JPH0472391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pin type amorphous silicon solar cell, and in particular to a novel amorphous silicon (a-Si) film obtained by decomposing a higher order silane than disilane as an i type a-Si layer. Regarding solar cells.

As shown in Figure 1, the pin type A-Si solar cell is
glass substrate 1, transparent conductive film 2, p-type a-Si layer 3,
It is composed of an i-type a-Si layer 4, an n-type a-Si layer 5, and a back electrode 6. When light enters this solar cell from the glass substrate side, electrons and holes are generated in the i-type a-Si layer in response to the light having energy exceeding the band gap of a-Si. These electrons and holes are separated by an internal electric field generated by the rectifying junction of the solar cell. Since the electrons are separated into electrons and holes in this way, a photocurrent and a photovoltage are generated. The separated electrons go to the n-type a-Si layer 5, and the holes go to the p-type a-Si layer 5.
It flows into the Si layer 3 and is collected by the electrode. In this way, it can be extracted to the outside as a photocurrent and a photovoltage. In other words, the efficiency of a solar cell depends on how efficiently electrons and holes, which are separated and generated by incident light, can be extracted to the outside.

It is known that the above objective can be achieved by increasing the width of the space charge region. For this reason, Japanese Patent Application Laid-open No. 56-4287 discloses that an i-type a-Si layer is
Compensation with type dopants is disclosed.

The present inventors have discovered that by forming the i-type A-SI layer of a pin-type solar cell using high-order silane, the width of the space charge region can be increased without using a p-type dopant. Ta.

That is, the pin type amorphous silicon solar cell of the present invention has a power generation region made of an amorphous silicon layer deposited on a substrate, and the p and n type semiconductor layers are composed of monosilane and p and n. It is formed by glow discharge decomposition of gases containing type impurities, and is characterized in that the undoped (i-type) amorphous silicon layer, which is a photoactive layer, is formed by decomposition of a higher-order silane higher than disilane. be.

In the present invention, p-type and n-type semiconductor layers are formed by glow discharge decomposition of gases containing monosilane and p- and n-type impurities, respectively. This is because the present inventors have found that when higher-order silane is used as a raw material, the doping effect is low.

In the present invention, as the silane higher than disilane (hereinafter referred to as disilane, etc.), either a chemically synthesized substance or a physically synthesized substance such as a silent discharge of monosilane can be used. The decomposition of disilane and the like is carried out under the application of electrical energy and thermal energy. A preferred example of decomposition is decomposition in a glow discharge atmosphere.

A method for manufacturing a solar cell according to the present invention will be explained with reference to FIG. A glass substrate 1 having a transparent conductive film is placed in a glow discharge device. 10 ^-2 Torr inside the device
Hereinafter, the pressure is preferably reduced to 10 ^-5 Torr or less and then heated. Preferably, a suitable amount of a reducing gas such as monosilane (SiH ₄ ) or hydrogen, for example 5 to
The substrate 1 is heated to 200 to 400° C. by flowing at a flow rate of 100 c.c./min. After the substrate temperature reaches the specified value, SiH ₄
Mix an appropriate amount of diborane (B ₂ H ₆ ) with water, add hydrogen as necessary, and set the pressure inside the device to an appropriate pressure for glow discharge to occur, e.g. 0.05 to 5 Torr.
and start glow discharge. The volume ratio of B ₂ H ₆ to SiH ₄ can be appropriately selected from 10 ⁻⁴ to 10 ⁻¹ , but is preferably from 10 ⁻³ to 10 ⁻² . This p-type a-
The thickness of the Si layer 3 is 50 to 1000 Å, preferably
It is 100-500 Å.

Next, an i-type a-Si layer 4 is deposited using Si ₂ H ₆ . The thickness of the i-type a-Si layer 4 can be increased by 2 to 5 times when deposited using SiH ₄ , probably due to the expansion of the space charge region. _{Si2H6 _}
can be used after being diluted with H ₂ , Ar, He, etc. The coexisting amount of SiH ₄ is preferably 10% or less.

That is, in the present invention, since an i-type a-Si layer with a thickness of 0.5 to 1 μm can be deposited, the energy of incident light can be utilized more effectively than in the prior art. Disilane etc. are more effective than SiH ₄ .
In a glow discharge atmosphere, it seems to be more easily decomposed and the deposition rate is also high. The fact that the deposition rate is high is disclosed in JP-A-56-83929. However, in the deposition of an a-Si layer made of disilane or the like, the doping effect of the a-Si layer is lower than that of an a-Si layer made of SiH ₄ in both p-type and n-type. In other words, adding the same amount of p-type or n-type dopant to disilane or the like as to SiH ₄ does not produce the same doping effect. If an i-type a-Si layer is deposited using disilane or the like, the space charge density due to defects will be reduced, resulting in a semiconductor layer that is closer to the intrinsic state, and this also makes it difficult to dope as mentioned above. It's probably related.

The decomposition conditions for disilane and the like may be the same as the decomposition conditions for SiH ₄ , but milder conditions may be used. That is, an atmospheric pressure of 0.01 to 5 Torr and a discharge power of 30 to 100 W are sufficient. It is also possible to microcrystallize part of the a-Si layer by increasing the discharge power.

Then, an n-type a-Si layer 5 is deposited. N-type dopants are phosphine (PH ₃ ) and arsine (AsH ₃ ).
etc. This n-type a-Si layer 5 ensures ohmic contact with the back electrode 6. n-type a-Si
When the layer 5 is located on the opposite side to the incident light as shown in FIG. 1, the thickness of the n-type a-Si layer 5 is not particularly limited, and a thickness of 100 to 500 Å is sufficient. . The volume ratio of _PH3 to _SiH4 is
It can be selected as appropriate from 10 ^-5 to 10 ^-1 , but preferably from 10 ^-4 to
10 ^-3 .

After depositing the n-type a-Si layer to a predetermined thickness, the back electrode 6 is deposited by a method known to those skilled in the art, such as vapor deposition or printing.

In the pin-type amorphous silicon solar cell of the present invention, the p-type and n-type semiconductor layers are formed using gases containing monosilane and p-type and n-type impurities, respectively, and the photoactive layer is formed using p-type and n-type semiconductor layers as raw materials. High photoelectric conversion efficiency can be obtained by forming the film using high-order silane as a raw material without using a mold doping agent.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A glass substrate coated with a transparent conductive film of indium tin oxide to a thickness of approximately 500 Å was placed in an RF/capacitively coupled plasma generator, and heated for approximately 300 Å while flowing SiH ₄ to facilitate heat transfer. heated to ℃.

Next _, SiH ₄ and B ₂ H ₆ were introduced so _{that the} mixing ratio of B ₂ H ₆ to SiH ₄ was 10 ^-2 ,
A p-type a-Si layer with a thickness of about 150 Å was formed.

Next, Si ₂ H ₆ (Si ₂ H 6 by gas chromatography method)
_An i _- type a _- Si layer was deposited to a _{predetermined} thickness.

Next, SiH ₄ and PH ₃ are mixed at a mixing ratio of PH ₃ to SiH ₄ .
SiH ₄ and PH ₃ were introduced to give a concentration of 10 ⁻³ to form an n-type a-Si layer with a thickness of about 500 Å. A thin aluminum film was deposited on this by vacuum evaporation to form a back electrode.

The thickness of the i-type a-Si layer is 3000 Å, 5000 Å, 7000 Å.
Four types were created: Å, 10000Å. This result is 5000～
A cell with a 10,000 Å i-type a-Si layer is
A short circuit current about 2 to 3 times higher than that of a cell with a 3000 Å a-Si layer was obtained under 15 W fluorescent lamp illumination. At this time, the open circuit voltage hardly changed, and it was confirmed that the photoelectric conversion efficiency was improved.

[Brief explanation of the drawing]

Figure 1 shows type i obtained by decomposition of disilane.
FIG. 2 is a longitudinal cross-sectional view of a pin-type a-Si solar cell including a -Si layer. 0... Incident light, 1... Glass substrate, 2... Transparent conductive film, 3... P-type a-Si layer, 4... I-type a-Si
layer, 5... n-type a-Si layer, 6... electrode.

Claims (1)

[Claims] 1. In a pin-type amorphous silicon solar cell having a power generation region consisting of an amorphous silicon layer deposited on a substrate, the p- and n-type semiconductor layers are formed by glow discharge decomposition of gases containing monosilane and p- and n-type impurities, respectively. 1. A pin-type amorphous silicon solar cell characterized in that an undoped (i-type) amorphous silicon layer serving as a photoactive layer is formed by decomposing a higher-order silane higher than disilane.