JPH06163957A - Thin film solar cell and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a thin film solar cell and its manufacturing method wherein sensitivity to the long wavelength side is improved, and optical deterioration is little. CONSTITUTION:In the title thin film solar cell, a transparent conducting film 2, a PIN semiconductor layer, and a rear electrode 6 are formed in this order on a glass substrate 1. A P-layer 3 of the PIN semiconductor layer is composed of thin film polycrystalline P-type silicon. An I-layer 4 of the PIN semiconductor layer is composed of I-layer amorphous silicon. An N-layer 5 of the PIN semiconductor layer is composed of N-type amorphous silicon or N-type microcrystal silicon. As to the manufacturing methode, the transparent conducting film 2, the PIN semiconductor layer, and the rear electrode 6 are formed in this order on the glass substrate 1. The P-layer 3 of the PIN semiconductor layer is the polycrystalline P-type silicon. The I-layer 4 is I-type amorphous silicon. The N-layer 5 of the PIN semiconductor layer 5 is N-type amorphous silicon or N-type microcrystal silicon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large area thin film solar cell formed on an inexpensive glass substrate and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in a thin film solar cell in which a transparent conductive film, a PIN semiconductor layer and a back electrode are formed in this order on a glass substrate, the P layer is formed of amorphous silicon carbide, amorphous silicon, or Amorphous silicon carbide or amorphous silicon containing fine crystals has been used.

When such a P layer is used, when the a-Si: H which is the I layer is formed next, boron in the P layer diffuses into the I layer, and the transparent conductive film forms the P layer or the I layer. Spread to. Therefore, in order to produce a high-performance amorphous silicon solar cell, film formation is performed at a film formation temperature of 250 ° C. or lower.

By limiting the film forming temperature of the I layer to 250 ° C. or less, hydrogen is contained in the I layer in an amount of about 15 atom%. As a result, there are problems that improvement in sensitivity on the long wavelength side cannot be expected and that photodegradation is large.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and provides a thin film solar cell having improved sensitivity on the long wavelength side and less photodegradation, and a method for producing the same. Is intended.

[0006]

The thin film solar cell of the present invention is a thin film solar cell in which a transparent conductive film, a PIN semiconductor layer and a back electrode are formed in this order on a glass substrate. The P layer of the semiconductor layer is made of thin film polycrystalline P type silicon, the I layer of the PIN semiconductor layer is made of I type amorphous silicon, and the N layer of the PIN semiconductor layer is made of N type amorphous silicon or N type microcrystal. It is characterized by being made of silicon.

In the thin film solar cell of the present invention, the P
The particle size of the layer is more than 200Å and its electrical resistivity is 1
It is preferably 00 Ωcm or less.

In the thin film solar cell of the present invention,
The P layer is a laser annealing method or plasma CVD
It is preferably formed by repeating the film formation by the method and the hydrogen plasma treatment.

Further, in the thin film solar cell of the present invention, it is preferable that the amount of hydrogen in the film of the P layer is 5 atomic% or less.

Moreover, in the thin-film solar cell of the present invention, for example, Pb,
It is preferable that an ultrathin metal film that does not store hydrogen, such as Ti, W, Mo, or TiC, is formed.

The method for producing a thin film solar cell of the present invention is a method for producing a thin film solar cell in which a transparent conductive film, a PIN semiconductor layer and a back electrode are formed in this order on a glass substrate. The layer is thin-film polycrystalline P-type silicon, the I layer of the PIN semiconductor layer is I-type amorphous silicon, and the N layer of the PIN semiconductor layer is N-type amorphous silicon or N-type microcrystalline silicon. I am trying.

In the method for producing a thin film solar cell of the present invention, it is preferable that the particle size of the P layer is 200 Å or more and the electrical resistivity thereof is 100 Ωcm or less.

In the method of manufacturing a thin film solar cell of the present invention, it is preferable that the P layer is formed by repeating a film formation by a laser annealing method or a plasma CVD method and a hydrogen plasma treatment.

Further, in the method for producing a thin film solar cell of the present invention, it is preferable that the amount of hydrogen in the film of the P layer is 5 atomic% or less.

Moreover, in the method for producing a thin film solar cell of the present invention, for example, P is provided between the transparent conductive film and the P layer.
It is preferable to form an ultrathin metal film that does not store hydrogen, such as b, Ti, W, Mo, or TiC.

[0016]

Since the thin film solar cell of the present invention uses the polycrystalline thin film silicon for the P layer, the I layer can be formed at a high temperature. Therefore, the sensitivity on the long wavelength side is improved, and the photodegradation property is also improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the accompanying drawings, but the present invention is not limited to such embodiments.

FIG. 1 is a schematic view of an embodiment of the present invention, and FIG. 2 is a schematic view of another embodiment of the present invention. In the figure, 1 is a glass substrate, 2 is a transparent conductive film (transparent electrode), 3 is a thin film polycrystalline P layer, 4 is amorphous silicon I layer, 5 is N-type amorphous silicon or N-type microcrystalline silicon, and 6 is a back electrode. , 7 are metal thin films which do not occlude hydrogen.

As shown in FIG. 1, the thin film solar cell of the present invention comprises a transparent conductive film (transparent electrode) on a glass substrate 1.
2, thin film polycrystalline P layer 3, amorphous silicon I layer 4,
The N-type amorphous silicon or the N-type microcrystalline amorphous silicon 5 and the back surface electrode 6 are formed in this order.

Here, the grain size of the thin film polycrystalline P layer is 200Å
Above, the electrical resistivity is set to 100 Ωcm or less. This is to improve the V _{oc of} this solar cell and to prevent hydrogen in the I layer from diffusing into the P layer when the I layer is formed at a high temperature.

As described above, the solar cell of the present invention has the P layer 3
In addition, the use of such thin film polycrystalline silicon is characteristic, and the method of forming the P layer 3 has the greatest characteristic.

The P layer 3 may be directly formed on the transparent electrode 2, but as shown in FIG. 2, it is formed on the ultrathin metal film 7 formed on the transparent electrode 2 and not storing hydrogen up to 30 Å. It is preferable that the transparent electrode 2 is formed in order to reduce the damage to the transparent electrode 2.

As a metal that does not absorb hydrogen, P
d, Ti, W, Mo, TiC and the like.

These ultra-thin metal films 7 are formed by, for example, a vapor deposition method, a sputtering method or the like.

Next, a method of forming the P-type thin film polycrystalline silicon 3 will be described. There are roughly two methods for forming the P-type thin film polycrystalline silicon 3.

(1) A method of obtaining a P-type thin film polycrystalline silicon 3 by repeating film formation of amorphous silicon by the plasma CVD method and hydrogen plasma treatment.

Specifically, boron-doped a was deposited at a substrate temperature of 150 ° C. to 500 ° C. by the RF plasma CVD method.
-Si: H is deposited to a film thickness of about 5Å to 50Å, and ECR hydrogen plasma is performed for 10 seconds to 60 seconds to perform hydrogen plasma treatment.

An important point in this hydrogen plasma treatment is adjustment of the amount of hydrogen atom flux reaching the substrate surface. This hydrogen atom flux amount is 4 × 10 ¹⁵ a
tom / cm ² · sec, preferably 1 × 10 ¹⁶ ato
m / cm ² · sec or more is required.

By repeating this film formation and hydrogen plasma treatment, the P-type thin film polycrystalline silicon 3 is obtained. This film thickness is 100Å to 1000Å, preferably 100Å to 50
It is 0Å.

(2) A method of obtaining the P-type thin film polycrystalline silicon 3 by the laser annealing method.

Concretely, 100-Å to 1000Å of boron-doped a-Si: H is formed by a plasma CVD method.
Deposited, then a energy density by using an excimer laser at 100mJ / cm ² ~400mJ / cm ²
-Si: H is laser-annealed to recrystallize. Here, as the excimer laser, KrF, A
rF, XeCl, F ₂ are used. The substrate temperature is set to room temperature to 500 ° C. during laser annealing.

Next, the I layer 4 is formed after the P layer 3 is formed. The I layer 4 is formed of an a-Si: H I layer by a usual method.

When the amorphous silicon P layer is used, the substrate temperature is limited to 250 ° C. or lower due to the diffusion of boron in the P layer and the diffusion of the transparent electrode, but polycrystalline silicon is used for the P layer. In that case, film formation up to 500 ° C. is possible.

In general, the I layer 4 is formed by plasma CVD at a substrate temperature of 250 ° C. to 450 ° C., preferably 250 ° C.
The film is formed at a temperature of ℃ to 350 ℃.

The N layer 5 is formed by N-type a-SiH or N-type a-Si: H containing microcrystalline silicon.

Finally, the back electrode 6 is formed to complete the solar cell.

It should be noted that the amorphous silicon of the I layer 4 formed on the thin film polycrystalline P-layer silicon 3 grows on the crystal especially at the interface, so that the amount of hydrogen is small and high-quality amorphous silicon is obtained. It is formed. Therefore, it is possible to form amorphous silicon, which is important for improving the photodegradation characteristics of the solar cell and has a small photodegradation at the P / I interface.

Hereinafter, the present invention will be described in more detail based on more specific examples.

Example 1 _On a glass substrate 1 on which SnO ₂ 2 was formed, a P-type a-S by RF plasma CVD method was formed under the following film forming conditions.
The thin film polycrystalline P-type silicon film 3 was formed by repeating the formation of the i: H film and the ECR hydrogen plasma treatment.

The film formation by the RF plasma CVD method is carried out at a substrate temperature of 230 ° C., SiH ₄ = 20 SCCM, H ₂ = 200.
SCCM, B ₂ H ₆ (diluted to 1000ppm)
= 2 SCCM, reaction chamber pressure 0.5 Torr, RF power density 30 mW / cm ^{2 for} 40 seconds. The film thickness thus obtained was 20Å.

Then, ECR hydrogen plasma treatment is performed. This treatment is H ₂ = 200 SCCM, reaction chamber pressure is 20 mT
Orr and ECR power 450W performed for 30 seconds. At this time, the hydrogen atom flux reaching the substrate 1 is 1
× 10 ¹⁶ atom / cm ² · sec or more.

The film formation by the RF plasma and the ECR hydrogen plasma treatment were repeated 12 times to obtain a P-type thin film polycrystalline silicon film 3 having a film thickness of 200 Å.

Next, the P-type silicon film 3 is transported in a vacuum, and the amorphous silicon film of the I layer 4 is plasma C
It was formed by the VD method.

As film forming conditions, SiH ₄ = 20 SCC
M, substrate temperature 300 ° C., reaction chamber pressure 0.2 Torr, R
F power density is 20 mW / cm ² and film thickness is 400
It was 0Å.

The N layer 5 was similarly formed by the plasma CVD method. The film forming conditions are as follows: substrate temperature 270 ° C., reaction chamber pressure 1 Torr, SiH ₄ = 10 SCCM, PH ₃ (10
(Diluted to 00 ppm) = 100 SCCM, H ₂ =
The film thickness was set to 250 Å, with 200 SCCM and RF power density of 0.2 W / cm ² .

On this N layer 5, a composite electrode (back surface electrode) consisting of a ZnO thin film 800Å and an Al thin film 1000Å
6 to form a solar cell,
Investigate the change in efficiency after photo-deterioration with a solar simulator of AM1.5, 100mW for 500 hours at ℃,
The results are shown in Table 1.

It can be seen that when the normal amorphous P layer is used, the deterioration rate is significantly reduced as compared with the comparative example described later.

Example 2 SiH ₄ = 20 SCCM, B ₂ by plasma CVD method
H ₆ (diluted to 1000 ppm) = 5 SCCM,
A P-type amorphous silicon film was formed on the transparent conductive film 2 of the glass substrate 1 at a pressure of 400 Torr at a reaction chamber pressure of 0.1 Torr, a substrate temperature of 200 ° C., and an RF power density of 30 mW / cm ² .

Next, laser annealing was performed at a substrate temperature of 350 ° C. using an excimer laser (KrF).
This laser annealing was performed in vacuum with the KrF wavelength of 248 nm and the laser energy density of 200 mJ / cm ² .

By this laser annealing, P-type thin film polycrystalline silicon 3 having a film thickness of 400 Å was obtained.

With the obtained film 3 held in vacuum, I layer 4, N layer 5 and back electrode 6 were formed by the same method as in Example 1 to complete a solar cell. The photodegradation characteristics of the obtained solar cell of Example 2 were investigated in the same manner as in Example 1, and the results are also shown in Table 1.

Example 3 Pd was vapor-deposited on a glass substrate 1 on which SnO ₂ 2 was formed at a substrate temperature of 250 ° C. by an electron beam vapor deposition method at a temperature of 20Å to form a metal thin film 7 that does not absorb hydrogen.

Next, in the same manner as in Example 1, RF plasma CVD and ECR hydrogen plasma treatment were performed under the same conditions to form a P layer 3. The I layer 4, the N layer 5, and the back electrode 6 were also formed under the same conditions to complete the solar cell. The photodegradation characteristics of the obtained solar cell of Example 3 were examined in the same manner as in Example 1, and the results are also shown in Table 1.

Comparative Example RF plasma C was formed on a glass substrate on which SnO ₂ was formed.
A P-type a-SiC: H film was formed at a substrate temperature of 200 by the VD method.
It was formed at a film thickness of 150Å at ℃.

As film forming conditions, SiH ₄ = 20 SCC
M, CH ₄ = 40 SCCM, H ₂ = 200 SCCM, B
₂ H ₆ (diluted to 1000 ppm) = 10 SCC
M, reaction chamber pressure 0.5 Torr, RF power density 30 m
It was set to W / cm ² .

In the same manner as in Example 1, the N layer, the I layer and the back surface electrode were prepared to complete the solar cell. The photodegradation characteristics of the obtained solar cell were investigated, and the results are also shown in Table 1.

Here, when the film formation temperature of the I layer is 300 ° C., since the P layer is amorphous, boron in the P layer diffuses into the I layer, and the initial characteristics are greatly deteriorated. Occurs. Further, even after light deterioration, the performance after deterioration is poor due to the blackness of the P / I interface.

[0058]

[Table 1]

[0059]

As described above, according to the thin film solar cell of the present invention, the sensitivity on the long wavelength side can be improved and the photodegradation characteristic can be greatly improved.

Further, according to the method for producing a thin film solar cell of the present invention, a thin film solar cell having improved long-wavelength side sensitivity and significantly improved photodegradation characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention.

FIG. 2 is a schematic view of another embodiment of the present invention.

[Explanation of sign]

1 Glass Substrate 2 Transparent Electrode 3 Thin Film Polycrystalline P Layer 4 Amorphous Silicon I Layer 5 N-type Amorphous Silicon or N-type Microcrystalline Silicon 6 Back Electrode 7 Metal Thin Film That Does Not Absorb Hydrogen

Claims (12)

[Claims] 1. A thin film solar cell comprising a transparent conductive film, a PIN semiconductor layer and a back electrode formed in this order on a glass substrate, wherein the P layer of the PIN semiconductor layer is a thin film polycrystalline P type. I of the PIN semiconductor layer, which is made of silicon
The layer is made of I-type amorphous silicon, and the PIN is
The N layer of the semiconductor layer is N-type amorphous silicon or N
A thin-film solar cell comprising microcrystalline silicon. 2. The thin-film solar cell according to claim 1, wherein the P layer has a grain size of 200 Å or more and an electrical resistivity of 100 Ωcm or less. 3. The P layer is formed by repeating a film formation by a laser annealing method or a plasma CVD method and a hydrogen plasma treatment.
Alternatively, the thin-film solar cell described in 2. 4. The amount of hydrogen in the P layer film is 5 atomi.
It is c% or less, Claim 1, 2 or 3 characterized by the above-mentioned.
The thin film solar cell described. 5. The thin-film solar cell according to claim 1, wherein an ultrathin metal film which does not absorb hydrogen is formed between the transparent conductive film and the P layer. . 6. The ultrathin metal that does not absorb hydrogen is P
The thin film solar cell according to claim 5, which is b, Ti, W, Mo or TiC. 7. A method of manufacturing a thin film solar cell, comprising a transparent conductive film, a PIN semiconductor layer and a back electrode formed in this order on a glass substrate, wherein the P layer of the PIN semiconductor layer is a thin film polycrystalline P type. A method of manufacturing a thin-film solar cell, comprising: silicon, the I layer of the PIN semiconductor layer is I type amorphous silicon, and the N layer of the PIN semiconductor layer is N type amorphous silicon or N type microcrystalline silicon. 8. The method for producing a thin-film solar cell according to claim 7, wherein the P layer has a grain size of 200 Å or more and an electrical resistivity of 100 Ωcm or less. 9. The method for producing a thin film solar cell according to claim 7, wherein the P layer is formed by repeating a film formation by a laser annealing method or a plasma CVD method and a hydrogen plasma treatment. 10. The amount of hydrogen in the P layer film is set to 5 atom.
ic% or less, The manufacturing method of the thin film solar cell of Claim 7, 8 or 9 characterized by the above-mentioned. 11. The method for producing a thin film solar cell according to claim 7, 8, 9 or 10, wherein an ultrathin metal film which does not absorb hydrogen is formed between the transparent conductive film and the P layer. . 12. The ultra-thin metal that does not absorb hydrogen,
The method for producing a thin-film solar cell according to claim 11, which is Pb, Ti, W, Mo or TiC.