown in the example in the figure, P type a-Si layer 3 and I type a
- A diffusion prevention layer 7 is provided between the silicon layer 4 and the silicon layer 4. In FIG. 3, the same parts as in FIG. 1 are given the same numbers. That is, due to the presence of the diffusion prevention layer 7, the P-type a-Si layer 3 is transferred from the I-type a-Si layer 3.
Impurity diffusion into layer 4 is prevented and therefore type I a-
A high resistance layer as in the conventional case does not occur in the Si layer 4.

The diffusion prevention layer 7 is preferably a thin film with good light transmittance and electrical conductivity, such as platinum or cermet (for example, platinum cermet) with a thickness of 10 to 40 Å. if there is,
Even if it is interposed between the P-type a-Si layer 3 and the I-type a-Si layer 4, it does not affect the formation of a bond between these two layers.

Figure 4 shows the relationship between photoelectric conversion efficiency and film thickness when platinum is used as the diffusion prevention layer 7, and as mentioned above, a shot barrier can be formed if the film thickness is in the range of about 10 to 40 Å. Even though platinum has a property, when there is no diffusion prevention layer 7, that is, when the platinum film thickness is zero in FIG. 4, a higher photoelectric conversion efficiency is obtained than in a photovoltaic device. In addition, P type a-
As the Si layer 3, B ₂ H ₆ /SiH ₄ =0.3% was used. From this, even if platinum is used as the diffusion prevention layer 7, if the film thickness is approximately 10 to 40 Å, there will be no adverse effect on the bond formation between the P-type a-Si layer 3 and the I-type a-Si layer 4. It turns out that there is no effect on

As yet another example of the diffusion prevention layer 7, an N-type a-Si layer with a low impurity concentration can also be used. That is, the impurities diffused from the a-Si layer 3 are compensated by the N-type a-Si layer as the diffusion prevention layer 7. Therefore, the N-type a-Si layer as the diffusion prevention layer 7 is for compensating the impurities diffused from the P-type a-Si layer 3, and the P-type a-Si layer 3 and I-type a-Si layer
It goes without saying that the N-type impurity concentration is selected to an extent that does not adversely affect the formation of a bond between the two layers with the -Si layer 4. The impurity concentration of _the N-type a-Si layer that acts as such a diffusion prevention layer 7 is shown in FIG. ,
Even if SiH ₄ is doped with PH ₃ , an N-type impurity gas, by about 10 ^-6 , the σRT of the region without PH ₃ doping (non-doped region) is almost the same.
P-type a is added to the diffusion prevention film 7 doped with about 10 ^-6 PH ₃ .
- Even if P-type impurities diffuse from the Si layer 3, the impurity concentration in the diffusion prevention film 7 only moves in the direction approaching the non-doped region, so the diffused impurities are absorbed by the σRT with high resistance. It can be compensated without making it into the area.

FIG. 5 shows the relationship between the diffusion prevention film 7 doped with N-type impurities at a gas volume ratio of about 10 ^-6 and the photoelectric conversion efficiency. In the measurement shown in FIG. 5, as in FIG. 4, the P-type a-Si layer 3 containing B ₂ H ₆ /SiH ₄ =0.3% was used.

In the above embodiment, after forming the P type a-Si layer 3, the I type a
- Although we have described the case of preventing diffusion when forming the Si layer 4, in the opposite case, that is, first forming an I-type a-Si layer on a stainless steel or other conductive substrate, and then
Of course, even when forming a type a-Si layer, the diffusion prevention film 7 provided at the interface between the I-type a-Si layer and the P-type a-Si layer works effectively. Therefore,
The present invention is not limited to the embodiment shown in FIG. 3 in which P-type, I-type, and N-type layers are sequentially laminated on the transparent first electrode film 2.

As is clear from the above explanation, according to the present invention, P is laminated by gas reaction in a silane atmosphere.
In photovoltaic devices having amorphous semiconductor layers of type I and type I, an undesirable high resistance layer due to impurity diffusion from the p type layer to the i type layer is not generated, so the series resistance of the device is reduced and the output characteristics are improved. is improved.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a conventional example, FIG. 2 is a conductivity characteristic diagram, and FIG. 3 is a side view showing an embodiment of the present invention.
Figure 4 is a characteristic diagram showing the relationship between photoelectric conversion efficiency and film thickness when platinum is used as the diffusion prevention film of the present invention, and Figure 5 is an N-type a-
FIG. 3 is a characteristic diagram showing the relationship between photoelectric conversion efficiency and film thickness when using a Si layer. 3...P type a-Si layer, 4...I type a-Si layer, 7
...Anti-diffusion film.

Claims (1)

[Claims] 1. In a photovoltaic device having P-type and I-type (intrinsic type) amorphous semiconductor layers stacked by gas reaction in a silicon compound atmosphere, adversely affecting the formation of a bond between the two layers. 1. A photovoltaic device characterized in that a diffusion prevention device is interposed to prevent diffusion of P-type impurities.